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 @gol
620 -mprototype -mno-prototype @gol
621 -msim -mmvme -mads -myellowknife -memb -msdata @gol
622 -msdata=@var{opt} -mvxworks -mwindiss -G @var{num} -pthread}
624 @emph{S/390 and zSeries Options}
625 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
626 -mhard-float -msoft-float -mbackchain -mno-backchain -mkernel-backchain @gol
627 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
628 -m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol
629 -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol
630 -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard}
633 @gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol
634 -m4-nofpu -m4-single-only -m4-single -m4 @gol
635 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol
636 -m5-64media -m5-64media-nofpu @gol
637 -m5-32media -m5-32media-nofpu @gol
638 -m5-compact -m5-compact-nofpu @gol
639 -mb -ml -mdalign -mrelax @gol
640 -mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol
641 -mieee -misize -mpadstruct -mspace @gol
642 -mprefergot -musermode}
645 @gccoptlist{-mcpu=@var{cpu-type} @gol
646 -mtune=@var{cpu-type} @gol
647 -mcmodel=@var{code-model} @gol
648 -m32 -m64 -mapp-regs -mno-app-regs @gol
649 -mfaster-structs -mno-faster-structs @gol
650 -mfpu -mno-fpu -mhard-float -msoft-float @gol
651 -mhard-quad-float -msoft-quad-float @gol
652 -mimpure-text -mno-impure-text -mlittle-endian @gol
653 -mstack-bias -mno-stack-bias @gol
654 -munaligned-doubles -mno-unaligned-doubles @gol
655 -mv8plus -mno-v8plus -mvis -mno-vis
658 @emph{System V Options}
659 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
661 @emph{TMS320C3x/C4x Options}
662 @gccoptlist{-mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol
663 -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol
664 -mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol
665 -mparallel-insns -mparallel-mpy -mpreserve-float}
668 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
669 -mprolog-function -mno-prolog-function -mspace @gol
670 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
671 -mapp-regs -mno-app-regs @gol
672 -mdisable-callt -mno-disable-callt @gol
678 @gccoptlist{-mg -mgnu -munix}
680 @emph{x86-64 Options}
681 See i386 and x86-64 Options.
683 @emph{Xstormy16 Options}
686 @emph{Xtensa Options}
687 @gccoptlist{-mconst16 -mno-const16 @gol
688 -mfused-madd -mno-fused-madd @gol
689 -mtext-section-literals -mno-text-section-literals @gol
690 -mtarget-align -mno-target-align @gol
691 -mlongcalls -mno-longcalls}
693 @emph{zSeries Options}
694 See S/390 and zSeries Options.
696 @item Code Generation Options
697 @xref{Code Gen Options,,Options for Code Generation Conventions}.
698 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
699 -ffixed-@var{reg} -fexceptions @gol
700 -fnon-call-exceptions -funwind-tables @gol
701 -fasynchronous-unwind-tables @gol
702 -finhibit-size-directive -finstrument-functions @gol
703 -fno-common -fno-ident @gol
704 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
705 -freg-struct-return -fshared-data -fshort-enums @gol
706 -fshort-double -fshort-wchar @gol
707 -fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol
708 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
709 -fargument-alias -fargument-noalias @gol
710 -fargument-noalias-global -fleading-underscore @gol
711 -ftls-model=@var{model} @gol
712 -ftrapv -fwrapv -fbounds-check @gol
717 * Overall Options:: Controlling the kind of output:
718 an executable, object files, assembler files,
719 or preprocessed source.
720 * C Dialect Options:: Controlling the variant of C language compiled.
721 * C++ Dialect Options:: Variations on C++.
722 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
724 * Language Independent Options:: Controlling how diagnostics should be
726 * Warning Options:: How picky should the compiler be?
727 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
728 * Optimize Options:: How much optimization?
729 * Preprocessor Options:: Controlling header files and macro definitions.
730 Also, getting dependency information for Make.
731 * Assembler Options:: Passing options to the assembler.
732 * Link Options:: Specifying libraries and so on.
733 * Directory Options:: Where to find header files and libraries.
734 Where to find the compiler executable files.
735 * Spec Files:: How to pass switches to sub-processes.
736 * Target Options:: Running a cross-compiler, or an old version of GCC.
739 @node Overall Options
740 @section Options Controlling the Kind of Output
742 Compilation can involve up to four stages: preprocessing, compilation
743 proper, assembly and linking, always in that order. GCC is capable of
744 preprocessing and compiling several files either into several
745 assembler input files, or into one assembler input file; then each
746 assembler input file produces an object file, and linking combines all
747 the object files (those newly compiled, and those specified as input)
748 into an executable file.
750 @cindex file name suffix
751 For any given input file, the file name suffix determines what kind of
756 C source code which must be preprocessed.
759 C source code which should not be preprocessed.
762 C++ source code which should not be preprocessed.
765 Objective-C source code. Note that you must link with the @file{libobjc}
766 library to make an Objective-C program work.
769 Objective-C source code which should not be preprocessed.
773 Objective-C++ source code. Note that you must link with the @file{libobjc}
774 library to make an Objective-C++ program work. Note that @samp{.M} refers
775 to a literal capital M@.
778 Objective-C++ source code which should not be preprocessed.
781 C, C++, Objective-C or Objective-C++ header file to be turned into a
786 @itemx @var{file}.cxx
787 @itemx @var{file}.cpp
788 @itemx @var{file}.CPP
789 @itemx @var{file}.c++
791 C++ source code which must be preprocessed. Note that in @samp{.cxx},
792 the last two letters must both be literally @samp{x}. Likewise,
793 @samp{.C} refers to a literal capital C@.
797 C++ header file to be turned into a precompiled header.
800 @itemx @var{file}.for
801 @itemx @var{file}.FOR
802 Fortran source code which should not be preprocessed.
805 @itemx @var{file}.fpp
806 @itemx @var{file}.FPP
807 Fortran source code which must be preprocessed (with the traditional
811 Fortran source code which must be preprocessed with a RATFOR
812 preprocessor (not included with GCC)@.
815 @itemx @var{file}.f95
816 Fortran 90/95 source code which should not be preprocessed.
818 @c FIXME: Descriptions of Java file types.
825 Ada source code file which contains a library unit declaration (a
826 declaration of a package, subprogram, or generic, or a generic
827 instantiation), or a library unit renaming declaration (a package,
828 generic, or subprogram renaming declaration). Such files are also
831 @itemx @var{file}.adb
832 Ada source code file containing a library unit body (a subprogram or
833 package body). Such files are also called @dfn{bodies}.
835 @c GCC also knows about some suffixes for languages not yet included:
844 Assembler code which must be preprocessed.
847 An object file to be fed straight into linking.
848 Any file name with no recognized suffix is treated this way.
852 You can specify the input language explicitly with the @option{-x} option:
855 @item -x @var{language}
856 Specify explicitly the @var{language} for the following input files
857 (rather than letting the compiler choose a default based on the file
858 name suffix). This option applies to all following input files until
859 the next @option{-x} option. Possible values for @var{language} are:
861 c c-header c-cpp-output
862 c++ c++-header c++-cpp-output
863 objective-c objective-c-header objective-c-cpp-output
864 objective-c++ objective-c++-header objective-c++-cpp-output
865 assembler assembler-with-cpp
867 f77 f77-cpp-input ratfor
874 Turn off any specification of a language, so that subsequent files are
875 handled according to their file name suffixes (as they are if @option{-x}
876 has not been used at all).
878 @item -pass-exit-codes
879 @opindex pass-exit-codes
880 Normally the @command{gcc} program will exit with the code of 1 if any
881 phase of the compiler returns a non-success return code. If you specify
882 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
883 numerically highest error produced by any phase that returned an error
887 If you only want some of the stages of compilation, you can use
888 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
889 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
890 @command{gcc} is to stop. Note that some combinations (for example,
891 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
896 Compile or assemble the source files, but do not link. The linking
897 stage simply is not done. The ultimate output is in the form of an
898 object file for each source file.
900 By default, the object file name for a source file is made by replacing
901 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
903 Unrecognized input files, not requiring compilation or assembly, are
908 Stop after the stage of compilation proper; do not assemble. The output
909 is in the form of an assembler code file for each non-assembler input
912 By default, the assembler file name for a source file is made by
913 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
915 Input files that don't require compilation are ignored.
919 Stop after the preprocessing stage; do not run the compiler proper. The
920 output is in the form of preprocessed source code, which is sent to the
923 Input files which don't require preprocessing are ignored.
925 @cindex output file option
928 Place output in file @var{file}. This applies regardless to whatever
929 sort of output is being produced, whether it be an executable file,
930 an object file, an assembler file or preprocessed C code.
932 If @option{-o} is not specified, the default is to put an executable
933 file in @file{a.out}, the object file for
934 @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its
935 assembler file in @file{@var{source}.s}, a precompiled header file in
936 @file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on
941 Print (on standard error output) the commands executed to run the stages
942 of compilation. Also print the version number of the compiler driver
943 program and of the preprocessor and the compiler proper.
947 Like @option{-v} except the commands are not executed and all command
948 arguments are quoted. This is useful for shell scripts to capture the
949 driver-generated command lines.
953 Use pipes rather than temporary files for communication between the
954 various stages of compilation. This fails to work on some systems where
955 the assembler is unable to read from a pipe; but the GNU assembler has
960 If you are compiling multiple source files, this option tells the driver
961 to pass all the source files to the compiler at once (for those
962 languages for which the compiler can handle this). This will allow
963 intermodule analysis (IMA) to be performed by the compiler. Currently the only
964 language for which this is supported is C. If you pass source files for
965 multiple languages to the driver, using this option, the driver will invoke
966 the compiler(s) that support IMA once each, passing each compiler all the
967 source files appropriate for it. For those languages that do not support
968 IMA this option will be ignored, and the compiler will be invoked once for
969 each source file in that language. If you use this option in conjunction
970 with -save-temps, the compiler will generate multiple pre-processed files
971 (one for each source file), but only one (combined) .o or .s file.
975 Print (on the standard output) a description of the command line options
976 understood by @command{gcc}. If the @option{-v} option is also specified
977 then @option{--help} will also be passed on to the various processes
978 invoked by @command{gcc}, so that they can display the command line options
979 they accept. If the @option{-Wextra} option is also specified then command
980 line options which have no documentation associated with them will also
985 Print (on the standard output) a description of target specific command
986 line options for each tool.
990 Display the version number and copyrights of the invoked GCC.
994 @section Compiling C++ Programs
996 @cindex suffixes for C++ source
997 @cindex C++ source file suffixes
998 C++ source files conventionally use one of the suffixes @samp{.C},
999 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
1000 @samp{.cxx}; C++ header files often use @samp{.hh} or @samp{.H}; and
1001 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
1002 files with these names and compiles them as C++ programs even if you
1003 call the compiler the same way as for compiling C programs (usually
1004 with the name @command{gcc}).
1008 However, C++ programs often require class libraries as well as a
1009 compiler that understands the C++ language---and under some
1010 circumstances, you might want to compile programs or header files from
1011 standard input, or otherwise without a suffix that flags them as C++
1012 programs. You might also like to precompile a C header file with a
1013 @samp{.h} extension to be used in C++ compilations. @command{g++} is a
1014 program that calls GCC with the default language set to C++, and
1015 automatically specifies linking against the C++ library. On many
1016 systems, @command{g++} is also installed with the name @command{c++}.
1018 @cindex invoking @command{g++}
1019 When you compile C++ programs, you may specify many of the same
1020 command-line options that you use for compiling programs in any
1021 language; or command-line options meaningful for C and related
1022 languages; or options that are meaningful only for C++ programs.
1023 @xref{C Dialect Options,,Options Controlling C Dialect}, for
1024 explanations of options for languages related to C@.
1025 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
1026 explanations of options that are meaningful only for C++ programs.
1028 @node C Dialect Options
1029 @section Options Controlling C Dialect
1030 @cindex dialect options
1031 @cindex language dialect options
1032 @cindex options, dialect
1034 The following options control the dialect of C (or languages derived
1035 from C, such as C++, Objective-C and Objective-C++) that the compiler
1039 @cindex ANSI support
1043 In C mode, support all ISO C90 programs. In C++ mode,
1044 remove GNU extensions that conflict with ISO C++.
1046 This turns off certain features of GCC that are incompatible with ISO
1047 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
1048 such as the @code{asm} and @code{typeof} keywords, and
1049 predefined macros such as @code{unix} and @code{vax} that identify the
1050 type of system you are using. It also enables the undesirable and
1051 rarely used ISO trigraph feature. For the C compiler,
1052 it disables recognition of C++ style @samp{//} comments as well as
1053 the @code{inline} keyword.
1055 The alternate keywords @code{__asm__}, @code{__extension__},
1056 @code{__inline__} and @code{__typeof__} continue to work despite
1057 @option{-ansi}. You would not want to use them in an ISO C program, of
1058 course, but it is useful to put them in header files that might be included
1059 in compilations done with @option{-ansi}. Alternate predefined macros
1060 such as @code{__unix__} and @code{__vax__} are also available, with or
1061 without @option{-ansi}.
1063 The @option{-ansi} option does not cause non-ISO programs to be
1064 rejected gratuitously. For that, @option{-pedantic} is required in
1065 addition to @option{-ansi}. @xref{Warning Options}.
1067 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1068 option is used. Some header files may notice this macro and refrain
1069 from declaring certain functions or defining certain macros that the
1070 ISO standard doesn't call for; this is to avoid interfering with any
1071 programs that might use these names for other things.
1073 Functions which would normally be built in but do not have semantics
1074 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1075 functions with @option{-ansi} is used. @xref{Other Builtins,,Other
1076 built-in functions provided by GCC}, for details of the functions
1081 Determine the language standard. This option is currently only
1082 supported when compiling C or C++. A value for this option must be
1083 provided; possible values are
1088 ISO C90 (same as @option{-ansi}).
1090 @item iso9899:199409
1091 ISO C90 as modified in amendment 1.
1097 ISO C99. Note that this standard is not yet fully supported; see
1098 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1099 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1102 Default, ISO C90 plus GNU extensions (including some C99 features).
1106 ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
1107 this will become the default. The name @samp{gnu9x} is deprecated.
1110 The 1998 ISO C++ standard plus amendments.
1113 The same as @option{-std=c++98} plus GNU extensions. This is the
1114 default for C++ code.
1117 Even when this option is not specified, you can still use some of the
1118 features of newer standards in so far as they do not conflict with
1119 previous C standards. For example, you may use @code{__restrict__} even
1120 when @option{-std=c99} is not specified.
1122 The @option{-std} options specifying some version of ISO C have the same
1123 effects as @option{-ansi}, except that features that were not in ISO C90
1124 but are in the specified version (for example, @samp{//} comments and
1125 the @code{inline} keyword in ISO C99) are not disabled.
1127 @xref{Standards,,Language Standards Supported by GCC}, for details of
1128 these standard versions.
1130 @item -aux-info @var{filename}
1132 Output to the given filename prototyped declarations for all functions
1133 declared and/or defined in a translation unit, including those in header
1134 files. This option is silently ignored in any language other than C@.
1136 Besides declarations, the file indicates, in comments, the origin of
1137 each declaration (source file and line), whether the declaration was
1138 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1139 @samp{O} for old, respectively, in the first character after the line
1140 number and the colon), and whether it came from a declaration or a
1141 definition (@samp{C} or @samp{F}, respectively, in the following
1142 character). In the case of function definitions, a K&R-style list of
1143 arguments followed by their declarations is also provided, inside
1144 comments, after the declaration.
1148 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1149 keyword, so that code can use these words as identifiers. You can use
1150 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1151 instead. @option{-ansi} implies @option{-fno-asm}.
1153 In C++, this switch only affects the @code{typeof} keyword, since
1154 @code{asm} and @code{inline} are standard keywords. You may want to
1155 use the @option{-fno-gnu-keywords} flag instead, which has the same
1156 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1157 switch only affects the @code{asm} and @code{typeof} keywords, since
1158 @code{inline} is a standard keyword in ISO C99.
1161 @itemx -fno-builtin-@var{function}
1162 @opindex fno-builtin
1163 @cindex built-in functions
1164 Don't recognize built-in functions that do not begin with
1165 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1166 functions provided by GCC}, for details of the functions affected,
1167 including those which are not built-in functions when @option{-ansi} or
1168 @option{-std} options for strict ISO C conformance are used because they
1169 do not have an ISO standard meaning.
1171 GCC normally generates special code to handle certain built-in functions
1172 more efficiently; for instance, calls to @code{alloca} may become single
1173 instructions that adjust the stack directly, and calls to @code{memcpy}
1174 may become inline copy loops. The resulting code is often both smaller
1175 and faster, but since the function calls no longer appear as such, you
1176 cannot set a breakpoint on those calls, nor can you change the behavior
1177 of the functions by linking with a different library. In addition,
1178 when a function is recognized as a built-in function, GCC may use
1179 information about that function to warn about problems with calls to
1180 that function, or to generate more efficient code, even if the
1181 resulting code still contains calls to that function. For example,
1182 warnings are given with @option{-Wformat} for bad calls to
1183 @code{printf}, when @code{printf} is built in, and @code{strlen} is
1184 known not to modify global memory.
1186 With the @option{-fno-builtin-@var{function}} option
1187 only the built-in function @var{function} is
1188 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1189 function is named this is not built-in in this version of GCC, this
1190 option is ignored. There is no corresponding
1191 @option{-fbuiltin-@var{function}} option; if you wish to enable
1192 built-in functions selectively when using @option{-fno-builtin} or
1193 @option{-ffreestanding}, you may define macros such as:
1196 #define abs(n) __builtin_abs ((n))
1197 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1202 @cindex hosted environment
1204 Assert that compilation takes place in a hosted environment. This implies
1205 @option{-fbuiltin}. A hosted environment is one in which the
1206 entire standard library is available, and in which @code{main} has a return
1207 type of @code{int}. Examples are nearly everything except a kernel.
1208 This is equivalent to @option{-fno-freestanding}.
1210 @item -ffreestanding
1211 @opindex ffreestanding
1212 @cindex hosted environment
1214 Assert that compilation takes place in a freestanding environment. This
1215 implies @option{-fno-builtin}. A freestanding environment
1216 is one in which the standard library may not exist, and program startup may
1217 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1218 This is equivalent to @option{-fno-hosted}.
1220 @xref{Standards,,Language Standards Supported by GCC}, for details of
1221 freestanding and hosted environments.
1223 @item -fms-extensions
1224 @opindex fms-extensions
1225 Accept some non-standard constructs used in Microsoft header files.
1227 Some cases of unnamed fields in structures and unions are only
1228 accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union
1229 fields within structs/unions}, for details.
1233 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1234 options for strict ISO C conformance) implies @option{-trigraphs}.
1236 @item -no-integrated-cpp
1237 @opindex no-integrated-cpp
1238 Performs a compilation in two passes: preprocessing and compiling. This
1239 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1240 @option{-B} option. The user supplied compilation step can then add in
1241 an additional preprocessing step after normal preprocessing but before
1242 compiling. The default is to use the integrated cpp (internal cpp)
1244 The semantics of this option will change if "cc1", "cc1plus", and
1245 "cc1obj" are merged.
1247 @cindex traditional C language
1248 @cindex C language, traditional
1250 @itemx -traditional-cpp
1251 @opindex traditional-cpp
1252 @opindex traditional
1253 Formerly, these options caused GCC to attempt to emulate a pre-standard
1254 C compiler. They are now only supported with the @option{-E} switch.
1255 The preprocessor continues to support a pre-standard mode. See the GNU
1256 CPP manual for details.
1258 @item -fcond-mismatch
1259 @opindex fcond-mismatch
1260 Allow conditional expressions with mismatched types in the second and
1261 third arguments. The value of such an expression is void. This option
1262 is not supported for C++.
1264 @item -funsigned-char
1265 @opindex funsigned-char
1266 Let the type @code{char} be unsigned, like @code{unsigned char}.
1268 Each kind of machine has a default for what @code{char} should
1269 be. It is either like @code{unsigned char} by default or like
1270 @code{signed char} by default.
1272 Ideally, a portable program should always use @code{signed char} or
1273 @code{unsigned char} when it depends on the signedness of an object.
1274 But many programs have been written to use plain @code{char} and
1275 expect it to be signed, or expect it to be unsigned, depending on the
1276 machines they were written for. This option, and its inverse, let you
1277 make such a program work with the opposite default.
1279 The type @code{char} is always a distinct type from each of
1280 @code{signed char} or @code{unsigned char}, even though its behavior
1281 is always just like one of those two.
1284 @opindex fsigned-char
1285 Let the type @code{char} be signed, like @code{signed char}.
1287 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1288 the negative form of @option{-funsigned-char}. Likewise, the option
1289 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1291 @item -fsigned-bitfields
1292 @itemx -funsigned-bitfields
1293 @itemx -fno-signed-bitfields
1294 @itemx -fno-unsigned-bitfields
1295 @opindex fsigned-bitfields
1296 @opindex funsigned-bitfields
1297 @opindex fno-signed-bitfields
1298 @opindex fno-unsigned-bitfields
1299 These options control whether a bit-field is signed or unsigned, when the
1300 declaration does not use either @code{signed} or @code{unsigned}. By
1301 default, such a bit-field is signed, because this is consistent: the
1302 basic integer types such as @code{int} are signed types.
1305 @node C++ Dialect Options
1306 @section Options Controlling C++ Dialect
1308 @cindex compiler options, C++
1309 @cindex C++ options, command line
1310 @cindex options, C++
1311 This section describes the command-line options that are only meaningful
1312 for C++ programs; but you can also use most of the GNU compiler options
1313 regardless of what language your program is in. For example, you
1314 might compile a file @code{firstClass.C} like this:
1317 g++ -g -frepo -O -c firstClass.C
1321 In this example, only @option{-frepo} is an option meant
1322 only for C++ programs; you can use the other options with any
1323 language supported by GCC@.
1325 Here is a list of options that are @emph{only} for compiling C++ programs:
1329 @item -fabi-version=@var{n}
1330 @opindex fabi-version
1331 Use version @var{n} of the C++ ABI. Version 2 is the version of the
1332 C++ ABI that first appeared in G++ 3.4. Version 1 is the version of
1333 the C++ ABI that first appeared in G++ 3.2. Version 0 will always be
1334 the version that conforms most closely to the C++ ABI specification.
1335 Therefore, the ABI obtained using version 0 will change as ABI bugs
1338 The default is version 2.
1340 @item -fno-access-control
1341 @opindex fno-access-control
1342 Turn off all access checking. This switch is mainly useful for working
1343 around bugs in the access control code.
1347 Check that the pointer returned by @code{operator new} is non-null
1348 before attempting to modify the storage allocated. This check is
1349 normally unnecessary because the C++ standard specifies that
1350 @code{operator new} will only return @code{0} if it is declared
1351 @samp{throw()}, in which case the compiler will always check the
1352 return value even without this option. In all other cases, when
1353 @code{operator new} has a non-empty exception specification, memory
1354 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1355 @samp{new (nothrow)}.
1357 @item -fconserve-space
1358 @opindex fconserve-space
1359 Put uninitialized or runtime-initialized global variables into the
1360 common segment, as C does. This saves space in the executable at the
1361 cost of not diagnosing duplicate definitions. If you compile with this
1362 flag and your program mysteriously crashes after @code{main()} has
1363 completed, you may have an object that is being destroyed twice because
1364 two definitions were merged.
1366 This option is no longer useful on most targets, now that support has
1367 been added for putting variables into BSS without making them common.
1369 @item -fno-const-strings
1370 @opindex fno-const-strings
1371 Give string constants type @code{char *} instead of type @code{const
1372 char *}. By default, G++ uses type @code{const char *} as required by
1373 the standard. Even if you use @option{-fno-const-strings}, you cannot
1374 actually modify the value of a string constant.
1376 This option might be removed in a future release of G++. For maximum
1377 portability, you should structure your code so that it works with
1378 string constants that have type @code{const char *}.
1380 @item -fno-elide-constructors
1381 @opindex fno-elide-constructors
1382 The C++ standard allows an implementation to omit creating a temporary
1383 which is only used to initialize another object of the same type.
1384 Specifying this option disables that optimization, and forces G++ to
1385 call the copy constructor in all cases.
1387 @item -fno-enforce-eh-specs
1388 @opindex fno-enforce-eh-specs
1389 Don't check for violation of exception specifications at runtime. This
1390 option violates the C++ standard, but may be useful for reducing code
1391 size in production builds, much like defining @samp{NDEBUG}. The compiler
1392 will still optimize based on the exception specifications.
1395 @itemx -fno-for-scope
1397 @opindex fno-for-scope
1398 If @option{-ffor-scope} is specified, the scope of variables declared in
1399 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1400 as specified by the C++ standard.
1401 If @option{-fno-for-scope} is specified, the scope of variables declared in
1402 a @i{for-init-statement} extends to the end of the enclosing scope,
1403 as was the case in old versions of G++, and other (traditional)
1404 implementations of C++.
1406 The default if neither flag is given to follow the standard,
1407 but to allow and give a warning for old-style code that would
1408 otherwise be invalid, or have different behavior.
1410 @item -fno-gnu-keywords
1411 @opindex fno-gnu-keywords
1412 Do not recognize @code{typeof} as a keyword, so that code can use this
1413 word as an identifier. You can use the keyword @code{__typeof__} instead.
1414 @option{-ansi} implies @option{-fno-gnu-keywords}.
1416 @item -fno-implicit-templates
1417 @opindex fno-implicit-templates
1418 Never emit code for non-inline templates which are instantiated
1419 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1420 @xref{Template Instantiation}, for more information.
1422 @item -fno-implicit-inline-templates
1423 @opindex fno-implicit-inline-templates
1424 Don't emit code for implicit instantiations of inline templates, either.
1425 The default is to handle inlines differently so that compiles with and
1426 without optimization will need the same set of explicit instantiations.
1428 @item -fno-implement-inlines
1429 @opindex fno-implement-inlines
1430 To save space, do not emit out-of-line copies of inline functions
1431 controlled by @samp{#pragma implementation}. This will cause linker
1432 errors if these functions are not inlined everywhere they are called.
1434 @item -fms-extensions
1435 @opindex fms-extensions
1436 Disable pedantic warnings about constructs used in MFC, such as implicit
1437 int and getting a pointer to member function via non-standard syntax.
1439 @item -fno-nonansi-builtins
1440 @opindex fno-nonansi-builtins
1441 Disable built-in declarations of functions that are not mandated by
1442 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1443 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1445 @item -fno-operator-names
1446 @opindex fno-operator-names
1447 Do not treat the operator name keywords @code{and}, @code{bitand},
1448 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1449 synonyms as keywords.
1451 @item -fno-optional-diags
1452 @opindex fno-optional-diags
1453 Disable diagnostics that the standard says a compiler does not need to
1454 issue. Currently, the only such diagnostic issued by G++ is the one for
1455 a name having multiple meanings within a class.
1458 @opindex fpermissive
1459 Downgrade some diagnostics about nonconformant code from errors to
1460 warnings. Thus, using @option{-fpermissive} will allow some
1461 nonconforming code to compile.
1465 Enable automatic template instantiation at link time. This option also
1466 implies @option{-fno-implicit-templates}. @xref{Template
1467 Instantiation}, for more information.
1471 Disable generation of information about every class with virtual
1472 functions for use by the C++ runtime type identification features
1473 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1474 of the language, you can save some space by using this flag. Note that
1475 exception handling uses the same information, but it will generate it as
1480 Emit statistics about front-end processing at the end of the compilation.
1481 This information is generally only useful to the G++ development team.
1483 @item -ftemplate-depth-@var{n}
1484 @opindex ftemplate-depth
1485 Set the maximum instantiation depth for template classes to @var{n}.
1486 A limit on the template instantiation depth is needed to detect
1487 endless recursions during template class instantiation. ANSI/ISO C++
1488 conforming programs must not rely on a maximum depth greater than 17.
1490 @item -fno-threadsafe-statics
1491 @opindex fno-threadsafe-statics
1492 Do not emit the extra code to use the routines specified in the C++
1493 ABI for thread-safe initialization of local statics. You can use this
1494 option to reduce code size slightly in code that doesn't need to be
1497 @item -fuse-cxa-atexit
1498 @opindex fuse-cxa-atexit
1499 Register destructors for objects with static storage duration with the
1500 @code{__cxa_atexit} function rather than the @code{atexit} function.
1501 This option is required for fully standards-compliant handling of static
1502 destructors, but will only work if your C library supports
1503 @code{__cxa_atexit}.
1505 @item -fvisibility-inlines-hidden
1506 @opindex fvisibility-inlines-hidden
1507 Causes all inlined methods to be marked with
1508 @code{__attribute__ ((visibility ("hidden")))} so that they do not
1509 appear in the export table of a DSO and do not require a PLT indirection
1510 when used within the DSO. Enabling this option can have a dramatic effect
1511 on load and link times of a DSO as it massively reduces the size of the
1512 dynamic export table when the library makes heavy use of templates. While
1513 it can cause bloating through duplication of code within each DSO where
1514 it is used, often the wastage is less than the considerable space occupied
1515 by a long symbol name in the export table which is typical when using
1516 templates and namespaces. For even more savings, combine with the
1517 @option{-fvisibility=hidden} switch.
1521 Do not use weak symbol support, even if it is provided by the linker.
1522 By default, G++ will use weak symbols if they are available. This
1523 option exists only for testing, and should not be used by end-users;
1524 it will result in inferior code and has no benefits. This option may
1525 be removed in a future release of G++.
1529 Do not search for header files in the standard directories specific to
1530 C++, but do still search the other standard directories. (This option
1531 is used when building the C++ library.)
1534 In addition, these optimization, warning, and code generation options
1535 have meanings only for C++ programs:
1538 @item -fno-default-inline
1539 @opindex fno-default-inline
1540 Do not assume @samp{inline} for functions defined inside a class scope.
1541 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1542 functions will have linkage like inline functions; they just won't be
1545 @item -Wabi @r{(C++ only)}
1547 Warn when G++ generates code that is probably not compatible with the
1548 vendor-neutral C++ ABI. Although an effort has been made to warn about
1549 all such cases, there are probably some cases that are not warned about,
1550 even though G++ is generating incompatible code. There may also be
1551 cases where warnings are emitted even though the code that is generated
1554 You should rewrite your code to avoid these warnings if you are
1555 concerned about the fact that code generated by G++ may not be binary
1556 compatible with code generated by other compilers.
1558 The known incompatibilities at this point include:
1563 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1564 pack data into the same byte as a base class. For example:
1567 struct A @{ virtual void f(); int f1 : 1; @};
1568 struct B : public A @{ int f2 : 1; @};
1572 In this case, G++ will place @code{B::f2} into the same byte
1573 as@code{A::f1}; other compilers will not. You can avoid this problem
1574 by explicitly padding @code{A} so that its size is a multiple of the
1575 byte size on your platform; that will cause G++ and other compilers to
1576 layout @code{B} identically.
1579 Incorrect handling of tail-padding for virtual bases. G++ does not use
1580 tail padding when laying out virtual bases. For example:
1583 struct A @{ virtual void f(); char c1; @};
1584 struct B @{ B(); char c2; @};
1585 struct C : public A, public virtual B @{@};
1589 In this case, G++ will not place @code{B} into the tail-padding for
1590 @code{A}; other compilers will. You can avoid this problem by
1591 explicitly padding @code{A} so that its size is a multiple of its
1592 alignment (ignoring virtual base classes); that will cause G++ and other
1593 compilers to layout @code{C} identically.
1596 Incorrect handling of bit-fields with declared widths greater than that
1597 of their underlying types, when the bit-fields appear in a union. For
1601 union U @{ int i : 4096; @};
1605 Assuming that an @code{int} does not have 4096 bits, G++ will make the
1606 union too small by the number of bits in an @code{int}.
1609 Empty classes can be placed at incorrect offsets. For example:
1619 struct C : public B, public A @{@};
1623 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
1624 it should be placed at offset zero. G++ mistakenly believes that the
1625 @code{A} data member of @code{B} is already at offset zero.
1628 Names of template functions whose types involve @code{typename} or
1629 template template parameters can be mangled incorrectly.
1632 template <typename Q>
1633 void f(typename Q::X) @{@}
1635 template <template <typename> class Q>
1636 void f(typename Q<int>::X) @{@}
1640 Instantiations of these templates may be mangled incorrectly.
1644 @item -Wctor-dtor-privacy @r{(C++ only)}
1645 @opindex Wctor-dtor-privacy
1646 Warn when a class seems unusable because all the constructors or
1647 destructors in that class are private, and it has neither friends nor
1648 public static member functions.
1650 @item -Wnon-virtual-dtor @r{(C++ only)}
1651 @opindex Wnon-virtual-dtor
1652 Warn when a class appears to be polymorphic, thereby requiring a virtual
1653 destructor, yet it declares a non-virtual one.
1654 This warning is enabled by @option{-Wall}.
1656 @item -Wreorder @r{(C++ only)}
1658 @cindex reordering, warning
1659 @cindex warning for reordering of member initializers
1660 Warn when the order of member initializers given in the code does not
1661 match the order in which they must be executed. For instance:
1667 A(): j (0), i (1) @{ @}
1671 The compiler will rearrange the member initializers for @samp{i}
1672 and @samp{j} to match the declaration order of the members, emitting
1673 a warning to that effect. This warning is enabled by @option{-Wall}.
1676 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
1679 @item -Weffc++ @r{(C++ only)}
1681 Warn about violations of the following style guidelines from Scott Meyers'
1682 @cite{Effective C++} book:
1686 Item 11: Define a copy constructor and an assignment operator for classes
1687 with dynamically allocated memory.
1690 Item 12: Prefer initialization to assignment in constructors.
1693 Item 14: Make destructors virtual in base classes.
1696 Item 15: Have @code{operator=} return a reference to @code{*this}.
1699 Item 23: Don't try to return a reference when you must return an object.
1703 Also warn about violations of the following style guidelines from
1704 Scott Meyers' @cite{More Effective C++} book:
1708 Item 6: Distinguish between prefix and postfix forms of increment and
1709 decrement operators.
1712 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
1716 When selecting this option, be aware that the standard library
1717 headers do not obey all of these guidelines; use @samp{grep -v}
1718 to filter out those warnings.
1720 @item -Wno-deprecated @r{(C++ only)}
1721 @opindex Wno-deprecated
1722 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
1724 @item -Wno-non-template-friend @r{(C++ only)}
1725 @opindex Wno-non-template-friend
1726 Disable warnings when non-templatized friend functions are declared
1727 within a template. Since the advent of explicit template specification
1728 support in G++, if the name of the friend is an unqualified-id (i.e.,
1729 @samp{friend foo(int)}), the C++ language specification demands that the
1730 friend declare or define an ordinary, nontemplate function. (Section
1731 14.5.3). Before G++ implemented explicit specification, unqualified-ids
1732 could be interpreted as a particular specialization of a templatized
1733 function. Because this non-conforming behavior is no longer the default
1734 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
1735 check existing code for potential trouble spots and is on by default.
1736 This new compiler behavior can be turned off with
1737 @option{-Wno-non-template-friend} which keeps the conformant compiler code
1738 but disables the helpful warning.
1740 @item -Wold-style-cast @r{(C++ only)}
1741 @opindex Wold-style-cast
1742 Warn if an old-style (C-style) cast to a non-void type is used within
1743 a C++ program. The new-style casts (@samp{static_cast},
1744 @samp{reinterpret_cast}, and @samp{const_cast}) are less vulnerable to
1745 unintended effects and much easier to search for.
1747 @item -Woverloaded-virtual @r{(C++ only)}
1748 @opindex Woverloaded-virtual
1749 @cindex overloaded virtual fn, warning
1750 @cindex warning for overloaded virtual fn
1751 Warn when a function declaration hides virtual functions from a
1752 base class. For example, in:
1759 struct B: public A @{
1764 the @code{A} class version of @code{f} is hidden in @code{B}, and code
1772 will fail to compile.
1774 @item -Wno-pmf-conversions @r{(C++ only)}
1775 @opindex Wno-pmf-conversions
1776 Disable the diagnostic for converting a bound pointer to member function
1779 @item -Wsign-promo @r{(C++ only)}
1780 @opindex Wsign-promo
1781 Warn when overload resolution chooses a promotion from unsigned or
1782 enumerated type to a signed type, over a conversion to an unsigned type of
1783 the same size. Previous versions of G++ would try to preserve
1784 unsignedness, but the standard mandates the current behavior.
1786 @item -Wsynth @r{(C++ only)}
1788 @cindex warning for synthesized methods
1789 @cindex synthesized methods, warning
1790 Warn when G++'s synthesis behavior does not match that of cfront. For
1796 A& operator = (int);
1806 In this example, G++ will synthesize a default @samp{A& operator =
1807 (const A&);}, while cfront will use the user-defined @samp{operator =}.
1810 @node Objective-C and Objective-C++ Dialect Options
1811 @section Options Controlling Objective-C and Objective-C++ Dialects
1813 @cindex compiler options, Objective-C and Objective-C++
1814 @cindex Objective-C and Objective-C++ options, command line
1815 @cindex options, Objective-C and Objective-C++
1816 (NOTE: This manual does not describe the Objective-C and Objective-C++
1817 languages themselves. See @xref{Standards,,Language Standards
1818 Supported by GCC}, for references.)
1820 This section describes the command-line options that are only meaningful
1821 for Objective-C and Objective-C++ programs, but you can also use most of
1822 the language-independent GNU compiler options.
1823 For example, you might compile a file @code{some_class.m} like this:
1826 gcc -g -fgnu-runtime -O -c some_class.m
1830 In this example, @option{-fgnu-runtime} is an option meant only for
1831 Objective-C and Objective-C++ programs; you can use the other options with
1832 any language supported by GCC@.
1834 Note that since Objective-C is an extension of the C language, Objective-C
1835 compilations may also use options specific to the C front-end (e.g.,
1836 @option{-Wtraditional}). Similarly, Objective-C++ compilations may use
1837 C++-specific options (e.g., @option{-Wabi}).
1839 Here is a list of options that are @emph{only} for compiling Objective-C
1840 and Objective-C++ programs:
1843 @item -fconstant-string-class=@var{class-name}
1844 @opindex fconstant-string-class
1845 Use @var{class-name} as the name of the class to instantiate for each
1846 literal string specified with the syntax @code{@@"@dots{}"}. The default
1847 class name is @code{NXConstantString} if the GNU runtime is being used, and
1848 @code{NSConstantString} if the NeXT runtime is being used (see below). The
1849 @option{-fconstant-cfstrings} option, if also present, will override the
1850 @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
1851 to be laid out as constant CoreFoundation strings.
1854 @opindex fgnu-runtime
1855 Generate object code compatible with the standard GNU Objective-C
1856 runtime. This is the default for most types of systems.
1858 @item -fnext-runtime
1859 @opindex fnext-runtime
1860 Generate output compatible with the NeXT runtime. This is the default
1861 for NeXT-based systems, including Darwin and Mac OS X@. The macro
1862 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
1865 @item -fno-nil-receivers
1866 @opindex fno-nil-receivers
1867 Assume that all Objective-C message dispatches (e.g.,
1868 @code{[receiver message:arg]}) in this translation unit ensure that the receiver
1869 is not @code{nil}. This allows for more efficient entry points in the runtime
1870 to be used. Currently, this option is only available in conjunction with
1871 the NeXT runtime on Mac OS X 10.3 and later.
1873 @item -fobjc-exceptions
1874 @opindex fobjc-exceptions
1875 Enable syntactic support for structured exception handling in Objective-C,
1876 similar to what is offered by C++ and Java. Currently, this option is only
1877 available in conjunction with the NeXT runtime on Mac OS X 10.3 and later.
1885 @@catch (AnObjCClass *exc) @{
1892 @@catch (AnotherClass *exc) @{
1895 @@catch (id allOthers) @{
1905 The @code{@@throw} statement may appear anywhere in an Objective-C or
1906 Objective-C++ program; when used inside of a @code{@@catch} block, the
1907 @code{@@throw} may appear without an argument (as shown above), in which case
1908 the object caught by the @code{@@catch} will be rethrown.
1910 Note that only (pointers to) Objective-C objects may be thrown and
1911 caught using this scheme. When an object is thrown, it will be caught
1912 by the nearest @code{@@catch} clause capable of handling objects of that type,
1913 analogously to how @code{catch} blocks work in C++ and Java. A
1914 @code{@@catch(id @dots{})} clause (as shown above) may also be provided to catch
1915 any and all Objective-C exceptions not caught by previous @code{@@catch}
1918 The @code{@@finally} clause, if present, will be executed upon exit from the
1919 immediately preceding @code{@@try @dots{} @@catch} section. This will happen
1920 regardless of whether any exceptions are thrown, caught or rethrown
1921 inside the @code{@@try @dots{} @@catch} section, analogously to the behavior
1922 of the @code{finally} clause in Java.
1924 There are several caveats to using the new exception mechanism:
1928 Although currently designed to be binary compatible with @code{NS_HANDLER}-style
1929 idioms provided by the @code{NSException} class, the new
1930 exceptions can only be used on Mac OS X 10.3 (Panther) and later
1931 systems, due to additional functionality needed in the (NeXT) Objective-C
1935 As mentioned above, the new exceptions do not support handling
1936 types other than Objective-C objects. Furthermore, when used from
1937 Objective-C++, the Objective-C exception model does not interoperate with C++
1938 exceptions at this time. This means you cannot @code{@@throw} an exception
1939 from Objective-C and @code{catch} it in C++, or vice versa
1940 (i.e., @code{throw @dots{} @@catch}).
1943 The @option{-fobjc-exceptions} switch also enables the use of synchronization
1944 blocks for thread-safe execution:
1947 @@synchronized (ObjCClass *guard) @{
1952 Upon entering the @code{@@synchronized} block, a thread of execution shall
1953 first check whether a lock has been placed on the corresponding @code{guard}
1954 object by another thread. If it has, the current thread shall wait until
1955 the other thread relinquishes its lock. Once @code{guard} becomes available,
1956 the current thread will place its own lock on it, execute the code contained in
1957 the @code{@@synchronized} block, and finally relinquish the lock (thereby
1958 making @code{guard} available to other threads).
1960 Unlike Java, Objective-C does not allow for entire methods to be marked
1961 @code{@@synchronized}. Note that throwing exceptions out of
1962 @code{@@synchronized} blocks is allowed, and will cause the guarding object
1963 to be unlocked properly.
1965 @item -freplace-objc-classes
1966 @opindex freplace-objc-classes
1967 Emit a special marker instructing @command{ld(1)} not to statically link in
1968 the resulting object file, and allow @command{dyld(1)} to load it in at
1969 run time instead. This is used in conjunction with the Fix-and-Continue
1970 debugging mode, where the object file in question may be recompiled and
1971 dynamically reloaded in the course of program execution, without the need
1972 to restart the program itself. Currently, Fix-and-Continue functionality
1973 is only available in conjunction with the NeXT runtime on Mac OS X 10.3
1978 When compiling for the NeXT runtime, the compiler ordinarily replaces calls
1979 to @code{objc_getClass("@dots{}")} (when the name of the class is known at
1980 compile time) with static class references that get initialized at load time,
1981 which improves run-time performance. Specifying the @option{-fzero-link} flag
1982 suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
1983 to be retained. This is useful in Zero-Link debugging mode, since it allows
1984 for individual class implementations to be modified during program execution.
1988 Dump interface declarations for all classes seen in the source file to a
1989 file named @file{@var{sourcename}.decl}.
1992 @opindex Wno-protocol
1993 If a class is declared to implement a protocol, a warning is issued for
1994 every method in the protocol that is not implemented by the class. The
1995 default behavior is to issue a warning for every method not explicitly
1996 implemented in the class, even if a method implementation is inherited
1997 from the superclass. If you use the @option{-Wno-protocol} option, then
1998 methods inherited from the superclass are considered to be implemented,
1999 and no warning is issued for them.
2003 Warn if multiple methods of different types for the same selector are
2004 found during compilation. The check is performed on the list of methods
2005 in the final stage of compilation. Additionally, a check is performed
2006 for each selector appearing in a @code{@@selector(@dots{})}
2007 expression, and a corresponding method for that selector has been found
2008 during compilation. Because these checks scan the method table only at
2009 the end of compilation, these warnings are not produced if the final
2010 stage of compilation is not reached, for example because an error is
2011 found during compilation, or because the @option{-fsyntax-only} option is
2014 @item -Wundeclared-selector
2015 @opindex Wundeclared-selector
2016 Warn if a @code{@@selector(@dots{})} expression referring to an
2017 undeclared selector is found. A selector is considered undeclared if no
2018 method with that name has been declared before the
2019 @code{@@selector(@dots{})} expression, either explicitly in an
2020 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
2021 an @code{@@implementation} section. This option always performs its
2022 checks as soon as a @code{@@selector(@dots{})} expression is found,
2023 while @option{-Wselector} only performs its checks in the final stage of
2024 compilation. This also enforces the coding style convention
2025 that methods and selectors must be declared before being used.
2027 @item -print-objc-runtime-info
2028 @opindex print-objc-runtime-info
2029 Generate C header describing the largest structure that is passed by
2034 @node Language Independent Options
2035 @section Options to Control Diagnostic Messages Formatting
2036 @cindex options to control diagnostics formatting
2037 @cindex diagnostic messages
2038 @cindex message formatting
2040 Traditionally, diagnostic messages have been formatted irrespective of
2041 the output device's aspect (e.g.@: its width, @dots{}). The options described
2042 below can be used to control the diagnostic messages formatting
2043 algorithm, e.g.@: how many characters per line, how often source location
2044 information should be reported. Right now, only the C++ front end can
2045 honor these options. However it is expected, in the near future, that
2046 the remaining front ends would be able to digest them correctly.
2049 @item -fmessage-length=@var{n}
2050 @opindex fmessage-length
2051 Try to format error messages so that they fit on lines of about @var{n}
2052 characters. The default is 72 characters for @command{g++} and 0 for the rest of
2053 the front ends supported by GCC@. If @var{n} is zero, then no
2054 line-wrapping will be done; each error message will appear on a single
2057 @opindex fdiagnostics-show-location
2058 @item -fdiagnostics-show-location=once
2059 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
2060 reporter to emit @emph{once} source location information; that is, in
2061 case the message is too long to fit on a single physical line and has to
2062 be wrapped, the source location won't be emitted (as prefix) again,
2063 over and over, in subsequent continuation lines. This is the default
2066 @item -fdiagnostics-show-location=every-line
2067 Only meaningful in line-wrapping mode. Instructs the diagnostic
2068 messages reporter to emit the same source location information (as
2069 prefix) for physical lines that result from the process of breaking
2070 a message which is too long to fit on a single line.
2074 @node Warning Options
2075 @section Options to Request or Suppress Warnings
2076 @cindex options to control warnings
2077 @cindex warning messages
2078 @cindex messages, warning
2079 @cindex suppressing warnings
2081 Warnings are diagnostic messages that report constructions which
2082 are not inherently erroneous but which are risky or suggest there
2083 may have been an error.
2085 You can request many specific warnings with options beginning @samp{-W},
2086 for example @option{-Wimplicit} to request warnings on implicit
2087 declarations. Each of these specific warning options also has a
2088 negative form beginning @samp{-Wno-} to turn off warnings;
2089 for example, @option{-Wno-implicit}. This manual lists only one of the
2090 two forms, whichever is not the default.
2092 The following options control the amount and kinds of warnings produced
2093 by GCC; for further, language-specific options also refer to
2094 @ref{C++ Dialect Options} and @ref{Objective-C and Objective-C++ Dialect
2098 @cindex syntax checking
2100 @opindex fsyntax-only
2101 Check the code for syntax errors, but don't do anything beyond that.
2105 Issue all the warnings demanded by strict ISO C and ISO C++;
2106 reject all programs that use forbidden extensions, and some other
2107 programs that do not follow ISO C and ISO C++. For ISO C, follows the
2108 version of the ISO C standard specified by any @option{-std} option used.
2110 Valid ISO C and ISO C++ programs should compile properly with or without
2111 this option (though a rare few will require @option{-ansi} or a
2112 @option{-std} option specifying the required version of ISO C)@. However,
2113 without this option, certain GNU extensions and traditional C and C++
2114 features are supported as well. With this option, they are rejected.
2116 @option{-pedantic} does not cause warning messages for use of the
2117 alternate keywords whose names begin and end with @samp{__}. Pedantic
2118 warnings are also disabled in the expression that follows
2119 @code{__extension__}. However, only system header files should use
2120 these escape routes; application programs should avoid them.
2121 @xref{Alternate Keywords}.
2123 Some users try to use @option{-pedantic} to check programs for strict ISO
2124 C conformance. They soon find that it does not do quite what they want:
2125 it finds some non-ISO practices, but not all---only those for which
2126 ISO C @emph{requires} a diagnostic, and some others for which
2127 diagnostics have been added.
2129 A feature to report any failure to conform to ISO C might be useful in
2130 some instances, but would require considerable additional work and would
2131 be quite different from @option{-pedantic}. We don't have plans to
2132 support such a feature in the near future.
2134 Where the standard specified with @option{-std} represents a GNU
2135 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
2136 corresponding @dfn{base standard}, the version of ISO C on which the GNU
2137 extended dialect is based. Warnings from @option{-pedantic} are given
2138 where they are required by the base standard. (It would not make sense
2139 for such warnings to be given only for features not in the specified GNU
2140 C dialect, since by definition the GNU dialects of C include all
2141 features the compiler supports with the given option, and there would be
2142 nothing to warn about.)
2144 @item -pedantic-errors
2145 @opindex pedantic-errors
2146 Like @option{-pedantic}, except that errors are produced rather than
2151 Inhibit all warning messages.
2155 Inhibit warning messages about the use of @samp{#import}.
2157 @item -Wchar-subscripts
2158 @opindex Wchar-subscripts
2159 Warn if an array subscript has type @code{char}. This is a common cause
2160 of error, as programmers often forget that this type is signed on some
2165 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
2166 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
2168 @item -Wfatal-errors
2169 @opindex Wfatal-errors
2170 This option causes the compiler to abort compilation on the first error
2171 occurred rather than trying to keep going and printing further error
2176 @opindex ffreestanding
2177 @opindex fno-builtin
2178 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
2179 the arguments supplied have types appropriate to the format string
2180 specified, and that the conversions specified in the format string make
2181 sense. This includes standard functions, and others specified by format
2182 attributes (@pxref{Function Attributes}), in the @code{printf},
2183 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
2184 not in the C standard) families (or other target-specific families).
2185 Which functions are checked without format attributes having been
2186 specified depends on the standard version selected, and such checks of
2187 functions without the attribute specified are disabled by
2188 @option{-ffreestanding} or @option{-fno-builtin}.
2190 The formats are checked against the format features supported by GNU
2191 libc version 2.2. These include all ISO C90 and C99 features, as well
2192 as features from the Single Unix Specification and some BSD and GNU
2193 extensions. Other library implementations may not support all these
2194 features; GCC does not support warning about features that go beyond a
2195 particular library's limitations. However, if @option{-pedantic} is used
2196 with @option{-Wformat}, warnings will be given about format features not
2197 in the selected standard version (but not for @code{strfmon} formats,
2198 since those are not in any version of the C standard). @xref{C Dialect
2199 Options,,Options Controlling C Dialect}.
2201 Since @option{-Wformat} also checks for null format arguments for
2202 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2204 @option{-Wformat} is included in @option{-Wall}. For more control over some
2205 aspects of format checking, the options @option{-Wformat-y2k},
2206 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2207 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2208 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2211 @opindex Wformat-y2k
2212 If @option{-Wformat} is specified, also warn about @code{strftime}
2213 formats which may yield only a two-digit year.
2215 @item -Wno-format-extra-args
2216 @opindex Wno-format-extra-args
2217 If @option{-Wformat} is specified, do not warn about excess arguments to a
2218 @code{printf} or @code{scanf} format function. The C standard specifies
2219 that such arguments are ignored.
2221 Where the unused arguments lie between used arguments that are
2222 specified with @samp{$} operand number specifications, normally
2223 warnings are still given, since the implementation could not know what
2224 type to pass to @code{va_arg} to skip the unused arguments. However,
2225 in the case of @code{scanf} formats, this option will suppress the
2226 warning if the unused arguments are all pointers, since the Single
2227 Unix Specification says that such unused arguments are allowed.
2229 @item -Wno-format-zero-length
2230 @opindex Wno-format-zero-length
2231 If @option{-Wformat} is specified, do not warn about zero-length formats.
2232 The C standard specifies that zero-length formats are allowed.
2234 @item -Wformat-nonliteral
2235 @opindex Wformat-nonliteral
2236 If @option{-Wformat} is specified, also warn if the format string is not a
2237 string literal and so cannot be checked, unless the format function
2238 takes its format arguments as a @code{va_list}.
2240 @item -Wformat-security
2241 @opindex Wformat-security
2242 If @option{-Wformat} is specified, also warn about uses of format
2243 functions that represent possible security problems. At present, this
2244 warns about calls to @code{printf} and @code{scanf} functions where the
2245 format string is not a string literal and there are no format arguments,
2246 as in @code{printf (foo);}. This may be a security hole if the format
2247 string came from untrusted input and contains @samp{%n}. (This is
2248 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2249 in future warnings may be added to @option{-Wformat-security} that are not
2250 included in @option{-Wformat-nonliteral}.)
2254 Enable @option{-Wformat} plus format checks not included in
2255 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2256 -Wformat-nonliteral -Wformat-security -Wformat-y2k}.
2260 Warn about passing a null pointer for arguments marked as
2261 requiring a non-null value by the @code{nonnull} function attribute.
2263 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2264 can be disabled with the @option{-Wno-nonnull} option.
2266 @item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
2268 Warn about uninitialized variables which are initialized with themselves.
2269 Note this option can only be used with the @option{-Wuninitialized} option,
2270 which in turn only works with @option{-O1} and above.
2272 For example, GCC will warn about @code{i} being uninitialized in the
2273 following snippet only when @option{-Winit-self} has been specified:
2284 @item -Wimplicit-int
2285 @opindex Wimplicit-int
2286 Warn when a declaration does not specify a type.
2288 @item -Wimplicit-function-declaration
2289 @itemx -Werror-implicit-function-declaration
2290 @opindex Wimplicit-function-declaration
2291 @opindex Werror-implicit-function-declaration
2292 Give a warning (or error) whenever a function is used before being
2293 declared. The form @option{-Wno-error-implicit-function-declaration}
2298 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2302 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
2303 function with external linkage, returning int, taking either zero
2304 arguments, two, or three arguments of appropriate types.
2306 @item -Wmissing-braces
2307 @opindex Wmissing-braces
2308 Warn if an aggregate or union initializer is not fully bracketed. In
2309 the following example, the initializer for @samp{a} is not fully
2310 bracketed, but that for @samp{b} is fully bracketed.
2313 int a[2][2] = @{ 0, 1, 2, 3 @};
2314 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2317 @item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)}
2318 @opindex Wmissing-include-dirs
2319 Warn if a user-supplied include directory does not exist.
2322 @opindex Wparentheses
2323 Warn if parentheses are omitted in certain contexts, such
2324 as when there is an assignment in a context where a truth value
2325 is expected, or when operators are nested whose precedence people
2326 often get confused about. Only the warning for an assignment used as
2327 a truth value is supported when compiling C++; the other warnings are
2328 only supported when compiling C@.
2330 Also warn if a comparison like @samp{x<=y<=z} appears; this is
2331 equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different
2332 interpretation from that of ordinary mathematical notation.
2334 Also warn about constructions where there may be confusion to which
2335 @code{if} statement an @code{else} branch belongs. Here is an example of
2350 In C, every @code{else} branch belongs to the innermost possible @code{if}
2351 statement, which in this example is @code{if (b)}. This is often not
2352 what the programmer expected, as illustrated in the above example by
2353 indentation the programmer chose. When there is the potential for this
2354 confusion, GCC will issue a warning when this flag is specified.
2355 To eliminate the warning, add explicit braces around the innermost
2356 @code{if} statement so there is no way the @code{else} could belong to
2357 the enclosing @code{if}. The resulting code would look like this:
2373 @item -Wsequence-point
2374 @opindex Wsequence-point
2375 Warn about code that may have undefined semantics because of violations
2376 of sequence point rules in the C standard.
2378 The C standard defines the order in which expressions in a C program are
2379 evaluated in terms of @dfn{sequence points}, which represent a partial
2380 ordering between the execution of parts of the program: those executed
2381 before the sequence point, and those executed after it. These occur
2382 after the evaluation of a full expression (one which is not part of a
2383 larger expression), after the evaluation of the first operand of a
2384 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
2385 function is called (but after the evaluation of its arguments and the
2386 expression denoting the called function), and in certain other places.
2387 Other than as expressed by the sequence point rules, the order of
2388 evaluation of subexpressions of an expression is not specified. All
2389 these rules describe only a partial order rather than a total order,
2390 since, for example, if two functions are called within one expression
2391 with no sequence point between them, the order in which the functions
2392 are called is not specified. However, the standards committee have
2393 ruled that function calls do not overlap.
2395 It is not specified when between sequence points modifications to the
2396 values of objects take effect. Programs whose behavior depends on this
2397 have undefined behavior; the C standard specifies that ``Between the
2398 previous and next sequence point an object shall have its stored value
2399 modified at most once by the evaluation of an expression. Furthermore,
2400 the prior value shall be read only to determine the value to be
2401 stored.''. If a program breaks these rules, the results on any
2402 particular implementation are entirely unpredictable.
2404 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
2405 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
2406 diagnosed by this option, and it may give an occasional false positive
2407 result, but in general it has been found fairly effective at detecting
2408 this sort of problem in programs.
2410 The present implementation of this option only works for C programs. A
2411 future implementation may also work for C++ programs.
2413 The C standard is worded confusingly, therefore there is some debate
2414 over the precise meaning of the sequence point rules in subtle cases.
2415 Links to discussions of the problem, including proposed formal
2416 definitions, may be found on the GCC readings page, at
2417 @w{@uref{http://gcc.gnu.org/readings.html}}.
2420 @opindex Wreturn-type
2421 Warn whenever a function is defined with a return-type that defaults to
2422 @code{int}. Also warn about any @code{return} statement with no
2423 return-value in a function whose return-type is not @code{void}.
2425 For C, also warn if the return type of a function has a type qualifier
2426 such as @code{const}. Such a type qualifier has no effect, since the
2427 value returned by a function is not an lvalue. ISO C prohibits
2428 qualified @code{void} return types on function definitions, so such
2429 return types always receive a warning even without this option.
2431 For C++, a function without return type always produces a diagnostic
2432 message, even when @option{-Wno-return-type} is specified. The only
2433 exceptions are @samp{main} and functions defined in system headers.
2437 Warn whenever a @code{switch} statement has an index of enumerated type
2438 and lacks a @code{case} for one or more of the named codes of that
2439 enumeration. (The presence of a @code{default} label prevents this
2440 warning.) @code{case} labels outside the enumeration range also
2441 provoke warnings when this option is used.
2443 @item -Wswitch-default
2444 @opindex Wswitch-switch
2445 Warn whenever a @code{switch} statement does not have a @code{default}
2449 @opindex Wswitch-enum
2450 Warn whenever a @code{switch} statement has an index of enumerated type
2451 and lacks a @code{case} for one or more of the named codes of that
2452 enumeration. @code{case} labels outside the enumeration range also
2453 provoke warnings when this option is used.
2457 Warn if any trigraphs are encountered that might change the meaning of
2458 the program (trigraphs within comments are not warned about).
2460 @item -Wunused-function
2461 @opindex Wunused-function
2462 Warn whenever a static function is declared but not defined or a
2463 non\-inline static function is unused.
2465 @item -Wunused-label
2466 @opindex Wunused-label
2467 Warn whenever a label is declared but not used.
2469 To suppress this warning use the @samp{unused} attribute
2470 (@pxref{Variable Attributes}).
2472 @item -Wunused-parameter
2473 @opindex Wunused-parameter
2474 Warn whenever a function parameter is unused aside from its declaration.
2476 To suppress this warning use the @samp{unused} attribute
2477 (@pxref{Variable Attributes}).
2479 @item -Wunused-variable
2480 @opindex Wunused-variable
2481 Warn whenever a local variable or non-constant static variable is unused
2482 aside from its declaration
2484 To suppress this warning use the @samp{unused} attribute
2485 (@pxref{Variable Attributes}).
2487 @item -Wunused-value
2488 @opindex Wunused-value
2489 Warn whenever a statement computes a result that is explicitly not used.
2491 To suppress this warning cast the expression to @samp{void}.
2495 All the above @option{-Wunused} options combined.
2497 In order to get a warning about an unused function parameter, you must
2498 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
2499 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
2501 @item -Wuninitialized
2502 @opindex Wuninitialized
2503 Warn if an automatic variable is used without first being initialized or
2504 if a variable may be clobbered by a @code{setjmp} call.
2506 These warnings are possible only in optimizing compilation,
2507 because they require data flow information that is computed only
2508 when optimizing. If you don't specify @option{-O}, you simply won't
2511 If you want to warn about code which uses the uninitialized value of the
2512 variable in its own initializer, use the @option{-Winit-self} option.
2514 These warnings occur only for variables that are candidates for
2515 register allocation. Therefore, they do not occur for a variable that
2516 is declared @code{volatile}, or whose address is taken, or whose size
2517 is other than 1, 2, 4 or 8 bytes. Also, they do not occur for
2518 structures, unions or arrays, even when they are in registers.
2520 Note that there may be no warning about a variable that is used only
2521 to compute a value that itself is never used, because such
2522 computations may be deleted by data flow analysis before the warnings
2525 These warnings are made optional because GCC is not smart
2526 enough to see all the reasons why the code might be correct
2527 despite appearing to have an error. Here is one example of how
2548 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
2549 always initialized, but GCC doesn't know this. Here is
2550 another common case:
2555 if (change_y) save_y = y, y = new_y;
2557 if (change_y) y = save_y;
2562 This has no bug because @code{save_y} is used only if it is set.
2564 @cindex @code{longjmp} warnings
2565 This option also warns when a non-volatile automatic variable might be
2566 changed by a call to @code{longjmp}. These warnings as well are possible
2567 only in optimizing compilation.
2569 The compiler sees only the calls to @code{setjmp}. It cannot know
2570 where @code{longjmp} will be called; in fact, a signal handler could
2571 call it at any point in the code. As a result, you may get a warning
2572 even when there is in fact no problem because @code{longjmp} cannot
2573 in fact be called at the place which would cause a problem.
2575 Some spurious warnings can be avoided if you declare all the functions
2576 you use that never return as @code{noreturn}. @xref{Function
2579 @item -Wunknown-pragmas
2580 @opindex Wunknown-pragmas
2581 @cindex warning for unknown pragmas
2582 @cindex unknown pragmas, warning
2583 @cindex pragmas, warning of unknown
2584 Warn when a #pragma directive is encountered which is not understood by
2585 GCC@. If this command line option is used, warnings will even be issued
2586 for unknown pragmas in system header files. This is not the case if
2587 the warnings were only enabled by the @option{-Wall} command line option.
2589 @item -Wstrict-aliasing
2590 @opindex Wstrict-aliasing
2591 This option is only active when @option{-fstrict-aliasing} is active.
2592 It warns about code which might break the strict aliasing rules that the
2593 compiler is using for optimization. The warning does not catch all
2594 cases, but does attempt to catch the more common pitfalls. It is
2595 included in @option{-Wall}.
2597 @item -Wstrict-aliasing=2
2598 @opindex Wstrict-aliasing=2
2599 This option is only active when @option{-fstrict-aliasing} is active.
2600 It warns about all code which might break the strict aliasing rules that the
2601 compiler is using for optimization. This warning catches all cases, but
2602 it will also give a warning for some ambiguous cases that are safe.
2606 All of the above @samp{-W} options combined. This enables all the
2607 warnings about constructions that some users consider questionable, and
2608 that are easy to avoid (or modify to prevent the warning), even in
2609 conjunction with macros. This also enables some language-specific
2610 warnings described in @ref{C++ Dialect Options} and
2611 @ref{Objective-C and Objective-C++ Dialect Options}.
2614 The following @option{-W@dots{}} options are not implied by @option{-Wall}.
2615 Some of them warn about constructions that users generally do not
2616 consider questionable, but which occasionally you might wish to check
2617 for; others warn about constructions that are necessary or hard to avoid
2618 in some cases, and there is no simple way to modify the code to suppress
2625 (This option used to be called @option{-W}. The older name is still
2626 supported, but the newer name is more descriptive.) Print extra warning
2627 messages for these events:
2631 A function can return either with or without a value. (Falling
2632 off the end of the function body is considered returning without
2633 a value.) For example, this function would evoke such a
2647 An expression-statement or the left-hand side of a comma expression
2648 contains no side effects.
2649 To suppress the warning, cast the unused expression to void.
2650 For example, an expression such as @samp{x[i,j]} will cause a warning,
2651 but @samp{x[(void)i,j]} will not.
2654 An unsigned value is compared against zero with @samp{<} or @samp{>=}.
2657 Storage-class specifiers like @code{static} are not the first things in
2658 a declaration. According to the C Standard, this usage is obsolescent.
2661 If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
2665 A comparison between signed and unsigned values could produce an
2666 incorrect result when the signed value is converted to unsigned.
2667 (But don't warn if @option{-Wno-sign-compare} is also specified.)
2670 An aggregate has an initializer which does not initialize all members.
2671 This warning can be independently controlled by
2672 @option{-Wmissing-field-initializers}.
2675 A function parameter is declared without a type specifier in K&R-style
2683 An empty body occurs in an @samp{if} or @samp{else} statement.
2686 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2687 @samp{>}, or @samp{>=}.
2690 A variable might be changed by @samp{longjmp} or @samp{vfork}.
2693 Any of several floating-point events that often indicate errors, such as
2694 overflow, underflow, loss of precision, etc.
2696 @item @r{(C++ only)}
2697 An enumerator and a non-enumerator both appear in a conditional expression.
2699 @item @r{(C++ only)}
2700 A non-static reference or non-static @samp{const} member appears in a
2701 class without constructors.
2703 @item @r{(C++ only)}
2704 Ambiguous virtual bases.
2706 @item @r{(C++ only)}
2707 Subscripting an array which has been declared @samp{register}.
2709 @item @r{(C++ only)}
2710 Taking the address of a variable which has been declared @samp{register}.
2712 @item @r{(C++ only)}
2713 A base class is not initialized in a derived class' copy constructor.
2716 @item -Wno-div-by-zero
2717 @opindex Wno-div-by-zero
2718 @opindex Wdiv-by-zero
2719 Do not warn about compile-time integer division by zero. Floating point
2720 division by zero is not warned about, as it can be a legitimate way of
2721 obtaining infinities and NaNs.
2723 @item -Wsystem-headers
2724 @opindex Wsystem-headers
2725 @cindex warnings from system headers
2726 @cindex system headers, warnings from
2727 Print warning messages for constructs found in system header files.
2728 Warnings from system headers are normally suppressed, on the assumption
2729 that they usually do not indicate real problems and would only make the
2730 compiler output harder to read. Using this command line option tells
2731 GCC to emit warnings from system headers as if they occurred in user
2732 code. However, note that using @option{-Wall} in conjunction with this
2733 option will @emph{not} warn about unknown pragmas in system
2734 headers---for that, @option{-Wunknown-pragmas} must also be used.
2737 @opindex Wfloat-equal
2738 Warn if floating point values are used in equality comparisons.
2740 The idea behind this is that sometimes it is convenient (for the
2741 programmer) to consider floating-point values as approximations to
2742 infinitely precise real numbers. If you are doing this, then you need
2743 to compute (by analyzing the code, or in some other way) the maximum or
2744 likely maximum error that the computation introduces, and allow for it
2745 when performing comparisons (and when producing output, but that's a
2746 different problem). In particular, instead of testing for equality, you
2747 would check to see whether the two values have ranges that overlap; and
2748 this is done with the relational operators, so equality comparisons are
2751 @item -Wtraditional @r{(C only)}
2752 @opindex Wtraditional
2753 Warn about certain constructs that behave differently in traditional and
2754 ISO C@. Also warn about ISO C constructs that have no traditional C
2755 equivalent, and/or problematic constructs which should be avoided.
2759 Macro parameters that appear within string literals in the macro body.
2760 In traditional C macro replacement takes place within string literals,
2761 but does not in ISO C@.
2764 In traditional C, some preprocessor directives did not exist.
2765 Traditional preprocessors would only consider a line to be a directive
2766 if the @samp{#} appeared in column 1 on the line. Therefore
2767 @option{-Wtraditional} warns about directives that traditional C
2768 understands but would ignore because the @samp{#} does not appear as the
2769 first character on the line. It also suggests you hide directives like
2770 @samp{#pragma} not understood by traditional C by indenting them. Some
2771 traditional implementations would not recognize @samp{#elif}, so it
2772 suggests avoiding it altogether.
2775 A function-like macro that appears without arguments.
2778 The unary plus operator.
2781 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
2782 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
2783 constants.) Note, these suffixes appear in macros defined in the system
2784 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
2785 Use of these macros in user code might normally lead to spurious
2786 warnings, however GCC's integrated preprocessor has enough context to
2787 avoid warning in these cases.
2790 A function declared external in one block and then used after the end of
2794 A @code{switch} statement has an operand of type @code{long}.
2797 A non-@code{static} function declaration follows a @code{static} one.
2798 This construct is not accepted by some traditional C compilers.
2801 The ISO type of an integer constant has a different width or
2802 signedness from its traditional type. This warning is only issued if
2803 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
2804 typically represent bit patterns, are not warned about.
2807 Usage of ISO string concatenation is detected.
2810 Initialization of automatic aggregates.
2813 Identifier conflicts with labels. Traditional C lacks a separate
2814 namespace for labels.
2817 Initialization of unions. If the initializer is zero, the warning is
2818 omitted. This is done under the assumption that the zero initializer in
2819 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
2820 initializer warnings and relies on default initialization to zero in the
2824 Conversions by prototypes between fixed/floating point values and vice
2825 versa. The absence of these prototypes when compiling with traditional
2826 C would cause serious problems. This is a subset of the possible
2827 conversion warnings, for the full set use @option{-Wconversion}.
2830 Use of ISO C style function definitions. This warning intentionally is
2831 @emph{not} issued for prototype declarations or variadic functions
2832 because these ISO C features will appear in your code when using
2833 libiberty's traditional C compatibility macros, @code{PARAMS} and
2834 @code{VPARAMS}. This warning is also bypassed for nested functions
2835 because that feature is already a GCC extension and thus not relevant to
2836 traditional C compatibility.
2839 @item -Wdeclaration-after-statement @r{(C only)}
2840 @opindex Wdeclaration-after-statement
2841 Warn when a declaration is found after a statement in a block. This
2842 construct, known from C++, was introduced with ISO C99 and is by default
2843 allowed in GCC@. It is not supported by ISO C90 and was not supported by
2844 GCC versions before GCC 3.0. @xref{Mixed Declarations}.
2848 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
2850 @item -Wendif-labels
2851 @opindex Wendif-labels
2852 Warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
2856 Warn whenever a local variable shadows another local variable, parameter or
2857 global variable or whenever a built-in function is shadowed.
2859 @item -Wlarger-than-@var{len}
2860 @opindex Wlarger-than
2861 Warn whenever an object of larger than @var{len} bytes is defined.
2863 @item -Wpointer-arith
2864 @opindex Wpointer-arith
2865 Warn about anything that depends on the ``size of'' a function type or
2866 of @code{void}. GNU C assigns these types a size of 1, for
2867 convenience in calculations with @code{void *} pointers and pointers
2870 @item -Wbad-function-cast @r{(C only)}
2871 @opindex Wbad-function-cast
2872 Warn whenever a function call is cast to a non-matching type.
2873 For example, warn if @code{int malloc()} is cast to @code{anything *}.
2877 Warn whenever a pointer is cast so as to remove a type qualifier from
2878 the target type. For example, warn if a @code{const char *} is cast
2879 to an ordinary @code{char *}.
2882 @opindex Wcast-align
2883 Warn whenever a pointer is cast such that the required alignment of the
2884 target is increased. For example, warn if a @code{char *} is cast to
2885 an @code{int *} on machines where integers can only be accessed at
2886 two- or four-byte boundaries.
2888 @item -Wwrite-strings
2889 @opindex Wwrite-strings
2890 When compiling C, give string constants the type @code{const
2891 char[@var{length}]} so that
2892 copying the address of one into a non-@code{const} @code{char *}
2893 pointer will get a warning; when compiling C++, warn about the
2894 deprecated conversion from string constants to @code{char *}.
2895 These warnings will help you find at
2896 compile time code that can try to write into a string constant, but
2897 only if you have been very careful about using @code{const} in
2898 declarations and prototypes. Otherwise, it will just be a nuisance;
2899 this is why we did not make @option{-Wall} request these warnings.
2902 @opindex Wconversion
2903 Warn if a prototype causes a type conversion that is different from what
2904 would happen to the same argument in the absence of a prototype. This
2905 includes conversions of fixed point to floating and vice versa, and
2906 conversions changing the width or signedness of a fixed point argument
2907 except when the same as the default promotion.
2909 Also, warn if a negative integer constant expression is implicitly
2910 converted to an unsigned type. For example, warn about the assignment
2911 @code{x = -1} if @code{x} is unsigned. But do not warn about explicit
2912 casts like @code{(unsigned) -1}.
2914 @item -Wsign-compare
2915 @opindex Wsign-compare
2916 @cindex warning for comparison of signed and unsigned values
2917 @cindex comparison of signed and unsigned values, warning
2918 @cindex signed and unsigned values, comparison warning
2919 Warn when a comparison between signed and unsigned values could produce
2920 an incorrect result when the signed value is converted to unsigned.
2921 This warning is also enabled by @option{-Wextra}; to get the other warnings
2922 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
2924 @item -Waggregate-return
2925 @opindex Waggregate-return
2926 Warn if any functions that return structures or unions are defined or
2927 called. (In languages where you can return an array, this also elicits
2930 @item -Wstrict-prototypes @r{(C only)}
2931 @opindex Wstrict-prototypes
2932 Warn if a function is declared or defined without specifying the
2933 argument types. (An old-style function definition is permitted without
2934 a warning if preceded by a declaration which specifies the argument
2937 @item -Wold-style-definition @r{(C only)}
2938 @opindex Wold-style-definition
2939 Warn if an old-style function definition is used. A warning is given
2940 even if there is a previous prototype.
2942 @item -Wmissing-prototypes @r{(C only)}
2943 @opindex Wmissing-prototypes
2944 Warn if a global function is defined without a previous prototype
2945 declaration. This warning is issued even if the definition itself
2946 provides a prototype. The aim is to detect global functions that fail
2947 to be declared in header files.
2949 @item -Wmissing-declarations @r{(C only)}
2950 @opindex Wmissing-declarations
2951 Warn if a global function is defined without a previous declaration.
2952 Do so even if the definition itself provides a prototype.
2953 Use this option to detect global functions that are not declared in
2956 @item -Wmissing-field-initializers
2957 @opindex Wmissing-field-initializers
2960 Warn if a structure's initializer has some fields missing. For
2961 example, the following code would cause such a warning, because
2962 @code{x.h} is implicitly zero:
2965 struct s @{ int f, g, h; @};
2966 struct s x = @{ 3, 4 @};
2969 This option does not warn about designated initializers, so the following
2970 modification would not trigger a warning:
2973 struct s @{ int f, g, h; @};
2974 struct s x = @{ .f = 3, .g = 4 @};
2977 This warning is included in @option{-Wextra}. To get other @option{-Wextra}
2978 warnings without this one, use @samp{-Wextra -Wno-missing-field-initializers}.
2980 @item -Wmissing-noreturn
2981 @opindex Wmissing-noreturn
2982 Warn about functions which might be candidates for attribute @code{noreturn}.
2983 Note these are only possible candidates, not absolute ones. Care should
2984 be taken to manually verify functions actually do not ever return before
2985 adding the @code{noreturn} attribute, otherwise subtle code generation
2986 bugs could be introduced. You will not get a warning for @code{main} in
2987 hosted C environments.
2989 @item -Wmissing-format-attribute
2990 @opindex Wmissing-format-attribute
2992 If @option{-Wformat} is enabled, also warn about functions which might be
2993 candidates for @code{format} attributes. Note these are only possible
2994 candidates, not absolute ones. GCC will guess that @code{format}
2995 attributes might be appropriate for any function that calls a function
2996 like @code{vprintf} or @code{vscanf}, but this might not always be the
2997 case, and some functions for which @code{format} attributes are
2998 appropriate may not be detected. This option has no effect unless
2999 @option{-Wformat} is enabled (possibly by @option{-Wall}).
3001 @item -Wno-multichar
3002 @opindex Wno-multichar
3004 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
3005 Usually they indicate a typo in the user's code, as they have
3006 implementation-defined values, and should not be used in portable code.
3008 @item -Wno-deprecated-declarations
3009 @opindex Wno-deprecated-declarations
3010 Do not warn about uses of functions, variables, and types marked as
3011 deprecated by using the @code{deprecated} attribute.
3012 (@pxref{Function Attributes}, @pxref{Variable Attributes},
3013 @pxref{Type Attributes}.)
3017 Warn if a structure is given the packed attribute, but the packed
3018 attribute has no effect on the layout or size of the structure.
3019 Such structures may be mis-aligned for little benefit. For
3020 instance, in this code, the variable @code{f.x} in @code{struct bar}
3021 will be misaligned even though @code{struct bar} does not itself
3022 have the packed attribute:
3029 @} __attribute__((packed));
3039 Warn if padding is included in a structure, either to align an element
3040 of the structure or to align the whole structure. Sometimes when this
3041 happens it is possible to rearrange the fields of the structure to
3042 reduce the padding and so make the structure smaller.
3044 @item -Wredundant-decls
3045 @opindex Wredundant-decls
3046 Warn if anything is declared more than once in the same scope, even in
3047 cases where multiple declaration is valid and changes nothing.
3049 @item -Wnested-externs @r{(C only)}
3050 @opindex Wnested-externs
3051 Warn if an @code{extern} declaration is encountered within a function.
3053 @item -Wunreachable-code
3054 @opindex Wunreachable-code
3055 Warn if the compiler detects that code will never be executed.
3057 This option is intended to warn when the compiler detects that at
3058 least a whole line of source code will never be executed, because
3059 some condition is never satisfied or because it is after a
3060 procedure that never returns.
3062 It is possible for this option to produce a warning even though there
3063 are circumstances under which part of the affected line can be executed,
3064 so care should be taken when removing apparently-unreachable code.
3066 For instance, when a function is inlined, a warning may mean that the
3067 line is unreachable in only one inlined copy of the function.
3069 This option is not made part of @option{-Wall} because in a debugging
3070 version of a program there is often substantial code which checks
3071 correct functioning of the program and is, hopefully, unreachable
3072 because the program does work. Another common use of unreachable
3073 code is to provide behavior which is selectable at compile-time.
3077 Warn if a function can not be inlined and it was declared as inline.
3078 Even with this option, the compiler will not warn about failures to
3079 inline functions declared in system headers.
3081 The compiler uses a variety of heuristics to determine whether or not
3082 to inline a function. For example, the compiler takes into account
3083 the size of the function being inlined and the the amount of inlining
3084 that has already been done in the current function. Therefore,
3085 seemingly insignificant changes in the source program can cause the
3086 warnings produced by @option{-Winline} to appear or disappear.
3088 @item -Wno-invalid-offsetof @r{(C++ only)}
3089 @opindex Wno-invalid-offsetof
3090 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
3091 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
3092 to a non-POD type is undefined. In existing C++ implementations,
3093 however, @samp{offsetof} typically gives meaningful results even when
3094 applied to certain kinds of non-POD types. (Such as a simple
3095 @samp{struct} that fails to be a POD type only by virtue of having a
3096 constructor.) This flag is for users who are aware that they are
3097 writing nonportable code and who have deliberately chosen to ignore the
3100 The restrictions on @samp{offsetof} may be relaxed in a future version
3101 of the C++ standard.
3104 @opindex Winvalid-pch
3105 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
3106 the search path but can't be used.
3110 @opindex Wno-long-long
3111 Warn if @samp{long long} type is used. This is default. To inhibit
3112 the warning messages, use @option{-Wno-long-long}. Flags
3113 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
3114 only when @option{-pedantic} flag is used.
3116 @item -Wvariadic-macros
3117 @opindex Wvariadic-macros
3118 @opindex Wno-variadic-macros
3119 Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU
3120 alternate syntax when in pedantic ISO C99 mode. This is default.
3121 To inhibit the warning messages, use @option{-Wno-variadic-macros}.
3123 @item -Wdisabled-optimization
3124 @opindex Wdisabled-optimization
3125 Warn if a requested optimization pass is disabled. This warning does
3126 not generally indicate that there is anything wrong with your code; it
3127 merely indicates that GCC's optimizers were unable to handle the code
3128 effectively. Often, the problem is that your code is too big or too
3129 complex; GCC will refuse to optimize programs when the optimization
3130 itself is likely to take inordinate amounts of time.
3134 Make all warnings into errors.
3137 @node Debugging Options
3138 @section Options for Debugging Your Program or GCC
3139 @cindex options, debugging
3140 @cindex debugging information options
3142 GCC has various special options that are used for debugging
3143 either your program or GCC:
3148 Produce debugging information in the operating system's native format
3149 (stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging
3152 On most systems that use stabs format, @option{-g} enables use of extra
3153 debugging information that only GDB can use; this extra information
3154 makes debugging work better in GDB but will probably make other debuggers
3156 refuse to read the program. If you want to control for certain whether
3157 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
3158 @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
3160 GCC allows you to use @option{-g} with
3161 @option{-O}. The shortcuts taken by optimized code may occasionally
3162 produce surprising results: some variables you declared may not exist
3163 at all; flow of control may briefly move where you did not expect it;
3164 some statements may not be executed because they compute constant
3165 results or their values were already at hand; some statements may
3166 execute in different places because they were moved out of loops.
3168 Nevertheless it proves possible to debug optimized output. This makes
3169 it reasonable to use the optimizer for programs that might have bugs.
3171 The following options are useful when GCC is generated with the
3172 capability for more than one debugging format.
3176 Produce debugging information for use by GDB@. This means to use the
3177 most expressive format available (DWARF 2, stabs, or the native format
3178 if neither of those are supported), including GDB extensions if at all
3183 Produce debugging information in stabs format (if that is supported),
3184 without GDB extensions. This is the format used by DBX on most BSD
3185 systems. On MIPS, Alpha and System V Release 4 systems this option
3186 produces stabs debugging output which is not understood by DBX or SDB@.
3187 On System V Release 4 systems this option requires the GNU assembler.
3189 @item -feliminate-unused-debug-symbols
3190 @opindex feliminate-unused-debug-symbols
3191 Produce debugging information in stabs format (if that is supported),
3192 for only symbols that are actually used.
3196 Produce debugging information in stabs format (if that is supported),
3197 using GNU extensions understood only by the GNU debugger (GDB)@. The
3198 use of these extensions is likely to make other debuggers crash or
3199 refuse to read the program.
3203 Produce debugging information in COFF format (if that is supported).
3204 This is the format used by SDB on most System V systems prior to
3209 Produce debugging information in XCOFF format (if that is supported).
3210 This is the format used by the DBX debugger on IBM RS/6000 systems.
3214 Produce debugging information in XCOFF format (if that is supported),
3215 using GNU extensions understood only by the GNU debugger (GDB)@. The
3216 use of these extensions is likely to make other debuggers crash or
3217 refuse to read the program, and may cause assemblers other than the GNU
3218 assembler (GAS) to fail with an error.
3222 Produce debugging information in DWARF version 2 format (if that is
3223 supported). This is the format used by DBX on IRIX 6. With this
3224 option, GCC uses features of DWARF version 3 when they are useful;
3225 version 3 is upward compatible with version 2, but may still cause
3226 problems for older debuggers.
3230 Produce debugging information in VMS debug format (if that is
3231 supported). This is the format used by DEBUG on VMS systems.
3234 @itemx -ggdb@var{level}
3235 @itemx -gstabs@var{level}
3236 @itemx -gcoff@var{level}
3237 @itemx -gxcoff@var{level}
3238 @itemx -gvms@var{level}
3239 Request debugging information and also use @var{level} to specify how
3240 much information. The default level is 2.
3242 Level 1 produces minimal information, enough for making backtraces in
3243 parts of the program that you don't plan to debug. This includes
3244 descriptions of functions and external variables, but no information
3245 about local variables and no line numbers.
3247 Level 3 includes extra information, such as all the macro definitions
3248 present in the program. Some debuggers support macro expansion when
3249 you use @option{-g3}.
3251 @option{-gdwarf-2} does not accept a concatenated debug level, because
3252 GCC used to support an option @option{-gdwarf} that meant to generate
3253 debug information in version 1 of the DWARF format (which is very
3254 different from version 2), and it would have been too confusing. That
3255 debug format is long obsolete, but the option cannot be changed now.
3256 Instead use an additional @option{-g@var{level}} option to change the
3257 debug level for DWARF2.
3259 @item -feliminate-dwarf2-dups
3260 @opindex feliminate-dwarf2-dups
3261 Compress DWARF2 debugging information by eliminating duplicated
3262 information about each symbol. This option only makes sense when
3263 generating DWARF2 debugging information with @option{-gdwarf-2}.
3265 @cindex @command{prof}
3268 Generate extra code to write profile information suitable for the
3269 analysis program @command{prof}. You must use this option when compiling
3270 the source files you want data about, and you must also use it when
3273 @cindex @command{gprof}
3276 Generate extra code to write profile information suitable for the
3277 analysis program @command{gprof}. You must use this option when compiling
3278 the source files you want data about, and you must also use it when
3283 Makes the compiler print out each function name as it is compiled, and
3284 print some statistics about each pass when it finishes.
3287 @opindex ftime-report
3288 Makes the compiler print some statistics about the time consumed by each
3289 pass when it finishes.
3292 @opindex fmem-report
3293 Makes the compiler print some statistics about permanent memory
3294 allocation when it finishes.
3296 @item -fprofile-arcs
3297 @opindex fprofile-arcs
3298 Add code so that program flow @dfn{arcs} are instrumented. During
3299 execution the program records how many times each branch and call is
3300 executed and how many times it is taken or returns. When the compiled
3301 program exits it saves this data to a file called
3302 @file{@var{auxname}.gcda} for each source file. The data may be used for
3303 profile-directed optimizations (@option{-fbranch-probabilities}), or for
3304 test coverage analysis (@option{-ftest-coverage}). Each object file's
3305 @var{auxname} is generated from the name of the output file, if
3306 explicitly specified and it is not the final executable, otherwise it is
3307 the basename of the source file. In both cases any suffix is removed
3308 (e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
3309 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
3314 Compile the source files with @option{-fprofile-arcs} plus optimization
3315 and code generation options. For test coverage analysis, use the
3316 additional @option{-ftest-coverage} option. You do not need to profile
3317 every source file in a program.
3320 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
3321 (the latter implies the former).
3324 Run the program on a representative workload to generate the arc profile
3325 information. This may be repeated any number of times. You can run
3326 concurrent instances of your program, and provided that the file system
3327 supports locking, the data files will be correctly updated. Also
3328 @code{fork} calls are detected and correctly handled (double counting
3332 For profile-directed optimizations, compile the source files again with
3333 the same optimization and code generation options plus
3334 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
3335 Control Optimization}).
3338 For test coverage analysis, use @command{gcov} to produce human readable
3339 information from the @file{.gcno} and @file{.gcda} files. Refer to the
3340 @command{gcov} documentation for further information.
3344 With @option{-fprofile-arcs}, for each function of your program GCC
3345 creates a program flow graph, then finds a spanning tree for the graph.
3346 Only arcs that are not on the spanning tree have to be instrumented: the
3347 compiler adds code to count the number of times that these arcs are
3348 executed. When an arc is the only exit or only entrance to a block, the
3349 instrumentation code can be added to the block; otherwise, a new basic
3350 block must be created to hold the instrumentation code.
3352 @item -ftree-based-profiling
3353 @opindex ftree-based-profiling
3354 This option is used in addition to @option{-fprofile-arcs} or
3355 @option{-fbranch-probabilities} to control whether those optimizations
3356 are performed on a tree-based or rtl-based internal representation.
3357 If you use this option when compiling with @option{-fprofile-arcs},
3358 you must also use it when compiling later with @option{-fbranch-probabilities}.
3359 Currently the tree-based optimization is in an early stage of
3360 development, and this option is recommended only for those people
3361 working on improving it.
3364 @item -ftest-coverage
3365 @opindex ftest-coverage
3366 Produce a notes file that the @command{gcov} code-coverage utility
3367 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
3368 show program coverage. Each source file's note file is called
3369 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
3370 above for a description of @var{auxname} and instructions on how to
3371 generate test coverage data. Coverage data will match the source files
3372 more closely, if you do not optimize.
3374 @item -d@var{letters}
3375 @item -fdump-rtl-@var{pass}
3377 Says to make debugging dumps during compilation at times specified by
3378 @var{letters}. This is used for debugging the RTL-based passes of the
3379 compiler. The file names for most of the dumps are made by appending a
3380 pass number and a word to the @var{dumpname}. @var{dumpname} is generated
3381 from the name of the output file, if explicitly specified and it is not
3382 an executable, otherwise it is the basename of the source file.
3384 Most debug dumps can be enabled either passing a letter to the @option{-d}
3385 option, or with a long @option{-fdump-rtl} switch; here are the possible
3386 letters for use in @var{letters} and @var{pass}, and their meanings:
3391 Annotate the assembler output with miscellaneous debugging information.
3394 @itemx -fdump-rtl-bp
3396 @opindex fdump-rtl-bp
3397 Dump after computing branch probabilities, to @file{@var{file}.09.bp}.
3400 @itemx -fdump-rtl-bbro
3402 @opindex fdump-rtl-bbro
3403 Dump after block reordering, to @file{@var{file}.30.bbro}.
3406 @itemx -fdump-rtl-combine
3408 @opindex fdump-rtl-combine
3409 Dump after instruction combination, to the file @file{@var{file}.17.combine}.
3412 @itemx -fdump-rtl-ce1
3413 @itemx -fdump-rtl-ce2
3415 @opindex fdump-rtl-ce1
3416 @opindex fdump-rtl-ce2
3417 @option{-dC} and @option{-fdump-rtl-ce1} enable dumping after the
3418 first if conversion, to the file @file{@var{file}.11.ce1}. @option{-dC}
3419 and @option{-fdump-rtl-ce2} enable dumping after the second if
3420 conversion, to the file @file{@var{file}.18.ce2}.
3423 @itemx -fdump-rtl-btl
3424 @itemx -fdump-rtl-dbr
3426 @opindex fdump-rtl-btl
3427 @opindex fdump-rtl-dbr
3428 @option{-dd} and @option{-fdump-rtl-btl} enable dumping after branch
3429 target load optimization, to to @file{@var{file}.31.btl}. @option{-dd}
3430 and @option{-fdump-rtl-dbr} enable dumping after delayed branch
3431 scheduling, to @file{@var{file}.36.dbr}.
3435 Dump all macro definitions, at the end of preprocessing, in addition to
3439 @itemx -fdump-rtl-ce3
3441 @opindex fdump-rtl-ce3
3442 Dump after the third if conversion, to @file{@var{file}.28.ce3}.
3445 @itemx -fdump-rtl-cfg
3446 @itemx -fdump-rtl-life
3448 @opindex fdump-rtl-cfg
3449 @opindex fdump-rtl-life
3450 @option{-df} and @option{-fdump-rtl-cfg} enable dumping after control
3451 and data flow analysis, to @file{@var{file}.08.cfg}. @option{-df}
3452 and @option{-fdump-rtl-cfg} enable dumping dump after life analysis,
3453 to @file{@var{file}.16.life}.
3456 @itemx -fdump-rtl-greg
3458 @opindex fdump-rtl-greg
3459 Dump after global register allocation, to @file{@var{file}.23.greg}.
3462 @itemx -fdump-rtl-gcse
3463 @itemx -fdump-rtl-bypass
3465 @opindex fdump-rtl-gcse
3466 @opindex fdump-rtl-bypass
3467 @option{-dG} and @option{-fdump-rtl-gcse} enable dumping after GCSE, to
3468 @file{@var{file}.05.gcse}. @option{-dG} and @option{-fdump-rtl-bypass}
3469 enable dumping after jump bypassing and control flow optimizations, to
3470 @file{@var{file}.07.bypass}.
3473 @itemx -fdump-rtl-eh
3475 @opindex fdump-rtl-eh
3476 Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
3479 @itemx -fdump-rtl-sibling
3481 @opindex fdump-rtl-sibling
3482 Dump after sibling call optimizations, to @file{@var{file}.01.sibling}.
3485 @itemx -fdump-rtl-jump
3487 @opindex fdump-rtl-jump
3488 Dump after the first jump optimization, to @file{@var{file}.03.jump}.
3491 @itemx -fdump-rtl-stack
3493 @opindex fdump-rtl-stack
3494 Dump after conversion from registers to stack, to @file{@var{file}.33.stack}.
3497 @itemx -fdump-rtl-lreg
3499 @opindex fdump-rtl-lreg
3500 Dump after local register allocation, to @file{@var{file}.22.lreg}.
3503 @itemx -fdump-rtl-loop
3504 @itemx -fdump-rtl-loop2
3506 @opindex fdump-rtl-loop
3507 @opindex fdump-rtl-loop2
3508 @option{-dL} and @option{-fdump-rtl-loop} enable dumping after the first
3509 loop optimization pass, to @file{@var{file}.06.loop}. @option{-dL} and
3510 @option{-fdump-rtl-loop2} enable dumping after the second pass, to
3511 @file{@var{file}.13.loop2}.
3514 @itemx -fdump-rtl-sms
3516 @opindex fdump-rtl-sms
3517 Dump after modulo scheduling, to @file{@var{file}.20.sms}.
3520 @itemx -fdump-rtl-mach
3522 @opindex fdump-rtl-mach
3523 Dump after performing the machine dependent reorganization pass, to
3524 @file{@var{file}.35.mach}.
3527 @itemx -fdump-rtl-rnreg
3529 @opindex fdump-rtl-rnreg
3530 Dump after register renumbering, to @file{@var{file}.29.rnreg}.
3533 @itemx -fdump-rtl-regmove
3535 @opindex fdump-rtl-regmove
3536 Dump after the register move pass, to @file{@var{file}.19.regmove}.
3539 @itemx -fdump-rtl-postreload
3541 @opindex fdump-rtl-postreload
3542 Dump after post-reload optimizations, to @file{@var{file}.24.postreload}.
3545 @itemx -fdump-rtl-expand
3547 @opindex fdump-rtl-expand
3548 Dump after RTL generation, to @file{@var{file}.00.expand}.
3551 @itemx -fdump-rtl-sched2
3553 @opindex fdump-rtl-sched2
3554 Dump after the second scheduling pass, to @file{@var{file}.32.sched2}.
3557 @itemx -fdump-rtl-cse
3559 @opindex fdump-rtl-cse
3560 Dump after CSE (including the jump optimization that sometimes follows
3561 CSE), to @file{@var{file}.04.cse}.
3564 @itemx -fdump-rtl-sched
3566 @opindex fdump-rtl-sched
3567 Dump after the first scheduling pass, to @file{@var{file}.21.sched}.
3570 @itemx -fdump-rtl-cse2
3572 @opindex fdump-rtl-cse2
3573 Dump after the second CSE pass (including the jump optimization that
3574 sometimes follows CSE), to @file{@var{file}.15.cse2}.
3577 @itemx -fdump-rtl-tracer
3579 @opindex fdump-rtl-tracer
3580 Dump after running tracer, to @file{@var{file}.12.tracer}.
3583 @itemx -fdump-rtl-vpt
3584 @itemx -fdump-rtl-vartrack
3586 @opindex fdump-rtl-vpt
3587 @opindex fdump-rtl-vartrack
3588 @option{-dV} and @option{-fdump-rtl-vpt} enable dumping after the value
3589 profile transformations, to @file{@var{file}.10.vpt}. @option{-dV}
3590 and @option{-fdump-rtl-vartrack} enable dumping after variable tracking,
3591 to @file{@var{file}.34.vartrack}.
3594 @itemx -fdump-rtl-flow2
3596 @opindex fdump-rtl-flow2
3597 Dump after the second flow pass, to @file{@var{file}.26.flow2}.
3600 @itemx -fdump-rtl-peephole2
3602 @opindex fdump-rtl-peephole2
3603 Dump after the peephole pass, to @file{@var{file}.27.peephole2}.
3606 @itemx -fdump-rtl-web
3608 @opindex fdump-rtl-web
3609 Dump after live range splitting, to @file{@var{file}.14.web}.
3612 @itemx -fdump-rtl-all
3614 @opindex fdump-rtl-all
3615 Produce all the dumps listed above.
3619 Produce a core dump whenever an error occurs.
3623 Print statistics on memory usage, at the end of the run, to
3628 Annotate the assembler output with a comment indicating which
3629 pattern and alternative was used. The length of each instruction is
3634 Dump the RTL in the assembler output as a comment before each instruction.
3635 Also turns on @option{-dp} annotation.
3639 For each of the other indicated dump files (either with @option{-d} or
3640 @option{-fdump-rtl-@var{pass}}), dump a representation of the control flow
3641 graph suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
3645 Just generate RTL for a function instead of compiling it. Usually used
3646 with @samp{r} (@option{-fdump-rtl-expand}).
3650 Dump debugging information during parsing, to standard error.
3653 @item -fdump-unnumbered
3654 @opindex fdump-unnumbered
3655 When doing debugging dumps (see @option{-d} option above), suppress instruction
3656 numbers and line number note output. This makes it more feasible to
3657 use diff on debugging dumps for compiler invocations with different
3658 options, in particular with and without @option{-g}.
3660 @item -fdump-translation-unit @r{(C and C++ only)}
3661 @itemx -fdump-translation-unit-@var{options} @r{(C and C++ only)}
3662 @opindex fdump-translation-unit
3663 Dump a representation of the tree structure for the entire translation
3664 unit to a file. The file name is made by appending @file{.tu} to the
3665 source file name. If the @samp{-@var{options}} form is used, @var{options}
3666 controls the details of the dump as described for the
3667 @option{-fdump-tree} options.
3669 @item -fdump-class-hierarchy @r{(C++ only)}
3670 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
3671 @opindex fdump-class-hierarchy
3672 Dump a representation of each class's hierarchy and virtual function
3673 table layout to a file. The file name is made by appending @file{.class}
3674 to the source file name. If the @samp{-@var{options}} form is used,
3675 @var{options} controls the details of the dump as described for the
3676 @option{-fdump-tree} options.
3678 @item -fdump-ipa-@var{switch}
3680 Control the dumping at various stages of inter-procedural analysis
3681 language tree to a file. The file name is generated by appending a switch
3682 specific suffix to the source file name. The following dumps are possible:
3686 Enables all inter-procedural analysis dumps; currently the only produced
3687 dump is the @samp{cgraph} dump.
3690 Dumps information about call-graph optimization, unused function removal,
3691 and inlining decisions.
3694 @item -fdump-tree-@var{switch} @r{(C and C++ only)}
3695 @itemx -fdump-tree-@var{switch}-@var{options} @r{(C and C++ only)}
3697 Control the dumping at various stages of processing the intermediate
3698 language tree to a file. The file name is generated by appending a switch
3699 specific suffix to the source file name. If the @samp{-@var{options}}
3700 form is used, @var{options} is a list of @samp{-} separated options that
3701 control the details of the dump. Not all options are applicable to all
3702 dumps, those which are not meaningful will be ignored. The following
3703 options are available
3707 Print the address of each node. Usually this is not meaningful as it
3708 changes according to the environment and source file. Its primary use
3709 is for tying up a dump file with a debug environment.
3711 Inhibit dumping of members of a scope or body of a function merely
3712 because that scope has been reached. Only dump such items when they
3713 are directly reachable by some other path. When dumping pretty-printed
3714 trees, this option inhibits dumping the bodies of control structures.
3716 Print a raw representation of the tree. By default, trees are
3717 pretty-printed into a C-like representation.
3719 Enable more detailed dumps (not honored by every dump option).
3721 Enable dumping various statistics about the pass (not honored by every dump
3724 Enable showing basic block boundaries (disabled in raw dumps).
3726 Enable showing virtual operands for every statement.
3728 Enable showing line numbers for statements.
3730 Enable showing the unique ID (@code{DECL_UID}) for each variable.
3732 Turn on all options, except @option{raw}, @option{slim} and @option{lineno}.
3735 The following tree dumps are possible:
3739 Dump before any tree based optimization, to @file{@var{file}.original}.
3742 Dump after all tree based optimization, to @file{@var{file}.optimized}.
3745 Dump after function inlining, to @file{@var{file}.inlined}.
3748 @opindex fdump-tree-gimple
3749 Dump each function before and after the gimplification pass to a file. The
3750 file name is made by appending @file{.gimple} to the source file name.
3753 @opindex fdump-tree-cfg
3754 Dump the control flow graph of each function to a file. The file name is
3755 made by appending @file{.cfg} to the source file name.
3758 @opindex fdump-tree-vcg
3759 Dump the control flow graph of each function to a file in VCG format. The
3760 file name is made by appending @file{.vcg} to the source file name. Note
3761 that if the file contains more than one function, the generated file cannot
3762 be used directly by VCG. You will need to cut and paste each function's
3763 graph into its own separate file first.
3766 @opindex fdump-tree-ch
3767 Dump each function after copying loop headers. The file name is made by
3768 appending @file{.ch} to the source file name.
3771 @opindex fdump-tree-ssa
3772 Dump SSA related information to a file. The file name is made by appending
3773 @file{.ssa} to the source file name.
3776 @opindex fdump-tree-alias
3777 Dump aliasing information for each function. The file name is made by
3778 appending @file{.alias} to the source file name.
3781 @opindex fdump-tree-ccp
3782 Dump each function after CCP. The file name is made by appending
3783 @file{.ccp} to the source file name.
3786 @opindex fdump-tree-pre
3787 Dump trees after partial redundancy elimination. The file name is made
3788 by appending @file{.pre} to the source file name.
3791 @opindex fdump-tree-fre
3792 Dump trees after full redundancy elimination. The file name is made
3793 by appending @file{.fre} to the source file name.
3796 @opindex fdump-tree-dce
3797 Dump each function after dead code elimination. The file name is made by
3798 appending @file{.dce} to the source file name.
3801 @opindex fdump-tree-mudflap
3802 Dump each function after adding mudflap instrumentation. The file name is
3803 made by appending @file{.mudflap} to the source file name.
3806 @opindex fdump-tree-sra
3807 Dump each function after performing scalar replacement of aggregates. The
3808 file name is made by appending @file{.sra} to the source file name.
3811 @opindex fdump-tree-dom
3812 Dump each function after applying dominator tree optimizations. The file
3813 name is made by appending @file{.dom} to the source file name.
3816 @opindex fdump-tree-dse
3817 Dump each function after applying dead store elimination. The file
3818 name is made by appending @file{.dse} to the source file name.
3821 @opindex fdump-tree-phiopt
3822 Dump each function after optimizing PHI nodes into straightline code. The file
3823 name is made by appending @file{.phiopt} to the source file name.
3826 @opindex fdump-tree-forwprop
3827 Dump each function after forward propagating single use variables. The file
3828 name is made by appending @file{.forwprop} to the source file name.
3831 @opindex fdump-tree-copyrename
3832 Dump each function after applying the copy rename optimization. The file
3833 name is made by appending @file{.copyrename} to the source file name.
3836 @opindex fdump-tree-nrv
3837 Dump each function after applying the named return value optimization on
3838 generic trees. The file name is made by appending @file{.nrv} to the source
3842 @opindex fdump-tree-vect
3843 Dump each function after applying vectorization of loops. The file name is
3844 made by appending @file{.vect} to the source file name.
3847 @opindex fdump-tree-all
3848 Enable all the available tree dumps with the flags provided in this option.
3851 @item -frandom-seed=@var{string}
3852 @opindex frandom-string
3853 This option provides a seed that GCC uses when it would otherwise use
3854 random numbers. It is used to generate certain symbol names
3855 that have to be different in every compiled file. It is also used to
3856 place unique stamps in coverage data files and the object files that
3857 produce them. You can use the @option{-frandom-seed} option to produce
3858 reproducibly identical object files.
3860 The @var{string} should be different for every file you compile.
3862 @item -fsched-verbose=@var{n}
3863 @opindex fsched-verbose
3864 On targets that use instruction scheduling, this option controls the
3865 amount of debugging output the scheduler prints. This information is
3866 written to standard error, unless @option{-dS} or @option{-dR} is
3867 specified, in which case it is output to the usual dump
3868 listing file, @file{.sched} or @file{.sched2} respectively. However
3869 for @var{n} greater than nine, the output is always printed to standard
3872 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
3873 same information as @option{-dRS}. For @var{n} greater than one, it
3874 also output basic block probabilities, detailed ready list information
3875 and unit/insn info. For @var{n} greater than two, it includes RTL
3876 at abort point, control-flow and regions info. And for @var{n} over
3877 four, @option{-fsched-verbose} also includes dependence info.
3881 Store the usual ``temporary'' intermediate files permanently; place them
3882 in the current directory and name them based on the source file. Thus,
3883 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
3884 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
3885 preprocessed @file{foo.i} output file even though the compiler now
3886 normally uses an integrated preprocessor.
3890 Report the CPU time taken by each subprocess in the compilation
3891 sequence. For C source files, this is the compiler proper and assembler
3892 (plus the linker if linking is done). The output looks like this:
3899 The first number on each line is the ``user time,'' that is time spent
3900 executing the program itself. The second number is ``system time,''
3901 time spent executing operating system routines on behalf of the program.
3902 Both numbers are in seconds.
3904 @item -fvar-tracking
3905 @opindex fvar-tracking
3906 Run variable tracking pass. It computes where variables are stored at each
3907 position in code. Better debugging information is then generated
3908 (if the debugging information format supports this information).
3910 It is enabled by default when compiling with optimization (@option{-Os},
3911 @option{-O}, @option{-O2}, ...), debugging information (@option{-g}) and
3912 the debug info format supports it.
3914 @item -print-file-name=@var{library}
3915 @opindex print-file-name
3916 Print the full absolute name of the library file @var{library} that
3917 would be used when linking---and don't do anything else. With this
3918 option, GCC does not compile or link anything; it just prints the
3921 @item -print-multi-directory
3922 @opindex print-multi-directory
3923 Print the directory name corresponding to the multilib selected by any
3924 other switches present in the command line. This directory is supposed
3925 to exist in @env{GCC_EXEC_PREFIX}.
3927 @item -print-multi-lib
3928 @opindex print-multi-lib
3929 Print the mapping from multilib directory names to compiler switches
3930 that enable them. The directory name is separated from the switches by
3931 @samp{;}, and each switch starts with an @samp{@@} instead of the
3932 @samp{-}, without spaces between multiple switches. This is supposed to
3933 ease shell-processing.
3935 @item -print-prog-name=@var{program}
3936 @opindex print-prog-name
3937 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
3939 @item -print-libgcc-file-name
3940 @opindex print-libgcc-file-name
3941 Same as @option{-print-file-name=libgcc.a}.
3943 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
3944 but you do want to link with @file{libgcc.a}. You can do
3947 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
3950 @item -print-search-dirs
3951 @opindex print-search-dirs
3952 Print the name of the configured installation directory and a list of
3953 program and library directories @command{gcc} will search---and don't do anything else.
3955 This is useful when @command{gcc} prints the error message
3956 @samp{installation problem, cannot exec cpp0: No such file or directory}.
3957 To resolve this you either need to put @file{cpp0} and the other compiler
3958 components where @command{gcc} expects to find them, or you can set the environment
3959 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
3960 Don't forget the trailing '/'.
3961 @xref{Environment Variables}.
3964 @opindex dumpmachine
3965 Print the compiler's target machine (for example,
3966 @samp{i686-pc-linux-gnu})---and don't do anything else.
3969 @opindex dumpversion
3970 Print the compiler version (for example, @samp{3.0})---and don't do
3975 Print the compiler's built-in specs---and don't do anything else. (This
3976 is used when GCC itself is being built.) @xref{Spec Files}.
3978 @item -feliminate-unused-debug-types
3979 @opindex feliminate-unused-debug-types
3980 Normally, when producing DWARF2 output, GCC will emit debugging
3981 information for all types declared in a compilation
3982 unit, regardless of whether or not they are actually used
3983 in that compilation unit. Sometimes this is useful, such as
3984 if, in the debugger, you want to cast a value to a type that is
3985 not actually used in your program (but is declared). More often,
3986 however, this results in a significant amount of wasted space.
3987 With this option, GCC will avoid producing debug symbol output
3988 for types that are nowhere used in the source file being compiled.
3991 @node Optimize Options
3992 @section Options That Control Optimization
3993 @cindex optimize options
3994 @cindex options, optimization
3996 These options control various sorts of optimizations.
3998 Without any optimization option, the compiler's goal is to reduce the
3999 cost of compilation and to make debugging produce the expected
4000 results. Statements are independent: if you stop the program with a
4001 breakpoint between statements, you can then assign a new value to any
4002 variable or change the program counter to any other statement in the
4003 function and get exactly the results you would expect from the source
4006 Turning on optimization flags makes the compiler attempt to improve
4007 the performance and/or code size at the expense of compilation time
4008 and possibly the ability to debug the program.
4010 The compiler performs optimization based on the knowledge it has of
4011 the program. Optimization levels @option{-O2} and above, in
4012 particular, enable @emph{unit-at-a-time} mode, which allows the
4013 compiler to consider information gained from later functions in
4014 the file when compiling a function. Compiling multiple files at
4015 once to a single output file in @emph{unit-at-a-time} mode allows
4016 the compiler to use information gained from all of the files when
4017 compiling each of them.
4019 Not all optimizations are controlled directly by a flag. Only
4020 optimizations that have a flag are listed.
4027 Optimize. Optimizing compilation takes somewhat more time, and a lot
4028 more memory for a large function.
4030 With @option{-O}, the compiler tries to reduce code size and execution
4031 time, without performing any optimizations that take a great deal of
4034 @option{-O} turns on the following optimization flags:
4035 @gccoptlist{-fdefer-pop @gol
4036 -fmerge-constants @gol
4038 -floop-optimize @gol
4039 -fif-conversion @gol
4040 -fif-conversion2 @gol
4041 -fdelayed-branch @gol
4042 -fguess-branch-probability @gol
4045 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
4046 where doing so does not interfere with debugging.
4050 Optimize even more. GCC performs nearly all supported optimizations
4051 that do not involve a space-speed tradeoff. The compiler does not
4052 perform loop unrolling or function inlining when you specify @option{-O2}.
4053 As compared to @option{-O}, this option increases both compilation time
4054 and the performance of the generated code.
4056 @option{-O2} turns on all optimization flags specified by @option{-O}. It
4057 also turns on the following optimization flags:
4058 @gccoptlist{-fforce-mem @gol
4059 -foptimize-sibling-calls @gol
4060 -fstrength-reduce @gol
4061 -fcse-follow-jumps -fcse-skip-blocks @gol
4062 -frerun-cse-after-loop -frerun-loop-opt @gol
4063 -fgcse -fgcse-lm -fgcse-sm -fgcse-las @gol
4064 -fdelete-null-pointer-checks @gol
4065 -fexpensive-optimizations @gol
4067 -fschedule-insns -fschedule-insns2 @gol
4068 -fsched-interblock -fsched-spec @gol
4071 -freorder-blocks -freorder-functions @gol
4072 -fstrict-aliasing @gol
4073 -funit-at-a-time @gol
4074 -falign-functions -falign-jumps @gol
4075 -falign-loops -falign-labels @gol
4078 Please note the warning under @option{-fgcse} about
4079 invoking @option{-O2} on programs that use computed gotos.
4083 Optimize yet more. @option{-O3} turns on all optimizations specified by
4084 @option{-O2} and also turns on the @option{-finline-functions},
4085 @option{-fweb} and @option{-fgcse-after-reload} options.
4089 Do not optimize. This is the default.
4093 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
4094 do not typically increase code size. It also performs further
4095 optimizations designed to reduce code size.
4097 @option{-Os} disables the following optimization flags:
4098 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
4099 -falign-labels -freorder-blocks -freorder-blocks-and-partition -fprefetch-loop-arrays}
4101 If you use multiple @option{-O} options, with or without level numbers,
4102 the last such option is the one that is effective.
4105 Options of the form @option{-f@var{flag}} specify machine-independent
4106 flags. Most flags have both positive and negative forms; the negative
4107 form of @option{-ffoo} would be @option{-fno-foo}. In the table
4108 below, only one of the forms is listed---the one you typically will
4109 use. You can figure out the other form by either removing @samp{no-}
4112 The following options control specific optimizations. They are either
4113 activated by @option{-O} options or are related to ones that are. You
4114 can use the following flags in the rare cases when ``fine-tuning'' of
4115 optimizations to be performed is desired.
4118 @item -fno-default-inline
4119 @opindex fno-default-inline
4120 Do not make member functions inline by default merely because they are
4121 defined inside the class scope (C++ only). Otherwise, when you specify
4122 @w{@option{-O}}, member functions defined inside class scope are compiled
4123 inline by default; i.e., you don't need to add @samp{inline} in front of
4124 the member function name.
4126 @item -fno-defer-pop
4127 @opindex fno-defer-pop
4128 Always pop the arguments to each function call as soon as that function
4129 returns. For machines which must pop arguments after a function call,
4130 the compiler normally lets arguments accumulate on the stack for several
4131 function calls and pops them all at once.
4133 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4137 Force memory operands to be copied into registers before doing
4138 arithmetic on them. This produces better code by making all memory
4139 references potential common subexpressions. When they are not common
4140 subexpressions, instruction combination should eliminate the separate
4143 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4146 @opindex fforce-addr
4147 Force memory address constants to be copied into registers before
4148 doing arithmetic on them. This may produce better code just as
4149 @option{-fforce-mem} may.
4151 @item -fomit-frame-pointer
4152 @opindex fomit-frame-pointer
4153 Don't keep the frame pointer in a register for functions that
4154 don't need one. This avoids the instructions to save, set up and
4155 restore frame pointers; it also makes an extra register available
4156 in many functions. @strong{It also makes debugging impossible on
4159 On some machines, such as the VAX, this flag has no effect, because
4160 the standard calling sequence automatically handles the frame pointer
4161 and nothing is saved by pretending it doesn't exist. The
4162 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
4163 whether a target machine supports this flag. @xref{Registers,,Register
4164 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
4166 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4168 @item -foptimize-sibling-calls
4169 @opindex foptimize-sibling-calls
4170 Optimize sibling and tail recursive calls.
4172 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4176 Don't pay attention to the @code{inline} keyword. Normally this option
4177 is used to keep the compiler from expanding any functions inline.
4178 Note that if you are not optimizing, no functions can be expanded inline.
4180 @item -finline-functions
4181 @opindex finline-functions
4182 Integrate all simple functions into their callers. The compiler
4183 heuristically decides which functions are simple enough to be worth
4184 integrating in this way.
4186 If all calls to a given function are integrated, and the function is
4187 declared @code{static}, then the function is normally not output as
4188 assembler code in its own right.
4190 Enabled at level @option{-O3}.
4192 @item -finline-limit=@var{n}
4193 @opindex finline-limit
4194 By default, GCC limits the size of functions that can be inlined. This flag
4195 allows the control of this limit for functions that are explicitly marked as
4196 inline (i.e., marked with the inline keyword or defined within the class
4197 definition in c++). @var{n} is the size of functions that can be inlined in
4198 number of pseudo instructions (not counting parameter handling). The default
4199 value of @var{n} is 600.
4200 Increasing this value can result in more inlined code at
4201 the cost of compilation time and memory consumption. Decreasing usually makes
4202 the compilation faster and less code will be inlined (which presumably
4203 means slower programs). This option is particularly useful for programs that
4204 use inlining heavily such as those based on recursive templates with C++.
4206 Inlining is actually controlled by a number of parameters, which may be
4207 specified individually by using @option{--param @var{name}=@var{value}}.
4208 The @option{-finline-limit=@var{n}} option sets some of these parameters
4212 @item max-inline-insns-single
4213 is set to @var{n}/2.
4214 @item max-inline-insns-auto
4215 is set to @var{n}/2.
4216 @item min-inline-insns
4217 is set to 130 or @var{n}/4, whichever is smaller.
4218 @item max-inline-insns-rtl
4222 See below for a documentation of the individual
4223 parameters controlling inlining.
4225 @emph{Note:} pseudo instruction represents, in this particular context, an
4226 abstract measurement of function's size. In no way, it represents a count
4227 of assembly instructions and as such its exact meaning might change from one
4228 release to an another.
4230 @item -fkeep-inline-functions
4231 @opindex fkeep-inline-functions
4232 In C, emit @code{static} functions that are declared @code{inline}
4233 into the object file, even if the function has been inlined into all
4234 of its callers. This switch does not affect functions using the
4235 @code{extern inline} extension in GNU C. In C++, emit any and all
4236 inline functions into the object file.
4238 @item -fkeep-static-consts
4239 @opindex fkeep-static-consts
4240 Emit variables declared @code{static const} when optimization isn't turned
4241 on, even if the variables aren't referenced.
4243 GCC enables this option by default. If you want to force the compiler to
4244 check if the variable was referenced, regardless of whether or not
4245 optimization is turned on, use the @option{-fno-keep-static-consts} option.
4247 @item -fmerge-constants
4248 Attempt to merge identical constants (string constants and floating point
4249 constants) across compilation units.
4251 This option is the default for optimized compilation if the assembler and
4252 linker support it. Use @option{-fno-merge-constants} to inhibit this
4255 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4257 @item -fmerge-all-constants
4258 Attempt to merge identical constants and identical variables.
4260 This option implies @option{-fmerge-constants}. In addition to
4261 @option{-fmerge-constants} this considers e.g.@: even constant initialized
4262 arrays or initialized constant variables with integral or floating point
4263 types. Languages like C or C++ require each non-automatic variable to
4264 have distinct location, so using this option will result in non-conforming
4267 @item -fmodulo-sched
4268 @opindex fmodulo-sched
4269 Perform swing modulo scheduling immediately before the first scheduling
4270 pass. This pass looks at innermost loops and reorders their
4271 instructions by overlapping different iterations.
4275 Use a graph coloring register allocator. Currently this option is meant
4276 only for testing. Users should not specify this option, since it is not
4277 yet ready for production use.
4279 @item -fno-branch-count-reg
4280 @opindex fno-branch-count-reg
4281 Do not use ``decrement and branch'' instructions on a count register,
4282 but instead generate a sequence of instructions that decrement a
4283 register, compare it against zero, then branch based upon the result.
4284 This option is only meaningful on architectures that support such
4285 instructions, which include x86, PowerPC, IA-64 and S/390.
4287 The default is @option{-fbranch-count-reg}, enabled when
4288 @option{-fstrength-reduce} is enabled.
4290 @item -fno-function-cse
4291 @opindex fno-function-cse
4292 Do not put function addresses in registers; make each instruction that
4293 calls a constant function contain the function's address explicitly.
4295 This option results in less efficient code, but some strange hacks
4296 that alter the assembler output may be confused by the optimizations
4297 performed when this option is not used.
4299 The default is @option{-ffunction-cse}
4301 @item -fno-zero-initialized-in-bss
4302 @opindex fno-zero-initialized-in-bss
4303 If the target supports a BSS section, GCC by default puts variables that
4304 are initialized to zero into BSS@. This can save space in the resulting
4307 This option turns off this behavior because some programs explicitly
4308 rely on variables going to the data section. E.g., so that the
4309 resulting executable can find the beginning of that section and/or make
4310 assumptions based on that.
4312 The default is @option{-fzero-initialized-in-bss}.
4314 @item -fbounds-check
4315 @opindex fbounds-check
4316 For front-ends that support it, generate additional code to check that
4317 indices used to access arrays are within the declared range. This is
4318 currently only supported by the Java and Fortran front-ends, where
4319 this option defaults to true and false respectively.
4321 @item -fmudflap -fmudflapth -fmudflapir
4325 @cindex bounds checking
4327 For front-ends that support it (C and C++), instrument all risky
4328 pointer/array dereferencing operations, some standard library
4329 string/heap functions, and some other associated constructs with
4330 range/validity tests. Modules so instrumented should be immune to
4331 buffer overflows, invalid heap use, and some other classes of C/C++
4332 programming errors. The instrumentation relies on a separate runtime
4333 library (@file{libmudflap}), which will be linked into a program if
4334 @option{-fmudflap} is given at link time. Run-time behavior of the
4335 instrumented program is controlled by the @env{MUDFLAP_OPTIONS}
4336 environment variable. See @code{env MUDFLAP_OPTIONS=-help a.out}
4339 Use @option{-fmudflapth} instead of @option{-fmudflap} to compile and to
4340 link if your program is multi-threaded. Use @option{-fmudflapir}, in
4341 addition to @option{-fmudflap} or @option{-fmudflapth}, if
4342 instrumentation should ignore pointer reads. This produces less
4343 instrumentation (and therefore faster execution) and still provides
4344 some protection against outright memory corrupting writes, but allows
4345 erroneously read data to propagate within a program.
4347 @item -fstrength-reduce
4348 @opindex fstrength-reduce
4349 Perform the optimizations of loop strength reduction and
4350 elimination of iteration variables.
4352 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4354 @item -fthread-jumps
4355 @opindex fthread-jumps
4356 Perform optimizations where we check to see if a jump branches to a
4357 location where another comparison subsumed by the first is found. If
4358 so, the first branch is redirected to either the destination of the
4359 second branch or a point immediately following it, depending on whether
4360 the condition is known to be true or false.
4362 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4364 @item -fcse-follow-jumps
4365 @opindex fcse-follow-jumps
4366 In common subexpression elimination, scan through jump instructions
4367 when the target of the jump is not reached by any other path. For
4368 example, when CSE encounters an @code{if} statement with an
4369 @code{else} clause, CSE will follow the jump when the condition
4372 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4374 @item -fcse-skip-blocks
4375 @opindex fcse-skip-blocks
4376 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
4377 follow jumps which conditionally skip over blocks. When CSE
4378 encounters a simple @code{if} statement with no else clause,
4379 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
4380 body of the @code{if}.
4382 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4384 @item -frerun-cse-after-loop
4385 @opindex frerun-cse-after-loop
4386 Re-run common subexpression elimination after loop optimizations has been
4389 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4391 @item -frerun-loop-opt
4392 @opindex frerun-loop-opt
4393 Run the loop optimizer twice.
4395 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4399 Perform a global common subexpression elimination pass.
4400 This pass also performs global constant and copy propagation.
4402 @emph{Note:} When compiling a program using computed gotos, a GCC
4403 extension, you may get better runtime performance if you disable
4404 the global common subexpression elimination pass by adding
4405 @option{-fno-gcse} to the command line.
4407 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4411 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
4412 attempt to move loads which are only killed by stores into themselves. This
4413 allows a loop containing a load/store sequence to be changed to a load outside
4414 the loop, and a copy/store within the loop.
4416 Enabled by default when gcse is enabled.
4420 When @option{-fgcse-sm} is enabled, a store motion pass is run after
4421 global common subexpression elimination. This pass will attempt to move
4422 stores out of loops. When used in conjunction with @option{-fgcse-lm},
4423 loops containing a load/store sequence can be changed to a load before
4424 the loop and a store after the loop.
4426 Enabled by default when gcse is enabled.
4430 When @option{-fgcse-las} is enabled, the global common subexpression
4431 elimination pass eliminates redundant loads that come after stores to the
4432 same memory location (both partial and full redundancies).
4434 Enabled by default when gcse is enabled.
4436 @item -fgcse-after-reload
4437 @opindex fgcse-after-reload
4438 When @option{-fgcse-after-reload} is enabled, a redundant load elimination
4439 pass is performed after reload. The purpose of this pass is to cleanup
4442 @item -floop-optimize
4443 @opindex floop-optimize
4444 Perform loop optimizations: move constant expressions out of loops, simplify
4445 exit test conditions and optionally do strength-reduction as well.
4447 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4449 @item -floop-optimize2
4450 @opindex floop-optimize2
4451 Perform loop optimizations using the new loop optimizer. The optimizations
4452 (loop unrolling, peeling and unswitching, loop invariant motion) are enabled
4455 @item -fcrossjumping
4456 @opindex crossjumping
4457 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
4458 resulting code may or may not perform better than without cross-jumping.
4460 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4462 @item -fif-conversion
4463 @opindex if-conversion
4464 Attempt to transform conditional jumps into branch-less equivalents. This
4465 include use of conditional moves, min, max, set flags and abs instructions, and
4466 some tricks doable by standard arithmetics. The use of conditional execution
4467 on chips where it is available is controlled by @code{if-conversion2}.
4469 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4471 @item -fif-conversion2
4472 @opindex if-conversion2
4473 Use conditional execution (where available) to transform conditional jumps into
4474 branch-less equivalents.
4476 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4478 @item -fdelete-null-pointer-checks
4479 @opindex fdelete-null-pointer-checks
4480 Use global dataflow analysis to identify and eliminate useless checks
4481 for null pointers. The compiler assumes that dereferencing a null
4482 pointer would have halted the program. If a pointer is checked after
4483 it has already been dereferenced, it cannot be null.
4485 In some environments, this assumption is not true, and programs can
4486 safely dereference null pointers. Use
4487 @option{-fno-delete-null-pointer-checks} to disable this optimization
4488 for programs which depend on that behavior.
4490 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4492 @item -fexpensive-optimizations
4493 @opindex fexpensive-optimizations
4494 Perform a number of minor optimizations that are relatively expensive.
4496 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4498 @item -foptimize-register-move
4500 @opindex foptimize-register-move
4502 Attempt to reassign register numbers in move instructions and as
4503 operands of other simple instructions in order to maximize the amount of
4504 register tying. This is especially helpful on machines with two-operand
4507 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
4510 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4512 @item -fdelayed-branch
4513 @opindex fdelayed-branch
4514 If supported for the target machine, attempt to reorder instructions
4515 to exploit instruction slots available after delayed branch
4518 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4520 @item -fschedule-insns
4521 @opindex fschedule-insns
4522 If supported for the target machine, attempt to reorder instructions to
4523 eliminate execution stalls due to required data being unavailable. This
4524 helps machines that have slow floating point or memory load instructions
4525 by allowing other instructions to be issued until the result of the load
4526 or floating point instruction is required.
4528 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4530 @item -fschedule-insns2
4531 @opindex fschedule-insns2
4532 Similar to @option{-fschedule-insns}, but requests an additional pass of
4533 instruction scheduling after register allocation has been done. This is
4534 especially useful on machines with a relatively small number of
4535 registers and where memory load instructions take more than one cycle.
4537 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4539 @item -fno-sched-interblock
4540 @opindex fno-sched-interblock
4541 Don't schedule instructions across basic blocks. This is normally
4542 enabled by default when scheduling before register allocation, i.e.@:
4543 with @option{-fschedule-insns} or at @option{-O2} or higher.
4545 @item -fno-sched-spec
4546 @opindex fno-sched-spec
4547 Don't allow speculative motion of non-load instructions. This is normally
4548 enabled by default when scheduling before register allocation, i.e.@:
4549 with @option{-fschedule-insns} or at @option{-O2} or higher.
4551 @item -fsched-spec-load
4552 @opindex fsched-spec-load
4553 Allow speculative motion of some load instructions. This only makes
4554 sense when scheduling before register allocation, i.e.@: with
4555 @option{-fschedule-insns} or at @option{-O2} or higher.
4557 @item -fsched-spec-load-dangerous
4558 @opindex fsched-spec-load-dangerous
4559 Allow speculative motion of more load instructions. This only makes
4560 sense when scheduling before register allocation, i.e.@: with
4561 @option{-fschedule-insns} or at @option{-O2} or higher.
4563 @item -fsched-stalled-insns=@var{n}
4564 @opindex fsched-stalled-insns
4565 Define how many insns (if any) can be moved prematurely from the queue
4566 of stalled insns into the ready list, during the second scheduling pass.
4568 @item -fsched-stalled-insns-dep=@var{n}
4569 @opindex fsched-stalled-insns-dep
4570 Define how many insn groups (cycles) will be examined for a dependency
4571 on a stalled insn that is candidate for premature removal from the queue
4572 of stalled insns. Has an effect only during the second scheduling pass,
4573 and only if @option{-fsched-stalled-insns} is used and its value is not zero.
4575 @item -fsched2-use-superblocks
4576 @opindex fsched2-use-superblocks
4577 When scheduling after register allocation, do use superblock scheduling
4578 algorithm. Superblock scheduling allows motion across basic block boundaries
4579 resulting on faster schedules. This option is experimental, as not all machine
4580 descriptions used by GCC model the CPU closely enough to avoid unreliable
4581 results from the algorithm.
4583 This only makes sense when scheduling after register allocation, i.e.@: with
4584 @option{-fschedule-insns2} or at @option{-O2} or higher.
4586 @item -fsched2-use-traces
4587 @opindex fsched2-use-traces
4588 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
4589 allocation and additionally perform code duplication in order to increase the
4590 size of superblocks using tracer pass. See @option{-ftracer} for details on
4593 This mode should produce faster but significantly longer programs. Also
4594 without @option{-fbranch-probabilities} the traces constructed may not
4595 match the reality and hurt the performance. This only makes
4596 sense when scheduling after register allocation, i.e.@: with
4597 @option{-fschedule-insns2} or at @option{-O2} or higher.
4599 @item -freschedule-modulo-scheduled-loops
4600 @opindex fscheduling-in-modulo-scheduled-loops
4601 The modulo scheduling comes before the traditional scheduling, if a loop was modulo scheduled
4602 we may want to prevent the later scheduling passes from changing its schedule, we use this
4603 option to control that.
4605 @item -fcaller-saves
4606 @opindex fcaller-saves
4607 Enable values to be allocated in registers that will be clobbered by
4608 function calls, by emitting extra instructions to save and restore the
4609 registers around such calls. Such allocation is done only when it
4610 seems to result in better code than would otherwise be produced.
4612 This option is always enabled by default on certain machines, usually
4613 those which have no call-preserved registers to use instead.
4615 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4618 Perform Partial Redundancy Elimination (PRE) on trees. This flag is
4619 enabled by default at @option{-O} and higher.
4622 Perform Full Redundancy Elimination (FRE) on trees. The difference
4623 between FRE and PRE is that FRE only considers expressions
4624 that are computed on all paths leading to the redundant computation.
4625 This analysis faster than PRE, though it exposes fewer redundancies.
4626 This flag is enabled by default at @option{-O} and higher.
4629 Perform sparse conditional constant propagation (CCP) on trees. This flag
4630 is enabled by default at @option{-O} and higher.
4633 Perform dead code elimination (DCE) on trees. This flag is enabled by
4634 default at @option{-O} and higher.
4636 @item -ftree-dominator-opts
4637 Perform dead code elimination (DCE) on trees. This flag is enabled by
4638 default at @option{-O} and higher.
4641 Perform loop header copying on trees. This is beneficial since it increases
4642 effectiveness of code motion optimizations. It also saves one jump. This flag
4643 is enabled by default at @option{-O} and higher. It is not enabled
4644 for @option{-Os}, since it usually increases code size.
4646 @item -ftree-loop-optimize
4647 Perform loop optimizations on trees. This flag is enabled by default
4648 at @option{-O} and higher.
4650 @item -ftree-loop-linear
4651 Perform linear loop transformations on tree. This flag can improve cache
4652 performance and allow further loop optimizations to take place.
4655 Perform loop invariant motion on trees. This pass moves only invartiants that
4656 would be hard to handle on rtl level (function calls, operations that expand to
4657 nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
4658 operands of conditions that are invariant out of the loop, so that we can use
4659 just trivial invariantness analysis in loop unswitching. The pass also includes
4663 Create a canonical counter for number of iterations in the loop for that
4664 determining number of iterations requires complicated analysis. Later
4665 optimizations then may determine the number easily. Useful especially
4666 in connection with unrolling.
4669 Perform induction variable optimizations (strength reduction, induction
4670 variable merging and induction variable elimination) on trees.
4673 Perform scalar replacement of aggregates. This pass replaces structure
4674 references with scalars to prevent committing structures to memory too
4675 early. This flag is enabled by default at @option{-O} and higher.
4677 @item -ftree-copyrename
4678 Perform copy renaming on trees. This pass attempts to rename compiler
4679 temporaries to other variables at copy locations, usually resulting in
4680 variable names which more closely resemble the original variables. This flag
4681 is enabled by default at @option{-O} and higher.
4684 Perform temporary expression replacement during the SSA->normal phase. Single
4685 use/single def temporaries are replaced at their use location with their
4686 defining expression. This results in non-GIMPLE code, but gives the expanders
4687 much more complex trees to work on resulting in better RTL generation. This is
4688 enabled by default at @option{-O} and higher.
4691 Perform live range splitting during the SSA->normal phase. Distinct live
4692 ranges of a variable are split into unique variables, allowing for better
4693 optimization later. This is enabled by default at @option{-O} and higher.
4695 @item -ftree-vectorize
4696 Perform loop vectorization on trees.
4700 Perform tail duplication to enlarge superblock size. This transformation
4701 simplifies the control flow of the function allowing other optimizations to do
4704 @item -funroll-loops
4705 @opindex funroll-loops
4706 Unroll loops whose number of iterations can be determined at compile
4707 time or upon entry to the loop. @option{-funroll-loops} implies both
4708 @option{-fstrength-reduce} and @option{-frerun-cse-after-loop}. This
4709 option makes code larger, and may or may not make it run faster.
4711 @item -funroll-all-loops
4712 @opindex funroll-all-loops
4713 Unroll all loops, even if their number of iterations is uncertain when
4714 the loop is entered. This usually makes programs run more slowly.
4715 @option{-funroll-all-loops} implies the same options as
4716 @option{-funroll-loops},
4718 @item -fsplit-ivs-in-unroller
4719 @opindex -fsplit-ivs-in-unroller
4720 Enables expressing of values of induction variables in later iterations
4721 of the unrolled loop using the value in the first iteration. This breaks
4722 long dependency chains, thus improving efficiency of the scheduling passes
4723 (for best results, @option{-fweb} should be used as well).
4725 Combination of @option{-fweb} and CSE is often sufficient to obtain the
4726 same effect. However in cases the loop body is more complicated than
4727 a single basic block, this is not reliable. It also does not work at all
4728 on some of the architectures due to restrictions in the CSE pass.
4730 This optimization is enabled by default.
4732 @item -fvariable-expansion-in-unroller
4733 @opindex -fvariable-expansion-in-unroller
4734 With this option, the compiler will create multiple copies of some
4735 local variables when unrolling a loop which can result in superior code.
4737 @item -fprefetch-loop-arrays
4738 @opindex fprefetch-loop-arrays
4739 If supported by the target machine, generate instructions to prefetch
4740 memory to improve the performance of loops that access large arrays.
4742 These options may generate better or worse code; results are highly
4743 dependent on the structure of loops within the source code.
4746 @itemx -fno-peephole2
4747 @opindex fno-peephole
4748 @opindex fno-peephole2
4749 Disable any machine-specific peephole optimizations. The difference
4750 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
4751 are implemented in the compiler; some targets use one, some use the
4752 other, a few use both.
4754 @option{-fpeephole} is enabled by default.
4755 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4757 @item -fno-guess-branch-probability
4758 @opindex fno-guess-branch-probability
4759 Do not guess branch probabilities using a randomized model.
4761 Sometimes GCC will opt to use a randomized model to guess branch
4762 probabilities, when none are available from either profiling feedback
4763 (@option{-fprofile-arcs}) or @samp{__builtin_expect}. This means that
4764 different runs of the compiler on the same program may produce different
4767 In a hard real-time system, people don't want different runs of the
4768 compiler to produce code that has different behavior; minimizing
4769 non-determinism is of paramount import. This switch allows users to
4770 reduce non-determinism, possibly at the expense of inferior
4773 The default is @option{-fguess-branch-probability} at levels
4774 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4776 @item -freorder-blocks
4777 @opindex freorder-blocks
4778 Reorder basic blocks in the compiled function in order to reduce number of
4779 taken branches and improve code locality.
4781 Enabled at levels @option{-O2}, @option{-O3}.
4783 @item -freorder-blocks-and-partition
4784 @opindex freorder-blocks-and-partition
4785 In addition to reordering basic blocks in the compiled function, in order
4786 to reduce number of taken branches, partitions hot and cold basic blocks
4787 into separate sections of the assembly and .o files, to improve
4788 paging and cache locality performance.
4790 This optimization is automatically turned off in the presence of
4791 exception handling, for linkonce sections, for functions with a user-defined
4792 section attribute and on any architecture that does not support named
4795 @item -freorder-functions
4796 @opindex freorder-functions
4797 Reorder basic blocks in the compiled function in order to reduce number of
4798 taken branches and improve code locality. This is implemented by using special
4799 subsections @code{.text.hot} for most frequently executed functions and
4800 @code{.text.unlikely} for unlikely executed functions. Reordering is done by
4801 the linker so object file format must support named sections and linker must
4802 place them in a reasonable way.
4804 Also profile feedback must be available in to make this option effective. See
4805 @option{-fprofile-arcs} for details.
4807 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4809 @item -fstrict-aliasing
4810 @opindex fstrict-aliasing
4811 Allows the compiler to assume the strictest aliasing rules applicable to
4812 the language being compiled. For C (and C++), this activates
4813 optimizations based on the type of expressions. In particular, an
4814 object of one type is assumed never to reside at the same address as an
4815 object of a different type, unless the types are almost the same. For
4816 example, an @code{unsigned int} can alias an @code{int}, but not a
4817 @code{void*} or a @code{double}. A character type may alias any other
4820 Pay special attention to code like this:
4833 The practice of reading from a different union member than the one most
4834 recently written to (called ``type-punning'') is common. Even with
4835 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
4836 is accessed through the union type. So, the code above will work as
4837 expected. However, this code might not:
4848 Every language that wishes to perform language-specific alias analysis
4849 should define a function that computes, given an @code{tree}
4850 node, an alias set for the node. Nodes in different alias sets are not
4851 allowed to alias. For an example, see the C front-end function
4852 @code{c_get_alias_set}.
4854 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4856 @item -falign-functions
4857 @itemx -falign-functions=@var{n}
4858 @opindex falign-functions
4859 Align the start of functions to the next power-of-two greater than
4860 @var{n}, skipping up to @var{n} bytes. For instance,
4861 @option{-falign-functions=32} aligns functions to the next 32-byte
4862 boundary, but @option{-falign-functions=24} would align to the next
4863 32-byte boundary only if this can be done by skipping 23 bytes or less.
4865 @option{-fno-align-functions} and @option{-falign-functions=1} are
4866 equivalent and mean that functions will not be aligned.
4868 Some assemblers only support this flag when @var{n} is a power of two;
4869 in that case, it is rounded up.
4871 If @var{n} is not specified or is zero, use a machine-dependent default.
4873 Enabled at levels @option{-O2}, @option{-O3}.
4875 @item -falign-labels
4876 @itemx -falign-labels=@var{n}
4877 @opindex falign-labels
4878 Align all branch targets to a power-of-two boundary, skipping up to
4879 @var{n} bytes like @option{-falign-functions}. This option can easily
4880 make code slower, because it must insert dummy operations for when the
4881 branch target is reached in the usual flow of the code.
4883 @option{-fno-align-labels} and @option{-falign-labels=1} are
4884 equivalent and mean that labels will not be aligned.
4886 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
4887 are greater than this value, then their values are used instead.
4889 If @var{n} is not specified or is zero, use a machine-dependent default
4890 which is very likely to be @samp{1}, meaning no alignment.
4892 Enabled at levels @option{-O2}, @option{-O3}.
4895 @itemx -falign-loops=@var{n}
4896 @opindex falign-loops
4897 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
4898 like @option{-falign-functions}. The hope is that the loop will be
4899 executed many times, which will make up for any execution of the dummy
4902 @option{-fno-align-loops} and @option{-falign-loops=1} are
4903 equivalent and mean that loops will not be aligned.
4905 If @var{n} is not specified or is zero, use a machine-dependent default.
4907 Enabled at levels @option{-O2}, @option{-O3}.
4910 @itemx -falign-jumps=@var{n}
4911 @opindex falign-jumps
4912 Align branch targets to a power-of-two boundary, for branch targets
4913 where the targets can only be reached by jumping, skipping up to @var{n}
4914 bytes like @option{-falign-functions}. In this case, no dummy operations
4917 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
4918 equivalent and mean that loops will not be aligned.
4920 If @var{n} is not specified or is zero, use a machine-dependent default.
4922 Enabled at levels @option{-O2}, @option{-O3}.
4924 @item -funit-at-a-time
4925 @opindex funit-at-a-time
4926 Parse the whole compilation unit before starting to produce code.
4927 This allows some extra optimizations to take place but consumes
4928 more memory (in general). There are some compatibility issues
4929 with @emph{unit-at-at-time} mode:
4932 enabling @emph{unit-at-a-time} mode may change the order
4933 in which functions, variables, and top-level @code{asm} statements
4934 are emitted, and will likely break code relying on some particular
4935 ordering. The majority of such top-level @code{asm} statements,
4936 though, can be replaced by @code{section} attributes.
4939 @emph{unit-at-a-time} mode removes unreferenced static variables
4940 and functions are removed. This may result in undefined references
4941 when an @code{asm} statement refers directly to variables or functions
4942 that are otherwise unused. In that case either the variable/function
4943 shall be listed as an operand of the @code{asm} statement operand or,
4944 in the case of top-level @code{asm} statements the attribute @code{used}
4945 shall be used on the declaration.
4948 Static functions now can use non-standard passing conventions that
4949 may break @code{asm} statements calling functions directly. Again,
4950 attribute @code{used} will prevent this behavior.
4953 As a temporary workaround, @option{-fno-unit-at-a-time} can be used,
4954 but this scheme may not be supported by future releases of GCC.
4956 Enabled at levels @option{-O2}, @option{-O3}.
4960 Constructs webs as commonly used for register allocation purposes and assign
4961 each web individual pseudo register. This allows the register allocation pass
4962 to operate on pseudos directly, but also strengthens several other optimization
4963 passes, such as CSE, loop optimizer and trivial dead code remover. It can,
4964 however, make debugging impossible, since variables will no longer stay in a
4967 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os},
4968 on targets where the default format for debugging information supports
4971 @item -fno-cprop-registers
4972 @opindex fno-cprop-registers
4973 After register allocation and post-register allocation instruction splitting,
4974 we perform a copy-propagation pass to try to reduce scheduling dependencies
4975 and occasionally eliminate the copy.
4977 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4979 @item -fprofile-generate
4980 @opindex fprofile-generate
4982 Enable options usually used for instrumenting application to produce
4983 profile useful for later recompilation with profile feedback based
4984 optimization. You must use @option{-fprofile-generate} both when
4985 compiling and when linking your program.
4987 The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}.
4990 @opindex fprofile-use
4991 Enable profile feedback directed optimizations, and optimizations
4992 generally profitable only with profile feedback available.
4994 The following options are enabled: @code{-fbranch-probabilities},
4995 @code{-fvpt}, @code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer}.
4999 The following options control compiler behavior regarding floating
5000 point arithmetic. These options trade off between speed and
5001 correctness. All must be specifically enabled.
5005 @opindex ffloat-store
5006 Do not store floating point variables in registers, and inhibit other
5007 options that might change whether a floating point value is taken from a
5010 @cindex floating point precision
5011 This option prevents undesirable excess precision on machines such as
5012 the 68000 where the floating registers (of the 68881) keep more
5013 precision than a @code{double} is supposed to have. Similarly for the
5014 x86 architecture. For most programs, the excess precision does only
5015 good, but a few programs rely on the precise definition of IEEE floating
5016 point. Use @option{-ffloat-store} for such programs, after modifying
5017 them to store all pertinent intermediate computations into variables.
5021 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, @*
5022 @option{-fno-trapping-math}, @option{-ffinite-math-only},
5023 @option{-fno-rounding-math} and @option{-fno-signaling-nans}.
5025 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
5027 This option should never be turned on by any @option{-O} option since
5028 it can result in incorrect output for programs which depend on
5029 an exact implementation of IEEE or ISO rules/specifications for
5032 @item -fno-math-errno
5033 @opindex fno-math-errno
5034 Do not set ERRNO after calling math functions that are executed
5035 with a single instruction, e.g., sqrt. A program that relies on
5036 IEEE exceptions for math error handling may want to use this flag
5037 for speed while maintaining IEEE arithmetic compatibility.
5039 This option should never be turned on by any @option{-O} option since
5040 it can result in incorrect output for programs which depend on
5041 an exact implementation of IEEE or ISO rules/specifications for
5044 The default is @option{-fmath-errno}.
5046 @item -funsafe-math-optimizations
5047 @opindex funsafe-math-optimizations
5048 Allow optimizations for floating-point arithmetic that (a) assume
5049 that arguments and results are valid and (b) may violate IEEE or
5050 ANSI standards. When used at link-time, it may include libraries
5051 or startup files that change the default FPU control word or other
5052 similar optimizations.
5054 This option should never be turned on by any @option{-O} option since
5055 it can result in incorrect output for programs which depend on
5056 an exact implementation of IEEE or ISO rules/specifications for
5059 The default is @option{-fno-unsafe-math-optimizations}.
5061 @item -ffinite-math-only
5062 @opindex ffinite-math-only
5063 Allow optimizations for floating-point arithmetic that assume
5064 that arguments and results are not NaNs or +-Infs.
5066 This option should never be turned on by any @option{-O} option since
5067 it can result in incorrect output for programs which depend on
5068 an exact implementation of IEEE or ISO rules/specifications.
5070 The default is @option{-fno-finite-math-only}.
5072 @item -fno-trapping-math
5073 @opindex fno-trapping-math
5074 Compile code assuming that floating-point operations cannot generate
5075 user-visible traps. These traps include division by zero, overflow,
5076 underflow, inexact result and invalid operation. This option implies
5077 @option{-fno-signaling-nans}. Setting this option may allow faster
5078 code if one relies on ``non-stop'' IEEE arithmetic, for example.
5080 This option should never be turned on by any @option{-O} option since
5081 it can result in incorrect output for programs which depend on
5082 an exact implementation of IEEE or ISO rules/specifications for
5085 The default is @option{-ftrapping-math}.
5087 @item -frounding-math
5088 @opindex frounding-math
5089 Disable transformations and optimizations that assume default floating
5090 point rounding behavior. This is round-to-zero for all floating point
5091 to integer conversions, and round-to-nearest for all other arithmetic
5092 truncations. This option should be specified for programs that change
5093 the FP rounding mode dynamically, or that may be executed with a
5094 non-default rounding mode. This option disables constant folding of
5095 floating point expressions at compile-time (which may be affected by
5096 rounding mode) and arithmetic transformations that are unsafe in the
5097 presence of sign-dependent rounding modes.
5099 The default is @option{-fno-rounding-math}.
5101 This option is experimental and does not currently guarantee to
5102 disable all GCC optimizations that are affected by rounding mode.
5103 Future versions of GCC may provide finer control of this setting
5104 using C99's @code{FENV_ACCESS} pragma. This command line option
5105 will be used to specify the default state for @code{FENV_ACCESS}.
5107 @item -fsignaling-nans
5108 @opindex fsignaling-nans
5109 Compile code assuming that IEEE signaling NaNs may generate user-visible
5110 traps during floating-point operations. Setting this option disables
5111 optimizations that may change the number of exceptions visible with
5112 signaling NaNs. This option implies @option{-ftrapping-math}.
5114 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
5117 The default is @option{-fno-signaling-nans}.
5119 This option is experimental and does not currently guarantee to
5120 disable all GCC optimizations that affect signaling NaN behavior.
5122 @item -fsingle-precision-constant
5123 @opindex fsingle-precision-constant
5124 Treat floating point constant as single precision constant instead of
5125 implicitly converting it to double precision constant.
5130 The following options control optimizations that may improve
5131 performance, but are not enabled by any @option{-O} options. This
5132 section includes experimental options that may produce broken code.
5135 @item -fbranch-probabilities
5136 @opindex fbranch-probabilities
5137 After running a program compiled with @option{-fprofile-arcs}
5138 (@pxref{Debugging Options,, Options for Debugging Your Program or
5139 @command{gcc}}), you can compile it a second time using
5140 @option{-fbranch-probabilities}, to improve optimizations based on
5141 the number of times each branch was taken. When the program
5142 compiled with @option{-fprofile-arcs} exits it saves arc execution
5143 counts to a file called @file{@var{sourcename}.gcda} for each source
5144 file The information in this data file is very dependent on the
5145 structure of the generated code, so you must use the same source code
5146 and the same optimization options for both compilations.
5148 With @option{-fbranch-probabilities}, GCC puts a
5149 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
5150 These can be used to improve optimization. Currently, they are only
5151 used in one place: in @file{reorg.c}, instead of guessing which path a
5152 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
5153 exactly determine which path is taken more often.
5155 @item -fprofile-values
5156 @opindex fprofile-values
5157 If combined with @option{-fprofile-arcs}, it adds code so that some
5158 data about values of expressions in the program is gathered.
5160 With @option{-fbranch-probabilities}, it reads back the data gathered
5161 from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
5162 notes to instructions for their later usage in optimizations.
5164 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
5168 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
5169 a code to gather information about values of expressions.
5171 With @option{-fbranch-probabilities}, it reads back the data gathered
5172 and actually performs the optimizations based on them.
5173 Currently the optimizations include specialization of division operation
5174 using the knowledge about the value of the denominator.
5176 @item -fspeculative-prefetching
5177 @opindex fspeculative-prefetching
5178 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
5179 a code to gather information about addresses of memory references in the
5182 With @option{-fbranch-probabilities}, it reads back the data gathered
5183 and issues prefetch instructions according to them. In addition to the opportunities
5184 noticed by @option{-fprefetch-loop-arrays}, it also notices more complicated
5185 memory access patterns -- for example accesses to the data stored in linked
5186 list whose elements are usually allocated sequentially.
5188 In order to prevent issuing double prefetches, usage of
5189 @option{-fspeculative-prefetching} implies @option{-fno-prefetch-loop-arrays}.
5191 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
5193 @item -frename-registers
5194 @opindex frename-registers
5195 Attempt to avoid false dependencies in scheduled code by making use
5196 of registers left over after register allocation. This optimization
5197 will most benefit processors with lots of registers. Depending on the
5198 debug information format adopted by the target, however, it can
5199 make debugging impossible, since variables will no longer stay in
5200 a ``home register''.
5202 Not enabled by default at any level because it has known bugs.
5206 Use a graph coloring register allocator. Currently this option is meant
5207 for testing, so we are interested to hear about miscompilations with
5212 Perform tail duplication to enlarge superblock size. This transformation
5213 simplifies the control flow of the function allowing other optimizations to do
5216 Enabled with @option{-fprofile-use}.
5218 @item -funroll-loops
5219 @opindex funroll-loops
5220 Unroll loops whose number of iterations can be determined at compile time or
5221 upon entry to the loop. @option{-funroll-loops} implies
5222 @option{-frerun-cse-after-loop}. It also turns on complete loop peeling
5223 (i.e.@: complete removal of loops with small constant number of iterations).
5224 This option makes code larger, and may or may not make it run faster.
5226 Enabled with @option{-fprofile-use}.
5228 @item -funroll-all-loops
5229 @opindex funroll-all-loops
5230 Unroll all loops, even if their number of iterations is uncertain when
5231 the loop is entered. This usually makes programs run more slowly.
5232 @option{-funroll-all-loops} implies the same options as
5233 @option{-funroll-loops}.
5236 @opindex fpeel-loops
5237 Peels the loops for that there is enough information that they do not
5238 roll much (from profile feedback). It also turns on complete loop peeling
5239 (i.e.@: complete removal of loops with small constant number of iterations).
5241 Enabled with @option{-fprofile-use}.
5243 @item -fmove-loop-invariants
5244 @opindex fmove-loop-invariants
5245 Enables the loop invariant motion pass in the new loop optimizer. Enabled
5246 at level @option{-O1}
5248 @item -funswitch-loops
5249 @opindex funswitch-loops
5250 Move branches with loop invariant conditions out of the loop, with duplicates
5251 of the loop on both branches (modified according to result of the condition).
5253 @item -fprefetch-loop-arrays
5254 @opindex fprefetch-loop-arrays
5255 If supported by the target machine, generate instructions to prefetch
5256 memory to improve the performance of loops that access large arrays.
5258 Disabled at level @option{-Os}.
5260 @item -ffunction-sections
5261 @itemx -fdata-sections
5262 @opindex ffunction-sections
5263 @opindex fdata-sections
5264 Place each function or data item into its own section in the output
5265 file if the target supports arbitrary sections. The name of the
5266 function or the name of the data item determines the section's name
5269 Use these options on systems where the linker can perform optimizations
5270 to improve locality of reference in the instruction space. Most systems
5271 using the ELF object format and SPARC processors running Solaris 2 have
5272 linkers with such optimizations. AIX may have these optimizations in
5275 Only use these options when there are significant benefits from doing
5276 so. When you specify these options, the assembler and linker will
5277 create larger object and executable files and will also be slower.
5278 You will not be able to use @code{gprof} on all systems if you
5279 specify this option and you may have problems with debugging if
5280 you specify both this option and @option{-g}.
5282 @item -fbranch-target-load-optimize
5283 @opindex fbranch-target-load-optimize
5284 Perform branch target register load optimization before prologue / epilogue
5286 The use of target registers can typically be exposed only during reload,
5287 thus hoisting loads out of loops and doing inter-block scheduling needs
5288 a separate optimization pass.
5290 @item -fbranch-target-load-optimize2
5291 @opindex fbranch-target-load-optimize2
5292 Perform branch target register load optimization after prologue / epilogue
5295 @item -fbtr-bb-exclusive
5296 @opindex fbtr-bb-exclusive
5297 When performing branch target register load optimization, don't reuse
5298 branch target registers in within any basic block.
5300 @item --param @var{name}=@var{value}
5302 In some places, GCC uses various constants to control the amount of
5303 optimization that is done. For example, GCC will not inline functions
5304 that contain more that a certain number of instructions. You can
5305 control some of these constants on the command-line using the
5306 @option{--param} option.
5308 The names of specific parameters, and the meaning of the values, are
5309 tied to the internals of the compiler, and are subject to change
5310 without notice in future releases.
5312 In each case, the @var{value} is an integer. The allowable choices for
5313 @var{name} are given in the following table:
5316 @item max-crossjump-edges
5317 The maximum number of incoming edges to consider for crossjumping.
5318 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
5319 the number of edges incoming to each block. Increasing values mean
5320 more aggressive optimization, making the compile time increase with
5321 probably small improvement in executable size.
5323 @item min-crossjump-insns
5324 The minimum number of instructions which must be matched at the end
5325 of two blocks before crossjumping will be performed on them. This
5326 value is ignored in the case where all instructions in the block being
5327 crossjumped from are matched. The default value is 5.
5329 @item max-delay-slot-insn-search
5330 The maximum number of instructions to consider when looking for an
5331 instruction to fill a delay slot. If more than this arbitrary number of
5332 instructions is searched, the time savings from filling the delay slot
5333 will be minimal so stop searching. Increasing values mean more
5334 aggressive optimization, making the compile time increase with probably
5335 small improvement in executable run time.
5337 @item max-delay-slot-live-search
5338 When trying to fill delay slots, the maximum number of instructions to
5339 consider when searching for a block with valid live register
5340 information. Increasing this arbitrarily chosen value means more
5341 aggressive optimization, increasing the compile time. This parameter
5342 should be removed when the delay slot code is rewritten to maintain the
5345 @item max-gcse-memory
5346 The approximate maximum amount of memory that will be allocated in
5347 order to perform the global common subexpression elimination
5348 optimization. If more memory than specified is required, the
5349 optimization will not be done.
5351 @item max-gcse-passes
5352 The maximum number of passes of GCSE to run. The default is 1.
5354 @item max-pending-list-length
5355 The maximum number of pending dependencies scheduling will allow
5356 before flushing the current state and starting over. Large functions
5357 with few branches or calls can create excessively large lists which
5358 needlessly consume memory and resources.
5360 @item max-inline-insns-single
5361 Several parameters control the tree inliner used in gcc.
5362 This number sets the maximum number of instructions (counted in GCC's
5363 internal representation) in a single function that the tree inliner
5364 will consider for inlining. This only affects functions declared
5365 inline and methods implemented in a class declaration (C++).
5366 The default value is 500.
5368 @item max-inline-insns-auto
5369 When you use @option{-finline-functions} (included in @option{-O3}),
5370 a lot of functions that would otherwise not be considered for inlining
5371 by the compiler will be investigated. To those functions, a different
5372 (more restrictive) limit compared to functions declared inline can
5374 The default value is 120.
5376 @item large-function-insns
5377 The limit specifying really large functions. For functions greater than this
5378 limit inlining is constrained by @option{--param large-function-growth}.
5379 This parameter is useful primarily to avoid extreme compilation time caused by non-linear
5380 algorithms used by the backend.
5381 This parameter is ignored when @option{-funit-at-a-time} is not used.
5382 The default value is 3000.
5384 @item large-function-growth
5385 Specifies maximal growth of large function caused by inlining in percents.
5386 This parameter is ignored when @option{-funit-at-a-time} is not used.
5387 The default value is 200.
5389 @item inline-unit-growth
5390 Specifies maximal overall growth of the compilation unit caused by inlining.
5391 This parameter is ignored when @option{-funit-at-a-time} is not used.
5392 The default value is 150.
5394 @item max-inline-insns-recursive
5395 @itemx max-inline-insns-recursive-auto
5396 Specifies maximum number of instructions out-of-line copy of self recursive inline
5397 function can grow into by performing recursive inlining.
5399 For functions declared inline @option{--param max-inline-insns-recursive} is
5400 taken into acount. For function not declared inline, recursive inlining
5401 happens only when @option{-finline-functions} (included in @option{-O3}) is
5402 enabled and @option{--param max-inline-insns-recursive-auto} is used. The
5403 default value is 500.
5405 @item max-inline-recursive-depth
5406 @itemx max-inline-recursive-depth-auto
5407 Specifies maximum recursion depth used by the recursive inlining.
5409 For functions declared inline @option{--param max-inline-recursive-depth} is
5410 taken into acount. For function not declared inline, recursive inlining
5411 happens only when @option{-finline-functions} (included in @option{-O3}) is
5412 enabled and @option{--param max-inline-recursive-depth-auto} is used. The
5413 default value is 500.
5415 @item max-inline-insns-rtl
5416 For languages that use the RTL inliner (this happens at a later stage
5417 than tree inlining), you can set the maximum allowable size (counted
5418 in RTL instructions) for the RTL inliner with this parameter.
5419 The default value is 600.
5421 @item max-unrolled-insns
5422 The maximum number of instructions that a loop should have if that loop
5423 is unrolled, and if the loop is unrolled, it determines how many times
5424 the loop code is unrolled.
5426 @item max-average-unrolled-insns
5427 The maximum number of instructions biased by probabilities of their execution
5428 that a loop should have if that loop is unrolled, and if the loop is unrolled,
5429 it determines how many times the loop code is unrolled.
5431 @item max-unroll-times
5432 The maximum number of unrollings of a single loop.
5434 @item max-peeled-insns
5435 The maximum number of instructions that a loop should have if that loop
5436 is peeled, and if the loop is peeled, it determines how many times
5437 the loop code is peeled.
5439 @item max-peel-times
5440 The maximum number of peelings of a single loop.
5442 @item max-completely-peeled-insns
5443 The maximum number of insns of a completely peeled loop.
5445 @item max-completely-peel-times
5446 The maximum number of iterations of a loop to be suitable for complete peeling.
5448 @item max-unswitch-insns
5449 The maximum number of insns of an unswitched loop.
5451 @item max-unswitch-level
5452 The maximum number of branches unswitched in a single loop.
5455 The minimum cost of an expensive expression in the loop invariant motion.
5457 @item iv-consider-all-candidates-bound
5458 Bound on number of candidates for induction variables below that
5459 all candidates are considered for each use in induction variable
5460 optimizations. Only the most relevant candidates are considered
5461 if there are more candidates, to avoid quadratic time complexity.
5463 @item iv-max-considered-uses
5464 The induction variable optimizations give up on loops that contain more
5465 induction variable uses.
5467 @item max-iterations-to-track
5469 The maximum number of iterations of a loop the brute force algorithm
5470 for analysis of # of iterations of the loop tries to evaluate.
5472 @item hot-bb-count-fraction
5473 Select fraction of the maximal count of repetitions of basic block in program
5474 given basic block needs to have to be considered hot.
5476 @item hot-bb-frequency-fraction
5477 Select fraction of the maximal frequency of executions of basic block in
5478 function given basic block needs to have to be considered hot
5480 @item tracer-dynamic-coverage
5481 @itemx tracer-dynamic-coverage-feedback
5483 This value is used to limit superblock formation once the given percentage of
5484 executed instructions is covered. This limits unnecessary code size
5487 The @option{tracer-dynamic-coverage-feedback} is used only when profile
5488 feedback is available. The real profiles (as opposed to statically estimated
5489 ones) are much less balanced allowing the threshold to be larger value.
5491 @item tracer-max-code-growth
5492 Stop tail duplication once code growth has reached given percentage. This is
5493 rather hokey argument, as most of the duplicates will be eliminated later in
5494 cross jumping, so it may be set to much higher values than is the desired code
5497 @item tracer-min-branch-ratio
5499 Stop reverse growth when the reverse probability of best edge is less than this
5500 threshold (in percent).
5502 @item tracer-min-branch-ratio
5503 @itemx tracer-min-branch-ratio-feedback
5505 Stop forward growth if the best edge do have probability lower than this
5508 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
5509 compilation for profile feedback and one for compilation without. The value
5510 for compilation with profile feedback needs to be more conservative (higher) in
5511 order to make tracer effective.
5513 @item max-cse-path-length
5515 Maximum number of basic blocks on path that cse considers. The default is 10.
5517 @item global-var-threshold
5519 Counts the number of function calls (N) and the number of
5520 call-clobbered variables (V). If NxV is larger than this limit, a
5521 single artificial variable will be created to represent all the
5522 call-clobbered variables at function call sites. This artificial
5523 variable will then be made to alias every call-clobbered variable.
5524 (done as int * size_t on the host machine; beware overflow).
5526 @item max-aliased-vops
5528 Maximum number of virtual operands allowed to represent aliases
5529 before triggering the alias grouping heuristic. Alias grouping
5530 reduces compile times and memory consumption needed for aliasing at
5531 the expense of precision loss in alias information.
5533 @item ggc-min-expand
5535 GCC uses a garbage collector to manage its own memory allocation. This
5536 parameter specifies the minimum percentage by which the garbage
5537 collector's heap should be allowed to expand between collections.
5538 Tuning this may improve compilation speed; it has no effect on code
5541 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
5542 RAM >= 1GB. If @code{getrlimit} is available, the notion of "RAM" is
5543 the smallest of actual RAM and RLIMIT_DATA or RLIMIT_AS. If
5544 GCC is not able to calculate RAM on a particular platform, the lower
5545 bound of 30% is used. Setting this parameter and
5546 @option{ggc-min-heapsize} to zero causes a full collection to occur at
5547 every opportunity. This is extremely slow, but can be useful for
5550 @item ggc-min-heapsize
5552 Minimum size of the garbage collector's heap before it begins bothering
5553 to collect garbage. The first collection occurs after the heap expands
5554 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
5555 tuning this may improve compilation speed, and has no effect on code
5558 The default is the smaller of RAM/8, RLIMIT_RSS, or a limit which
5559 tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
5560 with a lower bound of 4096 (four megabytes) and an upper bound of
5561 131072 (128 megabytes). If GCC is not able to calculate RAM on a
5562 particular platform, the lower bound is used. Setting this parameter
5563 very large effectively disables garbage collection. Setting this
5564 parameter and @option{ggc-min-expand} to zero causes a full collection
5565 to occur at every opportunity.
5567 @item max-reload-search-insns
5568 The maximum number of instruction reload should look backward for equivalent
5569 register. Increasing values mean more aggressive optimization, making the
5570 compile time increase with probably slightly better performance. The default
5573 @item max-cselib-memory-location
5574 The maximum number of memory locations cselib should take into acount.
5575 Increasing values mean more aggressive optimization, making the compile time
5576 increase with probably slightly better performance. The default value is 500.
5578 @item reorder-blocks-duplicate
5579 @itemx reorder-blocks-duplicate-feedback
5581 Used by basic block reordering pass to decide whether to use unconditional
5582 branch or duplicate the code on its destination. Code is duplicated when its
5583 estimated size is smaller than this value multiplied by the estimated size of
5584 unconditional jump in the hot spots of the program.
5586 The @option{reorder-block-duplicate-feedback} is used only when profile
5587 feedback is available and may be set to higher values than
5588 @option{reorder-block-duplicate} since information about the hot spots is more
5591 @item max-sched-region-blocks
5592 The maximum number of blocks in a region to be considered for
5593 interblock scheduling. The default value is 10.
5595 @item max-sched-region-insns
5596 The maximum number of insns in a region to be considered for
5597 interblock scheduling. The default value is 100.
5599 @item integer-share-limit
5600 Small integer constants can use a shared data structure, reducing the
5601 compiler's memory usage and increasing its speed. This sets the maximum
5602 value of a shared integer constant's. The default value is 256.
5607 @node Preprocessor Options
5608 @section Options Controlling the Preprocessor
5609 @cindex preprocessor options
5610 @cindex options, preprocessor
5612 These options control the C preprocessor, which is run on each C source
5613 file before actual compilation.
5615 If you use the @option{-E} option, nothing is done except preprocessing.
5616 Some of these options make sense only together with @option{-E} because
5617 they cause the preprocessor output to be unsuitable for actual
5622 You can use @option{-Wp,@var{option}} to bypass the compiler driver
5623 and pass @var{option} directly through to the preprocessor. If
5624 @var{option} contains commas, it is split into multiple options at the
5625 commas. However, many options are modified, translated or interpreted
5626 by the compiler driver before being passed to the preprocessor, and
5627 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
5628 interface is undocumented and subject to change, so whenever possible
5629 you should avoid using @option{-Wp} and let the driver handle the
5632 @item -Xpreprocessor @var{option}
5633 @opindex preprocessor
5634 Pass @var{option} as an option to the preprocessor. You can use this to
5635 supply system-specific preprocessor options which GCC does not know how to
5638 If you want to pass an option that takes an argument, you must use
5639 @option{-Xpreprocessor} twice, once for the option and once for the argument.
5642 @include cppopts.texi
5644 @node Assembler Options
5645 @section Passing Options to the Assembler
5647 @c prevent bad page break with this line
5648 You can pass options to the assembler.
5651 @item -Wa,@var{option}
5653 Pass @var{option} as an option to the assembler. If @var{option}
5654 contains commas, it is split into multiple options at the commas.
5656 @item -Xassembler @var{option}
5658 Pass @var{option} as an option to the assembler. You can use this to
5659 supply system-specific assembler options which GCC does not know how to
5662 If you want to pass an option that takes an argument, you must use
5663 @option{-Xassembler} twice, once for the option and once for the argument.
5668 @section Options for Linking
5669 @cindex link options
5670 @cindex options, linking
5672 These options come into play when the compiler links object files into
5673 an executable output file. They are meaningless if the compiler is
5674 not doing a link step.
5678 @item @var{object-file-name}
5679 A file name that does not end in a special recognized suffix is
5680 considered to name an object file or library. (Object files are
5681 distinguished from libraries by the linker according to the file
5682 contents.) If linking is done, these object files are used as input
5691 If any of these options is used, then the linker is not run, and
5692 object file names should not be used as arguments. @xref{Overall
5696 @item -l@var{library}
5697 @itemx -l @var{library}
5699 Search the library named @var{library} when linking. (The second
5700 alternative with the library as a separate argument is only for
5701 POSIX compliance and is not recommended.)
5703 It makes a difference where in the command you write this option; the
5704 linker searches and processes libraries and object files in the order they
5705 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
5706 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
5707 to functions in @samp{z}, those functions may not be loaded.
5709 The linker searches a standard list of directories for the library,
5710 which is actually a file named @file{lib@var{library}.a}. The linker
5711 then uses this file as if it had been specified precisely by name.
5713 The directories searched include several standard system directories
5714 plus any that you specify with @option{-L}.
5716 Normally the files found this way are library files---archive files
5717 whose members are object files. The linker handles an archive file by
5718 scanning through it for members which define symbols that have so far
5719 been referenced but not defined. But if the file that is found is an
5720 ordinary object file, it is linked in the usual fashion. The only
5721 difference between using an @option{-l} option and specifying a file name
5722 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
5723 and searches several directories.
5727 You need this special case of the @option{-l} option in order to
5728 link an Objective-C or Objective-C++ program.
5731 @opindex nostartfiles
5732 Do not use the standard system startup files when linking.
5733 The standard system libraries are used normally, unless @option{-nostdlib}
5734 or @option{-nodefaultlibs} is used.
5736 @item -nodefaultlibs
5737 @opindex nodefaultlibs
5738 Do not use the standard system libraries when linking.
5739 Only the libraries you specify will be passed to the linker.
5740 The standard startup files are used normally, unless @option{-nostartfiles}
5741 is used. The compiler may generate calls to @code{memcmp},
5742 @code{memset}, @code{memcpy} and @code{memmove}.
5743 These entries are usually resolved by entries in
5744 libc. These entry points should be supplied through some other
5745 mechanism when this option is specified.
5749 Do not use the standard system startup files or libraries when linking.
5750 No startup files and only the libraries you specify will be passed to
5751 the linker. The compiler may generate calls to @code{memcmp}, @code{memset},
5752 @code{memcpy} and @code{memmove}.
5753 These entries are usually resolved by entries in
5754 libc. These entry points should be supplied through some other
5755 mechanism when this option is specified.
5757 @cindex @option{-lgcc}, use with @option{-nostdlib}
5758 @cindex @option{-nostdlib} and unresolved references
5759 @cindex unresolved references and @option{-nostdlib}
5760 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
5761 @cindex @option{-nodefaultlibs} and unresolved references
5762 @cindex unresolved references and @option{-nodefaultlibs}
5763 One of the standard libraries bypassed by @option{-nostdlib} and
5764 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
5765 that GCC uses to overcome shortcomings of particular machines, or special
5766 needs for some languages.
5767 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
5768 Collection (GCC) Internals},
5769 for more discussion of @file{libgcc.a}.)
5770 In most cases, you need @file{libgcc.a} even when you want to avoid
5771 other standard libraries. In other words, when you specify @option{-nostdlib}
5772 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
5773 This ensures that you have no unresolved references to internal GCC
5774 library subroutines. (For example, @samp{__main}, used to ensure C++
5775 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
5776 GNU Compiler Collection (GCC) Internals}.)
5780 Produce a position independent executable on targets which support it.
5781 For predictable results, you must also specify the same set of options
5782 that were used to generate code (@option{-fpie}, @option{-fPIE},
5783 or model suboptions) when you specify this option.
5787 Remove all symbol table and relocation information from the executable.
5791 On systems that support dynamic linking, this prevents linking with the shared
5792 libraries. On other systems, this option has no effect.
5796 Produce a shared object which can then be linked with other objects to
5797 form an executable. Not all systems support this option. For predictable
5798 results, you must also specify the same set of options that were used to
5799 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
5800 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
5801 needs to build supplementary stub code for constructors to work. On
5802 multi-libbed systems, @samp{gcc -shared} must select the correct support
5803 libraries to link against. Failing to supply the correct flags may lead
5804 to subtle defects. Supplying them in cases where they are not necessary
5807 @item -shared-libgcc
5808 @itemx -static-libgcc
5809 @opindex shared-libgcc
5810 @opindex static-libgcc
5811 On systems that provide @file{libgcc} as a shared library, these options
5812 force the use of either the shared or static version respectively.
5813 If no shared version of @file{libgcc} was built when the compiler was
5814 configured, these options have no effect.
5816 There are several situations in which an application should use the
5817 shared @file{libgcc} instead of the static version. The most common
5818 of these is when the application wishes to throw and catch exceptions
5819 across different shared libraries. In that case, each of the libraries
5820 as well as the application itself should use the shared @file{libgcc}.
5822 Therefore, the G++ and GCJ drivers automatically add
5823 @option{-shared-libgcc} whenever you build a shared library or a main
5824 executable, because C++ and Java programs typically use exceptions, so
5825 this is the right thing to do.
5827 If, instead, you use the GCC driver to create shared libraries, you may
5828 find that they will not always be linked with the shared @file{libgcc}.
5829 If GCC finds, at its configuration time, that you have a non-GNU linker
5830 or a GNU linker that does not support option @option{--eh-frame-hdr},
5831 it will link the shared version of @file{libgcc} into shared libraries
5832 by default. Otherwise, it will take advantage of the linker and optimize
5833 away the linking with the shared version of @file{libgcc}, linking with
5834 the static version of libgcc by default. This allows exceptions to
5835 propagate through such shared libraries, without incurring relocation
5836 costs at library load time.
5838 However, if a library or main executable is supposed to throw or catch
5839 exceptions, you must link it using the G++ or GCJ driver, as appropriate
5840 for the languages used in the program, or using the option
5841 @option{-shared-libgcc}, such that it is linked with the shared
5846 Bind references to global symbols when building a shared object. Warn
5847 about any unresolved references (unless overridden by the link editor
5848 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
5851 @item -Xlinker @var{option}
5853 Pass @var{option} as an option to the linker. You can use this to
5854 supply system-specific linker options which GCC does not know how to
5857 If you want to pass an option that takes an argument, you must use
5858 @option{-Xlinker} twice, once for the option and once for the argument.
5859 For example, to pass @option{-assert definitions}, you must write
5860 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
5861 @option{-Xlinker "-assert definitions"}, because this passes the entire
5862 string as a single argument, which is not what the linker expects.
5864 @item -Wl,@var{option}
5866 Pass @var{option} as an option to the linker. If @var{option} contains
5867 commas, it is split into multiple options at the commas.
5869 @item -u @var{symbol}
5871 Pretend the symbol @var{symbol} is undefined, to force linking of
5872 library modules to define it. You can use @option{-u} multiple times with
5873 different symbols to force loading of additional library modules.
5876 @node Directory Options
5877 @section Options for Directory Search
5878 @cindex directory options
5879 @cindex options, directory search
5882 These options specify directories to search for header files, for
5883 libraries and for parts of the compiler:
5888 Add the directory @var{dir} to the head of the list of directories to be
5889 searched for header files. This can be used to override a system header
5890 file, substituting your own version, since these directories are
5891 searched before the system header file directories. However, you should
5892 not use this option to add directories that contain vendor-supplied
5893 system header files (use @option{-isystem} for that). If you use more than
5894 one @option{-I} option, the directories are scanned in left-to-right
5895 order; the standard system directories come after.
5897 If a standard system include directory, or a directory specified with
5898 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
5899 option will be ignored. The directory will still be searched but as a
5900 system directory at its normal position in the system include chain.
5901 This is to ensure that GCC's procedure to fix buggy system headers and
5902 the ordering for the include_next directive are not inadvertently changed.
5903 If you really need to change the search order for system directories,
5904 use the @option{-nostdinc} and/or @option{-isystem} options.
5906 @item -iquote@var{dir}
5908 Add the directory @var{dir} to the head of the list of directories to
5909 be searched for header files only for the case of @samp{#include
5910 "@var{file}"}; they are not searched for @samp{#include <@var{file}>},
5911 otherwise just like @option{-I}.
5915 Add directory @var{dir} to the list of directories to be searched
5918 @item -B@var{prefix}
5920 This option specifies where to find the executables, libraries,
5921 include files, and data files of the compiler itself.
5923 The compiler driver program runs one or more of the subprograms
5924 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
5925 @var{prefix} as a prefix for each program it tries to run, both with and
5926 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
5928 For each subprogram to be run, the compiler driver first tries the
5929 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
5930 was not specified, the driver tries two standard prefixes, which are
5931 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
5932 those results in a file name that is found, the unmodified program
5933 name is searched for using the directories specified in your
5934 @env{PATH} environment variable.
5936 The compiler will check to see if the path provided by the @option{-B}
5937 refers to a directory, and if necessary it will add a directory
5938 separator character at the end of the path.
5940 @option{-B} prefixes that effectively specify directory names also apply
5941 to libraries in the linker, because the compiler translates these
5942 options into @option{-L} options for the linker. They also apply to
5943 includes files in the preprocessor, because the compiler translates these
5944 options into @option{-isystem} options for the preprocessor. In this case,
5945 the compiler appends @samp{include} to the prefix.
5947 The run-time support file @file{libgcc.a} can also be searched for using
5948 the @option{-B} prefix, if needed. If it is not found there, the two
5949 standard prefixes above are tried, and that is all. The file is left
5950 out of the link if it is not found by those means.
5952 Another way to specify a prefix much like the @option{-B} prefix is to use
5953 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
5956 As a special kludge, if the path provided by @option{-B} is
5957 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
5958 9, then it will be replaced by @file{[dir/]include}. This is to help
5959 with boot-strapping the compiler.
5961 @item -specs=@var{file}
5963 Process @var{file} after the compiler reads in the standard @file{specs}
5964 file, in order to override the defaults that the @file{gcc} driver
5965 program uses when determining what switches to pass to @file{cc1},
5966 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
5967 @option{-specs=@var{file}} can be specified on the command line, and they
5968 are processed in order, from left to right.
5972 This option has been deprecated. Please use @option{-iquote} instead for
5973 @option{-I} directories before the @option{-I-} and remove the @option{-I-}.
5974 Any directories you specify with @option{-I} options before the @option{-I-}
5975 option are searched only for the case of @samp{#include "@var{file}"};
5976 they are not searched for @samp{#include <@var{file}>}.
5978 If additional directories are specified with @option{-I} options after
5979 the @option{-I-}, these directories are searched for all @samp{#include}
5980 directives. (Ordinarily @emph{all} @option{-I} directories are used
5983 In addition, the @option{-I-} option inhibits the use of the current
5984 directory (where the current input file came from) as the first search
5985 directory for @samp{#include "@var{file}"}. There is no way to
5986 override this effect of @option{-I-}. With @option{-I.} you can specify
5987 searching the directory which was current when the compiler was
5988 invoked. That is not exactly the same as what the preprocessor does
5989 by default, but it is often satisfactory.
5991 @option{-I-} does not inhibit the use of the standard system directories
5992 for header files. Thus, @option{-I-} and @option{-nostdinc} are
5999 @section Specifying subprocesses and the switches to pass to them
6002 @command{gcc} is a driver program. It performs its job by invoking a
6003 sequence of other programs to do the work of compiling, assembling and
6004 linking. GCC interprets its command-line parameters and uses these to
6005 deduce which programs it should invoke, and which command-line options
6006 it ought to place on their command lines. This behavior is controlled
6007 by @dfn{spec strings}. In most cases there is one spec string for each
6008 program that GCC can invoke, but a few programs have multiple spec
6009 strings to control their behavior. The spec strings built into GCC can
6010 be overridden by using the @option{-specs=} command-line switch to specify
6013 @dfn{Spec files} are plaintext files that are used to construct spec
6014 strings. They consist of a sequence of directives separated by blank
6015 lines. The type of directive is determined by the first non-whitespace
6016 character on the line and it can be one of the following:
6019 @item %@var{command}
6020 Issues a @var{command} to the spec file processor. The commands that can
6024 @item %include <@var{file}>
6026 Search for @var{file} and insert its text at the current point in the
6029 @item %include_noerr <@var{file}>
6030 @cindex %include_noerr
6031 Just like @samp{%include}, but do not generate an error message if the include
6032 file cannot be found.
6034 @item %rename @var{old_name} @var{new_name}
6036 Rename the spec string @var{old_name} to @var{new_name}.
6040 @item *[@var{spec_name}]:
6041 This tells the compiler to create, override or delete the named spec
6042 string. All lines after this directive up to the next directive or
6043 blank line are considered to be the text for the spec string. If this
6044 results in an empty string then the spec will be deleted. (Or, if the
6045 spec did not exist, then nothing will happened.) Otherwise, if the spec
6046 does not currently exist a new spec will be created. If the spec does
6047 exist then its contents will be overridden by the text of this
6048 directive, unless the first character of that text is the @samp{+}
6049 character, in which case the text will be appended to the spec.
6051 @item [@var{suffix}]:
6052 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
6053 and up to the next directive or blank line are considered to make up the
6054 spec string for the indicated suffix. When the compiler encounters an
6055 input file with the named suffix, it will processes the spec string in
6056 order to work out how to compile that file. For example:
6063 This says that any input file whose name ends in @samp{.ZZ} should be
6064 passed to the program @samp{z-compile}, which should be invoked with the
6065 command-line switch @option{-input} and with the result of performing the
6066 @samp{%i} substitution. (See below.)
6068 As an alternative to providing a spec string, the text that follows a
6069 suffix directive can be one of the following:
6072 @item @@@var{language}
6073 This says that the suffix is an alias for a known @var{language}. This is
6074 similar to using the @option{-x} command-line switch to GCC to specify a
6075 language explicitly. For example:
6082 Says that .ZZ files are, in fact, C++ source files.
6085 This causes an error messages saying:
6088 @var{name} compiler not installed on this system.
6092 GCC already has an extensive list of suffixes built into it.
6093 This directive will add an entry to the end of the list of suffixes, but
6094 since the list is searched from the end backwards, it is effectively
6095 possible to override earlier entries using this technique.
6099 GCC has the following spec strings built into it. Spec files can
6100 override these strings or create their own. Note that individual
6101 targets can also add their own spec strings to this list.
6104 asm Options to pass to the assembler
6105 asm_final Options to pass to the assembler post-processor
6106 cpp Options to pass to the C preprocessor
6107 cc1 Options to pass to the C compiler
6108 cc1plus Options to pass to the C++ compiler
6109 endfile Object files to include at the end of the link
6110 link Options to pass to the linker
6111 lib Libraries to include on the command line to the linker
6112 libgcc Decides which GCC support library to pass to the linker
6113 linker Sets the name of the linker
6114 predefines Defines to be passed to the C preprocessor
6115 signed_char Defines to pass to CPP to say whether @code{char} is signed
6117 startfile Object files to include at the start of the link
6120 Here is a small example of a spec file:
6126 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
6129 This example renames the spec called @samp{lib} to @samp{old_lib} and
6130 then overrides the previous definition of @samp{lib} with a new one.
6131 The new definition adds in some extra command-line options before
6132 including the text of the old definition.
6134 @dfn{Spec strings} are a list of command-line options to be passed to their
6135 corresponding program. In addition, the spec strings can contain
6136 @samp{%}-prefixed sequences to substitute variable text or to
6137 conditionally insert text into the command line. Using these constructs
6138 it is possible to generate quite complex command lines.
6140 Here is a table of all defined @samp{%}-sequences for spec
6141 strings. Note that spaces are not generated automatically around the
6142 results of expanding these sequences. Therefore you can concatenate them
6143 together or combine them with constant text in a single argument.
6147 Substitute one @samp{%} into the program name or argument.
6150 Substitute the name of the input file being processed.
6153 Substitute the basename of the input file being processed.
6154 This is the substring up to (and not including) the last period
6155 and not including the directory.
6158 This is the same as @samp{%b}, but include the file suffix (text after
6162 Marks the argument containing or following the @samp{%d} as a
6163 temporary file name, so that that file will be deleted if GCC exits
6164 successfully. Unlike @samp{%g}, this contributes no text to the
6167 @item %g@var{suffix}
6168 Substitute a file name that has suffix @var{suffix} and is chosen
6169 once per compilation, and mark the argument in the same way as
6170 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
6171 name is now chosen in a way that is hard to predict even when previously
6172 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
6173 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
6174 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
6175 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
6176 was simply substituted with a file name chosen once per compilation,
6177 without regard to any appended suffix (which was therefore treated
6178 just like ordinary text), making such attacks more likely to succeed.
6180 @item %u@var{suffix}
6181 Like @samp{%g}, but generates a new temporary file name even if
6182 @samp{%u@var{suffix}} was already seen.
6184 @item %U@var{suffix}
6185 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
6186 new one if there is no such last file name. In the absence of any
6187 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
6188 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
6189 would involve the generation of two distinct file names, one
6190 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
6191 simply substituted with a file name chosen for the previous @samp{%u},
6192 without regard to any appended suffix.
6194 @item %j@var{suffix}
6195 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
6196 writable, and if save-temps is off; otherwise, substitute the name
6197 of a temporary file, just like @samp{%u}. This temporary file is not
6198 meant for communication between processes, but rather as a junk
6201 @item %|@var{suffix}
6202 @itemx %m@var{suffix}
6203 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
6204 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
6205 all. These are the two most common ways to instruct a program that it
6206 should read from standard input or write to standard output. If you
6207 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
6208 construct: see for example @file{f/lang-specs.h}.
6210 @item %.@var{SUFFIX}
6211 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
6212 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
6213 terminated by the next space or %.
6216 Marks the argument containing or following the @samp{%w} as the
6217 designated output file of this compilation. This puts the argument
6218 into the sequence of arguments that @samp{%o} will substitute later.
6221 Substitutes the names of all the output files, with spaces
6222 automatically placed around them. You should write spaces
6223 around the @samp{%o} as well or the results are undefined.
6224 @samp{%o} is for use in the specs for running the linker.
6225 Input files whose names have no recognized suffix are not compiled
6226 at all, but they are included among the output files, so they will
6230 Substitutes the suffix for object files. Note that this is
6231 handled specially when it immediately follows @samp{%g, %u, or %U},
6232 because of the need for those to form complete file names. The
6233 handling is such that @samp{%O} is treated exactly as if it had already
6234 been substituted, except that @samp{%g, %u, and %U} do not currently
6235 support additional @var{suffix} characters following @samp{%O} as they would
6236 following, for example, @samp{.o}.
6239 Substitutes the standard macro predefinitions for the
6240 current target machine. Use this when running @code{cpp}.
6243 Like @samp{%p}, but puts @samp{__} before and after the name of each
6244 predefined macro, except for macros that start with @samp{__} or with
6245 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
6249 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
6250 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}), and
6251 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
6255 Current argument is the name of a library or startup file of some sort.
6256 Search for that file in a standard list of directories and substitute
6257 the full name found.
6260 Print @var{str} as an error message. @var{str} is terminated by a newline.
6261 Use this when inconsistent options are detected.
6264 Substitute the contents of spec string @var{name} at this point.
6267 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
6269 @item %x@{@var{option}@}
6270 Accumulate an option for @samp{%X}.
6273 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
6277 Output the accumulated assembler options specified by @option{-Wa}.
6280 Output the accumulated preprocessor options specified by @option{-Wp}.
6283 Process the @code{asm} spec. This is used to compute the
6284 switches to be passed to the assembler.
6287 Process the @code{asm_final} spec. This is a spec string for
6288 passing switches to an assembler post-processor, if such a program is
6292 Process the @code{link} spec. This is the spec for computing the
6293 command line passed to the linker. Typically it will make use of the
6294 @samp{%L %G %S %D and %E} sequences.
6297 Dump out a @option{-L} option for each directory that GCC believes might
6298 contain startup files. If the target supports multilibs then the
6299 current multilib directory will be prepended to each of these paths.
6302 Output the multilib directory with directory separators replaced with
6303 @samp{_}. If multilib directories are not set, or the multilib directory is
6304 @file{.} then this option emits nothing.
6307 Process the @code{lib} spec. This is a spec string for deciding which
6308 libraries should be included on the command line to the linker.
6311 Process the @code{libgcc} spec. This is a spec string for deciding
6312 which GCC support library should be included on the command line to the linker.
6315 Process the @code{startfile} spec. This is a spec for deciding which
6316 object files should be the first ones passed to the linker. Typically
6317 this might be a file named @file{crt0.o}.
6320 Process the @code{endfile} spec. This is a spec string that specifies
6321 the last object files that will be passed to the linker.
6324 Process the @code{cpp} spec. This is used to construct the arguments
6325 to be passed to the C preprocessor.
6328 Process the @code{cc1} spec. This is used to construct the options to be
6329 passed to the actual C compiler (@samp{cc1}).
6332 Process the @code{cc1plus} spec. This is used to construct the options to be
6333 passed to the actual C++ compiler (@samp{cc1plus}).
6336 Substitute the variable part of a matched option. See below.
6337 Note that each comma in the substituted string is replaced by
6341 Remove all occurrences of @code{-S} from the command line. Note---this
6342 command is position dependent. @samp{%} commands in the spec string
6343 before this one will see @code{-S}, @samp{%} commands in the spec string
6344 after this one will not.
6346 @item %:@var{function}(@var{args})
6347 Call the named function @var{function}, passing it @var{args}.
6348 @var{args} is first processed as a nested spec string, then split
6349 into an argument vector in the usual fashion. The function returns
6350 a string which is processed as if it had appeared literally as part
6351 of the current spec.
6353 The following built-in spec functions are provided:
6356 @item @code{if-exists}
6357 The @code{if-exists} spec function takes one argument, an absolute
6358 pathname to a file. If the file exists, @code{if-exists} returns the
6359 pathname. Here is a small example of its usage:
6363 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
6366 @item @code{if-exists-else}
6367 The @code{if-exists-else} spec function is similar to the @code{if-exists}
6368 spec function, except that it takes two arguments. The first argument is
6369 an absolute pathname to a file. If the file exists, @code{if-exists-else}
6370 returns the pathname. If it does not exist, it returns the second argument.
6371 This way, @code{if-exists-else} can be used to select one file or another,
6372 based on the existence of the first. Here is a small example of its usage:
6376 crt0%O%s %:if-exists(crti%O%s) \
6377 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
6380 @item @code{replace-outfile}
6381 The @code{replace-outfile} spec function takes two arguments. It looks for the
6382 first argument in the outfiles array and replaces it with the second argument. Here
6383 is a small example of its usage:
6386 %@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
6392 Substitutes the @code{-S} switch, if that switch was given to GCC@.
6393 If that switch was not specified, this substitutes nothing. Note that
6394 the leading dash is omitted when specifying this option, and it is
6395 automatically inserted if the substitution is performed. Thus the spec
6396 string @samp{%@{foo@}} would match the command-line option @option{-foo}
6397 and would output the command line option @option{-foo}.
6399 @item %W@{@code{S}@}
6400 Like %@{@code{S}@} but mark last argument supplied within as a file to be
6403 @item %@{@code{S}*@}
6404 Substitutes all the switches specified to GCC whose names start
6405 with @code{-S}, but which also take an argument. This is used for
6406 switches like @option{-o}, @option{-D}, @option{-I}, etc.
6407 GCC considers @option{-o foo} as being
6408 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
6409 text, including the space. Thus two arguments would be generated.
6411 @item %@{@code{S}*&@code{T}*@}
6412 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
6413 (the order of @code{S} and @code{T} in the spec is not significant).
6414 There can be any number of ampersand-separated variables; for each the
6415 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
6417 @item %@{@code{S}:@code{X}@}
6418 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
6420 @item %@{!@code{S}:@code{X}@}
6421 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
6423 @item %@{@code{S}*:@code{X}@}
6424 Substitutes @code{X} if one or more switches whose names start with
6425 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
6426 once, no matter how many such switches appeared. However, if @code{%*}
6427 appears somewhere in @code{X}, then @code{X} will be substituted once
6428 for each matching switch, with the @code{%*} replaced by the part of
6429 that switch that matched the @code{*}.
6431 @item %@{.@code{S}:@code{X}@}
6432 Substitutes @code{X}, if processing a file with suffix @code{S}.
6434 @item %@{!.@code{S}:@code{X}@}
6435 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
6437 @item %@{@code{S}|@code{P}:@code{X}@}
6438 Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@.
6439 This may be combined with @samp{!}, @samp{.}, and @code{*} sequences as well,
6440 although they have a stronger binding than the @samp{|}. If @code{%*}
6441 appears in @code{X}, all of the alternatives must be starred, and only
6442 the first matching alternative is substituted.
6444 For example, a spec string like this:
6447 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
6450 will output the following command-line options from the following input
6451 command-line options:
6456 -d fred.c -foo -baz -boggle
6457 -d jim.d -bar -baz -boggle
6460 @item %@{S:X; T:Y; :D@}
6462 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
6463 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
6464 be as many clauses as you need. This may be combined with @code{.},
6465 @code{!}, @code{|}, and @code{*} as needed.
6470 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
6471 construct may contain other nested @samp{%} constructs or spaces, or
6472 even newlines. They are processed as usual, as described above.
6473 Trailing white space in @code{X} is ignored. White space may also
6474 appear anywhere on the left side of the colon in these constructs,
6475 except between @code{.} or @code{*} and the corresponding word.
6477 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
6478 handled specifically in these constructs. If another value of
6479 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
6480 @option{-W} switch is found later in the command line, the earlier
6481 switch value is ignored, except with @{@code{S}*@} where @code{S} is
6482 just one letter, which passes all matching options.
6484 The character @samp{|} at the beginning of the predicate text is used to
6485 indicate that a command should be piped to the following command, but
6486 only if @option{-pipe} is specified.
6488 It is built into GCC which switches take arguments and which do not.
6489 (You might think it would be useful to generalize this to allow each
6490 compiler's spec to say which switches take arguments. But this cannot
6491 be done in a consistent fashion. GCC cannot even decide which input
6492 files have been specified without knowing which switches take arguments,
6493 and it must know which input files to compile in order to tell which
6496 GCC also knows implicitly that arguments starting in @option{-l} are to be
6497 treated as compiler output files, and passed to the linker in their
6498 proper position among the other output files.
6500 @c man begin OPTIONS
6502 @node Target Options
6503 @section Specifying Target Machine and Compiler Version
6504 @cindex target options
6505 @cindex cross compiling
6506 @cindex specifying machine version
6507 @cindex specifying compiler version and target machine
6508 @cindex compiler version, specifying
6509 @cindex target machine, specifying
6511 The usual way to run GCC is to run the executable called @file{gcc}, or
6512 @file{<machine>-gcc} when cross-compiling, or
6513 @file{<machine>-gcc-<version>} to run a version other than the one that
6514 was installed last. Sometimes this is inconvenient, so GCC provides
6515 options that will switch to another cross-compiler or version.
6518 @item -b @var{machine}
6520 The argument @var{machine} specifies the target machine for compilation.
6522 The value to use for @var{machine} is the same as was specified as the
6523 machine type when configuring GCC as a cross-compiler. For
6524 example, if a cross-compiler was configured with @samp{configure
6525 i386v}, meaning to compile for an 80386 running System V, then you
6526 would specify @option{-b i386v} to run that cross compiler.
6528 @item -V @var{version}
6530 The argument @var{version} specifies which version of GCC to run.
6531 This is useful when multiple versions are installed. For example,
6532 @var{version} might be @samp{2.0}, meaning to run GCC version 2.0.
6535 The @option{-V} and @option{-b} options work by running the
6536 @file{<machine>-gcc-<version>} executable, so there's no real reason to
6537 use them if you can just run that directly.
6539 @node Submodel Options
6540 @section Hardware Models and Configurations
6541 @cindex submodel options
6542 @cindex specifying hardware config
6543 @cindex hardware models and configurations, specifying
6544 @cindex machine dependent options
6546 Earlier we discussed the standard option @option{-b} which chooses among
6547 different installed compilers for completely different target
6548 machines, such as VAX vs.@: 68000 vs.@: 80386.
6550 In addition, each of these target machine types can have its own
6551 special options, starting with @samp{-m}, to choose among various
6552 hardware models or configurations---for example, 68010 vs 68020,
6553 floating coprocessor or none. A single installed version of the
6554 compiler can compile for any model or configuration, according to the
6557 Some configurations of the compiler also support additional special
6558 options, usually for compatibility with other compilers on the same
6561 These options are defined by the macro @code{TARGET_SWITCHES} in the
6562 machine description. The default for the options is also defined by
6563 that macro, which enables you to change the defaults.
6565 @c This list is ordered alphanumerically by subsection name.
6566 @c It should be the same order and spelling as these options are listed
6567 @c in Machine Dependent Options
6575 * DEC Alpha Options::
6576 * DEC Alpha/VMS Options::
6580 * i386 and x86-64 Options::
6592 * RS/6000 and PowerPC Options::
6593 * S/390 and zSeries Options::
6596 * System V Options::
6597 * TMS320C3x/C4x Options::
6601 * Xstormy16 Options::
6607 @subsection ARC Options
6610 These options are defined for ARC implementations:
6615 Compile code for little endian mode. This is the default.
6619 Compile code for big endian mode.
6622 @opindex mmangle-cpu
6623 Prepend the name of the cpu to all public symbol names.
6624 In multiple-processor systems, there are many ARC variants with different
6625 instruction and register set characteristics. This flag prevents code
6626 compiled for one cpu to be linked with code compiled for another.
6627 No facility exists for handling variants that are ``almost identical''.
6628 This is an all or nothing option.
6630 @item -mcpu=@var{cpu}
6632 Compile code for ARC variant @var{cpu}.
6633 Which variants are supported depend on the configuration.
6634 All variants support @option{-mcpu=base}, this is the default.
6636 @item -mtext=@var{text-section}
6637 @itemx -mdata=@var{data-section}
6638 @itemx -mrodata=@var{readonly-data-section}
6642 Put functions, data, and readonly data in @var{text-section},
6643 @var{data-section}, and @var{readonly-data-section} respectively
6644 by default. This can be overridden with the @code{section} attribute.
6645 @xref{Variable Attributes}.
6650 @subsection ARM Options
6653 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
6657 @item -mabi=@var{name}
6659 Generate code for the specified ABI. Permissible values are: @samp{apcs-gnu},
6660 @samp{atpcs}, @samp{aapcs} and @samp{iwmmxt}.
6663 @opindex mapcs-frame
6664 Generate a stack frame that is compliant with the ARM Procedure Call
6665 Standard for all functions, even if this is not strictly necessary for
6666 correct execution of the code. Specifying @option{-fomit-frame-pointer}
6667 with this option will cause the stack frames not to be generated for
6668 leaf functions. The default is @option{-mno-apcs-frame}.
6672 This is a synonym for @option{-mapcs-frame}.
6675 @c not currently implemented
6676 @item -mapcs-stack-check
6677 @opindex mapcs-stack-check
6678 Generate code to check the amount of stack space available upon entry to
6679 every function (that actually uses some stack space). If there is
6680 insufficient space available then either the function
6681 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
6682 called, depending upon the amount of stack space required. The run time
6683 system is required to provide these functions. The default is
6684 @option{-mno-apcs-stack-check}, since this produces smaller code.
6686 @c not currently implemented
6688 @opindex mapcs-float
6689 Pass floating point arguments using the float point registers. This is
6690 one of the variants of the APCS@. This option is recommended if the
6691 target hardware has a floating point unit or if a lot of floating point
6692 arithmetic is going to be performed by the code. The default is
6693 @option{-mno-apcs-float}, since integer only code is slightly increased in
6694 size if @option{-mapcs-float} is used.
6696 @c not currently implemented
6697 @item -mapcs-reentrant
6698 @opindex mapcs-reentrant
6699 Generate reentrant, position independent code. The default is
6700 @option{-mno-apcs-reentrant}.
6703 @item -mthumb-interwork
6704 @opindex mthumb-interwork
6705 Generate code which supports calling between the ARM and Thumb
6706 instruction sets. Without this option the two instruction sets cannot
6707 be reliably used inside one program. The default is
6708 @option{-mno-thumb-interwork}, since slightly larger code is generated
6709 when @option{-mthumb-interwork} is specified.
6711 @item -mno-sched-prolog
6712 @opindex mno-sched-prolog
6713 Prevent the reordering of instructions in the function prolog, or the
6714 merging of those instruction with the instructions in the function's
6715 body. This means that all functions will start with a recognizable set
6716 of instructions (or in fact one of a choice from a small set of
6717 different function prologues), and this information can be used to
6718 locate the start if functions inside an executable piece of code. The
6719 default is @option{-msched-prolog}.
6722 @opindex mhard-float
6723 Generate output containing floating point instructions. This is the
6727 @opindex msoft-float
6728 Generate output containing library calls for floating point.
6729 @strong{Warning:} the requisite libraries are not available for all ARM
6730 targets. Normally the facilities of the machine's usual C compiler are
6731 used, but this cannot be done directly in cross-compilation. You must make
6732 your own arrangements to provide suitable library functions for
6735 @option{-msoft-float} changes the calling convention in the output file;
6736 therefore, it is only useful if you compile @emph{all} of a program with
6737 this option. In particular, you need to compile @file{libgcc.a}, the
6738 library that comes with GCC, with @option{-msoft-float} in order for
6741 @item -mfloat-abi=@var{name}
6743 Specifies which ABI to use for floating point values. Permissible values
6744 are: @samp{soft}, @samp{softfp} and @samp{hard}.
6746 @samp{soft} and @samp{hard} are equivalent to @option{-msoft-float}
6747 and @option{-mhard-float} respectively. @samp{softfp} allows the generation
6748 of floating point instructions, but still uses the soft-float calling
6751 @item -mlittle-endian
6752 @opindex mlittle-endian
6753 Generate code for a processor running in little-endian mode. This is
6754 the default for all standard configurations.
6757 @opindex mbig-endian
6758 Generate code for a processor running in big-endian mode; the default is
6759 to compile code for a little-endian processor.
6761 @item -mwords-little-endian
6762 @opindex mwords-little-endian
6763 This option only applies when generating code for big-endian processors.
6764 Generate code for a little-endian word order but a big-endian byte
6765 order. That is, a byte order of the form @samp{32107654}. Note: this
6766 option should only be used if you require compatibility with code for
6767 big-endian ARM processors generated by versions of the compiler prior to
6770 @item -mcpu=@var{name}
6772 This specifies the name of the target ARM processor. GCC uses this name
6773 to determine what kind of instructions it can emit when generating
6774 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
6775 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
6776 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
6777 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
6778 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
6779 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s},
6780 @samp{arm8}, @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
6781 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
6782 @samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s},
6783 @samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi},
6784 @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s},
6785 @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e},
6786 @samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp},
6787 @samp{arm1176jz-s}, @samp{arm1176jzf-s}, @samp{xscale}, @samp{iwmmxt},
6790 @itemx -mtune=@var{name}
6792 This option is very similar to the @option{-mcpu=} option, except that
6793 instead of specifying the actual target processor type, and hence
6794 restricting which instructions can be used, it specifies that GCC should
6795 tune the performance of the code as if the target were of the type
6796 specified in this option, but still choosing the instructions that it
6797 will generate based on the cpu specified by a @option{-mcpu=} option.
6798 For some ARM implementations better performance can be obtained by using
6801 @item -march=@var{name}
6803 This specifies the name of the target ARM architecture. GCC uses this
6804 name to determine what kind of instructions it can emit when generating
6805 assembly code. This option can be used in conjunction with or instead
6806 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
6807 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
6808 @samp{armv5}, @samp{armv5t}, @samp{armv5te}, @samp{armv6}, @samp{armv6j},
6809 @samp{iwmmxt}, @samp{ep9312}.
6811 @item -mfpu=@var{name}
6812 @itemx -mfpe=@var{number}
6813 @itemx -mfp=@var{number}
6817 This specifies what floating point hardware (or hardware emulation) is
6818 available on the target. Permissible names are: @samp{fpa}, @samp{fpe2},
6819 @samp{fpe3}, @samp{maverick}, @samp{vfp}. @option{-mfp} and @option{-mfpe}
6820 are synonyms for @option{-mfpu}=@samp{fpe}@var{number}, for compatibility
6821 with older versions of GCC@.
6823 If @option{-msoft-float} is specified this specifies the format of
6824 floating point values.
6826 @item -mstructure-size-boundary=@var{n}
6827 @opindex mstructure-size-boundary
6828 The size of all structures and unions will be rounded up to a multiple
6829 of the number of bits set by this option. Permissible values are 8, 32
6830 and 64. The default value varies for different toolchains. For the COFF
6831 targeted toolchain the default value is 8. A value of 64 is only allowed
6832 if the underlying ABI supports it.
6834 Specifying the larger number can produce faster, more efficient code, but
6835 can also increase the size of the program. Different values are potentially
6836 incompatible. Code compiled with one value cannot necessarily expect to
6837 work with code or libraries compiled with another value, if they exchange
6838 information using structures or unions.
6840 @item -mabort-on-noreturn
6841 @opindex mabort-on-noreturn
6842 Generate a call to the function @code{abort} at the end of a
6843 @code{noreturn} function. It will be executed if the function tries to
6847 @itemx -mno-long-calls
6848 @opindex mlong-calls
6849 @opindex mno-long-calls
6850 Tells the compiler to perform function calls by first loading the
6851 address of the function into a register and then performing a subroutine
6852 call on this register. This switch is needed if the target function
6853 will lie outside of the 64 megabyte addressing range of the offset based
6854 version of subroutine call instruction.
6856 Even if this switch is enabled, not all function calls will be turned
6857 into long calls. The heuristic is that static functions, functions
6858 which have the @samp{short-call} attribute, functions that are inside
6859 the scope of a @samp{#pragma no_long_calls} directive and functions whose
6860 definitions have already been compiled within the current compilation
6861 unit, will not be turned into long calls. The exception to this rule is
6862 that weak function definitions, functions with the @samp{long-call}
6863 attribute or the @samp{section} attribute, and functions that are within
6864 the scope of a @samp{#pragma long_calls} directive, will always be
6865 turned into long calls.
6867 This feature is not enabled by default. Specifying
6868 @option{-mno-long-calls} will restore the default behavior, as will
6869 placing the function calls within the scope of a @samp{#pragma
6870 long_calls_off} directive. Note these switches have no effect on how
6871 the compiler generates code to handle function calls via function
6874 @item -mnop-fun-dllimport
6875 @opindex mnop-fun-dllimport
6876 Disable support for the @code{dllimport} attribute.
6878 @item -msingle-pic-base
6879 @opindex msingle-pic-base
6880 Treat the register used for PIC addressing as read-only, rather than
6881 loading it in the prologue for each function. The run-time system is
6882 responsible for initializing this register with an appropriate value
6883 before execution begins.
6885 @item -mpic-register=@var{reg}
6886 @opindex mpic-register
6887 Specify the register to be used for PIC addressing. The default is R10
6888 unless stack-checking is enabled, when R9 is used.
6890 @item -mcirrus-fix-invalid-insns
6891 @opindex mcirrus-fix-invalid-insns
6892 @opindex mno-cirrus-fix-invalid-insns
6893 Insert NOPs into the instruction stream to in order to work around
6894 problems with invalid Maverick instruction combinations. This option
6895 is only valid if the @option{-mcpu=ep9312} option has been used to
6896 enable generation of instructions for the Cirrus Maverick floating
6897 point co-processor. This option is not enabled by default, since the
6898 problem is only present in older Maverick implementations. The default
6899 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
6902 @item -mpoke-function-name
6903 @opindex mpoke-function-name
6904 Write the name of each function into the text section, directly
6905 preceding the function prologue. The generated code is similar to this:
6909 .ascii "arm_poke_function_name", 0
6912 .word 0xff000000 + (t1 - t0)
6913 arm_poke_function_name
6915 stmfd sp!, @{fp, ip, lr, pc@}
6919 When performing a stack backtrace, code can inspect the value of
6920 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
6921 location @code{pc - 12} and the top 8 bits are set, then we know that
6922 there is a function name embedded immediately preceding this location
6923 and has length @code{((pc[-3]) & 0xff000000)}.
6927 Generate code for the 16-bit Thumb instruction set. The default is to
6928 use the 32-bit ARM instruction set.
6931 @opindex mtpcs-frame
6932 Generate a stack frame that is compliant with the Thumb Procedure Call
6933 Standard for all non-leaf functions. (A leaf function is one that does
6934 not call any other functions.) The default is @option{-mno-tpcs-frame}.
6936 @item -mtpcs-leaf-frame
6937 @opindex mtpcs-leaf-frame
6938 Generate a stack frame that is compliant with the Thumb Procedure Call
6939 Standard for all leaf functions. (A leaf function is one that does
6940 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
6942 @item -mcallee-super-interworking
6943 @opindex mcallee-super-interworking
6944 Gives all externally visible functions in the file being compiled an ARM
6945 instruction set header which switches to Thumb mode before executing the
6946 rest of the function. This allows these functions to be called from
6947 non-interworking code.
6949 @item -mcaller-super-interworking
6950 @opindex mcaller-super-interworking
6951 Allows calls via function pointers (including virtual functions) to
6952 execute correctly regardless of whether the target code has been
6953 compiled for interworking or not. There is a small overhead in the cost
6954 of executing a function pointer if this option is enabled.
6959 @subsection AVR Options
6962 These options are defined for AVR implementations:
6965 @item -mmcu=@var{mcu}
6967 Specify ATMEL AVR instruction set or MCU type.
6969 Instruction set avr1 is for the minimal AVR core, not supported by the C
6970 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
6971 attiny11, attiny12, attiny15, attiny28).
6973 Instruction set avr2 (default) is for the classic AVR core with up to
6974 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
6975 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
6976 at90c8534, at90s8535).
6978 Instruction set avr3 is for the classic AVR core with up to 128K program
6979 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
6981 Instruction set avr4 is for the enhanced AVR core with up to 8K program
6982 memory space (MCU types: atmega8, atmega83, atmega85).
6984 Instruction set avr5 is for the enhanced AVR core with up to 128K program
6985 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
6986 atmega64, atmega128, at43usb355, at94k).
6990 Output instruction sizes to the asm file.
6992 @item -minit-stack=@var{N}
6993 @opindex minit-stack
6994 Specify the initial stack address, which may be a symbol or numeric value,
6995 @samp{__stack} is the default.
6997 @item -mno-interrupts
6998 @opindex mno-interrupts
6999 Generated code is not compatible with hardware interrupts.
7000 Code size will be smaller.
7002 @item -mcall-prologues
7003 @opindex mcall-prologues
7004 Functions prologues/epilogues expanded as call to appropriate
7005 subroutines. Code size will be smaller.
7007 @item -mno-tablejump
7008 @opindex mno-tablejump
7009 Do not generate tablejump insns which sometimes increase code size.
7012 @opindex mtiny-stack
7013 Change only the low 8 bits of the stack pointer.
7017 Assume int to be 8 bit integer. This affects the sizes of all types: A
7018 char will be 1 byte, an int will be 1 byte, an long will be 2 bytes
7019 and long long will be 4 bytes. Please note that this option does not
7020 comply to the C standards, but it will provide you with smaller code
7025 @subsection CRIS Options
7026 @cindex CRIS Options
7028 These options are defined specifically for the CRIS ports.
7031 @item -march=@var{architecture-type}
7032 @itemx -mcpu=@var{architecture-type}
7035 Generate code for the specified architecture. The choices for
7036 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
7037 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX.
7038 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
7041 @item -mtune=@var{architecture-type}
7043 Tune to @var{architecture-type} everything applicable about the generated
7044 code, except for the ABI and the set of available instructions. The
7045 choices for @var{architecture-type} are the same as for
7046 @option{-march=@var{architecture-type}}.
7048 @item -mmax-stack-frame=@var{n}
7049 @opindex mmax-stack-frame
7050 Warn when the stack frame of a function exceeds @var{n} bytes.
7052 @item -melinux-stacksize=@var{n}
7053 @opindex melinux-stacksize
7054 Only available with the @samp{cris-axis-aout} target. Arranges for
7055 indications in the program to the kernel loader that the stack of the
7056 program should be set to @var{n} bytes.
7062 The options @option{-metrax4} and @option{-metrax100} are synonyms for
7063 @option{-march=v3} and @option{-march=v8} respectively.
7065 @item -mmul-bug-workaround
7066 @itemx -mno-mul-bug-workaround
7067 @opindex mmul-bug-workaround
7068 @opindex mno-mul-bug-workaround
7069 Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
7070 models where it applies. This option is active by default.
7074 Enable CRIS-specific verbose debug-related information in the assembly
7075 code. This option also has the effect to turn off the @samp{#NO_APP}
7076 formatted-code indicator to the assembler at the beginning of the
7081 Do not use condition-code results from previous instruction; always emit
7082 compare and test instructions before use of condition codes.
7084 @item -mno-side-effects
7085 @opindex mno-side-effects
7086 Do not emit instructions with side-effects in addressing modes other than
7090 @itemx -mno-stack-align
7092 @itemx -mno-data-align
7093 @itemx -mconst-align
7094 @itemx -mno-const-align
7095 @opindex mstack-align
7096 @opindex mno-stack-align
7097 @opindex mdata-align
7098 @opindex mno-data-align
7099 @opindex mconst-align
7100 @opindex mno-const-align
7101 These options (no-options) arranges (eliminate arrangements) for the
7102 stack-frame, individual data and constants to be aligned for the maximum
7103 single data access size for the chosen CPU model. The default is to
7104 arrange for 32-bit alignment. ABI details such as structure layout are
7105 not affected by these options.
7113 Similar to the stack- data- and const-align options above, these options
7114 arrange for stack-frame, writable data and constants to all be 32-bit,
7115 16-bit or 8-bit aligned. The default is 32-bit alignment.
7117 @item -mno-prologue-epilogue
7118 @itemx -mprologue-epilogue
7119 @opindex mno-prologue-epilogue
7120 @opindex mprologue-epilogue
7121 With @option{-mno-prologue-epilogue}, the normal function prologue and
7122 epilogue that sets up the stack-frame are omitted and no return
7123 instructions or return sequences are generated in the code. Use this
7124 option only together with visual inspection of the compiled code: no
7125 warnings or errors are generated when call-saved registers must be saved,
7126 or storage for local variable needs to be allocated.
7132 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
7133 instruction sequences that load addresses for functions from the PLT part
7134 of the GOT rather than (traditional on other architectures) calls to the
7135 PLT. The default is @option{-mgotplt}.
7139 Legacy no-op option only recognized with the cris-axis-aout target.
7143 Legacy no-op option only recognized with the cris-axis-elf and
7144 cris-axis-linux-gnu targets.
7148 Only recognized with the cris-axis-aout target, where it selects a
7149 GNU/linux-like multilib, include files and instruction set for
7154 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
7158 This option, recognized for the cris-axis-aout and cris-axis-elf arranges
7159 to link with input-output functions from a simulator library. Code,
7160 initialized data and zero-initialized data are allocated consecutively.
7164 Like @option{-sim}, but pass linker options to locate initialized data at
7165 0x40000000 and zero-initialized data at 0x80000000.
7168 @node Darwin Options
7169 @subsection Darwin Options
7170 @cindex Darwin options
7172 These options are defined for all architectures running the Darwin operating
7173 system. They are useful for compatibility with other Mac OS compilers.
7178 Add the framework directory @var{dir} to the head of the list of
7179 directories to be searched for header files. These directories are
7180 interleaved with those specified by @option{-I} options and are
7181 scanned in a left-to-right order.
7183 A framework directory is a directory with frameworks in it. A
7184 framework is a directory with a @samp{"Headers"} and/or
7185 @samp{"PrivateHeaders"} directory contained directly in it that ends
7186 in @samp{".framework"}. The name of a framework is the name of this
7187 directory excluding the @samp{".framework"}. Headers associated with
7188 the framework are found in one of those two directories, with
7189 @samp{"Headers"} being searched first. A subframework is a framework
7190 directory that is in a framework's @samp{"Frameworks"} directory.
7191 Includes of subframework headers can only appear in a header of a
7192 framework that contains the subframework, or in a sibling subframework
7193 header. Two subframeworks are siblings if they occur in the same
7194 framework. A subframework should not have the same name as a
7195 framework, a warning will be issued if this is violated. Currently a
7196 subframework cannot have subframeworks, in the future, the mechanism
7197 may be extended to support this. The standard frameworks can be found
7198 in @samp{"/System/Library/Frameworks"} and
7199 @samp{"/Library/Frameworks"}. An example include looks like
7200 @code{#include <Framework/header.h>}, where @samp{Framework} denotes
7201 the name of the framework and header.h is found in the
7202 @samp{"PrivateHeaders"} or @samp{"Headers"} directory.
7206 Emit debugging information for symbols that are used. For STABS
7207 debugging format, this enables @option{-feliminate-unused-debug-symbols}.
7208 This is by default ON.
7212 Emit debugging information for all symbols and types.
7214 @item -mone-byte-bool
7215 @opindex -mone-byte-bool
7216 Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}.
7217 By default @samp{sizeof(bool)} is @samp{4} when compiling for
7218 Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this
7219 option has no effect on x86.
7221 @strong{Warning:} The @option{-mone-byte-bool} switch causes GCC
7222 to generate code that is not binary compatible with code generated
7223 without that switch. Using this switch may require recompiling all
7224 other modules in a program, including system libraries. Use this
7225 switch to conform to a non-default data model.
7227 @item -mfix-and-continue
7228 @itemx -ffix-and-continue
7229 @itemx -findirect-data
7230 @opindex mfix-and-continue
7231 @opindex ffix-and-continue
7232 @opindex findirect-data
7233 Generate code suitable for fast turn around development. Needed to
7234 enable gdb to dynamically load @code{.o} files into already running
7235 programs. @option{-findirect-data} and @option{-ffix-and-continue}
7236 are provided for backwards compatibility.
7240 Loads all members of static archive libraries.
7241 See man ld(1) for more information.
7243 @item -arch_errors_fatal
7244 @opindex arch_errors_fatal
7245 Cause the errors having to do with files that have the wrong architecture
7249 @opindex bind_at_load
7250 Causes the output file to be marked such that the dynamic linker will
7251 bind all undefined references when the file is loaded or launched.
7255 Produce a Mach-o bundle format file.
7256 See man ld(1) for more information.
7258 @item -bundle_loader @var{executable}
7259 @opindex bundle_loader
7260 This specifies the @var{executable} that will be loading the build
7261 output file being linked. See man ld(1) for more information.
7263 @item -allowable_client @var{client_name}
7267 @itemx -compatibility_version
7268 @itemx -current_version
7270 @itemx -dependency-file
7272 @itemx -dylinker_install_name
7275 @itemx -exported_symbols_list
7277 @itemx -flat_namespace
7278 @itemx -force_cpusubtype_ALL
7279 @itemx -force_flat_namespace
7280 @itemx -headerpad_max_install_names
7283 @itemx -install_name
7284 @itemx -keep_private_externs
7285 @itemx -multi_module
7286 @itemx -multiply_defined
7287 @itemx -multiply_defined_unused
7289 @itemx -no_dead_strip_inits_and_terms
7290 @itemx -nofixprebinding
7293 @itemx -noseglinkedit
7294 @itemx -pagezero_size
7296 @itemx -prebind_all_twolevel_modules
7297 @itemx -private_bundle
7298 @itemx -read_only_relocs
7300 @itemx -sectobjectsymbols
7304 @itemx -sectobjectsymbols
7307 @itemx -segs_read_only_addr
7308 @itemx -segs_read_write_addr
7309 @itemx -seg_addr_table
7310 @itemx -seg_addr_table_filename
7313 @itemx -segs_read_only_addr
7314 @itemx -segs_read_write_addr
7315 @itemx -single_module
7318 @itemx -sub_umbrella
7319 @itemx -twolevel_namespace
7322 @itemx -unexported_symbols_list
7323 @itemx -weak_reference_mismatches
7326 @opindex allowable_client
7328 @opindex client_name
7329 @opindex compatibility_version
7330 @opindex current_version
7332 @opindex dependency-file
7334 @opindex dylinker_install_name
7337 @opindex exported_symbols_list
7339 @opindex flat_namespace
7340 @opindex force_cpusubtype_ALL
7341 @opindex force_flat_namespace
7342 @opindex headerpad_max_install_names
7345 @opindex install_name
7346 @opindex keep_private_externs
7347 @opindex multi_module
7348 @opindex multiply_defined
7349 @opindex multiply_defined_unused
7351 @opindex no_dead_strip_inits_and_terms
7352 @opindex nofixprebinding
7353 @opindex nomultidefs
7355 @opindex noseglinkedit
7356 @opindex pagezero_size
7358 @opindex prebind_all_twolevel_modules
7359 @opindex private_bundle
7360 @opindex read_only_relocs
7362 @opindex sectobjectsymbols
7366 @opindex sectobjectsymbols
7369 @opindex segs_read_only_addr
7370 @opindex segs_read_write_addr
7371 @opindex seg_addr_table
7372 @opindex seg_addr_table_filename
7373 @opindex seglinkedit
7375 @opindex segs_read_only_addr
7376 @opindex segs_read_write_addr
7377 @opindex single_module
7379 @opindex sub_library
7380 @opindex sub_umbrella
7381 @opindex twolevel_namespace
7384 @opindex unexported_symbols_list
7385 @opindex weak_reference_mismatches
7386 @opindex whatsloaded
7388 These options are available for Darwin linker. Darwin linker man page
7389 describes them in detail.
7392 @node DEC Alpha Options
7393 @subsection DEC Alpha Options
7395 These @samp{-m} options are defined for the DEC Alpha implementations:
7398 @item -mno-soft-float
7400 @opindex mno-soft-float
7401 @opindex msoft-float
7402 Use (do not use) the hardware floating-point instructions for
7403 floating-point operations. When @option{-msoft-float} is specified,
7404 functions in @file{libgcc.a} will be used to perform floating-point
7405 operations. Unless they are replaced by routines that emulate the
7406 floating-point operations, or compiled in such a way as to call such
7407 emulations routines, these routines will issue floating-point
7408 operations. If you are compiling for an Alpha without floating-point
7409 operations, you must ensure that the library is built so as not to call
7412 Note that Alpha implementations without floating-point operations are
7413 required to have floating-point registers.
7418 @opindex mno-fp-regs
7419 Generate code that uses (does not use) the floating-point register set.
7420 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
7421 register set is not used, floating point operands are passed in integer
7422 registers as if they were integers and floating-point results are passed
7423 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
7424 so any function with a floating-point argument or return value called by code
7425 compiled with @option{-mno-fp-regs} must also be compiled with that
7428 A typical use of this option is building a kernel that does not use,
7429 and hence need not save and restore, any floating-point registers.
7433 The Alpha architecture implements floating-point hardware optimized for
7434 maximum performance. It is mostly compliant with the IEEE floating
7435 point standard. However, for full compliance, software assistance is
7436 required. This option generates code fully IEEE compliant code
7437 @emph{except} that the @var{inexact-flag} is not maintained (see below).
7438 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
7439 defined during compilation. The resulting code is less efficient but is
7440 able to correctly support denormalized numbers and exceptional IEEE
7441 values such as not-a-number and plus/minus infinity. Other Alpha
7442 compilers call this option @option{-ieee_with_no_inexact}.
7444 @item -mieee-with-inexact
7445 @opindex mieee-with-inexact
7446 This is like @option{-mieee} except the generated code also maintains
7447 the IEEE @var{inexact-flag}. Turning on this option causes the
7448 generated code to implement fully-compliant IEEE math. In addition to
7449 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
7450 macro. On some Alpha implementations the resulting code may execute
7451 significantly slower than the code generated by default. Since there is
7452 very little code that depends on the @var{inexact-flag}, you should
7453 normally not specify this option. Other Alpha compilers call this
7454 option @option{-ieee_with_inexact}.
7456 @item -mfp-trap-mode=@var{trap-mode}
7457 @opindex mfp-trap-mode
7458 This option controls what floating-point related traps are enabled.
7459 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
7460 The trap mode can be set to one of four values:
7464 This is the default (normal) setting. The only traps that are enabled
7465 are the ones that cannot be disabled in software (e.g., division by zero
7469 In addition to the traps enabled by @samp{n}, underflow traps are enabled
7473 Like @samp{su}, but the instructions are marked to be safe for software
7474 completion (see Alpha architecture manual for details).
7477 Like @samp{su}, but inexact traps are enabled as well.
7480 @item -mfp-rounding-mode=@var{rounding-mode}
7481 @opindex mfp-rounding-mode
7482 Selects the IEEE rounding mode. Other Alpha compilers call this option
7483 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
7488 Normal IEEE rounding mode. Floating point numbers are rounded towards
7489 the nearest machine number or towards the even machine number in case
7493 Round towards minus infinity.
7496 Chopped rounding mode. Floating point numbers are rounded towards zero.
7499 Dynamic rounding mode. A field in the floating point control register
7500 (@var{fpcr}, see Alpha architecture reference manual) controls the
7501 rounding mode in effect. The C library initializes this register for
7502 rounding towards plus infinity. Thus, unless your program modifies the
7503 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
7506 @item -mtrap-precision=@var{trap-precision}
7507 @opindex mtrap-precision
7508 In the Alpha architecture, floating point traps are imprecise. This
7509 means without software assistance it is impossible to recover from a
7510 floating trap and program execution normally needs to be terminated.
7511 GCC can generate code that can assist operating system trap handlers
7512 in determining the exact location that caused a floating point trap.
7513 Depending on the requirements of an application, different levels of
7514 precisions can be selected:
7518 Program precision. This option is the default and means a trap handler
7519 can only identify which program caused a floating point exception.
7522 Function precision. The trap handler can determine the function that
7523 caused a floating point exception.
7526 Instruction precision. The trap handler can determine the exact
7527 instruction that caused a floating point exception.
7530 Other Alpha compilers provide the equivalent options called
7531 @option{-scope_safe} and @option{-resumption_safe}.
7533 @item -mieee-conformant
7534 @opindex mieee-conformant
7535 This option marks the generated code as IEEE conformant. You must not
7536 use this option unless you also specify @option{-mtrap-precision=i} and either
7537 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
7538 is to emit the line @samp{.eflag 48} in the function prologue of the
7539 generated assembly file. Under DEC Unix, this has the effect that
7540 IEEE-conformant math library routines will be linked in.
7542 @item -mbuild-constants
7543 @opindex mbuild-constants
7544 Normally GCC examines a 32- or 64-bit integer constant to
7545 see if it can construct it from smaller constants in two or three
7546 instructions. If it cannot, it will output the constant as a literal and
7547 generate code to load it from the data segment at runtime.
7549 Use this option to require GCC to construct @emph{all} integer constants
7550 using code, even if it takes more instructions (the maximum is six).
7552 You would typically use this option to build a shared library dynamic
7553 loader. Itself a shared library, it must relocate itself in memory
7554 before it can find the variables and constants in its own data segment.
7560 Select whether to generate code to be assembled by the vendor-supplied
7561 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
7579 Indicate whether GCC should generate code to use the optional BWX,
7580 CIX, FIX and MAX instruction sets. The default is to use the instruction
7581 sets supported by the CPU type specified via @option{-mcpu=} option or that
7582 of the CPU on which GCC was built if none was specified.
7587 @opindex mfloat-ieee
7588 Generate code that uses (does not use) VAX F and G floating point
7589 arithmetic instead of IEEE single and double precision.
7591 @item -mexplicit-relocs
7592 @itemx -mno-explicit-relocs
7593 @opindex mexplicit-relocs
7594 @opindex mno-explicit-relocs
7595 Older Alpha assemblers provided no way to generate symbol relocations
7596 except via assembler macros. Use of these macros does not allow
7597 optimal instruction scheduling. GNU binutils as of version 2.12
7598 supports a new syntax that allows the compiler to explicitly mark
7599 which relocations should apply to which instructions. This option
7600 is mostly useful for debugging, as GCC detects the capabilities of
7601 the assembler when it is built and sets the default accordingly.
7605 @opindex msmall-data
7606 @opindex mlarge-data
7607 When @option{-mexplicit-relocs} is in effect, static data is
7608 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
7609 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
7610 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
7611 16-bit relocations off of the @code{$gp} register. This limits the
7612 size of the small data area to 64KB, but allows the variables to be
7613 directly accessed via a single instruction.
7615 The default is @option{-mlarge-data}. With this option the data area
7616 is limited to just below 2GB. Programs that require more than 2GB of
7617 data must use @code{malloc} or @code{mmap} to allocate the data in the
7618 heap instead of in the program's data segment.
7620 When generating code for shared libraries, @option{-fpic} implies
7621 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
7625 @opindex msmall-text
7626 @opindex mlarge-text
7627 When @option{-msmall-text} is used, the compiler assumes that the
7628 code of the entire program (or shared library) fits in 4MB, and is
7629 thus reachable with a branch instruction. When @option{-msmall-data}
7630 is used, the compiler can assume that all local symbols share the
7631 same @code{$gp} value, and thus reduce the number of instructions
7632 required for a function call from 4 to 1.
7634 The default is @option{-mlarge-text}.
7636 @item -mcpu=@var{cpu_type}
7638 Set the instruction set and instruction scheduling parameters for
7639 machine type @var{cpu_type}. You can specify either the @samp{EV}
7640 style name or the corresponding chip number. GCC supports scheduling
7641 parameters for the EV4, EV5 and EV6 family of processors and will
7642 choose the default values for the instruction set from the processor
7643 you specify. If you do not specify a processor type, GCC will default
7644 to the processor on which the compiler was built.
7646 Supported values for @var{cpu_type} are
7652 Schedules as an EV4 and has no instruction set extensions.
7656 Schedules as an EV5 and has no instruction set extensions.
7660 Schedules as an EV5 and supports the BWX extension.
7665 Schedules as an EV5 and supports the BWX and MAX extensions.
7669 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
7673 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
7676 @item -mtune=@var{cpu_type}
7678 Set only the instruction scheduling parameters for machine type
7679 @var{cpu_type}. The instruction set is not changed.
7681 @item -mmemory-latency=@var{time}
7682 @opindex mmemory-latency
7683 Sets the latency the scheduler should assume for typical memory
7684 references as seen by the application. This number is highly
7685 dependent on the memory access patterns used by the application
7686 and the size of the external cache on the machine.
7688 Valid options for @var{time} are
7692 A decimal number representing clock cycles.
7698 The compiler contains estimates of the number of clock cycles for
7699 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
7700 (also called Dcache, Scache, and Bcache), as well as to main memory.
7701 Note that L3 is only valid for EV5.
7706 @node DEC Alpha/VMS Options
7707 @subsection DEC Alpha/VMS Options
7709 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
7712 @item -mvms-return-codes
7713 @opindex mvms-return-codes
7714 Return VMS condition codes from main. The default is to return POSIX
7715 style condition (e.g.@ error) codes.
7719 @subsection FRV Options
7726 Only use the first 32 general purpose registers.
7731 Use all 64 general purpose registers.
7736 Use only the first 32 floating point registers.
7741 Use all 64 floating point registers
7744 @opindex mhard-float
7746 Use hardware instructions for floating point operations.
7749 @opindex msoft-float
7751 Use library routines for floating point operations.
7756 Dynamically allocate condition code registers.
7761 Do not try to dynamically allocate condition code registers, only
7762 use @code{icc0} and @code{fcc0}.
7767 Change ABI to use double word insns.
7772 Do not use double word instructions.
7777 Use floating point double instructions.
7782 Do not use floating point double instructions.
7787 Use media instructions.
7792 Do not use media instructions.
7797 Use multiply and add/subtract instructions.
7802 Do not use multiply and add/subtract instructions.
7807 Select the FDPIC ABI, that uses function descriptors to represent
7808 pointers to functions. Without any PIC/PIE-related options, it
7809 implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it
7810 assumes GOT entries and small data are within a 12-bit range from the
7811 GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets
7812 are computed with 32 bits.
7815 @opindex minline-plt
7817 Enable inlining of PLT entries in function calls to functions that are
7818 not known to bind locally. It has no effect without @option{-mfdpic}.
7819 It's enabled by default if optimizing for speed and compiling for
7820 shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an
7821 optimization option such as @option{-O3} or above is present in the
7827 Enable the use of @code{GPREL} relocations in the FDPIC ABI for data
7828 that is known to be in read-only sections. It's enabled by default,
7829 except for @option{-fpic} or @option{-fpie}: even though it may help
7830 make the global offset table smaller, it trades 1 instruction for 4.
7831 With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4,
7832 one of which may be shared by multiple symbols, and it avoids the need
7833 for a GOT entry for the referenced symbol, so it's more likely to be a
7834 win. If it is not, @option{-mno-gprel-ro} can be used to disable it.
7836 @item -multilib-library-pic
7837 @opindex multilib-library-pic
7839 Link with the (library, not FD) pic libraries. It's implied by
7840 @option{-mlibrary-pic}, as well as by @option{-fPIC} and
7841 @option{-fpic} without @option{-mfdpic}. You should never have to use
7847 Follow the EABI requirement of always creating a frame pointer whenever
7848 a stack frame is allocated. This option is enabled by default and can
7849 be disabled with @option{-mno-linked-fp}.
7852 @opindex mlong-calls
7854 Use indirect addressing to call functions outside the current
7855 compilation unit. This allows the functions to be placed anywhere
7856 within the 32-bit address space.
7858 @item -malign-labels
7859 @opindex malign-labels
7861 Try to align labels to an 8-byte boundary by inserting nops into the
7862 previous packet. This option only has an effect when VLIW packing
7863 is enabled. It doesn't create new packets; it merely adds nops to
7867 @opindex mlibrary-pic
7869 Generate position-independent EABI code.
7874 Use only the first four media accumulator registers.
7879 Use all eight media accumulator registers.
7884 Pack VLIW instructions.
7889 Do not pack VLIW instructions.
7894 Do not mark ABI switches in e_flags.
7899 Enable the use of conditional-move instructions (default).
7901 This switch is mainly for debugging the compiler and will likely be removed
7902 in a future version.
7904 @item -mno-cond-move
7905 @opindex mno-cond-move
7907 Disable the use of conditional-move instructions.
7909 This switch is mainly for debugging the compiler and will likely be removed
7910 in a future version.
7915 Enable the use of conditional set instructions (default).
7917 This switch is mainly for debugging the compiler and will likely be removed
7918 in a future version.
7923 Disable the use of conditional set instructions.
7925 This switch is mainly for debugging the compiler and will likely be removed
7926 in a future version.
7931 Enable the use of conditional execution (default).
7933 This switch is mainly for debugging the compiler and will likely be removed
7934 in a future version.
7936 @item -mno-cond-exec
7937 @opindex mno-cond-exec
7939 Disable the use of conditional execution.
7941 This switch is mainly for debugging the compiler and will likely be removed
7942 in a future version.
7945 @opindex mvliw-branch
7947 Run a pass to pack branches into VLIW instructions (default).
7949 This switch is mainly for debugging the compiler and will likely be removed
7950 in a future version.
7952 @item -mno-vliw-branch
7953 @opindex mno-vliw-branch
7955 Do not run a pass to pack branches into VLIW instructions.
7957 This switch is mainly for debugging the compiler and will likely be removed
7958 in a future version.
7960 @item -mmulti-cond-exec
7961 @opindex mmulti-cond-exec
7963 Enable optimization of @code{&&} and @code{||} in conditional execution
7966 This switch is mainly for debugging the compiler and will likely be removed
7967 in a future version.
7969 @item -mno-multi-cond-exec
7970 @opindex mno-multi-cond-exec
7972 Disable optimization of @code{&&} and @code{||} in conditional execution.
7974 This switch is mainly for debugging the compiler and will likely be removed
7975 in a future version.
7977 @item -mnested-cond-exec
7978 @opindex mnested-cond-exec
7980 Enable nested conditional execution optimizations (default).
7982 This switch is mainly for debugging the compiler and will likely be removed
7983 in a future version.
7985 @item -mno-nested-cond-exec
7986 @opindex mno-nested-cond-exec
7988 Disable nested conditional execution optimizations.
7990 This switch is mainly for debugging the compiler and will likely be removed
7991 in a future version.
7993 @item -mtomcat-stats
7994 @opindex mtomcat-stats
7996 Cause gas to print out tomcat statistics.
7998 @item -mcpu=@var{cpu}
8001 Select the processor type for which to generate code. Possible values are
8002 @samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450},
8003 @samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}.
8007 @node H8/300 Options
8008 @subsection H8/300 Options
8010 These @samp{-m} options are defined for the H8/300 implementations:
8015 Shorten some address references at link time, when possible; uses the
8016 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
8017 ld, Using ld}, for a fuller description.
8021 Generate code for the H8/300H@.
8025 Generate code for the H8S@.
8029 Generate code for the H8S and H8/300H in the normal mode. This switch
8030 must be used either with @option{-mh} or @option{-ms}.
8034 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
8038 Make @code{int} data 32 bits by default.
8042 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
8043 The default for the H8/300H and H8S is to align longs and floats on 4
8045 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
8046 This option has no effect on the H8/300.
8050 @subsection HPPA Options
8051 @cindex HPPA Options
8053 These @samp{-m} options are defined for the HPPA family of computers:
8056 @item -march=@var{architecture-type}
8058 Generate code for the specified architecture. The choices for
8059 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
8060 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
8061 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
8062 architecture option for your machine. Code compiled for lower numbered
8063 architectures will run on higher numbered architectures, but not the
8067 @itemx -mpa-risc-1-1
8068 @itemx -mpa-risc-2-0
8069 @opindex mpa-risc-1-0
8070 @opindex mpa-risc-1-1
8071 @opindex mpa-risc-2-0
8072 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
8075 @opindex mbig-switch
8076 Generate code suitable for big switch tables. Use this option only if
8077 the assembler/linker complain about out of range branches within a switch
8080 @item -mjump-in-delay
8081 @opindex mjump-in-delay
8082 Fill delay slots of function calls with unconditional jump instructions
8083 by modifying the return pointer for the function call to be the target
8084 of the conditional jump.
8086 @item -mdisable-fpregs
8087 @opindex mdisable-fpregs
8088 Prevent floating point registers from being used in any manner. This is
8089 necessary for compiling kernels which perform lazy context switching of
8090 floating point registers. If you use this option and attempt to perform
8091 floating point operations, the compiler will abort.
8093 @item -mdisable-indexing
8094 @opindex mdisable-indexing
8095 Prevent the compiler from using indexing address modes. This avoids some
8096 rather obscure problems when compiling MIG generated code under MACH@.
8098 @item -mno-space-regs
8099 @opindex mno-space-regs
8100 Generate code that assumes the target has no space registers. This allows
8101 GCC to generate faster indirect calls and use unscaled index address modes.
8103 Such code is suitable for level 0 PA systems and kernels.
8105 @item -mfast-indirect-calls
8106 @opindex mfast-indirect-calls
8107 Generate code that assumes calls never cross space boundaries. This
8108 allows GCC to emit code which performs faster indirect calls.
8110 This option will not work in the presence of shared libraries or nested
8113 @item -mfixed-range=@var{register-range}
8114 @opindex mfixed-range
8115 Generate code treating the given register range as fixed registers.
8116 A fixed register is one that the register allocator can not use. This is
8117 useful when compiling kernel code. A register range is specified as
8118 two registers separated by a dash. Multiple register ranges can be
8119 specified separated by a comma.
8121 @item -mlong-load-store
8122 @opindex mlong-load-store
8123 Generate 3-instruction load and store sequences as sometimes required by
8124 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
8127 @item -mportable-runtime
8128 @opindex mportable-runtime
8129 Use the portable calling conventions proposed by HP for ELF systems.
8133 Enable the use of assembler directives only GAS understands.
8135 @item -mschedule=@var{cpu-type}
8137 Schedule code according to the constraints for the machine type
8138 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
8139 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
8140 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
8141 proper scheduling option for your machine. The default scheduling is
8145 @opindex mlinker-opt
8146 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
8147 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
8148 linkers in which they give bogus error messages when linking some programs.
8151 @opindex msoft-float
8152 Generate output containing library calls for floating point.
8153 @strong{Warning:} the requisite libraries are not available for all HPPA
8154 targets. Normally the facilities of the machine's usual C compiler are
8155 used, but this cannot be done directly in cross-compilation. You must make
8156 your own arrangements to provide suitable library functions for
8157 cross-compilation. The embedded target @samp{hppa1.1-*-pro}
8158 does provide software floating point support.
8160 @option{-msoft-float} changes the calling convention in the output file;
8161 therefore, it is only useful if you compile @emph{all} of a program with
8162 this option. In particular, you need to compile @file{libgcc.a}, the
8163 library that comes with GCC, with @option{-msoft-float} in order for
8168 Generate the predefine, @code{_SIO}, for server IO. The default is
8169 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
8170 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO. These
8171 options are available under HP-UX and HI-UX.
8175 Use GNU ld specific options. This passes @option{-shared} to ld when
8176 building a shared library. It is the default when GCC is configured,
8177 explicitly or implicitly, with the GNU linker. This option does not
8178 have any affect on which ld is called, it only changes what parameters
8179 are passed to that ld. The ld that is called is determined by the
8180 @option{--with-ld} configure option, GCC's program search path, and
8181 finally by the user's @env{PATH}. The linker used by GCC can be printed
8182 using @samp{which `gcc -print-prog-name=ld`}.
8186 Use HP ld specific options. This passes @option{-b} to ld when building
8187 a shared library and passes @option{+Accept TypeMismatch} to ld on all
8188 links. It is the default when GCC is configured, explicitly or
8189 implicitly, with the HP linker. This option does not have any affect on
8190 which ld is called, it only changes what parameters are passed to that
8191 ld. The ld that is called is determined by the @option{--with-ld}
8192 configure option, GCC's program search path, and finally by the user's
8193 @env{PATH}. The linker used by GCC can be printed using @samp{which
8194 `gcc -print-prog-name=ld`}.
8197 @opindex mno-long-calls
8198 Generate code that uses long call sequences. This ensures that a call
8199 is always able to reach linker generated stubs. The default is to generate
8200 long calls only when the distance from the call site to the beginning
8201 of the function or translation unit, as the case may be, exceeds a
8202 predefined limit set by the branch type being used. The limits for
8203 normal calls are 7,600,000 and 240,000 bytes, respectively for the
8204 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
8207 Distances are measured from the beginning of functions when using the
8208 @option{-ffunction-sections} option, or when using the @option{-mgas}
8209 and @option{-mno-portable-runtime} options together under HP-UX with
8212 It is normally not desirable to use this option as it will degrade
8213 performance. However, it may be useful in large applications,
8214 particularly when partial linking is used to build the application.
8216 The types of long calls used depends on the capabilities of the
8217 assembler and linker, and the type of code being generated. The
8218 impact on systems that support long absolute calls, and long pic
8219 symbol-difference or pc-relative calls should be relatively small.
8220 However, an indirect call is used on 32-bit ELF systems in pic code
8221 and it is quite long.
8223 @item -munix=@var{unix-std}
8225 Generate compiler predefines and select a startfile for the specified
8226 UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95}
8227 and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95}
8228 is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX
8229 11.11 and later. The default values are @samp{93} for HP-UX 10.00,
8230 @samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11
8233 @option{-munix=93} provides the same predefines as GCC 3.3 and 3.4.
8234 @option{-munix=95} provides additional predefines for @code{XOPEN_UNIX}
8235 and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}.
8236 @option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX},
8237 @code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and
8238 @code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}.
8240 It is @emph{important} to note that this option changes the interfaces
8241 for various library routines. It also affects the operational behavior
8242 of the C library. Thus, @emph{extreme} care is needed in using this
8245 Library code that is intended to operate with more than one UNIX
8246 standard must test, set and restore the variable @var{__xpg4_extended_mask}
8247 as appropriate. Most GNU software doesn't provide this capability.
8251 Suppress the generation of link options to search libdld.sl when the
8252 @option{-static} option is specified on HP-UX 10 and later.
8256 The HP-UX implementation of setlocale in libc has a dependency on
8257 libdld.sl. There isn't an archive version of libdld.sl. Thus,
8258 when the @option{-static} option is specified, special link options
8259 are needed to resolve this dependency.
8261 On HP-UX 10 and later, the GCC driver adds the necessary options to
8262 link with libdld.sl when the @option{-static} option is specified.
8263 This causes the resulting binary to be dynamic. On the 64-bit port,
8264 the linkers generate dynamic binaries by default in any case. The
8265 @option{-nolibdld} option can be used to prevent the GCC driver from
8266 adding these link options.
8270 Add support for multithreading with the @dfn{dce thread} library
8271 under HP-UX. This option sets flags for both the preprocessor and
8275 @node i386 and x86-64 Options
8276 @subsection Intel 386 and AMD x86-64 Options
8277 @cindex i386 Options
8278 @cindex x86-64 Options
8279 @cindex Intel 386 Options
8280 @cindex AMD x86-64 Options
8282 These @samp{-m} options are defined for the i386 and x86-64 family of
8286 @item -mtune=@var{cpu-type}
8288 Tune to @var{cpu-type} everything applicable about the generated code, except
8289 for the ABI and the set of available instructions. The choices for
8293 Original Intel's i386 CPU.
8295 Intel's i486 CPU. (No scheduling is implemented for this chip.)
8297 Intel Pentium CPU with no MMX support.
8299 Intel PentiumMMX CPU based on Pentium core with MMX instruction set support.
8300 @item i686, pentiumpro
8301 Intel PentiumPro CPU.
8303 Intel Pentium2 CPU based on PentiumPro core with MMX instruction set support.
8304 @item pentium3, pentium3m
8305 Intel Pentium3 CPU based on PentiumPro core with MMX and SSE instruction set
8308 Low power version of Intel Pentium3 CPU with MMX, SSE and SSE2 instruction set
8309 support. Used by Centrino notebooks.
8310 @item pentium4, pentium4m
8311 Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set support.
8313 Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and SSE3 instruction
8316 Improved version of Intel Pentium4 CPU with 64-bit extensions, MMX, SSE,
8317 SSE2 and SSE3 instruction set support.
8319 AMD K6 CPU with MMX instruction set support.
8321 Improved versions of AMD K6 CPU with MMX and 3dNOW! instruction set support.
8322 @item athlon, athlon-tbird
8323 AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and SSE prefetch instructions
8325 @item athlon-4, athlon-xp, athlon-mp
8326 Improved AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and full SSE
8327 instruction set support.
8328 @item k8, opteron, athlon64, athlon-fx
8329 AMD K8 core based CPUs with x86-64 instruction set support. (This supersets
8330 MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW! and 64-bit instruction set extensions.)
8332 IDT Winchip C6 CPU, dealt in same way as i486 with additional MMX instruction
8335 IDT Winchip2 CPU, dealt in same way as i486 with additional MMX and 3dNOW!
8336 instruction set support.
8338 Via C3 CPU with MMX and 3dNOW! instruction set support. (No scheduling is
8339 implemented for this chip.)
8341 Via C3-2 CPU with MMX and SSE instruction set support. (No scheduling is
8342 implemented for this chip.)
8345 While picking a specific @var{cpu-type} will schedule things appropriately
8346 for that particular chip, the compiler will not generate any code that
8347 does not run on the i386 without the @option{-march=@var{cpu-type}} option
8350 @item -march=@var{cpu-type}
8352 Generate instructions for the machine type @var{cpu-type}. The choices
8353 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
8354 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
8356 @item -mcpu=@var{cpu-type}
8358 A deprecated synonym for @option{-mtune}.
8367 @opindex mpentiumpro
8368 These options are synonyms for @option{-mtune=i386}, @option{-mtune=i486},
8369 @option{-mtune=pentium}, and @option{-mtune=pentiumpro} respectively.
8370 These synonyms are deprecated.
8372 @item -mfpmath=@var{unit}
8374 Generate floating point arithmetics for selected unit @var{unit}. The choices
8379 Use the standard 387 floating point coprocessor present majority of chips and
8380 emulated otherwise. Code compiled with this option will run almost everywhere.
8381 The temporary results are computed in 80bit precision instead of precision
8382 specified by the type resulting in slightly different results compared to most
8383 of other chips. See @option{-ffloat-store} for more detailed description.
8385 This is the default choice for i386 compiler.
8388 Use scalar floating point instructions present in the SSE instruction set.
8389 This instruction set is supported by Pentium3 and newer chips, in the AMD line
8390 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
8391 instruction set supports only single precision arithmetics, thus the double and
8392 extended precision arithmetics is still done using 387. Later version, present
8393 only in Pentium4 and the future AMD x86-64 chips supports double precision
8396 For i387 you need to use @option{-march=@var{cpu-type}}, @option{-msse} or
8397 @option{-msse2} switches to enable SSE extensions and make this option
8398 effective. For x86-64 compiler, these extensions are enabled by default.
8400 The resulting code should be considerably faster in the majority of cases and avoid
8401 the numerical instability problems of 387 code, but may break some existing
8402 code that expects temporaries to be 80bit.
8404 This is the default choice for the x86-64 compiler.
8407 Attempt to utilize both instruction sets at once. This effectively double the
8408 amount of available registers and on chips with separate execution units for
8409 387 and SSE the execution resources too. Use this option with care, as it is
8410 still experimental, because the GCC register allocator does not model separate
8411 functional units well resulting in instable performance.
8414 @item -masm=@var{dialect}
8415 @opindex masm=@var{dialect}
8416 Output asm instructions using selected @var{dialect}. Supported choices are
8417 @samp{intel} or @samp{att} (the default one).
8422 @opindex mno-ieee-fp
8423 Control whether or not the compiler uses IEEE floating point
8424 comparisons. These handle correctly the case where the result of a
8425 comparison is unordered.
8428 @opindex msoft-float
8429 Generate output containing library calls for floating point.
8430 @strong{Warning:} the requisite libraries are not part of GCC@.
8431 Normally the facilities of the machine's usual C compiler are used, but
8432 this can't be done directly in cross-compilation. You must make your
8433 own arrangements to provide suitable library functions for
8436 On machines where a function returns floating point results in the 80387
8437 register stack, some floating point opcodes may be emitted even if
8438 @option{-msoft-float} is used.
8440 @item -mno-fp-ret-in-387
8441 @opindex mno-fp-ret-in-387
8442 Do not use the FPU registers for return values of functions.
8444 The usual calling convention has functions return values of types
8445 @code{float} and @code{double} in an FPU register, even if there
8446 is no FPU@. The idea is that the operating system should emulate
8449 The option @option{-mno-fp-ret-in-387} causes such values to be returned
8450 in ordinary CPU registers instead.
8452 @item -mno-fancy-math-387
8453 @opindex mno-fancy-math-387
8454 Some 387 emulators do not support the @code{sin}, @code{cos} and
8455 @code{sqrt} instructions for the 387. Specify this option to avoid
8456 generating those instructions. This option is the default on FreeBSD,
8457 OpenBSD and NetBSD@. This option is overridden when @option{-march}
8458 indicates that the target cpu will always have an FPU and so the
8459 instruction will not need emulation. As of revision 2.6.1, these
8460 instructions are not generated unless you also use the
8461 @option{-funsafe-math-optimizations} switch.
8463 @item -malign-double
8464 @itemx -mno-align-double
8465 @opindex malign-double
8466 @opindex mno-align-double
8467 Control whether GCC aligns @code{double}, @code{long double}, and
8468 @code{long long} variables on a two word boundary or a one word
8469 boundary. Aligning @code{double} variables on a two word boundary will
8470 produce code that runs somewhat faster on a @samp{Pentium} at the
8471 expense of more memory.
8473 @strong{Warning:} if you use the @option{-malign-double} switch,
8474 structures containing the above types will be aligned differently than
8475 the published application binary interface specifications for the 386
8476 and will not be binary compatible with structures in code compiled
8477 without that switch.
8479 @item -m96bit-long-double
8480 @itemx -m128bit-long-double
8481 @opindex m96bit-long-double
8482 @opindex m128bit-long-double
8483 These switches control the size of @code{long double} type. The i386
8484 application binary interface specifies the size to be 96 bits,
8485 so @option{-m96bit-long-double} is the default in 32 bit mode.
8487 Modern architectures (Pentium and newer) would prefer @code{long double}
8488 to be aligned to an 8 or 16 byte boundary. In arrays or structures
8489 conforming to the ABI, this would not be possible. So specifying a
8490 @option{-m128bit-long-double} will align @code{long double}
8491 to a 16 byte boundary by padding the @code{long double} with an additional
8494 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
8495 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
8497 Notice that neither of these options enable any extra precision over the x87
8498 standard of 80 bits for a @code{long double}.
8500 @strong{Warning:} if you override the default value for your target ABI, the
8501 structures and arrays containing @code{long double} variables will change
8502 their size as well as function calling convention for function taking
8503 @code{long double} will be modified. Hence they will not be binary
8504 compatible with arrays or structures in code compiled without that switch.
8508 @itemx -mno-svr3-shlib
8509 @opindex msvr3-shlib
8510 @opindex mno-svr3-shlib
8511 Control whether GCC places uninitialized local variables into the
8512 @code{bss} or @code{data} segments. @option{-msvr3-shlib} places them
8513 into @code{bss}. These options are meaningful only on System V Release 3.
8517 Use a different function-calling convention, in which functions that
8518 take a fixed number of arguments return with the @code{ret} @var{num}
8519 instruction, which pops their arguments while returning. This saves one
8520 instruction in the caller since there is no need to pop the arguments
8523 You can specify that an individual function is called with this calling
8524 sequence with the function attribute @samp{stdcall}. You can also
8525 override the @option{-mrtd} option by using the function attribute
8526 @samp{cdecl}. @xref{Function Attributes}.
8528 @strong{Warning:} this calling convention is incompatible with the one
8529 normally used on Unix, so you cannot use it if you need to call
8530 libraries compiled with the Unix compiler.
8532 Also, you must provide function prototypes for all functions that
8533 take variable numbers of arguments (including @code{printf});
8534 otherwise incorrect code will be generated for calls to those
8537 In addition, seriously incorrect code will result if you call a
8538 function with too many arguments. (Normally, extra arguments are
8539 harmlessly ignored.)
8541 @item -mregparm=@var{num}
8543 Control how many registers are used to pass integer arguments. By
8544 default, no registers are used to pass arguments, and at most 3
8545 registers can be used. You can control this behavior for a specific
8546 function by using the function attribute @samp{regparm}.
8547 @xref{Function Attributes}.
8549 @strong{Warning:} if you use this switch, and
8550 @var{num} is nonzero, then you must build all modules with the same
8551 value, including any libraries. This includes the system libraries and
8554 @item -mpreferred-stack-boundary=@var{num}
8555 @opindex mpreferred-stack-boundary
8556 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
8557 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
8558 the default is 4 (16 bytes or 128 bits), except when optimizing for code
8559 size (@option{-Os}), in which case the default is the minimum correct
8560 alignment (4 bytes for x86, and 8 bytes for x86-64).
8562 On Pentium and PentiumPro, @code{double} and @code{long double} values
8563 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
8564 suffer significant run time performance penalties. On Pentium III, the
8565 Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar
8566 penalties if it is not 16 byte aligned.
8568 To ensure proper alignment of this values on the stack, the stack boundary
8569 must be as aligned as that required by any value stored on the stack.
8570 Further, every function must be generated such that it keeps the stack
8571 aligned. Thus calling a function compiled with a higher preferred
8572 stack boundary from a function compiled with a lower preferred stack
8573 boundary will most likely misalign the stack. It is recommended that
8574 libraries that use callbacks always use the default setting.
8576 This extra alignment does consume extra stack space, and generally
8577 increases code size. Code that is sensitive to stack space usage, such
8578 as embedded systems and operating system kernels, may want to reduce the
8579 preferred alignment to @option{-mpreferred-stack-boundary=2}.
8597 These switches enable or disable the use of built-in functions that allow
8598 direct access to the MMX, SSE, SSE2, SSE3 and 3Dnow extensions of the
8601 @xref{X86 Built-in Functions}, for details of the functions enabled
8602 and disabled by these switches.
8604 To have SSE/SSE2 instructions generated automatically from floating-point
8605 code, see @option{-mfpmath=sse}.
8608 @itemx -mno-push-args
8610 @opindex mno-push-args
8611 Use PUSH operations to store outgoing parameters. This method is shorter
8612 and usually equally fast as method using SUB/MOV operations and is enabled
8613 by default. In some cases disabling it may improve performance because of
8614 improved scheduling and reduced dependencies.
8616 @item -maccumulate-outgoing-args
8617 @opindex maccumulate-outgoing-args
8618 If enabled, the maximum amount of space required for outgoing arguments will be
8619 computed in the function prologue. This is faster on most modern CPUs
8620 because of reduced dependencies, improved scheduling and reduced stack usage
8621 when preferred stack boundary is not equal to 2. The drawback is a notable
8622 increase in code size. This switch implies @option{-mno-push-args}.
8626 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
8627 on thread-safe exception handling must compile and link all code with the
8628 @option{-mthreads} option. When compiling, @option{-mthreads} defines
8629 @option{-D_MT}; when linking, it links in a special thread helper library
8630 @option{-lmingwthrd} which cleans up per thread exception handling data.
8632 @item -mno-align-stringops
8633 @opindex mno-align-stringops
8634 Do not align destination of inlined string operations. This switch reduces
8635 code size and improves performance in case the destination is already aligned,
8636 but GCC doesn't know about it.
8638 @item -minline-all-stringops
8639 @opindex minline-all-stringops
8640 By default GCC inlines string operations only when destination is known to be
8641 aligned at least to 4 byte boundary. This enables more inlining, increase code
8642 size, but may improve performance of code that depends on fast memcpy, strlen
8643 and memset for short lengths.
8645 @item -momit-leaf-frame-pointer
8646 @opindex momit-leaf-frame-pointer
8647 Don't keep the frame pointer in a register for leaf functions. This
8648 avoids the instructions to save, set up and restore frame pointers and
8649 makes an extra register available in leaf functions. The option
8650 @option{-fomit-frame-pointer} removes the frame pointer for all functions
8651 which might make debugging harder.
8653 @item -mtls-direct-seg-refs
8654 @itemx -mno-tls-direct-seg-refs
8655 @opindex mtls-direct-seg-refs
8656 Controls whether TLS variables may be accessed with offsets from the
8657 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
8658 or whether the thread base pointer must be added. Whether or not this
8659 is legal depends on the operating system, and whether it maps the
8660 segment to cover the entire TLS area.
8662 For systems that use GNU libc, the default is on.
8665 These @samp{-m} switches are supported in addition to the above
8666 on AMD x86-64 processors in 64-bit environments.
8673 Generate code for a 32-bit or 64-bit environment.
8674 The 32-bit environment sets int, long and pointer to 32 bits and
8675 generates code that runs on any i386 system.
8676 The 64-bit environment sets int to 32 bits and long and pointer
8677 to 64 bits and generates code for AMD's x86-64 architecture.
8680 @opindex no-red-zone
8681 Do not use a so called red zone for x86-64 code. The red zone is mandated
8682 by the x86-64 ABI, it is a 128-byte area beyond the location of the
8683 stack pointer that will not be modified by signal or interrupt handlers
8684 and therefore can be used for temporary data without adjusting the stack
8685 pointer. The flag @option{-mno-red-zone} disables this red zone.
8687 @item -mcmodel=small
8688 @opindex mcmodel=small
8689 Generate code for the small code model: the program and its symbols must
8690 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
8691 Programs can be statically or dynamically linked. This is the default
8694 @item -mcmodel=kernel
8695 @opindex mcmodel=kernel
8696 Generate code for the kernel code model. The kernel runs in the
8697 negative 2 GB of the address space.
8698 This model has to be used for Linux kernel code.
8700 @item -mcmodel=medium
8701 @opindex mcmodel=medium
8702 Generate code for the medium model: The program is linked in the lower 2
8703 GB of the address space but symbols can be located anywhere in the
8704 address space. Programs can be statically or dynamically linked, but
8705 building of shared libraries are not supported with the medium model.
8707 @item -mcmodel=large
8708 @opindex mcmodel=large
8709 Generate code for the large model: This model makes no assumptions
8710 about addresses and sizes of sections. Currently GCC does not implement
8715 @subsection IA-64 Options
8716 @cindex IA-64 Options
8718 These are the @samp{-m} options defined for the Intel IA-64 architecture.
8722 @opindex mbig-endian
8723 Generate code for a big endian target. This is the default for HP-UX@.
8725 @item -mlittle-endian
8726 @opindex mlittle-endian
8727 Generate code for a little endian target. This is the default for AIX5
8734 Generate (or don't) code for the GNU assembler. This is the default.
8735 @c Also, this is the default if the configure option @option{--with-gnu-as}
8742 Generate (or don't) code for the GNU linker. This is the default.
8743 @c Also, this is the default if the configure option @option{--with-gnu-ld}
8748 Generate code that does not use a global pointer register. The result
8749 is not position independent code, and violates the IA-64 ABI@.
8751 @item -mvolatile-asm-stop
8752 @itemx -mno-volatile-asm-stop
8753 @opindex mvolatile-asm-stop
8754 @opindex mno-volatile-asm-stop
8755 Generate (or don't) a stop bit immediately before and after volatile asm
8760 Generate code that works around Itanium B step errata.
8762 @item -mregister-names
8763 @itemx -mno-register-names
8764 @opindex mregister-names
8765 @opindex mno-register-names
8766 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
8767 the stacked registers. This may make assembler output more readable.
8773 Disable (or enable) optimizations that use the small data section. This may
8774 be useful for working around optimizer bugs.
8777 @opindex mconstant-gp
8778 Generate code that uses a single constant global pointer value. This is
8779 useful when compiling kernel code.
8783 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
8784 This is useful when compiling firmware code.
8786 @item -minline-float-divide-min-latency
8787 @opindex minline-float-divide-min-latency
8788 Generate code for inline divides of floating point values
8789 using the minimum latency algorithm.
8791 @item -minline-float-divide-max-throughput
8792 @opindex minline-float-divide-max-throughput
8793 Generate code for inline divides of floating point values
8794 using the maximum throughput algorithm.
8796 @item -minline-int-divide-min-latency
8797 @opindex minline-int-divide-min-latency
8798 Generate code for inline divides of integer values
8799 using the minimum latency algorithm.
8801 @item -minline-int-divide-max-throughput
8802 @opindex minline-int-divide-max-throughput
8803 Generate code for inline divides of integer values
8804 using the maximum throughput algorithm.
8806 @item -mno-dwarf2-asm
8808 @opindex mno-dwarf2-asm
8809 @opindex mdwarf2-asm
8810 Don't (or do) generate assembler code for the DWARF2 line number debugging
8811 info. This may be useful when not using the GNU assembler.
8813 @item -mfixed-range=@var{register-range}
8814 @opindex mfixed-range
8815 Generate code treating the given register range as fixed registers.
8816 A fixed register is one that the register allocator can not use. This is
8817 useful when compiling kernel code. A register range is specified as
8818 two registers separated by a dash. Multiple register ranges can be
8819 specified separated by a comma.
8821 @item -mearly-stop-bits
8822 @itemx -mno-early-stop-bits
8823 @opindex mearly-stop-bits
8824 @opindex mno-early-stop-bits
8825 Allow stop bits to be placed earlier than immediately preceding the
8826 instruction that triggered the stop bit. This can improve instruction
8827 scheduling, but does not always do so.
8830 @node M32R/D Options
8831 @subsection M32R/D Options
8832 @cindex M32R/D options
8834 These @option{-m} options are defined for Renesas M32R/D architectures:
8839 Generate code for the M32R/2@.
8843 Generate code for the M32R/X@.
8847 Generate code for the M32R@. This is the default.
8850 @opindex mmodel=small
8851 Assume all objects live in the lower 16MB of memory (so that their addresses
8852 can be loaded with the @code{ld24} instruction), and assume all subroutines
8853 are reachable with the @code{bl} instruction.
8854 This is the default.
8856 The addressability of a particular object can be set with the
8857 @code{model} attribute.
8859 @item -mmodel=medium
8860 @opindex mmodel=medium
8861 Assume objects may be anywhere in the 32-bit address space (the compiler
8862 will generate @code{seth/add3} instructions to load their addresses), and
8863 assume all subroutines are reachable with the @code{bl} instruction.
8866 @opindex mmodel=large
8867 Assume objects may be anywhere in the 32-bit address space (the compiler
8868 will generate @code{seth/add3} instructions to load their addresses), and
8869 assume subroutines may not be reachable with the @code{bl} instruction
8870 (the compiler will generate the much slower @code{seth/add3/jl}
8871 instruction sequence).
8874 @opindex msdata=none
8875 Disable use of the small data area. Variables will be put into
8876 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
8877 @code{section} attribute has been specified).
8878 This is the default.
8880 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
8881 Objects may be explicitly put in the small data area with the
8882 @code{section} attribute using one of these sections.
8885 @opindex msdata=sdata
8886 Put small global and static data in the small data area, but do not
8887 generate special code to reference them.
8891 Put small global and static data in the small data area, and generate
8892 special instructions to reference them.
8896 @cindex smaller data references
8897 Put global and static objects less than or equal to @var{num} bytes
8898 into the small data or bss sections instead of the normal data or bss
8899 sections. The default value of @var{num} is 8.
8900 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
8901 for this option to have any effect.
8903 All modules should be compiled with the same @option{-G @var{num}} value.
8904 Compiling with different values of @var{num} may or may not work; if it
8905 doesn't the linker will give an error message---incorrect code will not be
8910 Makes the M32R specific code in the compiler display some statistics
8911 that might help in debugging programs.
8914 @opindex malign-loops
8915 Align all loops to a 32-byte boundary.
8917 @item -mno-align-loops
8918 @opindex mno-align-loops
8919 Do not enforce a 32-byte alignment for loops. This is the default.
8921 @item -missue-rate=@var{number}
8922 @opindex missue-rate=@var{number}
8923 Issue @var{number} instructions per cycle. @var{number} can only be 1
8926 @item -mbranch-cost=@var{number}
8927 @opindex mbranch-cost=@var{number}
8928 @var{number} can only be 1 or 2. If it is 1 then branches will be
8929 preferred over conditional code, if it is 2, then the opposite will
8932 @item -mflush-trap=@var{number}
8933 @opindex mflush-trap=@var{number}
8934 Specifies the trap number to use to flush the cache. The default is
8935 12. Valid numbers are between 0 and 15 inclusive.
8937 @item -mno-flush-trap
8938 @opindex mno-flush-trap
8939 Specifies that the cache cannot be flushed by using a trap.
8941 @item -mflush-func=@var{name}
8942 @opindex mflush-func=@var{name}
8943 Specifies the name of the operating system function to call to flush
8944 the cache. The default is @emph{_flush_cache}, but a function call
8945 will only be used if a trap is not available.
8947 @item -mno-flush-func
8948 @opindex mno-flush-func
8949 Indicates that there is no OS function for flushing the cache.
8953 @node M680x0 Options
8954 @subsection M680x0 Options
8955 @cindex M680x0 options
8957 These are the @samp{-m} options defined for the 68000 series. The default
8958 values for these options depends on which style of 68000 was selected when
8959 the compiler was configured; the defaults for the most common choices are
8967 Generate output for a 68000. This is the default
8968 when the compiler is configured for 68000-based systems.
8970 Use this option for microcontrollers with a 68000 or EC000 core,
8971 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
8977 Generate output for a 68020. This is the default
8978 when the compiler is configured for 68020-based systems.
8982 Generate output containing 68881 instructions for floating point.
8983 This is the default for most 68020 systems unless @option{--nfp} was
8984 specified when the compiler was configured.
8988 Generate output for a 68030. This is the default when the compiler is
8989 configured for 68030-based systems.
8993 Generate output for a 68040. This is the default when the compiler is
8994 configured for 68040-based systems.
8996 This option inhibits the use of 68881/68882 instructions that have to be
8997 emulated by software on the 68040. Use this option if your 68040 does not
8998 have code to emulate those instructions.
9002 Generate output for a 68060. This is the default when the compiler is
9003 configured for 68060-based systems.
9005 This option inhibits the use of 68020 and 68881/68882 instructions that
9006 have to be emulated by software on the 68060. Use this option if your 68060
9007 does not have code to emulate those instructions.
9011 Generate output for a CPU32. This is the default
9012 when the compiler is configured for CPU32-based systems.
9014 Use this option for microcontrollers with a
9015 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
9016 68336, 68340, 68341, 68349 and 68360.
9020 Generate output for a 520X ``coldfire'' family cpu. This is the default
9021 when the compiler is configured for 520X-based systems.
9023 Use this option for microcontroller with a 5200 core, including
9024 the MCF5202, MCF5203, MCF5204 and MCF5202.
9029 Generate output for a 68040, without using any of the new instructions.
9030 This results in code which can run relatively efficiently on either a
9031 68020/68881 or a 68030 or a 68040. The generated code does use the
9032 68881 instructions that are emulated on the 68040.
9036 Generate output for a 68060, without using any of the new instructions.
9037 This results in code which can run relatively efficiently on either a
9038 68020/68881 or a 68030 or a 68040. The generated code does use the
9039 68881 instructions that are emulated on the 68060.
9042 @opindex msoft-float
9043 Generate output containing library calls for floating point.
9044 @strong{Warning:} the requisite libraries are not available for all m68k
9045 targets. Normally the facilities of the machine's usual C compiler are
9046 used, but this can't be done directly in cross-compilation. You must
9047 make your own arrangements to provide suitable library functions for
9048 cross-compilation. The embedded targets @samp{m68k-*-aout} and
9049 @samp{m68k-*-coff} do provide software floating point support.
9053 Consider type @code{int} to be 16 bits wide, like @code{short int}.
9054 Additionally, parameters passed on the stack are also aligned to a
9055 16-bit boundary even on targets whose API mandates promotion to 32-bit.
9058 @opindex mnobitfield
9059 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
9060 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
9064 Do use the bit-field instructions. The @option{-m68020} option implies
9065 @option{-mbitfield}. This is the default if you use a configuration
9066 designed for a 68020.
9070 Use a different function-calling convention, in which functions
9071 that take a fixed number of arguments return with the @code{rtd}
9072 instruction, which pops their arguments while returning. This
9073 saves one instruction in the caller since there is no need to pop
9074 the arguments there.
9076 This calling convention is incompatible with the one normally
9077 used on Unix, so you cannot use it if you need to call libraries
9078 compiled with the Unix compiler.
9080 Also, you must provide function prototypes for all functions that
9081 take variable numbers of arguments (including @code{printf});
9082 otherwise incorrect code will be generated for calls to those
9085 In addition, seriously incorrect code will result if you call a
9086 function with too many arguments. (Normally, extra arguments are
9087 harmlessly ignored.)
9089 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
9090 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
9093 @itemx -mno-align-int
9095 @opindex mno-align-int
9096 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
9097 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
9098 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
9099 Aligning variables on 32-bit boundaries produces code that runs somewhat
9100 faster on processors with 32-bit busses at the expense of more memory.
9102 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
9103 align structures containing the above types differently than
9104 most published application binary interface specifications for the m68k.
9108 Use the pc-relative addressing mode of the 68000 directly, instead of
9109 using a global offset table. At present, this option implies @option{-fpic},
9110 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
9111 not presently supported with @option{-mpcrel}, though this could be supported for
9112 68020 and higher processors.
9114 @item -mno-strict-align
9115 @itemx -mstrict-align
9116 @opindex mno-strict-align
9117 @opindex mstrict-align
9118 Do not (do) assume that unaligned memory references will be handled by
9122 Generate code that allows the data segment to be located in a different
9123 area of memory from the text segment. This allows for execute in place in
9124 an environment without virtual memory management. This option implies
9128 Generate code that assumes that the data segment follows the text segment.
9129 This is the default.
9131 @item -mid-shared-library
9132 Generate code that supports shared libraries via the library ID method.
9133 This allows for execute in place and shared libraries in an environment
9134 without virtual memory management. This option implies @option{-fPIC}.
9136 @item -mno-id-shared-library
9137 Generate code that doesn't assume ID based shared libraries are being used.
9138 This is the default.
9140 @item -mshared-library-id=n
9141 Specified the identification number of the ID based shared library being
9142 compiled. Specifying a value of 0 will generate more compact code, specifying
9143 other values will force the allocation of that number to the current
9144 library but is no more space or time efficient than omitting this option.
9148 @node M68hc1x Options
9149 @subsection M68hc1x Options
9150 @cindex M68hc1x options
9152 These are the @samp{-m} options defined for the 68hc11 and 68hc12
9153 microcontrollers. The default values for these options depends on
9154 which style of microcontroller was selected when the compiler was configured;
9155 the defaults for the most common choices are given below.
9162 Generate output for a 68HC11. This is the default
9163 when the compiler is configured for 68HC11-based systems.
9169 Generate output for a 68HC12. This is the default
9170 when the compiler is configured for 68HC12-based systems.
9176 Generate output for a 68HCS12.
9179 @opindex mauto-incdec
9180 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
9187 Enable the use of 68HC12 min and max instructions.
9190 @itemx -mno-long-calls
9191 @opindex mlong-calls
9192 @opindex mno-long-calls
9193 Treat all calls as being far away (near). If calls are assumed to be
9194 far away, the compiler will use the @code{call} instruction to
9195 call a function and the @code{rtc} instruction for returning.
9199 Consider type @code{int} to be 16 bits wide, like @code{short int}.
9201 @item -msoft-reg-count=@var{count}
9202 @opindex msoft-reg-count
9203 Specify the number of pseudo-soft registers which are used for the
9204 code generation. The maximum number is 32. Using more pseudo-soft
9205 register may or may not result in better code depending on the program.
9206 The default is 4 for 68HC11 and 2 for 68HC12.
9211 @subsection MCore Options
9212 @cindex MCore options
9214 These are the @samp{-m} options defined for the Motorola M*Core
9222 @opindex mno-hardlit
9223 Inline constants into the code stream if it can be done in two
9224 instructions or less.
9230 Use the divide instruction. (Enabled by default).
9232 @item -mrelax-immediate
9233 @itemx -mno-relax-immediate
9234 @opindex mrelax-immediate
9235 @opindex mno-relax-immediate
9236 Allow arbitrary sized immediates in bit operations.
9238 @item -mwide-bitfields
9239 @itemx -mno-wide-bitfields
9240 @opindex mwide-bitfields
9241 @opindex mno-wide-bitfields
9242 Always treat bit-fields as int-sized.
9244 @item -m4byte-functions
9245 @itemx -mno-4byte-functions
9246 @opindex m4byte-functions
9247 @opindex mno-4byte-functions
9248 Force all functions to be aligned to a four byte boundary.
9250 @item -mcallgraph-data
9251 @itemx -mno-callgraph-data
9252 @opindex mcallgraph-data
9253 @opindex mno-callgraph-data
9254 Emit callgraph information.
9257 @itemx -mno-slow-bytes
9258 @opindex mslow-bytes
9259 @opindex mno-slow-bytes
9260 Prefer word access when reading byte quantities.
9262 @item -mlittle-endian
9264 @opindex mlittle-endian
9265 @opindex mbig-endian
9266 Generate code for a little endian target.
9272 Generate code for the 210 processor.
9276 @subsection MIPS Options
9277 @cindex MIPS options
9283 Generate big-endian code.
9287 Generate little-endian code. This is the default for @samp{mips*el-*-*}
9290 @item -march=@var{arch}
9292 Generate code that will run on @var{arch}, which can be the name of a
9293 generic MIPS ISA, or the name of a particular processor.
9295 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
9296 @samp{mips32}, @samp{mips32r2}, and @samp{mips64}.
9297 The processor names are:
9298 @samp{4kc}, @samp{4kp}, @samp{5kc}, @samp{20kc},
9300 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
9301 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000}, @samp{rm7000},
9305 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300},
9306 @samp{vr5000}, @samp{vr5400} and @samp{vr5500}.
9307 The special value @samp{from-abi} selects the
9308 most compatible architecture for the selected ABI (that is,
9309 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
9311 In processor names, a final @samp{000} can be abbreviated as @samp{k}
9312 (for example, @samp{-march=r2k}). Prefixes are optional, and
9313 @samp{vr} may be written @samp{r}.
9315 GCC defines two macros based on the value of this option. The first
9316 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
9317 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
9318 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
9319 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
9320 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
9322 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
9323 above. In other words, it will have the full prefix and will not
9324 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
9325 the macro names the resolved architecture (either @samp{"mips1"} or
9326 @samp{"mips3"}). It names the default architecture when no
9327 @option{-march} option is given.
9329 @item -mtune=@var{arch}
9331 Optimize for @var{arch}. Among other things, this option controls
9332 the way instructions are scheduled, and the perceived cost of arithmetic
9333 operations. The list of @var{arch} values is the same as for
9336 When this option is not used, GCC will optimize for the processor
9337 specified by @option{-march}. By using @option{-march} and
9338 @option{-mtune} together, it is possible to generate code that will
9339 run on a family of processors, but optimize the code for one
9340 particular member of that family.
9342 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
9343 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
9344 @samp{-march} ones described above.
9348 Equivalent to @samp{-march=mips1}.
9352 Equivalent to @samp{-march=mips2}.
9356 Equivalent to @samp{-march=mips3}.
9360 Equivalent to @samp{-march=mips4}.
9364 Equivalent to @samp{-march=mips32}.
9368 Equivalent to @samp{-march=mips32r2}.
9372 Equivalent to @samp{-march=mips64}.
9378 Use (do not use) the MIPS16 ISA.
9390 Generate code for the given ABI@.
9392 Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
9393 generates 64-bit code when you select a 64-bit architecture, but you
9394 can use @option{-mgp32} to get 32-bit code instead.
9396 For information about the O64 ABI, see
9397 @w{@uref{http://gcc.gnu.org/projects/mipso64-abi.html}}.
9400 @itemx -mno-abicalls
9402 @opindex mno-abicalls
9403 Generate (do not generate) SVR4-style position-independent code.
9404 @option{-mabicalls} is the default for SVR4-based systems.
9410 Lift (do not lift) the usual restrictions on the size of the global
9413 GCC normally uses a single instruction to load values from the GOT.
9414 While this is relatively efficient, it will only work if the GOT
9415 is smaller than about 64k. Anything larger will cause the linker
9416 to report an error such as:
9418 @cindex relocation truncated to fit (MIPS)
9420 relocation truncated to fit: R_MIPS_GOT16 foobar
9423 If this happens, you should recompile your code with @option{-mxgot}.
9424 It should then work with very large GOTs, although it will also be
9425 less efficient, since it will take three instructions to fetch the
9426 value of a global symbol.
9428 Note that some linkers can create multiple GOTs. If you have such a
9429 linker, you should only need to use @option{-mxgot} when a single object
9430 file accesses more than 64k's worth of GOT entries. Very few do.
9432 These options have no effect unless GCC is generating position
9437 Assume that general-purpose registers are 32 bits wide.
9441 Assume that general-purpose registers are 64 bits wide.
9445 Assume that floating-point registers are 32 bits wide.
9449 Assume that floating-point registers are 64 bits wide.
9452 @opindex mhard-float
9453 Use floating-point coprocessor instructions.
9456 @opindex msoft-float
9457 Do not use floating-point coprocessor instructions. Implement
9458 floating-point calculations using library calls instead.
9460 @item -msingle-float
9461 @opindex msingle-float
9462 Assume that the floating-point coprocessor only supports single-precision
9465 @itemx -mdouble-float
9466 @opindex mdouble-float
9467 Assume that the floating-point coprocessor supports double-precision
9468 operations. This is the default.
9470 @itemx -mpaired-single
9471 @itemx -mno-paired-single
9472 @opindex mpaired-single
9473 @opindex mno-paired-single
9474 Use (do not use) paired-single floating-point instructions.
9475 @xref{MIPS Paired-Single Support}. This option can only be used
9476 when generating 64-bit code and requires hardware floating-point
9477 support to be enabled.
9483 Use (do not use) the MIPS-3D ASE. @xref{MIPS-3D Built-in Functions}.
9484 The option @option{-mips3d} implies @option{-mpaired-single}.
9488 Force @code{int} and @code{long} types to be 64 bits wide. See
9489 @option{-mlong32} for an explanation of the default and the way
9490 that the pointer size is determined.
9494 Force @code{long} types to be 64 bits wide. See @option{-mlong32} for
9495 an explanation of the default and the way that the pointer size is
9500 Force @code{long}, @code{int}, and pointer types to be 32 bits wide.
9502 The default size of @code{int}s, @code{long}s and pointers depends on
9503 the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI
9504 uses 64-bit @code{long}s, as does the 64-bit EABI; the others use
9505 32-bit @code{long}s. Pointers are the same size as @code{long}s,
9506 or the same size as integer registers, whichever is smaller.
9510 @cindex smaller data references (MIPS)
9511 @cindex gp-relative references (MIPS)
9512 Put global and static items less than or equal to @var{num} bytes into
9513 the small data or bss section instead of the normal data or bss section.
9514 This allows the data to be accessed using a single instruction.
9516 All modules should be compiled with the same @option{-G @var{num}}
9519 @item -membedded-data
9520 @itemx -mno-embedded-data
9521 @opindex membedded-data
9522 @opindex mno-embedded-data
9523 Allocate variables to the read-only data section first if possible, then
9524 next in the small data section if possible, otherwise in data. This gives
9525 slightly slower code than the default, but reduces the amount of RAM required
9526 when executing, and thus may be preferred for some embedded systems.
9528 @item -muninit-const-in-rodata
9529 @itemx -mno-uninit-const-in-rodata
9530 @opindex muninit-const-in-rodata
9531 @opindex mno-uninit-const-in-rodata
9532 Put uninitialized @code{const} variables in the read-only data section.
9533 This option is only meaningful in conjunction with @option{-membedded-data}.
9535 @item -msplit-addresses
9536 @itemx -mno-split-addresses
9537 @opindex msplit-addresses
9538 @opindex mno-split-addresses
9539 Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler
9540 relocation operators. This option has been superceded by
9541 @option{-mexplicit-relocs} but is retained for backwards compatibility.
9543 @item -mexplicit-relocs
9544 @itemx -mno-explicit-relocs
9545 @opindex mexplicit-relocs
9546 @opindex mno-explicit-relocs
9547 Use (do not use) assembler relocation operators when dealing with symbolic
9548 addresses. The alternative, selected by @option{-mno-explicit-relocs},
9549 is to use assembler macros instead.
9551 @option{-mexplicit-relocs} is the default if GCC was configured
9552 to use an assembler that supports relocation operators.
9554 @item -mcheck-zero-division
9555 @itemx -mno-check-zero-division
9556 @opindex mcheck-zero-division
9557 @opindex mno-check-zero-division
9558 Trap (do not trap) on integer division by zero. The default is
9559 @option{-mcheck-zero-division}.
9561 @item -mdivide-traps
9562 @itemx -mdivide-breaks
9563 @opindex mdivide-traps
9564 @opindex mdivide-breaks
9565 MIPS systems check for division by zero by generating either a
9566 conditional trap or a break instruction. Using traps results in
9567 smaller code, but is only supported on MIPS II and later. Also, some
9568 versions of the Linux kernel have a bug that prevents trap from
9569 generating the proper signal (SIGFPE). Use @option{-mdivide-traps} to
9570 allow conditional traps on architectures that support them and
9571 @option{-mdivide-breaks} to force the use of breaks.
9573 The default is usually @option{-mdivide-traps}, but this can be
9574 overridden at configure time using @option{--with-divide=breaks}.
9575 Divide-by-zero checks can be completely disabled using
9576 @option{-mno-check-zero-division}.
9582 Force (do not force) the use of @code{memcpy()} for non-trivial block
9583 moves. The default is @option{-mno-memcpy}, which allows GCC to inline
9584 most constant-sized copies.
9587 @itemx -mno-long-calls
9588 @opindex mlong-calls
9589 @opindex mno-long-calls
9590 Disable (do not disable) use of the @code{jal} instruction. Calling
9591 functions using @code{jal} is more efficient but requires the caller
9592 and callee to be in the same 256 megabyte segment.
9594 This option has no effect on abicalls code. The default is
9595 @option{-mno-long-calls}.
9601 Enable (disable) use of the @code{mad}, @code{madu} and @code{mul}
9602 instructions, as provided by the R4650 ISA.
9605 @itemx -mno-fused-madd
9606 @opindex mfused-madd
9607 @opindex mno-fused-madd
9608 Enable (disable) use of the floating point multiply-accumulate
9609 instructions, when they are available. The default is
9610 @option{-mfused-madd}.
9612 When multiply-accumulate instructions are used, the intermediate
9613 product is calculated to infinite precision and is not subject to
9614 the FCSR Flush to Zero bit. This may be undesirable in some
9619 Tell the MIPS assembler to not run its preprocessor over user
9620 assembler files (with a @samp{.s} suffix) when assembling them.
9623 @itemx -mno-fix-r4000
9625 @opindex mno-fix-r4000
9626 Work around certain R4000 CPU errata:
9629 A double-word or a variable shift may give an incorrect result if executed
9630 immediately after starting an integer division.
9632 A double-word or a variable shift may give an incorrect result if executed
9633 while an integer multiplication is in progress.
9635 An integer division may give an incorrect result if started in a delay slot
9636 of a taken branch or a jump.
9640 @itemx -mno-fix-r4400
9642 @opindex mno-fix-r4400
9643 Work around certain R4400 CPU errata:
9646 A double-word or a variable shift may give an incorrect result if executed
9647 immediately after starting an integer division.
9651 @itemx -mno-fix-vr4120
9652 @opindex mfix-vr4120
9653 Work around certain VR4120 errata:
9656 @code{dmultu} does not always produce the correct result.
9658 @code{div} and @code{ddiv} do not always produce the correct result if one
9659 of the operands is negative.
9661 The workarounds for the division errata rely on special functions in
9662 @file{libgcc.a}. At present, these functions are only provided by
9663 the @code{mips64vr*-elf} configurations.
9665 Other VR4120 errata require a nop to be inserted between certain pairs of
9666 instructions. These errata are handled by the assembler, not by GCC itself.
9671 Work around certain SB-1 CPU core errata.
9672 (This flag currently works around the SB-1 revision 2
9673 ``F1'' and ``F2'' floating point errata.)
9675 @item -mflush-func=@var{func}
9676 @itemx -mno-flush-func
9677 @opindex mflush-func
9678 Specifies the function to call to flush the I and D caches, or to not
9679 call any such function. If called, the function must take the same
9680 arguments as the common @code{_flush_func()}, that is, the address of the
9681 memory range for which the cache is being flushed, the size of the
9682 memory range, and the number 3 (to flush both caches). The default
9683 depends on the target GCC was configured for, but commonly is either
9684 @samp{_flush_func} or @samp{__cpu_flush}.
9686 @item -mbranch-likely
9687 @itemx -mno-branch-likely
9688 @opindex mbranch-likely
9689 @opindex mno-branch-likely
9690 Enable or disable use of Branch Likely instructions, regardless of the
9691 default for the selected architecture. By default, Branch Likely
9692 instructions may be generated if they are supported by the selected
9693 architecture. An exception is for the MIPS32 and MIPS64 architectures
9694 and processors which implement those architectures; for those, Branch
9695 Likely instructions will not be generated by default because the MIPS32
9696 and MIPS64 architectures specifically deprecate their use.
9698 @item -mfp-exceptions
9699 @itemx -mno-fp-exceptions
9700 @opindex mfp-exceptions
9701 Specifies whether FP exceptions are enabled. This affects how we schedule
9702 FP instructions for some processors. The default is that FP exceptions are
9705 For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
9706 64-bit code, then we can use both FP pipes. Otherwise, we can only use one
9709 @item -mvr4130-align
9710 @itemx -mno-vr4130-align
9711 @opindex mvr4130-align
9712 The VR4130 pipeline is two-way superscalar, but can only issue two
9713 instructions together if the first one is 8-byte aligned. When this
9714 option is enabled, GCC will align pairs of instructions that it
9715 thinks should execute in parallel.
9717 This option only has an effect when optimizing for the VR4130.
9718 It normally makes code faster, but at the expense of making it bigger.
9719 It is enabled by default at optimization level @option{-O3}.
9723 @subsection MMIX Options
9724 @cindex MMIX Options
9726 These options are defined for the MMIX:
9730 @itemx -mno-libfuncs
9732 @opindex mno-libfuncs
9733 Specify that intrinsic library functions are being compiled, passing all
9734 values in registers, no matter the size.
9739 @opindex mno-epsilon
9740 Generate floating-point comparison instructions that compare with respect
9741 to the @code{rE} epsilon register.
9743 @item -mabi=mmixware
9745 @opindex mabi-mmixware
9747 Generate code that passes function parameters and return values that (in
9748 the called function) are seen as registers @code{$0} and up, as opposed to
9749 the GNU ABI which uses global registers @code{$231} and up.
9752 @itemx -mno-zero-extend
9753 @opindex mzero-extend
9754 @opindex mno-zero-extend
9755 When reading data from memory in sizes shorter than 64 bits, use (do not
9756 use) zero-extending load instructions by default, rather than
9757 sign-extending ones.
9760 @itemx -mno-knuthdiv
9762 @opindex mno-knuthdiv
9763 Make the result of a division yielding a remainder have the same sign as
9764 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
9765 remainder follows the sign of the dividend. Both methods are
9766 arithmetically valid, the latter being almost exclusively used.
9768 @item -mtoplevel-symbols
9769 @itemx -mno-toplevel-symbols
9770 @opindex mtoplevel-symbols
9771 @opindex mno-toplevel-symbols
9772 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
9773 code can be used with the @code{PREFIX} assembly directive.
9777 Generate an executable in the ELF format, rather than the default
9778 @samp{mmo} format used by the @command{mmix} simulator.
9780 @item -mbranch-predict
9781 @itemx -mno-branch-predict
9782 @opindex mbranch-predict
9783 @opindex mno-branch-predict
9784 Use (do not use) the probable-branch instructions, when static branch
9785 prediction indicates a probable branch.
9787 @item -mbase-addresses
9788 @itemx -mno-base-addresses
9789 @opindex mbase-addresses
9790 @opindex mno-base-addresses
9791 Generate (do not generate) code that uses @emph{base addresses}. Using a
9792 base address automatically generates a request (handled by the assembler
9793 and the linker) for a constant to be set up in a global register. The
9794 register is used for one or more base address requests within the range 0
9795 to 255 from the value held in the register. The generally leads to short
9796 and fast code, but the number of different data items that can be
9797 addressed is limited. This means that a program that uses lots of static
9798 data may require @option{-mno-base-addresses}.
9801 @itemx -mno-single-exit
9802 @opindex msingle-exit
9803 @opindex mno-single-exit
9804 Force (do not force) generated code to have a single exit point in each
9808 @node MN10300 Options
9809 @subsection MN10300 Options
9810 @cindex MN10300 options
9812 These @option{-m} options are defined for Matsushita MN10300 architectures:
9817 Generate code to avoid bugs in the multiply instructions for the MN10300
9818 processors. This is the default.
9821 @opindex mno-mult-bug
9822 Do not generate code to avoid bugs in the multiply instructions for the
9827 Generate code which uses features specific to the AM33 processor.
9831 Do not generate code which uses features specific to the AM33 processor. This
9836 Do not link in the C run-time initialization object file.
9840 Indicate to the linker that it should perform a relaxation optimization pass
9841 to shorten branches, calls and absolute memory addresses. This option only
9842 has an effect when used on the command line for the final link step.
9844 This option makes symbolic debugging impossible.
9848 @subsection NS32K Options
9849 @cindex NS32K options
9851 These are the @samp{-m} options defined for the 32000 series. The default
9852 values for these options depends on which style of 32000 was selected when
9853 the compiler was configured; the defaults for the most common choices are
9861 Generate output for a 32032. This is the default
9862 when the compiler is configured for 32032 and 32016 based systems.
9868 Generate output for a 32332. This is the default
9869 when the compiler is configured for 32332-based systems.
9875 Generate output for a 32532. This is the default
9876 when the compiler is configured for 32532-based systems.
9880 Generate output containing 32081 instructions for floating point.
9881 This is the default for all systems.
9885 Generate output containing 32381 instructions for floating point. This
9886 also implies @option{-m32081}. The 32381 is only compatible with the 32332
9887 and 32532 cpus. This is the default for the pc532-netbsd configuration.
9891 Try and generate multiply-add floating point instructions @code{polyF}
9892 and @code{dotF}. This option is only available if the @option{-m32381}
9893 option is in effect. Using these instructions requires changes to
9894 register allocation which generally has a negative impact on
9895 performance. This option should only be enabled when compiling code
9896 particularly likely to make heavy use of multiply-add instructions.
9899 @opindex mnomulti-add
9900 Do not try and generate multiply-add floating point instructions
9901 @code{polyF} and @code{dotF}. This is the default on all platforms.
9904 @opindex msoft-float
9905 Generate output containing library calls for floating point.
9906 @strong{Warning:} the requisite libraries may not be available.
9908 @item -mieee-compare
9909 @itemx -mno-ieee-compare
9910 @opindex mieee-compare
9911 @opindex mno-ieee-compare
9912 Control whether or not the compiler uses IEEE floating point
9913 comparisons. These handle correctly the case where the result of a
9914 comparison is unordered.
9915 @strong{Warning:} the requisite kernel support may not be available.
9918 @opindex mnobitfield
9919 Do not use the bit-field instructions. On some machines it is faster to
9920 use shifting and masking operations. This is the default for the pc532.
9924 Do use the bit-field instructions. This is the default for all platforms
9929 Use a different function-calling convention, in which functions
9930 that take a fixed number of arguments return pop their
9931 arguments on return with the @code{ret} instruction.
9933 This calling convention is incompatible with the one normally
9934 used on Unix, so you cannot use it if you need to call libraries
9935 compiled with the Unix compiler.
9937 Also, you must provide function prototypes for all functions that
9938 take variable numbers of arguments (including @code{printf});
9939 otherwise incorrect code will be generated for calls to those
9942 In addition, seriously incorrect code will result if you call a
9943 function with too many arguments. (Normally, extra arguments are
9944 harmlessly ignored.)
9946 This option takes its name from the 680x0 @code{rtd} instruction.
9951 Use a different function-calling convention where the first two arguments
9952 are passed in registers.
9954 This calling convention is incompatible with the one normally
9955 used on Unix, so you cannot use it if you need to call libraries
9956 compiled with the Unix compiler.
9959 @opindex mnoregparam
9960 Do not pass any arguments in registers. This is the default for all
9965 It is OK to use the sb as an index register which is always loaded with
9966 zero. This is the default for the pc532-netbsd target.
9970 The sb register is not available for use or has not been initialized to
9971 zero by the run time system. This is the default for all targets except
9972 the pc532-netbsd. It is also implied whenever @option{-mhimem} or
9973 @option{-fpic} is set.
9977 Many ns32000 series addressing modes use displacements of up to 512MB@.
9978 If an address is above 512MB then displacements from zero can not be used.
9979 This option causes code to be generated which can be loaded above 512MB@.
9980 This may be useful for operating systems or ROM code.
9984 Assume code will be loaded in the first 512MB of virtual address space.
9985 This is the default for all platforms.
9989 @node PDP-11 Options
9990 @subsection PDP-11 Options
9991 @cindex PDP-11 Options
9993 These options are defined for the PDP-11:
9998 Use hardware FPP floating point. This is the default. (FIS floating
9999 point on the PDP-11/40 is not supported.)
10002 @opindex msoft-float
10003 Do not use hardware floating point.
10007 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
10011 Return floating-point results in memory. This is the default.
10015 Generate code for a PDP-11/40.
10019 Generate code for a PDP-11/45. This is the default.
10023 Generate code for a PDP-11/10.
10025 @item -mbcopy-builtin
10026 @opindex bcopy-builtin
10027 Use inline @code{movmemhi} patterns for copying memory. This is the
10032 Do not use inline @code{movmemhi} patterns for copying memory.
10038 Use 16-bit @code{int}. This is the default.
10044 Use 32-bit @code{int}.
10047 @itemx -mno-float32
10049 @opindex mno-float32
10050 Use 64-bit @code{float}. This is the default.
10053 @itemx -mno-float64
10055 @opindex mno-float64
10056 Use 32-bit @code{float}.
10060 Use @code{abshi2} pattern. This is the default.
10064 Do not use @code{abshi2} pattern.
10066 @item -mbranch-expensive
10067 @opindex mbranch-expensive
10068 Pretend that branches are expensive. This is for experimenting with
10069 code generation only.
10071 @item -mbranch-cheap
10072 @opindex mbranch-cheap
10073 Do not pretend that branches are expensive. This is the default.
10077 Generate code for a system with split I&D.
10081 Generate code for a system without split I&D. This is the default.
10085 Use Unix assembler syntax. This is the default when configured for
10086 @samp{pdp11-*-bsd}.
10090 Use DEC assembler syntax. This is the default when configured for any
10091 PDP-11 target other than @samp{pdp11-*-bsd}.
10094 @node PowerPC Options
10095 @subsection PowerPC Options
10096 @cindex PowerPC options
10098 These are listed under @xref{RS/6000 and PowerPC Options}.
10100 @node RS/6000 and PowerPC Options
10101 @subsection IBM RS/6000 and PowerPC Options
10102 @cindex RS/6000 and PowerPC Options
10103 @cindex IBM RS/6000 and PowerPC Options
10105 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
10112 @itemx -mno-powerpc
10113 @itemx -mpowerpc-gpopt
10114 @itemx -mno-powerpc-gpopt
10115 @itemx -mpowerpc-gfxopt
10116 @itemx -mno-powerpc-gfxopt
10118 @itemx -mno-powerpc64
10122 @opindex mno-power2
10124 @opindex mno-powerpc
10125 @opindex mpowerpc-gpopt
10126 @opindex mno-powerpc-gpopt
10127 @opindex mpowerpc-gfxopt
10128 @opindex mno-powerpc-gfxopt
10129 @opindex mpowerpc64
10130 @opindex mno-powerpc64
10131 GCC supports two related instruction set architectures for the
10132 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
10133 instructions supported by the @samp{rios} chip set used in the original
10134 RS/6000 systems and the @dfn{PowerPC} instruction set is the
10135 architecture of the Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and
10136 the IBM 4xx microprocessors.
10138 Neither architecture is a subset of the other. However there is a
10139 large common subset of instructions supported by both. An MQ
10140 register is included in processors supporting the POWER architecture.
10142 You use these options to specify which instructions are available on the
10143 processor you are using. The default value of these options is
10144 determined when configuring GCC@. Specifying the
10145 @option{-mcpu=@var{cpu_type}} overrides the specification of these
10146 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
10147 rather than the options listed above.
10149 The @option{-mpower} option allows GCC to generate instructions that
10150 are found only in the POWER architecture and to use the MQ register.
10151 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
10152 to generate instructions that are present in the POWER2 architecture but
10153 not the original POWER architecture.
10155 The @option{-mpowerpc} option allows GCC to generate instructions that
10156 are found only in the 32-bit subset of the PowerPC architecture.
10157 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
10158 GCC to use the optional PowerPC architecture instructions in the
10159 General Purpose group, including floating-point square root. Specifying
10160 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
10161 use the optional PowerPC architecture instructions in the Graphics
10162 group, including floating-point select.
10164 The @option{-mpowerpc64} option allows GCC to generate the additional
10165 64-bit instructions that are found in the full PowerPC64 architecture
10166 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
10167 @option{-mno-powerpc64}.
10169 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
10170 will use only the instructions in the common subset of both
10171 architectures plus some special AIX common-mode calls, and will not use
10172 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
10173 permits GCC to use any instruction from either architecture and to
10174 allow use of the MQ register; specify this for the Motorola MPC601.
10176 @item -mnew-mnemonics
10177 @itemx -mold-mnemonics
10178 @opindex mnew-mnemonics
10179 @opindex mold-mnemonics
10180 Select which mnemonics to use in the generated assembler code. With
10181 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
10182 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
10183 assembler mnemonics defined for the POWER architecture. Instructions
10184 defined in only one architecture have only one mnemonic; GCC uses that
10185 mnemonic irrespective of which of these options is specified.
10187 GCC defaults to the mnemonics appropriate for the architecture in
10188 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
10189 value of these option. Unless you are building a cross-compiler, you
10190 should normally not specify either @option{-mnew-mnemonics} or
10191 @option{-mold-mnemonics}, but should instead accept the default.
10193 @item -mcpu=@var{cpu_type}
10195 Set architecture type, register usage, choice of mnemonics, and
10196 instruction scheduling parameters for machine type @var{cpu_type}.
10197 Supported values for @var{cpu_type} are @samp{401}, @samp{403},
10198 @samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{505},
10199 @samp{601}, @samp{602}, @samp{603}, @samp{603e}, @samp{604},
10200 @samp{604e}, @samp{620}, @samp{630}, @samp{740}, @samp{7400},
10201 @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
10202 @samp{860}, @samp{970}, @samp{common}, @samp{ec603e}, @samp{G3},
10203 @samp{G4}, @samp{G5}, @samp{power}, @samp{power2}, @samp{power3},
10204 @samp{power4}, @samp{power5}, @samp{powerpc}, @samp{powerpc64},
10205 @samp{rios}, @samp{rios1}, @samp{rios2}, @samp{rsc}, and @samp{rs64a}.
10207 @option{-mcpu=common} selects a completely generic processor. Code
10208 generated under this option will run on any POWER or PowerPC processor.
10209 GCC will use only the instructions in the common subset of both
10210 architectures, and will not use the MQ register. GCC assumes a generic
10211 processor model for scheduling purposes.
10213 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
10214 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
10215 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
10216 types, with an appropriate, generic processor model assumed for
10217 scheduling purposes.
10219 The other options specify a specific processor. Code generated under
10220 those options will run best on that processor, and may not run at all on
10223 The @option{-mcpu} options automatically enable or disable the
10224 following options: @option{-maltivec}, @option{-mhard-float},
10225 @option{-mmfcrf}, @option{-mmultiple}, @option{-mnew-mnemonics},
10226 @option{-mpower}, @option{-mpower2}, @option{-mpowerpc64},
10227 @option{-mpowerpc-gpopt}, @option{-mpowerpc-gfxopt},
10228 @option{-mstring}. The particular options set for any particular CPU
10229 will vary between compiler versions, depending on what setting seems
10230 to produce optimal code for that CPU; it doesn't necessarily reflect
10231 the actual hardware's capabilities. If you wish to set an individual
10232 option to a particular value, you may specify it after the
10233 @option{-mcpu} option, like @samp{-mcpu=970 -mno-altivec}.
10235 On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are
10236 not enabled or disabled by the @option{-mcpu} option at present, since
10237 AIX does not have full support for these options. You may still
10238 enable or disable them individually if you're sure it'll work in your
10241 @item -mtune=@var{cpu_type}
10243 Set the instruction scheduling parameters for machine type
10244 @var{cpu_type}, but do not set the architecture type, register usage, or
10245 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
10246 values for @var{cpu_type} are used for @option{-mtune} as for
10247 @option{-mcpu}. If both are specified, the code generated will use the
10248 architecture, registers, and mnemonics set by @option{-mcpu}, but the
10249 scheduling parameters set by @option{-mtune}.
10252 @itemx -mno-altivec
10254 @opindex mno-altivec
10255 Generate code that uses (does not use) AltiVec instructions, and also
10256 enable the use of built-in functions that allow more direct access to
10257 the AltiVec instruction set. You may also need to set
10258 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
10263 Extend the current ABI with SPE ABI extensions. This does not change
10264 the default ABI, instead it adds the SPE ABI extensions to the current
10268 @opindex mabi=no-spe
10269 Disable Booke SPE ABI extensions for the current ABI.
10271 @item -misel=@var{yes/no}
10274 This switch enables or disables the generation of ISEL instructions.
10276 @item -mspe=@var{yes/no}
10279 This switch enables or disables the generation of SPE simd
10282 @item -mfloat-gprs=@var{yes/no}
10283 @itemx -mfloat-gprs
10284 @opindex mfloat-gprs
10285 This switch enables or disables the generation of floating point
10286 operations on the general purpose registers for architectures that
10287 support it. This option is currently only available on the MPC8540.
10293 Generate code for 32-bit or 64-bit environments of Darwin and SVR4
10294 targets (including GNU/Linux). The 32-bit environment sets int, long
10295 and pointer to 32 bits and generates code that runs on any PowerPC
10296 variant. The 64-bit environment sets int to 32 bits and long and
10297 pointer to 64 bits, and generates code for PowerPC64, as for
10298 @option{-mpowerpc64}.
10301 @itemx -mno-fp-in-toc
10302 @itemx -mno-sum-in-toc
10303 @itemx -mminimal-toc
10305 @opindex mno-fp-in-toc
10306 @opindex mno-sum-in-toc
10307 @opindex mminimal-toc
10308 Modify generation of the TOC (Table Of Contents), which is created for
10309 every executable file. The @option{-mfull-toc} option is selected by
10310 default. In that case, GCC will allocate at least one TOC entry for
10311 each unique non-automatic variable reference in your program. GCC
10312 will also place floating-point constants in the TOC@. However, only
10313 16,384 entries are available in the TOC@.
10315 If you receive a linker error message that saying you have overflowed
10316 the available TOC space, you can reduce the amount of TOC space used
10317 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
10318 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
10319 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
10320 generate code to calculate the sum of an address and a constant at
10321 run-time instead of putting that sum into the TOC@. You may specify one
10322 or both of these options. Each causes GCC to produce very slightly
10323 slower and larger code at the expense of conserving TOC space.
10325 If you still run out of space in the TOC even when you specify both of
10326 these options, specify @option{-mminimal-toc} instead. This option causes
10327 GCC to make only one TOC entry for every file. When you specify this
10328 option, GCC will produce code that is slower and larger but which
10329 uses extremely little TOC space. You may wish to use this option
10330 only on files that contain less frequently executed code.
10336 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
10337 @code{long} type, and the infrastructure needed to support them.
10338 Specifying @option{-maix64} implies @option{-mpowerpc64} and
10339 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
10340 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
10343 @itemx -mno-xl-call
10345 @opindex mno-xl-call
10346 On AIX, pass floating-point arguments to prototyped functions beyond the
10347 register save area (RSA) on the stack in addition to argument FPRs. The
10348 AIX calling convention was extended but not initially documented to
10349 handle an obscure K&R C case of calling a function that takes the
10350 address of its arguments with fewer arguments than declared. AIX XL
10351 compilers access floating point arguments which do not fit in the
10352 RSA from the stack when a subroutine is compiled without
10353 optimization. Because always storing floating-point arguments on the
10354 stack is inefficient and rarely needed, this option is not enabled by
10355 default and only is necessary when calling subroutines compiled by AIX
10356 XL compilers without optimization.
10360 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
10361 application written to use message passing with special startup code to
10362 enable the application to run. The system must have PE installed in the
10363 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
10364 must be overridden with the @option{-specs=} option to specify the
10365 appropriate directory location. The Parallel Environment does not
10366 support threads, so the @option{-mpe} option and the @option{-pthread}
10367 option are incompatible.
10369 @item -malign-natural
10370 @itemx -malign-power
10371 @opindex malign-natural
10372 @opindex malign-power
10373 On AIX, Darwin, and 64-bit PowerPC GNU/Linux, the option
10374 @option{-malign-natural} overrides the ABI-defined alignment of larger
10375 types, such as floating-point doubles, on their natural size-based boundary.
10376 The option @option{-malign-power} instructs GCC to follow the ABI-specified
10377 alignment rules. GCC defaults to the standard alignment defined in the ABI.
10380 @itemx -mhard-float
10381 @opindex msoft-float
10382 @opindex mhard-float
10383 Generate code that does not use (uses) the floating-point register set.
10384 Software floating point emulation is provided if you use the
10385 @option{-msoft-float} option, and pass the option to GCC when linking.
10388 @itemx -mno-multiple
10390 @opindex mno-multiple
10391 Generate code that uses (does not use) the load multiple word
10392 instructions and the store multiple word instructions. These
10393 instructions are generated by default on POWER systems, and not
10394 generated on PowerPC systems. Do not use @option{-mmultiple} on little
10395 endian PowerPC systems, since those instructions do not work when the
10396 processor is in little endian mode. The exceptions are PPC740 and
10397 PPC750 which permit the instructions usage in little endian mode.
10402 @opindex mno-string
10403 Generate code that uses (does not use) the load string instructions
10404 and the store string word instructions to save multiple registers and
10405 do small block moves. These instructions are generated by default on
10406 POWER systems, and not generated on PowerPC systems. Do not use
10407 @option{-mstring} on little endian PowerPC systems, since those
10408 instructions do not work when the processor is in little endian mode.
10409 The exceptions are PPC740 and PPC750 which permit the instructions
10410 usage in little endian mode.
10415 @opindex mno-update
10416 Generate code that uses (does not use) the load or store instructions
10417 that update the base register to the address of the calculated memory
10418 location. These instructions are generated by default. If you use
10419 @option{-mno-update}, there is a small window between the time that the
10420 stack pointer is updated and the address of the previous frame is
10421 stored, which means code that walks the stack frame across interrupts or
10422 signals may get corrupted data.
10425 @itemx -mno-fused-madd
10426 @opindex mfused-madd
10427 @opindex mno-fused-madd
10428 Generate code that uses (does not use) the floating point multiply and
10429 accumulate instructions. These instructions are generated by default if
10430 hardware floating is used.
10432 @item -mno-bit-align
10434 @opindex mno-bit-align
10435 @opindex mbit-align
10436 On System V.4 and embedded PowerPC systems do not (do) force structures
10437 and unions that contain bit-fields to be aligned to the base type of the
10440 For example, by default a structure containing nothing but 8
10441 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
10442 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
10443 the structure would be aligned to a 1 byte boundary and be one byte in
10446 @item -mno-strict-align
10447 @itemx -mstrict-align
10448 @opindex mno-strict-align
10449 @opindex mstrict-align
10450 On System V.4 and embedded PowerPC systems do not (do) assume that
10451 unaligned memory references will be handled by the system.
10453 @item -mrelocatable
10454 @itemx -mno-relocatable
10455 @opindex mrelocatable
10456 @opindex mno-relocatable
10457 On embedded PowerPC systems generate code that allows (does not allow)
10458 the program to be relocated to a different address at runtime. If you
10459 use @option{-mrelocatable} on any module, all objects linked together must
10460 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
10462 @item -mrelocatable-lib
10463 @itemx -mno-relocatable-lib
10464 @opindex mrelocatable-lib
10465 @opindex mno-relocatable-lib
10466 On embedded PowerPC systems generate code that allows (does not allow)
10467 the program to be relocated to a different address at runtime. Modules
10468 compiled with @option{-mrelocatable-lib} can be linked with either modules
10469 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
10470 with modules compiled with the @option{-mrelocatable} options.
10476 On System V.4 and embedded PowerPC systems do not (do) assume that
10477 register 2 contains a pointer to a global area pointing to the addresses
10478 used in the program.
10481 @itemx -mlittle-endian
10483 @opindex mlittle-endian
10484 On System V.4 and embedded PowerPC systems compile code for the
10485 processor in little endian mode. The @option{-mlittle-endian} option is
10486 the same as @option{-mlittle}.
10489 @itemx -mbig-endian
10491 @opindex mbig-endian
10492 On System V.4 and embedded PowerPC systems compile code for the
10493 processor in big endian mode. The @option{-mbig-endian} option is
10494 the same as @option{-mbig}.
10496 @item -mdynamic-no-pic
10497 @opindex mdynamic-no-pic
10498 On Darwin and Mac OS X systems, compile code so that it is not
10499 relocatable, but that its external references are relocatable. The
10500 resulting code is suitable for applications, but not shared
10503 @item -mprioritize-restricted-insns=@var{priority}
10504 @opindex mprioritize-restricted-insns
10505 This option controls the priority that is assigned to
10506 dispatch-slot restricted instructions during the second scheduling
10507 pass. The argument @var{priority} takes the value @var{0/1/2} to assign
10508 @var{no/highest/second-highest} priority to dispatch slot restricted
10511 @item -msched-costly-dep=@var{dependence_type}
10512 @opindex msched-costly-dep
10513 This option controls which dependences are considered costly
10514 by the target during instruction scheduling. The argument
10515 @var{dependence_type} takes one of the following values:
10516 @var{no}: no dependence is costly,
10517 @var{all}: all dependences are costly,
10518 @var{true_store_to_load}: a true dependence from store to load is costly,
10519 @var{store_to_load}: any dependence from store to load is costly,
10520 @var{number}: any dependence which latency >= @var{number} is costly.
10522 @item -minsert-sched-nops=@var{scheme}
10523 @opindex minsert-sched-nops
10524 This option controls which nop insertion scheme will be used during
10525 the second scheduling pass. The argument @var{scheme} takes one of the
10527 @var{no}: Don't insert nops.
10528 @var{pad}: Pad with nops any dispatch group which has vacant issue slots,
10529 according to the scheduler's grouping.
10530 @var{regroup_exact}: Insert nops to force costly dependent insns into
10531 separate groups. Insert exactly as many nops as needed to force an insn
10532 to a new group, according to the estimated processor grouping.
10533 @var{number}: Insert nops to force costly dependent insns into
10534 separate groups. Insert @var{number} nops to force an insn to a new group.
10537 @opindex mcall-sysv
10538 On System V.4 and embedded PowerPC systems compile code using calling
10539 conventions that adheres to the March 1995 draft of the System V
10540 Application Binary Interface, PowerPC processor supplement. This is the
10541 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
10543 @item -mcall-sysv-eabi
10544 @opindex mcall-sysv-eabi
10545 Specify both @option{-mcall-sysv} and @option{-meabi} options.
10547 @item -mcall-sysv-noeabi
10548 @opindex mcall-sysv-noeabi
10549 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
10551 @item -mcall-solaris
10552 @opindex mcall-solaris
10553 On System V.4 and embedded PowerPC systems compile code for the Solaris
10557 @opindex mcall-linux
10558 On System V.4 and embedded PowerPC systems compile code for the
10559 Linux-based GNU system.
10563 On System V.4 and embedded PowerPC systems compile code for the
10564 Hurd-based GNU system.
10566 @item -mcall-netbsd
10567 @opindex mcall-netbsd
10568 On System V.4 and embedded PowerPC systems compile code for the
10569 NetBSD operating system.
10571 @item -maix-struct-return
10572 @opindex maix-struct-return
10573 Return all structures in memory (as specified by the AIX ABI)@.
10575 @item -msvr4-struct-return
10576 @opindex msvr4-struct-return
10577 Return structures smaller than 8 bytes in registers (as specified by the
10580 @item -mabi=altivec
10581 @opindex mabi=altivec
10582 Extend the current ABI with AltiVec ABI extensions. This does not
10583 change the default ABI, instead it adds the AltiVec ABI extensions to
10586 @item -mabi=no-altivec
10587 @opindex mabi=no-altivec
10588 Disable AltiVec ABI extensions for the current ABI.
10591 @itemx -mno-prototype
10592 @opindex mprototype
10593 @opindex mno-prototype
10594 On System V.4 and embedded PowerPC systems assume that all calls to
10595 variable argument functions are properly prototyped. Otherwise, the
10596 compiler must insert an instruction before every non prototyped call to
10597 set or clear bit 6 of the condition code register (@var{CR}) to
10598 indicate whether floating point values were passed in the floating point
10599 registers in case the function takes a variable arguments. With
10600 @option{-mprototype}, only calls to prototyped variable argument functions
10601 will set or clear the bit.
10605 On embedded PowerPC systems, assume that the startup module is called
10606 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
10607 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
10612 On embedded PowerPC systems, assume that the startup module is called
10613 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
10618 On embedded PowerPC systems, assume that the startup module is called
10619 @file{crt0.o} and the standard C libraries are @file{libads.a} and
10622 @item -myellowknife
10623 @opindex myellowknife
10624 On embedded PowerPC systems, assume that the startup module is called
10625 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
10630 On System V.4 and embedded PowerPC systems, specify that you are
10631 compiling for a VxWorks system.
10635 Specify that you are compiling for the WindISS simulation environment.
10639 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
10640 header to indicate that @samp{eabi} extended relocations are used.
10646 On System V.4 and embedded PowerPC systems do (do not) adhere to the
10647 Embedded Applications Binary Interface (eabi) which is a set of
10648 modifications to the System V.4 specifications. Selecting @option{-meabi}
10649 means that the stack is aligned to an 8 byte boundary, a function
10650 @code{__eabi} is called to from @code{main} to set up the eabi
10651 environment, and the @option{-msdata} option can use both @code{r2} and
10652 @code{r13} to point to two separate small data areas. Selecting
10653 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
10654 do not call an initialization function from @code{main}, and the
10655 @option{-msdata} option will only use @code{r13} to point to a single
10656 small data area. The @option{-meabi} option is on by default if you
10657 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
10660 @opindex msdata=eabi
10661 On System V.4 and embedded PowerPC systems, put small initialized
10662 @code{const} global and static data in the @samp{.sdata2} section, which
10663 is pointed to by register @code{r2}. Put small initialized
10664 non-@code{const} global and static data in the @samp{.sdata} section,
10665 which is pointed to by register @code{r13}. Put small uninitialized
10666 global and static data in the @samp{.sbss} section, which is adjacent to
10667 the @samp{.sdata} section. The @option{-msdata=eabi} option is
10668 incompatible with the @option{-mrelocatable} option. The
10669 @option{-msdata=eabi} option also sets the @option{-memb} option.
10672 @opindex msdata=sysv
10673 On System V.4 and embedded PowerPC systems, put small global and static
10674 data in the @samp{.sdata} section, which is pointed to by register
10675 @code{r13}. Put small uninitialized global and static data in the
10676 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
10677 The @option{-msdata=sysv} option is incompatible with the
10678 @option{-mrelocatable} option.
10680 @item -msdata=default
10682 @opindex msdata=default
10684 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
10685 compile code the same as @option{-msdata=eabi}, otherwise compile code the
10686 same as @option{-msdata=sysv}.
10689 @opindex msdata-data
10690 On System V.4 and embedded PowerPC systems, put small global and static
10691 data in the @samp{.sdata} section. Put small uninitialized global and
10692 static data in the @samp{.sbss} section. Do not use register @code{r13}
10693 to address small data however. This is the default behavior unless
10694 other @option{-msdata} options are used.
10698 @opindex msdata=none
10700 On embedded PowerPC systems, put all initialized global and static data
10701 in the @samp{.data} section, and all uninitialized data in the
10702 @samp{.bss} section.
10706 @cindex smaller data references (PowerPC)
10707 @cindex .sdata/.sdata2 references (PowerPC)
10708 On embedded PowerPC systems, put global and static items less than or
10709 equal to @var{num} bytes into the small data or bss sections instead of
10710 the normal data or bss section. By default, @var{num} is 8. The
10711 @option{-G @var{num}} switch is also passed to the linker.
10712 All modules should be compiled with the same @option{-G @var{num}} value.
10715 @itemx -mno-regnames
10717 @opindex mno-regnames
10718 On System V.4 and embedded PowerPC systems do (do not) emit register
10719 names in the assembly language output using symbolic forms.
10722 @itemx -mno-longcall
10724 @opindex mno-longcall
10725 Default to making all function calls indirectly, using a register, so
10726 that functions which reside further than 32 megabytes (33,554,432
10727 bytes) from the current location can be called. This setting can be
10728 overridden by the @code{shortcall} function attribute, or by
10729 @code{#pragma longcall(0)}.
10731 Some linkers are capable of detecting out-of-range calls and generating
10732 glue code on the fly. On these systems, long calls are unnecessary and
10733 generate slower code. As of this writing, the AIX linker can do this,
10734 as can the GNU linker for PowerPC/64. It is planned to add this feature
10735 to the GNU linker for 32-bit PowerPC systems as well.
10737 On Darwin/PPC systems, @code{#pragma longcall} will generate ``jbsr
10738 callee, L42'', plus a ``branch island'' (glue code). The two target
10739 addresses represent the callee and the ``branch island.'' The
10740 Darwin/PPC linker will prefer the first address and generate a ``bl
10741 callee'' if the PPC ``bl'' instruction will reach the callee directly;
10742 otherwise, the linker will generate ``bl L42'' to call the ``branch
10743 island.'' The ``branch island'' is appended to the body of the
10744 calling function; it computes the full 32-bit address of the callee
10747 On Mach-O (Darwin) systems, this option directs the compiler emit to
10748 the glue for every direct call, and the Darwin linker decides whether
10749 to use or discard it.
10751 In the future, we may cause GCC to ignore all longcall specifications
10752 when the linker is known to generate glue.
10756 Adds support for multithreading with the @dfn{pthreads} library.
10757 This option sets flags for both the preprocessor and linker.
10761 @node S/390 and zSeries Options
10762 @subsection S/390 and zSeries Options
10763 @cindex S/390 and zSeries Options
10765 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
10769 @itemx -msoft-float
10770 @opindex mhard-float
10771 @opindex msoft-float
10772 Use (do not use) the hardware floating-point instructions and registers
10773 for floating-point operations. When @option{-msoft-float} is specified,
10774 functions in @file{libgcc.a} will be used to perform floating-point
10775 operations. When @option{-mhard-float} is specified, the compiler
10776 generates IEEE floating-point instructions. This is the default.
10779 @itemx -mno-backchain
10780 @itemx -mkernel-backchain
10781 @opindex mbackchain
10782 @opindex mno-backchain
10783 @opindex mkernel-backchain
10784 In order to provide a backchain the address of the caller's frame
10785 is stored within the callee's stack frame.
10786 A backchain may be needed to allow debugging using tools that do not understand
10787 DWARF-2 call frame information.
10788 For @option{-mno-backchain} no backchain is maintained at all which is the
10790 If one of the other options is present the backchain pointer is placed either
10791 on top of the stack frame (@option{-mkernel-backchain}) or on
10792 the bottom (@option{-mbackchain}).
10793 Beside the different backchain location @option{-mkernel-backchain}
10794 also changes stack frame layout breaking the ABI. This option
10795 is intended to be used for code which internally needs a backchain but has
10796 to get by with a limited stack size e.g.@: the linux kernel.
10797 Internal unwinding code not using DWARF-2 info has to be able to locate the
10798 return address of a function. That will be eased be the fact that
10799 the return address of a function is placed two words below the backchain
10803 @itemx -mno-small-exec
10804 @opindex msmall-exec
10805 @opindex mno-small-exec
10806 Generate (or do not generate) code using the @code{bras} instruction
10807 to do subroutine calls.
10808 This only works reliably if the total executable size does not
10809 exceed 64k. The default is to use the @code{basr} instruction instead,
10810 which does not have this limitation.
10816 When @option{-m31} is specified, generate code compliant to the
10817 GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate
10818 code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in
10819 particular to generate 64-bit instructions. For the @samp{s390}
10820 targets, the default is @option{-m31}, while the @samp{s390x}
10821 targets default to @option{-m64}.
10827 When @option{-mzarch} is specified, generate code using the
10828 instructions available on z/Architecture.
10829 When @option{-mesa} is specified, generate code using the
10830 instructions available on ESA/390. Note that @option{-mesa} is
10831 not possible with @option{-m64}.
10832 When generating code compliant to the GNU/Linux for S/390 ABI,
10833 the default is @option{-mesa}. When generating code compliant
10834 to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}.
10840 Generate (or do not generate) code using the @code{mvcle} instruction
10841 to perform block moves. When @option{-mno-mvcle} is specified,
10842 use a @code{mvc} loop instead. This is the default.
10848 Print (or do not print) additional debug information when compiling.
10849 The default is to not print debug information.
10851 @item -march=@var{cpu-type}
10853 Generate code that will run on @var{cpu-type}, which is the name of a system
10854 representing a certain processor type. Possible values for
10855 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, and @samp{z990}.
10856 When generating code using the instructions available on z/Architecture,
10857 the default is @option{-march=z900}. Otherwise, the default is
10858 @option{-march=g5}.
10860 @item -mtune=@var{cpu-type}
10862 Tune to @var{cpu-type} everything applicable about the generated code,
10863 except for the ABI and the set of available instructions.
10864 The list of @var{cpu-type} values is the same as for @option{-march}.
10865 The default is the value used for @option{-march}.
10868 @itemx -mno-tpf-trace
10869 @opindex mtpf-trace
10870 @opindex mno-tpf-trace
10871 Generate code that adds (does not add) in TPF OS specific branches to trace
10872 routines in the operating system. This option is off by default, even
10873 when compiling for the TPF OS.
10876 @itemx -mno-fused-madd
10877 @opindex mfused-madd
10878 @opindex mno-fused-madd
10879 Generate code that uses (does not use) the floating point multiply and
10880 accumulate instructions. These instructions are generated by default if
10881 hardware floating point is used.
10883 @item -mwarn-framesize=@var{framesize}
10884 @opindex mwarn-framesize
10885 Emit a warning if the current function exceeds the given frame size. Because
10886 this is a compile time check it doesn't need to be a real problem when the program
10887 runs. It is intended to identify functions which most probably cause
10888 a stack overflow. It is useful to be used in an environment with limited stack
10889 size e.g.@: the linux kernel.
10891 @item -mwarn-dynamicstack
10892 @opindex mwarn-dynamicstack
10893 Emit a warning if the function calls alloca or uses dynamically
10894 sized arrays. This is generally a bad idea with a limited stack size.
10896 @item -mstack-guard=@var{stack-guard}
10897 @item -mstack-size=@var{stack-size}
10898 @opindex mstack-guard
10899 @opindex mstack-size
10900 These arguments always have to be used in conjunction. If they are present the s390
10901 back end emits additional instructions in the function prologue which trigger a trap
10902 if the stack size is @var{stack-guard} bytes above the @var{stack-size}
10903 (remember that the stack on s390 grows downward). These options are intended to
10904 be used to help debugging stack overflow problems. The additionally emitted code
10905 cause only little overhead and hence can also be used in production like systems
10906 without greater performance degradation. The given values have to be exact
10907 powers of 2 and @var{stack-size} has to be greater than @var{stack-guard}.
10908 In order to be efficient the extra code makes the assumption that the stack starts
10909 at an address aligned to the value given by @var{stack-size}.
10913 @subsection SH Options
10915 These @samp{-m} options are defined for the SH implementations:
10920 Generate code for the SH1.
10924 Generate code for the SH2.
10927 Generate code for the SH2e.
10931 Generate code for the SH3.
10935 Generate code for the SH3e.
10939 Generate code for the SH4 without a floating-point unit.
10941 @item -m4-single-only
10942 @opindex m4-single-only
10943 Generate code for the SH4 with a floating-point unit that only
10944 supports single-precision arithmetic.
10948 Generate code for the SH4 assuming the floating-point unit is in
10949 single-precision mode by default.
10953 Generate code for the SH4.
10957 Generate code for the SH4al-dsp, or for a SH4a in such a way that the
10958 floating-point unit is not used.
10960 @item -m4a-single-only
10961 @opindex m4a-single-only
10962 Generate code for the SH4a, in such a way that no double-precision
10963 floating point operations are used.
10966 @opindex m4a-single
10967 Generate code for the SH4a assuming the floating-point unit is in
10968 single-precision mode by default.
10972 Generate code for the SH4a.
10976 Same as @option{-m4a-nofpu}, except that it implicitly passes
10977 @option{-dsp} to the assembler. GCC doesn't generate any DSP
10978 instructions at the moment.
10982 Compile code for the processor in big endian mode.
10986 Compile code for the processor in little endian mode.
10990 Align doubles at 64-bit boundaries. Note that this changes the calling
10991 conventions, and thus some functions from the standard C library will
10992 not work unless you recompile it first with @option{-mdalign}.
10996 Shorten some address references at link time, when possible; uses the
10997 linker option @option{-relax}.
11001 Use 32-bit offsets in @code{switch} tables. The default is to use
11006 Enable the use of the instruction @code{fmovd}.
11010 Comply with the calling conventions defined by Renesas.
11014 Comply with the calling conventions defined by Renesas.
11018 Comply with the calling conventions defined for GCC before the Renesas
11019 conventions were available. This option is the default for all
11020 targets of the SH toolchain except for @samp{sh-symbianelf}.
11023 @opindex mnomacsave
11024 Mark the @code{MAC} register as call-clobbered, even if
11025 @option{-mhitachi} is given.
11029 Increase IEEE-compliance of floating-point code.
11033 Dump instruction size and location in the assembly code.
11036 @opindex mpadstruct
11037 This option is deprecated. It pads structures to multiple of 4 bytes,
11038 which is incompatible with the SH ABI@.
11042 Optimize for space instead of speed. Implied by @option{-Os}.
11045 @opindex mprefergot
11046 When generating position-independent code, emit function calls using
11047 the Global Offset Table instead of the Procedure Linkage Table.
11051 Generate a library function call to invalidate instruction cache
11052 entries, after fixing up a trampoline. This library function call
11053 doesn't assume it can write to the whole memory address space. This
11054 is the default when the target is @code{sh-*-linux*}.
11057 @node SPARC Options
11058 @subsection SPARC Options
11059 @cindex SPARC options
11061 These @samp{-m} options are supported on the SPARC:
11064 @item -mno-app-regs
11066 @opindex mno-app-regs
11068 Specify @option{-mapp-regs} to generate output using the global registers
11069 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
11072 To be fully SVR4 ABI compliant at the cost of some performance loss,
11073 specify @option{-mno-app-regs}. You should compile libraries and system
11074 software with this option.
11077 @itemx -mhard-float
11079 @opindex mhard-float
11080 Generate output containing floating point instructions. This is the
11084 @itemx -msoft-float
11086 @opindex msoft-float
11087 Generate output containing library calls for floating point.
11088 @strong{Warning:} the requisite libraries are not available for all SPARC
11089 targets. Normally the facilities of the machine's usual C compiler are
11090 used, but this cannot be done directly in cross-compilation. You must make
11091 your own arrangements to provide suitable library functions for
11092 cross-compilation. The embedded targets @samp{sparc-*-aout} and
11093 @samp{sparclite-*-*} do provide software floating point support.
11095 @option{-msoft-float} changes the calling convention in the output file;
11096 therefore, it is only useful if you compile @emph{all} of a program with
11097 this option. In particular, you need to compile @file{libgcc.a}, the
11098 library that comes with GCC, with @option{-msoft-float} in order for
11101 @item -mhard-quad-float
11102 @opindex mhard-quad-float
11103 Generate output containing quad-word (long double) floating point
11106 @item -msoft-quad-float
11107 @opindex msoft-quad-float
11108 Generate output containing library calls for quad-word (long double)
11109 floating point instructions. The functions called are those specified
11110 in the SPARC ABI@. This is the default.
11112 As of this writing, there are no SPARC implementations that have hardware
11113 support for the quad-word floating point instructions. They all invoke
11114 a trap handler for one of these instructions, and then the trap handler
11115 emulates the effect of the instruction. Because of the trap handler overhead,
11116 this is much slower than calling the ABI library routines. Thus the
11117 @option{-msoft-quad-float} option is the default.
11119 @item -mno-unaligned-doubles
11120 @itemx -munaligned-doubles
11121 @opindex mno-unaligned-doubles
11122 @opindex munaligned-doubles
11123 Assume that doubles have 8 byte alignment. This is the default.
11125 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
11126 alignment only if they are contained in another type, or if they have an
11127 absolute address. Otherwise, it assumes they have 4 byte alignment.
11128 Specifying this option avoids some rare compatibility problems with code
11129 generated by other compilers. It is not the default because it results
11130 in a performance loss, especially for floating point code.
11132 @item -mno-faster-structs
11133 @itemx -mfaster-structs
11134 @opindex mno-faster-structs
11135 @opindex mfaster-structs
11136 With @option{-mfaster-structs}, the compiler assumes that structures
11137 should have 8 byte alignment. This enables the use of pairs of
11138 @code{ldd} and @code{std} instructions for copies in structure
11139 assignment, in place of twice as many @code{ld} and @code{st} pairs.
11140 However, the use of this changed alignment directly violates the SPARC
11141 ABI@. Thus, it's intended only for use on targets where the developer
11142 acknowledges that their resulting code will not be directly in line with
11143 the rules of the ABI@.
11145 @item -mimpure-text
11146 @opindex mimpure-text
11147 @option{-mimpure-text}, used in addition to @option{-shared}, tells
11148 the compiler to not pass @option{-z text} to the linker when linking a
11149 shared object. Using this option, you can link position-dependent
11150 code into a shared object.
11152 @option{-mimpure-text} suppresses the ``relocations remain against
11153 allocatable but non-writable sections'' linker error message.
11154 However, the necessary relocations will trigger copy-on-write, and the
11155 shared object is not actually shared across processes. Instead of
11156 using @option{-mimpure-text}, you should compile all source code with
11157 @option{-fpic} or @option{-fPIC}.
11159 This option is only available on SunOS and Solaris.
11161 @item -mcpu=@var{cpu_type}
11163 Set the instruction set, register set, and instruction scheduling parameters
11164 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
11165 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
11166 @samp{f930}, @samp{f934}, @samp{hypersparc}, @samp{sparclite86x},
11167 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc}, and
11168 @samp{ultrasparc3}.
11170 Default instruction scheduling parameters are used for values that select
11171 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
11172 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
11174 Here is a list of each supported architecture and their supported
11179 v8: supersparc, hypersparc
11180 sparclite: f930, f934, sparclite86x
11182 v9: ultrasparc, ultrasparc3
11185 By default (unless configured otherwise), GCC generates code for the V7
11186 variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler
11187 additionally optimizes it for the Cypress CY7C602 chip, as used in the
11188 SPARCStation/SPARCServer 3xx series. This is also appropriate for the older
11189 SPARCStation 1, 2, IPX etc.
11191 With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC
11192 architecture. The only difference from V7 code is that the compiler emits
11193 the integer multiply and integer divide instructions which exist in SPARC-V8
11194 but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally
11195 optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and
11198 With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of
11199 the SPARC architecture. This adds the integer multiply, integer divide step
11200 and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7.
11201 With @option{-mcpu=f930}, the compiler additionally optimizes it for the
11202 Fujitsu MB86930 chip, which is the original SPARClite, with no FPU. With
11203 @option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu
11204 MB86934 chip, which is the more recent SPARClite with FPU.
11206 With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of
11207 the SPARC architecture. This adds the integer multiply, multiply/accumulate,
11208 integer divide step and scan (@code{ffs}) instructions which exist in SPARClet
11209 but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally
11210 optimizes it for the TEMIC SPARClet chip.
11212 With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC
11213 architecture. This adds 64-bit integer and floating-point move instructions,
11214 3 additional floating-point condition code registers and conditional move
11215 instructions. With @option{-mcpu=ultrasparc}, the compiler additionally
11216 optimizes it for the Sun UltraSPARC I/II chips. With
11217 @option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the
11218 Sun UltraSPARC III chip.
11220 @item -mtune=@var{cpu_type}
11222 Set the instruction scheduling parameters for machine type
11223 @var{cpu_type}, but do not set the instruction set or register set that the
11224 option @option{-mcpu=@var{cpu_type}} would.
11226 The same values for @option{-mcpu=@var{cpu_type}} can be used for
11227 @option{-mtune=@var{cpu_type}}, but the only useful values are those
11228 that select a particular cpu implementation. Those are @samp{cypress},
11229 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
11230 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc}, and
11231 @samp{ultrasparc3}.
11236 @opindex mno-v8plus
11237 With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI. The
11238 difference from the V8 ABI is that the global and out registers are
11239 considered 64-bit wide. This is enabled by default on Solaris in 32-bit
11240 mode for all SPARC-V9 processors.
11246 With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC
11247 Visual Instruction Set extensions. The default is @option{-mno-vis}.
11250 These @samp{-m} options are supported in addition to the above
11251 on SPARC-V9 processors in 64-bit environments:
11254 @item -mlittle-endian
11255 @opindex mlittle-endian
11256 Generate code for a processor running in little-endian mode. It is only
11257 available for a few configurations and most notably not on Solaris.
11263 Generate code for a 32-bit or 64-bit environment.
11264 The 32-bit environment sets int, long and pointer to 32 bits.
11265 The 64-bit environment sets int to 32 bits and long and pointer
11268 @item -mcmodel=medlow
11269 @opindex mcmodel=medlow
11270 Generate code for the Medium/Low code model: 64-bit addresses, programs
11271 must be linked in the low 32 bits of memory. Programs can be statically
11272 or dynamically linked.
11274 @item -mcmodel=medmid
11275 @opindex mcmodel=medmid
11276 Generate code for the Medium/Middle code model: 64-bit addresses, programs
11277 must be linked in the low 44 bits of memory, the text and data segments must
11278 be less than 2GB in size and the data segment must be located within 2GB of
11281 @item -mcmodel=medany
11282 @opindex mcmodel=medany
11283 Generate code for the Medium/Anywhere code model: 64-bit addresses, programs
11284 may be linked anywhere in memory, the text and data segments must be less
11285 than 2GB in size and the data segment must be located within 2GB of the
11288 @item -mcmodel=embmedany
11289 @opindex mcmodel=embmedany
11290 Generate code for the Medium/Anywhere code model for embedded systems:
11291 64-bit addresses, the text and data segments must be less than 2GB in
11292 size, both starting anywhere in memory (determined at link time). The
11293 global register %g4 points to the base of the data segment. Programs
11294 are statically linked and PIC is not supported.
11297 @itemx -mno-stack-bias
11298 @opindex mstack-bias
11299 @opindex mno-stack-bias
11300 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
11301 frame pointer if present, are offset by @minus{}2047 which must be added back
11302 when making stack frame references. This is the default in 64-bit mode.
11303 Otherwise, assume no such offset is present.
11306 These switches are supported in addition to the above on Solaris:
11311 Add support for multithreading using the Solaris threads library. This
11312 option sets flags for both the preprocessor and linker. This option does
11313 not affect the thread safety of object code produced by the compiler or
11314 that of libraries supplied with it.
11318 Add support for multithreading using the POSIX threads library. This
11319 option sets flags for both the preprocessor and linker. This option does
11320 not affect the thread safety of object code produced by the compiler or
11321 that of libraries supplied with it.
11324 @node System V Options
11325 @subsection Options for System V
11327 These additional options are available on System V Release 4 for
11328 compatibility with other compilers on those systems:
11333 Create a shared object.
11334 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
11338 Identify the versions of each tool used by the compiler, in a
11339 @code{.ident} assembler directive in the output.
11343 Refrain from adding @code{.ident} directives to the output file (this is
11346 @item -YP,@var{dirs}
11348 Search the directories @var{dirs}, and no others, for libraries
11349 specified with @option{-l}.
11351 @item -Ym,@var{dir}
11353 Look in the directory @var{dir} to find the M4 preprocessor.
11354 The assembler uses this option.
11355 @c This is supposed to go with a -Yd for predefined M4 macro files, but
11356 @c the generic assembler that comes with Solaris takes just -Ym.
11359 @node TMS320C3x/C4x Options
11360 @subsection TMS320C3x/C4x Options
11361 @cindex TMS320C3x/C4x Options
11363 These @samp{-m} options are defined for TMS320C3x/C4x implementations:
11367 @item -mcpu=@var{cpu_type}
11369 Set the instruction set, register set, and instruction scheduling
11370 parameters for machine type @var{cpu_type}. Supported values for
11371 @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
11372 @samp{c44}. The default is @samp{c40} to generate code for the
11377 @itemx -msmall-memory
11379 @opindex mbig-memory
11381 @opindex msmall-memory
11383 Generates code for the big or small memory model. The small memory
11384 model assumed that all data fits into one 64K word page. At run-time
11385 the data page (DP) register must be set to point to the 64K page
11386 containing the .bss and .data program sections. The big memory model is
11387 the default and requires reloading of the DP register for every direct
11394 Allow (disallow) allocation of general integer operands into the block
11395 count register BK@.
11401 Enable (disable) generation of code using decrement and branch,
11402 DBcond(D), instructions. This is enabled by default for the C4x. To be
11403 on the safe side, this is disabled for the C3x, since the maximum
11404 iteration count on the C3x is @math{2^{23} + 1} (but who iterates loops more than
11405 @math{2^{23}} times on the C3x?). Note that GCC will try to reverse a loop so
11406 that it can utilize the decrement and branch instruction, but will give
11407 up if there is more than one memory reference in the loop. Thus a loop
11408 where the loop counter is decremented can generate slightly more
11409 efficient code, in cases where the RPTB instruction cannot be utilized.
11411 @item -mdp-isr-reload
11413 @opindex mdp-isr-reload
11415 Force the DP register to be saved on entry to an interrupt service
11416 routine (ISR), reloaded to point to the data section, and restored on
11417 exit from the ISR@. This should not be required unless someone has
11418 violated the small memory model by modifying the DP register, say within
11425 For the C3x use the 24-bit MPYI instruction for integer multiplies
11426 instead of a library call to guarantee 32-bit results. Note that if one
11427 of the operands is a constant, then the multiplication will be performed
11428 using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
11429 then squaring operations are performed inline instead of a library call.
11432 @itemx -mno-fast-fix
11434 @opindex mno-fast-fix
11435 The C3x/C4x FIX instruction to convert a floating point value to an
11436 integer value chooses the nearest integer less than or equal to the
11437 floating point value rather than to the nearest integer. Thus if the
11438 floating point number is negative, the result will be incorrectly
11439 truncated an additional code is necessary to detect and correct this
11440 case. This option can be used to disable generation of the additional
11441 code required to correct the result.
11447 Enable (disable) generation of repeat block sequences using the RPTB
11448 instruction for zero overhead looping. The RPTB construct is only used
11449 for innermost loops that do not call functions or jump across the loop
11450 boundaries. There is no advantage having nested RPTB loops due to the
11451 overhead required to save and restore the RC, RS, and RE registers.
11452 This is enabled by default with @option{-O2}.
11454 @item -mrpts=@var{count}
11458 Enable (disable) the use of the single instruction repeat instruction
11459 RPTS@. If a repeat block contains a single instruction, and the loop
11460 count can be guaranteed to be less than the value @var{count}, GCC will
11461 emit a RPTS instruction instead of a RPTB@. If no value is specified,
11462 then a RPTS will be emitted even if the loop count cannot be determined
11463 at compile time. Note that the repeated instruction following RPTS does
11464 not have to be reloaded from memory each iteration, thus freeing up the
11465 CPU buses for operands. However, since interrupts are blocked by this
11466 instruction, it is disabled by default.
11468 @item -mloop-unsigned
11469 @itemx -mno-loop-unsigned
11470 @opindex mloop-unsigned
11471 @opindex mno-loop-unsigned
11472 The maximum iteration count when using RPTS and RPTB (and DB on the C40)
11473 is @math{2^{31} + 1} since these instructions test if the iteration count is
11474 negative to terminate the loop. If the iteration count is unsigned
11475 there is a possibility than the @math{2^{31} + 1} maximum iteration count may be
11476 exceeded. This switch allows an unsigned iteration count.
11480 Try to emit an assembler syntax that the TI assembler (asm30) is happy
11481 with. This also enforces compatibility with the API employed by the TI
11482 C3x C compiler. For example, long doubles are passed as structures
11483 rather than in floating point registers.
11489 Generate code that uses registers (stack) for passing arguments to functions.
11490 By default, arguments are passed in registers where possible rather
11491 than by pushing arguments on to the stack.
11493 @item -mparallel-insns
11494 @itemx -mno-parallel-insns
11495 @opindex mparallel-insns
11496 @opindex mno-parallel-insns
11497 Allow the generation of parallel instructions. This is enabled by
11498 default with @option{-O2}.
11500 @item -mparallel-mpy
11501 @itemx -mno-parallel-mpy
11502 @opindex mparallel-mpy
11503 @opindex mno-parallel-mpy
11504 Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
11505 provided @option{-mparallel-insns} is also specified. These instructions have
11506 tight register constraints which can pessimize the code generation
11507 of large functions.
11512 @subsection V850 Options
11513 @cindex V850 Options
11515 These @samp{-m} options are defined for V850 implementations:
11519 @itemx -mno-long-calls
11520 @opindex mlong-calls
11521 @opindex mno-long-calls
11522 Treat all calls as being far away (near). If calls are assumed to be
11523 far away, the compiler will always load the functions address up into a
11524 register, and call indirect through the pointer.
11530 Do not optimize (do optimize) basic blocks that use the same index
11531 pointer 4 or more times to copy pointer into the @code{ep} register, and
11532 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
11533 option is on by default if you optimize.
11535 @item -mno-prolog-function
11536 @itemx -mprolog-function
11537 @opindex mno-prolog-function
11538 @opindex mprolog-function
11539 Do not use (do use) external functions to save and restore registers
11540 at the prologue and epilogue of a function. The external functions
11541 are slower, but use less code space if more than one function saves
11542 the same number of registers. The @option{-mprolog-function} option
11543 is on by default if you optimize.
11547 Try to make the code as small as possible. At present, this just turns
11548 on the @option{-mep} and @option{-mprolog-function} options.
11550 @item -mtda=@var{n}
11552 Put static or global variables whose size is @var{n} bytes or less into
11553 the tiny data area that register @code{ep} points to. The tiny data
11554 area can hold up to 256 bytes in total (128 bytes for byte references).
11556 @item -msda=@var{n}
11558 Put static or global variables whose size is @var{n} bytes or less into
11559 the small data area that register @code{gp} points to. The small data
11560 area can hold up to 64 kilobytes.
11562 @item -mzda=@var{n}
11564 Put static or global variables whose size is @var{n} bytes or less into
11565 the first 32 kilobytes of memory.
11569 Specify that the target processor is the V850.
11572 @opindex mbig-switch
11573 Generate code suitable for big switch tables. Use this option only if
11574 the assembler/linker complain about out of range branches within a switch
11579 This option will cause r2 and r5 to be used in the code generated by
11580 the compiler. This setting is the default.
11582 @item -mno-app-regs
11583 @opindex mno-app-regs
11584 This option will cause r2 and r5 to be treated as fixed registers.
11588 Specify that the target processor is the V850E1. The preprocessor
11589 constants @samp{__v850e1__} and @samp{__v850e__} will be defined if
11590 this option is used.
11594 Specify that the target processor is the V850E. The preprocessor
11595 constant @samp{__v850e__} will be defined if this option is used.
11597 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
11598 are defined then a default target processor will be chosen and the
11599 relevant @samp{__v850*__} preprocessor constant will be defined.
11601 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
11602 defined, regardless of which processor variant is the target.
11604 @item -mdisable-callt
11605 @opindex mdisable-callt
11606 This option will suppress generation of the CALLT instruction for the
11607 v850e and v850e1 flavors of the v850 architecture. The default is
11608 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
11613 @subsection VAX Options
11614 @cindex VAX options
11616 These @samp{-m} options are defined for the VAX:
11621 Do not output certain jump instructions (@code{aobleq} and so on)
11622 that the Unix assembler for the VAX cannot handle across long
11627 Do output those jump instructions, on the assumption that you
11628 will assemble with the GNU assembler.
11632 Output code for g-format floating point numbers instead of d-format.
11635 @node x86-64 Options
11636 @subsection x86-64 Options
11637 @cindex x86-64 options
11639 These are listed under @xref{i386 and x86-64 Options}.
11641 @node Xstormy16 Options
11642 @subsection Xstormy16 Options
11643 @cindex Xstormy16 Options
11645 These options are defined for Xstormy16:
11650 Choose startup files and linker script suitable for the simulator.
11653 @node Xtensa Options
11654 @subsection Xtensa Options
11655 @cindex Xtensa Options
11657 These options are supported for Xtensa targets:
11661 @itemx -mno-const16
11663 @opindex mno-const16
11664 Enable or disable use of @code{CONST16} instructions for loading
11665 constant values. The @code{CONST16} instruction is currently not a
11666 standard option from Tensilica. When enabled, @code{CONST16}
11667 instructions are always used in place of the standard @code{L32R}
11668 instructions. The use of @code{CONST16} is enabled by default only if
11669 the @code{L32R} instruction is not available.
11672 @itemx -mno-fused-madd
11673 @opindex mfused-madd
11674 @opindex mno-fused-madd
11675 Enable or disable use of fused multiply/add and multiply/subtract
11676 instructions in the floating-point option. This has no effect if the
11677 floating-point option is not also enabled. Disabling fused multiply/add
11678 and multiply/subtract instructions forces the compiler to use separate
11679 instructions for the multiply and add/subtract operations. This may be
11680 desirable in some cases where strict IEEE 754-compliant results are
11681 required: the fused multiply add/subtract instructions do not round the
11682 intermediate result, thereby producing results with @emph{more} bits of
11683 precision than specified by the IEEE standard. Disabling fused multiply
11684 add/subtract instructions also ensures that the program output is not
11685 sensitive to the compiler's ability to combine multiply and add/subtract
11688 @item -mtext-section-literals
11689 @itemx -mno-text-section-literals
11690 @opindex mtext-section-literals
11691 @opindex mno-text-section-literals
11692 Control the treatment of literal pools. The default is
11693 @option{-mno-text-section-literals}, which places literals in a separate
11694 section in the output file. This allows the literal pool to be placed
11695 in a data RAM/ROM, and it also allows the linker to combine literal
11696 pools from separate object files to remove redundant literals and
11697 improve code size. With @option{-mtext-section-literals}, the literals
11698 are interspersed in the text section in order to keep them as close as
11699 possible to their references. This may be necessary for large assembly
11702 @item -mtarget-align
11703 @itemx -mno-target-align
11704 @opindex mtarget-align
11705 @opindex mno-target-align
11706 When this option is enabled, GCC instructs the assembler to
11707 automatically align instructions to reduce branch penalties at the
11708 expense of some code density. The assembler attempts to widen density
11709 instructions to align branch targets and the instructions following call
11710 instructions. If there are not enough preceding safe density
11711 instructions to align a target, no widening will be performed. The
11712 default is @option{-mtarget-align}. These options do not affect the
11713 treatment of auto-aligned instructions like @code{LOOP}, which the
11714 assembler will always align, either by widening density instructions or
11715 by inserting no-op instructions.
11718 @itemx -mno-longcalls
11719 @opindex mlongcalls
11720 @opindex mno-longcalls
11721 When this option is enabled, GCC instructs the assembler to translate
11722 direct calls to indirect calls unless it can determine that the target
11723 of a direct call is in the range allowed by the call instruction. This
11724 translation typically occurs for calls to functions in other source
11725 files. Specifically, the assembler translates a direct @code{CALL}
11726 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
11727 The default is @option{-mno-longcalls}. This option should be used in
11728 programs where the call target can potentially be out of range. This
11729 option is implemented in the assembler, not the compiler, so the
11730 assembly code generated by GCC will still show direct call
11731 instructions---look at the disassembled object code to see the actual
11732 instructions. Note that the assembler will use an indirect call for
11733 every cross-file call, not just those that really will be out of range.
11736 @node zSeries Options
11737 @subsection zSeries Options
11738 @cindex zSeries options
11740 These are listed under @xref{S/390 and zSeries Options}.
11742 @node Code Gen Options
11743 @section Options for Code Generation Conventions
11744 @cindex code generation conventions
11745 @cindex options, code generation
11746 @cindex run-time options
11748 These machine-independent options control the interface conventions
11749 used in code generation.
11751 Most of them have both positive and negative forms; the negative form
11752 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
11753 one of the forms is listed---the one which is not the default. You
11754 can figure out the other form by either removing @samp{no-} or adding
11758 @item -fbounds-check
11759 @opindex fbounds-check
11760 For front-ends that support it, generate additional code to check that
11761 indices used to access arrays are within the declared range. This is
11762 currently only supported by the Java and Fortran 77 front-ends, where
11763 this option defaults to true and false respectively.
11767 This option generates traps for signed overflow on addition, subtraction,
11768 multiplication operations.
11772 This option instructs the compiler to assume that signed arithmetic
11773 overflow of addition, subtraction and multiplication wraps around
11774 using twos-complement representation. This flag enables some optimizations
11775 and disables other. This option is enabled by default for the Java
11776 front-end, as required by the Java language specification.
11779 @opindex fexceptions
11780 Enable exception handling. Generates extra code needed to propagate
11781 exceptions. For some targets, this implies GCC will generate frame
11782 unwind information for all functions, which can produce significant data
11783 size overhead, although it does not affect execution. If you do not
11784 specify this option, GCC will enable it by default for languages like
11785 C++ which normally require exception handling, and disable it for
11786 languages like C that do not normally require it. However, you may need
11787 to enable this option when compiling C code that needs to interoperate
11788 properly with exception handlers written in C++. You may also wish to
11789 disable this option if you are compiling older C++ programs that don't
11790 use exception handling.
11792 @item -fnon-call-exceptions
11793 @opindex fnon-call-exceptions
11794 Generate code that allows trapping instructions to throw exceptions.
11795 Note that this requires platform-specific runtime support that does
11796 not exist everywhere. Moreover, it only allows @emph{trapping}
11797 instructions to throw exceptions, i.e.@: memory references or floating
11798 point instructions. It does not allow exceptions to be thrown from
11799 arbitrary signal handlers such as @code{SIGALRM}.
11801 @item -funwind-tables
11802 @opindex funwind-tables
11803 Similar to @option{-fexceptions}, except that it will just generate any needed
11804 static data, but will not affect the generated code in any other way.
11805 You will normally not enable this option; instead, a language processor
11806 that needs this handling would enable it on your behalf.
11808 @item -fasynchronous-unwind-tables
11809 @opindex fasynchronous-unwind-tables
11810 Generate unwind table in dwarf2 format, if supported by target machine. The
11811 table is exact at each instruction boundary, so it can be used for stack
11812 unwinding from asynchronous events (such as debugger or garbage collector).
11814 @item -fpcc-struct-return
11815 @opindex fpcc-struct-return
11816 Return ``short'' @code{struct} and @code{union} values in memory like
11817 longer ones, rather than in registers. This convention is less
11818 efficient, but it has the advantage of allowing intercallability between
11819 GCC-compiled files and files compiled with other compilers, particularly
11820 the Portable C Compiler (pcc).
11822 The precise convention for returning structures in memory depends
11823 on the target configuration macros.
11825 Short structures and unions are those whose size and alignment match
11826 that of some integer type.
11828 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
11829 switch is not binary compatible with code compiled with the
11830 @option{-freg-struct-return} switch.
11831 Use it to conform to a non-default application binary interface.
11833 @item -freg-struct-return
11834 @opindex freg-struct-return
11835 Return @code{struct} and @code{union} values in registers when possible.
11836 This is more efficient for small structures than
11837 @option{-fpcc-struct-return}.
11839 If you specify neither @option{-fpcc-struct-return} nor
11840 @option{-freg-struct-return}, GCC defaults to whichever convention is
11841 standard for the target. If there is no standard convention, GCC
11842 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
11843 the principal compiler. In those cases, we can choose the standard, and
11844 we chose the more efficient register return alternative.
11846 @strong{Warning:} code compiled with the @option{-freg-struct-return}
11847 switch is not binary compatible with code compiled with the
11848 @option{-fpcc-struct-return} switch.
11849 Use it to conform to a non-default application binary interface.
11851 @item -fshort-enums
11852 @opindex fshort-enums
11853 Allocate to an @code{enum} type only as many bytes as it needs for the
11854 declared range of possible values. Specifically, the @code{enum} type
11855 will be equivalent to the smallest integer type which has enough room.
11857 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
11858 code that is not binary compatible with code generated without that switch.
11859 Use it to conform to a non-default application binary interface.
11861 @item -fshort-double
11862 @opindex fshort-double
11863 Use the same size for @code{double} as for @code{float}.
11865 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
11866 code that is not binary compatible with code generated without that switch.
11867 Use it to conform to a non-default application binary interface.
11869 @item -fshort-wchar
11870 @opindex fshort-wchar
11871 Override the underlying type for @samp{wchar_t} to be @samp{short
11872 unsigned int} instead of the default for the target. This option is
11873 useful for building programs to run under WINE@.
11875 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
11876 code that is not binary compatible with code generated without that switch.
11877 Use it to conform to a non-default application binary interface.
11879 @item -fshared-data
11880 @opindex fshared-data
11881 Requests that the data and non-@code{const} variables of this
11882 compilation be shared data rather than private data. The distinction
11883 makes sense only on certain operating systems, where shared data is
11884 shared between processes running the same program, while private data
11885 exists in one copy per process.
11888 @opindex fno-common
11889 In C, allocate even uninitialized global variables in the data section of the
11890 object file, rather than generating them as common blocks. This has the
11891 effect that if the same variable is declared (without @code{extern}) in
11892 two different compilations, you will get an error when you link them.
11893 The only reason this might be useful is if you wish to verify that the
11894 program will work on other systems which always work this way.
11898 Ignore the @samp{#ident} directive.
11900 @item -finhibit-size-directive
11901 @opindex finhibit-size-directive
11902 Don't output a @code{.size} assembler directive, or anything else that
11903 would cause trouble if the function is split in the middle, and the
11904 two halves are placed at locations far apart in memory. This option is
11905 used when compiling @file{crtstuff.c}; you should not need to use it
11908 @item -fverbose-asm
11909 @opindex fverbose-asm
11910 Put extra commentary information in the generated assembly code to
11911 make it more readable. This option is generally only of use to those
11912 who actually need to read the generated assembly code (perhaps while
11913 debugging the compiler itself).
11915 @option{-fno-verbose-asm}, the default, causes the
11916 extra information to be omitted and is useful when comparing two assembler
11921 @cindex global offset table
11923 Generate position-independent code (PIC) suitable for use in a shared
11924 library, if supported for the target machine. Such code accesses all
11925 constant addresses through a global offset table (GOT)@. The dynamic
11926 loader resolves the GOT entries when the program starts (the dynamic
11927 loader is not part of GCC; it is part of the operating system). If
11928 the GOT size for the linked executable exceeds a machine-specific
11929 maximum size, you get an error message from the linker indicating that
11930 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
11931 instead. (These maximums are 8k on the SPARC and 32k
11932 on the m68k and RS/6000. The 386 has no such limit.)
11934 Position-independent code requires special support, and therefore works
11935 only on certain machines. For the 386, GCC supports PIC for System V
11936 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
11937 position-independent.
11941 If supported for the target machine, emit position-independent code,
11942 suitable for dynamic linking and avoiding any limit on the size of the
11943 global offset table. This option makes a difference on the m68k
11946 Position-independent code requires special support, and therefore works
11947 only on certain machines.
11953 These options are similar to @option{-fpic} and @option{-fPIC}, but
11954 generated position independent code can be only linked into executables.
11955 Usually these options are used when @option{-pie} GCC option will be
11956 used during linking.
11958 @item -ffixed-@var{reg}
11960 Treat the register named @var{reg} as a fixed register; generated code
11961 should never refer to it (except perhaps as a stack pointer, frame
11962 pointer or in some other fixed role).
11964 @var{reg} must be the name of a register. The register names accepted
11965 are machine-specific and are defined in the @code{REGISTER_NAMES}
11966 macro in the machine description macro file.
11968 This flag does not have a negative form, because it specifies a
11971 @item -fcall-used-@var{reg}
11972 @opindex fcall-used
11973 Treat the register named @var{reg} as an allocable register that is
11974 clobbered by function calls. It may be allocated for temporaries or
11975 variables that do not live across a call. Functions compiled this way
11976 will not save and restore the register @var{reg}.
11978 It is an error to used this flag with the frame pointer or stack pointer.
11979 Use of this flag for other registers that have fixed pervasive roles in
11980 the machine's execution model will produce disastrous results.
11982 This flag does not have a negative form, because it specifies a
11985 @item -fcall-saved-@var{reg}
11986 @opindex fcall-saved
11987 Treat the register named @var{reg} as an allocable register saved by
11988 functions. It may be allocated even for temporaries or variables that
11989 live across a call. Functions compiled this way will save and restore
11990 the register @var{reg} if they use it.
11992 It is an error to used this flag with the frame pointer or stack pointer.
11993 Use of this flag for other registers that have fixed pervasive roles in
11994 the machine's execution model will produce disastrous results.
11996 A different sort of disaster will result from the use of this flag for
11997 a register in which function values may be returned.
11999 This flag does not have a negative form, because it specifies a
12002 @item -fpack-struct[=@var{n}]
12003 @opindex fpack-struct
12004 Without a value specified, pack all structure members together without
12005 holes. When a value is specified (which must be a small power of two), pack
12006 structure members according to this value, representing the maximum
12007 alignment (that is, objects with default alignment requirements larger than
12008 this will be output potentially unaligned at the next fitting location.
12010 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
12011 code that is not binary compatible with code generated without that switch.
12012 Additionally, it makes the code suboptimal.
12013 Use it to conform to a non-default application binary interface.
12015 @item -finstrument-functions
12016 @opindex finstrument-functions
12017 Generate instrumentation calls for entry and exit to functions. Just
12018 after function entry and just before function exit, the following
12019 profiling functions will be called with the address of the current
12020 function and its call site. (On some platforms,
12021 @code{__builtin_return_address} does not work beyond the current
12022 function, so the call site information may not be available to the
12023 profiling functions otherwise.)
12026 void __cyg_profile_func_enter (void *this_fn,
12028 void __cyg_profile_func_exit (void *this_fn,
12032 The first argument is the address of the start of the current function,
12033 which may be looked up exactly in the symbol table.
12035 This instrumentation is also done for functions expanded inline in other
12036 functions. The profiling calls will indicate where, conceptually, the
12037 inline function is entered and exited. This means that addressable
12038 versions of such functions must be available. If all your uses of a
12039 function are expanded inline, this may mean an additional expansion of
12040 code size. If you use @samp{extern inline} in your C code, an
12041 addressable version of such functions must be provided. (This is
12042 normally the case anyways, but if you get lucky and the optimizer always
12043 expands the functions inline, you might have gotten away without
12044 providing static copies.)
12046 A function may be given the attribute @code{no_instrument_function}, in
12047 which case this instrumentation will not be done. This can be used, for
12048 example, for the profiling functions listed above, high-priority
12049 interrupt routines, and any functions from which the profiling functions
12050 cannot safely be called (perhaps signal handlers, if the profiling
12051 routines generate output or allocate memory).
12053 @item -fstack-check
12054 @opindex fstack-check
12055 Generate code to verify that you do not go beyond the boundary of the
12056 stack. You should specify this flag if you are running in an
12057 environment with multiple threads, but only rarely need to specify it in
12058 a single-threaded environment since stack overflow is automatically
12059 detected on nearly all systems if there is only one stack.
12061 Note that this switch does not actually cause checking to be done; the
12062 operating system must do that. The switch causes generation of code
12063 to ensure that the operating system sees the stack being extended.
12065 @item -fstack-limit-register=@var{reg}
12066 @itemx -fstack-limit-symbol=@var{sym}
12067 @itemx -fno-stack-limit
12068 @opindex fstack-limit-register
12069 @opindex fstack-limit-symbol
12070 @opindex fno-stack-limit
12071 Generate code to ensure that the stack does not grow beyond a certain value,
12072 either the value of a register or the address of a symbol. If the stack
12073 would grow beyond the value, a signal is raised. For most targets,
12074 the signal is raised before the stack overruns the boundary, so
12075 it is possible to catch the signal without taking special precautions.
12077 For instance, if the stack starts at absolute address @samp{0x80000000}
12078 and grows downwards, you can use the flags
12079 @option{-fstack-limit-symbol=__stack_limit} and
12080 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
12081 of 128KB@. Note that this may only work with the GNU linker.
12083 @cindex aliasing of parameters
12084 @cindex parameters, aliased
12085 @item -fargument-alias
12086 @itemx -fargument-noalias
12087 @itemx -fargument-noalias-global
12088 @opindex fargument-alias
12089 @opindex fargument-noalias
12090 @opindex fargument-noalias-global
12091 Specify the possible relationships among parameters and between
12092 parameters and global data.
12094 @option{-fargument-alias} specifies that arguments (parameters) may
12095 alias each other and may alias global storage.@*
12096 @option{-fargument-noalias} specifies that arguments do not alias
12097 each other, but may alias global storage.@*
12098 @option{-fargument-noalias-global} specifies that arguments do not
12099 alias each other and do not alias global storage.
12101 Each language will automatically use whatever option is required by
12102 the language standard. You should not need to use these options yourself.
12104 @item -fleading-underscore
12105 @opindex fleading-underscore
12106 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
12107 change the way C symbols are represented in the object file. One use
12108 is to help link with legacy assembly code.
12110 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
12111 generate code that is not binary compatible with code generated without that
12112 switch. Use it to conform to a non-default application binary interface.
12113 Not all targets provide complete support for this switch.
12115 @item -ftls-model=@var{model}
12116 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
12117 The @var{model} argument should be one of @code{global-dynamic},
12118 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
12120 The default without @option{-fpic} is @code{initial-exec}; with
12121 @option{-fpic} the default is @code{global-dynamic}.
12123 @item -fvisibility=@var{default|internal|hidden|protected}
12124 @opindex fvisibility
12125 Set the default ELF image symbol visibility to the specified option - all
12126 symbols will be marked with this unless overridden within the code.
12127 Using this feature can very substantially improve linking and
12128 load times of shared object libraries, produce more optimized
12129 code, provide near-perfect API export and prevent symbol clashes.
12130 It is @strong{strongly} recommended that you use this in any shared objects
12133 Despite the nomenclature, @code{default} always means public ie;
12134 available to be linked against from outside the shared object.
12135 @code{protected} and @code{internal} are pretty useless in real-world
12136 usage so the only other commonly used option will be @code{hidden}.
12137 The default if -fvisibility isn't specified is @code{default} ie; make every
12138 symbol public - this causes the same behavior as previous versions of
12141 A good explanation of the benefits offered by ensuring ELF
12142 symbols have the correct visibility is given by ``How To Write
12143 Shared Libraries'' by Ulrich Drepper (which can be found at
12144 @w{@uref{http://people.redhat.com/~drepper/}}) - however a superior
12145 solution made possible by this option to marking things hidden when
12146 the default is public is to make the default hidden and mark things
12147 public. This is the norm with DLL's on Windows and with @option{-fvisibility=hidden}
12148 and @code{__attribute__ ((visibility("default")))} instead of
12149 @code{__declspec(dllexport)} you get almost identical semantics with
12150 identical syntax. This is a great boon to those working with
12151 cross-platform projects.
12153 For those adding visibility support to existing code, you may find
12154 @samp{#pragma GCC visibility} of use. This works by you enclosing
12155 the declarations you wish to set visibility for with (for example)
12156 @samp{#pragma GCC visibility push(hidden)} and
12157 @samp{#pragma GCC visibility pop}. These can be nested up to sixteen
12158 times. Bear in mind that symbol visibility should be viewed @strong{as
12159 part of the API interface contract} and thus all new code should
12160 always specify visibility when it is not the default ie; declarations
12161 only for use within the local DSO should @strong{always} be marked explicitly
12162 as hidden as so to avoid PLT indirection overheads - making this
12163 abundantly clear also aids readability and self-documentation of the code.
12164 Note that due to ISO C++ specification requirements, operator new and
12165 operator delete must always be of default visibility.
12167 An overview of these techniques, their benefits and how to use them
12168 is at @w{@uref{http://www.nedprod.com/programs/gccvisibility.html}}.
12174 @node Environment Variables
12175 @section Environment Variables Affecting GCC
12176 @cindex environment variables
12178 @c man begin ENVIRONMENT
12179 This section describes several environment variables that affect how GCC
12180 operates. Some of them work by specifying directories or prefixes to use
12181 when searching for various kinds of files. Some are used to specify other
12182 aspects of the compilation environment.
12184 Note that you can also specify places to search using options such as
12185 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
12186 take precedence over places specified using environment variables, which
12187 in turn take precedence over those specified by the configuration of GCC@.
12188 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
12189 GNU Compiler Collection (GCC) Internals}.
12194 @c @itemx LC_COLLATE
12196 @c @itemx LC_MONETARY
12197 @c @itemx LC_NUMERIC
12202 @c @findex LC_COLLATE
12203 @findex LC_MESSAGES
12204 @c @findex LC_MONETARY
12205 @c @findex LC_NUMERIC
12209 These environment variables control the way that GCC uses
12210 localization information that allow GCC to work with different
12211 national conventions. GCC inspects the locale categories
12212 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
12213 so. These locale categories can be set to any value supported by your
12214 installation. A typical value is @samp{en_GB.UTF-8} for English in the United
12215 Kingdom encoded in UTF-8.
12217 The @env{LC_CTYPE} environment variable specifies character
12218 classification. GCC uses it to determine the character boundaries in
12219 a string; this is needed for some multibyte encodings that contain quote
12220 and escape characters that would otherwise be interpreted as a string
12223 The @env{LC_MESSAGES} environment variable specifies the language to
12224 use in diagnostic messages.
12226 If the @env{LC_ALL} environment variable is set, it overrides the value
12227 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
12228 and @env{LC_MESSAGES} default to the value of the @env{LANG}
12229 environment variable. If none of these variables are set, GCC
12230 defaults to traditional C English behavior.
12234 If @env{TMPDIR} is set, it specifies the directory to use for temporary
12235 files. GCC uses temporary files to hold the output of one stage of
12236 compilation which is to be used as input to the next stage: for example,
12237 the output of the preprocessor, which is the input to the compiler
12240 @item GCC_EXEC_PREFIX
12241 @findex GCC_EXEC_PREFIX
12242 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
12243 names of the subprograms executed by the compiler. No slash is added
12244 when this prefix is combined with the name of a subprogram, but you can
12245 specify a prefix that ends with a slash if you wish.
12247 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
12248 an appropriate prefix to use based on the pathname it was invoked with.
12250 If GCC cannot find the subprogram using the specified prefix, it
12251 tries looking in the usual places for the subprogram.
12253 The default value of @env{GCC_EXEC_PREFIX} is
12254 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the value
12255 of @code{prefix} when you ran the @file{configure} script.
12257 Other prefixes specified with @option{-B} take precedence over this prefix.
12259 This prefix is also used for finding files such as @file{crt0.o} that are
12262 In addition, the prefix is used in an unusual way in finding the
12263 directories to search for header files. For each of the standard
12264 directories whose name normally begins with @samp{/usr/local/lib/gcc}
12265 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
12266 replacing that beginning with the specified prefix to produce an
12267 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
12268 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
12269 These alternate directories are searched first; the standard directories
12272 @item COMPILER_PATH
12273 @findex COMPILER_PATH
12274 The value of @env{COMPILER_PATH} is a colon-separated list of
12275 directories, much like @env{PATH}. GCC tries the directories thus
12276 specified when searching for subprograms, if it can't find the
12277 subprograms using @env{GCC_EXEC_PREFIX}.
12280 @findex LIBRARY_PATH
12281 The value of @env{LIBRARY_PATH} is a colon-separated list of
12282 directories, much like @env{PATH}. When configured as a native compiler,
12283 GCC tries the directories thus specified when searching for special
12284 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
12285 using GCC also uses these directories when searching for ordinary
12286 libraries for the @option{-l} option (but directories specified with
12287 @option{-L} come first).
12291 @cindex locale definition
12292 This variable is used to pass locale information to the compiler. One way in
12293 which this information is used is to determine the character set to be used
12294 when character literals, string literals and comments are parsed in C and C++.
12295 When the compiler is configured to allow multibyte characters,
12296 the following values for @env{LANG} are recognized:
12300 Recognize JIS characters.
12302 Recognize SJIS characters.
12304 Recognize EUCJP characters.
12307 If @env{LANG} is not defined, or if it has some other value, then the
12308 compiler will use mblen and mbtowc as defined by the default locale to
12309 recognize and translate multibyte characters.
12313 Some additional environments variables affect the behavior of the
12316 @include cppenv.texi
12320 @node Precompiled Headers
12321 @section Using Precompiled Headers
12322 @cindex precompiled headers
12323 @cindex speed of compilation
12325 Often large projects have many header files that are included in every
12326 source file. The time the compiler takes to process these header files
12327 over and over again can account for nearly all of the time required to
12328 build the project. To make builds faster, GCC allows users to
12329 `precompile' a header file; then, if builds can use the precompiled
12330 header file they will be much faster.
12332 @strong{Caution:} There are a few known situations where GCC will
12333 crash when trying to use a precompiled header. If you have trouble
12334 with a precompiled header, you should remove the precompiled header
12335 and compile without it. In addition, please use GCC's on-line
12336 defect-tracking system to report any problems you encounter with
12337 precompiled headers. @xref{Bugs}.
12339 To create a precompiled header file, simply compile it as you would any
12340 other file, if necessary using the @option{-x} option to make the driver
12341 treat it as a C or C++ header file. You will probably want to use a
12342 tool like @command{make} to keep the precompiled header up-to-date when
12343 the headers it contains change.
12345 A precompiled header file will be searched for when @code{#include} is
12346 seen in the compilation. As it searches for the included file
12347 (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
12348 compiler looks for a precompiled header in each directory just before it
12349 looks for the include file in that directory. The name searched for is
12350 the name specified in the @code{#include} with @samp{.gch} appended. If
12351 the precompiled header file can't be used, it is ignored.
12353 For instance, if you have @code{#include "all.h"}, and you have
12354 @file{all.h.gch} in the same directory as @file{all.h}, then the
12355 precompiled header file will be used if possible, and the original
12356 header will be used otherwise.
12358 Alternatively, you might decide to put the precompiled header file in a
12359 directory and use @option{-I} to ensure that directory is searched
12360 before (or instead of) the directory containing the original header.
12361 Then, if you want to check that the precompiled header file is always
12362 used, you can put a file of the same name as the original header in this
12363 directory containing an @code{#error} command.
12365 This also works with @option{-include}. So yet another way to use
12366 precompiled headers, good for projects not designed with precompiled
12367 header files in mind, is to simply take most of the header files used by
12368 a project, include them from another header file, precompile that header
12369 file, and @option{-include} the precompiled header. If the header files
12370 have guards against multiple inclusion, they will be skipped because
12371 they've already been included (in the precompiled header).
12373 If you need to precompile the same header file for different
12374 languages, targets, or compiler options, you can instead make a
12375 @emph{directory} named like @file{all.h.gch}, and put each precompiled
12376 header in the directory, perhaps using @option{-o}. It doesn't matter
12377 what you call the files in the directory, every precompiled header in
12378 the directory will be considered. The first precompiled header
12379 encountered in the directory that is valid for this compilation will
12380 be used; they're searched in no particular order.
12382 There are many other possibilities, limited only by your imagination,
12383 good sense, and the constraints of your build system.
12385 A precompiled header file can be used only when these conditions apply:
12389 Only one precompiled header can be used in a particular compilation.
12392 A precompiled header can't be used once the first C token is seen. You
12393 can have preprocessor directives before a precompiled header; you can
12394 even include a precompiled header from inside another header, so long as
12395 there are no C tokens before the @code{#include}.
12398 The precompiled header file must be produced for the same language as
12399 the current compilation. You can't use a C precompiled header for a C++
12403 The precompiled header file must be produced by the same compiler
12404 version and configuration as the current compilation is using.
12405 The easiest way to guarantee this is to use the same compiler binary
12406 for creating and using precompiled headers.
12409 Any macros defined before the precompiled header is included must
12410 either be defined in the same way as when the precompiled header was
12411 generated, or must not affect the precompiled header, which usually
12412 means that the they don't appear in the precompiled header at all.
12414 The @option{-D} option is one way to define a macro before a
12415 precompiled header is included; using a @code{#define} can also do it.
12416 There are also some options that define macros implicitly, like
12417 @option{-O} and @option{-Wdeprecated}; the same rule applies to macros
12420 @item If debugging information is output when using the precompiled
12421 header, using @option{-g} or similar, the same kind of debugging information
12422 must have been output when building the precompiled header. However,
12423 a precompiled header built using @option{-g} can be used in a compilation
12424 when no debugging information is being output.
12426 @item The same @option{-m} options must generally be used when building
12427 and using the precompiled header. @xref{Submodel Options},
12428 for any cases where this rule is relaxed.
12430 @item Each of the following options must be the same when building and using
12431 the precompiled header:
12433 @gccoptlist{-fexceptions -funit-at-a-time}
12436 Some other command-line options starting with @option{-f},
12437 @option{-p}, or @option{-O} must be defined in the same way as when
12438 the precompiled header was generated. At present, it's not clear
12439 which options are safe to change and which are not; the safest choice
12440 is to use exactly the same options when generating and using the
12441 precompiled header. The following are known to be safe:
12443 @gccoptlist{-fpreprocessed -pedantic-errors}
12447 For all of these except the last, the compiler will automatically
12448 ignore the precompiled header if the conditions aren't met. If you
12449 find an option combination that doesn't work and doesn't cause the
12450 precompiled header to be ignored, please consider filing a bug report,
12453 If you do use differing options when generating and using the
12454 precompiled header, the actual behavior will be a mixture of the
12455 behavior for the options. For instance, if you use @option{-g} to
12456 generate the precompiled header but not when using it, you may or may
12457 not get debugging information for routines in the precompiled header.
12459 @node Running Protoize
12460 @section Running Protoize
12462 The program @code{protoize} is an optional part of GCC@. You can use
12463 it to add prototypes to a program, thus converting the program to ISO
12464 C in one respect. The companion program @code{unprotoize} does the
12465 reverse: it removes argument types from any prototypes that are found.
12467 When you run these programs, you must specify a set of source files as
12468 command line arguments. The conversion programs start out by compiling
12469 these files to see what functions they define. The information gathered
12470 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
12472 After scanning comes actual conversion. The specified files are all
12473 eligible to be converted; any files they include (whether sources or
12474 just headers) are eligible as well.
12476 But not all the eligible files are converted. By default,
12477 @code{protoize} and @code{unprotoize} convert only source and header
12478 files in the current directory. You can specify additional directories
12479 whose files should be converted with the @option{-d @var{directory}}
12480 option. You can also specify particular files to exclude with the
12481 @option{-x @var{file}} option. A file is converted if it is eligible, its
12482 directory name matches one of the specified directory names, and its
12483 name within the directory has not been excluded.
12485 Basic conversion with @code{protoize} consists of rewriting most
12486 function definitions and function declarations to specify the types of
12487 the arguments. The only ones not rewritten are those for varargs
12490 @code{protoize} optionally inserts prototype declarations at the
12491 beginning of the source file, to make them available for any calls that
12492 precede the function's definition. Or it can insert prototype
12493 declarations with block scope in the blocks where undeclared functions
12496 Basic conversion with @code{unprotoize} consists of rewriting most
12497 function declarations to remove any argument types, and rewriting
12498 function definitions to the old-style pre-ISO form.
12500 Both conversion programs print a warning for any function declaration or
12501 definition that they can't convert. You can suppress these warnings
12504 The output from @code{protoize} or @code{unprotoize} replaces the
12505 original source file. The original file is renamed to a name ending
12506 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
12507 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
12508 for DOS) file already exists, then the source file is simply discarded.
12510 @code{protoize} and @code{unprotoize} both depend on GCC itself to
12511 scan the program and collect information about the functions it uses.
12512 So neither of these programs will work until GCC is installed.
12514 Here is a table of the options you can use with @code{protoize} and
12515 @code{unprotoize}. Each option works with both programs unless
12519 @item -B @var{directory}
12520 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
12521 usual directory (normally @file{/usr/local/lib}). This file contains
12522 prototype information about standard system functions. This option
12523 applies only to @code{protoize}.
12525 @item -c @var{compilation-options}
12526 Use @var{compilation-options} as the options when running @command{gcc} to
12527 produce the @samp{.X} files. The special option @option{-aux-info} is
12528 always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
12530 Note that the compilation options must be given as a single argument to
12531 @code{protoize} or @code{unprotoize}. If you want to specify several
12532 @command{gcc} options, you must quote the entire set of compilation options
12533 to make them a single word in the shell.
12535 There are certain @command{gcc} arguments that you cannot use, because they
12536 would produce the wrong kind of output. These include @option{-g},
12537 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
12538 the @var{compilation-options}, they are ignored.
12541 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
12542 systems) instead of @samp{.c}. This is convenient if you are converting
12543 a C program to C++. This option applies only to @code{protoize}.
12546 Add explicit global declarations. This means inserting explicit
12547 declarations at the beginning of each source file for each function
12548 that is called in the file and was not declared. These declarations
12549 precede the first function definition that contains a call to an
12550 undeclared function. This option applies only to @code{protoize}.
12552 @item -i @var{string}
12553 Indent old-style parameter declarations with the string @var{string}.
12554 This option applies only to @code{protoize}.
12556 @code{unprotoize} converts prototyped function definitions to old-style
12557 function definitions, where the arguments are declared between the
12558 argument list and the initial @samp{@{}. By default, @code{unprotoize}
12559 uses five spaces as the indentation. If you want to indent with just
12560 one space instead, use @option{-i " "}.
12563 Keep the @samp{.X} files. Normally, they are deleted after conversion
12567 Add explicit local declarations. @code{protoize} with @option{-l} inserts
12568 a prototype declaration for each function in each block which calls the
12569 function without any declaration. This option applies only to
12573 Make no real changes. This mode just prints information about the conversions
12574 that would have been done without @option{-n}.
12577 Make no @samp{.save} files. The original files are simply deleted.
12578 Use this option with caution.
12580 @item -p @var{program}
12581 Use the program @var{program} as the compiler. Normally, the name
12582 @file{gcc} is used.
12585 Work quietly. Most warnings are suppressed.
12588 Print the version number, just like @option{-v} for @command{gcc}.
12591 If you need special compiler options to compile one of your program's
12592 source files, then you should generate that file's @samp{.X} file
12593 specially, by running @command{gcc} on that source file with the
12594 appropriate options and the option @option{-aux-info}. Then run
12595 @code{protoize} on the entire set of files. @code{protoize} will use
12596 the existing @samp{.X} file because it is newer than the source file.
12600 gcc -Dfoo=bar file1.c -aux-info file1.X
12605 You need to include the special files along with the rest in the
12606 @code{protoize} command, even though their @samp{.X} files already
12607 exist, because otherwise they won't get converted.
12609 @xref{Protoize Caveats}, for more information on how to use
12610 @code{protoize} successfully.