1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2 @c 2000, 2001, 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
3 @c This is part of the GCC manual.
4 @c For copying conditions, see the file gcc.texi.
11 @c man begin COPYRIGHT
12 Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997,
13 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
15 Permission is granted to copy, distribute and/or modify this document
16 under the terms of the GNU Free Documentation License, Version 1.2 or
17 any later version published by the Free Software Foundation; with the
18 Invariant Sections being ``GNU General Public License'' and ``Funding
19 Free Software'', the Front-Cover texts being (a) (see below), and with
20 the Back-Cover Texts being (b) (see below). A copy of the license is
21 included in the gfdl(7) man page.
23 (a) The FSF's Front-Cover Text is:
27 (b) The FSF's Back-Cover Text is:
29 You have freedom to copy and modify this GNU Manual, like GNU
30 software. Copies published by the Free Software Foundation raise
31 funds for GNU development.
33 @c Set file name and title for the man page.
35 @settitle GNU project C and C++ compiler
37 gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
38 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
39 [@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
40 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
41 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
42 [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
43 [@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{}
45 Only the most useful options are listed here; see below for the
46 remainder. @samp{g++} accepts mostly the same options as @samp{gcc}.
49 gpl(7), gfdl(7), fsf-funding(7),
50 cpp(1), gcov(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
51 and the Info entries for @file{gcc}, @file{cpp}, @file{as},
52 @file{ld}, @file{binutils} and @file{gdb}.
55 For instructions on reporting bugs, see
56 @w{@uref{http://gcc.gnu.org/bugs.html}}.
59 See the Info entry for @command{gcc}, or
60 @w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}},
61 for contributors to GCC@.
66 @chapter GCC Command Options
67 @cindex GCC command options
68 @cindex command options
69 @cindex options, GCC command
71 @c man begin DESCRIPTION
72 When you invoke GCC, it normally does preprocessing, compilation,
73 assembly and linking. The ``overall options'' allow you to stop this
74 process at an intermediate stage. For example, the @option{-c} option
75 says not to run the linker. Then the output consists of object files
76 output by the assembler.
78 Other options are passed on to one stage of processing. Some options
79 control the preprocessor and others the compiler itself. Yet other
80 options control the assembler and linker; most of these are not
81 documented here, since you rarely need to use any of them.
83 @cindex C compilation options
84 Most of the command line options that you can use with GCC are useful
85 for C programs; when an option is only useful with another language
86 (usually C++), the explanation says so explicitly. If the description
87 for a particular option does not mention a source language, you can use
88 that option with all supported languages.
90 @cindex C++ compilation options
91 @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
92 options for compiling C++ programs.
94 @cindex grouping options
95 @cindex options, grouping
96 The @command{gcc} program accepts options and file names as operands. Many
97 options have multi-letter names; therefore multiple single-letter options
98 may @emph{not} be grouped: @option{-dr} is very different from @w{@samp{-d
101 @cindex order of options
102 @cindex options, order
103 You can mix options and other arguments. For the most part, the order
104 you use doesn't matter. Order does matter when you use several options
105 of the same kind; for example, if you specify @option{-L} more than once,
106 the directories are searched in the order specified.
108 Many options have long names starting with @samp{-f} or with
109 @samp{-W}---for example,
110 @option{-fstrength-reduce}, @option{-Wformat} and so on. Most of
111 these have both positive and negative forms; the negative form of
112 @option{-ffoo} would be @option{-fno-foo}. This manual documents
113 only one of these two forms, whichever one is not the default.
117 @xref{Option Index}, for an index to GCC's options.
120 * Option Summary:: Brief list of all options, without explanations.
121 * Overall Options:: Controlling the kind of output:
122 an executable, object files, assembler files,
123 or preprocessed source.
124 * Invoking G++:: Compiling C++ programs.
125 * C Dialect Options:: Controlling the variant of C language compiled.
126 * C++ Dialect Options:: Variations on C++.
127 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
129 * Language Independent Options:: Controlling how diagnostics should be
131 * Warning Options:: How picky should the compiler be?
132 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
133 * Optimize Options:: How much optimization?
134 * Preprocessor Options:: Controlling header files and macro definitions.
135 Also, getting dependency information for Make.
136 * Assembler Options:: Passing options to the assembler.
137 * Link Options:: Specifying libraries and so on.
138 * Directory Options:: Where to find header files and libraries.
139 Where to find the compiler executable files.
140 * Spec Files:: How to pass switches to sub-processes.
141 * Target Options:: Running a cross-compiler, or an old version of GCC.
142 * Submodel Options:: Specifying minor hardware or convention variations,
143 such as 68010 vs 68020.
144 * Code Gen Options:: Specifying conventions for function calls, data layout
146 * Environment Variables:: Env vars that affect GCC.
147 * Precompiled Headers:: Compiling a header once, and using it many times.
148 * Running Protoize:: Automatically adding or removing function prototypes.
154 @section Option Summary
156 Here is a summary of all the options, grouped by type. Explanations are
157 in the following sections.
160 @item Overall Options
161 @xref{Overall Options,,Options Controlling the Kind of Output}.
162 @gccoptlist{-c -S -E -o @var{file} -combine -pipe -pass-exit-codes @gol
163 -x @var{language} -v -### --help --target-help --version @@@var{file}}
165 @item C Language Options
166 @xref{C Dialect Options,,Options Controlling C Dialect}.
167 @gccoptlist{-ansi -std=@var{standard} -aux-info @var{filename} @gol
168 -fno-asm -fno-builtin -fno-builtin-@var{function} @gol
169 -fhosted -ffreestanding -fms-extensions @gol
170 -trigraphs -no-integrated-cpp -traditional -traditional-cpp @gol
171 -fallow-single-precision -fcond-mismatch @gol
172 -fsigned-bitfields -fsigned-char @gol
173 -funsigned-bitfields -funsigned-char}
175 @item C++ Language Options
176 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
177 @gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol
178 -fconserve-space -ffriend-injection -fno-const-strings @gol
179 -fno-elide-constructors @gol
180 -fno-enforce-eh-specs @gol
181 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
182 -fno-implicit-templates @gol
183 -fno-implicit-inline-templates @gol
184 -fno-implement-inlines -fms-extensions @gol
185 -fno-nonansi-builtins -fno-operator-names @gol
186 -fno-optional-diags -fpermissive @gol
187 -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
188 -fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ @gol
189 -fno-default-inline -fvisibility-inlines-hidden @gol
190 -Wabi -Wctor-dtor-privacy @gol
191 -Wnon-virtual-dtor -Wreorder @gol
192 -Weffc++ -Wno-deprecated -Wstrict-null-sentinel @gol
193 -Wno-non-template-friend -Wold-style-cast @gol
194 -Woverloaded-virtual -Wno-pmf-conversions @gol
197 @item Objective-C and Objective-C++ Language Options
198 @xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling
199 Objective-C and Objective-C++ Dialects}.
201 -fconstant-string-class=@var{class-name} @gol
202 -fgnu-runtime -fnext-runtime @gol
203 -fno-nil-receivers @gol
204 -fobjc-call-cxx-cdtors @gol
205 -fobjc-direct-dispatch @gol
206 -fobjc-exceptions @gol
208 -freplace-objc-classes @gol
211 -Wassign-intercept @gol
212 -Wno-protocol -Wselector @gol
213 -Wstrict-selector-match @gol
214 -Wundeclared-selector}
216 @item Language Independent Options
217 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
218 @gccoptlist{-fmessage-length=@var{n} @gol
219 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]}} @gol
220 -fdiagnostics-show-options
222 @item Warning Options
223 @xref{Warning Options,,Options to Request or Suppress Warnings}.
224 @gccoptlist{-fsyntax-only -pedantic -pedantic-errors @gol
225 -w -Wextra -Wall -Waggregate-return -Wno-attributes @gol
226 -Wc++-compat -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment @gol
227 -Wconversion -Wno-deprecated-declarations @gol
228 -Wdisabled-optimization -Wno-div-by-zero -Wno-endif-labels @gol
229 -Werror -Werror-implicit-function-declaration @gol
230 -Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 @gol
231 -Wno-format-extra-args -Wformat-nonliteral @gol
232 -Wformat-security -Wformat-y2k @gol
233 -Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol
234 -Wimport -Wno-import -Winit-self -Winline @gol
235 -Wno-int-to-pointer-cast @gol
236 -Wno-invalid-offsetof -Winvalid-pch @gol
237 -Wlarger-than-@var{len} -Wunsafe-loop-optimizations -Wlong-long @gol
238 -Wmain -Wmissing-braces -Wmissing-field-initializers @gol
239 -Wmissing-format-attribute -Wmissing-include-dirs @gol
240 -Wmissing-noreturn @gol
241 -Wno-multichar -Wnonnull -Wpacked -Wpadded @gol
242 -Wparentheses -Wpointer-arith -Wno-pointer-to-int-cast @gol
243 -Wredundant-decls @gol
244 -Wreturn-type -Wsequence-point -Wshadow @gol
245 -Wsign-compare -Wstack-protector @gol
246 -Wstrict-aliasing -Wstrict-aliasing=2 @gol
247 -Wstring-literal-comparison @gol
248 -Wswitch -Wswitch-default -Wswitch-enum @gol
249 -Wsystem-headers -Wtrigraphs -Wundef -Wuninitialized @gol
250 -Wunknown-pragmas -Wno-pragmas -Wunreachable-code @gol
251 -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
252 -Wunused-value -Wunused-variable -Wvariadic-macros @gol
253 -Wvolatile-register-var -Wwrite-strings}
255 @item C-only Warning Options
256 @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
257 -Wmissing-prototypes -Wnested-externs -Wold-style-definition @gol
258 -Wstrict-prototypes -Wtraditional @gol
259 -Wdeclaration-after-statement -Wno-pointer-sign}
261 @item Debugging Options
262 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
263 @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
264 -fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
265 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
266 -fdump-ipa-all -fdump-ipa-cgraph @gol
268 -fdump-tree-original@r{[}-@var{n}@r{]} @gol
269 -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
270 -fdump-tree-inlined@r{[}-@var{n}@r{]} @gol
271 -fdump-tree-cfg -fdump-tree-vcg -fdump-tree-alias @gol
273 -fdump-tree-ssa@r{[}-@var{n}@r{]} -fdump-tree-pre@r{[}-@var{n}@r{]} @gol
274 -fdump-tree-ccp@r{[}-@var{n}@r{]} -fdump-tree-dce@r{[}-@var{n}@r{]} @gol
275 -fdump-tree-gimple@r{[}-raw@r{]} -fdump-tree-mudflap@r{[}-@var{n}@r{]} @gol
276 -fdump-tree-dom@r{[}-@var{n}@r{]} @gol
277 -fdump-tree-dse@r{[}-@var{n}@r{]} @gol
278 -fdump-tree-phiopt@r{[}-@var{n}@r{]} @gol
279 -fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
280 -fdump-tree-copyrename@r{[}-@var{n}@r{]} @gol
281 -fdump-tree-nrv -fdump-tree-vect @gol
282 -fdump-tree-sink @gol
283 -fdump-tree-sra@r{[}-@var{n}@r{]} @gol
284 -fdump-tree-salias @gol
285 -fdump-tree-fre@r{[}-@var{n}@r{]} @gol
286 -fdump-tree-vrp@r{[}-@var{n}@r{]} @gol
287 -ftree-vectorizer-verbose=@var{n} @gol
288 -fdump-tree-storeccp@r{[}-@var{n}@r{]} @gol
289 -feliminate-dwarf2-dups -feliminate-unused-debug-types @gol
290 -feliminate-unused-debug-symbols -fmem-report -fprofile-arcs @gol
291 -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
292 -ftest-coverage -ftime-report -fvar-tracking @gol
293 -g -g@var{level} -gcoff -gdwarf-2 @gol
294 -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
295 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
296 -print-multi-directory -print-multi-lib @gol
297 -print-prog-name=@var{program} -print-search-dirs -Q @gol
300 @item Optimization Options
301 @xref{Optimize Options,,Options that Control Optimization}.
302 @gccoptlist{-falign-functions=@var{n} -falign-jumps=@var{n} @gol
303 -falign-labels=@var{n} -falign-loops=@var{n} @gol
304 -fbounds-check -fmudflap -fmudflapth -fmudflapir @gol
305 -fbranch-probabilities -fprofile-values -fvpt -fbranch-target-load-optimize @gol
306 -fbranch-target-load-optimize2 -fbtr-bb-exclusive @gol
307 -fcaller-saves -fcprop-registers -fcse-follow-jumps @gol
308 -fcse-skip-blocks -fcx-limited-range -fdata-sections @gol
309 -fdelayed-branch -fdelete-null-pointer-checks -fearly-inlining @gol
310 -fexpensive-optimizations -ffast-math -ffloat-store @gol
311 -fforce-addr -ffunction-sections @gol
312 -fgcse -fgcse-lm -fgcse-sm -fgcse-las -fgcse-after-reload @gol
313 -floop-optimize -fcrossjumping -fif-conversion -fif-conversion2 @gol
314 -finline-functions -finline-functions-called-once @gol
315 -finline-limit=@var{n} -fkeep-inline-functions @gol
316 -fkeep-static-consts -fmerge-constants -fmerge-all-constants @gol
317 -fmodulo-sched -fno-branch-count-reg @gol
318 -fno-default-inline -fno-defer-pop -floop-optimize2 -fmove-loop-invariants @gol
319 -fno-function-cse -fno-guess-branch-probability @gol
320 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
321 -funsafe-math-optimizations -funsafe-loop-optimizations -ffinite-math-only @gol
322 -fno-trapping-math -fno-zero-initialized-in-bss @gol
323 -fomit-frame-pointer -foptimize-register-move @gol
324 -foptimize-sibling-calls -fprefetch-loop-arrays @gol
325 -fprofile-generate -fprofile-use @gol
326 -fregmove -frename-registers @gol
327 -freorder-blocks -freorder-blocks-and-partition -freorder-functions @gol
328 -frerun-cse-after-loop -frerun-loop-opt @gol
329 -frounding-math -fschedule-insns -fschedule-insns2 @gol
330 -fno-sched-interblock -fno-sched-spec -fsched-spec-load @gol
331 -fsched-spec-load-dangerous @gol
332 -fsched-stalled-insns=@var{n} -fsched-stalled-insns-dep=@var{n} @gol
333 -fsched2-use-superblocks @gol
334 -fsched2-use-traces -freschedule-modulo-scheduled-loops @gol
335 -fsignaling-nans -fsingle-precision-constant @gol
336 -fstack-protector -fstack-protector-all @gol
337 -fstrength-reduce -fstrict-aliasing -ftracer -fthread-jumps @gol
338 -funroll-all-loops -funroll-loops -fpeel-loops @gol
339 -fsplit-ivs-in-unroller -funswitch-loops @gol
340 -fvariable-expansion-in-unroller @gol
341 -ftree-pre -ftree-ccp -ftree-dce -ftree-loop-optimize @gol
342 -ftree-loop-linear -ftree-loop-im -ftree-loop-ivcanon -fivopts @gol
343 -ftree-dominator-opts -ftree-dse -ftree-copyrename -ftree-sink @gol
344 -ftree-ch -ftree-sra -ftree-ter -ftree-lrs -ftree-fre -ftree-vectorize @gol
345 -ftree-vect-loop-version -ftree-salias -fweb @gol
346 -ftree-copy-prop -ftree-store-ccp -ftree-store-copy-prop -fwhole-program @gol
347 --param @var{name}=@var{value}
348 -O -O0 -O1 -O2 -O3 -Os}
350 @item Preprocessor Options
351 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
352 @gccoptlist{-A@var{question}=@var{answer} @gol
353 -A-@var{question}@r{[}=@var{answer}@r{]} @gol
354 -C -dD -dI -dM -dN @gol
355 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
356 -idirafter @var{dir} @gol
357 -include @var{file} -imacros @var{file} @gol
358 -iprefix @var{file} -iwithprefix @var{dir} @gol
359 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
360 -isysroot @var{dir} @gol
361 -M -MM -MF -MG -MP -MQ -MT -nostdinc @gol
362 -P -fworking-directory -remap @gol
363 -trigraphs -undef -U@var{macro} -Wp,@var{option} @gol
364 -Xpreprocessor @var{option}}
366 @item Assembler Option
367 @xref{Assembler Options,,Passing Options to the Assembler}.
368 @gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
371 @xref{Link Options,,Options for Linking}.
372 @gccoptlist{@var{object-file-name} -l@var{library} @gol
373 -nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic @gol
374 -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
375 -Wl,@var{option} -Xlinker @var{option} @gol
378 @item Directory Options
379 @xref{Directory Options,,Options for Directory Search}.
380 @gccoptlist{-B@var{prefix} -I@var{dir} -iquote@var{dir} -L@var{dir}
381 -specs=@var{file} -I- --sysroot=@var{dir}}
384 @c I wrote this xref this way to avoid overfull hbox. -- rms
385 @xref{Target Options}.
386 @gccoptlist{-V @var{version} -b @var{machine}}
388 @item Machine Dependent Options
389 @xref{Submodel Options,,Hardware Models and Configurations}.
390 @c This list is ordered alphanumerically by subsection name.
391 @c Try and put the significant identifier (CPU or system) first,
392 @c so users have a clue at guessing where the ones they want will be.
395 @gccoptlist{-EB -EL @gol
396 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
397 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
400 @gccoptlist{-mapcs-frame -mno-apcs-frame @gol
401 -mabi=@var{name} @gol
402 -mapcs-stack-check -mno-apcs-stack-check @gol
403 -mapcs-float -mno-apcs-float @gol
404 -mapcs-reentrant -mno-apcs-reentrant @gol
405 -msched-prolog -mno-sched-prolog @gol
406 -mlittle-endian -mbig-endian -mwords-little-endian @gol
407 -mfloat-abi=@var{name} -msoft-float -mhard-float -mfpe @gol
408 -mthumb-interwork -mno-thumb-interwork @gol
409 -mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol
410 -mstructure-size-boundary=@var{n} @gol
411 -mabort-on-noreturn @gol
412 -mlong-calls -mno-long-calls @gol
413 -msingle-pic-base -mno-single-pic-base @gol
414 -mpic-register=@var{reg} @gol
415 -mnop-fun-dllimport @gol
416 -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol
417 -mpoke-function-name @gol
419 -mtpcs-frame -mtpcs-leaf-frame @gol
420 -mcaller-super-interworking -mcallee-super-interworking @gol
424 @gccoptlist{-mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
425 -mcall-prologues -mno-tablejump -mtiny-stack -mint8}
427 @emph{Blackfin Options}
428 @gccoptlist{-momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol
429 -mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol
430 -mlow-64k -mno-low64k -mid-shared-library @gol
431 -mno-id-shared-library -mshared-library-id=@var{n} @gol
432 -mlong-calls -mno-long-calls}
435 @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
436 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
437 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
438 -mstack-align -mdata-align -mconst-align @gol
439 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
440 -melf -maout -melinux -mlinux -sim -sim2 @gol
441 -mmul-bug-workaround -mno-mul-bug-workaround}
444 @gccoptlist{-mmac -mpush-args}
446 @emph{Darwin Options}
447 @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
448 -arch_only -bind_at_load -bundle -bundle_loader @gol
449 -client_name -compatibility_version -current_version @gol
451 -dependency-file -dylib_file -dylinker_install_name @gol
452 -dynamic -dynamiclib -exported_symbols_list @gol
453 -filelist -flat_namespace -force_cpusubtype_ALL @gol
454 -force_flat_namespace -headerpad_max_install_names @gol
455 -image_base -init -install_name -keep_private_externs @gol
456 -multi_module -multiply_defined -multiply_defined_unused @gol
457 -noall_load -no_dead_strip_inits_and_terms @gol
458 -nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol
459 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
460 -private_bundle -read_only_relocs -sectalign @gol
461 -sectobjectsymbols -whyload -seg1addr @gol
462 -sectcreate -sectobjectsymbols -sectorder @gol
463 -segaddr -segs_read_only_addr -segs_read_write_addr @gol
464 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
465 -segprot -segs_read_only_addr -segs_read_write_addr @gol
466 -single_module -static -sub_library -sub_umbrella @gol
467 -twolevel_namespace -umbrella -undefined @gol
468 -unexported_symbols_list -weak_reference_mismatches @gol
469 -whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol
472 @emph{DEC Alpha Options}
473 @gccoptlist{-mno-fp-regs -msoft-float -malpha-as -mgas @gol
474 -mieee -mieee-with-inexact -mieee-conformant @gol
475 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
476 -mtrap-precision=@var{mode} -mbuild-constants @gol
477 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
478 -mbwx -mmax -mfix -mcix @gol
479 -mfloat-vax -mfloat-ieee @gol
480 -mexplicit-relocs -msmall-data -mlarge-data @gol
481 -msmall-text -mlarge-text @gol
482 -mmemory-latency=@var{time}}
484 @emph{DEC Alpha/VMS Options}
485 @gccoptlist{-mvms-return-codes}
488 @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
489 -mhard-float -msoft-float @gol
490 -malloc-cc -mfixed-cc -mdword -mno-dword @gol
491 -mdouble -mno-double @gol
492 -mmedia -mno-media -mmuladd -mno-muladd @gol
493 -mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol
494 -mlinked-fp -mlong-calls -malign-labels @gol
495 -mlibrary-pic -macc-4 -macc-8 @gol
496 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
497 -moptimize-membar -mno-optimize-membar @gol
498 -mscc -mno-scc -mcond-exec -mno-cond-exec @gol
499 -mvliw-branch -mno-vliw-branch @gol
500 -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
501 -mno-nested-cond-exec -mtomcat-stats @gol
505 @emph{H8/300 Options}
506 @gccoptlist{-mrelax -mh -ms -mn -mint32 -malign-300}
509 @gccoptlist{-march=@var{architecture-type} @gol
510 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
511 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
512 -mfixed-range=@var{register-range} @gol
513 -mjump-in-delay -mlinker-opt -mlong-calls @gol
514 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
515 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
516 -mno-jump-in-delay -mno-long-load-store @gol
517 -mno-portable-runtime -mno-soft-float @gol
518 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
519 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
520 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
521 -munix=@var{unix-std} -nolibdld -static -threads}
523 @emph{i386 and x86-64 Options}
524 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
525 -mfpmath=@var{unit} @gol
526 -masm=@var{dialect} -mno-fancy-math-387 @gol
527 -mno-fp-ret-in-387 -msoft-float -msvr3-shlib @gol
528 -mno-wide-multiply -mrtd -malign-double @gol
529 -mpreferred-stack-boundary=@var{num} @gol
530 -mmmx -msse -msse2 -msse3 -m3dnow @gol
531 -mthreads -mno-align-stringops -minline-all-stringops @gol
532 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
533 -m96bit-long-double -mregparm=@var{num} -msseregparm @gol
534 -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol
535 -mcmodel=@var{code-model} @gol
536 -m32 -m64 -mlarge-data-threshold=@var{num}}
539 @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
540 -mvolatile-asm-stop -mregister-names -mno-sdata @gol
541 -mconstant-gp -mauto-pic -minline-float-divide-min-latency @gol
542 -minline-float-divide-max-throughput @gol
543 -minline-int-divide-min-latency @gol
544 -minline-int-divide-max-throughput @gol
545 -minline-sqrt-min-latency -minline-sqrt-max-throughput @gol
546 -mno-dwarf2-asm -mearly-stop-bits @gol
547 -mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol
548 -mtune=@var{cpu-type} -mt -pthread -milp32 -mlp64}
550 @emph{M32R/D Options}
551 @gccoptlist{-m32r2 -m32rx -m32r @gol
553 -malign-loops -mno-align-loops @gol
554 -missue-rate=@var{number} @gol
555 -mbranch-cost=@var{number} @gol
556 -mmodel=@var{code-size-model-type} @gol
557 -msdata=@var{sdata-type} @gol
558 -mno-flush-func -mflush-func=@var{name} @gol
559 -mno-flush-trap -mflush-trap=@var{number} @gol
563 @gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}}
565 @emph{M680x0 Options}
566 @gccoptlist{-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
567 -m68060 -mcpu32 -m5200 -m68881 -mbitfield -mc68000 -mc68020 @gol
568 -mnobitfield -mrtd -mshort -msoft-float -mpcrel @gol
569 -malign-int -mstrict-align -msep-data -mno-sep-data @gol
570 -mshared-library-id=n -mid-shared-library -mno-id-shared-library}
572 @emph{M68hc1x Options}
573 @gccoptlist{-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 @gol
574 -mauto-incdec -minmax -mlong-calls -mshort @gol
575 -msoft-reg-count=@var{count}}
578 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
579 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
580 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
581 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
582 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
585 @gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol
586 -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips64 @gol
587 -mips16 -mno-mips16 -mabi=@var{abi} -mabicalls -mno-abicalls @gol
588 -mxgot -mno-xgot -mgp32 -mgp64 -mfp32 -mfp64 @gol
589 -mhard-float -msoft-float -msingle-float -mdouble-float @gol
590 -mdsp -mpaired-single -mips3d @gol
591 -mlong64 -mlong32 -msym32 -mno-sym32 @gol
592 -G@var{num} -membedded-data -mno-embedded-data @gol
593 -muninit-const-in-rodata -mno-uninit-const-in-rodata @gol
594 -msplit-addresses -mno-split-addresses @gol
595 -mexplicit-relocs -mno-explicit-relocs @gol
596 -mcheck-zero-division -mno-check-zero-division @gol
597 -mdivide-traps -mdivide-breaks @gol
598 -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol
599 -mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp @gol
600 -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol
601 -mfix-vr4120 -mno-fix-vr4120 -mfix-vr4130 @gol
602 -mfix-sb1 -mno-fix-sb1 @gol
603 -mflush-func=@var{func} -mno-flush-func @gol
604 -mbranch-likely -mno-branch-likely @gol
605 -mfp-exceptions -mno-fp-exceptions @gol
606 -mvr4130-align -mno-vr4130-align}
609 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
610 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
611 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
612 -mno-base-addresses -msingle-exit -mno-single-exit}
614 @emph{MN10300 Options}
615 @gccoptlist{-mmult-bug -mno-mult-bug @gol
616 -mam33 -mno-am33 @gol
617 -mam33-2 -mno-am33-2 @gol
618 -mreturn-pointer-on-d0 @gol
622 @gccoptlist{-mno-crt0 -mmul -mbacc -msim @gol
623 -march=@var{cpu-type} }
625 @emph{PDP-11 Options}
626 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
627 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
628 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
629 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
630 -mbranch-expensive -mbranch-cheap @gol
631 -msplit -mno-split -munix-asm -mdec-asm}
633 @emph{PowerPC Options}
634 See RS/6000 and PowerPC Options.
636 @emph{RS/6000 and PowerPC Options}
637 @gccoptlist{-mcpu=@var{cpu-type} @gol
638 -mtune=@var{cpu-type} @gol
639 -mpower -mno-power -mpower2 -mno-power2 @gol
640 -mpowerpc -mpowerpc64 -mno-powerpc @gol
641 -maltivec -mno-altivec @gol
642 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
643 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
644 -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mfprnd -mno-fprnd @gol
645 -mnew-mnemonics -mold-mnemonics @gol
646 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
647 -m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol
648 -malign-power -malign-natural @gol
649 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
650 -mstring -mno-string -mupdate -mno-update @gol
651 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
652 -mstrict-align -mno-strict-align -mrelocatable @gol
653 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
654 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
655 -mdynamic-no-pic -maltivec -mswdiv @gol
656 -mprioritize-restricted-insns=@var{priority} @gol
657 -msched-costly-dep=@var{dependence_type} @gol
658 -minsert-sched-nops=@var{scheme} @gol
659 -mcall-sysv -mcall-netbsd @gol
660 -maix-struct-return -msvr4-struct-return @gol
661 -mabi=@var{abi-type} -msecure-plt -mbss-plt @gol
662 -misel -mno-isel @gol
663 -misel=yes -misel=no @gol
665 -mspe=yes -mspe=no @gol
666 -mvrsave -mno-vrsave @gol
667 -mmulhw -mno-mulhw @gol
668 -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol
669 -mprototype -mno-prototype @gol
670 -msim -mmvme -mads -myellowknife -memb -msdata @gol
671 -msdata=@var{opt} -mvxworks -mwindiss -G @var{num} -pthread}
673 @emph{S/390 and zSeries Options}
674 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
675 -mhard-float -msoft-float -mbackchain -mno-backchain @gol
676 -mpacked-stack -mno-packed-stack @gol
677 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
678 -m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol
679 -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol
680 -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard}
683 @gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol
684 -m4-nofpu -m4-single-only -m4-single -m4 @gol
685 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol
686 -m5-64media -m5-64media-nofpu @gol
687 -m5-32media -m5-32media-nofpu @gol
688 -m5-compact -m5-compact-nofpu @gol
689 -mb -ml -mdalign -mrelax @gol
690 -mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol
691 -mieee -misize -mpadstruct -mspace @gol
692 -mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol
693 -mdivsi3_libfunc=@var{name} @gol
694 -madjust-unroll -mindexed-addressing -mgettrcost=@var{number} -mpt-fixed @gol
698 @gccoptlist{-mcpu=@var{cpu-type} @gol
699 -mtune=@var{cpu-type} @gol
700 -mcmodel=@var{code-model} @gol
701 -m32 -m64 -mapp-regs -mno-app-regs @gol
702 -mfaster-structs -mno-faster-structs @gol
703 -mfpu -mno-fpu -mhard-float -msoft-float @gol
704 -mhard-quad-float -msoft-quad-float @gol
705 -mimpure-text -mno-impure-text -mlittle-endian @gol
706 -mstack-bias -mno-stack-bias @gol
707 -munaligned-doubles -mno-unaligned-doubles @gol
708 -mv8plus -mno-v8plus -mvis -mno-vis
711 @emph{System V Options}
712 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
714 @emph{TMS320C3x/C4x Options}
715 @gccoptlist{-mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol
716 -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol
717 -mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol
718 -mparallel-insns -mparallel-mpy -mpreserve-float}
721 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
722 -mprolog-function -mno-prolog-function -mspace @gol
723 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
724 -mapp-regs -mno-app-regs @gol
725 -mdisable-callt -mno-disable-callt @gol
731 @gccoptlist{-mg -mgnu -munix}
733 @emph{x86-64 Options}
734 See i386 and x86-64 Options.
736 @emph{Xstormy16 Options}
739 @emph{Xtensa Options}
740 @gccoptlist{-mconst16 -mno-const16 @gol
741 -mfused-madd -mno-fused-madd @gol
742 -mtext-section-literals -mno-text-section-literals @gol
743 -mtarget-align -mno-target-align @gol
744 -mlongcalls -mno-longcalls}
746 @emph{zSeries Options}
747 See S/390 and zSeries Options.
749 @item Code Generation Options
750 @xref{Code Gen Options,,Options for Code Generation Conventions}.
751 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
752 -ffixed-@var{reg} -fexceptions @gol
753 -fnon-call-exceptions -funwind-tables @gol
754 -fasynchronous-unwind-tables @gol
755 -finhibit-size-directive -finstrument-functions @gol
756 -fno-common -fno-ident @gol
757 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
758 -fno-jump-tables @gol
759 -freg-struct-return -fshared-data -fshort-enums @gol
760 -fshort-double -fshort-wchar @gol
761 -fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol
762 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
763 -fargument-alias -fargument-noalias @gol
764 -fargument-noalias-global -fleading-underscore @gol
765 -ftls-model=@var{model} @gol
766 -ftrapv -fwrapv -fbounds-check @gol
771 * Overall Options:: Controlling the kind of output:
772 an executable, object files, assembler files,
773 or preprocessed source.
774 * C Dialect Options:: Controlling the variant of C language compiled.
775 * C++ Dialect Options:: Variations on C++.
776 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
778 * Language Independent Options:: Controlling how diagnostics should be
780 * Warning Options:: How picky should the compiler be?
781 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
782 * Optimize Options:: How much optimization?
783 * Preprocessor Options:: Controlling header files and macro definitions.
784 Also, getting dependency information for Make.
785 * Assembler Options:: Passing options to the assembler.
786 * Link Options:: Specifying libraries and so on.
787 * Directory Options:: Where to find header files and libraries.
788 Where to find the compiler executable files.
789 * Spec Files:: How to pass switches to sub-processes.
790 * Target Options:: Running a cross-compiler, or an old version of GCC.
793 @node Overall Options
794 @section Options Controlling the Kind of Output
796 Compilation can involve up to four stages: preprocessing, compilation
797 proper, assembly and linking, always in that order. GCC is capable of
798 preprocessing and compiling several files either into several
799 assembler input files, or into one assembler input file; then each
800 assembler input file produces an object file, and linking combines all
801 the object files (those newly compiled, and those specified as input)
802 into an executable file.
804 @cindex file name suffix
805 For any given input file, the file name suffix determines what kind of
810 C source code which must be preprocessed.
813 C source code which should not be preprocessed.
816 C++ source code which should not be preprocessed.
819 Objective-C source code. Note that you must link with the @file{libobjc}
820 library to make an Objective-C program work.
823 Objective-C source code which should not be preprocessed.
827 Objective-C++ source code. Note that you must link with the @file{libobjc}
828 library to make an Objective-C++ program work. Note that @samp{.M} refers
829 to a literal capital M@.
832 Objective-C++ source code which should not be preprocessed.
835 C, C++, Objective-C or Objective-C++ header file to be turned into a
840 @itemx @var{file}.cxx
841 @itemx @var{file}.cpp
842 @itemx @var{file}.CPP
843 @itemx @var{file}.c++
845 C++ source code which must be preprocessed. Note that in @samp{.cxx},
846 the last two letters must both be literally @samp{x}. Likewise,
847 @samp{.C} refers to a literal capital C@.
851 Objective-C++ source code which must be preprocessed.
854 Objective-C++ source code which should not be preprocessed.
858 C++ header file to be turned into a precompiled header.
861 @itemx @var{file}.for
862 @itemx @var{file}.FOR
863 Fixed form Fortran source code which should not be preprocessed.
866 @itemx @var{file}.fpp
867 @itemx @var{file}.FPP
868 Fixed form Fortran source code which must be preprocessed (with the traditional
872 @itemx @var{file}.f95
873 Free form Fortran source code which should not be preprocessed.
876 @itemx @var{file}.F95
877 Free form Fortran source code which must be preprocessed (with the
878 traditional preprocessor).
880 @c FIXME: Descriptions of Java file types.
887 Ada source code file which contains a library unit declaration (a
888 declaration of a package, subprogram, or generic, or a generic
889 instantiation), or a library unit renaming declaration (a package,
890 generic, or subprogram renaming declaration). Such files are also
893 @itemx @var{file}.adb
894 Ada source code file containing a library unit body (a subprogram or
895 package body). Such files are also called @dfn{bodies}.
897 @c GCC also knows about some suffixes for languages not yet included:
908 Assembler code which must be preprocessed.
911 An object file to be fed straight into linking.
912 Any file name with no recognized suffix is treated this way.
916 You can specify the input language explicitly with the @option{-x} option:
919 @item -x @var{language}
920 Specify explicitly the @var{language} for the following input files
921 (rather than letting the compiler choose a default based on the file
922 name suffix). This option applies to all following input files until
923 the next @option{-x} option. Possible values for @var{language} are:
925 c c-header c-cpp-output
926 c++ c++-header c++-cpp-output
927 objective-c objective-c-header objective-c-cpp-output
928 objective-c++ objective-c++-header objective-c++-cpp-output
929 assembler assembler-with-cpp
938 Turn off any specification of a language, so that subsequent files are
939 handled according to their file name suffixes (as they are if @option{-x}
940 has not been used at all).
942 @item -pass-exit-codes
943 @opindex pass-exit-codes
944 Normally the @command{gcc} program will exit with the code of 1 if any
945 phase of the compiler returns a non-success return code. If you specify
946 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
947 numerically highest error produced by any phase that returned an error
951 If you only want some of the stages of compilation, you can use
952 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
953 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
954 @command{gcc} is to stop. Note that some combinations (for example,
955 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
960 Compile or assemble the source files, but do not link. The linking
961 stage simply is not done. The ultimate output is in the form of an
962 object file for each source file.
964 By default, the object file name for a source file is made by replacing
965 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
967 Unrecognized input files, not requiring compilation or assembly, are
972 Stop after the stage of compilation proper; do not assemble. The output
973 is in the form of an assembler code file for each non-assembler input
976 By default, the assembler file name for a source file is made by
977 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
979 Input files that don't require compilation are ignored.
983 Stop after the preprocessing stage; do not run the compiler proper. The
984 output is in the form of preprocessed source code, which is sent to the
987 Input files which don't require preprocessing are ignored.
989 @cindex output file option
992 Place output in file @var{file}. This applies regardless to whatever
993 sort of output is being produced, whether it be an executable file,
994 an object file, an assembler file or preprocessed C code.
996 If @option{-o} is not specified, the default is to put an executable
997 file in @file{a.out}, the object file for
998 @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its
999 assembler file in @file{@var{source}.s}, a precompiled header file in
1000 @file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on
1005 Print (on standard error output) the commands executed to run the stages
1006 of compilation. Also print the version number of the compiler driver
1007 program and of the preprocessor and the compiler proper.
1011 Like @option{-v} except the commands are not executed and all command
1012 arguments are quoted. This is useful for shell scripts to capture the
1013 driver-generated command lines.
1017 Use pipes rather than temporary files for communication between the
1018 various stages of compilation. This fails to work on some systems where
1019 the assembler is unable to read from a pipe; but the GNU assembler has
1024 If you are compiling multiple source files, this option tells the driver
1025 to pass all the source files to the compiler at once (for those
1026 languages for which the compiler can handle this). This will allow
1027 intermodule analysis (IMA) to be performed by the compiler. Currently the only
1028 language for which this is supported is C@. If you pass source files for
1029 multiple languages to the driver, using this option, the driver will invoke
1030 the compiler(s) that support IMA once each, passing each compiler all the
1031 source files appropriate for it. For those languages that do not support
1032 IMA this option will be ignored, and the compiler will be invoked once for
1033 each source file in that language. If you use this option in conjunction
1034 with @option{-save-temps}, the compiler will generate multiple
1036 (one for each source file), but only one (combined) @file{.o} or
1041 Print (on the standard output) a description of the command line options
1042 understood by @command{gcc}. If the @option{-v} option is also specified
1043 then @option{--help} will also be passed on to the various processes
1044 invoked by @command{gcc}, so that they can display the command line options
1045 they accept. If the @option{-Wextra} option is also specified then command
1046 line options which have no documentation associated with them will also
1050 @opindex target-help
1051 Print (on the standard output) a description of target specific command
1052 line options for each tool.
1056 Display the version number and copyrights of the invoked GCC@.
1058 @include @value{srcdir}/../libiberty/at-file.texi
1062 @section Compiling C++ Programs
1064 @cindex suffixes for C++ source
1065 @cindex C++ source file suffixes
1066 C++ source files conventionally use one of the suffixes @samp{.C},
1067 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
1068 @samp{.cxx}; C++ header files often use @samp{.hh} or @samp{.H}; and
1069 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
1070 files with these names and compiles them as C++ programs even if you
1071 call the compiler the same way as for compiling C programs (usually
1072 with the name @command{gcc}).
1076 However, C++ programs often require class libraries as well as a
1077 compiler that understands the C++ language---and under some
1078 circumstances, you might want to compile programs or header files from
1079 standard input, or otherwise without a suffix that flags them as C++
1080 programs. You might also like to precompile a C header file with a
1081 @samp{.h} extension to be used in C++ compilations. @command{g++} is a
1082 program that calls GCC with the default language set to C++, and
1083 automatically specifies linking against the C++ library. On many
1084 systems, @command{g++} is also installed with the name @command{c++}.
1086 @cindex invoking @command{g++}
1087 When you compile C++ programs, you may specify many of the same
1088 command-line options that you use for compiling programs in any
1089 language; or command-line options meaningful for C and related
1090 languages; or options that are meaningful only for C++ programs.
1091 @xref{C Dialect Options,,Options Controlling C Dialect}, for
1092 explanations of options for languages related to C@.
1093 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
1094 explanations of options that are meaningful only for C++ programs.
1096 @node C Dialect Options
1097 @section Options Controlling C Dialect
1098 @cindex dialect options
1099 @cindex language dialect options
1100 @cindex options, dialect
1102 The following options control the dialect of C (or languages derived
1103 from C, such as C++, Objective-C and Objective-C++) that the compiler
1107 @cindex ANSI support
1111 In C mode, support all ISO C90 programs. In C++ mode,
1112 remove GNU extensions that conflict with ISO C++.
1114 This turns off certain features of GCC that are incompatible with ISO
1115 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
1116 such as the @code{asm} and @code{typeof} keywords, and
1117 predefined macros such as @code{unix} and @code{vax} that identify the
1118 type of system you are using. It also enables the undesirable and
1119 rarely used ISO trigraph feature. For the C compiler,
1120 it disables recognition of C++ style @samp{//} comments as well as
1121 the @code{inline} keyword.
1123 The alternate keywords @code{__asm__}, @code{__extension__},
1124 @code{__inline__} and @code{__typeof__} continue to work despite
1125 @option{-ansi}. You would not want to use them in an ISO C program, of
1126 course, but it is useful to put them in header files that might be included
1127 in compilations done with @option{-ansi}. Alternate predefined macros
1128 such as @code{__unix__} and @code{__vax__} are also available, with or
1129 without @option{-ansi}.
1131 The @option{-ansi} option does not cause non-ISO programs to be
1132 rejected gratuitously. For that, @option{-pedantic} is required in
1133 addition to @option{-ansi}. @xref{Warning Options}.
1135 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1136 option is used. Some header files may notice this macro and refrain
1137 from declaring certain functions or defining certain macros that the
1138 ISO standard doesn't call for; this is to avoid interfering with any
1139 programs that might use these names for other things.
1141 Functions which would normally be built in but do not have semantics
1142 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1143 functions with @option{-ansi} is used. @xref{Other Builtins,,Other
1144 built-in functions provided by GCC}, for details of the functions
1149 Determine the language standard. This option is currently only
1150 supported when compiling C or C++. A value for this option must be
1151 provided; possible values are
1156 ISO C90 (same as @option{-ansi}).
1158 @item iso9899:199409
1159 ISO C90 as modified in amendment 1.
1165 ISO C99. Note that this standard is not yet fully supported; see
1166 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1167 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1170 Default, ISO C90 plus GNU extensions (including some C99 features).
1174 ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
1175 this will become the default. The name @samp{gnu9x} is deprecated.
1178 The 1998 ISO C++ standard plus amendments.
1181 The same as @option{-std=c++98} plus GNU extensions. This is the
1182 default for C++ code.
1185 Even when this option is not specified, you can still use some of the
1186 features of newer standards in so far as they do not conflict with
1187 previous C standards. For example, you may use @code{__restrict__} even
1188 when @option{-std=c99} is not specified.
1190 The @option{-std} options specifying some version of ISO C have the same
1191 effects as @option{-ansi}, except that features that were not in ISO C90
1192 but are in the specified version (for example, @samp{//} comments and
1193 the @code{inline} keyword in ISO C99) are not disabled.
1195 @xref{Standards,,Language Standards Supported by GCC}, for details of
1196 these standard versions.
1198 @item -aux-info @var{filename}
1200 Output to the given filename prototyped declarations for all functions
1201 declared and/or defined in a translation unit, including those in header
1202 files. This option is silently ignored in any language other than C@.
1204 Besides declarations, the file indicates, in comments, the origin of
1205 each declaration (source file and line), whether the declaration was
1206 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1207 @samp{O} for old, respectively, in the first character after the line
1208 number and the colon), and whether it came from a declaration or a
1209 definition (@samp{C} or @samp{F}, respectively, in the following
1210 character). In the case of function definitions, a K&R-style list of
1211 arguments followed by their declarations is also provided, inside
1212 comments, after the declaration.
1216 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1217 keyword, so that code can use these words as identifiers. You can use
1218 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1219 instead. @option{-ansi} implies @option{-fno-asm}.
1221 In C++, this switch only affects the @code{typeof} keyword, since
1222 @code{asm} and @code{inline} are standard keywords. You may want to
1223 use the @option{-fno-gnu-keywords} flag instead, which has the same
1224 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1225 switch only affects the @code{asm} and @code{typeof} keywords, since
1226 @code{inline} is a standard keyword in ISO C99.
1229 @itemx -fno-builtin-@var{function}
1230 @opindex fno-builtin
1231 @cindex built-in functions
1232 Don't recognize built-in functions that do not begin with
1233 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1234 functions provided by GCC}, for details of the functions affected,
1235 including those which are not built-in functions when @option{-ansi} or
1236 @option{-std} options for strict ISO C conformance are used because they
1237 do not have an ISO standard meaning.
1239 GCC normally generates special code to handle certain built-in functions
1240 more efficiently; for instance, calls to @code{alloca} may become single
1241 instructions that adjust the stack directly, and calls to @code{memcpy}
1242 may become inline copy loops. The resulting code is often both smaller
1243 and faster, but since the function calls no longer appear as such, you
1244 cannot set a breakpoint on those calls, nor can you change the behavior
1245 of the functions by linking with a different library. In addition,
1246 when a function is recognized as a built-in function, GCC may use
1247 information about that function to warn about problems with calls to
1248 that function, or to generate more efficient code, even if the
1249 resulting code still contains calls to that function. For example,
1250 warnings are given with @option{-Wformat} for bad calls to
1251 @code{printf}, when @code{printf} is built in, and @code{strlen} is
1252 known not to modify global memory.
1254 With the @option{-fno-builtin-@var{function}} option
1255 only the built-in function @var{function} is
1256 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1257 function is named this is not built-in in this version of GCC, this
1258 option is ignored. There is no corresponding
1259 @option{-fbuiltin-@var{function}} option; if you wish to enable
1260 built-in functions selectively when using @option{-fno-builtin} or
1261 @option{-ffreestanding}, you may define macros such as:
1264 #define abs(n) __builtin_abs ((n))
1265 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1270 @cindex hosted environment
1272 Assert that compilation takes place in a hosted environment. This implies
1273 @option{-fbuiltin}. A hosted environment is one in which the
1274 entire standard library is available, and in which @code{main} has a return
1275 type of @code{int}. Examples are nearly everything except a kernel.
1276 This is equivalent to @option{-fno-freestanding}.
1278 @item -ffreestanding
1279 @opindex ffreestanding
1280 @cindex hosted environment
1282 Assert that compilation takes place in a freestanding environment. This
1283 implies @option{-fno-builtin}. A freestanding environment
1284 is one in which the standard library may not exist, and program startup may
1285 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1286 This is equivalent to @option{-fno-hosted}.
1288 @xref{Standards,,Language Standards Supported by GCC}, for details of
1289 freestanding and hosted environments.
1291 @item -fms-extensions
1292 @opindex fms-extensions
1293 Accept some non-standard constructs used in Microsoft header files.
1295 Some cases of unnamed fields in structures and unions are only
1296 accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union
1297 fields within structs/unions}, for details.
1301 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1302 options for strict ISO C conformance) implies @option{-trigraphs}.
1304 @item -no-integrated-cpp
1305 @opindex no-integrated-cpp
1306 Performs a compilation in two passes: preprocessing and compiling. This
1307 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1308 @option{-B} option. The user supplied compilation step can then add in
1309 an additional preprocessing step after normal preprocessing but before
1310 compiling. The default is to use the integrated cpp (internal cpp)
1312 The semantics of this option will change if "cc1", "cc1plus", and
1313 "cc1obj" are merged.
1315 @cindex traditional C language
1316 @cindex C language, traditional
1318 @itemx -traditional-cpp
1319 @opindex traditional-cpp
1320 @opindex traditional
1321 Formerly, these options caused GCC to attempt to emulate a pre-standard
1322 C compiler. They are now only supported with the @option{-E} switch.
1323 The preprocessor continues to support a pre-standard mode. See the GNU
1324 CPP manual for details.
1326 @item -fcond-mismatch
1327 @opindex fcond-mismatch
1328 Allow conditional expressions with mismatched types in the second and
1329 third arguments. The value of such an expression is void. This option
1330 is not supported for C++.
1332 @item -funsigned-char
1333 @opindex funsigned-char
1334 Let the type @code{char} be unsigned, like @code{unsigned char}.
1336 Each kind of machine has a default for what @code{char} should
1337 be. It is either like @code{unsigned char} by default or like
1338 @code{signed char} by default.
1340 Ideally, a portable program should always use @code{signed char} or
1341 @code{unsigned char} when it depends on the signedness of an object.
1342 But many programs have been written to use plain @code{char} and
1343 expect it to be signed, or expect it to be unsigned, depending on the
1344 machines they were written for. This option, and its inverse, let you
1345 make such a program work with the opposite default.
1347 The type @code{char} is always a distinct type from each of
1348 @code{signed char} or @code{unsigned char}, even though its behavior
1349 is always just like one of those two.
1352 @opindex fsigned-char
1353 Let the type @code{char} be signed, like @code{signed char}.
1355 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1356 the negative form of @option{-funsigned-char}. Likewise, the option
1357 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1359 @item -fsigned-bitfields
1360 @itemx -funsigned-bitfields
1361 @itemx -fno-signed-bitfields
1362 @itemx -fno-unsigned-bitfields
1363 @opindex fsigned-bitfields
1364 @opindex funsigned-bitfields
1365 @opindex fno-signed-bitfields
1366 @opindex fno-unsigned-bitfields
1367 These options control whether a bit-field is signed or unsigned, when the
1368 declaration does not use either @code{signed} or @code{unsigned}. By
1369 default, such a bit-field is signed, because this is consistent: the
1370 basic integer types such as @code{int} are signed types.
1373 @node C++ Dialect Options
1374 @section Options Controlling C++ Dialect
1376 @cindex compiler options, C++
1377 @cindex C++ options, command line
1378 @cindex options, C++
1379 This section describes the command-line options that are only meaningful
1380 for C++ programs; but you can also use most of the GNU compiler options
1381 regardless of what language your program is in. For example, you
1382 might compile a file @code{firstClass.C} like this:
1385 g++ -g -frepo -O -c firstClass.C
1389 In this example, only @option{-frepo} is an option meant
1390 only for C++ programs; you can use the other options with any
1391 language supported by GCC@.
1393 Here is a list of options that are @emph{only} for compiling C++ programs:
1397 @item -fabi-version=@var{n}
1398 @opindex fabi-version
1399 Use version @var{n} of the C++ ABI@. Version 2 is the version of the
1400 C++ ABI that first appeared in G++ 3.4. Version 1 is the version of
1401 the C++ ABI that first appeared in G++ 3.2. Version 0 will always be
1402 the version that conforms most closely to the C++ ABI specification.
1403 Therefore, the ABI obtained using version 0 will change as ABI bugs
1406 The default is version 2.
1408 @item -fno-access-control
1409 @opindex fno-access-control
1410 Turn off all access checking. This switch is mainly useful for working
1411 around bugs in the access control code.
1415 Check that the pointer returned by @code{operator new} is non-null
1416 before attempting to modify the storage allocated. This check is
1417 normally unnecessary because the C++ standard specifies that
1418 @code{operator new} will only return @code{0} if it is declared
1419 @samp{throw()}, in which case the compiler will always check the
1420 return value even without this option. In all other cases, when
1421 @code{operator new} has a non-empty exception specification, memory
1422 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1423 @samp{new (nothrow)}.
1425 @item -fconserve-space
1426 @opindex fconserve-space
1427 Put uninitialized or runtime-initialized global variables into the
1428 common segment, as C does. This saves space in the executable at the
1429 cost of not diagnosing duplicate definitions. If you compile with this
1430 flag and your program mysteriously crashes after @code{main()} has
1431 completed, you may have an object that is being destroyed twice because
1432 two definitions were merged.
1434 This option is no longer useful on most targets, now that support has
1435 been added for putting variables into BSS without making them common.
1437 @item -ffriend-injection
1438 @opindex ffriend-injection
1439 Inject friend functions into the enclosing namespace, so that they are
1440 visible outside the scope of the class in which they are declared.
1441 Friend functions were documented to work this way in the old Annotated
1442 C++ Reference Manual, and versions of G++ before 4.1 always worked
1443 that way. However, in ISO C++ a friend function which is not declared
1444 in an enclosing scope can only be found using argument dependent
1445 lookup. This option causes friends to be injected as they were in
1448 This option is for compatibility, and may be removed in a future
1451 @item -fno-const-strings
1452 @opindex fno-const-strings
1453 Give string constants type @code{char *} instead of type @code{const
1454 char *}. By default, G++ uses type @code{const char *} as required by
1455 the standard. Even if you use @option{-fno-const-strings}, you cannot
1456 actually modify the value of a string constant.
1458 This option might be removed in a future release of G++. For maximum
1459 portability, you should structure your code so that it works with
1460 string constants that have type @code{const char *}.
1462 @item -fno-elide-constructors
1463 @opindex fno-elide-constructors
1464 The C++ standard allows an implementation to omit creating a temporary
1465 which is only used to initialize another object of the same type.
1466 Specifying this option disables that optimization, and forces G++ to
1467 call the copy constructor in all cases.
1469 @item -fno-enforce-eh-specs
1470 @opindex fno-enforce-eh-specs
1471 Don't generate code to check for violation of exception specifications
1472 at runtime. This option violates the C++ standard, but may be useful
1473 for reducing code size in production builds, much like defining
1474 @samp{NDEBUG}. This does not give user code permission to throw
1475 exceptions in violation of the exception specifications; the compiler
1476 will still optimize based on the specifications, so throwing an
1477 unexpected exception will result in undefined behavior.
1480 @itemx -fno-for-scope
1482 @opindex fno-for-scope
1483 If @option{-ffor-scope} is specified, the scope of variables declared in
1484 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1485 as specified by the C++ standard.
1486 If @option{-fno-for-scope} is specified, the scope of variables declared in
1487 a @i{for-init-statement} extends to the end of the enclosing scope,
1488 as was the case in old versions of G++, and other (traditional)
1489 implementations of C++.
1491 The default if neither flag is given to follow the standard,
1492 but to allow and give a warning for old-style code that would
1493 otherwise be invalid, or have different behavior.
1495 @item -fno-gnu-keywords
1496 @opindex fno-gnu-keywords
1497 Do not recognize @code{typeof} as a keyword, so that code can use this
1498 word as an identifier. You can use the keyword @code{__typeof__} instead.
1499 @option{-ansi} implies @option{-fno-gnu-keywords}.
1501 @item -fno-implicit-templates
1502 @opindex fno-implicit-templates
1503 Never emit code for non-inline templates which are instantiated
1504 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1505 @xref{Template Instantiation}, for more information.
1507 @item -fno-implicit-inline-templates
1508 @opindex fno-implicit-inline-templates
1509 Don't emit code for implicit instantiations of inline templates, either.
1510 The default is to handle inlines differently so that compiles with and
1511 without optimization will need the same set of explicit instantiations.
1513 @item -fno-implement-inlines
1514 @opindex fno-implement-inlines
1515 To save space, do not emit out-of-line copies of inline functions
1516 controlled by @samp{#pragma implementation}. This will cause linker
1517 errors if these functions are not inlined everywhere they are called.
1519 @item -fms-extensions
1520 @opindex fms-extensions
1521 Disable pedantic warnings about constructs used in MFC, such as implicit
1522 int and getting a pointer to member function via non-standard syntax.
1524 @item -fno-nonansi-builtins
1525 @opindex fno-nonansi-builtins
1526 Disable built-in declarations of functions that are not mandated by
1527 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1528 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1530 @item -fno-operator-names
1531 @opindex fno-operator-names
1532 Do not treat the operator name keywords @code{and}, @code{bitand},
1533 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1534 synonyms as keywords.
1536 @item -fno-optional-diags
1537 @opindex fno-optional-diags
1538 Disable diagnostics that the standard says a compiler does not need to
1539 issue. Currently, the only such diagnostic issued by G++ is the one for
1540 a name having multiple meanings within a class.
1543 @opindex fpermissive
1544 Downgrade some diagnostics about nonconformant code from errors to
1545 warnings. Thus, using @option{-fpermissive} will allow some
1546 nonconforming code to compile.
1550 Enable automatic template instantiation at link time. This option also
1551 implies @option{-fno-implicit-templates}. @xref{Template
1552 Instantiation}, for more information.
1556 Disable generation of information about every class with virtual
1557 functions for use by the C++ runtime type identification features
1558 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1559 of the language, you can save some space by using this flag. Note that
1560 exception handling uses the same information, but it will generate it as
1565 Emit statistics about front-end processing at the end of the compilation.
1566 This information is generally only useful to the G++ development team.
1568 @item -ftemplate-depth-@var{n}
1569 @opindex ftemplate-depth
1570 Set the maximum instantiation depth for template classes to @var{n}.
1571 A limit on the template instantiation depth is needed to detect
1572 endless recursions during template class instantiation. ANSI/ISO C++
1573 conforming programs must not rely on a maximum depth greater than 17.
1575 @item -fno-threadsafe-statics
1576 @opindex fno-threadsafe-statics
1577 Do not emit the extra code to use the routines specified in the C++
1578 ABI for thread-safe initialization of local statics. You can use this
1579 option to reduce code size slightly in code that doesn't need to be
1582 @item -fuse-cxa-atexit
1583 @opindex fuse-cxa-atexit
1584 Register destructors for objects with static storage duration with the
1585 @code{__cxa_atexit} function rather than the @code{atexit} function.
1586 This option is required for fully standards-compliant handling of static
1587 destructors, but will only work if your C library supports
1588 @code{__cxa_atexit}.
1590 @item -fvisibility-inlines-hidden
1591 @opindex fvisibility-inlines-hidden
1592 Causes all inlined methods to be marked with
1593 @code{__attribute__ ((visibility ("hidden")))} so that they do not
1594 appear in the export table of a DSO and do not require a PLT indirection
1595 when used within the DSO@. Enabling this option can have a dramatic effect
1596 on load and link times of a DSO as it massively reduces the size of the
1597 dynamic export table when the library makes heavy use of templates. While
1598 it can cause bloating through duplication of code within each DSO where
1599 it is used, often the wastage is less than the considerable space occupied
1600 by a long symbol name in the export table which is typical when using
1601 templates and namespaces. For even more savings, combine with the
1602 @option{-fvisibility=hidden} switch.
1606 Do not use weak symbol support, even if it is provided by the linker.
1607 By default, G++ will use weak symbols if they are available. This
1608 option exists only for testing, and should not be used by end-users;
1609 it will result in inferior code and has no benefits. This option may
1610 be removed in a future release of G++.
1614 Do not search for header files in the standard directories specific to
1615 C++, but do still search the other standard directories. (This option
1616 is used when building the C++ library.)
1619 In addition, these optimization, warning, and code generation options
1620 have meanings only for C++ programs:
1623 @item -fno-default-inline
1624 @opindex fno-default-inline
1625 Do not assume @samp{inline} for functions defined inside a class scope.
1626 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1627 functions will have linkage like inline functions; they just won't be
1630 @item -Wabi @r{(C++ only)}
1632 Warn when G++ generates code that is probably not compatible with the
1633 vendor-neutral C++ ABI@. Although an effort has been made to warn about
1634 all such cases, there are probably some cases that are not warned about,
1635 even though G++ is generating incompatible code. There may also be
1636 cases where warnings are emitted even though the code that is generated
1639 You should rewrite your code to avoid these warnings if you are
1640 concerned about the fact that code generated by G++ may not be binary
1641 compatible with code generated by other compilers.
1643 The known incompatibilities at this point include:
1648 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1649 pack data into the same byte as a base class. For example:
1652 struct A @{ virtual void f(); int f1 : 1; @};
1653 struct B : public A @{ int f2 : 1; @};
1657 In this case, G++ will place @code{B::f2} into the same byte
1658 as@code{A::f1}; other compilers will not. You can avoid this problem
1659 by explicitly padding @code{A} so that its size is a multiple of the
1660 byte size on your platform; that will cause G++ and other compilers to
1661 layout @code{B} identically.
1664 Incorrect handling of tail-padding for virtual bases. G++ does not use
1665 tail padding when laying out virtual bases. For example:
1668 struct A @{ virtual void f(); char c1; @};
1669 struct B @{ B(); char c2; @};
1670 struct C : public A, public virtual B @{@};
1674 In this case, G++ will not place @code{B} into the tail-padding for
1675 @code{A}; other compilers will. You can avoid this problem by
1676 explicitly padding @code{A} so that its size is a multiple of its
1677 alignment (ignoring virtual base classes); that will cause G++ and other
1678 compilers to layout @code{C} identically.
1681 Incorrect handling of bit-fields with declared widths greater than that
1682 of their underlying types, when the bit-fields appear in a union. For
1686 union U @{ int i : 4096; @};
1690 Assuming that an @code{int} does not have 4096 bits, G++ will make the
1691 union too small by the number of bits in an @code{int}.
1694 Empty classes can be placed at incorrect offsets. For example:
1704 struct C : public B, public A @{@};
1708 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
1709 it should be placed at offset zero. G++ mistakenly believes that the
1710 @code{A} data member of @code{B} is already at offset zero.
1713 Names of template functions whose types involve @code{typename} or
1714 template template parameters can be mangled incorrectly.
1717 template <typename Q>
1718 void f(typename Q::X) @{@}
1720 template <template <typename> class Q>
1721 void f(typename Q<int>::X) @{@}
1725 Instantiations of these templates may be mangled incorrectly.
1729 @item -Wctor-dtor-privacy @r{(C++ only)}
1730 @opindex Wctor-dtor-privacy
1731 Warn when a class seems unusable because all the constructors or
1732 destructors in that class are private, and it has neither friends nor
1733 public static member functions.
1735 @item -Wnon-virtual-dtor @r{(C++ only)}
1736 @opindex Wnon-virtual-dtor
1737 Warn when a class appears to be polymorphic, thereby requiring a virtual
1738 destructor, yet it declares a non-virtual one.
1739 This warning is enabled by @option{-Wall}.
1741 @item -Wreorder @r{(C++ only)}
1743 @cindex reordering, warning
1744 @cindex warning for reordering of member initializers
1745 Warn when the order of member initializers given in the code does not
1746 match the order in which they must be executed. For instance:
1752 A(): j (0), i (1) @{ @}
1756 The compiler will rearrange the member initializers for @samp{i}
1757 and @samp{j} to match the declaration order of the members, emitting
1758 a warning to that effect. This warning is enabled by @option{-Wall}.
1761 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
1764 @item -Weffc++ @r{(C++ only)}
1766 Warn about violations of the following style guidelines from Scott Meyers'
1767 @cite{Effective C++} book:
1771 Item 11: Define a copy constructor and an assignment operator for classes
1772 with dynamically allocated memory.
1775 Item 12: Prefer initialization to assignment in constructors.
1778 Item 14: Make destructors virtual in base classes.
1781 Item 15: Have @code{operator=} return a reference to @code{*this}.
1784 Item 23: Don't try to return a reference when you must return an object.
1788 Also warn about violations of the following style guidelines from
1789 Scott Meyers' @cite{More Effective C++} book:
1793 Item 6: Distinguish between prefix and postfix forms of increment and
1794 decrement operators.
1797 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
1801 When selecting this option, be aware that the standard library
1802 headers do not obey all of these guidelines; use @samp{grep -v}
1803 to filter out those warnings.
1805 @item -Wno-deprecated @r{(C++ only)}
1806 @opindex Wno-deprecated
1807 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
1809 @item -Wstrict-null-sentinel @r{(C++ only)}
1810 @opindex Wstrict-null-sentinel
1811 Warn also about the use of an uncasted @code{NULL} as sentinel. When
1812 compiling only with GCC this is a valid sentinel, as @code{NULL} is defined
1813 to @code{__null}. Although it is a null pointer constant not a null pointer,
1814 it is guaranteed to of the same size as a pointer. But this use is
1815 not portable across different compilers.
1817 @item -Wno-non-template-friend @r{(C++ only)}
1818 @opindex Wno-non-template-friend
1819 Disable warnings when non-templatized friend functions are declared
1820 within a template. Since the advent of explicit template specification
1821 support in G++, if the name of the friend is an unqualified-id (i.e.,
1822 @samp{friend foo(int)}), the C++ language specification demands that the
1823 friend declare or define an ordinary, nontemplate function. (Section
1824 14.5.3). Before G++ implemented explicit specification, unqualified-ids
1825 could be interpreted as a particular specialization of a templatized
1826 function. Because this non-conforming behavior is no longer the default
1827 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
1828 check existing code for potential trouble spots and is on by default.
1829 This new compiler behavior can be turned off with
1830 @option{-Wno-non-template-friend} which keeps the conformant compiler code
1831 but disables the helpful warning.
1833 @item -Wold-style-cast @r{(C++ only)}
1834 @opindex Wold-style-cast
1835 Warn if an old-style (C-style) cast to a non-void type is used within
1836 a C++ program. The new-style casts (@samp{dynamic_cast},
1837 @samp{static_cast}, @samp{reinterpret_cast}, and @samp{const_cast}) are
1838 less vulnerable to unintended effects and much easier to search for.
1840 @item -Woverloaded-virtual @r{(C++ only)}
1841 @opindex Woverloaded-virtual
1842 @cindex overloaded virtual fn, warning
1843 @cindex warning for overloaded virtual fn
1844 Warn when a function declaration hides virtual functions from a
1845 base class. For example, in:
1852 struct B: public A @{
1857 the @code{A} class version of @code{f} is hidden in @code{B}, and code
1865 will fail to compile.
1867 @item -Wno-pmf-conversions @r{(C++ only)}
1868 @opindex Wno-pmf-conversions
1869 Disable the diagnostic for converting a bound pointer to member function
1872 @item -Wsign-promo @r{(C++ only)}
1873 @opindex Wsign-promo
1874 Warn when overload resolution chooses a promotion from unsigned or
1875 enumerated type to a signed type, over a conversion to an unsigned type of
1876 the same size. Previous versions of G++ would try to preserve
1877 unsignedness, but the standard mandates the current behavior.
1882 A& operator = (int);
1892 In this example, G++ will synthesize a default @samp{A& operator =
1893 (const A&);}, while cfront will use the user-defined @samp{operator =}.
1896 @node Objective-C and Objective-C++ Dialect Options
1897 @section Options Controlling Objective-C and Objective-C++ Dialects
1899 @cindex compiler options, Objective-C and Objective-C++
1900 @cindex Objective-C and Objective-C++ options, command line
1901 @cindex options, Objective-C and Objective-C++
1902 (NOTE: This manual does not describe the Objective-C and Objective-C++
1903 languages themselves. See @xref{Standards,,Language Standards
1904 Supported by GCC}, for references.)
1906 This section describes the command-line options that are only meaningful
1907 for Objective-C and Objective-C++ programs, but you can also use most of
1908 the language-independent GNU compiler options.
1909 For example, you might compile a file @code{some_class.m} like this:
1912 gcc -g -fgnu-runtime -O -c some_class.m
1916 In this example, @option{-fgnu-runtime} is an option meant only for
1917 Objective-C and Objective-C++ programs; you can use the other options with
1918 any language supported by GCC@.
1920 Note that since Objective-C is an extension of the C language, Objective-C
1921 compilations may also use options specific to the C front-end (e.g.,
1922 @option{-Wtraditional}). Similarly, Objective-C++ compilations may use
1923 C++-specific options (e.g., @option{-Wabi}).
1925 Here is a list of options that are @emph{only} for compiling Objective-C
1926 and Objective-C++ programs:
1929 @item -fconstant-string-class=@var{class-name}
1930 @opindex fconstant-string-class
1931 Use @var{class-name} as the name of the class to instantiate for each
1932 literal string specified with the syntax @code{@@"@dots{}"}. The default
1933 class name is @code{NXConstantString} if the GNU runtime is being used, and
1934 @code{NSConstantString} if the NeXT runtime is being used (see below). The
1935 @option{-fconstant-cfstrings} option, if also present, will override the
1936 @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
1937 to be laid out as constant CoreFoundation strings.
1940 @opindex fgnu-runtime
1941 Generate object code compatible with the standard GNU Objective-C
1942 runtime. This is the default for most types of systems.
1944 @item -fnext-runtime
1945 @opindex fnext-runtime
1946 Generate output compatible with the NeXT runtime. This is the default
1947 for NeXT-based systems, including Darwin and Mac OS X@. The macro
1948 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
1951 @item -fno-nil-receivers
1952 @opindex fno-nil-receivers
1953 Assume that all Objective-C message dispatches (e.g.,
1954 @code{[receiver message:arg]}) in this translation unit ensure that the receiver
1955 is not @code{nil}. This allows for more efficient entry points in the runtime
1956 to be used. Currently, this option is only available in conjunction with
1957 the NeXT runtime on Mac OS X 10.3 and later.
1959 @item -fobjc-call-cxx-cdtors
1960 @opindex fobjc-call-cxx-cdtors
1961 For each Objective-C class, check if any of its instance variables is a
1962 C++ object with a non-trivial default constructor. If so, synthesize a
1963 special @code{- (id) .cxx_construct} instance method that will run
1964 non-trivial default constructors on any such instance variables, in order,
1965 and then return @code{self}. Similarly, check if any instance variable
1966 is a C++ object with a non-trivial destructor, and if so, synthesize a
1967 special @code{- (void) .cxx_destruct} method that will run
1968 all such default destructors, in reverse order.
1970 The @code{- (id) .cxx_construct} and/or @code{- (void) .cxx_destruct} methods
1971 thusly generated will only operate on instance variables declared in the
1972 current Objective-C class, and not those inherited from superclasses. It
1973 is the responsibility of the Objective-C runtime to invoke all such methods
1974 in an object's inheritance hierarchy. The @code{- (id) .cxx_construct} methods
1975 will be invoked by the runtime immediately after a new object
1976 instance is allocated; the @code{- (void) .cxx_destruct} methods will
1977 be invoked immediately before the runtime deallocates an object instance.
1979 As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has
1980 support for invoking the @code{- (id) .cxx_construct} and
1981 @code{- (void) .cxx_destruct} methods.
1983 @item -fobjc-direct-dispatch
1984 @opindex fobjc-direct-dispatch
1985 Allow fast jumps to the message dispatcher. On Darwin this is
1986 accomplished via the comm page.
1988 @item -fobjc-exceptions
1989 @opindex fobjc-exceptions
1990 Enable syntactic support for structured exception handling in Objective-C,
1991 similar to what is offered by C++ and Java. Currently, this option is only
1992 available in conjunction with the NeXT runtime on Mac OS X 10.3 and later.
2000 @@catch (AnObjCClass *exc) @{
2007 @@catch (AnotherClass *exc) @{
2010 @@catch (id allOthers) @{
2020 The @code{@@throw} statement may appear anywhere in an Objective-C or
2021 Objective-C++ program; when used inside of a @code{@@catch} block, the
2022 @code{@@throw} may appear without an argument (as shown above), in which case
2023 the object caught by the @code{@@catch} will be rethrown.
2025 Note that only (pointers to) Objective-C objects may be thrown and
2026 caught using this scheme. When an object is thrown, it will be caught
2027 by the nearest @code{@@catch} clause capable of handling objects of that type,
2028 analogously to how @code{catch} blocks work in C++ and Java. A
2029 @code{@@catch(id @dots{})} clause (as shown above) may also be provided to catch
2030 any and all Objective-C exceptions not caught by previous @code{@@catch}
2033 The @code{@@finally} clause, if present, will be executed upon exit from the
2034 immediately preceding @code{@@try @dots{} @@catch} section. This will happen
2035 regardless of whether any exceptions are thrown, caught or rethrown
2036 inside the @code{@@try @dots{} @@catch} section, analogously to the behavior
2037 of the @code{finally} clause in Java.
2039 There are several caveats to using the new exception mechanism:
2043 Although currently designed to be binary compatible with @code{NS_HANDLER}-style
2044 idioms provided by the @code{NSException} class, the new
2045 exceptions can only be used on Mac OS X 10.3 (Panther) and later
2046 systems, due to additional functionality needed in the (NeXT) Objective-C
2050 As mentioned above, the new exceptions do not support handling
2051 types other than Objective-C objects. Furthermore, when used from
2052 Objective-C++, the Objective-C exception model does not interoperate with C++
2053 exceptions at this time. This means you cannot @code{@@throw} an exception
2054 from Objective-C and @code{catch} it in C++, or vice versa
2055 (i.e., @code{throw @dots{} @@catch}).
2058 The @option{-fobjc-exceptions} switch also enables the use of synchronization
2059 blocks for thread-safe execution:
2062 @@synchronized (ObjCClass *guard) @{
2067 Upon entering the @code{@@synchronized} block, a thread of execution shall
2068 first check whether a lock has been placed on the corresponding @code{guard}
2069 object by another thread. If it has, the current thread shall wait until
2070 the other thread relinquishes its lock. Once @code{guard} becomes available,
2071 the current thread will place its own lock on it, execute the code contained in
2072 the @code{@@synchronized} block, and finally relinquish the lock (thereby
2073 making @code{guard} available to other threads).
2075 Unlike Java, Objective-C does not allow for entire methods to be marked
2076 @code{@@synchronized}. Note that throwing exceptions out of
2077 @code{@@synchronized} blocks is allowed, and will cause the guarding object
2078 to be unlocked properly.
2082 Enable garbage collection (GC) in Objective-C and Objective-C++ programs.
2084 @item -freplace-objc-classes
2085 @opindex freplace-objc-classes
2086 Emit a special marker instructing @command{ld(1)} not to statically link in
2087 the resulting object file, and allow @command{dyld(1)} to load it in at
2088 run time instead. This is used in conjunction with the Fix-and-Continue
2089 debugging mode, where the object file in question may be recompiled and
2090 dynamically reloaded in the course of program execution, without the need
2091 to restart the program itself. Currently, Fix-and-Continue functionality
2092 is only available in conjunction with the NeXT runtime on Mac OS X 10.3
2097 When compiling for the NeXT runtime, the compiler ordinarily replaces calls
2098 to @code{objc_getClass("@dots{}")} (when the name of the class is known at
2099 compile time) with static class references that get initialized at load time,
2100 which improves run-time performance. Specifying the @option{-fzero-link} flag
2101 suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
2102 to be retained. This is useful in Zero-Link debugging mode, since it allows
2103 for individual class implementations to be modified during program execution.
2107 Dump interface declarations for all classes seen in the source file to a
2108 file named @file{@var{sourcename}.decl}.
2110 @item -Wassign-intercept
2111 @opindex Wassign-intercept
2112 Warn whenever an Objective-C assignment is being intercepted by the
2116 @opindex Wno-protocol
2117 If a class is declared to implement a protocol, a warning is issued for
2118 every method in the protocol that is not implemented by the class. The
2119 default behavior is to issue a warning for every method not explicitly
2120 implemented in the class, even if a method implementation is inherited
2121 from the superclass. If you use the @option{-Wno-protocol} option, then
2122 methods inherited from the superclass are considered to be implemented,
2123 and no warning is issued for them.
2127 Warn if multiple methods of different types for the same selector are
2128 found during compilation. The check is performed on the list of methods
2129 in the final stage of compilation. Additionally, a check is performed
2130 for each selector appearing in a @code{@@selector(@dots{})}
2131 expression, and a corresponding method for that selector has been found
2132 during compilation. Because these checks scan the method table only at
2133 the end of compilation, these warnings are not produced if the final
2134 stage of compilation is not reached, for example because an error is
2135 found during compilation, or because the @option{-fsyntax-only} option is
2138 @item -Wstrict-selector-match
2139 @opindex Wstrict-selector-match
2140 Warn if multiple methods with differing argument and/or return types are
2141 found for a given selector when attempting to send a message using this
2142 selector to a receiver of type @code{id} or @code{Class}. When this flag
2143 is off (which is the default behavior), the compiler will omit such warnings
2144 if any differences found are confined to types which share the same size
2147 @item -Wundeclared-selector
2148 @opindex Wundeclared-selector
2149 Warn if a @code{@@selector(@dots{})} expression referring to an
2150 undeclared selector is found. A selector is considered undeclared if no
2151 method with that name has been declared before the
2152 @code{@@selector(@dots{})} expression, either explicitly in an
2153 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
2154 an @code{@@implementation} section. This option always performs its
2155 checks as soon as a @code{@@selector(@dots{})} expression is found,
2156 while @option{-Wselector} only performs its checks in the final stage of
2157 compilation. This also enforces the coding style convention
2158 that methods and selectors must be declared before being used.
2160 @item -print-objc-runtime-info
2161 @opindex print-objc-runtime-info
2162 Generate C header describing the largest structure that is passed by
2167 @node Language Independent Options
2168 @section Options to Control Diagnostic Messages Formatting
2169 @cindex options to control diagnostics formatting
2170 @cindex diagnostic messages
2171 @cindex message formatting
2173 Traditionally, diagnostic messages have been formatted irrespective of
2174 the output device's aspect (e.g.@: its width, @dots{}). The options described
2175 below can be used to control the diagnostic messages formatting
2176 algorithm, e.g.@: how many characters per line, how often source location
2177 information should be reported. Right now, only the C++ front end can
2178 honor these options. However it is expected, in the near future, that
2179 the remaining front ends would be able to digest them correctly.
2182 @item -fmessage-length=@var{n}
2183 @opindex fmessage-length
2184 Try to format error messages so that they fit on lines of about @var{n}
2185 characters. The default is 72 characters for @command{g++} and 0 for the rest of
2186 the front ends supported by GCC@. If @var{n} is zero, then no
2187 line-wrapping will be done; each error message will appear on a single
2190 @opindex fdiagnostics-show-location
2191 @item -fdiagnostics-show-location=once
2192 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
2193 reporter to emit @emph{once} source location information; that is, in
2194 case the message is too long to fit on a single physical line and has to
2195 be wrapped, the source location won't be emitted (as prefix) again,
2196 over and over, in subsequent continuation lines. This is the default
2199 @item -fdiagnostics-show-location=every-line
2200 Only meaningful in line-wrapping mode. Instructs the diagnostic
2201 messages reporter to emit the same source location information (as
2202 prefix) for physical lines that result from the process of breaking
2203 a message which is too long to fit on a single line.
2205 @item -fdiagnostics-show-options
2206 @opindex fdiagnostics-show-options
2207 This option instructs the diagnostic machinery to add text to each
2208 diagnostic emitted, which indicates which command line option directly
2209 controls that diagnostic, when such an option is known to the
2210 diagnostic machinery.
2214 @node Warning Options
2215 @section Options to Request or Suppress Warnings
2216 @cindex options to control warnings
2217 @cindex warning messages
2218 @cindex messages, warning
2219 @cindex suppressing warnings
2221 Warnings are diagnostic messages that report constructions which
2222 are not inherently erroneous but which are risky or suggest there
2223 may have been an error.
2225 You can request many specific warnings with options beginning @samp{-W},
2226 for example @option{-Wimplicit} to request warnings on implicit
2227 declarations. Each of these specific warning options also has a
2228 negative form beginning @samp{-Wno-} to turn off warnings;
2229 for example, @option{-Wno-implicit}. This manual lists only one of the
2230 two forms, whichever is not the default.
2232 The following options control the amount and kinds of warnings produced
2233 by GCC; for further, language-specific options also refer to
2234 @ref{C++ Dialect Options} and @ref{Objective-C and Objective-C++ Dialect
2238 @cindex syntax checking
2240 @opindex fsyntax-only
2241 Check the code for syntax errors, but don't do anything beyond that.
2245 Issue all the warnings demanded by strict ISO C and ISO C++;
2246 reject all programs that use forbidden extensions, and some other
2247 programs that do not follow ISO C and ISO C++. For ISO C, follows the
2248 version of the ISO C standard specified by any @option{-std} option used.
2250 Valid ISO C and ISO C++ programs should compile properly with or without
2251 this option (though a rare few will require @option{-ansi} or a
2252 @option{-std} option specifying the required version of ISO C)@. However,
2253 without this option, certain GNU extensions and traditional C and C++
2254 features are supported as well. With this option, they are rejected.
2256 @option{-pedantic} does not cause warning messages for use of the
2257 alternate keywords whose names begin and end with @samp{__}. Pedantic
2258 warnings are also disabled in the expression that follows
2259 @code{__extension__}. However, only system header files should use
2260 these escape routes; application programs should avoid them.
2261 @xref{Alternate Keywords}.
2263 Some users try to use @option{-pedantic} to check programs for strict ISO
2264 C conformance. They soon find that it does not do quite what they want:
2265 it finds some non-ISO practices, but not all---only those for which
2266 ISO C @emph{requires} a diagnostic, and some others for which
2267 diagnostics have been added.
2269 A feature to report any failure to conform to ISO C might be useful in
2270 some instances, but would require considerable additional work and would
2271 be quite different from @option{-pedantic}. We don't have plans to
2272 support such a feature in the near future.
2274 Where the standard specified with @option{-std} represents a GNU
2275 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
2276 corresponding @dfn{base standard}, the version of ISO C on which the GNU
2277 extended dialect is based. Warnings from @option{-pedantic} are given
2278 where they are required by the base standard. (It would not make sense
2279 for such warnings to be given only for features not in the specified GNU
2280 C dialect, since by definition the GNU dialects of C include all
2281 features the compiler supports with the given option, and there would be
2282 nothing to warn about.)
2284 @item -pedantic-errors
2285 @opindex pedantic-errors
2286 Like @option{-pedantic}, except that errors are produced rather than
2291 Inhibit all warning messages.
2295 Inhibit warning messages about the use of @samp{#import}.
2297 @item -Wchar-subscripts
2298 @opindex Wchar-subscripts
2299 Warn if an array subscript has type @code{char}. This is a common cause
2300 of error, as programmers often forget that this type is signed on some
2302 This warning is enabled by @option{-Wall}.
2306 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
2307 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
2308 This warning is enabled by @option{-Wall}.
2310 @item -Wfatal-errors
2311 @opindex Wfatal-errors
2312 This option causes the compiler to abort compilation on the first error
2313 occurred rather than trying to keep going and printing further error
2318 @opindex ffreestanding
2319 @opindex fno-builtin
2320 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
2321 the arguments supplied have types appropriate to the format string
2322 specified, and that the conversions specified in the format string make
2323 sense. This includes standard functions, and others specified by format
2324 attributes (@pxref{Function Attributes}), in the @code{printf},
2325 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
2326 not in the C standard) families (or other target-specific families).
2327 Which functions are checked without format attributes having been
2328 specified depends on the standard version selected, and such checks of
2329 functions without the attribute specified are disabled by
2330 @option{-ffreestanding} or @option{-fno-builtin}.
2332 The formats are checked against the format features supported by GNU
2333 libc version 2.2. These include all ISO C90 and C99 features, as well
2334 as features from the Single Unix Specification and some BSD and GNU
2335 extensions. Other library implementations may not support all these
2336 features; GCC does not support warning about features that go beyond a
2337 particular library's limitations. However, if @option{-pedantic} is used
2338 with @option{-Wformat}, warnings will be given about format features not
2339 in the selected standard version (but not for @code{strfmon} formats,
2340 since those are not in any version of the C standard). @xref{C Dialect
2341 Options,,Options Controlling C Dialect}.
2343 Since @option{-Wformat} also checks for null format arguments for
2344 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2346 @option{-Wformat} is included in @option{-Wall}. For more control over some
2347 aspects of format checking, the options @option{-Wformat-y2k},
2348 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2349 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2350 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2353 @opindex Wformat-y2k
2354 If @option{-Wformat} is specified, also warn about @code{strftime}
2355 formats which may yield only a two-digit year.
2357 @item -Wno-format-extra-args
2358 @opindex Wno-format-extra-args
2359 If @option{-Wformat} is specified, do not warn about excess arguments to a
2360 @code{printf} or @code{scanf} format function. The C standard specifies
2361 that such arguments are ignored.
2363 Where the unused arguments lie between used arguments that are
2364 specified with @samp{$} operand number specifications, normally
2365 warnings are still given, since the implementation could not know what
2366 type to pass to @code{va_arg} to skip the unused arguments. However,
2367 in the case of @code{scanf} formats, this option will suppress the
2368 warning if the unused arguments are all pointers, since the Single
2369 Unix Specification says that such unused arguments are allowed.
2371 @item -Wno-format-zero-length
2372 @opindex Wno-format-zero-length
2373 If @option{-Wformat} is specified, do not warn about zero-length formats.
2374 The C standard specifies that zero-length formats are allowed.
2376 @item -Wformat-nonliteral
2377 @opindex Wformat-nonliteral
2378 If @option{-Wformat} is specified, also warn if the format string is not a
2379 string literal and so cannot be checked, unless the format function
2380 takes its format arguments as a @code{va_list}.
2382 @item -Wformat-security
2383 @opindex Wformat-security
2384 If @option{-Wformat} is specified, also warn about uses of format
2385 functions that represent possible security problems. At present, this
2386 warns about calls to @code{printf} and @code{scanf} functions where the
2387 format string is not a string literal and there are no format arguments,
2388 as in @code{printf (foo);}. This may be a security hole if the format
2389 string came from untrusted input and contains @samp{%n}. (This is
2390 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2391 in future warnings may be added to @option{-Wformat-security} that are not
2392 included in @option{-Wformat-nonliteral}.)
2396 Enable @option{-Wformat} plus format checks not included in
2397 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2398 -Wformat-nonliteral -Wformat-security -Wformat-y2k}.
2402 Warn about passing a null pointer for arguments marked as
2403 requiring a non-null value by the @code{nonnull} function attribute.
2405 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2406 can be disabled with the @option{-Wno-nonnull} option.
2408 @item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
2410 Warn about uninitialized variables which are initialized with themselves.
2411 Note this option can only be used with the @option{-Wuninitialized} option,
2412 which in turn only works with @option{-O1} and above.
2414 For example, GCC will warn about @code{i} being uninitialized in the
2415 following snippet only when @option{-Winit-self} has been specified:
2426 @item -Wimplicit-int
2427 @opindex Wimplicit-int
2428 Warn when a declaration does not specify a type.
2429 This warning is enabled by @option{-Wall}.
2431 @item -Wimplicit-function-declaration
2432 @itemx -Werror-implicit-function-declaration
2433 @opindex Wimplicit-function-declaration
2434 @opindex Werror-implicit-function-declaration
2435 Give a warning (or error) whenever a function is used before being
2436 declared. The form @option{-Wno-error-implicit-function-declaration}
2438 This warning is enabled by @option{-Wall} (as a warning, not an error).
2442 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2443 This warning is enabled by @option{-Wall}.
2447 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
2448 function with external linkage, returning int, taking either zero
2449 arguments, two, or three arguments of appropriate types.
2450 This warning is enabled by @option{-Wall}.
2452 @item -Wmissing-braces
2453 @opindex Wmissing-braces
2454 Warn if an aggregate or union initializer is not fully bracketed. In
2455 the following example, the initializer for @samp{a} is not fully
2456 bracketed, but that for @samp{b} is fully bracketed.
2459 int a[2][2] = @{ 0, 1, 2, 3 @};
2460 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2463 This warning is enabled by @option{-Wall}.
2465 @item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)}
2466 @opindex Wmissing-include-dirs
2467 Warn if a user-supplied include directory does not exist.
2470 @opindex Wparentheses
2471 Warn if parentheses are omitted in certain contexts, such
2472 as when there is an assignment in a context where a truth value
2473 is expected, or when operators are nested whose precedence people
2474 often get confused about. Only the warning for an assignment used as
2475 a truth value is supported when compiling C++; the other warnings are
2476 only supported when compiling C@.
2478 Also warn if a comparison like @samp{x<=y<=z} appears; this is
2479 equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different
2480 interpretation from that of ordinary mathematical notation.
2482 Also warn about constructions where there may be confusion to which
2483 @code{if} statement an @code{else} branch belongs. Here is an example of
2498 In C, every @code{else} branch belongs to the innermost possible @code{if}
2499 statement, which in this example is @code{if (b)}. This is often not
2500 what the programmer expected, as illustrated in the above example by
2501 indentation the programmer chose. When there is the potential for this
2502 confusion, GCC will issue a warning when this flag is specified.
2503 To eliminate the warning, add explicit braces around the innermost
2504 @code{if} statement so there is no way the @code{else} could belong to
2505 the enclosing @code{if}. The resulting code would look like this:
2521 This warning is enabled by @option{-Wall}.
2523 @item -Wsequence-point
2524 @opindex Wsequence-point
2525 Warn about code that may have undefined semantics because of violations
2526 of sequence point rules in the C standard.
2528 The C standard defines the order in which expressions in a C program are
2529 evaluated in terms of @dfn{sequence points}, which represent a partial
2530 ordering between the execution of parts of the program: those executed
2531 before the sequence point, and those executed after it. These occur
2532 after the evaluation of a full expression (one which is not part of a
2533 larger expression), after the evaluation of the first operand of a
2534 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
2535 function is called (but after the evaluation of its arguments and the
2536 expression denoting the called function), and in certain other places.
2537 Other than as expressed by the sequence point rules, the order of
2538 evaluation of subexpressions of an expression is not specified. All
2539 these rules describe only a partial order rather than a total order,
2540 since, for example, if two functions are called within one expression
2541 with no sequence point between them, the order in which the functions
2542 are called is not specified. However, the standards committee have
2543 ruled that function calls do not overlap.
2545 It is not specified when between sequence points modifications to the
2546 values of objects take effect. Programs whose behavior depends on this
2547 have undefined behavior; the C standard specifies that ``Between the
2548 previous and next sequence point an object shall have its stored value
2549 modified at most once by the evaluation of an expression. Furthermore,
2550 the prior value shall be read only to determine the value to be
2551 stored.''. If a program breaks these rules, the results on any
2552 particular implementation are entirely unpredictable.
2554 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
2555 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
2556 diagnosed by this option, and it may give an occasional false positive
2557 result, but in general it has been found fairly effective at detecting
2558 this sort of problem in programs.
2560 The present implementation of this option only works for C programs. A
2561 future implementation may also work for C++ programs.
2563 The C standard is worded confusingly, therefore there is some debate
2564 over the precise meaning of the sequence point rules in subtle cases.
2565 Links to discussions of the problem, including proposed formal
2566 definitions, may be found on the GCC readings page, at
2567 @w{@uref{http://gcc.gnu.org/readings.html}}.
2569 This warning is enabled by @option{-Wall}.
2572 @opindex Wreturn-type
2573 Warn whenever a function is defined with a return-type that defaults to
2574 @code{int}. Also warn about any @code{return} statement with no
2575 return-value in a function whose return-type is not @code{void}.
2577 For C, also warn if the return type of a function has a type qualifier
2578 such as @code{const}. Such a type qualifier has no effect, since the
2579 value returned by a function is not an lvalue. ISO C prohibits
2580 qualified @code{void} return types on function definitions, so such
2581 return types always receive a warning even without this option.
2583 For C++, a function without return type always produces a diagnostic
2584 message, even when @option{-Wno-return-type} is specified. The only
2585 exceptions are @samp{main} and functions defined in system headers.
2587 This warning is enabled by @option{-Wall}.
2591 Warn whenever a @code{switch} statement has an index of enumerated type
2592 and lacks a @code{case} for one or more of the named codes of that
2593 enumeration. (The presence of a @code{default} label prevents this
2594 warning.) @code{case} labels outside the enumeration range also
2595 provoke warnings when this option is used.
2596 This warning is enabled by @option{-Wall}.
2598 @item -Wswitch-default
2599 @opindex Wswitch-switch
2600 Warn whenever a @code{switch} statement does not have a @code{default}
2604 @opindex Wswitch-enum
2605 Warn whenever a @code{switch} statement has an index of enumerated type
2606 and lacks a @code{case} for one or more of the named codes of that
2607 enumeration. @code{case} labels outside the enumeration range also
2608 provoke warnings when this option is used.
2612 Warn if any trigraphs are encountered that might change the meaning of
2613 the program (trigraphs within comments are not warned about).
2614 This warning is enabled by @option{-Wall}.
2616 @item -Wunused-function
2617 @opindex Wunused-function
2618 Warn whenever a static function is declared but not defined or a
2619 non-inline static function is unused.
2620 This warning is enabled by @option{-Wall}.
2622 @item -Wunused-label
2623 @opindex Wunused-label
2624 Warn whenever a label is declared but not used.
2625 This warning is enabled by @option{-Wall}.
2627 To suppress this warning use the @samp{unused} attribute
2628 (@pxref{Variable Attributes}).
2630 @item -Wunused-parameter
2631 @opindex Wunused-parameter
2632 Warn whenever a function parameter is unused aside from its declaration.
2634 To suppress this warning use the @samp{unused} attribute
2635 (@pxref{Variable Attributes}).
2637 @item -Wunused-variable
2638 @opindex Wunused-variable
2639 Warn whenever a local variable or non-constant static variable is unused
2640 aside from its declaration
2641 This warning is enabled by @option{-Wall}.
2643 To suppress this warning use the @samp{unused} attribute
2644 (@pxref{Variable Attributes}).
2646 @item -Wunused-value
2647 @opindex Wunused-value
2648 Warn whenever a statement computes a result that is explicitly not used.
2649 This warning is enabled by @option{-Wall}.
2651 To suppress this warning cast the expression to @samp{void}.
2655 All the above @option{-Wunused} options combined.
2657 In order to get a warning about an unused function parameter, you must
2658 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
2659 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
2661 @item -Wuninitialized
2662 @opindex Wuninitialized
2663 Warn if an automatic variable is used without first being initialized or
2664 if a variable may be clobbered by a @code{setjmp} call.
2666 These warnings are possible only in optimizing compilation,
2667 because they require data flow information that is computed only
2668 when optimizing. If you don't specify @option{-O}, you simply won't
2671 If you want to warn about code which uses the uninitialized value of the
2672 variable in its own initializer, use the @option{-Winit-self} option.
2674 These warnings occur for individual uninitialized or clobbered
2675 elements of structure, union or array variables as well as for
2676 variables which are uninitialized or clobbered as a whole. They do
2677 not occur for variables or elements declared @code{volatile}. Because
2678 these warnings depend on optimization, the exact variables or elements
2679 for which there are warnings will depend on the precise optimization
2680 options and version of GCC used.
2682 Note that there may be no warning about a variable that is used only
2683 to compute a value that itself is never used, because such
2684 computations may be deleted by data flow analysis before the warnings
2687 These warnings are made optional because GCC is not smart
2688 enough to see all the reasons why the code might be correct
2689 despite appearing to have an error. Here is one example of how
2710 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
2711 always initialized, but GCC doesn't know this. Here is
2712 another common case:
2717 if (change_y) save_y = y, y = new_y;
2719 if (change_y) y = save_y;
2724 This has no bug because @code{save_y} is used only if it is set.
2726 @cindex @code{longjmp} warnings
2727 This option also warns when a non-volatile automatic variable might be
2728 changed by a call to @code{longjmp}. These warnings as well are possible
2729 only in optimizing compilation.
2731 The compiler sees only the calls to @code{setjmp}. It cannot know
2732 where @code{longjmp} will be called; in fact, a signal handler could
2733 call it at any point in the code. As a result, you may get a warning
2734 even when there is in fact no problem because @code{longjmp} cannot
2735 in fact be called at the place which would cause a problem.
2737 Some spurious warnings can be avoided if you declare all the functions
2738 you use that never return as @code{noreturn}. @xref{Function
2741 This warning is enabled by @option{-Wall}.
2743 @item -Wunknown-pragmas
2744 @opindex Wunknown-pragmas
2745 @cindex warning for unknown pragmas
2746 @cindex unknown pragmas, warning
2747 @cindex pragmas, warning of unknown
2748 Warn when a #pragma directive is encountered which is not understood by
2749 GCC@. If this command line option is used, warnings will even be issued
2750 for unknown pragmas in system header files. This is not the case if
2751 the warnings were only enabled by the @option{-Wall} command line option.
2754 @opindex Wno-pragmas
2756 Do not warn about misuses of pragmas, such as incorrect parameters,
2757 invalid syntax, or conflicts between pragmas. See also
2758 @samp{-Wunknown-pragmas}.
2760 @item -Wstrict-aliasing
2761 @opindex Wstrict-aliasing
2762 This option is only active when @option{-fstrict-aliasing} is active.
2763 It warns about code which might break the strict aliasing rules that the
2764 compiler is using for optimization. The warning does not catch all
2765 cases, but does attempt to catch the more common pitfalls. It is
2766 included in @option{-Wall}.
2768 @item -Wstrict-aliasing=2
2769 @opindex Wstrict-aliasing=2
2770 This option is only active when @option{-fstrict-aliasing} is active.
2771 It warns about code which might break the strict aliasing rules that the
2772 compiler is using for optimization. This warning catches more cases than
2773 @option{-Wstrict-aliasing}, but it will also give a warning for some ambiguous
2774 cases that are safe.
2778 All of the above @samp{-W} options combined. This enables all the
2779 warnings about constructions that some users consider questionable, and
2780 that are easy to avoid (or modify to prevent the warning), even in
2781 conjunction with macros. This also enables some language-specific
2782 warnings described in @ref{C++ Dialect Options} and
2783 @ref{Objective-C and Objective-C++ Dialect Options}.
2786 The following @option{-W@dots{}} options are not implied by @option{-Wall}.
2787 Some of them warn about constructions that users generally do not
2788 consider questionable, but which occasionally you might wish to check
2789 for; others warn about constructions that are necessary or hard to avoid
2790 in some cases, and there is no simple way to modify the code to suppress
2797 (This option used to be called @option{-W}. The older name is still
2798 supported, but the newer name is more descriptive.) Print extra warning
2799 messages for these events:
2803 A function can return either with or without a value. (Falling
2804 off the end of the function body is considered returning without
2805 a value.) For example, this function would evoke such a
2819 An expression-statement or the left-hand side of a comma expression
2820 contains no side effects.
2821 To suppress the warning, cast the unused expression to void.
2822 For example, an expression such as @samp{x[i,j]} will cause a warning,
2823 but @samp{x[(void)i,j]} will not.
2826 An unsigned value is compared against zero with @samp{<} or @samp{>=}.
2829 Storage-class specifiers like @code{static} are not the first things in
2830 a declaration. According to the C Standard, this usage is obsolescent.
2833 If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
2837 A comparison between signed and unsigned values could produce an
2838 incorrect result when the signed value is converted to unsigned.
2839 (But don't warn if @option{-Wno-sign-compare} is also specified.)
2842 An aggregate has an initializer which does not initialize all members.
2843 This warning can be independently controlled by
2844 @option{-Wmissing-field-initializers}.
2847 A function parameter is declared without a type specifier in K&R-style
2855 An empty body occurs in an @samp{if} or @samp{else} statement.
2858 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2859 @samp{>}, or @samp{>=}.
2862 A variable might be changed by @samp{longjmp} or @samp{vfork}.
2865 Any of several floating-point events that often indicate errors, such as
2866 overflow, underflow, loss of precision, etc.
2868 @item @r{(C++ only)}
2869 An enumerator and a non-enumerator both appear in a conditional expression.
2871 @item @r{(C++ only)}
2872 A non-static reference or non-static @samp{const} member appears in a
2873 class without constructors.
2875 @item @r{(C++ only)}
2876 Ambiguous virtual bases.
2878 @item @r{(C++ only)}
2879 Subscripting an array which has been declared @samp{register}.
2881 @item @r{(C++ only)}
2882 Taking the address of a variable which has been declared @samp{register}.
2884 @item @r{(C++ only)}
2885 A base class is not initialized in a derived class' copy constructor.
2888 @item -Wno-div-by-zero
2889 @opindex Wno-div-by-zero
2890 @opindex Wdiv-by-zero
2891 Do not warn about compile-time integer division by zero. Floating point
2892 division by zero is not warned about, as it can be a legitimate way of
2893 obtaining infinities and NaNs.
2895 @item -Wsystem-headers
2896 @opindex Wsystem-headers
2897 @cindex warnings from system headers
2898 @cindex system headers, warnings from
2899 Print warning messages for constructs found in system header files.
2900 Warnings from system headers are normally suppressed, on the assumption
2901 that they usually do not indicate real problems and would only make the
2902 compiler output harder to read. Using this command line option tells
2903 GCC to emit warnings from system headers as if they occurred in user
2904 code. However, note that using @option{-Wall} in conjunction with this
2905 option will @emph{not} warn about unknown pragmas in system
2906 headers---for that, @option{-Wunknown-pragmas} must also be used.
2909 @opindex Wfloat-equal
2910 Warn if floating point values are used in equality comparisons.
2912 The idea behind this is that sometimes it is convenient (for the
2913 programmer) to consider floating-point values as approximations to
2914 infinitely precise real numbers. If you are doing this, then you need
2915 to compute (by analyzing the code, or in some other way) the maximum or
2916 likely maximum error that the computation introduces, and allow for it
2917 when performing comparisons (and when producing output, but that's a
2918 different problem). In particular, instead of testing for equality, you
2919 would check to see whether the two values have ranges that overlap; and
2920 this is done with the relational operators, so equality comparisons are
2923 @item -Wtraditional @r{(C only)}
2924 @opindex Wtraditional
2925 Warn about certain constructs that behave differently in traditional and
2926 ISO C@. Also warn about ISO C constructs that have no traditional C
2927 equivalent, and/or problematic constructs which should be avoided.
2931 Macro parameters that appear within string literals in the macro body.
2932 In traditional C macro replacement takes place within string literals,
2933 but does not in ISO C@.
2936 In traditional C, some preprocessor directives did not exist.
2937 Traditional preprocessors would only consider a line to be a directive
2938 if the @samp{#} appeared in column 1 on the line. Therefore
2939 @option{-Wtraditional} warns about directives that traditional C
2940 understands but would ignore because the @samp{#} does not appear as the
2941 first character on the line. It also suggests you hide directives like
2942 @samp{#pragma} not understood by traditional C by indenting them. Some
2943 traditional implementations would not recognize @samp{#elif}, so it
2944 suggests avoiding it altogether.
2947 A function-like macro that appears without arguments.
2950 The unary plus operator.
2953 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
2954 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
2955 constants.) Note, these suffixes appear in macros defined in the system
2956 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
2957 Use of these macros in user code might normally lead to spurious
2958 warnings, however GCC's integrated preprocessor has enough context to
2959 avoid warning in these cases.
2962 A function declared external in one block and then used after the end of
2966 A @code{switch} statement has an operand of type @code{long}.
2969 A non-@code{static} function declaration follows a @code{static} one.
2970 This construct is not accepted by some traditional C compilers.
2973 The ISO type of an integer constant has a different width or
2974 signedness from its traditional type. This warning is only issued if
2975 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
2976 typically represent bit patterns, are not warned about.
2979 Usage of ISO string concatenation is detected.
2982 Initialization of automatic aggregates.
2985 Identifier conflicts with labels. Traditional C lacks a separate
2986 namespace for labels.
2989 Initialization of unions. If the initializer is zero, the warning is
2990 omitted. This is done under the assumption that the zero initializer in
2991 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
2992 initializer warnings and relies on default initialization to zero in the
2996 Conversions by prototypes between fixed/floating point values and vice
2997 versa. The absence of these prototypes when compiling with traditional
2998 C would cause serious problems. This is a subset of the possible
2999 conversion warnings, for the full set use @option{-Wconversion}.
3002 Use of ISO C style function definitions. This warning intentionally is
3003 @emph{not} issued for prototype declarations or variadic functions
3004 because these ISO C features will appear in your code when using
3005 libiberty's traditional C compatibility macros, @code{PARAMS} and
3006 @code{VPARAMS}. This warning is also bypassed for nested functions
3007 because that feature is already a GCC extension and thus not relevant to
3008 traditional C compatibility.
3011 @item -Wdeclaration-after-statement @r{(C only)}
3012 @opindex Wdeclaration-after-statement
3013 Warn when a declaration is found after a statement in a block. This
3014 construct, known from C++, was introduced with ISO C99 and is by default
3015 allowed in GCC@. It is not supported by ISO C90 and was not supported by
3016 GCC versions before GCC 3.0. @xref{Mixed Declarations}.
3020 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
3022 @item -Wno-endif-labels
3023 @opindex Wno-endif-labels
3024 @opindex Wendif-labels
3025 Do not warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
3029 Warn whenever a local variable shadows another local variable, parameter or
3030 global variable or whenever a built-in function is shadowed.
3032 @item -Wlarger-than-@var{len}
3033 @opindex Wlarger-than
3034 Warn whenever an object of larger than @var{len} bytes is defined.
3036 @item -Wunsafe-loop-optimizations
3037 @opindex Wunsafe-loop-optimizations
3038 Warn if the loop cannot be optimized because the compiler could not
3039 assume anything on the bounds of the loop indices. With
3040 @option{-funsafe-loop-optimizations} warn if the compiler made
3043 @item -Wpointer-arith
3044 @opindex Wpointer-arith
3045 Warn about anything that depends on the ``size of'' a function type or
3046 of @code{void}. GNU C assigns these types a size of 1, for
3047 convenience in calculations with @code{void *} pointers and pointers
3050 @item -Wbad-function-cast @r{(C only)}
3051 @opindex Wbad-function-cast
3052 Warn whenever a function call is cast to a non-matching type.
3053 For example, warn if @code{int malloc()} is cast to @code{anything *}.
3056 Warn about ISO C constructs that are outside of the common subset of
3057 ISO C and ISO C++, e.g.@: request for implicit conversion from
3058 @code{void *} to a pointer to non-@code{void} type.
3062 Warn whenever a pointer is cast so as to remove a type qualifier from
3063 the target type. For example, warn if a @code{const char *} is cast
3064 to an ordinary @code{char *}.
3067 @opindex Wcast-align
3068 Warn whenever a pointer is cast such that the required alignment of the
3069 target is increased. For example, warn if a @code{char *} is cast to
3070 an @code{int *} on machines where integers can only be accessed at
3071 two- or four-byte boundaries.
3073 @item -Wwrite-strings
3074 @opindex Wwrite-strings
3075 When compiling C, give string constants the type @code{const
3076 char[@var{length}]} so that
3077 copying the address of one into a non-@code{const} @code{char *}
3078 pointer will get a warning; when compiling C++, warn about the
3079 deprecated conversion from string constants to @code{char *}.
3080 These warnings will help you find at
3081 compile time code that can try to write into a string constant, but
3082 only if you have been very careful about using @code{const} in
3083 declarations and prototypes. Otherwise, it will just be a nuisance;
3084 this is why we did not make @option{-Wall} request these warnings.
3087 @opindex Wconversion
3088 Warn if a prototype causes a type conversion that is different from what
3089 would happen to the same argument in the absence of a prototype. This
3090 includes conversions of fixed point to floating and vice versa, and
3091 conversions changing the width or signedness of a fixed point argument
3092 except when the same as the default promotion.
3094 Also, warn if a negative integer constant expression is implicitly
3095 converted to an unsigned type. For example, warn about the assignment
3096 @code{x = -1} if @code{x} is unsigned. But do not warn about explicit
3097 casts like @code{(unsigned) -1}.
3099 @item -Wsign-compare
3100 @opindex Wsign-compare
3101 @cindex warning for comparison of signed and unsigned values
3102 @cindex comparison of signed and unsigned values, warning
3103 @cindex signed and unsigned values, comparison warning
3104 Warn when a comparison between signed and unsigned values could produce
3105 an incorrect result when the signed value is converted to unsigned.
3106 This warning is also enabled by @option{-Wextra}; to get the other warnings
3107 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
3109 @item -Waggregate-return
3110 @opindex Waggregate-return
3111 Warn if any functions that return structures or unions are defined or
3112 called. (In languages where you can return an array, this also elicits
3115 @item -Wno-attributes
3116 @opindex Wno-attributes
3117 @opindex Wattributes
3118 Do not warn if an unexpected @code{__attribute__} is used, such as
3119 unrecognized attributes, function attributes applied to variables,
3120 etc. This will not stop errors for incorrect use of supported
3123 @item -Wstrict-prototypes @r{(C only)}
3124 @opindex Wstrict-prototypes
3125 Warn if a function is declared or defined without specifying the
3126 argument types. (An old-style function definition is permitted without
3127 a warning if preceded by a declaration which specifies the argument
3130 @item -Wold-style-definition @r{(C only)}
3131 @opindex Wold-style-definition
3132 Warn if an old-style function definition is used. A warning is given
3133 even if there is a previous prototype.
3135 @item -Wmissing-prototypes @r{(C only)}
3136 @opindex Wmissing-prototypes
3137 Warn if a global function is defined without a previous prototype
3138 declaration. This warning is issued even if the definition itself
3139 provides a prototype. The aim is to detect global functions that fail
3140 to be declared in header files.
3142 @item -Wmissing-declarations @r{(C only)}
3143 @opindex Wmissing-declarations
3144 Warn if a global function is defined without a previous declaration.
3145 Do so even if the definition itself provides a prototype.
3146 Use this option to detect global functions that are not declared in
3149 @item -Wmissing-field-initializers
3150 @opindex Wmissing-field-initializers
3153 Warn if a structure's initializer has some fields missing. For
3154 example, the following code would cause such a warning, because
3155 @code{x.h} is implicitly zero:
3158 struct s @{ int f, g, h; @};
3159 struct s x = @{ 3, 4 @};
3162 This option does not warn about designated initializers, so the following
3163 modification would not trigger a warning:
3166 struct s @{ int f, g, h; @};
3167 struct s x = @{ .f = 3, .g = 4 @};
3170 This warning is included in @option{-Wextra}. To get other @option{-Wextra}
3171 warnings without this one, use @samp{-Wextra -Wno-missing-field-initializers}.
3173 @item -Wmissing-noreturn
3174 @opindex Wmissing-noreturn
3175 Warn about functions which might be candidates for attribute @code{noreturn}.
3176 Note these are only possible candidates, not absolute ones. Care should
3177 be taken to manually verify functions actually do not ever return before
3178 adding the @code{noreturn} attribute, otherwise subtle code generation
3179 bugs could be introduced. You will not get a warning for @code{main} in
3180 hosted C environments.
3182 @item -Wmissing-format-attribute
3183 @opindex Wmissing-format-attribute
3185 Warn about function pointers which might be candidates for @code{format}
3186 attributes. Note these are only possible candidates, not absolute ones.
3187 GCC will guess that function pointers with @code{format} attributes that
3188 are used in assignment, initialization, parameter passing or return
3189 statements should have a corresponding @code{format} attribute in the
3190 resulting type. I.e.@: the left-hand side of the assignment or
3191 initialization, the type of the parameter variable, or the return type
3192 of the containing function respectively should also have a @code{format}
3193 attribute to avoid the warning.
3195 GCC will also warn about function definitions which might be
3196 candidates for @code{format} attributes. Again, these are only
3197 possible candidates. GCC will guess that @code{format} attributes
3198 might be appropriate for any function that calls a function like
3199 @code{vprintf} or @code{vscanf}, but this might not always be the
3200 case, and some functions for which @code{format} attributes are
3201 appropriate may not be detected.
3203 @item -Wno-multichar
3204 @opindex Wno-multichar
3206 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
3207 Usually they indicate a typo in the user's code, as they have
3208 implementation-defined values, and should not be used in portable code.
3210 @item -Wnormalized=<none|id|nfc|nfkc>
3211 @opindex Wnormalized
3214 @cindex character set, input normalization
3215 In ISO C and ISO C++, two identifiers are different if they are
3216 different sequences of characters. However, sometimes when characters
3217 outside the basic ASCII character set are used, you can have two
3218 different character sequences that look the same. To avoid confusion,
3219 the ISO 10646 standard sets out some @dfn{normalization rules} which
3220 when applied ensure that two sequences that look the same are turned into
3221 the same sequence. GCC can warn you if you are using identifiers which
3222 have not been normalized; this option controls that warning.
3224 There are four levels of warning that GCC supports. The default is
3225 @option{-Wnormalized=nfc}, which warns about any identifier which is
3226 not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the
3227 recommended form for most uses.
3229 Unfortunately, there are some characters which ISO C and ISO C++ allow
3230 in identifiers that when turned into NFC aren't allowable as
3231 identifiers. That is, there's no way to use these symbols in portable
3232 ISO C or C++ and have all your identifiers in NFC.
3233 @option{-Wnormalized=id} suppresses the warning for these characters.
3234 It is hoped that future versions of the standards involved will correct
3235 this, which is why this option is not the default.
3237 You can switch the warning off for all characters by writing
3238 @option{-Wnormalized=none}. You would only want to do this if you
3239 were using some other normalization scheme (like ``D''), because
3240 otherwise you can easily create bugs that are literally impossible to see.
3242 Some characters in ISO 10646 have distinct meanings but look identical
3243 in some fonts or display methodologies, especially once formatting has
3244 been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL
3245 LETTER N'', will display just like a regular @code{n} which has been
3246 placed in a superscript. ISO 10646 defines the @dfn{NFKC}
3247 normalisation scheme to convert all these into a standard form as
3248 well, and GCC will warn if your code is not in NFKC if you use
3249 @option{-Wnormalized=nfkc}. This warning is comparable to warning
3250 about every identifier that contains the letter O because it might be
3251 confused with the digit 0, and so is not the default, but may be
3252 useful as a local coding convention if the programming environment is
3253 unable to be fixed to display these characters distinctly.
3255 @item -Wno-deprecated-declarations
3256 @opindex Wno-deprecated-declarations
3257 Do not warn about uses of functions, variables, and types marked as
3258 deprecated by using the @code{deprecated} attribute.
3259 (@pxref{Function Attributes}, @pxref{Variable Attributes},
3260 @pxref{Type Attributes}.)
3264 Warn if a structure is given the packed attribute, but the packed
3265 attribute has no effect on the layout or size of the structure.
3266 Such structures may be mis-aligned for little benefit. For
3267 instance, in this code, the variable @code{f.x} in @code{struct bar}
3268 will be misaligned even though @code{struct bar} does not itself
3269 have the packed attribute:
3276 @} __attribute__((packed));
3286 Warn if padding is included in a structure, either to align an element
3287 of the structure or to align the whole structure. Sometimes when this
3288 happens it is possible to rearrange the fields of the structure to
3289 reduce the padding and so make the structure smaller.
3291 @item -Wredundant-decls
3292 @opindex Wredundant-decls
3293 Warn if anything is declared more than once in the same scope, even in
3294 cases where multiple declaration is valid and changes nothing.
3296 @item -Wnested-externs @r{(C only)}
3297 @opindex Wnested-externs
3298 Warn if an @code{extern} declaration is encountered within a function.
3300 @item -Wunreachable-code
3301 @opindex Wunreachable-code
3302 Warn if the compiler detects that code will never be executed.
3304 This option is intended to warn when the compiler detects that at
3305 least a whole line of source code will never be executed, because
3306 some condition is never satisfied or because it is after a
3307 procedure that never returns.
3309 It is possible for this option to produce a warning even though there
3310 are circumstances under which part of the affected line can be executed,
3311 so care should be taken when removing apparently-unreachable code.
3313 For instance, when a function is inlined, a warning may mean that the
3314 line is unreachable in only one inlined copy of the function.
3316 This option is not made part of @option{-Wall} because in a debugging
3317 version of a program there is often substantial code which checks
3318 correct functioning of the program and is, hopefully, unreachable
3319 because the program does work. Another common use of unreachable
3320 code is to provide behavior which is selectable at compile-time.
3324 Warn if a function can not be inlined and it was declared as inline.
3325 Even with this option, the compiler will not warn about failures to
3326 inline functions declared in system headers.
3328 The compiler uses a variety of heuristics to determine whether or not
3329 to inline a function. For example, the compiler takes into account
3330 the size of the function being inlined and the amount of inlining
3331 that has already been done in the current function. Therefore,
3332 seemingly insignificant changes in the source program can cause the
3333 warnings produced by @option{-Winline} to appear or disappear.
3335 @item -Wno-invalid-offsetof @r{(C++ only)}
3336 @opindex Wno-invalid-offsetof
3337 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
3338 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
3339 to a non-POD type is undefined. In existing C++ implementations,
3340 however, @samp{offsetof} typically gives meaningful results even when
3341 applied to certain kinds of non-POD types. (Such as a simple
3342 @samp{struct} that fails to be a POD type only by virtue of having a
3343 constructor.) This flag is for users who are aware that they are
3344 writing nonportable code and who have deliberately chosen to ignore the
3347 The restrictions on @samp{offsetof} may be relaxed in a future version
3348 of the C++ standard.
3350 @item -Wno-int-to-pointer-cast @r{(C only)}
3351 @opindex Wno-int-to-pointer-cast
3352 Suppress warnings from casts to pointer type of an integer of a
3355 @item -Wno-pointer-to-int-cast @r{(C only)}
3356 @opindex Wno-pointer-to-int-cast
3357 Suppress warnings from casts from a pointer to an integer type of a
3361 @opindex Winvalid-pch
3362 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
3363 the search path but can't be used.
3367 @opindex Wno-long-long
3368 Warn if @samp{long long} type is used. This is default. To inhibit
3369 the warning messages, use @option{-Wno-long-long}. Flags
3370 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
3371 only when @option{-pedantic} flag is used.
3373 @item -Wvariadic-macros
3374 @opindex Wvariadic-macros
3375 @opindex Wno-variadic-macros
3376 Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU
3377 alternate syntax when in pedantic ISO C99 mode. This is default.
3378 To inhibit the warning messages, use @option{-Wno-variadic-macros}.
3380 @item -Wvolatile-register-var
3381 @opindex Wvolatile-register-var
3382 @opindex Wno-volatile-register-var
3383 Warn if a register variable is declared volatile. The volatile
3384 modifier does not inhibit all optimizations that may eliminate reads
3385 and/or writes to register variables.
3387 @item -Wdisabled-optimization
3388 @opindex Wdisabled-optimization
3389 Warn if a requested optimization pass is disabled. This warning does
3390 not generally indicate that there is anything wrong with your code; it
3391 merely indicates that GCC's optimizers were unable to handle the code
3392 effectively. Often, the problem is that your code is too big or too
3393 complex; GCC will refuse to optimize programs when the optimization
3394 itself is likely to take inordinate amounts of time.
3396 @item -Wno-pointer-sign
3397 @opindex Wno-pointer-sign
3398 Don't warn for pointer argument passing or assignment with different signedness.
3399 Only useful in the negative form since this warning is enabled by default.
3400 This option is only supported for C and Objective-C@.
3404 Make all warnings into errors.
3406 @item -Wstack-protector
3407 @opindex Wstack-protector
3408 This option is only active when @option{-fstack-protector} is active. It
3409 warns about functions that will not be protected against stack smashing.
3411 @item -Wstring-literal-comparison
3412 @opindex Wstring-literal-comparison
3413 Warn about suspicious comparisons to string literal constants. In C,
3414 direct comparisons against the memory address of a string literal, such
3415 as @code{if (x == "abc")}, typically indicate a programmer error, and
3416 even when intentional, result in unspecified behavior and are not portable.
3417 Usually these warnings alert that the programmer intended to use
3418 @code{strcmp}. This warning is enabled by @option{-Wall}.
3422 @node Debugging Options
3423 @section Options for Debugging Your Program or GCC
3424 @cindex options, debugging
3425 @cindex debugging information options
3427 GCC has various special options that are used for debugging
3428 either your program or GCC:
3433 Produce debugging information in the operating system's native format
3434 (stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging
3437 On most systems that use stabs format, @option{-g} enables use of extra
3438 debugging information that only GDB can use; this extra information
3439 makes debugging work better in GDB but will probably make other debuggers
3441 refuse to read the program. If you want to control for certain whether
3442 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
3443 @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
3445 GCC allows you to use @option{-g} with
3446 @option{-O}. The shortcuts taken by optimized code may occasionally
3447 produce surprising results: some variables you declared may not exist
3448 at all; flow of control may briefly move where you did not expect it;
3449 some statements may not be executed because they compute constant
3450 results or their values were already at hand; some statements may
3451 execute in different places because they were moved out of loops.
3453 Nevertheless it proves possible to debug optimized output. This makes
3454 it reasonable to use the optimizer for programs that might have bugs.
3456 The following options are useful when GCC is generated with the
3457 capability for more than one debugging format.
3461 Produce debugging information for use by GDB@. This means to use the
3462 most expressive format available (DWARF 2, stabs, or the native format
3463 if neither of those are supported), including GDB extensions if at all
3468 Produce debugging information in stabs format (if that is supported),
3469 without GDB extensions. This is the format used by DBX on most BSD
3470 systems. On MIPS, Alpha and System V Release 4 systems this option
3471 produces stabs debugging output which is not understood by DBX or SDB@.
3472 On System V Release 4 systems this option requires the GNU assembler.
3474 @item -feliminate-unused-debug-symbols
3475 @opindex feliminate-unused-debug-symbols
3476 Produce debugging information in stabs format (if that is supported),
3477 for only symbols that are actually used.
3481 Produce debugging information in stabs format (if that is supported),
3482 using GNU extensions understood only by the GNU debugger (GDB)@. The
3483 use of these extensions is likely to make other debuggers crash or
3484 refuse to read the program.
3488 Produce debugging information in COFF format (if that is supported).
3489 This is the format used by SDB on most System V systems prior to
3494 Produce debugging information in XCOFF format (if that is supported).
3495 This is the format used by the DBX debugger on IBM RS/6000 systems.
3499 Produce debugging information in XCOFF format (if that is supported),
3500 using GNU extensions understood only by the GNU debugger (GDB)@. The
3501 use of these extensions is likely to make other debuggers crash or
3502 refuse to read the program, and may cause assemblers other than the GNU
3503 assembler (GAS) to fail with an error.
3507 Produce debugging information in DWARF version 2 format (if that is
3508 supported). This is the format used by DBX on IRIX 6. With this
3509 option, GCC uses features of DWARF version 3 when they are useful;
3510 version 3 is upward compatible with version 2, but may still cause
3511 problems for older debuggers.
3515 Produce debugging information in VMS debug format (if that is
3516 supported). This is the format used by DEBUG on VMS systems.
3519 @itemx -ggdb@var{level}
3520 @itemx -gstabs@var{level}
3521 @itemx -gcoff@var{level}
3522 @itemx -gxcoff@var{level}
3523 @itemx -gvms@var{level}
3524 Request debugging information and also use @var{level} to specify how
3525 much information. The default level is 2.
3527 Level 1 produces minimal information, enough for making backtraces in
3528 parts of the program that you don't plan to debug. This includes
3529 descriptions of functions and external variables, but no information
3530 about local variables and no line numbers.
3532 Level 3 includes extra information, such as all the macro definitions
3533 present in the program. Some debuggers support macro expansion when
3534 you use @option{-g3}.
3536 @option{-gdwarf-2} does not accept a concatenated debug level, because
3537 GCC used to support an option @option{-gdwarf} that meant to generate
3538 debug information in version 1 of the DWARF format (which is very
3539 different from version 2), and it would have been too confusing. That
3540 debug format is long obsolete, but the option cannot be changed now.
3541 Instead use an additional @option{-g@var{level}} option to change the
3542 debug level for DWARF2.
3544 @item -feliminate-dwarf2-dups
3545 @opindex feliminate-dwarf2-dups
3546 Compress DWARF2 debugging information by eliminating duplicated
3547 information about each symbol. This option only makes sense when
3548 generating DWARF2 debugging information with @option{-gdwarf-2}.
3550 @cindex @command{prof}
3553 Generate extra code to write profile information suitable for the
3554 analysis program @command{prof}. You must use this option when compiling
3555 the source files you want data about, and you must also use it when
3558 @cindex @command{gprof}
3561 Generate extra code to write profile information suitable for the
3562 analysis program @command{gprof}. You must use this option when compiling
3563 the source files you want data about, and you must also use it when
3568 Makes the compiler print out each function name as it is compiled, and
3569 print some statistics about each pass when it finishes.
3572 @opindex ftime-report
3573 Makes the compiler print some statistics about the time consumed by each
3574 pass when it finishes.
3577 @opindex fmem-report
3578 Makes the compiler print some statistics about permanent memory
3579 allocation when it finishes.
3581 @item -fprofile-arcs
3582 @opindex fprofile-arcs
3583 Add code so that program flow @dfn{arcs} are instrumented. During
3584 execution the program records how many times each branch and call is
3585 executed and how many times it is taken or returns. When the compiled
3586 program exits it saves this data to a file called
3587 @file{@var{auxname}.gcda} for each source file. The data may be used for
3588 profile-directed optimizations (@option{-fbranch-probabilities}), or for
3589 test coverage analysis (@option{-ftest-coverage}). Each object file's
3590 @var{auxname} is generated from the name of the output file, if
3591 explicitly specified and it is not the final executable, otherwise it is
3592 the basename of the source file. In both cases any suffix is removed
3593 (e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
3594 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
3595 @xref{Cross-profiling}.
3597 @cindex @command{gcov}
3601 This option is used to compile and link code instrumented for coverage
3602 analysis. The option is a synonym for @option{-fprofile-arcs}
3603 @option{-ftest-coverage} (when compiling) and @option{-lgcov} (when
3604 linking). See the documentation for those options for more details.
3609 Compile the source files with @option{-fprofile-arcs} plus optimization
3610 and code generation options. For test coverage analysis, use the
3611 additional @option{-ftest-coverage} option. You do not need to profile
3612 every source file in a program.
3615 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
3616 (the latter implies the former).
3619 Run the program on a representative workload to generate the arc profile
3620 information. This may be repeated any number of times. You can run
3621 concurrent instances of your program, and provided that the file system
3622 supports locking, the data files will be correctly updated. Also
3623 @code{fork} calls are detected and correctly handled (double counting
3627 For profile-directed optimizations, compile the source files again with
3628 the same optimization and code generation options plus
3629 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
3630 Control Optimization}).
3633 For test coverage analysis, use @command{gcov} to produce human readable
3634 information from the @file{.gcno} and @file{.gcda} files. Refer to the
3635 @command{gcov} documentation for further information.
3639 With @option{-fprofile-arcs}, for each function of your program GCC
3640 creates a program flow graph, then finds a spanning tree for the graph.
3641 Only arcs that are not on the spanning tree have to be instrumented: the
3642 compiler adds code to count the number of times that these arcs are
3643 executed. When an arc is the only exit or only entrance to a block, the
3644 instrumentation code can be added to the block; otherwise, a new basic
3645 block must be created to hold the instrumentation code.
3648 @item -ftest-coverage
3649 @opindex ftest-coverage
3650 Produce a notes file that the @command{gcov} code-coverage utility
3651 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
3652 show program coverage. Each source file's note file is called
3653 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
3654 above for a description of @var{auxname} and instructions on how to
3655 generate test coverage data. Coverage data will match the source files
3656 more closely, if you do not optimize.
3658 @item -d@var{letters}
3659 @item -fdump-rtl-@var{pass}
3661 Says to make debugging dumps during compilation at times specified by
3662 @var{letters}. This is used for debugging the RTL-based passes of the
3663 compiler. The file names for most of the dumps are made by appending a
3664 pass number and a word to the @var{dumpname}. @var{dumpname} is generated
3665 from the name of the output file, if explicitly specified and it is not
3666 an executable, otherwise it is the basename of the source file.
3668 Most debug dumps can be enabled either passing a letter to the @option{-d}
3669 option, or with a long @option{-fdump-rtl} switch; here are the possible
3670 letters for use in @var{letters} and @var{pass}, and their meanings:
3675 Annotate the assembler output with miscellaneous debugging information.
3678 @itemx -fdump-rtl-bp
3680 @opindex fdump-rtl-bp
3681 Dump after computing branch probabilities, to @file{@var{file}.09.bp}.
3684 @itemx -fdump-rtl-bbro
3686 @opindex fdump-rtl-bbro
3687 Dump after block reordering, to @file{@var{file}.30.bbro}.
3690 @itemx -fdump-rtl-combine
3692 @opindex fdump-rtl-combine
3693 Dump after instruction combination, to the file @file{@var{file}.17.combine}.
3696 @itemx -fdump-rtl-ce1
3697 @itemx -fdump-rtl-ce2
3699 @opindex fdump-rtl-ce1
3700 @opindex fdump-rtl-ce2
3701 @option{-dC} and @option{-fdump-rtl-ce1} enable dumping after the
3702 first if conversion, to the file @file{@var{file}.11.ce1}. @option{-dC}
3703 and @option{-fdump-rtl-ce2} enable dumping after the second if
3704 conversion, to the file @file{@var{file}.18.ce2}.
3707 @itemx -fdump-rtl-btl
3708 @itemx -fdump-rtl-dbr
3710 @opindex fdump-rtl-btl
3711 @opindex fdump-rtl-dbr
3712 @option{-dd} and @option{-fdump-rtl-btl} enable dumping after branch
3713 target load optimization, to @file{@var{file}.31.btl}. @option{-dd}
3714 and @option{-fdump-rtl-dbr} enable dumping after delayed branch
3715 scheduling, to @file{@var{file}.36.dbr}.
3719 Dump all macro definitions, at the end of preprocessing, in addition to
3723 @itemx -fdump-rtl-ce3
3725 @opindex fdump-rtl-ce3
3726 Dump after the third if conversion, to @file{@var{file}.28.ce3}.
3729 @itemx -fdump-rtl-cfg
3730 @itemx -fdump-rtl-life
3732 @opindex fdump-rtl-cfg
3733 @opindex fdump-rtl-life
3734 @option{-df} and @option{-fdump-rtl-cfg} enable dumping after control
3735 and data flow analysis, to @file{@var{file}.08.cfg}. @option{-df}
3736 and @option{-fdump-rtl-cfg} enable dumping dump after life analysis,
3737 to @file{@var{file}.16.life}.
3740 @itemx -fdump-rtl-greg
3742 @opindex fdump-rtl-greg
3743 Dump after global register allocation, to @file{@var{file}.23.greg}.
3746 @itemx -fdump-rtl-gcse
3747 @itemx -fdump-rtl-bypass
3749 @opindex fdump-rtl-gcse
3750 @opindex fdump-rtl-bypass
3751 @option{-dG} and @option{-fdump-rtl-gcse} enable dumping after GCSE, to
3752 @file{@var{file}.05.gcse}. @option{-dG} and @option{-fdump-rtl-bypass}
3753 enable dumping after jump bypassing and control flow optimizations, to
3754 @file{@var{file}.07.bypass}.
3757 @itemx -fdump-rtl-eh
3759 @opindex fdump-rtl-eh
3760 Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
3763 @itemx -fdump-rtl-sibling
3765 @opindex fdump-rtl-sibling
3766 Dump after sibling call optimizations, to @file{@var{file}.01.sibling}.
3769 @itemx -fdump-rtl-jump
3771 @opindex fdump-rtl-jump
3772 Dump after the first jump optimization, to @file{@var{file}.03.jump}.
3775 @itemx -fdump-rtl-stack
3777 @opindex fdump-rtl-stack
3778 Dump after conversion from registers to stack, to @file{@var{file}.33.stack}.
3781 @itemx -fdump-rtl-lreg
3783 @opindex fdump-rtl-lreg
3784 Dump after local register allocation, to @file{@var{file}.22.lreg}.
3787 @itemx -fdump-rtl-loop
3788 @itemx -fdump-rtl-loop2
3790 @opindex fdump-rtl-loop
3791 @opindex fdump-rtl-loop2
3792 @option{-dL} and @option{-fdump-rtl-loop} enable dumping after the first
3793 loop optimization pass, to @file{@var{file}.06.loop}. @option{-dL} and
3794 @option{-fdump-rtl-loop2} enable dumping after the second pass, to
3795 @file{@var{file}.13.loop2}.
3798 @itemx -fdump-rtl-sms
3800 @opindex fdump-rtl-sms
3801 Dump after modulo scheduling, to @file{@var{file}.20.sms}.
3804 @itemx -fdump-rtl-mach
3806 @opindex fdump-rtl-mach
3807 Dump after performing the machine dependent reorganization pass, to
3808 @file{@var{file}.35.mach}.
3811 @itemx -fdump-rtl-rnreg
3813 @opindex fdump-rtl-rnreg
3814 Dump after register renumbering, to @file{@var{file}.29.rnreg}.
3817 @itemx -fdump-rtl-regmove
3819 @opindex fdump-rtl-regmove
3820 Dump after the register move pass, to @file{@var{file}.19.regmove}.
3823 @itemx -fdump-rtl-postreload
3825 @opindex fdump-rtl-postreload
3826 Dump after post-reload optimizations, to @file{@var{file}.24.postreload}.
3829 @itemx -fdump-rtl-expand
3831 @opindex fdump-rtl-expand
3832 Dump after RTL generation, to @file{@var{file}.00.expand}.
3835 @itemx -fdump-rtl-sched2
3837 @opindex fdump-rtl-sched2
3838 Dump after the second scheduling pass, to @file{@var{file}.32.sched2}.
3841 @itemx -fdump-rtl-cse
3843 @opindex fdump-rtl-cse
3844 Dump after CSE (including the jump optimization that sometimes follows
3845 CSE), to @file{@var{file}.04.cse}.
3848 @itemx -fdump-rtl-sched
3850 @opindex fdump-rtl-sched
3851 Dump after the first scheduling pass, to @file{@var{file}.21.sched}.
3854 @itemx -fdump-rtl-cse2
3856 @opindex fdump-rtl-cse2
3857 Dump after the second CSE pass (including the jump optimization that
3858 sometimes follows CSE), to @file{@var{file}.15.cse2}.
3861 @itemx -fdump-rtl-tracer
3863 @opindex fdump-rtl-tracer
3864 Dump after running tracer, to @file{@var{file}.12.tracer}.
3867 @itemx -fdump-rtl-vpt
3868 @itemx -fdump-rtl-vartrack
3870 @opindex fdump-rtl-vpt
3871 @opindex fdump-rtl-vartrack
3872 @option{-dV} and @option{-fdump-rtl-vpt} enable dumping after the value
3873 profile transformations, to @file{@var{file}.10.vpt}. @option{-dV}
3874 and @option{-fdump-rtl-vartrack} enable dumping after variable tracking,
3875 to @file{@var{file}.34.vartrack}.
3878 @itemx -fdump-rtl-flow2
3880 @opindex fdump-rtl-flow2
3881 Dump after the second flow pass, to @file{@var{file}.26.flow2}.
3884 @itemx -fdump-rtl-peephole2
3886 @opindex fdump-rtl-peephole2
3887 Dump after the peephole pass, to @file{@var{file}.27.peephole2}.
3890 @itemx -fdump-rtl-web
3892 @opindex fdump-rtl-web
3893 Dump after live range splitting, to @file{@var{file}.14.web}.
3896 @itemx -fdump-rtl-all
3898 @opindex fdump-rtl-all
3899 Produce all the dumps listed above.
3903 Produce a core dump whenever an error occurs.
3907 Print statistics on memory usage, at the end of the run, to
3912 Annotate the assembler output with a comment indicating which
3913 pattern and alternative was used. The length of each instruction is
3918 Dump the RTL in the assembler output as a comment before each instruction.
3919 Also turns on @option{-dp} annotation.
3923 For each of the other indicated dump files (either with @option{-d} or
3924 @option{-fdump-rtl-@var{pass}}), dump a representation of the control flow
3925 graph suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
3929 Just generate RTL for a function instead of compiling it. Usually used
3930 with @samp{r} (@option{-fdump-rtl-expand}).
3934 Dump debugging information during parsing, to standard error.
3937 @item -fdump-unnumbered
3938 @opindex fdump-unnumbered
3939 When doing debugging dumps (see @option{-d} option above), suppress instruction
3940 numbers and line number note output. This makes it more feasible to
3941 use diff on debugging dumps for compiler invocations with different
3942 options, in particular with and without @option{-g}.
3944 @item -fdump-translation-unit @r{(C++ only)}
3945 @itemx -fdump-translation-unit-@var{options} @r{(C++ only)}
3946 @opindex fdump-translation-unit
3947 Dump a representation of the tree structure for the entire translation
3948 unit to a file. The file name is made by appending @file{.tu} to the
3949 source file name. If the @samp{-@var{options}} form is used, @var{options}
3950 controls the details of the dump as described for the
3951 @option{-fdump-tree} options.
3953 @item -fdump-class-hierarchy @r{(C++ only)}
3954 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
3955 @opindex fdump-class-hierarchy
3956 Dump a representation of each class's hierarchy and virtual function
3957 table layout to a file. The file name is made by appending @file{.class}
3958 to the source file name. If the @samp{-@var{options}} form is used,
3959 @var{options} controls the details of the dump as described for the
3960 @option{-fdump-tree} options.
3962 @item -fdump-ipa-@var{switch}
3964 Control the dumping at various stages of inter-procedural analysis
3965 language tree to a file. The file name is generated by appending a switch
3966 specific suffix to the source file name. The following dumps are possible:
3970 Enables all inter-procedural analysis dumps; currently the only produced
3971 dump is the @samp{cgraph} dump.
3974 Dumps information about call-graph optimization, unused function removal,
3975 and inlining decisions.
3978 @item -fdump-tree-@var{switch} @r{(C and C++ only)}
3979 @itemx -fdump-tree-@var{switch}-@var{options} @r{(C and C++ only)}
3981 Control the dumping at various stages of processing the intermediate
3982 language tree to a file. The file name is generated by appending a switch
3983 specific suffix to the source file name. If the @samp{-@var{options}}
3984 form is used, @var{options} is a list of @samp{-} separated options that
3985 control the details of the dump. Not all options are applicable to all
3986 dumps, those which are not meaningful will be ignored. The following
3987 options are available
3991 Print the address of each node. Usually this is not meaningful as it
3992 changes according to the environment and source file. Its primary use
3993 is for tying up a dump file with a debug environment.
3995 Inhibit dumping of members of a scope or body of a function merely
3996 because that scope has been reached. Only dump such items when they
3997 are directly reachable by some other path. When dumping pretty-printed
3998 trees, this option inhibits dumping the bodies of control structures.
4000 Print a raw representation of the tree. By default, trees are
4001 pretty-printed into a C-like representation.
4003 Enable more detailed dumps (not honored by every dump option).
4005 Enable dumping various statistics about the pass (not honored by every dump
4008 Enable showing basic block boundaries (disabled in raw dumps).
4010 Enable showing virtual operands for every statement.
4012 Enable showing line numbers for statements.
4014 Enable showing the unique ID (@code{DECL_UID}) for each variable.
4016 Turn on all options, except @option{raw}, @option{slim} and @option{lineno}.
4019 The following tree dumps are possible:
4023 Dump before any tree based optimization, to @file{@var{file}.original}.
4026 Dump after all tree based optimization, to @file{@var{file}.optimized}.
4029 Dump after function inlining, to @file{@var{file}.inlined}.
4032 @opindex fdump-tree-gimple
4033 Dump each function before and after the gimplification pass to a file. The
4034 file name is made by appending @file{.gimple} to the source file name.
4037 @opindex fdump-tree-cfg
4038 Dump the control flow graph of each function to a file. The file name is
4039 made by appending @file{.cfg} to the source file name.
4042 @opindex fdump-tree-vcg
4043 Dump the control flow graph of each function to a file in VCG format. The
4044 file name is made by appending @file{.vcg} to the source file name. Note
4045 that if the file contains more than one function, the generated file cannot
4046 be used directly by VCG@. You will need to cut and paste each function's
4047 graph into its own separate file first.
4050 @opindex fdump-tree-ch
4051 Dump each function after copying loop headers. The file name is made by
4052 appending @file{.ch} to the source file name.
4055 @opindex fdump-tree-ssa
4056 Dump SSA related information to a file. The file name is made by appending
4057 @file{.ssa} to the source file name.
4060 @opindex fdump-tree-salias
4061 Dump structure aliasing variable information to a file. This file name
4062 is made by appending @file{.salias} to the source file name.
4065 @opindex fdump-tree-alias
4066 Dump aliasing information for each function. The file name is made by
4067 appending @file{.alias} to the source file name.
4070 @opindex fdump-tree-ccp
4071 Dump each function after CCP@. The file name is made by appending
4072 @file{.ccp} to the source file name.
4075 @opindex fdump-tree-storeccp
4076 Dump each function after STORE-CCP. The file name is made by appending
4077 @file{.storeccp} to the source file name.
4080 @opindex fdump-tree-pre
4081 Dump trees after partial redundancy elimination. The file name is made
4082 by appending @file{.pre} to the source file name.
4085 @opindex fdump-tree-fre
4086 Dump trees after full redundancy elimination. The file name is made
4087 by appending @file{.fre} to the source file name.
4090 @opindex fdump-tree-copyprop
4091 Dump trees after copy propagation. The file name is made
4092 by appending @file{.copyprop} to the source file name.
4094 @item store_copyprop
4095 @opindex fdump-tree-store_copyprop
4096 Dump trees after store copy-propagation. The file name is made
4097 by appending @file{.store_copyprop} to the source file name.
4100 @opindex fdump-tree-dce
4101 Dump each function after dead code elimination. The file name is made by
4102 appending @file{.dce} to the source file name.
4105 @opindex fdump-tree-mudflap
4106 Dump each function after adding mudflap instrumentation. The file name is
4107 made by appending @file{.mudflap} to the source file name.
4110 @opindex fdump-tree-sra
4111 Dump each function after performing scalar replacement of aggregates. The
4112 file name is made by appending @file{.sra} to the source file name.
4115 @opindex fdump-tree-sink
4116 Dump each function after performing code sinking. The file name is made
4117 by appending @file{.sink} to the source file name.
4120 @opindex fdump-tree-dom
4121 Dump each function after applying dominator tree optimizations. The file
4122 name is made by appending @file{.dom} to the source file name.
4125 @opindex fdump-tree-dse
4126 Dump each function after applying dead store elimination. The file
4127 name is made by appending @file{.dse} to the source file name.
4130 @opindex fdump-tree-phiopt
4131 Dump each function after optimizing PHI nodes into straightline code. The file
4132 name is made by appending @file{.phiopt} to the source file name.
4135 @opindex fdump-tree-forwprop
4136 Dump each function after forward propagating single use variables. The file
4137 name is made by appending @file{.forwprop} to the source file name.
4140 @opindex fdump-tree-copyrename
4141 Dump each function after applying the copy rename optimization. The file
4142 name is made by appending @file{.copyrename} to the source file name.
4145 @opindex fdump-tree-nrv
4146 Dump each function after applying the named return value optimization on
4147 generic trees. The file name is made by appending @file{.nrv} to the source
4151 @opindex fdump-tree-vect
4152 Dump each function after applying vectorization of loops. The file name is
4153 made by appending @file{.vect} to the source file name.
4156 @opindex fdump-tree-vrp
4157 Dump each function after Value Range Propagation (VRP). The file name
4158 is made by appending @file{.vrp} to the source file name.
4161 @opindex fdump-tree-all
4162 Enable all the available tree dumps with the flags provided in this option.
4165 @item -ftree-vectorizer-verbose=@var{n}
4166 @opindex ftree-vectorizer-verbose
4167 This option controls the amount of debugging output the vectorizer prints.
4168 This information is written to standard error, unless @option{-fdump-tree-all}
4169 or @option{-fdump-tree-vect} is specified, in which case it is output to the
4170 usual dump listing file, @file{.vect}.
4172 @item -frandom-seed=@var{string}
4173 @opindex frandom-string
4174 This option provides a seed that GCC uses when it would otherwise use
4175 random numbers. It is used to generate certain symbol names
4176 that have to be different in every compiled file. It is also used to
4177 place unique stamps in coverage data files and the object files that
4178 produce them. You can use the @option{-frandom-seed} option to produce
4179 reproducibly identical object files.
4181 The @var{string} should be different for every file you compile.
4183 @item -fsched-verbose=@var{n}
4184 @opindex fsched-verbose
4185 On targets that use instruction scheduling, this option controls the
4186 amount of debugging output the scheduler prints. This information is
4187 written to standard error, unless @option{-dS} or @option{-dR} is
4188 specified, in which case it is output to the usual dump
4189 listing file, @file{.sched} or @file{.sched2} respectively. However
4190 for @var{n} greater than nine, the output is always printed to standard
4193 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
4194 same information as @option{-dRS}. For @var{n} greater than one, it
4195 also output basic block probabilities, detailed ready list information
4196 and unit/insn info. For @var{n} greater than two, it includes RTL
4197 at abort point, control-flow and regions info. And for @var{n} over
4198 four, @option{-fsched-verbose} also includes dependence info.
4202 Store the usual ``temporary'' intermediate files permanently; place them
4203 in the current directory and name them based on the source file. Thus,
4204 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
4205 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
4206 preprocessed @file{foo.i} output file even though the compiler now
4207 normally uses an integrated preprocessor.
4209 When used in combination with the @option{-x} command line option,
4210 @option{-save-temps} is sensible enough to avoid over writing an
4211 input source file with the same extension as an intermediate file.
4212 The corresponding intermediate file may be obtained by renaming the
4213 source file before using @option{-save-temps}.
4217 Report the CPU time taken by each subprocess in the compilation
4218 sequence. For C source files, this is the compiler proper and assembler
4219 (plus the linker if linking is done). The output looks like this:
4226 The first number on each line is the ``user time'', that is time spent
4227 executing the program itself. The second number is ``system time'',
4228 time spent executing operating system routines on behalf of the program.
4229 Both numbers are in seconds.
4231 @item -fvar-tracking
4232 @opindex fvar-tracking
4233 Run variable tracking pass. It computes where variables are stored at each
4234 position in code. Better debugging information is then generated
4235 (if the debugging information format supports this information).
4237 It is enabled by default when compiling with optimization (@option{-Os},
4238 @option{-O}, @option{-O2}, ...), debugging information (@option{-g}) and
4239 the debug info format supports it.
4241 @item -print-file-name=@var{library}
4242 @opindex print-file-name
4243 Print the full absolute name of the library file @var{library} that
4244 would be used when linking---and don't do anything else. With this
4245 option, GCC does not compile or link anything; it just prints the
4248 @item -print-multi-directory
4249 @opindex print-multi-directory
4250 Print the directory name corresponding to the multilib selected by any
4251 other switches present in the command line. This directory is supposed
4252 to exist in @env{GCC_EXEC_PREFIX}.
4254 @item -print-multi-lib
4255 @opindex print-multi-lib
4256 Print the mapping from multilib directory names to compiler switches
4257 that enable them. The directory name is separated from the switches by
4258 @samp{;}, and each switch starts with an @samp{@@} instead of the
4259 @samp{-}, without spaces between multiple switches. This is supposed to
4260 ease shell-processing.
4262 @item -print-prog-name=@var{program}
4263 @opindex print-prog-name
4264 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
4266 @item -print-libgcc-file-name
4267 @opindex print-libgcc-file-name
4268 Same as @option{-print-file-name=libgcc.a}.
4270 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
4271 but you do want to link with @file{libgcc.a}. You can do
4274 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
4277 @item -print-search-dirs
4278 @opindex print-search-dirs
4279 Print the name of the configured installation directory and a list of
4280 program and library directories @command{gcc} will search---and don't do anything else.
4282 This is useful when @command{gcc} prints the error message
4283 @samp{installation problem, cannot exec cpp0: No such file or directory}.
4284 To resolve this you either need to put @file{cpp0} and the other compiler
4285 components where @command{gcc} expects to find them, or you can set the environment
4286 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
4287 Don't forget the trailing @samp{/}.
4288 @xref{Environment Variables}.
4291 @opindex dumpmachine
4292 Print the compiler's target machine (for example,
4293 @samp{i686-pc-linux-gnu})---and don't do anything else.
4296 @opindex dumpversion
4297 Print the compiler version (for example, @samp{3.0})---and don't do
4302 Print the compiler's built-in specs---and don't do anything else. (This
4303 is used when GCC itself is being built.) @xref{Spec Files}.
4305 @item -feliminate-unused-debug-types
4306 @opindex feliminate-unused-debug-types
4307 Normally, when producing DWARF2 output, GCC will emit debugging
4308 information for all types declared in a compilation
4309 unit, regardless of whether or not they are actually used
4310 in that compilation unit. Sometimes this is useful, such as
4311 if, in the debugger, you want to cast a value to a type that is
4312 not actually used in your program (but is declared). More often,
4313 however, this results in a significant amount of wasted space.
4314 With this option, GCC will avoid producing debug symbol output
4315 for types that are nowhere used in the source file being compiled.
4318 @node Optimize Options
4319 @section Options That Control Optimization
4320 @cindex optimize options
4321 @cindex options, optimization
4323 These options control various sorts of optimizations.
4325 Without any optimization option, the compiler's goal is to reduce the
4326 cost of compilation and to make debugging produce the expected
4327 results. Statements are independent: if you stop the program with a
4328 breakpoint between statements, you can then assign a new value to any
4329 variable or change the program counter to any other statement in the
4330 function and get exactly the results you would expect from the source
4333 Turning on optimization flags makes the compiler attempt to improve
4334 the performance and/or code size at the expense of compilation time
4335 and possibly the ability to debug the program.
4337 The compiler performs optimization based on the knowledge it has of
4338 the program. Optimization levels @option{-O2} and above, in
4339 particular, enable @emph{unit-at-a-time} mode, which allows the
4340 compiler to consider information gained from later functions in
4341 the file when compiling a function. Compiling multiple files at
4342 once to a single output file in @emph{unit-at-a-time} mode allows
4343 the compiler to use information gained from all of the files when
4344 compiling each of them.
4346 Not all optimizations are controlled directly by a flag. Only
4347 optimizations that have a flag are listed.
4354 Optimize. Optimizing compilation takes somewhat more time, and a lot
4355 more memory for a large function.
4357 With @option{-O}, the compiler tries to reduce code size and execution
4358 time, without performing any optimizations that take a great deal of
4361 @option{-O} turns on the following optimization flags:
4362 @gccoptlist{-fdefer-pop @gol
4363 -fdelayed-branch @gol
4364 -fguess-branch-probability @gol
4365 -fcprop-registers @gol
4366 -floop-optimize @gol
4367 -fif-conversion @gol
4368 -fif-conversion2 @gol
4371 -ftree-dominator-opts @gol
4376 -ftree-copyrename @gol
4381 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
4382 where doing so does not interfere with debugging.
4386 Optimize even more. GCC performs nearly all supported optimizations
4387 that do not involve a space-speed tradeoff. The compiler does not
4388 perform loop unrolling or function inlining when you specify @option{-O2}.
4389 As compared to @option{-O}, this option increases both compilation time
4390 and the performance of the generated code.
4392 @option{-O2} turns on all optimization flags specified by @option{-O}. It
4393 also turns on the following optimization flags:
4394 @gccoptlist{-fthread-jumps @gol
4396 -foptimize-sibling-calls @gol
4397 -fcse-follow-jumps -fcse-skip-blocks @gol
4398 -fgcse -fgcse-lm @gol
4399 -fexpensive-optimizations @gol
4400 -fstrength-reduce @gol
4401 -frerun-cse-after-loop -frerun-loop-opt @gol
4404 -fschedule-insns -fschedule-insns2 @gol
4405 -fsched-interblock -fsched-spec @gol
4407 -fstrict-aliasing @gol
4408 -fdelete-null-pointer-checks @gol
4409 -freorder-blocks -freorder-functions @gol
4410 -funit-at-a-time @gol
4411 -falign-functions -falign-jumps @gol
4412 -falign-loops -falign-labels @gol
4416 Please note the warning under @option{-fgcse} about
4417 invoking @option{-O2} on programs that use computed gotos.
4421 Optimize yet more. @option{-O3} turns on all optimizations specified by
4422 @option{-O2} and also turns on the @option{-finline-functions},
4423 @option{-funswitch-loops} and @option{-fgcse-after-reload} options.
4427 Do not optimize. This is the default.
4431 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
4432 do not typically increase code size. It also performs further
4433 optimizations designed to reduce code size.
4435 @option{-Os} disables the following optimization flags:
4436 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
4437 -falign-labels -freorder-blocks -freorder-blocks-and-partition @gol
4438 -fprefetch-loop-arrays -ftree-vect-loop-version}
4440 If you use multiple @option{-O} options, with or without level numbers,
4441 the last such option is the one that is effective.
4444 Options of the form @option{-f@var{flag}} specify machine-independent
4445 flags. Most flags have both positive and negative forms; the negative
4446 form of @option{-ffoo} would be @option{-fno-foo}. In the table
4447 below, only one of the forms is listed---the one you typically will
4448 use. You can figure out the other form by either removing @samp{no-}
4451 The following options control specific optimizations. They are either
4452 activated by @option{-O} options or are related to ones that are. You
4453 can use the following flags in the rare cases when ``fine-tuning'' of
4454 optimizations to be performed is desired.
4457 @item -fno-default-inline
4458 @opindex fno-default-inline
4459 Do not make member functions inline by default merely because they are
4460 defined inside the class scope (C++ only). Otherwise, when you specify
4461 @w{@option{-O}}, member functions defined inside class scope are compiled
4462 inline by default; i.e., you don't need to add @samp{inline} in front of
4463 the member function name.
4465 @item -fno-defer-pop
4466 @opindex fno-defer-pop
4467 Always pop the arguments to each function call as soon as that function
4468 returns. For machines which must pop arguments after a function call,
4469 the compiler normally lets arguments accumulate on the stack for several
4470 function calls and pops them all at once.
4472 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4476 Force memory operands to be copied into registers before doing
4477 arithmetic on them. This produces better code by making all memory
4478 references potential common subexpressions. When they are not common
4479 subexpressions, instruction combination should eliminate the separate
4480 register-load. This option is now a nop and will be removed in 4.2.
4483 @opindex fforce-addr
4484 Force memory address constants to be copied into registers before
4485 doing arithmetic on them.
4487 @item -fomit-frame-pointer
4488 @opindex fomit-frame-pointer
4489 Don't keep the frame pointer in a register for functions that
4490 don't need one. This avoids the instructions to save, set up and
4491 restore frame pointers; it also makes an extra register available
4492 in many functions. @strong{It also makes debugging impossible on
4495 On some machines, such as the VAX, this flag has no effect, because
4496 the standard calling sequence automatically handles the frame pointer
4497 and nothing is saved by pretending it doesn't exist. The
4498 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
4499 whether a target machine supports this flag. @xref{Registers,,Register
4500 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
4502 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4504 @item -foptimize-sibling-calls
4505 @opindex foptimize-sibling-calls
4506 Optimize sibling and tail recursive calls.
4508 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4512 Don't pay attention to the @code{inline} keyword. Normally this option
4513 is used to keep the compiler from expanding any functions inline.
4514 Note that if you are not optimizing, no functions can be expanded inline.
4516 @item -finline-functions
4517 @opindex finline-functions
4518 Integrate all simple functions into their callers. The compiler
4519 heuristically decides which functions are simple enough to be worth
4520 integrating in this way.
4522 If all calls to a given function are integrated, and the function is
4523 declared @code{static}, then the function is normally not output as
4524 assembler code in its own right.
4526 Enabled at level @option{-O3}.
4528 @item -finline-functions-called-once
4529 @opindex finline-functions-called-once
4530 Consider all @code{static} functions called once for inlining into their
4531 caller even if they are not marked @code{inline}. If a call to a given
4532 function is integrated, then the function is not output as assembler code
4535 Enabled if @option{-funit-at-a-time} is enabled.
4537 @item -fearly-inlining
4538 @opindex fearly-inlining
4539 Inline functions marked by @code{always_inline} and functions whose body seems
4540 smaller than the function call overhead early before doing
4541 @option{-fprofile-generate} instrumentation and real inlining pass. Doing so
4542 makes profiling significantly cheaper and usually inlining faster on programs
4543 having large chains of nested wrapper functions.
4547 @item -finline-limit=@var{n}
4548 @opindex finline-limit
4549 By default, GCC limits the size of functions that can be inlined. This flag
4550 allows the control of this limit for functions that are explicitly marked as
4551 inline (i.e., marked with the inline keyword or defined within the class
4552 definition in c++). @var{n} is the size of functions that can be inlined in
4553 number of pseudo instructions (not counting parameter handling). The default
4554 value of @var{n} is 600.
4555 Increasing this value can result in more inlined code at
4556 the cost of compilation time and memory consumption. Decreasing usually makes
4557 the compilation faster and less code will be inlined (which presumably
4558 means slower programs). This option is particularly useful for programs that
4559 use inlining heavily such as those based on recursive templates with C++.
4561 Inlining is actually controlled by a number of parameters, which may be
4562 specified individually by using @option{--param @var{name}=@var{value}}.
4563 The @option{-finline-limit=@var{n}} option sets some of these parameters
4567 @item max-inline-insns-single
4568 is set to @var{n}/2.
4569 @item max-inline-insns-auto
4570 is set to @var{n}/2.
4571 @item min-inline-insns
4572 is set to 130 or @var{n}/4, whichever is smaller.
4573 @item max-inline-insns-rtl
4577 See below for a documentation of the individual
4578 parameters controlling inlining.
4580 @emph{Note:} pseudo instruction represents, in this particular context, an
4581 abstract measurement of function's size. In no way does it represent a count
4582 of assembly instructions and as such its exact meaning might change from one
4583 release to an another.
4585 @item -fkeep-inline-functions
4586 @opindex fkeep-inline-functions
4587 In C, emit @code{static} functions that are declared @code{inline}
4588 into the object file, even if the function has been inlined into all
4589 of its callers. This switch does not affect functions using the
4590 @code{extern inline} extension in GNU C@. In C++, emit any and all
4591 inline functions into the object file.
4593 @item -fkeep-static-consts
4594 @opindex fkeep-static-consts
4595 Emit variables declared @code{static const} when optimization isn't turned
4596 on, even if the variables aren't referenced.
4598 GCC enables this option by default. If you want to force the compiler to
4599 check if the variable was referenced, regardless of whether or not
4600 optimization is turned on, use the @option{-fno-keep-static-consts} option.
4602 @item -fmerge-constants
4603 Attempt to merge identical constants (string constants and floating point
4604 constants) across compilation units.
4606 This option is the default for optimized compilation if the assembler and
4607 linker support it. Use @option{-fno-merge-constants} to inhibit this
4610 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4612 @item -fmerge-all-constants
4613 Attempt to merge identical constants and identical variables.
4615 This option implies @option{-fmerge-constants}. In addition to
4616 @option{-fmerge-constants} this considers e.g.@: even constant initialized
4617 arrays or initialized constant variables with integral or floating point
4618 types. Languages like C or C++ require each non-automatic variable to
4619 have distinct location, so using this option will result in non-conforming
4622 @item -fmodulo-sched
4623 @opindex fmodulo-sched
4624 Perform swing modulo scheduling immediately before the first scheduling
4625 pass. This pass looks at innermost loops and reorders their
4626 instructions by overlapping different iterations.
4628 @item -fno-branch-count-reg
4629 @opindex fno-branch-count-reg
4630 Do not use ``decrement and branch'' instructions on a count register,
4631 but instead generate a sequence of instructions that decrement a
4632 register, compare it against zero, then branch based upon the result.
4633 This option is only meaningful on architectures that support such
4634 instructions, which include x86, PowerPC, IA-64 and S/390.
4636 The default is @option{-fbranch-count-reg}, enabled when
4637 @option{-fstrength-reduce} is enabled.
4639 @item -fno-function-cse
4640 @opindex fno-function-cse
4641 Do not put function addresses in registers; make each instruction that
4642 calls a constant function contain the function's address explicitly.
4644 This option results in less efficient code, but some strange hacks
4645 that alter the assembler output may be confused by the optimizations
4646 performed when this option is not used.
4648 The default is @option{-ffunction-cse}
4650 @item -fno-zero-initialized-in-bss
4651 @opindex fno-zero-initialized-in-bss
4652 If the target supports a BSS section, GCC by default puts variables that
4653 are initialized to zero into BSS@. This can save space in the resulting
4656 This option turns off this behavior because some programs explicitly
4657 rely on variables going to the data section. E.g., so that the
4658 resulting executable can find the beginning of that section and/or make
4659 assumptions based on that.
4661 The default is @option{-fzero-initialized-in-bss}.
4663 @item -fbounds-check
4664 @opindex fbounds-check
4665 For front-ends that support it, generate additional code to check that
4666 indices used to access arrays are within the declared range. This is
4667 currently only supported by the Java and Fortran front-ends, where
4668 this option defaults to true and false respectively.
4670 @item -fmudflap -fmudflapth -fmudflapir
4674 @cindex bounds checking
4676 For front-ends that support it (C and C++), instrument all risky
4677 pointer/array dereferencing operations, some standard library
4678 string/heap functions, and some other associated constructs with
4679 range/validity tests. Modules so instrumented should be immune to
4680 buffer overflows, invalid heap use, and some other classes of C/C++
4681 programming errors. The instrumentation relies on a separate runtime
4682 library (@file{libmudflap}), which will be linked into a program if
4683 @option{-fmudflap} is given at link time. Run-time behavior of the
4684 instrumented program is controlled by the @env{MUDFLAP_OPTIONS}
4685 environment variable. See @code{env MUDFLAP_OPTIONS=-help a.out}
4688 Use @option{-fmudflapth} instead of @option{-fmudflap} to compile and to
4689 link if your program is multi-threaded. Use @option{-fmudflapir}, in
4690 addition to @option{-fmudflap} or @option{-fmudflapth}, if
4691 instrumentation should ignore pointer reads. This produces less
4692 instrumentation (and therefore faster execution) and still provides
4693 some protection against outright memory corrupting writes, but allows
4694 erroneously read data to propagate within a program.
4696 @item -fstrength-reduce
4697 @opindex fstrength-reduce
4698 Perform the optimizations of loop strength reduction and
4699 elimination of iteration variables.
4701 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4703 @item -fthread-jumps
4704 @opindex fthread-jumps
4705 Perform optimizations where we check to see if a jump branches to a
4706 location where another comparison subsumed by the first is found. If
4707 so, the first branch is redirected to either the destination of the
4708 second branch or a point immediately following it, depending on whether
4709 the condition is known to be true or false.
4711 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4713 @item -fcse-follow-jumps
4714 @opindex fcse-follow-jumps
4715 In common subexpression elimination, scan through jump instructions
4716 when the target of the jump is not reached by any other path. For
4717 example, when CSE encounters an @code{if} statement with an
4718 @code{else} clause, CSE will follow the jump when the condition
4721 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4723 @item -fcse-skip-blocks
4724 @opindex fcse-skip-blocks
4725 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
4726 follow jumps which conditionally skip over blocks. When CSE
4727 encounters a simple @code{if} statement with no else clause,
4728 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
4729 body of the @code{if}.
4731 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4733 @item -frerun-cse-after-loop
4734 @opindex frerun-cse-after-loop
4735 Re-run common subexpression elimination after loop optimizations has been
4738 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4740 @item -frerun-loop-opt
4741 @opindex frerun-loop-opt
4742 Run the loop optimizer twice.
4744 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4748 Perform a global common subexpression elimination pass.
4749 This pass also performs global constant and copy propagation.
4751 @emph{Note:} When compiling a program using computed gotos, a GCC
4752 extension, you may get better runtime performance if you disable
4753 the global common subexpression elimination pass by adding
4754 @option{-fno-gcse} to the command line.
4756 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4760 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
4761 attempt to move loads which are only killed by stores into themselves. This
4762 allows a loop containing a load/store sequence to be changed to a load outside
4763 the loop, and a copy/store within the loop.
4765 Enabled by default when gcse is enabled.
4769 When @option{-fgcse-sm} is enabled, a store motion pass is run after
4770 global common subexpression elimination. This pass will attempt to move
4771 stores out of loops. When used in conjunction with @option{-fgcse-lm},
4772 loops containing a load/store sequence can be changed to a load before
4773 the loop and a store after the loop.
4775 Not enabled at any optimization level.
4779 When @option{-fgcse-las} is enabled, the global common subexpression
4780 elimination pass eliminates redundant loads that come after stores to the
4781 same memory location (both partial and full redundancies).
4783 Not enabled at any optimization level.
4785 @item -fgcse-after-reload
4786 @opindex fgcse-after-reload
4787 When @option{-fgcse-after-reload} is enabled, a redundant load elimination
4788 pass is performed after reload. The purpose of this pass is to cleanup
4791 @item -floop-optimize
4792 @opindex floop-optimize
4793 Perform loop optimizations: move constant expressions out of loops, simplify
4794 exit test conditions and optionally do strength-reduction as well.
4796 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4798 @item -floop-optimize2
4799 @opindex floop-optimize2
4800 Perform loop optimizations using the new loop optimizer. The optimizations
4801 (loop unrolling, peeling and unswitching, loop invariant motion) are enabled
4804 @item -funsafe-loop-optimizations
4805 @opindex funsafe-loop-optimizations
4806 If given, the loop optimizer will assume that loop indices do not
4807 overflow, and that the loops with nontrivial exit condition are not
4808 infinite. This enables a wider range of loop optimizations even if
4809 the loop optimizer itself cannot prove that these assumptions are valid.
4810 Using @option{-Wunsafe-loop-optimizations}, the compiler will warn you
4811 if it finds this kind of loop.
4813 @item -fcrossjumping
4814 @opindex crossjumping
4815 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
4816 resulting code may or may not perform better than without cross-jumping.
4818 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4820 @item -fif-conversion
4821 @opindex if-conversion
4822 Attempt to transform conditional jumps into branch-less equivalents. This
4823 include use of conditional moves, min, max, set flags and abs instructions, and
4824 some tricks doable by standard arithmetics. The use of conditional execution
4825 on chips where it is available is controlled by @code{if-conversion2}.
4827 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4829 @item -fif-conversion2
4830 @opindex if-conversion2
4831 Use conditional execution (where available) to transform conditional jumps into
4832 branch-less equivalents.
4834 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4836 @item -fdelete-null-pointer-checks
4837 @opindex fdelete-null-pointer-checks
4838 Use global dataflow analysis to identify and eliminate useless checks
4839 for null pointers. The compiler assumes that dereferencing a null
4840 pointer would have halted the program. If a pointer is checked after
4841 it has already been dereferenced, it cannot be null.
4843 In some environments, this assumption is not true, and programs can
4844 safely dereference null pointers. Use
4845 @option{-fno-delete-null-pointer-checks} to disable this optimization
4846 for programs which depend on that behavior.
4848 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4850 @item -fexpensive-optimizations
4851 @opindex fexpensive-optimizations
4852 Perform a number of minor optimizations that are relatively expensive.
4854 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4856 @item -foptimize-register-move
4858 @opindex foptimize-register-move
4860 Attempt to reassign register numbers in move instructions and as
4861 operands of other simple instructions in order to maximize the amount of
4862 register tying. This is especially helpful on machines with two-operand
4865 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
4868 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4870 @item -fdelayed-branch
4871 @opindex fdelayed-branch
4872 If supported for the target machine, attempt to reorder instructions
4873 to exploit instruction slots available after delayed branch
4876 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4878 @item -fschedule-insns
4879 @opindex fschedule-insns
4880 If supported for the target machine, attempt to reorder instructions to
4881 eliminate execution stalls due to required data being unavailable. This
4882 helps machines that have slow floating point or memory load instructions
4883 by allowing other instructions to be issued until the result of the load
4884 or floating point instruction is required.
4886 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4888 @item -fschedule-insns2
4889 @opindex fschedule-insns2
4890 Similar to @option{-fschedule-insns}, but requests an additional pass of
4891 instruction scheduling after register allocation has been done. This is
4892 especially useful on machines with a relatively small number of
4893 registers and where memory load instructions take more than one cycle.
4895 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4897 @item -fno-sched-interblock
4898 @opindex fno-sched-interblock
4899 Don't schedule instructions across basic blocks. This is normally
4900 enabled by default when scheduling before register allocation, i.e.@:
4901 with @option{-fschedule-insns} or at @option{-O2} or higher.
4903 @item -fno-sched-spec
4904 @opindex fno-sched-spec
4905 Don't allow speculative motion of non-load instructions. This is normally
4906 enabled by default when scheduling before register allocation, i.e.@:
4907 with @option{-fschedule-insns} or at @option{-O2} or higher.
4909 @item -fsched-spec-load
4910 @opindex fsched-spec-load
4911 Allow speculative motion of some load instructions. This only makes
4912 sense when scheduling before register allocation, i.e.@: with
4913 @option{-fschedule-insns} or at @option{-O2} or higher.
4915 @item -fsched-spec-load-dangerous
4916 @opindex fsched-spec-load-dangerous
4917 Allow speculative motion of more load instructions. This only makes
4918 sense when scheduling before register allocation, i.e.@: with
4919 @option{-fschedule-insns} or at @option{-O2} or higher.
4921 @item -fsched-stalled-insns=@var{n}
4922 @opindex fsched-stalled-insns
4923 Define how many insns (if any) can be moved prematurely from the queue
4924 of stalled insns into the ready list, during the second scheduling pass.
4926 @item -fsched-stalled-insns-dep=@var{n}
4927 @opindex fsched-stalled-insns-dep
4928 Define how many insn groups (cycles) will be examined for a dependency
4929 on a stalled insn that is candidate for premature removal from the queue
4930 of stalled insns. Has an effect only during the second scheduling pass,
4931 and only if @option{-fsched-stalled-insns} is used and its value is not zero.
4933 @item -fsched2-use-superblocks
4934 @opindex fsched2-use-superblocks
4935 When scheduling after register allocation, do use superblock scheduling
4936 algorithm. Superblock scheduling allows motion across basic block boundaries
4937 resulting on faster schedules. This option is experimental, as not all machine
4938 descriptions used by GCC model the CPU closely enough to avoid unreliable
4939 results from the algorithm.
4941 This only makes sense when scheduling after register allocation, i.e.@: with
4942 @option{-fschedule-insns2} or at @option{-O2} or higher.
4944 @item -fsched2-use-traces
4945 @opindex fsched2-use-traces
4946 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
4947 allocation and additionally perform code duplication in order to increase the
4948 size of superblocks using tracer pass. See @option{-ftracer} for details on
4951 This mode should produce faster but significantly longer programs. Also
4952 without @option{-fbranch-probabilities} the traces constructed may not
4953 match the reality and hurt the performance. This only makes
4954 sense when scheduling after register allocation, i.e.@: with
4955 @option{-fschedule-insns2} or at @option{-O2} or higher.
4957 @item -freschedule-modulo-scheduled-loops
4958 @opindex fscheduling-in-modulo-scheduled-loops
4959 The modulo scheduling comes before the traditional scheduling, if a loop was modulo scheduled
4960 we may want to prevent the later scheduling passes from changing its schedule, we use this
4961 option to control that.
4963 @item -fcaller-saves
4964 @opindex fcaller-saves
4965 Enable values to be allocated in registers that will be clobbered by
4966 function calls, by emitting extra instructions to save and restore the
4967 registers around such calls. Such allocation is done only when it
4968 seems to result in better code than would otherwise be produced.
4970 This option is always enabled by default on certain machines, usually
4971 those which have no call-preserved registers to use instead.
4973 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4976 Perform Partial Redundancy Elimination (PRE) on trees. This flag is
4977 enabled by default at @option{-O2} and @option{-O3}.
4980 Perform Full Redundancy Elimination (FRE) on trees. The difference
4981 between FRE and PRE is that FRE only considers expressions
4982 that are computed on all paths leading to the redundant computation.
4983 This analysis faster than PRE, though it exposes fewer redundancies.
4984 This flag is enabled by default at @option{-O} and higher.
4986 @item -ftree-copy-prop
4987 Perform copy propagation on trees. This pass eliminates unnecessary
4988 copy operations. This flag is enabled by default at @option{-O} and
4991 @item -ftree-store-copy-prop
4992 Perform copy propagation of memory loads and stores. This pass
4993 eliminates unnecessary copy operations in memory references
4994 (structures, global variables, arrays, etc). This flag is enabled by
4995 default at @option{-O2} and higher.
4998 Perform structural alias analysis on trees. This flag
4999 is enabled by default at @option{-O} and higher.
5002 Perform forward store motion on trees. This flag is
5003 enabled by default at @option{-O} and higher.
5006 Perform sparse conditional constant propagation (CCP) on trees. This
5007 pass only operates on local scalar variables and is enabled by default
5008 at @option{-O} and higher.
5010 @item -ftree-store-ccp
5011 Perform sparse conditional constant propagation (CCP) on trees. This
5012 pass operates on both local scalar variables and memory stores and
5013 loads (global variables, structures, arrays, etc). This flag is
5014 enabled by default at @option{-O2} and higher.
5017 Perform dead code elimination (DCE) on trees. This flag is enabled by
5018 default at @option{-O} and higher.
5020 @item -ftree-dominator-opts
5021 Perform a variety of simple scalar cleanups (constant/copy
5022 propagation, redundancy elimination, range propagation and expression
5023 simplification) based on a dominator tree traversal. This also
5024 performs jump threading (to reduce jumps to jumps). This flag is
5025 enabled by default at @option{-O} and higher.
5028 Perform loop header copying on trees. This is beneficial since it increases
5029 effectiveness of code motion optimizations. It also saves one jump. This flag
5030 is enabled by default at @option{-O} and higher. It is not enabled
5031 for @option{-Os}, since it usually increases code size.
5033 @item -ftree-loop-optimize
5034 Perform loop optimizations on trees. This flag is enabled by default
5035 at @option{-O} and higher.
5037 @item -ftree-loop-linear
5038 Perform linear loop transformations on tree. This flag can improve cache
5039 performance and allow further loop optimizations to take place.
5041 @item -ftree-loop-im
5042 Perform loop invariant motion on trees. This pass moves only invariants that
5043 would be hard to handle at RTL level (function calls, operations that expand to
5044 nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
5045 operands of conditions that are invariant out of the loop, so that we can use
5046 just trivial invariantness analysis in loop unswitching. The pass also includes
5049 @item -ftree-loop-ivcanon
5050 Create a canonical counter for number of iterations in the loop for that
5051 determining number of iterations requires complicated analysis. Later
5052 optimizations then may determine the number easily. Useful especially
5053 in connection with unrolling.
5056 Perform induction variable optimizations (strength reduction, induction
5057 variable merging and induction variable elimination) on trees.
5060 Perform scalar replacement of aggregates. This pass replaces structure
5061 references with scalars to prevent committing structures to memory too
5062 early. This flag is enabled by default at @option{-O} and higher.
5064 @item -ftree-copyrename
5065 Perform copy renaming on trees. This pass attempts to rename compiler
5066 temporaries to other variables at copy locations, usually resulting in
5067 variable names which more closely resemble the original variables. This flag
5068 is enabled by default at @option{-O} and higher.
5071 Perform temporary expression replacement during the SSA->normal phase. Single
5072 use/single def temporaries are replaced at their use location with their
5073 defining expression. This results in non-GIMPLE code, but gives the expanders
5074 much more complex trees to work on resulting in better RTL generation. This is
5075 enabled by default at @option{-O} and higher.
5078 Perform live range splitting during the SSA->normal phase. Distinct live
5079 ranges of a variable are split into unique variables, allowing for better
5080 optimization later. This is enabled by default at @option{-O} and higher.
5082 @item -ftree-vectorize
5083 Perform loop vectorization on trees.
5085 @item -ftree-vect-loop-version
5086 @opindex ftree-vect-loop-version
5087 Perform loop versioning when doing loop vectorization on trees. When a loop
5088 appears to be vectorizable except that data alignment or data dependence cannot
5089 be determined at compile time then vectorized and non-vectorized versions of
5090 the loop are generated along with runtime checks for alignment or dependence
5091 to control which version is executed. This option is enabled by default
5092 except at level @option{-Os} where it is disabled.
5095 Perform Value Range Propagation on trees. This is similar to the
5096 constant propagation pass, but instead of values, ranges of values are
5097 propagated. This allows the optimizers to remove unnecessary range
5098 checks like array bound checks and null pointer checks. This is
5099 enabled by default at @option{-O2} and higher. Null pointer check
5100 elimination is only done if @option{-fdelete-null-pointer-checks} is
5105 Perform tail duplication to enlarge superblock size. This transformation
5106 simplifies the control flow of the function allowing other optimizations to do
5109 @item -funroll-loops
5110 @opindex funroll-loops
5111 Unroll loops whose number of iterations can be determined at compile
5112 time or upon entry to the loop. @option{-funroll-loops} implies both
5113 @option{-fstrength-reduce} and @option{-frerun-cse-after-loop}. This
5114 option makes code larger, and may or may not make it run faster.
5116 @item -funroll-all-loops
5117 @opindex funroll-all-loops
5118 Unroll all loops, even if their number of iterations is uncertain when
5119 the loop is entered. This usually makes programs run more slowly.
5120 @option{-funroll-all-loops} implies the same options as
5121 @option{-funroll-loops},
5123 @item -fsplit-ivs-in-unroller
5124 @opindex -fsplit-ivs-in-unroller
5125 Enables expressing of values of induction variables in later iterations
5126 of the unrolled loop using the value in the first iteration. This breaks
5127 long dependency chains, thus improving efficiency of the scheduling passes.
5129 Combination of @option{-fweb} and CSE is often sufficient to obtain the
5130 same effect. However in cases the loop body is more complicated than
5131 a single basic block, this is not reliable. It also does not work at all
5132 on some of the architectures due to restrictions in the CSE pass.
5134 This optimization is enabled by default.
5136 @item -fvariable-expansion-in-unroller
5137 @opindex -fvariable-expansion-in-unroller
5138 With this option, the compiler will create multiple copies of some
5139 local variables when unrolling a loop which can result in superior code.
5141 @item -fprefetch-loop-arrays
5142 @opindex fprefetch-loop-arrays
5143 If supported by the target machine, generate instructions to prefetch
5144 memory to improve the performance of loops that access large arrays.
5146 These options may generate better or worse code; results are highly
5147 dependent on the structure of loops within the source code.
5150 @itemx -fno-peephole2
5151 @opindex fno-peephole
5152 @opindex fno-peephole2
5153 Disable any machine-specific peephole optimizations. The difference
5154 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
5155 are implemented in the compiler; some targets use one, some use the
5156 other, a few use both.
5158 @option{-fpeephole} is enabled by default.
5159 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5161 @item -fno-guess-branch-probability
5162 @opindex fno-guess-branch-probability
5163 Do not guess branch probabilities using heuristics.
5165 GCC will use heuristics to guess branch probabilities if they are
5166 not provided by profiling feedback (@option{-fprofile-arcs}). These
5167 heuristics are based on the control flow graph. If some branch probabilities
5168 are specified by @samp{__builtin_expect}, then the heuristics will be
5169 used to guess branch probabilities for the rest of the control flow graph,
5170 taking the @samp{__builtin_expect} info into account. The interactions
5171 between the heuristics and @samp{__builtin_expect} can be complex, and in
5172 some cases, it may be useful to disable the heuristics so that the effects
5173 of @samp{__builtin_expect} are easier to understand.
5175 The default is @option{-fguess-branch-probability} at levels
5176 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5178 @item -freorder-blocks
5179 @opindex freorder-blocks
5180 Reorder basic blocks in the compiled function in order to reduce number of
5181 taken branches and improve code locality.
5183 Enabled at levels @option{-O2}, @option{-O3}.
5185 @item -freorder-blocks-and-partition
5186 @opindex freorder-blocks-and-partition
5187 In addition to reordering basic blocks in the compiled function, in order
5188 to reduce number of taken branches, partitions hot and cold basic blocks
5189 into separate sections of the assembly and .o files, to improve
5190 paging and cache locality performance.
5192 This optimization is automatically turned off in the presence of
5193 exception handling, for linkonce sections, for functions with a user-defined
5194 section attribute and on any architecture that does not support named
5197 @item -freorder-functions
5198 @opindex freorder-functions
5199 Reorder functions in the object file in order to
5200 improve code locality. This is implemented by using special
5201 subsections @code{.text.hot} for most frequently executed functions and
5202 @code{.text.unlikely} for unlikely executed functions. Reordering is done by
5203 the linker so object file format must support named sections and linker must
5204 place them in a reasonable way.
5206 Also profile feedback must be available in to make this option effective. See
5207 @option{-fprofile-arcs} for details.
5209 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5211 @item -fstrict-aliasing
5212 @opindex fstrict-aliasing
5213 Allows the compiler to assume the strictest aliasing rules applicable to
5214 the language being compiled. For C (and C++), this activates
5215 optimizations based on the type of expressions. In particular, an
5216 object of one type is assumed never to reside at the same address as an
5217 object of a different type, unless the types are almost the same. For
5218 example, an @code{unsigned int} can alias an @code{int}, but not a
5219 @code{void*} or a @code{double}. A character type may alias any other
5222 Pay special attention to code like this:
5235 The practice of reading from a different union member than the one most
5236 recently written to (called ``type-punning'') is common. Even with
5237 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
5238 is accessed through the union type. So, the code above will work as
5239 expected. However, this code might not:
5250 Every language that wishes to perform language-specific alias analysis
5251 should define a function that computes, given an @code{tree}
5252 node, an alias set for the node. Nodes in different alias sets are not
5253 allowed to alias. For an example, see the C front-end function
5254 @code{c_get_alias_set}.
5256 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5258 @item -falign-functions
5259 @itemx -falign-functions=@var{n}
5260 @opindex falign-functions
5261 Align the start of functions to the next power-of-two greater than
5262 @var{n}, skipping up to @var{n} bytes. For instance,
5263 @option{-falign-functions=32} aligns functions to the next 32-byte
5264 boundary, but @option{-falign-functions=24} would align to the next
5265 32-byte boundary only if this can be done by skipping 23 bytes or less.
5267 @option{-fno-align-functions} and @option{-falign-functions=1} are
5268 equivalent and mean that functions will not be aligned.
5270 Some assemblers only support this flag when @var{n} is a power of two;
5271 in that case, it is rounded up.
5273 If @var{n} is not specified or is zero, use a machine-dependent default.
5275 Enabled at levels @option{-O2}, @option{-O3}.
5277 @item -falign-labels
5278 @itemx -falign-labels=@var{n}
5279 @opindex falign-labels
5280 Align all branch targets to a power-of-two boundary, skipping up to
5281 @var{n} bytes like @option{-falign-functions}. This option can easily
5282 make code slower, because it must insert dummy operations for when the
5283 branch target is reached in the usual flow of the code.
5285 @option{-fno-align-labels} and @option{-falign-labels=1} are
5286 equivalent and mean that labels will not be aligned.
5288 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
5289 are greater than this value, then their values are used instead.
5291 If @var{n} is not specified or is zero, use a machine-dependent default
5292 which is very likely to be @samp{1}, meaning no alignment.
5294 Enabled at levels @option{-O2}, @option{-O3}.
5297 @itemx -falign-loops=@var{n}
5298 @opindex falign-loops
5299 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
5300 like @option{-falign-functions}. The hope is that the loop will be
5301 executed many times, which will make up for any execution of the dummy
5304 @option{-fno-align-loops} and @option{-falign-loops=1} are
5305 equivalent and mean that loops will not be aligned.
5307 If @var{n} is not specified or is zero, use a machine-dependent default.
5309 Enabled at levels @option{-O2}, @option{-O3}.
5312 @itemx -falign-jumps=@var{n}
5313 @opindex falign-jumps
5314 Align branch targets to a power-of-two boundary, for branch targets
5315 where the targets can only be reached by jumping, skipping up to @var{n}
5316 bytes like @option{-falign-functions}. In this case, no dummy operations
5319 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
5320 equivalent and mean that loops will not be aligned.
5322 If @var{n} is not specified or is zero, use a machine-dependent default.
5324 Enabled at levels @option{-O2}, @option{-O3}.
5326 @item -funit-at-a-time
5327 @opindex funit-at-a-time
5328 Parse the whole compilation unit before starting to produce code.
5329 This allows some extra optimizations to take place but consumes
5330 more memory (in general). There are some compatibility issues
5331 with @emph{unit-at-at-time} mode:
5334 enabling @emph{unit-at-a-time} mode may change the order
5335 in which functions, variables, and top-level @code{asm} statements
5336 are emitted, and will likely break code relying on some particular
5337 ordering. The majority of such top-level @code{asm} statements,
5338 though, can be replaced by @code{section} attributes.
5341 @emph{unit-at-a-time} mode removes unreferenced static variables
5342 and functions. This may result in undefined references
5343 when an @code{asm} statement refers directly to variables or functions
5344 that are otherwise unused. In that case either the variable/function
5345 shall be listed as an operand of the @code{asm} statement operand or,
5346 in the case of top-level @code{asm} statements the attribute @code{used}
5347 shall be used on the declaration.
5350 Static functions now can use non-standard passing conventions that
5351 may break @code{asm} statements calling functions directly. Again,
5352 attribute @code{used} will prevent this behavior.
5355 As a temporary workaround, @option{-fno-unit-at-a-time} can be used,
5356 but this scheme may not be supported by future releases of GCC@.
5358 Enabled at levels @option{-O2}, @option{-O3}.
5362 Constructs webs as commonly used for register allocation purposes and assign
5363 each web individual pseudo register. This allows the register allocation pass
5364 to operate on pseudos directly, but also strengthens several other optimization
5365 passes, such as CSE, loop optimizer and trivial dead code remover. It can,
5366 however, make debugging impossible, since variables will no longer stay in a
5369 Enabled by default with @option{-funroll-loops}.
5371 @item -fwhole-program
5372 @opindex fwhole-program
5373 Assume that the current compilation unit represents whole program being
5374 compiled. All public functions and variables with the exception of @code{main}
5375 and those merged by attribute @code{externally_visible} become static functions
5376 and in a affect gets more aggressively optimized by interprocedural optimizers.
5377 While this option is equivalent to proper use of @code{static} keyword for
5378 programs consisting of single file, in combination with option
5379 @option{--combine} this flag can be used to compile most of smaller scale C
5380 programs since the functions and variables become local for the whole combined
5381 compilation unit, not for the single source file itself.
5384 @item -fno-cprop-registers
5385 @opindex fno-cprop-registers
5386 After register allocation and post-register allocation instruction splitting,
5387 we perform a copy-propagation pass to try to reduce scheduling dependencies
5388 and occasionally eliminate the copy.
5390 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5392 @item -fprofile-generate
5393 @opindex fprofile-generate
5395 Enable options usually used for instrumenting application to produce
5396 profile useful for later recompilation with profile feedback based
5397 optimization. You must use @option{-fprofile-generate} both when
5398 compiling and when linking your program.
5400 The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}.
5403 @opindex fprofile-use
5404 Enable profile feedback directed optimizations, and optimizations
5405 generally profitable only with profile feedback available.
5407 The following options are enabled: @code{-fbranch-probabilities}, @code{-fvpt},
5408 @code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer},
5409 @code{-fno-loop-optimize}.
5413 The following options control compiler behavior regarding floating
5414 point arithmetic. These options trade off between speed and
5415 correctness. All must be specifically enabled.
5419 @opindex ffloat-store
5420 Do not store floating point variables in registers, and inhibit other
5421 options that might change whether a floating point value is taken from a
5424 @cindex floating point precision
5425 This option prevents undesirable excess precision on machines such as
5426 the 68000 where the floating registers (of the 68881) keep more
5427 precision than a @code{double} is supposed to have. Similarly for the
5428 x86 architecture. For most programs, the excess precision does only
5429 good, but a few programs rely on the precise definition of IEEE floating
5430 point. Use @option{-ffloat-store} for such programs, after modifying
5431 them to store all pertinent intermediate computations into variables.
5435 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, @*
5436 @option{-fno-trapping-math}, @option{-ffinite-math-only},
5437 @option{-fno-rounding-math}, @option{-fno-signaling-nans}
5438 and @option{fcx-limited-range}.
5440 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
5442 This option should never be turned on by any @option{-O} option since
5443 it can result in incorrect output for programs which depend on
5444 an exact implementation of IEEE or ISO rules/specifications for
5447 @item -fno-math-errno
5448 @opindex fno-math-errno
5449 Do not set ERRNO after calling math functions that are executed
5450 with a single instruction, e.g., sqrt. A program that relies on
5451 IEEE exceptions for math error handling may want to use this flag
5452 for speed while maintaining IEEE arithmetic compatibility.
5454 This option should never be turned on by any @option{-O} option since
5455 it can result in incorrect output for programs which depend on
5456 an exact implementation of IEEE or ISO rules/specifications for
5459 The default is @option{-fmath-errno}.
5461 On Darwin systems, the math library never sets @code{errno}. There is therefore
5462 no reason for the compiler to consider the possibility that it might,
5463 and @option{-fno-math-errno} is the default.
5465 @item -funsafe-math-optimizations
5466 @opindex funsafe-math-optimizations
5467 Allow optimizations for floating-point arithmetic that (a) assume
5468 that arguments and results are valid and (b) may violate IEEE or
5469 ANSI standards. When used at link-time, it may include libraries
5470 or startup files that change the default FPU control word or other
5471 similar optimizations.
5473 This option should never be turned on by any @option{-O} option since
5474 it can result in incorrect output for programs which depend on
5475 an exact implementation of IEEE or ISO rules/specifications for
5478 The default is @option{-fno-unsafe-math-optimizations}.
5480 @item -ffinite-math-only
5481 @opindex ffinite-math-only
5482 Allow optimizations for floating-point arithmetic that assume
5483 that arguments and results are not NaNs or +-Infs.
5485 This option should never be turned on by any @option{-O} option since
5486 it can result in incorrect output for programs which depend on
5487 an exact implementation of IEEE or ISO rules/specifications.
5489 The default is @option{-fno-finite-math-only}.
5491 @item -fno-trapping-math
5492 @opindex fno-trapping-math
5493 Compile code assuming that floating-point operations cannot generate
5494 user-visible traps. These traps include division by zero, overflow,
5495 underflow, inexact result and invalid operation. This option implies
5496 @option{-fno-signaling-nans}. Setting this option may allow faster
5497 code if one relies on ``non-stop'' IEEE arithmetic, for example.
5499 This option should never be turned on by any @option{-O} option since
5500 it can result in incorrect output for programs which depend on
5501 an exact implementation of IEEE or ISO rules/specifications for
5504 The default is @option{-ftrapping-math}.
5506 @item -frounding-math
5507 @opindex frounding-math
5508 Disable transformations and optimizations that assume default floating
5509 point rounding behavior. This is round-to-zero for all floating point
5510 to integer conversions, and round-to-nearest for all other arithmetic
5511 truncations. This option should be specified for programs that change
5512 the FP rounding mode dynamically, or that may be executed with a
5513 non-default rounding mode. This option disables constant folding of
5514 floating point expressions at compile-time (which may be affected by
5515 rounding mode) and arithmetic transformations that are unsafe in the
5516 presence of sign-dependent rounding modes.
5518 The default is @option{-fno-rounding-math}.
5520 This option is experimental and does not currently guarantee to
5521 disable all GCC optimizations that are affected by rounding mode.
5522 Future versions of GCC may provide finer control of this setting
5523 using C99's @code{FENV_ACCESS} pragma. This command line option
5524 will be used to specify the default state for @code{FENV_ACCESS}.
5526 @item -fsignaling-nans
5527 @opindex fsignaling-nans
5528 Compile code assuming that IEEE signaling NaNs may generate user-visible
5529 traps during floating-point operations. Setting this option disables
5530 optimizations that may change the number of exceptions visible with
5531 signaling NaNs. This option implies @option{-ftrapping-math}.
5533 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
5536 The default is @option{-fno-signaling-nans}.
5538 This option is experimental and does not currently guarantee to
5539 disable all GCC optimizations that affect signaling NaN behavior.
5541 @item -fsingle-precision-constant
5542 @opindex fsingle-precision-constant
5543 Treat floating point constant as single precision constant instead of
5544 implicitly converting it to double precision constant.
5546 @item -fcx-limited-range
5547 @itemx -fno-cx-limited-range
5548 @opindex fcx-limited-range
5549 @opindex fno-cx-limited-range
5550 When enabled, this option states that a range reduction step is not
5551 needed when performing complex division. The default is
5552 @option{-fno-cx-limited-range}, but is enabled by @option{-ffast-math}.
5554 This option controls the default setting of the ISO C99
5555 @code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to
5560 The following options control optimizations that may improve
5561 performance, but are not enabled by any @option{-O} options. This
5562 section includes experimental options that may produce broken code.
5565 @item -fbranch-probabilities
5566 @opindex fbranch-probabilities
5567 After running a program compiled with @option{-fprofile-arcs}
5568 (@pxref{Debugging Options,, Options for Debugging Your Program or
5569 @command{gcc}}), you can compile it a second time using
5570 @option{-fbranch-probabilities}, to improve optimizations based on
5571 the number of times each branch was taken. When the program
5572 compiled with @option{-fprofile-arcs} exits it saves arc execution
5573 counts to a file called @file{@var{sourcename}.gcda} for each source
5574 file The information in this data file is very dependent on the
5575 structure of the generated code, so you must use the same source code
5576 and the same optimization options for both compilations.
5578 With @option{-fbranch-probabilities}, GCC puts a
5579 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
5580 These can be used to improve optimization. Currently, they are only
5581 used in one place: in @file{reorg.c}, instead of guessing which path a
5582 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
5583 exactly determine which path is taken more often.
5585 @item -fprofile-values
5586 @opindex fprofile-values
5587 If combined with @option{-fprofile-arcs}, it adds code so that some
5588 data about values of expressions in the program is gathered.
5590 With @option{-fbranch-probabilities}, it reads back the data gathered
5591 from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
5592 notes to instructions for their later usage in optimizations.
5594 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
5598 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
5599 a code to gather information about values of expressions.
5601 With @option{-fbranch-probabilities}, it reads back the data gathered
5602 and actually performs the optimizations based on them.
5603 Currently the optimizations include specialization of division operation
5604 using the knowledge about the value of the denominator.
5606 @item -frename-registers
5607 @opindex frename-registers
5608 Attempt to avoid false dependencies in scheduled code by making use
5609 of registers left over after register allocation. This optimization
5610 will most benefit processors with lots of registers. Depending on the
5611 debug information format adopted by the target, however, it can
5612 make debugging impossible, since variables will no longer stay in
5613 a ``home register''.
5615 Enabled by default with @option{-funroll-loops}.
5619 Perform tail duplication to enlarge superblock size. This transformation
5620 simplifies the control flow of the function allowing other optimizations to do
5623 Enabled with @option{-fprofile-use}.
5625 @item -funroll-loops
5626 @opindex funroll-loops
5627 Unroll loops whose number of iterations can be determined at compile time or
5628 upon entry to the loop. @option{-funroll-loops} implies
5629 @option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}.
5630 It also turns on complete loop peeling (i.e.@: complete removal of loops with
5631 small constant number of iterations). This option makes code larger, and may
5632 or may not make it run faster.
5634 Enabled with @option{-fprofile-use}.
5636 @item -funroll-all-loops
5637 @opindex funroll-all-loops
5638 Unroll all loops, even if their number of iterations is uncertain when
5639 the loop is entered. This usually makes programs run more slowly.
5640 @option{-funroll-all-loops} implies the same options as
5641 @option{-funroll-loops}.
5644 @opindex fpeel-loops
5645 Peels the loops for that there is enough information that they do not
5646 roll much (from profile feedback). It also turns on complete loop peeling
5647 (i.e.@: complete removal of loops with small constant number of iterations).
5649 Enabled with @option{-fprofile-use}.
5651 @item -fmove-loop-invariants
5652 @opindex fmove-loop-invariants
5653 Enables the loop invariant motion pass in the new loop optimizer. Enabled
5654 at level @option{-O1}
5656 @item -funswitch-loops
5657 @opindex funswitch-loops
5658 Move branches with loop invariant conditions out of the loop, with duplicates
5659 of the loop on both branches (modified according to result of the condition).
5661 @item -fprefetch-loop-arrays
5662 @opindex fprefetch-loop-arrays
5663 If supported by the target machine, generate instructions to prefetch
5664 memory to improve the performance of loops that access large arrays.
5666 Disabled at level @option{-Os}.
5668 @item -ffunction-sections
5669 @itemx -fdata-sections
5670 @opindex ffunction-sections
5671 @opindex fdata-sections
5672 Place each function or data item into its own section in the output
5673 file if the target supports arbitrary sections. The name of the
5674 function or the name of the data item determines the section's name
5677 Use these options on systems where the linker can perform optimizations
5678 to improve locality of reference in the instruction space. Most systems
5679 using the ELF object format and SPARC processors running Solaris 2 have
5680 linkers with such optimizations. AIX may have these optimizations in
5683 Only use these options when there are significant benefits from doing
5684 so. When you specify these options, the assembler and linker will
5685 create larger object and executable files and will also be slower.
5686 You will not be able to use @code{gprof} on all systems if you
5687 specify this option and you may have problems with debugging if
5688 you specify both this option and @option{-g}.
5690 @item -fbranch-target-load-optimize
5691 @opindex fbranch-target-load-optimize
5692 Perform branch target register load optimization before prologue / epilogue
5694 The use of target registers can typically be exposed only during reload,
5695 thus hoisting loads out of loops and doing inter-block scheduling needs
5696 a separate optimization pass.
5698 @item -fbranch-target-load-optimize2
5699 @opindex fbranch-target-load-optimize2
5700 Perform branch target register load optimization after prologue / epilogue
5703 @item -fbtr-bb-exclusive
5704 @opindex fbtr-bb-exclusive
5705 When performing branch target register load optimization, don't reuse
5706 branch target registers in within any basic block.
5708 @item -fstack-protector
5709 Emit extra code to check for buffer overflows, such as stack smashing
5710 attacks. This is done by adding a guard variable to functions with
5711 vulnerable objects. This includes functions that call alloca, and
5712 functions with buffers larger than 8 bytes. The guards are initialized
5713 when a function is entered and then checked when the function exits.
5714 If a guard check fails, an error message is printed and the program exits.
5716 @item -fstack-protector-all
5717 Like @option{-fstack-protector} except that all functions are protected.
5719 @item --param @var{name}=@var{value}
5721 In some places, GCC uses various constants to control the amount of
5722 optimization that is done. For example, GCC will not inline functions
5723 that contain more that a certain number of instructions. You can
5724 control some of these constants on the command-line using the
5725 @option{--param} option.
5727 The names of specific parameters, and the meaning of the values, are
5728 tied to the internals of the compiler, and are subject to change
5729 without notice in future releases.
5731 In each case, the @var{value} is an integer. The allowable choices for
5732 @var{name} are given in the following table:
5735 @item salias-max-implicit-fields
5736 The maximum number of fields in a variable without direct
5737 structure accesses for which structure aliasing will consider trying
5738 to track each field. The default is 5
5740 @item sra-max-structure-size
5741 The maximum structure size, in bytes, at which the scalar replacement
5742 of aggregates (SRA) optimization will perform block copies. The
5743 default value, 0, implies that GCC will select the most appropriate
5746 @item sra-field-structure-ratio
5747 The threshold ratio (as a percentage) between instantiated fields and
5748 the complete structure size. We say that if the ratio of the number
5749 of bytes in instantiated fields to the number of bytes in the complete
5750 structure exceeds this parameter, then block copies are not used. The
5753 @item max-crossjump-edges
5754 The maximum number of incoming edges to consider for crossjumping.
5755 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
5756 the number of edges incoming to each block. Increasing values mean
5757 more aggressive optimization, making the compile time increase with
5758 probably small improvement in executable size.
5760 @item min-crossjump-insns
5761 The minimum number of instructions which must be matched at the end
5762 of two blocks before crossjumping will be performed on them. This
5763 value is ignored in the case where all instructions in the block being
5764 crossjumped from are matched. The default value is 5.
5766 @item max-grow-copy-bb-insns
5767 The maximum code size expansion factor when copying basic blocks
5768 instead of jumping. The expansion is relative to a jump instruction.
5769 The default value is 8.
5771 @item max-goto-duplication-insns
5772 The maximum number of instructions to duplicate to a block that jumps
5773 to a computed goto. To avoid @math{O(N^2)} behavior in a number of
5774 passes, GCC factors computed gotos early in the compilation process,
5775 and unfactors them as late as possible. Only computed jumps at the
5776 end of a basic blocks with no more than max-goto-duplication-insns are
5777 unfactored. The default value is 8.
5779 @item max-delay-slot-insn-search
5780 The maximum number of instructions to consider when looking for an
5781 instruction to fill a delay slot. If more than this arbitrary number of
5782 instructions is searched, the time savings from filling the delay slot
5783 will be minimal so stop searching. Increasing values mean more
5784 aggressive optimization, making the compile time increase with probably
5785 small improvement in executable run time.
5787 @item max-delay-slot-live-search
5788 When trying to fill delay slots, the maximum number of instructions to
5789 consider when searching for a block with valid live register
5790 information. Increasing this arbitrarily chosen value means more
5791 aggressive optimization, increasing the compile time. This parameter
5792 should be removed when the delay slot code is rewritten to maintain the
5795 @item max-gcse-memory
5796 The approximate maximum amount of memory that will be allocated in
5797 order to perform the global common subexpression elimination
5798 optimization. If more memory than specified is required, the
5799 optimization will not be done.
5801 @item max-gcse-passes
5802 The maximum number of passes of GCSE to run. The default is 1.
5804 @item max-pending-list-length
5805 The maximum number of pending dependencies scheduling will allow
5806 before flushing the current state and starting over. Large functions
5807 with few branches or calls can create excessively large lists which
5808 needlessly consume memory and resources.
5810 @item max-inline-insns-single
5811 Several parameters control the tree inliner used in gcc.
5812 This number sets the maximum number of instructions (counted in GCC's
5813 internal representation) in a single function that the tree inliner
5814 will consider for inlining. This only affects functions declared
5815 inline and methods implemented in a class declaration (C++).
5816 The default value is 450.
5818 @item max-inline-insns-auto
5819 When you use @option{-finline-functions} (included in @option{-O3}),
5820 a lot of functions that would otherwise not be considered for inlining
5821 by the compiler will be investigated. To those functions, a different
5822 (more restrictive) limit compared to functions declared inline can
5824 The default value is 90.
5826 @item large-function-insns
5827 The limit specifying really large functions. For functions larger than this
5828 limit after inlining inlining is constrained by
5829 @option{--param large-function-growth}. This parameter is useful primarily
5830 to avoid extreme compilation time caused by non-linear algorithms used by the
5832 This parameter is ignored when @option{-funit-at-a-time} is not used.
5833 The default value is 2700.
5835 @item large-function-growth
5836 Specifies maximal growth of large function caused by inlining in percents.
5837 This parameter is ignored when @option{-funit-at-a-time} is not used.
5838 The default value is 100 which limits large function growth to 2.0 times
5841 @item large-unit-insns
5842 The limit specifying large translation unit. Growth caused by inlining of
5843 units larger than this limit is limited by @option{--param inline-unit-growth}.
5844 For small units this might be too tight (consider unit consisting of function A
5845 that is inline and B that just calls A three time. If B is small relative to
5846 A, the growth of unit is 300\% and yet such inlining is very sane. For very
5847 large units consisting of small inlininable functions however the overall unit
5848 growth limit is needed to avoid exponential explosion of code size. Thus for
5849 smaller units, the size is increased to @option{--param large-unit-insns}
5850 before aplying @option{--param inline-unit-growth}. The default is 10000
5852 @item inline-unit-growth
5853 Specifies maximal overall growth of the compilation unit caused by inlining.
5854 This parameter is ignored when @option{-funit-at-a-time} is not used.
5855 The default value is 50 which limits unit growth to 1.5 times the original
5858 @item max-inline-insns-recursive
5859 @itemx max-inline-insns-recursive-auto
5860 Specifies maximum number of instructions out-of-line copy of self recursive inline
5861 function can grow into by performing recursive inlining.
5863 For functions declared inline @option{--param max-inline-insns-recursive} is
5864 taken into acount. For function not declared inline, recursive inlining
5865 happens only when @option{-finline-functions} (included in @option{-O3}) is
5866 enabled and @option{--param max-inline-insns-recursive-auto} is used. The
5867 default value is 450.
5869 @item max-inline-recursive-depth
5870 @itemx max-inline-recursive-depth-auto
5871 Specifies maximum recursion depth used by the recursive inlining.
5873 For functions declared inline @option{--param max-inline-recursive-depth} is
5874 taken into acount. For function not declared inline, recursive inlining
5875 happens only when @option{-finline-functions} (included in @option{-O3}) is
5876 enabled and @option{--param max-inline-recursive-depth-auto} is used. The
5877 default value is 450.
5879 @item min-inline-recursive-probability
5880 Recursive inlining is profitable only for function having deep recursion
5881 in average and can hurt for function having little recursion depth by
5882 increasing the prologue size or complexity of function body to other
5885 When profile feedback is available (see @option{-fprofile-generate}) the actual
5886 recursion depth can be guessed from probability that function will recurse via
5887 given call expression. This parameter limits inlining only to call expression
5888 whose probability exceeds given threshold (in percents). The default value is
5891 @item inline-call-cost
5892 Specify cost of call instruction relative to simple arithmetics operations
5893 (having cost of 1). Increasing this cost disqualifies inlining of non-leaf
5894 functions and at the same time increases size of leaf function that is believed to
5895 reduce function size by being inlined. In effect it increases amount of
5896 inlining for code having large abstraction penalty (many functions that just
5897 pass the arguments to other functions) and decrease inlining for code with low
5898 abstraction penalty. The default value is 16.
5900 @item max-unrolled-insns
5901 The maximum number of instructions that a loop should have if that loop
5902 is unrolled, and if the loop is unrolled, it determines how many times
5903 the loop code is unrolled.
5905 @item max-average-unrolled-insns
5906 The maximum number of instructions biased by probabilities of their execution
5907 that a loop should have if that loop is unrolled, and if the loop is unrolled,
5908 it determines how many times the loop code is unrolled.
5910 @item max-unroll-times
5911 The maximum number of unrollings of a single loop.
5913 @item max-peeled-insns
5914 The maximum number of instructions that a loop should have if that loop
5915 is peeled, and if the loop is peeled, it determines how many times
5916 the loop code is peeled.
5918 @item max-peel-times
5919 The maximum number of peelings of a single loop.
5921 @item max-completely-peeled-insns
5922 The maximum number of insns of a completely peeled loop.
5924 @item max-completely-peel-times
5925 The maximum number of iterations of a loop to be suitable for complete peeling.
5927 @item max-unswitch-insns
5928 The maximum number of insns of an unswitched loop.
5930 @item max-unswitch-level
5931 The maximum number of branches unswitched in a single loop.
5934 The minimum cost of an expensive expression in the loop invariant motion.
5936 @item iv-consider-all-candidates-bound
5937 Bound on number of candidates for induction variables below that
5938 all candidates are considered for each use in induction variable
5939 optimizations. Only the most relevant candidates are considered
5940 if there are more candidates, to avoid quadratic time complexity.
5942 @item iv-max-considered-uses
5943 The induction variable optimizations give up on loops that contain more
5944 induction variable uses.
5946 @item iv-always-prune-cand-set-bound
5947 If number of candidates in the set is smaller than this value,
5948 we always try to remove unnecessary ivs from the set during its
5949 optimization when a new iv is added to the set.
5951 @item scev-max-expr-size
5952 Bound on size of expressions used in the scalar evolutions analyzer.
5953 Large expressions slow the analyzer.
5955 @item vect-max-version-checks
5956 The maximum number of runtime checks that can be performed when doing
5957 loop versioning in the vectorizer. See option ftree-vect-loop-version
5958 for more information.
5960 @item max-iterations-to-track
5962 The maximum number of iterations of a loop the brute force algorithm
5963 for analysis of # of iterations of the loop tries to evaluate.
5965 @item hot-bb-count-fraction
5966 Select fraction of the maximal count of repetitions of basic block in program
5967 given basic block needs to have to be considered hot.
5969 @item hot-bb-frequency-fraction
5970 Select fraction of the maximal frequency of executions of basic block in
5971 function given basic block needs to have to be considered hot
5973 @item max-predicted-iterations
5974 The maximum number of loop iterations we predict statically. This is useful
5975 in cases where function contain single loop with known bound and other loop
5976 with unknown. We predict the known number of iterations correctly, while
5977 the unknown number of iterations average to roughly 10. This means that the
5978 loop without bounds would appear artificially cold relative to the other one.
5980 @item tracer-dynamic-coverage
5981 @itemx tracer-dynamic-coverage-feedback
5983 This value is used to limit superblock formation once the given percentage of
5984 executed instructions is covered. This limits unnecessary code size
5987 The @option{tracer-dynamic-coverage-feedback} is used only when profile
5988 feedback is available. The real profiles (as opposed to statically estimated
5989 ones) are much less balanced allowing the threshold to be larger value.
5991 @item tracer-max-code-growth
5992 Stop tail duplication once code growth has reached given percentage. This is
5993 rather hokey argument, as most of the duplicates will be eliminated later in
5994 cross jumping, so it may be set to much higher values than is the desired code
5997 @item tracer-min-branch-ratio
5999 Stop reverse growth when the reverse probability of best edge is less than this
6000 threshold (in percent).
6002 @item tracer-min-branch-ratio
6003 @itemx tracer-min-branch-ratio-feedback
6005 Stop forward growth if the best edge do have probability lower than this
6008 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
6009 compilation for profile feedback and one for compilation without. The value
6010 for compilation with profile feedback needs to be more conservative (higher) in
6011 order to make tracer effective.
6013 @item max-cse-path-length
6015 Maximum number of basic blocks on path that cse considers. The default is 10.
6018 The maximum instructions CSE process before flushing. The default is 1000.
6020 @item global-var-threshold
6022 Counts the number of function calls (@var{n}) and the number of
6023 call-clobbered variables (@var{v}). If @var{n}x@var{v} is larger than this limit, a
6024 single artificial variable will be created to represent all the
6025 call-clobbered variables at function call sites. This artificial
6026 variable will then be made to alias every call-clobbered variable.
6027 (done as @code{int * size_t} on the host machine; beware overflow).
6029 @item max-aliased-vops
6031 Maximum number of virtual operands allowed to represent aliases
6032 before triggering the alias grouping heuristic. Alias grouping
6033 reduces compile times and memory consumption needed for aliasing at
6034 the expense of precision loss in alias information.
6036 @item ggc-min-expand
6038 GCC uses a garbage collector to manage its own memory allocation. This
6039 parameter specifies the minimum percentage by which the garbage
6040 collector's heap should be allowed to expand between collections.
6041 Tuning this may improve compilation speed; it has no effect on code
6044 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
6045 RAM >= 1GB@. If @code{getrlimit} is available, the notion of "RAM" is
6046 the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If
6047 GCC is not able to calculate RAM on a particular platform, the lower
6048 bound of 30% is used. Setting this parameter and
6049 @option{ggc-min-heapsize} to zero causes a full collection to occur at
6050 every opportunity. This is extremely slow, but can be useful for
6053 @item ggc-min-heapsize
6055 Minimum size of the garbage collector's heap before it begins bothering
6056 to collect garbage. The first collection occurs after the heap expands
6057 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
6058 tuning this may improve compilation speed, and has no effect on code
6061 The default is the smaller of RAM/8, RLIMIT_RSS, or a limit which
6062 tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
6063 with a lower bound of 4096 (four megabytes) and an upper bound of
6064 131072 (128 megabytes). If GCC is not able to calculate RAM on a
6065 particular platform, the lower bound is used. Setting this parameter
6066 very large effectively disables garbage collection. Setting this
6067 parameter and @option{ggc-min-expand} to zero causes a full collection
6068 to occur at every opportunity.
6070 @item max-reload-search-insns
6071 The maximum number of instruction reload should look backward for equivalent
6072 register. Increasing values mean more aggressive optimization, making the
6073 compile time increase with probably slightly better performance. The default
6076 @item max-cselib-memory-location
6077 The maximum number of memory locations cselib should take into acount.
6078 Increasing values mean more aggressive optimization, making the compile time
6079 increase with probably slightly better performance. The default value is 500.
6081 @item max-flow-memory-location
6082 Similar as @option{max-cselib-memory-location} but for dataflow liveness.
6083 The default value is 100.
6085 @item reorder-blocks-duplicate
6086 @itemx reorder-blocks-duplicate-feedback
6088 Used by basic block reordering pass to decide whether to use unconditional
6089 branch or duplicate the code on its destination. Code is duplicated when its
6090 estimated size is smaller than this value multiplied by the estimated size of
6091 unconditional jump in the hot spots of the program.
6093 The @option{reorder-block-duplicate-feedback} is used only when profile
6094 feedback is available and may be set to higher values than
6095 @option{reorder-block-duplicate} since information about the hot spots is more
6098 @item max-sched-region-blocks
6099 The maximum number of blocks in a region to be considered for
6100 interblock scheduling. The default value is 10.
6102 @item max-sched-region-insns
6103 The maximum number of insns in a region to be considered for
6104 interblock scheduling. The default value is 100.
6106 @item min-sched-prob
6107 The minimum probability of reaching a source block for interblock
6108 speculative scheduling. The default value is 40.
6110 @item max-last-value-rtl
6112 The maximum size measured as number of RTLs that can be recorded in an expression
6113 in combiner for a pseudo register as last known value of that register. The default
6116 @item integer-share-limit
6117 Small integer constants can use a shared data structure, reducing the
6118 compiler's memory usage and increasing its speed. This sets the maximum
6119 value of a shared integer constant's. The default value is 256.
6121 @item min-virtual-mappings
6122 Specifies the minimum number of virtual mappings in the incremental
6123 SSA updater that should be registered to trigger the virtual mappings
6124 heuristic defined by virtual-mappings-ratio. The default value is
6127 @item virtual-mappings-ratio
6128 If the number of virtual mappings is virtual-mappings-ratio bigger
6129 than the number of virtual symbols to be updated, then the incremental
6130 SSA updater switches to a full update for those symbols. The default
6133 @item ssp-buffer-size
6134 The minimum size of buffers (i.e. arrays) that will receive stack smashing
6135 protection when @option{-fstack-protection} is used.
6137 @item max-jump-thread-duplication-stmts
6138 Maximum number of statements allowed in a block that needs to be
6139 duplicated when threading jumps.
6143 @node Preprocessor Options
6144 @section Options Controlling the Preprocessor
6145 @cindex preprocessor options
6146 @cindex options, preprocessor
6148 These options control the C preprocessor, which is run on each C source
6149 file before actual compilation.
6151 If you use the @option{-E} option, nothing is done except preprocessing.
6152 Some of these options make sense only together with @option{-E} because
6153 they cause the preprocessor output to be unsuitable for actual
6158 You can use @option{-Wp,@var{option}} to bypass the compiler driver
6159 and pass @var{option} directly through to the preprocessor. If
6160 @var{option} contains commas, it is split into multiple options at the
6161 commas. However, many options are modified, translated or interpreted
6162 by the compiler driver before being passed to the preprocessor, and
6163 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
6164 interface is undocumented and subject to change, so whenever possible
6165 you should avoid using @option{-Wp} and let the driver handle the
6168 @item -Xpreprocessor @var{option}
6169 @opindex preprocessor
6170 Pass @var{option} as an option to the preprocessor. You can use this to
6171 supply system-specific preprocessor options which GCC does not know how to
6174 If you want to pass an option that takes an argument, you must use
6175 @option{-Xpreprocessor} twice, once for the option and once for the argument.
6178 @include cppopts.texi
6180 @node Assembler Options
6181 @section Passing Options to the Assembler
6183 @c prevent bad page break with this line
6184 You can pass options to the assembler.
6187 @item -Wa,@var{option}
6189 Pass @var{option} as an option to the assembler. If @var{option}
6190 contains commas, it is split into multiple options at the commas.
6192 @item -Xassembler @var{option}
6194 Pass @var{option} as an option to the assembler. You can use this to
6195 supply system-specific assembler options which GCC does not know how to
6198 If you want to pass an option that takes an argument, you must use
6199 @option{-Xassembler} twice, once for the option and once for the argument.
6204 @section Options for Linking
6205 @cindex link options
6206 @cindex options, linking
6208 These options come into play when the compiler links object files into
6209 an executable output file. They are meaningless if the compiler is
6210 not doing a link step.
6214 @item @var{object-file-name}
6215 A file name that does not end in a special recognized suffix is
6216 considered to name an object file or library. (Object files are
6217 distinguished from libraries by the linker according to the file
6218 contents.) If linking is done, these object files are used as input
6227 If any of these options is used, then the linker is not run, and
6228 object file names should not be used as arguments. @xref{Overall
6232 @item -l@var{library}
6233 @itemx -l @var{library}
6235 Search the library named @var{library} when linking. (The second
6236 alternative with the library as a separate argument is only for
6237 POSIX compliance and is not recommended.)
6239 It makes a difference where in the command you write this option; the
6240 linker searches and processes libraries and object files in the order they
6241 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
6242 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
6243 to functions in @samp{z}, those functions may not be loaded.
6245 The linker searches a standard list of directories for the library,
6246 which is actually a file named @file{lib@var{library}.a}. The linker
6247 then uses this file as if it had been specified precisely by name.
6249 The directories searched include several standard system directories
6250 plus any that you specify with @option{-L}.
6252 Normally the files found this way are library files---archive files
6253 whose members are object files. The linker handles an archive file by
6254 scanning through it for members which define symbols that have so far
6255 been referenced but not defined. But if the file that is found is an
6256 ordinary object file, it is linked in the usual fashion. The only
6257 difference between using an @option{-l} option and specifying a file name
6258 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
6259 and searches several directories.
6263 You need this special case of the @option{-l} option in order to
6264 link an Objective-C or Objective-C++ program.
6267 @opindex nostartfiles
6268 Do not use the standard system startup files when linking.
6269 The standard system libraries are used normally, unless @option{-nostdlib}
6270 or @option{-nodefaultlibs} is used.
6272 @item -nodefaultlibs
6273 @opindex nodefaultlibs
6274 Do not use the standard system libraries when linking.
6275 Only the libraries you specify will be passed to the linker.
6276 The standard startup files are used normally, unless @option{-nostartfiles}
6277 is used. The compiler may generate calls to @code{memcmp},
6278 @code{memset}, @code{memcpy} and @code{memmove}.
6279 These entries are usually resolved by entries in
6280 libc. These entry points should be supplied through some other
6281 mechanism when this option is specified.
6285 Do not use the standard system startup files or libraries when linking.
6286 No startup files and only the libraries you specify will be passed to
6287 the linker. The compiler may generate calls to @code{memcmp}, @code{memset},
6288 @code{memcpy} and @code{memmove}.
6289 These entries are usually resolved by entries in
6290 libc. These entry points should be supplied through some other
6291 mechanism when this option is specified.
6293 @cindex @option{-lgcc}, use with @option{-nostdlib}
6294 @cindex @option{-nostdlib} and unresolved references
6295 @cindex unresolved references and @option{-nostdlib}
6296 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
6297 @cindex @option{-nodefaultlibs} and unresolved references
6298 @cindex unresolved references and @option{-nodefaultlibs}
6299 One of the standard libraries bypassed by @option{-nostdlib} and
6300 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
6301 that GCC uses to overcome shortcomings of particular machines, or special
6302 needs for some languages.
6303 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
6304 Collection (GCC) Internals},
6305 for more discussion of @file{libgcc.a}.)
6306 In most cases, you need @file{libgcc.a} even when you want to avoid
6307 other standard libraries. In other words, when you specify @option{-nostdlib}
6308 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
6309 This ensures that you have no unresolved references to internal GCC
6310 library subroutines. (For example, @samp{__main}, used to ensure C++
6311 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
6312 GNU Compiler Collection (GCC) Internals}.)
6316 Produce a position independent executable on targets which support it.
6317 For predictable results, you must also specify the same set of options
6318 that were used to generate code (@option{-fpie}, @option{-fPIE},
6319 or model suboptions) when you specify this option.
6323 Pass the flag @option{-export-dynamic} to the ELF linker, on targets
6324 that support it. This instructs the linker to add all symbols, not
6325 only used ones, to the dynamic symbol table. This option is needed
6326 for some uses of @code{dlopen} or to allow obtaining backtraces
6327 from within a program.
6331 Remove all symbol table and relocation information from the executable.
6335 On systems that support dynamic linking, this prevents linking with the shared
6336 libraries. On other systems, this option has no effect.
6340 Produce a shared object which can then be linked with other objects to
6341 form an executable. Not all systems support this option. For predictable
6342 results, you must also specify the same set of options that were used to
6343 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
6344 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
6345 needs to build supplementary stub code for constructors to work. On
6346 multi-libbed systems, @samp{gcc -shared} must select the correct support
6347 libraries to link against. Failing to supply the correct flags may lead
6348 to subtle defects. Supplying them in cases where they are not necessary
6351 @item -shared-libgcc
6352 @itemx -static-libgcc
6353 @opindex shared-libgcc
6354 @opindex static-libgcc
6355 On systems that provide @file{libgcc} as a shared library, these options
6356 force the use of either the shared or static version respectively.
6357 If no shared version of @file{libgcc} was built when the compiler was
6358 configured, these options have no effect.
6360 There are several situations in which an application should use the
6361 shared @file{libgcc} instead of the static version. The most common
6362 of these is when the application wishes to throw and catch exceptions
6363 across different shared libraries. In that case, each of the libraries
6364 as well as the application itself should use the shared @file{libgcc}.
6366 Therefore, the G++ and GCJ drivers automatically add
6367 @option{-shared-libgcc} whenever you build a shared library or a main
6368 executable, because C++ and Java programs typically use exceptions, so
6369 this is the right thing to do.
6371 If, instead, you use the GCC driver to create shared libraries, you may
6372 find that they will not always be linked with the shared @file{libgcc}.
6373 If GCC finds, at its configuration time, that you have a non-GNU linker
6374 or a GNU linker that does not support option @option{--eh-frame-hdr},
6375 it will link the shared version of @file{libgcc} into shared libraries
6376 by default. Otherwise, it will take advantage of the linker and optimize
6377 away the linking with the shared version of @file{libgcc}, linking with
6378 the static version of libgcc by default. This allows exceptions to
6379 propagate through such shared libraries, without incurring relocation
6380 costs at library load time.
6382 However, if a library or main executable is supposed to throw or catch
6383 exceptions, you must link it using the G++ or GCJ driver, as appropriate
6384 for the languages used in the program, or using the option
6385 @option{-shared-libgcc}, such that it is linked with the shared
6390 Bind references to global symbols when building a shared object. Warn
6391 about any unresolved references (unless overridden by the link editor
6392 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
6395 @item -Xlinker @var{option}
6397 Pass @var{option} as an option to the linker. You can use this to
6398 supply system-specific linker options which GCC does not know how to
6401 If you want to pass an option that takes an argument, you must use
6402 @option{-Xlinker} twice, once for the option and once for the argument.
6403 For example, to pass @option{-assert definitions}, you must write
6404 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
6405 @option{-Xlinker "-assert definitions"}, because this passes the entire
6406 string as a single argument, which is not what the linker expects.
6408 @item -Wl,@var{option}
6410 Pass @var{option} as an option to the linker. If @var{option} contains
6411 commas, it is split into multiple options at the commas.
6413 @item -u @var{symbol}
6415 Pretend the symbol @var{symbol} is undefined, to force linking of
6416 library modules to define it. You can use @option{-u} multiple times with
6417 different symbols to force loading of additional library modules.
6420 @node Directory Options
6421 @section Options for Directory Search
6422 @cindex directory options
6423 @cindex options, directory search
6426 These options specify directories to search for header files, for
6427 libraries and for parts of the compiler:
6432 Add the directory @var{dir} to the head of the list of directories to be
6433 searched for header files. This can be used to override a system header
6434 file, substituting your own version, since these directories are
6435 searched before the system header file directories. However, you should
6436 not use this option to add directories that contain vendor-supplied
6437 system header files (use @option{-isystem} for that). If you use more than
6438 one @option{-I} option, the directories are scanned in left-to-right
6439 order; the standard system directories come after.
6441 If a standard system include directory, or a directory specified with
6442 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
6443 option will be ignored. The directory will still be searched but as a
6444 system directory at its normal position in the system include chain.
6445 This is to ensure that GCC's procedure to fix buggy system headers and
6446 the ordering for the include_next directive are not inadvertently changed.
6447 If you really need to change the search order for system directories,
6448 use the @option{-nostdinc} and/or @option{-isystem} options.
6450 @item -iquote@var{dir}
6452 Add the directory @var{dir} to the head of the list of directories to
6453 be searched for header files only for the case of @samp{#include
6454 "@var{file}"}; they are not searched for @samp{#include <@var{file}>},
6455 otherwise just like @option{-I}.
6459 Add directory @var{dir} to the list of directories to be searched
6462 @item -B@var{prefix}
6464 This option specifies where to find the executables, libraries,
6465 include files, and data files of the compiler itself.
6467 The compiler driver program runs one or more of the subprograms
6468 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
6469 @var{prefix} as a prefix for each program it tries to run, both with and
6470 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
6472 For each subprogram to be run, the compiler driver first tries the
6473 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
6474 was not specified, the driver tries two standard prefixes, which are
6475 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
6476 those results in a file name that is found, the unmodified program
6477 name is searched for using the directories specified in your
6478 @env{PATH} environment variable.
6480 The compiler will check to see if the path provided by the @option{-B}
6481 refers to a directory, and if necessary it will add a directory
6482 separator character at the end of the path.
6484 @option{-B} prefixes that effectively specify directory names also apply
6485 to libraries in the linker, because the compiler translates these
6486 options into @option{-L} options for the linker. They also apply to
6487 includes files in the preprocessor, because the compiler translates these
6488 options into @option{-isystem} options for the preprocessor. In this case,
6489 the compiler appends @samp{include} to the prefix.
6491 The run-time support file @file{libgcc.a} can also be searched for using
6492 the @option{-B} prefix, if needed. If it is not found there, the two
6493 standard prefixes above are tried, and that is all. The file is left
6494 out of the link if it is not found by those means.
6496 Another way to specify a prefix much like the @option{-B} prefix is to use
6497 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
6500 As a special kludge, if the path provided by @option{-B} is
6501 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
6502 9, then it will be replaced by @file{[dir/]include}. This is to help
6503 with boot-strapping the compiler.
6505 @item -specs=@var{file}
6507 Process @var{file} after the compiler reads in the standard @file{specs}
6508 file, in order to override the defaults that the @file{gcc} driver
6509 program uses when determining what switches to pass to @file{cc1},
6510 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
6511 @option{-specs=@var{file}} can be specified on the command line, and they
6512 are processed in order, from left to right.
6514 @item --sysroot=@var{dir}
6516 Use @var{dir} as the logical root directory for headers and libraries.
6517 For example, if the compiler would normally search for headers in
6518 @file{/usr/include} and libraries in @file{/usr/lib}, it will instead
6519 search @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}.
6521 If you use both this option and the @option{-isysroot} option, then
6522 the @option{--sysroot} option will apply to libraries, but the
6523 @option{-isysroot} option will apply to header files.
6525 The GNU linker (beginning with version 2.16) has the necessary support
6526 for this option. If your linker does not support this option, the
6527 header file aspect of @option{--sysroot} will still work, but the
6528 library aspect will not.
6532 This option has been deprecated. Please use @option{-iquote} instead for
6533 @option{-I} directories before the @option{-I-} and remove the @option{-I-}.
6534 Any directories you specify with @option{-I} options before the @option{-I-}
6535 option are searched only for the case of @samp{#include "@var{file}"};
6536 they are not searched for @samp{#include <@var{file}>}.
6538 If additional directories are specified with @option{-I} options after
6539 the @option{-I-}, these directories are searched for all @samp{#include}
6540 directives. (Ordinarily @emph{all} @option{-I} directories are used
6543 In addition, the @option{-I-} option inhibits the use of the current
6544 directory (where the current input file came from) as the first search
6545 directory for @samp{#include "@var{file}"}. There is no way to
6546 override this effect of @option{-I-}. With @option{-I.} you can specify
6547 searching the directory which was current when the compiler was
6548 invoked. That is not exactly the same as what the preprocessor does
6549 by default, but it is often satisfactory.
6551 @option{-I-} does not inhibit the use of the standard system directories
6552 for header files. Thus, @option{-I-} and @option{-nostdinc} are
6559 @section Specifying subprocesses and the switches to pass to them
6562 @command{gcc} is a driver program. It performs its job by invoking a
6563 sequence of other programs to do the work of compiling, assembling and
6564 linking. GCC interprets its command-line parameters and uses these to
6565 deduce which programs it should invoke, and which command-line options
6566 it ought to place on their command lines. This behavior is controlled
6567 by @dfn{spec strings}. In most cases there is one spec string for each
6568 program that GCC can invoke, but a few programs have multiple spec
6569 strings to control their behavior. The spec strings built into GCC can
6570 be overridden by using the @option{-specs=} command-line switch to specify
6573 @dfn{Spec files} are plaintext files that are used to construct spec
6574 strings. They consist of a sequence of directives separated by blank
6575 lines. The type of directive is determined by the first non-whitespace
6576 character on the line and it can be one of the following:
6579 @item %@var{command}
6580 Issues a @var{command} to the spec file processor. The commands that can
6584 @item %include <@var{file}>
6586 Search for @var{file} and insert its text at the current point in the
6589 @item %include_noerr <@var{file}>
6590 @cindex %include_noerr
6591 Just like @samp{%include}, but do not generate an error message if the include
6592 file cannot be found.
6594 @item %rename @var{old_name} @var{new_name}
6596 Rename the spec string @var{old_name} to @var{new_name}.
6600 @item *[@var{spec_name}]:
6601 This tells the compiler to create, override or delete the named spec
6602 string. All lines after this directive up to the next directive or
6603 blank line are considered to be the text for the spec string. If this
6604 results in an empty string then the spec will be deleted. (Or, if the
6605 spec did not exist, then nothing will happened.) Otherwise, if the spec
6606 does not currently exist a new spec will be created. If the spec does
6607 exist then its contents will be overridden by the text of this
6608 directive, unless the first character of that text is the @samp{+}
6609 character, in which case the text will be appended to the spec.
6611 @item [@var{suffix}]:
6612 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
6613 and up to the next directive or blank line are considered to make up the
6614 spec string for the indicated suffix. When the compiler encounters an
6615 input file with the named suffix, it will processes the spec string in
6616 order to work out how to compile that file. For example:
6623 This says that any input file whose name ends in @samp{.ZZ} should be
6624 passed to the program @samp{z-compile}, which should be invoked with the
6625 command-line switch @option{-input} and with the result of performing the
6626 @samp{%i} substitution. (See below.)
6628 As an alternative to providing a spec string, the text that follows a
6629 suffix directive can be one of the following:
6632 @item @@@var{language}
6633 This says that the suffix is an alias for a known @var{language}. This is
6634 similar to using the @option{-x} command-line switch to GCC to specify a
6635 language explicitly. For example:
6642 Says that .ZZ files are, in fact, C++ source files.
6645 This causes an error messages saying:
6648 @var{name} compiler not installed on this system.
6652 GCC already has an extensive list of suffixes built into it.
6653 This directive will add an entry to the end of the list of suffixes, but
6654 since the list is searched from the end backwards, it is effectively
6655 possible to override earlier entries using this technique.
6659 GCC has the following spec strings built into it. Spec files can
6660 override these strings or create their own. Note that individual
6661 targets can also add their own spec strings to this list.
6664 asm Options to pass to the assembler
6665 asm_final Options to pass to the assembler post-processor
6666 cpp Options to pass to the C preprocessor
6667 cc1 Options to pass to the C compiler
6668 cc1plus Options to pass to the C++ compiler
6669 endfile Object files to include at the end of the link
6670 link Options to pass to the linker
6671 lib Libraries to include on the command line to the linker
6672 libgcc Decides which GCC support library to pass to the linker
6673 linker Sets the name of the linker
6674 predefines Defines to be passed to the C preprocessor
6675 signed_char Defines to pass to CPP to say whether @code{char} is signed
6677 startfile Object files to include at the start of the link
6680 Here is a small example of a spec file:
6686 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
6689 This example renames the spec called @samp{lib} to @samp{old_lib} and
6690 then overrides the previous definition of @samp{lib} with a new one.
6691 The new definition adds in some extra command-line options before
6692 including the text of the old definition.
6694 @dfn{Spec strings} are a list of command-line options to be passed to their
6695 corresponding program. In addition, the spec strings can contain
6696 @samp{%}-prefixed sequences to substitute variable text or to
6697 conditionally insert text into the command line. Using these constructs
6698 it is possible to generate quite complex command lines.
6700 Here is a table of all defined @samp{%}-sequences for spec
6701 strings. Note that spaces are not generated automatically around the
6702 results of expanding these sequences. Therefore you can concatenate them
6703 together or combine them with constant text in a single argument.
6707 Substitute one @samp{%} into the program name or argument.
6710 Substitute the name of the input file being processed.
6713 Substitute the basename of the input file being processed.
6714 This is the substring up to (and not including) the last period
6715 and not including the directory.
6718 This is the same as @samp{%b}, but include the file suffix (text after
6722 Marks the argument containing or following the @samp{%d} as a
6723 temporary file name, so that that file will be deleted if GCC exits
6724 successfully. Unlike @samp{%g}, this contributes no text to the
6727 @item %g@var{suffix}
6728 Substitute a file name that has suffix @var{suffix} and is chosen
6729 once per compilation, and mark the argument in the same way as
6730 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
6731 name is now chosen in a way that is hard to predict even when previously
6732 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
6733 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
6734 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
6735 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
6736 was simply substituted with a file name chosen once per compilation,
6737 without regard to any appended suffix (which was therefore treated
6738 just like ordinary text), making such attacks more likely to succeed.
6740 @item %u@var{suffix}
6741 Like @samp{%g}, but generates a new temporary file name even if
6742 @samp{%u@var{suffix}} was already seen.
6744 @item %U@var{suffix}
6745 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
6746 new one if there is no such last file name. In the absence of any
6747 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
6748 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
6749 would involve the generation of two distinct file names, one
6750 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
6751 simply substituted with a file name chosen for the previous @samp{%u},
6752 without regard to any appended suffix.
6754 @item %j@var{suffix}
6755 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
6756 writable, and if save-temps is off; otherwise, substitute the name
6757 of a temporary file, just like @samp{%u}. This temporary file is not
6758 meant for communication between processes, but rather as a junk
6761 @item %|@var{suffix}
6762 @itemx %m@var{suffix}
6763 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
6764 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
6765 all. These are the two most common ways to instruct a program that it
6766 should read from standard input or write to standard output. If you
6767 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
6768 construct: see for example @file{f/lang-specs.h}.
6770 @item %.@var{SUFFIX}
6771 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
6772 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
6773 terminated by the next space or %.
6776 Marks the argument containing or following the @samp{%w} as the
6777 designated output file of this compilation. This puts the argument
6778 into the sequence of arguments that @samp{%o} will substitute later.
6781 Substitutes the names of all the output files, with spaces
6782 automatically placed around them. You should write spaces
6783 around the @samp{%o} as well or the results are undefined.
6784 @samp{%o} is for use in the specs for running the linker.
6785 Input files whose names have no recognized suffix are not compiled
6786 at all, but they are included among the output files, so they will
6790 Substitutes the suffix for object files. Note that this is
6791 handled specially when it immediately follows @samp{%g, %u, or %U},
6792 because of the need for those to form complete file names. The
6793 handling is such that @samp{%O} is treated exactly as if it had already
6794 been substituted, except that @samp{%g, %u, and %U} do not currently
6795 support additional @var{suffix} characters following @samp{%O} as they would
6796 following, for example, @samp{.o}.
6799 Substitutes the standard macro predefinitions for the
6800 current target machine. Use this when running @code{cpp}.
6803 Like @samp{%p}, but puts @samp{__} before and after the name of each
6804 predefined macro, except for macros that start with @samp{__} or with
6805 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
6809 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
6810 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}), and
6811 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
6815 Current argument is the name of a library or startup file of some sort.
6816 Search for that file in a standard list of directories and substitute
6817 the full name found.
6820 Print @var{str} as an error message. @var{str} is terminated by a newline.
6821 Use this when inconsistent options are detected.
6824 Substitute the contents of spec string @var{name} at this point.
6827 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
6829 @item %x@{@var{option}@}
6830 Accumulate an option for @samp{%X}.
6833 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
6837 Output the accumulated assembler options specified by @option{-Wa}.
6840 Output the accumulated preprocessor options specified by @option{-Wp}.
6843 Process the @code{asm} spec. This is used to compute the
6844 switches to be passed to the assembler.
6847 Process the @code{asm_final} spec. This is a spec string for
6848 passing switches to an assembler post-processor, if such a program is
6852 Process the @code{link} spec. This is the spec for computing the
6853 command line passed to the linker. Typically it will make use of the
6854 @samp{%L %G %S %D and %E} sequences.
6857 Dump out a @option{-L} option for each directory that GCC believes might
6858 contain startup files. If the target supports multilibs then the
6859 current multilib directory will be prepended to each of these paths.
6862 Process the @code{lib} spec. This is a spec string for deciding which
6863 libraries should be included on the command line to the linker.
6866 Process the @code{libgcc} spec. This is a spec string for deciding
6867 which GCC support library should be included on the command line to the linker.
6870 Process the @code{startfile} spec. This is a spec for deciding which
6871 object files should be the first ones passed to the linker. Typically
6872 this might be a file named @file{crt0.o}.
6875 Process the @code{endfile} spec. This is a spec string that specifies
6876 the last object files that will be passed to the linker.
6879 Process the @code{cpp} spec. This is used to construct the arguments
6880 to be passed to the C preprocessor.
6883 Process the @code{cc1} spec. This is used to construct the options to be
6884 passed to the actual C compiler (@samp{cc1}).
6887 Process the @code{cc1plus} spec. This is used to construct the options to be
6888 passed to the actual C++ compiler (@samp{cc1plus}).
6891 Substitute the variable part of a matched option. See below.
6892 Note that each comma in the substituted string is replaced by
6896 Remove all occurrences of @code{-S} from the command line. Note---this
6897 command is position dependent. @samp{%} commands in the spec string
6898 before this one will see @code{-S}, @samp{%} commands in the spec string
6899 after this one will not.
6901 @item %:@var{function}(@var{args})
6902 Call the named function @var{function}, passing it @var{args}.
6903 @var{args} is first processed as a nested spec string, then split
6904 into an argument vector in the usual fashion. The function returns
6905 a string which is processed as if it had appeared literally as part
6906 of the current spec.
6908 The following built-in spec functions are provided:
6911 @item @code{if-exists}
6912 The @code{if-exists} spec function takes one argument, an absolute
6913 pathname to a file. If the file exists, @code{if-exists} returns the
6914 pathname. Here is a small example of its usage:
6918 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
6921 @item @code{if-exists-else}
6922 The @code{if-exists-else} spec function is similar to the @code{if-exists}
6923 spec function, except that it takes two arguments. The first argument is
6924 an absolute pathname to a file. If the file exists, @code{if-exists-else}
6925 returns the pathname. If it does not exist, it returns the second argument.
6926 This way, @code{if-exists-else} can be used to select one file or another,
6927 based on the existence of the first. Here is a small example of its usage:
6931 crt0%O%s %:if-exists(crti%O%s) \
6932 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
6935 @item @code{replace-outfile}
6936 The @code{replace-outfile} spec function takes two arguments. It looks for the
6937 first argument in the outfiles array and replaces it with the second argument. Here
6938 is a small example of its usage:
6941 %@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
6947 Substitutes the @code{-S} switch, if that switch was given to GCC@.
6948 If that switch was not specified, this substitutes nothing. Note that
6949 the leading dash is omitted when specifying this option, and it is
6950 automatically inserted if the substitution is performed. Thus the spec
6951 string @samp{%@{foo@}} would match the command-line option @option{-foo}
6952 and would output the command line option @option{-foo}.
6954 @item %W@{@code{S}@}
6955 Like %@{@code{S}@} but mark last argument supplied within as a file to be
6958 @item %@{@code{S}*@}
6959 Substitutes all the switches specified to GCC whose names start
6960 with @code{-S}, but which also take an argument. This is used for
6961 switches like @option{-o}, @option{-D}, @option{-I}, etc.
6962 GCC considers @option{-o foo} as being
6963 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
6964 text, including the space. Thus two arguments would be generated.
6966 @item %@{@code{S}*&@code{T}*@}
6967 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
6968 (the order of @code{S} and @code{T} in the spec is not significant).
6969 There can be any number of ampersand-separated variables; for each the
6970 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
6972 @item %@{@code{S}:@code{X}@}
6973 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
6975 @item %@{!@code{S}:@code{X}@}
6976 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
6978 @item %@{@code{S}*:@code{X}@}
6979 Substitutes @code{X} if one or more switches whose names start with
6980 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
6981 once, no matter how many such switches appeared. However, if @code{%*}
6982 appears somewhere in @code{X}, then @code{X} will be substituted once
6983 for each matching switch, with the @code{%*} replaced by the part of
6984 that switch that matched the @code{*}.
6986 @item %@{.@code{S}:@code{X}@}
6987 Substitutes @code{X}, if processing a file with suffix @code{S}.
6989 @item %@{!.@code{S}:@code{X}@}
6990 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
6992 @item %@{@code{S}|@code{P}:@code{X}@}
6993 Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@.
6994 This may be combined with @samp{!}, @samp{.}, and @code{*} sequences as well,
6995 although they have a stronger binding than the @samp{|}. If @code{%*}
6996 appears in @code{X}, all of the alternatives must be starred, and only
6997 the first matching alternative is substituted.
6999 For example, a spec string like this:
7002 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
7005 will output the following command-line options from the following input
7006 command-line options:
7011 -d fred.c -foo -baz -boggle
7012 -d jim.d -bar -baz -boggle
7015 @item %@{S:X; T:Y; :D@}
7017 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
7018 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
7019 be as many clauses as you need. This may be combined with @code{.},
7020 @code{!}, @code{|}, and @code{*} as needed.
7025 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
7026 construct may contain other nested @samp{%} constructs or spaces, or
7027 even newlines. They are processed as usual, as described above.
7028 Trailing white space in @code{X} is ignored. White space may also
7029 appear anywhere on the left side of the colon in these constructs,
7030 except between @code{.} or @code{*} and the corresponding word.
7032 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
7033 handled specifically in these constructs. If another value of
7034 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
7035 @option{-W} switch is found later in the command line, the earlier
7036 switch value is ignored, except with @{@code{S}*@} where @code{S} is
7037 just one letter, which passes all matching options.
7039 The character @samp{|} at the beginning of the predicate text is used to
7040 indicate that a command should be piped to the following command, but
7041 only if @option{-pipe} is specified.
7043 It is built into GCC which switches take arguments and which do not.
7044 (You might think it would be useful to generalize this to allow each
7045 compiler's spec to say which switches take arguments. But this cannot
7046 be done in a consistent fashion. GCC cannot even decide which input
7047 files have been specified without knowing which switches take arguments,
7048 and it must know which input files to compile in order to tell which
7051 GCC also knows implicitly that arguments starting in @option{-l} are to be
7052 treated as compiler output files, and passed to the linker in their
7053 proper position among the other output files.
7055 @c man begin OPTIONS
7057 @node Target Options
7058 @section Specifying Target Machine and Compiler Version
7059 @cindex target options
7060 @cindex cross compiling
7061 @cindex specifying machine version
7062 @cindex specifying compiler version and target machine
7063 @cindex compiler version, specifying
7064 @cindex target machine, specifying
7066 The usual way to run GCC is to run the executable called @file{gcc}, or
7067 @file{<machine>-gcc} when cross-compiling, or
7068 @file{<machine>-gcc-<version>} to run a version other than the one that
7069 was installed last. Sometimes this is inconvenient, so GCC provides
7070 options that will switch to another cross-compiler or version.
7073 @item -b @var{machine}
7075 The argument @var{machine} specifies the target machine for compilation.
7077 The value to use for @var{machine} is the same as was specified as the
7078 machine type when configuring GCC as a cross-compiler. For
7079 example, if a cross-compiler was configured with @samp{configure
7080 arm-elf}, meaning to compile for an arm processor with elf binaries,
7081 then you would specify @option{-b arm-elf} to run that cross compiler.
7082 Because there are other options beginning with @option{-b}, the
7083 configuration must contain a hyphen.
7085 @item -V @var{version}
7087 The argument @var{version} specifies which version of GCC to run.
7088 This is useful when multiple versions are installed. For example,
7089 @var{version} might be @samp{4.0}, meaning to run GCC version 4.0.
7092 The @option{-V} and @option{-b} options work by running the
7093 @file{<machine>-gcc-<version>} executable, so there's no real reason to
7094 use them if you can just run that directly.
7096 @node Submodel Options
7097 @section Hardware Models and Configurations
7098 @cindex submodel options
7099 @cindex specifying hardware config
7100 @cindex hardware models and configurations, specifying
7101 @cindex machine dependent options
7103 Earlier we discussed the standard option @option{-b} which chooses among
7104 different installed compilers for completely different target
7105 machines, such as VAX vs.@: 68000 vs.@: 80386.
7107 In addition, each of these target machine types can have its own
7108 special options, starting with @samp{-m}, to choose among various
7109 hardware models or configurations---for example, 68010 vs 68020,
7110 floating coprocessor or none. A single installed version of the
7111 compiler can compile for any model or configuration, according to the
7114 Some configurations of the compiler also support additional special
7115 options, usually for compatibility with other compilers on the same
7118 @c This list is ordered alphanumerically by subsection name.
7119 @c It should be the same order and spelling as these options are listed
7120 @c in Machine Dependent Options
7126 * Blackfin Options::
7130 * DEC Alpha Options::
7131 * DEC Alpha/VMS Options::
7135 * i386 and x86-64 Options::
7148 * RS/6000 and PowerPC Options::
7149 * S/390 and zSeries Options::
7152 * System V Options::
7153 * TMS320C3x/C4x Options::
7157 * Xstormy16 Options::
7163 @subsection ARC Options
7166 These options are defined for ARC implementations:
7171 Compile code for little endian mode. This is the default.
7175 Compile code for big endian mode.
7178 @opindex mmangle-cpu
7179 Prepend the name of the cpu to all public symbol names.
7180 In multiple-processor systems, there are many ARC variants with different
7181 instruction and register set characteristics. This flag prevents code
7182 compiled for one cpu to be linked with code compiled for another.
7183 No facility exists for handling variants that are ``almost identical''.
7184 This is an all or nothing option.
7186 @item -mcpu=@var{cpu}
7188 Compile code for ARC variant @var{cpu}.
7189 Which variants are supported depend on the configuration.
7190 All variants support @option{-mcpu=base}, this is the default.
7192 @item -mtext=@var{text-section}
7193 @itemx -mdata=@var{data-section}
7194 @itemx -mrodata=@var{readonly-data-section}
7198 Put functions, data, and readonly data in @var{text-section},
7199 @var{data-section}, and @var{readonly-data-section} respectively
7200 by default. This can be overridden with the @code{section} attribute.
7201 @xref{Variable Attributes}.
7206 @subsection ARM Options
7209 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
7213 @item -mabi=@var{name}
7215 Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu},
7216 @samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}.
7219 @opindex mapcs-frame
7220 Generate a stack frame that is compliant with the ARM Procedure Call
7221 Standard for all functions, even if this is not strictly necessary for
7222 correct execution of the code. Specifying @option{-fomit-frame-pointer}
7223 with this option will cause the stack frames not to be generated for
7224 leaf functions. The default is @option{-mno-apcs-frame}.
7228 This is a synonym for @option{-mapcs-frame}.
7231 @c not currently implemented
7232 @item -mapcs-stack-check
7233 @opindex mapcs-stack-check
7234 Generate code to check the amount of stack space available upon entry to
7235 every function (that actually uses some stack space). If there is
7236 insufficient space available then either the function
7237 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
7238 called, depending upon the amount of stack space required. The run time
7239 system is required to provide these functions. The default is
7240 @option{-mno-apcs-stack-check}, since this produces smaller code.
7242 @c not currently implemented
7244 @opindex mapcs-float
7245 Pass floating point arguments using the float point registers. This is
7246 one of the variants of the APCS@. This option is recommended if the
7247 target hardware has a floating point unit or if a lot of floating point
7248 arithmetic is going to be performed by the code. The default is
7249 @option{-mno-apcs-float}, since integer only code is slightly increased in
7250 size if @option{-mapcs-float} is used.
7252 @c not currently implemented
7253 @item -mapcs-reentrant
7254 @opindex mapcs-reentrant
7255 Generate reentrant, position independent code. The default is
7256 @option{-mno-apcs-reentrant}.
7259 @item -mthumb-interwork
7260 @opindex mthumb-interwork
7261 Generate code which supports calling between the ARM and Thumb
7262 instruction sets. Without this option the two instruction sets cannot
7263 be reliably used inside one program. The default is
7264 @option{-mno-thumb-interwork}, since slightly larger code is generated
7265 when @option{-mthumb-interwork} is specified.
7267 @item -mno-sched-prolog
7268 @opindex mno-sched-prolog
7269 Prevent the reordering of instructions in the function prolog, or the
7270 merging of those instruction with the instructions in the function's
7271 body. This means that all functions will start with a recognizable set
7272 of instructions (or in fact one of a choice from a small set of
7273 different function prologues), and this information can be used to
7274 locate the start if functions inside an executable piece of code. The
7275 default is @option{-msched-prolog}.
7278 @opindex mhard-float
7279 Generate output containing floating point instructions. This is the
7283 @opindex msoft-float
7284 Generate output containing library calls for floating point.
7285 @strong{Warning:} the requisite libraries are not available for all ARM
7286 targets. Normally the facilities of the machine's usual C compiler are
7287 used, but this cannot be done directly in cross-compilation. You must make
7288 your own arrangements to provide suitable library functions for
7291 @option{-msoft-float} changes the calling convention in the output file;
7292 therefore, it is only useful if you compile @emph{all} of a program with
7293 this option. In particular, you need to compile @file{libgcc.a}, the
7294 library that comes with GCC, with @option{-msoft-float} in order for
7297 @item -mfloat-abi=@var{name}
7299 Specifies which ABI to use for floating point values. Permissible values
7300 are: @samp{soft}, @samp{softfp} and @samp{hard}.
7302 @samp{soft} and @samp{hard} are equivalent to @option{-msoft-float}
7303 and @option{-mhard-float} respectively. @samp{softfp} allows the generation
7304 of floating point instructions, but still uses the soft-float calling
7307 @item -mlittle-endian
7308 @opindex mlittle-endian
7309 Generate code for a processor running in little-endian mode. This is
7310 the default for all standard configurations.
7313 @opindex mbig-endian
7314 Generate code for a processor running in big-endian mode; the default is
7315 to compile code for a little-endian processor.
7317 @item -mwords-little-endian
7318 @opindex mwords-little-endian
7319 This option only applies when generating code for big-endian processors.
7320 Generate code for a little-endian word order but a big-endian byte
7321 order. That is, a byte order of the form @samp{32107654}. Note: this
7322 option should only be used if you require compatibility with code for
7323 big-endian ARM processors generated by versions of the compiler prior to
7326 @item -mcpu=@var{name}
7328 This specifies the name of the target ARM processor. GCC uses this name
7329 to determine what kind of instructions it can emit when generating
7330 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
7331 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
7332 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
7333 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
7334 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
7335 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s},
7336 @samp{arm8}, @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
7337 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
7338 @samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s},
7339 @samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi},
7340 @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s},
7341 @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e},
7342 @samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp},
7343 @samp{arm1176jz-s}, @samp{arm1176jzf-s}, @samp{xscale}, @samp{iwmmxt},
7346 @itemx -mtune=@var{name}
7348 This option is very similar to the @option{-mcpu=} option, except that
7349 instead of specifying the actual target processor type, and hence
7350 restricting which instructions can be used, it specifies that GCC should
7351 tune the performance of the code as if the target were of the type
7352 specified in this option, but still choosing the instructions that it
7353 will generate based on the cpu specified by a @option{-mcpu=} option.
7354 For some ARM implementations better performance can be obtained by using
7357 @item -march=@var{name}
7359 This specifies the name of the target ARM architecture. GCC uses this
7360 name to determine what kind of instructions it can emit when generating
7361 assembly code. This option can be used in conjunction with or instead
7362 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
7363 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
7364 @samp{armv5}, @samp{armv5t}, @samp{armv5te}, @samp{armv6}, @samp{armv6j},
7365 @samp{iwmmxt}, @samp{ep9312}.
7367 @item -mfpu=@var{name}
7368 @itemx -mfpe=@var{number}
7369 @itemx -mfp=@var{number}
7373 This specifies what floating point hardware (or hardware emulation) is
7374 available on the target. Permissible names are: @samp{fpa}, @samp{fpe2},
7375 @samp{fpe3}, @samp{maverick}, @samp{vfp}. @option{-mfp} and @option{-mfpe}
7376 are synonyms for @option{-mfpu}=@samp{fpe}@var{number}, for compatibility
7377 with older versions of GCC@.
7379 If @option{-msoft-float} is specified this specifies the format of
7380 floating point values.
7382 @item -mstructure-size-boundary=@var{n}
7383 @opindex mstructure-size-boundary
7384 The size of all structures and unions will be rounded up to a multiple
7385 of the number of bits set by this option. Permissible values are 8, 32
7386 and 64. The default value varies for different toolchains. For the COFF
7387 targeted toolchain the default value is 8. A value of 64 is only allowed
7388 if the underlying ABI supports it.
7390 Specifying the larger number can produce faster, more efficient code, but
7391 can also increase the size of the program. Different values are potentially
7392 incompatible. Code compiled with one value cannot necessarily expect to
7393 work with code or libraries compiled with another value, if they exchange
7394 information using structures or unions.
7396 @item -mabort-on-noreturn
7397 @opindex mabort-on-noreturn
7398 Generate a call to the function @code{abort} at the end of a
7399 @code{noreturn} function. It will be executed if the function tries to
7403 @itemx -mno-long-calls
7404 @opindex mlong-calls
7405 @opindex mno-long-calls
7406 Tells the compiler to perform function calls by first loading the
7407 address of the function into a register and then performing a subroutine
7408 call on this register. This switch is needed if the target function
7409 will lie outside of the 64 megabyte addressing range of the offset based
7410 version of subroutine call instruction.
7412 Even if this switch is enabled, not all function calls will be turned
7413 into long calls. The heuristic is that static functions, functions
7414 which have the @samp{short-call} attribute, functions that are inside
7415 the scope of a @samp{#pragma no_long_calls} directive and functions whose
7416 definitions have already been compiled within the current compilation
7417 unit, will not be turned into long calls. The exception to this rule is
7418 that weak function definitions, functions with the @samp{long-call}
7419 attribute or the @samp{section} attribute, and functions that are within
7420 the scope of a @samp{#pragma long_calls} directive, will always be
7421 turned into long calls.
7423 This feature is not enabled by default. Specifying
7424 @option{-mno-long-calls} will restore the default behavior, as will
7425 placing the function calls within the scope of a @samp{#pragma
7426 long_calls_off} directive. Note these switches have no effect on how
7427 the compiler generates code to handle function calls via function
7430 @item -mnop-fun-dllimport
7431 @opindex mnop-fun-dllimport
7432 Disable support for the @code{dllimport} attribute.
7434 @item -msingle-pic-base
7435 @opindex msingle-pic-base
7436 Treat the register used for PIC addressing as read-only, rather than
7437 loading it in the prologue for each function. The run-time system is
7438 responsible for initializing this register with an appropriate value
7439 before execution begins.
7441 @item -mpic-register=@var{reg}
7442 @opindex mpic-register
7443 Specify the register to be used for PIC addressing. The default is R10
7444 unless stack-checking is enabled, when R9 is used.
7446 @item -mcirrus-fix-invalid-insns
7447 @opindex mcirrus-fix-invalid-insns
7448 @opindex mno-cirrus-fix-invalid-insns
7449 Insert NOPs into the instruction stream to in order to work around
7450 problems with invalid Maverick instruction combinations. This option
7451 is only valid if the @option{-mcpu=ep9312} option has been used to
7452 enable generation of instructions for the Cirrus Maverick floating
7453 point co-processor. This option is not enabled by default, since the
7454 problem is only present in older Maverick implementations. The default
7455 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
7458 @item -mpoke-function-name
7459 @opindex mpoke-function-name
7460 Write the name of each function into the text section, directly
7461 preceding the function prologue. The generated code is similar to this:
7465 .ascii "arm_poke_function_name", 0
7468 .word 0xff000000 + (t1 - t0)
7469 arm_poke_function_name
7471 stmfd sp!, @{fp, ip, lr, pc@}
7475 When performing a stack backtrace, code can inspect the value of
7476 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
7477 location @code{pc - 12} and the top 8 bits are set, then we know that
7478 there is a function name embedded immediately preceding this location
7479 and has length @code{((pc[-3]) & 0xff000000)}.
7483 Generate code for the 16-bit Thumb instruction set. The default is to
7484 use the 32-bit ARM instruction set.
7487 @opindex mtpcs-frame
7488 Generate a stack frame that is compliant with the Thumb Procedure Call
7489 Standard for all non-leaf functions. (A leaf function is one that does
7490 not call any other functions.) The default is @option{-mno-tpcs-frame}.
7492 @item -mtpcs-leaf-frame
7493 @opindex mtpcs-leaf-frame
7494 Generate a stack frame that is compliant with the Thumb Procedure Call
7495 Standard for all leaf functions. (A leaf function is one that does
7496 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
7498 @item -mcallee-super-interworking
7499 @opindex mcallee-super-interworking
7500 Gives all externally visible functions in the file being compiled an ARM
7501 instruction set header which switches to Thumb mode before executing the
7502 rest of the function. This allows these functions to be called from
7503 non-interworking code.
7505 @item -mcaller-super-interworking
7506 @opindex mcaller-super-interworking
7507 Allows calls via function pointers (including virtual functions) to
7508 execute correctly regardless of whether the target code has been
7509 compiled for interworking or not. There is a small overhead in the cost
7510 of executing a function pointer if this option is enabled.
7512 @item -mtp=@var{name}
7514 Specify the access model for the thread local storage pointer. The valid
7515 models are @option{soft}, which generates calls to @code{__aeabi_read_tp},
7516 @option{cp15}, which fetches the thread pointer from @code{cp15} directly
7517 (supported in the arm6k architecture), and @option{auto}, which uses the
7518 best available method for the selected processor. The default setting is
7524 @subsection AVR Options
7527 These options are defined for AVR implementations:
7530 @item -mmcu=@var{mcu}
7532 Specify ATMEL AVR instruction set or MCU type.
7534 Instruction set avr1 is for the minimal AVR core, not supported by the C
7535 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
7536 attiny11, attiny12, attiny15, attiny28).
7538 Instruction set avr2 (default) is for the classic AVR core with up to
7539 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
7540 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
7541 at90c8534, at90s8535).
7543 Instruction set avr3 is for the classic AVR core with up to 128K program
7544 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
7546 Instruction set avr4 is for the enhanced AVR core with up to 8K program
7547 memory space (MCU types: atmega8, atmega83, atmega85).
7549 Instruction set avr5 is for the enhanced AVR core with up to 128K program
7550 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
7551 atmega64, atmega128, at43usb355, at94k).
7555 Output instruction sizes to the asm file.
7557 @item -minit-stack=@var{N}
7558 @opindex minit-stack
7559 Specify the initial stack address, which may be a symbol or numeric value,
7560 @samp{__stack} is the default.
7562 @item -mno-interrupts
7563 @opindex mno-interrupts
7564 Generated code is not compatible with hardware interrupts.
7565 Code size will be smaller.
7567 @item -mcall-prologues
7568 @opindex mcall-prologues
7569 Functions prologues/epilogues expanded as call to appropriate
7570 subroutines. Code size will be smaller.
7572 @item -mno-tablejump
7573 @opindex mno-tablejump
7574 Do not generate tablejump insns which sometimes increase code size.
7577 @opindex mtiny-stack
7578 Change only the low 8 bits of the stack pointer.
7582 Assume int to be 8 bit integer. This affects the sizes of all types: A
7583 char will be 1 byte, an int will be 1 byte, an long will be 2 bytes
7584 and long long will be 4 bytes. Please note that this option does not
7585 comply to the C standards, but it will provide you with smaller code
7589 @node Blackfin Options
7590 @subsection Blackfin Options
7591 @cindex Blackfin Options
7594 @item -momit-leaf-frame-pointer
7595 @opindex momit-leaf-frame-pointer
7596 Don't keep the frame pointer in a register for leaf functions. This
7597 avoids the instructions to save, set up and restore frame pointers and
7598 makes an extra register available in leaf functions. The option
7599 @option{-fomit-frame-pointer} removes the frame pointer for all functions
7600 which might make debugging harder.
7602 @item -mspecld-anomaly
7603 @opindex mspecld-anomaly
7604 When enabled, the compiler will ensure that the generated code does not
7605 contain speculative loads after jump instructions. This option is enabled
7608 @item -mno-specld-anomaly
7609 @opindex mno-specld-anomaly
7610 Don't generate extra code to prevent speculative loads from occurring.
7612 @item -mcsync-anomaly
7613 @opindex mcsync-anomaly
7614 When enabled, the compiler will ensure that the generated code does not
7615 contain CSYNC or SSYNC instructions too soon after conditional branches.
7616 This option is enabled by default.
7618 @item -mno-csync-anomaly
7619 @opindex mno-csync-anomaly
7620 Don't generate extra code to prevent CSYNC or SSYNC instructions from
7621 occurring too soon after a conditional branch.
7625 When enabled, the compiler is free to take advantage of the knowledge that
7626 the entire program fits into the low 64k of memory.
7629 @opindex mno-low-64k
7630 Assume that the program is arbitrarily large. This is the default.
7632 @item -mid-shared-library
7633 @opindex mid-shared-library
7634 Generate code that supports shared libraries via the library ID method.
7635 This allows for execute in place and shared libraries in an environment
7636 without virtual memory management. This option implies @option{-fPIC}.
7638 @item -mno-id-shared-library
7639 @opindex mno-id-shared-library
7640 Generate code that doesn't assume ID based shared libraries are being used.
7641 This is the default.
7643 @item -mshared-library-id=n
7644 @opindex mshared-library-id
7645 Specified the identification number of the ID based shared library being
7646 compiled. Specifying a value of 0 will generate more compact code, specifying
7647 other values will force the allocation of that number to the current
7648 library but is no more space or time efficient than omitting this option.
7651 @itemx -mno-long-calls
7652 @opindex mlong-calls
7653 @opindex mno-long-calls
7654 Tells the compiler to perform function calls by first loading the
7655 address of the function into a register and then performing a subroutine
7656 call on this register. This switch is needed if the target function
7657 will lie outside of the 24 bit addressing range of the offset based
7658 version of subroutine call instruction.
7660 This feature is not enabled by default. Specifying
7661 @option{-mno-long-calls} will restore the default behavior. Note these
7662 switches have no effect on how the compiler generates code to handle
7663 function calls via function pointers.
7667 @subsection CRIS Options
7668 @cindex CRIS Options
7670 These options are defined specifically for the CRIS ports.
7673 @item -march=@var{architecture-type}
7674 @itemx -mcpu=@var{architecture-type}
7677 Generate code for the specified architecture. The choices for
7678 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
7679 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@.
7680 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
7683 @item -mtune=@var{architecture-type}
7685 Tune to @var{architecture-type} everything applicable about the generated
7686 code, except for the ABI and the set of available instructions. The
7687 choices for @var{architecture-type} are the same as for
7688 @option{-march=@var{architecture-type}}.
7690 @item -mmax-stack-frame=@var{n}
7691 @opindex mmax-stack-frame
7692 Warn when the stack frame of a function exceeds @var{n} bytes.
7694 @item -melinux-stacksize=@var{n}
7695 @opindex melinux-stacksize
7696 Only available with the @samp{cris-axis-aout} target. Arranges for
7697 indications in the program to the kernel loader that the stack of the
7698 program should be set to @var{n} bytes.
7704 The options @option{-metrax4} and @option{-metrax100} are synonyms for
7705 @option{-march=v3} and @option{-march=v8} respectively.
7707 @item -mmul-bug-workaround
7708 @itemx -mno-mul-bug-workaround
7709 @opindex mmul-bug-workaround
7710 @opindex mno-mul-bug-workaround
7711 Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
7712 models where it applies. This option is active by default.
7716 Enable CRIS-specific verbose debug-related information in the assembly
7717 code. This option also has the effect to turn off the @samp{#NO_APP}
7718 formatted-code indicator to the assembler at the beginning of the
7723 Do not use condition-code results from previous instruction; always emit
7724 compare and test instructions before use of condition codes.
7726 @item -mno-side-effects
7727 @opindex mno-side-effects
7728 Do not emit instructions with side-effects in addressing modes other than
7732 @itemx -mno-stack-align
7734 @itemx -mno-data-align
7735 @itemx -mconst-align
7736 @itemx -mno-const-align
7737 @opindex mstack-align
7738 @opindex mno-stack-align
7739 @opindex mdata-align
7740 @opindex mno-data-align
7741 @opindex mconst-align
7742 @opindex mno-const-align
7743 These options (no-options) arranges (eliminate arrangements) for the
7744 stack-frame, individual data and constants to be aligned for the maximum
7745 single data access size for the chosen CPU model. The default is to
7746 arrange for 32-bit alignment. ABI details such as structure layout are
7747 not affected by these options.
7755 Similar to the stack- data- and const-align options above, these options
7756 arrange for stack-frame, writable data and constants to all be 32-bit,
7757 16-bit or 8-bit aligned. The default is 32-bit alignment.
7759 @item -mno-prologue-epilogue
7760 @itemx -mprologue-epilogue
7761 @opindex mno-prologue-epilogue
7762 @opindex mprologue-epilogue
7763 With @option{-mno-prologue-epilogue}, the normal function prologue and
7764 epilogue that sets up the stack-frame are omitted and no return
7765 instructions or return sequences are generated in the code. Use this
7766 option only together with visual inspection of the compiled code: no
7767 warnings or errors are generated when call-saved registers must be saved,
7768 or storage for local variable needs to be allocated.
7774 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
7775 instruction sequences that load addresses for functions from the PLT part
7776 of the GOT rather than (traditional on other architectures) calls to the
7777 PLT@. The default is @option{-mgotplt}.
7781 Legacy no-op option only recognized with the cris-axis-aout target.
7785 Legacy no-op option only recognized with the cris-axis-elf and
7786 cris-axis-linux-gnu targets.
7790 Only recognized with the cris-axis-aout target, where it selects a
7791 GNU/linux-like multilib, include files and instruction set for
7796 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
7800 This option, recognized for the cris-axis-aout and cris-axis-elf arranges
7801 to link with input-output functions from a simulator library. Code,
7802 initialized data and zero-initialized data are allocated consecutively.
7806 Like @option{-sim}, but pass linker options to locate initialized data at
7807 0x40000000 and zero-initialized data at 0x80000000.
7811 @subsection CRX Options
7814 These options are defined specifically for the CRX ports.
7820 Enable the use of multiply-accumulate instructions. Disabled by default.
7824 Push instructions will be used to pass outgoing arguments when functions
7825 are called. Enabled by default.
7828 @node Darwin Options
7829 @subsection Darwin Options
7830 @cindex Darwin options
7832 These options are defined for all architectures running the Darwin operating
7835 FSF GCC on Darwin does not create ``fat'' object files; it will create
7836 an object file for the single architecture that it was built to
7837 target. Apple's GCC on Darwin does create ``fat'' files if multiple
7838 @option{-arch} options are used; it does so by running the compiler or
7839 linker multiple times and joining the results together with
7842 The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or
7843 @samp{i686}) is determined by the flags that specify the ISA
7844 that GCC is targetting, like @option{-mcpu} or @option{-march}. The
7845 @option{-force_cpusubtype_ALL} option can be used to override this.
7847 The Darwin tools vary in their behavior when presented with an ISA
7848 mismatch. The assembler, @file{as}, will only permit instructions to
7849 be used that are valid for the subtype of the file it is generating,
7850 so you cannot put 64-bit instructions in an @samp{ppc750} object file.
7851 The linker for shared libraries, @file{/usr/bin/libtool}, will fail
7852 and print an error if asked to create a shared library with a less
7853 restrictive subtype than its input files (for instance, trying to put
7854 a @samp{ppc970} object file in a @samp{ppc7400} library). The linker
7855 for executables, @file{ld}, will quietly give the executable the most
7856 restrictive subtype of any of its input files.
7861 Add the framework directory @var{dir} to the head of the list of
7862 directories to be searched for header files. These directories are
7863 interleaved with those specified by @option{-I} options and are
7864 scanned in a left-to-right order.
7866 A framework directory is a directory with frameworks in it. A
7867 framework is a directory with a @samp{"Headers"} and/or
7868 @samp{"PrivateHeaders"} directory contained directly in it that ends
7869 in @samp{".framework"}. The name of a framework is the name of this
7870 directory excluding the @samp{".framework"}. Headers associated with
7871 the framework are found in one of those two directories, with
7872 @samp{"Headers"} being searched first. A subframework is a framework
7873 directory that is in a framework's @samp{"Frameworks"} directory.
7874 Includes of subframework headers can only appear in a header of a
7875 framework that contains the subframework, or in a sibling subframework
7876 header. Two subframeworks are siblings if they occur in the same
7877 framework. A subframework should not have the same name as a
7878 framework, a warning will be issued if this is violated. Currently a
7879 subframework cannot have subframeworks, in the future, the mechanism
7880 may be extended to support this. The standard frameworks can be found
7881 in @samp{"/System/Library/Frameworks"} and
7882 @samp{"/Library/Frameworks"}. An example include looks like
7883 @code{#include <Framework/header.h>}, where @samp{Framework} denotes
7884 the name of the framework and header.h is found in the
7885 @samp{"PrivateHeaders"} or @samp{"Headers"} directory.
7889 Emit debugging information for symbols that are used. For STABS
7890 debugging format, this enables @option{-feliminate-unused-debug-symbols}.
7891 This is by default ON@.
7895 Emit debugging information for all symbols and types.
7897 @item -mmacosx-version-min=@var{version}
7898 The earliest version of MacOS X that this executable will run on
7899 is @var{version}. Typical values of @var{version} include @code{10.1},
7900 @code{10.2}, and @code{10.3.9}.
7902 The default for this option is to make choices that seem to be most
7905 @item -mone-byte-bool
7906 @opindex -mone-byte-bool
7907 Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}.
7908 By default @samp{sizeof(bool)} is @samp{4} when compiling for
7909 Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this
7910 option has no effect on x86.
7912 @strong{Warning:} The @option{-mone-byte-bool} switch causes GCC
7913 to generate code that is not binary compatible with code generated
7914 without that switch. Using this switch may require recompiling all
7915 other modules in a program, including system libraries. Use this
7916 switch to conform to a non-default data model.
7918 @item -mfix-and-continue
7919 @itemx -ffix-and-continue
7920 @itemx -findirect-data
7921 @opindex mfix-and-continue
7922 @opindex ffix-and-continue
7923 @opindex findirect-data
7924 Generate code suitable for fast turn around development. Needed to
7925 enable gdb to dynamically load @code{.o} files into already running
7926 programs. @option{-findirect-data} and @option{-ffix-and-continue}
7927 are provided for backwards compatibility.
7931 Loads all members of static archive libraries.
7932 See man ld(1) for more information.
7934 @item -arch_errors_fatal
7935 @opindex arch_errors_fatal
7936 Cause the errors having to do with files that have the wrong architecture
7940 @opindex bind_at_load
7941 Causes the output file to be marked such that the dynamic linker will
7942 bind all undefined references when the file is loaded or launched.
7946 Produce a Mach-o bundle format file.
7947 See man ld(1) for more information.
7949 @item -bundle_loader @var{executable}
7950 @opindex bundle_loader
7951 This option specifies the @var{executable} that will be loading the build
7952 output file being linked. See man ld(1) for more information.
7955 @opindex -dynamiclib
7956 When passed this option, GCC will produce a dynamic library instead of
7957 an executable when linking, using the Darwin @file{libtool} command.
7959 @item -force_cpusubtype_ALL
7960 @opindex -force_cpusubtype_ALL
7961 This causes GCC's output file to have the @var{ALL} subtype, instead of
7962 one controlled by the @option{-mcpu} or @option{-march} option.
7964 @item -allowable_client @var{client_name}
7966 @itemx -compatibility_version
7967 @itemx -current_version
7969 @itemx -dependency-file
7971 @itemx -dylinker_install_name
7973 @itemx -exported_symbols_list
7975 @itemx -flat_namespace
7976 @itemx -force_flat_namespace
7977 @itemx -headerpad_max_install_names
7980 @itemx -install_name
7981 @itemx -keep_private_externs
7982 @itemx -multi_module
7983 @itemx -multiply_defined
7984 @itemx -multiply_defined_unused
7986 @itemx -no_dead_strip_inits_and_terms
7987 @itemx -nofixprebinding
7990 @itemx -noseglinkedit
7991 @itemx -pagezero_size
7993 @itemx -prebind_all_twolevel_modules
7994 @itemx -private_bundle
7995 @itemx -read_only_relocs
7997 @itemx -sectobjectsymbols
8001 @itemx -sectobjectsymbols
8004 @itemx -segs_read_only_addr
8005 @itemx -segs_read_write_addr
8006 @itemx -seg_addr_table
8007 @itemx -seg_addr_table_filename
8010 @itemx -segs_read_only_addr
8011 @itemx -segs_read_write_addr
8012 @itemx -single_module
8015 @itemx -sub_umbrella
8016 @itemx -twolevel_namespace
8019 @itemx -unexported_symbols_list
8020 @itemx -weak_reference_mismatches
8023 @opindex allowable_client
8024 @opindex client_name
8025 @opindex compatibility_version
8026 @opindex current_version
8028 @opindex dependency-file
8030 @opindex dylinker_install_name
8032 @opindex exported_symbols_list
8034 @opindex flat_namespace
8035 @opindex force_flat_namespace
8036 @opindex headerpad_max_install_names
8039 @opindex install_name
8040 @opindex keep_private_externs
8041 @opindex multi_module
8042 @opindex multiply_defined
8043 @opindex multiply_defined_unused
8045 @opindex no_dead_strip_inits_and_terms
8046 @opindex nofixprebinding
8047 @opindex nomultidefs
8049 @opindex noseglinkedit
8050 @opindex pagezero_size
8052 @opindex prebind_all_twolevel_modules
8053 @opindex private_bundle
8054 @opindex read_only_relocs
8056 @opindex sectobjectsymbols
8060 @opindex sectobjectsymbols
8063 @opindex segs_read_only_addr
8064 @opindex segs_read_write_addr
8065 @opindex seg_addr_table
8066 @opindex seg_addr_table_filename
8067 @opindex seglinkedit
8069 @opindex segs_read_only_addr
8070 @opindex segs_read_write_addr
8071 @opindex single_module
8073 @opindex sub_library
8074 @opindex sub_umbrella
8075 @opindex twolevel_namespace
8078 @opindex unexported_symbols_list
8079 @opindex weak_reference_mismatches
8080 @opindex whatsloaded
8082 These options are passed to the Darwin linker. The Darwin linker man page
8083 describes them in detail.
8086 @node DEC Alpha Options
8087 @subsection DEC Alpha Options
8089 These @samp{-m} options are defined for the DEC Alpha implementations:
8092 @item -mno-soft-float
8094 @opindex mno-soft-float
8095 @opindex msoft-float
8096 Use (do not use) the hardware floating-point instructions for
8097 floating-point operations. When @option{-msoft-float} is specified,
8098 functions in @file{libgcc.a} will be used to perform floating-point
8099 operations. Unless they are replaced by routines that emulate the
8100 floating-point operations, or compiled in such a way as to call such
8101 emulations routines, these routines will issue floating-point
8102 operations. If you are compiling for an Alpha without floating-point
8103 operations, you must ensure that the library is built so as not to call
8106 Note that Alpha implementations without floating-point operations are
8107 required to have floating-point registers.
8112 @opindex mno-fp-regs
8113 Generate code that uses (does not use) the floating-point register set.
8114 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
8115 register set is not used, floating point operands are passed in integer
8116 registers as if they were integers and floating-point results are passed
8117 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
8118 so any function with a floating-point argument or return value called by code
8119 compiled with @option{-mno-fp-regs} must also be compiled with that
8122 A typical use of this option is building a kernel that does not use,
8123 and hence need not save and restore, any floating-point registers.
8127 The Alpha architecture implements floating-point hardware optimized for
8128 maximum performance. It is mostly compliant with the IEEE floating
8129 point standard. However, for full compliance, software assistance is
8130 required. This option generates code fully IEEE compliant code
8131 @emph{except} that the @var{inexact-flag} is not maintained (see below).
8132 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
8133 defined during compilation. The resulting code is less efficient but is
8134 able to correctly support denormalized numbers and exceptional IEEE
8135 values such as not-a-number and plus/minus infinity. Other Alpha
8136 compilers call this option @option{-ieee_with_no_inexact}.
8138 @item -mieee-with-inexact
8139 @opindex mieee-with-inexact
8140 This is like @option{-mieee} except the generated code also maintains
8141 the IEEE @var{inexact-flag}. Turning on this option causes the
8142 generated code to implement fully-compliant IEEE math. In addition to
8143 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
8144 macro. On some Alpha implementations the resulting code may execute
8145 significantly slower than the code generated by default. Since there is
8146 very little code that depends on the @var{inexact-flag}, you should
8147 normally not specify this option. Other Alpha compilers call this
8148 option @option{-ieee_with_inexact}.
8150 @item -mfp-trap-mode=@var{trap-mode}
8151 @opindex mfp-trap-mode
8152 This option controls what floating-point related traps are enabled.
8153 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
8154 The trap mode can be set to one of four values:
8158 This is the default (normal) setting. The only traps that are enabled
8159 are the ones that cannot be disabled in software (e.g., division by zero
8163 In addition to the traps enabled by @samp{n}, underflow traps are enabled
8167 Like @samp{su}, but the instructions are marked to be safe for software
8168 completion (see Alpha architecture manual for details).
8171 Like @samp{su}, but inexact traps are enabled as well.
8174 @item -mfp-rounding-mode=@var{rounding-mode}
8175 @opindex mfp-rounding-mode
8176 Selects the IEEE rounding mode. Other Alpha compilers call this option
8177 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
8182 Normal IEEE rounding mode. Floating point numbers are rounded towards
8183 the nearest machine number or towards the even machine number in case
8187 Round towards minus infinity.
8190 Chopped rounding mode. Floating point numbers are rounded towards zero.
8193 Dynamic rounding mode. A field in the floating point control register
8194 (@var{fpcr}, see Alpha architecture reference manual) controls the
8195 rounding mode in effect. The C library initializes this register for
8196 rounding towards plus infinity. Thus, unless your program modifies the
8197 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
8200 @item -mtrap-precision=@var{trap-precision}
8201 @opindex mtrap-precision
8202 In the Alpha architecture, floating point traps are imprecise. This
8203 means without software assistance it is impossible to recover from a
8204 floating trap and program execution normally needs to be terminated.
8205 GCC can generate code that can assist operating system trap handlers
8206 in determining the exact location that caused a floating point trap.
8207 Depending on the requirements of an application, different levels of
8208 precisions can be selected:
8212 Program precision. This option is the default and means a trap handler
8213 can only identify which program caused a floating point exception.
8216 Function precision. The trap handler can determine the function that
8217 caused a floating point exception.
8220 Instruction precision. The trap handler can determine the exact
8221 instruction that caused a floating point exception.
8224 Other Alpha compilers provide the equivalent options called
8225 @option{-scope_safe} and @option{-resumption_safe}.
8227 @item -mieee-conformant
8228 @opindex mieee-conformant
8229 This option marks the generated code as IEEE conformant. You must not
8230 use this option unless you also specify @option{-mtrap-precision=i} and either
8231 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
8232 is to emit the line @samp{.eflag 48} in the function prologue of the
8233 generated assembly file. Under DEC Unix, this has the effect that
8234 IEEE-conformant math library routines will be linked in.
8236 @item -mbuild-constants
8237 @opindex mbuild-constants
8238 Normally GCC examines a 32- or 64-bit integer constant to
8239 see if it can construct it from smaller constants in two or three
8240 instructions. If it cannot, it will output the constant as a literal and
8241 generate code to load it from the data segment at runtime.
8243 Use this option to require GCC to construct @emph{all} integer constants
8244 using code, even if it takes more instructions (the maximum is six).
8246 You would typically use this option to build a shared library dynamic
8247 loader. Itself a shared library, it must relocate itself in memory
8248 before it can find the variables and constants in its own data segment.
8254 Select whether to generate code to be assembled by the vendor-supplied
8255 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
8273 Indicate whether GCC should generate code to use the optional BWX,
8274 CIX, FIX and MAX instruction sets. The default is to use the instruction
8275 sets supported by the CPU type specified via @option{-mcpu=} option or that
8276 of the CPU on which GCC was built if none was specified.
8281 @opindex mfloat-ieee
8282 Generate code that uses (does not use) VAX F and G floating point
8283 arithmetic instead of IEEE single and double precision.
8285 @item -mexplicit-relocs
8286 @itemx -mno-explicit-relocs
8287 @opindex mexplicit-relocs
8288 @opindex mno-explicit-relocs
8289 Older Alpha assemblers provided no way to generate symbol relocations
8290 except via assembler macros. Use of these macros does not allow
8291 optimal instruction scheduling. GNU binutils as of version 2.12
8292 supports a new syntax that allows the compiler to explicitly mark
8293 which relocations should apply to which instructions. This option
8294 is mostly useful for debugging, as GCC detects the capabilities of
8295 the assembler when it is built and sets the default accordingly.
8299 @opindex msmall-data
8300 @opindex mlarge-data
8301 When @option{-mexplicit-relocs} is in effect, static data is
8302 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
8303 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
8304 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
8305 16-bit relocations off of the @code{$gp} register. This limits the
8306 size of the small data area to 64KB, but allows the variables to be
8307 directly accessed via a single instruction.
8309 The default is @option{-mlarge-data}. With this option the data area
8310 is limited to just below 2GB@. Programs that require more than 2GB of
8311 data must use @code{malloc} or @code{mmap} to allocate the data in the
8312 heap instead of in the program's data segment.
8314 When generating code for shared libraries, @option{-fpic} implies
8315 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
8319 @opindex msmall-text
8320 @opindex mlarge-text
8321 When @option{-msmall-text} is used, the compiler assumes that the
8322 code of the entire program (or shared library) fits in 4MB, and is
8323 thus reachable with a branch instruction. When @option{-msmall-data}
8324 is used, the compiler can assume that all local symbols share the
8325 same @code{$gp} value, and thus reduce the number of instructions
8326 required for a function call from 4 to 1.
8328 The default is @option{-mlarge-text}.
8330 @item -mcpu=@var{cpu_type}
8332 Set the instruction set and instruction scheduling parameters for
8333 machine type @var{cpu_type}. You can specify either the @samp{EV}
8334 style name or the corresponding chip number. GCC supports scheduling
8335 parameters for the EV4, EV5 and EV6 family of processors and will
8336 choose the default values for the instruction set from the processor
8337 you specify. If you do not specify a processor type, GCC will default
8338 to the processor on which the compiler was built.
8340 Supported values for @var{cpu_type} are
8346 Schedules as an EV4 and has no instruction set extensions.
8350 Schedules as an EV5 and has no instruction set extensions.
8354 Schedules as an EV5 and supports the BWX extension.
8359 Schedules as an EV5 and supports the BWX and MAX extensions.
8363 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
8367 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
8370 @item -mtune=@var{cpu_type}
8372 Set only the instruction scheduling parameters for machine type
8373 @var{cpu_type}. The instruction set is not changed.
8375 @item -mmemory-latency=@var{time}
8376 @opindex mmemory-latency
8377 Sets the latency the scheduler should assume for typical memory
8378 references as seen by the application. This number is highly
8379 dependent on the memory access patterns used by the application
8380 and the size of the external cache on the machine.
8382 Valid options for @var{time} are
8386 A decimal number representing clock cycles.
8392 The compiler contains estimates of the number of clock cycles for
8393 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
8394 (also called Dcache, Scache, and Bcache), as well as to main memory.
8395 Note that L3 is only valid for EV5.
8400 @node DEC Alpha/VMS Options
8401 @subsection DEC Alpha/VMS Options
8403 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
8406 @item -mvms-return-codes
8407 @opindex mvms-return-codes
8408 Return VMS condition codes from main. The default is to return POSIX
8409 style condition (e.g.@ error) codes.
8413 @subsection FRV Options
8420 Only use the first 32 general purpose registers.
8425 Use all 64 general purpose registers.
8430 Use only the first 32 floating point registers.
8435 Use all 64 floating point registers
8438 @opindex mhard-float
8440 Use hardware instructions for floating point operations.
8443 @opindex msoft-float
8445 Use library routines for floating point operations.
8450 Dynamically allocate condition code registers.
8455 Do not try to dynamically allocate condition code registers, only
8456 use @code{icc0} and @code{fcc0}.
8461 Change ABI to use double word insns.
8466 Do not use double word instructions.
8471 Use floating point double instructions.
8476 Do not use floating point double instructions.
8481 Use media instructions.
8486 Do not use media instructions.
8491 Use multiply and add/subtract instructions.
8496 Do not use multiply and add/subtract instructions.
8501 Select the FDPIC ABI, that uses function descriptors to represent
8502 pointers to functions. Without any PIC/PIE-related options, it
8503 implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it
8504 assumes GOT entries and small data are within a 12-bit range from the
8505 GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets
8506 are computed with 32 bits.
8509 @opindex minline-plt
8511 Enable inlining of PLT entries in function calls to functions that are
8512 not known to bind locally. It has no effect without @option{-mfdpic}.
8513 It's enabled by default if optimizing for speed and compiling for
8514 shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an
8515 optimization option such as @option{-O3} or above is present in the
8521 Assume a large TLS segment when generating thread-local code.
8526 Do not assume a large TLS segment when generating thread-local code.
8531 Enable the use of @code{GPREL} relocations in the FDPIC ABI for data
8532 that is known to be in read-only sections. It's enabled by default,
8533 except for @option{-fpic} or @option{-fpie}: even though it may help
8534 make the global offset table smaller, it trades 1 instruction for 4.
8535 With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4,
8536 one of which may be shared by multiple symbols, and it avoids the need
8537 for a GOT entry for the referenced symbol, so it's more likely to be a
8538 win. If it is not, @option{-mno-gprel-ro} can be used to disable it.
8540 @item -multilib-library-pic
8541 @opindex multilib-library-pic
8543 Link with the (library, not FD) pic libraries. It's implied by
8544 @option{-mlibrary-pic}, as well as by @option{-fPIC} and
8545 @option{-fpic} without @option{-mfdpic}. You should never have to use
8551 Follow the EABI requirement of always creating a frame pointer whenever
8552 a stack frame is allocated. This option is enabled by default and can
8553 be disabled with @option{-mno-linked-fp}.
8556 @opindex mlong-calls
8558 Use indirect addressing to call functions outside the current
8559 compilation unit. This allows the functions to be placed anywhere
8560 within the 32-bit address space.
8562 @item -malign-labels
8563 @opindex malign-labels
8565 Try to align labels to an 8-byte boundary by inserting nops into the
8566 previous packet. This option only has an effect when VLIW packing
8567 is enabled. It doesn't create new packets; it merely adds nops to
8571 @opindex mlibrary-pic
8573 Generate position-independent EABI code.
8578 Use only the first four media accumulator registers.
8583 Use all eight media accumulator registers.
8588 Pack VLIW instructions.
8593 Do not pack VLIW instructions.
8598 Do not mark ABI switches in e_flags.
8603 Enable the use of conditional-move instructions (default).
8605 This switch is mainly for debugging the compiler and will likely be removed
8606 in a future version.
8608 @item -mno-cond-move
8609 @opindex mno-cond-move
8611 Disable the use of conditional-move instructions.
8613 This switch is mainly for debugging the compiler and will likely be removed
8614 in a future version.
8619 Enable the use of conditional set instructions (default).
8621 This switch is mainly for debugging the compiler and will likely be removed
8622 in a future version.
8627 Disable the use of conditional set instructions.
8629 This switch is mainly for debugging the compiler and will likely be removed
8630 in a future version.
8635 Enable the use of conditional execution (default).
8637 This switch is mainly for debugging the compiler and will likely be removed
8638 in a future version.
8640 @item -mno-cond-exec
8641 @opindex mno-cond-exec
8643 Disable the use of conditional execution.
8645 This switch is mainly for debugging the compiler and will likely be removed
8646 in a future version.
8649 @opindex mvliw-branch
8651 Run a pass to pack branches into VLIW instructions (default).
8653 This switch is mainly for debugging the compiler and will likely be removed
8654 in a future version.
8656 @item -mno-vliw-branch
8657 @opindex mno-vliw-branch
8659 Do not run a pass to pack branches into VLIW instructions.
8661 This switch is mainly for debugging the compiler and will likely be removed
8662 in a future version.
8664 @item -mmulti-cond-exec
8665 @opindex mmulti-cond-exec
8667 Enable optimization of @code{&&} and @code{||} in conditional execution
8670 This switch is mainly for debugging the compiler and will likely be removed
8671 in a future version.
8673 @item -mno-multi-cond-exec
8674 @opindex mno-multi-cond-exec
8676 Disable optimization of @code{&&} and @code{||} in conditional execution.
8678 This switch is mainly for debugging the compiler and will likely be removed
8679 in a future version.
8681 @item -mnested-cond-exec
8682 @opindex mnested-cond-exec
8684 Enable nested conditional execution optimizations (default).
8686 This switch is mainly for debugging the compiler and will likely be removed
8687 in a future version.
8689 @item -mno-nested-cond-exec
8690 @opindex mno-nested-cond-exec
8692 Disable nested conditional execution optimizations.
8694 This switch is mainly for debugging the compiler and will likely be removed
8695 in a future version.
8697 @item -moptimize-membar
8698 @opindex moptimize-membar
8700 This switch removes redundant @code{membar} instructions from the
8701 compiler generated code. It is enabled by default.
8703 @item -mno-optimize-membar
8704 @opindex mno-optimize-membar
8706 This switch disables the automatic removal of redundant @code{membar}
8707 instructions from the generated code.
8709 @item -mtomcat-stats
8710 @opindex mtomcat-stats
8712 Cause gas to print out tomcat statistics.
8714 @item -mcpu=@var{cpu}
8717 Select the processor type for which to generate code. Possible values are
8718 @samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450},
8719 @samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}.
8723 @node H8/300 Options
8724 @subsection H8/300 Options
8726 These @samp{-m} options are defined for the H8/300 implementations:
8731 Shorten some address references at link time, when possible; uses the
8732 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
8733 ld, Using ld}, for a fuller description.
8737 Generate code for the H8/300H@.
8741 Generate code for the H8S@.
8745 Generate code for the H8S and H8/300H in the normal mode. This switch
8746 must be used either with @option{-mh} or @option{-ms}.
8750 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
8754 Make @code{int} data 32 bits by default.
8758 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
8759 The default for the H8/300H and H8S is to align longs and floats on 4
8761 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
8762 This option has no effect on the H8/300.
8766 @subsection HPPA Options
8767 @cindex HPPA Options
8769 These @samp{-m} options are defined for the HPPA family of computers:
8772 @item -march=@var{architecture-type}
8774 Generate code for the specified architecture. The choices for
8775 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
8776 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
8777 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
8778 architecture option for your machine. Code compiled for lower numbered
8779 architectures will run on higher numbered architectures, but not the
8783 @itemx -mpa-risc-1-1
8784 @itemx -mpa-risc-2-0
8785 @opindex mpa-risc-1-0
8786 @opindex mpa-risc-1-1
8787 @opindex mpa-risc-2-0
8788 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
8791 @opindex mbig-switch
8792 Generate code suitable for big switch tables. Use this option only if
8793 the assembler/linker complain about out of range branches within a switch
8796 @item -mjump-in-delay
8797 @opindex mjump-in-delay
8798 Fill delay slots of function calls with unconditional jump instructions
8799 by modifying the return pointer for the function call to be the target
8800 of the conditional jump.
8802 @item -mdisable-fpregs
8803 @opindex mdisable-fpregs
8804 Prevent floating point registers from being used in any manner. This is
8805 necessary for compiling kernels which perform lazy context switching of
8806 floating point registers. If you use this option and attempt to perform
8807 floating point operations, the compiler will abort.
8809 @item -mdisable-indexing
8810 @opindex mdisable-indexing
8811 Prevent the compiler from using indexing address modes. This avoids some
8812 rather obscure problems when compiling MIG generated code under MACH@.
8814 @item -mno-space-regs
8815 @opindex mno-space-regs
8816 Generate code that assumes the target has no space registers. This allows
8817 GCC to generate faster indirect calls and use unscaled index address modes.
8819 Such code is suitable for level 0 PA systems and kernels.
8821 @item -mfast-indirect-calls
8822 @opindex mfast-indirect-calls
8823 Generate code that assumes calls never cross space boundaries. This
8824 allows GCC to emit code which performs faster indirect calls.
8826 This option will not work in the presence of shared libraries or nested
8829 @item -mfixed-range=@var{register-range}
8830 @opindex mfixed-range
8831 Generate code treating the given register range as fixed registers.
8832 A fixed register is one that the register allocator can not use. This is
8833 useful when compiling kernel code. A register range is specified as
8834 two registers separated by a dash. Multiple register ranges can be
8835 specified separated by a comma.
8837 @item -mlong-load-store
8838 @opindex mlong-load-store
8839 Generate 3-instruction load and store sequences as sometimes required by
8840 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
8843 @item -mportable-runtime
8844 @opindex mportable-runtime
8845 Use the portable calling conventions proposed by HP for ELF systems.
8849 Enable the use of assembler directives only GAS understands.
8851 @item -mschedule=@var{cpu-type}
8853 Schedule code according to the constraints for the machine type
8854 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
8855 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
8856 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
8857 proper scheduling option for your machine. The default scheduling is
8861 @opindex mlinker-opt
8862 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
8863 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
8864 linkers in which they give bogus error messages when linking some programs.
8867 @opindex msoft-float
8868 Generate output containing library calls for floating point.
8869 @strong{Warning:} the requisite libraries are not available for all HPPA
8870 targets. Normally the facilities of the machine's usual C compiler are
8871 used, but this cannot be done directly in cross-compilation. You must make
8872 your own arrangements to provide suitable library functions for
8873 cross-compilation. The embedded target @samp{hppa1.1-*-pro}
8874 does provide software floating point support.
8876 @option{-msoft-float} changes the calling convention in the output file;
8877 therefore, it is only useful if you compile @emph{all} of a program with
8878 this option. In particular, you need to compile @file{libgcc.a}, the
8879 library that comes with GCC, with @option{-msoft-float} in order for
8884 Generate the predefine, @code{_SIO}, for server IO@. The default is
8885 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
8886 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These
8887 options are available under HP-UX and HI-UX@.
8891 Use GNU ld specific options. This passes @option{-shared} to ld when
8892 building a shared library. It is the default when GCC is configured,
8893 explicitly or implicitly, with the GNU linker. This option does not
8894 have any affect on which ld is called, it only changes what parameters
8895 are passed to that ld. The ld that is called is determined by the
8896 @option{--with-ld} configure option, GCC's program search path, and
8897 finally by the user's @env{PATH}. The linker used by GCC can be printed
8898 using @samp{which `gcc -print-prog-name=ld`}. This option is only available
8899 on the 64 bit HP-UX GCC, i.e. configured with @samp{hppa*64*-*-hpux*}.
8903 Use HP ld specific options. This passes @option{-b} to ld when building
8904 a shared library and passes @option{+Accept TypeMismatch} to ld on all
8905 links. It is the default when GCC is configured, explicitly or
8906 implicitly, with the HP linker. This option does not have any affect on
8907 which ld is called, it only changes what parameters are passed to that
8908 ld. The ld that is called is determined by the @option{--with-ld}
8909 configure option, GCC's program search path, and finally by the user's
8910 @env{PATH}. The linker used by GCC can be printed using @samp{which
8911 `gcc -print-prog-name=ld`}. This option is only available on the 64 bit
8912 HP-UX GCC, i.e. configured with @samp{hppa*64*-*-hpux*}.
8915 @opindex mno-long-calls
8916 Generate code that uses long call sequences. This ensures that a call
8917 is always able to reach linker generated stubs. The default is to generate
8918 long calls only when the distance from the call site to the beginning
8919 of the function or translation unit, as the case may be, exceeds a
8920 predefined limit set by the branch type being used. The limits for
8921 normal calls are 7,600,000 and 240,000 bytes, respectively for the
8922 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
8925 Distances are measured from the beginning of functions when using the
8926 @option{-ffunction-sections} option, or when using the @option{-mgas}
8927 and @option{-mno-portable-runtime} options together under HP-UX with
8930 It is normally not desirable to use this option as it will degrade
8931 performance. However, it may be useful in large applications,
8932 particularly when partial linking is used to build the application.
8934 The types of long calls used depends on the capabilities of the
8935 assembler and linker, and the type of code being generated. The
8936 impact on systems that support long absolute calls, and long pic
8937 symbol-difference or pc-relative calls should be relatively small.
8938 However, an indirect call is used on 32-bit ELF systems in pic code
8939 and it is quite long.
8941 @item -munix=@var{unix-std}
8943 Generate compiler predefines and select a startfile for the specified
8944 UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95}
8945 and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95}
8946 is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX
8947 11.11 and later. The default values are @samp{93} for HP-UX 10.00,
8948 @samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11
8951 @option{-munix=93} provides the same predefines as GCC 3.3 and 3.4.
8952 @option{-munix=95} provides additional predefines for @code{XOPEN_UNIX}
8953 and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}.
8954 @option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX},
8955 @code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and
8956 @code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}.
8958 It is @emph{important} to note that this option changes the interfaces
8959 for various library routines. It also affects the operational behavior
8960 of the C library. Thus, @emph{extreme} care is needed in using this
8963 Library code that is intended to operate with more than one UNIX
8964 standard must test, set and restore the variable @var{__xpg4_extended_mask}
8965 as appropriate. Most GNU software doesn't provide this capability.
8969 Suppress the generation of link options to search libdld.sl when the
8970 @option{-static} option is specified on HP-UX 10 and later.
8974 The HP-UX implementation of setlocale in libc has a dependency on
8975 libdld.sl. There isn't an archive version of libdld.sl. Thus,
8976 when the @option{-static} option is specified, special link options
8977 are needed to resolve this dependency.
8979 On HP-UX 10 and later, the GCC driver adds the necessary options to
8980 link with libdld.sl when the @option{-static} option is specified.
8981 This causes the resulting binary to be dynamic. On the 64-bit port,
8982 the linkers generate dynamic binaries by default in any case. The
8983 @option{-nolibdld} option can be used to prevent the GCC driver from
8984 adding these link options.
8988 Add support for multithreading with the @dfn{dce thread} library
8989 under HP-UX@. This option sets flags for both the preprocessor and
8993 @node i386 and x86-64 Options
8994 @subsection Intel 386 and AMD x86-64 Options
8995 @cindex i386 Options
8996 @cindex x86-64 Options
8997 @cindex Intel 386 Options
8998 @cindex AMD x86-64 Options
9000 These @samp{-m} options are defined for the i386 and x86-64 family of
9004 @item -mtune=@var{cpu-type}
9006 Tune to @var{cpu-type} everything applicable about the generated code, except
9007 for the ABI and the set of available instructions. The choices for
9011 Original Intel's i386 CPU@.
9013 Intel's i486 CPU@. (No scheduling is implemented for this chip.)
9015 Intel Pentium CPU with no MMX support.
9017 Intel PentiumMMX CPU based on Pentium core with MMX instruction set support.
9018 @item i686, pentiumpro
9019 Intel PentiumPro CPU@.
9021 Intel Pentium2 CPU based on PentiumPro core with MMX instruction set support.
9022 @item pentium3, pentium3m
9023 Intel Pentium3 CPU based on PentiumPro core with MMX and SSE instruction set
9026 Low power version of Intel Pentium3 CPU with MMX, SSE and SSE2 instruction set
9027 support. Used by Centrino notebooks.
9028 @item pentium4, pentium4m
9029 Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set support.
9031 Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and SSE3 instruction
9034 Improved version of Intel Pentium4 CPU with 64-bit extensions, MMX, SSE,
9035 SSE2 and SSE3 instruction set support.
9037 AMD K6 CPU with MMX instruction set support.
9039 Improved versions of AMD K6 CPU with MMX and 3dNOW! instruction set support.
9040 @item athlon, athlon-tbird
9041 AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and SSE prefetch instructions
9043 @item athlon-4, athlon-xp, athlon-mp
9044 Improved AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and full SSE
9045 instruction set support.
9046 @item k8, opteron, athlon64, athlon-fx
9047 AMD K8 core based CPUs with x86-64 instruction set support. (This supersets
9048 MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW! and 64-bit instruction set extensions.)
9050 IDT Winchip C6 CPU, dealt in same way as i486 with additional MMX instruction
9053 IDT Winchip2 CPU, dealt in same way as i486 with additional MMX and 3dNOW!
9054 instruction set support.
9056 Via C3 CPU with MMX and 3dNOW! instruction set support. (No scheduling is
9057 implemented for this chip.)
9059 Via C3-2 CPU with MMX and SSE instruction set support. (No scheduling is
9060 implemented for this chip.)
9063 While picking a specific @var{cpu-type} will schedule things appropriately
9064 for that particular chip, the compiler will not generate any code that
9065 does not run on the i386 without the @option{-march=@var{cpu-type}} option
9068 @item -march=@var{cpu-type}
9070 Generate instructions for the machine type @var{cpu-type}. The choices
9071 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
9072 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
9074 @item -mcpu=@var{cpu-type}
9076 A deprecated synonym for @option{-mtune}.
9085 @opindex mpentiumpro
9086 These options are synonyms for @option{-mtune=i386}, @option{-mtune=i486},
9087 @option{-mtune=pentium}, and @option{-mtune=pentiumpro} respectively.
9088 These synonyms are deprecated.
9090 @item -mfpmath=@var{unit}
9092 Generate floating point arithmetics for selected unit @var{unit}. The choices
9097 Use the standard 387 floating point coprocessor present majority of chips and
9098 emulated otherwise. Code compiled with this option will run almost everywhere.
9099 The temporary results are computed in 80bit precision instead of precision
9100 specified by the type resulting in slightly different results compared to most
9101 of other chips. See @option{-ffloat-store} for more detailed description.
9103 This is the default choice for i386 compiler.
9106 Use scalar floating point instructions present in the SSE instruction set.
9107 This instruction set is supported by Pentium3 and newer chips, in the AMD line
9108 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
9109 instruction set supports only single precision arithmetics, thus the double and
9110 extended precision arithmetics is still done using 387. Later version, present
9111 only in Pentium4 and the future AMD x86-64 chips supports double precision
9114 For the i386 compiler, you need to use @option{-march=@var{cpu-type}}, @option{-msse}
9115 or @option{-msse2} switches to enable SSE extensions and make this option
9116 effective. For the x86-64 compiler, these extensions are enabled by default.
9118 The resulting code should be considerably faster in the majority of cases and avoid
9119 the numerical instability problems of 387 code, but may break some existing
9120 code that expects temporaries to be 80bit.
9122 This is the default choice for the x86-64 compiler.
9125 Attempt to utilize both instruction sets at once. This effectively double the
9126 amount of available registers and on chips with separate execution units for
9127 387 and SSE the execution resources too. Use this option with care, as it is
9128 still experimental, because the GCC register allocator does not model separate
9129 functional units well resulting in instable performance.
9132 @item -masm=@var{dialect}
9133 @opindex masm=@var{dialect}
9134 Output asm instructions using selected @var{dialect}. Supported
9135 choices are @samp{intel} or @samp{att} (the default one). Darwin does
9136 not support @samp{intel}.
9141 @opindex mno-ieee-fp
9142 Control whether or not the compiler uses IEEE floating point
9143 comparisons. These handle correctly the case where the result of a
9144 comparison is unordered.
9147 @opindex msoft-float
9148 Generate output containing library calls for floating point.
9149 @strong{Warning:} the requisite libraries are not part of GCC@.
9150 Normally the facilities of the machine's usual C compiler are used, but
9151 this can't be done directly in cross-compilation. You must make your
9152 own arrangements to provide suitable library functions for
9155 On machines where a function returns floating point results in the 80387
9156 register stack, some floating point opcodes may be emitted even if
9157 @option{-msoft-float} is used.
9159 @item -mno-fp-ret-in-387
9160 @opindex mno-fp-ret-in-387
9161 Do not use the FPU registers for return values of functions.
9163 The usual calling convention has functions return values of types
9164 @code{float} and @code{double} in an FPU register, even if there
9165 is no FPU@. The idea is that the operating system should emulate
9168 The option @option{-mno-fp-ret-in-387} causes such values to be returned
9169 in ordinary CPU registers instead.
9171 @item -mno-fancy-math-387
9172 @opindex mno-fancy-math-387
9173 Some 387 emulators do not support the @code{sin}, @code{cos} and
9174 @code{sqrt} instructions for the 387. Specify this option to avoid
9175 generating those instructions. This option is the default on FreeBSD,
9176 OpenBSD and NetBSD@. This option is overridden when @option{-march}
9177 indicates that the target cpu will always have an FPU and so the
9178 instruction will not need emulation. As of revision 2.6.1, these
9179 instructions are not generated unless you also use the
9180 @option{-funsafe-math-optimizations} switch.
9182 @item -malign-double
9183 @itemx -mno-align-double
9184 @opindex malign-double
9185 @opindex mno-align-double
9186 Control whether GCC aligns @code{double}, @code{long double}, and
9187 @code{long long} variables on a two word boundary or a one word
9188 boundary. Aligning @code{double} variables on a two word boundary will
9189 produce code that runs somewhat faster on a @samp{Pentium} at the
9190 expense of more memory.
9192 @strong{Warning:} if you use the @option{-malign-double} switch,
9193 structures containing the above types will be aligned differently than
9194 the published application binary interface specifications for the 386
9195 and will not be binary compatible with structures in code compiled
9196 without that switch.
9198 @item -m96bit-long-double
9199 @itemx -m128bit-long-double
9200 @opindex m96bit-long-double
9201 @opindex m128bit-long-double
9202 These switches control the size of @code{long double} type. The i386
9203 application binary interface specifies the size to be 96 bits,
9204 so @option{-m96bit-long-double} is the default in 32 bit mode.
9206 Modern architectures (Pentium and newer) would prefer @code{long double}
9207 to be aligned to an 8 or 16 byte boundary. In arrays or structures
9208 conforming to the ABI, this would not be possible. So specifying a
9209 @option{-m128bit-long-double} will align @code{long double}
9210 to a 16 byte boundary by padding the @code{long double} with an additional
9213 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
9214 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
9216 Notice that neither of these options enable any extra precision over the x87
9217 standard of 80 bits for a @code{long double}.
9219 @strong{Warning:} if you override the default value for your target ABI, the
9220 structures and arrays containing @code{long double} variables will change
9221 their size as well as function calling convention for function taking
9222 @code{long double} will be modified. Hence they will not be binary
9223 compatible with arrays or structures in code compiled without that switch.
9225 @item -mmlarge-data-threshold=@var{number}
9226 @opindex mlarge-data-threshold=@var{number}
9227 When @option{-mcmodel=medium} is specified, the data greater than
9228 @var{threshold} are placed in large data section. This value must be the
9229 same across all object linked into the binary and defaults to 65535.
9232 @itemx -mno-svr3-shlib
9233 @opindex msvr3-shlib
9234 @opindex mno-svr3-shlib
9235 Control whether GCC places uninitialized local variables into the
9236 @code{bss} or @code{data} segments. @option{-msvr3-shlib} places them
9237 into @code{bss}. These options are meaningful only on System V Release 3.
9241 Use a different function-calling convention, in which functions that
9242 take a fixed number of arguments return with the @code{ret} @var{num}
9243 instruction, which pops their arguments while returning. This saves one
9244 instruction in the caller since there is no need to pop the arguments
9247 You can specify that an individual function is called with this calling
9248 sequence with the function attribute @samp{stdcall}. You can also
9249 override the @option{-mrtd} option by using the function attribute
9250 @samp{cdecl}. @xref{Function Attributes}.
9252 @strong{Warning:} this calling convention is incompatible with the one
9253 normally used on Unix, so you cannot use it if you need to call
9254 libraries compiled with the Unix compiler.
9256 Also, you must provide function prototypes for all functions that
9257 take variable numbers of arguments (including @code{printf});
9258 otherwise incorrect code will be generated for calls to those
9261 In addition, seriously incorrect code will result if you call a
9262 function with too many arguments. (Normally, extra arguments are
9263 harmlessly ignored.)
9265 @item -mregparm=@var{num}
9267 Control how many registers are used to pass integer arguments. By
9268 default, no registers are used to pass arguments, and at most 3
9269 registers can be used. You can control this behavior for a specific
9270 function by using the function attribute @samp{regparm}.
9271 @xref{Function Attributes}.
9273 @strong{Warning:} if you use this switch, and
9274 @var{num} is nonzero, then you must build all modules with the same
9275 value, including any libraries. This includes the system libraries and
9279 @opindex msseregparm
9280 Use SSE register passing conventions for float and double arguments
9281 and return values. You can control this behavior for a specific
9282 function by using the function attribute @samp{sseregparm}.
9283 @xref{Function Attributes}.
9285 @strong{Warning:} if you use this switch then you must build all
9286 modules with the same value, including any libraries. This includes
9287 the system libraries and startup modules.
9289 @item -mpreferred-stack-boundary=@var{num}
9290 @opindex mpreferred-stack-boundary
9291 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
9292 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
9293 the default is 4 (16 bytes or 128 bits), except when optimizing for code
9294 size (@option{-Os}), in which case the default is the minimum correct
9295 alignment (4 bytes for x86, and 8 bytes for x86-64).
9297 On Pentium and PentiumPro, @code{double} and @code{long double} values
9298 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
9299 suffer significant run time performance penalties. On Pentium III, the
9300 Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar
9301 penalties if it is not 16 byte aligned.
9303 To ensure proper alignment of this values on the stack, the stack boundary
9304 must be as aligned as that required by any value stored on the stack.
9305 Further, every function must be generated such that it keeps the stack
9306 aligned. Thus calling a function compiled with a higher preferred
9307 stack boundary from a function compiled with a lower preferred stack
9308 boundary will most likely misalign the stack. It is recommended that
9309 libraries that use callbacks always use the default setting.
9311 This extra alignment does consume extra stack space, and generally
9312 increases code size. Code that is sensitive to stack space usage, such
9313 as embedded systems and operating system kernels, may want to reduce the
9314 preferred alignment to @option{-mpreferred-stack-boundary=2}.
9332 These switches enable or disable the use of instructions in the MMX,
9333 SSE, SSE2 or 3DNow! extended instruction sets. These extensions are
9334 also available as built-in functions: see @ref{X86 Built-in Functions},
9335 for details of the functions enabled and disabled by these switches.
9337 To have SSE/SSE2 instructions generated automatically from floating-point
9338 code (as opposed to 387 instructions), see @option{-mfpmath=sse}.
9340 These options will enable GCC to use these extended instructions in
9341 generated code, even without @option{-mfpmath=sse}. Applications which
9342 perform runtime CPU detection must compile separate files for each
9343 supported architecture, using the appropriate flags. In particular,
9344 the file containing the CPU detection code should be compiled without
9348 @itemx -mno-push-args
9350 @opindex mno-push-args
9351 Use PUSH operations to store outgoing parameters. This method is shorter
9352 and usually equally fast as method using SUB/MOV operations and is enabled
9353 by default. In some cases disabling it may improve performance because of
9354 improved scheduling and reduced dependencies.
9356 @item -maccumulate-outgoing-args
9357 @opindex maccumulate-outgoing-args
9358 If enabled, the maximum amount of space required for outgoing arguments will be
9359 computed in the function prologue. This is faster on most modern CPUs
9360 because of reduced dependencies, improved scheduling and reduced stack usage
9361 when preferred stack boundary is not equal to 2. The drawback is a notable
9362 increase in code size. This switch implies @option{-mno-push-args}.
9366 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
9367 on thread-safe exception handling must compile and link all code with the
9368 @option{-mthreads} option. When compiling, @option{-mthreads} defines
9369 @option{-D_MT}; when linking, it links in a special thread helper library
9370 @option{-lmingwthrd} which cleans up per thread exception handling data.
9372 @item -mno-align-stringops
9373 @opindex mno-align-stringops
9374 Do not align destination of inlined string operations. This switch reduces
9375 code size and improves performance in case the destination is already aligned,
9376 but GCC doesn't know about it.
9378 @item -minline-all-stringops
9379 @opindex minline-all-stringops
9380 By default GCC inlines string operations only when destination is known to be
9381 aligned at least to 4 byte boundary. This enables more inlining, increase code
9382 size, but may improve performance of code that depends on fast memcpy, strlen
9383 and memset for short lengths.
9385 @item -momit-leaf-frame-pointer
9386 @opindex momit-leaf-frame-pointer
9387 Don't keep the frame pointer in a register for leaf functions. This
9388 avoids the instructions to save, set up and restore frame pointers and
9389 makes an extra register available in leaf functions. The option
9390 @option{-fomit-frame-pointer} removes the frame pointer for all functions
9391 which might make debugging harder.
9393 @item -mtls-direct-seg-refs
9394 @itemx -mno-tls-direct-seg-refs
9395 @opindex mtls-direct-seg-refs
9396 Controls whether TLS variables may be accessed with offsets from the
9397 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
9398 or whether the thread base pointer must be added. Whether or not this
9399 is legal depends on the operating system, and whether it maps the
9400 segment to cover the entire TLS area.
9402 For systems that use GNU libc, the default is on.
9405 These @samp{-m} switches are supported in addition to the above
9406 on AMD x86-64 processors in 64-bit environments.
9413 Generate code for a 32-bit or 64-bit environment.
9414 The 32-bit environment sets int, long and pointer to 32 bits and
9415 generates code that runs on any i386 system.
9416 The 64-bit environment sets int to 32 bits and long and pointer
9417 to 64 bits and generates code for AMD's x86-64 architecture.
9420 @opindex no-red-zone
9421 Do not use a so called red zone for x86-64 code. The red zone is mandated
9422 by the x86-64 ABI, it is a 128-byte area beyond the location of the
9423 stack pointer that will not be modified by signal or interrupt handlers
9424 and therefore can be used for temporary data without adjusting the stack
9425 pointer. The flag @option{-mno-red-zone} disables this red zone.
9427 @item -mcmodel=small
9428 @opindex mcmodel=small
9429 Generate code for the small code model: the program and its symbols must
9430 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
9431 Programs can be statically or dynamically linked. This is the default
9434 @item -mcmodel=kernel
9435 @opindex mcmodel=kernel
9436 Generate code for the kernel code model. The kernel runs in the
9437 negative 2 GB of the address space.
9438 This model has to be used for Linux kernel code.
9440 @item -mcmodel=medium
9441 @opindex mcmodel=medium
9442 Generate code for the medium model: The program is linked in the lower 2
9443 GB of the address space but symbols can be located anywhere in the
9444 address space. Programs can be statically or dynamically linked, but
9445 building of shared libraries are not supported with the medium model.
9447 @item -mcmodel=large
9448 @opindex mcmodel=large
9449 Generate code for the large model: This model makes no assumptions
9450 about addresses and sizes of sections. Currently GCC does not implement
9455 @subsection IA-64 Options
9456 @cindex IA-64 Options
9458 These are the @samp{-m} options defined for the Intel IA-64 architecture.
9462 @opindex mbig-endian
9463 Generate code for a big endian target. This is the default for HP-UX@.
9465 @item -mlittle-endian
9466 @opindex mlittle-endian
9467 Generate code for a little endian target. This is the default for AIX5
9474 Generate (or don't) code for the GNU assembler. This is the default.
9475 @c Also, this is the default if the configure option @option{--with-gnu-as}
9482 Generate (or don't) code for the GNU linker. This is the default.
9483 @c Also, this is the default if the configure option @option{--with-gnu-ld}
9488 Generate code that does not use a global pointer register. The result
9489 is not position independent code, and violates the IA-64 ABI@.
9491 @item -mvolatile-asm-stop
9492 @itemx -mno-volatile-asm-stop
9493 @opindex mvolatile-asm-stop
9494 @opindex mno-volatile-asm-stop
9495 Generate (or don't) a stop bit immediately before and after volatile asm
9498 @item -mregister-names
9499 @itemx -mno-register-names
9500 @opindex mregister-names
9501 @opindex mno-register-names
9502 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
9503 the stacked registers. This may make assembler output more readable.
9509 Disable (or enable) optimizations that use the small data section. This may
9510 be useful for working around optimizer bugs.
9513 @opindex mconstant-gp
9514 Generate code that uses a single constant global pointer value. This is
9515 useful when compiling kernel code.
9519 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
9520 This is useful when compiling firmware code.
9522 @item -minline-float-divide-min-latency
9523 @opindex minline-float-divide-min-latency
9524 Generate code for inline divides of floating point values
9525 using the minimum latency algorithm.
9527 @item -minline-float-divide-max-throughput
9528 @opindex minline-float-divide-max-throughput
9529 Generate code for inline divides of floating point values
9530 using the maximum throughput algorithm.
9532 @item -minline-int-divide-min-latency
9533 @opindex minline-int-divide-min-latency
9534 Generate code for inline divides of integer values
9535 using the minimum latency algorithm.
9537 @item -minline-int-divide-max-throughput
9538 @opindex minline-int-divide-max-throughput
9539 Generate code for inline divides of integer values
9540 using the maximum throughput algorithm.
9542 @item -minline-sqrt-min-latency
9543 @opindex minline-sqrt-min-latency
9544 Generate code for inline square roots
9545 using the minimum latency algorithm.
9547 @item -minline-sqrt-max-throughput
9548 @opindex minline-sqrt-max-throughput
9549 Generate code for inline square roots
9550 using the maximum throughput algorithm.
9552 @item -mno-dwarf2-asm
9554 @opindex mno-dwarf2-asm
9555 @opindex mdwarf2-asm
9556 Don't (or do) generate assembler code for the DWARF2 line number debugging
9557 info. This may be useful when not using the GNU assembler.
9559 @item -mearly-stop-bits
9560 @itemx -mno-early-stop-bits
9561 @opindex mearly-stop-bits
9562 @opindex mno-early-stop-bits
9563 Allow stop bits to be placed earlier than immediately preceding the
9564 instruction that triggered the stop bit. This can improve instruction
9565 scheduling, but does not always do so.
9567 @item -mfixed-range=@var{register-range}
9568 @opindex mfixed-range
9569 Generate code treating the given register range as fixed registers.
9570 A fixed register is one that the register allocator can not use. This is
9571 useful when compiling kernel code. A register range is specified as
9572 two registers separated by a dash. Multiple register ranges can be
9573 specified separated by a comma.
9575 @item -mtls-size=@var{tls-size}
9577 Specify bit size of immediate TLS offsets. Valid values are 14, 22, and
9580 @item -mtune=@var{cpu-type}
9582 Tune the instruction scheduling for a particular CPU, Valid values are
9583 itanium, itanium1, merced, itanium2, and mckinley.
9589 Add support for multithreading using the POSIX threads library. This
9590 option sets flags for both the preprocessor and linker. It does
9591 not affect the thread safety of object code produced by the compiler or
9592 that of libraries supplied with it. These are HP-UX specific flags.
9598 Generate code for a 32-bit or 64-bit environment.
9599 The 32-bit environment sets int, long and pointer to 32 bits.
9600 The 64-bit environment sets int to 32 bits and long and pointer
9601 to 64 bits. These are HP-UX specific flags.
9606 @subsection M32C Options
9607 @cindex M32C options
9610 @item -mcpu=@var{name}
9612 Select the CPU for which code is generated. @var{name} may be one of
9613 @samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to
9614 /60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for
9619 Specifies that the program will be run on the simulator. This causes
9620 an alternate runtime library to be linked in which supports, for
9621 example, file I/O. You must not use this option when generating
9622 programs that will run on real hardware; you must provide your own
9623 runtime library for whatever I/O functions are needed.
9625 @item -memregs=@var{number}
9627 Specifies the number of memory-based pseudo-registers GCC will use
9628 during code generation. These pseudo-registers will be used like real
9629 registers, so there is a tradeoff between GCC's ability to fit the
9630 code into available registers, and the performance penalty of using
9631 memory instead of registers. Note that all modules in a program must
9632 be compiled with the same value for this option. Because of that, you
9633 must not use this option with the default runtime libraries gcc
9638 @node M32R/D Options
9639 @subsection M32R/D Options
9640 @cindex M32R/D options
9642 These @option{-m} options are defined for Renesas M32R/D architectures:
9647 Generate code for the M32R/2@.
9651 Generate code for the M32R/X@.
9655 Generate code for the M32R@. This is the default.
9658 @opindex mmodel=small
9659 Assume all objects live in the lower 16MB of memory (so that their addresses
9660 can be loaded with the @code{ld24} instruction), and assume all subroutines
9661 are reachable with the @code{bl} instruction.
9662 This is the default.
9664 The addressability of a particular object can be set with the
9665 @code{model} attribute.
9667 @item -mmodel=medium
9668 @opindex mmodel=medium
9669 Assume objects may be anywhere in the 32-bit address space (the compiler
9670 will generate @code{seth/add3} instructions to load their addresses), and
9671 assume all subroutines are reachable with the @code{bl} instruction.
9674 @opindex mmodel=large
9675 Assume objects may be anywhere in the 32-bit address space (the compiler
9676 will generate @code{seth/add3} instructions to load their addresses), and
9677 assume subroutines may not be reachable with the @code{bl} instruction
9678 (the compiler will generate the much slower @code{seth/add3/jl}
9679 instruction sequence).
9682 @opindex msdata=none
9683 Disable use of the small data area. Variables will be put into
9684 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
9685 @code{section} attribute has been specified).
9686 This is the default.
9688 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
9689 Objects may be explicitly put in the small data area with the
9690 @code{section} attribute using one of these sections.
9693 @opindex msdata=sdata
9694 Put small global and static data in the small data area, but do not
9695 generate special code to reference them.
9699 Put small global and static data in the small data area, and generate
9700 special instructions to reference them.
9704 @cindex smaller data references
9705 Put global and static objects less than or equal to @var{num} bytes
9706 into the small data or bss sections instead of the normal data or bss
9707 sections. The default value of @var{num} is 8.
9708 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
9709 for this option to have any effect.
9711 All modules should be compiled with the same @option{-G @var{num}} value.
9712 Compiling with different values of @var{num} may or may not work; if it
9713 doesn't the linker will give an error message---incorrect code will not be
9718 Makes the M32R specific code in the compiler display some statistics
9719 that might help in debugging programs.
9722 @opindex malign-loops
9723 Align all loops to a 32-byte boundary.
9725 @item -mno-align-loops
9726 @opindex mno-align-loops
9727 Do not enforce a 32-byte alignment for loops. This is the default.
9729 @item -missue-rate=@var{number}
9730 @opindex missue-rate=@var{number}
9731 Issue @var{number} instructions per cycle. @var{number} can only be 1
9734 @item -mbranch-cost=@var{number}
9735 @opindex mbranch-cost=@var{number}
9736 @var{number} can only be 1 or 2. If it is 1 then branches will be
9737 preferred over conditional code, if it is 2, then the opposite will
9740 @item -mflush-trap=@var{number}
9741 @opindex mflush-trap=@var{number}
9742 Specifies the trap number to use to flush the cache. The default is
9743 12. Valid numbers are between 0 and 15 inclusive.
9745 @item -mno-flush-trap
9746 @opindex mno-flush-trap
9747 Specifies that the cache cannot be flushed by using a trap.
9749 @item -mflush-func=@var{name}
9750 @opindex mflush-func=@var{name}
9751 Specifies the name of the operating system function to call to flush
9752 the cache. The default is @emph{_flush_cache}, but a function call
9753 will only be used if a trap is not available.
9755 @item -mno-flush-func
9756 @opindex mno-flush-func
9757 Indicates that there is no OS function for flushing the cache.
9761 @node M680x0 Options
9762 @subsection M680x0 Options
9763 @cindex M680x0 options
9765 These are the @samp{-m} options defined for the 68000 series. The default
9766 values for these options depends on which style of 68000 was selected when
9767 the compiler was configured; the defaults for the most common choices are
9775 Generate output for a 68000. This is the default
9776 when the compiler is configured for 68000-based systems.
9778 Use this option for microcontrollers with a 68000 or EC000 core,
9779 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
9785 Generate output for a 68020. This is the default
9786 when the compiler is configured for 68020-based systems.
9790 Generate output containing 68881 instructions for floating point.
9791 This is the default for most 68020 systems unless @option{--nfp} was
9792 specified when the compiler was configured.
9796 Generate output for a 68030. This is the default when the compiler is
9797 configured for 68030-based systems.
9801 Generate output for a 68040. This is the default when the compiler is
9802 configured for 68040-based systems.
9804 This option inhibits the use of 68881/68882 instructions that have to be
9805 emulated by software on the 68040. Use this option if your 68040 does not
9806 have code to emulate those instructions.
9810 Generate output for a 68060. This is the default when the compiler is
9811 configured for 68060-based systems.
9813 This option inhibits the use of 68020 and 68881/68882 instructions that
9814 have to be emulated by software on the 68060. Use this option if your 68060
9815 does not have code to emulate those instructions.
9819 Generate output for a CPU32. This is the default
9820 when the compiler is configured for CPU32-based systems.
9822 Use this option for microcontrollers with a
9823 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
9824 68336, 68340, 68341, 68349 and 68360.
9828 Generate output for a 520X ``coldfire'' family cpu. This is the default
9829 when the compiler is configured for 520X-based systems.
9831 Use this option for microcontroller with a 5200 core, including
9832 the MCF5202, MCF5203, MCF5204 and MCF5202.
9837 Generate output for a 68040, without using any of the new instructions.
9838 This results in code which can run relatively efficiently on either a
9839 68020/68881 or a 68030 or a 68040. The generated code does use the
9840 68881 instructions that are emulated on the 68040.
9844 Generate output for a 68060, without using any of the new instructions.
9845 This results in code which can run relatively efficiently on either a
9846 68020/68881 or a 68030 or a 68040. The generated code does use the
9847 68881 instructions that are emulated on the 68060.
9850 @opindex msoft-float
9851 Generate output containing library calls for floating point.
9852 @strong{Warning:} the requisite libraries are not available for all m68k
9853 targets. Normally the facilities of the machine's usual C compiler are
9854 used, but this can't be done directly in cross-compilation. You must
9855 make your own arrangements to provide suitable library functions for
9856 cross-compilation. The embedded targets @samp{m68k-*-aout} and
9857 @samp{m68k-*-coff} do provide software floating point support.
9861 Consider type @code{int} to be 16 bits wide, like @code{short int}.
9862 Additionally, parameters passed on the stack are also aligned to a
9863 16-bit boundary even on targets whose API mandates promotion to 32-bit.
9866 @opindex mnobitfield
9867 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
9868 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
9872 Do use the bit-field instructions. The @option{-m68020} option implies
9873 @option{-mbitfield}. This is the default if you use a configuration
9874 designed for a 68020.
9878 Use a different function-calling convention, in which functions
9879 that take a fixed number of arguments return with the @code{rtd}
9880 instruction, which pops their arguments while returning. This
9881 saves one instruction in the caller since there is no need to pop
9882 the arguments there.
9884 This calling convention is incompatible with the one normally
9885 used on Unix, so you cannot use it if you need to call libraries
9886 compiled with the Unix compiler.
9888 Also, you must provide function prototypes for all functions that
9889 take variable numbers of arguments (including @code{printf});
9890 otherwise incorrect code will be generated for calls to those
9893 In addition, seriously incorrect code will result if you call a
9894 function with too many arguments. (Normally, extra arguments are
9895 harmlessly ignored.)
9897 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
9898 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
9901 @itemx -mno-align-int
9903 @opindex mno-align-int
9904 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
9905 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
9906 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
9907 Aligning variables on 32-bit boundaries produces code that runs somewhat
9908 faster on processors with 32-bit busses at the expense of more memory.
9910 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
9911 align structures containing the above types differently than
9912 most published application binary interface specifications for the m68k.
9916 Use the pc-relative addressing mode of the 68000 directly, instead of
9917 using a global offset table. At present, this option implies @option{-fpic},
9918 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
9919 not presently supported with @option{-mpcrel}, though this could be supported for
9920 68020 and higher processors.
9922 @item -mno-strict-align
9923 @itemx -mstrict-align
9924 @opindex mno-strict-align
9925 @opindex mstrict-align
9926 Do not (do) assume that unaligned memory references will be handled by
9930 Generate code that allows the data segment to be located in a different
9931 area of memory from the text segment. This allows for execute in place in
9932 an environment without virtual memory management. This option implies
9936 Generate code that assumes that the data segment follows the text segment.
9937 This is the default.
9939 @item -mid-shared-library
9940 Generate code that supports shared libraries via the library ID method.
9941 This allows for execute in place and shared libraries in an environment
9942 without virtual memory management. This option implies @option{-fPIC}.
9944 @item -mno-id-shared-library
9945 Generate code that doesn't assume ID based shared libraries are being used.
9946 This is the default.
9948 @item -mshared-library-id=n
9949 Specified the identification number of the ID based shared library being
9950 compiled. Specifying a value of 0 will generate more compact code, specifying
9951 other values will force the allocation of that number to the current
9952 library but is no more space or time efficient than omitting this option.
9956 @node M68hc1x Options
9957 @subsection M68hc1x Options
9958 @cindex M68hc1x options
9960 These are the @samp{-m} options defined for the 68hc11 and 68hc12
9961 microcontrollers. The default values for these options depends on
9962 which style of microcontroller was selected when the compiler was configured;
9963 the defaults for the most common choices are given below.
9970 Generate output for a 68HC11. This is the default
9971 when the compiler is configured for 68HC11-based systems.
9977 Generate output for a 68HC12. This is the default
9978 when the compiler is configured for 68HC12-based systems.
9984 Generate output for a 68HCS12.
9987 @opindex mauto-incdec
9988 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
9995 Enable the use of 68HC12 min and max instructions.
9998 @itemx -mno-long-calls
9999 @opindex mlong-calls
10000 @opindex mno-long-calls
10001 Treat all calls as being far away (near). If calls are assumed to be
10002 far away, the compiler will use the @code{call} instruction to
10003 call a function and the @code{rtc} instruction for returning.
10007 Consider type @code{int} to be 16 bits wide, like @code{short int}.
10009 @item -msoft-reg-count=@var{count}
10010 @opindex msoft-reg-count
10011 Specify the number of pseudo-soft registers which are used for the
10012 code generation. The maximum number is 32. Using more pseudo-soft
10013 register may or may not result in better code depending on the program.
10014 The default is 4 for 68HC11 and 2 for 68HC12.
10018 @node MCore Options
10019 @subsection MCore Options
10020 @cindex MCore options
10022 These are the @samp{-m} options defined for the Motorola M*Core
10028 @itemx -mno-hardlit
10030 @opindex mno-hardlit
10031 Inline constants into the code stream if it can be done in two
10032 instructions or less.
10038 Use the divide instruction. (Enabled by default).
10040 @item -mrelax-immediate
10041 @itemx -mno-relax-immediate
10042 @opindex mrelax-immediate
10043 @opindex mno-relax-immediate
10044 Allow arbitrary sized immediates in bit operations.
10046 @item -mwide-bitfields
10047 @itemx -mno-wide-bitfields
10048 @opindex mwide-bitfields
10049 @opindex mno-wide-bitfields
10050 Always treat bit-fields as int-sized.
10052 @item -m4byte-functions
10053 @itemx -mno-4byte-functions
10054 @opindex m4byte-functions
10055 @opindex mno-4byte-functions
10056 Force all functions to be aligned to a four byte boundary.
10058 @item -mcallgraph-data
10059 @itemx -mno-callgraph-data
10060 @opindex mcallgraph-data
10061 @opindex mno-callgraph-data
10062 Emit callgraph information.
10065 @itemx -mno-slow-bytes
10066 @opindex mslow-bytes
10067 @opindex mno-slow-bytes
10068 Prefer word access when reading byte quantities.
10070 @item -mlittle-endian
10071 @itemx -mbig-endian
10072 @opindex mlittle-endian
10073 @opindex mbig-endian
10074 Generate code for a little endian target.
10080 Generate code for the 210 processor.
10084 @subsection MIPS Options
10085 @cindex MIPS options
10091 Generate big-endian code.
10095 Generate little-endian code. This is the default for @samp{mips*el-*-*}
10098 @item -march=@var{arch}
10100 Generate code that will run on @var{arch}, which can be the name of a
10101 generic MIPS ISA, or the name of a particular processor.
10103 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
10104 @samp{mips32}, @samp{mips32r2}, and @samp{mips64}.
10105 The processor names are:
10106 @samp{4kc}, @samp{4km}, @samp{4kp},
10107 @samp{5kc}, @samp{5kf},
10109 @samp{24k}, @samp{24kc}, @samp{24kf}, @samp{24kx},
10112 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
10113 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000},
10114 @samp{rm7000}, @samp{rm9000},
10117 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300},
10118 @samp{vr5000}, @samp{vr5400} and @samp{vr5500}.
10119 The special value @samp{from-abi} selects the
10120 most compatible architecture for the selected ABI (that is,
10121 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
10123 In processor names, a final @samp{000} can be abbreviated as @samp{k}
10124 (for example, @samp{-march=r2k}). Prefixes are optional, and
10125 @samp{vr} may be written @samp{r}.
10127 GCC defines two macros based on the value of this option. The first
10128 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
10129 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
10130 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
10131 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
10132 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
10134 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
10135 above. In other words, it will have the full prefix and will not
10136 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
10137 the macro names the resolved architecture (either @samp{"mips1"} or
10138 @samp{"mips3"}). It names the default architecture when no
10139 @option{-march} option is given.
10141 @item -mtune=@var{arch}
10143 Optimize for @var{arch}. Among other things, this option controls
10144 the way instructions are scheduled, and the perceived cost of arithmetic
10145 operations. The list of @var{arch} values is the same as for
10148 When this option is not used, GCC will optimize for the processor
10149 specified by @option{-march}. By using @option{-march} and
10150 @option{-mtune} together, it is possible to generate code that will
10151 run on a family of processors, but optimize the code for one
10152 particular member of that family.
10154 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
10155 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
10156 @samp{-march} ones described above.
10160 Equivalent to @samp{-march=mips1}.
10164 Equivalent to @samp{-march=mips2}.
10168 Equivalent to @samp{-march=mips3}.
10172 Equivalent to @samp{-march=mips4}.
10176 Equivalent to @samp{-march=mips32}.
10180 Equivalent to @samp{-march=mips32r2}.
10184 Equivalent to @samp{-march=mips64}.
10189 @opindex mno-mips16
10190 Generate (do not generate) MIPS16 code. If GCC is targetting a
10191 MIPS32 or MIPS64 architecture, it will make use of the MIPS16e ASE@.
10203 Generate code for the given ABI@.
10205 Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
10206 generates 64-bit code when you select a 64-bit architecture, but you
10207 can use @option{-mgp32} to get 32-bit code instead.
10209 For information about the O64 ABI, see
10210 @w{@uref{http://gcc.gnu.org/projects/mipso64-abi.html}}.
10213 @itemx -mno-abicalls
10215 @opindex mno-abicalls
10216 Generate (do not generate) SVR4-style position-independent code.
10217 @option{-mabicalls} is the default for SVR4-based systems.
10223 Lift (do not lift) the usual restrictions on the size of the global
10226 GCC normally uses a single instruction to load values from the GOT@.
10227 While this is relatively efficient, it will only work if the GOT
10228 is smaller than about 64k. Anything larger will cause the linker
10229 to report an error such as:
10231 @cindex relocation truncated to fit (MIPS)
10233 relocation truncated to fit: R_MIPS_GOT16 foobar
10236 If this happens, you should recompile your code with @option{-mxgot}.
10237 It should then work with very large GOTs, although it will also be
10238 less efficient, since it will take three instructions to fetch the
10239 value of a global symbol.
10241 Note that some linkers can create multiple GOTs. If you have such a
10242 linker, you should only need to use @option{-mxgot} when a single object
10243 file accesses more than 64k's worth of GOT entries. Very few do.
10245 These options have no effect unless GCC is generating position
10250 Assume that general-purpose registers are 32 bits wide.
10254 Assume that general-purpose registers are 64 bits wide.
10258 Assume that floating-point registers are 32 bits wide.
10262 Assume that floating-point registers are 64 bits wide.
10265 @opindex mhard-float
10266 Use floating-point coprocessor instructions.
10269 @opindex msoft-float
10270 Do not use floating-point coprocessor instructions. Implement
10271 floating-point calculations using library calls instead.
10273 @item -msingle-float
10274 @opindex msingle-float
10275 Assume that the floating-point coprocessor only supports single-precision
10278 @itemx -mdouble-float
10279 @opindex mdouble-float
10280 Assume that the floating-point coprocessor supports double-precision
10281 operations. This is the default.
10287 Use (do not use) the MIPS DSP ASE. @xref{MIPS DSP Built-in Functions}.
10289 @itemx -mpaired-single
10290 @itemx -mno-paired-single
10291 @opindex mpaired-single
10292 @opindex mno-paired-single
10293 Use (do not use) paired-single floating-point instructions.
10294 @xref{MIPS Paired-Single Support}. This option can only be used
10295 when generating 64-bit code and requires hardware floating-point
10296 support to be enabled.
10301 @opindex mno-mips3d
10302 Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}.
10303 The option @option{-mips3d} implies @option{-mpaired-single}.
10307 Force @code{long} types to be 64 bits wide. See @option{-mlong32} for
10308 an explanation of the default and the way that the pointer size is
10313 Force @code{long}, @code{int}, and pointer types to be 32 bits wide.
10315 The default size of @code{int}s, @code{long}s and pointers depends on
10316 the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI
10317 uses 64-bit @code{long}s, as does the 64-bit EABI; the others use
10318 32-bit @code{long}s. Pointers are the same size as @code{long}s,
10319 or the same size as integer registers, whichever is smaller.
10325 Assume (do not assume) that all symbols have 32-bit values, regardless
10326 of the selected ABI@. This option is useful in combination with
10327 @option{-mabi=64} and @option{-mno-abicalls} because it allows GCC
10328 to generate shorter and faster references to symbolic addresses.
10332 @cindex smaller data references (MIPS)
10333 @cindex gp-relative references (MIPS)
10334 Put global and static items less than or equal to @var{num} bytes into
10335 the small data or bss section instead of the normal data or bss section.
10336 This allows the data to be accessed using a single instruction.
10338 All modules should be compiled with the same @option{-G @var{num}}
10341 @item -membedded-data
10342 @itemx -mno-embedded-data
10343 @opindex membedded-data
10344 @opindex mno-embedded-data
10345 Allocate variables to the read-only data section first if possible, then
10346 next in the small data section if possible, otherwise in data. This gives
10347 slightly slower code than the default, but reduces the amount of RAM required
10348 when executing, and thus may be preferred for some embedded systems.
10350 @item -muninit-const-in-rodata
10351 @itemx -mno-uninit-const-in-rodata
10352 @opindex muninit-const-in-rodata
10353 @opindex mno-uninit-const-in-rodata
10354 Put uninitialized @code{const} variables in the read-only data section.
10355 This option is only meaningful in conjunction with @option{-membedded-data}.
10357 @item -msplit-addresses
10358 @itemx -mno-split-addresses
10359 @opindex msplit-addresses
10360 @opindex mno-split-addresses
10361 Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler
10362 relocation operators. This option has been superseded by
10363 @option{-mexplicit-relocs} but is retained for backwards compatibility.
10365 @item -mexplicit-relocs
10366 @itemx -mno-explicit-relocs
10367 @opindex mexplicit-relocs
10368 @opindex mno-explicit-relocs
10369 Use (do not use) assembler relocation operators when dealing with symbolic
10370 addresses. The alternative, selected by @option{-mno-explicit-relocs},
10371 is to use assembler macros instead.
10373 @option{-mexplicit-relocs} is the default if GCC was configured
10374 to use an assembler that supports relocation operators.
10376 @item -mcheck-zero-division
10377 @itemx -mno-check-zero-division
10378 @opindex mcheck-zero-division
10379 @opindex mno-check-zero-division
10380 Trap (do not trap) on integer division by zero. The default is
10381 @option{-mcheck-zero-division}.
10383 @item -mdivide-traps
10384 @itemx -mdivide-breaks
10385 @opindex mdivide-traps
10386 @opindex mdivide-breaks
10387 MIPS systems check for division by zero by generating either a
10388 conditional trap or a break instruction. Using traps results in
10389 smaller code, but is only supported on MIPS II and later. Also, some
10390 versions of the Linux kernel have a bug that prevents trap from
10391 generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to
10392 allow conditional traps on architectures that support them and
10393 @option{-mdivide-breaks} to force the use of breaks.
10395 The default is usually @option{-mdivide-traps}, but this can be
10396 overridden at configure time using @option{--with-divide=breaks}.
10397 Divide-by-zero checks can be completely disabled using
10398 @option{-mno-check-zero-division}.
10403 @opindex mno-memcpy
10404 Force (do not force) the use of @code{memcpy()} for non-trivial block
10405 moves. The default is @option{-mno-memcpy}, which allows GCC to inline
10406 most constant-sized copies.
10409 @itemx -mno-long-calls
10410 @opindex mlong-calls
10411 @opindex mno-long-calls
10412 Disable (do not disable) use of the @code{jal} instruction. Calling
10413 functions using @code{jal} is more efficient but requires the caller
10414 and callee to be in the same 256 megabyte segment.
10416 This option has no effect on abicalls code. The default is
10417 @option{-mno-long-calls}.
10423 Enable (disable) use of the @code{mad}, @code{madu} and @code{mul}
10424 instructions, as provided by the R4650 ISA@.
10427 @itemx -mno-fused-madd
10428 @opindex mfused-madd
10429 @opindex mno-fused-madd
10430 Enable (disable) use of the floating point multiply-accumulate
10431 instructions, when they are available. The default is
10432 @option{-mfused-madd}.
10434 When multiply-accumulate instructions are used, the intermediate
10435 product is calculated to infinite precision and is not subject to
10436 the FCSR Flush to Zero bit. This may be undesirable in some
10441 Tell the MIPS assembler to not run its preprocessor over user
10442 assembler files (with a @samp{.s} suffix) when assembling them.
10445 @itemx -mno-fix-r4000
10446 @opindex mfix-r4000
10447 @opindex mno-fix-r4000
10448 Work around certain R4000 CPU errata:
10451 A double-word or a variable shift may give an incorrect result if executed
10452 immediately after starting an integer division.
10454 A double-word or a variable shift may give an incorrect result if executed
10455 while an integer multiplication is in progress.
10457 An integer division may give an incorrect result if started in a delay slot
10458 of a taken branch or a jump.
10462 @itemx -mno-fix-r4400
10463 @opindex mfix-r4400
10464 @opindex mno-fix-r4400
10465 Work around certain R4400 CPU errata:
10468 A double-word or a variable shift may give an incorrect result if executed
10469 immediately after starting an integer division.
10473 @itemx -mno-fix-vr4120
10474 @opindex mfix-vr4120
10475 Work around certain VR4120 errata:
10478 @code{dmultu} does not always produce the correct result.
10480 @code{div} and @code{ddiv} do not always produce the correct result if one
10481 of the operands is negative.
10483 The workarounds for the division errata rely on special functions in
10484 @file{libgcc.a}. At present, these functions are only provided by
10485 the @code{mips64vr*-elf} configurations.
10487 Other VR4120 errata require a nop to be inserted between certain pairs of
10488 instructions. These errata are handled by the assembler, not by GCC itself.
10491 @opindex mfix-vr4130
10492 Work around the VR4130 @code{mflo}/@code{mfhi} errata. The
10493 workarounds are implemented by the assembler rather than by GCC,
10494 although GCC will avoid using @code{mflo} and @code{mfhi} if the
10495 VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi}
10496 instructions are available instead.
10499 @itemx -mno-fix-sb1
10501 Work around certain SB-1 CPU core errata.
10502 (This flag currently works around the SB-1 revision 2
10503 ``F1'' and ``F2'' floating point errata.)
10505 @item -mflush-func=@var{func}
10506 @itemx -mno-flush-func
10507 @opindex mflush-func
10508 Specifies the function to call to flush the I and D caches, or to not
10509 call any such function. If called, the function must take the same
10510 arguments as the common @code{_flush_func()}, that is, the address of the
10511 memory range for which the cache is being flushed, the size of the
10512 memory range, and the number 3 (to flush both caches). The default
10513 depends on the target GCC was configured for, but commonly is either
10514 @samp{_flush_func} or @samp{__cpu_flush}.
10516 @item -mbranch-likely
10517 @itemx -mno-branch-likely
10518 @opindex mbranch-likely
10519 @opindex mno-branch-likely
10520 Enable or disable use of Branch Likely instructions, regardless of the
10521 default for the selected architecture. By default, Branch Likely
10522 instructions may be generated if they are supported by the selected
10523 architecture. An exception is for the MIPS32 and MIPS64 architectures
10524 and processors which implement those architectures; for those, Branch
10525 Likely instructions will not be generated by default because the MIPS32
10526 and MIPS64 architectures specifically deprecate their use.
10528 @item -mfp-exceptions
10529 @itemx -mno-fp-exceptions
10530 @opindex mfp-exceptions
10531 Specifies whether FP exceptions are enabled. This affects how we schedule
10532 FP instructions for some processors. The default is that FP exceptions are
10535 For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
10536 64-bit code, then we can use both FP pipes. Otherwise, we can only use one
10539 @item -mvr4130-align
10540 @itemx -mno-vr4130-align
10541 @opindex mvr4130-align
10542 The VR4130 pipeline is two-way superscalar, but can only issue two
10543 instructions together if the first one is 8-byte aligned. When this
10544 option is enabled, GCC will align pairs of instructions that it
10545 thinks should execute in parallel.
10547 This option only has an effect when optimizing for the VR4130.
10548 It normally makes code faster, but at the expense of making it bigger.
10549 It is enabled by default at optimization level @option{-O3}.
10553 @subsection MMIX Options
10554 @cindex MMIX Options
10556 These options are defined for the MMIX:
10560 @itemx -mno-libfuncs
10562 @opindex mno-libfuncs
10563 Specify that intrinsic library functions are being compiled, passing all
10564 values in registers, no matter the size.
10567 @itemx -mno-epsilon
10569 @opindex mno-epsilon
10570 Generate floating-point comparison instructions that compare with respect
10571 to the @code{rE} epsilon register.
10573 @item -mabi=mmixware
10575 @opindex mabi-mmixware
10577 Generate code that passes function parameters and return values that (in
10578 the called function) are seen as registers @code{$0} and up, as opposed to
10579 the GNU ABI which uses global registers @code{$231} and up.
10581 @item -mzero-extend
10582 @itemx -mno-zero-extend
10583 @opindex mzero-extend
10584 @opindex mno-zero-extend
10585 When reading data from memory in sizes shorter than 64 bits, use (do not
10586 use) zero-extending load instructions by default, rather than
10587 sign-extending ones.
10590 @itemx -mno-knuthdiv
10592 @opindex mno-knuthdiv
10593 Make the result of a division yielding a remainder have the same sign as
10594 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
10595 remainder follows the sign of the dividend. Both methods are
10596 arithmetically valid, the latter being almost exclusively used.
10598 @item -mtoplevel-symbols
10599 @itemx -mno-toplevel-symbols
10600 @opindex mtoplevel-symbols
10601 @opindex mno-toplevel-symbols
10602 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
10603 code can be used with the @code{PREFIX} assembly directive.
10607 Generate an executable in the ELF format, rather than the default
10608 @samp{mmo} format used by the @command{mmix} simulator.
10610 @item -mbranch-predict
10611 @itemx -mno-branch-predict
10612 @opindex mbranch-predict
10613 @opindex mno-branch-predict
10614 Use (do not use) the probable-branch instructions, when static branch
10615 prediction indicates a probable branch.
10617 @item -mbase-addresses
10618 @itemx -mno-base-addresses
10619 @opindex mbase-addresses
10620 @opindex mno-base-addresses
10621 Generate (do not generate) code that uses @emph{base addresses}. Using a
10622 base address automatically generates a request (handled by the assembler
10623 and the linker) for a constant to be set up in a global register. The
10624 register is used for one or more base address requests within the range 0
10625 to 255 from the value held in the register. The generally leads to short
10626 and fast code, but the number of different data items that can be
10627 addressed is limited. This means that a program that uses lots of static
10628 data may require @option{-mno-base-addresses}.
10630 @item -msingle-exit
10631 @itemx -mno-single-exit
10632 @opindex msingle-exit
10633 @opindex mno-single-exit
10634 Force (do not force) generated code to have a single exit point in each
10638 @node MN10300 Options
10639 @subsection MN10300 Options
10640 @cindex MN10300 options
10642 These @option{-m} options are defined for Matsushita MN10300 architectures:
10647 Generate code to avoid bugs in the multiply instructions for the MN10300
10648 processors. This is the default.
10650 @item -mno-mult-bug
10651 @opindex mno-mult-bug
10652 Do not generate code to avoid bugs in the multiply instructions for the
10653 MN10300 processors.
10657 Generate code which uses features specific to the AM33 processor.
10661 Do not generate code which uses features specific to the AM33 processor. This
10664 @item -mreturn-pointer-on-d0
10665 @opindex mreturn-pointer-on-d0
10666 When generating a function which returns a pointer, return the pointer
10667 in both @code{a0} and @code{d0}. Otherwise, the pointer is returned
10668 only in a0, and attempts to call such functions without a prototype
10669 would result in errors. Note that this option is on by default; use
10670 @option{-mno-return-pointer-on-d0} to disable it.
10674 Do not link in the C run-time initialization object file.
10678 Indicate to the linker that it should perform a relaxation optimization pass
10679 to shorten branches, calls and absolute memory addresses. This option only
10680 has an effect when used on the command line for the final link step.
10682 This option makes symbolic debugging impossible.
10686 @subsection MS1 Options
10687 @cindex MS1 options
10689 These @option{-m} options are defined for Morpho MS1 architectures:
10693 @item -march=@var{cpu-type}
10695 Generate code that will run on @var{cpu-type}, which is the name of a system
10696 representing a certain processor type. Possible values for
10697 @var{cpu-type} are @samp{MS1-64-001}, @samp{MS1-16-002}, and
10700 When this option is not used, the default is @option{-march=MS1-16-003}.
10704 Generate multiply instructions.
10708 Do not generate multiply instructions.
10712 Use byte loads and stores when generating code.
10716 Do not use byte loads and stores when generating code.
10720 Use simulator runtime
10724 Do not link in the C run-time initialization object file
10725 @file{crti.o}. Other run-time initialization and termination files
10726 such as @file{startup.o} and @file{exit.o} are still included on the
10727 linker command line.
10731 @node PDP-11 Options
10732 @subsection PDP-11 Options
10733 @cindex PDP-11 Options
10735 These options are defined for the PDP-11:
10740 Use hardware FPP floating point. This is the default. (FIS floating
10741 point on the PDP-11/40 is not supported.)
10744 @opindex msoft-float
10745 Do not use hardware floating point.
10749 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
10753 Return floating-point results in memory. This is the default.
10757 Generate code for a PDP-11/40.
10761 Generate code for a PDP-11/45. This is the default.
10765 Generate code for a PDP-11/10.
10767 @item -mbcopy-builtin
10768 @opindex bcopy-builtin
10769 Use inline @code{movmemhi} patterns for copying memory. This is the
10774 Do not use inline @code{movmemhi} patterns for copying memory.
10780 Use 16-bit @code{int}. This is the default.
10786 Use 32-bit @code{int}.
10789 @itemx -mno-float32
10791 @opindex mno-float32
10792 Use 64-bit @code{float}. This is the default.
10795 @itemx -mno-float64
10797 @opindex mno-float64
10798 Use 32-bit @code{float}.
10802 Use @code{abshi2} pattern. This is the default.
10806 Do not use @code{abshi2} pattern.
10808 @item -mbranch-expensive
10809 @opindex mbranch-expensive
10810 Pretend that branches are expensive. This is for experimenting with
10811 code generation only.
10813 @item -mbranch-cheap
10814 @opindex mbranch-cheap
10815 Do not pretend that branches are expensive. This is the default.
10819 Generate code for a system with split I&D@.
10823 Generate code for a system without split I&D@. This is the default.
10827 Use Unix assembler syntax. This is the default when configured for
10828 @samp{pdp11-*-bsd}.
10832 Use DEC assembler syntax. This is the default when configured for any
10833 PDP-11 target other than @samp{pdp11-*-bsd}.
10836 @node PowerPC Options
10837 @subsection PowerPC Options
10838 @cindex PowerPC options
10840 These are listed under @xref{RS/6000 and PowerPC Options}.
10842 @node RS/6000 and PowerPC Options
10843 @subsection IBM RS/6000 and PowerPC Options
10844 @cindex RS/6000 and PowerPC Options
10845 @cindex IBM RS/6000 and PowerPC Options
10847 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
10854 @itemx -mno-powerpc
10855 @itemx -mpowerpc-gpopt
10856 @itemx -mno-powerpc-gpopt
10857 @itemx -mpowerpc-gfxopt
10858 @itemx -mno-powerpc-gfxopt
10860 @itemx -mno-powerpc64
10864 @itemx -mno-popcntb
10870 @opindex mno-power2
10872 @opindex mno-powerpc
10873 @opindex mpowerpc-gpopt
10874 @opindex mno-powerpc-gpopt
10875 @opindex mpowerpc-gfxopt
10876 @opindex mno-powerpc-gfxopt
10877 @opindex mpowerpc64
10878 @opindex mno-powerpc64
10882 @opindex mno-popcntb
10885 GCC supports two related instruction set architectures for the
10886 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
10887 instructions supported by the @samp{rios} chip set used in the original
10888 RS/6000 systems and the @dfn{PowerPC} instruction set is the
10889 architecture of the Freescale MPC5xx, MPC6xx, MPC8xx microprocessors, and
10890 the IBM 4xx, 6xx, and follow-on microprocessors.
10892 Neither architecture is a subset of the other. However there is a
10893 large common subset of instructions supported by both. An MQ
10894 register is included in processors supporting the POWER architecture.
10896 You use these options to specify which instructions are available on the
10897 processor you are using. The default value of these options is
10898 determined when configuring GCC@. Specifying the
10899 @option{-mcpu=@var{cpu_type}} overrides the specification of these
10900 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
10901 rather than the options listed above.
10903 The @option{-mpower} option allows GCC to generate instructions that
10904 are found only in the POWER architecture and to use the MQ register.
10905 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
10906 to generate instructions that are present in the POWER2 architecture but
10907 not the original POWER architecture.
10909 The @option{-mpowerpc} option allows GCC to generate instructions that
10910 are found only in the 32-bit subset of the PowerPC architecture.
10911 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
10912 GCC to use the optional PowerPC architecture instructions in the
10913 General Purpose group, including floating-point square root. Specifying
10914 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
10915 use the optional PowerPC architecture instructions in the Graphics
10916 group, including floating-point select.
10918 The @option{-mmfcrf} option allows GCC to generate the move from
10919 condition register field instruction implemented on the POWER4
10920 processor and other processors that support the PowerPC V2.01
10922 The @option{-mpopcntb} option allows GCC to generate the popcount and
10923 double precision FP reciprocal estimate instruction implemented on the
10924 POWER5 processor and other processors that support the PowerPC V2.02
10926 The @option{-mfprnd} option allows GCC to generate the FP round to
10927 integer instructions implemented on the POWER5+ processor and other
10928 processors that support the PowerPC V2.03 architecture.
10930 The @option{-mpowerpc64} option allows GCC to generate the additional
10931 64-bit instructions that are found in the full PowerPC64 architecture
10932 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
10933 @option{-mno-powerpc64}.
10935 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
10936 will use only the instructions in the common subset of both
10937 architectures plus some special AIX common-mode calls, and will not use
10938 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
10939 permits GCC to use any instruction from either architecture and to
10940 allow use of the MQ register; specify this for the Motorola MPC601.
10942 @item -mnew-mnemonics
10943 @itemx -mold-mnemonics
10944 @opindex mnew-mnemonics
10945 @opindex mold-mnemonics
10946 Select which mnemonics to use in the generated assembler code. With
10947 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
10948 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
10949 assembler mnemonics defined for the POWER architecture. Instructions
10950 defined in only one architecture have only one mnemonic; GCC uses that
10951 mnemonic irrespective of which of these options is specified.
10953 GCC defaults to the mnemonics appropriate for the architecture in
10954 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
10955 value of these option. Unless you are building a cross-compiler, you
10956 should normally not specify either @option{-mnew-mnemonics} or
10957 @option{-mold-mnemonics}, but should instead accept the default.
10959 @item -mcpu=@var{cpu_type}
10961 Set architecture type, register usage, choice of mnemonics, and
10962 instruction scheduling parameters for machine type @var{cpu_type}.
10963 Supported values for @var{cpu_type} are @samp{401}, @samp{403},
10964 @samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{505},
10965 @samp{601}, @samp{602}, @samp{603}, @samp{603e}, @samp{604},
10966 @samp{604e}, @samp{620}, @samp{630}, @samp{740}, @samp{7400},
10967 @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
10968 @samp{860}, @samp{970}, @samp{8540}, @samp{ec603e}, @samp{G3},
10969 @samp{G4}, @samp{G5}, @samp{power}, @samp{power2}, @samp{power3},
10970 @samp{power4}, @samp{power5}, @samp{power5+},
10971 @samp{common}, @samp{powerpc}, @samp{powerpc64},
10972 @samp{rios}, @samp{rios1}, @samp{rios2}, @samp{rsc}, and @samp{rs64}.
10974 @option{-mcpu=common} selects a completely generic processor. Code
10975 generated under this option will run on any POWER or PowerPC processor.
10976 GCC will use only the instructions in the common subset of both
10977 architectures, and will not use the MQ register. GCC assumes a generic
10978 processor model for scheduling purposes.
10980 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
10981 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
10982 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
10983 types, with an appropriate, generic processor model assumed for
10984 scheduling purposes.
10986 The other options specify a specific processor. Code generated under
10987 those options will run best on that processor, and may not run at all on
10990 The @option{-mcpu} options automatically enable or disable the
10991 following options: @option{-maltivec}, @option{-mfprnd},
10992 @option{-mhard-float}, @option{-mmfcrf}, @option{-mmultiple},
10993 @option{-mnew-mnemonics}, @option{-mpopcntb}, @option{-mpower},
10994 @option{-mpower2}, @option{-mpowerpc64}, @option{-mpowerpc-gpopt},
10995 @option{-mpowerpc-gfxopt}, @option{-mstring}, @option{-mmulhw}.
10996 The particular options
10997 set for any particular CPU will vary between compiler versions,
10998 depending on what setting seems to produce optimal code for that CPU;
10999 it doesn't necessarily reflect the actual hardware's capabilities. If
11000 you wish to set an individual option to a particular value, you may
11001 specify it after the @option{-mcpu} option, like @samp{-mcpu=970
11004 On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are
11005 not enabled or disabled by the @option{-mcpu} option at present because
11006 AIX does not have full support for these options. You may still
11007 enable or disable them individually if you're sure it'll work in your
11010 @item -mtune=@var{cpu_type}
11012 Set the instruction scheduling parameters for machine type
11013 @var{cpu_type}, but do not set the architecture type, register usage, or
11014 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
11015 values for @var{cpu_type} are used for @option{-mtune} as for
11016 @option{-mcpu}. If both are specified, the code generated will use the
11017 architecture, registers, and mnemonics set by @option{-mcpu}, but the
11018 scheduling parameters set by @option{-mtune}.
11024 Generate code to compute division as reciprocal estimate and iterative
11025 refinement, creating opportunities for increased throughput. This
11026 feature requires: optional PowerPC Graphics instruction set for single
11027 precision and FRE instruction for double precision, assuming divides
11028 cannot generate user-visible traps, and the domain values not include
11029 Infinities, denormals or zero denominator.
11032 @itemx -mno-altivec
11034 @opindex mno-altivec
11035 Generate code that uses (does not use) AltiVec instructions, and also
11036 enable the use of built-in functions that allow more direct access to
11037 the AltiVec instruction set. You may also need to set
11038 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
11044 @opindex mno-vrsave
11045 Generate VRSAVE instructions when generating AltiVec code.
11049 Extend the current ABI with SPE ABI extensions. This does not change
11050 the default ABI, instead it adds the SPE ABI extensions to the current
11054 @opindex mabi=no-spe
11055 Disable Booke SPE ABI extensions for the current ABI@.
11058 @opindex msecure-plt
11059 Generate code that allows ld and ld.so to build executables and shared
11060 libraries with non-exec .plt and .got sections. This is a PowerPC
11061 32-bit SYSV ABI option.
11065 Generate code that uses a BSS .plt section that ld.so fills in, and
11066 requires .plt and .got sections that are both writable and executable.
11067 This is a PowerPC 32-bit SYSV ABI option.
11073 This switch enables or disables the generation of ISEL instructions.
11075 @item -misel=@var{yes/no}
11076 This switch has been deprecated. Use @option{-misel} and
11077 @option{-mno-isel} instead.
11083 This switch enables or disables the generation of SPE simd
11086 @item -mspe=@var{yes/no}
11087 This option has been deprecated. Use @option{-mspe} and
11088 @option{-mno-spe} instead.
11090 @item -mfloat-gprs=@var{yes/single/double/no}
11091 @itemx -mfloat-gprs
11092 @opindex mfloat-gprs
11093 This switch enables or disables the generation of floating point
11094 operations on the general purpose registers for architectures that
11097 The argument @var{yes} or @var{single} enables the use of
11098 single-precision floating point operations.
11100 The argument @var{double} enables the use of single and
11101 double-precision floating point operations.
11103 The argument @var{no} disables floating point operations on the
11104 general purpose registers.
11106 This option is currently only available on the MPC854x.
11112 Generate code for 32-bit or 64-bit environments of Darwin and SVR4
11113 targets (including GNU/Linux). The 32-bit environment sets int, long
11114 and pointer to 32 bits and generates code that runs on any PowerPC
11115 variant. The 64-bit environment sets int to 32 bits and long and
11116 pointer to 64 bits, and generates code for PowerPC64, as for
11117 @option{-mpowerpc64}.
11120 @itemx -mno-fp-in-toc
11121 @itemx -mno-sum-in-toc
11122 @itemx -mminimal-toc
11124 @opindex mno-fp-in-toc
11125 @opindex mno-sum-in-toc
11126 @opindex mminimal-toc
11127 Modify generation of the TOC (Table Of Contents), which is created for
11128 every executable file. The @option{-mfull-toc} option is selected by
11129 default. In that case, GCC will allocate at least one TOC entry for
11130 each unique non-automatic variable reference in your program. GCC
11131 will also place floating-point constants in the TOC@. However, only
11132 16,384 entries are available in the TOC@.
11134 If you receive a linker error message that saying you have overflowed
11135 the available TOC space, you can reduce the amount of TOC space used
11136 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
11137 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
11138 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
11139 generate code to calculate the sum of an address and a constant at
11140 run-time instead of putting that sum into the TOC@. You may specify one
11141 or both of these options. Each causes GCC to produce very slightly
11142 slower and larger code at the expense of conserving TOC space.
11144 If you still run out of space in the TOC even when you specify both of
11145 these options, specify @option{-mminimal-toc} instead. This option causes
11146 GCC to make only one TOC entry for every file. When you specify this
11147 option, GCC will produce code that is slower and larger but which
11148 uses extremely little TOC space. You may wish to use this option
11149 only on files that contain less frequently executed code.
11155 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
11156 @code{long} type, and the infrastructure needed to support them.
11157 Specifying @option{-maix64} implies @option{-mpowerpc64} and
11158 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
11159 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
11162 @itemx -mno-xl-compat
11163 @opindex mxl-compat
11164 @opindex mno-xl-compat
11165 Produce code that conforms more closely to IBM XLC semantics when using
11166 AIX-compatible ABI. Pass floating-point arguments to prototyped
11167 functions beyond the register save area (RSA) on the stack in addition
11168 to argument FPRs. Do not assume that most significant double in 128
11169 bit long double value is properly rounded when comparing values.
11171 The AIX calling convention was extended but not initially documented to
11172 handle an obscure K&R C case of calling a function that takes the
11173 address of its arguments with fewer arguments than declared. AIX XL
11174 compilers access floating point arguments which do not fit in the
11175 RSA from the stack when a subroutine is compiled without
11176 optimization. Because always storing floating-point arguments on the
11177 stack is inefficient and rarely needed, this option is not enabled by
11178 default and only is necessary when calling subroutines compiled by AIX
11179 XL compilers without optimization.
11183 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
11184 application written to use message passing with special startup code to
11185 enable the application to run. The system must have PE installed in the
11186 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
11187 must be overridden with the @option{-specs=} option to specify the
11188 appropriate directory location. The Parallel Environment does not
11189 support threads, so the @option{-mpe} option and the @option{-pthread}
11190 option are incompatible.
11192 @item -malign-natural
11193 @itemx -malign-power
11194 @opindex malign-natural
11195 @opindex malign-power
11196 On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
11197 @option{-malign-natural} overrides the ABI-defined alignment of larger
11198 types, such as floating-point doubles, on their natural size-based boundary.
11199 The option @option{-malign-power} instructs GCC to follow the ABI-specified
11200 alignment rules. GCC defaults to the standard alignment defined in the ABI@.
11202 On 64-bit Darwin, natural alignment is the default, and @option{-malign-power}
11206 @itemx -mhard-float
11207 @opindex msoft-float
11208 @opindex mhard-float
11209 Generate code that does not use (uses) the floating-point register set.
11210 Software floating point emulation is provided if you use the
11211 @option{-msoft-float} option, and pass the option to GCC when linking.
11214 @itemx -mno-multiple
11216 @opindex mno-multiple
11217 Generate code that uses (does not use) the load multiple word
11218 instructions and the store multiple word instructions. These
11219 instructions are generated by default on POWER systems, and not
11220 generated on PowerPC systems. Do not use @option{-mmultiple} on little
11221 endian PowerPC systems, since those instructions do not work when the
11222 processor is in little endian mode. The exceptions are PPC740 and
11223 PPC750 which permit the instructions usage in little endian mode.
11228 @opindex mno-string
11229 Generate code that uses (does not use) the load string instructions
11230 and the store string word instructions to save multiple registers and
11231 do small block moves. These instructions are generated by default on
11232 POWER systems, and not generated on PowerPC systems. Do not use
11233 @option{-mstring} on little endian PowerPC systems, since those
11234 instructions do not work when the processor is in little endian mode.
11235 The exceptions are PPC740 and PPC750 which permit the instructions
11236 usage in little endian mode.
11241 @opindex mno-update
11242 Generate code that uses (does not use) the load or store instructions
11243 that update the base register to the address of the calculated memory
11244 location. These instructions are generated by default. If you use
11245 @option{-mno-update}, there is a small window between the time that the
11246 stack pointer is updated and the address of the previous frame is
11247 stored, which means code that walks the stack frame across interrupts or
11248 signals may get corrupted data.
11251 @itemx -mno-fused-madd
11252 @opindex mfused-madd
11253 @opindex mno-fused-madd
11254 Generate code that uses (does not use) the floating point multiply and
11255 accumulate instructions. These instructions are generated by default if
11256 hardware floating is used.
11262 Generate code that uses (does not use) the half-word multiply and
11263 multiply-accumulate instructions on the IBM 405 and 440 processors.
11264 These instructions are generated by default when targetting those
11267 @item -mno-bit-align
11269 @opindex mno-bit-align
11270 @opindex mbit-align
11271 On System V.4 and embedded PowerPC systems do not (do) force structures
11272 and unions that contain bit-fields to be aligned to the base type of the
11275 For example, by default a structure containing nothing but 8
11276 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
11277 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
11278 the structure would be aligned to a 1 byte boundary and be one byte in
11281 @item -mno-strict-align
11282 @itemx -mstrict-align
11283 @opindex mno-strict-align
11284 @opindex mstrict-align
11285 On System V.4 and embedded PowerPC systems do not (do) assume that
11286 unaligned memory references will be handled by the system.
11288 @item -mrelocatable
11289 @itemx -mno-relocatable
11290 @opindex mrelocatable
11291 @opindex mno-relocatable
11292 On embedded PowerPC systems generate code that allows (does not allow)
11293 the program to be relocated to a different address at runtime. If you
11294 use @option{-mrelocatable} on any module, all objects linked together must
11295 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
11297 @item -mrelocatable-lib
11298 @itemx -mno-relocatable-lib
11299 @opindex mrelocatable-lib
11300 @opindex mno-relocatable-lib
11301 On embedded PowerPC systems generate code that allows (does not allow)
11302 the program to be relocated to a different address at runtime. Modules
11303 compiled with @option{-mrelocatable-lib} can be linked with either modules
11304 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
11305 with modules compiled with the @option{-mrelocatable} options.
11311 On System V.4 and embedded PowerPC systems do not (do) assume that
11312 register 2 contains a pointer to a global area pointing to the addresses
11313 used in the program.
11316 @itemx -mlittle-endian
11318 @opindex mlittle-endian
11319 On System V.4 and embedded PowerPC systems compile code for the
11320 processor in little endian mode. The @option{-mlittle-endian} option is
11321 the same as @option{-mlittle}.
11324 @itemx -mbig-endian
11326 @opindex mbig-endian
11327 On System V.4 and embedded PowerPC systems compile code for the
11328 processor in big endian mode. The @option{-mbig-endian} option is
11329 the same as @option{-mbig}.
11331 @item -mdynamic-no-pic
11332 @opindex mdynamic-no-pic
11333 On Darwin and Mac OS X systems, compile code so that it is not
11334 relocatable, but that its external references are relocatable. The
11335 resulting code is suitable for applications, but not shared
11338 @item -mprioritize-restricted-insns=@var{priority}
11339 @opindex mprioritize-restricted-insns
11340 This option controls the priority that is assigned to
11341 dispatch-slot restricted instructions during the second scheduling
11342 pass. The argument @var{priority} takes the value @var{0/1/2} to assign
11343 @var{no/highest/second-highest} priority to dispatch slot restricted
11346 @item -msched-costly-dep=@var{dependence_type}
11347 @opindex msched-costly-dep
11348 This option controls which dependences are considered costly
11349 by the target during instruction scheduling. The argument
11350 @var{dependence_type} takes one of the following values:
11351 @var{no}: no dependence is costly,
11352 @var{all}: all dependences are costly,
11353 @var{true_store_to_load}: a true dependence from store to load is costly,
11354 @var{store_to_load}: any dependence from store to load is costly,
11355 @var{number}: any dependence which latency >= @var{number} is costly.
11357 @item -minsert-sched-nops=@var{scheme}
11358 @opindex minsert-sched-nops
11359 This option controls which nop insertion scheme will be used during
11360 the second scheduling pass. The argument @var{scheme} takes one of the
11362 @var{no}: Don't insert nops.
11363 @var{pad}: Pad with nops any dispatch group which has vacant issue slots,
11364 according to the scheduler's grouping.
11365 @var{regroup_exact}: Insert nops to force costly dependent insns into
11366 separate groups. Insert exactly as many nops as needed to force an insn
11367 to a new group, according to the estimated processor grouping.
11368 @var{number}: Insert nops to force costly dependent insns into
11369 separate groups. Insert @var{number} nops to force an insn to a new group.
11372 @opindex mcall-sysv
11373 On System V.4 and embedded PowerPC systems compile code using calling
11374 conventions that adheres to the March 1995 draft of the System V
11375 Application Binary Interface, PowerPC processor supplement. This is the
11376 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
11378 @item -mcall-sysv-eabi
11379 @opindex mcall-sysv-eabi
11380 Specify both @option{-mcall-sysv} and @option{-meabi} options.
11382 @item -mcall-sysv-noeabi
11383 @opindex mcall-sysv-noeabi
11384 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
11386 @item -mcall-solaris
11387 @opindex mcall-solaris
11388 On System V.4 and embedded PowerPC systems compile code for the Solaris
11392 @opindex mcall-linux
11393 On System V.4 and embedded PowerPC systems compile code for the
11394 Linux-based GNU system.
11398 On System V.4 and embedded PowerPC systems compile code for the
11399 Hurd-based GNU system.
11401 @item -mcall-netbsd
11402 @opindex mcall-netbsd
11403 On System V.4 and embedded PowerPC systems compile code for the
11404 NetBSD operating system.
11406 @item -maix-struct-return
11407 @opindex maix-struct-return
11408 Return all structures in memory (as specified by the AIX ABI)@.
11410 @item -msvr4-struct-return
11411 @opindex msvr4-struct-return
11412 Return structures smaller than 8 bytes in registers (as specified by the
11415 @item -mabi=@var{abi-type}
11417 Extend the current ABI with a particular extension, or remove such extension.
11418 Valid values are @var{altivec}, @var{no-altivec}, @var{spe},
11422 @itemx -mno-prototype
11423 @opindex mprototype
11424 @opindex mno-prototype
11425 On System V.4 and embedded PowerPC systems assume that all calls to
11426 variable argument functions are properly prototyped. Otherwise, the
11427 compiler must insert an instruction before every non prototyped call to
11428 set or clear bit 6 of the condition code register (@var{CR}) to
11429 indicate whether floating point values were passed in the floating point
11430 registers in case the function takes a variable arguments. With
11431 @option{-mprototype}, only calls to prototyped variable argument functions
11432 will set or clear the bit.
11436 On embedded PowerPC systems, assume that the startup module is called
11437 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
11438 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
11443 On embedded PowerPC systems, assume that the startup module is called
11444 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
11449 On embedded PowerPC systems, assume that the startup module is called
11450 @file{crt0.o} and the standard C libraries are @file{libads.a} and
11453 @item -myellowknife
11454 @opindex myellowknife
11455 On embedded PowerPC systems, assume that the startup module is called
11456 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
11461 On System V.4 and embedded PowerPC systems, specify that you are
11462 compiling for a VxWorks system.
11466 Specify that you are compiling for the WindISS simulation environment.
11470 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
11471 header to indicate that @samp{eabi} extended relocations are used.
11477 On System V.4 and embedded PowerPC systems do (do not) adhere to the
11478 Embedded Applications Binary Interface (eabi) which is a set of
11479 modifications to the System V.4 specifications. Selecting @option{-meabi}
11480 means that the stack is aligned to an 8 byte boundary, a function
11481 @code{__eabi} is called to from @code{main} to set up the eabi
11482 environment, and the @option{-msdata} option can use both @code{r2} and
11483 @code{r13} to point to two separate small data areas. Selecting
11484 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
11485 do not call an initialization function from @code{main}, and the
11486 @option{-msdata} option will only use @code{r13} to point to a single
11487 small data area. The @option{-meabi} option is on by default if you
11488 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
11491 @opindex msdata=eabi
11492 On System V.4 and embedded PowerPC systems, put small initialized
11493 @code{const} global and static data in the @samp{.sdata2} section, which
11494 is pointed to by register @code{r2}. Put small initialized
11495 non-@code{const} global and static data in the @samp{.sdata} section,
11496 which is pointed to by register @code{r13}. Put small uninitialized
11497 global and static data in the @samp{.sbss} section, which is adjacent to
11498 the @samp{.sdata} section. The @option{-msdata=eabi} option is
11499 incompatible with the @option{-mrelocatable} option. The
11500 @option{-msdata=eabi} option also sets the @option{-memb} option.
11503 @opindex msdata=sysv
11504 On System V.4 and embedded PowerPC systems, put small global and static
11505 data in the @samp{.sdata} section, which is pointed to by register
11506 @code{r13}. Put small uninitialized global and static data in the
11507 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
11508 The @option{-msdata=sysv} option is incompatible with the
11509 @option{-mrelocatable} option.
11511 @item -msdata=default
11513 @opindex msdata=default
11515 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
11516 compile code the same as @option{-msdata=eabi}, otherwise compile code the
11517 same as @option{-msdata=sysv}.
11520 @opindex msdata-data
11521 On System V.4 and embedded PowerPC systems, put small global
11522 data in the @samp{.sdata} section. Put small uninitialized global
11523 data in the @samp{.sbss} section. Do not use register @code{r13}
11524 to address small data however. This is the default behavior unless
11525 other @option{-msdata} options are used.
11529 @opindex msdata=none
11531 On embedded PowerPC systems, put all initialized global and static data
11532 in the @samp{.data} section, and all uninitialized data in the
11533 @samp{.bss} section.
11537 @cindex smaller data references (PowerPC)
11538 @cindex .sdata/.sdata2 references (PowerPC)
11539 On embedded PowerPC systems, put global and static items less than or
11540 equal to @var{num} bytes into the small data or bss sections instead of
11541 the normal data or bss section. By default, @var{num} is 8. The
11542 @option{-G @var{num}} switch is also passed to the linker.
11543 All modules should be compiled with the same @option{-G @var{num}} value.
11546 @itemx -mno-regnames
11548 @opindex mno-regnames
11549 On System V.4 and embedded PowerPC systems do (do not) emit register
11550 names in the assembly language output using symbolic forms.
11553 @itemx -mno-longcall
11555 @opindex mno-longcall
11556 Default to making all function calls indirectly, using a register, so
11557 that functions which reside further than 32 megabytes (33,554,432
11558 bytes) from the current location can be called. This setting can be
11559 overridden by the @code{shortcall} function attribute, or by
11560 @code{#pragma longcall(0)}.
11562 Some linkers are capable of detecting out-of-range calls and generating
11563 glue code on the fly. On these systems, long calls are unnecessary and
11564 generate slower code. As of this writing, the AIX linker can do this,
11565 as can the GNU linker for PowerPC/64. It is planned to add this feature
11566 to the GNU linker for 32-bit PowerPC systems as well.
11568 On Darwin/PPC systems, @code{#pragma longcall} will generate ``jbsr
11569 callee, L42'', plus a ``branch island'' (glue code). The two target
11570 addresses represent the callee and the ``branch island''. The
11571 Darwin/PPC linker will prefer the first address and generate a ``bl
11572 callee'' if the PPC ``bl'' instruction will reach the callee directly;
11573 otherwise, the linker will generate ``bl L42'' to call the ``branch
11574 island''. The ``branch island'' is appended to the body of the
11575 calling function; it computes the full 32-bit address of the callee
11578 On Mach-O (Darwin) systems, this option directs the compiler emit to
11579 the glue for every direct call, and the Darwin linker decides whether
11580 to use or discard it.
11582 In the future, we may cause GCC to ignore all longcall specifications
11583 when the linker is known to generate glue.
11587 Adds support for multithreading with the @dfn{pthreads} library.
11588 This option sets flags for both the preprocessor and linker.
11592 @node S/390 and zSeries Options
11593 @subsection S/390 and zSeries Options
11594 @cindex S/390 and zSeries Options
11596 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
11600 @itemx -msoft-float
11601 @opindex mhard-float
11602 @opindex msoft-float
11603 Use (do not use) the hardware floating-point instructions and registers
11604 for floating-point operations. When @option{-msoft-float} is specified,
11605 functions in @file{libgcc.a} will be used to perform floating-point
11606 operations. When @option{-mhard-float} is specified, the compiler
11607 generates IEEE floating-point instructions. This is the default.
11610 @itemx -mno-backchain
11611 @opindex mbackchain
11612 @opindex mno-backchain
11613 Store (do not store) the address of the caller's frame as backchain pointer
11614 into the callee's stack frame.
11615 A backchain may be needed to allow debugging using tools that do not understand
11616 DWARF-2 call frame information.
11617 When @option{-mno-packed-stack} is in effect, the backchain pointer is stored
11618 at the bottom of the stack frame; when @option{-mpacked-stack} is in effect,
11619 the backchain is placed into the topmost word of the 96/160 byte register
11622 In general, code compiled with @option{-mbackchain} is call-compatible with
11623 code compiled with @option{-mmo-backchain}; however, use of the backchain
11624 for debugging purposes usually requires that the whole binary is built with
11625 @option{-mbackchain}. Note that the combination of @option{-mbackchain},
11626 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
11627 to build a linux kernel use @option{-msoft-float}.
11629 The default is to not maintain the backchain.
11631 @item -mpacked-stack
11632 @item -mno-packed-stack
11633 @opindex mpacked-stack
11634 @opindex mno-packed-stack
11635 Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is
11636 specified, the compiler uses the all fields of the 96/160 byte register save
11637 area only for their default purpose; unused fields still take up stack space.
11638 When @option{-mpacked-stack} is specified, register save slots are densely
11639 packed at the top of the register save area; unused space is reused for other
11640 purposes, allowing for more efficient use of the available stack space.
11641 However, when @option{-mbackchain} is also in effect, the topmost word of
11642 the save area is always used to store the backchain, and the return address
11643 register is always saved two words below the backchain.
11645 As long as the stack frame backchain is not used, code generated with
11646 @option{-mpacked-stack} is call-compatible with code generated with
11647 @option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for
11648 S/390 or zSeries generated code that uses the stack frame backchain at run
11649 time, not just for debugging purposes. Such code is not call-compatible
11650 with code compiled with @option{-mpacked-stack}. Also, note that the
11651 combination of @option{-mbackchain},
11652 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
11653 to build a linux kernel use @option{-msoft-float}.
11655 The default is to not use the packed stack layout.
11658 @itemx -mno-small-exec
11659 @opindex msmall-exec
11660 @opindex mno-small-exec
11661 Generate (or do not generate) code using the @code{bras} instruction
11662 to do subroutine calls.
11663 This only works reliably if the total executable size does not
11664 exceed 64k. The default is to use the @code{basr} instruction instead,
11665 which does not have this limitation.
11671 When @option{-m31} is specified, generate code compliant to the
11672 GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate
11673 code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in
11674 particular to generate 64-bit instructions. For the @samp{s390}
11675 targets, the default is @option{-m31}, while the @samp{s390x}
11676 targets default to @option{-m64}.
11682 When @option{-mzarch} is specified, generate code using the
11683 instructions available on z/Architecture.
11684 When @option{-mesa} is specified, generate code using the
11685 instructions available on ESA/390. Note that @option{-mesa} is
11686 not possible with @option{-m64}.
11687 When generating code compliant to the GNU/Linux for S/390 ABI,
11688 the default is @option{-mesa}. When generating code compliant
11689 to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}.
11695 Generate (or do not generate) code using the @code{mvcle} instruction
11696 to perform block moves. When @option{-mno-mvcle} is specified,
11697 use a @code{mvc} loop instead. This is the default unless optimizing for
11704 Print (or do not print) additional debug information when compiling.
11705 The default is to not print debug information.
11707 @item -march=@var{cpu-type}
11709 Generate code that will run on @var{cpu-type}, which is the name of a system
11710 representing a certain processor type. Possible values for
11711 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, and @samp{z990}.
11712 When generating code using the instructions available on z/Architecture,
11713 the default is @option{-march=z900}. Otherwise, the default is
11714 @option{-march=g5}.
11716 @item -mtune=@var{cpu-type}
11718 Tune to @var{cpu-type} everything applicable about the generated code,
11719 except for the ABI and the set of available instructions.
11720 The list of @var{cpu-type} values is the same as for @option{-march}.
11721 The default is the value used for @option{-march}.
11724 @itemx -mno-tpf-trace
11725 @opindex mtpf-trace
11726 @opindex mno-tpf-trace
11727 Generate code that adds (does not add) in TPF OS specific branches to trace
11728 routines in the operating system. This option is off by default, even
11729 when compiling for the TPF OS@.
11732 @itemx -mno-fused-madd
11733 @opindex mfused-madd
11734 @opindex mno-fused-madd
11735 Generate code that uses (does not use) the floating point multiply and
11736 accumulate instructions. These instructions are generated by default if
11737 hardware floating point is used.
11739 @item -mwarn-framesize=@var{framesize}
11740 @opindex mwarn-framesize
11741 Emit a warning if the current function exceeds the given frame size. Because
11742 this is a compile time check it doesn't need to be a real problem when the program
11743 runs. It is intended to identify functions which most probably cause
11744 a stack overflow. It is useful to be used in an environment with limited stack
11745 size e.g.@: the linux kernel.
11747 @item -mwarn-dynamicstack
11748 @opindex mwarn-dynamicstack
11749 Emit a warning if the function calls alloca or uses dynamically
11750 sized arrays. This is generally a bad idea with a limited stack size.
11752 @item -mstack-guard=@var{stack-guard}
11753 @item -mstack-size=@var{stack-size}
11754 @opindex mstack-guard
11755 @opindex mstack-size
11756 These arguments always have to be used in conjunction. If they are present the s390
11757 back end emits additional instructions in the function prologue which trigger a trap
11758 if the stack size is @var{stack-guard} bytes above the @var{stack-size}
11759 (remember that the stack on s390 grows downward). These options are intended to
11760 be used to help debugging stack overflow problems. The additionally emitted code
11761 causes only little overhead and hence can also be used in production like systems
11762 without greater performance degradation. The given values have to be exact
11763 powers of 2 and @var{stack-size} has to be greater than @var{stack-guard} without
11765 In order to be efficient the extra code makes the assumption that the stack starts
11766 at an address aligned to the value given by @var{stack-size}.
11770 @subsection SH Options
11772 These @samp{-m} options are defined for the SH implementations:
11777 Generate code for the SH1.
11781 Generate code for the SH2.
11784 Generate code for the SH2e.
11788 Generate code for the SH3.
11792 Generate code for the SH3e.
11796 Generate code for the SH4 without a floating-point unit.
11798 @item -m4-single-only
11799 @opindex m4-single-only
11800 Generate code for the SH4 with a floating-point unit that only
11801 supports single-precision arithmetic.
11805 Generate code for the SH4 assuming the floating-point unit is in
11806 single-precision mode by default.
11810 Generate code for the SH4.
11814 Generate code for the SH4al-dsp, or for a SH4a in such a way that the
11815 floating-point unit is not used.
11817 @item -m4a-single-only
11818 @opindex m4a-single-only
11819 Generate code for the SH4a, in such a way that no double-precision
11820 floating point operations are used.
11823 @opindex m4a-single
11824 Generate code for the SH4a assuming the floating-point unit is in
11825 single-precision mode by default.
11829 Generate code for the SH4a.
11833 Same as @option{-m4a-nofpu}, except that it implicitly passes
11834 @option{-dsp} to the assembler. GCC doesn't generate any DSP
11835 instructions at the moment.
11839 Compile code for the processor in big endian mode.
11843 Compile code for the processor in little endian mode.
11847 Align doubles at 64-bit boundaries. Note that this changes the calling
11848 conventions, and thus some functions from the standard C library will
11849 not work unless you recompile it first with @option{-mdalign}.
11853 Shorten some address references at link time, when possible; uses the
11854 linker option @option{-relax}.
11858 Use 32-bit offsets in @code{switch} tables. The default is to use
11863 Enable the use of the instruction @code{fmovd}.
11867 Comply with the calling conventions defined by Renesas.
11871 Comply with the calling conventions defined by Renesas.
11875 Comply with the calling conventions defined for GCC before the Renesas
11876 conventions were available. This option is the default for all
11877 targets of the SH toolchain except for @samp{sh-symbianelf}.
11880 @opindex mnomacsave
11881 Mark the @code{MAC} register as call-clobbered, even if
11882 @option{-mhitachi} is given.
11886 Increase IEEE-compliance of floating-point code.
11887 At the moment, this is equivalent to @option{-fno-finite-math-only}.
11888 When generating 16 bit SH opcodes, getting IEEE-conforming results for
11889 comparisons of NANs / infinities incurs extra overhead in every
11890 floating point comparison, therefore the default is set to
11891 @option{-ffinite-math-only}.
11895 Dump instruction size and location in the assembly code.
11898 @opindex mpadstruct
11899 This option is deprecated. It pads structures to multiple of 4 bytes,
11900 which is incompatible with the SH ABI@.
11904 Optimize for space instead of speed. Implied by @option{-Os}.
11907 @opindex mprefergot
11908 When generating position-independent code, emit function calls using
11909 the Global Offset Table instead of the Procedure Linkage Table.
11913 Generate a library function call to invalidate instruction cache
11914 entries, after fixing up a trampoline. This library function call
11915 doesn't assume it can write to the whole memory address space. This
11916 is the default when the target is @code{sh-*-linux*}.
11918 @item -multcost=@var{number}
11919 @opindex multcost=@var{number}
11920 Set the cost to assume for a multiply insn.
11922 @item -mdiv=@var{strategy}
11923 @opindex mdiv=@var{strategy}
11924 Set the division strategy to use for SHmedia code. @var{strategy} must be
11925 one of: call, call2, fp, inv, inv:minlat, inv20u, inv20l, inv:call,
11926 inv:call2, inv:fp .
11927 "fp" performs the operation in floating point. This has a very high latency,
11928 but needs only a few instructions, so it might be a good choice if
11929 your code has enough easily exploitable ILP to allow the compiler to
11930 schedule the floating point instructions together with other instructions.
11931 Division by zero causes a floating point exception.
11932 "inv" uses integer operations to calculate the inverse of the divisor,
11933 and then multiplies the dividend with the inverse. This strategy allows
11934 cse and hoisting of the inverse calculation. Division by zero calculates
11935 an unspecified result, but does not trap.
11936 "inv:minlat" is a variant of "inv" where if no cse / hoisting opportunities
11937 have been found, or if the entire operation has been hoisted to the same
11938 place, the last stages of the inverse calculation are intertwined with the
11939 final multiply to reduce the overall latency, at the expense of using a few
11940 more instructions, and thus offering fewer scheduling opportunities with
11942 "call" calls a library function that usually implements the inv:minlat
11944 This gives high code density for m5-*media-nofpu compilations.
11945 "call2" uses a different entry point of the same library function, where it
11946 assumes that a pointer to a lookup table has already been set up, which
11947 exposes the pointer load to cse / code hoisting optimizations.
11948 "inv:call", "inv:call2" and "inv:fp" all use the "inv" algorithm for initial
11949 code generation, but if the code stays unoptimized, revert to the "call",
11950 "call2", or "fp" strategies, respectively. Note that the
11951 potentially-trapping side effect of division by zero is carried by a
11952 separate instruction, so it is possible that all the integer instructions
11953 are hoisted out, but the marker for the side effect stays where it is.
11954 A recombination to fp operations or a call is not possible in that case.
11955 "inv20u" and "inv20l" are variants of the "inv:minlat" strategy. In the case
11956 that the inverse calculation was nor separated from the multiply, they speed
11957 up division where the dividend fits into 20 bits (plus sign where applicable),
11958 by inserting a test to skip a number of operations in this case; this test
11959 slows down the case of larger dividends. inv20u assumes the case of a such
11960 a small dividend to be unlikely, and inv20l assumes it to be likely.
11962 @item -mdivsi3_libfunc=@var{name}
11963 @opindex mdivsi3_libfunc=@var{name}
11964 Set the name of the library function used for 32 bit signed division to
11965 @var{name}. This only affect the name used in the call and inv:call
11966 division strategies, and the compiler will still expect the same
11967 sets of input/output/clobbered registers as if this option was not present.
11969 @item -madjust-unroll
11970 @opindex madjust-unroll
11971 Throttle unrolling to avoid thrashing target registers.
11972 This option only has an effect if the gcc code base supports the
11973 TARGET_ADJUST_UNROLL_MAX target hook.
11975 @item -mindexed-addressing
11976 @opindex mindexed-addressing
11977 Enable the use of the indexed addressing mode for SHmedia32/SHcompact.
11978 This is only safe if the hardware and/or OS implement 32 bit wrap-around
11979 semantics for the indexed addressing mode. The architecture allows the
11980 implementation of processors with 64 bit MMU, which the OS could use to
11981 get 32 bit addressing, but since no current hardware implementation supports
11982 this or any other way to make the indexed addressing mode safe to use in
11983 the 32 bit ABI, the default is -mno-indexed-addressing.
11985 @item -mgettrcost=@var{number}
11986 @opindex mgettrcost=@var{number}
11987 Set the cost assumed for the gettr instruction to @var{number}.
11988 The default is 2 if @option{-mpt-fixed} is in effect, 100 otherwise.
11992 Assume pt* instructions won't trap. This will generally generate better
11993 scheduled code, but is unsafe on current hardware. The current architecture
11994 definition says that ptabs and ptrel trap when the target anded with 3 is 3.
11995 This has the unintentional effect of making it unsafe to schedule ptabs /
11996 ptrel before a branch, or hoist it out of a loop. For example,
11997 __do_global_ctors, a part of libgcc that runs constructors at program
11998 startup, calls functions in a list which is delimited by -1. With the
11999 -mpt-fixed option, the ptabs will be done before testing against -1.
12000 That means that all the constructors will be run a bit quicker, but when
12001 the loop comes to the end of the list, the program crashes because ptabs
12002 loads -1 into a target register. Since this option is unsafe for any
12003 hardware implementing the current architecture specification, the default
12004 is -mno-pt-fixed. Unless the user specifies a specific cost with
12005 @option{-mgettrcost}, -mno-pt-fixed also implies @option{-mgettrcost=100};
12006 this deters register allocation using target registers for storing
12009 @item -minvalid-symbols
12010 @opindex minvalid-symbols
12011 Assume symbols might be invalid. Ordinary function symbols generated by
12012 the compiler will always be valid to load with movi/shori/ptabs or
12013 movi/shori/ptrel, but with assembler and/or linker tricks it is possible
12014 to generate symbols that will cause ptabs / ptrel to trap.
12015 This option is only meaningful when @option{-mno-pt-fixed} is in effect.
12016 It will then prevent cross-basic-block cse, hoisting and most scheduling
12017 of symbol loads. The default is @option{-mno-invalid-symbols}.
12020 @node SPARC Options
12021 @subsection SPARC Options
12022 @cindex SPARC options
12024 These @samp{-m} options are supported on the SPARC:
12027 @item -mno-app-regs
12029 @opindex mno-app-regs
12031 Specify @option{-mapp-regs} to generate output using the global registers
12032 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
12035 To be fully SVR4 ABI compliant at the cost of some performance loss,
12036 specify @option{-mno-app-regs}. You should compile libraries and system
12037 software with this option.
12040 @itemx -mhard-float
12042 @opindex mhard-float
12043 Generate output containing floating point instructions. This is the
12047 @itemx -msoft-float
12049 @opindex msoft-float
12050 Generate output containing library calls for floating point.
12051 @strong{Warning:} the requisite libraries are not available for all SPARC
12052 targets. Normally the facilities of the machine's usual C compiler are
12053 used, but this cannot be done directly in cross-compilation. You must make
12054 your own arrangements to provide suitable library functions for
12055 cross-compilation. The embedded targets @samp{sparc-*-aout} and
12056 @samp{sparclite-*-*} do provide software floating point support.
12058 @option{-msoft-float} changes the calling convention in the output file;
12059 therefore, it is only useful if you compile @emph{all} of a program with
12060 this option. In particular, you need to compile @file{libgcc.a}, the
12061 library that comes with GCC, with @option{-msoft-float} in order for
12064 @item -mhard-quad-float
12065 @opindex mhard-quad-float
12066 Generate output containing quad-word (long double) floating point
12069 @item -msoft-quad-float
12070 @opindex msoft-quad-float
12071 Generate output containing library calls for quad-word (long double)
12072 floating point instructions. The functions called are those specified
12073 in the SPARC ABI@. This is the default.
12075 As of this writing, there are no SPARC implementations that have hardware
12076 support for the quad-word floating point instructions. They all invoke
12077 a trap handler for one of these instructions, and then the trap handler
12078 emulates the effect of the instruction. Because of the trap handler overhead,
12079 this is much slower than calling the ABI library routines. Thus the
12080 @option{-msoft-quad-float} option is the default.
12082 @item -mno-unaligned-doubles
12083 @itemx -munaligned-doubles
12084 @opindex mno-unaligned-doubles
12085 @opindex munaligned-doubles
12086 Assume that doubles have 8 byte alignment. This is the default.
12088 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
12089 alignment only if they are contained in another type, or if they have an
12090 absolute address. Otherwise, it assumes they have 4 byte alignment.
12091 Specifying this option avoids some rare compatibility problems with code
12092 generated by other compilers. It is not the default because it results
12093 in a performance loss, especially for floating point code.
12095 @item -mno-faster-structs
12096 @itemx -mfaster-structs
12097 @opindex mno-faster-structs
12098 @opindex mfaster-structs
12099 With @option{-mfaster-structs}, the compiler assumes that structures
12100 should have 8 byte alignment. This enables the use of pairs of
12101 @code{ldd} and @code{std} instructions for copies in structure
12102 assignment, in place of twice as many @code{ld} and @code{st} pairs.
12103 However, the use of this changed alignment directly violates the SPARC
12104 ABI@. Thus, it's intended only for use on targets where the developer
12105 acknowledges that their resulting code will not be directly in line with
12106 the rules of the ABI@.
12108 @item -mimpure-text
12109 @opindex mimpure-text
12110 @option{-mimpure-text}, used in addition to @option{-shared}, tells
12111 the compiler to not pass @option{-z text} to the linker when linking a
12112 shared object. Using this option, you can link position-dependent
12113 code into a shared object.
12115 @option{-mimpure-text} suppresses the ``relocations remain against
12116 allocatable but non-writable sections'' linker error message.
12117 However, the necessary relocations will trigger copy-on-write, and the
12118 shared object is not actually shared across processes. Instead of
12119 using @option{-mimpure-text}, you should compile all source code with
12120 @option{-fpic} or @option{-fPIC}.
12122 This option is only available on SunOS and Solaris.
12124 @item -mcpu=@var{cpu_type}
12126 Set the instruction set, register set, and instruction scheduling parameters
12127 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
12128 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
12129 @samp{f930}, @samp{f934}, @samp{hypersparc}, @samp{sparclite86x},
12130 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc}, and
12131 @samp{ultrasparc3}.
12133 Default instruction scheduling parameters are used for values that select
12134 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
12135 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
12137 Here is a list of each supported architecture and their supported
12142 v8: supersparc, hypersparc
12143 sparclite: f930, f934, sparclite86x
12145 v9: ultrasparc, ultrasparc3
12148 By default (unless configured otherwise), GCC generates code for the V7
12149 variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler
12150 additionally optimizes it for the Cypress CY7C602 chip, as used in the
12151 SPARCStation/SPARCServer 3xx series. This is also appropriate for the older
12152 SPARCStation 1, 2, IPX etc.
12154 With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC
12155 architecture. The only difference from V7 code is that the compiler emits
12156 the integer multiply and integer divide instructions which exist in SPARC-V8
12157 but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally
12158 optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and
12161 With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of
12162 the SPARC architecture. This adds the integer multiply, integer divide step
12163 and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7.
12164 With @option{-mcpu=f930}, the compiler additionally optimizes it for the
12165 Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With
12166 @option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu
12167 MB86934 chip, which is the more recent SPARClite with FPU@.
12169 With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of
12170 the SPARC architecture. This adds the integer multiply, multiply/accumulate,
12171 integer divide step and scan (@code{ffs}) instructions which exist in SPARClet
12172 but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally
12173 optimizes it for the TEMIC SPARClet chip.
12175 With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC
12176 architecture. This adds 64-bit integer and floating-point move instructions,
12177 3 additional floating-point condition code registers and conditional move
12178 instructions. With @option{-mcpu=ultrasparc}, the compiler additionally
12179 optimizes it for the Sun UltraSPARC I/II chips. With
12180 @option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the
12181 Sun UltraSPARC III chip.
12183 @item -mtune=@var{cpu_type}
12185 Set the instruction scheduling parameters for machine type
12186 @var{cpu_type}, but do not set the instruction set or register set that the
12187 option @option{-mcpu=@var{cpu_type}} would.
12189 The same values for @option{-mcpu=@var{cpu_type}} can be used for
12190 @option{-mtune=@var{cpu_type}}, but the only useful values are those
12191 that select a particular cpu implementation. Those are @samp{cypress},
12192 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
12193 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc}, and
12194 @samp{ultrasparc3}.
12199 @opindex mno-v8plus
12200 With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The
12201 difference from the V8 ABI is that the global and out registers are
12202 considered 64-bit wide. This is enabled by default on Solaris in 32-bit
12203 mode for all SPARC-V9 processors.
12209 With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC
12210 Visual Instruction Set extensions. The default is @option{-mno-vis}.
12213 These @samp{-m} options are supported in addition to the above
12214 on SPARC-V9 processors in 64-bit environments:
12217 @item -mlittle-endian
12218 @opindex mlittle-endian
12219 Generate code for a processor running in little-endian mode. It is only
12220 available for a few configurations and most notably not on Solaris and Linux.
12226 Generate code for a 32-bit or 64-bit environment.
12227 The 32-bit environment sets int, long and pointer to 32 bits.
12228 The 64-bit environment sets int to 32 bits and long and pointer
12231 @item -mcmodel=medlow
12232 @opindex mcmodel=medlow
12233 Generate code for the Medium/Low code model: 64-bit addresses, programs
12234 must be linked in the low 32 bits of memory. Programs can be statically
12235 or dynamically linked.
12237 @item -mcmodel=medmid
12238 @opindex mcmodel=medmid
12239 Generate code for the Medium/Middle code model: 64-bit addresses, programs
12240 must be linked in the low 44 bits of memory, the text and data segments must
12241 be less than 2GB in size and the data segment must be located within 2GB of
12244 @item -mcmodel=medany
12245 @opindex mcmodel=medany
12246 Generate code for the Medium/Anywhere code model: 64-bit addresses, programs
12247 may be linked anywhere in memory, the text and data segments must be less
12248 than 2GB in size and the data segment must be located within 2GB of the
12251 @item -mcmodel=embmedany
12252 @opindex mcmodel=embmedany
12253 Generate code for the Medium/Anywhere code model for embedded systems:
12254 64-bit addresses, the text and data segments must be less than 2GB in
12255 size, both starting anywhere in memory (determined at link time). The
12256 global register %g4 points to the base of the data segment. Programs
12257 are statically linked and PIC is not supported.
12260 @itemx -mno-stack-bias
12261 @opindex mstack-bias
12262 @opindex mno-stack-bias
12263 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
12264 frame pointer if present, are offset by @minus{}2047 which must be added back
12265 when making stack frame references. This is the default in 64-bit mode.
12266 Otherwise, assume no such offset is present.
12269 These switches are supported in addition to the above on Solaris:
12274 Add support for multithreading using the Solaris threads library. This
12275 option sets flags for both the preprocessor and linker. This option does
12276 not affect the thread safety of object code produced by the compiler or
12277 that of libraries supplied with it.
12281 Add support for multithreading using the POSIX threads library. This
12282 option sets flags for both the preprocessor and linker. This option does
12283 not affect the thread safety of object code produced by the compiler or
12284 that of libraries supplied with it.
12287 @node System V Options
12288 @subsection Options for System V
12290 These additional options are available on System V Release 4 for
12291 compatibility with other compilers on those systems:
12296 Create a shared object.
12297 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
12301 Identify the versions of each tool used by the compiler, in a
12302 @code{.ident} assembler directive in the output.
12306 Refrain from adding @code{.ident} directives to the output file (this is
12309 @item -YP,@var{dirs}
12311 Search the directories @var{dirs}, and no others, for libraries
12312 specified with @option{-l}.
12314 @item -Ym,@var{dir}
12316 Look in the directory @var{dir} to find the M4 preprocessor.
12317 The assembler uses this option.
12318 @c This is supposed to go with a -Yd for predefined M4 macro files, but
12319 @c the generic assembler that comes with Solaris takes just -Ym.
12322 @node TMS320C3x/C4x Options
12323 @subsection TMS320C3x/C4x Options
12324 @cindex TMS320C3x/C4x Options
12326 These @samp{-m} options are defined for TMS320C3x/C4x implementations:
12330 @item -mcpu=@var{cpu_type}
12332 Set the instruction set, register set, and instruction scheduling
12333 parameters for machine type @var{cpu_type}. Supported values for
12334 @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
12335 @samp{c44}. The default is @samp{c40} to generate code for the
12340 @itemx -msmall-memory
12342 @opindex mbig-memory
12344 @opindex msmall-memory
12346 Generates code for the big or small memory model. The small memory
12347 model assumed that all data fits into one 64K word page. At run-time
12348 the data page (DP) register must be set to point to the 64K page
12349 containing the .bss and .data program sections. The big memory model is
12350 the default and requires reloading of the DP register for every direct
12357 Allow (disallow) allocation of general integer operands into the block
12358 count register BK@.
12364 Enable (disable) generation of code using decrement and branch,
12365 DBcond(D), instructions. This is enabled by default for the C4x. To be
12366 on the safe side, this is disabled for the C3x, since the maximum
12367 iteration count on the C3x is @math{2^{23} + 1} (but who iterates loops more than
12368 @math{2^{23}} times on the C3x?). Note that GCC will try to reverse a loop so
12369 that it can utilize the decrement and branch instruction, but will give
12370 up if there is more than one memory reference in the loop. Thus a loop
12371 where the loop counter is decremented can generate slightly more
12372 efficient code, in cases where the RPTB instruction cannot be utilized.
12374 @item -mdp-isr-reload
12376 @opindex mdp-isr-reload
12378 Force the DP register to be saved on entry to an interrupt service
12379 routine (ISR), reloaded to point to the data section, and restored on
12380 exit from the ISR@. This should not be required unless someone has
12381 violated the small memory model by modifying the DP register, say within
12388 For the C3x use the 24-bit MPYI instruction for integer multiplies
12389 instead of a library call to guarantee 32-bit results. Note that if one
12390 of the operands is a constant, then the multiplication will be performed
12391 using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
12392 then squaring operations are performed inline instead of a library call.
12395 @itemx -mno-fast-fix
12397 @opindex mno-fast-fix
12398 The C3x/C4x FIX instruction to convert a floating point value to an
12399 integer value chooses the nearest integer less than or equal to the
12400 floating point value rather than to the nearest integer. Thus if the
12401 floating point number is negative, the result will be incorrectly
12402 truncated an additional code is necessary to detect and correct this
12403 case. This option can be used to disable generation of the additional
12404 code required to correct the result.
12410 Enable (disable) generation of repeat block sequences using the RPTB
12411 instruction for zero overhead looping. The RPTB construct is only used
12412 for innermost loops that do not call functions or jump across the loop
12413 boundaries. There is no advantage having nested RPTB loops due to the
12414 overhead required to save and restore the RC, RS, and RE registers.
12415 This is enabled by default with @option{-O2}.
12417 @item -mrpts=@var{count}
12421 Enable (disable) the use of the single instruction repeat instruction
12422 RPTS@. If a repeat block contains a single instruction, and the loop
12423 count can be guaranteed to be less than the value @var{count}, GCC will
12424 emit a RPTS instruction instead of a RPTB@. If no value is specified,
12425 then a RPTS will be emitted even if the loop count cannot be determined
12426 at compile time. Note that the repeated instruction following RPTS does
12427 not have to be reloaded from memory each iteration, thus freeing up the
12428 CPU buses for operands. However, since interrupts are blocked by this
12429 instruction, it is disabled by default.
12431 @item -mloop-unsigned
12432 @itemx -mno-loop-unsigned
12433 @opindex mloop-unsigned
12434 @opindex mno-loop-unsigned
12435 The maximum iteration count when using RPTS and RPTB (and DB on the C40)
12436 is @math{2^{31} + 1} since these instructions test if the iteration count is
12437 negative to terminate the loop. If the iteration count is unsigned
12438 there is a possibility than the @math{2^{31} + 1} maximum iteration count may be
12439 exceeded. This switch allows an unsigned iteration count.
12443 Try to emit an assembler syntax that the TI assembler (asm30) is happy
12444 with. This also enforces compatibility with the API employed by the TI
12445 C3x C compiler. For example, long doubles are passed as structures
12446 rather than in floating point registers.
12452 Generate code that uses registers (stack) for passing arguments to functions.
12453 By default, arguments are passed in registers where possible rather
12454 than by pushing arguments on to the stack.
12456 @item -mparallel-insns
12457 @itemx -mno-parallel-insns
12458 @opindex mparallel-insns
12459 @opindex mno-parallel-insns
12460 Allow the generation of parallel instructions. This is enabled by
12461 default with @option{-O2}.
12463 @item -mparallel-mpy
12464 @itemx -mno-parallel-mpy
12465 @opindex mparallel-mpy
12466 @opindex mno-parallel-mpy
12467 Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
12468 provided @option{-mparallel-insns} is also specified. These instructions have
12469 tight register constraints which can pessimize the code generation
12470 of large functions.
12475 @subsection V850 Options
12476 @cindex V850 Options
12478 These @samp{-m} options are defined for V850 implementations:
12482 @itemx -mno-long-calls
12483 @opindex mlong-calls
12484 @opindex mno-long-calls
12485 Treat all calls as being far away (near). If calls are assumed to be
12486 far away, the compiler will always load the functions address up into a
12487 register, and call indirect through the pointer.
12493 Do not optimize (do optimize) basic blocks that use the same index
12494 pointer 4 or more times to copy pointer into the @code{ep} register, and
12495 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
12496 option is on by default if you optimize.
12498 @item -mno-prolog-function
12499 @itemx -mprolog-function
12500 @opindex mno-prolog-function
12501 @opindex mprolog-function
12502 Do not use (do use) external functions to save and restore registers
12503 at the prologue and epilogue of a function. The external functions
12504 are slower, but use less code space if more than one function saves
12505 the same number of registers. The @option{-mprolog-function} option
12506 is on by default if you optimize.
12510 Try to make the code as small as possible. At present, this just turns
12511 on the @option{-mep} and @option{-mprolog-function} options.
12513 @item -mtda=@var{n}
12515 Put static or global variables whose size is @var{n} bytes or less into
12516 the tiny data area that register @code{ep} points to. The tiny data
12517 area can hold up to 256 bytes in total (128 bytes for byte references).
12519 @item -msda=@var{n}
12521 Put static or global variables whose size is @var{n} bytes or less into
12522 the small data area that register @code{gp} points to. The small data
12523 area can hold up to 64 kilobytes.
12525 @item -mzda=@var{n}
12527 Put static or global variables whose size is @var{n} bytes or less into
12528 the first 32 kilobytes of memory.
12532 Specify that the target processor is the V850.
12535 @opindex mbig-switch
12536 Generate code suitable for big switch tables. Use this option only if
12537 the assembler/linker complain about out of range branches within a switch
12542 This option will cause r2 and r5 to be used in the code generated by
12543 the compiler. This setting is the default.
12545 @item -mno-app-regs
12546 @opindex mno-app-regs
12547 This option will cause r2 and r5 to be treated as fixed registers.
12551 Specify that the target processor is the V850E1. The preprocessor
12552 constants @samp{__v850e1__} and @samp{__v850e__} will be defined if
12553 this option is used.
12557 Specify that the target processor is the V850E@. The preprocessor
12558 constant @samp{__v850e__} will be defined if this option is used.
12560 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
12561 are defined then a default target processor will be chosen and the
12562 relevant @samp{__v850*__} preprocessor constant will be defined.
12564 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
12565 defined, regardless of which processor variant is the target.
12567 @item -mdisable-callt
12568 @opindex mdisable-callt
12569 This option will suppress generation of the CALLT instruction for the
12570 v850e and v850e1 flavors of the v850 architecture. The default is
12571 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
12576 @subsection VAX Options
12577 @cindex VAX options
12579 These @samp{-m} options are defined for the VAX:
12584 Do not output certain jump instructions (@code{aobleq} and so on)
12585 that the Unix assembler for the VAX cannot handle across long
12590 Do output those jump instructions, on the assumption that you
12591 will assemble with the GNU assembler.
12595 Output code for g-format floating point numbers instead of d-format.
12598 @node x86-64 Options
12599 @subsection x86-64 Options
12600 @cindex x86-64 options
12602 These are listed under @xref{i386 and x86-64 Options}.
12604 @node Xstormy16 Options
12605 @subsection Xstormy16 Options
12606 @cindex Xstormy16 Options
12608 These options are defined for Xstormy16:
12613 Choose startup files and linker script suitable for the simulator.
12616 @node Xtensa Options
12617 @subsection Xtensa Options
12618 @cindex Xtensa Options
12620 These options are supported for Xtensa targets:
12624 @itemx -mno-const16
12626 @opindex mno-const16
12627 Enable or disable use of @code{CONST16} instructions for loading
12628 constant values. The @code{CONST16} instruction is currently not a
12629 standard option from Tensilica. When enabled, @code{CONST16}
12630 instructions are always used in place of the standard @code{L32R}
12631 instructions. The use of @code{CONST16} is enabled by default only if
12632 the @code{L32R} instruction is not available.
12635 @itemx -mno-fused-madd
12636 @opindex mfused-madd
12637 @opindex mno-fused-madd
12638 Enable or disable use of fused multiply/add and multiply/subtract
12639 instructions in the floating-point option. This has no effect if the
12640 floating-point option is not also enabled. Disabling fused multiply/add
12641 and multiply/subtract instructions forces the compiler to use separate
12642 instructions for the multiply and add/subtract operations. This may be
12643 desirable in some cases where strict IEEE 754-compliant results are
12644 required: the fused multiply add/subtract instructions do not round the
12645 intermediate result, thereby producing results with @emph{more} bits of
12646 precision than specified by the IEEE standard. Disabling fused multiply
12647 add/subtract instructions also ensures that the program output is not
12648 sensitive to the compiler's ability to combine multiply and add/subtract
12651 @item -mtext-section-literals
12652 @itemx -mno-text-section-literals
12653 @opindex mtext-section-literals
12654 @opindex mno-text-section-literals
12655 Control the treatment of literal pools. The default is
12656 @option{-mno-text-section-literals}, which places literals in a separate
12657 section in the output file. This allows the literal pool to be placed
12658 in a data RAM/ROM, and it also allows the linker to combine literal
12659 pools from separate object files to remove redundant literals and
12660 improve code size. With @option{-mtext-section-literals}, the literals
12661 are interspersed in the text section in order to keep them as close as
12662 possible to their references. This may be necessary for large assembly
12665 @item -mtarget-align
12666 @itemx -mno-target-align
12667 @opindex mtarget-align
12668 @opindex mno-target-align
12669 When this option is enabled, GCC instructs the assembler to
12670 automatically align instructions to reduce branch penalties at the
12671 expense of some code density. The assembler attempts to widen density
12672 instructions to align branch targets and the instructions following call
12673 instructions. If there are not enough preceding safe density
12674 instructions to align a target, no widening will be performed. The
12675 default is @option{-mtarget-align}. These options do not affect the
12676 treatment of auto-aligned instructions like @code{LOOP}, which the
12677 assembler will always align, either by widening density instructions or
12678 by inserting no-op instructions.
12681 @itemx -mno-longcalls
12682 @opindex mlongcalls
12683 @opindex mno-longcalls
12684 When this option is enabled, GCC instructs the assembler to translate
12685 direct calls to indirect calls unless it can determine that the target
12686 of a direct call is in the range allowed by the call instruction. This
12687 translation typically occurs for calls to functions in other source
12688 files. Specifically, the assembler translates a direct @code{CALL}
12689 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
12690 The default is @option{-mno-longcalls}. This option should be used in
12691 programs where the call target can potentially be out of range. This
12692 option is implemented in the assembler, not the compiler, so the
12693 assembly code generated by GCC will still show direct call
12694 instructions---look at the disassembled object code to see the actual
12695 instructions. Note that the assembler will use an indirect call for
12696 every cross-file call, not just those that really will be out of range.
12699 @node zSeries Options
12700 @subsection zSeries Options
12701 @cindex zSeries options
12703 These are listed under @xref{S/390 and zSeries Options}.
12705 @node Code Gen Options
12706 @section Options for Code Generation Conventions
12707 @cindex code generation conventions
12708 @cindex options, code generation
12709 @cindex run-time options
12711 These machine-independent options control the interface conventions
12712 used in code generation.
12714 Most of them have both positive and negative forms; the negative form
12715 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
12716 one of the forms is listed---the one which is not the default. You
12717 can figure out the other form by either removing @samp{no-} or adding
12721 @item -fbounds-check
12722 @opindex fbounds-check
12723 For front-ends that support it, generate additional code to check that
12724 indices used to access arrays are within the declared range. This is
12725 currently only supported by the Java and Fortran 77 front-ends, where
12726 this option defaults to true and false respectively.
12730 This option generates traps for signed overflow on addition, subtraction,
12731 multiplication operations.
12735 This option instructs the compiler to assume that signed arithmetic
12736 overflow of addition, subtraction and multiplication wraps around
12737 using twos-complement representation. This flag enables some optimizations
12738 and disables others. This option is enabled by default for the Java
12739 front-end, as required by the Java language specification.
12742 @opindex fexceptions
12743 Enable exception handling. Generates extra code needed to propagate
12744 exceptions. For some targets, this implies GCC will generate frame
12745 unwind information for all functions, which can produce significant data
12746 size overhead, although it does not affect execution. If you do not
12747 specify this option, GCC will enable it by default for languages like
12748 C++ which normally require exception handling, and disable it for
12749 languages like C that do not normally require it. However, you may need
12750 to enable this option when compiling C code that needs to interoperate
12751 properly with exception handlers written in C++. You may also wish to
12752 disable this option if you are compiling older C++ programs that don't
12753 use exception handling.
12755 @item -fnon-call-exceptions
12756 @opindex fnon-call-exceptions
12757 Generate code that allows trapping instructions to throw exceptions.
12758 Note that this requires platform-specific runtime support that does
12759 not exist everywhere. Moreover, it only allows @emph{trapping}
12760 instructions to throw exceptions, i.e.@: memory references or floating
12761 point instructions. It does not allow exceptions to be thrown from
12762 arbitrary signal handlers such as @code{SIGALRM}.
12764 @item -funwind-tables
12765 @opindex funwind-tables
12766 Similar to @option{-fexceptions}, except that it will just generate any needed
12767 static data, but will not affect the generated code in any other way.
12768 You will normally not enable this option; instead, a language processor
12769 that needs this handling would enable it on your behalf.
12771 @item -fasynchronous-unwind-tables
12772 @opindex fasynchronous-unwind-tables
12773 Generate unwind table in dwarf2 format, if supported by target machine. The
12774 table is exact at each instruction boundary, so it can be used for stack
12775 unwinding from asynchronous events (such as debugger or garbage collector).
12777 @item -fpcc-struct-return
12778 @opindex fpcc-struct-return
12779 Return ``short'' @code{struct} and @code{union} values in memory like
12780 longer ones, rather than in registers. This convention is less
12781 efficient, but it has the advantage of allowing intercallability between
12782 GCC-compiled files and files compiled with other compilers, particularly
12783 the Portable C Compiler (pcc).
12785 The precise convention for returning structures in memory depends
12786 on the target configuration macros.
12788 Short structures and unions are those whose size and alignment match
12789 that of some integer type.
12791 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
12792 switch is not binary compatible with code compiled with the
12793 @option{-freg-struct-return} switch.
12794 Use it to conform to a non-default application binary interface.
12796 @item -freg-struct-return
12797 @opindex freg-struct-return
12798 Return @code{struct} and @code{union} values in registers when possible.
12799 This is more efficient for small structures than
12800 @option{-fpcc-struct-return}.
12802 If you specify neither @option{-fpcc-struct-return} nor
12803 @option{-freg-struct-return}, GCC defaults to whichever convention is
12804 standard for the target. If there is no standard convention, GCC
12805 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
12806 the principal compiler. In those cases, we can choose the standard, and
12807 we chose the more efficient register return alternative.
12809 @strong{Warning:} code compiled with the @option{-freg-struct-return}
12810 switch is not binary compatible with code compiled with the
12811 @option{-fpcc-struct-return} switch.
12812 Use it to conform to a non-default application binary interface.
12814 @item -fshort-enums
12815 @opindex fshort-enums
12816 Allocate to an @code{enum} type only as many bytes as it needs for the
12817 declared range of possible values. Specifically, the @code{enum} type
12818 will be equivalent to the smallest integer type which has enough room.
12820 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
12821 code that is not binary compatible with code generated without that switch.
12822 Use it to conform to a non-default application binary interface.
12824 @item -fshort-double
12825 @opindex fshort-double
12826 Use the same size for @code{double} as for @code{float}.
12828 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
12829 code that is not binary compatible with code generated without that switch.
12830 Use it to conform to a non-default application binary interface.
12832 @item -fshort-wchar
12833 @opindex fshort-wchar
12834 Override the underlying type for @samp{wchar_t} to be @samp{short
12835 unsigned int} instead of the default for the target. This option is
12836 useful for building programs to run under WINE@.
12838 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
12839 code that is not binary compatible with code generated without that switch.
12840 Use it to conform to a non-default application binary interface.
12842 @item -fshared-data
12843 @opindex fshared-data
12844 Requests that the data and non-@code{const} variables of this
12845 compilation be shared data rather than private data. The distinction
12846 makes sense only on certain operating systems, where shared data is
12847 shared between processes running the same program, while private data
12848 exists in one copy per process.
12851 @opindex fno-common
12852 In C, allocate even uninitialized global variables in the data section of the
12853 object file, rather than generating them as common blocks. This has the
12854 effect that if the same variable is declared (without @code{extern}) in
12855 two different compilations, you will get an error when you link them.
12856 The only reason this might be useful is if you wish to verify that the
12857 program will work on other systems which always work this way.
12861 Ignore the @samp{#ident} directive.
12863 @item -finhibit-size-directive
12864 @opindex finhibit-size-directive
12865 Don't output a @code{.size} assembler directive, or anything else that
12866 would cause trouble if the function is split in the middle, and the
12867 two halves are placed at locations far apart in memory. This option is
12868 used when compiling @file{crtstuff.c}; you should not need to use it
12871 @item -fverbose-asm
12872 @opindex fverbose-asm
12873 Put extra commentary information in the generated assembly code to
12874 make it more readable. This option is generally only of use to those
12875 who actually need to read the generated assembly code (perhaps while
12876 debugging the compiler itself).
12878 @option{-fno-verbose-asm}, the default, causes the
12879 extra information to be omitted and is useful when comparing two assembler
12884 @cindex global offset table
12886 Generate position-independent code (PIC) suitable for use in a shared
12887 library, if supported for the target machine. Such code accesses all
12888 constant addresses through a global offset table (GOT)@. The dynamic
12889 loader resolves the GOT entries when the program starts (the dynamic
12890 loader is not part of GCC; it is part of the operating system). If
12891 the GOT size for the linked executable exceeds a machine-specific
12892 maximum size, you get an error message from the linker indicating that
12893 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
12894 instead. (These maximums are 8k on the SPARC and 32k
12895 on the m68k and RS/6000. The 386 has no such limit.)
12897 Position-independent code requires special support, and therefore works
12898 only on certain machines. For the 386, GCC supports PIC for System V
12899 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
12900 position-independent.
12902 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
12907 If supported for the target machine, emit position-independent code,
12908 suitable for dynamic linking and avoiding any limit on the size of the
12909 global offset table. This option makes a difference on the m68k,
12910 PowerPC and SPARC@.
12912 Position-independent code requires special support, and therefore works
12913 only on certain machines.
12915 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
12922 These options are similar to @option{-fpic} and @option{-fPIC}, but
12923 generated position independent code can be only linked into executables.
12924 Usually these options are used when @option{-pie} GCC option will be
12925 used during linking.
12927 @item -fno-jump-tables
12928 @opindex fno-jump-tables
12929 Do not use jump tables for switch statements even where it would be
12930 more efficient than other code generation strategies. This option is
12931 of use in conjunction with @option{-fpic} or @option{-fPIC} for
12932 building code which forms part of a dynamic linker and cannot
12933 reference the address of a jump table. On some targets, jump tables
12934 do not require a GOT and this option is not needed.
12936 @item -ffixed-@var{reg}
12938 Treat the register named @var{reg} as a fixed register; generated code
12939 should never refer to it (except perhaps as a stack pointer, frame
12940 pointer or in some other fixed role).
12942 @var{reg} must be the name of a register. The register names accepted
12943 are machine-specific and are defined in the @code{REGISTER_NAMES}
12944 macro in the machine description macro file.
12946 This flag does not have a negative form, because it specifies a
12949 @item -fcall-used-@var{reg}
12950 @opindex fcall-used
12951 Treat the register named @var{reg} as an allocable register that is
12952 clobbered by function calls. It may be allocated for temporaries or
12953 variables that do not live across a call. Functions compiled this way
12954 will not save and restore the register @var{reg}.
12956 It is an error to used this flag with the frame pointer or stack pointer.
12957 Use of this flag for other registers that have fixed pervasive roles in
12958 the machine's execution model will produce disastrous results.
12960 This flag does not have a negative form, because it specifies a
12963 @item -fcall-saved-@var{reg}
12964 @opindex fcall-saved
12965 Treat the register named @var{reg} as an allocable register saved by
12966 functions. It may be allocated even for temporaries or variables that
12967 live across a call. Functions compiled this way will save and restore
12968 the register @var{reg} if they use it.
12970 It is an error to used this flag with the frame pointer or stack pointer.
12971 Use of this flag for other registers that have fixed pervasive roles in
12972 the machine's execution model will produce disastrous results.
12974 A different sort of disaster will result from the use of this flag for
12975 a register in which function values may be returned.
12977 This flag does not have a negative form, because it specifies a
12980 @item -fpack-struct[=@var{n}]
12981 @opindex fpack-struct
12982 Without a value specified, pack all structure members together without
12983 holes. When a value is specified (which must be a small power of two), pack
12984 structure members according to this value, representing the maximum
12985 alignment (that is, objects with default alignment requirements larger than
12986 this will be output potentially unaligned at the next fitting location.
12988 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
12989 code that is not binary compatible with code generated without that switch.
12990 Additionally, it makes the code suboptimal.
12991 Use it to conform to a non-default application binary interface.
12993 @item -finstrument-functions
12994 @opindex finstrument-functions
12995 Generate instrumentation calls for entry and exit to functions. Just
12996 after function entry and just before function exit, the following
12997 profiling functions will be called with the address of the current
12998 function and its call site. (On some platforms,
12999 @code{__builtin_return_address} does not work beyond the current
13000 function, so the call site information may not be available to the
13001 profiling functions otherwise.)
13004 void __cyg_profile_func_enter (void *this_fn,
13006 void __cyg_profile_func_exit (void *this_fn,
13010 The first argument is the address of the start of the current function,
13011 which may be looked up exactly in the symbol table.
13013 This instrumentation is also done for functions expanded inline in other
13014 functions. The profiling calls will indicate where, conceptually, the
13015 inline function is entered and exited. This means that addressable
13016 versions of such functions must be available. If all your uses of a
13017 function are expanded inline, this may mean an additional expansion of
13018 code size. If you use @samp{extern inline} in your C code, an
13019 addressable version of such functions must be provided. (This is
13020 normally the case anyways, but if you get lucky and the optimizer always
13021 expands the functions inline, you might have gotten away without
13022 providing static copies.)
13024 A function may be given the attribute @code{no_instrument_function}, in
13025 which case this instrumentation will not be done. This can be used, for
13026 example, for the profiling functions listed above, high-priority
13027 interrupt routines, and any functions from which the profiling functions
13028 cannot safely be called (perhaps signal handlers, if the profiling
13029 routines generate output or allocate memory).
13031 @item -fstack-check
13032 @opindex fstack-check
13033 Generate code to verify that you do not go beyond the boundary of the
13034 stack. You should specify this flag if you are running in an
13035 environment with multiple threads, but only rarely need to specify it in
13036 a single-threaded environment since stack overflow is automatically
13037 detected on nearly all systems if there is only one stack.
13039 Note that this switch does not actually cause checking to be done; the
13040 operating system must do that. The switch causes generation of code
13041 to ensure that the operating system sees the stack being extended.
13043 @item -fstack-limit-register=@var{reg}
13044 @itemx -fstack-limit-symbol=@var{sym}
13045 @itemx -fno-stack-limit
13046 @opindex fstack-limit-register
13047 @opindex fstack-limit-symbol
13048 @opindex fno-stack-limit
13049 Generate code to ensure that the stack does not grow beyond a certain value,
13050 either the value of a register or the address of a symbol. If the stack
13051 would grow beyond the value, a signal is raised. For most targets,
13052 the signal is raised before the stack overruns the boundary, so
13053 it is possible to catch the signal without taking special precautions.
13055 For instance, if the stack starts at absolute address @samp{0x80000000}
13056 and grows downwards, you can use the flags
13057 @option{-fstack-limit-symbol=__stack_limit} and
13058 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
13059 of 128KB@. Note that this may only work with the GNU linker.
13061 @cindex aliasing of parameters
13062 @cindex parameters, aliased
13063 @item -fargument-alias
13064 @itemx -fargument-noalias
13065 @itemx -fargument-noalias-global
13066 @opindex fargument-alias
13067 @opindex fargument-noalias
13068 @opindex fargument-noalias-global
13069 Specify the possible relationships among parameters and between
13070 parameters and global data.
13072 @option{-fargument-alias} specifies that arguments (parameters) may
13073 alias each other and may alias global storage.@*
13074 @option{-fargument-noalias} specifies that arguments do not alias
13075 each other, but may alias global storage.@*
13076 @option{-fargument-noalias-global} specifies that arguments do not
13077 alias each other and do not alias global storage.
13079 Each language will automatically use whatever option is required by
13080 the language standard. You should not need to use these options yourself.
13082 @item -fleading-underscore
13083 @opindex fleading-underscore
13084 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
13085 change the way C symbols are represented in the object file. One use
13086 is to help link with legacy assembly code.
13088 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
13089 generate code that is not binary compatible with code generated without that
13090 switch. Use it to conform to a non-default application binary interface.
13091 Not all targets provide complete support for this switch.
13093 @item -ftls-model=@var{model}
13094 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
13095 The @var{model} argument should be one of @code{global-dynamic},
13096 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
13098 The default without @option{-fpic} is @code{initial-exec}; with
13099 @option{-fpic} the default is @code{global-dynamic}.
13101 @item -fvisibility=@var{default|internal|hidden|protected}
13102 @opindex fvisibility
13103 Set the default ELF image symbol visibility to the specified option---all
13104 symbols will be marked with this unless overridden within the code.
13105 Using this feature can very substantially improve linking and
13106 load times of shared object libraries, produce more optimized
13107 code, provide near-perfect API export and prevent symbol clashes.
13108 It is @strong{strongly} recommended that you use this in any shared objects
13111 Despite the nomenclature, @code{default} always means public ie;
13112 available to be linked against from outside the shared object.
13113 @code{protected} and @code{internal} are pretty useless in real-world
13114 usage so the only other commonly used option will be @code{hidden}.
13115 The default if @option{-fvisibility} isn't specified is
13116 @code{default}, i.e., make every
13117 symbol public---this causes the same behavior as previous versions of
13120 A good explanation of the benefits offered by ensuring ELF
13121 symbols have the correct visibility is given by ``How To Write
13122 Shared Libraries'' by Ulrich Drepper (which can be found at
13123 @w{@uref{http://people.redhat.com/~drepper/}})---however a superior
13124 solution made possible by this option to marking things hidden when
13125 the default is public is to make the default hidden and mark things
13126 public. This is the norm with DLL's on Windows and with @option{-fvisibility=hidden}
13127 and @code{__attribute__ ((visibility("default")))} instead of
13128 @code{__declspec(dllexport)} you get almost identical semantics with
13129 identical syntax. This is a great boon to those working with
13130 cross-platform projects.
13132 For those adding visibility support to existing code, you may find
13133 @samp{#pragma GCC visibility} of use. This works by you enclosing
13134 the declarations you wish to set visibility for with (for example)
13135 @samp{#pragma GCC visibility push(hidden)} and
13136 @samp{#pragma GCC visibility pop}.
13137 Bear in mind that symbol visibility should be viewed @strong{as
13138 part of the API interface contract} and thus all new code should
13139 always specify visibility when it is not the default ie; declarations
13140 only for use within the local DSO should @strong{always} be marked explicitly
13141 as hidden as so to avoid PLT indirection overheads---making this
13142 abundantly clear also aids readability and self-documentation of the code.
13143 Note that due to ISO C++ specification requirements, operator new and
13144 operator delete must always be of default visibility.
13146 An overview of these techniques, their benefits and how to use them
13147 is at @w{@uref{http://gcc.gnu.org/wiki/Visibility}}.
13153 @node Environment Variables
13154 @section Environment Variables Affecting GCC
13155 @cindex environment variables
13157 @c man begin ENVIRONMENT
13158 This section describes several environment variables that affect how GCC
13159 operates. Some of them work by specifying directories or prefixes to use
13160 when searching for various kinds of files. Some are used to specify other
13161 aspects of the compilation environment.
13163 Note that you can also specify places to search using options such as
13164 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
13165 take precedence over places specified using environment variables, which
13166 in turn take precedence over those specified by the configuration of GCC@.
13167 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
13168 GNU Compiler Collection (GCC) Internals}.
13173 @c @itemx LC_COLLATE
13175 @c @itemx LC_MONETARY
13176 @c @itemx LC_NUMERIC
13181 @c @findex LC_COLLATE
13182 @findex LC_MESSAGES
13183 @c @findex LC_MONETARY
13184 @c @findex LC_NUMERIC
13188 These environment variables control the way that GCC uses
13189 localization information that allow GCC to work with different
13190 national conventions. GCC inspects the locale categories
13191 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
13192 so. These locale categories can be set to any value supported by your
13193 installation. A typical value is @samp{en_GB.UTF-8} for English in the United
13194 Kingdom encoded in UTF-8.
13196 The @env{LC_CTYPE} environment variable specifies character
13197 classification. GCC uses it to determine the character boundaries in
13198 a string; this is needed for some multibyte encodings that contain quote
13199 and escape characters that would otherwise be interpreted as a string
13202 The @env{LC_MESSAGES} environment variable specifies the language to
13203 use in diagnostic messages.
13205 If the @env{LC_ALL} environment variable is set, it overrides the value
13206 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
13207 and @env{LC_MESSAGES} default to the value of the @env{LANG}
13208 environment variable. If none of these variables are set, GCC
13209 defaults to traditional C English behavior.
13213 If @env{TMPDIR} is set, it specifies the directory to use for temporary
13214 files. GCC uses temporary files to hold the output of one stage of
13215 compilation which is to be used as input to the next stage: for example,
13216 the output of the preprocessor, which is the input to the compiler
13219 @item GCC_EXEC_PREFIX
13220 @findex GCC_EXEC_PREFIX
13221 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
13222 names of the subprograms executed by the compiler. No slash is added
13223 when this prefix is combined with the name of a subprogram, but you can
13224 specify a prefix that ends with a slash if you wish.
13226 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
13227 an appropriate prefix to use based on the pathname it was invoked with.
13229 If GCC cannot find the subprogram using the specified prefix, it
13230 tries looking in the usual places for the subprogram.
13232 The default value of @env{GCC_EXEC_PREFIX} is
13233 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the value
13234 of @code{prefix} when you ran the @file{configure} script.
13236 Other prefixes specified with @option{-B} take precedence over this prefix.
13238 This prefix is also used for finding files such as @file{crt0.o} that are
13241 In addition, the prefix is used in an unusual way in finding the
13242 directories to search for header files. For each of the standard
13243 directories whose name normally begins with @samp{/usr/local/lib/gcc}
13244 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
13245 replacing that beginning with the specified prefix to produce an
13246 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
13247 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
13248 These alternate directories are searched first; the standard directories
13251 @item COMPILER_PATH
13252 @findex COMPILER_PATH
13253 The value of @env{COMPILER_PATH} is a colon-separated list of
13254 directories, much like @env{PATH}. GCC tries the directories thus
13255 specified when searching for subprograms, if it can't find the
13256 subprograms using @env{GCC_EXEC_PREFIX}.
13259 @findex LIBRARY_PATH
13260 The value of @env{LIBRARY_PATH} is a colon-separated list of
13261 directories, much like @env{PATH}. When configured as a native compiler,
13262 GCC tries the directories thus specified when searching for special
13263 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
13264 using GCC also uses these directories when searching for ordinary
13265 libraries for the @option{-l} option (but directories specified with
13266 @option{-L} come first).
13270 @cindex locale definition
13271 This variable is used to pass locale information to the compiler. One way in
13272 which this information is used is to determine the character set to be used
13273 when character literals, string literals and comments are parsed in C and C++.
13274 When the compiler is configured to allow multibyte characters,
13275 the following values for @env{LANG} are recognized:
13279 Recognize JIS characters.
13281 Recognize SJIS characters.
13283 Recognize EUCJP characters.
13286 If @env{LANG} is not defined, or if it has some other value, then the
13287 compiler will use mblen and mbtowc as defined by the default locale to
13288 recognize and translate multibyte characters.
13292 Some additional environments variables affect the behavior of the
13295 @include cppenv.texi
13299 @node Precompiled Headers
13300 @section Using Precompiled Headers
13301 @cindex precompiled headers
13302 @cindex speed of compilation
13304 Often large projects have many header files that are included in every
13305 source file. The time the compiler takes to process these header files
13306 over and over again can account for nearly all of the time required to
13307 build the project. To make builds faster, GCC allows users to
13308 `precompile' a header file; then, if builds can use the precompiled
13309 header file they will be much faster.
13311 To create a precompiled header file, simply compile it as you would any
13312 other file, if necessary using the @option{-x} option to make the driver
13313 treat it as a C or C++ header file. You will probably want to use a
13314 tool like @command{make} to keep the precompiled header up-to-date when
13315 the headers it contains change.
13317 A precompiled header file will be searched for when @code{#include} is
13318 seen in the compilation. As it searches for the included file
13319 (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
13320 compiler looks for a precompiled header in each directory just before it
13321 looks for the include file in that directory. The name searched for is
13322 the name specified in the @code{#include} with @samp{.gch} appended. If
13323 the precompiled header file can't be used, it is ignored.
13325 For instance, if you have @code{#include "all.h"}, and you have
13326 @file{all.h.gch} in the same directory as @file{all.h}, then the
13327 precompiled header file will be used if possible, and the original
13328 header will be used otherwise.
13330 Alternatively, you might decide to put the precompiled header file in a
13331 directory and use @option{-I} to ensure that directory is searched
13332 before (or instead of) the directory containing the original header.
13333 Then, if you want to check that the precompiled header file is always
13334 used, you can put a file of the same name as the original header in this
13335 directory containing an @code{#error} command.
13337 This also works with @option{-include}. So yet another way to use
13338 precompiled headers, good for projects not designed with precompiled
13339 header files in mind, is to simply take most of the header files used by
13340 a project, include them from another header file, precompile that header
13341 file, and @option{-include} the precompiled header. If the header files
13342 have guards against multiple inclusion, they will be skipped because
13343 they've already been included (in the precompiled header).
13345 If you need to precompile the same header file for different
13346 languages, targets, or compiler options, you can instead make a
13347 @emph{directory} named like @file{all.h.gch}, and put each precompiled
13348 header in the directory, perhaps using @option{-o}. It doesn't matter
13349 what you call the files in the directory, every precompiled header in
13350 the directory will be considered. The first precompiled header
13351 encountered in the directory that is valid for this compilation will
13352 be used; they're searched in no particular order.
13354 There are many other possibilities, limited only by your imagination,
13355 good sense, and the constraints of your build system.
13357 A precompiled header file can be used only when these conditions apply:
13361 Only one precompiled header can be used in a particular compilation.
13364 A precompiled header can't be used once the first C token is seen. You
13365 can have preprocessor directives before a precompiled header; you can
13366 even include a precompiled header from inside another header, so long as
13367 there are no C tokens before the @code{#include}.
13370 The precompiled header file must be produced for the same language as
13371 the current compilation. You can't use a C precompiled header for a C++
13375 The precompiled header file must have been produced by the same compiler
13376 binary as the current compilation is using.
13379 Any macros defined before the precompiled header is included must
13380 either be defined in the same way as when the precompiled header was
13381 generated, or must not affect the precompiled header, which usually
13382 means that they don't appear in the precompiled header at all.
13384 The @option{-D} option is one way to define a macro before a
13385 precompiled header is included; using a @code{#define} can also do it.
13386 There are also some options that define macros implicitly, like
13387 @option{-O} and @option{-Wdeprecated}; the same rule applies to macros
13390 @item If debugging information is output when using the precompiled
13391 header, using @option{-g} or similar, the same kind of debugging information
13392 must have been output when building the precompiled header. However,
13393 a precompiled header built using @option{-g} can be used in a compilation
13394 when no debugging information is being output.
13396 @item The same @option{-m} options must generally be used when building
13397 and using the precompiled header. @xref{Submodel Options},
13398 for any cases where this rule is relaxed.
13400 @item Each of the following options must be the same when building and using
13401 the precompiled header:
13403 @gccoptlist{-fexceptions -funit-at-a-time}
13406 Some other command-line options starting with @option{-f},
13407 @option{-p}, or @option{-O} must be defined in the same way as when
13408 the precompiled header was generated. At present, it's not clear
13409 which options are safe to change and which are not; the safest choice
13410 is to use exactly the same options when generating and using the
13411 precompiled header. The following are known to be safe:
13413 @gccoptlist{-fmessage-length= -fpreprocessed
13414 -fsched-interblock -fsched-spec -fsched-spec-load -fsched-spec-load-dangerous
13415 -fsched-verbose=<number> -fschedule-insns -fvisibility=
13420 For all of these except the last, the compiler will automatically
13421 ignore the precompiled header if the conditions aren't met. If you
13422 find an option combination that doesn't work and doesn't cause the
13423 precompiled header to be ignored, please consider filing a bug report,
13426 If you do use differing options when generating and using the
13427 precompiled header, the actual behavior will be a mixture of the
13428 behavior for the options. For instance, if you use @option{-g} to
13429 generate the precompiled header but not when using it, you may or may
13430 not get debugging information for routines in the precompiled header.
13432 @node Running Protoize
13433 @section Running Protoize
13435 The program @code{protoize} is an optional part of GCC@. You can use
13436 it to add prototypes to a program, thus converting the program to ISO
13437 C in one respect. The companion program @code{unprotoize} does the
13438 reverse: it removes argument types from any prototypes that are found.
13440 When you run these programs, you must specify a set of source files as
13441 command line arguments. The conversion programs start out by compiling
13442 these files to see what functions they define. The information gathered
13443 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
13445 After scanning comes actual conversion. The specified files are all
13446 eligible to be converted; any files they include (whether sources or
13447 just headers) are eligible as well.
13449 But not all the eligible files are converted. By default,
13450 @code{protoize} and @code{unprotoize} convert only source and header
13451 files in the current directory. You can specify additional directories
13452 whose files should be converted with the @option{-d @var{directory}}
13453 option. You can also specify particular files to exclude with the
13454 @option{-x @var{file}} option. A file is converted if it is eligible, its
13455 directory name matches one of the specified directory names, and its
13456 name within the directory has not been excluded.
13458 Basic conversion with @code{protoize} consists of rewriting most
13459 function definitions and function declarations to specify the types of
13460 the arguments. The only ones not rewritten are those for varargs
13463 @code{protoize} optionally inserts prototype declarations at the
13464 beginning of the source file, to make them available for any calls that
13465 precede the function's definition. Or it can insert prototype
13466 declarations with block scope in the blocks where undeclared functions
13469 Basic conversion with @code{unprotoize} consists of rewriting most
13470 function declarations to remove any argument types, and rewriting
13471 function definitions to the old-style pre-ISO form.
13473 Both conversion programs print a warning for any function declaration or
13474 definition that they can't convert. You can suppress these warnings
13477 The output from @code{protoize} or @code{unprotoize} replaces the
13478 original source file. The original file is renamed to a name ending
13479 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
13480 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
13481 for DOS) file already exists, then the source file is simply discarded.
13483 @code{protoize} and @code{unprotoize} both depend on GCC itself to
13484 scan the program and collect information about the functions it uses.
13485 So neither of these programs will work until GCC is installed.
13487 Here is a table of the options you can use with @code{protoize} and
13488 @code{unprotoize}. Each option works with both programs unless
13492 @item -B @var{directory}
13493 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
13494 usual directory (normally @file{/usr/local/lib}). This file contains
13495 prototype information about standard system functions. This option
13496 applies only to @code{protoize}.
13498 @item -c @var{compilation-options}
13499 Use @var{compilation-options} as the options when running @command{gcc} to
13500 produce the @samp{.X} files. The special option @option{-aux-info} is
13501 always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
13503 Note that the compilation options must be given as a single argument to
13504 @code{protoize} or @code{unprotoize}. If you want to specify several
13505 @command{gcc} options, you must quote the entire set of compilation options
13506 to make them a single word in the shell.
13508 There are certain @command{gcc} arguments that you cannot use, because they
13509 would produce the wrong kind of output. These include @option{-g},
13510 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
13511 the @var{compilation-options}, they are ignored.
13514 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
13515 systems) instead of @samp{.c}. This is convenient if you are converting
13516 a C program to C++. This option applies only to @code{protoize}.
13519 Add explicit global declarations. This means inserting explicit
13520 declarations at the beginning of each source file for each function
13521 that is called in the file and was not declared. These declarations
13522 precede the first function definition that contains a call to an
13523 undeclared function. This option applies only to @code{protoize}.
13525 @item -i @var{string}
13526 Indent old-style parameter declarations with the string @var{string}.
13527 This option applies only to @code{protoize}.
13529 @code{unprotoize} converts prototyped function definitions to old-style
13530 function definitions, where the arguments are declared between the
13531 argument list and the initial @samp{@{}. By default, @code{unprotoize}
13532 uses five spaces as the indentation. If you want to indent with just
13533 one space instead, use @option{-i " "}.
13536 Keep the @samp{.X} files. Normally, they are deleted after conversion
13540 Add explicit local declarations. @code{protoize} with @option{-l} inserts
13541 a prototype declaration for each function in each block which calls the
13542 function without any declaration. This option applies only to
13546 Make no real changes. This mode just prints information about the conversions
13547 that would have been done without @option{-n}.
13550 Make no @samp{.save} files. The original files are simply deleted.
13551 Use this option with caution.
13553 @item -p @var{program}
13554 Use the program @var{program} as the compiler. Normally, the name
13555 @file{gcc} is used.
13558 Work quietly. Most warnings are suppressed.
13561 Print the version number, just like @option{-v} for @command{gcc}.
13564 If you need special compiler options to compile one of your program's
13565 source files, then you should generate that file's @samp{.X} file
13566 specially, by running @command{gcc} on that source file with the
13567 appropriate options and the option @option{-aux-info}. Then run
13568 @code{protoize} on the entire set of files. @code{protoize} will use
13569 the existing @samp{.X} file because it is newer than the source file.
13573 gcc -Dfoo=bar file1.c -aux-info file1.X
13578 You need to include the special files along with the rest in the
13579 @code{protoize} command, even though their @samp{.X} files already
13580 exist, because otherwise they won't get converted.
13582 @xref{Protoize Caveats}, for more information on how to use
13583 @code{protoize} successfully.