1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2 @c 2000, 2001, 2002, 2003 Free Software Foundation, Inc.
3 @c This is part of the GCC manual.
4 @c For copying conditions, see the file gcc.texi.
8 Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997,
9 1998, 1999, 2000, 2001, 2002, 2003 Free Software Foundation, Inc.
11 Permission is granted to copy, distribute and/or modify this document
12 under the terms of the GNU Free Documentation License, Version 1.2 or
13 any later version published by the Free Software Foundation; with the
14 Invariant Sections being ``GNU General Public License'' and ``Funding
15 Free Software'', the Front-Cover texts being (a) (see below), and with
16 the Back-Cover Texts being (b) (see below). A copy of the license is
17 included in the gfdl(7) man page.
19 (a) The FSF's Front-Cover Text is:
23 (b) The FSF's Back-Cover Text is:
25 You have freedom to copy and modify this GNU Manual, like GNU
26 software. Copies published by the Free Software Foundation raise
27 funds for GNU development.
29 @c Set file name and title for the man page.
31 @settitle GNU project C and C++ compiler
33 gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
34 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
35 [@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
36 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
37 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
38 [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
39 [@option{-o} @var{outfile}] @var{infile}@dots{}
41 Only the most useful options are listed here; see below for the
42 remainder. @samp{g++} accepts mostly the same options as @samp{gcc}.
45 gpl(7), gfdl(7), fsf-funding(7),
46 cpp(1), gcov(1), g77(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
47 and the Info entries for @file{gcc}, @file{cpp}, @file{g77}, @file{as},
48 @file{ld}, @file{binutils} and @file{gdb}.
51 For instructions on reporting bugs, see
52 @w{@uref{http://gcc.gnu.org/bugs.html}}. Use of the @command{gccbug}
53 script to report bugs is recommended.
56 See the Info entry for @command{gcc}, or
57 @w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}},
58 for contributors to GCC@.
63 @chapter GCC Command Options
64 @cindex GCC command options
65 @cindex command options
66 @cindex options, GCC command
68 @c man begin DESCRIPTION
69 When you invoke GCC, it normally does preprocessing, compilation,
70 assembly and linking. The ``overall options'' allow you to stop this
71 process at an intermediate stage. For example, the @option{-c} option
72 says not to run the linker. Then the output consists of object files
73 output by the assembler.
75 Other options are passed on to one stage of processing. Some options
76 control the preprocessor and others the compiler itself. Yet other
77 options control the assembler and linker; most of these are not
78 documented here, since you rarely need to use any of them.
80 @cindex C compilation options
81 Most of the command line options that you can use with GCC are useful
82 for C programs; when an option is only useful with another language
83 (usually C++), the explanation says so explicitly. If the description
84 for a particular option does not mention a source language, you can use
85 that option with all supported languages.
87 @cindex C++ compilation options
88 @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
89 options for compiling C++ programs.
91 @cindex grouping options
92 @cindex options, grouping
93 The @command{gcc} program accepts options and file names as operands. Many
94 options have multi-letter names; therefore multiple single-letter options
95 may @emph{not} be grouped: @option{-dr} is very different from @w{@samp{-d
98 @cindex order of options
99 @cindex options, order
100 You can mix options and other arguments. For the most part, the order
101 you use doesn't matter. Order does matter when you use several options
102 of the same kind; for example, if you specify @option{-L} more than once,
103 the directories are searched in the order specified.
105 Many options have long names starting with @samp{-f} or with
106 @samp{-W}---for example, @option{-fforce-mem},
107 @option{-fstrength-reduce}, @option{-Wformat} and so on. Most of
108 these have both positive and negative forms; the negative form of
109 @option{-ffoo} would be @option{-fno-foo}. This manual documents
110 only one of these two forms, whichever one is not the default.
114 @xref{Option Index}, for an index to GCC's options.
117 * Option Summary:: Brief list of all options, without explanations.
118 * Overall Options:: Controlling the kind of output:
119 an executable, object files, assembler files,
120 or preprocessed source.
121 * Invoking G++:: Compiling C++ programs.
122 * C Dialect Options:: Controlling the variant of C language compiled.
123 * C++ Dialect Options:: Variations on C++.
124 * Objective-C Dialect Options:: Variations on Objective-C.
125 * Language Independent Options:: Controlling how diagnostics should be
127 * Warning Options:: How picky should the compiler be?
128 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
129 * Optimize Options:: How much optimization?
130 * Preprocessor Options:: Controlling header files and macro definitions.
131 Also, getting dependency information for Make.
132 * Assembler Options:: Passing options to the assembler.
133 * Link Options:: Specifying libraries and so on.
134 * Directory Options:: Where to find header files and libraries.
135 Where to find the compiler executable files.
136 * Spec Files:: How to pass switches to sub-processes.
137 * Target Options:: Running a cross-compiler, or an old version of GCC.
138 * Submodel Options:: Specifying minor hardware or convention variations,
139 such as 68010 vs 68020.
140 * Code Gen Options:: Specifying conventions for function calls, data layout
142 * Environment Variables:: Env vars that affect GCC.
143 * Precompiled Headers:: Compiling a header once, and using it many times.
144 * Running Protoize:: Automatically adding or removing function prototypes.
150 @section Option Summary
152 Here is a summary of all the options, grouped by type. Explanations are
153 in the following sections.
156 @item Overall Options
157 @xref{Overall Options,,Options Controlling the Kind of Output}.
158 @gccoptlist{-c -S -E -o @var{file} -pipe -pass-exit-codes @gol
159 -x @var{language} -v -### --help --target-help --version}
161 @item C Language Options
162 @xref{C Dialect Options,,Options Controlling C Dialect}.
163 @gccoptlist{-ansi -std=@var{standard} -aux-info @var{filename} @gol
164 -fno-asm -fno-builtin -fno-builtin-@var{function} @gol
165 -fhosted -ffreestanding -fms-extensions @gol
166 -trigraphs -no-integrated-cpp -traditional -traditional-cpp @gol
167 -fallow-single-precision -fcond-mismatch @gol
168 -fsigned-bitfields -fsigned-char @gol
169 -funsigned-bitfields -funsigned-char @gol
172 @item C++ Language Options
173 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
174 @gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol
175 -fconserve-space -fno-const-strings @gol
176 -fno-elide-constructors @gol
177 -fno-enforce-eh-specs -fexternal-templates @gol
178 -falt-external-templates @gol
179 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
180 -fno-implicit-templates @gol
181 -fno-implicit-inline-templates @gol
182 -fno-implement-inlines -fms-extensions @gol
183 -fno-nonansi-builtins -fno-operator-names @gol
184 -fno-optional-diags -fpermissive @gol
185 -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
186 -fuse-cxa-atexit -fno-weak -nostdinc++ @gol
187 -fno-default-inline -Wabi -Wctor-dtor-privacy @gol
188 -Wnon-virtual-dtor -Wreorder @gol
189 -Weffc++ -Wno-deprecated @gol
190 -Wno-non-template-friend -Wold-style-cast @gol
191 -Woverloaded-virtual -Wno-pmf-conversions @gol
192 -Wsign-promo -Wsynth}
194 @item Objective-C Language Options
195 @xref{Objective-C Dialect Options,,Options Controlling Objective-C Dialect}.
196 @gccoptlist{-fconstant-string-class=@var{class-name} @gol
197 -fgnu-runtime -fnext-runtime -gen-decls @gol
198 -Wno-protocol -Wselector -Wundeclared-selector}
200 @item Language Independent Options
201 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
202 @gccoptlist{-fmessage-length=@var{n} @gol
203 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]}}
205 @item Warning Options
206 @xref{Warning Options,,Options to Request or Suppress Warnings}.
207 @gccoptlist{-fsyntax-only -pedantic -pedantic-errors @gol
208 -w -Wextra -Wall -Waggregate-return @gol
209 -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment @gol
210 -Wconversion -Wno-deprecated-declarations @gol
211 -Wdisabled-optimization -Wno-div-by-zero -Werror @gol
212 -Wfloat-equal -Wformat -Wformat=2 @gol
213 -Wformat-nonliteral -Wformat-security @gol
214 -Wimplicit -Wimplicit-int @gol
215 -Wimplicit-function-declaration @gol
216 -Werror-implicit-function-declaration @gol
217 -Wimport -Winline -Winvalid-pch -Wno-endif-labels @gol
218 -Wno-invalid-offsetof @gol
219 -Wlarger-than-@var{len} -Wlong-long @gol
220 -Wmain -Wmissing-braces @gol
221 -Wmissing-format-attribute -Wmissing-noreturn @gol
222 -Wno-multichar -Wno-format-extra-args -Wno-format-y2k @gol
223 -Wno-import -Wnonnull -Wpacked -Wpadded @gol
224 -Wparentheses -Wpointer-arith -Wredundant-decls @gol
225 -Wreturn-type -Wsequence-point -Wshadow @gol
226 -Wsign-compare -Wstrict-aliasing @gol
227 -Wswitch -Wswitch-default -Wswitch-enum @gol
228 -Wsystem-headers -Wtrigraphs -Wundef -Wuninitialized @gol
229 -Wunknown-pragmas -Wunreachable-code @gol
230 -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
231 -Wunused-value -Wunused-variable -Wwrite-strings}
233 @item C-only Warning Options
234 @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
235 -Wmissing-prototypes -Wnested-externs @gol
236 -Wstrict-prototypes -Wtraditional @gol
237 -Wdeclaration-after-statement}
239 @item Debugging Options
240 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
241 @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
242 -fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
243 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
244 -fdump-tree-original@r{[}-@var{n}@r{]} @gol
245 -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
246 -fdump-tree-inlined@r{[}-@var{n}@r{]} @gol
247 -feliminate-dwarf2-dups -feliminate-unused-debug-types @gol
248 -feliminate-unused-debug-symbols -fmem-report -fprofile-arcs @gol
249 -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
250 -ftest-coverage -ftime-report @gol
251 -g -g@var{level} -gcoff -gdwarf -gdwarf-1 -gdwarf-1+ -gdwarf-2 @gol
252 -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
253 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
254 -print-multi-directory -print-multi-lib @gol
255 -print-prog-name=@var{program} -print-search-dirs -Q @gol
258 @item Optimization Options
259 @xref{Optimize Options,,Options that Control Optimization}.
260 @gccoptlist{-falign-functions=@var{n} -falign-jumps=@var{n} @gol
261 -falign-labels=@var{n} -falign-loops=@var{n} @gol
262 -fbranch-probabilities -fprofile-values -fbranch-target-load-optimize @gol
263 -fbranch-target-load-optimize2 -fcaller-saves -fcprop-registers @gol
264 -fcse-follow-jumps -fcse-skip-blocks -fdata-sections @gol
265 -fdelayed-branch -fdelete-null-pointer-checks @gol
266 -fexpensive-optimizations -ffast-math -ffloat-store @gol
267 -fforce-addr -fforce-mem -ffunction-sections @gol
268 -fgcse -fgcse-lm -fgcse-sm -floop-optimize -fcrossjumping @gol
269 -fif-conversion -fif-conversion2 @gol
270 -finline-functions -finline-limit=@var{n} -fkeep-inline-functions @gol
271 -fkeep-static-consts -fmerge-constants -fmerge-all-constants @gol
272 -fmove-all-movables -fnew-ra -fno-branch-count-reg @gol
273 -fno-default-inline -fno-defer-pop @gol
274 -fno-function-cse -fno-guess-branch-probability @gol
275 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
276 -funsafe-math-optimizations -ffinite-math-only @gol
277 -fno-trapping-math -fno-zero-initialized-in-bss @gol
278 -fomit-frame-pointer -foptimize-register-move @gol
279 -foptimize-sibling-calls -fprefetch-loop-arrays @gol
280 -freduce-all-givs -fregmove -frename-registers @gol
281 -freorder-blocks -freorder-functions @gol
282 -frerun-cse-after-loop -frerun-loop-opt @gol
283 -fschedule-insns -fschedule-insns2 @gol
284 -fno-sched-interblock -fno-sched-spec -fsched-spec-load @gol
285 -fsched-spec-load-dangerous -fsched2-use-superblocks @gol
286 -fsched2-use-traces -fsignaling-nans @gol
287 -fsingle-precision-constant -fssa -fssa-ccp -fssa-dce @gol
288 -fstrength-reduce -fstrict-aliasing -ftracer -fthread-jumps @gol
289 -funroll-all-loops -funroll-loops -fpeel-loops @gol
290 -funswitch-loops -fold-unroll-loops -fold-unroll-all-loops @gol
291 --param @var{name}=@var{value}
292 -O -O0 -O1 -O2 -O3 -Os}
294 @item Preprocessor Options
295 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
296 @gccoptlist{-A@var{question}=@var{answer} @gol
297 -A-@var{question}@r{[}=@var{answer}@r{]} @gol
298 -C -dD -dI -dM -dN @gol
299 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
300 -idirafter @var{dir} @gol
301 -include @var{file} -imacros @var{file} @gol
302 -iprefix @var{file} -iwithprefix @var{dir} @gol
303 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
304 -M -MM -MF -MG -MP -MQ -MT -nostdinc @gol
305 -P -fworking-directory -remap @gol
306 -trigraphs -undef -U@var{macro} -Wp,@var{option} @gol
307 -Xpreprocessor @var{option}}
309 @item Assembler Option
310 @xref{Assembler Options,,Passing Options to the Assembler}.
311 @gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
314 @xref{Link Options,,Options for Linking}.
315 @gccoptlist{@var{object-file-name} -l@var{library} @gol
316 -nostartfiles -nodefaultlibs -nostdlib -pie @gol
317 -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
318 -Wl,@var{option} -Xlinker @var{option} @gol
321 @item Directory Options
322 @xref{Directory Options,,Options for Directory Search}.
323 @gccoptlist{-B@var{prefix} -I@var{dir} -I- -L@var{dir} -specs=@var{file}}
326 @c I wrote this xref this way to avoid overfull hbox. -- rms
327 @xref{Target Options}.
328 @gccoptlist{-V @var{version} -b @var{machine}}
330 @item Machine Dependent Options
331 @xref{Submodel Options,,Hardware Models and Configurations}.
333 @emph{M680x0 Options}
334 @gccoptlist{-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
335 -m68060 -mcpu32 -m5200 -m68881 -mbitfield -mc68000 -mc68020 @gol
336 -mnobitfield -mrtd -mshort -msoft-float -mpcrel @gol
337 -malign-int -mstrict-align}
339 @emph{M68hc1x Options}
340 @gccoptlist{-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 @gol
341 -mauto-incdec -minmax -mlong-calls -mshort @gol
342 -msoft-reg-count=@var{count}}
345 @gccoptlist{-mg -mgnu -munix}
348 @gccoptlist{-mcpu=@var{cpu-type} @gol
349 -mtune=@var{cpu-type} @gol
350 -mcmodel=@var{code-model} @gol
352 -mapp-regs -mbroken-saverestore -mcypress @gol
353 -mfaster-structs -mflat @gol
354 -mfpu -mhard-float -mhard-quad-float @gol
355 -mimpure-text -mlittle-endian -mlive-g0 -mno-app-regs @gol
356 -mno-faster-structs -mno-flat -mno-fpu @gol
357 -mno-impure-text -mno-stack-bias -mno-unaligned-doubles @gol
358 -msoft-float -msoft-quad-float -msparclite -mstack-bias @gol
359 -msupersparc -munaligned-doubles -mv8}
362 @gccoptlist{-mapcs-frame -mno-apcs-frame @gol
363 -mapcs-26 -mapcs-32 @gol
364 -mapcs-stack-check -mno-apcs-stack-check @gol
365 -mapcs-float -mno-apcs-float @gol
366 -mapcs-reentrant -mno-apcs-reentrant @gol
367 -msched-prolog -mno-sched-prolog @gol
368 -mlittle-endian -mbig-endian -mwords-little-endian @gol
369 -malignment-traps -mno-alignment-traps @gol
370 -msoft-float -mhard-float -mfpe @gol
371 -mthumb-interwork -mno-thumb-interwork @gol
372 -mcpu=@var{name} -march=@var{name} -mfpe=@var{name} @gol
373 -mstructure-size-boundary=@var{n} @gol
374 -mabort-on-noreturn @gol
375 -mlong-calls -mno-long-calls @gol
376 -msingle-pic-base -mno-single-pic-base @gol
377 -mpic-register=@var{reg} @gol
378 -mnop-fun-dllimport @gol
379 -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol
380 -mpoke-function-name @gol
382 -mtpcs-frame -mtpcs-leaf-frame @gol
383 -mcaller-super-interworking -mcallee-super-interworking}
385 @emph{MN10200 Options}
388 @emph{MN10300 Options}
389 @gccoptlist{-mmult-bug -mno-mult-bug @gol
390 -mam33 -mno-am33 @gol
391 -mam33-2 -mno-am33-2 @gol
394 @emph{M32R/D Options}
395 @gccoptlist{-m32rx -m32r -mcode-model=@var{model-type} @gol
396 -msdata=@var{sdata-type} -G @var{num}}
399 @gccoptlist{-m88000 -m88100 -m88110 -mbig-pic @gol
400 -mcheck-zero-division -mhandle-large-shift @gol
401 -midentify-revision -mno-check-zero-division @gol
402 -mno-ocs-debug-info -mno-ocs-frame-position @gol
403 -mno-optimize-arg-area -mno-serialize-volatile @gol
404 -mno-underscores -mocs-debug-info @gol
405 -mocs-frame-position -moptimize-arg-area @gol
406 -mserialize-volatile -mshort-data-@var{num} -msvr3 @gol
407 -msvr4 -mtrap-large-shift -muse-div-instruction @gol
408 -mversion-03.00 -mwarn-passed-structs}
410 @emph{RS/6000 and PowerPC Options}
411 @gccoptlist{-mcpu=@var{cpu-type} @gol
412 -mtune=@var{cpu-type} @gol
413 -mpower -mno-power -mpower2 -mno-power2 @gol
414 -mpowerpc -mpowerpc64 -mno-powerpc @gol
415 -maltivec -mno-altivec @gol
416 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
417 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
418 -mnew-mnemonics -mold-mnemonics @gol
419 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
420 -m64 -m32 -mxl-call -mno-xl-call -mpe @gol
421 -malign-power -malign-natural @gol
422 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
423 -mstring -mno-string -mupdate -mno-update @gol
424 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
425 -mstrict-align -mno-strict-align -mrelocatable @gol
426 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
427 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
428 -mdynamic-no-pic @gol
429 -mcall-sysv -mcall-netbsd @gol
430 -maix-struct-return -msvr4-struct-return @gol
431 -mabi=altivec -mabi=no-altivec @gol
432 -mabi=spe -mabi=no-spe @gol
433 -misel=yes -misel=no @gol
434 -mspe=yes -mspe=no @gol
435 -mfloat-gprs=yes -mfloat-gprs=no @gol
436 -mprototype -mno-prototype @gol
437 -msim -mmvme -mads -myellowknife -memb -msdata @gol
438 -msdata=@var{opt} -mvxworks -mwindiss -G @var{num} -pthread}
440 @emph{Darwin Options}
441 @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
442 -arch_only -bind_at_load -bundle -bundle_loader @gol
443 -client_name -compatibility_version -current_version @gol
444 -dependency-file -dylib_file -dylinker_install_name @gol
445 -dynamic -dynamiclib -exported_symbols_list @gol
446 -filelist -flat_namespace -force_cpusubtype_ALL @gol
447 -force_flat_namespace -headerpad_max_install_names @gol
448 -image_base -init -install_name -keep_private_externs @gol
449 -multi_module -multiply_defined -multiply_defined_unused @gol
450 -noall_load -nomultidefs -noprebind -noseglinkedit @gol
451 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
452 -private_bundle -read_only_relocs -sectalign @gol
453 -sectobjectsymbols -whyload -seg1addr @gol
454 -sectcreate -sectobjectsymbols -sectorder @gol
455 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
456 -segprot -segs_read_only_addr -segs_read_write_addr @gol
457 -single_module -static -sub_library -sub_umbrella @gol
458 -twolevel_namespace -umbrella -undefined @gol
459 -unexported_symbols_list -weak_reference_mismatches @gol
463 @gccoptlist{-mcall-lib-mul -mfp-arg-in-fpregs -mfp-arg-in-gregs @gol
464 -mfull-fp-blocks -mhc-struct-return -min-line-mul @gol
465 -mminimum-fp-blocks -mnohc-struct-return}
468 @gccoptlist{-mabicalls -march=@var{cpu-type} -mtune=@var{cpu=type} @gol
469 -mcpu=@var{cpu-type} -membedded-data -muninit-const-in-rodata @gol
470 -membedded-pic -mfp32 -mfp64 -mfused-madd -mno-fused-madd @gol
471 -mgas -mgp32 -mgp64 -mhard-float -mint64 -mips1 @gol
472 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips64 @gol
473 -mlong64 -mlong32 -mlong-calls -mmemcpy @gol
474 -mmips-as -mmips-tfile -mno-abicalls @gol
475 -mno-embedded-data -mno-uninit-const-in-rodata @gol
476 -mno-embedded-pic -mno-long-calls @gol
477 -mno-memcpy -mno-mips-tfile -mno-rnames @gol
478 -mrnames -msoft-float @gol
479 -m4650 -msingle-float -mmad @gol
480 -EL -EB -G @var{num} -nocpp @gol
481 -mabi=32 -mabi=n32 -mabi=64 -mabi=eabi -mabi-fake-default @gol
482 -mfix7000 -mno-crt0 -mflush-func=@var{func} -mno-flush-func @gol
483 -mbranch-likely -mno-branch-likely}
485 @emph{i386 and x86-64 Options}
486 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
487 -mfpmath=@var{unit} @gol
488 -masm=@var{dialect} -mno-fancy-math-387 @gol
489 -mno-fp-ret-in-387 -msoft-float -msvr3-shlib @gol
490 -mno-wide-multiply -mrtd -malign-double @gol
491 -mpreferred-stack-boundary=@var{num} @gol
492 -mmmx -msse -msse2 -mpni -m3dnow @gol
493 -mthreads -mno-align-stringops -minline-all-stringops @gol
494 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
495 -m96bit-long-double -mregparm=@var{num} -momit-leaf-frame-pointer @gol
496 -mno-red-zone -mno-tls-direct-seg-refs @gol
497 -mcmodel=@var{code-model} @gol
501 @gccoptlist{-march=@var{architecture-type} @gol
502 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
503 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
504 -mjump-in-delay -mlinker-opt -mlong-calls @gol
505 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
506 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
507 -mno-jump-in-delay -mno-long-load-store @gol
508 -mno-portable-runtime -mno-soft-float @gol
509 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
510 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
511 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
512 -nolibdld -static -threads}
514 @emph{Intel 960 Options}
515 @gccoptlist{-m@var{cpu-type} -masm-compat -mclean-linkage @gol
516 -mcode-align -mcomplex-addr -mleaf-procedures @gol
517 -mic-compat -mic2.0-compat -mic3.0-compat @gol
518 -mintel-asm -mno-clean-linkage -mno-code-align @gol
519 -mno-complex-addr -mno-leaf-procedures @gol
520 -mno-old-align -mno-strict-align -mno-tail-call @gol
521 -mnumerics -mold-align -msoft-float -mstrict-align @gol
524 @emph{DEC Alpha Options}
525 @gccoptlist{-mno-fp-regs -msoft-float -malpha-as -mgas @gol
526 -mieee -mieee-with-inexact -mieee-conformant @gol
527 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
528 -mtrap-precision=@var{mode} -mbuild-constants @gol
529 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
530 -mbwx -mmax -mfix -mcix @gol
531 -mfloat-vax -mfloat-ieee @gol
532 -mexplicit-relocs -msmall-data -mlarge-data @gol
533 -msmall-text -mlarge-text @gol
534 -mmemory-latency=@var{time}}
536 @emph{DEC Alpha/VMS Options}
537 @gccoptlist{-mvms-return-codes}
539 @emph{H8/300 Options}
540 @gccoptlist{-mrelax -mh -ms -mn -mint32 -malign-300}
543 @gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol
544 -m4-nofpu -m4-single-only -m4-single -m4 @gol
545 -m5-64media -m5-64media-nofpu @gol
546 -m5-32media -m5-32media-nofpu @gol
547 -m5-compact -m5-compact-nofpu @gol
548 -mb -ml -mdalign -mrelax @gol
549 -mbigtable -mfmovd -mhitachi -mnomacsave @gol
550 -mieee -misize -mpadstruct -mspace @gol
551 -mprefergot -musermode}
553 @emph{System V Options}
554 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
557 @gccoptlist{-EB -EL @gol
558 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
559 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
561 @emph{TMS320C3x/C4x Options}
562 @gccoptlist{-mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol
563 -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol
564 -mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol
565 -mparallel-insns -mparallel-mpy -mpreserve-float}
568 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
569 -mprolog-function -mno-prolog-function -mspace @gol
570 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
571 -mapp-regs -mno-app-regs @gol
572 -mdisable-callt -mno-disable-callt @gol
577 @gccoptlist{-m32032 -m32332 -m32532 -m32081 -m32381 @gol
578 -mmult-add -mnomult-add -msoft-float -mrtd -mnortd @gol
579 -mregparam -mnoregparam -msb -mnosb @gol
580 -mbitfield -mnobitfield -mhimem -mnohimem}
583 @gccoptlist{-mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
584 -mcall-prologues -mno-tablejump -mtiny-stack}
587 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
588 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
589 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
590 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
591 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
594 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
595 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
596 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
597 -mno-base-addresses -msingle-exit -mno-single-exit}
600 @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
601 -mvolatile-asm-stop -mb-step -mregister-names -mno-sdata @gol
602 -mconstant-gp -mauto-pic -minline-float-divide-min-latency @gol
603 -minline-float-divide-max-throughput @gol
604 -minline-int-divide-min-latency @gol
605 -minline-int-divide-max-throughput -mno-dwarf2-asm @gol
606 -mfixed-range=@var{register-range}}
609 @gccoptlist{-mextmem -mextmemory -monchip -mno-asm-optimize @gol
610 -masm-optimize -mbranch-cost=@var{n} -mcond-exec=@var{n}}
612 @emph{S/390 and zSeries Options}
613 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
614 -mhard-float -msoft-float -mbackchain -mno-backchain @gol
615 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
616 -m64 -m31 -mdebug -mno-debug -mesa -mzarch}
619 @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
620 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
621 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
622 -mstack-align -mdata-align -mconst-align @gol
623 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
624 -melf -maout -melinux -mlinux -sim -sim2}
626 @emph{PDP-11 Options}
627 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
628 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
629 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
630 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
631 -mbranch-expensive -mbranch-cheap @gol
632 -msplit -mno-split -munix-asm -mdec-asm}
634 @emph{Xstormy16 Options}
637 @emph{Xtensa Options}
638 @gccoptlist{-mbig-endian -mlittle-endian @gol
639 -mdensity -mno-density @gol
640 -mconst16 -mno-const16 @gol
642 -maddx -mno-addx @gol
643 -mmac16 -mno-mac16 @gol
644 -mmul16 -mno-mul16 @gol
645 -mmul32 -mno-mul32 @gol
647 -mminmax -mno-minmax @gol
648 -msext -mno-sext @gol
649 -mbooleans -mno-booleans @gol
650 -mhard-float -msoft-float @gol
651 -mfused-madd -mno-fused-madd @gol
652 -mtext-section-literals -mno-text-section-literals @gol
653 -mtarget-align -mno-target-align @gol
654 -mlongcalls -mno-longcalls}
657 @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
658 -mhard-float -msoft-float @gol
659 -malloc-cc -mfixed-cc -mdword -mno-dword @gol
660 -mdouble -mno-double @gol
661 -mmedia -mno-media -mmuladd -mno-muladd @gol
662 -mlibrary-pic -macc-4 -macc-8 @gol
663 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
664 -mscc -mno-scc -mcond-exec -mno-cond-exec @gol
665 -mvliw-branch -mno-vliw-branch @gol
666 -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
667 -mno-nested-cond-exec -mtomcat-stats @gol
670 @item Code Generation Options
671 @xref{Code Gen Options,,Options for Code Generation Conventions}.
672 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
673 -ffixed-@var{reg} -fexceptions @gol
674 -fnon-call-exceptions -funwind-tables @gol
675 -fasynchronous-unwind-tables @gol
676 -finhibit-size-directive -finstrument-functions @gol
677 -fno-common -fno-ident -fno-gnu-linker @gol
678 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
679 -freg-struct-return -fshared-data -fshort-enums @gol
680 -fshort-double -fshort-wchar @gol
681 -fverbose-asm -fpack-struct -fstack-check @gol
682 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
683 -fargument-alias -fargument-noalias @gol
684 -fargument-noalias-global -fleading-underscore @gol
685 -ftls-model=@var{model} @gol
686 -ftrapv -fwrapv -fbounds-check}
690 * Overall Options:: Controlling the kind of output:
691 an executable, object files, assembler files,
692 or preprocessed source.
693 * C Dialect Options:: Controlling the variant of C language compiled.
694 * C++ Dialect Options:: Variations on C++.
695 * Objective-C Dialect Options:: Variations on Objective-C.
696 * Language Independent Options:: Controlling how diagnostics should be
698 * Warning Options:: How picky should the compiler be?
699 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
700 * Optimize Options:: How much optimization?
701 * Preprocessor Options:: Controlling header files and macro definitions.
702 Also, getting dependency information for Make.
703 * Assembler Options:: Passing options to the assembler.
704 * Link Options:: Specifying libraries and so on.
705 * Directory Options:: Where to find header files and libraries.
706 Where to find the compiler executable files.
707 * Spec Files:: How to pass switches to sub-processes.
708 * Target Options:: Running a cross-compiler, or an old version of GCC.
711 @node Overall Options
712 @section Options Controlling the Kind of Output
714 Compilation can involve up to four stages: preprocessing, compilation
715 proper, assembly and linking, always in that order. GCC is capable of
716 preprocessing and compiling several files either into several
717 assembler input files, or into one assembler input file; then each
718 assembler input file produces an object file, and linking combines all
719 the object files (those newly compiled, and those specified as input)
720 into an executable file.
722 @cindex file name suffix
723 For any given input file, the file name suffix determines what kind of
728 C source code which must be preprocessed.
731 C source code which should not be preprocessed.
734 C++ source code which should not be preprocessed.
737 Objective-C source code. Note that you must link with the library
738 @file{libobjc.a} to make an Objective-C program work.
741 Objective-C source code which should not be preprocessed.
744 C or C++ header file to be turned into a precompiled header.
748 @itemx @var{file}.cxx
749 @itemx @var{file}.cpp
750 @itemx @var{file}.CPP
751 @itemx @var{file}.c++
753 C++ source code which must be preprocessed. Note that in @samp{.cxx},
754 the last two letters must both be literally @samp{x}. Likewise,
755 @samp{.C} refers to a literal capital C@.
759 C++ header file to be turned into a precompiled header.
762 @itemx @var{file}.for
763 @itemx @var{file}.FOR
764 Fortran source code which should not be preprocessed.
767 @itemx @var{file}.fpp
768 @itemx @var{file}.FPP
769 Fortran source code which must be preprocessed (with the traditional
773 Fortran source code which must be preprocessed with a RATFOR
774 preprocessor (not included with GCC)@.
776 @xref{Overall Options,,Options Controlling the Kind of Output, g77,
777 Using and Porting GNU Fortran}, for more details of the handling of
780 @c FIXME: Descriptions of Java file types.
787 Ada source code file which contains a library unit declaration (a
788 declaration of a package, subprogram, or generic, or a generic
789 instantiation), or a library unit renaming declaration (a package,
790 generic, or subprogram renaming declaration). Such files are also
793 @itemx @var{file}.adb
794 Ada source code file containing a library unit body (a subprogram or
795 package body). Such files are also called @dfn{bodies}.
797 @c GCC also knows about some suffixes for languages not yet included:
806 Assembler code which must be preprocessed.
809 An object file to be fed straight into linking.
810 Any file name with no recognized suffix is treated this way.
814 You can specify the input language explicitly with the @option{-x} option:
817 @item -x @var{language}
818 Specify explicitly the @var{language} for the following input files
819 (rather than letting the compiler choose a default based on the file
820 name suffix). This option applies to all following input files until
821 the next @option{-x} option. Possible values for @var{language} are:
823 c c-header cpp-output
824 c++ c++-header c++-cpp-output
825 objective-c objective-c-header objc-cpp-output
826 assembler assembler-with-cpp
828 f77 f77-cpp-input ratfor
834 Turn off any specification of a language, so that subsequent files are
835 handled according to their file name suffixes (as they are if @option{-x}
836 has not been used at all).
838 @item -pass-exit-codes
839 @opindex pass-exit-codes
840 Normally the @command{gcc} program will exit with the code of 1 if any
841 phase of the compiler returns a non-success return code. If you specify
842 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
843 numerically highest error produced by any phase that returned an error
847 If you only want some of the stages of compilation, you can use
848 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
849 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
850 @command{gcc} is to stop. Note that some combinations (for example,
851 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
856 Compile or assemble the source files, but do not link. The linking
857 stage simply is not done. The ultimate output is in the form of an
858 object file for each source file.
860 By default, the object file name for a source file is made by replacing
861 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
863 Unrecognized input files, not requiring compilation or assembly, are
868 Stop after the stage of compilation proper; do not assemble. The output
869 is in the form of an assembler code file for each non-assembler input
872 By default, the assembler file name for a source file is made by
873 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
875 Input files that don't require compilation are ignored.
879 Stop after the preprocessing stage; do not run the compiler proper. The
880 output is in the form of preprocessed source code, which is sent to the
883 Input files which don't require preprocessing are ignored.
885 @cindex output file option
888 Place output in file @var{file}. This applies regardless to whatever
889 sort of output is being produced, whether it be an executable file,
890 an object file, an assembler file or preprocessed C code.
892 If you specify @option{-o} when compiling more than one input file, or
893 you are producing an executable file as output, all the source files
894 on the command line will be compiled at once.
896 If @option{-o} is not specified, the default is to put an executable file
897 in @file{a.out}, the object file for @file{@var{source}.@var{suffix}} in
898 @file{@var{source}.o}, its assembler file in @file{@var{source}.s}, and
899 all preprocessed C source on standard output.
903 Print (on standard error output) the commands executed to run the stages
904 of compilation. Also print the version number of the compiler driver
905 program and of the preprocessor and the compiler proper.
909 Like @option{-v} except the commands are not executed and all command
910 arguments are quoted. This is useful for shell scripts to capture the
911 driver-generated command lines.
915 Use pipes rather than temporary files for communication between the
916 various stages of compilation. This fails to work on some systems where
917 the assembler is unable to read from a pipe; but the GNU assembler has
922 Print (on the standard output) a description of the command line options
923 understood by @command{gcc}. If the @option{-v} option is also specified
924 then @option{--help} will also be passed on to the various processes
925 invoked by @command{gcc}, so that they can display the command line options
926 they accept. If the @option{-Wextra} option is also specified then command
927 line options which have no documentation associated with them will also
932 Print (on the standard output) a description of target specific command
933 line options for each tool.
937 Display the version number and copyrights of the invoked GCC.
941 @section Compiling C++ Programs
943 @cindex suffixes for C++ source
944 @cindex C++ source file suffixes
945 C++ source files conventionally use one of the suffixes @samp{.C},
946 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
947 @samp{.cxx}; C++ header files often use @samp{.hh} or @samp{.H}; and
948 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
949 files with these names and compiles them as C++ programs even if you
950 call the compiler the same way as for compiling C programs (usually
951 with the name @command{gcc}).
955 However, C++ programs often require class libraries as well as a
956 compiler that understands the C++ language---and under some
957 circumstances, you might want to compile programs or header files from
958 standard input, or otherwise without a suffix that flags them as C++
959 programs. You might also like to precompile a C header file with a
960 @samp{.h} extension to be used in C++ compilations. @command{g++} is a
961 program that calls GCC with the default language set to C++, and
962 automatically specifies linking against the C++ library. On many
963 systems, @command{g++} is also installed with the name @command{c++}.
965 @cindex invoking @command{g++}
966 When you compile C++ programs, you may specify many of the same
967 command-line options that you use for compiling programs in any
968 language; or command-line options meaningful for C and related
969 languages; or options that are meaningful only for C++ programs.
970 @xref{C Dialect Options,,Options Controlling C Dialect}, for
971 explanations of options for languages related to C@.
972 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
973 explanations of options that are meaningful only for C++ programs.
975 @node C Dialect Options
976 @section Options Controlling C Dialect
977 @cindex dialect options
978 @cindex language dialect options
979 @cindex options, dialect
981 The following options control the dialect of C (or languages derived
982 from C, such as C++ and Objective-C) that the compiler accepts:
989 In C mode, support all ISO C90 programs. In C++ mode,
990 remove GNU extensions that conflict with ISO C++.
992 This turns off certain features of GCC that are incompatible with ISO
993 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
994 such as the @code{asm} and @code{typeof} keywords, and
995 predefined macros such as @code{unix} and @code{vax} that identify the
996 type of system you are using. It also enables the undesirable and
997 rarely used ISO trigraph feature. For the C compiler,
998 it disables recognition of C++ style @samp{//} comments as well as
999 the @code{inline} keyword.
1001 The alternate keywords @code{__asm__}, @code{__extension__},
1002 @code{__inline__} and @code{__typeof__} continue to work despite
1003 @option{-ansi}. You would not want to use them in an ISO C program, of
1004 course, but it is useful to put them in header files that might be included
1005 in compilations done with @option{-ansi}. Alternate predefined macros
1006 such as @code{__unix__} and @code{__vax__} are also available, with or
1007 without @option{-ansi}.
1009 The @option{-ansi} option does not cause non-ISO programs to be
1010 rejected gratuitously. For that, @option{-pedantic} is required in
1011 addition to @option{-ansi}. @xref{Warning Options}.
1013 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1014 option is used. Some header files may notice this macro and refrain
1015 from declaring certain functions or defining certain macros that the
1016 ISO standard doesn't call for; this is to avoid interfering with any
1017 programs that might use these names for other things.
1019 Functions which would normally be built in but do not have semantics
1020 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1021 functions with @option{-ansi} is used. @xref{Other Builtins,,Other
1022 built-in functions provided by GCC}, for details of the functions
1027 Determine the language standard. This option is currently only
1028 supported when compiling C or C++. A value for this option must be
1029 provided; possible values are
1034 ISO C90 (same as @option{-ansi}).
1036 @item iso9899:199409
1037 ISO C90 as modified in amendment 1.
1043 ISO C99. Note that this standard is not yet fully supported; see
1044 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1045 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1048 Default, ISO C90 plus GNU extensions (including some C99 features).
1052 ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
1053 this will become the default. The name @samp{gnu9x} is deprecated.
1056 The 1998 ISO C++ standard plus amendments.
1059 The same as @option{-std=c++98} plus GNU extensions. This is the
1060 default for C++ code.
1063 Even when this option is not specified, you can still use some of the
1064 features of newer standards in so far as they do not conflict with
1065 previous C standards. For example, you may use @code{__restrict__} even
1066 when @option{-std=c99} is not specified.
1068 The @option{-std} options specifying some version of ISO C have the same
1069 effects as @option{-ansi}, except that features that were not in ISO C90
1070 but are in the specified version (for example, @samp{//} comments and
1071 the @code{inline} keyword in ISO C99) are not disabled.
1073 @xref{Standards,,Language Standards Supported by GCC}, for details of
1074 these standard versions.
1076 @item -aux-info @var{filename}
1078 Output to the given filename prototyped declarations for all functions
1079 declared and/or defined in a translation unit, including those in header
1080 files. This option is silently ignored in any language other than C@.
1082 Besides declarations, the file indicates, in comments, the origin of
1083 each declaration (source file and line), whether the declaration was
1084 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1085 @samp{O} for old, respectively, in the first character after the line
1086 number and the colon), and whether it came from a declaration or a
1087 definition (@samp{C} or @samp{F}, respectively, in the following
1088 character). In the case of function definitions, a K&R-style list of
1089 arguments followed by their declarations is also provided, inside
1090 comments, after the declaration.
1094 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1095 keyword, so that code can use these words as identifiers. You can use
1096 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1097 instead. @option{-ansi} implies @option{-fno-asm}.
1099 In C++, this switch only affects the @code{typeof} keyword, since
1100 @code{asm} and @code{inline} are standard keywords. You may want to
1101 use the @option{-fno-gnu-keywords} flag instead, which has the same
1102 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1103 switch only affects the @code{asm} and @code{typeof} keywords, since
1104 @code{inline} is a standard keyword in ISO C99.
1107 @itemx -fno-builtin-@var{function}
1108 @opindex fno-builtin
1109 @cindex built-in functions
1110 Don't recognize built-in functions that do not begin with
1111 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1112 functions provided by GCC}, for details of the functions affected,
1113 including those which are not built-in functions when @option{-ansi} or
1114 @option{-std} options for strict ISO C conformance are used because they
1115 do not have an ISO standard meaning.
1117 GCC normally generates special code to handle certain built-in functions
1118 more efficiently; for instance, calls to @code{alloca} may become single
1119 instructions that adjust the stack directly, and calls to @code{memcpy}
1120 may become inline copy loops. The resulting code is often both smaller
1121 and faster, but since the function calls no longer appear as such, you
1122 cannot set a breakpoint on those calls, nor can you change the behavior
1123 of the functions by linking with a different library.
1125 With the @option{-fno-builtin-@var{function}} option
1126 only the built-in function @var{function} is
1127 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1128 function is named this is not built-in in this version of GCC, this
1129 option is ignored. There is no corresponding
1130 @option{-fbuiltin-@var{function}} option; if you wish to enable
1131 built-in functions selectively when using @option{-fno-builtin} or
1132 @option{-ffreestanding}, you may define macros such as:
1135 #define abs(n) __builtin_abs ((n))
1136 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1141 @cindex hosted environment
1143 Assert that compilation takes place in a hosted environment. This implies
1144 @option{-fbuiltin}. A hosted environment is one in which the
1145 entire standard library is available, and in which @code{main} has a return
1146 type of @code{int}. Examples are nearly everything except a kernel.
1147 This is equivalent to @option{-fno-freestanding}.
1149 @item -ffreestanding
1150 @opindex ffreestanding
1151 @cindex hosted environment
1153 Assert that compilation takes place in a freestanding environment. This
1154 implies @option{-fno-builtin}. A freestanding environment
1155 is one in which the standard library may not exist, and program startup may
1156 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1157 This is equivalent to @option{-fno-hosted}.
1159 @xref{Standards,,Language Standards Supported by GCC}, for details of
1160 freestanding and hosted environments.
1162 @item -fms-extensions
1163 @opindex fms-extensions
1164 Accept some non-standard constructs used in Microsoft header files.
1168 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1169 options for strict ISO C conformance) implies @option{-trigraphs}.
1171 @item -no-integrated-cpp
1172 @opindex no-integrated-cpp
1173 Performs a compilation in two passes: preprocessing and compiling. This
1174 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1175 @option{-B} option. The user supplied compilation step can then add in
1176 an additional preprocessing step after normal preprocessing but before
1177 compiling. The default is to use the integrated cpp (internal cpp)
1179 The semantics of this option will change if "cc1", "cc1plus", and
1180 "cc1obj" are merged.
1182 @cindex traditional C language
1183 @cindex C language, traditional
1185 @itemx -traditional-cpp
1186 @opindex traditional-cpp
1187 @opindex traditional
1188 Formerly, these options caused GCC to attempt to emulate a pre-standard
1189 C compiler. They are now only supported with the @option{-E} switch.
1190 The preprocessor continues to support a pre-standard mode. See the GNU
1191 CPP manual for details.
1193 @item -fcond-mismatch
1194 @opindex fcond-mismatch
1195 Allow conditional expressions with mismatched types in the second and
1196 third arguments. The value of such an expression is void. This option
1197 is not supported for C++.
1199 @item -funsigned-char
1200 @opindex funsigned-char
1201 Let the type @code{char} be unsigned, like @code{unsigned char}.
1203 Each kind of machine has a default for what @code{char} should
1204 be. It is either like @code{unsigned char} by default or like
1205 @code{signed char} by default.
1207 Ideally, a portable program should always use @code{signed char} or
1208 @code{unsigned char} when it depends on the signedness of an object.
1209 But many programs have been written to use plain @code{char} and
1210 expect it to be signed, or expect it to be unsigned, depending on the
1211 machines they were written for. This option, and its inverse, let you
1212 make such a program work with the opposite default.
1214 The type @code{char} is always a distinct type from each of
1215 @code{signed char} or @code{unsigned char}, even though its behavior
1216 is always just like one of those two.
1219 @opindex fsigned-char
1220 Let the type @code{char} be signed, like @code{signed char}.
1222 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1223 the negative form of @option{-funsigned-char}. Likewise, the option
1224 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1226 @item -fsigned-bitfields
1227 @itemx -funsigned-bitfields
1228 @itemx -fno-signed-bitfields
1229 @itemx -fno-unsigned-bitfields
1230 @opindex fsigned-bitfields
1231 @opindex funsigned-bitfields
1232 @opindex fno-signed-bitfields
1233 @opindex fno-unsigned-bitfields
1234 These options control whether a bit-field is signed or unsigned, when the
1235 declaration does not use either @code{signed} or @code{unsigned}. By
1236 default, such a bit-field is signed, because this is consistent: the
1237 basic integer types such as @code{int} are signed types.
1239 @item -fwritable-strings
1240 @opindex fwritable-strings
1241 Store string constants in the writable data segment and don't uniquize
1242 them. This is for compatibility with old programs which assume they can
1243 write into string constants.
1245 Writing into string constants is a very bad idea; ``constants'' should
1249 @node C++ Dialect Options
1250 @section Options Controlling C++ Dialect
1252 @cindex compiler options, C++
1253 @cindex C++ options, command line
1254 @cindex options, C++
1255 This section describes the command-line options that are only meaningful
1256 for C++ programs; but you can also use most of the GNU compiler options
1257 regardless of what language your program is in. For example, you
1258 might compile a file @code{firstClass.C} like this:
1261 g++ -g -frepo -O -c firstClass.C
1265 In this example, only @option{-frepo} is an option meant
1266 only for C++ programs; you can use the other options with any
1267 language supported by GCC@.
1269 Here is a list of options that are @emph{only} for compiling C++ programs:
1273 @item -fabi-version=@var{n}
1274 @opindex fabi-version
1275 Use version @var{n} of the C++ ABI. Version 1 is the version of the C++
1276 ABI that first appeared in G++ 3.2. Version 0 will always be the
1277 version that conforms most closely to the C++ ABI specification.
1278 Therefore, the ABI obtained using version 0 will change as ABI bugs are
1281 The default is version 1.
1283 @item -fno-access-control
1284 @opindex fno-access-control
1285 Turn off all access checking. This switch is mainly useful for working
1286 around bugs in the access control code.
1290 Check that the pointer returned by @code{operator new} is non-null
1291 before attempting to modify the storage allocated. This check is
1292 normally unnecessary because the C++ standard specifies that
1293 @code{operator new} will only return @code{0} if it is declared
1294 @samp{throw()}, in which case the compiler will always check the
1295 return value even without this option. In all other cases, when
1296 @code{operator new} has a non-empty exception specification, memory
1297 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1298 @samp{new (nothrow)}.
1300 @item -fconserve-space
1301 @opindex fconserve-space
1302 Put uninitialized or runtime-initialized global variables into the
1303 common segment, as C does. This saves space in the executable at the
1304 cost of not diagnosing duplicate definitions. If you compile with this
1305 flag and your program mysteriously crashes after @code{main()} has
1306 completed, you may have an object that is being destroyed twice because
1307 two definitions were merged.
1309 This option is no longer useful on most targets, now that support has
1310 been added for putting variables into BSS without making them common.
1312 @item -fno-const-strings
1313 @opindex fno-const-strings
1314 Give string constants type @code{char *} instead of type @code{const
1315 char *}. By default, G++ uses type @code{const char *} as required by
1316 the standard. Even if you use @option{-fno-const-strings}, you cannot
1317 actually modify the value of a string constant, unless you also use
1318 @option{-fwritable-strings}.
1320 This option might be removed in a future release of G++. For maximum
1321 portability, you should structure your code so that it works with
1322 string constants that have type @code{const char *}.
1324 @item -fno-elide-constructors
1325 @opindex fno-elide-constructors
1326 The C++ standard allows an implementation to omit creating a temporary
1327 which is only used to initialize another object of the same type.
1328 Specifying this option disables that optimization, and forces G++ to
1329 call the copy constructor in all cases.
1331 @item -fno-enforce-eh-specs
1332 @opindex fno-enforce-eh-specs
1333 Don't check for violation of exception specifications at runtime. This
1334 option violates the C++ standard, but may be useful for reducing code
1335 size in production builds, much like defining @samp{NDEBUG}. The compiler
1336 will still optimize based on the exception specifications.
1338 @item -fexternal-templates
1339 @opindex fexternal-templates
1341 Cause @samp{#pragma interface} and @samp{implementation} to apply to
1342 template instantiation; template instances are emitted or not according
1343 to the location of the template definition. @xref{Template
1344 Instantiation}, for more information.
1346 This option is deprecated.
1348 @item -falt-external-templates
1349 @opindex falt-external-templates
1350 Similar to @option{-fexternal-templates}, but template instances are
1351 emitted or not according to the place where they are first instantiated.
1352 @xref{Template Instantiation}, for more information.
1354 This option is deprecated.
1357 @itemx -fno-for-scope
1359 @opindex fno-for-scope
1360 If @option{-ffor-scope} is specified, the scope of variables declared in
1361 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1362 as specified by the C++ standard.
1363 If @option{-fno-for-scope} is specified, the scope of variables declared in
1364 a @i{for-init-statement} extends to the end of the enclosing scope,
1365 as was the case in old versions of G++, and other (traditional)
1366 implementations of C++.
1368 The default if neither flag is given to follow the standard,
1369 but to allow and give a warning for old-style code that would
1370 otherwise be invalid, or have different behavior.
1372 @item -fno-gnu-keywords
1373 @opindex fno-gnu-keywords
1374 Do not recognize @code{typeof} as a keyword, so that code can use this
1375 word as an identifier. You can use the keyword @code{__typeof__} instead.
1376 @option{-ansi} implies @option{-fno-gnu-keywords}.
1378 @item -fno-implicit-templates
1379 @opindex fno-implicit-templates
1380 Never emit code for non-inline templates which are instantiated
1381 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1382 @xref{Template Instantiation}, for more information.
1384 @item -fno-implicit-inline-templates
1385 @opindex fno-implicit-inline-templates
1386 Don't emit code for implicit instantiations of inline templates, either.
1387 The default is to handle inlines differently so that compiles with and
1388 without optimization will need the same set of explicit instantiations.
1390 @item -fno-implement-inlines
1391 @opindex fno-implement-inlines
1392 To save space, do not emit out-of-line copies of inline functions
1393 controlled by @samp{#pragma implementation}. This will cause linker
1394 errors if these functions are not inlined everywhere they are called.
1396 @item -fms-extensions
1397 @opindex fms-extensions
1398 Disable pedantic warnings about constructs used in MFC, such as implicit
1399 int and getting a pointer to member function via non-standard syntax.
1401 @item -fno-nonansi-builtins
1402 @opindex fno-nonansi-builtins
1403 Disable built-in declarations of functions that are not mandated by
1404 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1405 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1407 @item -fno-operator-names
1408 @opindex fno-operator-names
1409 Do not treat the operator name keywords @code{and}, @code{bitand},
1410 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1411 synonyms as keywords.
1413 @item -fno-optional-diags
1414 @opindex fno-optional-diags
1415 Disable diagnostics that the standard says a compiler does not need to
1416 issue. Currently, the only such diagnostic issued by G++ is the one for
1417 a name having multiple meanings within a class.
1420 @opindex fpermissive
1421 Downgrade some diagnostics about nonconformant code from errors to
1422 warnings. Thus, using @option{-fpermissive} will allow some
1423 nonconforming code to compile.
1427 Enable automatic template instantiation at link time. This option also
1428 implies @option{-fno-implicit-templates}. @xref{Template
1429 Instantiation}, for more information.
1433 Disable generation of information about every class with virtual
1434 functions for use by the C++ runtime type identification features
1435 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1436 of the language, you can save some space by using this flag. Note that
1437 exception handling uses the same information, but it will generate it as
1442 Emit statistics about front-end processing at the end of the compilation.
1443 This information is generally only useful to the G++ development team.
1445 @item -ftemplate-depth-@var{n}
1446 @opindex ftemplate-depth
1447 Set the maximum instantiation depth for template classes to @var{n}.
1448 A limit on the template instantiation depth is needed to detect
1449 endless recursions during template class instantiation. ANSI/ISO C++
1450 conforming programs must not rely on a maximum depth greater than 17.
1452 @item -fuse-cxa-atexit
1453 @opindex fuse-cxa-atexit
1454 Register destructors for objects with static storage duration with the
1455 @code{__cxa_atexit} function rather than the @code{atexit} function.
1456 This option is required for fully standards-compliant handling of static
1457 destructors, but will only work if your C library supports
1458 @code{__cxa_atexit}.
1462 Do not use weak symbol support, even if it is provided by the linker.
1463 By default, G++ will use weak symbols if they are available. This
1464 option exists only for testing, and should not be used by end-users;
1465 it will result in inferior code and has no benefits. This option may
1466 be removed in a future release of G++.
1470 Do not search for header files in the standard directories specific to
1471 C++, but do still search the other standard directories. (This option
1472 is used when building the C++ library.)
1475 In addition, these optimization, warning, and code generation options
1476 have meanings only for C++ programs:
1479 @item -fno-default-inline
1480 @opindex fno-default-inline
1481 Do not assume @samp{inline} for functions defined inside a class scope.
1482 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1483 functions will have linkage like inline functions; they just won't be
1486 @item -Wabi @r{(C++ only)}
1488 Warn when G++ generates code that is probably not compatible with the
1489 vendor-neutral C++ ABI. Although an effort has been made to warn about
1490 all such cases, there are probably some cases that are not warned about,
1491 even though G++ is generating incompatible code. There may also be
1492 cases where warnings are emitted even though the code that is generated
1495 You should rewrite your code to avoid these warnings if you are
1496 concerned about the fact that code generated by G++ may not be binary
1497 compatible with code generated by other compilers.
1499 The known incompatibilities at this point include:
1504 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1505 pack data into the same byte as a base class. For example:
1508 struct A @{ virtual void f(); int f1 : 1; @};
1509 struct B : public A @{ int f2 : 1; @};
1513 In this case, G++ will place @code{B::f2} into the same byte
1514 as@code{A::f1}; other compilers will not. You can avoid this problem
1515 by explicitly padding @code{A} so that its size is a multiple of the
1516 byte size on your platform; that will cause G++ and other compilers to
1517 layout @code{B} identically.
1520 Incorrect handling of tail-padding for virtual bases. G++ does not use
1521 tail padding when laying out virtual bases. For example:
1524 struct A @{ virtual void f(); char c1; @};
1525 struct B @{ B(); char c2; @};
1526 struct C : public A, public virtual B @{@};
1530 In this case, G++ will not place @code{B} into the tail-padding for
1531 @code{A}; other compilers will. You can avoid this problem by
1532 explicitly padding @code{A} so that its size is a multiple of its
1533 alignment (ignoring virtual base classes); that will cause G++ and other
1534 compilers to layout @code{C} identically.
1537 Incorrect handling of bit-fields with declared widths greater than that
1538 of their underlying types, when the bit-fields appear in a union. For
1542 union U @{ int i : 4096; @};
1546 Assuming that an @code{int} does not have 4096 bits, G++ will make the
1547 union too small by the number of bits in an @code{int}.
1550 Empty classes can be placed at incorrect offsets. For example:
1560 struct C : public B, public A @{@};
1564 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
1565 it should be placed at offset zero. G++ mistakenly believes that the
1566 @code{A} data member of @code{B} is already at offset zero.
1569 Names of template functions whose types involve @code{typename} or
1570 template template parameters can be mangled incorrectly.
1573 template <typename Q>
1574 void f(typename Q::X) @{@}
1576 template <template <typename> class Q>
1577 void f(typename Q<int>::X) @{@}
1581 Instantiations of these templates may be mangled incorrectly.
1585 @item -Wctor-dtor-privacy @r{(C++ only)}
1586 @opindex Wctor-dtor-privacy
1587 Warn when a class seems unusable because all the constructors or
1588 destructors in that class are private, and it has neither friends nor
1589 public static member functions.
1591 @item -Wnon-virtual-dtor @r{(C++ only)}
1592 @opindex Wnon-virtual-dtor
1593 Warn when a class appears to be polymorphic, thereby requiring a virtual
1594 destructor, yet it declares a non-virtual one.
1595 This warning is enabled by @option{-Wall}.
1597 @item -Wreorder @r{(C++ only)}
1599 @cindex reordering, warning
1600 @cindex warning for reordering of member initializers
1601 Warn when the order of member initializers given in the code does not
1602 match the order in which they must be executed. For instance:
1608 A(): j (0), i (1) @{ @}
1612 The compiler will rearrange the member initializers for @samp{i}
1613 and @samp{j} to match the declaration order of the members, emitting
1614 a warning to that effect. This warning is enabled by @option{-Wall}.
1617 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
1620 @item -Weffc++ @r{(C++ only)}
1622 Warn about violations of the following style guidelines from Scott Meyers'
1623 @cite{Effective C++} book:
1627 Item 11: Define a copy constructor and an assignment operator for classes
1628 with dynamically allocated memory.
1631 Item 12: Prefer initialization to assignment in constructors.
1634 Item 14: Make destructors virtual in base classes.
1637 Item 15: Have @code{operator=} return a reference to @code{*this}.
1640 Item 23: Don't try to return a reference when you must return an object.
1644 Also warn about violations of the following style guidelines from
1645 Scott Meyers' @cite{More Effective C++} book:
1649 Item 6: Distinguish between prefix and postfix forms of increment and
1650 decrement operators.
1653 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
1657 When selecting this option, be aware that the standard library
1658 headers do not obey all of these guidelines; use @samp{grep -v}
1659 to filter out those warnings.
1661 @item -Wno-deprecated @r{(C++ only)}
1662 @opindex Wno-deprecated
1663 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
1665 @item -Wno-non-template-friend @r{(C++ only)}
1666 @opindex Wno-non-template-friend
1667 Disable warnings when non-templatized friend functions are declared
1668 within a template. Since the advent of explicit template specification
1669 support in G++, if the name of the friend is an unqualified-id (i.e.,
1670 @samp{friend foo(int)}), the C++ language specification demands that the
1671 friend declare or define an ordinary, nontemplate function. (Section
1672 14.5.3). Before G++ implemented explicit specification, unqualified-ids
1673 could be interpreted as a particular specialization of a templatized
1674 function. Because this non-conforming behavior is no longer the default
1675 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
1676 check existing code for potential trouble spots and is on by default.
1677 This new compiler behavior can be turned off with
1678 @option{-Wno-non-template-friend} which keeps the conformant compiler code
1679 but disables the helpful warning.
1681 @item -Wold-style-cast @r{(C++ only)}
1682 @opindex Wold-style-cast
1683 Warn if an old-style (C-style) cast to a non-void type is used within
1684 a C++ program. The new-style casts (@samp{static_cast},
1685 @samp{reinterpret_cast}, and @samp{const_cast}) are less vulnerable to
1686 unintended effects and much easier to search for.
1688 @item -Woverloaded-virtual @r{(C++ only)}
1689 @opindex Woverloaded-virtual
1690 @cindex overloaded virtual fn, warning
1691 @cindex warning for overloaded virtual fn
1692 Warn when a function declaration hides virtual functions from a
1693 base class. For example, in:
1700 struct B: public A @{
1705 the @code{A} class version of @code{f} is hidden in @code{B}, and code
1713 will fail to compile.
1715 @item -Wno-pmf-conversions @r{(C++ only)}
1716 @opindex Wno-pmf-conversions
1717 Disable the diagnostic for converting a bound pointer to member function
1720 @item -Wsign-promo @r{(C++ only)}
1721 @opindex Wsign-promo
1722 Warn when overload resolution chooses a promotion from unsigned or
1723 enumeral type to a signed type, over a conversion to an unsigned type of
1724 the same size. Previous versions of G++ would try to preserve
1725 unsignedness, but the standard mandates the current behavior.
1727 @item -Wsynth @r{(C++ only)}
1729 @cindex warning for synthesized methods
1730 @cindex synthesized methods, warning
1731 Warn when G++'s synthesis behavior does not match that of cfront. For
1737 A& operator = (int);
1747 In this example, G++ will synthesize a default @samp{A& operator =
1748 (const A&);}, while cfront will use the user-defined @samp{operator =}.
1751 @node Objective-C Dialect Options
1752 @section Options Controlling Objective-C Dialect
1754 @cindex compiler options, Objective-C
1755 @cindex Objective-C options, command line
1756 @cindex options, Objective-C
1757 This section describes the command-line options that are only meaningful
1758 for Objective-C programs, but you can also use most of the GNU compiler
1759 options regardless of what language your program is in. For example,
1760 you might compile a file @code{some_class.m} like this:
1763 gcc -g -fgnu-runtime -O -c some_class.m
1767 In this example, @option{-fgnu-runtime} is an option meant only for
1768 Objective-C programs; you can use the other options with any language
1771 Here is a list of options that are @emph{only} for compiling Objective-C
1775 @item -fconstant-string-class=@var{class-name}
1776 @opindex fconstant-string-class
1777 Use @var{class-name} as the name of the class to instantiate for each
1778 literal string specified with the syntax @code{@@"@dots{}"}. The default
1779 class name is @code{NXConstantString}.
1782 @opindex fgnu-runtime
1783 Generate object code compatible with the standard GNU Objective-C
1784 runtime. This is the default for most types of systems.
1786 @item -fnext-runtime
1787 @opindex fnext-runtime
1788 Generate output compatible with the NeXT runtime. This is the default
1789 for NeXT-based systems, including Darwin and Mac OS X@. The macro
1790 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
1795 Dump interface declarations for all classes seen in the source file to a
1796 file named @file{@var{sourcename}.decl}.
1799 @opindex Wno-protocol
1800 If a class is declared to implement a protocol, a warning is issued for
1801 every method in the protocol that is not implemented by the class. The
1802 default behavior is to issue a warning for every method not explicitly
1803 implemented in the class, even if a method implementation is inherited
1804 from the superclass. If you use the @code{-Wno-protocol} option, then
1805 methods inherited from the superclass are considered to be implemented,
1806 and no warning is issued for them.
1810 Warn if multiple methods of different types for the same selector are
1811 found during compilation. The check is performed on the list of methods
1812 in the final stage of compilation. Additionally, a check is performed
1813 for each selector appearing in a @code{@@selector(@dots{})}
1814 expression, and a corresponding method for that selector has been found
1815 during compilation. Because these checks scan the method table only at
1816 the end of compilation, these warnings are not produced if the final
1817 stage of compilation is not reached, for example because an error is
1818 found during compilation, or because the @code{-fsyntax-only} option is
1821 @item -Wundeclared-selector
1822 @opindex Wundeclared-selector
1823 Warn if a @code{@@selector(@dots{})} expression referring to an
1824 undeclared selector is found. A selector is considered undeclared if no
1825 method with that name has been declared before the
1826 @code{@@selector(@dots{})} expression, either explicitly in an
1827 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
1828 an @code{@@implementation} section. This option always performs its
1829 checks as soon as a @code{@@selector(@dots{})} expression is found,
1830 while @code{-Wselector} only performs its checks in the final stage of
1831 compilation. This also enforces the coding style convention
1832 that methods and selectors must be declared before being used.
1834 @c not documented because only avail via -Wp
1835 @c @item -print-objc-runtime-info
1839 @node Language Independent Options
1840 @section Options to Control Diagnostic Messages Formatting
1841 @cindex options to control diagnostics formatting
1842 @cindex diagnostic messages
1843 @cindex message formatting
1845 Traditionally, diagnostic messages have been formatted irrespective of
1846 the output device's aspect (e.g.@: its width, @dots{}). The options described
1847 below can be used to control the diagnostic messages formatting
1848 algorithm, e.g.@: how many characters per line, how often source location
1849 information should be reported. Right now, only the C++ front end can
1850 honor these options. However it is expected, in the near future, that
1851 the remaining front ends would be able to digest them correctly.
1854 @item -fmessage-length=@var{n}
1855 @opindex fmessage-length
1856 Try to format error messages so that they fit on lines of about @var{n}
1857 characters. The default is 72 characters for @command{g++} and 0 for the rest of
1858 the front ends supported by GCC@. If @var{n} is zero, then no
1859 line-wrapping will be done; each error message will appear on a single
1862 @opindex fdiagnostics-show-location
1863 @item -fdiagnostics-show-location=once
1864 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
1865 reporter to emit @emph{once} source location information; that is, in
1866 case the message is too long to fit on a single physical line and has to
1867 be wrapped, the source location won't be emitted (as prefix) again,
1868 over and over, in subsequent continuation lines. This is the default
1871 @item -fdiagnostics-show-location=every-line
1872 Only meaningful in line-wrapping mode. Instructs the diagnostic
1873 messages reporter to emit the same source location information (as
1874 prefix) for physical lines that result from the process of breaking
1875 a message which is too long to fit on a single line.
1879 @node Warning Options
1880 @section Options to Request or Suppress Warnings
1881 @cindex options to control warnings
1882 @cindex warning messages
1883 @cindex messages, warning
1884 @cindex suppressing warnings
1886 Warnings are diagnostic messages that report constructions which
1887 are not inherently erroneous but which are risky or suggest there
1888 may have been an error.
1890 You can request many specific warnings with options beginning @samp{-W},
1891 for example @option{-Wimplicit} to request warnings on implicit
1892 declarations. Each of these specific warning options also has a
1893 negative form beginning @samp{-Wno-} to turn off warnings;
1894 for example, @option{-Wno-implicit}. This manual lists only one of the
1895 two forms, whichever is not the default.
1897 The following options control the amount and kinds of warnings produced
1898 by GCC; for further, language-specific options also refer to
1899 @ref{C++ Dialect Options} and @ref{Objective-C Dialect Options}.
1902 @cindex syntax checking
1904 @opindex fsyntax-only
1905 Check the code for syntax errors, but don't do anything beyond that.
1909 Issue all the warnings demanded by strict ISO C and ISO C++;
1910 reject all programs that use forbidden extensions, and some other
1911 programs that do not follow ISO C and ISO C++. For ISO C, follows the
1912 version of the ISO C standard specified by any @option{-std} option used.
1914 Valid ISO C and ISO C++ programs should compile properly with or without
1915 this option (though a rare few will require @option{-ansi} or a
1916 @option{-std} option specifying the required version of ISO C)@. However,
1917 without this option, certain GNU extensions and traditional C and C++
1918 features are supported as well. With this option, they are rejected.
1920 @option{-pedantic} does not cause warning messages for use of the
1921 alternate keywords whose names begin and end with @samp{__}. Pedantic
1922 warnings are also disabled in the expression that follows
1923 @code{__extension__}. However, only system header files should use
1924 these escape routes; application programs should avoid them.
1925 @xref{Alternate Keywords}.
1927 Some users try to use @option{-pedantic} to check programs for strict ISO
1928 C conformance. They soon find that it does not do quite what they want:
1929 it finds some non-ISO practices, but not all---only those for which
1930 ISO C @emph{requires} a diagnostic, and some others for which
1931 diagnostics have been added.
1933 A feature to report any failure to conform to ISO C might be useful in
1934 some instances, but would require considerable additional work and would
1935 be quite different from @option{-pedantic}. We don't have plans to
1936 support such a feature in the near future.
1938 Where the standard specified with @option{-std} represents a GNU
1939 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
1940 corresponding @dfn{base standard}, the version of ISO C on which the GNU
1941 extended dialect is based. Warnings from @option{-pedantic} are given
1942 where they are required by the base standard. (It would not make sense
1943 for such warnings to be given only for features not in the specified GNU
1944 C dialect, since by definition the GNU dialects of C include all
1945 features the compiler supports with the given option, and there would be
1946 nothing to warn about.)
1948 @item -pedantic-errors
1949 @opindex pedantic-errors
1950 Like @option{-pedantic}, except that errors are produced rather than
1955 Inhibit all warning messages.
1959 Inhibit warning messages about the use of @samp{#import}.
1961 @item -Wchar-subscripts
1962 @opindex Wchar-subscripts
1963 Warn if an array subscript has type @code{char}. This is a common cause
1964 of error, as programmers often forget that this type is signed on some
1969 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
1970 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
1974 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
1975 the arguments supplied have types appropriate to the format string
1976 specified, and that the conversions specified in the format string make
1977 sense. This includes standard functions, and others specified by format
1978 attributes (@pxref{Function Attributes}), in the @code{printf},
1979 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
1980 not in the C standard) families.
1982 The formats are checked against the format features supported by GNU
1983 libc version 2.2. These include all ISO C90 and C99 features, as well
1984 as features from the Single Unix Specification and some BSD and GNU
1985 extensions. Other library implementations may not support all these
1986 features; GCC does not support warning about features that go beyond a
1987 particular library's limitations. However, if @option{-pedantic} is used
1988 with @option{-Wformat}, warnings will be given about format features not
1989 in the selected standard version (but not for @code{strfmon} formats,
1990 since those are not in any version of the C standard). @xref{C Dialect
1991 Options,,Options Controlling C Dialect}.
1993 Since @option{-Wformat} also checks for null format arguments for
1994 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
1996 @option{-Wformat} is included in @option{-Wall}. For more control over some
1997 aspects of format checking, the options @option{-Wno-format-y2k},
1998 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
1999 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2000 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2002 @item -Wno-format-y2k
2003 @opindex Wno-format-y2k
2004 If @option{-Wformat} is specified, do not warn about @code{strftime}
2005 formats which may yield only a two-digit year.
2007 @item -Wno-format-extra-args
2008 @opindex Wno-format-extra-args
2009 If @option{-Wformat} is specified, do not warn about excess arguments to a
2010 @code{printf} or @code{scanf} format function. The C standard specifies
2011 that such arguments are ignored.
2013 Where the unused arguments lie between used arguments that are
2014 specified with @samp{$} operand number specifications, normally
2015 warnings are still given, since the implementation could not know what
2016 type to pass to @code{va_arg} to skip the unused arguments. However,
2017 in the case of @code{scanf} formats, this option will suppress the
2018 warning if the unused arguments are all pointers, since the Single
2019 Unix Specification says that such unused arguments are allowed.
2021 @item -Wno-format-zero-length
2022 @opindex Wno-format-zero-length
2023 If @option{-Wformat} is specified, do not warn about zero-length formats.
2024 The C standard specifies that zero-length formats are allowed.
2026 @item -Wformat-nonliteral
2027 @opindex Wformat-nonliteral
2028 If @option{-Wformat} is specified, also warn if the format string is not a
2029 string literal and so cannot be checked, unless the format function
2030 takes its format arguments as a @code{va_list}.
2032 @item -Wformat-security
2033 @opindex Wformat-security
2034 If @option{-Wformat} is specified, also warn about uses of format
2035 functions that represent possible security problems. At present, this
2036 warns about calls to @code{printf} and @code{scanf} functions where the
2037 format string is not a string literal and there are no format arguments,
2038 as in @code{printf (foo);}. This may be a security hole if the format
2039 string came from untrusted input and contains @samp{%n}. (This is
2040 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2041 in future warnings may be added to @option{-Wformat-security} that are not
2042 included in @option{-Wformat-nonliteral}.)
2046 Enable @option{-Wformat} plus format checks not included in
2047 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2048 -Wformat-nonliteral -Wformat-security}.
2052 Enable warning about passing a null pointer for arguments marked as
2053 requiring a non-null value by the @code{nonnull} function attribute.
2055 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2056 can be disabled with the @option{-Wno-nonnull} option.
2058 @item -Wimplicit-int
2059 @opindex Wimplicit-int
2060 Warn when a declaration does not specify a type.
2062 @item -Wimplicit-function-declaration
2063 @itemx -Werror-implicit-function-declaration
2064 @opindex Wimplicit-function-declaration
2065 @opindex Werror-implicit-function-declaration
2066 Give a warning (or error) whenever a function is used before being
2071 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2075 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
2076 function with external linkage, returning int, taking either zero
2077 arguments, two, or three arguments of appropriate types.
2079 @item -Wmissing-braces
2080 @opindex Wmissing-braces
2081 Warn if an aggregate or union initializer is not fully bracketed. In
2082 the following example, the initializer for @samp{a} is not fully
2083 bracketed, but that for @samp{b} is fully bracketed.
2086 int a[2][2] = @{ 0, 1, 2, 3 @};
2087 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2091 @opindex Wparentheses
2092 Warn if parentheses are omitted in certain contexts, such
2093 as when there is an assignment in a context where a truth value
2094 is expected, or when operators are nested whose precedence people
2095 often get confused about.
2097 Also warn about constructions where there may be confusion to which
2098 @code{if} statement an @code{else} branch belongs. Here is an example of
2113 In C, every @code{else} branch belongs to the innermost possible @code{if}
2114 statement, which in this example is @code{if (b)}. This is often not
2115 what the programmer expected, as illustrated in the above example by
2116 indentation the programmer chose. When there is the potential for this
2117 confusion, GCC will issue a warning when this flag is specified.
2118 To eliminate the warning, add explicit braces around the innermost
2119 @code{if} statement so there is no way the @code{else} could belong to
2120 the enclosing @code{if}. The resulting code would look like this:
2136 @item -Wsequence-point
2137 @opindex Wsequence-point
2138 Warn about code that may have undefined semantics because of violations
2139 of sequence point rules in the C standard.
2141 The C standard defines the order in which expressions in a C program are
2142 evaluated in terms of @dfn{sequence points}, which represent a partial
2143 ordering between the execution of parts of the program: those executed
2144 before the sequence point, and those executed after it. These occur
2145 after the evaluation of a full expression (one which is not part of a
2146 larger expression), after the evaluation of the first operand of a
2147 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
2148 function is called (but after the evaluation of its arguments and the
2149 expression denoting the called function), and in certain other places.
2150 Other than as expressed by the sequence point rules, the order of
2151 evaluation of subexpressions of an expression is not specified. All
2152 these rules describe only a partial order rather than a total order,
2153 since, for example, if two functions are called within one expression
2154 with no sequence point between them, the order in which the functions
2155 are called is not specified. However, the standards committee have
2156 ruled that function calls do not overlap.
2158 It is not specified when between sequence points modifications to the
2159 values of objects take effect. Programs whose behavior depends on this
2160 have undefined behavior; the C standard specifies that ``Between the
2161 previous and next sequence point an object shall have its stored value
2162 modified at most once by the evaluation of an expression. Furthermore,
2163 the prior value shall be read only to determine the value to be
2164 stored.''. If a program breaks these rules, the results on any
2165 particular implementation are entirely unpredictable.
2167 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
2168 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
2169 diagnosed by this option, and it may give an occasional false positive
2170 result, but in general it has been found fairly effective at detecting
2171 this sort of problem in programs.
2173 The present implementation of this option only works for C programs. A
2174 future implementation may also work for C++ programs.
2176 The C standard is worded confusingly, therefore there is some debate
2177 over the precise meaning of the sequence point rules in subtle cases.
2178 Links to discussions of the problem, including proposed formal
2179 definitions, may be found on our readings page, at
2180 @w{@uref{http://gcc.gnu.org/readings.html}}.
2183 @opindex Wreturn-type
2184 Warn whenever a function is defined with a return-type that defaults to
2185 @code{int}. Also warn about any @code{return} statement with no
2186 return-value in a function whose return-type is not @code{void}.
2188 For C++, a function without return type always produces a diagnostic
2189 message, even when @option{-Wno-return-type} is specified. The only
2190 exceptions are @samp{main} and functions defined in system headers.
2194 Warn whenever a @code{switch} statement has an index of enumeral type
2195 and lacks a @code{case} for one or more of the named codes of that
2196 enumeration. (The presence of a @code{default} label prevents this
2197 warning.) @code{case} labels outside the enumeration range also
2198 provoke warnings when this option is used.
2200 @item -Wswitch-default
2201 @opindex Wswitch-switch
2202 Warn whenever a @code{switch} statement does not have a @code{default}
2206 @opindex Wswitch-enum
2207 Warn whenever a @code{switch} statement has an index of enumeral type
2208 and lacks a @code{case} for one or more of the named codes of that
2209 enumeration. @code{case} labels outside the enumeration range also
2210 provoke warnings when this option is used.
2214 Warn if any trigraphs are encountered that might change the meaning of
2215 the program (trigraphs within comments are not warned about).
2217 @item -Wunused-function
2218 @opindex Wunused-function
2219 Warn whenever a static function is declared but not defined or a
2220 non\-inline static function is unused.
2222 @item -Wunused-label
2223 @opindex Wunused-label
2224 Warn whenever a label is declared but not used.
2226 To suppress this warning use the @samp{unused} attribute
2227 (@pxref{Variable Attributes}).
2229 @item -Wunused-parameter
2230 @opindex Wunused-parameter
2231 Warn whenever a function parameter is unused aside from its declaration.
2233 To suppress this warning use the @samp{unused} attribute
2234 (@pxref{Variable Attributes}).
2236 @item -Wunused-variable
2237 @opindex Wunused-variable
2238 Warn whenever a local variable or non-constant static variable is unused
2239 aside from its declaration
2241 To suppress this warning use the @samp{unused} attribute
2242 (@pxref{Variable Attributes}).
2244 @item -Wunused-value
2245 @opindex Wunused-value
2246 Warn whenever a statement computes a result that is explicitly not used.
2248 To suppress this warning cast the expression to @samp{void}.
2252 All the above @option{-Wunused} options combined.
2254 In order to get a warning about an unused function parameter, you must
2255 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
2256 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
2258 @item -Wuninitialized
2259 @opindex Wuninitialized
2260 Warn if an automatic variable is used without first being initialized or
2261 if a variable may be clobbered by a @code{setjmp} call.
2263 These warnings are possible only in optimizing compilation,
2264 because they require data flow information that is computed only
2265 when optimizing. If you don't specify @option{-O}, you simply won't
2268 These warnings occur only for variables that are candidates for
2269 register allocation. Therefore, they do not occur for a variable that
2270 is declared @code{volatile}, or whose address is taken, or whose size
2271 is other than 1, 2, 4 or 8 bytes. Also, they do not occur for
2272 structures, unions or arrays, even when they are in registers.
2274 Note that there may be no warning about a variable that is used only
2275 to compute a value that itself is never used, because such
2276 computations may be deleted by data flow analysis before the warnings
2279 These warnings are made optional because GCC is not smart
2280 enough to see all the reasons why the code might be correct
2281 despite appearing to have an error. Here is one example of how
2302 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
2303 always initialized, but GCC doesn't know this. Here is
2304 another common case:
2309 if (change_y) save_y = y, y = new_y;
2311 if (change_y) y = save_y;
2316 This has no bug because @code{save_y} is used only if it is set.
2318 @cindex @code{longjmp} warnings
2319 This option also warns when a non-volatile automatic variable might be
2320 changed by a call to @code{longjmp}. These warnings as well are possible
2321 only in optimizing compilation.
2323 The compiler sees only the calls to @code{setjmp}. It cannot know
2324 where @code{longjmp} will be called; in fact, a signal handler could
2325 call it at any point in the code. As a result, you may get a warning
2326 even when there is in fact no problem because @code{longjmp} cannot
2327 in fact be called at the place which would cause a problem.
2329 Some spurious warnings can be avoided if you declare all the functions
2330 you use that never return as @code{noreturn}. @xref{Function
2333 @item -Wunknown-pragmas
2334 @opindex Wunknown-pragmas
2335 @cindex warning for unknown pragmas
2336 @cindex unknown pragmas, warning
2337 @cindex pragmas, warning of unknown
2338 Warn when a #pragma directive is encountered which is not understood by
2339 GCC@. If this command line option is used, warnings will even be issued
2340 for unknown pragmas in system header files. This is not the case if
2341 the warnings were only enabled by the @option{-Wall} command line option.
2343 @item -Wstrict-aliasing
2344 @opindex Wstrict-aliasing
2345 This option is only active when @option{-fstrict-aliasing} is active.
2346 It warns about code which might break the strict aliasing rules that the
2347 compiler is using for optimization. The warning does not catch all
2348 cases, but does attempt to catch the more common pitfalls. It is
2349 included in @option{-Wall}.
2353 All of the above @samp{-W} options combined. This enables all the
2354 warnings about constructions that some users consider questionable, and
2355 that are easy to avoid (or modify to prevent the warning), even in
2356 conjunction with macros. This also enables some language-specific
2357 warnings described in @ref{C++ Dialect Options} and
2358 @ref{Objective-C Dialect Options}.
2361 The following @option{-W@dots{}} options are not implied by @option{-Wall}.
2362 Some of them warn about constructions that users generally do not
2363 consider questionable, but which occasionally you might wish to check
2364 for; others warn about constructions that are necessary or hard to avoid
2365 in some cases, and there is no simple way to modify the code to suppress
2372 (This option used to be called @option{-W}. The older name is still
2373 supported, but the newer name is more descriptive.) Print extra warning
2374 messages for these events:
2378 A function can return either with or without a value. (Falling
2379 off the end of the function body is considered returning without
2380 a value.) For example, this function would evoke such a
2394 An expression-statement or the left-hand side of a comma expression
2395 contains no side effects.
2396 To suppress the warning, cast the unused expression to void.
2397 For example, an expression such as @samp{x[i,j]} will cause a warning,
2398 but @samp{x[(void)i,j]} will not.
2401 An unsigned value is compared against zero with @samp{<} or @samp{>=}.
2404 A comparison like @samp{x<=y<=z} appears; this is equivalent to
2405 @samp{(x<=y ? 1 : 0) <= z}, which is a different interpretation from
2406 that of ordinary mathematical notation.
2409 Storage-class specifiers like @code{static} are not the first things in
2410 a declaration. According to the C Standard, this usage is obsolescent.
2413 The return type of a function has a type qualifier such as @code{const}.
2414 Such a type qualifier has no effect, since the value returned by a
2415 function is not an lvalue. (But don't warn about the GNU extension of
2416 @code{volatile void} return types. That extension will be warned about
2417 if @option{-pedantic} is specified.)
2420 If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
2424 A comparison between signed and unsigned values could produce an
2425 incorrect result when the signed value is converted to unsigned.
2426 (But don't warn if @option{-Wno-sign-compare} is also specified.)
2429 An aggregate has an initializer which does not initialize all members.
2430 For example, the following code would cause such a warning, because
2431 @code{x.h} would be implicitly initialized to zero:
2434 struct s @{ int f, g, h; @};
2435 struct s x = @{ 3, 4 @};
2439 A function parameter is declared without a type specifier in K&R-style
2447 An empty body occurs in an @samp{if} or @samp{else} statement.
2450 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2451 @samp{>}, or @samp{>=}.
2454 A variable might be changed by @samp{longjmp} or @samp{vfork}.
2457 Any of several floating-point events that often indicate errors, such as
2458 overflow, underflow, loss of precision, etc.
2460 @item @r{(C++ only)}
2461 An enumerator and a non-enumerator both appear in a conditional expression.
2463 @item @r{(C++ only)}
2464 A non-static reference or non-static @samp{const} member appears in a
2465 class without constructors.
2467 @item @r{(C++ only)}
2468 Ambiguous virtual bases.
2470 @item @r{(C++ only)}
2471 Subscripting an array which has been declared @samp{register}.
2473 @item @r{(C++ only)}
2474 Taking the address of a variable which has been declared @samp{register}.
2476 @item @r{(C++ only)}
2477 A base class is not initialized in a derived class' copy constructor.
2480 @item -Wno-div-by-zero
2481 @opindex Wno-div-by-zero
2482 @opindex Wdiv-by-zero
2483 Do not warn about compile-time integer division by zero. Floating point
2484 division by zero is not warned about, as it can be a legitimate way of
2485 obtaining infinities and NaNs.
2487 @item -Wsystem-headers
2488 @opindex Wsystem-headers
2489 @cindex warnings from system headers
2490 @cindex system headers, warnings from
2491 Print warning messages for constructs found in system header files.
2492 Warnings from system headers are normally suppressed, on the assumption
2493 that they usually do not indicate real problems and would only make the
2494 compiler output harder to read. Using this command line option tells
2495 GCC to emit warnings from system headers as if they occurred in user
2496 code. However, note that using @option{-Wall} in conjunction with this
2497 option will @emph{not} warn about unknown pragmas in system
2498 headers---for that, @option{-Wunknown-pragmas} must also be used.
2501 @opindex Wfloat-equal
2502 Warn if floating point values are used in equality comparisons.
2504 The idea behind this is that sometimes it is convenient (for the
2505 programmer) to consider floating-point values as approximations to
2506 infinitely precise real numbers. If you are doing this, then you need
2507 to compute (by analyzing the code, or in some other way) the maximum or
2508 likely maximum error that the computation introduces, and allow for it
2509 when performing comparisons (and when producing output, but that's a
2510 different problem). In particular, instead of testing for equality, you
2511 would check to see whether the two values have ranges that overlap; and
2512 this is done with the relational operators, so equality comparisons are
2515 @item -Wtraditional @r{(C only)}
2516 @opindex Wtraditional
2517 Warn about certain constructs that behave differently in traditional and
2518 ISO C@. Also warn about ISO C constructs that have no traditional C
2519 equivalent, and/or problematic constructs which should be avoided.
2523 Macro parameters that appear within string literals in the macro body.
2524 In traditional C macro replacement takes place within string literals,
2525 but does not in ISO C@.
2528 In traditional C, some preprocessor directives did not exist.
2529 Traditional preprocessors would only consider a line to be a directive
2530 if the @samp{#} appeared in column 1 on the line. Therefore
2531 @option{-Wtraditional} warns about directives that traditional C
2532 understands but would ignore because the @samp{#} does not appear as the
2533 first character on the line. It also suggests you hide directives like
2534 @samp{#pragma} not understood by traditional C by indenting them. Some
2535 traditional implementations would not recognize @samp{#elif}, so it
2536 suggests avoiding it altogether.
2539 A function-like macro that appears without arguments.
2542 The unary plus operator.
2545 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
2546 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
2547 constants.) Note, these suffixes appear in macros defined in the system
2548 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
2549 Use of these macros in user code might normally lead to spurious
2550 warnings, however gcc's integrated preprocessor has enough context to
2551 avoid warning in these cases.
2554 A function declared external in one block and then used after the end of
2558 A @code{switch} statement has an operand of type @code{long}.
2561 A non-@code{static} function declaration follows a @code{static} one.
2562 This construct is not accepted by some traditional C compilers.
2565 The ISO type of an integer constant has a different width or
2566 signedness from its traditional type. This warning is only issued if
2567 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
2568 typically represent bit patterns, are not warned about.
2571 Usage of ISO string concatenation is detected.
2574 Initialization of automatic aggregates.
2577 Identifier conflicts with labels. Traditional C lacks a separate
2578 namespace for labels.
2581 Initialization of unions. If the initializer is zero, the warning is
2582 omitted. This is done under the assumption that the zero initializer in
2583 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
2584 initializer warnings and relies on default initialization to zero in the
2588 Conversions by prototypes between fixed/floating point values and vice
2589 versa. The absence of these prototypes when compiling with traditional
2590 C would cause serious problems. This is a subset of the possible
2591 conversion warnings, for the full set use @option{-Wconversion}.
2594 Use of ISO C style function definitions. This warning intentionally is
2595 @emph{not} issued for prototype declarations or variadic functions
2596 because these ISO C features will appear in your code when using
2597 libiberty's traditional C compatibility macros, @code{PARAMS} and
2598 @code{VPARAMS}. This warning is also bypassed for nested functions
2599 because that feature is already a gcc extension and thus not relevant to
2600 traditional C compatibility.
2603 @item -Wdeclaration-after-statement @r{(C only)}
2604 @opindex Wdeclaration-after-statement
2605 Warn when a declaration is found after a statement in a block. This
2606 construct, known from C++, was introduced with ISO C99 and is by default
2607 allowed in GCC@. It is not supported by ISO C90 and was not supported by
2608 GCC versions before GCC 3.0. @xref{Mixed Declarations}.
2612 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
2614 @item -Wendif-labels
2615 @opindex Wendif-labels
2616 Warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
2620 Warn whenever a local variable shadows another local variable, parameter or
2621 global variable or whenever a built-in function is shadowed.
2623 @item -Wlarger-than-@var{len}
2624 @opindex Wlarger-than
2625 Warn whenever an object of larger than @var{len} bytes is defined.
2627 @item -Wpointer-arith
2628 @opindex Wpointer-arith
2629 Warn about anything that depends on the ``size of'' a function type or
2630 of @code{void}. GNU C assigns these types a size of 1, for
2631 convenience in calculations with @code{void *} pointers and pointers
2634 @item -Wbad-function-cast @r{(C only)}
2635 @opindex Wbad-function-cast
2636 Warn whenever a function call is cast to a non-matching type.
2637 For example, warn if @code{int malloc()} is cast to @code{anything *}.
2641 Warn whenever a pointer is cast so as to remove a type qualifier from
2642 the target type. For example, warn if a @code{const char *} is cast
2643 to an ordinary @code{char *}.
2646 @opindex Wcast-align
2647 Warn whenever a pointer is cast such that the required alignment of the
2648 target is increased. For example, warn if a @code{char *} is cast to
2649 an @code{int *} on machines where integers can only be accessed at
2650 two- or four-byte boundaries.
2652 @item -Wwrite-strings
2653 @opindex Wwrite-strings
2654 When compiling C, give string constants the type @code{const
2655 char[@var{length}]} so that
2656 copying the address of one into a non-@code{const} @code{char *}
2657 pointer will get a warning; when compiling C++, warn about the
2658 deprecated conversion from string constants to @code{char *}.
2659 These warnings will help you find at
2660 compile time code that can try to write into a string constant, but
2661 only if you have been very careful about using @code{const} in
2662 declarations and prototypes. Otherwise, it will just be a nuisance;
2663 this is why we did not make @option{-Wall} request these warnings.
2666 @opindex Wconversion
2667 Warn if a prototype causes a type conversion that is different from what
2668 would happen to the same argument in the absence of a prototype. This
2669 includes conversions of fixed point to floating and vice versa, and
2670 conversions changing the width or signedness of a fixed point argument
2671 except when the same as the default promotion.
2673 Also, warn if a negative integer constant expression is implicitly
2674 converted to an unsigned type. For example, warn about the assignment
2675 @code{x = -1} if @code{x} is unsigned. But do not warn about explicit
2676 casts like @code{(unsigned) -1}.
2678 @item -Wsign-compare
2679 @opindex Wsign-compare
2680 @cindex warning for comparison of signed and unsigned values
2681 @cindex comparison of signed and unsigned values, warning
2682 @cindex signed and unsigned values, comparison warning
2683 Warn when a comparison between signed and unsigned values could produce
2684 an incorrect result when the signed value is converted to unsigned.
2685 This warning is also enabled by @option{-Wextra}; to get the other warnings
2686 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
2688 @item -Waggregate-return
2689 @opindex Waggregate-return
2690 Warn if any functions that return structures or unions are defined or
2691 called. (In languages where you can return an array, this also elicits
2694 @item -Wstrict-prototypes @r{(C only)}
2695 @opindex Wstrict-prototypes
2696 Warn if a function is declared or defined without specifying the
2697 argument types. (An old-style function definition is permitted without
2698 a warning if preceded by a declaration which specifies the argument
2701 @item -Wmissing-prototypes @r{(C only)}
2702 @opindex Wmissing-prototypes
2703 Warn if a global function is defined without a previous prototype
2704 declaration. This warning is issued even if the definition itself
2705 provides a prototype. The aim is to detect global functions that fail
2706 to be declared in header files.
2708 @item -Wmissing-declarations @r{(C only)}
2709 @opindex Wmissing-declarations
2710 Warn if a global function is defined without a previous declaration.
2711 Do so even if the definition itself provides a prototype.
2712 Use this option to detect global functions that are not declared in
2715 @item -Wmissing-noreturn
2716 @opindex Wmissing-noreturn
2717 Warn about functions which might be candidates for attribute @code{noreturn}.
2718 Note these are only possible candidates, not absolute ones. Care should
2719 be taken to manually verify functions actually do not ever return before
2720 adding the @code{noreturn} attribute, otherwise subtle code generation
2721 bugs could be introduced. You will not get a warning for @code{main} in
2722 hosted C environments.
2724 @item -Wmissing-format-attribute
2725 @opindex Wmissing-format-attribute
2727 If @option{-Wformat} is enabled, also warn about functions which might be
2728 candidates for @code{format} attributes. Note these are only possible
2729 candidates, not absolute ones. GCC will guess that @code{format}
2730 attributes might be appropriate for any function that calls a function
2731 like @code{vprintf} or @code{vscanf}, but this might not always be the
2732 case, and some functions for which @code{format} attributes are
2733 appropriate may not be detected. This option has no effect unless
2734 @option{-Wformat} is enabled (possibly by @option{-Wall}).
2736 @item -Wno-multichar
2737 @opindex Wno-multichar
2739 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
2740 Usually they indicate a typo in the user's code, as they have
2741 implementation-defined values, and should not be used in portable code.
2743 @item -Wno-deprecated-declarations
2744 @opindex Wno-deprecated-declarations
2745 Do not warn about uses of functions, variables, and types marked as
2746 deprecated by using the @code{deprecated} attribute.
2747 (@pxref{Function Attributes}, @pxref{Variable Attributes},
2748 @pxref{Type Attributes}.)
2752 Warn if a structure is given the packed attribute, but the packed
2753 attribute has no effect on the layout or size of the structure.
2754 Such structures may be mis-aligned for little benefit. For
2755 instance, in this code, the variable @code{f.x} in @code{struct bar}
2756 will be misaligned even though @code{struct bar} does not itself
2757 have the packed attribute:
2764 @} __attribute__((packed));
2774 Warn if padding is included in a structure, either to align an element
2775 of the structure or to align the whole structure. Sometimes when this
2776 happens it is possible to rearrange the fields of the structure to
2777 reduce the padding and so make the structure smaller.
2779 @item -Wredundant-decls
2780 @opindex Wredundant-decls
2781 Warn if anything is declared more than once in the same scope, even in
2782 cases where multiple declaration is valid and changes nothing.
2784 @item -Wnested-externs @r{(C only)}
2785 @opindex Wnested-externs
2786 Warn if an @code{extern} declaration is encountered within a function.
2788 @item -Wunreachable-code
2789 @opindex Wunreachable-code
2790 Warn if the compiler detects that code will never be executed.
2792 This option is intended to warn when the compiler detects that at
2793 least a whole line of source code will never be executed, because
2794 some condition is never satisfied or because it is after a
2795 procedure that never returns.
2797 It is possible for this option to produce a warning even though there
2798 are circumstances under which part of the affected line can be executed,
2799 so care should be taken when removing apparently-unreachable code.
2801 For instance, when a function is inlined, a warning may mean that the
2802 line is unreachable in only one inlined copy of the function.
2804 This option is not made part of @option{-Wall} because in a debugging
2805 version of a program there is often substantial code which checks
2806 correct functioning of the program and is, hopefully, unreachable
2807 because the program does work. Another common use of unreachable
2808 code is to provide behavior which is selectable at compile-time.
2812 Warn if a function can not be inlined and it was declared as inline.
2813 Even with this option, the compiler will not warn about failures to
2814 inline functions declared in system headers.
2816 The compiler uses a variety of heuristics to determine whether or not
2817 to inline a function. For example, the compiler takes into account
2818 the size of the function being inlined and the the amount of inlining
2819 that has already been done in the current function. Therefore,
2820 seemingly insignificant changes in the source program can cause the
2821 warnings produced by @option{-Winline} to appear or disappear.
2823 @item -Wno-invalid-offsetof @r{(C++ only)}
2824 @opindex Wno-invalid-offsetof
2825 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
2826 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
2827 to a non-POD type is undefined. In existing C++ implementations,
2828 however, @samp{offsetof} typically gives meaningful results even when
2829 applied to certain kinds of non-POD types. (Such as a simple
2830 @samp{struct} that fails to be a POD type only by virtue of having a
2831 constructor.) This flag is for users who are aware that they are
2832 writing nonportable code and who have deliberately chosen to ignore the
2835 The restrictions on @samp{offsetof} may be relaxed in a future version
2836 of the C++ standard.
2839 @opindex Winvalid-pch
2840 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
2841 the search path but can't be used.
2845 @opindex Wno-long-long
2846 Warn if @samp{long long} type is used. This is default. To inhibit
2847 the warning messages, use @option{-Wno-long-long}. Flags
2848 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
2849 only when @option{-pedantic} flag is used.
2851 @item -Wdisabled-optimization
2852 @opindex Wdisabled-optimization
2853 Warn if a requested optimization pass is disabled. This warning does
2854 not generally indicate that there is anything wrong with your code; it
2855 merely indicates that GCC's optimizers were unable to handle the code
2856 effectively. Often, the problem is that your code is too big or too
2857 complex; GCC will refuse to optimize programs when the optimization
2858 itself is likely to take inordinate amounts of time.
2862 Make all warnings into errors.
2865 @node Debugging Options
2866 @section Options for Debugging Your Program or GCC
2867 @cindex options, debugging
2868 @cindex debugging information options
2870 GCC has various special options that are used for debugging
2871 either your program or GCC:
2876 Produce debugging information in the operating system's native format
2877 (stabs, COFF, XCOFF, or DWARF)@. GDB can work with this debugging
2880 On most systems that use stabs format, @option{-g} enables use of extra
2881 debugging information that only GDB can use; this extra information
2882 makes debugging work better in GDB but will probably make other debuggers
2884 refuse to read the program. If you want to control for certain whether
2885 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
2886 @option{-gxcoff+}, @option{-gxcoff}, @option{-gdwarf-1+}, @option{-gdwarf-1},
2887 or @option{-gvms} (see below).
2889 Unlike most other C compilers, GCC allows you to use @option{-g} with
2890 @option{-O}. The shortcuts taken by optimized code may occasionally
2891 produce surprising results: some variables you declared may not exist
2892 at all; flow of control may briefly move where you did not expect it;
2893 some statements may not be executed because they compute constant
2894 results or their values were already at hand; some statements may
2895 execute in different places because they were moved out of loops.
2897 Nevertheless it proves possible to debug optimized output. This makes
2898 it reasonable to use the optimizer for programs that might have bugs.
2900 The following options are useful when GCC is generated with the
2901 capability for more than one debugging format.
2905 Produce debugging information for use by GDB@. This means to use the
2906 most expressive format available (DWARF 2, stabs, or the native format
2907 if neither of those are supported), including GDB extensions if at all
2912 Produce debugging information in stabs format (if that is supported),
2913 without GDB extensions. This is the format used by DBX on most BSD
2914 systems. On MIPS, Alpha and System V Release 4 systems this option
2915 produces stabs debugging output which is not understood by DBX or SDB@.
2916 On System V Release 4 systems this option requires the GNU assembler.
2918 @item -feliminate-unused-debug-symbols
2919 @opindex feliminate-unused-debug-symbols
2920 Produce debugging information in stabs format (if that is supported),
2921 for only symbols that are actually used.
2925 Produce debugging information in stabs format (if that is supported),
2926 using GNU extensions understood only by the GNU debugger (GDB)@. The
2927 use of these extensions is likely to make other debuggers crash or
2928 refuse to read the program.
2932 Produce debugging information in COFF format (if that is supported).
2933 This is the format used by SDB on most System V systems prior to
2938 Produce debugging information in XCOFF format (if that is supported).
2939 This is the format used by the DBX debugger on IBM RS/6000 systems.
2943 Produce debugging information in XCOFF format (if that is supported),
2944 using GNU extensions understood only by the GNU debugger (GDB)@. The
2945 use of these extensions is likely to make other debuggers crash or
2946 refuse to read the program, and may cause assemblers other than the GNU
2947 assembler (GAS) to fail with an error.
2951 Produce debugging information in DWARF version 1 format (if that is
2952 supported). This is the format used by SDB on most System V Release 4
2955 This option is deprecated.
2959 Produce debugging information in DWARF version 1 format (if that is
2960 supported), using GNU extensions understood only by the GNU debugger
2961 (GDB)@. The use of these extensions is likely to make other debuggers
2962 crash or refuse to read the program.
2964 This option is deprecated.
2968 Produce debugging information in DWARF version 2 format (if that is
2969 supported). This is the format used by DBX on IRIX 6.
2973 Produce debugging information in VMS debug format (if that is
2974 supported). This is the format used by DEBUG on VMS systems.
2977 @itemx -ggdb@var{level}
2978 @itemx -gstabs@var{level}
2979 @itemx -gcoff@var{level}
2980 @itemx -gxcoff@var{level}
2981 @itemx -gvms@var{level}
2982 Request debugging information and also use @var{level} to specify how
2983 much information. The default level is 2.
2985 Level 1 produces minimal information, enough for making backtraces in
2986 parts of the program that you don't plan to debug. This includes
2987 descriptions of functions and external variables, but no information
2988 about local variables and no line numbers.
2990 Level 3 includes extra information, such as all the macro definitions
2991 present in the program. Some debuggers support macro expansion when
2992 you use @option{-g3}.
2994 Note that in order to avoid confusion between DWARF1 debug level 2,
2995 and DWARF2, neither @option{-gdwarf} nor @option{-gdwarf-2} accept
2996 a concatenated debug level. Instead use an additional @option{-g@var{level}}
2997 option to change the debug level for DWARF1 or DWARF2.
2999 @item -feliminate-dwarf2-dups
3000 @opindex feliminate-dwarf2-dups
3001 Compress DWARF2 debugging information by eliminating duplicated
3002 information about each symbol. This option only makes sense when
3003 generating DWARF2 debugging information with @option{-gdwarf-2}.
3005 @cindex @command{prof}
3008 Generate extra code to write profile information suitable for the
3009 analysis program @command{prof}. You must use this option when compiling
3010 the source files you want data about, and you must also use it when
3013 @cindex @command{gprof}
3016 Generate extra code to write profile information suitable for the
3017 analysis program @command{gprof}. You must use this option when compiling
3018 the source files you want data about, and you must also use it when
3023 Makes the compiler print out each function name as it is compiled, and
3024 print some statistics about each pass when it finishes.
3027 @opindex ftime-report
3028 Makes the compiler print some statistics about the time consumed by each
3029 pass when it finishes.
3032 @opindex fmem-report
3033 Makes the compiler print some statistics about permanent memory
3034 allocation when it finishes.
3036 @item -fprofile-arcs
3037 @opindex fprofile-arcs
3038 Add code so that program flow @dfn{arcs} are instrumented. During
3039 execution the program records how many times each branch and call is
3040 executed and how many times it is taken or returns. When the compiled
3041 program exits it saves this data to a file called
3042 @file{@var{auxname}.gcda} for each source file. The data may be used for
3043 profile-directed optimizations (@option{-fbranch-probabilities}), or for
3044 test coverage analysis (@option{-ftest-coverage}). Each object file's
3045 @var{auxname} is generated from the name of the output file, if
3046 explicitly specified and it is not the final executable, otherwise it is
3047 the basename of the source file. In both cases any suffix is removed
3048 (e.g. @file{foo.gcda} for input file @file{dir/foo.c}, or
3049 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
3054 Compile the source files with @option{-fprofile-arcs} plus optimization
3055 and code generation options. For test coverage analysis, use the
3056 additional @option{-ftest-coverage} option. You do not need to profile
3057 every source file in a program.
3060 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
3061 (the latter implies the former).
3064 Run the program on a representative workload to generate the arc profile
3065 information. This may be repeated any number of times. You can run
3066 concurrent instances of your program, and provided that the file system
3067 supports locking, the data files will be correctly updated. Also
3068 @code{fork} calls are detected and correctly handled (double counting
3072 For profile-directed optimizations, compile the source files again with
3073 the same optimization and code generation options plus
3074 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
3075 Control Optimization}).
3078 For test coverage analysis, use @command{gcov} to produce human readable
3079 information from the @file{.gcno} and @file{.gcda} files. Refer to the
3080 @command{gcov} documentation for further information.
3084 With @option{-fprofile-arcs}, for each function of your program GCC
3085 creates a program flow graph, then finds a spanning tree for the graph.
3086 Only arcs that are not on the spanning tree have to be instrumented: the
3087 compiler adds code to count the number of times that these arcs are
3088 executed. When an arc is the only exit or only entrance to a block, the
3089 instrumentation code can be added to the block; otherwise, a new basic
3090 block must be created to hold the instrumentation code.
3093 @item -ftest-coverage
3094 @opindex ftest-coverage
3095 Produce a notes file that the @command{gcov} code-coverage utility
3096 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
3097 show program coverage. Each source file's note file is called
3098 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
3099 above for a description of @var{auxname} and instructions on how to
3100 generate test coverage data. Coverage data will match the source files
3101 more closely, if you do not optimize.
3103 @item -d@var{letters}
3105 Says to make debugging dumps during compilation at times specified by
3106 @var{letters}. This is used for debugging the compiler. The file names
3107 for most of the dumps are made by appending a pass number and a word to
3108 the @var{dumpname}. @var{dumpname} is generated from the name of the
3109 output file, if explicitly specified and it is not an executable,
3110 otherwise it is the basename of the source file. In both cases any
3111 suffix is removed (e.g. @file{foo.00.rtl} or @file{foo.01.sibling}).
3112 Here are the possible letters for use in @var{letters}, and their
3118 Annotate the assembler output with miscellaneous debugging information.
3121 Dump after computing branch probabilities, to @file{@var{file}.16.bp}.
3124 Dump after block reordering, to @file{@var{file}.32.bbro}.
3127 Dump after instruction combination, to the file @file{@var{file}.22.combine}.
3130 Dump after the first if conversion, to the file @file{@var{file}.17.ce1}.
3131 Also dump after the second if conversion, to the file @file{@var{file}.23.ce2}.
3134 Dump after branch target load optimization, to to @file{@var{file}.34.btl}.
3135 Also dump after delayed branch scheduling, to @file{@var{file}.37.dbr}.
3138 Dump all macro definitions, at the end of preprocessing, in addition to
3142 Dump after SSA optimizations, to @file{@var{file}.05.ssa} and
3143 @file{@var{file}.010.ussa}.
3146 Dump after the second if conversion, to @file{@var{file}.33.ce3}.
3149 Dump after control and data flow analysis, to @file{@var{file}.15.cfg}.
3150 Also dump after life analysis, to @file{@var{file}.21.life}.
3153 Dump after purging @code{ADDRESSOF} codes, to @file{@var{file}.11.addressof}.
3156 Dump after global register allocation, to @file{@var{file}.27.greg}.
3159 Dump after GCSE, to @file{@var{file}.12.gcse}.
3160 Also dump after jump bypassing and control flow optimizations, to
3161 @file{@var{file}.14.bypass}.
3164 Dump after finalization of EH handling code, to @file{@var{file}.03.eh}.
3167 Dump after sibling call optimizations, to @file{@var{file}.02.sibling}.
3170 Dump after the first jump optimization, to @file{@var{file}.04.jump}.
3173 Dump after conversion from registers to stack, to @file{@var{file}.36.stack}.
3176 Dump after local register allocation, to @file{@var{file}.26.lreg}.
3179 Dump after loop optimization passes, to @file{@var{file}.13.loop} and
3180 @file{@var{file}.19.loop2}.
3183 Dump after performing the machine dependent reorganization pass, to
3184 @file{@var{file}.37.mach}.
3187 Dump after register renumbering, to @file{@var{file}.31.rnreg}.
3190 Dump after the register move pass, to @file{@var{file}.24.regmove}.
3193 Dump after post-reload optimizations, to @file{@var{file}.28.postreload}.
3196 Dump after RTL generation, to @file{@var{file}.01.rtl}.
3199 Dump after the second scheduling pass, to @file{@var{file}.35.sched2}.
3202 Dump after CSE (including the jump optimization that sometimes follows
3203 CSE), to @file{@var{file}.019.cse}.
3206 Dump after the first scheduling pass, to @file{@var{file}.25.sched}.
3209 Dump after the second CSE pass (including the jump optimization that
3210 sometimes follows CSE), to @file{@var{file}.20.cse2}.
3213 Dump after running tracer, to @file{@var{file}.18.tracer}.
3216 Dump after null pointer elimination pass to @file{@var{file}.018.null}.
3219 Dump callgraph and unit-at-a-time optimization @file{@var{file}.00.unit}.
3222 Dump after the second flow pass, to @file{@var{file}.29.flow2}.
3225 Dump after SSA conditional constant propagation, to
3226 @file{@var{file}.06.ssaccp}.
3229 Dump after SSA dead code elimination, to @file{@var{file}.07.ssadce}.
3232 Dump after the peephole pass, to @file{@var{file}.30.peephole2}.
3235 Produce all the dumps listed above.
3238 Produce a core dump whenever an error occurs.
3241 Print statistics on memory usage, at the end of the run, to
3245 Annotate the assembler output with a comment indicating which
3246 pattern and alternative was used. The length of each instruction is
3250 Dump the RTL in the assembler output as a comment before each instruction.
3251 Also turns on @option{-dp} annotation.
3254 For each of the other indicated dump files (except for
3255 @file{@var{file}.01.rtl}), dump a representation of the control flow graph
3256 suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
3259 Just generate RTL for a function instead of compiling it. Usually used
3263 Dump debugging information during parsing, to standard error.
3266 @item -fdump-unnumbered
3267 @opindex fdump-unnumbered
3268 When doing debugging dumps (see @option{-d} option above), suppress instruction
3269 numbers and line number note output. This makes it more feasible to
3270 use diff on debugging dumps for compiler invocations with different
3271 options, in particular with and without @option{-g}.
3273 @item -fdump-translation-unit @r{(C and C++ only)}
3274 @itemx -fdump-translation-unit-@var{options} @r{(C and C++ only)}
3275 @opindex fdump-translation-unit
3276 Dump a representation of the tree structure for the entire translation
3277 unit to a file. The file name is made by appending @file{.tu} to the
3278 source file name. If the @samp{-@var{options}} form is used, @var{options}
3279 controls the details of the dump as described for the
3280 @option{-fdump-tree} options.
3282 @item -fdump-class-hierarchy @r{(C++ only)}
3283 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
3284 @opindex fdump-class-hierarchy
3285 Dump a representation of each class's hierarchy and virtual function
3286 table layout to a file. The file name is made by appending @file{.class}
3287 to the source file name. If the @samp{-@var{options}} form is used,
3288 @var{options} controls the details of the dump as described for the
3289 @option{-fdump-tree} options.
3291 @item -fdump-tree-@var{switch} @r{(C++ only)}
3292 @itemx -fdump-tree-@var{switch}-@var{options} @r{(C++ only)}
3294 Control the dumping at various stages of processing the intermediate
3295 language tree to a file. The file name is generated by appending a switch
3296 specific suffix to the source file name. If the @samp{-@var{options}}
3297 form is used, @var{options} is a list of @samp{-} separated options that
3298 control the details of the dump. Not all options are applicable to all
3299 dumps, those which are not meaningful will be ignored. The following
3300 options are available
3304 Print the address of each node. Usually this is not meaningful as it
3305 changes according to the environment and source file. Its primary use
3306 is for tying up a dump file with a debug environment.
3308 Inhibit dumping of members of a scope or body of a function merely
3309 because that scope has been reached. Only dump such items when they
3310 are directly reachable by some other path.
3312 Turn on all options.
3315 The following tree dumps are possible:
3318 Dump before any tree based optimization, to @file{@var{file}.original}.
3320 Dump after all tree based optimization, to @file{@var{file}.optimized}.
3322 Dump after function inlining, to @file{@var{file}.inlined}.
3325 @item -frandom-seed=@var{string}
3326 @opindex frandom-string
3327 This option provides a seed that GCC uses when it would otherwise use
3328 random numbers. It is used to generate certain symbol names
3329 that have to be different in every compiled file. It is also used to
3330 place unique stamps in coverage data files and the object files that
3331 produce them. You can use the @option{-frandom-seed} option to produce
3332 reproducibly identical object files.
3334 The @var{string} should be different for every file you compile.
3336 @item -fsched-verbose=@var{n}
3337 @opindex fsched-verbose
3338 On targets that use instruction scheduling, this option controls the
3339 amount of debugging output the scheduler prints. This information is
3340 written to standard error, unless @option{-dS} or @option{-dR} is
3341 specified, in which case it is output to the usual dump
3342 listing file, @file{.sched} or @file{.sched2} respectively. However
3343 for @var{n} greater than nine, the output is always printed to standard
3346 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
3347 same information as @option{-dRS}. For @var{n} greater than one, it
3348 also output basic block probabilities, detailed ready list information
3349 and unit/insn info. For @var{n} greater than two, it includes RTL
3350 at abort point, control-flow and regions info. And for @var{n} over
3351 four, @option{-fsched-verbose} also includes dependence info.
3355 Store the usual ``temporary'' intermediate files permanently; place them
3356 in the current directory and name them based on the source file. Thus,
3357 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
3358 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
3359 preprocessed @file{foo.i} output file even though the compiler now
3360 normally uses an integrated preprocessor.
3364 Report the CPU time taken by each subprocess in the compilation
3365 sequence. For C source files, this is the compiler proper and assembler
3366 (plus the linker if linking is done). The output looks like this:
3373 The first number on each line is the ``user time,'' that is time spent
3374 executing the program itself. The second number is ``system time,''
3375 time spent executing operating system routines on behalf of the program.
3376 Both numbers are in seconds.
3378 @item -print-file-name=@var{library}
3379 @opindex print-file-name
3380 Print the full absolute name of the library file @var{library} that
3381 would be used when linking---and don't do anything else. With this
3382 option, GCC does not compile or link anything; it just prints the
3385 @item -print-multi-directory
3386 @opindex print-multi-directory
3387 Print the directory name corresponding to the multilib selected by any
3388 other switches present in the command line. This directory is supposed
3389 to exist in @env{GCC_EXEC_PREFIX}.
3391 @item -print-multi-lib
3392 @opindex print-multi-lib
3393 Print the mapping from multilib directory names to compiler switches
3394 that enable them. The directory name is separated from the switches by
3395 @samp{;}, and each switch starts with an @samp{@@} instead of the
3396 @samp{-}, without spaces between multiple switches. This is supposed to
3397 ease shell-processing.
3399 @item -print-prog-name=@var{program}
3400 @opindex print-prog-name
3401 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
3403 @item -print-libgcc-file-name
3404 @opindex print-libgcc-file-name
3405 Same as @option{-print-file-name=libgcc.a}.
3407 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
3408 but you do want to link with @file{libgcc.a}. You can do
3411 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
3414 @item -print-search-dirs
3415 @opindex print-search-dirs
3416 Print the name of the configured installation directory and a list of
3417 program and library directories gcc will search---and don't do anything else.
3419 This is useful when gcc prints the error message
3420 @samp{installation problem, cannot exec cpp0: No such file or directory}.
3421 To resolve this you either need to put @file{cpp0} and the other compiler
3422 components where gcc expects to find them, or you can set the environment
3423 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
3424 Don't forget the trailing '/'.
3425 @xref{Environment Variables}.
3428 @opindex dumpmachine
3429 Print the compiler's target machine (for example,
3430 @samp{i686-pc-linux-gnu})---and don't do anything else.
3433 @opindex dumpversion
3434 Print the compiler version (for example, @samp{3.0})---and don't do
3439 Print the compiler's built-in specs---and don't do anything else. (This
3440 is used when GCC itself is being built.) @xref{Spec Files}.
3442 @item -feliminate-unused-debug-types
3443 @opindex feliminate-unused-debug-types
3444 Normally, when producing DWARF2 output, GCC will emit debugging
3445 information for all types declared in a compilation
3446 unit, regardless of whether or not they are actually used
3447 in that compilation unit. Sometimes this is useful, such as
3448 if, in the debugger, you want to cast a value to a type that is
3449 not actually used in your program (but is declared). More often,
3450 however, this results in a significant amount of wasted space.
3451 With this option, GCC will avoid producing debug symbol output
3452 for types that are nowhere used in the source file being compiled.
3455 @node Optimize Options
3456 @section Options That Control Optimization
3457 @cindex optimize options
3458 @cindex options, optimization
3460 These options control various sorts of optimizations.
3462 Without any optimization option, the compiler's goal is to reduce the
3463 cost of compilation and to make debugging produce the expected
3464 results. Statements are independent: if you stop the program with a
3465 breakpoint between statements, you can then assign a new value to any
3466 variable or change the program counter to any other statement in the
3467 function and get exactly the results you would expect from the source
3470 Turning on optimization flags makes the compiler attempt to improve
3471 the performance and/or code size at the expense of compilation time
3472 and possibly the ability to debug the program.
3474 The compiler performs optimisation based on the knowledge it has of
3475 the program. Using the @option{-funit-at-a-time} flag will allow the
3476 compiler to consider information gained from later functions in the
3477 file when compiling a function. Compiling multiple files at once to a
3478 single output file (and using @option{-funit-at-a-time}) will allow
3479 the compiler to use information gained from all of the files when
3480 compiling each of them.
3482 Not all optimizations are controlled directly by a flag. Only
3483 optimizations that have a flag are listed.
3490 Optimize. Optimizing compilation takes somewhat more time, and a lot
3491 more memory for a large function.
3493 With @option{-O}, the compiler tries to reduce code size and execution
3494 time, without performing any optimizations that take a great deal of
3497 @option{-O} turns on the following optimization flags:
3498 @gccoptlist{-fdefer-pop @gol
3499 -fmerge-constants @gol
3501 -floop-optimize @gol
3503 -fif-conversion @gol
3504 -fif-conversion2 @gol
3505 -fdelayed-branch @gol
3506 -fguess-branch-probability @gol
3509 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
3510 where doing so does not interfere with debugging.
3514 Optimize even more. GCC performs nearly all supported optimizations
3515 that do not involve a space-speed tradeoff. The compiler does not
3516 perform loop unrolling or function inlining when you specify @option{-O2}.
3517 As compared to @option{-O}, this option increases both compilation time
3518 and the performance of the generated code.
3520 @option{-O2} turns on all optimization flags specified by @option{-O}. It
3521 also turns on the following optimization flags:
3522 @gccoptlist{-fforce-mem @gol
3523 -foptimize-sibling-calls @gol
3524 -fstrength-reduce @gol
3525 -fcse-follow-jumps -fcse-skip-blocks @gol
3526 -frerun-cse-after-loop -frerun-loop-opt @gol
3527 -fgcse -fgcse-lm -fgcse-sm @gol
3528 -fdelete-null-pointer-checks @gol
3529 -fexpensive-optimizations @gol
3531 -fschedule-insns -fschedule-insns2 @gol
3532 -fsched-interblock -fsched-spec @gol
3535 -freorder-blocks -freorder-functions @gol
3536 -fstrict-aliasing @gol
3537 -falign-functions -falign-jumps @gol
3538 -falign-loops -falign-labels}
3540 Please note the warning under @option{-fgcse} about
3541 invoking @option{-O2} on programs that use computed gotos.
3545 Optimize yet more. @option{-O3} turns on all optimizations specified by
3546 @option{-O2} and also turns on the @option{-finline-functions},
3547 @option{-funit-at-a-time} and @option{-frename-registers} options.
3551 Do not optimize. This is the default.
3555 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
3556 do not typically increase code size. It also performs further
3557 optimizations designed to reduce code size.
3559 @option{-Os} disables the following optimization flags:
3560 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
3561 -falign-labels -freorder-blocks -fprefetch-loop-arrays}
3563 If you use multiple @option{-O} options, with or without level numbers,
3564 the last such option is the one that is effective.
3567 Options of the form @option{-f@var{flag}} specify machine-independent
3568 flags. Most flags have both positive and negative forms; the negative
3569 form of @option{-ffoo} would be @option{-fno-foo}. In the table
3570 below, only one of the forms is listed---the one you typically will
3571 use. You can figure out the other form by either removing @samp{no-}
3574 The following options control specific optimizations. They are either
3575 activated by @option{-O} options or are related to ones that are. You
3576 can use the following flags in the rare cases when ``fine-tuning'' of
3577 optimizations to be performed is desired.
3580 @item -fno-default-inline
3581 @opindex fno-default-inline
3582 Do not make member functions inline by default merely because they are
3583 defined inside the class scope (C++ only). Otherwise, when you specify
3584 @w{@option{-O}}, member functions defined inside class scope are compiled
3585 inline by default; i.e., you don't need to add @samp{inline} in front of
3586 the member function name.
3588 @item -fno-defer-pop
3589 @opindex fno-defer-pop
3590 Always pop the arguments to each function call as soon as that function
3591 returns. For machines which must pop arguments after a function call,
3592 the compiler normally lets arguments accumulate on the stack for several
3593 function calls and pops them all at once.
3595 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3599 Force memory operands to be copied into registers before doing
3600 arithmetic on them. This produces better code by making all memory
3601 references potential common subexpressions. When they are not common
3602 subexpressions, instruction combination should eliminate the separate
3605 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3608 @opindex fforce-addr
3609 Force memory address constants to be copied into registers before
3610 doing arithmetic on them. This may produce better code just as
3611 @option{-fforce-mem} may.
3613 @item -fomit-frame-pointer
3614 @opindex fomit-frame-pointer
3615 Don't keep the frame pointer in a register for functions that
3616 don't need one. This avoids the instructions to save, set up and
3617 restore frame pointers; it also makes an extra register available
3618 in many functions. @strong{It also makes debugging impossible on
3621 On some machines, such as the VAX, this flag has no effect, because
3622 the standard calling sequence automatically handles the frame pointer
3623 and nothing is saved by pretending it doesn't exist. The
3624 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
3625 whether a target machine supports this flag. @xref{Registers,,Register
3626 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
3628 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3630 @item -foptimize-sibling-calls
3631 @opindex foptimize-sibling-calls
3632 Optimize sibling and tail recursive calls.
3634 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3638 Don't pay attention to the @code{inline} keyword. Normally this option
3639 is used to keep the compiler from expanding any functions inline.
3640 Note that if you are not optimizing, no functions can be expanded inline.
3642 @item -finline-functions
3643 @opindex finline-functions
3644 Integrate all simple functions into their callers. The compiler
3645 heuristically decides which functions are simple enough to be worth
3646 integrating in this way.
3648 If all calls to a given function are integrated, and the function is
3649 declared @code{static}, then the function is normally not output as
3650 assembler code in its own right.
3652 Enabled at level @option{-O3}.
3654 @item -finline-limit=@var{n}
3655 @opindex finline-limit
3656 By default, gcc limits the size of functions that can be inlined. This flag
3657 allows the control of this limit for functions that are explicitly marked as
3658 inline (i.e., marked with the inline keyword or defined within the class
3659 definition in c++). @var{n} is the size of functions that can be inlined in
3660 number of pseudo instructions (not counting parameter handling). The default
3661 value of @var{n} is 600.
3662 Increasing this value can result in more inlined code at
3663 the cost of compilation time and memory consumption. Decreasing usually makes
3664 the compilation faster and less code will be inlined (which presumably
3665 means slower programs). This option is particularly useful for programs that
3666 use inlining heavily such as those based on recursive templates with C++.
3668 Inlining is actually controlled by a number of parameters, which may be
3669 specified individually by using @option{--param @var{name}=@var{value}}.
3670 The @option{-finline-limit=@var{n}} option sets some of these parameters
3674 @item max-inline-insns
3676 @item max-inline-insns-single
3677 is set to @var{n}/2.
3678 @item max-inline-insns-auto
3679 is set to @var{n}/2.
3680 @item min-inline-insns
3681 is set to 130 or @var{n}/4, whichever is smaller.
3682 @item max-inline-insns-rtl
3686 Using @option{-finline-limit=600} thus results in the default settings
3687 for these parameters. See below for a documentation of the individual
3688 parameters controlling inlining.
3690 @emph{Note:} pseudo instruction represents, in this particular context, an
3691 abstract measurement of function's size. In no way, it represents a count
3692 of assembly instructions and as such its exact meaning might change from one
3693 release to an another.
3695 @item -fkeep-inline-functions
3696 @opindex fkeep-inline-functions
3697 Even if all calls to a given function are integrated, and the function
3698 is declared @code{static}, nevertheless output a separate run-time
3699 callable version of the function. This switch does not affect
3700 @code{extern inline} functions.
3702 @item -fkeep-static-consts
3703 @opindex fkeep-static-consts
3704 Emit variables declared @code{static const} when optimization isn't turned
3705 on, even if the variables aren't referenced.
3707 GCC enables this option by default. If you want to force the compiler to
3708 check if the variable was referenced, regardless of whether or not
3709 optimization is turned on, use the @option{-fno-keep-static-consts} option.
3711 @item -fmerge-constants
3712 Attempt to merge identical constants (string constants and floating point
3713 constants) across compilation units.
3715 This option is the default for optimized compilation if the assembler and
3716 linker support it. Use @option{-fno-merge-constants} to inhibit this
3719 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3721 @item -fmerge-all-constants
3722 Attempt to merge identical constants and identical variables.
3724 This option implies @option{-fmerge-constants}. In addition to
3725 @option{-fmerge-constants} this considers e.g. even constant initialized
3726 arrays or initialized constant variables with integral or floating point
3727 types. Languages like C or C++ require each non-automatic variable to
3728 have distinct location, so using this option will result in non-conforming
3733 Use a graph coloring register allocator. Currently this option is meant
3734 for testing, so we are interested to hear about miscompilations with
3737 @item -fno-branch-count-reg
3738 @opindex fno-branch-count-reg
3739 Do not use ``decrement and branch'' instructions on a count register,
3740 but instead generate a sequence of instructions that decrement a
3741 register, compare it against zero, then branch based upon the result.
3742 This option is only meaningful on architectures that support such
3743 instructions, which include x86, PowerPC, IA-64 and S/390.
3745 The default is @option{-fbranch-count-reg}, enabled when
3746 @option{-fstrength-reduce} is enabled.
3748 @item -fno-function-cse
3749 @opindex fno-function-cse
3750 Do not put function addresses in registers; make each instruction that
3751 calls a constant function contain the function's address explicitly.
3753 This option results in less efficient code, but some strange hacks
3754 that alter the assembler output may be confused by the optimizations
3755 performed when this option is not used.
3757 The default is @option{-ffunction-cse}
3759 @item -fno-zero-initialized-in-bss
3760 @opindex fno-zero-initialized-in-bss
3761 If the target supports a BSS section, GCC by default puts variables that
3762 are initialized to zero into BSS@. This can save space in the resulting
3765 This option turns off this behavior because some programs explicitly
3766 rely on variables going to the data section. E.g., so that the
3767 resulting executable can find the beginning of that section and/or make
3768 assumptions based on that.
3770 The default is @option{-fzero-initialized-in-bss}.
3772 @item -fstrength-reduce
3773 @opindex fstrength-reduce
3774 Perform the optimizations of loop strength reduction and
3775 elimination of iteration variables.
3777 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3779 @item -fthread-jumps
3780 @opindex fthread-jumps
3781 Perform optimizations where we check to see if a jump branches to a
3782 location where another comparison subsumed by the first is found. If
3783 so, the first branch is redirected to either the destination of the
3784 second branch or a point immediately following it, depending on whether
3785 the condition is known to be true or false.
3787 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3789 @item -fcse-follow-jumps
3790 @opindex fcse-follow-jumps
3791 In common subexpression elimination, scan through jump instructions
3792 when the target of the jump is not reached by any other path. For
3793 example, when CSE encounters an @code{if} statement with an
3794 @code{else} clause, CSE will follow the jump when the condition
3797 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3799 @item -fcse-skip-blocks
3800 @opindex fcse-skip-blocks
3801 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
3802 follow jumps which conditionally skip over blocks. When CSE
3803 encounters a simple @code{if} statement with no else clause,
3804 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
3805 body of the @code{if}.
3807 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3809 @item -frerun-cse-after-loop
3810 @opindex frerun-cse-after-loop
3811 Re-run common subexpression elimination after loop optimizations has been
3814 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3816 @item -frerun-loop-opt
3817 @opindex frerun-loop-opt
3818 Run the loop optimizer twice.
3820 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3824 Perform a global common subexpression elimination pass.
3825 This pass also performs global constant and copy propagation.
3827 @emph{Note:} When compiling a program using computed gotos, a GCC
3828 extension, you may get better runtime performance if you disable
3829 the global common subexpression elimination pass by adding
3830 @option{-fno-gcse} to the command line.
3832 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3836 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
3837 attempt to move loads which are only killed by stores into themselves. This
3838 allows a loop containing a load/store sequence to be changed to a load outside
3839 the loop, and a copy/store within the loop.
3841 Enabled by default when gcse is enabled.
3845 When @option{-fgcse-sm} is enabled, A store motion pass is run after global common
3846 subexpression elimination. This pass will attempt to move stores out of loops.
3847 When used in conjunction with @option{-fgcse-lm}, loops containing a load/store sequence
3848 can be changed to a load before the loop and a store after the loop.
3850 Enabled by default when gcse is enabled.
3852 @item -floop-optimize
3853 @opindex floop-optimize
3854 Perform loop optimizations: move constant expressions out of loops, simplify
3855 exit test conditions and optionally do strength-reduction and loop unrolling as
3858 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3860 @item -fcrossjumping
3861 @opindex crossjumping
3862 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
3863 resulting code may or may not perform better than without cross-jumping.
3865 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3867 @item -fif-conversion
3868 @opindex if-conversion
3869 Attempt to transform conditional jumps into branch-less equivalents. This
3870 include use of conditional moves, min, max, set flags and abs instructions, and
3871 some tricks doable by standard arithmetics. The use of conditional execution
3872 on chips where it is available is controlled by @code{if-conversion2}.
3874 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3876 @item -fif-conversion2
3877 @opindex if-conversion2
3878 Use conditional execution (where available) to transform conditional jumps into
3879 branch-less equivalents.
3881 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3883 @item -fdelete-null-pointer-checks
3884 @opindex fdelete-null-pointer-checks
3885 Use global dataflow analysis to identify and eliminate useless checks
3886 for null pointers. The compiler assumes that dereferencing a null
3887 pointer would have halted the program. If a pointer is checked after
3888 it has already been dereferenced, it cannot be null.
3890 In some environments, this assumption is not true, and programs can
3891 safely dereference null pointers. Use
3892 @option{-fno-delete-null-pointer-checks} to disable this optimization
3893 for programs which depend on that behavior.
3895 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3897 @item -fexpensive-optimizations
3898 @opindex fexpensive-optimizations
3899 Perform a number of minor optimizations that are relatively expensive.
3901 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3903 @item -foptimize-register-move
3905 @opindex foptimize-register-move
3907 Attempt to reassign register numbers in move instructions and as
3908 operands of other simple instructions in order to maximize the amount of
3909 register tying. This is especially helpful on machines with two-operand
3912 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
3915 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3917 @item -fdelayed-branch
3918 @opindex fdelayed-branch
3919 If supported for the target machine, attempt to reorder instructions
3920 to exploit instruction slots available after delayed branch
3923 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3925 @item -fschedule-insns
3926 @opindex fschedule-insns
3927 If supported for the target machine, attempt to reorder instructions to
3928 eliminate execution stalls due to required data being unavailable. This
3929 helps machines that have slow floating point or memory load instructions
3930 by allowing other instructions to be issued until the result of the load
3931 or floating point instruction is required.
3933 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3935 @item -fschedule-insns2
3936 @opindex fschedule-insns2
3937 Similar to @option{-fschedule-insns}, but requests an additional pass of
3938 instruction scheduling after register allocation has been done. This is
3939 especially useful on machines with a relatively small number of
3940 registers and where memory load instructions take more than one cycle.
3942 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3944 @item -fno-sched-interblock
3945 @opindex fno-sched-interblock
3946 Don't schedule instructions across basic blocks. This is normally
3947 enabled by default when scheduling before register allocation, i.e.@:
3948 with @option{-fschedule-insns} or at @option{-O2} or higher.
3950 @item -fno-sched-spec
3951 @opindex fno-sched-spec
3952 Don't allow speculative motion of non-load instructions. This is normally
3953 enabled by default when scheduling before register allocation, i.e.@:
3954 with @option{-fschedule-insns} or at @option{-O2} or higher.
3956 @item -fsched-spec-load
3957 @opindex fsched-spec-load
3958 Allow speculative motion of some load instructions. This only makes
3959 sense when scheduling before register allocation, i.e.@: with
3960 @option{-fschedule-insns} or at @option{-O2} or higher.
3962 @item -fsched-spec-load-dangerous
3963 @opindex fsched-spec-load-dangerous
3964 Allow speculative motion of more load instructions. This only makes
3965 sense when scheduling before register allocation, i.e.@: with
3966 @option{-fschedule-insns} or at @option{-O2} or higher.
3968 @item -fsched2-use-superblocks
3969 @opindex fsched2-use-superblocks
3970 When scheduling after register allocation, do use superblock scheduling
3971 algorithm. Superblock scheduling allows motion across basic block boundaries
3972 resulting on faster schedules. This option is experimental, as not all machine
3973 descriptions used by GCC model the CPU closely enough to avoid unreliable
3974 results from the algorithm.
3976 This only makes sense when scheduling after register allocation, i.e.@: with
3977 @option{-fschedule-insns2} or at @option{-O2} or higher.
3979 @item -fsched2-use-traces
3980 @opindex fsched2-use-traces
3981 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
3982 allocation and additionally perform code duplication in order to increase the
3983 size of superblocks using tracer pass. See @option{-ftracer} for details on
3986 This mode should produce faster but significantly longer programs. Also
3987 without @code{-fbranch-probabilities} the traces constructed may not match the
3988 reality and hurt the performance. This only makes
3989 sense when scheduling after register allocation, i.e.@: with
3990 @option{-fschedule-insns2} or at @option{-O2} or higher.
3992 @item -fcaller-saves
3993 @opindex fcaller-saves
3994 Enable values to be allocated in registers that will be clobbered by
3995 function calls, by emitting extra instructions to save and restore the
3996 registers around such calls. Such allocation is done only when it
3997 seems to result in better code than would otherwise be produced.
3999 This option is always enabled by default on certain machines, usually
4000 those which have no call-preserved registers to use instead.
4002 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4004 @item -fmove-all-movables
4005 @opindex fmove-all-movables
4006 Forces all invariant computations in loops to be moved
4009 @item -freduce-all-givs
4010 @opindex freduce-all-givs
4011 Forces all general-induction variables in loops to be
4014 @emph{Note:} When compiling programs written in Fortran,
4015 @option{-fmove-all-movables} and @option{-freduce-all-givs} are enabled
4016 by default when you use the optimizer.
4018 These options may generate better or worse code; results are highly
4019 dependent on the structure of loops within the source code.
4021 These two options are intended to be removed someday, once
4022 they have helped determine the efficacy of various
4023 approaches to improving loop optimizations.
4025 Please let us (@w{@email{gcc@@gcc.gnu.org}} and @w{@email{fortran@@gnu.org}})
4026 know how use of these options affects
4027 the performance of your production code.
4028 We're very interested in code that runs @emph{slower}
4029 when these options are @emph{enabled}.
4032 @itemx -fno-peephole2
4033 @opindex fno-peephole
4034 @opindex fno-peephole2
4035 Disable any machine-specific peephole optimizations. The difference
4036 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
4037 are implemented in the compiler; some targets use one, some use the
4038 other, a few use both.
4040 @option{-fpeephole} is enabled by default.
4041 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4043 @item -fno-guess-branch-probability
4044 @opindex fno-guess-branch-probability
4045 Do not guess branch probabilities using a randomized model.
4047 Sometimes gcc will opt to use a randomized model to guess branch
4048 probabilities, when none are available from either profiling feedback
4049 (@option{-fprofile-arcs}) or @samp{__builtin_expect}. This means that
4050 different runs of the compiler on the same program may produce different
4053 In a hard real-time system, people don't want different runs of the
4054 compiler to produce code that has different behavior; minimizing
4055 non-determinism is of paramount import. This switch allows users to
4056 reduce non-determinism, possibly at the expense of inferior
4059 The default is @option{-fguess-branch-probability} at levels
4060 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4062 @item -freorder-blocks
4063 @opindex freorder-blocks
4064 Reorder basic blocks in the compiled function in order to reduce number of
4065 taken branches and improve code locality.
4067 Enabled at levels @option{-O2}, @option{-O3}.
4069 @item -freorder-functions
4070 @opindex freorder-functions
4071 Reorder basic blocks in the compiled function in order to reduce number of
4072 taken branches and improve code locality. This is implemented by using special
4073 subsections @code{text.hot} for most frequently executed functions and
4074 @code{text.unlikely} for unlikely executed functions. Reordering is done by
4075 the linker so object file format must support named sections and linker must
4076 place them in a reasonable way.
4078 Also profile feedback must be available in to make this option effective. See
4079 @option{-fprofile-arcs} for details.
4081 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4083 @item -fstrict-aliasing
4084 @opindex fstrict-aliasing
4085 Allows the compiler to assume the strictest aliasing rules applicable to
4086 the language being compiled. For C (and C++), this activates
4087 optimizations based on the type of expressions. In particular, an
4088 object of one type is assumed never to reside at the same address as an
4089 object of a different type, unless the types are almost the same. For
4090 example, an @code{unsigned int} can alias an @code{int}, but not a
4091 @code{void*} or a @code{double}. A character type may alias any other
4094 Pay special attention to code like this:
4107 The practice of reading from a different union member than the one most
4108 recently written to (called ``type-punning'') is common. Even with
4109 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
4110 is accessed through the union type. So, the code above will work as
4111 expected. However, this code might not:
4122 Every language that wishes to perform language-specific alias analysis
4123 should define a function that computes, given an @code{tree}
4124 node, an alias set for the node. Nodes in different alias sets are not
4125 allowed to alias. For an example, see the C front-end function
4126 @code{c_get_alias_set}.
4128 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4130 @item -falign-functions
4131 @itemx -falign-functions=@var{n}
4132 @opindex falign-functions
4133 Align the start of functions to the next power-of-two greater than
4134 @var{n}, skipping up to @var{n} bytes. For instance,
4135 @option{-falign-functions=32} aligns functions to the next 32-byte
4136 boundary, but @option{-falign-functions=24} would align to the next
4137 32-byte boundary only if this can be done by skipping 23 bytes or less.
4139 @option{-fno-align-functions} and @option{-falign-functions=1} are
4140 equivalent and mean that functions will not be aligned.
4142 Some assemblers only support this flag when @var{n} is a power of two;
4143 in that case, it is rounded up.
4145 If @var{n} is not specified or is zero, use a machine-dependent default.
4147 Enabled at levels @option{-O2}, @option{-O3}.
4149 @item -falign-labels
4150 @itemx -falign-labels=@var{n}
4151 @opindex falign-labels
4152 Align all branch targets to a power-of-two boundary, skipping up to
4153 @var{n} bytes like @option{-falign-functions}. This option can easily
4154 make code slower, because it must insert dummy operations for when the
4155 branch target is reached in the usual flow of the code.
4157 @option{-fno-align-labels} and @option{-falign-labels=1} are
4158 equivalent and mean that labels will not be aligned.
4160 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
4161 are greater than this value, then their values are used instead.
4163 If @var{n} is not specified or is zero, use a machine-dependent default
4164 which is very likely to be @samp{1}, meaning no alignment.
4166 Enabled at levels @option{-O2}, @option{-O3}.
4169 @itemx -falign-loops=@var{n}
4170 @opindex falign-loops
4171 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
4172 like @option{-falign-functions}. The hope is that the loop will be
4173 executed many times, which will make up for any execution of the dummy
4176 @option{-fno-align-loops} and @option{-falign-loops=1} are
4177 equivalent and mean that loops will not be aligned.
4179 If @var{n} is not specified or is zero, use a machine-dependent default.
4181 Enabled at levels @option{-O2}, @option{-O3}.
4184 @itemx -falign-jumps=@var{n}
4185 @opindex falign-jumps
4186 Align branch targets to a power-of-two boundary, for branch targets
4187 where the targets can only be reached by jumping, skipping up to @var{n}
4188 bytes like @option{-falign-functions}. In this case, no dummy operations
4191 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
4192 equivalent and mean that loops will not be aligned.
4194 If @var{n} is not specified or is zero, use a machine-dependent default.
4196 Enabled at levels @option{-O2}, @option{-O3}.
4198 @item -frename-registers
4199 @opindex frename-registers
4200 Attempt to avoid false dependencies in scheduled code by making use
4201 of registers left over after register allocation. This optimization
4202 will most benefit processors with lots of registers. It can, however,
4203 make debugging impossible, since variables will no longer stay in
4204 a ``home register''.
4206 Enabled at levels @option{-O3}.
4208 @item -fno-cprop-registers
4209 @opindex fno-cprop-registers
4210 After register allocation and post-register allocation instruction splitting,
4211 we perform a copy-propagation pass to try to reduce scheduling dependencies
4212 and occasionally eliminate the copy.
4214 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4218 The following options control compiler behavior regarding floating
4219 point arithmetic. These options trade off between speed and
4220 correctness. All must be specifically enabled.
4224 @opindex ffloat-store
4225 Do not store floating point variables in registers, and inhibit other
4226 options that might change whether a floating point value is taken from a
4229 @cindex floating point precision
4230 This option prevents undesirable excess precision on machines such as
4231 the 68000 where the floating registers (of the 68881) keep more
4232 precision than a @code{double} is supposed to have. Similarly for the
4233 x86 architecture. For most programs, the excess precision does only
4234 good, but a few programs rely on the precise definition of IEEE floating
4235 point. Use @option{-ffloat-store} for such programs, after modifying
4236 them to store all pertinent intermediate computations into variables.
4240 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, @*
4241 @option{-fno-trapping-math}, @option{-ffinite-math-only} and @*
4242 @option{-fno-signaling-nans}.
4244 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
4246 This option should never be turned on by any @option{-O} option since
4247 it can result in incorrect output for programs which depend on
4248 an exact implementation of IEEE or ISO rules/specifications for
4251 @item -fno-math-errno
4252 @opindex fno-math-errno
4253 Do not set ERRNO after calling math functions that are executed
4254 with a single instruction, e.g., sqrt. A program that relies on
4255 IEEE exceptions for math error handling may want to use this flag
4256 for speed while maintaining IEEE arithmetic compatibility.
4258 This option should never be turned on by any @option{-O} option since
4259 it can result in incorrect output for programs which depend on
4260 an exact implementation of IEEE or ISO rules/specifications for
4263 The default is @option{-fmath-errno}.
4265 @item -funsafe-math-optimizations
4266 @opindex funsafe-math-optimizations
4267 Allow optimizations for floating-point arithmetic that (a) assume
4268 that arguments and results are valid and (b) may violate IEEE or
4269 ANSI standards. When used at link-time, it may include libraries
4270 or startup files that change the default FPU control word or other
4271 similar optimizations.
4273 This option should never be turned on by any @option{-O} option since
4274 it can result in incorrect output for programs which depend on
4275 an exact implementation of IEEE or ISO rules/specifications for
4278 The default is @option{-fno-unsafe-math-optimizations}.
4280 @item -ffinite-math-only
4281 @opindex ffinite-math-only
4282 Allow optimizations for floating-point arithmetic that assume
4283 that arguments and results are not NaNs or +-Infs.
4285 This option should never be turned on by any @option{-O} option since
4286 it can result in incorrect output for programs which depend on
4287 an exact implementation of IEEE or ISO rules/specifications.
4289 The default is @option{-fno-finite-math-only}.
4291 @item -fno-trapping-math
4292 @opindex fno-trapping-math
4293 Compile code assuming that floating-point operations cannot generate
4294 user-visible traps. These traps include division by zero, overflow,
4295 underflow, inexact result and invalid operation. This option implies
4296 @option{-fno-signaling-nans}. Setting this option may allow faster
4297 code if one relies on ``non-stop'' IEEE arithmetic, for example.
4299 This option should never be turned on by any @option{-O} option since
4300 it can result in incorrect output for programs which depend on
4301 an exact implementation of IEEE or ISO rules/specifications for
4304 The default is @option{-ftrapping-math}.
4306 @item -fsignaling-nans
4307 @opindex fsignaling-nans
4308 Compile code assuming that IEEE signaling NaNs may generate user-visible
4309 traps during floating-point operations. Setting this option disables
4310 optimizations that may change the number of exceptions visible with
4311 signaling NaNs. This option implies @option{-ftrapping-math}.
4313 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
4316 The default is @option{-fno-signaling-nans}.
4318 This option is experimental and does not currently guarantee to
4319 disable all GCC optimizations that affect signaling NaN behavior.
4321 @item -fsingle-precision-constant
4322 @opindex fsingle-precision-constant
4323 Treat floating point constant as single precision constant instead of
4324 implicitly converting it to double precision constant.
4329 The following options control optimizations that may improve
4330 performance, but are not enabled by any @option{-O} options. This
4331 section includes experimental options that may produce broken code.
4334 @item -fbranch-probabilities
4335 @opindex fbranch-probabilities
4336 After running a program compiled with @option{-fprofile-arcs}
4337 (@pxref{Debugging Options,, Options for Debugging Your Program or
4338 @command{gcc}}), you can compile it a second time using
4339 @option{-fbranch-probabilities}, to improve optimizations based on
4340 the number of times each branch was taken. When the program
4341 compiled with @option{-fprofile-arcs} exits it saves arc execution
4342 counts to a file called @file{@var{sourcename}.gcda} for each source
4343 file The information in this data file is very dependent on the
4344 structure of the generated code, so you must use the same source code
4345 and the same optimization options for both compilations.
4347 With @option{-fbranch-probabilities}, GCC puts a
4348 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
4349 These can be used to improve optimization. Currently, they are only
4350 used in one place: in @file{reorg.c}, instead of guessing which path a
4351 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
4352 exactly determine which path is taken more often.
4354 @item -fprofile-values
4355 @opindex fprofile-values
4356 If combined with @option{-fprofile-arcs}, it adds code so that some
4357 data about values of expressions in the program is gathered.
4359 With @option{-fbranch-probabilities}, it reads back the data gathered
4360 from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
4361 notes to instructions for their later usage in optimizations.
4365 Use a graph coloring register allocator. Currently this option is meant
4366 for testing, so we are interested to hear about miscompilations with
4371 Perform tail duplication to enlarge superblock size. This transformation
4372 simplifies the control flow of the function allowing other optimizations to do
4375 @item -funit-at-a-time
4376 @opindex funit-at-a-time
4377 Parse the whole compilation unit before starting to produce code.
4378 This allows some extra optimizations to take place but consumes more
4381 @item -funroll-loops
4382 @opindex funroll-loops
4383 Unroll loops whose number of iterations can be determined at compile time or
4384 upon entry to the loop. @option{-funroll-loops} implies
4385 @option{-frerun-cse-after-loop}. It also turns on complete loop peeling
4386 (i.e. complete removal of loops with small constant number of iterations).
4387 This option makes code larger, and may or may not make it run faster.
4389 @item -funroll-all-loops
4390 @opindex funroll-all-loops
4391 Unroll all loops, even if their number of iterations is uncertain when
4392 the loop is entered. This usually makes programs run more slowly.
4393 @option{-funroll-all-loops} implies the same options as
4394 @option{-funroll-loops}.
4397 @opindex fpeel-loops
4398 Peels the loops for that there is enough information that they do not
4399 roll much (from profile feedback). It also turns on complete loop peeling
4400 (i.e. complete removal of loops with small constant number of iterations).
4402 @item -funswitch-loops
4403 @opindex funswitch-loops
4404 Move branches with loop invariant conditions out of the loop, with duplicates
4405 of the loop on both branches (modified according to result of the condition).
4407 @item -fold-unroll-loops
4408 @opindex fold-unroll-loops
4409 Unroll loops whose number of iterations can be determined at compile
4410 time or upon entry to the loop, using the old loop unroller whose loop
4411 recognition is based on notes from frontend. @option{-fold-unroll-loops} implies
4412 both @option{-fstrength-reduce} and @option{-frerun-cse-after-loop}. This
4413 option makes code larger, and may or may not make it run faster.
4415 @item -fold-unroll-all-loops
4416 @opindex fold-unroll-all-loops
4417 Unroll all loops, even if their number of iterations is uncertain when
4418 the loop is entered. This is done using the old loop unroller whose loop
4419 recognition is based on notes from frontend. This usually makes programs run more slowly.
4420 @option{-fold-unroll-all-loops} implies the same options as
4421 @option{-fold-unroll-loops}.
4423 @item -funswitch-loops
4424 @opindex funswitch-loops
4425 Move branches with loop invariant conditions out of the loop, with duplicates
4426 of the loop on both branches (modified according to result of the condition).
4428 @item -funswitch-loops
4429 @opindex funswitch-loops
4430 Move branches with loop invariant conditions out of the loop, with duplicates
4431 of the loop on both branches (modified according to result of the condition).
4433 @item -fprefetch-loop-arrays
4434 @opindex fprefetch-loop-arrays
4435 If supported by the target machine, generate instructions to prefetch
4436 memory to improve the performance of loops that access large arrays.
4438 Disabled at level @option{-Os}.
4440 @item -ffunction-sections
4441 @itemx -fdata-sections
4442 @opindex ffunction-sections
4443 @opindex fdata-sections
4444 Place each function or data item into its own section in the output
4445 file if the target supports arbitrary sections. The name of the
4446 function or the name of the data item determines the section's name
4449 Use these options on systems where the linker can perform optimizations
4450 to improve locality of reference in the instruction space. Most systems
4451 using the ELF object format and SPARC processors running Solaris 2 have
4452 linkers with such optimizations. AIX may have these optimizations in
4455 Only use these options when there are significant benefits from doing
4456 so. When you specify these options, the assembler and linker will
4457 create larger object and executable files and will also be slower.
4458 You will not be able to use @code{gprof} on all systems if you
4459 specify this option and you may have problems with debugging if
4460 you specify both this option and @option{-g}.
4464 Perform optimizations in static single assignment form. Each function's
4465 flow graph is translated into SSA form, optimizations are performed, and
4466 the flow graph is translated back from SSA form. Users should not
4467 specify this option, since it is not yet ready for production use.
4471 Perform Sparse Conditional Constant Propagation in SSA form. Requires
4472 @option{-fssa}. Like @option{-fssa}, this is an experimental feature.
4476 Perform aggressive dead-code elimination in SSA form. Requires @option{-fssa}.
4477 Like @option{-fssa}, this is an experimental feature.
4479 @item -fbranch-target-load-optimize
4480 @opindex fbranch-target-load-optimize
4481 Perform branch target register load optimization before prologue / epilogue
4483 The use of target registers can typically be exposed only during reload,
4484 thus hoisting loads out of loops and doing inter-block scheduling needs
4485 a separate optimization pass.
4487 @item -fbranch-target-load-optimize2
4488 @opindex fbranch-target-load-optimize2
4489 Perform branch target register load optimization after prologue / epilogue
4495 @item --param @var{name}=@var{value}
4497 In some places, GCC uses various constants to control the amount of
4498 optimization that is done. For example, GCC will not inline functions
4499 that contain more that a certain number of instructions. You can
4500 control some of these constants on the command-line using the
4501 @option{--param} option.
4503 In each case, the @var{value} is an integer. The allowable choices for
4504 @var{name} are given in the following table:
4507 @item max-crossjump-edges
4508 The maximum number of incoming edges to consider for crossjumping.
4509 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
4510 the number of edges incoming to each block. Increasing values mean
4511 more aggressive optimization, making the compile time increase with
4512 probably small improvement in executable size.
4514 @item max-delay-slot-insn-search
4515 The maximum number of instructions to consider when looking for an
4516 instruction to fill a delay slot. If more than this arbitrary number of
4517 instructions is searched, the time savings from filling the delay slot
4518 will be minimal so stop searching. Increasing values mean more
4519 aggressive optimization, making the compile time increase with probably
4520 small improvement in executable run time.
4522 @item max-delay-slot-live-search
4523 When trying to fill delay slots, the maximum number of instructions to
4524 consider when searching for a block with valid live register
4525 information. Increasing this arbitrarily chosen value means more
4526 aggressive optimization, increasing the compile time. This parameter
4527 should be removed when the delay slot code is rewritten to maintain the
4530 @item max-gcse-memory
4531 The approximate maximum amount of memory that will be allocated in
4532 order to perform the global common subexpression elimination
4533 optimization. If more memory than specified is required, the
4534 optimization will not be done.
4536 @item max-gcse-passes
4537 The maximum number of passes of GCSE to run.
4539 @item max-pending-list-length
4540 The maximum number of pending dependencies scheduling will allow
4541 before flushing the current state and starting over. Large functions
4542 with few branches or calls can create excessively large lists which
4543 needlessly consume memory and resources.
4545 @item max-inline-insns-single
4546 Several parameters control the tree inliner used in gcc.
4547 This number sets the maximum number of instructions (counted in gcc's
4548 internal representation) in a single function that the tree inliner
4549 will consider for inlining. This only affects functions declared
4550 inline and methods implemented in a class declaration (C++).
4551 The default value is 100.
4553 @item max-inline-insns-auto
4554 When you use @option{-finline-functions} (included in @option{-O3}),
4555 a lot of functions that would otherwise not be considered for inlining
4556 by the compiler will be investigated. To those functions, a different
4557 (more restrictive) limit compared to functions declared inline can
4559 The default value is 100.
4561 @item max-inline-insns
4562 The tree inliner does decrease the allowable size for single functions
4563 to be inlined after we already inlined the number of instructions
4564 given here by repeated inlining. This number should be a factor of
4565 two or more larger than the single function limit.
4566 Higher numbers result in better runtime performance, but incur higher
4567 compile-time resource (CPU time, memory) requirements and result in
4568 larger binaries. Very high values are not advisable, as too large
4569 binaries may adversely affect runtime performance.
4570 The default value is 200.
4572 @item max-inline-slope
4573 After exceeding the maximum number of inlined instructions by repeated
4574 inlining, a linear function is used to decrease the allowable size
4575 for single functions. The slope of that function is the negative
4576 reciprocal of the number specified here.
4577 This parameter is ignored when @option{-funit-at-a-time} is used.
4578 The default value is 32.
4580 @item min-inline-insns
4581 The repeated inlining is throttled more and more by the linear function
4582 after exceeding the limit. To avoid too much throttling, a minimum for
4583 this function is specified here to allow repeated inlining for very small
4584 functions even when a lot of repeated inlining already has been done.
4585 This parameter is ignored when @option{-funit-at-a-time} is used.
4586 The default value is 10.
4588 @item large-function-insns
4589 The limit specifying really large functions. For functions greater than this
4590 limit inlining is constrained by @option{--param large-function-growth}.
4591 This parameter is usefull primarily to avoid extreme compilation time caused by non-linear
4592 algorithms used by the backend.
4593 This parameter is ignored when @option{-funit-at-a-time} is not used.
4594 The default value is 30000.
4596 @item large-function-growth
4597 Specifies maximal growth of large functtion caused by inlining in percents.
4598 This parameter is ignored when @option{-funit-at-a-time} is not used.
4599 The default value is 200.
4601 @item inline-unit-growth
4602 Specifies maximal overall growth of the compilation unit caused by inlining.
4603 This parameter is ignored when @option{-funit-at-a-time} is not used.
4604 The default value is 150.
4606 @item max-inline-insns-rtl
4607 For languages that use the RTL inliner (this happens at a later stage
4608 than tree inlining), you can set the maximum allowable size (counted
4609 in RTL instructions) for the RTL inliner with this parameter.
4610 The default value is 600.
4613 @item max-unrolled-insns
4614 The maximum number of instructions that a loop should have if that loop
4615 is unrolled, and if the loop is unrolled, it determines how many times
4616 the loop code is unrolled.
4618 @item max-average-unrolled-insns
4619 The maximum number of instructions biased by probabilities of their execution
4620 that a loop should have if that loop is unrolled, and if the loop is unrolled,
4621 it determines how many times the loop code is unrolled.
4623 @item max-unroll-times
4624 The maximum number of unrollings of a single loop.
4626 @item max-peeled-insns
4627 The maximum number of instructions that a loop should have if that loop
4628 is peeled, and if the loop is peeled, it determines how many times
4629 the loop code is peeled.
4631 @item max-peel-times
4632 The maximum number of peelings of a single loop.
4634 @item max-completely-peeled-insns
4635 The maximum number of insns of a completely peeled loop.
4637 @item max-completely-peel-times
4638 The maximum number of iterations of a loop to be suitable for complete peeling.
4640 @item max-unswitch-insns
4641 The maximum number of insns of an unswitched loop.
4643 @item max-unswitch-level
4644 The maximum number of branches unswitched in a single loop.
4646 @item hot-bb-count-fraction
4647 Select fraction of the maximal count of repetitions of basic block in program
4648 given basic block needs to have to be considered hot.
4650 @item hot-bb-frequency-fraction
4651 Select fraction of the maximal frequency of executions of basic block in
4652 function given basic block needs to have to be considered hot
4654 @item tracer-dynamic-coverage
4655 @itemx tracer-dynamic-coverage-feedback
4657 This value is used to limit superblock formation once the given percentage of
4658 executed instructions is covered. This limits unnecessary code size
4661 The @option{tracer-dynamic-coverage-feedback} is used only when profile
4662 feedback is available. The real profiles (as opposed to statically estimated
4663 ones) are much less balanced allowing the threshold to be larger value.
4665 @item tracer-max-code-growth
4666 Stop tail duplication once code growth has reached given percentage. This is
4667 rather hokey argument, as most of the duplicates will be eliminated later in
4668 cross jumping, so it may be set to much higher values than is the desired code
4671 @item tracer-min-branch-ratio
4673 Stop reverse growth when the reverse probability of best edge is less than this
4674 threshold (in percent).
4676 @item tracer-min-branch-ratio
4677 @itemx tracer-min-branch-ratio-feedback
4679 Stop forward growth if the best edge do have probability lower than this
4682 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
4683 compilation for profile feedback and one for compilation without. The value
4684 for compilation with profile feedback needs to be more conservative (higher) in
4685 order to make tracer effective.
4687 @item max-cse-path-length
4689 Maximum number of basic blocks on path that cse considers.
4691 @item ggc-min-expand
4693 GCC uses a garbage collector to manage its own memory allocation. This
4694 parameter specifies the minimum percentage by which the garbage
4695 collector's heap should be allowed to expand between collections.
4696 Tuning this may improve compilation speed; it has no effect on code
4699 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
4700 RAM >= 1GB. If @code{getrlimit} is available, the notion of "RAM" is
4701 the smallest of actual RAM, RLIMIT_RSS, RLIMIT_DATA and RLIMIT_AS. If
4702 GCC is not able to calculate RAM on a particular platform, the lower
4703 bound of 30% is used. Setting this parameter and
4704 @option{ggc-min-heapsize} to zero causes a full collection to occur at
4705 every opportunity. This is extremely slow, but can be useful for
4708 @item ggc-min-heapsize
4710 Minimum size of the garbage collector's heap before it begins bothering
4711 to collect garbage. The first collection occurs after the heap expands
4712 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
4713 tuning this may improve compilation speed, and has no effect on code
4716 The default is RAM/8, with a lower bound of 4096 (four megabytes) and an
4717 upper bound of 131072 (128 megabytes). If @code{getrlimit} is
4718 available, the notion of "RAM" is the smallest of actual RAM,
4719 RLIMIT_RSS, RLIMIT_DATA and RLIMIT_AS. If GCC is not able to calculate
4720 RAM on a particular platform, the lower bound is used. Setting this
4721 parameter very large effectively disables garbage collection. Setting
4722 this parameter and @option{ggc-min-expand} to zero causes a full
4723 collection to occur at every opportunity.
4725 @item reorder-blocks-duplicate
4726 @itemx reorder-blocks-duplicate-feedback
4728 Used by basic block reordering pass to decide whether to use unconditional
4729 branch or duplicate the code on its destination. Code is duplicated when its
4730 estimated size is smaller than this value multiplied by the estimated size of
4731 unconditional jump in the hot spots of the program.
4733 The @option{reorder-block-duplicate-feedback} is used only when profile
4734 feedback is available and may be set to higher values than
4735 @option{reorder-block-duplicate} since information about the hot spots is more
4740 @node Preprocessor Options
4741 @section Options Controlling the Preprocessor
4742 @cindex preprocessor options
4743 @cindex options, preprocessor
4745 These options control the C preprocessor, which is run on each C source
4746 file before actual compilation.
4748 If you use the @option{-E} option, nothing is done except preprocessing.
4749 Some of these options make sense only together with @option{-E} because
4750 they cause the preprocessor output to be unsuitable for actual
4755 You can use @option{-Wp,@var{option}} to bypass the compiler driver
4756 and pass @var{option} directly through to the preprocessor. If
4757 @var{option} contains commas, it is split into multiple options at the
4758 commas. However, many options are modified, translated or interpreted
4759 by the compiler driver before being passed to the preprocessor, and
4760 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
4761 interface is undocumented and subject to change, so whenever possible
4762 you should avoid using @option{-Wp} and let the driver handle the
4765 @item -Xpreprocessor @var{option}
4766 @opindex preprocessor
4767 Pass @var{option} as an option to the preprocessor. You can use this to
4768 supply system-specific preprocessor options which GCC does not know how to
4771 If you want to pass an option that takes an argument, you must use
4772 @option{-Xpreprocessor} twice, once for the option and once for the argument.
4775 @include cppopts.texi
4777 @node Assembler Options
4778 @section Passing Options to the Assembler
4780 @c prevent bad page break with this line
4781 You can pass options to the assembler.
4784 @item -Wa,@var{option}
4786 Pass @var{option} as an option to the assembler. If @var{option}
4787 contains commas, it is split into multiple options at the commas.
4789 @item -Xassembler @var{option}
4791 Pass @var{option} as an option to the assembler. You can use this to
4792 supply system-specific assembler options which GCC does not know how to
4795 If you want to pass an option that takes an argument, you must use
4796 @option{-Xassembler} twice, once for the option and once for the argument.
4801 @section Options for Linking
4802 @cindex link options
4803 @cindex options, linking
4805 These options come into play when the compiler links object files into
4806 an executable output file. They are meaningless if the compiler is
4807 not doing a link step.
4811 @item @var{object-file-name}
4812 A file name that does not end in a special recognized suffix is
4813 considered to name an object file or library. (Object files are
4814 distinguished from libraries by the linker according to the file
4815 contents.) If linking is done, these object files are used as input
4824 If any of these options is used, then the linker is not run, and
4825 object file names should not be used as arguments. @xref{Overall
4829 @item -l@var{library}
4830 @itemx -l @var{library}
4832 Search the library named @var{library} when linking. (The second
4833 alternative with the library as a separate argument is only for
4834 POSIX compliance and is not recommended.)
4836 It makes a difference where in the command you write this option; the
4837 linker searches and processes libraries and object files in the order they
4838 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
4839 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
4840 to functions in @samp{z}, those functions may not be loaded.
4842 The linker searches a standard list of directories for the library,
4843 which is actually a file named @file{lib@var{library}.a}. The linker
4844 then uses this file as if it had been specified precisely by name.
4846 The directories searched include several standard system directories
4847 plus any that you specify with @option{-L}.
4849 Normally the files found this way are library files---archive files
4850 whose members are object files. The linker handles an archive file by
4851 scanning through it for members which define symbols that have so far
4852 been referenced but not defined. But if the file that is found is an
4853 ordinary object file, it is linked in the usual fashion. The only
4854 difference between using an @option{-l} option and specifying a file name
4855 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
4856 and searches several directories.
4860 You need this special case of the @option{-l} option in order to
4861 link an Objective-C program.
4864 @opindex nostartfiles
4865 Do not use the standard system startup files when linking.
4866 The standard system libraries are used normally, unless @option{-nostdlib}
4867 or @option{-nodefaultlibs} is used.
4869 @item -nodefaultlibs
4870 @opindex nodefaultlibs
4871 Do not use the standard system libraries when linking.
4872 Only the libraries you specify will be passed to the linker.
4873 The standard startup files are used normally, unless @option{-nostartfiles}
4874 is used. The compiler may generate calls to memcmp, memset, and memcpy
4875 for System V (and ISO C) environments or to bcopy and bzero for
4876 BSD environments. These entries are usually resolved by entries in
4877 libc. These entry points should be supplied through some other
4878 mechanism when this option is specified.
4882 Do not use the standard system startup files or libraries when linking.
4883 No startup files and only the libraries you specify will be passed to
4884 the linker. The compiler may generate calls to memcmp, memset, and memcpy
4885 for System V (and ISO C) environments or to bcopy and bzero for
4886 BSD environments. These entries are usually resolved by entries in
4887 libc. These entry points should be supplied through some other
4888 mechanism when this option is specified.
4890 @cindex @option{-lgcc}, use with @option{-nostdlib}
4891 @cindex @option{-nostdlib} and unresolved references
4892 @cindex unresolved references and @option{-nostdlib}
4893 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
4894 @cindex @option{-nodefaultlibs} and unresolved references
4895 @cindex unresolved references and @option{-nodefaultlibs}
4896 One of the standard libraries bypassed by @option{-nostdlib} and
4897 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
4898 that GCC uses to overcome shortcomings of particular machines, or special
4899 needs for some languages.
4900 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
4901 Collection (GCC) Internals},
4902 for more discussion of @file{libgcc.a}.)
4903 In most cases, you need @file{libgcc.a} even when you want to avoid
4904 other standard libraries. In other words, when you specify @option{-nostdlib}
4905 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
4906 This ensures that you have no unresolved references to internal GCC
4907 library subroutines. (For example, @samp{__main}, used to ensure C++
4908 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
4909 GNU Compiler Collection (GCC) Internals}.)
4913 Produce a position independent executable on targets which support it.
4914 For predictable results, you must also specify the same set of options
4915 that were used to generate code (@option{-fpie}, @option{-fPIE},
4916 or model suboptions) when you specify this option.
4920 Remove all symbol table and relocation information from the executable.
4924 On systems that support dynamic linking, this prevents linking with the shared
4925 libraries. On other systems, this option has no effect.
4929 Produce a shared object which can then be linked with other objects to
4930 form an executable. Not all systems support this option. For predictable
4931 results, you must also specify the same set of options that were used to
4932 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
4933 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
4934 needs to build supplementary stub code for constructors to work. On
4935 multi-libbed systems, @samp{gcc -shared} must select the correct support
4936 libraries to link against. Failing to supply the correct flags may lead
4937 to subtle defects. Supplying them in cases where they are not necessary
4940 @item -shared-libgcc
4941 @itemx -static-libgcc
4942 @opindex shared-libgcc
4943 @opindex static-libgcc
4944 On systems that provide @file{libgcc} as a shared library, these options
4945 force the use of either the shared or static version respectively.
4946 If no shared version of @file{libgcc} was built when the compiler was
4947 configured, these options have no effect.
4949 There are several situations in which an application should use the
4950 shared @file{libgcc} instead of the static version. The most common
4951 of these is when the application wishes to throw and catch exceptions
4952 across different shared libraries. In that case, each of the libraries
4953 as well as the application itself should use the shared @file{libgcc}.
4955 Therefore, the G++ and GCJ drivers automatically add
4956 @option{-shared-libgcc} whenever you build a shared library or a main
4957 executable, because C++ and Java programs typically use exceptions, so
4958 this is the right thing to do.
4960 If, instead, you use the GCC driver to create shared libraries, you may
4961 find that they will not always be linked with the shared @file{libgcc}.
4962 If GCC finds, at its configuration time, that you have a GNU linker that
4963 does not support option @option{--eh-frame-hdr}, it will link the shared
4964 version of @file{libgcc} into shared libraries by default. Otherwise,
4965 it will take advantage of the linker and optimize away the linking with
4966 the shared version of @file{libgcc}, linking with the static version of
4967 libgcc by default. This allows exceptions to propagate through such
4968 shared libraries, without incurring relocation costs at library load
4971 However, if a library or main executable is supposed to throw or catch
4972 exceptions, you must link it using the G++ or GCJ driver, as appropriate
4973 for the languages used in the program, or using the option
4974 @option{-shared-libgcc}, such that it is linked with the shared
4979 Bind references to global symbols when building a shared object. Warn
4980 about any unresolved references (unless overridden by the link editor
4981 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
4984 @item -Xlinker @var{option}
4986 Pass @var{option} as an option to the linker. You can use this to
4987 supply system-specific linker options which GCC does not know how to
4990 If you want to pass an option that takes an argument, you must use
4991 @option{-Xlinker} twice, once for the option and once for the argument.
4992 For example, to pass @option{-assert definitions}, you must write
4993 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
4994 @option{-Xlinker "-assert definitions"}, because this passes the entire
4995 string as a single argument, which is not what the linker expects.
4997 @item -Wl,@var{option}
4999 Pass @var{option} as an option to the linker. If @var{option} contains
5000 commas, it is split into multiple options at the commas.
5002 @item -u @var{symbol}
5004 Pretend the symbol @var{symbol} is undefined, to force linking of
5005 library modules to define it. You can use @option{-u} multiple times with
5006 different symbols to force loading of additional library modules.
5009 @node Directory Options
5010 @section Options for Directory Search
5011 @cindex directory options
5012 @cindex options, directory search
5015 These options specify directories to search for header files, for
5016 libraries and for parts of the compiler:
5021 Add the directory @var{dir} to the head of the list of directories to be
5022 searched for header files. This can be used to override a system header
5023 file, substituting your own version, since these directories are
5024 searched before the system header file directories. However, you should
5025 not use this option to add directories that contain vendor-supplied
5026 system header files (use @option{-isystem} for that). If you use more than
5027 one @option{-I} option, the directories are scanned in left-to-right
5028 order; the standard system directories come after.
5030 If a standard system include directory, or a directory specified with
5031 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
5032 option will be ignored. The directory will still be searched but as a
5033 system directory at its normal position in the system include chain.
5034 This is to ensure that GCC's procedure to fix buggy system headers and
5035 the ordering for the include_next directive are not inadvertently changed.
5036 If you really need to change the search order for system directories,
5037 use the @option{-nostdinc} and/or @option{-isystem} options.
5041 Any directories you specify with @option{-I} options before the @option{-I-}
5042 option are searched only for the case of @samp{#include "@var{file}"};
5043 they are not searched for @samp{#include <@var{file}>}.
5045 If additional directories are specified with @option{-I} options after
5046 the @option{-I-}, these directories are searched for all @samp{#include}
5047 directives. (Ordinarily @emph{all} @option{-I} directories are used
5050 In addition, the @option{-I-} option inhibits the use of the current
5051 directory (where the current input file came from) as the first search
5052 directory for @samp{#include "@var{file}"}. There is no way to
5053 override this effect of @option{-I-}. With @option{-I.} you can specify
5054 searching the directory which was current when the compiler was
5055 invoked. That is not exactly the same as what the preprocessor does
5056 by default, but it is often satisfactory.
5058 @option{-I-} does not inhibit the use of the standard system directories
5059 for header files. Thus, @option{-I-} and @option{-nostdinc} are
5064 Add directory @var{dir} to the list of directories to be searched
5067 @item -B@var{prefix}
5069 This option specifies where to find the executables, libraries,
5070 include files, and data files of the compiler itself.
5072 The compiler driver program runs one or more of the subprograms
5073 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
5074 @var{prefix} as a prefix for each program it tries to run, both with and
5075 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
5077 For each subprogram to be run, the compiler driver first tries the
5078 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
5079 was not specified, the driver tries two standard prefixes, which are
5080 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
5081 those results in a file name that is found, the unmodified program
5082 name is searched for using the directories specified in your
5083 @env{PATH} environment variable.
5085 The compiler will check to see if the path provided by the @option{-B}
5086 refers to a directory, and if necessary it will add a directory
5087 separator character at the end of the path.
5089 @option{-B} prefixes that effectively specify directory names also apply
5090 to libraries in the linker, because the compiler translates these
5091 options into @option{-L} options for the linker. They also apply to
5092 includes files in the preprocessor, because the compiler translates these
5093 options into @option{-isystem} options for the preprocessor. In this case,
5094 the compiler appends @samp{include} to the prefix.
5096 The run-time support file @file{libgcc.a} can also be searched for using
5097 the @option{-B} prefix, if needed. If it is not found there, the two
5098 standard prefixes above are tried, and that is all. The file is left
5099 out of the link if it is not found by those means.
5101 Another way to specify a prefix much like the @option{-B} prefix is to use
5102 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
5105 As a special kludge, if the path provided by @option{-B} is
5106 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
5107 9, then it will be replaced by @file{[dir/]include}. This is to help
5108 with boot-strapping the compiler.
5110 @item -specs=@var{file}
5112 Process @var{file} after the compiler reads in the standard @file{specs}
5113 file, in order to override the defaults that the @file{gcc} driver
5114 program uses when determining what switches to pass to @file{cc1},
5115 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
5116 @option{-specs=@var{file}} can be specified on the command line, and they
5117 are processed in order, from left to right.
5123 @section Specifying subprocesses and the switches to pass to them
5126 @command{gcc} is a driver program. It performs its job by invoking a
5127 sequence of other programs to do the work of compiling, assembling and
5128 linking. GCC interprets its command-line parameters and uses these to
5129 deduce which programs it should invoke, and which command-line options
5130 it ought to place on their command lines. This behavior is controlled
5131 by @dfn{spec strings}. In most cases there is one spec string for each
5132 program that GCC can invoke, but a few programs have multiple spec
5133 strings to control their behavior. The spec strings built into GCC can
5134 be overridden by using the @option{-specs=} command-line switch to specify
5137 @dfn{Spec files} are plaintext files that are used to construct spec
5138 strings. They consist of a sequence of directives separated by blank
5139 lines. The type of directive is determined by the first non-whitespace
5140 character on the line and it can be one of the following:
5143 @item %@var{command}
5144 Issues a @var{command} to the spec file processor. The commands that can
5148 @item %include <@var{file}>
5150 Search for @var{file} and insert its text at the current point in the
5153 @item %include_noerr <@var{file}>
5154 @cindex %include_noerr
5155 Just like @samp{%include}, but do not generate an error message if the include
5156 file cannot be found.
5158 @item %rename @var{old_name} @var{new_name}
5160 Rename the spec string @var{old_name} to @var{new_name}.
5164 @item *[@var{spec_name}]:
5165 This tells the compiler to create, override or delete the named spec
5166 string. All lines after this directive up to the next directive or
5167 blank line are considered to be the text for the spec string. If this
5168 results in an empty string then the spec will be deleted. (Or, if the
5169 spec did not exist, then nothing will happened.) Otherwise, if the spec
5170 does not currently exist a new spec will be created. If the spec does
5171 exist then its contents will be overridden by the text of this
5172 directive, unless the first character of that text is the @samp{+}
5173 character, in which case the text will be appended to the spec.
5175 @item [@var{suffix}]:
5176 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
5177 and up to the next directive or blank line are considered to make up the
5178 spec string for the indicated suffix. When the compiler encounters an
5179 input file with the named suffix, it will processes the spec string in
5180 order to work out how to compile that file. For example:
5187 This says that any input file whose name ends in @samp{.ZZ} should be
5188 passed to the program @samp{z-compile}, which should be invoked with the
5189 command-line switch @option{-input} and with the result of performing the
5190 @samp{%i} substitution. (See below.)
5192 As an alternative to providing a spec string, the text that follows a
5193 suffix directive can be one of the following:
5196 @item @@@var{language}
5197 This says that the suffix is an alias for a known @var{language}. This is
5198 similar to using the @option{-x} command-line switch to GCC to specify a
5199 language explicitly. For example:
5206 Says that .ZZ files are, in fact, C++ source files.
5209 This causes an error messages saying:
5212 @var{name} compiler not installed on this system.
5216 GCC already has an extensive list of suffixes built into it.
5217 This directive will add an entry to the end of the list of suffixes, but
5218 since the list is searched from the end backwards, it is effectively
5219 possible to override earlier entries using this technique.
5223 GCC has the following spec strings built into it. Spec files can
5224 override these strings or create their own. Note that individual
5225 targets can also add their own spec strings to this list.
5228 asm Options to pass to the assembler
5229 asm_final Options to pass to the assembler post-processor
5230 cpp Options to pass to the C preprocessor
5231 cc1 Options to pass to the C compiler
5232 cc1plus Options to pass to the C++ compiler
5233 endfile Object files to include at the end of the link
5234 link Options to pass to the linker
5235 lib Libraries to include on the command line to the linker
5236 libgcc Decides which GCC support library to pass to the linker
5237 linker Sets the name of the linker
5238 predefines Defines to be passed to the C preprocessor
5239 signed_char Defines to pass to CPP to say whether @code{char} is signed
5241 startfile Object files to include at the start of the link
5244 Here is a small example of a spec file:
5250 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
5253 This example renames the spec called @samp{lib} to @samp{old_lib} and
5254 then overrides the previous definition of @samp{lib} with a new one.
5255 The new definition adds in some extra command-line options before
5256 including the text of the old definition.
5258 @dfn{Spec strings} are a list of command-line options to be passed to their
5259 corresponding program. In addition, the spec strings can contain
5260 @samp{%}-prefixed sequences to substitute variable text or to
5261 conditionally insert text into the command line. Using these constructs
5262 it is possible to generate quite complex command lines.
5264 Here is a table of all defined @samp{%}-sequences for spec
5265 strings. Note that spaces are not generated automatically around the
5266 results of expanding these sequences. Therefore you can concatenate them
5267 together or combine them with constant text in a single argument.
5271 Substitute one @samp{%} into the program name or argument.
5274 Substitute the name of the input file being processed.
5277 Substitute the basename of the input file being processed.
5278 This is the substring up to (and not including) the last period
5279 and not including the directory.
5282 This is the same as @samp{%b}, but include the file suffix (text after
5286 Marks the argument containing or following the @samp{%d} as a
5287 temporary file name, so that that file will be deleted if GCC exits
5288 successfully. Unlike @samp{%g}, this contributes no text to the
5291 @item %g@var{suffix}
5292 Substitute a file name that has suffix @var{suffix} and is chosen
5293 once per compilation, and mark the argument in the same way as
5294 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
5295 name is now chosen in a way that is hard to predict even when previously
5296 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
5297 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
5298 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
5299 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
5300 was simply substituted with a file name chosen once per compilation,
5301 without regard to any appended suffix (which was therefore treated
5302 just like ordinary text), making such attacks more likely to succeed.
5304 @item %u@var{suffix}
5305 Like @samp{%g}, but generates a new temporary file name even if
5306 @samp{%u@var{suffix}} was already seen.
5308 @item %U@var{suffix}
5309 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
5310 new one if there is no such last file name. In the absence of any
5311 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
5312 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
5313 would involve the generation of two distinct file names, one
5314 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
5315 simply substituted with a file name chosen for the previous @samp{%u},
5316 without regard to any appended suffix.
5318 @item %j@var{suffix}
5319 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
5320 writable, and if save-temps is off; otherwise, substitute the name
5321 of a temporary file, just like @samp{%u}. This temporary file is not
5322 meant for communication between processes, but rather as a junk
5325 @item %|@var{suffix}
5326 @itemx %m@var{suffix}
5327 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
5328 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
5329 all. These are the two most common ways to instruct a program that it
5330 should read from standard input or write to standard output. If you
5331 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
5332 construct: see for example @file{f/lang-specs.h}.
5334 @item %.@var{SUFFIX}
5335 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
5336 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
5337 terminated by the next space or %.
5340 Marks the argument containing or following the @samp{%w} as the
5341 designated output file of this compilation. This puts the argument
5342 into the sequence of arguments that @samp{%o} will substitute later.
5345 Substitutes the names of all the output files, with spaces
5346 automatically placed around them. You should write spaces
5347 around the @samp{%o} as well or the results are undefined.
5348 @samp{%o} is for use in the specs for running the linker.
5349 Input files whose names have no recognized suffix are not compiled
5350 at all, but they are included among the output files, so they will
5354 Substitutes the suffix for object files. Note that this is
5355 handled specially when it immediately follows @samp{%g, %u, or %U},
5356 because of the need for those to form complete file names. The
5357 handling is such that @samp{%O} is treated exactly as if it had already
5358 been substituted, except that @samp{%g, %u, and %U} do not currently
5359 support additional @var{suffix} characters following @samp{%O} as they would
5360 following, for example, @samp{.o}.
5363 Substitutes the standard macro predefinitions for the
5364 current target machine. Use this when running @code{cpp}.
5367 Like @samp{%p}, but puts @samp{__} before and after the name of each
5368 predefined macro, except for macros that start with @samp{__} or with
5369 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
5373 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
5374 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}), and
5375 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
5379 Current argument is the name of a library or startup file of some sort.
5380 Search for that file in a standard list of directories and substitute
5381 the full name found.
5384 Print @var{str} as an error message. @var{str} is terminated by a newline.
5385 Use this when inconsistent options are detected.
5388 Substitute the contents of spec string @var{name} at this point.
5391 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
5393 @item %x@{@var{option}@}
5394 Accumulate an option for @samp{%X}.
5397 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
5401 Output the accumulated assembler options specified by @option{-Wa}.
5404 Output the accumulated preprocessor options specified by @option{-Wp}.
5407 Process the @code{asm} spec. This is used to compute the
5408 switches to be passed to the assembler.
5411 Process the @code{asm_final} spec. This is a spec string for
5412 passing switches to an assembler post-processor, if such a program is
5416 Process the @code{link} spec. This is the spec for computing the
5417 command line passed to the linker. Typically it will make use of the
5418 @samp{%L %G %S %D and %E} sequences.
5421 Dump out a @option{-L} option for each directory that GCC believes might
5422 contain startup files. If the target supports multilibs then the
5423 current multilib directory will be prepended to each of these paths.
5426 Output the multilib directory with directory separators replaced with
5427 @samp{_}. If multilib directories are not set, or the multilib directory is
5428 @file{.} then this option emits nothing.
5431 Process the @code{lib} spec. This is a spec string for deciding which
5432 libraries should be included on the command line to the linker.
5435 Process the @code{libgcc} spec. This is a spec string for deciding
5436 which GCC support library should be included on the command line to the linker.
5439 Process the @code{startfile} spec. This is a spec for deciding which
5440 object files should be the first ones passed to the linker. Typically
5441 this might be a file named @file{crt0.o}.
5444 Process the @code{endfile} spec. This is a spec string that specifies
5445 the last object files that will be passed to the linker.
5448 Process the @code{cpp} spec. This is used to construct the arguments
5449 to be passed to the C preprocessor.
5452 Process the @code{signed_char} spec. This is intended to be used
5453 to tell cpp whether a char is signed. It typically has the definition:
5455 %@{funsigned-char:-D__CHAR_UNSIGNED__@}
5459 Process the @code{cc1} spec. This is used to construct the options to be
5460 passed to the actual C compiler (@samp{cc1}).
5463 Process the @code{cc1plus} spec. This is used to construct the options to be
5464 passed to the actual C++ compiler (@samp{cc1plus}).
5467 Substitute the variable part of a matched option. See below.
5468 Note that each comma in the substituted string is replaced by
5472 Remove all occurrences of @code{-S} from the command line. Note---this
5473 command is position dependent. @samp{%} commands in the spec string
5474 before this one will see @code{-S}, @samp{%} commands in the spec string
5475 after this one will not.
5477 @item %:@var{function}(@var{args})
5478 Call the named function @var{function}, passing it @var{args}.
5479 @var{args} is first processed as a nested spec string, then split
5480 into an argument vector in the usual fashion. The function returns
5481 a string which is processed as if it had appeared literally as part
5482 of the current spec.
5484 The following built-in spec functions are provided:
5487 @item @code{if-exists}
5488 The @code{if-exists} spec function takes one argument, an absolute
5489 pathname to a file. If the file exists, @code{if-exists} returns the
5490 pathname. Here is a small example of its usage:
5494 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
5497 @item @code{if-exists-else}
5498 The @code{if-exists-else} spec function is similar to the @code{if-exists}
5499 spec function, except that it takes two arguments. The first argument is
5500 an absolute pathname to a file. If the file exists, @code{if-exists-else}
5501 returns the pathname. If it does not exist, it returns the second argument.
5502 This way, @code{if-exists-else} can be used to select one file or another,
5503 based on the existence of the first. Here is a small example of its usage:
5507 crt0%O%s %:if-exists(crti%O%s) \
5508 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
5513 Substitutes the @code{-S} switch, if that switch was given to GCC@.
5514 If that switch was not specified, this substitutes nothing. Note that
5515 the leading dash is omitted when specifying this option, and it is
5516 automatically inserted if the substitution is performed. Thus the spec
5517 string @samp{%@{foo@}} would match the command-line option @option{-foo}
5518 and would output the command line option @option{-foo}.
5520 @item %W@{@code{S}@}
5521 Like %@{@code{S}@} but mark last argument supplied within as a file to be
5524 @item %@{@code{S}*@}
5525 Substitutes all the switches specified to GCC whose names start
5526 with @code{-S}, but which also take an argument. This is used for
5527 switches like @option{-o}, @option{-D}, @option{-I}, etc.
5528 GCC considers @option{-o foo} as being
5529 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
5530 text, including the space. Thus two arguments would be generated.
5532 @item %@{@code{S}*&@code{T}*@}
5533 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
5534 (the order of @code{S} and @code{T} in the spec is not significant).
5535 There can be any number of ampersand-separated variables; for each the
5536 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
5538 @item %@{@code{S}:@code{X}@}
5539 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
5541 @item %@{!@code{S}:@code{X}@}
5542 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
5544 @item %@{@code{S}*:@code{X}@}
5545 Substitutes @code{X} if one or more switches whose names start with
5546 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
5547 once, no matter how many such switches appeared. However, if @code{%*}
5548 appears somewhere in @code{X}, then @code{X} will be substituted once
5549 for each matching switch, with the @code{%*} replaced by the part of
5550 that switch that matched the @code{*}.
5552 @item %@{.@code{S}:@code{X}@}
5553 Substitutes @code{X}, if processing a file with suffix @code{S}.
5555 @item %@{!.@code{S}:@code{X}@}
5556 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
5558 @item %@{@code{S}|@code{P}:@code{X}@}
5559 Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@.
5560 This may be combined with @samp{!}, @samp{.}, and @code{*} sequences as well,
5561 although they have a stronger binding than the @samp{|}. If @code{%*}
5562 appears in @code{X}, all of the alternatives must be starred, and only
5563 the first matching alternative is substituted.
5565 For example, a spec string like this:
5568 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
5571 will output the following command-line options from the following input
5572 command-line options:
5577 -d fred.c -foo -baz -boggle
5578 -d jim.d -bar -baz -boggle
5581 @item %@{S:X; T:Y; :D@}
5583 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
5584 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
5585 be as many clauses as you need. This may be combined with @code{.},
5586 @code{!}, @code{|}, and @code{*} as needed.
5591 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
5592 construct may contain other nested @samp{%} constructs or spaces, or
5593 even newlines. They are processed as usual, as described above.
5594 Trailing white space in @code{X} is ignored. White space may also
5595 appear anywhere on the left side of the colon in these constructs,
5596 except between @code{.} or @code{*} and the corresponding word.
5598 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
5599 handled specifically in these constructs. If another value of
5600 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
5601 @option{-W} switch is found later in the command line, the earlier
5602 switch value is ignored, except with @{@code{S}*@} where @code{S} is
5603 just one letter, which passes all matching options.
5605 The character @samp{|} at the beginning of the predicate text is used to
5606 indicate that a command should be piped to the following command, but
5607 only if @option{-pipe} is specified.
5609 It is built into GCC which switches take arguments and which do not.
5610 (You might think it would be useful to generalize this to allow each
5611 compiler's spec to say which switches take arguments. But this cannot
5612 be done in a consistent fashion. GCC cannot even decide which input
5613 files have been specified without knowing which switches take arguments,
5614 and it must know which input files to compile in order to tell which
5617 GCC also knows implicitly that arguments starting in @option{-l} are to be
5618 treated as compiler output files, and passed to the linker in their
5619 proper position among the other output files.
5621 @c man begin OPTIONS
5623 @node Target Options
5624 @section Specifying Target Machine and Compiler Version
5625 @cindex target options
5626 @cindex cross compiling
5627 @cindex specifying machine version
5628 @cindex specifying compiler version and target machine
5629 @cindex compiler version, specifying
5630 @cindex target machine, specifying
5632 The usual way to run GCC is to run the executable called @file{gcc}, or
5633 @file{<machine>-gcc} when cross-compiling, or
5634 @file{<machine>-gcc-<version>} to run a version other than the one that
5635 was installed last. Sometimes this is inconvenient, so GCC provides
5636 options that will switch to another cross-compiler or version.
5639 @item -b @var{machine}
5641 The argument @var{machine} specifies the target machine for compilation.
5643 The value to use for @var{machine} is the same as was specified as the
5644 machine type when configuring GCC as a cross-compiler. For
5645 example, if a cross-compiler was configured with @samp{configure
5646 i386v}, meaning to compile for an 80386 running System V, then you
5647 would specify @option{-b i386v} to run that cross compiler.
5649 @item -V @var{version}
5651 The argument @var{version} specifies which version of GCC to run.
5652 This is useful when multiple versions are installed. For example,
5653 @var{version} might be @samp{2.0}, meaning to run GCC version 2.0.
5656 The @option{-V} and @option{-b} options work by running the
5657 @file{<machine>-gcc-<version>} executable, so there's no real reason to
5658 use them if you can just run that directly.
5660 @node Submodel Options
5661 @section Hardware Models and Configurations
5662 @cindex submodel options
5663 @cindex specifying hardware config
5664 @cindex hardware models and configurations, specifying
5665 @cindex machine dependent options
5667 Earlier we discussed the standard option @option{-b} which chooses among
5668 different installed compilers for completely different target
5669 machines, such as VAX vs.@: 68000 vs.@: 80386.
5671 In addition, each of these target machine types can have its own
5672 special options, starting with @samp{-m}, to choose among various
5673 hardware models or configurations---for example, 68010 vs 68020,
5674 floating coprocessor or none. A single installed version of the
5675 compiler can compile for any model or configuration, according to the
5678 Some configurations of the compiler also support additional special
5679 options, usually for compatibility with other compilers on the same
5682 These options are defined by the macro @code{TARGET_SWITCHES} in the
5683 machine description. The default for the options is also defined by
5684 that macro, which enables you to change the defaults.
5696 * RS/6000 and PowerPC Options::
5700 * i386 and x86-64 Options::
5702 * Intel 960 Options::
5703 * DEC Alpha Options::
5704 * DEC Alpha/VMS Options::
5707 * System V Options::
5708 * TMS320C3x/C4x Options::
5716 * S/390 and zSeries Options::
5720 * Xstormy16 Options::
5725 @node M680x0 Options
5726 @subsection M680x0 Options
5727 @cindex M680x0 options
5729 These are the @samp{-m} options defined for the 68000 series. The default
5730 values for these options depends on which style of 68000 was selected when
5731 the compiler was configured; the defaults for the most common choices are
5739 Generate output for a 68000. This is the default
5740 when the compiler is configured for 68000-based systems.
5742 Use this option for microcontrollers with a 68000 or EC000 core,
5743 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
5749 Generate output for a 68020. This is the default
5750 when the compiler is configured for 68020-based systems.
5754 Generate output containing 68881 instructions for floating point.
5755 This is the default for most 68020 systems unless @option{--nfp} was
5756 specified when the compiler was configured.
5760 Generate output for a 68030. This is the default when the compiler is
5761 configured for 68030-based systems.
5765 Generate output for a 68040. This is the default when the compiler is
5766 configured for 68040-based systems.
5768 This option inhibits the use of 68881/68882 instructions that have to be
5769 emulated by software on the 68040. Use this option if your 68040 does not
5770 have code to emulate those instructions.
5774 Generate output for a 68060. This is the default when the compiler is
5775 configured for 68060-based systems.
5777 This option inhibits the use of 68020 and 68881/68882 instructions that
5778 have to be emulated by software on the 68060. Use this option if your 68060
5779 does not have code to emulate those instructions.
5783 Generate output for a CPU32. This is the default
5784 when the compiler is configured for CPU32-based systems.
5786 Use this option for microcontrollers with a
5787 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
5788 68336, 68340, 68341, 68349 and 68360.
5792 Generate output for a 520X ``coldfire'' family cpu. This is the default
5793 when the compiler is configured for 520X-based systems.
5795 Use this option for microcontroller with a 5200 core, including
5796 the MCF5202, MCF5203, MCF5204 and MCF5202.
5801 Generate output for a 68040, without using any of the new instructions.
5802 This results in code which can run relatively efficiently on either a
5803 68020/68881 or a 68030 or a 68040. The generated code does use the
5804 68881 instructions that are emulated on the 68040.
5808 Generate output for a 68060, without using any of the new instructions.
5809 This results in code which can run relatively efficiently on either a
5810 68020/68881 or a 68030 or a 68040. The generated code does use the
5811 68881 instructions that are emulated on the 68060.
5814 @opindex msoft-float
5815 Generate output containing library calls for floating point.
5816 @strong{Warning:} the requisite libraries are not available for all m68k
5817 targets. Normally the facilities of the machine's usual C compiler are
5818 used, but this can't be done directly in cross-compilation. You must
5819 make your own arrangements to provide suitable library functions for
5820 cross-compilation. The embedded targets @samp{m68k-*-aout} and
5821 @samp{m68k-*-coff} do provide software floating point support.
5825 Consider type @code{int} to be 16 bits wide, like @code{short int}.
5828 @opindex mnobitfield
5829 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
5830 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
5834 Do use the bit-field instructions. The @option{-m68020} option implies
5835 @option{-mbitfield}. This is the default if you use a configuration
5836 designed for a 68020.
5840 Use a different function-calling convention, in which functions
5841 that take a fixed number of arguments return with the @code{rtd}
5842 instruction, which pops their arguments while returning. This
5843 saves one instruction in the caller since there is no need to pop
5844 the arguments there.
5846 This calling convention is incompatible with the one normally
5847 used on Unix, so you cannot use it if you need to call libraries
5848 compiled with the Unix compiler.
5850 Also, you must provide function prototypes for all functions that
5851 take variable numbers of arguments (including @code{printf});
5852 otherwise incorrect code will be generated for calls to those
5855 In addition, seriously incorrect code will result if you call a
5856 function with too many arguments. (Normally, extra arguments are
5857 harmlessly ignored.)
5859 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
5860 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
5863 @itemx -mno-align-int
5865 @opindex mno-align-int
5866 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
5867 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
5868 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
5869 Aligning variables on 32-bit boundaries produces code that runs somewhat
5870 faster on processors with 32-bit busses at the expense of more memory.
5872 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
5873 align structures containing the above types differently than
5874 most published application binary interface specifications for the m68k.
5878 Use the pc-relative addressing mode of the 68000 directly, instead of
5879 using a global offset table. At present, this option implies @option{-fpic},
5880 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
5881 not presently supported with @option{-mpcrel}, though this could be supported for
5882 68020 and higher processors.
5884 @item -mno-strict-align
5885 @itemx -mstrict-align
5886 @opindex mno-strict-align
5887 @opindex mstrict-align
5888 Do not (do) assume that unaligned memory references will be handled by
5893 @node M68hc1x Options
5894 @subsection M68hc1x Options
5895 @cindex M68hc1x options
5897 These are the @samp{-m} options defined for the 68hc11 and 68hc12
5898 microcontrollers. The default values for these options depends on
5899 which style of microcontroller was selected when the compiler was configured;
5900 the defaults for the most common choices are given below.
5907 Generate output for a 68HC11. This is the default
5908 when the compiler is configured for 68HC11-based systems.
5914 Generate output for a 68HC12. This is the default
5915 when the compiler is configured for 68HC12-based systems.
5921 Generate output for a 68HCS12.
5924 @opindex mauto-incdec
5925 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
5932 Enable the use of 68HC12 min and max instructions.
5935 @itemx -mno-long-calls
5936 @opindex mlong-calls
5937 @opindex mno-long-calls
5938 Treat all calls as being far away (near). If calls are assumed to be
5939 far away, the compiler will use the @code{call} instruction to
5940 call a function and the @code{rtc} instruction for returning.
5944 Consider type @code{int} to be 16 bits wide, like @code{short int}.
5946 @item -msoft-reg-count=@var{count}
5947 @opindex msoft-reg-count
5948 Specify the number of pseudo-soft registers which are used for the
5949 code generation. The maximum number is 32. Using more pseudo-soft
5950 register may or may not result in better code depending on the program.
5951 The default is 4 for 68HC11 and 2 for 68HC12.
5956 @subsection VAX Options
5959 These @samp{-m} options are defined for the VAX:
5964 Do not output certain jump instructions (@code{aobleq} and so on)
5965 that the Unix assembler for the VAX cannot handle across long
5970 Do output those jump instructions, on the assumption that you
5971 will assemble with the GNU assembler.
5975 Output code for g-format floating point numbers instead of d-format.
5979 @subsection SPARC Options
5980 @cindex SPARC options
5982 These @samp{-m} switches are supported on the SPARC:
5987 @opindex mno-app-regs
5989 Specify @option{-mapp-regs} to generate output using the global registers
5990 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
5993 To be fully SVR4 ABI compliant at the cost of some performance loss,
5994 specify @option{-mno-app-regs}. You should compile libraries and system
5995 software with this option.
6000 @opindex mhard-float
6001 Generate output containing floating point instructions. This is the
6007 @opindex msoft-float
6008 Generate output containing library calls for floating point.
6009 @strong{Warning:} the requisite libraries are not available for all SPARC
6010 targets. Normally the facilities of the machine's usual C compiler are
6011 used, but this cannot be done directly in cross-compilation. You must make
6012 your own arrangements to provide suitable library functions for
6013 cross-compilation. The embedded targets @samp{sparc-*-aout} and
6014 @samp{sparclite-*-*} do provide software floating point support.
6016 @option{-msoft-float} changes the calling convention in the output file;
6017 therefore, it is only useful if you compile @emph{all} of a program with
6018 this option. In particular, you need to compile @file{libgcc.a}, the
6019 library that comes with GCC, with @option{-msoft-float} in order for
6022 @item -mhard-quad-float
6023 @opindex mhard-quad-float
6024 Generate output containing quad-word (long double) floating point
6027 @item -msoft-quad-float
6028 @opindex msoft-quad-float
6029 Generate output containing library calls for quad-word (long double)
6030 floating point instructions. The functions called are those specified
6031 in the SPARC ABI@. This is the default.
6033 As of this writing, there are no sparc implementations that have hardware
6034 support for the quad-word floating point instructions. They all invoke
6035 a trap handler for one of these instructions, and then the trap handler
6036 emulates the effect of the instruction. Because of the trap handler overhead,
6037 this is much slower than calling the ABI library routines. Thus the
6038 @option{-msoft-quad-float} option is the default.
6044 With @option{-mflat}, the compiler does not generate save/restore instructions
6045 and will use a ``flat'' or single register window calling convention.
6046 This model uses %i7 as the frame pointer and is compatible with the normal
6047 register window model. Code from either may be intermixed.
6048 The local registers and the input registers (0--5) are still treated as
6049 ``call saved'' registers and will be saved on the stack as necessary.
6051 With @option{-mno-flat} (the default), the compiler emits save/restore
6052 instructions (except for leaf functions) and is the normal mode of operation.
6054 @item -mno-unaligned-doubles
6055 @itemx -munaligned-doubles
6056 @opindex mno-unaligned-doubles
6057 @opindex munaligned-doubles
6058 Assume that doubles have 8 byte alignment. This is the default.
6060 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
6061 alignment only if they are contained in another type, or if they have an
6062 absolute address. Otherwise, it assumes they have 4 byte alignment.
6063 Specifying this option avoids some rare compatibility problems with code
6064 generated by other compilers. It is not the default because it results
6065 in a performance loss, especially for floating point code.
6067 @item -mno-faster-structs
6068 @itemx -mfaster-structs
6069 @opindex mno-faster-structs
6070 @opindex mfaster-structs
6071 With @option{-mfaster-structs}, the compiler assumes that structures
6072 should have 8 byte alignment. This enables the use of pairs of
6073 @code{ldd} and @code{std} instructions for copies in structure
6074 assignment, in place of twice as many @code{ld} and @code{st} pairs.
6075 However, the use of this changed alignment directly violates the SPARC
6076 ABI@. Thus, it's intended only for use on targets where the developer
6077 acknowledges that their resulting code will not be directly in line with
6078 the rules of the ABI@.
6081 @opindex mimpure-text
6082 @option{-mimpure-text}, used in addition to @option{-shared}, tells
6083 the compiler to not pass @option{-z text} to the linker when linking a
6084 shared object. Using this option, you can link position-dependent
6085 code into a shared object.
6087 @option{-mimpure-text} suppresses the ``relocations remain against
6088 allocatable but non-writable sections'' linker error message.
6089 However, the necessary relocations will trigger copy-on-write, and the
6090 shared object is not actually shared across processes. Instead of
6091 using @option{-mimpure-text}, you should compile all source code with
6092 @option{-fpic} or @option{-fPIC}.
6094 This option is only available on SunOS and Solaris.
6100 These two options select variations on the SPARC architecture.
6102 By default (unless specifically configured for the Fujitsu SPARClite),
6103 GCC generates code for the v7 variant of the SPARC architecture.
6105 @option{-mv8} will give you SPARC v8 code. The only difference from v7
6106 code is that the compiler emits the integer multiply and integer
6107 divide instructions which exist in SPARC v8 but not in SPARC v7.
6109 @option{-msparclite} will give you SPARClite code. This adds the integer
6110 multiply, integer divide step and scan (@code{ffs}) instructions which
6111 exist in SPARClite but not in SPARC v7.
6113 These options are deprecated and will be deleted in a future GCC release.
6114 They have been replaced with @option{-mcpu=xxx}.
6119 @opindex msupersparc
6120 These two options select the processor for which the code is optimized.
6122 With @option{-mcypress} (the default), the compiler optimizes code for the
6123 Cypress CY7C602 chip, as used in the SPARCStation/SPARCServer 3xx series.
6124 This is also appropriate for the older SPARCStation 1, 2, IPX etc.
6126 With @option{-msupersparc} the compiler optimizes code for the SuperSPARC cpu, as
6127 used in the SPARCStation 10, 1000 and 2000 series. This flag also enables use
6128 of the full SPARC v8 instruction set.
6130 These options are deprecated and will be deleted in a future GCC release.
6131 They have been replaced with @option{-mcpu=xxx}.
6133 @item -mcpu=@var{cpu_type}
6135 Set the instruction set, register set, and instruction scheduling parameters
6136 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
6137 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
6138 @samp{hypersparc}, @samp{sparclite86x}, @samp{f930}, @samp{f934},
6139 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc}, and
6142 Default instruction scheduling parameters are used for values that select
6143 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
6144 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
6146 Here is a list of each supported architecture and their supported
6151 v8: supersparc, hypersparc
6152 sparclite: f930, f934, sparclite86x
6154 v9: ultrasparc, ultrasparc3
6157 @item -mtune=@var{cpu_type}
6159 Set the instruction scheduling parameters for machine type
6160 @var{cpu_type}, but do not set the instruction set or register set that the
6161 option @option{-mcpu=@var{cpu_type}} would.
6163 The same values for @option{-mcpu=@var{cpu_type}} can be used for
6164 @option{-mtune=@var{cpu_type}}, but the only useful values are those
6165 that select a particular cpu implementation. Those are @samp{cypress},
6166 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
6167 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc}, and
6172 These @samp{-m} switches are supported in addition to the above
6173 on the SPARCLET processor.
6176 @item -mlittle-endian
6177 @opindex mlittle-endian
6178 Generate code for a processor running in little-endian mode.
6182 Treat register @code{%g0} as a normal register.
6183 GCC will continue to clobber it as necessary but will not assume
6184 it always reads as 0.
6186 @item -mbroken-saverestore
6187 @opindex mbroken-saverestore
6188 Generate code that does not use non-trivial forms of the @code{save} and
6189 @code{restore} instructions. Early versions of the SPARCLET processor do
6190 not correctly handle @code{save} and @code{restore} instructions used with
6191 arguments. They correctly handle them used without arguments. A @code{save}
6192 instruction used without arguments increments the current window pointer
6193 but does not allocate a new stack frame. It is assumed that the window
6194 overflow trap handler will properly handle this case as will interrupt
6198 These @samp{-m} switches are supported in addition to the above
6199 on SPARC V9 processors in 64-bit environments.
6202 @item -mlittle-endian
6203 @opindex mlittle-endian
6204 Generate code for a processor running in little-endian mode. It is only
6205 available for a few configurations and most notably not on Solaris.
6211 Generate code for a 32-bit or 64-bit environment.
6212 The 32-bit environment sets int, long and pointer to 32 bits.
6213 The 64-bit environment sets int to 32 bits and long and pointer
6216 @item -mcmodel=medlow
6217 @opindex mcmodel=medlow
6218 Generate code for the Medium/Low code model: the program must be linked
6219 in the low 32 bits of the address space. Pointers are 64 bits.
6220 Programs can be statically or dynamically linked.
6222 @item -mcmodel=medmid
6223 @opindex mcmodel=medmid
6224 Generate code for the Medium/Middle code model: the program must be linked
6225 in the low 44 bits of the address space, the text segment must be less than
6226 2G bytes, and data segment must be within 2G of the text segment.
6227 Pointers are 64 bits.
6229 @item -mcmodel=medany
6230 @opindex mcmodel=medany
6231 Generate code for the Medium/Anywhere code model: the program may be linked
6232 anywhere in the address space, the text segment must be less than
6233 2G bytes, and data segment must be within 2G of the text segment.
6234 Pointers are 64 bits.
6236 @item -mcmodel=embmedany
6237 @opindex mcmodel=embmedany
6238 Generate code for the Medium/Anywhere code model for embedded systems:
6239 assume a 32-bit text and a 32-bit data segment, both starting anywhere
6240 (determined at link time). Register %g4 points to the base of the
6241 data segment. Pointers are still 64 bits.
6242 Programs are statically linked, PIC is not supported.
6245 @itemx -mno-stack-bias
6246 @opindex mstack-bias
6247 @opindex mno-stack-bias
6248 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
6249 frame pointer if present, are offset by @minus{}2047 which must be added back
6250 when making stack frame references.
6251 Otherwise, assume no such offset is present.
6255 @subsection ARM Options
6258 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
6263 @opindex mapcs-frame
6264 Generate a stack frame that is compliant with the ARM Procedure Call
6265 Standard for all functions, even if this is not strictly necessary for
6266 correct execution of the code. Specifying @option{-fomit-frame-pointer}
6267 with this option will cause the stack frames not to be generated for
6268 leaf functions. The default is @option{-mno-apcs-frame}.
6272 This is a synonym for @option{-mapcs-frame}.
6276 Generate code for a processor running with a 26-bit program counter,
6277 and conforming to the function calling standards for the APCS 26-bit
6278 option. This option replaces the @option{-m2} and @option{-m3} options
6279 of previous releases of the compiler.
6283 Generate code for a processor running with a 32-bit program counter,
6284 and conforming to the function calling standards for the APCS 32-bit
6285 option. This option replaces the @option{-m6} option of previous releases
6289 @c not currently implemented
6290 @item -mapcs-stack-check
6291 @opindex mapcs-stack-check
6292 Generate code to check the amount of stack space available upon entry to
6293 every function (that actually uses some stack space). If there is
6294 insufficient space available then either the function
6295 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
6296 called, depending upon the amount of stack space required. The run time
6297 system is required to provide these functions. The default is
6298 @option{-mno-apcs-stack-check}, since this produces smaller code.
6300 @c not currently implemented
6302 @opindex mapcs-float
6303 Pass floating point arguments using the float point registers. This is
6304 one of the variants of the APCS@. This option is recommended if the
6305 target hardware has a floating point unit or if a lot of floating point
6306 arithmetic is going to be performed by the code. The default is
6307 @option{-mno-apcs-float}, since integer only code is slightly increased in
6308 size if @option{-mapcs-float} is used.
6310 @c not currently implemented
6311 @item -mapcs-reentrant
6312 @opindex mapcs-reentrant
6313 Generate reentrant, position independent code. The default is
6314 @option{-mno-apcs-reentrant}.
6317 @item -mthumb-interwork
6318 @opindex mthumb-interwork
6319 Generate code which supports calling between the ARM and Thumb
6320 instruction sets. Without this option the two instruction sets cannot
6321 be reliably used inside one program. The default is
6322 @option{-mno-thumb-interwork}, since slightly larger code is generated
6323 when @option{-mthumb-interwork} is specified.
6325 @item -mno-sched-prolog
6326 @opindex mno-sched-prolog
6327 Prevent the reordering of instructions in the function prolog, or the
6328 merging of those instruction with the instructions in the function's
6329 body. This means that all functions will start with a recognizable set
6330 of instructions (or in fact one of a choice from a small set of
6331 different function prologues), and this information can be used to
6332 locate the start if functions inside an executable piece of code. The
6333 default is @option{-msched-prolog}.
6336 @opindex mhard-float
6337 Generate output containing floating point instructions. This is the
6341 @opindex msoft-float
6342 Generate output containing library calls for floating point.
6343 @strong{Warning:} the requisite libraries are not available for all ARM
6344 targets. Normally the facilities of the machine's usual C compiler are
6345 used, but this cannot be done directly in cross-compilation. You must make
6346 your own arrangements to provide suitable library functions for
6349 @option{-msoft-float} changes the calling convention in the output file;
6350 therefore, it is only useful if you compile @emph{all} of a program with
6351 this option. In particular, you need to compile @file{libgcc.a}, the
6352 library that comes with GCC, with @option{-msoft-float} in order for
6355 @item -mlittle-endian
6356 @opindex mlittle-endian
6357 Generate code for a processor running in little-endian mode. This is
6358 the default for all standard configurations.
6361 @opindex mbig-endian
6362 Generate code for a processor running in big-endian mode; the default is
6363 to compile code for a little-endian processor.
6365 @item -mwords-little-endian
6366 @opindex mwords-little-endian
6367 This option only applies when generating code for big-endian processors.
6368 Generate code for a little-endian word order but a big-endian byte
6369 order. That is, a byte order of the form @samp{32107654}. Note: this
6370 option should only be used if you require compatibility with code for
6371 big-endian ARM processors generated by versions of the compiler prior to
6374 @item -malignment-traps
6375 @opindex malignment-traps
6376 Generate code that will not trap if the MMU has alignment traps enabled.
6377 On ARM architectures prior to ARMv4, there were no instructions to
6378 access half-word objects stored in memory. However, when reading from
6379 memory a feature of the ARM architecture allows a word load to be used,
6380 even if the address is unaligned, and the processor core will rotate the
6381 data as it is being loaded. This option tells the compiler that such
6382 misaligned accesses will cause a MMU trap and that it should instead
6383 synthesize the access as a series of byte accesses. The compiler can
6384 still use word accesses to load half-word data if it knows that the
6385 address is aligned to a word boundary.
6387 This option is ignored when compiling for ARM architecture 4 or later,
6388 since these processors have instructions to directly access half-word
6391 @item -mno-alignment-traps
6392 @opindex mno-alignment-traps
6393 Generate code that assumes that the MMU will not trap unaligned
6394 accesses. This produces better code when the target instruction set
6395 does not have half-word memory operations (i.e.@: implementations prior to
6398 Note that you cannot use this option to access unaligned word objects,
6399 since the processor will only fetch one 32-bit aligned object from
6402 The default setting for most targets is @option{-mno-alignment-traps}, since
6403 this produces better code when there are no half-word memory
6404 instructions available.
6406 @item -mshort-load-bytes
6407 @itemx -mno-short-load-words
6408 @opindex mshort-load-bytes
6409 @opindex mno-short-load-words
6410 These are deprecated aliases for @option{-malignment-traps}.
6412 @item -mno-short-load-bytes
6413 @itemx -mshort-load-words
6414 @opindex mno-short-load-bytes
6415 @opindex mshort-load-words
6416 This are deprecated aliases for @option{-mno-alignment-traps}.
6418 @item -mcpu=@var{name}
6420 This specifies the name of the target ARM processor. GCC uses this name
6421 to determine what kind of instructions it can emit when generating
6422 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
6423 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
6424 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
6425 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
6426 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
6427 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm8},
6428 @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
6429 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
6430 @samp{arm920t}, @samp{arm940t}, @samp{arm9tdmi}, @samp{arm10tdmi},
6431 @samp{arm1020t}, @samp{xscale}, @samp{iwmmxt}, @samp{ep9312}.
6433 @itemx -mtune=@var{name}
6435 This option is very similar to the @option{-mcpu=} option, except that
6436 instead of specifying the actual target processor type, and hence
6437 restricting which instructions can be used, it specifies that GCC should
6438 tune the performance of the code as if the target were of the type
6439 specified in this option, but still choosing the instructions that it
6440 will generate based on the cpu specified by a @option{-mcpu=} option.
6441 For some ARM implementations better performance can be obtained by using
6444 @item -march=@var{name}
6446 This specifies the name of the target ARM architecture. GCC uses this
6447 name to determine what kind of instructions it can emit when generating
6448 assembly code. This option can be used in conjunction with or instead
6449 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
6450 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
6451 @samp{armv5}, @samp{armv5t}, @samp{armv5te}, @samp{iwmmxt}, @samp{ep9312}.
6453 @item -mfpe=@var{number}
6454 @itemx -mfp=@var{number}
6457 This specifies the version of the floating point emulation available on
6458 the target. Permissible values are 2 and 3. @option{-mfp=} is a synonym
6459 for @option{-mfpe=}, for compatibility with older versions of GCC@.
6461 @item -mstructure-size-boundary=@var{n}
6462 @opindex mstructure-size-boundary
6463 The size of all structures and unions will be rounded up to a multiple
6464 of the number of bits set by this option. Permissible values are 8 and
6465 32. The default value varies for different toolchains. For the COFF
6466 targeted toolchain the default value is 8. Specifying the larger number
6467 can produce faster, more efficient code, but can also increase the size
6468 of the program. The two values are potentially incompatible. Code
6469 compiled with one value cannot necessarily expect to work with code or
6470 libraries compiled with the other value, if they exchange information
6471 using structures or unions.
6473 @item -mabort-on-noreturn
6474 @opindex mabort-on-noreturn
6475 Generate a call to the function @code{abort} at the end of a
6476 @code{noreturn} function. It will be executed if the function tries to
6480 @itemx -mno-long-calls
6481 @opindex mlong-calls
6482 @opindex mno-long-calls
6483 Tells the compiler to perform function calls by first loading the
6484 address of the function into a register and then performing a subroutine
6485 call on this register. This switch is needed if the target function
6486 will lie outside of the 64 megabyte addressing range of the offset based
6487 version of subroutine call instruction.
6489 Even if this switch is enabled, not all function calls will be turned
6490 into long calls. The heuristic is that static functions, functions
6491 which have the @samp{short-call} attribute, functions that are inside
6492 the scope of a @samp{#pragma no_long_calls} directive and functions whose
6493 definitions have already been compiled within the current compilation
6494 unit, will not be turned into long calls. The exception to this rule is
6495 that weak function definitions, functions with the @samp{long-call}
6496 attribute or the @samp{section} attribute, and functions that are within
6497 the scope of a @samp{#pragma long_calls} directive, will always be
6498 turned into long calls.
6500 This feature is not enabled by default. Specifying
6501 @option{-mno-long-calls} will restore the default behavior, as will
6502 placing the function calls within the scope of a @samp{#pragma
6503 long_calls_off} directive. Note these switches have no effect on how
6504 the compiler generates code to handle function calls via function
6507 @item -mnop-fun-dllimport
6508 @opindex mnop-fun-dllimport
6509 Disable support for the @code{dllimport} attribute.
6511 @item -msingle-pic-base
6512 @opindex msingle-pic-base
6513 Treat the register used for PIC addressing as read-only, rather than
6514 loading it in the prologue for each function. The run-time system is
6515 responsible for initializing this register with an appropriate value
6516 before execution begins.
6518 @item -mpic-register=@var{reg}
6519 @opindex mpic-register
6520 Specify the register to be used for PIC addressing. The default is R10
6521 unless stack-checking is enabled, when R9 is used.
6523 @item -mcirrus-fix-invalid-insns
6524 @opindex mcirrus-fix-invalid-insns
6525 @opindex mno-cirrus-fix-invalid-insns
6526 Insert NOPs into the instruction stream to in order to work around
6527 problems with invalid Maverick instruction combinations. This option
6528 is only valid if the @option{-mcpu=ep9312} option has been used to
6529 enable generation of instructions for the Cirrus Maverick floating
6530 point co-processor. This option is not enabled by default, since the
6531 problem is only present in older Maverick implementations. The default
6532 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
6535 @item -mpoke-function-name
6536 @opindex mpoke-function-name
6537 Write the name of each function into the text section, directly
6538 preceding the function prologue. The generated code is similar to this:
6542 .ascii "arm_poke_function_name", 0
6545 .word 0xff000000 + (t1 - t0)
6546 arm_poke_function_name
6548 stmfd sp!, @{fp, ip, lr, pc@}
6552 When performing a stack backtrace, code can inspect the value of
6553 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
6554 location @code{pc - 12} and the top 8 bits are set, then we know that
6555 there is a function name embedded immediately preceding this location
6556 and has length @code{((pc[-3]) & 0xff000000)}.
6560 Generate code for the 16-bit Thumb instruction set. The default is to
6561 use the 32-bit ARM instruction set.
6564 @opindex mtpcs-frame
6565 Generate a stack frame that is compliant with the Thumb Procedure Call
6566 Standard for all non-leaf functions. (A leaf function is one that does
6567 not call any other functions.) The default is @option{-mno-tpcs-frame}.
6569 @item -mtpcs-leaf-frame
6570 @opindex mtpcs-leaf-frame
6571 Generate a stack frame that is compliant with the Thumb Procedure Call
6572 Standard for all leaf functions. (A leaf function is one that does
6573 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
6575 @item -mcallee-super-interworking
6576 @opindex mcallee-super-interworking
6577 Gives all externally visible functions in the file being compiled an ARM
6578 instruction set header which switches to Thumb mode before executing the
6579 rest of the function. This allows these functions to be called from
6580 non-interworking code.
6582 @item -mcaller-super-interworking
6583 @opindex mcaller-super-interworking
6584 Allows calls via function pointers (including virtual functions) to
6585 execute correctly regardless of whether the target code has been
6586 compiled for interworking or not. There is a small overhead in the cost
6587 of executing a function pointer if this option is enabled.
6591 @node MN10200 Options
6592 @subsection MN10200 Options
6593 @cindex MN10200 options
6595 These @option{-m} options are defined for Matsushita MN10200 architectures:
6600 Indicate to the linker that it should perform a relaxation optimization pass
6601 to shorten branches, calls and absolute memory addresses. This option only
6602 has an effect when used on the command line for the final link step.
6604 This option makes symbolic debugging impossible.
6607 @node MN10300 Options
6608 @subsection MN10300 Options
6609 @cindex MN10300 options
6611 These @option{-m} options are defined for Matsushita MN10300 architectures:
6616 Generate code to avoid bugs in the multiply instructions for the MN10300
6617 processors. This is the default.
6620 @opindex mno-mult-bug
6621 Do not generate code to avoid bugs in the multiply instructions for the
6626 Generate code which uses features specific to the AM33 processor.
6630 Do not generate code which uses features specific to the AM33 processor. This
6635 Do not link in the C run-time initialization object file.
6639 Indicate to the linker that it should perform a relaxation optimization pass
6640 to shorten branches, calls and absolute memory addresses. This option only
6641 has an effect when used on the command line for the final link step.
6643 This option makes symbolic debugging impossible.
6647 @node M32R/D Options
6648 @subsection M32R/D Options
6649 @cindex M32R/D options
6651 These @option{-m} options are defined for Mitsubishi M32R/D architectures:
6656 Generate code for the M32R/X@.
6660 Generate code for the M32R@. This is the default.
6662 @item -mcode-model=small
6663 @opindex mcode-model=small
6664 Assume all objects live in the lower 16MB of memory (so that their addresses
6665 can be loaded with the @code{ld24} instruction), and assume all subroutines
6666 are reachable with the @code{bl} instruction.
6667 This is the default.
6669 The addressability of a particular object can be set with the
6670 @code{model} attribute.
6672 @item -mcode-model=medium
6673 @opindex mcode-model=medium
6674 Assume objects may be anywhere in the 32-bit address space (the compiler
6675 will generate @code{seth/add3} instructions to load their addresses), and
6676 assume all subroutines are reachable with the @code{bl} instruction.
6678 @item -mcode-model=large
6679 @opindex mcode-model=large
6680 Assume objects may be anywhere in the 32-bit address space (the compiler
6681 will generate @code{seth/add3} instructions to load their addresses), and
6682 assume subroutines may not be reachable with the @code{bl} instruction
6683 (the compiler will generate the much slower @code{seth/add3/jl}
6684 instruction sequence).
6687 @opindex msdata=none
6688 Disable use of the small data area. Variables will be put into
6689 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
6690 @code{section} attribute has been specified).
6691 This is the default.
6693 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
6694 Objects may be explicitly put in the small data area with the
6695 @code{section} attribute using one of these sections.
6698 @opindex msdata=sdata
6699 Put small global and static data in the small data area, but do not
6700 generate special code to reference them.
6704 Put small global and static data in the small data area, and generate
6705 special instructions to reference them.
6709 @cindex smaller data references
6710 Put global and static objects less than or equal to @var{num} bytes
6711 into the small data or bss sections instead of the normal data or bss
6712 sections. The default value of @var{num} is 8.
6713 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
6714 for this option to have any effect.
6716 All modules should be compiled with the same @option{-G @var{num}} value.
6717 Compiling with different values of @var{num} may or may not work; if it
6718 doesn't the linker will give an error message---incorrect code will not be
6724 @subsection M88K Options
6725 @cindex M88k options
6727 These @samp{-m} options are defined for Motorola 88k architectures:
6732 Generate code that works well on both the m88100 and the
6737 Generate code that works best for the m88100, but that also
6742 Generate code that works best for the m88110, and may not run
6747 Obsolete option to be removed from the next revision.
6750 @item -midentify-revision
6751 @opindex midentify-revision
6752 @cindex identifying source, compiler (88k)
6753 Include an @code{ident} directive in the assembler output recording the
6754 source file name, compiler name and version, timestamp, and compilation
6757 @item -mno-underscores
6758 @opindex mno-underscores
6759 @cindex underscores, avoiding (88k)
6760 In assembler output, emit symbol names without adding an underscore
6761 character at the beginning of each name. The default is to use an
6762 underscore as prefix on each name.
6764 @item -mocs-debug-info
6765 @itemx -mno-ocs-debug-info
6766 @opindex mocs-debug-info
6767 @opindex mno-ocs-debug-info
6769 @cindex debugging, 88k OCS
6770 Include (or omit) additional debugging information (about registers used
6771 in each stack frame) as specified in the 88open Object Compatibility
6772 Standard, ``OCS''@. This extra information allows debugging of code that
6773 has had the frame pointer eliminated. The default for SVr4 and Delta 88
6774 SVr3.2 is to include this information; other 88k configurations omit this
6775 information by default.
6777 @item -mocs-frame-position
6778 @opindex mocs-frame-position
6779 @cindex register positions in frame (88k)
6780 When emitting COFF debugging information for automatic variables and
6781 parameters stored on the stack, use the offset from the canonical frame
6782 address, which is the stack pointer (register 31) on entry to the
6783 function. The SVr4 and Delta88 SVr3.2, and BCS configurations use
6784 @option{-mocs-frame-position}; other 88k configurations have the default
6785 @option{-mno-ocs-frame-position}.
6787 @item -mno-ocs-frame-position
6788 @opindex mno-ocs-frame-position
6789 @cindex register positions in frame (88k)
6790 When emitting COFF debugging information for automatic variables and
6791 parameters stored on the stack, use the offset from the frame pointer
6792 register (register 30). When this option is in effect, the frame
6793 pointer is not eliminated when debugging information is selected by the
6796 @item -moptimize-arg-area
6797 @opindex moptimize-arg-area
6798 @cindex arguments in frame (88k)
6799 Save space by reorganizing the stack frame. This option generates code
6800 that does not agree with the 88open specifications, but uses less
6803 @itemx -mno-optimize-arg-area
6804 @opindex mno-optimize-arg-area
6805 Do not reorganize the stack frame to save space. This is the default.
6806 The generated conforms to the specification, but uses more memory.
6808 @item -mshort-data-@var{num}
6809 @opindex mshort-data
6810 @cindex smaller data references (88k)
6811 @cindex r0-relative references (88k)
6812 Generate smaller data references by making them relative to @code{r0},
6813 which allows loading a value using a single instruction (rather than the
6814 usual two). You control which data references are affected by
6815 specifying @var{num} with this option. For example, if you specify
6816 @option{-mshort-data-512}, then the data references affected are those
6817 involving displacements of less than 512 bytes.
6818 @option{-mshort-data-@var{num}} is not effective for @var{num} greater
6821 @item -mserialize-volatile
6822 @opindex mserialize-volatile
6823 @itemx -mno-serialize-volatile
6824 @opindex mno-serialize-volatile
6825 @cindex sequential consistency on 88k
6826 Do, or don't, generate code to guarantee sequential consistency
6827 of volatile memory references. By default, consistency is
6830 The order of memory references made by the MC88110 processor does
6831 not always match the order of the instructions requesting those
6832 references. In particular, a load instruction may execute before
6833 a preceding store instruction. Such reordering violates
6834 sequential consistency of volatile memory references, when there
6835 are multiple processors. When consistency must be guaranteed,
6836 GCC generates special instructions, as needed, to force
6837 execution in the proper order.
6839 The MC88100 processor does not reorder memory references and so
6840 always provides sequential consistency. However, by default, GCC
6841 generates the special instructions to guarantee consistency
6842 even when you use @option{-m88100}, so that the code may be run on an
6843 MC88110 processor. If you intend to run your code only on the
6844 MC88100 processor, you may use @option{-mno-serialize-volatile}.
6846 The extra code generated to guarantee consistency may affect the
6847 performance of your application. If you know that you can safely
6848 forgo this guarantee, you may use @option{-mno-serialize-volatile}.
6854 @cindex assembler syntax, 88k
6856 Turn on (@option{-msvr4}) or off (@option{-msvr3}) compiler extensions
6857 related to System V release 4 (SVr4). This controls the following:
6861 Which variant of the assembler syntax to emit.
6863 @option{-msvr4} makes the C preprocessor recognize @samp{#pragma weak}
6864 that is used on System V release 4.
6866 @option{-msvr4} makes GCC issue additional declaration directives used in
6870 @option{-msvr4} is the default for the m88k-motorola-sysv4 configuration.
6871 @option{-msvr3} is the default for all other m88k configurations.
6873 @item -mversion-03.00
6874 @opindex mversion-03.00
6875 This option is obsolete, and is ignored.
6876 @c ??? which asm syntax better for GAS? option there too?
6878 @item -mno-check-zero-division
6879 @itemx -mcheck-zero-division
6880 @opindex mno-check-zero-division
6881 @opindex mcheck-zero-division
6882 @cindex zero division on 88k
6883 Do, or don't, generate code to guarantee that integer division by
6884 zero will be detected. By default, detection is guaranteed.
6886 Some models of the MC88100 processor fail to trap upon integer
6887 division by zero under certain conditions. By default, when
6888 compiling code that might be run on such a processor, GCC
6889 generates code that explicitly checks for zero-valued divisors
6890 and traps with exception number 503 when one is detected. Use of
6891 @option{-mno-check-zero-division} suppresses such checking for code
6892 generated to run on an MC88100 processor.
6894 GCC assumes that the MC88110 processor correctly detects all instances
6895 of integer division by zero. When @option{-m88110} is specified, no
6896 explicit checks for zero-valued divisors are generated, and both
6897 @option{-mcheck-zero-division} and @option{-mno-check-zero-division} are
6900 @item -muse-div-instruction
6901 @opindex muse-div-instruction
6902 @cindex divide instruction, 88k
6903 Use the div instruction for signed integer division on the
6904 MC88100 processor. By default, the div instruction is not used.
6906 On the MC88100 processor the signed integer division instruction
6907 div) traps to the operating system on a negative operand. The
6908 operating system transparently completes the operation, but at a
6909 large cost in execution time. By default, when compiling code
6910 that might be run on an MC88100 processor, GCC emulates signed
6911 integer division using the unsigned integer division instruction
6912 divu), thereby avoiding the large penalty of a trap to the
6913 operating system. Such emulation has its own, smaller, execution
6914 cost in both time and space. To the extent that your code's
6915 important signed integer division operations are performed on two
6916 nonnegative operands, it may be desirable to use the div
6917 instruction directly.
6919 On the MC88110 processor the div instruction (also known as the
6920 divs instruction) processes negative operands without trapping to
6921 the operating system. When @option{-m88110} is specified,
6922 @option{-muse-div-instruction} is ignored, and the div instruction is used
6923 for signed integer division.
6925 Note that the result of dividing @code{INT_MIN} by @minus{}1 is undefined. In
6926 particular, the behavior of such a division with and without
6927 @option{-muse-div-instruction} may differ.
6929 @item -mtrap-large-shift
6930 @itemx -mhandle-large-shift
6931 @opindex mtrap-large-shift
6932 @opindex mhandle-large-shift
6933 @cindex bit shift overflow (88k)
6934 @cindex large bit shifts (88k)
6935 Include code to detect bit-shifts of more than 31 bits; respectively,
6936 trap such shifts or emit code to handle them properly. By default GCC
6937 makes no special provision for large bit shifts.
6939 @item -mwarn-passed-structs
6940 @opindex mwarn-passed-structs
6941 @cindex structure passing (88k)
6942 Warn when a function passes a struct as an argument or result.
6943 Structure-passing conventions have changed during the evolution of the C
6944 language, and are often the source of portability problems. By default,
6945 GCC issues no such warning.
6948 @c break page here to avoid unsightly interparagraph stretch.
6952 @node RS/6000 and PowerPC Options
6953 @subsection IBM RS/6000 and PowerPC Options
6954 @cindex RS/6000 and PowerPC Options
6955 @cindex IBM RS/6000 and PowerPC Options
6957 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
6965 @itemx -mpowerpc-gpopt
6966 @itemx -mno-powerpc-gpopt
6967 @itemx -mpowerpc-gfxopt
6968 @itemx -mno-powerpc-gfxopt
6970 @itemx -mno-powerpc64
6976 @opindex mno-powerpc
6977 @opindex mpowerpc-gpopt
6978 @opindex mno-powerpc-gpopt
6979 @opindex mpowerpc-gfxopt
6980 @opindex mno-powerpc-gfxopt
6982 @opindex mno-powerpc64
6983 GCC supports two related instruction set architectures for the
6984 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
6985 instructions supported by the @samp{rios} chip set used in the original
6986 RS/6000 systems and the @dfn{PowerPC} instruction set is the
6987 architecture of the Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and
6988 the IBM 4xx microprocessors.
6990 Neither architecture is a subset of the other. However there is a
6991 large common subset of instructions supported by both. An MQ
6992 register is included in processors supporting the POWER architecture.
6994 You use these options to specify which instructions are available on the
6995 processor you are using. The default value of these options is
6996 determined when configuring GCC@. Specifying the
6997 @option{-mcpu=@var{cpu_type}} overrides the specification of these
6998 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
6999 rather than the options listed above.
7001 The @option{-mpower} option allows GCC to generate instructions that
7002 are found only in the POWER architecture and to use the MQ register.
7003 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
7004 to generate instructions that are present in the POWER2 architecture but
7005 not the original POWER architecture.
7007 The @option{-mpowerpc} option allows GCC to generate instructions that
7008 are found only in the 32-bit subset of the PowerPC architecture.
7009 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
7010 GCC to use the optional PowerPC architecture instructions in the
7011 General Purpose group, including floating-point square root. Specifying
7012 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
7013 use the optional PowerPC architecture instructions in the Graphics
7014 group, including floating-point select.
7016 The @option{-mpowerpc64} option allows GCC to generate the additional
7017 64-bit instructions that are found in the full PowerPC64 architecture
7018 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
7019 @option{-mno-powerpc64}.
7021 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
7022 will use only the instructions in the common subset of both
7023 architectures plus some special AIX common-mode calls, and will not use
7024 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
7025 permits GCC to use any instruction from either architecture and to
7026 allow use of the MQ register; specify this for the Motorola MPC601.
7028 @item -mnew-mnemonics
7029 @itemx -mold-mnemonics
7030 @opindex mnew-mnemonics
7031 @opindex mold-mnemonics
7032 Select which mnemonics to use in the generated assembler code. With
7033 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
7034 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
7035 assembler mnemonics defined for the POWER architecture. Instructions
7036 defined in only one architecture have only one mnemonic; GCC uses that
7037 mnemonic irrespective of which of these options is specified.
7039 GCC defaults to the mnemonics appropriate for the architecture in
7040 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
7041 value of these option. Unless you are building a cross-compiler, you
7042 should normally not specify either @option{-mnew-mnemonics} or
7043 @option{-mold-mnemonics}, but should instead accept the default.
7045 @item -mcpu=@var{cpu_type}
7047 Set architecture type, register usage, choice of mnemonics, and
7048 instruction scheduling parameters for machine type @var{cpu_type}.
7049 Supported values for @var{cpu_type} are @samp{rios}, @samp{rios1},
7050 @samp{rsc}, @samp{rios2}, @samp{rs64a}, @samp{601}, @samp{602},
7051 @samp{603}, @samp{603e}, @samp{604}, @samp{604e}, @samp{620},
7052 @samp{630}, @samp{740}, @samp{7400}, @samp{7450}, @samp{750},
7053 @samp{power}, @samp{power2}, @samp{powerpc}, @samp{403}, @samp{505},
7054 @samp{801}, @samp{821}, @samp{823}, and @samp{860} and @samp{common}.
7056 @option{-mcpu=common} selects a completely generic processor. Code
7057 generated under this option will run on any POWER or PowerPC processor.
7058 GCC will use only the instructions in the common subset of both
7059 architectures, and will not use the MQ register. GCC assumes a generic
7060 processor model for scheduling purposes.
7062 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
7063 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
7064 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
7065 types, with an appropriate, generic processor model assumed for
7066 scheduling purposes.
7068 The other options specify a specific processor. Code generated under
7069 those options will run best on that processor, and may not run at all on
7072 The @option{-mcpu} options automatically enable or disable other
7073 @option{-m} options as follows:
7077 @option{-mno-power}, @option{-mno-powerpc}
7084 @option{-mpower}, @option{-mno-powerpc}, @option{-mno-new-mnemonics}
7099 @option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics}
7102 @option{-mpower}, @option{-mpowerpc}, @option{-mnew-mnemonics}
7107 @option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics}, @option{-msoft-float}
7110 @item -mtune=@var{cpu_type}
7112 Set the instruction scheduling parameters for machine type
7113 @var{cpu_type}, but do not set the architecture type, register usage, or
7114 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
7115 values for @var{cpu_type} are used for @option{-mtune} as for
7116 @option{-mcpu}. If both are specified, the code generated will use the
7117 architecture, registers, and mnemonics set by @option{-mcpu}, but the
7118 scheduling parameters set by @option{-mtune}.
7123 @opindex mno-altivec
7124 These switches enable or disable the use of built-in functions that
7125 allow access to the AltiVec instruction set. You may also need to set
7126 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
7131 Extend the current ABI with SPE ABI extensions. This does not change
7132 the default ABI, instead it adds the SPE ABI extensions to the current
7136 @opindex mabi=no-spe
7137 Disable Booke SPE ABI extensions for the current ABI.
7139 @item -misel=@var{yes/no}
7142 This switch enables or disables the generation of ISEL instructions.
7144 @item -mspe=@var{yes/no}
7147 This switch enables or disables the generation of SPE simd
7150 @item -mfloat-gprs=@var{yes/no}
7152 @opindex mfloat-gprs
7153 This switch enables or disables the generation of floating point
7154 operations on the general purpose registers for architectures that
7155 support it. This option is currently only available on the MPC8540.
7158 @itemx -mno-fp-in-toc
7159 @itemx -mno-sum-in-toc
7160 @itemx -mminimal-toc
7162 @opindex mno-fp-in-toc
7163 @opindex mno-sum-in-toc
7164 @opindex mminimal-toc
7165 Modify generation of the TOC (Table Of Contents), which is created for
7166 every executable file. The @option{-mfull-toc} option is selected by
7167 default. In that case, GCC will allocate at least one TOC entry for
7168 each unique non-automatic variable reference in your program. GCC
7169 will also place floating-point constants in the TOC@. However, only
7170 16,384 entries are available in the TOC@.
7172 If you receive a linker error message that saying you have overflowed
7173 the available TOC space, you can reduce the amount of TOC space used
7174 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
7175 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
7176 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
7177 generate code to calculate the sum of an address and a constant at
7178 run-time instead of putting that sum into the TOC@. You may specify one
7179 or both of these options. Each causes GCC to produce very slightly
7180 slower and larger code at the expense of conserving TOC space.
7182 If you still run out of space in the TOC even when you specify both of
7183 these options, specify @option{-mminimal-toc} instead. This option causes
7184 GCC to make only one TOC entry for every file. When you specify this
7185 option, GCC will produce code that is slower and larger but which
7186 uses extremely little TOC space. You may wish to use this option
7187 only on files that contain less frequently executed code.
7193 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
7194 @code{long} type, and the infrastructure needed to support them.
7195 Specifying @option{-maix64} implies @option{-mpowerpc64} and
7196 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
7197 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
7202 @opindex mno-xl-call
7203 On AIX, pass floating-point arguments to prototyped functions beyond the
7204 register save area (RSA) on the stack in addition to argument FPRs. The
7205 AIX calling convention was extended but not initially documented to
7206 handle an obscure K&R C case of calling a function that takes the
7207 address of its arguments with fewer arguments than declared. AIX XL
7208 compilers access floating point arguments which do not fit in the
7209 RSA from the stack when a subroutine is compiled without
7210 optimization. Because always storing floating-point arguments on the
7211 stack is inefficient and rarely needed, this option is not enabled by
7212 default and only is necessary when calling subroutines compiled by AIX
7213 XL compilers without optimization.
7217 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
7218 application written to use message passing with special startup code to
7219 enable the application to run. The system must have PE installed in the
7220 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
7221 must be overridden with the @option{-specs=} option to specify the
7222 appropriate directory location. The Parallel Environment does not
7223 support threads, so the @option{-mpe} option and the @option{-pthread}
7224 option are incompatible.
7226 @item -malign-natural
7227 @itemx -malign-power
7228 @opindex malign-natural
7229 @opindex malign-power
7230 On AIX, Darwin, and 64-bit PowerPC Linux, the option
7231 @option{-malign-natural} overrides the ABI-defined alignment of larger
7232 types, such as floating-point doubles, on their natural size-based boundary.
7233 The option @option{-malign-power} instructs GCC to follow the ABI-specified
7234 alignment rules. GCC defaults to the standard alignment defined in the ABI.
7238 @opindex msoft-float
7239 @opindex mhard-float
7240 Generate code that does not use (uses) the floating-point register set.
7241 Software floating point emulation is provided if you use the
7242 @option{-msoft-float} option, and pass the option to GCC when linking.
7245 @itemx -mno-multiple
7247 @opindex mno-multiple
7248 Generate code that uses (does not use) the load multiple word
7249 instructions and the store multiple word instructions. These
7250 instructions are generated by default on POWER systems, and not
7251 generated on PowerPC systems. Do not use @option{-mmultiple} on little
7252 endian PowerPC systems, since those instructions do not work when the
7253 processor is in little endian mode. The exceptions are PPC740 and
7254 PPC750 which permit the instructions usage in little endian mode.
7260 Generate code that uses (does not use) the load string instructions
7261 and the store string word instructions to save multiple registers and
7262 do small block moves. These instructions are generated by default on
7263 POWER systems, and not generated on PowerPC systems. Do not use
7264 @option{-mstring} on little endian PowerPC systems, since those
7265 instructions do not work when the processor is in little endian mode.
7266 The exceptions are PPC740 and PPC750 which permit the instructions
7267 usage in little endian mode.
7273 Generate code that uses (does not use) the load or store instructions
7274 that update the base register to the address of the calculated memory
7275 location. These instructions are generated by default. If you use
7276 @option{-mno-update}, there is a small window between the time that the
7277 stack pointer is updated and the address of the previous frame is
7278 stored, which means code that walks the stack frame across interrupts or
7279 signals may get corrupted data.
7282 @itemx -mno-fused-madd
7283 @opindex mfused-madd
7284 @opindex mno-fused-madd
7285 Generate code that uses (does not use) the floating point multiply and
7286 accumulate instructions. These instructions are generated by default if
7287 hardware floating is used.
7289 @item -mno-bit-align
7291 @opindex mno-bit-align
7293 On System V.4 and embedded PowerPC systems do not (do) force structures
7294 and unions that contain bit-fields to be aligned to the base type of the
7297 For example, by default a structure containing nothing but 8
7298 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
7299 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
7300 the structure would be aligned to a 1 byte boundary and be one byte in
7303 @item -mno-strict-align
7304 @itemx -mstrict-align
7305 @opindex mno-strict-align
7306 @opindex mstrict-align
7307 On System V.4 and embedded PowerPC systems do not (do) assume that
7308 unaligned memory references will be handled by the system.
7311 @itemx -mno-relocatable
7312 @opindex mrelocatable
7313 @opindex mno-relocatable
7314 On embedded PowerPC systems generate code that allows (does not allow)
7315 the program to be relocated to a different address at runtime. If you
7316 use @option{-mrelocatable} on any module, all objects linked together must
7317 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
7319 @item -mrelocatable-lib
7320 @itemx -mno-relocatable-lib
7321 @opindex mrelocatable-lib
7322 @opindex mno-relocatable-lib
7323 On embedded PowerPC systems generate code that allows (does not allow)
7324 the program to be relocated to a different address at runtime. Modules
7325 compiled with @option{-mrelocatable-lib} can be linked with either modules
7326 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
7327 with modules compiled with the @option{-mrelocatable} options.
7333 On System V.4 and embedded PowerPC systems do not (do) assume that
7334 register 2 contains a pointer to a global area pointing to the addresses
7335 used in the program.
7338 @itemx -mlittle-endian
7340 @opindex mlittle-endian
7341 On System V.4 and embedded PowerPC systems compile code for the
7342 processor in little endian mode. The @option{-mlittle-endian} option is
7343 the same as @option{-mlittle}.
7348 @opindex mbig-endian
7349 On System V.4 and embedded PowerPC systems compile code for the
7350 processor in big endian mode. The @option{-mbig-endian} option is
7351 the same as @option{-mbig}.
7353 @item -mdynamic-no-pic
7354 @opindex mdynamic-no-pic
7355 On Darwin and Mac OS X systems, compile code so that it is not
7356 relocatable, but that its external references are relocatable. The
7357 resulting code is suitable for applications, but not shared
7362 On System V.4 and embedded PowerPC systems compile code using calling
7363 conventions that adheres to the March 1995 draft of the System V
7364 Application Binary Interface, PowerPC processor supplement. This is the
7365 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
7367 @item -mcall-sysv-eabi
7368 @opindex mcall-sysv-eabi
7369 Specify both @option{-mcall-sysv} and @option{-meabi} options.
7371 @item -mcall-sysv-noeabi
7372 @opindex mcall-sysv-noeabi
7373 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
7375 @item -mcall-solaris
7376 @opindex mcall-solaris
7377 On System V.4 and embedded PowerPC systems compile code for the Solaris
7381 @opindex mcall-linux
7382 On System V.4 and embedded PowerPC systems compile code for the
7383 Linux-based GNU system.
7387 On System V.4 and embedded PowerPC systems compile code for the
7388 Hurd-based GNU system.
7391 @opindex mcall-netbsd
7392 On System V.4 and embedded PowerPC systems compile code for the
7393 NetBSD operating system.
7395 @item -maix-struct-return
7396 @opindex maix-struct-return
7397 Return all structures in memory (as specified by the AIX ABI)@.
7399 @item -msvr4-struct-return
7400 @opindex msvr4-struct-return
7401 Return structures smaller than 8 bytes in registers (as specified by the
7405 @opindex mabi=altivec
7406 Extend the current ABI with AltiVec ABI extensions. This does not
7407 change the default ABI, instead it adds the AltiVec ABI extensions to
7410 @item -mabi=no-altivec
7411 @opindex mabi=no-altivec
7412 Disable AltiVec ABI extensions for the current ABI.
7415 @itemx -mno-prototype
7417 @opindex mno-prototype
7418 On System V.4 and embedded PowerPC systems assume that all calls to
7419 variable argument functions are properly prototyped. Otherwise, the
7420 compiler must insert an instruction before every non prototyped call to
7421 set or clear bit 6 of the condition code register (@var{CR}) to
7422 indicate whether floating point values were passed in the floating point
7423 registers in case the function takes a variable arguments. With
7424 @option{-mprototype}, only calls to prototyped variable argument functions
7425 will set or clear the bit.
7429 On embedded PowerPC systems, assume that the startup module is called
7430 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
7431 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
7436 On embedded PowerPC systems, assume that the startup module is called
7437 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
7442 On embedded PowerPC systems, assume that the startup module is called
7443 @file{crt0.o} and the standard C libraries are @file{libads.a} and
7447 @opindex myellowknife
7448 On embedded PowerPC systems, assume that the startup module is called
7449 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
7454 On System V.4 and embedded PowerPC systems, specify that you are
7455 compiling for a VxWorks system.
7459 Specify that you are compiling for the WindISS simulation environment.
7463 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
7464 header to indicate that @samp{eabi} extended relocations are used.
7470 On System V.4 and embedded PowerPC systems do (do not) adhere to the
7471 Embedded Applications Binary Interface (eabi) which is a set of
7472 modifications to the System V.4 specifications. Selecting @option{-meabi}
7473 means that the stack is aligned to an 8 byte boundary, a function
7474 @code{__eabi} is called to from @code{main} to set up the eabi
7475 environment, and the @option{-msdata} option can use both @code{r2} and
7476 @code{r13} to point to two separate small data areas. Selecting
7477 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
7478 do not call an initialization function from @code{main}, and the
7479 @option{-msdata} option will only use @code{r13} to point to a single
7480 small data area. The @option{-meabi} option is on by default if you
7481 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
7484 @opindex msdata=eabi
7485 On System V.4 and embedded PowerPC systems, put small initialized
7486 @code{const} global and static data in the @samp{.sdata2} section, which
7487 is pointed to by register @code{r2}. Put small initialized
7488 non-@code{const} global and static data in the @samp{.sdata} section,
7489 which is pointed to by register @code{r13}. Put small uninitialized
7490 global and static data in the @samp{.sbss} section, which is adjacent to
7491 the @samp{.sdata} section. The @option{-msdata=eabi} option is
7492 incompatible with the @option{-mrelocatable} option. The
7493 @option{-msdata=eabi} option also sets the @option{-memb} option.
7496 @opindex msdata=sysv
7497 On System V.4 and embedded PowerPC systems, put small global and static
7498 data in the @samp{.sdata} section, which is pointed to by register
7499 @code{r13}. Put small uninitialized global and static data in the
7500 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
7501 The @option{-msdata=sysv} option is incompatible with the
7502 @option{-mrelocatable} option.
7504 @item -msdata=default
7506 @opindex msdata=default
7508 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
7509 compile code the same as @option{-msdata=eabi}, otherwise compile code the
7510 same as @option{-msdata=sysv}.
7513 @opindex msdata-data
7514 On System V.4 and embedded PowerPC systems, put small global and static
7515 data in the @samp{.sdata} section. Put small uninitialized global and
7516 static data in the @samp{.sbss} section. Do not use register @code{r13}
7517 to address small data however. This is the default behavior unless
7518 other @option{-msdata} options are used.
7522 @opindex msdata=none
7524 On embedded PowerPC systems, put all initialized global and static data
7525 in the @samp{.data} section, and all uninitialized data in the
7526 @samp{.bss} section.
7530 @cindex smaller data references (PowerPC)
7531 @cindex .sdata/.sdata2 references (PowerPC)
7532 On embedded PowerPC systems, put global and static items less than or
7533 equal to @var{num} bytes into the small data or bss sections instead of
7534 the normal data or bss section. By default, @var{num} is 8. The
7535 @option{-G @var{num}} switch is also passed to the linker.
7536 All modules should be compiled with the same @option{-G @var{num}} value.
7539 @itemx -mno-regnames
7541 @opindex mno-regnames
7542 On System V.4 and embedded PowerPC systems do (do not) emit register
7543 names in the assembly language output using symbolic forms.
7546 @itemx -mno-longcall
7548 @opindex mno-longcall
7549 Default to making all function calls via pointers, so that functions
7550 which reside further than 64 megabytes (67,108,864 bytes) from the
7551 current location can be called. This setting can be overridden by the
7552 @code{shortcall} function attribute, or by @code{#pragma longcall(0)}.
7554 Some linkers are capable of detecting out-of-range calls and generating
7555 glue code on the fly. On these systems, long calls are unnecessary and
7556 generate slower code. As of this writing, the AIX linker can do this,
7557 as can the GNU linker for PowerPC/64. It is planned to add this feature
7558 to the GNU linker for 32-bit PowerPC systems as well.
7560 In the future, we may cause GCC to ignore all longcall specifications
7561 when the linker is known to generate glue.
7565 Adds support for multithreading with the @dfn{pthreads} library.
7566 This option sets flags for both the preprocessor and linker.
7570 @node Darwin Options
7571 @subsection Darwin Options
7572 @cindex Darwin options
7574 These options are defined for all architectures running the Darwin operating
7575 system. They are useful for compatibility with other Mac OS compilers.
7580 Loads all members of static archive libraries.
7581 See man ld(1) for more information.
7583 @item -arch_errors_fatal
7584 @opindex arch_errors_fatal
7585 Cause the errors having to do with files that have the wrong architecture
7589 @opindex bind_at_load
7590 Causes the output file to be marked such that the dynamic linker will
7591 bind all undefined references when the file is loaded or launched.
7595 Produce a Mach-o bundle format file.
7596 See man ld(1) for more information.
7598 @item -bundle_loader @var{executable}
7599 @opindex bundle_loader
7600 This specifies the @var{executable} that will be loading the build
7601 output file being linked. See man ld(1) for more information.
7603 @item -allowable_client @var{client_name}
7607 @item -compatibility_version
7608 @item -current_version
7609 @item -dependency-file
7611 @item -dylinker_install_name
7614 @item -exported_symbols_list
7616 @item -flat_namespace
7617 @item -force_cpusubtype_ALL
7618 @item -force_flat_namespace
7619 @item -headerpad_max_install_names
7623 @item -keep_private_externs
7625 @item -multiply_defined
7626 @item -multiply_defined_unused
7630 @item -noseglinkedit
7631 @item -pagezero_size
7633 @item -prebind_all_twolevel_modules
7634 @item -private_bundle
7635 @item -read_only_relocs
7637 @item -sectobjectsymbols
7641 @item -sectobjectsymbols
7643 @item -seg_addr_table
7644 @item -seg_addr_table_filename
7647 @item -segs_read_only_addr
7648 @item -segs_read_write_addr
7649 @item -single_module
7653 @item -twolevel_namespace
7656 @item -unexported_symbols_list
7657 @item -weak_reference_mismatches
7660 @opindex allowable_client
7662 @opindex client_name
7663 @opindex compatibility_version
7664 @opindex current_version
7665 @opindex dependency-file
7667 @opindex dylinker_install_name
7670 @opindex exported_symbols_list
7672 @opindex flat_namespace
7673 @opindex force_cpusubtype_ALL
7674 @opindex force_flat_namespace
7675 @opindex headerpad_max_install_names
7678 @opindex install_name
7679 @opindex keep_private_externs
7680 @opindex multi_module
7681 @opindex multiply_defined
7682 @opindex multiply_defined_unused
7684 @opindex nomultidefs
7686 @opindex noseglinkedit
7687 @opindex pagezero_size
7689 @opindex prebind_all_twolevel_modules
7690 @opindex private_bundle
7691 @opindex read_only_relocs
7693 @opindex sectobjectsymbols
7697 @opindex sectobjectsymbols
7699 @opindex seg_addr_table
7700 @opindex seg_addr_table_filename
7701 @opindex seglinkedit
7703 @opindex segs_read_only_addr
7704 @opindex segs_read_write_addr
7705 @opindex single_module
7707 @opindex sub_library
7708 @opindex sub_umbrella
7709 @opindex twolevel_namespace
7712 @opindex unexported_symbols_list
7713 @opindex weak_reference_mismatches
7714 @opindex whatsloaded
7716 This options are available for Darwin linker. Darwin linker man page
7717 describes them in detail.
7722 @subsection IBM RT Options
7724 @cindex IBM RT options
7726 These @samp{-m} options are defined for the IBM RT PC:
7730 @opindex min-line-mul
7731 Use an in-line code sequence for integer multiplies. This is the
7734 @item -mcall-lib-mul
7735 @opindex mcall-lib-mul
7736 Call @code{lmul$$} for integer multiples.
7738 @item -mfull-fp-blocks
7739 @opindex mfull-fp-blocks
7740 Generate full-size floating point data blocks, including the minimum
7741 amount of scratch space recommended by IBM@. This is the default.
7743 @item -mminimum-fp-blocks
7744 @opindex mminimum-fp-blocks
7745 Do not include extra scratch space in floating point data blocks. This
7746 results in smaller code, but slower execution, since scratch space must
7747 be allocated dynamically.
7749 @cindex @file{stdarg.h} and RT PC
7750 @item -mfp-arg-in-fpregs
7751 @opindex mfp-arg-in-fpregs
7752 Use a calling sequence incompatible with the IBM calling convention in
7753 which floating point arguments are passed in floating point registers.
7754 Note that @code{stdarg.h} will not work with floating point operands
7755 if this option is specified.
7757 @item -mfp-arg-in-gregs
7758 @opindex mfp-arg-in-gregs
7759 Use the normal calling convention for floating point arguments. This is
7762 @item -mhc-struct-return
7763 @opindex mhc-struct-return
7764 Return structures of more than one word in memory, rather than in a
7765 register. This provides compatibility with the MetaWare HighC (hc)
7766 compiler. Use the option @option{-fpcc-struct-return} for compatibility
7767 with the Portable C Compiler (pcc).
7769 @item -mnohc-struct-return
7770 @opindex mnohc-struct-return
7771 Return some structures of more than one word in registers, when
7772 convenient. This is the default. For compatibility with the
7773 IBM-supplied compilers, use the option @option{-fpcc-struct-return} or the
7774 option @option{-mhc-struct-return}.
7778 @subsection MIPS Options
7779 @cindex MIPS options
7781 These @samp{-m} options are defined for the MIPS family of computers:
7785 @item -march=@var{arch}
7787 Generate code that will run on @var{arch}, which can be the name of a
7788 generic MIPS ISA, or the name of a particular processor.
7790 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
7791 @samp{mips32}, @samp{mips32r2}, and @samp{mips64}.
7792 The processor names are:
7793 @samp{4kc}, @samp{4kp}, @samp{5kc}, @samp{20kc},
7795 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
7796 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000}, @samp{rm7000},
7800 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4300},
7801 @samp{vr5000}, @samp{vr5400} and @samp{vr5500}.
7802 The special value @samp{from-abi} selects the
7803 most compatible architecture for the selected ABI (that is,
7804 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
7806 In processor names, a final @samp{000} can be abbreviated as @samp{k}
7807 (for example, @samp{-march=r2k}). Prefixes are optional, and
7808 @samp{vr} may be written @samp{r}.
7810 GCC defines two macros based on the value of this option. The first
7811 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
7812 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
7813 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
7814 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
7815 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
7817 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
7818 above. In other words, it will have the full prefix and will not
7819 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
7820 the macro names the resolved architecture (either @samp{"mips1"} or
7821 @samp{"mips3"}). It names the default architecture when no
7822 @option{-march} option is given.
7824 @item -mtune=@var{arch}
7826 Optimize for @var{arch}. Among other things, this option controls
7827 the way instructions are scheduled, and the perceived cost of arithmetic
7828 operations. The list of @var{arch} values is the same as for
7831 When this option is not used, GCC will optimize for the processor
7832 specified by @option{-march}. By using @option{-march} and
7833 @option{-mtune} together, it is possible to generate code that will
7834 run on a family of processors, but optimize the code for one
7835 particular member of that family.
7837 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
7838 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
7839 @samp{-march} ones described above.
7843 Equivalent to @samp{-march=mips1}.
7847 Equivalent to @samp{-march=mips2}.
7851 Equivalent to @samp{-march=mips3}.
7855 Equivalent to @samp{-march=mips4}.
7859 Equivalent to @samp{-march=mips32}.
7863 Equivalent to @samp{-march=mips32r2}.
7867 Equivalent to @samp{-march=mips64}.
7870 @itemx -mno-fused-madd
7871 @opindex mfused-madd
7872 @opindex mno-fused-madd
7873 Generate code that uses (does not use) the floating point multiply and
7874 accumulate instructions, when they are available. These instructions
7875 are generated by default if they are available, but this may be
7876 undesirable if the extra precision causes problems or on certain chips
7877 in the mode where denormals are rounded to zero where denormals
7878 generated by multiply and accumulate instructions cause exceptions
7883 Assume that floating point registers are 32 bits wide.
7887 Assume that floating point registers are 64 bits wide.
7891 Assume that general purpose registers are 32 bits wide.
7895 Assume that general purpose registers are 64 bits wide.
7899 Force int and long types to be 64 bits wide. See @option{-mlong32} for an
7900 explanation of the default, and the width of pointers.
7904 Force long types to be 64 bits wide. See @option{-mlong32} for an
7905 explanation of the default, and the width of pointers.
7909 Force long, int, and pointer types to be 32 bits wide.
7911 The default size of ints, longs and pointers depends on the ABI@. All
7912 the supported ABIs use 32-bit ints. The n64 ABI uses 64-bit longs, as
7913 does the 64-bit Cygnus EABI; the others use 32-bit longs. Pointers
7914 are the same size as longs, or the same size as integer registers,
7915 whichever is smaller.
7929 Generate code for the given ABI@.
7931 Note that there are two embedded ABIs: @option{-mabi=eabi}
7932 selects the one defined by Cygnus while @option{-meabi=meabi}
7933 selects the one defined by MIPS@. Both these ABIs have
7934 32-bit and 64-bit variants. Normally, GCC will generate
7935 64-bit code when you select a 64-bit architecture, but you
7936 can use @option{-mgp32} to get 32-bit code instead.
7938 @item -mabi-fake-default
7939 @opindex mabi-fake-default
7940 You don't want to know what this option does. No, really. I mean
7941 it. Move on to the next option.
7943 What? You're still here? Oh, well@enddots{} Ok, here's the deal. GCC
7944 wants the default set of options to get the root of the multilib tree,
7945 and the shared library SONAMEs without any multilib-indicating
7946 suffixes. This is not convenience for @samp{mips64-linux-gnu}, since
7947 we want to default to the N32 ABI, while still being binary-compatible
7948 with @samp{mips-linux-gnu} if you stick to the O32 ABI@. Being
7949 binary-compatible means shared libraries should have the same SONAMEs,
7950 and libraries should live in the same location. Having O32 libraries
7951 in a sub-directory named say @file{o32} is not acceptable.
7953 So we trick GCC into believing that O32 is the default ABI, except
7954 that we override the default with some internal command-line
7955 processing magic. Problem is, if we stopped at that, and you then
7956 created a multilib-aware package that used the output of @command{gcc
7957 -print-multi-lib} to decide which multilibs to build, and how, and
7958 you'd find yourself in an awkward situation when you found out that
7959 some of the options listed ended up mapping to the same multilib, and
7960 none of your libraries was actually built for the multilib that
7961 @option{-print-multi-lib} claims to be the default. So we added this
7962 option that disables the default switcher, falling back to GCC's
7963 original notion of the default library. Confused yet?
7965 For short: don't ever use this option, unless you find it in the list
7966 of additional options to be used when building for multilibs, in the
7967 output of @option{gcc -print-multi-lib}.
7971 Generate code for the MIPS assembler, and invoke @file{mips-tfile} to
7972 add normal debug information. This is the default for all
7973 platforms except for the OSF/1 reference platform, using the OSF/rose
7974 object format. If the either of the @option{-gstabs} or @option{-gstabs+}
7975 switches are used, the @file{mips-tfile} program will encapsulate the
7976 stabs within MIPS ECOFF@.
7980 Generate code for the GNU assembler. This is the default on the OSF/1
7981 reference platform, using the OSF/rose object format. Also, this is
7982 the default if the configure option @option{--with-gnu-as} is used.
7984 @item -msplit-addresses
7985 @itemx -mno-split-addresses
7986 @opindex msplit-addresses
7987 @opindex mno-split-addresses
7988 Generate code to load the high and low parts of address constants separately.
7989 This allows GCC to optimize away redundant loads of the high order
7990 bits of addresses. This optimization requires GNU as and GNU ld.
7991 This optimization is enabled by default for some embedded targets where
7992 GNU as and GNU ld are standard.
7998 The @option{-mrnames} switch says to output code using the MIPS software
7999 names for the registers, instead of the hardware names (ie, @var{a0}
8000 instead of @var{$4}). The only known assembler that supports this option
8001 is the Algorithmics assembler.
8007 The @option{-mmemcpy} switch makes all block moves call the appropriate
8008 string function (@samp{memcpy} or @samp{bcopy}) instead of possibly
8009 generating inline code.
8012 @itemx -mno-mips-tfile
8013 @opindex mmips-tfile
8014 @opindex mno-mips-tfile
8015 The @option{-mno-mips-tfile} switch causes the compiler not
8016 postprocess the object file with the @file{mips-tfile} program,
8017 after the MIPS assembler has generated it to add debug support. If
8018 @file{mips-tfile} is not run, then no local variables will be
8019 available to the debugger. In addition, @file{stage2} and
8020 @file{stage3} objects will have the temporary file names passed to the
8021 assembler embedded in the object file, which means the objects will
8022 not compare the same. The @option{-mno-mips-tfile} switch should only
8023 be used when there are bugs in the @file{mips-tfile} program that
8024 prevents compilation.
8027 @opindex msoft-float
8028 Generate output containing library calls for floating point.
8029 @strong{Warning:} the requisite libraries are not part of GCC@.
8030 Normally the facilities of the machine's usual C compiler are used, but
8031 this can't be done directly in cross-compilation. You must make your
8032 own arrangements to provide suitable library functions for
8036 @opindex mhard-float
8037 Generate output containing floating point instructions. This is the
8038 default if you use the unmodified sources.
8041 @itemx -mno-abicalls
8043 @opindex mno-abicalls
8044 Emit (or do not emit) the pseudo operations @samp{.abicalls},
8045 @samp{.cpload}, and @samp{.cprestore} that some System V.4 ports use for
8046 position independent code.
8049 @itemx -mno-long-calls
8050 @opindex mlong-calls
8051 @opindex mno-long-calls
8052 Do all calls with the @samp{JALR} instruction, which requires
8053 loading up a function's address into a register before the call.
8054 You need to use this switch, if you call outside of the current
8055 512 megabyte segment to functions that are not through pointers.
8057 @item -membedded-pic
8058 @itemx -mno-embedded-pic
8059 @opindex membedded-pic
8060 @opindex mno-embedded-pic
8061 Generate PIC code suitable for some embedded systems. All calls are
8062 made using PC relative address, and all data is addressed using the $gp
8063 register. No more than 65536 bytes of global data may be used. This
8064 requires GNU as and GNU ld which do most of the work. This currently
8065 only works on targets which use ECOFF; it does not work with ELF@.
8067 @item -membedded-data
8068 @itemx -mno-embedded-data
8069 @opindex membedded-data
8070 @opindex mno-embedded-data
8071 Allocate variables to the read-only data section first if possible, then
8072 next in the small data section if possible, otherwise in data. This gives
8073 slightly slower code than the default, but reduces the amount of RAM required
8074 when executing, and thus may be preferred for some embedded systems.
8076 @item -muninit-const-in-rodata
8077 @itemx -mno-uninit-const-in-rodata
8078 @opindex muninit-const-in-rodata
8079 @opindex mno-uninit-const-in-rodata
8080 When used together with @option{-membedded-data}, it will always store uninitialized
8081 const variables in the read-only data section.
8083 @item -msingle-float
8084 @itemx -mdouble-float
8085 @opindex msingle-float
8086 @opindex mdouble-float
8087 The @option{-msingle-float} switch tells gcc to assume that the floating
8088 point coprocessor only supports single precision operations, as on the
8089 @samp{r4650} chip. The @option{-mdouble-float} switch permits gcc to use
8090 double precision operations. This is the default.
8096 Permit use of the @samp{mad}, @samp{madu} and @samp{mul} instructions,
8097 as on the @samp{r4650} chip.
8101 Turns on @option{-msingle-float}, @option{-mmad}, and, at least for now,
8102 @option{-mcpu=r4650}.
8108 Enable 16-bit instructions.
8112 Use the entry and exit pseudo ops. This option can only be used with
8117 Compile code for the processor in little endian mode.
8118 The requisite libraries are assumed to exist.
8122 Compile code for the processor in big endian mode.
8123 The requisite libraries are assumed to exist.
8127 @cindex smaller data references (MIPS)
8128 @cindex gp-relative references (MIPS)
8129 Put global and static items less than or equal to @var{num} bytes into
8130 the small data or bss sections instead of the normal data or bss
8131 section. This allows the assembler to emit one word memory reference
8132 instructions based on the global pointer (@var{gp} or @var{$28}),
8133 instead of the normal two words used. By default, @var{num} is 8 when
8134 the MIPS assembler is used, and 0 when the GNU assembler is used. The
8135 @option{-G @var{num}} switch is also passed to the assembler and linker.
8136 All modules should be compiled with the same @option{-G @var{num}}
8141 Tell the MIPS assembler to not run its preprocessor over user
8142 assembler files (with a @samp{.s} suffix) when assembling them.
8146 Pass an option to gas which will cause nops to be inserted if
8147 the read of the destination register of an mfhi or mflo instruction
8148 occurs in the following two instructions.
8152 Do not include the default crt0.
8154 @item -mflush-func=@var{func}
8155 @itemx -mno-flush-func
8156 @opindex mflush-func
8157 Specifies the function to call to flush the I and D caches, or to not
8158 call any such function. If called, the function must take the same
8159 arguments as the common @code{_flush_func()}, that is, the address of the
8160 memory range for which the cache is being flushed, the size of the
8161 memory range, and the number 3 (to flush both caches). The default
8162 depends on the target gcc was configured for, but commonly is either
8163 @samp{_flush_func} or @samp{__cpu_flush}.
8165 @item -mbranch-likely
8166 @itemx -mno-branch-likely
8167 @opindex mbranch-likely
8168 @opindex mno-branch-likely
8169 Enable or disable use of Branch Likely instructions, regardless of the
8170 default for the selected architecture. By default, Branch Likely
8171 instructions may be generated if they are supported by the selected
8172 architecture. An exception is for the MIPS32 and MIPS64 architectures
8173 and processors which implement those architectures; for those, Branch
8174 Likely instructions will not be generated by default because the MIPS32
8175 and MIPS64 architectures specifically deprecate their use.
8178 @node i386 and x86-64 Options
8179 @subsection Intel 386 and AMD x86-64 Options
8180 @cindex i386 Options
8181 @cindex x86-64 Options
8182 @cindex Intel 386 Options
8183 @cindex AMD x86-64 Options
8185 These @samp{-m} options are defined for the i386 and x86-64 family of
8189 @item -mtune=@var{cpu-type}
8191 Tune to @var{cpu-type} everything applicable about the generated code, except
8192 for the ABI and the set of available instructions. The choices for
8193 @var{cpu-type} are @samp{i386}, @samp{i486}, @samp{i586}, @samp{i686},
8194 @samp{pentium}, @samp{pentium-mmx}, @samp{pentiumpro}, @samp{pentium2},
8195 @samp{pentium3}, @samp{pentium4}, @samp{k6}, @samp{k6-2}, @samp{k6-3},
8196 @samp{athlon}, @samp{athlon-tbird}, @samp{athlon-4}, @samp{athlon-xp},
8197 @samp{athlon-mp}, @samp{winchip-c6}, @samp{winchip2}, @samp{k8}, @samp{c3}
8200 While picking a specific @var{cpu-type} will schedule things appropriately
8201 for that particular chip, the compiler will not generate any code that
8202 does not run on the i386 without the @option{-march=@var{cpu-type}} option
8203 being used. @samp{i586} is equivalent to @samp{pentium} and @samp{i686}
8204 is equivalent to @samp{pentiumpro}. @samp{k6} and @samp{athlon} are the
8205 AMD chips as opposed to the Intel ones.
8207 @item -march=@var{cpu-type}
8209 Generate instructions for the machine type @var{cpu-type}. The choices
8210 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
8211 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
8213 @item -mcpu=@var{cpu-type}
8215 A deprecated synonym for @option{-mtune}.
8224 @opindex mpentiumpro
8225 These options are synonyms for @option{-mtune=i386}, @option{-mtune=i486},
8226 @option{-mtune=pentium}, and @option{-mtune=pentiumpro} respectively.
8227 These synonyms are deprecated.
8229 @item -mfpmath=@var{unit}
8231 generate floating point arithmetics for selected unit @var{unit}. the choices
8236 Use the standard 387 floating point coprocessor present majority of chips and
8237 emulated otherwise. Code compiled with this option will run almost everywhere.
8238 The temporary results are computed in 80bit precision instead of precision
8239 specified by the type resulting in slightly different results compared to most
8240 of other chips. See @option{-ffloat-store} for more detailed description.
8242 This is the default choice for i386 compiler.
8245 Use scalar floating point instructions present in the SSE instruction set.
8246 This instruction set is supported by Pentium3 and newer chips, in the AMD line
8247 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
8248 instruction set supports only single precision arithmetics, thus the double and
8249 extended precision arithmetics is still done using 387. Later version, present
8250 only in Pentium4 and the future AMD x86-64 chips supports double precision
8253 For i387 you need to use @option{-march=@var{cpu-type}}, @option{-msse} or
8254 @option{-msse2} switches to enable SSE extensions and make this option
8255 effective. For x86-64 compiler, these extensions are enabled by default.
8257 The resulting code should be considerably faster in majority of cases and avoid
8258 the numerical instability problems of 387 code, but may break some existing
8259 code that expects temporaries to be 80bit.
8261 This is the default choice for x86-64 compiler.
8264 Use all SSE extensions enabled by @option{-msse2} as well as the new
8265 SSE extensions in Prescott New Instructions. @option{-mpni} also
8266 enables 2 builtin functions, @code{__builtin_ia32_monitor} and
8267 @code{__builtin_ia32_mwait}, for new instructions @code{monitor} and
8271 Attempt to utilize both instruction sets at once. This effectively double the
8272 amount of available registers and on chips with separate execution units for
8273 387 and SSE the execution resources too. Use this option with care, as it is
8274 still experimental, because gcc register allocator does not model separate
8275 functional units well resulting in instable performance.
8278 @item -masm=@var{dialect}
8279 @opindex masm=@var{dialect}
8280 Output asm instructions using selected @var{dialect}. Supported choices are
8281 @samp{intel} or @samp{att} (the default one).
8286 @opindex mno-ieee-fp
8287 Control whether or not the compiler uses IEEE floating point
8288 comparisons. These handle correctly the case where the result of a
8289 comparison is unordered.
8292 @opindex msoft-float
8293 Generate output containing library calls for floating point.
8294 @strong{Warning:} the requisite libraries are not part of GCC@.
8295 Normally the facilities of the machine's usual C compiler are used, but
8296 this can't be done directly in cross-compilation. You must make your
8297 own arrangements to provide suitable library functions for
8300 On machines where a function returns floating point results in the 80387
8301 register stack, some floating point opcodes may be emitted even if
8302 @option{-msoft-float} is used.
8304 @item -mno-fp-ret-in-387
8305 @opindex mno-fp-ret-in-387
8306 Do not use the FPU registers for return values of functions.
8308 The usual calling convention has functions return values of types
8309 @code{float} and @code{double} in an FPU register, even if there
8310 is no FPU@. The idea is that the operating system should emulate
8313 The option @option{-mno-fp-ret-in-387} causes such values to be returned
8314 in ordinary CPU registers instead.
8316 @item -mno-fancy-math-387
8317 @opindex mno-fancy-math-387
8318 Some 387 emulators do not support the @code{sin}, @code{cos} and
8319 @code{sqrt} instructions for the 387. Specify this option to avoid
8320 generating those instructions. This option is the default on FreeBSD,
8321 OpenBSD and NetBSD@. This option is overridden when @option{-march}
8322 indicates that the target cpu will always have an FPU and so the
8323 instruction will not need emulation. As of revision 2.6.1, these
8324 instructions are not generated unless you also use the
8325 @option{-funsafe-math-optimizations} switch.
8327 @item -malign-double
8328 @itemx -mno-align-double
8329 @opindex malign-double
8330 @opindex mno-align-double
8331 Control whether GCC aligns @code{double}, @code{long double}, and
8332 @code{long long} variables on a two word boundary or a one word
8333 boundary. Aligning @code{double} variables on a two word boundary will
8334 produce code that runs somewhat faster on a @samp{Pentium} at the
8335 expense of more memory.
8337 @strong{Warning:} if you use the @option{-malign-double} switch,
8338 structures containing the above types will be aligned differently than
8339 the published application binary interface specifications for the 386
8340 and will not be binary compatible with structures in code compiled
8341 without that switch.
8343 @item -m96bit-long-double
8344 @item -m128bit-long-double
8345 @opindex m96bit-long-double
8346 @opindex m128bit-long-double
8347 These switches control the size of @code{long double} type. The i386
8348 application binary interface specifies the size to be 96 bits,
8349 so @option{-m96bit-long-double} is the default in 32 bit mode.
8351 Modern architectures (Pentium and newer) would prefer @code{long double}
8352 to be aligned to an 8 or 16 byte boundary. In arrays or structures
8353 conforming to the ABI, this would not be possible. So specifying a
8354 @option{-m128bit-long-double} will align @code{long double}
8355 to a 16 byte boundary by padding the @code{long double} with an additional
8358 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
8359 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
8361 Notice that neither of these options enable any extra precision over the x87
8362 standard of 80 bits for a @code{long double}.
8364 @strong{Warning:} if you override the default value for your target ABI, the
8365 structures and arrays containing @code{long double} will change their size as
8366 well as function calling convention for function taking @code{long double}
8367 will be modified. Hence they will not be binary compatible with arrays or
8368 structures in code compiled without that switch.
8372 @itemx -mno-svr3-shlib
8373 @opindex msvr3-shlib
8374 @opindex mno-svr3-shlib
8375 Control whether GCC places uninitialized local variables into the
8376 @code{bss} or @code{data} segments. @option{-msvr3-shlib} places them
8377 into @code{bss}. These options are meaningful only on System V Release 3.
8381 Use a different function-calling convention, in which functions that
8382 take a fixed number of arguments return with the @code{ret} @var{num}
8383 instruction, which pops their arguments while returning. This saves one
8384 instruction in the caller since there is no need to pop the arguments
8387 You can specify that an individual function is called with this calling
8388 sequence with the function attribute @samp{stdcall}. You can also
8389 override the @option{-mrtd} option by using the function attribute
8390 @samp{cdecl}. @xref{Function Attributes}.
8392 @strong{Warning:} this calling convention is incompatible with the one
8393 normally used on Unix, so you cannot use it if you need to call
8394 libraries compiled with the Unix compiler.
8396 Also, you must provide function prototypes for all functions that
8397 take variable numbers of arguments (including @code{printf});
8398 otherwise incorrect code will be generated for calls to those
8401 In addition, seriously incorrect code will result if you call a
8402 function with too many arguments. (Normally, extra arguments are
8403 harmlessly ignored.)
8405 @item -mregparm=@var{num}
8407 Control how many registers are used to pass integer arguments. By
8408 default, no registers are used to pass arguments, and at most 3
8409 registers can be used. You can control this behavior for a specific
8410 function by using the function attribute @samp{regparm}.
8411 @xref{Function Attributes}.
8413 @strong{Warning:} if you use this switch, and
8414 @var{num} is nonzero, then you must build all modules with the same
8415 value, including any libraries. This includes the system libraries and
8418 @item -mpreferred-stack-boundary=@var{num}
8419 @opindex mpreferred-stack-boundary
8420 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
8421 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
8422 the default is 4 (16 bytes or 128 bits), except when optimizing for code
8423 size (@option{-Os}), in which case the default is the minimum correct
8424 alignment (4 bytes for x86, and 8 bytes for x86-64).
8426 On Pentium and PentiumPro, @code{double} and @code{long double} values
8427 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
8428 suffer significant run time performance penalties. On Pentium III, the
8429 Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar
8430 penalties if it is not 16 byte aligned.
8432 To ensure proper alignment of this values on the stack, the stack boundary
8433 must be as aligned as that required by any value stored on the stack.
8434 Further, every function must be generated such that it keeps the stack
8435 aligned. Thus calling a function compiled with a higher preferred
8436 stack boundary from a function compiled with a lower preferred stack
8437 boundary will most likely misalign the stack. It is recommended that
8438 libraries that use callbacks always use the default setting.
8440 This extra alignment does consume extra stack space, and generally
8441 increases code size. Code that is sensitive to stack space usage, such
8442 as embedded systems and operating system kernels, may want to reduce the
8443 preferred alignment to @option{-mpreferred-stack-boundary=2}.
8461 These switches enable or disable the use of built-in functions that allow
8462 direct access to the MMX, SSE and 3Dnow extensions of the instruction set.
8464 @xref{X86 Built-in Functions}, for details of the functions enabled
8465 and disabled by these switches.
8467 To have SSE/SSE2 instructions generated automatically from floating-point
8468 code, see @option{-mfpmath=sse}.
8471 @itemx -mno-push-args
8473 @opindex mno-push-args
8474 Use PUSH operations to store outgoing parameters. This method is shorter
8475 and usually equally fast as method using SUB/MOV operations and is enabled
8476 by default. In some cases disabling it may improve performance because of
8477 improved scheduling and reduced dependencies.
8479 @item -maccumulate-outgoing-args
8480 @opindex maccumulate-outgoing-args
8481 If enabled, the maximum amount of space required for outgoing arguments will be
8482 computed in the function prologue. This is faster on most modern CPUs
8483 because of reduced dependencies, improved scheduling and reduced stack usage
8484 when preferred stack boundary is not equal to 2. The drawback is a notable
8485 increase in code size. This switch implies @option{-mno-push-args}.
8489 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
8490 on thread-safe exception handling must compile and link all code with the
8491 @option{-mthreads} option. When compiling, @option{-mthreads} defines
8492 @option{-D_MT}; when linking, it links in a special thread helper library
8493 @option{-lmingwthrd} which cleans up per thread exception handling data.
8495 @item -mno-align-stringops
8496 @opindex mno-align-stringops
8497 Do not align destination of inlined string operations. This switch reduces
8498 code size and improves performance in case the destination is already aligned,
8499 but gcc don't know about it.
8501 @item -minline-all-stringops
8502 @opindex minline-all-stringops
8503 By default GCC inlines string operations only when destination is known to be
8504 aligned at least to 4 byte boundary. This enables more inlining, increase code
8505 size, but may improve performance of code that depends on fast memcpy, strlen
8506 and memset for short lengths.
8508 @item -momit-leaf-frame-pointer
8509 @opindex momit-leaf-frame-pointer
8510 Don't keep the frame pointer in a register for leaf functions. This
8511 avoids the instructions to save, set up and restore frame pointers and
8512 makes an extra register available in leaf functions. The option
8513 @option{-fomit-frame-pointer} removes the frame pointer for all functions
8514 which might make debugging harder.
8516 @item -mtls-direct-seg-refs
8517 @itemx -mno-tls-direct-seg-refs
8518 @opindex mtls-direct-seg-refs
8519 Controls whether TLS variables may be accessed with offsets from the
8520 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
8521 or whether the thread base pointer must be added. Whether or not this
8522 is legal depends on the operating system, and whether it maps the
8523 segment to cover the entire TLS area.
8525 For systems that use GNU libc, the default is on.
8528 These @samp{-m} switches are supported in addition to the above
8529 on AMD x86-64 processors in 64-bit environments.
8536 Generate code for a 32-bit or 64-bit environment.
8537 The 32-bit environment sets int, long and pointer to 32 bits and
8538 generates code that runs on any i386 system.
8539 The 64-bit environment sets int to 32 bits and long and pointer
8540 to 64 bits and generates code for AMD's x86-64 architecture.
8543 @opindex no-red-zone
8544 Do not use a so called red zone for x86-64 code. The red zone is mandated
8545 by the x86-64 ABI, it is a 128-byte area beyond the location of the
8546 stack pointer that will not be modified by signal or interrupt handlers
8547 and therefore can be used for temporary data without adjusting the stack
8548 pointer. The flag @option{-mno-red-zone} disables this red zone.
8550 @item -mcmodel=small
8551 @opindex mcmodel=small
8552 Generate code for the small code model: the program and its symbols must
8553 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
8554 Programs can be statically or dynamically linked. This is the default
8557 @item -mcmodel=kernel
8558 @opindex mcmodel=kernel
8559 Generate code for the kernel code model. The kernel runs in the
8560 negative 2 GB of the address space.
8561 This model has to be used for Linux kernel code.
8563 @item -mcmodel=medium
8564 @opindex mcmodel=medium
8565 Generate code for the medium model: The program is linked in the lower 2
8566 GB of the address space but symbols can be located anywhere in the
8567 address space. Programs can be statically or dynamically linked, but
8568 building of shared libraries are not supported with the medium model.
8570 @item -mcmodel=large
8571 @opindex mcmodel=large
8572 Generate code for the large model: This model makes no assumptions
8573 about addresses and sizes of sections. Currently GCC does not implement
8578 @subsection HPPA Options
8579 @cindex HPPA Options
8581 These @samp{-m} options are defined for the HPPA family of computers:
8584 @item -march=@var{architecture-type}
8586 Generate code for the specified architecture. The choices for
8587 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
8588 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
8589 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
8590 architecture option for your machine. Code compiled for lower numbered
8591 architectures will run on higher numbered architectures, but not the
8594 PA 2.0 support currently requires gas snapshot 19990413 or later. The
8595 next release of binutils (current is 2.9.1) will probably contain PA 2.0
8599 @itemx -mpa-risc-1-1
8600 @itemx -mpa-risc-2-0
8601 @opindex mpa-risc-1-0
8602 @opindex mpa-risc-1-1
8603 @opindex mpa-risc-2-0
8604 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
8607 @opindex mbig-switch
8608 Generate code suitable for big switch tables. Use this option only if
8609 the assembler/linker complain about out of range branches within a switch
8612 @item -mjump-in-delay
8613 @opindex mjump-in-delay
8614 Fill delay slots of function calls with unconditional jump instructions
8615 by modifying the return pointer for the function call to be the target
8616 of the conditional jump.
8618 @item -mdisable-fpregs
8619 @opindex mdisable-fpregs
8620 Prevent floating point registers from being used in any manner. This is
8621 necessary for compiling kernels which perform lazy context switching of
8622 floating point registers. If you use this option and attempt to perform
8623 floating point operations, the compiler will abort.
8625 @item -mdisable-indexing
8626 @opindex mdisable-indexing
8627 Prevent the compiler from using indexing address modes. This avoids some
8628 rather obscure problems when compiling MIG generated code under MACH@.
8630 @item -mno-space-regs
8631 @opindex mno-space-regs
8632 Generate code that assumes the target has no space registers. This allows
8633 GCC to generate faster indirect calls and use unscaled index address modes.
8635 Such code is suitable for level 0 PA systems and kernels.
8637 @item -mfast-indirect-calls
8638 @opindex mfast-indirect-calls
8639 Generate code that assumes calls never cross space boundaries. This
8640 allows GCC to emit code which performs faster indirect calls.
8642 This option will not work in the presence of shared libraries or nested
8645 @item -mlong-load-store
8646 @opindex mlong-load-store
8647 Generate 3-instruction load and store sequences as sometimes required by
8648 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
8651 @item -mportable-runtime
8652 @opindex mportable-runtime
8653 Use the portable calling conventions proposed by HP for ELF systems.
8657 Enable the use of assembler directives only GAS understands.
8659 @item -mschedule=@var{cpu-type}
8661 Schedule code according to the constraints for the machine type
8662 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
8663 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
8664 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
8665 proper scheduling option for your machine. The default scheduling is
8669 @opindex mlinker-opt
8670 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
8671 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
8672 linkers in which they give bogus error messages when linking some programs.
8675 @opindex msoft-float
8676 Generate output containing library calls for floating point.
8677 @strong{Warning:} the requisite libraries are not available for all HPPA
8678 targets. Normally the facilities of the machine's usual C compiler are
8679 used, but this cannot be done directly in cross-compilation. You must make
8680 your own arrangements to provide suitable library functions for
8681 cross-compilation. The embedded target @samp{hppa1.1-*-pro}
8682 does provide software floating point support.
8684 @option{-msoft-float} changes the calling convention in the output file;
8685 therefore, it is only useful if you compile @emph{all} of a program with
8686 this option. In particular, you need to compile @file{libgcc.a}, the
8687 library that comes with GCC, with @option{-msoft-float} in order for
8692 Generate the predefine, @code{_SIO}, for server IO. The default is
8693 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
8694 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO. These
8695 options are available under HP-UX and HI-UX.
8699 Use GNU ld specific options. This passes @option{-shared} to ld when
8700 building a shared library. It is the default when GCC is configured,
8701 explicitly or implicitly, with the GNU linker. This option does not
8702 have any affect on which ld is called, it only changes what parameters
8703 are passed to that ld. The ld that is called is determined by the
8704 @option{--with-ld} configure option, gcc's program search path, and
8705 finally by the user's @env{PATH}. The linker used by GCC can be printed
8706 using @samp{which `gcc -print-prog-name=ld`}.
8710 Use HP ld specific options. This passes @option{-b} to ld when building
8711 a shared library and passes @option{+Accept TypeMismatch} to ld on all
8712 links. It is the default when GCC is configured, explicitly or
8713 implicitly, with the HP linker. This option does not have any affect on
8714 which ld is called, it only changes what parameters are passed to that
8715 ld. The ld that is called is determined by the @option{--with-ld}
8716 configure option, gcc's program search path, and finally by the user's
8717 @env{PATH}. The linker used by GCC can be printed using @samp{which
8718 `gcc -print-prog-name=ld`}.
8721 @opindex mno-long-calls
8722 Generate code that uses long call sequences. This ensures that a call
8723 is always able to reach linker generated stubs. The default is to generate
8724 long calls only when the distance from the call site to the beginning
8725 of the function or translation unit, as the case may be, exceeds a
8726 predefined limit set by the branch type being used. The limits for
8727 normal calls are 7,600,000 and 240,000 bytes, respectively for the
8728 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
8731 Distances are measured from the beginning of functions when using the
8732 @option{-ffunction-sections} option, or when using the @option{-mgas}
8733 and @option{-mno-portable-runtime} options together under HP-UX with
8736 It is normally not desirable to use this option as it will degrade
8737 performance. However, it may be useful in large applications,
8738 particularly when partial linking is used to build the application.
8740 The types of long calls used depends on the capabilities of the
8741 assembler and linker, and the type of code being generated. The
8742 impact on systems that support long absolute calls, and long pic
8743 symbol-difference or pc-relative calls should be relatively small.
8744 However, an indirect call is used on 32-bit ELF systems in pic code
8745 and it is quite long.
8749 Suppress the generation of link options to search libdld.sl when the
8750 @option{-static} option is specified on HP-UX 10 and later.
8754 The HP-UX implementation of setlocale in libc has a dependency on
8755 libdld.sl. There isn't an archive version of libdld.sl. Thus,
8756 when the @option{-static} option is specified, special link options
8757 are needed to resolve this dependency.
8759 On HP-UX 10 and later, the GCC driver adds the necessary options to
8760 link with libdld.sl when the @option{-static} option is specified.
8761 This causes the resulting binary to be dynamic. On the 64-bit port,
8762 the linkers generate dynamic binaries by default in any case. The
8763 @option{-nolibdld} option can be used to prevent the GCC driver from
8764 adding these link options.
8768 Add support for multithreading with the @dfn{dce thread} library
8769 under HP-UX. This option sets flags for both the preprocessor and
8773 @node Intel 960 Options
8774 @subsection Intel 960 Options
8776 These @samp{-m} options are defined for the Intel 960 implementations:
8779 @item -m@var{cpu-type}
8787 Assume the defaults for the machine type @var{cpu-type} for some of
8788 the other options, including instruction scheduling, floating point
8789 support, and addressing modes. The choices for @var{cpu-type} are
8790 @samp{ka}, @samp{kb}, @samp{mc}, @samp{ca}, @samp{cf},
8791 @samp{sa}, and @samp{sb}.
8798 @opindex msoft-float
8799 The @option{-mnumerics} option indicates that the processor does support
8800 floating-point instructions. The @option{-msoft-float} option indicates
8801 that floating-point support should not be assumed.
8803 @item -mleaf-procedures
8804 @itemx -mno-leaf-procedures
8805 @opindex mleaf-procedures
8806 @opindex mno-leaf-procedures
8807 Do (or do not) attempt to alter leaf procedures to be callable with the
8808 @code{bal} instruction as well as @code{call}. This will result in more
8809 efficient code for explicit calls when the @code{bal} instruction can be
8810 substituted by the assembler or linker, but less efficient code in other
8811 cases, such as calls via function pointers, or using a linker that doesn't
8812 support this optimization.
8815 @itemx -mno-tail-call
8817 @opindex mno-tail-call
8818 Do (or do not) make additional attempts (beyond those of the
8819 machine-independent portions of the compiler) to optimize tail-recursive
8820 calls into branches. You may not want to do this because the detection of
8821 cases where this is not valid is not totally complete. The default is
8822 @option{-mno-tail-call}.
8824 @item -mcomplex-addr
8825 @itemx -mno-complex-addr
8826 @opindex mcomplex-addr
8827 @opindex mno-complex-addr
8828 Assume (or do not assume) that the use of a complex addressing mode is a
8829 win on this implementation of the i960. Complex addressing modes may not
8830 be worthwhile on the K-series, but they definitely are on the C-series.
8831 The default is currently @option{-mcomplex-addr} for all processors except
8835 @itemx -mno-code-align
8836 @opindex mcode-align
8837 @opindex mno-code-align
8838 Align code to 8-byte boundaries for faster fetching (or don't bother).
8839 Currently turned on by default for C-series implementations only.
8842 @item -mclean-linkage
8843 @itemx -mno-clean-linkage
8844 @opindex mclean-linkage
8845 @opindex mno-clean-linkage
8846 These options are not fully implemented.
8850 @itemx -mic2.0-compat
8851 @itemx -mic3.0-compat
8853 @opindex mic2.0-compat
8854 @opindex mic3.0-compat
8855 Enable compatibility with iC960 v2.0 or v3.0.
8859 @opindex masm-compat
8861 Enable compatibility with the iC960 assembler.
8863 @item -mstrict-align
8864 @itemx -mno-strict-align
8865 @opindex mstrict-align
8866 @opindex mno-strict-align
8867 Do not permit (do permit) unaligned accesses.
8871 Enable structure-alignment compatibility with Intel's gcc release version
8872 1.3 (based on gcc 1.37). This option implies @option{-mstrict-align}.
8874 @item -mlong-double-64
8875 @opindex mlong-double-64
8876 Implement type @samp{long double} as 64-bit floating point numbers.
8877 Without the option @samp{long double} is implemented by 80-bit
8878 floating point numbers. The only reason we have it because there is
8879 no 128-bit @samp{long double} support in @samp{fp-bit.c} yet. So it
8880 is only useful for people using soft-float targets. Otherwise, we
8881 should recommend against use of it.
8885 @node DEC Alpha Options
8886 @subsection DEC Alpha Options
8888 These @samp{-m} options are defined for the DEC Alpha implementations:
8891 @item -mno-soft-float
8893 @opindex mno-soft-float
8894 @opindex msoft-float
8895 Use (do not use) the hardware floating-point instructions for
8896 floating-point operations. When @option{-msoft-float} is specified,
8897 functions in @file{libgcc.a} will be used to perform floating-point
8898 operations. Unless they are replaced by routines that emulate the
8899 floating-point operations, or compiled in such a way as to call such
8900 emulations routines, these routines will issue floating-point
8901 operations. If you are compiling for an Alpha without floating-point
8902 operations, you must ensure that the library is built so as not to call
8905 Note that Alpha implementations without floating-point operations are
8906 required to have floating-point registers.
8911 @opindex mno-fp-regs
8912 Generate code that uses (does not use) the floating-point register set.
8913 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
8914 register set is not used, floating point operands are passed in integer
8915 registers as if they were integers and floating-point results are passed
8916 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
8917 so any function with a floating-point argument or return value called by code
8918 compiled with @option{-mno-fp-regs} must also be compiled with that
8921 A typical use of this option is building a kernel that does not use,
8922 and hence need not save and restore, any floating-point registers.
8926 The Alpha architecture implements floating-point hardware optimized for
8927 maximum performance. It is mostly compliant with the IEEE floating
8928 point standard. However, for full compliance, software assistance is
8929 required. This option generates code fully IEEE compliant code
8930 @emph{except} that the @var{inexact-flag} is not maintained (see below).
8931 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
8932 defined during compilation. The resulting code is less efficient but is
8933 able to correctly support denormalized numbers and exceptional IEEE
8934 values such as not-a-number and plus/minus infinity. Other Alpha
8935 compilers call this option @option{-ieee_with_no_inexact}.
8937 @item -mieee-with-inexact
8938 @opindex mieee-with-inexact
8939 This is like @option{-mieee} except the generated code also maintains
8940 the IEEE @var{inexact-flag}. Turning on this option causes the
8941 generated code to implement fully-compliant IEEE math. In addition to
8942 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
8943 macro. On some Alpha implementations the resulting code may execute
8944 significantly slower than the code generated by default. Since there is
8945 very little code that depends on the @var{inexact-flag}, you should
8946 normally not specify this option. Other Alpha compilers call this
8947 option @option{-ieee_with_inexact}.
8949 @item -mfp-trap-mode=@var{trap-mode}
8950 @opindex mfp-trap-mode
8951 This option controls what floating-point related traps are enabled.
8952 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
8953 The trap mode can be set to one of four values:
8957 This is the default (normal) setting. The only traps that are enabled
8958 are the ones that cannot be disabled in software (e.g., division by zero
8962 In addition to the traps enabled by @samp{n}, underflow traps are enabled
8966 Like @samp{su}, but the instructions are marked to be safe for software
8967 completion (see Alpha architecture manual for details).
8970 Like @samp{su}, but inexact traps are enabled as well.
8973 @item -mfp-rounding-mode=@var{rounding-mode}
8974 @opindex mfp-rounding-mode
8975 Selects the IEEE rounding mode. Other Alpha compilers call this option
8976 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
8981 Normal IEEE rounding mode. Floating point numbers are rounded towards
8982 the nearest machine number or towards the even machine number in case
8986 Round towards minus infinity.
8989 Chopped rounding mode. Floating point numbers are rounded towards zero.
8992 Dynamic rounding mode. A field in the floating point control register
8993 (@var{fpcr}, see Alpha architecture reference manual) controls the
8994 rounding mode in effect. The C library initializes this register for
8995 rounding towards plus infinity. Thus, unless your program modifies the
8996 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
8999 @item -mtrap-precision=@var{trap-precision}
9000 @opindex mtrap-precision
9001 In the Alpha architecture, floating point traps are imprecise. This
9002 means without software assistance it is impossible to recover from a
9003 floating trap and program execution normally needs to be terminated.
9004 GCC can generate code that can assist operating system trap handlers
9005 in determining the exact location that caused a floating point trap.
9006 Depending on the requirements of an application, different levels of
9007 precisions can be selected:
9011 Program precision. This option is the default and means a trap handler
9012 can only identify which program caused a floating point exception.
9015 Function precision. The trap handler can determine the function that
9016 caused a floating point exception.
9019 Instruction precision. The trap handler can determine the exact
9020 instruction that caused a floating point exception.
9023 Other Alpha compilers provide the equivalent options called
9024 @option{-scope_safe} and @option{-resumption_safe}.
9026 @item -mieee-conformant
9027 @opindex mieee-conformant
9028 This option marks the generated code as IEEE conformant. You must not
9029 use this option unless you also specify @option{-mtrap-precision=i} and either
9030 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
9031 is to emit the line @samp{.eflag 48} in the function prologue of the
9032 generated assembly file. Under DEC Unix, this has the effect that
9033 IEEE-conformant math library routines will be linked in.
9035 @item -mbuild-constants
9036 @opindex mbuild-constants
9037 Normally GCC examines a 32- or 64-bit integer constant to
9038 see if it can construct it from smaller constants in two or three
9039 instructions. If it cannot, it will output the constant as a literal and
9040 generate code to load it from the data segment at runtime.
9042 Use this option to require GCC to construct @emph{all} integer constants
9043 using code, even if it takes more instructions (the maximum is six).
9045 You would typically use this option to build a shared library dynamic
9046 loader. Itself a shared library, it must relocate itself in memory
9047 before it can find the variables and constants in its own data segment.
9053 Select whether to generate code to be assembled by the vendor-supplied
9054 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
9072 Indicate whether GCC should generate code to use the optional BWX,
9073 CIX, FIX and MAX instruction sets. The default is to use the instruction
9074 sets supported by the CPU type specified via @option{-mcpu=} option or that
9075 of the CPU on which GCC was built if none was specified.
9080 @opindex mfloat-ieee
9081 Generate code that uses (does not use) VAX F and G floating point
9082 arithmetic instead of IEEE single and double precision.
9084 @item -mexplicit-relocs
9085 @itemx -mno-explicit-relocs
9086 @opindex mexplicit-relocs
9087 @opindex mno-explicit-relocs
9088 Older Alpha assemblers provided no way to generate symbol relocations
9089 except via assembler macros. Use of these macros does not allow
9090 optimal instruction scheduling. GNU binutils as of version 2.12
9091 supports a new syntax that allows the compiler to explicitly mark
9092 which relocations should apply to which instructions. This option
9093 is mostly useful for debugging, as GCC detects the capabilities of
9094 the assembler when it is built and sets the default accordingly.
9098 @opindex msmall-data
9099 @opindex mlarge-data
9100 When @option{-mexplicit-relocs} is in effect, static data is
9101 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
9102 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
9103 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
9104 16-bit relocations off of the @code{$gp} register. This limits the
9105 size of the small data area to 64KB, but allows the variables to be
9106 directly accessed via a single instruction.
9108 The default is @option{-mlarge-data}. With this option the data area
9109 is limited to just below 2GB. Programs that require more than 2GB of
9110 data must use @code{malloc} or @code{mmap} to allocate the data in the
9111 heap instead of in the program's data segment.
9113 When generating code for shared libraries, @option{-fpic} implies
9114 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
9118 @opindex msmall-text
9119 @opindex mlarge-text
9120 When @option{-msmall-text} is used, the compiler assumes that the
9121 code of the entire program (or shared library) fits in 4MB, and is
9122 thus reachable with a branch instruction. When @option{-msmall-data}
9123 is used, the compiler can assume that all local symbols share the
9124 same @code{$gp} value, and thus reduce the number of instructions
9125 required for a function call from 4 to 1.
9127 The default is @option{-mlarge-text}.
9129 @item -mcpu=@var{cpu_type}
9131 Set the instruction set and instruction scheduling parameters for
9132 machine type @var{cpu_type}. You can specify either the @samp{EV}
9133 style name or the corresponding chip number. GCC supports scheduling
9134 parameters for the EV4, EV5 and EV6 family of processors and will
9135 choose the default values for the instruction set from the processor
9136 you specify. If you do not specify a processor type, GCC will default
9137 to the processor on which the compiler was built.
9139 Supported values for @var{cpu_type} are
9145 Schedules as an EV4 and has no instruction set extensions.
9149 Schedules as an EV5 and has no instruction set extensions.
9153 Schedules as an EV5 and supports the BWX extension.
9158 Schedules as an EV5 and supports the BWX and MAX extensions.
9162 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
9166 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
9169 @item -mtune=@var{cpu_type}
9171 Set only the instruction scheduling parameters for machine type
9172 @var{cpu_type}. The instruction set is not changed.
9174 @item -mmemory-latency=@var{time}
9175 @opindex mmemory-latency
9176 Sets the latency the scheduler should assume for typical memory
9177 references as seen by the application. This number is highly
9178 dependent on the memory access patterns used by the application
9179 and the size of the external cache on the machine.
9181 Valid options for @var{time} are
9185 A decimal number representing clock cycles.
9191 The compiler contains estimates of the number of clock cycles for
9192 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
9193 (also called Dcache, Scache, and Bcache), as well as to main memory.
9194 Note that L3 is only valid for EV5.
9199 @node DEC Alpha/VMS Options
9200 @subsection DEC Alpha/VMS Options
9202 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
9205 @item -mvms-return-codes
9206 @opindex mvms-return-codes
9207 Return VMS condition codes from main. The default is to return POSIX
9208 style condition (e.g.@ error) codes.
9211 @node H8/300 Options
9212 @subsection H8/300 Options
9214 These @samp{-m} options are defined for the H8/300 implementations:
9219 Shorten some address references at link time, when possible; uses the
9220 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
9221 ld.info, Using ld}, for a fuller description.
9225 Generate code for the H8/300H@.
9229 Generate code for the H8S@.
9233 Generate code for the H8S and H8/300H in the normal mode. This switch
9234 must be used either with -mh or -ms.
9238 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
9242 Make @code{int} data 32 bits by default.
9246 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
9247 The default for the H8/300H and H8S is to align longs and floats on 4
9249 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
9250 This option has no effect on the H8/300.
9254 @subsection SH Options
9256 These @samp{-m} options are defined for the SH implementations:
9261 Generate code for the SH1.
9265 Generate code for the SH2.
9268 Generate code for the SH2e.
9272 Generate code for the SH3.
9276 Generate code for the SH3e.
9280 Generate code for the SH4 without a floating-point unit.
9282 @item -m4-single-only
9283 @opindex m4-single-only
9284 Generate code for the SH4 with a floating-point unit that only
9285 supports single-precision arithmetic.
9289 Generate code for the SH4 assuming the floating-point unit is in
9290 single-precision mode by default.
9294 Generate code for the SH4.
9298 Compile code for the processor in big endian mode.
9302 Compile code for the processor in little endian mode.
9306 Align doubles at 64-bit boundaries. Note that this changes the calling
9307 conventions, and thus some functions from the standard C library will
9308 not work unless you recompile it first with @option{-mdalign}.
9312 Shorten some address references at link time, when possible; uses the
9313 linker option @option{-relax}.
9317 Use 32-bit offsets in @code{switch} tables. The default is to use
9322 Enable the use of the instruction @code{fmovd}.
9326 Comply with the calling conventions defined by Renesas.
9330 Mark the @code{MAC} register as call-clobbered, even if
9331 @option{-mhitachi} is given.
9335 Increase IEEE-compliance of floating-point code.
9339 Dump instruction size and location in the assembly code.
9343 This option is deprecated. It pads structures to multiple of 4 bytes,
9344 which is incompatible with the SH ABI@.
9348 Optimize for space instead of speed. Implied by @option{-Os}.
9352 When generating position-independent code, emit function calls using
9353 the Global Offset Table instead of the Procedure Linkage Table.
9357 Generate a library function call to invalidate instruction cache
9358 entries, after fixing up a trampoline. This library function call
9359 doesn't assume it can write to the whole memory address space. This
9360 is the default when the target is @code{sh-*-linux*}.
9363 @node System V Options
9364 @subsection Options for System V
9366 These additional options are available on System V Release 4 for
9367 compatibility with other compilers on those systems:
9372 Create a shared object.
9373 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
9377 Identify the versions of each tool used by the compiler, in a
9378 @code{.ident} assembler directive in the output.
9382 Refrain from adding @code{.ident} directives to the output file (this is
9385 @item -YP,@var{dirs}
9387 Search the directories @var{dirs}, and no others, for libraries
9388 specified with @option{-l}.
9392 Look in the directory @var{dir} to find the M4 preprocessor.
9393 The assembler uses this option.
9394 @c This is supposed to go with a -Yd for predefined M4 macro files, but
9395 @c the generic assembler that comes with Solaris takes just -Ym.
9398 @node TMS320C3x/C4x Options
9399 @subsection TMS320C3x/C4x Options
9400 @cindex TMS320C3x/C4x Options
9402 These @samp{-m} options are defined for TMS320C3x/C4x implementations:
9406 @item -mcpu=@var{cpu_type}
9408 Set the instruction set, register set, and instruction scheduling
9409 parameters for machine type @var{cpu_type}. Supported values for
9410 @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
9411 @samp{c44}. The default is @samp{c40} to generate code for the
9416 @itemx -msmall-memory
9418 @opindex mbig-memory
9420 @opindex msmall-memory
9422 Generates code for the big or small memory model. The small memory
9423 model assumed that all data fits into one 64K word page. At run-time
9424 the data page (DP) register must be set to point to the 64K page
9425 containing the .bss and .data program sections. The big memory model is
9426 the default and requires reloading of the DP register for every direct
9433 Allow (disallow) allocation of general integer operands into the block
9440 Enable (disable) generation of code using decrement and branch,
9441 DBcond(D), instructions. This is enabled by default for the C4x. To be
9442 on the safe side, this is disabled for the C3x, since the maximum
9443 iteration count on the C3x is @math{2^{23} + 1} (but who iterates loops more than
9444 @math{2^{23}} times on the C3x?). Note that GCC will try to reverse a loop so
9445 that it can utilize the decrement and branch instruction, but will give
9446 up if there is more than one memory reference in the loop. Thus a loop
9447 where the loop counter is decremented can generate slightly more
9448 efficient code, in cases where the RPTB instruction cannot be utilized.
9450 @item -mdp-isr-reload
9452 @opindex mdp-isr-reload
9454 Force the DP register to be saved on entry to an interrupt service
9455 routine (ISR), reloaded to point to the data section, and restored on
9456 exit from the ISR@. This should not be required unless someone has
9457 violated the small memory model by modifying the DP register, say within
9464 For the C3x use the 24-bit MPYI instruction for integer multiplies
9465 instead of a library call to guarantee 32-bit results. Note that if one
9466 of the operands is a constant, then the multiplication will be performed
9467 using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
9468 then squaring operations are performed inline instead of a library call.
9471 @itemx -mno-fast-fix
9473 @opindex mno-fast-fix
9474 The C3x/C4x FIX instruction to convert a floating point value to an
9475 integer value chooses the nearest integer less than or equal to the
9476 floating point value rather than to the nearest integer. Thus if the
9477 floating point number is negative, the result will be incorrectly
9478 truncated an additional code is necessary to detect and correct this
9479 case. This option can be used to disable generation of the additional
9480 code required to correct the result.
9486 Enable (disable) generation of repeat block sequences using the RPTB
9487 instruction for zero overhead looping. The RPTB construct is only used
9488 for innermost loops that do not call functions or jump across the loop
9489 boundaries. There is no advantage having nested RPTB loops due to the
9490 overhead required to save and restore the RC, RS, and RE registers.
9491 This is enabled by default with @option{-O2}.
9493 @item -mrpts=@var{count}
9497 Enable (disable) the use of the single instruction repeat instruction
9498 RPTS@. If a repeat block contains a single instruction, and the loop
9499 count can be guaranteed to be less than the value @var{count}, GCC will
9500 emit a RPTS instruction instead of a RPTB@. If no value is specified,
9501 then a RPTS will be emitted even if the loop count cannot be determined
9502 at compile time. Note that the repeated instruction following RPTS does
9503 not have to be reloaded from memory each iteration, thus freeing up the
9504 CPU buses for operands. However, since interrupts are blocked by this
9505 instruction, it is disabled by default.
9507 @item -mloop-unsigned
9508 @itemx -mno-loop-unsigned
9509 @opindex mloop-unsigned
9510 @opindex mno-loop-unsigned
9511 The maximum iteration count when using RPTS and RPTB (and DB on the C40)
9512 is @math{2^{31} + 1} since these instructions test if the iteration count is
9513 negative to terminate the loop. If the iteration count is unsigned
9514 there is a possibility than the @math{2^{31} + 1} maximum iteration count may be
9515 exceeded. This switch allows an unsigned iteration count.
9519 Try to emit an assembler syntax that the TI assembler (asm30) is happy
9520 with. This also enforces compatibility with the API employed by the TI
9521 C3x C compiler. For example, long doubles are passed as structures
9522 rather than in floating point registers.
9528 Generate code that uses registers (stack) for passing arguments to functions.
9529 By default, arguments are passed in registers where possible rather
9530 than by pushing arguments on to the stack.
9532 @item -mparallel-insns
9533 @itemx -mno-parallel-insns
9534 @opindex mparallel-insns
9535 @opindex mno-parallel-insns
9536 Allow the generation of parallel instructions. This is enabled by
9537 default with @option{-O2}.
9539 @item -mparallel-mpy
9540 @itemx -mno-parallel-mpy
9541 @opindex mparallel-mpy
9542 @opindex mno-parallel-mpy
9543 Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
9544 provided @option{-mparallel-insns} is also specified. These instructions have
9545 tight register constraints which can pessimize the code generation
9551 @subsection V850 Options
9552 @cindex V850 Options
9554 These @samp{-m} options are defined for V850 implementations:
9558 @itemx -mno-long-calls
9559 @opindex mlong-calls
9560 @opindex mno-long-calls
9561 Treat all calls as being far away (near). If calls are assumed to be
9562 far away, the compiler will always load the functions address up into a
9563 register, and call indirect through the pointer.
9569 Do not optimize (do optimize) basic blocks that use the same index
9570 pointer 4 or more times to copy pointer into the @code{ep} register, and
9571 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
9572 option is on by default if you optimize.
9574 @item -mno-prolog-function
9575 @itemx -mprolog-function
9576 @opindex mno-prolog-function
9577 @opindex mprolog-function
9578 Do not use (do use) external functions to save and restore registers
9579 at the prologue and epilogue of a function. The external functions
9580 are slower, but use less code space if more than one function saves
9581 the same number of registers. The @option{-mprolog-function} option
9582 is on by default if you optimize.
9586 Try to make the code as small as possible. At present, this just turns
9587 on the @option{-mep} and @option{-mprolog-function} options.
9591 Put static or global variables whose size is @var{n} bytes or less into
9592 the tiny data area that register @code{ep} points to. The tiny data
9593 area can hold up to 256 bytes in total (128 bytes for byte references).
9597 Put static or global variables whose size is @var{n} bytes or less into
9598 the small data area that register @code{gp} points to. The small data
9599 area can hold up to 64 kilobytes.
9603 Put static or global variables whose size is @var{n} bytes or less into
9604 the first 32 kilobytes of memory.
9608 Specify that the target processor is the V850.
9611 @opindex mbig-switch
9612 Generate code suitable for big switch tables. Use this option only if
9613 the assembler/linker complain about out of range branches within a switch
9618 This option will cause r2 and r5 to be used in the code generated by
9619 the compiler. This setting is the default.
9622 @opindex mno-app-regs
9623 This option will cause r2 and r5 to be treated as fixed registers.
9627 Specify that the target processor is the V850E. The preprocessor
9628 constant @samp{__v850e__} will be defined if this option is used.
9630 If neither @option{-mv850} nor @option{-mv850e} are defined
9631 then a default target processor will be chosen and the relevant
9632 @samp{__v850*__} preprocessor constant will be defined.
9634 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
9635 defined, regardless of which processor variant is the target.
9637 @item -mdisable-callt
9638 @opindex mdisable-callt
9639 This option will suppress generation of the CALLT instruction for the
9640 v850e flavors of the v850 architecture. The default is
9641 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
9646 @subsection ARC Options
9649 These options are defined for ARC implementations:
9654 Compile code for little endian mode. This is the default.
9658 Compile code for big endian mode.
9661 @opindex mmangle-cpu
9662 Prepend the name of the cpu to all public symbol names.
9663 In multiple-processor systems, there are many ARC variants with different
9664 instruction and register set characteristics. This flag prevents code
9665 compiled for one cpu to be linked with code compiled for another.
9666 No facility exists for handling variants that are ``almost identical''.
9667 This is an all or nothing option.
9669 @item -mcpu=@var{cpu}
9671 Compile code for ARC variant @var{cpu}.
9672 Which variants are supported depend on the configuration.
9673 All variants support @option{-mcpu=base}, this is the default.
9675 @item -mtext=@var{text-section}
9676 @itemx -mdata=@var{data-section}
9677 @itemx -mrodata=@var{readonly-data-section}
9681 Put functions, data, and readonly data in @var{text-section},
9682 @var{data-section}, and @var{readonly-data-section} respectively
9683 by default. This can be overridden with the @code{section} attribute.
9684 @xref{Variable Attributes}.
9689 @subsection NS32K Options
9690 @cindex NS32K options
9692 These are the @samp{-m} options defined for the 32000 series. The default
9693 values for these options depends on which style of 32000 was selected when
9694 the compiler was configured; the defaults for the most common choices are
9702 Generate output for a 32032. This is the default
9703 when the compiler is configured for 32032 and 32016 based systems.
9709 Generate output for a 32332. This is the default
9710 when the compiler is configured for 32332-based systems.
9716 Generate output for a 32532. This is the default
9717 when the compiler is configured for 32532-based systems.
9721 Generate output containing 32081 instructions for floating point.
9722 This is the default for all systems.
9726 Generate output containing 32381 instructions for floating point. This
9727 also implies @option{-m32081}. The 32381 is only compatible with the 32332
9728 and 32532 cpus. This is the default for the pc532-netbsd configuration.
9732 Try and generate multiply-add floating point instructions @code{polyF}
9733 and @code{dotF}. This option is only available if the @option{-m32381}
9734 option is in effect. Using these instructions requires changes to
9735 register allocation which generally has a negative impact on
9736 performance. This option should only be enabled when compiling code
9737 particularly likely to make heavy use of multiply-add instructions.
9740 @opindex mnomulti-add
9741 Do not try and generate multiply-add floating point instructions
9742 @code{polyF} and @code{dotF}. This is the default on all platforms.
9745 @opindex msoft-float
9746 Generate output containing library calls for floating point.
9747 @strong{Warning:} the requisite libraries may not be available.
9749 @item -mieee-compare
9750 @itemx -mno-ieee-compare
9751 @opindex mieee-compare
9752 @opindex mno-ieee-compare
9753 Control whether or not the compiler uses IEEE floating point
9754 comparisons. These handle correctly the case where the result of a
9755 comparison is unordered.
9756 @strong{Warning:} the requisite kernel support may not be available.
9759 @opindex mnobitfield
9760 Do not use the bit-field instructions. On some machines it is faster to
9761 use shifting and masking operations. This is the default for the pc532.
9765 Do use the bit-field instructions. This is the default for all platforms
9770 Use a different function-calling convention, in which functions
9771 that take a fixed number of arguments return pop their
9772 arguments on return with the @code{ret} instruction.
9774 This calling convention is incompatible with the one normally
9775 used on Unix, so you cannot use it if you need to call libraries
9776 compiled with the Unix compiler.
9778 Also, you must provide function prototypes for all functions that
9779 take variable numbers of arguments (including @code{printf});
9780 otherwise incorrect code will be generated for calls to those
9783 In addition, seriously incorrect code will result if you call a
9784 function with too many arguments. (Normally, extra arguments are
9785 harmlessly ignored.)
9787 This option takes its name from the 680x0 @code{rtd} instruction.
9792 Use a different function-calling convention where the first two arguments
9793 are passed in registers.
9795 This calling convention is incompatible with the one normally
9796 used on Unix, so you cannot use it if you need to call libraries
9797 compiled with the Unix compiler.
9800 @opindex mnoregparam
9801 Do not pass any arguments in registers. This is the default for all
9806 It is OK to use the sb as an index register which is always loaded with
9807 zero. This is the default for the pc532-netbsd target.
9811 The sb register is not available for use or has not been initialized to
9812 zero by the run time system. This is the default for all targets except
9813 the pc532-netbsd. It is also implied whenever @option{-mhimem} or
9814 @option{-fpic} is set.
9818 Many ns32000 series addressing modes use displacements of up to 512MB@.
9819 If an address is above 512MB then displacements from zero can not be used.
9820 This option causes code to be generated which can be loaded above 512MB@.
9821 This may be useful for operating systems or ROM code.
9825 Assume code will be loaded in the first 512MB of virtual address space.
9826 This is the default for all platforms.
9832 @subsection AVR Options
9835 These options are defined for AVR implementations:
9838 @item -mmcu=@var{mcu}
9840 Specify ATMEL AVR instruction set or MCU type.
9842 Instruction set avr1 is for the minimal AVR core, not supported by the C
9843 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
9844 attiny11, attiny12, attiny15, attiny28).
9846 Instruction set avr2 (default) is for the classic AVR core with up to
9847 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
9848 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
9849 at90c8534, at90s8535).
9851 Instruction set avr3 is for the classic AVR core with up to 128K program
9852 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
9854 Instruction set avr4 is for the enhanced AVR core with up to 8K program
9855 memory space (MCU types: atmega8, atmega83, atmega85).
9857 Instruction set avr5 is for the enhanced AVR core with up to 128K program
9858 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
9859 atmega64, atmega128, at43usb355, at94k).
9863 Output instruction sizes to the asm file.
9865 @item -minit-stack=@var{N}
9866 @opindex minit-stack
9867 Specify the initial stack address, which may be a symbol or numeric value,
9868 @samp{__stack} is the default.
9870 @item -mno-interrupts
9871 @opindex mno-interrupts
9872 Generated code is not compatible with hardware interrupts.
9873 Code size will be smaller.
9875 @item -mcall-prologues
9876 @opindex mcall-prologues
9877 Functions prologues/epilogues expanded as call to appropriate
9878 subroutines. Code size will be smaller.
9880 @item -mno-tablejump
9881 @opindex mno-tablejump
9882 Do not generate tablejump insns which sometimes increase code size.
9885 @opindex mtiny-stack
9886 Change only the low 8 bits of the stack pointer.
9890 @subsection MCore Options
9891 @cindex MCore options
9893 These are the @samp{-m} options defined for the Motorola M*Core
9901 @opindex mno-hardlit
9902 Inline constants into the code stream if it can be done in two
9903 instructions or less.
9909 Use the divide instruction. (Enabled by default).
9911 @item -mrelax-immediate
9912 @itemx -mno-relax-immediate
9913 @opindex mrelax-immediate
9914 @opindex mno-relax-immediate
9915 Allow arbitrary sized immediates in bit operations.
9917 @item -mwide-bitfields
9918 @itemx -mno-wide-bitfields
9919 @opindex mwide-bitfields
9920 @opindex mno-wide-bitfields
9921 Always treat bit-fields as int-sized.
9923 @item -m4byte-functions
9924 @itemx -mno-4byte-functions
9925 @opindex m4byte-functions
9926 @opindex mno-4byte-functions
9927 Force all functions to be aligned to a four byte boundary.
9929 @item -mcallgraph-data
9930 @itemx -mno-callgraph-data
9931 @opindex mcallgraph-data
9932 @opindex mno-callgraph-data
9933 Emit callgraph information.
9936 @itemx -mno-slow-bytes
9937 @opindex mslow-bytes
9938 @opindex mno-slow-bytes
9939 Prefer word access when reading byte quantities.
9941 @item -mlittle-endian
9943 @opindex mlittle-endian
9944 @opindex mbig-endian
9945 Generate code for a little endian target.
9951 Generate code for the 210 processor.
9955 @subsection IA-64 Options
9956 @cindex IA-64 Options
9958 These are the @samp{-m} options defined for the Intel IA-64 architecture.
9962 @opindex mbig-endian
9963 Generate code for a big endian target. This is the default for HP-UX@.
9965 @item -mlittle-endian
9966 @opindex mlittle-endian
9967 Generate code for a little endian target. This is the default for AIX5
9974 Generate (or don't) code for the GNU assembler. This is the default.
9975 @c Also, this is the default if the configure option @option{--with-gnu-as}
9982 Generate (or don't) code for the GNU linker. This is the default.
9983 @c Also, this is the default if the configure option @option{--with-gnu-ld}
9988 Generate code that does not use a global pointer register. The result
9989 is not position independent code, and violates the IA-64 ABI@.
9991 @item -mvolatile-asm-stop
9992 @itemx -mno-volatile-asm-stop
9993 @opindex mvolatile-asm-stop
9994 @opindex mno-volatile-asm-stop
9995 Generate (or don't) a stop bit immediately before and after volatile asm
10000 Generate code that works around Itanium B step errata.
10002 @item -mregister-names
10003 @itemx -mno-register-names
10004 @opindex mregister-names
10005 @opindex mno-register-names
10006 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
10007 the stacked registers. This may make assembler output more readable.
10013 Disable (or enable) optimizations that use the small data section. This may
10014 be useful for working around optimizer bugs.
10016 @item -mconstant-gp
10017 @opindex mconstant-gp
10018 Generate code that uses a single constant global pointer value. This is
10019 useful when compiling kernel code.
10023 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
10024 This is useful when compiling firmware code.
10026 @item -minline-float-divide-min-latency
10027 @opindex minline-float-divide-min-latency
10028 Generate code for inline divides of floating point values
10029 using the minimum latency algorithm.
10031 @item -minline-float-divide-max-throughput
10032 @opindex minline-float-divide-max-throughput
10033 Generate code for inline divides of floating point values
10034 using the maximum throughput algorithm.
10036 @item -minline-int-divide-min-latency
10037 @opindex minline-int-divide-min-latency
10038 Generate code for inline divides of integer values
10039 using the minimum latency algorithm.
10041 @item -minline-int-divide-max-throughput
10042 @opindex minline-int-divide-max-throughput
10043 Generate code for inline divides of integer values
10044 using the maximum throughput algorithm.
10046 @item -mno-dwarf2-asm
10047 @itemx -mdwarf2-asm
10048 @opindex mno-dwarf2-asm
10049 @opindex mdwarf2-asm
10050 Don't (or do) generate assembler code for the DWARF2 line number debugging
10051 info. This may be useful when not using the GNU assembler.
10053 @item -mfixed-range=@var{register-range}
10054 @opindex mfixed-range
10055 Generate code treating the given register range as fixed registers.
10056 A fixed register is one that the register allocator can not use. This is
10057 useful when compiling kernel code. A register range is specified as
10058 two registers separated by a dash. Multiple register ranges can be
10059 specified separated by a comma.
10061 @item -mearly-stop-bits
10062 @itemx -mno-early-stop-bits
10063 @opindex mearly-stop-bits
10064 @opindex mno-early-stop-bits
10065 Allow stop bits to be placed earlier than immediately preceding the
10066 instruction that triggered the stop bit. This can improve instruction
10067 scheduling, but does not always do so.
10071 @subsection D30V Options
10072 @cindex D30V Options
10074 These @samp{-m} options are defined for D30V implementations:
10079 Link the @samp{.text}, @samp{.data}, @samp{.bss}, @samp{.strings},
10080 @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections into external
10081 memory, which starts at location @code{0x80000000}.
10084 @opindex mextmemory
10085 Same as the @option{-mextmem} switch.
10089 Link the @samp{.text} section into onchip text memory, which starts at
10090 location @code{0x0}. Also link @samp{.data}, @samp{.bss},
10091 @samp{.strings}, @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections
10092 into onchip data memory, which starts at location @code{0x20000000}.
10094 @item -mno-asm-optimize
10095 @itemx -masm-optimize
10096 @opindex mno-asm-optimize
10097 @opindex masm-optimize
10098 Disable (enable) passing @option{-O} to the assembler when optimizing.
10099 The assembler uses the @option{-O} option to automatically parallelize
10100 adjacent short instructions where possible.
10102 @item -mbranch-cost=@var{n}
10103 @opindex mbranch-cost
10104 Increase the internal costs of branches to @var{n}. Higher costs means
10105 that the compiler will issue more instructions to avoid doing a branch.
10108 @item -mcond-exec=@var{n}
10109 @opindex mcond-exec
10110 Specify the maximum number of conditionally executed instructions that
10111 replace a branch. The default is 4.
10114 @node S/390 and zSeries Options
10115 @subsection S/390 and zSeries Options
10116 @cindex S/390 and zSeries Options
10118 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
10122 @itemx -msoft-float
10123 @opindex mhard-float
10124 @opindex msoft-float
10125 Use (do not use) the hardware floating-point instructions and registers
10126 for floating-point operations. When @option{-msoft-float} is specified,
10127 functions in @file{libgcc.a} will be used to perform floating-point
10128 operations. When @option{-mhard-float} is specified, the compiler
10129 generates IEEE floating-point instructions. This is the default.
10132 @itemx -mno-backchain
10133 @opindex mbackchain
10134 @opindex mno-backchain
10135 Generate (or do not generate) code which maintains an explicit
10136 backchain within the stack frame that points to the caller's frame.
10137 This is currently needed to allow debugging. The default is to
10138 generate the backchain.
10141 @itemx -mno-small-exec
10142 @opindex msmall-exec
10143 @opindex mno-small-exec
10144 Generate (or do not generate) code using the @code{bras} instruction
10145 to do subroutine calls.
10146 This only works reliably if the total executable size does not
10147 exceed 64k. The default is to use the @code{basr} instruction instead,
10148 which does not have this limitation.
10154 When @option{-m31} is specified, generate code compliant to the
10155 Linux for S/390 ABI@. When @option{-m64} is specified, generate
10156 code compliant to the Linux for zSeries ABI@. This allows GCC in
10157 particular to generate 64-bit instructions. For the @samp{s390}
10158 targets, the default is @option{-m31}, while the @samp{s390x}
10159 targets default to @option{-m64}.
10165 When @option{-mzarch} is specified, generate code using the
10166 instructions available on z/Architecture.
10167 When @option{-mesa} is specified, generate code using the
10168 instructions available on ESA/390. Note that @option{-mesa} is
10169 not possible with @option{-m64}.
10170 When generating code compliant to the Linux for S/390 ABI,
10171 the default is @option{-mesa}. When generating code compliant
10172 to the Linux for zSeries ABI, the default is @option{-mzarch}.
10178 Generate (or do not generate) code using the @code{mvcle} instruction
10179 to perform block moves. When @option{-mno-mvcle} is specified,
10180 use a @code{mvc} loop instead. This is the default.
10186 Print (or do not print) additional debug information when compiling.
10187 The default is to not print debug information.
10189 @item -march=@var{cpu-type}
10191 Generate code that will run on @var{cpu-type}, which is the name of a system
10192 representing a certain processor type. Possible values for
10193 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, and @samp{z990}.
10194 When generating code using the instructions available on z/Architecture,
10195 the default is @option{-march=z900}. Otherwise, the default is
10196 @option{-march=g5}.
10198 @item -mtune=@var{cpu-type}
10200 Tune to @var{cpu-type} everything applicable about the generated code,
10201 except for the ABI and the set of available instructions.
10202 The list of @var{cpu-type} values is the same as for @option{-march}.
10203 The default is the value used for @option{-march}.
10208 @subsection CRIS Options
10209 @cindex CRIS Options
10211 These options are defined specifically for the CRIS ports.
10214 @item -march=@var{architecture-type}
10215 @itemx -mcpu=@var{architecture-type}
10218 Generate code for the specified architecture. The choices for
10219 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
10220 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX.
10221 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
10224 @item -mtune=@var{architecture-type}
10226 Tune to @var{architecture-type} everything applicable about the generated
10227 code, except for the ABI and the set of available instructions. The
10228 choices for @var{architecture-type} are the same as for
10229 @option{-march=@var{architecture-type}}.
10231 @item -mmax-stack-frame=@var{n}
10232 @opindex mmax-stack-frame
10233 Warn when the stack frame of a function exceeds @var{n} bytes.
10235 @item -melinux-stacksize=@var{n}
10236 @opindex melinux-stacksize
10237 Only available with the @samp{cris-axis-aout} target. Arranges for
10238 indications in the program to the kernel loader that the stack of the
10239 program should be set to @var{n} bytes.
10245 The options @option{-metrax4} and @option{-metrax100} are synonyms for
10246 @option{-march=v3} and @option{-march=v8} respectively.
10250 Enable CRIS-specific verbose debug-related information in the assembly
10251 code. This option also has the effect to turn off the @samp{#NO_APP}
10252 formatted-code indicator to the assembler at the beginning of the
10257 Do not use condition-code results from previous instruction; always emit
10258 compare and test instructions before use of condition codes.
10260 @item -mno-side-effects
10261 @opindex mno-side-effects
10262 Do not emit instructions with side-effects in addressing modes other than
10265 @item -mstack-align
10266 @itemx -mno-stack-align
10267 @itemx -mdata-align
10268 @itemx -mno-data-align
10269 @itemx -mconst-align
10270 @itemx -mno-const-align
10271 @opindex mstack-align
10272 @opindex mno-stack-align
10273 @opindex mdata-align
10274 @opindex mno-data-align
10275 @opindex mconst-align
10276 @opindex mno-const-align
10277 These options (no-options) arranges (eliminate arrangements) for the
10278 stack-frame, individual data and constants to be aligned for the maximum
10279 single data access size for the chosen CPU model. The default is to
10280 arrange for 32-bit alignment. ABI details such as structure layout are
10281 not affected by these options.
10289 Similar to the stack- data- and const-align options above, these options
10290 arrange for stack-frame, writable data and constants to all be 32-bit,
10291 16-bit or 8-bit aligned. The default is 32-bit alignment.
10293 @item -mno-prologue-epilogue
10294 @itemx -mprologue-epilogue
10295 @opindex mno-prologue-epilogue
10296 @opindex mprologue-epilogue
10297 With @option{-mno-prologue-epilogue}, the normal function prologue and
10298 epilogue that sets up the stack-frame are omitted and no return
10299 instructions or return sequences are generated in the code. Use this
10300 option only together with visual inspection of the compiled code: no
10301 warnings or errors are generated when call-saved registers must be saved,
10302 or storage for local variable needs to be allocated.
10306 @opindex mno-gotplt
10308 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
10309 instruction sequences that load addresses for functions from the PLT part
10310 of the GOT rather than (traditional on other architectures) calls to the
10311 PLT. The default is @option{-mgotplt}.
10315 Legacy no-op option only recognized with the cris-axis-aout target.
10319 Legacy no-op option only recognized with the cris-axis-elf and
10320 cris-axis-linux-gnu targets.
10324 Only recognized with the cris-axis-aout target, where it selects a
10325 GNU/linux-like multilib, include files and instruction set for
10326 @option{-march=v8}.
10330 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
10334 This option, recognized for the cris-axis-aout and cris-axis-elf arranges
10335 to link with input-output functions from a simulator library. Code,
10336 initialized data and zero-initialized data are allocated consecutively.
10340 Like @option{-sim}, but pass linker options to locate initialized data at
10341 0x40000000 and zero-initialized data at 0x80000000.
10345 @subsection MMIX Options
10346 @cindex MMIX Options
10348 These options are defined for the MMIX:
10352 @itemx -mno-libfuncs
10354 @opindex mno-libfuncs
10355 Specify that intrinsic library functions are being compiled, passing all
10356 values in registers, no matter the size.
10359 @itemx -mno-epsilon
10361 @opindex mno-epsilon
10362 Generate floating-point comparison instructions that compare with respect
10363 to the @code{rE} epsilon register.
10365 @item -mabi=mmixware
10367 @opindex mabi-mmixware
10369 Generate code that passes function parameters and return values that (in
10370 the called function) are seen as registers @code{$0} and up, as opposed to
10371 the GNU ABI which uses global registers @code{$231} and up.
10373 @item -mzero-extend
10374 @itemx -mno-zero-extend
10375 @opindex mzero-extend
10376 @opindex mno-zero-extend
10377 When reading data from memory in sizes shorter than 64 bits, use (do not
10378 use) zero-extending load instructions by default, rather than
10379 sign-extending ones.
10382 @itemx -mno-knuthdiv
10384 @opindex mno-knuthdiv
10385 Make the result of a division yielding a remainder have the same sign as
10386 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
10387 remainder follows the sign of the dividend. Both methods are
10388 arithmetically valid, the latter being almost exclusively used.
10390 @item -mtoplevel-symbols
10391 @itemx -mno-toplevel-symbols
10392 @opindex mtoplevel-symbols
10393 @opindex mno-toplevel-symbols
10394 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
10395 code can be used with the @code{PREFIX} assembly directive.
10399 Generate an executable in the ELF format, rather than the default
10400 @samp{mmo} format used by the @command{mmix} simulator.
10402 @item -mbranch-predict
10403 @itemx -mno-branch-predict
10404 @opindex mbranch-predict
10405 @opindex mno-branch-predict
10406 Use (do not use) the probable-branch instructions, when static branch
10407 prediction indicates a probable branch.
10409 @item -mbase-addresses
10410 @itemx -mno-base-addresses
10411 @opindex mbase-addresses
10412 @opindex mno-base-addresses
10413 Generate (do not generate) code that uses @emph{base addresses}. Using a
10414 base address automatically generates a request (handled by the assembler
10415 and the linker) for a constant to be set up in a global register. The
10416 register is used for one or more base address requests within the range 0
10417 to 255 from the value held in the register. The generally leads to short
10418 and fast code, but the number of different data items that can be
10419 addressed is limited. This means that a program that uses lots of static
10420 data may require @option{-mno-base-addresses}.
10422 @item -msingle-exit
10423 @itemx -mno-single-exit
10424 @opindex msingle-exit
10425 @opindex mno-single-exit
10426 Force (do not force) generated code to have a single exit point in each
10430 @node PDP-11 Options
10431 @subsection PDP-11 Options
10432 @cindex PDP-11 Options
10434 These options are defined for the PDP-11:
10439 Use hardware FPP floating point. This is the default. (FIS floating
10440 point on the PDP-11/40 is not supported.)
10443 @opindex msoft-float
10444 Do not use hardware floating point.
10448 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
10452 Return floating-point results in memory. This is the default.
10456 Generate code for a PDP-11/40.
10460 Generate code for a PDP-11/45. This is the default.
10464 Generate code for a PDP-11/10.
10466 @item -mbcopy-builtin
10467 @opindex bcopy-builtin
10468 Use inline @code{movstrhi} patterns for copying memory. This is the
10473 Do not use inline @code{movstrhi} patterns for copying memory.
10479 Use 16-bit @code{int}. This is the default.
10485 Use 32-bit @code{int}.
10488 @itemx -mno-float32
10490 @opindex mno-float32
10491 Use 64-bit @code{float}. This is the default.
10496 @opindex mno-float64
10497 Use 32-bit @code{float}.
10501 Use @code{abshi2} pattern. This is the default.
10505 Do not use @code{abshi2} pattern.
10507 @item -mbranch-expensive
10508 @opindex mbranch-expensive
10509 Pretend that branches are expensive. This is for experimenting with
10510 code generation only.
10512 @item -mbranch-cheap
10513 @opindex mbranch-cheap
10514 Do not pretend that branches are expensive. This is the default.
10518 Generate code for a system with split I&D.
10522 Generate code for a system without split I&D. This is the default.
10526 Use Unix assembler syntax. This is the default when configured for
10527 @samp{pdp11-*-bsd}.
10531 Use DEC assembler syntax. This is the default when configured for any
10532 PDP-11 target other than @samp{pdp11-*-bsd}.
10535 @node Xstormy16 Options
10536 @subsection Xstormy16 Options
10537 @cindex Xstormy16 Options
10539 These options are defined for Xstormy16:
10544 Choose startup files and linker script suitable for the simulator.
10548 @subsection FRV Options
10549 @cindex FRV Options
10555 Only use the first 32 general purpose registers.
10560 Use all 64 general purpose registers.
10565 Use only the first 32 floating point registers.
10570 Use all 64 floating point registers
10573 @opindex mhard-float
10575 Use hardware instructions for floating point operations.
10578 @opindex msoft-float
10580 Use library routines for floating point operations.
10585 Dynamically allocate condition code registers.
10590 Do not try to dynamically allocate condition code registers, only
10591 use @code{icc0} and @code{fcc0}.
10596 Change ABI to use double word insns.
10601 Do not use double word instructions.
10606 Use floating point double instructions.
10609 @opindex mno-double
10611 Do not use floating point double instructions.
10616 Use media instructions.
10621 Do not use media instructions.
10626 Use multiply and add/subtract instructions.
10629 @opindex mno-muladd
10631 Do not use multiply and add/subtract instructions.
10633 @item -mlibrary-pic
10634 @opindex mlibrary-pic
10636 Enable PIC support for building libraries
10641 Use only the first four media accumulator registers.
10646 Use all eight media accumulator registers.
10651 Pack VLIW instructions.
10656 Do not pack VLIW instructions.
10659 @opindex mno-eflags
10661 Do not mark ABI switches in e_flags.
10664 @opindex mcond-move
10666 Enable the use of conditional-move instructions (default).
10668 This switch is mainly for debugging the compiler and will likely be removed
10669 in a future version.
10671 @item -mno-cond-move
10672 @opindex mno-cond-move
10674 Disable the use of conditional-move instructions.
10676 This switch is mainly for debugging the compiler and will likely be removed
10677 in a future version.
10682 Enable the use of conditional set instructions (default).
10684 This switch is mainly for debugging the compiler and will likely be removed
10685 in a future version.
10690 Disable the use of conditional set instructions.
10692 This switch is mainly for debugging the compiler and will likely be removed
10693 in a future version.
10696 @opindex mcond-exec
10698 Enable the use of conditional execution (default).
10700 This switch is mainly for debugging the compiler and will likely be removed
10701 in a future version.
10703 @item -mno-cond-exec
10704 @opindex mno-cond-exec
10706 Disable the use of conditional execution.
10708 This switch is mainly for debugging the compiler and will likely be removed
10709 in a future version.
10711 @item -mvliw-branch
10712 @opindex mvliw-branch
10714 Run a pass to pack branches into VLIW instructions (default).
10716 This switch is mainly for debugging the compiler and will likely be removed
10717 in a future version.
10719 @item -mno-vliw-branch
10720 @opindex mno-vliw-branch
10722 Do not run a pass to pack branches into VLIW instructions.
10724 This switch is mainly for debugging the compiler and will likely be removed
10725 in a future version.
10727 @item -mmulti-cond-exec
10728 @opindex mmulti-cond-exec
10730 Enable optimization of @code{&&} and @code{||} in conditional execution
10733 This switch is mainly for debugging the compiler and will likely be removed
10734 in a future version.
10736 @item -mno-multi-cond-exec
10737 @opindex mno-multi-cond-exec
10739 Disable optimization of @code{&&} and @code{||} in conditional execution.
10741 This switch is mainly for debugging the compiler and will likely be removed
10742 in a future version.
10744 @item -mnested-cond-exec
10745 @opindex mnested-cond-exec
10747 Enable nested conditional execution optimizations (default).
10749 This switch is mainly for debugging the compiler and will likely be removed
10750 in a future version.
10752 @item -mno-nested-cond-exec
10753 @opindex mno-nested-cond-exec
10755 Disable nested conditional execution optimizations.
10757 This switch is mainly for debugging the compiler and will likely be removed
10758 in a future version.
10760 @item -mtomcat-stats
10761 @opindex mtomcat-stats
10763 Cause gas to print out tomcat statistics.
10765 @item -mcpu=@var{cpu}
10768 Select the processor type for which to generate code. Possible values are
10769 @samp{simple}, @samp{tomcat}, @samp{fr500}, @samp{fr400}, @samp{fr300},
10774 @node Xtensa Options
10775 @subsection Xtensa Options
10776 @cindex Xtensa Options
10778 The Xtensa architecture is designed to support many different
10779 configurations. The compiler's default options can be set to match a
10780 particular Xtensa configuration by copying a configuration file into the
10781 GCC sources when building GCC@. The options below may be used to
10782 override the default options.
10786 @itemx -mlittle-endian
10787 @opindex mbig-endian
10788 @opindex mlittle-endian
10789 Specify big-endian or little-endian byte ordering for the target Xtensa
10793 @itemx -mno-density
10795 @opindex mno-density
10796 Enable or disable use of the optional Xtensa code density instructions.
10799 @itemx -mno-const16
10801 @opindex mno-const16
10802 Enable or disable use of @code{CONST16} instructions for loading
10803 constant values. The @code{CONST16} instruction is currently not a
10804 standard option from Tensilica. When enabled, @code{CONST16}
10805 instructions are always used in place of the standard @code{L32R}
10806 instructions. The use of @code{CONST16} is enabled by default only if
10807 the @code{L32R} instruction is not available.
10813 Enable or disable use of the Xtensa @code{ABS} instruction for absolute
10820 Enable or disable use of the Xtensa @code{ADDX} and @code{SUBX}
10827 Enable or disable use of the Xtensa MAC16 option. When enabled, GCC
10828 will generate MAC16 instructions from standard C code, with the
10829 limitation that it will use neither the MR register file nor any
10830 instruction that operates on the MR registers. When this option is
10831 disabled, GCC will translate 16-bit multiply/accumulate operations to a
10832 combination of core instructions and library calls, depending on whether
10833 any other multiplier options are enabled.
10839 Enable or disable use of the 16-bit integer multiplier option. When
10840 enabled, the compiler will generate 16-bit multiply instructions for
10841 multiplications of 16 bits or smaller in standard C code. When this
10842 option is disabled, the compiler will either use 32-bit multiply or
10843 MAC16 instructions if they are available or generate library calls to
10844 perform the multiply operations using shifts and adds.
10850 Enable or disable use of the 32-bit integer multiplier option. When
10851 enabled, the compiler will generate 32-bit multiply instructions for
10852 multiplications of 32 bits or smaller in standard C code. When this
10853 option is disabled, the compiler will generate library calls to perform
10854 the multiply operations using either shifts and adds or 16-bit multiply
10855 instructions if they are available.
10861 Enable or disable use of the optional normalization shift amount
10862 (@code{NSA}) instructions to implement the built-in @code{ffs} function.
10867 @opindex mno-minmax
10868 Enable or disable use of the optional minimum and maximum value
10875 Enable or disable use of the optional sign extend (@code{SEXT})
10879 @itemx -mno-booleans
10881 @opindex mno-booleans
10882 Enable or disable support for the boolean register file used by Xtensa
10883 coprocessors. This is not typically useful by itself but may be
10884 required for other options that make use of the boolean registers (e.g.,
10885 the floating-point option).
10888 @itemx -msoft-float
10889 @opindex mhard-float
10890 @opindex msoft-float
10891 Enable or disable use of the floating-point option. When enabled, GCC
10892 generates floating-point instructions for 32-bit @code{float}
10893 operations. When this option is disabled, GCC generates library calls
10894 to emulate 32-bit floating-point operations using integer instructions.
10895 Regardless of this option, 64-bit @code{double} operations are always
10896 emulated with calls to library functions.
10899 @itemx -mno-fused-madd
10900 @opindex mfused-madd
10901 @opindex mno-fused-madd
10902 Enable or disable use of fused multiply/add and multiply/subtract
10903 instructions in the floating-point option. This has no effect if the
10904 floating-point option is not also enabled. Disabling fused multiply/add
10905 and multiply/subtract instructions forces the compiler to use separate
10906 instructions for the multiply and add/subtract operations. This may be
10907 desirable in some cases where strict IEEE 754-compliant results are
10908 required: the fused multiply add/subtract instructions do not round the
10909 intermediate result, thereby producing results with @emph{more} bits of
10910 precision than specified by the IEEE standard. Disabling fused multiply
10911 add/subtract instructions also ensures that the program output is not
10912 sensitive to the compiler's ability to combine multiply and add/subtract
10915 @item -mtext-section-literals
10916 @itemx -mno-text-section-literals
10917 @opindex mtext-section-literals
10918 @opindex mno-text-section-literals
10919 Control the treatment of literal pools. The default is
10920 @option{-mno-text-section-literals}, which places literals in a separate
10921 section in the output file. This allows the literal pool to be placed
10922 in a data RAM/ROM, and it also allows the linker to combine literal
10923 pools from separate object files to remove redundant literals and
10924 improve code size. With @option{-mtext-section-literals}, the literals
10925 are interspersed in the text section in order to keep them as close as
10926 possible to their references. This may be necessary for large assembly
10929 @item -mtarget-align
10930 @itemx -mno-target-align
10931 @opindex mtarget-align
10932 @opindex mno-target-align
10933 When this option is enabled, GCC instructs the assembler to
10934 automatically align instructions to reduce branch penalties at the
10935 expense of some code density. The assembler attempts to widen density
10936 instructions to align branch targets and the instructions following call
10937 instructions. If there are not enough preceding safe density
10938 instructions to align a target, no widening will be performed. The
10939 default is @option{-mtarget-align}. These options do not affect the
10940 treatment of auto-aligned instructions like @code{LOOP}, which the
10941 assembler will always align, either by widening density instructions or
10942 by inserting no-op instructions.
10945 @itemx -mno-longcalls
10946 @opindex mlongcalls
10947 @opindex mno-longcalls
10948 When this option is enabled, GCC instructs the assembler to translate
10949 direct calls to indirect calls unless it can determine that the target
10950 of a direct call is in the range allowed by the call instruction. This
10951 translation typically occurs for calls to functions in other source
10952 files. Specifically, the assembler translates a direct @code{CALL}
10953 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
10954 The default is @option{-mno-longcalls}. This option should be used in
10955 programs where the call target can potentially be out of range. This
10956 option is implemented in the assembler, not the compiler, so the
10957 assembly code generated by GCC will still show direct call
10958 instructions---look at the disassembled object code to see the actual
10959 instructions. Note that the assembler will use an indirect call for
10960 every cross-file call, not just those that really will be out of range.
10963 @node Code Gen Options
10964 @section Options for Code Generation Conventions
10965 @cindex code generation conventions
10966 @cindex options, code generation
10967 @cindex run-time options
10969 These machine-independent options control the interface conventions
10970 used in code generation.
10972 Most of them have both positive and negative forms; the negative form
10973 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
10974 one of the forms is listed---the one which is not the default. You
10975 can figure out the other form by either removing @samp{no-} or adding
10979 @item -fbounds-check
10980 @opindex fbounds-check
10981 For front-ends that support it, generate additional code to check that
10982 indices used to access arrays are within the declared range. This is
10983 currently only supported by the Java and Fortran 77 front-ends, where
10984 this option defaults to true and false respectively.
10988 This option generates traps for signed overflow on addition, subtraction,
10989 multiplication operations.
10993 This option instructs the compiler to assume that signed arithmetic
10994 overflow of addition, subtraction and multiplication wraps around
10995 using twos-complement representation. This flag enables some optimizations
10996 and disables other. This option is enabled by default for the Java
10997 front-end, as required by the Java language specification.
11000 @opindex fexceptions
11001 Enable exception handling. Generates extra code needed to propagate
11002 exceptions. For some targets, this implies GCC will generate frame
11003 unwind information for all functions, which can produce significant data
11004 size overhead, although it does not affect execution. If you do not
11005 specify this option, GCC will enable it by default for languages like
11006 C++ which normally require exception handling, and disable it for
11007 languages like C that do not normally require it. However, you may need
11008 to enable this option when compiling C code that needs to interoperate
11009 properly with exception handlers written in C++. You may also wish to
11010 disable this option if you are compiling older C++ programs that don't
11011 use exception handling.
11013 @item -fnon-call-exceptions
11014 @opindex fnon-call-exceptions
11015 Generate code that allows trapping instructions to throw exceptions.
11016 Note that this requires platform-specific runtime support that does
11017 not exist everywhere. Moreover, it only allows @emph{trapping}
11018 instructions to throw exceptions, i.e.@: memory references or floating
11019 point instructions. It does not allow exceptions to be thrown from
11020 arbitrary signal handlers such as @code{SIGALRM}.
11022 @item -funwind-tables
11023 @opindex funwind-tables
11024 Similar to @option{-fexceptions}, except that it will just generate any needed
11025 static data, but will not affect the generated code in any other way.
11026 You will normally not enable this option; instead, a language processor
11027 that needs this handling would enable it on your behalf.
11029 @item -fasynchronous-unwind-tables
11030 @opindex funwind-tables
11031 Generate unwind table in dwarf2 format, if supported by target machine. The
11032 table is exact at each instruction boundary, so it can be used for stack
11033 unwinding from asynchronous events (such as debugger or garbage collector).
11035 @item -fpcc-struct-return
11036 @opindex fpcc-struct-return
11037 Return ``short'' @code{struct} and @code{union} values in memory like
11038 longer ones, rather than in registers. This convention is less
11039 efficient, but it has the advantage of allowing intercallability between
11040 GCC-compiled files and files compiled with other compilers, particularly
11041 the Portable C Compiler (pcc).
11043 The precise convention for returning structures in memory depends
11044 on the target configuration macros.
11046 Short structures and unions are those whose size and alignment match
11047 that of some integer type.
11049 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
11050 switch is not binary compatible with code compiled with the
11051 @option{-freg-struct-return} switch.
11052 Use it to conform to a non-default application binary interface.
11054 @item -freg-struct-return
11055 @opindex freg-struct-return
11056 Return @code{struct} and @code{union} values in registers when possible.
11057 This is more efficient for small structures than
11058 @option{-fpcc-struct-return}.
11060 If you specify neither @option{-fpcc-struct-return} nor
11061 @option{-freg-struct-return}, GCC defaults to whichever convention is
11062 standard for the target. If there is no standard convention, GCC
11063 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
11064 the principal compiler. In those cases, we can choose the standard, and
11065 we chose the more efficient register return alternative.
11067 @strong{Warning:} code compiled with the @option{-freg-struct-return}
11068 switch is not binary compatible with code compiled with the
11069 @option{-fpcc-struct-return} switch.
11070 Use it to conform to a non-default application binary interface.
11072 @item -fshort-enums
11073 @opindex fshort-enums
11074 Allocate to an @code{enum} type only as many bytes as it needs for the
11075 declared range of possible values. Specifically, the @code{enum} type
11076 will be equivalent to the smallest integer type which has enough room.
11078 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
11079 code that is not binary compatible with code generated without that switch.
11080 Use it to conform to a non-default application binary interface.
11082 @item -fshort-double
11083 @opindex fshort-double
11084 Use the same size for @code{double} as for @code{float}.
11086 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
11087 code that is not binary compatible with code generated without that switch.
11088 Use it to conform to a non-default application binary interface.
11090 @item -fshort-wchar
11091 @opindex fshort-wchar
11092 Override the underlying type for @samp{wchar_t} to be @samp{short
11093 unsigned int} instead of the default for the target. This option is
11094 useful for building programs to run under WINE@.
11096 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
11097 code that is not binary compatible with code generated without that switch.
11098 Use it to conform to a non-default application binary interface.
11100 @item -fshared-data
11101 @opindex fshared-data
11102 Requests that the data and non-@code{const} variables of this
11103 compilation be shared data rather than private data. The distinction
11104 makes sense only on certain operating systems, where shared data is
11105 shared between processes running the same program, while private data
11106 exists in one copy per process.
11109 @opindex fno-common
11110 In C, allocate even uninitialized global variables in the data section of the
11111 object file, rather than generating them as common blocks. This has the
11112 effect that if the same variable is declared (without @code{extern}) in
11113 two different compilations, you will get an error when you link them.
11114 The only reason this might be useful is if you wish to verify that the
11115 program will work on other systems which always work this way.
11119 Ignore the @samp{#ident} directive.
11121 @item -fno-gnu-linker
11122 @opindex fno-gnu-linker
11123 Do not output global initializations (such as C++ constructors and
11124 destructors) in the form used by the GNU linker (on systems where the GNU
11125 linker is the standard method of handling them). Use this option when
11126 you want to use a non-GNU linker, which also requires using the
11127 @command{collect2} program to make sure the system linker includes
11128 constructors and destructors. (@command{collect2} is included in the GCC
11129 distribution.) For systems which @emph{must} use @command{collect2}, the
11130 compiler driver @command{gcc} is configured to do this automatically.
11132 @item -finhibit-size-directive
11133 @opindex finhibit-size-directive
11134 Don't output a @code{.size} assembler directive, or anything else that
11135 would cause trouble if the function is split in the middle, and the
11136 two halves are placed at locations far apart in memory. This option is
11137 used when compiling @file{crtstuff.c}; you should not need to use it
11140 @item -fverbose-asm
11141 @opindex fverbose-asm
11142 Put extra commentary information in the generated assembly code to
11143 make it more readable. This option is generally only of use to those
11144 who actually need to read the generated assembly code (perhaps while
11145 debugging the compiler itself).
11147 @option{-fno-verbose-asm}, the default, causes the
11148 extra information to be omitted and is useful when comparing two assembler
11153 @cindex global offset table
11155 Generate position-independent code (PIC) suitable for use in a shared
11156 library, if supported for the target machine. Such code accesses all
11157 constant addresses through a global offset table (GOT)@. The dynamic
11158 loader resolves the GOT entries when the program starts (the dynamic
11159 loader is not part of GCC; it is part of the operating system). If
11160 the GOT size for the linked executable exceeds a machine-specific
11161 maximum size, you get an error message from the linker indicating that
11162 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
11163 instead. (These maximums are 16k on the m88k, 8k on the SPARC, and 32k
11164 on the m68k and RS/6000. The 386 has no such limit.)
11166 Position-independent code requires special support, and therefore works
11167 only on certain machines. For the 386, GCC supports PIC for System V
11168 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
11169 position-independent.
11173 If supported for the target machine, emit position-independent code,
11174 suitable for dynamic linking and avoiding any limit on the size of the
11175 global offset table. This option makes a difference on the m68k, m88k,
11178 Position-independent code requires special support, and therefore works
11179 only on certain machines.
11185 These options are similar to @option{-fpic} and @option{-fPIC}, but
11186 generated position independent code can be only linked into executables.
11187 Usually these options are used when @option{-pie} GCC option will be
11188 used during linking.
11190 @item -ffixed-@var{reg}
11192 Treat the register named @var{reg} as a fixed register; generated code
11193 should never refer to it (except perhaps as a stack pointer, frame
11194 pointer or in some other fixed role).
11196 @var{reg} must be the name of a register. The register names accepted
11197 are machine-specific and are defined in the @code{REGISTER_NAMES}
11198 macro in the machine description macro file.
11200 This flag does not have a negative form, because it specifies a
11203 @item -fcall-used-@var{reg}
11204 @opindex fcall-used
11205 Treat the register named @var{reg} as an allocable register that is
11206 clobbered by function calls. It may be allocated for temporaries or
11207 variables that do not live across a call. Functions compiled this way
11208 will not save and restore the register @var{reg}.
11210 It is an error to used this flag with the frame pointer or stack pointer.
11211 Use of this flag for other registers that have fixed pervasive roles in
11212 the machine's execution model will produce disastrous results.
11214 This flag does not have a negative form, because it specifies a
11217 @item -fcall-saved-@var{reg}
11218 @opindex fcall-saved
11219 Treat the register named @var{reg} as an allocable register saved by
11220 functions. It may be allocated even for temporaries or variables that
11221 live across a call. Functions compiled this way will save and restore
11222 the register @var{reg} if they use it.
11224 It is an error to used this flag with the frame pointer or stack pointer.
11225 Use of this flag for other registers that have fixed pervasive roles in
11226 the machine's execution model will produce disastrous results.
11228 A different sort of disaster will result from the use of this flag for
11229 a register in which function values may be returned.
11231 This flag does not have a negative form, because it specifies a
11234 @item -fpack-struct
11235 @opindex fpack-struct
11236 Pack all structure members together without holes.
11238 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
11239 code that is not binary compatible with code generated without that switch.
11240 Additionally, it makes the code suboptimal.
11241 Use it to conform to a non-default application binary interface.
11243 @item -finstrument-functions
11244 @opindex finstrument-functions
11245 Generate instrumentation calls for entry and exit to functions. Just
11246 after function entry and just before function exit, the following
11247 profiling functions will be called with the address of the current
11248 function and its call site. (On some platforms,
11249 @code{__builtin_return_address} does not work beyond the current
11250 function, so the call site information may not be available to the
11251 profiling functions otherwise.)
11254 void __cyg_profile_func_enter (void *this_fn,
11256 void __cyg_profile_func_exit (void *this_fn,
11260 The first argument is the address of the start of the current function,
11261 which may be looked up exactly in the symbol table.
11263 This instrumentation is also done for functions expanded inline in other
11264 functions. The profiling calls will indicate where, conceptually, the
11265 inline function is entered and exited. This means that addressable
11266 versions of such functions must be available. If all your uses of a
11267 function are expanded inline, this may mean an additional expansion of
11268 code size. If you use @samp{extern inline} in your C code, an
11269 addressable version of such functions must be provided. (This is
11270 normally the case anyways, but if you get lucky and the optimizer always
11271 expands the functions inline, you might have gotten away without
11272 providing static copies.)
11274 A function may be given the attribute @code{no_instrument_function}, in
11275 which case this instrumentation will not be done. This can be used, for
11276 example, for the profiling functions listed above, high-priority
11277 interrupt routines, and any functions from which the profiling functions
11278 cannot safely be called (perhaps signal handlers, if the profiling
11279 routines generate output or allocate memory).
11281 @item -fstack-check
11282 @opindex fstack-check
11283 Generate code to verify that you do not go beyond the boundary of the
11284 stack. You should specify this flag if you are running in an
11285 environment with multiple threads, but only rarely need to specify it in
11286 a single-threaded environment since stack overflow is automatically
11287 detected on nearly all systems if there is only one stack.
11289 Note that this switch does not actually cause checking to be done; the
11290 operating system must do that. The switch causes generation of code
11291 to ensure that the operating system sees the stack being extended.
11293 @item -fstack-limit-register=@var{reg}
11294 @itemx -fstack-limit-symbol=@var{sym}
11295 @itemx -fno-stack-limit
11296 @opindex fstack-limit-register
11297 @opindex fstack-limit-symbol
11298 @opindex fno-stack-limit
11299 Generate code to ensure that the stack does not grow beyond a certain value,
11300 either the value of a register or the address of a symbol. If the stack
11301 would grow beyond the value, a signal is raised. For most targets,
11302 the signal is raised before the stack overruns the boundary, so
11303 it is possible to catch the signal without taking special precautions.
11305 For instance, if the stack starts at absolute address @samp{0x80000000}
11306 and grows downwards, you can use the flags
11307 @option{-fstack-limit-symbol=__stack_limit} and
11308 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
11309 of 128KB@. Note that this may only work with the GNU linker.
11311 @cindex aliasing of parameters
11312 @cindex parameters, aliased
11313 @item -fargument-alias
11314 @itemx -fargument-noalias
11315 @itemx -fargument-noalias-global
11316 @opindex fargument-alias
11317 @opindex fargument-noalias
11318 @opindex fargument-noalias-global
11319 Specify the possible relationships among parameters and between
11320 parameters and global data.
11322 @option{-fargument-alias} specifies that arguments (parameters) may
11323 alias each other and may alias global storage.@*
11324 @option{-fargument-noalias} specifies that arguments do not alias
11325 each other, but may alias global storage.@*
11326 @option{-fargument-noalias-global} specifies that arguments do not
11327 alias each other and do not alias global storage.
11329 Each language will automatically use whatever option is required by
11330 the language standard. You should not need to use these options yourself.
11332 @item -fleading-underscore
11333 @opindex fleading-underscore
11334 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
11335 change the way C symbols are represented in the object file. One use
11336 is to help link with legacy assembly code.
11338 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
11339 generate code that is not binary compatible with code generated without that
11340 switch. Use it to conform to a non-default application binary interface.
11341 Not all targets provide complete support for this switch.
11343 @item -ftls-model=@var{model}
11344 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
11345 The @var{model} argument should be one of @code{global-dynamic},
11346 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
11348 The default without @option{-fpic} is @code{initial-exec}; with
11349 @option{-fpic} the default is @code{global-dynamic}.
11354 @node Environment Variables
11355 @section Environment Variables Affecting GCC
11356 @cindex environment variables
11358 @c man begin ENVIRONMENT
11359 This section describes several environment variables that affect how GCC
11360 operates. Some of them work by specifying directories or prefixes to use
11361 when searching for various kinds of files. Some are used to specify other
11362 aspects of the compilation environment.
11364 Note that you can also specify places to search using options such as
11365 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
11366 take precedence over places specified using environment variables, which
11367 in turn take precedence over those specified by the configuration of GCC@.
11368 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
11369 GNU Compiler Collection (GCC) Internals}.
11374 @c @itemx LC_COLLATE
11376 @c @itemx LC_MONETARY
11377 @c @itemx LC_NUMERIC
11382 @c @findex LC_COLLATE
11383 @findex LC_MESSAGES
11384 @c @findex LC_MONETARY
11385 @c @findex LC_NUMERIC
11389 These environment variables control the way that GCC uses
11390 localization information that allow GCC to work with different
11391 national conventions. GCC inspects the locale categories
11392 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
11393 so. These locale categories can be set to any value supported by your
11394 installation. A typical value is @samp{en_UK} for English in the United
11397 The @env{LC_CTYPE} environment variable specifies character
11398 classification. GCC uses it to determine the character boundaries in
11399 a string; this is needed for some multibyte encodings that contain quote
11400 and escape characters that would otherwise be interpreted as a string
11403 The @env{LC_MESSAGES} environment variable specifies the language to
11404 use in diagnostic messages.
11406 If the @env{LC_ALL} environment variable is set, it overrides the value
11407 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
11408 and @env{LC_MESSAGES} default to the value of the @env{LANG}
11409 environment variable. If none of these variables are set, GCC
11410 defaults to traditional C English behavior.
11414 If @env{TMPDIR} is set, it specifies the directory to use for temporary
11415 files. GCC uses temporary files to hold the output of one stage of
11416 compilation which is to be used as input to the next stage: for example,
11417 the output of the preprocessor, which is the input to the compiler
11420 @item GCC_EXEC_PREFIX
11421 @findex GCC_EXEC_PREFIX
11422 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
11423 names of the subprograms executed by the compiler. No slash is added
11424 when this prefix is combined with the name of a subprogram, but you can
11425 specify a prefix that ends with a slash if you wish.
11427 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
11428 an appropriate prefix to use based on the pathname it was invoked with.
11430 If GCC cannot find the subprogram using the specified prefix, it
11431 tries looking in the usual places for the subprogram.
11433 The default value of @env{GCC_EXEC_PREFIX} is
11434 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the value
11435 of @code{prefix} when you ran the @file{configure} script.
11437 Other prefixes specified with @option{-B} take precedence over this prefix.
11439 This prefix is also used for finding files such as @file{crt0.o} that are
11442 In addition, the prefix is used in an unusual way in finding the
11443 directories to search for header files. For each of the standard
11444 directories whose name normally begins with @samp{/usr/local/lib/gcc}
11445 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
11446 replacing that beginning with the specified prefix to produce an
11447 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
11448 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
11449 These alternate directories are searched first; the standard directories
11452 @item COMPILER_PATH
11453 @findex COMPILER_PATH
11454 The value of @env{COMPILER_PATH} is a colon-separated list of
11455 directories, much like @env{PATH}. GCC tries the directories thus
11456 specified when searching for subprograms, if it can't find the
11457 subprograms using @env{GCC_EXEC_PREFIX}.
11460 @findex LIBRARY_PATH
11461 The value of @env{LIBRARY_PATH} is a colon-separated list of
11462 directories, much like @env{PATH}. When configured as a native compiler,
11463 GCC tries the directories thus specified when searching for special
11464 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
11465 using GCC also uses these directories when searching for ordinary
11466 libraries for the @option{-l} option (but directories specified with
11467 @option{-L} come first).
11471 @cindex locale definition
11472 This variable is used to pass locale information to the compiler. One way in
11473 which this information is used is to determine the character set to be used
11474 when character literals, string literals and comments are parsed in C and C++.
11475 When the compiler is configured to allow multibyte characters,
11476 the following values for @env{LANG} are recognized:
11480 Recognize JIS characters.
11482 Recognize SJIS characters.
11484 Recognize EUCJP characters.
11487 If @env{LANG} is not defined, or if it has some other value, then the
11488 compiler will use mblen and mbtowc as defined by the default locale to
11489 recognize and translate multibyte characters.
11493 Some additional environments variables affect the behavior of the
11496 @include cppenv.texi
11500 @node Precompiled Headers
11501 @section Using Precompiled Headers
11502 @cindex precompiled headers
11503 @cindex speed of compilation
11505 Often large projects have many header files that are included in every
11506 source file. The time the compiler takes to process these header files
11507 over and over again can account for nearly all of the time required to
11508 build the project. To make builds faster, GCC allows users to
11509 `precompile' a header file; then, if builds can use the precompiled
11510 header file they will be much faster.
11512 To create a precompiled header file, simply compile it as you would any
11513 other file, if necessary using the @option{-x} option to make the driver
11514 treat it as a C or C++ header file. You will probably want to use a
11515 tool like @command{make} to keep the precompiled header up-to-date when
11516 the headers it contains change.
11518 A precompiled header file will be searched for when @code{#include} is
11519 seen in the compilation. As it searches for the included file
11520 (@pxref{Search Path,,Search Path,cpp.info,The C Preprocessor}) the
11521 compiler looks for a precompiled header in each directory just before it
11522 looks for the include file in that directory. The name searched for is
11523 the name specified in the @code{#include} with @samp{.gch} appended. If
11524 the precompiled header file can't be used, it is ignored.
11526 For instance, if you have @code{#include "all.h"}, and you have
11527 @file{all.h.gch} in the same directory as @file{all.h}, then the
11528 precompiled header file will be used if possible, and the original
11529 header will be used otherwise.
11531 Alternatively, you might decide to put the precompiled header file in a
11532 directory and use @option{-I} to ensure that directory is searched
11533 before (or instead of) the directory containing the original header.
11534 Then, if you want to check that the precompiled header file is always
11535 used, you can put a file of the same name as the original header in this
11536 directory containing an @code{#error} command.
11538 This also works with @option{-include}. So yet another way to use
11539 precompiled headers, good for projects not designed with precompiled
11540 header files in mind, is to simply take most of the header files used by
11541 a project, include them from another header file, precompile that header
11542 file, and @option{-include} the precompiled header. If the header files
11543 have guards against multiple inclusion, they will be skipped because
11544 they've already been included (in the precompiled header).
11546 If you need to precompile the same header file for different
11547 languages, targets, or compiler options, you can instead make a
11548 @emph{directory} named like @file{all.h.gch}, and put each precompiled
11549 header in the directory. (It doesn't matter what you call the files
11550 in the directory, every precompiled header in the directory will be
11551 considered.) The first precompiled header encountered in the
11552 directory that is valid for this compilation will be used; they're
11553 searched in no particular order.
11555 There are many other possibilities, limited only by your imagination,
11556 good sense, and the constraints of your build system.
11558 A precompiled header file can be used only when these conditions apply:
11562 Only one precompiled header can be used in a particular compilation.
11564 A precompiled header can't be used once the first C token is seen. You
11565 can have preprocessor directives before a precompiled header; you can
11566 even include a precompiled header from inside another header, so long as
11567 there are no C tokens before the @code{#include}.
11569 The precompiled header file must be produced for the same language as
11570 the current compilation. You can't use a C precompiled header for a C++
11573 The precompiled header file must be produced by the same compiler
11574 version and configuration as the current compilation is using.
11575 The easiest way to guarantee this is to use the same compiler binary
11576 for creating and using precompiled headers.
11578 Any macros defined before the precompiled header (including with
11579 @option{-D}) must either be defined in the same way as when the
11580 precompiled header was generated, or must not affect the precompiled
11581 header, which usually means that the they don't appear in the
11582 precompiled header at all.
11584 Certain command-line options must be defined in the same way as when the
11585 precompiled header was generated. At present, it's not clear which
11586 options are safe to change and which are not; the safest choice is to
11587 use exactly the same options when generating and using the precompiled
11591 For all of these but the last, the compiler will automatically ignore
11592 the precompiled header if the conditions aren't met. For the last item,
11593 some option changes will cause the precompiled header to be rejected,
11594 but not all incompatible option combinations have yet been found. If
11595 you find a new incompatible combination, please consider filing a bug
11596 report, see @ref{Bugs}.
11598 @node Running Protoize
11599 @section Running Protoize
11601 The program @code{protoize} is an optional part of GCC@. You can use
11602 it to add prototypes to a program, thus converting the program to ISO
11603 C in one respect. The companion program @code{unprotoize} does the
11604 reverse: it removes argument types from any prototypes that are found.
11606 When you run these programs, you must specify a set of source files as
11607 command line arguments. The conversion programs start out by compiling
11608 these files to see what functions they define. The information gathered
11609 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
11611 After scanning comes actual conversion. The specified files are all
11612 eligible to be converted; any files they include (whether sources or
11613 just headers) are eligible as well.
11615 But not all the eligible files are converted. By default,
11616 @code{protoize} and @code{unprotoize} convert only source and header
11617 files in the current directory. You can specify additional directories
11618 whose files should be converted with the @option{-d @var{directory}}
11619 option. You can also specify particular files to exclude with the
11620 @option{-x @var{file}} option. A file is converted if it is eligible, its
11621 directory name matches one of the specified directory names, and its
11622 name within the directory has not been excluded.
11624 Basic conversion with @code{protoize} consists of rewriting most
11625 function definitions and function declarations to specify the types of
11626 the arguments. The only ones not rewritten are those for varargs
11629 @code{protoize} optionally inserts prototype declarations at the
11630 beginning of the source file, to make them available for any calls that
11631 precede the function's definition. Or it can insert prototype
11632 declarations with block scope in the blocks where undeclared functions
11635 Basic conversion with @code{unprotoize} consists of rewriting most
11636 function declarations to remove any argument types, and rewriting
11637 function definitions to the old-style pre-ISO form.
11639 Both conversion programs print a warning for any function declaration or
11640 definition that they can't convert. You can suppress these warnings
11643 The output from @code{protoize} or @code{unprotoize} replaces the
11644 original source file. The original file is renamed to a name ending
11645 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
11646 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
11647 for DOS) file already exists, then the source file is simply discarded.
11649 @code{protoize} and @code{unprotoize} both depend on GCC itself to
11650 scan the program and collect information about the functions it uses.
11651 So neither of these programs will work until GCC is installed.
11653 Here is a table of the options you can use with @code{protoize} and
11654 @code{unprotoize}. Each option works with both programs unless
11658 @item -B @var{directory}
11659 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
11660 usual directory (normally @file{/usr/local/lib}). This file contains
11661 prototype information about standard system functions. This option
11662 applies only to @code{protoize}.
11664 @item -c @var{compilation-options}
11665 Use @var{compilation-options} as the options when running @command{gcc} to
11666 produce the @samp{.X} files. The special option @option{-aux-info} is
11667 always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
11669 Note that the compilation options must be given as a single argument to
11670 @code{protoize} or @code{unprotoize}. If you want to specify several
11671 @command{gcc} options, you must quote the entire set of compilation options
11672 to make them a single word in the shell.
11674 There are certain @command{gcc} arguments that you cannot use, because they
11675 would produce the wrong kind of output. These include @option{-g},
11676 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
11677 the @var{compilation-options}, they are ignored.
11680 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
11681 systems) instead of @samp{.c}. This is convenient if you are converting
11682 a C program to C++. This option applies only to @code{protoize}.
11685 Add explicit global declarations. This means inserting explicit
11686 declarations at the beginning of each source file for each function
11687 that is called in the file and was not declared. These declarations
11688 precede the first function definition that contains a call to an
11689 undeclared function. This option applies only to @code{protoize}.
11691 @item -i @var{string}
11692 Indent old-style parameter declarations with the string @var{string}.
11693 This option applies only to @code{protoize}.
11695 @code{unprotoize} converts prototyped function definitions to old-style
11696 function definitions, where the arguments are declared between the
11697 argument list and the initial @samp{@{}. By default, @code{unprotoize}
11698 uses five spaces as the indentation. If you want to indent with just
11699 one space instead, use @option{-i " "}.
11702 Keep the @samp{.X} files. Normally, they are deleted after conversion
11706 Add explicit local declarations. @code{protoize} with @option{-l} inserts
11707 a prototype declaration for each function in each block which calls the
11708 function without any declaration. This option applies only to
11712 Make no real changes. This mode just prints information about the conversions
11713 that would have been done without @option{-n}.
11716 Make no @samp{.save} files. The original files are simply deleted.
11717 Use this option with caution.
11719 @item -p @var{program}
11720 Use the program @var{program} as the compiler. Normally, the name
11721 @file{gcc} is used.
11724 Work quietly. Most warnings are suppressed.
11727 Print the version number, just like @option{-v} for @command{gcc}.
11730 If you need special compiler options to compile one of your program's
11731 source files, then you should generate that file's @samp{.X} file
11732 specially, by running @command{gcc} on that source file with the
11733 appropriate options and the option @option{-aux-info}. Then run
11734 @code{protoize} on the entire set of files. @code{protoize} will use
11735 the existing @samp{.X} file because it is newer than the source file.
11739 gcc -Dfoo=bar file1.c -aux-info file1.X
11744 You need to include the special files along with the rest in the
11745 @code{protoize} command, even though their @samp{.X} files already
11746 exist, because otherwise they won't get converted.
11748 @xref{Protoize Caveats}, for more information on how to use
11749 @code{protoize} successfully.