1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2 @c 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008
3 @c Free Software Foundation, Inc.
4 @c This is part of the GCC manual.
5 @c For copying conditions, see the file gcc.texi.
12 @c man begin COPYRIGHT
13 Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
14 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008
15 Free Software Foundation, Inc.
17 Permission is granted to copy, distribute and/or modify this document
18 under the terms of the GNU Free Documentation License, Version 1.2 or
19 any later version published by the Free Software Foundation; with the
20 Invariant Sections being ``GNU General Public License'' and ``Funding
21 Free Software'', the Front-Cover texts being (a) (see below), and with
22 the Back-Cover Texts being (b) (see below). A copy of the license is
23 included in the gfdl(7) man page.
25 (a) The FSF's Front-Cover Text is:
29 (b) The FSF's Back-Cover Text is:
31 You have freedom to copy and modify this GNU Manual, like GNU
32 software. Copies published by the Free Software Foundation raise
33 funds for GNU development.
35 @c Set file name and title for the man page.
37 @settitle GNU project C and C++ compiler
39 gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
40 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
41 [@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
42 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
43 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
44 [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
45 [@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{}
47 Only the most useful options are listed here; see below for the
48 remainder. @samp{g++} accepts mostly the same options as @samp{gcc}.
51 gpl(7), gfdl(7), fsf-funding(7),
52 cpp(1), gcov(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
53 and the Info entries for @file{gcc}, @file{cpp}, @file{as},
54 @file{ld}, @file{binutils} and @file{gdb}.
57 For instructions on reporting bugs, see
61 See the Info entry for @command{gcc}, or
62 @w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}},
63 for contributors to GCC@.
68 @chapter GCC Command Options
69 @cindex GCC command options
70 @cindex command options
71 @cindex options, GCC command
73 @c man begin DESCRIPTION
74 When you invoke GCC, it normally does preprocessing, compilation,
75 assembly and linking. The ``overall options'' allow you to stop this
76 process at an intermediate stage. For example, the @option{-c} option
77 says not to run the linker. Then the output consists of object files
78 output by the assembler.
80 Other options are passed on to one stage of processing. Some options
81 control the preprocessor and others the compiler itself. Yet other
82 options control the assembler and linker; most of these are not
83 documented here, since you rarely need to use any of them.
85 @cindex C compilation options
86 Most of the command line options that you can use with GCC are useful
87 for C programs; when an option is only useful with another language
88 (usually C++), the explanation says so explicitly. If the description
89 for a particular option does not mention a source language, you can use
90 that option with all supported languages.
92 @cindex C++ compilation options
93 @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
94 options for compiling C++ programs.
96 @cindex grouping options
97 @cindex options, grouping
98 The @command{gcc} program accepts options and file names as operands. Many
99 options have multi-letter names; therefore multiple single-letter options
100 may @emph{not} be grouped: @option{-dr} is very different from @w{@samp{-d
103 @cindex order of options
104 @cindex options, order
105 You can mix options and other arguments. For the most part, the order
106 you use doesn't matter. Order does matter when you use several
107 options of the same kind; for example, if you specify @option{-L} more
108 than once, the directories are searched in the order specified. Also,
109 the placement of the @option{-l} option is significant.
111 Many options have long names starting with @samp{-f} or with
112 @samp{-W}---for example,
113 @option{-fmove-loop-invariants}, @option{-Wformat} and so on. Most of
114 these have both positive and negative forms; the negative form of
115 @option{-ffoo} would be @option{-fno-foo}. This manual documents
116 only one of these two forms, whichever one is not the default.
120 @xref{Option Index}, for an index to GCC's options.
123 * Option Summary:: Brief list of all options, without explanations.
124 * Overall Options:: Controlling the kind of output:
125 an executable, object files, assembler files,
126 or preprocessed source.
127 * Invoking G++:: Compiling C++ programs.
128 * C Dialect Options:: Controlling the variant of C language compiled.
129 * C++ Dialect Options:: Variations on C++.
130 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
132 * Language Independent Options:: Controlling how diagnostics should be
134 * Warning Options:: How picky should the compiler be?
135 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
136 * Optimize Options:: How much optimization?
137 * Preprocessor Options:: Controlling header files and macro definitions.
138 Also, getting dependency information for Make.
139 * Assembler Options:: Passing options to the assembler.
140 * Link Options:: Specifying libraries and so on.
141 * Directory Options:: Where to find header files and libraries.
142 Where to find the compiler executable files.
143 * Spec Files:: How to pass switches to sub-processes.
144 * Target Options:: Running a cross-compiler, or an old version of GCC.
145 * Submodel Options:: Specifying minor hardware or convention variations,
146 such as 68010 vs 68020.
147 * Code Gen Options:: Specifying conventions for function calls, data layout
149 * Environment Variables:: Env vars that affect GCC.
150 * Precompiled Headers:: Compiling a header once, and using it many times.
151 * Running Protoize:: Automatically adding or removing function prototypes.
157 @section Option Summary
159 Here is a summary of all the options, grouped by type. Explanations are
160 in the following sections.
163 @item Overall Options
164 @xref{Overall Options,,Options Controlling the Kind of Output}.
165 @gccoptlist{-c -S -E -o @var{file} -combine -pipe -pass-exit-codes @gol
166 -x @var{language} -v -### --help@r{[}=@var{class}@r{]} --target-help @gol
167 --version -wrapper@@@var{file}}
169 @item C Language Options
170 @xref{C Dialect Options,,Options Controlling C Dialect}.
171 @gccoptlist{-ansi -std=@var{standard} -fgnu89-inline @gol
172 -aux-info @var{filename} @gol
173 -fno-asm -fno-builtin -fno-builtin-@var{function} @gol
174 -fhosted -ffreestanding -fopenmp -fms-extensions @gol
175 -trigraphs -no-integrated-cpp -traditional -traditional-cpp @gol
176 -fallow-single-precision -fcond-mismatch -flax-vector-conversions @gol
177 -fsigned-bitfields -fsigned-char @gol
178 -funsigned-bitfields -funsigned-char}
180 @item C++ Language Options
181 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
182 @gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol
183 -fconserve-space -ffriend-injection @gol
184 -fno-elide-constructors @gol
185 -fno-enforce-eh-specs @gol
186 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
187 -fno-implicit-templates @gol
188 -fno-implicit-inline-templates @gol
189 -fno-implement-inlines -fms-extensions @gol
190 -fno-nonansi-builtins -fno-operator-names @gol
191 -fno-optional-diags -fpermissive @gol
192 -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
193 -fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ @gol
194 -fno-default-inline -fvisibility-inlines-hidden @gol
195 -fvisibility-ms-compat @gol
196 -Wabi -Wctor-dtor-privacy @gol
197 -Wnon-virtual-dtor -Wreorder @gol
198 -Weffc++ -Wstrict-null-sentinel @gol
199 -Wno-non-template-friend -Wold-style-cast @gol
200 -Woverloaded-virtual -Wno-pmf-conversions @gol
203 @item Objective-C and Objective-C++ Language Options
204 @xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling
205 Objective-C and Objective-C++ Dialects}.
206 @gccoptlist{-fconstant-string-class=@var{class-name} @gol
207 -fgnu-runtime -fnext-runtime @gol
208 -fno-nil-receivers @gol
209 -fobjc-call-cxx-cdtors @gol
210 -fobjc-direct-dispatch @gol
211 -fobjc-exceptions @gol
213 -freplace-objc-classes @gol
216 -Wassign-intercept @gol
217 -Wno-protocol -Wselector @gol
218 -Wstrict-selector-match @gol
219 -Wundeclared-selector}
221 @item Language Independent Options
222 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
223 @gccoptlist{-fmessage-length=@var{n} @gol
224 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]} @gol
225 -fdiagnostics-show-option}
227 @item Warning Options
228 @xref{Warning Options,,Options to Request or Suppress Warnings}.
229 @gccoptlist{-fsyntax-only -pedantic -pedantic-errors @gol
230 -w -Wextra -Wall -Waddress -Waggregate-return -Warray-bounds @gol
231 -Wno-attributes -Wc++-compat -Wc++0x-compat -Wcast-align -Wcast-qual @gol
232 -Wchar-subscripts -Wclobbered -Wcomment @gol
233 -Wconversion -Wcoverage-mismatch -Wno-deprecated @gol
234 -Wno-deprecated-declarations -Wdisabled-optimization @gol
235 -Wdisallowed-function-list=@var{sym},@var{sym},@dots{} @gol
236 -Wno-div-by-zero -Wempty-body -Wenum-compare -Wno-endif-labels @gol
237 -Werror -Werror=* @gol
238 -Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 @gol
239 -Wno-format-contains-nul -Wno-format-extra-args -Wformat-nonliteral @gol
240 -Wformat-security -Wformat-y2k @gol
241 -Wframe-larger-than=@var{len} -Wignored-qualifiers @gol
242 -Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol
243 -Winit-self -Winline @gol
244 -Wno-int-to-pointer-cast -Wno-invalid-offsetof @gol
245 -Winvalid-pch -Wlarger-than=@var{len} -Wunsafe-loop-optimizations @gol
246 -Wlogical-op -Wlong-long @gol
247 -Wmain -Wmissing-braces -Wmissing-field-initializers @gol
248 -Wmissing-format-attribute -Wmissing-include-dirs @gol
249 -Wmissing-noreturn -Wno-mudflap @gol
250 -Wno-multichar -Wnonnull -Wno-overflow @gol
251 -Woverlength-strings -Wpacked -Wpadded @gol
252 -Wparentheses -Wpointer-arith -Wno-pointer-to-int-cast @gol
253 -Wredundant-decls @gol
254 -Wreturn-type -Wsequence-point -Wshadow @gol
255 -Wsign-compare -Wsign-conversion -Wstack-protector @gol
256 -Wstrict-aliasing -Wstrict-aliasing=n @gol
257 -Wstrict-overflow -Wstrict-overflow=@var{n} @gol
258 -Wswitch -Wswitch-default -Wswitch-enum @gol
259 -Wsystem-headers -Wtrigraphs -Wtype-limits -Wundef -Wuninitialized @gol
260 -Wunknown-pragmas -Wno-pragmas -Wunreachable-code @gol
261 -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
262 -Wunused-value -Wunused-variable @gol
263 -Wvariadic-macros -Wvla @gol
264 -Wvolatile-register-var -Wwrite-strings}
266 @item C and Objective-C-only Warning Options
267 @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
268 -Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs @gol
269 -Wold-style-declaration -Wold-style-definition @gol
270 -Wstrict-prototypes -Wtraditional -Wtraditional-conversion @gol
271 -Wdeclaration-after-statement -Wpointer-sign}
273 @item Debugging Options
274 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
275 @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
276 -fdbg-cnt-list -fdbg-cnt=@var{counter-value-list} @gol
277 -fdump-noaddr -fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
278 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
279 -fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline @gol
280 -fdump-statistics @gol
282 -fdump-tree-original@r{[}-@var{n}@r{]} @gol
283 -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
284 -fdump-tree-cfg -fdump-tree-vcg -fdump-tree-alias @gol
286 -fdump-tree-ssa@r{[}-@var{n}@r{]} -fdump-tree-pre@r{[}-@var{n}@r{]} @gol
287 -fdump-tree-ccp@r{[}-@var{n}@r{]} -fdump-tree-dce@r{[}-@var{n}@r{]} @gol
288 -fdump-tree-gimple@r{[}-raw@r{]} -fdump-tree-mudflap@r{[}-@var{n}@r{]} @gol
289 -fdump-tree-dom@r{[}-@var{n}@r{]} @gol
290 -fdump-tree-dse@r{[}-@var{n}@r{]} @gol
291 -fdump-tree-phiopt@r{[}-@var{n}@r{]} @gol
292 -fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
293 -fdump-tree-copyrename@r{[}-@var{n}@r{]} @gol
294 -fdump-tree-nrv -fdump-tree-vect @gol
295 -fdump-tree-sink @gol
296 -fdump-tree-sra@r{[}-@var{n}@r{]} @gol
297 -fdump-tree-fre@r{[}-@var{n}@r{]} @gol
298 -fdump-tree-vrp@r{[}-@var{n}@r{]} @gol
299 -ftree-vectorizer-verbose=@var{n} @gol
300 -fdump-tree-storeccp@r{[}-@var{n}@r{]} @gol
301 -feliminate-dwarf2-dups -feliminate-unused-debug-types @gol
302 -feliminate-unused-debug-symbols -femit-class-debug-always @gol
303 -fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report -fprofile-arcs @gol
304 -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
305 -ftest-coverage -ftime-report -fvar-tracking @gol
306 -g -g@var{level} -gcoff -gdwarf-2 @gol
307 -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
308 -fno-merge-debug-strings -fdebug-prefix-map=@var{old}=@var{new} @gol
309 -femit-struct-debug-baseonly -femit-struct-debug-reduced @gol
310 -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} @gol
311 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
312 -print-multi-directory -print-multi-lib @gol
313 -print-prog-name=@var{program} -print-search-dirs -Q @gol
314 -print-sysroot -print-sysroot-headers-suffix @gol
317 @item Optimization Options
318 @xref{Optimize Options,,Options that Control Optimization}.
320 -falign-functions[=@var{n}] -falign-jumps[=@var{n}] @gol
321 -falign-labels[=@var{n}] -falign-loops[=@var{n}] -fassociative-math @gol
322 -fauto-inc-dec -fbranch-probabilities -fbranch-target-load-optimize @gol
323 -fbranch-target-load-optimize2 -fbtr-bb-exclusive -fcaller-saves @gol
324 -fcheck-data-deps -fcprop-registers -fcrossjumping -fcse-follow-jumps @gol
325 -fcse-skip-blocks -fcx-fortran-rules -fcx-limited-range @gol
326 -fdata-sections -fdce -fdce @gol
327 -fdelayed-branch -fdelete-null-pointer-checks -fdse -fdse @gol
328 -fearly-inlining -fexpensive-optimizations -ffast-math @gol
329 -ffinite-math-only -ffloat-store -fforward-propagate @gol
330 -ffunction-sections -fgcse -fgcse-after-reload -fgcse-las -fgcse-lm @gol
331 -fgcse-sm -fif-conversion -fif-conversion2 -findirect-inlining @gol
332 -finline-functions -finline-functions-called-once -finline-limit=@var{n} @gol
333 -finline-small-functions -fipa-cp -fipa-marix-reorg -fipa-pta @gol
334 -fipa-pure-const -fipa-reference -fipa-struct-reorg @gol
335 -fipa-type-escape -fivopts -fkeep-inline-functions -fkeep-static-consts @gol
336 -fmerge-all-constants -fmerge-constants -fmodulo-sched @gol
337 -fmodulo-sched-allow-regmoves -fmove-loop-invariants -fmudflap @gol
338 -fmudflapir -fmudflapth -fno-branch-count-reg -fno-default-inline @gol
339 -fno-defer-pop -fno-function-cse -fno-guess-branch-probability @gol
340 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
341 -fno-sched-interblock -fno-sched-spec -fno-signed-zeros @gol
342 -fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol
343 -fomit-frame-pointer -foptimize-register-move -foptimize-sibling-calls @gol
344 -fpeel-loops -fpredictive-commoning -fprefetch-loop-arrays @gol
345 -fprofile-dir=@var{path} -fprofile-generate -fprofile-generate=@var{path} @gol
346 -fprofile-use -fprofile-use=@var{path} -fprofile-values @gol
347 -freciprocal-math -fregmove -frename-registers -freorder-blocks @gol
348 -freorder-blocks-and-partition -freorder-functions @gol
349 -frerun-cse-after-loop -freschedule-modulo-scheduled-loops @gol
350 -frounding-math -frtl-abstract-sequences -fsched2-use-superblocks @gol
351 -fsched2-use-traces -fsched-spec-load -fsched-spec-load-dangerous @gol
352 -fsched-stalled-insns-dep[=@var{n}] -fsched-stalled-insns[=@var{n}] @gol
353 -fschedule-insns -fschedule-insns2 -fsection-anchors -fsee @gol
354 -fsignaling-nans -fsingle-precision-constant -fsplit-ivs-in-unroller @gol
355 -fsplit-wide-types -fstack-protector -fstack-protector-all @gol
356 -fstrict-aliasing -fstrict-overflow -fthread-jumps -ftracer @gol
357 -ftree-builtin-call-dce -ftree-ccp -ftree-ch -ftree-copy-prop @gol
358 -ftree-copyrename -ftree-dce @gol
359 -ftree-dominator-opts -ftree-dse -ftree-fre -ftree-loop-im @gol
360 -ftree-loop-distribution @gol
361 -ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize @gol
362 -ftree-parallelize-loops=@var{n} -ftree-pre -ftree-reassoc @gol
363 -ftree-sink -ftree-sra -ftree-store-ccp -ftree-switch-conversion @gol
364 -ftree-ter -ftree-vect-loop-version -ftree-vectorize -ftree-vrp @gol
365 -funit-at-a-time -funroll-all-loops -funroll-loops @gol
366 -funsafe-loop-optimizations -funsafe-math-optimizations -funswitch-loops @gol
367 -fvariable-expansion-in-unroller -fvect-cost-model -fvpt -fweb @gol
369 --param @var{name}=@var{value}
370 -O -O0 -O1 -O2 -O3 -Os}
372 @item Preprocessor Options
373 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
374 @gccoptlist{-A@var{question}=@var{answer} @gol
375 -A-@var{question}@r{[}=@var{answer}@r{]} @gol
376 -C -dD -dI -dM -dN @gol
377 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
378 -idirafter @var{dir} @gol
379 -include @var{file} -imacros @var{file} @gol
380 -iprefix @var{file} -iwithprefix @var{dir} @gol
381 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
382 -imultilib @var{dir} -isysroot @var{dir} @gol
383 -M -MM -MF -MG -MP -MQ -MT -nostdinc @gol
384 -P -fworking-directory -remap @gol
385 -trigraphs -undef -U@var{macro} -Wp,@var{option} @gol
386 -Xpreprocessor @var{option}}
388 @item Assembler Option
389 @xref{Assembler Options,,Passing Options to the Assembler}.
390 @gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
393 @xref{Link Options,,Options for Linking}.
394 @gccoptlist{@var{object-file-name} -l@var{library} @gol
395 -nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic @gol
396 -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
397 -Wl,@var{option} -Xlinker @var{option} @gol
400 @item Directory Options
401 @xref{Directory Options,,Options for Directory Search}.
402 @gccoptlist{-B@var{prefix} -I@var{dir} -iquote@var{dir} -L@var{dir}
403 -specs=@var{file} -I- --sysroot=@var{dir}}
406 @c I wrote this xref this way to avoid overfull hbox. -- rms
407 @xref{Target Options}.
408 @gccoptlist{-V @var{version} -b @var{machine}}
410 @item Machine Dependent Options
411 @xref{Submodel Options,,Hardware Models and Configurations}.
412 @c This list is ordered alphanumerically by subsection name.
413 @c Try and put the significant identifier (CPU or system) first,
414 @c so users have a clue at guessing where the ones they want will be.
417 @gccoptlist{-EB -EL @gol
418 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
419 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
422 @gccoptlist{-mapcs-frame -mno-apcs-frame @gol
423 -mabi=@var{name} @gol
424 -mapcs-stack-check -mno-apcs-stack-check @gol
425 -mapcs-float -mno-apcs-float @gol
426 -mapcs-reentrant -mno-apcs-reentrant @gol
427 -msched-prolog -mno-sched-prolog @gol
428 -mlittle-endian -mbig-endian -mwords-little-endian @gol
429 -mfloat-abi=@var{name} -msoft-float -mhard-float -mfpe @gol
430 -mthumb-interwork -mno-thumb-interwork @gol
431 -mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol
432 -mstructure-size-boundary=@var{n} @gol
433 -mabort-on-noreturn @gol
434 -mlong-calls -mno-long-calls @gol
435 -msingle-pic-base -mno-single-pic-base @gol
436 -mpic-register=@var{reg} @gol
437 -mnop-fun-dllimport @gol
438 -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol
439 -mpoke-function-name @gol
441 -mtpcs-frame -mtpcs-leaf-frame @gol
442 -mcaller-super-interworking -mcallee-super-interworking @gol
446 @gccoptlist{-mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
447 -mcall-prologues -mno-tablejump -mtiny-stack -mint8}
449 @emph{Blackfin Options}
450 @gccoptlist{-mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} @gol
451 -msim -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol
452 -mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol
453 -mlow-64k -mno-low64k -mstack-check-l1 -mid-shared-library @gol
454 -mno-id-shared-library -mshared-library-id=@var{n} @gol
455 -mleaf-id-shared-library -mno-leaf-id-shared-library @gol
456 -msep-data -mno-sep-data -mlong-calls -mno-long-calls @gol
457 -mfast-fp -minline-plt -mmulticore -mcorea -mcoreb -msdram}
460 @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
461 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
462 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
463 -mstack-align -mdata-align -mconst-align @gol
464 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
465 -melf -maout -melinux -mlinux -sim -sim2 @gol
466 -mmul-bug-workaround -mno-mul-bug-workaround}
469 @gccoptlist{-mmac -mpush-args}
471 @emph{Darwin Options}
472 @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
473 -arch_only -bind_at_load -bundle -bundle_loader @gol
474 -client_name -compatibility_version -current_version @gol
476 -dependency-file -dylib_file -dylinker_install_name @gol
477 -dynamic -dynamiclib -exported_symbols_list @gol
478 -filelist -flat_namespace -force_cpusubtype_ALL @gol
479 -force_flat_namespace -headerpad_max_install_names @gol
481 -image_base -init -install_name -keep_private_externs @gol
482 -multi_module -multiply_defined -multiply_defined_unused @gol
483 -noall_load -no_dead_strip_inits_and_terms @gol
484 -nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol
485 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
486 -private_bundle -read_only_relocs -sectalign @gol
487 -sectobjectsymbols -whyload -seg1addr @gol
488 -sectcreate -sectobjectsymbols -sectorder @gol
489 -segaddr -segs_read_only_addr -segs_read_write_addr @gol
490 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
491 -segprot -segs_read_only_addr -segs_read_write_addr @gol
492 -single_module -static -sub_library -sub_umbrella @gol
493 -twolevel_namespace -umbrella -undefined @gol
494 -unexported_symbols_list -weak_reference_mismatches @gol
495 -whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol
496 -mkernel -mone-byte-bool}
498 @emph{DEC Alpha Options}
499 @gccoptlist{-mno-fp-regs -msoft-float -malpha-as -mgas @gol
500 -mieee -mieee-with-inexact -mieee-conformant @gol
501 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
502 -mtrap-precision=@var{mode} -mbuild-constants @gol
503 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
504 -mbwx -mmax -mfix -mcix @gol
505 -mfloat-vax -mfloat-ieee @gol
506 -mexplicit-relocs -msmall-data -mlarge-data @gol
507 -msmall-text -mlarge-text @gol
508 -mmemory-latency=@var{time}}
510 @emph{DEC Alpha/VMS Options}
511 @gccoptlist{-mvms-return-codes}
514 @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
515 -mhard-float -msoft-float @gol
516 -malloc-cc -mfixed-cc -mdword -mno-dword @gol
517 -mdouble -mno-double @gol
518 -mmedia -mno-media -mmuladd -mno-muladd @gol
519 -mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol
520 -mlinked-fp -mlong-calls -malign-labels @gol
521 -mlibrary-pic -macc-4 -macc-8 @gol
522 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
523 -moptimize-membar -mno-optimize-membar @gol
524 -mscc -mno-scc -mcond-exec -mno-cond-exec @gol
525 -mvliw-branch -mno-vliw-branch @gol
526 -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
527 -mno-nested-cond-exec -mtomcat-stats @gol
531 @emph{GNU/Linux Options}
532 @gccoptlist{-muclibc}
534 @emph{H8/300 Options}
535 @gccoptlist{-mrelax -mh -ms -mn -mint32 -malign-300}
538 @gccoptlist{-march=@var{architecture-type} @gol
539 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
540 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
541 -mfixed-range=@var{register-range} @gol
542 -mjump-in-delay -mlinker-opt -mlong-calls @gol
543 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
544 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
545 -mno-jump-in-delay -mno-long-load-store @gol
546 -mno-portable-runtime -mno-soft-float @gol
547 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
548 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
549 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
550 -munix=@var{unix-std} -nolibdld -static -threads}
552 @emph{i386 and x86-64 Options}
553 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
554 -mfpmath=@var{unit} @gol
555 -masm=@var{dialect} -mno-fancy-math-387 @gol
556 -mno-fp-ret-in-387 -msoft-float @gol
557 -mno-wide-multiply -mrtd -malign-double @gol
558 -mpreferred-stack-boundary=@var{num}
559 -mincoming-stack-boundary=@var{num}
560 -mcld -mcx16 -msahf -mrecip @gol
561 -mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 @gol
563 -msse4a -m3dnow -mpopcnt -mabm -msse5 @gol
564 -mthreads -mno-align-stringops -minline-all-stringops @gol
565 -minline-stringops-dynamically -mstringop-strategy=@var{alg} @gol
566 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
567 -m96bit-long-double -mregparm=@var{num} -msseregparm @gol
568 -mveclibabi=@var{type} -mpc32 -mpc64 -mpc80 -mstackrealign @gol
569 -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol
570 -mcmodel=@var{code-model} @gol
571 -m32 -m64 -mlarge-data-threshold=@var{num} @gol
572 -mfused-madd -mno-fused-madd}
575 @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
576 -mvolatile-asm-stop -mregister-names -mno-sdata @gol
577 -mconstant-gp -mauto-pic -minline-float-divide-min-latency @gol
578 -minline-float-divide-max-throughput @gol
579 -minline-int-divide-min-latency @gol
580 -minline-int-divide-max-throughput @gol
581 -minline-sqrt-min-latency -minline-sqrt-max-throughput @gol
582 -mno-dwarf2-asm -mearly-stop-bits @gol
583 -mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol
584 -mtune=@var{cpu-type} -mt -pthread -milp32 -mlp64 @gol
585 -mno-sched-br-data-spec -msched-ar-data-spec -mno-sched-control-spec @gol
586 -msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec @gol
587 -msched-ldc -mno-sched-control-ldc -mno-sched-spec-verbose @gol
588 -mno-sched-prefer-non-data-spec-insns @gol
589 -mno-sched-prefer-non-control-spec-insns @gol
590 -mno-sched-count-spec-in-critical-path}
592 @emph{M32R/D Options}
593 @gccoptlist{-m32r2 -m32rx -m32r @gol
595 -malign-loops -mno-align-loops @gol
596 -missue-rate=@var{number} @gol
597 -mbranch-cost=@var{number} @gol
598 -mmodel=@var{code-size-model-type} @gol
599 -msdata=@var{sdata-type} @gol
600 -mno-flush-func -mflush-func=@var{name} @gol
601 -mno-flush-trap -mflush-trap=@var{number} @gol
605 @gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}}
607 @emph{M680x0 Options}
608 @gccoptlist{-march=@var{arch} -mcpu=@var{cpu} -mtune=@var{tune}
609 -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
610 -m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407 @gol
611 -mcfv4e -mbitfield -mno-bitfield -mc68000 -mc68020 @gol
612 -mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort @gol
613 -mno-short -mhard-float -m68881 -msoft-float -mpcrel @gol
614 -malign-int -mstrict-align -msep-data -mno-sep-data @gol
615 -mshared-library-id=n -mid-shared-library -mno-id-shared-library @gol
618 @emph{M68hc1x Options}
619 @gccoptlist{-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 @gol
620 -mauto-incdec -minmax -mlong-calls -mshort @gol
621 -msoft-reg-count=@var{count}}
624 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
625 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
626 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
627 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
628 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
631 @gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol
632 -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 @gol
633 -mips64 -mips64r2 @gol
634 -mips16 -mno-mips16 -mflip-mips16 @gol
635 -minterlink-mips16 -mno-interlink-mips16 @gol
636 -mabi=@var{abi} -mabicalls -mno-abicalls @gol
637 -mshared -mno-shared -mxgot -mno-xgot -mgp32 -mgp64 @gol
638 -mfp32 -mfp64 -mhard-float -msoft-float @gol
639 -msingle-float -mdouble-float -mdsp -mno-dsp -mdspr2 -mno-dspr2 @gol
640 -msmartmips -mno-smartmips @gol
641 -mpaired-single -mno-paired-single -mdmx -mno-mdmx @gol
642 -mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc @gol
643 -mlong64 -mlong32 -msym32 -mno-sym32 @gol
644 -G@var{num} -mlocal-sdata -mno-local-sdata @gol
645 -mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt @gol
646 -membedded-data -mno-embedded-data @gol
647 -muninit-const-in-rodata -mno-uninit-const-in-rodata @gol
648 -mcode-readable=@var{setting} @gol
649 -msplit-addresses -mno-split-addresses @gol
650 -mexplicit-relocs -mno-explicit-relocs @gol
651 -mcheck-zero-division -mno-check-zero-division @gol
652 -mdivide-traps -mdivide-breaks @gol
653 -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol
654 -mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp @gol
655 -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol
656 -mfix-vr4120 -mno-fix-vr4120 -mfix-vr4130 -mno-fix-vr4130 @gol
657 -mfix-sb1 -mno-fix-sb1 @gol
658 -mflush-func=@var{func} -mno-flush-func @gol
659 -mbranch-cost=@var{num} -mbranch-likely -mno-branch-likely @gol
660 -mfp-exceptions -mno-fp-exceptions @gol
661 -mvr4130-align -mno-vr4130-align}
664 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
665 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
666 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
667 -mno-base-addresses -msingle-exit -mno-single-exit}
669 @emph{MN10300 Options}
670 @gccoptlist{-mmult-bug -mno-mult-bug @gol
671 -mam33 -mno-am33 @gol
672 -mam33-2 -mno-am33-2 @gol
673 -mreturn-pointer-on-d0 @gol
676 @emph{PDP-11 Options}
677 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
678 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
679 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
680 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
681 -mbranch-expensive -mbranch-cheap @gol
682 -msplit -mno-split -munix-asm -mdec-asm}
684 @emph{PowerPC Options}
685 See RS/6000 and PowerPC Options.
687 @emph{RS/6000 and PowerPC Options}
688 @gccoptlist{-mcpu=@var{cpu-type} @gol
689 -mtune=@var{cpu-type} @gol
690 -mpower -mno-power -mpower2 -mno-power2 @gol
691 -mpowerpc -mpowerpc64 -mno-powerpc @gol
692 -maltivec -mno-altivec @gol
693 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
694 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
695 -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mfprnd -mno-fprnd @gol
696 -mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mhard-dfp -mno-hard-dfp @gol
697 -mnew-mnemonics -mold-mnemonics @gol
698 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
699 -m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol
700 -malign-power -malign-natural @gol
701 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
702 -mstring -mno-string -mupdate -mno-update @gol
703 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
704 -mstrict-align -mno-strict-align -mrelocatable @gol
705 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
706 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
707 -mdynamic-no-pic -maltivec -mswdiv @gol
708 -mprioritize-restricted-insns=@var{priority} @gol
709 -msched-costly-dep=@var{dependence_type} @gol
710 -minsert-sched-nops=@var{scheme} @gol
711 -mcall-sysv -mcall-netbsd @gol
712 -maix-struct-return -msvr4-struct-return @gol
713 -mabi=@var{abi-type} -msecure-plt -mbss-plt @gol
714 -misel -mno-isel @gol
715 -misel=yes -misel=no @gol
717 -mspe=yes -mspe=no @gol
719 -mvrsave -mno-vrsave @gol
720 -mmulhw -mno-mulhw @gol
721 -mdlmzb -mno-dlmzb @gol
722 -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol
723 -mprototype -mno-prototype @gol
724 -msim -mmvme -mads -myellowknife -memb -msdata @gol
725 -msdata=@var{opt} -mvxworks -G @var{num} -pthread}
727 @emph{S/390 and zSeries Options}
728 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
729 -mhard-float -msoft-float -mlong-double-64 -mlong-double-128 @gol
730 -mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol
731 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
732 -m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol
733 -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol
734 -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard}
737 @gccoptlist{-meb -mel @gol
741 -mscore5 -mscore5u -mscore7 -mscore7d}
744 @gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol
745 -m4-nofpu -m4-single-only -m4-single -m4 @gol
746 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol
747 -m5-64media -m5-64media-nofpu @gol
748 -m5-32media -m5-32media-nofpu @gol
749 -m5-compact -m5-compact-nofpu @gol
750 -mb -ml -mdalign -mrelax @gol
751 -mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol
752 -mieee -mbitops -misize -minline-ic_invalidate -mpadstruct -mspace @gol
753 -mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol
754 -mdivsi3_libfunc=@var{name} -mfixed-range=@var{register-range} @gol
755 -madjust-unroll -mindexed-addressing -mgettrcost=@var{number} -mpt-fixed @gol
759 @gccoptlist{-mcpu=@var{cpu-type} @gol
760 -mtune=@var{cpu-type} @gol
761 -mcmodel=@var{code-model} @gol
762 -m32 -m64 -mapp-regs -mno-app-regs @gol
763 -mfaster-structs -mno-faster-structs @gol
764 -mfpu -mno-fpu -mhard-float -msoft-float @gol
765 -mhard-quad-float -msoft-quad-float @gol
766 -mimpure-text -mno-impure-text -mlittle-endian @gol
767 -mstack-bias -mno-stack-bias @gol
768 -munaligned-doubles -mno-unaligned-doubles @gol
769 -mv8plus -mno-v8plus -mvis -mno-vis
770 -threads -pthreads -pthread}
773 @gccoptlist{-mwarn-reloc -merror-reloc @gol
774 -msafe-dma -munsafe-dma @gol
776 -msmall-mem -mlarge-mem -mstdmain @gol
777 -mfixed-range=@var{register-range}}
779 @emph{System V Options}
780 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
783 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
784 -mprolog-function -mno-prolog-function -mspace @gol
785 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
786 -mapp-regs -mno-app-regs @gol
787 -mdisable-callt -mno-disable-callt @gol
793 @gccoptlist{-mg -mgnu -munix}
795 @emph{VxWorks Options}
796 @gccoptlist{-mrtp -non-static -Bstatic -Bdynamic @gol
797 -Xbind-lazy -Xbind-now}
799 @emph{x86-64 Options}
800 See i386 and x86-64 Options.
802 @emph{Xstormy16 Options}
805 @emph{Xtensa Options}
806 @gccoptlist{-mconst16 -mno-const16 @gol
807 -mfused-madd -mno-fused-madd @gol
808 -mserialize-volatile -mno-serialize-volatile @gol
809 -mtext-section-literals -mno-text-section-literals @gol
810 -mtarget-align -mno-target-align @gol
811 -mlongcalls -mno-longcalls}
813 @emph{zSeries Options}
814 See S/390 and zSeries Options.
816 @item Code Generation Options
817 @xref{Code Gen Options,,Options for Code Generation Conventions}.
818 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
819 -ffixed-@var{reg} -fexceptions @gol
820 -fnon-call-exceptions -funwind-tables @gol
821 -fasynchronous-unwind-tables @gol
822 -finhibit-size-directive -finstrument-functions @gol
823 -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} @gol
824 -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{} @gol
825 -fno-common -fno-ident @gol
826 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
827 -fno-jump-tables @gol
828 -frecord-gcc-switches @gol
829 -freg-struct-return -fshort-enums @gol
830 -fshort-double -fshort-wchar @gol
831 -fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol
832 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
833 -fno-stack-limit -fargument-alias -fargument-noalias @gol
834 -fargument-noalias-global -fargument-noalias-anything @gol
835 -fleading-underscore -ftls-model=@var{model} @gol
836 -ftrapv -fwrapv -fbounds-check @gol
841 * Overall Options:: Controlling the kind of output:
842 an executable, object files, assembler files,
843 or preprocessed source.
844 * C Dialect Options:: Controlling the variant of C language compiled.
845 * C++ Dialect Options:: Variations on C++.
846 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
848 * Language Independent Options:: Controlling how diagnostics should be
850 * Warning Options:: How picky should the compiler be?
851 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
852 * Optimize Options:: How much optimization?
853 * Preprocessor Options:: Controlling header files and macro definitions.
854 Also, getting dependency information for Make.
855 * Assembler Options:: Passing options to the assembler.
856 * Link Options:: Specifying libraries and so on.
857 * Directory Options:: Where to find header files and libraries.
858 Where to find the compiler executable files.
859 * Spec Files:: How to pass switches to sub-processes.
860 * Target Options:: Running a cross-compiler, or an old version of GCC.
863 @node Overall Options
864 @section Options Controlling the Kind of Output
866 Compilation can involve up to four stages: preprocessing, compilation
867 proper, assembly and linking, always in that order. GCC is capable of
868 preprocessing and compiling several files either into several
869 assembler input files, or into one assembler input file; then each
870 assembler input file produces an object file, and linking combines all
871 the object files (those newly compiled, and those specified as input)
872 into an executable file.
874 @cindex file name suffix
875 For any given input file, the file name suffix determines what kind of
880 C source code which must be preprocessed.
883 C source code which should not be preprocessed.
886 C++ source code which should not be preprocessed.
889 Objective-C source code. Note that you must link with the @file{libobjc}
890 library to make an Objective-C program work.
893 Objective-C source code which should not be preprocessed.
897 Objective-C++ source code. Note that you must link with the @file{libobjc}
898 library to make an Objective-C++ program work. Note that @samp{.M} refers
899 to a literal capital M@.
902 Objective-C++ source code which should not be preprocessed.
905 C, C++, Objective-C or Objective-C++ header file to be turned into a
910 @itemx @var{file}.cxx
911 @itemx @var{file}.cpp
912 @itemx @var{file}.CPP
913 @itemx @var{file}.c++
915 C++ source code which must be preprocessed. Note that in @samp{.cxx},
916 the last two letters must both be literally @samp{x}. Likewise,
917 @samp{.C} refers to a literal capital C@.
921 Objective-C++ source code which must be preprocessed.
924 Objective-C++ source code which should not be preprocessed.
929 @itemx @var{file}.hxx
930 @itemx @var{file}.hpp
931 @itemx @var{file}.HPP
932 @itemx @var{file}.h++
933 @itemx @var{file}.tcc
934 C++ header file to be turned into a precompiled header.
937 @itemx @var{file}.for
938 @itemx @var{file}.ftn
939 Fixed form Fortran source code which should not be preprocessed.
942 @itemx @var{file}.FOR
943 @itemx @var{file}.fpp
944 @itemx @var{file}.FPP
945 @itemx @var{file}.FTN
946 Fixed form Fortran source code which must be preprocessed (with the traditional
950 @itemx @var{file}.f95
951 @itemx @var{file}.f03
952 @itemx @var{file}.f08
953 Free form Fortran source code which should not be preprocessed.
956 @itemx @var{file}.F95
957 @itemx @var{file}.F03
958 @itemx @var{file}.F08
959 Free form Fortran source code which must be preprocessed (with the
960 traditional preprocessor).
962 @c FIXME: Descriptions of Java file types.
969 Ada source code file which contains a library unit declaration (a
970 declaration of a package, subprogram, or generic, or a generic
971 instantiation), or a library unit renaming declaration (a package,
972 generic, or subprogram renaming declaration). Such files are also
976 Ada source code file containing a library unit body (a subprogram or
977 package body). Such files are also called @dfn{bodies}.
979 @c GCC also knows about some suffixes for languages not yet included:
991 Assembler code which must be preprocessed.
994 An object file to be fed straight into linking.
995 Any file name with no recognized suffix is treated this way.
999 You can specify the input language explicitly with the @option{-x} option:
1002 @item -x @var{language}
1003 Specify explicitly the @var{language} for the following input files
1004 (rather than letting the compiler choose a default based on the file
1005 name suffix). This option applies to all following input files until
1006 the next @option{-x} option. Possible values for @var{language} are:
1008 c c-header c-cpp-output
1009 c++ c++-header c++-cpp-output
1010 objective-c objective-c-header objective-c-cpp-output
1011 objective-c++ objective-c++-header objective-c++-cpp-output
1012 assembler assembler-with-cpp
1014 f77 f77-cpp-input f95 f95-cpp-input
1019 Turn off any specification of a language, so that subsequent files are
1020 handled according to their file name suffixes (as they are if @option{-x}
1021 has not been used at all).
1023 @item -pass-exit-codes
1024 @opindex pass-exit-codes
1025 Normally the @command{gcc} program will exit with the code of 1 if any
1026 phase of the compiler returns a non-success return code. If you specify
1027 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
1028 numerically highest error produced by any phase that returned an error
1029 indication. The C, C++, and Fortran frontends return 4, if an internal
1030 compiler error is encountered.
1033 If you only want some of the stages of compilation, you can use
1034 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
1035 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
1036 @command{gcc} is to stop. Note that some combinations (for example,
1037 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
1042 Compile or assemble the source files, but do not link. The linking
1043 stage simply is not done. The ultimate output is in the form of an
1044 object file for each source file.
1046 By default, the object file name for a source file is made by replacing
1047 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
1049 Unrecognized input files, not requiring compilation or assembly, are
1054 Stop after the stage of compilation proper; do not assemble. The output
1055 is in the form of an assembler code file for each non-assembler input
1058 By default, the assembler file name for a source file is made by
1059 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
1061 Input files that don't require compilation are ignored.
1065 Stop after the preprocessing stage; do not run the compiler proper. The
1066 output is in the form of preprocessed source code, which is sent to the
1069 Input files which don't require preprocessing are ignored.
1071 @cindex output file option
1074 Place output in file @var{file}. This applies regardless to whatever
1075 sort of output is being produced, whether it be an executable file,
1076 an object file, an assembler file or preprocessed C code.
1078 If @option{-o} is not specified, the default is to put an executable
1079 file in @file{a.out}, the object file for
1080 @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its
1081 assembler file in @file{@var{source}.s}, a precompiled header file in
1082 @file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on
1087 Print (on standard error output) the commands executed to run the stages
1088 of compilation. Also print the version number of the compiler driver
1089 program and of the preprocessor and the compiler proper.
1093 Like @option{-v} except the commands are not executed and all command
1094 arguments are quoted. This is useful for shell scripts to capture the
1095 driver-generated command lines.
1099 Use pipes rather than temporary files for communication between the
1100 various stages of compilation. This fails to work on some systems where
1101 the assembler is unable to read from a pipe; but the GNU assembler has
1106 If you are compiling multiple source files, this option tells the driver
1107 to pass all the source files to the compiler at once (for those
1108 languages for which the compiler can handle this). This will allow
1109 intermodule analysis (IMA) to be performed by the compiler. Currently the only
1110 language for which this is supported is C@. If you pass source files for
1111 multiple languages to the driver, using this option, the driver will invoke
1112 the compiler(s) that support IMA once each, passing each compiler all the
1113 source files appropriate for it. For those languages that do not support
1114 IMA this option will be ignored, and the compiler will be invoked once for
1115 each source file in that language. If you use this option in conjunction
1116 with @option{-save-temps}, the compiler will generate multiple
1118 (one for each source file), but only one (combined) @file{.o} or
1123 Print (on the standard output) a description of the command line options
1124 understood by @command{gcc}. If the @option{-v} option is also specified
1125 then @option{--help} will also be passed on to the various processes
1126 invoked by @command{gcc}, so that they can display the command line options
1127 they accept. If the @option{-Wextra} option has also been specified
1128 (prior to the @option{--help} option), then command line options which
1129 have no documentation associated with them will also be displayed.
1132 @opindex target-help
1133 Print (on the standard output) a description of target-specific command
1134 line options for each tool. For some targets extra target-specific
1135 information may also be printed.
1137 @item --help=@var{class}@r{[},@var{qualifier}@r{]}
1138 Print (on the standard output) a description of the command line
1139 options understood by the compiler that fit into a specific class.
1140 The class can be one of @samp{optimizers}, @samp{warnings}, @samp{target},
1141 @samp{params}, or @var{language}:
1144 @item @samp{optimizers}
1145 This will display all of the optimization options supported by the
1148 @item @samp{warnings}
1149 This will display all of the options controlling warning messages
1150 produced by the compiler.
1153 This will display target-specific options. Unlike the
1154 @option{--target-help} option however, target-specific options of the
1155 linker and assembler will not be displayed. This is because those
1156 tools do not currently support the extended @option{--help=} syntax.
1159 This will display the values recognized by the @option{--param}
1162 @item @var{language}
1163 This will display the options supported for @var{language}, where
1164 @var{language} is the name of one of the languages supported in this
1168 This will display the options that are common to all languages.
1171 It is possible to further refine the output of the @option{--help=}
1172 option by adding a comma separated list of qualifiers after the
1173 class. These can be any from the following list:
1176 @item @samp{undocumented}
1177 Display only those options which are undocumented.
1180 Display options which take an argument that appears after an equal
1181 sign in the same continuous piece of text, such as:
1182 @samp{--help=target}.
1184 @item @samp{separate}
1185 Display options which take an argument that appears as a separate word
1186 following the original option, such as: @samp{-o output-file}.
1189 Thus for example to display all the undocumented target-specific
1190 switches supported by the compiler the following can be used:
1193 --help=target,undocumented
1196 The sense of a qualifier can be inverted by prefixing it with the
1197 @var{^} character, so for example to display all binary warning
1198 options (i.e., ones that are either on or off and that do not take an
1199 argument), which have a description the following can be used:
1202 --help=warnings,^joined,^undocumented
1205 A class can also be used as a qualifier, although this usually
1206 restricts the output by so much that there is nothing to display. One
1207 case where it does work however is when one of the classes is
1208 @var{target}. So for example to display all the target-specific
1209 optimization options the following can be used:
1212 --help=target,optimizers
1215 The @option{--help=} option can be repeated on the command line. Each
1216 successive use will display its requested class of options, skipping
1217 those that have already been displayed.
1219 If the @option{-Q} option appears on the command line before the
1220 @option{--help=} option, then the descriptive text displayed by
1221 @option{--help=} is changed. Instead of describing the displayed
1222 options, an indication is given as to whether the option is enabled,
1223 disabled or set to a specific value (assuming that the compiler
1224 knows this at the point where the @option{--help=} option is used).
1226 Here is a truncated example from the ARM port of @command{gcc}:
1229 % gcc -Q -mabi=2 --help=target -c
1230 The following options are target specific:
1232 -mabort-on-noreturn [disabled]
1236 The output is sensitive to the effects of previous command line
1237 options, so for example it is possible to find out which optimizations
1238 are enabled at @option{-O2} by using:
1241 -O2 --help=optimizers
1244 Alternatively you can discover which binary optimizations are enabled
1245 by @option{-O3} by using:
1248 gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
1249 gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
1250 diff /tmp/O2-opts /tmp/O3-opts | grep enabled
1255 Display the version number and copyrights of the invoked GCC@.
1259 Invoke all subcommands under a wrapper program. It takes a single
1260 comma separated list as an argument, which will be used to invoke
1264 gcc -c t.c -wrapper gdb,--args
1267 This will invoke all subprograms of gcc under "gdb --args",
1268 thus cc1 invocation will be "gdb --args cc1 ...".
1270 @include @value{srcdir}/../libiberty/at-file.texi
1274 @section Compiling C++ Programs
1276 @cindex suffixes for C++ source
1277 @cindex C++ source file suffixes
1278 C++ source files conventionally use one of the suffixes @samp{.C},
1279 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
1280 @samp{.cxx}; C++ header files often use @samp{.hh}, @samp{.hpp},
1281 @samp{.H}, or (for shared template code) @samp{.tcc}; and
1282 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
1283 files with these names and compiles them as C++ programs even if you
1284 call the compiler the same way as for compiling C programs (usually
1285 with the name @command{gcc}).
1289 However, the use of @command{gcc} does not add the C++ library.
1290 @command{g++} is a program that calls GCC and treats @samp{.c},
1291 @samp{.h} and @samp{.i} files as C++ source files instead of C source
1292 files unless @option{-x} is used, and automatically specifies linking
1293 against the C++ library. This program is also useful when
1294 precompiling a C header file with a @samp{.h} extension for use in C++
1295 compilations. On many systems, @command{g++} is also installed with
1296 the name @command{c++}.
1298 @cindex invoking @command{g++}
1299 When you compile C++ programs, you may specify many of the same
1300 command-line options that you use for compiling programs in any
1301 language; or command-line options meaningful for C and related
1302 languages; or options that are meaningful only for C++ programs.
1303 @xref{C Dialect Options,,Options Controlling C Dialect}, for
1304 explanations of options for languages related to C@.
1305 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
1306 explanations of options that are meaningful only for C++ programs.
1308 @node C Dialect Options
1309 @section Options Controlling C Dialect
1310 @cindex dialect options
1311 @cindex language dialect options
1312 @cindex options, dialect
1314 The following options control the dialect of C (or languages derived
1315 from C, such as C++, Objective-C and Objective-C++) that the compiler
1319 @cindex ANSI support
1323 In C mode, this is equivalent to @samp{-std=c89}. In C++ mode, it is
1324 equivalent to @samp{-std=c++98}.
1326 This turns off certain features of GCC that are incompatible with ISO
1327 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
1328 such as the @code{asm} and @code{typeof} keywords, and
1329 predefined macros such as @code{unix} and @code{vax} that identify the
1330 type of system you are using. It also enables the undesirable and
1331 rarely used ISO trigraph feature. For the C compiler,
1332 it disables recognition of C++ style @samp{//} comments as well as
1333 the @code{inline} keyword.
1335 The alternate keywords @code{__asm__}, @code{__extension__},
1336 @code{__inline__} and @code{__typeof__} continue to work despite
1337 @option{-ansi}. You would not want to use them in an ISO C program, of
1338 course, but it is useful to put them in header files that might be included
1339 in compilations done with @option{-ansi}. Alternate predefined macros
1340 such as @code{__unix__} and @code{__vax__} are also available, with or
1341 without @option{-ansi}.
1343 The @option{-ansi} option does not cause non-ISO programs to be
1344 rejected gratuitously. For that, @option{-pedantic} is required in
1345 addition to @option{-ansi}. @xref{Warning Options}.
1347 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1348 option is used. Some header files may notice this macro and refrain
1349 from declaring certain functions or defining certain macros that the
1350 ISO standard doesn't call for; this is to avoid interfering with any
1351 programs that might use these names for other things.
1353 Functions that would normally be built in but do not have semantics
1354 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1355 functions when @option{-ansi} is used. @xref{Other Builtins,,Other
1356 built-in functions provided by GCC}, for details of the functions
1361 Determine the language standard. @xref{Standards,,Language Standards
1362 Supported by GCC}, for details of these standard versions. This option
1363 is currently only supported when compiling C or C++.
1365 The compiler can accept several base standards, such as @samp{c89} or
1366 @samp{c++98}, and GNU dialects of those standards, such as
1367 @samp{gnu89} or @samp{gnu++98}. By specifing a base standard, the
1368 compiler will accept all programs following that standard and those
1369 using GNU extensions that do not contradict it. For example,
1370 @samp{-std=c89} turns off certain features of GCC that are
1371 incompatible with ISO C90, such as the @code{asm} and @code{typeof}
1372 keywords, but not other GNU extensions that do not have a meaning in
1373 ISO C90, such as omitting the middle term of a @code{?:}
1374 expression. On the other hand, by specifing a GNU dialect of a
1375 standard, all features the compiler support are enabled, even when
1376 those features change the meaning of the base standard and some
1377 strict-conforming programs may be rejected. The particular standard
1378 is used by @option{-pedantic} to identify which features are GNU
1379 extensions given that version of the standard. For example
1380 @samp{-std=gnu89 -pedantic} would warn about C++ style @samp{//}
1381 comments, while @samp{-std=gnu99 -pedantic} would not.
1383 A value for this option must be provided; possible values are
1388 Support all ISO C90 programs (certain GNU extensions that conflict
1389 with ISO C90 are disabled). Same as @option{-ansi} for C code.
1391 @item iso9899:199409
1392 ISO C90 as modified in amendment 1.
1398 ISO C99. Note that this standard is not yet fully supported; see
1399 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1400 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1403 GNU dialect of ISO C90 (including some C99 features). This
1404 is the default for C code.
1408 GNU dialect of ISO C99. When ISO C99 is fully implemented in GCC,
1409 this will become the default. The name @samp{gnu9x} is deprecated.
1412 The 1998 ISO C++ standard plus amendments. Same as @option{-ansi} for
1416 GNU dialect of @option{-std=c++98}. This is the default for
1420 The working draft of the upcoming ISO C++0x standard. This option
1421 enables experimental features that are likely to be included in
1422 C++0x. The working draft is constantly changing, and any feature that is
1423 enabled by this flag may be removed from future versions of GCC if it is
1424 not part of the C++0x standard.
1427 GNU dialect of @option{-std=c++0x}. This option enables
1428 experimental features that may be removed in future versions of GCC.
1431 @item -fgnu89-inline
1432 @opindex fgnu89-inline
1433 The option @option{-fgnu89-inline} tells GCC to use the traditional
1434 GNU semantics for @code{inline} functions when in C99 mode.
1435 @xref{Inline,,An Inline Function is As Fast As a Macro}. This option
1436 is accepted and ignored by GCC versions 4.1.3 up to but not including
1437 4.3. In GCC versions 4.3 and later it changes the behavior of GCC in
1438 C99 mode. Using this option is roughly equivalent to adding the
1439 @code{gnu_inline} function attribute to all inline functions
1440 (@pxref{Function Attributes}).
1442 The option @option{-fno-gnu89-inline} explicitly tells GCC to use the
1443 C99 semantics for @code{inline} when in C99 or gnu99 mode (i.e., it
1444 specifies the default behavior). This option was first supported in
1445 GCC 4.3. This option is not supported in C89 or gnu89 mode.
1447 The preprocessor macros @code{__GNUC_GNU_INLINE__} and
1448 @code{__GNUC_STDC_INLINE__} may be used to check which semantics are
1449 in effect for @code{inline} functions. @xref{Common Predefined
1450 Macros,,,cpp,The C Preprocessor}.
1452 @item -aux-info @var{filename}
1454 Output to the given filename prototyped declarations for all functions
1455 declared and/or defined in a translation unit, including those in header
1456 files. This option is silently ignored in any language other than C@.
1458 Besides declarations, the file indicates, in comments, the origin of
1459 each declaration (source file and line), whether the declaration was
1460 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1461 @samp{O} for old, respectively, in the first character after the line
1462 number and the colon), and whether it came from a declaration or a
1463 definition (@samp{C} or @samp{F}, respectively, in the following
1464 character). In the case of function definitions, a K&R-style list of
1465 arguments followed by their declarations is also provided, inside
1466 comments, after the declaration.
1470 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1471 keyword, so that code can use these words as identifiers. You can use
1472 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1473 instead. @option{-ansi} implies @option{-fno-asm}.
1475 In C++, this switch only affects the @code{typeof} keyword, since
1476 @code{asm} and @code{inline} are standard keywords. You may want to
1477 use the @option{-fno-gnu-keywords} flag instead, which has the same
1478 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1479 switch only affects the @code{asm} and @code{typeof} keywords, since
1480 @code{inline} is a standard keyword in ISO C99.
1483 @itemx -fno-builtin-@var{function}
1484 @opindex fno-builtin
1485 @cindex built-in functions
1486 Don't recognize built-in functions that do not begin with
1487 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1488 functions provided by GCC}, for details of the functions affected,
1489 including those which are not built-in functions when @option{-ansi} or
1490 @option{-std} options for strict ISO C conformance are used because they
1491 do not have an ISO standard meaning.
1493 GCC normally generates special code to handle certain built-in functions
1494 more efficiently; for instance, calls to @code{alloca} may become single
1495 instructions that adjust the stack directly, and calls to @code{memcpy}
1496 may become inline copy loops. The resulting code is often both smaller
1497 and faster, but since the function calls no longer appear as such, you
1498 cannot set a breakpoint on those calls, nor can you change the behavior
1499 of the functions by linking with a different library. In addition,
1500 when a function is recognized as a built-in function, GCC may use
1501 information about that function to warn about problems with calls to
1502 that function, or to generate more efficient code, even if the
1503 resulting code still contains calls to that function. For example,
1504 warnings are given with @option{-Wformat} for bad calls to
1505 @code{printf}, when @code{printf} is built in, and @code{strlen} is
1506 known not to modify global memory.
1508 With the @option{-fno-builtin-@var{function}} option
1509 only the built-in function @var{function} is
1510 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1511 function is named this is not built-in in this version of GCC, this
1512 option is ignored. There is no corresponding
1513 @option{-fbuiltin-@var{function}} option; if you wish to enable
1514 built-in functions selectively when using @option{-fno-builtin} or
1515 @option{-ffreestanding}, you may define macros such as:
1518 #define abs(n) __builtin_abs ((n))
1519 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1524 @cindex hosted environment
1526 Assert that compilation takes place in a hosted environment. This implies
1527 @option{-fbuiltin}. A hosted environment is one in which the
1528 entire standard library is available, and in which @code{main} has a return
1529 type of @code{int}. Examples are nearly everything except a kernel.
1530 This is equivalent to @option{-fno-freestanding}.
1532 @item -ffreestanding
1533 @opindex ffreestanding
1534 @cindex hosted environment
1536 Assert that compilation takes place in a freestanding environment. This
1537 implies @option{-fno-builtin}. A freestanding environment
1538 is one in which the standard library may not exist, and program startup may
1539 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1540 This is equivalent to @option{-fno-hosted}.
1542 @xref{Standards,,Language Standards Supported by GCC}, for details of
1543 freestanding and hosted environments.
1547 @cindex openmp parallel
1548 Enable handling of OpenMP directives @code{#pragma omp} in C/C++ and
1549 @code{!$omp} in Fortran. When @option{-fopenmp} is specified, the
1550 compiler generates parallel code according to the OpenMP Application
1551 Program Interface v2.5 @w{@uref{http://www.openmp.org/}}. This option
1552 implies @option{-pthread}, and thus is only supported on targets that
1553 have support for @option{-pthread}.
1555 @item -fms-extensions
1556 @opindex fms-extensions
1557 Accept some non-standard constructs used in Microsoft header files.
1559 Some cases of unnamed fields in structures and unions are only
1560 accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union
1561 fields within structs/unions}, for details.
1565 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1566 options for strict ISO C conformance) implies @option{-trigraphs}.
1568 @item -no-integrated-cpp
1569 @opindex no-integrated-cpp
1570 Performs a compilation in two passes: preprocessing and compiling. This
1571 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1572 @option{-B} option. The user supplied compilation step can then add in
1573 an additional preprocessing step after normal preprocessing but before
1574 compiling. The default is to use the integrated cpp (internal cpp)
1576 The semantics of this option will change if "cc1", "cc1plus", and
1577 "cc1obj" are merged.
1579 @cindex traditional C language
1580 @cindex C language, traditional
1582 @itemx -traditional-cpp
1583 @opindex traditional-cpp
1584 @opindex traditional
1585 Formerly, these options caused GCC to attempt to emulate a pre-standard
1586 C compiler. They are now only supported with the @option{-E} switch.
1587 The preprocessor continues to support a pre-standard mode. See the GNU
1588 CPP manual for details.
1590 @item -fcond-mismatch
1591 @opindex fcond-mismatch
1592 Allow conditional expressions with mismatched types in the second and
1593 third arguments. The value of such an expression is void. This option
1594 is not supported for C++.
1596 @item -flax-vector-conversions
1597 @opindex flax-vector-conversions
1598 Allow implicit conversions between vectors with differing numbers of
1599 elements and/or incompatible element types. This option should not be
1602 @item -funsigned-char
1603 @opindex funsigned-char
1604 Let the type @code{char} be unsigned, like @code{unsigned char}.
1606 Each kind of machine has a default for what @code{char} should
1607 be. It is either like @code{unsigned char} by default or like
1608 @code{signed char} by default.
1610 Ideally, a portable program should always use @code{signed char} or
1611 @code{unsigned char} when it depends on the signedness of an object.
1612 But many programs have been written to use plain @code{char} and
1613 expect it to be signed, or expect it to be unsigned, depending on the
1614 machines they were written for. This option, and its inverse, let you
1615 make such a program work with the opposite default.
1617 The type @code{char} is always a distinct type from each of
1618 @code{signed char} or @code{unsigned char}, even though its behavior
1619 is always just like one of those two.
1622 @opindex fsigned-char
1623 Let the type @code{char} be signed, like @code{signed char}.
1625 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1626 the negative form of @option{-funsigned-char}. Likewise, the option
1627 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1629 @item -fsigned-bitfields
1630 @itemx -funsigned-bitfields
1631 @itemx -fno-signed-bitfields
1632 @itemx -fno-unsigned-bitfields
1633 @opindex fsigned-bitfields
1634 @opindex funsigned-bitfields
1635 @opindex fno-signed-bitfields
1636 @opindex fno-unsigned-bitfields
1637 These options control whether a bit-field is signed or unsigned, when the
1638 declaration does not use either @code{signed} or @code{unsigned}. By
1639 default, such a bit-field is signed, because this is consistent: the
1640 basic integer types such as @code{int} are signed types.
1643 @node C++ Dialect Options
1644 @section Options Controlling C++ Dialect
1646 @cindex compiler options, C++
1647 @cindex C++ options, command line
1648 @cindex options, C++
1649 This section describes the command-line options that are only meaningful
1650 for C++ programs; but you can also use most of the GNU compiler options
1651 regardless of what language your program is in. For example, you
1652 might compile a file @code{firstClass.C} like this:
1655 g++ -g -frepo -O -c firstClass.C
1659 In this example, only @option{-frepo} is an option meant
1660 only for C++ programs; you can use the other options with any
1661 language supported by GCC@.
1663 Here is a list of options that are @emph{only} for compiling C++ programs:
1667 @item -fabi-version=@var{n}
1668 @opindex fabi-version
1669 Use version @var{n} of the C++ ABI@. Version 2 is the version of the
1670 C++ ABI that first appeared in G++ 3.4. Version 1 is the version of
1671 the C++ ABI that first appeared in G++ 3.2. Version 0 will always be
1672 the version that conforms most closely to the C++ ABI specification.
1673 Therefore, the ABI obtained using version 0 will change as ABI bugs
1676 The default is version 2.
1678 @item -fno-access-control
1679 @opindex fno-access-control
1680 Turn off all access checking. This switch is mainly useful for working
1681 around bugs in the access control code.
1685 Check that the pointer returned by @code{operator new} is non-null
1686 before attempting to modify the storage allocated. This check is
1687 normally unnecessary because the C++ standard specifies that
1688 @code{operator new} will only return @code{0} if it is declared
1689 @samp{throw()}, in which case the compiler will always check the
1690 return value even without this option. In all other cases, when
1691 @code{operator new} has a non-empty exception specification, memory
1692 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1693 @samp{new (nothrow)}.
1695 @item -fconserve-space
1696 @opindex fconserve-space
1697 Put uninitialized or runtime-initialized global variables into the
1698 common segment, as C does. This saves space in the executable at the
1699 cost of not diagnosing duplicate definitions. If you compile with this
1700 flag and your program mysteriously crashes after @code{main()} has
1701 completed, you may have an object that is being destroyed twice because
1702 two definitions were merged.
1704 This option is no longer useful on most targets, now that support has
1705 been added for putting variables into BSS without making them common.
1707 @item -ffriend-injection
1708 @opindex ffriend-injection
1709 Inject friend functions into the enclosing namespace, so that they are
1710 visible outside the scope of the class in which they are declared.
1711 Friend functions were documented to work this way in the old Annotated
1712 C++ Reference Manual, and versions of G++ before 4.1 always worked
1713 that way. However, in ISO C++ a friend function which is not declared
1714 in an enclosing scope can only be found using argument dependent
1715 lookup. This option causes friends to be injected as they were in
1718 This option is for compatibility, and may be removed in a future
1721 @item -fno-elide-constructors
1722 @opindex fno-elide-constructors
1723 The C++ standard allows an implementation to omit creating a temporary
1724 which is only used to initialize another object of the same type.
1725 Specifying this option disables that optimization, and forces G++ to
1726 call the copy constructor in all cases.
1728 @item -fno-enforce-eh-specs
1729 @opindex fno-enforce-eh-specs
1730 Don't generate code to check for violation of exception specifications
1731 at runtime. This option violates the C++ standard, but may be useful
1732 for reducing code size in production builds, much like defining
1733 @samp{NDEBUG}. This does not give user code permission to throw
1734 exceptions in violation of the exception specifications; the compiler
1735 will still optimize based on the specifications, so throwing an
1736 unexpected exception will result in undefined behavior.
1739 @itemx -fno-for-scope
1741 @opindex fno-for-scope
1742 If @option{-ffor-scope} is specified, the scope of variables declared in
1743 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1744 as specified by the C++ standard.
1745 If @option{-fno-for-scope} is specified, the scope of variables declared in
1746 a @i{for-init-statement} extends to the end of the enclosing scope,
1747 as was the case in old versions of G++, and other (traditional)
1748 implementations of C++.
1750 The default if neither flag is given to follow the standard,
1751 but to allow and give a warning for old-style code that would
1752 otherwise be invalid, or have different behavior.
1754 @item -fno-gnu-keywords
1755 @opindex fno-gnu-keywords
1756 Do not recognize @code{typeof} as a keyword, so that code can use this
1757 word as an identifier. You can use the keyword @code{__typeof__} instead.
1758 @option{-ansi} implies @option{-fno-gnu-keywords}.
1760 @item -fno-implicit-templates
1761 @opindex fno-implicit-templates
1762 Never emit code for non-inline templates which are instantiated
1763 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1764 @xref{Template Instantiation}, for more information.
1766 @item -fno-implicit-inline-templates
1767 @opindex fno-implicit-inline-templates
1768 Don't emit code for implicit instantiations of inline templates, either.
1769 The default is to handle inlines differently so that compiles with and
1770 without optimization will need the same set of explicit instantiations.
1772 @item -fno-implement-inlines
1773 @opindex fno-implement-inlines
1774 To save space, do not emit out-of-line copies of inline functions
1775 controlled by @samp{#pragma implementation}. This will cause linker
1776 errors if these functions are not inlined everywhere they are called.
1778 @item -fms-extensions
1779 @opindex fms-extensions
1780 Disable pedantic warnings about constructs used in MFC, such as implicit
1781 int and getting a pointer to member function via non-standard syntax.
1783 @item -fno-nonansi-builtins
1784 @opindex fno-nonansi-builtins
1785 Disable built-in declarations of functions that are not mandated by
1786 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1787 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1789 @item -fno-operator-names
1790 @opindex fno-operator-names
1791 Do not treat the operator name keywords @code{and}, @code{bitand},
1792 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1793 synonyms as keywords.
1795 @item -fno-optional-diags
1796 @opindex fno-optional-diags
1797 Disable diagnostics that the standard says a compiler does not need to
1798 issue. Currently, the only such diagnostic issued by G++ is the one for
1799 a name having multiple meanings within a class.
1802 @opindex fpermissive
1803 Downgrade some diagnostics about nonconformant code from errors to
1804 warnings. Thus, using @option{-fpermissive} will allow some
1805 nonconforming code to compile.
1809 Enable automatic template instantiation at link time. This option also
1810 implies @option{-fno-implicit-templates}. @xref{Template
1811 Instantiation}, for more information.
1815 Disable generation of information about every class with virtual
1816 functions for use by the C++ runtime type identification features
1817 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1818 of the language, you can save some space by using this flag. Note that
1819 exception handling uses the same information, but it will generate it as
1820 needed. The @samp{dynamic_cast} operator can still be used for casts that
1821 do not require runtime type information, i.e.@: casts to @code{void *} or to
1822 unambiguous base classes.
1826 Emit statistics about front-end processing at the end of the compilation.
1827 This information is generally only useful to the G++ development team.
1829 @item -ftemplate-depth-@var{n}
1830 @opindex ftemplate-depth
1831 Set the maximum instantiation depth for template classes to @var{n}.
1832 A limit on the template instantiation depth is needed to detect
1833 endless recursions during template class instantiation. ANSI/ISO C++
1834 conforming programs must not rely on a maximum depth greater than 17.
1836 @item -fno-threadsafe-statics
1837 @opindex fno-threadsafe-statics
1838 Do not emit the extra code to use the routines specified in the C++
1839 ABI for thread-safe initialization of local statics. You can use this
1840 option to reduce code size slightly in code that doesn't need to be
1843 @item -fuse-cxa-atexit
1844 @opindex fuse-cxa-atexit
1845 Register destructors for objects with static storage duration with the
1846 @code{__cxa_atexit} function rather than the @code{atexit} function.
1847 This option is required for fully standards-compliant handling of static
1848 destructors, but will only work if your C library supports
1849 @code{__cxa_atexit}.
1851 @item -fno-use-cxa-get-exception-ptr
1852 @opindex fno-use-cxa-get-exception-ptr
1853 Don't use the @code{__cxa_get_exception_ptr} runtime routine. This
1854 will cause @code{std::uncaught_exception} to be incorrect, but is necessary
1855 if the runtime routine is not available.
1857 @item -fvisibility-inlines-hidden
1858 @opindex fvisibility-inlines-hidden
1859 This switch declares that the user does not attempt to compare
1860 pointers to inline methods where the addresses of the two functions
1861 were taken in different shared objects.
1863 The effect of this is that GCC may, effectively, mark inline methods with
1864 @code{__attribute__ ((visibility ("hidden")))} so that they do not
1865 appear in the export table of a DSO and do not require a PLT indirection
1866 when used within the DSO@. Enabling this option can have a dramatic effect
1867 on load and link times of a DSO as it massively reduces the size of the
1868 dynamic export table when the library makes heavy use of templates.
1870 The behavior of this switch is not quite the same as marking the
1871 methods as hidden directly, because it does not affect static variables
1872 local to the function or cause the compiler to deduce that
1873 the function is defined in only one shared object.
1875 You may mark a method as having a visibility explicitly to negate the
1876 effect of the switch for that method. For example, if you do want to
1877 compare pointers to a particular inline method, you might mark it as
1878 having default visibility. Marking the enclosing class with explicit
1879 visibility will have no effect.
1881 Explicitly instantiated inline methods are unaffected by this option
1882 as their linkage might otherwise cross a shared library boundary.
1883 @xref{Template Instantiation}.
1885 @item -fvisibility-ms-compat
1886 @opindex fvisibility-ms-compat
1887 This flag attempts to use visibility settings to make GCC's C++
1888 linkage model compatible with that of Microsoft Visual Studio.
1890 The flag makes these changes to GCC's linkage model:
1894 It sets the default visibility to @code{hidden}, like
1895 @option{-fvisibility=hidden}.
1898 Types, but not their members, are not hidden by default.
1901 The One Definition Rule is relaxed for types without explicit
1902 visibility specifications which are defined in more than one different
1903 shared object: those declarations are permitted if they would have
1904 been permitted when this option was not used.
1907 In new code it is better to use @option{-fvisibility=hidden} and
1908 export those classes which are intended to be externally visible.
1909 Unfortunately it is possible for code to rely, perhaps accidentally,
1910 on the Visual Studio behavior.
1912 Among the consequences of these changes are that static data members
1913 of the same type with the same name but defined in different shared
1914 objects will be different, so changing one will not change the other;
1915 and that pointers to function members defined in different shared
1916 objects may not compare equal. When this flag is given, it is a
1917 violation of the ODR to define types with the same name differently.
1921 Do not use weak symbol support, even if it is provided by the linker.
1922 By default, G++ will use weak symbols if they are available. This
1923 option exists only for testing, and should not be used by end-users;
1924 it will result in inferior code and has no benefits. This option may
1925 be removed in a future release of G++.
1929 Do not search for header files in the standard directories specific to
1930 C++, but do still search the other standard directories. (This option
1931 is used when building the C++ library.)
1934 In addition, these optimization, warning, and code generation options
1935 have meanings only for C++ programs:
1938 @item -fno-default-inline
1939 @opindex fno-default-inline
1940 Do not assume @samp{inline} for functions defined inside a class scope.
1941 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1942 functions will have linkage like inline functions; they just won't be
1945 @item -Wabi @r{(C++ and Objective-C++ only)}
1948 Warn when G++ generates code that is probably not compatible with the
1949 vendor-neutral C++ ABI@. Although an effort has been made to warn about
1950 all such cases, there are probably some cases that are not warned about,
1951 even though G++ is generating incompatible code. There may also be
1952 cases where warnings are emitted even though the code that is generated
1955 You should rewrite your code to avoid these warnings if you are
1956 concerned about the fact that code generated by G++ may not be binary
1957 compatible with code generated by other compilers.
1959 The known incompatibilities at this point include:
1964 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1965 pack data into the same byte as a base class. For example:
1968 struct A @{ virtual void f(); int f1 : 1; @};
1969 struct B : public A @{ int f2 : 1; @};
1973 In this case, G++ will place @code{B::f2} into the same byte
1974 as@code{A::f1}; other compilers will not. You can avoid this problem
1975 by explicitly padding @code{A} so that its size is a multiple of the
1976 byte size on your platform; that will cause G++ and other compilers to
1977 layout @code{B} identically.
1980 Incorrect handling of tail-padding for virtual bases. G++ does not use
1981 tail padding when laying out virtual bases. For example:
1984 struct A @{ virtual void f(); char c1; @};
1985 struct B @{ B(); char c2; @};
1986 struct C : public A, public virtual B @{@};
1990 In this case, G++ will not place @code{B} into the tail-padding for
1991 @code{A}; other compilers will. You can avoid this problem by
1992 explicitly padding @code{A} so that its size is a multiple of its
1993 alignment (ignoring virtual base classes); that will cause G++ and other
1994 compilers to layout @code{C} identically.
1997 Incorrect handling of bit-fields with declared widths greater than that
1998 of their underlying types, when the bit-fields appear in a union. For
2002 union U @{ int i : 4096; @};
2006 Assuming that an @code{int} does not have 4096 bits, G++ will make the
2007 union too small by the number of bits in an @code{int}.
2010 Empty classes can be placed at incorrect offsets. For example:
2020 struct C : public B, public A @{@};
2024 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
2025 it should be placed at offset zero. G++ mistakenly believes that the
2026 @code{A} data member of @code{B} is already at offset zero.
2029 Names of template functions whose types involve @code{typename} or
2030 template template parameters can be mangled incorrectly.
2033 template <typename Q>
2034 void f(typename Q::X) @{@}
2036 template <template <typename> class Q>
2037 void f(typename Q<int>::X) @{@}
2041 Instantiations of these templates may be mangled incorrectly.
2045 @item -Wctor-dtor-privacy @r{(C++ and Objective-C++ only)}
2046 @opindex Wctor-dtor-privacy
2047 @opindex Wno-ctor-dtor-privacy
2048 Warn when a class seems unusable because all the constructors or
2049 destructors in that class are private, and it has neither friends nor
2050 public static member functions.
2052 @item -Wnon-virtual-dtor @r{(C++ and Objective-C++ only)}
2053 @opindex Wnon-virtual-dtor
2054 @opindex Wno-non-virtual-dtor
2055 Warn when a class has virtual functions and accessible non-virtual
2056 destructor, in which case it would be possible but unsafe to delete
2057 an instance of a derived class through a pointer to the base class.
2058 This warning is also enabled if -Weffc++ is specified.
2060 @item -Wreorder @r{(C++ and Objective-C++ only)}
2062 @opindex Wno-reorder
2063 @cindex reordering, warning
2064 @cindex warning for reordering of member initializers
2065 Warn when the order of member initializers given in the code does not
2066 match the order in which they must be executed. For instance:
2072 A(): j (0), i (1) @{ @}
2076 The compiler will rearrange the member initializers for @samp{i}
2077 and @samp{j} to match the declaration order of the members, emitting
2078 a warning to that effect. This warning is enabled by @option{-Wall}.
2081 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
2084 @item -Weffc++ @r{(C++ and Objective-C++ only)}
2087 Warn about violations of the following style guidelines from Scott Meyers'
2088 @cite{Effective C++} book:
2092 Item 11: Define a copy constructor and an assignment operator for classes
2093 with dynamically allocated memory.
2096 Item 12: Prefer initialization to assignment in constructors.
2099 Item 14: Make destructors virtual in base classes.
2102 Item 15: Have @code{operator=} return a reference to @code{*this}.
2105 Item 23: Don't try to return a reference when you must return an object.
2109 Also warn about violations of the following style guidelines from
2110 Scott Meyers' @cite{More Effective C++} book:
2114 Item 6: Distinguish between prefix and postfix forms of increment and
2115 decrement operators.
2118 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
2122 When selecting this option, be aware that the standard library
2123 headers do not obey all of these guidelines; use @samp{grep -v}
2124 to filter out those warnings.
2126 @item -Wstrict-null-sentinel @r{(C++ and Objective-C++ only)}
2127 @opindex Wstrict-null-sentinel
2128 @opindex Wno-strict-null-sentinel
2129 Warn also about the use of an uncasted @code{NULL} as sentinel. When
2130 compiling only with GCC this is a valid sentinel, as @code{NULL} is defined
2131 to @code{__null}. Although it is a null pointer constant not a null pointer,
2132 it is guaranteed to of the same size as a pointer. But this use is
2133 not portable across different compilers.
2135 @item -Wno-non-template-friend @r{(C++ and Objective-C++ only)}
2136 @opindex Wno-non-template-friend
2137 @opindex Wnon-template-friend
2138 Disable warnings when non-templatized friend functions are declared
2139 within a template. Since the advent of explicit template specification
2140 support in G++, if the name of the friend is an unqualified-id (i.e.,
2141 @samp{friend foo(int)}), the C++ language specification demands that the
2142 friend declare or define an ordinary, nontemplate function. (Section
2143 14.5.3). Before G++ implemented explicit specification, unqualified-ids
2144 could be interpreted as a particular specialization of a templatized
2145 function. Because this non-conforming behavior is no longer the default
2146 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
2147 check existing code for potential trouble spots and is on by default.
2148 This new compiler behavior can be turned off with
2149 @option{-Wno-non-template-friend} which keeps the conformant compiler code
2150 but disables the helpful warning.
2152 @item -Wold-style-cast @r{(C++ and Objective-C++ only)}
2153 @opindex Wold-style-cast
2154 @opindex Wno-old-style-cast
2155 Warn if an old-style (C-style) cast to a non-void type is used within
2156 a C++ program. The new-style casts (@samp{dynamic_cast},
2157 @samp{static_cast}, @samp{reinterpret_cast}, and @samp{const_cast}) are
2158 less vulnerable to unintended effects and much easier to search for.
2160 @item -Woverloaded-virtual @r{(C++ and Objective-C++ only)}
2161 @opindex Woverloaded-virtual
2162 @opindex Wno-overloaded-virtual
2163 @cindex overloaded virtual fn, warning
2164 @cindex warning for overloaded virtual fn
2165 Warn when a function declaration hides virtual functions from a
2166 base class. For example, in:
2173 struct B: public A @{
2178 the @code{A} class version of @code{f} is hidden in @code{B}, and code
2186 will fail to compile.
2188 @item -Wno-pmf-conversions @r{(C++ and Objective-C++ only)}
2189 @opindex Wno-pmf-conversions
2190 @opindex Wpmf-conversions
2191 Disable the diagnostic for converting a bound pointer to member function
2194 @item -Wsign-promo @r{(C++ and Objective-C++ only)}
2195 @opindex Wsign-promo
2196 @opindex Wno-sign-promo
2197 Warn when overload resolution chooses a promotion from unsigned or
2198 enumerated type to a signed type, over a conversion to an unsigned type of
2199 the same size. Previous versions of G++ would try to preserve
2200 unsignedness, but the standard mandates the current behavior.
2205 A& operator = (int);
2215 In this example, G++ will synthesize a default @samp{A& operator =
2216 (const A&);}, while cfront will use the user-defined @samp{operator =}.
2219 @node Objective-C and Objective-C++ Dialect Options
2220 @section Options Controlling Objective-C and Objective-C++ Dialects
2222 @cindex compiler options, Objective-C and Objective-C++
2223 @cindex Objective-C and Objective-C++ options, command line
2224 @cindex options, Objective-C and Objective-C++
2225 (NOTE: This manual does not describe the Objective-C and Objective-C++
2226 languages themselves. See @xref{Standards,,Language Standards
2227 Supported by GCC}, for references.)
2229 This section describes the command-line options that are only meaningful
2230 for Objective-C and Objective-C++ programs, but you can also use most of
2231 the language-independent GNU compiler options.
2232 For example, you might compile a file @code{some_class.m} like this:
2235 gcc -g -fgnu-runtime -O -c some_class.m
2239 In this example, @option{-fgnu-runtime} is an option meant only for
2240 Objective-C and Objective-C++ programs; you can use the other options with
2241 any language supported by GCC@.
2243 Note that since Objective-C is an extension of the C language, Objective-C
2244 compilations may also use options specific to the C front-end (e.g.,
2245 @option{-Wtraditional}). Similarly, Objective-C++ compilations may use
2246 C++-specific options (e.g., @option{-Wabi}).
2248 Here is a list of options that are @emph{only} for compiling Objective-C
2249 and Objective-C++ programs:
2252 @item -fconstant-string-class=@var{class-name}
2253 @opindex fconstant-string-class
2254 Use @var{class-name} as the name of the class to instantiate for each
2255 literal string specified with the syntax @code{@@"@dots{}"}. The default
2256 class name is @code{NXConstantString} if the GNU runtime is being used, and
2257 @code{NSConstantString} if the NeXT runtime is being used (see below). The
2258 @option{-fconstant-cfstrings} option, if also present, will override the
2259 @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
2260 to be laid out as constant CoreFoundation strings.
2263 @opindex fgnu-runtime
2264 Generate object code compatible with the standard GNU Objective-C
2265 runtime. This is the default for most types of systems.
2267 @item -fnext-runtime
2268 @opindex fnext-runtime
2269 Generate output compatible with the NeXT runtime. This is the default
2270 for NeXT-based systems, including Darwin and Mac OS X@. The macro
2271 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
2274 @item -fno-nil-receivers
2275 @opindex fno-nil-receivers
2276 Assume that all Objective-C message dispatches (e.g.,
2277 @code{[receiver message:arg]}) in this translation unit ensure that the receiver
2278 is not @code{nil}. This allows for more efficient entry points in the runtime
2279 to be used. Currently, this option is only available in conjunction with
2280 the NeXT runtime on Mac OS X 10.3 and later.
2282 @item -fobjc-call-cxx-cdtors
2283 @opindex fobjc-call-cxx-cdtors
2284 For each Objective-C class, check if any of its instance variables is a
2285 C++ object with a non-trivial default constructor. If so, synthesize a
2286 special @code{- (id) .cxx_construct} instance method that will run
2287 non-trivial default constructors on any such instance variables, in order,
2288 and then return @code{self}. Similarly, check if any instance variable
2289 is a C++ object with a non-trivial destructor, and if so, synthesize a
2290 special @code{- (void) .cxx_destruct} method that will run
2291 all such default destructors, in reverse order.
2293 The @code{- (id) .cxx_construct} and/or @code{- (void) .cxx_destruct} methods
2294 thusly generated will only operate on instance variables declared in the
2295 current Objective-C class, and not those inherited from superclasses. It
2296 is the responsibility of the Objective-C runtime to invoke all such methods
2297 in an object's inheritance hierarchy. The @code{- (id) .cxx_construct} methods
2298 will be invoked by the runtime immediately after a new object
2299 instance is allocated; the @code{- (void) .cxx_destruct} methods will
2300 be invoked immediately before the runtime deallocates an object instance.
2302 As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has
2303 support for invoking the @code{- (id) .cxx_construct} and
2304 @code{- (void) .cxx_destruct} methods.
2306 @item -fobjc-direct-dispatch
2307 @opindex fobjc-direct-dispatch
2308 Allow fast jumps to the message dispatcher. On Darwin this is
2309 accomplished via the comm page.
2311 @item -fobjc-exceptions
2312 @opindex fobjc-exceptions
2313 Enable syntactic support for structured exception handling in Objective-C,
2314 similar to what is offered by C++ and Java. This option is
2315 unavailable in conjunction with the NeXT runtime on Mac OS X 10.2 and
2324 @@catch (AnObjCClass *exc) @{
2331 @@catch (AnotherClass *exc) @{
2334 @@catch (id allOthers) @{
2344 The @code{@@throw} statement may appear anywhere in an Objective-C or
2345 Objective-C++ program; when used inside of a @code{@@catch} block, the
2346 @code{@@throw} may appear without an argument (as shown above), in which case
2347 the object caught by the @code{@@catch} will be rethrown.
2349 Note that only (pointers to) Objective-C objects may be thrown and
2350 caught using this scheme. When an object is thrown, it will be caught
2351 by the nearest @code{@@catch} clause capable of handling objects of that type,
2352 analogously to how @code{catch} blocks work in C++ and Java. A
2353 @code{@@catch(id @dots{})} clause (as shown above) may also be provided to catch
2354 any and all Objective-C exceptions not caught by previous @code{@@catch}
2357 The @code{@@finally} clause, if present, will be executed upon exit from the
2358 immediately preceding @code{@@try @dots{} @@catch} section. This will happen
2359 regardless of whether any exceptions are thrown, caught or rethrown
2360 inside the @code{@@try @dots{} @@catch} section, analogously to the behavior
2361 of the @code{finally} clause in Java.
2363 There are several caveats to using the new exception mechanism:
2367 Although currently designed to be binary compatible with @code{NS_HANDLER}-style
2368 idioms provided by the @code{NSException} class, the new
2369 exceptions can only be used on Mac OS X 10.3 (Panther) and later
2370 systems, due to additional functionality needed in the (NeXT) Objective-C
2374 As mentioned above, the new exceptions do not support handling
2375 types other than Objective-C objects. Furthermore, when used from
2376 Objective-C++, the Objective-C exception model does not interoperate with C++
2377 exceptions at this time. This means you cannot @code{@@throw} an exception
2378 from Objective-C and @code{catch} it in C++, or vice versa
2379 (i.e., @code{throw @dots{} @@catch}).
2382 The @option{-fobjc-exceptions} switch also enables the use of synchronization
2383 blocks for thread-safe execution:
2386 @@synchronized (ObjCClass *guard) @{
2391 Upon entering the @code{@@synchronized} block, a thread of execution shall
2392 first check whether a lock has been placed on the corresponding @code{guard}
2393 object by another thread. If it has, the current thread shall wait until
2394 the other thread relinquishes its lock. Once @code{guard} becomes available,
2395 the current thread will place its own lock on it, execute the code contained in
2396 the @code{@@synchronized} block, and finally relinquish the lock (thereby
2397 making @code{guard} available to other threads).
2399 Unlike Java, Objective-C does not allow for entire methods to be marked
2400 @code{@@synchronized}. Note that throwing exceptions out of
2401 @code{@@synchronized} blocks is allowed, and will cause the guarding object
2402 to be unlocked properly.
2406 Enable garbage collection (GC) in Objective-C and Objective-C++ programs.
2408 @item -freplace-objc-classes
2409 @opindex freplace-objc-classes
2410 Emit a special marker instructing @command{ld(1)} not to statically link in
2411 the resulting object file, and allow @command{dyld(1)} to load it in at
2412 run time instead. This is used in conjunction with the Fix-and-Continue
2413 debugging mode, where the object file in question may be recompiled and
2414 dynamically reloaded in the course of program execution, without the need
2415 to restart the program itself. Currently, Fix-and-Continue functionality
2416 is only available in conjunction with the NeXT runtime on Mac OS X 10.3
2421 When compiling for the NeXT runtime, the compiler ordinarily replaces calls
2422 to @code{objc_getClass("@dots{}")} (when the name of the class is known at
2423 compile time) with static class references that get initialized at load time,
2424 which improves run-time performance. Specifying the @option{-fzero-link} flag
2425 suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
2426 to be retained. This is useful in Zero-Link debugging mode, since it allows
2427 for individual class implementations to be modified during program execution.
2431 Dump interface declarations for all classes seen in the source file to a
2432 file named @file{@var{sourcename}.decl}.
2434 @item -Wassign-intercept @r{(Objective-C and Objective-C++ only)}
2435 @opindex Wassign-intercept
2436 @opindex Wno-assign-intercept
2437 Warn whenever an Objective-C assignment is being intercepted by the
2440 @item -Wno-protocol @r{(Objective-C and Objective-C++ only)}
2441 @opindex Wno-protocol
2443 If a class is declared to implement a protocol, a warning is issued for
2444 every method in the protocol that is not implemented by the class. The
2445 default behavior is to issue a warning for every method not explicitly
2446 implemented in the class, even if a method implementation is inherited
2447 from the superclass. If you use the @option{-Wno-protocol} option, then
2448 methods inherited from the superclass are considered to be implemented,
2449 and no warning is issued for them.
2451 @item -Wselector @r{(Objective-C and Objective-C++ only)}
2453 @opindex Wno-selector
2454 Warn if multiple methods of different types for the same selector are
2455 found during compilation. The check is performed on the list of methods
2456 in the final stage of compilation. Additionally, a check is performed
2457 for each selector appearing in a @code{@@selector(@dots{})}
2458 expression, and a corresponding method for that selector has been found
2459 during compilation. Because these checks scan the method table only at
2460 the end of compilation, these warnings are not produced if the final
2461 stage of compilation is not reached, for example because an error is
2462 found during compilation, or because the @option{-fsyntax-only} option is
2465 @item -Wstrict-selector-match @r{(Objective-C and Objective-C++ only)}
2466 @opindex Wstrict-selector-match
2467 @opindex Wno-strict-selector-match
2468 Warn if multiple methods with differing argument and/or return types are
2469 found for a given selector when attempting to send a message using this
2470 selector to a receiver of type @code{id} or @code{Class}. When this flag
2471 is off (which is the default behavior), the compiler will omit such warnings
2472 if any differences found are confined to types which share the same size
2475 @item -Wundeclared-selector @r{(Objective-C and Objective-C++ only)}
2476 @opindex Wundeclared-selector
2477 @opindex Wno-undeclared-selector
2478 Warn if a @code{@@selector(@dots{})} expression referring to an
2479 undeclared selector is found. A selector is considered undeclared if no
2480 method with that name has been declared before the
2481 @code{@@selector(@dots{})} expression, either explicitly in an
2482 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
2483 an @code{@@implementation} section. This option always performs its
2484 checks as soon as a @code{@@selector(@dots{})} expression is found,
2485 while @option{-Wselector} only performs its checks in the final stage of
2486 compilation. This also enforces the coding style convention
2487 that methods and selectors must be declared before being used.
2489 @item -print-objc-runtime-info
2490 @opindex print-objc-runtime-info
2491 Generate C header describing the largest structure that is passed by
2496 @node Language Independent Options
2497 @section Options to Control Diagnostic Messages Formatting
2498 @cindex options to control diagnostics formatting
2499 @cindex diagnostic messages
2500 @cindex message formatting
2502 Traditionally, diagnostic messages have been formatted irrespective of
2503 the output device's aspect (e.g.@: its width, @dots{}). The options described
2504 below can be used to control the diagnostic messages formatting
2505 algorithm, e.g.@: how many characters per line, how often source location
2506 information should be reported. Right now, only the C++ front end can
2507 honor these options. However it is expected, in the near future, that
2508 the remaining front ends would be able to digest them correctly.
2511 @item -fmessage-length=@var{n}
2512 @opindex fmessage-length
2513 Try to format error messages so that they fit on lines of about @var{n}
2514 characters. The default is 72 characters for @command{g++} and 0 for the rest of
2515 the front ends supported by GCC@. If @var{n} is zero, then no
2516 line-wrapping will be done; each error message will appear on a single
2519 @opindex fdiagnostics-show-location
2520 @item -fdiagnostics-show-location=once
2521 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
2522 reporter to emit @emph{once} source location information; that is, in
2523 case the message is too long to fit on a single physical line and has to
2524 be wrapped, the source location won't be emitted (as prefix) again,
2525 over and over, in subsequent continuation lines. This is the default
2528 @item -fdiagnostics-show-location=every-line
2529 Only meaningful in line-wrapping mode. Instructs the diagnostic
2530 messages reporter to emit the same source location information (as
2531 prefix) for physical lines that result from the process of breaking
2532 a message which is too long to fit on a single line.
2534 @item -fdiagnostics-show-option
2535 @opindex fdiagnostics-show-option
2536 This option instructs the diagnostic machinery to add text to each
2537 diagnostic emitted, which indicates which command line option directly
2538 controls that diagnostic, when such an option is known to the
2539 diagnostic machinery.
2541 @item -Wcoverage-mismatch
2542 @opindex Wcoverage-mismatch
2543 Warn if feedback profiles do not match when using the
2544 @option{-fprofile-use} option.
2545 If a source file was changed between @option{-fprofile-gen} and
2546 @option{-fprofile-use}, the files with the profile feedback can fail
2547 to match the source file and GCC can not use the profile feedback
2548 information. By default, GCC emits an error message in this case.
2549 The option @option{-Wcoverage-mismatch} emits a warning instead of an
2550 error. GCC does not use appropriate feedback profiles, so using this
2551 option can result in poorly optimized code. This option is useful
2552 only in the case of very minor changes such as bug fixes to an
2557 @node Warning Options
2558 @section Options to Request or Suppress Warnings
2559 @cindex options to control warnings
2560 @cindex warning messages
2561 @cindex messages, warning
2562 @cindex suppressing warnings
2564 Warnings are diagnostic messages that report constructions which
2565 are not inherently erroneous but which are risky or suggest there
2566 may have been an error.
2568 The following language-independent options do not enable specific
2569 warnings but control the kinds of diagnostics produced by GCC.
2572 @cindex syntax checking
2574 @opindex fsyntax-only
2575 Check the code for syntax errors, but don't do anything beyond that.
2579 Inhibit all warning messages.
2584 Make all warnings into errors.
2589 Make the specified warning into an error. The specifier for a warning
2590 is appended, for example @option{-Werror=switch} turns the warnings
2591 controlled by @option{-Wswitch} into errors. This switch takes a
2592 negative form, to be used to negate @option{-Werror} for specific
2593 warnings, for example @option{-Wno-error=switch} makes
2594 @option{-Wswitch} warnings not be errors, even when @option{-Werror}
2595 is in effect. You can use the @option{-fdiagnostics-show-option}
2596 option to have each controllable warning amended with the option which
2597 controls it, to determine what to use with this option.
2599 Note that specifying @option{-Werror=}@var{foo} automatically implies
2600 @option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not
2603 @item -Wfatal-errors
2604 @opindex Wfatal-errors
2605 @opindex Wno-fatal-errors
2606 This option causes the compiler to abort compilation on the first error
2607 occurred rather than trying to keep going and printing further error
2612 You can request many specific warnings with options beginning
2613 @samp{-W}, for example @option{-Wimplicit} to request warnings on
2614 implicit declarations. Each of these specific warning options also
2615 has a negative form beginning @samp{-Wno-} to turn off warnings; for
2616 example, @option{-Wno-implicit}. This manual lists only one of the
2617 two forms, whichever is not the default. For further,
2618 language-specific options also refer to @ref{C++ Dialect Options} and
2619 @ref{Objective-C and Objective-C++ Dialect Options}.
2624 Issue all the warnings demanded by strict ISO C and ISO C++;
2625 reject all programs that use forbidden extensions, and some other
2626 programs that do not follow ISO C and ISO C++. For ISO C, follows the
2627 version of the ISO C standard specified by any @option{-std} option used.
2629 Valid ISO C and ISO C++ programs should compile properly with or without
2630 this option (though a rare few will require @option{-ansi} or a
2631 @option{-std} option specifying the required version of ISO C)@. However,
2632 without this option, certain GNU extensions and traditional C and C++
2633 features are supported as well. With this option, they are rejected.
2635 @option{-pedantic} does not cause warning messages for use of the
2636 alternate keywords whose names begin and end with @samp{__}. Pedantic
2637 warnings are also disabled in the expression that follows
2638 @code{__extension__}. However, only system header files should use
2639 these escape routes; application programs should avoid them.
2640 @xref{Alternate Keywords}.
2642 Some users try to use @option{-pedantic} to check programs for strict ISO
2643 C conformance. They soon find that it does not do quite what they want:
2644 it finds some non-ISO practices, but not all---only those for which
2645 ISO C @emph{requires} a diagnostic, and some others for which
2646 diagnostics have been added.
2648 A feature to report any failure to conform to ISO C might be useful in
2649 some instances, but would require considerable additional work and would
2650 be quite different from @option{-pedantic}. We don't have plans to
2651 support such a feature in the near future.
2653 Where the standard specified with @option{-std} represents a GNU
2654 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
2655 corresponding @dfn{base standard}, the version of ISO C on which the GNU
2656 extended dialect is based. Warnings from @option{-pedantic} are given
2657 where they are required by the base standard. (It would not make sense
2658 for such warnings to be given only for features not in the specified GNU
2659 C dialect, since by definition the GNU dialects of C include all
2660 features the compiler supports with the given option, and there would be
2661 nothing to warn about.)
2663 @item -pedantic-errors
2664 @opindex pedantic-errors
2665 Like @option{-pedantic}, except that errors are produced rather than
2671 This enables all the warnings about constructions that some users
2672 consider questionable, and that are easy to avoid (or modify to
2673 prevent the warning), even in conjunction with macros. This also
2674 enables some language-specific warnings described in @ref{C++ Dialect
2675 Options} and @ref{Objective-C and Objective-C++ Dialect Options}.
2677 @option{-Wall} turns on the following warning flags:
2679 @gccoptlist{-Waddress @gol
2680 -Warray-bounds @r{(only with} @option{-O2}@r{)} @gol
2682 -Wchar-subscripts @gol
2684 -Wimplicit-function-declaration @gol
2687 -Wmain @r{(only for C/ObjC and unless} @option{-ffreestanding}@r{)} @gol
2688 -Wmissing-braces @gol
2694 -Wsequence-point @gol
2695 -Wsign-compare @r{(only in C++)} @gol
2696 -Wstrict-aliasing @gol
2697 -Wstrict-overflow=1 @gol
2700 -Wuninitialized @gol
2701 -Wunknown-pragmas @gol
2702 -Wunused-function @gol
2705 -Wunused-variable @gol
2706 -Wvolatile-register-var @gol
2709 Note that some warning flags are not implied by @option{-Wall}. Some of
2710 them warn about constructions that users generally do not consider
2711 questionable, but which occasionally you might wish to check for;
2712 others warn about constructions that are necessary or hard to avoid in
2713 some cases, and there is no simple way to modify the code to suppress
2714 the warning. Some of them are enabled by @option{-Wextra} but many of
2715 them must be enabled individually.
2721 This enables some extra warning flags that are not enabled by
2722 @option{-Wall}. (This option used to be called @option{-W}. The older
2723 name is still supported, but the newer name is more descriptive.)
2725 @gccoptlist{-Wclobbered @gol
2727 -Wignored-qualifiers @gol
2728 -Wmissing-field-initializers @gol
2729 -Wmissing-parameter-type @r{(C only)} @gol
2730 -Wold-style-declaration @r{(C only)} @gol
2731 -Woverride-init @gol
2734 -Wuninitialized @gol
2735 -Wunused-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol
2738 The option @option{-Wextra} also prints warning messages for the
2744 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2745 @samp{>}, or @samp{>=}.
2748 (C++ only) An enumerator and a non-enumerator both appear in a
2749 conditional expression.
2752 (C++ only) Ambiguous virtual bases.
2755 (C++ only) Subscripting an array which has been declared @samp{register}.
2758 (C++ only) Taking the address of a variable which has been declared
2762 (C++ only) A base class is not initialized in a derived class' copy
2767 @item -Wchar-subscripts
2768 @opindex Wchar-subscripts
2769 @opindex Wno-char-subscripts
2770 Warn if an array subscript has type @code{char}. This is a common cause
2771 of error, as programmers often forget that this type is signed on some
2773 This warning is enabled by @option{-Wall}.
2777 @opindex Wno-comment
2778 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
2779 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
2780 This warning is enabled by @option{-Wall}.
2785 @opindex ffreestanding
2786 @opindex fno-builtin
2787 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
2788 the arguments supplied have types appropriate to the format string
2789 specified, and that the conversions specified in the format string make
2790 sense. This includes standard functions, and others specified by format
2791 attributes (@pxref{Function Attributes}), in the @code{printf},
2792 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
2793 not in the C standard) families (or other target-specific families).
2794 Which functions are checked without format attributes having been
2795 specified depends on the standard version selected, and such checks of
2796 functions without the attribute specified are disabled by
2797 @option{-ffreestanding} or @option{-fno-builtin}.
2799 The formats are checked against the format features supported by GNU
2800 libc version 2.2. These include all ISO C90 and C99 features, as well
2801 as features from the Single Unix Specification and some BSD and GNU
2802 extensions. Other library implementations may not support all these
2803 features; GCC does not support warning about features that go beyond a
2804 particular library's limitations. However, if @option{-pedantic} is used
2805 with @option{-Wformat}, warnings will be given about format features not
2806 in the selected standard version (but not for @code{strfmon} formats,
2807 since those are not in any version of the C standard). @xref{C Dialect
2808 Options,,Options Controlling C Dialect}.
2810 Since @option{-Wformat} also checks for null format arguments for
2811 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2813 @option{-Wformat} is included in @option{-Wall}. For more control over some
2814 aspects of format checking, the options @option{-Wformat-y2k},
2815 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2816 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2817 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2820 @opindex Wformat-y2k
2821 @opindex Wno-format-y2k
2822 If @option{-Wformat} is specified, also warn about @code{strftime}
2823 formats which may yield only a two-digit year.
2825 @item -Wno-format-contains-nul
2826 @opindex Wno-format-contains-nul
2827 @opindex Wformat-contains-nul
2828 If @option{-Wformat} is specified, do not warn about format strings that
2831 @item -Wno-format-extra-args
2832 @opindex Wno-format-extra-args
2833 @opindex Wformat-extra-args
2834 If @option{-Wformat} is specified, do not warn about excess arguments to a
2835 @code{printf} or @code{scanf} format function. The C standard specifies
2836 that such arguments are ignored.
2838 Where the unused arguments lie between used arguments that are
2839 specified with @samp{$} operand number specifications, normally
2840 warnings are still given, since the implementation could not know what
2841 type to pass to @code{va_arg} to skip the unused arguments. However,
2842 in the case of @code{scanf} formats, this option will suppress the
2843 warning if the unused arguments are all pointers, since the Single
2844 Unix Specification says that such unused arguments are allowed.
2846 @item -Wno-format-zero-length @r{(C and Objective-C only)}
2847 @opindex Wno-format-zero-length
2848 @opindex Wformat-zero-length
2849 If @option{-Wformat} is specified, do not warn about zero-length formats.
2850 The C standard specifies that zero-length formats are allowed.
2852 @item -Wformat-nonliteral
2853 @opindex Wformat-nonliteral
2854 @opindex Wno-format-nonliteral
2855 If @option{-Wformat} is specified, also warn if the format string is not a
2856 string literal and so cannot be checked, unless the format function
2857 takes its format arguments as a @code{va_list}.
2859 @item -Wformat-security
2860 @opindex Wformat-security
2861 @opindex Wno-format-security
2862 If @option{-Wformat} is specified, also warn about uses of format
2863 functions that represent possible security problems. At present, this
2864 warns about calls to @code{printf} and @code{scanf} functions where the
2865 format string is not a string literal and there are no format arguments,
2866 as in @code{printf (foo);}. This may be a security hole if the format
2867 string came from untrusted input and contains @samp{%n}. (This is
2868 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2869 in future warnings may be added to @option{-Wformat-security} that are not
2870 included in @option{-Wformat-nonliteral}.)
2874 @opindex Wno-format=2
2875 Enable @option{-Wformat} plus format checks not included in
2876 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2877 -Wformat-nonliteral -Wformat-security -Wformat-y2k}.
2879 @item -Wnonnull @r{(C and Objective-C only)}
2881 @opindex Wno-nonnull
2882 Warn about passing a null pointer for arguments marked as
2883 requiring a non-null value by the @code{nonnull} function attribute.
2885 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2886 can be disabled with the @option{-Wno-nonnull} option.
2888 @item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
2890 @opindex Wno-init-self
2891 Warn about uninitialized variables which are initialized with themselves.
2892 Note this option can only be used with the @option{-Wuninitialized} option.
2894 For example, GCC will warn about @code{i} being uninitialized in the
2895 following snippet only when @option{-Winit-self} has been specified:
2906 @item -Wimplicit-int @r{(C and Objective-C only)}
2907 @opindex Wimplicit-int
2908 @opindex Wno-implicit-int
2909 Warn when a declaration does not specify a type.
2910 This warning is enabled by @option{-Wall}.
2912 @item -Wimplicit-function-declaration @r{(C and Objective-C only)}
2913 @opindex Wimplicit-function-declaration
2914 @opindex Wno-implicit-function-declaration
2915 Give a warning whenever a function is used before being declared. In
2916 C99 mode (@option{-std=c99} or @option{-std=gnu99}), this warning is
2917 enabled by default and it is made into an error by
2918 @option{-pedantic-errors}. This warning is also enabled by
2923 @opindex Wno-implicit
2924 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2925 This warning is enabled by @option{-Wall}.
2927 @item -Wignored-qualifiers @r{(C and C++ only)}
2928 @opindex Wignored-qualifiers
2929 @opindex Wno-ignored-qualifiers
2930 Warn if the return type of a function has a type qualifier
2931 such as @code{const}. For ISO C such a type qualifier has no effect,
2932 since the value returned by a function is not an lvalue.
2933 For C++, the warning is only emitted for scalar types or @code{void}.
2934 ISO C prohibits qualified @code{void} return types on function
2935 definitions, so such return types always receive a warning
2936 even without this option.
2938 This warning is also enabled by @option{-Wextra}.
2943 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
2944 function with external linkage, returning int, taking either zero
2945 arguments, two, or three arguments of appropriate types.
2946 This warning is enabled by @option{-Wall}.
2948 @item -Wmissing-braces
2949 @opindex Wmissing-braces
2950 @opindex Wno-missing-braces
2951 Warn if an aggregate or union initializer is not fully bracketed. In
2952 the following example, the initializer for @samp{a} is not fully
2953 bracketed, but that for @samp{b} is fully bracketed.
2956 int a[2][2] = @{ 0, 1, 2, 3 @};
2957 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2960 This warning is enabled by @option{-Wall}.
2962 @item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)}
2963 @opindex Wmissing-include-dirs
2964 @opindex Wno-missing-include-dirs
2965 Warn if a user-supplied include directory does not exist.
2968 @opindex Wparentheses
2969 @opindex Wno-parentheses
2970 Warn if parentheses are omitted in certain contexts, such
2971 as when there is an assignment in a context where a truth value
2972 is expected, or when operators are nested whose precedence people
2973 often get confused about.
2975 Also warn if a comparison like @samp{x<=y<=z} appears; this is
2976 equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different
2977 interpretation from that of ordinary mathematical notation.
2979 Also warn about constructions where there may be confusion to which
2980 @code{if} statement an @code{else} branch belongs. Here is an example of
2995 In C/C++, every @code{else} branch belongs to the innermost possible
2996 @code{if} statement, which in this example is @code{if (b)}. This is
2997 often not what the programmer expected, as illustrated in the above
2998 example by indentation the programmer chose. When there is the
2999 potential for this confusion, GCC will issue a warning when this flag
3000 is specified. To eliminate the warning, add explicit braces around
3001 the innermost @code{if} statement so there is no way the @code{else}
3002 could belong to the enclosing @code{if}. The resulting code would
3019 This warning is enabled by @option{-Wall}.
3021 @item -Wsequence-point
3022 @opindex Wsequence-point
3023 @opindex Wno-sequence-point
3024 Warn about code that may have undefined semantics because of violations
3025 of sequence point rules in the C and C++ standards.
3027 The C and C++ standards defines the order in which expressions in a C/C++
3028 program are evaluated in terms of @dfn{sequence points}, which represent
3029 a partial ordering between the execution of parts of the program: those
3030 executed before the sequence point, and those executed after it. These
3031 occur after the evaluation of a full expression (one which is not part
3032 of a larger expression), after the evaluation of the first operand of a
3033 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
3034 function is called (but after the evaluation of its arguments and the
3035 expression denoting the called function), and in certain other places.
3036 Other than as expressed by the sequence point rules, the order of
3037 evaluation of subexpressions of an expression is not specified. All
3038 these rules describe only a partial order rather than a total order,
3039 since, for example, if two functions are called within one expression
3040 with no sequence point between them, the order in which the functions
3041 are called is not specified. However, the standards committee have
3042 ruled that function calls do not overlap.
3044 It is not specified when between sequence points modifications to the
3045 values of objects take effect. Programs whose behavior depends on this
3046 have undefined behavior; the C and C++ standards specify that ``Between
3047 the previous and next sequence point an object shall have its stored
3048 value modified at most once by the evaluation of an expression.
3049 Furthermore, the prior value shall be read only to determine the value
3050 to be stored.''. If a program breaks these rules, the results on any
3051 particular implementation are entirely unpredictable.
3053 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
3054 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
3055 diagnosed by this option, and it may give an occasional false positive
3056 result, but in general it has been found fairly effective at detecting
3057 this sort of problem in programs.
3059 The standard is worded confusingly, therefore there is some debate
3060 over the precise meaning of the sequence point rules in subtle cases.
3061 Links to discussions of the problem, including proposed formal
3062 definitions, may be found on the GCC readings page, at
3063 @w{@uref{http://gcc.gnu.org/readings.html}}.
3065 This warning is enabled by @option{-Wall} for C and C++.
3068 @opindex Wreturn-type
3069 @opindex Wno-return-type
3070 Warn whenever a function is defined with a return-type that defaults
3071 to @code{int}. Also warn about any @code{return} statement with no
3072 return-value in a function whose return-type is not @code{void}
3073 (falling off the end of the function body is considered returning
3074 without a value), and about a @code{return} statement with a
3075 expression in a function whose return-type is @code{void}.
3077 For C++, a function without return type always produces a diagnostic
3078 message, even when @option{-Wno-return-type} is specified. The only
3079 exceptions are @samp{main} and functions defined in system headers.
3081 This warning is enabled by @option{-Wall}.
3086 Warn whenever a @code{switch} statement has an index of enumerated type
3087 and lacks a @code{case} for one or more of the named codes of that
3088 enumeration. (The presence of a @code{default} label prevents this
3089 warning.) @code{case} labels outside the enumeration range also
3090 provoke warnings when this option is used.
3091 This warning is enabled by @option{-Wall}.
3093 @item -Wswitch-default
3094 @opindex Wswitch-default
3095 @opindex Wno-switch-default
3096 Warn whenever a @code{switch} statement does not have a @code{default}
3100 @opindex Wswitch-enum
3101 @opindex Wno-switch-enum
3102 Warn whenever a @code{switch} statement has an index of enumerated type
3103 and lacks a @code{case} for one or more of the named codes of that
3104 enumeration. @code{case} labels outside the enumeration range also
3105 provoke warnings when this option is used.
3109 @opindex Wno-trigraphs
3110 Warn if any trigraphs are encountered that might change the meaning of
3111 the program (trigraphs within comments are not warned about).
3112 This warning is enabled by @option{-Wall}.
3114 @item -Wunused-function
3115 @opindex Wunused-function
3116 @opindex Wno-unused-function
3117 Warn whenever a static function is declared but not defined or a
3118 non-inline static function is unused.
3119 This warning is enabled by @option{-Wall}.
3121 @item -Wunused-label
3122 @opindex Wunused-label
3123 @opindex Wno-unused-label
3124 Warn whenever a label is declared but not used.
3125 This warning is enabled by @option{-Wall}.
3127 To suppress this warning use the @samp{unused} attribute
3128 (@pxref{Variable Attributes}).
3130 @item -Wunused-parameter
3131 @opindex Wunused-parameter
3132 @opindex Wno-unused-parameter
3133 Warn whenever a function parameter is unused aside from its declaration.
3135 To suppress this warning use the @samp{unused} attribute
3136 (@pxref{Variable Attributes}).
3138 @item -Wunused-variable
3139 @opindex Wunused-variable
3140 @opindex Wno-unused-variable
3141 Warn whenever a local variable or non-constant static variable is unused
3142 aside from its declaration.
3143 This warning is enabled by @option{-Wall}.
3145 To suppress this warning use the @samp{unused} attribute
3146 (@pxref{Variable Attributes}).
3148 @item -Wunused-value
3149 @opindex Wunused-value
3150 @opindex Wno-unused-value
3151 Warn whenever a statement computes a result that is explicitly not
3152 used. To suppress this warning cast the unused expression to
3153 @samp{void}. This includes an expression-statement or the left-hand
3154 side of a comma expression that contains no side effects. For example,
3155 an expression such as @samp{x[i,j]} will cause a warning, while
3156 @samp{x[(void)i,j]} will not.
3158 This warning is enabled by @option{-Wall}.
3163 All the above @option{-Wunused} options combined.
3165 In order to get a warning about an unused function parameter, you must
3166 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
3167 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
3169 @item -Wuninitialized
3170 @opindex Wuninitialized
3171 @opindex Wno-uninitialized
3172 Warn if an automatic variable is used without first being initialized
3173 or if a variable may be clobbered by a @code{setjmp} call. In C++,
3174 warn if a non-static reference or non-static @samp{const} member
3175 appears in a class without constructors.
3177 If you want to warn about code which uses the uninitialized value of the
3178 variable in its own initializer, use the @option{-Winit-self} option.
3180 These warnings occur for individual uninitialized or clobbered
3181 elements of structure, union or array variables as well as for
3182 variables which are uninitialized or clobbered as a whole. They do
3183 not occur for variables or elements declared @code{volatile}. Because
3184 these warnings depend on optimization, the exact variables or elements
3185 for which there are warnings will depend on the precise optimization
3186 options and version of GCC used.
3188 Note that there may be no warning about a variable that is used only
3189 to compute a value that itself is never used, because such
3190 computations may be deleted by data flow analysis before the warnings
3193 These warnings are made optional because GCC is not smart
3194 enough to see all the reasons why the code might be correct
3195 despite appearing to have an error. Here is one example of how
3216 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
3217 always initialized, but GCC doesn't know this. Here is
3218 another common case:
3223 if (change_y) save_y = y, y = new_y;
3225 if (change_y) y = save_y;
3230 This has no bug because @code{save_y} is used only if it is set.
3232 @cindex @code{longjmp} warnings
3233 This option also warns when a non-volatile automatic variable might be
3234 changed by a call to @code{longjmp}. These warnings as well are possible
3235 only in optimizing compilation.
3237 The compiler sees only the calls to @code{setjmp}. It cannot know
3238 where @code{longjmp} will be called; in fact, a signal handler could
3239 call it at any point in the code. As a result, you may get a warning
3240 even when there is in fact no problem because @code{longjmp} cannot
3241 in fact be called at the place which would cause a problem.
3243 Some spurious warnings can be avoided if you declare all the functions
3244 you use that never return as @code{noreturn}. @xref{Function
3247 This warning is enabled by @option{-Wall} or @option{-Wextra}.
3249 @item -Wunknown-pragmas
3250 @opindex Wunknown-pragmas
3251 @opindex Wno-unknown-pragmas
3252 @cindex warning for unknown pragmas
3253 @cindex unknown pragmas, warning
3254 @cindex pragmas, warning of unknown
3255 Warn when a #pragma directive is encountered which is not understood by
3256 GCC@. If this command line option is used, warnings will even be issued
3257 for unknown pragmas in system header files. This is not the case if
3258 the warnings were only enabled by the @option{-Wall} command line option.
3261 @opindex Wno-pragmas
3263 Do not warn about misuses of pragmas, such as incorrect parameters,
3264 invalid syntax, or conflicts between pragmas. See also
3265 @samp{-Wunknown-pragmas}.
3267 @item -Wstrict-aliasing
3268 @opindex Wstrict-aliasing
3269 @opindex Wno-strict-aliasing
3270 This option is only active when @option{-fstrict-aliasing} is active.
3271 It warns about code which might break the strict aliasing rules that the
3272 compiler is using for optimization. The warning does not catch all
3273 cases, but does attempt to catch the more common pitfalls. It is
3274 included in @option{-Wall}.
3275 It is equivalent to @option{-Wstrict-aliasing=3}
3277 @item -Wstrict-aliasing=n
3278 @opindex Wstrict-aliasing=n
3279 @opindex Wno-strict-aliasing=n
3280 This option is only active when @option{-fstrict-aliasing} is active.
3281 It warns about code which might break the strict aliasing rules that the
3282 compiler is using for optimization.
3283 Higher levels correspond to higher accuracy (fewer false positives).
3284 Higher levels also correspond to more effort, similar to the way -O works.
3285 @option{-Wstrict-aliasing} is equivalent to @option{-Wstrict-aliasing=n},
3288 Level 1: Most aggressive, quick, least accurate.
3289 Possibly useful when higher levels
3290 do not warn but -fstrict-aliasing still breaks the code, as it has very few
3291 false negatives. However, it has many false positives.
3292 Warns for all pointer conversions between possibly incompatible types,
3293 even if never dereferenced. Runs in the frontend only.
3295 Level 2: Aggressive, quick, not too precise.
3296 May still have many false positives (not as many as level 1 though),
3297 and few false negatives (but possibly more than level 1).
3298 Unlike level 1, it only warns when an address is taken. Warns about
3299 incomplete types. Runs in the frontend only.
3301 Level 3 (default for @option{-Wstrict-aliasing}):
3302 Should have very few false positives and few false
3303 negatives. Slightly slower than levels 1 or 2 when optimization is enabled.
3304 Takes care of the common punn+dereference pattern in the frontend:
3305 @code{*(int*)&some_float}.
3306 If optimization is enabled, it also runs in the backend, where it deals
3307 with multiple statement cases using flow-sensitive points-to information.
3308 Only warns when the converted pointer is dereferenced.
3309 Does not warn about incomplete types.
3311 @item -Wstrict-overflow
3312 @itemx -Wstrict-overflow=@var{n}
3313 @opindex Wstrict-overflow
3314 @opindex Wno-strict-overflow
3315 This option is only active when @option{-fstrict-overflow} is active.
3316 It warns about cases where the compiler optimizes based on the
3317 assumption that signed overflow does not occur. Note that it does not
3318 warn about all cases where the code might overflow: it only warns
3319 about cases where the compiler implements some optimization. Thus
3320 this warning depends on the optimization level.
3322 An optimization which assumes that signed overflow does not occur is
3323 perfectly safe if the values of the variables involved are such that
3324 overflow never does, in fact, occur. Therefore this warning can
3325 easily give a false positive: a warning about code which is not
3326 actually a problem. To help focus on important issues, several
3327 warning levels are defined. No warnings are issued for the use of
3328 undefined signed overflow when estimating how many iterations a loop
3329 will require, in particular when determining whether a loop will be
3333 @item -Wstrict-overflow=1
3334 Warn about cases which are both questionable and easy to avoid. For
3335 example: @code{x + 1 > x}; with @option{-fstrict-overflow}, the
3336 compiler will simplify this to @code{1}. This level of
3337 @option{-Wstrict-overflow} is enabled by @option{-Wall}; higher levels
3338 are not, and must be explicitly requested.
3340 @item -Wstrict-overflow=2
3341 Also warn about other cases where a comparison is simplified to a
3342 constant. For example: @code{abs (x) >= 0}. This can only be
3343 simplified when @option{-fstrict-overflow} is in effect, because
3344 @code{abs (INT_MIN)} overflows to @code{INT_MIN}, which is less than
3345 zero. @option{-Wstrict-overflow} (with no level) is the same as
3346 @option{-Wstrict-overflow=2}.
3348 @item -Wstrict-overflow=3
3349 Also warn about other cases where a comparison is simplified. For
3350 example: @code{x + 1 > 1} will be simplified to @code{x > 0}.
3352 @item -Wstrict-overflow=4
3353 Also warn about other simplifications not covered by the above cases.
3354 For example: @code{(x * 10) / 5} will be simplified to @code{x * 2}.
3356 @item -Wstrict-overflow=5
3357 Also warn about cases where the compiler reduces the magnitude of a
3358 constant involved in a comparison. For example: @code{x + 2 > y} will
3359 be simplified to @code{x + 1 >= y}. This is reported only at the
3360 highest warning level because this simplification applies to many
3361 comparisons, so this warning level will give a very large number of
3365 @item -Warray-bounds
3366 @opindex Wno-array-bounds
3367 @opindex Warray-bounds
3368 This option is only active when @option{-ftree-vrp} is active
3369 (default for -O2 and above). It warns about subscripts to arrays
3370 that are always out of bounds. This warning is enabled by @option{-Wall}.
3372 @item -Wno-div-by-zero
3373 @opindex Wno-div-by-zero
3374 @opindex Wdiv-by-zero
3375 Do not warn about compile-time integer division by zero. Floating point
3376 division by zero is not warned about, as it can be a legitimate way of
3377 obtaining infinities and NaNs.
3379 @item -Wsystem-headers
3380 @opindex Wsystem-headers
3381 @opindex Wno-system-headers
3382 @cindex warnings from system headers
3383 @cindex system headers, warnings from
3384 Print warning messages for constructs found in system header files.
3385 Warnings from system headers are normally suppressed, on the assumption
3386 that they usually do not indicate real problems and would only make the
3387 compiler output harder to read. Using this command line option tells
3388 GCC to emit warnings from system headers as if they occurred in user
3389 code. However, note that using @option{-Wall} in conjunction with this
3390 option will @emph{not} warn about unknown pragmas in system
3391 headers---for that, @option{-Wunknown-pragmas} must also be used.
3394 @opindex Wfloat-equal
3395 @opindex Wno-float-equal
3396 Warn if floating point values are used in equality comparisons.
3398 The idea behind this is that sometimes it is convenient (for the
3399 programmer) to consider floating-point values as approximations to
3400 infinitely precise real numbers. If you are doing this, then you need
3401 to compute (by analyzing the code, or in some other way) the maximum or
3402 likely maximum error that the computation introduces, and allow for it
3403 when performing comparisons (and when producing output, but that's a
3404 different problem). In particular, instead of testing for equality, you
3405 would check to see whether the two values have ranges that overlap; and
3406 this is done with the relational operators, so equality comparisons are
3409 @item -Wtraditional @r{(C and Objective-C only)}
3410 @opindex Wtraditional
3411 @opindex Wno-traditional
3412 Warn about certain constructs that behave differently in traditional and
3413 ISO C@. Also warn about ISO C constructs that have no traditional C
3414 equivalent, and/or problematic constructs which should be avoided.
3418 Macro parameters that appear within string literals in the macro body.
3419 In traditional C macro replacement takes place within string literals,
3420 but does not in ISO C@.
3423 In traditional C, some preprocessor directives did not exist.
3424 Traditional preprocessors would only consider a line to be a directive
3425 if the @samp{#} appeared in column 1 on the line. Therefore
3426 @option{-Wtraditional} warns about directives that traditional C
3427 understands but would ignore because the @samp{#} does not appear as the
3428 first character on the line. It also suggests you hide directives like
3429 @samp{#pragma} not understood by traditional C by indenting them. Some
3430 traditional implementations would not recognize @samp{#elif}, so it
3431 suggests avoiding it altogether.
3434 A function-like macro that appears without arguments.
3437 The unary plus operator.
3440 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
3441 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
3442 constants.) Note, these suffixes appear in macros defined in the system
3443 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
3444 Use of these macros in user code might normally lead to spurious
3445 warnings, however GCC's integrated preprocessor has enough context to
3446 avoid warning in these cases.
3449 A function declared external in one block and then used after the end of
3453 A @code{switch} statement has an operand of type @code{long}.
3456 A non-@code{static} function declaration follows a @code{static} one.
3457 This construct is not accepted by some traditional C compilers.
3460 The ISO type of an integer constant has a different width or
3461 signedness from its traditional type. This warning is only issued if
3462 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
3463 typically represent bit patterns, are not warned about.
3466 Usage of ISO string concatenation is detected.
3469 Initialization of automatic aggregates.
3472 Identifier conflicts with labels. Traditional C lacks a separate
3473 namespace for labels.
3476 Initialization of unions. If the initializer is zero, the warning is
3477 omitted. This is done under the assumption that the zero initializer in
3478 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
3479 initializer warnings and relies on default initialization to zero in the
3483 Conversions by prototypes between fixed/floating point values and vice
3484 versa. The absence of these prototypes when compiling with traditional
3485 C would cause serious problems. This is a subset of the possible
3486 conversion warnings, for the full set use @option{-Wtraditional-conversion}.
3489 Use of ISO C style function definitions. This warning intentionally is
3490 @emph{not} issued for prototype declarations or variadic functions
3491 because these ISO C features will appear in your code when using
3492 libiberty's traditional C compatibility macros, @code{PARAMS} and
3493 @code{VPARAMS}. This warning is also bypassed for nested functions
3494 because that feature is already a GCC extension and thus not relevant to
3495 traditional C compatibility.
3498 @item -Wtraditional-conversion @r{(C and Objective-C only)}
3499 @opindex Wtraditional-conversion
3500 @opindex Wno-traditional-conversion
3501 Warn if a prototype causes a type conversion that is different from what
3502 would happen to the same argument in the absence of a prototype. This
3503 includes conversions of fixed point to floating and vice versa, and
3504 conversions changing the width or signedness of a fixed point argument
3505 except when the same as the default promotion.
3507 @item -Wdeclaration-after-statement @r{(C and Objective-C only)}
3508 @opindex Wdeclaration-after-statement
3509 @opindex Wno-declaration-after-statement
3510 Warn when a declaration is found after a statement in a block. This
3511 construct, known from C++, was introduced with ISO C99 and is by default
3512 allowed in GCC@. It is not supported by ISO C90 and was not supported by
3513 GCC versions before GCC 3.0. @xref{Mixed Declarations}.
3518 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
3520 @item -Wno-endif-labels
3521 @opindex Wno-endif-labels
3522 @opindex Wendif-labels
3523 Do not warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
3528 Warn whenever a local variable shadows another local variable, parameter or
3529 global variable or whenever a built-in function is shadowed.
3531 @item -Wlarger-than=@var{len}
3532 @opindex Wlarger-than=@var{len}
3533 @opindex Wlarger-than-@var{len}
3534 Warn whenever an object of larger than @var{len} bytes is defined.
3536 @item -Wframe-larger-than=@var{len}
3537 @opindex Wframe-larger-than
3538 Warn if the size of a function frame is larger than @var{len} bytes.
3539 The computation done to determine the stack frame size is approximate
3540 and not conservative.
3541 The actual requirements may be somewhat greater than @var{len}
3542 even if you do not get a warning. In addition, any space allocated
3543 via @code{alloca}, variable-length arrays, or related constructs
3544 is not included by the compiler when determining
3545 whether or not to issue a warning.
3547 @item -Wunsafe-loop-optimizations
3548 @opindex Wunsafe-loop-optimizations
3549 @opindex Wno-unsafe-loop-optimizations
3550 Warn if the loop cannot be optimized because the compiler could not
3551 assume anything on the bounds of the loop indices. With
3552 @option{-funsafe-loop-optimizations} warn if the compiler made
3555 @item -Wpointer-arith
3556 @opindex Wpointer-arith
3557 @opindex Wno-pointer-arith
3558 Warn about anything that depends on the ``size of'' a function type or
3559 of @code{void}. GNU C assigns these types a size of 1, for
3560 convenience in calculations with @code{void *} pointers and pointers
3561 to functions. In C++, warn also when an arithmetic operation involves
3562 @code{NULL}. This warning is also enabled by @option{-pedantic}.
3565 @opindex Wtype-limits
3566 @opindex Wno-type-limits
3567 Warn if a comparison is always true or always false due to the limited
3568 range of the data type, but do not warn for constant expressions. For
3569 example, warn if an unsigned variable is compared against zero with
3570 @samp{<} or @samp{>=}. This warning is also enabled by
3573 @item -Wbad-function-cast @r{(C and Objective-C only)}
3574 @opindex Wbad-function-cast
3575 @opindex Wno-bad-function-cast
3576 Warn whenever a function call is cast to a non-matching type.
3577 For example, warn if @code{int malloc()} is cast to @code{anything *}.
3579 @item -Wc++-compat @r{(C and Objective-C only)}
3580 Warn about ISO C constructs that are outside of the common subset of
3581 ISO C and ISO C++, e.g.@: request for implicit conversion from
3582 @code{void *} to a pointer to non-@code{void} type.
3584 @item -Wc++0x-compat @r{(C++ and Objective-C++ only)}
3585 Warn about C++ constructs whose meaning differs between ISO C++ 1998 and
3586 ISO C++ 200x, e.g., identifiers in ISO C++ 1998 that will become keywords
3587 in ISO C++ 200x. This warning is enabled by @option{-Wall}.
3591 @opindex Wno-cast-qual
3592 Warn whenever a pointer is cast so as to remove a type qualifier from
3593 the target type. For example, warn if a @code{const char *} is cast
3594 to an ordinary @code{char *}.
3597 @opindex Wcast-align
3598 @opindex Wno-cast-align
3599 Warn whenever a pointer is cast such that the required alignment of the
3600 target is increased. For example, warn if a @code{char *} is cast to
3601 an @code{int *} on machines where integers can only be accessed at
3602 two- or four-byte boundaries.
3604 @item -Wwrite-strings
3605 @opindex Wwrite-strings
3606 @opindex Wno-write-strings
3607 When compiling C, give string constants the type @code{const
3608 char[@var{length}]} so that
3609 copying the address of one into a non-@code{const} @code{char *}
3610 pointer will get a warning; when compiling C++, warn about the
3611 deprecated conversion from string literals to @code{char *}. This
3612 warning, by default, is enabled for C++ programs.
3613 These warnings will help you find at
3614 compile time code that can try to write into a string constant, but
3615 only if you have been very careful about using @code{const} in
3616 declarations and prototypes. Otherwise, it will just be a nuisance;
3617 this is why we did not make @option{-Wall} request these warnings.
3621 @opindex Wno-clobbered
3622 Warn for variables that might be changed by @samp{longjmp} or
3623 @samp{vfork}. This warning is also enabled by @option{-Wextra}.
3626 @opindex Wconversion
3627 @opindex Wno-conversion
3628 Warn for implicit conversions that may alter a value. This includes
3629 conversions between real and integer, like @code{abs (x)} when
3630 @code{x} is @code{double}; conversions between signed and unsigned,
3631 like @code{unsigned ui = -1}; and conversions to smaller types, like
3632 @code{sqrtf (M_PI)}. Do not warn for explicit casts like @code{abs
3633 ((int) x)} and @code{ui = (unsigned) -1}, or if the value is not
3634 changed by the conversion like in @code{abs (2.0)}. Warnings about
3635 conversions between signed and unsigned integers can be disabled by
3636 using @option{-Wno-sign-conversion}.
3638 For C++, also warn for conversions between @code{NULL} and non-pointer
3639 types; confusing overload resolution for user-defined conversions; and
3640 conversions that will never use a type conversion operator:
3641 conversions to @code{void}, the same type, a base class or a reference
3642 to them. Warnings about conversions between signed and unsigned
3643 integers are disabled by default in C++ unless
3644 @option{-Wsign-conversion} is explicitly enabled.
3647 @opindex Wempty-body
3648 @opindex Wno-empty-body
3649 Warn if an empty body occurs in an @samp{if}, @samp{else} or @samp{do
3650 while} statement. Additionally, in C++, warn when an empty body occurs
3651 in a @samp{while} or @samp{for} statement with no whitespacing before
3652 the semicolon. This warning is also enabled by @option{-Wextra}.
3654 @item -Wenum-compare @r{(C++ and Objective-C++ only)}
3655 @opindex Wenum-compare
3656 @opindex Wno-enum-compare
3657 Warn about a comparison between values of different enum types. This
3658 warning is enabled by default.
3660 @item -Wsign-compare
3661 @opindex Wsign-compare
3662 @opindex Wno-sign-compare
3663 @cindex warning for comparison of signed and unsigned values
3664 @cindex comparison of signed and unsigned values, warning
3665 @cindex signed and unsigned values, comparison warning
3666 Warn when a comparison between signed and unsigned values could produce
3667 an incorrect result when the signed value is converted to unsigned.
3668 This warning is also enabled by @option{-Wextra}; to get the other warnings
3669 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
3671 @item -Wsign-conversion
3672 @opindex Wsign-conversion
3673 @opindex Wno-sign-conversion
3674 Warn for implicit conversions that may change the sign of an integer
3675 value, like assigning a signed integer expression to an unsigned
3676 integer variable. An explicit cast silences the warning. In C, this
3677 option is enabled also by @option{-Wconversion}.
3681 @opindex Wno-address
3682 Warn about suspicious uses of memory addresses. These include using
3683 the address of a function in a conditional expression, such as
3684 @code{void func(void); if (func)}, and comparisons against the memory
3685 address of a string literal, such as @code{if (x == "abc")}. Such
3686 uses typically indicate a programmer error: the address of a function
3687 always evaluates to true, so their use in a conditional usually
3688 indicate that the programmer forgot the parentheses in a function
3689 call; and comparisons against string literals result in unspecified
3690 behavior and are not portable in C, so they usually indicate that the
3691 programmer intended to use @code{strcmp}. This warning is enabled by
3695 @opindex Wlogical-op
3696 @opindex Wno-logical-op
3697 Warn about suspicious uses of logical operators in expressions.
3698 This includes using logical operators in contexts where a
3699 bit-wise operator is likely to be expected.
3701 @item -Waggregate-return
3702 @opindex Waggregate-return
3703 @opindex Wno-aggregate-return
3704 Warn if any functions that return structures or unions are defined or
3705 called. (In languages where you can return an array, this also elicits
3708 @item -Wno-attributes
3709 @opindex Wno-attributes
3710 @opindex Wattributes
3711 Do not warn if an unexpected @code{__attribute__} is used, such as
3712 unrecognized attributes, function attributes applied to variables,
3713 etc. This will not stop errors for incorrect use of supported
3716 @item -Wstrict-prototypes @r{(C and Objective-C only)}
3717 @opindex Wstrict-prototypes
3718 @opindex Wno-strict-prototypes
3719 Warn if a function is declared or defined without specifying the
3720 argument types. (An old-style function definition is permitted without
3721 a warning if preceded by a declaration which specifies the argument
3724 @item -Wold-style-declaration @r{(C and Objective-C only)}
3725 @opindex Wold-style-declaration
3726 @opindex Wno-old-style-declaration
3727 Warn for obsolescent usages, according to the C Standard, in a
3728 declaration. For example, warn if storage-class specifiers like
3729 @code{static} are not the first things in a declaration. This warning
3730 is also enabled by @option{-Wextra}.
3732 @item -Wold-style-definition @r{(C and Objective-C only)}
3733 @opindex Wold-style-definition
3734 @opindex Wno-old-style-definition
3735 Warn if an old-style function definition is used. A warning is given
3736 even if there is a previous prototype.
3738 @item -Wmissing-parameter-type @r{(C and Objective-C only)}
3739 @opindex Wmissing-parameter-type
3740 @opindex Wno-missing-parameter-type
3741 A function parameter is declared without a type specifier in K&R-style
3748 This warning is also enabled by @option{-Wextra}.
3750 @item -Wmissing-prototypes @r{(C and Objective-C only)}
3751 @opindex Wmissing-prototypes
3752 @opindex Wno-missing-prototypes
3753 Warn if a global function is defined without a previous prototype
3754 declaration. This warning is issued even if the definition itself
3755 provides a prototype. The aim is to detect global functions that fail
3756 to be declared in header files.
3758 @item -Wmissing-declarations
3759 @opindex Wmissing-declarations
3760 @opindex Wno-missing-declarations
3761 Warn if a global function is defined without a previous declaration.
3762 Do so even if the definition itself provides a prototype.
3763 Use this option to detect global functions that are not declared in
3764 header files. In C++, no warnings are issued for function templates,
3765 or for inline functions, or for functions in anonymous namespaces.
3767 @item -Wmissing-field-initializers
3768 @opindex Wmissing-field-initializers
3769 @opindex Wno-missing-field-initializers
3773 Warn if a structure's initializer has some fields missing. For
3774 example, the following code would cause such a warning, because
3775 @code{x.h} is implicitly zero:
3778 struct s @{ int f, g, h; @};
3779 struct s x = @{ 3, 4 @};
3782 This option does not warn about designated initializers, so the following
3783 modification would not trigger a warning:
3786 struct s @{ int f, g, h; @};
3787 struct s x = @{ .f = 3, .g = 4 @};
3790 This warning is included in @option{-Wextra}. To get other @option{-Wextra}
3791 warnings without this one, use @samp{-Wextra -Wno-missing-field-initializers}.
3793 @item -Wmissing-noreturn
3794 @opindex Wmissing-noreturn
3795 @opindex Wno-missing-noreturn
3796 Warn about functions which might be candidates for attribute @code{noreturn}.
3797 Note these are only possible candidates, not absolute ones. Care should
3798 be taken to manually verify functions actually do not ever return before
3799 adding the @code{noreturn} attribute, otherwise subtle code generation
3800 bugs could be introduced. You will not get a warning for @code{main} in
3801 hosted C environments.
3803 @item -Wmissing-format-attribute
3804 @opindex Wmissing-format-attribute
3805 @opindex Wno-missing-format-attribute
3808 Warn about function pointers which might be candidates for @code{format}
3809 attributes. Note these are only possible candidates, not absolute ones.
3810 GCC will guess that function pointers with @code{format} attributes that
3811 are used in assignment, initialization, parameter passing or return
3812 statements should have a corresponding @code{format} attribute in the
3813 resulting type. I.e.@: the left-hand side of the assignment or
3814 initialization, the type of the parameter variable, or the return type
3815 of the containing function respectively should also have a @code{format}
3816 attribute to avoid the warning.
3818 GCC will also warn about function definitions which might be
3819 candidates for @code{format} attributes. Again, these are only
3820 possible candidates. GCC will guess that @code{format} attributes
3821 might be appropriate for any function that calls a function like
3822 @code{vprintf} or @code{vscanf}, but this might not always be the
3823 case, and some functions for which @code{format} attributes are
3824 appropriate may not be detected.
3826 @item -Wno-multichar
3827 @opindex Wno-multichar
3829 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
3830 Usually they indicate a typo in the user's code, as they have
3831 implementation-defined values, and should not be used in portable code.
3833 @item -Wnormalized=<none|id|nfc|nfkc>
3834 @opindex Wnormalized=
3837 @cindex character set, input normalization
3838 In ISO C and ISO C++, two identifiers are different if they are
3839 different sequences of characters. However, sometimes when characters
3840 outside the basic ASCII character set are used, you can have two
3841 different character sequences that look the same. To avoid confusion,
3842 the ISO 10646 standard sets out some @dfn{normalization rules} which
3843 when applied ensure that two sequences that look the same are turned into
3844 the same sequence. GCC can warn you if you are using identifiers which
3845 have not been normalized; this option controls that warning.
3847 There are four levels of warning that GCC supports. The default is
3848 @option{-Wnormalized=nfc}, which warns about any identifier which is
3849 not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the
3850 recommended form for most uses.
3852 Unfortunately, there are some characters which ISO C and ISO C++ allow
3853 in identifiers that when turned into NFC aren't allowable as
3854 identifiers. That is, there's no way to use these symbols in portable
3855 ISO C or C++ and have all your identifiers in NFC@.
3856 @option{-Wnormalized=id} suppresses the warning for these characters.
3857 It is hoped that future versions of the standards involved will correct
3858 this, which is why this option is not the default.
3860 You can switch the warning off for all characters by writing
3861 @option{-Wnormalized=none}. You would only want to do this if you
3862 were using some other normalization scheme (like ``D''), because
3863 otherwise you can easily create bugs that are literally impossible to see.
3865 Some characters in ISO 10646 have distinct meanings but look identical
3866 in some fonts or display methodologies, especially once formatting has
3867 been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL
3868 LETTER N'', will display just like a regular @code{n} which has been
3869 placed in a superscript. ISO 10646 defines the @dfn{NFKC}
3870 normalization scheme to convert all these into a standard form as
3871 well, and GCC will warn if your code is not in NFKC if you use
3872 @option{-Wnormalized=nfkc}. This warning is comparable to warning
3873 about every identifier that contains the letter O because it might be
3874 confused with the digit 0, and so is not the default, but may be
3875 useful as a local coding convention if the programming environment is
3876 unable to be fixed to display these characters distinctly.
3878 @item -Wno-deprecated
3879 @opindex Wno-deprecated
3880 @opindex Wdeprecated
3881 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
3883 @item -Wno-deprecated-declarations
3884 @opindex Wno-deprecated-declarations
3885 @opindex Wdeprecated-declarations
3886 Do not warn about uses of functions (@pxref{Function Attributes}),
3887 variables (@pxref{Variable Attributes}), and types (@pxref{Type
3888 Attributes}) marked as deprecated by using the @code{deprecated}
3892 @opindex Wno-overflow
3894 Do not warn about compile-time overflow in constant expressions.
3896 @item -Woverride-init @r{(C and Objective-C only)}
3897 @opindex Woverride-init
3898 @opindex Wno-override-init
3902 Warn if an initialized field without side effects is overridden when
3903 using designated initializers (@pxref{Designated Inits, , Designated
3906 This warning is included in @option{-Wextra}. To get other
3907 @option{-Wextra} warnings without this one, use @samp{-Wextra
3908 -Wno-override-init}.
3913 Warn if a structure is given the packed attribute, but the packed
3914 attribute has no effect on the layout or size of the structure.
3915 Such structures may be mis-aligned for little benefit. For
3916 instance, in this code, the variable @code{f.x} in @code{struct bar}
3917 will be misaligned even though @code{struct bar} does not itself
3918 have the packed attribute:
3925 @} __attribute__((packed));
3936 Warn if padding is included in a structure, either to align an element
3937 of the structure or to align the whole structure. Sometimes when this
3938 happens it is possible to rearrange the fields of the structure to
3939 reduce the padding and so make the structure smaller.
3941 @item -Wredundant-decls
3942 @opindex Wredundant-decls
3943 @opindex Wno-redundant-decls
3944 Warn if anything is declared more than once in the same scope, even in
3945 cases where multiple declaration is valid and changes nothing.
3947 @item -Wnested-externs @r{(C and Objective-C only)}
3948 @opindex Wnested-externs
3949 @opindex Wno-nested-externs
3950 Warn if an @code{extern} declaration is encountered within a function.
3952 @item -Wunreachable-code
3953 @opindex Wunreachable-code
3954 @opindex Wno-unreachable-code
3955 Warn if the compiler detects that code will never be executed.
3957 This option is intended to warn when the compiler detects that at
3958 least a whole line of source code will never be executed, because
3959 some condition is never satisfied or because it is after a
3960 procedure that never returns.
3962 It is possible for this option to produce a warning even though there
3963 are circumstances under which part of the affected line can be executed,
3964 so care should be taken when removing apparently-unreachable code.
3966 For instance, when a function is inlined, a warning may mean that the
3967 line is unreachable in only one inlined copy of the function.
3969 This option is not made part of @option{-Wall} because in a debugging
3970 version of a program there is often substantial code which checks
3971 correct functioning of the program and is, hopefully, unreachable
3972 because the program does work. Another common use of unreachable
3973 code is to provide behavior which is selectable at compile-time.
3978 Warn if a function can not be inlined and it was declared as inline.
3979 Even with this option, the compiler will not warn about failures to
3980 inline functions declared in system headers.
3982 The compiler uses a variety of heuristics to determine whether or not
3983 to inline a function. For example, the compiler takes into account
3984 the size of the function being inlined and the amount of inlining
3985 that has already been done in the current function. Therefore,
3986 seemingly insignificant changes in the source program can cause the
3987 warnings produced by @option{-Winline} to appear or disappear.
3989 @item -Wno-invalid-offsetof @r{(C++ and Objective-C++ only)}
3990 @opindex Wno-invalid-offsetof
3991 @opindex Winvalid-offsetof
3992 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
3993 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
3994 to a non-POD type is undefined. In existing C++ implementations,
3995 however, @samp{offsetof} typically gives meaningful results even when
3996 applied to certain kinds of non-POD types. (Such as a simple
3997 @samp{struct} that fails to be a POD type only by virtue of having a
3998 constructor.) This flag is for users who are aware that they are
3999 writing nonportable code and who have deliberately chosen to ignore the
4002 The restrictions on @samp{offsetof} may be relaxed in a future version
4003 of the C++ standard.
4005 @item -Wno-int-to-pointer-cast @r{(C and Objective-C only)}
4006 @opindex Wno-int-to-pointer-cast
4007 @opindex Wint-to-pointer-cast
4008 Suppress warnings from casts to pointer type of an integer of a
4011 @item -Wno-pointer-to-int-cast @r{(C and Objective-C only)}
4012 @opindex Wno-pointer-to-int-cast
4013 @opindex Wpointer-to-int-cast
4014 Suppress warnings from casts from a pointer to an integer type of a
4018 @opindex Winvalid-pch
4019 @opindex Wno-invalid-pch
4020 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
4021 the search path but can't be used.
4025 @opindex Wno-long-long
4026 Warn if @samp{long long} type is used. This is default. To inhibit
4027 the warning messages, use @option{-Wno-long-long}. Flags
4028 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
4029 only when @option{-pedantic} flag is used.
4031 @item -Wvariadic-macros
4032 @opindex Wvariadic-macros
4033 @opindex Wno-variadic-macros
4034 Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU
4035 alternate syntax when in pedantic ISO C99 mode. This is default.
4036 To inhibit the warning messages, use @option{-Wno-variadic-macros}.
4041 Warn if variable length array is used in the code.
4042 @option{-Wno-vla} will prevent the @option{-pedantic} warning of
4043 the variable length array.
4045 @item -Wvolatile-register-var
4046 @opindex Wvolatile-register-var
4047 @opindex Wno-volatile-register-var
4048 Warn if a register variable is declared volatile. The volatile
4049 modifier does not inhibit all optimizations that may eliminate reads
4050 and/or writes to register variables. This warning is enabled by
4053 @item -Wdisabled-optimization
4054 @opindex Wdisabled-optimization
4055 @opindex Wno-disabled-optimization
4056 Warn if a requested optimization pass is disabled. This warning does
4057 not generally indicate that there is anything wrong with your code; it
4058 merely indicates that GCC's optimizers were unable to handle the code
4059 effectively. Often, the problem is that your code is too big or too
4060 complex; GCC will refuse to optimize programs when the optimization
4061 itself is likely to take inordinate amounts of time.
4063 @item -Wpointer-sign @r{(C and Objective-C only)}
4064 @opindex Wpointer-sign
4065 @opindex Wno-pointer-sign
4066 Warn for pointer argument passing or assignment with different signedness.
4067 This option is only supported for C and Objective-C@. It is implied by
4068 @option{-Wall} and by @option{-pedantic}, which can be disabled with
4069 @option{-Wno-pointer-sign}.
4071 @item -Wstack-protector
4072 @opindex Wstack-protector
4073 @opindex Wno-stack-protector
4074 This option is only active when @option{-fstack-protector} is active. It
4075 warns about functions that will not be protected against stack smashing.
4078 @opindex Wno-mudflap
4079 Suppress warnings about constructs that cannot be instrumented by
4082 @item -Woverlength-strings
4083 @opindex Woverlength-strings
4084 @opindex Wno-overlength-strings
4085 Warn about string constants which are longer than the ``minimum
4086 maximum'' length specified in the C standard. Modern compilers
4087 generally allow string constants which are much longer than the
4088 standard's minimum limit, but very portable programs should avoid
4089 using longer strings.
4091 The limit applies @emph{after} string constant concatenation, and does
4092 not count the trailing NUL@. In C89, the limit was 509 characters; in
4093 C99, it was raised to 4095. C++98 does not specify a normative
4094 minimum maximum, so we do not diagnose overlength strings in C++@.
4096 This option is implied by @option{-pedantic}, and can be disabled with
4097 @option{-Wno-overlength-strings}.
4099 @item -Wdisallowed-function-list=@var{sym},@var{sym},@dots{}
4100 @opindex Wdisallowed-function-list
4102 If any of @var{sym} is called, GCC will issue a warning. This can be useful
4103 in enforcing coding conventions that ban calls to certain functions, for
4104 example, @code{alloca}, @code{malloc}, etc.
4107 @node Debugging Options
4108 @section Options for Debugging Your Program or GCC
4109 @cindex options, debugging
4110 @cindex debugging information options
4112 GCC has various special options that are used for debugging
4113 either your program or GCC:
4118 Produce debugging information in the operating system's native format
4119 (stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging
4122 On most systems that use stabs format, @option{-g} enables use of extra
4123 debugging information that only GDB can use; this extra information
4124 makes debugging work better in GDB but will probably make other debuggers
4126 refuse to read the program. If you want to control for certain whether
4127 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
4128 @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
4130 GCC allows you to use @option{-g} with
4131 @option{-O}. The shortcuts taken by optimized code may occasionally
4132 produce surprising results: some variables you declared may not exist
4133 at all; flow of control may briefly move where you did not expect it;
4134 some statements may not be executed because they compute constant
4135 results or their values were already at hand; some statements may
4136 execute in different places because they were moved out of loops.
4138 Nevertheless it proves possible to debug optimized output. This makes
4139 it reasonable to use the optimizer for programs that might have bugs.
4141 The following options are useful when GCC is generated with the
4142 capability for more than one debugging format.
4146 Produce debugging information for use by GDB@. This means to use the
4147 most expressive format available (DWARF 2, stabs, or the native format
4148 if neither of those are supported), including GDB extensions if at all
4153 Produce debugging information in stabs format (if that is supported),
4154 without GDB extensions. This is the format used by DBX on most BSD
4155 systems. On MIPS, Alpha and System V Release 4 systems this option
4156 produces stabs debugging output which is not understood by DBX or SDB@.
4157 On System V Release 4 systems this option requires the GNU assembler.
4159 @item -feliminate-unused-debug-symbols
4160 @opindex feliminate-unused-debug-symbols
4161 Produce debugging information in stabs format (if that is supported),
4162 for only symbols that are actually used.
4164 @item -femit-class-debug-always
4165 Instead of emitting debugging information for a C++ class in only one
4166 object file, emit it in all object files using the class. This option
4167 should be used only with debuggers that are unable to handle the way GCC
4168 normally emits debugging information for classes because using this
4169 option will increase the size of debugging information by as much as a
4174 Produce debugging information in stabs format (if that is supported),
4175 using GNU extensions understood only by the GNU debugger (GDB)@. The
4176 use of these extensions is likely to make other debuggers crash or
4177 refuse to read the program.
4181 Produce debugging information in COFF format (if that is supported).
4182 This is the format used by SDB on most System V systems prior to
4187 Produce debugging information in XCOFF format (if that is supported).
4188 This is the format used by the DBX debugger on IBM RS/6000 systems.
4192 Produce debugging information in XCOFF format (if that is supported),
4193 using GNU extensions understood only by the GNU debugger (GDB)@. The
4194 use of these extensions is likely to make other debuggers crash or
4195 refuse to read the program, and may cause assemblers other than the GNU
4196 assembler (GAS) to fail with an error.
4200 Produce debugging information in DWARF version 2 format (if that is
4201 supported). This is the format used by DBX on IRIX 6. With this
4202 option, GCC uses features of DWARF version 3 when they are useful;
4203 version 3 is upward compatible with version 2, but may still cause
4204 problems for older debuggers.
4208 Produce debugging information in VMS debug format (if that is
4209 supported). This is the format used by DEBUG on VMS systems.
4212 @itemx -ggdb@var{level}
4213 @itemx -gstabs@var{level}
4214 @itemx -gcoff@var{level}
4215 @itemx -gxcoff@var{level}
4216 @itemx -gvms@var{level}
4217 Request debugging information and also use @var{level} to specify how
4218 much information. The default level is 2.
4220 Level 0 produces no debug information at all. Thus, @option{-g0} negates
4223 Level 1 produces minimal information, enough for making backtraces in
4224 parts of the program that you don't plan to debug. This includes
4225 descriptions of functions and external variables, but no information
4226 about local variables and no line numbers.
4228 Level 3 includes extra information, such as all the macro definitions
4229 present in the program. Some debuggers support macro expansion when
4230 you use @option{-g3}.
4232 @option{-gdwarf-2} does not accept a concatenated debug level, because
4233 GCC used to support an option @option{-gdwarf} that meant to generate
4234 debug information in version 1 of the DWARF format (which is very
4235 different from version 2), and it would have been too confusing. That
4236 debug format is long obsolete, but the option cannot be changed now.
4237 Instead use an additional @option{-g@var{level}} option to change the
4238 debug level for DWARF2.
4240 @item -feliminate-dwarf2-dups
4241 @opindex feliminate-dwarf2-dups
4242 Compress DWARF2 debugging information by eliminating duplicated
4243 information about each symbol. This option only makes sense when
4244 generating DWARF2 debugging information with @option{-gdwarf-2}.
4246 @item -femit-struct-debug-baseonly
4247 Emit debug information for struct-like types
4248 only when the base name of the compilation source file
4249 matches the base name of file in which the struct was defined.
4251 This option substantially reduces the size of debugging information,
4252 but at significant potential loss in type information to the debugger.
4253 See @option{-femit-struct-debug-reduced} for a less aggressive option.
4254 See @option{-femit-struct-debug-detailed} for more detailed control.
4256 This option works only with DWARF 2.
4258 @item -femit-struct-debug-reduced
4259 Emit debug information for struct-like types
4260 only when the base name of the compilation source file
4261 matches the base name of file in which the type was defined,
4262 unless the struct is a template or defined in a system header.
4264 This option significantly reduces the size of debugging information,
4265 with some potential loss in type information to the debugger.
4266 See @option{-femit-struct-debug-baseonly} for a more aggressive option.
4267 See @option{-femit-struct-debug-detailed} for more detailed control.
4269 This option works only with DWARF 2.
4271 @item -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]}
4272 Specify the struct-like types
4273 for which the compiler will generate debug information.
4274 The intent is to reduce duplicate struct debug information
4275 between different object files within the same program.
4277 This option is a detailed version of
4278 @option{-femit-struct-debug-reduced} and @option{-femit-struct-debug-baseonly},
4279 which will serve for most needs.
4281 A specification has the syntax
4282 [@samp{dir:}|@samp{ind:}][@samp{ord:}|@samp{gen:}](@samp{any}|@samp{sys}|@samp{base}|@samp{none})
4284 The optional first word limits the specification to
4285 structs that are used directly (@samp{dir:}) or used indirectly (@samp{ind:}).
4286 A struct type is used directly when it is the type of a variable, member.
4287 Indirect uses arise through pointers to structs.
4288 That is, when use of an incomplete struct would be legal, the use is indirect.
4290 @samp{struct one direct; struct two * indirect;}.
4292 The optional second word limits the specification to
4293 ordinary structs (@samp{ord:}) or generic structs (@samp{gen:}).
4294 Generic structs are a bit complicated to explain.
4295 For C++, these are non-explicit specializations of template classes,
4296 or non-template classes within the above.
4297 Other programming languages have generics,
4298 but @samp{-femit-struct-debug-detailed} does not yet implement them.
4300 The third word specifies the source files for those
4301 structs for which the compiler will emit debug information.
4302 The values @samp{none} and @samp{any} have the normal meaning.
4303 The value @samp{base} means that
4304 the base of name of the file in which the type declaration appears
4305 must match the base of the name of the main compilation file.
4306 In practice, this means that
4307 types declared in @file{foo.c} and @file{foo.h} will have debug information,
4308 but types declared in other header will not.
4309 The value @samp{sys} means those types satisfying @samp{base}
4310 or declared in system or compiler headers.
4312 You may need to experiment to determine the best settings for your application.
4314 The default is @samp{-femit-struct-debug-detailed=all}.
4316 This option works only with DWARF 2.
4318 @item -fno-merge-debug-strings
4319 @opindex fmerge-debug-strings
4320 @opindex fno-merge-debug-strings
4321 Direct the linker to merge together strings which are identical in
4322 different object files. This is not supported by all assemblers or
4323 linker. This decreases the size of the debug information in the
4324 output file at the cost of increasing link processing time. This is
4327 @item -fdebug-prefix-map=@var{old}=@var{new}
4328 @opindex fdebug-prefix-map
4329 When compiling files in directory @file{@var{old}}, record debugging
4330 information describing them as in @file{@var{new}} instead.
4332 @cindex @command{prof}
4335 Generate extra code to write profile information suitable for the
4336 analysis program @command{prof}. You must use this option when compiling
4337 the source files you want data about, and you must also use it when
4340 @cindex @command{gprof}
4343 Generate extra code to write profile information suitable for the
4344 analysis program @command{gprof}. You must use this option when compiling
4345 the source files you want data about, and you must also use it when
4350 Makes the compiler print out each function name as it is compiled, and
4351 print some statistics about each pass when it finishes.
4354 @opindex ftime-report
4355 Makes the compiler print some statistics about the time consumed by each
4356 pass when it finishes.
4359 @opindex fmem-report
4360 Makes the compiler print some statistics about permanent memory
4361 allocation when it finishes.
4363 @item -fpre-ipa-mem-report
4364 @opindex fpre-ipa-mem-report
4365 @item -fpost-ipa-mem-report
4366 @opindex fpost-ipa-mem-report
4367 Makes the compiler print some statistics about permanent memory
4368 allocation before or after interprocedural optimization.
4370 @item -fprofile-arcs
4371 @opindex fprofile-arcs
4372 Add code so that program flow @dfn{arcs} are instrumented. During
4373 execution the program records how many times each branch and call is
4374 executed and how many times it is taken or returns. When the compiled
4375 program exits it saves this data to a file called
4376 @file{@var{auxname}.gcda} for each source file. The data may be used for
4377 profile-directed optimizations (@option{-fbranch-probabilities}), or for
4378 test coverage analysis (@option{-ftest-coverage}). Each object file's
4379 @var{auxname} is generated from the name of the output file, if
4380 explicitly specified and it is not the final executable, otherwise it is
4381 the basename of the source file. In both cases any suffix is removed
4382 (e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
4383 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
4384 @xref{Cross-profiling}.
4386 @cindex @command{gcov}
4390 This option is used to compile and link code instrumented for coverage
4391 analysis. The option is a synonym for @option{-fprofile-arcs}
4392 @option{-ftest-coverage} (when compiling) and @option{-lgcov} (when
4393 linking). See the documentation for those options for more details.
4398 Compile the source files with @option{-fprofile-arcs} plus optimization
4399 and code generation options. For test coverage analysis, use the
4400 additional @option{-ftest-coverage} option. You do not need to profile
4401 every source file in a program.
4404 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
4405 (the latter implies the former).
4408 Run the program on a representative workload to generate the arc profile
4409 information. This may be repeated any number of times. You can run
4410 concurrent instances of your program, and provided that the file system
4411 supports locking, the data files will be correctly updated. Also
4412 @code{fork} calls are detected and correctly handled (double counting
4416 For profile-directed optimizations, compile the source files again with
4417 the same optimization and code generation options plus
4418 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
4419 Control Optimization}).
4422 For test coverage analysis, use @command{gcov} to produce human readable
4423 information from the @file{.gcno} and @file{.gcda} files. Refer to the
4424 @command{gcov} documentation for further information.
4428 With @option{-fprofile-arcs}, for each function of your program GCC
4429 creates a program flow graph, then finds a spanning tree for the graph.
4430 Only arcs that are not on the spanning tree have to be instrumented: the
4431 compiler adds code to count the number of times that these arcs are
4432 executed. When an arc is the only exit or only entrance to a block, the
4433 instrumentation code can be added to the block; otherwise, a new basic
4434 block must be created to hold the instrumentation code.
4437 @item -ftest-coverage
4438 @opindex ftest-coverage
4439 Produce a notes file that the @command{gcov} code-coverage utility
4440 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
4441 show program coverage. Each source file's note file is called
4442 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
4443 above for a description of @var{auxname} and instructions on how to
4444 generate test coverage data. Coverage data will match the source files
4445 more closely, if you do not optimize.
4447 @item -fdbg-cnt-list
4448 @opindex fdbg-cnt-list
4449 Print the name and the counter upperbound for all debug counters.
4451 @item -fdbg-cnt=@var{counter-value-list}
4453 Set the internal debug counter upperbound. @var{counter-value-list}
4454 is a comma-separated list of @var{name}:@var{value} pairs
4455 which sets the upperbound of each debug counter @var{name} to @var{value}.
4456 All debug counters have the initial upperbound of @var{UINT_MAX},
4457 thus dbg_cnt() returns true always unless the upperbound is set by this option.
4458 e.g. With -fdbg-cnt=dce:10,tail_call:0
4459 dbg_cnt(dce) will return true only for first 10 invocations
4460 and dbg_cnt(tail_call) will return false always.
4462 @item -d@var{letters}
4463 @itemx -fdump-rtl-@var{pass}
4465 Says to make debugging dumps during compilation at times specified by
4466 @var{letters}. This is used for debugging the RTL-based passes of the
4467 compiler. The file names for most of the dumps are made by appending a
4468 pass number and a word to the @var{dumpname}. @var{dumpname} is generated
4469 from the name of the output file, if explicitly specified and it is not
4470 an executable, otherwise it is the basename of the source file. These
4471 switches may have different effects when @option{-E} is used for
4474 Most debug dumps can be enabled either passing a letter to the @option{-d}
4475 option, or with a long @option{-fdump-rtl} switch; here are the possible
4476 letters for use in @var{letters} and @var{pass}, and their meanings:
4481 Annotate the assembler output with miscellaneous debugging information.
4483 @item -fdump-rtl-bbro
4484 @opindex fdump-rtl-bbro
4485 Dump after block reordering, to @file{@var{file}.148r.bbro}.
4487 @item -fdump-rtl-combine
4488 @opindex fdump-rtl-combine
4489 Dump after the RTL instruction combination pass, to the file
4490 @file{@var{file}.129r.combine}.
4492 @item -fdump-rtl-ce1
4493 @itemx -fdump-rtl-ce2
4494 @opindex fdump-rtl-ce1
4495 @opindex fdump-rtl-ce2
4496 @option{-fdump-rtl-ce1} enable dumping after the
4497 first if conversion, to the file @file{@var{file}.117r.ce1}.
4498 @option{-fdump-rtl-ce2} enable dumping after the second if
4499 conversion, to the file @file{@var{file}.130r.ce2}.
4501 @item -fdump-rtl-btl
4502 @itemx -fdump-rtl-dbr
4503 @opindex fdump-rtl-btl
4504 @opindex fdump-rtl-dbr
4505 @option{-fdump-rtl-btl} enable dumping after branch
4506 target load optimization, to @file{@var{file}.31.btl}.
4507 @option{-fdump-rtl-dbr} enable dumping after delayed branch
4508 scheduling, to @file{@var{file}.36.dbr}.
4512 Dump all macro definitions, at the end of preprocessing, in addition to
4515 @item -fdump-rtl-ce3
4516 @opindex fdump-rtl-ce3
4517 Dump after the third if conversion, to @file{@var{file}.146r.ce3}.
4519 @item -fdump-rtl-cfg
4520 @itemx -fdump-rtl-life
4521 @opindex fdump-rtl-cfg
4522 @opindex fdump-rtl-life
4523 @option{-fdump-rtl-cfg} enable dumping after control
4524 and data flow analysis, to @file{@var{file}.116r.cfg}.
4525 @option{-fdump-rtl-cfg} enable dumping dump after life analysis,
4526 to @file{@var{file}.128r.life1} and @file{@var{file}.135r.life2}.
4528 @item -fdump-rtl-greg
4529 @opindex fdump-rtl-greg
4530 Dump after global register allocation, to @file{@var{file}.139r.greg}.
4532 @item -fdump-rtl-gcse
4533 @itemx -fdump-rtl-bypass
4534 @opindex fdump-rtl-gcse
4535 @opindex fdump-rtl-bypass
4536 @option{-fdump-rtl-gcse} enable dumping after GCSE, to
4537 @file{@var{file}.114r.gcse}. @option{-fdump-rtl-bypass}
4538 enable dumping after jump bypassing and control flow optimizations, to
4539 @file{@var{file}.115r.bypass}.
4542 @opindex fdump-rtl-eh
4543 Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
4545 @item -fdump-rtl-sibling
4546 @opindex fdump-rtl-sibling
4547 Dump after sibling call optimizations, to @file{@var{file}.106r.sibling}.
4549 @item -fdump-rtl-jump
4550 @opindex fdump-rtl-jump
4551 Dump after the first jump optimization, to @file{@var{file}.112r.jump}.
4553 @item -fdump-rtl-stack
4554 @opindex fdump-rtl-stack
4555 Dump after conversion from GCC's "flat register file" registers to the
4556 x87's stack-like registers, to @file{@var{file}.152r.stack}.
4558 @item -fdump-rtl-lreg
4559 @opindex fdump-rtl-lreg
4560 Dump after local register allocation, to @file{@var{file}.138r.lreg}.
4562 @item -fdump-rtl-loop2
4563 @opindex fdump-rtl-loop2
4564 @option{-dL} and @option{-fdump-rtl-loop2} enable dumping after the
4565 loop optimization pass, to @file{@var{file}.119r.loop2},
4566 @file{@var{file}.120r.loop2_init},
4567 @file{@var{file}.121r.loop2_invariant}, and
4568 @file{@var{file}.125r.loop2_done}.
4570 @item -fdump-rtl-sms
4571 @opindex fdump-rtl-sms
4572 Dump after modulo scheduling, to @file{@var{file}.136r.sms}.
4574 @item -fdump-rtl-mach
4575 @opindex fdump-rtl-mach
4576 Dump after performing the machine dependent reorganization pass, to
4577 @file{@var{file}.155r.mach} if that pass exists.
4579 @item -fdump-rtl-rnreg
4580 @opindex fdump-rtl-rnreg
4581 Dump after register renumbering, to @file{@var{file}.147r.rnreg}.
4583 @item -fdump-rtl-regmove
4584 @opindex fdump-rtl-regmove
4585 Dump after the register move pass, to @file{@var{file}.132r.regmove}.
4587 @item -fdump-rtl-postreload
4588 @opindex fdump-rtl-postreload
4589 Dump after post-reload optimizations, to @file{@var{file}.24.postreload}.
4591 @item -fdump-rtl-expand
4592 @opindex fdump-rtl-expand
4593 Dump after RTL generation, to @file{@var{file}.104r.expand}.
4595 @item -fdump-rtl-sched2
4596 @opindex fdump-rtl-sched2
4597 Dump after the second scheduling pass, to @file{@var{file}.149r.sched2}.
4599 @item -fdump-rtl-cse
4600 @opindex fdump-rtl-cse
4601 Dump after CSE (including the jump optimization that sometimes follows
4602 CSE), to @file{@var{file}.113r.cse}.
4604 @item -fdump-rtl-sched1
4605 @opindex fdump-rtl-sched1
4606 Dump after the first scheduling pass, to @file{@var{file}.136r.sched1}.
4608 @item -fdump-rtl-cse2
4609 @opindex fdump-rtl-cse2
4610 Dump after the second CSE pass (including the jump optimization that
4611 sometimes follows CSE), to @file{@var{file}.127r.cse2}.
4613 @item -fdump-rtl-tracer
4614 @opindex fdump-rtl-tracer
4615 Dump after running tracer, to @file{@var{file}.118r.tracer}.
4617 @item -fdump-rtl-vpt
4618 @itemx -fdump-rtl-vartrack
4619 @opindex fdump-rtl-vpt
4620 @opindex fdump-rtl-vartrack
4621 @option{-fdump-rtl-vpt} enable dumping after the value
4622 profile transformations, to @file{@var{file}.10.vpt}.
4623 @option{-fdump-rtl-vartrack} enable dumping after variable tracking,
4624 to @file{@var{file}.154r.vartrack}.
4626 @item -fdump-rtl-flow2
4627 @opindex fdump-rtl-flow2
4628 Dump after the second flow pass, to @file{@var{file}.142r.flow2}.
4630 @item -fdump-rtl-peephole2
4631 @opindex fdump-rtl-peephole2
4632 Dump after the peephole pass, to @file{@var{file}.145r.peephole2}.
4634 @item -fdump-rtl-web
4635 @opindex fdump-rtl-web
4636 Dump after live range splitting, to @file{@var{file}.126r.web}.
4638 @item -fdump-rtl-all
4639 @opindex fdump-rtl-all
4640 Produce all the dumps listed above.
4644 Produce a core dump whenever an error occurs.
4648 Print statistics on memory usage, at the end of the run, to
4653 Annotate the assembler output with a comment indicating which
4654 pattern and alternative was used. The length of each instruction is
4659 Dump the RTL in the assembler output as a comment before each instruction.
4660 Also turns on @option{-dp} annotation.
4664 For each of the other indicated dump files (either with @option{-d} or
4665 @option{-fdump-rtl-@var{pass}}), dump a representation of the control flow
4666 graph suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
4670 Just generate RTL for a function instead of compiling it. Usually used
4671 with @samp{r} (@option{-fdump-rtl-expand}).
4675 Dump debugging information during parsing, to standard error.
4679 @opindex fdump-noaddr
4680 When doing debugging dumps (see @option{-d} option above), suppress
4681 address output. This makes it more feasible to use diff on debugging
4682 dumps for compiler invocations with different compiler binaries and/or
4683 different text / bss / data / heap / stack / dso start locations.
4685 @item -fdump-unnumbered
4686 @opindex fdump-unnumbered
4687 When doing debugging dumps (see @option{-d} option above), suppress instruction
4688 numbers and address output. This makes it more feasible to
4689 use diff on debugging dumps for compiler invocations with different
4690 options, in particular with and without @option{-g}.
4692 @item -fdump-translation-unit @r{(C++ only)}
4693 @itemx -fdump-translation-unit-@var{options} @r{(C++ only)}
4694 @opindex fdump-translation-unit
4695 Dump a representation of the tree structure for the entire translation
4696 unit to a file. The file name is made by appending @file{.tu} to the
4697 source file name. If the @samp{-@var{options}} form is used, @var{options}
4698 controls the details of the dump as described for the
4699 @option{-fdump-tree} options.
4701 @item -fdump-class-hierarchy @r{(C++ only)}
4702 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
4703 @opindex fdump-class-hierarchy
4704 Dump a representation of each class's hierarchy and virtual function
4705 table layout to a file. The file name is made by appending @file{.class}
4706 to the source file name. If the @samp{-@var{options}} form is used,
4707 @var{options} controls the details of the dump as described for the
4708 @option{-fdump-tree} options.
4710 @item -fdump-ipa-@var{switch}
4712 Control the dumping at various stages of inter-procedural analysis
4713 language tree to a file. The file name is generated by appending a switch
4714 specific suffix to the source file name. The following dumps are possible:
4718 Enables all inter-procedural analysis dumps.
4721 Dumps information about call-graph optimization, unused function removal,
4722 and inlining decisions.
4725 Dump after function inlining.
4729 @item -fdump-statistics-@var{option}
4730 @opindex -fdump-statistics
4731 Enable and control dumping of pass statistics in a separate file. The
4732 file name is generated by appending a suffix ending in @samp{.statistics}
4733 to the source file name. If the @samp{-@var{option}} form is used,
4734 @samp{-stats} will cause counters to be summed over the whole compilation unit
4735 while @samp{-details} will dump every event as the passes generate them.
4736 The default with no option is to sum counters for each function compiled.
4738 @item -fdump-tree-@var{switch}
4739 @itemx -fdump-tree-@var{switch}-@var{options}
4741 Control the dumping at various stages of processing the intermediate
4742 language tree to a file. The file name is generated by appending a switch
4743 specific suffix to the source file name. If the @samp{-@var{options}}
4744 form is used, @var{options} is a list of @samp{-} separated options that
4745 control the details of the dump. Not all options are applicable to all
4746 dumps, those which are not meaningful will be ignored. The following
4747 options are available
4751 Print the address of each node. Usually this is not meaningful as it
4752 changes according to the environment and source file. Its primary use
4753 is for tying up a dump file with a debug environment.
4755 Inhibit dumping of members of a scope or body of a function merely
4756 because that scope has been reached. Only dump such items when they
4757 are directly reachable by some other path. When dumping pretty-printed
4758 trees, this option inhibits dumping the bodies of control structures.
4760 Print a raw representation of the tree. By default, trees are
4761 pretty-printed into a C-like representation.
4763 Enable more detailed dumps (not honored by every dump option).
4765 Enable dumping various statistics about the pass (not honored by every dump
4768 Enable showing basic block boundaries (disabled in raw dumps).
4770 Enable showing virtual operands for every statement.
4772 Enable showing line numbers for statements.
4774 Enable showing the unique ID (@code{DECL_UID}) for each variable.
4776 Enable showing the tree dump for each statement.
4778 Turn on all options, except @option{raw}, @option{slim}, @option{verbose}
4779 and @option{lineno}.
4782 The following tree dumps are possible:
4786 Dump before any tree based optimization, to @file{@var{file}.original}.
4789 Dump after all tree based optimization, to @file{@var{file}.optimized}.
4792 @opindex fdump-tree-gimple
4793 Dump each function before and after the gimplification pass to a file. The
4794 file name is made by appending @file{.gimple} to the source file name.
4797 @opindex fdump-tree-cfg
4798 Dump the control flow graph of each function to a file. The file name is
4799 made by appending @file{.cfg} to the source file name.
4802 @opindex fdump-tree-vcg
4803 Dump the control flow graph of each function to a file in VCG format. The
4804 file name is made by appending @file{.vcg} to the source file name. Note
4805 that if the file contains more than one function, the generated file cannot
4806 be used directly by VCG@. You will need to cut and paste each function's
4807 graph into its own separate file first.
4810 @opindex fdump-tree-ch
4811 Dump each function after copying loop headers. The file name is made by
4812 appending @file{.ch} to the source file name.
4815 @opindex fdump-tree-ssa
4816 Dump SSA related information to a file. The file name is made by appending
4817 @file{.ssa} to the source file name.
4820 @opindex fdump-tree-alias
4821 Dump aliasing information for each function. The file name is made by
4822 appending @file{.alias} to the source file name.
4825 @opindex fdump-tree-ccp
4826 Dump each function after CCP@. The file name is made by appending
4827 @file{.ccp} to the source file name.
4830 @opindex fdump-tree-storeccp
4831 Dump each function after STORE-CCP@. The file name is made by appending
4832 @file{.storeccp} to the source file name.
4835 @opindex fdump-tree-pre
4836 Dump trees after partial redundancy elimination. The file name is made
4837 by appending @file{.pre} to the source file name.
4840 @opindex fdump-tree-fre
4841 Dump trees after full redundancy elimination. The file name is made
4842 by appending @file{.fre} to the source file name.
4845 @opindex fdump-tree-copyprop
4846 Dump trees after copy propagation. The file name is made
4847 by appending @file{.copyprop} to the source file name.
4849 @item store_copyprop
4850 @opindex fdump-tree-store_copyprop
4851 Dump trees after store copy-propagation. The file name is made
4852 by appending @file{.store_copyprop} to the source file name.
4855 @opindex fdump-tree-dce
4856 Dump each function after dead code elimination. The file name is made by
4857 appending @file{.dce} to the source file name.
4860 @opindex fdump-tree-mudflap
4861 Dump each function after adding mudflap instrumentation. The file name is
4862 made by appending @file{.mudflap} to the source file name.
4865 @opindex fdump-tree-sra
4866 Dump each function after performing scalar replacement of aggregates. The
4867 file name is made by appending @file{.sra} to the source file name.
4870 @opindex fdump-tree-sink
4871 Dump each function after performing code sinking. The file name is made
4872 by appending @file{.sink} to the source file name.
4875 @opindex fdump-tree-dom
4876 Dump each function after applying dominator tree optimizations. The file
4877 name is made by appending @file{.dom} to the source file name.
4880 @opindex fdump-tree-dse
4881 Dump each function after applying dead store elimination. The file
4882 name is made by appending @file{.dse} to the source file name.
4885 @opindex fdump-tree-phiopt
4886 Dump each function after optimizing PHI nodes into straightline code. The file
4887 name is made by appending @file{.phiopt} to the source file name.
4890 @opindex fdump-tree-forwprop
4891 Dump each function after forward propagating single use variables. The file
4892 name is made by appending @file{.forwprop} to the source file name.
4895 @opindex fdump-tree-copyrename
4896 Dump each function after applying the copy rename optimization. The file
4897 name is made by appending @file{.copyrename} to the source file name.
4900 @opindex fdump-tree-nrv
4901 Dump each function after applying the named return value optimization on
4902 generic trees. The file name is made by appending @file{.nrv} to the source
4906 @opindex fdump-tree-vect
4907 Dump each function after applying vectorization of loops. The file name is
4908 made by appending @file{.vect} to the source file name.
4911 @opindex fdump-tree-vrp
4912 Dump each function after Value Range Propagation (VRP). The file name
4913 is made by appending @file{.vrp} to the source file name.
4916 @opindex fdump-tree-all
4917 Enable all the available tree dumps with the flags provided in this option.
4920 @item -ftree-vectorizer-verbose=@var{n}
4921 @opindex ftree-vectorizer-verbose
4922 This option controls the amount of debugging output the vectorizer prints.
4923 This information is written to standard error, unless
4924 @option{-fdump-tree-all} or @option{-fdump-tree-vect} is specified,
4925 in which case it is output to the usual dump listing file, @file{.vect}.
4926 For @var{n}=0 no diagnostic information is reported.
4927 If @var{n}=1 the vectorizer reports each loop that got vectorized,
4928 and the total number of loops that got vectorized.
4929 If @var{n}=2 the vectorizer also reports non-vectorized loops that passed
4930 the first analysis phase (vect_analyze_loop_form) - i.e.@: countable,
4931 inner-most, single-bb, single-entry/exit loops. This is the same verbosity
4932 level that @option{-fdump-tree-vect-stats} uses.
4933 Higher verbosity levels mean either more information dumped for each
4934 reported loop, or same amount of information reported for more loops:
4935 If @var{n}=3, alignment related information is added to the reports.
4936 If @var{n}=4, data-references related information (e.g.@: memory dependences,
4937 memory access-patterns) is added to the reports.
4938 If @var{n}=5, the vectorizer reports also non-vectorized inner-most loops
4939 that did not pass the first analysis phase (i.e., may not be countable, or
4940 may have complicated control-flow).
4941 If @var{n}=6, the vectorizer reports also non-vectorized nested loops.
4942 For @var{n}=7, all the information the vectorizer generates during its
4943 analysis and transformation is reported. This is the same verbosity level
4944 that @option{-fdump-tree-vect-details} uses.
4946 @item -frandom-seed=@var{string}
4947 @opindex frandom-string
4948 This option provides a seed that GCC uses when it would otherwise use
4949 random numbers. It is used to generate certain symbol names
4950 that have to be different in every compiled file. It is also used to
4951 place unique stamps in coverage data files and the object files that
4952 produce them. You can use the @option{-frandom-seed} option to produce
4953 reproducibly identical object files.
4955 The @var{string} should be different for every file you compile.
4957 @item -fsched-verbose=@var{n}
4958 @opindex fsched-verbose
4959 On targets that use instruction scheduling, this option controls the
4960 amount of debugging output the scheduler prints. This information is
4961 written to standard error, unless @option{-dS} or @option{-dR} is
4962 specified, in which case it is output to the usual dump
4963 listing file, @file{.sched} or @file{.sched2} respectively. However
4964 for @var{n} greater than nine, the output is always printed to standard
4967 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
4968 same information as @option{-dRS}. For @var{n} greater than one, it
4969 also output basic block probabilities, detailed ready list information
4970 and unit/insn info. For @var{n} greater than two, it includes RTL
4971 at abort point, control-flow and regions info. And for @var{n} over
4972 four, @option{-fsched-verbose} also includes dependence info.
4976 Store the usual ``temporary'' intermediate files permanently; place them
4977 in the current directory and name them based on the source file. Thus,
4978 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
4979 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
4980 preprocessed @file{foo.i} output file even though the compiler now
4981 normally uses an integrated preprocessor.
4983 When used in combination with the @option{-x} command line option,
4984 @option{-save-temps} is sensible enough to avoid over writing an
4985 input source file with the same extension as an intermediate file.
4986 The corresponding intermediate file may be obtained by renaming the
4987 source file before using @option{-save-temps}.
4991 Report the CPU time taken by each subprocess in the compilation
4992 sequence. For C source files, this is the compiler proper and assembler
4993 (plus the linker if linking is done). The output looks like this:
5000 The first number on each line is the ``user time'', that is time spent
5001 executing the program itself. The second number is ``system time'',
5002 time spent executing operating system routines on behalf of the program.
5003 Both numbers are in seconds.
5005 @item -fvar-tracking
5006 @opindex fvar-tracking
5007 Run variable tracking pass. It computes where variables are stored at each
5008 position in code. Better debugging information is then generated
5009 (if the debugging information format supports this information).
5011 It is enabled by default when compiling with optimization (@option{-Os},
5012 @option{-O}, @option{-O2}, @dots{}), debugging information (@option{-g}) and
5013 the debug info format supports it.
5015 @item -print-file-name=@var{library}
5016 @opindex print-file-name
5017 Print the full absolute name of the library file @var{library} that
5018 would be used when linking---and don't do anything else. With this
5019 option, GCC does not compile or link anything; it just prints the
5022 @item -print-multi-directory
5023 @opindex print-multi-directory
5024 Print the directory name corresponding to the multilib selected by any
5025 other switches present in the command line. This directory is supposed
5026 to exist in @env{GCC_EXEC_PREFIX}.
5028 @item -print-multi-lib
5029 @opindex print-multi-lib
5030 Print the mapping from multilib directory names to compiler switches
5031 that enable them. The directory name is separated from the switches by
5032 @samp{;}, and each switch starts with an @samp{@@} instead of the
5033 @samp{-}, without spaces between multiple switches. This is supposed to
5034 ease shell-processing.
5036 @item -print-prog-name=@var{program}
5037 @opindex print-prog-name
5038 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
5040 @item -print-libgcc-file-name
5041 @opindex print-libgcc-file-name
5042 Same as @option{-print-file-name=libgcc.a}.
5044 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
5045 but you do want to link with @file{libgcc.a}. You can do
5048 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
5051 @item -print-search-dirs
5052 @opindex print-search-dirs
5053 Print the name of the configured installation directory and a list of
5054 program and library directories @command{gcc} will search---and don't do anything else.
5056 This is useful when @command{gcc} prints the error message
5057 @samp{installation problem, cannot exec cpp0: No such file or directory}.
5058 To resolve this you either need to put @file{cpp0} and the other compiler
5059 components where @command{gcc} expects to find them, or you can set the environment
5060 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
5061 Don't forget the trailing @samp{/}.
5062 @xref{Environment Variables}.
5064 @item -print-sysroot
5065 @opindex print-sysroot
5066 Print the target sysroot directory that will be used during
5067 compilation. This is the target sysroot specified either at configure
5068 time or or using the @option{--sysroot} option, possibly with an extra
5069 suffix that depends on compilation options. If no target sysroot is
5070 specified, the option prints nothing.
5072 @item -print-sysroot-headers-suffix
5073 @opindex print-sysroot-headers-suffix
5074 Print the suffix added to the target sysroot when searching for
5075 headers, or give an error if the compiler is not configured with such
5076 a suffix---and don't do anything else.
5079 @opindex dumpmachine
5080 Print the compiler's target machine (for example,
5081 @samp{i686-pc-linux-gnu})---and don't do anything else.
5084 @opindex dumpversion
5085 Print the compiler version (for example, @samp{3.0})---and don't do
5090 Print the compiler's built-in specs---and don't do anything else. (This
5091 is used when GCC itself is being built.) @xref{Spec Files}.
5093 @item -feliminate-unused-debug-types
5094 @opindex feliminate-unused-debug-types
5095 Normally, when producing DWARF2 output, GCC will emit debugging
5096 information for all types declared in a compilation
5097 unit, regardless of whether or not they are actually used
5098 in that compilation unit. Sometimes this is useful, such as
5099 if, in the debugger, you want to cast a value to a type that is
5100 not actually used in your program (but is declared). More often,
5101 however, this results in a significant amount of wasted space.
5102 With this option, GCC will avoid producing debug symbol output
5103 for types that are nowhere used in the source file being compiled.
5106 @node Optimize Options
5107 @section Options That Control Optimization
5108 @cindex optimize options
5109 @cindex options, optimization
5111 These options control various sorts of optimizations.
5113 Without any optimization option, the compiler's goal is to reduce the
5114 cost of compilation and to make debugging produce the expected
5115 results. Statements are independent: if you stop the program with a
5116 breakpoint between statements, you can then assign a new value to any
5117 variable or change the program counter to any other statement in the
5118 function and get exactly the results you would expect from the source
5121 Turning on optimization flags makes the compiler attempt to improve
5122 the performance and/or code size at the expense of compilation time
5123 and possibly the ability to debug the program.
5125 The compiler performs optimization based on the knowledge it has of the
5126 program. Compiling multiple files at once to a single output file mode allows
5127 the compiler to use information gained from all of the files when compiling
5130 Not all optimizations are controlled directly by a flag. Only
5131 optimizations that have a flag are listed.
5138 Optimize. Optimizing compilation takes somewhat more time, and a lot
5139 more memory for a large function.
5141 With @option{-O}, the compiler tries to reduce code size and execution
5142 time, without performing any optimizations that take a great deal of
5145 @option{-O} turns on the following optimization flags:
5148 -fcprop-registers @gol
5151 -fdelayed-branch @gol
5153 -fguess-branch-probability @gol
5154 -fif-conversion2 @gol
5155 -fif-conversion @gol
5156 -finline-small-functions @gol
5157 -fipa-pure-const @gol
5158 -fipa-reference @gol
5160 -fsplit-wide-types @gol
5161 -ftree-builtin-call-dce @gol
5164 -ftree-copyrename @gol
5166 -ftree-dominator-opts @gol
5173 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
5174 where doing so does not interfere with debugging.
5178 Optimize even more. GCC performs nearly all supported optimizations
5179 that do not involve a space-speed tradeoff. The compiler does not
5180 perform loop unrolling or function inlining when you specify @option{-O2}.
5181 As compared to @option{-O}, this option increases both compilation time
5182 and the performance of the generated code.
5184 @option{-O2} turns on all optimization flags specified by @option{-O}. It
5185 also turns on the following optimization flags:
5186 @gccoptlist{-fthread-jumps @gol
5187 -falign-functions -falign-jumps @gol
5188 -falign-loops -falign-labels @gol
5191 -fcse-follow-jumps -fcse-skip-blocks @gol
5192 -fdelete-null-pointer-checks @gol
5193 -fexpensive-optimizations @gol
5194 -fgcse -fgcse-lm @gol
5195 -findirect-inlining @gol
5196 -foptimize-sibling-calls @gol
5199 -freorder-blocks -freorder-functions @gol
5200 -frerun-cse-after-loop @gol
5201 -fsched-interblock -fsched-spec @gol
5202 -fschedule-insns -fschedule-insns2 @gol
5203 -fstrict-aliasing -fstrict-overflow @gol
5204 -ftree-switch-conversion @gol
5208 Please note the warning under @option{-fgcse} about
5209 invoking @option{-O2} on programs that use computed gotos.
5213 Optimize yet more. @option{-O3} turns on all optimizations specified
5214 by @option{-O2} and also turns on the @option{-finline-functions},
5215 @option{-funswitch-loops}, @option{-fpredictive-commoning},
5216 @option{-fgcse-after-reload} and @option{-ftree-vectorize} options.
5220 Reduce compilation time and make debugging produce the expected
5221 results. This is the default.
5225 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
5226 do not typically increase code size. It also performs further
5227 optimizations designed to reduce code size.
5229 @option{-Os} disables the following optimization flags:
5230 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
5231 -falign-labels -freorder-blocks -freorder-blocks-and-partition @gol
5232 -fprefetch-loop-arrays -ftree-vect-loop-version}
5234 If you use multiple @option{-O} options, with or without level numbers,
5235 the last such option is the one that is effective.
5238 Options of the form @option{-f@var{flag}} specify machine-independent
5239 flags. Most flags have both positive and negative forms; the negative
5240 form of @option{-ffoo} would be @option{-fno-foo}. In the table
5241 below, only one of the forms is listed---the one you typically will
5242 use. You can figure out the other form by either removing @samp{no-}
5245 The following options control specific optimizations. They are either
5246 activated by @option{-O} options or are related to ones that are. You
5247 can use the following flags in the rare cases when ``fine-tuning'' of
5248 optimizations to be performed is desired.
5251 @item -fno-default-inline
5252 @opindex fno-default-inline
5253 Do not make member functions inline by default merely because they are
5254 defined inside the class scope (C++ only). Otherwise, when you specify
5255 @w{@option{-O}}, member functions defined inside class scope are compiled
5256 inline by default; i.e., you don't need to add @samp{inline} in front of
5257 the member function name.
5259 @item -fno-defer-pop
5260 @opindex fno-defer-pop
5261 Always pop the arguments to each function call as soon as that function
5262 returns. For machines which must pop arguments after a function call,
5263 the compiler normally lets arguments accumulate on the stack for several
5264 function calls and pops them all at once.
5266 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5268 @item -fforward-propagate
5269 @opindex fforward-propagate
5270 Perform a forward propagation pass on RTL@. The pass tries to combine two
5271 instructions and checks if the result can be simplified. If loop unrolling
5272 is active, two passes are performed and the second is scheduled after
5275 This option is enabled by default at optimization levels @option{-O2},
5276 @option{-O3}, @option{-Os}.
5278 @item -fomit-frame-pointer
5279 @opindex fomit-frame-pointer
5280 Don't keep the frame pointer in a register for functions that
5281 don't need one. This avoids the instructions to save, set up and
5282 restore frame pointers; it also makes an extra register available
5283 in many functions. @strong{It also makes debugging impossible on
5286 On some machines, such as the VAX, this flag has no effect, because
5287 the standard calling sequence automatically handles the frame pointer
5288 and nothing is saved by pretending it doesn't exist. The
5289 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
5290 whether a target machine supports this flag. @xref{Registers,,Register
5291 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
5293 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5295 @item -foptimize-sibling-calls
5296 @opindex foptimize-sibling-calls
5297 Optimize sibling and tail recursive calls.
5299 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5303 Don't pay attention to the @code{inline} keyword. Normally this option
5304 is used to keep the compiler from expanding any functions inline.
5305 Note that if you are not optimizing, no functions can be expanded inline.
5307 @item -finline-small-functions
5308 @opindex finline-small-functions
5309 Integrate functions into their callers when their body is smaller than expected
5310 function call code (so overall size of program gets smaller). The compiler
5311 heuristically decides which functions are simple enough to be worth integrating
5314 Enabled at level @option{-O2}.
5316 @item -findirect-inlining
5317 @opindex findirect-inlining
5318 Inline also indirect calls that are discovered to be known at compile
5319 time thanks to previous inlining. This option has any effect only
5320 when inlining itself is turned on by the @option{-finline-functions}
5321 or @option{-finline-small-functions} options.
5323 Enabled at level @option{-O2}.
5325 @item -finline-functions
5326 @opindex finline-functions
5327 Integrate all simple functions into their callers. The compiler
5328 heuristically decides which functions are simple enough to be worth
5329 integrating in this way.
5331 If all calls to a given function are integrated, and the function is
5332 declared @code{static}, then the function is normally not output as
5333 assembler code in its own right.
5335 Enabled at level @option{-O3}.
5337 @item -finline-functions-called-once
5338 @opindex finline-functions-called-once
5339 Consider all @code{static} functions called once for inlining into their
5340 caller even if they are not marked @code{inline}. If a call to a given
5341 function is integrated, then the function is not output as assembler code
5344 Enabled at levels @option{-O1}, @option{-O2}, @option{-O3} and @option{-Os}.
5346 @item -fearly-inlining
5347 @opindex fearly-inlining
5348 Inline functions marked by @code{always_inline} and functions whose body seems
5349 smaller than the function call overhead early before doing
5350 @option{-fprofile-generate} instrumentation and real inlining pass. Doing so
5351 makes profiling significantly cheaper and usually inlining faster on programs
5352 having large chains of nested wrapper functions.
5356 @item -finline-limit=@var{n}
5357 @opindex finline-limit
5358 By default, GCC limits the size of functions that can be inlined. This flag
5359 allows coarse control of this limit. @var{n} is the size of functions that
5360 can be inlined in number of pseudo instructions.
5362 Inlining is actually controlled by a number of parameters, which may be
5363 specified individually by using @option{--param @var{name}=@var{value}}.
5364 The @option{-finline-limit=@var{n}} option sets some of these parameters
5368 @item max-inline-insns-single
5369 is set to @var{n}/2.
5370 @item max-inline-insns-auto
5371 is set to @var{n}/2.
5374 See below for a documentation of the individual
5375 parameters controlling inlining and for the defaults of these parameters.
5377 @emph{Note:} there may be no value to @option{-finline-limit} that results
5378 in default behavior.
5380 @emph{Note:} pseudo instruction represents, in this particular context, an
5381 abstract measurement of function's size. In no way does it represent a count
5382 of assembly instructions and as such its exact meaning might change from one
5383 release to an another.
5385 @item -fkeep-inline-functions
5386 @opindex fkeep-inline-functions
5387 In C, emit @code{static} functions that are declared @code{inline}
5388 into the object file, even if the function has been inlined into all
5389 of its callers. This switch does not affect functions using the
5390 @code{extern inline} extension in GNU C89@. In C++, emit any and all
5391 inline functions into the object file.
5393 @item -fkeep-static-consts
5394 @opindex fkeep-static-consts
5395 Emit variables declared @code{static const} when optimization isn't turned
5396 on, even if the variables aren't referenced.
5398 GCC enables this option by default. If you want to force the compiler to
5399 check if the variable was referenced, regardless of whether or not
5400 optimization is turned on, use the @option{-fno-keep-static-consts} option.
5402 @item -fmerge-constants
5403 @opindex fmerge-constants
5404 Attempt to merge identical constants (string constants and floating point
5405 constants) across compilation units.
5407 This option is the default for optimized compilation if the assembler and
5408 linker support it. Use @option{-fno-merge-constants} to inhibit this
5411 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5413 @item -fmerge-all-constants
5414 @opindex fmerge-all-constants
5415 Attempt to merge identical constants and identical variables.
5417 This option implies @option{-fmerge-constants}. In addition to
5418 @option{-fmerge-constants} this considers e.g.@: even constant initialized
5419 arrays or initialized constant variables with integral or floating point
5420 types. Languages like C or C++ require each non-automatic variable to
5421 have distinct location, so using this option will result in non-conforming
5424 @item -fmodulo-sched
5425 @opindex fmodulo-sched
5426 Perform swing modulo scheduling immediately before the first scheduling
5427 pass. This pass looks at innermost loops and reorders their
5428 instructions by overlapping different iterations.
5430 @item -fmodulo-sched-allow-regmoves
5431 @opindex fmodulo-sched-allow-regmoves
5432 Perform more aggressive SMS based modulo scheduling with register moves
5433 allowed. By setting this flag certain anti-dependences edges will be
5434 deleted which will trigger the generation of reg-moves based on the
5435 life-range analysis. This option is effective only with
5436 @option{-fmodulo-sched} enabled.
5438 @item -fno-branch-count-reg
5439 @opindex fno-branch-count-reg
5440 Do not use ``decrement and branch'' instructions on a count register,
5441 but instead generate a sequence of instructions that decrement a
5442 register, compare it against zero, then branch based upon the result.
5443 This option is only meaningful on architectures that support such
5444 instructions, which include x86, PowerPC, IA-64 and S/390.
5446 The default is @option{-fbranch-count-reg}.
5448 @item -fno-function-cse
5449 @opindex fno-function-cse
5450 Do not put function addresses in registers; make each instruction that
5451 calls a constant function contain the function's address explicitly.
5453 This option results in less efficient code, but some strange hacks
5454 that alter the assembler output may be confused by the optimizations
5455 performed when this option is not used.
5457 The default is @option{-ffunction-cse}
5459 @item -fno-zero-initialized-in-bss
5460 @opindex fno-zero-initialized-in-bss
5461 If the target supports a BSS section, GCC by default puts variables that
5462 are initialized to zero into BSS@. This can save space in the resulting
5465 This option turns off this behavior because some programs explicitly
5466 rely on variables going to the data section. E.g., so that the
5467 resulting executable can find the beginning of that section and/or make
5468 assumptions based on that.
5470 The default is @option{-fzero-initialized-in-bss}.
5472 @item -fmudflap -fmudflapth -fmudflapir
5476 @cindex bounds checking
5478 For front-ends that support it (C and C++), instrument all risky
5479 pointer/array dereferencing operations, some standard library
5480 string/heap functions, and some other associated constructs with
5481 range/validity tests. Modules so instrumented should be immune to
5482 buffer overflows, invalid heap use, and some other classes of C/C++
5483 programming errors. The instrumentation relies on a separate runtime
5484 library (@file{libmudflap}), which will be linked into a program if
5485 @option{-fmudflap} is given at link time. Run-time behavior of the
5486 instrumented program is controlled by the @env{MUDFLAP_OPTIONS}
5487 environment variable. See @code{env MUDFLAP_OPTIONS=-help a.out}
5490 Use @option{-fmudflapth} instead of @option{-fmudflap} to compile and to
5491 link if your program is multi-threaded. Use @option{-fmudflapir}, in
5492 addition to @option{-fmudflap} or @option{-fmudflapth}, if
5493 instrumentation should ignore pointer reads. This produces less
5494 instrumentation (and therefore faster execution) and still provides
5495 some protection against outright memory corrupting writes, but allows
5496 erroneously read data to propagate within a program.
5498 @item -fthread-jumps
5499 @opindex fthread-jumps
5500 Perform optimizations where we check to see if a jump branches to a
5501 location where another comparison subsumed by the first is found. If
5502 so, the first branch is redirected to either the destination of the
5503 second branch or a point immediately following it, depending on whether
5504 the condition is known to be true or false.
5506 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5508 @item -fsplit-wide-types
5509 @opindex fsplit-wide-types
5510 When using a type that occupies multiple registers, such as @code{long
5511 long} on a 32-bit system, split the registers apart and allocate them
5512 independently. This normally generates better code for those types,
5513 but may make debugging more difficult.
5515 Enabled at levels @option{-O}, @option{-O2}, @option{-O3},
5518 @item -fcse-follow-jumps
5519 @opindex fcse-follow-jumps
5520 In common subexpression elimination (CSE), scan through jump instructions
5521 when the target of the jump is not reached by any other path. For
5522 example, when CSE encounters an @code{if} statement with an
5523 @code{else} clause, CSE will follow the jump when the condition
5526 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5528 @item -fcse-skip-blocks
5529 @opindex fcse-skip-blocks
5530 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
5531 follow jumps which conditionally skip over blocks. When CSE
5532 encounters a simple @code{if} statement with no else clause,
5533 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
5534 body of the @code{if}.
5536 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5538 @item -frerun-cse-after-loop
5539 @opindex frerun-cse-after-loop
5540 Re-run common subexpression elimination after loop optimizations has been
5543 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5547 Perform a global common subexpression elimination pass.
5548 This pass also performs global constant and copy propagation.
5550 @emph{Note:} When compiling a program using computed gotos, a GCC
5551 extension, you may get better runtime performance if you disable
5552 the global common subexpression elimination pass by adding
5553 @option{-fno-gcse} to the command line.
5555 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5559 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
5560 attempt to move loads which are only killed by stores into themselves. This
5561 allows a loop containing a load/store sequence to be changed to a load outside
5562 the loop, and a copy/store within the loop.
5564 Enabled by default when gcse is enabled.
5568 When @option{-fgcse-sm} is enabled, a store motion pass is run after
5569 global common subexpression elimination. This pass will attempt to move
5570 stores out of loops. When used in conjunction with @option{-fgcse-lm},
5571 loops containing a load/store sequence can be changed to a load before
5572 the loop and a store after the loop.
5574 Not enabled at any optimization level.
5578 When @option{-fgcse-las} is enabled, the global common subexpression
5579 elimination pass eliminates redundant loads that come after stores to the
5580 same memory location (both partial and full redundancies).
5582 Not enabled at any optimization level.
5584 @item -fgcse-after-reload
5585 @opindex fgcse-after-reload
5586 When @option{-fgcse-after-reload} is enabled, a redundant load elimination
5587 pass is performed after reload. The purpose of this pass is to cleanup
5590 @item -funsafe-loop-optimizations
5591 @opindex funsafe-loop-optimizations
5592 If given, the loop optimizer will assume that loop indices do not
5593 overflow, and that the loops with nontrivial exit condition are not
5594 infinite. This enables a wider range of loop optimizations even if
5595 the loop optimizer itself cannot prove that these assumptions are valid.
5596 Using @option{-Wunsafe-loop-optimizations}, the compiler will warn you
5597 if it finds this kind of loop.
5599 @item -fcrossjumping
5600 @opindex fcrossjumping
5601 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
5602 resulting code may or may not perform better than without cross-jumping.
5604 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5606 @item -fauto-inc-dec
5607 @opindex fauto-inc-dec
5608 Combine increments or decrements of addresses with memory accesses.
5609 This pass is always skipped on architectures that do not have
5610 instructions to support this. Enabled by default at @option{-O} and
5611 higher on architectures that support this.
5615 Perform dead code elimination (DCE) on RTL@.
5616 Enabled by default at @option{-O} and higher.
5620 Perform dead store elimination (DSE) on RTL@.
5621 Enabled by default at @option{-O} and higher.
5623 @item -fif-conversion
5624 @opindex fif-conversion
5625 Attempt to transform conditional jumps into branch-less equivalents. This
5626 include use of conditional moves, min, max, set flags and abs instructions, and
5627 some tricks doable by standard arithmetics. The use of conditional execution
5628 on chips where it is available is controlled by @code{if-conversion2}.
5630 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5632 @item -fif-conversion2
5633 @opindex fif-conversion2
5634 Use conditional execution (where available) to transform conditional jumps into
5635 branch-less equivalents.
5637 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5639 @item -fdelete-null-pointer-checks
5640 @opindex fdelete-null-pointer-checks
5641 Use global dataflow analysis to identify and eliminate useless checks
5642 for null pointers. The compiler assumes that dereferencing a null
5643 pointer would have halted the program. If a pointer is checked after
5644 it has already been dereferenced, it cannot be null.
5646 In some environments, this assumption is not true, and programs can
5647 safely dereference null pointers. Use
5648 @option{-fno-delete-null-pointer-checks} to disable this optimization
5649 for programs which depend on that behavior.
5651 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5653 @item -fexpensive-optimizations
5654 @opindex fexpensive-optimizations
5655 Perform a number of minor optimizations that are relatively expensive.
5657 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5659 @item -foptimize-register-move
5661 @opindex foptimize-register-move
5663 Attempt to reassign register numbers in move instructions and as
5664 operands of other simple instructions in order to maximize the amount of
5665 register tying. This is especially helpful on machines with two-operand
5668 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
5671 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5673 @item -fdelayed-branch
5674 @opindex fdelayed-branch
5675 If supported for the target machine, attempt to reorder instructions
5676 to exploit instruction slots available after delayed branch
5679 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5681 @item -fschedule-insns
5682 @opindex fschedule-insns
5683 If supported for the target machine, attempt to reorder instructions to
5684 eliminate execution stalls due to required data being unavailable. This
5685 helps machines that have slow floating point or memory load instructions
5686 by allowing other instructions to be issued until the result of the load
5687 or floating point instruction is required.
5689 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5691 @item -fschedule-insns2
5692 @opindex fschedule-insns2
5693 Similar to @option{-fschedule-insns}, but requests an additional pass of
5694 instruction scheduling after register allocation has been done. This is
5695 especially useful on machines with a relatively small number of
5696 registers and where memory load instructions take more than one cycle.
5698 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5700 @item -fno-sched-interblock
5701 @opindex fno-sched-interblock
5702 Don't schedule instructions across basic blocks. This is normally
5703 enabled by default when scheduling before register allocation, i.e.@:
5704 with @option{-fschedule-insns} or at @option{-O2} or higher.
5706 @item -fno-sched-spec
5707 @opindex fno-sched-spec
5708 Don't allow speculative motion of non-load instructions. This is normally
5709 enabled by default when scheduling before register allocation, i.e.@:
5710 with @option{-fschedule-insns} or at @option{-O2} or higher.
5712 @item -fsched-spec-load
5713 @opindex fsched-spec-load
5714 Allow speculative motion of some load instructions. This only makes
5715 sense when scheduling before register allocation, i.e.@: with
5716 @option{-fschedule-insns} or at @option{-O2} or higher.
5718 @item -fsched-spec-load-dangerous
5719 @opindex fsched-spec-load-dangerous
5720 Allow speculative motion of more load instructions. This only makes
5721 sense when scheduling before register allocation, i.e.@: with
5722 @option{-fschedule-insns} or at @option{-O2} or higher.
5724 @item -fsched-stalled-insns
5725 @itemx -fsched-stalled-insns=@var{n}
5726 @opindex fsched-stalled-insns
5727 Define how many insns (if any) can be moved prematurely from the queue
5728 of stalled insns into the ready list, during the second scheduling pass.
5729 @option{-fno-sched-stalled-insns} means that no insns will be moved
5730 prematurely, @option{-fsched-stalled-insns=0} means there is no limit
5731 on how many queued insns can be moved prematurely.
5732 @option{-fsched-stalled-insns} without a value is equivalent to
5733 @option{-fsched-stalled-insns=1}.
5735 @item -fsched-stalled-insns-dep
5736 @itemx -fsched-stalled-insns-dep=@var{n}
5737 @opindex fsched-stalled-insns-dep
5738 Define how many insn groups (cycles) will be examined for a dependency
5739 on a stalled insn that is candidate for premature removal from the queue
5740 of stalled insns. This has an effect only during the second scheduling pass,
5741 and only if @option{-fsched-stalled-insns} is used.
5742 @option{-fno-sched-stalled-insns-dep} is equivalent to
5743 @option{-fsched-stalled-insns-dep=0}.
5744 @option{-fsched-stalled-insns-dep} without a value is equivalent to
5745 @option{-fsched-stalled-insns-dep=1}.
5747 @item -fsched2-use-superblocks
5748 @opindex fsched2-use-superblocks
5749 When scheduling after register allocation, do use superblock scheduling
5750 algorithm. Superblock scheduling allows motion across basic block boundaries
5751 resulting on faster schedules. This option is experimental, as not all machine
5752 descriptions used by GCC model the CPU closely enough to avoid unreliable
5753 results from the algorithm.
5755 This only makes sense when scheduling after register allocation, i.e.@: with
5756 @option{-fschedule-insns2} or at @option{-O2} or higher.
5758 @item -fsched2-use-traces
5759 @opindex fsched2-use-traces
5760 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
5761 allocation and additionally perform code duplication in order to increase the
5762 size of superblocks using tracer pass. See @option{-ftracer} for details on
5765 This mode should produce faster but significantly longer programs. Also
5766 without @option{-fbranch-probabilities} the traces constructed may not
5767 match the reality and hurt the performance. This only makes
5768 sense when scheduling after register allocation, i.e.@: with
5769 @option{-fschedule-insns2} or at @option{-O2} or higher.
5773 Eliminate redundant sign extension instructions and move the non-redundant
5774 ones to optimal placement using lazy code motion (LCM).
5776 @item -freschedule-modulo-scheduled-loops
5777 @opindex freschedule-modulo-scheduled-loops
5778 The modulo scheduling comes before the traditional scheduling, if a loop
5779 was modulo scheduled we may want to prevent the later scheduling passes
5780 from changing its schedule, we use this option to control that.
5782 @item -fcaller-saves
5783 @opindex fcaller-saves
5784 Enable values to be allocated in registers that will be clobbered by
5785 function calls, by emitting extra instructions to save and restore the
5786 registers around such calls. Such allocation is done only when it
5787 seems to result in better code than would otherwise be produced.
5789 This option is always enabled by default on certain machines, usually
5790 those which have no call-preserved registers to use instead.
5792 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5794 @item -ftree-reassoc
5795 @opindex ftree-reassoc
5796 Perform reassociation on trees. This flag is enabled by default
5797 at @option{-O} and higher.
5801 Perform partial redundancy elimination (PRE) on trees. This flag is
5802 enabled by default at @option{-O2} and @option{-O3}.
5806 Perform full redundancy elimination (FRE) on trees. The difference
5807 between FRE and PRE is that FRE only considers expressions
5808 that are computed on all paths leading to the redundant computation.
5809 This analysis is faster than PRE, though it exposes fewer redundancies.
5810 This flag is enabled by default at @option{-O} and higher.
5812 @item -ftree-copy-prop
5813 @opindex ftree-copy-prop
5814 Perform copy propagation on trees. This pass eliminates unnecessary
5815 copy operations. This flag is enabled by default at @option{-O} and
5818 @item -fipa-pure-const
5819 @opindex fipa-pure-const
5820 Discover which functions are pure or constant.
5821 Enabled by default at @option{-O} and higher.
5823 @item -fipa-reference
5824 @opindex fipa-reference
5825 Discover which static variables do not escape cannot escape the
5827 Enabled by default at @option{-O} and higher.
5829 @item -fipa-struct-reorg
5830 @opindex fipa-struct-reorg
5831 Perform structure reorganization optimization, that change C-like structures
5832 layout in order to better utilize spatial locality. This transformation is
5833 affective for programs containing arrays of structures. Available in two
5834 compilation modes: profile-based (enabled with @option{-fprofile-generate})
5835 or static (which uses built-in heuristics). Require @option{-fipa-type-escape}
5836 to provide the safety of this transformation. It works only in whole program
5837 mode, so it requires @option{-fwhole-program} and @option{-combine} to be
5838 enabled. Structures considered @samp{cold} by this transformation are not
5839 affected (see @option{--param struct-reorg-cold-struct-ratio=@var{value}}).
5841 With this flag, the program debug info reflects a new structure layout.
5845 Perform interprocedural pointer analysis. This option is experimental
5846 and does not affect generated code.
5850 Perform interprocedural constant propagation.
5851 This optimization analyzes the program to determine when values passed
5852 to functions are constants and then optimizes accordingly.
5853 This optimization can substantially increase performance
5854 if the application has constants passed to functions, but
5855 because this optimization can create multiple copies of functions,
5856 it may significantly increase code size.
5858 @item -fipa-matrix-reorg
5859 @opindex fipa-matrix-reorg
5860 Perform matrix flattening and transposing.
5861 Matrix flattening tries to replace a m-dimensional matrix
5862 with its equivalent n-dimensional matrix, where n < m.
5863 This reduces the level of indirection needed for accessing the elements
5864 of the matrix. The second optimization is matrix transposing that
5865 attemps to change the order of the matrix's dimensions in order to
5866 improve cache locality.
5867 Both optimizations need fwhole-program flag.
5868 Transposing is enabled only if profiling information is avaliable.
5873 Perform forward store motion on trees. This flag is
5874 enabled by default at @option{-O} and higher.
5878 Perform sparse conditional constant propagation (CCP) on trees. This
5879 pass only operates on local scalar variables and is enabled by default
5880 at @option{-O} and higher.
5882 @item -ftree-store-ccp
5883 @opindex ftree-store-ccp
5884 Perform sparse conditional constant propagation (CCP) on trees. This
5885 pass operates on both local scalar variables and memory stores and
5886 loads (global variables, structures, arrays, etc). This flag is
5887 enabled by default at @option{-O2} and higher.
5889 @item -ftree-switch-conversion
5890 Perform conversion of simple initializations in a switch to
5891 initializations from a scalar array. This flag is enabled by default
5892 at @option{-O2} and higher.
5896 Perform dead code elimination (DCE) on trees. This flag is enabled by
5897 default at @option{-O} and higher.
5899 @item -ftree-builtin-call-dce
5900 @opindex ftree-builtin-call-dce
5901 Perform conditional dead code elimination (DCE) for calls to builtin functions
5902 that may set @code{errno} but are otherwise side-effect free. This flag is
5903 enabled by default at @option{-O2} and higher if @option{-Os} is not also
5906 @item -ftree-dominator-opts
5907 @opindex ftree-dominator-opts
5908 Perform a variety of simple scalar cleanups (constant/copy
5909 propagation, redundancy elimination, range propagation and expression
5910 simplification) based on a dominator tree traversal. This also
5911 performs jump threading (to reduce jumps to jumps). This flag is
5912 enabled by default at @option{-O} and higher.
5916 Perform dead store elimination (DSE) on trees. A dead store is a store into
5917 a memory location which will later be overwritten by another store without
5918 any intervening loads. In this case the earlier store can be deleted. This
5919 flag is enabled by default at @option{-O} and higher.
5923 Perform loop header copying on trees. This is beneficial since it increases
5924 effectiveness of code motion optimizations. It also saves one jump. This flag
5925 is enabled by default at @option{-O} and higher. It is not enabled
5926 for @option{-Os}, since it usually increases code size.
5928 @item -ftree-loop-optimize
5929 @opindex ftree-loop-optimize
5930 Perform loop optimizations on trees. This flag is enabled by default
5931 at @option{-O} and higher.
5933 @item -ftree-loop-linear
5934 @opindex ftree-loop-linear
5935 Perform linear loop transformations on tree. This flag can improve cache
5936 performance and allow further loop optimizations to take place.
5938 @item -fcheck-data-deps
5939 @opindex fcheck-data-deps
5940 Compare the results of several data dependence analyzers. This option
5941 is used for debugging the data dependence analyzers.
5943 @item -ftree-loop-distribution
5944 Perform loop distribution. This flag can improve cache performance on
5945 big loop bodies and allow further loop optimizations, like
5946 parallelization or vectorization, to take place. For example, the loop
5963 @item -ftree-loop-im
5964 @opindex ftree-loop-im
5965 Perform loop invariant motion on trees. This pass moves only invariants that
5966 would be hard to handle at RTL level (function calls, operations that expand to
5967 nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
5968 operands of conditions that are invariant out of the loop, so that we can use
5969 just trivial invariantness analysis in loop unswitching. The pass also includes
5972 @item -ftree-loop-ivcanon
5973 @opindex ftree-loop-ivcanon
5974 Create a canonical counter for number of iterations in the loop for that
5975 determining number of iterations requires complicated analysis. Later
5976 optimizations then may determine the number easily. Useful especially
5977 in connection with unrolling.
5981 Perform induction variable optimizations (strength reduction, induction
5982 variable merging and induction variable elimination) on trees.
5984 @item -ftree-parallelize-loops=n
5985 @opindex ftree-parallelize-loops
5986 Parallelize loops, i.e., split their iteration space to run in n threads.
5987 This is only possible for loops whose iterations are independent
5988 and can be arbitrarily reordered. The optimization is only
5989 profitable on multiprocessor machines, for loops that are CPU-intensive,
5990 rather than constrained e.g.@: by memory bandwidth. This option
5991 implies @option{-pthread}, and thus is only supported on targets
5992 that have support for @option{-pthread}.
5996 Perform scalar replacement of aggregates. This pass replaces structure
5997 references with scalars to prevent committing structures to memory too
5998 early. This flag is enabled by default at @option{-O} and higher.
6000 @item -ftree-copyrename
6001 @opindex ftree-copyrename
6002 Perform copy renaming on trees. This pass attempts to rename compiler
6003 temporaries to other variables at copy locations, usually resulting in
6004 variable names which more closely resemble the original variables. This flag
6005 is enabled by default at @option{-O} and higher.
6009 Perform temporary expression replacement during the SSA->normal phase. Single
6010 use/single def temporaries are replaced at their use location with their
6011 defining expression. This results in non-GIMPLE code, but gives the expanders
6012 much more complex trees to work on resulting in better RTL generation. This is
6013 enabled by default at @option{-O} and higher.
6015 @item -ftree-vectorize
6016 @opindex ftree-vectorize
6017 Perform loop vectorization on trees. This flag is enabled by default at
6020 @item -ftree-vect-loop-version
6021 @opindex ftree-vect-loop-version
6022 Perform loop versioning when doing loop vectorization on trees. When a loop
6023 appears to be vectorizable except that data alignment or data dependence cannot
6024 be determined at compile time then vectorized and non-vectorized versions of
6025 the loop are generated along with runtime checks for alignment or dependence
6026 to control which version is executed. This option is enabled by default
6027 except at level @option{-Os} where it is disabled.
6029 @item -fvect-cost-model
6030 @opindex fvect-cost-model
6031 Enable cost model for vectorization.
6035 Perform Value Range Propagation on trees. This is similar to the
6036 constant propagation pass, but instead of values, ranges of values are
6037 propagated. This allows the optimizers to remove unnecessary range
6038 checks like array bound checks and null pointer checks. This is
6039 enabled by default at @option{-O2} and higher. Null pointer check
6040 elimination is only done if @option{-fdelete-null-pointer-checks} is
6045 Perform tail duplication to enlarge superblock size. This transformation
6046 simplifies the control flow of the function allowing other optimizations to do
6049 @item -funroll-loops
6050 @opindex funroll-loops
6051 Unroll loops whose number of iterations can be determined at compile
6052 time or upon entry to the loop. @option{-funroll-loops} implies
6053 @option{-frerun-cse-after-loop}. This option makes code larger,
6054 and may or may not make it run faster.
6056 @item -funroll-all-loops
6057 @opindex funroll-all-loops
6058 Unroll all loops, even if their number of iterations is uncertain when
6059 the loop is entered. This usually makes programs run more slowly.
6060 @option{-funroll-all-loops} implies the same options as
6061 @option{-funroll-loops},
6063 @item -fsplit-ivs-in-unroller
6064 @opindex fsplit-ivs-in-unroller
6065 Enables expressing of values of induction variables in later iterations
6066 of the unrolled loop using the value in the first iteration. This breaks
6067 long dependency chains, thus improving efficiency of the scheduling passes.
6069 Combination of @option{-fweb} and CSE is often sufficient to obtain the
6070 same effect. However in cases the loop body is more complicated than
6071 a single basic block, this is not reliable. It also does not work at all
6072 on some of the architectures due to restrictions in the CSE pass.
6074 This optimization is enabled by default.
6076 @item -fvariable-expansion-in-unroller
6077 @opindex fvariable-expansion-in-unroller
6078 With this option, the compiler will create multiple copies of some
6079 local variables when unrolling a loop which can result in superior code.
6081 @item -fpredictive-commoning
6082 @opindex fpredictive-commoning
6083 Perform predictive commoning optimization, i.e., reusing computations
6084 (especially memory loads and stores) performed in previous
6085 iterations of loops.
6087 This option is enabled at level @option{-O3}.
6089 @item -fprefetch-loop-arrays
6090 @opindex fprefetch-loop-arrays
6091 If supported by the target machine, generate instructions to prefetch
6092 memory to improve the performance of loops that access large arrays.
6094 This option may generate better or worse code; results are highly
6095 dependent on the structure of loops within the source code.
6097 Disabled at level @option{-Os}.
6100 @itemx -fno-peephole2
6101 @opindex fno-peephole
6102 @opindex fno-peephole2
6103 Disable any machine-specific peephole optimizations. The difference
6104 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
6105 are implemented in the compiler; some targets use one, some use the
6106 other, a few use both.
6108 @option{-fpeephole} is enabled by default.
6109 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6111 @item -fno-guess-branch-probability
6112 @opindex fno-guess-branch-probability
6113 Do not guess branch probabilities using heuristics.
6115 GCC will use heuristics to guess branch probabilities if they are
6116 not provided by profiling feedback (@option{-fprofile-arcs}). These
6117 heuristics are based on the control flow graph. If some branch probabilities
6118 are specified by @samp{__builtin_expect}, then the heuristics will be
6119 used to guess branch probabilities for the rest of the control flow graph,
6120 taking the @samp{__builtin_expect} info into account. The interactions
6121 between the heuristics and @samp{__builtin_expect} can be complex, and in
6122 some cases, it may be useful to disable the heuristics so that the effects
6123 of @samp{__builtin_expect} are easier to understand.
6125 The default is @option{-fguess-branch-probability} at levels
6126 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6128 @item -freorder-blocks
6129 @opindex freorder-blocks
6130 Reorder basic blocks in the compiled function in order to reduce number of
6131 taken branches and improve code locality.
6133 Enabled at levels @option{-O2}, @option{-O3}.
6135 @item -freorder-blocks-and-partition
6136 @opindex freorder-blocks-and-partition
6137 In addition to reordering basic blocks in the compiled function, in order
6138 to reduce number of taken branches, partitions hot and cold basic blocks
6139 into separate sections of the assembly and .o files, to improve
6140 paging and cache locality performance.
6142 This optimization is automatically turned off in the presence of
6143 exception handling, for linkonce sections, for functions with a user-defined
6144 section attribute and on any architecture that does not support named
6147 @item -freorder-functions
6148 @opindex freorder-functions
6149 Reorder functions in the object file in order to
6150 improve code locality. This is implemented by using special
6151 subsections @code{.text.hot} for most frequently executed functions and
6152 @code{.text.unlikely} for unlikely executed functions. Reordering is done by
6153 the linker so object file format must support named sections and linker must
6154 place them in a reasonable way.
6156 Also profile feedback must be available in to make this option effective. See
6157 @option{-fprofile-arcs} for details.
6159 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6161 @item -fstrict-aliasing
6162 @opindex fstrict-aliasing
6163 Allows the compiler to assume the strictest aliasing rules applicable to
6164 the language being compiled. For C (and C++), this activates
6165 optimizations based on the type of expressions. In particular, an
6166 object of one type is assumed never to reside at the same address as an
6167 object of a different type, unless the types are almost the same. For
6168 example, an @code{unsigned int} can alias an @code{int}, but not a
6169 @code{void*} or a @code{double}. A character type may alias any other
6172 @anchor{Type-punning}Pay special attention to code like this:
6185 The practice of reading from a different union member than the one most
6186 recently written to (called ``type-punning'') is common. Even with
6187 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
6188 is accessed through the union type. So, the code above will work as
6189 expected. @xref{Structures unions enumerations and bit-fields
6190 implementation}. However, this code might not:
6201 Similarly, access by taking the address, casting the resulting pointer
6202 and dereferencing the result has undefined behavior, even if the cast
6203 uses a union type, e.g.:
6207 return ((union a_union *) &d)->i;
6211 The @option{-fstrict-aliasing} option is enabled at levels
6212 @option{-O2}, @option{-O3}, @option{-Os}.
6214 @item -fstrict-overflow
6215 @opindex fstrict-overflow
6216 Allow the compiler to assume strict signed overflow rules, depending
6217 on the language being compiled. For C (and C++) this means that
6218 overflow when doing arithmetic with signed numbers is undefined, which
6219 means that the compiler may assume that it will not happen. This
6220 permits various optimizations. For example, the compiler will assume
6221 that an expression like @code{i + 10 > i} will always be true for
6222 signed @code{i}. This assumption is only valid if signed overflow is
6223 undefined, as the expression is false if @code{i + 10} overflows when
6224 using twos complement arithmetic. When this option is in effect any
6225 attempt to determine whether an operation on signed numbers will
6226 overflow must be written carefully to not actually involve overflow.
6228 This option also allows the compiler to assume strict pointer
6229 semantics: given a pointer to an object, if adding an offset to that
6230 pointer does not produce a pointer to the same object, the addition is
6231 undefined. This permits the compiler to conclude that @code{p + u >
6232 p} is always true for a pointer @code{p} and unsigned integer
6233 @code{u}. This assumption is only valid because pointer wraparound is
6234 undefined, as the expression is false if @code{p + u} overflows using
6235 twos complement arithmetic.
6237 See also the @option{-fwrapv} option. Using @option{-fwrapv} means
6238 that integer signed overflow is fully defined: it wraps. When
6239 @option{-fwrapv} is used, there is no difference between
6240 @option{-fstrict-overflow} and @option{-fno-strict-overflow} for
6241 integers. With @option{-fwrapv} certain types of overflow are
6242 permitted. For example, if the compiler gets an overflow when doing
6243 arithmetic on constants, the overflowed value can still be used with
6244 @option{-fwrapv}, but not otherwise.
6246 The @option{-fstrict-overflow} option is enabled at levels
6247 @option{-O2}, @option{-O3}, @option{-Os}.
6249 @item -falign-functions
6250 @itemx -falign-functions=@var{n}
6251 @opindex falign-functions
6252 Align the start of functions to the next power-of-two greater than
6253 @var{n}, skipping up to @var{n} bytes. For instance,
6254 @option{-falign-functions=32} aligns functions to the next 32-byte
6255 boundary, but @option{-falign-functions=24} would align to the next
6256 32-byte boundary only if this can be done by skipping 23 bytes or less.
6258 @option{-fno-align-functions} and @option{-falign-functions=1} are
6259 equivalent and mean that functions will not be aligned.
6261 Some assemblers only support this flag when @var{n} is a power of two;
6262 in that case, it is rounded up.
6264 If @var{n} is not specified or is zero, use a machine-dependent default.
6266 Enabled at levels @option{-O2}, @option{-O3}.
6268 @item -falign-labels
6269 @itemx -falign-labels=@var{n}
6270 @opindex falign-labels
6271 Align all branch targets to a power-of-two boundary, skipping up to
6272 @var{n} bytes like @option{-falign-functions}. This option can easily
6273 make code slower, because it must insert dummy operations for when the
6274 branch target is reached in the usual flow of the code.
6276 @option{-fno-align-labels} and @option{-falign-labels=1} are
6277 equivalent and mean that labels will not be aligned.
6279 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
6280 are greater than this value, then their values are used instead.
6282 If @var{n} is not specified or is zero, use a machine-dependent default
6283 which is very likely to be @samp{1}, meaning no alignment.
6285 Enabled at levels @option{-O2}, @option{-O3}.
6288 @itemx -falign-loops=@var{n}
6289 @opindex falign-loops
6290 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
6291 like @option{-falign-functions}. The hope is that the loop will be
6292 executed many times, which will make up for any execution of the dummy
6295 @option{-fno-align-loops} and @option{-falign-loops=1} are
6296 equivalent and mean that loops will not be aligned.
6298 If @var{n} is not specified or is zero, use a machine-dependent default.
6300 Enabled at levels @option{-O2}, @option{-O3}.
6303 @itemx -falign-jumps=@var{n}
6304 @opindex falign-jumps
6305 Align branch targets to a power-of-two boundary, for branch targets
6306 where the targets can only be reached by jumping, skipping up to @var{n}
6307 bytes like @option{-falign-functions}. In this case, no dummy operations
6310 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
6311 equivalent and mean that loops will not be aligned.
6313 If @var{n} is not specified or is zero, use a machine-dependent default.
6315 Enabled at levels @option{-O2}, @option{-O3}.
6317 @item -funit-at-a-time
6318 @opindex funit-at-a-time
6319 This option is left for compatibility reasons. @option{-funit-at-a-time}
6320 has no effect, while @option{-fno-unit-at-a-time} implies
6321 @option{-fno-toplevel-reorder} and @option{-fno-section-anchors}.
6325 @item -fno-toplevel-reorder
6326 @opindex fno-toplevel-reorder
6327 Do not reorder top-level functions, variables, and @code{asm}
6328 statements. Output them in the same order that they appear in the
6329 input file. When this option is used, unreferenced static variables
6330 will not be removed. This option is intended to support existing code
6331 which relies on a particular ordering. For new code, it is better to
6334 Enabled at level @option{-O0}. When disabled explicitly, it also imply
6335 @option{-fno-section-anchors} that is otherwise enabled at @option{-O0} on some
6340 Constructs webs as commonly used for register allocation purposes and assign
6341 each web individual pseudo register. This allows the register allocation pass
6342 to operate on pseudos directly, but also strengthens several other optimization
6343 passes, such as CSE, loop optimizer and trivial dead code remover. It can,
6344 however, make debugging impossible, since variables will no longer stay in a
6347 Enabled by default with @option{-funroll-loops}.
6349 @item -fwhole-program
6350 @opindex fwhole-program
6351 Assume that the current compilation unit represents whole program being
6352 compiled. All public functions and variables with the exception of @code{main}
6353 and those merged by attribute @code{externally_visible} become static functions
6354 and in a affect gets more aggressively optimized by interprocedural optimizers.
6355 While this option is equivalent to proper use of @code{static} keyword for
6356 programs consisting of single file, in combination with option
6357 @option{--combine} this flag can be used to compile most of smaller scale C
6358 programs since the functions and variables become local for the whole combined
6359 compilation unit, not for the single source file itself.
6361 This option is not supported for Fortran programs.
6363 @item -fcprop-registers
6364 @opindex fcprop-registers
6365 After register allocation and post-register allocation instruction splitting,
6366 we perform a copy-propagation pass to try to reduce scheduling dependencies
6367 and occasionally eliminate the copy.
6369 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6371 @item -fprofile-dir=@var{path}
6372 @opindex fprofile-dir
6374 Set the directory to search the profile data files in to @var{path}.
6375 This option affects only the profile data generated by
6376 @option{-fprofile-generate}, @option{-ftest-coverage}, @option{-fprofile-arcs}
6377 and used by @option{-fprofile-use} and @option{-fbranch-probabilities}
6378 and its related options.
6379 By default, GCC will use the current directory as @var{path}
6380 thus the profile data file will appear in the same directory as the object file.
6382 @item -fprofile-generate
6383 @itemx -fprofile-generate=@var{path}
6384 @opindex fprofile-generate
6386 Enable options usually used for instrumenting application to produce
6387 profile useful for later recompilation with profile feedback based
6388 optimization. You must use @option{-fprofile-generate} both when
6389 compiling and when linking your program.
6391 The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}.
6393 If @var{path} is specified, GCC will look at the @var{path} to find
6394 the profile feeedback data files. See @option{-fprofile-dir}.
6397 @itemx -fprofile-use=@var{path}
6398 @opindex fprofile-use
6399 Enable profile feedback directed optimizations, and optimizations
6400 generally profitable only with profile feedback available.
6402 The following options are enabled: @code{-fbranch-probabilities}, @code{-fvpt},
6403 @code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer}
6405 By default, GCC emits an error message if the feedback profiles do not
6406 match the source code. This error can be turned into a warning by using
6407 @option{-Wcoverage-mismatch}. Note this may result in poorly optimized
6410 If @var{path} is specified, GCC will look at the @var{path} to find
6411 the profile feedback data files. See @option{-fprofile-dir}.
6414 The following options control compiler behavior regarding floating
6415 point arithmetic. These options trade off between speed and
6416 correctness. All must be specifically enabled.
6420 @opindex ffloat-store
6421 Do not store floating point variables in registers, and inhibit other
6422 options that might change whether a floating point value is taken from a
6425 @cindex floating point precision
6426 This option prevents undesirable excess precision on machines such as
6427 the 68000 where the floating registers (of the 68881) keep more
6428 precision than a @code{double} is supposed to have. Similarly for the
6429 x86 architecture. For most programs, the excess precision does only
6430 good, but a few programs rely on the precise definition of IEEE floating
6431 point. Use @option{-ffloat-store} for such programs, after modifying
6432 them to store all pertinent intermediate computations into variables.
6436 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations},
6437 @option{-ffinite-math-only}, @option{-fno-rounding-math},
6438 @option{-fno-signaling-nans} and @option{-fcx-limited-range}.
6440 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
6442 This option is not turned on by any @option{-O} option since
6443 it can result in incorrect output for programs which depend on
6444 an exact implementation of IEEE or ISO rules/specifications for
6445 math functions. It may, however, yield faster code for programs
6446 that do not require the guarantees of these specifications.
6448 @item -fno-math-errno
6449 @opindex fno-math-errno
6450 Do not set ERRNO after calling math functions that are executed
6451 with a single instruction, e.g., sqrt. A program that relies on
6452 IEEE exceptions for math error handling may want to use this flag
6453 for speed while maintaining IEEE arithmetic compatibility.
6455 This option is not turned on by any @option{-O} option since
6456 it can result in incorrect output for programs which depend on
6457 an exact implementation of IEEE or ISO rules/specifications for
6458 math functions. It may, however, yield faster code for programs
6459 that do not require the guarantees of these specifications.
6461 The default is @option{-fmath-errno}.
6463 On Darwin systems, the math library never sets @code{errno}. There is
6464 therefore no reason for the compiler to consider the possibility that
6465 it might, and @option{-fno-math-errno} is the default.
6467 @item -funsafe-math-optimizations
6468 @opindex funsafe-math-optimizations
6470 Allow optimizations for floating-point arithmetic that (a) assume
6471 that arguments and results are valid and (b) may violate IEEE or
6472 ANSI standards. When used at link-time, it may include libraries
6473 or startup files that change the default FPU control word or other
6474 similar optimizations.
6476 This option is not turned on by any @option{-O} option since
6477 it can result in incorrect output for programs which depend on
6478 an exact implementation of IEEE or ISO rules/specifications for
6479 math functions. It may, however, yield faster code for programs
6480 that do not require the guarantees of these specifications.
6481 Enables @option{-fno-signed-zeros}, @option{-fno-trapping-math},
6482 @option{-fassociative-math} and @option{-freciprocal-math}.
6484 The default is @option{-fno-unsafe-math-optimizations}.
6486 @item -fassociative-math
6487 @opindex fassociative-math
6489 Allow re-association of operands in series of floating-point operations.
6490 This violates the ISO C and C++ language standard by possibly changing
6491 computation result. NOTE: re-ordering may change the sign of zero as
6492 well as ignore NaNs and inhibit or create underflow or overflow (and
6493 thus cannot be used on a code which relies on rounding behavior like
6494 @code{(x + 2**52) - 2**52)}. May also reorder floating-point comparisons
6495 and thus may not be used when ordered comparisons are required.
6496 This option requires that both @option{-fno-signed-zeros} and
6497 @option{-fno-trapping-math} be in effect. Moreover, it doesn't make
6498 much sense with @option{-frounding-math}.
6500 The default is @option{-fno-associative-math}.
6502 @item -freciprocal-math
6503 @opindex freciprocal-math
6505 Allow the reciprocal of a value to be used instead of dividing by
6506 the value if this enables optimizations. For example @code{x / y}
6507 can be replaced with @code{x * (1/y)} which is useful if @code{(1/y)}
6508 is subject to common subexpression elimination. Note that this loses
6509 precision and increases the number of flops operating on the value.
6511 The default is @option{-fno-reciprocal-math}.
6513 @item -ffinite-math-only
6514 @opindex ffinite-math-only
6515 Allow optimizations for floating-point arithmetic that assume
6516 that arguments and results are not NaNs or +-Infs.
6518 This option is not turned on by any @option{-O} option since
6519 it can result in incorrect output for programs which depend on
6520 an exact implementation of IEEE or ISO rules/specifications for
6521 math functions. It may, however, yield faster code for programs
6522 that do not require the guarantees of these specifications.
6524 The default is @option{-fno-finite-math-only}.
6526 @item -fno-signed-zeros
6527 @opindex fno-signed-zeros
6528 Allow optimizations for floating point arithmetic that ignore the
6529 signedness of zero. IEEE arithmetic specifies the behavior of
6530 distinct +0.0 and @minus{}0.0 values, which then prohibits simplification
6531 of expressions such as x+0.0 or 0.0*x (even with @option{-ffinite-math-only}).
6532 This option implies that the sign of a zero result isn't significant.
6534 The default is @option{-fsigned-zeros}.
6536 @item -fno-trapping-math
6537 @opindex fno-trapping-math
6538 Compile code assuming that floating-point operations cannot generate
6539 user-visible traps. These traps include division by zero, overflow,
6540 underflow, inexact result and invalid operation. This option requires
6541 that @option{-fno-signaling-nans} be in effect. Setting this option may
6542 allow faster code if one relies on ``non-stop'' IEEE arithmetic, for example.
6544 This option should never be turned on by any @option{-O} option since
6545 it can result in incorrect output for programs which depend on
6546 an exact implementation of IEEE or ISO rules/specifications for
6549 The default is @option{-ftrapping-math}.
6551 @item -frounding-math
6552 @opindex frounding-math
6553 Disable transformations and optimizations that assume default floating
6554 point rounding behavior. This is round-to-zero for all floating point
6555 to integer conversions, and round-to-nearest for all other arithmetic
6556 truncations. This option should be specified for programs that change
6557 the FP rounding mode dynamically, or that may be executed with a
6558 non-default rounding mode. This option disables constant folding of
6559 floating point expressions at compile-time (which may be affected by
6560 rounding mode) and arithmetic transformations that are unsafe in the
6561 presence of sign-dependent rounding modes.
6563 The default is @option{-fno-rounding-math}.
6565 This option is experimental and does not currently guarantee to
6566 disable all GCC optimizations that are affected by rounding mode.
6567 Future versions of GCC may provide finer control of this setting
6568 using C99's @code{FENV_ACCESS} pragma. This command line option
6569 will be used to specify the default state for @code{FENV_ACCESS}.
6571 @item -frtl-abstract-sequences
6572 @opindex frtl-abstract-sequences
6573 It is a size optimization method. This option is to find identical
6574 sequences of code, which can be turned into pseudo-procedures and
6575 then replace all occurrences with calls to the newly created
6576 subroutine. It is kind of an opposite of @option{-finline-functions}.
6577 This optimization runs at RTL level.
6579 @item -fsignaling-nans
6580 @opindex fsignaling-nans
6581 Compile code assuming that IEEE signaling NaNs may generate user-visible
6582 traps during floating-point operations. Setting this option disables
6583 optimizations that may change the number of exceptions visible with
6584 signaling NaNs. This option implies @option{-ftrapping-math}.
6586 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
6589 The default is @option{-fno-signaling-nans}.
6591 This option is experimental and does not currently guarantee to
6592 disable all GCC optimizations that affect signaling NaN behavior.
6594 @item -fsingle-precision-constant
6595 @opindex fsingle-precision-constant
6596 Treat floating point constant as single precision constant instead of
6597 implicitly converting it to double precision constant.
6599 @item -fcx-limited-range
6600 @opindex fcx-limited-range
6601 When enabled, this option states that a range reduction step is not
6602 needed when performing complex division. Also, there is no checking
6603 whether the result of a complex multiplication or division is @code{NaN
6604 + I*NaN}, with an attempt to rescue the situation in that case. The
6605 default is @option{-fno-cx-limited-range}, but is enabled by
6606 @option{-ffast-math}.
6608 This option controls the default setting of the ISO C99
6609 @code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to
6612 @item -fcx-fortran-rules
6613 @opindex fcx-fortran-rules
6614 Complex multiplication and division follow Fortran rules. Range
6615 reduction is done as part of complex division, but there is no checking
6616 whether the result of a complex multiplication or division is @code{NaN
6617 + I*NaN}, with an attempt to rescue the situation in that case.
6619 The default is @option{-fno-cx-fortran-rules}.
6623 The following options control optimizations that may improve
6624 performance, but are not enabled by any @option{-O} options. This
6625 section includes experimental options that may produce broken code.
6628 @item -fbranch-probabilities
6629 @opindex fbranch-probabilities
6630 After running a program compiled with @option{-fprofile-arcs}
6631 (@pxref{Debugging Options,, Options for Debugging Your Program or
6632 @command{gcc}}), you can compile it a second time using
6633 @option{-fbranch-probabilities}, to improve optimizations based on
6634 the number of times each branch was taken. When the program
6635 compiled with @option{-fprofile-arcs} exits it saves arc execution
6636 counts to a file called @file{@var{sourcename}.gcda} for each source
6637 file. The information in this data file is very dependent on the
6638 structure of the generated code, so you must use the same source code
6639 and the same optimization options for both compilations.
6641 With @option{-fbranch-probabilities}, GCC puts a
6642 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
6643 These can be used to improve optimization. Currently, they are only
6644 used in one place: in @file{reorg.c}, instead of guessing which path a
6645 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
6646 exactly determine which path is taken more often.
6648 @item -fprofile-values
6649 @opindex fprofile-values
6650 If combined with @option{-fprofile-arcs}, it adds code so that some
6651 data about values of expressions in the program is gathered.
6653 With @option{-fbranch-probabilities}, it reads back the data gathered
6654 from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
6655 notes to instructions for their later usage in optimizations.
6657 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
6661 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
6662 a code to gather information about values of expressions.
6664 With @option{-fbranch-probabilities}, it reads back the data gathered
6665 and actually performs the optimizations based on them.
6666 Currently the optimizations include specialization of division operation
6667 using the knowledge about the value of the denominator.
6669 @item -frename-registers
6670 @opindex frename-registers
6671 Attempt to avoid false dependencies in scheduled code by making use
6672 of registers left over after register allocation. This optimization
6673 will most benefit processors with lots of registers. Depending on the
6674 debug information format adopted by the target, however, it can
6675 make debugging impossible, since variables will no longer stay in
6676 a ``home register''.
6678 Enabled by default with @option{-funroll-loops}.
6682 Perform tail duplication to enlarge superblock size. This transformation
6683 simplifies the control flow of the function allowing other optimizations to do
6686 Enabled with @option{-fprofile-use}.
6688 @item -funroll-loops
6689 @opindex funroll-loops
6690 Unroll loops whose number of iterations can be determined at compile time or
6691 upon entry to the loop. @option{-funroll-loops} implies
6692 @option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}.
6693 It also turns on complete loop peeling (i.e.@: complete removal of loops with
6694 small constant number of iterations). This option makes code larger, and may
6695 or may not make it run faster.
6697 Enabled with @option{-fprofile-use}.
6699 @item -funroll-all-loops
6700 @opindex funroll-all-loops
6701 Unroll all loops, even if their number of iterations is uncertain when
6702 the loop is entered. This usually makes programs run more slowly.
6703 @option{-funroll-all-loops} implies the same options as
6704 @option{-funroll-loops}.
6707 @opindex fpeel-loops
6708 Peels the loops for that there is enough information that they do not
6709 roll much (from profile feedback). It also turns on complete loop peeling
6710 (i.e.@: complete removal of loops with small constant number of iterations).
6712 Enabled with @option{-fprofile-use}.
6714 @item -fmove-loop-invariants
6715 @opindex fmove-loop-invariants
6716 Enables the loop invariant motion pass in the RTL loop optimizer. Enabled
6717 at level @option{-O1}
6719 @item -funswitch-loops
6720 @opindex funswitch-loops
6721 Move branches with loop invariant conditions out of the loop, with duplicates
6722 of the loop on both branches (modified according to result of the condition).
6724 @item -ffunction-sections
6725 @itemx -fdata-sections
6726 @opindex ffunction-sections
6727 @opindex fdata-sections
6728 Place each function or data item into its own section in the output
6729 file if the target supports arbitrary sections. The name of the
6730 function or the name of the data item determines the section's name
6733 Use these options on systems where the linker can perform optimizations
6734 to improve locality of reference in the instruction space. Most systems
6735 using the ELF object format and SPARC processors running Solaris 2 have
6736 linkers with such optimizations. AIX may have these optimizations in
6739 Only use these options when there are significant benefits from doing
6740 so. When you specify these options, the assembler and linker will
6741 create larger object and executable files and will also be slower.
6742 You will not be able to use @code{gprof} on all systems if you
6743 specify this option and you may have problems with debugging if
6744 you specify both this option and @option{-g}.
6746 @item -fbranch-target-load-optimize
6747 @opindex fbranch-target-load-optimize
6748 Perform branch target register load optimization before prologue / epilogue
6750 The use of target registers can typically be exposed only during reload,
6751 thus hoisting loads out of loops and doing inter-block scheduling needs
6752 a separate optimization pass.
6754 @item -fbranch-target-load-optimize2
6755 @opindex fbranch-target-load-optimize2
6756 Perform branch target register load optimization after prologue / epilogue
6759 @item -fbtr-bb-exclusive
6760 @opindex fbtr-bb-exclusive
6761 When performing branch target register load optimization, don't reuse
6762 branch target registers in within any basic block.
6764 @item -fstack-protector
6765 @opindex fstack-protector
6766 Emit extra code to check for buffer overflows, such as stack smashing
6767 attacks. This is done by adding a guard variable to functions with
6768 vulnerable objects. This includes functions that call alloca, and
6769 functions with buffers larger than 8 bytes. The guards are initialized
6770 when a function is entered and then checked when the function exits.
6771 If a guard check fails, an error message is printed and the program exits.
6773 @item -fstack-protector-all
6774 @opindex fstack-protector-all
6775 Like @option{-fstack-protector} except that all functions are protected.
6777 @item -fsection-anchors
6778 @opindex fsection-anchors
6779 Try to reduce the number of symbolic address calculations by using
6780 shared ``anchor'' symbols to address nearby objects. This transformation
6781 can help to reduce the number of GOT entries and GOT accesses on some
6784 For example, the implementation of the following function @code{foo}:
6788 int foo (void) @{ return a + b + c; @}
6791 would usually calculate the addresses of all three variables, but if you
6792 compile it with @option{-fsection-anchors}, it will access the variables
6793 from a common anchor point instead. The effect is similar to the
6794 following pseudocode (which isn't valid C):
6799 register int *xr = &x;
6800 return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
6804 Not all targets support this option.
6806 @item --param @var{name}=@var{value}
6808 In some places, GCC uses various constants to control the amount of
6809 optimization that is done. For example, GCC will not inline functions
6810 that contain more that a certain number of instructions. You can
6811 control some of these constants on the command-line using the
6812 @option{--param} option.
6814 The names of specific parameters, and the meaning of the values, are
6815 tied to the internals of the compiler, and are subject to change
6816 without notice in future releases.
6818 In each case, the @var{value} is an integer. The allowable choices for
6819 @var{name} are given in the following table:
6822 @item sra-max-structure-size
6823 The maximum structure size, in bytes, at which the scalar replacement
6824 of aggregates (SRA) optimization will perform block copies. The
6825 default value, 0, implies that GCC will select the most appropriate
6828 @item sra-field-structure-ratio
6829 The threshold ratio (as a percentage) between instantiated fields and
6830 the complete structure size. We say that if the ratio of the number
6831 of bytes in instantiated fields to the number of bytes in the complete
6832 structure exceeds this parameter, then block copies are not used. The
6835 @item struct-reorg-cold-struct-ratio
6836 The threshold ratio (as a percentage) between a structure frequency
6837 and the frequency of the hottest structure in the program. This parameter
6838 is used by struct-reorg optimization enabled by @option{-fipa-struct-reorg}.
6839 We say that if the ratio of a structure frequency, calculated by profiling,
6840 to the hottest structure frequency in the program is less than this
6841 parameter, then structure reorganization is not applied to this structure.
6844 @item max-crossjump-edges
6845 The maximum number of incoming edges to consider for crossjumping.
6846 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
6847 the number of edges incoming to each block. Increasing values mean
6848 more aggressive optimization, making the compile time increase with
6849 probably small improvement in executable size.
6851 @item min-crossjump-insns
6852 The minimum number of instructions which must be matched at the end
6853 of two blocks before crossjumping will be performed on them. This
6854 value is ignored in the case where all instructions in the block being
6855 crossjumped from are matched. The default value is 5.
6857 @item max-grow-copy-bb-insns
6858 The maximum code size expansion factor when copying basic blocks
6859 instead of jumping. The expansion is relative to a jump instruction.
6860 The default value is 8.
6862 @item max-goto-duplication-insns
6863 The maximum number of instructions to duplicate to a block that jumps
6864 to a computed goto. To avoid @math{O(N^2)} behavior in a number of
6865 passes, GCC factors computed gotos early in the compilation process,
6866 and unfactors them as late as possible. Only computed jumps at the
6867 end of a basic blocks with no more than max-goto-duplication-insns are
6868 unfactored. The default value is 8.
6870 @item max-delay-slot-insn-search
6871 The maximum number of instructions to consider when looking for an
6872 instruction to fill a delay slot. If more than this arbitrary number of
6873 instructions is searched, the time savings from filling the delay slot
6874 will be minimal so stop searching. Increasing values mean more
6875 aggressive optimization, making the compile time increase with probably
6876 small improvement in executable run time.
6878 @item max-delay-slot-live-search
6879 When trying to fill delay slots, the maximum number of instructions to
6880 consider when searching for a block with valid live register
6881 information. Increasing this arbitrarily chosen value means more
6882 aggressive optimization, increasing the compile time. This parameter
6883 should be removed when the delay slot code is rewritten to maintain the
6886 @item max-gcse-memory
6887 The approximate maximum amount of memory that will be allocated in
6888 order to perform the global common subexpression elimination
6889 optimization. If more memory than specified is required, the
6890 optimization will not be done.
6892 @item max-gcse-passes
6893 The maximum number of passes of GCSE to run. The default is 1.
6895 @item max-pending-list-length
6896 The maximum number of pending dependencies scheduling will allow
6897 before flushing the current state and starting over. Large functions
6898 with few branches or calls can create excessively large lists which
6899 needlessly consume memory and resources.
6901 @item max-inline-insns-single
6902 Several parameters control the tree inliner used in gcc.
6903 This number sets the maximum number of instructions (counted in GCC's
6904 internal representation) in a single function that the tree inliner
6905 will consider for inlining. This only affects functions declared
6906 inline and methods implemented in a class declaration (C++).
6907 The default value is 450.
6909 @item max-inline-insns-auto
6910 When you use @option{-finline-functions} (included in @option{-O3}),
6911 a lot of functions that would otherwise not be considered for inlining
6912 by the compiler will be investigated. To those functions, a different
6913 (more restrictive) limit compared to functions declared inline can
6915 The default value is 90.
6917 @item large-function-insns
6918 The limit specifying really large functions. For functions larger than this
6919 limit after inlining inlining is constrained by
6920 @option{--param large-function-growth}. This parameter is useful primarily
6921 to avoid extreme compilation time caused by non-linear algorithms used by the
6923 The default value is 2700.
6925 @item large-function-growth
6926 Specifies maximal growth of large function caused by inlining in percents.
6927 The default value is 100 which limits large function growth to 2.0 times
6930 @item large-unit-insns
6931 The limit specifying large translation unit. Growth caused by inlining of
6932 units larger than this limit is limited by @option{--param inline-unit-growth}.
6933 For small units this might be too tight (consider unit consisting of function A
6934 that is inline and B that just calls A three time. If B is small relative to
6935 A, the growth of unit is 300\% and yet such inlining is very sane. For very
6936 large units consisting of small inlineable functions however the overall unit
6937 growth limit is needed to avoid exponential explosion of code size. Thus for
6938 smaller units, the size is increased to @option{--param large-unit-insns}
6939 before applying @option{--param inline-unit-growth}. The default is 10000
6941 @item inline-unit-growth
6942 Specifies maximal overall growth of the compilation unit caused by inlining.
6943 The default value is 30 which limits unit growth to 1.3 times the original
6946 @item large-stack-frame
6947 The limit specifying large stack frames. While inlining the algorithm is trying
6948 to not grow past this limit too much. Default value is 256 bytes.
6950 @item large-stack-frame-growth
6951 Specifies maximal growth of large stack frames caused by inlining in percents.
6952 The default value is 1000 which limits large stack frame growth to 11 times
6955 @item max-inline-insns-recursive
6956 @itemx max-inline-insns-recursive-auto
6957 Specifies maximum number of instructions out-of-line copy of self recursive inline
6958 function can grow into by performing recursive inlining.
6960 For functions declared inline @option{--param max-inline-insns-recursive} is
6961 taken into account. For function not declared inline, recursive inlining
6962 happens only when @option{-finline-functions} (included in @option{-O3}) is
6963 enabled and @option{--param max-inline-insns-recursive-auto} is used. The
6964 default value is 450.
6966 @item max-inline-recursive-depth
6967 @itemx max-inline-recursive-depth-auto
6968 Specifies maximum recursion depth used by the recursive inlining.
6970 For functions declared inline @option{--param max-inline-recursive-depth} is
6971 taken into account. For function not declared inline, recursive inlining
6972 happens only when @option{-finline-functions} (included in @option{-O3}) is
6973 enabled and @option{--param max-inline-recursive-depth-auto} is used. The
6976 @item min-inline-recursive-probability
6977 Recursive inlining is profitable only for function having deep recursion
6978 in average and can hurt for function having little recursion depth by
6979 increasing the prologue size or complexity of function body to other
6982 When profile feedback is available (see @option{-fprofile-generate}) the actual
6983 recursion depth can be guessed from probability that function will recurse via
6984 given call expression. This parameter limits inlining only to call expression
6985 whose probability exceeds given threshold (in percents). The default value is
6988 @item inline-call-cost
6989 Specify cost of call instruction relative to simple arithmetics operations
6990 (having cost of 1). Increasing this cost disqualifies inlining of non-leaf
6991 functions and at the same time increases size of leaf function that is believed to
6992 reduce function size by being inlined. In effect it increases amount of
6993 inlining for code having large abstraction penalty (many functions that just
6994 pass the arguments to other functions) and decrease inlining for code with low
6995 abstraction penalty. The default value is 12.
6997 @item min-vect-loop-bound
6998 The minimum number of iterations under which a loop will not get vectorized
6999 when @option{-ftree-vectorize} is used. The number of iterations after
7000 vectorization needs to be greater than the value specified by this option
7001 to allow vectorization. The default value is 0.
7003 @item max-unrolled-insns
7004 The maximum number of instructions that a loop should have if that loop
7005 is unrolled, and if the loop is unrolled, it determines how many times
7006 the loop code is unrolled.
7008 @item max-average-unrolled-insns
7009 The maximum number of instructions biased by probabilities of their execution
7010 that a loop should have if that loop is unrolled, and if the loop is unrolled,
7011 it determines how many times the loop code is unrolled.
7013 @item max-unroll-times
7014 The maximum number of unrollings of a single loop.
7016 @item max-peeled-insns
7017 The maximum number of instructions that a loop should have if that loop
7018 is peeled, and if the loop is peeled, it determines how many times
7019 the loop code is peeled.
7021 @item max-peel-times
7022 The maximum number of peelings of a single loop.
7024 @item max-completely-peeled-insns
7025 The maximum number of insns of a completely peeled loop.
7027 @item max-completely-peel-times
7028 The maximum number of iterations of a loop to be suitable for complete peeling.
7030 @item max-unswitch-insns
7031 The maximum number of insns of an unswitched loop.
7033 @item max-unswitch-level
7034 The maximum number of branches unswitched in a single loop.
7037 The minimum cost of an expensive expression in the loop invariant motion.
7039 @item iv-consider-all-candidates-bound
7040 Bound on number of candidates for induction variables below that
7041 all candidates are considered for each use in induction variable
7042 optimizations. Only the most relevant candidates are considered
7043 if there are more candidates, to avoid quadratic time complexity.
7045 @item iv-max-considered-uses
7046 The induction variable optimizations give up on loops that contain more
7047 induction variable uses.
7049 @item iv-always-prune-cand-set-bound
7050 If number of candidates in the set is smaller than this value,
7051 we always try to remove unnecessary ivs from the set during its
7052 optimization when a new iv is added to the set.
7054 @item scev-max-expr-size
7055 Bound on size of expressions used in the scalar evolutions analyzer.
7056 Large expressions slow the analyzer.
7058 @item omega-max-vars
7059 The maximum number of variables in an Omega constraint system.
7060 The default value is 128.
7062 @item omega-max-geqs
7063 The maximum number of inequalities in an Omega constraint system.
7064 The default value is 256.
7067 The maximum number of equalities in an Omega constraint system.
7068 The default value is 128.
7070 @item omega-max-wild-cards
7071 The maximum number of wildcard variables that the Omega solver will
7072 be able to insert. The default value is 18.
7074 @item omega-hash-table-size
7075 The size of the hash table in the Omega solver. The default value is
7078 @item omega-max-keys
7079 The maximal number of keys used by the Omega solver. The default
7082 @item omega-eliminate-redundant-constraints
7083 When set to 1, use expensive methods to eliminate all redundant
7084 constraints. The default value is 0.
7086 @item vect-max-version-for-alignment-checks
7087 The maximum number of runtime checks that can be performed when
7088 doing loop versioning for alignment in the vectorizer. See option
7089 ftree-vect-loop-version for more information.
7091 @item vect-max-version-for-alias-checks
7092 The maximum number of runtime checks that can be performed when
7093 doing loop versioning for alias in the vectorizer. See option
7094 ftree-vect-loop-version for more information.
7096 @item max-iterations-to-track
7098 The maximum number of iterations of a loop the brute force algorithm
7099 for analysis of # of iterations of the loop tries to evaluate.
7101 @item hot-bb-count-fraction
7102 Select fraction of the maximal count of repetitions of basic block in program
7103 given basic block needs to have to be considered hot.
7105 @item hot-bb-frequency-fraction
7106 Select fraction of the maximal frequency of executions of basic block in
7107 function given basic block needs to have to be considered hot
7109 @item max-predicted-iterations
7110 The maximum number of loop iterations we predict statically. This is useful
7111 in cases where function contain single loop with known bound and other loop
7112 with unknown. We predict the known number of iterations correctly, while
7113 the unknown number of iterations average to roughly 10. This means that the
7114 loop without bounds would appear artificially cold relative to the other one.
7116 @item align-threshold
7118 Select fraction of the maximal frequency of executions of basic block in
7119 function given basic block will get aligned.
7121 @item align-loop-iterations
7123 A loop expected to iterate at lest the selected number of iterations will get
7126 @item tracer-dynamic-coverage
7127 @itemx tracer-dynamic-coverage-feedback
7129 This value is used to limit superblock formation once the given percentage of
7130 executed instructions is covered. This limits unnecessary code size
7133 The @option{tracer-dynamic-coverage-feedback} is used only when profile
7134 feedback is available. The real profiles (as opposed to statically estimated
7135 ones) are much less balanced allowing the threshold to be larger value.
7137 @item tracer-max-code-growth
7138 Stop tail duplication once code growth has reached given percentage. This is
7139 rather hokey argument, as most of the duplicates will be eliminated later in
7140 cross jumping, so it may be set to much higher values than is the desired code
7143 @item tracer-min-branch-ratio
7145 Stop reverse growth when the reverse probability of best edge is less than this
7146 threshold (in percent).
7148 @item tracer-min-branch-ratio
7149 @itemx tracer-min-branch-ratio-feedback
7151 Stop forward growth if the best edge do have probability lower than this
7154 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
7155 compilation for profile feedback and one for compilation without. The value
7156 for compilation with profile feedback needs to be more conservative (higher) in
7157 order to make tracer effective.
7159 @item max-cse-path-length
7161 Maximum number of basic blocks on path that cse considers. The default is 10.
7164 The maximum instructions CSE process before flushing. The default is 1000.
7166 @item max-aliased-vops
7168 Maximum number of virtual operands per function allowed to represent
7169 aliases before triggering the alias partitioning heuristic. Alias
7170 partitioning reduces compile times and memory consumption needed for
7171 aliasing at the expense of precision loss in alias information. The
7172 default value for this parameter is 100 for -O1, 500 for -O2 and 1000
7175 Notice that if a function contains more memory statements than the
7176 value of this parameter, it is not really possible to achieve this
7177 reduction. In this case, the compiler will use the number of memory
7178 statements as the value for @option{max-aliased-vops}.
7180 @item avg-aliased-vops
7182 Average number of virtual operands per statement allowed to represent
7183 aliases before triggering the alias partitioning heuristic. This
7184 works in conjunction with @option{max-aliased-vops}. If a function
7185 contains more than @option{max-aliased-vops} virtual operators, then
7186 memory symbols will be grouped into memory partitions until either the
7187 total number of virtual operators is below @option{max-aliased-vops}
7188 or the average number of virtual operators per memory statement is
7189 below @option{avg-aliased-vops}. The default value for this parameter
7190 is 1 for -O1 and -O2, and 3 for -O3.
7192 @item ggc-min-expand
7194 GCC uses a garbage collector to manage its own memory allocation. This
7195 parameter specifies the minimum percentage by which the garbage
7196 collector's heap should be allowed to expand between collections.
7197 Tuning this may improve compilation speed; it has no effect on code
7200 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
7201 RAM >= 1GB@. If @code{getrlimit} is available, the notion of "RAM" is
7202 the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If
7203 GCC is not able to calculate RAM on a particular platform, the lower
7204 bound of 30% is used. Setting this parameter and
7205 @option{ggc-min-heapsize} to zero causes a full collection to occur at
7206 every opportunity. This is extremely slow, but can be useful for
7209 @item ggc-min-heapsize
7211 Minimum size of the garbage collector's heap before it begins bothering
7212 to collect garbage. The first collection occurs after the heap expands
7213 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
7214 tuning this may improve compilation speed, and has no effect on code
7217 The default is the smaller of RAM/8, RLIMIT_RSS, or a limit which
7218 tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
7219 with a lower bound of 4096 (four megabytes) and an upper bound of
7220 131072 (128 megabytes). If GCC is not able to calculate RAM on a
7221 particular platform, the lower bound is used. Setting this parameter
7222 very large effectively disables garbage collection. Setting this
7223 parameter and @option{ggc-min-expand} to zero causes a full collection
7224 to occur at every opportunity.
7226 @item max-reload-search-insns
7227 The maximum number of instruction reload should look backward for equivalent
7228 register. Increasing values mean more aggressive optimization, making the
7229 compile time increase with probably slightly better performance. The default
7232 @item max-cselib-memory-locations
7233 The maximum number of memory locations cselib should take into account.
7234 Increasing values mean more aggressive optimization, making the compile time
7235 increase with probably slightly better performance. The default value is 500.
7237 @item reorder-blocks-duplicate
7238 @itemx reorder-blocks-duplicate-feedback
7240 Used by basic block reordering pass to decide whether to use unconditional
7241 branch or duplicate the code on its destination. Code is duplicated when its
7242 estimated size is smaller than this value multiplied by the estimated size of
7243 unconditional jump in the hot spots of the program.
7245 The @option{reorder-block-duplicate-feedback} is used only when profile
7246 feedback is available and may be set to higher values than
7247 @option{reorder-block-duplicate} since information about the hot spots is more
7250 @item max-sched-ready-insns
7251 The maximum number of instructions ready to be issued the scheduler should
7252 consider at any given time during the first scheduling pass. Increasing
7253 values mean more thorough searches, making the compilation time increase
7254 with probably little benefit. The default value is 100.
7256 @item max-sched-region-blocks
7257 The maximum number of blocks in a region to be considered for
7258 interblock scheduling. The default value is 10.
7260 @item max-sched-region-insns
7261 The maximum number of insns in a region to be considered for
7262 interblock scheduling. The default value is 100.
7265 The minimum probability (in percents) of reaching a source block
7266 for interblock speculative scheduling. The default value is 40.
7268 @item max-sched-extend-regions-iters
7269 The maximum number of iterations through CFG to extend regions.
7270 0 - disable region extension,
7271 N - do at most N iterations.
7272 The default value is 0.
7274 @item max-sched-insn-conflict-delay
7275 The maximum conflict delay for an insn to be considered for speculative motion.
7276 The default value is 3.
7278 @item sched-spec-prob-cutoff
7279 The minimal probability of speculation success (in percents), so that
7280 speculative insn will be scheduled.
7281 The default value is 40.
7283 @item max-last-value-rtl
7285 The maximum size measured as number of RTLs that can be recorded in an expression
7286 in combiner for a pseudo register as last known value of that register. The default
7289 @item integer-share-limit
7290 Small integer constants can use a shared data structure, reducing the
7291 compiler's memory usage and increasing its speed. This sets the maximum
7292 value of a shared integer constant. The default value is 256.
7294 @item min-virtual-mappings
7295 Specifies the minimum number of virtual mappings in the incremental
7296 SSA updater that should be registered to trigger the virtual mappings
7297 heuristic defined by virtual-mappings-ratio. The default value is
7300 @item virtual-mappings-ratio
7301 If the number of virtual mappings is virtual-mappings-ratio bigger
7302 than the number of virtual symbols to be updated, then the incremental
7303 SSA updater switches to a full update for those symbols. The default
7306 @item ssp-buffer-size
7307 The minimum size of buffers (i.e.@: arrays) that will receive stack smashing
7308 protection when @option{-fstack-protection} is used.
7310 @item max-jump-thread-duplication-stmts
7311 Maximum number of statements allowed in a block that needs to be
7312 duplicated when threading jumps.
7314 @item max-fields-for-field-sensitive
7315 Maximum number of fields in a structure we will treat in
7316 a field sensitive manner during pointer analysis. The default is zero
7317 for -O0, and -O1 and 100 for -Os, -O2, and -O3.
7319 @item prefetch-latency
7320 Estimate on average number of instructions that are executed before
7321 prefetch finishes. The distance we prefetch ahead is proportional
7322 to this constant. Increasing this number may also lead to less
7323 streams being prefetched (see @option{simultaneous-prefetches}).
7325 @item simultaneous-prefetches
7326 Maximum number of prefetches that can run at the same time.
7328 @item l1-cache-line-size
7329 The size of cache line in L1 cache, in bytes.
7332 The size of L1 cache, in kilobytes.
7335 The size of L2 cache, in kilobytes.
7337 @item use-canonical-types
7338 Whether the compiler should use the ``canonical'' type system. By
7339 default, this should always be 1, which uses a more efficient internal
7340 mechanism for comparing types in C++ and Objective-C++. However, if
7341 bugs in the canonical type system are causing compilation failures,
7342 set this value to 0 to disable canonical types.
7344 @item switch-conversion-max-branch-ratio
7345 Switch initialization conversion will refuse to create arrays that are
7346 bigger than @option{switch-conversion-max-branch-ratio} times the number of
7347 branches in the switch.
7349 @item max-partial-antic-length
7350 Maximum length of the partial antic set computed during the tree
7351 partial redundancy elimination optimization (@option{-ftree-pre}) when
7352 optimizing at @option{-O3} and above. For some sorts of source code
7353 the enhanced partial redundancy elimination optimization can run away,
7354 consuming all of the memory available on the host machine. This
7355 parameter sets a limit on the length of the sets that are computed,
7356 which prevents the runaway behaviour. Setting a value of 0 for
7357 this paramter will allow an unlimited set length.
7359 @item sccvn-max-scc-size
7360 Maximum size of a strongly connected component (SCC) during SCCVN
7361 processing. If this limit is hit, SCCVN processing for the whole
7362 function will not be done and optimizations depending on it will
7363 be disabled. The default maximum SCC size is 10000.
7368 @node Preprocessor Options
7369 @section Options Controlling the Preprocessor
7370 @cindex preprocessor options
7371 @cindex options, preprocessor
7373 These options control the C preprocessor, which is run on each C source
7374 file before actual compilation.
7376 If you use the @option{-E} option, nothing is done except preprocessing.
7377 Some of these options make sense only together with @option{-E} because
7378 they cause the preprocessor output to be unsuitable for actual
7383 You can use @option{-Wp,@var{option}} to bypass the compiler driver
7384 and pass @var{option} directly through to the preprocessor. If
7385 @var{option} contains commas, it is split into multiple options at the
7386 commas. However, many options are modified, translated or interpreted
7387 by the compiler driver before being passed to the preprocessor, and
7388 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
7389 interface is undocumented and subject to change, so whenever possible
7390 you should avoid using @option{-Wp} and let the driver handle the
7393 @item -Xpreprocessor @var{option}
7394 @opindex preprocessor
7395 Pass @var{option} as an option to the preprocessor. You can use this to
7396 supply system-specific preprocessor options which GCC does not know how to
7399 If you want to pass an option that takes an argument, you must use
7400 @option{-Xpreprocessor} twice, once for the option and once for the argument.
7403 @include cppopts.texi
7405 @node Assembler Options
7406 @section Passing Options to the Assembler
7408 @c prevent bad page break with this line
7409 You can pass options to the assembler.
7412 @item -Wa,@var{option}
7414 Pass @var{option} as an option to the assembler. If @var{option}
7415 contains commas, it is split into multiple options at the commas.
7417 @item -Xassembler @var{option}
7419 Pass @var{option} as an option to the assembler. You can use this to
7420 supply system-specific assembler options which GCC does not know how to
7423 If you want to pass an option that takes an argument, you must use
7424 @option{-Xassembler} twice, once for the option and once for the argument.
7429 @section Options for Linking
7430 @cindex link options
7431 @cindex options, linking
7433 These options come into play when the compiler links object files into
7434 an executable output file. They are meaningless if the compiler is
7435 not doing a link step.
7439 @item @var{object-file-name}
7440 A file name that does not end in a special recognized suffix is
7441 considered to name an object file or library. (Object files are
7442 distinguished from libraries by the linker according to the file
7443 contents.) If linking is done, these object files are used as input
7452 If any of these options is used, then the linker is not run, and
7453 object file names should not be used as arguments. @xref{Overall
7457 @item -l@var{library}
7458 @itemx -l @var{library}
7460 Search the library named @var{library} when linking. (The second
7461 alternative with the library as a separate argument is only for
7462 POSIX compliance and is not recommended.)
7464 It makes a difference where in the command you write this option; the
7465 linker searches and processes libraries and object files in the order they
7466 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
7467 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
7468 to functions in @samp{z}, those functions may not be loaded.
7470 The linker searches a standard list of directories for the library,
7471 which is actually a file named @file{lib@var{library}.a}. The linker
7472 then uses this file as if it had been specified precisely by name.
7474 The directories searched include several standard system directories
7475 plus any that you specify with @option{-L}.
7477 Normally the files found this way are library files---archive files
7478 whose members are object files. The linker handles an archive file by
7479 scanning through it for members which define symbols that have so far
7480 been referenced but not defined. But if the file that is found is an
7481 ordinary object file, it is linked in the usual fashion. The only
7482 difference between using an @option{-l} option and specifying a file name
7483 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
7484 and searches several directories.
7488 You need this special case of the @option{-l} option in order to
7489 link an Objective-C or Objective-C++ program.
7492 @opindex nostartfiles
7493 Do not use the standard system startup files when linking.
7494 The standard system libraries are used normally, unless @option{-nostdlib}
7495 or @option{-nodefaultlibs} is used.
7497 @item -nodefaultlibs
7498 @opindex nodefaultlibs
7499 Do not use the standard system libraries when linking.
7500 Only the libraries you specify will be passed to the linker.
7501 The standard startup files are used normally, unless @option{-nostartfiles}
7502 is used. The compiler may generate calls to @code{memcmp},
7503 @code{memset}, @code{memcpy} and @code{memmove}.
7504 These entries are usually resolved by entries in
7505 libc. These entry points should be supplied through some other
7506 mechanism when this option is specified.
7510 Do not use the standard system startup files or libraries when linking.
7511 No startup files and only the libraries you specify will be passed to
7512 the linker. The compiler may generate calls to @code{memcmp}, @code{memset},
7513 @code{memcpy} and @code{memmove}.
7514 These entries are usually resolved by entries in
7515 libc. These entry points should be supplied through some other
7516 mechanism when this option is specified.
7518 @cindex @option{-lgcc}, use with @option{-nostdlib}
7519 @cindex @option{-nostdlib} and unresolved references
7520 @cindex unresolved references and @option{-nostdlib}
7521 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
7522 @cindex @option{-nodefaultlibs} and unresolved references
7523 @cindex unresolved references and @option{-nodefaultlibs}
7524 One of the standard libraries bypassed by @option{-nostdlib} and
7525 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
7526 that GCC uses to overcome shortcomings of particular machines, or special
7527 needs for some languages.
7528 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
7529 Collection (GCC) Internals},
7530 for more discussion of @file{libgcc.a}.)
7531 In most cases, you need @file{libgcc.a} even when you want to avoid
7532 other standard libraries. In other words, when you specify @option{-nostdlib}
7533 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
7534 This ensures that you have no unresolved references to internal GCC
7535 library subroutines. (For example, @samp{__main}, used to ensure C++
7536 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
7537 GNU Compiler Collection (GCC) Internals}.)
7541 Produce a position independent executable on targets which support it.
7542 For predictable results, you must also specify the same set of options
7543 that were used to generate code (@option{-fpie}, @option{-fPIE},
7544 or model suboptions) when you specify this option.
7548 Pass the flag @option{-export-dynamic} to the ELF linker, on targets
7549 that support it. This instructs the linker to add all symbols, not
7550 only used ones, to the dynamic symbol table. This option is needed
7551 for some uses of @code{dlopen} or to allow obtaining backtraces
7552 from within a program.
7556 Remove all symbol table and relocation information from the executable.
7560 On systems that support dynamic linking, this prevents linking with the shared
7561 libraries. On other systems, this option has no effect.
7565 Produce a shared object which can then be linked with other objects to
7566 form an executable. Not all systems support this option. For predictable
7567 results, you must also specify the same set of options that were used to
7568 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
7569 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
7570 needs to build supplementary stub code for constructors to work. On
7571 multi-libbed systems, @samp{gcc -shared} must select the correct support
7572 libraries to link against. Failing to supply the correct flags may lead
7573 to subtle defects. Supplying them in cases where they are not necessary
7576 @item -shared-libgcc
7577 @itemx -static-libgcc
7578 @opindex shared-libgcc
7579 @opindex static-libgcc
7580 On systems that provide @file{libgcc} as a shared library, these options
7581 force the use of either the shared or static version respectively.
7582 If no shared version of @file{libgcc} was built when the compiler was
7583 configured, these options have no effect.
7585 There are several situations in which an application should use the
7586 shared @file{libgcc} instead of the static version. The most common
7587 of these is when the application wishes to throw and catch exceptions
7588 across different shared libraries. In that case, each of the libraries
7589 as well as the application itself should use the shared @file{libgcc}.
7591 Therefore, the G++ and GCJ drivers automatically add
7592 @option{-shared-libgcc} whenever you build a shared library or a main
7593 executable, because C++ and Java programs typically use exceptions, so
7594 this is the right thing to do.
7596 If, instead, you use the GCC driver to create shared libraries, you may
7597 find that they will not always be linked with the shared @file{libgcc}.
7598 If GCC finds, at its configuration time, that you have a non-GNU linker
7599 or a GNU linker that does not support option @option{--eh-frame-hdr},
7600 it will link the shared version of @file{libgcc} into shared libraries
7601 by default. Otherwise, it will take advantage of the linker and optimize
7602 away the linking with the shared version of @file{libgcc}, linking with
7603 the static version of libgcc by default. This allows exceptions to
7604 propagate through such shared libraries, without incurring relocation
7605 costs at library load time.
7607 However, if a library or main executable is supposed to throw or catch
7608 exceptions, you must link it using the G++ or GCJ driver, as appropriate
7609 for the languages used in the program, or using the option
7610 @option{-shared-libgcc}, such that it is linked with the shared
7615 Bind references to global symbols when building a shared object. Warn
7616 about any unresolved references (unless overridden by the link editor
7617 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
7620 @item -Xlinker @var{option}
7622 Pass @var{option} as an option to the linker. You can use this to
7623 supply system-specific linker options which GCC does not know how to
7626 If you want to pass an option that takes an argument, you must use
7627 @option{-Xlinker} twice, once for the option and once for the argument.
7628 For example, to pass @option{-assert definitions}, you must write
7629 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
7630 @option{-Xlinker "-assert definitions"}, because this passes the entire
7631 string as a single argument, which is not what the linker expects.
7633 @item -Wl,@var{option}
7635 Pass @var{option} as an option to the linker. If @var{option} contains
7636 commas, it is split into multiple options at the commas.
7638 @item -u @var{symbol}
7640 Pretend the symbol @var{symbol} is undefined, to force linking of
7641 library modules to define it. You can use @option{-u} multiple times with
7642 different symbols to force loading of additional library modules.
7645 @node Directory Options
7646 @section Options for Directory Search
7647 @cindex directory options
7648 @cindex options, directory search
7651 These options specify directories to search for header files, for
7652 libraries and for parts of the compiler:
7657 Add the directory @var{dir} to the head of the list of directories to be
7658 searched for header files. This can be used to override a system header
7659 file, substituting your own version, since these directories are
7660 searched before the system header file directories. However, you should
7661 not use this option to add directories that contain vendor-supplied
7662 system header files (use @option{-isystem} for that). If you use more than
7663 one @option{-I} option, the directories are scanned in left-to-right
7664 order; the standard system directories come after.
7666 If a standard system include directory, or a directory specified with
7667 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
7668 option will be ignored. The directory will still be searched but as a
7669 system directory at its normal position in the system include chain.
7670 This is to ensure that GCC's procedure to fix buggy system headers and
7671 the ordering for the include_next directive are not inadvertently changed.
7672 If you really need to change the search order for system directories,
7673 use the @option{-nostdinc} and/or @option{-isystem} options.
7675 @item -iquote@var{dir}
7677 Add the directory @var{dir} to the head of the list of directories to
7678 be searched for header files only for the case of @samp{#include
7679 "@var{file}"}; they are not searched for @samp{#include <@var{file}>},
7680 otherwise just like @option{-I}.
7684 Add directory @var{dir} to the list of directories to be searched
7687 @item -B@var{prefix}
7689 This option specifies where to find the executables, libraries,
7690 include files, and data files of the compiler itself.
7692 The compiler driver program runs one or more of the subprograms
7693 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
7694 @var{prefix} as a prefix for each program it tries to run, both with and
7695 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
7697 For each subprogram to be run, the compiler driver first tries the
7698 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
7699 was not specified, the driver tries two standard prefixes, which are
7700 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
7701 those results in a file name that is found, the unmodified program
7702 name is searched for using the directories specified in your
7703 @env{PATH} environment variable.
7705 The compiler will check to see if the path provided by the @option{-B}
7706 refers to a directory, and if necessary it will add a directory
7707 separator character at the end of the path.
7709 @option{-B} prefixes that effectively specify directory names also apply
7710 to libraries in the linker, because the compiler translates these
7711 options into @option{-L} options for the linker. They also apply to
7712 includes files in the preprocessor, because the compiler translates these
7713 options into @option{-isystem} options for the preprocessor. In this case,
7714 the compiler appends @samp{include} to the prefix.
7716 The run-time support file @file{libgcc.a} can also be searched for using
7717 the @option{-B} prefix, if needed. If it is not found there, the two
7718 standard prefixes above are tried, and that is all. The file is left
7719 out of the link if it is not found by those means.
7721 Another way to specify a prefix much like the @option{-B} prefix is to use
7722 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
7725 As a special kludge, if the path provided by @option{-B} is
7726 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
7727 9, then it will be replaced by @file{[dir/]include}. This is to help
7728 with boot-strapping the compiler.
7730 @item -specs=@var{file}
7732 Process @var{file} after the compiler reads in the standard @file{specs}
7733 file, in order to override the defaults that the @file{gcc} driver
7734 program uses when determining what switches to pass to @file{cc1},
7735 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
7736 @option{-specs=@var{file}} can be specified on the command line, and they
7737 are processed in order, from left to right.
7739 @item --sysroot=@var{dir}
7741 Use @var{dir} as the logical root directory for headers and libraries.
7742 For example, if the compiler would normally search for headers in
7743 @file{/usr/include} and libraries in @file{/usr/lib}, it will instead
7744 search @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}.
7746 If you use both this option and the @option{-isysroot} option, then
7747 the @option{--sysroot} option will apply to libraries, but the
7748 @option{-isysroot} option will apply to header files.
7750 The GNU linker (beginning with version 2.16) has the necessary support
7751 for this option. If your linker does not support this option, the
7752 header file aspect of @option{--sysroot} will still work, but the
7753 library aspect will not.
7757 This option has been deprecated. Please use @option{-iquote} instead for
7758 @option{-I} directories before the @option{-I-} and remove the @option{-I-}.
7759 Any directories you specify with @option{-I} options before the @option{-I-}
7760 option are searched only for the case of @samp{#include "@var{file}"};
7761 they are not searched for @samp{#include <@var{file}>}.
7763 If additional directories are specified with @option{-I} options after
7764 the @option{-I-}, these directories are searched for all @samp{#include}
7765 directives. (Ordinarily @emph{all} @option{-I} directories are used
7768 In addition, the @option{-I-} option inhibits the use of the current
7769 directory (where the current input file came from) as the first search
7770 directory for @samp{#include "@var{file}"}. There is no way to
7771 override this effect of @option{-I-}. With @option{-I.} you can specify
7772 searching the directory which was current when the compiler was
7773 invoked. That is not exactly the same as what the preprocessor does
7774 by default, but it is often satisfactory.
7776 @option{-I-} does not inhibit the use of the standard system directories
7777 for header files. Thus, @option{-I-} and @option{-nostdinc} are
7784 @section Specifying subprocesses and the switches to pass to them
7787 @command{gcc} is a driver program. It performs its job by invoking a
7788 sequence of other programs to do the work of compiling, assembling and
7789 linking. GCC interprets its command-line parameters and uses these to
7790 deduce which programs it should invoke, and which command-line options
7791 it ought to place on their command lines. This behavior is controlled
7792 by @dfn{spec strings}. In most cases there is one spec string for each
7793 program that GCC can invoke, but a few programs have multiple spec
7794 strings to control their behavior. The spec strings built into GCC can
7795 be overridden by using the @option{-specs=} command-line switch to specify
7798 @dfn{Spec files} are plaintext files that are used to construct spec
7799 strings. They consist of a sequence of directives separated by blank
7800 lines. The type of directive is determined by the first non-whitespace
7801 character on the line and it can be one of the following:
7804 @item %@var{command}
7805 Issues a @var{command} to the spec file processor. The commands that can
7809 @item %include <@var{file}>
7811 Search for @var{file} and insert its text at the current point in the
7814 @item %include_noerr <@var{file}>
7815 @cindex %include_noerr
7816 Just like @samp{%include}, but do not generate an error message if the include
7817 file cannot be found.
7819 @item %rename @var{old_name} @var{new_name}
7821 Rename the spec string @var{old_name} to @var{new_name}.
7825 @item *[@var{spec_name}]:
7826 This tells the compiler to create, override or delete the named spec
7827 string. All lines after this directive up to the next directive or
7828 blank line are considered to be the text for the spec string. If this
7829 results in an empty string then the spec will be deleted. (Or, if the
7830 spec did not exist, then nothing will happened.) Otherwise, if the spec
7831 does not currently exist a new spec will be created. If the spec does
7832 exist then its contents will be overridden by the text of this
7833 directive, unless the first character of that text is the @samp{+}
7834 character, in which case the text will be appended to the spec.
7836 @item [@var{suffix}]:
7837 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
7838 and up to the next directive or blank line are considered to make up the
7839 spec string for the indicated suffix. When the compiler encounters an
7840 input file with the named suffix, it will processes the spec string in
7841 order to work out how to compile that file. For example:
7848 This says that any input file whose name ends in @samp{.ZZ} should be
7849 passed to the program @samp{z-compile}, which should be invoked with the
7850 command-line switch @option{-input} and with the result of performing the
7851 @samp{%i} substitution. (See below.)
7853 As an alternative to providing a spec string, the text that follows a
7854 suffix directive can be one of the following:
7857 @item @@@var{language}
7858 This says that the suffix is an alias for a known @var{language}. This is
7859 similar to using the @option{-x} command-line switch to GCC to specify a
7860 language explicitly. For example:
7867 Says that .ZZ files are, in fact, C++ source files.
7870 This causes an error messages saying:
7873 @var{name} compiler not installed on this system.
7877 GCC already has an extensive list of suffixes built into it.
7878 This directive will add an entry to the end of the list of suffixes, but
7879 since the list is searched from the end backwards, it is effectively
7880 possible to override earlier entries using this technique.
7884 GCC has the following spec strings built into it. Spec files can
7885 override these strings or create their own. Note that individual
7886 targets can also add their own spec strings to this list.
7889 asm Options to pass to the assembler
7890 asm_final Options to pass to the assembler post-processor
7891 cpp Options to pass to the C preprocessor
7892 cc1 Options to pass to the C compiler
7893 cc1plus Options to pass to the C++ compiler
7894 endfile Object files to include at the end of the link
7895 link Options to pass to the linker
7896 lib Libraries to include on the command line to the linker
7897 libgcc Decides which GCC support library to pass to the linker
7898 linker Sets the name of the linker
7899 predefines Defines to be passed to the C preprocessor
7900 signed_char Defines to pass to CPP to say whether @code{char} is signed
7902 startfile Object files to include at the start of the link
7905 Here is a small example of a spec file:
7911 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
7914 This example renames the spec called @samp{lib} to @samp{old_lib} and
7915 then overrides the previous definition of @samp{lib} with a new one.
7916 The new definition adds in some extra command-line options before
7917 including the text of the old definition.
7919 @dfn{Spec strings} are a list of command-line options to be passed to their
7920 corresponding program. In addition, the spec strings can contain
7921 @samp{%}-prefixed sequences to substitute variable text or to
7922 conditionally insert text into the command line. Using these constructs
7923 it is possible to generate quite complex command lines.
7925 Here is a table of all defined @samp{%}-sequences for spec
7926 strings. Note that spaces are not generated automatically around the
7927 results of expanding these sequences. Therefore you can concatenate them
7928 together or combine them with constant text in a single argument.
7932 Substitute one @samp{%} into the program name or argument.
7935 Substitute the name of the input file being processed.
7938 Substitute the basename of the input file being processed.
7939 This is the substring up to (and not including) the last period
7940 and not including the directory.
7943 This is the same as @samp{%b}, but include the file suffix (text after
7947 Marks the argument containing or following the @samp{%d} as a
7948 temporary file name, so that that file will be deleted if GCC exits
7949 successfully. Unlike @samp{%g}, this contributes no text to the
7952 @item %g@var{suffix}
7953 Substitute a file name that has suffix @var{suffix} and is chosen
7954 once per compilation, and mark the argument in the same way as
7955 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
7956 name is now chosen in a way that is hard to predict even when previously
7957 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
7958 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
7959 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
7960 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
7961 was simply substituted with a file name chosen once per compilation,
7962 without regard to any appended suffix (which was therefore treated
7963 just like ordinary text), making such attacks more likely to succeed.
7965 @item %u@var{suffix}
7966 Like @samp{%g}, but generates a new temporary file name even if
7967 @samp{%u@var{suffix}} was already seen.
7969 @item %U@var{suffix}
7970 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
7971 new one if there is no such last file name. In the absence of any
7972 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
7973 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
7974 would involve the generation of two distinct file names, one
7975 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
7976 simply substituted with a file name chosen for the previous @samp{%u},
7977 without regard to any appended suffix.
7979 @item %j@var{suffix}
7980 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
7981 writable, and if save-temps is off; otherwise, substitute the name
7982 of a temporary file, just like @samp{%u}. This temporary file is not
7983 meant for communication between processes, but rather as a junk
7986 @item %|@var{suffix}
7987 @itemx %m@var{suffix}
7988 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
7989 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
7990 all. These are the two most common ways to instruct a program that it
7991 should read from standard input or write to standard output. If you
7992 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
7993 construct: see for example @file{f/lang-specs.h}.
7995 @item %.@var{SUFFIX}
7996 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
7997 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
7998 terminated by the next space or %.
8001 Marks the argument containing or following the @samp{%w} as the
8002 designated output file of this compilation. This puts the argument
8003 into the sequence of arguments that @samp{%o} will substitute later.
8006 Substitutes the names of all the output files, with spaces
8007 automatically placed around them. You should write spaces
8008 around the @samp{%o} as well or the results are undefined.
8009 @samp{%o} is for use in the specs for running the linker.
8010 Input files whose names have no recognized suffix are not compiled
8011 at all, but they are included among the output files, so they will
8015 Substitutes the suffix for object files. Note that this is
8016 handled specially when it immediately follows @samp{%g, %u, or %U},
8017 because of the need for those to form complete file names. The
8018 handling is such that @samp{%O} is treated exactly as if it had already
8019 been substituted, except that @samp{%g, %u, and %U} do not currently
8020 support additional @var{suffix} characters following @samp{%O} as they would
8021 following, for example, @samp{.o}.
8024 Substitutes the standard macro predefinitions for the
8025 current target machine. Use this when running @code{cpp}.
8028 Like @samp{%p}, but puts @samp{__} before and after the name of each
8029 predefined macro, except for macros that start with @samp{__} or with
8030 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
8034 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
8035 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}),
8036 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
8037 and @option{-imultilib} as necessary.
8040 Current argument is the name of a library or startup file of some sort.
8041 Search for that file in a standard list of directories and substitute
8042 the full name found.
8045 Print @var{str} as an error message. @var{str} is terminated by a newline.
8046 Use this when inconsistent options are detected.
8049 Substitute the contents of spec string @var{name} at this point.
8052 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
8054 @item %x@{@var{option}@}
8055 Accumulate an option for @samp{%X}.
8058 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
8062 Output the accumulated assembler options specified by @option{-Wa}.
8065 Output the accumulated preprocessor options specified by @option{-Wp}.
8068 Process the @code{asm} spec. This is used to compute the
8069 switches to be passed to the assembler.
8072 Process the @code{asm_final} spec. This is a spec string for
8073 passing switches to an assembler post-processor, if such a program is
8077 Process the @code{link} spec. This is the spec for computing the
8078 command line passed to the linker. Typically it will make use of the
8079 @samp{%L %G %S %D and %E} sequences.
8082 Dump out a @option{-L} option for each directory that GCC believes might
8083 contain startup files. If the target supports multilibs then the
8084 current multilib directory will be prepended to each of these paths.
8087 Process the @code{lib} spec. This is a spec string for deciding which
8088 libraries should be included on the command line to the linker.
8091 Process the @code{libgcc} spec. This is a spec string for deciding
8092 which GCC support library should be included on the command line to the linker.
8095 Process the @code{startfile} spec. This is a spec for deciding which
8096 object files should be the first ones passed to the linker. Typically
8097 this might be a file named @file{crt0.o}.
8100 Process the @code{endfile} spec. This is a spec string that specifies
8101 the last object files that will be passed to the linker.
8104 Process the @code{cpp} spec. This is used to construct the arguments
8105 to be passed to the C preprocessor.
8108 Process the @code{cc1} spec. This is used to construct the options to be
8109 passed to the actual C compiler (@samp{cc1}).
8112 Process the @code{cc1plus} spec. This is used to construct the options to be
8113 passed to the actual C++ compiler (@samp{cc1plus}).
8116 Substitute the variable part of a matched option. See below.
8117 Note that each comma in the substituted string is replaced by
8121 Remove all occurrences of @code{-S} from the command line. Note---this
8122 command is position dependent. @samp{%} commands in the spec string
8123 before this one will see @code{-S}, @samp{%} commands in the spec string
8124 after this one will not.
8126 @item %:@var{function}(@var{args})
8127 Call the named function @var{function}, passing it @var{args}.
8128 @var{args} is first processed as a nested spec string, then split
8129 into an argument vector in the usual fashion. The function returns
8130 a string which is processed as if it had appeared literally as part
8131 of the current spec.
8133 The following built-in spec functions are provided:
8137 The @code{getenv} spec function takes two arguments: an environment
8138 variable name and a string. If the environment variable is not
8139 defined, a fatal error is issued. Otherwise, the return value is the
8140 value of the environment variable concatenated with the string. For
8141 example, if @env{TOPDIR} is defined as @file{/path/to/top}, then:
8144 %:getenv(TOPDIR /include)
8147 expands to @file{/path/to/top/include}.
8149 @item @code{if-exists}
8150 The @code{if-exists} spec function takes one argument, an absolute
8151 pathname to a file. If the file exists, @code{if-exists} returns the
8152 pathname. Here is a small example of its usage:
8156 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
8159 @item @code{if-exists-else}
8160 The @code{if-exists-else} spec function is similar to the @code{if-exists}
8161 spec function, except that it takes two arguments. The first argument is
8162 an absolute pathname to a file. If the file exists, @code{if-exists-else}
8163 returns the pathname. If it does not exist, it returns the second argument.
8164 This way, @code{if-exists-else} can be used to select one file or another,
8165 based on the existence of the first. Here is a small example of its usage:
8169 crt0%O%s %:if-exists(crti%O%s) \
8170 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
8173 @item @code{replace-outfile}
8174 The @code{replace-outfile} spec function takes two arguments. It looks for the
8175 first argument in the outfiles array and replaces it with the second argument. Here
8176 is a small example of its usage:
8179 %@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
8182 @item @code{print-asm-header}
8183 The @code{print-asm-header} function takes no arguments and simply
8184 prints a banner like:
8190 Use "-Wa,OPTION" to pass "OPTION" to the assembler.
8193 It is used to separate compiler options from assembler options
8194 in the @option{--target-help} output.
8198 Substitutes the @code{-S} switch, if that switch was given to GCC@.
8199 If that switch was not specified, this substitutes nothing. Note that
8200 the leading dash is omitted when specifying this option, and it is
8201 automatically inserted if the substitution is performed. Thus the spec
8202 string @samp{%@{foo@}} would match the command-line option @option{-foo}
8203 and would output the command line option @option{-foo}.
8205 @item %W@{@code{S}@}
8206 Like %@{@code{S}@} but mark last argument supplied within as a file to be
8209 @item %@{@code{S}*@}
8210 Substitutes all the switches specified to GCC whose names start
8211 with @code{-S}, but which also take an argument. This is used for
8212 switches like @option{-o}, @option{-D}, @option{-I}, etc.
8213 GCC considers @option{-o foo} as being
8214 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
8215 text, including the space. Thus two arguments would be generated.
8217 @item %@{@code{S}*&@code{T}*@}
8218 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
8219 (the order of @code{S} and @code{T} in the spec is not significant).
8220 There can be any number of ampersand-separated variables; for each the
8221 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
8223 @item %@{@code{S}:@code{X}@}
8224 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
8226 @item %@{!@code{S}:@code{X}@}
8227 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
8229 @item %@{@code{S}*:@code{X}@}
8230 Substitutes @code{X} if one or more switches whose names start with
8231 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
8232 once, no matter how many such switches appeared. However, if @code{%*}
8233 appears somewhere in @code{X}, then @code{X} will be substituted once
8234 for each matching switch, with the @code{%*} replaced by the part of
8235 that switch that matched the @code{*}.
8237 @item %@{.@code{S}:@code{X}@}
8238 Substitutes @code{X}, if processing a file with suffix @code{S}.
8240 @item %@{!.@code{S}:@code{X}@}
8241 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
8243 @item %@{,@code{S}:@code{X}@}
8244 Substitutes @code{X}, if processing a file for language @code{S}.
8246 @item %@{!,@code{S}:@code{X}@}
8247 Substitutes @code{X}, if not processing a file for language @code{S}.
8249 @item %@{@code{S}|@code{P}:@code{X}@}
8250 Substitutes @code{X} if either @code{-S} or @code{-P} was given to
8251 GCC@. This may be combined with @samp{!}, @samp{.}, @samp{,}, and
8252 @code{*} sequences as well, although they have a stronger binding than
8253 the @samp{|}. If @code{%*} appears in @code{X}, all of the
8254 alternatives must be starred, and only the first matching alternative
8257 For example, a spec string like this:
8260 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
8263 will output the following command-line options from the following input
8264 command-line options:
8269 -d fred.c -foo -baz -boggle
8270 -d jim.d -bar -baz -boggle
8273 @item %@{S:X; T:Y; :D@}
8275 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
8276 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
8277 be as many clauses as you need. This may be combined with @code{.},
8278 @code{,}, @code{!}, @code{|}, and @code{*} as needed.
8283 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
8284 construct may contain other nested @samp{%} constructs or spaces, or
8285 even newlines. They are processed as usual, as described above.
8286 Trailing white space in @code{X} is ignored. White space may also
8287 appear anywhere on the left side of the colon in these constructs,
8288 except between @code{.} or @code{*} and the corresponding word.
8290 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
8291 handled specifically in these constructs. If another value of
8292 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
8293 @option{-W} switch is found later in the command line, the earlier
8294 switch value is ignored, except with @{@code{S}*@} where @code{S} is
8295 just one letter, which passes all matching options.
8297 The character @samp{|} at the beginning of the predicate text is used to
8298 indicate that a command should be piped to the following command, but
8299 only if @option{-pipe} is specified.
8301 It is built into GCC which switches take arguments and which do not.
8302 (You might think it would be useful to generalize this to allow each
8303 compiler's spec to say which switches take arguments. But this cannot
8304 be done in a consistent fashion. GCC cannot even decide which input
8305 files have been specified without knowing which switches take arguments,
8306 and it must know which input files to compile in order to tell which
8309 GCC also knows implicitly that arguments starting in @option{-l} are to be
8310 treated as compiler output files, and passed to the linker in their
8311 proper position among the other output files.
8313 @c man begin OPTIONS
8315 @node Target Options
8316 @section Specifying Target Machine and Compiler Version
8317 @cindex target options
8318 @cindex cross compiling
8319 @cindex specifying machine version
8320 @cindex specifying compiler version and target machine
8321 @cindex compiler version, specifying
8322 @cindex target machine, specifying
8324 The usual way to run GCC is to run the executable called @file{gcc}, or
8325 @file{<machine>-gcc} when cross-compiling, or
8326 @file{<machine>-gcc-<version>} to run a version other than the one that
8327 was installed last. Sometimes this is inconvenient, so GCC provides
8328 options that will switch to another cross-compiler or version.
8331 @item -b @var{machine}
8333 The argument @var{machine} specifies the target machine for compilation.
8335 The value to use for @var{machine} is the same as was specified as the
8336 machine type when configuring GCC as a cross-compiler. For
8337 example, if a cross-compiler was configured with @samp{configure
8338 arm-elf}, meaning to compile for an arm processor with elf binaries,
8339 then you would specify @option{-b arm-elf} to run that cross compiler.
8340 Because there are other options beginning with @option{-b}, the
8341 configuration must contain a hyphen.
8343 @item -V @var{version}
8345 The argument @var{version} specifies which version of GCC to run.
8346 This is useful when multiple versions are installed. For example,
8347 @var{version} might be @samp{4.0}, meaning to run GCC version 4.0.
8350 The @option{-V} and @option{-b} options work by running the
8351 @file{<machine>-gcc-<version>} executable, so there's no real reason to
8352 use them if you can just run that directly.
8354 @node Submodel Options
8355 @section Hardware Models and Configurations
8356 @cindex submodel options
8357 @cindex specifying hardware config
8358 @cindex hardware models and configurations, specifying
8359 @cindex machine dependent options
8361 Earlier we discussed the standard option @option{-b} which chooses among
8362 different installed compilers for completely different target
8363 machines, such as VAX vs.@: 68000 vs.@: 80386.
8365 In addition, each of these target machine types can have its own
8366 special options, starting with @samp{-m}, to choose among various
8367 hardware models or configurations---for example, 68010 vs 68020,
8368 floating coprocessor or none. A single installed version of the
8369 compiler can compile for any model or configuration, according to the
8372 Some configurations of the compiler also support additional special
8373 options, usually for compatibility with other compilers on the same
8376 @c This list is ordered alphanumerically by subsection name.
8377 @c It should be the same order and spelling as these options are listed
8378 @c in Machine Dependent Options
8384 * Blackfin Options::
8388 * DEC Alpha Options::
8389 * DEC Alpha/VMS Options::
8391 * GNU/Linux Options::
8394 * i386 and x86-64 Options::
8406 * RS/6000 and PowerPC Options::
8407 * S/390 and zSeries Options::
8412 * System V Options::
8417 * Xstormy16 Options::
8423 @subsection ARC Options
8426 These options are defined for ARC implementations:
8431 Compile code for little endian mode. This is the default.
8435 Compile code for big endian mode.
8438 @opindex mmangle-cpu
8439 Prepend the name of the cpu to all public symbol names.
8440 In multiple-processor systems, there are many ARC variants with different
8441 instruction and register set characteristics. This flag prevents code
8442 compiled for one cpu to be linked with code compiled for another.
8443 No facility exists for handling variants that are ``almost identical''.
8444 This is an all or nothing option.
8446 @item -mcpu=@var{cpu}
8448 Compile code for ARC variant @var{cpu}.
8449 Which variants are supported depend on the configuration.
8450 All variants support @option{-mcpu=base}, this is the default.
8452 @item -mtext=@var{text-section}
8453 @itemx -mdata=@var{data-section}
8454 @itemx -mrodata=@var{readonly-data-section}
8458 Put functions, data, and readonly data in @var{text-section},
8459 @var{data-section}, and @var{readonly-data-section} respectively
8460 by default. This can be overridden with the @code{section} attribute.
8461 @xref{Variable Attributes}.
8466 @subsection ARM Options
8469 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
8473 @item -mabi=@var{name}
8475 Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu},
8476 @samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}.
8479 @opindex mapcs-frame
8480 Generate a stack frame that is compliant with the ARM Procedure Call
8481 Standard for all functions, even if this is not strictly necessary for
8482 correct execution of the code. Specifying @option{-fomit-frame-pointer}
8483 with this option will cause the stack frames not to be generated for
8484 leaf functions. The default is @option{-mno-apcs-frame}.
8488 This is a synonym for @option{-mapcs-frame}.
8491 @c not currently implemented
8492 @item -mapcs-stack-check
8493 @opindex mapcs-stack-check
8494 Generate code to check the amount of stack space available upon entry to
8495 every function (that actually uses some stack space). If there is
8496 insufficient space available then either the function
8497 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
8498 called, depending upon the amount of stack space required. The run time
8499 system is required to provide these functions. The default is
8500 @option{-mno-apcs-stack-check}, since this produces smaller code.
8502 @c not currently implemented
8504 @opindex mapcs-float
8505 Pass floating point arguments using the float point registers. This is
8506 one of the variants of the APCS@. This option is recommended if the
8507 target hardware has a floating point unit or if a lot of floating point
8508 arithmetic is going to be performed by the code. The default is
8509 @option{-mno-apcs-float}, since integer only code is slightly increased in
8510 size if @option{-mapcs-float} is used.
8512 @c not currently implemented
8513 @item -mapcs-reentrant
8514 @opindex mapcs-reentrant
8515 Generate reentrant, position independent code. The default is
8516 @option{-mno-apcs-reentrant}.
8519 @item -mthumb-interwork
8520 @opindex mthumb-interwork
8521 Generate code which supports calling between the ARM and Thumb
8522 instruction sets. Without this option the two instruction sets cannot
8523 be reliably used inside one program. The default is
8524 @option{-mno-thumb-interwork}, since slightly larger code is generated
8525 when @option{-mthumb-interwork} is specified.
8527 @item -mno-sched-prolog
8528 @opindex mno-sched-prolog
8529 Prevent the reordering of instructions in the function prolog, or the
8530 merging of those instruction with the instructions in the function's
8531 body. This means that all functions will start with a recognizable set
8532 of instructions (or in fact one of a choice from a small set of
8533 different function prologues), and this information can be used to
8534 locate the start if functions inside an executable piece of code. The
8535 default is @option{-msched-prolog}.
8538 @opindex mhard-float
8539 Generate output containing floating point instructions. This is the
8543 @opindex msoft-float
8544 Generate output containing library calls for floating point.
8545 @strong{Warning:} the requisite libraries are not available for all ARM
8546 targets. Normally the facilities of the machine's usual C compiler are
8547 used, but this cannot be done directly in cross-compilation. You must make
8548 your own arrangements to provide suitable library functions for
8551 @option{-msoft-float} changes the calling convention in the output file;
8552 therefore, it is only useful if you compile @emph{all} of a program with
8553 this option. In particular, you need to compile @file{libgcc.a}, the
8554 library that comes with GCC, with @option{-msoft-float} in order for
8557 @item -mfloat-abi=@var{name}
8559 Specifies which ABI to use for floating point values. Permissible values
8560 are: @samp{soft}, @samp{softfp} and @samp{hard}.
8562 @samp{soft} and @samp{hard} are equivalent to @option{-msoft-float}
8563 and @option{-mhard-float} respectively. @samp{softfp} allows the generation
8564 of floating point instructions, but still uses the soft-float calling
8567 @item -mlittle-endian
8568 @opindex mlittle-endian
8569 Generate code for a processor running in little-endian mode. This is
8570 the default for all standard configurations.
8573 @opindex mbig-endian
8574 Generate code for a processor running in big-endian mode; the default is
8575 to compile code for a little-endian processor.
8577 @item -mwords-little-endian
8578 @opindex mwords-little-endian
8579 This option only applies when generating code for big-endian processors.
8580 Generate code for a little-endian word order but a big-endian byte
8581 order. That is, a byte order of the form @samp{32107654}. Note: this
8582 option should only be used if you require compatibility with code for
8583 big-endian ARM processors generated by versions of the compiler prior to
8586 @item -mcpu=@var{name}
8588 This specifies the name of the target ARM processor. GCC uses this name
8589 to determine what kind of instructions it can emit when generating
8590 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
8591 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
8592 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
8593 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
8594 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
8595 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s},
8596 @samp{arm8}, @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
8597 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
8598 @samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s},
8599 @samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi},
8600 @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s},
8601 @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e},
8602 @samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp},
8603 @samp{arm1156t2-s}, @samp{arm1176jz-s}, @samp{arm1176jzf-s},
8604 @samp{cortex-a8}, @samp{cortex-r4}, @samp{cortex-r4f}, @samp{cortex-m3},
8606 @samp{xscale}, @samp{iwmmxt}, @samp{ep9312}.
8608 @item -mtune=@var{name}
8610 This option is very similar to the @option{-mcpu=} option, except that
8611 instead of specifying the actual target processor type, and hence
8612 restricting which instructions can be used, it specifies that GCC should
8613 tune the performance of the code as if the target were of the type
8614 specified in this option, but still choosing the instructions that it
8615 will generate based on the cpu specified by a @option{-mcpu=} option.
8616 For some ARM implementations better performance can be obtained by using
8619 @item -march=@var{name}
8621 This specifies the name of the target ARM architecture. GCC uses this
8622 name to determine what kind of instructions it can emit when generating
8623 assembly code. This option can be used in conjunction with or instead
8624 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
8625 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
8626 @samp{armv5}, @samp{armv5t}, @samp{armv5te}, @samp{armv6}, @samp{armv6j},
8627 @samp{armv6t2}, @samp{armv6z}, @samp{armv6zk}, @samp{armv6-m},
8628 @samp{armv7}, @samp{armv7-a}, @samp{armv7-r}, @samp{armv7-m},
8629 @samp{iwmmxt}, @samp{ep9312}.
8631 @item -mfpu=@var{name}
8632 @itemx -mfpe=@var{number}
8633 @itemx -mfp=@var{number}
8637 This specifies what floating point hardware (or hardware emulation) is
8638 available on the target. Permissible names are: @samp{fpa}, @samp{fpe2},
8639 @samp{fpe3}, @samp{maverick}, @samp{vfp}, @samp{vfpv3}, @samp{vfpv3-d16} and
8640 @samp{neon}. @option{-mfp} and @option{-mfpe}
8641 are synonyms for @option{-mfpu}=@samp{fpe}@var{number}, for compatibility
8642 with older versions of GCC@.
8644 If @option{-msoft-float} is specified this specifies the format of
8645 floating point values.
8647 @item -mstructure-size-boundary=@var{n}
8648 @opindex mstructure-size-boundary
8649 The size of all structures and unions will be rounded up to a multiple
8650 of the number of bits set by this option. Permissible values are 8, 32
8651 and 64. The default value varies for different toolchains. For the COFF
8652 targeted toolchain the default value is 8. A value of 64 is only allowed
8653 if the underlying ABI supports it.
8655 Specifying the larger number can produce faster, more efficient code, but
8656 can also increase the size of the program. Different values are potentially
8657 incompatible. Code compiled with one value cannot necessarily expect to
8658 work with code or libraries compiled with another value, if they exchange
8659 information using structures or unions.
8661 @item -mabort-on-noreturn
8662 @opindex mabort-on-noreturn
8663 Generate a call to the function @code{abort} at the end of a
8664 @code{noreturn} function. It will be executed if the function tries to
8668 @itemx -mno-long-calls
8669 @opindex mlong-calls
8670 @opindex mno-long-calls
8671 Tells the compiler to perform function calls by first loading the
8672 address of the function into a register and then performing a subroutine
8673 call on this register. This switch is needed if the target function
8674 will lie outside of the 64 megabyte addressing range of the offset based
8675 version of subroutine call instruction.
8677 Even if this switch is enabled, not all function calls will be turned
8678 into long calls. The heuristic is that static functions, functions
8679 which have the @samp{short-call} attribute, functions that are inside
8680 the scope of a @samp{#pragma no_long_calls} directive and functions whose
8681 definitions have already been compiled within the current compilation
8682 unit, will not be turned into long calls. The exception to this rule is
8683 that weak function definitions, functions with the @samp{long-call}
8684 attribute or the @samp{section} attribute, and functions that are within
8685 the scope of a @samp{#pragma long_calls} directive, will always be
8686 turned into long calls.
8688 This feature is not enabled by default. Specifying
8689 @option{-mno-long-calls} will restore the default behavior, as will
8690 placing the function calls within the scope of a @samp{#pragma
8691 long_calls_off} directive. Note these switches have no effect on how
8692 the compiler generates code to handle function calls via function
8695 @item -mnop-fun-dllimport
8696 @opindex mnop-fun-dllimport
8697 Disable support for the @code{dllimport} attribute.
8699 @item -msingle-pic-base
8700 @opindex msingle-pic-base
8701 Treat the register used for PIC addressing as read-only, rather than
8702 loading it in the prologue for each function. The run-time system is
8703 responsible for initializing this register with an appropriate value
8704 before execution begins.
8706 @item -mpic-register=@var{reg}
8707 @opindex mpic-register
8708 Specify the register to be used for PIC addressing. The default is R10
8709 unless stack-checking is enabled, when R9 is used.
8711 @item -mcirrus-fix-invalid-insns
8712 @opindex mcirrus-fix-invalid-insns
8713 @opindex mno-cirrus-fix-invalid-insns
8714 Insert NOPs into the instruction stream to in order to work around
8715 problems with invalid Maverick instruction combinations. This option
8716 is only valid if the @option{-mcpu=ep9312} option has been used to
8717 enable generation of instructions for the Cirrus Maverick floating
8718 point co-processor. This option is not enabled by default, since the
8719 problem is only present in older Maverick implementations. The default
8720 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
8723 @item -mpoke-function-name
8724 @opindex mpoke-function-name
8725 Write the name of each function into the text section, directly
8726 preceding the function prologue. The generated code is similar to this:
8730 .ascii "arm_poke_function_name", 0
8733 .word 0xff000000 + (t1 - t0)
8734 arm_poke_function_name
8736 stmfd sp!, @{fp, ip, lr, pc@}
8740 When performing a stack backtrace, code can inspect the value of
8741 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
8742 location @code{pc - 12} and the top 8 bits are set, then we know that
8743 there is a function name embedded immediately preceding this location
8744 and has length @code{((pc[-3]) & 0xff000000)}.
8748 Generate code for the Thumb instruction set. The default is to
8749 use the 32-bit ARM instruction set.
8750 This option automatically enables either 16-bit Thumb-1 or
8751 mixed 16/32-bit Thumb-2 instructions based on the @option{-mcpu=@var{name}}
8752 and @option{-march=@var{name}} options.
8755 @opindex mtpcs-frame
8756 Generate a stack frame that is compliant with the Thumb Procedure Call
8757 Standard for all non-leaf functions. (A leaf function is one that does
8758 not call any other functions.) The default is @option{-mno-tpcs-frame}.
8760 @item -mtpcs-leaf-frame
8761 @opindex mtpcs-leaf-frame
8762 Generate a stack frame that is compliant with the Thumb Procedure Call
8763 Standard for all leaf functions. (A leaf function is one that does
8764 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
8766 @item -mcallee-super-interworking
8767 @opindex mcallee-super-interworking
8768 Gives all externally visible functions in the file being compiled an ARM
8769 instruction set header which switches to Thumb mode before executing the
8770 rest of the function. This allows these functions to be called from
8771 non-interworking code.
8773 @item -mcaller-super-interworking
8774 @opindex mcaller-super-interworking
8775 Allows calls via function pointers (including virtual functions) to
8776 execute correctly regardless of whether the target code has been
8777 compiled for interworking or not. There is a small overhead in the cost
8778 of executing a function pointer if this option is enabled.
8780 @item -mtp=@var{name}
8782 Specify the access model for the thread local storage pointer. The valid
8783 models are @option{soft}, which generates calls to @code{__aeabi_read_tp},
8784 @option{cp15}, which fetches the thread pointer from @code{cp15} directly
8785 (supported in the arm6k architecture), and @option{auto}, which uses the
8786 best available method for the selected processor. The default setting is
8792 @subsection AVR Options
8795 These options are defined for AVR implementations:
8798 @item -mmcu=@var{mcu}
8800 Specify ATMEL AVR instruction set or MCU type.
8802 Instruction set avr1 is for the minimal AVR core, not supported by the C
8803 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
8804 attiny11, attiny12, attiny15, attiny28).
8806 Instruction set avr2 (default) is for the classic AVR core with up to
8807 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
8808 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
8809 at90c8534, at90s8535).
8811 Instruction set avr3 is for the classic AVR core with up to 128K program
8812 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
8814 Instruction set avr4 is for the enhanced AVR core with up to 8K program
8815 memory space (MCU types: atmega8, atmega83, atmega85).
8817 Instruction set avr5 is for the enhanced AVR core with up to 128K program
8818 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
8819 atmega64, atmega128, at43usb355, at94k).
8823 Output instruction sizes to the asm file.
8825 @item -minit-stack=@var{N}
8826 @opindex minit-stack
8827 Specify the initial stack address, which may be a symbol or numeric value,
8828 @samp{__stack} is the default.
8830 @item -mno-interrupts
8831 @opindex mno-interrupts
8832 Generated code is not compatible with hardware interrupts.
8833 Code size will be smaller.
8835 @item -mcall-prologues
8836 @opindex mcall-prologues
8837 Functions prologues/epilogues expanded as call to appropriate
8838 subroutines. Code size will be smaller.
8840 @item -mno-tablejump
8841 @opindex mno-tablejump
8842 Do not generate tablejump insns which sometimes increase code size.
8845 @opindex mtiny-stack
8846 Change only the low 8 bits of the stack pointer.
8850 Assume int to be 8 bit integer. This affects the sizes of all types: A
8851 char will be 1 byte, an int will be 1 byte, an long will be 2 bytes
8852 and long long will be 4 bytes. Please note that this option does not
8853 comply to the C standards, but it will provide you with smaller code
8857 @node Blackfin Options
8858 @subsection Blackfin Options
8859 @cindex Blackfin Options
8862 @item -mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]}
8864 Specifies the name of the target Blackfin processor. Currently, @var{cpu}
8865 can be one of @samp{bf522}, @samp{bf523}, @samp{bf524},
8866 @samp{bf525}, @samp{bf526}, @samp{bf527},
8867 @samp{bf531}, @samp{bf532}, @samp{bf533}, @samp{bf534},
8868 @samp{bf536}, @samp{bf537}, @samp{bf538}, @samp{bf539},
8869 @samp{bf542}, @samp{bf544}, @samp{bf547}, @samp{bf548}, @samp{bf549},
8871 The optional @var{sirevision} specifies the silicon revision of the target
8872 Blackfin processor. Any workarounds available for the targeted silicon revision
8873 will be enabled. If @var{sirevision} is @samp{none}, no workarounds are enabled.
8874 If @var{sirevision} is @samp{any}, all workarounds for the targeted processor
8875 will be enabled. The @code{__SILICON_REVISION__} macro is defined to two
8876 hexadecimal digits representing the major and minor numbers in the silicon
8877 revision. If @var{sirevision} is @samp{none}, the @code{__SILICON_REVISION__}
8878 is not defined. If @var{sirevision} is @samp{any}, the
8879 @code{__SILICON_REVISION__} is defined to be @code{0xffff}.
8880 If this optional @var{sirevision} is not used, GCC assumes the latest known
8881 silicon revision of the targeted Blackfin processor.
8883 Support for @samp{bf561} is incomplete. For @samp{bf561},
8884 Only the processor macro is defined.
8885 Without this option, @samp{bf532} is used as the processor by default.
8886 The corresponding predefined processor macros for @var{cpu} is to
8887 be defined. And for @samp{bfin-elf} toolchain, this causes the hardware BSP
8888 provided by libgloss to be linked in if @option{-msim} is not given.
8892 Specifies that the program will be run on the simulator. This causes
8893 the simulator BSP provided by libgloss to be linked in. This option
8894 has effect only for @samp{bfin-elf} toolchain.
8895 Certain other options, such as @option{-mid-shared-library} and
8896 @option{-mfdpic}, imply @option{-msim}.
8898 @item -momit-leaf-frame-pointer
8899 @opindex momit-leaf-frame-pointer
8900 Don't keep the frame pointer in a register for leaf functions. This
8901 avoids the instructions to save, set up and restore frame pointers and
8902 makes an extra register available in leaf functions. The option
8903 @option{-fomit-frame-pointer} removes the frame pointer for all functions
8904 which might make debugging harder.
8906 @item -mspecld-anomaly
8907 @opindex mspecld-anomaly
8908 When enabled, the compiler will ensure that the generated code does not
8909 contain speculative loads after jump instructions. If this option is used,
8910 @code{__WORKAROUND_SPECULATIVE_LOADS} is defined.
8912 @item -mno-specld-anomaly
8913 @opindex mno-specld-anomaly
8914 Don't generate extra code to prevent speculative loads from occurring.
8916 @item -mcsync-anomaly
8917 @opindex mcsync-anomaly
8918 When enabled, the compiler will ensure that the generated code does not
8919 contain CSYNC or SSYNC instructions too soon after conditional branches.
8920 If this option is used, @code{__WORKAROUND_SPECULATIVE_SYNCS} is defined.
8922 @item -mno-csync-anomaly
8923 @opindex mno-csync-anomaly
8924 Don't generate extra code to prevent CSYNC or SSYNC instructions from
8925 occurring too soon after a conditional branch.
8929 When enabled, the compiler is free to take advantage of the knowledge that
8930 the entire program fits into the low 64k of memory.
8933 @opindex mno-low-64k
8934 Assume that the program is arbitrarily large. This is the default.
8936 @item -mstack-check-l1
8937 @opindex mstack-check-l1
8938 Do stack checking using information placed into L1 scratchpad memory by the
8941 @item -mid-shared-library
8942 @opindex mid-shared-library
8943 Generate code that supports shared libraries via the library ID method.
8944 This allows for execute in place and shared libraries in an environment
8945 without virtual memory management. This option implies @option{-fPIC}.
8946 With a @samp{bfin-elf} target, this option implies @option{-msim}.
8948 @item -mno-id-shared-library
8949 @opindex mno-id-shared-library
8950 Generate code that doesn't assume ID based shared libraries are being used.
8951 This is the default.
8953 @item -mleaf-id-shared-library
8954 @opindex mleaf-id-shared-library
8955 Generate code that supports shared libraries via the library ID method,
8956 but assumes that this library or executable won't link against any other
8957 ID shared libraries. That allows the compiler to use faster code for jumps
8960 @item -mno-leaf-id-shared-library
8961 @opindex mno-leaf-id-shared-library
8962 Do not assume that the code being compiled won't link against any ID shared
8963 libraries. Slower code will be generated for jump and call insns.
8965 @item -mshared-library-id=n
8966 @opindex mshared-library-id
8967 Specified the identification number of the ID based shared library being
8968 compiled. Specifying a value of 0 will generate more compact code, specifying
8969 other values will force the allocation of that number to the current
8970 library but is no more space or time efficient than omitting this option.
8974 Generate code that allows the data segment to be located in a different
8975 area of memory from the text segment. This allows for execute in place in
8976 an environment without virtual memory management by eliminating relocations
8977 against the text section.
8980 @opindex mno-sep-data
8981 Generate code that assumes that the data segment follows the text segment.
8982 This is the default.
8985 @itemx -mno-long-calls
8986 @opindex mlong-calls
8987 @opindex mno-long-calls
8988 Tells the compiler to perform function calls by first loading the
8989 address of the function into a register and then performing a subroutine
8990 call on this register. This switch is needed if the target function
8991 will lie outside of the 24 bit addressing range of the offset based
8992 version of subroutine call instruction.
8994 This feature is not enabled by default. Specifying
8995 @option{-mno-long-calls} will restore the default behavior. Note these
8996 switches have no effect on how the compiler generates code to handle
8997 function calls via function pointers.
9001 Link with the fast floating-point library. This library relaxes some of
9002 the IEEE floating-point standard's rules for checking inputs against
9003 Not-a-Number (NAN), in the interest of performance.
9006 @opindex minline-plt
9007 Enable inlining of PLT entries in function calls to functions that are
9008 not known to bind locally. It has no effect without @option{-mfdpic}.
9012 Build standalone application for multicore Blackfin processor. Proper
9013 start files and link scripts will be used to support multicore.
9014 This option defines @code{__BFIN_MULTICORE}. It can only be used with
9015 @option{-mcpu=bf561@r{[}-@var{sirevision}@r{]}}. It can be used with
9016 @option{-mcorea} or @option{-mcoreb}. If it's used without
9017 @option{-mcorea} or @option{-mcoreb}, single application/dual core
9018 programming model is used. In this model, the main function of Core B
9019 should be named as coreb_main. If it's used with @option{-mcorea} or
9020 @option{-mcoreb}, one application per core programming model is used.
9021 If this option is not used, single core application programming
9026 Build standalone application for Core A of BF561 when using
9027 one application per core programming model. Proper start files
9028 and link scripts will be used to support Core A. This option
9029 defines @code{__BFIN_COREA}. It must be used with @option{-mmulticore}.
9033 Build standalone application for Core B of BF561 when using
9034 one application per core programming model. Proper start files
9035 and link scripts will be used to support Core B. This option
9036 defines @code{__BFIN_COREB}. When this option is used, coreb_main
9037 should be used instead of main. It must be used with
9038 @option{-mmulticore}.
9042 Build standalone application for SDRAM. Proper start files and
9043 link scripts will be used to put the application into SDRAM.
9044 Loader should initialize SDRAM before loading the application
9045 into SDRAM. This option defines @code{__BFIN_SDRAM}.
9049 @subsection CRIS Options
9050 @cindex CRIS Options
9052 These options are defined specifically for the CRIS ports.
9055 @item -march=@var{architecture-type}
9056 @itemx -mcpu=@var{architecture-type}
9059 Generate code for the specified architecture. The choices for
9060 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
9061 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@.
9062 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
9065 @item -mtune=@var{architecture-type}
9067 Tune to @var{architecture-type} everything applicable about the generated
9068 code, except for the ABI and the set of available instructions. The
9069 choices for @var{architecture-type} are the same as for
9070 @option{-march=@var{architecture-type}}.
9072 @item -mmax-stack-frame=@var{n}
9073 @opindex mmax-stack-frame
9074 Warn when the stack frame of a function exceeds @var{n} bytes.
9080 The options @option{-metrax4} and @option{-metrax100} are synonyms for
9081 @option{-march=v3} and @option{-march=v8} respectively.
9083 @item -mmul-bug-workaround
9084 @itemx -mno-mul-bug-workaround
9085 @opindex mmul-bug-workaround
9086 @opindex mno-mul-bug-workaround
9087 Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
9088 models where it applies. This option is active by default.
9092 Enable CRIS-specific verbose debug-related information in the assembly
9093 code. This option also has the effect to turn off the @samp{#NO_APP}
9094 formatted-code indicator to the assembler at the beginning of the
9099 Do not use condition-code results from previous instruction; always emit
9100 compare and test instructions before use of condition codes.
9102 @item -mno-side-effects
9103 @opindex mno-side-effects
9104 Do not emit instructions with side-effects in addressing modes other than
9108 @itemx -mno-stack-align
9110 @itemx -mno-data-align
9111 @itemx -mconst-align
9112 @itemx -mno-const-align
9113 @opindex mstack-align
9114 @opindex mno-stack-align
9115 @opindex mdata-align
9116 @opindex mno-data-align
9117 @opindex mconst-align
9118 @opindex mno-const-align
9119 These options (no-options) arranges (eliminate arrangements) for the
9120 stack-frame, individual data and constants to be aligned for the maximum
9121 single data access size for the chosen CPU model. The default is to
9122 arrange for 32-bit alignment. ABI details such as structure layout are
9123 not affected by these options.
9131 Similar to the stack- data- and const-align options above, these options
9132 arrange for stack-frame, writable data and constants to all be 32-bit,
9133 16-bit or 8-bit aligned. The default is 32-bit alignment.
9135 @item -mno-prologue-epilogue
9136 @itemx -mprologue-epilogue
9137 @opindex mno-prologue-epilogue
9138 @opindex mprologue-epilogue
9139 With @option{-mno-prologue-epilogue}, the normal function prologue and
9140 epilogue that sets up the stack-frame are omitted and no return
9141 instructions or return sequences are generated in the code. Use this
9142 option only together with visual inspection of the compiled code: no
9143 warnings or errors are generated when call-saved registers must be saved,
9144 or storage for local variable needs to be allocated.
9150 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
9151 instruction sequences that load addresses for functions from the PLT part
9152 of the GOT rather than (traditional on other architectures) calls to the
9153 PLT@. The default is @option{-mgotplt}.
9157 Legacy no-op option only recognized with the cris-axis-elf and
9158 cris-axis-linux-gnu targets.
9162 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
9166 This option, recognized for the cris-axis-elf arranges
9167 to link with input-output functions from a simulator library. Code,
9168 initialized data and zero-initialized data are allocated consecutively.
9172 Like @option{-sim}, but pass linker options to locate initialized data at
9173 0x40000000 and zero-initialized data at 0x80000000.
9177 @subsection CRX Options
9180 These options are defined specifically for the CRX ports.
9186 Enable the use of multiply-accumulate instructions. Disabled by default.
9190 Push instructions will be used to pass outgoing arguments when functions
9191 are called. Enabled by default.
9194 @node Darwin Options
9195 @subsection Darwin Options
9196 @cindex Darwin options
9198 These options are defined for all architectures running the Darwin operating
9201 FSF GCC on Darwin does not create ``fat'' object files; it will create
9202 an object file for the single architecture that it was built to
9203 target. Apple's GCC on Darwin does create ``fat'' files if multiple
9204 @option{-arch} options are used; it does so by running the compiler or
9205 linker multiple times and joining the results together with
9208 The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or
9209 @samp{i686}) is determined by the flags that specify the ISA
9210 that GCC is targetting, like @option{-mcpu} or @option{-march}. The
9211 @option{-force_cpusubtype_ALL} option can be used to override this.
9213 The Darwin tools vary in their behavior when presented with an ISA
9214 mismatch. The assembler, @file{as}, will only permit instructions to
9215 be used that are valid for the subtype of the file it is generating,
9216 so you cannot put 64-bit instructions in an @samp{ppc750} object file.
9217 The linker for shared libraries, @file{/usr/bin/libtool}, will fail
9218 and print an error if asked to create a shared library with a less
9219 restrictive subtype than its input files (for instance, trying to put
9220 a @samp{ppc970} object file in a @samp{ppc7400} library). The linker
9221 for executables, @file{ld}, will quietly give the executable the most
9222 restrictive subtype of any of its input files.
9227 Add the framework directory @var{dir} to the head of the list of
9228 directories to be searched for header files. These directories are
9229 interleaved with those specified by @option{-I} options and are
9230 scanned in a left-to-right order.
9232 A framework directory is a directory with frameworks in it. A
9233 framework is a directory with a @samp{"Headers"} and/or
9234 @samp{"PrivateHeaders"} directory contained directly in it that ends
9235 in @samp{".framework"}. The name of a framework is the name of this
9236 directory excluding the @samp{".framework"}. Headers associated with
9237 the framework are found in one of those two directories, with
9238 @samp{"Headers"} being searched first. A subframework is a framework
9239 directory that is in a framework's @samp{"Frameworks"} directory.
9240 Includes of subframework headers can only appear in a header of a
9241 framework that contains the subframework, or in a sibling subframework
9242 header. Two subframeworks are siblings if they occur in the same
9243 framework. A subframework should not have the same name as a
9244 framework, a warning will be issued if this is violated. Currently a
9245 subframework cannot have subframeworks, in the future, the mechanism
9246 may be extended to support this. The standard frameworks can be found
9247 in @samp{"/System/Library/Frameworks"} and
9248 @samp{"/Library/Frameworks"}. An example include looks like
9249 @code{#include <Framework/header.h>}, where @samp{Framework} denotes
9250 the name of the framework and header.h is found in the
9251 @samp{"PrivateHeaders"} or @samp{"Headers"} directory.
9253 @item -iframework@var{dir}
9255 Like @option{-F} except the directory is a treated as a system
9256 directory. The main difference between this @option{-iframework} and
9257 @option{-F} is that with @option{-iframework} the compiler does not
9258 warn about constructs contained within header files found via
9259 @var{dir}. This option is valid only for the C family of languages.
9263 Emit debugging information for symbols that are used. For STABS
9264 debugging format, this enables @option{-feliminate-unused-debug-symbols}.
9265 This is by default ON@.
9269 Emit debugging information for all symbols and types.
9271 @item -mmacosx-version-min=@var{version}
9272 The earliest version of MacOS X that this executable will run on
9273 is @var{version}. Typical values of @var{version} include @code{10.1},
9274 @code{10.2}, and @code{10.3.9}.
9276 If the compiler was built to use the system's headers by default,
9277 then the default for this option is the system version on which the
9278 compiler is running, otherwise the default is to make choices which
9279 are compatible with as many systems and code bases as possible.
9283 Enable kernel development mode. The @option{-mkernel} option sets
9284 @option{-static}, @option{-fno-common}, @option{-fno-cxa-atexit},
9285 @option{-fno-exceptions}, @option{-fno-non-call-exceptions},
9286 @option{-fapple-kext}, @option{-fno-weak} and @option{-fno-rtti} where
9287 applicable. This mode also sets @option{-mno-altivec},
9288 @option{-msoft-float}, @option{-fno-builtin} and
9289 @option{-mlong-branch} for PowerPC targets.
9291 @item -mone-byte-bool
9292 @opindex mone-byte-bool
9293 Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}.
9294 By default @samp{sizeof(bool)} is @samp{4} when compiling for
9295 Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this
9296 option has no effect on x86.
9298 @strong{Warning:} The @option{-mone-byte-bool} switch causes GCC
9299 to generate code that is not binary compatible with code generated
9300 without that switch. Using this switch may require recompiling all
9301 other modules in a program, including system libraries. Use this
9302 switch to conform to a non-default data model.
9304 @item -mfix-and-continue
9305 @itemx -ffix-and-continue
9306 @itemx -findirect-data
9307 @opindex mfix-and-continue
9308 @opindex ffix-and-continue
9309 @opindex findirect-data
9310 Generate code suitable for fast turn around development. Needed to
9311 enable gdb to dynamically load @code{.o} files into already running
9312 programs. @option{-findirect-data} and @option{-ffix-and-continue}
9313 are provided for backwards compatibility.
9317 Loads all members of static archive libraries.
9318 See man ld(1) for more information.
9320 @item -arch_errors_fatal
9321 @opindex arch_errors_fatal
9322 Cause the errors having to do with files that have the wrong architecture
9326 @opindex bind_at_load
9327 Causes the output file to be marked such that the dynamic linker will
9328 bind all undefined references when the file is loaded or launched.
9332 Produce a Mach-o bundle format file.
9333 See man ld(1) for more information.
9335 @item -bundle_loader @var{executable}
9336 @opindex bundle_loader
9337 This option specifies the @var{executable} that will be loading the build
9338 output file being linked. See man ld(1) for more information.
9342 When passed this option, GCC will produce a dynamic library instead of
9343 an executable when linking, using the Darwin @file{libtool} command.
9345 @item -force_cpusubtype_ALL
9346 @opindex force_cpusubtype_ALL
9347 This causes GCC's output file to have the @var{ALL} subtype, instead of
9348 one controlled by the @option{-mcpu} or @option{-march} option.
9350 @item -allowable_client @var{client_name}
9352 @itemx -compatibility_version
9353 @itemx -current_version
9355 @itemx -dependency-file
9357 @itemx -dylinker_install_name
9359 @itemx -exported_symbols_list
9361 @itemx -flat_namespace
9362 @itemx -force_flat_namespace
9363 @itemx -headerpad_max_install_names
9366 @itemx -install_name
9367 @itemx -keep_private_externs
9368 @itemx -multi_module
9369 @itemx -multiply_defined
9370 @itemx -multiply_defined_unused
9372 @itemx -no_dead_strip_inits_and_terms
9373 @itemx -nofixprebinding
9376 @itemx -noseglinkedit
9377 @itemx -pagezero_size
9379 @itemx -prebind_all_twolevel_modules
9380 @itemx -private_bundle
9381 @itemx -read_only_relocs
9383 @itemx -sectobjectsymbols
9387 @itemx -sectobjectsymbols
9390 @itemx -segs_read_only_addr
9391 @itemx -segs_read_write_addr
9392 @itemx -seg_addr_table
9393 @itemx -seg_addr_table_filename
9396 @itemx -segs_read_only_addr
9397 @itemx -segs_read_write_addr
9398 @itemx -single_module
9401 @itemx -sub_umbrella
9402 @itemx -twolevel_namespace
9405 @itemx -unexported_symbols_list
9406 @itemx -weak_reference_mismatches
9408 @opindex allowable_client
9409 @opindex client_name
9410 @opindex compatibility_version
9411 @opindex current_version
9413 @opindex dependency-file
9415 @opindex dylinker_install_name
9417 @opindex exported_symbols_list
9419 @opindex flat_namespace
9420 @opindex force_flat_namespace
9421 @opindex headerpad_max_install_names
9424 @opindex install_name
9425 @opindex keep_private_externs
9426 @opindex multi_module
9427 @opindex multiply_defined
9428 @opindex multiply_defined_unused
9430 @opindex no_dead_strip_inits_and_terms
9431 @opindex nofixprebinding
9432 @opindex nomultidefs
9434 @opindex noseglinkedit
9435 @opindex pagezero_size
9437 @opindex prebind_all_twolevel_modules
9438 @opindex private_bundle
9439 @opindex read_only_relocs
9441 @opindex sectobjectsymbols
9445 @opindex sectobjectsymbols
9448 @opindex segs_read_only_addr
9449 @opindex segs_read_write_addr
9450 @opindex seg_addr_table
9451 @opindex seg_addr_table_filename
9452 @opindex seglinkedit
9454 @opindex segs_read_only_addr
9455 @opindex segs_read_write_addr
9456 @opindex single_module
9458 @opindex sub_library
9459 @opindex sub_umbrella
9460 @opindex twolevel_namespace
9463 @opindex unexported_symbols_list
9464 @opindex weak_reference_mismatches
9465 @opindex whatsloaded
9466 These options are passed to the Darwin linker. The Darwin linker man page
9467 describes them in detail.
9470 @node DEC Alpha Options
9471 @subsection DEC Alpha Options
9473 These @samp{-m} options are defined for the DEC Alpha implementations:
9476 @item -mno-soft-float
9478 @opindex mno-soft-float
9479 @opindex msoft-float
9480 Use (do not use) the hardware floating-point instructions for
9481 floating-point operations. When @option{-msoft-float} is specified,
9482 functions in @file{libgcc.a} will be used to perform floating-point
9483 operations. Unless they are replaced by routines that emulate the
9484 floating-point operations, or compiled in such a way as to call such
9485 emulations routines, these routines will issue floating-point
9486 operations. If you are compiling for an Alpha without floating-point
9487 operations, you must ensure that the library is built so as not to call
9490 Note that Alpha implementations without floating-point operations are
9491 required to have floating-point registers.
9496 @opindex mno-fp-regs
9497 Generate code that uses (does not use) the floating-point register set.
9498 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
9499 register set is not used, floating point operands are passed in integer
9500 registers as if they were integers and floating-point results are passed
9501 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
9502 so any function with a floating-point argument or return value called by code
9503 compiled with @option{-mno-fp-regs} must also be compiled with that
9506 A typical use of this option is building a kernel that does not use,
9507 and hence need not save and restore, any floating-point registers.
9511 The Alpha architecture implements floating-point hardware optimized for
9512 maximum performance. It is mostly compliant with the IEEE floating
9513 point standard. However, for full compliance, software assistance is
9514 required. This option generates code fully IEEE compliant code
9515 @emph{except} that the @var{inexact-flag} is not maintained (see below).
9516 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
9517 defined during compilation. The resulting code is less efficient but is
9518 able to correctly support denormalized numbers and exceptional IEEE
9519 values such as not-a-number and plus/minus infinity. Other Alpha
9520 compilers call this option @option{-ieee_with_no_inexact}.
9522 @item -mieee-with-inexact
9523 @opindex mieee-with-inexact
9524 This is like @option{-mieee} except the generated code also maintains
9525 the IEEE @var{inexact-flag}. Turning on this option causes the
9526 generated code to implement fully-compliant IEEE math. In addition to
9527 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
9528 macro. On some Alpha implementations the resulting code may execute
9529 significantly slower than the code generated by default. Since there is
9530 very little code that depends on the @var{inexact-flag}, you should
9531 normally not specify this option. Other Alpha compilers call this
9532 option @option{-ieee_with_inexact}.
9534 @item -mfp-trap-mode=@var{trap-mode}
9535 @opindex mfp-trap-mode
9536 This option controls what floating-point related traps are enabled.
9537 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
9538 The trap mode can be set to one of four values:
9542 This is the default (normal) setting. The only traps that are enabled
9543 are the ones that cannot be disabled in software (e.g., division by zero
9547 In addition to the traps enabled by @samp{n}, underflow traps are enabled
9551 Like @samp{u}, but the instructions are marked to be safe for software
9552 completion (see Alpha architecture manual for details).
9555 Like @samp{su}, but inexact traps are enabled as well.
9558 @item -mfp-rounding-mode=@var{rounding-mode}
9559 @opindex mfp-rounding-mode
9560 Selects the IEEE rounding mode. Other Alpha compilers call this option
9561 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
9566 Normal IEEE rounding mode. Floating point numbers are rounded towards
9567 the nearest machine number or towards the even machine number in case
9571 Round towards minus infinity.
9574 Chopped rounding mode. Floating point numbers are rounded towards zero.
9577 Dynamic rounding mode. A field in the floating point control register
9578 (@var{fpcr}, see Alpha architecture reference manual) controls the
9579 rounding mode in effect. The C library initializes this register for
9580 rounding towards plus infinity. Thus, unless your program modifies the
9581 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
9584 @item -mtrap-precision=@var{trap-precision}
9585 @opindex mtrap-precision
9586 In the Alpha architecture, floating point traps are imprecise. This
9587 means without software assistance it is impossible to recover from a
9588 floating trap and program execution normally needs to be terminated.
9589 GCC can generate code that can assist operating system trap handlers
9590 in determining the exact location that caused a floating point trap.
9591 Depending on the requirements of an application, different levels of
9592 precisions can be selected:
9596 Program precision. This option is the default and means a trap handler
9597 can only identify which program caused a floating point exception.
9600 Function precision. The trap handler can determine the function that
9601 caused a floating point exception.
9604 Instruction precision. The trap handler can determine the exact
9605 instruction that caused a floating point exception.
9608 Other Alpha compilers provide the equivalent options called
9609 @option{-scope_safe} and @option{-resumption_safe}.
9611 @item -mieee-conformant
9612 @opindex mieee-conformant
9613 This option marks the generated code as IEEE conformant. You must not
9614 use this option unless you also specify @option{-mtrap-precision=i} and either
9615 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
9616 is to emit the line @samp{.eflag 48} in the function prologue of the
9617 generated assembly file. Under DEC Unix, this has the effect that
9618 IEEE-conformant math library routines will be linked in.
9620 @item -mbuild-constants
9621 @opindex mbuild-constants
9622 Normally GCC examines a 32- or 64-bit integer constant to
9623 see if it can construct it from smaller constants in two or three
9624 instructions. If it cannot, it will output the constant as a literal and
9625 generate code to load it from the data segment at runtime.
9627 Use this option to require GCC to construct @emph{all} integer constants
9628 using code, even if it takes more instructions (the maximum is six).
9630 You would typically use this option to build a shared library dynamic
9631 loader. Itself a shared library, it must relocate itself in memory
9632 before it can find the variables and constants in its own data segment.
9638 Select whether to generate code to be assembled by the vendor-supplied
9639 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
9657 Indicate whether GCC should generate code to use the optional BWX,
9658 CIX, FIX and MAX instruction sets. The default is to use the instruction
9659 sets supported by the CPU type specified via @option{-mcpu=} option or that
9660 of the CPU on which GCC was built if none was specified.
9665 @opindex mfloat-ieee
9666 Generate code that uses (does not use) VAX F and G floating point
9667 arithmetic instead of IEEE single and double precision.
9669 @item -mexplicit-relocs
9670 @itemx -mno-explicit-relocs
9671 @opindex mexplicit-relocs
9672 @opindex mno-explicit-relocs
9673 Older Alpha assemblers provided no way to generate symbol relocations
9674 except via assembler macros. Use of these macros does not allow
9675 optimal instruction scheduling. GNU binutils as of version 2.12
9676 supports a new syntax that allows the compiler to explicitly mark
9677 which relocations should apply to which instructions. This option
9678 is mostly useful for debugging, as GCC detects the capabilities of
9679 the assembler when it is built and sets the default accordingly.
9683 @opindex msmall-data
9684 @opindex mlarge-data
9685 When @option{-mexplicit-relocs} is in effect, static data is
9686 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
9687 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
9688 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
9689 16-bit relocations off of the @code{$gp} register. This limits the
9690 size of the small data area to 64KB, but allows the variables to be
9691 directly accessed via a single instruction.
9693 The default is @option{-mlarge-data}. With this option the data area
9694 is limited to just below 2GB@. Programs that require more than 2GB of
9695 data must use @code{malloc} or @code{mmap} to allocate the data in the
9696 heap instead of in the program's data segment.
9698 When generating code for shared libraries, @option{-fpic} implies
9699 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
9703 @opindex msmall-text
9704 @opindex mlarge-text
9705 When @option{-msmall-text} is used, the compiler assumes that the
9706 code of the entire program (or shared library) fits in 4MB, and is
9707 thus reachable with a branch instruction. When @option{-msmall-data}
9708 is used, the compiler can assume that all local symbols share the
9709 same @code{$gp} value, and thus reduce the number of instructions
9710 required for a function call from 4 to 1.
9712 The default is @option{-mlarge-text}.
9714 @item -mcpu=@var{cpu_type}
9716 Set the instruction set and instruction scheduling parameters for
9717 machine type @var{cpu_type}. You can specify either the @samp{EV}
9718 style name or the corresponding chip number. GCC supports scheduling
9719 parameters for the EV4, EV5 and EV6 family of processors and will
9720 choose the default values for the instruction set from the processor
9721 you specify. If you do not specify a processor type, GCC will default
9722 to the processor on which the compiler was built.
9724 Supported values for @var{cpu_type} are
9730 Schedules as an EV4 and has no instruction set extensions.
9734 Schedules as an EV5 and has no instruction set extensions.
9738 Schedules as an EV5 and supports the BWX extension.
9743 Schedules as an EV5 and supports the BWX and MAX extensions.
9747 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
9751 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
9754 @item -mtune=@var{cpu_type}
9756 Set only the instruction scheduling parameters for machine type
9757 @var{cpu_type}. The instruction set is not changed.
9759 @item -mmemory-latency=@var{time}
9760 @opindex mmemory-latency
9761 Sets the latency the scheduler should assume for typical memory
9762 references as seen by the application. This number is highly
9763 dependent on the memory access patterns used by the application
9764 and the size of the external cache on the machine.
9766 Valid options for @var{time} are
9770 A decimal number representing clock cycles.
9776 The compiler contains estimates of the number of clock cycles for
9777 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
9778 (also called Dcache, Scache, and Bcache), as well as to main memory.
9779 Note that L3 is only valid for EV5.
9784 @node DEC Alpha/VMS Options
9785 @subsection DEC Alpha/VMS Options
9787 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
9790 @item -mvms-return-codes
9791 @opindex mvms-return-codes
9792 Return VMS condition codes from main. The default is to return POSIX
9793 style condition (e.g.@: error) codes.
9797 @subsection FRV Options
9804 Only use the first 32 general purpose registers.
9809 Use all 64 general purpose registers.
9814 Use only the first 32 floating point registers.
9819 Use all 64 floating point registers
9822 @opindex mhard-float
9824 Use hardware instructions for floating point operations.
9827 @opindex msoft-float
9829 Use library routines for floating point operations.
9834 Dynamically allocate condition code registers.
9839 Do not try to dynamically allocate condition code registers, only
9840 use @code{icc0} and @code{fcc0}.
9845 Change ABI to use double word insns.
9850 Do not use double word instructions.
9855 Use floating point double instructions.
9860 Do not use floating point double instructions.
9865 Use media instructions.
9870 Do not use media instructions.
9875 Use multiply and add/subtract instructions.
9880 Do not use multiply and add/subtract instructions.
9885 Select the FDPIC ABI, that uses function descriptors to represent
9886 pointers to functions. Without any PIC/PIE-related options, it
9887 implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it
9888 assumes GOT entries and small data are within a 12-bit range from the
9889 GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets
9890 are computed with 32 bits.
9891 With a @samp{bfin-elf} target, this option implies @option{-msim}.
9894 @opindex minline-plt
9896 Enable inlining of PLT entries in function calls to functions that are
9897 not known to bind locally. It has no effect without @option{-mfdpic}.
9898 It's enabled by default if optimizing for speed and compiling for
9899 shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an
9900 optimization option such as @option{-O3} or above is present in the
9906 Assume a large TLS segment when generating thread-local code.
9911 Do not assume a large TLS segment when generating thread-local code.
9916 Enable the use of @code{GPREL} relocations in the FDPIC ABI for data
9917 that is known to be in read-only sections. It's enabled by default,
9918 except for @option{-fpic} or @option{-fpie}: even though it may help
9919 make the global offset table smaller, it trades 1 instruction for 4.
9920 With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4,
9921 one of which may be shared by multiple symbols, and it avoids the need
9922 for a GOT entry for the referenced symbol, so it's more likely to be a
9923 win. If it is not, @option{-mno-gprel-ro} can be used to disable it.
9925 @item -multilib-library-pic
9926 @opindex multilib-library-pic
9928 Link with the (library, not FD) pic libraries. It's implied by
9929 @option{-mlibrary-pic}, as well as by @option{-fPIC} and
9930 @option{-fpic} without @option{-mfdpic}. You should never have to use
9936 Follow the EABI requirement of always creating a frame pointer whenever
9937 a stack frame is allocated. This option is enabled by default and can
9938 be disabled with @option{-mno-linked-fp}.
9941 @opindex mlong-calls
9943 Use indirect addressing to call functions outside the current
9944 compilation unit. This allows the functions to be placed anywhere
9945 within the 32-bit address space.
9947 @item -malign-labels
9948 @opindex malign-labels
9950 Try to align labels to an 8-byte boundary by inserting nops into the
9951 previous packet. This option only has an effect when VLIW packing
9952 is enabled. It doesn't create new packets; it merely adds nops to
9956 @opindex mlibrary-pic
9958 Generate position-independent EABI code.
9963 Use only the first four media accumulator registers.
9968 Use all eight media accumulator registers.
9973 Pack VLIW instructions.
9978 Do not pack VLIW instructions.
9983 Do not mark ABI switches in e_flags.
9988 Enable the use of conditional-move instructions (default).
9990 This switch is mainly for debugging the compiler and will likely be removed
9991 in a future version.
9993 @item -mno-cond-move
9994 @opindex mno-cond-move
9996 Disable the use of conditional-move instructions.
9998 This switch is mainly for debugging the compiler and will likely be removed
9999 in a future version.
10004 Enable the use of conditional set instructions (default).
10006 This switch is mainly for debugging the compiler and will likely be removed
10007 in a future version.
10012 Disable the use of conditional set instructions.
10014 This switch is mainly for debugging the compiler and will likely be removed
10015 in a future version.
10018 @opindex mcond-exec
10020 Enable the use of conditional execution (default).
10022 This switch is mainly for debugging the compiler and will likely be removed
10023 in a future version.
10025 @item -mno-cond-exec
10026 @opindex mno-cond-exec
10028 Disable the use of conditional execution.
10030 This switch is mainly for debugging the compiler and will likely be removed
10031 in a future version.
10033 @item -mvliw-branch
10034 @opindex mvliw-branch
10036 Run a pass to pack branches into VLIW instructions (default).
10038 This switch is mainly for debugging the compiler and will likely be removed
10039 in a future version.
10041 @item -mno-vliw-branch
10042 @opindex mno-vliw-branch
10044 Do not run a pass to pack branches into VLIW instructions.
10046 This switch is mainly for debugging the compiler and will likely be removed
10047 in a future version.
10049 @item -mmulti-cond-exec
10050 @opindex mmulti-cond-exec
10052 Enable optimization of @code{&&} and @code{||} in conditional execution
10055 This switch is mainly for debugging the compiler and will likely be removed
10056 in a future version.
10058 @item -mno-multi-cond-exec
10059 @opindex mno-multi-cond-exec
10061 Disable optimization of @code{&&} and @code{||} in conditional execution.
10063 This switch is mainly for debugging the compiler and will likely be removed
10064 in a future version.
10066 @item -mnested-cond-exec
10067 @opindex mnested-cond-exec
10069 Enable nested conditional execution optimizations (default).
10071 This switch is mainly for debugging the compiler and will likely be removed
10072 in a future version.
10074 @item -mno-nested-cond-exec
10075 @opindex mno-nested-cond-exec
10077 Disable nested conditional execution optimizations.
10079 This switch is mainly for debugging the compiler and will likely be removed
10080 in a future version.
10082 @item -moptimize-membar
10083 @opindex moptimize-membar
10085 This switch removes redundant @code{membar} instructions from the
10086 compiler generated code. It is enabled by default.
10088 @item -mno-optimize-membar
10089 @opindex mno-optimize-membar
10091 This switch disables the automatic removal of redundant @code{membar}
10092 instructions from the generated code.
10094 @item -mtomcat-stats
10095 @opindex mtomcat-stats
10097 Cause gas to print out tomcat statistics.
10099 @item -mcpu=@var{cpu}
10102 Select the processor type for which to generate code. Possible values are
10103 @samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450},
10104 @samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}.
10108 @node GNU/Linux Options
10109 @subsection GNU/Linux Options
10111 These @samp{-m} options are defined for GNU/Linux targets:
10116 Use the GNU C library instead of uClibc. This is the default except
10117 on @samp{*-*-linux-*uclibc*} targets.
10121 Use uClibc instead of the GNU C library. This is the default on
10122 @samp{*-*-linux-*uclibc*} targets.
10125 @node H8/300 Options
10126 @subsection H8/300 Options
10128 These @samp{-m} options are defined for the H8/300 implementations:
10133 Shorten some address references at link time, when possible; uses the
10134 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
10135 ld, Using ld}, for a fuller description.
10139 Generate code for the H8/300H@.
10143 Generate code for the H8S@.
10147 Generate code for the H8S and H8/300H in the normal mode. This switch
10148 must be used either with @option{-mh} or @option{-ms}.
10152 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
10156 Make @code{int} data 32 bits by default.
10159 @opindex malign-300
10160 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
10161 The default for the H8/300H and H8S is to align longs and floats on 4
10163 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
10164 This option has no effect on the H8/300.
10168 @subsection HPPA Options
10169 @cindex HPPA Options
10171 These @samp{-m} options are defined for the HPPA family of computers:
10174 @item -march=@var{architecture-type}
10176 Generate code for the specified architecture. The choices for
10177 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
10178 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
10179 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
10180 architecture option for your machine. Code compiled for lower numbered
10181 architectures will run on higher numbered architectures, but not the
10184 @item -mpa-risc-1-0
10185 @itemx -mpa-risc-1-1
10186 @itemx -mpa-risc-2-0
10187 @opindex mpa-risc-1-0
10188 @opindex mpa-risc-1-1
10189 @opindex mpa-risc-2-0
10190 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
10193 @opindex mbig-switch
10194 Generate code suitable for big switch tables. Use this option only if
10195 the assembler/linker complain about out of range branches within a switch
10198 @item -mjump-in-delay
10199 @opindex mjump-in-delay
10200 Fill delay slots of function calls with unconditional jump instructions
10201 by modifying the return pointer for the function call to be the target
10202 of the conditional jump.
10204 @item -mdisable-fpregs
10205 @opindex mdisable-fpregs
10206 Prevent floating point registers from being used in any manner. This is
10207 necessary for compiling kernels which perform lazy context switching of
10208 floating point registers. If you use this option and attempt to perform
10209 floating point operations, the compiler will abort.
10211 @item -mdisable-indexing
10212 @opindex mdisable-indexing
10213 Prevent the compiler from using indexing address modes. This avoids some
10214 rather obscure problems when compiling MIG generated code under MACH@.
10216 @item -mno-space-regs
10217 @opindex mno-space-regs
10218 Generate code that assumes the target has no space registers. This allows
10219 GCC to generate faster indirect calls and use unscaled index address modes.
10221 Such code is suitable for level 0 PA systems and kernels.
10223 @item -mfast-indirect-calls
10224 @opindex mfast-indirect-calls
10225 Generate code that assumes calls never cross space boundaries. This
10226 allows GCC to emit code which performs faster indirect calls.
10228 This option will not work in the presence of shared libraries or nested
10231 @item -mfixed-range=@var{register-range}
10232 @opindex mfixed-range
10233 Generate code treating the given register range as fixed registers.
10234 A fixed register is one that the register allocator can not use. This is
10235 useful when compiling kernel code. A register range is specified as
10236 two registers separated by a dash. Multiple register ranges can be
10237 specified separated by a comma.
10239 @item -mlong-load-store
10240 @opindex mlong-load-store
10241 Generate 3-instruction load and store sequences as sometimes required by
10242 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
10245 @item -mportable-runtime
10246 @opindex mportable-runtime
10247 Use the portable calling conventions proposed by HP for ELF systems.
10251 Enable the use of assembler directives only GAS understands.
10253 @item -mschedule=@var{cpu-type}
10255 Schedule code according to the constraints for the machine type
10256 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
10257 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
10258 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
10259 proper scheduling option for your machine. The default scheduling is
10263 @opindex mlinker-opt
10264 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
10265 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
10266 linkers in which they give bogus error messages when linking some programs.
10269 @opindex msoft-float
10270 Generate output containing library calls for floating point.
10271 @strong{Warning:} the requisite libraries are not available for all HPPA
10272 targets. Normally the facilities of the machine's usual C compiler are
10273 used, but this cannot be done directly in cross-compilation. You must make
10274 your own arrangements to provide suitable library functions for
10277 @option{-msoft-float} changes the calling convention in the output file;
10278 therefore, it is only useful if you compile @emph{all} of a program with
10279 this option. In particular, you need to compile @file{libgcc.a}, the
10280 library that comes with GCC, with @option{-msoft-float} in order for
10285 Generate the predefine, @code{_SIO}, for server IO@. The default is
10286 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
10287 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These
10288 options are available under HP-UX and HI-UX@.
10292 Use GNU ld specific options. This passes @option{-shared} to ld when
10293 building a shared library. It is the default when GCC is configured,
10294 explicitly or implicitly, with the GNU linker. This option does not
10295 have any affect on which ld is called, it only changes what parameters
10296 are passed to that ld. The ld that is called is determined by the
10297 @option{--with-ld} configure option, GCC's program search path, and
10298 finally by the user's @env{PATH}. The linker used by GCC can be printed
10299 using @samp{which `gcc -print-prog-name=ld`}. This option is only available
10300 on the 64 bit HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}.
10304 Use HP ld specific options. This passes @option{-b} to ld when building
10305 a shared library and passes @option{+Accept TypeMismatch} to ld on all
10306 links. It is the default when GCC is configured, explicitly or
10307 implicitly, with the HP linker. This option does not have any affect on
10308 which ld is called, it only changes what parameters are passed to that
10309 ld. The ld that is called is determined by the @option{--with-ld}
10310 configure option, GCC's program search path, and finally by the user's
10311 @env{PATH}. The linker used by GCC can be printed using @samp{which
10312 `gcc -print-prog-name=ld`}. This option is only available on the 64 bit
10313 HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}.
10316 @opindex mno-long-calls
10317 Generate code that uses long call sequences. This ensures that a call
10318 is always able to reach linker generated stubs. The default is to generate
10319 long calls only when the distance from the call site to the beginning
10320 of the function or translation unit, as the case may be, exceeds a
10321 predefined limit set by the branch type being used. The limits for
10322 normal calls are 7,600,000 and 240,000 bytes, respectively for the
10323 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
10326 Distances are measured from the beginning of functions when using the
10327 @option{-ffunction-sections} option, or when using the @option{-mgas}
10328 and @option{-mno-portable-runtime} options together under HP-UX with
10331 It is normally not desirable to use this option as it will degrade
10332 performance. However, it may be useful in large applications,
10333 particularly when partial linking is used to build the application.
10335 The types of long calls used depends on the capabilities of the
10336 assembler and linker, and the type of code being generated. The
10337 impact on systems that support long absolute calls, and long pic
10338 symbol-difference or pc-relative calls should be relatively small.
10339 However, an indirect call is used on 32-bit ELF systems in pic code
10340 and it is quite long.
10342 @item -munix=@var{unix-std}
10344 Generate compiler predefines and select a startfile for the specified
10345 UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95}
10346 and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95}
10347 is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX
10348 11.11 and later. The default values are @samp{93} for HP-UX 10.00,
10349 @samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11
10352 @option{-munix=93} provides the same predefines as GCC 3.3 and 3.4.
10353 @option{-munix=95} provides additional predefines for @code{XOPEN_UNIX}
10354 and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}.
10355 @option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX},
10356 @code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and
10357 @code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}.
10359 It is @emph{important} to note that this option changes the interfaces
10360 for various library routines. It also affects the operational behavior
10361 of the C library. Thus, @emph{extreme} care is needed in using this
10364 Library code that is intended to operate with more than one UNIX
10365 standard must test, set and restore the variable @var{__xpg4_extended_mask}
10366 as appropriate. Most GNU software doesn't provide this capability.
10370 Suppress the generation of link options to search libdld.sl when the
10371 @option{-static} option is specified on HP-UX 10 and later.
10375 The HP-UX implementation of setlocale in libc has a dependency on
10376 libdld.sl. There isn't an archive version of libdld.sl. Thus,
10377 when the @option{-static} option is specified, special link options
10378 are needed to resolve this dependency.
10380 On HP-UX 10 and later, the GCC driver adds the necessary options to
10381 link with libdld.sl when the @option{-static} option is specified.
10382 This causes the resulting binary to be dynamic. On the 64-bit port,
10383 the linkers generate dynamic binaries by default in any case. The
10384 @option{-nolibdld} option can be used to prevent the GCC driver from
10385 adding these link options.
10389 Add support for multithreading with the @dfn{dce thread} library
10390 under HP-UX@. This option sets flags for both the preprocessor and
10394 @node i386 and x86-64 Options
10395 @subsection Intel 386 and AMD x86-64 Options
10396 @cindex i386 Options
10397 @cindex x86-64 Options
10398 @cindex Intel 386 Options
10399 @cindex AMD x86-64 Options
10401 These @samp{-m} options are defined for the i386 and x86-64 family of
10405 @item -mtune=@var{cpu-type}
10407 Tune to @var{cpu-type} everything applicable about the generated code, except
10408 for the ABI and the set of available instructions. The choices for
10409 @var{cpu-type} are:
10412 Produce code optimized for the most common IA32/AMD64/EM64T processors.
10413 If you know the CPU on which your code will run, then you should use
10414 the corresponding @option{-mtune} option instead of
10415 @option{-mtune=generic}. But, if you do not know exactly what CPU users
10416 of your application will have, then you should use this option.
10418 As new processors are deployed in the marketplace, the behavior of this
10419 option will change. Therefore, if you upgrade to a newer version of
10420 GCC, the code generated option will change to reflect the processors
10421 that were most common when that version of GCC was released.
10423 There is no @option{-march=generic} option because @option{-march}
10424 indicates the instruction set the compiler can use, and there is no
10425 generic instruction set applicable to all processors. In contrast,
10426 @option{-mtune} indicates the processor (or, in this case, collection of
10427 processors) for which the code is optimized.
10429 This selects the CPU to tune for at compilation time by determining
10430 the processor type of the compiling machine. Using @option{-mtune=native}
10431 will produce code optimized for the local machine under the constraints
10432 of the selected instruction set. Using @option{-march=native} will
10433 enable all instruction subsets supported by the local machine (hence
10434 the result might not run on different machines).
10436 Original Intel's i386 CPU@.
10438 Intel's i486 CPU@. (No scheduling is implemented for this chip.)
10439 @item i586, pentium
10440 Intel Pentium CPU with no MMX support.
10442 Intel PentiumMMX CPU based on Pentium core with MMX instruction set support.
10444 Intel PentiumPro CPU@.
10446 Same as @code{generic}, but when used as @code{march} option, PentiumPro
10447 instruction set will be used, so the code will run on all i686 family chips.
10449 Intel Pentium2 CPU based on PentiumPro core with MMX instruction set support.
10450 @item pentium3, pentium3m
10451 Intel Pentium3 CPU based on PentiumPro core with MMX and SSE instruction set
10454 Low power version of Intel Pentium3 CPU with MMX, SSE and SSE2 instruction set
10455 support. Used by Centrino notebooks.
10456 @item pentium4, pentium4m
10457 Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set support.
10459 Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and SSE3 instruction
10462 Improved version of Intel Pentium4 CPU with 64-bit extensions, MMX, SSE,
10463 SSE2 and SSE3 instruction set support.
10465 Intel Core2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3
10466 instruction set support.
10468 AMD K6 CPU with MMX instruction set support.
10470 Improved versions of AMD K6 CPU with MMX and 3dNOW!@: instruction set support.
10471 @item athlon, athlon-tbird
10472 AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW!@: and SSE prefetch instructions
10474 @item athlon-4, athlon-xp, athlon-mp
10475 Improved AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW!@: and full SSE
10476 instruction set support.
10477 @item k8, opteron, athlon64, athlon-fx
10478 AMD K8 core based CPUs with x86-64 instruction set support. (This supersets
10479 MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW!@: and 64-bit instruction set extensions.)
10480 @item k8-sse3, opteron-sse3, athlon64-sse3
10481 Improved versions of k8, opteron and athlon64 with SSE3 instruction set support.
10482 @item amdfam10, barcelona
10483 AMD Family 10h core based CPUs with x86-64 instruction set support. (This
10484 supersets MMX, SSE, SSE2, SSE3, SSE4A, 3dNOW!, enhanced 3dNOW!, ABM and 64-bit
10485 instruction set extensions.)
10487 IDT Winchip C6 CPU, dealt in same way as i486 with additional MMX instruction
10490 IDT Winchip2 CPU, dealt in same way as i486 with additional MMX and 3dNOW!@:
10491 instruction set support.
10493 Via C3 CPU with MMX and 3dNOW!@: instruction set support. (No scheduling is
10494 implemented for this chip.)
10496 Via C3-2 CPU with MMX and SSE instruction set support. (No scheduling is
10497 implemented for this chip.)
10499 Embedded AMD CPU with MMX and 3dNOW! instruction set support.
10502 While picking a specific @var{cpu-type} will schedule things appropriately
10503 for that particular chip, the compiler will not generate any code that
10504 does not run on the i386 without the @option{-march=@var{cpu-type}} option
10507 @item -march=@var{cpu-type}
10509 Generate instructions for the machine type @var{cpu-type}. The choices
10510 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
10511 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
10513 @item -mcpu=@var{cpu-type}
10515 A deprecated synonym for @option{-mtune}.
10517 @item -mfpmath=@var{unit}
10519 Generate floating point arithmetics for selected unit @var{unit}. The choices
10520 for @var{unit} are:
10524 Use the standard 387 floating point coprocessor present majority of chips and
10525 emulated otherwise. Code compiled with this option will run almost everywhere.
10526 The temporary results are computed in 80bit precision instead of precision
10527 specified by the type resulting in slightly different results compared to most
10528 of other chips. See @option{-ffloat-store} for more detailed description.
10530 This is the default choice for i386 compiler.
10533 Use scalar floating point instructions present in the SSE instruction set.
10534 This instruction set is supported by Pentium3 and newer chips, in the AMD line
10535 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
10536 instruction set supports only single precision arithmetics, thus the double and
10537 extended precision arithmetics is still done using 387. Later version, present
10538 only in Pentium4 and the future AMD x86-64 chips supports double precision
10541 For the i386 compiler, you need to use @option{-march=@var{cpu-type}}, @option{-msse}
10542 or @option{-msse2} switches to enable SSE extensions and make this option
10543 effective. For the x86-64 compiler, these extensions are enabled by default.
10545 The resulting code should be considerably faster in the majority of cases and avoid
10546 the numerical instability problems of 387 code, but may break some existing
10547 code that expects temporaries to be 80bit.
10549 This is the default choice for the x86-64 compiler.
10554 Attempt to utilize both instruction sets at once. This effectively double the
10555 amount of available registers and on chips with separate execution units for
10556 387 and SSE the execution resources too. Use this option with care, as it is
10557 still experimental, because the GCC register allocator does not model separate
10558 functional units well resulting in instable performance.
10561 @item -masm=@var{dialect}
10562 @opindex masm=@var{dialect}
10563 Output asm instructions using selected @var{dialect}. Supported
10564 choices are @samp{intel} or @samp{att} (the default one). Darwin does
10565 not support @samp{intel}.
10568 @itemx -mno-ieee-fp
10570 @opindex mno-ieee-fp
10571 Control whether or not the compiler uses IEEE floating point
10572 comparisons. These handle correctly the case where the result of a
10573 comparison is unordered.
10576 @opindex msoft-float
10577 Generate output containing library calls for floating point.
10578 @strong{Warning:} the requisite libraries are not part of GCC@.
10579 Normally the facilities of the machine's usual C compiler are used, but
10580 this can't be done directly in cross-compilation. You must make your
10581 own arrangements to provide suitable library functions for
10584 On machines where a function returns floating point results in the 80387
10585 register stack, some floating point opcodes may be emitted even if
10586 @option{-msoft-float} is used.
10588 @item -mno-fp-ret-in-387
10589 @opindex mno-fp-ret-in-387
10590 Do not use the FPU registers for return values of functions.
10592 The usual calling convention has functions return values of types
10593 @code{float} and @code{double} in an FPU register, even if there
10594 is no FPU@. The idea is that the operating system should emulate
10597 The option @option{-mno-fp-ret-in-387} causes such values to be returned
10598 in ordinary CPU registers instead.
10600 @item -mno-fancy-math-387
10601 @opindex mno-fancy-math-387
10602 Some 387 emulators do not support the @code{sin}, @code{cos} and
10603 @code{sqrt} instructions for the 387. Specify this option to avoid
10604 generating those instructions. This option is the default on FreeBSD,
10605 OpenBSD and NetBSD@. This option is overridden when @option{-march}
10606 indicates that the target cpu will always have an FPU and so the
10607 instruction will not need emulation. As of revision 2.6.1, these
10608 instructions are not generated unless you also use the
10609 @option{-funsafe-math-optimizations} switch.
10611 @item -malign-double
10612 @itemx -mno-align-double
10613 @opindex malign-double
10614 @opindex mno-align-double
10615 Control whether GCC aligns @code{double}, @code{long double}, and
10616 @code{long long} variables on a two word boundary or a one word
10617 boundary. Aligning @code{double} variables on a two word boundary will
10618 produce code that runs somewhat faster on a @samp{Pentium} at the
10619 expense of more memory.
10621 On x86-64, @option{-malign-double} is enabled by default.
10623 @strong{Warning:} if you use the @option{-malign-double} switch,
10624 structures containing the above types will be aligned differently than
10625 the published application binary interface specifications for the 386
10626 and will not be binary compatible with structures in code compiled
10627 without that switch.
10629 @item -m96bit-long-double
10630 @itemx -m128bit-long-double
10631 @opindex m96bit-long-double
10632 @opindex m128bit-long-double
10633 These switches control the size of @code{long double} type. The i386
10634 application binary interface specifies the size to be 96 bits,
10635 so @option{-m96bit-long-double} is the default in 32 bit mode.
10637 Modern architectures (Pentium and newer) would prefer @code{long double}
10638 to be aligned to an 8 or 16 byte boundary. In arrays or structures
10639 conforming to the ABI, this would not be possible. So specifying a
10640 @option{-m128bit-long-double} will align @code{long double}
10641 to a 16 byte boundary by padding the @code{long double} with an additional
10644 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
10645 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
10647 Notice that neither of these options enable any extra precision over the x87
10648 standard of 80 bits for a @code{long double}.
10650 @strong{Warning:} if you override the default value for your target ABI, the
10651 structures and arrays containing @code{long double} variables will change
10652 their size as well as function calling convention for function taking
10653 @code{long double} will be modified. Hence they will not be binary
10654 compatible with arrays or structures in code compiled without that switch.
10656 @item -mmlarge-data-threshold=@var{number}
10657 @opindex mlarge-data-threshold=@var{number}
10658 When @option{-mcmodel=medium} is specified, the data greater than
10659 @var{threshold} are placed in large data section. This value must be the
10660 same across all object linked into the binary and defaults to 65535.
10664 Use a different function-calling convention, in which functions that
10665 take a fixed number of arguments return with the @code{ret} @var{num}
10666 instruction, which pops their arguments while returning. This saves one
10667 instruction in the caller since there is no need to pop the arguments
10670 You can specify that an individual function is called with this calling
10671 sequence with the function attribute @samp{stdcall}. You can also
10672 override the @option{-mrtd} option by using the function attribute
10673 @samp{cdecl}. @xref{Function Attributes}.
10675 @strong{Warning:} this calling convention is incompatible with the one
10676 normally used on Unix, so you cannot use it if you need to call
10677 libraries compiled with the Unix compiler.
10679 Also, you must provide function prototypes for all functions that
10680 take variable numbers of arguments (including @code{printf});
10681 otherwise incorrect code will be generated for calls to those
10684 In addition, seriously incorrect code will result if you call a
10685 function with too many arguments. (Normally, extra arguments are
10686 harmlessly ignored.)
10688 @item -mregparm=@var{num}
10690 Control how many registers are used to pass integer arguments. By
10691 default, no registers are used to pass arguments, and at most 3
10692 registers can be used. You can control this behavior for a specific
10693 function by using the function attribute @samp{regparm}.
10694 @xref{Function Attributes}.
10696 @strong{Warning:} if you use this switch, and
10697 @var{num} is nonzero, then you must build all modules with the same
10698 value, including any libraries. This includes the system libraries and
10702 @opindex msseregparm
10703 Use SSE register passing conventions for float and double arguments
10704 and return values. You can control this behavior for a specific
10705 function by using the function attribute @samp{sseregparm}.
10706 @xref{Function Attributes}.
10708 @strong{Warning:} if you use this switch then you must build all
10709 modules with the same value, including any libraries. This includes
10710 the system libraries and startup modules.
10719 Set 80387 floating-point precision to 32, 64 or 80 bits. When @option{-mpc32}
10720 is specified, the significands of results of floating-point operations are
10721 rounded to 24 bits (single precision); @option{-mpc64} rounds the the
10722 significands of results of floating-point operations to 53 bits (double
10723 precision) and @option{-mpc80} rounds the significands of results of
10724 floating-point operations to 64 bits (extended double precision), which is
10725 the default. When this option is used, floating-point operations in higher
10726 precisions are not available to the programmer without setting the FPU
10727 control word explicitly.
10729 Setting the rounding of floating-point operations to less than the default
10730 80 bits can speed some programs by 2% or more. Note that some mathematical
10731 libraries assume that extended precision (80 bit) floating-point operations
10732 are enabled by default; routines in such libraries could suffer significant
10733 loss of accuracy, typically through so-called "catastrophic cancellation",
10734 when this option is used to set the precision to less than extended precision.
10736 @item -mstackrealign
10737 @opindex mstackrealign
10738 Realign the stack at entry. On the Intel x86, the @option{-mstackrealign}
10739 option will generate an alternate prologue and epilogue that realigns the
10740 runtime stack if necessary. This supports mixing legacy codes that keep
10741 a 4-byte aligned stack with modern codes that keep a 16-byte stack for
10742 SSE compatibility. See also the attribute @code{force_align_arg_pointer},
10743 applicable to individual functions.
10745 @item -mpreferred-stack-boundary=@var{num}
10746 @opindex mpreferred-stack-boundary
10747 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
10748 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
10749 the default is 4 (16 bytes or 128 bits).
10751 @item -mincoming-stack-boundary=@var{num}
10752 @opindex mincoming-stack-boundary
10753 Assume the incoming stack is aligned to a 2 raised to @var{num} byte
10754 boundary. If @option{-mincoming-stack-boundary} is not specified,
10755 the one specified by @option{-mpreferred-stack-boundary} will be used.
10757 On Pentium and PentiumPro, @code{double} and @code{long double} values
10758 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
10759 suffer significant run time performance penalties. On Pentium III, the
10760 Streaming SIMD Extension (SSE) data type @code{__m128} may not work
10761 properly if it is not 16 byte aligned.
10763 To ensure proper alignment of this values on the stack, the stack boundary
10764 must be as aligned as that required by any value stored on the stack.
10765 Further, every function must be generated such that it keeps the stack
10766 aligned. Thus calling a function compiled with a higher preferred
10767 stack boundary from a function compiled with a lower preferred stack
10768 boundary will most likely misalign the stack. It is recommended that
10769 libraries that use callbacks always use the default setting.
10771 This extra alignment does consume extra stack space, and generally
10772 increases code size. Code that is sensitive to stack space usage, such
10773 as embedded systems and operating system kernels, may want to reduce the
10774 preferred alignment to @option{-mpreferred-stack-boundary=2}.
10812 These switches enable or disable the use of instructions in the MMX,
10813 SSE, SSE2, SSE3, SSSE3, SSE4.1, AES, PCLMUL, SSE4A, SSE5, ABM or
10814 3DNow!@: extended instruction sets.
10815 These extensions are also available as built-in functions: see
10816 @ref{X86 Built-in Functions}, for details of the functions enabled and
10817 disabled by these switches.
10819 To have SSE/SSE2 instructions generated automatically from floating-point
10820 code (as opposed to 387 instructions), see @option{-mfpmath=sse}.
10822 These options will enable GCC to use these extended instructions in
10823 generated code, even without @option{-mfpmath=sse}. Applications which
10824 perform runtime CPU detection must compile separate files for each
10825 supported architecture, using the appropriate flags. In particular,
10826 the file containing the CPU detection code should be compiled without
10831 This option instructs GCC to emit a @code{cld} instruction in the prologue
10832 of functions that use string instructions. String instructions depend on
10833 the DF flag to select between autoincrement or autodecrement mode. While the
10834 ABI specifies the DF flag to be cleared on function entry, some operating
10835 systems violate this specification by not clearing the DF flag in their
10836 exception dispatchers. The exception handler can be invoked with the DF flag
10837 set which leads to wrong direction mode, when string instructions are used.
10838 This option can be enabled by default on 32-bit x86 targets by configuring
10839 GCC with the @option{--enable-cld} configure option. Generation of @code{cld}
10840 instructions can be suppressed with the @option{-mno-cld} compiler option
10845 This option will enable GCC to use CMPXCHG16B instruction in generated code.
10846 CMPXCHG16B allows for atomic operations on 128-bit double quadword (or oword)
10847 data types. This is useful for high resolution counters that could be updated
10848 by multiple processors (or cores). This instruction is generated as part of
10849 atomic built-in functions: see @ref{Atomic Builtins} for details.
10853 This option will enable GCC to use SAHF instruction in generated 64-bit code.
10854 Early Intel CPUs with Intel 64 lacked LAHF and SAHF instructions supported
10855 by AMD64 until introduction of Pentium 4 G1 step in December 2005. LAHF and
10856 SAHF are load and store instructions, respectively, for certain status flags.
10857 In 64-bit mode, SAHF instruction is used to optimize @code{fmod}, @code{drem}
10858 or @code{remainder} built-in functions: see @ref{Other Builtins} for details.
10862 This option will enable GCC to use RCPSS and RSQRTSS instructions (and their
10863 vectorized variants RCPPS and RSQRTPS) with an additional Newton-Rhapson step
10864 to increase precision instead of DIVSS and SQRTSS (and their vectorized
10865 variants) for single precision floating point arguments. These instructions
10866 are generated only when @option{-funsafe-math-optimizations} is enabled
10867 together with @option{-finite-math-only} and @option{-fno-trapping-math}.
10868 Note that while the throughput of the sequence is higher than the throughput
10869 of the non-reciprocal instruction, the precision of the sequence can be
10870 decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994).
10872 @item -mveclibabi=@var{type}
10873 @opindex mveclibabi
10874 Specifies the ABI type to use for vectorizing intrinsics using an
10875 external library. Supported types are @code{svml} for the Intel short
10876 vector math library and @code{acml} for the AMD math core library style
10877 of interfacing. GCC will currently emit calls to @code{vmldExp2},
10878 @code{vmldLn2}, @code{vmldLog102}, @code{vmldLog102}, @code{vmldPow2},
10879 @code{vmldTanh2}, @code{vmldTan2}, @code{vmldAtan2}, @code{vmldAtanh2},
10880 @code{vmldCbrt2}, @code{vmldSinh2}, @code{vmldSin2}, @code{vmldAsinh2},
10881 @code{vmldAsin2}, @code{vmldCosh2}, @code{vmldCos2}, @code{vmldAcosh2},
10882 @code{vmldAcos2}, @code{vmlsExp4}, @code{vmlsLn4}, @code{vmlsLog104},
10883 @code{vmlsLog104}, @code{vmlsPow4}, @code{vmlsTanh4}, @code{vmlsTan4},
10884 @code{vmlsAtan4}, @code{vmlsAtanh4}, @code{vmlsCbrt4}, @code{vmlsSinh4},
10885 @code{vmlsSin4}, @code{vmlsAsinh4}, @code{vmlsAsin4}, @code{vmlsCosh4},
10886 @code{vmlsCos4}, @code{vmlsAcosh4} and @code{vmlsAcos4} for corresponding
10887 function type when @option{-mveclibabi=svml} is used and @code{__vrd2_sin},
10888 @code{__vrd2_cos}, @code{__vrd2_exp}, @code{__vrd2_log}, @code{__vrd2_log2},
10889 @code{__vrd2_log10}, @code{__vrs4_sinf}, @code{__vrs4_cosf},
10890 @code{__vrs4_expf}, @code{__vrs4_logf}, @code{__vrs4_log2f},
10891 @code{__vrs4_log10f} and @code{__vrs4_powf} for corresponding function type
10892 when @option{-mveclibabi=acml} is used. Both @option{-ftree-vectorize} and
10893 @option{-funsafe-math-optimizations} have to be enabled. A SVML or ACML ABI
10894 compatible library will have to be specified at link time.
10897 @itemx -mno-push-args
10898 @opindex mpush-args
10899 @opindex mno-push-args
10900 Use PUSH operations to store outgoing parameters. This method is shorter
10901 and usually equally fast as method using SUB/MOV operations and is enabled
10902 by default. In some cases disabling it may improve performance because of
10903 improved scheduling and reduced dependencies.
10905 @item -maccumulate-outgoing-args
10906 @opindex maccumulate-outgoing-args
10907 If enabled, the maximum amount of space required for outgoing arguments will be
10908 computed in the function prologue. This is faster on most modern CPUs
10909 because of reduced dependencies, improved scheduling and reduced stack usage
10910 when preferred stack boundary is not equal to 2. The drawback is a notable
10911 increase in code size. This switch implies @option{-mno-push-args}.
10915 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
10916 on thread-safe exception handling must compile and link all code with the
10917 @option{-mthreads} option. When compiling, @option{-mthreads} defines
10918 @option{-D_MT}; when linking, it links in a special thread helper library
10919 @option{-lmingwthrd} which cleans up per thread exception handling data.
10921 @item -mno-align-stringops
10922 @opindex mno-align-stringops
10923 Do not align destination of inlined string operations. This switch reduces
10924 code size and improves performance in case the destination is already aligned,
10925 but GCC doesn't know about it.
10927 @item -minline-all-stringops
10928 @opindex minline-all-stringops
10929 By default GCC inlines string operations only when destination is known to be
10930 aligned at least to 4 byte boundary. This enables more inlining, increase code
10931 size, but may improve performance of code that depends on fast memcpy, strlen
10932 and memset for short lengths.
10934 @item -minline-stringops-dynamically
10935 @opindex minline-stringops-dynamically
10936 For string operation of unknown size, inline runtime checks so for small
10937 blocks inline code is used, while for large blocks library call is used.
10939 @item -mstringop-strategy=@var{alg}
10940 @opindex mstringop-strategy=@var{alg}
10941 Overwrite internal decision heuristic about particular algorithm to inline
10942 string operation with. The allowed values are @code{rep_byte},
10943 @code{rep_4byte}, @code{rep_8byte} for expanding using i386 @code{rep} prefix
10944 of specified size, @code{byte_loop}, @code{loop}, @code{unrolled_loop} for
10945 expanding inline loop, @code{libcall} for always expanding library call.
10947 @item -momit-leaf-frame-pointer
10948 @opindex momit-leaf-frame-pointer
10949 Don't keep the frame pointer in a register for leaf functions. This
10950 avoids the instructions to save, set up and restore frame pointers and
10951 makes an extra register available in leaf functions. The option
10952 @option{-fomit-frame-pointer} removes the frame pointer for all functions
10953 which might make debugging harder.
10955 @item -mtls-direct-seg-refs
10956 @itemx -mno-tls-direct-seg-refs
10957 @opindex mtls-direct-seg-refs
10958 Controls whether TLS variables may be accessed with offsets from the
10959 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
10960 or whether the thread base pointer must be added. Whether or not this
10961 is legal depends on the operating system, and whether it maps the
10962 segment to cover the entire TLS area.
10964 For systems that use GNU libc, the default is on.
10967 @itemx -mno-fused-madd
10968 @opindex mfused-madd
10969 Enable automatic generation of fused floating point multiply-add instructions
10970 if the ISA supports such instructions. The -mfused-madd option is on by
10971 default. The fused multiply-add instructions have a different
10972 rounding behavior compared to executing a multiply followed by an add.
10975 These @samp{-m} switches are supported in addition to the above
10976 on AMD x86-64 processors in 64-bit environments.
10983 Generate code for a 32-bit or 64-bit environment.
10984 The 32-bit environment sets int, long and pointer to 32 bits and
10985 generates code that runs on any i386 system.
10986 The 64-bit environment sets int to 32 bits and long and pointer
10987 to 64 bits and generates code for AMD's x86-64 architecture. For
10988 darwin only the -m64 option turns off the @option{-fno-pic} and
10989 @option{-mdynamic-no-pic} options.
10991 @item -mno-red-zone
10992 @opindex no-red-zone
10993 Do not use a so called red zone for x86-64 code. The red zone is mandated
10994 by the x86-64 ABI, it is a 128-byte area beyond the location of the
10995 stack pointer that will not be modified by signal or interrupt handlers
10996 and therefore can be used for temporary data without adjusting the stack
10997 pointer. The flag @option{-mno-red-zone} disables this red zone.
10999 @item -mcmodel=small
11000 @opindex mcmodel=small
11001 Generate code for the small code model: the program and its symbols must
11002 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
11003 Programs can be statically or dynamically linked. This is the default
11006 @item -mcmodel=kernel
11007 @opindex mcmodel=kernel
11008 Generate code for the kernel code model. The kernel runs in the
11009 negative 2 GB of the address space.
11010 This model has to be used for Linux kernel code.
11012 @item -mcmodel=medium
11013 @opindex mcmodel=medium
11014 Generate code for the medium model: The program is linked in the lower 2
11015 GB of the address space but symbols can be located anywhere in the
11016 address space. Programs can be statically or dynamically linked, but
11017 building of shared libraries are not supported with the medium model.
11019 @item -mcmodel=large
11020 @opindex mcmodel=large
11021 Generate code for the large model: This model makes no assumptions
11022 about addresses and sizes of sections.
11025 @node IA-64 Options
11026 @subsection IA-64 Options
11027 @cindex IA-64 Options
11029 These are the @samp{-m} options defined for the Intel IA-64 architecture.
11033 @opindex mbig-endian
11034 Generate code for a big endian target. This is the default for HP-UX@.
11036 @item -mlittle-endian
11037 @opindex mlittle-endian
11038 Generate code for a little endian target. This is the default for AIX5
11044 @opindex mno-gnu-as
11045 Generate (or don't) code for the GNU assembler. This is the default.
11046 @c Also, this is the default if the configure option @option{--with-gnu-as}
11052 @opindex mno-gnu-ld
11053 Generate (or don't) code for the GNU linker. This is the default.
11054 @c Also, this is the default if the configure option @option{--with-gnu-ld}
11059 Generate code that does not use a global pointer register. The result
11060 is not position independent code, and violates the IA-64 ABI@.
11062 @item -mvolatile-asm-stop
11063 @itemx -mno-volatile-asm-stop
11064 @opindex mvolatile-asm-stop
11065 @opindex mno-volatile-asm-stop
11066 Generate (or don't) a stop bit immediately before and after volatile asm
11069 @item -mregister-names
11070 @itemx -mno-register-names
11071 @opindex mregister-names
11072 @opindex mno-register-names
11073 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
11074 the stacked registers. This may make assembler output more readable.
11080 Disable (or enable) optimizations that use the small data section. This may
11081 be useful for working around optimizer bugs.
11083 @item -mconstant-gp
11084 @opindex mconstant-gp
11085 Generate code that uses a single constant global pointer value. This is
11086 useful when compiling kernel code.
11090 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
11091 This is useful when compiling firmware code.
11093 @item -minline-float-divide-min-latency
11094 @opindex minline-float-divide-min-latency
11095 Generate code for inline divides of floating point values
11096 using the minimum latency algorithm.
11098 @item -minline-float-divide-max-throughput
11099 @opindex minline-float-divide-max-throughput
11100 Generate code for inline divides of floating point values
11101 using the maximum throughput algorithm.
11103 @item -minline-int-divide-min-latency
11104 @opindex minline-int-divide-min-latency
11105 Generate code for inline divides of integer values
11106 using the minimum latency algorithm.
11108 @item -minline-int-divide-max-throughput
11109 @opindex minline-int-divide-max-throughput
11110 Generate code for inline divides of integer values
11111 using the maximum throughput algorithm.
11113 @item -minline-sqrt-min-latency
11114 @opindex minline-sqrt-min-latency
11115 Generate code for inline square roots
11116 using the minimum latency algorithm.
11118 @item -minline-sqrt-max-throughput
11119 @opindex minline-sqrt-max-throughput
11120 Generate code for inline square roots
11121 using the maximum throughput algorithm.
11123 @item -mno-dwarf2-asm
11124 @itemx -mdwarf2-asm
11125 @opindex mno-dwarf2-asm
11126 @opindex mdwarf2-asm
11127 Don't (or do) generate assembler code for the DWARF2 line number debugging
11128 info. This may be useful when not using the GNU assembler.
11130 @item -mearly-stop-bits
11131 @itemx -mno-early-stop-bits
11132 @opindex mearly-stop-bits
11133 @opindex mno-early-stop-bits
11134 Allow stop bits to be placed earlier than immediately preceding the
11135 instruction that triggered the stop bit. This can improve instruction
11136 scheduling, but does not always do so.
11138 @item -mfixed-range=@var{register-range}
11139 @opindex mfixed-range
11140 Generate code treating the given register range as fixed registers.
11141 A fixed register is one that the register allocator can not use. This is
11142 useful when compiling kernel code. A register range is specified as
11143 two registers separated by a dash. Multiple register ranges can be
11144 specified separated by a comma.
11146 @item -mtls-size=@var{tls-size}
11148 Specify bit size of immediate TLS offsets. Valid values are 14, 22, and
11151 @item -mtune=@var{cpu-type}
11153 Tune the instruction scheduling for a particular CPU, Valid values are
11154 itanium, itanium1, merced, itanium2, and mckinley.
11160 Add support for multithreading using the POSIX threads library. This
11161 option sets flags for both the preprocessor and linker. It does
11162 not affect the thread safety of object code produced by the compiler or
11163 that of libraries supplied with it. These are HP-UX specific flags.
11169 Generate code for a 32-bit or 64-bit environment.
11170 The 32-bit environment sets int, long and pointer to 32 bits.
11171 The 64-bit environment sets int to 32 bits and long and pointer
11172 to 64 bits. These are HP-UX specific flags.
11174 @item -mno-sched-br-data-spec
11175 @itemx -msched-br-data-spec
11176 @opindex mno-sched-br-data-spec
11177 @opindex msched-br-data-spec
11178 (Dis/En)able data speculative scheduling before reload.
11179 This will result in generation of the ld.a instructions and
11180 the corresponding check instructions (ld.c / chk.a).
11181 The default is 'disable'.
11183 @item -msched-ar-data-spec
11184 @itemx -mno-sched-ar-data-spec
11185 @opindex msched-ar-data-spec
11186 @opindex mno-sched-ar-data-spec
11187 (En/Dis)able data speculative scheduling after reload.
11188 This will result in generation of the ld.a instructions and
11189 the corresponding check instructions (ld.c / chk.a).
11190 The default is 'enable'.
11192 @item -mno-sched-control-spec
11193 @itemx -msched-control-spec
11194 @opindex mno-sched-control-spec
11195 @opindex msched-control-spec
11196 (Dis/En)able control speculative scheduling. This feature is
11197 available only during region scheduling (i.e.@: before reload).
11198 This will result in generation of the ld.s instructions and
11199 the corresponding check instructions chk.s .
11200 The default is 'disable'.
11202 @item -msched-br-in-data-spec
11203 @itemx -mno-sched-br-in-data-spec
11204 @opindex msched-br-in-data-spec
11205 @opindex mno-sched-br-in-data-spec
11206 (En/Dis)able speculative scheduling of the instructions that
11207 are dependent on the data speculative loads before reload.
11208 This is effective only with @option{-msched-br-data-spec} enabled.
11209 The default is 'enable'.
11211 @item -msched-ar-in-data-spec
11212 @itemx -mno-sched-ar-in-data-spec
11213 @opindex msched-ar-in-data-spec
11214 @opindex mno-sched-ar-in-data-spec
11215 (En/Dis)able speculative scheduling of the instructions that
11216 are dependent on the data speculative loads after reload.
11217 This is effective only with @option{-msched-ar-data-spec} enabled.
11218 The default is 'enable'.
11220 @item -msched-in-control-spec
11221 @itemx -mno-sched-in-control-spec
11222 @opindex msched-in-control-spec
11223 @opindex mno-sched-in-control-spec
11224 (En/Dis)able speculative scheduling of the instructions that
11225 are dependent on the control speculative loads.
11226 This is effective only with @option{-msched-control-spec} enabled.
11227 The default is 'enable'.
11230 @itemx -mno-sched-ldc
11231 @opindex msched-ldc
11232 @opindex mno-sched-ldc
11233 (En/Dis)able use of simple data speculation checks ld.c .
11234 If disabled, only chk.a instructions will be emitted to check
11235 data speculative loads.
11236 The default is 'enable'.
11238 @item -mno-sched-control-ldc
11239 @itemx -msched-control-ldc
11240 @opindex mno-sched-control-ldc
11241 @opindex msched-control-ldc
11242 (Dis/En)able use of ld.c instructions to check control speculative loads.
11243 If enabled, in case of control speculative load with no speculatively
11244 scheduled dependent instructions this load will be emitted as ld.sa and
11245 ld.c will be used to check it.
11246 The default is 'disable'.
11248 @item -mno-sched-spec-verbose
11249 @itemx -msched-spec-verbose
11250 @opindex mno-sched-spec-verbose
11251 @opindex msched-spec-verbose
11252 (Dis/En)able printing of the information about speculative motions.
11254 @item -mno-sched-prefer-non-data-spec-insns
11255 @itemx -msched-prefer-non-data-spec-insns
11256 @opindex mno-sched-prefer-non-data-spec-insns
11257 @opindex msched-prefer-non-data-spec-insns
11258 If enabled, data speculative instructions will be chosen for schedule
11259 only if there are no other choices at the moment. This will make
11260 the use of the data speculation much more conservative.
11261 The default is 'disable'.
11263 @item -mno-sched-prefer-non-control-spec-insns
11264 @itemx -msched-prefer-non-control-spec-insns
11265 @opindex mno-sched-prefer-non-control-spec-insns
11266 @opindex msched-prefer-non-control-spec-insns
11267 If enabled, control speculative instructions will be chosen for schedule
11268 only if there are no other choices at the moment. This will make
11269 the use of the control speculation much more conservative.
11270 The default is 'disable'.
11272 @item -mno-sched-count-spec-in-critical-path
11273 @itemx -msched-count-spec-in-critical-path
11274 @opindex mno-sched-count-spec-in-critical-path
11275 @opindex msched-count-spec-in-critical-path
11276 If enabled, speculative dependencies will be considered during
11277 computation of the instructions priorities. This will make the use of the
11278 speculation a bit more conservative.
11279 The default is 'disable'.
11284 @subsection M32C Options
11285 @cindex M32C options
11288 @item -mcpu=@var{name}
11290 Select the CPU for which code is generated. @var{name} may be one of
11291 @samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to
11292 /60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for
11293 the M32C/80 series.
11297 Specifies that the program will be run on the simulator. This causes
11298 an alternate runtime library to be linked in which supports, for
11299 example, file I/O@. You must not use this option when generating
11300 programs that will run on real hardware; you must provide your own
11301 runtime library for whatever I/O functions are needed.
11303 @item -memregs=@var{number}
11305 Specifies the number of memory-based pseudo-registers GCC will use
11306 during code generation. These pseudo-registers will be used like real
11307 registers, so there is a tradeoff between GCC's ability to fit the
11308 code into available registers, and the performance penalty of using
11309 memory instead of registers. Note that all modules in a program must
11310 be compiled with the same value for this option. Because of that, you
11311 must not use this option with the default runtime libraries gcc
11316 @node M32R/D Options
11317 @subsection M32R/D Options
11318 @cindex M32R/D options
11320 These @option{-m} options are defined for Renesas M32R/D architectures:
11325 Generate code for the M32R/2@.
11329 Generate code for the M32R/X@.
11333 Generate code for the M32R@. This is the default.
11335 @item -mmodel=small
11336 @opindex mmodel=small
11337 Assume all objects live in the lower 16MB of memory (so that their addresses
11338 can be loaded with the @code{ld24} instruction), and assume all subroutines
11339 are reachable with the @code{bl} instruction.
11340 This is the default.
11342 The addressability of a particular object can be set with the
11343 @code{model} attribute.
11345 @item -mmodel=medium
11346 @opindex mmodel=medium
11347 Assume objects may be anywhere in the 32-bit address space (the compiler
11348 will generate @code{seth/add3} instructions to load their addresses), and
11349 assume all subroutines are reachable with the @code{bl} instruction.
11351 @item -mmodel=large
11352 @opindex mmodel=large
11353 Assume objects may be anywhere in the 32-bit address space (the compiler
11354 will generate @code{seth/add3} instructions to load their addresses), and
11355 assume subroutines may not be reachable with the @code{bl} instruction
11356 (the compiler will generate the much slower @code{seth/add3/jl}
11357 instruction sequence).
11360 @opindex msdata=none
11361 Disable use of the small data area. Variables will be put into
11362 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
11363 @code{section} attribute has been specified).
11364 This is the default.
11366 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
11367 Objects may be explicitly put in the small data area with the
11368 @code{section} attribute using one of these sections.
11370 @item -msdata=sdata
11371 @opindex msdata=sdata
11372 Put small global and static data in the small data area, but do not
11373 generate special code to reference them.
11376 @opindex msdata=use
11377 Put small global and static data in the small data area, and generate
11378 special instructions to reference them.
11382 @cindex smaller data references
11383 Put global and static objects less than or equal to @var{num} bytes
11384 into the small data or bss sections instead of the normal data or bss
11385 sections. The default value of @var{num} is 8.
11386 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
11387 for this option to have any effect.
11389 All modules should be compiled with the same @option{-G @var{num}} value.
11390 Compiling with different values of @var{num} may or may not work; if it
11391 doesn't the linker will give an error message---incorrect code will not be
11396 Makes the M32R specific code in the compiler display some statistics
11397 that might help in debugging programs.
11399 @item -malign-loops
11400 @opindex malign-loops
11401 Align all loops to a 32-byte boundary.
11403 @item -mno-align-loops
11404 @opindex mno-align-loops
11405 Do not enforce a 32-byte alignment for loops. This is the default.
11407 @item -missue-rate=@var{number}
11408 @opindex missue-rate=@var{number}
11409 Issue @var{number} instructions per cycle. @var{number} can only be 1
11412 @item -mbranch-cost=@var{number}
11413 @opindex mbranch-cost=@var{number}
11414 @var{number} can only be 1 or 2. If it is 1 then branches will be
11415 preferred over conditional code, if it is 2, then the opposite will
11418 @item -mflush-trap=@var{number}
11419 @opindex mflush-trap=@var{number}
11420 Specifies the trap number to use to flush the cache. The default is
11421 12. Valid numbers are between 0 and 15 inclusive.
11423 @item -mno-flush-trap
11424 @opindex mno-flush-trap
11425 Specifies that the cache cannot be flushed by using a trap.
11427 @item -mflush-func=@var{name}
11428 @opindex mflush-func=@var{name}
11429 Specifies the name of the operating system function to call to flush
11430 the cache. The default is @emph{_flush_cache}, but a function call
11431 will only be used if a trap is not available.
11433 @item -mno-flush-func
11434 @opindex mno-flush-func
11435 Indicates that there is no OS function for flushing the cache.
11439 @node M680x0 Options
11440 @subsection M680x0 Options
11441 @cindex M680x0 options
11443 These are the @samp{-m} options defined for M680x0 and ColdFire processors.
11444 The default settings depend on which architecture was selected when
11445 the compiler was configured; the defaults for the most common choices
11449 @item -march=@var{arch}
11451 Generate code for a specific M680x0 or ColdFire instruction set
11452 architecture. Permissible values of @var{arch} for M680x0
11453 architectures are: @samp{68000}, @samp{68010}, @samp{68020},
11454 @samp{68030}, @samp{68040}, @samp{68060} and @samp{cpu32}. ColdFire
11455 architectures are selected according to Freescale's ISA classification
11456 and the permissible values are: @samp{isaa}, @samp{isaaplus},
11457 @samp{isab} and @samp{isac}.
11459 gcc defines a macro @samp{__mcf@var{arch}__} whenever it is generating
11460 code for a ColdFire target. The @var{arch} in this macro is one of the
11461 @option{-march} arguments given above.
11463 When used together, @option{-march} and @option{-mtune} select code
11464 that runs on a family of similar processors but that is optimized
11465 for a particular microarchitecture.
11467 @item -mcpu=@var{cpu}
11469 Generate code for a specific M680x0 or ColdFire processor.
11470 The M680x0 @var{cpu}s are: @samp{68000}, @samp{68010}, @samp{68020},
11471 @samp{68030}, @samp{68040}, @samp{68060}, @samp{68302}, @samp{68332}
11472 and @samp{cpu32}. The ColdFire @var{cpu}s are given by the table
11473 below, which also classifies the CPUs into families:
11475 @multitable @columnfractions 0.20 0.80
11476 @item @strong{Family} @tab @strong{@samp{-mcpu} arguments}
11477 @item @samp{51qe} @tab @samp{51qe}
11478 @item @samp{5206} @tab @samp{5202} @samp{5204} @samp{5206}
11479 @item @samp{5206e} @tab @samp{5206e}
11480 @item @samp{5208} @tab @samp{5207} @samp{5208}
11481 @item @samp{5211a} @tab @samp{5210a} @samp{5211a}
11482 @item @samp{5213} @tab @samp{5211} @samp{5212} @samp{5213}
11483 @item @samp{5216} @tab @samp{5214} @samp{5216}
11484 @item @samp{52235} @tab @samp{52230} @samp{52231} @samp{52232} @samp{52233} @samp{52234} @samp{52235}
11485 @item @samp{5225} @tab @samp{5224} @samp{5225}
11486 @item @samp{5235} @tab @samp{5232} @samp{5233} @samp{5234} @samp{5235} @samp{523x}
11487 @item @samp{5249} @tab @samp{5249}
11488 @item @samp{5250} @tab @samp{5250}
11489 @item @samp{5271} @tab @samp{5270} @samp{5271}
11490 @item @samp{5272} @tab @samp{5272}
11491 @item @samp{5275} @tab @samp{5274} @samp{5275}
11492 @item @samp{5282} @tab @samp{5280} @samp{5281} @samp{5282} @samp{528x}
11493 @item @samp{5307} @tab @samp{5307}
11494 @item @samp{5329} @tab @samp{5327} @samp{5328} @samp{5329} @samp{532x}
11495 @item @samp{5373} @tab @samp{5372} @samp{5373} @samp{537x}
11496 @item @samp{5407} @tab @samp{5407}
11497 @item @samp{5475} @tab @samp{5470} @samp{5471} @samp{5472} @samp{5473} @samp{5474} @samp{5475} @samp{547x} @samp{5480} @samp{5481} @samp{5482} @samp{5483} @samp{5484} @samp{5485}
11500 @option{-mcpu=@var{cpu}} overrides @option{-march=@var{arch}} if
11501 @var{arch} is compatible with @var{cpu}. Other combinations of
11502 @option{-mcpu} and @option{-march} are rejected.
11504 gcc defines the macro @samp{__mcf_cpu_@var{cpu}} when ColdFire target
11505 @var{cpu} is selected. It also defines @samp{__mcf_family_@var{family}},
11506 where the value of @var{family} is given by the table above.
11508 @item -mtune=@var{tune}
11510 Tune the code for a particular microarchitecture, within the
11511 constraints set by @option{-march} and @option{-mcpu}.
11512 The M680x0 microarchitectures are: @samp{68000}, @samp{68010},
11513 @samp{68020}, @samp{68030}, @samp{68040}, @samp{68060}
11514 and @samp{cpu32}. The ColdFire microarchitectures
11515 are: @samp{cfv1}, @samp{cfv2}, @samp{cfv3}, @samp{cfv4} and @samp{cfv4e}.
11517 You can also use @option{-mtune=68020-40} for code that needs
11518 to run relatively well on 68020, 68030 and 68040 targets.
11519 @option{-mtune=68020-60} is similar but includes 68060 targets
11520 as well. These two options select the same tuning decisions as
11521 @option{-m68020-40} and @option{-m68020-60} respectively.
11523 gcc defines the macros @samp{__mc@var{arch}} and @samp{__mc@var{arch}__}
11524 when tuning for 680x0 architecture @var{arch}. It also defines
11525 @samp{mc@var{arch}} unless either @option{-ansi} or a non-GNU @option{-std}
11526 option is used. If gcc is tuning for a range of architectures,
11527 as selected by @option{-mtune=68020-40} or @option{-mtune=68020-60},
11528 it defines the macros for every architecture in the range.
11530 gcc also defines the macro @samp{__m@var{uarch}__} when tuning for
11531 ColdFire microarchitecture @var{uarch}, where @var{uarch} is one
11532 of the arguments given above.
11538 Generate output for a 68000. This is the default
11539 when the compiler is configured for 68000-based systems.
11540 It is equivalent to @option{-march=68000}.
11542 Use this option for microcontrollers with a 68000 or EC000 core,
11543 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
11547 Generate output for a 68010. This is the default
11548 when the compiler is configured for 68010-based systems.
11549 It is equivalent to @option{-march=68010}.
11555 Generate output for a 68020. This is the default
11556 when the compiler is configured for 68020-based systems.
11557 It is equivalent to @option{-march=68020}.
11561 Generate output for a 68030. This is the default when the compiler is
11562 configured for 68030-based systems. It is equivalent to
11563 @option{-march=68030}.
11567 Generate output for a 68040. This is the default when the compiler is
11568 configured for 68040-based systems. It is equivalent to
11569 @option{-march=68040}.
11571 This option inhibits the use of 68881/68882 instructions that have to be
11572 emulated by software on the 68040. Use this option if your 68040 does not
11573 have code to emulate those instructions.
11577 Generate output for a 68060. This is the default when the compiler is
11578 configured for 68060-based systems. It is equivalent to
11579 @option{-march=68060}.
11581 This option inhibits the use of 68020 and 68881/68882 instructions that
11582 have to be emulated by software on the 68060. Use this option if your 68060
11583 does not have code to emulate those instructions.
11587 Generate output for a CPU32. This is the default
11588 when the compiler is configured for CPU32-based systems.
11589 It is equivalent to @option{-march=cpu32}.
11591 Use this option for microcontrollers with a
11592 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
11593 68336, 68340, 68341, 68349 and 68360.
11597 Generate output for a 520X ColdFire CPU@. This is the default
11598 when the compiler is configured for 520X-based systems.
11599 It is equivalent to @option{-mcpu=5206}, and is now deprecated
11600 in favor of that option.
11602 Use this option for microcontroller with a 5200 core, including
11603 the MCF5202, MCF5203, MCF5204 and MCF5206.
11607 Generate output for a 5206e ColdFire CPU@. The option is now
11608 deprecated in favor of the equivalent @option{-mcpu=5206e}.
11612 Generate output for a member of the ColdFire 528X family.
11613 The option is now deprecated in favor of the equivalent
11614 @option{-mcpu=528x}.
11618 Generate output for a ColdFire 5307 CPU@. The option is now deprecated
11619 in favor of the equivalent @option{-mcpu=5307}.
11623 Generate output for a ColdFire 5407 CPU@. The option is now deprecated
11624 in favor of the equivalent @option{-mcpu=5407}.
11628 Generate output for a ColdFire V4e family CPU (e.g.@: 547x/548x).
11629 This includes use of hardware floating point instructions.
11630 The option is equivalent to @option{-mcpu=547x}, and is now
11631 deprecated in favor of that option.
11635 Generate output for a 68040, without using any of the new instructions.
11636 This results in code which can run relatively efficiently on either a
11637 68020/68881 or a 68030 or a 68040. The generated code does use the
11638 68881 instructions that are emulated on the 68040.
11640 The option is equivalent to @option{-march=68020} @option{-mtune=68020-40}.
11644 Generate output for a 68060, without using any of the new instructions.
11645 This results in code which can run relatively efficiently on either a
11646 68020/68881 or a 68030 or a 68040. The generated code does use the
11647 68881 instructions that are emulated on the 68060.
11649 The option is equivalent to @option{-march=68020} @option{-mtune=68020-60}.
11653 @opindex mhard-float
11655 Generate floating-point instructions. This is the default for 68020
11656 and above, and for ColdFire devices that have an FPU@. It defines the
11657 macro @samp{__HAVE_68881__} on M680x0 targets and @samp{__mcffpu__}
11658 on ColdFire targets.
11661 @opindex msoft-float
11662 Do not generate floating-point instructions; use library calls instead.
11663 This is the default for 68000, 68010, and 68832 targets. It is also
11664 the default for ColdFire devices that have no FPU.
11670 Generate (do not generate) ColdFire hardware divide and remainder
11671 instructions. If @option{-march} is used without @option{-mcpu},
11672 the default is ``on'' for ColdFire architectures and ``off'' for M680x0
11673 architectures. Otherwise, the default is taken from the target CPU
11674 (either the default CPU, or the one specified by @option{-mcpu}). For
11675 example, the default is ``off'' for @option{-mcpu=5206} and ``on'' for
11676 @option{-mcpu=5206e}.
11678 gcc defines the macro @samp{__mcfhwdiv__} when this option is enabled.
11682 Consider type @code{int} to be 16 bits wide, like @code{short int}.
11683 Additionally, parameters passed on the stack are also aligned to a
11684 16-bit boundary even on targets whose API mandates promotion to 32-bit.
11688 Do not consider type @code{int} to be 16 bits wide. This is the default.
11691 @itemx -mno-bitfield
11692 @opindex mnobitfield
11693 @opindex mno-bitfield
11694 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
11695 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
11699 Do use the bit-field instructions. The @option{-m68020} option implies
11700 @option{-mbitfield}. This is the default if you use a configuration
11701 designed for a 68020.
11705 Use a different function-calling convention, in which functions
11706 that take a fixed number of arguments return with the @code{rtd}
11707 instruction, which pops their arguments while returning. This
11708 saves one instruction in the caller since there is no need to pop
11709 the arguments there.
11711 This calling convention is incompatible with the one normally
11712 used on Unix, so you cannot use it if you need to call libraries
11713 compiled with the Unix compiler.
11715 Also, you must provide function prototypes for all functions that
11716 take variable numbers of arguments (including @code{printf});
11717 otherwise incorrect code will be generated for calls to those
11720 In addition, seriously incorrect code will result if you call a
11721 function with too many arguments. (Normally, extra arguments are
11722 harmlessly ignored.)
11724 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
11725 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
11729 Do not use the calling conventions selected by @option{-mrtd}.
11730 This is the default.
11733 @itemx -mno-align-int
11734 @opindex malign-int
11735 @opindex mno-align-int
11736 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
11737 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
11738 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
11739 Aligning variables on 32-bit boundaries produces code that runs somewhat
11740 faster on processors with 32-bit busses at the expense of more memory.
11742 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
11743 align structures containing the above types differently than
11744 most published application binary interface specifications for the m68k.
11748 Use the pc-relative addressing mode of the 68000 directly, instead of
11749 using a global offset table. At present, this option implies @option{-fpic},
11750 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
11751 not presently supported with @option{-mpcrel}, though this could be supported for
11752 68020 and higher processors.
11754 @item -mno-strict-align
11755 @itemx -mstrict-align
11756 @opindex mno-strict-align
11757 @opindex mstrict-align
11758 Do not (do) assume that unaligned memory references will be handled by
11762 Generate code that allows the data segment to be located in a different
11763 area of memory from the text segment. This allows for execute in place in
11764 an environment without virtual memory management. This option implies
11767 @item -mno-sep-data
11768 Generate code that assumes that the data segment follows the text segment.
11769 This is the default.
11771 @item -mid-shared-library
11772 Generate code that supports shared libraries via the library ID method.
11773 This allows for execute in place and shared libraries in an environment
11774 without virtual memory management. This option implies @option{-fPIC}.
11776 @item -mno-id-shared-library
11777 Generate code that doesn't assume ID based shared libraries are being used.
11778 This is the default.
11780 @item -mshared-library-id=n
11781 Specified the identification number of the ID based shared library being
11782 compiled. Specifying a value of 0 will generate more compact code, specifying
11783 other values will force the allocation of that number to the current
11784 library but is no more space or time efficient than omitting this option.
11790 When generating position-independent code for ColdFire, generate code
11791 that works if the GOT has more than 8192 entries. This code is
11792 larger and slower than code generated without this option. On M680x0
11793 processors, this option is not needed; @option{-fPIC} suffices.
11795 GCC normally uses a single instruction to load values from the GOT@.
11796 While this is relatively efficient, it only works if the GOT
11797 is smaller than about 64k. Anything larger causes the linker
11798 to report an error such as:
11800 @cindex relocation truncated to fit (ColdFire)
11802 relocation truncated to fit: R_68K_GOT16O foobar
11805 If this happens, you should recompile your code with @option{-mxgot}.
11806 It should then work with very large GOTs. However, code generated with
11807 @option{-mxgot} is less efficient, since it takes 4 instructions to fetch
11808 the value of a global symbol.
11810 Note that some linkers, including newer versions of the GNU linker,
11811 can create multiple GOTs and sort GOT entries. If you have such a linker,
11812 you should only need to use @option{-mxgot} when compiling a single
11813 object file that accesses more than 8192 GOT entries. Very few do.
11815 These options have no effect unless GCC is generating
11816 position-independent code.
11820 @node M68hc1x Options
11821 @subsection M68hc1x Options
11822 @cindex M68hc1x options
11824 These are the @samp{-m} options defined for the 68hc11 and 68hc12
11825 microcontrollers. The default values for these options depends on
11826 which style of microcontroller was selected when the compiler was configured;
11827 the defaults for the most common choices are given below.
11834 Generate output for a 68HC11. This is the default
11835 when the compiler is configured for 68HC11-based systems.
11841 Generate output for a 68HC12. This is the default
11842 when the compiler is configured for 68HC12-based systems.
11848 Generate output for a 68HCS12.
11850 @item -mauto-incdec
11851 @opindex mauto-incdec
11852 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
11859 Enable the use of 68HC12 min and max instructions.
11862 @itemx -mno-long-calls
11863 @opindex mlong-calls
11864 @opindex mno-long-calls
11865 Treat all calls as being far away (near). If calls are assumed to be
11866 far away, the compiler will use the @code{call} instruction to
11867 call a function and the @code{rtc} instruction for returning.
11871 Consider type @code{int} to be 16 bits wide, like @code{short int}.
11873 @item -msoft-reg-count=@var{count}
11874 @opindex msoft-reg-count
11875 Specify the number of pseudo-soft registers which are used for the
11876 code generation. The maximum number is 32. Using more pseudo-soft
11877 register may or may not result in better code depending on the program.
11878 The default is 4 for 68HC11 and 2 for 68HC12.
11882 @node MCore Options
11883 @subsection MCore Options
11884 @cindex MCore options
11886 These are the @samp{-m} options defined for the Motorola M*Core
11892 @itemx -mno-hardlit
11894 @opindex mno-hardlit
11895 Inline constants into the code stream if it can be done in two
11896 instructions or less.
11902 Use the divide instruction. (Enabled by default).
11904 @item -mrelax-immediate
11905 @itemx -mno-relax-immediate
11906 @opindex mrelax-immediate
11907 @opindex mno-relax-immediate
11908 Allow arbitrary sized immediates in bit operations.
11910 @item -mwide-bitfields
11911 @itemx -mno-wide-bitfields
11912 @opindex mwide-bitfields
11913 @opindex mno-wide-bitfields
11914 Always treat bit-fields as int-sized.
11916 @item -m4byte-functions
11917 @itemx -mno-4byte-functions
11918 @opindex m4byte-functions
11919 @opindex mno-4byte-functions
11920 Force all functions to be aligned to a four byte boundary.
11922 @item -mcallgraph-data
11923 @itemx -mno-callgraph-data
11924 @opindex mcallgraph-data
11925 @opindex mno-callgraph-data
11926 Emit callgraph information.
11929 @itemx -mno-slow-bytes
11930 @opindex mslow-bytes
11931 @opindex mno-slow-bytes
11932 Prefer word access when reading byte quantities.
11934 @item -mlittle-endian
11935 @itemx -mbig-endian
11936 @opindex mlittle-endian
11937 @opindex mbig-endian
11938 Generate code for a little endian target.
11944 Generate code for the 210 processor.
11948 @subsection MIPS Options
11949 @cindex MIPS options
11955 Generate big-endian code.
11959 Generate little-endian code. This is the default for @samp{mips*el-*-*}
11962 @item -march=@var{arch}
11964 Generate code that will run on @var{arch}, which can be the name of a
11965 generic MIPS ISA, or the name of a particular processor.
11967 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
11968 @samp{mips32}, @samp{mips32r2}, @samp{mips64} and @samp{mips64r2}.
11969 The processor names are:
11970 @samp{4kc}, @samp{4km}, @samp{4kp}, @samp{4ksc},
11971 @samp{4kec}, @samp{4kem}, @samp{4kep}, @samp{4ksd},
11972 @samp{5kc}, @samp{5kf},
11974 @samp{24kc}, @samp{24kf2_1}, @samp{24kf1_1},
11975 @samp{24kec}, @samp{24kef2_1}, @samp{24kef1_1},
11976 @samp{34kc}, @samp{34kf2_1}, @samp{34kf1_1},
11977 @samp{74kc}, @samp{74kf2_1}, @samp{74kf1_1}, @samp{74kf3_2},
11978 @samp{loongson2e}, @samp{loongson2f},
11981 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
11982 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000},
11983 @samp{rm7000}, @samp{rm9000},
11986 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300},
11987 @samp{vr5000}, @samp{vr5400}, @samp{vr5500}
11989 The special value @samp{from-abi} selects the
11990 most compatible architecture for the selected ABI (that is,
11991 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
11993 Native Linux/GNU toolchains also support the value @samp{native},
11994 which selects the best architecture option for the host processor.
11995 @option{-march=native} has no effect if GCC does not recognize
11998 In processor names, a final @samp{000} can be abbreviated as @samp{k}
11999 (for example, @samp{-march=r2k}). Prefixes are optional, and
12000 @samp{vr} may be written @samp{r}.
12002 Names of the form @samp{@var{n}f2_1} refer to processors with
12003 FPUs clocked at half the rate of the core, names of the form
12004 @samp{@var{n}f1_1} refer to processors with FPUs clocked at the same
12005 rate as the core, and names of the form @samp{@var{n}f3_2} refer to
12006 processors with FPUs clocked a ratio of 3:2 with respect to the core.
12007 For compatibility reasons, @samp{@var{n}f} is accepted as a synonym
12008 for @samp{@var{n}f2_1} while @samp{@var{n}x} and @samp{@var{b}fx} are
12009 accepted as synonyms for @samp{@var{n}f1_1}.
12011 GCC defines two macros based on the value of this option. The first
12012 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
12013 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
12014 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
12015 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
12016 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
12018 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
12019 above. In other words, it will have the full prefix and will not
12020 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
12021 the macro names the resolved architecture (either @samp{"mips1"} or
12022 @samp{"mips3"}). It names the default architecture when no
12023 @option{-march} option is given.
12025 @item -mtune=@var{arch}
12027 Optimize for @var{arch}. Among other things, this option controls
12028 the way instructions are scheduled, and the perceived cost of arithmetic
12029 operations. The list of @var{arch} values is the same as for
12032 When this option is not used, GCC will optimize for the processor
12033 specified by @option{-march}. By using @option{-march} and
12034 @option{-mtune} together, it is possible to generate code that will
12035 run on a family of processors, but optimize the code for one
12036 particular member of that family.
12038 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
12039 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
12040 @samp{-march} ones described above.
12044 Equivalent to @samp{-march=mips1}.
12048 Equivalent to @samp{-march=mips2}.
12052 Equivalent to @samp{-march=mips3}.
12056 Equivalent to @samp{-march=mips4}.
12060 Equivalent to @samp{-march=mips32}.
12064 Equivalent to @samp{-march=mips32r2}.
12068 Equivalent to @samp{-march=mips64}.
12072 Equivalent to @samp{-march=mips64r2}.
12077 @opindex mno-mips16
12078 Generate (do not generate) MIPS16 code. If GCC is targetting a
12079 MIPS32 or MIPS64 architecture, it will make use of the MIPS16e ASE@.
12081 MIPS16 code generation can also be controlled on a per-function basis
12082 by means of @code{mips16} and @code{nomips16} attributes.
12083 @xref{Function Attributes}, for more information.
12085 @item -mflip-mips16
12086 @opindex mflip-mips16
12087 Generate MIPS16 code on alternating functions. This option is provided
12088 for regression testing of mixed MIPS16/non-MIPS16 code generation, and is
12089 not intended for ordinary use in compiling user code.
12091 @item -minterlink-mips16
12092 @itemx -mno-interlink-mips16
12093 @opindex minterlink-mips16
12094 @opindex mno-interlink-mips16
12095 Require (do not require) that non-MIPS16 code be link-compatible with
12098 For example, non-MIPS16 code cannot jump directly to MIPS16 code;
12099 it must either use a call or an indirect jump. @option{-minterlink-mips16}
12100 therefore disables direct jumps unless GCC knows that the target of the
12101 jump is not MIPS16.
12113 Generate code for the given ABI@.
12115 Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
12116 generates 64-bit code when you select a 64-bit architecture, but you
12117 can use @option{-mgp32} to get 32-bit code instead.
12119 For information about the O64 ABI, see
12120 @w{@uref{http://gcc.gnu.org/projects/mipso64-abi.html}}.
12122 GCC supports a variant of the o32 ABI in which floating-point registers
12123 are 64 rather than 32 bits wide. You can select this combination with
12124 @option{-mabi=32} @option{-mfp64}. This ABI relies on the @samp{mthc1}
12125 and @samp{mfhc1} instructions and is therefore only supported for
12126 MIPS32R2 processors.
12128 The register assignments for arguments and return values remain the
12129 same, but each scalar value is passed in a single 64-bit register
12130 rather than a pair of 32-bit registers. For example, scalar
12131 floating-point values are returned in @samp{$f0} only, not a
12132 @samp{$f0}/@samp{$f1} pair. The set of call-saved registers also
12133 remains the same, but all 64 bits are saved.
12136 @itemx -mno-abicalls
12138 @opindex mno-abicalls
12139 Generate (do not generate) code that is suitable for SVR4-style
12140 dynamic objects. @option{-mabicalls} is the default for SVR4-based
12145 Generate (do not generate) code that is fully position-independent,
12146 and that can therefore be linked into shared libraries. This option
12147 only affects @option{-mabicalls}.
12149 All @option{-mabicalls} code has traditionally been position-independent,
12150 regardless of options like @option{-fPIC} and @option{-fpic}. However,
12151 as an extension, the GNU toolchain allows executables to use absolute
12152 accesses for locally-binding symbols. It can also use shorter GP
12153 initialization sequences and generate direct calls to locally-defined
12154 functions. This mode is selected by @option{-mno-shared}.
12156 @option{-mno-shared} depends on binutils 2.16 or higher and generates
12157 objects that can only be linked by the GNU linker. However, the option
12158 does not affect the ABI of the final executable; it only affects the ABI
12159 of relocatable objects. Using @option{-mno-shared} will generally make
12160 executables both smaller and quicker.
12162 @option{-mshared} is the default.
12168 Lift (do not lift) the usual restrictions on the size of the global
12171 GCC normally uses a single instruction to load values from the GOT@.
12172 While this is relatively efficient, it will only work if the GOT
12173 is smaller than about 64k. Anything larger will cause the linker
12174 to report an error such as:
12176 @cindex relocation truncated to fit (MIPS)
12178 relocation truncated to fit: R_MIPS_GOT16 foobar
12181 If this happens, you should recompile your code with @option{-mxgot}.
12182 It should then work with very large GOTs, although it will also be
12183 less efficient, since it will take three instructions to fetch the
12184 value of a global symbol.
12186 Note that some linkers can create multiple GOTs. If you have such a
12187 linker, you should only need to use @option{-mxgot} when a single object
12188 file accesses more than 64k's worth of GOT entries. Very few do.
12190 These options have no effect unless GCC is generating position
12195 Assume that general-purpose registers are 32 bits wide.
12199 Assume that general-purpose registers are 64 bits wide.
12203 Assume that floating-point registers are 32 bits wide.
12207 Assume that floating-point registers are 64 bits wide.
12210 @opindex mhard-float
12211 Use floating-point coprocessor instructions.
12214 @opindex msoft-float
12215 Do not use floating-point coprocessor instructions. Implement
12216 floating-point calculations using library calls instead.
12218 @item -msingle-float
12219 @opindex msingle-float
12220 Assume that the floating-point coprocessor only supports single-precision
12223 @item -mdouble-float
12224 @opindex mdouble-float
12225 Assume that the floating-point coprocessor supports double-precision
12226 operations. This is the default.
12232 Use (do not use) @samp{ll}, @samp{sc}, and @samp{sync} instructions to
12233 implement atomic memory built-in functions. When neither option is
12234 specified, GCC will use the instructions if the target architecture
12237 @option{-mllsc} is useful if the runtime environment can emulate the
12238 instructions and @option{-mno-llsc} can be useful when compiling for
12239 nonstandard ISAs. You can make either option the default by
12240 configuring GCC with @option{--with-llsc} and @option{--without-llsc}
12241 respectively. @option{--with-llsc} is the default for some
12242 configurations; see the installation documentation for details.
12248 Use (do not use) revision 1 of the MIPS DSP ASE@.
12249 @xref{MIPS DSP Built-in Functions}. This option defines the
12250 preprocessor macro @samp{__mips_dsp}. It also defines
12251 @samp{__mips_dsp_rev} to 1.
12257 Use (do not use) revision 2 of the MIPS DSP ASE@.
12258 @xref{MIPS DSP Built-in Functions}. This option defines the
12259 preprocessor macros @samp{__mips_dsp} and @samp{__mips_dspr2}.
12260 It also defines @samp{__mips_dsp_rev} to 2.
12263 @itemx -mno-smartmips
12264 @opindex msmartmips
12265 @opindex mno-smartmips
12266 Use (do not use) the MIPS SmartMIPS ASE.
12268 @item -mpaired-single
12269 @itemx -mno-paired-single
12270 @opindex mpaired-single
12271 @opindex mno-paired-single
12272 Use (do not use) paired-single floating-point instructions.
12273 @xref{MIPS Paired-Single Support}. This option requires
12274 hardware floating-point support to be enabled.
12280 Use (do not use) MIPS Digital Media Extension instructions.
12281 This option can only be used when generating 64-bit code and requires
12282 hardware floating-point support to be enabled.
12287 @opindex mno-mips3d
12288 Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}.
12289 The option @option{-mips3d} implies @option{-mpaired-single}.
12295 Use (do not use) MT Multithreading instructions.
12299 Force @code{long} types to be 64 bits wide. See @option{-mlong32} for
12300 an explanation of the default and the way that the pointer size is
12305 Force @code{long}, @code{int}, and pointer types to be 32 bits wide.
12307 The default size of @code{int}s, @code{long}s and pointers depends on
12308 the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI
12309 uses 64-bit @code{long}s, as does the 64-bit EABI; the others use
12310 32-bit @code{long}s. Pointers are the same size as @code{long}s,
12311 or the same size as integer registers, whichever is smaller.
12317 Assume (do not assume) that all symbols have 32-bit values, regardless
12318 of the selected ABI@. This option is useful in combination with
12319 @option{-mabi=64} and @option{-mno-abicalls} because it allows GCC
12320 to generate shorter and faster references to symbolic addresses.
12324 Put definitions of externally-visible data in a small data section
12325 if that data is no bigger than @var{num} bytes. GCC can then access
12326 the data more efficiently; see @option{-mgpopt} for details.
12328 The default @option{-G} option depends on the configuration.
12330 @item -mlocal-sdata
12331 @itemx -mno-local-sdata
12332 @opindex mlocal-sdata
12333 @opindex mno-local-sdata
12334 Extend (do not extend) the @option{-G} behavior to local data too,
12335 such as to static variables in C@. @option{-mlocal-sdata} is the
12336 default for all configurations.
12338 If the linker complains that an application is using too much small data,
12339 you might want to try rebuilding the less performance-critical parts with
12340 @option{-mno-local-sdata}. You might also want to build large
12341 libraries with @option{-mno-local-sdata}, so that the libraries leave
12342 more room for the main program.
12344 @item -mextern-sdata
12345 @itemx -mno-extern-sdata
12346 @opindex mextern-sdata
12347 @opindex mno-extern-sdata
12348 Assume (do not assume) that externally-defined data will be in
12349 a small data section if that data is within the @option{-G} limit.
12350 @option{-mextern-sdata} is the default for all configurations.
12352 If you compile a module @var{Mod} with @option{-mextern-sdata} @option{-G
12353 @var{num}} @option{-mgpopt}, and @var{Mod} references a variable @var{Var}
12354 that is no bigger than @var{num} bytes, you must make sure that @var{Var}
12355 is placed in a small data section. If @var{Var} is defined by another
12356 module, you must either compile that module with a high-enough
12357 @option{-G} setting or attach a @code{section} attribute to @var{Var}'s
12358 definition. If @var{Var} is common, you must link the application
12359 with a high-enough @option{-G} setting.
12361 The easiest way of satisfying these restrictions is to compile
12362 and link every module with the same @option{-G} option. However,
12363 you may wish to build a library that supports several different
12364 small data limits. You can do this by compiling the library with
12365 the highest supported @option{-G} setting and additionally using
12366 @option{-mno-extern-sdata} to stop the library from making assumptions
12367 about externally-defined data.
12373 Use (do not use) GP-relative accesses for symbols that are known to be
12374 in a small data section; see @option{-G}, @option{-mlocal-sdata} and
12375 @option{-mextern-sdata}. @option{-mgpopt} is the default for all
12378 @option{-mno-gpopt} is useful for cases where the @code{$gp} register
12379 might not hold the value of @code{_gp}. For example, if the code is
12380 part of a library that might be used in a boot monitor, programs that
12381 call boot monitor routines will pass an unknown value in @code{$gp}.
12382 (In such situations, the boot monitor itself would usually be compiled
12383 with @option{-G0}.)
12385 @option{-mno-gpopt} implies @option{-mno-local-sdata} and
12386 @option{-mno-extern-sdata}.
12388 @item -membedded-data
12389 @itemx -mno-embedded-data
12390 @opindex membedded-data
12391 @opindex mno-embedded-data
12392 Allocate variables to the read-only data section first if possible, then
12393 next in the small data section if possible, otherwise in data. This gives
12394 slightly slower code than the default, but reduces the amount of RAM required
12395 when executing, and thus may be preferred for some embedded systems.
12397 @item -muninit-const-in-rodata
12398 @itemx -mno-uninit-const-in-rodata
12399 @opindex muninit-const-in-rodata
12400 @opindex mno-uninit-const-in-rodata
12401 Put uninitialized @code{const} variables in the read-only data section.
12402 This option is only meaningful in conjunction with @option{-membedded-data}.
12404 @item -mcode-readable=@var{setting}
12405 @opindex mcode-readable
12406 Specify whether GCC may generate code that reads from executable sections.
12407 There are three possible settings:
12410 @item -mcode-readable=yes
12411 Instructions may freely access executable sections. This is the
12414 @item -mcode-readable=pcrel
12415 MIPS16 PC-relative load instructions can access executable sections,
12416 but other instructions must not do so. This option is useful on 4KSc
12417 and 4KSd processors when the code TLBs have the Read Inhibit bit set.
12418 It is also useful on processors that can be configured to have a dual
12419 instruction/data SRAM interface and that, like the M4K, automatically
12420 redirect PC-relative loads to the instruction RAM.
12422 @item -mcode-readable=no
12423 Instructions must not access executable sections. This option can be
12424 useful on targets that are configured to have a dual instruction/data
12425 SRAM interface but that (unlike the M4K) do not automatically redirect
12426 PC-relative loads to the instruction RAM.
12429 @item -msplit-addresses
12430 @itemx -mno-split-addresses
12431 @opindex msplit-addresses
12432 @opindex mno-split-addresses
12433 Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler
12434 relocation operators. This option has been superseded by
12435 @option{-mexplicit-relocs} but is retained for backwards compatibility.
12437 @item -mexplicit-relocs
12438 @itemx -mno-explicit-relocs
12439 @opindex mexplicit-relocs
12440 @opindex mno-explicit-relocs
12441 Use (do not use) assembler relocation operators when dealing with symbolic
12442 addresses. The alternative, selected by @option{-mno-explicit-relocs},
12443 is to use assembler macros instead.
12445 @option{-mexplicit-relocs} is the default if GCC was configured
12446 to use an assembler that supports relocation operators.
12448 @item -mcheck-zero-division
12449 @itemx -mno-check-zero-division
12450 @opindex mcheck-zero-division
12451 @opindex mno-check-zero-division
12452 Trap (do not trap) on integer division by zero.
12454 The default is @option{-mcheck-zero-division}.
12456 @item -mdivide-traps
12457 @itemx -mdivide-breaks
12458 @opindex mdivide-traps
12459 @opindex mdivide-breaks
12460 MIPS systems check for division by zero by generating either a
12461 conditional trap or a break instruction. Using traps results in
12462 smaller code, but is only supported on MIPS II and later. Also, some
12463 versions of the Linux kernel have a bug that prevents trap from
12464 generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to
12465 allow conditional traps on architectures that support them and
12466 @option{-mdivide-breaks} to force the use of breaks.
12468 The default is usually @option{-mdivide-traps}, but this can be
12469 overridden at configure time using @option{--with-divide=breaks}.
12470 Divide-by-zero checks can be completely disabled using
12471 @option{-mno-check-zero-division}.
12476 @opindex mno-memcpy
12477 Force (do not force) the use of @code{memcpy()} for non-trivial block
12478 moves. The default is @option{-mno-memcpy}, which allows GCC to inline
12479 most constant-sized copies.
12482 @itemx -mno-long-calls
12483 @opindex mlong-calls
12484 @opindex mno-long-calls
12485 Disable (do not disable) use of the @code{jal} instruction. Calling
12486 functions using @code{jal} is more efficient but requires the caller
12487 and callee to be in the same 256 megabyte segment.
12489 This option has no effect on abicalls code. The default is
12490 @option{-mno-long-calls}.
12496 Enable (disable) use of the @code{mad}, @code{madu} and @code{mul}
12497 instructions, as provided by the R4650 ISA@.
12500 @itemx -mno-fused-madd
12501 @opindex mfused-madd
12502 @opindex mno-fused-madd
12503 Enable (disable) use of the floating point multiply-accumulate
12504 instructions, when they are available. The default is
12505 @option{-mfused-madd}.
12507 When multiply-accumulate instructions are used, the intermediate
12508 product is calculated to infinite precision and is not subject to
12509 the FCSR Flush to Zero bit. This may be undesirable in some
12514 Tell the MIPS assembler to not run its preprocessor over user
12515 assembler files (with a @samp{.s} suffix) when assembling them.
12518 @itemx -mno-fix-r4000
12519 @opindex mfix-r4000
12520 @opindex mno-fix-r4000
12521 Work around certain R4000 CPU errata:
12524 A double-word or a variable shift may give an incorrect result if executed
12525 immediately after starting an integer division.
12527 A double-word or a variable shift may give an incorrect result if executed
12528 while an integer multiplication is in progress.
12530 An integer division may give an incorrect result if started in a delay slot
12531 of a taken branch or a jump.
12535 @itemx -mno-fix-r4400
12536 @opindex mfix-r4400
12537 @opindex mno-fix-r4400
12538 Work around certain R4400 CPU errata:
12541 A double-word or a variable shift may give an incorrect result if executed
12542 immediately after starting an integer division.
12546 @itemx -mno-fix-vr4120
12547 @opindex mfix-vr4120
12548 Work around certain VR4120 errata:
12551 @code{dmultu} does not always produce the correct result.
12553 @code{div} and @code{ddiv} do not always produce the correct result if one
12554 of the operands is negative.
12556 The workarounds for the division errata rely on special functions in
12557 @file{libgcc.a}. At present, these functions are only provided by
12558 the @code{mips64vr*-elf} configurations.
12560 Other VR4120 errata require a nop to be inserted between certain pairs of
12561 instructions. These errata are handled by the assembler, not by GCC itself.
12564 @opindex mfix-vr4130
12565 Work around the VR4130 @code{mflo}/@code{mfhi} errata. The
12566 workarounds are implemented by the assembler rather than by GCC,
12567 although GCC will avoid using @code{mflo} and @code{mfhi} if the
12568 VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi}
12569 instructions are available instead.
12572 @itemx -mno-fix-sb1
12574 Work around certain SB-1 CPU core errata.
12575 (This flag currently works around the SB-1 revision 2
12576 ``F1'' and ``F2'' floating point errata.)
12578 @item -mflush-func=@var{func}
12579 @itemx -mno-flush-func
12580 @opindex mflush-func
12581 Specifies the function to call to flush the I and D caches, or to not
12582 call any such function. If called, the function must take the same
12583 arguments as the common @code{_flush_func()}, that is, the address of the
12584 memory range for which the cache is being flushed, the size of the
12585 memory range, and the number 3 (to flush both caches). The default
12586 depends on the target GCC was configured for, but commonly is either
12587 @samp{_flush_func} or @samp{__cpu_flush}.
12589 @item mbranch-cost=@var{num}
12590 @opindex mbranch-cost
12591 Set the cost of branches to roughly @var{num} ``simple'' instructions.
12592 This cost is only a heuristic and is not guaranteed to produce
12593 consistent results across releases. A zero cost redundantly selects
12594 the default, which is based on the @option{-mtune} setting.
12596 @item -mbranch-likely
12597 @itemx -mno-branch-likely
12598 @opindex mbranch-likely
12599 @opindex mno-branch-likely
12600 Enable or disable use of Branch Likely instructions, regardless of the
12601 default for the selected architecture. By default, Branch Likely
12602 instructions may be generated if they are supported by the selected
12603 architecture. An exception is for the MIPS32 and MIPS64 architectures
12604 and processors which implement those architectures; for those, Branch
12605 Likely instructions will not be generated by default because the MIPS32
12606 and MIPS64 architectures specifically deprecate their use.
12608 @item -mfp-exceptions
12609 @itemx -mno-fp-exceptions
12610 @opindex mfp-exceptions
12611 Specifies whether FP exceptions are enabled. This affects how we schedule
12612 FP instructions for some processors. The default is that FP exceptions are
12615 For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
12616 64-bit code, then we can use both FP pipes. Otherwise, we can only use one
12619 @item -mvr4130-align
12620 @itemx -mno-vr4130-align
12621 @opindex mvr4130-align
12622 The VR4130 pipeline is two-way superscalar, but can only issue two
12623 instructions together if the first one is 8-byte aligned. When this
12624 option is enabled, GCC will align pairs of instructions that it
12625 thinks should execute in parallel.
12627 This option only has an effect when optimizing for the VR4130.
12628 It normally makes code faster, but at the expense of making it bigger.
12629 It is enabled by default at optimization level @option{-O3}.
12633 @subsection MMIX Options
12634 @cindex MMIX Options
12636 These options are defined for the MMIX:
12640 @itemx -mno-libfuncs
12642 @opindex mno-libfuncs
12643 Specify that intrinsic library functions are being compiled, passing all
12644 values in registers, no matter the size.
12647 @itemx -mno-epsilon
12649 @opindex mno-epsilon
12650 Generate floating-point comparison instructions that compare with respect
12651 to the @code{rE} epsilon register.
12653 @item -mabi=mmixware
12655 @opindex mabi-mmixware
12657 Generate code that passes function parameters and return values that (in
12658 the called function) are seen as registers @code{$0} and up, as opposed to
12659 the GNU ABI which uses global registers @code{$231} and up.
12661 @item -mzero-extend
12662 @itemx -mno-zero-extend
12663 @opindex mzero-extend
12664 @opindex mno-zero-extend
12665 When reading data from memory in sizes shorter than 64 bits, use (do not
12666 use) zero-extending load instructions by default, rather than
12667 sign-extending ones.
12670 @itemx -mno-knuthdiv
12672 @opindex mno-knuthdiv
12673 Make the result of a division yielding a remainder have the same sign as
12674 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
12675 remainder follows the sign of the dividend. Both methods are
12676 arithmetically valid, the latter being almost exclusively used.
12678 @item -mtoplevel-symbols
12679 @itemx -mno-toplevel-symbols
12680 @opindex mtoplevel-symbols
12681 @opindex mno-toplevel-symbols
12682 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
12683 code can be used with the @code{PREFIX} assembly directive.
12687 Generate an executable in the ELF format, rather than the default
12688 @samp{mmo} format used by the @command{mmix} simulator.
12690 @item -mbranch-predict
12691 @itemx -mno-branch-predict
12692 @opindex mbranch-predict
12693 @opindex mno-branch-predict
12694 Use (do not use) the probable-branch instructions, when static branch
12695 prediction indicates a probable branch.
12697 @item -mbase-addresses
12698 @itemx -mno-base-addresses
12699 @opindex mbase-addresses
12700 @opindex mno-base-addresses
12701 Generate (do not generate) code that uses @emph{base addresses}. Using a
12702 base address automatically generates a request (handled by the assembler
12703 and the linker) for a constant to be set up in a global register. The
12704 register is used for one or more base address requests within the range 0
12705 to 255 from the value held in the register. The generally leads to short
12706 and fast code, but the number of different data items that can be
12707 addressed is limited. This means that a program that uses lots of static
12708 data may require @option{-mno-base-addresses}.
12710 @item -msingle-exit
12711 @itemx -mno-single-exit
12712 @opindex msingle-exit
12713 @opindex mno-single-exit
12714 Force (do not force) generated code to have a single exit point in each
12718 @node MN10300 Options
12719 @subsection MN10300 Options
12720 @cindex MN10300 options
12722 These @option{-m} options are defined for Matsushita MN10300 architectures:
12727 Generate code to avoid bugs in the multiply instructions for the MN10300
12728 processors. This is the default.
12730 @item -mno-mult-bug
12731 @opindex mno-mult-bug
12732 Do not generate code to avoid bugs in the multiply instructions for the
12733 MN10300 processors.
12737 Generate code which uses features specific to the AM33 processor.
12741 Do not generate code which uses features specific to the AM33 processor. This
12744 @item -mreturn-pointer-on-d0
12745 @opindex mreturn-pointer-on-d0
12746 When generating a function which returns a pointer, return the pointer
12747 in both @code{a0} and @code{d0}. Otherwise, the pointer is returned
12748 only in a0, and attempts to call such functions without a prototype
12749 would result in errors. Note that this option is on by default; use
12750 @option{-mno-return-pointer-on-d0} to disable it.
12754 Do not link in the C run-time initialization object file.
12758 Indicate to the linker that it should perform a relaxation optimization pass
12759 to shorten branches, calls and absolute memory addresses. This option only
12760 has an effect when used on the command line for the final link step.
12762 This option makes symbolic debugging impossible.
12765 @node PDP-11 Options
12766 @subsection PDP-11 Options
12767 @cindex PDP-11 Options
12769 These options are defined for the PDP-11:
12774 Use hardware FPP floating point. This is the default. (FIS floating
12775 point on the PDP-11/40 is not supported.)
12778 @opindex msoft-float
12779 Do not use hardware floating point.
12783 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
12787 Return floating-point results in memory. This is the default.
12791 Generate code for a PDP-11/40.
12795 Generate code for a PDP-11/45. This is the default.
12799 Generate code for a PDP-11/10.
12801 @item -mbcopy-builtin
12802 @opindex bcopy-builtin
12803 Use inline @code{movmemhi} patterns for copying memory. This is the
12808 Do not use inline @code{movmemhi} patterns for copying memory.
12814 Use 16-bit @code{int}. This is the default.
12820 Use 32-bit @code{int}.
12823 @itemx -mno-float32
12825 @opindex mno-float32
12826 Use 64-bit @code{float}. This is the default.
12829 @itemx -mno-float64
12831 @opindex mno-float64
12832 Use 32-bit @code{float}.
12836 Use @code{abshi2} pattern. This is the default.
12840 Do not use @code{abshi2} pattern.
12842 @item -mbranch-expensive
12843 @opindex mbranch-expensive
12844 Pretend that branches are expensive. This is for experimenting with
12845 code generation only.
12847 @item -mbranch-cheap
12848 @opindex mbranch-cheap
12849 Do not pretend that branches are expensive. This is the default.
12853 Generate code for a system with split I&D@.
12857 Generate code for a system without split I&D@. This is the default.
12861 Use Unix assembler syntax. This is the default when configured for
12862 @samp{pdp11-*-bsd}.
12866 Use DEC assembler syntax. This is the default when configured for any
12867 PDP-11 target other than @samp{pdp11-*-bsd}.
12870 @node PowerPC Options
12871 @subsection PowerPC Options
12872 @cindex PowerPC options
12874 These are listed under @xref{RS/6000 and PowerPC Options}.
12876 @node RS/6000 and PowerPC Options
12877 @subsection IBM RS/6000 and PowerPC Options
12878 @cindex RS/6000 and PowerPC Options
12879 @cindex IBM RS/6000 and PowerPC Options
12881 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
12888 @itemx -mno-powerpc
12889 @itemx -mpowerpc-gpopt
12890 @itemx -mno-powerpc-gpopt
12891 @itemx -mpowerpc-gfxopt
12892 @itemx -mno-powerpc-gfxopt
12894 @itemx -mno-powerpc64
12898 @itemx -mno-popcntb
12906 @itemx -mno-hard-dfp
12910 @opindex mno-power2
12912 @opindex mno-powerpc
12913 @opindex mpowerpc-gpopt
12914 @opindex mno-powerpc-gpopt
12915 @opindex mpowerpc-gfxopt
12916 @opindex mno-powerpc-gfxopt
12917 @opindex mpowerpc64
12918 @opindex mno-powerpc64
12922 @opindex mno-popcntb
12928 @opindex mno-mfpgpr
12930 @opindex mno-hard-dfp
12931 GCC supports two related instruction set architectures for the
12932 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
12933 instructions supported by the @samp{rios} chip set used in the original
12934 RS/6000 systems and the @dfn{PowerPC} instruction set is the
12935 architecture of the Freescale MPC5xx, MPC6xx, MPC8xx microprocessors, and
12936 the IBM 4xx, 6xx, and follow-on microprocessors.
12938 Neither architecture is a subset of the other. However there is a
12939 large common subset of instructions supported by both. An MQ
12940 register is included in processors supporting the POWER architecture.
12942 You use these options to specify which instructions are available on the
12943 processor you are using. The default value of these options is
12944 determined when configuring GCC@. Specifying the
12945 @option{-mcpu=@var{cpu_type}} overrides the specification of these
12946 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
12947 rather than the options listed above.
12949 The @option{-mpower} option allows GCC to generate instructions that
12950 are found only in the POWER architecture and to use the MQ register.
12951 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
12952 to generate instructions that are present in the POWER2 architecture but
12953 not the original POWER architecture.
12955 The @option{-mpowerpc} option allows GCC to generate instructions that
12956 are found only in the 32-bit subset of the PowerPC architecture.
12957 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
12958 GCC to use the optional PowerPC architecture instructions in the
12959 General Purpose group, including floating-point square root. Specifying
12960 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
12961 use the optional PowerPC architecture instructions in the Graphics
12962 group, including floating-point select.
12964 The @option{-mmfcrf} option allows GCC to generate the move from
12965 condition register field instruction implemented on the POWER4
12966 processor and other processors that support the PowerPC V2.01
12968 The @option{-mpopcntb} option allows GCC to generate the popcount and
12969 double precision FP reciprocal estimate instruction implemented on the
12970 POWER5 processor and other processors that support the PowerPC V2.02
12972 The @option{-mfprnd} option allows GCC to generate the FP round to
12973 integer instructions implemented on the POWER5+ processor and other
12974 processors that support the PowerPC V2.03 architecture.
12975 The @option{-mcmpb} option allows GCC to generate the compare bytes
12976 instruction implemented on the POWER6 processor and other processors
12977 that support the PowerPC V2.05 architecture.
12978 The @option{-mmfpgpr} option allows GCC to generate the FP move to/from
12979 general purpose register instructions implemented on the POWER6X
12980 processor and other processors that support the extended PowerPC V2.05
12982 The @option{-mhard-dfp} option allows GCC to generate the decimal floating
12983 point instructions implemented on some POWER processors.
12985 The @option{-mpowerpc64} option allows GCC to generate the additional
12986 64-bit instructions that are found in the full PowerPC64 architecture
12987 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
12988 @option{-mno-powerpc64}.
12990 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
12991 will use only the instructions in the common subset of both
12992 architectures plus some special AIX common-mode calls, and will not use
12993 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
12994 permits GCC to use any instruction from either architecture and to
12995 allow use of the MQ register; specify this for the Motorola MPC601.
12997 @item -mnew-mnemonics
12998 @itemx -mold-mnemonics
12999 @opindex mnew-mnemonics
13000 @opindex mold-mnemonics
13001 Select which mnemonics to use in the generated assembler code. With
13002 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
13003 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
13004 assembler mnemonics defined for the POWER architecture. Instructions
13005 defined in only one architecture have only one mnemonic; GCC uses that
13006 mnemonic irrespective of which of these options is specified.
13008 GCC defaults to the mnemonics appropriate for the architecture in
13009 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
13010 value of these option. Unless you are building a cross-compiler, you
13011 should normally not specify either @option{-mnew-mnemonics} or
13012 @option{-mold-mnemonics}, but should instead accept the default.
13014 @item -mcpu=@var{cpu_type}
13016 Set architecture type, register usage, choice of mnemonics, and
13017 instruction scheduling parameters for machine type @var{cpu_type}.
13018 Supported values for @var{cpu_type} are @samp{401}, @samp{403},
13019 @samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{464}, @samp{464fp},
13020 @samp{505}, @samp{601}, @samp{602}, @samp{603}, @samp{603e}, @samp{604},
13021 @samp{604e}, @samp{620}, @samp{630}, @samp{740}, @samp{7400},
13022 @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
13023 @samp{860}, @samp{970}, @samp{8540}, @samp{e300c2}, @samp{e300c3},
13024 @samp{e500mc}, @samp{ec603e}, @samp{G3}, @samp{G4}, @samp{G5},
13025 @samp{power}, @samp{power2}, @samp{power3}, @samp{power4},
13026 @samp{power5}, @samp{power5+}, @samp{power6}, @samp{power6x}, @samp{power7}
13027 @samp{common}, @samp{powerpc}, @samp{powerpc64}, @samp{rios},
13028 @samp{rios1}, @samp{rios2}, @samp{rsc}, and @samp{rs64}.
13030 @option{-mcpu=common} selects a completely generic processor. Code
13031 generated under this option will run on any POWER or PowerPC processor.
13032 GCC will use only the instructions in the common subset of both
13033 architectures, and will not use the MQ register. GCC assumes a generic
13034 processor model for scheduling purposes.
13036 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
13037 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
13038 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
13039 types, with an appropriate, generic processor model assumed for
13040 scheduling purposes.
13042 The other options specify a specific processor. Code generated under
13043 those options will run best on that processor, and may not run at all on
13046 The @option{-mcpu} options automatically enable or disable the
13049 @gccoptlist{-maltivec -mfprnd -mhard-float -mmfcrf -mmultiple @gol
13050 -mnew-mnemonics -mpopcntb -mpower -mpower2 -mpowerpc64 @gol
13051 -mpowerpc-gpopt -mpowerpc-gfxopt -mstring -mmulhw -mdlmzb -mmfpgpr}
13053 The particular options set for any particular CPU will vary between
13054 compiler versions, depending on what setting seems to produce optimal
13055 code for that CPU; it doesn't necessarily reflect the actual hardware's
13056 capabilities. If you wish to set an individual option to a particular
13057 value, you may specify it after the @option{-mcpu} option, like
13058 @samp{-mcpu=970 -mno-altivec}.
13060 On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are
13061 not enabled or disabled by the @option{-mcpu} option at present because
13062 AIX does not have full support for these options. You may still
13063 enable or disable them individually if you're sure it'll work in your
13066 @item -mtune=@var{cpu_type}
13068 Set the instruction scheduling parameters for machine type
13069 @var{cpu_type}, but do not set the architecture type, register usage, or
13070 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
13071 values for @var{cpu_type} are used for @option{-mtune} as for
13072 @option{-mcpu}. If both are specified, the code generated will use the
13073 architecture, registers, and mnemonics set by @option{-mcpu}, but the
13074 scheduling parameters set by @option{-mtune}.
13080 Generate code to compute division as reciprocal estimate and iterative
13081 refinement, creating opportunities for increased throughput. This
13082 feature requires: optional PowerPC Graphics instruction set for single
13083 precision and FRE instruction for double precision, assuming divides
13084 cannot generate user-visible traps, and the domain values not include
13085 Infinities, denormals or zero denominator.
13088 @itemx -mno-altivec
13090 @opindex mno-altivec
13091 Generate code that uses (does not use) AltiVec instructions, and also
13092 enable the use of built-in functions that allow more direct access to
13093 the AltiVec instruction set. You may also need to set
13094 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
13100 @opindex mno-vrsave
13101 Generate VRSAVE instructions when generating AltiVec code.
13104 @opindex msecure-plt
13105 Generate code that allows ld and ld.so to build executables and shared
13106 libraries with non-exec .plt and .got sections. This is a PowerPC
13107 32-bit SYSV ABI option.
13111 Generate code that uses a BSS .plt section that ld.so fills in, and
13112 requires .plt and .got sections that are both writable and executable.
13113 This is a PowerPC 32-bit SYSV ABI option.
13119 This switch enables or disables the generation of ISEL instructions.
13121 @item -misel=@var{yes/no}
13122 This switch has been deprecated. Use @option{-misel} and
13123 @option{-mno-isel} instead.
13129 This switch enables or disables the generation of SPE simd
13135 @opindex mno-paired
13136 This switch enables or disables the generation of PAIRED simd
13139 @item -mspe=@var{yes/no}
13140 This option has been deprecated. Use @option{-mspe} and
13141 @option{-mno-spe} instead.
13143 @item -mfloat-gprs=@var{yes/single/double/no}
13144 @itemx -mfloat-gprs
13145 @opindex mfloat-gprs
13146 This switch enables or disables the generation of floating point
13147 operations on the general purpose registers for architectures that
13150 The argument @var{yes} or @var{single} enables the use of
13151 single-precision floating point operations.
13153 The argument @var{double} enables the use of single and
13154 double-precision floating point operations.
13156 The argument @var{no} disables floating point operations on the
13157 general purpose registers.
13159 This option is currently only available on the MPC854x.
13165 Generate code for 32-bit or 64-bit environments of Darwin and SVR4
13166 targets (including GNU/Linux). The 32-bit environment sets int, long
13167 and pointer to 32 bits and generates code that runs on any PowerPC
13168 variant. The 64-bit environment sets int to 32 bits and long and
13169 pointer to 64 bits, and generates code for PowerPC64, as for
13170 @option{-mpowerpc64}.
13173 @itemx -mno-fp-in-toc
13174 @itemx -mno-sum-in-toc
13175 @itemx -mminimal-toc
13177 @opindex mno-fp-in-toc
13178 @opindex mno-sum-in-toc
13179 @opindex mminimal-toc
13180 Modify generation of the TOC (Table Of Contents), which is created for
13181 every executable file. The @option{-mfull-toc} option is selected by
13182 default. In that case, GCC will allocate at least one TOC entry for
13183 each unique non-automatic variable reference in your program. GCC
13184 will also place floating-point constants in the TOC@. However, only
13185 16,384 entries are available in the TOC@.
13187 If you receive a linker error message that saying you have overflowed
13188 the available TOC space, you can reduce the amount of TOC space used
13189 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
13190 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
13191 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
13192 generate code to calculate the sum of an address and a constant at
13193 run-time instead of putting that sum into the TOC@. You may specify one
13194 or both of these options. Each causes GCC to produce very slightly
13195 slower and larger code at the expense of conserving TOC space.
13197 If you still run out of space in the TOC even when you specify both of
13198 these options, specify @option{-mminimal-toc} instead. This option causes
13199 GCC to make only one TOC entry for every file. When you specify this
13200 option, GCC will produce code that is slower and larger but which
13201 uses extremely little TOC space. You may wish to use this option
13202 only on files that contain less frequently executed code.
13208 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
13209 @code{long} type, and the infrastructure needed to support them.
13210 Specifying @option{-maix64} implies @option{-mpowerpc64} and
13211 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
13212 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
13215 @itemx -mno-xl-compat
13216 @opindex mxl-compat
13217 @opindex mno-xl-compat
13218 Produce code that conforms more closely to IBM XL compiler semantics
13219 when using AIX-compatible ABI@. Pass floating-point arguments to
13220 prototyped functions beyond the register save area (RSA) on the stack
13221 in addition to argument FPRs. Do not assume that most significant
13222 double in 128-bit long double value is properly rounded when comparing
13223 values and converting to double. Use XL symbol names for long double
13226 The AIX calling convention was extended but not initially documented to
13227 handle an obscure K&R C case of calling a function that takes the
13228 address of its arguments with fewer arguments than declared. IBM XL
13229 compilers access floating point arguments which do not fit in the
13230 RSA from the stack when a subroutine is compiled without
13231 optimization. Because always storing floating-point arguments on the
13232 stack is inefficient and rarely needed, this option is not enabled by
13233 default and only is necessary when calling subroutines compiled by IBM
13234 XL compilers without optimization.
13238 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
13239 application written to use message passing with special startup code to
13240 enable the application to run. The system must have PE installed in the
13241 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
13242 must be overridden with the @option{-specs=} option to specify the
13243 appropriate directory location. The Parallel Environment does not
13244 support threads, so the @option{-mpe} option and the @option{-pthread}
13245 option are incompatible.
13247 @item -malign-natural
13248 @itemx -malign-power
13249 @opindex malign-natural
13250 @opindex malign-power
13251 On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
13252 @option{-malign-natural} overrides the ABI-defined alignment of larger
13253 types, such as floating-point doubles, on their natural size-based boundary.
13254 The option @option{-malign-power} instructs GCC to follow the ABI-specified
13255 alignment rules. GCC defaults to the standard alignment defined in the ABI@.
13257 On 64-bit Darwin, natural alignment is the default, and @option{-malign-power}
13261 @itemx -mhard-float
13262 @opindex msoft-float
13263 @opindex mhard-float
13264 Generate code that does not use (uses) the floating-point register set.
13265 Software floating point emulation is provided if you use the
13266 @option{-msoft-float} option, and pass the option to GCC when linking.
13269 @itemx -mno-multiple
13271 @opindex mno-multiple
13272 Generate code that uses (does not use) the load multiple word
13273 instructions and the store multiple word instructions. These
13274 instructions are generated by default on POWER systems, and not
13275 generated on PowerPC systems. Do not use @option{-mmultiple} on little
13276 endian PowerPC systems, since those instructions do not work when the
13277 processor is in little endian mode. The exceptions are PPC740 and
13278 PPC750 which permit the instructions usage in little endian mode.
13283 @opindex mno-string
13284 Generate code that uses (does not use) the load string instructions
13285 and the store string word instructions to save multiple registers and
13286 do small block moves. These instructions are generated by default on
13287 POWER systems, and not generated on PowerPC systems. Do not use
13288 @option{-mstring} on little endian PowerPC systems, since those
13289 instructions do not work when the processor is in little endian mode.
13290 The exceptions are PPC740 and PPC750 which permit the instructions
13291 usage in little endian mode.
13296 @opindex mno-update
13297 Generate code that uses (does not use) the load or store instructions
13298 that update the base register to the address of the calculated memory
13299 location. These instructions are generated by default. If you use
13300 @option{-mno-update}, there is a small window between the time that the
13301 stack pointer is updated and the address of the previous frame is
13302 stored, which means code that walks the stack frame across interrupts or
13303 signals may get corrupted data.
13306 @itemx -mno-fused-madd
13307 @opindex mfused-madd
13308 @opindex mno-fused-madd
13309 Generate code that uses (does not use) the floating point multiply and
13310 accumulate instructions. These instructions are generated by default if
13311 hardware floating is used.
13317 Generate code that uses (does not use) the half-word multiply and
13318 multiply-accumulate instructions on the IBM 405, 440 and 464 processors.
13319 These instructions are generated by default when targetting those
13326 Generate code that uses (does not use) the string-search @samp{dlmzb}
13327 instruction on the IBM 405, 440 and 464 processors. This instruction is
13328 generated by default when targetting those processors.
13330 @item -mno-bit-align
13332 @opindex mno-bit-align
13333 @opindex mbit-align
13334 On System V.4 and embedded PowerPC systems do not (do) force structures
13335 and unions that contain bit-fields to be aligned to the base type of the
13338 For example, by default a structure containing nothing but 8
13339 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
13340 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
13341 the structure would be aligned to a 1 byte boundary and be one byte in
13344 @item -mno-strict-align
13345 @itemx -mstrict-align
13346 @opindex mno-strict-align
13347 @opindex mstrict-align
13348 On System V.4 and embedded PowerPC systems do not (do) assume that
13349 unaligned memory references will be handled by the system.
13351 @item -mrelocatable
13352 @itemx -mno-relocatable
13353 @opindex mrelocatable
13354 @opindex mno-relocatable
13355 On embedded PowerPC systems generate code that allows (does not allow)
13356 the program to be relocated to a different address at runtime. If you
13357 use @option{-mrelocatable} on any module, all objects linked together must
13358 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
13360 @item -mrelocatable-lib
13361 @itemx -mno-relocatable-lib
13362 @opindex mrelocatable-lib
13363 @opindex mno-relocatable-lib
13364 On embedded PowerPC systems generate code that allows (does not allow)
13365 the program to be relocated to a different address at runtime. Modules
13366 compiled with @option{-mrelocatable-lib} can be linked with either modules
13367 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
13368 with modules compiled with the @option{-mrelocatable} options.
13374 On System V.4 and embedded PowerPC systems do not (do) assume that
13375 register 2 contains a pointer to a global area pointing to the addresses
13376 used in the program.
13379 @itemx -mlittle-endian
13381 @opindex mlittle-endian
13382 On System V.4 and embedded PowerPC systems compile code for the
13383 processor in little endian mode. The @option{-mlittle-endian} option is
13384 the same as @option{-mlittle}.
13387 @itemx -mbig-endian
13389 @opindex mbig-endian
13390 On System V.4 and embedded PowerPC systems compile code for the
13391 processor in big endian mode. The @option{-mbig-endian} option is
13392 the same as @option{-mbig}.
13394 @item -mdynamic-no-pic
13395 @opindex mdynamic-no-pic
13396 On Darwin and Mac OS X systems, compile code so that it is not
13397 relocatable, but that its external references are relocatable. The
13398 resulting code is suitable for applications, but not shared
13401 @item -mprioritize-restricted-insns=@var{priority}
13402 @opindex mprioritize-restricted-insns
13403 This option controls the priority that is assigned to
13404 dispatch-slot restricted instructions during the second scheduling
13405 pass. The argument @var{priority} takes the value @var{0/1/2} to assign
13406 @var{no/highest/second-highest} priority to dispatch slot restricted
13409 @item -msched-costly-dep=@var{dependence_type}
13410 @opindex msched-costly-dep
13411 This option controls which dependences are considered costly
13412 by the target during instruction scheduling. The argument
13413 @var{dependence_type} takes one of the following values:
13414 @var{no}: no dependence is costly,
13415 @var{all}: all dependences are costly,
13416 @var{true_store_to_load}: a true dependence from store to load is costly,
13417 @var{store_to_load}: any dependence from store to load is costly,
13418 @var{number}: any dependence which latency >= @var{number} is costly.
13420 @item -minsert-sched-nops=@var{scheme}
13421 @opindex minsert-sched-nops
13422 This option controls which nop insertion scheme will be used during
13423 the second scheduling pass. The argument @var{scheme} takes one of the
13425 @var{no}: Don't insert nops.
13426 @var{pad}: Pad with nops any dispatch group which has vacant issue slots,
13427 according to the scheduler's grouping.
13428 @var{regroup_exact}: Insert nops to force costly dependent insns into
13429 separate groups. Insert exactly as many nops as needed to force an insn
13430 to a new group, according to the estimated processor grouping.
13431 @var{number}: Insert nops to force costly dependent insns into
13432 separate groups. Insert @var{number} nops to force an insn to a new group.
13435 @opindex mcall-sysv
13436 On System V.4 and embedded PowerPC systems compile code using calling
13437 conventions that adheres to the March 1995 draft of the System V
13438 Application Binary Interface, PowerPC processor supplement. This is the
13439 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
13441 @item -mcall-sysv-eabi
13442 @opindex mcall-sysv-eabi
13443 Specify both @option{-mcall-sysv} and @option{-meabi} options.
13445 @item -mcall-sysv-noeabi
13446 @opindex mcall-sysv-noeabi
13447 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
13449 @item -mcall-solaris
13450 @opindex mcall-solaris
13451 On System V.4 and embedded PowerPC systems compile code for the Solaris
13455 @opindex mcall-linux
13456 On System V.4 and embedded PowerPC systems compile code for the
13457 Linux-based GNU system.
13461 On System V.4 and embedded PowerPC systems compile code for the
13462 Hurd-based GNU system.
13464 @item -mcall-netbsd
13465 @opindex mcall-netbsd
13466 On System V.4 and embedded PowerPC systems compile code for the
13467 NetBSD operating system.
13469 @item -maix-struct-return
13470 @opindex maix-struct-return
13471 Return all structures in memory (as specified by the AIX ABI)@.
13473 @item -msvr4-struct-return
13474 @opindex msvr4-struct-return
13475 Return structures smaller than 8 bytes in registers (as specified by the
13478 @item -mabi=@var{abi-type}
13480 Extend the current ABI with a particular extension, or remove such extension.
13481 Valid values are @var{altivec}, @var{no-altivec}, @var{spe},
13482 @var{no-spe}, @var{ibmlongdouble}, @var{ieeelongdouble}@.
13486 Extend the current ABI with SPE ABI extensions. This does not change
13487 the default ABI, instead it adds the SPE ABI extensions to the current
13491 @opindex mabi=no-spe
13492 Disable Booke SPE ABI extensions for the current ABI@.
13494 @item -mabi=ibmlongdouble
13495 @opindex mabi=ibmlongdouble
13496 Change the current ABI to use IBM extended precision long double.
13497 This is a PowerPC 32-bit SYSV ABI option.
13499 @item -mabi=ieeelongdouble
13500 @opindex mabi=ieeelongdouble
13501 Change the current ABI to use IEEE extended precision long double.
13502 This is a PowerPC 32-bit Linux ABI option.
13505 @itemx -mno-prototype
13506 @opindex mprototype
13507 @opindex mno-prototype
13508 On System V.4 and embedded PowerPC systems assume that all calls to
13509 variable argument functions are properly prototyped. Otherwise, the
13510 compiler must insert an instruction before every non prototyped call to
13511 set or clear bit 6 of the condition code register (@var{CR}) to
13512 indicate whether floating point values were passed in the floating point
13513 registers in case the function takes a variable arguments. With
13514 @option{-mprototype}, only calls to prototyped variable argument functions
13515 will set or clear the bit.
13519 On embedded PowerPC systems, assume that the startup module is called
13520 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
13521 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}
13526 On embedded PowerPC systems, assume that the startup module is called
13527 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
13532 On embedded PowerPC systems, assume that the startup module is called
13533 @file{crt0.o} and the standard C libraries are @file{libads.a} and
13536 @item -myellowknife
13537 @opindex myellowknife
13538 On embedded PowerPC systems, assume that the startup module is called
13539 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
13544 On System V.4 and embedded PowerPC systems, specify that you are
13545 compiling for a VxWorks system.
13549 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
13550 header to indicate that @samp{eabi} extended relocations are used.
13556 On System V.4 and embedded PowerPC systems do (do not) adhere to the
13557 Embedded Applications Binary Interface (eabi) which is a set of
13558 modifications to the System V.4 specifications. Selecting @option{-meabi}
13559 means that the stack is aligned to an 8 byte boundary, a function
13560 @code{__eabi} is called to from @code{main} to set up the eabi
13561 environment, and the @option{-msdata} option can use both @code{r2} and
13562 @code{r13} to point to two separate small data areas. Selecting
13563 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
13564 do not call an initialization function from @code{main}, and the
13565 @option{-msdata} option will only use @code{r13} to point to a single
13566 small data area. The @option{-meabi} option is on by default if you
13567 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
13570 @opindex msdata=eabi
13571 On System V.4 and embedded PowerPC systems, put small initialized
13572 @code{const} global and static data in the @samp{.sdata2} section, which
13573 is pointed to by register @code{r2}. Put small initialized
13574 non-@code{const} global and static data in the @samp{.sdata} section,
13575 which is pointed to by register @code{r13}. Put small uninitialized
13576 global and static data in the @samp{.sbss} section, which is adjacent to
13577 the @samp{.sdata} section. The @option{-msdata=eabi} option is
13578 incompatible with the @option{-mrelocatable} option. The
13579 @option{-msdata=eabi} option also sets the @option{-memb} option.
13582 @opindex msdata=sysv
13583 On System V.4 and embedded PowerPC systems, put small global and static
13584 data in the @samp{.sdata} section, which is pointed to by register
13585 @code{r13}. Put small uninitialized global and static data in the
13586 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
13587 The @option{-msdata=sysv} option is incompatible with the
13588 @option{-mrelocatable} option.
13590 @item -msdata=default
13592 @opindex msdata=default
13594 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
13595 compile code the same as @option{-msdata=eabi}, otherwise compile code the
13596 same as @option{-msdata=sysv}.
13599 @opindex msdata-data
13600 On System V.4 and embedded PowerPC systems, put small global
13601 data in the @samp{.sdata} section. Put small uninitialized global
13602 data in the @samp{.sbss} section. Do not use register @code{r13}
13603 to address small data however. This is the default behavior unless
13604 other @option{-msdata} options are used.
13608 @opindex msdata=none
13610 On embedded PowerPC systems, put all initialized global and static data
13611 in the @samp{.data} section, and all uninitialized data in the
13612 @samp{.bss} section.
13616 @cindex smaller data references (PowerPC)
13617 @cindex .sdata/.sdata2 references (PowerPC)
13618 On embedded PowerPC systems, put global and static items less than or
13619 equal to @var{num} bytes into the small data or bss sections instead of
13620 the normal data or bss section. By default, @var{num} is 8. The
13621 @option{-G @var{num}} switch is also passed to the linker.
13622 All modules should be compiled with the same @option{-G @var{num}} value.
13625 @itemx -mno-regnames
13627 @opindex mno-regnames
13628 On System V.4 and embedded PowerPC systems do (do not) emit register
13629 names in the assembly language output using symbolic forms.
13632 @itemx -mno-longcall
13634 @opindex mno-longcall
13635 By default assume that all calls are far away so that a longer more
13636 expensive calling sequence is required. This is required for calls
13637 further than 32 megabytes (33,554,432 bytes) from the current location.
13638 A short call will be generated if the compiler knows
13639 the call cannot be that far away. This setting can be overridden by
13640 the @code{shortcall} function attribute, or by @code{#pragma
13643 Some linkers are capable of detecting out-of-range calls and generating
13644 glue code on the fly. On these systems, long calls are unnecessary and
13645 generate slower code. As of this writing, the AIX linker can do this,
13646 as can the GNU linker for PowerPC/64. It is planned to add this feature
13647 to the GNU linker for 32-bit PowerPC systems as well.
13649 On Darwin/PPC systems, @code{#pragma longcall} will generate ``jbsr
13650 callee, L42'', plus a ``branch island'' (glue code). The two target
13651 addresses represent the callee and the ``branch island''. The
13652 Darwin/PPC linker will prefer the first address and generate a ``bl
13653 callee'' if the PPC ``bl'' instruction will reach the callee directly;
13654 otherwise, the linker will generate ``bl L42'' to call the ``branch
13655 island''. The ``branch island'' is appended to the body of the
13656 calling function; it computes the full 32-bit address of the callee
13659 On Mach-O (Darwin) systems, this option directs the compiler emit to
13660 the glue for every direct call, and the Darwin linker decides whether
13661 to use or discard it.
13663 In the future, we may cause GCC to ignore all longcall specifications
13664 when the linker is known to generate glue.
13668 Adds support for multithreading with the @dfn{pthreads} library.
13669 This option sets flags for both the preprocessor and linker.
13673 @node S/390 and zSeries Options
13674 @subsection S/390 and zSeries Options
13675 @cindex S/390 and zSeries Options
13677 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
13681 @itemx -msoft-float
13682 @opindex mhard-float
13683 @opindex msoft-float
13684 Use (do not use) the hardware floating-point instructions and registers
13685 for floating-point operations. When @option{-msoft-float} is specified,
13686 functions in @file{libgcc.a} will be used to perform floating-point
13687 operations. When @option{-mhard-float} is specified, the compiler
13688 generates IEEE floating-point instructions. This is the default.
13690 @item -mlong-double-64
13691 @itemx -mlong-double-128
13692 @opindex mlong-double-64
13693 @opindex mlong-double-128
13694 These switches control the size of @code{long double} type. A size
13695 of 64bit makes the @code{long double} type equivalent to the @code{double}
13696 type. This is the default.
13699 @itemx -mno-backchain
13700 @opindex mbackchain
13701 @opindex mno-backchain
13702 Store (do not store) the address of the caller's frame as backchain pointer
13703 into the callee's stack frame.
13704 A backchain may be needed to allow debugging using tools that do not understand
13705 DWARF-2 call frame information.
13706 When @option{-mno-packed-stack} is in effect, the backchain pointer is stored
13707 at the bottom of the stack frame; when @option{-mpacked-stack} is in effect,
13708 the backchain is placed into the topmost word of the 96/160 byte register
13711 In general, code compiled with @option{-mbackchain} is call-compatible with
13712 code compiled with @option{-mmo-backchain}; however, use of the backchain
13713 for debugging purposes usually requires that the whole binary is built with
13714 @option{-mbackchain}. Note that the combination of @option{-mbackchain},
13715 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
13716 to build a linux kernel use @option{-msoft-float}.
13718 The default is to not maintain the backchain.
13720 @item -mpacked-stack
13721 @itemx -mno-packed-stack
13722 @opindex mpacked-stack
13723 @opindex mno-packed-stack
13724 Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is
13725 specified, the compiler uses the all fields of the 96/160 byte register save
13726 area only for their default purpose; unused fields still take up stack space.
13727 When @option{-mpacked-stack} is specified, register save slots are densely
13728 packed at the top of the register save area; unused space is reused for other
13729 purposes, allowing for more efficient use of the available stack space.
13730 However, when @option{-mbackchain} is also in effect, the topmost word of
13731 the save area is always used to store the backchain, and the return address
13732 register is always saved two words below the backchain.
13734 As long as the stack frame backchain is not used, code generated with
13735 @option{-mpacked-stack} is call-compatible with code generated with
13736 @option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for
13737 S/390 or zSeries generated code that uses the stack frame backchain at run
13738 time, not just for debugging purposes. Such code is not call-compatible
13739 with code compiled with @option{-mpacked-stack}. Also, note that the
13740 combination of @option{-mbackchain},
13741 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
13742 to build a linux kernel use @option{-msoft-float}.
13744 The default is to not use the packed stack layout.
13747 @itemx -mno-small-exec
13748 @opindex msmall-exec
13749 @opindex mno-small-exec
13750 Generate (or do not generate) code using the @code{bras} instruction
13751 to do subroutine calls.
13752 This only works reliably if the total executable size does not
13753 exceed 64k. The default is to use the @code{basr} instruction instead,
13754 which does not have this limitation.
13760 When @option{-m31} is specified, generate code compliant to the
13761 GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate
13762 code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in
13763 particular to generate 64-bit instructions. For the @samp{s390}
13764 targets, the default is @option{-m31}, while the @samp{s390x}
13765 targets default to @option{-m64}.
13771 When @option{-mzarch} is specified, generate code using the
13772 instructions available on z/Architecture.
13773 When @option{-mesa} is specified, generate code using the
13774 instructions available on ESA/390. Note that @option{-mesa} is
13775 not possible with @option{-m64}.
13776 When generating code compliant to the GNU/Linux for S/390 ABI,
13777 the default is @option{-mesa}. When generating code compliant
13778 to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}.
13784 Generate (or do not generate) code using the @code{mvcle} instruction
13785 to perform block moves. When @option{-mno-mvcle} is specified,
13786 use a @code{mvc} loop instead. This is the default unless optimizing for
13793 Print (or do not print) additional debug information when compiling.
13794 The default is to not print debug information.
13796 @item -march=@var{cpu-type}
13798 Generate code that will run on @var{cpu-type}, which is the name of a system
13799 representing a certain processor type. Possible values for
13800 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, and @samp{z990}.
13801 When generating code using the instructions available on z/Architecture,
13802 the default is @option{-march=z900}. Otherwise, the default is
13803 @option{-march=g5}.
13805 @item -mtune=@var{cpu-type}
13807 Tune to @var{cpu-type} everything applicable about the generated code,
13808 except for the ABI and the set of available instructions.
13809 The list of @var{cpu-type} values is the same as for @option{-march}.
13810 The default is the value used for @option{-march}.
13813 @itemx -mno-tpf-trace
13814 @opindex mtpf-trace
13815 @opindex mno-tpf-trace
13816 Generate code that adds (does not add) in TPF OS specific branches to trace
13817 routines in the operating system. This option is off by default, even
13818 when compiling for the TPF OS@.
13821 @itemx -mno-fused-madd
13822 @opindex mfused-madd
13823 @opindex mno-fused-madd
13824 Generate code that uses (does not use) the floating point multiply and
13825 accumulate instructions. These instructions are generated by default if
13826 hardware floating point is used.
13828 @item -mwarn-framesize=@var{framesize}
13829 @opindex mwarn-framesize
13830 Emit a warning if the current function exceeds the given frame size. Because
13831 this is a compile time check it doesn't need to be a real problem when the program
13832 runs. It is intended to identify functions which most probably cause
13833 a stack overflow. It is useful to be used in an environment with limited stack
13834 size e.g.@: the linux kernel.
13836 @item -mwarn-dynamicstack
13837 @opindex mwarn-dynamicstack
13838 Emit a warning if the function calls alloca or uses dynamically
13839 sized arrays. This is generally a bad idea with a limited stack size.
13841 @item -mstack-guard=@var{stack-guard}
13842 @itemx -mstack-size=@var{stack-size}
13843 @opindex mstack-guard
13844 @opindex mstack-size
13845 If these options are provided the s390 back end emits additional instructions in
13846 the function prologue which trigger a trap if the stack size is @var{stack-guard}
13847 bytes above the @var{stack-size} (remember that the stack on s390 grows downward).
13848 If the @var{stack-guard} option is omitted the smallest power of 2 larger than
13849 the frame size of the compiled function is chosen.
13850 These options are intended to be used to help debugging stack overflow problems.
13851 The additionally emitted code causes only little overhead and hence can also be
13852 used in production like systems without greater performance degradation. The given
13853 values have to be exact powers of 2 and @var{stack-size} has to be greater than
13854 @var{stack-guard} without exceeding 64k.
13855 In order to be efficient the extra code makes the assumption that the stack starts
13856 at an address aligned to the value given by @var{stack-size}.
13857 The @var{stack-guard} option can only be used in conjunction with @var{stack-size}.
13860 @node Score Options
13861 @subsection Score Options
13862 @cindex Score Options
13864 These options are defined for Score implementations:
13869 Compile code for big endian mode. This is the default.
13873 Compile code for little endian mode.
13877 Disable generate bcnz instruction.
13881 Enable generate unaligned load and store instruction.
13885 Enable the use of multiply-accumulate instructions. Disabled by default.
13889 Specify the SCORE5 as the target architecture.
13893 Specify the SCORE5U of the target architecture.
13897 Specify the SCORE7 as the target architecture. This is the default.
13901 Specify the SCORE7D as the target architecture.
13905 @subsection SH Options
13907 These @samp{-m} options are defined for the SH implementations:
13912 Generate code for the SH1.
13916 Generate code for the SH2.
13919 Generate code for the SH2e.
13923 Generate code for the SH3.
13927 Generate code for the SH3e.
13931 Generate code for the SH4 without a floating-point unit.
13933 @item -m4-single-only
13934 @opindex m4-single-only
13935 Generate code for the SH4 with a floating-point unit that only
13936 supports single-precision arithmetic.
13940 Generate code for the SH4 assuming the floating-point unit is in
13941 single-precision mode by default.
13945 Generate code for the SH4.
13949 Generate code for the SH4al-dsp, or for a SH4a in such a way that the
13950 floating-point unit is not used.
13952 @item -m4a-single-only
13953 @opindex m4a-single-only
13954 Generate code for the SH4a, in such a way that no double-precision
13955 floating point operations are used.
13958 @opindex m4a-single
13959 Generate code for the SH4a assuming the floating-point unit is in
13960 single-precision mode by default.
13964 Generate code for the SH4a.
13968 Same as @option{-m4a-nofpu}, except that it implicitly passes
13969 @option{-dsp} to the assembler. GCC doesn't generate any DSP
13970 instructions at the moment.
13974 Compile code for the processor in big endian mode.
13978 Compile code for the processor in little endian mode.
13982 Align doubles at 64-bit boundaries. Note that this changes the calling
13983 conventions, and thus some functions from the standard C library will
13984 not work unless you recompile it first with @option{-mdalign}.
13988 Shorten some address references at link time, when possible; uses the
13989 linker option @option{-relax}.
13993 Use 32-bit offsets in @code{switch} tables. The default is to use
13998 Enable the use of bit manipulation instructions on SH2A.
14002 Enable the use of the instruction @code{fmovd}.
14006 Comply with the calling conventions defined by Renesas.
14010 Comply with the calling conventions defined by Renesas.
14014 Comply with the calling conventions defined for GCC before the Renesas
14015 conventions were available. This option is the default for all
14016 targets of the SH toolchain except for @samp{sh-symbianelf}.
14019 @opindex mnomacsave
14020 Mark the @code{MAC} register as call-clobbered, even if
14021 @option{-mhitachi} is given.
14025 Increase IEEE-compliance of floating-point code.
14026 At the moment, this is equivalent to @option{-fno-finite-math-only}.
14027 When generating 16 bit SH opcodes, getting IEEE-conforming results for
14028 comparisons of NANs / infinities incurs extra overhead in every
14029 floating point comparison, therefore the default is set to
14030 @option{-ffinite-math-only}.
14032 @item -minline-ic_invalidate
14033 @opindex minline-ic_invalidate
14034 Inline code to invalidate instruction cache entries after setting up
14035 nested function trampolines.
14036 This option has no effect if -musermode is in effect and the selected
14037 code generation option (e.g. -m4) does not allow the use of the icbi
14039 If the selected code generation option does not allow the use of the icbi
14040 instruction, and -musermode is not in effect, the inlined code will
14041 manipulate the instruction cache address array directly with an associative
14042 write. This not only requires privileged mode, but it will also
14043 fail if the cache line had been mapped via the TLB and has become unmapped.
14047 Dump instruction size and location in the assembly code.
14050 @opindex mpadstruct
14051 This option is deprecated. It pads structures to multiple of 4 bytes,
14052 which is incompatible with the SH ABI@.
14056 Optimize for space instead of speed. Implied by @option{-Os}.
14059 @opindex mprefergot
14060 When generating position-independent code, emit function calls using
14061 the Global Offset Table instead of the Procedure Linkage Table.
14065 Don't generate privileged mode only code; implies -mno-inline-ic_invalidate
14066 if the inlined code would not work in user mode.
14067 This is the default when the target is @code{sh-*-linux*}.
14069 @item -multcost=@var{number}
14070 @opindex multcost=@var{number}
14071 Set the cost to assume for a multiply insn.
14073 @item -mdiv=@var{strategy}
14074 @opindex mdiv=@var{strategy}
14075 Set the division strategy to use for SHmedia code. @var{strategy} must be
14076 one of: call, call2, fp, inv, inv:minlat, inv20u, inv20l, inv:call,
14077 inv:call2, inv:fp .
14078 "fp" performs the operation in floating point. This has a very high latency,
14079 but needs only a few instructions, so it might be a good choice if
14080 your code has enough easily exploitable ILP to allow the compiler to
14081 schedule the floating point instructions together with other instructions.
14082 Division by zero causes a floating point exception.
14083 "inv" uses integer operations to calculate the inverse of the divisor,
14084 and then multiplies the dividend with the inverse. This strategy allows
14085 cse and hoisting of the inverse calculation. Division by zero calculates
14086 an unspecified result, but does not trap.
14087 "inv:minlat" is a variant of "inv" where if no cse / hoisting opportunities
14088 have been found, or if the entire operation has been hoisted to the same
14089 place, the last stages of the inverse calculation are intertwined with the
14090 final multiply to reduce the overall latency, at the expense of using a few
14091 more instructions, and thus offering fewer scheduling opportunities with
14093 "call" calls a library function that usually implements the inv:minlat
14095 This gives high code density for m5-*media-nofpu compilations.
14096 "call2" uses a different entry point of the same library function, where it
14097 assumes that a pointer to a lookup table has already been set up, which
14098 exposes the pointer load to cse / code hoisting optimizations.
14099 "inv:call", "inv:call2" and "inv:fp" all use the "inv" algorithm for initial
14100 code generation, but if the code stays unoptimized, revert to the "call",
14101 "call2", or "fp" strategies, respectively. Note that the
14102 potentially-trapping side effect of division by zero is carried by a
14103 separate instruction, so it is possible that all the integer instructions
14104 are hoisted out, but the marker for the side effect stays where it is.
14105 A recombination to fp operations or a call is not possible in that case.
14106 "inv20u" and "inv20l" are variants of the "inv:minlat" strategy. In the case
14107 that the inverse calculation was nor separated from the multiply, they speed
14108 up division where the dividend fits into 20 bits (plus sign where applicable),
14109 by inserting a test to skip a number of operations in this case; this test
14110 slows down the case of larger dividends. inv20u assumes the case of a such
14111 a small dividend to be unlikely, and inv20l assumes it to be likely.
14113 @item -mdivsi3_libfunc=@var{name}
14114 @opindex mdivsi3_libfunc=@var{name}
14115 Set the name of the library function used for 32 bit signed division to
14116 @var{name}. This only affect the name used in the call and inv:call
14117 division strategies, and the compiler will still expect the same
14118 sets of input/output/clobbered registers as if this option was not present.
14120 @item -mfixed-range=@var{register-range}
14121 @opindex mfixed-range
14122 Generate code treating the given register range as fixed registers.
14123 A fixed register is one that the register allocator can not use. This is
14124 useful when compiling kernel code. A register range is specified as
14125 two registers separated by a dash. Multiple register ranges can be
14126 specified separated by a comma.
14128 @item -madjust-unroll
14129 @opindex madjust-unroll
14130 Throttle unrolling to avoid thrashing target registers.
14131 This option only has an effect if the gcc code base supports the
14132 TARGET_ADJUST_UNROLL_MAX target hook.
14134 @item -mindexed-addressing
14135 @opindex mindexed-addressing
14136 Enable the use of the indexed addressing mode for SHmedia32/SHcompact.
14137 This is only safe if the hardware and/or OS implement 32 bit wrap-around
14138 semantics for the indexed addressing mode. The architecture allows the
14139 implementation of processors with 64 bit MMU, which the OS could use to
14140 get 32 bit addressing, but since no current hardware implementation supports
14141 this or any other way to make the indexed addressing mode safe to use in
14142 the 32 bit ABI, the default is -mno-indexed-addressing.
14144 @item -mgettrcost=@var{number}
14145 @opindex mgettrcost=@var{number}
14146 Set the cost assumed for the gettr instruction to @var{number}.
14147 The default is 2 if @option{-mpt-fixed} is in effect, 100 otherwise.
14151 Assume pt* instructions won't trap. This will generally generate better
14152 scheduled code, but is unsafe on current hardware. The current architecture
14153 definition says that ptabs and ptrel trap when the target anded with 3 is 3.
14154 This has the unintentional effect of making it unsafe to schedule ptabs /
14155 ptrel before a branch, or hoist it out of a loop. For example,
14156 __do_global_ctors, a part of libgcc that runs constructors at program
14157 startup, calls functions in a list which is delimited by @minus{}1. With the
14158 -mpt-fixed option, the ptabs will be done before testing against @minus{}1.
14159 That means that all the constructors will be run a bit quicker, but when
14160 the loop comes to the end of the list, the program crashes because ptabs
14161 loads @minus{}1 into a target register. Since this option is unsafe for any
14162 hardware implementing the current architecture specification, the default
14163 is -mno-pt-fixed. Unless the user specifies a specific cost with
14164 @option{-mgettrcost}, -mno-pt-fixed also implies @option{-mgettrcost=100};
14165 this deters register allocation using target registers for storing
14168 @item -minvalid-symbols
14169 @opindex minvalid-symbols
14170 Assume symbols might be invalid. Ordinary function symbols generated by
14171 the compiler will always be valid to load with movi/shori/ptabs or
14172 movi/shori/ptrel, but with assembler and/or linker tricks it is possible
14173 to generate symbols that will cause ptabs / ptrel to trap.
14174 This option is only meaningful when @option{-mno-pt-fixed} is in effect.
14175 It will then prevent cross-basic-block cse, hoisting and most scheduling
14176 of symbol loads. The default is @option{-mno-invalid-symbols}.
14179 @node SPARC Options
14180 @subsection SPARC Options
14181 @cindex SPARC options
14183 These @samp{-m} options are supported on the SPARC:
14186 @item -mno-app-regs
14188 @opindex mno-app-regs
14190 Specify @option{-mapp-regs} to generate output using the global registers
14191 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
14194 To be fully SVR4 ABI compliant at the cost of some performance loss,
14195 specify @option{-mno-app-regs}. You should compile libraries and system
14196 software with this option.
14199 @itemx -mhard-float
14201 @opindex mhard-float
14202 Generate output containing floating point instructions. This is the
14206 @itemx -msoft-float
14208 @opindex msoft-float
14209 Generate output containing library calls for floating point.
14210 @strong{Warning:} the requisite libraries are not available for all SPARC
14211 targets. Normally the facilities of the machine's usual C compiler are
14212 used, but this cannot be done directly in cross-compilation. You must make
14213 your own arrangements to provide suitable library functions for
14214 cross-compilation. The embedded targets @samp{sparc-*-aout} and
14215 @samp{sparclite-*-*} do provide software floating point support.
14217 @option{-msoft-float} changes the calling convention in the output file;
14218 therefore, it is only useful if you compile @emph{all} of a program with
14219 this option. In particular, you need to compile @file{libgcc.a}, the
14220 library that comes with GCC, with @option{-msoft-float} in order for
14223 @item -mhard-quad-float
14224 @opindex mhard-quad-float
14225 Generate output containing quad-word (long double) floating point
14228 @item -msoft-quad-float
14229 @opindex msoft-quad-float
14230 Generate output containing library calls for quad-word (long double)
14231 floating point instructions. The functions called are those specified
14232 in the SPARC ABI@. This is the default.
14234 As of this writing, there are no SPARC implementations that have hardware
14235 support for the quad-word floating point instructions. They all invoke
14236 a trap handler for one of these instructions, and then the trap handler
14237 emulates the effect of the instruction. Because of the trap handler overhead,
14238 this is much slower than calling the ABI library routines. Thus the
14239 @option{-msoft-quad-float} option is the default.
14241 @item -mno-unaligned-doubles
14242 @itemx -munaligned-doubles
14243 @opindex mno-unaligned-doubles
14244 @opindex munaligned-doubles
14245 Assume that doubles have 8 byte alignment. This is the default.
14247 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
14248 alignment only if they are contained in another type, or if they have an
14249 absolute address. Otherwise, it assumes they have 4 byte alignment.
14250 Specifying this option avoids some rare compatibility problems with code
14251 generated by other compilers. It is not the default because it results
14252 in a performance loss, especially for floating point code.
14254 @item -mno-faster-structs
14255 @itemx -mfaster-structs
14256 @opindex mno-faster-structs
14257 @opindex mfaster-structs
14258 With @option{-mfaster-structs}, the compiler assumes that structures
14259 should have 8 byte alignment. This enables the use of pairs of
14260 @code{ldd} and @code{std} instructions for copies in structure
14261 assignment, in place of twice as many @code{ld} and @code{st} pairs.
14262 However, the use of this changed alignment directly violates the SPARC
14263 ABI@. Thus, it's intended only for use on targets where the developer
14264 acknowledges that their resulting code will not be directly in line with
14265 the rules of the ABI@.
14267 @item -mimpure-text
14268 @opindex mimpure-text
14269 @option{-mimpure-text}, used in addition to @option{-shared}, tells
14270 the compiler to not pass @option{-z text} to the linker when linking a
14271 shared object. Using this option, you can link position-dependent
14272 code into a shared object.
14274 @option{-mimpure-text} suppresses the ``relocations remain against
14275 allocatable but non-writable sections'' linker error message.
14276 However, the necessary relocations will trigger copy-on-write, and the
14277 shared object is not actually shared across processes. Instead of
14278 using @option{-mimpure-text}, you should compile all source code with
14279 @option{-fpic} or @option{-fPIC}.
14281 This option is only available on SunOS and Solaris.
14283 @item -mcpu=@var{cpu_type}
14285 Set the instruction set, register set, and instruction scheduling parameters
14286 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
14287 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
14288 @samp{f930}, @samp{f934}, @samp{hypersparc}, @samp{sparclite86x},
14289 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc},
14290 @samp{ultrasparc3}, @samp{niagara} and @samp{niagara2}.
14292 Default instruction scheduling parameters are used for values that select
14293 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
14294 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
14296 Here is a list of each supported architecture and their supported
14301 v8: supersparc, hypersparc
14302 sparclite: f930, f934, sparclite86x
14304 v9: ultrasparc, ultrasparc3, niagara, niagara2
14307 By default (unless configured otherwise), GCC generates code for the V7
14308 variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler
14309 additionally optimizes it for the Cypress CY7C602 chip, as used in the
14310 SPARCStation/SPARCServer 3xx series. This is also appropriate for the older
14311 SPARCStation 1, 2, IPX etc.
14313 With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC
14314 architecture. The only difference from V7 code is that the compiler emits
14315 the integer multiply and integer divide instructions which exist in SPARC-V8
14316 but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally
14317 optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and
14320 With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of
14321 the SPARC architecture. This adds the integer multiply, integer divide step
14322 and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7.
14323 With @option{-mcpu=f930}, the compiler additionally optimizes it for the
14324 Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With
14325 @option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu
14326 MB86934 chip, which is the more recent SPARClite with FPU@.
14328 With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of
14329 the SPARC architecture. This adds the integer multiply, multiply/accumulate,
14330 integer divide step and scan (@code{ffs}) instructions which exist in SPARClet
14331 but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally
14332 optimizes it for the TEMIC SPARClet chip.
14334 With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC
14335 architecture. This adds 64-bit integer and floating-point move instructions,
14336 3 additional floating-point condition code registers and conditional move
14337 instructions. With @option{-mcpu=ultrasparc}, the compiler additionally
14338 optimizes it for the Sun UltraSPARC I/II/IIi chips. With
14339 @option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the
14340 Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With
14341 @option{-mcpu=niagara}, the compiler additionally optimizes it for
14342 Sun UltraSPARC T1 chips. With @option{-mcpu=niagara2}, the compiler
14343 additionally optimizes it for Sun UltraSPARC T2 chips.
14345 @item -mtune=@var{cpu_type}
14347 Set the instruction scheduling parameters for machine type
14348 @var{cpu_type}, but do not set the instruction set or register set that the
14349 option @option{-mcpu=@var{cpu_type}} would.
14351 The same values for @option{-mcpu=@var{cpu_type}} can be used for
14352 @option{-mtune=@var{cpu_type}}, but the only useful values are those
14353 that select a particular cpu implementation. Those are @samp{cypress},
14354 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
14355 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc},
14356 @samp{ultrasparc3}, @samp{niagara}, and @samp{niagara2}.
14361 @opindex mno-v8plus
14362 With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The
14363 difference from the V8 ABI is that the global and out registers are
14364 considered 64-bit wide. This is enabled by default on Solaris in 32-bit
14365 mode for all SPARC-V9 processors.
14371 With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC
14372 Visual Instruction Set extensions. The default is @option{-mno-vis}.
14375 These @samp{-m} options are supported in addition to the above
14376 on SPARC-V9 processors in 64-bit environments:
14379 @item -mlittle-endian
14380 @opindex mlittle-endian
14381 Generate code for a processor running in little-endian mode. It is only
14382 available for a few configurations and most notably not on Solaris and Linux.
14388 Generate code for a 32-bit or 64-bit environment.
14389 The 32-bit environment sets int, long and pointer to 32 bits.
14390 The 64-bit environment sets int to 32 bits and long and pointer
14393 @item -mcmodel=medlow
14394 @opindex mcmodel=medlow
14395 Generate code for the Medium/Low code model: 64-bit addresses, programs
14396 must be linked in the low 32 bits of memory. Programs can be statically
14397 or dynamically linked.
14399 @item -mcmodel=medmid
14400 @opindex mcmodel=medmid
14401 Generate code for the Medium/Middle code model: 64-bit addresses, programs
14402 must be linked in the low 44 bits of memory, the text and data segments must
14403 be less than 2GB in size and the data segment must be located within 2GB of
14406 @item -mcmodel=medany
14407 @opindex mcmodel=medany
14408 Generate code for the Medium/Anywhere code model: 64-bit addresses, programs
14409 may be linked anywhere in memory, the text and data segments must be less
14410 than 2GB in size and the data segment must be located within 2GB of the
14413 @item -mcmodel=embmedany
14414 @opindex mcmodel=embmedany
14415 Generate code for the Medium/Anywhere code model for embedded systems:
14416 64-bit addresses, the text and data segments must be less than 2GB in
14417 size, both starting anywhere in memory (determined at link time). The
14418 global register %g4 points to the base of the data segment. Programs
14419 are statically linked and PIC is not supported.
14422 @itemx -mno-stack-bias
14423 @opindex mstack-bias
14424 @opindex mno-stack-bias
14425 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
14426 frame pointer if present, are offset by @minus{}2047 which must be added back
14427 when making stack frame references. This is the default in 64-bit mode.
14428 Otherwise, assume no such offset is present.
14431 These switches are supported in addition to the above on Solaris:
14436 Add support for multithreading using the Solaris threads library. This
14437 option sets flags for both the preprocessor and linker. This option does
14438 not affect the thread safety of object code produced by the compiler or
14439 that of libraries supplied with it.
14443 Add support for multithreading using the POSIX threads library. This
14444 option sets flags for both the preprocessor and linker. This option does
14445 not affect the thread safety of object code produced by the compiler or
14446 that of libraries supplied with it.
14450 This is a synonym for @option{-pthreads}.
14454 @subsection SPU Options
14455 @cindex SPU options
14457 These @samp{-m} options are supported on the SPU:
14461 @itemx -merror-reloc
14462 @opindex mwarn-reloc
14463 @opindex merror-reloc
14465 The loader for SPU does not handle dynamic relocations. By default, GCC
14466 will give an error when it generates code that requires a dynamic
14467 relocation. @option{-mno-error-reloc} disables the error,
14468 @option{-mwarn-reloc} will generate a warning instead.
14471 @itemx -munsafe-dma
14473 @opindex munsafe-dma
14475 Instructions which initiate or test completion of DMA must not be
14476 reordered with respect to loads and stores of the memory which is being
14477 accessed. Users typically address this problem using the volatile
14478 keyword, but that can lead to inefficient code in places where the
14479 memory is known to not change. Rather than mark the memory as volatile
14480 we treat the DMA instructions as potentially effecting all memory. With
14481 @option{-munsafe-dma} users must use the volatile keyword to protect
14484 @item -mbranch-hints
14485 @opindex mbranch-hints
14487 By default, GCC will generate a branch hint instruction to avoid
14488 pipeline stalls for always taken or probably taken branches. A hint
14489 will not be generated closer than 8 instructions away from its branch.
14490 There is little reason to disable them, except for debugging purposes,
14491 or to make an object a little bit smaller.
14495 @opindex msmall-mem
14496 @opindex mlarge-mem
14498 By default, GCC generates code assuming that addresses are never larger
14499 than 18 bits. With @option{-mlarge-mem} code is generated that assumes
14500 a full 32 bit address.
14505 By default, GCC links against startup code that assumes the SPU-style
14506 main function interface (which has an unconventional parameter list).
14507 With @option{-mstdmain}, GCC will link your program against startup
14508 code that assumes a C99-style interface to @code{main}, including a
14509 local copy of @code{argv} strings.
14511 @item -mfixed-range=@var{register-range}
14512 @opindex mfixed-range
14513 Generate code treating the given register range as fixed registers.
14514 A fixed register is one that the register allocator can not use. This is
14515 useful when compiling kernel code. A register range is specified as
14516 two registers separated by a dash. Multiple register ranges can be
14517 specified separated by a comma.
14521 @node System V Options
14522 @subsection Options for System V
14524 These additional options are available on System V Release 4 for
14525 compatibility with other compilers on those systems:
14530 Create a shared object.
14531 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
14535 Identify the versions of each tool used by the compiler, in a
14536 @code{.ident} assembler directive in the output.
14540 Refrain from adding @code{.ident} directives to the output file (this is
14543 @item -YP,@var{dirs}
14545 Search the directories @var{dirs}, and no others, for libraries
14546 specified with @option{-l}.
14548 @item -Ym,@var{dir}
14550 Look in the directory @var{dir} to find the M4 preprocessor.
14551 The assembler uses this option.
14552 @c This is supposed to go with a -Yd for predefined M4 macro files, but
14553 @c the generic assembler that comes with Solaris takes just -Ym.
14557 @subsection V850 Options
14558 @cindex V850 Options
14560 These @samp{-m} options are defined for V850 implementations:
14564 @itemx -mno-long-calls
14565 @opindex mlong-calls
14566 @opindex mno-long-calls
14567 Treat all calls as being far away (near). If calls are assumed to be
14568 far away, the compiler will always load the functions address up into a
14569 register, and call indirect through the pointer.
14575 Do not optimize (do optimize) basic blocks that use the same index
14576 pointer 4 or more times to copy pointer into the @code{ep} register, and
14577 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
14578 option is on by default if you optimize.
14580 @item -mno-prolog-function
14581 @itemx -mprolog-function
14582 @opindex mno-prolog-function
14583 @opindex mprolog-function
14584 Do not use (do use) external functions to save and restore registers
14585 at the prologue and epilogue of a function. The external functions
14586 are slower, but use less code space if more than one function saves
14587 the same number of registers. The @option{-mprolog-function} option
14588 is on by default if you optimize.
14592 Try to make the code as small as possible. At present, this just turns
14593 on the @option{-mep} and @option{-mprolog-function} options.
14595 @item -mtda=@var{n}
14597 Put static or global variables whose size is @var{n} bytes or less into
14598 the tiny data area that register @code{ep} points to. The tiny data
14599 area can hold up to 256 bytes in total (128 bytes for byte references).
14601 @item -msda=@var{n}
14603 Put static or global variables whose size is @var{n} bytes or less into
14604 the small data area that register @code{gp} points to. The small data
14605 area can hold up to 64 kilobytes.
14607 @item -mzda=@var{n}
14609 Put static or global variables whose size is @var{n} bytes or less into
14610 the first 32 kilobytes of memory.
14614 Specify that the target processor is the V850.
14617 @opindex mbig-switch
14618 Generate code suitable for big switch tables. Use this option only if
14619 the assembler/linker complain about out of range branches within a switch
14624 This option will cause r2 and r5 to be used in the code generated by
14625 the compiler. This setting is the default.
14627 @item -mno-app-regs
14628 @opindex mno-app-regs
14629 This option will cause r2 and r5 to be treated as fixed registers.
14633 Specify that the target processor is the V850E1. The preprocessor
14634 constants @samp{__v850e1__} and @samp{__v850e__} will be defined if
14635 this option is used.
14639 Specify that the target processor is the V850E@. The preprocessor
14640 constant @samp{__v850e__} will be defined if this option is used.
14642 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
14643 are defined then a default target processor will be chosen and the
14644 relevant @samp{__v850*__} preprocessor constant will be defined.
14646 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
14647 defined, regardless of which processor variant is the target.
14649 @item -mdisable-callt
14650 @opindex mdisable-callt
14651 This option will suppress generation of the CALLT instruction for the
14652 v850e and v850e1 flavors of the v850 architecture. The default is
14653 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
14658 @subsection VAX Options
14659 @cindex VAX options
14661 These @samp{-m} options are defined for the VAX:
14666 Do not output certain jump instructions (@code{aobleq} and so on)
14667 that the Unix assembler for the VAX cannot handle across long
14672 Do output those jump instructions, on the assumption that you
14673 will assemble with the GNU assembler.
14677 Output code for g-format floating point numbers instead of d-format.
14680 @node VxWorks Options
14681 @subsection VxWorks Options
14682 @cindex VxWorks Options
14684 The options in this section are defined for all VxWorks targets.
14685 Options specific to the target hardware are listed with the other
14686 options for that target.
14691 GCC can generate code for both VxWorks kernels and real time processes
14692 (RTPs). This option switches from the former to the latter. It also
14693 defines the preprocessor macro @code{__RTP__}.
14696 @opindex non-static
14697 Link an RTP executable against shared libraries rather than static
14698 libraries. The options @option{-static} and @option{-shared} can
14699 also be used for RTPs (@pxref{Link Options}); @option{-static}
14706 These options are passed down to the linker. They are defined for
14707 compatibility with Diab.
14710 @opindex Xbind-lazy
14711 Enable lazy binding of function calls. This option is equivalent to
14712 @option{-Wl,-z,now} and is defined for compatibility with Diab.
14716 Disable lazy binding of function calls. This option is the default and
14717 is defined for compatibility with Diab.
14720 @node x86-64 Options
14721 @subsection x86-64 Options
14722 @cindex x86-64 options
14724 These are listed under @xref{i386 and x86-64 Options}.
14726 @node Xstormy16 Options
14727 @subsection Xstormy16 Options
14728 @cindex Xstormy16 Options
14730 These options are defined for Xstormy16:
14735 Choose startup files and linker script suitable for the simulator.
14738 @node Xtensa Options
14739 @subsection Xtensa Options
14740 @cindex Xtensa Options
14742 These options are supported for Xtensa targets:
14746 @itemx -mno-const16
14748 @opindex mno-const16
14749 Enable or disable use of @code{CONST16} instructions for loading
14750 constant values. The @code{CONST16} instruction is currently not a
14751 standard option from Tensilica. When enabled, @code{CONST16}
14752 instructions are always used in place of the standard @code{L32R}
14753 instructions. The use of @code{CONST16} is enabled by default only if
14754 the @code{L32R} instruction is not available.
14757 @itemx -mno-fused-madd
14758 @opindex mfused-madd
14759 @opindex mno-fused-madd
14760 Enable or disable use of fused multiply/add and multiply/subtract
14761 instructions in the floating-point option. This has no effect if the
14762 floating-point option is not also enabled. Disabling fused multiply/add
14763 and multiply/subtract instructions forces the compiler to use separate
14764 instructions for the multiply and add/subtract operations. This may be
14765 desirable in some cases where strict IEEE 754-compliant results are
14766 required: the fused multiply add/subtract instructions do not round the
14767 intermediate result, thereby producing results with @emph{more} bits of
14768 precision than specified by the IEEE standard. Disabling fused multiply
14769 add/subtract instructions also ensures that the program output is not
14770 sensitive to the compiler's ability to combine multiply and add/subtract
14773 @item -mserialize-volatile
14774 @itemx -mno-serialize-volatile
14775 @opindex mserialize-volatile
14776 @opindex mno-serialize-volatile
14777 When this option is enabled, GCC inserts @code{MEMW} instructions before
14778 @code{volatile} memory references to guarantee sequential consistency.
14779 The default is @option{-mserialize-volatile}. Use
14780 @option{-mno-serialize-volatile} to omit the @code{MEMW} instructions.
14782 @item -mtext-section-literals
14783 @itemx -mno-text-section-literals
14784 @opindex mtext-section-literals
14785 @opindex mno-text-section-literals
14786 Control the treatment of literal pools. The default is
14787 @option{-mno-text-section-literals}, which places literals in a separate
14788 section in the output file. This allows the literal pool to be placed
14789 in a data RAM/ROM, and it also allows the linker to combine literal
14790 pools from separate object files to remove redundant literals and
14791 improve code size. With @option{-mtext-section-literals}, the literals
14792 are interspersed in the text section in order to keep them as close as
14793 possible to their references. This may be necessary for large assembly
14796 @item -mtarget-align
14797 @itemx -mno-target-align
14798 @opindex mtarget-align
14799 @opindex mno-target-align
14800 When this option is enabled, GCC instructs the assembler to
14801 automatically align instructions to reduce branch penalties at the
14802 expense of some code density. The assembler attempts to widen density
14803 instructions to align branch targets and the instructions following call
14804 instructions. If there are not enough preceding safe density
14805 instructions to align a target, no widening will be performed. The
14806 default is @option{-mtarget-align}. These options do not affect the
14807 treatment of auto-aligned instructions like @code{LOOP}, which the
14808 assembler will always align, either by widening density instructions or
14809 by inserting no-op instructions.
14812 @itemx -mno-longcalls
14813 @opindex mlongcalls
14814 @opindex mno-longcalls
14815 When this option is enabled, GCC instructs the assembler to translate
14816 direct calls to indirect calls unless it can determine that the target
14817 of a direct call is in the range allowed by the call instruction. This
14818 translation typically occurs for calls to functions in other source
14819 files. Specifically, the assembler translates a direct @code{CALL}
14820 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
14821 The default is @option{-mno-longcalls}. This option should be used in
14822 programs where the call target can potentially be out of range. This
14823 option is implemented in the assembler, not the compiler, so the
14824 assembly code generated by GCC will still show direct call
14825 instructions---look at the disassembled object code to see the actual
14826 instructions. Note that the assembler will use an indirect call for
14827 every cross-file call, not just those that really will be out of range.
14830 @node zSeries Options
14831 @subsection zSeries Options
14832 @cindex zSeries options
14834 These are listed under @xref{S/390 and zSeries Options}.
14836 @node Code Gen Options
14837 @section Options for Code Generation Conventions
14838 @cindex code generation conventions
14839 @cindex options, code generation
14840 @cindex run-time options
14842 These machine-independent options control the interface conventions
14843 used in code generation.
14845 Most of them have both positive and negative forms; the negative form
14846 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
14847 one of the forms is listed---the one which is not the default. You
14848 can figure out the other form by either removing @samp{no-} or adding
14852 @item -fbounds-check
14853 @opindex fbounds-check
14854 For front-ends that support it, generate additional code to check that
14855 indices used to access arrays are within the declared range. This is
14856 currently only supported by the Java and Fortran front-ends, where
14857 this option defaults to true and false respectively.
14861 This option generates traps for signed overflow on addition, subtraction,
14862 multiplication operations.
14866 This option instructs the compiler to assume that signed arithmetic
14867 overflow of addition, subtraction and multiplication wraps around
14868 using twos-complement representation. This flag enables some optimizations
14869 and disables others. This option is enabled by default for the Java
14870 front-end, as required by the Java language specification.
14873 @opindex fexceptions
14874 Enable exception handling. Generates extra code needed to propagate
14875 exceptions. For some targets, this implies GCC will generate frame
14876 unwind information for all functions, which can produce significant data
14877 size overhead, although it does not affect execution. If you do not
14878 specify this option, GCC will enable it by default for languages like
14879 C++ which normally require exception handling, and disable it for
14880 languages like C that do not normally require it. However, you may need
14881 to enable this option when compiling C code that needs to interoperate
14882 properly with exception handlers written in C++. You may also wish to
14883 disable this option if you are compiling older C++ programs that don't
14884 use exception handling.
14886 @item -fnon-call-exceptions
14887 @opindex fnon-call-exceptions
14888 Generate code that allows trapping instructions to throw exceptions.
14889 Note that this requires platform-specific runtime support that does
14890 not exist everywhere. Moreover, it only allows @emph{trapping}
14891 instructions to throw exceptions, i.e.@: memory references or floating
14892 point instructions. It does not allow exceptions to be thrown from
14893 arbitrary signal handlers such as @code{SIGALRM}.
14895 @item -funwind-tables
14896 @opindex funwind-tables
14897 Similar to @option{-fexceptions}, except that it will just generate any needed
14898 static data, but will not affect the generated code in any other way.
14899 You will normally not enable this option; instead, a language processor
14900 that needs this handling would enable it on your behalf.
14902 @item -fasynchronous-unwind-tables
14903 @opindex fasynchronous-unwind-tables
14904 Generate unwind table in dwarf2 format, if supported by target machine. The
14905 table is exact at each instruction boundary, so it can be used for stack
14906 unwinding from asynchronous events (such as debugger or garbage collector).
14908 @item -fpcc-struct-return
14909 @opindex fpcc-struct-return
14910 Return ``short'' @code{struct} and @code{union} values in memory like
14911 longer ones, rather than in registers. This convention is less
14912 efficient, but it has the advantage of allowing intercallability between
14913 GCC-compiled files and files compiled with other compilers, particularly
14914 the Portable C Compiler (pcc).
14916 The precise convention for returning structures in memory depends
14917 on the target configuration macros.
14919 Short structures and unions are those whose size and alignment match
14920 that of some integer type.
14922 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
14923 switch is not binary compatible with code compiled with the
14924 @option{-freg-struct-return} switch.
14925 Use it to conform to a non-default application binary interface.
14927 @item -freg-struct-return
14928 @opindex freg-struct-return
14929 Return @code{struct} and @code{union} values in registers when possible.
14930 This is more efficient for small structures than
14931 @option{-fpcc-struct-return}.
14933 If you specify neither @option{-fpcc-struct-return} nor
14934 @option{-freg-struct-return}, GCC defaults to whichever convention is
14935 standard for the target. If there is no standard convention, GCC
14936 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
14937 the principal compiler. In those cases, we can choose the standard, and
14938 we chose the more efficient register return alternative.
14940 @strong{Warning:} code compiled with the @option{-freg-struct-return}
14941 switch is not binary compatible with code compiled with the
14942 @option{-fpcc-struct-return} switch.
14943 Use it to conform to a non-default application binary interface.
14945 @item -fshort-enums
14946 @opindex fshort-enums
14947 Allocate to an @code{enum} type only as many bytes as it needs for the
14948 declared range of possible values. Specifically, the @code{enum} type
14949 will be equivalent to the smallest integer type which has enough room.
14951 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
14952 code that is not binary compatible with code generated without that switch.
14953 Use it to conform to a non-default application binary interface.
14955 @item -fshort-double
14956 @opindex fshort-double
14957 Use the same size for @code{double} as for @code{float}.
14959 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
14960 code that is not binary compatible with code generated without that switch.
14961 Use it to conform to a non-default application binary interface.
14963 @item -fshort-wchar
14964 @opindex fshort-wchar
14965 Override the underlying type for @samp{wchar_t} to be @samp{short
14966 unsigned int} instead of the default for the target. This option is
14967 useful for building programs to run under WINE@.
14969 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
14970 code that is not binary compatible with code generated without that switch.
14971 Use it to conform to a non-default application binary interface.
14974 @opindex fno-common
14975 In C, allocate even uninitialized global variables in the data section of the
14976 object file, rather than generating them as common blocks. This has the
14977 effect that if the same variable is declared (without @code{extern}) in
14978 two different compilations, you will get an error when you link them.
14979 The only reason this might be useful is if you wish to verify that the
14980 program will work on other systems which always work this way.
14984 Ignore the @samp{#ident} directive.
14986 @item -finhibit-size-directive
14987 @opindex finhibit-size-directive
14988 Don't output a @code{.size} assembler directive, or anything else that
14989 would cause trouble if the function is split in the middle, and the
14990 two halves are placed at locations far apart in memory. This option is
14991 used when compiling @file{crtstuff.c}; you should not need to use it
14994 @item -fverbose-asm
14995 @opindex fverbose-asm
14996 Put extra commentary information in the generated assembly code to
14997 make it more readable. This option is generally only of use to those
14998 who actually need to read the generated assembly code (perhaps while
14999 debugging the compiler itself).
15001 @option{-fno-verbose-asm}, the default, causes the
15002 extra information to be omitted and is useful when comparing two assembler
15005 @item -frecord-gcc-switches
15006 @opindex frecord-gcc-switches
15007 This switch causes the command line that was used to invoke the
15008 compiler to be recorded into the object file that is being created.
15009 This switch is only implemented on some targets and the exact format
15010 of the recording is target and binary file format dependent, but it
15011 usually takes the form of a section containing ASCII text. This
15012 switch is related to the @option{-fverbose-asm} switch, but that
15013 switch only records information in the assembler output file as
15014 comments, so it never reaches the object file.
15018 @cindex global offset table
15020 Generate position-independent code (PIC) suitable for use in a shared
15021 library, if supported for the target machine. Such code accesses all
15022 constant addresses through a global offset table (GOT)@. The dynamic
15023 loader resolves the GOT entries when the program starts (the dynamic
15024 loader is not part of GCC; it is part of the operating system). If
15025 the GOT size for the linked executable exceeds a machine-specific
15026 maximum size, you get an error message from the linker indicating that
15027 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
15028 instead. (These maximums are 8k on the SPARC and 32k
15029 on the m68k and RS/6000. The 386 has no such limit.)
15031 Position-independent code requires special support, and therefore works
15032 only on certain machines. For the 386, GCC supports PIC for System V
15033 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
15034 position-independent.
15036 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
15041 If supported for the target machine, emit position-independent code,
15042 suitable for dynamic linking and avoiding any limit on the size of the
15043 global offset table. This option makes a difference on the m68k,
15044 PowerPC and SPARC@.
15046 Position-independent code requires special support, and therefore works
15047 only on certain machines.
15049 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
15056 These options are similar to @option{-fpic} and @option{-fPIC}, but
15057 generated position independent code can be only linked into executables.
15058 Usually these options are used when @option{-pie} GCC option will be
15059 used during linking.
15061 @option{-fpie} and @option{-fPIE} both define the macros
15062 @code{__pie__} and @code{__PIE__}. The macros have the value 1
15063 for @option{-fpie} and 2 for @option{-fPIE}.
15065 @item -fno-jump-tables
15066 @opindex fno-jump-tables
15067 Do not use jump tables for switch statements even where it would be
15068 more efficient than other code generation strategies. This option is
15069 of use in conjunction with @option{-fpic} or @option{-fPIC} for
15070 building code which forms part of a dynamic linker and cannot
15071 reference the address of a jump table. On some targets, jump tables
15072 do not require a GOT and this option is not needed.
15074 @item -ffixed-@var{reg}
15076 Treat the register named @var{reg} as a fixed register; generated code
15077 should never refer to it (except perhaps as a stack pointer, frame
15078 pointer or in some other fixed role).
15080 @var{reg} must be the name of a register. The register names accepted
15081 are machine-specific and are defined in the @code{REGISTER_NAMES}
15082 macro in the machine description macro file.
15084 This flag does not have a negative form, because it specifies a
15087 @item -fcall-used-@var{reg}
15088 @opindex fcall-used
15089 Treat the register named @var{reg} as an allocable register that is
15090 clobbered by function calls. It may be allocated for temporaries or
15091 variables that do not live across a call. Functions compiled this way
15092 will not save and restore the register @var{reg}.
15094 It is an error to used this flag with the frame pointer or stack pointer.
15095 Use of this flag for other registers that have fixed pervasive roles in
15096 the machine's execution model will produce disastrous results.
15098 This flag does not have a negative form, because it specifies a
15101 @item -fcall-saved-@var{reg}
15102 @opindex fcall-saved
15103 Treat the register named @var{reg} as an allocable register saved by
15104 functions. It may be allocated even for temporaries or variables that
15105 live across a call. Functions compiled this way will save and restore
15106 the register @var{reg} if they use it.
15108 It is an error to used this flag with the frame pointer or stack pointer.
15109 Use of this flag for other registers that have fixed pervasive roles in
15110 the machine's execution model will produce disastrous results.
15112 A different sort of disaster will result from the use of this flag for
15113 a register in which function values may be returned.
15115 This flag does not have a negative form, because it specifies a
15118 @item -fpack-struct[=@var{n}]
15119 @opindex fpack-struct
15120 Without a value specified, pack all structure members together without
15121 holes. When a value is specified (which must be a small power of two), pack
15122 structure members according to this value, representing the maximum
15123 alignment (that is, objects with default alignment requirements larger than
15124 this will be output potentially unaligned at the next fitting location.
15126 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
15127 code that is not binary compatible with code generated without that switch.
15128 Additionally, it makes the code suboptimal.
15129 Use it to conform to a non-default application binary interface.
15131 @item -finstrument-functions
15132 @opindex finstrument-functions
15133 Generate instrumentation calls for entry and exit to functions. Just
15134 after function entry and just before function exit, the following
15135 profiling functions will be called with the address of the current
15136 function and its call site. (On some platforms,
15137 @code{__builtin_return_address} does not work beyond the current
15138 function, so the call site information may not be available to the
15139 profiling functions otherwise.)
15142 void __cyg_profile_func_enter (void *this_fn,
15144 void __cyg_profile_func_exit (void *this_fn,
15148 The first argument is the address of the start of the current function,
15149 which may be looked up exactly in the symbol table.
15151 This instrumentation is also done for functions expanded inline in other
15152 functions. The profiling calls will indicate where, conceptually, the
15153 inline function is entered and exited. This means that addressable
15154 versions of such functions must be available. If all your uses of a
15155 function are expanded inline, this may mean an additional expansion of
15156 code size. If you use @samp{extern inline} in your C code, an
15157 addressable version of such functions must be provided. (This is
15158 normally the case anyways, but if you get lucky and the optimizer always
15159 expands the functions inline, you might have gotten away without
15160 providing static copies.)
15162 A function may be given the attribute @code{no_instrument_function}, in
15163 which case this instrumentation will not be done. This can be used, for
15164 example, for the profiling functions listed above, high-priority
15165 interrupt routines, and any functions from which the profiling functions
15166 cannot safely be called (perhaps signal handlers, if the profiling
15167 routines generate output or allocate memory).
15169 @item -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{}
15170 @opindex finstrument-functions-exclude-file-list
15172 Set the list of functions that are excluded from instrumentation (see
15173 the description of @code{-finstrument-functions}). If the file that
15174 contains a function definition matches with one of @var{file}, then
15175 that function is not instrumented. The match is done on substrings:
15176 if the @var{file} parameter is a substring of the file name, it is
15177 considered to be a match.
15180 @code{-finstrument-functions-exclude-file-list=/bits/stl,include/sys}
15181 will exclude any inline function defined in files whose pathnames
15182 contain @code{/bits/stl} or @code{include/sys}.
15184 If, for some reason, you want to include letter @code{','} in one of
15185 @var{sym}, write @code{'\,'}. For example,
15186 @code{-finstrument-functions-exclude-file-list='\,\,tmp'}
15187 (note the single quote surrounding the option).
15189 @item -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{}
15190 @opindex finstrument-functions-exclude-function-list
15192 This is similar to @code{-finstrument-functions-exclude-file-list},
15193 but this option sets the list of function names to be excluded from
15194 instrumentation. The function name to be matched is its user-visible
15195 name, such as @code{vector<int> blah(const vector<int> &)}, not the
15196 internal mangled name (e.g., @code{_Z4blahRSt6vectorIiSaIiEE}). The
15197 match is done on substrings: if the @var{sym} parameter is a substring
15198 of the function name, it is considered to be a match.
15200 @item -fstack-check
15201 @opindex fstack-check
15202 Generate code to verify that you do not go beyond the boundary of the
15203 stack. You should specify this flag if you are running in an
15204 environment with multiple threads, but only rarely need to specify it in
15205 a single-threaded environment since stack overflow is automatically
15206 detected on nearly all systems if there is only one stack.
15208 Note that this switch does not actually cause checking to be done; the
15209 operating system must do that. The switch causes generation of code
15210 to ensure that the operating system sees the stack being extended.
15212 @item -fstack-limit-register=@var{reg}
15213 @itemx -fstack-limit-symbol=@var{sym}
15214 @itemx -fno-stack-limit
15215 @opindex fstack-limit-register
15216 @opindex fstack-limit-symbol
15217 @opindex fno-stack-limit
15218 Generate code to ensure that the stack does not grow beyond a certain value,
15219 either the value of a register or the address of a symbol. If the stack
15220 would grow beyond the value, a signal is raised. For most targets,
15221 the signal is raised before the stack overruns the boundary, so
15222 it is possible to catch the signal without taking special precautions.
15224 For instance, if the stack starts at absolute address @samp{0x80000000}
15225 and grows downwards, you can use the flags
15226 @option{-fstack-limit-symbol=__stack_limit} and
15227 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
15228 of 128KB@. Note that this may only work with the GNU linker.
15230 @cindex aliasing of parameters
15231 @cindex parameters, aliased
15232 @item -fargument-alias
15233 @itemx -fargument-noalias
15234 @itemx -fargument-noalias-global
15235 @itemx -fargument-noalias-anything
15236 @opindex fargument-alias
15237 @opindex fargument-noalias
15238 @opindex fargument-noalias-global
15239 @opindex fargument-noalias-anything
15240 Specify the possible relationships among parameters and between
15241 parameters and global data.
15243 @option{-fargument-alias} specifies that arguments (parameters) may
15244 alias each other and may alias global storage.@*
15245 @option{-fargument-noalias} specifies that arguments do not alias
15246 each other, but may alias global storage.@*
15247 @option{-fargument-noalias-global} specifies that arguments do not
15248 alias each other and do not alias global storage.
15249 @option{-fargument-noalias-anything} specifies that arguments do not
15250 alias any other storage.
15252 Each language will automatically use whatever option is required by
15253 the language standard. You should not need to use these options yourself.
15255 @item -fleading-underscore
15256 @opindex fleading-underscore
15257 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
15258 change the way C symbols are represented in the object file. One use
15259 is to help link with legacy assembly code.
15261 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
15262 generate code that is not binary compatible with code generated without that
15263 switch. Use it to conform to a non-default application binary interface.
15264 Not all targets provide complete support for this switch.
15266 @item -ftls-model=@var{model}
15267 @opindex ftls-model
15268 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
15269 The @var{model} argument should be one of @code{global-dynamic},
15270 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
15272 The default without @option{-fpic} is @code{initial-exec}; with
15273 @option{-fpic} the default is @code{global-dynamic}.
15275 @item -fvisibility=@var{default|internal|hidden|protected}
15276 @opindex fvisibility
15277 Set the default ELF image symbol visibility to the specified option---all
15278 symbols will be marked with this unless overridden within the code.
15279 Using this feature can very substantially improve linking and
15280 load times of shared object libraries, produce more optimized
15281 code, provide near-perfect API export and prevent symbol clashes.
15282 It is @strong{strongly} recommended that you use this in any shared objects
15285 Despite the nomenclature, @code{default} always means public ie;
15286 available to be linked against from outside the shared object.
15287 @code{protected} and @code{internal} are pretty useless in real-world
15288 usage so the only other commonly used option will be @code{hidden}.
15289 The default if @option{-fvisibility} isn't specified is
15290 @code{default}, i.e., make every
15291 symbol public---this causes the same behavior as previous versions of
15294 A good explanation of the benefits offered by ensuring ELF
15295 symbols have the correct visibility is given by ``How To Write
15296 Shared Libraries'' by Ulrich Drepper (which can be found at
15297 @w{@uref{http://people.redhat.com/~drepper/}})---however a superior
15298 solution made possible by this option to marking things hidden when
15299 the default is public is to make the default hidden and mark things
15300 public. This is the norm with DLL's on Windows and with @option{-fvisibility=hidden}
15301 and @code{__attribute__ ((visibility("default")))} instead of
15302 @code{__declspec(dllexport)} you get almost identical semantics with
15303 identical syntax. This is a great boon to those working with
15304 cross-platform projects.
15306 For those adding visibility support to existing code, you may find
15307 @samp{#pragma GCC visibility} of use. This works by you enclosing
15308 the declarations you wish to set visibility for with (for example)
15309 @samp{#pragma GCC visibility push(hidden)} and
15310 @samp{#pragma GCC visibility pop}.
15311 Bear in mind that symbol visibility should be viewed @strong{as
15312 part of the API interface contract} and thus all new code should
15313 always specify visibility when it is not the default ie; declarations
15314 only for use within the local DSO should @strong{always} be marked explicitly
15315 as hidden as so to avoid PLT indirection overheads---making this
15316 abundantly clear also aids readability and self-documentation of the code.
15317 Note that due to ISO C++ specification requirements, operator new and
15318 operator delete must always be of default visibility.
15320 Be aware that headers from outside your project, in particular system
15321 headers and headers from any other library you use, may not be
15322 expecting to be compiled with visibility other than the default. You
15323 may need to explicitly say @samp{#pragma GCC visibility push(default)}
15324 before including any such headers.
15326 @samp{extern} declarations are not affected by @samp{-fvisibility}, so
15327 a lot of code can be recompiled with @samp{-fvisibility=hidden} with
15328 no modifications. However, this means that calls to @samp{extern}
15329 functions with no explicit visibility will use the PLT, so it is more
15330 effective to use @samp{__attribute ((visibility))} and/or
15331 @samp{#pragma GCC visibility} to tell the compiler which @samp{extern}
15332 declarations should be treated as hidden.
15334 Note that @samp{-fvisibility} does affect C++ vague linkage
15335 entities. This means that, for instance, an exception class that will
15336 be thrown between DSOs must be explicitly marked with default
15337 visibility so that the @samp{type_info} nodes will be unified between
15340 An overview of these techniques, their benefits and how to use them
15341 is at @w{@uref{http://gcc.gnu.org/wiki/Visibility}}.
15347 @node Environment Variables
15348 @section Environment Variables Affecting GCC
15349 @cindex environment variables
15351 @c man begin ENVIRONMENT
15352 This section describes several environment variables that affect how GCC
15353 operates. Some of them work by specifying directories or prefixes to use
15354 when searching for various kinds of files. Some are used to specify other
15355 aspects of the compilation environment.
15357 Note that you can also specify places to search using options such as
15358 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
15359 take precedence over places specified using environment variables, which
15360 in turn take precedence over those specified by the configuration of GCC@.
15361 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
15362 GNU Compiler Collection (GCC) Internals}.
15367 @c @itemx LC_COLLATE
15369 @c @itemx LC_MONETARY
15370 @c @itemx LC_NUMERIC
15375 @c @findex LC_COLLATE
15376 @findex LC_MESSAGES
15377 @c @findex LC_MONETARY
15378 @c @findex LC_NUMERIC
15382 These environment variables control the way that GCC uses
15383 localization information that allow GCC to work with different
15384 national conventions. GCC inspects the locale categories
15385 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
15386 so. These locale categories can be set to any value supported by your
15387 installation. A typical value is @samp{en_GB.UTF-8} for English in the United
15388 Kingdom encoded in UTF-8.
15390 The @env{LC_CTYPE} environment variable specifies character
15391 classification. GCC uses it to determine the character boundaries in
15392 a string; this is needed for some multibyte encodings that contain quote
15393 and escape characters that would otherwise be interpreted as a string
15396 The @env{LC_MESSAGES} environment variable specifies the language to
15397 use in diagnostic messages.
15399 If the @env{LC_ALL} environment variable is set, it overrides the value
15400 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
15401 and @env{LC_MESSAGES} default to the value of the @env{LANG}
15402 environment variable. If none of these variables are set, GCC
15403 defaults to traditional C English behavior.
15407 If @env{TMPDIR} is set, it specifies the directory to use for temporary
15408 files. GCC uses temporary files to hold the output of one stage of
15409 compilation which is to be used as input to the next stage: for example,
15410 the output of the preprocessor, which is the input to the compiler
15413 @item GCC_EXEC_PREFIX
15414 @findex GCC_EXEC_PREFIX
15415 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
15416 names of the subprograms executed by the compiler. No slash is added
15417 when this prefix is combined with the name of a subprogram, but you can
15418 specify a prefix that ends with a slash if you wish.
15420 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
15421 an appropriate prefix to use based on the pathname it was invoked with.
15423 If GCC cannot find the subprogram using the specified prefix, it
15424 tries looking in the usual places for the subprogram.
15426 The default value of @env{GCC_EXEC_PREFIX} is
15427 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the prefix to
15428 the installed compiler. In many cases @var{prefix} is the value
15429 of @code{prefix} when you ran the @file{configure} script.
15431 Other prefixes specified with @option{-B} take precedence over this prefix.
15433 This prefix is also used for finding files such as @file{crt0.o} that are
15436 In addition, the prefix is used in an unusual way in finding the
15437 directories to search for header files. For each of the standard
15438 directories whose name normally begins with @samp{/usr/local/lib/gcc}
15439 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
15440 replacing that beginning with the specified prefix to produce an
15441 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
15442 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
15443 These alternate directories are searched first; the standard directories
15444 come next. If a standard directory begins with the configured
15445 @var{prefix} then the value of @var{prefix} is replaced by
15446 @env{GCC_EXEC_PREFIX} when looking for header files.
15448 @item COMPILER_PATH
15449 @findex COMPILER_PATH
15450 The value of @env{COMPILER_PATH} is a colon-separated list of
15451 directories, much like @env{PATH}. GCC tries the directories thus
15452 specified when searching for subprograms, if it can't find the
15453 subprograms using @env{GCC_EXEC_PREFIX}.
15456 @findex LIBRARY_PATH
15457 The value of @env{LIBRARY_PATH} is a colon-separated list of
15458 directories, much like @env{PATH}. When configured as a native compiler,
15459 GCC tries the directories thus specified when searching for special
15460 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
15461 using GCC also uses these directories when searching for ordinary
15462 libraries for the @option{-l} option (but directories specified with
15463 @option{-L} come first).
15467 @cindex locale definition
15468 This variable is used to pass locale information to the compiler. One way in
15469 which this information is used is to determine the character set to be used
15470 when character literals, string literals and comments are parsed in C and C++.
15471 When the compiler is configured to allow multibyte characters,
15472 the following values for @env{LANG} are recognized:
15476 Recognize JIS characters.
15478 Recognize SJIS characters.
15480 Recognize EUCJP characters.
15483 If @env{LANG} is not defined, or if it has some other value, then the
15484 compiler will use mblen and mbtowc as defined by the default locale to
15485 recognize and translate multibyte characters.
15489 Some additional environments variables affect the behavior of the
15492 @include cppenv.texi
15496 @node Precompiled Headers
15497 @section Using Precompiled Headers
15498 @cindex precompiled headers
15499 @cindex speed of compilation
15501 Often large projects have many header files that are included in every
15502 source file. The time the compiler takes to process these header files
15503 over and over again can account for nearly all of the time required to
15504 build the project. To make builds faster, GCC allows users to
15505 `precompile' a header file; then, if builds can use the precompiled
15506 header file they will be much faster.
15508 To create a precompiled header file, simply compile it as you would any
15509 other file, if necessary using the @option{-x} option to make the driver
15510 treat it as a C or C++ header file. You will probably want to use a
15511 tool like @command{make} to keep the precompiled header up-to-date when
15512 the headers it contains change.
15514 A precompiled header file will be searched for when @code{#include} is
15515 seen in the compilation. As it searches for the included file
15516 (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
15517 compiler looks for a precompiled header in each directory just before it
15518 looks for the include file in that directory. The name searched for is
15519 the name specified in the @code{#include} with @samp{.gch} appended. If
15520 the precompiled header file can't be used, it is ignored.
15522 For instance, if you have @code{#include "all.h"}, and you have
15523 @file{all.h.gch} in the same directory as @file{all.h}, then the
15524 precompiled header file will be used if possible, and the original
15525 header will be used otherwise.
15527 Alternatively, you might decide to put the precompiled header file in a
15528 directory and use @option{-I} to ensure that directory is searched
15529 before (or instead of) the directory containing the original header.
15530 Then, if you want to check that the precompiled header file is always
15531 used, you can put a file of the same name as the original header in this
15532 directory containing an @code{#error} command.
15534 This also works with @option{-include}. So yet another way to use
15535 precompiled headers, good for projects not designed with precompiled
15536 header files in mind, is to simply take most of the header files used by
15537 a project, include them from another header file, precompile that header
15538 file, and @option{-include} the precompiled header. If the header files
15539 have guards against multiple inclusion, they will be skipped because
15540 they've already been included (in the precompiled header).
15542 If you need to precompile the same header file for different
15543 languages, targets, or compiler options, you can instead make a
15544 @emph{directory} named like @file{all.h.gch}, and put each precompiled
15545 header in the directory, perhaps using @option{-o}. It doesn't matter
15546 what you call the files in the directory, every precompiled header in
15547 the directory will be considered. The first precompiled header
15548 encountered in the directory that is valid for this compilation will
15549 be used; they're searched in no particular order.
15551 There are many other possibilities, limited only by your imagination,
15552 good sense, and the constraints of your build system.
15554 A precompiled header file can be used only when these conditions apply:
15558 Only one precompiled header can be used in a particular compilation.
15561 A precompiled header can't be used once the first C token is seen. You
15562 can have preprocessor directives before a precompiled header; you can
15563 even include a precompiled header from inside another header, so long as
15564 there are no C tokens before the @code{#include}.
15567 The precompiled header file must be produced for the same language as
15568 the current compilation. You can't use a C precompiled header for a C++
15572 The precompiled header file must have been produced by the same compiler
15573 binary as the current compilation is using.
15576 Any macros defined before the precompiled header is included must
15577 either be defined in the same way as when the precompiled header was
15578 generated, or must not affect the precompiled header, which usually
15579 means that they don't appear in the precompiled header at all.
15581 The @option{-D} option is one way to define a macro before a
15582 precompiled header is included; using a @code{#define} can also do it.
15583 There are also some options that define macros implicitly, like
15584 @option{-O} and @option{-Wdeprecated}; the same rule applies to macros
15587 @item If debugging information is output when using the precompiled
15588 header, using @option{-g} or similar, the same kind of debugging information
15589 must have been output when building the precompiled header. However,
15590 a precompiled header built using @option{-g} can be used in a compilation
15591 when no debugging information is being output.
15593 @item The same @option{-m} options must generally be used when building
15594 and using the precompiled header. @xref{Submodel Options},
15595 for any cases where this rule is relaxed.
15597 @item Each of the following options must be the same when building and using
15598 the precompiled header:
15600 @gccoptlist{-fexceptions}
15603 Some other command-line options starting with @option{-f},
15604 @option{-p}, or @option{-O} must be defined in the same way as when
15605 the precompiled header was generated. At present, it's not clear
15606 which options are safe to change and which are not; the safest choice
15607 is to use exactly the same options when generating and using the
15608 precompiled header. The following are known to be safe:
15610 @gccoptlist{-fmessage-length= -fpreprocessed -fsched-interblock @gol
15611 -fsched-spec -fsched-spec-load -fsched-spec-load-dangerous @gol
15612 -fsched-verbose=<number> -fschedule-insns -fvisibility= @gol
15617 For all of these except the last, the compiler will automatically
15618 ignore the precompiled header if the conditions aren't met. If you
15619 find an option combination that doesn't work and doesn't cause the
15620 precompiled header to be ignored, please consider filing a bug report,
15623 If you do use differing options when generating and using the
15624 precompiled header, the actual behavior will be a mixture of the
15625 behavior for the options. For instance, if you use @option{-g} to
15626 generate the precompiled header but not when using it, you may or may
15627 not get debugging information for routines in the precompiled header.
15629 @node Running Protoize
15630 @section Running Protoize
15632 The program @code{protoize} is an optional part of GCC@. You can use
15633 it to add prototypes to a program, thus converting the program to ISO
15634 C in one respect. The companion program @code{unprotoize} does the
15635 reverse: it removes argument types from any prototypes that are found.
15637 When you run these programs, you must specify a set of source files as
15638 command line arguments. The conversion programs start out by compiling
15639 these files to see what functions they define. The information gathered
15640 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
15642 After scanning comes actual conversion. The specified files are all
15643 eligible to be converted; any files they include (whether sources or
15644 just headers) are eligible as well.
15646 But not all the eligible files are converted. By default,
15647 @code{protoize} and @code{unprotoize} convert only source and header
15648 files in the current directory. You can specify additional directories
15649 whose files should be converted with the @option{-d @var{directory}}
15650 option. You can also specify particular files to exclude with the
15651 @option{-x @var{file}} option. A file is converted if it is eligible, its
15652 directory name matches one of the specified directory names, and its
15653 name within the directory has not been excluded.
15655 Basic conversion with @code{protoize} consists of rewriting most
15656 function definitions and function declarations to specify the types of
15657 the arguments. The only ones not rewritten are those for varargs
15660 @code{protoize} optionally inserts prototype declarations at the
15661 beginning of the source file, to make them available for any calls that
15662 precede the function's definition. Or it can insert prototype
15663 declarations with block scope in the blocks where undeclared functions
15666 Basic conversion with @code{unprotoize} consists of rewriting most
15667 function declarations to remove any argument types, and rewriting
15668 function definitions to the old-style pre-ISO form.
15670 Both conversion programs print a warning for any function declaration or
15671 definition that they can't convert. You can suppress these warnings
15674 The output from @code{protoize} or @code{unprotoize} replaces the
15675 original source file. The original file is renamed to a name ending
15676 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
15677 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
15678 for DOS) file already exists, then the source file is simply discarded.
15680 @code{protoize} and @code{unprotoize} both depend on GCC itself to
15681 scan the program and collect information about the functions it uses.
15682 So neither of these programs will work until GCC is installed.
15684 Here is a table of the options you can use with @code{protoize} and
15685 @code{unprotoize}. Each option works with both programs unless
15689 @item -B @var{directory}
15690 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
15691 usual directory (normally @file{/usr/local/lib}). This file contains
15692 prototype information about standard system functions. This option
15693 applies only to @code{protoize}.
15695 @item -c @var{compilation-options}
15696 Use @var{compilation-options} as the options when running @command{gcc} to
15697 produce the @samp{.X} files. The special option @option{-aux-info} is
15698 always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
15700 Note that the compilation options must be given as a single argument to
15701 @code{protoize} or @code{unprotoize}. If you want to specify several
15702 @command{gcc} options, you must quote the entire set of compilation options
15703 to make them a single word in the shell.
15705 There are certain @command{gcc} arguments that you cannot use, because they
15706 would produce the wrong kind of output. These include @option{-g},
15707 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
15708 the @var{compilation-options}, they are ignored.
15711 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
15712 systems) instead of @samp{.c}. This is convenient if you are converting
15713 a C program to C++. This option applies only to @code{protoize}.
15716 Add explicit global declarations. This means inserting explicit
15717 declarations at the beginning of each source file for each function
15718 that is called in the file and was not declared. These declarations
15719 precede the first function definition that contains a call to an
15720 undeclared function. This option applies only to @code{protoize}.
15722 @item -i @var{string}
15723 Indent old-style parameter declarations with the string @var{string}.
15724 This option applies only to @code{protoize}.
15726 @code{unprotoize} converts prototyped function definitions to old-style
15727 function definitions, where the arguments are declared between the
15728 argument list and the initial @samp{@{}. By default, @code{unprotoize}
15729 uses five spaces as the indentation. If you want to indent with just
15730 one space instead, use @option{-i " "}.
15733 Keep the @samp{.X} files. Normally, they are deleted after conversion
15737 Add explicit local declarations. @code{protoize} with @option{-l} inserts
15738 a prototype declaration for each function in each block which calls the
15739 function without any declaration. This option applies only to
15743 Make no real changes. This mode just prints information about the conversions
15744 that would have been done without @option{-n}.
15747 Make no @samp{.save} files. The original files are simply deleted.
15748 Use this option with caution.
15750 @item -p @var{program}
15751 Use the program @var{program} as the compiler. Normally, the name
15752 @file{gcc} is used.
15755 Work quietly. Most warnings are suppressed.
15758 Print the version number, just like @option{-v} for @command{gcc}.
15761 If you need special compiler options to compile one of your program's
15762 source files, then you should generate that file's @samp{.X} file
15763 specially, by running @command{gcc} on that source file with the
15764 appropriate options and the option @option{-aux-info}. Then run
15765 @code{protoize} on the entire set of files. @code{protoize} will use
15766 the existing @samp{.X} file because it is newer than the source file.
15770 gcc -Dfoo=bar file1.c -aux-info file1.X
15775 You need to include the special files along with the rest in the
15776 @code{protoize} command, even though their @samp{.X} files already
15777 exist, because otherwise they won't get converted.
15779 @xref{Protoize Caveats}, for more information on how to use
15780 @code{protoize} successfully.