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 @gol
506 -minline-sqrt-min-latency -minline-sqrt-max-throughput @gol
507 -mno-dwarf2-asm -mearly-stop-bits @gol
508 -mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol
509 -mtune=@var{cpu-type} -mt -pthread -milp32 -mlp64}
511 @emph{M32R/D Options}
512 @gccoptlist{-m32r2 -m32rx -m32r @gol
514 -malign-loops -mno-align-loops @gol
515 -missue-rate=@var{number} @gol
516 -mbranch-cost=@var{number} @gol
517 -mmodel=@var{code-size-model-type} @gol
518 -msdata=@var{sdata-type} @gol
519 -mno-flush-func -mflush-func=@var{name} @gol
520 -mno-flush-trap -mflush-trap=@var{number} @gol
523 @emph{M680x0 Options}
524 @gccoptlist{-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
525 -m68060 -mcpu32 -m5200 -m68881 -mbitfield -mc68000 -mc68020 @gol
526 -mnobitfield -mrtd -mshort -msoft-float -mpcrel @gol
527 -malign-int -mstrict-align -msep-data -mno-sep-data @gol
528 -mshared-library-id=n -mid-shared-library -mno-id-shared-library}
530 @emph{M68hc1x Options}
531 @gccoptlist{-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 @gol
532 -mauto-incdec -minmax -mlong-calls -mshort @gol
533 -msoft-reg-count=@var{count}}
536 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
537 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
538 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
539 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
540 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
543 @gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol
544 -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips64 @gol
545 -mips16 -mno-mips16 -mabi=@var{abi} -mabicalls -mno-abicalls @gol
546 -mxgot -mno-xgot -mgp32 -mgp64 -mfp32 -mfp64 @gol
547 -mhard-float -msoft-float -msingle-float -mdouble-float @gol
548 -mpaired-single -mips3d @gol
549 -mint64 -mlong64 -mlong32 @gol
550 -G@var{num} -membedded-data -mno-embedded-data @gol
551 -muninit-const-in-rodata -mno-uninit-const-in-rodata @gol
552 -msplit-addresses -mno-split-addresses @gol
553 -mexplicit-relocs -mno-explicit-relocs @gol
554 -mcheck-zero-division -mno-check-zero-division @gol
555 -mdivide-traps -mdivide-breaks @gol
556 -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol
557 -mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp @gol
558 -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol
559 -mfix-vr4120 -mno-fix-vr4120 -mfix-sb1 -mno-fix-sb1 @gol
560 -mflush-func=@var{func} -mno-flush-func @gol
561 -mbranch-likely -mno-branch-likely @gol
562 -mfp-exceptions -mno-fp-exceptions @gol
563 -mvr4130-align -mno-vr4130-align}
566 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
567 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
568 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
569 -mno-base-addresses -msingle-exit -mno-single-exit}
571 @emph{MN10300 Options}
572 @gccoptlist{-mmult-bug -mno-mult-bug @gol
573 -mam33 -mno-am33 @gol
574 -mam33-2 -mno-am33-2 @gol
578 @gccoptlist{-m32032 -m32332 -m32532 -m32081 -m32381 @gol
579 -mmult-add -mnomult-add -msoft-float -mrtd -mnortd @gol
580 -mregparam -mnoregparam -msb -mnosb @gol
581 -mbitfield -mnobitfield -mhimem -mnohimem}
583 @emph{PDP-11 Options}
584 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
585 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
586 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
587 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
588 -mbranch-expensive -mbranch-cheap @gol
589 -msplit -mno-split -munix-asm -mdec-asm}
591 @emph{PowerPC Options}
592 See RS/6000 and PowerPC Options.
594 @emph{RS/6000 and PowerPC Options}
595 @gccoptlist{-mcpu=@var{cpu-type} @gol
596 -mtune=@var{cpu-type} @gol
597 -mpower -mno-power -mpower2 -mno-power2 @gol
598 -mpowerpc -mpowerpc64 -mno-powerpc @gol
599 -maltivec -mno-altivec @gol
600 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
601 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
602 -mnew-mnemonics -mold-mnemonics @gol
603 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
604 -m64 -m32 -mxl-call -mno-xl-call -mpe @gol
605 -malign-power -malign-natural @gol
606 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
607 -mstring -mno-string -mupdate -mno-update @gol
608 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
609 -mstrict-align -mno-strict-align -mrelocatable @gol
610 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
611 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
612 -mdynamic-no-pic @gol
613 -mprioritize-restricted-insns=@var{priority} @gol
614 -msched-costly-dep=@var{dependence_type} @gol
615 -minsert-sched-nops=@var{scheme} @gol
616 -mcall-sysv -mcall-netbsd @gol
617 -maix-struct-return -msvr4-struct-return @gol
618 -mabi=altivec -mabi=no-altivec @gol
619 -mabi=spe -mabi=no-spe @gol
620 -misel=yes -misel=no @gol
621 -mspe=yes -mspe=no @gol
622 -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol
623 -mprototype -mno-prototype @gol
624 -msim -mmvme -mads -myellowknife -memb -msdata @gol
625 -msdata=@var{opt} -mvxworks -mwindiss -G @var{num} -pthread}
627 @emph{S/390 and zSeries Options}
628 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
629 -mhard-float -msoft-float -mbackchain -mno-backchain @gol
630 -mpacked-stack -mno-packed-stack @gol
631 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
632 -m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol
633 -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol
634 -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard}
637 @gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol
638 -m4-nofpu -m4-single-only -m4-single -m4 @gol
639 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol
640 -m5-64media -m5-64media-nofpu @gol
641 -m5-32media -m5-32media-nofpu @gol
642 -m5-compact -m5-compact-nofpu @gol
643 -mb -ml -mdalign -mrelax @gol
644 -mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol
645 -mieee -misize -mpadstruct -mspace @gol
646 -mprefergot -musermode}
649 @gccoptlist{-mcpu=@var{cpu-type} @gol
650 -mtune=@var{cpu-type} @gol
651 -mcmodel=@var{code-model} @gol
652 -m32 -m64 -mapp-regs -mno-app-regs @gol
653 -mfaster-structs -mno-faster-structs @gol
654 -mfpu -mno-fpu -mhard-float -msoft-float @gol
655 -mhard-quad-float -msoft-quad-float @gol
656 -mimpure-text -mno-impure-text -mlittle-endian @gol
657 -mstack-bias -mno-stack-bias @gol
658 -munaligned-doubles -mno-unaligned-doubles @gol
659 -mv8plus -mno-v8plus -mvis -mno-vis
662 @emph{System V Options}
663 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
665 @emph{TMS320C3x/C4x Options}
666 @gccoptlist{-mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol
667 -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol
668 -mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol
669 -mparallel-insns -mparallel-mpy -mpreserve-float}
672 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
673 -mprolog-function -mno-prolog-function -mspace @gol
674 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
675 -mapp-regs -mno-app-regs @gol
676 -mdisable-callt -mno-disable-callt @gol
682 @gccoptlist{-mg -mgnu -munix}
684 @emph{x86-64 Options}
685 See i386 and x86-64 Options.
687 @emph{Xstormy16 Options}
690 @emph{Xtensa Options}
691 @gccoptlist{-mconst16 -mno-const16 @gol
692 -mfused-madd -mno-fused-madd @gol
693 -mtext-section-literals -mno-text-section-literals @gol
694 -mtarget-align -mno-target-align @gol
695 -mlongcalls -mno-longcalls}
697 @emph{zSeries Options}
698 See S/390 and zSeries Options.
700 @item Code Generation Options
701 @xref{Code Gen Options,,Options for Code Generation Conventions}.
702 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
703 -ffixed-@var{reg} -fexceptions @gol
704 -fnon-call-exceptions -funwind-tables @gol
705 -fasynchronous-unwind-tables @gol
706 -finhibit-size-directive -finstrument-functions @gol
707 -fno-common -fno-ident @gol
708 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
709 -freg-struct-return -fshared-data -fshort-enums @gol
710 -fshort-double -fshort-wchar @gol
711 -fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol
712 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
713 -fargument-alias -fargument-noalias @gol
714 -fargument-noalias-global -fleading-underscore @gol
715 -ftls-model=@var{model} @gol
716 -ftrapv -fwrapv -fbounds-check @gol
721 * Overall Options:: Controlling the kind of output:
722 an executable, object files, assembler files,
723 or preprocessed source.
724 * C Dialect Options:: Controlling the variant of C language compiled.
725 * C++ Dialect Options:: Variations on C++.
726 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
728 * Language Independent Options:: Controlling how diagnostics should be
730 * Warning Options:: How picky should the compiler be?
731 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
732 * Optimize Options:: How much optimization?
733 * Preprocessor Options:: Controlling header files and macro definitions.
734 Also, getting dependency information for Make.
735 * Assembler Options:: Passing options to the assembler.
736 * Link Options:: Specifying libraries and so on.
737 * Directory Options:: Where to find header files and libraries.
738 Where to find the compiler executable files.
739 * Spec Files:: How to pass switches to sub-processes.
740 * Target Options:: Running a cross-compiler, or an old version of GCC.
743 @node Overall Options
744 @section Options Controlling the Kind of Output
746 Compilation can involve up to four stages: preprocessing, compilation
747 proper, assembly and linking, always in that order. GCC is capable of
748 preprocessing and compiling several files either into several
749 assembler input files, or into one assembler input file; then each
750 assembler input file produces an object file, and linking combines all
751 the object files (those newly compiled, and those specified as input)
752 into an executable file.
754 @cindex file name suffix
755 For any given input file, the file name suffix determines what kind of
760 C source code which must be preprocessed.
763 C source code which should not be preprocessed.
766 C++ source code which should not be preprocessed.
769 Objective-C source code. Note that you must link with the @file{libobjc}
770 library to make an Objective-C program work.
773 Objective-C source code which should not be preprocessed.
777 Objective-C++ source code. Note that you must link with the @file{libobjc}
778 library to make an Objective-C++ program work. Note that @samp{.M} refers
779 to a literal capital M@.
782 Objective-C++ source code which should not be preprocessed.
785 C, C++, Objective-C or Objective-C++ header file to be turned into a
790 @itemx @var{file}.cxx
791 @itemx @var{file}.cpp
792 @itemx @var{file}.CPP
793 @itemx @var{file}.c++
795 C++ source code which must be preprocessed. Note that in @samp{.cxx},
796 the last two letters must both be literally @samp{x}. Likewise,
797 @samp{.C} refers to a literal capital C@.
801 C++ header file to be turned into a precompiled header.
804 @itemx @var{file}.for
805 @itemx @var{file}.FOR
806 Fortran source code which should not be preprocessed.
809 @itemx @var{file}.fpp
810 @itemx @var{file}.FPP
811 Fortran source code which must be preprocessed (with the traditional
815 Fortran source code which must be preprocessed with a RATFOR
816 preprocessor (not included with GCC)@.
819 @itemx @var{file}.f95
820 Fortran 90/95 source code which should not be preprocessed.
822 @c FIXME: Descriptions of Java file types.
829 Ada source code file which contains a library unit declaration (a
830 declaration of a package, subprogram, or generic, or a generic
831 instantiation), or a library unit renaming declaration (a package,
832 generic, or subprogram renaming declaration). Such files are also
835 @itemx @var{file}.adb
836 Ada source code file containing a library unit body (a subprogram or
837 package body). Such files are also called @dfn{bodies}.
839 @c GCC also knows about some suffixes for languages not yet included:
848 Assembler code which must be preprocessed.
851 An object file to be fed straight into linking.
852 Any file name with no recognized suffix is treated this way.
856 You can specify the input language explicitly with the @option{-x} option:
859 @item -x @var{language}
860 Specify explicitly the @var{language} for the following input files
861 (rather than letting the compiler choose a default based on the file
862 name suffix). This option applies to all following input files until
863 the next @option{-x} option. Possible values for @var{language} are:
865 c c-header c-cpp-output
866 c++ c++-header c++-cpp-output
867 objective-c objective-c-header objective-c-cpp-output
868 objective-c++ objective-c++-header objective-c++-cpp-output
869 assembler assembler-with-cpp
871 f77 f77-cpp-input ratfor
878 Turn off any specification of a language, so that subsequent files are
879 handled according to their file name suffixes (as they are if @option{-x}
880 has not been used at all).
882 @item -pass-exit-codes
883 @opindex pass-exit-codes
884 Normally the @command{gcc} program will exit with the code of 1 if any
885 phase of the compiler returns a non-success return code. If you specify
886 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
887 numerically highest error produced by any phase that returned an error
891 If you only want some of the stages of compilation, you can use
892 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
893 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
894 @command{gcc} is to stop. Note that some combinations (for example,
895 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
900 Compile or assemble the source files, but do not link. The linking
901 stage simply is not done. The ultimate output is in the form of an
902 object file for each source file.
904 By default, the object file name for a source file is made by replacing
905 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
907 Unrecognized input files, not requiring compilation or assembly, are
912 Stop after the stage of compilation proper; do not assemble. The output
913 is in the form of an assembler code file for each non-assembler input
916 By default, the assembler file name for a source file is made by
917 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
919 Input files that don't require compilation are ignored.
923 Stop after the preprocessing stage; do not run the compiler proper. The
924 output is in the form of preprocessed source code, which is sent to the
927 Input files which don't require preprocessing are ignored.
929 @cindex output file option
932 Place output in file @var{file}. This applies regardless to whatever
933 sort of output is being produced, whether it be an executable file,
934 an object file, an assembler file or preprocessed C code.
936 If @option{-o} is not specified, the default is to put an executable
937 file in @file{a.out}, the object file for
938 @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its
939 assembler file in @file{@var{source}.s}, a precompiled header file in
940 @file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on
945 Print (on standard error output) the commands executed to run the stages
946 of compilation. Also print the version number of the compiler driver
947 program and of the preprocessor and the compiler proper.
951 Like @option{-v} except the commands are not executed and all command
952 arguments are quoted. This is useful for shell scripts to capture the
953 driver-generated command lines.
957 Use pipes rather than temporary files for communication between the
958 various stages of compilation. This fails to work on some systems where
959 the assembler is unable to read from a pipe; but the GNU assembler has
964 If you are compiling multiple source files, this option tells the driver
965 to pass all the source files to the compiler at once (for those
966 languages for which the compiler can handle this). This will allow
967 intermodule analysis (IMA) to be performed by the compiler. Currently the only
968 language for which this is supported is C@. If you pass source files for
969 multiple languages to the driver, using this option, the driver will invoke
970 the compiler(s) that support IMA once each, passing each compiler all the
971 source files appropriate for it. For those languages that do not support
972 IMA this option will be ignored, and the compiler will be invoked once for
973 each source file in that language. If you use this option in conjunction
974 with @option{-save-temps}, the compiler will generate multiple
976 (one for each source file), but only one (combined) @file{.o} or
981 Print (on the standard output) a description of the command line options
982 understood by @command{gcc}. If the @option{-v} option is also specified
983 then @option{--help} will also be passed on to the various processes
984 invoked by @command{gcc}, so that they can display the command line options
985 they accept. If the @option{-Wextra} option is also specified then command
986 line options which have no documentation associated with them will also
991 Print (on the standard output) a description of target specific command
992 line options for each tool.
996 Display the version number and copyrights of the invoked GCC@.
1000 @section Compiling C++ Programs
1002 @cindex suffixes for C++ source
1003 @cindex C++ source file suffixes
1004 C++ source files conventionally use one of the suffixes @samp{.C},
1005 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
1006 @samp{.cxx}; C++ header files often use @samp{.hh} or @samp{.H}; and
1007 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
1008 files with these names and compiles them as C++ programs even if you
1009 call the compiler the same way as for compiling C programs (usually
1010 with the name @command{gcc}).
1014 However, C++ programs often require class libraries as well as a
1015 compiler that understands the C++ language---and under some
1016 circumstances, you might want to compile programs or header files from
1017 standard input, or otherwise without a suffix that flags them as C++
1018 programs. You might also like to precompile a C header file with a
1019 @samp{.h} extension to be used in C++ compilations. @command{g++} is a
1020 program that calls GCC with the default language set to C++, and
1021 automatically specifies linking against the C++ library. On many
1022 systems, @command{g++} is also installed with the name @command{c++}.
1024 @cindex invoking @command{g++}
1025 When you compile C++ programs, you may specify many of the same
1026 command-line options that you use for compiling programs in any
1027 language; or command-line options meaningful for C and related
1028 languages; or options that are meaningful only for C++ programs.
1029 @xref{C Dialect Options,,Options Controlling C Dialect}, for
1030 explanations of options for languages related to C@.
1031 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
1032 explanations of options that are meaningful only for C++ programs.
1034 @node C Dialect Options
1035 @section Options Controlling C Dialect
1036 @cindex dialect options
1037 @cindex language dialect options
1038 @cindex options, dialect
1040 The following options control the dialect of C (or languages derived
1041 from C, such as C++, Objective-C and Objective-C++) that the compiler
1045 @cindex ANSI support
1049 In C mode, support all ISO C90 programs. In C++ mode,
1050 remove GNU extensions that conflict with ISO C++.
1052 This turns off certain features of GCC that are incompatible with ISO
1053 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
1054 such as the @code{asm} and @code{typeof} keywords, and
1055 predefined macros such as @code{unix} and @code{vax} that identify the
1056 type of system you are using. It also enables the undesirable and
1057 rarely used ISO trigraph feature. For the C compiler,
1058 it disables recognition of C++ style @samp{//} comments as well as
1059 the @code{inline} keyword.
1061 The alternate keywords @code{__asm__}, @code{__extension__},
1062 @code{__inline__} and @code{__typeof__} continue to work despite
1063 @option{-ansi}. You would not want to use them in an ISO C program, of
1064 course, but it is useful to put them in header files that might be included
1065 in compilations done with @option{-ansi}. Alternate predefined macros
1066 such as @code{__unix__} and @code{__vax__} are also available, with or
1067 without @option{-ansi}.
1069 The @option{-ansi} option does not cause non-ISO programs to be
1070 rejected gratuitously. For that, @option{-pedantic} is required in
1071 addition to @option{-ansi}. @xref{Warning Options}.
1073 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1074 option is used. Some header files may notice this macro and refrain
1075 from declaring certain functions or defining certain macros that the
1076 ISO standard doesn't call for; this is to avoid interfering with any
1077 programs that might use these names for other things.
1079 Functions which would normally be built in but do not have semantics
1080 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1081 functions with @option{-ansi} is used. @xref{Other Builtins,,Other
1082 built-in functions provided by GCC}, for details of the functions
1087 Determine the language standard. This option is currently only
1088 supported when compiling C or C++. A value for this option must be
1089 provided; possible values are
1094 ISO C90 (same as @option{-ansi}).
1096 @item iso9899:199409
1097 ISO C90 as modified in amendment 1.
1103 ISO C99. Note that this standard is not yet fully supported; see
1104 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1105 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1108 Default, ISO C90 plus GNU extensions (including some C99 features).
1112 ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
1113 this will become the default. The name @samp{gnu9x} is deprecated.
1116 The 1998 ISO C++ standard plus amendments.
1119 The same as @option{-std=c++98} plus GNU extensions. This is the
1120 default for C++ code.
1123 Even when this option is not specified, you can still use some of the
1124 features of newer standards in so far as they do not conflict with
1125 previous C standards. For example, you may use @code{__restrict__} even
1126 when @option{-std=c99} is not specified.
1128 The @option{-std} options specifying some version of ISO C have the same
1129 effects as @option{-ansi}, except that features that were not in ISO C90
1130 but are in the specified version (for example, @samp{//} comments and
1131 the @code{inline} keyword in ISO C99) are not disabled.
1133 @xref{Standards,,Language Standards Supported by GCC}, for details of
1134 these standard versions.
1136 @item -aux-info @var{filename}
1138 Output to the given filename prototyped declarations for all functions
1139 declared and/or defined in a translation unit, including those in header
1140 files. This option is silently ignored in any language other than C@.
1142 Besides declarations, the file indicates, in comments, the origin of
1143 each declaration (source file and line), whether the declaration was
1144 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1145 @samp{O} for old, respectively, in the first character after the line
1146 number and the colon), and whether it came from a declaration or a
1147 definition (@samp{C} or @samp{F}, respectively, in the following
1148 character). In the case of function definitions, a K&R-style list of
1149 arguments followed by their declarations is also provided, inside
1150 comments, after the declaration.
1154 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1155 keyword, so that code can use these words as identifiers. You can use
1156 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1157 instead. @option{-ansi} implies @option{-fno-asm}.
1159 In C++, this switch only affects the @code{typeof} keyword, since
1160 @code{asm} and @code{inline} are standard keywords. You may want to
1161 use the @option{-fno-gnu-keywords} flag instead, which has the same
1162 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1163 switch only affects the @code{asm} and @code{typeof} keywords, since
1164 @code{inline} is a standard keyword in ISO C99.
1167 @itemx -fno-builtin-@var{function}
1168 @opindex fno-builtin
1169 @cindex built-in functions
1170 Don't recognize built-in functions that do not begin with
1171 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1172 functions provided by GCC}, for details of the functions affected,
1173 including those which are not built-in functions when @option{-ansi} or
1174 @option{-std} options for strict ISO C conformance are used because they
1175 do not have an ISO standard meaning.
1177 GCC normally generates special code to handle certain built-in functions
1178 more efficiently; for instance, calls to @code{alloca} may become single
1179 instructions that adjust the stack directly, and calls to @code{memcpy}
1180 may become inline copy loops. The resulting code is often both smaller
1181 and faster, but since the function calls no longer appear as such, you
1182 cannot set a breakpoint on those calls, nor can you change the behavior
1183 of the functions by linking with a different library. In addition,
1184 when a function is recognized as a built-in function, GCC may use
1185 information about that function to warn about problems with calls to
1186 that function, or to generate more efficient code, even if the
1187 resulting code still contains calls to that function. For example,
1188 warnings are given with @option{-Wformat} for bad calls to
1189 @code{printf}, when @code{printf} is built in, and @code{strlen} is
1190 known not to modify global memory.
1192 With the @option{-fno-builtin-@var{function}} option
1193 only the built-in function @var{function} is
1194 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1195 function is named this is not built-in in this version of GCC, this
1196 option is ignored. There is no corresponding
1197 @option{-fbuiltin-@var{function}} option; if you wish to enable
1198 built-in functions selectively when using @option{-fno-builtin} or
1199 @option{-ffreestanding}, you may define macros such as:
1202 #define abs(n) __builtin_abs ((n))
1203 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1208 @cindex hosted environment
1210 Assert that compilation takes place in a hosted environment. This implies
1211 @option{-fbuiltin}. A hosted environment is one in which the
1212 entire standard library is available, and in which @code{main} has a return
1213 type of @code{int}. Examples are nearly everything except a kernel.
1214 This is equivalent to @option{-fno-freestanding}.
1216 @item -ffreestanding
1217 @opindex ffreestanding
1218 @cindex hosted environment
1220 Assert that compilation takes place in a freestanding environment. This
1221 implies @option{-fno-builtin}. A freestanding environment
1222 is one in which the standard library may not exist, and program startup may
1223 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1224 This is equivalent to @option{-fno-hosted}.
1226 @xref{Standards,,Language Standards Supported by GCC}, for details of
1227 freestanding and hosted environments.
1229 @item -fms-extensions
1230 @opindex fms-extensions
1231 Accept some non-standard constructs used in Microsoft header files.
1233 Some cases of unnamed fields in structures and unions are only
1234 accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union
1235 fields within structs/unions}, for details.
1239 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1240 options for strict ISO C conformance) implies @option{-trigraphs}.
1242 @item -no-integrated-cpp
1243 @opindex no-integrated-cpp
1244 Performs a compilation in two passes: preprocessing and compiling. This
1245 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1246 @option{-B} option. The user supplied compilation step can then add in
1247 an additional preprocessing step after normal preprocessing but before
1248 compiling. The default is to use the integrated cpp (internal cpp)
1250 The semantics of this option will change if "cc1", "cc1plus", and
1251 "cc1obj" are merged.
1253 @cindex traditional C language
1254 @cindex C language, traditional
1256 @itemx -traditional-cpp
1257 @opindex traditional-cpp
1258 @opindex traditional
1259 Formerly, these options caused GCC to attempt to emulate a pre-standard
1260 C compiler. They are now only supported with the @option{-E} switch.
1261 The preprocessor continues to support a pre-standard mode. See the GNU
1262 CPP manual for details.
1264 @item -fcond-mismatch
1265 @opindex fcond-mismatch
1266 Allow conditional expressions with mismatched types in the second and
1267 third arguments. The value of such an expression is void. This option
1268 is not supported for C++.
1270 @item -funsigned-char
1271 @opindex funsigned-char
1272 Let the type @code{char} be unsigned, like @code{unsigned char}.
1274 Each kind of machine has a default for what @code{char} should
1275 be. It is either like @code{unsigned char} by default or like
1276 @code{signed char} by default.
1278 Ideally, a portable program should always use @code{signed char} or
1279 @code{unsigned char} when it depends on the signedness of an object.
1280 But many programs have been written to use plain @code{char} and
1281 expect it to be signed, or expect it to be unsigned, depending on the
1282 machines they were written for. This option, and its inverse, let you
1283 make such a program work with the opposite default.
1285 The type @code{char} is always a distinct type from each of
1286 @code{signed char} or @code{unsigned char}, even though its behavior
1287 is always just like one of those two.
1290 @opindex fsigned-char
1291 Let the type @code{char} be signed, like @code{signed char}.
1293 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1294 the negative form of @option{-funsigned-char}. Likewise, the option
1295 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1297 @item -fsigned-bitfields
1298 @itemx -funsigned-bitfields
1299 @itemx -fno-signed-bitfields
1300 @itemx -fno-unsigned-bitfields
1301 @opindex fsigned-bitfields
1302 @opindex funsigned-bitfields
1303 @opindex fno-signed-bitfields
1304 @opindex fno-unsigned-bitfields
1305 These options control whether a bit-field is signed or unsigned, when the
1306 declaration does not use either @code{signed} or @code{unsigned}. By
1307 default, such a bit-field is signed, because this is consistent: the
1308 basic integer types such as @code{int} are signed types.
1311 @node C++ Dialect Options
1312 @section Options Controlling C++ Dialect
1314 @cindex compiler options, C++
1315 @cindex C++ options, command line
1316 @cindex options, C++
1317 This section describes the command-line options that are only meaningful
1318 for C++ programs; but you can also use most of the GNU compiler options
1319 regardless of what language your program is in. For example, you
1320 might compile a file @code{firstClass.C} like this:
1323 g++ -g -frepo -O -c firstClass.C
1327 In this example, only @option{-frepo} is an option meant
1328 only for C++ programs; you can use the other options with any
1329 language supported by GCC@.
1331 Here is a list of options that are @emph{only} for compiling C++ programs:
1335 @item -fabi-version=@var{n}
1336 @opindex fabi-version
1337 Use version @var{n} of the C++ ABI@. Version 2 is the version of the
1338 C++ ABI that first appeared in G++ 3.4. Version 1 is the version of
1339 the C++ ABI that first appeared in G++ 3.2. Version 0 will always be
1340 the version that conforms most closely to the C++ ABI specification.
1341 Therefore, the ABI obtained using version 0 will change as ABI bugs
1344 The default is version 2.
1346 @item -fno-access-control
1347 @opindex fno-access-control
1348 Turn off all access checking. This switch is mainly useful for working
1349 around bugs in the access control code.
1353 Check that the pointer returned by @code{operator new} is non-null
1354 before attempting to modify the storage allocated. This check is
1355 normally unnecessary because the C++ standard specifies that
1356 @code{operator new} will only return @code{0} if it is declared
1357 @samp{throw()}, in which case the compiler will always check the
1358 return value even without this option. In all other cases, when
1359 @code{operator new} has a non-empty exception specification, memory
1360 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1361 @samp{new (nothrow)}.
1363 @item -fconserve-space
1364 @opindex fconserve-space
1365 Put uninitialized or runtime-initialized global variables into the
1366 common segment, as C does. This saves space in the executable at the
1367 cost of not diagnosing duplicate definitions. If you compile with this
1368 flag and your program mysteriously crashes after @code{main()} has
1369 completed, you may have an object that is being destroyed twice because
1370 two definitions were merged.
1372 This option is no longer useful on most targets, now that support has
1373 been added for putting variables into BSS without making them common.
1375 @item -fno-const-strings
1376 @opindex fno-const-strings
1377 Give string constants type @code{char *} instead of type @code{const
1378 char *}. By default, G++ uses type @code{const char *} as required by
1379 the standard. Even if you use @option{-fno-const-strings}, you cannot
1380 actually modify the value of a string constant.
1382 This option might be removed in a future release of G++. For maximum
1383 portability, you should structure your code so that it works with
1384 string constants that have type @code{const char *}.
1386 @item -fno-elide-constructors
1387 @opindex fno-elide-constructors
1388 The C++ standard allows an implementation to omit creating a temporary
1389 which is only used to initialize another object of the same type.
1390 Specifying this option disables that optimization, and forces G++ to
1391 call the copy constructor in all cases.
1393 @item -fno-enforce-eh-specs
1394 @opindex fno-enforce-eh-specs
1395 Don't check for violation of exception specifications at runtime. This
1396 option violates the C++ standard, but may be useful for reducing code
1397 size in production builds, much like defining @samp{NDEBUG}. The compiler
1398 will still optimize based on the exception specifications.
1401 @itemx -fno-for-scope
1403 @opindex fno-for-scope
1404 If @option{-ffor-scope} is specified, the scope of variables declared in
1405 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1406 as specified by the C++ standard.
1407 If @option{-fno-for-scope} is specified, the scope of variables declared in
1408 a @i{for-init-statement} extends to the end of the enclosing scope,
1409 as was the case in old versions of G++, and other (traditional)
1410 implementations of C++.
1412 The default if neither flag is given to follow the standard,
1413 but to allow and give a warning for old-style code that would
1414 otherwise be invalid, or have different behavior.
1416 @item -fno-gnu-keywords
1417 @opindex fno-gnu-keywords
1418 Do not recognize @code{typeof} as a keyword, so that code can use this
1419 word as an identifier. You can use the keyword @code{__typeof__} instead.
1420 @option{-ansi} implies @option{-fno-gnu-keywords}.
1422 @item -fno-implicit-templates
1423 @opindex fno-implicit-templates
1424 Never emit code for non-inline templates which are instantiated
1425 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1426 @xref{Template Instantiation}, for more information.
1428 @item -fno-implicit-inline-templates
1429 @opindex fno-implicit-inline-templates
1430 Don't emit code for implicit instantiations of inline templates, either.
1431 The default is to handle inlines differently so that compiles with and
1432 without optimization will need the same set of explicit instantiations.
1434 @item -fno-implement-inlines
1435 @opindex fno-implement-inlines
1436 To save space, do not emit out-of-line copies of inline functions
1437 controlled by @samp{#pragma implementation}. This will cause linker
1438 errors if these functions are not inlined everywhere they are called.
1440 @item -fms-extensions
1441 @opindex fms-extensions
1442 Disable pedantic warnings about constructs used in MFC, such as implicit
1443 int and getting a pointer to member function via non-standard syntax.
1445 @item -fno-nonansi-builtins
1446 @opindex fno-nonansi-builtins
1447 Disable built-in declarations of functions that are not mandated by
1448 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1449 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1451 @item -fno-operator-names
1452 @opindex fno-operator-names
1453 Do not treat the operator name keywords @code{and}, @code{bitand},
1454 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1455 synonyms as keywords.
1457 @item -fno-optional-diags
1458 @opindex fno-optional-diags
1459 Disable diagnostics that the standard says a compiler does not need to
1460 issue. Currently, the only such diagnostic issued by G++ is the one for
1461 a name having multiple meanings within a class.
1464 @opindex fpermissive
1465 Downgrade some diagnostics about nonconformant code from errors to
1466 warnings. Thus, using @option{-fpermissive} will allow some
1467 nonconforming code to compile.
1471 Enable automatic template instantiation at link time. This option also
1472 implies @option{-fno-implicit-templates}. @xref{Template
1473 Instantiation}, for more information.
1477 Disable generation of information about every class with virtual
1478 functions for use by the C++ runtime type identification features
1479 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1480 of the language, you can save some space by using this flag. Note that
1481 exception handling uses the same information, but it will generate it as
1486 Emit statistics about front-end processing at the end of the compilation.
1487 This information is generally only useful to the G++ development team.
1489 @item -ftemplate-depth-@var{n}
1490 @opindex ftemplate-depth
1491 Set the maximum instantiation depth for template classes to @var{n}.
1492 A limit on the template instantiation depth is needed to detect
1493 endless recursions during template class instantiation. ANSI/ISO C++
1494 conforming programs must not rely on a maximum depth greater than 17.
1496 @item -fno-threadsafe-statics
1497 @opindex fno-threadsafe-statics
1498 Do not emit the extra code to use the routines specified in the C++
1499 ABI for thread-safe initialization of local statics. You can use this
1500 option to reduce code size slightly in code that doesn't need to be
1503 @item -fuse-cxa-atexit
1504 @opindex fuse-cxa-atexit
1505 Register destructors for objects with static storage duration with the
1506 @code{__cxa_atexit} function rather than the @code{atexit} function.
1507 This option is required for fully standards-compliant handling of static
1508 destructors, but will only work if your C library supports
1509 @code{__cxa_atexit}.
1511 @item -fvisibility-inlines-hidden
1512 @opindex fvisibility-inlines-hidden
1513 Causes all inlined methods to be marked with
1514 @code{__attribute__ ((visibility ("hidden")))} so that they do not
1515 appear in the export table of a DSO and do not require a PLT indirection
1516 when used within the DSO@. Enabling this option can have a dramatic effect
1517 on load and link times of a DSO as it massively reduces the size of the
1518 dynamic export table when the library makes heavy use of templates. While
1519 it can cause bloating through duplication of code within each DSO where
1520 it is used, often the wastage is less than the considerable space occupied
1521 by a long symbol name in the export table which is typical when using
1522 templates and namespaces. For even more savings, combine with the
1523 @option{-fvisibility=hidden} switch.
1527 Do not use weak symbol support, even if it is provided by the linker.
1528 By default, G++ will use weak symbols if they are available. This
1529 option exists only for testing, and should not be used by end-users;
1530 it will result in inferior code and has no benefits. This option may
1531 be removed in a future release of G++.
1535 Do not search for header files in the standard directories specific to
1536 C++, but do still search the other standard directories. (This option
1537 is used when building the C++ library.)
1540 In addition, these optimization, warning, and code generation options
1541 have meanings only for C++ programs:
1544 @item -fno-default-inline
1545 @opindex fno-default-inline
1546 Do not assume @samp{inline} for functions defined inside a class scope.
1547 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1548 functions will have linkage like inline functions; they just won't be
1551 @item -Wabi @r{(C++ only)}
1553 Warn when G++ generates code that is probably not compatible with the
1554 vendor-neutral C++ ABI@. Although an effort has been made to warn about
1555 all such cases, there are probably some cases that are not warned about,
1556 even though G++ is generating incompatible code. There may also be
1557 cases where warnings are emitted even though the code that is generated
1560 You should rewrite your code to avoid these warnings if you are
1561 concerned about the fact that code generated by G++ may not be binary
1562 compatible with code generated by other compilers.
1564 The known incompatibilities at this point include:
1569 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1570 pack data into the same byte as a base class. For example:
1573 struct A @{ virtual void f(); int f1 : 1; @};
1574 struct B : public A @{ int f2 : 1; @};
1578 In this case, G++ will place @code{B::f2} into the same byte
1579 as@code{A::f1}; other compilers will not. You can avoid this problem
1580 by explicitly padding @code{A} so that its size is a multiple of the
1581 byte size on your platform; that will cause G++ and other compilers to
1582 layout @code{B} identically.
1585 Incorrect handling of tail-padding for virtual bases. G++ does not use
1586 tail padding when laying out virtual bases. For example:
1589 struct A @{ virtual void f(); char c1; @};
1590 struct B @{ B(); char c2; @};
1591 struct C : public A, public virtual B @{@};
1595 In this case, G++ will not place @code{B} into the tail-padding for
1596 @code{A}; other compilers will. You can avoid this problem by
1597 explicitly padding @code{A} so that its size is a multiple of its
1598 alignment (ignoring virtual base classes); that will cause G++ and other
1599 compilers to layout @code{C} identically.
1602 Incorrect handling of bit-fields with declared widths greater than that
1603 of their underlying types, when the bit-fields appear in a union. For
1607 union U @{ int i : 4096; @};
1611 Assuming that an @code{int} does not have 4096 bits, G++ will make the
1612 union too small by the number of bits in an @code{int}.
1615 Empty classes can be placed at incorrect offsets. For example:
1625 struct C : public B, public A @{@};
1629 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
1630 it should be placed at offset zero. G++ mistakenly believes that the
1631 @code{A} data member of @code{B} is already at offset zero.
1634 Names of template functions whose types involve @code{typename} or
1635 template template parameters can be mangled incorrectly.
1638 template <typename Q>
1639 void f(typename Q::X) @{@}
1641 template <template <typename> class Q>
1642 void f(typename Q<int>::X) @{@}
1646 Instantiations of these templates may be mangled incorrectly.
1650 @item -Wctor-dtor-privacy @r{(C++ only)}
1651 @opindex Wctor-dtor-privacy
1652 Warn when a class seems unusable because all the constructors or
1653 destructors in that class are private, and it has neither friends nor
1654 public static member functions.
1656 @item -Wnon-virtual-dtor @r{(C++ only)}
1657 @opindex Wnon-virtual-dtor
1658 Warn when a class appears to be polymorphic, thereby requiring a virtual
1659 destructor, yet it declares a non-virtual one.
1660 This warning is enabled by @option{-Wall}.
1662 @item -Wreorder @r{(C++ only)}
1664 @cindex reordering, warning
1665 @cindex warning for reordering of member initializers
1666 Warn when the order of member initializers given in the code does not
1667 match the order in which they must be executed. For instance:
1673 A(): j (0), i (1) @{ @}
1677 The compiler will rearrange the member initializers for @samp{i}
1678 and @samp{j} to match the declaration order of the members, emitting
1679 a warning to that effect. This warning is enabled by @option{-Wall}.
1682 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
1685 @item -Weffc++ @r{(C++ only)}
1687 Warn about violations of the following style guidelines from Scott Meyers'
1688 @cite{Effective C++} book:
1692 Item 11: Define a copy constructor and an assignment operator for classes
1693 with dynamically allocated memory.
1696 Item 12: Prefer initialization to assignment in constructors.
1699 Item 14: Make destructors virtual in base classes.
1702 Item 15: Have @code{operator=} return a reference to @code{*this}.
1705 Item 23: Don't try to return a reference when you must return an object.
1709 Also warn about violations of the following style guidelines from
1710 Scott Meyers' @cite{More Effective C++} book:
1714 Item 6: Distinguish between prefix and postfix forms of increment and
1715 decrement operators.
1718 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
1722 When selecting this option, be aware that the standard library
1723 headers do not obey all of these guidelines; use @samp{grep -v}
1724 to filter out those warnings.
1726 @item -Wno-deprecated @r{(C++ only)}
1727 @opindex Wno-deprecated
1728 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
1730 @item -Wno-non-template-friend @r{(C++ only)}
1731 @opindex Wno-non-template-friend
1732 Disable warnings when non-templatized friend functions are declared
1733 within a template. Since the advent of explicit template specification
1734 support in G++, if the name of the friend is an unqualified-id (i.e.,
1735 @samp{friend foo(int)}), the C++ language specification demands that the
1736 friend declare or define an ordinary, nontemplate function. (Section
1737 14.5.3). Before G++ implemented explicit specification, unqualified-ids
1738 could be interpreted as a particular specialization of a templatized
1739 function. Because this non-conforming behavior is no longer the default
1740 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
1741 check existing code for potential trouble spots and is on by default.
1742 This new compiler behavior can be turned off with
1743 @option{-Wno-non-template-friend} which keeps the conformant compiler code
1744 but disables the helpful warning.
1746 @item -Wold-style-cast @r{(C++ only)}
1747 @opindex Wold-style-cast
1748 Warn if an old-style (C-style) cast to a non-void type is used within
1749 a C++ program. The new-style casts (@samp{static_cast},
1750 @samp{reinterpret_cast}, and @samp{const_cast}) are less vulnerable to
1751 unintended effects and much easier to search for.
1753 @item -Woverloaded-virtual @r{(C++ only)}
1754 @opindex Woverloaded-virtual
1755 @cindex overloaded virtual fn, warning
1756 @cindex warning for overloaded virtual fn
1757 Warn when a function declaration hides virtual functions from a
1758 base class. For example, in:
1765 struct B: public A @{
1770 the @code{A} class version of @code{f} is hidden in @code{B}, and code
1778 will fail to compile.
1780 @item -Wno-pmf-conversions @r{(C++ only)}
1781 @opindex Wno-pmf-conversions
1782 Disable the diagnostic for converting a bound pointer to member function
1785 @item -Wsign-promo @r{(C++ only)}
1786 @opindex Wsign-promo
1787 Warn when overload resolution chooses a promotion from unsigned or
1788 enumerated type to a signed type, over a conversion to an unsigned type of
1789 the same size. Previous versions of G++ would try to preserve
1790 unsignedness, but the standard mandates the current behavior.
1792 @item -Wsynth @r{(C++ only)}
1794 @cindex warning for synthesized methods
1795 @cindex synthesized methods, warning
1796 Warn when G++'s synthesis behavior does not match that of cfront. For
1802 A& operator = (int);
1812 In this example, G++ will synthesize a default @samp{A& operator =
1813 (const A&);}, while cfront will use the user-defined @samp{operator =}.
1816 @node Objective-C and Objective-C++ Dialect Options
1817 @section Options Controlling Objective-C and Objective-C++ Dialects
1819 @cindex compiler options, Objective-C and Objective-C++
1820 @cindex Objective-C and Objective-C++ options, command line
1821 @cindex options, Objective-C and Objective-C++
1822 (NOTE: This manual does not describe the Objective-C and Objective-C++
1823 languages themselves. See @xref{Standards,,Language Standards
1824 Supported by GCC}, for references.)
1826 This section describes the command-line options that are only meaningful
1827 for Objective-C and Objective-C++ programs, but you can also use most of
1828 the language-independent GNU compiler options.
1829 For example, you might compile a file @code{some_class.m} like this:
1832 gcc -g -fgnu-runtime -O -c some_class.m
1836 In this example, @option{-fgnu-runtime} is an option meant only for
1837 Objective-C and Objective-C++ programs; you can use the other options with
1838 any language supported by GCC@.
1840 Note that since Objective-C is an extension of the C language, Objective-C
1841 compilations may also use options specific to the C front-end (e.g.,
1842 @option{-Wtraditional}). Similarly, Objective-C++ compilations may use
1843 C++-specific options (e.g., @option{-Wabi}).
1845 Here is a list of options that are @emph{only} for compiling Objective-C
1846 and Objective-C++ programs:
1849 @item -fconstant-string-class=@var{class-name}
1850 @opindex fconstant-string-class
1851 Use @var{class-name} as the name of the class to instantiate for each
1852 literal string specified with the syntax @code{@@"@dots{}"}. The default
1853 class name is @code{NXConstantString} if the GNU runtime is being used, and
1854 @code{NSConstantString} if the NeXT runtime is being used (see below). The
1855 @option{-fconstant-cfstrings} option, if also present, will override the
1856 @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
1857 to be laid out as constant CoreFoundation strings.
1860 @opindex fgnu-runtime
1861 Generate object code compatible with the standard GNU Objective-C
1862 runtime. This is the default for most types of systems.
1864 @item -fnext-runtime
1865 @opindex fnext-runtime
1866 Generate output compatible with the NeXT runtime. This is the default
1867 for NeXT-based systems, including Darwin and Mac OS X@. The macro
1868 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
1871 @item -fno-nil-receivers
1872 @opindex fno-nil-receivers
1873 Assume that all Objective-C message dispatches (e.g.,
1874 @code{[receiver message:arg]}) in this translation unit ensure that the receiver
1875 is not @code{nil}. This allows for more efficient entry points in the runtime
1876 to be used. Currently, this option is only available in conjunction with
1877 the NeXT runtime on Mac OS X 10.3 and later.
1879 @item -fobjc-exceptions
1880 @opindex fobjc-exceptions
1881 Enable syntactic support for structured exception handling in Objective-C,
1882 similar to what is offered by C++ and Java. Currently, this option is only
1883 available in conjunction with the NeXT runtime on Mac OS X 10.3 and later.
1891 @@catch (AnObjCClass *exc) @{
1898 @@catch (AnotherClass *exc) @{
1901 @@catch (id allOthers) @{
1911 The @code{@@throw} statement may appear anywhere in an Objective-C or
1912 Objective-C++ program; when used inside of a @code{@@catch} block, the
1913 @code{@@throw} may appear without an argument (as shown above), in which case
1914 the object caught by the @code{@@catch} will be rethrown.
1916 Note that only (pointers to) Objective-C objects may be thrown and
1917 caught using this scheme. When an object is thrown, it will be caught
1918 by the nearest @code{@@catch} clause capable of handling objects of that type,
1919 analogously to how @code{catch} blocks work in C++ and Java. A
1920 @code{@@catch(id @dots{})} clause (as shown above) may also be provided to catch
1921 any and all Objective-C exceptions not caught by previous @code{@@catch}
1924 The @code{@@finally} clause, if present, will be executed upon exit from the
1925 immediately preceding @code{@@try @dots{} @@catch} section. This will happen
1926 regardless of whether any exceptions are thrown, caught or rethrown
1927 inside the @code{@@try @dots{} @@catch} section, analogously to the behavior
1928 of the @code{finally} clause in Java.
1930 There are several caveats to using the new exception mechanism:
1934 Although currently designed to be binary compatible with @code{NS_HANDLER}-style
1935 idioms provided by the @code{NSException} class, the new
1936 exceptions can only be used on Mac OS X 10.3 (Panther) and later
1937 systems, due to additional functionality needed in the (NeXT) Objective-C
1941 As mentioned above, the new exceptions do not support handling
1942 types other than Objective-C objects. Furthermore, when used from
1943 Objective-C++, the Objective-C exception model does not interoperate with C++
1944 exceptions at this time. This means you cannot @code{@@throw} an exception
1945 from Objective-C and @code{catch} it in C++, or vice versa
1946 (i.e., @code{throw @dots{} @@catch}).
1949 The @option{-fobjc-exceptions} switch also enables the use of synchronization
1950 blocks for thread-safe execution:
1953 @@synchronized (ObjCClass *guard) @{
1958 Upon entering the @code{@@synchronized} block, a thread of execution shall
1959 first check whether a lock has been placed on the corresponding @code{guard}
1960 object by another thread. If it has, the current thread shall wait until
1961 the other thread relinquishes its lock. Once @code{guard} becomes available,
1962 the current thread will place its own lock on it, execute the code contained in
1963 the @code{@@synchronized} block, and finally relinquish the lock (thereby
1964 making @code{guard} available to other threads).
1966 Unlike Java, Objective-C does not allow for entire methods to be marked
1967 @code{@@synchronized}. Note that throwing exceptions out of
1968 @code{@@synchronized} blocks is allowed, and will cause the guarding object
1969 to be unlocked properly.
1971 @item -freplace-objc-classes
1972 @opindex freplace-objc-classes
1973 Emit a special marker instructing @command{ld(1)} not to statically link in
1974 the resulting object file, and allow @command{dyld(1)} to load it in at
1975 run time instead. This is used in conjunction with the Fix-and-Continue
1976 debugging mode, where the object file in question may be recompiled and
1977 dynamically reloaded in the course of program execution, without the need
1978 to restart the program itself. Currently, Fix-and-Continue functionality
1979 is only available in conjunction with the NeXT runtime on Mac OS X 10.3
1984 When compiling for the NeXT runtime, the compiler ordinarily replaces calls
1985 to @code{objc_getClass("@dots{}")} (when the name of the class is known at
1986 compile time) with static class references that get initialized at load time,
1987 which improves run-time performance. Specifying the @option{-fzero-link} flag
1988 suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
1989 to be retained. This is useful in Zero-Link debugging mode, since it allows
1990 for individual class implementations to be modified during program execution.
1994 Dump interface declarations for all classes seen in the source file to a
1995 file named @file{@var{sourcename}.decl}.
1998 @opindex Wno-protocol
1999 If a class is declared to implement a protocol, a warning is issued for
2000 every method in the protocol that is not implemented by the class. The
2001 default behavior is to issue a warning for every method not explicitly
2002 implemented in the class, even if a method implementation is inherited
2003 from the superclass. If you use the @option{-Wno-protocol} option, then
2004 methods inherited from the superclass are considered to be implemented,
2005 and no warning is issued for them.
2009 Warn if multiple methods of different types for the same selector are
2010 found during compilation. The check is performed on the list of methods
2011 in the final stage of compilation. Additionally, a check is performed
2012 for each selector appearing in a @code{@@selector(@dots{})}
2013 expression, and a corresponding method for that selector has been found
2014 during compilation. Because these checks scan the method table only at
2015 the end of compilation, these warnings are not produced if the final
2016 stage of compilation is not reached, for example because an error is
2017 found during compilation, or because the @option{-fsyntax-only} option is
2020 @item -Wundeclared-selector
2021 @opindex Wundeclared-selector
2022 Warn if a @code{@@selector(@dots{})} expression referring to an
2023 undeclared selector is found. A selector is considered undeclared if no
2024 method with that name has been declared before the
2025 @code{@@selector(@dots{})} expression, either explicitly in an
2026 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
2027 an @code{@@implementation} section. This option always performs its
2028 checks as soon as a @code{@@selector(@dots{})} expression is found,
2029 while @option{-Wselector} only performs its checks in the final stage of
2030 compilation. This also enforces the coding style convention
2031 that methods and selectors must be declared before being used.
2033 @item -print-objc-runtime-info
2034 @opindex print-objc-runtime-info
2035 Generate C header describing the largest structure that is passed by
2040 @node Language Independent Options
2041 @section Options to Control Diagnostic Messages Formatting
2042 @cindex options to control diagnostics formatting
2043 @cindex diagnostic messages
2044 @cindex message formatting
2046 Traditionally, diagnostic messages have been formatted irrespective of
2047 the output device's aspect (e.g.@: its width, @dots{}). The options described
2048 below can be used to control the diagnostic messages formatting
2049 algorithm, e.g.@: how many characters per line, how often source location
2050 information should be reported. Right now, only the C++ front end can
2051 honor these options. However it is expected, in the near future, that
2052 the remaining front ends would be able to digest them correctly.
2055 @item -fmessage-length=@var{n}
2056 @opindex fmessage-length
2057 Try to format error messages so that they fit on lines of about @var{n}
2058 characters. The default is 72 characters for @command{g++} and 0 for the rest of
2059 the front ends supported by GCC@. If @var{n} is zero, then no
2060 line-wrapping will be done; each error message will appear on a single
2063 @opindex fdiagnostics-show-location
2064 @item -fdiagnostics-show-location=once
2065 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
2066 reporter to emit @emph{once} source location information; that is, in
2067 case the message is too long to fit on a single physical line and has to
2068 be wrapped, the source location won't be emitted (as prefix) again,
2069 over and over, in subsequent continuation lines. This is the default
2072 @item -fdiagnostics-show-location=every-line
2073 Only meaningful in line-wrapping mode. Instructs the diagnostic
2074 messages reporter to emit the same source location information (as
2075 prefix) for physical lines that result from the process of breaking
2076 a message which is too long to fit on a single line.
2080 @node Warning Options
2081 @section Options to Request or Suppress Warnings
2082 @cindex options to control warnings
2083 @cindex warning messages
2084 @cindex messages, warning
2085 @cindex suppressing warnings
2087 Warnings are diagnostic messages that report constructions which
2088 are not inherently erroneous but which are risky or suggest there
2089 may have been an error.
2091 You can request many specific warnings with options beginning @samp{-W},
2092 for example @option{-Wimplicit} to request warnings on implicit
2093 declarations. Each of these specific warning options also has a
2094 negative form beginning @samp{-Wno-} to turn off warnings;
2095 for example, @option{-Wno-implicit}. This manual lists only one of the
2096 two forms, whichever is not the default.
2098 The following options control the amount and kinds of warnings produced
2099 by GCC; for further, language-specific options also refer to
2100 @ref{C++ Dialect Options} and @ref{Objective-C and Objective-C++ Dialect
2104 @cindex syntax checking
2106 @opindex fsyntax-only
2107 Check the code for syntax errors, but don't do anything beyond that.
2111 Issue all the warnings demanded by strict ISO C and ISO C++;
2112 reject all programs that use forbidden extensions, and some other
2113 programs that do not follow ISO C and ISO C++. For ISO C, follows the
2114 version of the ISO C standard specified by any @option{-std} option used.
2116 Valid ISO C and ISO C++ programs should compile properly with or without
2117 this option (though a rare few will require @option{-ansi} or a
2118 @option{-std} option specifying the required version of ISO C)@. However,
2119 without this option, certain GNU extensions and traditional C and C++
2120 features are supported as well. With this option, they are rejected.
2122 @option{-pedantic} does not cause warning messages for use of the
2123 alternate keywords whose names begin and end with @samp{__}. Pedantic
2124 warnings are also disabled in the expression that follows
2125 @code{__extension__}. However, only system header files should use
2126 these escape routes; application programs should avoid them.
2127 @xref{Alternate Keywords}.
2129 Some users try to use @option{-pedantic} to check programs for strict ISO
2130 C conformance. They soon find that it does not do quite what they want:
2131 it finds some non-ISO practices, but not all---only those for which
2132 ISO C @emph{requires} a diagnostic, and some others for which
2133 diagnostics have been added.
2135 A feature to report any failure to conform to ISO C might be useful in
2136 some instances, but would require considerable additional work and would
2137 be quite different from @option{-pedantic}. We don't have plans to
2138 support such a feature in the near future.
2140 Where the standard specified with @option{-std} represents a GNU
2141 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
2142 corresponding @dfn{base standard}, the version of ISO C on which the GNU
2143 extended dialect is based. Warnings from @option{-pedantic} are given
2144 where they are required by the base standard. (It would not make sense
2145 for such warnings to be given only for features not in the specified GNU
2146 C dialect, since by definition the GNU dialects of C include all
2147 features the compiler supports with the given option, and there would be
2148 nothing to warn about.)
2150 @item -pedantic-errors
2151 @opindex pedantic-errors
2152 Like @option{-pedantic}, except that errors are produced rather than
2157 Inhibit all warning messages.
2161 Inhibit warning messages about the use of @samp{#import}.
2163 @item -Wchar-subscripts
2164 @opindex Wchar-subscripts
2165 Warn if an array subscript has type @code{char}. This is a common cause
2166 of error, as programmers often forget that this type is signed on some
2171 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
2172 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
2174 @item -Wfatal-errors
2175 @opindex Wfatal-errors
2176 This option causes the compiler to abort compilation on the first error
2177 occurred rather than trying to keep going and printing further error
2182 @opindex ffreestanding
2183 @opindex fno-builtin
2184 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
2185 the arguments supplied have types appropriate to the format string
2186 specified, and that the conversions specified in the format string make
2187 sense. This includes standard functions, and others specified by format
2188 attributes (@pxref{Function Attributes}), in the @code{printf},
2189 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
2190 not in the C standard) families (or other target-specific families).
2191 Which functions are checked without format attributes having been
2192 specified depends on the standard version selected, and such checks of
2193 functions without the attribute specified are disabled by
2194 @option{-ffreestanding} or @option{-fno-builtin}.
2196 The formats are checked against the format features supported by GNU
2197 libc version 2.2. These include all ISO C90 and C99 features, as well
2198 as features from the Single Unix Specification and some BSD and GNU
2199 extensions. Other library implementations may not support all these
2200 features; GCC does not support warning about features that go beyond a
2201 particular library's limitations. However, if @option{-pedantic} is used
2202 with @option{-Wformat}, warnings will be given about format features not
2203 in the selected standard version (but not for @code{strfmon} formats,
2204 since those are not in any version of the C standard). @xref{C Dialect
2205 Options,,Options Controlling C Dialect}.
2207 Since @option{-Wformat} also checks for null format arguments for
2208 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2210 @option{-Wformat} is included in @option{-Wall}. For more control over some
2211 aspects of format checking, the options @option{-Wformat-y2k},
2212 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2213 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2214 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2217 @opindex Wformat-y2k
2218 If @option{-Wformat} is specified, also warn about @code{strftime}
2219 formats which may yield only a two-digit year.
2221 @item -Wno-format-extra-args
2222 @opindex Wno-format-extra-args
2223 If @option{-Wformat} is specified, do not warn about excess arguments to a
2224 @code{printf} or @code{scanf} format function. The C standard specifies
2225 that such arguments are ignored.
2227 Where the unused arguments lie between used arguments that are
2228 specified with @samp{$} operand number specifications, normally
2229 warnings are still given, since the implementation could not know what
2230 type to pass to @code{va_arg} to skip the unused arguments. However,
2231 in the case of @code{scanf} formats, this option will suppress the
2232 warning if the unused arguments are all pointers, since the Single
2233 Unix Specification says that such unused arguments are allowed.
2235 @item -Wno-format-zero-length
2236 @opindex Wno-format-zero-length
2237 If @option{-Wformat} is specified, do not warn about zero-length formats.
2238 The C standard specifies that zero-length formats are allowed.
2240 @item -Wformat-nonliteral
2241 @opindex Wformat-nonliteral
2242 If @option{-Wformat} is specified, also warn if the format string is not a
2243 string literal and so cannot be checked, unless the format function
2244 takes its format arguments as a @code{va_list}.
2246 @item -Wformat-security
2247 @opindex Wformat-security
2248 If @option{-Wformat} is specified, also warn about uses of format
2249 functions that represent possible security problems. At present, this
2250 warns about calls to @code{printf} and @code{scanf} functions where the
2251 format string is not a string literal and there are no format arguments,
2252 as in @code{printf (foo);}. This may be a security hole if the format
2253 string came from untrusted input and contains @samp{%n}. (This is
2254 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2255 in future warnings may be added to @option{-Wformat-security} that are not
2256 included in @option{-Wformat-nonliteral}.)
2260 Enable @option{-Wformat} plus format checks not included in
2261 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2262 -Wformat-nonliteral -Wformat-security -Wformat-y2k}.
2266 Warn about passing a null pointer for arguments marked as
2267 requiring a non-null value by the @code{nonnull} function attribute.
2269 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2270 can be disabled with the @option{-Wno-nonnull} option.
2272 @item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
2274 Warn about uninitialized variables which are initialized with themselves.
2275 Note this option can only be used with the @option{-Wuninitialized} option,
2276 which in turn only works with @option{-O1} and above.
2278 For example, GCC will warn about @code{i} being uninitialized in the
2279 following snippet only when @option{-Winit-self} has been specified:
2290 @item -Wimplicit-int
2291 @opindex Wimplicit-int
2292 Warn when a declaration does not specify a type.
2294 @item -Wimplicit-function-declaration
2295 @itemx -Werror-implicit-function-declaration
2296 @opindex Wimplicit-function-declaration
2297 @opindex Werror-implicit-function-declaration
2298 Give a warning (or error) whenever a function is used before being
2299 declared. The form @option{-Wno-error-implicit-function-declaration}
2304 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2308 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
2309 function with external linkage, returning int, taking either zero
2310 arguments, two, or three arguments of appropriate types.
2312 @item -Wmissing-braces
2313 @opindex Wmissing-braces
2314 Warn if an aggregate or union initializer is not fully bracketed. In
2315 the following example, the initializer for @samp{a} is not fully
2316 bracketed, but that for @samp{b} is fully bracketed.
2319 int a[2][2] = @{ 0, 1, 2, 3 @};
2320 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2323 @item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)}
2324 @opindex Wmissing-include-dirs
2325 Warn if a user-supplied include directory does not exist.
2328 @opindex Wparentheses
2329 Warn if parentheses are omitted in certain contexts, such
2330 as when there is an assignment in a context where a truth value
2331 is expected, or when operators are nested whose precedence people
2332 often get confused about. Only the warning for an assignment used as
2333 a truth value is supported when compiling C++; the other warnings are
2334 only supported when compiling C@.
2336 Also warn if a comparison like @samp{x<=y<=z} appears; this is
2337 equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different
2338 interpretation from that of ordinary mathematical notation.
2340 Also warn about constructions where there may be confusion to which
2341 @code{if} statement an @code{else} branch belongs. Here is an example of
2356 In C, every @code{else} branch belongs to the innermost possible @code{if}
2357 statement, which in this example is @code{if (b)}. This is often not
2358 what the programmer expected, as illustrated in the above example by
2359 indentation the programmer chose. When there is the potential for this
2360 confusion, GCC will issue a warning when this flag is specified.
2361 To eliminate the warning, add explicit braces around the innermost
2362 @code{if} statement so there is no way the @code{else} could belong to
2363 the enclosing @code{if}. The resulting code would look like this:
2379 @item -Wsequence-point
2380 @opindex Wsequence-point
2381 Warn about code that may have undefined semantics because of violations
2382 of sequence point rules in the C standard.
2384 The C standard defines the order in which expressions in a C program are
2385 evaluated in terms of @dfn{sequence points}, which represent a partial
2386 ordering between the execution of parts of the program: those executed
2387 before the sequence point, and those executed after it. These occur
2388 after the evaluation of a full expression (one which is not part of a
2389 larger expression), after the evaluation of the first operand of a
2390 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
2391 function is called (but after the evaluation of its arguments and the
2392 expression denoting the called function), and in certain other places.
2393 Other than as expressed by the sequence point rules, the order of
2394 evaluation of subexpressions of an expression is not specified. All
2395 these rules describe only a partial order rather than a total order,
2396 since, for example, if two functions are called within one expression
2397 with no sequence point between them, the order in which the functions
2398 are called is not specified. However, the standards committee have
2399 ruled that function calls do not overlap.
2401 It is not specified when between sequence points modifications to the
2402 values of objects take effect. Programs whose behavior depends on this
2403 have undefined behavior; the C standard specifies that ``Between the
2404 previous and next sequence point an object shall have its stored value
2405 modified at most once by the evaluation of an expression. Furthermore,
2406 the prior value shall be read only to determine the value to be
2407 stored.''. If a program breaks these rules, the results on any
2408 particular implementation are entirely unpredictable.
2410 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
2411 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
2412 diagnosed by this option, and it may give an occasional false positive
2413 result, but in general it has been found fairly effective at detecting
2414 this sort of problem in programs.
2416 The present implementation of this option only works for C programs. A
2417 future implementation may also work for C++ programs.
2419 The C standard is worded confusingly, therefore there is some debate
2420 over the precise meaning of the sequence point rules in subtle cases.
2421 Links to discussions of the problem, including proposed formal
2422 definitions, may be found on the GCC readings page, at
2423 @w{@uref{http://gcc.gnu.org/readings.html}}.
2426 @opindex Wreturn-type
2427 Warn whenever a function is defined with a return-type that defaults to
2428 @code{int}. Also warn about any @code{return} statement with no
2429 return-value in a function whose return-type is not @code{void}.
2431 For C, also warn if the return type of a function has a type qualifier
2432 such as @code{const}. Such a type qualifier has no effect, since the
2433 value returned by a function is not an lvalue. ISO C prohibits
2434 qualified @code{void} return types on function definitions, so such
2435 return types always receive a warning even without this option.
2437 For C++, a function without return type always produces a diagnostic
2438 message, even when @option{-Wno-return-type} is specified. The only
2439 exceptions are @samp{main} and functions defined in system headers.
2443 Warn whenever a @code{switch} statement has an index of enumerated type
2444 and lacks a @code{case} for one or more of the named codes of that
2445 enumeration. (The presence of a @code{default} label prevents this
2446 warning.) @code{case} labels outside the enumeration range also
2447 provoke warnings when this option is used.
2449 @item -Wswitch-default
2450 @opindex Wswitch-switch
2451 Warn whenever a @code{switch} statement does not have a @code{default}
2455 @opindex Wswitch-enum
2456 Warn whenever a @code{switch} statement has an index of enumerated type
2457 and lacks a @code{case} for one or more of the named codes of that
2458 enumeration. @code{case} labels outside the enumeration range also
2459 provoke warnings when this option is used.
2463 Warn if any trigraphs are encountered that might change the meaning of
2464 the program (trigraphs within comments are not warned about).
2466 @item -Wunused-function
2467 @opindex Wunused-function
2468 Warn whenever a static function is declared but not defined or a
2469 non\-inline static function is unused.
2471 @item -Wunused-label
2472 @opindex Wunused-label
2473 Warn whenever a label is declared but not used.
2475 To suppress this warning use the @samp{unused} attribute
2476 (@pxref{Variable Attributes}).
2478 @item -Wunused-parameter
2479 @opindex Wunused-parameter
2480 Warn whenever a function parameter is unused aside from its declaration.
2482 To suppress this warning use the @samp{unused} attribute
2483 (@pxref{Variable Attributes}).
2485 @item -Wunused-variable
2486 @opindex Wunused-variable
2487 Warn whenever a local variable or non-constant static variable is unused
2488 aside from its declaration
2490 To suppress this warning use the @samp{unused} attribute
2491 (@pxref{Variable Attributes}).
2493 @item -Wunused-value
2494 @opindex Wunused-value
2495 Warn whenever a statement computes a result that is explicitly not used.
2497 To suppress this warning cast the expression to @samp{void}.
2501 All the above @option{-Wunused} options combined.
2503 In order to get a warning about an unused function parameter, you must
2504 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
2505 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
2507 @item -Wuninitialized
2508 @opindex Wuninitialized
2509 Warn if an automatic variable is used without first being initialized or
2510 if a variable may be clobbered by a @code{setjmp} call.
2512 These warnings are possible only in optimizing compilation,
2513 because they require data flow information that is computed only
2514 when optimizing. If you don't specify @option{-O}, you simply won't
2517 If you want to warn about code which uses the uninitialized value of the
2518 variable in its own initializer, use the @option{-Winit-self} option.
2520 These warnings occur only for variables that are candidates for
2521 register allocation. Therefore, they do not occur for a variable that
2522 is declared @code{volatile}, or whose address is taken, or whose size
2523 is other than 1, 2, 4 or 8 bytes. Also, they do not occur for
2524 structures, unions or arrays, even when they are in registers.
2526 Note that there may be no warning about a variable that is used only
2527 to compute a value that itself is never used, because such
2528 computations may be deleted by data flow analysis before the warnings
2531 These warnings are made optional because GCC is not smart
2532 enough to see all the reasons why the code might be correct
2533 despite appearing to have an error. Here is one example of how
2554 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
2555 always initialized, but GCC doesn't know this. Here is
2556 another common case:
2561 if (change_y) save_y = y, y = new_y;
2563 if (change_y) y = save_y;
2568 This has no bug because @code{save_y} is used only if it is set.
2570 @cindex @code{longjmp} warnings
2571 This option also warns when a non-volatile automatic variable might be
2572 changed by a call to @code{longjmp}. These warnings as well are possible
2573 only in optimizing compilation.
2575 The compiler sees only the calls to @code{setjmp}. It cannot know
2576 where @code{longjmp} will be called; in fact, a signal handler could
2577 call it at any point in the code. As a result, you may get a warning
2578 even when there is in fact no problem because @code{longjmp} cannot
2579 in fact be called at the place which would cause a problem.
2581 Some spurious warnings can be avoided if you declare all the functions
2582 you use that never return as @code{noreturn}. @xref{Function
2585 @item -Wunknown-pragmas
2586 @opindex Wunknown-pragmas
2587 @cindex warning for unknown pragmas
2588 @cindex unknown pragmas, warning
2589 @cindex pragmas, warning of unknown
2590 Warn when a #pragma directive is encountered which is not understood by
2591 GCC@. If this command line option is used, warnings will even be issued
2592 for unknown pragmas in system header files. This is not the case if
2593 the warnings were only enabled by the @option{-Wall} command line option.
2595 @item -Wstrict-aliasing
2596 @opindex Wstrict-aliasing
2597 This option is only active when @option{-fstrict-aliasing} is active.
2598 It warns about code which might break the strict aliasing rules that the
2599 compiler is using for optimization. The warning does not catch all
2600 cases, but does attempt to catch the more common pitfalls. It is
2601 included in @option{-Wall}.
2603 @item -Wstrict-aliasing=2
2604 @opindex Wstrict-aliasing=2
2605 This option is only active when @option{-fstrict-aliasing} is active.
2606 It warns about all code which might break the strict aliasing rules that the
2607 compiler is using for optimization. This warning catches all cases, but
2608 it will also give a warning for some ambiguous cases that are safe.
2612 All of the above @samp{-W} options combined. This enables all the
2613 warnings about constructions that some users consider questionable, and
2614 that are easy to avoid (or modify to prevent the warning), even in
2615 conjunction with macros. This also enables some language-specific
2616 warnings described in @ref{C++ Dialect Options} and
2617 @ref{Objective-C and Objective-C++ Dialect Options}.
2620 The following @option{-W@dots{}} options are not implied by @option{-Wall}.
2621 Some of them warn about constructions that users generally do not
2622 consider questionable, but which occasionally you might wish to check
2623 for; others warn about constructions that are necessary or hard to avoid
2624 in some cases, and there is no simple way to modify the code to suppress
2631 (This option used to be called @option{-W}. The older name is still
2632 supported, but the newer name is more descriptive.) Print extra warning
2633 messages for these events:
2637 A function can return either with or without a value. (Falling
2638 off the end of the function body is considered returning without
2639 a value.) For example, this function would evoke such a
2653 An expression-statement or the left-hand side of a comma expression
2654 contains no side effects.
2655 To suppress the warning, cast the unused expression to void.
2656 For example, an expression such as @samp{x[i,j]} will cause a warning,
2657 but @samp{x[(void)i,j]} will not.
2660 An unsigned value is compared against zero with @samp{<} or @samp{>=}.
2663 Storage-class specifiers like @code{static} are not the first things in
2664 a declaration. According to the C Standard, this usage is obsolescent.
2667 If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
2671 A comparison between signed and unsigned values could produce an
2672 incorrect result when the signed value is converted to unsigned.
2673 (But don't warn if @option{-Wno-sign-compare} is also specified.)
2676 An aggregate has an initializer which does not initialize all members.
2677 This warning can be independently controlled by
2678 @option{-Wmissing-field-initializers}.
2681 A function parameter is declared without a type specifier in K&R-style
2689 An empty body occurs in an @samp{if} or @samp{else} statement.
2692 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2693 @samp{>}, or @samp{>=}.
2696 A variable might be changed by @samp{longjmp} or @samp{vfork}.
2699 Any of several floating-point events that often indicate errors, such as
2700 overflow, underflow, loss of precision, etc.
2702 @item @r{(C++ only)}
2703 An enumerator and a non-enumerator both appear in a conditional expression.
2705 @item @r{(C++ only)}
2706 A non-static reference or non-static @samp{const} member appears in a
2707 class without constructors.
2709 @item @r{(C++ only)}
2710 Ambiguous virtual bases.
2712 @item @r{(C++ only)}
2713 Subscripting an array which has been declared @samp{register}.
2715 @item @r{(C++ only)}
2716 Taking the address of a variable which has been declared @samp{register}.
2718 @item @r{(C++ only)}
2719 A base class is not initialized in a derived class' copy constructor.
2722 @item -Wno-div-by-zero
2723 @opindex Wno-div-by-zero
2724 @opindex Wdiv-by-zero
2725 Do not warn about compile-time integer division by zero. Floating point
2726 division by zero is not warned about, as it can be a legitimate way of
2727 obtaining infinities and NaNs.
2729 @item -Wsystem-headers
2730 @opindex Wsystem-headers
2731 @cindex warnings from system headers
2732 @cindex system headers, warnings from
2733 Print warning messages for constructs found in system header files.
2734 Warnings from system headers are normally suppressed, on the assumption
2735 that they usually do not indicate real problems and would only make the
2736 compiler output harder to read. Using this command line option tells
2737 GCC to emit warnings from system headers as if they occurred in user
2738 code. However, note that using @option{-Wall} in conjunction with this
2739 option will @emph{not} warn about unknown pragmas in system
2740 headers---for that, @option{-Wunknown-pragmas} must also be used.
2743 @opindex Wfloat-equal
2744 Warn if floating point values are used in equality comparisons.
2746 The idea behind this is that sometimes it is convenient (for the
2747 programmer) to consider floating-point values as approximations to
2748 infinitely precise real numbers. If you are doing this, then you need
2749 to compute (by analyzing the code, or in some other way) the maximum or
2750 likely maximum error that the computation introduces, and allow for it
2751 when performing comparisons (and when producing output, but that's a
2752 different problem). In particular, instead of testing for equality, you
2753 would check to see whether the two values have ranges that overlap; and
2754 this is done with the relational operators, so equality comparisons are
2757 @item -Wtraditional @r{(C only)}
2758 @opindex Wtraditional
2759 Warn about certain constructs that behave differently in traditional and
2760 ISO C@. Also warn about ISO C constructs that have no traditional C
2761 equivalent, and/or problematic constructs which should be avoided.
2765 Macro parameters that appear within string literals in the macro body.
2766 In traditional C macro replacement takes place within string literals,
2767 but does not in ISO C@.
2770 In traditional C, some preprocessor directives did not exist.
2771 Traditional preprocessors would only consider a line to be a directive
2772 if the @samp{#} appeared in column 1 on the line. Therefore
2773 @option{-Wtraditional} warns about directives that traditional C
2774 understands but would ignore because the @samp{#} does not appear as the
2775 first character on the line. It also suggests you hide directives like
2776 @samp{#pragma} not understood by traditional C by indenting them. Some
2777 traditional implementations would not recognize @samp{#elif}, so it
2778 suggests avoiding it altogether.
2781 A function-like macro that appears without arguments.
2784 The unary plus operator.
2787 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
2788 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
2789 constants.) Note, these suffixes appear in macros defined in the system
2790 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
2791 Use of these macros in user code might normally lead to spurious
2792 warnings, however GCC's integrated preprocessor has enough context to
2793 avoid warning in these cases.
2796 A function declared external in one block and then used after the end of
2800 A @code{switch} statement has an operand of type @code{long}.
2803 A non-@code{static} function declaration follows a @code{static} one.
2804 This construct is not accepted by some traditional C compilers.
2807 The ISO type of an integer constant has a different width or
2808 signedness from its traditional type. This warning is only issued if
2809 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
2810 typically represent bit patterns, are not warned about.
2813 Usage of ISO string concatenation is detected.
2816 Initialization of automatic aggregates.
2819 Identifier conflicts with labels. Traditional C lacks a separate
2820 namespace for labels.
2823 Initialization of unions. If the initializer is zero, the warning is
2824 omitted. This is done under the assumption that the zero initializer in
2825 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
2826 initializer warnings and relies on default initialization to zero in the
2830 Conversions by prototypes between fixed/floating point values and vice
2831 versa. The absence of these prototypes when compiling with traditional
2832 C would cause serious problems. This is a subset of the possible
2833 conversion warnings, for the full set use @option{-Wconversion}.
2836 Use of ISO C style function definitions. This warning intentionally is
2837 @emph{not} issued for prototype declarations or variadic functions
2838 because these ISO C features will appear in your code when using
2839 libiberty's traditional C compatibility macros, @code{PARAMS} and
2840 @code{VPARAMS}. This warning is also bypassed for nested functions
2841 because that feature is already a GCC extension and thus not relevant to
2842 traditional C compatibility.
2845 @item -Wdeclaration-after-statement @r{(C only)}
2846 @opindex Wdeclaration-after-statement
2847 Warn when a declaration is found after a statement in a block. This
2848 construct, known from C++, was introduced with ISO C99 and is by default
2849 allowed in GCC@. It is not supported by ISO C90 and was not supported by
2850 GCC versions before GCC 3.0. @xref{Mixed Declarations}.
2854 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
2856 @item -Wendif-labels
2857 @opindex Wendif-labels
2858 Warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
2862 Warn whenever a local variable shadows another local variable, parameter or
2863 global variable or whenever a built-in function is shadowed.
2865 @item -Wlarger-than-@var{len}
2866 @opindex Wlarger-than
2867 Warn whenever an object of larger than @var{len} bytes is defined.
2869 @item -Wpointer-arith
2870 @opindex Wpointer-arith
2871 Warn about anything that depends on the ``size of'' a function type or
2872 of @code{void}. GNU C assigns these types a size of 1, for
2873 convenience in calculations with @code{void *} pointers and pointers
2876 @item -Wbad-function-cast @r{(C only)}
2877 @opindex Wbad-function-cast
2878 Warn whenever a function call is cast to a non-matching type.
2879 For example, warn if @code{int malloc()} is cast to @code{anything *}.
2883 Warn whenever a pointer is cast so as to remove a type qualifier from
2884 the target type. For example, warn if a @code{const char *} is cast
2885 to an ordinary @code{char *}.
2888 @opindex Wcast-align
2889 Warn whenever a pointer is cast such that the required alignment of the
2890 target is increased. For example, warn if a @code{char *} is cast to
2891 an @code{int *} on machines where integers can only be accessed at
2892 two- or four-byte boundaries.
2894 @item -Wwrite-strings
2895 @opindex Wwrite-strings
2896 When compiling C, give string constants the type @code{const
2897 char[@var{length}]} so that
2898 copying the address of one into a non-@code{const} @code{char *}
2899 pointer will get a warning; when compiling C++, warn about the
2900 deprecated conversion from string constants to @code{char *}.
2901 These warnings will help you find at
2902 compile time code that can try to write into a string constant, but
2903 only if you have been very careful about using @code{const} in
2904 declarations and prototypes. Otherwise, it will just be a nuisance;
2905 this is why we did not make @option{-Wall} request these warnings.
2908 @opindex Wconversion
2909 Warn if a prototype causes a type conversion that is different from what
2910 would happen to the same argument in the absence of a prototype. This
2911 includes conversions of fixed point to floating and vice versa, and
2912 conversions changing the width or signedness of a fixed point argument
2913 except when the same as the default promotion.
2915 Also, warn if a negative integer constant expression is implicitly
2916 converted to an unsigned type. For example, warn about the assignment
2917 @code{x = -1} if @code{x} is unsigned. But do not warn about explicit
2918 casts like @code{(unsigned) -1}.
2920 @item -Wsign-compare
2921 @opindex Wsign-compare
2922 @cindex warning for comparison of signed and unsigned values
2923 @cindex comparison of signed and unsigned values, warning
2924 @cindex signed and unsigned values, comparison warning
2925 Warn when a comparison between signed and unsigned values could produce
2926 an incorrect result when the signed value is converted to unsigned.
2927 This warning is also enabled by @option{-Wextra}; to get the other warnings
2928 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
2930 @item -Waggregate-return
2931 @opindex Waggregate-return
2932 Warn if any functions that return structures or unions are defined or
2933 called. (In languages where you can return an array, this also elicits
2936 @item -Wstrict-prototypes @r{(C only)}
2937 @opindex Wstrict-prototypes
2938 Warn if a function is declared or defined without specifying the
2939 argument types. (An old-style function definition is permitted without
2940 a warning if preceded by a declaration which specifies the argument
2943 @item -Wold-style-definition @r{(C only)}
2944 @opindex Wold-style-definition
2945 Warn if an old-style function definition is used. A warning is given
2946 even if there is a previous prototype.
2948 @item -Wmissing-prototypes @r{(C only)}
2949 @opindex Wmissing-prototypes
2950 Warn if a global function is defined without a previous prototype
2951 declaration. This warning is issued even if the definition itself
2952 provides a prototype. The aim is to detect global functions that fail
2953 to be declared in header files.
2955 @item -Wmissing-declarations @r{(C only)}
2956 @opindex Wmissing-declarations
2957 Warn if a global function is defined without a previous declaration.
2958 Do so even if the definition itself provides a prototype.
2959 Use this option to detect global functions that are not declared in
2962 @item -Wmissing-field-initializers
2963 @opindex Wmissing-field-initializers
2966 Warn if a structure's initializer has some fields missing. For
2967 example, the following code would cause such a warning, because
2968 @code{x.h} is implicitly zero:
2971 struct s @{ int f, g, h; @};
2972 struct s x = @{ 3, 4 @};
2975 This option does not warn about designated initializers, so the following
2976 modification would not trigger a warning:
2979 struct s @{ int f, g, h; @};
2980 struct s x = @{ .f = 3, .g = 4 @};
2983 This warning is included in @option{-Wextra}. To get other @option{-Wextra}
2984 warnings without this one, use @samp{-Wextra -Wno-missing-field-initializers}.
2986 @item -Wmissing-noreturn
2987 @opindex Wmissing-noreturn
2988 Warn about functions which might be candidates for attribute @code{noreturn}.
2989 Note these are only possible candidates, not absolute ones. Care should
2990 be taken to manually verify functions actually do not ever return before
2991 adding the @code{noreturn} attribute, otherwise subtle code generation
2992 bugs could be introduced. You will not get a warning for @code{main} in
2993 hosted C environments.
2995 @item -Wmissing-format-attribute
2996 @opindex Wmissing-format-attribute
2998 If @option{-Wformat} is enabled, also warn about functions which might be
2999 candidates for @code{format} attributes. Note these are only possible
3000 candidates, not absolute ones. GCC will guess that @code{format}
3001 attributes might be appropriate for any function that calls a function
3002 like @code{vprintf} or @code{vscanf}, but this might not always be the
3003 case, and some functions for which @code{format} attributes are
3004 appropriate may not be detected. This option has no effect unless
3005 @option{-Wformat} is enabled (possibly by @option{-Wall}).
3007 @item -Wno-multichar
3008 @opindex Wno-multichar
3010 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
3011 Usually they indicate a typo in the user's code, as they have
3012 implementation-defined values, and should not be used in portable code.
3014 @item -Wno-deprecated-declarations
3015 @opindex Wno-deprecated-declarations
3016 Do not warn about uses of functions, variables, and types marked as
3017 deprecated by using the @code{deprecated} attribute.
3018 (@pxref{Function Attributes}, @pxref{Variable Attributes},
3019 @pxref{Type Attributes}.)
3023 Warn if a structure is given the packed attribute, but the packed
3024 attribute has no effect on the layout or size of the structure.
3025 Such structures may be mis-aligned for little benefit. For
3026 instance, in this code, the variable @code{f.x} in @code{struct bar}
3027 will be misaligned even though @code{struct bar} does not itself
3028 have the packed attribute:
3035 @} __attribute__((packed));
3045 Warn if padding is included in a structure, either to align an element
3046 of the structure or to align the whole structure. Sometimes when this
3047 happens it is possible to rearrange the fields of the structure to
3048 reduce the padding and so make the structure smaller.
3050 @item -Wredundant-decls
3051 @opindex Wredundant-decls
3052 Warn if anything is declared more than once in the same scope, even in
3053 cases where multiple declaration is valid and changes nothing.
3055 @item -Wnested-externs @r{(C only)}
3056 @opindex Wnested-externs
3057 Warn if an @code{extern} declaration is encountered within a function.
3059 @item -Wunreachable-code
3060 @opindex Wunreachable-code
3061 Warn if the compiler detects that code will never be executed.
3063 This option is intended to warn when the compiler detects that at
3064 least a whole line of source code will never be executed, because
3065 some condition is never satisfied or because it is after a
3066 procedure that never returns.
3068 It is possible for this option to produce a warning even though there
3069 are circumstances under which part of the affected line can be executed,
3070 so care should be taken when removing apparently-unreachable code.
3072 For instance, when a function is inlined, a warning may mean that the
3073 line is unreachable in only one inlined copy of the function.
3075 This option is not made part of @option{-Wall} because in a debugging
3076 version of a program there is often substantial code which checks
3077 correct functioning of the program and is, hopefully, unreachable
3078 because the program does work. Another common use of unreachable
3079 code is to provide behavior which is selectable at compile-time.
3083 Warn if a function can not be inlined and it was declared as inline.
3084 Even with this option, the compiler will not warn about failures to
3085 inline functions declared in system headers.
3087 The compiler uses a variety of heuristics to determine whether or not
3088 to inline a function. For example, the compiler takes into account
3089 the size of the function being inlined and the the amount of inlining
3090 that has already been done in the current function. Therefore,
3091 seemingly insignificant changes in the source program can cause the
3092 warnings produced by @option{-Winline} to appear or disappear.
3094 @item -Wno-invalid-offsetof @r{(C++ only)}
3095 @opindex Wno-invalid-offsetof
3096 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
3097 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
3098 to a non-POD type is undefined. In existing C++ implementations,
3099 however, @samp{offsetof} typically gives meaningful results even when
3100 applied to certain kinds of non-POD types. (Such as a simple
3101 @samp{struct} that fails to be a POD type only by virtue of having a
3102 constructor.) This flag is for users who are aware that they are
3103 writing nonportable code and who have deliberately chosen to ignore the
3106 The restrictions on @samp{offsetof} may be relaxed in a future version
3107 of the C++ standard.
3110 @opindex Winvalid-pch
3111 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
3112 the search path but can't be used.
3116 @opindex Wno-long-long
3117 Warn if @samp{long long} type is used. This is default. To inhibit
3118 the warning messages, use @option{-Wno-long-long}. Flags
3119 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
3120 only when @option{-pedantic} flag is used.
3122 @item -Wvariadic-macros
3123 @opindex Wvariadic-macros
3124 @opindex Wno-variadic-macros
3125 Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU
3126 alternate syntax when in pedantic ISO C99 mode. This is default.
3127 To inhibit the warning messages, use @option{-Wno-variadic-macros}.
3129 @item -Wdisabled-optimization
3130 @opindex Wdisabled-optimization
3131 Warn if a requested optimization pass is disabled. This warning does
3132 not generally indicate that there is anything wrong with your code; it
3133 merely indicates that GCC's optimizers were unable to handle the code
3134 effectively. Often, the problem is that your code is too big or too
3135 complex; GCC will refuse to optimize programs when the optimization
3136 itself is likely to take inordinate amounts of time.
3140 Make all warnings into errors.
3143 @node Debugging Options
3144 @section Options for Debugging Your Program or GCC
3145 @cindex options, debugging
3146 @cindex debugging information options
3148 GCC has various special options that are used for debugging
3149 either your program or GCC:
3154 Produce debugging information in the operating system's native format
3155 (stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging
3158 On most systems that use stabs format, @option{-g} enables use of extra
3159 debugging information that only GDB can use; this extra information
3160 makes debugging work better in GDB but will probably make other debuggers
3162 refuse to read the program. If you want to control for certain whether
3163 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
3164 @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
3166 GCC allows you to use @option{-g} with
3167 @option{-O}. The shortcuts taken by optimized code may occasionally
3168 produce surprising results: some variables you declared may not exist
3169 at all; flow of control may briefly move where you did not expect it;
3170 some statements may not be executed because they compute constant
3171 results or their values were already at hand; some statements may
3172 execute in different places because they were moved out of loops.
3174 Nevertheless it proves possible to debug optimized output. This makes
3175 it reasonable to use the optimizer for programs that might have bugs.
3177 The following options are useful when GCC is generated with the
3178 capability for more than one debugging format.
3182 Produce debugging information for use by GDB@. This means to use the
3183 most expressive format available (DWARF 2, stabs, or the native format
3184 if neither of those are supported), including GDB extensions if at all
3189 Produce debugging information in stabs format (if that is supported),
3190 without GDB extensions. This is the format used by DBX on most BSD
3191 systems. On MIPS, Alpha and System V Release 4 systems this option
3192 produces stabs debugging output which is not understood by DBX or SDB@.
3193 On System V Release 4 systems this option requires the GNU assembler.
3195 @item -feliminate-unused-debug-symbols
3196 @opindex feliminate-unused-debug-symbols
3197 Produce debugging information in stabs format (if that is supported),
3198 for only symbols that are actually used.
3202 Produce debugging information in stabs format (if that is supported),
3203 using GNU extensions understood only by the GNU debugger (GDB)@. The
3204 use of these extensions is likely to make other debuggers crash or
3205 refuse to read the program.
3209 Produce debugging information in COFF format (if that is supported).
3210 This is the format used by SDB on most System V systems prior to
3215 Produce debugging information in XCOFF format (if that is supported).
3216 This is the format used by the DBX debugger on IBM RS/6000 systems.
3220 Produce debugging information in XCOFF format (if that is supported),
3221 using GNU extensions understood only by the GNU debugger (GDB)@. The
3222 use of these extensions is likely to make other debuggers crash or
3223 refuse to read the program, and may cause assemblers other than the GNU
3224 assembler (GAS) to fail with an error.
3228 Produce debugging information in DWARF version 2 format (if that is
3229 supported). This is the format used by DBX on IRIX 6. With this
3230 option, GCC uses features of DWARF version 3 when they are useful;
3231 version 3 is upward compatible with version 2, but may still cause
3232 problems for older debuggers.
3236 Produce debugging information in VMS debug format (if that is
3237 supported). This is the format used by DEBUG on VMS systems.
3240 @itemx -ggdb@var{level}
3241 @itemx -gstabs@var{level}
3242 @itemx -gcoff@var{level}
3243 @itemx -gxcoff@var{level}
3244 @itemx -gvms@var{level}
3245 Request debugging information and also use @var{level} to specify how
3246 much information. The default level is 2.
3248 Level 1 produces minimal information, enough for making backtraces in
3249 parts of the program that you don't plan to debug. This includes
3250 descriptions of functions and external variables, but no information
3251 about local variables and no line numbers.
3253 Level 3 includes extra information, such as all the macro definitions
3254 present in the program. Some debuggers support macro expansion when
3255 you use @option{-g3}.
3257 @option{-gdwarf-2} does not accept a concatenated debug level, because
3258 GCC used to support an option @option{-gdwarf} that meant to generate
3259 debug information in version 1 of the DWARF format (which is very
3260 different from version 2), and it would have been too confusing. That
3261 debug format is long obsolete, but the option cannot be changed now.
3262 Instead use an additional @option{-g@var{level}} option to change the
3263 debug level for DWARF2.
3265 @item -feliminate-dwarf2-dups
3266 @opindex feliminate-dwarf2-dups
3267 Compress DWARF2 debugging information by eliminating duplicated
3268 information about each symbol. This option only makes sense when
3269 generating DWARF2 debugging information with @option{-gdwarf-2}.
3271 @cindex @command{prof}
3274 Generate extra code to write profile information suitable for the
3275 analysis program @command{prof}. You must use this option when compiling
3276 the source files you want data about, and you must also use it when
3279 @cindex @command{gprof}
3282 Generate extra code to write profile information suitable for the
3283 analysis program @command{gprof}. You must use this option when compiling
3284 the source files you want data about, and you must also use it when
3289 Makes the compiler print out each function name as it is compiled, and
3290 print some statistics about each pass when it finishes.
3293 @opindex ftime-report
3294 Makes the compiler print some statistics about the time consumed by each
3295 pass when it finishes.
3298 @opindex fmem-report
3299 Makes the compiler print some statistics about permanent memory
3300 allocation when it finishes.
3302 @item -fprofile-arcs
3303 @opindex fprofile-arcs
3304 Add code so that program flow @dfn{arcs} are instrumented. During
3305 execution the program records how many times each branch and call is
3306 executed and how many times it is taken or returns. When the compiled
3307 program exits it saves this data to a file called
3308 @file{@var{auxname}.gcda} for each source file. The data may be used for
3309 profile-directed optimizations (@option{-fbranch-probabilities}), or for
3310 test coverage analysis (@option{-ftest-coverage}). Each object file's
3311 @var{auxname} is generated from the name of the output file, if
3312 explicitly specified and it is not the final executable, otherwise it is
3313 the basename of the source file. In both cases any suffix is removed
3314 (e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
3315 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
3320 Compile the source files with @option{-fprofile-arcs} plus optimization
3321 and code generation options. For test coverage analysis, use the
3322 additional @option{-ftest-coverage} option. You do not need to profile
3323 every source file in a program.
3326 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
3327 (the latter implies the former).
3330 Run the program on a representative workload to generate the arc profile
3331 information. This may be repeated any number of times. You can run
3332 concurrent instances of your program, and provided that the file system
3333 supports locking, the data files will be correctly updated. Also
3334 @code{fork} calls are detected and correctly handled (double counting
3338 For profile-directed optimizations, compile the source files again with
3339 the same optimization and code generation options plus
3340 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
3341 Control Optimization}).
3344 For test coverage analysis, use @command{gcov} to produce human readable
3345 information from the @file{.gcno} and @file{.gcda} files. Refer to the
3346 @command{gcov} documentation for further information.
3350 With @option{-fprofile-arcs}, for each function of your program GCC
3351 creates a program flow graph, then finds a spanning tree for the graph.
3352 Only arcs that are not on the spanning tree have to be instrumented: the
3353 compiler adds code to count the number of times that these arcs are
3354 executed. When an arc is the only exit or only entrance to a block, the
3355 instrumentation code can be added to the block; otherwise, a new basic
3356 block must be created to hold the instrumentation code.
3358 @item -ftree-based-profiling
3359 @opindex ftree-based-profiling
3360 This option is used in addition to @option{-fprofile-arcs} or
3361 @option{-fbranch-probabilities} to control whether those optimizations
3362 are performed on a tree-based or rtl-based internal representation.
3363 If you use this option when compiling with @option{-fprofile-arcs},
3364 you must also use it when compiling later with @option{-fbranch-probabilities}.
3365 Currently the tree-based optimization is in an early stage of
3366 development, and this option is recommended only for those people
3367 working on improving it.
3370 @item -ftest-coverage
3371 @opindex ftest-coverage
3372 Produce a notes file that the @command{gcov} code-coverage utility
3373 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
3374 show program coverage. Each source file's note file is called
3375 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
3376 above for a description of @var{auxname} and instructions on how to
3377 generate test coverage data. Coverage data will match the source files
3378 more closely, if you do not optimize.
3380 @item -d@var{letters}
3381 @item -fdump-rtl-@var{pass}
3383 Says to make debugging dumps during compilation at times specified by
3384 @var{letters}. This is used for debugging the RTL-based passes of the
3385 compiler. The file names for most of the dumps are made by appending a
3386 pass number and a word to the @var{dumpname}. @var{dumpname} is generated
3387 from the name of the output file, if explicitly specified and it is not
3388 an executable, otherwise it is the basename of the source file.
3390 Most debug dumps can be enabled either passing a letter to the @option{-d}
3391 option, or with a long @option{-fdump-rtl} switch; here are the possible
3392 letters for use in @var{letters} and @var{pass}, and their meanings:
3397 Annotate the assembler output with miscellaneous debugging information.
3400 @itemx -fdump-rtl-bp
3402 @opindex fdump-rtl-bp
3403 Dump after computing branch probabilities, to @file{@var{file}.09.bp}.
3406 @itemx -fdump-rtl-bbro
3408 @opindex fdump-rtl-bbro
3409 Dump after block reordering, to @file{@var{file}.30.bbro}.
3412 @itemx -fdump-rtl-combine
3414 @opindex fdump-rtl-combine
3415 Dump after instruction combination, to the file @file{@var{file}.17.combine}.
3418 @itemx -fdump-rtl-ce1
3419 @itemx -fdump-rtl-ce2
3421 @opindex fdump-rtl-ce1
3422 @opindex fdump-rtl-ce2
3423 @option{-dC} and @option{-fdump-rtl-ce1} enable dumping after the
3424 first if conversion, to the file @file{@var{file}.11.ce1}. @option{-dC}
3425 and @option{-fdump-rtl-ce2} enable dumping after the second if
3426 conversion, to the file @file{@var{file}.18.ce2}.
3429 @itemx -fdump-rtl-btl
3430 @itemx -fdump-rtl-dbr
3432 @opindex fdump-rtl-btl
3433 @opindex fdump-rtl-dbr
3434 @option{-dd} and @option{-fdump-rtl-btl} enable dumping after branch
3435 target load optimization, to to @file{@var{file}.31.btl}. @option{-dd}
3436 and @option{-fdump-rtl-dbr} enable dumping after delayed branch
3437 scheduling, to @file{@var{file}.36.dbr}.
3441 Dump all macro definitions, at the end of preprocessing, in addition to
3445 @itemx -fdump-rtl-ce3
3447 @opindex fdump-rtl-ce3
3448 Dump after the third if conversion, to @file{@var{file}.28.ce3}.
3451 @itemx -fdump-rtl-cfg
3452 @itemx -fdump-rtl-life
3454 @opindex fdump-rtl-cfg
3455 @opindex fdump-rtl-life
3456 @option{-df} and @option{-fdump-rtl-cfg} enable dumping after control
3457 and data flow analysis, to @file{@var{file}.08.cfg}. @option{-df}
3458 and @option{-fdump-rtl-cfg} enable dumping dump after life analysis,
3459 to @file{@var{file}.16.life}.
3462 @itemx -fdump-rtl-greg
3464 @opindex fdump-rtl-greg
3465 Dump after global register allocation, to @file{@var{file}.23.greg}.
3468 @itemx -fdump-rtl-gcse
3469 @itemx -fdump-rtl-bypass
3471 @opindex fdump-rtl-gcse
3472 @opindex fdump-rtl-bypass
3473 @option{-dG} and @option{-fdump-rtl-gcse} enable dumping after GCSE, to
3474 @file{@var{file}.05.gcse}. @option{-dG} and @option{-fdump-rtl-bypass}
3475 enable dumping after jump bypassing and control flow optimizations, to
3476 @file{@var{file}.07.bypass}.
3479 @itemx -fdump-rtl-eh
3481 @opindex fdump-rtl-eh
3482 Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
3485 @itemx -fdump-rtl-sibling
3487 @opindex fdump-rtl-sibling
3488 Dump after sibling call optimizations, to @file{@var{file}.01.sibling}.
3491 @itemx -fdump-rtl-jump
3493 @opindex fdump-rtl-jump
3494 Dump after the first jump optimization, to @file{@var{file}.03.jump}.
3497 @itemx -fdump-rtl-stack
3499 @opindex fdump-rtl-stack
3500 Dump after conversion from registers to stack, to @file{@var{file}.33.stack}.
3503 @itemx -fdump-rtl-lreg
3505 @opindex fdump-rtl-lreg
3506 Dump after local register allocation, to @file{@var{file}.22.lreg}.
3509 @itemx -fdump-rtl-loop
3510 @itemx -fdump-rtl-loop2
3512 @opindex fdump-rtl-loop
3513 @opindex fdump-rtl-loop2
3514 @option{-dL} and @option{-fdump-rtl-loop} enable dumping after the first
3515 loop optimization pass, to @file{@var{file}.06.loop}. @option{-dL} and
3516 @option{-fdump-rtl-loop2} enable dumping after the second pass, to
3517 @file{@var{file}.13.loop2}.
3520 @itemx -fdump-rtl-sms
3522 @opindex fdump-rtl-sms
3523 Dump after modulo scheduling, to @file{@var{file}.20.sms}.
3526 @itemx -fdump-rtl-mach
3528 @opindex fdump-rtl-mach
3529 Dump after performing the machine dependent reorganization pass, to
3530 @file{@var{file}.35.mach}.
3533 @itemx -fdump-rtl-rnreg
3535 @opindex fdump-rtl-rnreg
3536 Dump after register renumbering, to @file{@var{file}.29.rnreg}.
3539 @itemx -fdump-rtl-regmove
3541 @opindex fdump-rtl-regmove
3542 Dump after the register move pass, to @file{@var{file}.19.regmove}.
3545 @itemx -fdump-rtl-postreload
3547 @opindex fdump-rtl-postreload
3548 Dump after post-reload optimizations, to @file{@var{file}.24.postreload}.
3551 @itemx -fdump-rtl-expand
3553 @opindex fdump-rtl-expand
3554 Dump after RTL generation, to @file{@var{file}.00.expand}.
3557 @itemx -fdump-rtl-sched2
3559 @opindex fdump-rtl-sched2
3560 Dump after the second scheduling pass, to @file{@var{file}.32.sched2}.
3563 @itemx -fdump-rtl-cse
3565 @opindex fdump-rtl-cse
3566 Dump after CSE (including the jump optimization that sometimes follows
3567 CSE), to @file{@var{file}.04.cse}.
3570 @itemx -fdump-rtl-sched
3572 @opindex fdump-rtl-sched
3573 Dump after the first scheduling pass, to @file{@var{file}.21.sched}.
3576 @itemx -fdump-rtl-cse2
3578 @opindex fdump-rtl-cse2
3579 Dump after the second CSE pass (including the jump optimization that
3580 sometimes follows CSE), to @file{@var{file}.15.cse2}.
3583 @itemx -fdump-rtl-tracer
3585 @opindex fdump-rtl-tracer
3586 Dump after running tracer, to @file{@var{file}.12.tracer}.
3589 @itemx -fdump-rtl-vpt
3590 @itemx -fdump-rtl-vartrack
3592 @opindex fdump-rtl-vpt
3593 @opindex fdump-rtl-vartrack
3594 @option{-dV} and @option{-fdump-rtl-vpt} enable dumping after the value
3595 profile transformations, to @file{@var{file}.10.vpt}. @option{-dV}
3596 and @option{-fdump-rtl-vartrack} enable dumping after variable tracking,
3597 to @file{@var{file}.34.vartrack}.
3600 @itemx -fdump-rtl-flow2
3602 @opindex fdump-rtl-flow2
3603 Dump after the second flow pass, to @file{@var{file}.26.flow2}.
3606 @itemx -fdump-rtl-peephole2
3608 @opindex fdump-rtl-peephole2
3609 Dump after the peephole pass, to @file{@var{file}.27.peephole2}.
3612 @itemx -fdump-rtl-web
3614 @opindex fdump-rtl-web
3615 Dump after live range splitting, to @file{@var{file}.14.web}.
3618 @itemx -fdump-rtl-all
3620 @opindex fdump-rtl-all
3621 Produce all the dumps listed above.
3625 Produce a core dump whenever an error occurs.
3629 Print statistics on memory usage, at the end of the run, to
3634 Annotate the assembler output with a comment indicating which
3635 pattern and alternative was used. The length of each instruction is
3640 Dump the RTL in the assembler output as a comment before each instruction.
3641 Also turns on @option{-dp} annotation.
3645 For each of the other indicated dump files (either with @option{-d} or
3646 @option{-fdump-rtl-@var{pass}}), dump a representation of the control flow
3647 graph suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
3651 Just generate RTL for a function instead of compiling it. Usually used
3652 with @samp{r} (@option{-fdump-rtl-expand}).
3656 Dump debugging information during parsing, to standard error.
3659 @item -fdump-unnumbered
3660 @opindex fdump-unnumbered
3661 When doing debugging dumps (see @option{-d} option above), suppress instruction
3662 numbers and line number note output. This makes it more feasible to
3663 use diff on debugging dumps for compiler invocations with different
3664 options, in particular with and without @option{-g}.
3666 @item -fdump-translation-unit @r{(C and C++ only)}
3667 @itemx -fdump-translation-unit-@var{options} @r{(C and C++ only)}
3668 @opindex fdump-translation-unit
3669 Dump a representation of the tree structure for the entire translation
3670 unit to a file. The file name is made by appending @file{.tu} to the
3671 source file name. If the @samp{-@var{options}} form is used, @var{options}
3672 controls the details of the dump as described for the
3673 @option{-fdump-tree} options.
3675 @item -fdump-class-hierarchy @r{(C++ only)}
3676 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
3677 @opindex fdump-class-hierarchy
3678 Dump a representation of each class's hierarchy and virtual function
3679 table layout to a file. The file name is made by appending @file{.class}
3680 to the source file name. If the @samp{-@var{options}} form is used,
3681 @var{options} controls the details of the dump as described for the
3682 @option{-fdump-tree} options.
3684 @item -fdump-ipa-@var{switch}
3686 Control the dumping at various stages of inter-procedural analysis
3687 language tree to a file. The file name is generated by appending a switch
3688 specific suffix to the source file name. The following dumps are possible:
3692 Enables all inter-procedural analysis dumps; currently the only produced
3693 dump is the @samp{cgraph} dump.
3696 Dumps information about call-graph optimization, unused function removal,
3697 and inlining decisions.
3700 @item -fdump-tree-@var{switch} @r{(C and C++ only)}
3701 @itemx -fdump-tree-@var{switch}-@var{options} @r{(C and C++ only)}
3703 Control the dumping at various stages of processing the intermediate
3704 language tree to a file. The file name is generated by appending a switch
3705 specific suffix to the source file name. If the @samp{-@var{options}}
3706 form is used, @var{options} is a list of @samp{-} separated options that
3707 control the details of the dump. Not all options are applicable to all
3708 dumps, those which are not meaningful will be ignored. The following
3709 options are available
3713 Print the address of each node. Usually this is not meaningful as it
3714 changes according to the environment and source file. Its primary use
3715 is for tying up a dump file with a debug environment.
3717 Inhibit dumping of members of a scope or body of a function merely
3718 because that scope has been reached. Only dump such items when they
3719 are directly reachable by some other path. When dumping pretty-printed
3720 trees, this option inhibits dumping the bodies of control structures.
3722 Print a raw representation of the tree. By default, trees are
3723 pretty-printed into a C-like representation.
3725 Enable more detailed dumps (not honored by every dump option).
3727 Enable dumping various statistics about the pass (not honored by every dump
3730 Enable showing basic block boundaries (disabled in raw dumps).
3732 Enable showing virtual operands for every statement.
3734 Enable showing line numbers for statements.
3736 Enable showing the unique ID (@code{DECL_UID}) for each variable.
3738 Turn on all options, except @option{raw}, @option{slim} and @option{lineno}.
3741 The following tree dumps are possible:
3745 Dump before any tree based optimization, to @file{@var{file}.original}.
3748 Dump after all tree based optimization, to @file{@var{file}.optimized}.
3751 Dump after function inlining, to @file{@var{file}.inlined}.
3754 @opindex fdump-tree-gimple
3755 Dump each function before and after the gimplification pass to a file. The
3756 file name is made by appending @file{.gimple} to the source file name.
3759 @opindex fdump-tree-cfg
3760 Dump the control flow graph of each function to a file. The file name is
3761 made by appending @file{.cfg} to the source file name.
3764 @opindex fdump-tree-vcg
3765 Dump the control flow graph of each function to a file in VCG format. The
3766 file name is made by appending @file{.vcg} to the source file name. Note
3767 that if the file contains more than one function, the generated file cannot
3768 be used directly by VCG@. You will need to cut and paste each function's
3769 graph into its own separate file first.
3772 @opindex fdump-tree-ch
3773 Dump each function after copying loop headers. The file name is made by
3774 appending @file{.ch} to the source file name.
3777 @opindex fdump-tree-ssa
3778 Dump SSA related information to a file. The file name is made by appending
3779 @file{.ssa} to the source file name.
3782 @opindex fdump-tree-alias
3783 Dump aliasing information for each function. The file name is made by
3784 appending @file{.alias} to the source file name.
3787 @opindex fdump-tree-ccp
3788 Dump each function after CCP@. The file name is made by appending
3789 @file{.ccp} to the source file name.
3792 @opindex fdump-tree-pre
3793 Dump trees after partial redundancy elimination. The file name is made
3794 by appending @file{.pre} to the source file name.
3797 @opindex fdump-tree-fre
3798 Dump trees after full redundancy elimination. The file name is made
3799 by appending @file{.fre} to the source file name.
3802 @opindex fdump-tree-dce
3803 Dump each function after dead code elimination. The file name is made by
3804 appending @file{.dce} to the source file name.
3807 @opindex fdump-tree-mudflap
3808 Dump each function after adding mudflap instrumentation. The file name is
3809 made by appending @file{.mudflap} to the source file name.
3812 @opindex fdump-tree-sra
3813 Dump each function after performing scalar replacement of aggregates. The
3814 file name is made by appending @file{.sra} to the source file name.
3817 @opindex fdump-tree-dom
3818 Dump each function after applying dominator tree optimizations. The file
3819 name is made by appending @file{.dom} to the source file name.
3822 @opindex fdump-tree-dse
3823 Dump each function after applying dead store elimination. The file
3824 name is made by appending @file{.dse} to the source file name.
3827 @opindex fdump-tree-phiopt
3828 Dump each function after optimizing PHI nodes into straightline code. The file
3829 name is made by appending @file{.phiopt} to the source file name.
3832 @opindex fdump-tree-forwprop
3833 Dump each function after forward propagating single use variables. The file
3834 name is made by appending @file{.forwprop} to the source file name.
3837 @opindex fdump-tree-copyrename
3838 Dump each function after applying the copy rename optimization. The file
3839 name is made by appending @file{.copyrename} to the source file name.
3842 @opindex fdump-tree-nrv
3843 Dump each function after applying the named return value optimization on
3844 generic trees. The file name is made by appending @file{.nrv} to the source
3848 @opindex fdump-tree-vect
3849 Dump each function after applying vectorization of loops. The file name is
3850 made by appending @file{.vect} to the source file name.
3853 @opindex fdump-tree-all
3854 Enable all the available tree dumps with the flags provided in this option.
3857 @item -frandom-seed=@var{string}
3858 @opindex frandom-string
3859 This option provides a seed that GCC uses when it would otherwise use
3860 random numbers. It is used to generate certain symbol names
3861 that have to be different in every compiled file. It is also used to
3862 place unique stamps in coverage data files and the object files that
3863 produce them. You can use the @option{-frandom-seed} option to produce
3864 reproducibly identical object files.
3866 The @var{string} should be different for every file you compile.
3868 @item -fsched-verbose=@var{n}
3869 @opindex fsched-verbose
3870 On targets that use instruction scheduling, this option controls the
3871 amount of debugging output the scheduler prints. This information is
3872 written to standard error, unless @option{-dS} or @option{-dR} is
3873 specified, in which case it is output to the usual dump
3874 listing file, @file{.sched} or @file{.sched2} respectively. However
3875 for @var{n} greater than nine, the output is always printed to standard
3878 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
3879 same information as @option{-dRS}. For @var{n} greater than one, it
3880 also output basic block probabilities, detailed ready list information
3881 and unit/insn info. For @var{n} greater than two, it includes RTL
3882 at abort point, control-flow and regions info. And for @var{n} over
3883 four, @option{-fsched-verbose} also includes dependence info.
3887 Store the usual ``temporary'' intermediate files permanently; place them
3888 in the current directory and name them based on the source file. Thus,
3889 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
3890 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
3891 preprocessed @file{foo.i} output file even though the compiler now
3892 normally uses an integrated preprocessor.
3896 Report the CPU time taken by each subprocess in the compilation
3897 sequence. For C source files, this is the compiler proper and assembler
3898 (plus the linker if linking is done). The output looks like this:
3905 The first number on each line is the ``user time'', that is time spent
3906 executing the program itself. The second number is ``system time'',
3907 time spent executing operating system routines on behalf of the program.
3908 Both numbers are in seconds.
3910 @item -fvar-tracking
3911 @opindex fvar-tracking
3912 Run variable tracking pass. It computes where variables are stored at each
3913 position in code. Better debugging information is then generated
3914 (if the debugging information format supports this information).
3916 It is enabled by default when compiling with optimization (@option{-Os},
3917 @option{-O}, @option{-O2}, ...), debugging information (@option{-g}) and
3918 the debug info format supports it.
3920 @item -print-file-name=@var{library}
3921 @opindex print-file-name
3922 Print the full absolute name of the library file @var{library} that
3923 would be used when linking---and don't do anything else. With this
3924 option, GCC does not compile or link anything; it just prints the
3927 @item -print-multi-directory
3928 @opindex print-multi-directory
3929 Print the directory name corresponding to the multilib selected by any
3930 other switches present in the command line. This directory is supposed
3931 to exist in @env{GCC_EXEC_PREFIX}.
3933 @item -print-multi-lib
3934 @opindex print-multi-lib
3935 Print the mapping from multilib directory names to compiler switches
3936 that enable them. The directory name is separated from the switches by
3937 @samp{;}, and each switch starts with an @samp{@@} instead of the
3938 @samp{-}, without spaces between multiple switches. This is supposed to
3939 ease shell-processing.
3941 @item -print-prog-name=@var{program}
3942 @opindex print-prog-name
3943 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
3945 @item -print-libgcc-file-name
3946 @opindex print-libgcc-file-name
3947 Same as @option{-print-file-name=libgcc.a}.
3949 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
3950 but you do want to link with @file{libgcc.a}. You can do
3953 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
3956 @item -print-search-dirs
3957 @opindex print-search-dirs
3958 Print the name of the configured installation directory and a list of
3959 program and library directories @command{gcc} will search---and don't do anything else.
3961 This is useful when @command{gcc} prints the error message
3962 @samp{installation problem, cannot exec cpp0: No such file or directory}.
3963 To resolve this you either need to put @file{cpp0} and the other compiler
3964 components where @command{gcc} expects to find them, or you can set the environment
3965 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
3966 Don't forget the trailing @samp{/}.
3967 @xref{Environment Variables}.
3970 @opindex dumpmachine
3971 Print the compiler's target machine (for example,
3972 @samp{i686-pc-linux-gnu})---and don't do anything else.
3975 @opindex dumpversion
3976 Print the compiler version (for example, @samp{3.0})---and don't do
3981 Print the compiler's built-in specs---and don't do anything else. (This
3982 is used when GCC itself is being built.) @xref{Spec Files}.
3984 @item -feliminate-unused-debug-types
3985 @opindex feliminate-unused-debug-types
3986 Normally, when producing DWARF2 output, GCC will emit debugging
3987 information for all types declared in a compilation
3988 unit, regardless of whether or not they are actually used
3989 in that compilation unit. Sometimes this is useful, such as
3990 if, in the debugger, you want to cast a value to a type that is
3991 not actually used in your program (but is declared). More often,
3992 however, this results in a significant amount of wasted space.
3993 With this option, GCC will avoid producing debug symbol output
3994 for types that are nowhere used in the source file being compiled.
3997 @node Optimize Options
3998 @section Options That Control Optimization
3999 @cindex optimize options
4000 @cindex options, optimization
4002 These options control various sorts of optimizations.
4004 Without any optimization option, the compiler's goal is to reduce the
4005 cost of compilation and to make debugging produce the expected
4006 results. Statements are independent: if you stop the program with a
4007 breakpoint between statements, you can then assign a new value to any
4008 variable or change the program counter to any other statement in the
4009 function and get exactly the results you would expect from the source
4012 Turning on optimization flags makes the compiler attempt to improve
4013 the performance and/or code size at the expense of compilation time
4014 and possibly the ability to debug the program.
4016 The compiler performs optimization based on the knowledge it has of
4017 the program. Optimization levels @option{-O2} and above, in
4018 particular, enable @emph{unit-at-a-time} mode, which allows the
4019 compiler to consider information gained from later functions in
4020 the file when compiling a function. Compiling multiple files at
4021 once to a single output file in @emph{unit-at-a-time} mode allows
4022 the compiler to use information gained from all of the files when
4023 compiling each of them.
4025 Not all optimizations are controlled directly by a flag. Only
4026 optimizations that have a flag are listed.
4033 Optimize. Optimizing compilation takes somewhat more time, and a lot
4034 more memory for a large function.
4036 With @option{-O}, the compiler tries to reduce code size and execution
4037 time, without performing any optimizations that take a great deal of
4040 @option{-O} turns on the following optimization flags:
4041 @gccoptlist{-fdefer-pop @gol
4042 -fmerge-constants @gol
4044 -floop-optimize @gol
4045 -fif-conversion @gol
4046 -fif-conversion2 @gol
4047 -fdelayed-branch @gol
4048 -fguess-branch-probability @gol
4051 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
4052 where doing so does not interfere with debugging.
4056 Optimize even more. GCC performs nearly all supported optimizations
4057 that do not involve a space-speed tradeoff. The compiler does not
4058 perform loop unrolling or function inlining when you specify @option{-O2}.
4059 As compared to @option{-O}, this option increases both compilation time
4060 and the performance of the generated code.
4062 @option{-O2} turns on all optimization flags specified by @option{-O}. It
4063 also turns on the following optimization flags:
4064 @gccoptlist{-fforce-mem @gol
4065 -foptimize-sibling-calls @gol
4066 -fstrength-reduce @gol
4067 -fcse-follow-jumps -fcse-skip-blocks @gol
4068 -frerun-cse-after-loop -frerun-loop-opt @gol
4069 -fgcse -fgcse-lm -fgcse-sm -fgcse-las @gol
4070 -fdelete-null-pointer-checks @gol
4071 -fexpensive-optimizations @gol
4073 -fschedule-insns -fschedule-insns2 @gol
4074 -fsched-interblock -fsched-spec @gol
4077 -freorder-blocks -freorder-functions @gol
4078 -fstrict-aliasing @gol
4079 -funit-at-a-time @gol
4080 -falign-functions -falign-jumps @gol
4081 -falign-loops -falign-labels @gol
4084 Please note the warning under @option{-fgcse} about
4085 invoking @option{-O2} on programs that use computed gotos.
4089 Optimize yet more. @option{-O3} turns on all optimizations specified by
4090 @option{-O2} and also turns on the @option{-finline-functions},
4091 @option{-fweb} and @option{-fgcse-after-reload} options.
4095 Do not optimize. This is the default.
4099 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
4100 do not typically increase code size. It also performs further
4101 optimizations designed to reduce code size.
4103 @option{-Os} disables the following optimization flags:
4104 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
4105 -falign-labels -freorder-blocks -freorder-blocks-and-partition -fprefetch-loop-arrays}
4107 If you use multiple @option{-O} options, with or without level numbers,
4108 the last such option is the one that is effective.
4111 Options of the form @option{-f@var{flag}} specify machine-independent
4112 flags. Most flags have both positive and negative forms; the negative
4113 form of @option{-ffoo} would be @option{-fno-foo}. In the table
4114 below, only one of the forms is listed---the one you typically will
4115 use. You can figure out the other form by either removing @samp{no-}
4118 The following options control specific optimizations. They are either
4119 activated by @option{-O} options or are related to ones that are. You
4120 can use the following flags in the rare cases when ``fine-tuning'' of
4121 optimizations to be performed is desired.
4124 @item -fno-default-inline
4125 @opindex fno-default-inline
4126 Do not make member functions inline by default merely because they are
4127 defined inside the class scope (C++ only). Otherwise, when you specify
4128 @w{@option{-O}}, member functions defined inside class scope are compiled
4129 inline by default; i.e., you don't need to add @samp{inline} in front of
4130 the member function name.
4132 @item -fno-defer-pop
4133 @opindex fno-defer-pop
4134 Always pop the arguments to each function call as soon as that function
4135 returns. For machines which must pop arguments after a function call,
4136 the compiler normally lets arguments accumulate on the stack for several
4137 function calls and pops them all at once.
4139 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4143 Force memory operands to be copied into registers before doing
4144 arithmetic on them. This produces better code by making all memory
4145 references potential common subexpressions. When they are not common
4146 subexpressions, instruction combination should eliminate the separate
4149 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4152 @opindex fforce-addr
4153 Force memory address constants to be copied into registers before
4154 doing arithmetic on them. This may produce better code just as
4155 @option{-fforce-mem} may.
4157 @item -fomit-frame-pointer
4158 @opindex fomit-frame-pointer
4159 Don't keep the frame pointer in a register for functions that
4160 don't need one. This avoids the instructions to save, set up and
4161 restore frame pointers; it also makes an extra register available
4162 in many functions. @strong{It also makes debugging impossible on
4165 On some machines, such as the VAX, this flag has no effect, because
4166 the standard calling sequence automatically handles the frame pointer
4167 and nothing is saved by pretending it doesn't exist. The
4168 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
4169 whether a target machine supports this flag. @xref{Registers,,Register
4170 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
4172 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4174 @item -foptimize-sibling-calls
4175 @opindex foptimize-sibling-calls
4176 Optimize sibling and tail recursive calls.
4178 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4182 Don't pay attention to the @code{inline} keyword. Normally this option
4183 is used to keep the compiler from expanding any functions inline.
4184 Note that if you are not optimizing, no functions can be expanded inline.
4186 @item -finline-functions
4187 @opindex finline-functions
4188 Integrate all simple functions into their callers. The compiler
4189 heuristically decides which functions are simple enough to be worth
4190 integrating in this way.
4192 If all calls to a given function are integrated, and the function is
4193 declared @code{static}, then the function is normally not output as
4194 assembler code in its own right.
4196 Enabled at level @option{-O3}.
4198 @item -finline-limit=@var{n}
4199 @opindex finline-limit
4200 By default, GCC limits the size of functions that can be inlined. This flag
4201 allows the control of this limit for functions that are explicitly marked as
4202 inline (i.e., marked with the inline keyword or defined within the class
4203 definition in c++). @var{n} is the size of functions that can be inlined in
4204 number of pseudo instructions (not counting parameter handling). The default
4205 value of @var{n} is 600.
4206 Increasing this value can result in more inlined code at
4207 the cost of compilation time and memory consumption. Decreasing usually makes
4208 the compilation faster and less code will be inlined (which presumably
4209 means slower programs). This option is particularly useful for programs that
4210 use inlining heavily such as those based on recursive templates with C++.
4212 Inlining is actually controlled by a number of parameters, which may be
4213 specified individually by using @option{--param @var{name}=@var{value}}.
4214 The @option{-finline-limit=@var{n}} option sets some of these parameters
4218 @item max-inline-insns-single
4219 is set to @var{n}/2.
4220 @item max-inline-insns-auto
4221 is set to @var{n}/2.
4222 @item min-inline-insns
4223 is set to 130 or @var{n}/4, whichever is smaller.
4224 @item max-inline-insns-rtl
4228 See below for a documentation of the individual
4229 parameters controlling inlining.
4231 @emph{Note:} pseudo instruction represents, in this particular context, an
4232 abstract measurement of function's size. In no way, it represents a count
4233 of assembly instructions and as such its exact meaning might change from one
4234 release to an another.
4236 @item -fkeep-inline-functions
4237 @opindex fkeep-inline-functions
4238 In C, emit @code{static} functions that are declared @code{inline}
4239 into the object file, even if the function has been inlined into all
4240 of its callers. This switch does not affect functions using the
4241 @code{extern inline} extension in GNU C@. In C++, emit any and all
4242 inline functions into the object file.
4244 @item -fkeep-static-consts
4245 @opindex fkeep-static-consts
4246 Emit variables declared @code{static const} when optimization isn't turned
4247 on, even if the variables aren't referenced.
4249 GCC enables this option by default. If you want to force the compiler to
4250 check if the variable was referenced, regardless of whether or not
4251 optimization is turned on, use the @option{-fno-keep-static-consts} option.
4253 @item -fmerge-constants
4254 Attempt to merge identical constants (string constants and floating point
4255 constants) across compilation units.
4257 This option is the default for optimized compilation if the assembler and
4258 linker support it. Use @option{-fno-merge-constants} to inhibit this
4261 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4263 @item -fmerge-all-constants
4264 Attempt to merge identical constants and identical variables.
4266 This option implies @option{-fmerge-constants}. In addition to
4267 @option{-fmerge-constants} this considers e.g.@: even constant initialized
4268 arrays or initialized constant variables with integral or floating point
4269 types. Languages like C or C++ require each non-automatic variable to
4270 have distinct location, so using this option will result in non-conforming
4273 @item -fmodulo-sched
4274 @opindex fmodulo-sched
4275 Perform swing modulo scheduling immediately before the first scheduling
4276 pass. This pass looks at innermost loops and reorders their
4277 instructions by overlapping different iterations.
4281 Use a graph coloring register allocator. Currently this option is meant
4282 only for testing. Users should not specify this option, since it is not
4283 yet ready for production use.
4285 @item -fno-branch-count-reg
4286 @opindex fno-branch-count-reg
4287 Do not use ``decrement and branch'' instructions on a count register,
4288 but instead generate a sequence of instructions that decrement a
4289 register, compare it against zero, then branch based upon the result.
4290 This option is only meaningful on architectures that support such
4291 instructions, which include x86, PowerPC, IA-64 and S/390.
4293 The default is @option{-fbranch-count-reg}, enabled when
4294 @option{-fstrength-reduce} is enabled.
4296 @item -fno-function-cse
4297 @opindex fno-function-cse
4298 Do not put function addresses in registers; make each instruction that
4299 calls a constant function contain the function's address explicitly.
4301 This option results in less efficient code, but some strange hacks
4302 that alter the assembler output may be confused by the optimizations
4303 performed when this option is not used.
4305 The default is @option{-ffunction-cse}
4307 @item -fno-zero-initialized-in-bss
4308 @opindex fno-zero-initialized-in-bss
4309 If the target supports a BSS section, GCC by default puts variables that
4310 are initialized to zero into BSS@. This can save space in the resulting
4313 This option turns off this behavior because some programs explicitly
4314 rely on variables going to the data section. E.g., so that the
4315 resulting executable can find the beginning of that section and/or make
4316 assumptions based on that.
4318 The default is @option{-fzero-initialized-in-bss}.
4320 @item -fbounds-check
4321 @opindex fbounds-check
4322 For front-ends that support it, generate additional code to check that
4323 indices used to access arrays are within the declared range. This is
4324 currently only supported by the Java and Fortran front-ends, where
4325 this option defaults to true and false respectively.
4327 @item -fmudflap -fmudflapth -fmudflapir
4331 @cindex bounds checking
4333 For front-ends that support it (C and C++), instrument all risky
4334 pointer/array dereferencing operations, some standard library
4335 string/heap functions, and some other associated constructs with
4336 range/validity tests. Modules so instrumented should be immune to
4337 buffer overflows, invalid heap use, and some other classes of C/C++
4338 programming errors. The instrumentation relies on a separate runtime
4339 library (@file{libmudflap}), which will be linked into a program if
4340 @option{-fmudflap} is given at link time. Run-time behavior of the
4341 instrumented program is controlled by the @env{MUDFLAP_OPTIONS}
4342 environment variable. See @code{env MUDFLAP_OPTIONS=-help a.out}
4345 Use @option{-fmudflapth} instead of @option{-fmudflap} to compile and to
4346 link if your program is multi-threaded. Use @option{-fmudflapir}, in
4347 addition to @option{-fmudflap} or @option{-fmudflapth}, if
4348 instrumentation should ignore pointer reads. This produces less
4349 instrumentation (and therefore faster execution) and still provides
4350 some protection against outright memory corrupting writes, but allows
4351 erroneously read data to propagate within a program.
4353 @item -fstrength-reduce
4354 @opindex fstrength-reduce
4355 Perform the optimizations of loop strength reduction and
4356 elimination of iteration variables.
4358 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4360 @item -fthread-jumps
4361 @opindex fthread-jumps
4362 Perform optimizations where we check to see if a jump branches to a
4363 location where another comparison subsumed by the first is found. If
4364 so, the first branch is redirected to either the destination of the
4365 second branch or a point immediately following it, depending on whether
4366 the condition is known to be true or false.
4368 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4370 @item -fcse-follow-jumps
4371 @opindex fcse-follow-jumps
4372 In common subexpression elimination, scan through jump instructions
4373 when the target of the jump is not reached by any other path. For
4374 example, when CSE encounters an @code{if} statement with an
4375 @code{else} clause, CSE will follow the jump when the condition
4378 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4380 @item -fcse-skip-blocks
4381 @opindex fcse-skip-blocks
4382 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
4383 follow jumps which conditionally skip over blocks. When CSE
4384 encounters a simple @code{if} statement with no else clause,
4385 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
4386 body of the @code{if}.
4388 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4390 @item -frerun-cse-after-loop
4391 @opindex frerun-cse-after-loop
4392 Re-run common subexpression elimination after loop optimizations has been
4395 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4397 @item -frerun-loop-opt
4398 @opindex frerun-loop-opt
4399 Run the loop optimizer twice.
4401 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4405 Perform a global common subexpression elimination pass.
4406 This pass also performs global constant and copy propagation.
4408 @emph{Note:} When compiling a program using computed gotos, a GCC
4409 extension, you may get better runtime performance if you disable
4410 the global common subexpression elimination pass by adding
4411 @option{-fno-gcse} to the command line.
4413 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4417 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
4418 attempt to move loads which are only killed by stores into themselves. This
4419 allows a loop containing a load/store sequence to be changed to a load outside
4420 the loop, and a copy/store within the loop.
4422 Enabled by default when gcse is enabled.
4426 When @option{-fgcse-sm} is enabled, a store motion pass is run after
4427 global common subexpression elimination. This pass will attempt to move
4428 stores out of loops. When used in conjunction with @option{-fgcse-lm},
4429 loops containing a load/store sequence can be changed to a load before
4430 the loop and a store after the loop.
4432 Enabled by default when gcse is enabled.
4436 When @option{-fgcse-las} is enabled, the global common subexpression
4437 elimination pass eliminates redundant loads that come after stores to the
4438 same memory location (both partial and full redundancies).
4440 Enabled by default when gcse is enabled.
4442 @item -fgcse-after-reload
4443 @opindex fgcse-after-reload
4444 When @option{-fgcse-after-reload} is enabled, a redundant load elimination
4445 pass is performed after reload. The purpose of this pass is to cleanup
4448 @item -floop-optimize
4449 @opindex floop-optimize
4450 Perform loop optimizations: move constant expressions out of loops, simplify
4451 exit test conditions and optionally do strength-reduction as well.
4453 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4455 @item -floop-optimize2
4456 @opindex floop-optimize2
4457 Perform loop optimizations using the new loop optimizer. The optimizations
4458 (loop unrolling, peeling and unswitching, loop invariant motion) are enabled
4461 @item -fcrossjumping
4462 @opindex crossjumping
4463 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
4464 resulting code may or may not perform better than without cross-jumping.
4466 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4468 @item -fif-conversion
4469 @opindex if-conversion
4470 Attempt to transform conditional jumps into branch-less equivalents. This
4471 include use of conditional moves, min, max, set flags and abs instructions, and
4472 some tricks doable by standard arithmetics. The use of conditional execution
4473 on chips where it is available is controlled by @code{if-conversion2}.
4475 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4477 @item -fif-conversion2
4478 @opindex if-conversion2
4479 Use conditional execution (where available) to transform conditional jumps into
4480 branch-less equivalents.
4482 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4484 @item -fdelete-null-pointer-checks
4485 @opindex fdelete-null-pointer-checks
4486 Use global dataflow analysis to identify and eliminate useless checks
4487 for null pointers. The compiler assumes that dereferencing a null
4488 pointer would have halted the program. If a pointer is checked after
4489 it has already been dereferenced, it cannot be null.
4491 In some environments, this assumption is not true, and programs can
4492 safely dereference null pointers. Use
4493 @option{-fno-delete-null-pointer-checks} to disable this optimization
4494 for programs which depend on that behavior.
4496 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4498 @item -fexpensive-optimizations
4499 @opindex fexpensive-optimizations
4500 Perform a number of minor optimizations that are relatively expensive.
4502 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4504 @item -foptimize-register-move
4506 @opindex foptimize-register-move
4508 Attempt to reassign register numbers in move instructions and as
4509 operands of other simple instructions in order to maximize the amount of
4510 register tying. This is especially helpful on machines with two-operand
4513 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
4516 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4518 @item -fdelayed-branch
4519 @opindex fdelayed-branch
4520 If supported for the target machine, attempt to reorder instructions
4521 to exploit instruction slots available after delayed branch
4524 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4526 @item -fschedule-insns
4527 @opindex fschedule-insns
4528 If supported for the target machine, attempt to reorder instructions to
4529 eliminate execution stalls due to required data being unavailable. This
4530 helps machines that have slow floating point or memory load instructions
4531 by allowing other instructions to be issued until the result of the load
4532 or floating point instruction is required.
4534 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4536 @item -fschedule-insns2
4537 @opindex fschedule-insns2
4538 Similar to @option{-fschedule-insns}, but requests an additional pass of
4539 instruction scheduling after register allocation has been done. This is
4540 especially useful on machines with a relatively small number of
4541 registers and where memory load instructions take more than one cycle.
4543 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4545 @item -fno-sched-interblock
4546 @opindex fno-sched-interblock
4547 Don't schedule instructions across basic blocks. 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 -fno-sched-spec
4552 @opindex fno-sched-spec
4553 Don't allow speculative motion of non-load instructions. This is normally
4554 enabled by default when scheduling before register allocation, i.e.@:
4555 with @option{-fschedule-insns} or at @option{-O2} or higher.
4557 @item -fsched-spec-load
4558 @opindex fsched-spec-load
4559 Allow speculative motion of some 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-spec-load-dangerous
4564 @opindex fsched-spec-load-dangerous
4565 Allow speculative motion of more load instructions. This only makes
4566 sense when scheduling before register allocation, i.e.@: with
4567 @option{-fschedule-insns} or at @option{-O2} or higher.
4569 @item -fsched-stalled-insns=@var{n}
4570 @opindex fsched-stalled-insns
4571 Define how many insns (if any) can be moved prematurely from the queue
4572 of stalled insns into the ready list, during the second scheduling pass.
4574 @item -fsched-stalled-insns-dep=@var{n}
4575 @opindex fsched-stalled-insns-dep
4576 Define how many insn groups (cycles) will be examined for a dependency
4577 on a stalled insn that is candidate for premature removal from the queue
4578 of stalled insns. Has an effect only during the second scheduling pass,
4579 and only if @option{-fsched-stalled-insns} is used and its value is not zero.
4581 @item -fsched2-use-superblocks
4582 @opindex fsched2-use-superblocks
4583 When scheduling after register allocation, do use superblock scheduling
4584 algorithm. Superblock scheduling allows motion across basic block boundaries
4585 resulting on faster schedules. This option is experimental, as not all machine
4586 descriptions used by GCC model the CPU closely enough to avoid unreliable
4587 results from the algorithm.
4589 This only makes sense when scheduling after register allocation, i.e.@: with
4590 @option{-fschedule-insns2} or at @option{-O2} or higher.
4592 @item -fsched2-use-traces
4593 @opindex fsched2-use-traces
4594 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
4595 allocation and additionally perform code duplication in order to increase the
4596 size of superblocks using tracer pass. See @option{-ftracer} for details on
4599 This mode should produce faster but significantly longer programs. Also
4600 without @option{-fbranch-probabilities} the traces constructed may not
4601 match the reality and hurt the performance. This only makes
4602 sense when scheduling after register allocation, i.e.@: with
4603 @option{-fschedule-insns2} or at @option{-O2} or higher.
4605 @item -freschedule-modulo-scheduled-loops
4606 @opindex fscheduling-in-modulo-scheduled-loops
4607 The modulo scheduling comes before the traditional scheduling, if a loop was modulo scheduled
4608 we may want to prevent the later scheduling passes from changing its schedule, we use this
4609 option to control that.
4611 @item -fcaller-saves
4612 @opindex fcaller-saves
4613 Enable values to be allocated in registers that will be clobbered by
4614 function calls, by emitting extra instructions to save and restore the
4615 registers around such calls. Such allocation is done only when it
4616 seems to result in better code than would otherwise be produced.
4618 This option is always enabled by default on certain machines, usually
4619 those which have no call-preserved registers to use instead.
4621 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4624 Perform Partial Redundancy Elimination (PRE) on trees. This flag is
4625 enabled by default at @option{-O} and higher.
4628 Perform Full Redundancy Elimination (FRE) on trees. The difference
4629 between FRE and PRE is that FRE only considers expressions
4630 that are computed on all paths leading to the redundant computation.
4631 This analysis faster than PRE, though it exposes fewer redundancies.
4632 This flag is enabled by default at @option{-O} and higher.
4635 Perform sparse conditional constant propagation (CCP) on trees. This flag
4636 is enabled by default at @option{-O} and higher.
4639 Perform dead code elimination (DCE) on trees. This flag is enabled by
4640 default at @option{-O} and higher.
4642 @item -ftree-dominator-opts
4643 Perform dead code elimination (DCE) on trees. This flag is enabled by
4644 default at @option{-O} and higher.
4647 Perform loop header copying on trees. This is beneficial since it increases
4648 effectiveness of code motion optimizations. It also saves one jump. This flag
4649 is enabled by default at @option{-O} and higher. It is not enabled
4650 for @option{-Os}, since it usually increases code size.
4652 @item -ftree-loop-optimize
4653 Perform loop optimizations on trees. This flag is enabled by default
4654 at @option{-O} and higher.
4656 @item -ftree-loop-linear
4657 Perform linear loop transformations on tree. This flag can improve cache
4658 performance and allow further loop optimizations to take place.
4661 Perform loop invariant motion on trees. This pass moves only invartiants that
4662 would be hard to handle on rtl level (function calls, operations that expand to
4663 nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
4664 operands of conditions that are invariant out of the loop, so that we can use
4665 just trivial invariantness analysis in loop unswitching. The pass also includes
4669 Create a canonical counter for number of iterations in the loop for that
4670 determining number of iterations requires complicated analysis. Later
4671 optimizations then may determine the number easily. Useful especially
4672 in connection with unrolling.
4675 Perform induction variable optimizations (strength reduction, induction
4676 variable merging and induction variable elimination) on trees.
4679 Perform scalar replacement of aggregates. This pass replaces structure
4680 references with scalars to prevent committing structures to memory too
4681 early. This flag is enabled by default at @option{-O} and higher.
4683 @item -ftree-copyrename
4684 Perform copy renaming on trees. This pass attempts to rename compiler
4685 temporaries to other variables at copy locations, usually resulting in
4686 variable names which more closely resemble the original variables. This flag
4687 is enabled by default at @option{-O} and higher.
4690 Perform temporary expression replacement during the SSA->normal phase. Single
4691 use/single def temporaries are replaced at their use location with their
4692 defining expression. This results in non-GIMPLE code, but gives the expanders
4693 much more complex trees to work on resulting in better RTL generation. This is
4694 enabled by default at @option{-O} and higher.
4697 Perform live range splitting during the SSA->normal phase. Distinct live
4698 ranges of a variable are split into unique variables, allowing for better
4699 optimization later. This is enabled by default at @option{-O} and higher.
4701 @item -ftree-vectorize
4702 Perform loop vectorization on trees.
4706 Perform tail duplication to enlarge superblock size. This transformation
4707 simplifies the control flow of the function allowing other optimizations to do
4710 @item -funroll-loops
4711 @opindex funroll-loops
4712 Unroll loops whose number of iterations can be determined at compile
4713 time or upon entry to the loop. @option{-funroll-loops} implies both
4714 @option{-fstrength-reduce} and @option{-frerun-cse-after-loop}. This
4715 option makes code larger, and may or may not make it run faster.
4717 @item -funroll-all-loops
4718 @opindex funroll-all-loops
4719 Unroll all loops, even if their number of iterations is uncertain when
4720 the loop is entered. This usually makes programs run more slowly.
4721 @option{-funroll-all-loops} implies the same options as
4722 @option{-funroll-loops},
4724 @item -fsplit-ivs-in-unroller
4725 @opindex -fsplit-ivs-in-unroller
4726 Enables expressing of values of induction variables in later iterations
4727 of the unrolled loop using the value in the first iteration. This breaks
4728 long dependency chains, thus improving efficiency of the scheduling passes
4729 (for best results, @option{-fweb} should be used as well).
4731 Combination of @option{-fweb} and CSE is often sufficient to obtain the
4732 same effect. However in cases the loop body is more complicated than
4733 a single basic block, this is not reliable. It also does not work at all
4734 on some of the architectures due to restrictions in the CSE pass.
4736 This optimization is enabled by default.
4738 @item -fvariable-expansion-in-unroller
4739 @opindex -fvariable-expansion-in-unroller
4740 With this option, the compiler will create multiple copies of some
4741 local variables when unrolling a loop which can result in superior code.
4743 @item -fprefetch-loop-arrays
4744 @opindex fprefetch-loop-arrays
4745 If supported by the target machine, generate instructions to prefetch
4746 memory to improve the performance of loops that access large arrays.
4748 These options may generate better or worse code; results are highly
4749 dependent on the structure of loops within the source code.
4752 @itemx -fno-peephole2
4753 @opindex fno-peephole
4754 @opindex fno-peephole2
4755 Disable any machine-specific peephole optimizations. The difference
4756 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
4757 are implemented in the compiler; some targets use one, some use the
4758 other, a few use both.
4760 @option{-fpeephole} is enabled by default.
4761 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4763 @item -fno-guess-branch-probability
4764 @opindex fno-guess-branch-probability
4765 Do not guess branch probabilities using heuristics.
4767 GCC will use heuristics to guess branch probabilities if they are
4768 not provided by profiling feedback (@option{-fprofile-arcs}). These
4769 heuristics are based on the control flow graph. If some branch probabilities
4770 are specified by @samp{__builtin_expect}, then the heuristics will be
4771 used to guess branch probabilities for the rest of the control flow graph,
4772 taking the @samp{__builtin_expect} info into account. The interactions
4773 between the heuristics and @samp{__builtin_expect} can be complex, and in
4774 some cases, it may be useful to disable the heuristics so that the effects
4775 of @samp{__builtin_expect} are easier to understand.
4777 The default is @option{-fguess-branch-probability} at levels
4778 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4780 @item -freorder-blocks
4781 @opindex freorder-blocks
4782 Reorder basic blocks in the compiled function in order to reduce number of
4783 taken branches and improve code locality.
4785 Enabled at levels @option{-O2}, @option{-O3}.
4787 @item -freorder-blocks-and-partition
4788 @opindex freorder-blocks-and-partition
4789 In addition to reordering basic blocks in the compiled function, in order
4790 to reduce number of taken branches, partitions hot and cold basic blocks
4791 into separate sections of the assembly and .o files, to improve
4792 paging and cache locality performance.
4794 This optimization is automatically turned off in the presence of
4795 exception handling, for linkonce sections, for functions with a user-defined
4796 section attribute and on any architecture that does not support named
4799 @item -freorder-functions
4800 @opindex freorder-functions
4801 Reorder basic blocks in the compiled function in order to reduce number of
4802 taken branches and improve code locality. This is implemented by using special
4803 subsections @code{.text.hot} for most frequently executed functions and
4804 @code{.text.unlikely} for unlikely executed functions. Reordering is done by
4805 the linker so object file format must support named sections and linker must
4806 place them in a reasonable way.
4808 Also profile feedback must be available in to make this option effective. See
4809 @option{-fprofile-arcs} for details.
4811 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4813 @item -fstrict-aliasing
4814 @opindex fstrict-aliasing
4815 Allows the compiler to assume the strictest aliasing rules applicable to
4816 the language being compiled. For C (and C++), this activates
4817 optimizations based on the type of expressions. In particular, an
4818 object of one type is assumed never to reside at the same address as an
4819 object of a different type, unless the types are almost the same. For
4820 example, an @code{unsigned int} can alias an @code{int}, but not a
4821 @code{void*} or a @code{double}. A character type may alias any other
4824 Pay special attention to code like this:
4837 The practice of reading from a different union member than the one most
4838 recently written to (called ``type-punning'') is common. Even with
4839 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
4840 is accessed through the union type. So, the code above will work as
4841 expected. However, this code might not:
4852 Every language that wishes to perform language-specific alias analysis
4853 should define a function that computes, given an @code{tree}
4854 node, an alias set for the node. Nodes in different alias sets are not
4855 allowed to alias. For an example, see the C front-end function
4856 @code{c_get_alias_set}.
4858 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4860 @item -falign-functions
4861 @itemx -falign-functions=@var{n}
4862 @opindex falign-functions
4863 Align the start of functions to the next power-of-two greater than
4864 @var{n}, skipping up to @var{n} bytes. For instance,
4865 @option{-falign-functions=32} aligns functions to the next 32-byte
4866 boundary, but @option{-falign-functions=24} would align to the next
4867 32-byte boundary only if this can be done by skipping 23 bytes or less.
4869 @option{-fno-align-functions} and @option{-falign-functions=1} are
4870 equivalent and mean that functions will not be aligned.
4872 Some assemblers only support this flag when @var{n} is a power of two;
4873 in that case, it is rounded up.
4875 If @var{n} is not specified or is zero, use a machine-dependent default.
4877 Enabled at levels @option{-O2}, @option{-O3}.
4879 @item -falign-labels
4880 @itemx -falign-labels=@var{n}
4881 @opindex falign-labels
4882 Align all branch targets to a power-of-two boundary, skipping up to
4883 @var{n} bytes like @option{-falign-functions}. This option can easily
4884 make code slower, because it must insert dummy operations for when the
4885 branch target is reached in the usual flow of the code.
4887 @option{-fno-align-labels} and @option{-falign-labels=1} are
4888 equivalent and mean that labels will not be aligned.
4890 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
4891 are greater than this value, then their values are used instead.
4893 If @var{n} is not specified or is zero, use a machine-dependent default
4894 which is very likely to be @samp{1}, meaning no alignment.
4896 Enabled at levels @option{-O2}, @option{-O3}.
4899 @itemx -falign-loops=@var{n}
4900 @opindex falign-loops
4901 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
4902 like @option{-falign-functions}. The hope is that the loop will be
4903 executed many times, which will make up for any execution of the dummy
4906 @option{-fno-align-loops} and @option{-falign-loops=1} are
4907 equivalent and mean that loops will not be aligned.
4909 If @var{n} is not specified or is zero, use a machine-dependent default.
4911 Enabled at levels @option{-O2}, @option{-O3}.
4914 @itemx -falign-jumps=@var{n}
4915 @opindex falign-jumps
4916 Align branch targets to a power-of-two boundary, for branch targets
4917 where the targets can only be reached by jumping, skipping up to @var{n}
4918 bytes like @option{-falign-functions}. In this case, no dummy operations
4921 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
4922 equivalent and mean that loops will not be aligned.
4924 If @var{n} is not specified or is zero, use a machine-dependent default.
4926 Enabled at levels @option{-O2}, @option{-O3}.
4928 @item -funit-at-a-time
4929 @opindex funit-at-a-time
4930 Parse the whole compilation unit before starting to produce code.
4931 This allows some extra optimizations to take place but consumes
4932 more memory (in general). There are some compatibility issues
4933 with @emph{unit-at-at-time} mode:
4936 enabling @emph{unit-at-a-time} mode may change the order
4937 in which functions, variables, and top-level @code{asm} statements
4938 are emitted, and will likely break code relying on some particular
4939 ordering. The majority of such top-level @code{asm} statements,
4940 though, can be replaced by @code{section} attributes.
4943 @emph{unit-at-a-time} mode removes unreferenced static variables
4944 and functions are removed. This may result in undefined references
4945 when an @code{asm} statement refers directly to variables or functions
4946 that are otherwise unused. In that case either the variable/function
4947 shall be listed as an operand of the @code{asm} statement operand or,
4948 in the case of top-level @code{asm} statements the attribute @code{used}
4949 shall be used on the declaration.
4952 Static functions now can use non-standard passing conventions that
4953 may break @code{asm} statements calling functions directly. Again,
4954 attribute @code{used} will prevent this behavior.
4957 As a temporary workaround, @option{-fno-unit-at-a-time} can be used,
4958 but this scheme may not be supported by future releases of GCC@.
4960 Enabled at levels @option{-O2}, @option{-O3}.
4964 Constructs webs as commonly used for register allocation purposes and assign
4965 each web individual pseudo register. This allows the register allocation pass
4966 to operate on pseudos directly, but also strengthens several other optimization
4967 passes, such as CSE, loop optimizer and trivial dead code remover. It can,
4968 however, make debugging impossible, since variables will no longer stay in a
4971 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os},
4972 on targets where the default format for debugging information supports
4975 @item -fno-cprop-registers
4976 @opindex fno-cprop-registers
4977 After register allocation and post-register allocation instruction splitting,
4978 we perform a copy-propagation pass to try to reduce scheduling dependencies
4979 and occasionally eliminate the copy.
4981 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4983 @item -fprofile-generate
4984 @opindex fprofile-generate
4986 Enable options usually used for instrumenting application to produce
4987 profile useful for later recompilation with profile feedback based
4988 optimization. You must use @option{-fprofile-generate} both when
4989 compiling and when linking your program.
4991 The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}.
4994 @opindex fprofile-use
4995 Enable profile feedback directed optimizations, and optimizations
4996 generally profitable only with profile feedback available.
4998 The following options are enabled: @code{-fbranch-probabilities},
4999 @code{-fvpt}, @code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer}.
5003 The following options control compiler behavior regarding floating
5004 point arithmetic. These options trade off between speed and
5005 correctness. All must be specifically enabled.
5009 @opindex ffloat-store
5010 Do not store floating point variables in registers, and inhibit other
5011 options that might change whether a floating point value is taken from a
5014 @cindex floating point precision
5015 This option prevents undesirable excess precision on machines such as
5016 the 68000 where the floating registers (of the 68881) keep more
5017 precision than a @code{double} is supposed to have. Similarly for the
5018 x86 architecture. For most programs, the excess precision does only
5019 good, but a few programs rely on the precise definition of IEEE floating
5020 point. Use @option{-ffloat-store} for such programs, after modifying
5021 them to store all pertinent intermediate computations into variables.
5025 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, @*
5026 @option{-fno-trapping-math}, @option{-ffinite-math-only},
5027 @option{-fno-rounding-math} and @option{-fno-signaling-nans}.
5029 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
5031 This option should never be turned on by any @option{-O} option since
5032 it can result in incorrect output for programs which depend on
5033 an exact implementation of IEEE or ISO rules/specifications for
5036 @item -fno-math-errno
5037 @opindex fno-math-errno
5038 Do not set ERRNO after calling math functions that are executed
5039 with a single instruction, e.g., sqrt. A program that relies on
5040 IEEE exceptions for math error handling may want to use this flag
5041 for speed while maintaining IEEE arithmetic compatibility.
5043 This option should never be turned on by any @option{-O} option since
5044 it can result in incorrect output for programs which depend on
5045 an exact implementation of IEEE or ISO rules/specifications for
5048 The default is @option{-fmath-errno}.
5050 @item -funsafe-math-optimizations
5051 @opindex funsafe-math-optimizations
5052 Allow optimizations for floating-point arithmetic that (a) assume
5053 that arguments and results are valid and (b) may violate IEEE or
5054 ANSI standards. When used at link-time, it may include libraries
5055 or startup files that change the default FPU control word or other
5056 similar optimizations.
5058 This option should never be turned on by any @option{-O} option since
5059 it can result in incorrect output for programs which depend on
5060 an exact implementation of IEEE or ISO rules/specifications for
5063 The default is @option{-fno-unsafe-math-optimizations}.
5065 @item -ffinite-math-only
5066 @opindex ffinite-math-only
5067 Allow optimizations for floating-point arithmetic that assume
5068 that arguments and results are not NaNs or +-Infs.
5070 This option should never be turned on by any @option{-O} option since
5071 it can result in incorrect output for programs which depend on
5072 an exact implementation of IEEE or ISO rules/specifications.
5074 The default is @option{-fno-finite-math-only}.
5076 @item -fno-trapping-math
5077 @opindex fno-trapping-math
5078 Compile code assuming that floating-point operations cannot generate
5079 user-visible traps. These traps include division by zero, overflow,
5080 underflow, inexact result and invalid operation. This option implies
5081 @option{-fno-signaling-nans}. Setting this option may allow faster
5082 code if one relies on ``non-stop'' IEEE arithmetic, for example.
5084 This option should never be turned on by any @option{-O} option since
5085 it can result in incorrect output for programs which depend on
5086 an exact implementation of IEEE or ISO rules/specifications for
5089 The default is @option{-ftrapping-math}.
5091 @item -frounding-math
5092 @opindex frounding-math
5093 Disable transformations and optimizations that assume default floating
5094 point rounding behavior. This is round-to-zero for all floating point
5095 to integer conversions, and round-to-nearest for all other arithmetic
5096 truncations. This option should be specified for programs that change
5097 the FP rounding mode dynamically, or that may be executed with a
5098 non-default rounding mode. This option disables constant folding of
5099 floating point expressions at compile-time (which may be affected by
5100 rounding mode) and arithmetic transformations that are unsafe in the
5101 presence of sign-dependent rounding modes.
5103 The default is @option{-fno-rounding-math}.
5105 This option is experimental and does not currently guarantee to
5106 disable all GCC optimizations that are affected by rounding mode.
5107 Future versions of GCC may provide finer control of this setting
5108 using C99's @code{FENV_ACCESS} pragma. This command line option
5109 will be used to specify the default state for @code{FENV_ACCESS}.
5111 @item -fsignaling-nans
5112 @opindex fsignaling-nans
5113 Compile code assuming that IEEE signaling NaNs may generate user-visible
5114 traps during floating-point operations. Setting this option disables
5115 optimizations that may change the number of exceptions visible with
5116 signaling NaNs. This option implies @option{-ftrapping-math}.
5118 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
5121 The default is @option{-fno-signaling-nans}.
5123 This option is experimental and does not currently guarantee to
5124 disable all GCC optimizations that affect signaling NaN behavior.
5126 @item -fsingle-precision-constant
5127 @opindex fsingle-precision-constant
5128 Treat floating point constant as single precision constant instead of
5129 implicitly converting it to double precision constant.
5134 The following options control optimizations that may improve
5135 performance, but are not enabled by any @option{-O} options. This
5136 section includes experimental options that may produce broken code.
5139 @item -fbranch-probabilities
5140 @opindex fbranch-probabilities
5141 After running a program compiled with @option{-fprofile-arcs}
5142 (@pxref{Debugging Options,, Options for Debugging Your Program or
5143 @command{gcc}}), you can compile it a second time using
5144 @option{-fbranch-probabilities}, to improve optimizations based on
5145 the number of times each branch was taken. When the program
5146 compiled with @option{-fprofile-arcs} exits it saves arc execution
5147 counts to a file called @file{@var{sourcename}.gcda} for each source
5148 file The information in this data file is very dependent on the
5149 structure of the generated code, so you must use the same source code
5150 and the same optimization options for both compilations.
5152 With @option{-fbranch-probabilities}, GCC puts a
5153 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
5154 These can be used to improve optimization. Currently, they are only
5155 used in one place: in @file{reorg.c}, instead of guessing which path a
5156 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
5157 exactly determine which path is taken more often.
5159 @item -fprofile-values
5160 @opindex fprofile-values
5161 If combined with @option{-fprofile-arcs}, it adds code so that some
5162 data about values of expressions in the program is gathered.
5164 With @option{-fbranch-probabilities}, it reads back the data gathered
5165 from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
5166 notes to instructions for their later usage in optimizations.
5168 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
5172 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
5173 a code to gather information about values of expressions.
5175 With @option{-fbranch-probabilities}, it reads back the data gathered
5176 and actually performs the optimizations based on them.
5177 Currently the optimizations include specialization of division operation
5178 using the knowledge about the value of the denominator.
5180 @item -fspeculative-prefetching
5181 @opindex fspeculative-prefetching
5182 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
5183 a code to gather information about addresses of memory references in the
5186 With @option{-fbranch-probabilities}, it reads back the data gathered
5187 and issues prefetch instructions according to them. In addition to the opportunities
5188 noticed by @option{-fprefetch-loop-arrays}, it also notices more complicated
5189 memory access patterns---for example accesses to the data stored in linked
5190 list whose elements are usually allocated sequentially.
5192 In order to prevent issuing double prefetches, usage of
5193 @option{-fspeculative-prefetching} implies @option{-fno-prefetch-loop-arrays}.
5195 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
5197 @item -frename-registers
5198 @opindex frename-registers
5199 Attempt to avoid false dependencies in scheduled code by making use
5200 of registers left over after register allocation. This optimization
5201 will most benefit processors with lots of registers. Depending on the
5202 debug information format adopted by the target, however, it can
5203 make debugging impossible, since variables will no longer stay in
5204 a ``home register''.
5206 Not enabled by default at any level because it has known bugs.
5210 Use a graph coloring register allocator. Currently this option is meant
5211 for testing, so we are interested to hear about miscompilations with
5216 Perform tail duplication to enlarge superblock size. This transformation
5217 simplifies the control flow of the function allowing other optimizations to do
5220 Enabled with @option{-fprofile-use}.
5222 @item -funroll-loops
5223 @opindex funroll-loops
5224 Unroll loops whose number of iterations can be determined at compile time or
5225 upon entry to the loop. @option{-funroll-loops} implies
5226 @option{-frerun-cse-after-loop}. It also turns on complete loop peeling
5227 (i.e.@: complete removal of loops with small constant number of iterations).
5228 This option makes code larger, and may or may not make it run faster.
5230 Enabled with @option{-fprofile-use}.
5232 @item -funroll-all-loops
5233 @opindex funroll-all-loops
5234 Unroll all loops, even if their number of iterations is uncertain when
5235 the loop is entered. This usually makes programs run more slowly.
5236 @option{-funroll-all-loops} implies the same options as
5237 @option{-funroll-loops}.
5240 @opindex fpeel-loops
5241 Peels the loops for that there is enough information that they do not
5242 roll much (from profile feedback). It also turns on complete loop peeling
5243 (i.e.@: complete removal of loops with small constant number of iterations).
5245 Enabled with @option{-fprofile-use}.
5247 @item -fmove-loop-invariants
5248 @opindex fmove-loop-invariants
5249 Enables the loop invariant motion pass in the new loop optimizer. Enabled
5250 at level @option{-O1}
5252 @item -funswitch-loops
5253 @opindex funswitch-loops
5254 Move branches with loop invariant conditions out of the loop, with duplicates
5255 of the loop on both branches (modified according to result of the condition).
5257 @item -fprefetch-loop-arrays
5258 @opindex fprefetch-loop-arrays
5259 If supported by the target machine, generate instructions to prefetch
5260 memory to improve the performance of loops that access large arrays.
5262 Disabled at level @option{-Os}.
5264 @item -ffunction-sections
5265 @itemx -fdata-sections
5266 @opindex ffunction-sections
5267 @opindex fdata-sections
5268 Place each function or data item into its own section in the output
5269 file if the target supports arbitrary sections. The name of the
5270 function or the name of the data item determines the section's name
5273 Use these options on systems where the linker can perform optimizations
5274 to improve locality of reference in the instruction space. Most systems
5275 using the ELF object format and SPARC processors running Solaris 2 have
5276 linkers with such optimizations. AIX may have these optimizations in
5279 Only use these options when there are significant benefits from doing
5280 so. When you specify these options, the assembler and linker will
5281 create larger object and executable files and will also be slower.
5282 You will not be able to use @code{gprof} on all systems if you
5283 specify this option and you may have problems with debugging if
5284 you specify both this option and @option{-g}.
5286 @item -fbranch-target-load-optimize
5287 @opindex fbranch-target-load-optimize
5288 Perform branch target register load optimization before prologue / epilogue
5290 The use of target registers can typically be exposed only during reload,
5291 thus hoisting loads out of loops and doing inter-block scheduling needs
5292 a separate optimization pass.
5294 @item -fbranch-target-load-optimize2
5295 @opindex fbranch-target-load-optimize2
5296 Perform branch target register load optimization after prologue / epilogue
5299 @item -fbtr-bb-exclusive
5300 @opindex fbtr-bb-exclusive
5301 When performing branch target register load optimization, don't reuse
5302 branch target registers in within any basic block.
5304 @item --param @var{name}=@var{value}
5306 In some places, GCC uses various constants to control the amount of
5307 optimization that is done. For example, GCC will not inline functions
5308 that contain more that a certain number of instructions. You can
5309 control some of these constants on the command-line using the
5310 @option{--param} option.
5312 The names of specific parameters, and the meaning of the values, are
5313 tied to the internals of the compiler, and are subject to change
5314 without notice in future releases.
5316 In each case, the @var{value} is an integer. The allowable choices for
5317 @var{name} are given in the following table:
5320 @item sra-max-structure-size
5321 The maximum structure size, in bytes, at which the scalar replacement
5322 of aggregates (SRA) optimization will perform block copies. The
5323 default value, 0, implies that GCC will select the most appropriate
5326 @item sra-field-structure-ratio
5327 The threshold ratio (as a percentage) between instantiated fields and
5328 the complete structure size. We say that if the ratio of the number
5329 of bytes in instantiated fields to the number of bytes in the complete
5330 structure exceeds this parameter, then block copies are not used. The
5333 @item max-crossjump-edges
5334 The maximum number of incoming edges to consider for crossjumping.
5335 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
5336 the number of edges incoming to each block. Increasing values mean
5337 more aggressive optimization, making the compile time increase with
5338 probably small improvement in executable size.
5340 @item min-crossjump-insns
5341 The minimum number of instructions which must be matched at the end
5342 of two blocks before crossjumping will be performed on them. This
5343 value is ignored in the case where all instructions in the block being
5344 crossjumped from are matched. The default value is 5.
5346 @item max-delay-slot-insn-search
5347 The maximum number of instructions to consider when looking for an
5348 instruction to fill a delay slot. If more than this arbitrary number of
5349 instructions is searched, the time savings from filling the delay slot
5350 will be minimal so stop searching. Increasing values mean more
5351 aggressive optimization, making the compile time increase with probably
5352 small improvement in executable run time.
5354 @item max-delay-slot-live-search
5355 When trying to fill delay slots, the maximum number of instructions to
5356 consider when searching for a block with valid live register
5357 information. Increasing this arbitrarily chosen value means more
5358 aggressive optimization, increasing the compile time. This parameter
5359 should be removed when the delay slot code is rewritten to maintain the
5362 @item max-gcse-memory
5363 The approximate maximum amount of memory that will be allocated in
5364 order to perform the global common subexpression elimination
5365 optimization. If more memory than specified is required, the
5366 optimization will not be done.
5368 @item max-gcse-passes
5369 The maximum number of passes of GCSE to run. The default is 1.
5371 @item max-pending-list-length
5372 The maximum number of pending dependencies scheduling will allow
5373 before flushing the current state and starting over. Large functions
5374 with few branches or calls can create excessively large lists which
5375 needlessly consume memory and resources.
5377 @item max-inline-insns-single
5378 Several parameters control the tree inliner used in gcc.
5379 This number sets the maximum number of instructions (counted in GCC's
5380 internal representation) in a single function that the tree inliner
5381 will consider for inlining. This only affects functions declared
5382 inline and methods implemented in a class declaration (C++).
5383 The default value is 500.
5385 @item max-inline-insns-auto
5386 When you use @option{-finline-functions} (included in @option{-O3}),
5387 a lot of functions that would otherwise not be considered for inlining
5388 by the compiler will be investigated. To those functions, a different
5389 (more restrictive) limit compared to functions declared inline can
5391 The default value is 120.
5393 @item large-function-insns
5394 The limit specifying really large functions. For functions larger than this
5395 limit after inlining inlining is constrained by
5396 @option{--param large-function-growth}. This parameter is useful primarily
5397 to avoid extreme compilation time caused by non-linear algorithms used by the
5399 This parameter is ignored when @option{-funit-at-a-time} is not used.
5400 The default value is 3000.
5402 @item large-function-growth
5403 Specifies maximal growth of large function caused by inlining in percents.
5404 This parameter is ignored when @option{-funit-at-a-time} is not used.
5405 The default value is 100 which limits large function growth to 2.0 times
5408 @item inline-unit-growth
5409 Specifies maximal overall growth of the compilation unit caused by inlining.
5410 This parameter is ignored when @option{-funit-at-a-time} is not used.
5411 The default value is 50 which limits unit growth to 1.5 times the original
5414 @item max-inline-insns-recursive
5415 @itemx max-inline-insns-recursive-auto
5416 Specifies maximum number of instructions out-of-line copy of self recursive inline
5417 function can grow into by performing recursive inlining.
5419 For functions declared inline @option{--param max-inline-insns-recursive} is
5420 taken into acount. For function not declared inline, recursive inlining
5421 happens only when @option{-finline-functions} (included in @option{-O3}) is
5422 enabled and @option{--param max-inline-insns-recursive-auto} is used. The
5423 default value is 500.
5425 @item max-inline-recursive-depth
5426 @itemx max-inline-recursive-depth-auto
5427 Specifies maximum recursion depth used by the recursive inlining.
5429 For functions declared inline @option{--param max-inline-recursive-depth} is
5430 taken into acount. For function not declared inline, recursive inlining
5431 happens only when @option{-finline-functions} (included in @option{-O3}) is
5432 enabled and @option{--param max-inline-recursive-depth-auto} is used. The
5433 default value is 500.
5435 @item max-unrolled-insns
5436 The maximum number of instructions that a loop should have if that loop
5437 is unrolled, and if the loop is unrolled, it determines how many times
5438 the loop code is unrolled.
5440 @item max-average-unrolled-insns
5441 The maximum number of instructions biased by probabilities of their execution
5442 that a loop should have if that loop is unrolled, and if the loop is unrolled,
5443 it determines how many times the loop code is unrolled.
5445 @item max-unroll-times
5446 The maximum number of unrollings of a single loop.
5448 @item max-peeled-insns
5449 The maximum number of instructions that a loop should have if that loop
5450 is peeled, and if the loop is peeled, it determines how many times
5451 the loop code is peeled.
5453 @item max-peel-times
5454 The maximum number of peelings of a single loop.
5456 @item max-completely-peeled-insns
5457 The maximum number of insns of a completely peeled loop.
5459 @item max-completely-peel-times
5460 The maximum number of iterations of a loop to be suitable for complete peeling.
5462 @item max-unswitch-insns
5463 The maximum number of insns of an unswitched loop.
5465 @item max-unswitch-level
5466 The maximum number of branches unswitched in a single loop.
5469 The minimum cost of an expensive expression in the loop invariant motion.
5471 @item iv-consider-all-candidates-bound
5472 Bound on number of candidates for induction variables below that
5473 all candidates are considered for each use in induction variable
5474 optimizations. Only the most relevant candidates are considered
5475 if there are more candidates, to avoid quadratic time complexity.
5477 @item iv-max-considered-uses
5478 The induction variable optimizations give up on loops that contain more
5479 induction variable uses.
5481 @item iv-always-prune-cand-set-bound
5482 If number of candidates in the set is smaller than this value,
5483 we always try to remove unnecessary ivs from the set during its
5484 optimization when a new iv is added to the set.
5486 @item max-iterations-to-track
5488 The maximum number of iterations of a loop the brute force algorithm
5489 for analysis of # of iterations of the loop tries to evaluate.
5491 @item hot-bb-count-fraction
5492 Select fraction of the maximal count of repetitions of basic block in program
5493 given basic block needs to have to be considered hot.
5495 @item hot-bb-frequency-fraction
5496 Select fraction of the maximal frequency of executions of basic block in
5497 function given basic block needs to have to be considered hot
5499 @item tracer-dynamic-coverage
5500 @itemx tracer-dynamic-coverage-feedback
5502 This value is used to limit superblock formation once the given percentage of
5503 executed instructions is covered. This limits unnecessary code size
5506 The @option{tracer-dynamic-coverage-feedback} is used only when profile
5507 feedback is available. The real profiles (as opposed to statically estimated
5508 ones) are much less balanced allowing the threshold to be larger value.
5510 @item tracer-max-code-growth
5511 Stop tail duplication once code growth has reached given percentage. This is
5512 rather hokey argument, as most of the duplicates will be eliminated later in
5513 cross jumping, so it may be set to much higher values than is the desired code
5516 @item tracer-min-branch-ratio
5518 Stop reverse growth when the reverse probability of best edge is less than this
5519 threshold (in percent).
5521 @item tracer-min-branch-ratio
5522 @itemx tracer-min-branch-ratio-feedback
5524 Stop forward growth if the best edge do have probability lower than this
5527 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
5528 compilation for profile feedback and one for compilation without. The value
5529 for compilation with profile feedback needs to be more conservative (higher) in
5530 order to make tracer effective.
5532 @item max-cse-path-length
5534 Maximum number of basic blocks on path that cse considers. The default is 10.
5536 @item global-var-threshold
5538 Counts the number of function calls (@var{n}) and the number of
5539 call-clobbered variables (@var{v}). If @var{n}x@var{v} is larger than this limit, a
5540 single artificial variable will be created to represent all the
5541 call-clobbered variables at function call sites. This artificial
5542 variable will then be made to alias every call-clobbered variable.
5543 (done as @code{int * size_t} on the host machine; beware overflow).
5545 @item max-aliased-vops
5547 Maximum number of virtual operands allowed to represent aliases
5548 before triggering the alias grouping heuristic. Alias grouping
5549 reduces compile times and memory consumption needed for aliasing at
5550 the expense of precision loss in alias information.
5552 @item ggc-min-expand
5554 GCC uses a garbage collector to manage its own memory allocation. This
5555 parameter specifies the minimum percentage by which the garbage
5556 collector's heap should be allowed to expand between collections.
5557 Tuning this may improve compilation speed; it has no effect on code
5560 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
5561 RAM >= 1GB@. If @code{getrlimit} is available, the notion of "RAM" is
5562 the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If
5563 GCC is not able to calculate RAM on a particular platform, the lower
5564 bound of 30% is used. Setting this parameter and
5565 @option{ggc-min-heapsize} to zero causes a full collection to occur at
5566 every opportunity. This is extremely slow, but can be useful for
5569 @item ggc-min-heapsize
5571 Minimum size of the garbage collector's heap before it begins bothering
5572 to collect garbage. The first collection occurs after the heap expands
5573 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
5574 tuning this may improve compilation speed, and has no effect on code
5577 The default is the smaller of RAM/8, RLIMIT_RSS, or a limit which
5578 tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
5579 with a lower bound of 4096 (four megabytes) and an upper bound of
5580 131072 (128 megabytes). If GCC is not able to calculate RAM on a
5581 particular platform, the lower bound is used. Setting this parameter
5582 very large effectively disables garbage collection. Setting this
5583 parameter and @option{ggc-min-expand} to zero causes a full collection
5584 to occur at every opportunity.
5586 @item max-reload-search-insns
5587 The maximum number of instruction reload should look backward for equivalent
5588 register. Increasing values mean more aggressive optimization, making the
5589 compile time increase with probably slightly better performance. The default
5592 @item max-cselib-memory-location
5593 The maximum number of memory locations cselib should take into acount.
5594 Increasing values mean more aggressive optimization, making the compile time
5595 increase with probably slightly better performance. The default value is 500.
5597 @item reorder-blocks-duplicate
5598 @itemx reorder-blocks-duplicate-feedback
5600 Used by basic block reordering pass to decide whether to use unconditional
5601 branch or duplicate the code on its destination. Code is duplicated when its
5602 estimated size is smaller than this value multiplied by the estimated size of
5603 unconditional jump in the hot spots of the program.
5605 The @option{reorder-block-duplicate-feedback} is used only when profile
5606 feedback is available and may be set to higher values than
5607 @option{reorder-block-duplicate} since information about the hot spots is more
5610 @item max-sched-region-blocks
5611 The maximum number of blocks in a region to be considered for
5612 interblock scheduling. The default value is 10.
5614 @item max-sched-region-insns
5615 The maximum number of insns in a region to be considered for
5616 interblock scheduling. The default value is 100.
5618 @item integer-share-limit
5619 Small integer constants can use a shared data structure, reducing the
5620 compiler's memory usage and increasing its speed. This sets the maximum
5621 value of a shared integer constant's. The default value is 256.
5626 @node Preprocessor Options
5627 @section Options Controlling the Preprocessor
5628 @cindex preprocessor options
5629 @cindex options, preprocessor
5631 These options control the C preprocessor, which is run on each C source
5632 file before actual compilation.
5634 If you use the @option{-E} option, nothing is done except preprocessing.
5635 Some of these options make sense only together with @option{-E} because
5636 they cause the preprocessor output to be unsuitable for actual
5641 You can use @option{-Wp,@var{option}} to bypass the compiler driver
5642 and pass @var{option} directly through to the preprocessor. If
5643 @var{option} contains commas, it is split into multiple options at the
5644 commas. However, many options are modified, translated or interpreted
5645 by the compiler driver before being passed to the preprocessor, and
5646 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
5647 interface is undocumented and subject to change, so whenever possible
5648 you should avoid using @option{-Wp} and let the driver handle the
5651 @item -Xpreprocessor @var{option}
5652 @opindex preprocessor
5653 Pass @var{option} as an option to the preprocessor. You can use this to
5654 supply system-specific preprocessor options which GCC does not know how to
5657 If you want to pass an option that takes an argument, you must use
5658 @option{-Xpreprocessor} twice, once for the option and once for the argument.
5661 @include cppopts.texi
5663 @node Assembler Options
5664 @section Passing Options to the Assembler
5666 @c prevent bad page break with this line
5667 You can pass options to the assembler.
5670 @item -Wa,@var{option}
5672 Pass @var{option} as an option to the assembler. If @var{option}
5673 contains commas, it is split into multiple options at the commas.
5675 @item -Xassembler @var{option}
5677 Pass @var{option} as an option to the assembler. You can use this to
5678 supply system-specific assembler options which GCC does not know how to
5681 If you want to pass an option that takes an argument, you must use
5682 @option{-Xassembler} twice, once for the option and once for the argument.
5687 @section Options for Linking
5688 @cindex link options
5689 @cindex options, linking
5691 These options come into play when the compiler links object files into
5692 an executable output file. They are meaningless if the compiler is
5693 not doing a link step.
5697 @item @var{object-file-name}
5698 A file name that does not end in a special recognized suffix is
5699 considered to name an object file or library. (Object files are
5700 distinguished from libraries by the linker according to the file
5701 contents.) If linking is done, these object files are used as input
5710 If any of these options is used, then the linker is not run, and
5711 object file names should not be used as arguments. @xref{Overall
5715 @item -l@var{library}
5716 @itemx -l @var{library}
5718 Search the library named @var{library} when linking. (The second
5719 alternative with the library as a separate argument is only for
5720 POSIX compliance and is not recommended.)
5722 It makes a difference where in the command you write this option; the
5723 linker searches and processes libraries and object files in the order they
5724 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
5725 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
5726 to functions in @samp{z}, those functions may not be loaded.
5728 The linker searches a standard list of directories for the library,
5729 which is actually a file named @file{lib@var{library}.a}. The linker
5730 then uses this file as if it had been specified precisely by name.
5732 The directories searched include several standard system directories
5733 plus any that you specify with @option{-L}.
5735 Normally the files found this way are library files---archive files
5736 whose members are object files. The linker handles an archive file by
5737 scanning through it for members which define symbols that have so far
5738 been referenced but not defined. But if the file that is found is an
5739 ordinary object file, it is linked in the usual fashion. The only
5740 difference between using an @option{-l} option and specifying a file name
5741 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
5742 and searches several directories.
5746 You need this special case of the @option{-l} option in order to
5747 link an Objective-C or Objective-C++ program.
5750 @opindex nostartfiles
5751 Do not use the standard system startup files when linking.
5752 The standard system libraries are used normally, unless @option{-nostdlib}
5753 or @option{-nodefaultlibs} is used.
5755 @item -nodefaultlibs
5756 @opindex nodefaultlibs
5757 Do not use the standard system libraries when linking.
5758 Only the libraries you specify will be passed to the linker.
5759 The standard startup files are used normally, unless @option{-nostartfiles}
5760 is used. The compiler may generate calls to @code{memcmp},
5761 @code{memset}, @code{memcpy} and @code{memmove}.
5762 These entries are usually resolved by entries in
5763 libc. These entry points should be supplied through some other
5764 mechanism when this option is specified.
5768 Do not use the standard system startup files or libraries when linking.
5769 No startup files and only the libraries you specify will be passed to
5770 the linker. The compiler may generate calls to @code{memcmp}, @code{memset},
5771 @code{memcpy} and @code{memmove}.
5772 These entries are usually resolved by entries in
5773 libc. These entry points should be supplied through some other
5774 mechanism when this option is specified.
5776 @cindex @option{-lgcc}, use with @option{-nostdlib}
5777 @cindex @option{-nostdlib} and unresolved references
5778 @cindex unresolved references and @option{-nostdlib}
5779 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
5780 @cindex @option{-nodefaultlibs} and unresolved references
5781 @cindex unresolved references and @option{-nodefaultlibs}
5782 One of the standard libraries bypassed by @option{-nostdlib} and
5783 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
5784 that GCC uses to overcome shortcomings of particular machines, or special
5785 needs for some languages.
5786 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
5787 Collection (GCC) Internals},
5788 for more discussion of @file{libgcc.a}.)
5789 In most cases, you need @file{libgcc.a} even when you want to avoid
5790 other standard libraries. In other words, when you specify @option{-nostdlib}
5791 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
5792 This ensures that you have no unresolved references to internal GCC
5793 library subroutines. (For example, @samp{__main}, used to ensure C++
5794 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
5795 GNU Compiler Collection (GCC) Internals}.)
5799 Produce a position independent executable on targets which support it.
5800 For predictable results, you must also specify the same set of options
5801 that were used to generate code (@option{-fpie}, @option{-fPIE},
5802 or model suboptions) when you specify this option.
5806 Remove all symbol table and relocation information from the executable.
5810 On systems that support dynamic linking, this prevents linking with the shared
5811 libraries. On other systems, this option has no effect.
5815 Produce a shared object which can then be linked with other objects to
5816 form an executable. Not all systems support this option. For predictable
5817 results, you must also specify the same set of options that were used to
5818 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
5819 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
5820 needs to build supplementary stub code for constructors to work. On
5821 multi-libbed systems, @samp{gcc -shared} must select the correct support
5822 libraries to link against. Failing to supply the correct flags may lead
5823 to subtle defects. Supplying them in cases where they are not necessary
5826 @item -shared-libgcc
5827 @itemx -static-libgcc
5828 @opindex shared-libgcc
5829 @opindex static-libgcc
5830 On systems that provide @file{libgcc} as a shared library, these options
5831 force the use of either the shared or static version respectively.
5832 If no shared version of @file{libgcc} was built when the compiler was
5833 configured, these options have no effect.
5835 There are several situations in which an application should use the
5836 shared @file{libgcc} instead of the static version. The most common
5837 of these is when the application wishes to throw and catch exceptions
5838 across different shared libraries. In that case, each of the libraries
5839 as well as the application itself should use the shared @file{libgcc}.
5841 Therefore, the G++ and GCJ drivers automatically add
5842 @option{-shared-libgcc} whenever you build a shared library or a main
5843 executable, because C++ and Java programs typically use exceptions, so
5844 this is the right thing to do.
5846 If, instead, you use the GCC driver to create shared libraries, you may
5847 find that they will not always be linked with the shared @file{libgcc}.
5848 If GCC finds, at its configuration time, that you have a non-GNU linker
5849 or a GNU linker that does not support option @option{--eh-frame-hdr},
5850 it will link the shared version of @file{libgcc} into shared libraries
5851 by default. Otherwise, it will take advantage of the linker and optimize
5852 away the linking with the shared version of @file{libgcc}, linking with
5853 the static version of libgcc by default. This allows exceptions to
5854 propagate through such shared libraries, without incurring relocation
5855 costs at library load time.
5857 However, if a library or main executable is supposed to throw or catch
5858 exceptions, you must link it using the G++ or GCJ driver, as appropriate
5859 for the languages used in the program, or using the option
5860 @option{-shared-libgcc}, such that it is linked with the shared
5865 Bind references to global symbols when building a shared object. Warn
5866 about any unresolved references (unless overridden by the link editor
5867 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
5870 @item -Xlinker @var{option}
5872 Pass @var{option} as an option to the linker. You can use this to
5873 supply system-specific linker options which GCC does not know how to
5876 If you want to pass an option that takes an argument, you must use
5877 @option{-Xlinker} twice, once for the option and once for the argument.
5878 For example, to pass @option{-assert definitions}, you must write
5879 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
5880 @option{-Xlinker "-assert definitions"}, because this passes the entire
5881 string as a single argument, which is not what the linker expects.
5883 @item -Wl,@var{option}
5885 Pass @var{option} as an option to the linker. If @var{option} contains
5886 commas, it is split into multiple options at the commas.
5888 @item -u @var{symbol}
5890 Pretend the symbol @var{symbol} is undefined, to force linking of
5891 library modules to define it. You can use @option{-u} multiple times with
5892 different symbols to force loading of additional library modules.
5895 @node Directory Options
5896 @section Options for Directory Search
5897 @cindex directory options
5898 @cindex options, directory search
5901 These options specify directories to search for header files, for
5902 libraries and for parts of the compiler:
5907 Add the directory @var{dir} to the head of the list of directories to be
5908 searched for header files. This can be used to override a system header
5909 file, substituting your own version, since these directories are
5910 searched before the system header file directories. However, you should
5911 not use this option to add directories that contain vendor-supplied
5912 system header files (use @option{-isystem} for that). If you use more than
5913 one @option{-I} option, the directories are scanned in left-to-right
5914 order; the standard system directories come after.
5916 If a standard system include directory, or a directory specified with
5917 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
5918 option will be ignored. The directory will still be searched but as a
5919 system directory at its normal position in the system include chain.
5920 This is to ensure that GCC's procedure to fix buggy system headers and
5921 the ordering for the include_next directive are not inadvertently changed.
5922 If you really need to change the search order for system directories,
5923 use the @option{-nostdinc} and/or @option{-isystem} options.
5925 @item -iquote@var{dir}
5927 Add the directory @var{dir} to the head of the list of directories to
5928 be searched for header files only for the case of @samp{#include
5929 "@var{file}"}; they are not searched for @samp{#include <@var{file}>},
5930 otherwise just like @option{-I}.
5934 Add directory @var{dir} to the list of directories to be searched
5937 @item -B@var{prefix}
5939 This option specifies where to find the executables, libraries,
5940 include files, and data files of the compiler itself.
5942 The compiler driver program runs one or more of the subprograms
5943 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
5944 @var{prefix} as a prefix for each program it tries to run, both with and
5945 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
5947 For each subprogram to be run, the compiler driver first tries the
5948 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
5949 was not specified, the driver tries two standard prefixes, which are
5950 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
5951 those results in a file name that is found, the unmodified program
5952 name is searched for using the directories specified in your
5953 @env{PATH} environment variable.
5955 The compiler will check to see if the path provided by the @option{-B}
5956 refers to a directory, and if necessary it will add a directory
5957 separator character at the end of the path.
5959 @option{-B} prefixes that effectively specify directory names also apply
5960 to libraries in the linker, because the compiler translates these
5961 options into @option{-L} options for the linker. They also apply to
5962 includes files in the preprocessor, because the compiler translates these
5963 options into @option{-isystem} options for the preprocessor. In this case,
5964 the compiler appends @samp{include} to the prefix.
5966 The run-time support file @file{libgcc.a} can also be searched for using
5967 the @option{-B} prefix, if needed. If it is not found there, the two
5968 standard prefixes above are tried, and that is all. The file is left
5969 out of the link if it is not found by those means.
5971 Another way to specify a prefix much like the @option{-B} prefix is to use
5972 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
5975 As a special kludge, if the path provided by @option{-B} is
5976 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
5977 9, then it will be replaced by @file{[dir/]include}. This is to help
5978 with boot-strapping the compiler.
5980 @item -specs=@var{file}
5982 Process @var{file} after the compiler reads in the standard @file{specs}
5983 file, in order to override the defaults that the @file{gcc} driver
5984 program uses when determining what switches to pass to @file{cc1},
5985 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
5986 @option{-specs=@var{file}} can be specified on the command line, and they
5987 are processed in order, from left to right.
5991 This option has been deprecated. Please use @option{-iquote} instead for
5992 @option{-I} directories before the @option{-I-} and remove the @option{-I-}.
5993 Any directories you specify with @option{-I} options before the @option{-I-}
5994 option are searched only for the case of @samp{#include "@var{file}"};
5995 they are not searched for @samp{#include <@var{file}>}.
5997 If additional directories are specified with @option{-I} options after
5998 the @option{-I-}, these directories are searched for all @samp{#include}
5999 directives. (Ordinarily @emph{all} @option{-I} directories are used
6002 In addition, the @option{-I-} option inhibits the use of the current
6003 directory (where the current input file came from) as the first search
6004 directory for @samp{#include "@var{file}"}. There is no way to
6005 override this effect of @option{-I-}. With @option{-I.} you can specify
6006 searching the directory which was current when the compiler was
6007 invoked. That is not exactly the same as what the preprocessor does
6008 by default, but it is often satisfactory.
6010 @option{-I-} does not inhibit the use of the standard system directories
6011 for header files. Thus, @option{-I-} and @option{-nostdinc} are
6018 @section Specifying subprocesses and the switches to pass to them
6021 @command{gcc} is a driver program. It performs its job by invoking a
6022 sequence of other programs to do the work of compiling, assembling and
6023 linking. GCC interprets its command-line parameters and uses these to
6024 deduce which programs it should invoke, and which command-line options
6025 it ought to place on their command lines. This behavior is controlled
6026 by @dfn{spec strings}. In most cases there is one spec string for each
6027 program that GCC can invoke, but a few programs have multiple spec
6028 strings to control their behavior. The spec strings built into GCC can
6029 be overridden by using the @option{-specs=} command-line switch to specify
6032 @dfn{Spec files} are plaintext files that are used to construct spec
6033 strings. They consist of a sequence of directives separated by blank
6034 lines. The type of directive is determined by the first non-whitespace
6035 character on the line and it can be one of the following:
6038 @item %@var{command}
6039 Issues a @var{command} to the spec file processor. The commands that can
6043 @item %include <@var{file}>
6045 Search for @var{file} and insert its text at the current point in the
6048 @item %include_noerr <@var{file}>
6049 @cindex %include_noerr
6050 Just like @samp{%include}, but do not generate an error message if the include
6051 file cannot be found.
6053 @item %rename @var{old_name} @var{new_name}
6055 Rename the spec string @var{old_name} to @var{new_name}.
6059 @item *[@var{spec_name}]:
6060 This tells the compiler to create, override or delete the named spec
6061 string. All lines after this directive up to the next directive or
6062 blank line are considered to be the text for the spec string. If this
6063 results in an empty string then the spec will be deleted. (Or, if the
6064 spec did not exist, then nothing will happened.) Otherwise, if the spec
6065 does not currently exist a new spec will be created. If the spec does
6066 exist then its contents will be overridden by the text of this
6067 directive, unless the first character of that text is the @samp{+}
6068 character, in which case the text will be appended to the spec.
6070 @item [@var{suffix}]:
6071 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
6072 and up to the next directive or blank line are considered to make up the
6073 spec string for the indicated suffix. When the compiler encounters an
6074 input file with the named suffix, it will processes the spec string in
6075 order to work out how to compile that file. For example:
6082 This says that any input file whose name ends in @samp{.ZZ} should be
6083 passed to the program @samp{z-compile}, which should be invoked with the
6084 command-line switch @option{-input} and with the result of performing the
6085 @samp{%i} substitution. (See below.)
6087 As an alternative to providing a spec string, the text that follows a
6088 suffix directive can be one of the following:
6091 @item @@@var{language}
6092 This says that the suffix is an alias for a known @var{language}. This is
6093 similar to using the @option{-x} command-line switch to GCC to specify a
6094 language explicitly. For example:
6101 Says that .ZZ files are, in fact, C++ source files.
6104 This causes an error messages saying:
6107 @var{name} compiler not installed on this system.
6111 GCC already has an extensive list of suffixes built into it.
6112 This directive will add an entry to the end of the list of suffixes, but
6113 since the list is searched from the end backwards, it is effectively
6114 possible to override earlier entries using this technique.
6118 GCC has the following spec strings built into it. Spec files can
6119 override these strings or create their own. Note that individual
6120 targets can also add their own spec strings to this list.
6123 asm Options to pass to the assembler
6124 asm_final Options to pass to the assembler post-processor
6125 cpp Options to pass to the C preprocessor
6126 cc1 Options to pass to the C compiler
6127 cc1plus Options to pass to the C++ compiler
6128 endfile Object files to include at the end of the link
6129 link Options to pass to the linker
6130 lib Libraries to include on the command line to the linker
6131 libgcc Decides which GCC support library to pass to the linker
6132 linker Sets the name of the linker
6133 predefines Defines to be passed to the C preprocessor
6134 signed_char Defines to pass to CPP to say whether @code{char} is signed
6136 startfile Object files to include at the start of the link
6139 Here is a small example of a spec file:
6145 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
6148 This example renames the spec called @samp{lib} to @samp{old_lib} and
6149 then overrides the previous definition of @samp{lib} with a new one.
6150 The new definition adds in some extra command-line options before
6151 including the text of the old definition.
6153 @dfn{Spec strings} are a list of command-line options to be passed to their
6154 corresponding program. In addition, the spec strings can contain
6155 @samp{%}-prefixed sequences to substitute variable text or to
6156 conditionally insert text into the command line. Using these constructs
6157 it is possible to generate quite complex command lines.
6159 Here is a table of all defined @samp{%}-sequences for spec
6160 strings. Note that spaces are not generated automatically around the
6161 results of expanding these sequences. Therefore you can concatenate them
6162 together or combine them with constant text in a single argument.
6166 Substitute one @samp{%} into the program name or argument.
6169 Substitute the name of the input file being processed.
6172 Substitute the basename of the input file being processed.
6173 This is the substring up to (and not including) the last period
6174 and not including the directory.
6177 This is the same as @samp{%b}, but include the file suffix (text after
6181 Marks the argument containing or following the @samp{%d} as a
6182 temporary file name, so that that file will be deleted if GCC exits
6183 successfully. Unlike @samp{%g}, this contributes no text to the
6186 @item %g@var{suffix}
6187 Substitute a file name that has suffix @var{suffix} and is chosen
6188 once per compilation, and mark the argument in the same way as
6189 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
6190 name is now chosen in a way that is hard to predict even when previously
6191 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
6192 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
6193 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
6194 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
6195 was simply substituted with a file name chosen once per compilation,
6196 without regard to any appended suffix (which was therefore treated
6197 just like ordinary text), making such attacks more likely to succeed.
6199 @item %u@var{suffix}
6200 Like @samp{%g}, but generates a new temporary file name even if
6201 @samp{%u@var{suffix}} was already seen.
6203 @item %U@var{suffix}
6204 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
6205 new one if there is no such last file name. In the absence of any
6206 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
6207 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
6208 would involve the generation of two distinct file names, one
6209 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
6210 simply substituted with a file name chosen for the previous @samp{%u},
6211 without regard to any appended suffix.
6213 @item %j@var{suffix}
6214 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
6215 writable, and if save-temps is off; otherwise, substitute the name
6216 of a temporary file, just like @samp{%u}. This temporary file is not
6217 meant for communication between processes, but rather as a junk
6220 @item %|@var{suffix}
6221 @itemx %m@var{suffix}
6222 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
6223 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
6224 all. These are the two most common ways to instruct a program that it
6225 should read from standard input or write to standard output. If you
6226 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
6227 construct: see for example @file{f/lang-specs.h}.
6229 @item %.@var{SUFFIX}
6230 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
6231 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
6232 terminated by the next space or %.
6235 Marks the argument containing or following the @samp{%w} as the
6236 designated output file of this compilation. This puts the argument
6237 into the sequence of arguments that @samp{%o} will substitute later.
6240 Substitutes the names of all the output files, with spaces
6241 automatically placed around them. You should write spaces
6242 around the @samp{%o} as well or the results are undefined.
6243 @samp{%o} is for use in the specs for running the linker.
6244 Input files whose names have no recognized suffix are not compiled
6245 at all, but they are included among the output files, so they will
6249 Substitutes the suffix for object files. Note that this is
6250 handled specially when it immediately follows @samp{%g, %u, or %U},
6251 because of the need for those to form complete file names. The
6252 handling is such that @samp{%O} is treated exactly as if it had already
6253 been substituted, except that @samp{%g, %u, and %U} do not currently
6254 support additional @var{suffix} characters following @samp{%O} as they would
6255 following, for example, @samp{.o}.
6258 Substitutes the standard macro predefinitions for the
6259 current target machine. Use this when running @code{cpp}.
6262 Like @samp{%p}, but puts @samp{__} before and after the name of each
6263 predefined macro, except for macros that start with @samp{__} or with
6264 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
6268 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
6269 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}), and
6270 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
6274 Current argument is the name of a library or startup file of some sort.
6275 Search for that file in a standard list of directories and substitute
6276 the full name found.
6279 Print @var{str} as an error message. @var{str} is terminated by a newline.
6280 Use this when inconsistent options are detected.
6283 Substitute the contents of spec string @var{name} at this point.
6286 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
6288 @item %x@{@var{option}@}
6289 Accumulate an option for @samp{%X}.
6292 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
6296 Output the accumulated assembler options specified by @option{-Wa}.
6299 Output the accumulated preprocessor options specified by @option{-Wp}.
6302 Process the @code{asm} spec. This is used to compute the
6303 switches to be passed to the assembler.
6306 Process the @code{asm_final} spec. This is a spec string for
6307 passing switches to an assembler post-processor, if such a program is
6311 Process the @code{link} spec. This is the spec for computing the
6312 command line passed to the linker. Typically it will make use of the
6313 @samp{%L %G %S %D and %E} sequences.
6316 Dump out a @option{-L} option for each directory that GCC believes might
6317 contain startup files. If the target supports multilibs then the
6318 current multilib directory will be prepended to each of these paths.
6321 Output the multilib directory with directory separators replaced with
6322 @samp{_}. If multilib directories are not set, or the multilib directory is
6323 @file{.} then this option emits nothing.
6326 Process the @code{lib} spec. This is a spec string for deciding which
6327 libraries should be included on the command line to the linker.
6330 Process the @code{libgcc} spec. This is a spec string for deciding
6331 which GCC support library should be included on the command line to the linker.
6334 Process the @code{startfile} spec. This is a spec for deciding which
6335 object files should be the first ones passed to the linker. Typically
6336 this might be a file named @file{crt0.o}.
6339 Process the @code{endfile} spec. This is a spec string that specifies
6340 the last object files that will be passed to the linker.
6343 Process the @code{cpp} spec. This is used to construct the arguments
6344 to be passed to the C preprocessor.
6347 Process the @code{cc1} spec. This is used to construct the options to be
6348 passed to the actual C compiler (@samp{cc1}).
6351 Process the @code{cc1plus} spec. This is used to construct the options to be
6352 passed to the actual C++ compiler (@samp{cc1plus}).
6355 Substitute the variable part of a matched option. See below.
6356 Note that each comma in the substituted string is replaced by
6360 Remove all occurrences of @code{-S} from the command line. Note---this
6361 command is position dependent. @samp{%} commands in the spec string
6362 before this one will see @code{-S}, @samp{%} commands in the spec string
6363 after this one will not.
6365 @item %:@var{function}(@var{args})
6366 Call the named function @var{function}, passing it @var{args}.
6367 @var{args} is first processed as a nested spec string, then split
6368 into an argument vector in the usual fashion. The function returns
6369 a string which is processed as if it had appeared literally as part
6370 of the current spec.
6372 The following built-in spec functions are provided:
6375 @item @code{if-exists}
6376 The @code{if-exists} spec function takes one argument, an absolute
6377 pathname to a file. If the file exists, @code{if-exists} returns the
6378 pathname. Here is a small example of its usage:
6382 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
6385 @item @code{if-exists-else}
6386 The @code{if-exists-else} spec function is similar to the @code{if-exists}
6387 spec function, except that it takes two arguments. The first argument is
6388 an absolute pathname to a file. If the file exists, @code{if-exists-else}
6389 returns the pathname. If it does not exist, it returns the second argument.
6390 This way, @code{if-exists-else} can be used to select one file or another,
6391 based on the existence of the first. Here is a small example of its usage:
6395 crt0%O%s %:if-exists(crti%O%s) \
6396 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
6399 @item @code{replace-outfile}
6400 The @code{replace-outfile} spec function takes two arguments. It looks for the
6401 first argument in the outfiles array and replaces it with the second argument. Here
6402 is a small example of its usage:
6405 %@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
6411 Substitutes the @code{-S} switch, if that switch was given to GCC@.
6412 If that switch was not specified, this substitutes nothing. Note that
6413 the leading dash is omitted when specifying this option, and it is
6414 automatically inserted if the substitution is performed. Thus the spec
6415 string @samp{%@{foo@}} would match the command-line option @option{-foo}
6416 and would output the command line option @option{-foo}.
6418 @item %W@{@code{S}@}
6419 Like %@{@code{S}@} but mark last argument supplied within as a file to be
6422 @item %@{@code{S}*@}
6423 Substitutes all the switches specified to GCC whose names start
6424 with @code{-S}, but which also take an argument. This is used for
6425 switches like @option{-o}, @option{-D}, @option{-I}, etc.
6426 GCC considers @option{-o foo} as being
6427 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
6428 text, including the space. Thus two arguments would be generated.
6430 @item %@{@code{S}*&@code{T}*@}
6431 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
6432 (the order of @code{S} and @code{T} in the spec is not significant).
6433 There can be any number of ampersand-separated variables; for each the
6434 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
6436 @item %@{@code{S}:@code{X}@}
6437 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
6439 @item %@{!@code{S}:@code{X}@}
6440 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
6442 @item %@{@code{S}*:@code{X}@}
6443 Substitutes @code{X} if one or more switches whose names start with
6444 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
6445 once, no matter how many such switches appeared. However, if @code{%*}
6446 appears somewhere in @code{X}, then @code{X} will be substituted once
6447 for each matching switch, with the @code{%*} replaced by the part of
6448 that switch that matched the @code{*}.
6450 @item %@{.@code{S}:@code{X}@}
6451 Substitutes @code{X}, if processing a file with suffix @code{S}.
6453 @item %@{!.@code{S}:@code{X}@}
6454 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
6456 @item %@{@code{S}|@code{P}:@code{X}@}
6457 Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@.
6458 This may be combined with @samp{!}, @samp{.}, and @code{*} sequences as well,
6459 although they have a stronger binding than the @samp{|}. If @code{%*}
6460 appears in @code{X}, all of the alternatives must be starred, and only
6461 the first matching alternative is substituted.
6463 For example, a spec string like this:
6466 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
6469 will output the following command-line options from the following input
6470 command-line options:
6475 -d fred.c -foo -baz -boggle
6476 -d jim.d -bar -baz -boggle
6479 @item %@{S:X; T:Y; :D@}
6481 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
6482 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
6483 be as many clauses as you need. This may be combined with @code{.},
6484 @code{!}, @code{|}, and @code{*} as needed.
6489 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
6490 construct may contain other nested @samp{%} constructs or spaces, or
6491 even newlines. They are processed as usual, as described above.
6492 Trailing white space in @code{X} is ignored. White space may also
6493 appear anywhere on the left side of the colon in these constructs,
6494 except between @code{.} or @code{*} and the corresponding word.
6496 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
6497 handled specifically in these constructs. If another value of
6498 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
6499 @option{-W} switch is found later in the command line, the earlier
6500 switch value is ignored, except with @{@code{S}*@} where @code{S} is
6501 just one letter, which passes all matching options.
6503 The character @samp{|} at the beginning of the predicate text is used to
6504 indicate that a command should be piped to the following command, but
6505 only if @option{-pipe} is specified.
6507 It is built into GCC which switches take arguments and which do not.
6508 (You might think it would be useful to generalize this to allow each
6509 compiler's spec to say which switches take arguments. But this cannot
6510 be done in a consistent fashion. GCC cannot even decide which input
6511 files have been specified without knowing which switches take arguments,
6512 and it must know which input files to compile in order to tell which
6515 GCC also knows implicitly that arguments starting in @option{-l} are to be
6516 treated as compiler output files, and passed to the linker in their
6517 proper position among the other output files.
6519 @c man begin OPTIONS
6521 @node Target Options
6522 @section Specifying Target Machine and Compiler Version
6523 @cindex target options
6524 @cindex cross compiling
6525 @cindex specifying machine version
6526 @cindex specifying compiler version and target machine
6527 @cindex compiler version, specifying
6528 @cindex target machine, specifying
6530 The usual way to run GCC is to run the executable called @file{gcc}, or
6531 @file{<machine>-gcc} when cross-compiling, or
6532 @file{<machine>-gcc-<version>} to run a version other than the one that
6533 was installed last. Sometimes this is inconvenient, so GCC provides
6534 options that will switch to another cross-compiler or version.
6537 @item -b @var{machine}
6539 The argument @var{machine} specifies the target machine for compilation.
6541 The value to use for @var{machine} is the same as was specified as the
6542 machine type when configuring GCC as a cross-compiler. For
6543 example, if a cross-compiler was configured with @samp{configure
6544 i386v}, meaning to compile for an 80386 running System V, then you
6545 would specify @option{-b i386v} to run that cross compiler.
6547 @item -V @var{version}
6549 The argument @var{version} specifies which version of GCC to run.
6550 This is useful when multiple versions are installed. For example,
6551 @var{version} might be @samp{2.0}, meaning to run GCC version 2.0.
6554 The @option{-V} and @option{-b} options work by running the
6555 @file{<machine>-gcc-<version>} executable, so there's no real reason to
6556 use them if you can just run that directly.
6558 @node Submodel Options
6559 @section Hardware Models and Configurations
6560 @cindex submodel options
6561 @cindex specifying hardware config
6562 @cindex hardware models and configurations, specifying
6563 @cindex machine dependent options
6565 Earlier we discussed the standard option @option{-b} which chooses among
6566 different installed compilers for completely different target
6567 machines, such as VAX vs.@: 68000 vs.@: 80386.
6569 In addition, each of these target machine types can have its own
6570 special options, starting with @samp{-m}, to choose among various
6571 hardware models or configurations---for example, 68010 vs 68020,
6572 floating coprocessor or none. A single installed version of the
6573 compiler can compile for any model or configuration, according to the
6576 Some configurations of the compiler also support additional special
6577 options, usually for compatibility with other compilers on the same
6580 These options are defined by the macro @code{TARGET_SWITCHES} in the
6581 machine description. The default for the options is also defined by
6582 that macro, which enables you to change the defaults.
6584 @c This list is ordered alphanumerically by subsection name.
6585 @c It should be the same order and spelling as these options are listed
6586 @c in Machine Dependent Options
6594 * DEC Alpha Options::
6595 * DEC Alpha/VMS Options::
6599 * i386 and x86-64 Options::
6611 * RS/6000 and PowerPC Options::
6612 * S/390 and zSeries Options::
6615 * System V Options::
6616 * TMS320C3x/C4x Options::
6620 * Xstormy16 Options::
6626 @subsection ARC Options
6629 These options are defined for ARC implementations:
6634 Compile code for little endian mode. This is the default.
6638 Compile code for big endian mode.
6641 @opindex mmangle-cpu
6642 Prepend the name of the cpu to all public symbol names.
6643 In multiple-processor systems, there are many ARC variants with different
6644 instruction and register set characteristics. This flag prevents code
6645 compiled for one cpu to be linked with code compiled for another.
6646 No facility exists for handling variants that are ``almost identical''.
6647 This is an all or nothing option.
6649 @item -mcpu=@var{cpu}
6651 Compile code for ARC variant @var{cpu}.
6652 Which variants are supported depend on the configuration.
6653 All variants support @option{-mcpu=base}, this is the default.
6655 @item -mtext=@var{text-section}
6656 @itemx -mdata=@var{data-section}
6657 @itemx -mrodata=@var{readonly-data-section}
6661 Put functions, data, and readonly data in @var{text-section},
6662 @var{data-section}, and @var{readonly-data-section} respectively
6663 by default. This can be overridden with the @code{section} attribute.
6664 @xref{Variable Attributes}.
6669 @subsection ARM Options
6672 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
6676 @item -mabi=@var{name}
6678 Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu},
6679 @samp{atpcs}, @samp{aapcs} and @samp{iwmmxt}.
6682 @opindex mapcs-frame
6683 Generate a stack frame that is compliant with the ARM Procedure Call
6684 Standard for all functions, even if this is not strictly necessary for
6685 correct execution of the code. Specifying @option{-fomit-frame-pointer}
6686 with this option will cause the stack frames not to be generated for
6687 leaf functions. The default is @option{-mno-apcs-frame}.
6691 This is a synonym for @option{-mapcs-frame}.
6694 @c not currently implemented
6695 @item -mapcs-stack-check
6696 @opindex mapcs-stack-check
6697 Generate code to check the amount of stack space available upon entry to
6698 every function (that actually uses some stack space). If there is
6699 insufficient space available then either the function
6700 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
6701 called, depending upon the amount of stack space required. The run time
6702 system is required to provide these functions. The default is
6703 @option{-mno-apcs-stack-check}, since this produces smaller code.
6705 @c not currently implemented
6707 @opindex mapcs-float
6708 Pass floating point arguments using the float point registers. This is
6709 one of the variants of the APCS@. This option is recommended if the
6710 target hardware has a floating point unit or if a lot of floating point
6711 arithmetic is going to be performed by the code. The default is
6712 @option{-mno-apcs-float}, since integer only code is slightly increased in
6713 size if @option{-mapcs-float} is used.
6715 @c not currently implemented
6716 @item -mapcs-reentrant
6717 @opindex mapcs-reentrant
6718 Generate reentrant, position independent code. The default is
6719 @option{-mno-apcs-reentrant}.
6722 @item -mthumb-interwork
6723 @opindex mthumb-interwork
6724 Generate code which supports calling between the ARM and Thumb
6725 instruction sets. Without this option the two instruction sets cannot
6726 be reliably used inside one program. The default is
6727 @option{-mno-thumb-interwork}, since slightly larger code is generated
6728 when @option{-mthumb-interwork} is specified.
6730 @item -mno-sched-prolog
6731 @opindex mno-sched-prolog
6732 Prevent the reordering of instructions in the function prolog, or the
6733 merging of those instruction with the instructions in the function's
6734 body. This means that all functions will start with a recognizable set
6735 of instructions (or in fact one of a choice from a small set of
6736 different function prologues), and this information can be used to
6737 locate the start if functions inside an executable piece of code. The
6738 default is @option{-msched-prolog}.
6741 @opindex mhard-float
6742 Generate output containing floating point instructions. This is the
6746 @opindex msoft-float
6747 Generate output containing library calls for floating point.
6748 @strong{Warning:} the requisite libraries are not available for all ARM
6749 targets. Normally the facilities of the machine's usual C compiler are
6750 used, but this cannot be done directly in cross-compilation. You must make
6751 your own arrangements to provide suitable library functions for
6754 @option{-msoft-float} changes the calling convention in the output file;
6755 therefore, it is only useful if you compile @emph{all} of a program with
6756 this option. In particular, you need to compile @file{libgcc.a}, the
6757 library that comes with GCC, with @option{-msoft-float} in order for
6760 @item -mfloat-abi=@var{name}
6762 Specifies which ABI to use for floating point values. Permissible values
6763 are: @samp{soft}, @samp{softfp} and @samp{hard}.
6765 @samp{soft} and @samp{hard} are equivalent to @option{-msoft-float}
6766 and @option{-mhard-float} respectively. @samp{softfp} allows the generation
6767 of floating point instructions, but still uses the soft-float calling
6770 @item -mlittle-endian
6771 @opindex mlittle-endian
6772 Generate code for a processor running in little-endian mode. This is
6773 the default for all standard configurations.
6776 @opindex mbig-endian
6777 Generate code for a processor running in big-endian mode; the default is
6778 to compile code for a little-endian processor.
6780 @item -mwords-little-endian
6781 @opindex mwords-little-endian
6782 This option only applies when generating code for big-endian processors.
6783 Generate code for a little-endian word order but a big-endian byte
6784 order. That is, a byte order of the form @samp{32107654}. Note: this
6785 option should only be used if you require compatibility with code for
6786 big-endian ARM processors generated by versions of the compiler prior to
6789 @item -mcpu=@var{name}
6791 This specifies the name of the target ARM processor. GCC uses this name
6792 to determine what kind of instructions it can emit when generating
6793 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
6794 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
6795 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
6796 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
6797 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
6798 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s},
6799 @samp{arm8}, @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
6800 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
6801 @samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s},
6802 @samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi},
6803 @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s},
6804 @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e},
6805 @samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp},
6806 @samp{arm1176jz-s}, @samp{arm1176jzf-s}, @samp{xscale}, @samp{iwmmxt},
6809 @itemx -mtune=@var{name}
6811 This option is very similar to the @option{-mcpu=} option, except that
6812 instead of specifying the actual target processor type, and hence
6813 restricting which instructions can be used, it specifies that GCC should
6814 tune the performance of the code as if the target were of the type
6815 specified in this option, but still choosing the instructions that it
6816 will generate based on the cpu specified by a @option{-mcpu=} option.
6817 For some ARM implementations better performance can be obtained by using
6820 @item -march=@var{name}
6822 This specifies the name of the target ARM architecture. GCC uses this
6823 name to determine what kind of instructions it can emit when generating
6824 assembly code. This option can be used in conjunction with or instead
6825 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
6826 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
6827 @samp{armv5}, @samp{armv5t}, @samp{armv5te}, @samp{armv6}, @samp{armv6j},
6828 @samp{iwmmxt}, @samp{ep9312}.
6830 @item -mfpu=@var{name}
6831 @itemx -mfpe=@var{number}
6832 @itemx -mfp=@var{number}
6836 This specifies what floating point hardware (or hardware emulation) is
6837 available on the target. Permissible names are: @samp{fpa}, @samp{fpe2},
6838 @samp{fpe3}, @samp{maverick}, @samp{vfp}. @option{-mfp} and @option{-mfpe}
6839 are synonyms for @option{-mfpu}=@samp{fpe}@var{number}, for compatibility
6840 with older versions of GCC@.
6842 If @option{-msoft-float} is specified this specifies the format of
6843 floating point values.
6845 @item -mstructure-size-boundary=@var{n}
6846 @opindex mstructure-size-boundary
6847 The size of all structures and unions will be rounded up to a multiple
6848 of the number of bits set by this option. Permissible values are 8, 32
6849 and 64. The default value varies for different toolchains. For the COFF
6850 targeted toolchain the default value is 8. A value of 64 is only allowed
6851 if the underlying ABI supports it.
6853 Specifying the larger number can produce faster, more efficient code, but
6854 can also increase the size of the program. Different values are potentially
6855 incompatible. Code compiled with one value cannot necessarily expect to
6856 work with code or libraries compiled with another value, if they exchange
6857 information using structures or unions.
6859 @item -mabort-on-noreturn
6860 @opindex mabort-on-noreturn
6861 Generate a call to the function @code{abort} at the end of a
6862 @code{noreturn} function. It will be executed if the function tries to
6866 @itemx -mno-long-calls
6867 @opindex mlong-calls
6868 @opindex mno-long-calls
6869 Tells the compiler to perform function calls by first loading the
6870 address of the function into a register and then performing a subroutine
6871 call on this register. This switch is needed if the target function
6872 will lie outside of the 64 megabyte addressing range of the offset based
6873 version of subroutine call instruction.
6875 Even if this switch is enabled, not all function calls will be turned
6876 into long calls. The heuristic is that static functions, functions
6877 which have the @samp{short-call} attribute, functions that are inside
6878 the scope of a @samp{#pragma no_long_calls} directive and functions whose
6879 definitions have already been compiled within the current compilation
6880 unit, will not be turned into long calls. The exception to this rule is
6881 that weak function definitions, functions with the @samp{long-call}
6882 attribute or the @samp{section} attribute, and functions that are within
6883 the scope of a @samp{#pragma long_calls} directive, will always be
6884 turned into long calls.
6886 This feature is not enabled by default. Specifying
6887 @option{-mno-long-calls} will restore the default behavior, as will
6888 placing the function calls within the scope of a @samp{#pragma
6889 long_calls_off} directive. Note these switches have no effect on how
6890 the compiler generates code to handle function calls via function
6893 @item -mnop-fun-dllimport
6894 @opindex mnop-fun-dllimport
6895 Disable support for the @code{dllimport} attribute.
6897 @item -msingle-pic-base
6898 @opindex msingle-pic-base
6899 Treat the register used for PIC addressing as read-only, rather than
6900 loading it in the prologue for each function. The run-time system is
6901 responsible for initializing this register with an appropriate value
6902 before execution begins.
6904 @item -mpic-register=@var{reg}
6905 @opindex mpic-register
6906 Specify the register to be used for PIC addressing. The default is R10
6907 unless stack-checking is enabled, when R9 is used.
6909 @item -mcirrus-fix-invalid-insns
6910 @opindex mcirrus-fix-invalid-insns
6911 @opindex mno-cirrus-fix-invalid-insns
6912 Insert NOPs into the instruction stream to in order to work around
6913 problems with invalid Maverick instruction combinations. This option
6914 is only valid if the @option{-mcpu=ep9312} option has been used to
6915 enable generation of instructions for the Cirrus Maverick floating
6916 point co-processor. This option is not enabled by default, since the
6917 problem is only present in older Maverick implementations. The default
6918 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
6921 @item -mpoke-function-name
6922 @opindex mpoke-function-name
6923 Write the name of each function into the text section, directly
6924 preceding the function prologue. The generated code is similar to this:
6928 .ascii "arm_poke_function_name", 0
6931 .word 0xff000000 + (t1 - t0)
6932 arm_poke_function_name
6934 stmfd sp!, @{fp, ip, lr, pc@}
6938 When performing a stack backtrace, code can inspect the value of
6939 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
6940 location @code{pc - 12} and the top 8 bits are set, then we know that
6941 there is a function name embedded immediately preceding this location
6942 and has length @code{((pc[-3]) & 0xff000000)}.
6946 Generate code for the 16-bit Thumb instruction set. The default is to
6947 use the 32-bit ARM instruction set.
6950 @opindex mtpcs-frame
6951 Generate a stack frame that is compliant with the Thumb Procedure Call
6952 Standard for all non-leaf functions. (A leaf function is one that does
6953 not call any other functions.) The default is @option{-mno-tpcs-frame}.
6955 @item -mtpcs-leaf-frame
6956 @opindex mtpcs-leaf-frame
6957 Generate a stack frame that is compliant with the Thumb Procedure Call
6958 Standard for all leaf functions. (A leaf function is one that does
6959 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
6961 @item -mcallee-super-interworking
6962 @opindex mcallee-super-interworking
6963 Gives all externally visible functions in the file being compiled an ARM
6964 instruction set header which switches to Thumb mode before executing the
6965 rest of the function. This allows these functions to be called from
6966 non-interworking code.
6968 @item -mcaller-super-interworking
6969 @opindex mcaller-super-interworking
6970 Allows calls via function pointers (including virtual functions) to
6971 execute correctly regardless of whether the target code has been
6972 compiled for interworking or not. There is a small overhead in the cost
6973 of executing a function pointer if this option is enabled.
6978 @subsection AVR Options
6981 These options are defined for AVR implementations:
6984 @item -mmcu=@var{mcu}
6986 Specify ATMEL AVR instruction set or MCU type.
6988 Instruction set avr1 is for the minimal AVR core, not supported by the C
6989 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
6990 attiny11, attiny12, attiny15, attiny28).
6992 Instruction set avr2 (default) is for the classic AVR core with up to
6993 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
6994 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
6995 at90c8534, at90s8535).
6997 Instruction set avr3 is for the classic AVR core with up to 128K program
6998 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
7000 Instruction set avr4 is for the enhanced AVR core with up to 8K program
7001 memory space (MCU types: atmega8, atmega83, atmega85).
7003 Instruction set avr5 is for the enhanced AVR core with up to 128K program
7004 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
7005 atmega64, atmega128, at43usb355, at94k).
7009 Output instruction sizes to the asm file.
7011 @item -minit-stack=@var{N}
7012 @opindex minit-stack
7013 Specify the initial stack address, which may be a symbol or numeric value,
7014 @samp{__stack} is the default.
7016 @item -mno-interrupts
7017 @opindex mno-interrupts
7018 Generated code is not compatible with hardware interrupts.
7019 Code size will be smaller.
7021 @item -mcall-prologues
7022 @opindex mcall-prologues
7023 Functions prologues/epilogues expanded as call to appropriate
7024 subroutines. Code size will be smaller.
7026 @item -mno-tablejump
7027 @opindex mno-tablejump
7028 Do not generate tablejump insns which sometimes increase code size.
7031 @opindex mtiny-stack
7032 Change only the low 8 bits of the stack pointer.
7036 Assume int to be 8 bit integer. This affects the sizes of all types: A
7037 char will be 1 byte, an int will be 1 byte, an long will be 2 bytes
7038 and long long will be 4 bytes. Please note that this option does not
7039 comply to the C standards, but it will provide you with smaller code
7044 @subsection CRIS Options
7045 @cindex CRIS Options
7047 These options are defined specifically for the CRIS ports.
7050 @item -march=@var{architecture-type}
7051 @itemx -mcpu=@var{architecture-type}
7054 Generate code for the specified architecture. The choices for
7055 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
7056 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@.
7057 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
7060 @item -mtune=@var{architecture-type}
7062 Tune to @var{architecture-type} everything applicable about the generated
7063 code, except for the ABI and the set of available instructions. The
7064 choices for @var{architecture-type} are the same as for
7065 @option{-march=@var{architecture-type}}.
7067 @item -mmax-stack-frame=@var{n}
7068 @opindex mmax-stack-frame
7069 Warn when the stack frame of a function exceeds @var{n} bytes.
7071 @item -melinux-stacksize=@var{n}
7072 @opindex melinux-stacksize
7073 Only available with the @samp{cris-axis-aout} target. Arranges for
7074 indications in the program to the kernel loader that the stack of the
7075 program should be set to @var{n} bytes.
7081 The options @option{-metrax4} and @option{-metrax100} are synonyms for
7082 @option{-march=v3} and @option{-march=v8} respectively.
7084 @item -mmul-bug-workaround
7085 @itemx -mno-mul-bug-workaround
7086 @opindex mmul-bug-workaround
7087 @opindex mno-mul-bug-workaround
7088 Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
7089 models where it applies. This option is active by default.
7093 Enable CRIS-specific verbose debug-related information in the assembly
7094 code. This option also has the effect to turn off the @samp{#NO_APP}
7095 formatted-code indicator to the assembler at the beginning of the
7100 Do not use condition-code results from previous instruction; always emit
7101 compare and test instructions before use of condition codes.
7103 @item -mno-side-effects
7104 @opindex mno-side-effects
7105 Do not emit instructions with side-effects in addressing modes other than
7109 @itemx -mno-stack-align
7111 @itemx -mno-data-align
7112 @itemx -mconst-align
7113 @itemx -mno-const-align
7114 @opindex mstack-align
7115 @opindex mno-stack-align
7116 @opindex mdata-align
7117 @opindex mno-data-align
7118 @opindex mconst-align
7119 @opindex mno-const-align
7120 These options (no-options) arranges (eliminate arrangements) for the
7121 stack-frame, individual data and constants to be aligned for the maximum
7122 single data access size for the chosen CPU model. The default is to
7123 arrange for 32-bit alignment. ABI details such as structure layout are
7124 not affected by these options.
7132 Similar to the stack- data- and const-align options above, these options
7133 arrange for stack-frame, writable data and constants to all be 32-bit,
7134 16-bit or 8-bit aligned. The default is 32-bit alignment.
7136 @item -mno-prologue-epilogue
7137 @itemx -mprologue-epilogue
7138 @opindex mno-prologue-epilogue
7139 @opindex mprologue-epilogue
7140 With @option{-mno-prologue-epilogue}, the normal function prologue and
7141 epilogue that sets up the stack-frame are omitted and no return
7142 instructions or return sequences are generated in the code. Use this
7143 option only together with visual inspection of the compiled code: no
7144 warnings or errors are generated when call-saved registers must be saved,
7145 or storage for local variable needs to be allocated.
7151 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
7152 instruction sequences that load addresses for functions from the PLT part
7153 of the GOT rather than (traditional on other architectures) calls to the
7154 PLT@. The default is @option{-mgotplt}.
7158 Legacy no-op option only recognized with the cris-axis-aout target.
7162 Legacy no-op option only recognized with the cris-axis-elf and
7163 cris-axis-linux-gnu targets.
7167 Only recognized with the cris-axis-aout target, where it selects a
7168 GNU/linux-like multilib, include files and instruction set for
7173 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
7177 This option, recognized for the cris-axis-aout and cris-axis-elf arranges
7178 to link with input-output functions from a simulator library. Code,
7179 initialized data and zero-initialized data are allocated consecutively.
7183 Like @option{-sim}, but pass linker options to locate initialized data at
7184 0x40000000 and zero-initialized data at 0x80000000.
7187 @node Darwin Options
7188 @subsection Darwin Options
7189 @cindex Darwin options
7191 These options are defined for all architectures running the Darwin operating
7194 FSF GCC on Darwin does not create ``fat'' object files; it will create
7195 an object file for the single architecture that it was built to
7196 target. Apple's GCC on Darwin does create ``fat'' files if multiple
7197 @option{-arch} options are used; it does so by running the compiler or
7198 linker multiple times and joining the results together with
7201 The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or
7202 @samp{i686}) is determined by the flags that specify the ISA
7203 that GCC is targetting, like @option{-mcpu} or @option{-march}. The
7204 @option{-force_cpusubtype_ALL} option can be used to override this.
7206 The Darwin tools vary in their behaviour when presented with an ISA
7207 mismatch. The assembler, @file{as}, will only permit instructions to
7208 be used that are valid for the subtype of the file it is generating,
7209 so you cannot put 64-bit instructions in an @samp{ppc750} object file.
7210 The linker for shared libraries, @file{/usr/bin/libtool}, will fail
7211 and print an error if asked to create a shared library with a less
7212 restrictive subtype than its input files (for instance, trying to put
7213 a @samp{ppc970} object file in a @samp{ppc7400} library). The linker
7214 for executables, @file{ld}, will quietly give the executable the most
7215 restrictive subtype of any of its input files.
7220 Add the framework directory @var{dir} to the head of the list of
7221 directories to be searched for header files. These directories are
7222 interleaved with those specified by @option{-I} options and are
7223 scanned in a left-to-right order.
7225 A framework directory is a directory with frameworks in it. A
7226 framework is a directory with a @samp{"Headers"} and/or
7227 @samp{"PrivateHeaders"} directory contained directly in it that ends
7228 in @samp{".framework"}. The name of a framework is the name of this
7229 directory excluding the @samp{".framework"}. Headers associated with
7230 the framework are found in one of those two directories, with
7231 @samp{"Headers"} being searched first. A subframework is a framework
7232 directory that is in a framework's @samp{"Frameworks"} directory.
7233 Includes of subframework headers can only appear in a header of a
7234 framework that contains the subframework, or in a sibling subframework
7235 header. Two subframeworks are siblings if they occur in the same
7236 framework. A subframework should not have the same name as a
7237 framework, a warning will be issued if this is violated. Currently a
7238 subframework cannot have subframeworks, in the future, the mechanism
7239 may be extended to support this. The standard frameworks can be found
7240 in @samp{"/System/Library/Frameworks"} and
7241 @samp{"/Library/Frameworks"}. An example include looks like
7242 @code{#include <Framework/header.h>}, where @samp{Framework} denotes
7243 the name of the framework and header.h is found in the
7244 @samp{"PrivateHeaders"} or @samp{"Headers"} directory.
7248 Emit debugging information for symbols that are used. For STABS
7249 debugging format, this enables @option{-feliminate-unused-debug-symbols}.
7250 This is by default ON@.
7254 Emit debugging information for all symbols and types.
7256 @item -mone-byte-bool
7257 @opindex -mone-byte-bool
7258 Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}.
7259 By default @samp{sizeof(bool)} is @samp{4} when compiling for
7260 Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this
7261 option has no effect on x86.
7263 @strong{Warning:} The @option{-mone-byte-bool} switch causes GCC
7264 to generate code that is not binary compatible with code generated
7265 without that switch. Using this switch may require recompiling all
7266 other modules in a program, including system libraries. Use this
7267 switch to conform to a non-default data model.
7269 @item -mfix-and-continue
7270 @itemx -ffix-and-continue
7271 @itemx -findirect-data
7272 @opindex mfix-and-continue
7273 @opindex ffix-and-continue
7274 @opindex findirect-data
7275 Generate code suitable for fast turn around development. Needed to
7276 enable gdb to dynamically load @code{.o} files into already running
7277 programs. @option{-findirect-data} and @option{-ffix-and-continue}
7278 are provided for backwards compatibility.
7282 Loads all members of static archive libraries.
7283 See man ld(1) for more information.
7285 @item -arch_errors_fatal
7286 @opindex arch_errors_fatal
7287 Cause the errors having to do with files that have the wrong architecture
7291 @opindex bind_at_load
7292 Causes the output file to be marked such that the dynamic linker will
7293 bind all undefined references when the file is loaded or launched.
7297 Produce a Mach-o bundle format file.
7298 See man ld(1) for more information.
7300 @item -bundle_loader @var{executable}
7301 @opindex bundle_loader
7302 This option specifies the @var{executable} that will be loading the build
7303 output file being linked. See man ld(1) for more information.
7306 @opindex -dynamiclib
7307 When passed this option, GCC will produce a dynamic library instead of
7308 an executable when linking, using the Darwin @file{libtool} command.
7310 @item -force_cpusubtype_ALL
7311 @opindex -force_cpusubtype_ALL
7312 This causes GCC's output file to have the @var{ALL} subtype, instead of
7313 one controlled by the @option{-mcpu} or @option{-march} option.
7315 @item -allowable_client @var{client_name}
7317 @itemx -compatibility_version
7318 @itemx -current_version
7320 @itemx -dependency-file
7322 @itemx -dylinker_install_name
7324 @itemx -exported_symbols_list
7326 @itemx -flat_namespace
7327 @itemx -force_flat_namespace
7328 @itemx -headerpad_max_install_names
7331 @itemx -install_name
7332 @itemx -keep_private_externs
7333 @itemx -multi_module
7334 @itemx -multiply_defined
7335 @itemx -multiply_defined_unused
7337 @itemx -no_dead_strip_inits_and_terms
7338 @itemx -nofixprebinding
7341 @itemx -noseglinkedit
7342 @itemx -pagezero_size
7344 @itemx -prebind_all_twolevel_modules
7345 @itemx -private_bundle
7346 @itemx -read_only_relocs
7348 @itemx -sectobjectsymbols
7352 @itemx -sectobjectsymbols
7355 @itemx -segs_read_only_addr
7356 @itemx -segs_read_write_addr
7357 @itemx -seg_addr_table
7358 @itemx -seg_addr_table_filename
7361 @itemx -segs_read_only_addr
7362 @itemx -segs_read_write_addr
7363 @itemx -single_module
7366 @itemx -sub_umbrella
7367 @itemx -twolevel_namespace
7370 @itemx -unexported_symbols_list
7371 @itemx -weak_reference_mismatches
7374 @opindex allowable_client
7375 @opindex client_name
7376 @opindex compatibility_version
7377 @opindex current_version
7379 @opindex dependency-file
7381 @opindex dylinker_install_name
7383 @opindex exported_symbols_list
7385 @opindex flat_namespace
7386 @opindex force_flat_namespace
7387 @opindex headerpad_max_install_names
7390 @opindex install_name
7391 @opindex keep_private_externs
7392 @opindex multi_module
7393 @opindex multiply_defined
7394 @opindex multiply_defined_unused
7396 @opindex no_dead_strip_inits_and_terms
7397 @opindex nofixprebinding
7398 @opindex nomultidefs
7400 @opindex noseglinkedit
7401 @opindex pagezero_size
7403 @opindex prebind_all_twolevel_modules
7404 @opindex private_bundle
7405 @opindex read_only_relocs
7407 @opindex sectobjectsymbols
7411 @opindex sectobjectsymbols
7414 @opindex segs_read_only_addr
7415 @opindex segs_read_write_addr
7416 @opindex seg_addr_table
7417 @opindex seg_addr_table_filename
7418 @opindex seglinkedit
7420 @opindex segs_read_only_addr
7421 @opindex segs_read_write_addr
7422 @opindex single_module
7424 @opindex sub_library
7425 @opindex sub_umbrella
7426 @opindex twolevel_namespace
7429 @opindex unexported_symbols_list
7430 @opindex weak_reference_mismatches
7431 @opindex whatsloaded
7433 These options are passed to the Darwin linker. The Darwin linker man page
7434 describes them in detail.
7437 @node DEC Alpha Options
7438 @subsection DEC Alpha Options
7440 These @samp{-m} options are defined for the DEC Alpha implementations:
7443 @item -mno-soft-float
7445 @opindex mno-soft-float
7446 @opindex msoft-float
7447 Use (do not use) the hardware floating-point instructions for
7448 floating-point operations. When @option{-msoft-float} is specified,
7449 functions in @file{libgcc.a} will be used to perform floating-point
7450 operations. Unless they are replaced by routines that emulate the
7451 floating-point operations, or compiled in such a way as to call such
7452 emulations routines, these routines will issue floating-point
7453 operations. If you are compiling for an Alpha without floating-point
7454 operations, you must ensure that the library is built so as not to call
7457 Note that Alpha implementations without floating-point operations are
7458 required to have floating-point registers.
7463 @opindex mno-fp-regs
7464 Generate code that uses (does not use) the floating-point register set.
7465 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
7466 register set is not used, floating point operands are passed in integer
7467 registers as if they were integers and floating-point results are passed
7468 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
7469 so any function with a floating-point argument or return value called by code
7470 compiled with @option{-mno-fp-regs} must also be compiled with that
7473 A typical use of this option is building a kernel that does not use,
7474 and hence need not save and restore, any floating-point registers.
7478 The Alpha architecture implements floating-point hardware optimized for
7479 maximum performance. It is mostly compliant with the IEEE floating
7480 point standard. However, for full compliance, software assistance is
7481 required. This option generates code fully IEEE compliant code
7482 @emph{except} that the @var{inexact-flag} is not maintained (see below).
7483 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
7484 defined during compilation. The resulting code is less efficient but is
7485 able to correctly support denormalized numbers and exceptional IEEE
7486 values such as not-a-number and plus/minus infinity. Other Alpha
7487 compilers call this option @option{-ieee_with_no_inexact}.
7489 @item -mieee-with-inexact
7490 @opindex mieee-with-inexact
7491 This is like @option{-mieee} except the generated code also maintains
7492 the IEEE @var{inexact-flag}. Turning on this option causes the
7493 generated code to implement fully-compliant IEEE math. In addition to
7494 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
7495 macro. On some Alpha implementations the resulting code may execute
7496 significantly slower than the code generated by default. Since there is
7497 very little code that depends on the @var{inexact-flag}, you should
7498 normally not specify this option. Other Alpha compilers call this
7499 option @option{-ieee_with_inexact}.
7501 @item -mfp-trap-mode=@var{trap-mode}
7502 @opindex mfp-trap-mode
7503 This option controls what floating-point related traps are enabled.
7504 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
7505 The trap mode can be set to one of four values:
7509 This is the default (normal) setting. The only traps that are enabled
7510 are the ones that cannot be disabled in software (e.g., division by zero
7514 In addition to the traps enabled by @samp{n}, underflow traps are enabled
7518 Like @samp{su}, but the instructions are marked to be safe for software
7519 completion (see Alpha architecture manual for details).
7522 Like @samp{su}, but inexact traps are enabled as well.
7525 @item -mfp-rounding-mode=@var{rounding-mode}
7526 @opindex mfp-rounding-mode
7527 Selects the IEEE rounding mode. Other Alpha compilers call this option
7528 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
7533 Normal IEEE rounding mode. Floating point numbers are rounded towards
7534 the nearest machine number or towards the even machine number in case
7538 Round towards minus infinity.
7541 Chopped rounding mode. Floating point numbers are rounded towards zero.
7544 Dynamic rounding mode. A field in the floating point control register
7545 (@var{fpcr}, see Alpha architecture reference manual) controls the
7546 rounding mode in effect. The C library initializes this register for
7547 rounding towards plus infinity. Thus, unless your program modifies the
7548 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
7551 @item -mtrap-precision=@var{trap-precision}
7552 @opindex mtrap-precision
7553 In the Alpha architecture, floating point traps are imprecise. This
7554 means without software assistance it is impossible to recover from a
7555 floating trap and program execution normally needs to be terminated.
7556 GCC can generate code that can assist operating system trap handlers
7557 in determining the exact location that caused a floating point trap.
7558 Depending on the requirements of an application, different levels of
7559 precisions can be selected:
7563 Program precision. This option is the default and means a trap handler
7564 can only identify which program caused a floating point exception.
7567 Function precision. The trap handler can determine the function that
7568 caused a floating point exception.
7571 Instruction precision. The trap handler can determine the exact
7572 instruction that caused a floating point exception.
7575 Other Alpha compilers provide the equivalent options called
7576 @option{-scope_safe} and @option{-resumption_safe}.
7578 @item -mieee-conformant
7579 @opindex mieee-conformant
7580 This option marks the generated code as IEEE conformant. You must not
7581 use this option unless you also specify @option{-mtrap-precision=i} and either
7582 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
7583 is to emit the line @samp{.eflag 48} in the function prologue of the
7584 generated assembly file. Under DEC Unix, this has the effect that
7585 IEEE-conformant math library routines will be linked in.
7587 @item -mbuild-constants
7588 @opindex mbuild-constants
7589 Normally GCC examines a 32- or 64-bit integer constant to
7590 see if it can construct it from smaller constants in two or three
7591 instructions. If it cannot, it will output the constant as a literal and
7592 generate code to load it from the data segment at runtime.
7594 Use this option to require GCC to construct @emph{all} integer constants
7595 using code, even if it takes more instructions (the maximum is six).
7597 You would typically use this option to build a shared library dynamic
7598 loader. Itself a shared library, it must relocate itself in memory
7599 before it can find the variables and constants in its own data segment.
7605 Select whether to generate code to be assembled by the vendor-supplied
7606 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
7624 Indicate whether GCC should generate code to use the optional BWX,
7625 CIX, FIX and MAX instruction sets. The default is to use the instruction
7626 sets supported by the CPU type specified via @option{-mcpu=} option or that
7627 of the CPU on which GCC was built if none was specified.
7632 @opindex mfloat-ieee
7633 Generate code that uses (does not use) VAX F and G floating point
7634 arithmetic instead of IEEE single and double precision.
7636 @item -mexplicit-relocs
7637 @itemx -mno-explicit-relocs
7638 @opindex mexplicit-relocs
7639 @opindex mno-explicit-relocs
7640 Older Alpha assemblers provided no way to generate symbol relocations
7641 except via assembler macros. Use of these macros does not allow
7642 optimal instruction scheduling. GNU binutils as of version 2.12
7643 supports a new syntax that allows the compiler to explicitly mark
7644 which relocations should apply to which instructions. This option
7645 is mostly useful for debugging, as GCC detects the capabilities of
7646 the assembler when it is built and sets the default accordingly.
7650 @opindex msmall-data
7651 @opindex mlarge-data
7652 When @option{-mexplicit-relocs} is in effect, static data is
7653 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
7654 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
7655 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
7656 16-bit relocations off of the @code{$gp} register. This limits the
7657 size of the small data area to 64KB, but allows the variables to be
7658 directly accessed via a single instruction.
7660 The default is @option{-mlarge-data}. With this option the data area
7661 is limited to just below 2GB@. Programs that require more than 2GB of
7662 data must use @code{malloc} or @code{mmap} to allocate the data in the
7663 heap instead of in the program's data segment.
7665 When generating code for shared libraries, @option{-fpic} implies
7666 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
7670 @opindex msmall-text
7671 @opindex mlarge-text
7672 When @option{-msmall-text} is used, the compiler assumes that the
7673 code of the entire program (or shared library) fits in 4MB, and is
7674 thus reachable with a branch instruction. When @option{-msmall-data}
7675 is used, the compiler can assume that all local symbols share the
7676 same @code{$gp} value, and thus reduce the number of instructions
7677 required for a function call from 4 to 1.
7679 The default is @option{-mlarge-text}.
7681 @item -mcpu=@var{cpu_type}
7683 Set the instruction set and instruction scheduling parameters for
7684 machine type @var{cpu_type}. You can specify either the @samp{EV}
7685 style name or the corresponding chip number. GCC supports scheduling
7686 parameters for the EV4, EV5 and EV6 family of processors and will
7687 choose the default values for the instruction set from the processor
7688 you specify. If you do not specify a processor type, GCC will default
7689 to the processor on which the compiler was built.
7691 Supported values for @var{cpu_type} are
7697 Schedules as an EV4 and has no instruction set extensions.
7701 Schedules as an EV5 and has no instruction set extensions.
7705 Schedules as an EV5 and supports the BWX extension.
7710 Schedules as an EV5 and supports the BWX and MAX extensions.
7714 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
7718 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
7721 @item -mtune=@var{cpu_type}
7723 Set only the instruction scheduling parameters for machine type
7724 @var{cpu_type}. The instruction set is not changed.
7726 @item -mmemory-latency=@var{time}
7727 @opindex mmemory-latency
7728 Sets the latency the scheduler should assume for typical memory
7729 references as seen by the application. This number is highly
7730 dependent on the memory access patterns used by the application
7731 and the size of the external cache on the machine.
7733 Valid options for @var{time} are
7737 A decimal number representing clock cycles.
7743 The compiler contains estimates of the number of clock cycles for
7744 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
7745 (also called Dcache, Scache, and Bcache), as well as to main memory.
7746 Note that L3 is only valid for EV5.
7751 @node DEC Alpha/VMS Options
7752 @subsection DEC Alpha/VMS Options
7754 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
7757 @item -mvms-return-codes
7758 @opindex mvms-return-codes
7759 Return VMS condition codes from main. The default is to return POSIX
7760 style condition (e.g.@ error) codes.
7764 @subsection FRV Options
7771 Only use the first 32 general purpose registers.
7776 Use all 64 general purpose registers.
7781 Use only the first 32 floating point registers.
7786 Use all 64 floating point registers
7789 @opindex mhard-float
7791 Use hardware instructions for floating point operations.
7794 @opindex msoft-float
7796 Use library routines for floating point operations.
7801 Dynamically allocate condition code registers.
7806 Do not try to dynamically allocate condition code registers, only
7807 use @code{icc0} and @code{fcc0}.
7812 Change ABI to use double word insns.
7817 Do not use double word instructions.
7822 Use floating point double instructions.
7827 Do not use floating point double instructions.
7832 Use media instructions.
7837 Do not use media instructions.
7842 Use multiply and add/subtract instructions.
7847 Do not use multiply and add/subtract instructions.
7852 Select the FDPIC ABI, that uses function descriptors to represent
7853 pointers to functions. Without any PIC/PIE-related options, it
7854 implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it
7855 assumes GOT entries and small data are within a 12-bit range from the
7856 GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets
7857 are computed with 32 bits.
7860 @opindex minline-plt
7862 Enable inlining of PLT entries in function calls to functions that are
7863 not known to bind locally. It has no effect without @option{-mfdpic}.
7864 It's enabled by default if optimizing for speed and compiling for
7865 shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an
7866 optimization option such as @option{-O3} or above is present in the
7872 Enable the use of @code{GPREL} relocations in the FDPIC ABI for data
7873 that is known to be in read-only sections. It's enabled by default,
7874 except for @option{-fpic} or @option{-fpie}: even though it may help
7875 make the global offset table smaller, it trades 1 instruction for 4.
7876 With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4,
7877 one of which may be shared by multiple symbols, and it avoids the need
7878 for a GOT entry for the referenced symbol, so it's more likely to be a
7879 win. If it is not, @option{-mno-gprel-ro} can be used to disable it.
7881 @item -multilib-library-pic
7882 @opindex multilib-library-pic
7884 Link with the (library, not FD) pic libraries. It's implied by
7885 @option{-mlibrary-pic}, as well as by @option{-fPIC} and
7886 @option{-fpic} without @option{-mfdpic}. You should never have to use
7892 Follow the EABI requirement of always creating a frame pointer whenever
7893 a stack frame is allocated. This option is enabled by default and can
7894 be disabled with @option{-mno-linked-fp}.
7897 @opindex mlong-calls
7899 Use indirect addressing to call functions outside the current
7900 compilation unit. This allows the functions to be placed anywhere
7901 within the 32-bit address space.
7903 @item -malign-labels
7904 @opindex malign-labels
7906 Try to align labels to an 8-byte boundary by inserting nops into the
7907 previous packet. This option only has an effect when VLIW packing
7908 is enabled. It doesn't create new packets; it merely adds nops to
7912 @opindex mlibrary-pic
7914 Generate position-independent EABI code.
7919 Use only the first four media accumulator registers.
7924 Use all eight media accumulator registers.
7929 Pack VLIW instructions.
7934 Do not pack VLIW instructions.
7939 Do not mark ABI switches in e_flags.
7944 Enable the use of conditional-move instructions (default).
7946 This switch is mainly for debugging the compiler and will likely be removed
7947 in a future version.
7949 @item -mno-cond-move
7950 @opindex mno-cond-move
7952 Disable the use of conditional-move instructions.
7954 This switch is mainly for debugging the compiler and will likely be removed
7955 in a future version.
7960 Enable the use of conditional set instructions (default).
7962 This switch is mainly for debugging the compiler and will likely be removed
7963 in a future version.
7968 Disable the use of conditional set instructions.
7970 This switch is mainly for debugging the compiler and will likely be removed
7971 in a future version.
7976 Enable the use of conditional execution (default).
7978 This switch is mainly for debugging the compiler and will likely be removed
7979 in a future version.
7981 @item -mno-cond-exec
7982 @opindex mno-cond-exec
7984 Disable the use of conditional execution.
7986 This switch is mainly for debugging the compiler and will likely be removed
7987 in a future version.
7990 @opindex mvliw-branch
7992 Run a pass to pack branches into VLIW instructions (default).
7994 This switch is mainly for debugging the compiler and will likely be removed
7995 in a future version.
7997 @item -mno-vliw-branch
7998 @opindex mno-vliw-branch
8000 Do not run a pass to pack branches into VLIW instructions.
8002 This switch is mainly for debugging the compiler and will likely be removed
8003 in a future version.
8005 @item -mmulti-cond-exec
8006 @opindex mmulti-cond-exec
8008 Enable optimization of @code{&&} and @code{||} in conditional execution
8011 This switch is mainly for debugging the compiler and will likely be removed
8012 in a future version.
8014 @item -mno-multi-cond-exec
8015 @opindex mno-multi-cond-exec
8017 Disable optimization of @code{&&} and @code{||} in conditional execution.
8019 This switch is mainly for debugging the compiler and will likely be removed
8020 in a future version.
8022 @item -mnested-cond-exec
8023 @opindex mnested-cond-exec
8025 Enable nested conditional execution optimizations (default).
8027 This switch is mainly for debugging the compiler and will likely be removed
8028 in a future version.
8030 @item -mno-nested-cond-exec
8031 @opindex mno-nested-cond-exec
8033 Disable nested conditional execution optimizations.
8035 This switch is mainly for debugging the compiler and will likely be removed
8036 in a future version.
8038 @item -mtomcat-stats
8039 @opindex mtomcat-stats
8041 Cause gas to print out tomcat statistics.
8043 @item -mcpu=@var{cpu}
8046 Select the processor type for which to generate code. Possible values are
8047 @samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450},
8048 @samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}.
8052 @node H8/300 Options
8053 @subsection H8/300 Options
8055 These @samp{-m} options are defined for the H8/300 implementations:
8060 Shorten some address references at link time, when possible; uses the
8061 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
8062 ld, Using ld}, for a fuller description.
8066 Generate code for the H8/300H@.
8070 Generate code for the H8S@.
8074 Generate code for the H8S and H8/300H in the normal mode. This switch
8075 must be used either with @option{-mh} or @option{-ms}.
8079 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
8083 Make @code{int} data 32 bits by default.
8087 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
8088 The default for the H8/300H and H8S is to align longs and floats on 4
8090 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
8091 This option has no effect on the H8/300.
8095 @subsection HPPA Options
8096 @cindex HPPA Options
8098 These @samp{-m} options are defined for the HPPA family of computers:
8101 @item -march=@var{architecture-type}
8103 Generate code for the specified architecture. The choices for
8104 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
8105 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
8106 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
8107 architecture option for your machine. Code compiled for lower numbered
8108 architectures will run on higher numbered architectures, but not the
8112 @itemx -mpa-risc-1-1
8113 @itemx -mpa-risc-2-0
8114 @opindex mpa-risc-1-0
8115 @opindex mpa-risc-1-1
8116 @opindex mpa-risc-2-0
8117 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
8120 @opindex mbig-switch
8121 Generate code suitable for big switch tables. Use this option only if
8122 the assembler/linker complain about out of range branches within a switch
8125 @item -mjump-in-delay
8126 @opindex mjump-in-delay
8127 Fill delay slots of function calls with unconditional jump instructions
8128 by modifying the return pointer for the function call to be the target
8129 of the conditional jump.
8131 @item -mdisable-fpregs
8132 @opindex mdisable-fpregs
8133 Prevent floating point registers from being used in any manner. This is
8134 necessary for compiling kernels which perform lazy context switching of
8135 floating point registers. If you use this option and attempt to perform
8136 floating point operations, the compiler will abort.
8138 @item -mdisable-indexing
8139 @opindex mdisable-indexing
8140 Prevent the compiler from using indexing address modes. This avoids some
8141 rather obscure problems when compiling MIG generated code under MACH@.
8143 @item -mno-space-regs
8144 @opindex mno-space-regs
8145 Generate code that assumes the target has no space registers. This allows
8146 GCC to generate faster indirect calls and use unscaled index address modes.
8148 Such code is suitable for level 0 PA systems and kernels.
8150 @item -mfast-indirect-calls
8151 @opindex mfast-indirect-calls
8152 Generate code that assumes calls never cross space boundaries. This
8153 allows GCC to emit code which performs faster indirect calls.
8155 This option will not work in the presence of shared libraries or nested
8158 @item -mfixed-range=@var{register-range}
8159 @opindex mfixed-range
8160 Generate code treating the given register range as fixed registers.
8161 A fixed register is one that the register allocator can not use. This is
8162 useful when compiling kernel code. A register range is specified as
8163 two registers separated by a dash. Multiple register ranges can be
8164 specified separated by a comma.
8166 @item -mlong-load-store
8167 @opindex mlong-load-store
8168 Generate 3-instruction load and store sequences as sometimes required by
8169 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
8172 @item -mportable-runtime
8173 @opindex mportable-runtime
8174 Use the portable calling conventions proposed by HP for ELF systems.
8178 Enable the use of assembler directives only GAS understands.
8180 @item -mschedule=@var{cpu-type}
8182 Schedule code according to the constraints for the machine type
8183 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
8184 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
8185 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
8186 proper scheduling option for your machine. The default scheduling is
8190 @opindex mlinker-opt
8191 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
8192 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
8193 linkers in which they give bogus error messages when linking some programs.
8196 @opindex msoft-float
8197 Generate output containing library calls for floating point.
8198 @strong{Warning:} the requisite libraries are not available for all HPPA
8199 targets. Normally the facilities of the machine's usual C compiler are
8200 used, but this cannot be done directly in cross-compilation. You must make
8201 your own arrangements to provide suitable library functions for
8202 cross-compilation. The embedded target @samp{hppa1.1-*-pro}
8203 does provide software floating point support.
8205 @option{-msoft-float} changes the calling convention in the output file;
8206 therefore, it is only useful if you compile @emph{all} of a program with
8207 this option. In particular, you need to compile @file{libgcc.a}, the
8208 library that comes with GCC, with @option{-msoft-float} in order for
8213 Generate the predefine, @code{_SIO}, for server IO@. The default is
8214 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
8215 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These
8216 options are available under HP-UX and HI-UX@.
8220 Use GNU ld specific options. This passes @option{-shared} to ld when
8221 building a shared library. It is the default when GCC is configured,
8222 explicitly or implicitly, with the GNU linker. This option does not
8223 have any affect on which ld is called, it only changes what parameters
8224 are passed to that ld. The ld that is called is determined by the
8225 @option{--with-ld} configure option, GCC's program search path, and
8226 finally by the user's @env{PATH}. The linker used by GCC can be printed
8227 using @samp{which `gcc -print-prog-name=ld`}.
8231 Use HP ld specific options. This passes @option{-b} to ld when building
8232 a shared library and passes @option{+Accept TypeMismatch} to ld on all
8233 links. It is the default when GCC is configured, explicitly or
8234 implicitly, with the HP linker. This option does not have any affect on
8235 which ld is called, it only changes what parameters are passed to that
8236 ld. The ld that is called is determined by the @option{--with-ld}
8237 configure option, GCC's program search path, and finally by the user's
8238 @env{PATH}. The linker used by GCC can be printed using @samp{which
8239 `gcc -print-prog-name=ld`}.
8242 @opindex mno-long-calls
8243 Generate code that uses long call sequences. This ensures that a call
8244 is always able to reach linker generated stubs. The default is to generate
8245 long calls only when the distance from the call site to the beginning
8246 of the function or translation unit, as the case may be, exceeds a
8247 predefined limit set by the branch type being used. The limits for
8248 normal calls are 7,600,000 and 240,000 bytes, respectively for the
8249 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
8252 Distances are measured from the beginning of functions when using the
8253 @option{-ffunction-sections} option, or when using the @option{-mgas}
8254 and @option{-mno-portable-runtime} options together under HP-UX with
8257 It is normally not desirable to use this option as it will degrade
8258 performance. However, it may be useful in large applications,
8259 particularly when partial linking is used to build the application.
8261 The types of long calls used depends on the capabilities of the
8262 assembler and linker, and the type of code being generated. The
8263 impact on systems that support long absolute calls, and long pic
8264 symbol-difference or pc-relative calls should be relatively small.
8265 However, an indirect call is used on 32-bit ELF systems in pic code
8266 and it is quite long.
8268 @item -munix=@var{unix-std}
8270 Generate compiler predefines and select a startfile for the specified
8271 UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95}
8272 and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95}
8273 is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX
8274 11.11 and later. The default values are @samp{93} for HP-UX 10.00,
8275 @samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11
8278 @option{-munix=93} provides the same predefines as GCC 3.3 and 3.4.
8279 @option{-munix=95} provides additional predefines for @code{XOPEN_UNIX}
8280 and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}.
8281 @option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX},
8282 @code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and
8283 @code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}.
8285 It is @emph{important} to note that this option changes the interfaces
8286 for various library routines. It also affects the operational behavior
8287 of the C library. Thus, @emph{extreme} care is needed in using this
8290 Library code that is intended to operate with more than one UNIX
8291 standard must test, set and restore the variable @var{__xpg4_extended_mask}
8292 as appropriate. Most GNU software doesn't provide this capability.
8296 Suppress the generation of link options to search libdld.sl when the
8297 @option{-static} option is specified on HP-UX 10 and later.
8301 The HP-UX implementation of setlocale in libc has a dependency on
8302 libdld.sl. There isn't an archive version of libdld.sl. Thus,
8303 when the @option{-static} option is specified, special link options
8304 are needed to resolve this dependency.
8306 On HP-UX 10 and later, the GCC driver adds the necessary options to
8307 link with libdld.sl when the @option{-static} option is specified.
8308 This causes the resulting binary to be dynamic. On the 64-bit port,
8309 the linkers generate dynamic binaries by default in any case. The
8310 @option{-nolibdld} option can be used to prevent the GCC driver from
8311 adding these link options.
8315 Add support for multithreading with the @dfn{dce thread} library
8316 under HP-UX@. This option sets flags for both the preprocessor and
8320 @node i386 and x86-64 Options
8321 @subsection Intel 386 and AMD x86-64 Options
8322 @cindex i386 Options
8323 @cindex x86-64 Options
8324 @cindex Intel 386 Options
8325 @cindex AMD x86-64 Options
8327 These @samp{-m} options are defined for the i386 and x86-64 family of
8331 @item -mtune=@var{cpu-type}
8333 Tune to @var{cpu-type} everything applicable about the generated code, except
8334 for the ABI and the set of available instructions. The choices for
8338 Original Intel's i386 CPU@.
8340 Intel's i486 CPU@. (No scheduling is implemented for this chip.)
8342 Intel Pentium CPU with no MMX support.
8344 Intel PentiumMMX CPU based on Pentium core with MMX instruction set support.
8345 @item i686, pentiumpro
8346 Intel PentiumPro CPU@.
8348 Intel Pentium2 CPU based on PentiumPro core with MMX instruction set support.
8349 @item pentium3, pentium3m
8350 Intel Pentium3 CPU based on PentiumPro core with MMX and SSE instruction set
8353 Low power version of Intel Pentium3 CPU with MMX, SSE and SSE2 instruction set
8354 support. Used by Centrino notebooks.
8355 @item pentium4, pentium4m
8356 Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set support.
8358 Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and SSE3 instruction
8361 Improved version of Intel Pentium4 CPU with 64-bit extensions, MMX, SSE,
8362 SSE2 and SSE3 instruction set support.
8364 AMD K6 CPU with MMX instruction set support.
8366 Improved versions of AMD K6 CPU with MMX and 3dNOW! instruction set support.
8367 @item athlon, athlon-tbird
8368 AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and SSE prefetch instructions
8370 @item athlon-4, athlon-xp, athlon-mp
8371 Improved AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and full SSE
8372 instruction set support.
8373 @item k8, opteron, athlon64, athlon-fx
8374 AMD K8 core based CPUs with x86-64 instruction set support. (This supersets
8375 MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW! and 64-bit instruction set extensions.)
8377 IDT Winchip C6 CPU, dealt in same way as i486 with additional MMX instruction
8380 IDT Winchip2 CPU, dealt in same way as i486 with additional MMX and 3dNOW!
8381 instruction set support.
8383 Via C3 CPU with MMX and 3dNOW! instruction set support. (No scheduling is
8384 implemented for this chip.)
8386 Via C3-2 CPU with MMX and SSE instruction set support. (No scheduling is
8387 implemented for this chip.)
8390 While picking a specific @var{cpu-type} will schedule things appropriately
8391 for that particular chip, the compiler will not generate any code that
8392 does not run on the i386 without the @option{-march=@var{cpu-type}} option
8395 @item -march=@var{cpu-type}
8397 Generate instructions for the machine type @var{cpu-type}. The choices
8398 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
8399 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
8401 @item -mcpu=@var{cpu-type}
8403 A deprecated synonym for @option{-mtune}.
8412 @opindex mpentiumpro
8413 These options are synonyms for @option{-mtune=i386}, @option{-mtune=i486},
8414 @option{-mtune=pentium}, and @option{-mtune=pentiumpro} respectively.
8415 These synonyms are deprecated.
8417 @item -mfpmath=@var{unit}
8419 Generate floating point arithmetics for selected unit @var{unit}. The choices
8424 Use the standard 387 floating point coprocessor present majority of chips and
8425 emulated otherwise. Code compiled with this option will run almost everywhere.
8426 The temporary results are computed in 80bit precision instead of precision
8427 specified by the type resulting in slightly different results compared to most
8428 of other chips. See @option{-ffloat-store} for more detailed description.
8430 This is the default choice for i386 compiler.
8433 Use scalar floating point instructions present in the SSE instruction set.
8434 This instruction set is supported by Pentium3 and newer chips, in the AMD line
8435 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
8436 instruction set supports only single precision arithmetics, thus the double and
8437 extended precision arithmetics is still done using 387. Later version, present
8438 only in Pentium4 and the future AMD x86-64 chips supports double precision
8441 For i387 you need to use @option{-march=@var{cpu-type}}, @option{-msse} or
8442 @option{-msse2} switches to enable SSE extensions and make this option
8443 effective. For x86-64 compiler, these extensions are enabled by default.
8445 The resulting code should be considerably faster in the majority of cases and avoid
8446 the numerical instability problems of 387 code, but may break some existing
8447 code that expects temporaries to be 80bit.
8449 This is the default choice for the x86-64 compiler.
8452 Attempt to utilize both instruction sets at once. This effectively double the
8453 amount of available registers and on chips with separate execution units for
8454 387 and SSE the execution resources too. Use this option with care, as it is
8455 still experimental, because the GCC register allocator does not model separate
8456 functional units well resulting in instable performance.
8459 @item -masm=@var{dialect}
8460 @opindex masm=@var{dialect}
8461 Output asm instructions using selected @var{dialect}. Supported choices are
8462 @samp{intel} or @samp{att} (the default one).
8467 @opindex mno-ieee-fp
8468 Control whether or not the compiler uses IEEE floating point
8469 comparisons. These handle correctly the case where the result of a
8470 comparison is unordered.
8473 @opindex msoft-float
8474 Generate output containing library calls for floating point.
8475 @strong{Warning:} the requisite libraries are not part of GCC@.
8476 Normally the facilities of the machine's usual C compiler are used, but
8477 this can't be done directly in cross-compilation. You must make your
8478 own arrangements to provide suitable library functions for
8481 On machines where a function returns floating point results in the 80387
8482 register stack, some floating point opcodes may be emitted even if
8483 @option{-msoft-float} is used.
8485 @item -mno-fp-ret-in-387
8486 @opindex mno-fp-ret-in-387
8487 Do not use the FPU registers for return values of functions.
8489 The usual calling convention has functions return values of types
8490 @code{float} and @code{double} in an FPU register, even if there
8491 is no FPU@. The idea is that the operating system should emulate
8494 The option @option{-mno-fp-ret-in-387} causes such values to be returned
8495 in ordinary CPU registers instead.
8497 @item -mno-fancy-math-387
8498 @opindex mno-fancy-math-387
8499 Some 387 emulators do not support the @code{sin}, @code{cos} and
8500 @code{sqrt} instructions for the 387. Specify this option to avoid
8501 generating those instructions. This option is the default on FreeBSD,
8502 OpenBSD and NetBSD@. This option is overridden when @option{-march}
8503 indicates that the target cpu will always have an FPU and so the
8504 instruction will not need emulation. As of revision 2.6.1, these
8505 instructions are not generated unless you also use the
8506 @option{-funsafe-math-optimizations} switch.
8508 @item -malign-double
8509 @itemx -mno-align-double
8510 @opindex malign-double
8511 @opindex mno-align-double
8512 Control whether GCC aligns @code{double}, @code{long double}, and
8513 @code{long long} variables on a two word boundary or a one word
8514 boundary. Aligning @code{double} variables on a two word boundary will
8515 produce code that runs somewhat faster on a @samp{Pentium} at the
8516 expense of more memory.
8518 @strong{Warning:} if you use the @option{-malign-double} switch,
8519 structures containing the above types will be aligned differently than
8520 the published application binary interface specifications for the 386
8521 and will not be binary compatible with structures in code compiled
8522 without that switch.
8524 @item -m96bit-long-double
8525 @itemx -m128bit-long-double
8526 @opindex m96bit-long-double
8527 @opindex m128bit-long-double
8528 These switches control the size of @code{long double} type. The i386
8529 application binary interface specifies the size to be 96 bits,
8530 so @option{-m96bit-long-double} is the default in 32 bit mode.
8532 Modern architectures (Pentium and newer) would prefer @code{long double}
8533 to be aligned to an 8 or 16 byte boundary. In arrays or structures
8534 conforming to the ABI, this would not be possible. So specifying a
8535 @option{-m128bit-long-double} will align @code{long double}
8536 to a 16 byte boundary by padding the @code{long double} with an additional
8539 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
8540 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
8542 Notice that neither of these options enable any extra precision over the x87
8543 standard of 80 bits for a @code{long double}.
8545 @strong{Warning:} if you override the default value for your target ABI, the
8546 structures and arrays containing @code{long double} variables will change
8547 their size as well as function calling convention for function taking
8548 @code{long double} will be modified. Hence they will not be binary
8549 compatible with arrays or structures in code compiled without that switch.
8553 @itemx -mno-svr3-shlib
8554 @opindex msvr3-shlib
8555 @opindex mno-svr3-shlib
8556 Control whether GCC places uninitialized local variables into the
8557 @code{bss} or @code{data} segments. @option{-msvr3-shlib} places them
8558 into @code{bss}. These options are meaningful only on System V Release 3.
8562 Use a different function-calling convention, in which functions that
8563 take a fixed number of arguments return with the @code{ret} @var{num}
8564 instruction, which pops their arguments while returning. This saves one
8565 instruction in the caller since there is no need to pop the arguments
8568 You can specify that an individual function is called with this calling
8569 sequence with the function attribute @samp{stdcall}. You can also
8570 override the @option{-mrtd} option by using the function attribute
8571 @samp{cdecl}. @xref{Function Attributes}.
8573 @strong{Warning:} this calling convention is incompatible with the one
8574 normally used on Unix, so you cannot use it if you need to call
8575 libraries compiled with the Unix compiler.
8577 Also, you must provide function prototypes for all functions that
8578 take variable numbers of arguments (including @code{printf});
8579 otherwise incorrect code will be generated for calls to those
8582 In addition, seriously incorrect code will result if you call a
8583 function with too many arguments. (Normally, extra arguments are
8584 harmlessly ignored.)
8586 @item -mregparm=@var{num}
8588 Control how many registers are used to pass integer arguments. By
8589 default, no registers are used to pass arguments, and at most 3
8590 registers can be used. You can control this behavior for a specific
8591 function by using the function attribute @samp{regparm}.
8592 @xref{Function Attributes}.
8594 @strong{Warning:} if you use this switch, and
8595 @var{num} is nonzero, then you must build all modules with the same
8596 value, including any libraries. This includes the system libraries and
8599 @item -mpreferred-stack-boundary=@var{num}
8600 @opindex mpreferred-stack-boundary
8601 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
8602 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
8603 the default is 4 (16 bytes or 128 bits), except when optimizing for code
8604 size (@option{-Os}), in which case the default is the minimum correct
8605 alignment (4 bytes for x86, and 8 bytes for x86-64).
8607 On Pentium and PentiumPro, @code{double} and @code{long double} values
8608 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
8609 suffer significant run time performance penalties. On Pentium III, the
8610 Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar
8611 penalties if it is not 16 byte aligned.
8613 To ensure proper alignment of this values on the stack, the stack boundary
8614 must be as aligned as that required by any value stored on the stack.
8615 Further, every function must be generated such that it keeps the stack
8616 aligned. Thus calling a function compiled with a higher preferred
8617 stack boundary from a function compiled with a lower preferred stack
8618 boundary will most likely misalign the stack. It is recommended that
8619 libraries that use callbacks always use the default setting.
8621 This extra alignment does consume extra stack space, and generally
8622 increases code size. Code that is sensitive to stack space usage, such
8623 as embedded systems and operating system kernels, may want to reduce the
8624 preferred alignment to @option{-mpreferred-stack-boundary=2}.
8642 These switches enable or disable the use of built-in functions that allow
8643 direct access to the MMX, SSE, SSE2, SSE3 and 3Dnow extensions of the
8646 @xref{X86 Built-in Functions}, for details of the functions enabled
8647 and disabled by these switches.
8649 To have SSE/SSE2 instructions generated automatically from floating-point
8650 code, see @option{-mfpmath=sse}.
8653 @itemx -mno-push-args
8655 @opindex mno-push-args
8656 Use PUSH operations to store outgoing parameters. This method is shorter
8657 and usually equally fast as method using SUB/MOV operations and is enabled
8658 by default. In some cases disabling it may improve performance because of
8659 improved scheduling and reduced dependencies.
8661 @item -maccumulate-outgoing-args
8662 @opindex maccumulate-outgoing-args
8663 If enabled, the maximum amount of space required for outgoing arguments will be
8664 computed in the function prologue. This is faster on most modern CPUs
8665 because of reduced dependencies, improved scheduling and reduced stack usage
8666 when preferred stack boundary is not equal to 2. The drawback is a notable
8667 increase in code size. This switch implies @option{-mno-push-args}.
8671 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
8672 on thread-safe exception handling must compile and link all code with the
8673 @option{-mthreads} option. When compiling, @option{-mthreads} defines
8674 @option{-D_MT}; when linking, it links in a special thread helper library
8675 @option{-lmingwthrd} which cleans up per thread exception handling data.
8677 @item -mno-align-stringops
8678 @opindex mno-align-stringops
8679 Do not align destination of inlined string operations. This switch reduces
8680 code size and improves performance in case the destination is already aligned,
8681 but GCC doesn't know about it.
8683 @item -minline-all-stringops
8684 @opindex minline-all-stringops
8685 By default GCC inlines string operations only when destination is known to be
8686 aligned at least to 4 byte boundary. This enables more inlining, increase code
8687 size, but may improve performance of code that depends on fast memcpy, strlen
8688 and memset for short lengths.
8690 @item -momit-leaf-frame-pointer
8691 @opindex momit-leaf-frame-pointer
8692 Don't keep the frame pointer in a register for leaf functions. This
8693 avoids the instructions to save, set up and restore frame pointers and
8694 makes an extra register available in leaf functions. The option
8695 @option{-fomit-frame-pointer} removes the frame pointer for all functions
8696 which might make debugging harder.
8698 @item -mtls-direct-seg-refs
8699 @itemx -mno-tls-direct-seg-refs
8700 @opindex mtls-direct-seg-refs
8701 Controls whether TLS variables may be accessed with offsets from the
8702 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
8703 or whether the thread base pointer must be added. Whether or not this
8704 is legal depends on the operating system, and whether it maps the
8705 segment to cover the entire TLS area.
8707 For systems that use GNU libc, the default is on.
8710 These @samp{-m} switches are supported in addition to the above
8711 on AMD x86-64 processors in 64-bit environments.
8718 Generate code for a 32-bit or 64-bit environment.
8719 The 32-bit environment sets int, long and pointer to 32 bits and
8720 generates code that runs on any i386 system.
8721 The 64-bit environment sets int to 32 bits and long and pointer
8722 to 64 bits and generates code for AMD's x86-64 architecture.
8725 @opindex no-red-zone
8726 Do not use a so called red zone for x86-64 code. The red zone is mandated
8727 by the x86-64 ABI, it is a 128-byte area beyond the location of the
8728 stack pointer that will not be modified by signal or interrupt handlers
8729 and therefore can be used for temporary data without adjusting the stack
8730 pointer. The flag @option{-mno-red-zone} disables this red zone.
8732 @item -mcmodel=small
8733 @opindex mcmodel=small
8734 Generate code for the small code model: the program and its symbols must
8735 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
8736 Programs can be statically or dynamically linked. This is the default
8739 @item -mcmodel=kernel
8740 @opindex mcmodel=kernel
8741 Generate code for the kernel code model. The kernel runs in the
8742 negative 2 GB of the address space.
8743 This model has to be used for Linux kernel code.
8745 @item -mcmodel=medium
8746 @opindex mcmodel=medium
8747 Generate code for the medium model: The program is linked in the lower 2
8748 GB of the address space but symbols can be located anywhere in the
8749 address space. Programs can be statically or dynamically linked, but
8750 building of shared libraries are not supported with the medium model.
8752 @item -mcmodel=large
8753 @opindex mcmodel=large
8754 Generate code for the large model: This model makes no assumptions
8755 about addresses and sizes of sections. Currently GCC does not implement
8760 @subsection IA-64 Options
8761 @cindex IA-64 Options
8763 These are the @samp{-m} options defined for the Intel IA-64 architecture.
8767 @opindex mbig-endian
8768 Generate code for a big endian target. This is the default for HP-UX@.
8770 @item -mlittle-endian
8771 @opindex mlittle-endian
8772 Generate code for a little endian target. This is the default for AIX5
8779 Generate (or don't) code for the GNU assembler. This is the default.
8780 @c Also, this is the default if the configure option @option{--with-gnu-as}
8787 Generate (or don't) code for the GNU linker. This is the default.
8788 @c Also, this is the default if the configure option @option{--with-gnu-ld}
8793 Generate code that does not use a global pointer register. The result
8794 is not position independent code, and violates the IA-64 ABI@.
8796 @item -mvolatile-asm-stop
8797 @itemx -mno-volatile-asm-stop
8798 @opindex mvolatile-asm-stop
8799 @opindex mno-volatile-asm-stop
8800 Generate (or don't) a stop bit immediately before and after volatile asm
8805 Generate code that works around Itanium B step errata.
8807 @item -mregister-names
8808 @itemx -mno-register-names
8809 @opindex mregister-names
8810 @opindex mno-register-names
8811 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
8812 the stacked registers. This may make assembler output more readable.
8818 Disable (or enable) optimizations that use the small data section. This may
8819 be useful for working around optimizer bugs.
8822 @opindex mconstant-gp
8823 Generate code that uses a single constant global pointer value. This is
8824 useful when compiling kernel code.
8828 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
8829 This is useful when compiling firmware code.
8831 @item -minline-float-divide-min-latency
8832 @opindex minline-float-divide-min-latency
8833 Generate code for inline divides of floating point values
8834 using the minimum latency algorithm.
8836 @item -minline-float-divide-max-throughput
8837 @opindex minline-float-divide-max-throughput
8838 Generate code for inline divides of floating point values
8839 using the maximum throughput algorithm.
8841 @item -minline-int-divide-min-latency
8842 @opindex minline-int-divide-min-latency
8843 Generate code for inline divides of integer values
8844 using the minimum latency algorithm.
8846 @item -minline-int-divide-max-throughput
8847 @opindex minline-int-divide-max-throughput
8848 Generate code for inline divides of integer values
8849 using the maximum throughput algorithm.
8851 @item -minline-sqrt-min-latency
8852 @opindex minline-sqrt-min-latency
8853 Generate code for inline square roots
8854 using the minimum latency algorithm.
8856 @item -minline-sqrt-max-throughput
8857 @opindex minline-sqrt-max-throughput
8858 Generate code for inline square roots
8859 using the maximum throughput algorithm.
8861 @item -mno-dwarf2-asm
8863 @opindex mno-dwarf2-asm
8864 @opindex mdwarf2-asm
8865 Don't (or do) generate assembler code for the DWARF2 line number debugging
8866 info. This may be useful when not using the GNU assembler.
8868 @item -mearly-stop-bits
8869 @itemx -mno-early-stop-bits
8870 @opindex mearly-stop-bits
8871 @opindex mno-early-stop-bits
8872 Allow stop bits to be placed earlier than immediately preceding the
8873 instruction that triggered the stop bit. This can improve instruction
8874 scheduling, but does not always do so.
8876 @item -mfixed-range=@var{register-range}
8877 @opindex mfixed-range
8878 Generate code treating the given register range as fixed registers.
8879 A fixed register is one that the register allocator can not use. This is
8880 useful when compiling kernel code. A register range is specified as
8881 two registers separated by a dash. Multiple register ranges can be
8882 specified separated by a comma.
8884 @item -mtls-size=@var{tls-size}
8886 Specify bit size of immediate TLS offsets. Valid values are 14, 22, and
8889 @item -mtune-arch=@var{cpu-type}
8891 Tune the instruction scheduling for a particular CPU, Valid values are
8892 itanium, itanium1, merced, itanium2, and mckinley.
8898 Add support for multithreading using the POSIX threads library. This
8899 option sets flags for both the preprocessor and linker. It does
8900 not affect the thread safety of object code produced by the compiler or
8901 that of libraries supplied with it. These are HP-UX specific flags.
8907 Generate code for a 32-bit or 64-bit environment.
8908 The 32-bit environment sets int, long and pointer to 32 bits.
8909 The 64-bit environment sets int to 32 bits and long and pointer
8910 to 64 bits. These are HP-UX specific flags.
8914 @node M32R/D Options
8915 @subsection M32R/D Options
8916 @cindex M32R/D options
8918 These @option{-m} options are defined for Renesas M32R/D architectures:
8923 Generate code for the M32R/2@.
8927 Generate code for the M32R/X@.
8931 Generate code for the M32R@. This is the default.
8934 @opindex mmodel=small
8935 Assume all objects live in the lower 16MB of memory (so that their addresses
8936 can be loaded with the @code{ld24} instruction), and assume all subroutines
8937 are reachable with the @code{bl} instruction.
8938 This is the default.
8940 The addressability of a particular object can be set with the
8941 @code{model} attribute.
8943 @item -mmodel=medium
8944 @opindex mmodel=medium
8945 Assume objects may be anywhere in the 32-bit address space (the compiler
8946 will generate @code{seth/add3} instructions to load their addresses), and
8947 assume all subroutines are reachable with the @code{bl} instruction.
8950 @opindex mmodel=large
8951 Assume objects may be anywhere in the 32-bit address space (the compiler
8952 will generate @code{seth/add3} instructions to load their addresses), and
8953 assume subroutines may not be reachable with the @code{bl} instruction
8954 (the compiler will generate the much slower @code{seth/add3/jl}
8955 instruction sequence).
8958 @opindex msdata=none
8959 Disable use of the small data area. Variables will be put into
8960 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
8961 @code{section} attribute has been specified).
8962 This is the default.
8964 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
8965 Objects may be explicitly put in the small data area with the
8966 @code{section} attribute using one of these sections.
8969 @opindex msdata=sdata
8970 Put small global and static data in the small data area, but do not
8971 generate special code to reference them.
8975 Put small global and static data in the small data area, and generate
8976 special instructions to reference them.
8980 @cindex smaller data references
8981 Put global and static objects less than or equal to @var{num} bytes
8982 into the small data or bss sections instead of the normal data or bss
8983 sections. The default value of @var{num} is 8.
8984 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
8985 for this option to have any effect.
8987 All modules should be compiled with the same @option{-G @var{num}} value.
8988 Compiling with different values of @var{num} may or may not work; if it
8989 doesn't the linker will give an error message---incorrect code will not be
8994 Makes the M32R specific code in the compiler display some statistics
8995 that might help in debugging programs.
8998 @opindex malign-loops
8999 Align all loops to a 32-byte boundary.
9001 @item -mno-align-loops
9002 @opindex mno-align-loops
9003 Do not enforce a 32-byte alignment for loops. This is the default.
9005 @item -missue-rate=@var{number}
9006 @opindex missue-rate=@var{number}
9007 Issue @var{number} instructions per cycle. @var{number} can only be 1
9010 @item -mbranch-cost=@var{number}
9011 @opindex mbranch-cost=@var{number}
9012 @var{number} can only be 1 or 2. If it is 1 then branches will be
9013 preferred over conditional code, if it is 2, then the opposite will
9016 @item -mflush-trap=@var{number}
9017 @opindex mflush-trap=@var{number}
9018 Specifies the trap number to use to flush the cache. The default is
9019 12. Valid numbers are between 0 and 15 inclusive.
9021 @item -mno-flush-trap
9022 @opindex mno-flush-trap
9023 Specifies that the cache cannot be flushed by using a trap.
9025 @item -mflush-func=@var{name}
9026 @opindex mflush-func=@var{name}
9027 Specifies the name of the operating system function to call to flush
9028 the cache. The default is @emph{_flush_cache}, but a function call
9029 will only be used if a trap is not available.
9031 @item -mno-flush-func
9032 @opindex mno-flush-func
9033 Indicates that there is no OS function for flushing the cache.
9037 @node M680x0 Options
9038 @subsection M680x0 Options
9039 @cindex M680x0 options
9041 These are the @samp{-m} options defined for the 68000 series. The default
9042 values for these options depends on which style of 68000 was selected when
9043 the compiler was configured; the defaults for the most common choices are
9051 Generate output for a 68000. This is the default
9052 when the compiler is configured for 68000-based systems.
9054 Use this option for microcontrollers with a 68000 or EC000 core,
9055 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
9061 Generate output for a 68020. This is the default
9062 when the compiler is configured for 68020-based systems.
9066 Generate output containing 68881 instructions for floating point.
9067 This is the default for most 68020 systems unless @option{--nfp} was
9068 specified when the compiler was configured.
9072 Generate output for a 68030. This is the default when the compiler is
9073 configured for 68030-based systems.
9077 Generate output for a 68040. This is the default when the compiler is
9078 configured for 68040-based systems.
9080 This option inhibits the use of 68881/68882 instructions that have to be
9081 emulated by software on the 68040. Use this option if your 68040 does not
9082 have code to emulate those instructions.
9086 Generate output for a 68060. This is the default when the compiler is
9087 configured for 68060-based systems.
9089 This option inhibits the use of 68020 and 68881/68882 instructions that
9090 have to be emulated by software on the 68060. Use this option if your 68060
9091 does not have code to emulate those instructions.
9095 Generate output for a CPU32. This is the default
9096 when the compiler is configured for CPU32-based systems.
9098 Use this option for microcontrollers with a
9099 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
9100 68336, 68340, 68341, 68349 and 68360.
9104 Generate output for a 520X ``coldfire'' family cpu. This is the default
9105 when the compiler is configured for 520X-based systems.
9107 Use this option for microcontroller with a 5200 core, including
9108 the MCF5202, MCF5203, MCF5204 and MCF5202.
9113 Generate output for a 68040, without using any of the new instructions.
9114 This results in code which can run relatively efficiently on either a
9115 68020/68881 or a 68030 or a 68040. The generated code does use the
9116 68881 instructions that are emulated on the 68040.
9120 Generate output for a 68060, without using any of the new instructions.
9121 This results in code which can run relatively efficiently on either a
9122 68020/68881 or a 68030 or a 68040. The generated code does use the
9123 68881 instructions that are emulated on the 68060.
9126 @opindex msoft-float
9127 Generate output containing library calls for floating point.
9128 @strong{Warning:} the requisite libraries are not available for all m68k
9129 targets. Normally the facilities of the machine's usual C compiler are
9130 used, but this can't be done directly in cross-compilation. You must
9131 make your own arrangements to provide suitable library functions for
9132 cross-compilation. The embedded targets @samp{m68k-*-aout} and
9133 @samp{m68k-*-coff} do provide software floating point support.
9137 Consider type @code{int} to be 16 bits wide, like @code{short int}.
9138 Additionally, parameters passed on the stack are also aligned to a
9139 16-bit boundary even on targets whose API mandates promotion to 32-bit.
9142 @opindex mnobitfield
9143 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
9144 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
9148 Do use the bit-field instructions. The @option{-m68020} option implies
9149 @option{-mbitfield}. This is the default if you use a configuration
9150 designed for a 68020.
9154 Use a different function-calling convention, in which functions
9155 that take a fixed number of arguments return with the @code{rtd}
9156 instruction, which pops their arguments while returning. This
9157 saves one instruction in the caller since there is no need to pop
9158 the arguments there.
9160 This calling convention is incompatible with the one normally
9161 used on Unix, so you cannot use it if you need to call libraries
9162 compiled with the Unix compiler.
9164 Also, you must provide function prototypes for all functions that
9165 take variable numbers of arguments (including @code{printf});
9166 otherwise incorrect code will be generated for calls to those
9169 In addition, seriously incorrect code will result if you call a
9170 function with too many arguments. (Normally, extra arguments are
9171 harmlessly ignored.)
9173 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
9174 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
9177 @itemx -mno-align-int
9179 @opindex mno-align-int
9180 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
9181 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
9182 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
9183 Aligning variables on 32-bit boundaries produces code that runs somewhat
9184 faster on processors with 32-bit busses at the expense of more memory.
9186 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
9187 align structures containing the above types differently than
9188 most published application binary interface specifications for the m68k.
9192 Use the pc-relative addressing mode of the 68000 directly, instead of
9193 using a global offset table. At present, this option implies @option{-fpic},
9194 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
9195 not presently supported with @option{-mpcrel}, though this could be supported for
9196 68020 and higher processors.
9198 @item -mno-strict-align
9199 @itemx -mstrict-align
9200 @opindex mno-strict-align
9201 @opindex mstrict-align
9202 Do not (do) assume that unaligned memory references will be handled by
9206 Generate code that allows the data segment to be located in a different
9207 area of memory from the text segment. This allows for execute in place in
9208 an environment without virtual memory management. This option implies
9212 Generate code that assumes that the data segment follows the text segment.
9213 This is the default.
9215 @item -mid-shared-library
9216 Generate code that supports shared libraries via the library ID method.
9217 This allows for execute in place and shared libraries in an environment
9218 without virtual memory management. This option implies @option{-fPIC}.
9220 @item -mno-id-shared-library
9221 Generate code that doesn't assume ID based shared libraries are being used.
9222 This is the default.
9224 @item -mshared-library-id=n
9225 Specified the identification number of the ID based shared library being
9226 compiled. Specifying a value of 0 will generate more compact code, specifying
9227 other values will force the allocation of that number to the current
9228 library but is no more space or time efficient than omitting this option.
9232 @node M68hc1x Options
9233 @subsection M68hc1x Options
9234 @cindex M68hc1x options
9236 These are the @samp{-m} options defined for the 68hc11 and 68hc12
9237 microcontrollers. The default values for these options depends on
9238 which style of microcontroller was selected when the compiler was configured;
9239 the defaults for the most common choices are given below.
9246 Generate output for a 68HC11. This is the default
9247 when the compiler is configured for 68HC11-based systems.
9253 Generate output for a 68HC12. This is the default
9254 when the compiler is configured for 68HC12-based systems.
9260 Generate output for a 68HCS12.
9263 @opindex mauto-incdec
9264 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
9271 Enable the use of 68HC12 min and max instructions.
9274 @itemx -mno-long-calls
9275 @opindex mlong-calls
9276 @opindex mno-long-calls
9277 Treat all calls as being far away (near). If calls are assumed to be
9278 far away, the compiler will use the @code{call} instruction to
9279 call a function and the @code{rtc} instruction for returning.
9283 Consider type @code{int} to be 16 bits wide, like @code{short int}.
9285 @item -msoft-reg-count=@var{count}
9286 @opindex msoft-reg-count
9287 Specify the number of pseudo-soft registers which are used for the
9288 code generation. The maximum number is 32. Using more pseudo-soft
9289 register may or may not result in better code depending on the program.
9290 The default is 4 for 68HC11 and 2 for 68HC12.
9295 @subsection MCore Options
9296 @cindex MCore options
9298 These are the @samp{-m} options defined for the Motorola M*Core
9306 @opindex mno-hardlit
9307 Inline constants into the code stream if it can be done in two
9308 instructions or less.
9314 Use the divide instruction. (Enabled by default).
9316 @item -mrelax-immediate
9317 @itemx -mno-relax-immediate
9318 @opindex mrelax-immediate
9319 @opindex mno-relax-immediate
9320 Allow arbitrary sized immediates in bit operations.
9322 @item -mwide-bitfields
9323 @itemx -mno-wide-bitfields
9324 @opindex mwide-bitfields
9325 @opindex mno-wide-bitfields
9326 Always treat bit-fields as int-sized.
9328 @item -m4byte-functions
9329 @itemx -mno-4byte-functions
9330 @opindex m4byte-functions
9331 @opindex mno-4byte-functions
9332 Force all functions to be aligned to a four byte boundary.
9334 @item -mcallgraph-data
9335 @itemx -mno-callgraph-data
9336 @opindex mcallgraph-data
9337 @opindex mno-callgraph-data
9338 Emit callgraph information.
9341 @itemx -mno-slow-bytes
9342 @opindex mslow-bytes
9343 @opindex mno-slow-bytes
9344 Prefer word access when reading byte quantities.
9346 @item -mlittle-endian
9348 @opindex mlittle-endian
9349 @opindex mbig-endian
9350 Generate code for a little endian target.
9356 Generate code for the 210 processor.
9360 @subsection MIPS Options
9361 @cindex MIPS options
9367 Generate big-endian code.
9371 Generate little-endian code. This is the default for @samp{mips*el-*-*}
9374 @item -march=@var{arch}
9376 Generate code that will run on @var{arch}, which can be the name of a
9377 generic MIPS ISA, or the name of a particular processor.
9379 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
9380 @samp{mips32}, @samp{mips32r2}, and @samp{mips64}.
9381 The processor names are:
9382 @samp{4kc}, @samp{4kp}, @samp{5kc}, @samp{20kc},
9384 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
9385 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000}, @samp{rm7000},
9389 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300},
9390 @samp{vr5000}, @samp{vr5400} and @samp{vr5500}.
9391 The special value @samp{from-abi} selects the
9392 most compatible architecture for the selected ABI (that is,
9393 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
9395 In processor names, a final @samp{000} can be abbreviated as @samp{k}
9396 (for example, @samp{-march=r2k}). Prefixes are optional, and
9397 @samp{vr} may be written @samp{r}.
9399 GCC defines two macros based on the value of this option. The first
9400 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
9401 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
9402 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
9403 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
9404 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
9406 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
9407 above. In other words, it will have the full prefix and will not
9408 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
9409 the macro names the resolved architecture (either @samp{"mips1"} or
9410 @samp{"mips3"}). It names the default architecture when no
9411 @option{-march} option is given.
9413 @item -mtune=@var{arch}
9415 Optimize for @var{arch}. Among other things, this option controls
9416 the way instructions are scheduled, and the perceived cost of arithmetic
9417 operations. The list of @var{arch} values is the same as for
9420 When this option is not used, GCC will optimize for the processor
9421 specified by @option{-march}. By using @option{-march} and
9422 @option{-mtune} together, it is possible to generate code that will
9423 run on a family of processors, but optimize the code for one
9424 particular member of that family.
9426 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
9427 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
9428 @samp{-march} ones described above.
9432 Equivalent to @samp{-march=mips1}.
9436 Equivalent to @samp{-march=mips2}.
9440 Equivalent to @samp{-march=mips3}.
9444 Equivalent to @samp{-march=mips4}.
9448 Equivalent to @samp{-march=mips32}.
9452 Equivalent to @samp{-march=mips32r2}.
9456 Equivalent to @samp{-march=mips64}.
9462 Use (do not use) the MIPS16 ISA@.
9474 Generate code for the given ABI@.
9476 Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
9477 generates 64-bit code when you select a 64-bit architecture, but you
9478 can use @option{-mgp32} to get 32-bit code instead.
9480 For information about the O64 ABI, see
9481 @w{@uref{http://gcc.gnu.org/projects/mipso64-abi.html}}.
9484 @itemx -mno-abicalls
9486 @opindex mno-abicalls
9487 Generate (do not generate) SVR4-style position-independent code.
9488 @option{-mabicalls} is the default for SVR4-based systems.
9494 Lift (do not lift) the usual restrictions on the size of the global
9497 GCC normally uses a single instruction to load values from the GOT@.
9498 While this is relatively efficient, it will only work if the GOT
9499 is smaller than about 64k. Anything larger will cause the linker
9500 to report an error such as:
9502 @cindex relocation truncated to fit (MIPS)
9504 relocation truncated to fit: R_MIPS_GOT16 foobar
9507 If this happens, you should recompile your code with @option{-mxgot}.
9508 It should then work with very large GOTs, although it will also be
9509 less efficient, since it will take three instructions to fetch the
9510 value of a global symbol.
9512 Note that some linkers can create multiple GOTs. If you have such a
9513 linker, you should only need to use @option{-mxgot} when a single object
9514 file accesses more than 64k's worth of GOT entries. Very few do.
9516 These options have no effect unless GCC is generating position
9521 Assume that general-purpose registers are 32 bits wide.
9525 Assume that general-purpose registers are 64 bits wide.
9529 Assume that floating-point registers are 32 bits wide.
9533 Assume that floating-point registers are 64 bits wide.
9536 @opindex mhard-float
9537 Use floating-point coprocessor instructions.
9540 @opindex msoft-float
9541 Do not use floating-point coprocessor instructions. Implement
9542 floating-point calculations using library calls instead.
9544 @item -msingle-float
9545 @opindex msingle-float
9546 Assume that the floating-point coprocessor only supports single-precision
9549 @itemx -mdouble-float
9550 @opindex mdouble-float
9551 Assume that the floating-point coprocessor supports double-precision
9552 operations. This is the default.
9554 @itemx -mpaired-single
9555 @itemx -mno-paired-single
9556 @opindex mpaired-single
9557 @opindex mno-paired-single
9558 Use (do not use) paired-single floating-point instructions.
9559 @xref{MIPS Paired-Single Support}. This option can only be used
9560 when generating 64-bit code and requires hardware floating-point
9561 support to be enabled.
9567 Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}.
9568 The option @option{-mips3d} implies @option{-mpaired-single}.
9572 Force @code{int} and @code{long} types to be 64 bits wide. See
9573 @option{-mlong32} for an explanation of the default and the way
9574 that the pointer size is determined.
9578 Force @code{long} types to be 64 bits wide. See @option{-mlong32} for
9579 an explanation of the default and the way that the pointer size is
9584 Force @code{long}, @code{int}, and pointer types to be 32 bits wide.
9586 The default size of @code{int}s, @code{long}s and pointers depends on
9587 the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI
9588 uses 64-bit @code{long}s, as does the 64-bit EABI; the others use
9589 32-bit @code{long}s. Pointers are the same size as @code{long}s,
9590 or the same size as integer registers, whichever is smaller.
9594 @cindex smaller data references (MIPS)
9595 @cindex gp-relative references (MIPS)
9596 Put global and static items less than or equal to @var{num} bytes into
9597 the small data or bss section instead of the normal data or bss section.
9598 This allows the data to be accessed using a single instruction.
9600 All modules should be compiled with the same @option{-G @var{num}}
9603 @item -membedded-data
9604 @itemx -mno-embedded-data
9605 @opindex membedded-data
9606 @opindex mno-embedded-data
9607 Allocate variables to the read-only data section first if possible, then
9608 next in the small data section if possible, otherwise in data. This gives
9609 slightly slower code than the default, but reduces the amount of RAM required
9610 when executing, and thus may be preferred for some embedded systems.
9612 @item -muninit-const-in-rodata
9613 @itemx -mno-uninit-const-in-rodata
9614 @opindex muninit-const-in-rodata
9615 @opindex mno-uninit-const-in-rodata
9616 Put uninitialized @code{const} variables in the read-only data section.
9617 This option is only meaningful in conjunction with @option{-membedded-data}.
9619 @item -msplit-addresses
9620 @itemx -mno-split-addresses
9621 @opindex msplit-addresses
9622 @opindex mno-split-addresses
9623 Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler
9624 relocation operators. This option has been superceded by
9625 @option{-mexplicit-relocs} but is retained for backwards compatibility.
9627 @item -mexplicit-relocs
9628 @itemx -mno-explicit-relocs
9629 @opindex mexplicit-relocs
9630 @opindex mno-explicit-relocs
9631 Use (do not use) assembler relocation operators when dealing with symbolic
9632 addresses. The alternative, selected by @option{-mno-explicit-relocs},
9633 is to use assembler macros instead.
9635 @option{-mexplicit-relocs} is the default if GCC was configured
9636 to use an assembler that supports relocation operators.
9638 @item -mcheck-zero-division
9639 @itemx -mno-check-zero-division
9640 @opindex mcheck-zero-division
9641 @opindex mno-check-zero-division
9642 Trap (do not trap) on integer division by zero. The default is
9643 @option{-mcheck-zero-division}.
9645 @item -mdivide-traps
9646 @itemx -mdivide-breaks
9647 @opindex mdivide-traps
9648 @opindex mdivide-breaks
9649 MIPS systems check for division by zero by generating either a
9650 conditional trap or a break instruction. Using traps results in
9651 smaller code, but is only supported on MIPS II and later. Also, some
9652 versions of the Linux kernel have a bug that prevents trap from
9653 generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to
9654 allow conditional traps on architectures that support them and
9655 @option{-mdivide-breaks} to force the use of breaks.
9657 The default is usually @option{-mdivide-traps}, but this can be
9658 overridden at configure time using @option{--with-divide=breaks}.
9659 Divide-by-zero checks can be completely disabled using
9660 @option{-mno-check-zero-division}.
9666 Force (do not force) the use of @code{memcpy()} for non-trivial block
9667 moves. The default is @option{-mno-memcpy}, which allows GCC to inline
9668 most constant-sized copies.
9671 @itemx -mno-long-calls
9672 @opindex mlong-calls
9673 @opindex mno-long-calls
9674 Disable (do not disable) use of the @code{jal} instruction. Calling
9675 functions using @code{jal} is more efficient but requires the caller
9676 and callee to be in the same 256 megabyte segment.
9678 This option has no effect on abicalls code. The default is
9679 @option{-mno-long-calls}.
9685 Enable (disable) use of the @code{mad}, @code{madu} and @code{mul}
9686 instructions, as provided by the R4650 ISA@.
9689 @itemx -mno-fused-madd
9690 @opindex mfused-madd
9691 @opindex mno-fused-madd
9692 Enable (disable) use of the floating point multiply-accumulate
9693 instructions, when they are available. The default is
9694 @option{-mfused-madd}.
9696 When multiply-accumulate instructions are used, the intermediate
9697 product is calculated to infinite precision and is not subject to
9698 the FCSR Flush to Zero bit. This may be undesirable in some
9703 Tell the MIPS assembler to not run its preprocessor over user
9704 assembler files (with a @samp{.s} suffix) when assembling them.
9707 @itemx -mno-fix-r4000
9709 @opindex mno-fix-r4000
9710 Work around certain R4000 CPU errata:
9713 A double-word or a variable shift may give an incorrect result if executed
9714 immediately after starting an integer division.
9716 A double-word or a variable shift may give an incorrect result if executed
9717 while an integer multiplication is in progress.
9719 An integer division may give an incorrect result if started in a delay slot
9720 of a taken branch or a jump.
9724 @itemx -mno-fix-r4400
9726 @opindex mno-fix-r4400
9727 Work around certain R4400 CPU errata:
9730 A double-word or a variable shift may give an incorrect result if executed
9731 immediately after starting an integer division.
9735 @itemx -mno-fix-vr4120
9736 @opindex mfix-vr4120
9737 Work around certain VR4120 errata:
9740 @code{dmultu} does not always produce the correct result.
9742 @code{div} and @code{ddiv} do not always produce the correct result if one
9743 of the operands is negative.
9745 The workarounds for the division errata rely on special functions in
9746 @file{libgcc.a}. At present, these functions are only provided by
9747 the @code{mips64vr*-elf} configurations.
9749 Other VR4120 errata require a nop to be inserted between certain pairs of
9750 instructions. These errata are handled by the assembler, not by GCC itself.
9755 Work around certain SB-1 CPU core errata.
9756 (This flag currently works around the SB-1 revision 2
9757 ``F1'' and ``F2'' floating point errata.)
9759 @item -mflush-func=@var{func}
9760 @itemx -mno-flush-func
9761 @opindex mflush-func
9762 Specifies the function to call to flush the I and D caches, or to not
9763 call any such function. If called, the function must take the same
9764 arguments as the common @code{_flush_func()}, that is, the address of the
9765 memory range for which the cache is being flushed, the size of the
9766 memory range, and the number 3 (to flush both caches). The default
9767 depends on the target GCC was configured for, but commonly is either
9768 @samp{_flush_func} or @samp{__cpu_flush}.
9770 @item -mbranch-likely
9771 @itemx -mno-branch-likely
9772 @opindex mbranch-likely
9773 @opindex mno-branch-likely
9774 Enable or disable use of Branch Likely instructions, regardless of the
9775 default for the selected architecture. By default, Branch Likely
9776 instructions may be generated if they are supported by the selected
9777 architecture. An exception is for the MIPS32 and MIPS64 architectures
9778 and processors which implement those architectures; for those, Branch
9779 Likely instructions will not be generated by default because the MIPS32
9780 and MIPS64 architectures specifically deprecate their use.
9782 @item -mfp-exceptions
9783 @itemx -mno-fp-exceptions
9784 @opindex mfp-exceptions
9785 Specifies whether FP exceptions are enabled. This affects how we schedule
9786 FP instructions for some processors. The default is that FP exceptions are
9789 For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
9790 64-bit code, then we can use both FP pipes. Otherwise, we can only use one
9793 @item -mvr4130-align
9794 @itemx -mno-vr4130-align
9795 @opindex mvr4130-align
9796 The VR4130 pipeline is two-way superscalar, but can only issue two
9797 instructions together if the first one is 8-byte aligned. When this
9798 option is enabled, GCC will align pairs of instructions that it
9799 thinks should execute in parallel.
9801 This option only has an effect when optimizing for the VR4130.
9802 It normally makes code faster, but at the expense of making it bigger.
9803 It is enabled by default at optimization level @option{-O3}.
9807 @subsection MMIX Options
9808 @cindex MMIX Options
9810 These options are defined for the MMIX:
9814 @itemx -mno-libfuncs
9816 @opindex mno-libfuncs
9817 Specify that intrinsic library functions are being compiled, passing all
9818 values in registers, no matter the size.
9823 @opindex mno-epsilon
9824 Generate floating-point comparison instructions that compare with respect
9825 to the @code{rE} epsilon register.
9827 @item -mabi=mmixware
9829 @opindex mabi-mmixware
9831 Generate code that passes function parameters and return values that (in
9832 the called function) are seen as registers @code{$0} and up, as opposed to
9833 the GNU ABI which uses global registers @code{$231} and up.
9836 @itemx -mno-zero-extend
9837 @opindex mzero-extend
9838 @opindex mno-zero-extend
9839 When reading data from memory in sizes shorter than 64 bits, use (do not
9840 use) zero-extending load instructions by default, rather than
9841 sign-extending ones.
9844 @itemx -mno-knuthdiv
9846 @opindex mno-knuthdiv
9847 Make the result of a division yielding a remainder have the same sign as
9848 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
9849 remainder follows the sign of the dividend. Both methods are
9850 arithmetically valid, the latter being almost exclusively used.
9852 @item -mtoplevel-symbols
9853 @itemx -mno-toplevel-symbols
9854 @opindex mtoplevel-symbols
9855 @opindex mno-toplevel-symbols
9856 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
9857 code can be used with the @code{PREFIX} assembly directive.
9861 Generate an executable in the ELF format, rather than the default
9862 @samp{mmo} format used by the @command{mmix} simulator.
9864 @item -mbranch-predict
9865 @itemx -mno-branch-predict
9866 @opindex mbranch-predict
9867 @opindex mno-branch-predict
9868 Use (do not use) the probable-branch instructions, when static branch
9869 prediction indicates a probable branch.
9871 @item -mbase-addresses
9872 @itemx -mno-base-addresses
9873 @opindex mbase-addresses
9874 @opindex mno-base-addresses
9875 Generate (do not generate) code that uses @emph{base addresses}. Using a
9876 base address automatically generates a request (handled by the assembler
9877 and the linker) for a constant to be set up in a global register. The
9878 register is used for one or more base address requests within the range 0
9879 to 255 from the value held in the register. The generally leads to short
9880 and fast code, but the number of different data items that can be
9881 addressed is limited. This means that a program that uses lots of static
9882 data may require @option{-mno-base-addresses}.
9885 @itemx -mno-single-exit
9886 @opindex msingle-exit
9887 @opindex mno-single-exit
9888 Force (do not force) generated code to have a single exit point in each
9892 @node MN10300 Options
9893 @subsection MN10300 Options
9894 @cindex MN10300 options
9896 These @option{-m} options are defined for Matsushita MN10300 architectures:
9901 Generate code to avoid bugs in the multiply instructions for the MN10300
9902 processors. This is the default.
9905 @opindex mno-mult-bug
9906 Do not generate code to avoid bugs in the multiply instructions for the
9911 Generate code which uses features specific to the AM33 processor.
9915 Do not generate code which uses features specific to the AM33 processor. This
9920 Do not link in the C run-time initialization object file.
9924 Indicate to the linker that it should perform a relaxation optimization pass
9925 to shorten branches, calls and absolute memory addresses. This option only
9926 has an effect when used on the command line for the final link step.
9928 This option makes symbolic debugging impossible.
9932 @subsection NS32K Options
9933 @cindex NS32K options
9935 These are the @samp{-m} options defined for the 32000 series. The default
9936 values for these options depends on which style of 32000 was selected when
9937 the compiler was configured; the defaults for the most common choices are
9945 Generate output for a 32032. This is the default
9946 when the compiler is configured for 32032 and 32016 based systems.
9952 Generate output for a 32332. This is the default
9953 when the compiler is configured for 32332-based systems.
9959 Generate output for a 32532. This is the default
9960 when the compiler is configured for 32532-based systems.
9964 Generate output containing 32081 instructions for floating point.
9965 This is the default for all systems.
9969 Generate output containing 32381 instructions for floating point. This
9970 also implies @option{-m32081}. The 32381 is only compatible with the 32332
9971 and 32532 cpus. This is the default for the pc532-netbsd configuration.
9975 Try and generate multiply-add floating point instructions @code{polyF}
9976 and @code{dotF}. This option is only available if the @option{-m32381}
9977 option is in effect. Using these instructions requires changes to
9978 register allocation which generally has a negative impact on
9979 performance. This option should only be enabled when compiling code
9980 particularly likely to make heavy use of multiply-add instructions.
9983 @opindex mnomulti-add
9984 Do not try and generate multiply-add floating point instructions
9985 @code{polyF} and @code{dotF}. This is the default on all platforms.
9988 @opindex msoft-float
9989 Generate output containing library calls for floating point.
9990 @strong{Warning:} the requisite libraries may not be available.
9992 @item -mieee-compare
9993 @itemx -mno-ieee-compare
9994 @opindex mieee-compare
9995 @opindex mno-ieee-compare
9996 Control whether or not the compiler uses IEEE floating point
9997 comparisons. These handle correctly the case where the result of a
9998 comparison is unordered.
9999 @strong{Warning:} the requisite kernel support may not be available.
10002 @opindex mnobitfield
10003 Do not use the bit-field instructions. On some machines it is faster to
10004 use shifting and masking operations. This is the default for the pc532.
10008 Do use the bit-field instructions. This is the default for all platforms
10013 Use a different function-calling convention, in which functions
10014 that take a fixed number of arguments return pop their
10015 arguments on return with the @code{ret} instruction.
10017 This calling convention is incompatible with the one normally
10018 used on Unix, so you cannot use it if you need to call libraries
10019 compiled with the Unix compiler.
10021 Also, you must provide function prototypes for all functions that
10022 take variable numbers of arguments (including @code{printf});
10023 otherwise incorrect code will be generated for calls to those
10026 In addition, seriously incorrect code will result if you call a
10027 function with too many arguments. (Normally, extra arguments are
10028 harmlessly ignored.)
10030 This option takes its name from the 680x0 @code{rtd} instruction.
10035 Use a different function-calling convention where the first two arguments
10036 are passed in registers.
10038 This calling convention is incompatible with the one normally
10039 used on Unix, so you cannot use it if you need to call libraries
10040 compiled with the Unix compiler.
10043 @opindex mnoregparam
10044 Do not pass any arguments in registers. This is the default for all
10049 It is OK to use the sb as an index register which is always loaded with
10050 zero. This is the default for the pc532-netbsd target.
10054 The sb register is not available for use or has not been initialized to
10055 zero by the run time system. This is the default for all targets except
10056 the pc532-netbsd. It is also implied whenever @option{-mhimem} or
10057 @option{-fpic} is set.
10061 Many ns32000 series addressing modes use displacements of up to 512MB@.
10062 If an address is above 512MB then displacements from zero can not be used.
10063 This option causes code to be generated which can be loaded above 512MB@.
10064 This may be useful for operating systems or ROM code.
10068 Assume code will be loaded in the first 512MB of virtual address space.
10069 This is the default for all platforms.
10073 @node PDP-11 Options
10074 @subsection PDP-11 Options
10075 @cindex PDP-11 Options
10077 These options are defined for the PDP-11:
10082 Use hardware FPP floating point. This is the default. (FIS floating
10083 point on the PDP-11/40 is not supported.)
10086 @opindex msoft-float
10087 Do not use hardware floating point.
10091 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
10095 Return floating-point results in memory. This is the default.
10099 Generate code for a PDP-11/40.
10103 Generate code for a PDP-11/45. This is the default.
10107 Generate code for a PDP-11/10.
10109 @item -mbcopy-builtin
10110 @opindex bcopy-builtin
10111 Use inline @code{movmemhi} patterns for copying memory. This is the
10116 Do not use inline @code{movmemhi} patterns for copying memory.
10122 Use 16-bit @code{int}. This is the default.
10128 Use 32-bit @code{int}.
10131 @itemx -mno-float32
10133 @opindex mno-float32
10134 Use 64-bit @code{float}. This is the default.
10137 @itemx -mno-float64
10139 @opindex mno-float64
10140 Use 32-bit @code{float}.
10144 Use @code{abshi2} pattern. This is the default.
10148 Do not use @code{abshi2} pattern.
10150 @item -mbranch-expensive
10151 @opindex mbranch-expensive
10152 Pretend that branches are expensive. This is for experimenting with
10153 code generation only.
10155 @item -mbranch-cheap
10156 @opindex mbranch-cheap
10157 Do not pretend that branches are expensive. This is the default.
10161 Generate code for a system with split I&D@.
10165 Generate code for a system without split I&D@. This is the default.
10169 Use Unix assembler syntax. This is the default when configured for
10170 @samp{pdp11-*-bsd}.
10174 Use DEC assembler syntax. This is the default when configured for any
10175 PDP-11 target other than @samp{pdp11-*-bsd}.
10178 @node PowerPC Options
10179 @subsection PowerPC Options
10180 @cindex PowerPC options
10182 These are listed under @xref{RS/6000 and PowerPC Options}.
10184 @node RS/6000 and PowerPC Options
10185 @subsection IBM RS/6000 and PowerPC Options
10186 @cindex RS/6000 and PowerPC Options
10187 @cindex IBM RS/6000 and PowerPC Options
10189 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
10196 @itemx -mno-powerpc
10197 @itemx -mpowerpc-gpopt
10198 @itemx -mno-powerpc-gpopt
10199 @itemx -mpowerpc-gfxopt
10200 @itemx -mno-powerpc-gfxopt
10202 @itemx -mno-powerpc64
10206 @opindex mno-power2
10208 @opindex mno-powerpc
10209 @opindex mpowerpc-gpopt
10210 @opindex mno-powerpc-gpopt
10211 @opindex mpowerpc-gfxopt
10212 @opindex mno-powerpc-gfxopt
10213 @opindex mpowerpc64
10214 @opindex mno-powerpc64
10215 GCC supports two related instruction set architectures for the
10216 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
10217 instructions supported by the @samp{rios} chip set used in the original
10218 RS/6000 systems and the @dfn{PowerPC} instruction set is the
10219 architecture of the Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and
10220 the IBM 4xx microprocessors.
10222 Neither architecture is a subset of the other. However there is a
10223 large common subset of instructions supported by both. An MQ
10224 register is included in processors supporting the POWER architecture.
10226 You use these options to specify which instructions are available on the
10227 processor you are using. The default value of these options is
10228 determined when configuring GCC@. Specifying the
10229 @option{-mcpu=@var{cpu_type}} overrides the specification of these
10230 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
10231 rather than the options listed above.
10233 The @option{-mpower} option allows GCC to generate instructions that
10234 are found only in the POWER architecture and to use the MQ register.
10235 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
10236 to generate instructions that are present in the POWER2 architecture but
10237 not the original POWER architecture.
10239 The @option{-mpowerpc} option allows GCC to generate instructions that
10240 are found only in the 32-bit subset of the PowerPC architecture.
10241 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
10242 GCC to use the optional PowerPC architecture instructions in the
10243 General Purpose group, including floating-point square root. Specifying
10244 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
10245 use the optional PowerPC architecture instructions in the Graphics
10246 group, including floating-point select.
10248 The @option{-mpowerpc64} option allows GCC to generate the additional
10249 64-bit instructions that are found in the full PowerPC64 architecture
10250 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
10251 @option{-mno-powerpc64}.
10253 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
10254 will use only the instructions in the common subset of both
10255 architectures plus some special AIX common-mode calls, and will not use
10256 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
10257 permits GCC to use any instruction from either architecture and to
10258 allow use of the MQ register; specify this for the Motorola MPC601.
10260 @item -mnew-mnemonics
10261 @itemx -mold-mnemonics
10262 @opindex mnew-mnemonics
10263 @opindex mold-mnemonics
10264 Select which mnemonics to use in the generated assembler code. With
10265 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
10266 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
10267 assembler mnemonics defined for the POWER architecture. Instructions
10268 defined in only one architecture have only one mnemonic; GCC uses that
10269 mnemonic irrespective of which of these options is specified.
10271 GCC defaults to the mnemonics appropriate for the architecture in
10272 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
10273 value of these option. Unless you are building a cross-compiler, you
10274 should normally not specify either @option{-mnew-mnemonics} or
10275 @option{-mold-mnemonics}, but should instead accept the default.
10277 @item -mcpu=@var{cpu_type}
10279 Set architecture type, register usage, choice of mnemonics, and
10280 instruction scheduling parameters for machine type @var{cpu_type}.
10281 Supported values for @var{cpu_type} are @samp{401}, @samp{403},
10282 @samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{505},
10283 @samp{601}, @samp{602}, @samp{603}, @samp{603e}, @samp{604},
10284 @samp{604e}, @samp{620}, @samp{630}, @samp{740}, @samp{7400},
10285 @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
10286 @samp{860}, @samp{970}, @samp{common}, @samp{ec603e}, @samp{G3},
10287 @samp{G4}, @samp{G5}, @samp{power}, @samp{power2}, @samp{power3},
10288 @samp{power4}, @samp{power5}, @samp{powerpc}, @samp{powerpc64},
10289 @samp{rios}, @samp{rios1}, @samp{rios2}, @samp{rsc}, and @samp{rs64a}.
10291 @option{-mcpu=common} selects a completely generic processor. Code
10292 generated under this option will run on any POWER or PowerPC processor.
10293 GCC will use only the instructions in the common subset of both
10294 architectures, and will not use the MQ register. GCC assumes a generic
10295 processor model for scheduling purposes.
10297 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
10298 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
10299 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
10300 types, with an appropriate, generic processor model assumed for
10301 scheduling purposes.
10303 The other options specify a specific processor. Code generated under
10304 those options will run best on that processor, and may not run at all on
10307 The @option{-mcpu} options automatically enable or disable the
10308 following options: @option{-maltivec}, @option{-mhard-float},
10309 @option{-mmfcrf}, @option{-mmultiple}, @option{-mnew-mnemonics},
10310 @option{-mpower}, @option{-mpower2}, @option{-mpowerpc64},
10311 @option{-mpowerpc-gpopt}, @option{-mpowerpc-gfxopt},
10312 @option{-mstring}. The particular options set for any particular CPU
10313 will vary between compiler versions, depending on what setting seems
10314 to produce optimal code for that CPU; it doesn't necessarily reflect
10315 the actual hardware's capabilities. If you wish to set an individual
10316 option to a particular value, you may specify it after the
10317 @option{-mcpu} option, like @samp{-mcpu=970 -mno-altivec}.
10319 On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are
10320 not enabled or disabled by the @option{-mcpu} option at present, since
10321 AIX does not have full support for these options. You may still
10322 enable or disable them individually if you're sure it'll work in your
10325 @item -mtune=@var{cpu_type}
10327 Set the instruction scheduling parameters for machine type
10328 @var{cpu_type}, but do not set the architecture type, register usage, or
10329 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
10330 values for @var{cpu_type} are used for @option{-mtune} as for
10331 @option{-mcpu}. If both are specified, the code generated will use the
10332 architecture, registers, and mnemonics set by @option{-mcpu}, but the
10333 scheduling parameters set by @option{-mtune}.
10336 @itemx -mno-altivec
10338 @opindex mno-altivec
10339 Generate code that uses (does not use) AltiVec instructions, and also
10340 enable the use of built-in functions that allow more direct access to
10341 the AltiVec instruction set. You may also need to set
10342 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
10347 Extend the current ABI with SPE ABI extensions. This does not change
10348 the default ABI, instead it adds the SPE ABI extensions to the current
10352 @opindex mabi=no-spe
10353 Disable Booke SPE ABI extensions for the current ABI@.
10355 @item -misel=@var{yes/no}
10358 This switch enables or disables the generation of ISEL instructions.
10360 @item -mspe=@var{yes/no}
10363 This switch enables or disables the generation of SPE simd
10366 @item -mfloat-gprs=@var{yes/single/double/no}
10367 @itemx -mfloat-gprs
10368 @opindex mfloat-gprs
10369 This switch enables or disables the generation of floating point
10370 operations on the general purpose registers for architectures that
10373 The argument @var{yes} or @var{single} enables the use of
10374 single-precision floating point operations.
10376 The argument @var{double} enables the use of single and
10377 double-precision floating point operations.
10379 The argument @var{no} disables floating point operations on the
10380 general purpose registers.
10382 This option is currently only available on the MPC854x.
10388 Generate code for 32-bit or 64-bit environments of Darwin and SVR4
10389 targets (including GNU/Linux). The 32-bit environment sets int, long
10390 and pointer to 32 bits and generates code that runs on any PowerPC
10391 variant. The 64-bit environment sets int to 32 bits and long and
10392 pointer to 64 bits, and generates code for PowerPC64, as for
10393 @option{-mpowerpc64}.
10396 @itemx -mno-fp-in-toc
10397 @itemx -mno-sum-in-toc
10398 @itemx -mminimal-toc
10400 @opindex mno-fp-in-toc
10401 @opindex mno-sum-in-toc
10402 @opindex mminimal-toc
10403 Modify generation of the TOC (Table Of Contents), which is created for
10404 every executable file. The @option{-mfull-toc} option is selected by
10405 default. In that case, GCC will allocate at least one TOC entry for
10406 each unique non-automatic variable reference in your program. GCC
10407 will also place floating-point constants in the TOC@. However, only
10408 16,384 entries are available in the TOC@.
10410 If you receive a linker error message that saying you have overflowed
10411 the available TOC space, you can reduce the amount of TOC space used
10412 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
10413 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
10414 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
10415 generate code to calculate the sum of an address and a constant at
10416 run-time instead of putting that sum into the TOC@. You may specify one
10417 or both of these options. Each causes GCC to produce very slightly
10418 slower and larger code at the expense of conserving TOC space.
10420 If you still run out of space in the TOC even when you specify both of
10421 these options, specify @option{-mminimal-toc} instead. This option causes
10422 GCC to make only one TOC entry for every file. When you specify this
10423 option, GCC will produce code that is slower and larger but which
10424 uses extremely little TOC space. You may wish to use this option
10425 only on files that contain less frequently executed code.
10431 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
10432 @code{long} type, and the infrastructure needed to support them.
10433 Specifying @option{-maix64} implies @option{-mpowerpc64} and
10434 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
10435 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
10438 @itemx -mno-xl-call
10440 @opindex mno-xl-call
10441 On AIX, pass floating-point arguments to prototyped functions beyond the
10442 register save area (RSA) on the stack in addition to argument FPRs. The
10443 AIX calling convention was extended but not initially documented to
10444 handle an obscure K&R C case of calling a function that takes the
10445 address of its arguments with fewer arguments than declared. AIX XL
10446 compilers access floating point arguments which do not fit in the
10447 RSA from the stack when a subroutine is compiled without
10448 optimization. Because always storing floating-point arguments on the
10449 stack is inefficient and rarely needed, this option is not enabled by
10450 default and only is necessary when calling subroutines compiled by AIX
10451 XL compilers without optimization.
10455 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
10456 application written to use message passing with special startup code to
10457 enable the application to run. The system must have PE installed in the
10458 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
10459 must be overridden with the @option{-specs=} option to specify the
10460 appropriate directory location. The Parallel Environment does not
10461 support threads, so the @option{-mpe} option and the @option{-pthread}
10462 option are incompatible.
10464 @item -malign-natural
10465 @itemx -malign-power
10466 @opindex malign-natural
10467 @opindex malign-power
10468 On AIX, Darwin, and 64-bit PowerPC GNU/Linux, the option
10469 @option{-malign-natural} overrides the ABI-defined alignment of larger
10470 types, such as floating-point doubles, on their natural size-based boundary.
10471 The option @option{-malign-power} instructs GCC to follow the ABI-specified
10472 alignment rules. GCC defaults to the standard alignment defined in the ABI@.
10475 @itemx -mhard-float
10476 @opindex msoft-float
10477 @opindex mhard-float
10478 Generate code that does not use (uses) the floating-point register set.
10479 Software floating point emulation is provided if you use the
10480 @option{-msoft-float} option, and pass the option to GCC when linking.
10483 @itemx -mno-multiple
10485 @opindex mno-multiple
10486 Generate code that uses (does not use) the load multiple word
10487 instructions and the store multiple word instructions. These
10488 instructions are generated by default on POWER systems, and not
10489 generated on PowerPC systems. Do not use @option{-mmultiple} on little
10490 endian PowerPC systems, since those instructions do not work when the
10491 processor is in little endian mode. The exceptions are PPC740 and
10492 PPC750 which permit the instructions usage in little endian mode.
10497 @opindex mno-string
10498 Generate code that uses (does not use) the load string instructions
10499 and the store string word instructions to save multiple registers and
10500 do small block moves. These instructions are generated by default on
10501 POWER systems, and not generated on PowerPC systems. Do not use
10502 @option{-mstring} on little endian PowerPC systems, since those
10503 instructions do not work when the processor is in little endian mode.
10504 The exceptions are PPC740 and PPC750 which permit the instructions
10505 usage in little endian mode.
10510 @opindex mno-update
10511 Generate code that uses (does not use) the load or store instructions
10512 that update the base register to the address of the calculated memory
10513 location. These instructions are generated by default. If you use
10514 @option{-mno-update}, there is a small window between the time that the
10515 stack pointer is updated and the address of the previous frame is
10516 stored, which means code that walks the stack frame across interrupts or
10517 signals may get corrupted data.
10520 @itemx -mno-fused-madd
10521 @opindex mfused-madd
10522 @opindex mno-fused-madd
10523 Generate code that uses (does not use) the floating point multiply and
10524 accumulate instructions. These instructions are generated by default if
10525 hardware floating is used.
10527 @item -mno-bit-align
10529 @opindex mno-bit-align
10530 @opindex mbit-align
10531 On System V.4 and embedded PowerPC systems do not (do) force structures
10532 and unions that contain bit-fields to be aligned to the base type of the
10535 For example, by default a structure containing nothing but 8
10536 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
10537 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
10538 the structure would be aligned to a 1 byte boundary and be one byte in
10541 @item -mno-strict-align
10542 @itemx -mstrict-align
10543 @opindex mno-strict-align
10544 @opindex mstrict-align
10545 On System V.4 and embedded PowerPC systems do not (do) assume that
10546 unaligned memory references will be handled by the system.
10548 @item -mrelocatable
10549 @itemx -mno-relocatable
10550 @opindex mrelocatable
10551 @opindex mno-relocatable
10552 On embedded PowerPC systems generate code that allows (does not allow)
10553 the program to be relocated to a different address at runtime. If you
10554 use @option{-mrelocatable} on any module, all objects linked together must
10555 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
10557 @item -mrelocatable-lib
10558 @itemx -mno-relocatable-lib
10559 @opindex mrelocatable-lib
10560 @opindex mno-relocatable-lib
10561 On embedded PowerPC systems generate code that allows (does not allow)
10562 the program to be relocated to a different address at runtime. Modules
10563 compiled with @option{-mrelocatable-lib} can be linked with either modules
10564 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
10565 with modules compiled with the @option{-mrelocatable} options.
10571 On System V.4 and embedded PowerPC systems do not (do) assume that
10572 register 2 contains a pointer to a global area pointing to the addresses
10573 used in the program.
10576 @itemx -mlittle-endian
10578 @opindex mlittle-endian
10579 On System V.4 and embedded PowerPC systems compile code for the
10580 processor in little endian mode. The @option{-mlittle-endian} option is
10581 the same as @option{-mlittle}.
10584 @itemx -mbig-endian
10586 @opindex mbig-endian
10587 On System V.4 and embedded PowerPC systems compile code for the
10588 processor in big endian mode. The @option{-mbig-endian} option is
10589 the same as @option{-mbig}.
10591 @item -mdynamic-no-pic
10592 @opindex mdynamic-no-pic
10593 On Darwin and Mac OS X systems, compile code so that it is not
10594 relocatable, but that its external references are relocatable. The
10595 resulting code is suitable for applications, but not shared
10598 @item -mprioritize-restricted-insns=@var{priority}
10599 @opindex mprioritize-restricted-insns
10600 This option controls the priority that is assigned to
10601 dispatch-slot restricted instructions during the second scheduling
10602 pass. The argument @var{priority} takes the value @var{0/1/2} to assign
10603 @var{no/highest/second-highest} priority to dispatch slot restricted
10606 @item -msched-costly-dep=@var{dependence_type}
10607 @opindex msched-costly-dep
10608 This option controls which dependences are considered costly
10609 by the target during instruction scheduling. The argument
10610 @var{dependence_type} takes one of the following values:
10611 @var{no}: no dependence is costly,
10612 @var{all}: all dependences are costly,
10613 @var{true_store_to_load}: a true dependence from store to load is costly,
10614 @var{store_to_load}: any dependence from store to load is costly,
10615 @var{number}: any dependence which latency >= @var{number} is costly.
10617 @item -minsert-sched-nops=@var{scheme}
10618 @opindex minsert-sched-nops
10619 This option controls which nop insertion scheme will be used during
10620 the second scheduling pass. The argument @var{scheme} takes one of the
10622 @var{no}: Don't insert nops.
10623 @var{pad}: Pad with nops any dispatch group which has vacant issue slots,
10624 according to the scheduler's grouping.
10625 @var{regroup_exact}: Insert nops to force costly dependent insns into
10626 separate groups. Insert exactly as many nops as needed to force an insn
10627 to a new group, according to the estimated processor grouping.
10628 @var{number}: Insert nops to force costly dependent insns into
10629 separate groups. Insert @var{number} nops to force an insn to a new group.
10632 @opindex mcall-sysv
10633 On System V.4 and embedded PowerPC systems compile code using calling
10634 conventions that adheres to the March 1995 draft of the System V
10635 Application Binary Interface, PowerPC processor supplement. This is the
10636 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
10638 @item -mcall-sysv-eabi
10639 @opindex mcall-sysv-eabi
10640 Specify both @option{-mcall-sysv} and @option{-meabi} options.
10642 @item -mcall-sysv-noeabi
10643 @opindex mcall-sysv-noeabi
10644 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
10646 @item -mcall-solaris
10647 @opindex mcall-solaris
10648 On System V.4 and embedded PowerPC systems compile code for the Solaris
10652 @opindex mcall-linux
10653 On System V.4 and embedded PowerPC systems compile code for the
10654 Linux-based GNU system.
10658 On System V.4 and embedded PowerPC systems compile code for the
10659 Hurd-based GNU system.
10661 @item -mcall-netbsd
10662 @opindex mcall-netbsd
10663 On System V.4 and embedded PowerPC systems compile code for the
10664 NetBSD operating system.
10666 @item -maix-struct-return
10667 @opindex maix-struct-return
10668 Return all structures in memory (as specified by the AIX ABI)@.
10670 @item -msvr4-struct-return
10671 @opindex msvr4-struct-return
10672 Return structures smaller than 8 bytes in registers (as specified by the
10675 @item -mabi=altivec
10676 @opindex mabi=altivec
10677 Extend the current ABI with AltiVec ABI extensions. This does not
10678 change the default ABI, instead it adds the AltiVec ABI extensions to
10681 @item -mabi=no-altivec
10682 @opindex mabi=no-altivec
10683 Disable AltiVec ABI extensions for the current ABI@.
10686 @itemx -mno-prototype
10687 @opindex mprototype
10688 @opindex mno-prototype
10689 On System V.4 and embedded PowerPC systems assume that all calls to
10690 variable argument functions are properly prototyped. Otherwise, the
10691 compiler must insert an instruction before every non prototyped call to
10692 set or clear bit 6 of the condition code register (@var{CR}) to
10693 indicate whether floating point values were passed in the floating point
10694 registers in case the function takes a variable arguments. With
10695 @option{-mprototype}, only calls to prototyped variable argument functions
10696 will set or clear the bit.
10700 On embedded PowerPC systems, assume that the startup module is called
10701 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
10702 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
10707 On embedded PowerPC systems, assume that the startup module is called
10708 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
10713 On embedded PowerPC systems, assume that the startup module is called
10714 @file{crt0.o} and the standard C libraries are @file{libads.a} and
10717 @item -myellowknife
10718 @opindex myellowknife
10719 On embedded PowerPC systems, assume that the startup module is called
10720 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
10725 On System V.4 and embedded PowerPC systems, specify that you are
10726 compiling for a VxWorks system.
10730 Specify that you are compiling for the WindISS simulation environment.
10734 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
10735 header to indicate that @samp{eabi} extended relocations are used.
10741 On System V.4 and embedded PowerPC systems do (do not) adhere to the
10742 Embedded Applications Binary Interface (eabi) which is a set of
10743 modifications to the System V.4 specifications. Selecting @option{-meabi}
10744 means that the stack is aligned to an 8 byte boundary, a function
10745 @code{__eabi} is called to from @code{main} to set up the eabi
10746 environment, and the @option{-msdata} option can use both @code{r2} and
10747 @code{r13} to point to two separate small data areas. Selecting
10748 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
10749 do not call an initialization function from @code{main}, and the
10750 @option{-msdata} option will only use @code{r13} to point to a single
10751 small data area. The @option{-meabi} option is on by default if you
10752 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
10755 @opindex msdata=eabi
10756 On System V.4 and embedded PowerPC systems, put small initialized
10757 @code{const} global and static data in the @samp{.sdata2} section, which
10758 is pointed to by register @code{r2}. Put small initialized
10759 non-@code{const} global and static data in the @samp{.sdata} section,
10760 which is pointed to by register @code{r13}. Put small uninitialized
10761 global and static data in the @samp{.sbss} section, which is adjacent to
10762 the @samp{.sdata} section. The @option{-msdata=eabi} option is
10763 incompatible with the @option{-mrelocatable} option. The
10764 @option{-msdata=eabi} option also sets the @option{-memb} option.
10767 @opindex msdata=sysv
10768 On System V.4 and embedded PowerPC systems, put small global and static
10769 data in the @samp{.sdata} section, which is pointed to by register
10770 @code{r13}. Put small uninitialized global and static data in the
10771 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
10772 The @option{-msdata=sysv} option is incompatible with the
10773 @option{-mrelocatable} option.
10775 @item -msdata=default
10777 @opindex msdata=default
10779 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
10780 compile code the same as @option{-msdata=eabi}, otherwise compile code the
10781 same as @option{-msdata=sysv}.
10784 @opindex msdata-data
10785 On System V.4 and embedded PowerPC systems, put small global and static
10786 data in the @samp{.sdata} section. Put small uninitialized global and
10787 static data in the @samp{.sbss} section. Do not use register @code{r13}
10788 to address small data however. This is the default behavior unless
10789 other @option{-msdata} options are used.
10793 @opindex msdata=none
10795 On embedded PowerPC systems, put all initialized global and static data
10796 in the @samp{.data} section, and all uninitialized data in the
10797 @samp{.bss} section.
10801 @cindex smaller data references (PowerPC)
10802 @cindex .sdata/.sdata2 references (PowerPC)
10803 On embedded PowerPC systems, put global and static items less than or
10804 equal to @var{num} bytes into the small data or bss sections instead of
10805 the normal data or bss section. By default, @var{num} is 8. The
10806 @option{-G @var{num}} switch is also passed to the linker.
10807 All modules should be compiled with the same @option{-G @var{num}} value.
10810 @itemx -mno-regnames
10812 @opindex mno-regnames
10813 On System V.4 and embedded PowerPC systems do (do not) emit register
10814 names in the assembly language output using symbolic forms.
10817 @itemx -mno-longcall
10819 @opindex mno-longcall
10820 Default to making all function calls indirectly, using a register, so
10821 that functions which reside further than 32 megabytes (33,554,432
10822 bytes) from the current location can be called. This setting can be
10823 overridden by the @code{shortcall} function attribute, or by
10824 @code{#pragma longcall(0)}.
10826 Some linkers are capable of detecting out-of-range calls and generating
10827 glue code on the fly. On these systems, long calls are unnecessary and
10828 generate slower code. As of this writing, the AIX linker can do this,
10829 as can the GNU linker for PowerPC/64. It is planned to add this feature
10830 to the GNU linker for 32-bit PowerPC systems as well.
10832 On Darwin/PPC systems, @code{#pragma longcall} will generate ``jbsr
10833 callee, L42'', plus a ``branch island'' (glue code). The two target
10834 addresses represent the callee and the ``branch island''. The
10835 Darwin/PPC linker will prefer the first address and generate a ``bl
10836 callee'' if the PPC ``bl'' instruction will reach the callee directly;
10837 otherwise, the linker will generate ``bl L42'' to call the ``branch
10838 island''. The ``branch island'' is appended to the body of the
10839 calling function; it computes the full 32-bit address of the callee
10842 On Mach-O (Darwin) systems, this option directs the compiler emit to
10843 the glue for every direct call, and the Darwin linker decides whether
10844 to use or discard it.
10846 In the future, we may cause GCC to ignore all longcall specifications
10847 when the linker is known to generate glue.
10851 Adds support for multithreading with the @dfn{pthreads} library.
10852 This option sets flags for both the preprocessor and linker.
10856 @node S/390 and zSeries Options
10857 @subsection S/390 and zSeries Options
10858 @cindex S/390 and zSeries Options
10860 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
10864 @itemx -msoft-float
10865 @opindex mhard-float
10866 @opindex msoft-float
10867 Use (do not use) the hardware floating-point instructions and registers
10868 for floating-point operations. When @option{-msoft-float} is specified,
10869 functions in @file{libgcc.a} will be used to perform floating-point
10870 operations. When @option{-mhard-float} is specified, the compiler
10871 generates IEEE floating-point instructions. This is the default.
10874 @itemx -mno-backchain
10875 @opindex mbackchain
10876 @opindex mno-backchain
10877 Store (do not store) the address of the caller's frame as backchain pointer
10878 into the callee's stack frame.
10879 A backchain may be needed to allow debugging using tools that do not understand
10880 DWARF-2 call frame information.
10881 When @option{-mno-packed-stack} is in effect, the backchain pointer is stored
10882 at the bottom of the stack frame; when @option{-mpacked-stack} is in effect,
10883 the backchain is placed into the topmost word of the 96/160 byte register
10886 In general, code compiled with @option{-mbackchain} is call-compatible with
10887 code compiled with @option{-mmo-backchain}; however, use of the backchain
10888 for debugging purposes usually requires that the whole binary is built with
10889 @option{-mbackchain}. Note that the combination of @option{-mbackchain} and
10890 @option{-mpacked-stack} generates code that is not ABI-compatible.
10892 The default is to not maintain the backchain.
10894 @item -mpacked-stack
10895 @item -mno-packed-stack
10896 @opindex mpacked-stack
10897 @opindex mno-packed-stack
10898 Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is
10899 specified, the compiler uses the all fields of the 96/160 byte register save
10900 area only for their default purpose; unused fields still take up stack space.
10901 When @option{-mpacked-stack} is specified, register save slots are densely
10902 packed at the top of the register save area; unused space is reused for other
10903 purposes, allowing for more efficient use of the available stack space.
10904 However, when @option{-mbackchain} is also in effect, the topmost word of
10905 the save area is always used to store the backchain, and the return address
10906 register is always saved two words below the backchain.
10908 As long as the stack frame backchain is not used, code generated with
10909 @option{-mpacked-stack} is call-compatible with code generated with
10910 @option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for
10911 S/390 or zSeries generated code that uses the stack frame backchain at run
10912 time, not just for debugging purposes. Such code is not call-compatible
10913 with code compiled with @option{-mpacked-stack}. Also, note that the
10914 combination of @option{-mbackchain} and @option{-mpacked-stack} generates code
10915 that is not ABI-compatible.
10917 The default is to not use the packed stack layout.
10920 @itemx -mno-small-exec
10921 @opindex msmall-exec
10922 @opindex mno-small-exec
10923 Generate (or do not generate) code using the @code{bras} instruction
10924 to do subroutine calls.
10925 This only works reliably if the total executable size does not
10926 exceed 64k. The default is to use the @code{basr} instruction instead,
10927 which does not have this limitation.
10933 When @option{-m31} is specified, generate code compliant to the
10934 GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate
10935 code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in
10936 particular to generate 64-bit instructions. For the @samp{s390}
10937 targets, the default is @option{-m31}, while the @samp{s390x}
10938 targets default to @option{-m64}.
10944 When @option{-mzarch} is specified, generate code using the
10945 instructions available on z/Architecture.
10946 When @option{-mesa} is specified, generate code using the
10947 instructions available on ESA/390. Note that @option{-mesa} is
10948 not possible with @option{-m64}.
10949 When generating code compliant to the GNU/Linux for S/390 ABI,
10950 the default is @option{-mesa}. When generating code compliant
10951 to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}.
10957 Generate (or do not generate) code using the @code{mvcle} instruction
10958 to perform block moves. When @option{-mno-mvcle} is specified,
10959 use a @code{mvc} loop instead. This is the default.
10965 Print (or do not print) additional debug information when compiling.
10966 The default is to not print debug information.
10968 @item -march=@var{cpu-type}
10970 Generate code that will run on @var{cpu-type}, which is the name of a system
10971 representing a certain processor type. Possible values for
10972 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, and @samp{z990}.
10973 When generating code using the instructions available on z/Architecture,
10974 the default is @option{-march=z900}. Otherwise, the default is
10975 @option{-march=g5}.
10977 @item -mtune=@var{cpu-type}
10979 Tune to @var{cpu-type} everything applicable about the generated code,
10980 except for the ABI and the set of available instructions.
10981 The list of @var{cpu-type} values is the same as for @option{-march}.
10982 The default is the value used for @option{-march}.
10985 @itemx -mno-tpf-trace
10986 @opindex mtpf-trace
10987 @opindex mno-tpf-trace
10988 Generate code that adds (does not add) in TPF OS specific branches to trace
10989 routines in the operating system. This option is off by default, even
10990 when compiling for the TPF OS@.
10993 @itemx -mno-fused-madd
10994 @opindex mfused-madd
10995 @opindex mno-fused-madd
10996 Generate code that uses (does not use) the floating point multiply and
10997 accumulate instructions. These instructions are generated by default if
10998 hardware floating point is used.
11000 @item -mwarn-framesize=@var{framesize}
11001 @opindex mwarn-framesize
11002 Emit a warning if the current function exceeds the given frame size. Because
11003 this is a compile time check it doesn't need to be a real problem when the program
11004 runs. It is intended to identify functions which most probably cause
11005 a stack overflow. It is useful to be used in an environment with limited stack
11006 size e.g.@: the linux kernel.
11008 @item -mwarn-dynamicstack
11009 @opindex mwarn-dynamicstack
11010 Emit a warning if the function calls alloca or uses dynamically
11011 sized arrays. This is generally a bad idea with a limited stack size.
11013 @item -mstack-guard=@var{stack-guard}
11014 @item -mstack-size=@var{stack-size}
11015 @opindex mstack-guard
11016 @opindex mstack-size
11017 These arguments always have to be used in conjunction. If they are present the s390
11018 back end emits additional instructions in the function prologue which trigger a trap
11019 if the stack size is @var{stack-guard} bytes above the @var{stack-size}
11020 (remember that the stack on s390 grows downward). These options are intended to
11021 be used to help debugging stack overflow problems. The additionally emitted code
11022 cause only little overhead and hence can also be used in production like systems
11023 without greater performance degradation. The given values have to be exact
11024 powers of 2 and @var{stack-size} has to be greater than @var{stack-guard}.
11025 In order to be efficient the extra code makes the assumption that the stack starts
11026 at an address aligned to the value given by @var{stack-size}.
11030 @subsection SH Options
11032 These @samp{-m} options are defined for the SH implementations:
11037 Generate code for the SH1.
11041 Generate code for the SH2.
11044 Generate code for the SH2e.
11048 Generate code for the SH3.
11052 Generate code for the SH3e.
11056 Generate code for the SH4 without a floating-point unit.
11058 @item -m4-single-only
11059 @opindex m4-single-only
11060 Generate code for the SH4 with a floating-point unit that only
11061 supports single-precision arithmetic.
11065 Generate code for the SH4 assuming the floating-point unit is in
11066 single-precision mode by default.
11070 Generate code for the SH4.
11074 Generate code for the SH4al-dsp, or for a SH4a in such a way that the
11075 floating-point unit is not used.
11077 @item -m4a-single-only
11078 @opindex m4a-single-only
11079 Generate code for the SH4a, in such a way that no double-precision
11080 floating point operations are used.
11083 @opindex m4a-single
11084 Generate code for the SH4a assuming the floating-point unit is in
11085 single-precision mode by default.
11089 Generate code for the SH4a.
11093 Same as @option{-m4a-nofpu}, except that it implicitly passes
11094 @option{-dsp} to the assembler. GCC doesn't generate any DSP
11095 instructions at the moment.
11099 Compile code for the processor in big endian mode.
11103 Compile code for the processor in little endian mode.
11107 Align doubles at 64-bit boundaries. Note that this changes the calling
11108 conventions, and thus some functions from the standard C library will
11109 not work unless you recompile it first with @option{-mdalign}.
11113 Shorten some address references at link time, when possible; uses the
11114 linker option @option{-relax}.
11118 Use 32-bit offsets in @code{switch} tables. The default is to use
11123 Enable the use of the instruction @code{fmovd}.
11127 Comply with the calling conventions defined by Renesas.
11131 Comply with the calling conventions defined by Renesas.
11135 Comply with the calling conventions defined for GCC before the Renesas
11136 conventions were available. This option is the default for all
11137 targets of the SH toolchain except for @samp{sh-symbianelf}.
11140 @opindex mnomacsave
11141 Mark the @code{MAC} register as call-clobbered, even if
11142 @option{-mhitachi} is given.
11146 Increase IEEE-compliance of floating-point code.
11150 Dump instruction size and location in the assembly code.
11153 @opindex mpadstruct
11154 This option is deprecated. It pads structures to multiple of 4 bytes,
11155 which is incompatible with the SH ABI@.
11159 Optimize for space instead of speed. Implied by @option{-Os}.
11162 @opindex mprefergot
11163 When generating position-independent code, emit function calls using
11164 the Global Offset Table instead of the Procedure Linkage Table.
11168 Generate a library function call to invalidate instruction cache
11169 entries, after fixing up a trampoline. This library function call
11170 doesn't assume it can write to the whole memory address space. This
11171 is the default when the target is @code{sh-*-linux*}.
11174 @node SPARC Options
11175 @subsection SPARC Options
11176 @cindex SPARC options
11178 These @samp{-m} options are supported on the SPARC:
11181 @item -mno-app-regs
11183 @opindex mno-app-regs
11185 Specify @option{-mapp-regs} to generate output using the global registers
11186 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
11189 To be fully SVR4 ABI compliant at the cost of some performance loss,
11190 specify @option{-mno-app-regs}. You should compile libraries and system
11191 software with this option.
11194 @itemx -mhard-float
11196 @opindex mhard-float
11197 Generate output containing floating point instructions. This is the
11201 @itemx -msoft-float
11203 @opindex msoft-float
11204 Generate output containing library calls for floating point.
11205 @strong{Warning:} the requisite libraries are not available for all SPARC
11206 targets. Normally the facilities of the machine's usual C compiler are
11207 used, but this cannot be done directly in cross-compilation. You must make
11208 your own arrangements to provide suitable library functions for
11209 cross-compilation. The embedded targets @samp{sparc-*-aout} and
11210 @samp{sparclite-*-*} do provide software floating point support.
11212 @option{-msoft-float} changes the calling convention in the output file;
11213 therefore, it is only useful if you compile @emph{all} of a program with
11214 this option. In particular, you need to compile @file{libgcc.a}, the
11215 library that comes with GCC, with @option{-msoft-float} in order for
11218 @item -mhard-quad-float
11219 @opindex mhard-quad-float
11220 Generate output containing quad-word (long double) floating point
11223 @item -msoft-quad-float
11224 @opindex msoft-quad-float
11225 Generate output containing library calls for quad-word (long double)
11226 floating point instructions. The functions called are those specified
11227 in the SPARC ABI@. This is the default.
11229 As of this writing, there are no SPARC implementations that have hardware
11230 support for the quad-word floating point instructions. They all invoke
11231 a trap handler for one of these instructions, and then the trap handler
11232 emulates the effect of the instruction. Because of the trap handler overhead,
11233 this is much slower than calling the ABI library routines. Thus the
11234 @option{-msoft-quad-float} option is the default.
11236 @item -mno-unaligned-doubles
11237 @itemx -munaligned-doubles
11238 @opindex mno-unaligned-doubles
11239 @opindex munaligned-doubles
11240 Assume that doubles have 8 byte alignment. This is the default.
11242 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
11243 alignment only if they are contained in another type, or if they have an
11244 absolute address. Otherwise, it assumes they have 4 byte alignment.
11245 Specifying this option avoids some rare compatibility problems with code
11246 generated by other compilers. It is not the default because it results
11247 in a performance loss, especially for floating point code.
11249 @item -mno-faster-structs
11250 @itemx -mfaster-structs
11251 @opindex mno-faster-structs
11252 @opindex mfaster-structs
11253 With @option{-mfaster-structs}, the compiler assumes that structures
11254 should have 8 byte alignment. This enables the use of pairs of
11255 @code{ldd} and @code{std} instructions for copies in structure
11256 assignment, in place of twice as many @code{ld} and @code{st} pairs.
11257 However, the use of this changed alignment directly violates the SPARC
11258 ABI@. Thus, it's intended only for use on targets where the developer
11259 acknowledges that their resulting code will not be directly in line with
11260 the rules of the ABI@.
11262 @item -mimpure-text
11263 @opindex mimpure-text
11264 @option{-mimpure-text}, used in addition to @option{-shared}, tells
11265 the compiler to not pass @option{-z text} to the linker when linking a
11266 shared object. Using this option, you can link position-dependent
11267 code into a shared object.
11269 @option{-mimpure-text} suppresses the ``relocations remain against
11270 allocatable but non-writable sections'' linker error message.
11271 However, the necessary relocations will trigger copy-on-write, and the
11272 shared object is not actually shared across processes. Instead of
11273 using @option{-mimpure-text}, you should compile all source code with
11274 @option{-fpic} or @option{-fPIC}.
11276 This option is only available on SunOS and Solaris.
11278 @item -mcpu=@var{cpu_type}
11280 Set the instruction set, register set, and instruction scheduling parameters
11281 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
11282 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
11283 @samp{f930}, @samp{f934}, @samp{hypersparc}, @samp{sparclite86x},
11284 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc}, and
11285 @samp{ultrasparc3}.
11287 Default instruction scheduling parameters are used for values that select
11288 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
11289 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
11291 Here is a list of each supported architecture and their supported
11296 v8: supersparc, hypersparc
11297 sparclite: f930, f934, sparclite86x
11299 v9: ultrasparc, ultrasparc3
11302 By default (unless configured otherwise), GCC generates code for the V7
11303 variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler
11304 additionally optimizes it for the Cypress CY7C602 chip, as used in the
11305 SPARCStation/SPARCServer 3xx series. This is also appropriate for the older
11306 SPARCStation 1, 2, IPX etc.
11308 With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC
11309 architecture. The only difference from V7 code is that the compiler emits
11310 the integer multiply and integer divide instructions which exist in SPARC-V8
11311 but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally
11312 optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and
11315 With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of
11316 the SPARC architecture. This adds the integer multiply, integer divide step
11317 and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7.
11318 With @option{-mcpu=f930}, the compiler additionally optimizes it for the
11319 Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With
11320 @option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu
11321 MB86934 chip, which is the more recent SPARClite with FPU@.
11323 With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of
11324 the SPARC architecture. This adds the integer multiply, multiply/accumulate,
11325 integer divide step and scan (@code{ffs}) instructions which exist in SPARClet
11326 but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally
11327 optimizes it for the TEMIC SPARClet chip.
11329 With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC
11330 architecture. This adds 64-bit integer and floating-point move instructions,
11331 3 additional floating-point condition code registers and conditional move
11332 instructions. With @option{-mcpu=ultrasparc}, the compiler additionally
11333 optimizes it for the Sun UltraSPARC I/II chips. With
11334 @option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the
11335 Sun UltraSPARC III chip.
11337 @item -mtune=@var{cpu_type}
11339 Set the instruction scheduling parameters for machine type
11340 @var{cpu_type}, but do not set the instruction set or register set that the
11341 option @option{-mcpu=@var{cpu_type}} would.
11343 The same values for @option{-mcpu=@var{cpu_type}} can be used for
11344 @option{-mtune=@var{cpu_type}}, but the only useful values are those
11345 that select a particular cpu implementation. Those are @samp{cypress},
11346 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
11347 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc}, and
11348 @samp{ultrasparc3}.
11353 @opindex mno-v8plus
11354 With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The
11355 difference from the V8 ABI is that the global and out registers are
11356 considered 64-bit wide. This is enabled by default on Solaris in 32-bit
11357 mode for all SPARC-V9 processors.
11363 With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC
11364 Visual Instruction Set extensions. The default is @option{-mno-vis}.
11367 These @samp{-m} options are supported in addition to the above
11368 on SPARC-V9 processors in 64-bit environments:
11371 @item -mlittle-endian
11372 @opindex mlittle-endian
11373 Generate code for a processor running in little-endian mode. It is only
11374 available for a few configurations and most notably not on Solaris.
11380 Generate code for a 32-bit or 64-bit environment.
11381 The 32-bit environment sets int, long and pointer to 32 bits.
11382 The 64-bit environment sets int to 32 bits and long and pointer
11385 @item -mcmodel=medlow
11386 @opindex mcmodel=medlow
11387 Generate code for the Medium/Low code model: 64-bit addresses, programs
11388 must be linked in the low 32 bits of memory. Programs can be statically
11389 or dynamically linked.
11391 @item -mcmodel=medmid
11392 @opindex mcmodel=medmid
11393 Generate code for the Medium/Middle code model: 64-bit addresses, programs
11394 must be linked in the low 44 bits of memory, the text and data segments must
11395 be less than 2GB in size and the data segment must be located within 2GB of
11398 @item -mcmodel=medany
11399 @opindex mcmodel=medany
11400 Generate code for the Medium/Anywhere code model: 64-bit addresses, programs
11401 may be linked anywhere in memory, the text and data segments must be less
11402 than 2GB in size and the data segment must be located within 2GB of the
11405 @item -mcmodel=embmedany
11406 @opindex mcmodel=embmedany
11407 Generate code for the Medium/Anywhere code model for embedded systems:
11408 64-bit addresses, the text and data segments must be less than 2GB in
11409 size, both starting anywhere in memory (determined at link time). The
11410 global register %g4 points to the base of the data segment. Programs
11411 are statically linked and PIC is not supported.
11414 @itemx -mno-stack-bias
11415 @opindex mstack-bias
11416 @opindex mno-stack-bias
11417 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
11418 frame pointer if present, are offset by @minus{}2047 which must be added back
11419 when making stack frame references. This is the default in 64-bit mode.
11420 Otherwise, assume no such offset is present.
11423 These switches are supported in addition to the above on Solaris:
11428 Add support for multithreading using the Solaris threads library. This
11429 option sets flags for both the preprocessor and linker. This option does
11430 not affect the thread safety of object code produced by the compiler or
11431 that of libraries supplied with it.
11435 Add support for multithreading using the POSIX threads library. This
11436 option sets flags for both the preprocessor and linker. This option does
11437 not affect the thread safety of object code produced by the compiler or
11438 that of libraries supplied with it.
11441 @node System V Options
11442 @subsection Options for System V
11444 These additional options are available on System V Release 4 for
11445 compatibility with other compilers on those systems:
11450 Create a shared object.
11451 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
11455 Identify the versions of each tool used by the compiler, in a
11456 @code{.ident} assembler directive in the output.
11460 Refrain from adding @code{.ident} directives to the output file (this is
11463 @item -YP,@var{dirs}
11465 Search the directories @var{dirs}, and no others, for libraries
11466 specified with @option{-l}.
11468 @item -Ym,@var{dir}
11470 Look in the directory @var{dir} to find the M4 preprocessor.
11471 The assembler uses this option.
11472 @c This is supposed to go with a -Yd for predefined M4 macro files, but
11473 @c the generic assembler that comes with Solaris takes just -Ym.
11476 @node TMS320C3x/C4x Options
11477 @subsection TMS320C3x/C4x Options
11478 @cindex TMS320C3x/C4x Options
11480 These @samp{-m} options are defined for TMS320C3x/C4x implementations:
11484 @item -mcpu=@var{cpu_type}
11486 Set the instruction set, register set, and instruction scheduling
11487 parameters for machine type @var{cpu_type}. Supported values for
11488 @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
11489 @samp{c44}. The default is @samp{c40} to generate code for the
11494 @itemx -msmall-memory
11496 @opindex mbig-memory
11498 @opindex msmall-memory
11500 Generates code for the big or small memory model. The small memory
11501 model assumed that all data fits into one 64K word page. At run-time
11502 the data page (DP) register must be set to point to the 64K page
11503 containing the .bss and .data program sections. The big memory model is
11504 the default and requires reloading of the DP register for every direct
11511 Allow (disallow) allocation of general integer operands into the block
11512 count register BK@.
11518 Enable (disable) generation of code using decrement and branch,
11519 DBcond(D), instructions. This is enabled by default for the C4x. To be
11520 on the safe side, this is disabled for the C3x, since the maximum
11521 iteration count on the C3x is @math{2^{23} + 1} (but who iterates loops more than
11522 @math{2^{23}} times on the C3x?). Note that GCC will try to reverse a loop so
11523 that it can utilize the decrement and branch instruction, but will give
11524 up if there is more than one memory reference in the loop. Thus a loop
11525 where the loop counter is decremented can generate slightly more
11526 efficient code, in cases where the RPTB instruction cannot be utilized.
11528 @item -mdp-isr-reload
11530 @opindex mdp-isr-reload
11532 Force the DP register to be saved on entry to an interrupt service
11533 routine (ISR), reloaded to point to the data section, and restored on
11534 exit from the ISR@. This should not be required unless someone has
11535 violated the small memory model by modifying the DP register, say within
11542 For the C3x use the 24-bit MPYI instruction for integer multiplies
11543 instead of a library call to guarantee 32-bit results. Note that if one
11544 of the operands is a constant, then the multiplication will be performed
11545 using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
11546 then squaring operations are performed inline instead of a library call.
11549 @itemx -mno-fast-fix
11551 @opindex mno-fast-fix
11552 The C3x/C4x FIX instruction to convert a floating point value to an
11553 integer value chooses the nearest integer less than or equal to the
11554 floating point value rather than to the nearest integer. Thus if the
11555 floating point number is negative, the result will be incorrectly
11556 truncated an additional code is necessary to detect and correct this
11557 case. This option can be used to disable generation of the additional
11558 code required to correct the result.
11564 Enable (disable) generation of repeat block sequences using the RPTB
11565 instruction for zero overhead looping. The RPTB construct is only used
11566 for innermost loops that do not call functions or jump across the loop
11567 boundaries. There is no advantage having nested RPTB loops due to the
11568 overhead required to save and restore the RC, RS, and RE registers.
11569 This is enabled by default with @option{-O2}.
11571 @item -mrpts=@var{count}
11575 Enable (disable) the use of the single instruction repeat instruction
11576 RPTS@. If a repeat block contains a single instruction, and the loop
11577 count can be guaranteed to be less than the value @var{count}, GCC will
11578 emit a RPTS instruction instead of a RPTB@. If no value is specified,
11579 then a RPTS will be emitted even if the loop count cannot be determined
11580 at compile time. Note that the repeated instruction following RPTS does
11581 not have to be reloaded from memory each iteration, thus freeing up the
11582 CPU buses for operands. However, since interrupts are blocked by this
11583 instruction, it is disabled by default.
11585 @item -mloop-unsigned
11586 @itemx -mno-loop-unsigned
11587 @opindex mloop-unsigned
11588 @opindex mno-loop-unsigned
11589 The maximum iteration count when using RPTS and RPTB (and DB on the C40)
11590 is @math{2^{31} + 1} since these instructions test if the iteration count is
11591 negative to terminate the loop. If the iteration count is unsigned
11592 there is a possibility than the @math{2^{31} + 1} maximum iteration count may be
11593 exceeded. This switch allows an unsigned iteration count.
11597 Try to emit an assembler syntax that the TI assembler (asm30) is happy
11598 with. This also enforces compatibility with the API employed by the TI
11599 C3x C compiler. For example, long doubles are passed as structures
11600 rather than in floating point registers.
11606 Generate code that uses registers (stack) for passing arguments to functions.
11607 By default, arguments are passed in registers where possible rather
11608 than by pushing arguments on to the stack.
11610 @item -mparallel-insns
11611 @itemx -mno-parallel-insns
11612 @opindex mparallel-insns
11613 @opindex mno-parallel-insns
11614 Allow the generation of parallel instructions. This is enabled by
11615 default with @option{-O2}.
11617 @item -mparallel-mpy
11618 @itemx -mno-parallel-mpy
11619 @opindex mparallel-mpy
11620 @opindex mno-parallel-mpy
11621 Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
11622 provided @option{-mparallel-insns} is also specified. These instructions have
11623 tight register constraints which can pessimize the code generation
11624 of large functions.
11629 @subsection V850 Options
11630 @cindex V850 Options
11632 These @samp{-m} options are defined for V850 implementations:
11636 @itemx -mno-long-calls
11637 @opindex mlong-calls
11638 @opindex mno-long-calls
11639 Treat all calls as being far away (near). If calls are assumed to be
11640 far away, the compiler will always load the functions address up into a
11641 register, and call indirect through the pointer.
11647 Do not optimize (do optimize) basic blocks that use the same index
11648 pointer 4 or more times to copy pointer into the @code{ep} register, and
11649 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
11650 option is on by default if you optimize.
11652 @item -mno-prolog-function
11653 @itemx -mprolog-function
11654 @opindex mno-prolog-function
11655 @opindex mprolog-function
11656 Do not use (do use) external functions to save and restore registers
11657 at the prologue and epilogue of a function. The external functions
11658 are slower, but use less code space if more than one function saves
11659 the same number of registers. The @option{-mprolog-function} option
11660 is on by default if you optimize.
11664 Try to make the code as small as possible. At present, this just turns
11665 on the @option{-mep} and @option{-mprolog-function} options.
11667 @item -mtda=@var{n}
11669 Put static or global variables whose size is @var{n} bytes or less into
11670 the tiny data area that register @code{ep} points to. The tiny data
11671 area can hold up to 256 bytes in total (128 bytes for byte references).
11673 @item -msda=@var{n}
11675 Put static or global variables whose size is @var{n} bytes or less into
11676 the small data area that register @code{gp} points to. The small data
11677 area can hold up to 64 kilobytes.
11679 @item -mzda=@var{n}
11681 Put static or global variables whose size is @var{n} bytes or less into
11682 the first 32 kilobytes of memory.
11686 Specify that the target processor is the V850.
11689 @opindex mbig-switch
11690 Generate code suitable for big switch tables. Use this option only if
11691 the assembler/linker complain about out of range branches within a switch
11696 This option will cause r2 and r5 to be used in the code generated by
11697 the compiler. This setting is the default.
11699 @item -mno-app-regs
11700 @opindex mno-app-regs
11701 This option will cause r2 and r5 to be treated as fixed registers.
11705 Specify that the target processor is the V850E1. The preprocessor
11706 constants @samp{__v850e1__} and @samp{__v850e__} will be defined if
11707 this option is used.
11711 Specify that the target processor is the V850E@. The preprocessor
11712 constant @samp{__v850e__} will be defined if this option is used.
11714 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
11715 are defined then a default target processor will be chosen and the
11716 relevant @samp{__v850*__} preprocessor constant will be defined.
11718 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
11719 defined, regardless of which processor variant is the target.
11721 @item -mdisable-callt
11722 @opindex mdisable-callt
11723 This option will suppress generation of the CALLT instruction for the
11724 v850e and v850e1 flavors of the v850 architecture. The default is
11725 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
11730 @subsection VAX Options
11731 @cindex VAX options
11733 These @samp{-m} options are defined for the VAX:
11738 Do not output certain jump instructions (@code{aobleq} and so on)
11739 that the Unix assembler for the VAX cannot handle across long
11744 Do output those jump instructions, on the assumption that you
11745 will assemble with the GNU assembler.
11749 Output code for g-format floating point numbers instead of d-format.
11752 @node x86-64 Options
11753 @subsection x86-64 Options
11754 @cindex x86-64 options
11756 These are listed under @xref{i386 and x86-64 Options}.
11758 @node Xstormy16 Options
11759 @subsection Xstormy16 Options
11760 @cindex Xstormy16 Options
11762 These options are defined for Xstormy16:
11767 Choose startup files and linker script suitable for the simulator.
11770 @node Xtensa Options
11771 @subsection Xtensa Options
11772 @cindex Xtensa Options
11774 These options are supported for Xtensa targets:
11778 @itemx -mno-const16
11780 @opindex mno-const16
11781 Enable or disable use of @code{CONST16} instructions for loading
11782 constant values. The @code{CONST16} instruction is currently not a
11783 standard option from Tensilica. When enabled, @code{CONST16}
11784 instructions are always used in place of the standard @code{L32R}
11785 instructions. The use of @code{CONST16} is enabled by default only if
11786 the @code{L32R} instruction is not available.
11789 @itemx -mno-fused-madd
11790 @opindex mfused-madd
11791 @opindex mno-fused-madd
11792 Enable or disable use of fused multiply/add and multiply/subtract
11793 instructions in the floating-point option. This has no effect if the
11794 floating-point option is not also enabled. Disabling fused multiply/add
11795 and multiply/subtract instructions forces the compiler to use separate
11796 instructions for the multiply and add/subtract operations. This may be
11797 desirable in some cases where strict IEEE 754-compliant results are
11798 required: the fused multiply add/subtract instructions do not round the
11799 intermediate result, thereby producing results with @emph{more} bits of
11800 precision than specified by the IEEE standard. Disabling fused multiply
11801 add/subtract instructions also ensures that the program output is not
11802 sensitive to the compiler's ability to combine multiply and add/subtract
11805 @item -mtext-section-literals
11806 @itemx -mno-text-section-literals
11807 @opindex mtext-section-literals
11808 @opindex mno-text-section-literals
11809 Control the treatment of literal pools. The default is
11810 @option{-mno-text-section-literals}, which places literals in a separate
11811 section in the output file. This allows the literal pool to be placed
11812 in a data RAM/ROM, and it also allows the linker to combine literal
11813 pools from separate object files to remove redundant literals and
11814 improve code size. With @option{-mtext-section-literals}, the literals
11815 are interspersed in the text section in order to keep them as close as
11816 possible to their references. This may be necessary for large assembly
11819 @item -mtarget-align
11820 @itemx -mno-target-align
11821 @opindex mtarget-align
11822 @opindex mno-target-align
11823 When this option is enabled, GCC instructs the assembler to
11824 automatically align instructions to reduce branch penalties at the
11825 expense of some code density. The assembler attempts to widen density
11826 instructions to align branch targets and the instructions following call
11827 instructions. If there are not enough preceding safe density
11828 instructions to align a target, no widening will be performed. The
11829 default is @option{-mtarget-align}. These options do not affect the
11830 treatment of auto-aligned instructions like @code{LOOP}, which the
11831 assembler will always align, either by widening density instructions or
11832 by inserting no-op instructions.
11835 @itemx -mno-longcalls
11836 @opindex mlongcalls
11837 @opindex mno-longcalls
11838 When this option is enabled, GCC instructs the assembler to translate
11839 direct calls to indirect calls unless it can determine that the target
11840 of a direct call is in the range allowed by the call instruction. This
11841 translation typically occurs for calls to functions in other source
11842 files. Specifically, the assembler translates a direct @code{CALL}
11843 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
11844 The default is @option{-mno-longcalls}. This option should be used in
11845 programs where the call target can potentially be out of range. This
11846 option is implemented in the assembler, not the compiler, so the
11847 assembly code generated by GCC will still show direct call
11848 instructions---look at the disassembled object code to see the actual
11849 instructions. Note that the assembler will use an indirect call for
11850 every cross-file call, not just those that really will be out of range.
11853 @node zSeries Options
11854 @subsection zSeries Options
11855 @cindex zSeries options
11857 These are listed under @xref{S/390 and zSeries Options}.
11859 @node Code Gen Options
11860 @section Options for Code Generation Conventions
11861 @cindex code generation conventions
11862 @cindex options, code generation
11863 @cindex run-time options
11865 These machine-independent options control the interface conventions
11866 used in code generation.
11868 Most of them have both positive and negative forms; the negative form
11869 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
11870 one of the forms is listed---the one which is not the default. You
11871 can figure out the other form by either removing @samp{no-} or adding
11875 @item -fbounds-check
11876 @opindex fbounds-check
11877 For front-ends that support it, generate additional code to check that
11878 indices used to access arrays are within the declared range. This is
11879 currently only supported by the Java and Fortran 77 front-ends, where
11880 this option defaults to true and false respectively.
11884 This option generates traps for signed overflow on addition, subtraction,
11885 multiplication operations.
11889 This option instructs the compiler to assume that signed arithmetic
11890 overflow of addition, subtraction and multiplication wraps around
11891 using twos-complement representation. This flag enables some optimizations
11892 and disables other. This option is enabled by default for the Java
11893 front-end, as required by the Java language specification.
11896 @opindex fexceptions
11897 Enable exception handling. Generates extra code needed to propagate
11898 exceptions. For some targets, this implies GCC will generate frame
11899 unwind information for all functions, which can produce significant data
11900 size overhead, although it does not affect execution. If you do not
11901 specify this option, GCC will enable it by default for languages like
11902 C++ which normally require exception handling, and disable it for
11903 languages like C that do not normally require it. However, you may need
11904 to enable this option when compiling C code that needs to interoperate
11905 properly with exception handlers written in C++. You may also wish to
11906 disable this option if you are compiling older C++ programs that don't
11907 use exception handling.
11909 @item -fnon-call-exceptions
11910 @opindex fnon-call-exceptions
11911 Generate code that allows trapping instructions to throw exceptions.
11912 Note that this requires platform-specific runtime support that does
11913 not exist everywhere. Moreover, it only allows @emph{trapping}
11914 instructions to throw exceptions, i.e.@: memory references or floating
11915 point instructions. It does not allow exceptions to be thrown from
11916 arbitrary signal handlers such as @code{SIGALRM}.
11918 @item -funwind-tables
11919 @opindex funwind-tables
11920 Similar to @option{-fexceptions}, except that it will just generate any needed
11921 static data, but will not affect the generated code in any other way.
11922 You will normally not enable this option; instead, a language processor
11923 that needs this handling would enable it on your behalf.
11925 @item -fasynchronous-unwind-tables
11926 @opindex fasynchronous-unwind-tables
11927 Generate unwind table in dwarf2 format, if supported by target machine. The
11928 table is exact at each instruction boundary, so it can be used for stack
11929 unwinding from asynchronous events (such as debugger or garbage collector).
11931 @item -fpcc-struct-return
11932 @opindex fpcc-struct-return
11933 Return ``short'' @code{struct} and @code{union} values in memory like
11934 longer ones, rather than in registers. This convention is less
11935 efficient, but it has the advantage of allowing intercallability between
11936 GCC-compiled files and files compiled with other compilers, particularly
11937 the Portable C Compiler (pcc).
11939 The precise convention for returning structures in memory depends
11940 on the target configuration macros.
11942 Short structures and unions are those whose size and alignment match
11943 that of some integer type.
11945 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
11946 switch is not binary compatible with code compiled with the
11947 @option{-freg-struct-return} switch.
11948 Use it to conform to a non-default application binary interface.
11950 @item -freg-struct-return
11951 @opindex freg-struct-return
11952 Return @code{struct} and @code{union} values in registers when possible.
11953 This is more efficient for small structures than
11954 @option{-fpcc-struct-return}.
11956 If you specify neither @option{-fpcc-struct-return} nor
11957 @option{-freg-struct-return}, GCC defaults to whichever convention is
11958 standard for the target. If there is no standard convention, GCC
11959 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
11960 the principal compiler. In those cases, we can choose the standard, and
11961 we chose the more efficient register return alternative.
11963 @strong{Warning:} code compiled with the @option{-freg-struct-return}
11964 switch is not binary compatible with code compiled with the
11965 @option{-fpcc-struct-return} switch.
11966 Use it to conform to a non-default application binary interface.
11968 @item -fshort-enums
11969 @opindex fshort-enums
11970 Allocate to an @code{enum} type only as many bytes as it needs for the
11971 declared range of possible values. Specifically, the @code{enum} type
11972 will be equivalent to the smallest integer type which has enough room.
11974 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
11975 code that is not binary compatible with code generated without that switch.
11976 Use it to conform to a non-default application binary interface.
11978 @item -fshort-double
11979 @opindex fshort-double
11980 Use the same size for @code{double} as for @code{float}.
11982 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
11983 code that is not binary compatible with code generated without that switch.
11984 Use it to conform to a non-default application binary interface.
11986 @item -fshort-wchar
11987 @opindex fshort-wchar
11988 Override the underlying type for @samp{wchar_t} to be @samp{short
11989 unsigned int} instead of the default for the target. This option is
11990 useful for building programs to run under WINE@.
11992 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
11993 code that is not binary compatible with code generated without that switch.
11994 Use it to conform to a non-default application binary interface.
11996 @item -fshared-data
11997 @opindex fshared-data
11998 Requests that the data and non-@code{const} variables of this
11999 compilation be shared data rather than private data. The distinction
12000 makes sense only on certain operating systems, where shared data is
12001 shared between processes running the same program, while private data
12002 exists in one copy per process.
12005 @opindex fno-common
12006 In C, allocate even uninitialized global variables in the data section of the
12007 object file, rather than generating them as common blocks. This has the
12008 effect that if the same variable is declared (without @code{extern}) in
12009 two different compilations, you will get an error when you link them.
12010 The only reason this might be useful is if you wish to verify that the
12011 program will work on other systems which always work this way.
12015 Ignore the @samp{#ident} directive.
12017 @item -finhibit-size-directive
12018 @opindex finhibit-size-directive
12019 Don't output a @code{.size} assembler directive, or anything else that
12020 would cause trouble if the function is split in the middle, and the
12021 two halves are placed at locations far apart in memory. This option is
12022 used when compiling @file{crtstuff.c}; you should not need to use it
12025 @item -fverbose-asm
12026 @opindex fverbose-asm
12027 Put extra commentary information in the generated assembly code to
12028 make it more readable. This option is generally only of use to those
12029 who actually need to read the generated assembly code (perhaps while
12030 debugging the compiler itself).
12032 @option{-fno-verbose-asm}, the default, causes the
12033 extra information to be omitted and is useful when comparing two assembler
12038 @cindex global offset table
12040 Generate position-independent code (PIC) suitable for use in a shared
12041 library, if supported for the target machine. Such code accesses all
12042 constant addresses through a global offset table (GOT)@. The dynamic
12043 loader resolves the GOT entries when the program starts (the dynamic
12044 loader is not part of GCC; it is part of the operating system). If
12045 the GOT size for the linked executable exceeds a machine-specific
12046 maximum size, you get an error message from the linker indicating that
12047 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
12048 instead. (These maximums are 8k on the SPARC and 32k
12049 on the m68k and RS/6000. The 386 has no such limit.)
12051 Position-independent code requires special support, and therefore works
12052 only on certain machines. For the 386, GCC supports PIC for System V
12053 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
12054 position-independent.
12058 If supported for the target machine, emit position-independent code,
12059 suitable for dynamic linking and avoiding any limit on the size of the
12060 global offset table. This option makes a difference on the m68k
12063 Position-independent code requires special support, and therefore works
12064 only on certain machines.
12070 These options are similar to @option{-fpic} and @option{-fPIC}, but
12071 generated position independent code can be only linked into executables.
12072 Usually these options are used when @option{-pie} GCC option will be
12073 used during linking.
12075 @item -ffixed-@var{reg}
12077 Treat the register named @var{reg} as a fixed register; generated code
12078 should never refer to it (except perhaps as a stack pointer, frame
12079 pointer or in some other fixed role).
12081 @var{reg} must be the name of a register. The register names accepted
12082 are machine-specific and are defined in the @code{REGISTER_NAMES}
12083 macro in the machine description macro file.
12085 This flag does not have a negative form, because it specifies a
12088 @item -fcall-used-@var{reg}
12089 @opindex fcall-used
12090 Treat the register named @var{reg} as an allocable register that is
12091 clobbered by function calls. It may be allocated for temporaries or
12092 variables that do not live across a call. Functions compiled this way
12093 will not save and restore the register @var{reg}.
12095 It is an error to used this flag with the frame pointer or stack pointer.
12096 Use of this flag for other registers that have fixed pervasive roles in
12097 the machine's execution model will produce disastrous results.
12099 This flag does not have a negative form, because it specifies a
12102 @item -fcall-saved-@var{reg}
12103 @opindex fcall-saved
12104 Treat the register named @var{reg} as an allocable register saved by
12105 functions. It may be allocated even for temporaries or variables that
12106 live across a call. Functions compiled this way will save and restore
12107 the register @var{reg} if they use it.
12109 It is an error to used this flag with the frame pointer or stack pointer.
12110 Use of this flag for other registers that have fixed pervasive roles in
12111 the machine's execution model will produce disastrous results.
12113 A different sort of disaster will result from the use of this flag for
12114 a register in which function values may be returned.
12116 This flag does not have a negative form, because it specifies a
12119 @item -fpack-struct[=@var{n}]
12120 @opindex fpack-struct
12121 Without a value specified, pack all structure members together without
12122 holes. When a value is specified (which must be a small power of two), pack
12123 structure members according to this value, representing the maximum
12124 alignment (that is, objects with default alignment requirements larger than
12125 this will be output potentially unaligned at the next fitting location.
12127 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
12128 code that is not binary compatible with code generated without that switch.
12129 Additionally, it makes the code suboptimal.
12130 Use it to conform to a non-default application binary interface.
12132 @item -finstrument-functions
12133 @opindex finstrument-functions
12134 Generate instrumentation calls for entry and exit to functions. Just
12135 after function entry and just before function exit, the following
12136 profiling functions will be called with the address of the current
12137 function and its call site. (On some platforms,
12138 @code{__builtin_return_address} does not work beyond the current
12139 function, so the call site information may not be available to the
12140 profiling functions otherwise.)
12143 void __cyg_profile_func_enter (void *this_fn,
12145 void __cyg_profile_func_exit (void *this_fn,
12149 The first argument is the address of the start of the current function,
12150 which may be looked up exactly in the symbol table.
12152 This instrumentation is also done for functions expanded inline in other
12153 functions. The profiling calls will indicate where, conceptually, the
12154 inline function is entered and exited. This means that addressable
12155 versions of such functions must be available. If all your uses of a
12156 function are expanded inline, this may mean an additional expansion of
12157 code size. If you use @samp{extern inline} in your C code, an
12158 addressable version of such functions must be provided. (This is
12159 normally the case anyways, but if you get lucky and the optimizer always
12160 expands the functions inline, you might have gotten away without
12161 providing static copies.)
12163 A function may be given the attribute @code{no_instrument_function}, in
12164 which case this instrumentation will not be done. This can be used, for
12165 example, for the profiling functions listed above, high-priority
12166 interrupt routines, and any functions from which the profiling functions
12167 cannot safely be called (perhaps signal handlers, if the profiling
12168 routines generate output or allocate memory).
12170 @item -fstack-check
12171 @opindex fstack-check
12172 Generate code to verify that you do not go beyond the boundary of the
12173 stack. You should specify this flag if you are running in an
12174 environment with multiple threads, but only rarely need to specify it in
12175 a single-threaded environment since stack overflow is automatically
12176 detected on nearly all systems if there is only one stack.
12178 Note that this switch does not actually cause checking to be done; the
12179 operating system must do that. The switch causes generation of code
12180 to ensure that the operating system sees the stack being extended.
12182 @item -fstack-limit-register=@var{reg}
12183 @itemx -fstack-limit-symbol=@var{sym}
12184 @itemx -fno-stack-limit
12185 @opindex fstack-limit-register
12186 @opindex fstack-limit-symbol
12187 @opindex fno-stack-limit
12188 Generate code to ensure that the stack does not grow beyond a certain value,
12189 either the value of a register or the address of a symbol. If the stack
12190 would grow beyond the value, a signal is raised. For most targets,
12191 the signal is raised before the stack overruns the boundary, so
12192 it is possible to catch the signal without taking special precautions.
12194 For instance, if the stack starts at absolute address @samp{0x80000000}
12195 and grows downwards, you can use the flags
12196 @option{-fstack-limit-symbol=__stack_limit} and
12197 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
12198 of 128KB@. Note that this may only work with the GNU linker.
12200 @cindex aliasing of parameters
12201 @cindex parameters, aliased
12202 @item -fargument-alias
12203 @itemx -fargument-noalias
12204 @itemx -fargument-noalias-global
12205 @opindex fargument-alias
12206 @opindex fargument-noalias
12207 @opindex fargument-noalias-global
12208 Specify the possible relationships among parameters and between
12209 parameters and global data.
12211 @option{-fargument-alias} specifies that arguments (parameters) may
12212 alias each other and may alias global storage.@*
12213 @option{-fargument-noalias} specifies that arguments do not alias
12214 each other, but may alias global storage.@*
12215 @option{-fargument-noalias-global} specifies that arguments do not
12216 alias each other and do not alias global storage.
12218 Each language will automatically use whatever option is required by
12219 the language standard. You should not need to use these options yourself.
12221 @item -fleading-underscore
12222 @opindex fleading-underscore
12223 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
12224 change the way C symbols are represented in the object file. One use
12225 is to help link with legacy assembly code.
12227 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
12228 generate code that is not binary compatible with code generated without that
12229 switch. Use it to conform to a non-default application binary interface.
12230 Not all targets provide complete support for this switch.
12232 @item -ftls-model=@var{model}
12233 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
12234 The @var{model} argument should be one of @code{global-dynamic},
12235 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
12237 The default without @option{-fpic} is @code{initial-exec}; with
12238 @option{-fpic} the default is @code{global-dynamic}.
12240 @item -fvisibility=@var{default|internal|hidden|protected}
12241 @opindex fvisibility
12242 Set the default ELF image symbol visibility to the specified option---all
12243 symbols will be marked with this unless overridden within the code.
12244 Using this feature can very substantially improve linking and
12245 load times of shared object libraries, produce more optimized
12246 code, provide near-perfect API export and prevent symbol clashes.
12247 It is @strong{strongly} recommended that you use this in any shared objects
12250 Despite the nomenclature, @code{default} always means public ie;
12251 available to be linked against from outside the shared object.
12252 @code{protected} and @code{internal} are pretty useless in real-world
12253 usage so the only other commonly used option will be @code{hidden}.
12254 The default if @option{-fvisibility} isn't specified is
12255 @code{default}, i.e., make every
12256 symbol public---this causes the same behavior as previous versions of
12259 A good explanation of the benefits offered by ensuring ELF
12260 symbols have the correct visibility is given by ``How To Write
12261 Shared Libraries'' by Ulrich Drepper (which can be found at
12262 @w{@uref{http://people.redhat.com/~drepper/}})---however a superior
12263 solution made possible by this option to marking things hidden when
12264 the default is public is to make the default hidden and mark things
12265 public. This is the norm with DLL's on Windows and with @option{-fvisibility=hidden}
12266 and @code{__attribute__ ((visibility("default")))} instead of
12267 @code{__declspec(dllexport)} you get almost identical semantics with
12268 identical syntax. This is a great boon to those working with
12269 cross-platform projects.
12271 For those adding visibility support to existing code, you may find
12272 @samp{#pragma GCC visibility} of use. This works by you enclosing
12273 the declarations you wish to set visibility for with (for example)
12274 @samp{#pragma GCC visibility push(hidden)} and
12275 @samp{#pragma GCC visibility pop}. These can be nested up to sixteen
12276 times. Bear in mind that symbol visibility should be viewed @strong{as
12277 part of the API interface contract} and thus all new code should
12278 always specify visibility when it is not the default ie; declarations
12279 only for use within the local DSO should @strong{always} be marked explicitly
12280 as hidden as so to avoid PLT indirection overheads---making this
12281 abundantly clear also aids readability and self-documentation of the code.
12282 Note that due to ISO C++ specification requirements, operator new and
12283 operator delete must always be of default visibility.
12285 An overview of these techniques, their benefits and how to use them
12286 is at @w{@uref{http://www.nedprod.com/programs/gccvisibility.html}}.
12292 @node Environment Variables
12293 @section Environment Variables Affecting GCC
12294 @cindex environment variables
12296 @c man begin ENVIRONMENT
12297 This section describes several environment variables that affect how GCC
12298 operates. Some of them work by specifying directories or prefixes to use
12299 when searching for various kinds of files. Some are used to specify other
12300 aspects of the compilation environment.
12302 Note that you can also specify places to search using options such as
12303 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
12304 take precedence over places specified using environment variables, which
12305 in turn take precedence over those specified by the configuration of GCC@.
12306 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
12307 GNU Compiler Collection (GCC) Internals}.
12312 @c @itemx LC_COLLATE
12314 @c @itemx LC_MONETARY
12315 @c @itemx LC_NUMERIC
12320 @c @findex LC_COLLATE
12321 @findex LC_MESSAGES
12322 @c @findex LC_MONETARY
12323 @c @findex LC_NUMERIC
12327 These environment variables control the way that GCC uses
12328 localization information that allow GCC to work with different
12329 national conventions. GCC inspects the locale categories
12330 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
12331 so. These locale categories can be set to any value supported by your
12332 installation. A typical value is @samp{en_GB.UTF-8} for English in the United
12333 Kingdom encoded in UTF-8.
12335 The @env{LC_CTYPE} environment variable specifies character
12336 classification. GCC uses it to determine the character boundaries in
12337 a string; this is needed for some multibyte encodings that contain quote
12338 and escape characters that would otherwise be interpreted as a string
12341 The @env{LC_MESSAGES} environment variable specifies the language to
12342 use in diagnostic messages.
12344 If the @env{LC_ALL} environment variable is set, it overrides the value
12345 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
12346 and @env{LC_MESSAGES} default to the value of the @env{LANG}
12347 environment variable. If none of these variables are set, GCC
12348 defaults to traditional C English behavior.
12352 If @env{TMPDIR} is set, it specifies the directory to use for temporary
12353 files. GCC uses temporary files to hold the output of one stage of
12354 compilation which is to be used as input to the next stage: for example,
12355 the output of the preprocessor, which is the input to the compiler
12358 @item GCC_EXEC_PREFIX
12359 @findex GCC_EXEC_PREFIX
12360 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
12361 names of the subprograms executed by the compiler. No slash is added
12362 when this prefix is combined with the name of a subprogram, but you can
12363 specify a prefix that ends with a slash if you wish.
12365 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
12366 an appropriate prefix to use based on the pathname it was invoked with.
12368 If GCC cannot find the subprogram using the specified prefix, it
12369 tries looking in the usual places for the subprogram.
12371 The default value of @env{GCC_EXEC_PREFIX} is
12372 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the value
12373 of @code{prefix} when you ran the @file{configure} script.
12375 Other prefixes specified with @option{-B} take precedence over this prefix.
12377 This prefix is also used for finding files such as @file{crt0.o} that are
12380 In addition, the prefix is used in an unusual way in finding the
12381 directories to search for header files. For each of the standard
12382 directories whose name normally begins with @samp{/usr/local/lib/gcc}
12383 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
12384 replacing that beginning with the specified prefix to produce an
12385 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
12386 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
12387 These alternate directories are searched first; the standard directories
12390 @item COMPILER_PATH
12391 @findex COMPILER_PATH
12392 The value of @env{COMPILER_PATH} is a colon-separated list of
12393 directories, much like @env{PATH}. GCC tries the directories thus
12394 specified when searching for subprograms, if it can't find the
12395 subprograms using @env{GCC_EXEC_PREFIX}.
12398 @findex LIBRARY_PATH
12399 The value of @env{LIBRARY_PATH} is a colon-separated list of
12400 directories, much like @env{PATH}. When configured as a native compiler,
12401 GCC tries the directories thus specified when searching for special
12402 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
12403 using GCC also uses these directories when searching for ordinary
12404 libraries for the @option{-l} option (but directories specified with
12405 @option{-L} come first).
12409 @cindex locale definition
12410 This variable is used to pass locale information to the compiler. One way in
12411 which this information is used is to determine the character set to be used
12412 when character literals, string literals and comments are parsed in C and C++.
12413 When the compiler is configured to allow multibyte characters,
12414 the following values for @env{LANG} are recognized:
12418 Recognize JIS characters.
12420 Recognize SJIS characters.
12422 Recognize EUCJP characters.
12425 If @env{LANG} is not defined, or if it has some other value, then the
12426 compiler will use mblen and mbtowc as defined by the default locale to
12427 recognize and translate multibyte characters.
12431 Some additional environments variables affect the behavior of the
12434 @include cppenv.texi
12438 @node Precompiled Headers
12439 @section Using Precompiled Headers
12440 @cindex precompiled headers
12441 @cindex speed of compilation
12443 Often large projects have many header files that are included in every
12444 source file. The time the compiler takes to process these header files
12445 over and over again can account for nearly all of the time required to
12446 build the project. To make builds faster, GCC allows users to
12447 `precompile' a header file; then, if builds can use the precompiled
12448 header file they will be much faster.
12450 @strong{Caution:} There are a few known situations where GCC will
12451 crash when trying to use a precompiled header. If you have trouble
12452 with a precompiled header, you should remove the precompiled header
12453 and compile without it. In addition, please use GCC's on-line
12454 defect-tracking system to report any problems you encounter with
12455 precompiled headers. @xref{Bugs}.
12457 To create a precompiled header file, simply compile it as you would any
12458 other file, if necessary using the @option{-x} option to make the driver
12459 treat it as a C or C++ header file. You will probably want to use a
12460 tool like @command{make} to keep the precompiled header up-to-date when
12461 the headers it contains change.
12463 A precompiled header file will be searched for when @code{#include} is
12464 seen in the compilation. As it searches for the included file
12465 (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
12466 compiler looks for a precompiled header in each directory just before it
12467 looks for the include file in that directory. The name searched for is
12468 the name specified in the @code{#include} with @samp{.gch} appended. If
12469 the precompiled header file can't be used, it is ignored.
12471 For instance, if you have @code{#include "all.h"}, and you have
12472 @file{all.h.gch} in the same directory as @file{all.h}, then the
12473 precompiled header file will be used if possible, and the original
12474 header will be used otherwise.
12476 Alternatively, you might decide to put the precompiled header file in a
12477 directory and use @option{-I} to ensure that directory is searched
12478 before (or instead of) the directory containing the original header.
12479 Then, if you want to check that the precompiled header file is always
12480 used, you can put a file of the same name as the original header in this
12481 directory containing an @code{#error} command.
12483 This also works with @option{-include}. So yet another way to use
12484 precompiled headers, good for projects not designed with precompiled
12485 header files in mind, is to simply take most of the header files used by
12486 a project, include them from another header file, precompile that header
12487 file, and @option{-include} the precompiled header. If the header files
12488 have guards against multiple inclusion, they will be skipped because
12489 they've already been included (in the precompiled header).
12491 If you need to precompile the same header file for different
12492 languages, targets, or compiler options, you can instead make a
12493 @emph{directory} named like @file{all.h.gch}, and put each precompiled
12494 header in the directory, perhaps using @option{-o}. It doesn't matter
12495 what you call the files in the directory, every precompiled header in
12496 the directory will be considered. The first precompiled header
12497 encountered in the directory that is valid for this compilation will
12498 be used; they're searched in no particular order.
12500 There are many other possibilities, limited only by your imagination,
12501 good sense, and the constraints of your build system.
12503 A precompiled header file can be used only when these conditions apply:
12507 Only one precompiled header can be used in a particular compilation.
12510 A precompiled header can't be used once the first C token is seen. You
12511 can have preprocessor directives before a precompiled header; you can
12512 even include a precompiled header from inside another header, so long as
12513 there are no C tokens before the @code{#include}.
12516 The precompiled header file must be produced for the same language as
12517 the current compilation. You can't use a C precompiled header for a C++
12521 The precompiled header file must be produced by the same compiler
12522 version and configuration as the current compilation is using.
12523 The easiest way to guarantee this is to use the same compiler binary
12524 for creating and using precompiled headers.
12527 Any macros defined before the precompiled header is included must
12528 either be defined in the same way as when the precompiled header was
12529 generated, or must not affect the precompiled header, which usually
12530 means that the they don't appear in the precompiled header at all.
12532 The @option{-D} option is one way to define a macro before a
12533 precompiled header is included; using a @code{#define} can also do it.
12534 There are also some options that define macros implicitly, like
12535 @option{-O} and @option{-Wdeprecated}; the same rule applies to macros
12538 @item If debugging information is output when using the precompiled
12539 header, using @option{-g} or similar, the same kind of debugging information
12540 must have been output when building the precompiled header. However,
12541 a precompiled header built using @option{-g} can be used in a compilation
12542 when no debugging information is being output.
12544 @item The same @option{-m} options must generally be used when building
12545 and using the precompiled header. @xref{Submodel Options},
12546 for any cases where this rule is relaxed.
12548 @item Each of the following options must be the same when building and using
12549 the precompiled header:
12551 @gccoptlist{-fexceptions -funit-at-a-time}
12554 Some other command-line options starting with @option{-f},
12555 @option{-p}, or @option{-O} must be defined in the same way as when
12556 the precompiled header was generated. At present, it's not clear
12557 which options are safe to change and which are not; the safest choice
12558 is to use exactly the same options when generating and using the
12559 precompiled header. The following are known to be safe:
12561 @gccoptlist{-fpreprocessed -pedantic-errors}
12565 For all of these except the last, the compiler will automatically
12566 ignore the precompiled header if the conditions aren't met. If you
12567 find an option combination that doesn't work and doesn't cause the
12568 precompiled header to be ignored, please consider filing a bug report,
12571 If you do use differing options when generating and using the
12572 precompiled header, the actual behavior will be a mixture of the
12573 behavior for the options. For instance, if you use @option{-g} to
12574 generate the precompiled header but not when using it, you may or may
12575 not get debugging information for routines in the precompiled header.
12577 @node Running Protoize
12578 @section Running Protoize
12580 The program @code{protoize} is an optional part of GCC@. You can use
12581 it to add prototypes to a program, thus converting the program to ISO
12582 C in one respect. The companion program @code{unprotoize} does the
12583 reverse: it removes argument types from any prototypes that are found.
12585 When you run these programs, you must specify a set of source files as
12586 command line arguments. The conversion programs start out by compiling
12587 these files to see what functions they define. The information gathered
12588 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
12590 After scanning comes actual conversion. The specified files are all
12591 eligible to be converted; any files they include (whether sources or
12592 just headers) are eligible as well.
12594 But not all the eligible files are converted. By default,
12595 @code{protoize} and @code{unprotoize} convert only source and header
12596 files in the current directory. You can specify additional directories
12597 whose files should be converted with the @option{-d @var{directory}}
12598 option. You can also specify particular files to exclude with the
12599 @option{-x @var{file}} option. A file is converted if it is eligible, its
12600 directory name matches one of the specified directory names, and its
12601 name within the directory has not been excluded.
12603 Basic conversion with @code{protoize} consists of rewriting most
12604 function definitions and function declarations to specify the types of
12605 the arguments. The only ones not rewritten are those for varargs
12608 @code{protoize} optionally inserts prototype declarations at the
12609 beginning of the source file, to make them available for any calls that
12610 precede the function's definition. Or it can insert prototype
12611 declarations with block scope in the blocks where undeclared functions
12614 Basic conversion with @code{unprotoize} consists of rewriting most
12615 function declarations to remove any argument types, and rewriting
12616 function definitions to the old-style pre-ISO form.
12618 Both conversion programs print a warning for any function declaration or
12619 definition that they can't convert. You can suppress these warnings
12622 The output from @code{protoize} or @code{unprotoize} replaces the
12623 original source file. The original file is renamed to a name ending
12624 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
12625 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
12626 for DOS) file already exists, then the source file is simply discarded.
12628 @code{protoize} and @code{unprotoize} both depend on GCC itself to
12629 scan the program and collect information about the functions it uses.
12630 So neither of these programs will work until GCC is installed.
12632 Here is a table of the options you can use with @code{protoize} and
12633 @code{unprotoize}. Each option works with both programs unless
12637 @item -B @var{directory}
12638 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
12639 usual directory (normally @file{/usr/local/lib}). This file contains
12640 prototype information about standard system functions. This option
12641 applies only to @code{protoize}.
12643 @item -c @var{compilation-options}
12644 Use @var{compilation-options} as the options when running @command{gcc} to
12645 produce the @samp{.X} files. The special option @option{-aux-info} is
12646 always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
12648 Note that the compilation options must be given as a single argument to
12649 @code{protoize} or @code{unprotoize}. If you want to specify several
12650 @command{gcc} options, you must quote the entire set of compilation options
12651 to make them a single word in the shell.
12653 There are certain @command{gcc} arguments that you cannot use, because they
12654 would produce the wrong kind of output. These include @option{-g},
12655 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
12656 the @var{compilation-options}, they are ignored.
12659 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
12660 systems) instead of @samp{.c}. This is convenient if you are converting
12661 a C program to C++. This option applies only to @code{protoize}.
12664 Add explicit global declarations. This means inserting explicit
12665 declarations at the beginning of each source file for each function
12666 that is called in the file and was not declared. These declarations
12667 precede the first function definition that contains a call to an
12668 undeclared function. This option applies only to @code{protoize}.
12670 @item -i @var{string}
12671 Indent old-style parameter declarations with the string @var{string}.
12672 This option applies only to @code{protoize}.
12674 @code{unprotoize} converts prototyped function definitions to old-style
12675 function definitions, where the arguments are declared between the
12676 argument list and the initial @samp{@{}. By default, @code{unprotoize}
12677 uses five spaces as the indentation. If you want to indent with just
12678 one space instead, use @option{-i " "}.
12681 Keep the @samp{.X} files. Normally, they are deleted after conversion
12685 Add explicit local declarations. @code{protoize} with @option{-l} inserts
12686 a prototype declaration for each function in each block which calls the
12687 function without any declaration. This option applies only to
12691 Make no real changes. This mode just prints information about the conversions
12692 that would have been done without @option{-n}.
12695 Make no @samp{.save} files. The original files are simply deleted.
12696 Use this option with caution.
12698 @item -p @var{program}
12699 Use the program @var{program} as the compiler. Normally, the name
12700 @file{gcc} is used.
12703 Work quietly. Most warnings are suppressed.
12706 Print the version number, just like @option{-v} for @command{gcc}.
12709 If you need special compiler options to compile one of your program's
12710 source files, then you should generate that file's @samp{.X} file
12711 specially, by running @command{gcc} on that source file with the
12712 appropriate options and the option @option{-aux-info}. Then run
12713 @code{protoize} on the entire set of files. @code{protoize} will use
12714 the existing @samp{.X} file because it is newer than the source file.
12718 gcc -Dfoo=bar file1.c -aux-info file1.X
12723 You need to include the special files along with the rest in the
12724 @code{protoize} command, even though their @samp{.X} files already
12725 exist, because otherwise they won't get converted.
12727 @xref{Protoize Caveats}, for more information on how to use
12728 @code{protoize} successfully.