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diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi deleted file mode 100644 index 975ee64..0000000 --- a/gcc/doc/invoke.texi +++ /dev/null @@ -1,35442 +0,0 @@ -@c Copyright (C) 1988-2022 Free Software Foundation, Inc. -@c This is part of the GCC manual. -@c For copying conditions, see the file gcc.texi. - -@ignore -@c man begin INCLUDE -@include gcc-vers.texi -@c man end - -@c man begin COPYRIGHT -Copyright @copyright{} 1988-2022 Free Software Foundation, Inc. - -Permission is granted to copy, distribute and/or modify this document -under the terms of the GNU Free Documentation License, Version 1.3 or -any later version published by the Free Software Foundation; with the -Invariant Sections being ``GNU General Public License'' and ``Funding -Free Software'', the Front-Cover texts being (a) (see below), and with -the Back-Cover Texts being (b) (see below). A copy of the license is -included in the gfdl(7) man page. - -(a) The FSF's Front-Cover Text is: - - A GNU Manual - -(b) The FSF's Back-Cover Text is: - - You have freedom to copy and modify this GNU Manual, like GNU - software. Copies published by the Free Software Foundation raise - funds for GNU development. -@c man end -@c Set file name and title for the man page. -@setfilename gcc -@settitle GNU project C and C++ compiler -@c man begin SYNOPSIS -gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}] - [@option{-g}] [@option{-pg}] [@option{-O}@var{level}] - [@option{-W}@var{warn}@dots{}] [@option{-Wpedantic}] - [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}] - [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}] - [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}] - [@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{} - -Only the most useful options are listed here; see below for the -remainder. @command{g++} accepts mostly the same options as @command{gcc}. -@c man end -@c man begin SEEALSO -gpl(7), gfdl(7), fsf-funding(7), -cpp(1), gcov(1), as(1), ld(1), gdb(1) -and the Info entries for @file{gcc}, @file{cpp}, @file{as}, -@file{ld}, @file{binutils} and @file{gdb}. -@c man end -@c man begin BUGS -For instructions on reporting bugs, see -@w{@value{BUGURL}}. -@c man end -@c man begin AUTHOR -See the Info entry for @command{gcc}, or -@w{@uref{https://gcc.gnu.org/onlinedocs/gcc/Contributors.html}}, -for contributors to GCC@. -@c man end -@end ignore - -@node Invoking GCC -@chapter GCC Command Options -@cindex GCC command options -@cindex command options -@cindex options, GCC command - -@c man begin DESCRIPTION -When you invoke GCC, it normally does preprocessing, compilation, -assembly and linking. The ``overall options'' allow you to stop this -process at an intermediate stage. For example, the @option{-c} option -says not to run the linker. Then the output consists of object files -output by the assembler. -@xref{Overall Options,,Options Controlling the Kind of Output}. - -Other options are passed on to one or more stages of processing. Some options -control the preprocessor and others the compiler itself. Yet other -options control the assembler and linker; most of these are not -documented here, since you rarely need to use any of them. - -@cindex C compilation options -Most of the command-line options that you can use with GCC are useful -for C programs; when an option is only useful with another language -(usually C++), the explanation says so explicitly. If the description -for a particular option does not mention a source language, you can use -that option with all supported languages. - -@cindex cross compiling -@cindex specifying machine version -@cindex specifying compiler version and target machine -@cindex compiler version, specifying -@cindex target machine, specifying -The usual way to run GCC is to run the executable called @command{gcc}, or -@command{@var{machine}-gcc} when cross-compiling, or -@command{@var{machine}-gcc-@var{version}} to run a specific version of GCC. -When you compile C++ programs, you should invoke GCC as @command{g++} -instead. @xref{Invoking G++,,Compiling C++ Programs}, -for information about the differences in behavior between @command{gcc} -and @command{g++} when compiling C++ programs. - -@cindex grouping options -@cindex options, grouping -The @command{gcc} program accepts options and file names as operands. Many -options have multi-letter names; therefore multiple single-letter options -may @emph{not} be grouped: @option{-dv} is very different from @w{@samp{-d --v}}. - -@cindex order of options -@cindex options, order -You can mix options and other arguments. For the most part, the order -you use doesn't matter. Order does matter when you use several -options of the same kind; for example, if you specify @option{-L} more -than once, the directories are searched in the order specified. Also, -the placement of the @option{-l} option is significant. - -Many options have long names starting with @samp{-f} or with -@samp{-W}---for example, -@option{-fmove-loop-invariants}, @option{-Wformat} and so on. Most of -these have both positive and negative forms; the negative form of -@option{-ffoo} is @option{-fno-foo}. This manual documents -only one of these two forms, whichever one is not the default. - -Some options take one or more arguments typically separated either -by a space or by the equals sign (@samp{=}) from the option name. -Unless documented otherwise, an argument can be either numeric or -a string. Numeric arguments must typically be small unsigned decimal -or hexadecimal integers. Hexadecimal arguments must begin with -the @samp{0x} prefix. Arguments to options that specify a size -threshold of some sort may be arbitrarily large decimal or hexadecimal -integers followed by a byte size suffix designating a multiple of bytes -such as @code{kB} and @code{KiB} for kilobyte and kibibyte, respectively, -@code{MB} and @code{MiB} for megabyte and mebibyte, @code{GB} and -@code{GiB} for gigabyte and gigibyte, and so on. Such arguments are -designated by @var{byte-size} in the following text. Refer to the NIST, -IEC, and other relevant national and international standards for the full -listing and explanation of the binary and decimal byte size prefixes. - -@c man end - -@xref{Option Index}, for an index to GCC's options. - -@menu -* Option Summary:: Brief list of all options, without explanations. -* Overall Options:: Controlling the kind of output: - an executable, object files, assembler files, - or preprocessed source. -* Invoking G++:: Compiling C++ programs. -* C Dialect Options:: Controlling the variant of C language compiled. -* C++ Dialect Options:: Variations on C++. -* Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C - and Objective-C++. -* Diagnostic Message Formatting Options:: Controlling how diagnostics should - be formatted. -* Warning Options:: How picky should the compiler be? -* Static Analyzer Options:: More expensive warnings. -* Debugging Options:: Producing debuggable code. -* Optimize Options:: How much optimization? -* Instrumentation Options:: Enabling profiling and extra run-time error checking. -* Preprocessor Options:: Controlling header files and macro definitions. - Also, getting dependency information for Make. -* Assembler Options:: Passing options to the assembler. -* Link Options:: Specifying libraries and so on. -* Directory Options:: Where to find header files and libraries. - Where to find the compiler executable files. -* Code Gen Options:: Specifying conventions for function calls, data layout - and register usage. -* Developer Options:: Printing GCC configuration info, statistics, and - debugging dumps. -* Submodel Options:: Target-specific options, such as compiling for a - specific processor variant. -* Spec Files:: How to pass switches to sub-processes. -* Environment Variables:: Env vars that affect GCC. -* Precompiled Headers:: Compiling a header once, and using it many times. -* C++ Modules:: Experimental C++20 module system. -@end menu - -@c man begin OPTIONS - -@node Option Summary -@section Option Summary - -Here is a summary of all the options, grouped by type. Explanations are -in the following sections. - -@table @emph -@item Overall Options -@xref{Overall Options,,Options Controlling the Kind of Output}. -@gccoptlist{-c -S -E -o @var{file} @gol --dumpbase @var{dumpbase} -dumpbase-ext @var{auxdropsuf} @gol --dumpdir @var{dumppfx} -x @var{language} @gol --v -### --help@r{[}=@var{class}@r{[},@dots{}@r{]]} --target-help --version @gol --pass-exit-codes -pipe -specs=@var{file} -wrapper @gol -@@@var{file} -ffile-prefix-map=@var{old}=@var{new} @gol --fplugin=@var{file} -fplugin-arg-@var{name}=@var{arg} @gol --fdump-ada-spec@r{[}-slim@r{]} -fada-spec-parent=@var{unit} -fdump-go-spec=@var{file}} - -@item C Language Options -@xref{C Dialect Options,,Options Controlling C Dialect}. -@gccoptlist{-ansi -std=@var{standard} -aux-info @var{filename} @gol --fno-asm @gol --fno-builtin -fno-builtin-@var{function} -fcond-mismatch @gol --ffreestanding -fgimple -fgnu-tm -fgnu89-inline -fhosted @gol --flax-vector-conversions -fms-extensions @gol --foffload=@var{arg} -foffload-options=@var{arg} @gol --fopenacc -fopenacc-dim=@var{geom} @gol --fopenmp -fopenmp-simd @gol --fpermitted-flt-eval-methods=@var{standard} @gol --fplan9-extensions -fsigned-bitfields -funsigned-bitfields @gol --fsigned-char -funsigned-char -fstrict-flex-arrays[=@var{n}] @gol --fsso-struct=@var{endianness}} - -@item C++ Language Options -@xref{C++ Dialect Options,,Options Controlling C++ Dialect}. -@gccoptlist{-fabi-version=@var{n} -fno-access-control @gol --faligned-new=@var{n} -fargs-in-order=@var{n} -fchar8_t -fcheck-new @gol --fconstexpr-depth=@var{n} -fconstexpr-cache-depth=@var{n} @gol --fconstexpr-loop-limit=@var{n} -fconstexpr-ops-limit=@var{n} @gol --fno-elide-constructors @gol --fno-enforce-eh-specs @gol --fno-gnu-keywords @gol --fno-implicit-templates @gol --fno-implicit-inline-templates @gol --fno-implement-inlines @gol --fmodule-header@r{[}=@var{kind}@r{]} -fmodule-only -fmodules-ts @gol --fmodule-implicit-inline @gol --fno-module-lazy @gol --fmodule-mapper=@var{specification} @gol --fmodule-version-ignore @gol --fms-extensions @gol --fnew-inheriting-ctors @gol --fnew-ttp-matching @gol --fno-nonansi-builtins -fnothrow-opt -fno-operator-names @gol --fno-optional-diags -fpermissive @gol --fno-pretty-templates @gol --fno-rtti -fsized-deallocation @gol --ftemplate-backtrace-limit=@var{n} @gol --ftemplate-depth=@var{n} @gol --fno-threadsafe-statics -fuse-cxa-atexit @gol --fno-weak -nostdinc++ @gol --fvisibility-inlines-hidden @gol --fvisibility-ms-compat @gol --fext-numeric-literals @gol --flang-info-include-translate@r{[}=@var{header}@r{]} @gol --flang-info-include-translate-not @gol --flang-info-module-cmi@r{[}=@var{module}@r{]} @gol --stdlib=@var{libstdc++,libc++} @gol --Wabi-tag -Wcatch-value -Wcatch-value=@var{n} @gol --Wno-class-conversion -Wclass-memaccess @gol --Wcomma-subscript -Wconditionally-supported @gol --Wno-conversion-null -Wctad-maybe-unsupported @gol --Wctor-dtor-privacy -Wdangling-reference @gol --Wno-delete-incomplete @gol --Wdelete-non-virtual-dtor -Wno-deprecated-array-compare @gol --Wdeprecated-copy -Wdeprecated-copy-dtor @gol --Wno-deprecated-enum-enum-conversion -Wno-deprecated-enum-float-conversion @gol --Weffc++ -Wno-exceptions -Wextra-semi -Wno-inaccessible-base @gol --Wno-inherited-variadic-ctor -Wno-init-list-lifetime @gol --Winvalid-imported-macros @gol --Wno-invalid-offsetof -Wno-literal-suffix @gol --Wmismatched-new-delete -Wmismatched-tags @gol --Wmultiple-inheritance -Wnamespaces -Wnarrowing @gol --Wnoexcept -Wnoexcept-type -Wnon-virtual-dtor @gol --Wpessimizing-move -Wno-placement-new -Wplacement-new=@var{n} @gol --Wrange-loop-construct -Wredundant-move -Wredundant-tags @gol --Wreorder -Wregister @gol --Wstrict-null-sentinel -Wno-subobject-linkage -Wtemplates @gol --Wno-non-template-friend -Wold-style-cast @gol --Woverloaded-virtual -Wno-pmf-conversions -Wself-move -Wsign-promo @gol --Wsized-deallocation -Wsuggest-final-methods @gol --Wsuggest-final-types -Wsuggest-override @gol --Wno-terminate -Wuseless-cast -Wno-vexing-parse @gol --Wvirtual-inheritance @gol --Wno-virtual-move-assign -Wvolatile -Wzero-as-null-pointer-constant} - -@item Objective-C and Objective-C++ Language Options -@xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling -Objective-C and Objective-C++ Dialects}. -@gccoptlist{-fconstant-string-class=@var{class-name} @gol --fgnu-runtime -fnext-runtime @gol --fno-nil-receivers @gol --fobjc-abi-version=@var{n} @gol --fobjc-call-cxx-cdtors @gol --fobjc-direct-dispatch @gol --fobjc-exceptions @gol --fobjc-gc @gol --fobjc-nilcheck @gol --fobjc-std=objc1 @gol --fno-local-ivars @gol --fivar-visibility=@r{[}public@r{|}protected@r{|}private@r{|}package@r{]} @gol --freplace-objc-classes @gol --fzero-link @gol --gen-decls @gol --Wassign-intercept -Wno-property-assign-default @gol --Wno-protocol -Wobjc-root-class -Wselector @gol --Wstrict-selector-match @gol --Wundeclared-selector} - -@item Diagnostic Message Formatting Options -@xref{Diagnostic Message Formatting Options,,Options to Control Diagnostic Messages Formatting}. -@gccoptlist{-fmessage-length=@var{n} @gol --fdiagnostics-plain-output @gol --fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]} @gol --fdiagnostics-color=@r{[}auto@r{|}never@r{|}always@r{]} @gol --fdiagnostics-urls=@r{[}auto@r{|}never@r{|}always@r{]} @gol --fdiagnostics-format=@r{[}text@r{|}sarif-stderr@r{|}sarif-file@r{|}json@r{|}json-stderr@r{|}json-file@r{]} @gol --fno-diagnostics-show-option -fno-diagnostics-show-caret @gol --fno-diagnostics-show-labels -fno-diagnostics-show-line-numbers @gol --fno-diagnostics-show-cwe @gol --fno-diagnostics-show-rule @gol --fdiagnostics-minimum-margin-width=@var{width} @gol --fdiagnostics-parseable-fixits -fdiagnostics-generate-patch @gol --fdiagnostics-show-template-tree -fno-elide-type @gol --fdiagnostics-path-format=@r{[}none@r{|}separate-events@r{|}inline-events@r{]} @gol --fdiagnostics-show-path-depths @gol --fno-show-column @gol --fdiagnostics-column-unit=@r{[}display@r{|}byte@r{]} @gol --fdiagnostics-column-origin=@var{origin} @gol --fdiagnostics-escape-format=@r{[}unicode@r{|}bytes@r{]}} - -@item Warning Options -@xref{Warning Options,,Options to Request or Suppress Warnings}. -@gccoptlist{-fsyntax-only -fmax-errors=@var{n} -Wpedantic @gol --pedantic-errors @gol --w -Wextra -Wall -Wabi=@var{n} @gol --Waddress -Wno-address-of-packed-member -Waggregate-return @gol --Walloc-size-larger-than=@var{byte-size} -Walloc-zero @gol --Walloca -Walloca-larger-than=@var{byte-size} @gol --Wno-aggressive-loop-optimizations @gol --Warith-conversion @gol --Warray-bounds -Warray-bounds=@var{n} -Warray-compare @gol --Wno-attributes -Wattribute-alias=@var{n} -Wno-attribute-alias @gol --Wno-attribute-warning @gol --Wbidi-chars=@r{[}none@r{|}unpaired@r{|}any@r{|}ucn@r{]} @gol --Wbool-compare -Wbool-operation @gol --Wno-builtin-declaration-mismatch @gol --Wno-builtin-macro-redefined -Wc90-c99-compat -Wc99-c11-compat @gol --Wc11-c2x-compat @gol --Wc++-compat -Wc++11-compat -Wc++14-compat -Wc++17-compat @gol --Wc++20-compat @gol --Wno-c++11-extensions -Wno-c++14-extensions -Wno-c++17-extensions @gol --Wno-c++20-extensions -Wno-c++23-extensions @gol --Wcast-align -Wcast-align=strict -Wcast-function-type -Wcast-qual @gol --Wchar-subscripts @gol --Wclobbered -Wcomment @gol --Wconversion -Wno-coverage-mismatch -Wno-cpp @gol --Wdangling-else -Wdangling-pointer -Wdangling-pointer=@var{n} @gol --Wdate-time @gol --Wno-deprecated -Wno-deprecated-declarations -Wno-designated-init @gol --Wdisabled-optimization @gol --Wno-discarded-array-qualifiers -Wno-discarded-qualifiers @gol --Wno-div-by-zero -Wdouble-promotion @gol --Wduplicated-branches -Wduplicated-cond @gol --Wempty-body -Wno-endif-labels -Wenum-compare -Wenum-conversion @gol --Wenum-int-mismatch @gol --Werror -Werror=* -Wexpansion-to-defined -Wfatal-errors @gol --Wfloat-conversion -Wfloat-equal -Wformat -Wformat=2 @gol --Wno-format-contains-nul -Wno-format-extra-args @gol --Wformat-nonliteral -Wformat-overflow=@var{n} @gol --Wformat-security -Wformat-signedness -Wformat-truncation=@var{n} @gol --Wformat-y2k -Wframe-address @gol --Wframe-larger-than=@var{byte-size} -Wno-free-nonheap-object @gol --Wno-if-not-aligned -Wno-ignored-attributes @gol --Wignored-qualifiers -Wno-incompatible-pointer-types @gol --Wimplicit -Wimplicit-fallthrough -Wimplicit-fallthrough=@var{n} @gol --Wno-implicit-function-declaration -Wno-implicit-int @gol --Winfinite-recursion @gol --Winit-self -Winline -Wno-int-conversion -Wint-in-bool-context @gol --Wno-int-to-pointer-cast -Wno-invalid-memory-model @gol --Winvalid-pch -Winvalid-utf8 -Wno-unicode -Wjump-misses-init @gol --Wlarger-than=@var{byte-size} -Wlogical-not-parentheses -Wlogical-op @gol --Wlong-long -Wno-lto-type-mismatch -Wmain -Wmaybe-uninitialized @gol --Wmemset-elt-size -Wmemset-transposed-args @gol --Wmisleading-indentation -Wmissing-attributes -Wmissing-braces @gol --Wmissing-field-initializers -Wmissing-format-attribute @gol --Wmissing-include-dirs -Wmissing-noreturn -Wno-missing-profile @gol --Wno-multichar -Wmultistatement-macros -Wnonnull -Wnonnull-compare @gol --Wnormalized=@r{[}none@r{|}id@r{|}nfc@r{|}nfkc@r{]} @gol --Wnull-dereference -Wno-odr @gol --Wopenacc-parallelism @gol --Wopenmp-simd @gol --Wno-overflow -Woverlength-strings -Wno-override-init-side-effects @gol --Wpacked -Wno-packed-bitfield-compat -Wpacked-not-aligned -Wpadded @gol --Wparentheses -Wno-pedantic-ms-format @gol --Wpointer-arith -Wno-pointer-compare -Wno-pointer-to-int-cast @gol --Wno-pragmas -Wno-prio-ctor-dtor -Wredundant-decls @gol --Wrestrict -Wno-return-local-addr -Wreturn-type @gol --Wno-scalar-storage-order -Wsequence-point @gol --Wshadow -Wshadow=global -Wshadow=local -Wshadow=compatible-local @gol --Wno-shadow-ivar @gol --Wno-shift-count-negative -Wno-shift-count-overflow -Wshift-negative-value @gol --Wno-shift-overflow -Wshift-overflow=@var{n} @gol --Wsign-compare -Wsign-conversion @gol --Wno-sizeof-array-argument @gol --Wsizeof-array-div @gol --Wsizeof-pointer-div -Wsizeof-pointer-memaccess @gol --Wstack-protector -Wstack-usage=@var{byte-size} -Wstrict-aliasing @gol --Wstrict-aliasing=n -Wstrict-overflow -Wstrict-overflow=@var{n} @gol --Wstring-compare @gol --Wno-stringop-overflow -Wno-stringop-overread @gol --Wno-stringop-truncation @gol --Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{|}malloc@r{]} @gol --Wswitch -Wno-switch-bool -Wswitch-default -Wswitch-enum @gol --Wno-switch-outside-range -Wno-switch-unreachable -Wsync-nand @gol --Wsystem-headers -Wtautological-compare -Wtrampolines -Wtrigraphs @gol --Wtrivial-auto-var-init -Wtsan -Wtype-limits -Wundef @gol --Wuninitialized -Wunknown-pragmas @gol --Wunsuffixed-float-constants -Wunused @gol --Wunused-but-set-parameter -Wunused-but-set-variable @gol --Wunused-const-variable -Wunused-const-variable=@var{n} @gol --Wunused-function -Wunused-label -Wunused-local-typedefs @gol --Wunused-macros @gol --Wunused-parameter -Wno-unused-result @gol --Wunused-value -Wunused-variable @gol --Wno-varargs -Wvariadic-macros @gol --Wvector-operation-performance @gol --Wvla -Wvla-larger-than=@var{byte-size} -Wno-vla-larger-than @gol --Wvolatile-register-var -Wwrite-strings @gol --Wxor-used-as-pow @gol --Wzero-length-bounds} - -@item Static Analyzer Options -@gccoptlist{ --fanalyzer @gol --fanalyzer-call-summaries @gol --fanalyzer-checker=@var{name} @gol --fno-analyzer-feasibility @gol --fanalyzer-fine-grained @gol --fno-analyzer-state-merge @gol --fno-analyzer-state-purge @gol --fanalyzer-transitivity @gol --fno-analyzer-undo-inlining @gol --fanalyzer-verbose-edges @gol --fanalyzer-verbose-state-changes @gol --fanalyzer-verbosity=@var{level} @gol --fdump-analyzer @gol --fdump-analyzer-callgraph @gol --fdump-analyzer-exploded-graph @gol --fdump-analyzer-exploded-nodes @gol --fdump-analyzer-exploded-nodes-2 @gol --fdump-analyzer-exploded-nodes-3 @gol --fdump-analyzer-exploded-paths @gol --fdump-analyzer-feasibility @gol --fdump-analyzer-json @gol --fdump-analyzer-state-purge @gol --fdump-analyzer-stderr @gol --fdump-analyzer-supergraph @gol --fdump-analyzer-untracked @gol --Wno-analyzer-double-fclose @gol --Wno-analyzer-double-free @gol --Wno-analyzer-exposure-through-output-file @gol --Wno-analyzer-exposure-through-uninit-copy @gol --Wno-analyzer-fd-access-mode-mismatch @gol --Wno-analyzer-fd-double-close @gol --Wno-analyzer-fd-leak @gol --Wno-analyzer-fd-use-after-close @gol --Wno-analyzer-fd-use-without-check @gol --Wno-analyzer-file-leak @gol --Wno-analyzer-free-of-non-heap @gol --Wno-analyzer-imprecise-fp-arithmetic @gol --Wno-analyzer-jump-through-null @gol --Wno-analyzer-malloc-leak @gol --Wno-analyzer-mismatching-deallocation @gol --Wno-analyzer-null-argument @gol --Wno-analyzer-null-dereference @gol --Wno-analyzer-out-of-bounds @gol --Wno-analyzer-possible-null-argument @gol --Wno-analyzer-possible-null-dereference @gol --Wno-analyzer-putenv-of-auto-var @gol --Wno-analyzer-shift-count-negative @gol --Wno-analyzer-shift-count-overflow @gol --Wno-analyzer-stale-setjmp-buffer @gol --Wno-analyzer-tainted-allocation-size @gol --Wno-analyzer-tainted-array-index @gol --Wno-analyzer-tainted-divisor @gol --Wno-analyzer-tainted-offset @gol --Wno-analyzer-tainted-size @gol --Wanalyzer-too-complex @gol --Wno-analyzer-unsafe-call-within-signal-handler @gol --Wno-analyzer-use-after-free @gol --Wno-analyzer-use-of-pointer-in-stale-stack-frame @gol --Wno-analyzer-use-of-uninitialized-value @gol --Wno-analyzer-va-arg-type-mismatch @gol --Wno-analyzer-va-list-exhausted @gol --Wno-analyzer-va-list-leak @gol --Wno-analyzer-va-list-use-after-va-end @gol --Wno-analyzer-write-to-const @gol --Wno-analyzer-write-to-string-literal @gol -} - -@item C and Objective-C-only Warning Options -@gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol --Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs @gol --Wold-style-declaration -Wold-style-definition @gol --Wstrict-prototypes -Wtraditional -Wtraditional-conversion @gol --Wdeclaration-after-statement -Wpointer-sign} - -@item Debugging Options -@xref{Debugging Options,,Options for Debugging Your Program}. -@gccoptlist{-g -g@var{level} -gdwarf -gdwarf-@var{version} @gol --gbtf -gctf -gctf@var{level} @gol --ggdb -grecord-gcc-switches -gno-record-gcc-switches @gol --gstrict-dwarf -gno-strict-dwarf @gol --gas-loc-support -gno-as-loc-support @gol --gas-locview-support -gno-as-locview-support @gol --gcolumn-info -gno-column-info -gdwarf32 -gdwarf64 @gol --gstatement-frontiers -gno-statement-frontiers @gol --gvariable-location-views -gno-variable-location-views @gol --ginternal-reset-location-views -gno-internal-reset-location-views @gol --ginline-points -gno-inline-points @gol --gvms -gz@r{[}=@var{type}@r{]} @gol --gsplit-dwarf -gdescribe-dies -gno-describe-dies @gol --fdebug-prefix-map=@var{old}=@var{new} -fdebug-types-section @gol --fno-eliminate-unused-debug-types @gol --femit-struct-debug-baseonly -femit-struct-debug-reduced @gol --femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} @gol --fno-eliminate-unused-debug-symbols -femit-class-debug-always @gol --fno-merge-debug-strings -fno-dwarf2-cfi-asm @gol --fvar-tracking -fvar-tracking-assignments} - -@item Optimization Options -@xref{Optimize Options,,Options that Control Optimization}. -@gccoptlist{-faggressive-loop-optimizations @gol --falign-functions[=@var{n}[:@var{m}:[@var{n2}[:@var{m2}]]]] @gol --falign-jumps[=@var{n}[:@var{m}:[@var{n2}[:@var{m2}]]]] @gol --falign-labels[=@var{n}[:@var{m}:[@var{n2}[:@var{m2}]]]] @gol --falign-loops[=@var{n}[:@var{m}:[@var{n2}[:@var{m2}]]]] @gol --fno-allocation-dce -fallow-store-data-races @gol --fassociative-math -fauto-profile -fauto-profile[=@var{path}] @gol --fauto-inc-dec -fbranch-probabilities @gol --fcaller-saves @gol --fcombine-stack-adjustments -fconserve-stack @gol --fcompare-elim -fcprop-registers -fcrossjumping @gol --fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules @gol --fcx-limited-range @gol --fdata-sections -fdce -fdelayed-branch @gol --fdelete-null-pointer-checks -fdevirtualize -fdevirtualize-speculatively @gol --fdevirtualize-at-ltrans -fdse @gol --fearly-inlining -fipa-sra -fexpensive-optimizations -ffat-lto-objects @gol --ffast-math -ffinite-math-only -ffloat-store -fexcess-precision=@var{style} @gol --ffinite-loops @gol --fforward-propagate -ffp-contract=@var{style} -ffunction-sections @gol --fgcse -fgcse-after-reload -fgcse-las -fgcse-lm -fgraphite-identity @gol --fgcse-sm -fhoist-adjacent-loads -fif-conversion @gol --fif-conversion2 -findirect-inlining @gol --finline-functions -finline-functions-called-once -finline-limit=@var{n} @gol --finline-small-functions -fipa-modref -fipa-cp -fipa-cp-clone @gol --fipa-bit-cp -fipa-vrp -fipa-pta -fipa-profile -fipa-pure-const @gol --fipa-reference -fipa-reference-addressable @gol --fipa-stack-alignment -fipa-icf -fira-algorithm=@var{algorithm} @gol --flive-patching=@var{level} @gol --fira-region=@var{region} -fira-hoist-pressure @gol --fira-loop-pressure -fno-ira-share-save-slots @gol --fno-ira-share-spill-slots @gol --fisolate-erroneous-paths-dereference -fisolate-erroneous-paths-attribute @gol --fivopts -fkeep-inline-functions -fkeep-static-functions @gol --fkeep-static-consts -flimit-function-alignment -flive-range-shrinkage @gol --floop-block -floop-interchange -floop-strip-mine @gol --floop-unroll-and-jam -floop-nest-optimize @gol --floop-parallelize-all -flra-remat -flto -flto-compression-level @gol --flto-partition=@var{alg} -fmerge-all-constants @gol --fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves @gol --fmove-loop-invariants -fmove-loop-stores -fno-branch-count-reg @gol --fno-defer-pop -fno-fp-int-builtin-inexact -fno-function-cse @gol --fno-guess-branch-probability -fno-inline -fno-math-errno -fno-peephole @gol --fno-peephole2 -fno-printf-return-value -fno-sched-interblock @gol --fno-sched-spec -fno-signed-zeros @gol --fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol --fomit-frame-pointer -foptimize-sibling-calls @gol --fpartial-inlining -fpeel-loops -fpredictive-commoning @gol --fprefetch-loop-arrays @gol --fprofile-correction @gol --fprofile-use -fprofile-use=@var{path} -fprofile-partial-training @gol --fprofile-values -fprofile-reorder-functions @gol --freciprocal-math -free -frename-registers -freorder-blocks @gol --freorder-blocks-algorithm=@var{algorithm} @gol --freorder-blocks-and-partition -freorder-functions @gol --frerun-cse-after-loop -freschedule-modulo-scheduled-loops @gol --frounding-math -fsave-optimization-record @gol --fsched2-use-superblocks -fsched-pressure @gol --fsched-spec-load -fsched-spec-load-dangerous @gol --fsched-stalled-insns-dep[=@var{n}] -fsched-stalled-insns[=@var{n}] @gol --fsched-group-heuristic -fsched-critical-path-heuristic @gol --fsched-spec-insn-heuristic -fsched-rank-heuristic @gol --fsched-last-insn-heuristic -fsched-dep-count-heuristic @gol --fschedule-fusion @gol --fschedule-insns -fschedule-insns2 -fsection-anchors @gol --fselective-scheduling -fselective-scheduling2 @gol --fsel-sched-pipelining -fsel-sched-pipelining-outer-loops @gol --fsemantic-interposition -fshrink-wrap -fshrink-wrap-separate @gol --fsignaling-nans @gol --fsingle-precision-constant -fsplit-ivs-in-unroller -fsplit-loops@gol --fsplit-paths @gol --fsplit-wide-types -fsplit-wide-types-early -fssa-backprop -fssa-phiopt @gol --fstdarg-opt -fstore-merging -fstrict-aliasing -fipa-strict-aliasing @gol --fthread-jumps -ftracer -ftree-bit-ccp @gol --ftree-builtin-call-dce -ftree-ccp -ftree-ch @gol --ftree-coalesce-vars -ftree-copy-prop -ftree-dce -ftree-dominator-opts @gol --ftree-dse -ftree-forwprop -ftree-fre -fcode-hoisting @gol --ftree-loop-if-convert -ftree-loop-im @gol --ftree-phiprop -ftree-loop-distribution -ftree-loop-distribute-patterns @gol --ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize @gol --ftree-loop-vectorize @gol --ftree-parallelize-loops=@var{n} -ftree-pre -ftree-partial-pre -ftree-pta @gol --ftree-reassoc -ftree-scev-cprop -ftree-sink -ftree-slsr -ftree-sra @gol --ftree-switch-conversion -ftree-tail-merge @gol --ftree-ter -ftree-vectorize -ftree-vrp -ftrivial-auto-var-init @gol --funconstrained-commons -funit-at-a-time -funroll-all-loops @gol --funroll-loops -funsafe-math-optimizations -funswitch-loops @gol --fipa-ra -fvariable-expansion-in-unroller -fvect-cost-model -fvpt @gol --fweb -fwhole-program -fwpa -fuse-linker-plugin -fzero-call-used-regs @gol ---param @var{name}=@var{value} --O -O0 -O1 -O2 -O3 -Os -Ofast -Og -Oz} - -@item Program Instrumentation Options -@xref{Instrumentation Options,,Program Instrumentation Options}. -@gccoptlist{-p -pg -fprofile-arcs --coverage -ftest-coverage @gol --fprofile-abs-path @gol --fprofile-dir=@var{path} -fprofile-generate -fprofile-generate=@var{path} @gol --fprofile-info-section -fprofile-info-section=@var{name} @gol --fprofile-note=@var{path} -fprofile-prefix-path=@var{path} @gol --fprofile-update=@var{method} -fprofile-filter-files=@var{regex} @gol --fprofile-exclude-files=@var{regex} @gol --fprofile-reproducible=@r{[}multithreaded@r{|}parallel-runs@r{|}serial@r{]} @gol --fsanitize=@var{style} -fsanitize-recover -fsanitize-recover=@var{style} @gol --fsanitize-trap -fsanitize-trap=@var{style} @gol --fasan-shadow-offset=@var{number} -fsanitize-sections=@var{s1},@var{s2},... @gol --fsanitize-undefined-trap-on-error -fbounds-check @gol --fcf-protection=@r{[}full@r{|}branch@r{|}return@r{|}none@r{|}check@r{]} @gol --fharden-compares -fharden-conditional-branches @gol --fstack-protector -fstack-protector-all -fstack-protector-strong @gol --fstack-protector-explicit -fstack-check @gol --fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol --fno-stack-limit -fsplit-stack @gol --fvtable-verify=@r{[}std@r{|}preinit@r{|}none@r{]} @gol --fvtv-counts -fvtv-debug @gol --finstrument-functions -finstrument-functions-once @gol --finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} @gol --finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{}} @gol --fprofile-prefix-map=@var{old}=@var{new} - -@item Preprocessor Options -@xref{Preprocessor Options,,Options Controlling the Preprocessor}. -@gccoptlist{-A@var{question}=@var{answer} @gol --A-@var{question}@r{[}=@var{answer}@r{]} @gol --C -CC -D@var{macro}@r{[}=@var{defn}@r{]} @gol --dD -dI -dM -dN -dU @gol --fdebug-cpp -fdirectives-only -fdollars-in-identifiers @gol --fexec-charset=@var{charset} -fextended-identifiers @gol --finput-charset=@var{charset} -flarge-source-files @gol --fmacro-prefix-map=@var{old}=@var{new} -fmax-include-depth=@var{depth} @gol --fno-canonical-system-headers -fpch-deps -fpch-preprocess @gol --fpreprocessed -ftabstop=@var{width} -ftrack-macro-expansion @gol --fwide-exec-charset=@var{charset} -fworking-directory @gol --H -imacros @var{file} -include @var{file} @gol --M -MD -MF -MG -MM -MMD -MP -MQ -MT -Mno-modules @gol --no-integrated-cpp -P -pthread -remap @gol --traditional -traditional-cpp -trigraphs @gol --U@var{macro} -undef @gol --Wp,@var{option} -Xpreprocessor @var{option}} - -@item Assembler Options -@xref{Assembler Options,,Passing Options to the Assembler}. -@gccoptlist{-Wa,@var{option} -Xassembler @var{option}} - -@item Linker Options -@xref{Link Options,,Options for Linking}. -@gccoptlist{@var{object-file-name} -fuse-ld=@var{linker} -l@var{library} @gol --nostartfiles -nodefaultlibs -nolibc -nostdlib -nostdlib++ @gol --e @var{entry} --entry=@var{entry} @gol --pie -pthread -r -rdynamic @gol --s -static -static-pie -static-libgcc -static-libstdc++ @gol --static-libasan -static-libtsan -static-liblsan -static-libubsan @gol --shared -shared-libgcc -symbolic @gol --T @var{script} -Wl,@var{option} -Xlinker @var{option} @gol --u @var{symbol} -z @var{keyword}} - -@item Directory Options -@xref{Directory Options,,Options for Directory Search}. -@gccoptlist{-B@var{prefix} -I@var{dir} -I- @gol --idirafter @var{dir} @gol --imacros @var{file} -imultilib @var{dir} @gol --iplugindir=@var{dir} -iprefix @var{file} @gol --iquote @var{dir} -isysroot @var{dir} -isystem @var{dir} @gol --iwithprefix @var{dir} -iwithprefixbefore @var{dir} @gol --L@var{dir} -no-canonical-prefixes --no-sysroot-suffix @gol --nostdinc -nostdinc++ --sysroot=@var{dir}} - -@item Code Generation Options -@xref{Code Gen Options,,Options for Code Generation Conventions}. -@gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol --ffixed-@var{reg} -fexceptions @gol --fnon-call-exceptions -fdelete-dead-exceptions -funwind-tables @gol --fasynchronous-unwind-tables @gol --fno-gnu-unique @gol --finhibit-size-directive -fcommon -fno-ident @gol --fpcc-struct-return -fpic -fPIC -fpie -fPIE -fno-plt @gol --fno-jump-tables -fno-bit-tests @gol --frecord-gcc-switches @gol --freg-struct-return -fshort-enums -fshort-wchar @gol --fverbose-asm -fpack-struct[=@var{n}] @gol --fleading-underscore -ftls-model=@var{model} @gol --fstack-reuse=@var{reuse_level} @gol --ftrampolines -ftrapv -fwrapv @gol --fvisibility=@r{[}default@r{|}internal@r{|}hidden@r{|}protected@r{]} @gol --fstrict-volatile-bitfields -fsync-libcalls} - -@item Developer Options -@xref{Developer Options,,GCC Developer Options}. -@gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol --dumpfullversion -fcallgraph-info@r{[}=su,da@r{]} --fchecking -fchecking=@var{n} --fdbg-cnt-list @gol -fdbg-cnt=@var{counter-value-list} @gol --fdisable-ipa-@var{pass_name} @gol --fdisable-rtl-@var{pass_name} @gol --fdisable-rtl-@var{pass-name}=@var{range-list} @gol --fdisable-tree-@var{pass_name} @gol --fdisable-tree-@var{pass-name}=@var{range-list} @gol --fdump-debug -fdump-earlydebug @gol --fdump-noaddr -fdump-unnumbered -fdump-unnumbered-links @gol --fdump-final-insns@r{[}=@var{file}@r{]} @gol --fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline @gol --fdump-lang-all @gol --fdump-lang-@var{switch} @gol --fdump-lang-@var{switch}-@var{options} @gol --fdump-lang-@var{switch}-@var{options}=@var{filename} @gol --fdump-passes @gol --fdump-rtl-@var{pass} -fdump-rtl-@var{pass}=@var{filename} @gol --fdump-statistics @gol --fdump-tree-all @gol --fdump-tree-@var{switch} @gol --fdump-tree-@var{switch}-@var{options} @gol --fdump-tree-@var{switch}-@var{options}=@var{filename} @gol --fcompare-debug@r{[}=@var{opts}@r{]} -fcompare-debug-second @gol --fenable-@var{kind}-@var{pass} @gol --fenable-@var{kind}-@var{pass}=@var{range-list} @gol --fira-verbose=@var{n} @gol --flto-report -flto-report-wpa -fmem-report-wpa @gol --fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report @gol --fopt-info -fopt-info-@var{options}@r{[}=@var{file}@r{]} @gol --fmultiflags -fprofile-report @gol --frandom-seed=@var{string} -fsched-verbose=@var{n} @gol --fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose @gol --fstats -fstack-usage -ftime-report -ftime-report-details @gol --fvar-tracking-assignments-toggle -gtoggle @gol --print-file-name=@var{library} -print-libgcc-file-name @gol --print-multi-directory -print-multi-lib -print-multi-os-directory @gol --print-prog-name=@var{program} -print-search-dirs -Q @gol --print-sysroot -print-sysroot-headers-suffix @gol --save-temps -save-temps=cwd -save-temps=obj -time@r{[}=@var{file}@r{]}} - -@item Machine-Dependent Options -@xref{Submodel Options,,Machine-Dependent Options}. -@c This list is ordered alphanumerically by subsection name. -@c Try and put the significant identifier (CPU or system) first, -@c so users have a clue at guessing where the ones they want will be. - -@emph{AArch64 Options} -@gccoptlist{-mabi=@var{name} -mbig-endian -mlittle-endian @gol --mgeneral-regs-only @gol --mcmodel=tiny -mcmodel=small -mcmodel=large @gol --mstrict-align -mno-strict-align @gol --momit-leaf-frame-pointer @gol --mtls-dialect=desc -mtls-dialect=traditional @gol --mtls-size=@var{size} @gol --mfix-cortex-a53-835769 -mfix-cortex-a53-843419 @gol --mlow-precision-recip-sqrt -mlow-precision-sqrt -mlow-precision-div @gol --mpc-relative-literal-loads @gol --msign-return-address=@var{scope} @gol --mbranch-protection=@var{none}|@var{standard}|@var{pac-ret}[+@var{leaf} -+@var{b-key}]|@var{bti} @gol --mharden-sls=@var{opts} @gol --march=@var{name} -mcpu=@var{name} -mtune=@var{name} @gol --moverride=@var{string} -mverbose-cost-dump @gol --mstack-protector-guard=@var{guard} -mstack-protector-guard-reg=@var{sysreg} @gol --mstack-protector-guard-offset=@var{offset} -mtrack-speculation @gol --moutline-atomics } - -@emph{Adapteva Epiphany Options} -@gccoptlist{-mhalf-reg-file -mprefer-short-insn-regs @gol --mbranch-cost=@var{num} -mcmove -mnops=@var{num} -msoft-cmpsf @gol --msplit-lohi -mpost-inc -mpost-modify -mstack-offset=@var{num} @gol --mround-nearest -mlong-calls -mshort-calls -msmall16 @gol --mfp-mode=@var{mode} -mvect-double -max-vect-align=@var{num} @gol --msplit-vecmove-early -m1reg-@var{reg}} - -@emph{AMD GCN Options} -@gccoptlist{-march=@var{gpu} -mtune=@var{gpu} -mstack-size=@var{bytes}} - -@emph{ARC Options} -@gccoptlist{-mbarrel-shifter -mjli-always @gol --mcpu=@var{cpu} -mA6 -mARC600 -mA7 -mARC700 @gol --mdpfp -mdpfp-compact -mdpfp-fast -mno-dpfp-lrsr @gol --mea -mno-mpy -mmul32x16 -mmul64 -matomic @gol --mnorm -mspfp -mspfp-compact -mspfp-fast -msimd -msoft-float -mswap @gol --mcrc -mdsp-packa -mdvbf -mlock -mmac-d16 -mmac-24 -mrtsc -mswape @gol --mtelephony -mxy -misize -mannotate-align -marclinux -marclinux_prof @gol --mlong-calls -mmedium-calls -msdata -mirq-ctrl-saved @gol --mrgf-banked-regs -mlpc-width=@var{width} -G @var{num} @gol --mvolatile-cache -mtp-regno=@var{regno} @gol --malign-call -mauto-modify-reg -mbbit-peephole -mno-brcc @gol --mcase-vector-pcrel -mcompact-casesi -mno-cond-exec -mearly-cbranchsi @gol --mexpand-adddi -mindexed-loads -mlra -mlra-priority-none @gol --mlra-priority-compact -mlra-priority-noncompact -mmillicode @gol --mmixed-code -mq-class -mRcq -mRcw -msize-level=@var{level} @gol --mtune=@var{cpu} -mmultcost=@var{num} -mcode-density-frame @gol --munalign-prob-threshold=@var{probability} -mmpy-option=@var{multo} @gol --mdiv-rem -mcode-density -mll64 -mfpu=@var{fpu} -mrf16 -mbranch-index} - -@emph{ARM Options} -@gccoptlist{-mapcs-frame -mno-apcs-frame @gol --mabi=@var{name} @gol --mapcs-stack-check -mno-apcs-stack-check @gol --mapcs-reentrant -mno-apcs-reentrant @gol --mgeneral-regs-only @gol --msched-prolog -mno-sched-prolog @gol --mlittle-endian -mbig-endian @gol --mbe8 -mbe32 @gol --mfloat-abi=@var{name} @gol --mfp16-format=@var{name} --mthumb-interwork -mno-thumb-interwork @gol --mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol --mtune=@var{name} -mprint-tune-info @gol --mstructure-size-boundary=@var{n} @gol --mabort-on-noreturn @gol --mlong-calls -mno-long-calls @gol --msingle-pic-base -mno-single-pic-base @gol --mpic-register=@var{reg} @gol --mnop-fun-dllimport @gol --mpoke-function-name @gol --mthumb -marm -mflip-thumb @gol --mtpcs-frame -mtpcs-leaf-frame @gol --mcaller-super-interworking -mcallee-super-interworking @gol --mtp=@var{name} -mtls-dialect=@var{dialect} @gol --mword-relocations @gol --mfix-cortex-m3-ldrd @gol --mfix-cortex-a57-aes-1742098 @gol --mfix-cortex-a72-aes-1655431 @gol --munaligned-access @gol --mneon-for-64bits @gol --mslow-flash-data @gol --masm-syntax-unified @gol --mrestrict-it @gol --mverbose-cost-dump @gol --mpure-code @gol --mcmse @gol --mfix-cmse-cve-2021-35465 @gol --mstack-protector-guard=@var{guard} -mstack-protector-guard-offset=@var{offset} @gol --mfdpic} - -@emph{AVR Options} -@gccoptlist{-mmcu=@var{mcu} -mabsdata -maccumulate-args @gol --mbranch-cost=@var{cost} @gol --mcall-prologues -mgas-isr-prologues -mint8 @gol --mdouble=@var{bits} -mlong-double=@var{bits} @gol --mn_flash=@var{size} -mno-interrupts @gol --mmain-is-OS_task -mrelax -mrmw -mstrict-X -mtiny-stack @gol --mfract-convert-truncate @gol --mshort-calls -nodevicelib -nodevicespecs @gol --Waddr-space-convert -Wmisspelled-isr} - -@emph{Blackfin Options} -@gccoptlist{-mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} @gol --msim -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol --mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol --mlow-64k -mno-low64k -mstack-check-l1 -mid-shared-library @gol --mno-id-shared-library -mshared-library-id=@var{n} @gol --mleaf-id-shared-library -mno-leaf-id-shared-library @gol --msep-data -mno-sep-data -mlong-calls -mno-long-calls @gol --mfast-fp -minline-plt -mmulticore -mcorea -mcoreb -msdram @gol --micplb} - -@emph{C6X Options} -@gccoptlist{-mbig-endian -mlittle-endian -march=@var{cpu} @gol --msim -msdata=@var{sdata-type}} - -@emph{CRIS Options} -@gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} --mtune=@var{cpu} -mmax-stack-frame=@var{n} @gol --metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol --mstack-align -mdata-align -mconst-align @gol --m32-bit -m16-bit -m8-bit -mno-prologue-epilogue @gol --melf -maout -sim -sim2 @gol --mmul-bug-workaround -mno-mul-bug-workaround} - -@emph{C-SKY Options} -@gccoptlist{-march=@var{arch} -mcpu=@var{cpu} @gol --mbig-endian -EB -mlittle-endian -EL @gol --mhard-float -msoft-float -mfpu=@var{fpu} -mdouble-float -mfdivdu @gol --mfloat-abi=@var{name} @gol --melrw -mistack -mmp -mcp -mcache -msecurity -mtrust @gol --mdsp -medsp -mvdsp @gol --mdiv -msmart -mhigh-registers -manchor @gol --mpushpop -mmultiple-stld -mconstpool -mstack-size -mccrt @gol --mbranch-cost=@var{n} -mcse-cc -msched-prolog -msim} - -@emph{Darwin Options} -@gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol --arch_only -bind_at_load -bundle -bundle_loader @gol --client_name -compatibility_version -current_version @gol --dead_strip @gol --dependency-file -dylib_file -dylinker_install_name @gol --dynamic -dynamiclib -exported_symbols_list @gol --filelist -flat_namespace -force_cpusubtype_ALL @gol --force_flat_namespace -headerpad_max_install_names @gol --iframework @gol --image_base -init -install_name -keep_private_externs @gol --multi_module -multiply_defined -multiply_defined_unused @gol --noall_load -no_dead_strip_inits_and_terms @gol --nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol --pagezero_size -prebind -prebind_all_twolevel_modules @gol --private_bundle -read_only_relocs -sectalign @gol --sectobjectsymbols -whyload -seg1addr @gol --sectcreate -sectobjectsymbols -sectorder @gol --segaddr -segs_read_only_addr -segs_read_write_addr @gol --seg_addr_table -seg_addr_table_filename -seglinkedit @gol --segprot -segs_read_only_addr -segs_read_write_addr @gol --single_module -static -sub_library -sub_umbrella @gol --twolevel_namespace -umbrella -undefined @gol --unexported_symbols_list -weak_reference_mismatches @gol --whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol --mkernel -mone-byte-bool} - -@emph{DEC Alpha Options} -@gccoptlist{-mno-fp-regs -msoft-float @gol --mieee -mieee-with-inexact -mieee-conformant @gol --mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol --mtrap-precision=@var{mode} -mbuild-constants @gol --mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol --mbwx -mmax -mfix -mcix @gol --mfloat-vax -mfloat-ieee @gol --mexplicit-relocs -msmall-data -mlarge-data @gol --msmall-text -mlarge-text @gol --mmemory-latency=@var{time}} - -@emph{eBPF Options} -@gccoptlist{-mbig-endian -mlittle-endian -mkernel=@var{version} --mframe-limit=@var{bytes} -mxbpf -mco-re -mno-co-re --mjmpext -mjmp32 -malu32 -mcpu=@var{version}} - -@emph{FR30 Options} -@gccoptlist{-msmall-model -mno-lsim} - -@emph{FT32 Options} -@gccoptlist{-msim -mlra -mnodiv -mft32b -mcompress -mnopm} - -@emph{FRV Options} -@gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol --mhard-float -msoft-float @gol --malloc-cc -mfixed-cc -mdword -mno-dword @gol --mdouble -mno-double @gol --mmedia -mno-media -mmuladd -mno-muladd @gol --mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol --mlinked-fp -mlong-calls -malign-labels @gol --mlibrary-pic -macc-4 -macc-8 @gol --mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol --moptimize-membar -mno-optimize-membar @gol --mscc -mno-scc -mcond-exec -mno-cond-exec @gol --mvliw-branch -mno-vliw-branch @gol --mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol --mno-nested-cond-exec -mtomcat-stats @gol --mTLS -mtls @gol --mcpu=@var{cpu}} - -@emph{GNU/Linux Options} -@gccoptlist{-mglibc -muclibc -mmusl -mbionic -mandroid @gol --tno-android-cc -tno-android-ld} - -@emph{H8/300 Options} -@gccoptlist{-mrelax -mh -ms -mn -mexr -mno-exr -mint32 -malign-300} - -@emph{HPPA Options} -@gccoptlist{-march=@var{architecture-type} @gol --mcaller-copies -mdisable-fpregs -mdisable-indexing @gol --mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol --mfixed-range=@var{register-range} @gol --mjump-in-delay -mlinker-opt -mlong-calls @gol --mlong-load-store -mno-disable-fpregs @gol --mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol --mno-jump-in-delay -mno-long-load-store @gol --mno-portable-runtime -mno-soft-float @gol --mno-space-regs -msoft-float -mpa-risc-1-0 @gol --mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol --mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol --munix=@var{unix-std} -nolibdld -static -threads} - -@emph{IA-64 Options} -@gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol --mvolatile-asm-stop -mregister-names -msdata -mno-sdata @gol --mconstant-gp -mauto-pic -mfused-madd @gol --minline-float-divide-min-latency @gol --minline-float-divide-max-throughput @gol --mno-inline-float-divide @gol --minline-int-divide-min-latency @gol --minline-int-divide-max-throughput @gol --mno-inline-int-divide @gol --minline-sqrt-min-latency -minline-sqrt-max-throughput @gol --mno-inline-sqrt @gol --mdwarf2-asm -mearly-stop-bits @gol --mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol --mtune=@var{cpu-type} -milp32 -mlp64 @gol --msched-br-data-spec -msched-ar-data-spec -msched-control-spec @gol --msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec @gol --msched-spec-ldc -msched-spec-control-ldc @gol --msched-prefer-non-data-spec-insns -msched-prefer-non-control-spec-insns @gol --msched-stop-bits-after-every-cycle -msched-count-spec-in-critical-path @gol --msel-sched-dont-check-control-spec -msched-fp-mem-deps-zero-cost @gol --msched-max-memory-insns-hard-limit -msched-max-memory-insns=@var{max-insns}} - -@emph{LM32 Options} -@gccoptlist{-mbarrel-shift-enabled -mdivide-enabled -mmultiply-enabled @gol --msign-extend-enabled -muser-enabled} - -@emph{LoongArch Options} -@gccoptlist{-march=@var{cpu-type} -mtune=@var{cpu-type} -mabi=@var{base-abi-type} @gol --mfpu=@var{fpu-type} -msoft-float -msingle-float -mdouble-float @gol --mbranch-cost=@var{n} -mcheck-zero-division -mno-check-zero-division @gol --mcond-move-int -mno-cond-move-int @gol --mcond-move-float -mno-cond-move-float @gol --memcpy -mno-memcpy -mstrict-align -mno-strict-align @gol --mmax-inline-memcpy-size=@var{n} @gol --mexplicit-relocs -mno-explicit-relocs @gol --mdirect-extern-access -mno-direct-extern-access @gol --mcmodel=@var{code-model}} - -@emph{M32R/D Options} -@gccoptlist{-m32r2 -m32rx -m32r @gol --mdebug @gol --malign-loops -mno-align-loops @gol --missue-rate=@var{number} @gol --mbranch-cost=@var{number} @gol --mmodel=@var{code-size-model-type} @gol --msdata=@var{sdata-type} @gol --mno-flush-func -mflush-func=@var{name} @gol --mno-flush-trap -mflush-trap=@var{number} @gol --G @var{num}} - -@emph{M32C Options} -@gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}} - -@emph{M680x0 Options} -@gccoptlist{-march=@var{arch} -mcpu=@var{cpu} -mtune=@var{tune} @gol --m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol --m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407 @gol --mcfv4e -mbitfield -mno-bitfield -mc68000 -mc68020 @gol --mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort @gol --mno-short -mhard-float -m68881 -msoft-float -mpcrel @gol --malign-int -mstrict-align -msep-data -mno-sep-data @gol --mshared-library-id=n -mid-shared-library -mno-id-shared-library @gol --mxgot -mno-xgot -mlong-jump-table-offsets} - -@emph{MCore Options} -@gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol --mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol --m4byte-functions -mno-4byte-functions -mcallgraph-data @gol --mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol --mlittle-endian -mbig-endian -m210 -m340 -mstack-increment} - -@emph{MeP Options} -@gccoptlist{-mabsdiff -mall-opts -maverage -mbased=@var{n} -mbitops @gol --mc=@var{n} -mclip -mconfig=@var{name} -mcop -mcop32 -mcop64 -mivc2 @gol --mdc -mdiv -meb -mel -mio-volatile -ml -mleadz -mm -mminmax @gol --mmult -mno-opts -mrepeat -ms -msatur -msdram -msim -msimnovec -mtf @gol --mtiny=@var{n}} - -@emph{MicroBlaze Options} -@gccoptlist{-msoft-float -mhard-float -msmall-divides -mcpu=@var{cpu} @gol --mmemcpy -mxl-soft-mul -mxl-soft-div -mxl-barrel-shift @gol --mxl-pattern-compare -mxl-stack-check -mxl-gp-opt -mno-clearbss @gol --mxl-multiply-high -mxl-float-convert -mxl-float-sqrt @gol --mbig-endian -mlittle-endian -mxl-reorder -mxl-mode-@var{app-model} @gol --mpic-data-is-text-relative} - -@emph{MIPS Options} -@gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol --mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips32r3 -mips32r5 @gol --mips32r6 -mips64 -mips64r2 -mips64r3 -mips64r5 -mips64r6 @gol --mips16 -mno-mips16 -mflip-mips16 @gol --minterlink-compressed -mno-interlink-compressed @gol --minterlink-mips16 -mno-interlink-mips16 @gol --mabi=@var{abi} -mabicalls -mno-abicalls @gol --mshared -mno-shared -mplt -mno-plt -mxgot -mno-xgot @gol --mgp32 -mgp64 -mfp32 -mfpxx -mfp64 -mhard-float -msoft-float @gol --mno-float -msingle-float -mdouble-float @gol --modd-spreg -mno-odd-spreg @gol --mabs=@var{mode} -mnan=@var{encoding} @gol --mdsp -mno-dsp -mdspr2 -mno-dspr2 @gol --mmcu -mmno-mcu @gol --meva -mno-eva @gol --mvirt -mno-virt @gol --mxpa -mno-xpa @gol --mcrc -mno-crc @gol --mginv -mno-ginv @gol --mmicromips -mno-micromips @gol --mmsa -mno-msa @gol --mloongson-mmi -mno-loongson-mmi @gol --mloongson-ext -mno-loongson-ext @gol --mloongson-ext2 -mno-loongson-ext2 @gol --mfpu=@var{fpu-type} @gol --msmartmips -mno-smartmips @gol --mpaired-single -mno-paired-single -mdmx -mno-mdmx @gol --mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc @gol --mlong64 -mlong32 -msym32 -mno-sym32 @gol --G@var{num} -mlocal-sdata -mno-local-sdata @gol --mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt @gol --membedded-data -mno-embedded-data @gol --muninit-const-in-rodata -mno-uninit-const-in-rodata @gol --mcode-readable=@var{setting} @gol --msplit-addresses -mno-split-addresses @gol --mexplicit-relocs -mno-explicit-relocs @gol --mcheck-zero-division -mno-check-zero-division @gol --mdivide-traps -mdivide-breaks @gol --mload-store-pairs -mno-load-store-pairs @gol --munaligned-access -mno-unaligned-access @gol --mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol --mmad -mno-mad -mimadd -mno-imadd -mfused-madd -mno-fused-madd -nocpp @gol --mfix-24k -mno-fix-24k @gol --mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol --mfix-r5900 -mno-fix-r5900 @gol --mfix-r10000 -mno-fix-r10000 -mfix-rm7000 -mno-fix-rm7000 @gol --mfix-vr4120 -mno-fix-vr4120 @gol --mfix-vr4130 -mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1 @gol --mflush-func=@var{func} -mno-flush-func @gol --mbranch-cost=@var{num} -mbranch-likely -mno-branch-likely @gol --mcompact-branches=@var{policy} @gol --mfp-exceptions -mno-fp-exceptions @gol --mvr4130-align -mno-vr4130-align -msynci -mno-synci @gol --mlxc1-sxc1 -mno-lxc1-sxc1 -mmadd4 -mno-madd4 @gol --mrelax-pic-calls -mno-relax-pic-calls -mmcount-ra-address @gol --mframe-header-opt -mno-frame-header-opt} - -@emph{MMIX Options} -@gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol --mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol --melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol --mno-base-addresses -msingle-exit -mno-single-exit} - -@emph{MN10300 Options} -@gccoptlist{-mmult-bug -mno-mult-bug @gol --mno-am33 -mam33 -mam33-2 -mam34 @gol --mtune=@var{cpu-type} @gol --mreturn-pointer-on-d0 @gol --mno-crt0 -mrelax -mliw -msetlb} - -@emph{Moxie Options} -@gccoptlist{-meb -mel -mmul.x -mno-crt0} - -@emph{MSP430 Options} -@gccoptlist{-msim -masm-hex -mmcu= -mcpu= -mlarge -msmall -mrelax @gol --mwarn-mcu @gol --mcode-region= -mdata-region= @gol --msilicon-errata= -msilicon-errata-warn= @gol --mhwmult= -minrt -mtiny-printf -mmax-inline-shift=} - -@emph{NDS32 Options} -@gccoptlist{-mbig-endian -mlittle-endian @gol --mreduced-regs -mfull-regs @gol --mcmov -mno-cmov @gol --mext-perf -mno-ext-perf @gol --mext-perf2 -mno-ext-perf2 @gol --mext-string -mno-ext-string @gol --mv3push -mno-v3push @gol --m16bit -mno-16bit @gol --misr-vector-size=@var{num} @gol --mcache-block-size=@var{num} @gol --march=@var{arch} @gol --mcmodel=@var{code-model} @gol --mctor-dtor -mrelax} - -@emph{Nios II Options} -@gccoptlist{-G @var{num} -mgpopt=@var{option} -mgpopt -mno-gpopt @gol --mgprel-sec=@var{regexp} -mr0rel-sec=@var{regexp} @gol --mel -meb @gol --mno-bypass-cache -mbypass-cache @gol --mno-cache-volatile -mcache-volatile @gol --mno-fast-sw-div -mfast-sw-div @gol --mhw-mul -mno-hw-mul -mhw-mulx -mno-hw-mulx -mno-hw-div -mhw-div @gol --mcustom-@var{insn}=@var{N} -mno-custom-@var{insn} @gol --mcustom-fpu-cfg=@var{name} @gol --mhal -msmallc -msys-crt0=@var{name} -msys-lib=@var{name} @gol --march=@var{arch} -mbmx -mno-bmx -mcdx -mno-cdx} - -@emph{Nvidia PTX Options} -@gccoptlist{-m64 -mmainkernel -moptimize} - -@emph{OpenRISC Options} -@gccoptlist{-mboard=@var{name} -mnewlib -mhard-mul -mhard-div @gol --msoft-mul -msoft-div @gol --msoft-float -mhard-float -mdouble-float -munordered-float @gol --mcmov -mror -mrori -msext -msfimm -mshftimm @gol --mcmodel=@var{code-model}} - -@emph{PDP-11 Options} -@gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol --mint32 -mno-int16 -mint16 -mno-int32 @gol --msplit -munix-asm -mdec-asm -mgnu-asm -mlra} - -@emph{picoChip Options} -@gccoptlist{-mae=@var{ae_type} -mvliw-lookahead=@var{N} @gol --msymbol-as-address -mno-inefficient-warnings} - -@emph{PowerPC Options} -See RS/6000 and PowerPC Options. - -@emph{PRU Options} -@gccoptlist{-mmcu=@var{mcu} -minrt -mno-relax -mloop @gol --mabi=@var{variant} @gol} - -@emph{RISC-V Options} -@gccoptlist{-mbranch-cost=@var{N-instruction} @gol --mplt -mno-plt @gol --mabi=@var{ABI-string} @gol --mfdiv -mno-fdiv @gol --mdiv -mno-div @gol --misa-spec=@var{ISA-spec-string} @gol --march=@var{ISA-string} @gol --mtune=@var{processor-string} @gol --mpreferred-stack-boundary=@var{num} @gol --msmall-data-limit=@var{N-bytes} @gol --msave-restore -mno-save-restore @gol --mshorten-memrefs -mno-shorten-memrefs @gol --mstrict-align -mno-strict-align @gol --mcmodel=medlow -mcmodel=medany @gol --mexplicit-relocs -mno-explicit-relocs @gol --mrelax -mno-relax @gol --mriscv-attribute -mno-riscv-attribute @gol --malign-data=@var{type} @gol --mbig-endian -mlittle-endian @gol --mstack-protector-guard=@var{guard} -mstack-protector-guard-reg=@var{reg} @gol --mstack-protector-guard-offset=@var{offset}} --mcsr-check -mno-csr-check @gol - -@emph{RL78 Options} -@gccoptlist{-msim -mmul=none -mmul=g13 -mmul=g14 -mallregs @gol --mcpu=g10 -mcpu=g13 -mcpu=g14 -mg10 -mg13 -mg14 @gol --m64bit-doubles -m32bit-doubles -msave-mduc-in-interrupts} - -@emph{RS/6000 and PowerPC Options} -@gccoptlist{-mcpu=@var{cpu-type} @gol --mtune=@var{cpu-type} @gol --mcmodel=@var{code-model} @gol --mpowerpc64 @gol --maltivec -mno-altivec @gol --mpowerpc-gpopt -mno-powerpc-gpopt @gol --mpowerpc-gfxopt -mno-powerpc-gfxopt @gol --mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mpopcntd -mno-popcntd @gol --mfprnd -mno-fprnd @gol --mcmpb -mno-cmpb -mhard-dfp -mno-hard-dfp @gol --mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol --m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol --malign-power -malign-natural @gol --msoft-float -mhard-float -mmultiple -mno-multiple @gol --mupdate -mno-update @gol --mavoid-indexed-addresses -mno-avoid-indexed-addresses @gol --mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol --mstrict-align -mno-strict-align -mrelocatable @gol --mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol --mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol --mdynamic-no-pic -mswdiv -msingle-pic-base @gol --mprioritize-restricted-insns=@var{priority} @gol --msched-costly-dep=@var{dependence_type} @gol --minsert-sched-nops=@var{scheme} @gol --mcall-aixdesc -mcall-eabi -mcall-freebsd @gol --mcall-linux -mcall-netbsd -mcall-openbsd @gol --mcall-sysv -mcall-sysv-eabi -mcall-sysv-noeabi @gol --mtraceback=@var{traceback_type} @gol --maix-struct-return -msvr4-struct-return @gol --mabi=@var{abi-type} -msecure-plt -mbss-plt @gol --mlongcall -mno-longcall -mpltseq -mno-pltseq @gol --mblock-move-inline-limit=@var{num} @gol --mblock-compare-inline-limit=@var{num} @gol --mblock-compare-inline-loop-limit=@var{num} @gol --mno-block-ops-unaligned-vsx @gol --mstring-compare-inline-limit=@var{num} @gol --misel -mno-isel @gol --mvrsave -mno-vrsave @gol --mmulhw -mno-mulhw @gol --mdlmzb -mno-dlmzb @gol --mprototype -mno-prototype @gol --msim -mmvme -mads -myellowknife -memb -msdata @gol --msdata=@var{opt} -mreadonly-in-sdata -mvxworks -G @var{num} @gol --mrecip -mrecip=@var{opt} -mno-recip -mrecip-precision @gol --mno-recip-precision @gol --mveclibabi=@var{type} -mfriz -mno-friz @gol --mpointers-to-nested-functions -mno-pointers-to-nested-functions @gol --msave-toc-indirect -mno-save-toc-indirect @gol --mpower8-fusion -mno-mpower8-fusion -mpower8-vector -mno-power8-vector @gol --mcrypto -mno-crypto -mhtm -mno-htm @gol --mquad-memory -mno-quad-memory @gol --mquad-memory-atomic -mno-quad-memory-atomic @gol --mcompat-align-parm -mno-compat-align-parm @gol --mfloat128 -mno-float128 -mfloat128-hardware -mno-float128-hardware @gol --mgnu-attribute -mno-gnu-attribute @gol --mstack-protector-guard=@var{guard} -mstack-protector-guard-reg=@var{reg} @gol --mstack-protector-guard-offset=@var{offset} -mprefixed -mno-prefixed @gol --mpcrel -mno-pcrel -mmma -mno-mmma -mrop-protect -mno-rop-protect @gol --mprivileged -mno-privileged} - -@emph{RX Options} -@gccoptlist{-m64bit-doubles -m32bit-doubles -fpu -nofpu@gol --mcpu=@gol --mbig-endian-data -mlittle-endian-data @gol --msmall-data @gol --msim -mno-sim@gol --mas100-syntax -mno-as100-syntax@gol --mrelax@gol --mmax-constant-size=@gol --mint-register=@gol --mpid@gol --mallow-string-insns -mno-allow-string-insns@gol --mjsr@gol --mno-warn-multiple-fast-interrupts@gol --msave-acc-in-interrupts} - -@emph{S/390 and zSeries Options} -@gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol --mhard-float -msoft-float -mhard-dfp -mno-hard-dfp @gol --mlong-double-64 -mlong-double-128 @gol --mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol --msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol --m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol --mhtm -mvx -mzvector @gol --mtpf-trace -mno-tpf-trace -mtpf-trace-skip -mno-tpf-trace-skip @gol --mfused-madd -mno-fused-madd @gol --mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard @gol --mhotpatch=@var{halfwords},@var{halfwords}} - -@emph{Score Options} -@gccoptlist{-meb -mel @gol --mnhwloop @gol --muls @gol --mmac @gol --mscore5 -mscore5u -mscore7 -mscore7d} - -@emph{SH Options} -@gccoptlist{-m1 -m2 -m2e @gol --m2a-nofpu -m2a-single-only -m2a-single -m2a @gol --m3 -m3e @gol --m4-nofpu -m4-single-only -m4-single -m4 @gol --m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol --mb -ml -mdalign -mrelax @gol --mbigtable -mfmovd -mrenesas -mno-renesas -mnomacsave @gol --mieee -mno-ieee -mbitops -misize -minline-ic_invalidate -mpadstruct @gol --mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol --mdivsi3_libfunc=@var{name} -mfixed-range=@var{register-range} @gol --maccumulate-outgoing-args @gol --matomic-model=@var{atomic-model} @gol --mbranch-cost=@var{num} -mzdcbranch -mno-zdcbranch @gol --mcbranch-force-delay-slot @gol --mfused-madd -mno-fused-madd -mfsca -mno-fsca -mfsrra -mno-fsrra @gol --mpretend-cmove -mtas} - -@emph{Solaris 2 Options} -@gccoptlist{-mclear-hwcap -mno-clear-hwcap -mimpure-text -mno-impure-text @gol --pthreads} - -@emph{SPARC Options} -@gccoptlist{-mcpu=@var{cpu-type} @gol --mtune=@var{cpu-type} @gol --mcmodel=@var{code-model} @gol --mmemory-model=@var{mem-model} @gol --m32 -m64 -mapp-regs -mno-app-regs @gol --mfaster-structs -mno-faster-structs -mflat -mno-flat @gol --mfpu -mno-fpu -mhard-float -msoft-float @gol --mhard-quad-float -msoft-quad-float @gol --mstack-bias -mno-stack-bias @gol --mstd-struct-return -mno-std-struct-return @gol --munaligned-doubles -mno-unaligned-doubles @gol --muser-mode -mno-user-mode @gol --mv8plus -mno-v8plus -mvis -mno-vis @gol --mvis2 -mno-vis2 -mvis3 -mno-vis3 @gol --mvis4 -mno-vis4 -mvis4b -mno-vis4b @gol --mcbcond -mno-cbcond -mfmaf -mno-fmaf -mfsmuld -mno-fsmuld @gol --mpopc -mno-popc -msubxc -mno-subxc @gol --mfix-at697f -mfix-ut699 -mfix-ut700 -mfix-gr712rc @gol --mlra -mno-lra} - -@emph{System V Options} -@gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}} - -@emph{V850 Options} -@gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol --mprolog-function -mno-prolog-function -mspace @gol --mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol --mapp-regs -mno-app-regs @gol --mdisable-callt -mno-disable-callt @gol --mv850e2v3 -mv850e2 -mv850e1 -mv850es @gol --mv850e -mv850 -mv850e3v5 @gol --mloop @gol --mrelax @gol --mlong-jumps @gol --msoft-float @gol --mhard-float @gol --mgcc-abi @gol --mrh850-abi @gol --mbig-switch} - -@emph{VAX Options} -@gccoptlist{-mg -mgnu -munix -mlra} - -@emph{Visium Options} -@gccoptlist{-mdebug -msim -mfpu -mno-fpu -mhard-float -msoft-float @gol --mcpu=@var{cpu-type} -mtune=@var{cpu-type} -msv-mode -muser-mode} - -@emph{VMS Options} -@gccoptlist{-mvms-return-codes -mdebug-main=@var{prefix} -mmalloc64 @gol --mpointer-size=@var{size}} - -@emph{VxWorks Options} -@gccoptlist{-mrtp -non-static -Bstatic -Bdynamic @gol --Xbind-lazy -Xbind-now} - -@emph{x86 Options} -@gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol --mtune-ctrl=@var{feature-list} -mdump-tune-features -mno-default @gol --mfpmath=@var{unit} @gol --masm=@var{dialect} -mno-fancy-math-387 @gol --mno-fp-ret-in-387 -m80387 -mhard-float -msoft-float @gol --mno-wide-multiply -mrtd -malign-double @gol --mpreferred-stack-boundary=@var{num} @gol --mincoming-stack-boundary=@var{num} @gol --mcld -mcx16 -msahf -mmovbe -mcrc32 -mmwait @gol --mrecip -mrecip=@var{opt} @gol --mvzeroupper -mprefer-avx128 -mprefer-vector-width=@var{opt} @gol --mmove-max=@var{bits} -mstore-max=@var{bits} @gol --mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx @gol --mavx2 -mavx512f -mavx512pf -mavx512er -mavx512cd -mavx512vl @gol --mavx512bw -mavx512dq -mavx512ifma -mavx512vbmi -msha -maes @gol --mpclmul -mfsgsbase -mrdrnd -mf16c -mfma -mpconfig -mwbnoinvd @gol --mptwrite -mprefetchwt1 -mclflushopt -mclwb -mxsavec -mxsaves @gol --msse4a -m3dnow -m3dnowa -mpopcnt -mabm -mbmi -mtbm -mfma4 -mxop @gol --madx -mlzcnt -mbmi2 -mfxsr -mxsave -mxsaveopt -mrtm -mhle -mlwp @gol --mmwaitx -mclzero -mpku -mthreads -mgfni -mvaes -mwaitpkg @gol --mshstk -mmanual-endbr -mcet-switch -mforce-indirect-call @gol --mavx512vbmi2 -mavx512bf16 -menqcmd @gol --mvpclmulqdq -mavx512bitalg -mmovdiri -mmovdir64b -mavx512vpopcntdq @gol --mavx5124fmaps -mavx512vnni -mavx5124vnniw -mprfchw -mrdpid @gol --mrdseed -msgx -mavx512vp2intersect -mserialize -mtsxldtrk@gol --mamx-tile -mamx-int8 -mamx-bf16 -muintr -mhreset -mavxvnni@gol --mavx512fp16 -mavxifma -mavxvnniint8 -mavxneconvert -mcmpccxadd -mamx-fp16 @gol --mprefetchi -mraoint @gol --mcldemote -mms-bitfields -mno-align-stringops -minline-all-stringops @gol --minline-stringops-dynamically -mstringop-strategy=@var{alg} @gol --mkl -mwidekl @gol --mmemcpy-strategy=@var{strategy} -mmemset-strategy=@var{strategy} @gol --mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol --m96bit-long-double -mlong-double-64 -mlong-double-80 -mlong-double-128 @gol --mregparm=@var{num} -msseregparm @gol --mveclibabi=@var{type} -mvect8-ret-in-mem @gol --mpc32 -mpc64 -mpc80 -mstackrealign @gol --momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol --mcmodel=@var{code-model} -mabi=@var{name} -maddress-mode=@var{mode} @gol --m32 -m64 -mx32 -m16 -miamcu -mlarge-data-threshold=@var{num} @gol --msse2avx -mfentry -mrecord-mcount -mnop-mcount -m8bit-idiv @gol --minstrument-return=@var{type} -mfentry-name=@var{name} -mfentry-section=@var{name} @gol --mavx256-split-unaligned-load -mavx256-split-unaligned-store @gol --malign-data=@var{type} -mstack-protector-guard=@var{guard} @gol --mstack-protector-guard-reg=@var{reg} @gol --mstack-protector-guard-offset=@var{offset} @gol --mstack-protector-guard-symbol=@var{symbol} @gol --mgeneral-regs-only -mcall-ms2sysv-xlogues -mrelax-cmpxchg-loop @gol --mindirect-branch=@var{choice} -mfunction-return=@var{choice} @gol --mindirect-branch-register -mharden-sls=@var{choice} @gol --mindirect-branch-cs-prefix -mneeded -mno-direct-extern-access} - -@emph{x86 Windows Options} -@gccoptlist{-mconsole -mcygwin -mno-cygwin -mdll @gol --mnop-fun-dllimport -mthread @gol --municode -mwin32 -mwindows -fno-set-stack-executable} - -@emph{Xstormy16 Options} -@gccoptlist{-msim} - -@emph{Xtensa Options} -@gccoptlist{-mconst16 -mno-const16 @gol --mfused-madd -mno-fused-madd @gol --mforce-no-pic @gol --mserialize-volatile -mno-serialize-volatile @gol --mtext-section-literals -mno-text-section-literals @gol --mauto-litpools -mno-auto-litpools @gol --mtarget-align -mno-target-align @gol --mlongcalls -mno-longcalls @gol --mabi=@var{abi-type} @gol --mextra-l32r-costs=@var{cycles}} - -@emph{zSeries Options} -See S/390 and zSeries Options. -@end table - - -@node Overall Options -@section Options Controlling the Kind of Output - -Compilation can involve up to four stages: preprocessing, compilation -proper, assembly and linking, always in that order. GCC is capable of -preprocessing and compiling several files either into several -assembler input files, or into one assembler input file; then each -assembler input file produces an object file, and linking combines all -the object files (those newly compiled, and those specified as input) -into an executable file. - -@cindex file name suffix -For any given input file, the file name suffix determines what kind of -compilation is done: - -@table @gcctabopt -@item @var{file}.c -C source code that must be preprocessed. - -@item @var{file}.i -C source code that should not be preprocessed. - -@item @var{file}.ii -C++ source code that should not be preprocessed. - -@item @var{file}.m -Objective-C source code. Note that you must link with the @file{libobjc} -library to make an Objective-C program work. - -@item @var{file}.mi -Objective-C source code that should not be preprocessed. - -@item @var{file}.mm -@itemx @var{file}.M -Objective-C++ source code. Note that you must link with the @file{libobjc} -library to make an Objective-C++ program work. Note that @samp{.M} refers -to a literal capital M@. - -@item @var{file}.mii -Objective-C++ source code that should not be preprocessed. - -@item @var{file}.h -C, C++, Objective-C or Objective-C++ header file to be turned into a -precompiled header (default), or C, C++ header file to be turned into an -Ada spec (via the @option{-fdump-ada-spec} switch). - -@item @var{file}.cc -@itemx @var{file}.cp -@itemx @var{file}.cxx -@itemx @var{file}.cpp -@itemx @var{file}.CPP -@itemx @var{file}.c++ -@itemx @var{file}.C -C++ source code that must be preprocessed. Note that in @samp{.cxx}, -the last two letters must both be literally @samp{x}. Likewise, -@samp{.C} refers to a literal capital C@. - -@item @var{file}.mm -@itemx @var{file}.M -Objective-C++ source code that must be preprocessed. - -@item @var{file}.mii -Objective-C++ source code that should not be preprocessed. - -@item @var{file}.hh -@itemx @var{file}.H -@itemx @var{file}.hp -@itemx @var{file}.hxx -@itemx @var{file}.hpp -@itemx @var{file}.HPP -@itemx @var{file}.h++ -@itemx @var{file}.tcc -C++ header file to be turned into a precompiled header or Ada spec. - -@item @var{file}.f -@itemx @var{file}.for -@itemx @var{file}.ftn -Fixed form Fortran source code that should not be preprocessed. - -@item @var{file}.F -@itemx @var{file}.FOR -@itemx @var{file}.fpp -@itemx @var{file}.FPP -@itemx @var{file}.FTN -Fixed form Fortran source code that must be preprocessed (with the traditional -preprocessor). - -@item @var{file}.f90 -@itemx @var{file}.f95 -@itemx @var{file}.f03 -@itemx @var{file}.f08 -Free form Fortran source code that should not be preprocessed. - -@item @var{file}.F90 -@itemx @var{file}.F95 -@itemx @var{file}.F03 -@itemx @var{file}.F08 -Free form Fortran source code that must be preprocessed (with the -traditional preprocessor). - -@item @var{file}.go -Go source code. - -@item @var{file}.d -D source code. - -@item @var{file}.di -D interface file. - -@item @var{file}.dd -D documentation code (Ddoc). - -@item @var{file}.ads -Ada source code file that contains a library unit declaration (a -declaration of a package, subprogram, or generic, or a generic -instantiation), or a library unit renaming declaration (a package, -generic, or subprogram renaming declaration). Such files are also -called @dfn{specs}. - -@item @var{file}.adb -Ada source code file containing a library unit body (a subprogram or -package body). Such files are also called @dfn{bodies}. - -@c GCC also knows about some suffixes for languages not yet included: -@c Ratfor: -@c @var{file}.r - -@item @var{file}.s -Assembler code. - -@item @var{file}.S -@itemx @var{file}.sx -Assembler code that must be preprocessed. - -@item @var{other} -An object file to be fed straight into linking. -Any file name with no recognized suffix is treated this way. -@end table - -@opindex x -You can specify the input language explicitly with the @option{-x} option: - -@table @gcctabopt -@item -x @var{language} -Specify explicitly the @var{language} for the following input files -(rather than letting the compiler choose a default based on the file -name suffix). This option applies to all following input files until -the next @option{-x} option. Possible values for @var{language} are: -@smallexample -c c-header cpp-output -c++ c++-header c++-system-header c++-user-header c++-cpp-output -objective-c objective-c-header objective-c-cpp-output -objective-c++ objective-c++-header objective-c++-cpp-output -assembler assembler-with-cpp -ada -d -f77 f77-cpp-input f95 f95-cpp-input -go -@end smallexample - -@item -x none -Turn off any specification of a language, so that subsequent files are -handled according to their file name suffixes (as they are if @option{-x} -has not been used at all). -@end table - -If you only want some of the stages of compilation, you can use -@option{-x} (or filename suffixes) to tell @command{gcc} where to start, and -one of the options @option{-c}, @option{-S}, or @option{-E} to say where -@command{gcc} is to stop. Note that some combinations (for example, -@samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all. - -@table @gcctabopt -@item -c -@opindex c -Compile or assemble the source files, but do not link. The linking -stage simply is not done. The ultimate output is in the form of an -object file for each source file. - -By default, the object file name for a source file is made by replacing -the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}. - -Unrecognized input files, not requiring compilation or assembly, are -ignored. - -@item -S -@opindex S -Stop after the stage of compilation proper; do not assemble. The output -is in the form of an assembler code file for each non-assembler input -file specified. - -By default, the assembler file name for a source file is made by -replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}. - -Input files that don't require compilation are ignored. - -@item -E -@opindex E -Stop after the preprocessing stage; do not run the compiler proper. The -output is in the form of preprocessed source code, which is sent to the -standard output. - -Input files that don't require preprocessing are ignored. - -@cindex output file option -@item -o @var{file} -@opindex o -Place the primary output in file @var{file}. This applies to whatever -sort of output is being produced, whether it be an executable file, an -object file, an assembler file or preprocessed C code. - -If @option{-o} is not specified, the default is to put an executable -file in @file{a.out}, the object file for -@file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its -assembler file in @file{@var{source}.s}, a precompiled header file in -@file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on -standard output. - -Though @option{-o} names only the primary output, it also affects the -naming of auxiliary and dump outputs. See the examples below. Unless -overridden, both auxiliary outputs and dump outputs are placed in the -same directory as the primary output. In auxiliary outputs, the suffix -of the input file is replaced with that of the auxiliary output file -type; in dump outputs, the suffix of the dump file is appended to the -input file suffix. In compilation commands, the base name of both -auxiliary and dump outputs is that of the primary output; in compile and -link commands, the primary output name, minus the executable suffix, is -combined with the input file name. If both share the same base name, -disregarding the suffix, the result of the combination is that base -name, otherwise, they are concatenated, separated by a dash. - -@smallexample -gcc -c foo.c ... -@end smallexample - -will use @file{foo.o} as the primary output, and place aux outputs and -dumps next to it, e.g., aux file @file{foo.dwo} for -@option{-gsplit-dwarf}, and dump file @file{foo.c.???r.final} for -@option{-fdump-rtl-final}. - -If a non-linker output file is explicitly specified, aux and dump files -by default take the same base name: - -@smallexample -gcc -c foo.c -o dir/foobar.o ... -@end smallexample - -will name aux outputs @file{dir/foobar.*} and dump outputs -@file{dir/foobar.c.*}. - -A linker output will instead prefix aux and dump outputs: - -@smallexample -gcc foo.c bar.c -o dir/foobar ... -@end smallexample - -will generally name aux outputs @file{dir/foobar-foo.*} and -@file{dir/foobar-bar.*}, and dump outputs @file{dir/foobar-foo.c.*} and -@file{dir/foobar-bar.c.*}. - -The one exception to the above is when the executable shares the base -name with the single input: - -@smallexample -gcc foo.c -o dir/foo ... -@end smallexample - -in which case aux outputs are named @file{dir/foo.*} and dump outputs -named @file{dir/foo.c.*}. - -The location and the names of auxiliary and dump outputs can be adjusted -by the options @option{-dumpbase}, @option{-dumpbase-ext}, -@option{-dumpdir}, @option{-save-temps=cwd}, and -@option{-save-temps=obj}. - - -@item -dumpbase @var{dumpbase} -@opindex dumpbase -This option sets the base name for auxiliary and dump output files. It -does not affect the name of the primary output file. Intermediate -outputs, when preserved, are not regarded as primary outputs, but as -auxiliary outputs: - -@smallexample -gcc -save-temps -S foo.c -@end smallexample - -saves the (no longer) temporary preprocessed file in @file{foo.i}, and -then compiles to the (implied) output file @file{foo.s}, whereas: - -@smallexample -gcc -save-temps -dumpbase save-foo -c foo.c -@end smallexample - -preprocesses to in @file{save-foo.i}, compiles to @file{save-foo.s} (now -an intermediate, thus auxiliary output), and then assembles to the -(implied) output file @file{foo.o}. - -Absent this option, dump and aux files take their names from the input -file, or from the (non-linker) output file, if one is explicitly -specified: dump output files (e.g. those requested by @option{-fdump-*} -options) with the input name suffix, and aux output files (those -requested by other non-dump options, e.g. @code{-save-temps}, -@code{-gsplit-dwarf}, @code{-fcallgraph-info}) without it. - -Similar suffix differentiation of dump and aux outputs can be attained -for explicitly-given @option{-dumpbase basename.suf} by also specifying -@option{-dumpbase-ext .suf}. - -If @var{dumpbase} is explicitly specified with any directory component, -any @var{dumppfx} specification (e.g. @option{-dumpdir} or -@option{-save-temps=*}) is ignored, and instead of appending to it, -@var{dumpbase} fully overrides it: - -@smallexample -gcc foo.c -c -o dir/foo.o -dumpbase alt/foo \ - -dumpdir pfx- -save-temps=cwd ... -@end smallexample - -creates auxiliary and dump outputs named @file{alt/foo.*}, disregarding -@file{dir/} in @option{-o}, the @file{./} prefix implied by -@option{-save-temps=cwd}, and @file{pfx-} in @option{-dumpdir}. - -When @option{-dumpbase} is specified in a command that compiles multiple -inputs, or that compiles and then links, it may be combined with -@var{dumppfx}, as specified under @option{-dumpdir}. Then, each input -file is compiled using the combined @var{dumppfx}, and default values -for @var{dumpbase} and @var{auxdropsuf} are computed for each input -file: - -@smallexample -gcc foo.c bar.c -c -dumpbase main ... -@end smallexample - -creates @file{foo.o} and @file{bar.o} as primary outputs, and avoids -overwriting the auxiliary and dump outputs by using the @var{dumpbase} -as a prefix, creating auxiliary and dump outputs named @file{main-foo.*} -and @file{main-bar.*}. - -An empty string specified as @var{dumpbase} avoids the influence of the -output basename in the naming of auxiliary and dump outputs during -compilation, computing default values : - -@smallexample -gcc -c foo.c -o dir/foobar.o -dumpbase '' ... -@end smallexample - -will name aux outputs @file{dir/foo.*} and dump outputs -@file{dir/foo.c.*}. Note how their basenames are taken from the input -name, but the directory still defaults to that of the output. - -The empty-string dumpbase does not prevent the use of the output -basename for outputs during linking: - -@smallexample -gcc foo.c bar.c -o dir/foobar -dumpbase '' -flto ... -@end smallexample - -The compilation of the source files will name auxiliary outputs -@file{dir/foo.*} and @file{dir/bar.*}, and dump outputs -@file{dir/foo.c.*} and @file{dir/bar.c.*}. LTO recompilation during -linking will use @file{dir/foobar.} as the prefix for dumps and -auxiliary files. - - -@item -dumpbase-ext @var{auxdropsuf} -@opindex dumpbase-ext -When forming the name of an auxiliary (but not a dump) output file, drop -trailing @var{auxdropsuf} from @var{dumpbase} before appending any -suffixes. If not specified, this option defaults to the suffix of a -default @var{dumpbase}, i.e., the suffix of the input file when -@option{-dumpbase} is not present in the command line, or @var{dumpbase} -is combined with @var{dumppfx}. - -@smallexample -gcc foo.c -c -o dir/foo.o -dumpbase x-foo.c -dumpbase-ext .c ... -@end smallexample - -creates @file{dir/foo.o} as the main output, and generates auxiliary -outputs in @file{dir/x-foo.*}, taking the location of the primary -output, and dropping the @file{.c} suffix from the @var{dumpbase}. Dump -outputs retain the suffix: @file{dir/x-foo.c.*}. - -This option is disregarded if it does not match the suffix of a -specified @var{dumpbase}, except as an alternative to the executable -suffix when appending the linker output base name to @var{dumppfx}, as -specified below: - -@smallexample -gcc foo.c bar.c -o main.out -dumpbase-ext .out ... -@end smallexample - -creates @file{main.out} as the primary output, and avoids overwriting -the auxiliary and dump outputs by using the executable name minus -@var{auxdropsuf} as a prefix, creating auxiliary outputs named -@file{main-foo.*} and @file{main-bar.*} and dump outputs named -@file{main-foo.c.*} and @file{main-bar.c.*}. - - -@item -dumpdir @var{dumppfx} -@opindex dumpdir -When forming the name of an auxiliary or dump output file, use -@var{dumppfx} as a prefix: - -@smallexample -gcc -dumpdir pfx- -c foo.c ... -@end smallexample - -creates @file{foo.o} as the primary output, and auxiliary outputs named -@file{pfx-foo.*}, combining the given @var{dumppfx} with the default -@var{dumpbase} derived from the default primary output, derived in turn -from the input name. Dump outputs also take the input name suffix: -@file{pfx-foo.c.*}. - -If @var{dumppfx} is to be used as a directory name, it must end with a -directory separator: - -@smallexample -gcc -dumpdir dir/ -c foo.c -o obj/bar.o ... -@end smallexample - -creates @file{obj/bar.o} as the primary output, and auxiliary outputs -named @file{dir/bar.*}, combining the given @var{dumppfx} with the -default @var{dumpbase} derived from the primary output name. Dump -outputs also take the input name suffix: @file{dir/bar.c.*}. - -It defaults to the location of the output file, unless the output -file is a special file like @code{/dev/null}. Options -@option{-save-temps=cwd} and @option{-save-temps=obj} override this -default, just like an explicit @option{-dumpdir} option. In case -multiple such options are given, the last one prevails: - -@smallexample -gcc -dumpdir pfx- -c foo.c -save-temps=obj ... -@end smallexample - -outputs @file{foo.o}, with auxiliary outputs named @file{foo.*} because -@option{-save-temps=*} overrides the @var{dumppfx} given by the earlier -@option{-dumpdir} option. It does not matter that @option{=obj} is the -default for @option{-save-temps}, nor that the output directory is -implicitly the current directory. Dump outputs are named -@file{foo.c.*}. - -When compiling from multiple input files, if @option{-dumpbase} is -specified, @var{dumpbase}, minus a @var{auxdropsuf} suffix, and a dash -are appended to (or override, if containing any directory components) an -explicit or defaulted @var{dumppfx}, so that each of the multiple -compilations gets differently-named aux and dump outputs. - -@smallexample -gcc foo.c bar.c -c -dumpdir dir/pfx- -dumpbase main ... -@end smallexample - -outputs auxiliary dumps to @file{dir/pfx-main-foo.*} and -@file{dir/pfx-main-bar.*}, appending @var{dumpbase}- to @var{dumppfx}. -Dump outputs retain the input file suffix: @file{dir/pfx-main-foo.c.*} -and @file{dir/pfx-main-bar.c.*}, respectively. Contrast with the -single-input compilation: - -@smallexample -gcc foo.c -c -dumpdir dir/pfx- -dumpbase main ... -@end smallexample - -that, applying @option{-dumpbase} to a single source, does not compute -and append a separate @var{dumpbase} per input file. Its auxiliary and -dump outputs go in @file{dir/pfx-main.*}. - -When compiling and then linking from multiple input files, a defaulted -or explicitly specified @var{dumppfx} also undergoes the @var{dumpbase}- -transformation above (e.g. the compilation of @file{foo.c} and -@file{bar.c} above, but without @option{-c}). If neither -@option{-dumpdir} nor @option{-dumpbase} are given, the linker output -base name, minus @var{auxdropsuf}, if specified, or the executable -suffix otherwise, plus a dash is appended to the default @var{dumppfx} -instead. Note, however, that unlike earlier cases of linking: - -@smallexample -gcc foo.c bar.c -dumpdir dir/pfx- -o main ... -@end smallexample - -does not append the output name @file{main} to @var{dumppfx}, because -@option{-dumpdir} is explicitly specified. The goal is that the -explicitly-specified @var{dumppfx} may contain the specified output name -as part of the prefix, if desired; only an explicitly-specified -@option{-dumpbase} would be combined with it, in order to avoid simply -discarding a meaningful option. - -When compiling and then linking from a single input file, the linker -output base name will only be appended to the default @var{dumppfx} as -above if it does not share the base name with the single input file -name. This has been covered in single-input linking cases above, but -not with an explicit @option{-dumpdir} that inhibits the combination, -even if overridden by @option{-save-temps=*}: - -@smallexample -gcc foo.c -dumpdir alt/pfx- -o dir/main.exe -save-temps=cwd ... -@end smallexample - -Auxiliary outputs are named @file{foo.*}, and dump outputs -@file{foo.c.*}, in the current working directory as ultimately requested -by @option{-save-temps=cwd}. - -Summing it all up for an intuitive though slightly imprecise data flow: -the primary output name is broken into a directory part and a basename -part; @var{dumppfx} is set to the former, unless overridden by -@option{-dumpdir} or @option{-save-temps=*}, and @var{dumpbase} is set -to the latter, unless overriden by @option{-dumpbase}. If there are -multiple inputs or linking, this @var{dumpbase} may be combined with -@var{dumppfx} and taken from each input file. Auxiliary output names -for each input are formed by combining @var{dumppfx}, @var{dumpbase} -minus suffix, and the auxiliary output suffix; dump output names are -only different in that the suffix from @var{dumpbase} is retained. - -When it comes to auxiliary and dump outputs created during LTO -recompilation, a combination of @var{dumppfx} and @var{dumpbase}, as -given or as derived from the linker output name but not from inputs, -even in cases in which this combination would not otherwise be used as -such, is passed down with a trailing period replacing the compiler-added -dash, if any, as a @option{-dumpdir} option to @command{lto-wrapper}; -being involved in linking, this program does not normally get any -@option{-dumpbase} and @option{-dumpbase-ext}, and it ignores them. - -When running sub-compilers, @command{lto-wrapper} appends LTO stage -names to the received @var{dumppfx}, ensures it contains a directory -component so that it overrides any @option{-dumpdir}, and passes that as -@option{-dumpbase} to sub-compilers. - -@item -v -@opindex v -Print (on standard error output) the commands executed to run the stages -of compilation. Also print the version number of the compiler driver -program and of the preprocessor and the compiler proper. - -@item -### -@opindex ### -Like @option{-v} except the commands are not executed and arguments -are quoted unless they contain only alphanumeric characters or @code{./-_}. -This is useful for shell scripts to capture the driver-generated command lines. - -@item --help -@opindex help -Print (on the standard output) a description of the command-line options -understood by @command{gcc}. If the @option{-v} option is also specified -then @option{--help} is also passed on to the various processes -invoked by @command{gcc}, so that they can display the command-line options -they accept. If the @option{-Wextra} option has also been specified -(prior to the @option{--help} option), then command-line options that -have no documentation associated with them are also displayed. - -@item --target-help -@opindex target-help -Print (on the standard output) a description of target-specific command-line -options for each tool. For some targets extra target-specific -information may also be printed. - -@item --help=@{@var{class}@r{|[}^@r{]}@var{qualifier}@}@r{[},@dots{}@r{]} -Print (on the standard output) a description of the command-line -options understood by the compiler that fit into all specified classes -and qualifiers. These are the supported classes: - -@table @asis -@item @samp{optimizers} -Display all of the optimization options supported by the -compiler. - -@item @samp{warnings} -Display all of the options controlling warning messages -produced by the compiler. - -@item @samp{target} -Display target-specific options. Unlike the -@option{--target-help} option however, target-specific options of the -linker and assembler are not displayed. This is because those -tools do not currently support the extended @option{--help=} syntax. - -@item @samp{params} -Display the values recognized by the @option{--param} -option. - -@item @var{language} -Display the options supported for @var{language}, where -@var{language} is the name of one of the languages supported in this -version of GCC@. If an option is supported by all languages, one needs -to select @samp{common} class. - -@item @samp{common} -Display the options that are common to all languages. -@end table - -These are the supported qualifiers: - -@table @asis -@item @samp{undocumented} -Display only those options that are undocumented. - -@item @samp{joined} -Display options taking an argument that appears after an equal -sign in the same continuous piece of text, such as: -@samp{--help=target}. - -@item @samp{separate} -Display options taking an argument that appears as a separate word -following the original option, such as: @samp{-o output-file}. -@end table - -Thus for example to display all the undocumented target-specific -switches supported by the compiler, use: - -@smallexample ---help=target,undocumented -@end smallexample - -The sense of a qualifier can be inverted by prefixing it with the -@samp{^} character, so for example to display all binary warning -options (i.e., ones that are either on or off and that do not take an -argument) that have a description, use: - -@smallexample ---help=warnings,^joined,^undocumented -@end smallexample - -The argument to @option{--help=} should not consist solely of inverted -qualifiers. - -Combining several classes is possible, although this usually -restricts the output so much that there is nothing to display. One -case where it does work, however, is when one of the classes is -@var{target}. For example, to display all the target-specific -optimization options, use: - -@smallexample ---help=target,optimizers -@end smallexample - -The @option{--help=} option can be repeated on the command line. Each -successive use displays its requested class of options, skipping -those that have already been displayed. If @option{--help} is also -specified anywhere on the command line then this takes precedence -over any @option{--help=} option. - -If the @option{-Q} option appears on the command line before the -@option{--help=} option, then the descriptive text displayed by -@option{--help=} is changed. Instead of describing the displayed -options, an indication is given as to whether the option is enabled, -disabled or set to a specific value (assuming that the compiler -knows this at the point where the @option{--help=} option is used). - -Here is a truncated example from the ARM port of @command{gcc}: - -@smallexample - % gcc -Q -mabi=2 --help=target -c - The following options are target specific: - -mabi= 2 - -mabort-on-noreturn [disabled] - -mapcs [disabled] -@end smallexample - -The output is sensitive to the effects of previous command-line -options, so for example it is possible to find out which optimizations -are enabled at @option{-O2} by using: - -@smallexample --Q -O2 --help=optimizers -@end smallexample - -Alternatively you can discover which binary optimizations are enabled -by @option{-O3} by using: - -@smallexample -gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts -gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts -diff /tmp/O2-opts /tmp/O3-opts | grep enabled -@end smallexample - -@item --version -@opindex version -Display the version number and copyrights of the invoked GCC@. - -@item -pass-exit-codes -@opindex pass-exit-codes -Normally the @command{gcc} program exits with the code of 1 if any -phase of the compiler returns a non-success return code. If you specify -@option{-pass-exit-codes}, the @command{gcc} program instead returns with -the numerically highest error produced by any phase returning an error -indication. The C, C++, and Fortran front ends return 4 if an internal -compiler error is encountered. - -@item -pipe -@opindex pipe -Use pipes rather than temporary files for communication between the -various stages of compilation. This fails to work on some systems where -the assembler is unable to read from a pipe; but the GNU assembler has -no trouble. - -@item -specs=@var{file} -@opindex specs -Process @var{file} after the compiler reads in the standard @file{specs} -file, in order to override the defaults which the @command{gcc} driver -program uses when determining what switches to pass to @command{cc1}, -@command{cc1plus}, @command{as}, @command{ld}, etc. More than one -@option{-specs=@var{file}} can be specified on the command line, and they -are processed in order, from left to right. @xref{Spec Files}, for -information about the format of the @var{file}. - -@item -wrapper -@opindex wrapper -Invoke all subcommands under a wrapper program. The name of the -wrapper program and its parameters are passed as a comma separated -list. - -@smallexample -gcc -c t.c -wrapper gdb,--args -@end smallexample - -@noindent -This invokes all subprograms of @command{gcc} under -@samp{gdb --args}, thus the invocation of @command{cc1} is -@samp{gdb --args cc1 @dots{}}. - -@item -ffile-prefix-map=@var{old}=@var{new} -@opindex ffile-prefix-map -When compiling files residing in directory @file{@var{old}}, record -any references to them in the result of the compilation as if the -files resided in directory @file{@var{new}} instead. Specifying this -option is equivalent to specifying all the individual -@option{-f*-prefix-map} options. This can be used to make reproducible -builds that are location independent. See also -@option{-fmacro-prefix-map}, @option{-fdebug-prefix-map} and -@option{-fprofile-prefix-map}. - -@item -fplugin=@var{name}.so -@opindex fplugin -Load the plugin code in file @var{name}.so, assumed to be a -shared object to be dlopen'd by the compiler. The base name of -the shared object file is used to identify the plugin for the -purposes of argument parsing (See -@option{-fplugin-arg-@var{name}-@var{key}=@var{value}} below). -Each plugin should define the callback functions specified in the -Plugins API. - -@item -fplugin-arg-@var{name}-@var{key}=@var{value} -@opindex fplugin-arg -Define an argument called @var{key} with a value of @var{value} -for the plugin called @var{name}. - -@item -fdump-ada-spec@r{[}-slim@r{]} -@opindex fdump-ada-spec -For C and C++ source and include files, generate corresponding Ada specs. -@xref{Generating Ada Bindings for C and C++ headers,,, gnat_ugn, -GNAT User's Guide}, which provides detailed documentation on this feature. - -@item -fada-spec-parent=@var{unit} -@opindex fada-spec-parent -In conjunction with @option{-fdump-ada-spec@r{[}-slim@r{]}} above, generate -Ada specs as child units of parent @var{unit}. - -@item -fdump-go-spec=@var{file} -@opindex fdump-go-spec -For input files in any language, generate corresponding Go -declarations in @var{file}. This generates Go @code{const}, -@code{type}, @code{var}, and @code{func} declarations which may be a -useful way to start writing a Go interface to code written in some -other language. - -@include @value{srcdir}/../libiberty/at-file.texi -@end table - -@node Invoking G++ -@section Compiling C++ Programs - -@cindex suffixes for C++ source -@cindex C++ source file suffixes -C++ source files conventionally use one of the suffixes @samp{.C}, -@samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or -@samp{.cxx}; C++ header files often use @samp{.hh}, @samp{.hpp}, -@samp{.H}, or (for shared template code) @samp{.tcc}; and -preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes -files with these names and compiles them as C++ programs even if you -call the compiler the same way as for compiling C programs (usually -with the name @command{gcc}). - -@findex g++ -@findex c++ -However, the use of @command{gcc} does not add the C++ library. -@command{g++} is a program that calls GCC and automatically specifies linking -against the C++ library. It treats @samp{.c}, -@samp{.h} and @samp{.i} files as C++ source files instead of C source -files unless @option{-x} is used. This program is also useful when -precompiling a C header file with a @samp{.h} extension for use in C++ -compilations. On many systems, @command{g++} is also installed with -the name @command{c++}. - -@cindex invoking @command{g++} -When you compile C++ programs, you may specify many of the same -command-line options that you use for compiling programs in any -language; or command-line options meaningful for C and related -languages; or options that are meaningful only for C++ programs. -@xref{C Dialect Options,,Options Controlling C Dialect}, for -explanations of options for languages related to C@. -@xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for -explanations of options that are meaningful only for C++ programs. - -@node C Dialect Options -@section Options Controlling C Dialect -@cindex dialect options -@cindex language dialect options -@cindex options, dialect - -The following options control the dialect of C (or languages derived -from C, such as C++, Objective-C and Objective-C++) that the compiler -accepts: - -@table @gcctabopt -@cindex ANSI support -@cindex ISO support -@item -ansi -@opindex ansi -In C mode, this is equivalent to @option{-std=c90}. In C++ mode, it is -equivalent to @option{-std=c++98}. - -This turns off certain features of GCC that are incompatible with ISO -C90 (when compiling C code), or of standard C++ (when compiling C++ code), -such as the @code{asm} and @code{typeof} keywords, and -predefined macros such as @code{unix} and @code{vax} that identify the -type of system you are using. It also enables the undesirable and -rarely used ISO trigraph feature. For the C compiler, -it disables recognition of C++ style @samp{//} comments as well as -the @code{inline} keyword. - -The alternate keywords @code{__asm__}, @code{__extension__}, -@code{__inline__} and @code{__typeof__} continue to work despite -@option{-ansi}. You would not want to use them in an ISO C program, of -course, but it is useful to put them in header files that might be included -in compilations done with @option{-ansi}. Alternate predefined macros -such as @code{__unix__} and @code{__vax__} are also available, with or -without @option{-ansi}. - -The @option{-ansi} option does not cause non-ISO programs to be -rejected gratuitously. For that, @option{-Wpedantic} is required in -addition to @option{-ansi}. @xref{Warning Options}. - -The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi} -option is used. Some header files may notice this macro and refrain -from declaring certain functions or defining certain macros that the -ISO standard doesn't call for; this is to avoid interfering with any -programs that might use these names for other things. - -Functions that are normally built in but do not have semantics -defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in -functions when @option{-ansi} is used. @xref{Other Builtins,,Other -built-in functions provided by GCC}, for details of the functions -affected. - -@item -std= -@opindex std -Determine the language standard. @xref{Standards,,Language Standards -Supported by GCC}, for details of these standard versions. This option -is currently only supported when compiling C or C++. - -The compiler can accept several base standards, such as @samp{c90} or -@samp{c++98}, and GNU dialects of those standards, such as -@samp{gnu90} or @samp{gnu++98}. When a base standard is specified, the -compiler accepts all programs following that standard plus those -using GNU extensions that do not contradict it. For example, -@option{-std=c90} turns off certain features of GCC that are -incompatible with ISO C90, such as the @code{asm} and @code{typeof} -keywords, but not other GNU extensions that do not have a meaning in -ISO C90, such as omitting the middle term of a @code{?:} -expression. On the other hand, when a GNU dialect of a standard is -specified, all features supported by the compiler are enabled, even when -those features change the meaning of the base standard. As a result, some -strict-conforming programs may be rejected. The particular standard -is used by @option{-Wpedantic} to identify which features are GNU -extensions given that version of the standard. For example -@option{-std=gnu90 -Wpedantic} warns about C++ style @samp{//} -comments, while @option{-std=gnu99 -Wpedantic} does not. - -A value for this option must be provided; possible values are - -@table @samp -@item c90 -@itemx c89 -@itemx iso9899:1990 -Support all ISO C90 programs (certain GNU extensions that conflict -with ISO C90 are disabled). Same as @option{-ansi} for C code. - -@item iso9899:199409 -ISO C90 as modified in amendment 1. - -@item c99 -@itemx c9x -@itemx iso9899:1999 -@itemx iso9899:199x -ISO C99. This standard is substantially completely supported, modulo -bugs and floating-point issues -(mainly but not entirely relating to optional C99 features from -Annexes F and G). See -@w{@uref{https://gcc.gnu.org/c99status.html}} for more information. The -names @samp{c9x} and @samp{iso9899:199x} are deprecated. - -@item c11 -@itemx c1x -@itemx iso9899:2011 -ISO C11, the 2011 revision of the ISO C standard. This standard is -substantially completely supported, modulo bugs, floating-point issues -(mainly but not entirely relating to optional C11 features from -Annexes F and G) and the optional Annexes K (Bounds-checking -interfaces) and L (Analyzability). The name @samp{c1x} is deprecated. - -@item c17 -@itemx c18 -@itemx iso9899:2017 -@itemx iso9899:2018 -ISO C17, the 2017 revision of the ISO C standard -(published in 2018). This standard is -same as C11 except for corrections of defects (all of which are also -applied with @option{-std=c11}) and a new value of -@code{__STDC_VERSION__}, and so is supported to the same extent as C11. - -@item c2x -The next version of the ISO C standard, still under development. The -support for this version is experimental and incomplete. - -@item gnu90 -@itemx gnu89 -GNU dialect of ISO C90 (including some C99 features). - -@item gnu99 -@itemx gnu9x -GNU dialect of ISO C99. The name @samp{gnu9x} is deprecated. - -@item gnu11 -@itemx gnu1x -GNU dialect of ISO C11. -The name @samp{gnu1x} is deprecated. - -@item gnu17 -@itemx gnu18 -GNU dialect of ISO C17. This is the default for C code. - -@item gnu2x -The next version of the ISO C standard, still under development, plus -GNU extensions. The support for this version is experimental and -incomplete. - -@item c++98 -@itemx c++03 -The 1998 ISO C++ standard plus the 2003 technical corrigendum and some -additional defect reports. Same as @option{-ansi} for C++ code. - -@item gnu++98 -@itemx gnu++03 -GNU dialect of @option{-std=c++98}. - -@item c++11 -@itemx c++0x -The 2011 ISO C++ standard plus amendments. -The name @samp{c++0x} is deprecated. - -@item gnu++11 -@itemx gnu++0x -GNU dialect of @option{-std=c++11}. -The name @samp{gnu++0x} is deprecated. - -@item c++14 -@itemx c++1y -The 2014 ISO C++ standard plus amendments. -The name @samp{c++1y} is deprecated. - -@item gnu++14 -@itemx gnu++1y -GNU dialect of @option{-std=c++14}. -The name @samp{gnu++1y} is deprecated. - -@item c++17 -@itemx c++1z -The 2017 ISO C++ standard plus amendments. -The name @samp{c++1z} is deprecated. - -@item gnu++17 -@itemx gnu++1z -GNU dialect of @option{-std=c++17}. -This is the default for C++ code. -The name @samp{gnu++1z} is deprecated. - -@item c++20 -@itemx c++2a -The 2020 ISO C++ standard plus amendments. -Support is experimental, and could change in incompatible ways in -future releases. -The name @samp{c++2a} is deprecated. - -@item gnu++20 -@itemx gnu++2a -GNU dialect of @option{-std=c++20}. -Support is experimental, and could change in incompatible ways in -future releases. -The name @samp{gnu++2a} is deprecated. - -@item c++2b -@itemx c++23 -The next revision of the ISO C++ standard, planned for -2023. Support is highly experimental, and will almost certainly -change in incompatible ways in future releases. - -@item gnu++2b -@itemx gnu++23 -GNU dialect of @option{-std=c++2b}. Support is highly experimental, -and will almost certainly change in incompatible ways in future -releases. -@end table - -@item -aux-info @var{filename} -@opindex aux-info -Output to the given filename prototyped declarations for all functions -declared and/or defined in a translation unit, including those in header -files. This option is silently ignored in any language other than C@. - -Besides declarations, the file indicates, in comments, the origin of -each declaration (source file and line), whether the declaration was -implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or -@samp{O} for old, respectively, in the first character after the line -number and the colon), and whether it came from a declaration or a -definition (@samp{C} or @samp{F}, respectively, in the following -character). In the case of function definitions, a K&R-style list of -arguments followed by their declarations is also provided, inside -comments, after the declaration. - -@item -fno-asm -@opindex fno-asm -@opindex fasm -Do not recognize @code{asm}, @code{inline} or @code{typeof} as a -keyword, so that code can use these words as identifiers. You can use -the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__} -instead. In C, @option{-ansi} implies @option{-fno-asm}. - -In C++, @code{inline} is a standard keyword and is not affected by -this switch. You may want to use the @option{-fno-gnu-keywords} flag -instead, which disables @code{typeof} but not @code{asm} and -@code{inline}. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), -this switch only affects the @code{asm} and @code{typeof} keywords, -since @code{inline} is a standard keyword in ISO C99. In C2X mode -(@option{-std=c2x} or @option{-std=gnu2x}), this switch only affects -the @code{asm} keyword, since @code{typeof} is a standard keyword in -ISO C2X. - -@item -fno-builtin -@itemx -fno-builtin-@var{function} -@opindex fno-builtin -@opindex fbuiltin -@cindex built-in functions -Don't recognize built-in functions that do not begin with -@samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in -functions provided by GCC}, for details of the functions affected, -including those which are not built-in functions when @option{-ansi} or -@option{-std} options for strict ISO C conformance are used because they -do not have an ISO standard meaning. - -GCC normally generates special code to handle certain built-in functions -more efficiently; for instance, calls to @code{alloca} may become single -instructions which adjust the stack directly, and calls to @code{memcpy} -may become inline copy loops. The resulting code is often both smaller -and faster, but since the function calls no longer appear as such, you -cannot set a breakpoint on those calls, nor can you change the behavior -of the functions by linking with a different library. In addition, -when a function is recognized as a built-in function, GCC may use -information about that function to warn about problems with calls to -that function, or to generate more efficient code, even if the -resulting code still contains calls to that function. For example, -warnings are given with @option{-Wformat} for bad calls to -@code{printf} when @code{printf} is built in and @code{strlen} is -known not to modify global memory. - -With the @option{-fno-builtin-@var{function}} option -only the built-in function @var{function} is -disabled. @var{function} must not begin with @samp{__builtin_}. If a -function is named that is not built-in in this version of GCC, this -option is ignored. There is no corresponding -@option{-fbuiltin-@var{function}} option; if you wish to enable -built-in functions selectively when using @option{-fno-builtin} or -@option{-ffreestanding}, you may define macros such as: - -@smallexample -#define abs(n) __builtin_abs ((n)) -#define strcpy(d, s) __builtin_strcpy ((d), (s)) -@end smallexample - -@item -fcond-mismatch -@opindex fcond-mismatch -Allow conditional expressions with mismatched types in the second and -third arguments. The value of such an expression is void. This option -is not supported for C++. - -@item -ffreestanding -@opindex ffreestanding -@cindex hosted environment - -Assert that compilation targets a freestanding environment. This -implies @option{-fno-builtin}. A freestanding environment -is one in which the standard library may not exist, and program startup may -not necessarily be at @code{main}. The most obvious example is an OS kernel. -This is equivalent to @option{-fno-hosted}. - -@xref{Standards,,Language Standards Supported by GCC}, for details of -freestanding and hosted environments. - -@item -fgimple -@opindex fgimple - -Enable parsing of function definitions marked with @code{__GIMPLE}. -This is an experimental feature that allows unit testing of GIMPLE -passes. - -@item -fgnu-tm -@opindex fgnu-tm -When the option @option{-fgnu-tm} is specified, the compiler -generates code for the Linux variant of Intel's current Transactional -Memory ABI specification document (Revision 1.1, May 6 2009). This is -an experimental feature whose interface may change in future versions -of GCC, as the official specification changes. Please note that not -all architectures are supported for this feature. - -For more information on GCC's support for transactional memory, -@xref{Enabling libitm,,The GNU Transactional Memory Library,libitm,GNU -Transactional Memory Library}. - -Note that the transactional memory feature is not supported with -non-call exceptions (@option{-fnon-call-exceptions}). - -@item -fgnu89-inline -@opindex fgnu89-inline -The option @option{-fgnu89-inline} tells GCC to use the traditional -GNU semantics for @code{inline} functions when in C99 mode. -@xref{Inline,,An Inline Function is As Fast As a Macro}. -Using this option is roughly equivalent to adding the -@code{gnu_inline} function attribute to all inline functions -(@pxref{Function Attributes}). - -The option @option{-fno-gnu89-inline} explicitly tells GCC to use the -C99 semantics for @code{inline} when in C99 or gnu99 mode (i.e., it -specifies the default behavior). -This option is not supported in @option{-std=c90} or -@option{-std=gnu90} mode. - -The preprocessor macros @code{__GNUC_GNU_INLINE__} and -@code{__GNUC_STDC_INLINE__} may be used to check which semantics are -in effect for @code{inline} functions. @xref{Common Predefined -Macros,,,cpp,The C Preprocessor}. - -@item -fhosted -@opindex fhosted -@cindex hosted environment - -Assert that compilation targets a hosted environment. This implies -@option{-fbuiltin}. A hosted environment is one in which the -entire standard library is available, and in which @code{main} has a return -type of @code{int}. Examples are nearly everything except a kernel. -This is equivalent to @option{-fno-freestanding}. - -@item -flax-vector-conversions -@opindex flax-vector-conversions -Allow implicit conversions between vectors with differing numbers of -elements and/or incompatible element types. This option should not be -used for new code. - -@item -fms-extensions -@opindex fms-extensions -Accept some non-standard constructs used in Microsoft header files. - -In C++ code, this allows member names in structures to be similar -to previous types declarations. - -@smallexample -typedef int UOW; -struct ABC @{ - UOW UOW; -@}; -@end smallexample - -Some cases of unnamed fields in structures and unions are only -accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union -fields within structs/unions}, for details. - -Note that this option is off for all targets except for x86 -targets using ms-abi. - -@item -foffload=disable -@itemx -foffload=default -@itemx -foffload=@var{target-list} -@opindex foffload -@cindex Offloading targets -@cindex OpenACC offloading targets -@cindex OpenMP offloading targets -Specify for which OpenMP and OpenACC offload targets code should be generated. -The default behavior, equivalent to @option{-foffload=default}, is to generate -code for all supported offload targets. The @option{-foffload=disable} form -generates code only for the host fallback, while -@option{-foffload=@var{target-list}} generates code only for the specified -comma-separated list of offload targets. - -Offload targets are specified in GCC's internal target-triplet format. You can -run the compiler with @option{-v} to show the list of configured offload targets -under @code{OFFLOAD_TARGET_NAMES}. - -@item -foffload-options=@var{options} -@itemx -foffload-options=@var{target-triplet-list}=@var{options} -@opindex foffload-options -@cindex Offloading options -@cindex OpenACC offloading options -@cindex OpenMP offloading options - -With @option{-foffload-options=@var{options}}, GCC passes the specified -@var{options} to the compilers for all enabled offloading targets. You can -specify options that apply only to a specific target or targets by using -the @option{-foffload-options=@var{target-list}=@var{options}} form. The -@var{target-list} is a comma-separated list in the same format as for the -@option{-foffload=} option. - -Typical command lines are - -@smallexample --foffload-options=-lgfortran -foffload-options=-lm --foffload-options="-lgfortran -lm" -foffload-options=nvptx-none=-latomic --foffload-options=amdgcn-amdhsa=-march=gfx906 -foffload-options=-lm -@end smallexample - -@item -fopenacc -@opindex fopenacc -@cindex OpenACC accelerator programming -Enable handling of OpenACC directives @code{#pragma acc} in C/C++ and -@code{!$acc} in Fortran. When @option{-fopenacc} is specified, the -compiler generates accelerated code according to the OpenACC Application -Programming Interface v2.6 @w{@uref{https://www.openacc.org}}. This option -implies @option{-pthread}, and thus is only supported on targets that -have support for @option{-pthread}. - -@item -fopenacc-dim=@var{geom} -@opindex fopenacc-dim -@cindex OpenACC accelerator programming -Specify default compute dimensions for parallel offload regions that do -not explicitly specify. The @var{geom} value is a triple of -':'-separated sizes, in order 'gang', 'worker' and, 'vector'. A size -can be omitted, to use a target-specific default value. - -@item -fopenmp -@opindex fopenmp -@cindex OpenMP parallel -Enable handling of OpenMP directives @code{#pragma omp} in C/C++, -@code{[[omp::directive(...)]]} and @code{[[omp::sequence(...)]]} in C++ and -@code{!$omp} in Fortran. When @option{-fopenmp} is specified, the -compiler generates parallel code according to the OpenMP Application -Program Interface v4.5 @w{@uref{https://www.openmp.org}}. This option -implies @option{-pthread}, and thus is only supported on targets that -have support for @option{-pthread}. @option{-fopenmp} implies -@option{-fopenmp-simd}. - -@item -fopenmp-simd -@opindex fopenmp-simd -@cindex OpenMP SIMD -@cindex SIMD -Enable handling of OpenMP's @code{simd}, @code{declare simd}, -@code{declare reduction}, @code{assume}, @code{ordered}, @code{scan}, -@code{loop} directives and combined or composite directives with -@code{simd} as constituent with @code{#pragma omp} in C/C++, -@code{[[omp::directive(...)]]} and @code{[[omp::sequence(...)]]} in C++ -and @code{!$omp} in Fortran. Other OpenMP directives are ignored. - -@item -fpermitted-flt-eval-methods=@var{style} -@opindex fpermitted-flt-eval-methods -@opindex fpermitted-flt-eval-methods=c11 -@opindex fpermitted-flt-eval-methods=ts-18661-3 -ISO/IEC TS 18661-3 defines new permissible values for -@code{FLT_EVAL_METHOD} that indicate that operations and constants with -a semantic type that is an interchange or extended format should be -evaluated to the precision and range of that type. These new values are -a superset of those permitted under C99/C11, which does not specify the -meaning of other positive values of @code{FLT_EVAL_METHOD}. As such, code -conforming to C11 may not have been written expecting the possibility of -the new values. - -@option{-fpermitted-flt-eval-methods} specifies whether the compiler -should allow only the values of @code{FLT_EVAL_METHOD} specified in C99/C11, -or the extended set of values specified in ISO/IEC TS 18661-3. - -@var{style} is either @code{c11} or @code{ts-18661-3} as appropriate. - -The default when in a standards compliant mode (@option{-std=c11} or similar) -is @option{-fpermitted-flt-eval-methods=c11}. The default when in a GNU -dialect (@option{-std=gnu11} or similar) is -@option{-fpermitted-flt-eval-methods=ts-18661-3}. - -@item -fplan9-extensions -@opindex fplan9-extensions -Accept some non-standard constructs used in Plan 9 code. - -This enables @option{-fms-extensions}, permits passing pointers to -structures with anonymous fields to functions that expect pointers to -elements of the type of the field, and permits referring to anonymous -fields declared using a typedef. @xref{Unnamed Fields,,Unnamed -struct/union fields within structs/unions}, for details. This is only -supported for C, not C++. - -@item -fsigned-bitfields -@itemx -funsigned-bitfields -@itemx -fno-signed-bitfields -@itemx -fno-unsigned-bitfields -@opindex fsigned-bitfields -@opindex funsigned-bitfields -@opindex fno-signed-bitfields -@opindex fno-unsigned-bitfields -These options control whether a bit-field is signed or unsigned, when the -declaration does not use either @code{signed} or @code{unsigned}. By -default, such a bit-field is signed, because this is consistent: the -basic integer types such as @code{int} are signed types. - -@item -fsigned-char -@opindex fsigned-char -Let the type @code{char} be signed, like @code{signed char}. - -Note that this is equivalent to @option{-fno-unsigned-char}, which is -the negative form of @option{-funsigned-char}. Likewise, the option -@option{-fno-signed-char} is equivalent to @option{-funsigned-char}. - -@item -funsigned-char -@opindex funsigned-char -Let the type @code{char} be unsigned, like @code{unsigned char}. - -Each kind of machine has a default for what @code{char} should -be. It is either like @code{unsigned char} by default or like -@code{signed char} by default. - -Ideally, a portable program should always use @code{signed char} or -@code{unsigned char} when it depends on the signedness of an object. -But many programs have been written to use plain @code{char} and -expect it to be signed, or expect it to be unsigned, depending on the -machines they were written for. This option, and its inverse, let you -make such a program work with the opposite default. - -The type @code{char} is always a distinct type from each of -@code{signed char} or @code{unsigned char}, even though its behavior -is always just like one of those two. - -@item -fstrict-flex-arrays -@opindex fstrict-flex-arrays -@opindex fno-strict-flex-arrays -Control when to treat the trailing array of a structure as a flexible array -member for the purpose of accessing the elements of such an array. -The positive form is equivalent to @option{-fstrict-flex-arrays=3}, which is the -strictest. A trailing array is treated as a flexible array member only when it -is declared as a flexible array member per C99 standard onwards. -The negative form is equivalent to @option{-fstrict-flex-arrays=0}, which is the -least strict. All trailing arrays of structures are treated as flexible array -members. - -@item -fstrict-flex-arrays=@var{level} -@opindex fstrict-flex-arrays=@var{level} -Control when to treat the trailing array of a structure as a flexible array -member for the purpose of accessing the elements of such an array. The value -of @var{level} controls the level of strictness. - -The possible values of @var{level} are the same as for the -@code{strict_flex_array} attribute (@pxref{Variable Attributes}). - -You can control this behavior for a specific trailing array field of a -structure by using the variable attribute @code{strict_flex_array} attribute -(@pxref{Variable Attributes}). - -@item -fsso-struct=@var{endianness} -@opindex fsso-struct -Set the default scalar storage order of structures and unions to the -specified endianness. The accepted values are @samp{big-endian}, -@samp{little-endian} and @samp{native} for the native endianness of -the target (the default). This option is not supported for C++. - -@strong{Warning:} the @option{-fsso-struct} switch causes GCC to generate -code that is not binary compatible with code generated without it if the -specified endianness is not the native endianness of the target. -@end table - -@node C++ Dialect Options -@section Options Controlling C++ Dialect - -@cindex compiler options, C++ -@cindex C++ options, command-line -@cindex options, C++ -This section describes the command-line options that are only meaningful -for C++ programs. You can also use most of the GNU compiler options -regardless of what language your program is in. For example, you -might compile a file @file{firstClass.C} like this: - -@smallexample -g++ -g -fstrict-enums -O -c firstClass.C -@end smallexample - -@noindent -In this example, only @option{-fstrict-enums} is an option meant -only for C++ programs; you can use the other options with any -language supported by GCC@. - -Some options for compiling C programs, such as @option{-std}, are also -relevant for C++ programs. -@xref{C Dialect Options,,Options Controlling C Dialect}. - -Here is a list of options that are @emph{only} for compiling C++ programs: - -@table @gcctabopt - -@item -fabi-version=@var{n} -@opindex fabi-version -Use version @var{n} of the C++ ABI@. The default is version 0. - -Version 0 refers to the version conforming most closely to -the C++ ABI specification. Therefore, the ABI obtained using version 0 -will change in different versions of G++ as ABI bugs are fixed. - -Version 1 is the version of the C++ ABI that first appeared in G++ 3.2. - -Version 2 is the version of the C++ ABI that first appeared in G++ -3.4, and was the default through G++ 4.9. - -Version 3 corrects an error in mangling a constant address as a -template argument. - -Version 4, which first appeared in G++ 4.5, implements a standard -mangling for vector types. - -Version 5, which first appeared in G++ 4.6, corrects the mangling of -attribute const/volatile on function pointer types, decltype of a -plain decl, and use of a function parameter in the declaration of -another parameter. - -Version 6, which first appeared in G++ 4.7, corrects the promotion -behavior of C++11 scoped enums and the mangling of template argument -packs, const/static_cast, prefix ++ and --, and a class scope function -used as a template argument. - -Version 7, which first appeared in G++ 4.8, that treats nullptr_t as a -builtin type and corrects the mangling of lambdas in default argument -scope. - -Version 8, which first appeared in G++ 4.9, corrects the substitution -behavior of function types with function-cv-qualifiers. - -Version 9, which first appeared in G++ 5.2, corrects the alignment of -@code{nullptr_t}. - -Version 10, which first appeared in G++ 6.1, adds mangling of -attributes that affect type identity, such as ia32 calling convention -attributes (e.g.@: @samp{stdcall}). - -Version 11, which first appeared in G++ 7, corrects the mangling of -sizeof... expressions and operator names. For multiple entities with -the same name within a function, that are declared in different scopes, -the mangling now changes starting with the twelfth occurrence. It also -implies @option{-fnew-inheriting-ctors}. - -Version 12, which first appeared in G++ 8, corrects the calling -conventions for empty classes on the x86_64 target and for classes -with only deleted copy/move constructors. It accidentally changes the -calling convention for classes with a deleted copy constructor and a -trivial move constructor. - -Version 13, which first appeared in G++ 8.2, fixes the accidental -change in version 12. - -Version 14, which first appeared in G++ 10, corrects the mangling of -the nullptr expression. - -Version 15, which first appeared in G++ 10.3, corrects G++ 10 ABI -tag regression. - -Version 16, which first appeared in G++ 11, changes the mangling of -@code{__alignof__} to be distinct from that of @code{alignof}, and -dependent operator names. - -Version 17, which first appeared in G++ 12, fixes layout of classes -that inherit from aggregate classes with default member initializers -in C++14 and up. - -Version 18, which first appeard in G++ 13, fixes manglings of lambdas -that have additional context. - -See also @option{-Wabi}. - -@item -fabi-compat-version=@var{n} -@opindex fabi-compat-version -On targets that support strong aliases, G++ -works around mangling changes by creating an alias with the correct -mangled name when defining a symbol with an incorrect mangled name. -This switch specifies which ABI version to use for the alias. - -With @option{-fabi-version=0} (the default), this defaults to 13 (GCC 8.2 -compatibility). If another ABI version is explicitly selected, this -defaults to 0. For compatibility with GCC versions 3.2 through 4.9, -use @option{-fabi-compat-version=2}. - -If this option is not provided but @option{-Wabi=@var{n}} is, that -version is used for compatibility aliases. If this option is provided -along with @option{-Wabi} (without the version), the version from this -option is used for the warning. - -@item -fno-access-control -@opindex fno-access-control -@opindex faccess-control -Turn off all access checking. This switch is mainly useful for working -around bugs in the access control code. - -@item -faligned-new -@opindex faligned-new -Enable support for C++17 @code{new} of types that require more -alignment than @code{void* ::operator new(std::size_t)} provides. A -numeric argument such as @code{-faligned-new=32} can be used to -specify how much alignment (in bytes) is provided by that function, -but few users will need to override the default of -@code{alignof(std::max_align_t)}. - -This flag is enabled by default for @option{-std=c++17}. - -@item -fchar8_t -@itemx -fno-char8_t -@opindex fchar8_t -@opindex fno-char8_t -Enable support for @code{char8_t} as adopted for C++20. This includes -the addition of a new @code{char8_t} fundamental type, changes to the -types of UTF-8 string and character literals, new signatures for -user-defined literals, associated standard library updates, and new -@code{__cpp_char8_t} and @code{__cpp_lib_char8_t} feature test macros. - -This option enables functions to be overloaded for ordinary and UTF-8 -strings: - -@smallexample -int f(const char *); // #1 -int f(const char8_t *); // #2 -int v1 = f("text"); // Calls #1 -int v2 = f(u8"text"); // Calls #2 -@end smallexample - -@noindent -and introduces new signatures for user-defined literals: - -@smallexample -int operator""_udl1(char8_t); -int v3 = u8'x'_udl1; -int operator""_udl2(const char8_t*, std::size_t); -int v4 = u8"text"_udl2; -template<typename T, T...> int operator""_udl3(); -int v5 = u8"text"_udl3; -@end smallexample - -@noindent -The change to the types of UTF-8 string and character literals introduces -incompatibilities with ISO C++11 and later standards. For example, the -following code is well-formed under ISO C++11, but is ill-formed when -@option{-fchar8_t} is specified. - -@smallexample -char ca[] = u8"xx"; // error: char-array initialized from wide - // string -const char *cp = u8"xx";// error: invalid conversion from - // `const char8_t*' to `const char*' -int f(const char*); -auto v = f(u8"xx"); // error: invalid conversion from - // `const char8_t*' to `const char*' -std::string s@{u8"xx"@}; // error: no matching function for call to - // `std::basic_string<char>::basic_string()' -using namespace std::literals; -s = u8"xx"s; // error: conversion from - // `basic_string<char8_t>' to non-scalar - // type `basic_string<char>' requested -@end smallexample - -@item -fcheck-new -@opindex fcheck-new -Check that the pointer returned by @code{operator new} is non-null -before attempting to modify the storage allocated. This check is -normally unnecessary because the C++ standard specifies that -@code{operator new} only returns @code{0} if it is declared -@code{throw()}, in which case the compiler always checks the -return value even without this option. In all other cases, when -@code{operator new} has a non-empty exception specification, memory -exhaustion is signalled by throwing @code{std::bad_alloc}. See also -@samp{new (nothrow)}. - -@item -fconcepts -@itemx -fconcepts-ts -@opindex fconcepts -@opindex fconcepts-ts -Enable support for the C++ Concepts feature for constraining template -arguments. With @option{-std=c++20} and above, Concepts are part of -the language standard, so @option{-fconcepts} defaults to on. - -Some constructs that were allowed by the earlier C++ Extensions for -Concepts Technical Specification, ISO 19217 (2015), but didn't make it -into the standard, can additionally be enabled by -@option{-fconcepts-ts}. - -@item -fconstexpr-depth=@var{n} -@opindex fconstexpr-depth -Set the maximum nested evaluation depth for C++11 constexpr functions -to @var{n}. A limit is needed to detect endless recursion during -constant expression evaluation. The minimum specified by the standard -is 512. - -@item -fconstexpr-cache-depth=@var{n} -@opindex fconstexpr-cache-depth -Set the maximum level of nested evaluation depth for C++11 constexpr -functions that will be cached to @var{n}. This is a heuristic that -trades off compilation speed (when the cache avoids repeated -calculations) against memory consumption (when the cache grows very -large from highly recursive evaluations). The default is 8. Very few -users are likely to want to adjust it, but if your code does heavy -constexpr calculations you might want to experiment to find which -value works best for you. - -@item -fconstexpr-fp-except -@opindex fconstexpr-fp-except -Annex F of the C standard specifies that IEC559 floating point -exceptions encountered at compile time should not stop compilation. -C++ compilers have historically not followed this guidance, instead -treating floating point division by zero as non-constant even though -it has a well defined value. This flag tells the compiler to give -Annex F priority over other rules saying that a particular operation -is undefined. - -@smallexample -constexpr float inf = 1./0.; // OK with -fconstexpr-fp-except -@end smallexample - -@item -fconstexpr-loop-limit=@var{n} -@opindex fconstexpr-loop-limit -Set the maximum number of iterations for a loop in C++14 constexpr functions -to @var{n}. A limit is needed to detect infinite loops during -constant expression evaluation. The default is 262144 (1<<18). - -@item -fconstexpr-ops-limit=@var{n} -@opindex fconstexpr-ops-limit -Set the maximum number of operations during a single constexpr evaluation. -Even when number of iterations of a single loop is limited with the above limit, -if there are several nested loops and each of them has many iterations but still -smaller than the above limit, or if in a body of some loop or even outside -of a loop too many expressions need to be evaluated, the resulting constexpr -evaluation might take too long. -The default is 33554432 (1<<25). - -@item -fcoroutines -@opindex fcoroutines -Enable support for the C++ coroutines extension (experimental). - -@item -fno-elide-constructors -@opindex fno-elide-constructors -@opindex felide-constructors -The C++ standard allows an implementation to omit creating a temporary -that is only used to initialize another object of the same type. -Specifying this option disables that optimization, and forces G++ to -call the copy constructor in all cases. This option also causes G++ -to call trivial member functions which otherwise would be expanded inline. - -In C++17, the compiler is required to omit these temporaries, but this -option still affects trivial member functions. - -@item -fno-enforce-eh-specs -@opindex fno-enforce-eh-specs -@opindex fenforce-eh-specs -Don't generate code to check for violation of exception specifications -at run time. This option violates the C++ standard, but may be useful -for reducing code size in production builds, much like defining -@code{NDEBUG}. This does not give user code permission to throw -exceptions in violation of the exception specifications; the compiler -still optimizes based on the specifications, so throwing an -unexpected exception results in undefined behavior at run time. - -@item -fextern-tls-init -@itemx -fno-extern-tls-init -@opindex fextern-tls-init -@opindex fno-extern-tls-init -The C++11 and OpenMP standards allow @code{thread_local} and -@code{threadprivate} variables to have dynamic (runtime) -initialization. To support this, any use of such a variable goes -through a wrapper function that performs any necessary initialization. -When the use and definition of the variable are in the same -translation unit, this overhead can be optimized away, but when the -use is in a different translation unit there is significant overhead -even if the variable doesn't actually need dynamic initialization. If -the programmer can be sure that no use of the variable in a -non-defining TU needs to trigger dynamic initialization (either -because the variable is statically initialized, or a use of the -variable in the defining TU will be executed before any uses in -another TU), they can avoid this overhead with the -@option{-fno-extern-tls-init} option. - -On targets that support symbol aliases, the default is -@option{-fextern-tls-init}. On targets that do not support symbol -aliases, the default is @option{-fno-extern-tls-init}. - -@item -ffold-simple-inlines -@itemx -fno-fold-simple-inlines -@opindex ffold-simple-inlines -@opindex fno-fold-simple-inlines -Permit the C++ frontend to fold calls to @code{std::move}, @code{std::forward}, -@code{std::addressof} and @code{std::as_const}. In contrast to inlining, this -means no debug information will be generated for such calls. Since these -functions are rarely interesting to debug, this flag is enabled by default -unless @option{-fno-inline} is active. - -@item -fno-gnu-keywords -@opindex fno-gnu-keywords -@opindex fgnu-keywords -Do not recognize @code{typeof} as a keyword, so that code can use this -word as an identifier. You can use the keyword @code{__typeof__} instead. -This option is implied by the strict ISO C++ dialects: @option{-ansi}, -@option{-std=c++98}, @option{-std=c++11}, etc. - -@item -fimplicit-constexpr -@opindex fimplicit-constexpr -Make inline functions implicitly constexpr, if they satisfy the -requirements for a constexpr function. This option can be used in -C++14 mode or later. This can result in initialization changing from -dynamic to static and other optimizations. - -@item -fno-implicit-templates -@opindex fno-implicit-templates -@opindex fimplicit-templates -Never emit code for non-inline templates that are instantiated -implicitly (i.e.@: by use); only emit code for explicit instantiations. -If you use this option, you must take care to structure your code to -include all the necessary explicit instantiations to avoid getting -undefined symbols at link time. -@xref{Template Instantiation}, for more information. - -@item -fno-implicit-inline-templates -@opindex fno-implicit-inline-templates -@opindex fimplicit-inline-templates -Don't emit code for implicit instantiations of inline templates, either. -The default is to handle inlines differently so that compiles with and -without optimization need the same set of explicit instantiations. - -@item -fno-implement-inlines -@opindex fno-implement-inlines -@opindex fimplement-inlines -To save space, do not emit out-of-line copies of inline functions -controlled by @code{#pragma implementation}. This causes linker -errors if these functions are not inlined everywhere they are called. - -@item -fmodules-ts -@itemx -fno-modules-ts -@opindex fmodules-ts -@opindex fno-modules-ts -Enable support for C++20 modules (@pxref{C++ Modules}). The -@option{-fno-modules-ts} is usually not needed, as that is the -default. Even though this is a C++20 feature, it is not currently -implicitly enabled by selecting that standard version. - -@item -fmodule-header -@itemx -fmodule-header=user -@itemx -fmodule-header=system -@opindex fmodule-header -Compile a header file to create an importable header unit. - -@item -fmodule-implicit-inline -@opindex fmodule-implicit-inline -Member functions defined in their class definitions are not implicitly -inline for modular code. This is different to traditional C++ -behavior, for good reasons. However, it may result in a difficulty -during code porting. This option makes such function definitions -implicitly inline. It does however generate an ABI incompatibility, -so you must use it everywhere or nowhere. (Such definitions outside -of a named module remain implicitly inline, regardless.) - -@item -fno-module-lazy -@opindex fno-module-lazy -@opindex fmodule-lazy -Disable lazy module importing and module mapper creation. - -@item -fmodule-mapper=@r{[}@var{hostname}@r{]}:@var{port}@r{[}?@var{ident}@r{]} -@itemx -fmodule-mapper=|@var{program}@r{[}?@var{ident}@r{]} @var{args...} -@itemx -fmodule-mapper==@var{socket}@r{[}?@var{ident}@r{]} -@itemx -fmodule-mapper=<>@r{[}@var{inout}@r{]}@r{[}?@var{ident}@r{]} -@itemx -fmodule-mapper=<@var{in}>@var{out}@r{[}?@var{ident}@r{]} -@itemx -fmodule-mapper=@var{file}@r{[}?@var{ident}@r{]} -@vindex CXX_MODULE_MAPPER @r{environment variable} -@opindex fmodule-mapper -An oracle to query for module name to filename mappings. If -unspecified the @env{CXX_MODULE_MAPPER} environment variable is used, -and if that is unset, an in-process default is provided. - -@item -fmodule-only -@opindex fmodule-only -Only emit the Compiled Module Interface, inhibiting any object file. - -@item -fms-extensions -@opindex fms-extensions -Disable Wpedantic warnings about constructs used in MFC, such as implicit -int and getting a pointer to member function via non-standard syntax. - -@item -fnew-inheriting-ctors -@opindex fnew-inheriting-ctors -Enable the P0136 adjustment to the semantics of C++11 constructor -inheritance. This is part of C++17 but also considered to be a Defect -Report against C++11 and C++14. This flag is enabled by default -unless @option{-fabi-version=10} or lower is specified. - -@item -fnew-ttp-matching -@opindex fnew-ttp-matching -Enable the P0522 resolution to Core issue 150, template template -parameters and default arguments: this allows a template with default -template arguments as an argument for a template template parameter -with fewer template parameters. This flag is enabled by default for -@option{-std=c++17}. - -@item -fno-nonansi-builtins -@opindex fno-nonansi-builtins -@opindex fnonansi-builtins -Disable built-in declarations of functions that are not mandated by -ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit}, -@code{index}, @code{bzero}, @code{conjf}, and other related functions. - -@item -fnothrow-opt -@opindex fnothrow-opt -Treat a @code{throw()} exception specification as if it were a -@code{noexcept} specification to reduce or eliminate the text size -overhead relative to a function with no exception specification. If -the function has local variables of types with non-trivial -destructors, the exception specification actually makes the -function smaller because the EH cleanups for those variables can be -optimized away. The semantic effect is that an exception thrown out of -a function with such an exception specification results in a call -to @code{terminate} rather than @code{unexpected}. - -@item -fno-operator-names -@opindex fno-operator-names -@opindex foperator-names -Do not treat the operator name keywords @code{and}, @code{bitand}, -@code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as -synonyms as keywords. - -@item -fno-optional-diags -@opindex fno-optional-diags -@opindex foptional-diags -Disable diagnostics that the standard says a compiler does not need to -issue. Currently, the only such diagnostic issued by G++ is the one for -a name having multiple meanings within a class. - -@item -fpermissive -@opindex fpermissive -Downgrade some diagnostics about nonconformant code from errors to -warnings. Thus, using @option{-fpermissive} allows some -nonconforming code to compile. - -@item -fno-pretty-templates -@opindex fno-pretty-templates -@opindex fpretty-templates -When an error message refers to a specialization of a function -template, the compiler normally prints the signature of the -template followed by the template arguments and any typedefs or -typenames in the signature (e.g.@: @code{void f(T) [with T = int]} -rather than @code{void f(int)}) so that it's clear which template is -involved. When an error message refers to a specialization of a class -template, the compiler omits any template arguments that match -the default template arguments for that template. If either of these -behaviors make it harder to understand the error message rather than -easier, you can use @option{-fno-pretty-templates} to disable them. - -@item -fno-rtti -@opindex fno-rtti -@opindex frtti -Disable generation of information about every class with virtual -functions for use by the C++ run-time type identification features -(@code{dynamic_cast} and @code{typeid}). If you don't use those parts -of the language, you can save some space by using this flag. Note that -exception handling uses the same information, but G++ generates it as -needed. The @code{dynamic_cast} operator can still be used for casts that -do not require run-time type information, i.e.@: casts to @code{void *} or to -unambiguous base classes. - -Mixing code compiled with @option{-frtti} with that compiled with -@option{-fno-rtti} may not work. For example, programs may -fail to link if a class compiled with @option{-fno-rtti} is used as a base -for a class compiled with @option{-frtti}. - -@item -fsized-deallocation -@opindex fsized-deallocation -Enable the built-in global declarations -@smallexample -void operator delete (void *, std::size_t) noexcept; -void operator delete[] (void *, std::size_t) noexcept; -@end smallexample -as introduced in C++14. This is useful for user-defined replacement -deallocation functions that, for example, use the size of the object -to make deallocation faster. Enabled by default under -@option{-std=c++14} and above. The flag @option{-Wsized-deallocation} -warns about places that might want to add a definition. - -@item -fstrict-enums -@opindex fstrict-enums -Allow the compiler to optimize using the assumption that a value of -enumerated type can only be one of the values of the enumeration (as -defined in the C++ standard; basically, a value that can be -represented in the minimum number of bits needed to represent all the -enumerators). This assumption may not be valid if the program uses a -cast to convert an arbitrary integer value to the enumerated type. - -@item -fstrong-eval-order -@opindex fstrong-eval-order -Evaluate member access, array subscripting, and shift expressions in -left-to-right order, and evaluate assignment in right-to-left order, -as adopted for C++17. Enabled by default with @option{-std=c++17}. -@option{-fstrong-eval-order=some} enables just the ordering of member -access and shift expressions, and is the default without -@option{-std=c++17}. - -@item -ftemplate-backtrace-limit=@var{n} -@opindex ftemplate-backtrace-limit -Set the maximum number of template instantiation notes for a single -warning or error to @var{n}. The default value is 10. - -@item -ftemplate-depth=@var{n} -@opindex ftemplate-depth -Set the maximum instantiation depth for template classes to @var{n}. -A limit on the template instantiation depth is needed to detect -endless recursions during template class instantiation. ANSI/ISO C++ -conforming programs must not rely on a maximum depth greater than 17 -(changed to 1024 in C++11). The default value is 900, as the compiler -can run out of stack space before hitting 1024 in some situations. - -@item -fno-threadsafe-statics -@opindex fno-threadsafe-statics -@opindex fthreadsafe-statics -Do not emit the extra code to use the routines specified in the C++ -ABI for thread-safe initialization of local statics. You can use this -option to reduce code size slightly in code that doesn't need to be -thread-safe. - -@item -fuse-cxa-atexit -@opindex fuse-cxa-atexit -Register destructors for objects with static storage duration with the -@code{__cxa_atexit} function rather than the @code{atexit} function. -This option is required for fully standards-compliant handling of static -destructors, but only works if your C library supports -@code{__cxa_atexit}. - -@item -fno-use-cxa-get-exception-ptr -@opindex fno-use-cxa-get-exception-ptr -@opindex fuse-cxa-get-exception-ptr -Don't use the @code{__cxa_get_exception_ptr} runtime routine. This -causes @code{std::uncaught_exception} to be incorrect, but is necessary -if the runtime routine is not available. - -@item -fvisibility-inlines-hidden -@opindex fvisibility-inlines-hidden -This switch declares that the user does not attempt to compare -pointers to inline functions or methods where the addresses of the two functions -are taken in different shared objects. - -The effect of this is that GCC may, effectively, mark inline methods with -@code{__attribute__ ((visibility ("hidden")))} so that they do not -appear in the export table of a DSO and do not require a PLT indirection -when used within the DSO@. Enabling this option can have a dramatic effect -on load and link times of a DSO as it massively reduces the size of the -dynamic export table when the library makes heavy use of templates. - -The behavior of this switch is not quite the same as marking the -methods as hidden directly, because it does not affect static variables -local to the function or cause the compiler to deduce that -the function is defined in only one shared object. - -You may mark a method as having a visibility explicitly to negate the -effect of the switch for that method. For example, if you do want to -compare pointers to a particular inline method, you might mark it as -having default visibility. Marking the enclosing class with explicit -visibility has no effect. - -Explicitly instantiated inline methods are unaffected by this option -as their linkage might otherwise cross a shared library boundary. -@xref{Template Instantiation}. - -@item -fvisibility-ms-compat -@opindex fvisibility-ms-compat -This flag attempts to use visibility settings to make GCC's C++ -linkage model compatible with that of Microsoft Visual Studio. - -The flag makes these changes to GCC's linkage model: - -@enumerate -@item -It sets the default visibility to @code{hidden}, like -@option{-fvisibility=hidden}. - -@item -Types, but not their members, are not hidden by default. - -@item -The One Definition Rule is relaxed for types without explicit -visibility specifications that are defined in more than one -shared object: those declarations are permitted if they are -permitted when this option is not used. -@end enumerate - -In new code it is better to use @option{-fvisibility=hidden} and -export those classes that are intended to be externally visible. -Unfortunately it is possible for code to rely, perhaps accidentally, -on the Visual Studio behavior. - -Among the consequences of these changes are that static data members -of the same type with the same name but defined in different shared -objects are different, so changing one does not change the other; -and that pointers to function members defined in different shared -objects may not compare equal. When this flag is given, it is a -violation of the ODR to define types with the same name differently. - -@item -fno-weak -@opindex fno-weak -@opindex fweak -Do not use weak symbol support, even if it is provided by the linker. -By default, G++ uses weak symbols if they are available. This -option exists only for testing, and should not be used by end-users; -it results in inferior code and has no benefits. This option may -be removed in a future release of G++. - -@item -fext-numeric-literals @r{(C++ and Objective-C++ only)} -@opindex fext-numeric-literals -@opindex fno-ext-numeric-literals -Accept imaginary, fixed-point, or machine-defined -literal number suffixes as GNU extensions. -When this option is turned off these suffixes are treated -as C++11 user-defined literal numeric suffixes. -This is on by default for all pre-C++11 dialects and all GNU dialects: -@option{-std=c++98}, @option{-std=gnu++98}, @option{-std=gnu++11}, -@option{-std=gnu++14}. -This option is off by default -for ISO C++11 onwards (@option{-std=c++11}, ...). - -@item -nostdinc++ -@opindex nostdinc++ -Do not search for header files in the standard directories specific to -C++, but do still search the other standard directories. (This option -is used when building the C++ library.) - -@item -flang-info-include-translate -@itemx -flang-info-include-translate-not -@itemx -flang-info-include-translate=@var{header} -@opindex flang-info-include-translate -@opindex flang-info-include-translate-not -Inform of include translation events. The first will note accepted -include translations, the second will note declined include -translations. The @var{header} form will inform of include -translations relating to that specific header. If @var{header} is of -the form @code{"user"} or @code{<system>} it will be resolved to a -specific user or system header using the include path. - -@item -flang-info-module-cmi -@itemx -flang-info-module-cmi=@var{module} -@opindex flang-info-module-cmi -Inform of Compiled Module Interface pathnames. The first will note -all read CMI pathnames. The @var{module} form will not reading a -specific module's CMI. @var{module} may be a named module or a -header-unit (the latter indicated by either being a pathname containing -directory separators or enclosed in @code{<>} or @code{""}). - -@item -stdlib=@var{libstdc++,libc++} -@opindex stdlib -When G++ is configured to support this option, it allows specification of -alternate C++ runtime libraries. Two options are available: @var{libstdc++} -(the default, native C++ runtime for G++) and @var{libc++} which is the -C++ runtime installed on some operating systems (e.g. Darwin versions from -Darwin11 onwards). The option switches G++ to use the headers from the -specified library and to emit @code{-lstdc++} or @code{-lc++} respectively, -when a C++ runtime is required for linking. -@end table - -In addition, these warning options have meanings only for C++ programs: - -@table @gcctabopt -@item -Wabi-tag @r{(C++ and Objective-C++ only)} -@opindex Wabi-tag -Warn when a type with an ABI tag is used in a context that does not -have that ABI tag. See @ref{C++ Attributes} for more information -about ABI tags. - -@item -Wcomma-subscript @r{(C++ and Objective-C++ only)} -@opindex Wcomma-subscript -@opindex Wno-comma-subscript -Warn about uses of a comma expression within a subscripting expression. -This usage was deprecated in C++20 and is going to be removed in C++23. -However, a comma expression wrapped in @code{( )} is not deprecated. Example: - -@smallexample -@group -void f(int *a, int b, int c) @{ - a[b,c]; // deprecated in C++20, invalid in C++23 - a[(b,c)]; // OK -@} -@end group -@end smallexample - -In C++23 it is valid to have comma separated expressions in a subscript -when an overloaded subscript operator is found and supports the right -number and types of arguments. G++ will accept the formerly valid syntax -for code that is not valid in C++23 but used to be valid but deprecated -in C++20 with a pedantic warning that can be disabled with -@option{-Wno-comma-subscript}. - -Enabled by default with @option{-std=c++20} unless @option{-Wno-deprecated}, -and with @option{-std=c++23} regardless of @option{-Wno-deprecated}. - -@item -Wctad-maybe-unsupported @r{(C++ and Objective-C++ only)} -@opindex Wctad-maybe-unsupported -@opindex Wno-ctad-maybe-unsupported -Warn when performing class template argument deduction (CTAD) on a type with -no explicitly written deduction guides. This warning will point out cases -where CTAD succeeded only because the compiler synthesized the implicit -deduction guides, which might not be what the programmer intended. Certain -style guides allow CTAD only on types that specifically "opt-in"; i.e., on -types that are designed to support CTAD. This warning can be suppressed with -the following pattern: - -@smallexample -struct allow_ctad_t; // any name works -template <typename T> struct S @{ - S(T) @{ @} -@}; -S(allow_ctad_t) -> S<void>; // guide with incomplete parameter type will never be considered -@end smallexample - -@item -Wctor-dtor-privacy @r{(C++ and Objective-C++ only)} -@opindex Wctor-dtor-privacy -@opindex Wno-ctor-dtor-privacy -Warn when a class seems unusable because all the constructors or -destructors in that class are private, and it has neither friends nor -public static member functions. Also warn if there are no non-private -methods, and there's at least one private member function that isn't -a constructor or destructor. - -@item -Wdangling-reference @r{(C++ and Objective-C++ only)} -@opindex Wdangling-reference -@opindex Wno-dangling-reference -Warn when a reference is bound to a temporary whose lifetime has ended. -For example: - -@smallexample -int n = 1; -const int& r = std::max(n - 1, n + 1); // r is dangling -@end smallexample - -In the example above, two temporaries are created, one for each -argument, and a reference to one of the temporaries is returned. -However, both temporaries are destroyed at the end of the full -expression, so the reference @code{r} is dangling. This warning -also detects dangling references in member initializer lists: - -@smallexample -const int& f(const int& i) @{ return i; @} -struct S @{ - const int &r; // r is dangling - S() : r(f(10)) @{ @} -@}; -@end smallexample - -Member functions are checked as well, but only their object argument: - -@smallexample -struct S @{ - const S& self () @{ return *this; @} -@}; -const S& s = S().self(); // s is dangling -@end smallexample - -Certain functions are safe in this respect, for example @code{std::use_facet}: -they take and return a reference, but they don't return one of its arguments, -which can fool the warning. Such functions can be excluded from the warning -by wrapping them in a @code{#pragma}: - -@smallexample -#pragma GCC diagnostic push -#pragma GCC diagnostic ignored "-Wdangling-reference" -const T& foo (const T&) @{ @dots{} @} -#pragma GCC diagnostic pop -@end smallexample - -This warning is enabled by @option{-Wall}. - -@item -Wdelete-non-virtual-dtor @r{(C++ and Objective-C++ only)} -@opindex Wdelete-non-virtual-dtor -@opindex Wno-delete-non-virtual-dtor -Warn when @code{delete} is used to destroy an instance of a class that -has virtual functions and non-virtual destructor. It is unsafe to delete -an instance of a derived class through a pointer to a base class if the -base class does not have a virtual destructor. This warning is enabled -by @option{-Wall}. - -@item -Wdeprecated-copy @r{(C++ and Objective-C++ only)} -@opindex Wdeprecated-copy -@opindex Wno-deprecated-copy -Warn that the implicit declaration of a copy constructor or copy -assignment operator is deprecated if the class has a user-provided -copy constructor or copy assignment operator, in C++11 and up. This -warning is enabled by @option{-Wextra}. With -@option{-Wdeprecated-copy-dtor}, also deprecate if the class has a -user-provided destructor. - -@item -Wno-deprecated-enum-enum-conversion @r{(C++ and Objective-C++ only)} -@opindex Wdeprecated-enum-enum-conversion -@opindex Wno-deprecated-enum-enum-conversion -Disable the warning about the case when the usual arithmetic conversions -are applied on operands where one is of enumeration type and the other is -of a different enumeration type. This conversion was deprecated in C++20. -For example: - -@smallexample -enum E1 @{ e @}; -enum E2 @{ f @}; -int k = f - e; -@end smallexample - -@option{-Wdeprecated-enum-enum-conversion} is enabled by default with -@option{-std=c++20}. In pre-C++20 dialects, this warning can be enabled -by @option{-Wenum-conversion}. - -@item -Wno-deprecated-enum-float-conversion @r{(C++ and Objective-C++ only)} -@opindex Wdeprecated-enum-float-conversion -@opindex Wno-deprecated-enum-float-conversion -Disable the warning about the case when the usual arithmetic conversions -are applied on operands where one is of enumeration type and the other is -of a floating-point type. This conversion was deprecated in C++20. For -example: - -@smallexample -enum E1 @{ e @}; -enum E2 @{ f @}; -bool b = e <= 3.7; -@end smallexample - -@option{-Wdeprecated-enum-float-conversion} is enabled by default with -@option{-std=c++20}. In pre-C++20 dialects, this warning can be enabled -by @option{-Wenum-conversion}. - -@item -Wno-init-list-lifetime @r{(C++ and Objective-C++ only)} -@opindex Winit-list-lifetime -@opindex Wno-init-list-lifetime -Do not warn about uses of @code{std::initializer_list} that are likely -to result in dangling pointers. Since the underlying array for an -@code{initializer_list} is handled like a normal C++ temporary object, -it is easy to inadvertently keep a pointer to the array past the end -of the array's lifetime. For example: - -@itemize @bullet -@item -If a function returns a temporary @code{initializer_list}, or a local -@code{initializer_list} variable, the array's lifetime ends at the end -of the return statement, so the value returned has a dangling pointer. - -@item -If a new-expression creates an @code{initializer_list}, the array only -lives until the end of the enclosing full-expression, so the -@code{initializer_list} in the heap has a dangling pointer. - -@item -When an @code{initializer_list} variable is assigned from a -brace-enclosed initializer list, the temporary array created for the -right side of the assignment only lives until the end of the -full-expression, so at the next statement the @code{initializer_list} -variable has a dangling pointer. - -@smallexample -// li's initial underlying array lives as long as li -std::initializer_list<int> li = @{ 1,2,3 @}; -// assignment changes li to point to a temporary array -li = @{ 4, 5 @}; -// now the temporary is gone and li has a dangling pointer -int i = li.begin()[0] // undefined behavior -@end smallexample - -@item -When a list constructor stores the @code{begin} pointer from the -@code{initializer_list} argument, this doesn't extend the lifetime of -the array, so if a class variable is constructed from a temporary -@code{initializer_list}, the pointer is left dangling by the end of -the variable declaration statement. - -@end itemize - -@item -Winvalid-imported-macros -@opindex Winvalid-imported-macros -@opindex Wno-invalid-imported-macros -Verify all imported macro definitions are valid at the end of -compilation. This is not enabled by default, as it requires -additional processing to determine. It may be useful when preparing -sets of header-units to ensure consistent macros. - -@item -Wno-literal-suffix @r{(C++ and Objective-C++ only)} -@opindex Wliteral-suffix -@opindex Wno-literal-suffix -Do not warn when a string or character literal is followed by a -ud-suffix which does not begin with an underscore. As a conforming -extension, GCC treats such suffixes as separate preprocessing tokens -in order to maintain backwards compatibility with code that uses -formatting macros from @code{<inttypes.h>}. For example: - -@smallexample -#define __STDC_FORMAT_MACROS -#include <inttypes.h> -#include <stdio.h> - -int main() @{ - int64_t i64 = 123; - printf("My int64: %" PRId64"\n", i64); -@} -@end smallexample - -In this case, @code{PRId64} is treated as a separate preprocessing token. - -This option also controls warnings when a user-defined literal -operator is declared with a literal suffix identifier that doesn't -begin with an underscore. Literal suffix identifiers that don't begin -with an underscore are reserved for future standardization. - -These warnings are enabled by default. - -@item -Wno-narrowing @r{(C++ and Objective-C++ only)} -@opindex Wnarrowing -@opindex Wno-narrowing -For C++11 and later standards, narrowing conversions are diagnosed by default, -as required by the standard. A narrowing conversion from a constant produces -an error, and a narrowing conversion from a non-constant produces a warning, -but @option{-Wno-narrowing} suppresses the diagnostic. -Note that this does not affect the meaning of well-formed code; -narrowing conversions are still considered ill-formed in SFINAE contexts. - -With @option{-Wnarrowing} in C++98, warn when a narrowing -conversion prohibited by C++11 occurs within -@samp{@{ @}}, e.g. - -@smallexample -int i = @{ 2.2 @}; // error: narrowing from double to int -@end smallexample - -This flag is included in @option{-Wall} and @option{-Wc++11-compat}. - -@item -Wnoexcept @r{(C++ and Objective-C++ only)} -@opindex Wnoexcept -@opindex Wno-noexcept -Warn when a noexcept-expression evaluates to false because of a call -to a function that does not have a non-throwing exception -specification (i.e. @code{throw()} or @code{noexcept}) but is known by -the compiler to never throw an exception. - -@item -Wnoexcept-type @r{(C++ and Objective-C++ only)} -@opindex Wnoexcept-type -@opindex Wno-noexcept-type -Warn if the C++17 feature making @code{noexcept} part of a function -type changes the mangled name of a symbol relative to C++14. Enabled -by @option{-Wabi} and @option{-Wc++17-compat}. - -As an example: - -@smallexample -template <class T> void f(T t) @{ t(); @}; -void g() noexcept; -void h() @{ f(g); @} -@end smallexample - -@noindent -In C++14, @code{f} calls @code{f<void(*)()>}, but in -C++17 it calls @code{f<void(*)()noexcept>}. - -@item -Wclass-memaccess @r{(C++ and Objective-C++ only)} -@opindex Wclass-memaccess -@opindex Wno-class-memaccess -Warn when the destination of a call to a raw memory function such as -@code{memset} or @code{memcpy} is an object of class type, and when writing -into such an object might bypass the class non-trivial or deleted constructor -or copy assignment, violate const-correctness or encapsulation, or corrupt -virtual table pointers. Modifying the representation of such objects may -violate invariants maintained by member functions of the class. For example, -the call to @code{memset} below is undefined because it modifies a non-trivial -class object and is, therefore, diagnosed. The safe way to either initialize -or clear the storage of objects of such types is by using the appropriate -constructor or assignment operator, if one is available. -@smallexample -std::string str = "abc"; -memset (&str, 0, sizeof str); -@end smallexample -The @option{-Wclass-memaccess} option is enabled by @option{-Wall}. -Explicitly casting the pointer to the class object to @code{void *} or -to a type that can be safely accessed by the raw memory function suppresses -the warning. - -@item -Wnon-virtual-dtor @r{(C++ and Objective-C++ only)} -@opindex Wnon-virtual-dtor -@opindex Wno-non-virtual-dtor -Warn when a class has virtual functions and an accessible non-virtual -destructor itself or in an accessible polymorphic base class, in which -case it is possible but unsafe to delete an instance of a derived -class through a pointer to the class itself or base class. This -warning is automatically enabled if @option{-Weffc++} is specified. - -@item -Wregister @r{(C++ and Objective-C++ only)} -@opindex Wregister -@opindex Wno-register -Warn on uses of the @code{register} storage class specifier, except -when it is part of the GNU @ref{Explicit Register Variables} extension. -The use of the @code{register} keyword as storage class specifier has -been deprecated in C++11 and removed in C++17. -Enabled by default with @option{-std=c++17}. - -@item -Wreorder @r{(C++ and Objective-C++ only)} -@opindex Wreorder -@opindex Wno-reorder -@cindex reordering, warning -@cindex warning for reordering of member initializers -Warn when the order of member initializers given in the code does not -match the order in which they must be executed. For instance: - -@smallexample -struct A @{ - int i; - int j; - A(): j (0), i (1) @{ @} -@}; -@end smallexample - -@noindent -The compiler rearranges the member initializers for @code{i} -and @code{j} to match the declaration order of the members, emitting -a warning to that effect. This warning is enabled by @option{-Wall}. - -@item -Wno-pessimizing-move @r{(C++ and Objective-C++ only)} -@opindex Wpessimizing-move -@opindex Wno-pessimizing-move -This warning warns when a call to @code{std::move} prevents copy -elision. A typical scenario when copy elision can occur is when returning in -a function with a class return type, when the expression being returned is the -name of a non-volatile automatic object, and is not a function parameter, and -has the same type as the function return type. - -@smallexample -struct T @{ -@dots{} -@}; -T fn() -@{ - T t; - @dots{} - return std::move (t); -@} -@end smallexample - -But in this example, the @code{std::move} call prevents copy elision. - -This warning is enabled by @option{-Wall}. - -@item -Wno-redundant-move @r{(C++ and Objective-C++ only)} -@opindex Wredundant-move -@opindex Wno-redundant-move -This warning warns about redundant calls to @code{std::move}; that is, when -a move operation would have been performed even without the @code{std::move} -call. This happens because the compiler is forced to treat the object as if -it were an rvalue in certain situations such as returning a local variable, -where copy elision isn't applicable. Consider: - -@smallexample -struct T @{ -@dots{} -@}; -T fn(T t) -@{ - @dots{} - return std::move (t); -@} -@end smallexample - -Here, the @code{std::move} call is redundant. Because G++ implements Core -Issue 1579, another example is: - -@smallexample -struct T @{ // convertible to U -@dots{} -@}; -struct U @{ -@dots{} -@}; -U fn() -@{ - T t; - @dots{} - return std::move (t); -@} -@end smallexample -In this example, copy elision isn't applicable because the type of the -expression being returned and the function return type differ, yet G++ -treats the return value as if it were designated by an rvalue. - -This warning is enabled by @option{-Wextra}. - -@item -Wrange-loop-construct @r{(C++ and Objective-C++ only)} -@opindex Wrange-loop-construct -@opindex Wno-range-loop-construct -This warning warns when a C++ range-based for-loop is creating an unnecessary -copy. This can happen when the range declaration is not a reference, but -probably should be. For example: - -@smallexample -struct S @{ char arr[128]; @}; -void fn () @{ - S arr[5]; - for (const auto x : arr) @{ @dots{} @} -@} -@end smallexample - -It does not warn when the type being copied is a trivially-copyable type whose -size is less than 64 bytes. - -This warning also warns when a loop variable in a range-based for-loop is -initialized with a value of a different type resulting in a copy. For example: - -@smallexample -void fn() @{ - int arr[10]; - for (const double &x : arr) @{ @dots{} @} -@} -@end smallexample - -In the example above, in every iteration of the loop a temporary value of -type @code{double} is created and destroyed, to which the reference -@code{const double &} is bound. - -This warning is enabled by @option{-Wall}. - -@item -Wredundant-tags @r{(C++ and Objective-C++ only)} -@opindex Wredundant-tags -@opindex Wno-redundant-tags -Warn about redundant class-key and enum-key in references to class types -and enumerated types in contexts where the key can be eliminated without -causing an ambiguity. For example: - -@smallexample -struct foo; -struct foo *p; // warn that keyword struct can be eliminated -@end smallexample - -@noindent -On the other hand, in this example there is no warning: - -@smallexample -struct foo; -void foo (); // "hides" struct foo -void bar (struct foo&); // no warning, keyword struct is necessary -@end smallexample - -@item -Wno-subobject-linkage @r{(C++ and Objective-C++ only)} -@opindex Wsubobject-linkage -@opindex Wno-subobject-linkage -Do not warn -if a class type has a base or a field whose type uses the anonymous -namespace or depends on a type with no linkage. If a type A depends on -a type B with no or internal linkage, defining it in multiple -translation units would be an ODR violation because the meaning of B -is different in each translation unit. If A only appears in a single -translation unit, the best way to silence the warning is to give it -internal linkage by putting it in an anonymous namespace as well. The -compiler doesn't give this warning for types defined in the main .C -file, as those are unlikely to have multiple definitions. -@option{-Wsubobject-linkage} is enabled by default. - -@item -Weffc++ @r{(C++ and Objective-C++ only)} -@opindex Weffc++ -@opindex Wno-effc++ -Warn about violations of the following style guidelines from Scott Meyers' -@cite{Effective C++} series of books: - -@itemize @bullet -@item -Define a copy constructor and an assignment operator for classes -with dynamically-allocated memory. - -@item -Prefer initialization to assignment in constructors. - -@item -Have @code{operator=} return a reference to @code{*this}. - -@item -Don't try to return a reference when you must return an object. - -@item -Distinguish between prefix and postfix forms of increment and -decrement operators. - -@item -Never overload @code{&&}, @code{||}, or @code{,}. - -@end itemize - -This option also enables @option{-Wnon-virtual-dtor}, which is also -one of the effective C++ recommendations. However, the check is -extended to warn about the lack of virtual destructor in accessible -non-polymorphic bases classes too. - -When selecting this option, be aware that the standard library -headers do not obey all of these guidelines; use @samp{grep -v} -to filter out those warnings. - -@item -Wno-exceptions @r{(C++ and Objective-C++ only)} -@opindex Wexceptions -@opindex Wno-exceptions -Disable the warning about the case when an exception handler is shadowed by -another handler, which can point out a wrong ordering of exception handlers. - -@item -Wstrict-null-sentinel @r{(C++ and Objective-C++ only)} -@opindex Wstrict-null-sentinel -@opindex Wno-strict-null-sentinel -Warn about the use of an uncasted @code{NULL} as sentinel. When -compiling only with GCC this is a valid sentinel, as @code{NULL} is defined -to @code{__null}. Although it is a null pointer constant rather than a -null pointer, it is guaranteed to be of the same size as a pointer. -But this use is not portable across different compilers. - -@item -Wno-non-template-friend @r{(C++ and Objective-C++ only)} -@opindex Wno-non-template-friend -@opindex Wnon-template-friend -Disable warnings when non-template friend functions are declared -within a template. In very old versions of GCC that predate implementation -of the ISO standard, declarations such as -@samp{friend int foo(int)}, where the name of the friend is an unqualified-id, -could be interpreted as a particular specialization of a template -function; the warning exists to diagnose compatibility problems, -and is enabled by default. - -@item -Wold-style-cast @r{(C++ and Objective-C++ only)} -@opindex Wold-style-cast -@opindex Wno-old-style-cast -Warn if an old-style (C-style) cast to a non-void type is used within -a C++ program. The new-style casts (@code{dynamic_cast}, -@code{static_cast}, @code{reinterpret_cast}, and @code{const_cast}) are -less vulnerable to unintended effects and much easier to search for. - -@item -Woverloaded-virtual @r{(C++ and Objective-C++ only)} -@itemx -Woverloaded-virtual=@var{n} -@opindex Woverloaded-virtual -@opindex Wno-overloaded-virtual -@cindex overloaded virtual function, warning -@cindex warning for overloaded virtual function -Warn when a function declaration hides virtual functions from a -base class. For example, in: - -@smallexample -struct A @{ - virtual void f(); -@}; - -struct B: public A @{ - void f(int); // does not override -@}; -@end smallexample - -the @code{A} class version of @code{f} is hidden in @code{B}, and code -like: - -@smallexample -B* b; -b->f(); -@end smallexample - -@noindent -fails to compile. - -The optional level suffix controls the behavior when all the -declarations in the derived class override virtual functions in the -base class, even if not all of the base functions are overridden: - -@smallexample -struct C @{ - virtual void f(); - virtual void f(int); -@}; - -struct D: public C @{ - void f(int); // does override -@} -@end smallexample - -This pattern is less likely to be a mistake; if D is only used -virtually, the user might have decided that the base class semantics -for some of the overloads are fine. - -At level 1, this case does not warn; at level 2, it does. -@option{-Woverloaded-virtual} by itself selects level 2. Level 1 is -included in @option{-Wall}. - -@item -Wno-pmf-conversions @r{(C++ and Objective-C++ only)} -@opindex Wno-pmf-conversions -@opindex Wpmf-conversions -Disable the diagnostic for converting a bound pointer to member function -to a plain pointer. - -@item -Wsign-promo @r{(C++ and Objective-C++ only)} -@opindex Wsign-promo -@opindex Wno-sign-promo -Warn when overload resolution chooses a promotion from unsigned or -enumerated type to a signed type, over a conversion to an unsigned type of -the same size. Previous versions of G++ tried to preserve -unsignedness, but the standard mandates the current behavior. - -@item -Wtemplates @r{(C++ and Objective-C++ only)} -@opindex Wtemplates -@opindex Wno-templates -Warn when a primary template declaration is encountered. Some coding -rules disallow templates, and this may be used to enforce that rule. -The warning is inactive inside a system header file, such as the STL, so -one can still use the STL. One may also instantiate or specialize -templates. - -@item -Wmismatched-new-delete @r{(C++ and Objective-C++ only)} -@opindex Wmismatched-new-delete -@opindex Wno-mismatched-new-delete -Warn for mismatches between calls to @code{operator new} or @code{operator -delete} and the corresponding call to the allocation or deallocation function. -This includes invocations of C++ @code{operator delete} with pointers -returned from either mismatched forms of @code{operator new}, or from other -functions that allocate objects for which the @code{operator delete} isn't -a suitable deallocator, as well as calls to other deallocation functions -with pointers returned from @code{operator new} for which the deallocation -function isn't suitable. - -For example, the @code{delete} expression in the function below is diagnosed -because it doesn't match the array form of the @code{new} expression -the pointer argument was returned from. Similarly, the call to @code{free} -is also diagnosed. - -@smallexample -void f () -@{ - int *a = new int[n]; - delete a; // warning: mismatch in array forms of expressions - - char *p = new char[n]; - free (p); // warning: mismatch between new and free -@} -@end smallexample - -The related option @option{-Wmismatched-dealloc} diagnoses mismatches -involving allocation and deallocation functions other than @code{operator -new} and @code{operator delete}. - -@option{-Wmismatched-new-delete} is included in @option{-Wall}. - -@item -Wmismatched-tags @r{(C++ and Objective-C++ only)} -@opindex Wmismatched-tags -@opindex Wno-mismatched-tags -Warn for declarations of structs, classes, and class templates and their -specializations with a class-key that does not match either the definition -or the first declaration if no definition is provided. - -For example, the declaration of @code{struct Object} in the argument list -of @code{draw} triggers the warning. To avoid it, either remove the redundant -class-key @code{struct} or replace it with @code{class} to match its definition. -@smallexample -class Object @{ -public: - virtual ~Object () = 0; -@}; -void draw (struct Object*); -@end smallexample - -It is not wrong to declare a class with the class-key @code{struct} as -the example above shows. The @option{-Wmismatched-tags} option is intended -to help achieve a consistent style of class declarations. In code that is -intended to be portable to Windows-based compilers the warning helps prevent -unresolved references due to the difference in the mangling of symbols -declared with different class-keys. The option can be used either on its -own or in conjunction with @option{-Wredundant-tags}. - -@item -Wmultiple-inheritance @r{(C++ and Objective-C++ only)} -@opindex Wmultiple-inheritance -@opindex Wno-multiple-inheritance -Warn when a class is defined with multiple direct base classes. Some -coding rules disallow multiple inheritance, and this may be used to -enforce that rule. The warning is inactive inside a system header file, -such as the STL, so one can still use the STL. One may also define -classes that indirectly use multiple inheritance. - -@item -Wvirtual-inheritance -@opindex Wvirtual-inheritance -@opindex Wno-virtual-inheritance -Warn when a class is defined with a virtual direct base class. Some -coding rules disallow multiple inheritance, and this may be used to -enforce that rule. The warning is inactive inside a system header file, -such as the STL, so one can still use the STL. One may also define -classes that indirectly use virtual inheritance. - -@item -Wno-virtual-move-assign -@opindex Wvirtual-move-assign -@opindex Wno-virtual-move-assign -Suppress warnings about inheriting from a virtual base with a -non-trivial C++11 move assignment operator. This is dangerous because -if the virtual base is reachable along more than one path, it is -moved multiple times, which can mean both objects end up in the -moved-from state. If the move assignment operator is written to avoid -moving from a moved-from object, this warning can be disabled. - -@item -Wnamespaces -@opindex Wnamespaces -@opindex Wno-namespaces -Warn when a namespace definition is opened. Some coding rules disallow -namespaces, and this may be used to enforce that rule. The warning is -inactive inside a system header file, such as the STL, so one can still -use the STL. One may also use using directives and qualified names. - -@item -Wno-terminate @r{(C++ and Objective-C++ only)} -@opindex Wterminate -@opindex Wno-terminate -Disable the warning about a throw-expression that will immediately -result in a call to @code{terminate}. - -@item -Wno-vexing-parse @r{(C++ and Objective-C++ only)} -@opindex Wvexing-parse -@opindex Wno-vexing-parse -Warn about the most vexing parse syntactic ambiguity. This warns about -the cases when a declaration looks like a variable definition, but the -C++ language requires it to be interpreted as a function declaration. -For instance: - -@smallexample -void f(double a) @{ - int i(); // extern int i (void); - int n(int(a)); // extern int n (int); -@} -@end smallexample - -Another example: - -@smallexample -struct S @{ S(int); @}; -void f(double a) @{ - S x(int(a)); // extern struct S x (int); - S y(int()); // extern struct S y (int (*) (void)); - S z(); // extern struct S z (void); -@} -@end smallexample - -The warning will suggest options how to deal with such an ambiguity; e.g., -it can suggest removing the parentheses or using braces instead. - -This warning is enabled by default. - -@item -Wno-class-conversion @r{(C++ and Objective-C++ only)} -@opindex Wno-class-conversion -@opindex Wclass-conversion -Do not warn when a conversion function converts an -object to the same type, to a base class of that type, or to void; such -a conversion function will never be called. - -@item -Wvolatile @r{(C++ and Objective-C++ only)} -@opindex Wvolatile -@opindex Wno-volatile -Warn about deprecated uses of the @code{volatile} qualifier. This includes -postfix and prefix @code{++} and @code{--} expressions of -@code{volatile}-qualified types, using simple assignments where the left -operand is a @code{volatile}-qualified non-class type for their value, -compound assignments where the left operand is a @code{volatile}-qualified -non-class type, @code{volatile}-qualified function return type, -@code{volatile}-qualified parameter type, and structured bindings of a -@code{volatile}-qualified type. This usage was deprecated in C++20. - -Enabled by default with @option{-std=c++20}. - -@item -Wzero-as-null-pointer-constant @r{(C++ and Objective-C++ only)} -@opindex Wzero-as-null-pointer-constant -@opindex Wno-zero-as-null-pointer-constant -Warn when a literal @samp{0} is used as null pointer constant. This can -be useful to facilitate the conversion to @code{nullptr} in C++11. - -@item -Waligned-new -@opindex Waligned-new -@opindex Wno-aligned-new -Warn about a new-expression of a type that requires greater alignment -than the @code{alignof(std::max_align_t)} but uses an allocation -function without an explicit alignment parameter. This option is -enabled by @option{-Wall}. - -Normally this only warns about global allocation functions, but -@option{-Waligned-new=all} also warns about class member allocation -functions. - -@item -Wno-placement-new -@itemx -Wplacement-new=@var{n} -@opindex Wplacement-new -@opindex Wno-placement-new -Warn about placement new expressions with undefined behavior, such as -constructing an object in a buffer that is smaller than the type of -the object. For example, the placement new expression below is diagnosed -because it attempts to construct an array of 64 integers in a buffer only -64 bytes large. -@smallexample -char buf [64]; -new (buf) int[64]; -@end smallexample -This warning is enabled by default. - -@table @gcctabopt -@item -Wplacement-new=1 -This is the default warning level of @option{-Wplacement-new}. At this -level the warning is not issued for some strictly undefined constructs that -GCC allows as extensions for compatibility with legacy code. For example, -the following @code{new} expression is not diagnosed at this level even -though it has undefined behavior according to the C++ standard because -it writes past the end of the one-element array. -@smallexample -struct S @{ int n, a[1]; @}; -S *s = (S *)malloc (sizeof *s + 31 * sizeof s->a[0]); -new (s->a)int [32](); -@end smallexample - -@item -Wplacement-new=2 -At this level, in addition to diagnosing all the same constructs as at level -1, a diagnostic is also issued for placement new expressions that construct -an object in the last member of structure whose type is an array of a single -element and whose size is less than the size of the object being constructed. -While the previous example would be diagnosed, the following construct makes -use of the flexible member array extension to avoid the warning at level 2. -@smallexample -struct S @{ int n, a[]; @}; -S *s = (S *)malloc (sizeof *s + 32 * sizeof s->a[0]); -new (s->a)int [32](); -@end smallexample - -@end table - -@item -Wcatch-value -@itemx -Wcatch-value=@var{n} @r{(C++ and Objective-C++ only)} -@opindex Wcatch-value -@opindex Wno-catch-value -Warn about catch handlers that do not catch via reference. -With @option{-Wcatch-value=1} (or @option{-Wcatch-value} for short) -warn about polymorphic class types that are caught by value. -With @option{-Wcatch-value=2} warn about all class types that are caught -by value. With @option{-Wcatch-value=3} warn about all types that are -not caught by reference. @option{-Wcatch-value} is enabled by @option{-Wall}. - -@item -Wconditionally-supported @r{(C++ and Objective-C++ only)} -@opindex Wconditionally-supported -@opindex Wno-conditionally-supported -Warn for conditionally-supported (C++11 [intro.defs]) constructs. - -@item -Wno-delete-incomplete @r{(C++ and Objective-C++ only)} -@opindex Wdelete-incomplete -@opindex Wno-delete-incomplete -Do not warn when deleting a pointer to incomplete type, which may cause -undefined behavior at runtime. This warning is enabled by default. - -@item -Wextra-semi @r{(C++, Objective-C++ only)} -@opindex Wextra-semi -@opindex Wno-extra-semi -Warn about redundant semicolons after in-class function definitions. - -@item -Wno-inaccessible-base @r{(C++, Objective-C++ only)} -@opindex Winaccessible-base -@opindex Wno-inaccessible-base -This option controls warnings -when a base class is inaccessible in a class derived from it due to -ambiguity. The warning is enabled by default. -Note that the warning for ambiguous virtual -bases is enabled by the @option{-Wextra} option. -@smallexample -@group -struct A @{ int a; @}; - -struct B : A @{ @}; - -struct C : B, A @{ @}; -@end group -@end smallexample - -@item -Wno-inherited-variadic-ctor -@opindex Winherited-variadic-ctor -@opindex Wno-inherited-variadic-ctor -Suppress warnings about use of C++11 inheriting constructors when the -base class inherited from has a C variadic constructor; the warning is -on by default because the ellipsis is not inherited. - -@item -Wno-invalid-offsetof @r{(C++ and Objective-C++ only)} -@opindex Wno-invalid-offsetof -@opindex Winvalid-offsetof -Suppress warnings from applying the @code{offsetof} macro to a non-POD -type. According to the 2014 ISO C++ standard, applying @code{offsetof} -to a non-standard-layout type is undefined. In existing C++ implementations, -however, @code{offsetof} typically gives meaningful results. -This flag is for users who are aware that they are -writing nonportable code and who have deliberately chosen to ignore the -warning about it. - -The restrictions on @code{offsetof} may be relaxed in a future version -of the C++ standard. - -@item -Wsized-deallocation @r{(C++ and Objective-C++ only)} -@opindex Wsized-deallocation -@opindex Wno-sized-deallocation -Warn about a definition of an unsized deallocation function -@smallexample -void operator delete (void *) noexcept; -void operator delete[] (void *) noexcept; -@end smallexample -without a definition of the corresponding sized deallocation function -@smallexample -void operator delete (void *, std::size_t) noexcept; -void operator delete[] (void *, std::size_t) noexcept; -@end smallexample -or vice versa. Enabled by @option{-Wextra} along with -@option{-fsized-deallocation}. - -@item -Wsuggest-final-types -@opindex Wno-suggest-final-types -@opindex Wsuggest-final-types -Warn about types with virtual methods where code quality would be improved -if the type were declared with the C++11 @code{final} specifier, -or, if possible, -declared in an anonymous namespace. This allows GCC to more aggressively -devirtualize the polymorphic calls. This warning is more effective with -link-time optimization, -where the information about the class hierarchy graph is -more complete. - -@item -Wsuggest-final-methods -@opindex Wno-suggest-final-methods -@opindex Wsuggest-final-methods -Warn about virtual methods where code quality would be improved if the method -were declared with the C++11 @code{final} specifier, -or, if possible, its type were -declared in an anonymous namespace or with the @code{final} specifier. -This warning is -more effective with link-time optimization, where the information about the -class hierarchy graph is more complete. It is recommended to first consider -suggestions of @option{-Wsuggest-final-types} and then rebuild with new -annotations. - -@item -Wsuggest-override -@opindex Wsuggest-override -@opindex Wno-suggest-override -Warn about overriding virtual functions that are not marked with the -@code{override} keyword. - -@item -Wuse-after-free -@itemx -Wuse-after-free=@var{n} -@opindex Wuse-after-free -@opindex Wno-use-after-free -Warn about uses of pointers to dynamically allocated objects that have -been rendered indeterminate by a call to a deallocation function. -The warning is enabled at all optimization levels but may yield different -results with optimization than without. - -@table @gcctabopt -@item -Wuse-after-free=1 -At level 1 the warning attempts to diagnose only unconditional uses -of pointers made indeterminate by a deallocation call or a successful -call to @code{realloc}, regardless of whether or not the call resulted -in an actual reallocatio of memory. This includes double-@code{free} -calls as well as uses in arithmetic and relational expressions. Although -undefined, uses of indeterminate pointers in equality (or inequality) -expressions are not diagnosed at this level. -@item -Wuse-after-free=2 -At level 2, in addition to unconditional uses, the warning also diagnoses -conditional uses of pointers made indeterminate by a deallocation call. -As at level 2, uses in equality (or inequality) expressions are not -diagnosed. For example, the second call to @code{free} in the following -function is diagnosed at this level: -@smallexample -struct A @{ int refcount; void *data; @}; - -void release (struct A *p) -@{ - int refcount = --p->refcount; - free (p); - if (refcount == 0) - free (p->data); // warning: p may be used after free -@} -@end smallexample -@item -Wuse-after-free=3 -At level 3, the warning also diagnoses uses of indeterminate pointers in -equality expressions. All uses of indeterminate pointers are undefined -but equality tests sometimes appear after calls to @code{realloc} as -an attempt to determine whether the call resulted in relocating the object -to a different address. They are diagnosed at a separate level to aid -legacy code gradually transition to safe alternatives. For example, -the equality test in the function below is diagnosed at this level: -@smallexample -void adjust_pointers (int**, int); - -void grow (int **p, int n) -@{ - int **q = (int**)realloc (p, n *= 2); - if (q == p) - return; - adjust_pointers ((int**)q, n); -@} -@end smallexample -To avoid the warning at this level, store offsets into allocated memory -instead of pointers. This approach obviates needing to adjust the stored -pointers after reallocation. -@end table - -@option{-Wuse-after-free=2} is included in @option{-Wall}. - -@item -Wuseless-cast @r{(C++ and Objective-C++ only)} -@opindex Wuseless-cast -@opindex Wno-useless-cast -Warn when an expression is cast to its own type. This warning does not -occur when a class object is converted to a non-reference type as that -is a way to create a temporary: - -@smallexample -struct S @{ @}; -void g (S&&); -void f (S&& arg) -@{ - g (S(arg)); // make arg prvalue so that it can bind to S&& -@} -@end smallexample - -@item -Wno-conversion-null @r{(C++ and Objective-C++ only)} -@opindex Wconversion-null -@opindex Wno-conversion-null -Do not warn for conversions between @code{NULL} and non-pointer -types. @option{-Wconversion-null} is enabled by default. - -@end table - -@node Objective-C and Objective-C++ Dialect Options -@section Options Controlling Objective-C and Objective-C++ Dialects - -@cindex compiler options, Objective-C and Objective-C++ -@cindex Objective-C and Objective-C++ options, command-line -@cindex options, Objective-C and Objective-C++ -(NOTE: This manual does not describe the Objective-C and Objective-C++ -languages themselves. @xref{Standards,,Language Standards -Supported by GCC}, for references.) - -This section describes the command-line options that are only meaningful -for Objective-C and Objective-C++ programs. You can also use most of -the language-independent GNU compiler options. -For example, you might compile a file @file{some_class.m} like this: - -@smallexample -gcc -g -fgnu-runtime -O -c some_class.m -@end smallexample - -@noindent -In this example, @option{-fgnu-runtime} is an option meant only for -Objective-C and Objective-C++ programs; you can use the other options with -any language supported by GCC@. - -Note that since Objective-C is an extension of the C language, Objective-C -compilations may also use options specific to the C front-end (e.g., -@option{-Wtraditional}). Similarly, Objective-C++ compilations may use -C++-specific options (e.g., @option{-Wabi}). - -Here is a list of options that are @emph{only} for compiling Objective-C -and Objective-C++ programs: - -@table @gcctabopt -@item -fconstant-string-class=@var{class-name} -@opindex fconstant-string-class -Use @var{class-name} as the name of the class to instantiate for each -literal string specified with the syntax @code{@@"@dots{}"}. The default -class name is @code{NXConstantString} if the GNU runtime is being used, and -@code{NSConstantString} if the NeXT runtime is being used (see below). The -@option{-fconstant-cfstrings} option, if also present, overrides the -@option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals -to be laid out as constant CoreFoundation strings. - -@item -fgnu-runtime -@opindex fgnu-runtime -Generate object code compatible with the standard GNU Objective-C -runtime. This is the default for most types of systems. - -@item -fnext-runtime -@opindex fnext-runtime -Generate output compatible with the NeXT runtime. This is the default -for NeXT-based systems, including Darwin and Mac OS X@. The macro -@code{__NEXT_RUNTIME__} is predefined if (and only if) this option is -used. - -@item -fno-nil-receivers -@opindex fno-nil-receivers -@opindex fnil-receivers -Assume that all Objective-C message dispatches (@code{[receiver -message:arg]}) in this translation unit ensure that the receiver is -not @code{nil}. This allows for more efficient entry points in the -runtime to be used. This option is only available in conjunction with -the NeXT runtime and ABI version 0 or 1. - -@item -fobjc-abi-version=@var{n} -@opindex fobjc-abi-version -Use version @var{n} of the Objective-C ABI for the selected runtime. -This option is currently supported only for the NeXT runtime. In that -case, Version 0 is the traditional (32-bit) ABI without support for -properties and other Objective-C 2.0 additions. Version 1 is the -traditional (32-bit) ABI with support for properties and other -Objective-C 2.0 additions. Version 2 is the modern (64-bit) ABI. If -nothing is specified, the default is Version 0 on 32-bit target -machines, and Version 2 on 64-bit target machines. - -@item -fobjc-call-cxx-cdtors -@opindex fobjc-call-cxx-cdtors -For each Objective-C class, check if any of its instance variables is a -C++ object with a non-trivial default constructor. If so, synthesize a -special @code{- (id) .cxx_construct} instance method which runs -non-trivial default constructors on any such instance variables, in order, -and then return @code{self}. Similarly, check if any instance variable -is a C++ object with a non-trivial destructor, and if so, synthesize a -special @code{- (void) .cxx_destruct} method which runs -all such default destructors, in reverse order. - -The @code{- (id) .cxx_construct} and @code{- (void) .cxx_destruct} -methods thusly generated only operate on instance variables -declared in the current Objective-C class, and not those inherited -from superclasses. It is the responsibility of the Objective-C -runtime to invoke all such methods in an object's inheritance -hierarchy. The @code{- (id) .cxx_construct} methods are invoked -by the runtime immediately after a new object instance is allocated; -the @code{- (void) .cxx_destruct} methods are invoked immediately -before the runtime deallocates an object instance. - -As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has -support for invoking the @code{- (id) .cxx_construct} and -@code{- (void) .cxx_destruct} methods. - -@item -fobjc-direct-dispatch -@opindex fobjc-direct-dispatch -Allow fast jumps to the message dispatcher. On Darwin this is -accomplished via the comm page. - -@item -fobjc-exceptions -@opindex fobjc-exceptions -Enable syntactic support for structured exception handling in -Objective-C, similar to what is offered by C++. This option -is required to use the Objective-C keywords @code{@@try}, -@code{@@throw}, @code{@@catch}, @code{@@finally} and -@code{@@synchronized}. This option is available with both the GNU -runtime and the NeXT runtime (but not available in conjunction with -the NeXT runtime on Mac OS X 10.2 and earlier). - -@item -fobjc-gc -@opindex fobjc-gc -Enable garbage collection (GC) in Objective-C and Objective-C++ -programs. This option is only available with the NeXT runtime; the -GNU runtime has a different garbage collection implementation that -does not require special compiler flags. - -@item -fobjc-nilcheck -@opindex fobjc-nilcheck -For the NeXT runtime with version 2 of the ABI, check for a nil -receiver in method invocations before doing the actual method call. -This is the default and can be disabled using -@option{-fno-objc-nilcheck}. Class methods and super calls are never -checked for nil in this way no matter what this flag is set to. -Currently this flag does nothing when the GNU runtime, or an older -version of the NeXT runtime ABI, is used. - -@item -fobjc-std=objc1 -@opindex fobjc-std -Conform to the language syntax of Objective-C 1.0, the language -recognized by GCC 4.0. This only affects the Objective-C additions to -the C/C++ language; it does not affect conformance to C/C++ standards, -which is controlled by the separate C/C++ dialect option flags. When -this option is used with the Objective-C or Objective-C++ compiler, -any Objective-C syntax that is not recognized by GCC 4.0 is rejected. -This is useful if you need to make sure that your Objective-C code can -be compiled with older versions of GCC@. - -@item -freplace-objc-classes -@opindex freplace-objc-classes -Emit a special marker instructing @command{ld(1)} not to statically link in -the resulting object file, and allow @command{dyld(1)} to load it in at -run time instead. This is used in conjunction with the Fix-and-Continue -debugging mode, where the object file in question may be recompiled and -dynamically reloaded in the course of program execution, without the need -to restart the program itself. Currently, Fix-and-Continue functionality -is only available in conjunction with the NeXT runtime on Mac OS X 10.3 -and later. - -@item -fzero-link -@opindex fzero-link -When compiling for the NeXT runtime, the compiler ordinarily replaces calls -to @code{objc_getClass("@dots{}")} (when the name of the class is known at -compile time) with static class references that get initialized at load time, -which improves run-time performance. Specifying the @option{-fzero-link} flag -suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")} -to be retained. This is useful in Zero-Link debugging mode, since it allows -for individual class implementations to be modified during program execution. -The GNU runtime currently always retains calls to @code{objc_get_class("@dots{}")} -regardless of command-line options. - -@item -fno-local-ivars -@opindex fno-local-ivars -@opindex flocal-ivars -By default instance variables in Objective-C can be accessed as if -they were local variables from within the methods of the class they're -declared in. This can lead to shadowing between instance variables -and other variables declared either locally inside a class method or -globally with the same name. Specifying the @option{-fno-local-ivars} -flag disables this behavior thus avoiding variable shadowing issues. - -@item -fivar-visibility=@r{[}public@r{|}protected@r{|}private@r{|}package@r{]} -@opindex fivar-visibility -Set the default instance variable visibility to the specified option -so that instance variables declared outside the scope of any access -modifier directives default to the specified visibility. - -@item -gen-decls -@opindex gen-decls -Dump interface declarations for all classes seen in the source file to a -file named @file{@var{sourcename}.decl}. - -@item -Wassign-intercept @r{(Objective-C and Objective-C++ only)} -@opindex Wassign-intercept -@opindex Wno-assign-intercept -Warn whenever an Objective-C assignment is being intercepted by the -garbage collector. - -@item -Wno-property-assign-default @r{(Objective-C and Objective-C++ only)} -@opindex Wproperty-assign-default -@opindex Wno-property-assign-default -Do not warn if a property for an Objective-C object has no assign -semantics specified. - -@item -Wno-protocol @r{(Objective-C and Objective-C++ only)} -@opindex Wno-protocol -@opindex Wprotocol -If a class is declared to implement a protocol, a warning is issued for -every method in the protocol that is not implemented by the class. The -default behavior is to issue a warning for every method not explicitly -implemented in the class, even if a method implementation is inherited -from the superclass. If you use the @option{-Wno-protocol} option, then -methods inherited from the superclass are considered to be implemented, -and no warning is issued for them. - -@item -Wobjc-root-class @r{(Objective-C and Objective-C++ only)} -@opindex Wobjc-root-class -Warn if a class interface lacks a superclass. Most classes will inherit -from @code{NSObject} (or @code{Object}) for example. When declaring -classes intended to be root classes, the warning can be suppressed by -marking their interfaces with @code{__attribute__((objc_root_class))}. - -@item -Wselector @r{(Objective-C and Objective-C++ only)} -@opindex Wselector -@opindex Wno-selector -Warn if multiple methods of different types for the same selector are -found during compilation. The check is performed on the list of methods -in the final stage of compilation. Additionally, a check is performed -for each selector appearing in a @code{@@selector(@dots{})} -expression, and a corresponding method for that selector has been found -during compilation. Because these checks scan the method table only at -the end of compilation, these warnings are not produced if the final -stage of compilation is not reached, for example because an error is -found during compilation, or because the @option{-fsyntax-only} option is -being used. - -@item -Wstrict-selector-match @r{(Objective-C and Objective-C++ only)} -@opindex Wstrict-selector-match -@opindex Wno-strict-selector-match -Warn if multiple methods with differing argument and/or return types are -found for a given selector when attempting to send a message using this -selector to a receiver of type @code{id} or @code{Class}. When this flag -is off (which is the default behavior), the compiler omits such warnings -if any differences found are confined to types that share the same size -and alignment. - -@item -Wundeclared-selector @r{(Objective-C and Objective-C++ only)} -@opindex Wundeclared-selector -@opindex Wno-undeclared-selector -Warn if a @code{@@selector(@dots{})} expression referring to an -undeclared selector is found. A selector is considered undeclared if no -method with that name has been declared before the -@code{@@selector(@dots{})} expression, either explicitly in an -@code{@@interface} or @code{@@protocol} declaration, or implicitly in -an @code{@@implementation} section. This option always performs its -checks as soon as a @code{@@selector(@dots{})} expression is found, -while @option{-Wselector} only performs its checks in the final stage of -compilation. This also enforces the coding style convention -that methods and selectors must be declared before being used. - -@item -print-objc-runtime-info -@opindex print-objc-runtime-info -Generate C header describing the largest structure that is passed by -value, if any. - -@end table - -@node Diagnostic Message Formatting Options -@section Options to Control Diagnostic Messages Formatting -@cindex options to control diagnostics formatting -@cindex diagnostic messages -@cindex message formatting - -Traditionally, diagnostic messages have been formatted irrespective of -the output device's aspect (e.g.@: its width, @dots{}). You can use the -options described below -to control the formatting algorithm for diagnostic messages, -e.g.@: how many characters per line, how often source location -information should be reported. Note that some language front ends may not -honor these options. - -@table @gcctabopt -@item -fmessage-length=@var{n} -@opindex fmessage-length -Try to format error messages so that they fit on lines of about -@var{n} characters. If @var{n} is zero, then no line-wrapping is -done; each error message appears on a single line. This is the -default for all front ends. - -Note - this option also affects the display of the @samp{#error} and -@samp{#warning} pre-processor directives, and the @samp{deprecated} -function/type/variable attribute. It does not however affect the -@samp{pragma GCC warning} and @samp{pragma GCC error} pragmas. - -@item -fdiagnostics-plain-output -This option requests that diagnostic output look as plain as possible, which -may be useful when running @command{dejagnu} or other utilities that need to -parse diagnostics output and prefer that it remain more stable over time. -@option{-fdiagnostics-plain-output} is currently equivalent to the following -options: -@gccoptlist{-fno-diagnostics-show-caret @gol --fno-diagnostics-show-line-numbers @gol --fdiagnostics-color=never @gol --fdiagnostics-urls=never @gol --fdiagnostics-path-format=separate-events} -In the future, if GCC changes the default appearance of its diagnostics, the -corresponding option to disable the new behavior will be added to this list. - -@item -fdiagnostics-show-location=once -@opindex fdiagnostics-show-location -Only meaningful in line-wrapping mode. Instructs the diagnostic messages -reporter to emit source location information @emph{once}; that is, in -case the message is too long to fit on a single physical line and has to -be wrapped, the source location won't be emitted (as prefix) again, -over and over, in subsequent continuation lines. This is the default -behavior. - -@item -fdiagnostics-show-location=every-line -Only meaningful in line-wrapping mode. Instructs the diagnostic -messages reporter to emit the same source location information (as -prefix) for physical lines that result from the process of breaking -a message which is too long to fit on a single line. - -@item -fdiagnostics-color[=@var{WHEN}] -@itemx -fno-diagnostics-color -@opindex fdiagnostics-color -@cindex highlight, color -@vindex GCC_COLORS @r{environment variable} -Use color in diagnostics. @var{WHEN} is @samp{never}, @samp{always}, -or @samp{auto}. The default depends on how the compiler has been configured, -it can be any of the above @var{WHEN} options or also @samp{never} -if @env{GCC_COLORS} environment variable isn't present in the environment, -and @samp{auto} otherwise. -@samp{auto} makes GCC use color only when the standard error is a terminal, -and when not executing in an emacs shell. -The forms @option{-fdiagnostics-color} and @option{-fno-diagnostics-color} are -aliases for @option{-fdiagnostics-color=always} and -@option{-fdiagnostics-color=never}, respectively. - -The colors are defined by the environment variable @env{GCC_COLORS}. -Its value is a colon-separated list of capabilities and Select Graphic -Rendition (SGR) substrings. SGR commands are interpreted by the -terminal or terminal emulator. (See the section in the documentation -of your text terminal for permitted values and their meanings as -character attributes.) These substring values are integers in decimal -representation and can be concatenated with semicolons. -Common values to concatenate include -@samp{1} for bold, -@samp{4} for underline, -@samp{5} for blink, -@samp{7} for inverse, -@samp{39} for default foreground color, -@samp{30} to @samp{37} for foreground colors, -@samp{90} to @samp{97} for 16-color mode foreground colors, -@samp{38;5;0} to @samp{38;5;255} -for 88-color and 256-color modes foreground colors, -@samp{49} for default background color, -@samp{40} to @samp{47} for background colors, -@samp{100} to @samp{107} for 16-color mode background colors, -and @samp{48;5;0} to @samp{48;5;255} -for 88-color and 256-color modes background colors. - -The default @env{GCC_COLORS} is -@smallexample -error=01;31:warning=01;35:note=01;36:range1=32:range2=34:locus=01:\ -quote=01:path=01;36:fixit-insert=32:fixit-delete=31:\ -diff-filename=01:diff-hunk=32:diff-delete=31:diff-insert=32:\ -type-diff=01;32:fnname=01;32:targs=35 -@end smallexample -@noindent -where @samp{01;31} is bold red, @samp{01;35} is bold magenta, -@samp{01;36} is bold cyan, @samp{32} is green, @samp{34} is blue, -@samp{01} is bold, and @samp{31} is red. -Setting @env{GCC_COLORS} to the empty string disables colors. -Supported capabilities are as follows. - -@table @code -@item error= -@vindex error GCC_COLORS @r{capability} -SGR substring for error: markers. - -@item warning= -@vindex warning GCC_COLORS @r{capability} -SGR substring for warning: markers. - -@item note= -@vindex note GCC_COLORS @r{capability} -SGR substring for note: markers. - -@item path= -@vindex path GCC_COLORS @r{capability} -SGR substring for colorizing paths of control-flow events as printed -via @option{-fdiagnostics-path-format=}, such as the identifiers of -individual events and lines indicating interprocedural calls and returns. - -@item range1= -@vindex range1 GCC_COLORS @r{capability} -SGR substring for first additional range. - -@item range2= -@vindex range2 GCC_COLORS @r{capability} -SGR substring for second additional range. - -@item locus= -@vindex locus GCC_COLORS @r{capability} -SGR substring for location information, @samp{file:line} or -@samp{file:line:column} etc. - -@item quote= -@vindex quote GCC_COLORS @r{capability} -SGR substring for information printed within quotes. - -@item fnname= -@vindex fnname GCC_COLORS @r{capability} -SGR substring for names of C++ functions. - -@item targs= -@vindex targs GCC_COLORS @r{capability} -SGR substring for C++ function template parameter bindings. - -@item fixit-insert= -@vindex fixit-insert GCC_COLORS @r{capability} -SGR substring for fix-it hints suggesting text to -be inserted or replaced. - -@item fixit-delete= -@vindex fixit-delete GCC_COLORS @r{capability} -SGR substring for fix-it hints suggesting text to -be deleted. - -@item diff-filename= -@vindex diff-filename GCC_COLORS @r{capability} -SGR substring for filename headers within generated patches. - -@item diff-hunk= -@vindex diff-hunk GCC_COLORS @r{capability} -SGR substring for the starts of hunks within generated patches. - -@item diff-delete= -@vindex diff-delete GCC_COLORS @r{capability} -SGR substring for deleted lines within generated patches. - -@item diff-insert= -@vindex diff-insert GCC_COLORS @r{capability} -SGR substring for inserted lines within generated patches. - -@item type-diff= -@vindex type-diff GCC_COLORS @r{capability} -SGR substring for highlighting mismatching types within template -arguments in the C++ frontend. -@end table - -@item -fdiagnostics-urls[=@var{WHEN}] -@opindex fdiagnostics-urls -@cindex urls -@vindex GCC_URLS @r{environment variable} -@vindex TERM_URLS @r{environment variable} -Use escape sequences to embed URLs in diagnostics. For example, when -@option{-fdiagnostics-show-option} emits text showing the command-line -option controlling a diagnostic, embed a URL for documentation of that -option. - -@var{WHEN} is @samp{never}, @samp{always}, or @samp{auto}. -@samp{auto} makes GCC use URL escape sequences only when the standard error -is a terminal, and when not executing in an emacs shell or any graphical -terminal which is known to be incompatible with this feature, see below. - -The default depends on how the compiler has been configured. -It can be any of the above @var{WHEN} options. - -GCC can also be configured (via the -@option{--with-diagnostics-urls=auto-if-env} configure-time option) -so that the default is affected by environment variables. -Under such a configuration, GCC defaults to using @samp{auto} -if either @env{GCC_URLS} or @env{TERM_URLS} environment variables are -present and non-empty in the environment of the compiler, or @samp{never} -if neither are. - -However, even with @option{-fdiagnostics-urls=always} the behavior is -dependent on those environment variables: -If @env{GCC_URLS} is set to empty or @samp{no}, do not embed URLs in -diagnostics. If set to @samp{st}, URLs use ST escape sequences. -If set to @samp{bel}, the default, URLs use BEL escape sequences. -Any other non-empty value enables the feature. -If @env{GCC_URLS} is not set, use @env{TERM_URLS} as a fallback. -Note: ST is an ANSI escape sequence, string terminator @samp{ESC \}, -BEL is an ASCII character, CTRL-G that usually sounds like a beep. - -At this time GCC tries to detect also a few terminals that are known to -not implement the URL feature, and have bugs or at least had bugs in -some versions that are still in use, where the URL escapes are likely -to misbehave, i.e. print garbage on the screen. -That list is currently xfce4-terminal, certain known to be buggy -gnome-terminal versions, the linux console, and mingw. -This check can be skipped with the @option{-fdiagnostics-urls=always}. - -@item -fno-diagnostics-show-option -@opindex fno-diagnostics-show-option -@opindex fdiagnostics-show-option -By default, each diagnostic emitted includes text indicating the -command-line option that directly controls the diagnostic (if such an -option is known to the diagnostic machinery). Specifying the -@option{-fno-diagnostics-show-option} flag suppresses that behavior. - -@item -fno-diagnostics-show-caret -@opindex fno-diagnostics-show-caret -@opindex fdiagnostics-show-caret -By default, each diagnostic emitted includes the original source line -and a caret @samp{^} indicating the column. This option suppresses this -information. The source line is truncated to @var{n} characters, if -the @option{-fmessage-length=n} option is given. When the output is done -to the terminal, the width is limited to the width given by the -@env{COLUMNS} environment variable or, if not set, to the terminal width. - -@item -fno-diagnostics-show-labels -@opindex fno-diagnostics-show-labels -@opindex fdiagnostics-show-labels -By default, when printing source code (via @option{-fdiagnostics-show-caret}), -diagnostics can label ranges of source code with pertinent information, such -as the types of expressions: - -@smallexample - printf ("foo %s bar", long_i + long_j); - ~^ ~~~~~~~~~~~~~~~ - | | - char * long int -@end smallexample - -This option suppresses the printing of these labels (in the example above, -the vertical bars and the ``char *'' and ``long int'' text). - -@item -fno-diagnostics-show-cwe -@opindex fno-diagnostics-show-cwe -@opindex fdiagnostics-show-cwe -Diagnostic messages can optionally have an associated -@uref{https://cwe.mitre.org/index.html, CWE} identifier. -GCC itself only provides such metadata for some of the @option{-fanalyzer} -diagnostics. GCC plugins may also provide diagnostics with such metadata. -By default, if this information is present, it will be printed with -the diagnostic. This option suppresses the printing of this metadata. - -@item -fno-diagnostics-show-rules -@opindex fno-diagnostics-show-rules -@opindex fdiagnostics-show-rules -Diagnostic messages can optionally have rules associated with them, such -as from a coding standard, or a specification. -GCC itself does not do this for any of its diagnostics, but plugins may do so. -By default, if this information is present, it will be printed with -the diagnostic. This option suppresses the printing of this metadata. - -@item -fno-diagnostics-show-line-numbers -@opindex fno-diagnostics-show-line-numbers -@opindex fdiagnostics-show-line-numbers -By default, when printing source code (via @option{-fdiagnostics-show-caret}), -a left margin is printed, showing line numbers. This option suppresses this -left margin. - -@item -fdiagnostics-minimum-margin-width=@var{width} -@opindex fdiagnostics-minimum-margin-width -This option controls the minimum width of the left margin printed by -@option{-fdiagnostics-show-line-numbers}. It defaults to 6. - -@item -fdiagnostics-parseable-fixits -@opindex fdiagnostics-parseable-fixits -Emit fix-it hints in a machine-parseable format, suitable for consumption -by IDEs. For each fix-it, a line will be printed after the relevant -diagnostic, starting with the string ``fix-it:''. For example: - -@smallexample -fix-it:"test.c":@{45:3-45:21@}:"gtk_widget_show_all" -@end smallexample - -The location is expressed as a half-open range, expressed as a count of -bytes, starting at byte 1 for the initial column. In the above example, -bytes 3 through 20 of line 45 of ``test.c'' are to be replaced with the -given string: - -@smallexample -00000000011111111112222222222 -12345678901234567890123456789 - gtk_widget_showall (dlg); - ^^^^^^^^^^^^^^^^^^ - gtk_widget_show_all -@end smallexample - -The filename and replacement string escape backslash as ``\\", tab as ``\t'', -newline as ``\n'', double quotes as ``\"'', non-printable characters as octal -(e.g. vertical tab as ``\013''). - -An empty replacement string indicates that the given range is to be removed. -An empty range (e.g. ``45:3-45:3'') indicates that the string is to -be inserted at the given position. - -@item -fdiagnostics-generate-patch -@opindex fdiagnostics-generate-patch -Print fix-it hints to stderr in unified diff format, after any diagnostics -are printed. For example: - -@smallexample ---- test.c -+++ test.c -@@ -42,5 +42,5 @@ - - void show_cb(GtkDialog *dlg) - @{ -- gtk_widget_showall(dlg); -+ gtk_widget_show_all(dlg); - @} - -@end smallexample - -The diff may or may not be colorized, following the same rules -as for diagnostics (see @option{-fdiagnostics-color}). - -@item -fdiagnostics-show-template-tree -@opindex fdiagnostics-show-template-tree - -In the C++ frontend, when printing diagnostics showing mismatching -template types, such as: - -@smallexample - could not convert 'std::map<int, std::vector<double> >()' - from 'map<[...],vector<double>>' to 'map<[...],vector<float>> -@end smallexample - -the @option{-fdiagnostics-show-template-tree} flag enables printing a -tree-like structure showing the common and differing parts of the types, -such as: - -@smallexample - map< - [...], - vector< - [double != float]>> -@end smallexample - -The parts that differ are highlighted with color (``double'' and -``float'' in this case). - -@item -fno-elide-type -@opindex fno-elide-type -@opindex felide-type -By default when the C++ frontend prints diagnostics showing mismatching -template types, common parts of the types are printed as ``[...]'' to -simplify the error message. For example: - -@smallexample - could not convert 'std::map<int, std::vector<double> >()' - from 'map<[...],vector<double>>' to 'map<[...],vector<float>> -@end smallexample - -Specifying the @option{-fno-elide-type} flag suppresses that behavior. -This flag also affects the output of the -@option{-fdiagnostics-show-template-tree} flag. - -@item -fdiagnostics-path-format=@var{KIND} -@opindex fdiagnostics-path-format -Specify how to print paths of control-flow events for diagnostics that -have such a path associated with them. - -@var{KIND} is @samp{none}, @samp{separate-events}, or @samp{inline-events}, -the default. - -@samp{none} means to not print diagnostic paths. - -@samp{separate-events} means to print a separate ``note'' diagnostic for -each event within the diagnostic. For example: - -@smallexample -test.c:29:5: error: passing NULL as argument 1 to 'PyList_Append' which requires a non-NULL parameter -test.c:25:10: note: (1) when 'PyList_New' fails, returning NULL -test.c:27:3: note: (2) when 'i < count' -test.c:29:5: note: (3) when calling 'PyList_Append', passing NULL from (1) as argument 1 -@end smallexample - -@samp{inline-events} means to print the events ``inline'' within the source -code. This view attempts to consolidate the events into runs of -sufficiently-close events, printing them as labelled ranges within the source. - -For example, the same events as above might be printed as: - -@smallexample - 'test': events 1-3 - | - | 25 | list = PyList_New(0); - | | ^~~~~~~~~~~~~ - | | | - | | (1) when 'PyList_New' fails, returning NULL - | 26 | - | 27 | for (i = 0; i < count; i++) @{ - | | ~~~ - | | | - | | (2) when 'i < count' - | 28 | item = PyLong_FromLong(random()); - | 29 | PyList_Append(list, item); - | | ~~~~~~~~~~~~~~~~~~~~~~~~~ - | | | - | | (3) when calling 'PyList_Append', passing NULL from (1) as argument 1 - | -@end smallexample - -Interprocedural control flow is shown by grouping the events by stack frame, -and using indentation to show how stack frames are nested, pushed, and popped. - -For example: - -@smallexample - 'test': events 1-2 - | - | 133 | @{ - | | ^ - | | | - | | (1) entering 'test' - | 134 | boxed_int *obj = make_boxed_int (i); - | | ~~~~~~~~~~~~~~~~~~ - | | | - | | (2) calling 'make_boxed_int' - | - +--> 'make_boxed_int': events 3-4 - | - | 120 | @{ - | | ^ - | | | - | | (3) entering 'make_boxed_int' - | 121 | boxed_int *result = (boxed_int *)wrapped_malloc (sizeof (boxed_int)); - | | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - | | | - | | (4) calling 'wrapped_malloc' - | - +--> 'wrapped_malloc': events 5-6 - | - | 7 | @{ - | | ^ - | | | - | | (5) entering 'wrapped_malloc' - | 8 | return malloc (size); - | | ~~~~~~~~~~~~~ - | | | - | | (6) calling 'malloc' - | - <-------------+ - | - 'test': event 7 - | - | 138 | free_boxed_int (obj); - | | ^~~~~~~~~~~~~~~~~~~~ - | | | - | | (7) calling 'free_boxed_int' - | -(etc) -@end smallexample - -@item -fdiagnostics-show-path-depths -@opindex fdiagnostics-show-path-depths -This option provides additional information when printing control-flow paths -associated with a diagnostic. - -If this is option is provided then the stack depth will be printed for -each run of events within @option{-fdiagnostics-path-format=inline-events}. -If provided with @option{-fdiagnostics-path-format=separate-events}, then -the stack depth and function declaration will be appended when printing -each event. - -This is intended for use by GCC developers and plugin developers when -debugging diagnostics that report interprocedural control flow. - -@item -fno-show-column -@opindex fno-show-column -@opindex fshow-column -Do not print column numbers in diagnostics. This may be necessary if -diagnostics are being scanned by a program that does not understand the -column numbers, such as @command{dejagnu}. - -@item -fdiagnostics-column-unit=@var{UNIT} -@opindex fdiagnostics-column-unit -Select the units for the column number. This affects traditional diagnostics -(in the absence of @option{-fno-show-column}), as well as JSON format -diagnostics if requested. - -The default @var{UNIT}, @samp{display}, considers the number of display -columns occupied by each character. This may be larger than the number -of bytes required to encode the character, in the case of tab -characters, or it may be smaller, in the case of multibyte characters. -For example, the character ``GREEK SMALL LETTER PI (U+03C0)'' occupies one -display column, and its UTF-8 encoding requires two bytes; the character -``SLIGHTLY SMILING FACE (U+1F642)'' occupies two display columns, and -its UTF-8 encoding requires four bytes. - -Setting @var{UNIT} to @samp{byte} changes the column number to the raw byte -count in all cases, as was traditionally output by GCC prior to version 11.1.0. - -@item -fdiagnostics-column-origin=@var{ORIGIN} -@opindex fdiagnostics-column-origin -Select the origin for column numbers, i.e. the column number assigned to the -first column. The default value of 1 corresponds to traditional GCC -behavior and to the GNU style guide. Some utilities may perform better with an -origin of 0; any non-negative value may be specified. - -@item -fdiagnostics-escape-format=@var{FORMAT} -@opindex fdiagnostics-escape-format -When GCC prints pertinent source lines for a diagnostic it normally attempts -to print the source bytes directly. However, some diagnostics relate to encoding -issues in the source file, such as malformed UTF-8, or issues with Unicode -normalization. These diagnostics are flagged so that GCC will escape bytes -that are not printable ASCII when printing their pertinent source lines. - -This option controls how such bytes should be escaped. - -The default @var{FORMAT}, @samp{unicode} displays Unicode characters that -are not printable ASCII in the form @samp{<U+XXXX>}, and bytes that do not -correspond to a Unicode character validly-encoded in UTF-8-encoded will be -displayed as hexadecimal in the form @samp{<XX>}. - -For example, a source line containing the string @samp{before} followed by the -Unicode character U+03C0 (``GREEK SMALL LETTER PI'', with UTF-8 encoding -0xCF 0x80) followed by the byte 0xBF (a stray UTF-8 trailing byte), followed by -the string @samp{after} will be printed for such a diagnostic as: - -@smallexample - before<U+03C0><BF>after -@end smallexample - -Setting @var{FORMAT} to @samp{bytes} will display all non-printable-ASCII bytes -in the form @samp{<XX>}, thus showing the underlying encoding of non-ASCII -Unicode characters. For the example above, the following will be printed: - -@smallexample - before<CF><80><BF>after -@end smallexample - -@item -fdiagnostics-format=@var{FORMAT} -@opindex fdiagnostics-format -Select a different format for printing diagnostics. -@var{FORMAT} is @samp{text}, @samp{sarif-stderr}, @samp{sarif-file}, -@samp{json}, @samp{json-stderr}, or @samp{json-file}. - -The default is @samp{text}. - -The @samp{sarif-stderr} and @samp{sarif-file} formats both emit -diagnostics in SARIF Version 2.1.0 format, either to stderr, or to a file -named @file{@var{source}.sarif}, respectively. - -The @samp{json} format is a synonym for @samp{json-stderr}. -The @samp{json-stderr} and @samp{json-file} formats are identical, apart from -where the JSON is emitted to - with the former, the JSON is emitted to stderr, -whereas with @samp{json-file} it is written to @file{@var{source}.gcc.json}. - -The emitted JSON consists of a top-level JSON array containing JSON objects -representing the diagnostics. The JSON is emitted as one line, without -formatting; the examples below have been formatted for clarity. - -Diagnostics can have child diagnostics. For example, this error and note: - -@smallexample -misleading-indentation.c:15:3: warning: this 'if' clause does not - guard... [-Wmisleading-indentation] - 15 | if (flag) - | ^~ -misleading-indentation.c:17:5: note: ...this statement, but the latter - is misleadingly indented as if it were guarded by the 'if' - 17 | y = 2; - | ^ -@end smallexample - -@noindent -might be printed in JSON form (after formatting) like this: - -@smallexample -[ - @{ - "kind": "warning", - "locations": [ - @{ - "caret": @{ - "display-column": 3, - "byte-column": 3, - "column": 3, - "file": "misleading-indentation.c", - "line": 15 - @}, - "finish": @{ - "display-column": 4, - "byte-column": 4, - "column": 4, - "file": "misleading-indentation.c", - "line": 15 - @} - @} - ], - "message": "this \u2018if\u2019 clause does not guard...", - "option": "-Wmisleading-indentation", - "option_url": "https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wmisleading-indentation", - "children": [ - @{ - "kind": "note", - "locations": [ - @{ - "caret": @{ - "display-column": 5, - "byte-column": 5, - "column": 5, - "file": "misleading-indentation.c", - "line": 17 - @} - @} - ], - "escape-source": false, - "message": "...this statement, but the latter is @dots{}" - @} - ] - "escape-source": false, - "column-origin": 1, - @} -] -@end smallexample - -@noindent -where the @code{note} is a child of the @code{warning}. - -A diagnostic has a @code{kind}. If this is @code{warning}, then there is -an @code{option} key describing the command-line option controlling the -warning. - -A diagnostic can contain zero or more locations. Each location has an -optional @code{label} string and up to three positions within it: a -@code{caret} position and optional @code{start} and @code{finish} positions. -A position is described by a @code{file} name, a @code{line} number, and -three numbers indicating a column position: -@itemize @bullet - -@item -@code{display-column} counts display columns, accounting for tabs and -multibyte characters. - -@item -@code{byte-column} counts raw bytes. - -@item -@code{column} is equal to one of -the previous two, as dictated by the @option{-fdiagnostics-column-unit} -option. - -@end itemize -All three columns are relative to the origin specified by -@option{-fdiagnostics-column-origin}, which is typically equal to 1 but may -be set, for instance, to 0 for compatibility with other utilities that -number columns from 0. The column origin is recorded in the JSON output in -the @code{column-origin} tag. In the remaining examples below, the extra -column number outputs have been omitted for brevity. - -For example, this error: - -@smallexample -bad-binary-ops.c:64:23: error: invalid operands to binary + (have 'S' @{aka - 'struct s'@} and 'T' @{aka 'struct t'@}) - 64 | return callee_4a () + callee_4b (); - | ~~~~~~~~~~~~ ^ ~~~~~~~~~~~~ - | | | - | | T @{aka struct t@} - | S @{aka struct s@} -@end smallexample - -@noindent -has three locations. Its primary location is at the ``+'' token at column -23. It has two secondary locations, describing the left and right-hand sides -of the expression, which have labels. It might be printed in JSON form as: - -@smallexample - @{ - "children": [], - "kind": "error", - "locations": [ - @{ - "caret": @{ - "column": 23, "file": "bad-binary-ops.c", "line": 64 - @} - @}, - @{ - "caret": @{ - "column": 10, "file": "bad-binary-ops.c", "line": 64 - @}, - "finish": @{ - "column": 21, "file": "bad-binary-ops.c", "line": 64 - @}, - "label": "S @{aka struct s@}" - @}, - @{ - "caret": @{ - "column": 25, "file": "bad-binary-ops.c", "line": 64 - @}, - "finish": @{ - "column": 36, "file": "bad-binary-ops.c", "line": 64 - @}, - "label": "T @{aka struct t@}" - @} - ], - "escape-source": false, - "message": "invalid operands to binary + @dots{}" - @} -@end smallexample - -If a diagnostic contains fix-it hints, it has a @code{fixits} array, -consisting of half-open intervals, similar to the output of -@option{-fdiagnostics-parseable-fixits}. For example, this diagnostic -with a replacement fix-it hint: - -@smallexample -demo.c:8:15: error: 'struct s' has no member named 'colour'; did you - mean 'color'? - 8 | return ptr->colour; - | ^~~~~~ - | color -@end smallexample - -@noindent -might be printed in JSON form as: - -@smallexample - @{ - "children": [], - "fixits": [ - @{ - "next": @{ - "column": 21, - "file": "demo.c", - "line": 8 - @}, - "start": @{ - "column": 15, - "file": "demo.c", - "line": 8 - @}, - "string": "color" - @} - ], - "kind": "error", - "locations": [ - @{ - "caret": @{ - "column": 15, - "file": "demo.c", - "line": 8 - @}, - "finish": @{ - "column": 20, - "file": "demo.c", - "line": 8 - @} - @} - ], - "escape-source": false, - "message": "\u2018struct s\u2019 has no member named @dots{}" - @} -@end smallexample - -@noindent -where the fix-it hint suggests replacing the text from @code{start} up -to but not including @code{next} with @code{string}'s value. Deletions -are expressed via an empty value for @code{string}, insertions by -having @code{start} equal @code{next}. - -If the diagnostic has a path of control-flow events associated with it, -it has a @code{path} array of objects representing the events. Each -event object has a @code{description} string, a @code{location} object, -along with a @code{function} string and a @code{depth} number for -representing interprocedural paths. The @code{function} represents the -current function at that event, and the @code{depth} represents the -stack depth relative to some baseline: the higher, the more frames are -within the stack. - -For example, the intraprocedural example shown for -@option{-fdiagnostics-path-format=} might have this JSON for its path: - -@smallexample - "path": [ - @{ - "depth": 0, - "description": "when 'PyList_New' fails, returning NULL", - "function": "test", - "location": @{ - "column": 10, - "file": "test.c", - "line": 25 - @} - @}, - @{ - "depth": 0, - "description": "when 'i < count'", - "function": "test", - "location": @{ - "column": 3, - "file": "test.c", - "line": 27 - @} - @}, - @{ - "depth": 0, - "description": "when calling 'PyList_Append', passing NULL from (1) as argument 1", - "function": "test", - "location": @{ - "column": 5, - "file": "test.c", - "line": 29 - @} - @} - ] -@end smallexample - -Diagnostics have a boolean attribute @code{escape-source}, hinting whether -non-ASCII bytes should be escaped when printing the pertinent lines of -source code (@code{true} for diagnostics involving source encoding issues). - -@end table - -@node Warning Options -@section Options to Request or Suppress Warnings -@cindex options to control warnings -@cindex warning messages -@cindex messages, warning -@cindex suppressing warnings - -Warnings are diagnostic messages that report constructions that -are not inherently erroneous but that are risky or suggest there -may have been an error. - -The following language-independent options do not enable specific -warnings but control the kinds of diagnostics produced by GCC@. - -@table @gcctabopt -@cindex syntax checking -@item -fsyntax-only -@opindex fsyntax-only -Check the code for syntax errors, but don't do anything beyond that. - -@item -fmax-errors=@var{n} -@opindex fmax-errors -Limits the maximum number of error messages to @var{n}, at which point -GCC bails out rather than attempting to continue processing the source -code. If @var{n} is 0 (the default), there is no limit on the number -of error messages produced. If @option{-Wfatal-errors} is also -specified, then @option{-Wfatal-errors} takes precedence over this -option. - -@item -w -@opindex w -Inhibit all warning messages. - -@item -Werror -@opindex Werror -@opindex Wno-error -Make all warnings into errors. - -@item -Werror= -@opindex Werror= -@opindex Wno-error= -Make the specified warning into an error. The specifier for a warning -is appended; for example @option{-Werror=switch} turns the warnings -controlled by @option{-Wswitch} into errors. This switch takes a -negative form, to be used to negate @option{-Werror} for specific -warnings; for example @option{-Wno-error=switch} makes -@option{-Wswitch} warnings not be errors, even when @option{-Werror} -is in effect. - -The warning message for each controllable warning includes the -option that controls the warning. That option can then be used with -@option{-Werror=} and @option{-Wno-error=} as described above. -(Printing of the option in the warning message can be disabled using the -@option{-fno-diagnostics-show-option} flag.) - -Note that specifying @option{-Werror=}@var{foo} automatically implies -@option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not -imply anything. - -@item -Wfatal-errors -@opindex Wfatal-errors -@opindex Wno-fatal-errors -This option causes the compiler to abort compilation on the first error -occurred rather than trying to keep going and printing further error -messages. - -@end table - -You can request many specific warnings with options beginning with -@samp{-W}, for example @option{-Wimplicit} to request warnings on -implicit declarations. Each of these specific warning options also -has a negative form beginning @samp{-Wno-} to turn off warnings; for -example, @option{-Wno-implicit}. This manual lists only one of the -two forms, whichever is not the default. For further -language-specific options also refer to @ref{C++ Dialect Options} and -@ref{Objective-C and Objective-C++ Dialect Options}. -Additional warnings can be produced by enabling the static analyzer; -@xref{Static Analyzer Options}. - -Some options, such as @option{-Wall} and @option{-Wextra}, turn on other -options, such as @option{-Wunused}, which may turn on further options, -such as @option{-Wunused-value}. The combined effect of positive and -negative forms is that more specific options have priority over less -specific ones, independently of their position in the command-line. For -options of the same specificity, the last one takes effect. Options -enabled or disabled via pragmas (@pxref{Diagnostic Pragmas}) take effect -as if they appeared at the end of the command-line. - -When an unrecognized warning option is requested (e.g., -@option{-Wunknown-warning}), GCC emits a diagnostic stating -that the option is not recognized. However, if the @option{-Wno-} form -is used, the behavior is slightly different: no diagnostic is -produced for @option{-Wno-unknown-warning} unless other diagnostics -are being produced. This allows the use of new @option{-Wno-} options -with old compilers, but if something goes wrong, the compiler -warns that an unrecognized option is present. - -The effectiveness of some warnings depends on optimizations also being -enabled. For example @option{-Wsuggest-final-types} is more effective -with link-time optimization and some instances of other warnings may -not be issued at all unless optimization is enabled. While optimization -in general improves the efficacy of control and data flow sensitive -warnings, in some cases it may also cause false positives. - -@table @gcctabopt -@item -Wpedantic -@itemx -pedantic -@opindex pedantic -@opindex Wpedantic -@opindex Wno-pedantic -Issue all the warnings demanded by strict ISO C and ISO C++; -reject all programs that use forbidden extensions, and some other -programs that do not follow ISO C and ISO C++. For ISO C, follows the -version of the ISO C standard specified by any @option{-std} option used. - -Valid ISO C and ISO C++ programs should compile properly with or without -this option (though a rare few require @option{-ansi} or a -@option{-std} option specifying the required version of ISO C)@. However, -without this option, certain GNU extensions and traditional C and C++ -features are supported as well. With this option, they are rejected. - -@option{-Wpedantic} does not cause warning messages for use of the -alternate keywords whose names begin and end with @samp{__}. This alternate -format can also be used to disable warnings for non-ISO @samp{__intN} types, -i.e. @samp{__intN__}. -Pedantic warnings are also disabled in the expression that follows -@code{__extension__}. However, only system header files should use -these escape routes; application programs should avoid them. -@xref{Alternate Keywords}. - -Some users try to use @option{-Wpedantic} to check programs for strict ISO -C conformance. They soon find that it does not do quite what they want: -it finds some non-ISO practices, but not all---only those for which -ISO C @emph{requires} a diagnostic, and some others for which -diagnostics have been added. - -A feature to report any failure to conform to ISO C might be useful in -some instances, but would require considerable additional work and would -be quite different from @option{-Wpedantic}. We don't have plans to -support such a feature in the near future. - -Where the standard specified with @option{-std} represents a GNU -extended dialect of C, such as @samp{gnu90} or @samp{gnu99}, there is a -corresponding @dfn{base standard}, the version of ISO C on which the GNU -extended dialect is based. Warnings from @option{-Wpedantic} are given -where they are required by the base standard. (It does not make sense -for such warnings to be given only for features not in the specified GNU -C dialect, since by definition the GNU dialects of C include all -features the compiler supports with the given option, and there would be -nothing to warn about.) - -@item -pedantic-errors -@opindex pedantic-errors -Give an error whenever the @dfn{base standard} (see @option{-Wpedantic}) -requires a diagnostic, in some cases where there is undefined behavior -at compile-time and in some other cases that do not prevent compilation -of programs that are valid according to the standard. This is not -equivalent to @option{-Werror=pedantic}, since there are errors enabled -by this option and not enabled by the latter and vice versa. - -@item -Wall -@opindex Wall -@opindex Wno-all -This enables all the warnings about constructions that some users -consider questionable, and that are easy to avoid (or modify to -prevent the warning), even in conjunction with macros. This also -enables some language-specific warnings described in @ref{C++ Dialect -Options} and @ref{Objective-C and Objective-C++ Dialect Options}. - -@option{-Wall} turns on the following warning flags: - -@gccoptlist{-Waddress @gol --Warray-bounds=1 @r{(only with} @option{-O2}@r{)} @gol --Warray-compare @gol --Warray-parameter=2 @r{(C and Objective-C only)} @gol --Wbool-compare @gol --Wbool-operation @gol --Wc++11-compat -Wc++14-compat @gol --Wcatch-value @r{(C++ and Objective-C++ only)} @gol --Wchar-subscripts @gol --Wcomment @gol --Wdangling-pointer=2 @gol --Wduplicate-decl-specifier @r{(C and Objective-C only)} @gol --Wenum-compare @r{(in C/ObjC; this is on by default in C++)} @gol --Wenum-int-mismatch @r{(C and Objective-C only)} @gol --Wformat @gol --Wformat-overflow @gol --Wformat-truncation @gol --Wint-in-bool-context @gol --Wimplicit @r{(C and Objective-C only)} @gol --Wimplicit-int @r{(C and Objective-C only)} @gol --Wimplicit-function-declaration @r{(C and Objective-C only)} @gol --Winit-self @r{(only for C++)} @gol --Wlogical-not-parentheses @gol --Wmain @r{(only for C/ObjC and unless} @option{-ffreestanding}@r{)} @gol --Wmaybe-uninitialized @gol --Wmemset-elt-size @gol --Wmemset-transposed-args @gol --Wmisleading-indentation @r{(only for C/C++)} @gol --Wmismatched-dealloc @gol --Wmismatched-new-delete @r{(only for C/C++)} @gol --Wmissing-attributes @gol --Wmissing-braces @r{(only for C/ObjC)} @gol --Wmultistatement-macros @gol --Wnarrowing @r{(only for C++)} @gol --Wnonnull @gol --Wnonnull-compare @gol --Wopenmp-simd @gol --Wparentheses @gol --Wpessimizing-move @r{(only for C++)} @gol --Wpointer-sign @gol --Wrange-loop-construct @r{(only for C++)} @gol --Wreorder @gol --Wrestrict @gol --Wreturn-type @gol --Wself-move @r{(only for C++)} @gol --Wsequence-point @gol --Wsign-compare @r{(only in C++)} @gol --Wsizeof-array-div @gol --Wsizeof-pointer-div @gol --Wsizeof-pointer-memaccess @gol --Wstrict-aliasing @gol --Wstrict-overflow=1 @gol --Wswitch @gol --Wtautological-compare @gol --Wtrigraphs @gol --Wuninitialized @gol --Wunknown-pragmas @gol --Wunused-function @gol --Wunused-label @gol --Wunused-value @gol --Wunused-variable @gol --Wuse-after-free=3 @gol --Wvla-parameter @r{(C and Objective-C only)} @gol --Wvolatile-register-var @gol --Wzero-length-bounds} - -Note that some warning flags are not implied by @option{-Wall}. Some of -them warn about constructions that users generally do not consider -questionable, but which occasionally you might wish to check for; -others warn about constructions that are necessary or hard to avoid in -some cases, and there is no simple way to modify the code to suppress -the warning. Some of them are enabled by @option{-Wextra} but many of -them must be enabled individually. - -@item -Wextra -@opindex W -@opindex Wextra -@opindex Wno-extra -This enables some extra warning flags that are not enabled by -@option{-Wall}. (This option used to be called @option{-W}. The older -name is still supported, but the newer name is more descriptive.) - -@gccoptlist{-Wclobbered @gol --Wcast-function-type @gol --Wdeprecated-copy @r{(C++ only)} @gol --Wempty-body @gol --Wenum-conversion @r{(C only)} @gol --Wignored-qualifiers @gol --Wimplicit-fallthrough=3 @gol --Wmissing-field-initializers @gol --Wmissing-parameter-type @r{(C only)} @gol --Wold-style-declaration @r{(C only)} @gol --Woverride-init @gol --Wsign-compare @r{(C only)} @gol --Wstring-compare @gol --Wredundant-move @r{(only for C++)} @gol --Wtype-limits @gol --Wuninitialized @gol --Wshift-negative-value @r{(in C++11 to C++17 and in C99 and newer)} @gol --Wunused-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol --Wunused-but-set-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)}} - - -The option @option{-Wextra} also prints warning messages for the -following cases: - -@itemize @bullet - -@item -A pointer is compared against integer zero with @code{<}, @code{<=}, -@code{>}, or @code{>=}. - -@item -(C++ only) An enumerator and a non-enumerator both appear in a -conditional expression. - -@item -(C++ only) Ambiguous virtual bases. - -@item -(C++ only) Subscripting an array that has been declared @code{register}. - -@item -(C++ only) Taking the address of a variable that has been declared -@code{register}. - -@item -(C++ only) A base class is not initialized in the copy constructor -of a derived class. - -@end itemize - -@item -Wabi @r{(C, Objective-C, C++ and Objective-C++ only)} -@opindex Wabi -@opindex Wno-abi - -Warn about code affected by ABI changes. This includes code that may -not be compatible with the vendor-neutral C++ ABI as well as the psABI -for the particular target. - -Since G++ now defaults to updating the ABI with each major release, -normally @option{-Wabi} warns only about C++ ABI compatibility -problems if there is a check added later in a release series for an -ABI issue discovered since the initial release. @option{-Wabi} warns -about more things if an older ABI version is selected (with -@option{-fabi-version=@var{n}}). - -@option{-Wabi} can also be used with an explicit version number to -warn about C++ ABI compatibility with a particular @option{-fabi-version} -level, e.g.@: @option{-Wabi=2} to warn about changes relative to -@option{-fabi-version=2}. - -If an explicit version number is provided and -@option{-fabi-compat-version} is not specified, the version number -from this option is used for compatibility aliases. If no explicit -version number is provided with this option, but -@option{-fabi-compat-version} is specified, that version number is -used for C++ ABI warnings. - -Although an effort has been made to warn about -all such cases, there are probably some cases that are not warned about, -even though G++ is generating incompatible code. There may also be -cases where warnings are emitted even though the code that is generated -is compatible. - -You should rewrite your code to avoid these warnings if you are -concerned about the fact that code generated by G++ may not be binary -compatible with code generated by other compilers. - -Known incompatibilities in @option{-fabi-version=2} (which was the -default from GCC 3.4 to 4.9) include: - -@itemize @bullet - -@item -A template with a non-type template parameter of reference type was -mangled incorrectly: -@smallexample -extern int N; -template <int &> struct S @{@}; -void n (S<N>) @{2@} -@end smallexample - -This was fixed in @option{-fabi-version=3}. - -@item -SIMD vector types declared using @code{__attribute ((vector_size))} were -mangled in a non-standard way that does not allow for overloading of -functions taking vectors of different sizes. - -The mangling was changed in @option{-fabi-version=4}. - -@item -@code{__attribute ((const))} and @code{noreturn} were mangled as type -qualifiers, and @code{decltype} of a plain declaration was folded away. - -These mangling issues were fixed in @option{-fabi-version=5}. - -@item -Scoped enumerators passed as arguments to a variadic function are -promoted like unscoped enumerators, causing @code{va_arg} to complain. -On most targets this does not actually affect the parameter passing -ABI, as there is no way to pass an argument smaller than @code{int}. - -Also, the ABI changed the mangling of template argument packs, -@code{const_cast}, @code{static_cast}, prefix increment/decrement, and -a class scope function used as a template argument. - -These issues were corrected in @option{-fabi-version=6}. - -@item -Lambdas in default argument scope were mangled incorrectly, and the -ABI changed the mangling of @code{nullptr_t}. - -These issues were corrected in @option{-fabi-version=7}. - -@item -When mangling a function type with function-cv-qualifiers, the -un-qualified function type was incorrectly treated as a substitution -candidate. - -This was fixed in @option{-fabi-version=8}, the default for GCC 5.1. - -@item -@code{decltype(nullptr)} incorrectly had an alignment of 1, leading to -unaligned accesses. Note that this did not affect the ABI of a -function with a @code{nullptr_t} parameter, as parameters have a -minimum alignment. - -This was fixed in @option{-fabi-version=9}, the default for GCC 5.2. - -@item -Target-specific attributes that affect the identity of a type, such as -ia32 calling conventions on a function type (stdcall, regparm, etc.), -did not affect the mangled name, leading to name collisions when -function pointers were used as template arguments. - -This was fixed in @option{-fabi-version=10}, the default for GCC 6.1. - -@end itemize - -This option also enables warnings about psABI-related changes. -The known psABI changes at this point include: - -@itemize @bullet - -@item -For SysV/x86-64, unions with @code{long double} members are -passed in memory as specified in psABI. Prior to GCC 4.4, this was not -the case. For example: - -@smallexample -union U @{ - long double ld; - int i; -@}; -@end smallexample - -@noindent -@code{union U} is now always passed in memory. - -@end itemize - -@item -Wchar-subscripts -@opindex Wchar-subscripts -@opindex Wno-char-subscripts -Warn if an array subscript has type @code{char}. This is a common cause -of error, as programmers often forget that this type is signed on some -machines. -This warning is enabled by @option{-Wall}. - -@item -Wno-coverage-mismatch -@opindex Wno-coverage-mismatch -@opindex Wcoverage-mismatch -Warn if feedback profiles do not match when using the -@option{-fprofile-use} option. -If a source file is changed between compiling with @option{-fprofile-generate} -and with @option{-fprofile-use}, the files with the profile feedback can fail -to match the source file and GCC cannot use the profile feedback -information. By default, this warning is enabled and is treated as an -error. @option{-Wno-coverage-mismatch} can be used to disable the -warning or @option{-Wno-error=coverage-mismatch} can be used to -disable the error. Disabling the error for this warning can result in -poorly optimized code and is useful only in the -case of very minor changes such as bug fixes to an existing code-base. -Completely disabling the warning is not recommended. - -@item -Wno-coverage-invalid-line-number -@opindex Wno-coverage-invalid-line-number -@opindex Wcoverage-invalid-line-number -Warn in case a function ends earlier than it begins due -to an invalid linenum macros. The warning is emitted only -with @option{--coverage} enabled. - -By default, this warning is enabled and is treated as an -error. @option{-Wno-coverage-invalid-line-number} can be used to disable the -warning or @option{-Wno-error=coverage-invalid-line-number} can be used to -disable the error. - -@item -Wno-cpp @r{(C, Objective-C, C++, Objective-C++ and Fortran only)} -@opindex Wno-cpp -@opindex Wcpp -Suppress warning messages emitted by @code{#warning} directives. - -@item -Wdouble-promotion @r{(C, C++, Objective-C and Objective-C++ only)} -@opindex Wdouble-promotion -@opindex Wno-double-promotion -Give a warning when a value of type @code{float} is implicitly -promoted to @code{double}. CPUs with a 32-bit ``single-precision'' -floating-point unit implement @code{float} in hardware, but emulate -@code{double} in software. On such a machine, doing computations -using @code{double} values is much more expensive because of the -overhead required for software emulation. - -It is easy to accidentally do computations with @code{double} because -floating-point literals are implicitly of type @code{double}. For -example, in: -@smallexample -@group -float area(float radius) -@{ - return 3.14159 * radius * radius; -@} -@end group -@end smallexample -the compiler performs the entire computation with @code{double} -because the floating-point literal is a @code{double}. - -@item -Wduplicate-decl-specifier @r{(C and Objective-C only)} -@opindex Wduplicate-decl-specifier -@opindex Wno-duplicate-decl-specifier -Warn if a declaration has duplicate @code{const}, @code{volatile}, -@code{restrict} or @code{_Atomic} specifier. This warning is enabled by -@option{-Wall}. - -@item -Wformat -@itemx -Wformat=@var{n} -@opindex Wformat -@opindex Wno-format -@opindex ffreestanding -@opindex fno-builtin -@opindex Wformat= -Check calls to @code{printf} and @code{scanf}, etc., to make sure that -the arguments supplied have types appropriate to the format string -specified, and that the conversions specified in the format string make -sense. This includes standard functions, and others specified by format -attributes (@pxref{Function Attributes}), in the @code{printf}, -@code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension, -not in the C standard) families (or other target-specific families). -Which functions are checked without format attributes having been -specified depends on the standard version selected, and such checks of -functions without the attribute specified are disabled by -@option{-ffreestanding} or @option{-fno-builtin}. - -The formats are checked against the format features supported by GNU -libc version 2.2. These include all ISO C90 and C99 features, as well -as features from the Single Unix Specification and some BSD and GNU -extensions. Other library implementations may not support all these -features; GCC does not support warning about features that go beyond a -particular library's limitations. However, if @option{-Wpedantic} is used -with @option{-Wformat}, warnings are given about format features not -in the selected standard version (but not for @code{strfmon} formats, -since those are not in any version of the C standard). @xref{C Dialect -Options,,Options Controlling C Dialect}. - -@table @gcctabopt -@item -Wformat=1 -@itemx -Wformat -@opindex Wformat -@opindex Wformat=1 -Option @option{-Wformat} is equivalent to @option{-Wformat=1}, and -@option{-Wno-format} is equivalent to @option{-Wformat=0}. Since -@option{-Wformat} also checks for null format arguments for several -functions, @option{-Wformat} also implies @option{-Wnonnull}. Some -aspects of this level of format checking can be disabled by the -options: @option{-Wno-format-contains-nul}, -@option{-Wno-format-extra-args}, and @option{-Wno-format-zero-length}. -@option{-Wformat} is enabled by @option{-Wall}. - -@item -Wformat=2 -@opindex Wformat=2 -Enable @option{-Wformat} plus additional format checks. Currently -equivalent to @option{-Wformat -Wformat-nonliteral -Wformat-security --Wformat-y2k}. -@end table - -@item -Wno-format-contains-nul -@opindex Wno-format-contains-nul -@opindex Wformat-contains-nul -If @option{-Wformat} is specified, do not warn about format strings that -contain NUL bytes. - -@item -Wno-format-extra-args -@opindex Wno-format-extra-args -@opindex Wformat-extra-args -If @option{-Wformat} is specified, do not warn about excess arguments to a -@code{printf} or @code{scanf} format function. The C standard specifies -that such arguments are ignored. - -Where the unused arguments lie between used arguments that are -specified with @samp{$} operand number specifications, normally -warnings are still given, since the implementation could not know what -type to pass to @code{va_arg} to skip the unused arguments. However, -in the case of @code{scanf} formats, this option suppresses the -warning if the unused arguments are all pointers, since the Single -Unix Specification says that such unused arguments are allowed. - -@item -Wformat-overflow -@itemx -Wformat-overflow=@var{level} -@opindex Wformat-overflow -@opindex Wno-format-overflow -Warn about calls to formatted input/output functions such as @code{sprintf} -and @code{vsprintf} that might overflow the destination buffer. When the -exact number of bytes written by a format directive cannot be determined -at compile-time it is estimated based on heuristics that depend on the -@var{level} argument and on optimization. While enabling optimization -will in most cases improve the accuracy of the warning, it may also -result in false positives. - -@table @gcctabopt -@item -Wformat-overflow -@itemx -Wformat-overflow=1 -@opindex Wformat-overflow -@opindex Wno-format-overflow -Level @var{1} of @option{-Wformat-overflow} enabled by @option{-Wformat} -employs a conservative approach that warns only about calls that most -likely overflow the buffer. At this level, numeric arguments to format -directives with unknown values are assumed to have the value of one, and -strings of unknown length to be empty. Numeric arguments that are known -to be bounded to a subrange of their type, or string arguments whose output -is bounded either by their directive's precision or by a finite set of -string literals, are assumed to take on the value within the range that -results in the most bytes on output. For example, the call to @code{sprintf} -below is diagnosed because even with both @var{a} and @var{b} equal to zero, -the terminating NUL character (@code{'\0'}) appended by the function -to the destination buffer will be written past its end. Increasing -the size of the buffer by a single byte is sufficient to avoid the -warning, though it may not be sufficient to avoid the overflow. - -@smallexample -void f (int a, int b) -@{ - char buf [13]; - sprintf (buf, "a = %i, b = %i\n", a, b); -@} -@end smallexample - -@item -Wformat-overflow=2 -Level @var{2} warns also about calls that might overflow the destination -buffer given an argument of sufficient length or magnitude. At level -@var{2}, unknown numeric arguments are assumed to have the minimum -representable value for signed types with a precision greater than 1, and -the maximum representable value otherwise. Unknown string arguments whose -length cannot be assumed to be bounded either by the directive's precision, -or by a finite set of string literals they may evaluate to, or the character -array they may point to, are assumed to be 1 character long. - -At level @var{2}, the call in the example above is again diagnosed, but -this time because with @var{a} equal to a 32-bit @code{INT_MIN} the first -@code{%i} directive will write some of its digits beyond the end of -the destination buffer. To make the call safe regardless of the values -of the two variables, the size of the destination buffer must be increased -to at least 34 bytes. GCC includes the minimum size of the buffer in -an informational note following the warning. - -An alternative to increasing the size of the destination buffer is to -constrain the range of formatted values. The maximum length of string -arguments can be bounded by specifying the precision in the format -directive. When numeric arguments of format directives can be assumed -to be bounded by less than the precision of their type, choosing -an appropriate length modifier to the format specifier will reduce -the required buffer size. For example, if @var{a} and @var{b} in the -example above can be assumed to be within the precision of -the @code{short int} type then using either the @code{%hi} format -directive or casting the argument to @code{short} reduces the maximum -required size of the buffer to 24 bytes. - -@smallexample -void f (int a, int b) -@{ - char buf [23]; - sprintf (buf, "a = %hi, b = %i\n", a, (short)b); -@} -@end smallexample -@end table - -@item -Wno-format-zero-length -@opindex Wno-format-zero-length -@opindex Wformat-zero-length -If @option{-Wformat} is specified, do not warn about zero-length formats. -The C standard specifies that zero-length formats are allowed. - -@item -Wformat-nonliteral -@opindex Wformat-nonliteral -@opindex Wno-format-nonliteral -If @option{-Wformat} is specified, also warn if the format string is not a -string literal and so cannot be checked, unless the format function -takes its format arguments as a @code{va_list}. - -@item -Wformat-security -@opindex Wformat-security -@opindex Wno-format-security -If @option{-Wformat} is specified, also warn about uses of format -functions that represent possible security problems. At present, this -warns about calls to @code{printf} and @code{scanf} functions where the -format string is not a string literal and there are no format arguments, -as in @code{printf (foo);}. This may be a security hole if the format -string came from untrusted input and contains @samp{%n}. (This is -currently a subset of what @option{-Wformat-nonliteral} warns about, but -in future warnings may be added to @option{-Wformat-security} that are not -included in @option{-Wformat-nonliteral}.) - -@item -Wformat-signedness -@opindex Wformat-signedness -@opindex Wno-format-signedness -If @option{-Wformat} is specified, also warn if the format string -requires an unsigned argument and the argument is signed and vice versa. - -@item -Wformat-truncation -@itemx -Wformat-truncation=@var{level} -@opindex Wformat-truncation -@opindex Wno-format-truncation -Warn about calls to formatted input/output functions such as @code{snprintf} -and @code{vsnprintf} that might result in output truncation. When the exact -number of bytes written by a format directive cannot be determined at -compile-time it is estimated based on heuristics that depend on -the @var{level} argument and on optimization. While enabling optimization -will in most cases improve the accuracy of the warning, it may also result -in false positives. Except as noted otherwise, the option uses the same -logic @option{-Wformat-overflow}. - -@table @gcctabopt -@item -Wformat-truncation -@itemx -Wformat-truncation=1 -@opindex Wformat-truncation -@opindex Wno-format-truncation -Level @var{1} of @option{-Wformat-truncation} enabled by @option{-Wformat} -employs a conservative approach that warns only about calls to bounded -functions whose return value is unused and that will most likely result -in output truncation. - -@item -Wformat-truncation=2 -Level @var{2} warns also about calls to bounded functions whose return -value is used and that might result in truncation given an argument of -sufficient length or magnitude. -@end table - -@item -Wformat-y2k -@opindex Wformat-y2k -@opindex Wno-format-y2k -If @option{-Wformat} is specified, also warn about @code{strftime} -formats that may yield only a two-digit year. - -@item -Wnonnull -@opindex Wnonnull -@opindex Wno-nonnull -Warn about passing a null pointer for arguments marked as -requiring a non-null value by the @code{nonnull} function attribute. - -@option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It -can be disabled with the @option{-Wno-nonnull} option. - -@item -Wnonnull-compare -@opindex Wnonnull-compare -@opindex Wno-nonnull-compare -Warn when comparing an argument marked with the @code{nonnull} -function attribute against null inside the function. - -@option{-Wnonnull-compare} is included in @option{-Wall}. It -can be disabled with the @option{-Wno-nonnull-compare} option. - -@item -Wnull-dereference -@opindex Wnull-dereference -@opindex Wno-null-dereference -Warn if the compiler detects paths that trigger erroneous or -undefined behavior due to dereferencing a null pointer. This option -is only active when @option{-fdelete-null-pointer-checks} is active, -which is enabled by optimizations in most targets. The precision of -the warnings depends on the optimization options used. - -@item -Winfinite-recursion -@opindex Winfinite-recursion -@opindex Wno-infinite-recursion -Warn about infinitely recursive calls. The warning is effective at all -optimization levels but requires optimization in order to detect infinite -recursion in calls between two or more functions. -@option{-Winfinite-recursion} is included in @option{-Wall}. - -@item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)} -@opindex Winit-self -@opindex Wno-init-self -Warn about uninitialized variables that are initialized with themselves. -Note this option can only be used with the @option{-Wuninitialized} option. - -For example, GCC warns about @code{i} being uninitialized in the -following snippet only when @option{-Winit-self} has been specified: -@smallexample -@group -int f() -@{ - int i = i; - return i; -@} -@end group -@end smallexample - -This warning is enabled by @option{-Wall} in C++. - -@item -Wno-implicit-int @r{(C and Objective-C only)} -@opindex Wimplicit-int -@opindex Wno-implicit-int -This option controls warnings when a declaration does not specify a type. -This warning is enabled by default in C99 and later dialects of C, -and also by @option{-Wall}. - -@item -Wno-implicit-function-declaration @r{(C and Objective-C only)} -@opindex Wimplicit-function-declaration -@opindex Wno-implicit-function-declaration -This option controls warnings when a function is used before being declared. -This warning is enabled by default in C99 and later dialects of C, -and also by @option{-Wall}. -The warning is made into an error by @option{-pedantic-errors}. - -@item -Wimplicit @r{(C and Objective-C only)} -@opindex Wimplicit -@opindex Wno-implicit -Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}. -This warning is enabled by @option{-Wall}. - -@item -Wimplicit-fallthrough -@opindex Wimplicit-fallthrough -@opindex Wno-implicit-fallthrough -@option{-Wimplicit-fallthrough} is the same as @option{-Wimplicit-fallthrough=3} -and @option{-Wno-implicit-fallthrough} is the same as -@option{-Wimplicit-fallthrough=0}. - -@item -Wimplicit-fallthrough=@var{n} -@opindex Wimplicit-fallthrough= -Warn when a switch case falls through. For example: - -@smallexample -@group -switch (cond) - @{ - case 1: - a = 1; - break; - case 2: - a = 2; - case 3: - a = 3; - break; - @} -@end group -@end smallexample - -This warning does not warn when the last statement of a case cannot -fall through, e.g. when there is a return statement or a call to function -declared with the noreturn attribute. @option{-Wimplicit-fallthrough=} -also takes into account control flow statements, such as ifs, and only -warns when appropriate. E.g.@: - -@smallexample -@group -switch (cond) - @{ - case 1: - if (i > 3) @{ - bar (5); - break; - @} else if (i < 1) @{ - bar (0); - @} else - return; - default: - @dots{} - @} -@end group -@end smallexample - -Since there are occasions where a switch case fall through is desirable, -GCC provides an attribute, @code{__attribute__ ((fallthrough))}, that is -to be used along with a null statement to suppress this warning that -would normally occur: - -@smallexample -@group -switch (cond) - @{ - case 1: - bar (0); - __attribute__ ((fallthrough)); - default: - @dots{} - @} -@end group -@end smallexample - -C++17 provides a standard way to suppress the @option{-Wimplicit-fallthrough} -warning using @code{[[fallthrough]];} instead of the GNU attribute. In C++11 -or C++14 users can use @code{[[gnu::fallthrough]];}, which is a GNU extension. -Instead of these attributes, it is also possible to add a fallthrough comment -to silence the warning. The whole body of the C or C++ style comment should -match the given regular expressions listed below. The option argument @var{n} -specifies what kind of comments are accepted: - -@itemize @bullet - -@item @option{-Wimplicit-fallthrough=0} disables the warning altogether. - -@item @option{-Wimplicit-fallthrough=1} matches @code{.*} regular -expression, any comment is used as fallthrough comment. - -@item @option{-Wimplicit-fallthrough=2} case insensitively matches -@code{.*falls?[ \t-]*thr(ough|u).*} regular expression. - -@item @option{-Wimplicit-fallthrough=3} case sensitively matches one of the -following regular expressions: - -@itemize @bullet - -@item @code{-fallthrough} - -@item @code{@@fallthrough@@} - -@item @code{lint -fallthrough[ \t]*} - -@item @code{[ \t.!]*(ELSE,? |INTENTIONAL(LY)? )?@*FALL(S | |-)?THR(OUGH|U)[ \t.!]*(-[^\n\r]*)?} - -@item @code{[ \t.!]*(Else,? |Intentional(ly)? )?@*Fall((s | |-)[Tt]|t)hr(ough|u)[ \t.!]*(-[^\n\r]*)?} - -@item @code{[ \t.!]*([Ee]lse,? |[Ii]ntentional(ly)? )?@*fall(s | |-)?thr(ough|u)[ \t.!]*(-[^\n\r]*)?} - -@end itemize - -@item @option{-Wimplicit-fallthrough=4} case sensitively matches one of the -following regular expressions: - -@itemize @bullet - -@item @code{-fallthrough} - -@item @code{@@fallthrough@@} - -@item @code{lint -fallthrough[ \t]*} - -@item @code{[ \t]*FALLTHR(OUGH|U)[ \t]*} - -@end itemize - -@item @option{-Wimplicit-fallthrough=5} doesn't recognize any comments as -fallthrough comments, only attributes disable the warning. - -@end itemize - -The comment needs to be followed after optional whitespace and other comments -by @code{case} or @code{default} keywords or by a user label that precedes some -@code{case} or @code{default} label. - -@smallexample -@group -switch (cond) - @{ - case 1: - bar (0); - /* FALLTHRU */ - default: - @dots{} - @} -@end group -@end smallexample - -The @option{-Wimplicit-fallthrough=3} warning is enabled by @option{-Wextra}. - -@item -Wno-if-not-aligned @r{(C, C++, Objective-C and Objective-C++ only)} -@opindex Wif-not-aligned -@opindex Wno-if-not-aligned -Control if warnings triggered by the @code{warn_if_not_aligned} attribute -should be issued. These warnings are enabled by default. - -@item -Wignored-qualifiers @r{(C and C++ only)} -@opindex Wignored-qualifiers -@opindex Wno-ignored-qualifiers -Warn if the return type of a function has a type qualifier -such as @code{const}. For ISO C such a type qualifier has no effect, -since the value returned by a function is not an lvalue. -For C++, the warning is only emitted for scalar types or @code{void}. -ISO C prohibits qualified @code{void} return types on function -definitions, so such return types always receive a warning -even without this option. - -This warning is also enabled by @option{-Wextra}. - -@item -Wno-ignored-attributes @r{(C and C++ only)} -@opindex Wignored-attributes -@opindex Wno-ignored-attributes -This option controls warnings when an attribute is ignored. -This is different from the -@option{-Wattributes} option in that it warns whenever the compiler decides -to drop an attribute, not that the attribute is either unknown, used in a -wrong place, etc. This warning is enabled by default. - -@item -Wmain -@opindex Wmain -@opindex Wno-main -Warn if the type of @code{main} is suspicious. @code{main} should be -a function with external linkage, returning int, taking either zero -arguments, two, or three arguments of appropriate types. This warning -is enabled by default in C++ and is enabled by either @option{-Wall} -or @option{-Wpedantic}. - -@item -Wmisleading-indentation @r{(C and C++ only)} -@opindex Wmisleading-indentation -@opindex Wno-misleading-indentation -Warn when the indentation of the code does not reflect the block structure. -Specifically, a warning is issued for @code{if}, @code{else}, @code{while}, and -@code{for} clauses with a guarded statement that does not use braces, -followed by an unguarded statement with the same indentation. - -In the following example, the call to ``bar'' is misleadingly indented as -if it were guarded by the ``if'' conditional. - -@smallexample - if (some_condition ()) - foo (); - bar (); /* Gotcha: this is not guarded by the "if". */ -@end smallexample - -In the case of mixed tabs and spaces, the warning uses the -@option{-ftabstop=} option to determine if the statements line up -(defaulting to 8). - -The warning is not issued for code involving multiline preprocessor logic -such as the following example. - -@smallexample - if (flagA) - foo (0); -#if SOME_CONDITION_THAT_DOES_NOT_HOLD - if (flagB) -#endif - foo (1); -@end smallexample - -The warning is not issued after a @code{#line} directive, since this -typically indicates autogenerated code, and no assumptions can be made -about the layout of the file that the directive references. - -This warning is enabled by @option{-Wall} in C and C++. - -@item -Wmissing-attributes -@opindex Wmissing-attributes -@opindex Wno-missing-attributes -Warn when a declaration of a function is missing one or more attributes -that a related function is declared with and whose absence may adversely -affect the correctness or efficiency of generated code. For example, -the warning is issued for declarations of aliases that use attributes -to specify less restrictive requirements than those of their targets. -This typically represents a potential optimization opportunity. -By contrast, the @option{-Wattribute-alias=2} option controls warnings -issued when the alias is more restrictive than the target, which could -lead to incorrect code generation. -Attributes considered include @code{alloc_align}, @code{alloc_size}, -@code{cold}, @code{const}, @code{hot}, @code{leaf}, @code{malloc}, -@code{nonnull}, @code{noreturn}, @code{nothrow}, @code{pure}, -@code{returns_nonnull}, and @code{returns_twice}. - -In C++, the warning is issued when an explicit specialization of a primary -template declared with attribute @code{alloc_align}, @code{alloc_size}, -@code{assume_aligned}, @code{format}, @code{format_arg}, @code{malloc}, -or @code{nonnull} is declared without it. Attributes @code{deprecated}, -@code{error}, and @code{warning} suppress the warning. -(@pxref{Function Attributes}). - -You can use the @code{copy} attribute to apply the same -set of attributes to a declaration as that on another declaration without -explicitly enumerating the attributes. This attribute can be applied -to declarations of functions (@pxref{Common Function Attributes}), -variables (@pxref{Common Variable Attributes}), or types -(@pxref{Common Type Attributes}). - -@option{-Wmissing-attributes} is enabled by @option{-Wall}. - -For example, since the declaration of the primary function template -below makes use of both attribute @code{malloc} and @code{alloc_size} -the declaration of the explicit specialization of the template is -diagnosed because it is missing one of the attributes. - -@smallexample -template <class T> -T* __attribute__ ((malloc, alloc_size (1))) -allocate (size_t); - -template <> -void* __attribute__ ((malloc)) // missing alloc_size -allocate<void> (size_t); -@end smallexample - -@item -Wmissing-braces -@opindex Wmissing-braces -@opindex Wno-missing-braces -Warn if an aggregate or union initializer is not fully bracketed. In -the following example, the initializer for @code{a} is not fully -bracketed, but that for @code{b} is fully bracketed. - -@smallexample -int a[2][2] = @{ 0, 1, 2, 3 @}; -int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @}; -@end smallexample - -This warning is enabled by @option{-Wall}. - -@item -Wmissing-include-dirs @r{(C, C++, Objective-C, Objective-C++ and Fortran only)} -@opindex Wmissing-include-dirs -@opindex Wno-missing-include-dirs -Warn if a user-supplied include directory does not exist. This opions is disabled -by default for C, C++, Objective-C and Objective-C++. For Fortran, it is partially -enabled by default by warning for -I and -J, only. - -@item -Wno-missing-profile -@opindex Wmissing-profile -@opindex Wno-missing-profile -This option controls warnings if feedback profiles are missing when using the -@option{-fprofile-use} option. -This option diagnoses those cases where a new function or a new file is added -between compiling with @option{-fprofile-generate} and with -@option{-fprofile-use}, without regenerating the profiles. -In these cases, the profile feedback data files do not contain any -profile feedback information for -the newly added function or file respectively. Also, in the case when profile -count data (.gcda) files are removed, GCC cannot use any profile feedback -information. In all these cases, warnings are issued to inform you that a -profile generation step is due. -Ignoring the warning can result in poorly optimized code. -@option{-Wno-missing-profile} can be used to -disable the warning, but this is not recommended and should be done only -when non-existent profile data is justified. - -@item -Wmismatched-dealloc -@opindex Wmismatched-dealloc -@opindex Wno-mismatched-dealloc - -Warn for calls to deallocation functions with pointer arguments returned -from from allocations functions for which the former isn't a suitable -deallocator. A pair of functions can be associated as matching allocators -and deallocators by use of attribute @code{malloc}. Unless disabled by -the @option{-fno-builtin} option the standard functions @code{calloc}, -@code{malloc}, @code{realloc}, and @code{free}, as well as the corresponding -forms of C++ @code{operator new} and @code{operator delete} are implicitly -associated as matching allocators and deallocators. In the following -example @code{mydealloc} is the deallocator for pointers returned from -@code{myalloc}. - -@smallexample -void mydealloc (void*); - -__attribute__ ((malloc (mydealloc, 1))) void* -myalloc (size_t); - -void f (void) -@{ - void *p = myalloc (32); - // @dots{}use p@dots{} - free (p); // warning: not a matching deallocator for myalloc - mydealloc (p); // ok -@} -@end smallexample - -In C++, the related option @option{-Wmismatched-new-delete} diagnoses -mismatches involving either @code{operator new} or @code{operator delete}. - -Option @option{-Wmismatched-dealloc} is included in @option{-Wall}. - -@item -Wmultistatement-macros -@opindex Wmultistatement-macros -@opindex Wno-multistatement-macros -Warn about unsafe multiple statement macros that appear to be guarded -by a clause such as @code{if}, @code{else}, @code{for}, @code{switch}, or -@code{while}, in which only the first statement is actually guarded after -the macro is expanded. - -For example: - -@smallexample -#define DOIT x++; y++ -if (c) - DOIT; -@end smallexample - -will increment @code{y} unconditionally, not just when @code{c} holds. -The can usually be fixed by wrapping the macro in a do-while loop: -@smallexample -#define DOIT do @{ x++; y++; @} while (0) -if (c) - DOIT; -@end smallexample - -This warning is enabled by @option{-Wall} in C and C++. - -@item -Wparentheses -@opindex Wparentheses -@opindex Wno-parentheses -Warn if parentheses are omitted in certain contexts, such -as when there is an assignment in a context where a truth value -is expected, or when operators are nested whose precedence people -often get confused about. - -Also warn if a comparison like @code{x<=y<=z} appears; this is -equivalent to @code{(x<=y ? 1 : 0) <= z}, which is a different -interpretation from that of ordinary mathematical notation. - -Also warn for dangerous uses of the GNU extension to -@code{?:} with omitted middle operand. When the condition -in the @code{?}: operator is a boolean expression, the omitted value is -always 1. Often programmers expect it to be a value computed -inside the conditional expression instead. - -For C++ this also warns for some cases of unnecessary parentheses in -declarations, which can indicate an attempt at a function call instead -of a declaration: -@smallexample -@{ - // Declares a local variable called mymutex. - std::unique_lock<std::mutex> (mymutex); - // User meant std::unique_lock<std::mutex> lock (mymutex); -@} -@end smallexample - -This warning is enabled by @option{-Wall}. - -@item -Wno-self-move @r{(C++ and Objective-C++ only)} -@opindex Wself-move -@opindex Wno-self-move -This warning warns when a value is moved to itself with @code{std::move}. -Such a @code{std::move} typically has no effect. - -@smallexample -struct T @{ -@dots{} -@}; -void fn() -@{ - T t; - @dots{} - t = std::move (t); -@} -@end smallexample - -This warning is enabled by @option{-Wall}. - -@item -Wsequence-point -@opindex Wsequence-point -@opindex Wno-sequence-point -Warn about code that may have undefined semantics because of violations -of sequence point rules in the C and C++ standards. - -The C and C++ standards define the order in which expressions in a C/C++ -program are evaluated in terms of @dfn{sequence points}, which represent -a partial ordering between the execution of parts of the program: those -executed before the sequence point, and those executed after it. These -occur after the evaluation of a full expression (one which is not part -of a larger expression), after the evaluation of the first operand of a -@code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a -function is called (but after the evaluation of its arguments and the -expression denoting the called function), and in certain other places. -Other than as expressed by the sequence point rules, the order of -evaluation of subexpressions of an expression is not specified. All -these rules describe only a partial order rather than a total order, -since, for example, if two functions are called within one expression -with no sequence point between them, the order in which the functions -are called is not specified. However, the standards committee have -ruled that function calls do not overlap. - -It is not specified when between sequence points modifications to the -values of objects take effect. Programs whose behavior depends on this -have undefined behavior; the C and C++ standards specify that ``Between -the previous and next sequence point an object shall have its stored -value modified at most once by the evaluation of an expression. -Furthermore, the prior value shall be read only to determine the value -to be stored.''. If a program breaks these rules, the results on any -particular implementation are entirely unpredictable. - -Examples of code with undefined behavior are @code{a = a++;}, @code{a[n] -= b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not -diagnosed by this option, and it may give an occasional false positive -result, but in general it has been found fairly effective at detecting -this sort of problem in programs. - -The C++17 standard will define the order of evaluation of operands in -more cases: in particular it requires that the right-hand side of an -assignment be evaluated before the left-hand side, so the above -examples are no longer undefined. But this option will still warn -about them, to help people avoid writing code that is undefined in C -and earlier revisions of C++. - -The standard is worded confusingly, therefore there is some debate -over the precise meaning of the sequence point rules in subtle cases. -Links to discussions of the problem, including proposed formal -definitions, may be found on the GCC readings page, at -@uref{https://gcc.gnu.org/@/readings.html}. - -This warning is enabled by @option{-Wall} for C and C++. - -@item -Wno-return-local-addr -@opindex Wno-return-local-addr -@opindex Wreturn-local-addr -Do not warn about returning a pointer (or in C++, a reference) to a -variable that goes out of scope after the function returns. - -@item -Wreturn-type -@opindex Wreturn-type -@opindex Wno-return-type -Warn whenever a function is defined with a return type that defaults -to @code{int}. Also warn about any @code{return} statement with no -return value in a function whose return type is not @code{void} -(falling off the end of the function body is considered returning -without a value). - -For C only, warn about a @code{return} statement with an expression in a -function whose return type is @code{void}, unless the expression type is -also @code{void}. As a GNU extension, the latter case is accepted -without a warning unless @option{-Wpedantic} is used. Attempting -to use the return value of a non-@code{void} function other than @code{main} -that flows off the end by reaching the closing curly brace that terminates -the function is undefined. - -Unlike in C, in C++, flowing off the end of a non-@code{void} function other -than @code{main} results in undefined behavior even when the value of -the function is not used. - -This warning is enabled by default in C++ and by @option{-Wall} otherwise. - -@item -Wno-shift-count-negative -@opindex Wshift-count-negative -@opindex Wno-shift-count-negative -Controls warnings if a shift count is negative. -This warning is enabled by default. - -@item -Wno-shift-count-overflow -@opindex Wshift-count-overflow -@opindex Wno-shift-count-overflow -Controls warnings if a shift count is greater than or equal to the bit width -of the type. This warning is enabled by default. - -@item -Wshift-negative-value -@opindex Wshift-negative-value -@opindex Wno-shift-negative-value -Warn if left shifting a negative value. This warning is enabled by -@option{-Wextra} in C99 (and newer) and C++11 to C++17 modes. - -@item -Wno-shift-overflow -@itemx -Wshift-overflow=@var{n} -@opindex Wshift-overflow -@opindex Wno-shift-overflow -These options control warnings about left shift overflows. - -@table @gcctabopt -@item -Wshift-overflow=1 -This is the warning level of @option{-Wshift-overflow} and is enabled -by default in C99 and C++11 modes (and newer). This warning level does -not warn about left-shifting 1 into the sign bit. (However, in C, such -an overflow is still rejected in contexts where an integer constant expression -is required.) No warning is emitted in C++20 mode (and newer), as signed left -shifts always wrap. - -@item -Wshift-overflow=2 -This warning level also warns about left-shifting 1 into the sign bit, -unless C++14 mode (or newer) is active. -@end table - -@item -Wswitch -@opindex Wswitch -@opindex Wno-switch -Warn whenever a @code{switch} statement has an index of enumerated type -and lacks a @code{case} for one or more of the named codes of that -enumeration. (The presence of a @code{default} label prevents this -warning.) @code{case} labels outside the enumeration range also -provoke warnings when this option is used (even if there is a -@code{default} label). -This warning is enabled by @option{-Wall}. - -@item -Wswitch-default -@opindex Wswitch-default -@opindex Wno-switch-default -Warn whenever a @code{switch} statement does not have a @code{default} -case. - -@item -Wswitch-enum -@opindex Wswitch-enum -@opindex Wno-switch-enum -Warn whenever a @code{switch} statement has an index of enumerated type -and lacks a @code{case} for one or more of the named codes of that -enumeration. @code{case} labels outside the enumeration range also -provoke warnings when this option is used. The only difference -between @option{-Wswitch} and this option is that this option gives a -warning about an omitted enumeration code even if there is a -@code{default} label. - -@item -Wno-switch-bool -@opindex Wswitch-bool -@opindex Wno-switch-bool -Do not warn when a @code{switch} statement has an index of boolean type -and the case values are outside the range of a boolean type. -It is possible to suppress this warning by casting the controlling -expression to a type other than @code{bool}. For example: -@smallexample -@group -switch ((int) (a == 4)) - @{ - @dots{} - @} -@end group -@end smallexample -This warning is enabled by default for C and C++ programs. - -@item -Wno-switch-outside-range -@opindex Wswitch-outside-range -@opindex Wno-switch-outside-range -This option controls warnings when a @code{switch} case has a value -that is outside of its -respective type range. This warning is enabled by default for -C and C++ programs. - -@item -Wno-switch-unreachable -@opindex Wswitch-unreachable -@opindex Wno-switch-unreachable -Do not warn when a @code{switch} statement contains statements between the -controlling expression and the first case label, which will never be -executed. For example: -@smallexample -@group -switch (cond) - @{ - i = 15; - @dots{} - case 5: - @dots{} - @} -@end group -@end smallexample -@option{-Wswitch-unreachable} does not warn if the statement between the -controlling expression and the first case label is just a declaration: -@smallexample -@group -switch (cond) - @{ - int i; - @dots{} - case 5: - i = 5; - @dots{} - @} -@end group -@end smallexample -This warning is enabled by default for C and C++ programs. - -@item -Wsync-nand @r{(C and C++ only)} -@opindex Wsync-nand -@opindex Wno-sync-nand -Warn when @code{__sync_fetch_and_nand} and @code{__sync_nand_and_fetch} -built-in functions are used. These functions changed semantics in GCC 4.4. - -@item -Wtrivial-auto-var-init -@opindex Wtrivial-auto-var-init -@opindex Wno-trivial-auto-var-init -Warn when @code{-ftrivial-auto-var-init} cannot initialize the automatic -variable. A common situation is an automatic variable that is declared -between the controlling expression and the first case label of a @code{switch} -statement. - -@item -Wunused-but-set-parameter -@opindex Wunused-but-set-parameter -@opindex Wno-unused-but-set-parameter -Warn whenever a function parameter is assigned to, but otherwise unused -(aside from its declaration). - -To suppress this warning use the @code{unused} attribute -(@pxref{Variable Attributes}). - -This warning is also enabled by @option{-Wunused} together with -@option{-Wextra}. - -@item -Wunused-but-set-variable -@opindex Wunused-but-set-variable -@opindex Wno-unused-but-set-variable -Warn whenever a local variable is assigned to, but otherwise unused -(aside from its declaration). -This warning is enabled by @option{-Wall}. - -To suppress this warning use the @code{unused} attribute -(@pxref{Variable Attributes}). - -This warning is also enabled by @option{-Wunused}, which is enabled -by @option{-Wall}. - -@item -Wunused-function -@opindex Wunused-function -@opindex Wno-unused-function -Warn whenever a static function is declared but not defined or a -non-inline static function is unused. -This warning is enabled by @option{-Wall}. - -@item -Wunused-label -@opindex Wunused-label -@opindex Wno-unused-label -Warn whenever a label is declared but not used. -This warning is enabled by @option{-Wall}. - -To suppress this warning use the @code{unused} attribute -(@pxref{Variable Attributes}). - -@item -Wunused-local-typedefs @r{(C, Objective-C, C++ and Objective-C++ only)} -@opindex Wunused-local-typedefs -@opindex Wno-unused-local-typedefs -Warn when a typedef locally defined in a function is not used. -This warning is enabled by @option{-Wall}. - -@item -Wunused-parameter -@opindex Wunused-parameter -@opindex Wno-unused-parameter -Warn whenever a function parameter is unused aside from its declaration. - -To suppress this warning use the @code{unused} attribute -(@pxref{Variable Attributes}). - -@item -Wno-unused-result -@opindex Wunused-result -@opindex Wno-unused-result -Do not warn if a caller of a function marked with attribute -@code{warn_unused_result} (@pxref{Function Attributes}) does not use -its return value. The default is @option{-Wunused-result}. - -@item -Wunused-variable -@opindex Wunused-variable -@opindex Wno-unused-variable -Warn whenever a local or static variable is unused aside from its -declaration. This option implies @option{-Wunused-const-variable=1} for C, -but not for C++. This warning is enabled by @option{-Wall}. - -To suppress this warning use the @code{unused} attribute -(@pxref{Variable Attributes}). - -@item -Wunused-const-variable -@itemx -Wunused-const-variable=@var{n} -@opindex Wunused-const-variable -@opindex Wno-unused-const-variable -Warn whenever a constant static variable is unused aside from its declaration. -@option{-Wunused-const-variable=1} is enabled by @option{-Wunused-variable} -for C, but not for C++. In C this declares variable storage, but in C++ this -is not an error since const variables take the place of @code{#define}s. - -To suppress this warning use the @code{unused} attribute -(@pxref{Variable Attributes}). - -@table @gcctabopt -@item -Wunused-const-variable=1 -This is the warning level that is enabled by @option{-Wunused-variable} for -C. It warns only about unused static const variables defined in the main -compilation unit, but not about static const variables declared in any -header included. - -@item -Wunused-const-variable=2 -This warning level also warns for unused constant static variables in -headers (excluding system headers). This is the warning level of -@option{-Wunused-const-variable} and must be explicitly requested since -in C++ this isn't an error and in C it might be harder to clean up all -headers included. -@end table - -@item -Wunused-value -@opindex Wunused-value -@opindex Wno-unused-value -Warn whenever a statement computes a result that is explicitly not -used. To suppress this warning cast the unused expression to -@code{void}. This includes an expression-statement or the left-hand -side of a comma expression that contains no side effects. For example, -an expression such as @code{x[i,j]} causes a warning, while -@code{x[(void)i,j]} does not. - -This warning is enabled by @option{-Wall}. - -@item -Wunused -@opindex Wunused -@opindex Wno-unused -All the above @option{-Wunused} options combined. - -In order to get a warning about an unused function parameter, you must -either specify @option{-Wextra -Wunused} (note that @option{-Wall} implies -@option{-Wunused}), or separately specify @option{-Wunused-parameter}. - -@item -Wuninitialized -@opindex Wuninitialized -@opindex Wno-uninitialized -Warn if an object with automatic or allocated storage duration is used -without having been initialized. In C++, also warn if a non-static -reference or non-static @code{const} member appears in a class without -constructors. - -In addition, passing a pointer (or in C++, a reference) to an uninitialized -object to a @code{const}-qualified argument of a built-in function known to -read the object is also diagnosed by this warning. -(@option{-Wmaybe-uninitialized} is issued for ordinary functions.) - -If you want to warn about code that uses the uninitialized value of the -variable in its own initializer, use the @option{-Winit-self} option. - -These warnings occur for individual uninitialized elements of -structure, union or array variables as well as for variables that are -uninitialized as a whole. They do not occur for variables or elements -declared @code{volatile}. Because these warnings depend on -optimization, the exact variables or elements for which there are -warnings depend on the precise optimization options and version of GCC -used. - -Note that there may be no warning about a variable that is used only -to compute a value that itself is never used, because such -computations may be deleted by data flow analysis before the warnings -are printed. - -In C++, this warning also warns about using uninitialized objects in -member-initializer-lists. For example, GCC warns about @code{b} being -uninitialized in the following snippet: - -@smallexample -struct A @{ - int a; - int b; - A() : a(b) @{ @} -@}; -@end smallexample - -@item -Wno-invalid-memory-model -@opindex Winvalid-memory-model -@opindex Wno-invalid-memory-model -This option controls warnings -for invocations of @ref{__atomic Builtins}, @ref{__sync Builtins}, -and the C11 atomic generic functions with a memory consistency argument -that is either invalid for the operation or outside the range of values -of the @code{memory_order} enumeration. For example, since the -@code{__atomic_store} and @code{__atomic_store_n} built-ins are only -defined for the relaxed, release, and sequentially consistent memory -orders the following code is diagnosed: - -@smallexample -void store (int *i) -@{ - __atomic_store_n (i, 0, memory_order_consume); -@} -@end smallexample - -@option{-Winvalid-memory-model} is enabled by default. - -@item -Wmaybe-uninitialized -@opindex Wmaybe-uninitialized -@opindex Wno-maybe-uninitialized -For an object with automatic or allocated storage duration, if there exists -a path from the function entry to a use of the object that is initialized, -but there exist some other paths for which the object is not initialized, -the compiler emits a warning if it cannot prove the uninitialized paths -are not executed at run time. - -In addition, passing a pointer (or in C++, a reference) to an uninitialized -object to a @code{const}-qualified function argument is also diagnosed by -this warning. (@option{-Wuninitialized} is issued for built-in functions -known to read the object.) Annotating the function with attribute -@code{access (none)} indicates that the argument isn't used to access -the object and avoids the warning (@pxref{Common Function Attributes}). - -These warnings are only possible in optimizing compilation, because otherwise -GCC does not keep track of the state of variables. - -These warnings are made optional because GCC may not be able to determine when -the code is correct in spite of appearing to have an error. Here is one -example of how this can happen: - -@smallexample -@group -@{ - int x; - switch (y) - @{ - case 1: x = 1; - break; - case 2: x = 4; - break; - case 3: x = 5; - @} - foo (x); -@} -@end group -@end smallexample - -@noindent -If the value of @code{y} is always 1, 2 or 3, then @code{x} is -always initialized, but GCC doesn't know this. To suppress the -warning, you need to provide a default case with assert(0) or -similar code. - -@cindex @code{longjmp} warnings -This option also warns when a non-volatile automatic variable might be -changed by a call to @code{longjmp}. -The compiler sees only the calls to @code{setjmp}. It cannot know -where @code{longjmp} will be called; in fact, a signal handler could -call it at any point in the code. As a result, you may get a warning -even when there is in fact no problem because @code{longjmp} cannot -in fact be called at the place that would cause a problem. - -Some spurious warnings can be avoided if you declare all the functions -you use that never return as @code{noreturn}. @xref{Function -Attributes}. - -This warning is enabled by @option{-Wall} or @option{-Wextra}. - -@item -Wunknown-pragmas -@opindex Wunknown-pragmas -@opindex Wno-unknown-pragmas -@cindex warning for unknown pragmas -@cindex unknown pragmas, warning -@cindex pragmas, warning of unknown -Warn when a @code{#pragma} directive is encountered that is not understood by -GCC@. If this command-line option is used, warnings are even issued -for unknown pragmas in system header files. This is not the case if -the warnings are only enabled by the @option{-Wall} command-line option. - -@item -Wno-pragmas -@opindex Wno-pragmas -@opindex Wpragmas -Do not warn about misuses of pragmas, such as incorrect parameters, -invalid syntax, or conflicts between pragmas. See also -@option{-Wunknown-pragmas}. - -@item -Wno-prio-ctor-dtor -@opindex Wno-prio-ctor-dtor -@opindex Wprio-ctor-dtor -Do not warn if a priority from 0 to 100 is used for constructor or destructor. -The use of constructor and destructor attributes allow you to assign a -priority to the constructor/destructor to control its order of execution -before @code{main} is called or after it returns. The priority values must be -greater than 100 as the compiler reserves priority values between 0--100 for -the implementation. - -@item -Wstrict-aliasing -@opindex Wstrict-aliasing -@opindex Wno-strict-aliasing -This option is only active when @option{-fstrict-aliasing} is active. -It warns about code that might break the strict aliasing rules that the -compiler is using for optimization. The warning does not catch all -cases, but does attempt to catch the more common pitfalls. It is -included in @option{-Wall}. -It is equivalent to @option{-Wstrict-aliasing=3} - -@item -Wstrict-aliasing=n -@opindex Wstrict-aliasing=n -This option is only active when @option{-fstrict-aliasing} is active. -It warns about code that might break the strict aliasing rules that the -compiler is using for optimization. -Higher levels correspond to higher accuracy (fewer false positives). -Higher levels also correspond to more effort, similar to the way @option{-O} -works. -@option{-Wstrict-aliasing} is equivalent to @option{-Wstrict-aliasing=3}. - -Level 1: Most aggressive, quick, least accurate. -Possibly useful when higher levels -do not warn but @option{-fstrict-aliasing} still breaks the code, as it has very few -false negatives. However, it has many false positives. -Warns for all pointer conversions between possibly incompatible types, -even if never dereferenced. Runs in the front end only. - -Level 2: Aggressive, quick, not too precise. -May still have many false positives (not as many as level 1 though), -and few false negatives (but possibly more than level 1). -Unlike level 1, it only warns when an address is taken. Warns about -incomplete types. Runs in the front end only. - -Level 3 (default for @option{-Wstrict-aliasing}): -Should have very few false positives and few false -negatives. Slightly slower than levels 1 or 2 when optimization is enabled. -Takes care of the common pun+dereference pattern in the front end: -@code{*(int*)&some_float}. -If optimization is enabled, it also runs in the back end, where it deals -with multiple statement cases using flow-sensitive points-to information. -Only warns when the converted pointer is dereferenced. -Does not warn about incomplete types. - -@item -Wstrict-overflow -@itemx -Wstrict-overflow=@var{n} -@opindex Wstrict-overflow -@opindex Wno-strict-overflow -This option is only active when signed overflow is undefined. -It warns about cases where the compiler optimizes based on the -assumption that signed overflow does not occur. Note that it does not -warn about all cases where the code might overflow: it only warns -about cases where the compiler implements some optimization. Thus -this warning depends on the optimization level. - -An optimization that assumes that signed overflow does not occur is -perfectly safe if the values of the variables involved are such that -overflow never does, in fact, occur. Therefore this warning can -easily give a false positive: a warning about code that is not -actually a problem. To help focus on important issues, several -warning levels are defined. No warnings are issued for the use of -undefined signed overflow when estimating how many iterations a loop -requires, in particular when determining whether a loop will be -executed at all. - -@table @gcctabopt -@item -Wstrict-overflow=1 -Warn about cases that are both questionable and easy to avoid. For -example the compiler simplifies -@code{x + 1 > x} to @code{1}. This level of -@option{-Wstrict-overflow} is enabled by @option{-Wall}; higher levels -are not, and must be explicitly requested. - -@item -Wstrict-overflow=2 -Also warn about other cases where a comparison is simplified to a -constant. For example: @code{abs (x) >= 0}. This can only be -simplified when signed integer overflow is undefined, because -@code{abs (INT_MIN)} overflows to @code{INT_MIN}, which is less than -zero. @option{-Wstrict-overflow} (with no level) is the same as -@option{-Wstrict-overflow=2}. - -@item -Wstrict-overflow=3 -Also warn about other cases where a comparison is simplified. For -example: @code{x + 1 > 1} is simplified to @code{x > 0}. - -@item -Wstrict-overflow=4 -Also warn about other simplifications not covered by the above cases. -For example: @code{(x * 10) / 5} is simplified to @code{x * 2}. - -@item -Wstrict-overflow=5 -Also warn about cases where the compiler reduces the magnitude of a -constant involved in a comparison. For example: @code{x + 2 > y} is -simplified to @code{x + 1 >= y}. This is reported only at the -highest warning level because this simplification applies to many -comparisons, so this warning level gives a very large number of -false positives. -@end table - -@item -Wstring-compare -@opindex Wstring-compare -@opindex Wno-string-compare -Warn for calls to @code{strcmp} and @code{strncmp} whose result is -determined to be either zero or non-zero in tests for such equality -owing to the length of one argument being greater than the size of -the array the other argument is stored in (or the bound in the case -of @code{strncmp}). Such calls could be mistakes. For example, -the call to @code{strcmp} below is diagnosed because its result is -necessarily non-zero irrespective of the contents of the array @code{a}. - -@smallexample -extern char a[4]; -void f (char *d) -@{ - strcpy (d, "string"); - @dots{} - if (0 == strcmp (a, d)) // cannot be true - puts ("a and d are the same"); -@} -@end smallexample - -@option{-Wstring-compare} is enabled by @option{-Wextra}. - -@item -Wno-stringop-overflow -@item -Wstringop-overflow -@itemx -Wstringop-overflow=@var{type} -@opindex Wstringop-overflow -@opindex Wno-stringop-overflow -Warn for calls to string manipulation functions such as @code{memcpy} and -@code{strcpy} that are determined to overflow the destination buffer. The -optional argument is one greater than the type of Object Size Checking to -perform to determine the size of the destination. @xref{Object Size Checking}. -The argument is meaningful only for functions that operate on character arrays -but not for raw memory functions like @code{memcpy} which always make use -of Object Size type-0. The option also warns for calls that specify a size -in excess of the largest possible object or at most @code{SIZE_MAX / 2} bytes. -The option produces the best results with optimization enabled but can detect -a small subset of simple buffer overflows even without optimization in -calls to the GCC built-in functions like @code{__builtin_memcpy} that -correspond to the standard functions. In any case, the option warns about -just a subset of buffer overflows detected by the corresponding overflow -checking built-ins. For example, the option issues a warning for -the @code{strcpy} call below because it copies at least 5 characters -(the string @code{"blue"} including the terminating NUL) into the buffer -of size 4. - -@smallexample -enum Color @{ blue, purple, yellow @}; -const char* f (enum Color clr) -@{ - static char buf [4]; - const char *str; - switch (clr) - @{ - case blue: str = "blue"; break; - case purple: str = "purple"; break; - case yellow: str = "yellow"; break; - @} - - return strcpy (buf, str); // warning here -@} -@end smallexample - -Option @option{-Wstringop-overflow=2} is enabled by default. - -@table @gcctabopt -@item -Wstringop-overflow -@itemx -Wstringop-overflow=1 -@opindex Wstringop-overflow -@opindex Wno-stringop-overflow -The @option{-Wstringop-overflow=1} option uses type-zero Object Size Checking -to determine the sizes of destination objects. At this setting the option -does not warn for writes past the end of subobjects of larger objects accessed -by pointers unless the size of the largest surrounding object is known. When -the destination may be one of several objects it is assumed to be the largest -one of them. On Linux systems, when optimization is enabled at this setting -the option warns for the same code as when the @code{_FORTIFY_SOURCE} macro -is defined to a non-zero value. - -@item -Wstringop-overflow=2 -The @option{-Wstringop-overflow=2} option uses type-one Object Size Checking -to determine the sizes of destination objects. At this setting the option -warns about overflows when writing to members of the largest complete -objects whose exact size is known. However, it does not warn for excessive -writes to the same members of unknown objects referenced by pointers since -they may point to arrays containing unknown numbers of elements. This is -the default setting of the option. - -@item -Wstringop-overflow=3 -The @option{-Wstringop-overflow=3} option uses type-two Object Size Checking -to determine the sizes of destination objects. At this setting the option -warns about overflowing the smallest object or data member. This is the -most restrictive setting of the option that may result in warnings for safe -code. - -@item -Wstringop-overflow=4 -The @option{-Wstringop-overflow=4} option uses type-three Object Size Checking -to determine the sizes of destination objects. At this setting the option -warns about overflowing any data members, and when the destination is -one of several objects it uses the size of the largest of them to decide -whether to issue a warning. Similarly to @option{-Wstringop-overflow=3} this -setting of the option may result in warnings for benign code. -@end table - -@item -Wno-stringop-overread -@opindex Wstringop-overread -@opindex Wno-stringop-overread -Warn for calls to string manipulation functions such as @code{memchr}, or -@code{strcpy} that are determined to read past the end of the source -sequence. - -Option @option{-Wstringop-overread} is enabled by default. - -@item -Wno-stringop-truncation -@opindex Wstringop-truncation -@opindex Wno-stringop-truncation -Do not warn for calls to bounded string manipulation functions -such as @code{strncat}, -@code{strncpy}, and @code{stpncpy} that may either truncate the copied string -or leave the destination unchanged. - -In the following example, the call to @code{strncat} specifies a bound that -is less than the length of the source string. As a result, the copy of -the source will be truncated and so the call is diagnosed. To avoid the -warning use @code{bufsize - strlen (buf) - 1)} as the bound. - -@smallexample -void append (char *buf, size_t bufsize) -@{ - strncat (buf, ".txt", 3); -@} -@end smallexample - -As another example, the following call to @code{strncpy} results in copying -to @code{d} just the characters preceding the terminating NUL, without -appending the NUL to the end. Assuming the result of @code{strncpy} is -necessarily a NUL-terminated string is a common mistake, and so the call -is diagnosed. To avoid the warning when the result is not expected to be -NUL-terminated, call @code{memcpy} instead. - -@smallexample -void copy (char *d, const char *s) -@{ - strncpy (d, s, strlen (s)); -@} -@end smallexample - -In the following example, the call to @code{strncpy} specifies the size -of the destination buffer as the bound. If the length of the source -string is equal to or greater than this size the result of the copy will -not be NUL-terminated. Therefore, the call is also diagnosed. To avoid -the warning, specify @code{sizeof buf - 1} as the bound and set the last -element of the buffer to @code{NUL}. - -@smallexample -void copy (const char *s) -@{ - char buf[80]; - strncpy (buf, s, sizeof buf); - @dots{} -@} -@end smallexample - -In situations where a character array is intended to store a sequence -of bytes with no terminating @code{NUL} such an array may be annotated -with attribute @code{nonstring} to avoid this warning. Such arrays, -however, are not suitable arguments to functions that expect -@code{NUL}-terminated strings. To help detect accidental misuses of -such arrays GCC issues warnings unless it can prove that the use is -safe. @xref{Common Variable Attributes}. - -@item -Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{|}cold@r{|}malloc@r{]} -@opindex Wsuggest-attribute= -@opindex Wno-suggest-attribute= -Warn for cases where adding an attribute may be beneficial. The -attributes currently supported are listed below. - -@table @gcctabopt -@item -Wsuggest-attribute=pure -@itemx -Wsuggest-attribute=const -@itemx -Wsuggest-attribute=noreturn -@itemx -Wmissing-noreturn -@itemx -Wsuggest-attribute=malloc -@opindex Wsuggest-attribute=pure -@opindex Wno-suggest-attribute=pure -@opindex Wsuggest-attribute=const -@opindex Wno-suggest-attribute=const -@opindex Wsuggest-attribute=noreturn -@opindex Wno-suggest-attribute=noreturn -@opindex Wmissing-noreturn -@opindex Wno-missing-noreturn -@opindex Wsuggest-attribute=malloc -@opindex Wno-suggest-attribute=malloc - -Warn about functions that might be candidates for attributes -@code{pure}, @code{const} or @code{noreturn} or @code{malloc}. The compiler -only warns for functions visible in other compilation units or (in the case of -@code{pure} and @code{const}) if it cannot prove that the function returns -normally. A function returns normally if it doesn't contain an infinite loop or -return abnormally by throwing, calling @code{abort} or trapping. This analysis -requires option @option{-fipa-pure-const}, which is enabled by default at -@option{-O} and higher. Higher optimization levels improve the accuracy -of the analysis. - -@item -Wsuggest-attribute=format -@itemx -Wmissing-format-attribute -@opindex Wsuggest-attribute=format -@opindex Wmissing-format-attribute -@opindex Wno-suggest-attribute=format -@opindex Wno-missing-format-attribute -@opindex Wformat -@opindex Wno-format - -Warn about function pointers that might be candidates for @code{format} -attributes. Note these are only possible candidates, not absolute ones. -GCC guesses that function pointers with @code{format} attributes that -are used in assignment, initialization, parameter passing or return -statements should have a corresponding @code{format} attribute in the -resulting type. I.e.@: the left-hand side of the assignment or -initialization, the type of the parameter variable, or the return type -of the containing function respectively should also have a @code{format} -attribute to avoid the warning. - -GCC also warns about function definitions that might be -candidates for @code{format} attributes. Again, these are only -possible candidates. GCC guesses that @code{format} attributes -might be appropriate for any function that calls a function like -@code{vprintf} or @code{vscanf}, but this might not always be the -case, and some functions for which @code{format} attributes are -appropriate may not be detected. - -@item -Wsuggest-attribute=cold -@opindex Wsuggest-attribute=cold -@opindex Wno-suggest-attribute=cold - -Warn about functions that might be candidates for @code{cold} attribute. This -is based on static detection and generally only warns about functions which -always leads to a call to another @code{cold} function such as wrappers of -C++ @code{throw} or fatal error reporting functions leading to @code{abort}. -@end table - -@item -Walloc-zero -@opindex Wno-alloc-zero -@opindex Walloc-zero -Warn about calls to allocation functions decorated with attribute -@code{alloc_size} that specify zero bytes, including those to the built-in -forms of the functions @code{aligned_alloc}, @code{alloca}, @code{calloc}, -@code{malloc}, and @code{realloc}. Because the behavior of these functions -when called with a zero size differs among implementations (and in the case -of @code{realloc} has been deprecated) relying on it may result in subtle -portability bugs and should be avoided. - -@item -Walloc-size-larger-than=@var{byte-size} -@opindex Walloc-size-larger-than= -@opindex Wno-alloc-size-larger-than -Warn about calls to functions decorated with attribute @code{alloc_size} -that attempt to allocate objects larger than the specified number of bytes, -or where the result of the size computation in an integer type with infinite -precision would exceed the value of @samp{PTRDIFF_MAX} on the target. -@option{-Walloc-size-larger-than=}@samp{PTRDIFF_MAX} is enabled by default. -Warnings controlled by the option can be disabled either by specifying -@var{byte-size} of @samp{SIZE_MAX} or more or by -@option{-Wno-alloc-size-larger-than}. -@xref{Function Attributes}. - -@item -Wno-alloc-size-larger-than -@opindex Wno-alloc-size-larger-than -Disable @option{-Walloc-size-larger-than=} warnings. The option is -equivalent to @option{-Walloc-size-larger-than=}@samp{SIZE_MAX} or -larger. - -@item -Walloca -@opindex Wno-alloca -@opindex Walloca -This option warns on all uses of @code{alloca} in the source. - -@item -Walloca-larger-than=@var{byte-size} -@opindex Walloca-larger-than= -@opindex Wno-alloca-larger-than -This option warns on calls to @code{alloca} with an integer argument whose -value is either zero, or that is not bounded by a controlling predicate -that limits its value to at most @var{byte-size}. It also warns for calls -to @code{alloca} where the bound value is unknown. Arguments of non-integer -types are considered unbounded even if they appear to be constrained to -the expected range. - -For example, a bounded case of @code{alloca} could be: - -@smallexample -void func (size_t n) -@{ - void *p; - if (n <= 1000) - p = alloca (n); - else - p = malloc (n); - f (p); -@} -@end smallexample - -In the above example, passing @code{-Walloca-larger-than=1000} would not -issue a warning because the call to @code{alloca} is known to be at most -1000 bytes. However, if @code{-Walloca-larger-than=500} were passed, -the compiler would emit a warning. - -Unbounded uses, on the other hand, are uses of @code{alloca} with no -controlling predicate constraining its integer argument. For example: - -@smallexample -void func () -@{ - void *p = alloca (n); - f (p); -@} -@end smallexample - -If @code{-Walloca-larger-than=500} were passed, the above would trigger -a warning, but this time because of the lack of bounds checking. - -Note, that even seemingly correct code involving signed integers could -cause a warning: - -@smallexample -void func (signed int n) -@{ - if (n < 500) - @{ - p = alloca (n); - f (p); - @} -@} -@end smallexample - -In the above example, @var{n} could be negative, causing a larger than -expected argument to be implicitly cast into the @code{alloca} call. - -This option also warns when @code{alloca} is used in a loop. - -@option{-Walloca-larger-than=}@samp{PTRDIFF_MAX} is enabled by default -but is usually only effective when @option{-ftree-vrp} is active (default -for @option{-O2} and above). - -See also @option{-Wvla-larger-than=}@samp{byte-size}. - -@item -Wno-alloca-larger-than -@opindex Wno-alloca-larger-than -Disable @option{-Walloca-larger-than=} warnings. The option is -equivalent to @option{-Walloca-larger-than=}@samp{SIZE_MAX} or larger. - -@item -Warith-conversion -@opindex Warith-conversion -@opindex Wno-arith-conversion -Do warn about implicit conversions from arithmetic operations even -when conversion of the operands to the same type cannot change their -values. This affects warnings from @option{-Wconversion}, -@option{-Wfloat-conversion}, and @option{-Wsign-conversion}. - -@smallexample -@group -void f (char c, int i) -@{ - c = c + i; // warns with @option{-Wconversion} - c = c + 1; // only warns with @option{-Warith-conversion} -@} -@end group -@end smallexample - -@item -Warray-bounds -@itemx -Warray-bounds=@var{n} -@opindex Wno-array-bounds -@opindex Warray-bounds -Warn about out of bounds subscripts or offsets into arrays. This warning -is enabled by @option{-Wall}. It is more effective when @option{-ftree-vrp} -is active (the default for @option{-O2} and above) but a subset of instances -are issued even without optimization. - -@table @gcctabopt -@item -Warray-bounds=1 -This is the default warning level of @option{-Warray-bounds} and is enabled -by @option{-Wall}; higher levels are not, and must be explicitly requested. - -@item -Warray-bounds=2 -This warning level also warns about out of bounds accesses to trailing -struct members of one-element array types (@pxref{Zero Length}) and about -the intermediate results of pointer arithmetic that may yield out of bounds -values. This warning level may give a larger number of false positives and -is deactivated by default. -@end table - -@item -Warray-compare -@opindex Warray-compare -@opindex Wno-array-compare -Warn about equality and relational comparisons between two operands of array -type. This comparison was deprecated in C++20. For example: - -@smallexample -int arr1[5]; -int arr2[5]; -bool same = arr1 == arr2; -@end smallexample - -@option{-Warray-compare} is enabled by @option{-Wall}. - -@item -Warray-parameter -@itemx -Warray-parameter=@var{n} -@opindex Wno-array-parameter -Warn about redeclarations of functions involving arguments of array or -pointer types of inconsistent kinds or forms, and enable the detection -of out-of-bounds accesses to such parameters by warnings such as -@option{-Warray-bounds}. - -If the first function declaration uses the array form the bound specified -in the array is assumed to be the minimum number of elements expected to -be provided in calls to the function and the maximum number of elements -accessed by it. Failing to provide arguments of sufficient size or accessing -more than the maximum number of elements may be diagnosed by warnings such -as @option{-Warray-bounds}. At level 1 the warning diagnoses inconsistencies -involving array parameters declared using the @code{T[static N]} form. - -For example, the warning triggers for the following redeclarations because -the first one allows an array of any size to be passed to @code{f} while -the second one with the keyword @code{static} specifies that the array -argument must have at least four elements. - -@smallexample -void f (int[static 4]); -void f (int[]); // warning (inconsistent array form) - -void g (void) -@{ - int *p = (int *)malloc (4); - f (p); // warning (array too small) - @dots{} -@} -@end smallexample - -At level 2 the warning also triggers for redeclarations involving any other -inconsistency in array or pointer argument forms denoting array sizes. -Pointers and arrays of unspecified bound are considered equivalent and do -not trigger a warning. - -@smallexample -void g (int*); -void g (int[]); // no warning -void g (int[8]); // warning (inconsistent array bound) -@end smallexample - -@option{-Warray-parameter=2} is included in @option{-Wall}. The -@option{-Wvla-parameter} option triggers warnings for similar inconsistencies -involving Variable Length Array arguments. - -@item -Wattribute-alias=@var{n} -@itemx -Wno-attribute-alias -@opindex Wattribute-alias -@opindex Wno-attribute-alias -Warn about declarations using the @code{alias} and similar attributes whose -target is incompatible with the type of the alias. -@xref{Function Attributes,,Declaring Attributes of Functions}. - -@table @gcctabopt -@item -Wattribute-alias=1 -The default warning level of the @option{-Wattribute-alias} option diagnoses -incompatibilities between the type of the alias declaration and that of its -target. Such incompatibilities are typically indicative of bugs. - -@item -Wattribute-alias=2 - -At this level @option{-Wattribute-alias} also diagnoses cases where -the attributes of the alias declaration are more restrictive than the -attributes applied to its target. These mismatches can potentially -result in incorrect code generation. In other cases they may be -benign and could be resolved simply by adding the missing attribute to -the target. For comparison, see the @option{-Wmissing-attributes} -option, which controls diagnostics when the alias declaration is less -restrictive than the target, rather than more restrictive. - -Attributes considered include @code{alloc_align}, @code{alloc_size}, -@code{cold}, @code{const}, @code{hot}, @code{leaf}, @code{malloc}, -@code{nonnull}, @code{noreturn}, @code{nothrow}, @code{pure}, -@code{returns_nonnull}, and @code{returns_twice}. -@end table - -@option{-Wattribute-alias} is equivalent to @option{-Wattribute-alias=1}. -This is the default. You can disable these warnings with either -@option{-Wno-attribute-alias} or @option{-Wattribute-alias=0}. - -@item -Wbidi-chars=@r{[}none@r{|}unpaired@r{|}any@r{|}ucn@r{]} -@opindex Wbidi-chars= -@opindex Wbidi-chars -@opindex Wno-bidi-chars -Warn about possibly misleading UTF-8 bidirectional control characters in -comments, string literals, character constants, and identifiers. Such -characters can change left-to-right writing direction into right-to-left -(and vice versa), which can cause confusion between the logical order and -visual order. This may be dangerous; for instance, it may seem that a piece -of code is not commented out, whereas it in fact is. - -There are three levels of warning supported by GCC@. The default is -@option{-Wbidi-chars=unpaired}, which warns about improperly terminated -bidi contexts. @option{-Wbidi-chars=none} turns the warning off. -@option{-Wbidi-chars=any} warns about any use of bidirectional control -characters. - -By default, this warning does not warn about UCNs. It is, however, possible -to turn on such checking by using @option{-Wbidi-chars=unpaired,ucn} or -@option{-Wbidi-chars=any,ucn}. Using @option{-Wbidi-chars=ucn} is valid, -and is equivalent to @option{-Wbidi-chars=unpaired,ucn}, if no previous -@option{-Wbidi-chars=any} was specified. - -@item -Wbool-compare -@opindex Wno-bool-compare -@opindex Wbool-compare -Warn about boolean expression compared with an integer value different from -@code{true}/@code{false}. For instance, the following comparison is -always false: -@smallexample -int n = 5; -@dots{} -if ((n > 1) == 2) @{ @dots{} @} -@end smallexample -This warning is enabled by @option{-Wall}. - -@item -Wbool-operation -@opindex Wno-bool-operation -@opindex Wbool-operation -Warn about suspicious operations on expressions of a boolean type. For -instance, bitwise negation of a boolean is very likely a bug in the program. -For C, this warning also warns about incrementing or decrementing a boolean, -which rarely makes sense. (In C++, decrementing a boolean is always invalid. -Incrementing a boolean is invalid in C++17, and deprecated otherwise.) - -This warning is enabled by @option{-Wall}. - -@item -Wduplicated-branches -@opindex Wno-duplicated-branches -@opindex Wduplicated-branches -Warn when an if-else has identical branches. This warning detects cases like -@smallexample -if (p != NULL) - return 0; -else - return 0; -@end smallexample -It doesn't warn when both branches contain just a null statement. This warning -also warn for conditional operators: -@smallexample - int i = x ? *p : *p; -@end smallexample - -@item -Wduplicated-cond -@opindex Wno-duplicated-cond -@opindex Wduplicated-cond -Warn about duplicated conditions in an if-else-if chain. For instance, -warn for the following code: -@smallexample -if (p->q != NULL) @{ @dots{} @} -else if (p->q != NULL) @{ @dots{} @} -@end smallexample - -@item -Wframe-address -@opindex Wno-frame-address -@opindex Wframe-address -Warn when the @samp{__builtin_frame_address} or @samp{__builtin_return_address} -is called with an argument greater than 0. Such calls may return indeterminate -values or crash the program. The warning is included in @option{-Wall}. - -@item -Wno-discarded-qualifiers @r{(C and Objective-C only)} -@opindex Wno-discarded-qualifiers -@opindex Wdiscarded-qualifiers -Do not warn if type qualifiers on pointers are being discarded. -Typically, the compiler warns if a @code{const char *} variable is -passed to a function that takes a @code{char *} parameter. This option -can be used to suppress such a warning. - -@item -Wno-discarded-array-qualifiers @r{(C and Objective-C only)} -@opindex Wno-discarded-array-qualifiers -@opindex Wdiscarded-array-qualifiers -Do not warn if type qualifiers on arrays which are pointer targets -are being discarded. Typically, the compiler warns if a -@code{const int (*)[]} variable is passed to a function that -takes a @code{int (*)[]} parameter. This option can be used to -suppress such a warning. - -@item -Wno-incompatible-pointer-types @r{(C and Objective-C only)} -@opindex Wno-incompatible-pointer-types -@opindex Wincompatible-pointer-types -Do not warn when there is a conversion between pointers that have incompatible -types. This warning is for cases not covered by @option{-Wno-pointer-sign}, -which warns for pointer argument passing or assignment with different -signedness. - -@item -Wno-int-conversion @r{(C and Objective-C only)} -@opindex Wno-int-conversion -@opindex Wint-conversion -Do not warn about incompatible integer to pointer and pointer to integer -conversions. This warning is about implicit conversions; for explicit -conversions the warnings @option{-Wno-int-to-pointer-cast} and -@option{-Wno-pointer-to-int-cast} may be used. - -@item -Wzero-length-bounds -@opindex Wzero-length-bounds -@opindex Wzero-length-bounds -Warn about accesses to elements of zero-length array members that might -overlap other members of the same object. Declaring interior zero-length -arrays is discouraged because accesses to them are undefined. See -@xref{Zero Length}. - -For example, the first two stores in function @code{bad} are diagnosed -because the array elements overlap the subsequent members @code{b} and -@code{c}. The third store is diagnosed by @option{-Warray-bounds} -because it is beyond the bounds of the enclosing object. - -@smallexample -struct X @{ int a[0]; int b, c; @}; -struct X x; - -void bad (void) -@{ - x.a[0] = 0; // -Wzero-length-bounds - x.a[1] = 1; // -Wzero-length-bounds - x.a[2] = 2; // -Warray-bounds -@} -@end smallexample - -Option @option{-Wzero-length-bounds} is enabled by @option{-Warray-bounds}. - -@item -Wno-div-by-zero -@opindex Wno-div-by-zero -@opindex Wdiv-by-zero -Do not warn about compile-time integer division by zero. Floating-point -division by zero is not warned about, as it can be a legitimate way of -obtaining infinities and NaNs. - -@item -Wsystem-headers -@opindex Wsystem-headers -@opindex Wno-system-headers -@cindex warnings from system headers -@cindex system headers, warnings from -Print warning messages for constructs found in system header files. -Warnings from system headers are normally suppressed, on the assumption -that they usually do not indicate real problems and would only make the -compiler output harder to read. Using this command-line option tells -GCC to emit warnings from system headers as if they occurred in user -code. However, note that using @option{-Wall} in conjunction with this -option does @emph{not} warn about unknown pragmas in system -headers---for that, @option{-Wunknown-pragmas} must also be used. - -@item -Wtautological-compare -@opindex Wtautological-compare -@opindex Wno-tautological-compare -Warn if a self-comparison always evaluates to true or false. This -warning detects various mistakes such as: -@smallexample -int i = 1; -@dots{} -if (i > i) @{ @dots{} @} -@end smallexample - -This warning also warns about bitwise comparisons that always evaluate -to true or false, for instance: -@smallexample -if ((a & 16) == 10) @{ @dots{} @} -@end smallexample -will always be false. - -This warning is enabled by @option{-Wall}. - -@item -Wtrampolines -@opindex Wtrampolines -@opindex Wno-trampolines -Warn about trampolines generated for pointers to nested functions. -A trampoline is a small piece of data or code that is created at run -time on the stack when the address of a nested function is taken, and is -used to call the nested function indirectly. For some targets, it is -made up of data only and thus requires no special treatment. But, for -most targets, it is made up of code and thus requires the stack to be -made executable in order for the program to work properly. - -@item -Wfloat-equal -@opindex Wfloat-equal -@opindex Wno-float-equal -Warn if floating-point values are used in equality comparisons. - -The idea behind this is that sometimes it is convenient (for the -programmer) to consider floating-point values as approximations to -infinitely precise real numbers. If you are doing this, then you need -to compute (by analyzing the code, or in some other way) the maximum or -likely maximum error that the computation introduces, and allow for it -when performing comparisons (and when producing output, but that's a -different problem). In particular, instead of testing for equality, you -should check to see whether the two values have ranges that overlap; and -this is done with the relational operators, so equality comparisons are -probably mistaken. - -@item -Wtraditional @r{(C and Objective-C only)} -@opindex Wtraditional -@opindex Wno-traditional -Warn about certain constructs that behave differently in traditional and -ISO C@. Also warn about ISO C constructs that have no traditional C -equivalent, and/or problematic constructs that should be avoided. - -@itemize @bullet -@item -Macro parameters that appear within string literals in the macro body. -In traditional C macro replacement takes place within string literals, -but in ISO C it does not. - -@item -In traditional C, some preprocessor directives did not exist. -Traditional preprocessors only considered a line to be a directive -if the @samp{#} appeared in column 1 on the line. Therefore -@option{-Wtraditional} warns about directives that traditional C -understands but ignores because the @samp{#} does not appear as the -first character on the line. It also suggests you hide directives like -@code{#pragma} not understood by traditional C by indenting them. Some -traditional implementations do not recognize @code{#elif}, so this option -suggests avoiding it altogether. - -@item -A function-like macro that appears without arguments. - -@item -The unary plus operator. - -@item -The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating-point -constant suffixes. (Traditional C does support the @samp{L} suffix on integer -constants.) Note, these suffixes appear in macros defined in the system -headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}. -Use of these macros in user code might normally lead to spurious -warnings, however GCC's integrated preprocessor has enough context to -avoid warning in these cases. - -@item -A function declared external in one block and then used after the end of -the block. - -@item -A @code{switch} statement has an operand of type @code{long}. - -@item -A non-@code{static} function declaration follows a @code{static} one. -This construct is not accepted by some traditional C compilers. - -@item -The ISO type of an integer constant has a different width or -signedness from its traditional type. This warning is only issued if -the base of the constant is ten. I.e.@: hexadecimal or octal values, which -typically represent bit patterns, are not warned about. - -@item -Usage of ISO string concatenation is detected. - -@item -Initialization of automatic aggregates. - -@item -Identifier conflicts with labels. Traditional C lacks a separate -namespace for labels. - -@item -Initialization of unions. If the initializer is zero, the warning is -omitted. This is done under the assumption that the zero initializer in -user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing -initializer warnings and relies on default initialization to zero in the -traditional C case. - -@item -Conversions by prototypes between fixed/floating-point values and vice -versa. The absence of these prototypes when compiling with traditional -C causes serious problems. This is a subset of the possible -conversion warnings; for the full set use @option{-Wtraditional-conversion}. - -@item -Use of ISO C style function definitions. This warning intentionally is -@emph{not} issued for prototype declarations or variadic functions -because these ISO C features appear in your code when using -libiberty's traditional C compatibility macros, @code{PARAMS} and -@code{VPARAMS}. This warning is also bypassed for nested functions -because that feature is already a GCC extension and thus not relevant to -traditional C compatibility. -@end itemize - -@item -Wtraditional-conversion @r{(C and Objective-C only)} -@opindex Wtraditional-conversion -@opindex Wno-traditional-conversion -Warn if a prototype causes a type conversion that is different from what -would happen to the same argument in the absence of a prototype. This -includes conversions of fixed point to floating and vice versa, and -conversions changing the width or signedness of a fixed-point argument -except when the same as the default promotion. - -@item -Wdeclaration-after-statement @r{(C and Objective-C only)} -@opindex Wdeclaration-after-statement -@opindex Wno-declaration-after-statement -Warn when a declaration is found after a statement in a block. This -construct, known from C++, was introduced with ISO C99 and is by default -allowed in GCC@. It is not supported by ISO C90. @xref{Mixed Labels and Declarations}. - -@item -Wshadow -@opindex Wshadow -@opindex Wno-shadow -Warn whenever a local variable or type declaration shadows another -variable, parameter, type, class member (in C++), or instance variable -(in Objective-C) or whenever a built-in function is shadowed. Note -that in C++, the compiler warns if a local variable shadows an -explicit typedef, but not if it shadows a struct/class/enum. -If this warning is enabled, it includes also all instances of -local shadowing. This means that @option{-Wno-shadow=local} -and @option{-Wno-shadow=compatible-local} are ignored when -@option{-Wshadow} is used. -Same as @option{-Wshadow=global}. - -@item -Wno-shadow-ivar @r{(Objective-C only)} -@opindex Wno-shadow-ivar -@opindex Wshadow-ivar -Do not warn whenever a local variable shadows an instance variable in an -Objective-C method. - -@item -Wshadow=global -@opindex Wshadow=global -Warn for any shadowing. -Same as @option{-Wshadow}. - -@item -Wshadow=local -@opindex Wshadow=local -Warn when a local variable shadows another local variable or parameter. - -@item -Wshadow=compatible-local -@opindex Wshadow=compatible-local -Warn when a local variable shadows another local variable or parameter -whose type is compatible with that of the shadowing variable. In C++, -type compatibility here means the type of the shadowing variable can be -converted to that of the shadowed variable. The creation of this flag -(in addition to @option{-Wshadow=local}) is based on the idea that when -a local variable shadows another one of incompatible type, it is most -likely intentional, not a bug or typo, as shown in the following example: - -@smallexample -@group -for (SomeIterator i = SomeObj.begin(); i != SomeObj.end(); ++i) -@{ - for (int i = 0; i < N; ++i) - @{ - ... - @} - ... -@} -@end group -@end smallexample - -Since the two variable @code{i} in the example above have incompatible types, -enabling only @option{-Wshadow=compatible-local} does not emit a warning. -Because their types are incompatible, if a programmer accidentally uses one -in place of the other, type checking is expected to catch that and emit an -error or warning. Use of this flag instead of @option{-Wshadow=local} can -possibly reduce the number of warnings triggered by intentional shadowing. -Note that this also means that shadowing @code{const char *i} by -@code{char *i} does not emit a warning. - -This warning is also enabled by @option{-Wshadow=local}. - -@item -Wlarger-than=@var{byte-size} -@opindex Wlarger-than= -@opindex Wlarger-than-@var{byte-size} -Warn whenever an object is defined whose size exceeds @var{byte-size}. -@option{-Wlarger-than=}@samp{PTRDIFF_MAX} is enabled by default. -Warnings controlled by the option can be disabled either by specifying -@var{byte-size} of @samp{SIZE_MAX} or more or by @option{-Wno-larger-than}. - -Also warn for calls to bounded functions such as @code{memchr} or -@code{strnlen} that specify a bound greater than the largest possible -object, which is @samp{PTRDIFF_MAX} bytes by default. These warnings -can only be disabled by @option{-Wno-larger-than}. - -@item -Wno-larger-than -@opindex Wno-larger-than -Disable @option{-Wlarger-than=} warnings. The option is equivalent -to @option{-Wlarger-than=}@samp{SIZE_MAX} or larger. - -@item -Wframe-larger-than=@var{byte-size} -@opindex Wframe-larger-than= -@opindex Wno-frame-larger-than -Warn if the size of a function frame exceeds @var{byte-size}. -The computation done to determine the stack frame size is approximate -and not conservative. -The actual requirements may be somewhat greater than @var{byte-size} -even if you do not get a warning. In addition, any space allocated -via @code{alloca}, variable-length arrays, or related constructs -is not included by the compiler when determining -whether or not to issue a warning. -@option{-Wframe-larger-than=}@samp{PTRDIFF_MAX} is enabled by default. -Warnings controlled by the option can be disabled either by specifying -@var{byte-size} of @samp{SIZE_MAX} or more or by -@option{-Wno-frame-larger-than}. - -@item -Wno-frame-larger-than -@opindex Wno-frame-larger-than -Disable @option{-Wframe-larger-than=} warnings. The option is equivalent -to @option{-Wframe-larger-than=}@samp{SIZE_MAX} or larger. - -@item -Wfree-nonheap-object -@opindex Wfree-nonheap-object -@opindex Wno-free-nonheap-object -Warn when attempting to deallocate an object that was either not allocated -on the heap, or by using a pointer that was not returned from a prior call -to the corresponding allocation function. For example, because the call -to @code{stpcpy} returns a pointer to the terminating nul character and -not to the beginning of the object, the call to @code{free} below is -diagnosed. - -@smallexample -void f (char *p) -@{ - p = stpcpy (p, "abc"); - // ... - free (p); // warning -@} -@end smallexample - -@option{-Wfree-nonheap-object} is included in @option{-Wall}. - -@item -Wstack-usage=@var{byte-size} -@opindex Wstack-usage -@opindex Wno-stack-usage -Warn if the stack usage of a function might exceed @var{byte-size}. -The computation done to determine the stack usage is conservative. -Any space allocated via @code{alloca}, variable-length arrays, or related -constructs is included by the compiler when determining whether or not to -issue a warning. - -The message is in keeping with the output of @option{-fstack-usage}. - -@itemize -@item -If the stack usage is fully static but exceeds the specified amount, it's: - -@smallexample - warning: stack usage is 1120 bytes -@end smallexample -@item -If the stack usage is (partly) dynamic but bounded, it's: - -@smallexample - warning: stack usage might be 1648 bytes -@end smallexample -@item -If the stack usage is (partly) dynamic and not bounded, it's: - -@smallexample - warning: stack usage might be unbounded -@end smallexample -@end itemize - -@option{-Wstack-usage=}@samp{PTRDIFF_MAX} is enabled by default. -Warnings controlled by the option can be disabled either by specifying -@var{byte-size} of @samp{SIZE_MAX} or more or by -@option{-Wno-stack-usage}. - -@item -Wno-stack-usage -@opindex Wno-stack-usage -Disable @option{-Wstack-usage=} warnings. The option is equivalent -to @option{-Wstack-usage=}@samp{SIZE_MAX} or larger. - -@item -Wunsafe-loop-optimizations -@opindex Wunsafe-loop-optimizations -@opindex Wno-unsafe-loop-optimizations -Warn if the loop cannot be optimized because the compiler cannot -assume anything on the bounds of the loop indices. With -@option{-funsafe-loop-optimizations} warn if the compiler makes -such assumptions. - -@item -Wno-pedantic-ms-format @r{(MinGW targets only)} -@opindex Wno-pedantic-ms-format -@opindex Wpedantic-ms-format -When used in combination with @option{-Wformat} -and @option{-pedantic} without GNU extensions, this option -disables the warnings about non-ISO @code{printf} / @code{scanf} format -width specifiers @code{I32}, @code{I64}, and @code{I} used on Windows targets, -which depend on the MS runtime. - -@item -Wpointer-arith -@opindex Wpointer-arith -@opindex Wno-pointer-arith -Warn about anything that depends on the ``size of'' a function type or -of @code{void}. GNU C assigns these types a size of 1, for -convenience in calculations with @code{void *} pointers and pointers -to functions. In C++, warn also when an arithmetic operation involves -@code{NULL}. This warning is also enabled by @option{-Wpedantic}. - -@item -Wno-pointer-compare -@opindex Wpointer-compare -@opindex Wno-pointer-compare -Do not warn if a pointer is compared with a zero character constant. -This usually -means that the pointer was meant to be dereferenced. For example: - -@smallexample -const char *p = foo (); -if (p == '\0') - return 42; -@end smallexample - -Note that the code above is invalid in C++11. - -This warning is enabled by default. - -@item -Wtsan -@opindex Wtsan -@opindex Wno-tsan -Warn about unsupported features in ThreadSanitizer. - -ThreadSanitizer does not support @code{std::atomic_thread_fence} and -can report false positives. - -This warning is enabled by default. - -@item -Wtype-limits -@opindex Wtype-limits -@opindex Wno-type-limits -Warn if a comparison is always true or always false due to the limited -range of the data type, but do not warn for constant expressions. For -example, warn if an unsigned variable is compared against zero with -@code{<} or @code{>=}. This warning is also enabled by -@option{-Wextra}. - -@item -Wabsolute-value @r{(C and Objective-C only)} -@opindex Wabsolute-value -@opindex Wno-absolute-value -Warn for calls to standard functions that compute the absolute value -of an argument when a more appropriate standard function is available. -For example, calling @code{abs(3.14)} triggers the warning because the -appropriate function to call to compute the absolute value of a double -argument is @code{fabs}. The option also triggers warnings when the -argument in a call to such a function has an unsigned type. This -warning can be suppressed with an explicit type cast and it is also -enabled by @option{-Wextra}. - -@include cppwarnopts.texi - -@item -Wbad-function-cast @r{(C and Objective-C only)} -@opindex Wbad-function-cast -@opindex Wno-bad-function-cast -Warn when a function call is cast to a non-matching type. -For example, warn if a call to a function returning an integer type -is cast to a pointer type. - -@item -Wc90-c99-compat @r{(C and Objective-C only)} -@opindex Wc90-c99-compat -@opindex Wno-c90-c99-compat -Warn about features not present in ISO C90, but present in ISO C99. -For instance, warn about use of variable length arrays, @code{long long} -type, @code{bool} type, compound literals, designated initializers, and so -on. This option is independent of the standards mode. Warnings are disabled -in the expression that follows @code{__extension__}. - -@item -Wc99-c11-compat @r{(C and Objective-C only)} -@opindex Wc99-c11-compat -@opindex Wno-c99-c11-compat -Warn about features not present in ISO C99, but present in ISO C11. -For instance, warn about use of anonymous structures and unions, -@code{_Atomic} type qualifier, @code{_Thread_local} storage-class specifier, -@code{_Alignas} specifier, @code{Alignof} operator, @code{_Generic} keyword, -and so on. This option is independent of the standards mode. Warnings are -disabled in the expression that follows @code{__extension__}. - -@item -Wc11-c2x-compat @r{(C and Objective-C only)} -@opindex Wc11-c2x-compat -@opindex Wno-c11-c2x-compat -Warn about features not present in ISO C11, but present in ISO C2X. -For instance, warn about omitting the string in @code{_Static_assert}, -use of @samp{[[]]} syntax for attributes, use of decimal -floating-point types, and so on. This option is independent of the -standards mode. Warnings are disabled in the expression that follows -@code{__extension__}. - -@item -Wc++-compat @r{(C and Objective-C only)} -@opindex Wc++-compat -@opindex Wno-c++-compat -Warn about ISO C constructs that are outside of the common subset of -ISO C and ISO C++, e.g.@: request for implicit conversion from -@code{void *} to a pointer to non-@code{void} type. - -@item -Wc++11-compat @r{(C++ and Objective-C++ only)} -@opindex Wc++11-compat -@opindex Wno-c++11-compat -Warn about C++ constructs whose meaning differs between ISO C++ 1998 -and ISO C++ 2011, e.g., identifiers in ISO C++ 1998 that are keywords -in ISO C++ 2011. This warning turns on @option{-Wnarrowing} and is -enabled by @option{-Wall}. - -@item -Wc++14-compat @r{(C++ and Objective-C++ only)} -@opindex Wc++14-compat -@opindex Wno-c++14-compat -Warn about C++ constructs whose meaning differs between ISO C++ 2011 -and ISO C++ 2014. This warning is enabled by @option{-Wall}. - -@item -Wc++17-compat @r{(C++ and Objective-C++ only)} -@opindex Wc++17-compat -@opindex Wno-c++17-compat -Warn about C++ constructs whose meaning differs between ISO C++ 2014 -and ISO C++ 2017. This warning is enabled by @option{-Wall}. - -@item -Wc++20-compat @r{(C++ and Objective-C++ only)} -@opindex Wc++20-compat -@opindex Wno-c++20-compat -Warn about C++ constructs whose meaning differs between ISO C++ 2017 -and ISO C++ 2020. This warning is enabled by @option{-Wall}. - -@item -Wno-c++11-extensions @r{(C++ and Objective-C++ only)} -@opindex Wc++11-extensions -@opindex Wno-c++11-extensions -Do not warn about C++11 constructs in code being compiled using -an older C++ standard. Even without this option, some C++11 constructs -will only be diagnosed if @option{-Wpedantic} is used. - -@item -Wno-c++14-extensions @r{(C++ and Objective-C++ only)} -@opindex Wc++14-extensions -@opindex Wno-c++14-extensions -Do not warn about C++14 constructs in code being compiled using -an older C++ standard. Even without this option, some C++14 constructs -will only be diagnosed if @option{-Wpedantic} is used. - -@item -Wno-c++17-extensions @r{(C++ and Objective-C++ only)} -@opindex Wc++17-extensions -@opindex Wno-c++17-extensions -Do not warn about C++17 constructs in code being compiled using -an older C++ standard. Even without this option, some C++17 constructs -will only be diagnosed if @option{-Wpedantic} is used. - -@item -Wno-c++20-extensions @r{(C++ and Objective-C++ only)} -@opindex Wc++20-extensions -@opindex Wno-c++20-extensions -Do not warn about C++20 constructs in code being compiled using -an older C++ standard. Even without this option, some C++20 constructs -will only be diagnosed if @option{-Wpedantic} is used. - -@item -Wno-c++23-extensions @r{(C++ and Objective-C++ only)} -@opindex Wc++23-extensions -@opindex Wno-c++23-extensions -Do not warn about C++23 constructs in code being compiled using -an older C++ standard. Even without this option, some C++23 constructs -will only be diagnosed if @option{-Wpedantic} is used. - -@item -Wcast-qual -@opindex Wcast-qual -@opindex Wno-cast-qual -Warn whenever a pointer is cast so as to remove a type qualifier from -the target type. For example, warn if a @code{const char *} is cast -to an ordinary @code{char *}. - -Also warn when making a cast that introduces a type qualifier in an -unsafe way. For example, casting @code{char **} to @code{const char **} -is unsafe, as in this example: - -@smallexample - /* p is char ** value. */ - const char **q = (const char **) p; - /* Assignment of readonly string to const char * is OK. */ - *q = "string"; - /* Now char** pointer points to read-only memory. */ - **p = 'b'; -@end smallexample - -@item -Wcast-align -@opindex Wcast-align -@opindex Wno-cast-align -Warn whenever a pointer is cast such that the required alignment of the -target is increased. For example, warn if a @code{char *} is cast to -an @code{int *} on machines where integers can only be accessed at -two- or four-byte boundaries. - -@item -Wcast-align=strict -@opindex Wcast-align=strict -Warn whenever a pointer is cast such that the required alignment of the -target is increased. For example, warn if a @code{char *} is cast to -an @code{int *} regardless of the target machine. - -@item -Wcast-function-type -@opindex Wcast-function-type -@opindex Wno-cast-function-type -Warn when a function pointer is cast to an incompatible function pointer. -In a cast involving function types with a variable argument list only -the types of initial arguments that are provided are considered. -Any parameter of pointer-type matches any other pointer-type. Any benign -differences in integral types are ignored, like @code{int} vs.@: @code{long} -on ILP32 targets. Likewise type qualifiers are ignored. The function -type @code{void (*) (void)} is special and matches everything, which can -be used to suppress this warning. -In a cast involving pointer to member types this warning warns whenever -the type cast is changing the pointer to member type. -This warning is enabled by @option{-Wextra}. - -@item -Wwrite-strings -@opindex Wwrite-strings -@opindex Wno-write-strings -When compiling C, give string constants the type @code{const -char[@var{length}]} so that copying the address of one into a -non-@code{const} @code{char *} pointer produces a warning. These -warnings help you find at compile time code that can try to write -into a string constant, but only if you have been very careful about -using @code{const} in declarations and prototypes. Otherwise, it is -just a nuisance. This is why we did not make @option{-Wall} request -these warnings. - -When compiling C++, warn about the deprecated conversion from string -literals to @code{char *}. This warning is enabled by default for C++ -programs. - -@item -Wclobbered -@opindex Wclobbered -@opindex Wno-clobbered -Warn for variables that might be changed by @code{longjmp} or -@code{vfork}. This warning is also enabled by @option{-Wextra}. - -@item -Wconversion -@opindex Wconversion -@opindex Wno-conversion -Warn for implicit conversions that may alter a value. This includes -conversions between real and integer, like @code{abs (x)} when -@code{x} is @code{double}; conversions between signed and unsigned, -like @code{unsigned ui = -1}; and conversions to smaller types, like -@code{sqrtf (M_PI)}. Do not warn for explicit casts like @code{abs -((int) x)} and @code{ui = (unsigned) -1}, or if the value is not -changed by the conversion like in @code{abs (2.0)}. Warnings about -conversions between signed and unsigned integers can be disabled by -using @option{-Wno-sign-conversion}. - -For C++, also warn for confusing overload resolution for user-defined -conversions; and conversions that never use a type conversion -operator: conversions to @code{void}, the same type, a base class or a -reference to them. Warnings about conversions between signed and -unsigned integers are disabled by default in C++ unless -@option{-Wsign-conversion} is explicitly enabled. - -Warnings about conversion from arithmetic on a small type back to that -type are only given with @option{-Warith-conversion}. - -@item -Wdangling-else -@opindex Wdangling-else -@opindex Wno-dangling-else -Warn about constructions where there may be confusion to which -@code{if} statement an @code{else} branch belongs. Here is an example of -such a case: - -@smallexample -@group -@{ - if (a) - if (b) - foo (); - else - bar (); -@} -@end group -@end smallexample - -In C/C++, every @code{else} branch belongs to the innermost possible -@code{if} statement, which in this example is @code{if (b)}. This is -often not what the programmer expected, as illustrated in the above -example by indentation the programmer chose. When there is the -potential for this confusion, GCC issues a warning when this flag -is specified. To eliminate the warning, add explicit braces around -the innermost @code{if} statement so there is no way the @code{else} -can belong to the enclosing @code{if}. The resulting code -looks like this: - -@smallexample -@group -@{ - if (a) - @{ - if (b) - foo (); - else - bar (); - @} -@} -@end group -@end smallexample - -This warning is enabled by @option{-Wparentheses}. - -@item -Wdangling-pointer -@itemx -Wdangling-pointer=@var{n} -@opindex Wdangling-pointer -@opindex Wno-dangling-pointer -Warn about uses of pointers (or C++ references) to objects with automatic -storage duration after their lifetime has ended. This includes local -variables declared in nested blocks, compound literals and other unnamed -temporary objects. In addition, warn about storing the address of such -objects in escaped pointers. The warning is enabled at all optimization -levels but may yield different results with optimization than without. - -@table @gcctabopt -@item -Wdangling-pointer=1 -At level 1 the warning diagnoses only unconditional uses of dangling pointers. -For example -@smallexample -int f (int c1, int c2, x) -@{ - char *p = strchr ((char[])@{ c1, c2 @}, c3); - return p ? *p : 'x'; // warning: dangling pointer to a compound literal -@} -@end smallexample -In the following function the store of the address of the local variable -@code{x} in the escaped pointer @code{*p} also triggers the warning. -@smallexample -void g (int **p) -@{ - int x = 7; - *p = &x; // warning: storing the address of a local variable in *p -@} -@end smallexample - -@item -Wdangling-pointer=2 -At level 2, in addition to unconditional uses the warning also diagnoses -conditional uses of dangling pointers. - -For example, because the array @var{a} in the following function is out of -scope when the pointer @var{s} that was set to point is used, the warning -triggers at this level. - -@smallexample -void f (char *s) -@{ - if (!s) - @{ - char a[12] = "tmpname"; - s = a; - @} - strcat (s, ".tmp"); // warning: dangling pointer to a may be used - ... -@} -@end smallexample -@end table - -@option{-Wdangling-pointer=2} is included in @option{-Wall}. - -@item -Wdate-time -@opindex Wdate-time -@opindex Wno-date-time -Warn when macros @code{__TIME__}, @code{__DATE__} or @code{__TIMESTAMP__} -are encountered as they might prevent bit-wise-identical reproducible -compilations. - -@item -Wempty-body -@opindex Wempty-body -@opindex Wno-empty-body -Warn if an empty body occurs in an @code{if}, @code{else} or @code{do -while} statement. This warning is also enabled by @option{-Wextra}. - -@item -Wno-endif-labels -@opindex Wendif-labels -@opindex Wno-endif-labels -Do not warn about stray tokens after @code{#else} and @code{#endif}. - -@item -Wenum-compare -@opindex Wenum-compare -@opindex Wno-enum-compare -Warn about a comparison between values of different enumerated types. -In C++ enumerated type mismatches in conditional expressions are also -diagnosed and the warning is enabled by default. In C this warning is -enabled by @option{-Wall}. - -@item -Wenum-conversion -@opindex Wenum-conversion -@opindex Wno-enum-conversion -Warn when a value of enumerated type is implicitly converted to a -different enumerated type. This warning is enabled by @option{-Wextra} -in C@. - -@item -Wenum-int-mismatch @r{(C and Objective-C only)} -@opindex Wenum-int-mismatch -@opindex Wno-enum-int-mismatch -Warn about mismatches between an enumerated type and an integer type in -declarations. For example: - -@smallexample -enum E @{ l = -1, z = 0, g = 1 @}; -int foo(void); -enum E foo(void); -@end smallexample - -In C, an enumerated type is compatible with @code{char}, a signed -integer type, or an unsigned integer type. However, since the choice -of the underlying type of an enumerated type is implementation-defined, -such mismatches may cause portability issues. In C++, such mismatches -are an error. In C, this warning is enabled by @option{-Wall} and -@option{-Wc++-compat}. - -@item -Wjump-misses-init @r{(C, Objective-C only)} -@opindex Wjump-misses-init -@opindex Wno-jump-misses-init -Warn if a @code{goto} statement or a @code{switch} statement jumps -forward across the initialization of a variable, or jumps backward to a -label after the variable has been initialized. This only warns about -variables that are initialized when they are declared. This warning is -only supported for C and Objective-C; in C++ this sort of branch is an -error in any case. - -@option{-Wjump-misses-init} is included in @option{-Wc++-compat}. It -can be disabled with the @option{-Wno-jump-misses-init} option. - -@item -Wsign-compare -@opindex Wsign-compare -@opindex Wno-sign-compare -@cindex warning for comparison of signed and unsigned values -@cindex comparison of signed and unsigned values, warning -@cindex signed and unsigned values, comparison warning -Warn when a comparison between signed and unsigned values could produce -an incorrect result when the signed value is converted to unsigned. -In C++, this warning is also enabled by @option{-Wall}. In C, it is -also enabled by @option{-Wextra}. - -@item -Wsign-conversion -@opindex Wsign-conversion -@opindex Wno-sign-conversion -Warn for implicit conversions that may change the sign of an integer -value, like assigning a signed integer expression to an unsigned -integer variable. An explicit cast silences the warning. In C, this -option is enabled also by @option{-Wconversion}. - -@item -Wfloat-conversion -@opindex Wfloat-conversion -@opindex Wno-float-conversion -Warn for implicit conversions that reduce the precision of a real value. -This includes conversions from real to integer, and from higher precision -real to lower precision real values. This option is also enabled by -@option{-Wconversion}. - -@item -Wno-scalar-storage-order -@opindex Wno-scalar-storage-order -@opindex Wscalar-storage-order -Do not warn on suspicious constructs involving reverse scalar storage order. - -@item -Wsizeof-array-div -@opindex Wsizeof-array-div -@opindex Wno-sizeof-array-div -Warn about divisions of two sizeof operators when the first one is applied -to an array and the divisor does not equal the size of the array element. -In such a case, the computation will not yield the number of elements in the -array, which is likely what the user intended. This warning warns e.g. about -@smallexample -int fn () -@{ - int arr[10]; - return sizeof (arr) / sizeof (short); -@} -@end smallexample - -This warning is enabled by @option{-Wall}. - -@item -Wsizeof-pointer-div -@opindex Wsizeof-pointer-div -@opindex Wno-sizeof-pointer-div -Warn for suspicious divisions of two sizeof expressions that divide -the pointer size by the element size, which is the usual way to compute -the array size but won't work out correctly with pointers. This warning -warns e.g.@: about @code{sizeof (ptr) / sizeof (ptr[0])} if @code{ptr} is -not an array, but a pointer. This warning is enabled by @option{-Wall}. - -@item -Wsizeof-pointer-memaccess -@opindex Wsizeof-pointer-memaccess -@opindex Wno-sizeof-pointer-memaccess -Warn for suspicious length parameters to certain string and memory built-in -functions if the argument uses @code{sizeof}. This warning triggers for -example for @code{memset (ptr, 0, sizeof (ptr));} if @code{ptr} is not -an array, but a pointer, and suggests a possible fix, or about -@code{memcpy (&foo, ptr, sizeof (&foo));}. @option{-Wsizeof-pointer-memaccess} -also warns about calls to bounded string copy functions like @code{strncat} -or @code{strncpy} that specify as the bound a @code{sizeof} expression of -the source array. For example, in the following function the call to -@code{strncat} specifies the size of the source string as the bound. That -is almost certainly a mistake and so the call is diagnosed. -@smallexample -void make_file (const char *name) -@{ - char path[PATH_MAX]; - strncpy (path, name, sizeof path - 1); - strncat (path, ".text", sizeof ".text"); - @dots{} -@} -@end smallexample - -The @option{-Wsizeof-pointer-memaccess} option is enabled by @option{-Wall}. - -@item -Wno-sizeof-array-argument -@opindex Wsizeof-array-argument -@opindex Wno-sizeof-array-argument -Do not warn when the @code{sizeof} operator is applied to a parameter that is -declared as an array in a function definition. This warning is enabled by -default for C and C++ programs. - -@item -Wmemset-elt-size -@opindex Wmemset-elt-size -@opindex Wno-memset-elt-size -Warn for suspicious calls to the @code{memset} built-in function, if the -first argument references an array, and the third argument is a number -equal to the number of elements, but not equal to the size of the array -in memory. This indicates that the user has omitted a multiplication by -the element size. This warning is enabled by @option{-Wall}. - -@item -Wmemset-transposed-args -@opindex Wmemset-transposed-args -@opindex Wno-memset-transposed-args -Warn for suspicious calls to the @code{memset} built-in function where -the second argument is not zero and the third argument is zero. For -example, the call @code{memset (buf, sizeof buf, 0)} is diagnosed because -@code{memset (buf, 0, sizeof buf)} was meant instead. The diagnostic -is only emitted if the third argument is a literal zero. Otherwise, if -it is an expression that is folded to zero, or a cast of zero to some -type, it is far less likely that the arguments have been mistakenly -transposed and no warning is emitted. This warning is enabled -by @option{-Wall}. - -@item -Waddress -@opindex Waddress -@opindex Wno-address -Warn about suspicious uses of address expressions. These include comparing -the address of a function or a declared object to the null pointer constant -such as in -@smallexample -void f (void); -void g (void) -@{ - if (!f) // warning: expression evaluates to false - abort (); -@} -@end smallexample -comparisons of a pointer to a string literal, such as in -@smallexample -void f (const char *x) -@{ - if (x == "abc") // warning: expression evaluates to false - puts ("equal"); -@} -@end smallexample -and tests of the results of pointer addition or subtraction for equality -to null, such as in -@smallexample -void f (const int *p, int i) -@{ - return p + i == NULL; -@} -@end smallexample -Such uses typically indicate a programmer error: the address of most -functions and objects necessarily evaluates to true (the exception are -weak symbols), so their use in a conditional might indicate missing -parentheses in a function call or a missing dereference in an array -expression. The subset of the warning for object pointers can be -suppressed by casting the pointer operand to an integer type such -as @code{intptr_t} or @code{uintptr_t}. -Comparisons against string literals result in unspecified behavior -and are not portable, and suggest the intent was to call @code{strcmp}. -The warning is suppressed if the suspicious expression is the result -of macro expansion. -@option{-Waddress} warning is enabled by @option{-Wall}. - -@item -Wno-address-of-packed-member -@opindex Waddress-of-packed-member -@opindex Wno-address-of-packed-member -Do not warn when the address of packed member of struct or union is taken, -which usually results in an unaligned pointer value. This is -enabled by default. - -@item -Wlogical-op -@opindex Wlogical-op -@opindex Wno-logical-op -Warn about suspicious uses of logical operators in expressions. -This includes using logical operators in contexts where a -bit-wise operator is likely to be expected. Also warns when -the operands of a logical operator are the same: -@smallexample -extern int a; -if (a < 0 && a < 0) @{ @dots{} @} -@end smallexample - -@item -Wlogical-not-parentheses -@opindex Wlogical-not-parentheses -@opindex Wno-logical-not-parentheses -Warn about logical not used on the left hand side operand of a comparison. -This option does not warn if the right operand is considered to be a boolean -expression. Its purpose is to detect suspicious code like the following: -@smallexample -int a; -@dots{} -if (!a > 1) @{ @dots{} @} -@end smallexample - -It is possible to suppress the warning by wrapping the LHS into -parentheses: -@smallexample -if ((!a) > 1) @{ @dots{} @} -@end smallexample - -This warning is enabled by @option{-Wall}. - -@item -Waggregate-return -@opindex Waggregate-return -@opindex Wno-aggregate-return -Warn if any functions that return structures or unions are defined or -called. (In languages where you can return an array, this also elicits -a warning.) - -@item -Wno-aggressive-loop-optimizations -@opindex Wno-aggressive-loop-optimizations -@opindex Waggressive-loop-optimizations -Warn if in a loop with constant number of iterations the compiler detects -undefined behavior in some statement during one or more of the iterations. - -@item -Wno-attributes -@opindex Wno-attributes -@opindex Wattributes -Do not warn if an unexpected @code{__attribute__} is used, such as -unrecognized attributes, function attributes applied to variables, -etc. This does not stop errors for incorrect use of supported -attributes. - -Additionally, using @option{-Wno-attributes=}, it is possible to suppress -warnings about unknown scoped attributes (in C++11 and C2X). For example, -@option{-Wno-attributes=vendor::attr} disables warning about the following -declaration: - -@smallexample -[[vendor::attr]] void f(); -@end smallexample - -It is also possible to disable warning about all attributes in a namespace -using @option{-Wno-attributes=vendor::} which prevents warning about both -of these declarations: - -@smallexample -[[vendor::safe]] void f(); -[[vendor::unsafe]] void f2(); -@end smallexample - -Note that @option{-Wno-attributes=} does not imply @option{-Wno-attributes}. - -@item -Wno-builtin-declaration-mismatch -@opindex Wno-builtin-declaration-mismatch -@opindex Wbuiltin-declaration-mismatch -Warn if a built-in function is declared with an incompatible signature -or as a non-function, or when a built-in function declared with a type -that does not include a prototype is called with arguments whose promoted -types do not match those expected by the function. When @option{-Wextra} -is specified, also warn when a built-in function that takes arguments is -declared without a prototype. The @option{-Wbuiltin-declaration-mismatch} -warning is enabled by default. To avoid the warning include the appropriate -header to bring the prototypes of built-in functions into scope. - -For example, the call to @code{memset} below is diagnosed by the warning -because the function expects a value of type @code{size_t} as its argument -but the type of @code{32} is @code{int}. With @option{-Wextra}, -the declaration of the function is diagnosed as well. -@smallexample -extern void* memset (); -void f (void *d) -@{ - memset (d, '\0', 32); -@} -@end smallexample - -@item -Wno-builtin-macro-redefined -@opindex Wno-builtin-macro-redefined -@opindex Wbuiltin-macro-redefined -Do not warn if certain built-in macros are redefined. This suppresses -warnings for redefinition of @code{__TIMESTAMP__}, @code{__TIME__}, -@code{__DATE__}, @code{__FILE__}, and @code{__BASE_FILE__}. - -@item -Wstrict-prototypes @r{(C and Objective-C only)} -@opindex Wstrict-prototypes -@opindex Wno-strict-prototypes -Warn if a function is declared or defined without specifying the -argument types. (An old-style function definition is permitted without -a warning if preceded by a declaration that specifies the argument -types.) - -@item -Wold-style-declaration @r{(C and Objective-C only)} -@opindex Wold-style-declaration -@opindex Wno-old-style-declaration -Warn for obsolescent usages, according to the C Standard, in a -declaration. For example, warn if storage-class specifiers like -@code{static} are not the first things in a declaration. This warning -is also enabled by @option{-Wextra}. - -@item -Wold-style-definition @r{(C and Objective-C only)} -@opindex Wold-style-definition -@opindex Wno-old-style-definition -Warn if an old-style function definition is used. A warning is given -even if there is a previous prototype. A definition using @samp{()} -is not considered an old-style definition in C2X mode, because it is -equivalent to @samp{(void)} in that case, but is considered an -old-style definition for older standards. - -@item -Wmissing-parameter-type @r{(C and Objective-C only)} -@opindex Wmissing-parameter-type -@opindex Wno-missing-parameter-type -A function parameter is declared without a type specifier in K&R-style -functions: - -@smallexample -void foo(bar) @{ @} -@end smallexample - -This warning is also enabled by @option{-Wextra}. - -@item -Wmissing-prototypes @r{(C and Objective-C only)} -@opindex Wmissing-prototypes -@opindex Wno-missing-prototypes -Warn if a global function is defined without a previous prototype -declaration. This warning is issued even if the definition itself -provides a prototype. Use this option to detect global functions -that do not have a matching prototype declaration in a header file. -This option is not valid for C++ because all function declarations -provide prototypes and a non-matching declaration declares an -overload rather than conflict with an earlier declaration. -Use @option{-Wmissing-declarations} to detect missing declarations in C++. - -@item -Wmissing-declarations -@opindex Wmissing-declarations -@opindex Wno-missing-declarations -Warn if a global function is defined without a previous declaration. -Do so even if the definition itself provides a prototype. -Use this option to detect global functions that are not declared in -header files. In C, no warnings are issued for functions with previous -non-prototype declarations; use @option{-Wmissing-prototypes} to detect -missing prototypes. In C++, no warnings are issued for function templates, -or for inline functions, or for functions in anonymous namespaces. - -@item -Wmissing-field-initializers -@opindex Wmissing-field-initializers -@opindex Wno-missing-field-initializers -@opindex W -@opindex Wextra -@opindex Wno-extra -Warn if a structure's initializer has some fields missing. For -example, the following code causes such a warning, because -@code{x.h} is implicitly zero: - -@smallexample -struct s @{ int f, g, h; @}; -struct s x = @{ 3, 4 @}; -@end smallexample - -This option does not warn about designated initializers, so the following -modification does not trigger a warning: - -@smallexample -struct s @{ int f, g, h; @}; -struct s x = @{ .f = 3, .g = 4 @}; -@end smallexample - -In C this option does not warn about the universal zero initializer -@samp{@{ 0 @}}: - -@smallexample -struct s @{ int f, g, h; @}; -struct s x = @{ 0 @}; -@end smallexample - -Likewise, in C++ this option does not warn about the empty @{ @} -initializer, for example: - -@smallexample -struct s @{ int f, g, h; @}; -s x = @{ @}; -@end smallexample - -This warning is included in @option{-Wextra}. To get other @option{-Wextra} -warnings without this one, use @option{-Wextra -Wno-missing-field-initializers}. - -@item -Wno-missing-requires -@opindex Wmissing-requires -@opindex Wno-missing-requires - -By default, the compiler warns about a concept-id appearing as a C++20 simple-requirement: - -@smallexample -bool satisfied = requires @{ C<T> @}; -@end smallexample - -Here @samp{satisfied} will be true if @samp{C<T>} is a valid -expression, which it is for all T. Presumably the user meant to write - -@smallexample -bool satisfied = requires @{ requires C<T> @}; -@end smallexample - -so @samp{satisfied} is only true if concept @samp{C} is satisfied for -type @samp{T}. - -This warning can be disabled with @option{-Wno-missing-requires}. - -@item -Wno-missing-template-keyword -@opindex Wmissing-template-keyword -@opindex Wno-missing-template-keyword - -The member access tokens ., -> and :: must be followed by the @code{template} -keyword if the parent object is dependent and the member being named is a -template. - -@smallexample -template <class X> -void DoStuff (X x) -@{ - x.template DoSomeOtherStuff<X>(); // Good. - x.DoMoreStuff<X>(); // Warning, x is dependent. -@} -@end smallexample - -In rare cases it is possible to get false positives. To silence this, wrap -the expression in parentheses. For example, the following is treated as a -template, even where m and N are integers: - -@smallexample -void NotATemplate (my_class t) -@{ - int N = 5; - - bool test = t.m < N > (0); // Treated as a template. - test = (t.m < N) > (0); // Same meaning, but not treated as a template. -@} -@end smallexample - -This warning can be disabled with @option{-Wno-missing-template-keyword}. - -@item -Wno-multichar -@opindex Wno-multichar -@opindex Wmultichar -Do not warn if a multicharacter constant (@samp{'FOOF'}) is used. -Usually they indicate a typo in the user's code, as they have -implementation-defined values, and should not be used in portable code. - -@item -Wnormalized=@r{[}none@r{|}id@r{|}nfc@r{|}nfkc@r{]} -@opindex Wnormalized= -@opindex Wnormalized -@opindex Wno-normalized -@cindex NFC -@cindex NFKC -@cindex character set, input normalization -In ISO C and ISO C++, two identifiers are different if they are -different sequences of characters. However, sometimes when characters -outside the basic ASCII character set are used, you can have two -different character sequences that look the same. To avoid confusion, -the ISO 10646 standard sets out some @dfn{normalization rules} which -when applied ensure that two sequences that look the same are turned into -the same sequence. GCC can warn you if you are using identifiers that -have not been normalized; this option controls that warning. - -There are four levels of warning supported by GCC@. The default is -@option{-Wnormalized=nfc}, which warns about any identifier that is -not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the -recommended form for most uses. It is equivalent to -@option{-Wnormalized}. - -Unfortunately, there are some characters allowed in identifiers by -ISO C and ISO C++ that, when turned into NFC, are not allowed in -identifiers. That is, there's no way to use these symbols in portable -ISO C or C++ and have all your identifiers in NFC@. -@option{-Wnormalized=id} suppresses the warning for these characters. -It is hoped that future versions of the standards involved will correct -this, which is why this option is not the default. - -You can switch the warning off for all characters by writing -@option{-Wnormalized=none} or @option{-Wno-normalized}. You should -only do this if you are using some other normalization scheme (like -``D''), because otherwise you can easily create bugs that are -literally impossible to see. - -Some characters in ISO 10646 have distinct meanings but look identical -in some fonts or display methodologies, especially once formatting has -been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL -LETTER N'', displays just like a regular @code{n} that has been -placed in a superscript. ISO 10646 defines the @dfn{NFKC} -normalization scheme to convert all these into a standard form as -well, and GCC warns if your code is not in NFKC if you use -@option{-Wnormalized=nfkc}. This warning is comparable to warning -about every identifier that contains the letter O because it might be -confused with the digit 0, and so is not the default, but may be -useful as a local coding convention if the programming environment -cannot be fixed to display these characters distinctly. - -@item -Wno-attribute-warning -@opindex Wno-attribute-warning -@opindex Wattribute-warning -Do not warn about usage of functions (@pxref{Function Attributes}) -declared with @code{warning} attribute. By default, this warning is -enabled. @option{-Wno-attribute-warning} can be used to disable the -warning or @option{-Wno-error=attribute-warning} can be used to -disable the error when compiled with @option{-Werror} flag. - -@item -Wno-deprecated -@opindex Wno-deprecated -@opindex Wdeprecated -Do not warn about usage of deprecated features. @xref{Deprecated Features}. - -@item -Wno-deprecated-declarations -@opindex Wno-deprecated-declarations -@opindex Wdeprecated-declarations -Do not warn about uses of functions (@pxref{Function Attributes}), -variables (@pxref{Variable Attributes}), and types (@pxref{Type -Attributes}) marked as deprecated by using the @code{deprecated} -attribute. - -@item -Wno-overflow -@opindex Wno-overflow -@opindex Woverflow -Do not warn about compile-time overflow in constant expressions. - -@item -Wno-odr -@opindex Wno-odr -@opindex Wodr -Warn about One Definition Rule violations during link-time optimization. -Enabled by default. - -@item -Wopenacc-parallelism -@opindex Wopenacc-parallelism -@opindex Wno-openacc-parallelism -@cindex OpenACC accelerator programming -Warn about potentially suboptimal choices related to OpenACC parallelism. - -@item -Wopenmp-simd -@opindex Wopenmp-simd -@opindex Wno-openmp-simd -Warn if the vectorizer cost model overrides the OpenMP -simd directive set by user. The @option{-fsimd-cost-model=unlimited} -option can be used to relax the cost model. - -@item -Woverride-init @r{(C and Objective-C only)} -@opindex Woverride-init -@opindex Wno-override-init -@opindex W -@opindex Wextra -@opindex Wno-extra -Warn if an initialized field without side effects is overridden when -using designated initializers (@pxref{Designated Inits, , Designated -Initializers}). - -This warning is included in @option{-Wextra}. To get other -@option{-Wextra} warnings without this one, use @option{-Wextra --Wno-override-init}. - -@item -Wno-override-init-side-effects @r{(C and Objective-C only)} -@opindex Woverride-init-side-effects -@opindex Wno-override-init-side-effects -Do not warn if an initialized field with side effects is overridden when -using designated initializers (@pxref{Designated Inits, , Designated -Initializers}). This warning is enabled by default. - -@item -Wpacked -@opindex Wpacked -@opindex Wno-packed -Warn if a structure is given the packed attribute, but the packed -attribute has no effect on the layout or size of the structure. -Such structures may be mis-aligned for little benefit. For -instance, in this code, the variable @code{f.x} in @code{struct bar} -is misaligned even though @code{struct bar} does not itself -have the packed attribute: - -@smallexample -@group -struct foo @{ - int x; - char a, b, c, d; -@} __attribute__((packed)); -struct bar @{ - char z; - struct foo f; -@}; -@end group -@end smallexample - -@item -Wnopacked-bitfield-compat -@opindex Wpacked-bitfield-compat -@opindex Wno-packed-bitfield-compat -The 4.1, 4.2 and 4.3 series of GCC ignore the @code{packed} attribute -on bit-fields of type @code{char}. This was fixed in GCC 4.4 but -the change can lead to differences in the structure layout. GCC -informs you when the offset of such a field has changed in GCC 4.4. -For example there is no longer a 4-bit padding between field @code{a} -and @code{b} in this structure: - -@smallexample -struct foo -@{ - char a:4; - char b:8; -@} __attribute__ ((packed)); -@end smallexample - -This warning is enabled by default. Use -@option{-Wno-packed-bitfield-compat} to disable this warning. - -@item -Wpacked-not-aligned @r{(C, C++, Objective-C and Objective-C++ only)} -@opindex Wpacked-not-aligned -@opindex Wno-packed-not-aligned -Warn if a structure field with explicitly specified alignment in a -packed struct or union is misaligned. For example, a warning will -be issued on @code{struct S}, like, @code{warning: alignment 1 of -'struct S' is less than 8}, in this code: - -@smallexample -@group -struct __attribute__ ((aligned (8))) S8 @{ char a[8]; @}; -struct __attribute__ ((packed)) S @{ - struct S8 s8; -@}; -@end group -@end smallexample - -This warning is enabled by @option{-Wall}. - -@item -Wpadded -@opindex Wpadded -@opindex Wno-padded -Warn if padding is included in a structure, either to align an element -of the structure or to align the whole structure. Sometimes when this -happens it is possible to rearrange the fields of the structure to -reduce the padding and so make the structure smaller. - -@item -Wredundant-decls -@opindex Wredundant-decls -@opindex Wno-redundant-decls -Warn if anything is declared more than once in the same scope, even in -cases where multiple declaration is valid and changes nothing. - -@item -Wrestrict -@opindex Wrestrict -@opindex Wno-restrict -Warn when an object referenced by a @code{restrict}-qualified parameter -(or, in C++, a @code{__restrict}-qualified parameter) is aliased by another -argument, or when copies between such objects overlap. For example, -the call to the @code{strcpy} function below attempts to truncate the string -by replacing its initial characters with the last four. However, because -the call writes the terminating NUL into @code{a[4]}, the copies overlap and -the call is diagnosed. - -@smallexample -void foo (void) -@{ - char a[] = "abcd1234"; - strcpy (a, a + 4); - @dots{} -@} -@end smallexample -The @option{-Wrestrict} option detects some instances of simple overlap -even without optimization but works best at @option{-O2} and above. It -is included in @option{-Wall}. - -@item -Wnested-externs @r{(C and Objective-C only)} -@opindex Wnested-externs -@opindex Wno-nested-externs -Warn if an @code{extern} declaration is encountered within a function. - -@item -Winline -@opindex Winline -@opindex Wno-inline -Warn if a function that is declared as inline cannot be inlined. -Even with this option, the compiler does not warn about failures to -inline functions declared in system headers. - -The compiler uses a variety of heuristics to determine whether or not -to inline a function. For example, the compiler takes into account -the size of the function being inlined and the amount of inlining -that has already been done in the current function. Therefore, -seemingly insignificant changes in the source program can cause the -warnings produced by @option{-Winline} to appear or disappear. - -@item -Winterference-size -@opindex Winterference-size -Warn about use of C++17 @code{std::hardware_destructive_interference_size} -without specifying its value with @option{--param destructive-interference-size}. -Also warn about questionable values for that option. - -This variable is intended to be used for controlling class layout, to -avoid false sharing in concurrent code: - -@smallexample -struct independent_fields @{ - alignas(std::hardware_destructive_interference_size) std::atomic<int> one; - alignas(std::hardware_destructive_interference_size) std::atomic<int> two; -@}; -@end smallexample - -Here @samp{one} and @samp{two} are intended to be far enough apart -that stores to one won't require accesses to the other to reload the -cache line. - -By default, @option{--param destructive-interference-size} and -@option{--param constructive-interference-size} are set based on the -current @option{-mtune} option, typically to the L1 cache line size -for the particular target CPU, sometimes to a range if tuning for a -generic target. So all translation units that depend on ABI -compatibility for the use of these variables must be compiled with -the same @option{-mtune} (or @option{-mcpu}). - -If ABI stability is important, such as if the use is in a header for a -library, you should probably not use the hardware interference size -variables at all. Alternatively, you can force a particular value -with @option{--param}. - -If you are confident that your use of the variable does not affect ABI -outside a single build of your project, you can turn off the warning -with @option{-Wno-interference-size}. - -@item -Wint-in-bool-context -@opindex Wint-in-bool-context -@opindex Wno-int-in-bool-context -Warn for suspicious use of integer values where boolean values are expected, -such as conditional expressions (?:) using non-boolean integer constants in -boolean context, like @code{if (a <= b ? 2 : 3)}. Or left shifting of signed -integers in boolean context, like @code{for (a = 0; 1 << a; a++);}. Likewise -for all kinds of multiplications regardless of the data type. -This warning is enabled by @option{-Wall}. - -@item -Wno-int-to-pointer-cast -@opindex Wno-int-to-pointer-cast -@opindex Wint-to-pointer-cast -Suppress warnings from casts to pointer type of an integer of a -different size. In C++, casting to a pointer type of smaller size is -an error. @option{Wint-to-pointer-cast} is enabled by default. - - -@item -Wno-pointer-to-int-cast @r{(C and Objective-C only)} -@opindex Wno-pointer-to-int-cast -@opindex Wpointer-to-int-cast -Suppress warnings from casts from a pointer to an integer type of a -different size. - -@item -Winvalid-pch -@opindex Winvalid-pch -@opindex Wno-invalid-pch -Warn if a precompiled header (@pxref{Precompiled Headers}) is found in -the search path but cannot be used. - -@item -Winvalid-utf8 -@opindex Winvalid-utf8 -@opindex Wno-invalid-utf8 -Warn if an invalid UTF-8 character is found. -This warning is on by default for C++23 if @option{-finput-charset=UTF-8} -is used and turned into error with @option{-pedantic-errors}. - -@item -Wno-unicode -@opindex Wunicode -@opindex Wno-unicode -Don't diagnose invalid forms of delimited or named escape sequences which are -treated as separate tokens. @option{Wunicode} is enabled by default. - -@item -Wlong-long -@opindex Wlong-long -@opindex Wno-long-long -Warn if @code{long long} type is used. This is enabled by either -@option{-Wpedantic} or @option{-Wtraditional} in ISO C90 and C++98 -modes. To inhibit the warning messages, use @option{-Wno-long-long}. - -@item -Wvariadic-macros -@opindex Wvariadic-macros -@opindex Wno-variadic-macros -Warn if variadic macros are used in ISO C90 mode, or if the GNU -alternate syntax is used in ISO C99 mode. This is enabled by either -@option{-Wpedantic} or @option{-Wtraditional}. To inhibit the warning -messages, use @option{-Wno-variadic-macros}. - -@item -Wno-varargs -@opindex Wvarargs -@opindex Wno-varargs -Do not warn upon questionable usage of the macros used to handle variable -arguments like @code{va_start}. These warnings are enabled by default. - -@item -Wvector-operation-performance -@opindex Wvector-operation-performance -@opindex Wno-vector-operation-performance -Warn if vector operation is not implemented via SIMD capabilities of the -architecture. Mainly useful for the performance tuning. -Vector operation can be implemented @code{piecewise}, which means that the -scalar operation is performed on every vector element; -@code{in parallel}, which means that the vector operation is implemented -using scalars of wider type, which normally is more performance efficient; -and @code{as a single scalar}, which means that vector fits into a -scalar type. - -@item -Wvla -@opindex Wvla -@opindex Wno-vla -Warn if a variable-length array is used in the code. -@option{-Wno-vla} prevents the @option{-Wpedantic} warning of -the variable-length array. - -@item -Wvla-larger-than=@var{byte-size} -@opindex Wvla-larger-than= -@opindex Wno-vla-larger-than -If this option is used, the compiler warns for declarations of -variable-length arrays whose size is either unbounded, or bounded -by an argument that allows the array size to exceed @var{byte-size} -bytes. This is similar to how @option{-Walloca-larger-than=}@var{byte-size} -works, but with variable-length arrays. - -Note that GCC may optimize small variable-length arrays of a known -value into plain arrays, so this warning may not get triggered for -such arrays. - -@option{-Wvla-larger-than=}@samp{PTRDIFF_MAX} is enabled by default but -is typically only effective when @option{-ftree-vrp} is active (default -for @option{-O2} and above). - -See also @option{-Walloca-larger-than=@var{byte-size}}. - -@item -Wno-vla-larger-than -@opindex Wno-vla-larger-than -Disable @option{-Wvla-larger-than=} warnings. The option is equivalent -to @option{-Wvla-larger-than=}@samp{SIZE_MAX} or larger. - -@item -Wvla-parameter -@opindex Wno-vla-parameter -Warn about redeclarations of functions involving arguments of Variable -Length Array types of inconsistent kinds or forms, and enable the detection -of out-of-bounds accesses to such parameters by warnings such as -@option{-Warray-bounds}. - -If the first function declaration uses the VLA form the bound specified -in the array is assumed to be the minimum number of elements expected to -be provided in calls to the function and the maximum number of elements -accessed by it. Failing to provide arguments of sufficient size or -accessing more than the maximum number of elements may be diagnosed. - -For example, the warning triggers for the following redeclarations because -the first one allows an array of any size to be passed to @code{f} while -the second one specifies that the array argument must have at least @code{n} -elements. In addition, calling @code{f} with the associated VLA bound -parameter in excess of the actual VLA bound triggers a warning as well. - -@smallexample -void f (int n, int[n]); -void f (int, int[]); // warning: argument 2 previously declared as a VLA - -void g (int n) -@{ - if (n > 4) - return; - int a[n]; - f (sizeof a, a); // warning: access to a by f may be out of bounds - @dots{} -@} - -@end smallexample - -@option{-Wvla-parameter} is included in @option{-Wall}. The -@option{-Warray-parameter} option triggers warnings for similar problems -involving ordinary array arguments. - -@item -Wvolatile-register-var -@opindex Wvolatile-register-var -@opindex Wno-volatile-register-var -Warn if a register variable is declared volatile. The volatile -modifier does not inhibit all optimizations that may eliminate reads -and/or writes to register variables. This warning is enabled by -@option{-Wall}. - -@item -Wxor-used-as-pow @r{(C, C++, Objective-C and Objective-C++ only)} -@opindex Wxor-used-as-pow -@opindex Wno-xor-used-as-pow -Warn about uses of @code{^}, the exclusive or operator, where it appears -the user meant exponentiation. Specifically, the warning occurs when the -left-hand side is the decimal constant 2 or 10 and the right-hand side -is also a decimal constant. - -In C and C++, @code{^} means exclusive or, whereas in some other languages -(e.g. TeX and some versions of BASIC) it means exponentiation. - -This warning is enabled by default. It can be silenced by converting one -of the operands to hexadecimal. - -@item -Wdisabled-optimization -@opindex Wdisabled-optimization -@opindex Wno-disabled-optimization -Warn if a requested optimization pass is disabled. This warning does -not generally indicate that there is anything wrong with your code; it -merely indicates that GCC's optimizers are unable to handle the code -effectively. Often, the problem is that your code is too big or too -complex; GCC refuses to optimize programs when the optimization -itself is likely to take inordinate amounts of time. - -@item -Wpointer-sign @r{(C and Objective-C only)} -@opindex Wpointer-sign -@opindex Wno-pointer-sign -Warn for pointer argument passing or assignment with different signedness. -This option is only supported for C and Objective-C@. It is implied by -@option{-Wall} and by @option{-Wpedantic}, which can be disabled with -@option{-Wno-pointer-sign}. - -@item -Wstack-protector -@opindex Wstack-protector -@opindex Wno-stack-protector -This option is only active when @option{-fstack-protector} is active. It -warns about functions that are not protected against stack smashing. - -@item -Woverlength-strings -@opindex Woverlength-strings -@opindex Wno-overlength-strings -Warn about string constants that are longer than the ``minimum -maximum'' length specified in the C standard. Modern compilers -generally allow string constants that are much longer than the -standard's minimum limit, but very portable programs should avoid -using longer strings. - -The limit applies @emph{after} string constant concatenation, and does -not count the trailing NUL@. In C90, the limit was 509 characters; in -C99, it was raised to 4095. C++98 does not specify a normative -minimum maximum, so we do not diagnose overlength strings in C++@. - -This option is implied by @option{-Wpedantic}, and can be disabled with -@option{-Wno-overlength-strings}. - -@item -Wunsuffixed-float-constants @r{(C and Objective-C only)} -@opindex Wunsuffixed-float-constants -@opindex Wno-unsuffixed-float-constants - -Issue a warning for any floating constant that does not have -a suffix. When used together with @option{-Wsystem-headers} it -warns about such constants in system header files. This can be useful -when preparing code to use with the @code{FLOAT_CONST_DECIMAL64} pragma -from the decimal floating-point extension to C99. - -@item -Wno-lto-type-mismatch -@opindex Wlto-type-mismatch -@opindex Wno-lto-type-mismatch - -During the link-time optimization, do not warn about type mismatches in -global declarations from different compilation units. -Requires @option{-flto} to be enabled. Enabled by default. - -@item -Wno-designated-init @r{(C and Objective-C only)} -@opindex Wdesignated-init -@opindex Wno-designated-init -Suppress warnings when a positional initializer is used to initialize -a structure that has been marked with the @code{designated_init} -attribute. - -@end table - -@node Static Analyzer Options -@section Options That Control Static Analysis - -@table @gcctabopt -@item -fanalyzer -@opindex analyzer -@opindex fanalyzer -@opindex fno-analyzer -This option enables an static analysis of program flow which looks -for ``interesting'' interprocedural paths through the -code, and issues warnings for problems found on them. - -This analysis is much more expensive than other GCC warnings. - -Enabling this option effectively enables the following warnings: - -@gccoptlist{ @gol --Wanalyzer-allocation-size @gol --Wanalyzer-double-fclose @gol --Wanalyzer-double-free @gol --Wanalyzer-exposure-through-output-file @gol --Wanalyzer-exposure-through-uninit-copy @gol --Wanalyzer-fd-access-mode-mismatch @gol --Wanalyzer-fd-double-close @gol --Wanalyzer-fd-leak @gol --Wanalyzer-fd-use-after-close @gol --Wanalyzer-fd-use-without-check @gol --Wanalyzer-file-leak @gol --Wanalyzer-free-of-non-heap @gol --Wanalyzer-imprecise-fp-arithmetic @gol --Wanalyzer-jump-through-null @gol --Wanalyzer-malloc-leak @gol --Wanalyzer-mismatching-deallocation @gol --Wanalyzer-null-argument @gol --Wanalyzer-null-dereference @gol --Wanalyzer-out-of-bounds @gol --Wanalyzer-possible-null-argument @gol --Wanalyzer-possible-null-dereference @gol --Wanalyzer-putenv-of-auto-var @gol --Wanalyzer-shift-count-negative @gol --Wanalyzer-shift-count-overflow @gol --Wanalyzer-stale-setjmp-buffer @gol --Wanalyzer-unsafe-call-within-signal-handler @gol --Wanalyzer-use-after-free @gol --Wanalyzer-use-of-pointer-in-stale-stack-frame @gol --Wanalyzer-use-of-uninitialized-value @gol --Wanalyzer-va-arg-type-mismatch @gol --Wanalyzer-va-list-exhausted @gol --Wanalyzer-va-list-leak @gol --Wanalyzer-va-list-use-after-va-end @gol --Wanalyzer-write-to-const @gol --Wanalyzer-write-to-string-literal @gol -} -@ignore --Wanalyzer-tainted-allocation-size @gol --Wanalyzer-tainted-array-index @gol --Wanalyzer-tainted-divisor @gol --Wanalyzer-tainted-offset @gol --Wanalyzer-tainted-size @gol -@end ignore - -This option is only available if GCC was configured with analyzer -support enabled. - -@item -Wanalyzer-too-complex -@opindex Wanalyzer-too-complex -@opindex Wno-analyzer-too-complex -If @option{-fanalyzer} is enabled, the analyzer uses various heuristics -to attempt to explore the control flow and data flow in the program, -but these can be defeated by sufficiently complicated code. - -By default, the analysis silently stops if the code is too -complicated for the analyzer to fully explore and it reaches an internal -limit. The @option{-Wanalyzer-too-complex} option warns if this occurs. - -@item -Wno-analyzer-allocation-size -@opindex Wanalyzer-allocation-size -@opindex Wno-analyzer-allocation-size -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-allocation-size} -to disable it. - -This diagnostic warns for paths through the code in which a pointer to -a buffer is assigned to point at a buffer with a size that is not a -multiple of @code{sizeof (*pointer)}. - -See @uref{https://cwe.mitre.org/data/definitions/131.html, CWE-131: Incorrect Calculation of Buffer Size}. - -@item -Wno-analyzer-double-fclose -@opindex Wanalyzer-double-fclose -@opindex Wno-analyzer-double-fclose -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-double-fclose} to disable it. - -This diagnostic warns for paths through the code in which a @code{FILE *} -can have @code{fclose} called on it more than once. - -See @uref{https://cwe.mitre.org/data/definitions/1341.html, CWE-1341: Multiple Releases of Same Resource or Handle}. - -@item -Wno-analyzer-double-free -@opindex Wanalyzer-double-free -@opindex Wno-analyzer-double-free -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-double-free} to disable it. - -This diagnostic warns for paths through the code in which a pointer -can have a deallocator called on it more than once, either @code{free}, -or a deallocator referenced by attribute @code{malloc}. - -See @uref{https://cwe.mitre.org/data/definitions/415.html, CWE-415: Double Free}. - -@item -Wno-analyzer-exposure-through-output-file -@opindex Wanalyzer-exposure-through-output-file -@opindex Wno-analyzer-exposure-through-output-file -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-exposure-through-output-file} -to disable it. - -This diagnostic warns for paths through the code in which a -security-sensitive value is written to an output file -(such as writing a password to a log file). - -See @uref{https://cwe.mitre.org/data/definitions/532.html, CWE-532: Information Exposure Through Log Files}. - -@item -Wanalyzer-exposure-through-uninit-copy -@opindex Wanalyzer-exposure-through-uninit-copy -@opindex Wno-analyzer-exposure-through-uninit-copy -This warning requires both @option{-fanalyzer} and the use of a plugin -to specify a function that copies across a ``trust boundary''. Use -@option{-Wno-analyzer-exposure-through-uninit-copy} to disable it. - -This diagnostic warns for ``infoleaks'' - paths through the code in which -uninitialized values are copied across a security boundary -(such as code within an OS kernel that copies a partially-initialized -struct on the stack to user space). - -See @uref{https://cwe.mitre.org/data/definitions/200.html, CWE-200: Exposure of Sensitive Information to an Unauthorized Actor}. - -@item -Wno-analyzer-fd-access-mode-mismatch -@opindex Wanalyzer-fd-access-mode-mismatch -@opindex Wno-analyzer-fd-access-mode-mismatch -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-fd-access-mode-mismatch} -to disable it. - -This diagnostic warns for paths through code in which a -@code{read} on a write-only file descriptor is attempted, or vice versa. - -This diagnostic also warns for code paths in a which a function with attribute -@code{fd_arg_read (N)} is called with a file descriptor opened with -@code{O_WRONLY} at referenced argument @code{N} or a function with attribute -@code{fd_arg_write (N)} is called with a file descriptor opened with -@code{O_RDONLY} at referenced argument @var{N}. - -@item -Wno-analyzer-fd-double-close -@opindex Wanalyzer-fd-double-close -@opindex Wno-analyzer-fd-double-close -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-fd-double-close} -to disable it. - -This diagnostic warns for paths through code in which a -file descriptor can be closed more than once. - -See @uref{https://cwe.mitre.org/data/definitions/1341.html, CWE-1341: Multiple Releases of Same Resource or Handle}. - -@item -Wno-analyzer-fd-leak -@opindex Wanalyzer-fd-leak -@opindex Wno-analyzer-fd-leak -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-fd-leak} -to disable it. - -This diagnostic warns for paths through code in which an -open file descriptor is leaked. - -See @uref{https://cwe.mitre.org/data/definitions/775.html, CWE-775: Missing Release of File Descriptor or Handle after Effective Lifetime}. - -@item -Wno-analyzer-fd-use-after-close -@opindex Wanalyzer-fd-use-after-close -@opindex Wno-analyzer-fd-use-after-close -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-fd-use-after-close} -to disable it. - -This diagnostic warns for paths through code in which a -read or write is called on a closed file descriptor. - -This diagnostic also warns for paths through code in which -a function with attribute @code{fd_arg (N)} or @code{fd_arg_read (N)} -or @code{fd_arg_write (N)} is called with a closed file descriptor at -referenced argument @code{N}. - -@item -Wno-analyzer-fd-use-without-check -@opindex Wanalyzer-fd-use-without-check -@opindex Wno-analyzer-fd-use-without-check -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-fd-use-without-check} -to disable it. - -This diagnostic warns for paths through code in which a -file descriptor is used without being checked for validity. - -This diagnostic also warns for paths through code in which -a function with attribute @code{fd_arg (N)} or @code{fd_arg_read (N)} -or @code{fd_arg_write (N)} is called with a file descriptor, at referenced -argument @code{N}, without being checked for validity. - -@item -Wno-analyzer-file-leak -@opindex Wanalyzer-file-leak -@opindex Wno-analyzer-file-leak -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-file-leak} -to disable it. - -This diagnostic warns for paths through the code in which a -@code{<stdio.h>} @code{FILE *} stream object is leaked. - -See @uref{https://cwe.mitre.org/data/definitions/775.html, CWE-775: Missing Release of File Descriptor or Handle after Effective Lifetime}. - -@item -Wno-analyzer-free-of-non-heap -@opindex Wanalyzer-free-of-non-heap -@opindex Wno-analyzer-free-of-non-heap -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-free-of-non-heap} -to disable it. - -This diagnostic warns for paths through the code in which @code{free} -is called on a non-heap pointer (e.g. an on-stack buffer, or a global). - -See @uref{https://cwe.mitre.org/data/definitions/590.html, CWE-590: Free of Memory not on the Heap}. - -@item -Wno-analyzer-imprecise-fp-arithmetic -@opindex Wanalyzer-imprecise-fp-arithmetic -@opindex Wno-analyzer-imprecise-fp-arithmetic -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-imprecise-fp-arithmetic} -to disable it. - -This diagnostic warns for paths through the code in which floating-point -arithmetic is used in locations where precise computation is needed. This -diagnostic only warns on use of floating-point operands inside the -calculation of an allocation size at the moment. - -@item -Wno-analyzer-jump-through-null -@opindex Wanalyzer-jump-through-null -@opindex Wno-analyzer-jump-through-null -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-jump-through-null} -to disable it. - -This diagnostic warns for paths through the code in which a @code{NULL} -function pointer is called. - -@item -Wno-analyzer-malloc-leak -@opindex Wanalyzer-malloc-leak -@opindex Wno-analyzer-malloc-leak -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-malloc-leak} -to disable it. - -This diagnostic warns for paths through the code in which a -pointer allocated via an allocator is leaked: either @code{malloc}, -or a function marked with attribute @code{malloc}. - -See @uref{https://cwe.mitre.org/data/definitions/401.html, CWE-401: Missing Release of Memory after Effective Lifetime}. - -@item -Wno-analyzer-mismatching-deallocation -@opindex Wanalyzer-mismatching-deallocation -@opindex Wno-analyzer-mismatching-deallocation -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-mismatching-deallocation} -to disable it. - -This diagnostic warns for paths through the code in which the -wrong deallocation function is called on a pointer value, based on -which function was used to allocate the pointer value. The diagnostic -will warn about mismatches between @code{free}, scalar @code{delete} -and vector @code{delete[]}, and those marked as allocator/deallocator -pairs using attribute @code{malloc}. - -See @uref{https://cwe.mitre.org/data/definitions/762.html, CWE-762: Mismatched Memory Management Routines}. - -@item -Wno-analyzer-out-of-bounds -@opindex Wanalyzer-out-of-bounds -@opindex Wno-analyzer-out-of-bounds -This warning requires @option{-fanalyzer} to enable it; use -@option{-Wno-analyzer-out-of-bounds} to disable it. - -This diagnostic warns for path through the code in which a buffer is -definitely read or written out-of-bounds. The diagnostic applies for -cases where the analyzer is able to determine a constant offset and for -accesses past the end of a buffer, also a constant capacity. Further, -the diagnostic does limited checking for accesses past the end when the -offset as well as the capacity is symbolic. - -See @uref{https://cwe.mitre.org/data/definitions/119.html, CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer}. - -@item -Wno-analyzer-possible-null-argument -@opindex Wanalyzer-possible-null-argument -@opindex Wno-analyzer-possible-null-argument -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-possible-null-argument} to disable it. - -This diagnostic warns for paths through the code in which a -possibly-NULL value is passed to a function argument marked -with @code{__attribute__((nonnull))} as requiring a non-NULL -value. - -See @uref{https://cwe.mitre.org/data/definitions/690.html, CWE-690: Unchecked Return Value to NULL Pointer Dereference}. - -@item -Wno-analyzer-possible-null-dereference -@opindex Wanalyzer-possible-null-dereference -@opindex Wno-analyzer-possible-null-dereference -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-possible-null-dereference} to disable it. - -This diagnostic warns for paths through the code in which a -possibly-NULL value is dereferenced. - -See @uref{https://cwe.mitre.org/data/definitions/690.html, CWE-690: Unchecked Return Value to NULL Pointer Dereference}. - -@item -Wno-analyzer-null-argument -@opindex Wanalyzer-null-argument -@opindex Wno-analyzer-null-argument -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-null-argument} to disable it. - -This diagnostic warns for paths through the code in which a -value known to be NULL is passed to a function argument marked -with @code{__attribute__((nonnull))} as requiring a non-NULL -value. - -See @uref{https://cwe.mitre.org/data/definitions/476.html, CWE-476: NULL Pointer Dereference}. - -@item -Wno-analyzer-null-dereference -@opindex Wanalyzer-null-dereference -@opindex Wno-analyzer-null-dereference -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-null-dereference} to disable it. - -This diagnostic warns for paths through the code in which a -value known to be NULL is dereferenced. - -See @uref{https://cwe.mitre.org/data/definitions/476.html, CWE-476: NULL Pointer Dereference}. - -@item -Wno-analyzer-putenv-of-auto-var -@opindex Wanalyzer-putenv-of-auto-var -@opindex Wno-analyzer-putenv-of-auto-var -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-putenv-of-auto-var} to disable it. - -This diagnostic warns for paths through the code in which a -call to @code{putenv} is passed a pointer to an automatic variable -or an on-stack buffer. - -See @uref{https://wiki.sei.cmu.edu/confluence/x/6NYxBQ, POS34-C. Do not call putenv() with a pointer to an automatic variable as the argument}. - -@item -Wno-analyzer-shift-count-negative -@opindex Wanalyzer-shift-count-negative -@opindex Wno-analyzer-shift-count-negative -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-shift-count-negative} to disable it. - -This diagnostic warns for paths through the code in which a -shift is attempted with a negative count. It is analogous to -the @option{-Wshift-count-negative} diagnostic implemented in -the C/C++ front ends, but is implemented based on analyzing -interprocedural paths, rather than merely parsing the syntax tree. -However, the analyzer does not prioritize detection of such paths, so -false negatives are more likely relative to other warnings. - -@item -Wno-analyzer-shift-count-overflow -@opindex Wanalyzer-shift-count-overflow -@opindex Wno-analyzer-shift-count-overflow -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-shift-count-overflow} to disable it. - -This diagnostic warns for paths through the code in which a -shift is attempted with a count greater than or equal to the -precision of the operand's type. It is analogous to -the @option{-Wshift-count-overflow} diagnostic implemented in -the C/C++ front ends, but is implemented based on analyzing -interprocedural paths, rather than merely parsing the syntax tree. -However, the analyzer does not prioritize detection of such paths, so -false negatives are more likely relative to other warnings. - -@item -Wno-analyzer-stale-setjmp-buffer -@opindex Wanalyzer-stale-setjmp-buffer -@opindex Wno-analyzer-stale-setjmp-buffer -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-stale-setjmp-buffer} to disable it. - -This diagnostic warns for paths through the code in which -@code{longjmp} is called to rewind to a @code{jmp_buf} relating -to a @code{setjmp} call in a function that has returned. - -When @code{setjmp} is called on a @code{jmp_buf} to record a rewind -location, it records the stack frame. The stack frame becomes invalid -when the function containing the @code{setjmp} call returns. Attempting -to rewind to it via @code{longjmp} would reference a stack frame that -no longer exists, and likely lead to a crash (or worse). - -@item -Wno-analyzer-tainted-allocation-size -@opindex Wanalyzer-tainted-allocation-size -@opindex Wno-analyzer-tainted-allocation-size -This warning requires both @option{-fanalyzer} and -@option{-fanalyzer-checker=taint} to enable it; -use @option{-Wno-analyzer-tainted-allocation-size} to disable it. - -This diagnostic warns for paths through the code in which a value -that could be under an attacker's control is used as the size -of an allocation without being sanitized, so that an attacker could -inject an excessively large allocation and potentially cause a denial -of service attack. - -See @uref{https://cwe.mitre.org/data/definitions/789.html, CWE-789: Memory Allocation with Excessive Size Value}. - -@item -Wno-analyzer-tainted-array-index -@opindex Wanalyzer-tainted-array-index -@opindex Wno-analyzer-tainted-array-index -This warning requires both @option{-fanalyzer} and -@option{-fanalyzer-checker=taint} to enable it; -use @option{-Wno-analyzer-tainted-array-index} to disable it. - -This diagnostic warns for paths through the code in which a value -that could be under an attacker's control is used as the index -of an array access without being sanitized, so that an attacker -could inject an out-of-bounds access. - -See @uref{https://cwe.mitre.org/data/definitions/129.html, CWE-129: Improper Validation of Array Index}. - -@item -Wno-analyzer-tainted-divisor -@opindex Wanalyzer-tainted-divisor -@opindex Wno-analyzer-tainted-divisor -This warning requires both @option{-fanalyzer} and -@option{-fanalyzer-checker=taint} to enable it; -use @option{-Wno-analyzer-tainted-divisor} to disable it. - -This diagnostic warns for paths through the code in which a value -that could be under an attacker's control is used as the divisor -in a division or modulus operation without being sanitized, so that -an attacker could inject a division-by-zero. - -See @uref{https://cwe.mitre.org/data/definitions/369.html, CWE-369: Divide By Zero}. - -@item -Wno-analyzer-tainted-offset -@opindex Wanalyzer-tainted-offset -@opindex Wno-analyzer-tainted-offset -This warning requires both @option{-fanalyzer} and -@option{-fanalyzer-checker=taint} to enable it; -use @option{-Wno-analyzer-tainted-offset} to disable it. - -This diagnostic warns for paths through the code in which a value -that could be under an attacker's control is used as a pointer offset -without being sanitized, so that an attacker could inject an out-of-bounds -access. - -See @uref{https://cwe.mitre.org/data/definitions/823.html, CWE-823: Use of Out-of-range Pointer Offset}. - -@item -Wno-analyzer-tainted-size -@opindex Wanalyzer-tainted-size -@opindex Wno-analyzer-tainted-size -This warning requires both @option{-fanalyzer} and -@option{-fanalyzer-checker=taint} to enable it; -use @option{-Wno-analyzer-tainted-size} to disable it. - -This diagnostic warns for paths through the code in which a value -that could be under an attacker's control is used as the size of -an operation such as @code{memset} without being sanitized, so that an -attacker could inject an out-of-bounds access. - -See @uref{https://cwe.mitre.org/data/definitions/129.html, CWE-129: Improper Validation of Array Index}. - -@item -Wno-analyzer-unsafe-call-within-signal-handler -@opindex Wanalyzer-unsafe-call-within-signal-handler -@opindex Wno-analyzer-unsafe-call-within-signal-handler -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-unsafe-call-within-signal-handler} to disable it. - -This diagnostic warns for paths through the code in which a -function known to be async-signal-unsafe (such as @code{fprintf}) is -called from a signal handler. - -See @uref{https://cwe.mitre.org/data/definitions/479.html, CWE-479: Signal Handler Use of a Non-reentrant Function}. - -@item -Wno-analyzer-use-after-free -@opindex Wanalyzer-use-after-free -@opindex Wno-analyzer-use-after-free -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-use-after-free} to disable it. - -This diagnostic warns for paths through the code in which a -pointer is used after a deallocator is called on it: either @code{free}, -or a deallocator referenced by attribute @code{malloc}. - -See @uref{https://cwe.mitre.org/data/definitions/416.html, CWE-416: Use After Free}. - -@item -Wno-analyzer-use-of-pointer-in-stale-stack-frame -@opindex Wanalyzer-use-of-pointer-in-stale-stack-frame -@opindex Wno-analyzer-use-of-pointer-in-stale-stack-frame -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-use-of-pointer-in-stale-stack-frame} -to disable it. - -This diagnostic warns for paths through the code in which a pointer -is dereferenced that points to a variable in a stale stack frame. - -@item -Wno-analyzer-va-arg-type-mismatch -@opindex Wanalyzer-va-arg-type-mismatch -@opindex Wno-analyzer-va-arg-type-mismatch -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-va-arg-type-mismatch} -to disable it. - -This diagnostic warns for interprocedural paths through the code for which -the analyzer detects an attempt to use @code{va_arg} to extract a value -passed to a variadic call, but uses a type that does not match that of -the expression passed to the call. - -See @uref{https://cwe.mitre.org/data/definitions/686.html, CWE-686: Function Call With Incorrect Argument Type}. - -@item -Wno-analyzer-va-list-exhausted -@opindex Wanalyzer-va-list-exhausted -@opindex Wno-analyzer-va-list-exhausted -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-va-list-exhausted} -to disable it. - -This diagnostic warns for interprocedural paths through the code for which -the analyzer detects an attempt to use @code{va_arg} to access the next -value passed to a variadic call, but all of the values in the -@code{va_list} have already been consumed. - -See @uref{https://cwe.mitre.org/data/definitions/685.html, CWE-685: Function Call With Incorrect Number of Arguments}. - -@item -Wno-analyzer-va-list-leak -@opindex Wanalyzer-va-list-leak -@opindex Wno-analyzer-va-list-leak -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-va-list-leak} -to disable it. - -This diagnostic warns for interprocedural paths through the code for which -the analyzer detects that @code{va_start} or @code{va_copy} has been called -on a @code{va_list} without a corresponding call to @code{va_end}. - -@item -Wno-analyzer-va-list-use-after-va-end -@opindex Wanalyzer-va-list-use-after-va-end -@opindex Wno-analyzer-va-list-use-after-va-end -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-va-list-use-after-va-end} -to disable it. - -This diagnostic warns for interprocedural paths through the code for which -the analyzer detects an attempt to use a @code{va_list} after -@code{va_end} has been called on it. -@code{va_list}. - -@item -Wno-analyzer-write-to-const -@opindex Wanalyzer-write-to-const -@opindex Wno-analyzer-write-to-const -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-write-to-const} -to disable it. - -This diagnostic warns for paths through the code in which the analyzer -detects an attempt to write through a pointer to a @code{const} object. -However, the analyzer does not prioritize detection of such paths, so -false negatives are more likely relative to other warnings. - -@item -Wno-analyzer-write-to-string-literal -@opindex Wanalyzer-write-to-string-literal -@opindex Wno-analyzer-write-to-string-literal -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-write-to-string-literal} -to disable it. - -This diagnostic warns for paths through the code in which the analyzer -detects an attempt to write through a pointer to a string literal. -However, the analyzer does not prioritize detection of such paths, so -false negatives are more likely relative to other warnings. - -@item -Wno-analyzer-use-of-uninitialized-value -@opindex Wanalyzer-use-of-uninitialized-value -@opindex Wno-analyzer-use-of-uninitialized-value -This warning requires @option{-fanalyzer}, which enables it; use -@option{-Wno-analyzer-use-of-uninitialized-value} to disable it. - -This diagnostic warns for paths through the code in which an uninitialized -value is used. - -See @uref{https://cwe.mitre.org/data/definitions/457.html, CWE-457: Use of Uninitialized Variable}. - -@end table - -The analyzer has hardcoded knowledge about the behavior of the following -memory-management functions: - -@itemize @bullet -@item @code{alloca} -@item The built-in functions @code{__builtin_alloc}, -@code{__builtin_alloc_with_align}, @item @code{__builtin_calloc}, -@code{__builtin_free}, @code{__builtin_malloc}, @code{__builtin_memcpy}, -@code{__builtin_memcpy_chk}, @code{__builtin_memset}, -@code{__builtin_memset_chk}, @code{__builtin_realloc}, -@code{__builtin_stack_restore}, and @code{__builtin_stack_save} -@item @code{calloc} -@item @code{free} -@item @code{malloc} -@item @code{memset} -@item @code{operator delete} -@item @code{operator delete []} -@item @code{operator new} -@item @code{operator new []} -@item @code{realloc} -@item @code{strdup} -@item @code{strndup} -@end itemize - -of the following functions for working with file descriptors: - -@itemize @bullet -@item @code{open} -@item @code{close} -@item @code{creat} -@item @code{dup}, @code{dup2} and @code{dup3} -@item @code{pipe}, and @code{pipe2} -@item @code{read} -@item @code{write} -@end itemize - -of the following functions for working with @code{<stdio.h>} streams: -@itemize @bullet -@item The built-in functions @code{__builtin_fprintf}, -@code{__builtin_fprintf_unlocked}, @code{__builtin_fputc}, -@code{__builtin_fputc_unlocked}, @code{__builtin_fputs}, -@code{__builtin_fputs_unlocked}, @code{__builtin_fwrite}, -@code{__builtin_fwrite_unlocked}, @code{__builtin_printf}, -@code{__builtin_printf_unlocked}, @code{__builtin_putc}, -@code{__builtin_putchar}, @code{__builtin_putchar_unlocked}, -@code{__builtin_putc_unlocked}, @code{__builtin_puts}, -@code{__builtin_puts_unlocked}, @code{__builtin_vfprintf}, and -@code{__builtin_vprintf} -@item @code{fopen} -@item @code{fclose} -@item @code{fgets} -@item @code{fgets_unlocked} -@item @code{fread} -@item @code{getchar} -@item @code{fprintf} -@item @code{printf} -@item @code{fwrite} -@end itemize - -and of the following functions: - -@itemize @bullet -@item The built-in functions @code{__builtin_expect}, -@code{__builtin_expect_with_probability}, @code{__builtin_strchr}, -@code{__builtin_strcpy}, @code{__builtin_strcpy_chk}, -@code{__builtin_strlen}, @code{__builtin_va_copy}, and -@code{__builtin_va_start} -@item The GNU extensions @code{error} and @code{error_at_line} -@item @code{getpass} -@item @code{longjmp} -@item @code{putenv} -@item @code{setjmp} -@item @code{siglongjmp} -@item @code{signal} -@item @code{sigsetjmp} -@item @code{strchr} -@item @code{strlen} -@end itemize - -In addition, various functions with an @code{__analyzer_} prefix have -special meaning to the analyzer, described in the GCC Internals manual. - -Pertinent parameters for controlling the exploration are: -@option{--param analyzer-bb-explosion-factor=@var{value}}, -@option{--param analyzer-max-enodes-per-program-point=@var{value}}, -@option{--param analyzer-max-recursion-depth=@var{value}}, and -@option{--param analyzer-min-snodes-for-call-summary=@var{value}}. - -The following options control the analyzer. - -@table @gcctabopt - -@item -fanalyzer-call-summaries -@opindex fanalyzer-call-summaries -@opindex fno-analyzer-call-summaries -Simplify interprocedural analysis by computing the effect of certain calls, -rather than exploring all paths through the function from callsite to each -possible return. - -If enabled, call summaries are only used for functions with more than one -call site, and that are sufficiently complicated (as per -@option{--param analyzer-min-snodes-for-call-summary=@var{value}}). - -@item -fanalyzer-checker=@var{name} -@opindex fanalyzer-checker -Restrict the analyzer to run just the named checker, and enable it. - -Some checkers are disabled by default (even with @option{-fanalyzer}), -such as the @code{taint} checker that implements -@option{-Wanalyzer-tainted-array-index}, and this option is required -to enable them. - -@emph{Note:} currently, @option{-fanalyzer-checker=taint} disables the -following warnings from @option{-fanalyzer}: - -@gccoptlist{ @gol --Wanalyzer-double-fclose @gol --Wanalyzer-double-free @gol --Wanalyzer-exposure-through-output-file @gol --Wanalyzer-fd-access-mode-mismatch @gol --Wanalyzer-fd-double-close @gol --Wanalyzer-fd-leak @gol --Wanalyzer-fd-use-after-close @gol --Wanalyzer-fd-use-without-check @gol --Wanalyzer-file-leak @gol --Wanalyzer-free-of-non-heap @gol --Wanalyzer-malloc-leak @gol --Wanalyzer-mismatching-deallocation @gol --Wanalyzer-null-argument @gol --Wanalyzer-null-dereference @gol --Wanalyzer-possible-null-argument @gol --Wanalyzer-possible-null-dereference @gol --Wanalyzer-unsafe-call-within-signal-handler @gol --Wanalyzer-use-after-free @gol --Wanalyzer-va-list-leak @gol --Wanalyzer-va-list-use-after-va-end @gol -} - -@item -fno-analyzer-feasibility -@opindex fanalyzer-feasibility -@opindex fno-analyzer-feasibility -This option is intended for analyzer developers. - -By default the analyzer verifies that there is a feasible control flow path -for each diagnostic it emits: that the conditions that hold are not mutually -exclusive. Diagnostics for which no feasible path can be found are rejected. -This filtering can be suppressed with @option{-fno-analyzer-feasibility}, for -debugging issues in this code. - -@item -fanalyzer-fine-grained -@opindex fanalyzer-fine-grained -@opindex fno-analyzer-fine-grained -This option is intended for analyzer developers. - -Internally the analyzer builds an ``exploded graph'' that combines -control flow graphs with data flow information. - -By default, an edge in this graph can contain the effects of a run -of multiple statements within a basic block. With -@option{-fanalyzer-fine-grained}, each statement gets its own edge. - -@item -fanalyzer-show-duplicate-count -@opindex fanalyzer-show-duplicate-count -@opindex fno-analyzer-show-duplicate-count -This option is intended for analyzer developers: if multiple diagnostics -have been detected as being duplicates of each other, it emits a note when -reporting the best diagnostic, giving the number of additional diagnostics -that were suppressed by the deduplication logic. - -@item -fno-analyzer-state-merge -@opindex fanalyzer-state-merge -@opindex fno-analyzer-state-merge -This option is intended for analyzer developers. - -By default the analyzer attempts to simplify analysis by merging -sufficiently similar states at each program point as it builds its -``exploded graph''. With @option{-fno-analyzer-state-merge} this -merging can be suppressed, for debugging state-handling issues. - -@item -fno-analyzer-state-purge -@opindex fanalyzer-state-purge -@opindex fno-analyzer-state-purge -This option is intended for analyzer developers. - -By default the analyzer attempts to simplify analysis by purging -aspects of state at a program point that appear to no longer be relevant -e.g. the values of locals that aren't accessed later in the function -and which aren't relevant to leak analysis. - -With @option{-fno-analyzer-state-purge} this purging of state can -be suppressed, for debugging state-handling issues. - -@item -fanalyzer-transitivity -@opindex fanalyzer-transitivity -@opindex fno-analyzer-transitivity -This option enables transitivity of constraints within the analyzer. - -@item -fno-analyzer-undo-inlining -@opindex fanalyzer-undo-inlining -@opindex fno-analyzer-undo-inlining -This option is intended for analyzer developers. - -@option{-fanalyzer} runs relatively late compared to other code analysis -tools, and some optimizations have already been applied to the code. In -particular function inlining may have occurred, leading to the -interprocedural execution paths emitted by the analyzer containing -function frames that don't correspond to those in the original source -code. - -By default the analyzer attempts to reconstruct the original function -frames, and to emit events showing the inlined calls. - -With @option{-fno-analyzer-undo-inlining} this attempt to reconstruct -the original frame information can be be disabled, which may be of help -when debugging issues in the analyzer. - -@item -fanalyzer-verbose-edges -This option is intended for analyzer developers. It enables more -verbose, lower-level detail in the descriptions of control flow -within diagnostic paths. - -@item -fanalyzer-verbose-state-changes -This option is intended for analyzer developers. It enables more -verbose, lower-level detail in the descriptions of events relating -to state machines within diagnostic paths. - -@item -fanalyzer-verbosity=@var{level} -This option controls the complexity of the control flow paths that are -emitted for analyzer diagnostics. - -The @var{level} can be one of: - -@table @samp -@item 0 -At this level, interprocedural call and return events are displayed, -along with the most pertinent state-change events relating to -a diagnostic. For example, for a double-@code{free} diagnostic, -both calls to @code{free} will be shown. - -@item 1 -As per the previous level, but also show events for the entry -to each function. - -@item 2 -As per the previous level, but also show events relating to -control flow that are significant to triggering the issue -(e.g. ``true path taken'' at a conditional). - -This level is the default. - -@item 3 -As per the previous level, but show all control flow events, not -just significant ones. - -@item 4 -This level is intended for analyzer developers; it adds various -other events intended for debugging the analyzer. - -@end table - -@item -fdump-analyzer -@opindex fdump-analyzer -Dump internal details about what the analyzer is doing to -@file{@var{file}.analyzer.txt}. -This option is overridden by @option{-fdump-analyzer-stderr}. - -@item -fdump-analyzer-stderr -@opindex fdump-analyzer-stderr -Dump internal details about what the analyzer is doing to stderr. -This option overrides @option{-fdump-analyzer}. - -@item -fdump-analyzer-callgraph -@opindex fdump-analyzer-callgraph -Dump a representation of the call graph suitable for viewing with -GraphViz to @file{@var{file}.callgraph.dot}. - -@item -fdump-analyzer-exploded-graph -@opindex fdump-analyzer-exploded-graph -Dump a representation of the ``exploded graph'' suitable for viewing with -GraphViz to @file{@var{file}.eg.dot}. -Nodes are color-coded based on state-machine states to emphasize -state changes. - -@item -fdump-analyzer-exploded-nodes -@opindex dump-analyzer-exploded-nodes -Emit diagnostics showing where nodes in the ``exploded graph'' are -in relation to the program source. - -@item -fdump-analyzer-exploded-nodes-2 -@opindex dump-analyzer-exploded-nodes-2 -Dump a textual representation of the ``exploded graph'' to -@file{@var{file}.eg.txt}. - -@item -fdump-analyzer-exploded-nodes-3 -@opindex dump-analyzer-exploded-nodes-3 -Dump a textual representation of the ``exploded graph'' to -one dump file per node, to @file{@var{file}.eg-@var{id}.txt}. -This is typically a large number of dump files. - -@item -fdump-analyzer-exploded-paths -@opindex fdump-analyzer-exploded-paths -Dump a textual representation of the ``exploded path'' for each -diagnostic to @file{@var{file}.@var{idx}.@var{kind}.epath.txt}. - -@item -fdump-analyzer-feasibility -@opindex dump-analyzer-feasibility -Dump internal details about the analyzer's search for feasible paths. -The details are written in a form suitable for viewing with GraphViz -to filenames of the form @file{@var{file}.*.fg.dot}, -@file{@var{file}.*.tg.dot}, and @file{@var{file}.*.fpath.txt}. - -@item -fdump-analyzer-json -@opindex fdump-analyzer-json -Dump a compressed JSON representation of analyzer internals to -@file{@var{file}.analyzer.json.gz}. The precise format is subject -to change. - -@item -fdump-analyzer-state-purge -@opindex fdump-analyzer-state-purge -As per @option{-fdump-analyzer-supergraph}, dump a representation of the -``supergraph'' suitable for viewing with GraphViz, but annotate the -graph with information on what state will be purged at each node. -The graph is written to @file{@var{file}.state-purge.dot}. - -@item -fdump-analyzer-supergraph -@opindex fdump-analyzer-supergraph -Dump representations of the ``supergraph'' suitable for viewing with -GraphViz to @file{@var{file}.supergraph.dot} and to -@file{@var{file}.supergraph-eg.dot}. These show all of the -control flow graphs in the program, with interprocedural edges for -calls and returns. The second dump contains annotations showing nodes -in the ``exploded graph'' and diagnostics associated with them. - -@item -fdump-analyzer-untracked -@opindex fdump-analyzer-untracked -Emit custom warnings with internal details intended for analyzer developers. - -@end table - -@node Debugging Options -@section Options for Debugging Your Program -@cindex options, debugging -@cindex debugging information options - -To tell GCC to emit extra information for use by a debugger, in almost -all cases you need only to add @option{-g} to your other options. Some debug -formats can co-exist (like DWARF with CTF) when each of them is enabled -explicitly by adding the respective command line option to your other options. - -GCC allows you to use @option{-g} with -@option{-O}. The shortcuts taken by optimized code may occasionally -be surprising: some variables you declared may not exist -at all; flow of control may briefly move where you did not expect it; -some statements may not be executed because they compute constant -results or their values are already at hand; some statements may -execute in different places because they have been moved out of loops. -Nevertheless it is possible to debug optimized output. This makes -it reasonable to use the optimizer for programs that might have bugs. - -If you are not using some other optimization option, consider -using @option{-Og} (@pxref{Optimize Options}) with @option{-g}. -With no @option{-O} option at all, some compiler passes that collect -information useful for debugging do not run at all, so that -@option{-Og} may result in a better debugging experience. - -@table @gcctabopt -@item -g -@opindex g -Produce debugging information in the operating system's native format -(stabs, COFF, XCOFF, or DWARF)@. GDB can work with this debugging -information. - -On most systems that use stabs format, @option{-g} enables use of extra -debugging information that only GDB can use; this extra information -makes debugging work better in GDB but probably makes other debuggers -crash or refuse to read the program. If you want to control for certain whether -to generate the extra information, use @option{-gvms} (see below). - -@item -ggdb -@opindex ggdb -Produce debugging information for use by GDB@. This means to use the -most expressive format available (DWARF, stabs, or the native format -if neither of those are supported), including GDB extensions if at all -possible. - -@item -gdwarf -@itemx -gdwarf-@var{version} -@opindex gdwarf -Produce debugging information in DWARF format (if that is supported). -The value of @var{version} may be either 2, 3, 4 or 5; the default -version for most targets is 5 (with the exception of VxWorks, TPF and -Darwin/Mac OS X, which default to version 2, and AIX, which defaults -to version 4). - -Note that with DWARF Version 2, some ports require and always -use some non-conflicting DWARF 3 extensions in the unwind tables. - -Version 4 may require GDB 7.0 and @option{-fvar-tracking-assignments} -for maximum benefit. Version 5 requires GDB 8.0 or higher. - -GCC no longer supports DWARF Version 1, which is substantially -different than Version 2 and later. For historical reasons, some -other DWARF-related options such as -@option{-fno-dwarf2-cfi-asm}) retain a reference to DWARF Version 2 -in their names, but apply to all currently-supported versions of DWARF. - -@item -gbtf -@opindex gbtf -Request BTF debug information. BTF is the default debugging format for the -eBPF target. On other targets, like x86, BTF debug information can be -generated along with DWARF debug information when both of the debug formats are -enabled explicitly via their respective command line options. - -@item -gctf -@itemx -gctf@var{level} -@opindex gctf -Request CTF debug information and use level to specify how much CTF debug -information should be produced. If @option{-gctf} is specified -without a value for level, the default level of CTF debug information is 2. - -CTF debug information can be generated along with DWARF debug information when -both of the debug formats are enabled explicitly via their respective command -line options. - -Level 0 produces no CTF debug information at all. Thus, @option{-gctf0} -negates @option{-gctf}. - -Level 1 produces CTF information for tracebacks only. This includes callsite -information, but does not include type information. - -Level 2 produces type information for entities (functions, data objects etc.) -at file-scope or global-scope only. - -@item -gvms -@opindex gvms -Produce debugging information in Alpha/VMS debug format (if that is -supported). This is the format used by DEBUG on Alpha/VMS systems. - -@item -g@var{level} -@itemx -ggdb@var{level} -@itemx -gvms@var{level} -Request debugging information and also use @var{level} to specify how -much information. The default level is 2. - -Level 0 produces no debug information at all. Thus, @option{-g0} negates -@option{-g}. - -Level 1 produces minimal information, enough for making backtraces in -parts of the program that you don't plan to debug. This includes -descriptions of functions and external variables, and line number -tables, but no information about local variables. - -Level 3 includes extra information, such as all the macro definitions -present in the program. Some debuggers support macro expansion when -you use @option{-g3}. - -If you use multiple @option{-g} options, with or without level numbers, -the last such option is the one that is effective. - -@option{-gdwarf} does not accept a concatenated debug level, to avoid -confusion with @option{-gdwarf-@var{level}}. -Instead use an additional @option{-g@var{level}} option to change the -debug level for DWARF. - -@item -fno-eliminate-unused-debug-symbols -@opindex feliminate-unused-debug-symbols -@opindex fno-eliminate-unused-debug-symbols -By default, no debug information is produced for symbols that are not actually -used. Use this option if you want debug information for all symbols. - -@item -femit-class-debug-always -@opindex femit-class-debug-always -Instead of emitting debugging information for a C++ class in only one -object file, emit it in all object files using the class. This option -should be used only with debuggers that are unable to handle the way GCC -normally emits debugging information for classes because using this -option increases the size of debugging information by as much as a -factor of two. - -@item -fno-merge-debug-strings -@opindex fmerge-debug-strings -@opindex fno-merge-debug-strings -Direct the linker to not merge together strings in the debugging -information that are identical in different object files. Merging is -not supported by all assemblers or linkers. Merging decreases the size -of the debug information in the output file at the cost of increasing -link processing time. Merging is enabled by default. - -@item -fdebug-prefix-map=@var{old}=@var{new} -@opindex fdebug-prefix-map -When compiling files residing in directory @file{@var{old}}, record -debugging information describing them as if the files resided in -directory @file{@var{new}} instead. This can be used to replace a -build-time path with an install-time path in the debug info. It can -also be used to change an absolute path to a relative path by using -@file{.} for @var{new}. This can give more reproducible builds, which -are location independent, but may require an extra command to tell GDB -where to find the source files. See also @option{-ffile-prefix-map}. - -@item -fvar-tracking -@opindex fvar-tracking -Run variable tracking pass. It computes where variables are stored at each -position in code. Better debugging information is then generated -(if the debugging information format supports this information). - -It is enabled by default when compiling with optimization (@option{-Os}, -@option{-O}, @option{-O2}, @dots{}), debugging information (@option{-g}) and -the debug info format supports it. - -@item -fvar-tracking-assignments -@opindex fvar-tracking-assignments -@opindex fno-var-tracking-assignments -Annotate assignments to user variables early in the compilation and -attempt to carry the annotations over throughout the compilation all the -way to the end, in an attempt to improve debug information while -optimizing. Use of @option{-gdwarf-4} is recommended along with it. - -It can be enabled even if var-tracking is disabled, in which case -annotations are created and maintained, but discarded at the end. -By default, this flag is enabled together with @option{-fvar-tracking}, -except when selective scheduling is enabled. - -@item -gsplit-dwarf -@opindex gsplit-dwarf -If DWARF debugging information is enabled, separate as much debugging -information as possible into a separate output file with the extension -@file{.dwo}. This option allows the build system to avoid linking files with -debug information. To be useful, this option requires a debugger capable of -reading @file{.dwo} files. - -@item -gdwarf32 -@itemx -gdwarf64 -@opindex gdwarf32 -@opindex gdwarf64 -If DWARF debugging information is enabled, the @option{-gdwarf32} selects -the 32-bit DWARF format and the @option{-gdwarf64} selects the 64-bit -DWARF format. The default is target specific, on most targets it is -@option{-gdwarf32} though. The 32-bit DWARF format is smaller, but -can't support more than 2GiB of debug information in any of the DWARF -debug information sections. The 64-bit DWARF format allows larger debug -information and might not be well supported by all consumers yet. - -@item -gdescribe-dies -@opindex gdescribe-dies -Add description attributes to some DWARF DIEs that have no name attribute, -such as artificial variables, external references and call site -parameter DIEs. - -@item -gpubnames -@opindex gpubnames -Generate DWARF @code{.debug_pubnames} and @code{.debug_pubtypes} sections. - -@item -ggnu-pubnames -@opindex ggnu-pubnames -Generate @code{.debug_pubnames} and @code{.debug_pubtypes} sections in a format -suitable for conversion into a GDB@ index. This option is only useful -with a linker that can produce GDB@ index version 7. - -@item -fdebug-types-section -@opindex fdebug-types-section -@opindex fno-debug-types-section -When using DWARF Version 4 or higher, type DIEs can be put into -their own @code{.debug_types} section instead of making them part of the -@code{.debug_info} section. It is more efficient to put them in a separate -comdat section since the linker can then remove duplicates. -But not all DWARF consumers support @code{.debug_types} sections yet -and on some objects @code{.debug_types} produces larger instead of smaller -debugging information. - -@item -grecord-gcc-switches -@itemx -gno-record-gcc-switches -@opindex grecord-gcc-switches -@opindex gno-record-gcc-switches -This switch causes the command-line options used to invoke the -compiler that may affect code generation to be appended to the -DW_AT_producer attribute in DWARF debugging information. The options -are concatenated with spaces separating them from each other and from -the compiler version. -It is enabled by default. -See also @option{-frecord-gcc-switches} for another -way of storing compiler options into the object file. - -@item -gstrict-dwarf -@opindex gstrict-dwarf -Disallow using extensions of later DWARF standard version than selected -with @option{-gdwarf-@var{version}}. On most targets using non-conflicting -DWARF extensions from later standard versions is allowed. - -@item -gno-strict-dwarf -@opindex gno-strict-dwarf -Allow using extensions of later DWARF standard version than selected with -@option{-gdwarf-@var{version}}. - -@item -gas-loc-support -@opindex gas-loc-support -Inform the compiler that the assembler supports @code{.loc} directives. -It may then use them for the assembler to generate DWARF2+ line number -tables. - -This is generally desirable, because assembler-generated line-number -tables are a lot more compact than those the compiler can generate -itself. - -This option will be enabled by default if, at GCC configure time, the -assembler was found to support such directives. - -@item -gno-as-loc-support -@opindex gno-as-loc-support -Force GCC to generate DWARF2+ line number tables internally, if DWARF2+ -line number tables are to be generated. - -@item -gas-locview-support -@opindex gas-locview-support -Inform the compiler that the assembler supports @code{view} assignment -and reset assertion checking in @code{.loc} directives. - -This option will be enabled by default if, at GCC configure time, the -assembler was found to support them. - -@item -gno-as-locview-support -Force GCC to assign view numbers internally, if -@option{-gvariable-location-views} are explicitly requested. - -@item -gcolumn-info -@itemx -gno-column-info -@opindex gcolumn-info -@opindex gno-column-info -Emit location column information into DWARF debugging information, rather -than just file and line. -This option is enabled by default. - -@item -gstatement-frontiers -@itemx -gno-statement-frontiers -@opindex gstatement-frontiers -@opindex gno-statement-frontiers -This option causes GCC to create markers in the internal representation -at the beginning of statements, and to keep them roughly in place -throughout compilation, using them to guide the output of @code{is_stmt} -markers in the line number table. This is enabled by default when -compiling with optimization (@option{-Os}, @option{-O1}, @option{-O2}, -@dots{}), and outputting DWARF 2 debug information at the normal level. - -@item -gvariable-location-views -@itemx -gvariable-location-views=incompat5 -@itemx -gno-variable-location-views -@opindex gvariable-location-views -@opindex gvariable-location-views=incompat5 -@opindex gno-variable-location-views -Augment variable location lists with progressive view numbers implied -from the line number table. This enables debug information consumers to -inspect state at certain points of the program, even if no instructions -associated with the corresponding source locations are present at that -point. If the assembler lacks support for view numbers in line number -tables, this will cause the compiler to emit the line number table, -which generally makes them somewhat less compact. The augmented line -number tables and location lists are fully backward-compatible, so they -can be consumed by debug information consumers that are not aware of -these augmentations, but they won't derive any benefit from them either. - -This is enabled by default when outputting DWARF 2 debug information at -the normal level, as long as there is assembler support, -@option{-fvar-tracking-assignments} is enabled and -@option{-gstrict-dwarf} is not. When assembler support is not -available, this may still be enabled, but it will force GCC to output -internal line number tables, and if -@option{-ginternal-reset-location-views} is not enabled, that will most -certainly lead to silently mismatching location views. - -There is a proposed representation for view numbers that is not backward -compatible with the location list format introduced in DWARF 5, that can -be enabled with @option{-gvariable-location-views=incompat5}. This -option may be removed in the future, is only provided as a reference -implementation of the proposed representation. Debug information -consumers are not expected to support this extended format, and they -would be rendered unable to decode location lists using it. - -@item -ginternal-reset-location-views -@itemx -gno-internal-reset-location-views -@opindex ginternal-reset-location-views -@opindex gno-internal-reset-location-views -Attempt to determine location views that can be omitted from location -view lists. This requires the compiler to have very accurate insn -length estimates, which isn't always the case, and it may cause -incorrect view lists to be generated silently when using an assembler -that does not support location view lists. The GNU assembler will flag -any such error as a @code{view number mismatch}. This is only enabled -on ports that define a reliable estimation function. - -@item -ginline-points -@itemx -gno-inline-points -@opindex ginline-points -@opindex gno-inline-points -Generate extended debug information for inlined functions. Location -view tracking markers are inserted at inlined entry points, so that -address and view numbers can be computed and output in debug -information. This can be enabled independently of location views, in -which case the view numbers won't be output, but it can only be enabled -along with statement frontiers, and it is only enabled by default if -location views are enabled. - -@item -gz@r{[}=@var{type}@r{]} -@opindex gz -Produce compressed debug sections in DWARF format, if that is supported. -If @var{type} is not given, the default type depends on the capabilities -of the assembler and linker used. @var{type} may be one of -@samp{none} (don't compress debug sections), or @samp{zlib} (use zlib -compression in ELF gABI format). If the linker doesn't support writing -compressed debug sections, the option is rejected. Otherwise, if the -assembler does not support them, @option{-gz} is silently ignored when -producing object files. - -@item -femit-struct-debug-baseonly -@opindex femit-struct-debug-baseonly -Emit debug information for struct-like types -only when the base name of the compilation source file -matches the base name of file in which the struct is defined. - -This option substantially reduces the size of debugging information, -but at significant potential loss in type information to the debugger. -See @option{-femit-struct-debug-reduced} for a less aggressive option. -See @option{-femit-struct-debug-detailed} for more detailed control. - -This option works only with DWARF debug output. - -@item -femit-struct-debug-reduced -@opindex femit-struct-debug-reduced -Emit debug information for struct-like types -only when the base name of the compilation source file -matches the base name of file in which the type is defined, -unless the struct is a template or defined in a system header. - -This option significantly reduces the size of debugging information, -with some potential loss in type information to the debugger. -See @option{-femit-struct-debug-baseonly} for a more aggressive option. -See @option{-femit-struct-debug-detailed} for more detailed control. - -This option works only with DWARF debug output. - -@item -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} -@opindex femit-struct-debug-detailed -Specify the struct-like types -for which the compiler generates debug information. -The intent is to reduce duplicate struct debug information -between different object files within the same program. - -This option is a detailed version of -@option{-femit-struct-debug-reduced} and @option{-femit-struct-debug-baseonly}, -which serves for most needs. - -A specification has the syntax@* -[@samp{dir:}|@samp{ind:}][@samp{ord:}|@samp{gen:}](@samp{any}|@samp{sys}|@samp{base}|@samp{none}) - -The optional first word limits the specification to -structs that are used directly (@samp{dir:}) or used indirectly (@samp{ind:}). -A struct type is used directly when it is the type of a variable, member. -Indirect uses arise through pointers to structs. -That is, when use of an incomplete struct is valid, the use is indirect. -An example is -@samp{struct one direct; struct two * indirect;}. - -The optional second word limits the specification to -ordinary structs (@samp{ord:}) or generic structs (@samp{gen:}). -Generic structs are a bit complicated to explain. -For C++, these are non-explicit specializations of template classes, -or non-template classes within the above. -Other programming languages have generics, -but @option{-femit-struct-debug-detailed} does not yet implement them. - -The third word specifies the source files for those -structs for which the compiler should emit debug information. -The values @samp{none} and @samp{any} have the normal meaning. -The value @samp{base} means that -the base of name of the file in which the type declaration appears -must match the base of the name of the main compilation file. -In practice, this means that when compiling @file{foo.c}, debug information -is generated for types declared in that file and @file{foo.h}, -but not other header files. -The value @samp{sys} means those types satisfying @samp{base} -or declared in system or compiler headers. - -You may need to experiment to determine the best settings for your application. - -The default is @option{-femit-struct-debug-detailed=all}. - -This option works only with DWARF debug output. - -@item -fno-dwarf2-cfi-asm -@opindex fdwarf2-cfi-asm -@opindex fno-dwarf2-cfi-asm -Emit DWARF unwind info as compiler generated @code{.eh_frame} section -instead of using GAS @code{.cfi_*} directives. - -@item -fno-eliminate-unused-debug-types -@opindex feliminate-unused-debug-types -@opindex fno-eliminate-unused-debug-types -Normally, when producing DWARF output, GCC avoids producing debug symbol -output for types that are nowhere used in the source file being compiled. -Sometimes it is useful to have GCC emit debugging -information for all types declared in a compilation -unit, regardless of whether or not they are actually used -in that compilation unit, for example -if, in the debugger, you want to cast a value to a type that is -not actually used in your program (but is declared). More often, -however, this results in a significant amount of wasted space. -@end table - -@node Optimize Options -@section Options That Control Optimization -@cindex optimize options -@cindex options, optimization - -These options control various sorts of optimizations. - -Without any optimization option, the compiler's goal is to reduce the -cost of compilation and to make debugging produce the expected -results. Statements are independent: if you stop the program with a -breakpoint between statements, you can then assign a new value to any -variable or change the program counter to any other statement in the -function and get exactly the results you expect from the source -code. - -Turning on optimization flags makes the compiler attempt to improve -the performance and/or code size at the expense of compilation time -and possibly the ability to debug the program. - -The compiler performs optimization based on the knowledge it has of the -program. Compiling multiple files at once to a single output file mode allows -the compiler to use information gained from all of the files when compiling -each of them. - -Not all optimizations are controlled directly by a flag. Only -optimizations that have a flag are listed in this section. - -Most optimizations are completely disabled at @option{-O0} or if an -@option{-O} level is not set on the command line, even if individual -optimization flags are specified. Similarly, @option{-Og} suppresses -many optimization passes. - -Depending on the target and how GCC was configured, a slightly different -set of optimizations may be enabled at each @option{-O} level than -those listed here. You can invoke GCC with @option{-Q --help=optimizers} -to find out the exact set of optimizations that are enabled at each level. -@xref{Overall Options}, for examples. - -@table @gcctabopt -@item -O -@itemx -O1 -@opindex O -@opindex O1 -Optimize. Optimizing compilation takes somewhat more time, and a lot -more memory for a large function. - -With @option{-O}, the compiler tries to reduce code size and execution -time, without performing any optimizations that take a great deal of -compilation time. - -@c Note that in addition to the default_options_table list in opts.cc, -@c several optimization flags default to true but control optimization -@c passes that are explicitly disabled at -O0. - -@option{-O} turns on the following optimization flags: - -@c Please keep the following list alphabetized. -@gccoptlist{-fauto-inc-dec @gol --fbranch-count-reg @gol --fcombine-stack-adjustments @gol --fcompare-elim @gol --fcprop-registers @gol --fdce @gol --fdefer-pop @gol --fdelayed-branch @gol --fdse @gol --fforward-propagate @gol --fguess-branch-probability @gol --fif-conversion @gol --fif-conversion2 @gol --finline-functions-called-once @gol --fipa-modref @gol --fipa-profile @gol --fipa-pure-const @gol --fipa-reference @gol --fipa-reference-addressable @gol --fmerge-constants @gol --fmove-loop-invariants @gol --fmove-loop-stores@gol --fomit-frame-pointer @gol --freorder-blocks @gol --fshrink-wrap @gol --fshrink-wrap-separate @gol --fsplit-wide-types @gol --fssa-backprop @gol --fssa-phiopt @gol --ftree-bit-ccp @gol --ftree-ccp @gol --ftree-ch @gol --ftree-coalesce-vars @gol --ftree-copy-prop @gol --ftree-dce @gol --ftree-dominator-opts @gol --ftree-dse @gol --ftree-forwprop @gol --ftree-fre @gol --ftree-phiprop @gol --ftree-pta @gol --ftree-scev-cprop @gol --ftree-sink @gol --ftree-slsr @gol --ftree-sra @gol --ftree-ter @gol --funit-at-a-time} - -@item -O2 -@opindex O2 -Optimize even more. GCC performs nearly all supported optimizations -that do not involve a space-speed tradeoff. -As compared to @option{-O}, this option increases both compilation time -and the performance of the generated code. - -@option{-O2} turns on all optimization flags specified by @option{-O1}. It -also turns on the following optimization flags: - -@c Please keep the following list alphabetized! -@gccoptlist{-falign-functions -falign-jumps @gol --falign-labels -falign-loops @gol --fcaller-saves @gol --fcode-hoisting @gol --fcrossjumping @gol --fcse-follow-jumps -fcse-skip-blocks @gol --fdelete-null-pointer-checks @gol --fdevirtualize -fdevirtualize-speculatively @gol --fexpensive-optimizations @gol --ffinite-loops @gol --fgcse -fgcse-lm @gol --fhoist-adjacent-loads @gol --finline-functions @gol --finline-small-functions @gol --findirect-inlining @gol --fipa-bit-cp -fipa-cp -fipa-icf @gol --fipa-ra -fipa-sra -fipa-vrp @gol --fisolate-erroneous-paths-dereference @gol --flra-remat @gol --foptimize-sibling-calls @gol --foptimize-strlen @gol --fpartial-inlining @gol --fpeephole2 @gol --freorder-blocks-algorithm=stc @gol --freorder-blocks-and-partition -freorder-functions @gol --frerun-cse-after-loop @gol --fschedule-insns -fschedule-insns2 @gol --fsched-interblock -fsched-spec @gol --fstore-merging @gol --fstrict-aliasing @gol --fthread-jumps @gol --ftree-builtin-call-dce @gol --ftree-loop-vectorize @gol --ftree-pre @gol --ftree-slp-vectorize @gol --ftree-switch-conversion -ftree-tail-merge @gol --ftree-vrp @gol --fvect-cost-model=very-cheap} - -Please note the warning under @option{-fgcse} about -invoking @option{-O2} on programs that use computed gotos. - -@item -O3 -@opindex O3 -Optimize yet more. @option{-O3} turns on all optimizations specified -by @option{-O2} and also turns on the following optimization flags: - -@c Please keep the following list alphabetized! -@gccoptlist{-fgcse-after-reload @gol --fipa-cp-clone --floop-interchange @gol --floop-unroll-and-jam @gol --fpeel-loops @gol --fpredictive-commoning @gol --fsplit-loops @gol --fsplit-paths @gol --ftree-loop-distribution @gol --ftree-partial-pre @gol --funswitch-loops @gol --fvect-cost-model=dynamic @gol --fversion-loops-for-strides} - -@item -O0 -@opindex O0 -Reduce compilation time and make debugging produce the expected -results. This is the default. - -@item -Os -@opindex Os -Optimize for size. @option{-Os} enables all @option{-O2} optimizations -except those that often increase code size: - -@gccoptlist{-falign-functions -falign-jumps @gol --falign-labels -falign-loops @gol --fprefetch-loop-arrays -freorder-blocks-algorithm=stc} - -It also enables @option{-finline-functions}, causes the compiler to tune for -code size rather than execution speed, and performs further optimizations -designed to reduce code size. - -@item -Ofast -@opindex Ofast -Disregard strict standards compliance. @option{-Ofast} enables all -@option{-O3} optimizations. It also enables optimizations that are not -valid for all standard-compliant programs. -It turns on @option{-ffast-math}, @option{-fallow-store-data-races} -and the Fortran-specific @option{-fstack-arrays}, unless -@option{-fmax-stack-var-size} is specified, and @option{-fno-protect-parens}. -It turns off @option{-fsemantic-interposition}. - -@item -Og -@opindex Og -Optimize debugging experience. @option{-Og} should be the optimization -level of choice for the standard edit-compile-debug cycle, offering -a reasonable level of optimization while maintaining fast compilation -and a good debugging experience. It is a better choice than @option{-O0} -for producing debuggable code because some compiler passes -that collect debug information are disabled at @option{-O0}. - -Like @option{-O0}, @option{-Og} completely disables a number of -optimization passes so that individual options controlling them have -no effect. Otherwise @option{-Og} enables all @option{-O1} -optimization flags except for those that may interfere with debugging: - -@gccoptlist{-fbranch-count-reg -fdelayed-branch @gol --fdse -fif-conversion -fif-conversion2 @gol --finline-functions-called-once @gol --fmove-loop-invariants -fmove-loop-stores -fssa-phiopt @gol --ftree-bit-ccp -ftree-dse -ftree-pta -ftree-sra} - -@item -Oz -@opindex Oz -Optimize aggressively for size rather than speed. This may increase -the number of instructions executed if those instructions require -fewer bytes to encode. @option{-Oz} behaves similarly to @option{-Os} -including enabling most @option{-O2} optimizations. - -@end table - -If you use multiple @option{-O} options, with or without level numbers, -the last such option is the one that is effective. - -Options of the form @option{-f@var{flag}} specify machine-independent -flags. Most flags have both positive and negative forms; the negative -form of @option{-ffoo} is @option{-fno-foo}. In the table -below, only one of the forms is listed---the one you typically -use. You can figure out the other form by either removing @samp{no-} -or adding it. - -The following options control specific optimizations. They are either -activated by @option{-O} options or are related to ones that are. You -can use the following flags in the rare cases when ``fine-tuning'' of -optimizations to be performed is desired. - -@table @gcctabopt -@item -fno-defer-pop -@opindex fno-defer-pop -@opindex fdefer-pop -For machines that must pop arguments after a function call, always pop -the arguments as soon as each function returns. -At levels @option{-O1} and higher, @option{-fdefer-pop} is the default; -this allows the compiler to let arguments accumulate on the stack for several -function calls and pop them all at once. - -@item -fforward-propagate -@opindex fforward-propagate -Perform a forward propagation pass on RTL@. The pass tries to combine two -instructions and checks if the result can be simplified. If loop unrolling -is active, two passes are performed and the second is scheduled after -loop unrolling. - -This option is enabled by default at optimization levels @option{-O1}, -@option{-O2}, @option{-O3}, @option{-Os}. - -@item -ffp-contract=@var{style} -@opindex ffp-contract -@option{-ffp-contract=off} disables floating-point expression contraction. -@option{-ffp-contract=fast} enables floating-point expression contraction -such as forming of fused multiply-add operations if the target has -native support for them. -@option{-ffp-contract=on} enables floating-point expression contraction -if allowed by the language standard. This is currently not implemented -and treated equal to @option{-ffp-contract=off}. - -The default is @option{-ffp-contract=fast}. - -@item -fomit-frame-pointer -@opindex fomit-frame-pointer -Omit the frame pointer in functions that don't need one. This avoids the -instructions to save, set up and restore the frame pointer; on many targets -it also makes an extra register available. - -On some targets this flag has no effect because the standard calling sequence -always uses a frame pointer, so it cannot be omitted. - -Note that @option{-fno-omit-frame-pointer} doesn't guarantee the frame pointer -is used in all functions. Several targets always omit the frame pointer in -leaf functions. - -Enabled by default at @option{-O1} and higher. - -@item -foptimize-sibling-calls -@opindex foptimize-sibling-calls -Optimize sibling and tail recursive calls. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -foptimize-strlen -@opindex foptimize-strlen -Optimize various standard C string functions (e.g.@: @code{strlen}, -@code{strchr} or @code{strcpy}) and -their @code{_FORTIFY_SOURCE} counterparts into faster alternatives. - -Enabled at levels @option{-O2}, @option{-O3}. - -@item -fno-inline -@opindex fno-inline -@opindex finline -Do not expand any functions inline apart from those marked with -the @code{always_inline} attribute. This is the default when not -optimizing. - -Single functions can be exempted from inlining by marking them -with the @code{noinline} attribute. - -@item -finline-small-functions -@opindex finline-small-functions -Integrate functions into their callers when their body is smaller than expected -function call code (so overall size of program gets smaller). The compiler -heuristically decides which functions are simple enough to be worth integrating -in this way. This inlining applies to all functions, even those not declared -inline. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -findirect-inlining -@opindex findirect-inlining -Inline also indirect calls that are discovered to be known at compile -time thanks to previous inlining. This option has any effect only -when inlining itself is turned on by the @option{-finline-functions} -or @option{-finline-small-functions} options. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -finline-functions -@opindex finline-functions -Consider all functions for inlining, even if they are not declared inline. -The compiler heuristically decides which functions are worth integrating -in this way. - -If all calls to a given function are integrated, and the function is -declared @code{static}, then the function is normally not output as -assembler code in its own right. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. Also enabled -by @option{-fprofile-use} and @option{-fauto-profile}. - -@item -finline-functions-called-once -@opindex finline-functions-called-once -Consider all @code{static} functions called once for inlining into their -caller even if they are not marked @code{inline}. If a call to a given -function is integrated, then the function is not output as assembler code -in its own right. - -Enabled at levels @option{-O1}, @option{-O2}, @option{-O3} and @option{-Os}, -but not @option{-Og}. - -@item -fearly-inlining -@opindex fearly-inlining -Inline functions marked by @code{always_inline} and functions whose body seems -smaller than the function call overhead early before doing -@option{-fprofile-generate} instrumentation and real inlining pass. Doing so -makes profiling significantly cheaper and usually inlining faster on programs -having large chains of nested wrapper functions. - -Enabled by default. - -@item -fipa-sra -@opindex fipa-sra -Perform interprocedural scalar replacement of aggregates, removal of -unused parameters and replacement of parameters passed by reference -by parameters passed by value. - -Enabled at levels @option{-O2}, @option{-O3} and @option{-Os}. - -@item -finline-limit=@var{n} -@opindex finline-limit -By default, GCC limits the size of functions that can be inlined. This flag -allows coarse control of this limit. @var{n} is the size of functions that -can be inlined in number of pseudo instructions. - -Inlining is actually controlled by a number of parameters, which may be -specified individually by using @option{--param @var{name}=@var{value}}. -The @option{-finline-limit=@var{n}} option sets some of these parameters -as follows: - -@table @gcctabopt -@item max-inline-insns-single -is set to @var{n}/2. -@item max-inline-insns-auto -is set to @var{n}/2. -@end table - -See below for a documentation of the individual -parameters controlling inlining and for the defaults of these parameters. - -@emph{Note:} there may be no value to @option{-finline-limit} that results -in default behavior. - -@emph{Note:} pseudo instruction represents, in this particular context, an -abstract measurement of function's size. In no way does it represent a count -of assembly instructions and as such its exact meaning might change from one -release to an another. - -@item -fno-keep-inline-dllexport -@opindex fno-keep-inline-dllexport -@opindex fkeep-inline-dllexport -This is a more fine-grained version of @option{-fkeep-inline-functions}, -which applies only to functions that are declared using the @code{dllexport} -attribute or declspec. @xref{Function Attributes,,Declaring Attributes of -Functions}. - -@item -fkeep-inline-functions -@opindex fkeep-inline-functions -In C, emit @code{static} functions that are declared @code{inline} -into the object file, even if the function has been inlined into all -of its callers. This switch does not affect functions using the -@code{extern inline} extension in GNU C90@. In C++, emit any and all -inline functions into the object file. - -@item -fkeep-static-functions -@opindex fkeep-static-functions -Emit @code{static} functions into the object file, even if the function -is never used. - -@item -fkeep-static-consts -@opindex fkeep-static-consts -Emit variables declared @code{static const} when optimization isn't turned -on, even if the variables aren't referenced. - -GCC enables this option by default. If you want to force the compiler to -check if a variable is referenced, regardless of whether or not -optimization is turned on, use the @option{-fno-keep-static-consts} option. - -@item -fmerge-constants -@opindex fmerge-constants -Attempt to merge identical constants (string constants and floating-point -constants) across compilation units. - -This option is the default for optimized compilation if the assembler and -linker support it. Use @option{-fno-merge-constants} to inhibit this -behavior. - -Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fmerge-all-constants -@opindex fmerge-all-constants -Attempt to merge identical constants and identical variables. - -This option implies @option{-fmerge-constants}. In addition to -@option{-fmerge-constants} this considers e.g.@: even constant initialized -arrays or initialized constant variables with integral or floating-point -types. Languages like C or C++ require each variable, including multiple -instances of the same variable in recursive calls, to have distinct locations, -so using this option results in non-conforming -behavior. - -@item -fmodulo-sched -@opindex fmodulo-sched -Perform swing modulo scheduling immediately before the first scheduling -pass. This pass looks at innermost loops and reorders their -instructions by overlapping different iterations. - -@item -fmodulo-sched-allow-regmoves -@opindex fmodulo-sched-allow-regmoves -Perform more aggressive SMS-based modulo scheduling with register moves -allowed. By setting this flag certain anti-dependences edges are -deleted, which triggers the generation of reg-moves based on the -life-range analysis. This option is effective only with -@option{-fmodulo-sched} enabled. - -@item -fno-branch-count-reg -@opindex fno-branch-count-reg -@opindex fbranch-count-reg -Disable the optimization pass that scans for opportunities to use -``decrement and branch'' instructions on a count register instead of -instruction sequences that decrement a register, compare it against zero, and -then branch based upon the result. This option is only meaningful on -architectures that support such instructions, which include x86, PowerPC, -IA-64 and S/390. Note that the @option{-fno-branch-count-reg} option -doesn't remove the decrement and branch instructions from the generated -instruction stream introduced by other optimization passes. - -The default is @option{-fbranch-count-reg} at @option{-O1} and higher, -except for @option{-Og}. - -@item -fno-function-cse -@opindex fno-function-cse -@opindex ffunction-cse -Do not put function addresses in registers; make each instruction that -calls a constant function contain the function's address explicitly. - -This option results in less efficient code, but some strange hacks -that alter the assembler output may be confused by the optimizations -performed when this option is not used. - -The default is @option{-ffunction-cse} - -@item -fno-zero-initialized-in-bss -@opindex fno-zero-initialized-in-bss -@opindex fzero-initialized-in-bss -If the target supports a BSS section, GCC by default puts variables that -are initialized to zero into BSS@. This can save space in the resulting -code. - -This option turns off this behavior because some programs explicitly -rely on variables going to the data section---e.g., so that the -resulting executable can find the beginning of that section and/or make -assumptions based on that. - -The default is @option{-fzero-initialized-in-bss}. - -@item -fthread-jumps -@opindex fthread-jumps -Perform optimizations that check to see if a jump branches to a -location where another comparison subsumed by the first is found. If -so, the first branch is redirected to either the destination of the -second branch or a point immediately following it, depending on whether -the condition is known to be true or false. - -Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fsplit-wide-types -@opindex fsplit-wide-types -When using a type that occupies multiple registers, such as @code{long -long} on a 32-bit system, split the registers apart and allocate them -independently. This normally generates better code for those types, -but may make debugging more difficult. - -Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, -@option{-Os}. - -@item -fsplit-wide-types-early -@opindex fsplit-wide-types-early -Fully split wide types early, instead of very late. -This option has no effect unless @option{-fsplit-wide-types} is turned on. - -This is the default on some targets. - -@item -fcse-follow-jumps -@opindex fcse-follow-jumps -In common subexpression elimination (CSE), scan through jump instructions -when the target of the jump is not reached by any other path. For -example, when CSE encounters an @code{if} statement with an -@code{else} clause, CSE follows the jump when the condition -tested is false. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fcse-skip-blocks -@opindex fcse-skip-blocks -This is similar to @option{-fcse-follow-jumps}, but causes CSE to -follow jumps that conditionally skip over blocks. When CSE -encounters a simple @code{if} statement with no else clause, -@option{-fcse-skip-blocks} causes CSE to follow the jump around the -body of the @code{if}. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -frerun-cse-after-loop -@opindex frerun-cse-after-loop -Re-run common subexpression elimination after loop optimizations are -performed. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fgcse -@opindex fgcse -Perform a global common subexpression elimination pass. -This pass also performs global constant and copy propagation. - -@emph{Note:} When compiling a program using computed gotos, a GCC -extension, you may get better run-time performance if you disable -the global common subexpression elimination pass by adding -@option{-fno-gcse} to the command line. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fgcse-lm -@opindex fgcse-lm -When @option{-fgcse-lm} is enabled, global common subexpression elimination -attempts to move loads that are only killed by stores into themselves. This -allows a loop containing a load/store sequence to be changed to a load outside -the loop, and a copy/store within the loop. - -Enabled by default when @option{-fgcse} is enabled. - -@item -fgcse-sm -@opindex fgcse-sm -When @option{-fgcse-sm} is enabled, a store motion pass is run after -global common subexpression elimination. This pass attempts to move -stores out of loops. When used in conjunction with @option{-fgcse-lm}, -loops containing a load/store sequence can be changed to a load before -the loop and a store after the loop. - -Not enabled at any optimization level. - -@item -fgcse-las -@opindex fgcse-las -When @option{-fgcse-las} is enabled, the global common subexpression -elimination pass eliminates redundant loads that come after stores to the -same memory location (both partial and full redundancies). - -Not enabled at any optimization level. - -@item -fgcse-after-reload -@opindex fgcse-after-reload -When @option{-fgcse-after-reload} is enabled, a redundant load elimination -pass is performed after reload. The purpose of this pass is to clean up -redundant spilling. - -Enabled by @option{-O3}, @option{-fprofile-use} and @option{-fauto-profile}. - -@item -faggressive-loop-optimizations -@opindex faggressive-loop-optimizations -This option tells the loop optimizer to use language constraints to -derive bounds for the number of iterations of a loop. This assumes that -loop code does not invoke undefined behavior by for example causing signed -integer overflows or out-of-bound array accesses. The bounds for the -number of iterations of a loop are used to guide loop unrolling and peeling -and loop exit test optimizations. -This option is enabled by default. - -@item -funconstrained-commons -@opindex funconstrained-commons -This option tells the compiler that variables declared in common blocks -(e.g.@: Fortran) may later be overridden with longer trailing arrays. This -prevents certain optimizations that depend on knowing the array bounds. - -@item -fcrossjumping -@opindex fcrossjumping -Perform cross-jumping transformation. -This transformation unifies equivalent code and saves code size. The -resulting code may or may not perform better than without cross-jumping. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fauto-inc-dec -@opindex fauto-inc-dec -Combine increments or decrements of addresses with memory accesses. -This pass is always skipped on architectures that do not have -instructions to support this. Enabled by default at @option{-O1} and -higher on architectures that support this. - -@item -fdce -@opindex fdce -Perform dead code elimination (DCE) on RTL@. -Enabled by default at @option{-O1} and higher. - -@item -fdse -@opindex fdse -Perform dead store elimination (DSE) on RTL@. -Enabled by default at @option{-O1} and higher. - -@item -fif-conversion -@opindex fif-conversion -Attempt to transform conditional jumps into branch-less equivalents. This -includes use of conditional moves, min, max, set flags and abs instructions, and -some tricks doable by standard arithmetics. The use of conditional execution -on chips where it is available is controlled by @option{-fif-conversion2}. - -Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, @option{-Os}, but -not with @option{-Og}. - -@item -fif-conversion2 -@opindex fif-conversion2 -Use conditional execution (where available) to transform conditional jumps into -branch-less equivalents. - -Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, @option{-Os}, but -not with @option{-Og}. - -@item -fdeclone-ctor-dtor -@opindex fdeclone-ctor-dtor -The C++ ABI requires multiple entry points for constructors and -destructors: one for a base subobject, one for a complete object, and -one for a virtual destructor that calls operator delete afterwards. -For a hierarchy with virtual bases, the base and complete variants are -clones, which means two copies of the function. With this option, the -base and complete variants are changed to be thunks that call a common -implementation. - -Enabled by @option{-Os}. - -@item -fdelete-null-pointer-checks -@opindex fdelete-null-pointer-checks -Assume that programs cannot safely dereference null pointers, and that -no code or data element resides at address zero. -This option enables simple constant -folding optimizations at all optimization levels. In addition, other -optimization passes in GCC use this flag to control global dataflow -analyses that eliminate useless checks for null pointers; these assume -that a memory access to address zero always results in a trap, so -that if a pointer is checked after it has already been dereferenced, -it cannot be null. - -Note however that in some environments this assumption is not true. -Use @option{-fno-delete-null-pointer-checks} to disable this optimization -for programs that depend on that behavior. - -This option is enabled by default on most targets. On Nios II ELF, it -defaults to off. On AVR and MSP430, this option is completely disabled. - -Passes that use the dataflow information -are enabled independently at different optimization levels. - -@item -fdevirtualize -@opindex fdevirtualize -Attempt to convert calls to virtual functions to direct calls. This -is done both within a procedure and interprocedurally as part of -indirect inlining (@option{-findirect-inlining}) and interprocedural constant -propagation (@option{-fipa-cp}). -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fdevirtualize-speculatively -@opindex fdevirtualize-speculatively -Attempt to convert calls to virtual functions to speculative direct calls. -Based on the analysis of the type inheritance graph, determine for a given call -the set of likely targets. If the set is small, preferably of size 1, change -the call into a conditional deciding between direct and indirect calls. The -speculative calls enable more optimizations, such as inlining. When they seem -useless after further optimization, they are converted back into original form. - -@item -fdevirtualize-at-ltrans -@opindex fdevirtualize-at-ltrans -Stream extra information needed for aggressive devirtualization when running -the link-time optimizer in local transformation mode. -This option enables more devirtualization but -significantly increases the size of streamed data. For this reason it is -disabled by default. - -@item -fexpensive-optimizations -@opindex fexpensive-optimizations -Perform a number of minor optimizations that are relatively expensive. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -free -@opindex free -Attempt to remove redundant extension instructions. This is especially -helpful for the x86-64 architecture, which implicitly zero-extends in 64-bit -registers after writing to their lower 32-bit half. - -Enabled for Alpha, AArch64 and x86 at levels @option{-O2}, -@option{-O3}, @option{-Os}. - -@item -fno-lifetime-dse -@opindex fno-lifetime-dse -@opindex flifetime-dse -In C++ the value of an object is only affected by changes within its -lifetime: when the constructor begins, the object has an indeterminate -value, and any changes during the lifetime of the object are dead when -the object is destroyed. Normally dead store elimination will take -advantage of this; if your code relies on the value of the object -storage persisting beyond the lifetime of the object, you can use this -flag to disable this optimization. To preserve stores before the -constructor starts (e.g.@: because your operator new clears the object -storage) but still treat the object as dead after the destructor, you -can use @option{-flifetime-dse=1}. The default behavior can be -explicitly selected with @option{-flifetime-dse=2}. -@option{-flifetime-dse=0} is equivalent to @option{-fno-lifetime-dse}. - -@item -flive-range-shrinkage -@opindex flive-range-shrinkage -Attempt to decrease register pressure through register live range -shrinkage. This is helpful for fast processors with small or moderate -size register sets. - -@item -fira-algorithm=@var{algorithm} -@opindex fira-algorithm -Use the specified coloring algorithm for the integrated register -allocator. The @var{algorithm} argument can be @samp{priority}, which -specifies Chow's priority coloring, or @samp{CB}, which specifies -Chaitin-Briggs coloring. Chaitin-Briggs coloring is not implemented -for all architectures, but for those targets that do support it, it is -the default because it generates better code. - -@item -fira-region=@var{region} -@opindex fira-region -Use specified regions for the integrated register allocator. The -@var{region} argument should be one of the following: - -@table @samp - -@item all -Use all loops as register allocation regions. -This can give the best results for machines with a small and/or -irregular register set. - -@item mixed -Use all loops except for loops with small register pressure -as the regions. This value usually gives -the best results in most cases and for most architectures, -and is enabled by default when compiling with optimization for speed -(@option{-O}, @option{-O2}, @dots{}). - -@item one -Use all functions as a single region. -This typically results in the smallest code size, and is enabled by default for -@option{-Os} or @option{-O0}. - -@end table - -@item -fira-hoist-pressure -@opindex fira-hoist-pressure -Use IRA to evaluate register pressure in the code hoisting pass for -decisions to hoist expressions. This option usually results in smaller -code, but it can slow the compiler down. - -This option is enabled at level @option{-Os} for all targets. - -@item -fira-loop-pressure -@opindex fira-loop-pressure -Use IRA to evaluate register pressure in loops for decisions to move -loop invariants. This option usually results in generation -of faster and smaller code on machines with large register files (>= 32 -registers), but it can slow the compiler down. - -This option is enabled at level @option{-O3} for some targets. - -@item -fno-ira-share-save-slots -@opindex fno-ira-share-save-slots -@opindex fira-share-save-slots -Disable sharing of stack slots used for saving call-used hard -registers living through a call. Each hard register gets a -separate stack slot, and as a result function stack frames are -larger. - -@item -fno-ira-share-spill-slots -@opindex fno-ira-share-spill-slots -@opindex fira-share-spill-slots -Disable sharing of stack slots allocated for pseudo-registers. Each -pseudo-register that does not get a hard register gets a separate -stack slot, and as a result function stack frames are larger. - -@item -flra-remat -@opindex flra-remat -Enable CFG-sensitive rematerialization in LRA. Instead of loading -values of spilled pseudos, LRA tries to rematerialize (recalculate) -values if it is profitable. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fdelayed-branch -@opindex fdelayed-branch -If supported for the target machine, attempt to reorder instructions -to exploit instruction slots available after delayed branch -instructions. - -Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, @option{-Os}, -but not at @option{-Og}. - -@item -fschedule-insns -@opindex fschedule-insns -If supported for the target machine, attempt to reorder instructions to -eliminate execution stalls due to required data being unavailable. This -helps machines that have slow floating point or memory load instructions -by allowing other instructions to be issued until the result of the load -or floating-point instruction is required. - -Enabled at levels @option{-O2}, @option{-O3}. - -@item -fschedule-insns2 -@opindex fschedule-insns2 -Similar to @option{-fschedule-insns}, but requests an additional pass of -instruction scheduling after register allocation has been done. This is -especially useful on machines with a relatively small number of -registers and where memory load instructions take more than one cycle. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fno-sched-interblock -@opindex fno-sched-interblock -@opindex fsched-interblock -Disable instruction scheduling across basic blocks, which -is normally enabled when scheduling before register allocation, i.e.@: -with @option{-fschedule-insns} or at @option{-O2} or higher. - -@item -fno-sched-spec -@opindex fno-sched-spec -@opindex fsched-spec -Disable speculative motion of non-load instructions, which -is normally enabled when scheduling before register allocation, i.e.@: -with @option{-fschedule-insns} or at @option{-O2} or higher. - -@item -fsched-pressure -@opindex fsched-pressure -Enable register pressure sensitive insn scheduling before register -allocation. This only makes sense when scheduling before register -allocation is enabled, i.e.@: with @option{-fschedule-insns} or at -@option{-O2} or higher. Usage of this option can improve the -generated code and decrease its size by preventing register pressure -increase above the number of available hard registers and subsequent -spills in register allocation. - -@item -fsched-spec-load -@opindex fsched-spec-load -Allow speculative motion of some load instructions. This only makes -sense when scheduling before register allocation, i.e.@: with -@option{-fschedule-insns} or at @option{-O2} or higher. - -@item -fsched-spec-load-dangerous -@opindex fsched-spec-load-dangerous -Allow speculative motion of more load instructions. This only makes -sense when scheduling before register allocation, i.e.@: with -@option{-fschedule-insns} or at @option{-O2} or higher. - -@item -fsched-stalled-insns -@itemx -fsched-stalled-insns=@var{n} -@opindex fsched-stalled-insns -Define how many insns (if any) can be moved prematurely from the queue -of stalled insns into the ready list during the second scheduling pass. -@option{-fno-sched-stalled-insns} means that no insns are moved -prematurely, @option{-fsched-stalled-insns=0} means there is no limit -on how many queued insns can be moved prematurely. -@option{-fsched-stalled-insns} without a value is equivalent to -@option{-fsched-stalled-insns=1}. - -@item -fsched-stalled-insns-dep -@itemx -fsched-stalled-insns-dep=@var{n} -@opindex fsched-stalled-insns-dep -Define how many insn groups (cycles) are examined for a dependency -on a stalled insn that is a candidate for premature removal from the queue -of stalled insns. This has an effect only during the second scheduling pass, -and only if @option{-fsched-stalled-insns} is used. -@option{-fno-sched-stalled-insns-dep} is equivalent to -@option{-fsched-stalled-insns-dep=0}. -@option{-fsched-stalled-insns-dep} without a value is equivalent to -@option{-fsched-stalled-insns-dep=1}. - -@item -fsched2-use-superblocks -@opindex fsched2-use-superblocks -When scheduling after register allocation, use superblock scheduling. -This allows motion across basic block boundaries, -resulting in faster schedules. This option is experimental, as not all machine -descriptions used by GCC model the CPU closely enough to avoid unreliable -results from the algorithm. - -This only makes sense when scheduling after register allocation, i.e.@: with -@option{-fschedule-insns2} or at @option{-O2} or higher. - -@item -fsched-group-heuristic -@opindex fsched-group-heuristic -Enable the group heuristic in the scheduler. This heuristic favors -the instruction that belongs to a schedule group. This is enabled -by default when scheduling is enabled, i.e.@: with @option{-fschedule-insns} -or @option{-fschedule-insns2} or at @option{-O2} or higher. - -@item -fsched-critical-path-heuristic -@opindex fsched-critical-path-heuristic -Enable the critical-path heuristic in the scheduler. This heuristic favors -instructions on the critical path. This is enabled by default when -scheduling is enabled, i.e.@: with @option{-fschedule-insns} -or @option{-fschedule-insns2} or at @option{-O2} or higher. - -@item -fsched-spec-insn-heuristic -@opindex fsched-spec-insn-heuristic -Enable the speculative instruction heuristic in the scheduler. This -heuristic favors speculative instructions with greater dependency weakness. -This is enabled by default when scheduling is enabled, i.e.@: -with @option{-fschedule-insns} or @option{-fschedule-insns2} -or at @option{-O2} or higher. - -@item -fsched-rank-heuristic -@opindex fsched-rank-heuristic -Enable the rank heuristic in the scheduler. This heuristic favors -the instruction belonging to a basic block with greater size or frequency. -This is enabled by default when scheduling is enabled, i.e.@: -with @option{-fschedule-insns} or @option{-fschedule-insns2} or -at @option{-O2} or higher. - -@item -fsched-last-insn-heuristic -@opindex fsched-last-insn-heuristic -Enable the last-instruction heuristic in the scheduler. This heuristic -favors the instruction that is less dependent on the last instruction -scheduled. This is enabled by default when scheduling is enabled, -i.e.@: with @option{-fschedule-insns} or @option{-fschedule-insns2} or -at @option{-O2} or higher. - -@item -fsched-dep-count-heuristic -@opindex fsched-dep-count-heuristic -Enable the dependent-count heuristic in the scheduler. This heuristic -favors the instruction that has more instructions depending on it. -This is enabled by default when scheduling is enabled, i.e.@: -with @option{-fschedule-insns} or @option{-fschedule-insns2} or -at @option{-O2} or higher. - -@item -freschedule-modulo-scheduled-loops -@opindex freschedule-modulo-scheduled-loops -Modulo scheduling is performed before traditional scheduling. If a loop -is modulo scheduled, later scheduling passes may change its schedule. -Use this option to control that behavior. - -@item -fselective-scheduling -@opindex fselective-scheduling -Schedule instructions using selective scheduling algorithm. Selective -scheduling runs instead of the first scheduler pass. - -@item -fselective-scheduling2 -@opindex fselective-scheduling2 -Schedule instructions using selective scheduling algorithm. Selective -scheduling runs instead of the second scheduler pass. - -@item -fsel-sched-pipelining -@opindex fsel-sched-pipelining -Enable software pipelining of innermost loops during selective scheduling. -This option has no effect unless one of @option{-fselective-scheduling} or -@option{-fselective-scheduling2} is turned on. - -@item -fsel-sched-pipelining-outer-loops -@opindex fsel-sched-pipelining-outer-loops -When pipelining loops during selective scheduling, also pipeline outer loops. -This option has no effect unless @option{-fsel-sched-pipelining} is turned on. - -@item -fsemantic-interposition -@opindex fsemantic-interposition -Some object formats, like ELF, allow interposing of symbols by the -dynamic linker. -This means that for symbols exported from the DSO, the compiler cannot perform -interprocedural propagation, inlining and other optimizations in anticipation -that the function or variable in question may change. While this feature is -useful, for example, to rewrite memory allocation functions by a debugging -implementation, it is expensive in the terms of code quality. -With @option{-fno-semantic-interposition} the compiler assumes that -if interposition happens for functions the overwriting function will have -precisely the same semantics (and side effects). -Similarly if interposition happens -for variables, the constructor of the variable will be the same. The flag -has no effect for functions explicitly declared inline -(where it is never allowed for interposition to change semantics) -and for symbols explicitly declared weak. - -@item -fshrink-wrap -@opindex fshrink-wrap -Emit function prologues only before parts of the function that need it, -rather than at the top of the function. This flag is enabled by default at -@option{-O} and higher. - -@item -fshrink-wrap-separate -@opindex fshrink-wrap-separate -Shrink-wrap separate parts of the prologue and epilogue separately, so that -those parts are only executed when needed. -This option is on by default, but has no effect unless @option{-fshrink-wrap} -is also turned on and the target supports this. - -@item -fcaller-saves -@opindex fcaller-saves -Enable allocation of values to registers that are clobbered by -function calls, by emitting extra instructions to save and restore the -registers around such calls. Such allocation is done only when it -seems to result in better code. - -This option is always enabled by default on certain machines, usually -those which have no call-preserved registers to use instead. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fcombine-stack-adjustments -@opindex fcombine-stack-adjustments -Tracks stack adjustments (pushes and pops) and stack memory references -and then tries to find ways to combine them. - -Enabled by default at @option{-O1} and higher. - -@item -fipa-ra -@opindex fipa-ra -Use caller save registers for allocation if those registers are not used by -any called function. In that case it is not necessary to save and restore -them around calls. This is only possible if called functions are part of -same compilation unit as current function and they are compiled before it. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}, however the option -is disabled if generated code will be instrumented for profiling -(@option{-p}, or @option{-pg}) or if callee's register usage cannot be known -exactly (this happens on targets that do not expose prologues -and epilogues in RTL). - -@item -fconserve-stack -@opindex fconserve-stack -Attempt to minimize stack usage. The compiler attempts to use less -stack space, even if that makes the program slower. This option -implies setting the @option{large-stack-frame} parameter to 100 -and the @option{large-stack-frame-growth} parameter to 400. - -@item -ftree-reassoc -@opindex ftree-reassoc -Perform reassociation on trees. This flag is enabled by default -at @option{-O1} and higher. - -@item -fcode-hoisting -@opindex fcode-hoisting -Perform code hoisting. Code hoisting tries to move the -evaluation of expressions executed on all paths to the function exit -as early as possible. This is especially useful as a code size -optimization, but it often helps for code speed as well. -This flag is enabled by default at @option{-O2} and higher. - -@item -ftree-pre -@opindex ftree-pre -Perform partial redundancy elimination (PRE) on trees. This flag is -enabled by default at @option{-O2} and @option{-O3}. - -@item -ftree-partial-pre -@opindex ftree-partial-pre -Make partial redundancy elimination (PRE) more aggressive. This flag is -enabled by default at @option{-O3}. - -@item -ftree-forwprop -@opindex ftree-forwprop -Perform forward propagation on trees. This flag is enabled by default -at @option{-O1} and higher. - -@item -ftree-fre -@opindex ftree-fre -Perform full redundancy elimination (FRE) on trees. The difference -between FRE and PRE is that FRE only considers expressions -that are computed on all paths leading to the redundant computation. -This analysis is faster than PRE, though it exposes fewer redundancies. -This flag is enabled by default at @option{-O1} and higher. - -@item -ftree-phiprop -@opindex ftree-phiprop -Perform hoisting of loads from conditional pointers on trees. This -pass is enabled by default at @option{-O1} and higher. - -@item -fhoist-adjacent-loads -@opindex fhoist-adjacent-loads -Speculatively hoist loads from both branches of an if-then-else if the -loads are from adjacent locations in the same structure and the target -architecture has a conditional move instruction. This flag is enabled -by default at @option{-O2} and higher. - -@item -ftree-copy-prop -@opindex ftree-copy-prop -Perform copy propagation on trees. This pass eliminates unnecessary -copy operations. This flag is enabled by default at @option{-O1} and -higher. - -@item -fipa-pure-const -@opindex fipa-pure-const -Discover which functions are pure or constant. -Enabled by default at @option{-O1} and higher. - -@item -fipa-reference -@opindex fipa-reference -Discover which static variables do not escape the -compilation unit. -Enabled by default at @option{-O1} and higher. - -@item -fipa-reference-addressable -@opindex fipa-reference-addressable -Discover read-only, write-only and non-addressable static variables. -Enabled by default at @option{-O1} and higher. - -@item -fipa-stack-alignment -@opindex fipa-stack-alignment -Reduce stack alignment on call sites if possible. -Enabled by default. - -@item -fipa-pta -@opindex fipa-pta -Perform interprocedural pointer analysis and interprocedural modification -and reference analysis. This option can cause excessive memory and -compile-time usage on large compilation units. It is not enabled by -default at any optimization level. - -@item -fipa-profile -@opindex fipa-profile -Perform interprocedural profile propagation. The functions called only from -cold functions are marked as cold. Also functions executed once (such as -@code{cold}, @code{noreturn}, static constructors or destructors) are -identified. Cold functions and loop less parts of functions executed once are -then optimized for size. -Enabled by default at @option{-O1} and higher. - -@item -fipa-modref -@opindex fipa-modref -Perform interprocedural mod/ref analysis. This optimization analyzes the side -effects of functions (memory locations that are modified or referenced) and -enables better optimization across the function call boundary. This flag is -enabled by default at @option{-O1} and higher. - -@item -fipa-cp -@opindex fipa-cp -Perform interprocedural constant propagation. -This optimization analyzes the program to determine when values passed -to functions are constants and then optimizes accordingly. -This optimization can substantially increase performance -if the application has constants passed to functions. -This flag is enabled by default at @option{-O2}, @option{-Os} and @option{-O3}. -It is also enabled by @option{-fprofile-use} and @option{-fauto-profile}. - -@item -fipa-cp-clone -@opindex fipa-cp-clone -Perform function cloning to make interprocedural constant propagation stronger. -When enabled, interprocedural constant propagation performs function cloning -when externally visible function can be called with constant arguments. -Because this optimization can create multiple copies of functions, -it may significantly increase code size -(see @option{--param ipa-cp-unit-growth=@var{value}}). -This flag is enabled by default at @option{-O3}. -It is also enabled by @option{-fprofile-use} and @option{-fauto-profile}. - -@item -fipa-bit-cp -@opindex fipa-bit-cp -When enabled, perform interprocedural bitwise constant -propagation. This flag is enabled by default at @option{-O2} and -by @option{-fprofile-use} and @option{-fauto-profile}. -It requires that @option{-fipa-cp} is enabled. - -@item -fipa-vrp -@opindex fipa-vrp -When enabled, perform interprocedural propagation of value -ranges. This flag is enabled by default at @option{-O2}. It requires -that @option{-fipa-cp} is enabled. - -@item -fipa-icf -@opindex fipa-icf -Perform Identical Code Folding for functions and read-only variables. -The optimization reduces code size and may disturb unwind stacks by replacing -a function by equivalent one with a different name. The optimization works -more effectively with link-time optimization enabled. - -Although the behavior is similar to the Gold Linker's ICF optimization, GCC ICF -works on different levels and thus the optimizations are not same - there are -equivalences that are found only by GCC and equivalences found only by Gold. - -This flag is enabled by default at @option{-O2} and @option{-Os}. - -@item -flive-patching=@var{level} -@opindex flive-patching -Control GCC's optimizations to produce output suitable for live-patching. - -If the compiler's optimization uses a function's body or information extracted -from its body to optimize/change another function, the latter is called an -impacted function of the former. If a function is patched, its impacted -functions should be patched too. - -The impacted functions are determined by the compiler's interprocedural -optimizations. For example, a caller is impacted when inlining a function -into its caller, -cloning a function and changing its caller to call this new clone, -or extracting a function's pureness/constness information to optimize -its direct or indirect callers, etc. - -Usually, the more IPA optimizations enabled, the larger the number of -impacted functions for each function. In order to control the number of -impacted functions and more easily compute the list of impacted function, -IPA optimizations can be partially enabled at two different levels. - -The @var{level} argument should be one of the following: - -@table @samp - -@item inline-clone - -Only enable inlining and cloning optimizations, which includes inlining, -cloning, interprocedural scalar replacement of aggregates and partial inlining. -As a result, when patching a function, all its callers and its clones' -callers are impacted, therefore need to be patched as well. - -@option{-flive-patching=inline-clone} disables the following optimization flags: -@gccoptlist{-fwhole-program -fipa-pta -fipa-reference -fipa-ra @gol --fipa-icf -fipa-icf-functions -fipa-icf-variables @gol --fipa-bit-cp -fipa-vrp -fipa-pure-const -fipa-reference-addressable @gol --fipa-stack-alignment -fipa-modref} - -@item inline-only-static - -Only enable inlining of static functions. -As a result, when patching a static function, all its callers are impacted -and so need to be patched as well. - -In addition to all the flags that @option{-flive-patching=inline-clone} -disables, -@option{-flive-patching=inline-only-static} disables the following additional -optimization flags: -@gccoptlist{-fipa-cp-clone -fipa-sra -fpartial-inlining -fipa-cp} - -@end table - -When @option{-flive-patching} is specified without any value, the default value -is @var{inline-clone}. - -This flag is disabled by default. - -Note that @option{-flive-patching} is not supported with link-time optimization -(@option{-flto}). - -@item -fisolate-erroneous-paths-dereference -@opindex fisolate-erroneous-paths-dereference -Detect paths that trigger erroneous or undefined behavior due to -dereferencing a null pointer. Isolate those paths from the main control -flow and turn the statement with erroneous or undefined behavior into a trap. -This flag is enabled by default at @option{-O2} and higher and depends on -@option{-fdelete-null-pointer-checks} also being enabled. - -@item -fisolate-erroneous-paths-attribute -@opindex fisolate-erroneous-paths-attribute -Detect paths that trigger erroneous or undefined behavior due to a null value -being used in a way forbidden by a @code{returns_nonnull} or @code{nonnull} -attribute. Isolate those paths from the main control flow and turn the -statement with erroneous or undefined behavior into a trap. This is not -currently enabled, but may be enabled by @option{-O2} in the future. - -@item -ftree-sink -@opindex ftree-sink -Perform forward store motion on trees. This flag is -enabled by default at @option{-O1} and higher. - -@item -ftree-bit-ccp -@opindex ftree-bit-ccp -Perform sparse conditional bit constant propagation on trees and propagate -pointer alignment information. -This pass only operates on local scalar variables and is enabled by default -at @option{-O1} and higher, except for @option{-Og}. -It requires that @option{-ftree-ccp} is enabled. - -@item -ftree-ccp -@opindex ftree-ccp -Perform sparse conditional constant propagation (CCP) on trees. This -pass only operates on local scalar variables and is enabled by default -at @option{-O1} and higher. - -@item -fssa-backprop -@opindex fssa-backprop -Propagate information about uses of a value up the definition chain -in order to simplify the definitions. For example, this pass strips -sign operations if the sign of a value never matters. The flag is -enabled by default at @option{-O1} and higher. - -@item -fssa-phiopt -@opindex fssa-phiopt -Perform pattern matching on SSA PHI nodes to optimize conditional -code. This pass is enabled by default at @option{-O1} and higher, -except for @option{-Og}. - -@item -ftree-switch-conversion -@opindex ftree-switch-conversion -Perform conversion of simple initializations in a switch to -initializations from a scalar array. This flag is enabled by default -at @option{-O2} and higher. - -@item -ftree-tail-merge -@opindex ftree-tail-merge -Look for identical code sequences. When found, replace one with a jump to the -other. This optimization is known as tail merging or cross jumping. This flag -is enabled by default at @option{-O2} and higher. The compilation time -in this pass can -be limited using @option{max-tail-merge-comparisons} parameter and -@option{max-tail-merge-iterations} parameter. - -@item -ftree-dce -@opindex ftree-dce -Perform dead code elimination (DCE) on trees. This flag is enabled by -default at @option{-O1} and higher. - -@item -ftree-builtin-call-dce -@opindex ftree-builtin-call-dce -Perform conditional dead code elimination (DCE) for calls to built-in functions -that may set @code{errno} but are otherwise free of side effects. This flag is -enabled by default at @option{-O2} and higher if @option{-Os} is not also -specified. - -@item -ffinite-loops -@opindex ffinite-loops -@opindex fno-finite-loops -Assume that a loop with an exit will eventually take the exit and not loop -indefinitely. This allows the compiler to remove loops that otherwise have -no side-effects, not considering eventual endless looping as such. - -This option is enabled by default at @option{-O2} for C++ with -std=c++11 -or higher. - -@item -ftree-dominator-opts -@opindex ftree-dominator-opts -Perform a variety of simple scalar cleanups (constant/copy -propagation, redundancy elimination, range propagation and expression -simplification) based on a dominator tree traversal. This also -performs jump threading (to reduce jumps to jumps). This flag is -enabled by default at @option{-O1} and higher. - -@item -ftree-dse -@opindex ftree-dse -Perform dead store elimination (DSE) on trees. A dead store is a store into -a memory location that is later overwritten by another store without -any intervening loads. In this case the earlier store can be deleted. This -flag is enabled by default at @option{-O1} and higher. - -@item -ftree-ch -@opindex ftree-ch -Perform loop header copying on trees. This is beneficial since it increases -effectiveness of code motion optimizations. It also saves one jump. This flag -is enabled by default at @option{-O1} and higher. It is not enabled -for @option{-Os}, since it usually increases code size. - -@item -ftree-loop-optimize -@opindex ftree-loop-optimize -Perform loop optimizations on trees. This flag is enabled by default -at @option{-O1} and higher. - -@item -ftree-loop-linear -@itemx -floop-strip-mine -@itemx -floop-block -@opindex ftree-loop-linear -@opindex floop-strip-mine -@opindex floop-block -Perform loop nest optimizations. Same as -@option{-floop-nest-optimize}. To use this code transformation, GCC has -to be configured with @option{--with-isl} to enable the Graphite loop -transformation infrastructure. - -@item -fgraphite-identity -@opindex fgraphite-identity -Enable the identity transformation for graphite. For every SCoP we generate -the polyhedral representation and transform it back to gimple. Using -@option{-fgraphite-identity} we can check the costs or benefits of the -GIMPLE -> GRAPHITE -> GIMPLE transformation. Some minimal optimizations -are also performed by the code generator isl, like index splitting and -dead code elimination in loops. - -@item -floop-nest-optimize -@opindex floop-nest-optimize -Enable the isl based loop nest optimizer. This is a generic loop nest -optimizer based on the Pluto optimization algorithms. It calculates a loop -structure optimized for data-locality and parallelism. This option -is experimental. - -@item -floop-parallelize-all -@opindex floop-parallelize-all -Use the Graphite data dependence analysis to identify loops that can -be parallelized. Parallelize all the loops that can be analyzed to -not contain loop carried dependences without checking that it is -profitable to parallelize the loops. - -@item -ftree-coalesce-vars -@opindex ftree-coalesce-vars -While transforming the program out of the SSA representation, attempt to -reduce copying by coalescing versions of different user-defined -variables, instead of just compiler temporaries. This may severely -limit the ability to debug an optimized program compiled with -@option{-fno-var-tracking-assignments}. In the negated form, this flag -prevents SSA coalescing of user variables. This option is enabled by -default if optimization is enabled, and it does very little otherwise. - -@item -ftree-loop-if-convert -@opindex ftree-loop-if-convert -Attempt to transform conditional jumps in the innermost loops to -branch-less equivalents. The intent is to remove control-flow from -the innermost loops in order to improve the ability of the -vectorization pass to handle these loops. This is enabled by default -if vectorization is enabled. - -@item -ftree-loop-distribution -@opindex ftree-loop-distribution -Perform loop distribution. This flag can improve cache performance on -big loop bodies and allow further loop optimizations, like -parallelization or vectorization, to take place. For example, the loop -@smallexample -DO I = 1, N - A(I) = B(I) + C - D(I) = E(I) * F -ENDDO -@end smallexample -is transformed to -@smallexample -DO I = 1, N - A(I) = B(I) + C -ENDDO -DO I = 1, N - D(I) = E(I) * F -ENDDO -@end smallexample -This flag is enabled by default at @option{-O3}. -It is also enabled by @option{-fprofile-use} and @option{-fauto-profile}. - -@item -ftree-loop-distribute-patterns -@opindex ftree-loop-distribute-patterns -Perform loop distribution of patterns that can be code generated with -calls to a library. This flag is enabled by default at @option{-O2} and -higher, and by @option{-fprofile-use} and @option{-fauto-profile}. - -This pass distributes the initialization loops and generates a call to -memset zero. For example, the loop -@smallexample -DO I = 1, N - A(I) = 0 - B(I) = A(I) + I -ENDDO -@end smallexample -is transformed to -@smallexample -DO I = 1, N - A(I) = 0 -ENDDO -DO I = 1, N - B(I) = A(I) + I -ENDDO -@end smallexample -and the initialization loop is transformed into a call to memset zero. -This flag is enabled by default at @option{-O3}. -It is also enabled by @option{-fprofile-use} and @option{-fauto-profile}. - -@item -floop-interchange -@opindex floop-interchange -Perform loop interchange outside of graphite. This flag can improve cache -performance on loop nest and allow further loop optimizations, like -vectorization, to take place. For example, the loop -@smallexample -for (int i = 0; i < N; i++) - for (int j = 0; j < N; j++) - for (int k = 0; k < N; k++) - c[i][j] = c[i][j] + a[i][k]*b[k][j]; -@end smallexample -is transformed to -@smallexample -for (int i = 0; i < N; i++) - for (int k = 0; k < N; k++) - for (int j = 0; j < N; j++) - c[i][j] = c[i][j] + a[i][k]*b[k][j]; -@end smallexample -This flag is enabled by default at @option{-O3}. -It is also enabled by @option{-fprofile-use} and @option{-fauto-profile}. - -@item -floop-unroll-and-jam -@opindex floop-unroll-and-jam -Apply unroll and jam transformations on feasible loops. In a loop -nest this unrolls the outer loop by some factor and fuses the resulting -multiple inner loops. This flag is enabled by default at @option{-O3}. -It is also enabled by @option{-fprofile-use} and @option{-fauto-profile}. - -@item -ftree-loop-im -@opindex ftree-loop-im -Perform loop invariant motion on trees. This pass moves only invariants that -are hard to handle at RTL level (function calls, operations that expand to -nontrivial sequences of insns). With @option{-funswitch-loops} it also moves -operands of conditions that are invariant out of the loop, so that we can use -just trivial invariantness analysis in loop unswitching. The pass also includes -store motion. - -@item -ftree-loop-ivcanon -@opindex ftree-loop-ivcanon -Create a canonical counter for number of iterations in loops for which -determining number of iterations requires complicated analysis. Later -optimizations then may determine the number easily. Useful especially -in connection with unrolling. - -@item -ftree-scev-cprop -@opindex ftree-scev-cprop -Perform final value replacement. If a variable is modified in a loop -in such a way that its value when exiting the loop can be determined using -only its initial value and the number of loop iterations, replace uses of -the final value by such a computation, provided it is sufficiently cheap. -This reduces data dependencies and may allow further simplifications. -Enabled by default at @option{-O1} and higher. - -@item -fivopts -@opindex fivopts -Perform induction variable optimizations (strength reduction, induction -variable merging and induction variable elimination) on trees. - -@item -ftree-parallelize-loops=n -@opindex ftree-parallelize-loops -Parallelize loops, i.e., split their iteration space to run in n threads. -This is only possible for loops whose iterations are independent -and can be arbitrarily reordered. The optimization is only -profitable on multiprocessor machines, for loops that are CPU-intensive, -rather than constrained e.g.@: by memory bandwidth. This option -implies @option{-pthread}, and thus is only supported on targets -that have support for @option{-pthread}. - -@item -ftree-pta -@opindex ftree-pta -Perform function-local points-to analysis on trees. This flag is -enabled by default at @option{-O1} and higher, except for @option{-Og}. - -@item -ftree-sra -@opindex ftree-sra -Perform scalar replacement of aggregates. This pass replaces structure -references with scalars to prevent committing structures to memory too -early. This flag is enabled by default at @option{-O1} and higher, -except for @option{-Og}. - -@item -fstore-merging -@opindex fstore-merging -Perform merging of narrow stores to consecutive memory addresses. This pass -merges contiguous stores of immediate values narrower than a word into fewer -wider stores to reduce the number of instructions. This is enabled by default -at @option{-O2} and higher as well as @option{-Os}. - -@item -ftree-ter -@opindex ftree-ter -Perform temporary expression replacement during the SSA->normal phase. Single -use/single def temporaries are replaced at their use location with their -defining expression. This results in non-GIMPLE code, but gives the expanders -much more complex trees to work on resulting in better RTL generation. This is -enabled by default at @option{-O1} and higher. - -@item -ftree-slsr -@opindex ftree-slsr -Perform straight-line strength reduction on trees. This recognizes related -expressions involving multiplications and replaces them by less expensive -calculations when possible. This is enabled by default at @option{-O1} and -higher. - -@item -ftree-vectorize -@opindex ftree-vectorize -Perform vectorization on trees. This flag enables @option{-ftree-loop-vectorize} -and @option{-ftree-slp-vectorize} if not explicitly specified. - -@item -ftree-loop-vectorize -@opindex ftree-loop-vectorize -Perform loop vectorization on trees. This flag is enabled by default at -@option{-O2} and by @option{-ftree-vectorize}, @option{-fprofile-use}, -and @option{-fauto-profile}. - -@item -ftree-slp-vectorize -@opindex ftree-slp-vectorize -Perform basic block vectorization on trees. This flag is enabled by default at -@option{-O2} and by @option{-ftree-vectorize}, @option{-fprofile-use}, -and @option{-fauto-profile}. - -@item -ftrivial-auto-var-init=@var{choice} -@opindex ftrivial-auto-var-init -Initialize automatic variables with either a pattern or with zeroes to increase -the security and predictability of a program by preventing uninitialized memory -disclosure and use. -GCC still considers an automatic variable that doesn't have an explicit -initializer as uninitialized, @option{-Wuninitialized} and -@option{-Wanalyzer-use-of-uninitialized-value} will still report -warning messages on such automatic variables. -With this option, GCC will also initialize any padding of automatic variables -that have structure or union types to zeroes. -However, the current implementation cannot initialize automatic variables that -are declared between the controlling expression and the first case of a -@code{switch} statement. Using @option{-Wtrivial-auto-var-init} to report all -such cases. - -The three values of @var{choice} are: - -@itemize @bullet -@item -@samp{uninitialized} doesn't initialize any automatic variables. -This is C and C++'s default. - -@item -@samp{pattern} Initialize automatic variables with values which will likely -transform logic bugs into crashes down the line, are easily recognized in a -crash dump and without being values that programmers can rely on for useful -program semantics. -The current value is byte-repeatable pattern with byte "0xFE". -The values used for pattern initialization might be changed in the future. - -@item -@samp{zero} Initialize automatic variables with zeroes. -@end itemize - -The default is @samp{uninitialized}. - -You can control this behavior for a specific variable by using the variable -attribute @code{uninitialized} (@pxref{Variable Attributes}). - -@item -fvect-cost-model=@var{model} -@opindex fvect-cost-model -Alter the cost model used for vectorization. The @var{model} argument -should be one of @samp{unlimited}, @samp{dynamic}, @samp{cheap} or -@samp{very-cheap}. -With the @samp{unlimited} model the vectorized code-path is assumed -to be profitable while with the @samp{dynamic} model a runtime check -guards the vectorized code-path to enable it only for iteration -counts that will likely execute faster than when executing the original -scalar loop. The @samp{cheap} model disables vectorization of -loops where doing so would be cost prohibitive for example due to -required runtime checks for data dependence or alignment but otherwise -is equal to the @samp{dynamic} model. The @samp{very-cheap} model only -allows vectorization if the vector code would entirely replace the -scalar code that is being vectorized. For example, if each iteration -of a vectorized loop would only be able to handle exactly four iterations -of the scalar loop, the @samp{very-cheap} model would only allow -vectorization if the scalar iteration count is known to be a multiple -of four. - -The default cost model depends on other optimization flags and is -either @samp{dynamic} or @samp{cheap}. - -@item -fsimd-cost-model=@var{model} -@opindex fsimd-cost-model -Alter the cost model used for vectorization of loops marked with the OpenMP -simd directive. The @var{model} argument should be one of -@samp{unlimited}, @samp{dynamic}, @samp{cheap}. All values of @var{model} -have the same meaning as described in @option{-fvect-cost-model} and by -default a cost model defined with @option{-fvect-cost-model} is used. - -@item -ftree-vrp -@opindex ftree-vrp -Perform Value Range Propagation on trees. This is similar to the -constant propagation pass, but instead of values, ranges of values are -propagated. This allows the optimizers to remove unnecessary range -checks like array bound checks and null pointer checks. This is -enabled by default at @option{-O2} and higher. Null pointer check -elimination is only done if @option{-fdelete-null-pointer-checks} is -enabled. - -@item -fsplit-paths -@opindex fsplit-paths -Split paths leading to loop backedges. This can improve dead code -elimination and common subexpression elimination. This is enabled by -default at @option{-O3} and above. - -@item -fsplit-ivs-in-unroller -@opindex fsplit-ivs-in-unroller -Enables expression of values of induction variables in later iterations -of the unrolled loop using the value in the first iteration. This breaks -long dependency chains, thus improving efficiency of the scheduling passes. - -A combination of @option{-fweb} and CSE is often sufficient to obtain the -same effect. However, that is not reliable in cases where the loop body -is more complicated than a single basic block. It also does not work at all -on some architectures due to restrictions in the CSE pass. - -This optimization is enabled by default. - -@item -fvariable-expansion-in-unroller -@opindex fvariable-expansion-in-unroller -With this option, the compiler creates multiple copies of some -local variables when unrolling a loop, which can result in superior code. - -This optimization is enabled by default for PowerPC targets, but disabled -by default otherwise. - -@item -fpartial-inlining -@opindex fpartial-inlining -Inline parts of functions. This option has any effect only -when inlining itself is turned on by the @option{-finline-functions} -or @option{-finline-small-functions} options. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fpredictive-commoning -@opindex fpredictive-commoning -Perform predictive commoning optimization, i.e., reusing computations -(especially memory loads and stores) performed in previous -iterations of loops. - -This option is enabled at level @option{-O3}. -It is also enabled by @option{-fprofile-use} and @option{-fauto-profile}. - -@item -fprefetch-loop-arrays -@opindex fprefetch-loop-arrays -If supported by the target machine, generate instructions to prefetch -memory to improve the performance of loops that access large arrays. - -This option may generate better or worse code; results are highly -dependent on the structure of loops within the source code. - -Disabled at level @option{-Os}. - -@item -fno-printf-return-value -@opindex fno-printf-return-value -@opindex fprintf-return-value -Do not substitute constants for known return value of formatted output -functions such as @code{sprintf}, @code{snprintf}, @code{vsprintf}, and -@code{vsnprintf} (but not @code{printf} of @code{fprintf}). This -transformation allows GCC to optimize or even eliminate branches based -on the known return value of these functions called with arguments that -are either constant, or whose values are known to be in a range that -makes determining the exact return value possible. For example, when -@option{-fprintf-return-value} is in effect, both the branch and the -body of the @code{if} statement (but not the call to @code{snprint}) -can be optimized away when @code{i} is a 32-bit or smaller integer -because the return value is guaranteed to be at most 8. - -@smallexample -char buf[9]; -if (snprintf (buf, "%08x", i) >= sizeof buf) - @dots{} -@end smallexample - -The @option{-fprintf-return-value} option relies on other optimizations -and yields best results with @option{-O2} and above. It works in tandem -with the @option{-Wformat-overflow} and @option{-Wformat-truncation} -options. The @option{-fprintf-return-value} option is enabled by default. - -@item -fno-peephole -@itemx -fno-peephole2 -@opindex fno-peephole -@opindex fpeephole -@opindex fno-peephole2 -@opindex fpeephole2 -Disable any machine-specific peephole optimizations. The difference -between @option{-fno-peephole} and @option{-fno-peephole2} is in how they -are implemented in the compiler; some targets use one, some use the -other, a few use both. - -@option{-fpeephole} is enabled by default. -@option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fno-guess-branch-probability -@opindex fno-guess-branch-probability -@opindex fguess-branch-probability -Do not guess branch probabilities using heuristics. - -GCC uses heuristics to guess branch probabilities if they are -not provided by profiling feedback (@option{-fprofile-arcs}). These -heuristics are based on the control flow graph. If some branch probabilities -are specified by @code{__builtin_expect}, then the heuristics are -used to guess branch probabilities for the rest of the control flow graph, -taking the @code{__builtin_expect} info into account. The interactions -between the heuristics and @code{__builtin_expect} can be complex, and in -some cases, it may be useful to disable the heuristics so that the effects -of @code{__builtin_expect} are easier to understand. - -It is also possible to specify expected probability of the expression -with @code{__builtin_expect_with_probability} built-in function. - -The default is @option{-fguess-branch-probability} at levels -@option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. - -@item -freorder-blocks -@opindex freorder-blocks -Reorder basic blocks in the compiled function in order to reduce number of -taken branches and improve code locality. - -Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, @option{-Os}. - -@item -freorder-blocks-algorithm=@var{algorithm} -@opindex freorder-blocks-algorithm -Use the specified algorithm for basic block reordering. The -@var{algorithm} argument can be @samp{simple}, which does not increase -code size (except sometimes due to secondary effects like alignment), -or @samp{stc}, the ``software trace cache'' algorithm, which tries to -put all often executed code together, minimizing the number of branches -executed by making extra copies of code. - -The default is @samp{simple} at levels @option{-O1}, @option{-Os}, and -@samp{stc} at levels @option{-O2}, @option{-O3}. - -@item -freorder-blocks-and-partition -@opindex freorder-blocks-and-partition -In addition to reordering basic blocks in the compiled function, in order -to reduce number of taken branches, partitions hot and cold basic blocks -into separate sections of the assembly and @file{.o} files, to improve -paging and cache locality performance. - -This optimization is automatically turned off in the presence of -exception handling or unwind tables (on targets using setjump/longjump or target specific scheme), for linkonce sections, for functions with a user-defined -section attribute and on any architecture that does not support named -sections. When @option{-fsplit-stack} is used this option is not -enabled by default (to avoid linker errors), but may be enabled -explicitly (if using a working linker). - -Enabled for x86 at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -freorder-functions -@opindex freorder-functions -Reorder functions in the object file in order to -improve code locality. This is implemented by using special -subsections @code{.text.hot} for most frequently executed functions and -@code{.text.unlikely} for unlikely executed functions. Reordering is done by -the linker so object file format must support named sections and linker must -place them in a reasonable way. - -This option isn't effective unless you either provide profile feedback -(see @option{-fprofile-arcs} for details) or manually annotate functions with -@code{hot} or @code{cold} attributes (@pxref{Common Function Attributes}). - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fstrict-aliasing -@opindex fstrict-aliasing -Allow the compiler to assume the strictest aliasing rules applicable to -the language being compiled. For C (and C++), this activates -optimizations based on the type of expressions. In particular, an -object of one type is assumed never to reside at the same address as an -object of a different type, unless the types are almost the same. For -example, an @code{unsigned int} can alias an @code{int}, but not a -@code{void*} or a @code{double}. A character type may alias any other -type. - -@anchor{Type-punning}Pay special attention to code like this: -@smallexample -union a_union @{ - int i; - double d; -@}; - -int f() @{ - union a_union t; - t.d = 3.0; - return t.i; -@} -@end smallexample -The practice of reading from a different union member than the one most -recently written to (called ``type-punning'') is common. Even with -@option{-fstrict-aliasing}, type-punning is allowed, provided the memory -is accessed through the union type. So, the code above works as -expected. @xref{Structures unions enumerations and bit-fields -implementation}. However, this code might not: -@smallexample -int f() @{ - union a_union t; - int* ip; - t.d = 3.0; - ip = &t.i; - return *ip; -@} -@end smallexample - -Similarly, access by taking the address, casting the resulting pointer -and dereferencing the result has undefined behavior, even if the cast -uses a union type, e.g.: -@smallexample -int f() @{ - double d = 3.0; - return ((union a_union *) &d)->i; -@} -@end smallexample - -The @option{-fstrict-aliasing} option is enabled at levels -@option{-O2}, @option{-O3}, @option{-Os}. - -@item -fipa-strict-aliasing -@opindex fipa-strict-aliasing -Controls whether rules of @option{-fstrict-aliasing} are applied across -function boundaries. Note that if multiple functions gets inlined into a -single function the memory accesses are no longer considered to be crossing a -function boundary. - -The @option{-fipa-strict-aliasing} option is enabled by default and is -effective only in combination with @option{-fstrict-aliasing}. - -@item -falign-functions -@itemx -falign-functions=@var{n} -@itemx -falign-functions=@var{n}:@var{m} -@itemx -falign-functions=@var{n}:@var{m}:@var{n2} -@itemx -falign-functions=@var{n}:@var{m}:@var{n2}:@var{m2} -@opindex falign-functions -Align the start of functions to the next power-of-two greater than or -equal to @var{n}, skipping up to @var{m}-1 bytes. This ensures that at -least the first @var{m} bytes of the function can be fetched by the CPU -without crossing an @var{n}-byte alignment boundary. - -If @var{m} is not specified, it defaults to @var{n}. - -Examples: @option{-falign-functions=32} aligns functions to the next -32-byte boundary, @option{-falign-functions=24} aligns to the next -32-byte boundary only if this can be done by skipping 23 bytes or less, -@option{-falign-functions=32:7} aligns to the next -32-byte boundary only if this can be done by skipping 6 bytes or less. - -The second pair of @var{n2}:@var{m2} values allows you to specify -a secondary alignment: @option{-falign-functions=64:7:32:3} aligns to -the next 64-byte boundary if this can be done by skipping 6 bytes or less, -otherwise aligns to the next 32-byte boundary if this can be done -by skipping 2 bytes or less. -If @var{m2} is not specified, it defaults to @var{n2}. - -Some assemblers only support this flag when @var{n} is a power of two; -in that case, it is rounded up. - -@option{-fno-align-functions} and @option{-falign-functions=1} are -equivalent and mean that functions are not aligned. - -If @var{n} is not specified or is zero, use a machine-dependent default. -The maximum allowed @var{n} option value is 65536. - -Enabled at levels @option{-O2}, @option{-O3}. - -@item -flimit-function-alignment -If this option is enabled, the compiler tries to avoid unnecessarily -overaligning functions. It attempts to instruct the assembler to align -by the amount specified by @option{-falign-functions}, but not to -skip more bytes than the size of the function. - -@item -falign-labels -@itemx -falign-labels=@var{n} -@itemx -falign-labels=@var{n}:@var{m} -@itemx -falign-labels=@var{n}:@var{m}:@var{n2} -@itemx -falign-labels=@var{n}:@var{m}:@var{n2}:@var{m2} -@opindex falign-labels -Align all branch targets to a power-of-two boundary. - -Parameters of this option are analogous to the @option{-falign-functions} option. -@option{-fno-align-labels} and @option{-falign-labels=1} are -equivalent and mean that labels are not aligned. - -If @option{-falign-loops} or @option{-falign-jumps} are applicable and -are greater than this value, then their values are used instead. - -If @var{n} is not specified or is zero, use a machine-dependent default -which is very likely to be @samp{1}, meaning no alignment. -The maximum allowed @var{n} option value is 65536. - -Enabled at levels @option{-O2}, @option{-O3}. - -@item -falign-loops -@itemx -falign-loops=@var{n} -@itemx -falign-loops=@var{n}:@var{m} -@itemx -falign-loops=@var{n}:@var{m}:@var{n2} -@itemx -falign-loops=@var{n}:@var{m}:@var{n2}:@var{m2} -@opindex falign-loops -Align loops to a power-of-two boundary. If the loops are executed -many times, this makes up for any execution of the dummy padding -instructions. - -If @option{-falign-labels} is greater than this value, then its value -is used instead. - -Parameters of this option are analogous to the @option{-falign-functions} option. -@option{-fno-align-loops} and @option{-falign-loops=1} are -equivalent and mean that loops are not aligned. -The maximum allowed @var{n} option value is 65536. - -If @var{n} is not specified or is zero, use a machine-dependent default. - -Enabled at levels @option{-O2}, @option{-O3}. - -@item -falign-jumps -@itemx -falign-jumps=@var{n} -@itemx -falign-jumps=@var{n}:@var{m} -@itemx -falign-jumps=@var{n}:@var{m}:@var{n2} -@itemx -falign-jumps=@var{n}:@var{m}:@var{n2}:@var{m2} -@opindex falign-jumps -Align branch targets to a power-of-two boundary, for branch targets -where the targets can only be reached by jumping. In this case, -no dummy operations need be executed. - -If @option{-falign-labels} is greater than this value, then its value -is used instead. - -Parameters of this option are analogous to the @option{-falign-functions} option. -@option{-fno-align-jumps} and @option{-falign-jumps=1} are -equivalent and mean that loops are not aligned. - -If @var{n} is not specified or is zero, use a machine-dependent default. -The maximum allowed @var{n} option value is 65536. - -Enabled at levels @option{-O2}, @option{-O3}. - -@item -fno-allocation-dce -@opindex fno-allocation-dce -Do not remove unused C++ allocations in dead code elimination. - -@item -fallow-store-data-races -@opindex fallow-store-data-races -Allow the compiler to perform optimizations that may introduce new data races -on stores, without proving that the variable cannot be concurrently accessed -by other threads. Does not affect optimization of local data. It is safe to -use this option if it is known that global data will not be accessed by -multiple threads. - -Examples of optimizations enabled by @option{-fallow-store-data-races} include -hoisting or if-conversions that may cause a value that was already in memory -to be re-written with that same value. Such re-writing is safe in a single -threaded context but may be unsafe in a multi-threaded context. Note that on -some processors, if-conversions may be required in order to enable -vectorization. - -Enabled at level @option{-Ofast}. - -@item -funit-at-a-time -@opindex funit-at-a-time -This option is left for compatibility reasons. @option{-funit-at-a-time} -has no effect, while @option{-fno-unit-at-a-time} implies -@option{-fno-toplevel-reorder} and @option{-fno-section-anchors}. - -Enabled by default. - -@item -fno-toplevel-reorder -@opindex fno-toplevel-reorder -@opindex ftoplevel-reorder -Do not reorder top-level functions, variables, and @code{asm} -statements. Output them in the same order that they appear in the -input file. When this option is used, unreferenced static variables -are not removed. This option is intended to support existing code -that relies on a particular ordering. For new code, it is better to -use attributes when possible. - -@option{-ftoplevel-reorder} is the default at @option{-O1} and higher, and -also at @option{-O0} if @option{-fsection-anchors} is explicitly requested. -Additionally @option{-fno-toplevel-reorder} implies -@option{-fno-section-anchors}. - -@item -funreachable-traps -@opindex funreachable-traps -With this option, the compiler turns calls to -@code{__builtin_unreachable} into traps, instead of using them for -optimization. This also affects any such calls implicitly generated -by the compiler. - -This option has the same effect as @option{-fsanitize=unreachable --fsanitize-trap=unreachable}, but does not affect the values of those -options. If @option{-fsanitize=unreachable} is enabled, that option -takes priority over this one. - -This option is enabled by default at @option{-O0} and @option{-Og}. - -@item -fweb -@opindex fweb -Constructs webs as commonly used for register allocation purposes and assign -each web individual pseudo register. This allows the register allocation pass -to operate on pseudos directly, but also strengthens several other optimization -passes, such as CSE, loop optimizer and trivial dead code remover. It can, -however, make debugging impossible, since variables no longer stay in a -``home register''. - -Enabled by default with @option{-funroll-loops}. - -@item -fwhole-program -@opindex fwhole-program -Assume that the current compilation unit represents the whole program being -compiled. All public functions and variables with the exception of @code{main} -and those merged by attribute @code{externally_visible} become static functions -and in effect are optimized more aggressively by interprocedural optimizers. - -This option should not be used in combination with @option{-flto}. -Instead relying on a linker plugin should provide safer and more precise -information. - -@item -flto[=@var{n}] -@opindex flto -This option runs the standard link-time optimizer. When invoked -with source code, it generates GIMPLE (one of GCC's internal -representations) and writes it to special ELF sections in the object -file. When the object files are linked together, all the function -bodies are read from these ELF sections and instantiated as if they -had been part of the same translation unit. - -To use the link-time optimizer, @option{-flto} and optimization -options should be specified at compile time and during the final link. -It is recommended that you compile all the files participating in the -same link with the same options and also specify those options at -link time. -For example: - -@smallexample -gcc -c -O2 -flto foo.c -gcc -c -O2 -flto bar.c -gcc -o myprog -flto -O2 foo.o bar.o -@end smallexample - -The first two invocations to GCC save a bytecode representation -of GIMPLE into special ELF sections inside @file{foo.o} and -@file{bar.o}. The final invocation reads the GIMPLE bytecode from -@file{foo.o} and @file{bar.o}, merges the two files into a single -internal image, and compiles the result as usual. Since both -@file{foo.o} and @file{bar.o} are merged into a single image, this -causes all the interprocedural analyses and optimizations in GCC to -work across the two files as if they were a single one. This means, -for example, that the inliner is able to inline functions in -@file{bar.o} into functions in @file{foo.o} and vice-versa. - -Another (simpler) way to enable link-time optimization is: - -@smallexample -gcc -o myprog -flto -O2 foo.c bar.c -@end smallexample - -The above generates bytecode for @file{foo.c} and @file{bar.c}, -merges them together into a single GIMPLE representation and optimizes -them as usual to produce @file{myprog}. - -The important thing to keep in mind is that to enable link-time -optimizations you need to use the GCC driver to perform the link step. -GCC automatically performs link-time optimization if any of the -objects involved were compiled with the @option{-flto} command-line option. -You can always override -the automatic decision to do link-time optimization -by passing @option{-fno-lto} to the link command. - -To make whole program optimization effective, it is necessary to make -certain whole program assumptions. The compiler needs to know -what functions and variables can be accessed by libraries and runtime -outside of the link-time optimized unit. When supported by the linker, -the linker plugin (see @option{-fuse-linker-plugin}) passes information -to the compiler about used and externally visible symbols. When -the linker plugin is not available, @option{-fwhole-program} should be -used to allow the compiler to make these assumptions, which leads -to more aggressive optimization decisions. - -When a file is compiled with @option{-flto} without -@option{-fuse-linker-plugin}, the generated object file is larger than -a regular object file because it contains GIMPLE bytecodes and the usual -final code (see @option{-ffat-lto-objects}). This means that -object files with LTO information can be linked as normal object -files; if @option{-fno-lto} is passed to the linker, no -interprocedural optimizations are applied. Note that when -@option{-fno-fat-lto-objects} is enabled the compile stage is faster -but you cannot perform a regular, non-LTO link on them. - -When producing the final binary, GCC only -applies link-time optimizations to those files that contain bytecode. -Therefore, you can mix and match object files and libraries with -GIMPLE bytecodes and final object code. GCC automatically selects -which files to optimize in LTO mode and which files to link without -further processing. - -Generally, options specified at link time override those -specified at compile time, although in some cases GCC attempts to infer -link-time options from the settings used to compile the input files. - -If you do not specify an optimization level option @option{-O} at -link time, then GCC uses the highest optimization level -used when compiling the object files. Note that it is generally -ineffective to specify an optimization level option only at link time and -not at compile time, for two reasons. First, compiling without -optimization suppresses compiler passes that gather information -needed for effective optimization at link time. Second, some early -optimization passes can be performed only at compile time and -not at link time. - -There are some code generation flags preserved by GCC when -generating bytecodes, as they need to be used during the final link. -Currently, the following options and their settings are taken from -the first object file that explicitly specifies them: -@option{-fcommon}, @option{-fexceptions}, @option{-fnon-call-exceptions}, -@option{-fgnu-tm} and all the @option{-m} target flags. - -The following options @option{-fPIC}, @option{-fpic}, @option{-fpie} and -@option{-fPIE} are combined based on the following scheme: - -@smallexample -@option{-fPIC} + @option{-fpic} = @option{-fpic} -@option{-fPIC} + @option{-fno-pic} = @option{-fno-pic} -@option{-fpic/-fPIC} + (no option) = (no option) -@option{-fPIC} + @option{-fPIE} = @option{-fPIE} -@option{-fpic} + @option{-fPIE} = @option{-fpie} -@option{-fPIC/-fpic} + @option{-fpie} = @option{-fpie} -@end smallexample - -Certain ABI-changing flags are required to match in all compilation units, -and trying to override this at link time with a conflicting value -is ignored. This includes options such as @option{-freg-struct-return} -and @option{-fpcc-struct-return}. - -Other options such as @option{-ffp-contract}, @option{-fno-strict-overflow}, -@option{-fwrapv}, @option{-fno-trapv} or @option{-fno-strict-aliasing} -are passed through to the link stage and merged conservatively for -conflicting translation units. Specifically -@option{-fno-strict-overflow}, @option{-fwrapv} and @option{-fno-trapv} take -precedence; and for example @option{-ffp-contract=off} takes precedence -over @option{-ffp-contract=fast}. You can override them at link time. - -Diagnostic options such as @option{-Wstringop-overflow} are passed -through to the link stage and their setting matches that of the -compile-step at function granularity. Note that this matters only -for diagnostics emitted during optimization. Note that code -transforms such as inlining can lead to warnings being enabled -or disabled for regions if code not consistent with the setting -at compile time. - -When you need to pass options to the assembler via @option{-Wa} or -@option{-Xassembler} make sure to either compile such translation -units with @option{-fno-lto} or consistently use the same assembler -options on all translation units. You can alternatively also -specify assembler options at LTO link time. - -To enable debug info generation you need to supply @option{-g} at -compile time. If any of the input files at link time were built -with debug info generation enabled the link will enable debug info -generation as well. Any elaborate debug info settings -like the dwarf level @option{-gdwarf-5} need to be explicitly repeated -at the linker command line and mixing different settings in different -translation units is discouraged. - -If LTO encounters objects with C linkage declared with incompatible -types in separate translation units to be linked together (undefined -behavior according to ISO C99 6.2.7), a non-fatal diagnostic may be -issued. The behavior is still undefined at run time. Similar -diagnostics may be raised for other languages. - -Another feature of LTO is that it is possible to apply interprocedural -optimizations on files written in different languages: - -@smallexample -gcc -c -flto foo.c -g++ -c -flto bar.cc -gfortran -c -flto baz.f90 -g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran -@end smallexample - -Notice that the final link is done with @command{g++} to get the C++ -runtime libraries and @option{-lgfortran} is added to get the Fortran -runtime libraries. In general, when mixing languages in LTO mode, you -should use the same link command options as when mixing languages in a -regular (non-LTO) compilation. - -If object files containing GIMPLE bytecode are stored in a library archive, say -@file{libfoo.a}, it is possible to extract and use them in an LTO link if you -are using a linker with plugin support. To create static libraries suitable -for LTO, use @command{gcc-ar} and @command{gcc-ranlib} instead of @command{ar} -and @command{ranlib}; -to show the symbols of object files with GIMPLE bytecode, use -@command{gcc-nm}. Those commands require that @command{ar}, @command{ranlib} -and @command{nm} have been compiled with plugin support. At link time, use the -flag @option{-fuse-linker-plugin} to ensure that the library participates in -the LTO optimization process: - -@smallexample -gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo -@end smallexample - -With the linker plugin enabled, the linker extracts the needed -GIMPLE files from @file{libfoo.a} and passes them on to the running GCC -to make them part of the aggregated GIMPLE image to be optimized. - -If you are not using a linker with plugin support and/or do not -enable the linker plugin, then the objects inside @file{libfoo.a} -are extracted and linked as usual, but they do not participate -in the LTO optimization process. In order to make a static library suitable -for both LTO optimization and usual linkage, compile its object files with -@option{-flto} @option{-ffat-lto-objects}. - -Link-time optimizations do not require the presence of the whole program to -operate. If the program does not require any symbols to be exported, it is -possible to combine @option{-flto} and @option{-fwhole-program} to allow -the interprocedural optimizers to use more aggressive assumptions which may -lead to improved optimization opportunities. -Use of @option{-fwhole-program} is not needed when linker plugin is -active (see @option{-fuse-linker-plugin}). - -The current implementation of LTO makes no -attempt to generate bytecode that is portable between different -types of hosts. The bytecode files are versioned and there is a -strict version check, so bytecode files generated in one version of -GCC do not work with an older or newer version of GCC. - -Link-time optimization does not work well with generation of debugging -information on systems other than those using a combination of ELF and -DWARF. - -If you specify the optional @var{n}, the optimization and code -generation done at link time is executed in parallel using @var{n} -parallel jobs by utilizing an installed @command{make} program. The -environment variable @env{MAKE} may be used to override the program -used. - -You can also specify @option{-flto=jobserver} to use GNU make's -job server mode to determine the number of parallel jobs. This -is useful when the Makefile calling GCC is already executing in parallel. -You must prepend a @samp{+} to the command recipe in the parent Makefile -for this to work. This option likely only works if @env{MAKE} is -GNU make. Even without the option value, GCC tries to automatically -detect a running GNU make's job server. - -Use @option{-flto=auto} to use GNU make's job server, if available, -or otherwise fall back to autodetection of the number of CPU threads -present in your system. - -@item -flto-partition=@var{alg} -@opindex flto-partition -Specify the partitioning algorithm used by the link-time optimizer. -The value is either @samp{1to1} to specify a partitioning mirroring -the original source files or @samp{balanced} to specify partitioning -into equally sized chunks (whenever possible) or @samp{max} to create -new partition for every symbol where possible. Specifying @samp{none} -as an algorithm disables partitioning and streaming completely. -The default value is @samp{balanced}. While @samp{1to1} can be used -as an workaround for various code ordering issues, the @samp{max} -partitioning is intended for internal testing only. -The value @samp{one} specifies that exactly one partition should be -used while the value @samp{none} bypasses partitioning and executes -the link-time optimization step directly from the WPA phase. - -@item -flto-compression-level=@var{n} -@opindex flto-compression-level -This option specifies the level of compression used for intermediate -language written to LTO object files, and is only meaningful in -conjunction with LTO mode (@option{-flto}). GCC currently supports two -LTO compression algorithms. For zstd, valid values are 0 (no compression) -to 19 (maximum compression), while zlib supports values from 0 to 9. -Values outside this range are clamped to either minimum or maximum -of the supported values. If the option is not given, -a default balanced compression setting is used. - -@item -fuse-linker-plugin -@opindex fuse-linker-plugin -Enables the use of a linker plugin during link-time optimization. This -option relies on plugin support in the linker, which is available in gold -or in GNU ld 2.21 or newer. - -This option enables the extraction of object files with GIMPLE bytecode out -of library archives. This improves the quality of optimization by exposing -more code to the link-time optimizer. This information specifies what -symbols can be accessed externally (by non-LTO object or during dynamic -linking). Resulting code quality improvements on binaries (and shared -libraries that use hidden visibility) are similar to @option{-fwhole-program}. -See @option{-flto} for a description of the effect of this flag and how to -use it. - -This option is enabled by default when LTO support in GCC is enabled -and GCC was configured for use with -a linker supporting plugins (GNU ld 2.21 or newer or gold). - -@item -ffat-lto-objects -@opindex ffat-lto-objects -Fat LTO objects are object files that contain both the intermediate language -and the object code. This makes them usable for both LTO linking and normal -linking. This option is effective only when compiling with @option{-flto} -and is ignored at link time. - -@option{-fno-fat-lto-objects} improves compilation time over plain LTO, but -requires the complete toolchain to be aware of LTO. It requires a linker with -linker plugin support for basic functionality. Additionally, -@command{nm}, @command{ar} and @command{ranlib} -need to support linker plugins to allow a full-featured build environment -(capable of building static libraries etc). GCC provides the @command{gcc-ar}, -@command{gcc-nm}, @command{gcc-ranlib} wrappers to pass the right options -to these tools. With non fat LTO makefiles need to be modified to use them. - -Note that modern binutils provide plugin auto-load mechanism. -Installing the linker plugin into @file{$libdir/bfd-plugins} has the same -effect as usage of the command wrappers (@command{gcc-ar}, @command{gcc-nm} and -@command{gcc-ranlib}). - -The default is @option{-fno-fat-lto-objects} on targets with linker plugin -support. - -@item -fcompare-elim -@opindex fcompare-elim -After register allocation and post-register allocation instruction splitting, -identify arithmetic instructions that compute processor flags similar to a -comparison operation based on that arithmetic. If possible, eliminate the -explicit comparison operation. - -This pass only applies to certain targets that cannot explicitly represent -the comparison operation before register allocation is complete. - -Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fcprop-registers -@opindex fcprop-registers -After register allocation and post-register allocation instruction splitting, -perform a copy-propagation pass to try to reduce scheduling dependencies -and occasionally eliminate the copy. - -Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fprofile-correction -@opindex fprofile-correction -Profiles collected using an instrumented binary for multi-threaded programs may -be inconsistent due to missed counter updates. When this option is specified, -GCC uses heuristics to correct or smooth out such inconsistencies. By -default, GCC emits an error message when an inconsistent profile is detected. - -This option is enabled by @option{-fauto-profile}. - -@item -fprofile-partial-training -@opindex fprofile-partial-training -With @code{-fprofile-use} all portions of programs not executed during train -run are optimized agressively for size rather than speed. In some cases it is -not practical to train all possible hot paths in the program. (For -example, program may contain functions specific for a given hardware and -trianing may not cover all hardware configurations program is run on.) With -@code{-fprofile-partial-training} profile feedback will be ignored for all -functions not executed during the train run leading them to be optimized as if -they were compiled without profile feedback. This leads to better performance -when train run is not representative but also leads to significantly bigger -code. - -@item -fprofile-use -@itemx -fprofile-use=@var{path} -@opindex fprofile-use -Enable profile feedback-directed optimizations, -and the following optimizations, many of which -are generally profitable only with profile feedback available: - -@gccoptlist{-fbranch-probabilities -fprofile-values @gol --funroll-loops -fpeel-loops -ftracer -fvpt @gol --finline-functions -fipa-cp -fipa-cp-clone -fipa-bit-cp @gol --fpredictive-commoning -fsplit-loops -funswitch-loops @gol --fgcse-after-reload -ftree-loop-vectorize -ftree-slp-vectorize @gol --fvect-cost-model=dynamic -ftree-loop-distribute-patterns @gol --fprofile-reorder-functions} - -Before you can use this option, you must first generate profiling information. -@xref{Instrumentation Options}, for information about the -@option{-fprofile-generate} option. - -By default, GCC emits an error message if the feedback profiles do not -match the source code. This error can be turned into a warning by using -@option{-Wno-error=coverage-mismatch}. Note this may result in poorly -optimized code. Additionally, by default, GCC also emits a warning message if -the feedback profiles do not exist (see @option{-Wmissing-profile}). - -If @var{path} is specified, GCC looks at the @var{path} to find -the profile feedback data files. See @option{-fprofile-dir}. - -@item -fauto-profile -@itemx -fauto-profile=@var{path} -@opindex fauto-profile -Enable sampling-based feedback-directed optimizations, -and the following optimizations, -many of which are generally profitable only with profile feedback available: - -@gccoptlist{-fbranch-probabilities -fprofile-values @gol --funroll-loops -fpeel-loops -ftracer -fvpt @gol --finline-functions -fipa-cp -fipa-cp-clone -fipa-bit-cp @gol --fpredictive-commoning -fsplit-loops -funswitch-loops @gol --fgcse-after-reload -ftree-loop-vectorize -ftree-slp-vectorize @gol --fvect-cost-model=dynamic -ftree-loop-distribute-patterns @gol --fprofile-correction} - -@var{path} is the name of a file containing AutoFDO profile information. -If omitted, it defaults to @file{fbdata.afdo} in the current directory. - -Producing an AutoFDO profile data file requires running your program -with the @command{perf} utility on a supported GNU/Linux target system. -For more information, see @uref{https://perf.wiki.kernel.org/}. - -E.g. -@smallexample -perf record -e br_inst_retired:near_taken -b -o perf.data \ - -- your_program -@end smallexample - -Then use the @command{create_gcov} tool to convert the raw profile data -to a format that can be used by GCC.@ You must also supply the -unstripped binary for your program to this tool. -See @uref{https://github.com/google/autofdo}. - -E.g. -@smallexample -create_gcov --binary=your_program.unstripped --profile=perf.data \ - --gcov=profile.afdo -@end smallexample -@end table - -The following options control compiler behavior regarding floating-point -arithmetic. These options trade off between speed and -correctness. All must be specifically enabled. - -@table @gcctabopt -@item -ffloat-store -@opindex ffloat-store -Do not store floating-point variables in registers, and inhibit other -options that might change whether a floating-point value is taken from a -register or memory. - -@cindex floating-point precision -This option prevents undesirable excess precision on machines such as -the 68000 where the floating registers (of the 68881) keep more -precision than a @code{double} is supposed to have. Similarly for the -x86 architecture. For most programs, the excess precision does only -good, but a few programs rely on the precise definition of IEEE floating -point. Use @option{-ffloat-store} for such programs, after modifying -them to store all pertinent intermediate computations into variables. - -@item -fexcess-precision=@var{style} -@opindex fexcess-precision -This option allows further control over excess precision on machines -where floating-point operations occur in a format with more precision or -range than the IEEE standard and interchange floating-point types. By -default, @option{-fexcess-precision=fast} is in effect; this means that -operations may be carried out in a wider precision than the types specified -in the source if that would result in faster code, and it is unpredictable -when rounding to the types specified in the source code takes place. -When compiling C or C++, if @option{-fexcess-precision=standard} is specified -then excess precision follows the rules specified in ISO C99 or C++; in particular, -both casts and assignments cause values to be rounded to their -semantic types (whereas @option{-ffloat-store} only affects -assignments). This option is enabled by default for C or C++ if a strict -conformance option such as @option{-std=c99} or @option{-std=c++17} is used. -@option{-ffast-math} enables @option{-fexcess-precision=fast} by default -regardless of whether a strict conformance option is used. - -@opindex mfpmath -@option{-fexcess-precision=standard} is not implemented for languages -other than C or C++. On the x86, it has no effect if @option{-mfpmath=sse} -or @option{-mfpmath=sse+387} is specified; in the former case, IEEE -semantics apply without excess precision, and in the latter, rounding -is unpredictable. - -@item -ffast-math -@opindex ffast-math -Sets the options @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, -@option{-ffinite-math-only}, @option{-fno-rounding-math}, -@option{-fno-signaling-nans}, @option{-fcx-limited-range} and -@option{-fexcess-precision=fast}. - -This option causes the preprocessor macro @code{__FAST_MATH__} to be defined. - -This option is not turned on by any @option{-O} option besides -@option{-Ofast} since it can result in incorrect output for programs -that depend on an exact implementation of IEEE or ISO rules/specifications -for math functions. It may, however, yield faster code for programs -that do not require the guarantees of these specifications. - -@item -fno-math-errno -@opindex fno-math-errno -@opindex fmath-errno -Do not set @code{errno} after calling math functions that are executed -with a single instruction, e.g., @code{sqrt}. A program that relies on -IEEE exceptions for math error handling may want to use this flag -for speed while maintaining IEEE arithmetic compatibility. - -This option is not turned on by any @option{-O} option since -it can result in incorrect output for programs that depend on -an exact implementation of IEEE or ISO rules/specifications for -math functions. It may, however, yield faster code for programs -that do not require the guarantees of these specifications. - -The default is @option{-fmath-errno}. - -On Darwin systems, the math library never sets @code{errno}. There is -therefore no reason for the compiler to consider the possibility that -it might, and @option{-fno-math-errno} is the default. - -@item -funsafe-math-optimizations -@opindex funsafe-math-optimizations - -Allow optimizations for floating-point arithmetic that (a) assume -that arguments and results are valid and (b) may violate IEEE or -ANSI standards. When used at link time, it may include libraries -or startup files that change the default FPU control word or other -similar optimizations. - -This option is not turned on by any @option{-O} option since -it can result in incorrect output for programs that depend on -an exact implementation of IEEE or ISO rules/specifications for -math functions. It may, however, yield faster code for programs -that do not require the guarantees of these specifications. -Enables @option{-fno-signed-zeros}, @option{-fno-trapping-math}, -@option{-fassociative-math} and @option{-freciprocal-math}. - -The default is @option{-fno-unsafe-math-optimizations}. - -@item -fassociative-math -@opindex fassociative-math - -Allow re-association of operands in series of floating-point operations. -This violates the ISO C and C++ language standard by possibly changing -computation result. NOTE: re-ordering may change the sign of zero as -well as ignore NaNs and inhibit or create underflow or overflow (and -thus cannot be used on code that relies on rounding behavior like -@code{(x + 2**52) - 2**52}. May also reorder floating-point comparisons -and thus may not be used when ordered comparisons are required. -This option requires that both @option{-fno-signed-zeros} and -@option{-fno-trapping-math} be in effect. Moreover, it doesn't make -much sense with @option{-frounding-math}. For Fortran the option -is automatically enabled when both @option{-fno-signed-zeros} and -@option{-fno-trapping-math} are in effect. - -The default is @option{-fno-associative-math}. - -@item -freciprocal-math -@opindex freciprocal-math - -Allow the reciprocal of a value to be used instead of dividing by -the value if this enables optimizations. For example @code{x / y} -can be replaced with @code{x * (1/y)}, which is useful if @code{(1/y)} -is subject to common subexpression elimination. Note that this loses -precision and increases the number of flops operating on the value. - -The default is @option{-fno-reciprocal-math}. - -@item -ffinite-math-only -@opindex ffinite-math-only -Allow optimizations for floating-point arithmetic that assume -that arguments and results are not NaNs or +-Infs. - -This option is not turned on by any @option{-O} option since -it can result in incorrect output for programs that depend on -an exact implementation of IEEE or ISO rules/specifications for -math functions. It may, however, yield faster code for programs -that do not require the guarantees of these specifications. - -The default is @option{-fno-finite-math-only}. - -@item -fno-signed-zeros -@opindex fno-signed-zeros -@opindex fsigned-zeros -Allow optimizations for floating-point arithmetic that ignore the -signedness of zero. IEEE arithmetic specifies the behavior of -distinct +0.0 and @minus{}0.0 values, which then prohibits simplification -of expressions such as x+0.0 or 0.0*x (even with @option{-ffinite-math-only}). -This option implies that the sign of a zero result isn't significant. - -The default is @option{-fsigned-zeros}. - -@item -fno-trapping-math -@opindex fno-trapping-math -@opindex ftrapping-math -Compile code assuming that floating-point operations cannot generate -user-visible traps. These traps include division by zero, overflow, -underflow, inexact result and invalid operation. This option requires -that @option{-fno-signaling-nans} be in effect. Setting this option may -allow faster code if one relies on ``non-stop'' IEEE arithmetic, for example. - -This option should never be turned on by any @option{-O} option since -it can result in incorrect output for programs that depend on -an exact implementation of IEEE or ISO rules/specifications for -math functions. - -The default is @option{-ftrapping-math}. - -Future versions of GCC may provide finer control of this setting -using C99's @code{FENV_ACCESS} pragma. This command-line option -will be used along with @option{-frounding-math} to specify the -default state for @code{FENV_ACCESS}. - -@item -frounding-math -@opindex frounding-math -Disable transformations and optimizations that assume default floating-point -rounding behavior. This is round-to-zero for all floating point -to integer conversions, and round-to-nearest for all other arithmetic -truncations. This option should be specified for programs that change -the FP rounding mode dynamically, or that may be executed with a -non-default rounding mode. This option disables constant folding of -floating-point expressions at compile time (which may be affected by -rounding mode) and arithmetic transformations that are unsafe in the -presence of sign-dependent rounding modes. - -The default is @option{-fno-rounding-math}. - -This option is experimental and does not currently guarantee to -disable all GCC optimizations that are affected by rounding mode. -Future versions of GCC may provide finer control of this setting -using C99's @code{FENV_ACCESS} pragma. This command-line option -will be used along with @option{-ftrapping-math} to specify the -default state for @code{FENV_ACCESS}. - -@item -fsignaling-nans -@opindex fsignaling-nans -Compile code assuming that IEEE signaling NaNs may generate user-visible -traps during floating-point operations. Setting this option disables -optimizations that may change the number of exceptions visible with -signaling NaNs. This option implies @option{-ftrapping-math}. - -This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to -be defined. - -The default is @option{-fno-signaling-nans}. - -This option is experimental and does not currently guarantee to -disable all GCC optimizations that affect signaling NaN behavior. - -@item -fno-fp-int-builtin-inexact -@opindex fno-fp-int-builtin-inexact -@opindex ffp-int-builtin-inexact -Do not allow the built-in functions @code{ceil}, @code{floor}, -@code{round} and @code{trunc}, and their @code{float} and @code{long -double} variants, to generate code that raises the ``inexact'' -floating-point exception for noninteger arguments. ISO C99 and C11 -allow these functions to raise the ``inexact'' exception, but ISO/IEC -TS 18661-1:2014, the C bindings to IEEE 754-2008, as integrated into -ISO C2X, does not allow these functions to do so. - -The default is @option{-ffp-int-builtin-inexact}, allowing the -exception to be raised, unless C2X or a later C standard is selected. -This option does nothing unless @option{-ftrapping-math} is in effect. - -Even if @option{-fno-fp-int-builtin-inexact} is used, if the functions -generate a call to a library function then the ``inexact'' exception -may be raised if the library implementation does not follow TS 18661. - -@item -fsingle-precision-constant -@opindex fsingle-precision-constant -Treat floating-point constants as single precision instead of -implicitly converting them to double-precision constants. - -@item -fcx-limited-range -@opindex fcx-limited-range -When enabled, this option states that a range reduction step is not -needed when performing complex division. Also, there is no checking -whether the result of a complex multiplication or division is @code{NaN -+ I*NaN}, with an attempt to rescue the situation in that case. The -default is @option{-fno-cx-limited-range}, but is enabled by -@option{-ffast-math}. - -This option controls the default setting of the ISO C99 -@code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to -all languages. - -@item -fcx-fortran-rules -@opindex fcx-fortran-rules -Complex multiplication and division follow Fortran rules. Range -reduction is done as part of complex division, but there is no checking -whether the result of a complex multiplication or division is @code{NaN -+ I*NaN}, with an attempt to rescue the situation in that case. - -The default is @option{-fno-cx-fortran-rules}. - -@end table - -The following options control optimizations that may improve -performance, but are not enabled by any @option{-O} options. This -section includes experimental options that may produce broken code. - -@table @gcctabopt -@item -fbranch-probabilities -@opindex fbranch-probabilities -After running a program compiled with @option{-fprofile-arcs} -(@pxref{Instrumentation Options}), -you can compile it a second time using -@option{-fbranch-probabilities}, to improve optimizations based on -the number of times each branch was taken. When a program -compiled with @option{-fprofile-arcs} exits, it saves arc execution -counts to a file called @file{@var{sourcename}.gcda} for each source -file. The information in this data file is very dependent on the -structure of the generated code, so you must use the same source code -and the same optimization options for both compilations. -See details about the file naming in @option{-fprofile-arcs}. - -With @option{-fbranch-probabilities}, GCC puts a -@samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}. -These can be used to improve optimization. Currently, they are only -used in one place: in @file{reorg.cc}, instead of guessing which path a -branch is most likely to take, the @samp{REG_BR_PROB} values are used to -exactly determine which path is taken more often. - -Enabled by @option{-fprofile-use} and @option{-fauto-profile}. - -@item -fprofile-values -@opindex fprofile-values -If combined with @option{-fprofile-arcs}, it adds code so that some -data about values of expressions in the program is gathered. - -With @option{-fbranch-probabilities}, it reads back the data gathered -from profiling values of expressions for usage in optimizations. - -Enabled by @option{-fprofile-generate}, @option{-fprofile-use}, and -@option{-fauto-profile}. - -@item -fprofile-reorder-functions -@opindex fprofile-reorder-functions -Function reordering based on profile instrumentation collects -first time of execution of a function and orders these functions -in ascending order. - -Enabled with @option{-fprofile-use}. - -@item -fvpt -@opindex fvpt -If combined with @option{-fprofile-arcs}, this option instructs the compiler -to add code to gather information about values of expressions. - -With @option{-fbranch-probabilities}, it reads back the data gathered -and actually performs the optimizations based on them. -Currently the optimizations include specialization of division operations -using the knowledge about the value of the denominator. - -Enabled with @option{-fprofile-use} and @option{-fauto-profile}. - -@item -frename-registers -@opindex frename-registers -Attempt to avoid false dependencies in scheduled code by making use -of registers left over after register allocation. This optimization -most benefits processors with lots of registers. Depending on the -debug information format adopted by the target, however, it can -make debugging impossible, since variables no longer stay in -a ``home register''. - -Enabled by default with @option{-funroll-loops}. - -@item -fschedule-fusion -@opindex fschedule-fusion -Performs a target dependent pass over the instruction stream to schedule -instructions of same type together because target machine can execute them -more efficiently if they are adjacent to each other in the instruction flow. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -ftracer -@opindex ftracer -Perform tail duplication to enlarge superblock size. This transformation -simplifies the control flow of the function allowing other optimizations to do -a better job. - -Enabled by @option{-fprofile-use} and @option{-fauto-profile}. - -@item -funroll-loops -@opindex funroll-loops -Unroll loops whose number of iterations can be determined at compile time or -upon entry to the loop. @option{-funroll-loops} implies -@option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}. -It also turns on complete loop peeling (i.e.@: complete removal of loops with -a small constant number of iterations). This option makes code larger, and may -or may not make it run faster. - -Enabled by @option{-fprofile-use} and @option{-fauto-profile}. - -@item -funroll-all-loops -@opindex funroll-all-loops -Unroll all loops, even if their number of iterations is uncertain when -the loop is entered. This usually makes programs run more slowly. -@option{-funroll-all-loops} implies the same options as -@option{-funroll-loops}. - -@item -fpeel-loops -@opindex fpeel-loops -Peels loops for which there is enough information that they do not -roll much (from profile feedback or static analysis). It also turns on -complete loop peeling (i.e.@: complete removal of loops with small constant -number of iterations). - -Enabled by @option{-O3}, @option{-fprofile-use}, and @option{-fauto-profile}. - -@item -fmove-loop-invariants -@opindex fmove-loop-invariants -Enables the loop invariant motion pass in the RTL loop optimizer. Enabled -at level @option{-O1} and higher, except for @option{-Og}. - -@item -fmove-loop-stores -@opindex fmove-loop-stores -Enables the loop store motion pass in the GIMPLE loop optimizer. This -moves invariant stores to after the end of the loop in exchange for -carrying the stored value in a register across the iteration. -Note for this option to have an effect @option{-ftree-loop-im} has to -be enabled as well. Enabled at level @option{-O1} and higher, except -for @option{-Og}. - -@item -fsplit-loops -@opindex fsplit-loops -Split a loop into two if it contains a condition that's always true -for one side of the iteration space and false for the other. - -Enabled by @option{-fprofile-use} and @option{-fauto-profile}. - -@item -funswitch-loops -@opindex funswitch-loops -Move branches with loop invariant conditions out of the loop, with duplicates -of the loop on both branches (modified according to result of the condition). - -Enabled by @option{-fprofile-use} and @option{-fauto-profile}. - -@item -fversion-loops-for-strides -@opindex fversion-loops-for-strides -If a loop iterates over an array with a variable stride, create another -version of the loop that assumes the stride is always one. For example: - -@smallexample -for (int i = 0; i < n; ++i) - x[i * stride] = @dots{}; -@end smallexample - -becomes: - -@smallexample -if (stride == 1) - for (int i = 0; i < n; ++i) - x[i] = @dots{}; -else - for (int i = 0; i < n; ++i) - x[i * stride] = @dots{}; -@end smallexample - -This is particularly useful for assumed-shape arrays in Fortran where -(for example) it allows better vectorization assuming contiguous accesses. -This flag is enabled by default at @option{-O3}. -It is also enabled by @option{-fprofile-use} and @option{-fauto-profile}. - -@item -ffunction-sections -@itemx -fdata-sections -@opindex ffunction-sections -@opindex fdata-sections -Place each function or data item into its own section in the output -file if the target supports arbitrary sections. The name of the -function or the name of the data item determines the section's name -in the output file. - -Use these options on systems where the linker can perform optimizations to -improve locality of reference in the instruction space. Most systems using the -ELF object format have linkers with such optimizations. On AIX, the linker -rearranges sections (CSECTs) based on the call graph. The performance impact -varies. - -Together with a linker garbage collection (linker @option{--gc-sections} -option) these options may lead to smaller statically-linked executables (after -stripping). - -On ELF/DWARF systems these options do not degenerate the quality of the debug -information. There could be issues with other object files/debug info formats. - -Only use these options when there are significant benefits from doing so. When -you specify these options, the assembler and linker create larger object and -executable files and are also slower. These options affect code generation. -They prevent optimizations by the compiler and assembler using relative -locations inside a translation unit since the locations are unknown until -link time. An example of such an optimization is relaxing calls to short call -instructions. - -@item -fstdarg-opt -@opindex fstdarg-opt -Optimize the prologue of variadic argument functions with respect to usage of -those arguments. - -@item -fsection-anchors -@opindex fsection-anchors -Try to reduce the number of symbolic address calculations by using -shared ``anchor'' symbols to address nearby objects. This transformation -can help to reduce the number of GOT entries and GOT accesses on some -targets. - -For example, the implementation of the following function @code{foo}: - -@smallexample -static int a, b, c; -int foo (void) @{ return a + b + c; @} -@end smallexample - -@noindent -usually calculates the addresses of all three variables, but if you -compile it with @option{-fsection-anchors}, it accesses the variables -from a common anchor point instead. The effect is similar to the -following pseudocode (which isn't valid C): - -@smallexample -int foo (void) -@{ - register int *xr = &x; - return xr[&a - &x] + xr[&b - &x] + xr[&c - &x]; -@} -@end smallexample - -Not all targets support this option. - -@item -fzero-call-used-regs=@var{choice} -@opindex fzero-call-used-regs -Zero call-used registers at function return to increase program -security by either mitigating Return-Oriented Programming (ROP) -attacks or preventing information leakage through registers. - -The possible values of @var{choice} are the same as for the -@code{zero_call_used_regs} attribute (@pxref{Function Attributes}). -The default is @samp{skip}. - -You can control this behavior for a specific function by using the function -attribute @code{zero_call_used_regs} (@pxref{Function Attributes}). - -@item --param @var{name}=@var{value} -@opindex param -In some places, GCC uses various constants to control the amount of -optimization that is done. For example, GCC does not inline functions -that contain more than a certain number of instructions. You can -control some of these constants on the command line using the -@option{--param} option. - -The names of specific parameters, and the meaning of the values, are -tied to the internals of the compiler, and are subject to change -without notice in future releases. - -In order to get minimal, maximal and default value of a parameter, -one can use @option{--help=param -Q} options. - -In each case, the @var{value} is an integer. The following choices -of @var{name} are recognized for all targets: - -@table @gcctabopt -@item predictable-branch-outcome -When branch is predicted to be taken with probability lower than this threshold -(in percent), then it is considered well predictable. - -@item max-rtl-if-conversion-insns -RTL if-conversion tries to remove conditional branches around a block and -replace them with conditionally executed instructions. This parameter -gives the maximum number of instructions in a block which should be -considered for if-conversion. The compiler will -also use other heuristics to decide whether if-conversion is likely to be -profitable. - -@item max-rtl-if-conversion-predictable-cost -RTL if-conversion will try to remove conditional branches around a block -and replace them with conditionally executed instructions. These parameters -give the maximum permissible cost for the sequence that would be generated -by if-conversion depending on whether the branch is statically determined -to be predictable or not. The units for this parameter are the same as -those for the GCC internal seq_cost metric. The compiler will try to -provide a reasonable default for this parameter using the BRANCH_COST -target macro. - -@item max-crossjump-edges -The maximum number of incoming edges to consider for cross-jumping. -The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in -the number of edges incoming to each block. Increasing values mean -more aggressive optimization, making the compilation time increase with -probably small improvement in executable size. - -@item min-crossjump-insns -The minimum number of instructions that must be matched at the end -of two blocks before cross-jumping is performed on them. This -value is ignored in the case where all instructions in the block being -cross-jumped from are matched. - -@item max-grow-copy-bb-insns -The maximum code size expansion factor when copying basic blocks -instead of jumping. The expansion is relative to a jump instruction. - -@item max-goto-duplication-insns -The maximum number of instructions to duplicate to a block that jumps -to a computed goto. To avoid @math{O(N^2)} behavior in a number of -passes, GCC factors computed gotos early in the compilation process, -and unfactors them as late as possible. Only computed jumps at the -end of a basic blocks with no more than max-goto-duplication-insns are -unfactored. - -@item max-delay-slot-insn-search -The maximum number of instructions to consider when looking for an -instruction to fill a delay slot. If more than this arbitrary number of -instructions are searched, the time savings from filling the delay slot -are minimal, so stop searching. Increasing values mean more -aggressive optimization, making the compilation time increase with probably -small improvement in execution time. - -@item max-delay-slot-live-search -When trying to fill delay slots, the maximum number of instructions to -consider when searching for a block with valid live register -information. Increasing this arbitrarily chosen value means more -aggressive optimization, increasing the compilation time. This parameter -should be removed when the delay slot code is rewritten to maintain the -control-flow graph. - -@item max-gcse-memory -The approximate maximum amount of memory in @code{kB} that can be allocated in -order to perform the global common subexpression elimination -optimization. If more memory than specified is required, the -optimization is not done. - -@item max-gcse-insertion-ratio -If the ratio of expression insertions to deletions is larger than this value -for any expression, then RTL PRE inserts or removes the expression and thus -leaves partially redundant computations in the instruction stream. - -@item max-pending-list-length -The maximum number of pending dependencies scheduling allows -before flushing the current state and starting over. Large functions -with few branches or calls can create excessively large lists which -needlessly consume memory and resources. - -@item max-modulo-backtrack-attempts -The maximum number of backtrack attempts the scheduler should make -when modulo scheduling a loop. Larger values can exponentially increase -compilation time. - -@item max-inline-functions-called-once-loop-depth -Maximal loop depth of a call considered by inline heuristics that tries to -inline all functions called once. - -@item max-inline-functions-called-once-insns -Maximal estimated size of functions produced while inlining functions called -once. - -@item max-inline-insns-single -Several parameters control the tree inliner used in GCC@. This number sets the -maximum number of instructions (counted in GCC's internal representation) in a -single function that the tree inliner considers for inlining. This only -affects functions declared inline and methods implemented in a class -declaration (C++). - - -@item max-inline-insns-auto -When you use @option{-finline-functions} (included in @option{-O3}), -a lot of functions that would otherwise not be considered for inlining -by the compiler are investigated. To those functions, a different -(more restrictive) limit compared to functions declared inline can -be applied (@option{--param max-inline-insns-auto}). - -@item max-inline-insns-small -This is bound applied to calls which are considered relevant with -@option{-finline-small-functions}. - -@item max-inline-insns-size -This is bound applied to calls which are optimized for size. Small growth -may be desirable to anticipate optimization oppurtunities exposed by inlining. - -@item uninlined-function-insns -Number of instructions accounted by inliner for function overhead such as -function prologue and epilogue. - -@item uninlined-function-time -Extra time accounted by inliner for function overhead such as time needed to -execute function prologue and epilogue. - -@item inline-heuristics-hint-percent -The scale (in percents) applied to @option{inline-insns-single}, -@option{inline-insns-single-O2}, @option{inline-insns-auto} -when inline heuristics hints that inlining is -very profitable (will enable later optimizations). - -@item uninlined-thunk-insns -@item uninlined-thunk-time -Same as @option{--param uninlined-function-insns} and -@option{--param uninlined-function-time} but applied to function thunks. - -@item inline-min-speedup -When estimated performance improvement of caller + callee runtime exceeds this -threshold (in percent), the function can be inlined regardless of the limit on -@option{--param max-inline-insns-single} and @option{--param -max-inline-insns-auto}. - -@item large-function-insns -The limit specifying really large functions. For functions larger than this -limit after inlining, inlining is constrained by -@option{--param large-function-growth}. This parameter is useful primarily -to avoid extreme compilation time caused by non-linear algorithms used by the -back end. - -@item large-function-growth -Specifies maximal growth of large function caused by inlining in percents. -For example, parameter value 100 limits large function growth to 2.0 times -the original size. - -@item large-unit-insns -The limit specifying large translation unit. Growth caused by inlining of -units larger than this limit is limited by @option{--param inline-unit-growth}. -For small units this might be too tight. -For example, consider a unit consisting of function A -that is inline and B that just calls A three times. If B is small relative to -A, the growth of unit is 300\% and yet such inlining is very sane. For very -large units consisting of small inlineable functions, however, the overall unit -growth limit is needed to avoid exponential explosion of code size. Thus for -smaller units, the size is increased to @option{--param large-unit-insns} -before applying @option{--param inline-unit-growth}. - -@item lazy-modules -Maximum number of concurrently open C++ module files when lazy loading. - -@item inline-unit-growth -Specifies maximal overall growth of the compilation unit caused by inlining. -For example, parameter value 20 limits unit growth to 1.2 times the original -size. Cold functions (either marked cold via an attribute or by profile -feedback) are not accounted into the unit size. - -@item ipa-cp-unit-growth -Specifies maximal overall growth of the compilation unit caused by -interprocedural constant propagation. For example, parameter value 10 limits -unit growth to 1.1 times the original size. - -@item ipa-cp-large-unit-insns -The size of translation unit that IPA-CP pass considers large. - -@item large-stack-frame -The limit specifying large stack frames. While inlining the algorithm is trying -to not grow past this limit too much. - -@item large-stack-frame-growth -Specifies maximal growth of large stack frames caused by inlining in percents. -For example, parameter value 1000 limits large stack frame growth to 11 times -the original size. - -@item max-inline-insns-recursive -@itemx max-inline-insns-recursive-auto -Specifies the maximum number of instructions an out-of-line copy of a -self-recursive inline -function can grow into by performing recursive inlining. - -@option{--param max-inline-insns-recursive} applies to functions -declared inline. -For functions not declared inline, recursive inlining -happens only when @option{-finline-functions} (included in @option{-O3}) is -enabled; @option{--param max-inline-insns-recursive-auto} applies instead. - -@item max-inline-recursive-depth -@itemx max-inline-recursive-depth-auto -Specifies the maximum recursion depth used for recursive inlining. - -@option{--param max-inline-recursive-depth} applies to functions -declared inline. For functions not declared inline, recursive inlining -happens only when @option{-finline-functions} (included in @option{-O3}) is -enabled; @option{--param max-inline-recursive-depth-auto} applies instead. - -@item min-inline-recursive-probability -Recursive inlining is profitable only for function having deep recursion -in average and can hurt for function having little recursion depth by -increasing the prologue size or complexity of function body to other -optimizers. - -When profile feedback is available (see @option{-fprofile-generate}) the actual -recursion depth can be guessed from the probability that function recurses -via a given call expression. This parameter limits inlining only to call -expressions whose probability exceeds the given threshold (in percents). - -@item early-inlining-insns -Specify growth that the early inliner can make. In effect it increases -the amount of inlining for code having a large abstraction penalty. - -@item max-early-inliner-iterations -Limit of iterations of the early inliner. This basically bounds -the number of nested indirect calls the early inliner can resolve. -Deeper chains are still handled by late inlining. - -@item comdat-sharing-probability -Probability (in percent) that C++ inline function with comdat visibility -are shared across multiple compilation units. - -@item modref-max-bases -@item modref-max-refs -@item modref-max-accesses -Specifies the maximal number of base pointers, references and accesses stored -for a single function by mod/ref analysis. - -@item modref-max-tests -Specifies the maxmal number of tests alias oracle can perform to disambiguate -memory locations using the mod/ref information. This parameter ought to be -bigger than @option{--param modref-max-bases} and @option{--param -modref-max-refs}. - -@item modref-max-depth -Specifies the maximum depth of DFS walk used by modref escape analysis. -Setting to 0 disables the analysis completely. - -@item modref-max-escape-points -Specifies the maximum number of escape points tracked by modref per SSA-name. - -@item modref-max-adjustments -Specifies the maximum number the access range is enlarged during modref dataflow -analysis. - -@item profile-func-internal-id -A parameter to control whether to use function internal id in profile -database lookup. If the value is 0, the compiler uses an id that -is based on function assembler name and filename, which makes old profile -data more tolerant to source changes such as function reordering etc. - -@item min-vect-loop-bound -The minimum number of iterations under which loops are not vectorized -when @option{-ftree-vectorize} is used. The number of iterations after -vectorization needs to be greater than the value specified by this option -to allow vectorization. - -@item gcse-cost-distance-ratio -Scaling factor in calculation of maximum distance an expression -can be moved by GCSE optimizations. This is currently supported only in the -code hoisting pass. The bigger the ratio, the more aggressive code hoisting -is with simple expressions, i.e., the expressions that have cost -less than @option{gcse-unrestricted-cost}. Specifying 0 disables -hoisting of simple expressions. - -@item gcse-unrestricted-cost -Cost, roughly measured as the cost of a single typical machine -instruction, at which GCSE optimizations do not constrain -the distance an expression can travel. This is currently -supported only in the code hoisting pass. The lesser the cost, -the more aggressive code hoisting is. Specifying 0 -allows all expressions to travel unrestricted distances. - -@item max-hoist-depth -The depth of search in the dominator tree for expressions to hoist. -This is used to avoid quadratic behavior in hoisting algorithm. -The value of 0 does not limit on the search, but may slow down compilation -of huge functions. - -@item max-tail-merge-comparisons -The maximum amount of similar bbs to compare a bb with. This is used to -avoid quadratic behavior in tree tail merging. - -@item max-tail-merge-iterations -The maximum amount of iterations of the pass over the function. This is used to -limit compilation time in tree tail merging. - -@item store-merging-allow-unaligned -Allow the store merging pass to introduce unaligned stores if it is legal to -do so. - -@item max-stores-to-merge -The maximum number of stores to attempt to merge into wider stores in the store -merging pass. - -@item max-store-chains-to-track -The maximum number of store chains to track at the same time in the attempt -to merge them into wider stores in the store merging pass. - -@item max-stores-to-track -The maximum number of stores to track at the same time in the attemt to -to merge them into wider stores in the store merging pass. - -@item max-unrolled-insns -The maximum number of instructions that a loop may have to be unrolled. -If a loop is unrolled, this parameter also determines how many times -the loop code is unrolled. - -@item max-average-unrolled-insns -The maximum number of instructions biased by probabilities of their execution -that a loop may have to be unrolled. If a loop is unrolled, -this parameter also determines how many times the loop code is unrolled. - -@item max-unroll-times -The maximum number of unrollings of a single loop. - -@item max-peeled-insns -The maximum number of instructions that a loop may have to be peeled. -If a loop is peeled, this parameter also determines how many times -the loop code is peeled. - -@item max-peel-times -The maximum number of peelings of a single loop. - -@item max-peel-branches -The maximum number of branches on the hot path through the peeled sequence. - -@item max-completely-peeled-insns -The maximum number of insns of a completely peeled loop. - -@item max-completely-peel-times -The maximum number of iterations of a loop to be suitable for complete peeling. - -@item max-completely-peel-loop-nest-depth -The maximum depth of a loop nest suitable for complete peeling. - -@item max-unswitch-insns -The maximum number of insns of an unswitched loop. - -@item lim-expensive -The minimum cost of an expensive expression in the loop invariant motion. - -@item min-loop-cond-split-prob -When FDO profile information is available, @option{min-loop-cond-split-prob} -specifies minimum threshold for probability of semi-invariant condition -statement to trigger loop split. - -@item iv-consider-all-candidates-bound -Bound on number of candidates for induction variables, below which -all candidates are considered for each use in induction variable -optimizations. If there are more candidates than this, -only the most relevant ones are considered to avoid quadratic time complexity. - -@item iv-max-considered-uses -The induction variable optimizations give up on loops that contain more -induction variable uses. - -@item iv-always-prune-cand-set-bound -If the number of candidates in the set is smaller than this value, -always try to remove unnecessary ivs from the set -when adding a new one. - -@item avg-loop-niter -Average number of iterations of a loop. - -@item dse-max-object-size -Maximum size (in bytes) of objects tracked bytewise by dead store elimination. -Larger values may result in larger compilation times. - -@item dse-max-alias-queries-per-store -Maximum number of queries into the alias oracle per store. -Larger values result in larger compilation times and may result in more -removed dead stores. - -@item scev-max-expr-size -Bound on size of expressions used in the scalar evolutions analyzer. -Large expressions slow the analyzer. - -@item scev-max-expr-complexity -Bound on the complexity of the expressions in the scalar evolutions analyzer. -Complex expressions slow the analyzer. - -@item max-tree-if-conversion-phi-args -Maximum number of arguments in a PHI supported by TREE if conversion -unless the loop is marked with simd pragma. - -@item vect-max-layout-candidates -The maximum number of possible vector layouts (such as permutations) -to consider when optimizing to-be-vectorized code. - -@item vect-max-version-for-alignment-checks -The maximum number of run-time checks that can be performed when -doing loop versioning for alignment in the vectorizer. - -@item vect-max-version-for-alias-checks -The maximum number of run-time checks that can be performed when -doing loop versioning for alias in the vectorizer. - -@item vect-max-peeling-for-alignment -The maximum number of loop peels to enhance access alignment -for vectorizer. Value -1 means no limit. - -@item max-iterations-to-track -The maximum number of iterations of a loop the brute-force algorithm -for analysis of the number of iterations of the loop tries to evaluate. - -@item hot-bb-count-fraction -The denominator n of fraction 1/n of the maximal execution count of a -basic block in the entire program that a basic block needs to at least -have in order to be considered hot. The default is 10000, which means -that a basic block is considered hot if its execution count is greater -than 1/10000 of the maximal execution count. 0 means that it is never -considered hot. Used in non-LTO mode. - -@item hot-bb-count-ws-permille -The number of most executed permilles, ranging from 0 to 1000, of the -profiled execution of the entire program to which the execution count -of a basic block must be part of in order to be considered hot. The -default is 990, which means that a basic block is considered hot if -its execution count contributes to the upper 990 permilles, or 99.0%, -of the profiled execution of the entire program. 0 means that it is -never considered hot. Used in LTO mode. - -@item hot-bb-frequency-fraction -The denominator n of fraction 1/n of the execution frequency of the -entry block of a function that a basic block of this function needs -to at least have in order to be considered hot. The default is 1000, -which means that a basic block is considered hot in a function if it -is executed more frequently than 1/1000 of the frequency of the entry -block of the function. 0 means that it is never considered hot. - -@item unlikely-bb-count-fraction -The denominator n of fraction 1/n of the number of profiled runs of -the entire program below which the execution count of a basic block -must be in order for the basic block to be considered unlikely executed. -The default is 20, which means that a basic block is considered unlikely -executed if it is executed in fewer than 1/20, or 5%, of the runs of -the program. 0 means that it is always considered unlikely executed. - -@item max-predicted-iterations -The maximum number of loop iterations we predict statically. This is useful -in cases where a function contains a single loop with known bound and -another loop with unknown bound. -The known number of iterations is predicted correctly, while -the unknown number of iterations average to roughly 10. This means that the -loop without bounds appears artificially cold relative to the other one. - -@item builtin-expect-probability -Control the probability of the expression having the specified value. This -parameter takes a percentage (i.e.@: 0 ... 100) as input. - -@item builtin-string-cmp-inline-length -The maximum length of a constant string for a builtin string cmp call -eligible for inlining. - -@item align-threshold - -Select fraction of the maximal frequency of executions of a basic block in -a function to align the basic block. - -@item align-loop-iterations - -A loop expected to iterate at least the selected number of iterations is -aligned. - -@item tracer-dynamic-coverage -@itemx tracer-dynamic-coverage-feedback - -This value is used to limit superblock formation once the given percentage of -executed instructions is covered. This limits unnecessary code size -expansion. - -The @option{tracer-dynamic-coverage-feedback} parameter -is used only when profile -feedback is available. The real profiles (as opposed to statically estimated -ones) are much less balanced allowing the threshold to be larger value. - -@item tracer-max-code-growth -Stop tail duplication once code growth has reached given percentage. This is -a rather artificial limit, as most of the duplicates are eliminated later in -cross jumping, so it may be set to much higher values than is the desired code -growth. - -@item tracer-min-branch-ratio - -Stop reverse growth when the reverse probability of best edge is less than this -threshold (in percent). - -@item tracer-min-branch-probability -@itemx tracer-min-branch-probability-feedback - -Stop forward growth if the best edge has probability lower than this -threshold. - -Similarly to @option{tracer-dynamic-coverage} two parameters are -provided. @option{tracer-min-branch-probability-feedback} is used for -compilation with profile feedback and @option{tracer-min-branch-probability} -compilation without. The value for compilation with profile feedback -needs to be more conservative (higher) in order to make tracer -effective. - -@item stack-clash-protection-guard-size -Specify the size of the operating system provided stack guard as -2 raised to @var{num} bytes. Higher values may reduce the -number of explicit probes, but a value larger than the operating system -provided guard will leave code vulnerable to stack clash style attacks. - -@item stack-clash-protection-probe-interval -Stack clash protection involves probing stack space as it is allocated. This -param controls the maximum distance between probes into the stack as 2 raised -to @var{num} bytes. Higher values may reduce the number of explicit probes, but a value -larger than the operating system provided guard will leave code vulnerable to -stack clash style attacks. - -@item max-cse-path-length - -The maximum number of basic blocks on path that CSE considers. - -@item max-cse-insns -The maximum number of instructions CSE processes before flushing. - -@item ggc-min-expand - -GCC uses a garbage collector to manage its own memory allocation. This -parameter specifies the minimum percentage by which the garbage -collector's heap should be allowed to expand between collections. -Tuning this may improve compilation speed; it has no effect on code -generation. - -The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when -RAM >= 1GB@. If @code{getrlimit} is available, the notion of ``RAM'' is -the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If -GCC is not able to calculate RAM on a particular platform, the lower -bound of 30% is used. Setting this parameter and -@option{ggc-min-heapsize} to zero causes a full collection to occur at -every opportunity. This is extremely slow, but can be useful for -debugging. - -@item ggc-min-heapsize - -Minimum size of the garbage collector's heap before it begins bothering -to collect garbage. The first collection occurs after the heap expands -by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again, -tuning this may improve compilation speed, and has no effect on code -generation. - -The default is the smaller of RAM/8, RLIMIT_RSS, or a limit that -tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but -with a lower bound of 4096 (four megabytes) and an upper bound of -131072 (128 megabytes). If GCC is not able to calculate RAM on a -particular platform, the lower bound is used. Setting this parameter -very large effectively disables garbage collection. Setting this -parameter and @option{ggc-min-expand} to zero causes a full collection -to occur at every opportunity. - -@item max-reload-search-insns -The maximum number of instruction reload should look backward for equivalent -register. Increasing values mean more aggressive optimization, making the -compilation time increase with probably slightly better performance. - -@item max-cselib-memory-locations -The maximum number of memory locations cselib should take into account. -Increasing values mean more aggressive optimization, making the compilation time -increase with probably slightly better performance. - -@item max-sched-ready-insns -The maximum number of instructions ready to be issued the scheduler should -consider at any given time during the first scheduling pass. Increasing -values mean more thorough searches, making the compilation time increase -with probably little benefit. - -@item max-sched-region-blocks -The maximum number of blocks in a region to be considered for -interblock scheduling. - -@item max-pipeline-region-blocks -The maximum number of blocks in a region to be considered for -pipelining in the selective scheduler. - -@item max-sched-region-insns -The maximum number of insns in a region to be considered for -interblock scheduling. - -@item max-pipeline-region-insns -The maximum number of insns in a region to be considered for -pipelining in the selective scheduler. - -@item min-spec-prob -The minimum probability (in percents) of reaching a source block -for interblock speculative scheduling. - -@item max-sched-extend-regions-iters -The maximum number of iterations through CFG to extend regions. -A value of 0 disables region extensions. - -@item max-sched-insn-conflict-delay -The maximum conflict delay for an insn to be considered for speculative motion. - -@item sched-spec-prob-cutoff -The minimal probability of speculation success (in percents), so that -speculative insns are scheduled. - -@item sched-state-edge-prob-cutoff -The minimum probability an edge must have for the scheduler to save its -state across it. - -@item sched-mem-true-dep-cost -Minimal distance (in CPU cycles) between store and load targeting same -memory locations. - -@item selsched-max-lookahead -The maximum size of the lookahead window of selective scheduling. It is a -depth of search for available instructions. - -@item selsched-max-sched-times -The maximum number of times that an instruction is scheduled during -selective scheduling. This is the limit on the number of iterations -through which the instruction may be pipelined. - -@item selsched-insns-to-rename -The maximum number of best instructions in the ready list that are considered -for renaming in the selective scheduler. - -@item sms-min-sc -The minimum value of stage count that swing modulo scheduler -generates. - -@item max-last-value-rtl -The maximum size measured as number of RTLs that can be recorded in an expression -in combiner for a pseudo register as last known value of that register. - -@item max-combine-insns -The maximum number of instructions the RTL combiner tries to combine. - -@item integer-share-limit -Small integer constants can use a shared data structure, reducing the -compiler's memory usage and increasing its speed. This sets the maximum -value of a shared integer constant. - -@item ssp-buffer-size -The minimum size of buffers (i.e.@: arrays) that receive stack smashing -protection when @option{-fstack-protector} is used. - -@item min-size-for-stack-sharing -The minimum size of variables taking part in stack slot sharing when not -optimizing. - -@item max-jump-thread-duplication-stmts -Maximum number of statements allowed in a block that needs to be -duplicated when threading jumps. - -@item max-jump-thread-paths -The maximum number of paths to consider when searching for jump threading -opportunities. When arriving at a block, incoming edges are only considered -if the number of paths to be searched so far multiplied by the number of -incoming edges does not exhaust the specified maximum number of paths to -consider. - -@item max-fields-for-field-sensitive -Maximum number of fields in a structure treated in -a field sensitive manner during pointer analysis. - -@item prefetch-latency -Estimate on average number of instructions that are executed before -prefetch finishes. The distance prefetched ahead is proportional -to this constant. Increasing this number may also lead to less -streams being prefetched (see @option{simultaneous-prefetches}). - -@item simultaneous-prefetches -Maximum number of prefetches that can run at the same time. - -@item l1-cache-line-size -The size of cache line in L1 data cache, in bytes. - -@item l1-cache-size -The size of L1 data cache, in kilobytes. - -@item l2-cache-size -The size of L2 data cache, in kilobytes. - -@item prefetch-dynamic-strides -Whether the loop array prefetch pass should issue software prefetch hints -for strides that are non-constant. In some cases this may be -beneficial, though the fact the stride is non-constant may make it -hard to predict when there is clear benefit to issuing these hints. - -Set to 1 if the prefetch hints should be issued for non-constant -strides. Set to 0 if prefetch hints should be issued only for strides that -are known to be constant and below @option{prefetch-minimum-stride}. - -@item prefetch-minimum-stride -Minimum constant stride, in bytes, to start using prefetch hints for. If -the stride is less than this threshold, prefetch hints will not be issued. - -This setting is useful for processors that have hardware prefetchers, in -which case there may be conflicts between the hardware prefetchers and -the software prefetchers. If the hardware prefetchers have a maximum -stride they can handle, it should be used here to improve the use of -software prefetchers. - -A value of -1 means we don't have a threshold and therefore -prefetch hints can be issued for any constant stride. - -This setting is only useful for strides that are known and constant. - -@item destructive-interference-size -@item constructive-interference-size -The values for the C++17 variables -@code{std::hardware_destructive_interference_size} and -@code{std::hardware_constructive_interference_size}. The destructive -interference size is the minimum recommended offset between two -independent concurrently-accessed objects; the constructive -interference size is the maximum recommended size of contiguous memory -accessed together. Typically both will be the size of an L1 cache -line for the target, in bytes. For a generic target covering a range of L1 -cache line sizes, typically the constructive interference size will be -the small end of the range and the destructive size will be the large -end. - -The destructive interference size is intended to be used for layout, -and thus has ABI impact. The default value is not expected to be -stable, and on some targets varies with @option{-mtune}, so use of -this variable in a context where ABI stability is important, such as -the public interface of a library, is strongly discouraged; if it is -used in that context, users can stabilize the value using this -option. - -The constructive interference size is less sensitive, as it is -typically only used in a @samp{static_assert} to make sure that a type -fits within a cache line. - -See also @option{-Winterference-size}. - -@item loop-interchange-max-num-stmts -The maximum number of stmts in a loop to be interchanged. - -@item loop-interchange-stride-ratio -The minimum ratio between stride of two loops for interchange to be profitable. - -@item min-insn-to-prefetch-ratio -The minimum ratio between the number of instructions and the -number of prefetches to enable prefetching in a loop. - -@item prefetch-min-insn-to-mem-ratio -The minimum ratio between the number of instructions and the -number of memory references to enable prefetching in a loop. - -@item use-canonical-types -Whether the compiler should use the ``canonical'' type system. -Should always be 1, which uses a more efficient internal -mechanism for comparing types in C++ and Objective-C++. However, if -bugs in the canonical type system are causing compilation failures, -set this value to 0 to disable canonical types. - -@item switch-conversion-max-branch-ratio -Switch initialization conversion refuses to create arrays that are -bigger than @option{switch-conversion-max-branch-ratio} times the number of -branches in the switch. - -@item max-partial-antic-length -Maximum length of the partial antic set computed during the tree -partial redundancy elimination optimization (@option{-ftree-pre}) when -optimizing at @option{-O3} and above. For some sorts of source code -the enhanced partial redundancy elimination optimization can run away, -consuming all of the memory available on the host machine. This -parameter sets a limit on the length of the sets that are computed, -which prevents the runaway behavior. Setting a value of 0 for -this parameter allows an unlimited set length. - -@item rpo-vn-max-loop-depth -Maximum loop depth that is value-numbered optimistically. -When the limit hits the innermost -@var{rpo-vn-max-loop-depth} loops and the outermost loop in the -loop nest are value-numbered optimistically and the remaining ones not. - -@item sccvn-max-alias-queries-per-access -Maximum number of alias-oracle queries we perform when looking for -redundancies for loads and stores. If this limit is hit the search -is aborted and the load or store is not considered redundant. The -number of queries is algorithmically limited to the number of -stores on all paths from the load to the function entry. - -@item ira-max-loops-num -IRA uses regional register allocation by default. If a function -contains more loops than the number given by this parameter, only at most -the given number of the most frequently-executed loops form regions -for regional register allocation. - -@item ira-max-conflict-table-size -Although IRA uses a sophisticated algorithm to compress the conflict -table, the table can still require excessive amounts of memory for -huge functions. If the conflict table for a function could be more -than the size in MB given by this parameter, the register allocator -instead uses a faster, simpler, and lower-quality -algorithm that does not require building a pseudo-register conflict table. - -@item ira-loop-reserved-regs -IRA can be used to evaluate more accurate register pressure in loops -for decisions to move loop invariants (see @option{-O3}). The number -of available registers reserved for some other purposes is given -by this parameter. Default of the parameter -is the best found from numerous experiments. - -@item ira-consider-dup-in-all-alts -Make IRA to consider matching constraint (duplicated operand number) -heavily in all available alternatives for preferred register class. -If it is set as zero, it means IRA only respects the matching -constraint when it's in the only available alternative with an -appropriate register class. Otherwise, it means IRA will check all -available alternatives for preferred register class even if it has -found some choice with an appropriate register class and respect the -found qualified matching constraint. - -@item lra-inheritance-ebb-probability-cutoff -LRA tries to reuse values reloaded in registers in subsequent insns. -This optimization is called inheritance. EBB is used as a region to -do this optimization. The parameter defines a minimal fall-through -edge probability in percentage used to add BB to inheritance EBB in -LRA. The default value was chosen -from numerous runs of SPEC2000 on x86-64. - -@item loop-invariant-max-bbs-in-loop -Loop invariant motion can be very expensive, both in compilation time and -in amount of needed compile-time memory, with very large loops. Loops -with more basic blocks than this parameter won't have loop invariant -motion optimization performed on them. - -@item loop-max-datarefs-for-datadeps -Building data dependencies is expensive for very large loops. This -parameter limits the number of data references in loops that are -considered for data dependence analysis. These large loops are no -handled by the optimizations using loop data dependencies. - -@item max-vartrack-size -Sets a maximum number of hash table slots to use during variable -tracking dataflow analysis of any function. If this limit is exceeded -with variable tracking at assignments enabled, analysis for that -function is retried without it, after removing all debug insns from -the function. If the limit is exceeded even without debug insns, var -tracking analysis is completely disabled for the function. Setting -the parameter to zero makes it unlimited. - -@item max-vartrack-expr-depth -Sets a maximum number of recursion levels when attempting to map -variable names or debug temporaries to value expressions. This trades -compilation time for more complete debug information. If this is set too -low, value expressions that are available and could be represented in -debug information may end up not being used; setting this higher may -enable the compiler to find more complex debug expressions, but compile -time and memory use may grow. - -@item max-debug-marker-count -Sets a threshold on the number of debug markers (e.g.@: begin stmt -markers) to avoid complexity explosion at inlining or expanding to RTL. -If a function has more such gimple stmts than the set limit, such stmts -will be dropped from the inlined copy of a function, and from its RTL -expansion. - -@item min-nondebug-insn-uid -Use uids starting at this parameter for nondebug insns. The range below -the parameter is reserved exclusively for debug insns created by -@option{-fvar-tracking-assignments}, but debug insns may get -(non-overlapping) uids above it if the reserved range is exhausted. - -@item ipa-sra-ptr-growth-factor -IPA-SRA replaces a pointer to an aggregate with one or more new -parameters only when their cumulative size is less or equal to -@option{ipa-sra-ptr-growth-factor} times the size of the original -pointer parameter. - -@item ipa-sra-max-replacements -Maximum pieces of an aggregate that IPA-SRA tracks. As a -consequence, it is also the maximum number of replacements of a formal -parameter. - -@item sra-max-scalarization-size-Ospeed -@itemx sra-max-scalarization-size-Osize -The two Scalar Reduction of Aggregates passes (SRA and IPA-SRA) aim to -replace scalar parts of aggregates with uses of independent scalar -variables. These parameters control the maximum size, in storage units, -of aggregate which is considered for replacement when compiling for -speed -(@option{sra-max-scalarization-size-Ospeed}) or size -(@option{sra-max-scalarization-size-Osize}) respectively. - -@item sra-max-propagations -The maximum number of artificial accesses that Scalar Replacement of -Aggregates (SRA) will track, per one local variable, in order to -facilitate copy propagation. - -@item tm-max-aggregate-size -When making copies of thread-local variables in a transaction, this -parameter specifies the size in bytes after which variables are -saved with the logging functions as opposed to save/restore code -sequence pairs. This option only applies when using -@option{-fgnu-tm}. - -@item graphite-max-nb-scop-params -To avoid exponential effects in the Graphite loop transforms, the -number of parameters in a Static Control Part (SCoP) is bounded. -A value of zero can be used to lift -the bound. A variable whose value is unknown at compilation time and -defined outside a SCoP is a parameter of the SCoP. - -@item loop-block-tile-size -Loop blocking or strip mining transforms, enabled with -@option{-floop-block} or @option{-floop-strip-mine}, strip mine each -loop in the loop nest by a given number of iterations. The strip -length can be changed using the @option{loop-block-tile-size} -parameter. - -@item ipa-jump-function-lookups -Specifies number of statements visited during jump function offset discovery. - -@item ipa-cp-value-list-size -IPA-CP attempts to track all possible values and types passed to a function's -parameter in order to propagate them and perform devirtualization. -@option{ipa-cp-value-list-size} is the maximum number of values and types it -stores per one formal parameter of a function. - -@item ipa-cp-eval-threshold -IPA-CP calculates its own score of cloning profitability heuristics -and performs those cloning opportunities with scores that exceed -@option{ipa-cp-eval-threshold}. - -@item ipa-cp-max-recursive-depth -Maximum depth of recursive cloning for self-recursive function. - -@item ipa-cp-min-recursive-probability -Recursive cloning only when the probability of call being executed exceeds -the parameter. - -@item ipa-cp-profile-count-base -When using @option{-fprofile-use} option, IPA-CP will consider the measured -execution count of a call graph edge at this percentage position in their -histogram as the basis for its heuristics calculation. - -@item ipa-cp-recursive-freq-factor -The number of times interprocedural copy propagation expects recursive -functions to call themselves. - -@item ipa-cp-recursion-penalty -Percentage penalty the recursive functions will receive when they -are evaluated for cloning. - -@item ipa-cp-single-call-penalty -Percentage penalty functions containing a single call to another -function will receive when they are evaluated for cloning. - -@item ipa-max-agg-items -IPA-CP is also capable to propagate a number of scalar values passed -in an aggregate. @option{ipa-max-agg-items} controls the maximum -number of such values per one parameter. - -@item ipa-cp-loop-hint-bonus -When IPA-CP determines that a cloning candidate would make the number -of iterations of a loop known, it adds a bonus of -@option{ipa-cp-loop-hint-bonus} to the profitability score of -the candidate. - -@item ipa-max-loop-predicates -The maximum number of different predicates IPA will use to describe when -loops in a function have known properties. - -@item ipa-max-aa-steps -During its analysis of function bodies, IPA-CP employs alias analysis -in order to track values pointed to by function parameters. In order -not spend too much time analyzing huge functions, it gives up and -consider all memory clobbered after examining -@option{ipa-max-aa-steps} statements modifying memory. - -@item ipa-max-switch-predicate-bounds -Maximal number of boundary endpoints of case ranges of switch statement. -For switch exceeding this limit, IPA-CP will not construct cloning cost -predicate, which is used to estimate cloning benefit, for default case -of the switch statement. - -@item ipa-max-param-expr-ops -IPA-CP will analyze conditional statement that references some function -parameter to estimate benefit for cloning upon certain constant value. -But if number of operations in a parameter expression exceeds -@option{ipa-max-param-expr-ops}, the expression is treated as complicated -one, and is not handled by IPA analysis. - -@item lto-partitions -Specify desired number of partitions produced during WHOPR compilation. -The number of partitions should exceed the number of CPUs used for compilation. - -@item lto-min-partition -Size of minimal partition for WHOPR (in estimated instructions). -This prevents expenses of splitting very small programs into too many -partitions. - -@item lto-max-partition -Size of max partition for WHOPR (in estimated instructions). -to provide an upper bound for individual size of partition. -Meant to be used only with balanced partitioning. - -@item lto-max-streaming-parallelism -Maximal number of parallel processes used for LTO streaming. - -@item cxx-max-namespaces-for-diagnostic-help -The maximum number of namespaces to consult for suggestions when C++ -name lookup fails for an identifier. - -@item sink-frequency-threshold -The maximum relative execution frequency (in percents) of the target block -relative to a statement's original block to allow statement sinking of a -statement. Larger numbers result in more aggressive statement sinking. -A small positive adjustment is applied for -statements with memory operands as those are even more profitable so sink. - -@item max-stores-to-sink -The maximum number of conditional store pairs that can be sunk. Set to 0 -if either vectorization (@option{-ftree-vectorize}) or if-conversion -(@option{-ftree-loop-if-convert}) is disabled. - -@item case-values-threshold -The smallest number of different values for which it is best to use a -jump-table instead of a tree of conditional branches. If the value is -0, use the default for the machine. - -@item jump-table-max-growth-ratio-for-size -The maximum code size growth ratio when expanding -into a jump table (in percent). The parameter is used when -optimizing for size. - -@item jump-table-max-growth-ratio-for-speed -The maximum code size growth ratio when expanding -into a jump table (in percent). The parameter is used when -optimizing for speed. - -@item tree-reassoc-width -Set the maximum number of instructions executed in parallel in -reassociated tree. This parameter overrides target dependent -heuristics used by default if has non zero value. - -@item sched-pressure-algorithm -Choose between the two available implementations of -@option{-fsched-pressure}. Algorithm 1 is the original implementation -and is the more likely to prevent instructions from being reordered. -Algorithm 2 was designed to be a compromise between the relatively -conservative approach taken by algorithm 1 and the rather aggressive -approach taken by the default scheduler. It relies more heavily on -having a regular register file and accurate register pressure classes. -See @file{haifa-sched.cc} in the GCC sources for more details. - -The default choice depends on the target. - -@item max-slsr-cand-scan -Set the maximum number of existing candidates that are considered when -seeking a basis for a new straight-line strength reduction candidate. - -@item asan-globals -Enable buffer overflow detection for global objects. This kind -of protection is enabled by default if you are using -@option{-fsanitize=address} option. -To disable global objects protection use @option{--param asan-globals=0}. - -@item asan-stack -Enable buffer overflow detection for stack objects. This kind of -protection is enabled by default when using @option{-fsanitize=address}. -To disable stack protection use @option{--param asan-stack=0} option. - -@item asan-instrument-reads -Enable buffer overflow detection for memory reads. This kind of -protection is enabled by default when using @option{-fsanitize=address}. -To disable memory reads protection use -@option{--param asan-instrument-reads=0}. - -@item asan-instrument-writes -Enable buffer overflow detection for memory writes. This kind of -protection is enabled by default when using @option{-fsanitize=address}. -To disable memory writes protection use -@option{--param asan-instrument-writes=0} option. - -@item asan-memintrin -Enable detection for built-in functions. This kind of protection -is enabled by default when using @option{-fsanitize=address}. -To disable built-in functions protection use -@option{--param asan-memintrin=0}. - -@item asan-use-after-return -Enable detection of use-after-return. This kind of protection -is enabled by default when using the @option{-fsanitize=address} option. -To disable it use @option{--param asan-use-after-return=0}. - -Note: By default the check is disabled at run time. To enable it, -add @code{detect_stack_use_after_return=1} to the environment variable -@env{ASAN_OPTIONS}. - -@item asan-instrumentation-with-call-threshold -If number of memory accesses in function being instrumented -is greater or equal to this number, use callbacks instead of inline checks. -E.g. to disable inline code use -@option{--param asan-instrumentation-with-call-threshold=0}. - -@item hwasan-instrument-stack -Enable hwasan instrumentation of statically sized stack-allocated variables. -This kind of instrumentation is enabled by default when using -@option{-fsanitize=hwaddress} and disabled by default when using -@option{-fsanitize=kernel-hwaddress}. -To disable stack instrumentation use -@option{--param hwasan-instrument-stack=0}, and to enable it use -@option{--param hwasan-instrument-stack=1}. - -@item hwasan-random-frame-tag -When using stack instrumentation, decide tags for stack variables using a -deterministic sequence beginning at a random tag for each frame. With this -parameter unset tags are chosen using the same sequence but beginning from 1. -This is enabled by default for @option{-fsanitize=hwaddress} and unavailable -for @option{-fsanitize=kernel-hwaddress}. -To disable it use @option{--param hwasan-random-frame-tag=0}. - -@item hwasan-instrument-allocas -Enable hwasan instrumentation of dynamically sized stack-allocated variables. -This kind of instrumentation is enabled by default when using -@option{-fsanitize=hwaddress} and disabled by default when using -@option{-fsanitize=kernel-hwaddress}. -To disable instrumentation of such variables use -@option{--param hwasan-instrument-allocas=0}, and to enable it use -@option{--param hwasan-instrument-allocas=1}. - -@item hwasan-instrument-reads -Enable hwasan checks on memory reads. Instrumentation of reads is enabled by -default for both @option{-fsanitize=hwaddress} and -@option{-fsanitize=kernel-hwaddress}. -To disable checking memory reads use -@option{--param hwasan-instrument-reads=0}. - -@item hwasan-instrument-writes -Enable hwasan checks on memory writes. Instrumentation of writes is enabled by -default for both @option{-fsanitize=hwaddress} and -@option{-fsanitize=kernel-hwaddress}. -To disable checking memory writes use -@option{--param hwasan-instrument-writes=0}. - -@item hwasan-instrument-mem-intrinsics -Enable hwasan instrumentation of builtin functions. Instrumentation of these -builtin functions is enabled by default for both @option{-fsanitize=hwaddress} -and @option{-fsanitize=kernel-hwaddress}. -To disable instrumentation of builtin functions use -@option{--param hwasan-instrument-mem-intrinsics=0}. - -@item use-after-scope-direct-emission-threshold -If the size of a local variable in bytes is smaller or equal to this -number, directly poison (or unpoison) shadow memory instead of using -run-time callbacks. - -@item tsan-distinguish-volatile -Emit special instrumentation for accesses to volatiles. - -@item tsan-instrument-func-entry-exit -Emit instrumentation calls to __tsan_func_entry() and __tsan_func_exit(). - -@item max-fsm-thread-path-insns -Maximum number of instructions to copy when duplicating blocks on a -finite state automaton jump thread path. - -@item threader-debug -threader-debug=[none|all] Enables verbose dumping of the threader solver. - -@item parloops-chunk-size -Chunk size of omp schedule for loops parallelized by parloops. - -@item parloops-schedule -Schedule type of omp schedule for loops parallelized by parloops (static, -dynamic, guided, auto, runtime). - -@item parloops-min-per-thread -The minimum number of iterations per thread of an innermost parallelized -loop for which the parallelized variant is preferred over the single threaded -one. Note that for a parallelized loop nest the -minimum number of iterations of the outermost loop per thread is two. - -@item max-ssa-name-query-depth -Maximum depth of recursion when querying properties of SSA names in things -like fold routines. One level of recursion corresponds to following a -use-def chain. - -@item max-speculative-devirt-maydefs -The maximum number of may-defs we analyze when looking for a must-def -specifying the dynamic type of an object that invokes a virtual call -we may be able to devirtualize speculatively. - -@item max-vrp-switch-assertions -The maximum number of assertions to add along the default edge of a switch -statement during VRP. - -@item evrp-sparse-threshold -Maximum number of basic blocks before EVRP uses a sparse cache. - -@item vrp1-mode -Specifies the mode VRP pass 1 should operate in. - -@item vrp2-mode -Specifies the mode VRP pass 2 should operate in. - -@item ranger-debug -Specifies the type of debug output to be issued for ranges. - -@item evrp-switch-limit -Specifies the maximum number of switch cases before EVRP ignores a switch. - -@item unroll-jam-min-percent -The minimum percentage of memory references that must be optimized -away for the unroll-and-jam transformation to be considered profitable. - -@item unroll-jam-max-unroll -The maximum number of times the outer loop should be unrolled by -the unroll-and-jam transformation. - -@item max-rtl-if-conversion-unpredictable-cost -Maximum permissible cost for the sequence that would be generated -by the RTL if-conversion pass for a branch that is considered unpredictable. - -@item max-variable-expansions-in-unroller -If @option{-fvariable-expansion-in-unroller} is used, the maximum number -of times that an individual variable will be expanded during loop unrolling. - -@item partial-inlining-entry-probability -Maximum probability of the entry BB of split region -(in percent relative to entry BB of the function) -to make partial inlining happen. - -@item max-tracked-strlens -Maximum number of strings for which strlen optimization pass will -track string lengths. - -@item gcse-after-reload-partial-fraction -The threshold ratio for performing partial redundancy -elimination after reload. - -@item gcse-after-reload-critical-fraction -The threshold ratio of critical edges execution count that -permit performing redundancy elimination after reload. - -@item max-loop-header-insns -The maximum number of insns in loop header duplicated -by the copy loop headers pass. - -@item vect-epilogues-nomask -Enable loop epilogue vectorization using smaller vector size. - -@item vect-partial-vector-usage -Controls when the loop vectorizer considers using partial vector loads -and stores as an alternative to falling back to scalar code. 0 stops -the vectorizer from ever using partial vector loads and stores. 1 allows -partial vector loads and stores if vectorization removes the need for the -code to iterate. 2 allows partial vector loads and stores in all loops. -The parameter only has an effect on targets that support partial -vector loads and stores. - -@item vect-inner-loop-cost-factor -The maximum factor which the loop vectorizer applies to the cost of statements -in an inner loop relative to the loop being vectorized. The factor applied -is the maximum of the estimated number of iterations of the inner loop and -this parameter. The default value of this parameter is 50. - -@item vect-induction-float -Enable loop vectorization of floating point inductions. - -@item avoid-fma-max-bits -Maximum number of bits for which we avoid creating FMAs. - -@item sms-loop-average-count-threshold -A threshold on the average loop count considered by the swing modulo scheduler. - -@item sms-dfa-history -The number of cycles the swing modulo scheduler considers when checking -conflicts using DFA. - -@item graphite-allow-codegen-errors -Whether codegen errors should be ICEs when @option{-fchecking}. - -@item sms-max-ii-factor -A factor for tuning the upper bound that swing modulo scheduler -uses for scheduling a loop. - -@item lra-max-considered-reload-pseudos -The max number of reload pseudos which are considered during -spilling a non-reload pseudo. - -@item max-pow-sqrt-depth -Maximum depth of sqrt chains to use when synthesizing exponentiation -by a real constant. - -@item max-dse-active-local-stores -Maximum number of active local stores in RTL dead store elimination. - -@item asan-instrument-allocas -Enable asan allocas/VLAs protection. - -@item max-iterations-computation-cost -Bound on the cost of an expression to compute the number of iterations. - -@item max-isl-operations -Maximum number of isl operations, 0 means unlimited. - -@item graphite-max-arrays-per-scop -Maximum number of arrays per scop. - -@item max-vartrack-reverse-op-size -Max. size of loc list for which reverse ops should be added. - -@item fsm-scale-path-stmts -Scale factor to apply to the number of statements in a threading path -when comparing to the number of (scaled) blocks. - -@item uninit-control-dep-attempts -Maximum number of nested calls to search for control dependencies -during uninitialized variable analysis. - -@item fsm-scale-path-blocks -Scale factor to apply to the number of blocks in a threading path -when comparing to the number of (scaled) statements. - -@item sched-autopref-queue-depth -Hardware autoprefetcher scheduler model control flag. -Number of lookahead cycles the model looks into; at ' -' only enable instruction sorting heuristic. - -@item loop-versioning-max-inner-insns -The maximum number of instructions that an inner loop can have -before the loop versioning pass considers it too big to copy. - -@item loop-versioning-max-outer-insns -The maximum number of instructions that an outer loop can have -before the loop versioning pass considers it too big to copy, -discounting any instructions in inner loops that directly benefit -from versioning. - -@item ssa-name-def-chain-limit -The maximum number of SSA_NAME assignments to follow in determining -a property of a variable such as its value. This limits the number -of iterations or recursive calls GCC performs when optimizing certain -statements or when determining their validity prior to issuing -diagnostics. - -@item store-merging-max-size -Maximum size of a single store merging region in bytes. - -@item hash-table-verification-limit -The number of elements for which hash table verification is done -for each searched element. - -@item max-find-base-term-values -Maximum number of VALUEs handled during a single find_base_term call. - -@item analyzer-max-enodes-per-program-point -The maximum number of exploded nodes per program point within -the analyzer, before terminating analysis of that point. - -@item analyzer-max-constraints -The maximum number of constraints per state. - -@item analyzer-min-snodes-for-call-summary -The minimum number of supernodes within a function for the -analyzer to consider summarizing its effects at call sites. - -@item analyzer-max-enodes-for-full-dump -The maximum depth of exploded nodes that should appear in a dot dump -before switching to a less verbose format. - -@item analyzer-max-recursion-depth -The maximum number of times a callsite can appear in a call stack -within the analyzer, before terminating analysis of a call that would -recurse deeper. - -@item analyzer-max-svalue-depth -The maximum depth of a symbolic value, before approximating -the value as unknown. - -@item analyzer-max-infeasible-edges -The maximum number of infeasible edges to reject before declaring -a diagnostic as infeasible. - -@item gimple-fe-computed-hot-bb-threshold -The number of executions of a basic block which is considered hot. -The parameter is used only in GIMPLE FE. - -@item analyzer-bb-explosion-factor -The maximum number of 'after supernode' exploded nodes within the analyzer -per supernode, before terminating analysis. - -@item ranger-logical-depth -Maximum depth of logical expression evaluation ranger will look through -when evaluating outgoing edge ranges. - -@item relation-block-limit -Maximum number of relations the oracle will register in a basic block. - -@item min-pagesize -Minimum page size for warning purposes. - -@item openacc-kernels -Specify mode of OpenACC `kernels' constructs handling. -With @option{--param=openacc-kernels=decompose}, OpenACC `kernels' -constructs are decomposed into parts, a sequence of compute -constructs, each then handled individually. -This is work in progress. -With @option{--param=openacc-kernels=parloops}, OpenACC `kernels' -constructs are handled by the @samp{parloops} pass, en bloc. -This is the current default. - -@item openacc-privatization -Specify mode of OpenACC privatization diagnostics for -@option{-fopt-info-omp-note} and applicable -@option{-fdump-tree-*-details}. -With @option{--param=openacc-privatization=quiet}, don't diagnose. -This is the current default. -With @option{--param=openacc-privatization=noisy}, do diagnose. - -@end table - -The following choices of @var{name} are available on AArch64 targets: - -@table @gcctabopt -@item aarch64-sve-compare-costs -When vectorizing for SVE, consider using ``unpacked'' vectors for -smaller elements and use the cost model to pick the cheapest approach. -Also use the cost model to choose between SVE and Advanced SIMD vectorization. - -Using unpacked vectors includes storing smaller elements in larger -containers and accessing elements with extending loads and truncating -stores. - -@item aarch64-float-recp-precision -The number of Newton iterations for calculating the reciprocal for float type. -The precision of division is proportional to this param when division -approximation is enabled. The default value is 1. - -@item aarch64-double-recp-precision -The number of Newton iterations for calculating the reciprocal for double type. -The precision of division is propotional to this param when division -approximation is enabled. The default value is 2. - -@item aarch64-autovec-preference -Force an ISA selection strategy for auto-vectorization. Accepts values from -0 to 4, inclusive. -@table @samp -@item 0 -Use the default heuristics. -@item 1 -Use only Advanced SIMD for auto-vectorization. -@item 2 -Use only SVE for auto-vectorization. -@item 3 -Use both Advanced SIMD and SVE. Prefer Advanced SIMD when the costs are -deemed equal. -@item 4 -Use both Advanced SIMD and SVE. Prefer SVE when the costs are deemed equal. -@end table -The default value is 0. - -@item aarch64-loop-vect-issue-rate-niters -The tuning for some AArch64 CPUs tries to take both latencies and issue -rates into account when deciding whether a loop should be vectorized -using SVE, vectorized using Advanced SIMD, or not vectorized at all. -If this parameter is set to @var{n}, GCC will not use this heuristic -for loops that are known to execute in fewer than @var{n} Advanced -SIMD iterations. - -@item aarch64-vect-unroll-limit -The vectorizer will use available tuning information to determine whether it -would be beneficial to unroll the main vectorized loop and by how much. This -parameter set's the upper bound of how much the vectorizer will unroll the main -loop. The default value is four. - -@end table - -The following choices of @var{name} are available on i386 and x86_64 targets: - -@table @gcctabopt -@item x86-stlf-window-ninsns -Instructions number above which STFL stall penalty can be compensated. - -@end table - -@end table - -@node Instrumentation Options -@section Program Instrumentation Options -@cindex instrumentation options -@cindex program instrumentation options -@cindex run-time error checking options -@cindex profiling options -@cindex options, program instrumentation -@cindex options, run-time error checking -@cindex options, profiling - -GCC supports a number of command-line options that control adding -run-time instrumentation to the code it normally generates. -For example, one purpose of instrumentation is collect profiling -statistics for use in finding program hot spots, code coverage -analysis, or profile-guided optimizations. -Another class of program instrumentation is adding run-time checking -to detect programming errors like invalid pointer -dereferences or out-of-bounds array accesses, as well as deliberately -hostile attacks such as stack smashing or C++ vtable hijacking. -There is also a general hook which can be used to implement other -forms of tracing or function-level instrumentation for debug or -program analysis purposes. - -@table @gcctabopt -@cindex @command{prof} -@cindex @command{gprof} -@item -p -@itemx -pg -@opindex p -@opindex pg -Generate extra code to write profile information suitable for the -analysis program @command{prof} (for @option{-p}) or @command{gprof} -(for @option{-pg}). You must use this option when compiling -the source files you want data about, and you must also use it when -linking. - -You can use the function attribute @code{no_instrument_function} to -suppress profiling of individual functions when compiling with these options. -@xref{Common Function Attributes}. - -@item -fprofile-arcs -@opindex fprofile-arcs -Add code so that program flow @dfn{arcs} are instrumented. During -execution the program records how many times each branch and call is -executed and how many times it is taken or returns. On targets that support -constructors with priority support, profiling properly handles constructors, -destructors and C++ constructors (and destructors) of classes which are used -as a type of a global variable. - -When the compiled -program exits it saves this data to a file called -@file{@var{auxname}.gcda} for each source file. The data may be used for -profile-directed optimizations (@option{-fbranch-probabilities}), or for -test coverage analysis (@option{-ftest-coverage}). Each object file's -@var{auxname} is generated from the name of the output file, if -explicitly specified and it is not the final executable, otherwise it is -the basename of the source file. In both cases any suffix is removed -(e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or -@file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}). - -Note that if a command line directly links source files, the corresponding -@var{.gcda} files will be prefixed with the unsuffixed name of the output file. -E.g. @code{gcc a.c b.c -o binary} would generate @file{binary-a.gcda} and -@file{binary-b.gcda} files. - -@xref{Cross-profiling}. - -@cindex @command{gcov} -@item --coverage -@opindex coverage - -This option is used to compile and link code instrumented for coverage -analysis. The option is a synonym for @option{-fprofile-arcs} -@option{-ftest-coverage} (when compiling) and @option{-lgcov} (when -linking). See the documentation for those options for more details. - -@itemize - -@item -Compile the source files with @option{-fprofile-arcs} plus optimization -and code generation options. For test coverage analysis, use the -additional @option{-ftest-coverage} option. You do not need to profile -every source file in a program. - -@item -Compile the source files additionally with @option{-fprofile-abs-path} -to create absolute path names in the @file{.gcno} files. This allows -@command{gcov} to find the correct sources in projects where compilations -occur with different working directories. - -@item -Link your object files with @option{-lgcov} or @option{-fprofile-arcs} -(the latter implies the former). - -@item -Run the program on a representative workload to generate the arc profile -information. This may be repeated any number of times. You can run -concurrent instances of your program, and provided that the file system -supports locking, the data files will be correctly updated. Unless -a strict ISO C dialect option is in effect, @code{fork} calls are -detected and correctly handled without double counting. - -Moreover, an object file can be recompiled multiple times -and the corresponding @file{.gcda} file merges as long as -the source file and the compiler options are unchanged. - -@item -For profile-directed optimizations, compile the source files again with -the same optimization and code generation options plus -@option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that -Control Optimization}). - -@item -For test coverage analysis, use @command{gcov} to produce human readable -information from the @file{.gcno} and @file{.gcda} files. Refer to the -@command{gcov} documentation for further information. - -@end itemize - -With @option{-fprofile-arcs}, for each function of your program GCC -creates a program flow graph, then finds a spanning tree for the graph. -Only arcs that are not on the spanning tree have to be instrumented: the -compiler adds code to count the number of times that these arcs are -executed. When an arc is the only exit or only entrance to a block, the -instrumentation code can be added to the block; otherwise, a new basic -block must be created to hold the instrumentation code. - -@need 2000 -@item -ftest-coverage -@opindex ftest-coverage -Produce a notes file that the @command{gcov} code-coverage utility -(@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to -show program coverage. Each source file's note file is called -@file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option -above for a description of @var{auxname} and instructions on how to -generate test coverage data. Coverage data matches the source files -more closely if you do not optimize. - -@item -fprofile-abs-path -@opindex fprofile-abs-path -Automatically convert relative source file names to absolute path names -in the @file{.gcno} files. This allows @command{gcov} to find the correct -sources in projects where compilations occur with different working -directories. - -@item -fprofile-dir=@var{path} -@opindex fprofile-dir - -Set the directory to search for the profile data files in to @var{path}. -This option affects only the profile data generated by -@option{-fprofile-generate}, @option{-ftest-coverage}, @option{-fprofile-arcs} -and used by @option{-fprofile-use} and @option{-fbranch-probabilities} -and its related options. Both absolute and relative paths can be used. -By default, GCC uses the current directory as @var{path}, thus the -profile data file appears in the same directory as the object file. -In order to prevent the file name clashing, if the object file name is -not an absolute path, we mangle the absolute path of the -@file{@var{sourcename}.gcda} file and use it as the file name of a -@file{.gcda} file. See details about the file naming in @option{-fprofile-arcs}. -See similar option @option{-fprofile-note}. - -When an executable is run in a massive parallel environment, it is recommended -to save profile to different folders. That can be done with variables -in @var{path} that are exported during run-time: - -@table @gcctabopt - -@item %p -process ID. - -@item %q@{VAR@} -value of environment variable @var{VAR} - -@end table - -@item -fprofile-generate -@itemx -fprofile-generate=@var{path} -@opindex fprofile-generate - -Enable options usually used for instrumenting application to produce -profile useful for later recompilation with profile feedback based -optimization. You must use @option{-fprofile-generate} both when -compiling and when linking your program. - -The following options are enabled: -@option{-fprofile-arcs}, @option{-fprofile-values}, -@option{-finline-functions}, and @option{-fipa-bit-cp}. - -If @var{path} is specified, GCC looks at the @var{path} to find -the profile feedback data files. See @option{-fprofile-dir}. - -To optimize the program based on the collected profile information, use -@option{-fprofile-use}. @xref{Optimize Options}, for more information. - -@item -fprofile-info-section -@itemx -fprofile-info-section=@var{name} -@opindex fprofile-info-section - -Register the profile information in the specified section instead of using a -constructor/destructor. The section name is @var{name} if it is specified, -otherwise the section name defaults to @code{.gcov_info}. A pointer to the -profile information generated by @option{-fprofile-arcs} is placed in the -specified section for each translation unit. This option disables the profile -information registration through a constructor and it disables the profile -information processing through a destructor. This option is not intended to be -used in hosted environments such as GNU/Linux. It targets freestanding -environments (for example embedded systems) with limited resources which do not -support constructors/destructors or the C library file I/O. - -The linker could collect the input sections in a continuous memory block and -define start and end symbols. A GNU linker script example which defines a -linker output section follows: - -@smallexample - .gcov_info : - @{ - PROVIDE (__gcov_info_start = .); - KEEP (*(.gcov_info)) - PROVIDE (__gcov_info_end = .); - @} -@end smallexample - -The program could dump the profiling information registered in this linker set -for example like this: - -@smallexample -#include <gcov.h> -#include <stdio.h> -#include <stdlib.h> - -extern const struct gcov_info *const __gcov_info_start[]; -extern const struct gcov_info *const __gcov_info_end[]; - -static void -dump (const void *d, unsigned n, void *arg) -@{ - const unsigned char *c = d; - - for (unsigned i = 0; i < n; ++i) - printf ("%02x", c[i]); -@} - -static void -filename (const char *f, void *arg) -@{ - __gcov_filename_to_gcfn (f, dump, arg ); -@} - -static void * -allocate (unsigned length, void *arg) -@{ - return malloc (length); -@} - -static void -dump_gcov_info (void) -@{ - const struct gcov_info *const *info = __gcov_info_start; - const struct gcov_info *const *end = __gcov_info_end; - - /* Obfuscate variable to prevent compiler optimizations. */ - __asm__ ("" : "+r" (info)); - - while (info != end) - @{ - void *arg = NULL; - __gcov_info_to_gcda (*info, filename, dump, allocate, arg); - putchar ('\n'); - ++info; - @} -@} - -int -main (void) -@{ - dump_gcov_info (); - return 0; -@} -@end smallexample - -The @command{merge-stream} subcommand of @command{gcov-tool} may be used to -deserialize the data stream generated by the @code{__gcov_filename_to_gcfn} and -@code{__gcov_info_to_gcda} functions and merge the profile information into -@file{.gcda} files on the host filesystem. - -@item -fprofile-note=@var{path} -@opindex fprofile-note - -If @var{path} is specified, GCC saves @file{.gcno} file into @var{path} -location. If you combine the option with multiple source files, -the @file{.gcno} file will be overwritten. - -@item -fprofile-prefix-path=@var{path} -@opindex fprofile-prefix-path - -This option can be used in combination with -@option{profile-generate=}@var{profile_dir} and -@option{profile-use=}@var{profile_dir} to inform GCC where is the base -directory of built source tree. By default @var{profile_dir} will contain -files with mangled absolute paths of all object files in the built project. -This is not desirable when directory used to build the instrumented binary -differs from the directory used to build the binary optimized with profile -feedback because the profile data will not be found during the optimized build. -In such setups @option{-fprofile-prefix-path=}@var{path} with @var{path} -pointing to the base directory of the build can be used to strip the irrelevant -part of the path and keep all file names relative to the main build directory. - -@item -fprofile-prefix-map=@var{old}=@var{new} -@opindex fprofile-prefix-map -When compiling files residing in directory @file{@var{old}}, record -profiling information (with @option{--coverage}) -describing them as if the files resided in -directory @file{@var{new}} instead. -See also @option{-ffile-prefix-map}. - -@item -fprofile-update=@var{method} -@opindex fprofile-update - -Alter the update method for an application instrumented for profile -feedback based optimization. The @var{method} argument should be one of -@samp{single}, @samp{atomic} or @samp{prefer-atomic}. -The first one is useful for single-threaded applications, -while the second one prevents profile corruption by emitting thread-safe code. - -@strong{Warning:} When an application does not properly join all threads -(or creates an detached thread), a profile file can be still corrupted. - -Using @samp{prefer-atomic} would be transformed either to @samp{atomic}, -when supported by a target, or to @samp{single} otherwise. The GCC driver -automatically selects @samp{prefer-atomic} when @option{-pthread} -is present in the command line. - -@item -fprofile-filter-files=@var{regex} -@opindex fprofile-filter-files - -Instrument only functions from files whose name matches -any of the regular expressions (separated by semi-colons). - -For example, @option{-fprofile-filter-files=main\.c;module.*\.c} will instrument -only @file{main.c} and all C files starting with 'module'. - -@item -fprofile-exclude-files=@var{regex} -@opindex fprofile-exclude-files - -Instrument only functions from files whose name does not match -any of the regular expressions (separated by semi-colons). - -For example, @option{-fprofile-exclude-files=/usr/.*} will prevent instrumentation -of all files that are located in the @file{/usr/} folder. - -@item -fprofile-reproducible=@r{[}multithreaded@r{|}parallel-runs@r{|}serial@r{]} -@opindex fprofile-reproducible -Control level of reproducibility of profile gathered by -@code{-fprofile-generate}. This makes it possible to rebuild program -with same outcome which is useful, for example, for distribution -packages. - -With @option{-fprofile-reproducible=serial} the profile gathered by -@option{-fprofile-generate} is reproducible provided the trained program -behaves the same at each invocation of the train run, it is not -multi-threaded and profile data streaming is always done in the same -order. Note that profile streaming happens at the end of program run but -also before @code{fork} function is invoked. - -Note that it is quite common that execution counts of some part of -programs depends, for example, on length of temporary file names or -memory space randomization (that may affect hash-table collision rate). -Such non-reproducible part of programs may be annotated by -@code{no_instrument_function} function attribute. @command{gcov-dump} with -@option{-l} can be used to dump gathered data and verify that they are -indeed reproducible. - -With @option{-fprofile-reproducible=parallel-runs} collected profile -stays reproducible regardless the order of streaming of the data into -gcda files. This setting makes it possible to run multiple instances of -instrumented program in parallel (such as with @code{make -j}). This -reduces quality of gathered data, in particular of indirect call -profiling. - -@item -fsanitize=address -@opindex fsanitize=address -Enable AddressSanitizer, a fast memory error detector. -Memory access instructions are instrumented to detect -out-of-bounds and use-after-free bugs. -The option enables @option{-fsanitize-address-use-after-scope}. -See @uref{https://github.com/google/sanitizers/wiki/AddressSanitizer} for -more details. The run-time behavior can be influenced using the -@env{ASAN_OPTIONS} environment variable. When set to @code{help=1}, -the available options are shown at startup of the instrumented program. See -@url{https://github.com/google/sanitizers/wiki/AddressSanitizerFlags#run-time-flags} -for a list of supported options. -The option cannot be combined with @option{-fsanitize=thread} or -@option{-fsanitize=hwaddress}. Note that the only target -@option{-fsanitize=hwaddress} is currently supported on is AArch64. - -@item -fsanitize=kernel-address -@opindex fsanitize=kernel-address -Enable AddressSanitizer for Linux kernel. -See @uref{https://github.com/google/kasan} for more details. - -@item -fsanitize=hwaddress -@opindex fsanitize=hwaddress -Enable Hardware-assisted AddressSanitizer, which uses a hardware ability to -ignore the top byte of a pointer to allow the detection of memory errors with -a low memory overhead. -Memory access instructions are instrumented to detect out-of-bounds and -use-after-free bugs. -The option enables @option{-fsanitize-address-use-after-scope}. -See -@uref{https://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html} -for more details. The run-time behavior can be influenced using the -@env{HWASAN_OPTIONS} environment variable. When set to @code{help=1}, -the available options are shown at startup of the instrumented program. -The option cannot be combined with @option{-fsanitize=thread} or -@option{-fsanitize=address}, and is currently only available on AArch64. - -@item -fsanitize=kernel-hwaddress -@opindex fsanitize=kernel-hwaddress -Enable Hardware-assisted AddressSanitizer for compilation of the Linux kernel. -Similar to @option{-fsanitize=kernel-address} but using an alternate -instrumentation method, and similar to @option{-fsanitize=hwaddress} but with -instrumentation differences necessary for compiling the Linux kernel. -These differences are to avoid hwasan library initialization calls and to -account for the stack pointer having a different value in its top byte. - -@emph{Note:} This option has different defaults to the @option{-fsanitize=hwaddress}. -Instrumenting the stack and alloca calls are not on by default but are still -possible by specifying the command-line options -@option{--param hwasan-instrument-stack=1} and -@option{--param hwasan-instrument-allocas=1} respectively. Using a random frame -tag is not implemented for kernel instrumentation. - -@item -fsanitize=pointer-compare -@opindex fsanitize=pointer-compare -Instrument comparison operation (<, <=, >, >=) with pointer operands. -The option must be combined with either @option{-fsanitize=kernel-address} or -@option{-fsanitize=address} -The option cannot be combined with @option{-fsanitize=thread}. -Note: By default the check is disabled at run time. To enable it, -add @code{detect_invalid_pointer_pairs=2} to the environment variable -@env{ASAN_OPTIONS}. Using @code{detect_invalid_pointer_pairs=1} detects -invalid operation only when both pointers are non-null. - -@item -fsanitize=pointer-subtract -@opindex fsanitize=pointer-subtract -Instrument subtraction with pointer operands. -The option must be combined with either @option{-fsanitize=kernel-address} or -@option{-fsanitize=address} -The option cannot be combined with @option{-fsanitize=thread}. -Note: By default the check is disabled at run time. To enable it, -add @code{detect_invalid_pointer_pairs=2} to the environment variable -@env{ASAN_OPTIONS}. Using @code{detect_invalid_pointer_pairs=1} detects -invalid operation only when both pointers are non-null. - -@item -fsanitize=shadow-call-stack -@opindex fsanitize=shadow-call-stack -Enable ShadowCallStack, a security enhancement mechanism used to protect -programs against return address overwrites (e.g. stack buffer overflows.) -It works by saving a function's return address to a separately allocated -shadow call stack in the function prologue and restoring the return address -from the shadow call stack in the function epilogue. Instrumentation only -occurs in functions that need to save the return address to the stack. - -Currently it only supports the aarch64 platform. It is specifically -designed for linux kernels that enable the CONFIG_SHADOW_CALL_STACK option. -For the user space programs, runtime support is not currently provided -in libc and libgcc. Users who want to use this feature in user space need -to provide their own support for the runtime. It should be noted that -this may cause the ABI rules to be broken. - -On aarch64, the instrumentation makes use of the platform register @code{x18}. -This generally means that any code that may run on the same thread as code -compiled with ShadowCallStack must be compiled with the flag -@option{-ffixed-x18}, otherwise functions compiled without -@option{-ffixed-x18} might clobber @code{x18} and so corrupt the shadow -stack pointer. - -Also, because there is no userspace runtime support, code compiled with -ShadowCallStack cannot use exception handling. Use @option{-fno-exceptions} -to turn off exceptions. - -See @uref{https://clang.llvm.org/docs/ShadowCallStack.html} for more -details. - -@item -fsanitize=thread -@opindex fsanitize=thread -Enable ThreadSanitizer, a fast data race detector. -Memory access instructions are instrumented to detect -data race bugs. See @uref{https://github.com/google/sanitizers/wiki#threadsanitizer} for more -details. The run-time behavior can be influenced using the @env{TSAN_OPTIONS} -environment variable; see -@url{https://github.com/google/sanitizers/wiki/ThreadSanitizerFlags} for a list of -supported options. -The option cannot be combined with @option{-fsanitize=address}, -@option{-fsanitize=leak}. - -Note that sanitized atomic builtins cannot throw exceptions when -operating on invalid memory addresses with non-call exceptions -(@option{-fnon-call-exceptions}). - -@item -fsanitize=leak -@opindex fsanitize=leak -Enable LeakSanitizer, a memory leak detector. -This option only matters for linking of executables and -the executable is linked against a library that overrides @code{malloc} -and other allocator functions. See -@uref{https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer} for more -details. The run-time behavior can be influenced using the -@env{LSAN_OPTIONS} environment variable. -The option cannot be combined with @option{-fsanitize=thread}. - -@item -fsanitize=undefined -@opindex fsanitize=undefined -Enable UndefinedBehaviorSanitizer, a fast undefined behavior detector. -Various computations are instrumented to detect undefined behavior -at runtime. See @uref{https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html} for more details. The run-time behavior can be influenced using the -@env{UBSAN_OPTIONS} environment variable. Current suboptions are: - -@table @gcctabopt - -@item -fsanitize=shift -@opindex fsanitize=shift -This option enables checking that the result of a shift operation is -not undefined. Note that what exactly is considered undefined differs -slightly between C and C++, as well as between ISO C90 and C99, etc. -This option has two suboptions, @option{-fsanitize=shift-base} and -@option{-fsanitize=shift-exponent}. - -@item -fsanitize=shift-exponent -@opindex fsanitize=shift-exponent -This option enables checking that the second argument of a shift operation -is not negative and is smaller than the precision of the promoted first -argument. - -@item -fsanitize=shift-base -@opindex fsanitize=shift-base -If the second argument of a shift operation is within range, check that the -result of a shift operation is not undefined. Note that what exactly is -considered undefined differs slightly between C and C++, as well as between -ISO C90 and C99, etc. - -@item -fsanitize=integer-divide-by-zero -@opindex fsanitize=integer-divide-by-zero -Detect integer division by zero. - -@item -fsanitize=unreachable -@opindex fsanitize=unreachable -With this option, the compiler turns the @code{__builtin_unreachable} -call into a diagnostics message call instead. When reaching the -@code{__builtin_unreachable} call, the behavior is undefined. - -@item -fsanitize=vla-bound -@opindex fsanitize=vla-bound -This option instructs the compiler to check that the size of a variable -length array is positive. - -@item -fsanitize=null -@opindex fsanitize=null -This option enables pointer checking. Particularly, the application -built with this option turned on will issue an error message when it -tries to dereference a NULL pointer, or if a reference (possibly an -rvalue reference) is bound to a NULL pointer, or if a method is invoked -on an object pointed by a NULL pointer. - -@item -fsanitize=return -@opindex fsanitize=return -This option enables return statement checking. Programs -built with this option turned on will issue an error message -when the end of a non-void function is reached without actually -returning a value. This option works in C++ only. - -@item -fsanitize=signed-integer-overflow -@opindex fsanitize=signed-integer-overflow -This option enables signed integer overflow checking. We check that -the result of @code{+}, @code{*}, and both unary and binary @code{-} -does not overflow in the signed arithmetics. This also detects -@code{INT_MIN / -1} signed division. Note, integer promotion -rules must be taken into account. That is, the following is not an -overflow: -@smallexample -signed char a = SCHAR_MAX; -a++; -@end smallexample - -@item -fsanitize=bounds -@opindex fsanitize=bounds -This option enables instrumentation of array bounds. Various out of bounds -accesses are detected. Flexible array members, flexible array member-like -arrays, and initializers of variables with static storage are not instrumented. - -@item -fsanitize=bounds-strict -@opindex fsanitize=bounds-strict -This option enables strict instrumentation of array bounds. Most out of bounds -accesses are detected, including flexible array members and flexible array -member-like arrays. Initializers of variables with static storage are not -instrumented. - -@item -fsanitize=alignment -@opindex fsanitize=alignment - -This option enables checking of alignment of pointers when they are -dereferenced, or when a reference is bound to insufficiently aligned target, -or when a method or constructor is invoked on insufficiently aligned object. - -@item -fsanitize=object-size -@opindex fsanitize=object-size -This option enables instrumentation of memory references using the -@code{__builtin_object_size} function. Various out of bounds pointer -accesses are detected. - -@item -fsanitize=float-divide-by-zero -@opindex fsanitize=float-divide-by-zero -Detect floating-point division by zero. Unlike other similar options, -@option{-fsanitize=float-divide-by-zero} is not enabled by -@option{-fsanitize=undefined}, since floating-point division by zero can -be a legitimate way of obtaining infinities and NaNs. - -@item -fsanitize=float-cast-overflow -@opindex fsanitize=float-cast-overflow -This option enables floating-point type to integer conversion checking. -We check that the result of the conversion does not overflow. -Unlike other similar options, @option{-fsanitize=float-cast-overflow} is -not enabled by @option{-fsanitize=undefined}. -This option does not work well with @code{FE_INVALID} exceptions enabled. - -@item -fsanitize=nonnull-attribute -@opindex fsanitize=nonnull-attribute - -This option enables instrumentation of calls, checking whether null values -are not passed to arguments marked as requiring a non-null value by the -@code{nonnull} function attribute. - -@item -fsanitize=returns-nonnull-attribute -@opindex fsanitize=returns-nonnull-attribute - -This option enables instrumentation of return statements in functions -marked with @code{returns_nonnull} function attribute, to detect returning -of null values from such functions. - -@item -fsanitize=bool -@opindex fsanitize=bool - -This option enables instrumentation of loads from bool. If a value other -than 0/1 is loaded, a run-time error is issued. - -@item -fsanitize=enum -@opindex fsanitize=enum - -This option enables instrumentation of loads from an enum type. If -a value outside the range of values for the enum type is loaded, -a run-time error is issued. - -@item -fsanitize=vptr -@opindex fsanitize=vptr - -This option enables instrumentation of C++ member function calls, member -accesses and some conversions between pointers to base and derived classes, -to verify the referenced object has the correct dynamic type. - -@item -fsanitize=pointer-overflow -@opindex fsanitize=pointer-overflow - -This option enables instrumentation of pointer arithmetics. If the pointer -arithmetics overflows, a run-time error is issued. - -@item -fsanitize=builtin -@opindex fsanitize=builtin - -This option enables instrumentation of arguments to selected builtin -functions. If an invalid value is passed to such arguments, a run-time -error is issued. E.g.@ passing 0 as the argument to @code{__builtin_ctz} -or @code{__builtin_clz} invokes undefined behavior and is diagnosed -by this option. - -@end table - -Note that sanitizers tend to increase the rate of false positive -warnings, most notably those around @option{-Wmaybe-uninitialized}. -We recommend against combining @option{-Werror} and [the use of] -sanitizers. - -While @option{-ftrapv} causes traps for signed overflows to be emitted, -@option{-fsanitize=undefined} gives a diagnostic message. -This currently works only for the C family of languages. - -@item -fno-sanitize=all -@opindex fno-sanitize=all - -This option disables all previously enabled sanitizers. -@option{-fsanitize=all} is not allowed, as some sanitizers cannot be used -together. - -@item -fasan-shadow-offset=@var{number} -@opindex fasan-shadow-offset -This option forces GCC to use custom shadow offset in AddressSanitizer checks. -It is useful for experimenting with different shadow memory layouts in -Kernel AddressSanitizer. - -@item -fsanitize-sections=@var{s1},@var{s2},... -@opindex fsanitize-sections -Sanitize global variables in selected user-defined sections. @var{si} may -contain wildcards. - -@item -fsanitize-recover@r{[}=@var{opts}@r{]} -@opindex fsanitize-recover -@opindex fno-sanitize-recover -@option{-fsanitize-recover=} controls error recovery mode for sanitizers -mentioned in comma-separated list of @var{opts}. Enabling this option -for a sanitizer component causes it to attempt to continue -running the program as if no error happened. This means multiple -runtime errors can be reported in a single program run, and the exit -code of the program may indicate success even when errors -have been reported. The @option{-fno-sanitize-recover=} option -can be used to alter -this behavior: only the first detected error is reported -and program then exits with a non-zero exit code. - -Currently this feature only works for @option{-fsanitize=undefined} (and its suboptions -except for @option{-fsanitize=unreachable} and @option{-fsanitize=return}), -@option{-fsanitize=float-cast-overflow}, @option{-fsanitize=float-divide-by-zero}, -@option{-fsanitize=bounds-strict}, -@option{-fsanitize=kernel-address} and @option{-fsanitize=address}. -For these sanitizers error recovery is turned on by default, -except @option{-fsanitize=address}, for which this feature is experimental. -@option{-fsanitize-recover=all} and @option{-fno-sanitize-recover=all} is also -accepted, the former enables recovery for all sanitizers that support it, -the latter disables recovery for all sanitizers that support it. - -Even if a recovery mode is turned on the compiler side, it needs to be also -enabled on the runtime library side, otherwise the failures are still fatal. -The runtime library defaults to @code{halt_on_error=0} for -ThreadSanitizer and UndefinedBehaviorSanitizer, while default value for -AddressSanitizer is @code{halt_on_error=1}. This can be overridden through -setting the @code{halt_on_error} flag in the corresponding environment variable. - -Syntax without an explicit @var{opts} parameter is deprecated. It is -equivalent to specifying an @var{opts} list of: - -@smallexample -undefined,float-cast-overflow,float-divide-by-zero,bounds-strict -@end smallexample - -@item -fsanitize-address-use-after-scope -@opindex fsanitize-address-use-after-scope -Enable sanitization of local variables to detect use-after-scope bugs. -The option sets @option{-fstack-reuse} to @samp{none}. - -@item -fsanitize-trap@r{[}=@var{opts}@r{]} -@opindex fsanitize-trap -@opindex fno-sanitize-trap -The @option{-fsanitize-trap=} option instructs the compiler to -report for sanitizers mentioned in comma-separated list of @var{opts} -undefined behavior using @code{__builtin_trap} rather than a @code{libubsan} -library routine. If this option is enabled for certain sanitizer, -it takes precedence over the @option{-fsanitizer-recover=} for that -sanitizer, @code{__builtin_trap} will be emitted and be fatal regardless -of whether recovery is enabled or disabled using @option{-fsanitize-recover=}. - -The advantage of this is that the @code{libubsan} library is not needed -and is not linked in, so this is usable even in freestanding environments. - -Currently this feature works with @option{-fsanitize=undefined} (and its suboptions -except for @option{-fsanitize=vptr}), @option{-fsanitize=float-cast-overflow}, -@option{-fsanitize=float-divide-by-zero} and -@option{-fsanitize=bounds-strict}. @code{-fsanitize-trap=all} can be also -specified, which enables it for @code{undefined} suboptions, -@option{-fsanitize=float-cast-overflow}, -@option{-fsanitize=float-divide-by-zero} and -@option{-fsanitize=bounds-strict}. -If @code{-fsanitize-trap=undefined} or @code{-fsanitize-trap=all} is used -and @code{-fsanitize=vptr} is enabled on the command line, the -instrumentation is silently ignored as the instrumentation always needs -@code{libubsan} support, @option{-fsanitize-trap=vptr} is not allowed. - -@item -fsanitize-undefined-trap-on-error -@opindex fsanitize-undefined-trap-on-error -The @option{-fsanitize-undefined-trap-on-error} option is deprecated -equivalent of @option{-fsanitize-trap=all}. - -@item -fsanitize-coverage=trace-pc -@opindex fsanitize-coverage=trace-pc -Enable coverage-guided fuzzing code instrumentation. -Inserts a call to @code{__sanitizer_cov_trace_pc} into every basic block. - -@item -fsanitize-coverage=trace-cmp -@opindex fsanitize-coverage=trace-cmp -Enable dataflow guided fuzzing code instrumentation. -Inserts a call to @code{__sanitizer_cov_trace_cmp1}, -@code{__sanitizer_cov_trace_cmp2}, @code{__sanitizer_cov_trace_cmp4} or -@code{__sanitizer_cov_trace_cmp8} for integral comparison with both operands -variable or @code{__sanitizer_cov_trace_const_cmp1}, -@code{__sanitizer_cov_trace_const_cmp2}, -@code{__sanitizer_cov_trace_const_cmp4} or -@code{__sanitizer_cov_trace_const_cmp8} for integral comparison with one -operand constant, @code{__sanitizer_cov_trace_cmpf} or -@code{__sanitizer_cov_trace_cmpd} for float or double comparisons and -@code{__sanitizer_cov_trace_switch} for switch statements. - -@item -fcf-protection=@r{[}full@r{|}branch@r{|}return@r{|}none@r{|}check@r{]} -@opindex fcf-protection -Enable code instrumentation of control-flow transfers to increase -program security by checking that target addresses of control-flow -transfer instructions (such as indirect function call, function return, -indirect jump) are valid. This prevents diverting the flow of control -to an unexpected target. This is intended to protect against such -threats as Return-oriented Programming (ROP), and similarly -call/jmp-oriented programming (COP/JOP). - -The value @code{branch} tells the compiler to implement checking of -validity of control-flow transfer at the point of indirect branch -instructions, i.e.@: call/jmp instructions. The value @code{return} -implements checking of validity at the point of returning from a -function. The value @code{full} is an alias for specifying both -@code{branch} and @code{return}. The value @code{none} turns off -instrumentation. - -The value @code{check} is used for the final link with link-time -optimization (LTO). An error is issued if LTO object files are -compiled with different @option{-fcf-protection} values. The -value @code{check} is ignored at the compile time. - -The macro @code{__CET__} is defined when @option{-fcf-protection} is -used. The first bit of @code{__CET__} is set to 1 for the value -@code{branch} and the second bit of @code{__CET__} is set to 1 for -the @code{return}. - -You can also use the @code{nocf_check} attribute to identify -which functions and calls should be skipped from instrumentation -(@pxref{Function Attributes}). - -Currently the x86 GNU/Linux target provides an implementation based -on Intel Control-flow Enforcement Technology (CET) which works for -i686 processor or newer. - -@item -fharden-compares -@opindex fharden-compares -For every logical test that survives gimple optimizations and is -@emph{not} the condition in a conditional branch (for example, -conditions tested for conditional moves, or to store in boolean -variables), emit extra code to compute and verify the reversed -condition, and to call @code{__builtin_trap} if the results do not -match. Use with @samp{-fharden-conditional-branches} to cover all -conditionals. - -@item -fharden-conditional-branches -@opindex fharden-conditional-branches -For every non-vectorized conditional branch that survives gimple -optimizations, emit extra code to compute and verify the reversed -condition, and to call @code{__builtin_trap} if the result is -unexpected. Use with @samp{-fharden-compares} to cover all -conditionals. - -@item -fstack-protector -@opindex fstack-protector -Emit extra code to check for buffer overflows, such as stack smashing -attacks. This is done by adding a guard variable to functions with -vulnerable objects. This includes functions that call @code{alloca}, and -functions with buffers larger than or equal to 8 bytes. The guards are -initialized when a function is entered and then checked when the function -exits. If a guard check fails, an error message is printed and the program -exits. Only variables that are actually allocated on the stack are -considered, optimized away variables or variables allocated in registers -don't count. - -@item -fstack-protector-all -@opindex fstack-protector-all -Like @option{-fstack-protector} except that all functions are protected. - -@item -fstack-protector-strong -@opindex fstack-protector-strong -Like @option{-fstack-protector} but includes additional functions to -be protected --- those that have local array definitions, or have -references to local frame addresses. Only variables that are actually -allocated on the stack are considered, optimized away variables or variables -allocated in registers don't count. - -@item -fstack-protector-explicit -@opindex fstack-protector-explicit -Like @option{-fstack-protector} but only protects those functions which -have the @code{stack_protect} attribute. - -@item -fstack-check -@opindex fstack-check -Generate code to verify that you do not go beyond the boundary of the -stack. You should specify this flag if you are running in an -environment with multiple threads, but you only rarely need to specify it in -a single-threaded environment since stack overflow is automatically -detected on nearly all systems if there is only one stack. - -Note that this switch does not actually cause checking to be done; the -operating system or the language runtime must do that. The switch causes -generation of code to ensure that they see the stack being extended. - -You can additionally specify a string parameter: @samp{no} means no -checking, @samp{generic} means force the use of old-style checking, -@samp{specific} means use the best checking method and is equivalent -to bare @option{-fstack-check}. - -Old-style checking is a generic mechanism that requires no specific -target support in the compiler but comes with the following drawbacks: - -@enumerate -@item -Modified allocation strategy for large objects: they are always -allocated dynamically if their size exceeds a fixed threshold. Note this -may change the semantics of some code. - -@item -Fixed limit on the size of the static frame of functions: when it is -topped by a particular function, stack checking is not reliable and -a warning is issued by the compiler. - -@item -Inefficiency: because of both the modified allocation strategy and the -generic implementation, code performance is hampered. -@end enumerate - -Note that old-style stack checking is also the fallback method for -@samp{specific} if no target support has been added in the compiler. - -@samp{-fstack-check=} is designed for Ada's needs to detect infinite recursion -and stack overflows. @samp{specific} is an excellent choice when compiling -Ada code. It is not generally sufficient to protect against stack-clash -attacks. To protect against those you want @samp{-fstack-clash-protection}. - -@item -fstack-clash-protection -@opindex fstack-clash-protection -Generate code to prevent stack clash style attacks. When this option is -enabled, the compiler will only allocate one page of stack space at a time -and each page is accessed immediately after allocation. Thus, it prevents -allocations from jumping over any stack guard page provided by the -operating system. - -Most targets do not fully support stack clash protection. However, on -those targets @option{-fstack-clash-protection} will protect dynamic stack -allocations. @option{-fstack-clash-protection} may also provide limited -protection for static stack allocations if the target supports -@option{-fstack-check=specific}. - -@item -fstack-limit-register=@var{reg} -@itemx -fstack-limit-symbol=@var{sym} -@itemx -fno-stack-limit -@opindex fstack-limit-register -@opindex fstack-limit-symbol -@opindex fno-stack-limit -Generate code to ensure that the stack does not grow beyond a certain value, -either the value of a register or the address of a symbol. If a larger -stack is required, a signal is raised at run time. For most targets, -the signal is raised before the stack overruns the boundary, so -it is possible to catch the signal without taking special precautions. - -For instance, if the stack starts at absolute address @samp{0x80000000} -and grows downwards, you can use the flags -@option{-fstack-limit-symbol=__stack_limit} and -@option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit -of 128KB@. Note that this may only work with the GNU linker. - -You can locally override stack limit checking by using the -@code{no_stack_limit} function attribute (@pxref{Function Attributes}). - -@item -fsplit-stack -@opindex fsplit-stack -Generate code to automatically split the stack before it overflows. -The resulting program has a discontiguous stack which can only -overflow if the program is unable to allocate any more memory. This -is most useful when running threaded programs, as it is no longer -necessary to calculate a good stack size to use for each thread. This -is currently only implemented for the x86 targets running -GNU/Linux. - -When code compiled with @option{-fsplit-stack} calls code compiled -without @option{-fsplit-stack}, there may not be much stack space -available for the latter code to run. If compiling all code, -including library code, with @option{-fsplit-stack} is not an option, -then the linker can fix up these calls so that the code compiled -without @option{-fsplit-stack} always has a large stack. Support for -this is implemented in the gold linker in GNU binutils release 2.21 -and later. - -@item -fvtable-verify=@r{[}std@r{|}preinit@r{|}none@r{]} -@opindex fvtable-verify -This option is only available when compiling C++ code. -It turns on (or off, if using @option{-fvtable-verify=none}) the security -feature that verifies at run time, for every virtual call, that -the vtable pointer through which the call is made is valid for the type of -the object, and has not been corrupted or overwritten. If an invalid vtable -pointer is detected at run time, an error is reported and execution of the -program is immediately halted. - -This option causes run-time data structures to be built at program startup, -which are used for verifying the vtable pointers. -The options @samp{std} and @samp{preinit} -control the timing of when these data structures are built. In both cases the -data structures are built before execution reaches @code{main}. Using -@option{-fvtable-verify=std} causes the data structures to be built after -shared libraries have been loaded and initialized. -@option{-fvtable-verify=preinit} causes them to be built before shared -libraries have been loaded and initialized. - -If this option appears multiple times in the command line with different -values specified, @samp{none} takes highest priority over both @samp{std} and -@samp{preinit}; @samp{preinit} takes priority over @samp{std}. - -@item -fvtv-debug -@opindex fvtv-debug -When used in conjunction with @option{-fvtable-verify=std} or -@option{-fvtable-verify=preinit}, causes debug versions of the -runtime functions for the vtable verification feature to be called. -This flag also causes the compiler to log information about which -vtable pointers it finds for each class. -This information is written to a file named @file{vtv_set_ptr_data.log} -in the directory named by the environment variable @env{VTV_LOGS_DIR} -if that is defined or the current working directory otherwise. - -Note: This feature @emph{appends} data to the log file. If you want a fresh log -file, be sure to delete any existing one. - -@item -fvtv-counts -@opindex fvtv-counts -This is a debugging flag. When used in conjunction with -@option{-fvtable-verify=std} or @option{-fvtable-verify=preinit}, this -causes the compiler to keep track of the total number of virtual calls -it encounters and the number of verifications it inserts. It also -counts the number of calls to certain run-time library functions -that it inserts and logs this information for each compilation unit. -The compiler writes this information to a file named -@file{vtv_count_data.log} in the directory named by the environment -variable @env{VTV_LOGS_DIR} if that is defined or the current working -directory otherwise. It also counts the size of the vtable pointer sets -for each class, and writes this information to @file{vtv_class_set_sizes.log} -in the same directory. - -Note: This feature @emph{appends} data to the log files. To get fresh log -files, be sure to delete any existing ones. - -@item -finstrument-functions -@opindex finstrument-functions -Generate instrumentation calls for entry and exit to functions. Just -after function entry and just before function exit, the following -profiling functions are called with the address of the current -function and its call site. (On some platforms, -@code{__builtin_return_address} does not work beyond the current -function, so the call site information may not be available to the -profiling functions otherwise.) - -@smallexample -void __cyg_profile_func_enter (void *this_fn, - void *call_site); -void __cyg_profile_func_exit (void *this_fn, - void *call_site); -@end smallexample - -The first argument is the address of the start of the current function, -which may be looked up exactly in the symbol table. - -This instrumentation is also done for functions expanded inline in other -functions. The profiling calls indicate where, conceptually, the -inline function is entered and exited. This means that addressable -versions of such functions must be available. If all your uses of a -function are expanded inline, this may mean an additional expansion of -code size. If you use @code{extern inline} in your C code, an -addressable version of such functions must be provided. (This is -normally the case anyway, but if you get lucky and the optimizer always -expands the functions inline, you might have gotten away without -providing static copies.) - -A function may be given the attribute @code{no_instrument_function}, in -which case this instrumentation is not done. This can be used, for -example, for the profiling functions listed above, high-priority -interrupt routines, and any functions from which the profiling functions -cannot safely be called (perhaps signal handlers, if the profiling -routines generate output or allocate memory). -@xref{Common Function Attributes}. - -@item -finstrument-functions-once -@opindex -finstrument-functions-once -This is similar to @option{-finstrument-functions}, but the profiling -functions are called only once per instrumented function, i.e. the first -profiling function is called after the first entry into the instrumented -function and the second profiling function is called before the exit -corresponding to this first entry. - -The definition of @code{once} for the purpose of this option is a little -vague because the implementation is not protected against data races. -As a result, the implementation only guarantees that the profiling -functions are called at @emph{least} once per process and at @emph{most} -once per thread, but the calls are always paired, that is to say, if a -thread calls the first function, then it will call the second function, -unless it never reaches the exit of the instrumented function. - -@item -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{} -@opindex finstrument-functions-exclude-file-list - -Set the list of functions that are excluded from instrumentation (see -the description of @option{-finstrument-functions}). If the file that -contains a function definition matches with one of @var{file}, then -that function is not instrumented. The match is done on substrings: -if the @var{file} parameter is a substring of the file name, it is -considered to be a match. - -For example: - -@smallexample --finstrument-functions-exclude-file-list=/bits/stl,include/sys -@end smallexample - -@noindent -excludes any inline function defined in files whose pathnames -contain @file{/bits/stl} or @file{include/sys}. - -If, for some reason, you want to include letter @samp{,} in one of -@var{sym}, write @samp{\,}. For example, -@option{-finstrument-functions-exclude-file-list='\,\,tmp'} -(note the single quote surrounding the option). - -@item -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} -@opindex finstrument-functions-exclude-function-list - -This is similar to @option{-finstrument-functions-exclude-file-list}, -but this option sets the list of function names to be excluded from -instrumentation. The function name to be matched is its user-visible -name, such as @code{vector<int> blah(const vector<int> &)}, not the -internal mangled name (e.g., @code{_Z4blahRSt6vectorIiSaIiEE}). The -match is done on substrings: if the @var{sym} parameter is a substring -of the function name, it is considered to be a match. For C99 and C++ -extended identifiers, the function name must be given in UTF-8, not -using universal character names. - -@item -fpatchable-function-entry=@var{N}[,@var{M}] -@opindex fpatchable-function-entry -Generate @var{N} NOPs right at the beginning -of each function, with the function entry point before the @var{M}th NOP. -If @var{M} is omitted, it defaults to @code{0} so the -function entry points to the address just at the first NOP. -The NOP instructions reserve extra space which can be used to patch in -any desired instrumentation at run time, provided that the code segment -is writable. The amount of space is controllable indirectly via -the number of NOPs; the NOP instruction used corresponds to the instruction -emitted by the internal GCC back-end interface @code{gen_nop}. This behavior -is target-specific and may also depend on the architecture variant and/or -other compilation options. - -For run-time identification, the starting addresses of these areas, -which correspond to their respective function entries minus @var{M}, -are additionally collected in the @code{__patchable_function_entries} -section of the resulting binary. - -Note that the value of @code{__attribute__ ((patchable_function_entry -(N,M)))} takes precedence over command-line option -@option{-fpatchable-function-entry=N,M}. This can be used to increase -the area size or to remove it completely on a single function. -If @code{N=0}, no pad location is recorded. - -The NOP instructions are inserted at---and maybe before, depending on -@var{M}---the function entry address, even before the prologue. On -PowerPC with the ELFv2 ABI, for a function with dual entry points, -the local entry point is this function entry address. - -The maximum value of @var{N} and @var{M} is 65535. On PowerPC with the -ELFv2 ABI, for a function with dual entry points, the supported values -for @var{M} are 0, 2, 6 and 14. -@end table - - -@node Preprocessor Options -@section Options Controlling the Preprocessor -@cindex preprocessor options -@cindex options, preprocessor - -These options control the C preprocessor, which is run on each C source -file before actual compilation. - -If you use the @option{-E} option, nothing is done except preprocessing. -Some of these options make sense only together with @option{-E} because -they cause the preprocessor output to be unsuitable for actual -compilation. - -In addition to the options listed here, there are a number of options -to control search paths for include files documented in -@ref{Directory Options}. -Options to control preprocessor diagnostics are listed in -@ref{Warning Options}. - -@table @gcctabopt -@include cppopts.texi - -@item -Wp,@var{option} -@opindex Wp -You can use @option{-Wp,@var{option}} to bypass the compiler driver -and pass @var{option} directly through to the preprocessor. If -@var{option} contains commas, it is split into multiple options at the -commas. However, many options are modified, translated or interpreted -by the compiler driver before being passed to the preprocessor, and -@option{-Wp} forcibly bypasses this phase. The preprocessor's direct -interface is undocumented and subject to change, so whenever possible -you should avoid using @option{-Wp} and let the driver handle the -options instead. - -@item -Xpreprocessor @var{option} -@opindex Xpreprocessor -Pass @var{option} as an option to the preprocessor. You can use this to -supply system-specific preprocessor options that GCC does not -recognize. - -If you want to pass an option that takes an argument, you must use -@option{-Xpreprocessor} twice, once for the option and once for the argument. - -@item -no-integrated-cpp -@opindex no-integrated-cpp -Perform preprocessing as a separate pass before compilation. -By default, GCC performs preprocessing as an integrated part of -input tokenization and parsing. -If this option is provided, the appropriate language front end -(@command{cc1}, @command{cc1plus}, or @command{cc1obj} for C, C++, -and Objective-C, respectively) is instead invoked twice, -once for preprocessing only and once for actual compilation -of the preprocessed input. -This option may be useful in conjunction with the @option{-B} or -@option{-wrapper} options to specify an alternate preprocessor or -perform additional processing of the program source between -normal preprocessing and compilation. - -@item -flarge-source-files -@opindex flarge-source-files -Adjust GCC to expect large source files, at the expense of slower -compilation and higher memory usage. - -Specifically, GCC normally tracks both column numbers and line numbers -within source files and it normally prints both of these numbers in -diagnostics. However, once it has processed a certain number of source -lines, it stops tracking column numbers and only tracks line numbers. -This means that diagnostics for later lines do not include column numbers. -It also means that options like @option{-Wmisleading-indentation} cease to work -at that point, although the compiler prints a note if this happens. -Passing @option{-flarge-source-files} significantly increases the number -of source lines that GCC can process before it stops tracking columns. - -@end table - -@node Assembler Options -@section Passing Options to the Assembler - -@c prevent bad page break with this line -You can pass options to the assembler. - -@table @gcctabopt -@item -Wa,@var{option} -@opindex Wa -Pass @var{option} as an option to the assembler. If @var{option} -contains commas, it is split into multiple options at the commas. - -@item -Xassembler @var{option} -@opindex Xassembler -Pass @var{option} as an option to the assembler. You can use this to -supply system-specific assembler options that GCC does not -recognize. - -If you want to pass an option that takes an argument, you must use -@option{-Xassembler} twice, once for the option and once for the argument. - -@end table - -@node Link Options -@section Options for Linking -@cindex link options -@cindex options, linking - -These options come into play when the compiler links object files into -an executable output file. They are meaningless if the compiler is -not doing a link step. - -@table @gcctabopt -@cindex file names -@item @var{object-file-name} -A file name that does not end in a special recognized suffix is -considered to name an object file or library. (Object files are -distinguished from libraries by the linker according to the file -contents.) If linking is done, these object files are used as input -to the linker. - -@item -c -@itemx -S -@itemx -E -@opindex c -@opindex S -@opindex E -If any of these options is used, then the linker is not run, and -object file names should not be used as arguments. @xref{Overall -Options}. - -@item -flinker-output=@var{type} -@opindex flinker-output -This option controls code generation of the link-time optimizer. By -default the linker output is automatically determined by the linker -plugin. For debugging the compiler and if incremental linking with a -non-LTO object file is desired, it may be useful to control the type -manually. - -If @var{type} is @samp{exec}, code generation produces a static -binary. In this case @option{-fpic} and @option{-fpie} are both -disabled. - -If @var{type} is @samp{dyn}, code generation produces a shared -library. In this case @option{-fpic} or @option{-fPIC} is preserved, -but not enabled automatically. This allows to build shared libraries -without position-independent code on architectures where this is -possible, i.e.@: on x86. - -If @var{type} is @samp{pie}, code generation produces an @option{-fpie} -executable. This results in similar optimizations as @samp{exec} -except that @option{-fpie} is not disabled if specified at compilation -time. - -If @var{type} is @samp{rel}, the compiler assumes that incremental linking is -done. The sections containing intermediate code for link-time optimization are -merged, pre-optimized, and output to the resulting object file. In addition, if -@option{-ffat-lto-objects} is specified, binary code is produced for future -non-LTO linking. The object file produced by incremental linking is smaller -than a static library produced from the same object files. At link time the -result of incremental linking also loads faster than a static -library assuming that the majority of objects in the library are used. - -Finally @samp{nolto-rel} configures the compiler for incremental linking where -code generation is forced, a final binary is produced, and the intermediate -code for later link-time optimization is stripped. When multiple object files -are linked together the resulting code is better optimized than with -link-time optimizations disabled (for example, cross-module inlining -happens), but most of benefits of whole program optimizations are lost. - -During the incremental link (by @option{-r}) the linker plugin defaults to -@option{rel}. With current interfaces to GNU Binutils it is however not -possible to incrementally link LTO objects and non-LTO objects into a single -mixed object file. If any of object files in incremental link cannot -be used for link-time optimization, the linker plugin issues a warning and -uses @samp{nolto-rel}. To maintain whole program optimization, it is -recommended to link such objects into static library instead. Alternatively it -is possible to use H.J. Lu's binutils with support for mixed objects. - -@item -fuse-ld=bfd -@opindex fuse-ld=bfd -Use the @command{bfd} linker instead of the default linker. - -@item -fuse-ld=gold -@opindex fuse-ld=gold -Use the @command{gold} linker instead of the default linker. - -@item -fuse-ld=lld -@opindex fuse-ld=lld -Use the LLVM @command{lld} linker instead of the default linker. - -@item -fuse-ld=mold -@opindex fuse-ld=mold -Use the Modern Linker (@command{mold}) instead of the default linker. - -@cindex Libraries -@item -l@var{library} -@itemx -l @var{library} -@opindex l -Search the library named @var{library} when linking. (The second -alternative with the library as a separate argument is only for -POSIX compliance and is not recommended.) - -The @option{-l} option is passed directly to the linker by GCC. Refer -to your linker documentation for exact details. The general -description below applies to the GNU linker. - -The linker searches a standard list of directories for the library. -The directories searched include several standard system directories -plus any that you specify with @option{-L}. - -Static libraries are archives of object files, and have file names -like @file{lib@var{library}.a}. Some targets also support shared -libraries, which typically have names like @file{lib@var{library}.so}. -If both static and shared libraries are found, the linker gives -preference to linking with the shared library unless the -@option{-static} option is used. - -It makes a difference where in the command you write this option; the -linker searches and processes libraries and object files in the order they -are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z} -after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers -to functions in @samp{z}, those functions may not be loaded. - -@item -lobjc -@opindex lobjc -You need this special case of the @option{-l} option in order to -link an Objective-C or Objective-C++ program. - -@item -nostartfiles -@opindex nostartfiles -Do not use the standard system startup files when linking. -The standard system libraries are used normally, unless @option{-nostdlib}, -@option{-nolibc}, or @option{-nodefaultlibs} is used. - -@item -nodefaultlibs -@opindex nodefaultlibs -Do not use the standard system libraries when linking. -Only the libraries you specify are passed to the linker, and options -specifying linkage of the system libraries, such as @option{-static-libgcc} -or @option{-shared-libgcc}, are ignored. -The standard startup files are used normally, unless @option{-nostartfiles} -is used. - -The compiler may generate calls to @code{memcmp}, -@code{memset}, @code{memcpy} and @code{memmove}. -These entries are usually resolved by entries in -libc. These entry points should be supplied through some other -mechanism when this option is specified. - -@item -nolibc -@opindex nolibc -Do not use the C library or system libraries tightly coupled with it when -linking. Still link with the startup files, @file{libgcc} or toolchain -provided language support libraries such as @file{libgnat}, @file{libgfortran} -or @file{libstdc++} unless options preventing their inclusion are used as -well. This typically removes @option{-lc} from the link command line, as well -as system libraries that normally go with it and become meaningless when -absence of a C library is assumed, for example @option{-lpthread} or -@option{-lm} in some configurations. This is intended for bare-board -targets when there is indeed no C library available. - -@item -nostdlib -@opindex nostdlib -Do not use the standard system startup files or libraries when linking. -No startup files and only the libraries you specify are passed to -the linker, and options specifying linkage of the system libraries, such as -@option{-static-libgcc} or @option{-shared-libgcc}, are ignored. - -The compiler may generate calls to @code{memcmp}, @code{memset}, -@code{memcpy} and @code{memmove}. -These entries are usually resolved by entries in -libc. These entry points should be supplied through some other -mechanism when this option is specified. - -@cindex @option{-lgcc}, use with @option{-nostdlib} -@cindex @option{-nostdlib} and unresolved references -@cindex unresolved references and @option{-nostdlib} -@cindex @option{-lgcc}, use with @option{-nodefaultlibs} -@cindex @option{-nodefaultlibs} and unresolved references -@cindex unresolved references and @option{-nodefaultlibs} -One of the standard libraries bypassed by @option{-nostdlib} and -@option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines -which GCC uses to overcome shortcomings of particular machines, or special -needs for some languages. -(@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler -Collection (GCC) Internals}, -for more discussion of @file{libgcc.a}.) -In most cases, you need @file{libgcc.a} even when you want to avoid -other standard libraries. In other words, when you specify @option{-nostdlib} -or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well. -This ensures that you have no unresolved references to internal GCC -library subroutines. -(An example of such an internal subroutine is @code{__main}, used to ensure C++ -constructors are called; @pxref{Collect2,,@code{collect2}, gccint, -GNU Compiler Collection (GCC) Internals}.) - -@item -nostdlib++ -@opindex nostdlib++ -Do not implicitly link with standard C++ libraries. - -@item -e @var{entry} -@itemx --entry=@var{entry} -@opindex e -@opindex entry - -Specify that the program entry point is @var{entry}. The argument is -interpreted by the linker; the GNU linker accepts either a symbol name -or an address. - -@item -pie -@opindex pie -Produce a dynamically linked position independent executable on targets -that support it. For predictable results, you must also specify the same -set of options used for compilation (@option{-fpie}, @option{-fPIE}, -or model suboptions) when you specify this linker option. - -@item -no-pie -@opindex no-pie -Don't produce a dynamically linked position independent executable. - -@item -static-pie -@opindex static-pie -Produce a static position independent executable on targets that support -it. A static position independent executable is similar to a static -executable, but can be loaded at any address without a dynamic linker. -For predictable results, you must also specify the same set of options -used for compilation (@option{-fpie}, @option{-fPIE}, or model -suboptions) when you specify this linker option. - -@item -pthread -@opindex pthread -Link with the POSIX threads library. This option is supported on -GNU/Linux targets, most other Unix derivatives, and also on -x86 Cygwin and MinGW targets. On some targets this option also sets -flags for the preprocessor, so it should be used consistently for both -compilation and linking. - -@item -r -@opindex r -Produce a relocatable object as output. This is also known as partial -linking. - -@item -rdynamic -@opindex rdynamic -Pass the flag @option{-export-dynamic} to the ELF linker, on targets -that support it. This instructs the linker to add all symbols, not -only used ones, to the dynamic symbol table. This option is needed -for some uses of @code{dlopen} or to allow obtaining backtraces -from within a program. - -@item -s -@opindex s -Remove all symbol table and relocation information from the executable. - -@item -static -@opindex static -On systems that support dynamic linking, this overrides @option{-pie} -and prevents linking with the shared libraries. On other systems, this -option has no effect. - -@item -shared -@opindex shared -Produce a shared object which can then be linked with other objects to -form an executable. Not all systems support this option. For predictable -results, you must also specify the same set of options used for compilation -(@option{-fpic}, @option{-fPIC}, or model suboptions) when -you specify this linker option.@footnote{On some systems, @samp{gcc -shared} -needs to build supplementary stub code for constructors to work. On -multi-libbed systems, @samp{gcc -shared} must select the correct support -libraries to link against. Failing to supply the correct flags may lead -to subtle defects. Supplying them in cases where they are not necessary -is innocuous.} - -@item -shared-libgcc -@itemx -static-libgcc -@opindex shared-libgcc -@opindex static-libgcc -On systems that provide @file{libgcc} as a shared library, these options -force the use of either the shared or static version, respectively. -If no shared version of @file{libgcc} was built when the compiler was -configured, these options have no effect. - -There are several situations in which an application should use the -shared @file{libgcc} instead of the static version. The most common -of these is when the application wishes to throw and catch exceptions -across different shared libraries. In that case, each of the libraries -as well as the application itself should use the shared @file{libgcc}. - -Therefore, the G++ driver automatically adds @option{-shared-libgcc} -whenever you build a shared library or a main executable, because C++ -programs typically use exceptions, so this is the right thing to do. - -If, instead, you use the GCC driver to create shared libraries, you may -find that they are not always linked with the shared @file{libgcc}. -If GCC finds, at its configuration time, that you have a non-GNU linker -or a GNU linker that does not support option @option{--eh-frame-hdr}, -it links the shared version of @file{libgcc} into shared libraries -by default. Otherwise, it takes advantage of the linker and optimizes -away the linking with the shared version of @file{libgcc}, linking with -the static version of libgcc by default. This allows exceptions to -propagate through such shared libraries, without incurring relocation -costs at library load time. - -However, if a library or main executable is supposed to throw or catch -exceptions, you must link it using the G++ driver, or using the option -@option{-shared-libgcc}, such that it is linked with the shared -@file{libgcc}. - -@item -static-libasan -@opindex static-libasan -When the @option{-fsanitize=address} option is used to link a program, -the GCC driver automatically links against @option{libasan}. If -@file{libasan} is available as a shared library, and the @option{-static} -option is not used, then this links against the shared version of -@file{libasan}. The @option{-static-libasan} option directs the GCC -driver to link @file{libasan} statically, without necessarily linking -other libraries statically. - -@item -static-libtsan -@opindex static-libtsan -When the @option{-fsanitize=thread} option is used to link a program, -the GCC driver automatically links against @option{libtsan}. If -@file{libtsan} is available as a shared library, and the @option{-static} -option is not used, then this links against the shared version of -@file{libtsan}. The @option{-static-libtsan} option directs the GCC -driver to link @file{libtsan} statically, without necessarily linking -other libraries statically. - -@item -static-liblsan -@opindex static-liblsan -When the @option{-fsanitize=leak} option is used to link a program, -the GCC driver automatically links against @option{liblsan}. If -@file{liblsan} is available as a shared library, and the @option{-static} -option is not used, then this links against the shared version of -@file{liblsan}. The @option{-static-liblsan} option directs the GCC -driver to link @file{liblsan} statically, without necessarily linking -other libraries statically. - -@item -static-libubsan -@opindex static-libubsan -When the @option{-fsanitize=undefined} option is used to link a program, -the GCC driver automatically links against @option{libubsan}. If -@file{libubsan} is available as a shared library, and the @option{-static} -option is not used, then this links against the shared version of -@file{libubsan}. The @option{-static-libubsan} option directs the GCC -driver to link @file{libubsan} statically, without necessarily linking -other libraries statically. - -@item -static-libstdc++ -@opindex static-libstdc++ -When the @command{g++} program is used to link a C++ program, it -normally automatically links against @option{libstdc++}. If -@file{libstdc++} is available as a shared library, and the -@option{-static} option is not used, then this links against the -shared version of @file{libstdc++}. That is normally fine. However, it -is sometimes useful to freeze the version of @file{libstdc++} used by -the program without going all the way to a fully static link. The -@option{-static-libstdc++} option directs the @command{g++} driver to -link @file{libstdc++} statically, without necessarily linking other -libraries statically. - -@item -symbolic -@opindex symbolic -Bind references to global symbols when building a shared object. Warn -about any unresolved references (unless overridden by the link editor -option @option{-Xlinker -z -Xlinker defs}). Only a few systems support -this option. - -@item -T @var{script} -@opindex T -@cindex linker script -Use @var{script} as the linker script. This option is supported by most -systems using the GNU linker. On some targets, such as bare-board -targets without an operating system, the @option{-T} option may be required -when linking to avoid references to undefined symbols. - -@item -Xlinker @var{option} -@opindex Xlinker -Pass @var{option} as an option to the linker. You can use this to -supply system-specific linker options that GCC does not recognize. - -If you want to pass an option that takes a separate argument, you must use -@option{-Xlinker} twice, once for the option and once for the argument. -For example, to pass @option{-assert definitions}, you must write -@option{-Xlinker -assert -Xlinker definitions}. It does not work to write -@option{-Xlinker "-assert definitions"}, because this passes the entire -string as a single argument, which is not what the linker expects. - -When using the GNU linker, it is usually more convenient to pass -arguments to linker options using the @option{@var{option}=@var{value}} -syntax than as separate arguments. For example, you can specify -@option{-Xlinker -Map=output.map} rather than -@option{-Xlinker -Map -Xlinker output.map}. Other linkers may not support -this syntax for command-line options. - -@item -Wl,@var{option} -@opindex Wl -Pass @var{option} as an option to the linker. If @var{option} contains -commas, it is split into multiple options at the commas. You can use this -syntax to pass an argument to the option. -For example, @option{-Wl,-Map,output.map} passes @option{-Map output.map} to the -linker. When using the GNU linker, you can also get the same effect with -@option{-Wl,-Map=output.map}. - -@item -u @var{symbol} -@opindex u -Pretend the symbol @var{symbol} is undefined, to force linking of -library modules to define it. You can use @option{-u} multiple times with -different symbols to force loading of additional library modules. - -@item -z @var{keyword} -@opindex z -@option{-z} is passed directly on to the linker along with the keyword -@var{keyword}. See the section in the documentation of your linker for -permitted values and their meanings. -@end table - -@node Directory Options -@section Options for Directory Search -@cindex directory options -@cindex options, directory search -@cindex search path - -These options specify directories to search for header files, for -libraries and for parts of the compiler: - -@table @gcctabopt -@include cppdiropts.texi - -@item -iplugindir=@var{dir} -@opindex iplugindir= -Set the directory to search for plugins that are passed -by @option{-fplugin=@var{name}} instead of -@option{-fplugin=@var{path}/@var{name}.so}. This option is not meant -to be used by the user, but only passed by the driver. - -@item -L@var{dir} -@opindex L -Add directory @var{dir} to the list of directories to be searched -for @option{-l}. - -@item -B@var{prefix} -@opindex B -This option specifies where to find the executables, libraries, -include files, and data files of the compiler itself. - -The compiler driver program runs one or more of the subprograms -@command{cpp}, @command{cc1}, @command{as} and @command{ld}. It tries -@var{prefix} as a prefix for each program it tries to run, both with and -without @samp{@var{machine}/@var{version}/} for the corresponding target -machine and compiler version. - -For each subprogram to be run, the compiler driver first tries the -@option{-B} prefix, if any. If that name is not found, or if @option{-B} -is not specified, the driver tries two standard prefixes, -@file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of -those results in a file name that is found, the unmodified program -name is searched for using the directories specified in your -@env{PATH} environment variable. - -The compiler checks to see if the path provided by @option{-B} -refers to a directory, and if necessary it adds a directory -separator character at the end of the path. - -@option{-B} prefixes that effectively specify directory names also apply -to libraries in the linker, because the compiler translates these -options into @option{-L} options for the linker. They also apply to -include files in the preprocessor, because the compiler translates these -options into @option{-isystem} options for the preprocessor. In this case, -the compiler appends @samp{include} to the prefix. - -The runtime support file @file{libgcc.a} can also be searched for using -the @option{-B} prefix, if needed. If it is not found there, the two -standard prefixes above are tried, and that is all. The file is left -out of the link if it is not found by those means. - -Another way to specify a prefix much like the @option{-B} prefix is to use -the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment -Variables}. - -As a special kludge, if the path provided by @option{-B} is -@file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to -9, then it is replaced by @file{[dir/]include}. This is to help -with boot-strapping the compiler. - -@item -no-canonical-prefixes -@opindex no-canonical-prefixes -Do not expand any symbolic links, resolve references to @samp{/../} -or @samp{/./}, or make the path absolute when generating a relative -prefix. - -@item --sysroot=@var{dir} -@opindex sysroot -Use @var{dir} as the logical root directory for headers and libraries. -For example, if the compiler normally searches for headers in -@file{/usr/include} and libraries in @file{/usr/lib}, it instead -searches @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}. - -If you use both this option and the @option{-isysroot} option, then -the @option{--sysroot} option applies to libraries, but the -@option{-isysroot} option applies to header files. - -The GNU linker (beginning with version 2.16) has the necessary support -for this option. If your linker does not support this option, the -header file aspect of @option{--sysroot} still works, but the -library aspect does not. - -@item --no-sysroot-suffix -@opindex no-sysroot-suffix -For some targets, a suffix is added to the root directory specified -with @option{--sysroot}, depending on the other options used, so that -headers may for example be found in -@file{@var{dir}/@var{suffix}/usr/include} instead of -@file{@var{dir}/usr/include}. This option disables the addition of -such a suffix. - -@end table - -@node Code Gen Options -@section Options for Code Generation Conventions -@cindex code generation conventions -@cindex options, code generation -@cindex run-time options - -These machine-independent options control the interface conventions -used in code generation. - -Most of them have both positive and negative forms; the negative form -of @option{-ffoo} is @option{-fno-foo}. In the table below, only -one of the forms is listed---the one that is not the default. You -can figure out the other form by either removing @samp{no-} or adding -it. - -@table @gcctabopt -@item -fstack-reuse=@var{reuse-level} -@opindex fstack_reuse -This option controls stack space reuse for user declared local/auto variables -and compiler generated temporaries. @var{reuse_level} can be @samp{all}, -@samp{named_vars}, or @samp{none}. @samp{all} enables stack reuse for all -local variables and temporaries, @samp{named_vars} enables the reuse only for -user defined local variables with names, and @samp{none} disables stack reuse -completely. The default value is @samp{all}. The option is needed when the -program extends the lifetime of a scoped local variable or a compiler generated -temporary beyond the end point defined by the language. When a lifetime of -a variable ends, and if the variable lives in memory, the optimizing compiler -has the freedom to reuse its stack space with other temporaries or scoped -local variables whose live range does not overlap with it. Legacy code extending -local lifetime is likely to break with the stack reuse optimization. - -For example, - -@smallexample - int *p; - @{ - int local1; - - p = &local1; - local1 = 10; - .... - @} - @{ - int local2; - local2 = 20; - ... - @} - - if (*p == 10) // out of scope use of local1 - @{ - - @} -@end smallexample - -Another example: -@smallexample - - struct A - @{ - A(int k) : i(k), j(k) @{ @} - int i; - int j; - @}; - - A *ap; - - void foo(const A& ar) - @{ - ap = &ar; - @} - - void bar() - @{ - foo(A(10)); // temp object's lifetime ends when foo returns - - @{ - A a(20); - .... - @} - ap->i+= 10; // ap references out of scope temp whose space - // is reused with a. What is the value of ap->i? - @} - -@end smallexample - -The lifetime of a compiler generated temporary is well defined by the C++ -standard. When a lifetime of a temporary ends, and if the temporary lives -in memory, the optimizing compiler has the freedom to reuse its stack -space with other temporaries or scoped local variables whose live range -does not overlap with it. However some of the legacy code relies on -the behavior of older compilers in which temporaries' stack space is -not reused, the aggressive stack reuse can lead to runtime errors. This -option is used to control the temporary stack reuse optimization. - -@item -ftrapv -@opindex ftrapv -This option generates traps for signed overflow on addition, subtraction, -multiplication operations. -The options @option{-ftrapv} and @option{-fwrapv} override each other, so using -@option{-ftrapv} @option{-fwrapv} on the command-line results in -@option{-fwrapv} being effective. Note that only active options override, so -using @option{-ftrapv} @option{-fwrapv} @option{-fno-wrapv} on the command-line -results in @option{-ftrapv} being effective. - -@item -fwrapv -@opindex fwrapv -This option instructs the compiler to assume that signed arithmetic -overflow of addition, subtraction and multiplication wraps around -using twos-complement representation. This flag enables some optimizations -and disables others. -The options @option{-ftrapv} and @option{-fwrapv} override each other, so using -@option{-ftrapv} @option{-fwrapv} on the command-line results in -@option{-fwrapv} being effective. Note that only active options override, so -using @option{-ftrapv} @option{-fwrapv} @option{-fno-wrapv} on the command-line -results in @option{-ftrapv} being effective. - -@item -fwrapv-pointer -@opindex fwrapv-pointer -This option instructs the compiler to assume that pointer arithmetic -overflow on addition and subtraction wraps around using twos-complement -representation. This flag disables some optimizations which assume -pointer overflow is invalid. - -@item -fstrict-overflow -@opindex fstrict-overflow -This option implies @option{-fno-wrapv} @option{-fno-wrapv-pointer} and when -negated implies @option{-fwrapv} @option{-fwrapv-pointer}. - -@item -fexceptions -@opindex fexceptions -Enable exception handling. Generates extra code needed to propagate -exceptions. For some targets, this implies GCC generates frame -unwind information for all functions, which can produce significant data -size overhead, although it does not affect execution. If you do not -specify this option, GCC enables it by default for languages like -C++ that normally require exception handling, and disables it for -languages like C that do not normally require it. However, you may need -to enable this option when compiling C code that needs to interoperate -properly with exception handlers written in C++. You may also wish to -disable this option if you are compiling older C++ programs that don't -use exception handling. - -@item -fnon-call-exceptions -@opindex fnon-call-exceptions -Generate code that allows trapping instructions to throw exceptions. -Note that this requires platform-specific runtime support that does -not exist everywhere. Moreover, it only allows @emph{trapping} -instructions to throw exceptions, i.e.@: memory references or floating-point -instructions. It does not allow exceptions to be thrown from -arbitrary signal handlers such as @code{SIGALRM}. This enables -@option{-fexceptions}. - -@item -fdelete-dead-exceptions -@opindex fdelete-dead-exceptions -Consider that instructions that may throw exceptions but don't otherwise -contribute to the execution of the program can be optimized away. -This does not affect calls to functions except those with the -@code{pure} or @code{const} attributes. -This option is enabled by default for the Ada and C++ compilers, as permitted by -the language specifications. -Optimization passes that cause dead exceptions to be removed are enabled independently at different optimization levels. - -@item -funwind-tables -@opindex funwind-tables -Similar to @option{-fexceptions}, except that it just generates any needed -static data, but does not affect the generated code in any other way. -You normally do not need to enable this option; instead, a language processor -that needs this handling enables it on your behalf. - -@item -fasynchronous-unwind-tables -@opindex fasynchronous-unwind-tables -Generate unwind table in DWARF format, if supported by target machine. The -table is exact at each instruction boundary, so it can be used for stack -unwinding from asynchronous events (such as debugger or garbage collector). - -@item -fno-gnu-unique -@opindex fno-gnu-unique -@opindex fgnu-unique -On systems with recent GNU assembler and C library, the C++ compiler -uses the @code{STB_GNU_UNIQUE} binding to make sure that definitions -of template static data members and static local variables in inline -functions are unique even in the presence of @code{RTLD_LOCAL}; this -is necessary to avoid problems with a library used by two different -@code{RTLD_LOCAL} plugins depending on a definition in one of them and -therefore disagreeing with the other one about the binding of the -symbol. But this causes @code{dlclose} to be ignored for affected -DSOs; if your program relies on reinitialization of a DSO via -@code{dlclose} and @code{dlopen}, you can use -@option{-fno-gnu-unique}. - -@item -fpcc-struct-return -@opindex fpcc-struct-return -Return ``short'' @code{struct} and @code{union} values in memory like -longer ones, rather than in registers. This convention is less -efficient, but it has the advantage of allowing intercallability between -GCC-compiled files and files compiled with other compilers, particularly -the Portable C Compiler (pcc). - -The precise convention for returning structures in memory depends -on the target configuration macros. - -Short structures and unions are those whose size and alignment match -that of some integer type. - -@strong{Warning:} code compiled with the @option{-fpcc-struct-return} -switch is not binary compatible with code compiled with the -@option{-freg-struct-return} switch. -Use it to conform to a non-default application binary interface. - -@item -freg-struct-return -@opindex freg-struct-return -Return @code{struct} and @code{union} values in registers when possible. -This is more efficient for small structures than -@option{-fpcc-struct-return}. - -If you specify neither @option{-fpcc-struct-return} nor -@option{-freg-struct-return}, GCC defaults to whichever convention is -standard for the target. If there is no standard convention, GCC -defaults to @option{-fpcc-struct-return}, except on targets where GCC is -the principal compiler. In those cases, we can choose the standard, and -we chose the more efficient register return alternative. - -@strong{Warning:} code compiled with the @option{-freg-struct-return} -switch is not binary compatible with code compiled with the -@option{-fpcc-struct-return} switch. -Use it to conform to a non-default application binary interface. - -@item -fshort-enums -@opindex fshort-enums -Allocate to an @code{enum} type only as many bytes as it needs for the -declared range of possible values. Specifically, the @code{enum} type -is equivalent to the smallest integer type that has enough room. - -@strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate -code that is not binary compatible with code generated without that switch. -Use it to conform to a non-default application binary interface. - -@item -fshort-wchar -@opindex fshort-wchar -Override the underlying type for @code{wchar_t} to be @code{short -unsigned int} instead of the default for the target. This option is -useful for building programs to run under WINE@. - -@strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate -code that is not binary compatible with code generated without that switch. -Use it to conform to a non-default application binary interface. - -@item -fcommon -@opindex fcommon -@opindex fno-common -@cindex tentative definitions -In C code, this option controls the placement of global variables -defined without an initializer, known as @dfn{tentative definitions} -in the C standard. Tentative definitions are distinct from declarations -of a variable with the @code{extern} keyword, which do not allocate storage. - -The default is @option{-fno-common}, which specifies that the compiler places -uninitialized global variables in the BSS section of the object file. -This inhibits the merging of tentative definitions by the linker so you get a -multiple-definition error if the same variable is accidentally defined in more -than one compilation unit. - -The @option{-fcommon} places uninitialized global variables in a common block. -This allows the linker to resolve all tentative definitions of the same variable -in different compilation units to the same object, or to a non-tentative -definition. This behavior is inconsistent with C++, and on many targets implies -a speed and code size penalty on global variable references. It is mainly -useful to enable legacy code to link without errors. - -@item -fno-ident -@opindex fno-ident -@opindex fident -Ignore the @code{#ident} directive. - -@item -finhibit-size-directive -@opindex finhibit-size-directive -Don't output a @code{.size} assembler directive, or anything else that -would cause trouble if the function is split in the middle, and the -two halves are placed at locations far apart in memory. This option is -used when compiling @file{crtstuff.c}; you should not need to use it -for anything else. - -@item -fverbose-asm -@opindex fverbose-asm -Put extra commentary information in the generated assembly code to -make it more readable. This option is generally only of use to those -who actually need to read the generated assembly code (perhaps while -debugging the compiler itself). - -@option{-fno-verbose-asm}, the default, causes the -extra information to be omitted and is useful when comparing two assembler -files. - -The added comments include: - -@itemize @bullet - -@item -information on the compiler version and command-line options, - -@item -the source code lines associated with the assembly instructions, -in the form FILENAME:LINENUMBER:CONTENT OF LINE, - -@item -hints on which high-level expressions correspond to -the various assembly instruction operands. - -@end itemize - -For example, given this C source file: - -@smallexample -int test (int n) -@{ - int i; - int total = 0; - - for (i = 0; i < n; i++) - total += i * i; - - return total; -@} -@end smallexample - -compiling to (x86_64) assembly via @option{-S} and emitting the result -direct to stdout via @option{-o} @option{-} - -@smallexample -gcc -S test.c -fverbose-asm -Os -o - -@end smallexample - -gives output similar to this: - -@smallexample - .file "test.c" -# GNU C11 (GCC) version 7.0.0 20160809 (experimental) (x86_64-pc-linux-gnu) - [...snip...] -# options passed: - [...snip...] - - .text - .globl test - .type test, @@function -test: -.LFB0: - .cfi_startproc -# test.c:4: int total = 0; - xorl %eax, %eax # <retval> -# test.c:6: for (i = 0; i < n; i++) - xorl %edx, %edx # i -.L2: -# test.c:6: for (i = 0; i < n; i++) - cmpl %edi, %edx # n, i - jge .L5 #, -# test.c:7: total += i * i; - movl %edx, %ecx # i, tmp92 - imull %edx, %ecx # i, tmp92 -# test.c:6: for (i = 0; i < n; i++) - incl %edx # i -# test.c:7: total += i * i; - addl %ecx, %eax # tmp92, <retval> - jmp .L2 # -.L5: -# test.c:10: @} - ret - .cfi_endproc -.LFE0: - .size test, .-test - .ident "GCC: (GNU) 7.0.0 20160809 (experimental)" - .section .note.GNU-stack,"",@@progbits -@end smallexample - -The comments are intended for humans rather than machines and hence the -precise format of the comments is subject to change. - -@item -frecord-gcc-switches -@opindex frecord-gcc-switches -This switch causes the command line used to invoke the -compiler to be recorded into the object file that is being created. -This switch is only implemented on some targets and the exact format -of the recording is target and binary file format dependent, but it -usually takes the form of a section containing ASCII text. This -switch is related to the @option{-fverbose-asm} switch, but that -switch only records information in the assembler output file as -comments, so it never reaches the object file. -See also @option{-grecord-gcc-switches} for another -way of storing compiler options into the object file. - -@item -fpic -@opindex fpic -@cindex global offset table -@cindex PIC -Generate position-independent code (PIC) suitable for use in a shared -library, if supported for the target machine. Such code accesses all -constant addresses through a global offset table (GOT)@. The dynamic -loader resolves the GOT entries when the program starts (the dynamic -loader is not part of GCC; it is part of the operating system). If -the GOT size for the linked executable exceeds a machine-specific -maximum size, you get an error message from the linker indicating that -@option{-fpic} does not work; in that case, recompile with @option{-fPIC} -instead. (These maximums are 8k on the SPARC, 28k on AArch64 and 32k -on the m68k and RS/6000. The x86 has no such limit.) - -Position-independent code requires special support, and therefore works -only on certain machines. For the x86, GCC supports PIC for System V -but not for the Sun 386i. Code generated for the IBM RS/6000 is always -position-independent. - -When this flag is set, the macros @code{__pic__} and @code{__PIC__} -are defined to 1. - -@item -fPIC -@opindex fPIC -If supported for the target machine, emit position-independent code, -suitable for dynamic linking and avoiding any limit on the size of the -global offset table. This option makes a difference on AArch64, m68k, -PowerPC and SPARC@. - -Position-independent code requires special support, and therefore works -only on certain machines. - -When this flag is set, the macros @code{__pic__} and @code{__PIC__} -are defined to 2. - -@item -fpie -@itemx -fPIE -@opindex fpie -@opindex fPIE -These options are similar to @option{-fpic} and @option{-fPIC}, but the -generated position-independent code can be only linked into executables. -Usually these options are used to compile code that will be linked using -the @option{-pie} GCC option. - -@option{-fpie} and @option{-fPIE} both define the macros -@code{__pie__} and @code{__PIE__}. The macros have the value 1 -for @option{-fpie} and 2 for @option{-fPIE}. - -@item -fno-plt -@opindex fno-plt -@opindex fplt -Do not use the PLT for external function calls in position-independent code. -Instead, load the callee address at call sites from the GOT and branch to it. -This leads to more efficient code by eliminating PLT stubs and exposing -GOT loads to optimizations. On architectures such as 32-bit x86 where -PLT stubs expect the GOT pointer in a specific register, this gives more -register allocation freedom to the compiler. -Lazy binding requires use of the PLT; -with @option{-fno-plt} all external symbols are resolved at load time. - -Alternatively, the function attribute @code{noplt} can be used to avoid calls -through the PLT for specific external functions. - -In position-dependent code, a few targets also convert calls to -functions that are marked to not use the PLT to use the GOT instead. - -@item -fno-jump-tables -@opindex fno-jump-tables -@opindex fjump-tables -Do not use jump tables for switch statements even where it would be -more efficient than other code generation strategies. This option is -of use in conjunction with @option{-fpic} or @option{-fPIC} for -building code that forms part of a dynamic linker and cannot -reference the address of a jump table. On some targets, jump tables -do not require a GOT and this option is not needed. - -@item -fno-bit-tests -@opindex fno-bit-tests -@opindex fbit-tests -Do not use bit tests for switch statements even where it would be -more efficient than other code generation strategies. - -@item -ffixed-@var{reg} -@opindex ffixed -Treat the register named @var{reg} as a fixed register; generated code -should never refer to it (except perhaps as a stack pointer, frame -pointer or in some other fixed role). - -@var{reg} must be the name of a register. The register names accepted -are machine-specific and are defined in the @code{REGISTER_NAMES} -macro in the machine description macro file. - -This flag does not have a negative form, because it specifies a -three-way choice. - -@item -fcall-used-@var{reg} -@opindex fcall-used -Treat the register named @var{reg} as an allocable register that is -clobbered by function calls. It may be allocated for temporaries or -variables that do not live across a call. Functions compiled this way -do not save and restore the register @var{reg}. - -It is an error to use this flag with the frame pointer or stack pointer. -Use of this flag for other registers that have fixed pervasive roles in -the machine's execution model produces disastrous results. - -This flag does not have a negative form, because it specifies a -three-way choice. - -@item -fcall-saved-@var{reg} -@opindex fcall-saved -Treat the register named @var{reg} as an allocable register saved by -functions. It may be allocated even for temporaries or variables that -live across a call. Functions compiled this way save and restore -the register @var{reg} if they use it. - -It is an error to use this flag with the frame pointer or stack pointer. -Use of this flag for other registers that have fixed pervasive roles in -the machine's execution model produces disastrous results. - -A different sort of disaster results from the use of this flag for -a register in which function values may be returned. - -This flag does not have a negative form, because it specifies a -three-way choice. - -@item -fpack-struct[=@var{n}] -@opindex fpack-struct -Without a value specified, pack all structure members together without -holes. When a value is specified (which must be a small power of two), pack -structure members according to this value, representing the maximum -alignment (that is, objects with default alignment requirements larger than -this are output potentially unaligned at the next fitting location. - -@strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate -code that is not binary compatible with code generated without that switch. -Additionally, it makes the code suboptimal. -Use it to conform to a non-default application binary interface. - -@item -fleading-underscore -@opindex fleading-underscore -This option and its counterpart, @option{-fno-leading-underscore}, forcibly -change the way C symbols are represented in the object file. One use -is to help link with legacy assembly code. - -@strong{Warning:} the @option{-fleading-underscore} switch causes GCC to -generate code that is not binary compatible with code generated without that -switch. Use it to conform to a non-default application binary interface. -Not all targets provide complete support for this switch. - -@item -ftls-model=@var{model} -@opindex ftls-model -Alter the thread-local storage model to be used (@pxref{Thread-Local}). -The @var{model} argument should be one of @samp{global-dynamic}, -@samp{local-dynamic}, @samp{initial-exec} or @samp{local-exec}. -Note that the choice is subject to optimization: the compiler may use -a more efficient model for symbols not visible outside of the translation -unit, or if @option{-fpic} is not given on the command line. - -The default without @option{-fpic} is @samp{initial-exec}; with -@option{-fpic} the default is @samp{global-dynamic}. - -@item -ftrampolines -@opindex ftrampolines -For targets that normally need trampolines for nested functions, always -generate them instead of using descriptors. Otherwise, for targets that -do not need them, like for example HP-PA or IA-64, do nothing. - -A trampoline is a small piece of code that is created at run time on the -stack when the address of a nested function is taken, and is used to call -the nested function indirectly. Therefore, it requires the stack to be -made executable in order for the program to work properly. - -@option{-fno-trampolines} is enabled by default on a language by language -basis to let the compiler avoid generating them, if it computes that this -is safe, and replace them with descriptors. Descriptors are made up of data -only, but the generated code must be prepared to deal with them. As of this -writing, @option{-fno-trampolines} is enabled by default only for Ada. - -Moreover, code compiled with @option{-ftrampolines} and code compiled with -@option{-fno-trampolines} are not binary compatible if nested functions are -present. This option must therefore be used on a program-wide basis and be -manipulated with extreme care. - -For languages other than Ada, the @code{-ftrampolines} and -@code{-fno-trampolines} options currently have no effect, and -trampolines are always generated on platforms that need them -for nested functions. - -@item -fvisibility=@r{[}default@r{|}internal@r{|}hidden@r{|}protected@r{]} -@opindex fvisibility -Set the default ELF image symbol visibility to the specified option---all -symbols are marked with this unless overridden within the code. -Using this feature can very substantially improve linking and -load times of shared object libraries, produce more optimized -code, provide near-perfect API export and prevent symbol clashes. -It is @strong{strongly} recommended that you use this in any shared objects -you distribute. - -Despite the nomenclature, @samp{default} always means public; i.e., -available to be linked against from outside the shared object. -@samp{protected} and @samp{internal} are pretty useless in real-world -usage so the only other commonly used option is @samp{hidden}. -The default if @option{-fvisibility} isn't specified is -@samp{default}, i.e., make every symbol public. - -A good explanation of the benefits offered by ensuring ELF -symbols have the correct visibility is given by ``How To Write -Shared Libraries'' by Ulrich Drepper (which can be found at -@w{@uref{https://www.akkadia.org/drepper/}})---however a superior -solution made possible by this option to marking things hidden when -the default is public is to make the default hidden and mark things -public. This is the norm with DLLs on Windows and with @option{-fvisibility=hidden} -and @code{__attribute__ ((visibility("default")))} instead of -@code{__declspec(dllexport)} you get almost identical semantics with -identical syntax. This is a great boon to those working with -cross-platform projects. - -For those adding visibility support to existing code, you may find -@code{#pragma GCC visibility} of use. This works by you enclosing -the declarations you wish to set visibility for with (for example) -@code{#pragma GCC visibility push(hidden)} and -@code{#pragma GCC visibility pop}. -Bear in mind that symbol visibility should be viewed @strong{as -part of the API interface contract} and thus all new code should -always specify visibility when it is not the default; i.e., declarations -only for use within the local DSO should @strong{always} be marked explicitly -as hidden as so to avoid PLT indirection overheads---making this -abundantly clear also aids readability and self-documentation of the code. -Note that due to ISO C++ specification requirements, @code{operator new} and -@code{operator delete} must always be of default visibility. - -Be aware that headers from outside your project, in particular system -headers and headers from any other library you use, may not be -expecting to be compiled with visibility other than the default. You -may need to explicitly say @code{#pragma GCC visibility push(default)} -before including any such headers. - -@code{extern} declarations are not affected by @option{-fvisibility}, so -a lot of code can be recompiled with @option{-fvisibility=hidden} with -no modifications. However, this means that calls to @code{extern} -functions with no explicit visibility use the PLT, so it is more -effective to use @code{__attribute ((visibility))} and/or -@code{#pragma GCC visibility} to tell the compiler which @code{extern} -declarations should be treated as hidden. - -Note that @option{-fvisibility} does affect C++ vague linkage -entities. This means that, for instance, an exception class that is -be thrown between DSOs must be explicitly marked with default -visibility so that the @samp{type_info} nodes are unified between -the DSOs. - -An overview of these techniques, their benefits and how to use them -is at @uref{https://gcc.gnu.org/@/wiki/@/Visibility}. - -@item -fstrict-volatile-bitfields -@opindex fstrict-volatile-bitfields -This option should be used if accesses to volatile bit-fields (or other -structure fields, although the compiler usually honors those types -anyway) should use a single access of the width of the -field's type, aligned to a natural alignment if possible. For -example, targets with memory-mapped peripheral registers might require -all such accesses to be 16 bits wide; with this flag you can -declare all peripheral bit-fields as @code{unsigned short} (assuming short -is 16 bits on these targets) to force GCC to use 16-bit accesses -instead of, perhaps, a more efficient 32-bit access. - -If this option is disabled, the compiler uses the most efficient -instruction. In the previous example, that might be a 32-bit load -instruction, even though that accesses bytes that do not contain -any portion of the bit-field, or memory-mapped registers unrelated to -the one being updated. - -In some cases, such as when the @code{packed} attribute is applied to a -structure field, it may not be possible to access the field with a single -read or write that is correctly aligned for the target machine. In this -case GCC falls back to generating multiple accesses rather than code that -will fault or truncate the result at run time. - -Note: Due to restrictions of the C/C++11 memory model, write accesses are -not allowed to touch non bit-field members. It is therefore recommended -to define all bits of the field's type as bit-field members. - -The default value of this option is determined by the application binary -interface for the target processor. - -@item -fsync-libcalls -@opindex fsync-libcalls -This option controls whether any out-of-line instance of the @code{__sync} -family of functions may be used to implement the C++11 @code{__atomic} -family of functions. - -The default value of this option is enabled, thus the only useful form -of the option is @option{-fno-sync-libcalls}. This option is used in -the implementation of the @file{libatomic} runtime library. - -@end table - -@node Developer Options -@section GCC Developer Options -@cindex developer options -@cindex debugging GCC -@cindex debug dump options -@cindex dump options -@cindex compilation statistics - -This section describes command-line options that are primarily of -interest to GCC developers, including options to support compiler -testing and investigation of compiler bugs and compile-time -performance problems. This includes options that produce debug dumps -at various points in the compilation; that print statistics such as -memory use and execution time; and that print information about GCC's -configuration, such as where it searches for libraries. You should -rarely need to use any of these options for ordinary compilation and -linking tasks. - -Many developer options that cause GCC to dump output to a file take an -optional @samp{=@var{filename}} suffix. You can specify @samp{stdout} -or @samp{-} to dump to standard output, and @samp{stderr} for standard -error. - -If @samp{=@var{filename}} is omitted, a default dump file name is -constructed by concatenating the base dump file name, a pass number, -phase letter, and pass name. The base dump file name is the name of -output file produced by the compiler if explicitly specified and not -an executable; otherwise it is the source file name. -The pass number is determined by the order passes are registered with -the compiler's pass manager. -This is generally the same as the order of execution, but passes -registered by plugins, target-specific passes, or passes that are -otherwise registered late are numbered higher than the pass named -@samp{final}, even if they are executed earlier. The phase letter is -one of @samp{i} (inter-procedural analysis), @samp{l} -(language-specific), @samp{r} (RTL), or @samp{t} (tree). -The files are created in the directory of the output file. - -@table @gcctabopt - -@item -fcallgraph-info -@itemx -fcallgraph-info=@var{MARKERS} -@opindex fcallgraph-info -Makes the compiler output callgraph information for the program, on a -per-object-file basis. The information is generated in the common VCG -format. It can be decorated with additional, per-node and/or per-edge -information, if a list of comma-separated markers is additionally -specified. When the @code{su} marker is specified, the callgraph is -decorated with stack usage information; it is equivalent to -@option{-fstack-usage}. When the @code{da} marker is specified, the -callgraph is decorated with information about dynamically allocated -objects. - -When compiling with @option{-flto}, no callgraph information is output -along with the object file. At LTO link time, @option{-fcallgraph-info} -may generate multiple callgraph information files next to intermediate -LTO output files. - -@item -d@var{letters} -@itemx -fdump-rtl-@var{pass} -@itemx -fdump-rtl-@var{pass}=@var{filename} -@opindex d -@opindex fdump-rtl-@var{pass} -Says to make debugging dumps during compilation at times specified by -@var{letters}. This is used for debugging the RTL-based passes of the -compiler. - -Some @option{-d@var{letters}} switches have different meaning when -@option{-E} is used for preprocessing. @xref{Preprocessor Options}, -for information about preprocessor-specific dump options. - -Debug dumps can be enabled with a @option{-fdump-rtl} switch or some -@option{-d} option @var{letters}. Here are the possible -letters for use in @var{pass} and @var{letters}, and their meanings: - -@table @gcctabopt - -@item -fdump-rtl-alignments -@opindex fdump-rtl-alignments -Dump after branch alignments have been computed. - -@item -fdump-rtl-asmcons -@opindex fdump-rtl-asmcons -Dump after fixing rtl statements that have unsatisfied in/out constraints. - -@item -fdump-rtl-auto_inc_dec -@opindex fdump-rtl-auto_inc_dec -Dump after auto-inc-dec discovery. This pass is only run on -architectures that have auto inc or auto dec instructions. - -@item -fdump-rtl-barriers -@opindex fdump-rtl-barriers -Dump after cleaning up the barrier instructions. - -@item -fdump-rtl-bbpart -@opindex fdump-rtl-bbpart -Dump after partitioning hot and cold basic blocks. - -@item -fdump-rtl-bbro -@opindex fdump-rtl-bbro -Dump after block reordering. - -@item -fdump-rtl-btl1 -@itemx -fdump-rtl-btl2 -@opindex fdump-rtl-btl2 -@opindex fdump-rtl-btl2 -@option{-fdump-rtl-btl1} and @option{-fdump-rtl-btl2} enable dumping -after the two branch -target load optimization passes. - -@item -fdump-rtl-bypass -@opindex fdump-rtl-bypass -Dump after jump bypassing and control flow optimizations. - -@item -fdump-rtl-combine -@opindex fdump-rtl-combine -Dump after the RTL instruction combination pass. - -@item -fdump-rtl-compgotos -@opindex fdump-rtl-compgotos -Dump after duplicating the computed gotos. - -@item -fdump-rtl-ce1 -@itemx -fdump-rtl-ce2 -@itemx -fdump-rtl-ce3 -@opindex fdump-rtl-ce1 -@opindex fdump-rtl-ce2 -@opindex fdump-rtl-ce3 -@option{-fdump-rtl-ce1}, @option{-fdump-rtl-ce2}, and -@option{-fdump-rtl-ce3} enable dumping after the three -if conversion passes. - -@item -fdump-rtl-cprop_hardreg -@opindex fdump-rtl-cprop_hardreg -Dump after hard register copy propagation. - -@item -fdump-rtl-csa -@opindex fdump-rtl-csa -Dump after combining stack adjustments. - -@item -fdump-rtl-cse1 -@itemx -fdump-rtl-cse2 -@opindex fdump-rtl-cse1 -@opindex fdump-rtl-cse2 -@option{-fdump-rtl-cse1} and @option{-fdump-rtl-cse2} enable dumping after -the two common subexpression elimination passes. - -@item -fdump-rtl-dce -@opindex fdump-rtl-dce -Dump after the standalone dead code elimination passes. - -@item -fdump-rtl-dbr -@opindex fdump-rtl-dbr -Dump after delayed branch scheduling. - -@item -fdump-rtl-dce1 -@itemx -fdump-rtl-dce2 -@opindex fdump-rtl-dce1 -@opindex fdump-rtl-dce2 -@option{-fdump-rtl-dce1} and @option{-fdump-rtl-dce2} enable dumping after -the two dead store elimination passes. - -@item -fdump-rtl-eh -@opindex fdump-rtl-eh -Dump after finalization of EH handling code. - -@item -fdump-rtl-eh_ranges -@opindex fdump-rtl-eh_ranges -Dump after conversion of EH handling range regions. - -@item -fdump-rtl-expand -@opindex fdump-rtl-expand -Dump after RTL generation. - -@item -fdump-rtl-fwprop1 -@itemx -fdump-rtl-fwprop2 -@opindex fdump-rtl-fwprop1 -@opindex fdump-rtl-fwprop2 -@option{-fdump-rtl-fwprop1} and @option{-fdump-rtl-fwprop2} enable -dumping after the two forward propagation passes. - -@item -fdump-rtl-gcse1 -@itemx -fdump-rtl-gcse2 -@opindex fdump-rtl-gcse1 -@opindex fdump-rtl-gcse2 -@option{-fdump-rtl-gcse1} and @option{-fdump-rtl-gcse2} enable dumping -after global common subexpression elimination. - -@item -fdump-rtl-init-regs -@opindex fdump-rtl-init-regs -Dump after the initialization of the registers. - -@item -fdump-rtl-initvals -@opindex fdump-rtl-initvals -Dump after the computation of the initial value sets. - -@item -fdump-rtl-into_cfglayout -@opindex fdump-rtl-into_cfglayout -Dump after converting to cfglayout mode. - -@item -fdump-rtl-ira -@opindex fdump-rtl-ira -Dump after iterated register allocation. - -@item -fdump-rtl-jump -@opindex fdump-rtl-jump -Dump after the second jump optimization. - -@item -fdump-rtl-loop2 -@opindex fdump-rtl-loop2 -@option{-fdump-rtl-loop2} enables dumping after the rtl -loop optimization passes. - -@item -fdump-rtl-mach -@opindex fdump-rtl-mach -Dump after performing the machine dependent reorganization pass, if that -pass exists. - -@item -fdump-rtl-mode_sw -@opindex fdump-rtl-mode_sw -Dump after removing redundant mode switches. - -@item -fdump-rtl-rnreg -@opindex fdump-rtl-rnreg -Dump after register renumbering. - -@item -fdump-rtl-outof_cfglayout -@opindex fdump-rtl-outof_cfglayout -Dump after converting from cfglayout mode. - -@item -fdump-rtl-peephole2 -@opindex fdump-rtl-peephole2 -Dump after the peephole pass. - -@item -fdump-rtl-postreload -@opindex fdump-rtl-postreload -Dump after post-reload optimizations. - -@item -fdump-rtl-pro_and_epilogue -@opindex fdump-rtl-pro_and_epilogue -Dump after generating the function prologues and epilogues. - -@item -fdump-rtl-sched1 -@itemx -fdump-rtl-sched2 -@opindex fdump-rtl-sched1 -@opindex fdump-rtl-sched2 -@option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2} enable dumping -after the basic block scheduling passes. - -@item -fdump-rtl-ree -@opindex fdump-rtl-ree -Dump after sign/zero extension elimination. - -@item -fdump-rtl-seqabstr -@opindex fdump-rtl-seqabstr -Dump after common sequence discovery. - -@item -fdump-rtl-shorten -@opindex fdump-rtl-shorten -Dump after shortening branches. - -@item -fdump-rtl-sibling -@opindex fdump-rtl-sibling -Dump after sibling call optimizations. - -@item -fdump-rtl-split1 -@itemx -fdump-rtl-split2 -@itemx -fdump-rtl-split3 -@itemx -fdump-rtl-split4 -@itemx -fdump-rtl-split5 -@opindex fdump-rtl-split1 -@opindex fdump-rtl-split2 -@opindex fdump-rtl-split3 -@opindex fdump-rtl-split4 -@opindex fdump-rtl-split5 -These options enable dumping after five rounds of -instruction splitting. - -@item -fdump-rtl-sms -@opindex fdump-rtl-sms -Dump after modulo scheduling. This pass is only run on some -architectures. - -@item -fdump-rtl-stack -@opindex fdump-rtl-stack -Dump after conversion from GCC's ``flat register file'' registers to the -x87's stack-like registers. This pass is only run on x86 variants. - -@item -fdump-rtl-subreg1 -@itemx -fdump-rtl-subreg2 -@opindex fdump-rtl-subreg1 -@opindex fdump-rtl-subreg2 -@option{-fdump-rtl-subreg1} and @option{-fdump-rtl-subreg2} enable dumping after -the two subreg expansion passes. - -@item -fdump-rtl-unshare -@opindex fdump-rtl-unshare -Dump after all rtl has been unshared. - -@item -fdump-rtl-vartrack -@opindex fdump-rtl-vartrack -Dump after variable tracking. - -@item -fdump-rtl-vregs -@opindex fdump-rtl-vregs -Dump after converting virtual registers to hard registers. - -@item -fdump-rtl-web -@opindex fdump-rtl-web -Dump after live range splitting. - -@item -fdump-rtl-regclass -@itemx -fdump-rtl-subregs_of_mode_init -@itemx -fdump-rtl-subregs_of_mode_finish -@itemx -fdump-rtl-dfinit -@itemx -fdump-rtl-dfinish -@opindex fdump-rtl-regclass -@opindex fdump-rtl-subregs_of_mode_init -@opindex fdump-rtl-subregs_of_mode_finish -@opindex fdump-rtl-dfinit -@opindex fdump-rtl-dfinish -These dumps are defined but always produce empty files. - -@item -da -@itemx -fdump-rtl-all -@opindex da -@opindex fdump-rtl-all -Produce all the dumps listed above. - -@item -dA -@opindex dA -Annotate the assembler output with miscellaneous debugging information. - -@item -dD -@opindex dD -Dump all macro definitions, at the end of preprocessing, in addition to -normal output. - -@item -dH -@opindex dH -Produce a core dump whenever an error occurs. - -@item -dp -@opindex dp -Annotate the assembler output with a comment indicating which -pattern and alternative is used. The length and cost of each instruction are -also printed. - -@item -dP -@opindex dP -Dump the RTL in the assembler output as a comment before each instruction. -Also turns on @option{-dp} annotation. - -@item -dx -@opindex dx -Just generate RTL for a function instead of compiling it. Usually used -with @option{-fdump-rtl-expand}. -@end table - -@item -fdump-debug -@opindex fdump-debug -Dump debugging information generated during the debug -generation phase. - -@item -fdump-earlydebug -@opindex fdump-earlydebug -Dump debugging information generated during the early debug -generation phase. - -@item -fdump-noaddr -@opindex fdump-noaddr -When doing debugging dumps, suppress address output. This makes it more -feasible to use diff on debugging dumps for compiler invocations with -different compiler binaries and/or different -text / bss / data / heap / stack / dso start locations. - -@item -freport-bug -@opindex freport-bug -Collect and dump debug information into a temporary file if an -internal compiler error (ICE) occurs. - -@item -fdump-unnumbered -@opindex fdump-unnumbered -When doing debugging dumps, suppress instruction numbers and address output. -This makes it more feasible to use diff on debugging dumps for compiler -invocations with different options, in particular with and without -@option{-g}. - -@item -fdump-unnumbered-links -@opindex fdump-unnumbered-links -When doing debugging dumps (see @option{-d} option above), suppress -instruction numbers for the links to the previous and next instructions -in a sequence. - -@item -fdump-ipa-@var{switch} -@itemx -fdump-ipa-@var{switch}-@var{options} -@opindex fdump-ipa -Control the dumping at various stages of inter-procedural analysis -language tree to a file. The file name is generated by appending a -switch specific suffix to the source file name, and the file is created -in the same directory as the output file. The following dumps are -possible: - -@table @samp -@item all -Enables all inter-procedural analysis dumps. - -@item cgraph -Dumps information about call-graph optimization, unused function removal, -and inlining decisions. - -@item inline -Dump after function inlining. - -@end table - -Additionally, the options @option{-optimized}, @option{-missed}, -@option{-note}, and @option{-all} can be provided, with the same meaning -as for @option{-fopt-info}, defaulting to @option{-optimized}. - -For example, @option{-fdump-ipa-inline-optimized-missed} will emit -information on callsites that were inlined, along with callsites -that were not inlined. - -By default, the dump will contain messages about successful -optimizations (equivalent to @option{-optimized}) together with -low-level details about the analysis. - -@item -fdump-lang -@opindex fdump-lang -Dump language-specific information. The file name is made by appending -@file{.lang} to the source file name. - -@item -fdump-lang-all -@itemx -fdump-lang-@var{switch} -@itemx -fdump-lang-@var{switch}-@var{options} -@itemx -fdump-lang-@var{switch}-@var{options}=@var{filename} -@opindex fdump-lang-all -@opindex fdump-lang -Control the dumping of language-specific information. The @var{options} -and @var{filename} portions behave as described in the -@option{-fdump-tree} option. The following @var{switch} values are -accepted: - -@table @samp -@item all - -Enable all language-specific dumps. - -@item class -Dump class hierarchy information. Virtual table information is emitted -unless '@option{slim}' is specified. This option is applicable to C++ only. - -@item module -Dump module information. Options @option{lineno} (locations), -@option{graph} (reachability), @option{blocks} (clusters), -@option{uid} (serialization), @option{alias} (mergeable), -@option{asmname} (Elrond), @option{eh} (mapper) & @option{vops} -(macros) may provide additional information. This option is -applicable to C++ only. - -@item raw -Dump the raw internal tree data. This option is applicable to C++ only. - -@end table - -@item -fdump-passes -@opindex fdump-passes -Print on @file{stderr} the list of optimization passes that are turned -on and off by the current command-line options. - -@item -fdump-statistics-@var{option} -@opindex fdump-statistics -Enable and control dumping of pass statistics in a separate file. The -file name is generated by appending a suffix ending in -@samp{.statistics} to the source file name, and the file is created in -the same directory as the output file. If the @samp{-@var{option}} -form is used, @samp{-stats} causes counters to be summed over the -whole compilation unit while @samp{-details} dumps every event as -the passes generate them. The default with no option is to sum -counters for each function compiled. - -@item -fdump-tree-all -@itemx -fdump-tree-@var{switch} -@itemx -fdump-tree-@var{switch}-@var{options} -@itemx -fdump-tree-@var{switch}-@var{options}=@var{filename} -@opindex fdump-tree-all -@opindex fdump-tree -Control the dumping at various stages of processing the intermediate -language tree to a file. If the @samp{-@var{options}} -form is used, @var{options} is a list of @samp{-} separated options -which control the details of the dump. Not all options are applicable -to all dumps; those that are not meaningful are ignored. The -following options are available - -@table @samp -@item address -Print the address of each node. Usually this is not meaningful as it -changes according to the environment and source file. Its primary use -is for tying up a dump file with a debug environment. -@item asmname -If @code{DECL_ASSEMBLER_NAME} has been set for a given decl, use that -in the dump instead of @code{DECL_NAME}. Its primary use is ease of -use working backward from mangled names in the assembly file. -@item slim -When dumping front-end intermediate representations, inhibit dumping -of members of a scope or body of a function merely because that scope -has been reached. Only dump such items when they are directly reachable -by some other path. - -When dumping pretty-printed trees, this option inhibits dumping the -bodies of control structures. - -When dumping RTL, print the RTL in slim (condensed) form instead of -the default LISP-like representation. -@item raw -Print a raw representation of the tree. By default, trees are -pretty-printed into a C-like representation. -@item details -Enable more detailed dumps (not honored by every dump option). Also -include information from the optimization passes. -@item stats -Enable dumping various statistics about the pass (not honored by every dump -option). -@item blocks -Enable showing basic block boundaries (disabled in raw dumps). -@item graph -For each of the other indicated dump files (@option{-fdump-rtl-@var{pass}}), -dump a representation of the control flow graph suitable for viewing with -GraphViz to @file{@var{file}.@var{passid}.@var{pass}.dot}. Each function in -the file is pretty-printed as a subgraph, so that GraphViz can render them -all in a single plot. - -This option currently only works for RTL dumps, and the RTL is always -dumped in slim form. -@item vops -Enable showing virtual operands for every statement. -@item lineno -Enable showing line numbers for statements. -@item uid -Enable showing the unique ID (@code{DECL_UID}) for each variable. -@item verbose -Enable showing the tree dump for each statement. -@item eh -Enable showing the EH region number holding each statement. -@item scev -Enable showing scalar evolution analysis details. -@item optimized -Enable showing optimization information (only available in certain -passes). -@item missed -Enable showing missed optimization information (only available in certain -passes). -@item note -Enable other detailed optimization information (only available in -certain passes). -@item all -Turn on all options, except @option{raw}, @option{slim}, @option{verbose} -and @option{lineno}. -@item optall -Turn on all optimization options, i.e., @option{optimized}, -@option{missed}, and @option{note}. -@end table - -To determine what tree dumps are available or find the dump for a pass -of interest follow the steps below. - -@enumerate -@item -Invoke GCC with @option{-fdump-passes} and in the @file{stderr} output -look for a code that corresponds to the pass you are interested in. -For example, the codes @code{tree-evrp}, @code{tree-vrp1}, and -@code{tree-vrp2} correspond to the three Value Range Propagation passes. -The number at the end distinguishes distinct invocations of the same pass. -@item -To enable the creation of the dump file, append the pass code to -the @option{-fdump-} option prefix and invoke GCC with it. For example, -to enable the dump from the Early Value Range Propagation pass, invoke -GCC with the @option{-fdump-tree-evrp} option. Optionally, you may -specify the name of the dump file. If you don't specify one, GCC -creates as described below. -@item -Find the pass dump in a file whose name is composed of three components -separated by a period: the name of the source file GCC was invoked to -compile, a numeric suffix indicating the pass number followed by the -letter @samp{t} for tree passes (and the letter @samp{r} for RTL passes), -and finally the pass code. For example, the Early VRP pass dump might -be in a file named @file{myfile.c.038t.evrp} in the current working -directory. Note that the numeric codes are not stable and may change -from one version of GCC to another. -@end enumerate - -@item -fopt-info -@itemx -fopt-info-@var{options} -@itemx -fopt-info-@var{options}=@var{filename} -@opindex fopt-info -Controls optimization dumps from various optimization passes. If the -@samp{-@var{options}} form is used, @var{options} is a list of -@samp{-} separated option keywords to select the dump details and -optimizations. - -The @var{options} can be divided into three groups: -@enumerate -@item -options describing what kinds of messages should be emitted, -@item -options describing the verbosity of the dump, and -@item -options describing which optimizations should be included. -@end enumerate -The options from each group can be freely mixed as they are -non-overlapping. However, in case of any conflicts, -the later options override the earlier options on the command -line. - -The following options control which kinds of messages should be emitted: - -@table @samp -@item optimized -Print information when an optimization is successfully applied. It is -up to a pass to decide which information is relevant. For example, the -vectorizer passes print the source location of loops which are -successfully vectorized. -@item missed -Print information about missed optimizations. Individual passes -control which information to include in the output. -@item note -Print verbose information about optimizations, such as certain -transformations, more detailed messages about decisions etc. -@item all -Print detailed optimization information. This includes -@samp{optimized}, @samp{missed}, and @samp{note}. -@end table - -The following option controls the dump verbosity: - -@table @samp -@item internals -By default, only ``high-level'' messages are emitted. This option enables -additional, more detailed, messages, which are likely to only be of interest -to GCC developers. -@end table - -One or more of the following option keywords can be used to describe a -group of optimizations: - -@table @samp -@item ipa -Enable dumps from all interprocedural optimizations. -@item loop -Enable dumps from all loop optimizations. -@item inline -Enable dumps from all inlining optimizations. -@item omp -Enable dumps from all OMP (Offloading and Multi Processing) optimizations. -@item vec -Enable dumps from all vectorization optimizations. -@item optall -Enable dumps from all optimizations. This is a superset of -the optimization groups listed above. -@end table - -If @var{options} is -omitted, it defaults to @samp{optimized-optall}, which means to dump messages -about successful optimizations from all the passes, omitting messages -that are treated as ``internals''. - -If the @var{filename} is provided, then the dumps from all the -applicable optimizations are concatenated into the @var{filename}. -Otherwise the dump is output onto @file{stderr}. Though multiple -@option{-fopt-info} options are accepted, only one of them can include -a @var{filename}. If other filenames are provided then all but the -first such option are ignored. - -Note that the output @var{filename} is overwritten -in case of multiple translation units. If a combined output from -multiple translation units is desired, @file{stderr} should be used -instead. - -In the following example, the optimization info is output to -@file{stderr}: - -@smallexample -gcc -O3 -fopt-info -@end smallexample - -This example: -@smallexample -gcc -O3 -fopt-info-missed=missed.all -@end smallexample - -@noindent -outputs missed optimization report from all the passes into -@file{missed.all}, and this one: - -@smallexample -gcc -O2 -ftree-vectorize -fopt-info-vec-missed -@end smallexample - -@noindent -prints information about missed optimization opportunities from -vectorization passes on @file{stderr}. -Note that @option{-fopt-info-vec-missed} is equivalent to -@option{-fopt-info-missed-vec}. The order of the optimization group -names and message types listed after @option{-fopt-info} does not matter. - -As another example, -@smallexample -gcc -O3 -fopt-info-inline-optimized-missed=inline.txt -@end smallexample - -@noindent -outputs information about missed optimizations as well as -optimized locations from all the inlining passes into -@file{inline.txt}. - -Finally, consider: - -@smallexample -gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt -@end smallexample - -@noindent -Here the two output filenames @file{vec.miss} and @file{loop.opt} are -in conflict since only one output file is allowed. In this case, only -the first option takes effect and the subsequent options are -ignored. Thus only @file{vec.miss} is produced which contains -dumps from the vectorizer about missed opportunities. - -@item -fsave-optimization-record -@opindex fsave-optimization-record -Write a SRCFILE.opt-record.json.gz file detailing what optimizations -were performed, for those optimizations that support @option{-fopt-info}. - -This option is experimental and the format of the data within the -compressed JSON file is subject to change. - -It is roughly equivalent to a machine-readable version of -@option{-fopt-info-all}, as a collection of messages with source file, -line number and column number, with the following additional data for -each message: - -@itemize @bullet - -@item -the execution count of the code being optimized, along with metadata about -whether this was from actual profile data, or just an estimate, allowing -consumers to prioritize messages by code hotness, - -@item -the function name of the code being optimized, where applicable, - -@item -the ``inlining chain'' for the code being optimized, so that when -a function is inlined into several different places (which might -themselves be inlined), the reader can distinguish between the copies, - -@item -objects identifying those parts of the message that refer to expressions, -statements or symbol-table nodes, which of these categories they are, and, -when available, their source code location, - -@item -the GCC pass that emitted the message, and - -@item -the location in GCC's own code from which the message was emitted - -@end itemize - -Additionally, some messages are logically nested within other -messages, reflecting implementation details of the optimization -passes. - -@item -fsched-verbose=@var{n} -@opindex fsched-verbose -On targets that use instruction scheduling, this option controls the -amount of debugging output the scheduler prints to the dump files. - -For @var{n} greater than zero, @option{-fsched-verbose} outputs the -same information as @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2}. -For @var{n} greater than one, it also output basic block probabilities, -detailed ready list information and unit/insn info. For @var{n} greater -than two, it includes RTL at abort point, control-flow and regions info. -And for @var{n} over four, @option{-fsched-verbose} also includes -dependence info. - - - -@item -fenable-@var{kind}-@var{pass} -@itemx -fdisable-@var{kind}-@var{pass}=@var{range-list} -@opindex fdisable- -@opindex fenable- - -This is a set of options that are used to explicitly disable/enable -optimization passes. These options are intended for use for debugging GCC. -Compiler users should use regular options for enabling/disabling -passes instead. - -@table @gcctabopt - -@item -fdisable-ipa-@var{pass} -Disable IPA pass @var{pass}. @var{pass} is the pass name. If the same pass is -statically invoked in the compiler multiple times, the pass name should be -appended with a sequential number starting from 1. - -@item -fdisable-rtl-@var{pass} -@itemx -fdisable-rtl-@var{pass}=@var{range-list} -Disable RTL pass @var{pass}. @var{pass} is the pass name. If the same pass is -statically invoked in the compiler multiple times, the pass name should be -appended with a sequential number starting from 1. @var{range-list} is a -comma-separated list of function ranges or assembler names. Each range is a number -pair separated by a colon. The range is inclusive in both ends. If the range -is trivial, the number pair can be simplified as a single number. If the -function's call graph node's @var{uid} falls within one of the specified ranges, -the @var{pass} is disabled for that function. The @var{uid} is shown in the -function header of a dump file, and the pass names can be dumped by using -option @option{-fdump-passes}. - -@item -fdisable-tree-@var{pass} -@itemx -fdisable-tree-@var{pass}=@var{range-list} -Disable tree pass @var{pass}. See @option{-fdisable-rtl} for the description of -option arguments. - -@item -fenable-ipa-@var{pass} -Enable IPA pass @var{pass}. @var{pass} is the pass name. If the same pass is -statically invoked in the compiler multiple times, the pass name should be -appended with a sequential number starting from 1. - -@item -fenable-rtl-@var{pass} -@itemx -fenable-rtl-@var{pass}=@var{range-list} -Enable RTL pass @var{pass}. See @option{-fdisable-rtl} for option argument -description and examples. - -@item -fenable-tree-@var{pass} -@itemx -fenable-tree-@var{pass}=@var{range-list} -Enable tree pass @var{pass}. See @option{-fdisable-rtl} for the description -of option arguments. - -@end table - -Here are some examples showing uses of these options. - -@smallexample - -# disable ccp1 for all functions - -fdisable-tree-ccp1 -# disable complete unroll for function whose cgraph node uid is 1 - -fenable-tree-cunroll=1 -# disable gcse2 for functions at the following ranges [1,1], -# [300,400], and [400,1000] -# disable gcse2 for functions foo and foo2 - -fdisable-rtl-gcse2=foo,foo2 -# disable early inlining - -fdisable-tree-einline -# disable ipa inlining - -fdisable-ipa-inline -# enable tree full unroll - -fenable-tree-unroll - -@end smallexample - -@item -fchecking -@itemx -fchecking=@var{n} -@opindex fchecking -@opindex fno-checking -Enable internal consistency checking. The default depends on -the compiler configuration. @option{-fchecking=2} enables further -internal consistency checking that might affect code generation. - -@item -frandom-seed=@var{string} -@opindex frandom-seed -This option provides a seed that GCC uses in place of -random numbers in generating certain symbol names -that have to be different in every compiled file. It is also used to -place unique stamps in coverage data files and the object files that -produce them. You can use the @option{-frandom-seed} option to produce -reproducibly identical object files. - -The @var{string} can either be a number (decimal, octal or hex) or an -arbitrary string (in which case it's converted to a number by -computing CRC32). - -The @var{string} should be different for every file you compile. - -@item -save-temps -@opindex save-temps -Store the usual ``temporary'' intermediate files permanently; name them -as auxiliary output files, as specified described under -@option{-dumpbase} and @option{-dumpdir}. - -When used in combination with the @option{-x} command-line option, -@option{-save-temps} is sensible enough to avoid overwriting an -input source file with the same extension as an intermediate file. -The corresponding intermediate file may be obtained by renaming the -source file before using @option{-save-temps}. - -@item -save-temps=cwd -@opindex save-temps=cwd -Equivalent to @option{-save-temps -dumpdir ./}. - -@item -save-temps=obj -@opindex save-temps=obj -Equivalent to @option{-save-temps -dumpdir @file{outdir/}}, where -@file{outdir/} is the directory of the output file specified after the -@option{-o} option, including any directory separators. If the -@option{-o} option is not used, the @option{-save-temps=obj} switch -behaves like @option{-save-temps=cwd}. - -@item -time@r{[}=@var{file}@r{]} -@opindex time -Report the CPU time taken by each subprocess in the compilation -sequence. For C source files, this is the compiler proper and assembler -(plus the linker if linking is done). - -Without the specification of an output file, the output looks like this: - -@smallexample -# cc1 0.12 0.01 -# as 0.00 0.01 -@end smallexample - -The first number on each line is the ``user time'', that is time spent -executing the program itself. The second number is ``system time'', -time spent executing operating system routines on behalf of the program. -Both numbers are in seconds. - -With the specification of an output file, the output is appended to the -named file, and it looks like this: - -@smallexample -0.12 0.01 cc1 @var{options} -0.00 0.01 as @var{options} -@end smallexample - -The ``user time'' and the ``system time'' are moved before the program -name, and the options passed to the program are displayed, so that one -can later tell what file was being compiled, and with which options. - -@item -fdump-final-insns@r{[}=@var{file}@r{]} -@opindex fdump-final-insns -Dump the final internal representation (RTL) to @var{file}. If the -optional argument is omitted (or if @var{file} is @code{.}), the name -of the dump file is determined by appending @code{.gkd} to the -dump base name, see @option{-dumpbase}. - -@item -fcompare-debug@r{[}=@var{opts}@r{]} -@opindex fcompare-debug -@opindex fno-compare-debug -If no error occurs during compilation, run the compiler a second time, -adding @var{opts} and @option{-fcompare-debug-second} to the arguments -passed to the second compilation. Dump the final internal -representation in both compilations, and print an error if they differ. - -If the equal sign is omitted, the default @option{-gtoggle} is used. - -The environment variable @env{GCC_COMPARE_DEBUG}, if defined, non-empty -and nonzero, implicitly enables @option{-fcompare-debug}. If -@env{GCC_COMPARE_DEBUG} is defined to a string starting with a dash, -then it is used for @var{opts}, otherwise the default @option{-gtoggle} -is used. - -@option{-fcompare-debug=}, with the equal sign but without @var{opts}, -is equivalent to @option{-fno-compare-debug}, which disables the dumping -of the final representation and the second compilation, preventing even -@env{GCC_COMPARE_DEBUG} from taking effect. - -To verify full coverage during @option{-fcompare-debug} testing, set -@env{GCC_COMPARE_DEBUG} to say @option{-fcompare-debug-not-overridden}, -which GCC rejects as an invalid option in any actual compilation -(rather than preprocessing, assembly or linking). To get just a -warning, setting @env{GCC_COMPARE_DEBUG} to @samp{-w%n-fcompare-debug -not overridden} will do. - -@item -fcompare-debug-second -@opindex fcompare-debug-second -This option is implicitly passed to the compiler for the second -compilation requested by @option{-fcompare-debug}, along with options to -silence warnings, and omitting other options that would cause the compiler -to produce output to files or to standard output as a side effect. Dump -files and preserved temporary files are renamed so as to contain the -@code{.gk} additional extension during the second compilation, to avoid -overwriting those generated by the first. - -When this option is passed to the compiler driver, it causes the -@emph{first} compilation to be skipped, which makes it useful for little -other than debugging the compiler proper. - -@item -gtoggle -@opindex gtoggle -Turn off generation of debug info, if leaving out this option -generates it, or turn it on at level 2 otherwise. The position of this -argument in the command line does not matter; it takes effect after all -other options are processed, and it does so only once, no matter how -many times it is given. This is mainly intended to be used with -@option{-fcompare-debug}. - -@item -fvar-tracking-assignments-toggle -@opindex fvar-tracking-assignments-toggle -@opindex fno-var-tracking-assignments-toggle -Toggle @option{-fvar-tracking-assignments}, in the same way that -@option{-gtoggle} toggles @option{-g}. - -@item -Q -@opindex Q -Makes the compiler print out each function name as it is compiled, and -print some statistics about each pass when it finishes. - -@item -ftime-report -@opindex ftime-report -Makes the compiler print some statistics about the time consumed by each -pass when it finishes. - -@item -ftime-report-details -@opindex ftime-report-details -Record the time consumed by infrastructure parts separately for each pass. - -@item -fira-verbose=@var{n} -@opindex fira-verbose -Control the verbosity of the dump file for the integrated register allocator. -The default value is 5. If the value @var{n} is greater or equal to 10, -the dump output is sent to stderr using the same format as @var{n} minus 10. - -@item -flto-report -@opindex flto-report -Prints a report with internal details on the workings of the link-time -optimizer. The contents of this report vary from version to version. -It is meant to be useful to GCC developers when processing object -files in LTO mode (via @option{-flto}). - -Disabled by default. - -@item -flto-report-wpa -@opindex flto-report-wpa -Like @option{-flto-report}, but only print for the WPA phase of link-time -optimization. - -@item -fmem-report -@opindex fmem-report -Makes the compiler print some statistics about permanent memory -allocation when it finishes. - -@item -fmem-report-wpa -@opindex fmem-report-wpa -Makes the compiler print some statistics about permanent memory -allocation for the WPA phase only. - -@item -fpre-ipa-mem-report -@opindex fpre-ipa-mem-report -@item -fpost-ipa-mem-report -@opindex fpost-ipa-mem-report -Makes the compiler print some statistics about permanent memory -allocation before or after interprocedural optimization. - -@item -fmultiflags -@opindex fmultiflags -This option enables multilib-aware @code{TFLAGS} to be used to build -target libraries with options different from those the compiler is -configured to use by default, through the use of specs (@xref{Spec -Files}) set up by compiler internals, by the target, or by builders at -configure time. - -Like @code{TFLAGS}, this allows the target libraries to be built for -portable baseline environments, while the compiler defaults to more -demanding ones. That's useful because users can easily override the -defaults the compiler is configured to use to build their own programs, -if the defaults are not ideal for their target environment, whereas -rebuilding the runtime libraries is usually not as easy or desirable. - -Unlike @code{TFLAGS}, the use of specs enables different flags to be -selected for different multilibs. The way to accomplish that is to -build with @samp{make TFLAGS=-fmultiflags}, after configuring -@samp{--with-specs=%@{fmultiflags:...@}}. - -This option is discarded by the driver once it's done processing driver -self spec. - -It is also useful to check that @code{TFLAGS} are being used to build -all target libraries, by configuring a non-bootstrap compiler -@samp{--with-specs='%@{!fmultiflags:%emissing TFLAGS@}'} and building -the compiler and target libraries. - -@item -fprofile-report -@opindex fprofile-report -Makes the compiler print some statistics about consistency of the -(estimated) profile and effect of individual passes. - -@item -fstack-usage -@opindex fstack-usage -Makes the compiler output stack usage information for the program, on a -per-function basis. The filename for the dump is made by appending -@file{.su} to the @var{auxname}. @var{auxname} is generated from the name of -the output file, if explicitly specified and it is not an executable, -otherwise it is the basename of the source file. An entry is made up -of three fields: - -@itemize -@item -The name of the function. -@item -A number of bytes. -@item -One or more qualifiers: @code{static}, @code{dynamic}, @code{bounded}. -@end itemize - -The qualifier @code{static} means that the function manipulates the stack -statically: a fixed number of bytes are allocated for the frame on function -entry and released on function exit; no stack adjustments are otherwise made -in the function. The second field is this fixed number of bytes. - -The qualifier @code{dynamic} means that the function manipulates the stack -dynamically: in addition to the static allocation described above, stack -adjustments are made in the body of the function, for example to push/pop -arguments around function calls. If the qualifier @code{bounded} is also -present, the amount of these adjustments is bounded at compile time and -the second field is an upper bound of the total amount of stack used by -the function. If it is not present, the amount of these adjustments is -not bounded at compile time and the second field only represents the -bounded part. - -@item -fstats -@opindex fstats -Emit statistics about front-end processing at the end of the compilation. -This option is supported only by the C++ front end, and -the information is generally only useful to the G++ development team. - -@item -fdbg-cnt-list -@opindex fdbg-cnt-list -Print the name and the counter upper bound for all debug counters. - - -@item -fdbg-cnt=@var{counter-value-list} -@opindex fdbg-cnt -Set the internal debug counter lower and upper bound. @var{counter-value-list} -is a comma-separated list of @var{name}:@var{lower_bound1}-@var{upper_bound1} -[:@var{lower_bound2}-@var{upper_bound2}...] tuples which sets -the name of the counter and list of closed intervals. -The @var{lower_bound} is optional and is zero -initialized if not set. -For example, with @option{-fdbg-cnt=dce:2-4:10-11,tail_call:10}, -@code{dbg_cnt(dce)} returns true only for second, third, fourth, tenth and -eleventh invocation. -For @code{dbg_cnt(tail_call)} true is returned for first 10 invocations. - -@item -print-file-name=@var{library} -@opindex print-file-name -Print the full absolute name of the library file @var{library} that -would be used when linking---and don't do anything else. With this -option, GCC does not compile or link anything; it just prints the -file name. - -@item -print-multi-directory -@opindex print-multi-directory -Print the directory name corresponding to the multilib selected by any -other switches present in the command line. This directory is supposed -to exist in @env{GCC_EXEC_PREFIX}. - -@item -print-multi-lib -@opindex print-multi-lib -Print the mapping from multilib directory names to compiler switches -that enable them. The directory name is separated from the switches by -@samp{;}, and each switch starts with an @samp{@@} instead of the -@samp{-}, without spaces between multiple switches. This is supposed to -ease shell processing. - -@item -print-multi-os-directory -@opindex print-multi-os-directory -Print the path to OS libraries for the selected -multilib, relative to some @file{lib} subdirectory. If OS libraries are -present in the @file{lib} subdirectory and no multilibs are used, this is -usually just @file{.}, if OS libraries are present in @file{lib@var{suffix}} -sibling directories this prints e.g.@: @file{../lib64}, @file{../lib} or -@file{../lib32}, or if OS libraries are present in @file{lib/@var{subdir}} -subdirectories it prints e.g.@: @file{amd64}, @file{sparcv9} or @file{ev6}. - -@item -print-multiarch -@opindex print-multiarch -Print the path to OS libraries for the selected multiarch, -relative to some @file{lib} subdirectory. - -@item -print-prog-name=@var{program} -@opindex print-prog-name -Like @option{-print-file-name}, but searches for a program such as @command{cpp}. - -@item -print-libgcc-file-name -@opindex print-libgcc-file-name -Same as @option{-print-file-name=libgcc.a}. - -This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs} -but you do want to link with @file{libgcc.a}. You can do: - -@smallexample -gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name` -@end smallexample - -@item -print-search-dirs -@opindex print-search-dirs -Print the name of the configured installation directory and a list of -program and library directories @command{gcc} searches---and don't do anything else. - -This is useful when @command{gcc} prints the error message -@samp{installation problem, cannot exec cpp0: No such file or directory}. -To resolve this you either need to put @file{cpp0} and the other compiler -components where @command{gcc} expects to find them, or you can set the environment -variable @env{GCC_EXEC_PREFIX} to the directory where you installed them. -Don't forget the trailing @samp{/}. -@xref{Environment Variables}. - -@item -print-sysroot -@opindex print-sysroot -Print the target sysroot directory that is used during -compilation. This is the target sysroot specified either at configure -time or using the @option{--sysroot} option, possibly with an extra -suffix that depends on compilation options. If no target sysroot is -specified, the option prints nothing. - -@item -print-sysroot-headers-suffix -@opindex print-sysroot-headers-suffix -Print the suffix added to the target sysroot when searching for -headers, or give an error if the compiler is not configured with such -a suffix---and don't do anything else. - -@item -dumpmachine -@opindex dumpmachine -Print the compiler's target machine (for example, -@samp{i686-pc-linux-gnu})---and don't do anything else. - -@item -dumpversion -@opindex dumpversion -Print the compiler version (for example, @code{3.0}, @code{6.3.0} or @code{7})---and don't do -anything else. This is the compiler version used in filesystem paths and -specs. Depending on how the compiler has been configured it can be just -a single number (major version), two numbers separated by a dot (major and -minor version) or three numbers separated by dots (major, minor and patchlevel -version). - -@item -dumpfullversion -@opindex dumpfullversion -Print the full compiler version---and don't do anything else. The output is -always three numbers separated by dots, major, minor and patchlevel version. - -@item -dumpspecs -@opindex dumpspecs -Print the compiler's built-in specs---and don't do anything else. (This -is used when GCC itself is being built.) @xref{Spec Files}. -@end table - -@node Submodel Options -@section Machine-Dependent Options -@cindex submodel options -@cindex specifying hardware config -@cindex hardware models and configurations, specifying -@cindex target-dependent options -@cindex machine-dependent options - -Each target machine supported by GCC can have its own options---for -example, to allow you to compile for a particular processor variant or -ABI, or to control optimizations specific to that machine. By -convention, the names of machine-specific options start with -@samp{-m}. - -Some configurations of the compiler also support additional target-specific -options, usually for compatibility with other compilers on the same -platform. - -@c This list is ordered alphanumerically by subsection name. -@c It should be the same order and spelling as these options are listed -@c in Machine Dependent Options - -@menu -* AArch64 Options:: -* Adapteva Epiphany Options:: -* AMD GCN Options:: -* ARC Options:: -* ARM Options:: -* AVR Options:: -* Blackfin Options:: -* C6X Options:: -* CRIS Options:: -* C-SKY Options:: -* Darwin Options:: -* DEC Alpha Options:: -* eBPF Options:: -* FR30 Options:: -* FT32 Options:: -* FRV Options:: -* GNU/Linux Options:: -* H8/300 Options:: -* HPPA Options:: -* IA-64 Options:: -* LM32 Options:: -* LoongArch Options:: -* M32C Options:: -* M32R/D Options:: -* M680x0 Options:: -* MCore Options:: -* MeP Options:: -* MicroBlaze Options:: -* MIPS Options:: -* MMIX Options:: -* MN10300 Options:: -* Moxie Options:: -* MSP430 Options:: -* NDS32 Options:: -* Nios II Options:: -* Nvidia PTX Options:: -* OpenRISC Options:: -* PDP-11 Options:: -* picoChip Options:: -* PowerPC Options:: -* PRU Options:: -* RISC-V Options:: -* RL78 Options:: -* RS/6000 and PowerPC Options:: -* RX Options:: -* S/390 and zSeries Options:: -* Score Options:: -* SH Options:: -* Solaris 2 Options:: -* SPARC Options:: -* System V Options:: -* V850 Options:: -* VAX Options:: -* Visium Options:: -* VMS Options:: -* VxWorks Options:: -* x86 Options:: -* x86 Windows Options:: -* Xstormy16 Options:: -* Xtensa Options:: -* zSeries Options:: -@end menu - -@node AArch64 Options -@subsection AArch64 Options -@cindex AArch64 Options - -These options are defined for AArch64 implementations: - -@table @gcctabopt - -@item -mabi=@var{name} -@opindex mabi -Generate code for the specified data model. Permissible values -are @samp{ilp32} for SysV-like data model where int, long int and pointers -are 32 bits, and @samp{lp64} for SysV-like data model where int is 32 bits, -but long int and pointers are 64 bits. - -The default depends on the specific target configuration. Note that -the LP64 and ILP32 ABIs are not link-compatible; you must compile your -entire program with the same ABI, and link with a compatible set of libraries. - -@item -mbig-endian -@opindex mbig-endian -Generate big-endian code. This is the default when GCC is configured for an -@samp{aarch64_be-*-*} target. - -@item -mgeneral-regs-only -@opindex mgeneral-regs-only -Generate code which uses only the general-purpose registers. This will prevent -the compiler from using floating-point and Advanced SIMD registers but will not -impose any restrictions on the assembler. - -@item -mlittle-endian -@opindex mlittle-endian -Generate little-endian code. This is the default when GCC is configured for an -@samp{aarch64-*-*} but not an @samp{aarch64_be-*-*} target. - -@item -mcmodel=tiny -@opindex mcmodel=tiny -Generate code for the tiny code model. The program and its statically defined -symbols must be within 1MB of each other. Programs can be statically or -dynamically linked. - -@item -mcmodel=small -@opindex mcmodel=small -Generate code for the small code model. The program and its statically defined -symbols must be within 4GB of each other. Programs can be statically or -dynamically linked. This is the default code model. - -@item -mcmodel=large -@opindex mcmodel=large -Generate code for the large code model. This makes no assumptions about -addresses and sizes of sections. Programs can be statically linked only. The -@option{-mcmodel=large} option is incompatible with @option{-mabi=ilp32}, -@option{-fpic} and @option{-fPIC}. - -@item -mstrict-align -@itemx -mno-strict-align -@opindex mstrict-align -@opindex mno-strict-align -Avoid or allow generating memory accesses that may not be aligned on a natural -object boundary as described in the architecture specification. - -@item -momit-leaf-frame-pointer -@itemx -mno-omit-leaf-frame-pointer -@opindex momit-leaf-frame-pointer -@opindex mno-omit-leaf-frame-pointer -Omit or keep the frame pointer in leaf functions. The former behavior is the -default. - -@item -mstack-protector-guard=@var{guard} -@itemx -mstack-protector-guard-reg=@var{reg} -@itemx -mstack-protector-guard-offset=@var{offset} -@opindex mstack-protector-guard -@opindex mstack-protector-guard-reg -@opindex mstack-protector-guard-offset -Generate stack protection code using canary at @var{guard}. Supported -locations are @samp{global} for a global canary or @samp{sysreg} for a -canary in an appropriate system register. - -With the latter choice the options -@option{-mstack-protector-guard-reg=@var{reg}} and -@option{-mstack-protector-guard-offset=@var{offset}} furthermore specify -which system register to use as base register for reading the canary, -and from what offset from that base register. There is no default -register or offset as this is entirely for use within the Linux -kernel. - -@item -mtls-dialect=desc -@opindex mtls-dialect=desc -Use TLS descriptors as the thread-local storage mechanism for dynamic accesses -of TLS variables. This is the default. - -@item -mtls-dialect=traditional -@opindex mtls-dialect=traditional -Use traditional TLS as the thread-local storage mechanism for dynamic accesses -of TLS variables. - -@item -mtls-size=@var{size} -@opindex mtls-size -Specify bit size of immediate TLS offsets. Valid values are 12, 24, 32, 48. -This option requires binutils 2.26 or newer. - -@item -mfix-cortex-a53-835769 -@itemx -mno-fix-cortex-a53-835769 -@opindex mfix-cortex-a53-835769 -@opindex mno-fix-cortex-a53-835769 -Enable or disable the workaround for the ARM Cortex-A53 erratum number 835769. -This involves inserting a NOP instruction between memory instructions and -64-bit integer multiply-accumulate instructions. - -@item -mfix-cortex-a53-843419 -@itemx -mno-fix-cortex-a53-843419 -@opindex mfix-cortex-a53-843419 -@opindex mno-fix-cortex-a53-843419 -Enable or disable the workaround for the ARM Cortex-A53 erratum number 843419. -This erratum workaround is made at link time and this will only pass the -corresponding flag to the linker. - -@item -mlow-precision-recip-sqrt -@itemx -mno-low-precision-recip-sqrt -@opindex mlow-precision-recip-sqrt -@opindex mno-low-precision-recip-sqrt -Enable or disable the reciprocal square root approximation. -This option only has an effect if @option{-ffast-math} or -@option{-funsafe-math-optimizations} is used as well. Enabling this reduces -precision of reciprocal square root results to about 16 bits for -single precision and to 32 bits for double precision. - -@item -mlow-precision-sqrt -@itemx -mno-low-precision-sqrt -@opindex mlow-precision-sqrt -@opindex mno-low-precision-sqrt -Enable or disable the square root approximation. -This option only has an effect if @option{-ffast-math} or -@option{-funsafe-math-optimizations} is used as well. Enabling this reduces -precision of square root results to about 16 bits for -single precision and to 32 bits for double precision. -If enabled, it implies @option{-mlow-precision-recip-sqrt}. - -@item -mlow-precision-div -@itemx -mno-low-precision-div -@opindex mlow-precision-div -@opindex mno-low-precision-div -Enable or disable the division approximation. -This option only has an effect if @option{-ffast-math} or -@option{-funsafe-math-optimizations} is used as well. Enabling this reduces -precision of division results to about 16 bits for -single precision and to 32 bits for double precision. - -@item -mtrack-speculation -@itemx -mno-track-speculation -Enable or disable generation of additional code to track speculative -execution through conditional branches. The tracking state can then -be used by the compiler when expanding calls to -@code{__builtin_speculation_safe_copy} to permit a more efficient code -sequence to be generated. - -@item -moutline-atomics -@itemx -mno-outline-atomics -Enable or disable calls to out-of-line helpers to implement atomic operations. -These helpers will, at runtime, determine if the LSE instructions from -ARMv8.1-A can be used; if not, they will use the load/store-exclusive -instructions that are present in the base ARMv8.0 ISA. - -This option is only applicable when compiling for the base ARMv8.0 -instruction set. If using a later revision, e.g. @option{-march=armv8.1-a} -or @option{-march=armv8-a+lse}, the ARMv8.1-Atomics instructions will be -used directly. The same applies when using @option{-mcpu=} when the -selected cpu supports the @samp{lse} feature. -This option is on by default. - -@item -march=@var{name} -@opindex march -Specify the name of the target architecture and, optionally, one or -more feature modifiers. This option has the form -@option{-march=@var{arch}@r{@{}+@r{[}no@r{]}@var{feature}@r{@}*}}. - -The table below summarizes the permissible values for @var{arch} -and the features that they enable by default: - -@multitable @columnfractions 0.20 0.20 0.60 -@headitem @var{arch} value @tab Architecture @tab Includes by default -@item @samp{armv8-a} @tab Armv8-A @tab @samp{+fp}, @samp{+simd} -@item @samp{armv8.1-a} @tab Armv8.1-A @tab @samp{armv8-a}, @samp{+crc}, @samp{+lse}, @samp{+rdma} -@item @samp{armv8.2-a} @tab Armv8.2-A @tab @samp{armv8.1-a} -@item @samp{armv8.3-a} @tab Armv8.3-A @tab @samp{armv8.2-a}, @samp{+pauth} -@item @samp{armv8.4-a} @tab Armv8.4-A @tab @samp{armv8.3-a}, @samp{+flagm}, @samp{+fp16fml}, @samp{+dotprod} -@item @samp{armv8.5-a} @tab Armv8.5-A @tab @samp{armv8.4-a}, @samp{+sb}, @samp{+ssbs}, @samp{+predres} -@item @samp{armv8.6-a} @tab Armv8.6-A @tab @samp{armv8.5-a}, @samp{+bf16}, @samp{+i8mm} -@item @samp{armv8.7-a} @tab Armv8.7-A @tab @samp{armv8.6-a}, @samp{+ls64} -@item @samp{armv8.8-a} @tab Armv8.8-a @tab @samp{armv8.7-a}, @samp{+mops} -@item @samp{armv9-a} @tab Armv9-A @tab @samp{armv8.5-a}, @samp{+sve}, @samp{+sve2} -@item @samp{armv9.1-a} @tab Armv9.1-A @tab @samp{armv9-a}, @samp{+bf16}, @samp{+i8mm} -@item @samp{armv9.2-a} @tab Armv9.2-A @tab @samp{armv9.1-a}, @samp{+ls64} -@item @samp{armv9.3-a} @tab Armv9.3-A @tab @samp{armv9.2-a}, @samp{+mops} -@item @samp{armv8-r} @tab Armv8-R @tab @samp{armv8-r} -@end multitable - -The value @samp{native} is available on native AArch64 GNU/Linux and -causes the compiler to pick the architecture of the host system. This -option has no effect if the compiler is unable to recognize the -architecture of the host system, - -The permissible values for @var{feature} are listed in the sub-section -on @ref{aarch64-feature-modifiers,,@option{-march} and @option{-mcpu} -Feature Modifiers}. Where conflicting feature modifiers are -specified, the right-most feature is used. - -GCC uses @var{name} to determine what kind of instructions it can emit -when generating assembly code. If @option{-march} is specified -without either of @option{-mtune} or @option{-mcpu} also being -specified, the code is tuned to perform well across a range of target -processors implementing the target architecture. - -@item -mtune=@var{name} -@opindex mtune -Specify the name of the target processor for which GCC should tune the -performance of the code. Permissible values for this option are: -@samp{generic}, @samp{cortex-a35}, @samp{cortex-a53}, @samp{cortex-a55}, -@samp{cortex-a57}, @samp{cortex-a72}, @samp{cortex-a73}, @samp{cortex-a75}, -@samp{cortex-a76}, @samp{cortex-a76ae}, @samp{cortex-a77}, -@samp{cortex-a65}, @samp{cortex-a65ae}, @samp{cortex-a34}, -@samp{cortex-a78}, @samp{cortex-a78ae}, @samp{cortex-a78c}, -@samp{ares}, @samp{exynos-m1}, @samp{emag}, @samp{falkor}, -@samp{neoverse-512tvb}, @samp{neoverse-e1}, @samp{neoverse-n1}, -@samp{neoverse-n2}, @samp{neoverse-v1}, @samp{neoverse-v2}, @samp{qdf24xx}, -@samp{saphira}, @samp{phecda}, @samp{xgene1}, @samp{vulcan}, -@samp{octeontx}, @samp{octeontx81}, @samp{octeontx83}, -@samp{octeontx2}, @samp{octeontx2t98}, @samp{octeontx2t96} -@samp{octeontx2t93}, @samp{octeontx2f95}, @samp{octeontx2f95n}, -@samp{octeontx2f95mm}, -@samp{a64fx}, -@samp{thunderx}, @samp{thunderxt88}, -@samp{thunderxt88p1}, @samp{thunderxt81}, @samp{tsv110}, -@samp{thunderxt83}, @samp{thunderx2t99}, @samp{thunderx3t110}, @samp{zeus}, -@samp{cortex-a57.cortex-a53}, @samp{cortex-a72.cortex-a53}, -@samp{cortex-a73.cortex-a35}, @samp{cortex-a73.cortex-a53}, -@samp{cortex-a75.cortex-a55}, @samp{cortex-a76.cortex-a55}, -@samp{cortex-r82}, @samp{cortex-x1}, @samp{cortex-x2}, -@samp{cortex-a510}, @samp{cortex-a710}, @samp{ampere1}, @samp{native}. - -The values @samp{cortex-a57.cortex-a53}, @samp{cortex-a72.cortex-a53}, -@samp{cortex-a73.cortex-a35}, @samp{cortex-a73.cortex-a53}, -@samp{cortex-a75.cortex-a55}, @samp{cortex-a76.cortex-a55} specify that GCC -should tune for a big.LITTLE system. - -The value @samp{neoverse-512tvb} specifies that GCC should tune -for Neoverse cores that (a) implement SVE and (b) have a total vector -bandwidth of 512 bits per cycle. In other words, the option tells GCC to -tune for Neoverse cores that can execute 4 128-bit Advanced SIMD arithmetic -instructions a cycle and that can execute an equivalent number of SVE -arithmetic instructions per cycle (2 for 256-bit SVE, 4 for 128-bit SVE). -This is more general than tuning for a specific core like Neoverse V1 -but is more specific than the default tuning described below. - -Additionally on native AArch64 GNU/Linux systems the value -@samp{native} tunes performance to the host system. This option has no effect -if the compiler is unable to recognize the processor of the host system. - -Where none of @option{-mtune=}, @option{-mcpu=} or @option{-march=} -are specified, the code is tuned to perform well across a range -of target processors. - -This option cannot be suffixed by feature modifiers. - -@item -mcpu=@var{name} -@opindex mcpu -Specify the name of the target processor, optionally suffixed by one -or more feature modifiers. This option has the form -@option{-mcpu=@var{cpu}@r{@{}+@r{[}no@r{]}@var{feature}@r{@}*}}, where -the permissible values for @var{cpu} are the same as those available -for @option{-mtune}. The permissible values for @var{feature} are -documented in the sub-section on -@ref{aarch64-feature-modifiers,,@option{-march} and @option{-mcpu} -Feature Modifiers}. Where conflicting feature modifiers are -specified, the right-most feature is used. - -GCC uses @var{name} to determine what kind of instructions it can emit when -generating assembly code (as if by @option{-march}) and to determine -the target processor for which to tune for performance (as if -by @option{-mtune}). Where this option is used in conjunction -with @option{-march} or @option{-mtune}, those options take precedence -over the appropriate part of this option. - -@option{-mcpu=neoverse-512tvb} is special in that it does not refer -to a specific core, but instead refers to all Neoverse cores that -(a) implement SVE and (b) have a total vector bandwidth of 512 bits -a cycle. Unless overridden by @option{-march}, -@option{-mcpu=neoverse-512tvb} generates code that can run on a -Neoverse V1 core, since Neoverse V1 is the first Neoverse core with -these properties. Unless overridden by @option{-mtune}, -@option{-mcpu=neoverse-512tvb} tunes code in the same way as for -@option{-mtune=neoverse-512tvb}. - -@item -moverride=@var{string} -@opindex moverride -Override tuning decisions made by the back-end in response to a -@option{-mtune=} switch. The syntax, semantics, and accepted values -for @var{string} in this option are not guaranteed to be consistent -across releases. - -This option is only intended to be useful when developing GCC. - -@item -mverbose-cost-dump -@opindex mverbose-cost-dump -Enable verbose cost model dumping in the debug dump files. This option is -provided for use in debugging the compiler. - -@item -mpc-relative-literal-loads -@itemx -mno-pc-relative-literal-loads -@opindex mpc-relative-literal-loads -@opindex mno-pc-relative-literal-loads -Enable or disable PC-relative literal loads. With this option literal pools are -accessed using a single instruction and emitted after each function. This -limits the maximum size of functions to 1MB. This is enabled by default for -@option{-mcmodel=tiny}. - -@item -msign-return-address=@var{scope} -@opindex msign-return-address -Select the function scope on which return address signing will be applied. -Permissible values are @samp{none}, which disables return address signing, -@samp{non-leaf}, which enables pointer signing for functions which are not leaf -functions, and @samp{all}, which enables pointer signing for all functions. The -default value is @samp{none}. This option has been deprecated by --mbranch-protection. - -@item -mbranch-protection=@var{none}|@var{standard}|@var{pac-ret}[+@var{leaf}+@var{b-key}]|@var{bti} -@opindex mbranch-protection -Select the branch protection features to use. -@samp{none} is the default and turns off all types of branch protection. -@samp{standard} turns on all types of branch protection features. If a feature -has additional tuning options, then @samp{standard} sets it to its standard -level. -@samp{pac-ret[+@var{leaf}]} turns on return address signing to its standard -level: signing functions that save the return address to memory (non-leaf -functions will practically always do this) using the a-key. The optional -argument @samp{leaf} can be used to extend the signing to include leaf -functions. The optional argument @samp{b-key} can be used to sign the functions -with the B-key instead of the A-key. -@samp{bti} turns on branch target identification mechanism. - -@item -mharden-sls=@var{opts} -@opindex mharden-sls -Enable compiler hardening against straight line speculation (SLS). -@var{opts} is a comma-separated list of the following options: -@table @samp -@item retbr -@item blr -@end table -In addition, @samp{-mharden-sls=all} enables all SLS hardening while -@samp{-mharden-sls=none} disables all SLS hardening. - -@item -msve-vector-bits=@var{bits} -@opindex msve-vector-bits -Specify the number of bits in an SVE vector register. This option only has -an effect when SVE is enabled. - -GCC supports two forms of SVE code generation: ``vector-length -agnostic'' output that works with any size of vector register and -``vector-length specific'' output that allows GCC to make assumptions -about the vector length when it is useful for optimization reasons. -The possible values of @samp{bits} are: @samp{scalable}, @samp{128}, -@samp{256}, @samp{512}, @samp{1024} and @samp{2048}. -Specifying @samp{scalable} selects vector-length agnostic -output. At present @samp{-msve-vector-bits=128} also generates vector-length -agnostic output for big-endian targets. All other values generate -vector-length specific code. The behavior of these values may change -in future releases and no value except @samp{scalable} should be -relied on for producing code that is portable across different -hardware SVE vector lengths. - -The default is @samp{-msve-vector-bits=scalable}, which produces -vector-length agnostic code. -@end table - -@subsubsection @option{-march} and @option{-mcpu} Feature Modifiers -@anchor{aarch64-feature-modifiers} -@cindex @option{-march} feature modifiers -@cindex @option{-mcpu} feature modifiers -Feature modifiers used with @option{-march} and @option{-mcpu} can be any of -the following and their inverses @option{no@var{feature}}: - -@table @samp -@item crc -Enable CRC extension. This is on by default for -@option{-march=armv8.1-a}. -@item crypto -Enable Crypto extension. This also enables Advanced SIMD and floating-point -instructions. -@item fp -Enable floating-point instructions. This is on by default for all possible -values for options @option{-march} and @option{-mcpu}. -@item simd -Enable Advanced SIMD instructions. This also enables floating-point -instructions. This is on by default for all possible values for options -@option{-march} and @option{-mcpu}. -@item sve -Enable Scalable Vector Extension instructions. This also enables Advanced -SIMD and floating-point instructions. -@item lse -Enable Large System Extension instructions. This is on by default for -@option{-march=armv8.1-a}. -@item rdma -Enable Round Double Multiply Accumulate instructions. This is on by default -for @option{-march=armv8.1-a}. -@item fp16 -Enable FP16 extension. This also enables floating-point instructions. -@item fp16fml -Enable FP16 fmla extension. This also enables FP16 extensions and -floating-point instructions. This option is enabled by default for @option{-march=armv8.4-a}. Use of this option with architectures prior to Armv8.2-A is not supported. - -@item rcpc -Enable the RcPc extension. This does not change code generation from GCC, -but is passed on to the assembler, enabling inline asm statements to use -instructions from the RcPc extension. -@item dotprod -Enable the Dot Product extension. This also enables Advanced SIMD instructions. -@item aes -Enable the Armv8-a aes and pmull crypto extension. This also enables Advanced -SIMD instructions. -@item sha2 -Enable the Armv8-a sha2 crypto extension. This also enables Advanced SIMD instructions. -@item sha3 -Enable the sha512 and sha3 crypto extension. This also enables Advanced SIMD -instructions. Use of this option with architectures prior to Armv8.2-A is not supported. -@item sm4 -Enable the sm3 and sm4 crypto extension. This also enables Advanced SIMD instructions. -Use of this option with architectures prior to Armv8.2-A is not supported. -@item profile -Enable the Statistical Profiling extension. This option is only to enable the -extension at the assembler level and does not affect code generation. -@item rng -Enable the Armv8.5-a Random Number instructions. This option is only to -enable the extension at the assembler level and does not affect code -generation. -@item memtag -Enable the Armv8.5-a Memory Tagging Extensions. -Use of this option with architectures prior to Armv8.5-A is not supported. -@item sb -Enable the Armv8-a Speculation Barrier instruction. This option is only to -enable the extension at the assembler level and does not affect code -generation. This option is enabled by default for @option{-march=armv8.5-a}. -@item ssbs -Enable the Armv8-a Speculative Store Bypass Safe instruction. This option -is only to enable the extension at the assembler level and does not affect code -generation. This option is enabled by default for @option{-march=armv8.5-a}. -@item predres -Enable the Armv8-a Execution and Data Prediction Restriction instructions. -This option is only to enable the extension at the assembler level and does -not affect code generation. This option is enabled by default for -@option{-march=armv8.5-a}. -@item sve2 -Enable the Armv8-a Scalable Vector Extension 2. This also enables SVE -instructions. -@item sve2-bitperm -Enable SVE2 bitperm instructions. This also enables SVE2 instructions. -@item sve2-sm4 -Enable SVE2 sm4 instructions. This also enables SVE2 instructions. -@item sve2-aes -Enable SVE2 aes instructions. This also enables SVE2 instructions. -@item sve2-sha3 -Enable SVE2 sha3 instructions. This also enables SVE2 instructions. -@item tme -Enable the Transactional Memory Extension. -@item i8mm -Enable 8-bit Integer Matrix Multiply instructions. This also enables -Advanced SIMD and floating-point instructions. This option is enabled by -default for @option{-march=armv8.6-a}. Use of this option with architectures -prior to Armv8.2-A is not supported. -@item f32mm -Enable 32-bit Floating point Matrix Multiply instructions. This also enables -SVE instructions. Use of this option with architectures prior to Armv8.2-A is -not supported. -@item f64mm -Enable 64-bit Floating point Matrix Multiply instructions. This also enables -SVE instructions. Use of this option with architectures prior to Armv8.2-A is -not supported. -@item bf16 -Enable brain half-precision floating-point instructions. This also enables -Advanced SIMD and floating-point instructions. This option is enabled by -default for @option{-march=armv8.6-a}. Use of this option with architectures -prior to Armv8.2-A is not supported. -@item ls64 -Enable the 64-byte atomic load and store instructions for accelerators. -This option is enabled by default for @option{-march=armv8.7-a}. -@item mops -Enable the instructions to accelerate memory operations like @code{memcpy}, -@code{memmove}, @code{memset}. This option is enabled by default for -@option{-march=armv8.8-a} -@item flagm -Enable the Flag Manipulation instructions Extension. -@item pauth -Enable the Pointer Authentication Extension. - -@end table - -Feature @option{crypto} implies @option{aes}, @option{sha2}, and @option{simd}, -which implies @option{fp}. -Conversely, @option{nofp} implies @option{nosimd}, which implies -@option{nocrypto}, @option{noaes} and @option{nosha2}. - -@node Adapteva Epiphany Options -@subsection Adapteva Epiphany Options - -These @samp{-m} options are defined for Adapteva Epiphany: - -@table @gcctabopt -@item -mhalf-reg-file -@opindex mhalf-reg-file -Don't allocate any register in the range @code{r32}@dots{}@code{r63}. -That allows code to run on hardware variants that lack these registers. - -@item -mprefer-short-insn-regs -@opindex mprefer-short-insn-regs -Preferentially allocate registers that allow short instruction generation. -This can result in increased instruction count, so this may either reduce or -increase overall code size. - -@item -mbranch-cost=@var{num} -@opindex mbranch-cost -Set the cost of branches to roughly @var{num} ``simple'' instructions. -This cost is only a heuristic and is not guaranteed to produce -consistent results across releases. - -@item -mcmove -@opindex mcmove -Enable the generation of conditional moves. - -@item -mnops=@var{num} -@opindex mnops -Emit @var{num} NOPs before every other generated instruction. - -@item -mno-soft-cmpsf -@opindex mno-soft-cmpsf -@opindex msoft-cmpsf -For single-precision floating-point comparisons, emit an @code{fsub} instruction -and test the flags. This is faster than a software comparison, but can -get incorrect results in the presence of NaNs, or when two different small -numbers are compared such that their difference is calculated as zero. -The default is @option{-msoft-cmpsf}, which uses slower, but IEEE-compliant, -software comparisons. - -@item -mstack-offset=@var{num} -@opindex mstack-offset -Set the offset between the top of the stack and the stack pointer. -E.g., a value of 8 means that the eight bytes in the range @code{sp+0@dots{}sp+7} -can be used by leaf functions without stack allocation. -Values other than @samp{8} or @samp{16} are untested and unlikely to work. -Note also that this option changes the ABI; compiling a program with a -different stack offset than the libraries have been compiled with -generally does not work. -This option can be useful if you want to evaluate if a different stack -offset would give you better code, but to actually use a different stack -offset to build working programs, it is recommended to configure the -toolchain with the appropriate @option{--with-stack-offset=@var{num}} option. - -@item -mno-round-nearest -@opindex mno-round-nearest -@opindex mround-nearest -Make the scheduler assume that the rounding mode has been set to -truncating. The default is @option{-mround-nearest}. - -@item -mlong-calls -@opindex mlong-calls -If not otherwise specified by an attribute, assume all calls might be beyond -the offset range of the @code{b} / @code{bl} instructions, and therefore load the -function address into a register before performing a (otherwise direct) call. -This is the default. - -@item -mshort-calls -@opindex short-calls -If not otherwise specified by an attribute, assume all direct calls are -in the range of the @code{b} / @code{bl} instructions, so use these instructions -for direct calls. The default is @option{-mlong-calls}. - -@item -msmall16 -@opindex msmall16 -Assume addresses can be loaded as 16-bit unsigned values. This does not -apply to function addresses for which @option{-mlong-calls} semantics -are in effect. - -@item -mfp-mode=@var{mode} -@opindex mfp-mode -Set the prevailing mode of the floating-point unit. -This determines the floating-point mode that is provided and expected -at function call and return time. Making this mode match the mode you -predominantly need at function start can make your programs smaller and -faster by avoiding unnecessary mode switches. - -@var{mode} can be set to one the following values: - -@table @samp -@item caller -Any mode at function entry is valid, and retained or restored when -the function returns, and when it calls other functions. -This mode is useful for compiling libraries or other compilation units -you might want to incorporate into different programs with different -prevailing FPU modes, and the convenience of being able to use a single -object file outweighs the size and speed overhead for any extra -mode switching that might be needed, compared with what would be needed -with a more specific choice of prevailing FPU mode. - -@item truncate -This is the mode used for floating-point calculations with -truncating (i.e.@: round towards zero) rounding mode. That includes -conversion from floating point to integer. - -@item round-nearest -This is the mode used for floating-point calculations with -round-to-nearest-or-even rounding mode. - -@item int -This is the mode used to perform integer calculations in the FPU, e.g.@: -integer multiply, or integer multiply-and-accumulate. -@end table - -The default is @option{-mfp-mode=caller} - -@item -mno-split-lohi -@itemx -mno-postinc -@itemx -mno-postmodify -@opindex mno-split-lohi -@opindex msplit-lohi -@opindex mno-postinc -@opindex mpostinc -@opindex mno-postmodify -@opindex mpostmodify -Code generation tweaks that disable, respectively, splitting of 32-bit -loads, generation of post-increment addresses, and generation of -post-modify addresses. The defaults are @option{msplit-lohi}, -@option{-mpost-inc}, and @option{-mpost-modify}. - -@item -mnovect-double -@opindex mno-vect-double -@opindex mvect-double -Change the preferred SIMD mode to SImode. The default is -@option{-mvect-double}, which uses DImode as preferred SIMD mode. - -@item -max-vect-align=@var{num} -@opindex max-vect-align -The maximum alignment for SIMD vector mode types. -@var{num} may be 4 or 8. The default is 8. -Note that this is an ABI change, even though many library function -interfaces are unaffected if they don't use SIMD vector modes -in places that affect size and/or alignment of relevant types. - -@item -msplit-vecmove-early -@opindex msplit-vecmove-early -Split vector moves into single word moves before reload. In theory this -can give better register allocation, but so far the reverse seems to be -generally the case. - -@item -m1reg-@var{reg} -@opindex m1reg- -Specify a register to hold the constant @minus{}1, which makes loading small negative -constants and certain bitmasks faster. -Allowable values for @var{reg} are @samp{r43} and @samp{r63}, -which specify use of that register as a fixed register, -and @samp{none}, which means that no register is used for this -purpose. The default is @option{-m1reg-none}. - -@end table - -@node AMD GCN Options -@subsection AMD GCN Options -@cindex AMD GCN Options - -These options are defined specifically for the AMD GCN port. - -@table @gcctabopt - -@item -march=@var{gpu} -@opindex march -@itemx -mtune=@var{gpu} -@opindex mtune -Set architecture type or tuning for @var{gpu}. Supported values for @var{gpu} -are - -@table @samp -@item fiji -Compile for GCN3 Fiji devices (gfx803). - -@item gfx900 -Compile for GCN5 Vega 10 devices (gfx900). - -@item gfx906 -Compile for GCN5 Vega 20 devices (gfx906). - -@item gfx908 -Compile for CDNA1 Instinct MI100 series devices (gfx908). - -@item gfx90a -Compile for CDNA2 Instinct MI200 series devices (gfx90a). - -@end table - -@item -msram-ecc=on -@itemx -msram-ecc=off -@itemx -msram-ecc=any -@opindex msram-ecc -Compile binaries suitable for devices with the SRAM-ECC feature enabled, -disabled, or either mode. This feature can be enabled per-process on some -devices. The compiled code must match the device mode. The default is -@samp{any}, for devices that support it. - -@item -mstack-size=@var{bytes} -@opindex mstack-size -Specify how many @var{bytes} of stack space will be requested for each GPU -thread (wave-front). Beware that there may be many threads and limited memory -available. The size of the stack allocation may also have an impact on -run-time performance. The default is 32KB when using OpenACC or OpenMP, and -1MB otherwise. - -@item -mxnack -@opindex mxnack -Compile binaries suitable for devices with the XNACK feature enabled. Some -devices always require XNACK and some allow the user to configure XNACK. The -compiled code must match the device mode. The default is @samp{-mno-xnack}. -At present this option is a placeholder for support that is not yet -implemented. - -@end table - -@node ARC Options -@subsection ARC Options -@cindex ARC options - -The following options control the architecture variant for which code -is being compiled: - -@c architecture variants -@table @gcctabopt - -@item -mbarrel-shifter -@opindex mbarrel-shifter -Generate instructions supported by barrel shifter. This is the default -unless @option{-mcpu=ARC601} or @samp{-mcpu=ARCEM} is in effect. - -@item -mjli-always -@opindex mjli-always -Force to call a function using jli_s instruction. This option is -valid only for ARCv2 architecture. - -@item -mcpu=@var{cpu} -@opindex mcpu -Set architecture type, register usage, and instruction scheduling -parameters for @var{cpu}. There are also shortcut alias options -available for backward compatibility and convenience. Supported -values for @var{cpu} are - -@table @samp -@opindex mA6 -@opindex mARC600 -@item arc600 -Compile for ARC600. Aliases: @option{-mA6}, @option{-mARC600}. - -@item arc601 -@opindex mARC601 -Compile for ARC601. Alias: @option{-mARC601}. - -@item arc700 -@opindex mA7 -@opindex mARC700 -Compile for ARC700. Aliases: @option{-mA7}, @option{-mARC700}. -This is the default when configured with @option{--with-cpu=arc700}@. - -@item arcem -Compile for ARC EM. - -@item archs -Compile for ARC HS. - -@item em -Compile for ARC EM CPU with no hardware extensions. - -@item em4 -Compile for ARC EM4 CPU. - -@item em4_dmips -Compile for ARC EM4 DMIPS CPU. - -@item em4_fpus -Compile for ARC EM4 DMIPS CPU with the single-precision floating-point -extension. - -@item em4_fpuda -Compile for ARC EM4 DMIPS CPU with single-precision floating-point and -double assist instructions. - -@item hs -Compile for ARC HS CPU with no hardware extensions except the atomic -instructions. - -@item hs34 -Compile for ARC HS34 CPU. - -@item hs38 -Compile for ARC HS38 CPU. - -@item hs38_linux -Compile for ARC HS38 CPU with all hardware extensions on. - -@item hs4x -Compile for ARC HS4x CPU. - -@item hs4xd -Compile for ARC HS4xD CPU. - -@item hs4x_rel31 -Compile for ARC HS4x CPU release 3.10a. - -@item arc600_norm -Compile for ARC 600 CPU with @code{norm} instructions enabled. - -@item arc600_mul32x16 -Compile for ARC 600 CPU with @code{norm} and 32x16-bit multiply -instructions enabled. - -@item arc600_mul64 -Compile for ARC 600 CPU with @code{norm} and @code{mul64}-family -instructions enabled. - -@item arc601_norm -Compile for ARC 601 CPU with @code{norm} instructions enabled. - -@item arc601_mul32x16 -Compile for ARC 601 CPU with @code{norm} and 32x16-bit multiply -instructions enabled. - -@item arc601_mul64 -Compile for ARC 601 CPU with @code{norm} and @code{mul64}-family -instructions enabled. - -@item nps400 -Compile for ARC 700 on NPS400 chip. - -@item em_mini -Compile for ARC EM minimalist configuration featuring reduced register -set. - -@end table - -@item -mdpfp -@opindex mdpfp -@itemx -mdpfp-compact -@opindex mdpfp-compact -Generate double-precision FPX instructions, tuned for the compact -implementation. - -@item -mdpfp-fast -@opindex mdpfp-fast -Generate double-precision FPX instructions, tuned for the fast -implementation. - -@item -mno-dpfp-lrsr -@opindex mno-dpfp-lrsr -Disable @code{lr} and @code{sr} instructions from using FPX extension -aux registers. - -@item -mea -@opindex mea -Generate extended arithmetic instructions. Currently only -@code{divaw}, @code{adds}, @code{subs}, and @code{sat16} are -supported. Only valid for @option{-mcpu=ARC700}. - -@item -mno-mpy -@opindex mno-mpy -@opindex mmpy -Do not generate @code{mpy}-family instructions for ARC700. This option is -deprecated. - -@item -mmul32x16 -@opindex mmul32x16 -Generate 32x16-bit multiply and multiply-accumulate instructions. - -@item -mmul64 -@opindex mmul64 -Generate @code{mul64} and @code{mulu64} instructions. -Only valid for @option{-mcpu=ARC600}. - -@item -mnorm -@opindex mnorm -Generate @code{norm} instructions. This is the default if @option{-mcpu=ARC700} -is in effect. - -@item -mspfp -@opindex mspfp -@itemx -mspfp-compact -@opindex mspfp-compact -Generate single-precision FPX instructions, tuned for the compact -implementation. - -@item -mspfp-fast -@opindex mspfp-fast -Generate single-precision FPX instructions, tuned for the fast -implementation. - -@item -msimd -@opindex msimd -Enable generation of ARC SIMD instructions via target-specific -builtins. Only valid for @option{-mcpu=ARC700}. - -@item -msoft-float -@opindex msoft-float -This option ignored; it is provided for compatibility purposes only. -Software floating-point code is emitted by default, and this default -can overridden by FPX options; @option{-mspfp}, @option{-mspfp-compact}, or -@option{-mspfp-fast} for single precision, and @option{-mdpfp}, -@option{-mdpfp-compact}, or @option{-mdpfp-fast} for double precision. - -@item -mswap -@opindex mswap -Generate @code{swap} instructions. - -@item -matomic -@opindex matomic -This enables use of the locked load/store conditional extension to implement -atomic memory built-in functions. Not available for ARC 6xx or ARC -EM cores. - -@item -mdiv-rem -@opindex mdiv-rem -Enable @code{div} and @code{rem} instructions for ARCv2 cores. - -@item -mcode-density -@opindex mcode-density -Enable code density instructions for ARC EM. -This option is on by default for ARC HS. - -@item -mll64 -@opindex mll64 -Enable double load/store operations for ARC HS cores. - -@item -mtp-regno=@var{regno} -@opindex mtp-regno -Specify thread pointer register number. - -@item -mmpy-option=@var{multo} -@opindex mmpy-option -Compile ARCv2 code with a multiplier design option. You can specify -the option using either a string or numeric value for @var{multo}. -@samp{wlh1} is the default value. The recognized values are: - -@table @samp -@item 0 -@itemx none -No multiplier available. - -@item 1 -@itemx w -16x16 multiplier, fully pipelined. -The following instructions are enabled: @code{mpyw} and @code{mpyuw}. - -@item 2 -@itemx wlh1 -32x32 multiplier, fully -pipelined (1 stage). The following instructions are additionally -enabled: @code{mpy}, @code{mpyu}, @code{mpym}, @code{mpymu}, and @code{mpy_s}. - -@item 3 -@itemx wlh2 -32x32 multiplier, fully pipelined -(2 stages). The following instructions are additionally enabled: @code{mpy}, -@code{mpyu}, @code{mpym}, @code{mpymu}, and @code{mpy_s}. - -@item 4 -@itemx wlh3 -Two 16x16 multipliers, blocking, -sequential. The following instructions are additionally enabled: @code{mpy}, -@code{mpyu}, @code{mpym}, @code{mpymu}, and @code{mpy_s}. - -@item 5 -@itemx wlh4 -One 16x16 multiplier, blocking, -sequential. The following instructions are additionally enabled: @code{mpy}, -@code{mpyu}, @code{mpym}, @code{mpymu}, and @code{mpy_s}. - -@item 6 -@itemx wlh5 -One 32x4 multiplier, blocking, -sequential. The following instructions are additionally enabled: @code{mpy}, -@code{mpyu}, @code{mpym}, @code{mpymu}, and @code{mpy_s}. - -@item 7 -@itemx plus_dmpy -ARC HS SIMD support. - -@item 8 -@itemx plus_macd -ARC HS SIMD support. - -@item 9 -@itemx plus_qmacw -ARC HS SIMD support. - -@end table - -This option is only available for ARCv2 cores@. - -@item -mfpu=@var{fpu} -@opindex mfpu -Enables support for specific floating-point hardware extensions for ARCv2 -cores. Supported values for @var{fpu} are: - -@table @samp - -@item fpus -Enables support for single-precision floating-point hardware -extensions@. - -@item fpud -Enables support for double-precision floating-point hardware -extensions. The single-precision floating-point extension is also -enabled. Not available for ARC EM@. - -@item fpuda -Enables support for double-precision floating-point hardware -extensions using double-precision assist instructions. The single-precision -floating-point extension is also enabled. This option is -only available for ARC EM@. - -@item fpuda_div -Enables support for double-precision floating-point hardware -extensions using double-precision assist instructions. -The single-precision floating-point, square-root, and divide -extensions are also enabled. This option is -only available for ARC EM@. - -@item fpuda_fma -Enables support for double-precision floating-point hardware -extensions using double-precision assist instructions. -The single-precision floating-point and fused multiply and add -hardware extensions are also enabled. This option is -only available for ARC EM@. - -@item fpuda_all -Enables support for double-precision floating-point hardware -extensions using double-precision assist instructions. -All single-precision floating-point hardware extensions are also -enabled. This option is only available for ARC EM@. - -@item fpus_div -Enables support for single-precision floating-point, square-root and divide -hardware extensions@. - -@item fpud_div -Enables support for double-precision floating-point, square-root and divide -hardware extensions. This option -includes option @samp{fpus_div}. Not available for ARC EM@. - -@item fpus_fma -Enables support for single-precision floating-point and -fused multiply and add hardware extensions@. - -@item fpud_fma -Enables support for double-precision floating-point and -fused multiply and add hardware extensions. This option -includes option @samp{fpus_fma}. Not available for ARC EM@. - -@item fpus_all -Enables support for all single-precision floating-point hardware -extensions@. - -@item fpud_all -Enables support for all single- and double-precision floating-point -hardware extensions. Not available for ARC EM@. - -@end table - -@item -mirq-ctrl-saved=@var{register-range}, @var{blink}, @var{lp_count} -@opindex mirq-ctrl-saved -Specifies general-purposes registers that the processor automatically -saves/restores on interrupt entry and exit. @var{register-range} is -specified as two registers separated by a dash. The register range -always starts with @code{r0}, the upper limit is @code{fp} register. -@var{blink} and @var{lp_count} are optional. This option is only -valid for ARC EM and ARC HS cores. - -@item -mrgf-banked-regs=@var{number} -@opindex mrgf-banked-regs -Specifies the number of registers replicated in second register bank -on entry to fast interrupt. Fast interrupts are interrupts with the -highest priority level P0. These interrupts save only PC and STATUS32 -registers to avoid memory transactions during interrupt entry and exit -sequences. Use this option when you are using fast interrupts in an -ARC V2 family processor. Permitted values are 4, 8, 16, and 32. - -@item -mlpc-width=@var{width} -@opindex mlpc-width -Specify the width of the @code{lp_count} register. Valid values for -@var{width} are 8, 16, 20, 24, 28 and 32 bits. The default width is -fixed to 32 bits. If the width is less than 32, the compiler does not -attempt to transform loops in your program to use the zero-delay loop -mechanism unless it is known that the @code{lp_count} register can -hold the required loop-counter value. Depending on the width -specified, the compiler and run-time library might continue to use the -loop mechanism for various needs. This option defines macro -@code{__ARC_LPC_WIDTH__} with the value of @var{width}. - -@item -mrf16 -@opindex mrf16 -This option instructs the compiler to generate code for a 16-entry -register file. This option defines the @code{__ARC_RF16__} -preprocessor macro. - -@item -mbranch-index -@opindex mbranch-index -Enable use of @code{bi} or @code{bih} instructions to implement jump -tables. - -@end table - -The following options are passed through to the assembler, and also -define preprocessor macro symbols. - -@c Flags used by the assembler, but for which we define preprocessor -@c macro symbols as well. -@table @gcctabopt -@item -mdsp-packa -@opindex mdsp-packa -Passed down to the assembler to enable the DSP Pack A extensions. -Also sets the preprocessor symbol @code{__Xdsp_packa}. This option is -deprecated. - -@item -mdvbf -@opindex mdvbf -Passed down to the assembler to enable the dual Viterbi butterfly -extension. Also sets the preprocessor symbol @code{__Xdvbf}. This -option is deprecated. - -@c ARC700 4.10 extension instruction -@item -mlock -@opindex mlock -Passed down to the assembler to enable the locked load/store -conditional extension. Also sets the preprocessor symbol -@code{__Xlock}. - -@item -mmac-d16 -@opindex mmac-d16 -Passed down to the assembler. Also sets the preprocessor symbol -@code{__Xxmac_d16}. This option is deprecated. - -@item -mmac-24 -@opindex mmac-24 -Passed down to the assembler. Also sets the preprocessor symbol -@code{__Xxmac_24}. This option is deprecated. - -@c ARC700 4.10 extension instruction -@item -mrtsc -@opindex mrtsc -Passed down to the assembler to enable the 64-bit time-stamp counter -extension instruction. Also sets the preprocessor symbol -@code{__Xrtsc}. This option is deprecated. - -@c ARC700 4.10 extension instruction -@item -mswape -@opindex mswape -Passed down to the assembler to enable the swap byte ordering -extension instruction. Also sets the preprocessor symbol -@code{__Xswape}. - -@item -mtelephony -@opindex mtelephony -Passed down to the assembler to enable dual- and single-operand -instructions for telephony. Also sets the preprocessor symbol -@code{__Xtelephony}. This option is deprecated. - -@item -mxy -@opindex mxy -Passed down to the assembler to enable the XY memory extension. Also -sets the preprocessor symbol @code{__Xxy}. - -@end table - -The following options control how the assembly code is annotated: - -@c Assembly annotation options -@table @gcctabopt -@item -misize -@opindex misize -Annotate assembler instructions with estimated addresses. - -@item -mannotate-align -@opindex mannotate-align -Explain what alignment considerations lead to the decision to make an -instruction short or long. - -@end table - -The following options are passed through to the linker: - -@c options passed through to the linker -@table @gcctabopt -@item -marclinux -@opindex marclinux -Passed through to the linker, to specify use of the @code{arclinux} emulation. -This option is enabled by default in tool chains built for -@w{@code{arc-linux-uclibc}} and @w{@code{arceb-linux-uclibc}} targets -when profiling is not requested. - -@item -marclinux_prof -@opindex marclinux_prof -Passed through to the linker, to specify use of the -@code{arclinux_prof} emulation. This option is enabled by default in -tool chains built for @w{@code{arc-linux-uclibc}} and -@w{@code{arceb-linux-uclibc}} targets when profiling is requested. - -@end table - -The following options control the semantics of generated code: - -@c semantically relevant code generation options -@table @gcctabopt -@item -mlong-calls -@opindex mlong-calls -Generate calls as register indirect calls, thus providing access -to the full 32-bit address range. - -@item -mmedium-calls -@opindex mmedium-calls -Don't use less than 25-bit addressing range for calls, which is the -offset available for an unconditional branch-and-link -instruction. Conditional execution of function calls is suppressed, to -allow use of the 25-bit range, rather than the 21-bit range with -conditional branch-and-link. This is the default for tool chains built -for @w{@code{arc-linux-uclibc}} and @w{@code{arceb-linux-uclibc}} targets. - -@item -G @var{num} -@opindex G -Put definitions of externally-visible data in a small data section if -that data is no bigger than @var{num} bytes. The default value of -@var{num} is 4 for any ARC configuration, or 8 when we have double -load/store operations. - -@item -mno-sdata -@opindex mno-sdata -@opindex msdata -Do not generate sdata references. This is the default for tool chains -built for @w{@code{arc-linux-uclibc}} and @w{@code{arceb-linux-uclibc}} -targets. - -@item -mvolatile-cache -@opindex mvolatile-cache -Use ordinarily cached memory accesses for volatile references. This is the -default. - -@item -mno-volatile-cache -@opindex mno-volatile-cache -@opindex mvolatile-cache -Enable cache bypass for volatile references. - -@end table - -The following options fine tune code generation: -@c code generation tuning options -@table @gcctabopt -@item -malign-call -@opindex malign-call -Does nothing. Preserved for backward compatibility. - -@item -mauto-modify-reg -@opindex mauto-modify-reg -Enable the use of pre/post modify with register displacement. - -@item -mbbit-peephole -@opindex mbbit-peephole -Enable bbit peephole2. - -@item -mno-brcc -@opindex mno-brcc -This option disables a target-specific pass in @file{arc_reorg} to -generate compare-and-branch (@code{br@var{cc}}) instructions. -It has no effect on -generation of these instructions driven by the combiner pass. - -@item -mcase-vector-pcrel -@opindex mcase-vector-pcrel -Use PC-relative switch case tables to enable case table shortening. -This is the default for @option{-Os}. - -@item -mcompact-casesi -@opindex mcompact-casesi -Enable compact @code{casesi} pattern. This is the default for @option{-Os}, -and only available for ARCv1 cores. This option is deprecated. - -@item -mno-cond-exec -@opindex mno-cond-exec -Disable the ARCompact-specific pass to generate conditional -execution instructions. - -Due to delay slot scheduling and interactions between operand numbers, -literal sizes, instruction lengths, and the support for conditional execution, -the target-independent pass to generate conditional execution is often lacking, -so the ARC port has kept a special pass around that tries to find more -conditional execution generation opportunities after register allocation, -branch shortening, and delay slot scheduling have been done. This pass -generally, but not always, improves performance and code size, at the cost of -extra compilation time, which is why there is an option to switch it off. -If you have a problem with call instructions exceeding their allowable -offset range because they are conditionalized, you should consider using -@option{-mmedium-calls} instead. - -@item -mearly-cbranchsi -@opindex mearly-cbranchsi -Enable pre-reload use of the @code{cbranchsi} pattern. - -@item -mexpand-adddi -@opindex mexpand-adddi -Expand @code{adddi3} and @code{subdi3} at RTL generation time into -@code{add.f}, @code{adc} etc. This option is deprecated. - -@item -mindexed-loads -@opindex mindexed-loads -Enable the use of indexed loads. This can be problematic because some -optimizers then assume that indexed stores exist, which is not -the case. - -@item -mlra -@opindex mlra -Enable Local Register Allocation. This is still experimental for ARC, -so by default the compiler uses standard reload -(i.e.@: @option{-mno-lra}). - -@item -mlra-priority-none -@opindex mlra-priority-none -Don't indicate any priority for target registers. - -@item -mlra-priority-compact -@opindex mlra-priority-compact -Indicate target register priority for r0..r3 / r12..r15. - -@item -mlra-priority-noncompact -@opindex mlra-priority-noncompact -Reduce target register priority for r0..r3 / r12..r15. - -@item -mmillicode -@opindex mmillicode -When optimizing for size (using @option{-Os}), prologues and epilogues -that have to save or restore a large number of registers are often -shortened by using call to a special function in libgcc; this is -referred to as a @emph{millicode} call. As these calls can pose -performance issues, and/or cause linking issues when linking in a -nonstandard way, this option is provided to turn on or off millicode -call generation. - -@item -mcode-density-frame -@opindex mcode-density-frame -This option enable the compiler to emit @code{enter} and @code{leave} -instructions. These instructions are only valid for CPUs with -code-density feature. - -@item -mmixed-code -@opindex mmixed-code -Does nothing. Preserved for backward compatibility. - -@item -mq-class -@opindex mq-class -Ths option is deprecated. Enable @samp{q} instruction alternatives. -This is the default for @option{-Os}. - -@item -mRcq -@opindex mRcq -Does nothing. Preserved for backward compatibility. - -@item -mRcw -@opindex mRcw -Does nothing. Preserved for backward compatibility. - -@item -msize-level=@var{level} -@opindex msize-level -Fine-tune size optimization with regards to instruction lengths and alignment. -The recognized values for @var{level} are: -@table @samp -@item 0 -No size optimization. This level is deprecated and treated like @samp{1}. - -@item 1 -Short instructions are used opportunistically. - -@item 2 -In addition, alignment of loops and of code after barriers are dropped. - -@item 3 -In addition, optional data alignment is dropped, and the option @option{Os} is enabled. - -@end table - -This defaults to @samp{3} when @option{-Os} is in effect. Otherwise, -the behavior when this is not set is equivalent to level @samp{1}. - -@item -mtune=@var{cpu} -@opindex mtune -Set instruction scheduling parameters for @var{cpu}, overriding any implied -by @option{-mcpu=}. - -Supported values for @var{cpu} are - -@table @samp -@item ARC600 -Tune for ARC600 CPU. - -@item ARC601 -Tune for ARC601 CPU. - -@item ARC700 -Tune for ARC700 CPU with standard multiplier block. - -@item ARC700-xmac -Tune for ARC700 CPU with XMAC block. - -@item ARC725D -Tune for ARC725D CPU. - -@item ARC750D -Tune for ARC750D CPU. - -@item core3 -Tune for ARCv2 core3 type CPU. This option enable usage of -@code{dbnz} instruction. - -@item release31a -Tune for ARC4x release 3.10a. - -@end table - -@item -mmultcost=@var{num} -@opindex mmultcost -Cost to assume for a multiply instruction, with @samp{4} being equal to a -normal instruction. - -@item -munalign-prob-threshold=@var{probability} -@opindex munalign-prob-threshold -Does nothing. Preserved for backward compatibility. - -@end table - -The following options are maintained for backward compatibility, but -are now deprecated and will be removed in a future release: - -@c Deprecated options -@table @gcctabopt - -@item -margonaut -@opindex margonaut -Obsolete FPX. - -@item -mbig-endian -@opindex mbig-endian -@itemx -EB -@opindex EB -Compile code for big-endian targets. Use of these options is now -deprecated. Big-endian code is supported by configuring GCC to build -@w{@code{arceb-elf32}} and @w{@code{arceb-linux-uclibc}} targets, -for which big endian is the default. - -@item -mlittle-endian -@opindex mlittle-endian -@itemx -EL -@opindex EL -Compile code for little-endian targets. Use of these options is now -deprecated. Little-endian code is supported by configuring GCC to build -@w{@code{arc-elf32}} and @w{@code{arc-linux-uclibc}} targets, -for which little endian is the default. - -@item -mbarrel_shifter -@opindex mbarrel_shifter -Replaced by @option{-mbarrel-shifter}. - -@item -mdpfp_compact -@opindex mdpfp_compact -Replaced by @option{-mdpfp-compact}. - -@item -mdpfp_fast -@opindex mdpfp_fast -Replaced by @option{-mdpfp-fast}. - -@item -mdsp_packa -@opindex mdsp_packa -Replaced by @option{-mdsp-packa}. - -@item -mEA -@opindex mEA -Replaced by @option{-mea}. - -@item -mmac_24 -@opindex mmac_24 -Replaced by @option{-mmac-24}. - -@item -mmac_d16 -@opindex mmac_d16 -Replaced by @option{-mmac-d16}. - -@item -mspfp_compact -@opindex mspfp_compact -Replaced by @option{-mspfp-compact}. - -@item -mspfp_fast -@opindex mspfp_fast -Replaced by @option{-mspfp-fast}. - -@item -mtune=@var{cpu} -@opindex mtune -Values @samp{arc600}, @samp{arc601}, @samp{arc700} and -@samp{arc700-xmac} for @var{cpu} are replaced by @samp{ARC600}, -@samp{ARC601}, @samp{ARC700} and @samp{ARC700-xmac} respectively. - -@item -multcost=@var{num} -@opindex multcost -Replaced by @option{-mmultcost}. - -@end table - -@node ARM Options -@subsection ARM Options -@cindex ARM options - -These @samp{-m} options are defined for the ARM port: - -@table @gcctabopt -@item -mabi=@var{name} -@opindex mabi -Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu}, -@samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}. - -@item -mapcs-frame -@opindex mapcs-frame -Generate a stack frame that is compliant with the ARM Procedure Call -Standard for all functions, even if this is not strictly necessary for -correct execution of the code. Specifying @option{-fomit-frame-pointer} -with this option causes the stack frames not to be generated for -leaf functions. The default is @option{-mno-apcs-frame}. -This option is deprecated. - -@item -mapcs -@opindex mapcs -This is a synonym for @option{-mapcs-frame} and is deprecated. - -@ignore -@c not currently implemented -@item -mapcs-stack-check -@opindex mapcs-stack-check -Generate code to check the amount of stack space available upon entry to -every function (that actually uses some stack space). If there is -insufficient space available then either the function -@code{__rt_stkovf_split_small} or @code{__rt_stkovf_split_big} is -called, depending upon the amount of stack space required. The runtime -system is required to provide these functions. The default is -@option{-mno-apcs-stack-check}, since this produces smaller code. - -@c not currently implemented -@item -mapcs-reentrant -@opindex mapcs-reentrant -Generate reentrant, position-independent code. The default is -@option{-mno-apcs-reentrant}. -@end ignore - -@item -mthumb-interwork -@opindex mthumb-interwork -Generate code that supports calling between the ARM and Thumb -instruction sets. Without this option, on pre-v5 architectures, the -two instruction sets cannot be reliably used inside one program. The -default is @option{-mno-thumb-interwork}, since slightly larger code -is generated when @option{-mthumb-interwork} is specified. In AAPCS -configurations this option is meaningless. - -@item -mno-sched-prolog -@opindex mno-sched-prolog -@opindex msched-prolog -Prevent the reordering of instructions in the function prologue, or the -merging of those instruction with the instructions in the function's -body. This means that all functions start with a recognizable set -of instructions (or in fact one of a choice from a small set of -different function prologues), and this information can be used to -locate the start of functions inside an executable piece of code. The -default is @option{-msched-prolog}. - -@item -mfloat-abi=@var{name} -@opindex mfloat-abi -Specifies which floating-point ABI to use. Permissible values -are: @samp{soft}, @samp{softfp} and @samp{hard}. - -Specifying @samp{soft} causes GCC to generate output containing -library calls for floating-point operations. -@samp{softfp} allows the generation of code using hardware floating-point -instructions, but still uses the soft-float calling conventions. -@samp{hard} allows generation of floating-point instructions -and uses FPU-specific calling conventions. - -The default depends on the specific target configuration. Note that -the hard-float and soft-float ABIs are not link-compatible; you must -compile your entire program with the same ABI, and link with a -compatible set of libraries. - -@item -mgeneral-regs-only -@opindex mgeneral-regs-only -Generate code which uses only the general-purpose registers. This will prevent -the compiler from using floating-point and Advanced SIMD registers but will not -impose any restrictions on the assembler. - -@item -mlittle-endian -@opindex mlittle-endian -Generate code for a processor running in little-endian mode. This is -the default for all standard configurations. - -@item -mbig-endian -@opindex mbig-endian -Generate code for a processor running in big-endian mode; the default is -to compile code for a little-endian processor. - -@item -mbe8 -@itemx -mbe32 -@opindex mbe8 -When linking a big-endian image select between BE8 and BE32 formats. -The option has no effect for little-endian images and is ignored. The -default is dependent on the selected target architecture. For ARMv6 -and later architectures the default is BE8, for older architectures -the default is BE32. BE32 format has been deprecated by ARM. - -@item -march=@var{name}@r{[}+extension@dots{}@r{]} -@opindex march -This specifies the name of the target ARM architecture. GCC uses this -name to determine what kind of instructions it can emit when generating -assembly code. This option can be used in conjunction with or instead -of the @option{-mcpu=} option. - -Permissible names are: -@samp{armv4t}, -@samp{armv5t}, @samp{armv5te}, -@samp{armv6}, @samp{armv6j}, @samp{armv6k}, @samp{armv6kz}, @samp{armv6t2}, -@samp{armv6z}, @samp{armv6zk}, -@samp{armv7}, @samp{armv7-a}, @samp{armv7ve}, -@samp{armv8-a}, @samp{armv8.1-a}, @samp{armv8.2-a}, @samp{armv8.3-a}, -@samp{armv8.4-a}, -@samp{armv8.5-a}, -@samp{armv8.6-a}, -@samp{armv9-a}, -@samp{armv7-r}, -@samp{armv8-r}, -@samp{armv6-m}, @samp{armv6s-m}, -@samp{armv7-m}, @samp{armv7e-m}, -@samp{armv8-m.base}, @samp{armv8-m.main}, -@samp{armv8.1-m.main}, -@samp{armv9-a}, -@samp{iwmmxt} and @samp{iwmmxt2}. - -Additionally, the following architectures, which lack support for the -Thumb execution state, are recognized but support is deprecated: @samp{armv4}. - -Many of the architectures support extensions. These can be added by -appending @samp{+@var{extension}} to the architecture name. Extension -options are processed in order and capabilities accumulate. An extension -will also enable any necessary base extensions -upon which it depends. For example, the @samp{+crypto} extension -will always enable the @samp{+simd} extension. The exception to the -additive construction is for extensions that are prefixed with -@samp{+no@dots{}}: these extensions disable the specified option and -any other extensions that may depend on the presence of that -extension. - -For example, @samp{-march=armv7-a+simd+nofp+vfpv4} is equivalent to -writing @samp{-march=armv7-a+vfpv4} since the @samp{+simd} option is -entirely disabled by the @samp{+nofp} option that follows it. - -Most extension names are generically named, but have an effect that is -dependent upon the architecture to which it is applied. For example, -the @samp{+simd} option can be applied to both @samp{armv7-a} and -@samp{armv8-a} architectures, but will enable the original ARMv7-A -Advanced SIMD (Neon) extensions for @samp{armv7-a} and the ARMv8-A -variant for @samp{armv8-a}. - -The table below lists the supported extensions for each architecture. -Architectures not mentioned do not support any extensions. - -@table @samp -@item armv5te -@itemx armv6 -@itemx armv6j -@itemx armv6k -@itemx armv6kz -@itemx armv6t2 -@itemx armv6z -@itemx armv6zk -@table @samp -@item +fp -The VFPv2 floating-point instructions. The extension @samp{+vfpv2} can be -used as an alias for this extension. - -@item +nofp -Disable the floating-point instructions. -@end table - -@item armv7 -The common subset of the ARMv7-A, ARMv7-R and ARMv7-M architectures. -@table @samp -@item +fp -The VFPv3 floating-point instructions, with 16 double-precision -registers. The extension @samp{+vfpv3-d16} can be used as an alias -for this extension. Note that floating-point is not supported by the -base ARMv7-M architecture, but is compatible with both the ARMv7-A and -ARMv7-R architectures. - -@item +nofp -Disable the floating-point instructions. -@end table - -@item armv7-a -@table @samp -@item +mp -The multiprocessing extension. - -@item +sec -The security extension. - -@item +fp -The VFPv3 floating-point instructions, with 16 double-precision -registers. The extension @samp{+vfpv3-d16} can be used as an alias -for this extension. - -@item +simd -The Advanced SIMD (Neon) v1 and the VFPv3 floating-point instructions. -The extensions @samp{+neon} and @samp{+neon-vfpv3} can be used as aliases -for this extension. - -@item +vfpv3 -The VFPv3 floating-point instructions, with 32 double-precision -registers. - -@item +vfpv3-d16-fp16 -The VFPv3 floating-point instructions, with 16 double-precision -registers and the half-precision floating-point conversion operations. - -@item +vfpv3-fp16 -The VFPv3 floating-point instructions, with 32 double-precision -registers and the half-precision floating-point conversion operations. - -@item +vfpv4-d16 -The VFPv4 floating-point instructions, with 16 double-precision -registers. - -@item +vfpv4 -The VFPv4 floating-point instructions, with 32 double-precision -registers. - -@item +neon-fp16 -The Advanced SIMD (Neon) v1 and the VFPv3 floating-point instructions, with -the half-precision floating-point conversion operations. - -@item +neon-vfpv4 -The Advanced SIMD (Neon) v2 and the VFPv4 floating-point instructions. - -@item +nosimd -Disable the Advanced SIMD instructions (does not disable floating point). - -@item +nofp -Disable the floating-point and Advanced SIMD instructions. -@end table - -@item armv7ve -The extended version of the ARMv7-A architecture with support for -virtualization. -@table @samp -@item +fp -The VFPv4 floating-point instructions, with 16 double-precision registers. -The extension @samp{+vfpv4-d16} can be used as an alias for this extension. - -@item +simd -The Advanced SIMD (Neon) v2 and the VFPv4 floating-point instructions. The -extension @samp{+neon-vfpv4} can be used as an alias for this extension. - -@item +vfpv3-d16 -The VFPv3 floating-point instructions, with 16 double-precision -registers. - -@item +vfpv3 -The VFPv3 floating-point instructions, with 32 double-precision -registers. - -@item +vfpv3-d16-fp16 -The VFPv3 floating-point instructions, with 16 double-precision -registers and the half-precision floating-point conversion operations. - -@item +vfpv3-fp16 -The VFPv3 floating-point instructions, with 32 double-precision -registers and the half-precision floating-point conversion operations. - -@item +vfpv4-d16 -The VFPv4 floating-point instructions, with 16 double-precision -registers. - -@item +vfpv4 -The VFPv4 floating-point instructions, with 32 double-precision -registers. - -@item +neon -The Advanced SIMD (Neon) v1 and the VFPv3 floating-point instructions. -The extension @samp{+neon-vfpv3} can be used as an alias for this extension. - -@item +neon-fp16 -The Advanced SIMD (Neon) v1 and the VFPv3 floating-point instructions, with -the half-precision floating-point conversion operations. - -@item +nosimd -Disable the Advanced SIMD instructions (does not disable floating point). - -@item +nofp -Disable the floating-point and Advanced SIMD instructions. -@end table - -@item armv8-a -@table @samp -@item +crc -The Cyclic Redundancy Check (CRC) instructions. -@item +simd -The ARMv8-A Advanced SIMD and floating-point instructions. -@item +crypto -The cryptographic instructions. -@item +nocrypto -Disable the cryptographic instructions. -@item +nofp -Disable the floating-point, Advanced SIMD and cryptographic instructions. -@item +sb -Speculation Barrier Instruction. -@item +predres -Execution and Data Prediction Restriction Instructions. -@end table - -@item armv8.1-a -@table @samp -@item +simd -The ARMv8.1-A Advanced SIMD and floating-point instructions. - -@item +crypto -The cryptographic instructions. This also enables the Advanced SIMD and -floating-point instructions. - -@item +nocrypto -Disable the cryptographic instructions. - -@item +nofp -Disable the floating-point, Advanced SIMD and cryptographic instructions. - -@item +sb -Speculation Barrier Instruction. - -@item +predres -Execution and Data Prediction Restriction Instructions. -@end table - -@item armv8.2-a -@itemx armv8.3-a -@table @samp -@item +fp16 -The half-precision floating-point data processing instructions. -This also enables the Advanced SIMD and floating-point instructions. - -@item +fp16fml -The half-precision floating-point fmla extension. This also enables -the half-precision floating-point extension and Advanced SIMD and -floating-point instructions. - -@item +simd -The ARMv8.1-A Advanced SIMD and floating-point instructions. - -@item +crypto -The cryptographic instructions. This also enables the Advanced SIMD and -floating-point instructions. - -@item +dotprod -Enable the Dot Product extension. This also enables Advanced SIMD instructions. - -@item +nocrypto -Disable the cryptographic extension. - -@item +nofp -Disable the floating-point, Advanced SIMD and cryptographic instructions. - -@item +sb -Speculation Barrier Instruction. - -@item +predres -Execution and Data Prediction Restriction Instructions. - -@item +i8mm -8-bit Integer Matrix Multiply instructions. -This also enables Advanced SIMD and floating-point instructions. - -@item +bf16 -Brain half-precision floating-point instructions. -This also enables Advanced SIMD and floating-point instructions. -@end table - -@item armv8.4-a -@table @samp -@item +fp16 -The half-precision floating-point data processing instructions. -This also enables the Advanced SIMD and floating-point instructions as well -as the Dot Product extension and the half-precision floating-point fmla -extension. - -@item +simd -The ARMv8.3-A Advanced SIMD and floating-point instructions as well as the -Dot Product extension. - -@item +crypto -The cryptographic instructions. This also enables the Advanced SIMD and -floating-point instructions as well as the Dot Product extension. - -@item +nocrypto -Disable the cryptographic extension. - -@item +nofp -Disable the floating-point, Advanced SIMD and cryptographic instructions. - -@item +sb -Speculation Barrier Instruction. - -@item +predres -Execution and Data Prediction Restriction Instructions. - -@item +i8mm -8-bit Integer Matrix Multiply instructions. -This also enables Advanced SIMD and floating-point instructions. - -@item +bf16 -Brain half-precision floating-point instructions. -This also enables Advanced SIMD and floating-point instructions. -@end table - -@item armv8.5-a -@table @samp -@item +fp16 -The half-precision floating-point data processing instructions. -This also enables the Advanced SIMD and floating-point instructions as well -as the Dot Product extension and the half-precision floating-point fmla -extension. - -@item +simd -The ARMv8.3-A Advanced SIMD and floating-point instructions as well as the -Dot Product extension. - -@item +crypto -The cryptographic instructions. This also enables the Advanced SIMD and -floating-point instructions as well as the Dot Product extension. - -@item +nocrypto -Disable the cryptographic extension. - -@item +nofp -Disable the floating-point, Advanced SIMD and cryptographic instructions. - -@item +i8mm -8-bit Integer Matrix Multiply instructions. -This also enables Advanced SIMD and floating-point instructions. - -@item +bf16 -Brain half-precision floating-point instructions. -This also enables Advanced SIMD and floating-point instructions. -@end table - -@item armv8.6-a -@table @samp -@item +fp16 -The half-precision floating-point data processing instructions. -This also enables the Advanced SIMD and floating-point instructions as well -as the Dot Product extension and the half-precision floating-point fmla -extension. - -@item +simd -The ARMv8.3-A Advanced SIMD and floating-point instructions as well as the -Dot Product extension. - -@item +crypto -The cryptographic instructions. This also enables the Advanced SIMD and -floating-point instructions as well as the Dot Product extension. - -@item +nocrypto -Disable the cryptographic extension. - -@item +nofp -Disable the floating-point, Advanced SIMD and cryptographic instructions. - -@item +i8mm -8-bit Integer Matrix Multiply instructions. -This also enables Advanced SIMD and floating-point instructions. - -@item +bf16 -Brain half-precision floating-point instructions. -This also enables Advanced SIMD and floating-point instructions. -@end table - -@item armv7-r -@table @samp -@item +fp.sp -The single-precision VFPv3 floating-point instructions. The extension -@samp{+vfpv3xd} can be used as an alias for this extension. - -@item +fp -The VFPv3 floating-point instructions with 16 double-precision registers. -The extension +vfpv3-d16 can be used as an alias for this extension. - -@item +vfpv3xd-d16-fp16 -The single-precision VFPv3 floating-point instructions with 16 double-precision -registers and the half-precision floating-point conversion operations. - -@item +vfpv3-d16-fp16 -The VFPv3 floating-point instructions with 16 double-precision -registers and the half-precision floating-point conversion operations. - -@item +nofp -Disable the floating-point extension. - -@item +idiv -The ARM-state integer division instructions. - -@item +noidiv -Disable the ARM-state integer division extension. -@end table - -@item armv7e-m -@table @samp -@item +fp -The single-precision VFPv4 floating-point instructions. - -@item +fpv5 -The single-precision FPv5 floating-point instructions. - -@item +fp.dp -The single- and double-precision FPv5 floating-point instructions. - -@item +nofp -Disable the floating-point extensions. -@end table - -@item armv8.1-m.main -@table @samp - -@item +dsp -The DSP instructions. - -@item +mve -The M-Profile Vector Extension (MVE) integer instructions. - -@item +mve.fp -The M-Profile Vector Extension (MVE) integer and single precision -floating-point instructions. - -@item +fp -The single-precision floating-point instructions. - -@item +fp.dp -The single- and double-precision floating-point instructions. - -@item +nofp -Disable the floating-point extension. - -@item +cdecp0, +cdecp1, ... , +cdecp7 -Enable the Custom Datapath Extension (CDE) on selected coprocessors according -to the numbers given in the options in the range 0 to 7. -@end table - -@item armv8-m.main -@table @samp -@item +dsp -The DSP instructions. - -@item +nodsp -Disable the DSP extension. - -@item +fp -The single-precision floating-point instructions. - -@item +fp.dp -The single- and double-precision floating-point instructions. - -@item +nofp -Disable the floating-point extension. - -@item +cdecp0, +cdecp1, ... , +cdecp7 -Enable the Custom Datapath Extension (CDE) on selected coprocessors according -to the numbers given in the options in the range 0 to 7. -@end table - -@item armv8-r -@table @samp -@item +crc -The Cyclic Redundancy Check (CRC) instructions. -@item +fp.sp -The single-precision FPv5 floating-point instructions. -@item +simd -The ARMv8-A Advanced SIMD and floating-point instructions. -@item +crypto -The cryptographic instructions. -@item +nocrypto -Disable the cryptographic instructions. -@item +nofp -Disable the floating-point, Advanced SIMD and cryptographic instructions. -@end table - -@end table - -@option{-march=native} causes the compiler to auto-detect the architecture -of the build computer. At present, this feature is only supported on -GNU/Linux, and not all architectures are recognized. If the auto-detect -is unsuccessful the option has no effect. - -@item -mtune=@var{name} -@opindex mtune -This option specifies the name of the target ARM processor for -which GCC should tune the performance of the code. -For some ARM implementations better performance can be obtained by using -this option. -Permissible names are: @samp{arm7tdmi}, @samp{arm7tdmi-s}, @samp{arm710t}, -@samp{arm720t}, @samp{arm740t}, @samp{strongarm}, @samp{strongarm110}, -@samp{strongarm1100}, @samp{strongarm1110}, @samp{arm8}, @samp{arm810}, -@samp{arm9}, @samp{arm9e}, @samp{arm920}, @samp{arm920t}, @samp{arm922t}, -@samp{arm946e-s}, @samp{arm966e-s}, @samp{arm968e-s}, @samp{arm926ej-s}, -@samp{arm940t}, @samp{arm9tdmi}, @samp{arm10tdmi}, @samp{arm1020t}, -@samp{arm1026ej-s}, @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e}, -@samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp}, -@samp{arm1156t2-s}, @samp{arm1156t2f-s}, @samp{arm1176jz-s}, @samp{arm1176jzf-s}, -@samp{generic-armv7-a}, @samp{cortex-a5}, @samp{cortex-a7}, @samp{cortex-a8}, -@samp{cortex-a9}, @samp{cortex-a12}, @samp{cortex-a15}, @samp{cortex-a17}, -@samp{cortex-a32}, @samp{cortex-a35}, @samp{cortex-a53}, @samp{cortex-a55}, -@samp{cortex-a57}, @samp{cortex-a72}, @samp{cortex-a73}, @samp{cortex-a75}, -@samp{cortex-a76}, @samp{cortex-a76ae}, @samp{cortex-a77}, -@samp{cortex-a78}, @samp{cortex-a78ae}, @samp{cortex-a78c}, @samp{cortex-a710}, -@samp{ares}, @samp{cortex-r4}, @samp{cortex-r4f}, @samp{cortex-r5}, -@samp{cortex-r7}, @samp{cortex-r8}, @samp{cortex-r52}, @samp{cortex-r52plus}, -@samp{cortex-m0}, @samp{cortex-m0plus}, @samp{cortex-m1}, @samp{cortex-m3}, -@samp{cortex-m4}, @samp{cortex-m7}, @samp{cortex-m23}, @samp{cortex-m33}, -@samp{cortex-m35p}, @samp{cortex-m55}, @samp{cortex-x1}, -@samp{cortex-m1.small-multiply}, @samp{cortex-m0.small-multiply}, -@samp{cortex-m0plus.small-multiply}, @samp{exynos-m1}, @samp{marvell-pj4}, -@samp{neoverse-n1}, @samp{neoverse-n2}, @samp{neoverse-v1}, @samp{xscale}, -@samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}, @samp{fa526}, @samp{fa626}, -@samp{fa606te}, @samp{fa626te}, @samp{fmp626}, @samp{fa726te}, @samp{star-mc1}, -@samp{xgene1}. - -Additionally, this option can specify that GCC should tune the performance -of the code for a big.LITTLE system. Permissible names are: -@samp{cortex-a15.cortex-a7}, @samp{cortex-a17.cortex-a7}, -@samp{cortex-a57.cortex-a53}, @samp{cortex-a72.cortex-a53}, -@samp{cortex-a72.cortex-a35}, @samp{cortex-a73.cortex-a53}, -@samp{cortex-a75.cortex-a55}, @samp{cortex-a76.cortex-a55}. - -@option{-mtune=generic-@var{arch}} specifies that GCC should tune the -performance for a blend of processors within architecture @var{arch}. -The aim is to generate code that run well on the current most popular -processors, balancing between optimizations that benefit some CPUs in the -range, and avoiding performance pitfalls of other CPUs. The effects of -this option may change in future GCC versions as CPU models come and go. - -@option{-mtune} permits the same extension options as @option{-mcpu}, but -the extension options do not affect the tuning of the generated code. - -@option{-mtune=native} causes the compiler to auto-detect the CPU -of the build computer. At present, this feature is only supported on -GNU/Linux, and not all architectures are recognized. If the auto-detect is -unsuccessful the option has no effect. - -@item -mcpu=@var{name}@r{[}+extension@dots{}@r{]} -@opindex mcpu -This specifies the name of the target ARM processor. GCC uses this name -to derive the name of the target ARM architecture (as if specified -by @option{-march}) and the ARM processor type for which to tune for -performance (as if specified by @option{-mtune}). Where this option -is used in conjunction with @option{-march} or @option{-mtune}, -those options take precedence over the appropriate part of this option. - -Many of the supported CPUs implement optional architectural -extensions. Where this is so the architectural extensions are -normally enabled by default. If implementations that lack the -extension exist, then the extension syntax can be used to disable -those extensions that have been omitted. For floating-point and -Advanced SIMD (Neon) instructions, the settings of the options -@option{-mfloat-abi} and @option{-mfpu} must also be considered: -floating-point and Advanced SIMD instructions will only be used if -@option{-mfloat-abi} is not set to @samp{soft}; and any setting of -@option{-mfpu} other than @samp{auto} will override the available -floating-point and SIMD extension instructions. - -For example, @samp{cortex-a9} can be found in three major -configurations: integer only, with just a floating-point unit or with -floating-point and Advanced SIMD. The default is to enable all the -instructions, but the extensions @samp{+nosimd} and @samp{+nofp} can -be used to disable just the SIMD or both the SIMD and floating-point -instructions respectively. - -Permissible names for this option are the same as those for -@option{-mtune}. - -The following extension options are common to the listed CPUs: - -@table @samp -@item +nodsp -Disable the DSP instructions on @samp{cortex-m33}, @samp{cortex-m35p} -and @samp{cortex-m55}. Also disable the M-Profile Vector Extension (MVE) -integer and single precision floating-point instructions on @samp{cortex-m55}. - -@item +nomve -Disable the M-Profile Vector Extension (MVE) integer and single precision -floating-point instructions on @samp{cortex-m55}. - -@item +nomve.fp -Disable the M-Profile Vector Extension (MVE) single precision floating-point -instructions on @samp{cortex-m55}. - -@item +nofp -Disables the floating-point instructions on @samp{arm9e}, -@samp{arm946e-s}, @samp{arm966e-s}, @samp{arm968e-s}, @samp{arm10e}, -@samp{arm1020e}, @samp{arm1022e}, @samp{arm926ej-s}, -@samp{arm1026ej-s}, @samp{cortex-r5}, @samp{cortex-r7}, @samp{cortex-r8}, -@samp{cortex-m4}, @samp{cortex-m7}, @samp{cortex-m33}, @samp{cortex-m35p} -and @samp{cortex-m55}. -Disables the floating-point and SIMD instructions on -@samp{generic-armv7-a}, @samp{cortex-a5}, @samp{cortex-a7}, -@samp{cortex-a8}, @samp{cortex-a9}, @samp{cortex-a12}, -@samp{cortex-a15}, @samp{cortex-a17}, @samp{cortex-a15.cortex-a7}, -@samp{cortex-a17.cortex-a7}, @samp{cortex-a32}, @samp{cortex-a35}, -@samp{cortex-a53} and @samp{cortex-a55}. - -@item +nofp.dp -Disables the double-precision component of the floating-point instructions -on @samp{cortex-r5}, @samp{cortex-r7}, @samp{cortex-r8}, @samp{cortex-r52}, -@samp{cortex-r52plus} and @samp{cortex-m7}. - -@item +nosimd -Disables the SIMD (but not floating-point) instructions on -@samp{generic-armv7-a}, @samp{cortex-a5}, @samp{cortex-a7} -and @samp{cortex-a9}. - -@item +crypto -Enables the cryptographic instructions on @samp{cortex-a32}, -@samp{cortex-a35}, @samp{cortex-a53}, @samp{cortex-a55}, @samp{cortex-a57}, -@samp{cortex-a72}, @samp{cortex-a73}, @samp{cortex-a75}, @samp{exynos-m1}, -@samp{xgene1}, @samp{cortex-a57.cortex-a53}, @samp{cortex-a72.cortex-a53}, -@samp{cortex-a73.cortex-a35}, @samp{cortex-a73.cortex-a53} and -@samp{cortex-a75.cortex-a55}. -@end table - -Additionally the @samp{generic-armv7-a} pseudo target defaults to -VFPv3 with 16 double-precision registers. It supports the following -extension options: @samp{mp}, @samp{sec}, @samp{vfpv3-d16}, -@samp{vfpv3}, @samp{vfpv3-d16-fp16}, @samp{vfpv3-fp16}, -@samp{vfpv4-d16}, @samp{vfpv4}, @samp{neon}, @samp{neon-vfpv3}, -@samp{neon-fp16}, @samp{neon-vfpv4}. The meanings are the same as for -the extensions to @option{-march=armv7-a}. - -@option{-mcpu=generic-@var{arch}} is also permissible, and is -equivalent to @option{-march=@var{arch} -mtune=generic-@var{arch}}. -See @option{-mtune} for more information. - -@option{-mcpu=native} causes the compiler to auto-detect the CPU -of the build computer. At present, this feature is only supported on -GNU/Linux, and not all architectures are recognized. If the auto-detect -is unsuccessful the option has no effect. - -@item -mfpu=@var{name} -@opindex mfpu -This specifies what floating-point hardware (or hardware emulation) is -available on the target. Permissible names are: @samp{auto}, @samp{vfpv2}, -@samp{vfpv3}, -@samp{vfpv3-fp16}, @samp{vfpv3-d16}, @samp{vfpv3-d16-fp16}, @samp{vfpv3xd}, -@samp{vfpv3xd-fp16}, @samp{neon-vfpv3}, @samp{neon-fp16}, @samp{vfpv4}, -@samp{vfpv4-d16}, @samp{fpv4-sp-d16}, @samp{neon-vfpv4}, -@samp{fpv5-d16}, @samp{fpv5-sp-d16}, -@samp{fp-armv8}, @samp{neon-fp-armv8} and @samp{crypto-neon-fp-armv8}. -Note that @samp{neon} is an alias for @samp{neon-vfpv3} and @samp{vfp} -is an alias for @samp{vfpv2}. - -The setting @samp{auto} is the default and is special. It causes the -compiler to select the floating-point and Advanced SIMD instructions -based on the settings of @option{-mcpu} and @option{-march}. - -If the selected floating-point hardware includes the NEON extension -(e.g.@: @option{-mfpu=neon}), note that floating-point -operations are not generated by GCC's auto-vectorization pass unless -@option{-funsafe-math-optimizations} is also specified. This is -because NEON hardware does not fully implement the IEEE 754 standard for -floating-point arithmetic (in particular denormal values are treated as -zero), so the use of NEON instructions may lead to a loss of precision. - -You can also set the fpu name at function level by using the @code{target("fpu=")} function attributes (@pxref{ARM Function Attributes}) or pragmas (@pxref{Function Specific Option Pragmas}). - -@item -mfp16-format=@var{name} -@opindex mfp16-format -Specify the format of the @code{__fp16} half-precision floating-point type. -Permissible names are @samp{none}, @samp{ieee}, and @samp{alternative}; -the default is @samp{none}, in which case the @code{__fp16} type is not -defined. @xref{Half-Precision}, for more information. - -@item -mstructure-size-boundary=@var{n} -@opindex mstructure-size-boundary -The sizes of all structures and unions are rounded up to a multiple -of the number of bits set by this option. Permissible values are 8, 32 -and 64. The default value varies for different toolchains. For the COFF -targeted toolchain the default value is 8. A value of 64 is only allowed -if the underlying ABI supports it. - -Specifying a larger number can produce faster, more efficient code, but -can also increase the size of the program. Different values are potentially -incompatible. Code compiled with one value cannot necessarily expect to -work with code or libraries compiled with another value, if they exchange -information using structures or unions. - -This option is deprecated. - -@item -mabort-on-noreturn -@opindex mabort-on-noreturn -Generate a call to the function @code{abort} at the end of a -@code{noreturn} function. It is executed if the function tries to -return. - -@item -mlong-calls -@itemx -mno-long-calls -@opindex mlong-calls -@opindex mno-long-calls -Tells the compiler to perform function calls by first loading the -address of the function into a register and then performing a subroutine -call on this register. This switch is needed if the target function -lies outside of the 64-megabyte addressing range of the offset-based -version of subroutine call instruction. - -Even if this switch is enabled, not all function calls are turned -into long calls. The heuristic is that static functions, functions -that have the @code{short_call} attribute, functions that are inside -the scope of a @code{#pragma no_long_calls} directive, and functions whose -definitions have already been compiled within the current compilation -unit are not turned into long calls. The exceptions to this rule are -that weak function definitions, functions with the @code{long_call} -attribute or the @code{section} attribute, and functions that are within -the scope of a @code{#pragma long_calls} directive are always -turned into long calls. - -This feature is not enabled by default. Specifying -@option{-mno-long-calls} restores the default behavior, as does -placing the function calls within the scope of a @code{#pragma -long_calls_off} directive. Note these switches have no effect on how -the compiler generates code to handle function calls via function -pointers. - -@item -msingle-pic-base -@opindex msingle-pic-base -Treat the register used for PIC addressing as read-only, rather than -loading it in the prologue for each function. The runtime system is -responsible for initializing this register with an appropriate value -before execution begins. - -@item -mpic-register=@var{reg} -@opindex mpic-register -Specify the register to be used for PIC addressing. -For standard PIC base case, the default is any suitable register -determined by compiler. For single PIC base case, the default is -@samp{R9} if target is EABI based or stack-checking is enabled, -otherwise the default is @samp{R10}. - -@item -mpic-data-is-text-relative -@opindex mpic-data-is-text-relative -Assume that the displacement between the text and data segments is fixed -at static link time. This permits using PC-relative addressing -operations to access data known to be in the data segment. For -non-VxWorks RTP targets, this option is enabled by default. When -disabled on such targets, it will enable @option{-msingle-pic-base} by -default. - -@item -mpoke-function-name -@opindex mpoke-function-name -Write the name of each function into the text section, directly -preceding the function prologue. The generated code is similar to this: - -@smallexample - t0 - .ascii "arm_poke_function_name", 0 - .align - t1 - .word 0xff000000 + (t1 - t0) - arm_poke_function_name - mov ip, sp - stmfd sp!, @{fp, ip, lr, pc@} - sub fp, ip, #4 -@end smallexample - -When performing a stack backtrace, code can inspect the value of -@code{pc} stored at @code{fp + 0}. If the trace function then looks at -location @code{pc - 12} and the top 8 bits are set, then we know that -there is a function name embedded immediately preceding this location -and has length @code{((pc[-3]) & 0xff000000)}. - -@item -mthumb -@itemx -marm -@opindex marm -@opindex mthumb - -Select between generating code that executes in ARM and Thumb -states. The default for most configurations is to generate code -that executes in ARM state, but the default can be changed by -configuring GCC with the @option{--with-mode=}@var{state} -configure option. - -You can also override the ARM and Thumb mode for each function -by using the @code{target("thumb")} and @code{target("arm")} function attributes -(@pxref{ARM Function Attributes}) or pragmas (@pxref{Function Specific Option Pragmas}). - -@item -mflip-thumb -@opindex mflip-thumb -Switch ARM/Thumb modes on alternating functions. -This option is provided for regression testing of mixed Thumb/ARM code -generation, and is not intended for ordinary use in compiling code. - -@item -mtpcs-frame -@opindex mtpcs-frame -Generate a stack frame that is compliant with the Thumb Procedure Call -Standard for all non-leaf functions. (A leaf function is one that does -not call any other functions.) The default is @option{-mno-tpcs-frame}. - -@item -mtpcs-leaf-frame -@opindex mtpcs-leaf-frame -Generate a stack frame that is compliant with the Thumb Procedure Call -Standard for all leaf functions. (A leaf function is one that does -not call any other functions.) The default is @option{-mno-apcs-leaf-frame}. - -@item -mcallee-super-interworking -@opindex mcallee-super-interworking -Gives all externally visible functions in the file being compiled an ARM -instruction set header which switches to Thumb mode before executing the -rest of the function. This allows these functions to be called from -non-interworking code. This option is not valid in AAPCS configurations -because interworking is enabled by default. - -@item -mcaller-super-interworking -@opindex mcaller-super-interworking -Allows calls via function pointers (including virtual functions) to -execute correctly regardless of whether the target code has been -compiled for interworking or not. There is a small overhead in the cost -of executing a function pointer if this option is enabled. This option -is not valid in AAPCS configurations because interworking is enabled -by default. - -@item -mtp=@var{name} -@opindex mtp -Specify the access model for the thread local storage pointer. The valid -models are @samp{soft}, which generates calls to @code{__aeabi_read_tp}, -@samp{cp15}, which fetches the thread pointer from @code{cp15} directly -(supported in the arm6k architecture), and @samp{auto}, which uses the -best available method for the selected processor. The default setting is -@samp{auto}. - -@item -mtls-dialect=@var{dialect} -@opindex mtls-dialect -Specify the dialect to use for accessing thread local storage. Two -@var{dialect}s are supported---@samp{gnu} and @samp{gnu2}. The -@samp{gnu} dialect selects the original GNU scheme for supporting -local and global dynamic TLS models. The @samp{gnu2} dialect -selects the GNU descriptor scheme, which provides better performance -for shared libraries. The GNU descriptor scheme is compatible with -the original scheme, but does require new assembler, linker and -library support. Initial and local exec TLS models are unaffected by -this option and always use the original scheme. - -@item -mword-relocations -@opindex mword-relocations -Only generate absolute relocations on word-sized values (i.e.@: R_ARM_ABS32). -This is enabled by default on targets (uClinux, SymbianOS) where the runtime -loader imposes this restriction, and when @option{-fpic} or @option{-fPIC} -is specified. This option conflicts with @option{-mslow-flash-data}. - -@item -mfix-cortex-m3-ldrd -@opindex mfix-cortex-m3-ldrd -Some Cortex-M3 cores can cause data corruption when @code{ldrd} instructions -with overlapping destination and base registers are used. This option avoids -generating these instructions. This option is enabled by default when -@option{-mcpu=cortex-m3} is specified. - -@item -mfix-cortex-a57-aes-1742098 -@itemx -mno-fix-cortex-a57-aes-1742098 -@itemx -mfix-cortex-a72-aes-1655431 -@itemx -mno-fix-cortex-a72-aes-1655431 -Enable (disable) mitigation for an erratum on Cortex-A57 and -Cortex-A72 that affects the AES cryptographic instructions. This -option is enabled by default when either @option{-mcpu=cortex-a57} or -@option{-mcpu=cortex-a72} is specified. - -@item -munaligned-access -@itemx -mno-unaligned-access -@opindex munaligned-access -@opindex mno-unaligned-access -Enables (or disables) reading and writing of 16- and 32- bit values -from addresses that are not 16- or 32- bit aligned. By default -unaligned access is disabled for all pre-ARMv6, all ARMv6-M and for -ARMv8-M Baseline architectures, and enabled for all other -architectures. If unaligned access is not enabled then words in packed -data structures are accessed a byte at a time. - -The ARM attribute @code{Tag_CPU_unaligned_access} is set in the -generated object file to either true or false, depending upon the -setting of this option. If unaligned access is enabled then the -preprocessor symbol @code{__ARM_FEATURE_UNALIGNED} is also -defined. - -@item -mneon-for-64bits -@opindex mneon-for-64bits -This option is deprecated and has no effect. - -@item -mslow-flash-data -@opindex mslow-flash-data -Assume loading data from flash is slower than fetching instruction. -Therefore literal load is minimized for better performance. -This option is only supported when compiling for ARMv7 M-profile and -off by default. It conflicts with @option{-mword-relocations}. - -@item -masm-syntax-unified -@opindex masm-syntax-unified -Assume inline assembler is using unified asm syntax. The default is -currently off which implies divided syntax. This option has no impact -on Thumb2. However, this may change in future releases of GCC. -Divided syntax should be considered deprecated. - -@item -mrestrict-it -@opindex mrestrict-it -Restricts generation of IT blocks to conform to the rules of ARMv8-A. -IT blocks can only contain a single 16-bit instruction from a select -set of instructions. This option is on by default for ARMv8-A Thumb mode. - -@item -mprint-tune-info -@opindex mprint-tune-info -Print CPU tuning information as comment in assembler file. This is -an option used only for regression testing of the compiler and not -intended for ordinary use in compiling code. This option is disabled -by default. - -@item -mverbose-cost-dump -@opindex mverbose-cost-dump -Enable verbose cost model dumping in the debug dump files. This option is -provided for use in debugging the compiler. - -@item -mpure-code -@opindex mpure-code -Do not allow constant data to be placed in code sections. -Additionally, when compiling for ELF object format give all text sections the -ELF processor-specific section attribute @code{SHF_ARM_PURECODE}. This option -is only available when generating non-pic code for M-profile targets. - -@item -mcmse -@opindex mcmse -Generate secure code as per the "ARMv8-M Security Extensions: Requirements on -Development Tools Engineering Specification", which can be found on -@url{https://developer.arm.com/documentation/ecm0359818/latest/}. - -@item -mfix-cmse-cve-2021-35465 -@opindex mfix-cmse-cve-2021-35465 -Mitigate against a potential security issue with the @code{VLLDM} instruction -in some M-profile devices when using CMSE (CVE-2021-365465). This option is -enabled by default when the option @option{-mcpu=} is used with -@code{cortex-m33}, @code{cortex-m35p}, @code{cortex-m55} or @code{star-mc1}. -The option @option{-mno-fix-cmse-cve-2021-35465} can be used to disable -the mitigation. - -@item -mstack-protector-guard=@var{guard} -@itemx -mstack-protector-guard-offset=@var{offset} -@opindex mstack-protector-guard -@opindex mstack-protector-guard-offset -Generate stack protection code using canary at @var{guard}. Supported -locations are @samp{global} for a global canary or @samp{tls} for a -canary accessible via the TLS register. The option -@option{-mstack-protector-guard-offset=} is for use with -@option{-fstack-protector-guard=tls} and not for use in user-land code. - -@item -mfdpic -@itemx -mno-fdpic -@opindex mfdpic -@opindex mno-fdpic -Select the FDPIC ABI, which uses 64-bit function descriptors to -represent pointers to functions. When the compiler is configured for -@code{arm-*-uclinuxfdpiceabi} targets, this option is on by default -and implies @option{-fPIE} if none of the PIC/PIE-related options is -provided. On other targets, it only enables the FDPIC-specific code -generation features, and the user should explicitly provide the -PIC/PIE-related options as needed. - -Note that static linking is not supported because it would still -involve the dynamic linker when the program self-relocates. If such -behavior is acceptable, use -static and -Wl,-dynamic-linker options. - -The opposite @option{-mno-fdpic} option is useful (and required) to -build the Linux kernel using the same (@code{arm-*-uclinuxfdpiceabi}) -toolchain as the one used to build the userland programs. - -@end table - -@node AVR Options -@subsection AVR Options -@cindex AVR Options - -These options are defined for AVR implementations: - -@table @gcctabopt -@item -mmcu=@var{mcu} -@opindex mmcu -Specify Atmel AVR instruction set architectures (ISA) or MCU type. - -The default for this option is@tie{}@samp{avr2}. - -GCC supports the following AVR devices and ISAs: - -@include avr-mmcu.texi - -@item -mabsdata -@opindex mabsdata - -Assume that all data in static storage can be accessed by LDS / STS -instructions. This option has only an effect on reduced Tiny devices like -ATtiny40. See also the @code{absdata} -@ref{AVR Variable Attributes,variable attribute}. - -@item -maccumulate-args -@opindex maccumulate-args -Accumulate outgoing function arguments and acquire/release the needed -stack space for outgoing function arguments once in function -prologue/epilogue. Without this option, outgoing arguments are pushed -before calling a function and popped afterwards. - -Popping the arguments after the function call can be expensive on -AVR so that accumulating the stack space might lead to smaller -executables because arguments need not be removed from the -stack after such a function call. - -This option can lead to reduced code size for functions that perform -several calls to functions that get their arguments on the stack like -calls to printf-like functions. - -@item -mbranch-cost=@var{cost} -@opindex mbranch-cost -Set the branch costs for conditional branch instructions to -@var{cost}. Reasonable values for @var{cost} are small, non-negative -integers. The default branch cost is 0. - -@item -mcall-prologues -@opindex mcall-prologues -Functions prologues/epilogues are expanded as calls to appropriate -subroutines. Code size is smaller. - -@item -mdouble=@var{bits} -@itemx -mlong-double=@var{bits} -@opindex mdouble -@opindex mlong-double -Set the size (in bits) of the @code{double} or @code{long double} type, -respectively. Possible values for @var{bits} are 32 and 64. -Whether or not a specific value for @var{bits} is allowed depends on -the @code{--with-double=} and @code{--with-long-double=} -@w{@uref{https://gcc.gnu.org/install/configure.html#avr,configure options}}, -and the same applies for the default values of the options. - -@item -mgas-isr-prologues -@opindex mgas-isr-prologues -Interrupt service routines (ISRs) may use the @code{__gcc_isr} pseudo -instruction supported by GNU Binutils. -If this option is on, the feature can still be disabled for individual -ISRs by means of the @ref{AVR Function Attributes,,@code{no_gccisr}} -function attribute. This feature is activated per default -if optimization is on (but not with @option{-Og}, @pxref{Optimize Options}), -and if GNU Binutils support @w{@uref{https://sourceware.org/PR21683,PR21683}}. - -@item -mint8 -@opindex mint8 -Assume @code{int} to be 8-bit integer. This affects the sizes of all types: a -@code{char} is 1 byte, an @code{int} is 1 byte, a @code{long} is 2 bytes, -and @code{long long} is 4 bytes. Please note that this option does not -conform to the C standards, but it results in smaller code -size. - -@item -mmain-is-OS_task -@opindex mmain-is-OS_task -Do not save registers in @code{main}. The effect is the same like -attaching attribute @ref{AVR Function Attributes,,@code{OS_task}} -to @code{main}. It is activated per default if optimization is on. - -@item -mn-flash=@var{num} -@opindex mn-flash -Assume that the flash memory has a size of -@var{num} times 64@tie{}KiB. - -@item -mno-interrupts -@opindex mno-interrupts -Generated code is not compatible with hardware interrupts. -Code size is smaller. - -@item -mrelax -@opindex mrelax -Try to replace @code{CALL} resp.@: @code{JMP} instruction by the shorter -@code{RCALL} resp.@: @code{RJMP} instruction if applicable. -Setting @option{-mrelax} just adds the @option{--mlink-relax} option to -the assembler's command line and the @option{--relax} option to the -linker's command line. - -Jump relaxing is performed by the linker because jump offsets are not -known before code is located. Therefore, the assembler code generated by the -compiler is the same, but the instructions in the executable may -differ from instructions in the assembler code. - -Relaxing must be turned on if linker stubs are needed, see the -section on @code{EIND} and linker stubs below. - -@item -mrmw -@opindex mrmw -Assume that the device supports the Read-Modify-Write -instructions @code{XCH}, @code{LAC}, @code{LAS} and @code{LAT}. - -@item -mshort-calls -@opindex mshort-calls - -Assume that @code{RJMP} and @code{RCALL} can target the whole -program memory. - -This option is used internally for multilib selection. It is -not an optimization option, and you don't need to set it by hand. - -@item -msp8 -@opindex msp8 -Treat the stack pointer register as an 8-bit register, -i.e.@: assume the high byte of the stack pointer is zero. -In general, you don't need to set this option by hand. - -This option is used internally by the compiler to select and -build multilibs for architectures @code{avr2} and @code{avr25}. -These architectures mix devices with and without @code{SPH}. -For any setting other than @option{-mmcu=avr2} or @option{-mmcu=avr25} -the compiler driver adds or removes this option from the compiler -proper's command line, because the compiler then knows if the device -or architecture has an 8-bit stack pointer and thus no @code{SPH} -register or not. - -@item -mstrict-X -@opindex mstrict-X -Use address register @code{X} in a way proposed by the hardware. This means -that @code{X} is only used in indirect, post-increment or -pre-decrement addressing. - -Without this option, the @code{X} register may be used in the same way -as @code{Y} or @code{Z} which then is emulated by additional -instructions. -For example, loading a value with @code{X+const} addressing with a -small non-negative @code{const < 64} to a register @var{Rn} is -performed as - -@example -adiw r26, const ; X += const -ld @var{Rn}, X ; @var{Rn} = *X -sbiw r26, const ; X -= const -@end example - -@item -mtiny-stack -@opindex mtiny-stack -Only change the lower 8@tie{}bits of the stack pointer. - -@item -mfract-convert-truncate -@opindex mfract-convert-truncate -Allow to use truncation instead of rounding towards zero for fractional fixed-point types. - -@item -nodevicelib -@opindex nodevicelib -Don't link against AVR-LibC's device specific library @code{lib<mcu>.a}. - -@item -nodevicespecs -@opindex nodevicespecs -Don't add @option{-specs=device-specs/specs-@var{mcu}} to the compiler driver's -command line. The user takes responsibility for supplying the sub-processes -like compiler proper, assembler and linker with appropriate command line -options. This means that the user has to supply her private device specs -file by means of @option{-specs=@var{path-to-specs-file}}. There is no -more need for option @option{-mmcu=@var{mcu}}. - -This option can also serve as a replacement for the older way of -specifying custom device-specs files that needed @option{-B @var{some-path}} to point to a directory -which contains a folder named @code{device-specs} which contains a specs file named -@code{specs-@var{mcu}}, where @var{mcu} was specified by @option{-mmcu=@var{mcu}}. - -@item -Waddr-space-convert -@opindex Waddr-space-convert -@opindex Wno-addr-space-convert -Warn about conversions between address spaces in the case where the -resulting address space is not contained in the incoming address space. - -@item -Wmisspelled-isr -@opindex Wmisspelled-isr -@opindex Wno-misspelled-isr -Warn if the ISR is misspelled, i.e.@: without __vector prefix. -Enabled by default. -@end table - -@subsubsection @code{EIND} and Devices with More Than 128 Ki Bytes of Flash -@cindex @code{EIND} -Pointers in the implementation are 16@tie{}bits wide. -The address of a function or label is represented as word address so -that indirect jumps and calls can target any code address in the -range of 64@tie{}Ki words. - -In order to facilitate indirect jump on devices with more than 128@tie{}Ki -bytes of program memory space, there is a special function register called -@code{EIND} that serves as most significant part of the target address -when @code{EICALL} or @code{EIJMP} instructions are used. - -Indirect jumps and calls on these devices are handled as follows by -the compiler and are subject to some limitations: - -@itemize @bullet - -@item -The compiler never sets @code{EIND}. - -@item -The compiler uses @code{EIND} implicitly in @code{EICALL}/@code{EIJMP} -instructions or might read @code{EIND} directly in order to emulate an -indirect call/jump by means of a @code{RET} instruction. - -@item -The compiler assumes that @code{EIND} never changes during the startup -code or during the application. In particular, @code{EIND} is not -saved/restored in function or interrupt service routine -prologue/epilogue. - -@item -For indirect calls to functions and computed goto, the linker -generates @emph{stubs}. Stubs are jump pads sometimes also called -@emph{trampolines}. Thus, the indirect call/jump jumps to such a stub. -The stub contains a direct jump to the desired address. - -@item -Linker relaxation must be turned on so that the linker generates -the stubs correctly in all situations. See the compiler option -@option{-mrelax} and the linker option @option{--relax}. -There are corner cases where the linker is supposed to generate stubs -but aborts without relaxation and without a helpful error message. - -@item -The default linker script is arranged for code with @code{EIND = 0}. -If code is supposed to work for a setup with @code{EIND != 0}, a custom -linker script has to be used in order to place the sections whose -name start with @code{.trampolines} into the segment where @code{EIND} -points to. - -@item -The startup code from libgcc never sets @code{EIND}. -Notice that startup code is a blend of code from libgcc and AVR-LibC. -For the impact of AVR-LibC on @code{EIND}, see the -@w{@uref{http://nongnu.org/avr-libc/user-manual/,AVR-LibC user manual}}. - -@item -It is legitimate for user-specific startup code to set up @code{EIND} -early, for example by means of initialization code located in -section @code{.init3}. Such code runs prior to general startup code -that initializes RAM and calls constructors, but after the bit -of startup code from AVR-LibC that sets @code{EIND} to the segment -where the vector table is located. -@example -#include <avr/io.h> - -static void -__attribute__((section(".init3"),naked,used,no_instrument_function)) -init3_set_eind (void) -@{ - __asm volatile ("ldi r24,pm_hh8(__trampolines_start)\n\t" - "out %i0,r24" :: "n" (&EIND) : "r24","memory"); -@} -@end example - -@noindent -The @code{__trampolines_start} symbol is defined in the linker script. - -@item -Stubs are generated automatically by the linker if -the following two conditions are met: -@itemize @minus - -@item The address of a label is taken by means of the @code{gs} modifier -(short for @emph{generate stubs}) like so: -@example -LDI r24, lo8(gs(@var{func})) -LDI r25, hi8(gs(@var{func})) -@end example -@item The final location of that label is in a code segment -@emph{outside} the segment where the stubs are located. -@end itemize - -@item -The compiler emits such @code{gs} modifiers for code labels in the -following situations: -@itemize @minus -@item Taking address of a function or code label. -@item Computed goto. -@item If prologue-save function is used, see @option{-mcall-prologues} -command-line option. -@item Switch/case dispatch tables. If you do not want such dispatch -tables you can specify the @option{-fno-jump-tables} command-line option. -@item C and C++ constructors/destructors called during startup/shutdown. -@item If the tools hit a @code{gs()} modifier explained above. -@end itemize - -@item -Jumping to non-symbolic addresses like so is @emph{not} supported: - -@example -int main (void) -@{ - /* Call function at word address 0x2 */ - return ((int(*)(void)) 0x2)(); -@} -@end example - -Instead, a stub has to be set up, i.e.@: the function has to be called -through a symbol (@code{func_4} in the example): - -@example -int main (void) -@{ - extern int func_4 (void); - - /* Call function at byte address 0x4 */ - return func_4(); -@} -@end example - -and the application be linked with @option{-Wl,--defsym,func_4=0x4}. -Alternatively, @code{func_4} can be defined in the linker script. -@end itemize - -@subsubsection Handling of the @code{RAMPD}, @code{RAMPX}, @code{RAMPY} and @code{RAMPZ} Special Function Registers -@cindex @code{RAMPD} -@cindex @code{RAMPX} -@cindex @code{RAMPY} -@cindex @code{RAMPZ} -Some AVR devices support memories larger than the 64@tie{}KiB range -that can be accessed with 16-bit pointers. To access memory locations -outside this 64@tie{}KiB range, the content of a @code{RAMP} -register is used as high part of the address: -The @code{X}, @code{Y}, @code{Z} address register is concatenated -with the @code{RAMPX}, @code{RAMPY}, @code{RAMPZ} special function -register, respectively, to get a wide address. Similarly, -@code{RAMPD} is used together with direct addressing. - -@itemize -@item -The startup code initializes the @code{RAMP} special function -registers with zero. - -@item -If a @ref{AVR Named Address Spaces,named address space} other than -generic or @code{__flash} is used, then @code{RAMPZ} is set -as needed before the operation. - -@item -If the device supports RAM larger than 64@tie{}KiB and the compiler -needs to change @code{RAMPZ} to accomplish an operation, @code{RAMPZ} -is reset to zero after the operation. - -@item -If the device comes with a specific @code{RAMP} register, the ISR -prologue/epilogue saves/restores that SFR and initializes it with -zero in case the ISR code might (implicitly) use it. - -@item -RAM larger than 64@tie{}KiB is not supported by GCC for AVR targets. -If you use inline assembler to read from locations outside the -16-bit address range and change one of the @code{RAMP} registers, -you must reset it to zero after the access. - -@end itemize - -@subsubsection AVR Built-in Macros - -GCC defines several built-in macros so that the user code can test -for the presence or absence of features. Almost any of the following -built-in macros are deduced from device capabilities and thus -triggered by the @option{-mmcu=} command-line option. - -For even more AVR-specific built-in macros see -@ref{AVR Named Address Spaces} and @ref{AVR Built-in Functions}. - -@table @code - -@item __AVR_ARCH__ -Build-in macro that resolves to a decimal number that identifies the -architecture and depends on the @option{-mmcu=@var{mcu}} option. -Possible values are: - -@code{2}, @code{25}, @code{3}, @code{31}, @code{35}, -@code{4}, @code{5}, @code{51}, @code{6} - -for @var{mcu}=@code{avr2}, @code{avr25}, @code{avr3}, @code{avr31}, -@code{avr35}, @code{avr4}, @code{avr5}, @code{avr51}, @code{avr6}, - -respectively and - -@code{100}, -@code{102}, @code{103}, @code{104}, -@code{105}, @code{106}, @code{107} - -for @var{mcu}=@code{avrtiny}, -@code{avrxmega2}, @code{avrxmega3}, @code{avrxmega4}, -@code{avrxmega5}, @code{avrxmega6}, @code{avrxmega7}, respectively. -If @var{mcu} specifies a device, this built-in macro is set -accordingly. For example, with @option{-mmcu=atmega8} the macro is -defined to @code{4}. - -@item __AVR_@var{Device}__ -Setting @option{-mmcu=@var{device}} defines this built-in macro which reflects -the device's name. For example, @option{-mmcu=atmega8} defines the -built-in macro @code{__AVR_ATmega8__}, @option{-mmcu=attiny261a} defines -@code{__AVR_ATtiny261A__}, etc. - -The built-in macros' names follow -the scheme @code{__AVR_@var{Device}__} where @var{Device} is -the device name as from the AVR user manual. The difference between -@var{Device} in the built-in macro and @var{device} in -@option{-mmcu=@var{device}} is that the latter is always lowercase. - -If @var{device} is not a device but only a core architecture like -@samp{avr51}, this macro is not defined. - -@item __AVR_DEVICE_NAME__ -Setting @option{-mmcu=@var{device}} defines this built-in macro to -the device's name. For example, with @option{-mmcu=atmega8} the macro -is defined to @code{atmega8}. - -If @var{device} is not a device but only a core architecture like -@samp{avr51}, this macro is not defined. - -@item __AVR_XMEGA__ -The device / architecture belongs to the XMEGA family of devices. - -@item __AVR_HAVE_ELPM__ -The device has the @code{ELPM} instruction. - -@item __AVR_HAVE_ELPMX__ -The device has the @code{ELPM R@var{n},Z} and @code{ELPM -R@var{n},Z+} instructions. - -@item __AVR_HAVE_MOVW__ -The device has the @code{MOVW} instruction to perform 16-bit -register-register moves. - -@item __AVR_HAVE_LPMX__ -The device has the @code{LPM R@var{n},Z} and -@code{LPM R@var{n},Z+} instructions. - -@item __AVR_HAVE_MUL__ -The device has a hardware multiplier. - -@item __AVR_HAVE_JMP_CALL__ -The device has the @code{JMP} and @code{CALL} instructions. -This is the case for devices with more than 8@tie{}KiB of program -memory. - -@item __AVR_HAVE_EIJMP_EICALL__ -@itemx __AVR_3_BYTE_PC__ -The device has the @code{EIJMP} and @code{EICALL} instructions. -This is the case for devices with more than 128@tie{}KiB of program memory. -This also means that the program counter -(PC) is 3@tie{}bytes wide. - -@item __AVR_2_BYTE_PC__ -The program counter (PC) is 2@tie{}bytes wide. This is the case for devices -with up to 128@tie{}KiB of program memory. - -@item __AVR_HAVE_8BIT_SP__ -@itemx __AVR_HAVE_16BIT_SP__ -The stack pointer (SP) register is treated as 8-bit respectively -16-bit register by the compiler. -The definition of these macros is affected by @option{-mtiny-stack}. - -@item __AVR_HAVE_SPH__ -@itemx __AVR_SP8__ -The device has the SPH (high part of stack pointer) special function -register or has an 8-bit stack pointer, respectively. -The definition of these macros is affected by @option{-mmcu=} and -in the cases of @option{-mmcu=avr2} and @option{-mmcu=avr25} also -by @option{-msp8}. - -@item __AVR_HAVE_RAMPD__ -@itemx __AVR_HAVE_RAMPX__ -@itemx __AVR_HAVE_RAMPY__ -@itemx __AVR_HAVE_RAMPZ__ -The device has the @code{RAMPD}, @code{RAMPX}, @code{RAMPY}, -@code{RAMPZ} special function register, respectively. - -@item __NO_INTERRUPTS__ -This macro reflects the @option{-mno-interrupts} command-line option. - -@item __AVR_ERRATA_SKIP__ -@itemx __AVR_ERRATA_SKIP_JMP_CALL__ -Some AVR devices (AT90S8515, ATmega103) must not skip 32-bit -instructions because of a hardware erratum. Skip instructions are -@code{SBRS}, @code{SBRC}, @code{SBIS}, @code{SBIC} and @code{CPSE}. -The second macro is only defined if @code{__AVR_HAVE_JMP_CALL__} is also -set. - -@item __AVR_ISA_RMW__ -The device has Read-Modify-Write instructions (XCH, LAC, LAS and LAT). - -@item __AVR_SFR_OFFSET__=@var{offset} -Instructions that can address I/O special function registers directly -like @code{IN}, @code{OUT}, @code{SBI}, etc.@: may use a different -address as if addressed by an instruction to access RAM like @code{LD} -or @code{STS}. This offset depends on the device architecture and has -to be subtracted from the RAM address in order to get the -respective I/O@tie{}address. - -@item __AVR_SHORT_CALLS__ -The @option{-mshort-calls} command line option is set. - -@item __AVR_PM_BASE_ADDRESS__=@var{addr} -Some devices support reading from flash memory by means of @code{LD*} -instructions. The flash memory is seen in the data address space -at an offset of @code{__AVR_PM_BASE_ADDRESS__}. If this macro -is not defined, this feature is not available. If defined, -the address space is linear and there is no need to put -@code{.rodata} into RAM. This is handled by the default linker -description file, and is currently available for -@code{avrtiny} and @code{avrxmega3}. Even more convenient, -there is no need to use address spaces like @code{__flash} or -features like attribute @code{progmem} and @code{pgm_read_*}. - -@item __WITH_AVRLIBC__ -The compiler is configured to be used together with AVR-Libc. -See the @option{--with-avrlibc} configure option. - -@item __HAVE_DOUBLE_MULTILIB__ -Defined if @option{-mdouble=} acts as a multilib option. - -@item __HAVE_DOUBLE32__ -@itemx __HAVE_DOUBLE64__ -Defined if the compiler supports 32-bit double resp. 64-bit double. -The actual layout is specified by option @option{-mdouble=}. - -@item __DEFAULT_DOUBLE__ -The size in bits of @code{double} if @option{-mdouble=} is not set. -To test the layout of @code{double} in a program, use the built-in -macro @code{__SIZEOF_DOUBLE__}. - -@item __HAVE_LONG_DOUBLE32__ -@itemx __HAVE_LONG_DOUBLE64__ -@itemx __HAVE_LONG_DOUBLE_MULTILIB__ -@itemx __DEFAULT_LONG_DOUBLE__ -Same as above, but for @code{long double} instead of @code{double}. - -@item __WITH_DOUBLE_COMPARISON__ -Reflects the @code{--with-double-comparison=@{tristate|bool|libf7@}} -@w{@uref{https://gcc.gnu.org/install/configure.html#avr,configure option}} -and is defined to @code{2} or @code{3}. - -@item __WITH_LIBF7_LIBGCC__ -@itemx __WITH_LIBF7_MATH__ -@itemx __WITH_LIBF7_MATH_SYMBOLS__ -Reflects the @code{--with-libf7=@{libgcc|math|math-symbols@}} -@w{@uref{https://gcc.gnu.org/install/configure.html#avr,configure option}}. - -@end table - -@node Blackfin Options -@subsection Blackfin Options -@cindex Blackfin Options - -@table @gcctabopt -@item -mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} -@opindex mcpu= -Specifies the name of the target Blackfin processor. Currently, @var{cpu} -can be one of @samp{bf512}, @samp{bf514}, @samp{bf516}, @samp{bf518}, -@samp{bf522}, @samp{bf523}, @samp{bf524}, @samp{bf525}, @samp{bf526}, -@samp{bf527}, @samp{bf531}, @samp{bf532}, @samp{bf533}, -@samp{bf534}, @samp{bf536}, @samp{bf537}, @samp{bf538}, @samp{bf539}, -@samp{bf542}, @samp{bf544}, @samp{bf547}, @samp{bf548}, @samp{bf549}, -@samp{bf542m}, @samp{bf544m}, @samp{bf547m}, @samp{bf548m}, @samp{bf549m}, -@samp{bf561}, @samp{bf592}. - -The optional @var{sirevision} specifies the silicon revision of the target -Blackfin processor. Any workarounds available for the targeted silicon revision -are enabled. If @var{sirevision} is @samp{none}, no workarounds are enabled. -If @var{sirevision} is @samp{any}, all workarounds for the targeted processor -are enabled. The @code{__SILICON_REVISION__} macro is defined to two -hexadecimal digits representing the major and minor numbers in the silicon -revision. If @var{sirevision} is @samp{none}, the @code{__SILICON_REVISION__} -is not defined. If @var{sirevision} is @samp{any}, the -@code{__SILICON_REVISION__} is defined to be @code{0xffff}. -If this optional @var{sirevision} is not used, GCC assumes the latest known -silicon revision of the targeted Blackfin processor. - -GCC defines a preprocessor macro for the specified @var{cpu}. -For the @samp{bfin-elf} toolchain, this option causes the hardware BSP -provided by libgloss to be linked in if @option{-msim} is not given. - -Without this option, @samp{bf532} is used as the processor by default. - -Note that support for @samp{bf561} is incomplete. For @samp{bf561}, -only the preprocessor macro is defined. - -@item -msim -@opindex msim -Specifies that the program will be run on the simulator. This causes -the simulator BSP provided by libgloss to be linked in. This option -has effect only for @samp{bfin-elf} toolchain. -Certain other options, such as @option{-mid-shared-library} and -@option{-mfdpic}, imply @option{-msim}. - -@item -momit-leaf-frame-pointer -@opindex momit-leaf-frame-pointer -Don't keep the frame pointer in a register for leaf functions. This -avoids the instructions to save, set up and restore frame pointers and -makes an extra register available in leaf functions. - -@item -mspecld-anomaly -@opindex mspecld-anomaly -When enabled, the compiler ensures that the generated code does not -contain speculative loads after jump instructions. If this option is used, -@code{__WORKAROUND_SPECULATIVE_LOADS} is defined. - -@item -mno-specld-anomaly -@opindex mno-specld-anomaly -@opindex mspecld-anomaly -Don't generate extra code to prevent speculative loads from occurring. - -@item -mcsync-anomaly -@opindex mcsync-anomaly -When enabled, the compiler ensures that the generated code does not -contain CSYNC or SSYNC instructions too soon after conditional branches. -If this option is used, @code{__WORKAROUND_SPECULATIVE_SYNCS} is defined. - -@item -mno-csync-anomaly -@opindex mno-csync-anomaly -@opindex mcsync-anomaly -Don't generate extra code to prevent CSYNC or SSYNC instructions from -occurring too soon after a conditional branch. - -@item -mlow64k -@opindex mlow64k -When enabled, the compiler is free to take advantage of the knowledge that -the entire program fits into the low 64k of memory. - -@item -mno-low64k -@opindex mno-low64k -Assume that the program is arbitrarily large. This is the default. - -@item -mstack-check-l1 -@opindex mstack-check-l1 -Do stack checking using information placed into L1 scratchpad memory by the -uClinux kernel. - -@item -mid-shared-library -@opindex mid-shared-library -Generate code that supports shared libraries via the library ID method. -This allows for execute in place and shared libraries in an environment -without virtual memory management. This option implies @option{-fPIC}. -With a @samp{bfin-elf} target, this option implies @option{-msim}. - -@item -mno-id-shared-library -@opindex mno-id-shared-library -@opindex mid-shared-library -Generate code that doesn't assume ID-based shared libraries are being used. -This is the default. - -@item -mleaf-id-shared-library -@opindex mleaf-id-shared-library -Generate code that supports shared libraries via the library ID method, -but assumes that this library or executable won't link against any other -ID shared libraries. That allows the compiler to use faster code for jumps -and calls. - -@item -mno-leaf-id-shared-library -@opindex mno-leaf-id-shared-library -@opindex mleaf-id-shared-library -Do not assume that the code being compiled won't link against any ID shared -libraries. Slower code is generated for jump and call insns. - -@item -mshared-library-id=n -@opindex mshared-library-id -Specifies the identification number of the ID-based shared library being -compiled. Specifying a value of 0 generates more compact code; specifying -other values forces the allocation of that number to the current -library but is no more space- or time-efficient than omitting this option. - -@item -msep-data -@opindex msep-data -Generate code that allows the data segment to be located in a different -area of memory from the text segment. This allows for execute in place in -an environment without virtual memory management by eliminating relocations -against the text section. - -@item -mno-sep-data -@opindex mno-sep-data -@opindex msep-data -Generate code that assumes that the data segment follows the text segment. -This is the default. - -@item -mlong-calls -@itemx -mno-long-calls -@opindex mlong-calls -@opindex mno-long-calls -Tells the compiler to perform function calls by first loading the -address of the function into a register and then performing a subroutine -call on this register. This switch is needed if the target function -lies outside of the 24-bit addressing range of the offset-based -version of subroutine call instruction. - -This feature is not enabled by default. Specifying -@option{-mno-long-calls} restores the default behavior. Note these -switches have no effect on how the compiler generates code to handle -function calls via function pointers. - -@item -mfast-fp -@opindex mfast-fp -Link with the fast floating-point library. This library relaxes some of -the IEEE floating-point standard's rules for checking inputs against -Not-a-Number (NAN), in the interest of performance. - -@item -minline-plt -@opindex minline-plt -Enable inlining of PLT entries in function calls to functions that are -not known to bind locally. It has no effect without @option{-mfdpic}. - -@item -mmulticore -@opindex mmulticore -Build a standalone application for multicore Blackfin processors. -This option causes proper start files and link scripts supporting -multicore to be used, and defines the macro @code{__BFIN_MULTICORE}. -It can only be used with @option{-mcpu=bf561@r{[}-@var{sirevision}@r{]}}. - -This option can be used with @option{-mcorea} or @option{-mcoreb}, which -selects the one-application-per-core programming model. Without -@option{-mcorea} or @option{-mcoreb}, the single-application/dual-core -programming model is used. In this model, the main function of Core B -should be named as @code{coreb_main}. - -If this option is not used, the single-core application programming -model is used. - -@item -mcorea -@opindex mcorea -Build a standalone application for Core A of BF561 when using -the one-application-per-core programming model. Proper start files -and link scripts are used to support Core A, and the macro -@code{__BFIN_COREA} is defined. -This option can only be used in conjunction with @option{-mmulticore}. - -@item -mcoreb -@opindex mcoreb -Build a standalone application for Core B of BF561 when using -the one-application-per-core programming model. Proper start files -and link scripts are used to support Core B, and the macro -@code{__BFIN_COREB} is defined. When this option is used, @code{coreb_main} -should be used instead of @code{main}. -This option can only be used in conjunction with @option{-mmulticore}. - -@item -msdram -@opindex msdram -Build a standalone application for SDRAM. Proper start files and -link scripts are used to put the application into SDRAM, and the macro -@code{__BFIN_SDRAM} is defined. -The loader should initialize SDRAM before loading the application. - -@item -micplb -@opindex micplb -Assume that ICPLBs are enabled at run time. This has an effect on certain -anomaly workarounds. For Linux targets, the default is to assume ICPLBs -are enabled; for standalone applications the default is off. -@end table - -@node C6X Options -@subsection C6X Options -@cindex C6X Options - -@table @gcctabopt -@item -march=@var{name} -@opindex march -This specifies the name of the target architecture. GCC uses this -name to determine what kind of instructions it can emit when generating -assembly code. Permissible names are: @samp{c62x}, -@samp{c64x}, @samp{c64x+}, @samp{c67x}, @samp{c67x+}, @samp{c674x}. - -@item -mbig-endian -@opindex mbig-endian -Generate code for a big-endian target. - -@item -mlittle-endian -@opindex mlittle-endian -Generate code for a little-endian target. This is the default. - -@item -msim -@opindex msim -Choose startup files and linker script suitable for the simulator. - -@item -msdata=default -@opindex msdata=default -Put small global and static data in the @code{.neardata} section, -which is pointed to by register @code{B14}. Put small uninitialized -global and static data in the @code{.bss} section, which is adjacent -to the @code{.neardata} section. Put small read-only data into the -@code{.rodata} section. The corresponding sections used for large -pieces of data are @code{.fardata}, @code{.far} and @code{.const}. - -@item -msdata=all -@opindex msdata=all -Put all data, not just small objects, into the sections reserved for -small data, and use addressing relative to the @code{B14} register to -access them. - -@item -msdata=none -@opindex msdata=none -Make no use of the sections reserved for small data, and use absolute -addresses to access all data. Put all initialized global and static -data in the @code{.fardata} section, and all uninitialized data in the -@code{.far} section. Put all constant data into the @code{.const} -section. -@end table - -@node CRIS Options -@subsection CRIS Options -@cindex CRIS Options - -These options are defined specifically for the CRIS ports. - -@table @gcctabopt -@item -march=@var{architecture-type} -@itemx -mcpu=@var{architecture-type} -@opindex march -@opindex mcpu -Generate code for the specified architecture. The choices for -@var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for -respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@. -Default is @samp{v0}. - -@item -mtune=@var{architecture-type} -@opindex mtune -Tune to @var{architecture-type} everything applicable about the generated -code, except for the ABI and the set of available instructions. The -choices for @var{architecture-type} are the same as for -@option{-march=@var{architecture-type}}. - -@item -mmax-stack-frame=@var{n} -@opindex mmax-stack-frame -Warn when the stack frame of a function exceeds @var{n} bytes. - -@item -metrax4 -@itemx -metrax100 -@opindex metrax4 -@opindex metrax100 -The options @option{-metrax4} and @option{-metrax100} are synonyms for -@option{-march=v3} and @option{-march=v8} respectively. - -@item -mmul-bug-workaround -@itemx -mno-mul-bug-workaround -@opindex mmul-bug-workaround -@opindex mno-mul-bug-workaround -Work around a bug in the @code{muls} and @code{mulu} instructions for CPU -models where it applies. This option is disabled by default. - -@item -mpdebug -@opindex mpdebug -Enable CRIS-specific verbose debug-related information in the assembly -code. This option also has the effect of turning off the @samp{#NO_APP} -formatted-code indicator to the assembler at the beginning of the -assembly file. - -@item -mcc-init -@opindex mcc-init -Do not use condition-code results from previous instruction; always emit -compare and test instructions before use of condition codes. - -@item -mno-side-effects -@opindex mno-side-effects -@opindex mside-effects -Do not emit instructions with side effects in addressing modes other than -post-increment. - -@item -mstack-align -@itemx -mno-stack-align -@itemx -mdata-align -@itemx -mno-data-align -@itemx -mconst-align -@itemx -mno-const-align -@opindex mstack-align -@opindex mno-stack-align -@opindex mdata-align -@opindex mno-data-align -@opindex mconst-align -@opindex mno-const-align -These options (@samp{no-} options) arrange (eliminate arrangements) for the -stack frame, individual data and constants to be aligned for the maximum -single data access size for the chosen CPU model. The default is to -arrange for 32-bit alignment. ABI details such as structure layout are -not affected by these options. - -@item -m32-bit -@itemx -m16-bit -@itemx -m8-bit -@opindex m32-bit -@opindex m16-bit -@opindex m8-bit -Similar to the stack- data- and const-align options above, these options -arrange for stack frame, writable data and constants to all be 32-bit, -16-bit or 8-bit aligned. The default is 32-bit alignment. - -@item -mno-prologue-epilogue -@itemx -mprologue-epilogue -@opindex mno-prologue-epilogue -@opindex mprologue-epilogue -With @option{-mno-prologue-epilogue}, the normal function prologue and -epilogue which set up the stack frame are omitted and no return -instructions or return sequences are generated in the code. Use this -option only together with visual inspection of the compiled code: no -warnings or errors are generated when call-saved registers must be saved, -or storage for local variables needs to be allocated. - -@item -melf -@opindex melf -Legacy no-op option. - -@item -sim -@opindex sim -This option arranges -to link with input-output functions from a simulator library. Code, -initialized data and zero-initialized data are allocated consecutively. - -@item -sim2 -@opindex sim2 -Like @option{-sim}, but pass linker options to locate initialized data at -0x40000000 and zero-initialized data at 0x80000000. -@end table - -@node C-SKY Options -@subsection C-SKY Options -@cindex C-SKY Options - -GCC supports these options when compiling for C-SKY V2 processors. - -@table @gcctabopt - -@item -march=@var{arch} -@opindex march= -Specify the C-SKY target architecture. Valid values for @var{arch} are: -@samp{ck801}, @samp{ck802}, @samp{ck803}, @samp{ck807}, and @samp{ck810}. -The default is @samp{ck810}. - -@item -mcpu=@var{cpu} -@opindex mcpu= -Specify the C-SKY target processor. Valid values for @var{cpu} are: -@samp{ck801}, @samp{ck801t}, -@samp{ck802}, @samp{ck802t}, @samp{ck802j}, -@samp{ck803}, @samp{ck803h}, @samp{ck803t}, @samp{ck803ht}, -@samp{ck803f}, @samp{ck803fh}, @samp{ck803e}, @samp{ck803eh}, -@samp{ck803et}, @samp{ck803eht}, @samp{ck803ef}, @samp{ck803efh}, -@samp{ck803ft}, @samp{ck803eft}, @samp{ck803efht}, @samp{ck803r1}, -@samp{ck803hr1}, @samp{ck803tr1}, @samp{ck803htr1}, @samp{ck803fr1}, -@samp{ck803fhr1}, @samp{ck803er1}, @samp{ck803ehr1}, @samp{ck803etr1}, -@samp{ck803ehtr1}, @samp{ck803efr1}, @samp{ck803efhr1}, @samp{ck803ftr1}, -@samp{ck803eftr1}, @samp{ck803efhtr1}, -@samp{ck803s}, @samp{ck803st}, @samp{ck803se}, @samp{ck803sf}, -@samp{ck803sef}, @samp{ck803seft}, -@samp{ck807e}, @samp{ck807ef}, @samp{ck807}, @samp{ck807f}, -@samp{ck810e}, @samp{ck810et}, @samp{ck810ef}, @samp{ck810eft}, -@samp{ck810}, @samp{ck810v}, @samp{ck810f}, @samp{ck810t}, @samp{ck810fv}, -@samp{ck810tv}, @samp{ck810ft}, and @samp{ck810ftv}. - -@item -mbig-endian -@opindex mbig-endian -@itemx -EB -@opindex EB -@itemx -mlittle-endian -@opindex mlittle-endian -@itemx -EL -@opindex EL - -Select big- or little-endian code. The default is little-endian. - -@item -mfloat-abi=@var{name} -@opindex mfloat-abi -Specifies which floating-point ABI to use. Permissible values -are: @samp{soft}, @samp{softfp} and @samp{hard}. - -Specifying @samp{soft} causes GCC to generate output containing -library calls for floating-point operations. -@samp{softfp} allows the generation of code using hardware floating-point -instructions, but still uses the soft-float calling conventions. -@samp{hard} allows generation of floating-point instructions -and uses FPU-specific calling conventions. - -The default depends on the specific target configuration. Note that -the hard-float and soft-float ABIs are not link-compatible; you must -compile your entire program with the same ABI, and link with a -compatible set of libraries. - -@item -mhard-float -@opindex mhard-float -@itemx -msoft-float -@opindex msoft-float - -Select hardware or software floating-point implementations. -The default is soft float. - -@item -mdouble-float -@itemx -mno-double-float -@opindex mdouble-float -When @option{-mhard-float} is in effect, enable generation of -double-precision float instructions. This is the default except -when compiling for CK803. - -@item -mfdivdu -@itemx -mno-fdivdu -@opindex mfdivdu -When @option{-mhard-float} is in effect, enable generation of -@code{frecipd}, @code{fsqrtd}, and @code{fdivd} instructions. -This is the default except when compiling for CK803. - -@item -mfpu=@var{fpu} -@opindex mfpu= -Select the floating-point processor. This option can only be used with -@option{-mhard-float}. -Values for @var{fpu} are -@samp{fpv2_sf} (equivalent to @samp{-mno-double-float -mno-fdivdu}), -@samp{fpv2} (@samp{-mdouble-float -mno-divdu}), and -@samp{fpv2_divd} (@samp{-mdouble-float -mdivdu}). - -@item -melrw -@itemx -mno-elrw -@opindex melrw -Enable the extended @code{lrw} instruction. This option defaults to on -for CK801 and off otherwise. - -@item -mistack -@itemx -mno-istack -@opindex mistack -Enable interrupt stack instructions; the default is off. - -The @option{-mistack} option is required to handle the -@code{interrupt} and @code{isr} function attributes -(@pxref{C-SKY Function Attributes}). - -@item -mmp -@opindex mmp -Enable multiprocessor instructions; the default is off. - -@item -mcp -@opindex mcp -Enable coprocessor instructions; the default is off. - -@item -mcache -@opindex mcache -Enable coprocessor instructions; the default is off. - -@item -msecurity -@opindex msecurity -Enable C-SKY security instructions; the default is off. - -@item -mtrust -@opindex mtrust -Enable C-SKY trust instructions; the default is off. - -@item -mdsp -@opindex mdsp -@itemx -medsp -@opindex medsp -@itemx -mvdsp -@opindex mvdsp -Enable C-SKY DSP, Enhanced DSP, or Vector DSP instructions, respectively. -All of these options default to off. - -@item -mdiv -@itemx -mno-div -@opindex mdiv -Generate divide instructions. Default is off. - -@item -msmart -@itemx -mno-smart -@opindex msmart -Generate code for Smart Mode, using only registers numbered 0-7 to allow -use of 16-bit instructions. This option is ignored for CK801 where this -is the required behavior, and it defaults to on for CK802. -For other targets, the default is off. - -@item -mhigh-registers -@itemx -mno-high-registers -@opindex mhigh-registers -Generate code using the high registers numbered 16-31. This option -is not supported on CK801, CK802, or CK803, and is enabled by default -for other processors. - -@item -manchor -@itemx -mno-anchor -@opindex manchor -Generate code using global anchor symbol addresses. - -@item -mpushpop -@itemx -mno-pushpop -@opindex mpushpop -Generate code using @code{push} and @code{pop} instructions. This option -defaults to on. - -@item -mmultiple-stld -@itemx -mstm -@itemx -mno-multiple-stld -@itemx -mno-stm -@opindex mmultiple-stld -Generate code using @code{stm} and @code{ldm} instructions. This option -isn't supported on CK801 but is enabled by default on other processors. - -@item -mconstpool -@itemx -mno-constpool -@opindex mconstpool -Create constant pools in the compiler instead of deferring it to the -assembler. This option is the default and required for correct code -generation on CK801 and CK802, and is optional on other processors. - -@item -mstack-size -@item -mno-stack-size -@opindex mstack-size -Emit @code{.stack_size} directives for each function in the assembly -output. This option defaults to off. - -@item -mccrt -@itemx -mno-ccrt -@opindex mccrt -Generate code for the C-SKY compiler runtime instead of libgcc. This -option defaults to off. - -@item -mbranch-cost=@var{n} -@opindex mbranch-cost= -Set the branch costs to roughly @code{n} instructions. The default is 1. - -@item -msched-prolog -@itemx -mno-sched-prolog -@opindex msched-prolog -Permit scheduling of function prologue and epilogue sequences. Using -this option can result in code that is not compliant with the C-SKY V2 ABI -prologue requirements and that cannot be debugged or backtraced. -It is disabled by default. - -@item -msim -@opindex msim -Links the library libsemi.a which is in compatible with simulator. Applicable -to ELF compiler only. - -@end table - -@node Darwin Options -@subsection Darwin Options -@cindex Darwin options - -These options are defined for all architectures running the Darwin operating -system. - -FSF GCC on Darwin does not create ``fat'' object files; it creates -an object file for the single architecture that GCC was built to -target. Apple's GCC on Darwin does create ``fat'' files if multiple -@option{-arch} options are used; it does so by running the compiler or -linker multiple times and joining the results together with -@file{lipo}. - -The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or -@samp{i686}) is determined by the flags that specify the ISA -that GCC is targeting, like @option{-mcpu} or @option{-march}. The -@option{-force_cpusubtype_ALL} option can be used to override this. - -The Darwin tools vary in their behavior when presented with an ISA -mismatch. The assembler, @file{as}, only permits instructions to -be used that are valid for the subtype of the file it is generating, -so you cannot put 64-bit instructions in a @samp{ppc750} object file. -The linker for shared libraries, @file{/usr/bin/libtool}, fails -and prints an error if asked to create a shared library with a less -restrictive subtype than its input files (for instance, trying to put -a @samp{ppc970} object file in a @samp{ppc7400} library). The linker -for executables, @command{ld}, quietly gives the executable the most -restrictive subtype of any of its input files. - -@table @gcctabopt -@item -F@var{dir} -@opindex F -Add the framework directory @var{dir} to the head of the list of -directories to be searched for header files. These directories are -interleaved with those specified by @option{-I} options and are -scanned in a left-to-right order. - -A framework directory is a directory with frameworks in it. A -framework is a directory with a @file{Headers} and/or -@file{PrivateHeaders} directory contained directly in it that ends -in @file{.framework}. The name of a framework is the name of this -directory excluding the @file{.framework}. Headers associated with -the framework are found in one of those two directories, with -@file{Headers} being searched first. A subframework is a framework -directory that is in a framework's @file{Frameworks} directory. -Includes of subframework headers can only appear in a header of a -framework that contains the subframework, or in a sibling subframework -header. Two subframeworks are siblings if they occur in the same -framework. A subframework should not have the same name as a -framework; a warning is issued if this is violated. Currently a -subframework cannot have subframeworks; in the future, the mechanism -may be extended to support this. The standard frameworks can be found -in @file{/System/Library/Frameworks} and -@file{/Library/Frameworks}. An example include looks like -@code{#include <Framework/header.h>}, where @file{Framework} denotes -the name of the framework and @file{header.h} is found in the -@file{PrivateHeaders} or @file{Headers} directory. - -@item -iframework@var{dir} -@opindex iframework -Like @option{-F} except the directory is a treated as a system -directory. The main difference between this @option{-iframework} and -@option{-F} is that with @option{-iframework} the compiler does not -warn about constructs contained within header files found via -@var{dir}. This option is valid only for the C family of languages. - -@item -gused -@opindex gused -Emit debugging information for symbols that are used. For stabs -debugging format, this enables @option{-feliminate-unused-debug-symbols}. -This is by default ON@. - -@item -gfull -@opindex gfull -Emit debugging information for all symbols and types. - -@item -mmacosx-version-min=@var{version} -The earliest version of MacOS X that this executable will run on -is @var{version}. Typical values of @var{version} include @code{10.1}, -@code{10.2}, and @code{10.3.9}. - -If the compiler was built to use the system's headers by default, -then the default for this option is the system version on which the -compiler is running, otherwise the default is to make choices that -are compatible with as many systems and code bases as possible. - -@item -mkernel -@opindex mkernel -Enable kernel development mode. The @option{-mkernel} option sets -@option{-static}, @option{-fno-common}, @option{-fno-use-cxa-atexit}, -@option{-fno-exceptions}, @option{-fno-non-call-exceptions}, -@option{-fapple-kext}, @option{-fno-weak} and @option{-fno-rtti} where -applicable. This mode also sets @option{-mno-altivec}, -@option{-msoft-float}, @option{-fno-builtin} and -@option{-mlong-branch} for PowerPC targets. - -@item -mone-byte-bool -@opindex mone-byte-bool -Override the defaults for @code{bool} so that @code{sizeof(bool)==1}. -By default @code{sizeof(bool)} is @code{4} when compiling for -Darwin/PowerPC and @code{1} when compiling for Darwin/x86, so this -option has no effect on x86. - -@strong{Warning:} The @option{-mone-byte-bool} switch causes GCC -to generate code that is not binary compatible with code generated -without that switch. Using this switch may require recompiling all -other modules in a program, including system libraries. Use this -switch to conform to a non-default data model. - -@item -mfix-and-continue -@itemx -ffix-and-continue -@itemx -findirect-data -@opindex mfix-and-continue -@opindex ffix-and-continue -@opindex findirect-data -Generate code suitable for fast turnaround development, such as to -allow GDB to dynamically load @file{.o} files into already-running -programs. @option{-findirect-data} and @option{-ffix-and-continue} -are provided for backwards compatibility. - -@item -all_load -@opindex all_load -Loads all members of static archive libraries. -See man ld(1) for more information. - -@item -arch_errors_fatal -@opindex arch_errors_fatal -Cause the errors having to do with files that have the wrong architecture -to be fatal. - -@item -bind_at_load -@opindex bind_at_load -Causes the output file to be marked such that the dynamic linker will -bind all undefined references when the file is loaded or launched. - -@item -bundle -@opindex bundle -Produce a Mach-o bundle format file. -See man ld(1) for more information. - -@item -bundle_loader @var{executable} -@opindex bundle_loader -This option specifies the @var{executable} that will load the build -output file being linked. See man ld(1) for more information. - -@item -dynamiclib -@opindex dynamiclib -When passed this option, GCC produces a dynamic library instead of -an executable when linking, using the Darwin @file{libtool} command. - -@item -force_cpusubtype_ALL -@opindex force_cpusubtype_ALL -This causes GCC's output file to have the @samp{ALL} subtype, instead of -one controlled by the @option{-mcpu} or @option{-march} option. - -@item -allowable_client @var{client_name} -@itemx -client_name -@itemx -compatibility_version -@itemx -current_version -@itemx -dead_strip -@itemx -dependency-file -@itemx -dylib_file -@itemx -dylinker_install_name -@itemx -dynamic -@itemx -exported_symbols_list -@itemx -filelist -@need 800 -@itemx -flat_namespace -@itemx -force_flat_namespace -@itemx -headerpad_max_install_names -@itemx -image_base -@itemx -init -@itemx -install_name -@itemx -keep_private_externs -@itemx -multi_module -@itemx -multiply_defined -@itemx -multiply_defined_unused -@need 800 -@itemx -noall_load -@itemx -no_dead_strip_inits_and_terms -@itemx -nofixprebinding -@itemx -nomultidefs -@itemx -noprebind -@itemx -noseglinkedit -@itemx -pagezero_size -@itemx -prebind -@itemx -prebind_all_twolevel_modules -@itemx -private_bundle -@need 800 -@itemx -read_only_relocs -@itemx -sectalign -@itemx -sectobjectsymbols -@itemx -whyload -@itemx -seg1addr -@itemx -sectcreate -@itemx -sectobjectsymbols -@itemx -sectorder -@itemx -segaddr -@itemx -segs_read_only_addr -@need 800 -@itemx -segs_read_write_addr -@itemx -seg_addr_table -@itemx -seg_addr_table_filename -@itemx -seglinkedit -@itemx -segprot -@itemx -segs_read_only_addr -@itemx -segs_read_write_addr -@itemx -single_module -@itemx -static -@itemx -sub_library -@need 800 -@itemx -sub_umbrella -@itemx -twolevel_namespace -@itemx -umbrella -@itemx -undefined -@itemx -unexported_symbols_list -@itemx -weak_reference_mismatches -@itemx -whatsloaded -@opindex allowable_client -@opindex client_name -@opindex compatibility_version -@opindex current_version -@opindex dead_strip -@opindex dependency-file -@opindex dylib_file -@opindex dylinker_install_name -@opindex dynamic -@opindex exported_symbols_list -@opindex filelist -@opindex flat_namespace -@opindex force_flat_namespace -@opindex headerpad_max_install_names -@opindex image_base -@opindex init -@opindex install_name -@opindex keep_private_externs -@opindex multi_module -@opindex multiply_defined -@opindex multiply_defined_unused -@opindex noall_load -@opindex no_dead_strip_inits_and_terms -@opindex nofixprebinding -@opindex nomultidefs -@opindex noprebind -@opindex noseglinkedit -@opindex pagezero_size -@opindex prebind -@opindex prebind_all_twolevel_modules -@opindex private_bundle -@opindex read_only_relocs -@opindex sectalign -@opindex sectobjectsymbols -@opindex whyload -@opindex seg1addr -@opindex sectcreate -@opindex sectobjectsymbols -@opindex sectorder -@opindex segaddr -@opindex segs_read_only_addr -@opindex segs_read_write_addr -@opindex seg_addr_table -@opindex seg_addr_table_filename -@opindex seglinkedit -@opindex segprot -@opindex segs_read_only_addr -@opindex segs_read_write_addr -@opindex single_module -@opindex static -@opindex sub_library -@opindex sub_umbrella -@opindex twolevel_namespace -@opindex umbrella -@opindex undefined -@opindex unexported_symbols_list -@opindex weak_reference_mismatches -@opindex whatsloaded -These options are passed to the Darwin linker. The Darwin linker man page -describes them in detail. -@end table - -@node DEC Alpha Options -@subsection DEC Alpha Options - -These @samp{-m} options are defined for the DEC Alpha implementations: - -@table @gcctabopt -@item -mno-soft-float -@itemx -msoft-float -@opindex mno-soft-float -@opindex msoft-float -Use (do not use) the hardware floating-point instructions for -floating-point operations. When @option{-msoft-float} is specified, -functions in @file{libgcc.a} are used to perform floating-point -operations. Unless they are replaced by routines that emulate the -floating-point operations, or compiled in such a way as to call such -emulations routines, these routines issue floating-point -operations. If you are compiling for an Alpha without floating-point -operations, you must ensure that the library is built so as not to call -them. - -Note that Alpha implementations without floating-point operations are -required to have floating-point registers. - -@item -mfp-reg -@itemx -mno-fp-regs -@opindex mfp-reg -@opindex mno-fp-regs -Generate code that uses (does not use) the floating-point register set. -@option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point -register set is not used, floating-point operands are passed in integer -registers as if they were integers and floating-point results are passed -in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence, -so any function with a floating-point argument or return value called by code -compiled with @option{-mno-fp-regs} must also be compiled with that -option. - -A typical use of this option is building a kernel that does not use, -and hence need not save and restore, any floating-point registers. - -@item -mieee -@opindex mieee -The Alpha architecture implements floating-point hardware optimized for -maximum performance. It is mostly compliant with the IEEE floating-point -standard. However, for full compliance, software assistance is -required. This option generates code fully IEEE-compliant code -@emph{except} that the @var{inexact-flag} is not maintained (see below). -If this option is turned on, the preprocessor macro @code{_IEEE_FP} is -defined during compilation. The resulting code is less efficient but is -able to correctly support denormalized numbers and exceptional IEEE -values such as not-a-number and plus/minus infinity. Other Alpha -compilers call this option @option{-ieee_with_no_inexact}. - -@item -mieee-with-inexact -@opindex mieee-with-inexact -This is like @option{-mieee} except the generated code also maintains -the IEEE @var{inexact-flag}. Turning on this option causes the -generated code to implement fully-compliant IEEE math. In addition to -@code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor -macro. On some Alpha implementations the resulting code may execute -significantly slower than the code generated by default. Since there is -very little code that depends on the @var{inexact-flag}, you should -normally not specify this option. Other Alpha compilers call this -option @option{-ieee_with_inexact}. - -@item -mfp-trap-mode=@var{trap-mode} -@opindex mfp-trap-mode -This option controls what floating-point related traps are enabled. -Other Alpha compilers call this option @option{-fptm @var{trap-mode}}. -The trap mode can be set to one of four values: - -@table @samp -@item n -This is the default (normal) setting. The only traps that are enabled -are the ones that cannot be disabled in software (e.g., division by zero -trap). - -@item u -In addition to the traps enabled by @samp{n}, underflow traps are enabled -as well. - -@item su -Like @samp{u}, but the instructions are marked to be safe for software -completion (see Alpha architecture manual for details). - -@item sui -Like @samp{su}, but inexact traps are enabled as well. -@end table - -@item -mfp-rounding-mode=@var{rounding-mode} -@opindex mfp-rounding-mode -Selects the IEEE rounding mode. Other Alpha compilers call this option -@option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one -of: - -@table @samp -@item n -Normal IEEE rounding mode. Floating-point numbers are rounded towards -the nearest machine number or towards the even machine number in case -of a tie. - -@item m -Round towards minus infinity. - -@item c -Chopped rounding mode. Floating-point numbers are rounded towards zero. - -@item d -Dynamic rounding mode. A field in the floating-point control register -(@var{fpcr}, see Alpha architecture reference manual) controls the -rounding mode in effect. The C library initializes this register for -rounding towards plus infinity. Thus, unless your program modifies the -@var{fpcr}, @samp{d} corresponds to round towards plus infinity. -@end table - -@item -mtrap-precision=@var{trap-precision} -@opindex mtrap-precision -In the Alpha architecture, floating-point traps are imprecise. This -means without software assistance it is impossible to recover from a -floating trap and program execution normally needs to be terminated. -GCC can generate code that can assist operating system trap handlers -in determining the exact location that caused a floating-point trap. -Depending on the requirements of an application, different levels of -precisions can be selected: - -@table @samp -@item p -Program precision. This option is the default and means a trap handler -can only identify which program caused a floating-point exception. - -@item f -Function precision. The trap handler can determine the function that -caused a floating-point exception. - -@item i -Instruction precision. The trap handler can determine the exact -instruction that caused a floating-point exception. -@end table - -Other Alpha compilers provide the equivalent options called -@option{-scope_safe} and @option{-resumption_safe}. - -@item -mieee-conformant -@opindex mieee-conformant -This option marks the generated code as IEEE conformant. You must not -use this option unless you also specify @option{-mtrap-precision=i} and either -@option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect -is to emit the line @samp{.eflag 48} in the function prologue of the -generated assembly file. - -@item -mbuild-constants -@opindex mbuild-constants -Normally GCC examines a 32- or 64-bit integer constant to -see if it can construct it from smaller constants in two or three -instructions. If it cannot, it outputs the constant as a literal and -generates code to load it from the data segment at run time. - -Use this option to require GCC to construct @emph{all} integer constants -using code, even if it takes more instructions (the maximum is six). - -You typically use this option to build a shared library dynamic -loader. Itself a shared library, it must relocate itself in memory -before it can find the variables and constants in its own data segment. - -@item -mbwx -@itemx -mno-bwx -@itemx -mcix -@itemx -mno-cix -@itemx -mfix -@itemx -mno-fix -@itemx -mmax -@itemx -mno-max -@opindex mbwx -@opindex mno-bwx -@opindex mcix -@opindex mno-cix -@opindex mfix -@opindex mno-fix -@opindex mmax -@opindex mno-max -Indicate whether GCC should generate code to use the optional BWX, -CIX, FIX and MAX instruction sets. The default is to use the instruction -sets supported by the CPU type specified via @option{-mcpu=} option or that -of the CPU on which GCC was built if none is specified. - -@item -mfloat-vax -@itemx -mfloat-ieee -@opindex mfloat-vax -@opindex mfloat-ieee -Generate code that uses (does not use) VAX F and G floating-point -arithmetic instead of IEEE single and double precision. - -@item -mexplicit-relocs -@itemx -mno-explicit-relocs -@opindex mexplicit-relocs -@opindex mno-explicit-relocs -Older Alpha assemblers provided no way to generate symbol relocations -except via assembler macros. Use of these macros does not allow -optimal instruction scheduling. GNU binutils as of version 2.12 -supports a new syntax that allows the compiler to explicitly mark -which relocations should apply to which instructions. This option -is mostly useful for debugging, as GCC detects the capabilities of -the assembler when it is built and sets the default accordingly. - -@item -msmall-data -@itemx -mlarge-data -@opindex msmall-data -@opindex mlarge-data -When @option{-mexplicit-relocs} is in effect, static data is -accessed via @dfn{gp-relative} relocations. When @option{-msmall-data} -is used, objects 8 bytes long or smaller are placed in a @dfn{small data area} -(the @code{.sdata} and @code{.sbss} sections) and are accessed via -16-bit relocations off of the @code{$gp} register. This limits the -size of the small data area to 64KB, but allows the variables to be -directly accessed via a single instruction. - -The default is @option{-mlarge-data}. With this option the data area -is limited to just below 2GB@. Programs that require more than 2GB of -data must use @code{malloc} or @code{mmap} to allocate the data in the -heap instead of in the program's data segment. - -When generating code for shared libraries, @option{-fpic} implies -@option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}. - -@item -msmall-text -@itemx -mlarge-text -@opindex msmall-text -@opindex mlarge-text -When @option{-msmall-text} is used, the compiler assumes that the -code of the entire program (or shared library) fits in 4MB, and is -thus reachable with a branch instruction. When @option{-msmall-data} -is used, the compiler can assume that all local symbols share the -same @code{$gp} value, and thus reduce the number of instructions -required for a function call from 4 to 1. - -The default is @option{-mlarge-text}. - -@item -mcpu=@var{cpu_type} -@opindex mcpu -Set the instruction set and instruction scheduling parameters for -machine type @var{cpu_type}. You can specify either the @samp{EV} -style name or the corresponding chip number. GCC supports scheduling -parameters for the EV4, EV5 and EV6 family of processors and -chooses the default values for the instruction set from the processor -you specify. If you do not specify a processor type, GCC defaults -to the processor on which the compiler was built. - -Supported values for @var{cpu_type} are - -@table @samp -@item ev4 -@itemx ev45 -@itemx 21064 -Schedules as an EV4 and has no instruction set extensions. - -@item ev5 -@itemx 21164 -Schedules as an EV5 and has no instruction set extensions. - -@item ev56 -@itemx 21164a -Schedules as an EV5 and supports the BWX extension. - -@item pca56 -@itemx 21164pc -@itemx 21164PC -Schedules as an EV5 and supports the BWX and MAX extensions. - -@item ev6 -@itemx 21264 -Schedules as an EV6 and supports the BWX, FIX, and MAX extensions. - -@item ev67 -@itemx 21264a -Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions. -@end table - -Native toolchains also support the value @samp{native}, -which selects the best architecture option for the host processor. -@option{-mcpu=native} has no effect if GCC does not recognize -the processor. - -@item -mtune=@var{cpu_type} -@opindex mtune -Set only the instruction scheduling parameters for machine type -@var{cpu_type}. The instruction set is not changed. - -Native toolchains also support the value @samp{native}, -which selects the best architecture option for the host processor. -@option{-mtune=native} has no effect if GCC does not recognize -the processor. - -@item -mmemory-latency=@var{time} -@opindex mmemory-latency -Sets the latency the scheduler should assume for typical memory -references as seen by the application. This number is highly -dependent on the memory access patterns used by the application -and the size of the external cache on the machine. - -Valid options for @var{time} are - -@table @samp -@item @var{number} -A decimal number representing clock cycles. - -@item L1 -@itemx L2 -@itemx L3 -@itemx main -The compiler contains estimates of the number of clock cycles for -``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches -(also called Dcache, Scache, and Bcache), as well as to main memory. -Note that L3 is only valid for EV5. - -@end table -@end table - -@node eBPF Options -@subsection eBPF Options -@cindex eBPF Options - -@table @gcctabopt -@item -mframe-limit=@var{bytes} -This specifies the hard limit for frame sizes, in bytes. Currently, -the value that can be specified should be less than or equal to -@samp{32767}. Defaults to whatever limit is imposed by the version of -the Linux kernel targeted. - -@item -mkernel=@var{version} -@opindex mkernel -This specifies the minimum version of the kernel that will run the -compiled program. GCC uses this version to determine which -instructions to use, what kernel helpers to allow, etc. Currently, -@var{version} can be one of @samp{4.0}, @samp{4.1}, @samp{4.2}, -@samp{4.3}, @samp{4.4}, @samp{4.5}, @samp{4.6}, @samp{4.7}, -@samp{4.8}, @samp{4.9}, @samp{4.10}, @samp{4.11}, @samp{4.12}, -@samp{4.13}, @samp{4.14}, @samp{4.15}, @samp{4.16}, @samp{4.17}, -@samp{4.18}, @samp{4.19}, @samp{4.20}, @samp{5.0}, @samp{5.1}, -@samp{5.2}, @samp{latest} and @samp{native}. - -@item -mbig-endian -@opindex mbig-endian -Generate code for a big-endian target. - -@item -mlittle-endian -@opindex mlittle-endian -Generate code for a little-endian target. This is the default. - -@item -mjmpext -@opindex mjmpext -Enable generation of extra conditional-branch instructions. -Enabled for CPU v2 and above. - -@item -mjmp32 -@opindex mjmp32 -Enable 32-bit jump instructions. Enabled for CPU v3 and above. - -@item -malu32 -@opindex malu32 -Enable 32-bit ALU instructions. Enabled for CPU v3 and above. - -@item -mcpu=@var{version} -@opindex mcpu -This specifies which version of the eBPF ISA to target. Newer versions -may not be supported by all kernels. The default is @samp{v3}. - -Supported values for @var{version} are: - -@table @samp -@item v1 -The first stable eBPF ISA with no special features or extensions. - -@item v2 -Supports the jump extensions, as in @option{-mjmpext}. - -@item v3 -All features of v2, plus: -@itemize @minus -@item 32-bit jump operations, as in @option{-mjmp32} -@item 32-bit ALU operations, as in @option{-malu32} -@end itemize - -@end table - -@item -mco-re -@opindex mco-re -Enable BPF Compile Once - Run Everywhere (CO-RE) support. Requires and -is implied by @option{-gbtf}. - -@item -mno-co-re -@opindex mno-co-re -Disable BPF Compile Once - Run Everywhere (CO-RE) support. BPF CO-RE -support is enabled by default when generating BTF debug information for -the BPF target. - -@item -mxbpf -Generate code for an expanded version of BPF, which relaxes some of -the restrictions imposed by the BPF architecture: -@itemize @minus -@item Save and restore callee-saved registers at function entry and -exit, respectively. -@end itemize -@end table - -@node FR30 Options -@subsection FR30 Options -@cindex FR30 Options - -These options are defined specifically for the FR30 port. - -@table @gcctabopt - -@item -msmall-model -@opindex msmall-model -Use the small address space model. This can produce smaller code, but -it does assume that all symbolic values and addresses fit into a -20-bit range. - -@item -mno-lsim -@opindex mno-lsim -Assume that runtime support has been provided and so there is no need -to include the simulator library (@file{libsim.a}) on the linker -command line. - -@end table - -@node FT32 Options -@subsection FT32 Options -@cindex FT32 Options - -These options are defined specifically for the FT32 port. - -@table @gcctabopt - -@item -msim -@opindex msim -Specifies that the program will be run on the simulator. This causes -an alternate runtime startup and library to be linked. -You must not use this option when generating programs that will run on -real hardware; you must provide your own runtime library for whatever -I/O functions are needed. - -@item -mlra -@opindex mlra -Enable Local Register Allocation. This is still experimental for FT32, -so by default the compiler uses standard reload. - -@item -mnodiv -@opindex mnodiv -Do not use div and mod instructions. - -@item -mft32b -@opindex mft32b -Enable use of the extended instructions of the FT32B processor. - -@item -mcompress -@opindex mcompress -Compress all code using the Ft32B code compression scheme. - -@item -mnopm -@opindex mnopm -Do not generate code that reads program memory. - -@end table - -@node FRV Options -@subsection FRV Options -@cindex FRV Options - -@table @gcctabopt -@item -mgpr-32 -@opindex mgpr-32 - -Only use the first 32 general-purpose registers. - -@item -mgpr-64 -@opindex mgpr-64 - -Use all 64 general-purpose registers. - -@item -mfpr-32 -@opindex mfpr-32 - -Use only the first 32 floating-point registers. - -@item -mfpr-64 -@opindex mfpr-64 - -Use all 64 floating-point registers. - -@item -mhard-float -@opindex mhard-float - -Use hardware instructions for floating-point operations. - -@item -msoft-float -@opindex msoft-float - -Use library routines for floating-point operations. - -@item -malloc-cc -@opindex malloc-cc - -Dynamically allocate condition code registers. - -@item -mfixed-cc -@opindex mfixed-cc - -Do not try to dynamically allocate condition code registers, only -use @code{icc0} and @code{fcc0}. - -@item -mdword -@opindex mdword - -Change ABI to use double word insns. - -@item -mno-dword -@opindex mno-dword -@opindex mdword - -Do not use double word instructions. - -@item -mdouble -@opindex mdouble - -Use floating-point double instructions. - -@item -mno-double -@opindex mno-double - -Do not use floating-point double instructions. - -@item -mmedia -@opindex mmedia - -Use media instructions. - -@item -mno-media -@opindex mno-media - -Do not use media instructions. - -@item -mmuladd -@opindex mmuladd - -Use multiply and add/subtract instructions. - -@item -mno-muladd -@opindex mno-muladd - -Do not use multiply and add/subtract instructions. - -@item -mfdpic -@opindex mfdpic - -Select the FDPIC ABI, which uses function descriptors to represent -pointers to functions. Without any PIC/PIE-related options, it -implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it -assumes GOT entries and small data are within a 12-bit range from the -GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets -are computed with 32 bits. -With a @samp{bfin-elf} target, this option implies @option{-msim}. - -@item -minline-plt -@opindex minline-plt - -Enable inlining of PLT entries in function calls to functions that are -not known to bind locally. It has no effect without @option{-mfdpic}. -It's enabled by default if optimizing for speed and compiling for -shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an -optimization option such as @option{-O3} or above is present in the -command line. - -@item -mTLS -@opindex mTLS - -Assume a large TLS segment when generating thread-local code. - -@item -mtls -@opindex mtls - -Do not assume a large TLS segment when generating thread-local code. - -@item -mgprel-ro -@opindex mgprel-ro - -Enable the use of @code{GPREL} relocations in the FDPIC ABI for data -that is known to be in read-only sections. It's enabled by default, -except for @option{-fpic} or @option{-fpie}: even though it may help -make the global offset table smaller, it trades 1 instruction for 4. -With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4, -one of which may be shared by multiple symbols, and it avoids the need -for a GOT entry for the referenced symbol, so it's more likely to be a -win. If it is not, @option{-mno-gprel-ro} can be used to disable it. - -@item -multilib-library-pic -@opindex multilib-library-pic - -Link with the (library, not FD) pic libraries. It's implied by -@option{-mlibrary-pic}, as well as by @option{-fPIC} and -@option{-fpic} without @option{-mfdpic}. You should never have to use -it explicitly. - -@item -mlinked-fp -@opindex mlinked-fp - -Follow the EABI requirement of always creating a frame pointer whenever -a stack frame is allocated. This option is enabled by default and can -be disabled with @option{-mno-linked-fp}. - -@item -mlong-calls -@opindex mlong-calls - -Use indirect addressing to call functions outside the current -compilation unit. This allows the functions to be placed anywhere -within the 32-bit address space. - -@item -malign-labels -@opindex malign-labels - -Try to align labels to an 8-byte boundary by inserting NOPs into the -previous packet. This option only has an effect when VLIW packing -is enabled. It doesn't create new packets; it merely adds NOPs to -existing ones. - -@item -mlibrary-pic -@opindex mlibrary-pic - -Generate position-independent EABI code. - -@item -macc-4 -@opindex macc-4 - -Use only the first four media accumulator registers. - -@item -macc-8 -@opindex macc-8 - -Use all eight media accumulator registers. - -@item -mpack -@opindex mpack - -Pack VLIW instructions. - -@item -mno-pack -@opindex mno-pack - -Do not pack VLIW instructions. - -@item -mno-eflags -@opindex mno-eflags - -Do not mark ABI switches in e_flags. - -@item -mcond-move -@opindex mcond-move - -Enable the use of conditional-move instructions (default). - -This switch is mainly for debugging the compiler and will likely be removed -in a future version. - -@item -mno-cond-move -@opindex mno-cond-move - -Disable the use of conditional-move instructions. - -This switch is mainly for debugging the compiler and will likely be removed -in a future version. - -@item -mscc -@opindex mscc - -Enable the use of conditional set instructions (default). - -This switch is mainly for debugging the compiler and will likely be removed -in a future version. - -@item -mno-scc -@opindex mno-scc - -Disable the use of conditional set instructions. - -This switch is mainly for debugging the compiler and will likely be removed -in a future version. - -@item -mcond-exec -@opindex mcond-exec - -Enable the use of conditional execution (default). - -This switch is mainly for debugging the compiler and will likely be removed -in a future version. - -@item -mno-cond-exec -@opindex mno-cond-exec - -Disable the use of conditional execution. - -This switch is mainly for debugging the compiler and will likely be removed -in a future version. - -@item -mvliw-branch -@opindex mvliw-branch - -Run a pass to pack branches into VLIW instructions (default). - -This switch is mainly for debugging the compiler and will likely be removed -in a future version. - -@item -mno-vliw-branch -@opindex mno-vliw-branch - -Do not run a pass to pack branches into VLIW instructions. - -This switch is mainly for debugging the compiler and will likely be removed -in a future version. - -@item -mmulti-cond-exec -@opindex mmulti-cond-exec - -Enable optimization of @code{&&} and @code{||} in conditional execution -(default). - -This switch is mainly for debugging the compiler and will likely be removed -in a future version. - -@item -mno-multi-cond-exec -@opindex mno-multi-cond-exec - -Disable optimization of @code{&&} and @code{||} in conditional execution. - -This switch is mainly for debugging the compiler and will likely be removed -in a future version. - -@item -mnested-cond-exec -@opindex mnested-cond-exec - -Enable nested conditional execution optimizations (default). - -This switch is mainly for debugging the compiler and will likely be removed -in a future version. - -@item -mno-nested-cond-exec -@opindex mno-nested-cond-exec - -Disable nested conditional execution optimizations. - -This switch is mainly for debugging the compiler and will likely be removed -in a future version. - -@item -moptimize-membar -@opindex moptimize-membar - -This switch removes redundant @code{membar} instructions from the -compiler-generated code. It is enabled by default. - -@item -mno-optimize-membar -@opindex mno-optimize-membar -@opindex moptimize-membar - -This switch disables the automatic removal of redundant @code{membar} -instructions from the generated code. - -@item -mtomcat-stats -@opindex mtomcat-stats - -Cause gas to print out tomcat statistics. - -@item -mcpu=@var{cpu} -@opindex mcpu - -Select the processor type for which to generate code. Possible values are -@samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450}, -@samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}. - -@end table - -@node GNU/Linux Options -@subsection GNU/Linux Options - -These @samp{-m} options are defined for GNU/Linux targets: - -@table @gcctabopt -@item -mglibc -@opindex mglibc -Use the GNU C library. This is the default except -on @samp{*-*-linux-*uclibc*}, @samp{*-*-linux-*musl*} and -@samp{*-*-linux-*android*} targets. - -@item -muclibc -@opindex muclibc -Use uClibc C library. This is the default on -@samp{*-*-linux-*uclibc*} targets. - -@item -mmusl -@opindex mmusl -Use the musl C library. This is the default on -@samp{*-*-linux-*musl*} targets. - -@item -mbionic -@opindex mbionic -Use Bionic C library. This is the default on -@samp{*-*-linux-*android*} targets. - -@item -mandroid -@opindex mandroid -Compile code compatible with Android platform. This is the default on -@samp{*-*-linux-*android*} targets. - -When compiling, this option enables @option{-mbionic}, @option{-fPIC}, -@option{-fno-exceptions} and @option{-fno-rtti} by default. When linking, -this option makes the GCC driver pass Android-specific options to the linker. -Finally, this option causes the preprocessor macro @code{__ANDROID__} -to be defined. - -@item -tno-android-cc -@opindex tno-android-cc -Disable compilation effects of @option{-mandroid}, i.e., do not enable -@option{-mbionic}, @option{-fPIC}, @option{-fno-exceptions} and -@option{-fno-rtti} by default. - -@item -tno-android-ld -@opindex tno-android-ld -Disable linking effects of @option{-mandroid}, i.e., pass standard Linux -linking options to the linker. - -@end table - -@node H8/300 Options -@subsection H8/300 Options - -These @samp{-m} options are defined for the H8/300 implementations: - -@table @gcctabopt -@item -mrelax -@opindex mrelax -Shorten some address references at link time, when possible; uses the -linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300, -ld, Using ld}, for a fuller description. - -@item -mh -@opindex mh -Generate code for the H8/300H@. - -@item -ms -@opindex ms -Generate code for the H8S@. - -@item -mn -@opindex mn -Generate code for the H8S and H8/300H in the normal mode. This switch -must be used either with @option{-mh} or @option{-ms}. - -@item -ms2600 -@opindex ms2600 -Generate code for the H8S/2600. This switch must be used with @option{-ms}. - -@item -mexr -@opindex mexr -Extended registers are stored on stack before execution of function -with monitor attribute. Default option is @option{-mexr}. -This option is valid only for H8S targets. - -@item -mno-exr -@opindex mno-exr -@opindex mexr -Extended registers are not stored on stack before execution of function -with monitor attribute. Default option is @option{-mno-exr}. -This option is valid only for H8S targets. - -@item -mint32 -@opindex mint32 -Make @code{int} data 32 bits by default. - -@item -malign-300 -@opindex malign-300 -On the H8/300H and H8S, use the same alignment rules as for the H8/300. -The default for the H8/300H and H8S is to align longs and floats on -4-byte boundaries. -@option{-malign-300} causes them to be aligned on 2-byte boundaries. -This option has no effect on the H8/300. -@end table - -@node HPPA Options -@subsection HPPA Options -@cindex HPPA Options - -These @samp{-m} options are defined for the HPPA family of computers: - -@table @gcctabopt -@item -march=@var{architecture-type} -@opindex march -Generate code for the specified architecture. The choices for -@var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA -1.1, and @samp{2.0} for PA 2.0 processors. Refer to -@file{/usr/lib/sched.models} on an HP-UX system to determine the proper -architecture option for your machine. Code compiled for lower numbered -architectures runs on higher numbered architectures, but not the -other way around. - -@item -mpa-risc-1-0 -@itemx -mpa-risc-1-1 -@itemx -mpa-risc-2-0 -@opindex mpa-risc-1-0 -@opindex mpa-risc-1-1 -@opindex mpa-risc-2-0 -Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively. - -@item -mcaller-copies -@opindex mcaller-copies -The caller copies function arguments passed by hidden reference. This -option should be used with care as it is not compatible with the default -32-bit runtime. However, only aggregates larger than eight bytes are -passed by hidden reference and the option provides better compatibility -with OpenMP. - -@item -mjump-in-delay -@opindex mjump-in-delay -This option is ignored and provided for compatibility purposes only. - -@item -mdisable-fpregs -@opindex mdisable-fpregs -Prevent floating-point registers from being used in any manner. This is -necessary for compiling kernels that perform lazy context switching of -floating-point registers. If you use this option and attempt to perform -floating-point operations, the compiler aborts. - -@item -mdisable-indexing -@opindex mdisable-indexing -Prevent the compiler from using indexing address modes. This avoids some -rather obscure problems when compiling MIG generated code under MACH@. - -@item -mno-space-regs -@opindex mno-space-regs -@opindex mspace-regs -Generate code that assumes the target has no space registers. This allows -GCC to generate faster indirect calls and use unscaled index address modes. - -Such code is suitable for level 0 PA systems and kernels. - -@item -mfast-indirect-calls -@opindex mfast-indirect-calls -Generate code that assumes calls never cross space boundaries. This -allows GCC to emit code that performs faster indirect calls. - -This option does not work in the presence of shared libraries or nested -functions. - -@item -mfixed-range=@var{register-range} -@opindex mfixed-range -Generate code treating the given register range as fixed registers. -A fixed register is one that the register allocator cannot use. This is -useful when compiling kernel code. A register range is specified as -two registers separated by a dash. Multiple register ranges can be -specified separated by a comma. - -@item -mlong-load-store -@opindex mlong-load-store -Generate 3-instruction load and store sequences as sometimes required by -the HP-UX 10 linker. This is equivalent to the @samp{+k} option to -the HP compilers. - -@item -mportable-runtime -@opindex mportable-runtime -Use the portable calling conventions proposed by HP for ELF systems. - -@item -mgas -@opindex mgas -Enable the use of assembler directives only GAS understands. - -@item -mschedule=@var{cpu-type} -@opindex mschedule -Schedule code according to the constraints for the machine type -@var{cpu-type}. The choices for @var{cpu-type} are @samp{700} -@samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer -to @file{/usr/lib/sched.models} on an HP-UX system to determine the -proper scheduling option for your machine. The default scheduling is -@samp{8000}. - -@item -mlinker-opt -@opindex mlinker-opt -Enable the optimization pass in the HP-UX linker. Note this makes symbolic -debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9 -linkers in which they give bogus error messages when linking some programs. - -@item -msoft-float -@opindex msoft-float -Generate output containing library calls for floating point. -@strong{Warning:} the requisite libraries are not available for all HPPA -targets. Normally the facilities of the machine's usual C compiler are -used, but this cannot be done directly in cross-compilation. You must make -your own arrangements to provide suitable library functions for -cross-compilation. - -@option{-msoft-float} changes the calling convention in the output file; -therefore, it is only useful if you compile @emph{all} of a program with -this option. In particular, you need to compile @file{libgcc.a}, the -library that comes with GCC, with @option{-msoft-float} in order for -this to work. - -@item -msio -@opindex msio -Generate the predefine, @code{_SIO}, for server IO@. The default is -@option{-mwsio}. This generates the predefines, @code{__hp9000s700}, -@code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These -options are available under HP-UX and HI-UX@. - -@item -mgnu-ld -@opindex mgnu-ld -Use options specific to GNU @command{ld}. -This passes @option{-shared} to @command{ld} when -building a shared library. It is the default when GCC is configured, -explicitly or implicitly, with the GNU linker. This option does not -affect which @command{ld} is called; it only changes what parameters -are passed to that @command{ld}. -The @command{ld} that is called is determined by the -@option{--with-ld} configure option, GCC's program search path, and -finally by the user's @env{PATH}. The linker used by GCC can be printed -using @samp{which `gcc -print-prog-name=ld`}. This option is only available -on the 64-bit HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}. - -@item -mhp-ld -@opindex mhp-ld -Use options specific to HP @command{ld}. -This passes @option{-b} to @command{ld} when building -a shared library and passes @option{+Accept TypeMismatch} to @command{ld} on all -links. It is the default when GCC is configured, explicitly or -implicitly, with the HP linker. This option does not affect -which @command{ld} is called; it only changes what parameters are passed to that -@command{ld}. -The @command{ld} that is called is determined by the @option{--with-ld} -configure option, GCC's program search path, and finally by the user's -@env{PATH}. The linker used by GCC can be printed using @samp{which -`gcc -print-prog-name=ld`}. This option is only available on the 64-bit -HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}. - -@item -mlong-calls -@opindex mno-long-calls -@opindex mlong-calls -Generate code that uses long call sequences. This ensures that a call -is always able to reach linker generated stubs. The default is to generate -long calls only when the distance from the call site to the beginning -of the function or translation unit, as the case may be, exceeds a -predefined limit set by the branch type being used. The limits for -normal calls are 7,600,000 and 240,000 bytes, respectively for the -PA 2.0 and PA 1.X architectures. Sibcalls are always limited at -240,000 bytes. - -Distances are measured from the beginning of functions when using the -@option{-ffunction-sections} option, or when using the @option{-mgas} -and @option{-mno-portable-runtime} options together under HP-UX with -the SOM linker. - -It is normally not desirable to use this option as it degrades -performance. However, it may be useful in large applications, -particularly when partial linking is used to build the application. - -The types of long calls used depends on the capabilities of the -assembler and linker, and the type of code being generated. The -impact on systems that support long absolute calls, and long pic -symbol-difference or pc-relative calls should be relatively small. -However, an indirect call is used on 32-bit ELF systems in pic code -and it is quite long. - -@item -munix=@var{unix-std} -@opindex march -Generate compiler predefines and select a startfile for the specified -UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95} -and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95} -is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX -11.11 and later. The default values are @samp{93} for HP-UX 10.00, -@samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11 -and later. - -@option{-munix=93} provides the same predefines as GCC 3.3 and 3.4. -@option{-munix=95} provides additional predefines for @code{XOPEN_UNIX} -and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}. -@option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX}, -@code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and -@code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}. - -It is @emph{important} to note that this option changes the interfaces -for various library routines. It also affects the operational behavior -of the C library. Thus, @emph{extreme} care is needed in using this -option. - -Library code that is intended to operate with more than one UNIX -standard must test, set and restore the variable @code{__xpg4_extended_mask} -as appropriate. Most GNU software doesn't provide this capability. - -@item -nolibdld -@opindex nolibdld -Suppress the generation of link options to search libdld.sl when the -@option{-static} option is specified on HP-UX 10 and later. - -@item -static -@opindex static -The HP-UX implementation of setlocale in libc has a dependency on -libdld.sl. There isn't an archive version of libdld.sl. Thus, -when the @option{-static} option is specified, special link options -are needed to resolve this dependency. - -On HP-UX 10 and later, the GCC driver adds the necessary options to -link with libdld.sl when the @option{-static} option is specified. -This causes the resulting binary to be dynamic. On the 64-bit port, -the linkers generate dynamic binaries by default in any case. The -@option{-nolibdld} option can be used to prevent the GCC driver from -adding these link options. - -@item -threads -@opindex threads -Add support for multithreading with the @dfn{dce thread} library -under HP-UX@. This option sets flags for both the preprocessor and -linker. -@end table - -@node IA-64 Options -@subsection IA-64 Options -@cindex IA-64 Options - -These are the @samp{-m} options defined for the Intel IA-64 architecture. - -@table @gcctabopt -@item -mbig-endian -@opindex mbig-endian -Generate code for a big-endian target. This is the default for HP-UX@. - -@item -mlittle-endian -@opindex mlittle-endian -Generate code for a little-endian target. This is the default for AIX5 -and GNU/Linux. - -@item -mgnu-as -@itemx -mno-gnu-as -@opindex mgnu-as -@opindex mno-gnu-as -Generate (or don't) code for the GNU assembler. This is the default. -@c Also, this is the default if the configure option @option{--with-gnu-as} -@c is used. - -@item -mgnu-ld -@itemx -mno-gnu-ld -@opindex mgnu-ld -@opindex mno-gnu-ld -Generate (or don't) code for the GNU linker. This is the default. -@c Also, this is the default if the configure option @option{--with-gnu-ld} -@c is used. - -@item -mno-pic -@opindex mno-pic -Generate code that does not use a global pointer register. The result -is not position independent code, and violates the IA-64 ABI@. - -@item -mvolatile-asm-stop -@itemx -mno-volatile-asm-stop -@opindex mvolatile-asm-stop -@opindex mno-volatile-asm-stop -Generate (or don't) a stop bit immediately before and after volatile asm -statements. - -@item -mregister-names -@itemx -mno-register-names -@opindex mregister-names -@opindex mno-register-names -Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for -the stacked registers. This may make assembler output more readable. - -@item -mno-sdata -@itemx -msdata -@opindex mno-sdata -@opindex msdata -Disable (or enable) optimizations that use the small data section. This may -be useful for working around optimizer bugs. - -@item -mconstant-gp -@opindex mconstant-gp -Generate code that uses a single constant global pointer value. This is -useful when compiling kernel code. - -@item -mauto-pic -@opindex mauto-pic -Generate code that is self-relocatable. This implies @option{-mconstant-gp}. -This is useful when compiling firmware code. - -@item -minline-float-divide-min-latency -@opindex minline-float-divide-min-latency -Generate code for inline divides of floating-point values -using the minimum latency algorithm. - -@item -minline-float-divide-max-throughput -@opindex minline-float-divide-max-throughput -Generate code for inline divides of floating-point values -using the maximum throughput algorithm. - -@item -mno-inline-float-divide -@opindex mno-inline-float-divide -Do not generate inline code for divides of floating-point values. - -@item -minline-int-divide-min-latency -@opindex minline-int-divide-min-latency -Generate code for inline divides of integer values -using the minimum latency algorithm. - -@item -minline-int-divide-max-throughput -@opindex minline-int-divide-max-throughput -Generate code for inline divides of integer values -using the maximum throughput algorithm. - -@item -mno-inline-int-divide -@opindex mno-inline-int-divide -@opindex minline-int-divide -Do not generate inline code for divides of integer values. - -@item -minline-sqrt-min-latency -@opindex minline-sqrt-min-latency -Generate code for inline square roots -using the minimum latency algorithm. - -@item -minline-sqrt-max-throughput -@opindex minline-sqrt-max-throughput -Generate code for inline square roots -using the maximum throughput algorithm. - -@item -mno-inline-sqrt -@opindex mno-inline-sqrt -Do not generate inline code for @code{sqrt}. - -@item -mfused-madd -@itemx -mno-fused-madd -@opindex mfused-madd -@opindex mno-fused-madd -Do (don't) generate code that uses the fused multiply/add or multiply/subtract -instructions. The default is to use these instructions. - -@item -mno-dwarf2-asm -@itemx -mdwarf2-asm -@opindex mno-dwarf2-asm -@opindex mdwarf2-asm -Don't (or do) generate assembler code for the DWARF line number debugging -info. This may be useful when not using the GNU assembler. - -@item -mearly-stop-bits -@itemx -mno-early-stop-bits -@opindex mearly-stop-bits -@opindex mno-early-stop-bits -Allow stop bits to be placed earlier than immediately preceding the -instruction that triggered the stop bit. This can improve instruction -scheduling, but does not always do so. - -@item -mfixed-range=@var{register-range} -@opindex mfixed-range -Generate code treating the given register range as fixed registers. -A fixed register is one that the register allocator cannot use. This is -useful when compiling kernel code. A register range is specified as -two registers separated by a dash. Multiple register ranges can be -specified separated by a comma. - -@item -mtls-size=@var{tls-size} -@opindex mtls-size -Specify bit size of immediate TLS offsets. Valid values are 14, 22, and -64. - -@item -mtune=@var{cpu-type} -@opindex mtune -Tune the instruction scheduling for a particular CPU, Valid values are -@samp{itanium}, @samp{itanium1}, @samp{merced}, @samp{itanium2}, -and @samp{mckinley}. - -@item -milp32 -@itemx -mlp64 -@opindex milp32 -@opindex mlp64 -Generate code for a 32-bit or 64-bit environment. -The 32-bit environment sets int, long and pointer to 32 bits. -The 64-bit environment sets int to 32 bits and long and pointer -to 64 bits. These are HP-UX specific flags. - -@item -mno-sched-br-data-spec -@itemx -msched-br-data-spec -@opindex mno-sched-br-data-spec -@opindex msched-br-data-spec -(Dis/En)able data speculative scheduling before reload. -This results in generation of @code{ld.a} instructions and -the corresponding check instructions (@code{ld.c} / @code{chk.a}). -The default setting is disabled. - -@item -msched-ar-data-spec -@itemx -mno-sched-ar-data-spec -@opindex msched-ar-data-spec -@opindex mno-sched-ar-data-spec -(En/Dis)able data speculative scheduling after reload. -This results in generation of @code{ld.a} instructions and -the corresponding check instructions (@code{ld.c} / @code{chk.a}). -The default setting is enabled. - -@item -mno-sched-control-spec -@itemx -msched-control-spec -@opindex mno-sched-control-spec -@opindex msched-control-spec -(Dis/En)able control speculative scheduling. This feature is -available only during region scheduling (i.e.@: before reload). -This results in generation of the @code{ld.s} instructions and -the corresponding check instructions @code{chk.s}. -The default setting is disabled. - -@item -msched-br-in-data-spec -@itemx -mno-sched-br-in-data-spec -@opindex msched-br-in-data-spec -@opindex mno-sched-br-in-data-spec -(En/Dis)able speculative scheduling of the instructions that -are dependent on the data speculative loads before reload. -This is effective only with @option{-msched-br-data-spec} enabled. -The default setting is enabled. - -@item -msched-ar-in-data-spec -@itemx -mno-sched-ar-in-data-spec -@opindex msched-ar-in-data-spec -@opindex mno-sched-ar-in-data-spec -(En/Dis)able speculative scheduling of the instructions that -are dependent on the data speculative loads after reload. -This is effective only with @option{-msched-ar-data-spec} enabled. -The default setting is enabled. - -@item -msched-in-control-spec -@itemx -mno-sched-in-control-spec -@opindex msched-in-control-spec -@opindex mno-sched-in-control-spec -(En/Dis)able speculative scheduling of the instructions that -are dependent on the control speculative loads. -This is effective only with @option{-msched-control-spec} enabled. -The default setting is enabled. - -@item -mno-sched-prefer-non-data-spec-insns -@itemx -msched-prefer-non-data-spec-insns -@opindex mno-sched-prefer-non-data-spec-insns -@opindex msched-prefer-non-data-spec-insns -If enabled, data-speculative instructions are chosen for schedule -only if there are no other choices at the moment. This makes -the use of the data speculation much more conservative. -The default setting is disabled. - -@item -mno-sched-prefer-non-control-spec-insns -@itemx -msched-prefer-non-control-spec-insns -@opindex mno-sched-prefer-non-control-spec-insns -@opindex msched-prefer-non-control-spec-insns -If enabled, control-speculative instructions are chosen for schedule -only if there are no other choices at the moment. This makes -the use of the control speculation much more conservative. -The default setting is disabled. - -@item -mno-sched-count-spec-in-critical-path -@itemx -msched-count-spec-in-critical-path -@opindex mno-sched-count-spec-in-critical-path -@opindex msched-count-spec-in-critical-path -If enabled, speculative dependencies are considered during -computation of the instructions priorities. This makes the use of the -speculation a bit more conservative. -The default setting is disabled. - -@item -msched-spec-ldc -@opindex msched-spec-ldc -Use a simple data speculation check. This option is on by default. - -@item -msched-control-spec-ldc -@opindex msched-spec-ldc -Use a simple check for control speculation. This option is on by default. - -@item -msched-stop-bits-after-every-cycle -@opindex msched-stop-bits-after-every-cycle -Place a stop bit after every cycle when scheduling. This option is on -by default. - -@item -msched-fp-mem-deps-zero-cost -@opindex msched-fp-mem-deps-zero-cost -Assume that floating-point stores and loads are not likely to cause a conflict -when placed into the same instruction group. This option is disabled by -default. - -@item -msel-sched-dont-check-control-spec -@opindex msel-sched-dont-check-control-spec -Generate checks for control speculation in selective scheduling. -This flag is disabled by default. - -@item -msched-max-memory-insns=@var{max-insns} -@opindex msched-max-memory-insns -Limit on the number of memory insns per instruction group, giving lower -priority to subsequent memory insns attempting to schedule in the same -instruction group. Frequently useful to prevent cache bank conflicts. -The default value is 1. - -@item -msched-max-memory-insns-hard-limit -@opindex msched-max-memory-insns-hard-limit -Makes the limit specified by @option{msched-max-memory-insns} a hard limit, -disallowing more than that number in an instruction group. -Otherwise, the limit is ``soft'', meaning that non-memory operations -are preferred when the limit is reached, but memory operations may still -be scheduled. - -@end table - -@node LM32 Options -@subsection LM32 Options -@cindex LM32 options - -These @option{-m} options are defined for the LatticeMico32 architecture: - -@table @gcctabopt -@item -mbarrel-shift-enabled -@opindex mbarrel-shift-enabled -Enable barrel-shift instructions. - -@item -mdivide-enabled -@opindex mdivide-enabled -Enable divide and modulus instructions. - -@item -mmultiply-enabled -@opindex multiply-enabled -Enable multiply instructions. - -@item -msign-extend-enabled -@opindex msign-extend-enabled -Enable sign extend instructions. - -@item -muser-enabled -@opindex muser-enabled -Enable user-defined instructions. - -@end table - -@node LoongArch Options -@subsection LoongArch Options -@cindex LoongArch Options - -These command-line options are defined for LoongArch targets: - -@table @gcctabopt -@item -march=@var{cpu-type} -@opindex -march -Generate instructions for the machine type @var{cpu-type}. In contrast to -@option{-mtune=@var{cpu-type}}, which merely tunes the generated code -for the specified @var{cpu-type}, @option{-march=@var{cpu-type}} allows GCC -to generate code that may not run at all on processors other than the one -indicated. Specifying @option{-march=@var{cpu-type}} implies -@option{-mtune=@var{cpu-type}}, except where noted otherwise. - -The choices for @var{cpu-type} are: - -@table @samp -@item native -This selects the CPU to generate code for at compilation time by determining -the processor type of the compiling machine. Using @option{-march=native} -enables all instruction subsets supported by the local machine (hence -the result might not run on different machines). Using @option{-mtune=native} -produces code optimized for the local machine under the constraints -of the selected instruction set. -@item loongarch64 -A generic CPU with 64-bit extensions. -@item la464 -LoongArch LA464 CPU with LBT, LSX, LASX, LVZ. -@end table - -@item -mtune=@var{cpu-type} -@opindex mtune -Optimize the output for the given processor, specified by microarchitecture -name. - -@item -mabi=@var{base-abi-type} -@opindex mabi -Generate code for the specified calling convention. -@var{base-abi-type} can be one of: -@table @samp -@item lp64d -Uses 64-bit general purpose registers and 32/64-bit floating-point -registers for parameter passing. Data model is LP64, where @samp{int} -is 32 bits, while @samp{long int} and pointers are 64 bits. -@item lp64f -Uses 64-bit general purpose registers and 32-bit floating-point -registers for parameter passing. Data model is LP64, where @samp{int} -is 32 bits, while @samp{long int} and pointers are 64 bits. -@item lp64s -Uses 64-bit general purpose registers and no floating-point -registers for parameter passing. Data model is LP64, where @samp{int} -is 32 bits, while @samp{long int} and pointers are 64 bits. -@end table - -@item -mfpu=@var{fpu-type} -@opindex mfpu -Generate code for the specified FPU type, which can be one of: -@table @samp -@item 64 -Allow the use of hardware floating-point instructions for 32-bit -and 64-bit operations. -@item 32 -Allow the use of hardware floating-point instructions for 32-bit -operations. -@item none -@item 0 -Prevent the use of hardware floating-point instructions. -@end table - -@item -msoft-float -@opindex msoft-float -Force @option{-mfpu=none} and prevents the use of floating-point -registers for parameter passing. This option may change the target -ABI. - -@item -msingle-float -@opindex -msingle-float -Force @option{-mfpu=32} and allow the use of 32-bit floating-point -registers for parameter passing. This option may change the target -ABI. - -@item -mdouble-float -@opindex -mdouble-float -Force @option{-mfpu=64} and allow the use of 32/64-bit floating-point -registers for parameter passing. This option may change the target -ABI. - -@item -mbranch-cost=@var{n} -@opindex -mbranch-cost -Set the cost of branches to roughly @var{n} instructions. - -@item -mcheck-zero-division -@itemx -mno-check-zero-divison -@opindex -mcheck-zero-division -Trap (do not trap) on integer division by zero. The default is -@option{-mcheck-zero-division} for @option{-O0} or @option{-Og}, and -@option{-mno-check-zero-division} for other optimization levels. - -@item -mcond-move-int -@itemx -mno-cond-move-int -@opindex -mcond-move-int -Conditional moves for integral data in general-purpose registers -are enabled (disabled). The default is @option{-mcond-move-int}. - -@item -mcond-move-float -@itemx -mno-cond-move-float -@opindex -mcond-move-float -Conditional moves for floating-point registers are enabled (disabled). -The default is @option{-mcond-move-float}. - -@item -mmemcpy -@itemx -mno-memcpy -@opindex -mmemcpy -Force (do not force) the use of @code{memcpy} for non-trivial block moves. -The default is @option{-mno-memcpy}, which allows GCC to inline most -constant-sized copies. Setting optimization level to @option{-Os} also -forces the use of @code{memcpy}, but @option{-mno-memcpy} may override this -behavior if explicitly specified, regardless of the order these options on -the command line. - -@item -mstrict-align -@itemx -mno-strict-align -@opindex -mstrict-align -Avoid or allow generating memory accesses that may not be aligned on a natural -object boundary as described in the architecture specification. The default is -@option{-mno-strict-align}. - -@item -msmall-data-limit=@var{number} -@opindex -msmall-data-limit -Put global and static data smaller than @var{number} bytes into a special -section (on some targets). The default value is 0. - -@item -mmax-inline-memcpy-size=@var{n} -@opindex -mmax-inline-memcpy-size -Inline all block moves (such as calls to @code{memcpy} or structure copies) -less than or equal to @var{n} bytes. The default value of @var{n} is 1024. - -@item -mcmodel=@var{code-model} -Set the code model to one of: -@table @samp -@item tiny-static (Not implemented yet) -@item tiny (Not implemented yet) - -@item normal -The text segment must be within 128MB addressing space. The data segment must -be within 2GB addressing space. - -@item medium -The text segment and data segment must be within 2GB addressing space. - -@item large (Not implemented yet) - -@item extreme -This mode does not limit the size of the code segment and data segment. -The @option{-mcmodel=extreme} option is incompatible with @option{-fplt} and -@option{-mno-explicit-relocs}. -@end table -The default code model is @code{normal}. - -@item -mexplicit-relocs -@itemx -mno-explicit-relocs -@opindex mexplicit-relocs -@opindex mno-explicit-relocs -Use or do not use assembler relocation operators when dealing with symbolic -addresses. The alternative is to use assembler macros instead, which may -limit optimization. The default value for the option is determined during -GCC build-time by detecting corresponding assembler support: -@code{-mexplicit-relocs} if said support is present, -@code{-mno-explicit-relocs} otherwise. This option is mostly useful for -debugging, or interoperation with assemblers different from the build-time -one. - -@item -mdirect-extern-access -@itemx -mno-direct-extern-access -@opindex mdirect-extern-access -Do not use or use GOT to access external symbols. The default is -@option{-mno-direct-extern-access}: GOT is used for external symbols with -default visibility, but not used for other external symbols. - -With @option{-mdirect-extern-access}, GOT is not used and all external -symbols are PC-relatively addressed. It is @strong{only} suitable for -environments where no dynamic link is performed, like firmwares, OS -kernels, executables linked with @option{-static} or @option{-static-pie}. -@option{-mdirect-extern-access} is not compatible with @option{-fPIC} or -@option{-fpic}. -@end table - -@node M32C Options -@subsection M32C Options -@cindex M32C options - -@table @gcctabopt -@item -mcpu=@var{name} -@opindex mcpu= -Select the CPU for which code is generated. @var{name} may be one of -@samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to -/60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for -the M32C/80 series. - -@item -msim -@opindex msim -Specifies that the program will be run on the simulator. This causes -an alternate runtime library to be linked in which supports, for -example, file I/O@. You must not use this option when generating -programs that will run on real hardware; you must provide your own -runtime library for whatever I/O functions are needed. - -@item -memregs=@var{number} -@opindex memregs= -Specifies the number of memory-based pseudo-registers GCC uses -during code generation. These pseudo-registers are used like real -registers, so there is a tradeoff between GCC's ability to fit the -code into available registers, and the performance penalty of using -memory instead of registers. Note that all modules in a program must -be compiled with the same value for this option. Because of that, you -must not use this option with GCC's default runtime libraries. - -@end table - -@node M32R/D Options -@subsection M32R/D Options -@cindex M32R/D options - -These @option{-m} options are defined for Renesas M32R/D architectures: - -@table @gcctabopt -@item -m32r2 -@opindex m32r2 -Generate code for the M32R/2@. - -@item -m32rx -@opindex m32rx -Generate code for the M32R/X@. - -@item -m32r -@opindex m32r -Generate code for the M32R@. This is the default. - -@item -mmodel=small -@opindex mmodel=small -Assume all objects live in the lower 16MB of memory (so that their addresses -can be loaded with the @code{ld24} instruction), and assume all subroutines -are reachable with the @code{bl} instruction. -This is the default. - -The addressability of a particular object can be set with the -@code{model} attribute. - -@item -mmodel=medium -@opindex mmodel=medium -Assume objects may be anywhere in the 32-bit address space (the compiler -generates @code{seth/add3} instructions to load their addresses), and -assume all subroutines are reachable with the @code{bl} instruction. - -@item -mmodel=large -@opindex mmodel=large -Assume objects may be anywhere in the 32-bit address space (the compiler -generates @code{seth/add3} instructions to load their addresses), and -assume subroutines may not be reachable with the @code{bl} instruction -(the compiler generates the much slower @code{seth/add3/jl} -instruction sequence). - -@item -msdata=none -@opindex msdata=none -Disable use of the small data area. Variables are put into -one of @code{.data}, @code{.bss}, or @code{.rodata} (unless the -@code{section} attribute has been specified). -This is the default. - -The small data area consists of sections @code{.sdata} and @code{.sbss}. -Objects may be explicitly put in the small data area with the -@code{section} attribute using one of these sections. - -@item -msdata=sdata -@opindex msdata=sdata -Put small global and static data in the small data area, but do not -generate special code to reference them. - -@item -msdata=use -@opindex msdata=use -Put small global and static data in the small data area, and generate -special instructions to reference them. - -@item -G @var{num} -@opindex G -@cindex smaller data references -Put global and static objects less than or equal to @var{num} bytes -into the small data or BSS sections instead of the normal data or BSS -sections. The default value of @var{num} is 8. -The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use} -for this option to have any effect. - -All modules should be compiled with the same @option{-G @var{num}} value. -Compiling with different values of @var{num} may or may not work; if it -doesn't the linker gives an error message---incorrect code is not -generated. - -@item -mdebug -@opindex mdebug -Makes the M32R-specific code in the compiler display some statistics -that might help in debugging programs. - -@item -malign-loops -@opindex malign-loops -Align all loops to a 32-byte boundary. - -@item -mno-align-loops -@opindex mno-align-loops -Do not enforce a 32-byte alignment for loops. This is the default. - -@item -missue-rate=@var{number} -@opindex missue-rate=@var{number} -Issue @var{number} instructions per cycle. @var{number} can only be 1 -or 2. - -@item -mbranch-cost=@var{number} -@opindex mbranch-cost=@var{number} -@var{number} can only be 1 or 2. If it is 1 then branches are -preferred over conditional code, if it is 2, then the opposite applies. - -@item -mflush-trap=@var{number} -@opindex mflush-trap=@var{number} -Specifies the trap number to use to flush the cache. The default is -12. Valid numbers are between 0 and 15 inclusive. - -@item -mno-flush-trap -@opindex mno-flush-trap -Specifies that the cache cannot be flushed by using a trap. - -@item -mflush-func=@var{name} -@opindex mflush-func=@var{name} -Specifies the name of the operating system function to call to flush -the cache. The default is @samp{_flush_cache}, but a function call -is only used if a trap is not available. - -@item -mno-flush-func -@opindex mno-flush-func -Indicates that there is no OS function for flushing the cache. - -@end table - -@node M680x0 Options -@subsection M680x0 Options -@cindex M680x0 options - -These are the @samp{-m} options defined for M680x0 and ColdFire processors. -The default settings depend on which architecture was selected when -the compiler was configured; the defaults for the most common choices -are given below. - -@table @gcctabopt -@item -march=@var{arch} -@opindex march -Generate code for a specific M680x0 or ColdFire instruction set -architecture. Permissible values of @var{arch} for M680x0 -architectures are: @samp{68000}, @samp{68010}, @samp{68020}, -@samp{68030}, @samp{68040}, @samp{68060} and @samp{cpu32}. ColdFire -architectures are selected according to Freescale's ISA classification -and the permissible values are: @samp{isaa}, @samp{isaaplus}, -@samp{isab} and @samp{isac}. - -GCC defines a macro @code{__mcf@var{arch}__} whenever it is generating -code for a ColdFire target. The @var{arch} in this macro is one of the -@option{-march} arguments given above. - -When used together, @option{-march} and @option{-mtune} select code -that runs on a family of similar processors but that is optimized -for a particular microarchitecture. - -@item -mcpu=@var{cpu} -@opindex mcpu -Generate code for a specific M680x0 or ColdFire processor. -The M680x0 @var{cpu}s are: @samp{68000}, @samp{68010}, @samp{68020}, -@samp{68030}, @samp{68040}, @samp{68060}, @samp{68302}, @samp{68332} -and @samp{cpu32}. The ColdFire @var{cpu}s are given by the table -below, which also classifies the CPUs into families: - -@multitable @columnfractions 0.20 0.80 -@headitem @strong{Family} @tab @strong{@samp{-mcpu} arguments} -@item @samp{51} @tab @samp{51} @samp{51ac} @samp{51ag} @samp{51cn} @samp{51em} @samp{51je} @samp{51jf} @samp{51jg} @samp{51jm} @samp{51mm} @samp{51qe} @samp{51qm} -@item @samp{5206} @tab @samp{5202} @samp{5204} @samp{5206} -@item @samp{5206e} @tab @samp{5206e} -@item @samp{5208} @tab @samp{5207} @samp{5208} -@item @samp{5211a} @tab @samp{5210a} @samp{5211a} -@item @samp{5213} @tab @samp{5211} @samp{5212} @samp{5213} -@item @samp{5216} @tab @samp{5214} @samp{5216} -@item @samp{52235} @tab @samp{52230} @samp{52231} @samp{52232} @samp{52233} @samp{52234} @samp{52235} -@item @samp{5225} @tab @samp{5224} @samp{5225} -@item @samp{52259} @tab @samp{52252} @samp{52254} @samp{52255} @samp{52256} @samp{52258} @samp{52259} -@item @samp{5235} @tab @samp{5232} @samp{5233} @samp{5234} @samp{5235} @samp{523x} -@item @samp{5249} @tab @samp{5249} -@item @samp{5250} @tab @samp{5250} -@item @samp{5271} @tab @samp{5270} @samp{5271} -@item @samp{5272} @tab @samp{5272} -@item @samp{5275} @tab @samp{5274} @samp{5275} -@item @samp{5282} @tab @samp{5280} @samp{5281} @samp{5282} @samp{528x} -@item @samp{53017} @tab @samp{53011} @samp{53012} @samp{53013} @samp{53014} @samp{53015} @samp{53016} @samp{53017} -@item @samp{5307} @tab @samp{5307} -@item @samp{5329} @tab @samp{5327} @samp{5328} @samp{5329} @samp{532x} -@item @samp{5373} @tab @samp{5372} @samp{5373} @samp{537x} -@item @samp{5407} @tab @samp{5407} -@item @samp{5475} @tab @samp{5470} @samp{5471} @samp{5472} @samp{5473} @samp{5474} @samp{5475} @samp{547x} @samp{5480} @samp{5481} @samp{5482} @samp{5483} @samp{5484} @samp{5485} -@end multitable - -@option{-mcpu=@var{cpu}} overrides @option{-march=@var{arch}} if -@var{arch} is compatible with @var{cpu}. Other combinations of -@option{-mcpu} and @option{-march} are rejected. - -GCC defines the macro @code{__mcf_cpu_@var{cpu}} when ColdFire target -@var{cpu} is selected. It also defines @code{__mcf_family_@var{family}}, -where the value of @var{family} is given by the table above. - -@item -mtune=@var{tune} -@opindex mtune -Tune the code for a particular microarchitecture within the -constraints set by @option{-march} and @option{-mcpu}. -The M680x0 microarchitectures are: @samp{68000}, @samp{68010}, -@samp{68020}, @samp{68030}, @samp{68040}, @samp{68060} -and @samp{cpu32}. The ColdFire microarchitectures -are: @samp{cfv1}, @samp{cfv2}, @samp{cfv3}, @samp{cfv4} and @samp{cfv4e}. - -You can also use @option{-mtune=68020-40} for code that needs -to run relatively well on 68020, 68030 and 68040 targets. -@option{-mtune=68020-60} is similar but includes 68060 targets -as well. These two options select the same tuning decisions as -@option{-m68020-40} and @option{-m68020-60} respectively. - -GCC defines the macros @code{__mc@var{arch}} and @code{__mc@var{arch}__} -when tuning for 680x0 architecture @var{arch}. It also defines -@code{mc@var{arch}} unless either @option{-ansi} or a non-GNU @option{-std} -option is used. If GCC is tuning for a range of architectures, -as selected by @option{-mtune=68020-40} or @option{-mtune=68020-60}, -it defines the macros for every architecture in the range. - -GCC also defines the macro @code{__m@var{uarch}__} when tuning for -ColdFire microarchitecture @var{uarch}, where @var{uarch} is one -of the arguments given above. - -@item -m68000 -@itemx -mc68000 -@opindex m68000 -@opindex mc68000 -Generate output for a 68000. This is the default -when the compiler is configured for 68000-based systems. -It is equivalent to @option{-march=68000}. - -Use this option for microcontrollers with a 68000 or EC000 core, -including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356. - -@item -m68010 -@opindex m68010 -Generate output for a 68010. This is the default -when the compiler is configured for 68010-based systems. -It is equivalent to @option{-march=68010}. - -@item -m68020 -@itemx -mc68020 -@opindex m68020 -@opindex mc68020 -Generate output for a 68020. This is the default -when the compiler is configured for 68020-based systems. -It is equivalent to @option{-march=68020}. - -@item -m68030 -@opindex m68030 -Generate output for a 68030. This is the default when the compiler is -configured for 68030-based systems. It is equivalent to -@option{-march=68030}. - -@item -m68040 -@opindex m68040 -Generate output for a 68040. This is the default when the compiler is -configured for 68040-based systems. It is equivalent to -@option{-march=68040}. - -This option inhibits the use of 68881/68882 instructions that have to be -emulated by software on the 68040. Use this option if your 68040 does not -have code to emulate those instructions. - -@item -m68060 -@opindex m68060 -Generate output for a 68060. This is the default when the compiler is -configured for 68060-based systems. It is equivalent to -@option{-march=68060}. - -This option inhibits the use of 68020 and 68881/68882 instructions that -have to be emulated by software on the 68060. Use this option if your 68060 -does not have code to emulate those instructions. - -@item -mcpu32 -@opindex mcpu32 -Generate output for a CPU32. This is the default -when the compiler is configured for CPU32-based systems. -It is equivalent to @option{-march=cpu32}. - -Use this option for microcontrollers with a -CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334, -68336, 68340, 68341, 68349 and 68360. - -@item -m5200 -@opindex m5200 -Generate output for a 520X ColdFire CPU@. This is the default -when the compiler is configured for 520X-based systems. -It is equivalent to @option{-mcpu=5206}, and is now deprecated -in favor of that option. - -Use this option for microcontroller with a 5200 core, including -the MCF5202, MCF5203, MCF5204 and MCF5206. - -@item -m5206e -@opindex m5206e -Generate output for a 5206e ColdFire CPU@. The option is now -deprecated in favor of the equivalent @option{-mcpu=5206e}. - -@item -m528x -@opindex m528x -Generate output for a member of the ColdFire 528X family. -The option is now deprecated in favor of the equivalent -@option{-mcpu=528x}. - -@item -m5307 -@opindex m5307 -Generate output for a ColdFire 5307 CPU@. The option is now deprecated -in favor of the equivalent @option{-mcpu=5307}. - -@item -m5407 -@opindex m5407 -Generate output for a ColdFire 5407 CPU@. The option is now deprecated -in favor of the equivalent @option{-mcpu=5407}. - -@item -mcfv4e -@opindex mcfv4e -Generate output for a ColdFire V4e family CPU (e.g.@: 547x/548x). -This includes use of hardware floating-point instructions. -The option is equivalent to @option{-mcpu=547x}, and is now -deprecated in favor of that option. - -@item -m68020-40 -@opindex m68020-40 -Generate output for a 68040, without using any of the new instructions. -This results in code that can run relatively efficiently on either a -68020/68881 or a 68030 or a 68040. The generated code does use the -68881 instructions that are emulated on the 68040. - -The option is equivalent to @option{-march=68020} @option{-mtune=68020-40}. - -@item -m68020-60 -@opindex m68020-60 -Generate output for a 68060, without using any of the new instructions. -This results in code that can run relatively efficiently on either a -68020/68881 or a 68030 or a 68040. The generated code does use the -68881 instructions that are emulated on the 68060. - -The option is equivalent to @option{-march=68020} @option{-mtune=68020-60}. - -@item -mhard-float -@itemx -m68881 -@opindex mhard-float -@opindex m68881 -Generate floating-point instructions. This is the default for 68020 -and above, and for ColdFire devices that have an FPU@. It defines the -macro @code{__HAVE_68881__} on M680x0 targets and @code{__mcffpu__} -on ColdFire targets. - -@item -msoft-float -@opindex msoft-float -Do not generate floating-point instructions; use library calls instead. -This is the default for 68000, 68010, and 68832 targets. It is also -the default for ColdFire devices that have no FPU. - -@item -mdiv -@itemx -mno-div -@opindex mdiv -@opindex mno-div -Generate (do not generate) ColdFire hardware divide and remainder -instructions. If @option{-march} is used without @option{-mcpu}, -the default is ``on'' for ColdFire architectures and ``off'' for M680x0 -architectures. Otherwise, the default is taken from the target CPU -(either the default CPU, or the one specified by @option{-mcpu}). For -example, the default is ``off'' for @option{-mcpu=5206} and ``on'' for -@option{-mcpu=5206e}. - -GCC defines the macro @code{__mcfhwdiv__} when this option is enabled. - -@item -mshort -@opindex mshort -Consider type @code{int} to be 16 bits wide, like @code{short int}. -Additionally, parameters passed on the stack are also aligned to a -16-bit boundary even on targets whose API mandates promotion to 32-bit. - -@item -mno-short -@opindex mno-short -Do not consider type @code{int} to be 16 bits wide. This is the default. - -@item -mnobitfield -@itemx -mno-bitfield -@opindex mnobitfield -@opindex mno-bitfield -Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32} -and @option{-m5200} options imply @w{@option{-mnobitfield}}. - -@item -mbitfield -@opindex mbitfield -Do use the bit-field instructions. The @option{-m68020} option implies -@option{-mbitfield}. This is the default if you use a configuration -designed for a 68020. - -@item -mrtd -@opindex mrtd -Use a different function-calling convention, in which functions -that take a fixed number of arguments return with the @code{rtd} -instruction, which pops their arguments while returning. This -saves one instruction in the caller since there is no need to pop -the arguments there. - -This calling convention is incompatible with the one normally -used on Unix, so you cannot use it if you need to call libraries -compiled with the Unix compiler. - -Also, you must provide function prototypes for all functions that -take variable numbers of arguments (including @code{printf}); -otherwise incorrect code is generated for calls to those -functions. - -In addition, seriously incorrect code results if you call a -function with too many arguments. (Normally, extra arguments are -harmlessly ignored.) - -The @code{rtd} instruction is supported by the 68010, 68020, 68030, -68040, 68060 and CPU32 processors, but not by the 68000 or 5200. - -The default is @option{-mno-rtd}. - -@item -malign-int -@itemx -mno-align-int -@opindex malign-int -@opindex mno-align-int -Control whether GCC aligns @code{int}, @code{long}, @code{long long}, -@code{float}, @code{double}, and @code{long double} variables on a 32-bit -boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}). -Aligning variables on 32-bit boundaries produces code that runs somewhat -faster on processors with 32-bit busses at the expense of more memory. - -@strong{Warning:} if you use the @option{-malign-int} switch, GCC -aligns structures containing the above types differently than -most published application binary interface specifications for the m68k. - -@opindex mpcrel -Use the pc-relative addressing mode of the 68000 directly, instead of -using a global offset table. At present, this option implies @option{-fpic}, -allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is -not presently supported with @option{-mpcrel}, though this could be supported for -68020 and higher processors. - -@item -mno-strict-align -@itemx -mstrict-align -@opindex mno-strict-align -@opindex mstrict-align -Do not (do) assume that unaligned memory references are handled by -the system. - -@item -msep-data -Generate code that allows the data segment to be located in a different -area of memory from the text segment. This allows for execute-in-place in -an environment without virtual memory management. This option implies -@option{-fPIC}. - -@item -mno-sep-data -Generate code that assumes that the data segment follows the text segment. -This is the default. - -@item -mid-shared-library -Generate code that supports shared libraries via the library ID method. -This allows for execute-in-place and shared libraries in an environment -without virtual memory management. This option implies @option{-fPIC}. - -@item -mno-id-shared-library -Generate code that doesn't assume ID-based shared libraries are being used. -This is the default. - -@item -mshared-library-id=n -Specifies the identification number of the ID-based shared library being -compiled. Specifying a value of 0 generates more compact code; specifying -other values forces the allocation of that number to the current -library, but is no more space- or time-efficient than omitting this option. - -@item -mxgot -@itemx -mno-xgot -@opindex mxgot -@opindex mno-xgot -When generating position-independent code for ColdFire, generate code -that works if the GOT has more than 8192 entries. This code is -larger and slower than code generated without this option. On M680x0 -processors, this option is not needed; @option{-fPIC} suffices. - -GCC normally uses a single instruction to load values from the GOT@. -While this is relatively efficient, it only works if the GOT -is smaller than about 64k. Anything larger causes the linker -to report an error such as: - -@cindex relocation truncated to fit (ColdFire) -@smallexample -relocation truncated to fit: R_68K_GOT16O foobar -@end smallexample - -If this happens, you should recompile your code with @option{-mxgot}. -It should then work with very large GOTs. However, code generated with -@option{-mxgot} is less efficient, since it takes 4 instructions to fetch -the value of a global symbol. - -Note that some linkers, including newer versions of the GNU linker, -can create multiple GOTs and sort GOT entries. If you have such a linker, -you should only need to use @option{-mxgot} when compiling a single -object file that accesses more than 8192 GOT entries. Very few do. - -These options have no effect unless GCC is generating -position-independent code. - -@item -mlong-jump-table-offsets -@opindex mlong-jump-table-offsets -Use 32-bit offsets in @code{switch} tables. The default is to use -16-bit offsets. - -@end table - -@node MCore Options -@subsection MCore Options -@cindex MCore options - -These are the @samp{-m} options defined for the Motorola M*Core -processors. - -@table @gcctabopt - -@item -mhardlit -@itemx -mno-hardlit -@opindex mhardlit -@opindex mno-hardlit -Inline constants into the code stream if it can be done in two -instructions or less. - -@item -mdiv -@itemx -mno-div -@opindex mdiv -@opindex mno-div -Use the divide instruction. (Enabled by default). - -@item -mrelax-immediate -@itemx -mno-relax-immediate -@opindex mrelax-immediate -@opindex mno-relax-immediate -Allow arbitrary-sized immediates in bit operations. - -@item -mwide-bitfields -@itemx -mno-wide-bitfields -@opindex mwide-bitfields -@opindex mno-wide-bitfields -Always treat bit-fields as @code{int}-sized. - -@item -m4byte-functions -@itemx -mno-4byte-functions -@opindex m4byte-functions -@opindex mno-4byte-functions -Force all functions to be aligned to a 4-byte boundary. - -@item -mcallgraph-data -@itemx -mno-callgraph-data -@opindex mcallgraph-data -@opindex mno-callgraph-data -Emit callgraph information. - -@item -mslow-bytes -@itemx -mno-slow-bytes -@opindex mslow-bytes -@opindex mno-slow-bytes -Prefer word access when reading byte quantities. - -@item -mlittle-endian -@itemx -mbig-endian -@opindex mlittle-endian -@opindex mbig-endian -Generate code for a little-endian target. - -@item -m210 -@itemx -m340 -@opindex m210 -@opindex m340 -Generate code for the 210 processor. - -@item -mno-lsim -@opindex mno-lsim -Assume that runtime support has been provided and so omit the -simulator library (@file{libsim.a)} from the linker command line. - -@item -mstack-increment=@var{size} -@opindex mstack-increment -Set the maximum amount for a single stack increment operation. Large -values can increase the speed of programs that contain functions -that need a large amount of stack space, but they can also trigger a -segmentation fault if the stack is extended too much. The default -value is 0x1000. - -@end table - -@node MeP Options -@subsection MeP Options -@cindex MeP options - -@table @gcctabopt - -@item -mabsdiff -@opindex mabsdiff -Enables the @code{abs} instruction, which is the absolute difference -between two registers. - -@item -mall-opts -@opindex mall-opts -Enables all the optional instructions---average, multiply, divide, bit -operations, leading zero, absolute difference, min/max, clip, and -saturation. - - -@item -maverage -@opindex maverage -Enables the @code{ave} instruction, which computes the average of two -registers. - -@item -mbased=@var{n} -@opindex mbased= -Variables of size @var{n} bytes or smaller are placed in the -@code{.based} section by default. Based variables use the @code{$tp} -register as a base register, and there is a 128-byte limit to the -@code{.based} section. - -@item -mbitops -@opindex mbitops -Enables the bit operation instructions---bit test (@code{btstm}), set -(@code{bsetm}), clear (@code{bclrm}), invert (@code{bnotm}), and -test-and-set (@code{tas}). - -@item -mc=@var{name} -@opindex mc= -Selects which section constant data is placed in. @var{name} may -be @samp{tiny}, @samp{near}, or @samp{far}. - -@item -mclip -@opindex mclip -Enables the @code{clip} instruction. Note that @option{-mclip} is not -useful unless you also provide @option{-mminmax}. - -@item -mconfig=@var{name} -@opindex mconfig= -Selects one of the built-in core configurations. Each MeP chip has -one or more modules in it; each module has a core CPU and a variety of -coprocessors, optional instructions, and peripherals. The -@code{MeP-Integrator} tool, not part of GCC, provides these -configurations through this option; using this option is the same as -using all the corresponding command-line options. The default -configuration is @samp{default}. - -@item -mcop -@opindex mcop -Enables the coprocessor instructions. By default, this is a 32-bit -coprocessor. Note that the coprocessor is normally enabled via the -@option{-mconfig=} option. - -@item -mcop32 -@opindex mcop32 -Enables the 32-bit coprocessor's instructions. - -@item -mcop64 -@opindex mcop64 -Enables the 64-bit coprocessor's instructions. - -@item -mivc2 -@opindex mivc2 -Enables IVC2 scheduling. IVC2 is a 64-bit VLIW coprocessor. - -@item -mdc -@opindex mdc -Causes constant variables to be placed in the @code{.near} section. - -@item -mdiv -@opindex mdiv -Enables the @code{div} and @code{divu} instructions. - -@item -meb -@opindex meb -Generate big-endian code. - -@item -mel -@opindex mel -Generate little-endian code. - -@item -mio-volatile -@opindex mio-volatile -Tells the compiler that any variable marked with the @code{io} -attribute is to be considered volatile. - -@item -ml -@opindex ml -Causes variables to be assigned to the @code{.far} section by default. - -@item -mleadz -@opindex mleadz -Enables the @code{leadz} (leading zero) instruction. - -@item -mm -@opindex mm -Causes variables to be assigned to the @code{.near} section by default. - -@item -mminmax -@opindex mminmax -Enables the @code{min} and @code{max} instructions. - -@item -mmult -@opindex mmult -Enables the multiplication and multiply-accumulate instructions. - -@item -mno-opts -@opindex mno-opts -Disables all the optional instructions enabled by @option{-mall-opts}. - -@item -mrepeat -@opindex mrepeat -Enables the @code{repeat} and @code{erepeat} instructions, used for -low-overhead looping. - -@item -ms -@opindex ms -Causes all variables to default to the @code{.tiny} section. Note -that there is a 65536-byte limit to this section. Accesses to these -variables use the @code{%gp} base register. - -@item -msatur -@opindex msatur -Enables the saturation instructions. Note that the compiler does not -currently generate these itself, but this option is included for -compatibility with other tools, like @code{as}. - -@item -msdram -@opindex msdram -Link the SDRAM-based runtime instead of the default ROM-based runtime. - -@item -msim -@opindex msim -Link the simulator run-time libraries. - -@item -msimnovec -@opindex msimnovec -Link the simulator runtime libraries, excluding built-in support -for reset and exception vectors and tables. - -@item -mtf -@opindex mtf -Causes all functions to default to the @code{.far} section. Without -this option, functions default to the @code{.near} section. - -@item -mtiny=@var{n} -@opindex mtiny= -Variables that are @var{n} bytes or smaller are allocated to the -@code{.tiny} section. These variables use the @code{$gp} base -register. The default for this option is 4, but note that there's a -65536-byte limit to the @code{.tiny} section. - -@end table - -@node MicroBlaze Options -@subsection MicroBlaze Options -@cindex MicroBlaze Options - -@table @gcctabopt - -@item -msoft-float -@opindex msoft-float -Use software emulation for floating point (default). - -@item -mhard-float -@opindex mhard-float -Use hardware floating-point instructions. - -@item -mmemcpy -@opindex mmemcpy -Do not optimize block moves, use @code{memcpy}. - -@item -mno-clearbss -@opindex mno-clearbss -This option is deprecated. Use @option{-fno-zero-initialized-in-bss} instead. - -@item -mcpu=@var{cpu-type} -@opindex mcpu= -Use features of, and schedule code for, the given CPU. -Supported values are in the format @samp{v@var{X}.@var{YY}.@var{Z}}, -where @var{X} is a major version, @var{YY} is the minor version, and -@var{Z} is compatibility code. Example values are @samp{v3.00.a}, -@samp{v4.00.b}, @samp{v5.00.a}, @samp{v5.00.b}, @samp{v6.00.a}. - -@item -mxl-soft-mul -@opindex mxl-soft-mul -Use software multiply emulation (default). - -@item -mxl-soft-div -@opindex mxl-soft-div -Use software emulation for divides (default). - -@item -mxl-barrel-shift -@opindex mxl-barrel-shift -Use the hardware barrel shifter. - -@item -mxl-pattern-compare -@opindex mxl-pattern-compare -Use pattern compare instructions. - -@item -msmall-divides -@opindex msmall-divides -Use table lookup optimization for small signed integer divisions. - -@item -mxl-stack-check -@opindex mxl-stack-check -This option is deprecated. Use @option{-fstack-check} instead. - -@item -mxl-gp-opt -@opindex mxl-gp-opt -Use GP-relative @code{.sdata}/@code{.sbss} sections. - -@item -mxl-multiply-high -@opindex mxl-multiply-high -Use multiply high instructions for high part of 32x32 multiply. - -@item -mxl-float-convert -@opindex mxl-float-convert -Use hardware floating-point conversion instructions. - -@item -mxl-float-sqrt -@opindex mxl-float-sqrt -Use hardware floating-point square root instruction. - -@item -mbig-endian -@opindex mbig-endian -Generate code for a big-endian target. - -@item -mlittle-endian -@opindex mlittle-endian -Generate code for a little-endian target. - -@item -mxl-reorder -@opindex mxl-reorder -Use reorder instructions (swap and byte reversed load/store). - -@item -mxl-mode-@var{app-model} -Select application model @var{app-model}. Valid models are -@table @samp -@item executable -normal executable (default), uses startup code @file{crt0.o}. - -@item xmdstub -for use with Xilinx Microprocessor Debugger (XMD) based -software intrusive debug agent called xmdstub. This uses startup file -@file{crt1.o} and sets the start address of the program to 0x800. - -@item bootstrap -for applications that are loaded using a bootloader. -This model uses startup file @file{crt2.o} which does not contain a processor -reset vector handler. This is suitable for transferring control on a -processor reset to the bootloader rather than the application. - -@item novectors -for applications that do not require any of the -MicroBlaze vectors. This option may be useful for applications running -within a monitoring application. This model uses @file{crt3.o} as a startup file. -@end table - -Option @option{-xl-mode-@var{app-model}} is a deprecated alias for -@option{-mxl-mode-@var{app-model}}. - -@item -mpic-data-is-text-relative -@opindex mpic-data-is-text-relative -Assume that the displacement between the text and data segments is fixed -at static link time. This allows data to be referenced by offset from start of -text address instead of GOT since PC-relative addressing is not supported. - -@end table - -@node MIPS Options -@subsection MIPS Options -@cindex MIPS options - -@table @gcctabopt - -@item -EB -@opindex EB -Generate big-endian code. - -@item -EL -@opindex EL -Generate little-endian code. This is the default for @samp{mips*el-*-*} -configurations. - -@item -march=@var{arch} -@opindex march -Generate code that runs on @var{arch}, which can be the name of a -generic MIPS ISA, or the name of a particular processor. -The ISA names are: -@samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4}, -@samp{mips32}, @samp{mips32r2}, @samp{mips32r3}, @samp{mips32r5}, -@samp{mips32r6}, @samp{mips64}, @samp{mips64r2}, @samp{mips64r3}, -@samp{mips64r5} and @samp{mips64r6}. -The processor names are: -@samp{4kc}, @samp{4km}, @samp{4kp}, @samp{4ksc}, -@samp{4kec}, @samp{4kem}, @samp{4kep}, @samp{4ksd}, -@samp{5kc}, @samp{5kf}, -@samp{20kc}, -@samp{24kc}, @samp{24kf2_1}, @samp{24kf1_1}, -@samp{24kec}, @samp{24kef2_1}, @samp{24kef1_1}, -@samp{34kc}, @samp{34kf2_1}, @samp{34kf1_1}, @samp{34kn}, -@samp{74kc}, @samp{74kf2_1}, @samp{74kf1_1}, @samp{74kf3_2}, -@samp{1004kc}, @samp{1004kf2_1}, @samp{1004kf1_1}, -@samp{i6400}, @samp{i6500}, -@samp{interaptiv}, -@samp{loongson2e}, @samp{loongson2f}, @samp{loongson3a}, @samp{gs464}, -@samp{gs464e}, @samp{gs264e}, -@samp{m4k}, -@samp{m14k}, @samp{m14kc}, @samp{m14ke}, @samp{m14kec}, -@samp{m5100}, @samp{m5101}, -@samp{octeon}, @samp{octeon+}, @samp{octeon2}, @samp{octeon3}, -@samp{orion}, -@samp{p5600}, @samp{p6600}, -@samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400}, -@samp{r4600}, @samp{r4650}, @samp{r4700}, @samp{r5900}, -@samp{r6000}, @samp{r8000}, -@samp{rm7000}, @samp{rm9000}, -@samp{r10000}, @samp{r12000}, @samp{r14000}, @samp{r16000}, -@samp{sb1}, -@samp{sr71000}, -@samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300}, -@samp{vr5000}, @samp{vr5400}, @samp{vr5500}, -@samp{xlr} and @samp{xlp}. -The special value @samp{from-abi} selects the -most compatible architecture for the selected ABI (that is, -@samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@. - -The native Linux/GNU toolchain also supports the value @samp{native}, -which selects the best architecture option for the host processor. -@option{-march=native} has no effect if GCC does not recognize -the processor. - -In processor names, a final @samp{000} can be abbreviated as @samp{k} -(for example, @option{-march=r2k}). Prefixes are optional, and -@samp{vr} may be written @samp{r}. - -Names of the form @samp{@var{n}f2_1} refer to processors with -FPUs clocked at half the rate of the core, names of the form -@samp{@var{n}f1_1} refer to processors with FPUs clocked at the same -rate as the core, and names of the form @samp{@var{n}f3_2} refer to -processors with FPUs clocked a ratio of 3:2 with respect to the core. -For compatibility reasons, @samp{@var{n}f} is accepted as a synonym -for @samp{@var{n}f2_1} while @samp{@var{n}x} and @samp{@var{b}fx} are -accepted as synonyms for @samp{@var{n}f1_1}. - -GCC defines two macros based on the value of this option. The first -is @code{_MIPS_ARCH}, which gives the name of target architecture, as -a string. The second has the form @code{_MIPS_ARCH_@var{foo}}, -where @var{foo} is the capitalized value of @code{_MIPS_ARCH}@. -For example, @option{-march=r2000} sets @code{_MIPS_ARCH} -to @code{"r2000"} and defines the macro @code{_MIPS_ARCH_R2000}. - -Note that the @code{_MIPS_ARCH} macro uses the processor names given -above. In other words, it has the full prefix and does not -abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi}, -the macro names the resolved architecture (either @code{"mips1"} or -@code{"mips3"}). It names the default architecture when no -@option{-march} option is given. - -@item -mtune=@var{arch} -@opindex mtune -Optimize for @var{arch}. Among other things, this option controls -the way instructions are scheduled, and the perceived cost of arithmetic -operations. The list of @var{arch} values is the same as for -@option{-march}. - -When this option is not used, GCC optimizes for the processor -specified by @option{-march}. By using @option{-march} and -@option{-mtune} together, it is possible to generate code that -runs on a family of processors, but optimize the code for one -particular member of that family. - -@option{-mtune} defines the macros @code{_MIPS_TUNE} and -@code{_MIPS_TUNE_@var{foo}}, which work in the same way as the -@option{-march} ones described above. - -@item -mips1 -@opindex mips1 -Equivalent to @option{-march=mips1}. - -@item -mips2 -@opindex mips2 -Equivalent to @option{-march=mips2}. - -@item -mips3 -@opindex mips3 -Equivalent to @option{-march=mips3}. - -@item -mips4 -@opindex mips4 -Equivalent to @option{-march=mips4}. - -@item -mips32 -@opindex mips32 -Equivalent to @option{-march=mips32}. - -@item -mips32r3 -@opindex mips32r3 -Equivalent to @option{-march=mips32r3}. - -@item -mips32r5 -@opindex mips32r5 -Equivalent to @option{-march=mips32r5}. - -@item -mips32r6 -@opindex mips32r6 -Equivalent to @option{-march=mips32r6}. - -@item -mips64 -@opindex mips64 -Equivalent to @option{-march=mips64}. - -@item -mips64r2 -@opindex mips64r2 -Equivalent to @option{-march=mips64r2}. - -@item -mips64r3 -@opindex mips64r3 -Equivalent to @option{-march=mips64r3}. - -@item -mips64r5 -@opindex mips64r5 -Equivalent to @option{-march=mips64r5}. - -@item -mips64r6 -@opindex mips64r6 -Equivalent to @option{-march=mips64r6}. - -@item -mips16 -@itemx -mno-mips16 -@opindex mips16 -@opindex mno-mips16 -Generate (do not generate) MIPS16 code. If GCC is targeting a -MIPS32 or MIPS64 architecture, it makes use of the MIPS16e ASE@. - -MIPS16 code generation can also be controlled on a per-function basis -by means of @code{mips16} and @code{nomips16} attributes. -@xref{Function Attributes}, for more information. - -@item -mflip-mips16 -@opindex mflip-mips16 -Generate MIPS16 code on alternating functions. This option is provided -for regression testing of mixed MIPS16/non-MIPS16 code generation, and is -not intended for ordinary use in compiling user code. - -@item -minterlink-compressed -@itemx -mno-interlink-compressed -@opindex minterlink-compressed -@opindex mno-interlink-compressed -Require (do not require) that code using the standard (uncompressed) MIPS ISA -be link-compatible with MIPS16 and microMIPS code, and vice versa. - -For example, code using the standard ISA encoding cannot jump directly -to MIPS16 or microMIPS code; it must either use a call or an indirect jump. -@option{-minterlink-compressed} therefore disables direct jumps unless GCC -knows that the target of the jump is not compressed. - -@item -minterlink-mips16 -@itemx -mno-interlink-mips16 -@opindex minterlink-mips16 -@opindex mno-interlink-mips16 -Aliases of @option{-minterlink-compressed} and -@option{-mno-interlink-compressed}. These options predate the microMIPS ASE -and are retained for backwards compatibility. - -@item -mabi=32 -@itemx -mabi=o64 -@itemx -mabi=n32 -@itemx -mabi=64 -@itemx -mabi=eabi -@opindex mabi=32 -@opindex mabi=o64 -@opindex mabi=n32 -@opindex mabi=64 -@opindex mabi=eabi -Generate code for the given ABI@. - -Note that the EABI has a 32-bit and a 64-bit variant. GCC normally -generates 64-bit code when you select a 64-bit architecture, but you -can use @option{-mgp32} to get 32-bit code instead. - -For information about the O64 ABI, see -@uref{https://gcc.gnu.org/@/projects/@/mipso64-abi.html}. - -GCC supports a variant of the o32 ABI in which floating-point registers -are 64 rather than 32 bits wide. You can select this combination with -@option{-mabi=32} @option{-mfp64}. This ABI relies on the @code{mthc1} -and @code{mfhc1} instructions and is therefore only supported for -MIPS32R2, MIPS32R3 and MIPS32R5 processors. - -The register assignments for arguments and return values remain the -same, but each scalar value is passed in a single 64-bit register -rather than a pair of 32-bit registers. For example, scalar -floating-point values are returned in @samp{$f0} only, not a -@samp{$f0}/@samp{$f1} pair. The set of call-saved registers also -remains the same in that the even-numbered double-precision registers -are saved. - -Two additional variants of the o32 ABI are supported to enable -a transition from 32-bit to 64-bit registers. These are FPXX -(@option{-mfpxx}) and FP64A (@option{-mfp64} @option{-mno-odd-spreg}). -The FPXX extension mandates that all code must execute correctly -when run using 32-bit or 64-bit registers. The code can be interlinked -with either FP32 or FP64, but not both. -The FP64A extension is similar to the FP64 extension but forbids the -use of odd-numbered single-precision registers. This can be used -in conjunction with the @code{FRE} mode of FPUs in MIPS32R5 -processors and allows both FP32 and FP64A code to interlink and -run in the same process without changing FPU modes. - -@item -mabicalls -@itemx -mno-abicalls -@opindex mabicalls -@opindex mno-abicalls -Generate (do not generate) code that is suitable for SVR4-style -dynamic objects. @option{-mabicalls} is the default for SVR4-based -systems. - -@item -mshared -@itemx -mno-shared -Generate (do not generate) code that is fully position-independent, -and that can therefore be linked into shared libraries. This option -only affects @option{-mabicalls}. - -All @option{-mabicalls} code has traditionally been position-independent, -regardless of options like @option{-fPIC} and @option{-fpic}. However, -as an extension, the GNU toolchain allows executables to use absolute -accesses for locally-binding symbols. It can also use shorter GP -initialization sequences and generate direct calls to locally-defined -functions. This mode is selected by @option{-mno-shared}. - -@option{-mno-shared} depends on binutils 2.16 or higher and generates -objects that can only be linked by the GNU linker. However, the option -does not affect the ABI of the final executable; it only affects the ABI -of relocatable objects. Using @option{-mno-shared} generally makes -executables both smaller and quicker. - -@option{-mshared} is the default. - -@item -mplt -@itemx -mno-plt -@opindex mplt -@opindex mno-plt -Assume (do not assume) that the static and dynamic linkers -support PLTs and copy relocations. This option only affects -@option{-mno-shared -mabicalls}. For the n64 ABI, this option -has no effect without @option{-msym32}. - -You can make @option{-mplt} the default by configuring -GCC with @option{--with-mips-plt}. The default is -@option{-mno-plt} otherwise. - -@item -mxgot -@itemx -mno-xgot -@opindex mxgot -@opindex mno-xgot -Lift (do not lift) the usual restrictions on the size of the global -offset table. - -GCC normally uses a single instruction to load values from the GOT@. -While this is relatively efficient, it only works if the GOT -is smaller than about 64k. Anything larger causes the linker -to report an error such as: - -@cindex relocation truncated to fit (MIPS) -@smallexample -relocation truncated to fit: R_MIPS_GOT16 foobar -@end smallexample - -If this happens, you should recompile your code with @option{-mxgot}. -This works with very large GOTs, although the code is also -less efficient, since it takes three instructions to fetch the -value of a global symbol. - -Note that some linkers can create multiple GOTs. If you have such a -linker, you should only need to use @option{-mxgot} when a single object -file accesses more than 64k's worth of GOT entries. Very few do. - -These options have no effect unless GCC is generating position -independent code. - -@item -mgp32 -@opindex mgp32 -Assume that general-purpose registers are 32 bits wide. - -@item -mgp64 -@opindex mgp64 -Assume that general-purpose registers are 64 bits wide. - -@item -mfp32 -@opindex mfp32 -Assume that floating-point registers are 32 bits wide. - -@item -mfp64 -@opindex mfp64 -Assume that floating-point registers are 64 bits wide. - -@item -mfpxx -@opindex mfpxx -Do not assume the width of floating-point registers. - -@item -mhard-float -@opindex mhard-float -Use floating-point coprocessor instructions. - -@item -msoft-float -@opindex msoft-float -Do not use floating-point coprocessor instructions. Implement -floating-point calculations using library calls instead. - -@item -mno-float -@opindex mno-float -Equivalent to @option{-msoft-float}, but additionally asserts that the -program being compiled does not perform any floating-point operations. -This option is presently supported only by some bare-metal MIPS -configurations, where it may select a special set of libraries -that lack all floating-point support (including, for example, the -floating-point @code{printf} formats). -If code compiled with @option{-mno-float} accidentally contains -floating-point operations, it is likely to suffer a link-time -or run-time failure. - -@item -msingle-float -@opindex msingle-float -Assume that the floating-point coprocessor only supports single-precision -operations. - -@item -mdouble-float -@opindex mdouble-float -Assume that the floating-point coprocessor supports double-precision -operations. This is the default. - -@item -modd-spreg -@itemx -mno-odd-spreg -@opindex modd-spreg -@opindex mno-odd-spreg -Enable the use of odd-numbered single-precision floating-point registers -for the o32 ABI. This is the default for processors that are known to -support these registers. When using the o32 FPXX ABI, @option{-mno-odd-spreg} -is set by default. - -@item -mabs=2008 -@itemx -mabs=legacy -@opindex mabs=2008 -@opindex mabs=legacy -These options control the treatment of the special not-a-number (NaN) -IEEE 754 floating-point data with the @code{abs.@i{fmt}} and -@code{neg.@i{fmt}} machine instructions. - -By default or when @option{-mabs=legacy} is used the legacy -treatment is selected. In this case these instructions are considered -arithmetic and avoided where correct operation is required and the -input operand might be a NaN. A longer sequence of instructions that -manipulate the sign bit of floating-point datum manually is used -instead unless the @option{-ffinite-math-only} option has also been -specified. - -The @option{-mabs=2008} option selects the IEEE 754-2008 treatment. In -this case these instructions are considered non-arithmetic and therefore -operating correctly in all cases, including in particular where the -input operand is a NaN. These instructions are therefore always used -for the respective operations. - -@item -mnan=2008 -@itemx -mnan=legacy -@opindex mnan=2008 -@opindex mnan=legacy -These options control the encoding of the special not-a-number (NaN) -IEEE 754 floating-point data. - -The @option{-mnan=legacy} option selects the legacy encoding. In this -case quiet NaNs (qNaNs) are denoted by the first bit of their trailing -significand field being 0, whereas signaling NaNs (sNaNs) are denoted -by the first bit of their trailing significand field being 1. - -The @option{-mnan=2008} option selects the IEEE 754-2008 encoding. In -this case qNaNs are denoted by the first bit of their trailing -significand field being 1, whereas sNaNs are denoted by the first bit of -their trailing significand field being 0. - -The default is @option{-mnan=legacy} unless GCC has been configured with -@option{--with-nan=2008}. - -@item -mllsc -@itemx -mno-llsc -@opindex mllsc -@opindex mno-llsc -Use (do not use) @samp{ll}, @samp{sc}, and @samp{sync} instructions to -implement atomic memory built-in functions. When neither option is -specified, GCC uses the instructions if the target architecture -supports them. - -@option{-mllsc} is useful if the runtime environment can emulate the -instructions and @option{-mno-llsc} can be useful when compiling for -nonstandard ISAs. You can make either option the default by -configuring GCC with @option{--with-llsc} and @option{--without-llsc} -respectively. @option{--with-llsc} is the default for some -configurations; see the installation documentation for details. - -@item -mdsp -@itemx -mno-dsp -@opindex mdsp -@opindex mno-dsp -Use (do not use) revision 1 of the MIPS DSP ASE@. -@xref{MIPS DSP Built-in Functions}. This option defines the -preprocessor macro @code{__mips_dsp}. It also defines -@code{__mips_dsp_rev} to 1. - -@item -mdspr2 -@itemx -mno-dspr2 -@opindex mdspr2 -@opindex mno-dspr2 -Use (do not use) revision 2 of the MIPS DSP ASE@. -@xref{MIPS DSP Built-in Functions}. This option defines the -preprocessor macros @code{__mips_dsp} and @code{__mips_dspr2}. -It also defines @code{__mips_dsp_rev} to 2. - -@item -msmartmips -@itemx -mno-smartmips -@opindex msmartmips -@opindex mno-smartmips -Use (do not use) the MIPS SmartMIPS ASE. - -@item -mpaired-single -@itemx -mno-paired-single -@opindex mpaired-single -@opindex mno-paired-single -Use (do not use) paired-single floating-point instructions. -@xref{MIPS Paired-Single Support}. This option requires -hardware floating-point support to be enabled. - -@item -mdmx -@itemx -mno-mdmx -@opindex mdmx -@opindex mno-mdmx -Use (do not use) MIPS Digital Media Extension instructions. -This option can only be used when generating 64-bit code and requires -hardware floating-point support to be enabled. - -@item -mips3d -@itemx -mno-mips3d -@opindex mips3d -@opindex mno-mips3d -Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}. -The option @option{-mips3d} implies @option{-mpaired-single}. - -@item -mmicromips -@itemx -mno-micromips -@opindex mmicromips -@opindex mno-mmicromips -Generate (do not generate) microMIPS code. - -MicroMIPS code generation can also be controlled on a per-function basis -by means of @code{micromips} and @code{nomicromips} attributes. -@xref{Function Attributes}, for more information. - -@item -mmt -@itemx -mno-mt -@opindex mmt -@opindex mno-mt -Use (do not use) MT Multithreading instructions. - -@item -mmcu -@itemx -mno-mcu -@opindex mmcu -@opindex mno-mcu -Use (do not use) the MIPS MCU ASE instructions. - -@item -meva -@itemx -mno-eva -@opindex meva -@opindex mno-eva -Use (do not use) the MIPS Enhanced Virtual Addressing instructions. - -@item -mvirt -@itemx -mno-virt -@opindex mvirt -@opindex mno-virt -Use (do not use) the MIPS Virtualization (VZ) instructions. - -@item -mxpa -@itemx -mno-xpa -@opindex mxpa -@opindex mno-xpa -Use (do not use) the MIPS eXtended Physical Address (XPA) instructions. - -@item -mcrc -@itemx -mno-crc -@opindex mcrc -@opindex mno-crc -Use (do not use) the MIPS Cyclic Redundancy Check (CRC) instructions. - -@item -mginv -@itemx -mno-ginv -@opindex mginv -@opindex mno-ginv -Use (do not use) the MIPS Global INValidate (GINV) instructions. - -@item -mloongson-mmi -@itemx -mno-loongson-mmi -@opindex mloongson-mmi -@opindex mno-loongson-mmi -Use (do not use) the MIPS Loongson MultiMedia extensions Instructions (MMI). - -@item -mloongson-ext -@itemx -mno-loongson-ext -@opindex mloongson-ext -@opindex mno-loongson-ext -Use (do not use) the MIPS Loongson EXTensions (EXT) instructions. - -@item -mloongson-ext2 -@itemx -mno-loongson-ext2 -@opindex mloongson-ext2 -@opindex mno-loongson-ext2 -Use (do not use) the MIPS Loongson EXTensions r2 (EXT2) instructions. - -@item -mlong64 -@opindex mlong64 -Force @code{long} types to be 64 bits wide. See @option{-mlong32} for -an explanation of the default and the way that the pointer size is -determined. - -@item -mlong32 -@opindex mlong32 -Force @code{long}, @code{int}, and pointer types to be 32 bits wide. - -The default size of @code{int}s, @code{long}s and pointers depends on -the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI -uses 64-bit @code{long}s, as does the 64-bit EABI; the others use -32-bit @code{long}s. Pointers are the same size as @code{long}s, -or the same size as integer registers, whichever is smaller. - -@item -msym32 -@itemx -mno-sym32 -@opindex msym32 -@opindex mno-sym32 -Assume (do not assume) that all symbols have 32-bit values, regardless -of the selected ABI@. This option is useful in combination with -@option{-mabi=64} and @option{-mno-abicalls} because it allows GCC -to generate shorter and faster references to symbolic addresses. - -@item -G @var{num} -@opindex G -Put definitions of externally-visible data in a small data section -if that data is no bigger than @var{num} bytes. GCC can then generate -more efficient accesses to the data; see @option{-mgpopt} for details. - -The default @option{-G} option depends on the configuration. - -@item -mlocal-sdata -@itemx -mno-local-sdata -@opindex mlocal-sdata -@opindex mno-local-sdata -Extend (do not extend) the @option{-G} behavior to local data too, -such as to static variables in C@. @option{-mlocal-sdata} is the -default for all configurations. - -If the linker complains that an application is using too much small data, -you might want to try rebuilding the less performance-critical parts with -@option{-mno-local-sdata}. You might also want to build large -libraries with @option{-mno-local-sdata}, so that the libraries leave -more room for the main program. - -@item -mextern-sdata -@itemx -mno-extern-sdata -@opindex mextern-sdata -@opindex mno-extern-sdata -Assume (do not assume) that externally-defined data is in -a small data section if the size of that data is within the @option{-G} limit. -@option{-mextern-sdata} is the default for all configurations. - -If you compile a module @var{Mod} with @option{-mextern-sdata} @option{-G -@var{num}} @option{-mgpopt}, and @var{Mod} references a variable @var{Var} -that is no bigger than @var{num} bytes, you must make sure that @var{Var} -is placed in a small data section. If @var{Var} is defined by another -module, you must either compile that module with a high-enough -@option{-G} setting or attach a @code{section} attribute to @var{Var}'s -definition. If @var{Var} is common, you must link the application -with a high-enough @option{-G} setting. - -The easiest way of satisfying these restrictions is to compile -and link every module with the same @option{-G} option. However, -you may wish to build a library that supports several different -small data limits. You can do this by compiling the library with -the highest supported @option{-G} setting and additionally using -@option{-mno-extern-sdata} to stop the library from making assumptions -about externally-defined data. - -@item -mgpopt -@itemx -mno-gpopt -@opindex mgpopt -@opindex mno-gpopt -Use (do not use) GP-relative accesses for symbols that are known to be -in a small data section; see @option{-G}, @option{-mlocal-sdata} and -@option{-mextern-sdata}. @option{-mgpopt} is the default for all -configurations. - -@option{-mno-gpopt} is useful for cases where the @code{$gp} register -might not hold the value of @code{_gp}. For example, if the code is -part of a library that might be used in a boot monitor, programs that -call boot monitor routines pass an unknown value in @code{$gp}. -(In such situations, the boot monitor itself is usually compiled -with @option{-G0}.) - -@option{-mno-gpopt} implies @option{-mno-local-sdata} and -@option{-mno-extern-sdata}. - -@item -membedded-data -@itemx -mno-embedded-data -@opindex membedded-data -@opindex mno-embedded-data -Allocate variables to the read-only data section first if possible, then -next in the small data section if possible, otherwise in data. This gives -slightly slower code than the default, but reduces the amount of RAM required -when executing, and thus may be preferred for some embedded systems. - -@item -muninit-const-in-rodata -@itemx -mno-uninit-const-in-rodata -@opindex muninit-const-in-rodata -@opindex mno-uninit-const-in-rodata -Put uninitialized @code{const} variables in the read-only data section. -This option is only meaningful in conjunction with @option{-membedded-data}. - -@item -mcode-readable=@var{setting} -@opindex mcode-readable -Specify whether GCC may generate code that reads from executable sections. -There are three possible settings: - -@table @gcctabopt -@item -mcode-readable=yes -Instructions may freely access executable sections. This is the -default setting. - -@item -mcode-readable=pcrel -MIPS16 PC-relative load instructions can access executable sections, -but other instructions must not do so. This option is useful on 4KSc -and 4KSd processors when the code TLBs have the Read Inhibit bit set. -It is also useful on processors that can be configured to have a dual -instruction/data SRAM interface and that, like the M4K, automatically -redirect PC-relative loads to the instruction RAM. - -@item -mcode-readable=no -Instructions must not access executable sections. This option can be -useful on targets that are configured to have a dual instruction/data -SRAM interface but that (unlike the M4K) do not automatically redirect -PC-relative loads to the instruction RAM. -@end table - -@item -msplit-addresses -@itemx -mno-split-addresses -@opindex msplit-addresses -@opindex mno-split-addresses -Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler -relocation operators. This option has been superseded by -@option{-mexplicit-relocs} but is retained for backwards compatibility. - -@item -mexplicit-relocs -@itemx -mno-explicit-relocs -@opindex mexplicit-relocs -@opindex mno-explicit-relocs -Use (do not use) assembler relocation operators when dealing with symbolic -addresses. The alternative, selected by @option{-mno-explicit-relocs}, -is to use assembler macros instead. - -@option{-mexplicit-relocs} is the default if GCC was configured -to use an assembler that supports relocation operators. - -@item -mcheck-zero-division -@itemx -mno-check-zero-division -@opindex mcheck-zero-division -@opindex mno-check-zero-division -Trap (do not trap) on integer division by zero. - -The default is @option{-mcheck-zero-division}. - -@item -mdivide-traps -@itemx -mdivide-breaks -@opindex mdivide-traps -@opindex mdivide-breaks -MIPS systems check for division by zero by generating either a -conditional trap or a break instruction. Using traps results in -smaller code, but is only supported on MIPS II and later. Also, some -versions of the Linux kernel have a bug that prevents trap from -generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to -allow conditional traps on architectures that support them and -@option{-mdivide-breaks} to force the use of breaks. - -The default is usually @option{-mdivide-traps}, but this can be -overridden at configure time using @option{--with-divide=breaks}. -Divide-by-zero checks can be completely disabled using -@option{-mno-check-zero-division}. - -@item -mload-store-pairs -@itemx -mno-load-store-pairs -@opindex mload-store-pairs -@opindex mno-load-store-pairs -Enable (disable) an optimization that pairs consecutive load or store -instructions to enable load/store bonding. This option is enabled by -default but only takes effect when the selected architecture is known -to support bonding. - -@item -munaligned-access -@itemx -mno-unaligned-access -@opindex munaligned-access -@opindex mno-unaligned-access -Enable (disable) direct unaligned access for MIPS Release 6. -MIPSr6 requires load/store unaligned-access support, -by hardware or trap&emulate. -So @option{-mno-unaligned-access} may be needed by kernel. - -@item -mmemcpy -@itemx -mno-memcpy -@opindex mmemcpy -@opindex mno-memcpy -Force (do not force) the use of @code{memcpy} for non-trivial block -moves. The default is @option{-mno-memcpy}, which allows GCC to inline -most constant-sized copies. - -@item -mlong-calls -@itemx -mno-long-calls -@opindex mlong-calls -@opindex mno-long-calls -Disable (do not disable) use of the @code{jal} instruction. Calling -functions using @code{jal} is more efficient but requires the caller -and callee to be in the same 256 megabyte segment. - -This option has no effect on abicalls code. The default is -@option{-mno-long-calls}. - -@item -mmad -@itemx -mno-mad -@opindex mmad -@opindex mno-mad -Enable (disable) use of the @code{mad}, @code{madu} and @code{mul} -instructions, as provided by the R4650 ISA@. - -@item -mimadd -@itemx -mno-imadd -@opindex mimadd -@opindex mno-imadd -Enable (disable) use of the @code{madd} and @code{msub} integer -instructions. The default is @option{-mimadd} on architectures -that support @code{madd} and @code{msub} except for the 74k -architecture where it was found to generate slower code. - -@item -mfused-madd -@itemx -mno-fused-madd -@opindex mfused-madd -@opindex mno-fused-madd -Enable (disable) use of the floating-point multiply-accumulate -instructions, when they are available. The default is -@option{-mfused-madd}. - -On the R8000 CPU when multiply-accumulate instructions are used, -the intermediate product is calculated to infinite precision -and is not subject to the FCSR Flush to Zero bit. This may be -undesirable in some circumstances. On other processors the result -is numerically identical to the equivalent computation using -separate multiply, add, subtract and negate instructions. - -@item -nocpp -@opindex nocpp -Tell the MIPS assembler to not run its preprocessor over user -assembler files (with a @samp{.s} suffix) when assembling them. - -@item -mfix-24k -@itemx -mno-fix-24k -@opindex mfix-24k -@opindex mno-fix-24k -Work around the 24K E48 (lost data on stores during refill) errata. -The workarounds are implemented by the assembler rather than by GCC@. - -@item -mfix-r4000 -@itemx -mno-fix-r4000 -@opindex mfix-r4000 -@opindex mno-fix-r4000 -Work around certain R4000 CPU errata: -@itemize @minus -@item -A double-word or a variable shift may give an incorrect result if executed -immediately after starting an integer division. -@item -A double-word or a variable shift may give an incorrect result if executed -while an integer multiplication is in progress. -@item -An integer division may give an incorrect result if started in a delay slot -of a taken branch or a jump. -@end itemize - -@item -mfix-r4400 -@itemx -mno-fix-r4400 -@opindex mfix-r4400 -@opindex mno-fix-r4400 -Work around certain R4400 CPU errata: -@itemize @minus -@item -A double-word or a variable shift may give an incorrect result if executed -immediately after starting an integer division. -@end itemize - -@item -mfix-r10000 -@itemx -mno-fix-r10000 -@opindex mfix-r10000 -@opindex mno-fix-r10000 -Work around certain R10000 errata: -@itemize @minus -@item -@code{ll}/@code{sc} sequences may not behave atomically on revisions -prior to 3.0. They may deadlock on revisions 2.6 and earlier. -@end itemize - -This option can only be used if the target architecture supports -branch-likely instructions. @option{-mfix-r10000} is the default when -@option{-march=r10000} is used; @option{-mno-fix-r10000} is the default -otherwise. - -@item -mfix-r5900 -@itemx -mno-fix-r5900 -@opindex mfix-r5900 -Do not attempt to schedule the preceding instruction into the delay slot -of a branch instruction placed at the end of a short loop of six -instructions or fewer and always schedule a @code{nop} instruction there -instead. The short loop bug under certain conditions causes loops to -execute only once or twice, due to a hardware bug in the R5900 chip. The -workaround is implemented by the assembler rather than by GCC@. - -@item -mfix-rm7000 -@itemx -mno-fix-rm7000 -@opindex mfix-rm7000 -Work around the RM7000 @code{dmult}/@code{dmultu} errata. The -workarounds are implemented by the assembler rather than by GCC@. - -@item -mfix-vr4120 -@itemx -mno-fix-vr4120 -@opindex mfix-vr4120 -Work around certain VR4120 errata: -@itemize @minus -@item -@code{dmultu} does not always produce the correct result. -@item -@code{div} and @code{ddiv} do not always produce the correct result if one -of the operands is negative. -@end itemize -The workarounds for the division errata rely on special functions in -@file{libgcc.a}. At present, these functions are only provided by -the @code{mips64vr*-elf} configurations. - -Other VR4120 errata require a NOP to be inserted between certain pairs of -instructions. These errata are handled by the assembler, not by GCC itself. - -@item -mfix-vr4130 -@opindex mfix-vr4130 -Work around the VR4130 @code{mflo}/@code{mfhi} errata. The -workarounds are implemented by the assembler rather than by GCC, -although GCC avoids using @code{mflo} and @code{mfhi} if the -VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi} -instructions are available instead. - -@item -mfix-sb1 -@itemx -mno-fix-sb1 -@opindex mfix-sb1 -Work around certain SB-1 CPU core errata. -(This flag currently works around the SB-1 revision 2 -``F1'' and ``F2'' floating-point errata.) - -@item -mr10k-cache-barrier=@var{setting} -@opindex mr10k-cache-barrier -Specify whether GCC should insert cache barriers to avoid the -side effects of speculation on R10K processors. - -In common with many processors, the R10K tries to predict the outcome -of a conditional branch and speculatively executes instructions from -the ``taken'' branch. It later aborts these instructions if the -predicted outcome is wrong. However, on the R10K, even aborted -instructions can have side effects. - -This problem only affects kernel stores and, depending on the system, -kernel loads. As an example, a speculatively-executed store may load -the target memory into cache and mark the cache line as dirty, even if -the store itself is later aborted. If a DMA operation writes to the -same area of memory before the ``dirty'' line is flushed, the cached -data overwrites the DMA-ed data. See the R10K processor manual -for a full description, including other potential problems. - -One workaround is to insert cache barrier instructions before every memory -access that might be speculatively executed and that might have side -effects even if aborted. @option{-mr10k-cache-barrier=@var{setting}} -controls GCC's implementation of this workaround. It assumes that -aborted accesses to any byte in the following regions does not have -side effects: - -@enumerate -@item -the memory occupied by the current function's stack frame; - -@item -the memory occupied by an incoming stack argument; - -@item -the memory occupied by an object with a link-time-constant address. -@end enumerate - -It is the kernel's responsibility to ensure that speculative -accesses to these regions are indeed safe. - -If the input program contains a function declaration such as: - -@smallexample -void foo (void); -@end smallexample - -then the implementation of @code{foo} must allow @code{j foo} and -@code{jal foo} to be executed speculatively. GCC honors this -restriction for functions it compiles itself. It expects non-GCC -functions (such as hand-written assembly code) to do the same. - -The option has three forms: - -@table @gcctabopt -@item -mr10k-cache-barrier=load-store -Insert a cache barrier before a load or store that might be -speculatively executed and that might have side effects even -if aborted. - -@item -mr10k-cache-barrier=store -Insert a cache barrier before a store that might be speculatively -executed and that might have side effects even if aborted. - -@item -mr10k-cache-barrier=none -Disable the insertion of cache barriers. This is the default setting. -@end table - -@item -mflush-func=@var{func} -@itemx -mno-flush-func -@opindex mflush-func -Specifies the function to call to flush the I and D caches, or to not -call any such function. If called, the function must take the same -arguments as the common @code{_flush_func}, that is, the address of the -memory range for which the cache is being flushed, the size of the -memory range, and the number 3 (to flush both caches). The default -depends on the target GCC was configured for, but commonly is either -@code{_flush_func} or @code{__cpu_flush}. - -@item mbranch-cost=@var{num} -@opindex mbranch-cost -Set the cost of branches to roughly @var{num} ``simple'' instructions. -This cost is only a heuristic and is not guaranteed to produce -consistent results across releases. A zero cost redundantly selects -the default, which is based on the @option{-mtune} setting. - -@item -mbranch-likely -@itemx -mno-branch-likely -@opindex mbranch-likely -@opindex mno-branch-likely -Enable or disable use of Branch Likely instructions, regardless of the -default for the selected architecture. By default, Branch Likely -instructions may be generated if they are supported by the selected -architecture. An exception is for the MIPS32 and MIPS64 architectures -and processors that implement those architectures; for those, Branch -Likely instructions are not be generated by default because the MIPS32 -and MIPS64 architectures specifically deprecate their use. - -@item -mcompact-branches=never -@itemx -mcompact-branches=optimal -@itemx -mcompact-branches=always -@opindex mcompact-branches=never -@opindex mcompact-branches=optimal -@opindex mcompact-branches=always -These options control which form of branches will be generated. The -default is @option{-mcompact-branches=optimal}. - -The @option{-mcompact-branches=never} option ensures that compact branch -instructions will never be generated. - -The @option{-mcompact-branches=always} option ensures that a compact -branch instruction will be generated if available for MIPS Release 6 onwards. -If a compact branch instruction is not available (or pre-R6), -a delay slot form of the branch will be used instead. - -If it is used for MIPS16/microMIPS targets, it will be just ignored now. -The behaviour for MIPS16/microMIPS may change in future, -since they do have some compact branch instructions. - -The @option{-mcompact-branches=optimal} option will cause a delay slot -branch to be used if one is available in the current ISA and the delay -slot is successfully filled. If the delay slot is not filled, a compact -branch will be chosen if one is available. - -@item -mfp-exceptions -@itemx -mno-fp-exceptions -@opindex mfp-exceptions -Specifies whether FP exceptions are enabled. This affects how -FP instructions are scheduled for some processors. -The default is that FP exceptions are -enabled. - -For instance, on the SB-1, if FP exceptions are disabled, and we are emitting -64-bit code, then we can use both FP pipes. Otherwise, we can only use one -FP pipe. - -@item -mvr4130-align -@itemx -mno-vr4130-align -@opindex mvr4130-align -The VR4130 pipeline is two-way superscalar, but can only issue two -instructions together if the first one is 8-byte aligned. When this -option is enabled, GCC aligns pairs of instructions that it -thinks should execute in parallel. - -This option only has an effect when optimizing for the VR4130. -It normally makes code faster, but at the expense of making it bigger. -It is enabled by default at optimization level @option{-O3}. - -@item -msynci -@itemx -mno-synci -@opindex msynci -Enable (disable) generation of @code{synci} instructions on -architectures that support it. The @code{synci} instructions (if -enabled) are generated when @code{__builtin___clear_cache} is -compiled. - -This option defaults to @option{-mno-synci}, but the default can be -overridden by configuring GCC with @option{--with-synci}. - -When compiling code for single processor systems, it is generally safe -to use @code{synci}. However, on many multi-core (SMP) systems, it -does not invalidate the instruction caches on all cores and may lead -to undefined behavior. - -@item -mrelax-pic-calls -@itemx -mno-relax-pic-calls -@opindex mrelax-pic-calls -Try to turn PIC calls that are normally dispatched via register -@code{$25} into direct calls. This is only possible if the linker can -resolve the destination at link time and if the destination is within -range for a direct call. - -@option{-mrelax-pic-calls} is the default if GCC was configured to use -an assembler and a linker that support the @code{.reloc} assembly -directive and @option{-mexplicit-relocs} is in effect. With -@option{-mno-explicit-relocs}, this optimization can be performed by the -assembler and the linker alone without help from the compiler. - -@item -mmcount-ra-address -@itemx -mno-mcount-ra-address -@opindex mmcount-ra-address -@opindex mno-mcount-ra-address -Emit (do not emit) code that allows @code{_mcount} to modify the -calling function's return address. When enabled, this option extends -the usual @code{_mcount} interface with a new @var{ra-address} -parameter, which has type @code{intptr_t *} and is passed in register -@code{$12}. @code{_mcount} can then modify the return address by -doing both of the following: -@itemize -@item -Returning the new address in register @code{$31}. -@item -Storing the new address in @code{*@var{ra-address}}, -if @var{ra-address} is nonnull. -@end itemize - -The default is @option{-mno-mcount-ra-address}. - -@item -mframe-header-opt -@itemx -mno-frame-header-opt -@opindex mframe-header-opt -Enable (disable) frame header optimization in the o32 ABI. When using the -o32 ABI, calling functions will allocate 16 bytes on the stack for the called -function to write out register arguments. When enabled, this optimization -will suppress the allocation of the frame header if it can be determined that -it is unused. - -This optimization is off by default at all optimization levels. - -@item -mlxc1-sxc1 -@itemx -mno-lxc1-sxc1 -@opindex mlxc1-sxc1 -When applicable, enable (disable) the generation of @code{lwxc1}, -@code{swxc1}, @code{ldxc1}, @code{sdxc1} instructions. Enabled by default. - -@item -mmadd4 -@itemx -mno-madd4 -@opindex mmadd4 -When applicable, enable (disable) the generation of 4-operand @code{madd.s}, -@code{madd.d} and related instructions. Enabled by default. - -@end table - -@node MMIX Options -@subsection MMIX Options -@cindex MMIX Options - -These options are defined for the MMIX: - -@table @gcctabopt -@item -mlibfuncs -@itemx -mno-libfuncs -@opindex mlibfuncs -@opindex mno-libfuncs -Specify that intrinsic library functions are being compiled, passing all -values in registers, no matter the size. - -@item -mepsilon -@itemx -mno-epsilon -@opindex mepsilon -@opindex mno-epsilon -Generate floating-point comparison instructions that compare with respect -to the @code{rE} epsilon register. - -@item -mabi=mmixware -@itemx -mabi=gnu -@opindex mabi=mmixware -@opindex mabi=gnu -Generate code that passes function parameters and return values that (in -the called function) are seen as registers @code{$0} and up, as opposed to -the GNU ABI which uses global registers @code{$231} and up. - -@item -mzero-extend -@itemx -mno-zero-extend -@opindex mzero-extend -@opindex mno-zero-extend -When reading data from memory in sizes shorter than 64 bits, use (do not -use) zero-extending load instructions by default, rather than -sign-extending ones. - -@item -mknuthdiv -@itemx -mno-knuthdiv -@opindex mknuthdiv -@opindex mno-knuthdiv -Make the result of a division yielding a remainder have the same sign as -the divisor. With the default, @option{-mno-knuthdiv}, the sign of the -remainder follows the sign of the dividend. Both methods are -arithmetically valid, the latter being almost exclusively used. - -@item -mtoplevel-symbols -@itemx -mno-toplevel-symbols -@opindex mtoplevel-symbols -@opindex mno-toplevel-symbols -Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly -code can be used with the @code{PREFIX} assembly directive. - -@item -melf -@opindex melf -Generate an executable in the ELF format, rather than the default -@samp{mmo} format used by the @command{mmix} simulator. - -@item -mbranch-predict -@itemx -mno-branch-predict -@opindex mbranch-predict -@opindex mno-branch-predict -Use (do not use) the probable-branch instructions, when static branch -prediction indicates a probable branch. - -@item -mbase-addresses -@itemx -mno-base-addresses -@opindex mbase-addresses -@opindex mno-base-addresses -Generate (do not generate) code that uses @emph{base addresses}. Using a -base address automatically generates a request (handled by the assembler -and the linker) for a constant to be set up in a global register. The -register is used for one or more base address requests within the range 0 -to 255 from the value held in the register. The generally leads to short -and fast code, but the number of different data items that can be -addressed is limited. This means that a program that uses lots of static -data may require @option{-mno-base-addresses}. - -@item -msingle-exit -@itemx -mno-single-exit -@opindex msingle-exit -@opindex mno-single-exit -Force (do not force) generated code to have a single exit point in each -function. -@end table - -@node MN10300 Options -@subsection MN10300 Options -@cindex MN10300 options - -These @option{-m} options are defined for Matsushita MN10300 architectures: - -@table @gcctabopt -@item -mmult-bug -@opindex mmult-bug -Generate code to avoid bugs in the multiply instructions for the MN10300 -processors. This is the default. - -@item -mno-mult-bug -@opindex mno-mult-bug -Do not generate code to avoid bugs in the multiply instructions for the -MN10300 processors. - -@item -mam33 -@opindex mam33 -Generate code using features specific to the AM33 processor. - -@item -mno-am33 -@opindex mno-am33 -Do not generate code using features specific to the AM33 processor. This -is the default. - -@item -mam33-2 -@opindex mam33-2 -Generate code using features specific to the AM33/2.0 processor. - -@item -mam34 -@opindex mam34 -Generate code using features specific to the AM34 processor. - -@item -mtune=@var{cpu-type} -@opindex mtune -Use the timing characteristics of the indicated CPU type when -scheduling instructions. This does not change the targeted processor -type. The CPU type must be one of @samp{mn10300}, @samp{am33}, -@samp{am33-2} or @samp{am34}. - -@item -mreturn-pointer-on-d0 -@opindex mreturn-pointer-on-d0 -When generating a function that returns a pointer, return the pointer -in both @code{a0} and @code{d0}. Otherwise, the pointer is returned -only in @code{a0}, and attempts to call such functions without a prototype -result in errors. Note that this option is on by default; use -@option{-mno-return-pointer-on-d0} to disable it. - -@item -mno-crt0 -@opindex mno-crt0 -Do not link in the C run-time initialization object file. - -@item -mrelax -@opindex mrelax -Indicate to the linker that it should perform a relaxation optimization pass -to shorten branches, calls and absolute memory addresses. This option only -has an effect when used on the command line for the final link step. - -This option makes symbolic debugging impossible. - -@item -mliw -@opindex mliw -Allow the compiler to generate @emph{Long Instruction Word} -instructions if the target is the @samp{AM33} or later. This is the -default. This option defines the preprocessor macro @code{__LIW__}. - -@item -mno-liw -@opindex mno-liw -Do not allow the compiler to generate @emph{Long Instruction Word} -instructions. This option defines the preprocessor macro -@code{__NO_LIW__}. - -@item -msetlb -@opindex msetlb -Allow the compiler to generate the @emph{SETLB} and @emph{Lcc} -instructions if the target is the @samp{AM33} or later. This is the -default. This option defines the preprocessor macro @code{__SETLB__}. - -@item -mno-setlb -@opindex mno-setlb -Do not allow the compiler to generate @emph{SETLB} or @emph{Lcc} -instructions. This option defines the preprocessor macro -@code{__NO_SETLB__}. - -@end table - -@node Moxie Options -@subsection Moxie Options -@cindex Moxie Options - -@table @gcctabopt - -@item -meb -@opindex meb -Generate big-endian code. This is the default for @samp{moxie-*-*} -configurations. - -@item -mel -@opindex mel -Generate little-endian code. - -@item -mmul.x -@opindex mmul.x -Generate mul.x and umul.x instructions. This is the default for -@samp{moxiebox-*-*} configurations. - -@item -mno-crt0 -@opindex mno-crt0 -Do not link in the C run-time initialization object file. - -@end table - -@node MSP430 Options -@subsection MSP430 Options -@cindex MSP430 Options - -These options are defined for the MSP430: - -@table @gcctabopt - -@item -masm-hex -@opindex masm-hex -Force assembly output to always use hex constants. Normally such -constants are signed decimals, but this option is available for -testsuite and/or aesthetic purposes. - -@item -mmcu= -@opindex mmcu= -Select the MCU to target. This is used to create a C preprocessor -symbol based upon the MCU name, converted to upper case and pre- and -post-fixed with @samp{__}. This in turn is used by the -@file{msp430.h} header file to select an MCU-specific supplementary -header file. - -The option also sets the ISA to use. If the MCU name is one that is -known to only support the 430 ISA then that is selected, otherwise the -430X ISA is selected. A generic MCU name of @samp{msp430} can also be -used to select the 430 ISA. Similarly the generic @samp{msp430x} MCU -name selects the 430X ISA. - -In addition an MCU-specific linker script is added to the linker -command line. The script's name is the name of the MCU with -@file{.ld} appended. Thus specifying @option{-mmcu=xxx} on the @command{gcc} -command line defines the C preprocessor symbol @code{__XXX__} and -cause the linker to search for a script called @file{xxx.ld}. - -The ISA and hardware multiply supported for the different MCUs is hard-coded -into GCC. However, an external @samp{devices.csv} file can be used to -extend device support beyond those that have been hard-coded. - -GCC searches for the @samp{devices.csv} file using the following methods in the -given precedence order, where the first method takes precendence over the -second which takes precedence over the third. - -@table @asis -@item Include path specified with @code{-I} and @code{-L} -@samp{devices.csv} will be searched for in each of the directories specified by -include paths and linker library search paths. -@item Path specified by the environment variable @samp{MSP430_GCC_INCLUDE_DIR} -Define the value of the global environment variable -@samp{MSP430_GCC_INCLUDE_DIR} -to the full path to the directory containing devices.csv, and GCC will search -this directory for devices.csv. If devices.csv is found, this directory will -also be registered as an include path, and linker library path. Header files -and linker scripts in this directory can therefore be used without manually -specifying @code{-I} and @code{-L} on the command line. -@item The @samp{msp430-elf@{,bare@}/include/devices} directory -Finally, GCC will examine @samp{msp430-elf@{,bare@}/include/devices} from the -toolchain root directory. This directory does not exist in a default -installation, but if the user has created it and copied @samp{devices.csv} -there, then the MCU data will be read. As above, this directory will -also be registered as an include path, and linker library path. - -@end table -If none of the above search methods find @samp{devices.csv}, then the -hard-coded MCU data is used. - - -@item -mwarn-mcu -@itemx -mno-warn-mcu -@opindex mwarn-mcu -@opindex mno-warn-mcu -This option enables or disables warnings about conflicts between the -MCU name specified by the @option{-mmcu} option and the ISA set by the -@option{-mcpu} option and/or the hardware multiply support set by the -@option{-mhwmult} option. It also toggles warnings about unrecognized -MCU names. This option is on by default. - -@item -mcpu= -@opindex mcpu= -Specifies the ISA to use. Accepted values are @samp{msp430}, -@samp{msp430x} and @samp{msp430xv2}. This option is deprecated. The -@option{-mmcu=} option should be used to select the ISA. - -@item -msim -@opindex msim -Link to the simulator runtime libraries and linker script. Overrides -any scripts that would be selected by the @option{-mmcu=} option. - -@item -mlarge -@opindex mlarge -Use large-model addressing (20-bit pointers, 20-bit @code{size_t}). - -@item -msmall -@opindex msmall -Use small-model addressing (16-bit pointers, 16-bit @code{size_t}). - -@item -mrelax -@opindex mrelax -This option is passed to the assembler and linker, and allows the -linker to perform certain optimizations that cannot be done until -the final link. - -@item mhwmult= -@opindex mhwmult= -Describes the type of hardware multiply supported by the target. -Accepted values are @samp{none} for no hardware multiply, @samp{16bit} -for the original 16-bit-only multiply supported by early MCUs. -@samp{32bit} for the 16/32-bit multiply supported by later MCUs and -@samp{f5series} for the 16/32-bit multiply supported by F5-series MCUs. -A value of @samp{auto} can also be given. This tells GCC to deduce -the hardware multiply support based upon the MCU name provided by the -@option{-mmcu} option. If no @option{-mmcu} option is specified or if -the MCU name is not recognized then no hardware multiply support is -assumed. @code{auto} is the default setting. - -Hardware multiplies are normally performed by calling a library -routine. This saves space in the generated code. When compiling at -@option{-O3} or higher however the hardware multiplier is invoked -inline. This makes for bigger, but faster code. - -The hardware multiply routines disable interrupts whilst running and -restore the previous interrupt state when they finish. This makes -them safe to use inside interrupt handlers as well as in normal code. - -@item -minrt -@opindex minrt -Enable the use of a minimum runtime environment - no static -initializers or constructors. This is intended for memory-constrained -devices. The compiler includes special symbols in some objects -that tell the linker and runtime which code fragments are required. - -@item -mtiny-printf -@opindex mtiny-printf -Enable reduced code size @code{printf} and @code{puts} library functions. -The @samp{tiny} implementations of these functions are not reentrant, so -must be used with caution in multi-threaded applications. - -Support for streams has been removed and the string to be printed will -always be sent to stdout via the @code{write} syscall. The string is not -buffered before it is sent to write. - -This option requires Newlib Nano IO, so GCC must be configured with -@samp{--enable-newlib-nano-formatted-io}. - -@item -mmax-inline-shift= -@opindex mmax-inline-shift= -This option takes an integer between 0 and 64 inclusive, and sets -the maximum number of inline shift instructions which should be emitted to -perform a shift operation by a constant amount. When this value needs to be -exceeded, an mspabi helper function is used instead. The default value is 4. - -This only affects cases where a shift by multiple positions cannot be -completed with a single instruction (e.g. all shifts >1 on the 430 ISA). - -Shifts of a 32-bit value are at least twice as costly, so the value passed for -this option is divided by 2 and the resulting value used instead. - -@item -mcode-region= -@itemx -mdata-region= -@opindex mcode-region -@opindex mdata-region -These options tell the compiler where to place functions and data that -do not have one of the @code{lower}, @code{upper}, @code{either} or -@code{section} attributes. Possible values are @code{lower}, -@code{upper}, @code{either} or @code{any}. The first three behave -like the corresponding attribute. The fourth possible value - -@code{any} - is the default. It leaves placement entirely up to the -linker script and how it assigns the standard sections -(@code{.text}, @code{.data}, etc) to the memory regions. - -@item -msilicon-errata= -@opindex msilicon-errata -This option passes on a request to assembler to enable the fixes for -the named silicon errata. - -@item -msilicon-errata-warn= -@opindex msilicon-errata-warn -This option passes on a request to the assembler to enable warning -messages when a silicon errata might need to be applied. - -@item -mwarn-devices-csv -@itemx -mno-warn-devices-csv -@opindex mwarn-devices-csv -@opindex mno-warn-devices-csv -Warn if @samp{devices.csv} is not found or there are problem parsing it -(default: on). - -@end table - -@node NDS32 Options -@subsection NDS32 Options -@cindex NDS32 Options - -These options are defined for NDS32 implementations: - -@table @gcctabopt - -@item -mbig-endian -@opindex mbig-endian -Generate code in big-endian mode. - -@item -mlittle-endian -@opindex mlittle-endian -Generate code in little-endian mode. - -@item -mreduced-regs -@opindex mreduced-regs -Use reduced-set registers for register allocation. - -@item -mfull-regs -@opindex mfull-regs -Use full-set registers for register allocation. - -@item -mcmov -@opindex mcmov -Generate conditional move instructions. - -@item -mno-cmov -@opindex mno-cmov -Do not generate conditional move instructions. - -@item -mext-perf -@opindex mext-perf -Generate performance extension instructions. - -@item -mno-ext-perf -@opindex mno-ext-perf -Do not generate performance extension instructions. - -@item -mext-perf2 -@opindex mext-perf2 -Generate performance extension 2 instructions. - -@item -mno-ext-perf2 -@opindex mno-ext-perf2 -Do not generate performance extension 2 instructions. - -@item -mext-string -@opindex mext-string -Generate string extension instructions. - -@item -mno-ext-string -@opindex mno-ext-string -Do not generate string extension instructions. - -@item -mv3push -@opindex mv3push -Generate v3 push25/pop25 instructions. - -@item -mno-v3push -@opindex mno-v3push -Do not generate v3 push25/pop25 instructions. - -@item -m16-bit -@opindex m16-bit -Generate 16-bit instructions. - -@item -mno-16-bit -@opindex mno-16-bit -Do not generate 16-bit instructions. - -@item -misr-vector-size=@var{num} -@opindex misr-vector-size -Specify the size of each interrupt vector, which must be 4 or 16. - -@item -mcache-block-size=@var{num} -@opindex mcache-block-size -Specify the size of each cache block, -which must be a power of 2 between 4 and 512. - -@item -march=@var{arch} -@opindex march -Specify the name of the target architecture. - -@item -mcmodel=@var{code-model} -@opindex mcmodel -Set the code model to one of -@table @asis -@item @samp{small} -All the data and read-only data segments must be within 512KB addressing space. -The text segment must be within 16MB addressing space. -@item @samp{medium} -The data segment must be within 512KB while the read-only data segment can be -within 4GB addressing space. The text segment should be still within 16MB -addressing space. -@item @samp{large} -All the text and data segments can be within 4GB addressing space. -@end table - -@item -mctor-dtor -@opindex mctor-dtor -Enable constructor/destructor feature. - -@item -mrelax -@opindex mrelax -Guide linker to relax instructions. - -@end table - -@node Nios II Options -@subsection Nios II Options -@cindex Nios II options -@cindex Altera Nios II options - -These are the options defined for the Altera Nios II processor. - -@table @gcctabopt - -@item -G @var{num} -@opindex G -@cindex smaller data references -Put global and static objects less than or equal to @var{num} bytes -into the small data or BSS sections instead of the normal data or BSS -sections. The default value of @var{num} is 8. - -@item -mgpopt=@var{option} -@itemx -mgpopt -@itemx -mno-gpopt -@opindex mgpopt -@opindex mno-gpopt -Generate (do not generate) GP-relative accesses. The following -@var{option} names are recognized: - -@table @samp - -@item none -Do not generate GP-relative accesses. - -@item local -Generate GP-relative accesses for small data objects that are not -external, weak, or uninitialized common symbols. -Also use GP-relative addressing for objects that -have been explicitly placed in a small data section via a @code{section} -attribute. - -@item global -As for @samp{local}, but also generate GP-relative accesses for -small data objects that are external, weak, or common. If you use this option, -you must ensure that all parts of your program (including libraries) are -compiled with the same @option{-G} setting. - -@item data -Generate GP-relative accesses for all data objects in the program. If you -use this option, the entire data and BSS segments -of your program must fit in 64K of memory and you must use an appropriate -linker script to allocate them within the addressable range of the -global pointer. - -@item all -Generate GP-relative addresses for function pointers as well as data -pointers. If you use this option, the entire text, data, and BSS segments -of your program must fit in 64K of memory and you must use an appropriate -linker script to allocate them within the addressable range of the -global pointer. - -@end table - -@option{-mgpopt} is equivalent to @option{-mgpopt=local}, and -@option{-mno-gpopt} is equivalent to @option{-mgpopt=none}. - -The default is @option{-mgpopt} except when @option{-fpic} or -@option{-fPIC} is specified to generate position-independent code. -Note that the Nios II ABI does not permit GP-relative accesses from -shared libraries. - -You may need to specify @option{-mno-gpopt} explicitly when building -programs that include large amounts of small data, including large -GOT data sections. In this case, the 16-bit offset for GP-relative -addressing may not be large enough to allow access to the entire -small data section. - -@item -mgprel-sec=@var{regexp} -@opindex mgprel-sec -This option specifies additional section names that can be accessed via -GP-relative addressing. It is most useful in conjunction with -@code{section} attributes on variable declarations -(@pxref{Common Variable Attributes}) and a custom linker script. -The @var{regexp} is a POSIX Extended Regular Expression. - -This option does not affect the behavior of the @option{-G} option, and -the specified sections are in addition to the standard @code{.sdata} -and @code{.sbss} small-data sections that are recognized by @option{-mgpopt}. - -@item -mr0rel-sec=@var{regexp} -@opindex mr0rel-sec -This option specifies names of sections that can be accessed via a -16-bit offset from @code{r0}; that is, in the low 32K or high 32K -of the 32-bit address space. It is most useful in conjunction with -@code{section} attributes on variable declarations -(@pxref{Common Variable Attributes}) and a custom linker script. -The @var{regexp} is a POSIX Extended Regular Expression. - -In contrast to the use of GP-relative addressing for small data, -zero-based addressing is never generated by default and there are no -conventional section names used in standard linker scripts for sections -in the low or high areas of memory. - -@item -mel -@itemx -meb -@opindex mel -@opindex meb -Generate little-endian (default) or big-endian (experimental) code, -respectively. - -@item -march=@var{arch} -@opindex march -This specifies the name of the target Nios II architecture. GCC uses this -name to determine what kind of instructions it can emit when generating -assembly code. Permissible names are: @samp{r1}, @samp{r2}. - -The preprocessor macro @code{__nios2_arch__} is available to programs, -with value 1 or 2, indicating the targeted ISA level. - -@item -mbypass-cache -@itemx -mno-bypass-cache -@opindex mno-bypass-cache -@opindex mbypass-cache -Force all load and store instructions to always bypass cache by -using I/O variants of the instructions. The default is not to -bypass the cache. - -@item -mno-cache-volatile -@itemx -mcache-volatile -@opindex mcache-volatile -@opindex mno-cache-volatile -Volatile memory access bypass the cache using the I/O variants of -the load and store instructions. The default is not to bypass the cache. - -@item -mno-fast-sw-div -@itemx -mfast-sw-div -@opindex mno-fast-sw-div -@opindex mfast-sw-div -Do not use table-based fast divide for small numbers. The default -is to use the fast divide at @option{-O3} and above. - -@item -mno-hw-mul -@itemx -mhw-mul -@itemx -mno-hw-mulx -@itemx -mhw-mulx -@itemx -mno-hw-div -@itemx -mhw-div -@opindex mno-hw-mul -@opindex mhw-mul -@opindex mno-hw-mulx -@opindex mhw-mulx -@opindex mno-hw-div -@opindex mhw-div -Enable or disable emitting @code{mul}, @code{mulx} and @code{div} family of -instructions by the compiler. The default is to emit @code{mul} -and not emit @code{div} and @code{mulx}. - -@item -mbmx -@itemx -mno-bmx -@itemx -mcdx -@itemx -mno-cdx -Enable or disable generation of Nios II R2 BMX (bit manipulation) and -CDX (code density) instructions. Enabling these instructions also -requires @option{-march=r2}. Since these instructions are optional -extensions to the R2 architecture, the default is not to emit them. - -@item -mcustom-@var{insn}=@var{N} -@itemx -mno-custom-@var{insn} -@opindex mcustom-@var{insn} -@opindex mno-custom-@var{insn} -Each @option{-mcustom-@var{insn}=@var{N}} option enables use of a -custom instruction with encoding @var{N} when generating code that uses -@var{insn}. For example, @option{-mcustom-fadds=253} generates custom -instruction 253 for single-precision floating-point add operations instead -of the default behavior of using a library call. - -The following values of @var{insn} are supported. Except as otherwise -noted, floating-point operations are expected to be implemented with -normal IEEE 754 semantics and correspond directly to the C operators or the -equivalent GCC built-in functions (@pxref{Other Builtins}). - -Single-precision floating point: -@table @asis - -@item @samp{fadds}, @samp{fsubs}, @samp{fdivs}, @samp{fmuls} -Binary arithmetic operations. - -@item @samp{fnegs} -Unary negation. - -@item @samp{fabss} -Unary absolute value. - -@item @samp{fcmpeqs}, @samp{fcmpges}, @samp{fcmpgts}, @samp{fcmples}, @samp{fcmplts}, @samp{fcmpnes} -Comparison operations. - -@item @samp{fmins}, @samp{fmaxs} -Floating-point minimum and maximum. These instructions are only -generated if @option{-ffinite-math-only} is specified. - -@item @samp{fsqrts} -Unary square root operation. - -@item @samp{fcoss}, @samp{fsins}, @samp{ftans}, @samp{fatans}, @samp{fexps}, @samp{flogs} -Floating-point trigonometric and exponential functions. These instructions -are only generated if @option{-funsafe-math-optimizations} is also specified. - -@end table - -Double-precision floating point: -@table @asis - -@item @samp{faddd}, @samp{fsubd}, @samp{fdivd}, @samp{fmuld} -Binary arithmetic operations. - -@item @samp{fnegd} -Unary negation. - -@item @samp{fabsd} -Unary absolute value. - -@item @samp{fcmpeqd}, @samp{fcmpged}, @samp{fcmpgtd}, @samp{fcmpled}, @samp{fcmpltd}, @samp{fcmpned} -Comparison operations. - -@item @samp{fmind}, @samp{fmaxd} -Double-precision minimum and maximum. These instructions are only -generated if @option{-ffinite-math-only} is specified. - -@item @samp{fsqrtd} -Unary square root operation. - -@item @samp{fcosd}, @samp{fsind}, @samp{ftand}, @samp{fatand}, @samp{fexpd}, @samp{flogd} -Double-precision trigonometric and exponential functions. These instructions -are only generated if @option{-funsafe-math-optimizations} is also specified. - -@end table - -Conversions: -@table @asis -@item @samp{fextsd} -Conversion from single precision to double precision. - -@item @samp{ftruncds} -Conversion from double precision to single precision. - -@item @samp{fixsi}, @samp{fixsu}, @samp{fixdi}, @samp{fixdu} -Conversion from floating point to signed or unsigned integer types, with -truncation towards zero. - -@item @samp{round} -Conversion from single-precision floating point to signed integer, -rounding to the nearest integer and ties away from zero. -This corresponds to the @code{__builtin_lroundf} function when -@option{-fno-math-errno} is used. - -@item @samp{floatis}, @samp{floatus}, @samp{floatid}, @samp{floatud} -Conversion from signed or unsigned integer types to floating-point types. - -@end table - -In addition, all of the following transfer instructions for internal -registers X and Y must be provided to use any of the double-precision -floating-point instructions. Custom instructions taking two -double-precision source operands expect the first operand in the -64-bit register X. The other operand (or only operand of a unary -operation) is given to the custom arithmetic instruction with the -least significant half in source register @var{src1} and the most -significant half in @var{src2}. A custom instruction that returns a -double-precision result returns the most significant 32 bits in the -destination register and the other half in 32-bit register Y. -GCC automatically generates the necessary code sequences to write -register X and/or read register Y when double-precision floating-point -instructions are used. - -@table @asis - -@item @samp{fwrx} -Write @var{src1} into the least significant half of X and @var{src2} into -the most significant half of X. - -@item @samp{fwry} -Write @var{src1} into Y. - -@item @samp{frdxhi}, @samp{frdxlo} -Read the most or least (respectively) significant half of X and store it in -@var{dest}. - -@item @samp{frdy} -Read the value of Y and store it into @var{dest}. -@end table - -Note that you can gain more local control over generation of Nios II custom -instructions by using the @code{target("custom-@var{insn}=@var{N}")} -and @code{target("no-custom-@var{insn}")} function attributes -(@pxref{Function Attributes}) -or pragmas (@pxref{Function Specific Option Pragmas}). - -@item -mcustom-fpu-cfg=@var{name} -@opindex mcustom-fpu-cfg - -This option enables a predefined, named set of custom instruction encodings -(see @option{-mcustom-@var{insn}} above). -Currently, the following sets are defined: - -@option{-mcustom-fpu-cfg=60-1} is equivalent to: -@gccoptlist{-mcustom-fmuls=252 @gol --mcustom-fadds=253 @gol --mcustom-fsubs=254 @gol --fsingle-precision-constant} - -@option{-mcustom-fpu-cfg=60-2} is equivalent to: -@gccoptlist{-mcustom-fmuls=252 @gol --mcustom-fadds=253 @gol --mcustom-fsubs=254 @gol --mcustom-fdivs=255 @gol --fsingle-precision-constant} - -@option{-mcustom-fpu-cfg=72-3} is equivalent to: -@gccoptlist{-mcustom-floatus=243 @gol --mcustom-fixsi=244 @gol --mcustom-floatis=245 @gol --mcustom-fcmpgts=246 @gol --mcustom-fcmples=249 @gol --mcustom-fcmpeqs=250 @gol --mcustom-fcmpnes=251 @gol --mcustom-fmuls=252 @gol --mcustom-fadds=253 @gol --mcustom-fsubs=254 @gol --mcustom-fdivs=255 @gol --fsingle-precision-constant} - -@option{-mcustom-fpu-cfg=fph2} is equivalent to: -@gccoptlist{-mcustom-fabss=224 @gol --mcustom-fnegs=225 @gol --mcustom-fcmpnes=226 @gol --mcustom-fcmpeqs=227 @gol --mcustom-fcmpges=228 @gol --mcustom-fcmpgts=229 @gol --mcustom-fcmples=230 @gol --mcustom-fcmplts=231 @gol --mcustom-fmaxs=232 @gol --mcustom-fmins=233 @gol --mcustom-round=248 @gol --mcustom-fixsi=249 @gol --mcustom-floatis=250 @gol --mcustom-fsqrts=251 @gol --mcustom-fmuls=252 @gol --mcustom-fadds=253 @gol --mcustom-fsubs=254 @gol --mcustom-fdivs=255 @gol} - -Custom instruction assignments given by individual -@option{-mcustom-@var{insn}=} options override those given by -@option{-mcustom-fpu-cfg=}, regardless of the -order of the options on the command line. - -Note that you can gain more local control over selection of a FPU -configuration by using the @code{target("custom-fpu-cfg=@var{name}")} -function attribute (@pxref{Function Attributes}) -or pragma (@pxref{Function Specific Option Pragmas}). - -The name @var{fph2} is an abbreviation for @emph{Nios II Floating Point -Hardware 2 Component}. Please note that the custom instructions enabled by -@option{-mcustom-fmins=233} and @option{-mcustom-fmaxs=234} are only generated -if @option{-ffinite-math-only} is specified. The custom instruction enabled by -@option{-mcustom-round=248} is only generated if @option{-fno-math-errno} is -specified. In contrast to the other configurations, -@option{-fsingle-precision-constant} is not set. - -@end table - -These additional @samp{-m} options are available for the Altera Nios II -ELF (bare-metal) target: - -@table @gcctabopt - -@item -mhal -@opindex mhal -Link with HAL BSP. This suppresses linking with the GCC-provided C runtime -startup and termination code, and is typically used in conjunction with -@option{-msys-crt0=} to specify the location of the alternate startup code -provided by the HAL BSP. - -@item -msmallc -@opindex msmallc -Link with a limited version of the C library, @option{-lsmallc}, rather than -Newlib. - -@item -msys-crt0=@var{startfile} -@opindex msys-crt0 -@var{startfile} is the file name of the startfile (crt0) to use -when linking. This option is only useful in conjunction with @option{-mhal}. - -@item -msys-lib=@var{systemlib} -@opindex msys-lib -@var{systemlib} is the library name of the library that provides -low-level system calls required by the C library, -e.g.@: @code{read} and @code{write}. -This option is typically used to link with a library provided by a HAL BSP. - -@end table - -@node Nvidia PTX Options -@subsection Nvidia PTX Options -@cindex Nvidia PTX options -@cindex nvptx options - -These options are defined for Nvidia PTX: - -@table @gcctabopt - -@item -m64 -@opindex m64 -Ignored, but preserved for backward compatibility. Only 64-bit ABI is -supported. - -@item -march=@var{architecture-string} -@opindex march -Generate code for the specified PTX ISA target architecture -(e.g.@: @samp{sm_35}). Valid architecture strings are @samp{sm_30}, -@samp{sm_35}, @samp{sm_53}, @samp{sm_70}, @samp{sm_75} and -@samp{sm_80}. -The default depends on how the compiler has been configured, see -@option{--with-arch}. - -This option sets the value of the preprocessor macro -@code{__PTX_SM__}; for instance, for @samp{sm_35}, it has the value -@samp{350}. - -@item -misa=@var{architecture-string} -@opindex misa -Alias of @option{-march=}. - -@item -march-map=@var{architecture-string} -@opindex march -Select the closest available @option{-march=} value that is not more -capable. For instance, for @option{-march-map=sm_50} select -@option{-march=sm_35}, and for @option{-march-map=sm_53} select -@option{-march=sm_53}. - -@item -mptx=@var{version-string} -@opindex mptx -Generate code for the specified PTX ISA version (e.g.@: @samp{7.0}). -Valid version strings include @samp{3.1}, @samp{6.0}, @samp{6.3}, and -@samp{7.0}. The default PTX ISA version is 6.0, unless a higher -version is required for specified PTX ISA target architecture via -option @option{-march=}. - -This option sets the values of the preprocessor macros -@code{__PTX_ISA_VERSION_MAJOR__} and @code{__PTX_ISA_VERSION_MINOR__}; -for instance, for @samp{3.1} the macros have the values @samp{3} and -@samp{1}, respectively. - -@item -mmainkernel -@opindex mmainkernel -Link in code for a __main kernel. This is for stand-alone instead of -offloading execution. - -@item -moptimize -@opindex moptimize -Apply partitioned execution optimizations. This is the default when any -level of optimization is selected. - -@item -msoft-stack -@opindex msoft-stack -Generate code that does not use @code{.local} memory -directly for stack storage. Instead, a per-warp stack pointer is -maintained explicitly. This enables variable-length stack allocation (with -variable-length arrays or @code{alloca}), and when global memory is used for -underlying storage, makes it possible to access automatic variables from other -threads, or with atomic instructions. This code generation variant is used -for OpenMP offloading, but the option is exposed on its own for the purpose -of testing the compiler; to generate code suitable for linking into programs -using OpenMP offloading, use option @option{-mgomp}. - -@item -muniform-simt -@opindex muniform-simt -Switch to code generation variant that allows to execute all threads in each -warp, while maintaining memory state and side effects as if only one thread -in each warp was active outside of OpenMP SIMD regions. All atomic operations -and calls to runtime (malloc, free, vprintf) are conditionally executed (iff -current lane index equals the master lane index), and the register being -assigned is copied via a shuffle instruction from the master lane. Outside of -SIMD regions lane 0 is the master; inside, each thread sees itself as the -master. Shared memory array @code{int __nvptx_uni[]} stores all-zeros or -all-ones bitmasks for each warp, indicating current mode (0 outside of SIMD -regions). Each thread can bitwise-and the bitmask at position @code{tid.y} -with current lane index to compute the master lane index. - -@item -mgomp -@opindex mgomp -Generate code for use in OpenMP offloading: enables @option{-msoft-stack} and -@option{-muniform-simt} options, and selects corresponding multilib variant. - -@end table - -@node OpenRISC Options -@subsection OpenRISC Options -@cindex OpenRISC Options - -These options are defined for OpenRISC: - -@table @gcctabopt - -@item -mboard=@var{name} -@opindex mboard -Configure a board specific runtime. This will be passed to the linker for -newlib board library linking. The default is @code{or1ksim}. - -@item -mnewlib -@opindex mnewlib -This option is ignored; it is for compatibility purposes only. This used to -select linker and preprocessor options for use with newlib. - -@item -msoft-div -@itemx -mhard-div -@opindex msoft-div -@opindex mhard-div -Select software or hardware divide (@code{l.div}, @code{l.divu}) instructions. -This default is hardware divide. - -@item -msoft-mul -@itemx -mhard-mul -@opindex msoft-mul -@opindex mhard-mul -Select software or hardware multiply (@code{l.mul}, @code{l.muli}) instructions. -This default is hardware multiply. - -@item -msoft-float -@itemx -mhard-float -@opindex msoft-float -@opindex mhard-float -Select software or hardware for floating point operations. -The default is software. - -@item -mdouble-float -@opindex mdouble-float -When @option{-mhard-float} is selected, enables generation of double-precision -floating point instructions. By default functions from @file{libgcc} are used -to perform double-precision floating point operations. - -@item -munordered-float -@opindex munordered-float -When @option{-mhard-float} is selected, enables generation of unordered -floating point compare and set flag (@code{lf.sfun*}) instructions. By default -functions from @file{libgcc} are used to perform unordered floating point -compare and set flag operations. - -@item -mcmov -@opindex mcmov -Enable generation of conditional move (@code{l.cmov}) instructions. By -default the equivalent will be generated using set and branch. - -@item -mror -@opindex mror -Enable generation of rotate right (@code{l.ror}) instructions. By default -functions from @file{libgcc} are used to perform rotate right operations. - -@item -mrori -@opindex mrori -Enable generation of rotate right with immediate (@code{l.rori}) instructions. -By default functions from @file{libgcc} are used to perform rotate right with -immediate operations. - -@item -msext -@opindex msext -Enable generation of sign extension (@code{l.ext*}) instructions. By default -memory loads are used to perform sign extension. - -@item -msfimm -@opindex msfimm -Enable generation of compare and set flag with immediate (@code{l.sf*i}) -instructions. By default extra instructions will be generated to store the -immediate to a register first. - -@item -mshftimm -@opindex mshftimm -Enable generation of shift with immediate (@code{l.srai}, @code{l.srli}, -@code{l.slli}) instructions. By default extra instructions will be generated -to store the immediate to a register first. - -@item -mcmodel=small -@opindex mcmodel=small -Generate OpenRISC code for the small model: The GOT is limited to 64k. This is -the default model. - -@item -mcmodel=large -@opindex mcmodel=large -Generate OpenRISC code for the large model: The GOT may grow up to 4G in size. - - -@end table - -@node PDP-11 Options -@subsection PDP-11 Options -@cindex PDP-11 Options - -These options are defined for the PDP-11: - -@table @gcctabopt -@item -mfpu -@opindex mfpu -Use hardware FPP floating point. This is the default. (FIS floating -point on the PDP-11/40 is not supported.) Implies -m45. - -@item -msoft-float -@opindex msoft-float -Do not use hardware floating point. - -@item -mac0 -@opindex mac0 -Return floating-point results in ac0 (fr0 in Unix assembler syntax). - -@item -mno-ac0 -@opindex mno-ac0 -Return floating-point results in memory. This is the default. - -@item -m40 -@opindex m40 -Generate code for a PDP-11/40. Implies -msoft-float -mno-split. - -@item -m45 -@opindex m45 -Generate code for a PDP-11/45. This is the default. - -@item -m10 -@opindex m10 -Generate code for a PDP-11/10. Implies -msoft-float -mno-split. - -@item -mint16 -@itemx -mno-int32 -@opindex mint16 -@opindex mno-int32 -Use 16-bit @code{int}. This is the default. - -@item -mint32 -@itemx -mno-int16 -@opindex mint32 -@opindex mno-int16 -Use 32-bit @code{int}. - -@item -msplit -@opindex msplit -Target has split instruction and data space. Implies -m45. - -@item -munix-asm -@opindex munix-asm -Use Unix assembler syntax. - -@item -mdec-asm -@opindex mdec-asm -Use DEC assembler syntax. - -@item -mgnu-asm -@opindex mgnu-asm -Use GNU assembler syntax. This is the default. - -@item -mlra -@opindex mlra -Use the new LRA register allocator. By default, the old ``reload'' -allocator is used. -@end table - -@node picoChip Options -@subsection picoChip Options -@cindex picoChip options - -These @samp{-m} options are defined for picoChip implementations: - -@table @gcctabopt - -@item -mae=@var{ae_type} -@opindex mcpu -Set the instruction set, register set, and instruction scheduling -parameters for array element type @var{ae_type}. Supported values -for @var{ae_type} are @samp{ANY}, @samp{MUL}, and @samp{MAC}. - -@option{-mae=ANY} selects a completely generic AE type. Code -generated with this option runs on any of the other AE types. The -code is not as efficient as it would be if compiled for a specific -AE type, and some types of operation (e.g., multiplication) do not -work properly on all types of AE. - -@option{-mae=MUL} selects a MUL AE type. This is the most useful AE type -for compiled code, and is the default. - -@option{-mae=MAC} selects a DSP-style MAC AE. Code compiled with this -option may suffer from poor performance of byte (char) manipulation, -since the DSP AE does not provide hardware support for byte load/stores. - -@item -msymbol-as-address -Enable the compiler to directly use a symbol name as an address in a -load/store instruction, without first loading it into a -register. Typically, the use of this option generates larger -programs, which run faster than when the option isn't used. However, the -results vary from program to program, so it is left as a user option, -rather than being permanently enabled. - -@item -mno-inefficient-warnings -Disables warnings about the generation of inefficient code. These -warnings can be generated, for example, when compiling code that -performs byte-level memory operations on the MAC AE type. The MAC AE has -no hardware support for byte-level memory operations, so all byte -load/stores must be synthesized from word load/store operations. This is -inefficient and a warning is generated to indicate -that you should rewrite the code to avoid byte operations, or to target -an AE type that has the necessary hardware support. This option disables -these warnings. - -@end table - -@node PowerPC Options -@subsection PowerPC Options -@cindex PowerPC options - -These are listed under @xref{RS/6000 and PowerPC Options}. - -@node PRU Options -@subsection PRU Options -@cindex PRU Options - -These command-line options are defined for PRU target: - -@table @gcctabopt -@item -minrt -@opindex minrt -Link with a minimum runtime environment, with no support for static -initializers and constructors. Using this option can significantly reduce -the size of the final ELF binary. Beware that the compiler could still -generate code with static initializers and constructors. It is up to the -programmer to ensure that the source program will not use those features. - -@item -mmcu=@var{mcu} -@opindex mmcu -Specify the PRU MCU variant to use. Check Newlib for the exact list of -supported MCUs. - -@item -mno-relax -@opindex mno-relax -Make GCC pass the @option{--no-relax} command-line option to the linker -instead of the @option{--relax} option. - -@item -mloop -@opindex mloop -Allow (or do not allow) GCC to use the LOOP instruction. - -@item -mabi=@var{variant} -@opindex mabi -Specify the ABI variant to output code for. @option{-mabi=ti} selects the -unmodified TI ABI while @option{-mabi=gnu} selects a GNU variant that copes -more naturally with certain GCC assumptions. These are the differences: - -@table @samp -@item Function Pointer Size -TI ABI specifies that function (code) pointers are 16-bit, whereas GNU -supports only 32-bit data and code pointers. - -@item Optional Return Value Pointer -Function return values larger than 64 bits are passed by using a hidden -pointer as the first argument of the function. TI ABI, though, mandates that -the pointer can be NULL in case the caller is not using the returned value. -GNU always passes and expects a valid return value pointer. - -@end table - -The current @option{-mabi=ti} implementation simply raises a compile error -when any of the above code constructs is detected. As a consequence -the standard C library cannot be built and it is omitted when linking with -@option{-mabi=ti}. - -Relaxation is a GNU feature and for safety reasons is disabled when using -@option{-mabi=ti}. The TI toolchain does not emit relocations for QBBx -instructions, so the GNU linker cannot adjust them when shortening adjacent -LDI32 pseudo instructions. - -@end table - -@node RISC-V Options -@subsection RISC-V Options -@cindex RISC-V Options - -These command-line options are defined for RISC-V targets: - -@table @gcctabopt -@item -mbranch-cost=@var{n} -@opindex mbranch-cost -Set the cost of branches to roughly @var{n} instructions. - -@item -mplt -@itemx -mno-plt -@opindex plt -When generating PIC code, do or don't allow the use of PLTs. Ignored for -non-PIC. The default is @option{-mplt}. - -@item -mabi=@var{ABI-string} -@opindex mabi -Specify integer and floating-point calling convention. @var{ABI-string} -contains two parts: the size of integer types and the registers used for -floating-point types. For example @samp{-march=rv64ifd -mabi=lp64d} means that -@samp{long} and pointers are 64-bit (implicitly defining @samp{int} to be -32-bit), and that floating-point values up to 64 bits wide are passed in F -registers. Contrast this with @samp{-march=rv64ifd -mabi=lp64f}, which still -allows the compiler to generate code that uses the F and D extensions but only -allows floating-point values up to 32 bits long to be passed in registers; or -@samp{-march=rv64ifd -mabi=lp64}, in which no floating-point arguments will be -passed in registers. - -The default for this argument is system dependent, users who want a specific -calling convention should specify one explicitly. The valid calling -conventions are: @samp{ilp32}, @samp{ilp32f}, @samp{ilp32d}, @samp{lp64}, -@samp{lp64f}, and @samp{lp64d}. Some calling conventions are impossible to -implement on some ISAs: for example, @samp{-march=rv32if -mabi=ilp32d} is -invalid because the ABI requires 64-bit values be passed in F registers, but F -registers are only 32 bits wide. There is also the @samp{ilp32e} ABI that can -only be used with the @samp{rv32e} architecture. This ABI is not well -specified at present, and is subject to change. - -@item -mfdiv -@itemx -mno-fdiv -@opindex mfdiv -Do or don't use hardware floating-point divide and square root instructions. -This requires the F or D extensions for floating-point registers. The default -is to use them if the specified architecture has these instructions. - -@item -mdiv -@itemx -mno-div -@opindex mdiv -Do or don't use hardware instructions for integer division. This requires the -M extension. The default is to use them if the specified architecture has -these instructions. - -@item -misa-spec=@var{ISA-spec-string} -@opindex misa-spec -Specify the version of the RISC-V Unprivileged (formerly User-Level) -ISA specification to produce code conforming to. The possibilities -for @var{ISA-spec-string} are: -@table @code -@item 2.2 -Produce code conforming to version 2.2. -@item 20190608 -Produce code conforming to version 20190608. -@item 20191213 -Produce code conforming to version 20191213. -@end table -The default is @option{-misa-spec=20191213} unless GCC has been configured -with @option{--with-isa-spec=} specifying a different default version. - -@item -march=@var{ISA-string} -@opindex march -Generate code for given RISC-V ISA (e.g.@: @samp{rv64im}). ISA strings must be -lower-case. Examples include @samp{rv64i}, @samp{rv32g}, @samp{rv32e}, and -@samp{rv32imaf}. - -When @option{-march=} is not specified, use the setting from @option{-mcpu}. - -If both @option{-march} and @option{-mcpu=} are not specified, the default for -this argument is system dependent, users who want a specific architecture -extensions should specify one explicitly. - -@item -mcpu=@var{processor-string} -@opindex mcpu -Use architecture of and optimize the output for the given processor, specified -by particular CPU name. -Permissible values for this option are: @samp{sifive-e20}, @samp{sifive-e21}, -@samp{sifive-e24}, @samp{sifive-e31}, @samp{sifive-e34}, @samp{sifive-e76}, -@samp{sifive-s21}, @samp{sifive-s51}, @samp{sifive-s54}, @samp{sifive-s76}, -@samp{sifive-u54}, and @samp{sifive-u74}. - -@item -mtune=@var{processor-string} -@opindex mtune -Optimize the output for the given processor, specified by microarchitecture or -particular CPU name. Permissible values for this option are: @samp{rocket}, -@samp{sifive-3-series}, @samp{sifive-5-series}, @samp{sifive-7-series}, -@samp{thead-c906}, @samp{size}, and all valid options for @option{-mcpu=}. - -When @option{-mtune=} is not specified, use the setting from @option{-mcpu}, -the default is @samp{rocket} if both are not specified. - -The @samp{size} choice is not intended for use by end-users. This is used -when @option{-Os} is specified. It overrides the instruction cost info -provided by @option{-mtune=}, but does not override the pipeline info. This -helps reduce code size while still giving good performance. - -@item -mpreferred-stack-boundary=@var{num} -@opindex mpreferred-stack-boundary -Attempt to keep the stack boundary aligned to a 2 raised to @var{num} -byte boundary. If @option{-mpreferred-stack-boundary} is not specified, -the default is 4 (16 bytes or 128-bits). - -@strong{Warning:} If you use this switch, then you must build all modules with -the same value, including any libraries. This includes the system libraries -and startup modules. - -@item -msmall-data-limit=@var{n} -@opindex msmall-data-limit -Put global and static data smaller than @var{n} bytes into a special section -(on some targets). - -@item -msave-restore -@itemx -mno-save-restore -@opindex msave-restore -Do or don't use smaller but slower prologue and epilogue code that uses -library function calls. The default is to use fast inline prologues and -epilogues. - -@item -mshorten-memrefs -@itemx -mno-shorten-memrefs -@opindex mshorten-memrefs -Do or do not attempt to make more use of compressed load/store instructions by -replacing a load/store of 'base register + large offset' with a new load/store -of 'new base + small offset'. If the new base gets stored in a compressed -register, then the new load/store can be compressed. Currently targets 32-bit -integer load/stores only. - -@item -mstrict-align -@itemx -mno-strict-align -@opindex mstrict-align -Do not or do generate unaligned memory accesses. The default is set depending -on whether the processor we are optimizing for supports fast unaligned access -or not. - -@item -mcmodel=medlow -@opindex mcmodel=medlow -Generate code for the medium-low code model. The program and its statically -defined symbols must lie within a single 2 GiB address range and must lie -between absolute addresses @minus{}2 GiB and +2 GiB. Programs can be -statically or dynamically linked. This is the default code model. - -@item -mcmodel=medany -@opindex mcmodel=medany -Generate code for the medium-any code model. The program and its statically -defined symbols must be within any single 2 GiB address range. Programs can be -statically or dynamically linked. - -The code generated by the medium-any code model is position-independent, but is -not guaranteed to function correctly when linked into position-independent -executables or libraries. - -@item -mexplicit-relocs -@itemx -mno-exlicit-relocs -Use or do not use assembler relocation operators when dealing with symbolic -addresses. The alternative is to use assembler macros instead, which may -limit optimization. - -@item -mrelax -@itemx -mno-relax -@opindex mrelax -Take advantage of linker relaxations to reduce the number of instructions -required to materialize symbol addresses. The default is to take advantage of -linker relaxations. - -@item -mriscv-attribute -@itemx -mno-riscv-attribute -@opindex mriscv-attribute -Emit (do not emit) RISC-V attribute to record extra information into ELF -objects. This feature requires at least binutils 2.32. - -@item -mcsr-check -@itemx -mno-csr-check -@opindex mcsr-check -Enables or disables the CSR checking. - -@item -malign-data=@var{type} -@opindex malign-data -Control how GCC aligns variables and constants of array, structure, or union -types. Supported values for @var{type} are @samp{xlen} which uses x register -width as the alignment value, and @samp{natural} which uses natural alignment. -@samp{xlen} is the default. - -@item -mbig-endian -@opindex mbig-endian -Generate big-endian code. This is the default when GCC is configured for a -@samp{riscv64be-*-*} or @samp{riscv32be-*-*} target. - -@item -mlittle-endian -@opindex mlittle-endian -Generate little-endian code. This is the default when GCC is configured for a -@samp{riscv64-*-*} or @samp{riscv32-*-*} but not a @samp{riscv64be-*-*} or -@samp{riscv32be-*-*} target. - -@item -mstack-protector-guard=@var{guard} -@itemx -mstack-protector-guard-reg=@var{reg} -@itemx -mstack-protector-guard-offset=@var{offset} -@opindex mstack-protector-guard -@opindex mstack-protector-guard-reg -@opindex mstack-protector-guard-offset -Generate stack protection code using canary at @var{guard}. Supported -locations are @samp{global} for a global canary or @samp{tls} for per-thread -canary in the TLS block. - -With the latter choice the options -@option{-mstack-protector-guard-reg=@var{reg}} and -@option{-mstack-protector-guard-offset=@var{offset}} furthermore specify -which register to use as base register for reading the canary, -and from what offset from that base register. There is no default -register or offset as this is entirely for use within the Linux -kernel. -@end table - -@node RL78 Options -@subsection RL78 Options -@cindex RL78 Options - -@table @gcctabopt - -@item -msim -@opindex msim -Links in additional target libraries to support operation within a -simulator. - -@item -mmul=none -@itemx -mmul=g10 -@itemx -mmul=g13 -@itemx -mmul=g14 -@itemx -mmul=rl78 -@opindex mmul -Specifies the type of hardware multiplication and division support to -be used. The simplest is @code{none}, which uses software for both -multiplication and division. This is the default. The @code{g13} -value is for the hardware multiply/divide peripheral found on the -RL78/G13 (S2 core) targets. The @code{g14} value selects the use of -the multiplication and division instructions supported by the RL78/G14 -(S3 core) parts. The value @code{rl78} is an alias for @code{g14} and -the value @code{mg10} is an alias for @code{none}. - -In addition a C preprocessor macro is defined, based upon the setting -of this option. Possible values are: @code{__RL78_MUL_NONE__}, -@code{__RL78_MUL_G13__} or @code{__RL78_MUL_G14__}. - -@item -mcpu=g10 -@itemx -mcpu=g13 -@itemx -mcpu=g14 -@itemx -mcpu=rl78 -@opindex mcpu -Specifies the RL78 core to target. The default is the G14 core, also -known as an S3 core or just RL78. The G13 or S2 core does not have -multiply or divide instructions, instead it uses a hardware peripheral -for these operations. The G10 or S1 core does not have register -banks, so it uses a different calling convention. - -If this option is set it also selects the type of hardware multiply -support to use, unless this is overridden by an explicit -@option{-mmul=none} option on the command line. Thus specifying -@option{-mcpu=g13} enables the use of the G13 hardware multiply -peripheral and specifying @option{-mcpu=g10} disables the use of -hardware multiplications altogether. - -Note, although the RL78/G14 core is the default target, specifying -@option{-mcpu=g14} or @option{-mcpu=rl78} on the command line does -change the behavior of the toolchain since it also enables G14 -hardware multiply support. If these options are not specified on the -command line then software multiplication routines will be used even -though the code targets the RL78 core. This is for backwards -compatibility with older toolchains which did not have hardware -multiply and divide support. - -In addition a C preprocessor macro is defined, based upon the setting -of this option. Possible values are: @code{__RL78_G10__}, -@code{__RL78_G13__} or @code{__RL78_G14__}. - -@item -mg10 -@itemx -mg13 -@itemx -mg14 -@itemx -mrl78 -@opindex mg10 -@opindex mg13 -@opindex mg14 -@opindex mrl78 -These are aliases for the corresponding @option{-mcpu=} option. They -are provided for backwards compatibility. - -@item -mallregs -@opindex mallregs -Allow the compiler to use all of the available registers. By default -registers @code{r24..r31} are reserved for use in interrupt handlers. -With this option enabled these registers can be used in ordinary -functions as well. - -@item -m64bit-doubles -@itemx -m32bit-doubles -@opindex m64bit-doubles -@opindex m32bit-doubles -Make the @code{double} data type be 64 bits (@option{-m64bit-doubles}) -or 32 bits (@option{-m32bit-doubles}) in size. The default is -@option{-m32bit-doubles}. - -@item -msave-mduc-in-interrupts -@itemx -mno-save-mduc-in-interrupts -@opindex msave-mduc-in-interrupts -@opindex mno-save-mduc-in-interrupts -Specifies that interrupt handler functions should preserve the -MDUC registers. This is only necessary if normal code might use -the MDUC registers, for example because it performs multiplication -and division operations. The default is to ignore the MDUC registers -as this makes the interrupt handlers faster. The target option -mg13 -needs to be passed for this to work as this feature is only available -on the G13 target (S2 core). The MDUC registers will only be saved -if the interrupt handler performs a multiplication or division -operation or it calls another function. - -@end table - -@node RS/6000 and PowerPC Options -@subsection IBM RS/6000 and PowerPC Options -@cindex RS/6000 and PowerPC Options -@cindex IBM RS/6000 and PowerPC Options - -These @samp{-m} options are defined for the IBM RS/6000 and PowerPC: -@table @gcctabopt -@item -mpowerpc-gpopt -@itemx -mno-powerpc-gpopt -@itemx -mpowerpc-gfxopt -@itemx -mno-powerpc-gfxopt -@need 800 -@itemx -mpowerpc64 -@itemx -mno-powerpc64 -@itemx -mmfcrf -@itemx -mno-mfcrf -@itemx -mpopcntb -@itemx -mno-popcntb -@itemx -mpopcntd -@itemx -mno-popcntd -@itemx -mfprnd -@itemx -mno-fprnd -@need 800 -@itemx -mcmpb -@itemx -mno-cmpb -@itemx -mhard-dfp -@itemx -mno-hard-dfp -@opindex mpowerpc-gpopt -@opindex mno-powerpc-gpopt -@opindex mpowerpc-gfxopt -@opindex mno-powerpc-gfxopt -@opindex mpowerpc64 -@opindex mno-powerpc64 -@opindex mmfcrf -@opindex mno-mfcrf -@opindex mpopcntb -@opindex mno-popcntb -@opindex mpopcntd -@opindex mno-popcntd -@opindex mfprnd -@opindex mno-fprnd -@opindex mcmpb -@opindex mno-cmpb -@opindex mhard-dfp -@opindex mno-hard-dfp -You use these options to specify which instructions are available on the -processor you are using. The default value of these options is -determined when configuring GCC@. Specifying the -@option{-mcpu=@var{cpu_type}} overrides the specification of these -options. We recommend you use the @option{-mcpu=@var{cpu_type}} option -rather than the options listed above. - -Specifying @option{-mpowerpc-gpopt} allows -GCC to use the optional PowerPC architecture instructions in the -General Purpose group, including floating-point square root. Specifying -@option{-mpowerpc-gfxopt} allows GCC to -use the optional PowerPC architecture instructions in the Graphics -group, including floating-point select. - -The @option{-mmfcrf} option allows GCC to generate the move from -condition register field instruction implemented on the POWER4 -processor and other processors that support the PowerPC V2.01 -architecture. -The @option{-mpopcntb} option allows GCC to generate the popcount and -double-precision FP reciprocal estimate instruction implemented on the -POWER5 processor and other processors that support the PowerPC V2.02 -architecture. -The @option{-mpopcntd} option allows GCC to generate the popcount -instruction implemented on the POWER7 processor and other processors -that support the PowerPC V2.06 architecture. -The @option{-mfprnd} option allows GCC to generate the FP round to -integer instructions implemented on the POWER5+ processor and other -processors that support the PowerPC V2.03 architecture. -The @option{-mcmpb} option allows GCC to generate the compare bytes -instruction implemented on the POWER6 processor and other processors -that support the PowerPC V2.05 architecture. -The @option{-mhard-dfp} option allows GCC to generate the decimal -floating-point instructions implemented on some POWER processors. - -The @option{-mpowerpc64} option allows GCC to generate the additional -64-bit instructions that are found in the full PowerPC64 architecture -and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to -@option{-mno-powerpc64}. - -@item -mcpu=@var{cpu_type} -@opindex mcpu -Set architecture type, register usage, and -instruction scheduling parameters for machine type @var{cpu_type}. -Supported values for @var{cpu_type} are @samp{401}, @samp{403}, -@samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{464}, @samp{464fp}, -@samp{476}, @samp{476fp}, @samp{505}, @samp{601}, @samp{602}, @samp{603}, -@samp{603e}, @samp{604}, @samp{604e}, @samp{620}, @samp{630}, @samp{740}, -@samp{7400}, @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823}, -@samp{860}, @samp{970}, @samp{8540}, @samp{a2}, @samp{e300c2}, -@samp{e300c3}, @samp{e500mc}, @samp{e500mc64}, @samp{e5500}, -@samp{e6500}, @samp{ec603e}, @samp{G3}, @samp{G4}, @samp{G5}, -@samp{titan}, @samp{power3}, @samp{power4}, @samp{power5}, @samp{power5+}, -@samp{power6}, @samp{power6x}, @samp{power7}, @samp{power8}, -@samp{power9}, @samp{power10}, @samp{powerpc}, @samp{powerpc64}, -@samp{powerpc64le}, @samp{rs64}, and @samp{native}. - -@option{-mcpu=powerpc}, @option{-mcpu=powerpc64}, and -@option{-mcpu=powerpc64le} specify pure 32-bit PowerPC (either -endian), 64-bit big endian PowerPC and 64-bit little endian PowerPC -architecture machine types, with an appropriate, generic processor -model assumed for scheduling purposes. - -Specifying @samp{native} as cpu type detects and selects the -architecture option that corresponds to the host processor of the -system performing the compilation. -@option{-mcpu=native} has no effect if GCC does not recognize the -processor. - -The other options specify a specific processor. Code generated under -those options runs best on that processor, and may not run at all on -others. - -The @option{-mcpu} options automatically enable or disable the -following options: - -@gccoptlist{-maltivec -mfprnd -mhard-float -mmfcrf -mmultiple @gol --mpopcntb -mpopcntd -mpowerpc64 @gol --mpowerpc-gpopt -mpowerpc-gfxopt @gol --mmulhw -mdlmzb -mmfpgpr -mvsx @gol --mcrypto -mhtm -mpower8-fusion -mpower8-vector @gol --mquad-memory -mquad-memory-atomic -mfloat128 @gol --mfloat128-hardware -mprefixed -mpcrel -mmma @gol --mrop-protect} - -The particular options set for any particular CPU varies between -compiler versions, depending on what setting seems to produce optimal -code for that CPU; it doesn't necessarily reflect the actual hardware's -capabilities. If you wish to set an individual option to a particular -value, you may specify it after the @option{-mcpu} option, like -@option{-mcpu=970 -mno-altivec}. - -On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are -not enabled or disabled by the @option{-mcpu} option at present because -AIX does not have full support for these options. You may still -enable or disable them individually if you're sure it'll work in your -environment. - -@item -mtune=@var{cpu_type} -@opindex mtune -Set the instruction scheduling parameters for machine type -@var{cpu_type}, but do not set the architecture type or register usage, -as @option{-mcpu=@var{cpu_type}} does. The same -values for @var{cpu_type} are used for @option{-mtune} as for -@option{-mcpu}. If both are specified, the code generated uses the -architecture and registers set by @option{-mcpu}, but the -scheduling parameters set by @option{-mtune}. - -@item -mcmodel=small -@opindex mcmodel=small -Generate PowerPC64 code for the small model: The TOC is limited to -64k. - -@item -mcmodel=medium -@opindex mcmodel=medium -Generate PowerPC64 code for the medium model: The TOC and other static -data may be up to a total of 4G in size. This is the default for 64-bit -Linux. - -@item -mcmodel=large -@opindex mcmodel=large -Generate PowerPC64 code for the large model: The TOC may be up to 4G -in size. Other data and code is only limited by the 64-bit address -space. - -@item -maltivec -@itemx -mno-altivec -@opindex maltivec -@opindex mno-altivec -Generate code that uses (does not use) AltiVec instructions, and also -enable the use of built-in functions that allow more direct access to -the AltiVec instruction set. You may also need to set -@option{-mabi=altivec} to adjust the current ABI with AltiVec ABI -enhancements. - -When @option{-maltivec} is used, the element order for AltiVec intrinsics -such as @code{vec_splat}, @code{vec_extract}, and @code{vec_insert} -match array element order corresponding to the endianness of the -target. That is, element zero identifies the leftmost element in a -vector register when targeting a big-endian platform, and identifies -the rightmost element in a vector register when targeting a -little-endian platform. - -@item -mvrsave -@itemx -mno-vrsave -@opindex mvrsave -@opindex mno-vrsave -Generate VRSAVE instructions when generating AltiVec code. - -@item -msecure-plt -@opindex msecure-plt -Generate code that allows @command{ld} and @command{ld.so} -to build executables and shared -libraries with non-executable @code{.plt} and @code{.got} sections. -This is a PowerPC -32-bit SYSV ABI option. - -@item -mbss-plt -@opindex mbss-plt -Generate code that uses a BSS @code{.plt} section that @command{ld.so} -fills in, and -requires @code{.plt} and @code{.got} -sections that are both writable and executable. -This is a PowerPC 32-bit SYSV ABI option. - -@item -misel -@itemx -mno-isel -@opindex misel -@opindex mno-isel -This switch enables or disables the generation of ISEL instructions. - -@item -mvsx -@itemx -mno-vsx -@opindex mvsx -@opindex mno-vsx -Generate code that uses (does not use) vector/scalar (VSX) -instructions, and also enable the use of built-in functions that allow -more direct access to the VSX instruction set. - -@item -mcrypto -@itemx -mno-crypto -@opindex mcrypto -@opindex mno-crypto -Enable the use (disable) of the built-in functions that allow direct -access to the cryptographic instructions that were added in version -2.07 of the PowerPC ISA. - -@item -mhtm -@itemx -mno-htm -@opindex mhtm -@opindex mno-htm -Enable (disable) the use of the built-in functions that allow direct -access to the Hardware Transactional Memory (HTM) instructions that -were added in version 2.07 of the PowerPC ISA. - -@item -mpower8-fusion -@itemx -mno-power8-fusion -@opindex mpower8-fusion -@opindex mno-power8-fusion -Generate code that keeps (does not keeps) some integer operations -adjacent so that the instructions can be fused together on power8 and -later processors. - -@item -mpower8-vector -@itemx -mno-power8-vector -@opindex mpower8-vector -@opindex mno-power8-vector -Generate code that uses (does not use) the vector and scalar -instructions that were added in version 2.07 of the PowerPC ISA. Also -enable the use of built-in functions that allow more direct access to -the vector instructions. - -@item -mquad-memory -@itemx -mno-quad-memory -@opindex mquad-memory -@opindex mno-quad-memory -Generate code that uses (does not use) the non-atomic quad word memory -instructions. The @option{-mquad-memory} option requires use of -64-bit mode. - -@item -mquad-memory-atomic -@itemx -mno-quad-memory-atomic -@opindex mquad-memory-atomic -@opindex mno-quad-memory-atomic -Generate code that uses (does not use) the atomic quad word memory -instructions. The @option{-mquad-memory-atomic} option requires use of -64-bit mode. - -@item -mfloat128 -@itemx -mno-float128 -@opindex mfloat128 -@opindex mno-float128 -Enable/disable the @var{__float128} keyword for IEEE 128-bit floating point -and use either software emulation for IEEE 128-bit floating point or -hardware instructions. - -The VSX instruction set (@option{-mvsx}) must be enabled to use the IEEE -128-bit floating point support. The IEEE 128-bit floating point is only -supported on Linux. - -The default for @option{-mfloat128} is enabled on PowerPC Linux -systems using the VSX instruction set, and disabled on other systems. - -If you use the ISA 3.0 instruction set (@option{-mpower9-vector} or -@option{-mcpu=power9}) on a 64-bit system, the IEEE 128-bit floating -point support will also enable the generation of ISA 3.0 IEEE 128-bit -floating point instructions. Otherwise, if you do not specify to -generate ISA 3.0 instructions or you are targeting a 32-bit big endian -system, IEEE 128-bit floating point will be done with software -emulation. - -@item -mfloat128-hardware -@itemx -mno-float128-hardware -@opindex mfloat128-hardware -@opindex mno-float128-hardware -Enable/disable using ISA 3.0 hardware instructions to support the -@var{__float128} data type. - -The default for @option{-mfloat128-hardware} is enabled on PowerPC -Linux systems using the ISA 3.0 instruction set, and disabled on other -systems. - -@item -m32 -@itemx -m64 -@opindex m32 -@opindex m64 -Generate code for 32-bit or 64-bit environments of Darwin and SVR4 -targets (including GNU/Linux). The 32-bit environment sets int, long -and pointer to 32 bits and generates code that runs on any PowerPC -variant. The 64-bit environment sets int to 32 bits and long and -pointer to 64 bits, and generates code for PowerPC64, as for -@option{-mpowerpc64}. - -@item -mfull-toc -@itemx -mno-fp-in-toc -@itemx -mno-sum-in-toc -@itemx -mminimal-toc -@opindex mfull-toc -@opindex mno-fp-in-toc -@opindex mno-sum-in-toc -@opindex mminimal-toc -Modify generation of the TOC (Table Of Contents), which is created for -every executable file. The @option{-mfull-toc} option is selected by -default. In that case, GCC allocates at least one TOC entry for -each unique non-automatic variable reference in your program. GCC -also places floating-point constants in the TOC@. However, only -16,384 entries are available in the TOC@. - -If you receive a linker error message that saying you have overflowed -the available TOC space, you can reduce the amount of TOC space used -with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options. -@option{-mno-fp-in-toc} prevents GCC from putting floating-point -constants in the TOC and @option{-mno-sum-in-toc} forces GCC to -generate code to calculate the sum of an address and a constant at -run time instead of putting that sum into the TOC@. You may specify one -or both of these options. Each causes GCC to produce very slightly -slower and larger code at the expense of conserving TOC space. - -If you still run out of space in the TOC even when you specify both of -these options, specify @option{-mminimal-toc} instead. This option causes -GCC to make only one TOC entry for every file. When you specify this -option, GCC produces code that is slower and larger but which -uses extremely little TOC space. You may wish to use this option -only on files that contain less frequently-executed code. - -@item -maix64 -@itemx -maix32 -@opindex maix64 -@opindex maix32 -Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit -@code{long} type, and the infrastructure needed to support them. -Specifying @option{-maix64} implies @option{-mpowerpc64}, -while @option{-maix32} disables the 64-bit ABI and -implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}. - -@item -mxl-compat -@itemx -mno-xl-compat -@opindex mxl-compat -@opindex mno-xl-compat -Produce code that conforms more closely to IBM XL compiler semantics -when using AIX-compatible ABI@. Pass floating-point arguments to -prototyped functions beyond the register save area (RSA) on the stack -in addition to argument FPRs. Do not assume that most significant -double in 128-bit long double value is properly rounded when comparing -values and converting to double. Use XL symbol names for long double -support routines. - -The AIX calling convention was extended but not initially documented to -handle an obscure K&R C case of calling a function that takes the -address of its arguments with fewer arguments than declared. IBM XL -compilers access floating-point arguments that do not fit in the -RSA from the stack when a subroutine is compiled without -optimization. Because always storing floating-point arguments on the -stack is inefficient and rarely needed, this option is not enabled by -default and only is necessary when calling subroutines compiled by IBM -XL compilers without optimization. - -@item -mpe -@opindex mpe -Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an -application written to use message passing with special startup code to -enable the application to run. The system must have PE installed in the -standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file -must be overridden with the @option{-specs=} option to specify the -appropriate directory location. The Parallel Environment does not -support threads, so the @option{-mpe} option and the @option{-pthread} -option are incompatible. - -@item -malign-natural -@itemx -malign-power -@opindex malign-natural -@opindex malign-power -On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option -@option{-malign-natural} overrides the ABI-defined alignment of larger -types, such as floating-point doubles, on their natural size-based boundary. -The option @option{-malign-power} instructs GCC to follow the ABI-specified -alignment rules. GCC defaults to the standard alignment defined in the ABI@. - -On 64-bit Darwin, natural alignment is the default, and @option{-malign-power} -is not supported. - -@item -msoft-float -@itemx -mhard-float -@opindex msoft-float -@opindex mhard-float -Generate code that does not use (uses) the floating-point register set. -Software floating-point emulation is provided if you use the -@option{-msoft-float} option, and pass the option to GCC when linking. - -@item -mmultiple -@itemx -mno-multiple -@opindex mmultiple -@opindex mno-multiple -Generate code that uses (does not use) the load multiple word -instructions and the store multiple word instructions. These -instructions are generated by default on POWER systems, and not -generated on PowerPC systems. Do not use @option{-mmultiple} on little-endian -PowerPC systems, since those instructions do not work when the -processor is in little-endian mode. The exceptions are PPC740 and -PPC750 which permit these instructions in little-endian mode. - -@item -mupdate -@itemx -mno-update -@opindex mupdate -@opindex mno-update -Generate code that uses (does not use) the load or store instructions -that update the base register to the address of the calculated memory -location. These instructions are generated by default. If you use -@option{-mno-update}, there is a small window between the time that the -stack pointer is updated and the address of the previous frame is -stored, which means code that walks the stack frame across interrupts or -signals may get corrupted data. - -@item -mavoid-indexed-addresses -@itemx -mno-avoid-indexed-addresses -@opindex mavoid-indexed-addresses -@opindex mno-avoid-indexed-addresses -Generate code that tries to avoid (not avoid) the use of indexed load -or store instructions. These instructions can incur a performance -penalty on Power6 processors in certain situations, such as when -stepping through large arrays that cross a 16M boundary. This option -is enabled by default when targeting Power6 and disabled otherwise. - -@item -mfused-madd -@itemx -mno-fused-madd -@opindex mfused-madd -@opindex mno-fused-madd -Generate code that uses (does not use) the floating-point multiply and -accumulate instructions. These instructions are generated by default -if hardware floating point is used. The machine-dependent -@option{-mfused-madd} option is now mapped to the machine-independent -@option{-ffp-contract=fast} option, and @option{-mno-fused-madd} is -mapped to @option{-ffp-contract=off}. - -@item -mmulhw -@itemx -mno-mulhw -@opindex mmulhw -@opindex mno-mulhw -Generate code that uses (does not use) the half-word multiply and -multiply-accumulate instructions on the IBM 405, 440, 464 and 476 processors. -These instructions are generated by default when targeting those -processors. - -@item -mdlmzb -@itemx -mno-dlmzb -@opindex mdlmzb -@opindex mno-dlmzb -Generate code that uses (does not use) the string-search @samp{dlmzb} -instruction on the IBM 405, 440, 464 and 476 processors. This instruction is -generated by default when targeting those processors. - -@item -mno-bit-align -@itemx -mbit-align -@opindex mno-bit-align -@opindex mbit-align -On System V.4 and embedded PowerPC systems do not (do) force structures -and unions that contain bit-fields to be aligned to the base type of the -bit-field. - -For example, by default a structure containing nothing but 8 -@code{unsigned} bit-fields of length 1 is aligned to a 4-byte -boundary and has a size of 4 bytes. By using @option{-mno-bit-align}, -the structure is aligned to a 1-byte boundary and is 1 byte in -size. - -@item -mno-strict-align -@itemx -mstrict-align -@opindex mno-strict-align -@opindex mstrict-align -On System V.4 and embedded PowerPC systems do not (do) assume that -unaligned memory references are handled by the system. - -@item -mrelocatable -@itemx -mno-relocatable -@opindex mrelocatable -@opindex mno-relocatable -Generate code that allows (does not allow) a static executable to be -relocated to a different address at run time. A simple embedded -PowerPC system loader should relocate the entire contents of -@code{.got2} and 4-byte locations listed in the @code{.fixup} section, -a table of 32-bit addresses generated by this option. For this to -work, all objects linked together must be compiled with -@option{-mrelocatable} or @option{-mrelocatable-lib}. -@option{-mrelocatable} code aligns the stack to an 8-byte boundary. - -@item -mrelocatable-lib -@itemx -mno-relocatable-lib -@opindex mrelocatable-lib -@opindex mno-relocatable-lib -Like @option{-mrelocatable}, @option{-mrelocatable-lib} generates a -@code{.fixup} section to allow static executables to be relocated at -run time, but @option{-mrelocatable-lib} does not use the smaller stack -alignment of @option{-mrelocatable}. Objects compiled with -@option{-mrelocatable-lib} may be linked with objects compiled with -any combination of the @option{-mrelocatable} options. - -@item -mno-toc -@itemx -mtoc -@opindex mno-toc -@opindex mtoc -On System V.4 and embedded PowerPC systems do not (do) assume that -register 2 contains a pointer to a global area pointing to the addresses -used in the program. - -@item -mlittle -@itemx -mlittle-endian -@opindex mlittle -@opindex mlittle-endian -On System V.4 and embedded PowerPC systems compile code for the -processor in little-endian mode. The @option{-mlittle-endian} option is -the same as @option{-mlittle}. - -@item -mbig -@itemx -mbig-endian -@opindex mbig -@opindex mbig-endian -On System V.4 and embedded PowerPC systems compile code for the -processor in big-endian mode. The @option{-mbig-endian} option is -the same as @option{-mbig}. - -@item -mdynamic-no-pic -@opindex mdynamic-no-pic -On Darwin and Mac OS X systems, compile code so that it is not -relocatable, but that its external references are relocatable. The -resulting code is suitable for applications, but not shared -libraries. - -@item -msingle-pic-base -@opindex msingle-pic-base -Treat the register used for PIC addressing as read-only, rather than -loading it in the prologue for each function. The runtime system is -responsible for initializing this register with an appropriate value -before execution begins. - -@item -mprioritize-restricted-insns=@var{priority} -@opindex mprioritize-restricted-insns -This option controls the priority that is assigned to -dispatch-slot restricted instructions during the second scheduling -pass. The argument @var{priority} takes the value @samp{0}, @samp{1}, -or @samp{2} to assign no, highest, or second-highest (respectively) -priority to dispatch-slot restricted -instructions. - -@item -msched-costly-dep=@var{dependence_type} -@opindex msched-costly-dep -This option controls which dependences are considered costly -by the target during instruction scheduling. The argument -@var{dependence_type} takes one of the following values: - -@table @asis -@item @samp{no} -No dependence is costly. - -@item @samp{all} -All dependences are costly. - -@item @samp{true_store_to_load} -A true dependence from store to load is costly. - -@item @samp{store_to_load} -Any dependence from store to load is costly. - -@item @var{number} -Any dependence for which the latency is greater than or equal to -@var{number} is costly. -@end table - -@item -minsert-sched-nops=@var{scheme} -@opindex minsert-sched-nops -This option controls which NOP insertion scheme is used during -the second scheduling pass. The argument @var{scheme} takes one of the -following values: - -@table @asis -@item @samp{no} -Don't insert NOPs. - -@item @samp{pad} -Pad with NOPs any dispatch group that has vacant issue slots, -according to the scheduler's grouping. - -@item @samp{regroup_exact} -Insert NOPs to force costly dependent insns into -separate groups. Insert exactly as many NOPs as needed to force an insn -to a new group, according to the estimated processor grouping. - -@item @var{number} -Insert NOPs to force costly dependent insns into -separate groups. Insert @var{number} NOPs to force an insn to a new group. -@end table - -@item -mcall-sysv -@opindex mcall-sysv -On System V.4 and embedded PowerPC systems compile code using calling -conventions that adhere to the March 1995 draft of the System V -Application Binary Interface, PowerPC processor supplement. This is the -default unless you configured GCC using @samp{powerpc-*-eabiaix}. - -@item -mcall-sysv-eabi -@itemx -mcall-eabi -@opindex mcall-sysv-eabi -@opindex mcall-eabi -Specify both @option{-mcall-sysv} and @option{-meabi} options. - -@item -mcall-sysv-noeabi -@opindex mcall-sysv-noeabi -Specify both @option{-mcall-sysv} and @option{-mno-eabi} options. - -@item -mcall-aixdesc -@opindex m -On System V.4 and embedded PowerPC systems compile code for the AIX -operating system. - -@item -mcall-linux -@opindex mcall-linux -On System V.4 and embedded PowerPC systems compile code for the -Linux-based GNU system. - -@item -mcall-freebsd -@opindex mcall-freebsd -On System V.4 and embedded PowerPC systems compile code for the -FreeBSD operating system. - -@item -mcall-netbsd -@opindex mcall-netbsd -On System V.4 and embedded PowerPC systems compile code for the -NetBSD operating system. - -@item -mcall-openbsd -@opindex mcall-netbsd -On System V.4 and embedded PowerPC systems compile code for the -OpenBSD operating system. - -@item -mtraceback=@var{traceback_type} -@opindex mtraceback -Select the type of traceback table. Valid values for @var{traceback_type} -are @samp{full}, @samp{part}, and @samp{no}. - -@item -maix-struct-return -@opindex maix-struct-return -Return all structures in memory (as specified by the AIX ABI)@. - -@item -msvr4-struct-return -@opindex msvr4-struct-return -Return structures smaller than 8 bytes in registers (as specified by the -SVR4 ABI)@. - -@item -mabi=@var{abi-type} -@opindex mabi -Extend the current ABI with a particular extension, or remove such extension. -Valid values are: @samp{altivec}, @samp{no-altivec}, -@samp{ibmlongdouble}, @samp{ieeelongdouble}, -@samp{elfv1}, @samp{elfv2}, -and for AIX: @samp{vec-extabi}, @samp{vec-default}@. - -@item -mabi=ibmlongdouble -@opindex mabi=ibmlongdouble -Change the current ABI to use IBM extended-precision long double. -This is not likely to work if your system defaults to using IEEE -extended-precision long double. If you change the long double type -from IEEE extended-precision, the compiler will issue a warning unless -you use the @option{-Wno-psabi} option. Requires @option{-mlong-double-128} -to be enabled. - -@item -mabi=ieeelongdouble -@opindex mabi=ieeelongdouble -Change the current ABI to use IEEE extended-precision long double. -This is not likely to work if your system defaults to using IBM -extended-precision long double. If you change the long double type -from IBM extended-precision, the compiler will issue a warning unless -you use the @option{-Wno-psabi} option. Requires @option{-mlong-double-128} -to be enabled. - -@item -mabi=elfv1 -@opindex mabi=elfv1 -Change the current ABI to use the ELFv1 ABI. -This is the default ABI for big-endian PowerPC 64-bit Linux. -Overriding the default ABI requires special system support and is -likely to fail in spectacular ways. - -@item -mabi=elfv2 -@opindex mabi=elfv2 -Change the current ABI to use the ELFv2 ABI. -This is the default ABI for little-endian PowerPC 64-bit Linux. -Overriding the default ABI requires special system support and is -likely to fail in spectacular ways. - -@item -mgnu-attribute -@itemx -mno-gnu-attribute -@opindex mgnu-attribute -@opindex mno-gnu-attribute -Emit .gnu_attribute assembly directives to set tag/value pairs in a -.gnu.attributes section that specify ABI variations in function -parameters or return values. - -@item -mprototype -@itemx -mno-prototype -@opindex mprototype -@opindex mno-prototype -On System V.4 and embedded PowerPC systems assume that all calls to -variable argument functions are properly prototyped. Otherwise, the -compiler must insert an instruction before every non-prototyped call to -set or clear bit 6 of the condition code register (@code{CR}) to -indicate whether floating-point values are passed in the floating-point -registers in case the function takes variable arguments. With -@option{-mprototype}, only calls to prototyped variable argument functions -set or clear the bit. - -@item -msim -@opindex msim -On embedded PowerPC systems, assume that the startup module is called -@file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and -@file{libc.a}. This is the default for @samp{powerpc-*-eabisim} -configurations. - -@item -mmvme -@opindex mmvme -On embedded PowerPC systems, assume that the startup module is called -@file{crt0.o} and the standard C libraries are @file{libmvme.a} and -@file{libc.a}. - -@item -mads -@opindex mads -On embedded PowerPC systems, assume that the startup module is called -@file{crt0.o} and the standard C libraries are @file{libads.a} and -@file{libc.a}. - -@item -myellowknife -@opindex myellowknife -On embedded PowerPC systems, assume that the startup module is called -@file{crt0.o} and the standard C libraries are @file{libyk.a} and -@file{libc.a}. - -@item -mvxworks -@opindex mvxworks -On System V.4 and embedded PowerPC systems, specify that you are -compiling for a VxWorks system. - -@item -memb -@opindex memb -On embedded PowerPC systems, set the @code{PPC_EMB} bit in the ELF flags -header to indicate that @samp{eabi} extended relocations are used. - -@item -meabi -@itemx -mno-eabi -@opindex meabi -@opindex mno-eabi -On System V.4 and embedded PowerPC systems do (do not) adhere to the -Embedded Applications Binary Interface (EABI), which is a set of -modifications to the System V.4 specifications. Selecting @option{-meabi} -means that the stack is aligned to an 8-byte boundary, a function -@code{__eabi} is called from @code{main} to set up the EABI -environment, and the @option{-msdata} option can use both @code{r2} and -@code{r13} to point to two separate small data areas. Selecting -@option{-mno-eabi} means that the stack is aligned to a 16-byte boundary, -no EABI initialization function is called from @code{main}, and the -@option{-msdata} option only uses @code{r13} to point to a single -small data area. The @option{-meabi} option is on by default if you -configured GCC using one of the @samp{powerpc*-*-eabi*} options. - -@item -msdata=eabi -@opindex msdata=eabi -On System V.4 and embedded PowerPC systems, put small initialized -@code{const} global and static data in the @code{.sdata2} section, which -is pointed to by register @code{r2}. Put small initialized -non-@code{const} global and static data in the @code{.sdata} section, -which is pointed to by register @code{r13}. Put small uninitialized -global and static data in the @code{.sbss} section, which is adjacent to -the @code{.sdata} section. The @option{-msdata=eabi} option is -incompatible with the @option{-mrelocatable} option. The -@option{-msdata=eabi} option also sets the @option{-memb} option. - -@item -msdata=sysv -@opindex msdata=sysv -On System V.4 and embedded PowerPC systems, put small global and static -data in the @code{.sdata} section, which is pointed to by register -@code{r13}. Put small uninitialized global and static data in the -@code{.sbss} section, which is adjacent to the @code{.sdata} section. -The @option{-msdata=sysv} option is incompatible with the -@option{-mrelocatable} option. - -@item -msdata=default -@itemx -msdata -@opindex msdata=default -@opindex msdata -On System V.4 and embedded PowerPC systems, if @option{-meabi} is used, -compile code the same as @option{-msdata=eabi}, otherwise compile code the -same as @option{-msdata=sysv}. - -@item -msdata=data -@opindex msdata=data -On System V.4 and embedded PowerPC systems, put small global -data in the @code{.sdata} section. Put small uninitialized global -data in the @code{.sbss} section. Do not use register @code{r13} -to address small data however. This is the default behavior unless -other @option{-msdata} options are used. - -@item -msdata=none -@itemx -mno-sdata -@opindex msdata=none -@opindex mno-sdata -On embedded PowerPC systems, put all initialized global and static data -in the @code{.data} section, and all uninitialized data in the -@code{.bss} section. - -@item -mreadonly-in-sdata -@opindex mreadonly-in-sdata -@opindex mno-readonly-in-sdata -Put read-only objects in the @code{.sdata} section as well. This is the -default. - -@item -mblock-move-inline-limit=@var{num} -@opindex mblock-move-inline-limit -Inline all block moves (such as calls to @code{memcpy} or structure -copies) less than or equal to @var{num} bytes. The minimum value for -@var{num} is 32 bytes on 32-bit targets and 64 bytes on 64-bit -targets. The default value is target-specific. - -@item -mblock-compare-inline-limit=@var{num} -@opindex mblock-compare-inline-limit -Generate non-looping inline code for all block compares (such as calls -to @code{memcmp} or structure compares) less than or equal to @var{num} -bytes. If @var{num} is 0, all inline expansion (non-loop and loop) of -block compare is disabled. The default value is target-specific. - -@item -mblock-compare-inline-loop-limit=@var{num} -@opindex mblock-compare-inline-loop-limit -Generate an inline expansion using loop code for all block compares that -are less than or equal to @var{num} bytes, but greater than the limit -for non-loop inline block compare expansion. If the block length is not -constant, at most @var{num} bytes will be compared before @code{memcmp} -is called to compare the remainder of the block. The default value is -target-specific. - -@item -mstring-compare-inline-limit=@var{num} -@opindex mstring-compare-inline-limit -Compare at most @var{num} string bytes with inline code. -If the difference or end of string is not found at the -end of the inline compare a call to @code{strcmp} or @code{strncmp} will -take care of the rest of the comparison. The default is 64 bytes. - -@item -G @var{num} -@opindex G -@cindex smaller data references (PowerPC) -@cindex .sdata/.sdata2 references (PowerPC) -On embedded PowerPC systems, put global and static items less than or -equal to @var{num} bytes into the small data or BSS sections instead of -the normal data or BSS section. By default, @var{num} is 8. The -@option{-G @var{num}} switch is also passed to the linker. -All modules should be compiled with the same @option{-G @var{num}} value. - -@item -mregnames -@itemx -mno-regnames -@opindex mregnames -@opindex mno-regnames -On System V.4 and embedded PowerPC systems do (do not) emit register -names in the assembly language output using symbolic forms. - -@item -mlongcall -@itemx -mno-longcall -@opindex mlongcall -@opindex mno-longcall -By default assume that all calls are far away so that a longer and more -expensive calling sequence is required. This is required for calls -farther than 32 megabytes (33,554,432 bytes) from the current location. -A short call is generated if the compiler knows -the call cannot be that far away. This setting can be overridden by -the @code{shortcall} function attribute, or by @code{#pragma -longcall(0)}. - -Some linkers are capable of detecting out-of-range calls and generating -glue code on the fly. On these systems, long calls are unnecessary and -generate slower code. As of this writing, the AIX linker can do this, -as can the GNU linker for PowerPC/64. It is planned to add this feature -to the GNU linker for 32-bit PowerPC systems as well. - -On PowerPC64 ELFv2 and 32-bit PowerPC systems with newer GNU linkers, -GCC can generate long calls using an inline PLT call sequence (see -@option{-mpltseq}). PowerPC with @option{-mbss-plt} and PowerPC64 -ELFv1 (big-endian) do not support inline PLT calls. - -On Darwin/PPC systems, @code{#pragma longcall} generates @code{jbsr -callee, L42}, plus a @dfn{branch island} (glue code). The two target -addresses represent the callee and the branch island. The -Darwin/PPC linker prefers the first address and generates a @code{bl -callee} if the PPC @code{bl} instruction reaches the callee directly; -otherwise, the linker generates @code{bl L42} to call the branch -island. The branch island is appended to the body of the -calling function; it computes the full 32-bit address of the callee -and jumps to it. - -On Mach-O (Darwin) systems, this option directs the compiler emit to -the glue for every direct call, and the Darwin linker decides whether -to use or discard it. - -In the future, GCC may ignore all longcall specifications -when the linker is known to generate glue. - -@item -mpltseq -@itemx -mno-pltseq -@opindex mpltseq -@opindex mno-pltseq -Implement (do not implement) -fno-plt and long calls using an inline -PLT call sequence that supports lazy linking and long calls to -functions in dlopen'd shared libraries. Inline PLT calls are only -supported on PowerPC64 ELFv2 and 32-bit PowerPC systems with newer GNU -linkers, and are enabled by default if the support is detected when -configuring GCC, and, in the case of 32-bit PowerPC, if GCC is -configured with @option{--enable-secureplt}. @option{-mpltseq} code -and @option{-mbss-plt} 32-bit PowerPC relocatable objects may not be -linked together. - -@item -mtls-markers -@itemx -mno-tls-markers -@opindex mtls-markers -@opindex mno-tls-markers -Mark (do not mark) calls to @code{__tls_get_addr} with a relocation -specifying the function argument. The relocation allows the linker to -reliably associate function call with argument setup instructions for -TLS optimization, which in turn allows GCC to better schedule the -sequence. - -@item -mrecip -@itemx -mno-recip -@opindex mrecip -This option enables use of the reciprocal estimate and -reciprocal square root estimate instructions with additional -Newton-Raphson steps to increase precision instead of doing a divide or -square root and divide for floating-point arguments. You should use -the @option{-ffast-math} option when using @option{-mrecip} (or at -least @option{-funsafe-math-optimizations}, -@option{-ffinite-math-only}, @option{-freciprocal-math} and -@option{-fno-trapping-math}). Note that while the throughput of the -sequence is generally higher than the throughput of the non-reciprocal -instruction, the precision of the sequence can be decreased by up to 2 -ulp (i.e.@: the inverse of 1.0 equals 0.99999994) for reciprocal square -roots. - -@item -mrecip=@var{opt} -@opindex mrecip=opt -This option controls which reciprocal estimate instructions -may be used. @var{opt} is a comma-separated list of options, which may -be preceded by a @code{!} to invert the option: - -@table @samp - -@item all -Enable all estimate instructions. - -@item default -Enable the default instructions, equivalent to @option{-mrecip}. - -@item none -Disable all estimate instructions, equivalent to @option{-mno-recip}. - -@item div -Enable the reciprocal approximation instructions for both -single and double precision. - -@item divf -Enable the single-precision reciprocal approximation instructions. - -@item divd -Enable the double-precision reciprocal approximation instructions. - -@item rsqrt -Enable the reciprocal square root approximation instructions for both -single and double precision. - -@item rsqrtf -Enable the single-precision reciprocal square root approximation instructions. - -@item rsqrtd -Enable the double-precision reciprocal square root approximation instructions. - -@end table - -So, for example, @option{-mrecip=all,!rsqrtd} enables -all of the reciprocal estimate instructions, except for the -@code{FRSQRTE}, @code{XSRSQRTEDP}, and @code{XVRSQRTEDP} instructions -which handle the double-precision reciprocal square root calculations. - -@item -mrecip-precision -@itemx -mno-recip-precision -@opindex mrecip-precision -Assume (do not assume) that the reciprocal estimate instructions -provide higher-precision estimates than is mandated by the PowerPC -ABI. Selecting @option{-mcpu=power6}, @option{-mcpu=power7} or -@option{-mcpu=power8} automatically selects @option{-mrecip-precision}. -The double-precision square root estimate instructions are not generated by -default on low-precision machines, since they do not provide an -estimate that converges after three steps. - -@item -mveclibabi=@var{type} -@opindex mveclibabi -Specifies the ABI type to use for vectorizing intrinsics using an -external library. The only type supported at present is @samp{mass}, -which specifies to use IBM's Mathematical Acceleration Subsystem -(MASS) libraries for vectorizing intrinsics using external libraries. -GCC currently emits calls to @code{acosd2}, @code{acosf4}, -@code{acoshd2}, @code{acoshf4}, @code{asind2}, @code{asinf4}, -@code{asinhd2}, @code{asinhf4}, @code{atan2d2}, @code{atan2f4}, -@code{atand2}, @code{atanf4}, @code{atanhd2}, @code{atanhf4}, -@code{cbrtd2}, @code{cbrtf4}, @code{cosd2}, @code{cosf4}, -@code{coshd2}, @code{coshf4}, @code{erfcd2}, @code{erfcf4}, -@code{erfd2}, @code{erff4}, @code{exp2d2}, @code{exp2f4}, -@code{expd2}, @code{expf4}, @code{expm1d2}, @code{expm1f4}, -@code{hypotd2}, @code{hypotf4}, @code{lgammad2}, @code{lgammaf4}, -@code{log10d2}, @code{log10f4}, @code{log1pd2}, @code{log1pf4}, -@code{log2d2}, @code{log2f4}, @code{logd2}, @code{logf4}, -@code{powd2}, @code{powf4}, @code{sind2}, @code{sinf4}, @code{sinhd2}, -@code{sinhf4}, @code{sqrtd2}, @code{sqrtf4}, @code{tand2}, -@code{tanf4}, @code{tanhd2}, and @code{tanhf4} when generating code -for power7. Both @option{-ftree-vectorize} and -@option{-funsafe-math-optimizations} must also be enabled. The MASS -libraries must be specified at link time. - -@item -mfriz -@itemx -mno-friz -@opindex mfriz -Generate (do not generate) the @code{friz} instruction when the -@option{-funsafe-math-optimizations} option is used to optimize -rounding of floating-point values to 64-bit integer and back to floating -point. The @code{friz} instruction does not return the same value if -the floating-point number is too large to fit in an integer. - -@item -mpointers-to-nested-functions -@itemx -mno-pointers-to-nested-functions -@opindex mpointers-to-nested-functions -Generate (do not generate) code to load up the static chain register -(@code{r11}) when calling through a pointer on AIX and 64-bit Linux -systems where a function pointer points to a 3-word descriptor giving -the function address, TOC value to be loaded in register @code{r2}, and -static chain value to be loaded in register @code{r11}. The -@option{-mpointers-to-nested-functions} is on by default. You cannot -call through pointers to nested functions or pointers -to functions compiled in other languages that use the static chain if -you use @option{-mno-pointers-to-nested-functions}. - -@item -msave-toc-indirect -@itemx -mno-save-toc-indirect -@opindex msave-toc-indirect -Generate (do not generate) code to save the TOC value in the reserved -stack location in the function prologue if the function calls through -a pointer on AIX and 64-bit Linux systems. If the TOC value is not -saved in the prologue, it is saved just before the call through the -pointer. The @option{-mno-save-toc-indirect} option is the default. - -@item -mcompat-align-parm -@itemx -mno-compat-align-parm -@opindex mcompat-align-parm -Generate (do not generate) code to pass structure parameters with a -maximum alignment of 64 bits, for compatibility with older versions -of GCC. - -Older versions of GCC (prior to 4.9.0) incorrectly did not align a -structure parameter on a 128-bit boundary when that structure contained -a member requiring 128-bit alignment. This is corrected in more -recent versions of GCC. This option may be used to generate code -that is compatible with functions compiled with older versions of -GCC. - -The @option{-mno-compat-align-parm} option is the default. - -@item -mstack-protector-guard=@var{guard} -@itemx -mstack-protector-guard-reg=@var{reg} -@itemx -mstack-protector-guard-offset=@var{offset} -@itemx -mstack-protector-guard-symbol=@var{symbol} -@opindex mstack-protector-guard -@opindex mstack-protector-guard-reg -@opindex mstack-protector-guard-offset -@opindex mstack-protector-guard-symbol -Generate stack protection code using canary at @var{guard}. Supported -locations are @samp{global} for global canary or @samp{tls} for per-thread -canary in the TLS block (the default with GNU libc version 2.4 or later). - -With the latter choice the options -@option{-mstack-protector-guard-reg=@var{reg}} and -@option{-mstack-protector-guard-offset=@var{offset}} furthermore specify -which register to use as base register for reading the canary, and from what -offset from that base register. The default for those is as specified in the -relevant ABI. @option{-mstack-protector-guard-symbol=@var{symbol}} overrides -the offset with a symbol reference to a canary in the TLS block. - -@item -mpcrel -@itemx -mno-pcrel -@opindex mpcrel -@opindex mno-pcrel -Generate (do not generate) pc-relative addressing. The @option{-mpcrel} -option requires that the medium code model (@option{-mcmodel=medium}) -and prefixed addressing (@option{-mprefixed}) options are enabled. - -@item -mprefixed -@itemx -mno-prefixed -@opindex mprefixed -@opindex mno-prefixed -Generate (do not generate) addressing modes using prefixed load and -store instructions. The @option{-mprefixed} option requires that -the option @option{-mcpu=power10} (or later) is enabled. - -@item -mmma -@itemx -mno-mma -@opindex mmma -@opindex mno-mma -Generate (do not generate) the MMA instructions. The @option{-mma} -option requires that the option @option{-mcpu=power10} (or later) -is enabled. - -@item -mrop-protect -@itemx -mno-rop-protect -@opindex mrop-protect -@opindex mno-rop-protect -Generate (do not generate) ROP protection instructions when the target -processor supports them. Currently this option disables the shrink-wrap -optimization (@option{-fshrink-wrap}). - -@item -mprivileged -@itemx -mno-privileged -@opindex mprivileged -@opindex mno-privileged -Generate (do not generate) code that will run in privileged state. - -@item -mblock-ops-unaligned-vsx -@itemx -mno-block-ops-unaligned-vsx -@opindex block-ops-unaligned-vsx -@opindex no-block-ops-unaligned-vsx -Generate (do not generate) unaligned vsx loads and stores for -inline expansion of @code{memcpy} and @code{memmove}. - -@item --param rs6000-vect-unroll-limit= -The vectorizer will check with target information to determine whether it -would be beneficial to unroll the main vectorized loop and by how much. This -parameter sets the upper bound of how much the vectorizer will unroll the main -loop. The default value is four. - -@end table - -@node RX Options -@subsection RX Options -@cindex RX Options - -These command-line options are defined for RX targets: - -@table @gcctabopt -@item -m64bit-doubles -@itemx -m32bit-doubles -@opindex m64bit-doubles -@opindex m32bit-doubles -Make the @code{double} data type be 64 bits (@option{-m64bit-doubles}) -or 32 bits (@option{-m32bit-doubles}) in size. The default is -@option{-m32bit-doubles}. @emph{Note} RX floating-point hardware only -works on 32-bit values, which is why the default is -@option{-m32bit-doubles}. - -@item -fpu -@itemx -nofpu -@opindex fpu -@opindex nofpu -Enables (@option{-fpu}) or disables (@option{-nofpu}) the use of RX -floating-point hardware. The default is enabled for the RX600 -series and disabled for the RX200 series. - -Floating-point instructions are only generated for 32-bit floating-point -values, however, so the FPU hardware is not used for doubles if the -@option{-m64bit-doubles} option is used. - -@emph{Note} If the @option{-fpu} option is enabled then -@option{-funsafe-math-optimizations} is also enabled automatically. -This is because the RX FPU instructions are themselves unsafe. - -@item -mcpu=@var{name} -@opindex mcpu -Selects the type of RX CPU to be targeted. Currently three types are -supported, the generic @samp{RX600} and @samp{RX200} series hardware and -the specific @samp{RX610} CPU. The default is @samp{RX600}. - -The only difference between @samp{RX600} and @samp{RX610} is that the -@samp{RX610} does not support the @code{MVTIPL} instruction. - -The @samp{RX200} series does not have a hardware floating-point unit -and so @option{-nofpu} is enabled by default when this type is -selected. - -@item -mbig-endian-data -@itemx -mlittle-endian-data -@opindex mbig-endian-data -@opindex mlittle-endian-data -Store data (but not code) in the big-endian format. The default is -@option{-mlittle-endian-data}, i.e.@: to store data in the little-endian -format. - -@item -msmall-data-limit=@var{N} -@opindex msmall-data-limit -Specifies the maximum size in bytes of global and static variables -which can be placed into the small data area. Using the small data -area can lead to smaller and faster code, but the size of area is -limited and it is up to the programmer to ensure that the area does -not overflow. Also when the small data area is used one of the RX's -registers (usually @code{r13}) is reserved for use pointing to this -area, so it is no longer available for use by the compiler. This -could result in slower and/or larger code if variables are pushed onto -the stack instead of being held in this register. - -Note, common variables (variables that have not been initialized) and -constants are not placed into the small data area as they are assigned -to other sections in the output executable. - -The default value is zero, which disables this feature. Note, this -feature is not enabled by default with higher optimization levels -(@option{-O2} etc) because of the potentially detrimental effects of -reserving a register. It is up to the programmer to experiment and -discover whether this feature is of benefit to their program. See the -description of the @option{-mpid} option for a description of how the -actual register to hold the small data area pointer is chosen. - -@item -msim -@itemx -mno-sim -@opindex msim -@opindex mno-sim -Use the simulator runtime. The default is to use the libgloss -board-specific runtime. - -@item -mas100-syntax -@itemx -mno-as100-syntax -@opindex mas100-syntax -@opindex mno-as100-syntax -When generating assembler output use a syntax that is compatible with -Renesas's AS100 assembler. This syntax can also be handled by the GAS -assembler, but it has some restrictions so it is not generated by default. - -@item -mmax-constant-size=@var{N} -@opindex mmax-constant-size -Specifies the maximum size, in bytes, of a constant that can be used as -an operand in a RX instruction. Although the RX instruction set does -allow constants of up to 4 bytes in length to be used in instructions, -a longer value equates to a longer instruction. Thus in some -circumstances it can be beneficial to restrict the size of constants -that are used in instructions. Constants that are too big are instead -placed into a constant pool and referenced via register indirection. - -The value @var{N} can be between 0 and 4. A value of 0 (the default) -or 4 means that constants of any size are allowed. - -@item -mrelax -@opindex mrelax -Enable linker relaxation. Linker relaxation is a process whereby the -linker attempts to reduce the size of a program by finding shorter -versions of various instructions. Disabled by default. - -@item -mint-register=@var{N} -@opindex mint-register -Specify the number of registers to reserve for fast interrupt handler -functions. The value @var{N} can be between 0 and 4. A value of 1 -means that register @code{r13} is reserved for the exclusive use -of fast interrupt handlers. A value of 2 reserves @code{r13} and -@code{r12}. A value of 3 reserves @code{r13}, @code{r12} and -@code{r11}, and a value of 4 reserves @code{r13} through @code{r10}. -A value of 0, the default, does not reserve any registers. - -@item -msave-acc-in-interrupts -@opindex msave-acc-in-interrupts -Specifies that interrupt handler functions should preserve the -accumulator register. This is only necessary if normal code might use -the accumulator register, for example because it performs 64-bit -multiplications. The default is to ignore the accumulator as this -makes the interrupt handlers faster. - -@item -mpid -@itemx -mno-pid -@opindex mpid -@opindex mno-pid -Enables the generation of position independent data. When enabled any -access to constant data is done via an offset from a base address -held in a register. This allows the location of constant data to be -determined at run time without requiring the executable to be -relocated, which is a benefit to embedded applications with tight -memory constraints. Data that can be modified is not affected by this -option. - -Note, using this feature reserves a register, usually @code{r13}, for -the constant data base address. This can result in slower and/or -larger code, especially in complicated functions. - -The actual register chosen to hold the constant data base address -depends upon whether the @option{-msmall-data-limit} and/or the -@option{-mint-register} command-line options are enabled. Starting -with register @code{r13} and proceeding downwards, registers are -allocated first to satisfy the requirements of @option{-mint-register}, -then @option{-mpid} and finally @option{-msmall-data-limit}. Thus it -is possible for the small data area register to be @code{r8} if both -@option{-mint-register=4} and @option{-mpid} are specified on the -command line. - -By default this feature is not enabled. The default can be restored -via the @option{-mno-pid} command-line option. - -@item -mno-warn-multiple-fast-interrupts -@itemx -mwarn-multiple-fast-interrupts -@opindex mno-warn-multiple-fast-interrupts -@opindex mwarn-multiple-fast-interrupts -Prevents GCC from issuing a warning message if it finds more than one -fast interrupt handler when it is compiling a file. The default is to -issue a warning for each extra fast interrupt handler found, as the RX -only supports one such interrupt. - -@item -mallow-string-insns -@itemx -mno-allow-string-insns -@opindex mallow-string-insns -@opindex mno-allow-string-insns -Enables or disables the use of the string manipulation instructions -@code{SMOVF}, @code{SCMPU}, @code{SMOVB}, @code{SMOVU}, @code{SUNTIL} -@code{SWHILE} and also the @code{RMPA} instruction. These -instructions may prefetch data, which is not safe to do if accessing -an I/O register. (See section 12.2.7 of the RX62N Group User's Manual -for more information). - -The default is to allow these instructions, but it is not possible for -GCC to reliably detect all circumstances where a string instruction -might be used to access an I/O register, so their use cannot be -disabled automatically. Instead it is reliant upon the programmer to -use the @option{-mno-allow-string-insns} option if their program -accesses I/O space. - -When the instructions are enabled GCC defines the C preprocessor -symbol @code{__RX_ALLOW_STRING_INSNS__}, otherwise it defines the -symbol @code{__RX_DISALLOW_STRING_INSNS__}. - -@item -mjsr -@itemx -mno-jsr -@opindex mjsr -@opindex mno-jsr -Use only (or not only) @code{JSR} instructions to access functions. -This option can be used when code size exceeds the range of @code{BSR} -instructions. Note that @option{-mno-jsr} does not mean to not use -@code{JSR} but instead means that any type of branch may be used. -@end table - -@emph{Note:} The generic GCC command-line option @option{-ffixed-@var{reg}} -has special significance to the RX port when used with the -@code{interrupt} function attribute. This attribute indicates a -function intended to process fast interrupts. GCC ensures -that it only uses the registers @code{r10}, @code{r11}, @code{r12} -and/or @code{r13} and only provided that the normal use of the -corresponding registers have been restricted via the -@option{-ffixed-@var{reg}} or @option{-mint-register} command-line -options. - -@node S/390 and zSeries Options -@subsection S/390 and zSeries Options -@cindex S/390 and zSeries Options - -These are the @samp{-m} options defined for the S/390 and zSeries architecture. - -@table @gcctabopt -@item -mhard-float -@itemx -msoft-float -@opindex mhard-float -@opindex msoft-float -Use (do not use) the hardware floating-point instructions and registers -for floating-point operations. When @option{-msoft-float} is specified, -functions in @file{libgcc.a} are used to perform floating-point -operations. When @option{-mhard-float} is specified, the compiler -generates IEEE floating-point instructions. This is the default. - -@item -mhard-dfp -@itemx -mno-hard-dfp -@opindex mhard-dfp -@opindex mno-hard-dfp -Use (do not use) the hardware decimal-floating-point instructions for -decimal-floating-point operations. When @option{-mno-hard-dfp} is -specified, functions in @file{libgcc.a} are used to perform -decimal-floating-point operations. When @option{-mhard-dfp} is -specified, the compiler generates decimal-floating-point hardware -instructions. This is the default for @option{-march=z9-ec} or higher. - -@item -mlong-double-64 -@itemx -mlong-double-128 -@opindex mlong-double-64 -@opindex mlong-double-128 -These switches control the size of @code{long double} type. A size -of 64 bits makes the @code{long double} type equivalent to the @code{double} -type. This is the default. - -@item -mbackchain -@itemx -mno-backchain -@opindex mbackchain -@opindex mno-backchain -Store (do not store) the address of the caller's frame as backchain pointer -into the callee's stack frame. -A backchain may be needed to allow debugging using tools that do not understand -DWARF call frame information. -When @option{-mno-packed-stack} is in effect, the backchain pointer is stored -at the bottom of the stack frame; when @option{-mpacked-stack} is in effect, -the backchain is placed into the topmost word of the 96/160 byte register -save area. - -In general, code compiled with @option{-mbackchain} is call-compatible with -code compiled with @option{-mno-backchain}; however, use of the backchain -for debugging purposes usually requires that the whole binary is built with -@option{-mbackchain}. Note that the combination of @option{-mbackchain}, -@option{-mpacked-stack} and @option{-mhard-float} is not supported. In order -to build a linux kernel use @option{-msoft-float}. - -The default is to not maintain the backchain. - -@item -mpacked-stack -@itemx -mno-packed-stack -@opindex mpacked-stack -@opindex mno-packed-stack -Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is -specified, the compiler uses the all fields of the 96/160 byte register save -area only for their default purpose; unused fields still take up stack space. -When @option{-mpacked-stack} is specified, register save slots are densely -packed at the top of the register save area; unused space is reused for other -purposes, allowing for more efficient use of the available stack space. -However, when @option{-mbackchain} is also in effect, the topmost word of -the save area is always used to store the backchain, and the return address -register is always saved two words below the backchain. - -As long as the stack frame backchain is not used, code generated with -@option{-mpacked-stack} is call-compatible with code generated with -@option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for -S/390 or zSeries generated code that uses the stack frame backchain at run -time, not just for debugging purposes. Such code is not call-compatible -with code compiled with @option{-mpacked-stack}. Also, note that the -combination of @option{-mbackchain}, -@option{-mpacked-stack} and @option{-mhard-float} is not supported. In order -to build a linux kernel use @option{-msoft-float}. - -The default is to not use the packed stack layout. - -@item -msmall-exec -@itemx -mno-small-exec -@opindex msmall-exec -@opindex mno-small-exec -Generate (or do not generate) code using the @code{bras} instruction -to do subroutine calls. -This only works reliably if the total executable size does not -exceed 64k. The default is to use the @code{basr} instruction instead, -which does not have this limitation. - -@item -m64 -@itemx -m31 -@opindex m64 -@opindex m31 -When @option{-m31} is specified, generate code compliant to the -GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate -code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in -particular to generate 64-bit instructions. For the @samp{s390} -targets, the default is @option{-m31}, while the @samp{s390x} -targets default to @option{-m64}. - -@item -mzarch -@itemx -mesa -@opindex mzarch -@opindex mesa -When @option{-mzarch} is specified, generate code using the -instructions available on z/Architecture. -When @option{-mesa} is specified, generate code using the -instructions available on ESA/390. Note that @option{-mesa} is -not possible with @option{-m64}. -When generating code compliant to the GNU/Linux for S/390 ABI, -the default is @option{-mesa}. When generating code compliant -to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}. - -@item -mhtm -@itemx -mno-htm -@opindex mhtm -@opindex mno-htm -The @option{-mhtm} option enables a set of builtins making use of -instructions available with the transactional execution facility -introduced with the IBM zEnterprise EC12 machine generation -@ref{S/390 System z Built-in Functions}. -@option{-mhtm} is enabled by default when using @option{-march=zEC12}. - -@item -mvx -@itemx -mno-vx -@opindex mvx -@opindex mno-vx -When @option{-mvx} is specified, generate code using the instructions -available with the vector extension facility introduced with the IBM -z13 machine generation. -This option changes the ABI for some vector type values with regard to -alignment and calling conventions. In case vector type values are -being used in an ABI-relevant context a GAS @samp{.gnu_attribute} -command will be added to mark the resulting binary with the ABI used. -@option{-mvx} is enabled by default when using @option{-march=z13}. - -@item -mzvector -@itemx -mno-zvector -@opindex mzvector -@opindex mno-zvector -The @option{-mzvector} option enables vector language extensions and -builtins using instructions available with the vector extension -facility introduced with the IBM z13 machine generation. -This option adds support for @samp{vector} to be used as a keyword to -define vector type variables and arguments. @samp{vector} is only -available when GNU extensions are enabled. It will not be expanded -when requesting strict standard compliance e.g.@: with @option{-std=c99}. -In addition to the GCC low-level builtins @option{-mzvector} enables -a set of builtins added for compatibility with AltiVec-style -implementations like Power and Cell. In order to make use of these -builtins the header file @file{vecintrin.h} needs to be included. -@option{-mzvector} is disabled by default. - -@item -mmvcle -@itemx -mno-mvcle -@opindex mmvcle -@opindex mno-mvcle -Generate (or do not generate) code using the @code{mvcle} instruction -to perform block moves. When @option{-mno-mvcle} is specified, -use a @code{mvc} loop instead. This is the default unless optimizing for -size. - -@item -mdebug -@itemx -mno-debug -@opindex mdebug -@opindex mno-debug -Print (or do not print) additional debug information when compiling. -The default is to not print debug information. - -@item -march=@var{cpu-type} -@opindex march -Generate code that runs on @var{cpu-type}, which is the name of a -system representing a certain processor type. Possible values for -@var{cpu-type} are @samp{z900}/@samp{arch5}, @samp{z990}/@samp{arch6}, -@samp{z9-109}, @samp{z9-ec}/@samp{arch7}, @samp{z10}/@samp{arch8}, -@samp{z196}/@samp{arch9}, @samp{zEC12}, @samp{z13}/@samp{arch11}, -@samp{z14}/@samp{arch12}, @samp{z15}/@samp{arch13}, -@samp{z16}/@samp{arch14}, and @samp{native}. - -The default is @option{-march=z900}. - -Specifying @samp{native} as cpu type can be used to select the best -architecture option for the host processor. -@option{-march=native} has no effect if GCC does not recognize the -processor. - -@item -mtune=@var{cpu-type} -@opindex mtune -Tune to @var{cpu-type} everything applicable about the generated code, -except for the ABI and the set of available instructions. -The list of @var{cpu-type} values is the same as for @option{-march}. -The default is the value used for @option{-march}. - -@item -mtpf-trace -@itemx -mno-tpf-trace -@opindex mtpf-trace -@opindex mno-tpf-trace -Generate code that adds (does not add) in TPF OS specific branches to trace -routines in the operating system. This option is off by default, even -when compiling for the TPF OS@. - -@item -mtpf-trace-skip -@itemx -mno-tpf-trace-skip -@opindex mtpf-trace-skip -@opindex mno-tpf-trace-skip -Generate code that changes (does not change) the default branch -targets enabled by @option{-mtpf-trace} to point to specialized trace -routines providing the ability of selectively skipping function trace -entries for the TPF OS. This option is off by default, even when -compiling for the TPF OS and specifying @option{-mtpf-trace}. - -@item -mfused-madd -@itemx -mno-fused-madd -@opindex mfused-madd -@opindex mno-fused-madd -Generate code that uses (does not use) the floating-point multiply and -accumulate instructions. These instructions are generated by default if -hardware floating point is used. - -@item -mwarn-framesize=@var{framesize} -@opindex mwarn-framesize -Emit a warning if the current function exceeds the given frame size. Because -this is a compile-time check it doesn't need to be a real problem when the program -runs. It is intended to identify functions that most probably cause -a stack overflow. It is useful to be used in an environment with limited stack -size e.g.@: the linux kernel. - -@item -mwarn-dynamicstack -@opindex mwarn-dynamicstack -Emit a warning if the function calls @code{alloca} or uses dynamically-sized -arrays. This is generally a bad idea with a limited stack size. - -@item -mstack-guard=@var{stack-guard} -@itemx -mstack-size=@var{stack-size} -@opindex mstack-guard -@opindex mstack-size -If these options are provided the S/390 back end emits additional instructions in -the function prologue that trigger a trap if the stack size is @var{stack-guard} -bytes above the @var{stack-size} (remember that the stack on S/390 grows downward). -If the @var{stack-guard} option is omitted the smallest power of 2 larger than -the frame size of the compiled function is chosen. -These options are intended to be used to help debugging stack overflow problems. -The additionally emitted code causes only little overhead and hence can also be -used in production-like systems without greater performance degradation. The given -values have to be exact powers of 2 and @var{stack-size} has to be greater than -@var{stack-guard} without exceeding 64k. -In order to be efficient the extra code makes the assumption that the stack starts -at an address aligned to the value given by @var{stack-size}. -The @var{stack-guard} option can only be used in conjunction with @var{stack-size}. - -@item -mhotpatch=@var{pre-halfwords},@var{post-halfwords} -@opindex mhotpatch -If the hotpatch option is enabled, a ``hot-patching'' function -prologue is generated for all functions in the compilation unit. -The funtion label is prepended with the given number of two-byte -NOP instructions (@var{pre-halfwords}, maximum 1000000). After -the label, 2 * @var{post-halfwords} bytes are appended, using the -largest NOP like instructions the architecture allows (maximum -1000000). - -If both arguments are zero, hotpatching is disabled. - -This option can be overridden for individual functions with the -@code{hotpatch} attribute. -@end table - -@node Score Options -@subsection Score Options -@cindex Score Options - -These options are defined for Score implementations: - -@table @gcctabopt -@item -meb -@opindex meb -Compile code for big-endian mode. This is the default. - -@item -mel -@opindex mel -Compile code for little-endian mode. - -@item -mnhwloop -@opindex mnhwloop -Disable generation of @code{bcnz} instructions. - -@item -muls -@opindex muls -Enable generation of unaligned load and store instructions. - -@item -mmac -@opindex mmac -Enable the use of multiply-accumulate instructions. Disabled by default. - -@item -mscore5 -@opindex mscore5 -Specify the SCORE5 as the target architecture. - -@item -mscore5u -@opindex mscore5u -Specify the SCORE5U of the target architecture. - -@item -mscore7 -@opindex mscore7 -Specify the SCORE7 as the target architecture. This is the default. - -@item -mscore7d -@opindex mscore7d -Specify the SCORE7D as the target architecture. -@end table - -@node SH Options -@subsection SH Options - -These @samp{-m} options are defined for the SH implementations: - -@table @gcctabopt -@item -m1 -@opindex m1 -Generate code for the SH1. - -@item -m2 -@opindex m2 -Generate code for the SH2. - -@item -m2e -Generate code for the SH2e. - -@item -m2a-nofpu -@opindex m2a-nofpu -Generate code for the SH2a without FPU, or for a SH2a-FPU in such a way -that the floating-point unit is not used. - -@item -m2a-single-only -@opindex m2a-single-only -Generate code for the SH2a-FPU, in such a way that no double-precision -floating-point operations are used. - -@item -m2a-single -@opindex m2a-single -Generate code for the SH2a-FPU assuming the floating-point unit is in -single-precision mode by default. - -@item -m2a -@opindex m2a -Generate code for the SH2a-FPU assuming the floating-point unit is in -double-precision mode by default. - -@item -m3 -@opindex m3 -Generate code for the SH3. - -@item -m3e -@opindex m3e -Generate code for the SH3e. - -@item -m4-nofpu -@opindex m4-nofpu -Generate code for the SH4 without a floating-point unit. - -@item -m4-single-only -@opindex m4-single-only -Generate code for the SH4 with a floating-point unit that only -supports single-precision arithmetic. - -@item -m4-single -@opindex m4-single -Generate code for the SH4 assuming the floating-point unit is in -single-precision mode by default. - -@item -m4 -@opindex m4 -Generate code for the SH4. - -@item -m4-100 -@opindex m4-100 -Generate code for SH4-100. - -@item -m4-100-nofpu -@opindex m4-100-nofpu -Generate code for SH4-100 in such a way that the -floating-point unit is not used. - -@item -m4-100-single -@opindex m4-100-single -Generate code for SH4-100 assuming the floating-point unit is in -single-precision mode by default. - -@item -m4-100-single-only -@opindex m4-100-single-only -Generate code for SH4-100 in such a way that no double-precision -floating-point operations are used. - -@item -m4-200 -@opindex m4-200 -Generate code for SH4-200. - -@item -m4-200-nofpu -@opindex m4-200-nofpu -Generate code for SH4-200 without in such a way that the -floating-point unit is not used. - -@item -m4-200-single -@opindex m4-200-single -Generate code for SH4-200 assuming the floating-point unit is in -single-precision mode by default. - -@item -m4-200-single-only -@opindex m4-200-single-only -Generate code for SH4-200 in such a way that no double-precision -floating-point operations are used. - -@item -m4-300 -@opindex m4-300 -Generate code for SH4-300. - -@item -m4-300-nofpu -@opindex m4-300-nofpu -Generate code for SH4-300 without in such a way that the -floating-point unit is not used. - -@item -m4-300-single -@opindex m4-300-single -Generate code for SH4-300 in such a way that no double-precision -floating-point operations are used. - -@item -m4-300-single-only -@opindex m4-300-single-only -Generate code for SH4-300 in such a way that no double-precision -floating-point operations are used. - -@item -m4-340 -@opindex m4-340 -Generate code for SH4-340 (no MMU, no FPU). - -@item -m4-500 -@opindex m4-500 -Generate code for SH4-500 (no FPU). Passes @option{-isa=sh4-nofpu} to the -assembler. - -@item -m4a-nofpu -@opindex m4a-nofpu -Generate code for the SH4al-dsp, or for a SH4a in such a way that the -floating-point unit is not used. - -@item -m4a-single-only -@opindex m4a-single-only -Generate code for the SH4a, in such a way that no double-precision -floating-point operations are used. - -@item -m4a-single -@opindex m4a-single -Generate code for the SH4a assuming the floating-point unit is in -single-precision mode by default. - -@item -m4a -@opindex m4a -Generate code for the SH4a. - -@item -m4al -@opindex m4al -Same as @option{-m4a-nofpu}, except that it implicitly passes -@option{-dsp} to the assembler. GCC doesn't generate any DSP -instructions at the moment. - -@item -mb -@opindex mb -Compile code for the processor in big-endian mode. - -@item -ml -@opindex ml -Compile code for the processor in little-endian mode. - -@item -mdalign -@opindex mdalign -Align doubles at 64-bit boundaries. Note that this changes the calling -conventions, and thus some functions from the standard C library do -not work unless you recompile it first with @option{-mdalign}. - -@item -mrelax -@opindex mrelax -Shorten some address references at link time, when possible; uses the -linker option @option{-relax}. - -@item -mbigtable -@opindex mbigtable -Use 32-bit offsets in @code{switch} tables. The default is to use -16-bit offsets. - -@item -mbitops -@opindex mbitops -Enable the use of bit manipulation instructions on SH2A. - -@item -mfmovd -@opindex mfmovd -Enable the use of the instruction @code{fmovd}. Check @option{-mdalign} for -alignment constraints. - -@item -mrenesas -@opindex mrenesas -Comply with the calling conventions defined by Renesas. - -@item -mno-renesas -@opindex mno-renesas -Comply with the calling conventions defined for GCC before the Renesas -conventions were available. This option is the default for all -targets of the SH toolchain. - -@item -mnomacsave -@opindex mnomacsave -Mark the @code{MAC} register as call-clobbered, even if -@option{-mrenesas} is given. - -@item -mieee -@itemx -mno-ieee -@opindex mieee -@opindex mno-ieee -Control the IEEE compliance of floating-point comparisons, which affects the -handling of cases where the result of a comparison is unordered. By default -@option{-mieee} is implicitly enabled. If @option{-ffinite-math-only} is -enabled @option{-mno-ieee} is implicitly set, which results in faster -floating-point greater-equal and less-equal comparisons. The implicit settings -can be overridden by specifying either @option{-mieee} or @option{-mno-ieee}. - -@item -minline-ic_invalidate -@opindex minline-ic_invalidate -Inline code to invalidate instruction cache entries after setting up -nested function trampolines. -This option has no effect if @option{-musermode} is in effect and the selected -code generation option (e.g.@: @option{-m4}) does not allow the use of the @code{icbi} -instruction. -If the selected code generation option does not allow the use of the @code{icbi} -instruction, and @option{-musermode} is not in effect, the inlined code -manipulates the instruction cache address array directly with an associative -write. This not only requires privileged mode at run time, but it also -fails if the cache line had been mapped via the TLB and has become unmapped. - -@item -misize -@opindex misize -Dump instruction size and location in the assembly code. - -@item -mpadstruct -@opindex mpadstruct -This option is deprecated. It pads structures to multiple of 4 bytes, -which is incompatible with the SH ABI@. - -@item -matomic-model=@var{model} -@opindex matomic-model=@var{model} -Sets the model of atomic operations and additional parameters as a comma -separated list. For details on the atomic built-in functions see -@ref{__atomic Builtins}. The following models and parameters are supported: - -@table @samp - -@item none -Disable compiler generated atomic sequences and emit library calls for atomic -operations. This is the default if the target is not @code{sh*-*-linux*}. - -@item soft-gusa -Generate GNU/Linux compatible gUSA software atomic sequences for the atomic -built-in functions. The generated atomic sequences require additional support -from the interrupt/exception handling code of the system and are only suitable -for SH3* and SH4* single-core systems. This option is enabled by default when -the target is @code{sh*-*-linux*} and SH3* or SH4*. When the target is SH4A, -this option also partially utilizes the hardware atomic instructions -@code{movli.l} and @code{movco.l} to create more efficient code, unless -@samp{strict} is specified. - -@item soft-tcb -Generate software atomic sequences that use a variable in the thread control -block. This is a variation of the gUSA sequences which can also be used on -SH1* and SH2* targets. The generated atomic sequences require additional -support from the interrupt/exception handling code of the system and are only -suitable for single-core systems. When using this model, the @samp{gbr-offset=} -parameter has to be specified as well. - -@item soft-imask -Generate software atomic sequences that temporarily disable interrupts by -setting @code{SR.IMASK = 1111}. This model works only when the program runs -in privileged mode and is only suitable for single-core systems. Additional -support from the interrupt/exception handling code of the system is not -required. This model is enabled by default when the target is -@code{sh*-*-linux*} and SH1* or SH2*. - -@item hard-llcs -Generate hardware atomic sequences using the @code{movli.l} and @code{movco.l} -instructions only. This is only available on SH4A and is suitable for -multi-core systems. Since the hardware instructions support only 32 bit atomic -variables access to 8 or 16 bit variables is emulated with 32 bit accesses. -Code compiled with this option is also compatible with other software -atomic model interrupt/exception handling systems if executed on an SH4A -system. Additional support from the interrupt/exception handling code of the -system is not required for this model. - -@item gbr-offset= -This parameter specifies the offset in bytes of the variable in the thread -control block structure that should be used by the generated atomic sequences -when the @samp{soft-tcb} model has been selected. For other models this -parameter is ignored. The specified value must be an integer multiple of four -and in the range 0-1020. - -@item strict -This parameter prevents mixed usage of multiple atomic models, even if they -are compatible, and makes the compiler generate atomic sequences of the -specified model only. - -@end table - -@item -mtas -@opindex mtas -Generate the @code{tas.b} opcode for @code{__atomic_test_and_set}. -Notice that depending on the particular hardware and software configuration -this can degrade overall performance due to the operand cache line flushes -that are implied by the @code{tas.b} instruction. On multi-core SH4A -processors the @code{tas.b} instruction must be used with caution since it -can result in data corruption for certain cache configurations. - -@item -mprefergot -@opindex mprefergot -When generating position-independent code, emit function calls using -the Global Offset Table instead of the Procedure Linkage Table. - -@item -musermode -@itemx -mno-usermode -@opindex musermode -@opindex mno-usermode -Don't allow (allow) the compiler generating privileged mode code. Specifying -@option{-musermode} also implies @option{-mno-inline-ic_invalidate} if the -inlined code would not work in user mode. @option{-musermode} is the default -when the target is @code{sh*-*-linux*}. If the target is SH1* or SH2* -@option{-musermode} has no effect, since there is no user mode. - -@item -multcost=@var{number} -@opindex multcost=@var{number} -Set the cost to assume for a multiply insn. - -@item -mdiv=@var{strategy} -@opindex mdiv=@var{strategy} -Set the division strategy to be used for integer division operations. -@var{strategy} can be one of: - -@table @samp - -@item call-div1 -Calls a library function that uses the single-step division instruction -@code{div1} to perform the operation. Division by zero calculates an -unspecified result and does not trap. This is the default except for SH4, -SH2A and SHcompact. - -@item call-fp -Calls a library function that performs the operation in double precision -floating point. Division by zero causes a floating-point exception. This is -the default for SHcompact with FPU. Specifying this for targets that do not -have a double precision FPU defaults to @code{call-div1}. - -@item call-table -Calls a library function that uses a lookup table for small divisors and -the @code{div1} instruction with case distinction for larger divisors. Division -by zero calculates an unspecified result and does not trap. This is the default -for SH4. Specifying this for targets that do not have dynamic shift -instructions defaults to @code{call-div1}. - -@end table - -When a division strategy has not been specified the default strategy is -selected based on the current target. For SH2A the default strategy is to -use the @code{divs} and @code{divu} instructions instead of library function -calls. - -@item -maccumulate-outgoing-args -@opindex maccumulate-outgoing-args -Reserve space once for outgoing arguments in the function prologue rather -than around each call. Generally beneficial for performance and size. Also -needed for unwinding to avoid changing the stack frame around conditional code. - -@item -mdivsi3_libfunc=@var{name} -@opindex mdivsi3_libfunc=@var{name} -Set the name of the library function used for 32-bit signed division to -@var{name}. -This only affects the name used in the @samp{call} division strategies, and -the compiler still expects the same sets of input/output/clobbered registers as -if this option were not present. - -@item -mfixed-range=@var{register-range} -@opindex mfixed-range -Generate code treating the given register range as fixed registers. -A fixed register is one that the register allocator cannot use. This is -useful when compiling kernel code. A register range is specified as -two registers separated by a dash. Multiple register ranges can be -specified separated by a comma. - -@item -mbranch-cost=@var{num} -@opindex mbranch-cost=@var{num} -Assume @var{num} to be the cost for a branch instruction. Higher numbers -make the compiler try to generate more branch-free code if possible. -If not specified the value is selected depending on the processor type that -is being compiled for. - -@item -mzdcbranch -@itemx -mno-zdcbranch -@opindex mzdcbranch -@opindex mno-zdcbranch -Assume (do not assume) that zero displacement conditional branch instructions -@code{bt} and @code{bf} are fast. If @option{-mzdcbranch} is specified, the -compiler prefers zero displacement branch code sequences. This is -enabled by default when generating code for SH4 and SH4A. It can be explicitly -disabled by specifying @option{-mno-zdcbranch}. - -@item -mcbranch-force-delay-slot -@opindex mcbranch-force-delay-slot -Force the usage of delay slots for conditional branches, which stuffs the delay -slot with a @code{nop} if a suitable instruction cannot be found. By default -this option is disabled. It can be enabled to work around hardware bugs as -found in the original SH7055. - -@item -mfused-madd -@itemx -mno-fused-madd -@opindex mfused-madd -@opindex mno-fused-madd -Generate code that uses (does not use) the floating-point multiply and -accumulate instructions. These instructions are generated by default -if hardware floating point is used. The machine-dependent -@option{-mfused-madd} option is now mapped to the machine-independent -@option{-ffp-contract=fast} option, and @option{-mno-fused-madd} is -mapped to @option{-ffp-contract=off}. - -@item -mfsca -@itemx -mno-fsca -@opindex mfsca -@opindex mno-fsca -Allow or disallow the compiler to emit the @code{fsca} instruction for sine -and cosine approximations. The option @option{-mfsca} must be used in -combination with @option{-funsafe-math-optimizations}. It is enabled by default -when generating code for SH4A. Using @option{-mno-fsca} disables sine and cosine -approximations even if @option{-funsafe-math-optimizations} is in effect. - -@item -mfsrra -@itemx -mno-fsrra -@opindex mfsrra -@opindex mno-fsrra -Allow or disallow the compiler to emit the @code{fsrra} instruction for -reciprocal square root approximations. The option @option{-mfsrra} must be used -in combination with @option{-funsafe-math-optimizations} and -@option{-ffinite-math-only}. It is enabled by default when generating code for -SH4A. Using @option{-mno-fsrra} disables reciprocal square root approximations -even if @option{-funsafe-math-optimizations} and @option{-ffinite-math-only} are -in effect. - -@item -mpretend-cmove -@opindex mpretend-cmove -Prefer zero-displacement conditional branches for conditional move instruction -patterns. This can result in faster code on the SH4 processor. - -@item -mfdpic -@opindex fdpic -Generate code using the FDPIC ABI. - -@end table - -@node Solaris 2 Options -@subsection Solaris 2 Options -@cindex Solaris 2 options - -These @samp{-m} options are supported on Solaris 2: - -@table @gcctabopt -@item -mclear-hwcap -@opindex mclear-hwcap -@option{-mclear-hwcap} tells the compiler to remove the hardware -capabilities generated by the Solaris assembler. This is only necessary -when object files use ISA extensions not supported by the current -machine, but check at runtime whether or not to use them. - -@item -mimpure-text -@opindex mimpure-text -@option{-mimpure-text}, used in addition to @option{-shared}, tells -the compiler to not pass @option{-z text} to the linker when linking a -shared object. Using this option, you can link position-dependent -code into a shared object. - -@option{-mimpure-text} suppresses the ``relocations remain against -allocatable but non-writable sections'' linker error message. -However, the necessary relocations trigger copy-on-write, and the -shared object is not actually shared across processes. Instead of -using @option{-mimpure-text}, you should compile all source code with -@option{-fpic} or @option{-fPIC}. - -@end table - -These switches are supported in addition to the above on Solaris 2: - -@table @gcctabopt -@item -pthreads -@opindex pthreads -This is a synonym for @option{-pthread}. -@end table - -@node SPARC Options -@subsection SPARC Options -@cindex SPARC options - -These @samp{-m} options are supported on the SPARC: - -@table @gcctabopt -@item -mno-app-regs -@itemx -mapp-regs -@opindex mno-app-regs -@opindex mapp-regs -Specify @option{-mapp-regs} to generate output using the global registers -2 through 4, which the SPARC SVR4 ABI reserves for applications. Like the -global register 1, each global register 2 through 4 is then treated as an -allocable register that is clobbered by function calls. This is the default. - -To be fully SVR4 ABI-compliant at the cost of some performance loss, -specify @option{-mno-app-regs}. You should compile libraries and system -software with this option. - -@item -mflat -@itemx -mno-flat -@opindex mflat -@opindex mno-flat -With @option{-mflat}, the compiler does not generate save/restore instructions -and uses a ``flat'' or single register window model. This model is compatible -with the regular register window model. The local registers and the input -registers (0--5) are still treated as ``call-saved'' registers and are -saved on the stack as needed. - -With @option{-mno-flat} (the default), the compiler generates save/restore -instructions (except for leaf functions). This is the normal operating mode. - -@item -mfpu -@itemx -mhard-float -@opindex mfpu -@opindex mhard-float -Generate output containing floating-point instructions. This is the -default. - -@item -mno-fpu -@itemx -msoft-float -@opindex mno-fpu -@opindex msoft-float -Generate output containing library calls for floating point. -@strong{Warning:} the requisite libraries are not available for all SPARC -targets. Normally the facilities of the machine's usual C compiler are -used, but this cannot be done directly in cross-compilation. You must make -your own arrangements to provide suitable library functions for -cross-compilation. The embedded targets @samp{sparc-*-aout} and -@samp{sparclite-*-*} do provide software floating-point support. - -@option{-msoft-float} changes the calling convention in the output file; -therefore, it is only useful if you compile @emph{all} of a program with -this option. In particular, you need to compile @file{libgcc.a}, the -library that comes with GCC, with @option{-msoft-float} in order for -this to work. - -@item -mhard-quad-float -@opindex mhard-quad-float -Generate output containing quad-word (long double) floating-point -instructions. - -@item -msoft-quad-float -@opindex msoft-quad-float -Generate output containing library calls for quad-word (long double) -floating-point instructions. The functions called are those specified -in the SPARC ABI@. This is the default. - -As of this writing, there are no SPARC implementations that have hardware -support for the quad-word floating-point instructions. They all invoke -a trap handler for one of these instructions, and then the trap handler -emulates the effect of the instruction. Because of the trap handler overhead, -this is much slower than calling the ABI library routines. Thus the -@option{-msoft-quad-float} option is the default. - -@item -mno-unaligned-doubles -@itemx -munaligned-doubles -@opindex mno-unaligned-doubles -@opindex munaligned-doubles -Assume that doubles have 8-byte alignment. This is the default. - -With @option{-munaligned-doubles}, GCC assumes that doubles have 8-byte -alignment only if they are contained in another type, or if they have an -absolute address. Otherwise, it assumes they have 4-byte alignment. -Specifying this option avoids some rare compatibility problems with code -generated by other compilers. It is not the default because it results -in a performance loss, especially for floating-point code. - -@item -muser-mode -@itemx -mno-user-mode -@opindex muser-mode -@opindex mno-user-mode -Do not generate code that can only run in supervisor mode. This is relevant -only for the @code{casa} instruction emitted for the LEON3 processor. This -is the default. - -@item -mfaster-structs -@itemx -mno-faster-structs -@opindex mfaster-structs -@opindex mno-faster-structs -With @option{-mfaster-structs}, the compiler assumes that structures -should have 8-byte alignment. This enables the use of pairs of -@code{ldd} and @code{std} instructions for copies in structure -assignment, in place of twice as many @code{ld} and @code{st} pairs. -However, the use of this changed alignment directly violates the SPARC -ABI@. Thus, it's intended only for use on targets where the developer -acknowledges that their resulting code is not directly in line with -the rules of the ABI@. - -@item -mstd-struct-return -@itemx -mno-std-struct-return -@opindex mstd-struct-return -@opindex mno-std-struct-return -With @option{-mstd-struct-return}, the compiler generates checking code -in functions returning structures or unions to detect size mismatches -between the two sides of function calls, as per the 32-bit ABI@. - -The default is @option{-mno-std-struct-return}. This option has no effect -in 64-bit mode. - -@item -mlra -@itemx -mno-lra -@opindex mlra -@opindex mno-lra -Enable Local Register Allocation. This is the default for SPARC since GCC 7 -so @option{-mno-lra} needs to be passed to get old Reload. - -@item -mcpu=@var{cpu_type} -@opindex mcpu -Set the instruction set, register set, and instruction scheduling parameters -for machine type @var{cpu_type}. Supported values for @var{cpu_type} are -@samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{hypersparc}, -@samp{leon}, @samp{leon3}, @samp{leon3v7}, @samp{leon5}, @samp{sparclite}, -@samp{f930}, @samp{f934}, @samp{sparclite86x}, @samp{sparclet}, @samp{tsc701}, -@samp{v9}, @samp{ultrasparc}, @samp{ultrasparc3}, @samp{niagara}, -@samp{niagara2}, @samp{niagara3}, @samp{niagara4}, @samp{niagara7} and -@samp{m8}. - -Native Solaris and GNU/Linux toolchains also support the value @samp{native}, -which selects the best architecture option for the host processor. -@option{-mcpu=native} has no effect if GCC does not recognize -the processor. - -Default instruction scheduling parameters are used for values that select -an architecture and not an implementation. These are @samp{v7}, @samp{v8}, -@samp{sparclite}, @samp{sparclet}, @samp{v9}. - -Here is a list of each supported architecture and their supported -implementations. - -@table @asis -@item v7 -cypress, leon3v7 - -@item v8 -supersparc, hypersparc, leon, leon3, leon5 - -@item sparclite -f930, f934, sparclite86x - -@item sparclet -tsc701 - -@item v9 -ultrasparc, ultrasparc3, niagara, niagara2, niagara3, niagara4, -niagara7, m8 -@end table - -By default (unless configured otherwise), GCC generates code for the V7 -variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler -additionally optimizes it for the Cypress CY7C602 chip, as used in the -SPARCStation/SPARCServer 3xx series. This is also appropriate for the older -SPARCStation 1, 2, IPX etc. - -With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC -architecture. The only difference from V7 code is that the compiler emits -the integer multiply and integer divide instructions which exist in SPARC-V8 -but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally -optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and -2000 series. - -With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of -the SPARC architecture. This adds the integer multiply, integer divide step -and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7. -With @option{-mcpu=f930}, the compiler additionally optimizes it for the -Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With -@option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu -MB86934 chip, which is the more recent SPARClite with FPU@. - -With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of -the SPARC architecture. This adds the integer multiply, multiply/accumulate, -integer divide step and scan (@code{ffs}) instructions which exist in SPARClet -but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally -optimizes it for the TEMIC SPARClet chip. - -With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC -architecture. This adds 64-bit integer and floating-point move instructions, -3 additional floating-point condition code registers and conditional move -instructions. With @option{-mcpu=ultrasparc}, the compiler additionally -optimizes it for the Sun UltraSPARC I/II/IIi chips. With -@option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the -Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With -@option{-mcpu=niagara}, the compiler additionally optimizes it for -Sun UltraSPARC T1 chips. With @option{-mcpu=niagara2}, the compiler -additionally optimizes it for Sun UltraSPARC T2 chips. With -@option{-mcpu=niagara3}, the compiler additionally optimizes it for Sun -UltraSPARC T3 chips. With @option{-mcpu=niagara4}, the compiler -additionally optimizes it for Sun UltraSPARC T4 chips. With -@option{-mcpu=niagara7}, the compiler additionally optimizes it for -Oracle SPARC M7 chips. With @option{-mcpu=m8}, the compiler -additionally optimizes it for Oracle M8 chips. - -@item -mtune=@var{cpu_type} -@opindex mtune -Set the instruction scheduling parameters for machine type -@var{cpu_type}, but do not set the instruction set or register set that the -option @option{-mcpu=@var{cpu_type}} does. - -The same values for @option{-mcpu=@var{cpu_type}} can be used for -@option{-mtune=@var{cpu_type}}, but the only useful values are those -that select a particular CPU implementation. Those are -@samp{cypress}, @samp{supersparc}, @samp{hypersparc}, @samp{leon}, -@samp{leon3}, @samp{leon3v7}, @samp{leon5}, @samp{f930}, @samp{f934}, -@samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc}, -@samp{ultrasparc3}, @samp{niagara}, @samp{niagara2}, @samp{niagara3}, -@samp{niagara4}, @samp{niagara7} and @samp{m8}. With native Solaris -and GNU/Linux toolchains, @samp{native} can also be used. - -@item -mv8plus -@itemx -mno-v8plus -@opindex mv8plus -@opindex mno-v8plus -With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The -difference from the V8 ABI is that the global and out registers are -considered 64 bits wide. This is enabled by default on Solaris in 32-bit -mode for all SPARC-V9 processors. - -@item -mvis -@itemx -mno-vis -@opindex mvis -@opindex mno-vis -With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC -Visual Instruction Set extensions. The default is @option{-mno-vis}. - -@item -mvis2 -@itemx -mno-vis2 -@opindex mvis2 -@opindex mno-vis2 -With @option{-mvis2}, GCC generates code that takes advantage of -version 2.0 of the UltraSPARC Visual Instruction Set extensions. The -default is @option{-mvis2} when targeting a cpu that supports such -instructions, such as UltraSPARC-III and later. Setting @option{-mvis2} -also sets @option{-mvis}. - -@item -mvis3 -@itemx -mno-vis3 -@opindex mvis3 -@opindex mno-vis3 -With @option{-mvis3}, GCC generates code that takes advantage of -version 3.0 of the UltraSPARC Visual Instruction Set extensions. The -default is @option{-mvis3} when targeting a cpu that supports such -instructions, such as niagara-3 and later. Setting @option{-mvis3} -also sets @option{-mvis2} and @option{-mvis}. - -@item -mvis4 -@itemx -mno-vis4 -@opindex mvis4 -@opindex mno-vis4 -With @option{-mvis4}, GCC generates code that takes advantage of -version 4.0 of the UltraSPARC Visual Instruction Set extensions. The -default is @option{-mvis4} when targeting a cpu that supports such -instructions, such as niagara-7 and later. Setting @option{-mvis4} -also sets @option{-mvis3}, @option{-mvis2} and @option{-mvis}. - -@item -mvis4b -@itemx -mno-vis4b -@opindex mvis4b -@opindex mno-vis4b -With @option{-mvis4b}, GCC generates code that takes advantage of -version 4.0 of the UltraSPARC Visual Instruction Set extensions, plus -the additional VIS instructions introduced in the Oracle SPARC -Architecture 2017. The default is @option{-mvis4b} when targeting a -cpu that supports such instructions, such as m8 and later. Setting -@option{-mvis4b} also sets @option{-mvis4}, @option{-mvis3}, -@option{-mvis2} and @option{-mvis}. - -@item -mcbcond -@itemx -mno-cbcond -@opindex mcbcond -@opindex mno-cbcond -With @option{-mcbcond}, GCC generates code that takes advantage of the UltraSPARC -Compare-and-Branch-on-Condition instructions. The default is @option{-mcbcond} -when targeting a CPU that supports such instructions, such as Niagara-4 and -later. - -@item -mfmaf -@itemx -mno-fmaf -@opindex mfmaf -@opindex mno-fmaf -With @option{-mfmaf}, GCC generates code that takes advantage of the UltraSPARC -Fused Multiply-Add Floating-point instructions. The default is @option{-mfmaf} -when targeting a CPU that supports such instructions, such as Niagara-3 and -later. - -@item -mfsmuld -@itemx -mno-fsmuld -@opindex mfsmuld -@opindex mno-fsmuld -With @option{-mfsmuld}, GCC generates code that takes advantage of the -Floating-point Multiply Single to Double (FsMULd) instruction. The default is -@option{-mfsmuld} when targeting a CPU supporting the architecture versions V8 -or V9 with FPU except @option{-mcpu=leon}. - -@item -mpopc -@itemx -mno-popc -@opindex mpopc -@opindex mno-popc -With @option{-mpopc}, GCC generates code that takes advantage of the UltraSPARC -Population Count instruction. The default is @option{-mpopc} -when targeting a CPU that supports such an instruction, such as Niagara-2 and -later. - -@item -msubxc -@itemx -mno-subxc -@opindex msubxc -@opindex mno-subxc -With @option{-msubxc}, GCC generates code that takes advantage of the UltraSPARC -Subtract-Extended-with-Carry instruction. The default is @option{-msubxc} -when targeting a CPU that supports such an instruction, such as Niagara-7 and -later. - -@item -mfix-at697f -@opindex mfix-at697f -Enable the documented workaround for the single erratum of the Atmel AT697F -processor (which corresponds to erratum #13 of the AT697E processor). - -@item -mfix-ut699 -@opindex mfix-ut699 -Enable the documented workarounds for the floating-point errata and the data -cache nullify errata of the UT699 processor. - -@item -mfix-ut700 -@opindex mfix-ut700 -Enable the documented workaround for the back-to-back store errata of -the UT699E/UT700 processor. - -@item -mfix-gr712rc -@opindex mfix-gr712rc -Enable the documented workaround for the back-to-back store errata of -the GR712RC processor. -@end table - -These @samp{-m} options are supported in addition to the above -on SPARC-V9 processors in 64-bit environments: - -@table @gcctabopt -@item -m32 -@itemx -m64 -@opindex m32 -@opindex m64 -Generate code for a 32-bit or 64-bit environment. -The 32-bit environment sets int, long and pointer to 32 bits. -The 64-bit environment sets int to 32 bits and long and pointer -to 64 bits. - -@item -mcmodel=@var{which} -@opindex mcmodel -Set the code model to one of - -@table @samp -@item medlow -The Medium/Low code model: 64-bit addresses, programs -must be linked in the low 32 bits of memory. Programs can be statically -or dynamically linked. - -@item medmid -The Medium/Middle code model: 64-bit addresses, programs -must be linked in the low 44 bits of memory, the text and data segments must -be less than 2GB in size and the data segment must be located within 2GB of -the text segment. - -@item medany -The Medium/Anywhere code model: 64-bit addresses, programs -may be linked anywhere in memory, the text and data segments must be less -than 2GB in size and the data segment must be located within 2GB of the -text segment. - -@item embmedany -The Medium/Anywhere code model for embedded systems: -64-bit addresses, the text and data segments must be less than 2GB in -size, both starting anywhere in memory (determined at link time). The -global register %g4 points to the base of the data segment. Programs -are statically linked and PIC is not supported. -@end table - -@item -mmemory-model=@var{mem-model} -@opindex mmemory-model -Set the memory model in force on the processor to one of - -@table @samp -@item default -The default memory model for the processor and operating system. - -@item rmo -Relaxed Memory Order - -@item pso -Partial Store Order - -@item tso -Total Store Order - -@item sc -Sequential Consistency -@end table - -These memory models are formally defined in Appendix D of the SPARC-V9 -architecture manual, as set in the processor's @code{PSTATE.MM} field. - -@item -mstack-bias -@itemx -mno-stack-bias -@opindex mstack-bias -@opindex mno-stack-bias -With @option{-mstack-bias}, GCC assumes that the stack pointer, and -frame pointer if present, are offset by @minus{}2047 which must be added back -when making stack frame references. This is the default in 64-bit mode. -Otherwise, assume no such offset is present. -@end table - -@node System V Options -@subsection Options for System V - -These additional options are available on System V Release 4 for -compatibility with other compilers on those systems: - -@table @gcctabopt -@item -G -@opindex G -Create a shared object. -It is recommended that @option{-symbolic} or @option{-shared} be used instead. - -@item -Qy -@opindex Qy -Identify the versions of each tool used by the compiler, in a -@code{.ident} assembler directive in the output. - -@item -Qn -@opindex Qn -Refrain from adding @code{.ident} directives to the output file (this is -the default). - -@item -YP,@var{dirs} -@opindex YP -Search the directories @var{dirs}, and no others, for libraries -specified with @option{-l}. - -@item -Ym,@var{dir} -@opindex Ym -Look in the directory @var{dir} to find the M4 preprocessor. -The assembler uses this option. -@c This is supposed to go with a -Yd for predefined M4 macro files, but -@c the generic assembler that comes with Solaris takes just -Ym. -@end table - -@node V850 Options -@subsection V850 Options -@cindex V850 Options - -These @samp{-m} options are defined for V850 implementations: - -@table @gcctabopt -@item -mlong-calls -@itemx -mno-long-calls -@opindex mlong-calls -@opindex mno-long-calls -Treat all calls as being far away (near). If calls are assumed to be -far away, the compiler always loads the function's address into a -register, and calls indirect through the pointer. - -@item -mno-ep -@itemx -mep -@opindex mno-ep -@opindex mep -Do not optimize (do optimize) basic blocks that use the same index -pointer 4 or more times to copy pointer into the @code{ep} register, and -use the shorter @code{sld} and @code{sst} instructions. The @option{-mep} -option is on by default if you optimize. - -@item -mno-prolog-function -@itemx -mprolog-function -@opindex mno-prolog-function -@opindex mprolog-function -Do not use (do use) external functions to save and restore registers -at the prologue and epilogue of a function. The external functions -are slower, but use less code space if more than one function saves -the same number of registers. The @option{-mprolog-function} option -is on by default if you optimize. - -@item -mspace -@opindex mspace -Try to make the code as small as possible. At present, this just turns -on the @option{-mep} and @option{-mprolog-function} options. - -@item -mtda=@var{n} -@opindex mtda -Put static or global variables whose size is @var{n} bytes or less into -the tiny data area that register @code{ep} points to. The tiny data -area can hold up to 256 bytes in total (128 bytes for byte references). - -@item -msda=@var{n} -@opindex msda -Put static or global variables whose size is @var{n} bytes or less into -the small data area that register @code{gp} points to. The small data -area can hold up to 64 kilobytes. - -@item -mzda=@var{n} -@opindex mzda -Put static or global variables whose size is @var{n} bytes or less into -the first 32 kilobytes of memory. - -@item -mv850 -@opindex mv850 -Specify that the target processor is the V850. - -@item -mv850e3v5 -@opindex mv850e3v5 -Specify that the target processor is the V850E3V5. The preprocessor -constant @code{__v850e3v5__} is defined if this option is used. - -@item -mv850e2v4 -@opindex mv850e2v4 -Specify that the target processor is the V850E3V5. This is an alias for -the @option{-mv850e3v5} option. - -@item -mv850e2v3 -@opindex mv850e2v3 -Specify that the target processor is the V850E2V3. The preprocessor -constant @code{__v850e2v3__} is defined if this option is used. - -@item -mv850e2 -@opindex mv850e2 -Specify that the target processor is the V850E2. The preprocessor -constant @code{__v850e2__} is defined if this option is used. - -@item -mv850e1 -@opindex mv850e1 -Specify that the target processor is the V850E1. The preprocessor -constants @code{__v850e1__} and @code{__v850e__} are defined if -this option is used. - -@item -mv850es -@opindex mv850es -Specify that the target processor is the V850ES. This is an alias for -the @option{-mv850e1} option. - -@item -mv850e -@opindex mv850e -Specify that the target processor is the V850E@. The preprocessor -constant @code{__v850e__} is defined if this option is used. - -If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1} -nor @option{-mv850e2} nor @option{-mv850e2v3} nor @option{-mv850e3v5} -are defined then a default target processor is chosen and the -relevant @samp{__v850*__} preprocessor constant is defined. - -The preprocessor constants @code{__v850} and @code{__v851__} are always -defined, regardless of which processor variant is the target. - -@item -mdisable-callt -@itemx -mno-disable-callt -@opindex mdisable-callt -@opindex mno-disable-callt -This option suppresses generation of the @code{CALLT} instruction for the -v850e, v850e1, v850e2, v850e2v3 and v850e3v5 flavors of the v850 -architecture. - -This option is enabled by default when the RH850 ABI is -in use (see @option{-mrh850-abi}), and disabled by default when the -GCC ABI is in use. If @code{CALLT} instructions are being generated -then the C preprocessor symbol @code{__V850_CALLT__} is defined. - -@item -mrelax -@itemx -mno-relax -@opindex mrelax -@opindex mno-relax -Pass on (or do not pass on) the @option{-mrelax} command-line option -to the assembler. - -@item -mlong-jumps -@itemx -mno-long-jumps -@opindex mlong-jumps -@opindex mno-long-jumps -Disable (or re-enable) the generation of PC-relative jump instructions. - -@item -msoft-float -@itemx -mhard-float -@opindex msoft-float -@opindex mhard-float -Disable (or re-enable) the generation of hardware floating point -instructions. This option is only significant when the target -architecture is @samp{V850E2V3} or higher. If hardware floating point -instructions are being generated then the C preprocessor symbol -@code{__FPU_OK__} is defined, otherwise the symbol -@code{__NO_FPU__} is defined. - -@item -mloop -@opindex mloop -Enables the use of the e3v5 LOOP instruction. The use of this -instruction is not enabled by default when the e3v5 architecture is -selected because its use is still experimental. - -@item -mrh850-abi -@itemx -mghs -@opindex mrh850-abi -@opindex mghs -Enables support for the RH850 version of the V850 ABI. This is the -default. With this version of the ABI the following rules apply: - -@itemize -@item -Integer sized structures and unions are returned via a memory pointer -rather than a register. - -@item -Large structures and unions (more than 8 bytes in size) are passed by -value. - -@item -Functions are aligned to 16-bit boundaries. - -@item -The @option{-m8byte-align} command-line option is supported. - -@item -The @option{-mdisable-callt} command-line option is enabled by -default. The @option{-mno-disable-callt} command-line option is not -supported. -@end itemize - -When this version of the ABI is enabled the C preprocessor symbol -@code{__V850_RH850_ABI__} is defined. - -@item -mgcc-abi -@opindex mgcc-abi -Enables support for the old GCC version of the V850 ABI. With this -version of the ABI the following rules apply: - -@itemize -@item -Integer sized structures and unions are returned in register @code{r10}. - -@item -Large structures and unions (more than 8 bytes in size) are passed by -reference. - -@item -Functions are aligned to 32-bit boundaries, unless optimizing for -size. - -@item -The @option{-m8byte-align} command-line option is not supported. - -@item -The @option{-mdisable-callt} command-line option is supported but not -enabled by default. -@end itemize - -When this version of the ABI is enabled the C preprocessor symbol -@code{__V850_GCC_ABI__} is defined. - -@item -m8byte-align -@itemx -mno-8byte-align -@opindex m8byte-align -@opindex mno-8byte-align -Enables support for @code{double} and @code{long long} types to be -aligned on 8-byte boundaries. The default is to restrict the -alignment of all objects to at most 4-bytes. When -@option{-m8byte-align} is in effect the C preprocessor symbol -@code{__V850_8BYTE_ALIGN__} is defined. - -@item -mbig-switch -@opindex mbig-switch -Generate code suitable for big switch tables. Use this option only if -the assembler/linker complain about out of range branches within a switch -table. - -@item -mapp-regs -@opindex mapp-regs -This option causes r2 and r5 to be used in the code generated by -the compiler. This setting is the default. - -@item -mno-app-regs -@opindex mno-app-regs -This option causes r2 and r5 to be treated as fixed registers. - -@end table - -@node VAX Options -@subsection VAX Options -@cindex VAX options - -These @samp{-m} options are defined for the VAX: - -@table @gcctabopt -@item -munix -@opindex munix -Do not output certain jump instructions (@code{aobleq} and so on) -that the Unix assembler for the VAX cannot handle across long -ranges. - -@item -mgnu -@opindex mgnu -Do output those jump instructions, on the assumption that the -GNU assembler is being used. - -@item -mg -@opindex mg -Output code for G-format floating-point numbers instead of D-format. - -@item -mlra -@itemx -mno-lra -@opindex mlra -@opindex mno-lra -Enable Local Register Allocation. This is still experimental for the VAX, -so by default the compiler uses standard reload. -@end table - -@node Visium Options -@subsection Visium Options -@cindex Visium options - -@table @gcctabopt - -@item -mdebug -@opindex mdebug -A program which performs file I/O and is destined to run on an MCM target -should be linked with this option. It causes the libraries libc.a and -libdebug.a to be linked. The program should be run on the target under -the control of the GDB remote debugging stub. - -@item -msim -@opindex msim -A program which performs file I/O and is destined to run on the simulator -should be linked with option. This causes libraries libc.a and libsim.a to -be linked. - -@item -mfpu -@itemx -mhard-float -@opindex mfpu -@opindex mhard-float -Generate code containing floating-point instructions. This is the -default. - -@item -mno-fpu -@itemx -msoft-float -@opindex mno-fpu -@opindex msoft-float -Generate code containing library calls for floating-point. - -@option{-msoft-float} changes the calling convention in the output file; -therefore, it is only useful if you compile @emph{all} of a program with -this option. In particular, you need to compile @file{libgcc.a}, the -library that comes with GCC, with @option{-msoft-float} in order for -this to work. - -@item -mcpu=@var{cpu_type} -@opindex mcpu -Set the instruction set, register set, and instruction scheduling parameters -for machine type @var{cpu_type}. Supported values for @var{cpu_type} are -@samp{mcm}, @samp{gr5} and @samp{gr6}. - -@samp{mcm} is a synonym of @samp{gr5} present for backward compatibility. - -By default (unless configured otherwise), GCC generates code for the GR5 -variant of the Visium architecture. - -With @option{-mcpu=gr6}, GCC generates code for the GR6 variant of the Visium -architecture. The only difference from GR5 code is that the compiler will -generate block move instructions. - -@item -mtune=@var{cpu_type} -@opindex mtune -Set the instruction scheduling parameters for machine type @var{cpu_type}, -but do not set the instruction set or register set that the option -@option{-mcpu=@var{cpu_type}} would. - -@item -msv-mode -@opindex msv-mode -Generate code for the supervisor mode, where there are no restrictions on -the access to general registers. This is the default. - -@item -muser-mode -@opindex muser-mode -Generate code for the user mode, where the access to some general registers -is forbidden: on the GR5, registers r24 to r31 cannot be accessed in this -mode; on the GR6, only registers r29 to r31 are affected. -@end table - -@node VMS Options -@subsection VMS Options - -These @samp{-m} options are defined for the VMS implementations: - -@table @gcctabopt -@item -mvms-return-codes -@opindex mvms-return-codes -Return VMS condition codes from @code{main}. The default is to return POSIX-style -condition (e.g.@: error) codes. - -@item -mdebug-main=@var{prefix} -@opindex mdebug-main=@var{prefix} -Flag the first routine whose name starts with @var{prefix} as the main -routine for the debugger. - -@item -mmalloc64 -@opindex mmalloc64 -Default to 64-bit memory allocation routines. - -@item -mpointer-size=@var{size} -@opindex mpointer-size=@var{size} -Set the default size of pointers. Possible options for @var{size} are -@samp{32} or @samp{short} for 32 bit pointers, @samp{64} or @samp{long} -for 64 bit pointers, and @samp{no} for supporting only 32 bit pointers. -The later option disables @code{pragma pointer_size}. -@end table - -@node VxWorks Options -@subsection VxWorks Options -@cindex VxWorks Options - -The options in this section are defined for all VxWorks targets. -Options specific to the target hardware are listed with the other -options for that target. - -@table @gcctabopt -@item -mrtp -@opindex mrtp -GCC can generate code for both VxWorks kernels and real time processes -(RTPs). This option switches from the former to the latter. It also -defines the preprocessor macro @code{__RTP__}. - -@item -non-static -@opindex non-static -Link an RTP executable against shared libraries rather than static -libraries. The options @option{-static} and @option{-shared} can -also be used for RTPs (@pxref{Link Options}); @option{-static} -is the default. - -@item -Bstatic -@itemx -Bdynamic -@opindex Bstatic -@opindex Bdynamic -These options are passed down to the linker. They are defined for -compatibility with Diab. - -@item -Xbind-lazy -@opindex Xbind-lazy -Enable lazy binding of function calls. This option is equivalent to -@option{-Wl,-z,now} and is defined for compatibility with Diab. - -@item -Xbind-now -@opindex Xbind-now -Disable lazy binding of function calls. This option is the default and -is defined for compatibility with Diab. -@end table - -@node x86 Options -@subsection x86 Options -@cindex x86 Options - -These @samp{-m} options are defined for the x86 family of computers. - -@table @gcctabopt - -@item -march=@var{cpu-type} -@opindex march -Generate instructions for the machine type @var{cpu-type}. In contrast to -@option{-mtune=@var{cpu-type}}, which merely tunes the generated code -for the specified @var{cpu-type}, @option{-march=@var{cpu-type}} allows GCC -to generate code that may not run at all on processors other than the one -indicated. Specifying @option{-march=@var{cpu-type}} implies -@option{-mtune=@var{cpu-type}}, except where noted otherwise. - -The choices for @var{cpu-type} are: - -@table @samp -@item native -This selects the CPU to generate code for at compilation time by determining -the processor type of the compiling machine. Using @option{-march=native} -enables all instruction subsets supported by the local machine (hence -the result might not run on different machines). Using @option{-mtune=native} -produces code optimized for the local machine under the constraints -of the selected instruction set. - -@item x86-64 -A generic CPU with 64-bit extensions. - -@item x86-64-v2 -@itemx x86-64-v3 -@itemx x86-64-v4 -These choices for @var{cpu-type} select the corresponding -micro-architecture level from the x86-64 psABI. On ABIs other than -the x86-64 psABI they select the same CPU features as the x86-64 psABI -documents for the particular micro-architecture level. - -Since these @var{cpu-type} values do not have a corresponding -@option{-mtune} setting, using @option{-march} with these values enables -generic tuning. Specific tuning can be enabled using the -@option{-mtune=@var{other-cpu-type}} option with an appropriate -@var{other-cpu-type} value. - -@item i386 -Original Intel i386 CPU@. - -@item i486 -Intel i486 CPU@. (No scheduling is implemented for this chip.) - -@item i586 -@itemx pentium -Intel Pentium CPU with no MMX support. - -@item lakemont -Intel Lakemont MCU, based on Intel Pentium CPU. - -@item pentium-mmx -Intel Pentium MMX CPU, based on Pentium core with MMX instruction set support. - -@item pentiumpro -Intel Pentium Pro CPU@. - -@item i686 -When used with @option{-march}, the Pentium Pro -instruction set is used, so the code runs on all i686 family chips. -When used with @option{-mtune}, it has the same meaning as @samp{generic}. - -@item pentium2 -Intel Pentium II CPU, based on Pentium Pro core with MMX and FXSR instruction -set support. - -@item pentium3 -@itemx pentium3m -Intel Pentium III CPU, based on Pentium Pro core with MMX, FXSR and SSE -instruction set support. - -@item pentium-m -Intel Pentium M; low-power version of Intel Pentium III CPU -with MMX, SSE, SSE2 and FXSR instruction set support. Used by Centrino -notebooks. - -@item pentium4 -@itemx pentium4m -Intel Pentium 4 CPU with MMX, SSE, SSE2 and FXSR instruction set support. - -@item prescott -Improved version of Intel Pentium 4 CPU with MMX, SSE, SSE2, SSE3 and FXSR -instruction set support. - -@item nocona -Improved version of Intel Pentium 4 CPU with 64-bit extensions, MMX, SSE, -SSE2, SSE3 and FXSR instruction set support. - -@item core2 -Intel Core 2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, CX16, -SAHF and FXSR instruction set support. - -@item nehalem -Intel Nehalem CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, -SSE4.1, SSE4.2, POPCNT, CX16, SAHF and FXSR instruction set support. - -@item westmere -Intel Westmere CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, -SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR and PCLMUL instruction set support. - -@item sandybridge -Intel Sandy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, -SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE and PCLMUL instruction set -support. - -@item ivybridge -Intel Ivy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, -SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND -and F16C instruction set support. - -@item haswell -Intel Haswell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, -SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, -F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE and HLE instruction set support. - -@item broadwell -Intel Broadwell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, -SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, -F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX and PREFETCHW -instruction set support. - -@item skylake -Intel Skylake CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, -SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, -F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES, -CLFLUSHOPT, XSAVEC, XSAVES and SGX instruction set support. - -@item bonnell -Intel Bonnell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3 and SSSE3 -instruction set support. - -@item silvermont -Intel Silvermont CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, -SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, PCLMUL, PREFETCHW and RDRND -instruction set support. - -@item goldmont -Intel Goldmont CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, -SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, PCLMUL, PREFETCHW, RDRND, AES, SHA, -RDSEED, XSAVE, XSAVEC, XSAVES, XSAVEOPT, CLFLUSHOPT and FSGSBASE instruction -set support. - -@item goldmont-plus -Intel Goldmont Plus CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, -SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, PCLMUL, PREFETCHW, RDRND, AES, -SHA, RDSEED, XSAVE, XSAVEC, XSAVES, XSAVEOPT, CLFLUSHOPT, FSGSBASE, PTWRITE, -RDPID and SGX instruction set support. - -@item tremont -Intel Tremont CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, -SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, PCLMUL, PREFETCHW, RDRND, AES, SHA, -RDSEED, XSAVE, XSAVEC, XSAVES, XSAVEOPT, CLFLUSHOPT, FSGSBASE, PTWRITE, RDPID, -SGX, CLWB, GFNI-SSE, MOVDIRI, MOVDIR64B, CLDEMOTE and WAITPKG instruction set -support. - -@item sierraforest -Intel Sierra Forest CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, -SSSE3, SSE4.1, SSE4.2, POPCNT, AES, PREFETCHW, PCLMUL, RDRND, XSAVE, XSAVEC, -XSAVES, XSAVEOPT, FSGSBASE, PTWRITE, RDPID, SGX, GFNI-SSE, CLWB, MOVDIRI, -MOVDIR64B, CLDEMOTE, WAITPKG, ADCX, AVX, AVX2, BMI, BMI2, F16C, FMA, LZCNT, -PCONFIG, PKU, VAES, VPCLMULQDQ, SERIALIZE, HRESET, KL, WIDEKL, AVX-VNNI, -AVXIFMA, AVXVNNIINT8, AVXNECONVERT and CMPCCXADD instruction set support. - -@item grandridge -Intel Grand Ridge CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, -SSSE3, SSE4.1, SSE4.2, POPCNT, AES, PREFETCHW, PCLMUL, RDRND, XSAVE, XSAVEC, -XSAVES, XSAVEOPT, FSGSBASE, PTWRITE, RDPID, SGX, GFNI-SSE, CLWB, MOVDIRI, -MOVDIR64B, CLDEMOTE, WAITPKG, ADCX, AVX, AVX2, BMI, BMI2, F16C, FMA, LZCNT, -PCONFIG, PKU, VAES, VPCLMULQDQ, SERIALIZE, HRESET, KL, WIDEKL, AVX-VNNI, -AVXIFMA, AVXVNNIINT8, AVXNECONVERT, CMPCCXADD and RAOINT instruction set -support. - -@item knl -Intel Knight's Landing CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, -SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, -RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, -AVX512PF, AVX512ER, AVX512F, AVX512CD and PREFETCHWT1 instruction set support. - -@item knm -Intel Knights Mill CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, -SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, -RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, -AVX512PF, AVX512ER, AVX512F, AVX512CD and PREFETCHWT1, AVX5124VNNIW, -AVX5124FMAPS and AVX512VPOPCNTDQ instruction set support. - -@item skylake-avx512 -Intel Skylake Server CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, -SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, -RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, -AES, CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, CLWB, AVX512VL, AVX512BW, -AVX512DQ and AVX512CD instruction set support. - -@item cannonlake -Intel Cannonlake Server CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, -SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, -FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, -PREFETCHW, AES, CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW, -AVX512DQ, AVX512CD, PKU, AVX512VBMI, AVX512IFMA and SHA instruction set -support. - -@item icelake-client -Intel Icelake Client CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, -SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, -RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, -AES, CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW, AVX512DQ, -AVX512CD, PKU, AVX512VBMI, AVX512IFMA, SHA, AVX512VNNI, GFNI, VAES, AVX512VBMI2 -, VPCLMULQDQ, AVX512BITALG, RDPID and AVX512VPOPCNTDQ instruction set support. - -@item icelake-server -Intel Icelake Server CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, -SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, -RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, -AES, CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW, AVX512DQ, -AVX512CD, PKU, AVX512VBMI, AVX512IFMA, SHA, AVX512VNNI, GFNI, VAES, AVX512VBMI2 -, VPCLMULQDQ, AVX512BITALG, RDPID, AVX512VPOPCNTDQ, PCONFIG, WBNOINVD and CLWB -instruction set support. - -@item cascadelake -Intel Cascadelake CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, -SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, -F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES, -CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, CLWB, AVX512VL, AVX512BW, AVX512DQ, -AVX512CD and AVX512VNNI instruction set support. - -@item cooperlake -Intel cooperlake CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, -SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, -F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES, -CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, CLWB, AVX512VL, AVX512BW, AVX512DQ, -AVX512CD, AVX512VNNI and AVX512BF16 instruction set support. - -@item tigerlake -Intel Tigerlake CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, -SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, -F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES, -CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW, AVX512DQ, AVX512CD -PKU, AVX512VBMI, AVX512IFMA, SHA, AVX512VNNI, GFNI, VAES, AVX512VBMI2, -VPCLMULQDQ, AVX512BITALG, RDPID, AVX512VPOPCNTDQ, MOVDIRI, MOVDIR64B, CLWB, -AVX512VP2INTERSECT and KEYLOCKER instruction set support. - -@item sapphirerapids -Intel sapphirerapids CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, -SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, -RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, -AES, CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW, AVX512DQ, -AVX512CD, PKU, AVX512VBMI, AVX512IFMA, SHA, AVX512VNNI, GFNI, VAES, AVX512VBMI2, -VPCLMULQDQ, AVX512BITALG, RDPID, AVX512VPOPCNTDQ, PCONFIG, WBNOINVD, CLWB, -MOVDIRI, MOVDIR64B, ENQCMD, CLDEMOTE, PTWRITE, WAITPKG, SERIALIZE, TSXLDTRK, -UINTR, AMX-BF16, AMX-TILE, AMX-INT8, AVX-VNNI, AVX512FP16 and AVX512BF16 -instruction set support. - -@item alderlake -Intel Alderlake CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, -SSE4.1, SSE4.2, POPCNT, AES, PREFETCHW, PCLMUL, RDRND, XSAVE, XSAVEC, XSAVES, -XSAVEOPT, FSGSBASE, PTWRITE, RDPID, SGX, GFNI-SSE, CLWB, MOVDIRI, MOVDIR64B, -CLDEMOTE, WAITPKG, ADCX, AVX, AVX2, BMI, BMI2, F16C, FMA, LZCNT, PCONFIG, PKU, -VAES, VPCLMULQDQ, SERIALIZE, HRESET, KL, WIDEKL and AVX-VNNI instruction set -support. - -@item rocketlake -Intel Rocketlake CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3 -, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, -F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES, -CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, AVX512VL, AVX512BW, AVX512DQ, AVX512CD -PKU, AVX512VBMI, AVX512IFMA, SHA, AVX512VNNI, GFNI, VAES, AVX512VBMI2, -VPCLMULQDQ, AVX512BITALG, RDPID and AVX512VPOPCNTDQ instruction set support. - -@item graniterapids -Intel graniterapids CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, -SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, -RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, -AES, CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW, AVX512DQ, -AVX512CD, PKU, AVX512VBMI, AVX512IFMA, SHA, AVX512VNNI, GFNI, VAES, AVX512VBMI2, -VPCLMULQDQ, AVX512BITALG, RDPID, AVX512VPOPCNTDQ, PCONFIG, WBNOINVD, CLWB, -MOVDIRI, MOVDIR64B, AVX512VP2INTERSECT, ENQCMD, CLDEMOTE, PTWRITE, WAITPKG, -SERIALIZE, TSXLDTRK, UINTR, AMX-BF16, AMX-TILE, AMX-INT8, AVX-VNNI, AVX512FP16, -AVX512BF16, AMX-FP16 and PREFETCHI instruction set support. - -@item k6 -AMD K6 CPU with MMX instruction set support. - -@item k6-2 -@itemx k6-3 -Improved versions of AMD K6 CPU with MMX and 3DNow!@: instruction set support. - -@item athlon -@itemx athlon-tbird -AMD Athlon CPU with MMX, 3dNOW!, enhanced 3DNow!@: and SSE prefetch instructions -support. - -@item athlon-4 -@itemx athlon-xp -@itemx athlon-mp -Improved AMD Athlon CPU with MMX, 3DNow!, enhanced 3DNow!@: and full SSE -instruction set support. - -@item k8 -@itemx opteron -@itemx athlon64 -@itemx athlon-fx -Processors based on the AMD K8 core with x86-64 instruction set support, -including the AMD Opteron, Athlon 64, and Athlon 64 FX processors. -(This supersets MMX, SSE, SSE2, 3DNow!, enhanced 3DNow!@: and 64-bit -instruction set extensions.) - -@item k8-sse3 -@itemx opteron-sse3 -@itemx athlon64-sse3 -Improved versions of AMD K8 cores with SSE3 instruction set support. - -@item amdfam10 -@itemx barcelona -CPUs based on AMD Family 10h cores with x86-64 instruction set support. (This -supersets MMX, SSE, SSE2, SSE3, SSE4A, 3DNow!, enhanced 3DNow!, ABM and 64-bit -instruction set extensions.) - -@item bdver1 -CPUs based on AMD Family 15h cores with x86-64 instruction set support. (This -supersets FMA4, AVX, XOP, LWP, AES, PCLMUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, -SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.) - -@item bdver2 -AMD Family 15h core based CPUs with x86-64 instruction set support. (This -supersets BMI, TBM, F16C, FMA, FMA4, AVX, XOP, LWP, AES, PCLMUL, CX16, MMX, -SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set -extensions.) - -@item bdver3 -AMD Family 15h core based CPUs with x86-64 instruction set support. (This -supersets BMI, TBM, F16C, FMA, FMA4, FSGSBASE, AVX, XOP, LWP, AES, -PCLMUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and -64-bit instruction set extensions.) - -@item bdver4 -AMD Family 15h core based CPUs with x86-64 instruction set support. (This -supersets BMI, BMI2, TBM, F16C, FMA, FMA4, FSGSBASE, AVX, AVX2, XOP, LWP, -AES, PCLMUL, CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, -SSE4.2, ABM and 64-bit instruction set extensions.) - -@item znver1 -AMD Family 17h core based CPUs with x86-64 instruction set support. (This -supersets BMI, BMI2, F16C, FMA, FSGSBASE, AVX, AVX2, ADCX, RDSEED, MWAITX, -SHA, CLZERO, AES, PCLMUL, CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, -SSE4.1, SSE4.2, ABM, XSAVEC, XSAVES, CLFLUSHOPT, POPCNT, and 64-bit -instruction set extensions.) - -@item znver2 -AMD Family 17h core based CPUs with x86-64 instruction set support. (This -supersets BMI, BMI2, CLWB, F16C, FMA, FSGSBASE, AVX, AVX2, ADCX, RDSEED, -MWAITX, SHA, CLZERO, AES, PCLMUL, CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, -SSSE3, SSE4.1, SSE4.2, ABM, XSAVEC, XSAVES, CLFLUSHOPT, POPCNT, RDPID, -WBNOINVD, and 64-bit instruction set extensions.) - -@item znver3 -AMD Family 19h core based CPUs with x86-64 instruction set support. (This -supersets BMI, BMI2, CLWB, F16C, FMA, FSGSBASE, AVX, AVX2, ADCX, RDSEED, -MWAITX, SHA, CLZERO, AES, PCLMUL, CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, -SSSE3, SSE4.1, SSE4.2, ABM, XSAVEC, XSAVES, CLFLUSHOPT, POPCNT, RDPID, -WBNOINVD, PKU, VPCLMULQDQ, VAES, and 64-bit instruction set extensions.) - -@item znver4 -AMD Family 19h core based CPUs with x86-64 instruction set support. (This -supersets BMI, BMI2, CLWB, F16C, FMA, FSGSBASE, AVX, AVX2, ADCX, RDSEED, -MWAITX, SHA, CLZERO, AES, PCLMUL, CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, -SSSE3, SSE4.1, SSE4.2, ABM, XSAVEC, XSAVES, CLFLUSHOPT, POPCNT, RDPID, -WBNOINVD, PKU, VPCLMULQDQ, VAES, AVX512F, AVX512DQ, AVX512IFMA, AVX512CD, -AVX512BW, AVX512VL, AVX512BF16, AVX512VBMI, AVX512VBMI2, AVX512VNNI, -AVX512BITALG, AVX512VPOPCNTDQ, GFNI and 64-bit instruction set extensions.) - -@item btver1 -CPUs based on AMD Family 14h cores with x86-64 instruction set support. (This -supersets MMX, SSE, SSE2, SSE3, SSSE3, SSE4A, CX16, ABM and 64-bit -instruction set extensions.) - -@item btver2 -CPUs based on AMD Family 16h cores with x86-64 instruction set support. This -includes MOVBE, F16C, BMI, AVX, PCLMUL, AES, SSE4.2, SSE4.1, CX16, ABM, -SSE4A, SSSE3, SSE3, SSE2, SSE, MMX and 64-bit instruction set extensions. - -@item winchip-c6 -IDT WinChip C6 CPU, dealt in same way as i486 with additional MMX instruction -set support. - -@item winchip2 -IDT WinChip 2 CPU, dealt in same way as i486 with additional MMX and 3DNow!@: -instruction set support. - -@item c3 -VIA C3 CPU with MMX and 3DNow!@: instruction set support. -(No scheduling is implemented for this chip.) - -@item c3-2 -VIA C3-2 (Nehemiah/C5XL) CPU with MMX and SSE instruction set support. -(No scheduling is implemented for this chip.) - -@item c7 -VIA C7 (Esther) CPU with MMX, SSE, SSE2 and SSE3 instruction set support. -(No scheduling is implemented for this chip.) - -@item samuel-2 -VIA Eden Samuel 2 CPU with MMX and 3DNow!@: instruction set support. -(No scheduling is implemented for this chip.) - -@item nehemiah -VIA Eden Nehemiah CPU with MMX and SSE instruction set support. -(No scheduling is implemented for this chip.) - -@item esther -VIA Eden Esther CPU with MMX, SSE, SSE2 and SSE3 instruction set support. -(No scheduling is implemented for this chip.) - -@item eden-x2 -VIA Eden X2 CPU with x86-64, MMX, SSE, SSE2 and SSE3 instruction set support. -(No scheduling is implemented for this chip.) - -@item eden-x4 -VIA Eden X4 CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, -AVX and AVX2 instruction set support. -(No scheduling is implemented for this chip.) - -@item nano -Generic VIA Nano CPU with x86-64, MMX, SSE, SSE2, SSE3 and SSSE3 -instruction set support. -(No scheduling is implemented for this chip.) - -@item nano-1000 -VIA Nano 1xxx CPU with x86-64, MMX, SSE, SSE2, SSE3 and SSSE3 -instruction set support. -(No scheduling is implemented for this chip.) - -@item nano-2000 -VIA Nano 2xxx CPU with x86-64, MMX, SSE, SSE2, SSE3 and SSSE3 -instruction set support. -(No scheduling is implemented for this chip.) - -@item nano-3000 -VIA Nano 3xxx CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3 and SSE4.1 -instruction set support. -(No scheduling is implemented for this chip.) - -@item nano-x2 -VIA Nano Dual Core CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3 and SSE4.1 -instruction set support. -(No scheduling is implemented for this chip.) - -@item nano-x4 -VIA Nano Quad Core CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3 and SSE4.1 -instruction set support. -(No scheduling is implemented for this chip.) - -@item lujiazui -ZHAOXIN lujiazui CPU with x86-64, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, -SSE4.2, AVX, POPCNT, AES, PCLMUL, RDRND, XSAVE, XSAVEOPT, FSGSBASE, CX16, -ABM, BMI, BMI2, F16C, FXSR, RDSEED instruction set support. - -@item geode -AMD Geode embedded processor with MMX and 3DNow!@: instruction set support. -@end table - -@item -mtune=@var{cpu-type} -@opindex mtune -Tune to @var{cpu-type} everything applicable about the generated code, except -for the ABI and the set of available instructions. -While picking a specific @var{cpu-type} schedules things appropriately -for that particular chip, the compiler does not generate any code that -cannot run on the default machine type unless you use a -@option{-march=@var{cpu-type}} option. -For example, if GCC is configured for i686-pc-linux-gnu -then @option{-mtune=pentium4} generates code that is tuned for Pentium 4 -but still runs on i686 machines. - -The choices for @var{cpu-type} are the same as for @option{-march}. -In addition, @option{-mtune} supports 2 extra choices for @var{cpu-type}: - -@table @samp -@item generic -Produce code optimized for the most common IA32/@/AMD64/@/EM64T processors. -If you know the CPU on which your code will run, then you should use -the corresponding @option{-mtune} or @option{-march} option instead of -@option{-mtune=generic}. But, if you do not know exactly what CPU users -of your application will have, then you should use this option. - -As new processors are deployed in the marketplace, the behavior of this -option will change. Therefore, if you upgrade to a newer version of -GCC, code generation controlled by this option will change to reflect -the processors -that are most common at the time that version of GCC is released. - -There is no @option{-march=generic} option because @option{-march} -indicates the instruction set the compiler can use, and there is no -generic instruction set applicable to all processors. In contrast, -@option{-mtune} indicates the processor (or, in this case, collection of -processors) for which the code is optimized. - -@item intel -Produce code optimized for the most current Intel processors, which are -Haswell and Silvermont for this version of GCC. If you know the CPU -on which your code will run, then you should use the corresponding -@option{-mtune} or @option{-march} option instead of @option{-mtune=intel}. -But, if you want your application performs better on both Haswell and -Silvermont, then you should use this option. - -As new Intel processors are deployed in the marketplace, the behavior of -this option will change. Therefore, if you upgrade to a newer version of -GCC, code generation controlled by this option will change to reflect -the most current Intel processors at the time that version of GCC is -released. - -There is no @option{-march=intel} option because @option{-march} indicates -the instruction set the compiler can use, and there is no common -instruction set applicable to all processors. In contrast, -@option{-mtune} indicates the processor (or, in this case, collection of -processors) for which the code is optimized. -@end table - -@item -mcpu=@var{cpu-type} -@opindex mcpu -A deprecated synonym for @option{-mtune}. - -@item -mfpmath=@var{unit} -@opindex mfpmath -Generate floating-point arithmetic for selected unit @var{unit}. The choices -for @var{unit} are: - -@table @samp -@item 387 -Use the standard 387 floating-point coprocessor present on the majority of chips and -emulated otherwise. Code compiled with this option runs almost everywhere. -The temporary results are computed in 80-bit precision instead of the precision -specified by the type, resulting in slightly different results compared to most -of other chips. See @option{-ffloat-store} for more detailed description. - -This is the default choice for non-Darwin x86-32 targets. - -@item sse -Use scalar floating-point instructions present in the SSE instruction set. -This instruction set is supported by Pentium III and newer chips, -and in the AMD line -by Athlon-4, Athlon XP and Athlon MP chips. The earlier version of the SSE -instruction set supports only single-precision arithmetic, thus the double and -extended-precision arithmetic are still done using 387. A later version, present -only in Pentium 4 and AMD x86-64 chips, supports double-precision -arithmetic too. - -For the x86-32 compiler, you must use @option{-march=@var{cpu-type}}, @option{-msse} -or @option{-msse2} switches to enable SSE extensions and make this option -effective. For the x86-64 compiler, these extensions are enabled by default. - -The resulting code should be considerably faster in the majority of cases and avoid -the numerical instability problems of 387 code, but may break some existing -code that expects temporaries to be 80 bits. - -This is the default choice for the x86-64 compiler, Darwin x86-32 targets, -and the default choice for x86-32 targets with the SSE2 instruction set -when @option{-ffast-math} is enabled. - -@item sse,387 -@itemx sse+387 -@itemx both -Attempt to utilize both instruction sets at once. This effectively doubles the -amount of available registers, and on chips with separate execution units for -387 and SSE the execution resources too. Use this option with care, as it is -still experimental, because the GCC register allocator does not model separate -functional units well, resulting in unstable performance. -@end table - -@item -masm=@var{dialect} -@opindex masm=@var{dialect} -Output assembly instructions using selected @var{dialect}. Also affects -which dialect is used for basic @code{asm} (@pxref{Basic Asm}) and -extended @code{asm} (@pxref{Extended Asm}). Supported choices (in dialect -order) are @samp{att} or @samp{intel}. The default is @samp{att}. Darwin does -not support @samp{intel}. - -@item -mieee-fp -@itemx -mno-ieee-fp -@opindex mieee-fp -@opindex mno-ieee-fp -Control whether or not the compiler uses IEEE floating-point -comparisons. These correctly handle the case where the result of a -comparison is unordered. - -@item -m80387 -@itemx -mhard-float -@opindex 80387 -@opindex mhard-float -Generate output containing 80387 instructions for floating point. - -@item -mno-80387 -@itemx -msoft-float -@opindex no-80387 -@opindex msoft-float -Generate output containing library calls for floating point. - -@strong{Warning:} the requisite libraries are not part of GCC@. -Normally the facilities of the machine's usual C compiler are used, but -this cannot be done directly in cross-compilation. You must make your -own arrangements to provide suitable library functions for -cross-compilation. - -On machines where a function returns floating-point results in the 80387 -register stack, some floating-point opcodes may be emitted even if -@option{-msoft-float} is used. - -@item -mno-fp-ret-in-387 -@opindex mno-fp-ret-in-387 -@opindex mfp-ret-in-387 -Do not use the FPU registers for return values of functions. - -The usual calling convention has functions return values of types -@code{float} and @code{double} in an FPU register, even if there -is no FPU@. The idea is that the operating system should emulate -an FPU@. - -The option @option{-mno-fp-ret-in-387} causes such values to be returned -in ordinary CPU registers instead. - -@item -mno-fancy-math-387 -@opindex mno-fancy-math-387 -@opindex mfancy-math-387 -Some 387 emulators do not support the @code{sin}, @code{cos} and -@code{sqrt} instructions for the 387. Specify this option to avoid -generating those instructions. -This option is overridden when @option{-march} -indicates that the target CPU always has an FPU and so the -instruction does not need emulation. These -instructions are not generated unless you also use the -@option{-funsafe-math-optimizations} switch. - -@item -malign-double -@itemx -mno-align-double -@opindex malign-double -@opindex mno-align-double -Control whether GCC aligns @code{double}, @code{long double}, and -@code{long long} variables on a two-word boundary or a one-word -boundary. Aligning @code{double} variables on a two-word boundary -produces code that runs somewhat faster on a Pentium at the -expense of more memory. - -On x86-64, @option{-malign-double} is enabled by default. - -@strong{Warning:} if you use the @option{-malign-double} switch, -structures containing the above types are aligned differently than -the published application binary interface specifications for the x86-32 -and are not binary compatible with structures in code compiled -without that switch. - -@item -m96bit-long-double -@itemx -m128bit-long-double -@opindex m96bit-long-double -@opindex m128bit-long-double -These switches control the size of @code{long double} type. The x86-32 -application binary interface specifies the size to be 96 bits, -so @option{-m96bit-long-double} is the default in 32-bit mode. - -Modern architectures (Pentium and newer) prefer @code{long double} -to be aligned to an 8- or 16-byte boundary. In arrays or structures -conforming to the ABI, this is not possible. So specifying -@option{-m128bit-long-double} aligns @code{long double} -to a 16-byte boundary by padding the @code{long double} with an additional -32-bit zero. - -In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as -its ABI specifies that @code{long double} is aligned on 16-byte boundary. - -Notice that neither of these options enable any extra precision over the x87 -standard of 80 bits for a @code{long double}. - -@strong{Warning:} if you override the default value for your target ABI, this -changes the size of -structures and arrays containing @code{long double} variables, -as well as modifying the function calling convention for functions taking -@code{long double}. Hence they are not binary-compatible -with code compiled without that switch. - -@item -mlong-double-64 -@itemx -mlong-double-80 -@itemx -mlong-double-128 -@opindex mlong-double-64 -@opindex mlong-double-80 -@opindex mlong-double-128 -These switches control the size of @code{long double} type. A size -of 64 bits makes the @code{long double} type equivalent to the @code{double} -type. This is the default for 32-bit Bionic C library. A size -of 128 bits makes the @code{long double} type equivalent to the -@code{__float128} type. This is the default for 64-bit Bionic C library. - -@strong{Warning:} if you override the default value for your target ABI, this -changes the size of -structures and arrays containing @code{long double} variables, -as well as modifying the function calling convention for functions taking -@code{long double}. Hence they are not binary-compatible -with code compiled without that switch. - -@item -malign-data=@var{type} -@opindex malign-data -Control how GCC aligns variables. Supported values for @var{type} are -@samp{compat} uses increased alignment value compatible uses GCC 4.8 -and earlier, @samp{abi} uses alignment value as specified by the -psABI, and @samp{cacheline} uses increased alignment value to match -the cache line size. @samp{compat} is the default. - -@item -mlarge-data-threshold=@var{threshold} -@opindex mlarge-data-threshold -When @option{-mcmodel=medium} is specified, data objects larger than -@var{threshold} are placed in the large data section. This value must be the -same across all objects linked into the binary, and defaults to 65535. - -@item -mrtd -@opindex mrtd -Use a different function-calling convention, in which functions that -take a fixed number of arguments return with the @code{ret @var{num}} -instruction, which pops their arguments while returning. This saves one -instruction in the caller since there is no need to pop the arguments -there. - -You can specify that an individual function is called with this calling -sequence with the function attribute @code{stdcall}. You can also -override the @option{-mrtd} option by using the function attribute -@code{cdecl}. @xref{Function Attributes}. - -@strong{Warning:} this calling convention is incompatible with the one -normally used on Unix, so you cannot use it if you need to call -libraries compiled with the Unix compiler. - -Also, you must provide function prototypes for all functions that -take variable numbers of arguments (including @code{printf}); -otherwise incorrect code is generated for calls to those -functions. - -In addition, seriously incorrect code results if you call a -function with too many arguments. (Normally, extra arguments are -harmlessly ignored.) - -@item -mregparm=@var{num} -@opindex mregparm -Control how many registers are used to pass integer arguments. By -default, no registers are used to pass arguments, and at most 3 -registers can be used. You can control this behavior for a specific -function by using the function attribute @code{regparm}. -@xref{Function Attributes}. - -@strong{Warning:} if you use this switch, and -@var{num} is nonzero, then you must build all modules with the same -value, including any libraries. This includes the system libraries and -startup modules. - -@item -msseregparm -@opindex msseregparm -Use SSE register passing conventions for float and double arguments -and return values. You can control this behavior for a specific -function by using the function attribute @code{sseregparm}. -@xref{Function Attributes}. - -@strong{Warning:} if you use this switch then you must build all -modules with the same value, including any libraries. This includes -the system libraries and startup modules. - -@item -mvect8-ret-in-mem -@opindex mvect8-ret-in-mem -Return 8-byte vectors in memory instead of MMX registers. This is the -default on VxWorks to match the ABI of the Sun Studio compilers until -version 12. @emph{Only} use this option if you need to remain -compatible with existing code produced by those previous compiler -versions or older versions of GCC@. - -@item -mpc32 -@itemx -mpc64 -@itemx -mpc80 -@opindex mpc32 -@opindex mpc64 -@opindex mpc80 - -Set 80387 floating-point precision to 32, 64 or 80 bits. When @option{-mpc32} -is specified, the significands of results of floating-point operations are -rounded to 24 bits (single precision); @option{-mpc64} rounds the -significands of results of floating-point operations to 53 bits (double -precision) and @option{-mpc80} rounds the significands of results of -floating-point operations to 64 bits (extended double precision), which is -the default. When this option is used, floating-point operations in higher -precisions are not available to the programmer without setting the FPU -control word explicitly. - -Setting the rounding of floating-point operations to less than the default -80 bits can speed some programs by 2% or more. Note that some mathematical -libraries assume that extended-precision (80-bit) floating-point operations -are enabled by default; routines in such libraries could suffer significant -loss of accuracy, typically through so-called ``catastrophic cancellation'', -when this option is used to set the precision to less than extended precision. - -@item -mstackrealign -@opindex mstackrealign -Realign the stack at entry. On the x86, the @option{-mstackrealign} -option generates an alternate prologue and epilogue that realigns the -run-time stack if necessary. This supports mixing legacy codes that keep -4-byte stack alignment with modern codes that keep 16-byte stack alignment for -SSE compatibility. See also the attribute @code{force_align_arg_pointer}, -applicable to individual functions. - -@item -mpreferred-stack-boundary=@var{num} -@opindex mpreferred-stack-boundary -Attempt to keep the stack boundary aligned to a 2 raised to @var{num} -byte boundary. If @option{-mpreferred-stack-boundary} is not specified, -the default is 4 (16 bytes or 128 bits). - -@strong{Warning:} When generating code for the x86-64 architecture with -SSE extensions disabled, @option{-mpreferred-stack-boundary=3} can be -used to keep the stack boundary aligned to 8 byte boundary. Since -x86-64 ABI require 16 byte stack alignment, this is ABI incompatible and -intended to be used in controlled environment where stack space is -important limitation. This option leads to wrong code when functions -compiled with 16 byte stack alignment (such as functions from a standard -library) are called with misaligned stack. In this case, SSE -instructions may lead to misaligned memory access traps. In addition, -variable arguments are handled incorrectly for 16 byte aligned -objects (including x87 long double and __int128), leading to wrong -results. You must build all modules with -@option{-mpreferred-stack-boundary=3}, including any libraries. This -includes the system libraries and startup modules. - -@item -mincoming-stack-boundary=@var{num} -@opindex mincoming-stack-boundary -Assume the incoming stack is aligned to a 2 raised to @var{num} byte -boundary. If @option{-mincoming-stack-boundary} is not specified, -the one specified by @option{-mpreferred-stack-boundary} is used. - -On Pentium and Pentium Pro, @code{double} and @code{long double} values -should be aligned to an 8-byte boundary (see @option{-malign-double}) or -suffer significant run time performance penalties. On Pentium III, the -Streaming SIMD Extension (SSE) data type @code{__m128} may not work -properly if it is not 16-byte aligned. - -To ensure proper alignment of this values on the stack, the stack boundary -must be as aligned as that required by any value stored on the stack. -Further, every function must be generated such that it keeps the stack -aligned. Thus calling a function compiled with a higher preferred -stack boundary from a function compiled with a lower preferred stack -boundary most likely misaligns the stack. It is recommended that -libraries that use callbacks always use the default setting. - -This extra alignment does consume extra stack space, and generally -increases code size. Code that is sensitive to stack space usage, such -as embedded systems and operating system kernels, may want to reduce the -preferred alignment to @option{-mpreferred-stack-boundary=2}. - -@need 200 -@item -mmmx -@opindex mmmx -@need 200 -@itemx -msse -@opindex msse -@need 200 -@itemx -msse2 -@opindex msse2 -@need 200 -@itemx -msse3 -@opindex msse3 -@need 200 -@itemx -mssse3 -@opindex mssse3 -@need 200 -@itemx -msse4 -@opindex msse4 -@need 200 -@itemx -msse4a -@opindex msse4a -@need 200 -@itemx -msse4.1 -@opindex msse4.1 -@need 200 -@itemx -msse4.2 -@opindex msse4.2 -@need 200 -@itemx -mavx -@opindex mavx -@need 200 -@itemx -mavx2 -@opindex mavx2 -@need 200 -@itemx -mavx512f -@opindex mavx512f -@need 200 -@itemx -mavx512pf -@opindex mavx512pf -@need 200 -@itemx -mavx512er -@opindex mavx512er -@need 200 -@itemx -mavx512cd -@opindex mavx512cd -@need 200 -@itemx -mavx512vl -@opindex mavx512vl -@need 200 -@itemx -mavx512bw -@opindex mavx512bw -@need 200 -@itemx -mavx512dq -@opindex mavx512dq -@need 200 -@itemx -mavx512ifma -@opindex mavx512ifma -@need 200 -@itemx -mavx512vbmi -@opindex mavx512vbmi -@need 200 -@itemx -msha -@opindex msha -@need 200 -@itemx -maes -@opindex maes -@need 200 -@itemx -mpclmul -@opindex mpclmul -@need 200 -@itemx -mclflushopt -@opindex mclflushopt -@need 200 -@itemx -mclwb -@opindex mclwb -@need 200 -@itemx -mfsgsbase -@opindex mfsgsbase -@need 200 -@itemx -mptwrite -@opindex mptwrite -@need 200 -@itemx -mrdrnd -@opindex mrdrnd -@need 200 -@itemx -mf16c -@opindex mf16c -@need 200 -@itemx -mfma -@opindex mfma -@need 200 -@itemx -mpconfig -@opindex mpconfig -@need 200 -@itemx -mwbnoinvd -@opindex mwbnoinvd -@need 200 -@itemx -mfma4 -@opindex mfma4 -@need 200 -@itemx -mprfchw -@opindex mprfchw -@need 200 -@itemx -mrdpid -@opindex mrdpid -@need 200 -@itemx -mprefetchwt1 -@opindex mprefetchwt1 -@need 200 -@itemx -mrdseed -@opindex mrdseed -@need 200 -@itemx -msgx -@opindex msgx -@need 200 -@itemx -mxop -@opindex mxop -@need 200 -@itemx -mlwp -@opindex mlwp -@need 200 -@itemx -m3dnow -@opindex m3dnow -@need 200 -@itemx -m3dnowa -@opindex m3dnowa -@need 200 -@itemx -mpopcnt -@opindex mpopcnt -@need 200 -@itemx -mabm -@opindex mabm -@need 200 -@itemx -madx -@opindex madx -@need 200 -@itemx -mbmi -@opindex mbmi -@need 200 -@itemx -mbmi2 -@opindex mbmi2 -@need 200 -@itemx -mlzcnt -@opindex mlzcnt -@need 200 -@itemx -mfxsr -@opindex mfxsr -@need 200 -@itemx -mxsave -@opindex mxsave -@need 200 -@itemx -mxsaveopt -@opindex mxsaveopt -@need 200 -@itemx -mxsavec -@opindex mxsavec -@need 200 -@itemx -mxsaves -@opindex mxsaves -@need 200 -@itemx -mrtm -@opindex mrtm -@need 200 -@itemx -mhle -@opindex mhle -@need 200 -@itemx -mtbm -@opindex mtbm -@need 200 -@itemx -mmwaitx -@opindex mmwaitx -@need 200 -@itemx -mclzero -@opindex mclzero -@need 200 -@itemx -mpku -@opindex mpku -@need 200 -@itemx -mavx512vbmi2 -@opindex mavx512vbmi2 -@need 200 -@itemx -mavx512bf16 -@opindex mavx512bf16 -@need 200 -@itemx -mavx512fp16 -@opindex mavx512fp16 -@need 200 -@itemx -mgfni -@opindex mgfni -@need 200 -@itemx -mvaes -@opindex mvaes -@need 200 -@itemx -mwaitpkg -@opindex mwaitpkg -@need 200 -@itemx -mvpclmulqdq -@opindex mvpclmulqdq -@need 200 -@itemx -mavx512bitalg -@opindex mavx512bitalg -@need 200 -@itemx -mmovdiri -@opindex mmovdiri -@need 200 -@itemx -mmovdir64b -@opindex mmovdir64b -@need 200 -@itemx -menqcmd -@opindex menqcmd -@itemx -muintr -@opindex muintr -@need 200 -@itemx -mtsxldtrk -@opindex mtsxldtrk -@need 200 -@itemx -mavx512vpopcntdq -@opindex mavx512vpopcntdq -@need 200 -@itemx -mavx512vp2intersect -@opindex mavx512vp2intersect -@need 200 -@itemx -mavx5124fmaps -@opindex mavx5124fmaps -@need 200 -@itemx -mavx512vnni -@opindex mavx512vnni -@need 200 -@itemx -mavxvnni -@opindex mavxvnni -@need 200 -@itemx -mavx5124vnniw -@opindex mavx5124vnniw -@need 200 -@itemx -mcldemote -@opindex mcldemote -@need 200 -@itemx -mserialize -@opindex mserialize -@need 200 -@itemx -mamx-tile -@opindex mamx-tile -@need 200 -@itemx -mamx-int8 -@opindex mamx-int8 -@need 200 -@itemx -mamx-bf16 -@opindex mamx-bf16 -@need 200 -@itemx -mhreset -@opindex mhreset -@itemx -mkl -@opindex mkl -@need 200 -@itemx -mwidekl -@opindex mwidekl -@need 200 -@itemx -mavxifma -@opindex mavxifma -@need 200 -@itemx -mavxvnniint8 -@opindex mavxvnniint8 -@need 200 -@itemx -mavxneconvert -@opindex mavxneconvert -@need 200 -@itemx -mcmpccxadd -@opindex mcmpccxadd -@need 200 -@itemx -mamx-fp16 -@opindex mamx-fp16 -@need 200 -@itemx -mprefetchi -@opindex mprefetchi -@need 200 -@itemx -mraoint -@opindex mraoint -These switches enable the use of instructions in the MMX, SSE, -SSE2, SSE3, SSSE3, SSE4, SSE4A, SSE4.1, SSE4.2, AVX, AVX2, AVX512F, AVX512PF, -AVX512ER, AVX512CD, AVX512VL, AVX512BW, AVX512DQ, AVX512IFMA, AVX512VBMI, SHA, -AES, PCLMUL, CLFLUSHOPT, CLWB, FSGSBASE, PTWRITE, RDRND, F16C, FMA, PCONFIG, -WBNOINVD, FMA4, PREFETCHW, RDPID, PREFETCHWT1, RDSEED, SGX, XOP, LWP, -3DNow!@:, enhanced 3DNow!@:, POPCNT, ABM, ADX, BMI, BMI2, LZCNT, FXSR, XSAVE, -XSAVEOPT, XSAVEC, XSAVES, RTM, HLE, TBM, MWAITX, CLZERO, PKU, AVX512VBMI2, -GFNI, VAES, WAITPKG, VPCLMULQDQ, AVX512BITALG, MOVDIRI, MOVDIR64B, AVX512BF16, -ENQCMD, AVX512VPOPCNTDQ, AVX5124FMAPS, AVX512VNNI, AVX5124VNNIW, SERIALIZE, -UINTR, HRESET, AMXTILE, AMXINT8, AMXBF16, KL, WIDEKL, AVXVNNI, AVX512FP16, -AVXIFMA, AVXVNNIINT8, AVXNECONVERT, CMPCCXADD, AMX-FP16, PREFETCHI, RAOINT or -CLDEMOTE extended instruction sets. Each has a corresponding @option{-mno-} -option to disable use of these instructions. - -These extensions are also available as built-in functions: see -@ref{x86 Built-in Functions}, for details of the functions enabled and -disabled by these switches. - -To generate SSE/SSE2 instructions automatically from floating-point -code (as opposed to 387 instructions), see @option{-mfpmath=sse}. - -GCC depresses SSEx instructions when @option{-mavx} is used. Instead, it -generates new AVX instructions or AVX equivalence for all SSEx instructions -when needed. - -These options enable GCC to use these extended instructions in -generated code, even without @option{-mfpmath=sse}. Applications that -perform run-time CPU detection must compile separate files for each -supported architecture, using the appropriate flags. In particular, -the file containing the CPU detection code should be compiled without -these options. - -@item -mdump-tune-features -@opindex mdump-tune-features -This option instructs GCC to dump the names of the x86 performance -tuning features and default settings. The names can be used in -@option{-mtune-ctrl=@var{feature-list}}. - -@item -mtune-ctrl=@var{feature-list} -@opindex mtune-ctrl=@var{feature-list} -This option is used to do fine grain control of x86 code generation features. -@var{feature-list} is a comma separated list of @var{feature} names. See also -@option{-mdump-tune-features}. When specified, the @var{feature} is turned -on if it is not preceded with @samp{^}, otherwise, it is turned off. -@option{-mtune-ctrl=@var{feature-list}} is intended to be used by GCC -developers. Using it may lead to code paths not covered by testing and can -potentially result in compiler ICEs or runtime errors. - -@item -mno-default -@opindex mno-default -This option instructs GCC to turn off all tunable features. See also -@option{-mtune-ctrl=@var{feature-list}} and @option{-mdump-tune-features}. - -@item -mcld -@opindex mcld -This option instructs GCC to emit a @code{cld} instruction in the prologue -of functions that use string instructions. String instructions depend on -the DF flag to select between autoincrement or autodecrement mode. While the -ABI specifies the DF flag to be cleared on function entry, some operating -systems violate this specification by not clearing the DF flag in their -exception dispatchers. The exception handler can be invoked with the DF flag -set, which leads to wrong direction mode when string instructions are used. -This option can be enabled by default on 32-bit x86 targets by configuring -GCC with the @option{--enable-cld} configure option. Generation of @code{cld} -instructions can be suppressed with the @option{-mno-cld} compiler option -in this case. - -@item -mvzeroupper -@opindex mvzeroupper -This option instructs GCC to emit a @code{vzeroupper} instruction -before a transfer of control flow out of the function to minimize -the AVX to SSE transition penalty as well as remove unnecessary @code{zeroupper} -intrinsics. - -@item -mprefer-avx128 -@opindex mprefer-avx128 -This option instructs GCC to use 128-bit AVX instructions instead of -256-bit AVX instructions in the auto-vectorizer. - -@item -mprefer-vector-width=@var{opt} -@opindex mprefer-vector-width -This option instructs GCC to use @var{opt}-bit vector width in instructions -instead of default on the selected platform. - -@item -mmove-max=@var{bits} -@opindex mmove-max -This option instructs GCC to set the maximum number of bits can be -moved from memory to memory efficiently to @var{bits}. The valid -@var{bits} are 128, 256 and 512. - -@item -mstore-max=@var{bits} -@opindex mstore-max -This option instructs GCC to set the maximum number of bits can be -stored to memory efficiently to @var{bits}. The valid @var{bits} are -128, 256 and 512. - -@table @samp -@item none -No extra limitations applied to GCC other than defined by the selected platform. - -@item 128 -Prefer 128-bit vector width for instructions. - -@item 256 -Prefer 256-bit vector width for instructions. - -@item 512 -Prefer 512-bit vector width for instructions. -@end table - -@item -mcx16 -@opindex mcx16 -This option enables GCC to generate @code{CMPXCHG16B} instructions in 64-bit -code to implement compare-and-exchange operations on 16-byte aligned 128-bit -objects. This is useful for atomic updates of data structures exceeding one -machine word in size. The compiler uses this instruction to implement -@ref{__sync Builtins}. However, for @ref{__atomic Builtins} operating on -128-bit integers, a library call is always used. - -@item -msahf -@opindex msahf -This option enables generation of @code{SAHF} instructions in 64-bit code. -Early Intel Pentium 4 CPUs with Intel 64 support, -prior to the introduction of Pentium 4 G1 step in December 2005, -lacked the @code{LAHF} and @code{SAHF} instructions -which are supported by AMD64. -These are load and store instructions, respectively, for certain status flags. -In 64-bit mode, the @code{SAHF} instruction is used to optimize @code{fmod}, -@code{drem}, and @code{remainder} built-in functions; -see @ref{Other Builtins} for details. - -@item -mmovbe -@opindex mmovbe -This option enables use of the @code{movbe} instruction to implement -@code{__builtin_bswap32} and @code{__builtin_bswap64}. - -@item -mshstk -@opindex mshstk -The @option{-mshstk} option enables shadow stack built-in functions -from x86 Control-flow Enforcement Technology (CET). - -@item -mcrc32 -@opindex mcrc32 -This option enables built-in functions @code{__builtin_ia32_crc32qi}, -@code{__builtin_ia32_crc32hi}, @code{__builtin_ia32_crc32si} and -@code{__builtin_ia32_crc32di} to generate the @code{crc32} machine instruction. - -@item -mmwait -@opindex mmwait -This option enables built-in functions @code{__builtin_ia32_monitor}, -and @code{__builtin_ia32_mwait} to generate the @code{monitor} and -@code{mwait} machine instructions. - -@item -mrecip -@opindex mrecip -This option enables use of @code{RCPSS} and @code{RSQRTSS} instructions -(and their vectorized variants @code{RCPPS} and @code{RSQRTPS}) -with an additional Newton-Raphson step -to increase precision instead of @code{DIVSS} and @code{SQRTSS} -(and their vectorized -variants) for single-precision floating-point arguments. These instructions -are generated only when @option{-funsafe-math-optimizations} is enabled -together with @option{-ffinite-math-only} and @option{-fno-trapping-math}. -Note that while the throughput of the sequence is higher than the throughput -of the non-reciprocal instruction, the precision of the sequence can be -decreased by up to 2 ulp (i.e.@: the inverse of 1.0 equals 0.99999994). - -Note that GCC implements @code{1.0f/sqrtf(@var{x})} in terms of @code{RSQRTSS} -(or @code{RSQRTPS}) already with @option{-ffast-math} (or the above option -combination), and doesn't need @option{-mrecip}. - -Also note that GCC emits the above sequence with additional Newton-Raphson step -for vectorized single-float division and vectorized @code{sqrtf(@var{x})} -already with @option{-ffast-math} (or the above option combination), and -doesn't need @option{-mrecip}. - -@item -mrecip=@var{opt} -@opindex mrecip=opt -This option controls which reciprocal estimate instructions -may be used. @var{opt} is a comma-separated list of options, which may -be preceded by a @samp{!} to invert the option: - -@table @samp -@item all -Enable all estimate instructions. - -@item default -Enable the default instructions, equivalent to @option{-mrecip}. - -@item none -Disable all estimate instructions, equivalent to @option{-mno-recip}. - -@item div -Enable the approximation for scalar division. - -@item vec-div -Enable the approximation for vectorized division. - -@item sqrt -Enable the approximation for scalar square root. - -@item vec-sqrt -Enable the approximation for vectorized square root. -@end table - -So, for example, @option{-mrecip=all,!sqrt} enables -all of the reciprocal approximations, except for square root. - -@item -mveclibabi=@var{type} -@opindex mveclibabi -Specifies the ABI type to use for vectorizing intrinsics using an -external library. Supported values for @var{type} are @samp{svml} -for the Intel short -vector math library and @samp{acml} for the AMD math core library. -To use this option, both @option{-ftree-vectorize} and -@option{-funsafe-math-optimizations} have to be enabled, and an SVML or ACML -ABI-compatible library must be specified at link time. - -GCC currently emits calls to @code{vmldExp2}, -@code{vmldLn2}, @code{vmldLog102}, @code{vmldPow2}, -@code{vmldTanh2}, @code{vmldTan2}, @code{vmldAtan2}, @code{vmldAtanh2}, -@code{vmldCbrt2}, @code{vmldSinh2}, @code{vmldSin2}, @code{vmldAsinh2}, -@code{vmldAsin2}, @code{vmldCosh2}, @code{vmldCos2}, @code{vmldAcosh2}, -@code{vmldAcos2}, @code{vmlsExp4}, @code{vmlsLn4}, -@code{vmlsLog104}, @code{vmlsPow4}, @code{vmlsTanh4}, @code{vmlsTan4}, -@code{vmlsAtan4}, @code{vmlsAtanh4}, @code{vmlsCbrt4}, @code{vmlsSinh4}, -@code{vmlsSin4}, @code{vmlsAsinh4}, @code{vmlsAsin4}, @code{vmlsCosh4}, -@code{vmlsCos4}, @code{vmlsAcosh4} and @code{vmlsAcos4} for corresponding -function type when @option{-mveclibabi=svml} is used, and @code{__vrd2_sin}, -@code{__vrd2_cos}, @code{__vrd2_exp}, @code{__vrd2_log}, @code{__vrd2_log2}, -@code{__vrd2_log10}, @code{__vrs4_sinf}, @code{__vrs4_cosf}, -@code{__vrs4_expf}, @code{__vrs4_logf}, @code{__vrs4_log2f}, -@code{__vrs4_log10f} and @code{__vrs4_powf} for the corresponding function type -when @option{-mveclibabi=acml} is used. - -@item -mabi=@var{name} -@opindex mabi -Generate code for the specified calling convention. Permissible values -are @samp{sysv} for the ABI used on GNU/Linux and other systems, and -@samp{ms} for the Microsoft ABI. The default is to use the Microsoft -ABI when targeting Microsoft Windows and the SysV ABI on all other systems. -You can control this behavior for specific functions by -using the function attributes @code{ms_abi} and @code{sysv_abi}. -@xref{Function Attributes}. - -@item -mforce-indirect-call -@opindex mforce-indirect-call -Force all calls to functions to be indirect. This is useful -when using Intel Processor Trace where it generates more precise timing -information for function calls. - -@item -mmanual-endbr -@opindex mmanual-endbr -Insert ENDBR instruction at function entry only via the @code{cf_check} -function attribute. This is useful when used with the option -@option{-fcf-protection=branch} to control ENDBR insertion at the -function entry. - -@item -mcet-switch -@opindex mcet-switch -By default, CET instrumentation is turned off on switch statements that -use a jump table and indirect branch track is disabled. Since jump -tables are stored in read-only memory, this does not result in a direct -loss of hardening. But if the jump table index is attacker-controlled, -the indirect jump may not be constrained by CET. This option turns on -CET instrumentation to enable indirect branch track for switch statements -with jump tables which leads to the jump targets reachable via any indirect -jumps. - -@item -mcall-ms2sysv-xlogues -@opindex mcall-ms2sysv-xlogues -@opindex mno-call-ms2sysv-xlogues -Due to differences in 64-bit ABIs, any Microsoft ABI function that calls a -System V ABI function must consider RSI, RDI and XMM6-15 as clobbered. By -default, the code for saving and restoring these registers is emitted inline, -resulting in fairly lengthy prologues and epilogues. Using -@option{-mcall-ms2sysv-xlogues} emits prologues and epilogues that -use stubs in the static portion of libgcc to perform these saves and restores, -thus reducing function size at the cost of a few extra instructions. - -@item -mtls-dialect=@var{type} -@opindex mtls-dialect -Generate code to access thread-local storage using the @samp{gnu} or -@samp{gnu2} conventions. @samp{gnu} is the conservative default; -@samp{gnu2} is more efficient, but it may add compile- and run-time -requirements that cannot be satisfied on all systems. - -@item -mpush-args -@itemx -mno-push-args -@opindex mpush-args -@opindex mno-push-args -Use PUSH operations to store outgoing parameters. This method is shorter -and usually equally fast as method using SUB/MOV operations and is enabled -by default. In some cases disabling it may improve performance because of -improved scheduling and reduced dependencies. - -@item -maccumulate-outgoing-args -@opindex maccumulate-outgoing-args -If enabled, the maximum amount of space required for outgoing arguments is -computed in the function prologue. This is faster on most modern CPUs -because of reduced dependencies, improved scheduling and reduced stack usage -when the preferred stack boundary is not equal to 2. The drawback is a notable -increase in code size. This switch implies @option{-mno-push-args}. - -@item -mthreads -@opindex mthreads -Support thread-safe exception handling on MinGW. Programs that rely -on thread-safe exception handling must compile and link all code with the -@option{-mthreads} option. When compiling, @option{-mthreads} defines -@option{-D_MT}; when linking, it links in a special thread helper library -@option{-lmingwthrd} which cleans up per-thread exception-handling data. - -@item -mms-bitfields -@itemx -mno-ms-bitfields -@opindex mms-bitfields -@opindex mno-ms-bitfields - -Enable/disable bit-field layout compatible with the native Microsoft -Windows compiler. - -If @code{packed} is used on a structure, or if bit-fields are used, -it may be that the Microsoft ABI lays out the structure differently -than the way GCC normally does. Particularly when moving packed -data between functions compiled with GCC and the native Microsoft compiler -(either via function call or as data in a file), it may be necessary to access -either format. - -This option is enabled by default for Microsoft Windows -targets. This behavior can also be controlled locally by use of variable -or type attributes. For more information, see @ref{x86 Variable Attributes} -and @ref{x86 Type Attributes}. - -The Microsoft structure layout algorithm is fairly simple with the exception -of the bit-field packing. -The padding and alignment of members of structures and whether a bit-field -can straddle a storage-unit boundary are determine by these rules: - -@enumerate -@item Structure members are stored sequentially in the order in which they are -declared: the first member has the lowest memory address and the last member -the highest. - -@item Every data object has an alignment requirement. The alignment requirement -for all data except structures, unions, and arrays is either the size of the -object or the current packing size (specified with either the -@code{aligned} attribute or the @code{pack} pragma), -whichever is less. For structures, unions, and arrays, -the alignment requirement is the largest alignment requirement of its members. -Every object is allocated an offset so that: - -@smallexample -offset % alignment_requirement == 0 -@end smallexample - -@item Adjacent bit-fields are packed into the same 1-, 2-, or 4-byte allocation -unit if the integral types are the same size and if the next bit-field fits -into the current allocation unit without crossing the boundary imposed by the -common alignment requirements of the bit-fields. -@end enumerate - -MSVC interprets zero-length bit-fields in the following ways: - -@enumerate -@item If a zero-length bit-field is inserted between two bit-fields that -are normally coalesced, the bit-fields are not coalesced. - -For example: - -@smallexample -struct - @{ - unsigned long bf_1 : 12; - unsigned long : 0; - unsigned long bf_2 : 12; - @} t1; -@end smallexample - -@noindent -The size of @code{t1} is 8 bytes with the zero-length bit-field. If the -zero-length bit-field were removed, @code{t1}'s size would be 4 bytes. - -@item If a zero-length bit-field is inserted after a bit-field, @code{foo}, and the -alignment of the zero-length bit-field is greater than the member that follows it, -@code{bar}, @code{bar} is aligned as the type of the zero-length bit-field. - -For example: - -@smallexample -struct - @{ - char foo : 4; - short : 0; - char bar; - @} t2; - -struct - @{ - char foo : 4; - short : 0; - double bar; - @} t3; -@end smallexample - -@noindent -For @code{t2}, @code{bar} is placed at offset 2, rather than offset 1. -Accordingly, the size of @code{t2} is 4. For @code{t3}, the zero-length -bit-field does not affect the alignment of @code{bar} or, as a result, the size -of the structure. - -Taking this into account, it is important to note the following: - -@enumerate -@item If a zero-length bit-field follows a normal bit-field, the type of the -zero-length bit-field may affect the alignment of the structure as whole. For -example, @code{t2} has a size of 4 bytes, since the zero-length bit-field follows a -normal bit-field, and is of type short. - -@item Even if a zero-length bit-field is not followed by a normal bit-field, it may -still affect the alignment of the structure: - -@smallexample -struct - @{ - char foo : 6; - long : 0; - @} t4; -@end smallexample - -@noindent -Here, @code{t4} takes up 4 bytes. -@end enumerate - -@item Zero-length bit-fields following non-bit-field members are ignored: - -@smallexample -struct - @{ - char foo; - long : 0; - char bar; - @} t5; -@end smallexample - -@noindent -Here, @code{t5} takes up 2 bytes. -@end enumerate - - -@item -mno-align-stringops -@opindex mno-align-stringops -@opindex malign-stringops -Do not align the destination of inlined string operations. This switch reduces -code size and improves performance in case the destination is already aligned, -but GCC doesn't know about it. - -@item -minline-all-stringops -@opindex minline-all-stringops -By default GCC inlines string operations only when the destination is -known to be aligned to least a 4-byte boundary. -This enables more inlining and increases code -size, but may improve performance of code that depends on fast -@code{memcpy} and @code{memset} for short lengths. -The option enables inline expansion of @code{strlen} for all -pointer alignments. - -@item -minline-stringops-dynamically -@opindex minline-stringops-dynamically -For string operations of unknown size, use run-time checks with -inline code for small blocks and a library call for large blocks. - -@item -mstringop-strategy=@var{alg} -@opindex mstringop-strategy=@var{alg} -Override the internal decision heuristic for the particular algorithm to use -for inlining string operations. The allowed values for @var{alg} are: - -@table @samp -@item rep_byte -@itemx rep_4byte -@itemx rep_8byte -Expand using i386 @code{rep} prefix of the specified size. - -@item byte_loop -@itemx loop -@itemx unrolled_loop -Expand into an inline loop. - -@item libcall -Always use a library call. -@end table - -@item -mmemcpy-strategy=@var{strategy} -@opindex mmemcpy-strategy=@var{strategy} -Override the internal decision heuristic to decide if @code{__builtin_memcpy} -should be inlined and what inline algorithm to use when the expected size -of the copy operation is known. @var{strategy} -is a comma-separated list of @var{alg}:@var{max_size}:@var{dest_align} triplets. -@var{alg} is specified in @option{-mstringop-strategy}, @var{max_size} specifies -the max byte size with which inline algorithm @var{alg} is allowed. For the last -triplet, the @var{max_size} must be @code{-1}. The @var{max_size} of the triplets -in the list must be specified in increasing order. The minimal byte size for -@var{alg} is @code{0} for the first triplet and @code{@var{max_size} + 1} of the -preceding range. - -@item -mmemset-strategy=@var{strategy} -@opindex mmemset-strategy=@var{strategy} -The option is similar to @option{-mmemcpy-strategy=} except that it is to control -@code{__builtin_memset} expansion. - -@item -momit-leaf-frame-pointer -@opindex momit-leaf-frame-pointer -Don't keep the frame pointer in a register for leaf functions. This -avoids the instructions to save, set up, and restore frame pointers and -makes an extra register available in leaf functions. The option -@option{-fomit-leaf-frame-pointer} removes the frame pointer for leaf functions, -which might make debugging harder. - -@item -mtls-direct-seg-refs -@itemx -mno-tls-direct-seg-refs -@opindex mtls-direct-seg-refs -Controls whether TLS variables may be accessed with offsets from the -TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit), -or whether the thread base pointer must be added. Whether or not this -is valid depends on the operating system, and whether it maps the -segment to cover the entire TLS area. - -For systems that use the GNU C Library, the default is on. - -@item -msse2avx -@itemx -mno-sse2avx -@opindex msse2avx -Specify that the assembler should encode SSE instructions with VEX -prefix. The option @option{-mavx} turns this on by default. - -@item -mfentry -@itemx -mno-fentry -@opindex mfentry -If profiling is active (@option{-pg}), put the profiling -counter call before the prologue. -Note: On x86 architectures the attribute @code{ms_hook_prologue} -isn't possible at the moment for @option{-mfentry} and @option{-pg}. - -@item -mrecord-mcount -@itemx -mno-record-mcount -@opindex mrecord-mcount -If profiling is active (@option{-pg}), generate a __mcount_loc section -that contains pointers to each profiling call. This is useful for -automatically patching and out calls. - -@item -mnop-mcount -@itemx -mno-nop-mcount -@opindex mnop-mcount -If profiling is active (@option{-pg}), generate the calls to -the profiling functions as NOPs. This is useful when they -should be patched in later dynamically. This is likely only -useful together with @option{-mrecord-mcount}. - -@item -minstrument-return=@var{type} -@opindex minstrument-return -Instrument function exit in -pg -mfentry instrumented functions with -call to specified function. This only instruments true returns ending -with ret, but not sibling calls ending with jump. Valid types -are @var{none} to not instrument, @var{call} to generate a call to __return__, -or @var{nop5} to generate a 5 byte nop. - -@item -mrecord-return -@itemx -mno-record-return -@opindex mrecord-return -Generate a __return_loc section pointing to all return instrumentation code. - -@item -mfentry-name=@var{name} -@opindex mfentry-name -Set name of __fentry__ symbol called at function entry for -pg -mfentry functions. - -@item -mfentry-section=@var{name} -@opindex mfentry-section -Set name of section to record -mrecord-mcount calls (default __mcount_loc). - -@item -mskip-rax-setup -@itemx -mno-skip-rax-setup -@opindex mskip-rax-setup -When generating code for the x86-64 architecture with SSE extensions -disabled, @option{-mskip-rax-setup} can be used to skip setting up RAX -register when there are no variable arguments passed in vector registers. - -@strong{Warning:} Since RAX register is used to avoid unnecessarily -saving vector registers on stack when passing variable arguments, the -impacts of this option are callees may waste some stack space, -misbehave or jump to a random location. GCC 4.4 or newer don't have -those issues, regardless the RAX register value. - -@item -m8bit-idiv -@itemx -mno-8bit-idiv -@opindex m8bit-idiv -On some processors, like Intel Atom, 8-bit unsigned integer divide is -much faster than 32-bit/64-bit integer divide. This option generates a -run-time check. If both dividend and divisor are within range of 0 -to 255, 8-bit unsigned integer divide is used instead of -32-bit/64-bit integer divide. - -@item -mavx256-split-unaligned-load -@itemx -mavx256-split-unaligned-store -@opindex mavx256-split-unaligned-load -@opindex mavx256-split-unaligned-store -Split 32-byte AVX unaligned load and store. - -@item -mstack-protector-guard=@var{guard} -@itemx -mstack-protector-guard-reg=@var{reg} -@itemx -mstack-protector-guard-offset=@var{offset} -@opindex mstack-protector-guard -@opindex mstack-protector-guard-reg -@opindex mstack-protector-guard-offset -Generate stack protection code using canary at @var{guard}. Supported -locations are @samp{global} for global canary or @samp{tls} for per-thread -canary in the TLS block (the default). This option has effect only when -@option{-fstack-protector} or @option{-fstack-protector-all} is specified. - -With the latter choice the options -@option{-mstack-protector-guard-reg=@var{reg}} and -@option{-mstack-protector-guard-offset=@var{offset}} furthermore specify -which segment register (@code{%fs} or @code{%gs}) to use as base register -for reading the canary, and from what offset from that base register. -The default for those is as specified in the relevant ABI. - -@item -mgeneral-regs-only -@opindex mgeneral-regs-only -Generate code that uses only the general-purpose registers. This -prevents the compiler from using floating-point, vector, mask and bound -registers. - -@item -mrelax-cmpxchg-loop -@opindex mrelax-cmpxchg-loop -Relax cmpxchg loop by emitting an early load and compare before cmpxchg, -execute pause if load value is not expected. This reduces excessive -cachline bouncing when and works for all atomic logic fetch builtins -that generates compare and swap loop. - -@item -mindirect-branch=@var{choice} -@opindex mindirect-branch -Convert indirect call and jump with @var{choice}. The default is -@samp{keep}, which keeps indirect call and jump unmodified. -@samp{thunk} converts indirect call and jump to call and return thunk. -@samp{thunk-inline} converts indirect call and jump to inlined call -and return thunk. @samp{thunk-extern} converts indirect call and jump -to external call and return thunk provided in a separate object file. -You can control this behavior for a specific function by using the -function attribute @code{indirect_branch}. @xref{Function Attributes}. - -Note that @option{-mcmodel=large} is incompatible with -@option{-mindirect-branch=thunk} and -@option{-mindirect-branch=thunk-extern} since the thunk function may -not be reachable in the large code model. - -Note that @option{-mindirect-branch=thunk-extern} is compatible with -@option{-fcf-protection=branch} since the external thunk can be made -to enable control-flow check. - -@item -mfunction-return=@var{choice} -@opindex mfunction-return -Convert function return with @var{choice}. The default is @samp{keep}, -which keeps function return unmodified. @samp{thunk} converts function -return to call and return thunk. @samp{thunk-inline} converts function -return to inlined call and return thunk. @samp{thunk-extern} converts -function return to external call and return thunk provided in a separate -object file. You can control this behavior for a specific function by -using the function attribute @code{function_return}. -@xref{Function Attributes}. - -Note that @option{-mindirect-return=thunk-extern} is compatible with -@option{-fcf-protection=branch} since the external thunk can be made -to enable control-flow check. - -Note that @option{-mcmodel=large} is incompatible with -@option{-mfunction-return=thunk} and -@option{-mfunction-return=thunk-extern} since the thunk function may -not be reachable in the large code model. - - -@item -mindirect-branch-register -@opindex mindirect-branch-register -Force indirect call and jump via register. - -@item -mharden-sls=@var{choice} -@opindex mharden-sls -Generate code to mitigate against straight line speculation (SLS) with -@var{choice}. The default is @samp{none} which disables all SLS -hardening. @samp{return} enables SLS hardening for function returns. -@samp{indirect-jmp} enables SLS hardening for indirect jumps. -@samp{all} enables all SLS hardening. - -@item -mindirect-branch-cs-prefix -@opindex mindirect-branch-cs-prefix -Add CS prefix to call and jmp to indirect thunk with branch target in -r8-r15 registers so that the call and jmp instruction length is 6 bytes -to allow them to be replaced with @samp{lfence; call *%r8-r15} or -@samp{lfence; jmp *%r8-r15} at run-time. - -@end table - -These @samp{-m} switches are supported in addition to the above -on x86-64 processors in 64-bit environments. - -@table @gcctabopt -@item -m32 -@itemx -m64 -@itemx -mx32 -@itemx -m16 -@itemx -miamcu -@opindex m32 -@opindex m64 -@opindex mx32 -@opindex m16 -@opindex miamcu -Generate code for a 16-bit, 32-bit or 64-bit environment. -The @option{-m32} option sets @code{int}, @code{long}, and pointer types -to 32 bits, and -generates code that runs on any i386 system. - -The @option{-m64} option sets @code{int} to 32 bits and @code{long} and pointer -types to 64 bits, and generates code for the x86-64 architecture. -For Darwin only the @option{-m64} option also turns off the @option{-fno-pic} -and @option{-mdynamic-no-pic} options. - -The @option{-mx32} option sets @code{int}, @code{long}, and pointer types -to 32 bits, and -generates code for the x86-64 architecture. - -The @option{-m16} option is the same as @option{-m32}, except for that -it outputs the @code{.code16gcc} assembly directive at the beginning of -the assembly output so that the binary can run in 16-bit mode. - -The @option{-miamcu} option generates code which conforms to Intel MCU -psABI. It requires the @option{-m32} option to be turned on. - -@item -mno-red-zone -@opindex mno-red-zone -@opindex mred-zone -Do not use a so-called ``red zone'' for x86-64 code. The red zone is mandated -by the x86-64 ABI; it is a 128-byte area beyond the location of the -stack pointer that is not modified by signal or interrupt handlers -and therefore can be used for temporary data without adjusting the stack -pointer. The flag @option{-mno-red-zone} disables this red zone. - -@item -mcmodel=small -@opindex mcmodel=small -Generate code for the small code model: the program and its symbols must -be linked in the lower 2 GB of the address space. Pointers are 64 bits. -Programs can be statically or dynamically linked. This is the default -code model. - -@item -mcmodel=kernel -@opindex mcmodel=kernel -Generate code for the kernel code model. The kernel runs in the -negative 2 GB of the address space. -This model has to be used for Linux kernel code. - -@item -mcmodel=medium -@opindex mcmodel=medium -Generate code for the medium model: the program is linked in the lower 2 -GB of the address space. Small symbols are also placed there. Symbols -with sizes larger than @option{-mlarge-data-threshold} are put into -large data or BSS sections and can be located above 2GB. Programs can -be statically or dynamically linked. - -@item -mcmodel=large -@opindex mcmodel=large -Generate code for the large model. This model makes no assumptions -about addresses and sizes of sections. - -@item -maddress-mode=long -@opindex maddress-mode=long -Generate code for long address mode. This is only supported for 64-bit -and x32 environments. It is the default address mode for 64-bit -environments. - -@item -maddress-mode=short -@opindex maddress-mode=short -Generate code for short address mode. This is only supported for 32-bit -and x32 environments. It is the default address mode for 32-bit and -x32 environments. - -@item -mneeded -@itemx -mno-needed -@opindex mneeded -Emit GNU_PROPERTY_X86_ISA_1_NEEDED GNU property for Linux target to -indicate the micro-architecture ISA level required to execute the binary. - -@item -mno-direct-extern-access -@opindex mno-direct-extern-access -@opindex mdirect-extern-access -Without @option{-fpic} nor @option{-fPIC}, always use the GOT pointer -to access external symbols. With @option{-fpic} or @option{-fPIC}, -treat access to protected symbols as local symbols. The default is -@option{-mdirect-extern-access}. - -@strong{Warning:} shared libraries compiled with -@option{-mno-direct-extern-access} and executable compiled with -@option{-mdirect-extern-access} may not be binary compatible if -protected symbols are used in shared libraries and executable. -@end table - -@node x86 Windows Options -@subsection x86 Windows Options -@cindex x86 Windows Options -@cindex Windows Options for x86 - -These additional options are available for Microsoft Windows targets: - -@table @gcctabopt -@item -mconsole -@opindex mconsole -This option -specifies that a console application is to be generated, by -instructing the linker to set the PE header subsystem type -required for console applications. -This option is available for Cygwin and MinGW targets and is -enabled by default on those targets. - -@item -mdll -@opindex mdll -This option is available for Cygwin and MinGW targets. It -specifies that a DLL---a dynamic link library---is to be -generated, enabling the selection of the required runtime -startup object and entry point. - -@item -mnop-fun-dllimport -@opindex mnop-fun-dllimport -This option is available for Cygwin and MinGW targets. It -specifies that the @code{dllimport} attribute should be ignored. - -@item -mthreads -@opindex mthreads -This option is available for MinGW targets. It specifies -that MinGW-specific thread support is to be used. - -@item -municode -@opindex municode -This option is available for MinGW-w64 targets. It causes -the @code{UNICODE} preprocessor macro to be predefined, and -chooses Unicode-capable runtime startup code. - -@item -mwin32 -@opindex mwin32 -This option is available for Cygwin and MinGW targets. It -specifies that the typical Microsoft Windows predefined macros are to -be set in the pre-processor, but does not influence the choice -of runtime library/startup code. - -@item -mwindows -@opindex mwindows -This option is available for Cygwin and MinGW targets. It -specifies that a GUI application is to be generated by -instructing the linker to set the PE header subsystem type -appropriately. - -@item -fno-set-stack-executable -@opindex fno-set-stack-executable -@opindex fset-stack-executable -This option is available for MinGW targets. It specifies that -the executable flag for the stack used by nested functions isn't -set. This is necessary for binaries running in kernel mode of -Microsoft Windows, as there the User32 API, which is used to set executable -privileges, isn't available. - -@item -fwritable-relocated-rdata -@opindex fno-writable-relocated-rdata -@opindex fwritable-relocated-rdata -This option is available for MinGW and Cygwin targets. It specifies -that relocated-data in read-only section is put into the @code{.data} -section. This is a necessary for older runtimes not supporting -modification of @code{.rdata} sections for pseudo-relocation. - -@item -mpe-aligned-commons -@opindex mpe-aligned-commons -This option is available for Cygwin and MinGW targets. It -specifies that the GNU extension to the PE file format that -permits the correct alignment of COMMON variables should be -used when generating code. It is enabled by default if -GCC detects that the target assembler found during configuration -supports the feature. -@end table - -See also under @ref{x86 Options} for standard options. - -@node Xstormy16 Options -@subsection Xstormy16 Options -@cindex Xstormy16 Options - -These options are defined for Xstormy16: - -@table @gcctabopt -@item -msim -@opindex msim -Choose startup files and linker script suitable for the simulator. -@end table - -@node Xtensa Options -@subsection Xtensa Options -@cindex Xtensa Options - -These options are supported for Xtensa targets: - -@table @gcctabopt -@item -mconst16 -@itemx -mno-const16 -@opindex mconst16 -@opindex mno-const16 -Enable or disable use of @code{CONST16} instructions for loading -constant values. The @code{CONST16} instruction is currently not a -standard option from Tensilica. When enabled, @code{CONST16} -instructions are always used in place of the standard @code{L32R} -instructions. The use of @code{CONST16} is enabled by default only if -the @code{L32R} instruction is not available. - -@item -mfused-madd -@itemx -mno-fused-madd -@opindex mfused-madd -@opindex mno-fused-madd -Enable or disable use of fused multiply/add and multiply/subtract -instructions in the floating-point option. This has no effect if the -floating-point option is not also enabled. Disabling fused multiply/add -and multiply/subtract instructions forces the compiler to use separate -instructions for the multiply and add/subtract operations. This may be -desirable in some cases where strict IEEE 754-compliant results are -required: the fused multiply add/subtract instructions do not round the -intermediate result, thereby producing results with @emph{more} bits of -precision than specified by the IEEE standard. Disabling fused multiply -add/subtract instructions also ensures that the program output is not -sensitive to the compiler's ability to combine multiply and add/subtract -operations. - -@item -mserialize-volatile -@itemx -mno-serialize-volatile -@opindex mserialize-volatile -@opindex mno-serialize-volatile -When this option is enabled, GCC inserts @code{MEMW} instructions before -@code{volatile} memory references to guarantee sequential consistency. -The default is @option{-mserialize-volatile}. Use -@option{-mno-serialize-volatile} to omit the @code{MEMW} instructions. - -@item -mforce-no-pic -@opindex mforce-no-pic -For targets, like GNU/Linux, where all user-mode Xtensa code must be -position-independent code (PIC), this option disables PIC for compiling -kernel code. - -@item -mtext-section-literals -@itemx -mno-text-section-literals -@opindex mtext-section-literals -@opindex mno-text-section-literals -These options control the treatment of literal pools. The default is -@option{-mno-text-section-literals}, which places literals in a separate -section in the output file. This allows the literal pool to be placed -in a data RAM/ROM, and it also allows the linker to combine literal -pools from separate object files to remove redundant literals and -improve code size. With @option{-mtext-section-literals}, the literals -are interspersed in the text section in order to keep them as close as -possible to their references. This may be necessary for large assembly -files. Literals for each function are placed right before that function. - -@item -mauto-litpools -@itemx -mno-auto-litpools -@opindex mauto-litpools -@opindex mno-auto-litpools -These options control the treatment of literal pools. The default is -@option{-mno-auto-litpools}, which places literals in a separate -section in the output file unless @option{-mtext-section-literals} is -used. With @option{-mauto-litpools} the literals are interspersed in -the text section by the assembler. Compiler does not produce explicit -@code{.literal} directives and loads literals into registers with -@code{MOVI} instructions instead of @code{L32R} to let the assembler -do relaxation and place literals as necessary. This option allows -assembler to create several literal pools per function and assemble -very big functions, which may not be possible with -@option{-mtext-section-literals}. - -@item -mtarget-align -@itemx -mno-target-align -@opindex mtarget-align -@opindex mno-target-align -When this option is enabled, GCC instructs the assembler to -automatically align instructions to reduce branch penalties at the -expense of some code density. The assembler attempts to widen density -instructions to align branch targets and the instructions following call -instructions. If there are not enough preceding safe density -instructions to align a target, no widening is performed. The -default is @option{-mtarget-align}. These options do not affect the -treatment of auto-aligned instructions like @code{LOOP}, which the -assembler always aligns, either by widening density instructions or -by inserting NOP instructions. - -@item -mlongcalls -@itemx -mno-longcalls -@opindex mlongcalls -@opindex mno-longcalls -When this option is enabled, GCC instructs the assembler to translate -direct calls to indirect calls unless it can determine that the target -of a direct call is in the range allowed by the call instruction. This -translation typically occurs for calls to functions in other source -files. Specifically, the assembler translates a direct @code{CALL} -instruction into an @code{L32R} followed by a @code{CALLX} instruction. -The default is @option{-mno-longcalls}. This option should be used in -programs where the call target can potentially be out of range. This -option is implemented in the assembler, not the compiler, so the -assembly code generated by GCC still shows direct call -instructions---look at the disassembled object code to see the actual -instructions. Note that the assembler uses an indirect call for -every cross-file call, not just those that really are out of range. - -@item -mabi=@var{name} -@opindex mabi -Generate code for the specified ABI@. Permissible values are: @samp{call0}, -@samp{windowed}. Default ABI is chosen by the Xtensa core configuration. - -@item -mabi=call0 -@opindex mabi=call0 -When this option is enabled function parameters are passed in registers -@code{a2} through @code{a7}, registers @code{a12} through @code{a15} are -caller-saved, and register @code{a15} may be used as a frame pointer. -When this version of the ABI is enabled the C preprocessor symbol -@code{__XTENSA_CALL0_ABI__} is defined. - -@item -mabi=windowed -@opindex mabi=windowed -When this option is enabled function parameters are passed in registers -@code{a10} through @code{a15}, and called function rotates register window -by 8 registers on entry so that its arguments are found in registers -@code{a2} through @code{a7}. Register @code{a7} may be used as a frame -pointer. Register window is rotated 8 registers back upon return. -When this version of the ABI is enabled the C preprocessor symbol -@code{__XTENSA_WINDOWED_ABI__} is defined. - -@item -mextra-l32r-costs=@var{n} -@opindex mextra-l32r-costs -Specify an extra cost of instruction RAM/ROM access for @code{L32R} -instructions, in clock cycles. This affects, when optimizing for speed, -whether loading a constant from literal pool using @code{L32R} or -synthesizing the constant from a small one with a couple of arithmetic -instructions. The default value is 0. -@end table - -@node zSeries Options -@subsection zSeries Options -@cindex zSeries options - -These are listed under @xref{S/390 and zSeries Options}. - - -@c man end - -@node Spec Files -@section Specifying Subprocesses and the Switches to Pass to Them -@cindex Spec Files - -@command{gcc} is a driver program. It performs its job by invoking a -sequence of other programs to do the work of compiling, assembling and -linking. GCC interprets its command-line parameters and uses these to -deduce which programs it should invoke, and which command-line options -it ought to place on their command lines. This behavior is controlled -by @dfn{spec strings}. In most cases there is one spec string for each -program that GCC can invoke, but a few programs have multiple spec -strings to control their behavior. The spec strings built into GCC can -be overridden by using the @option{-specs=} command-line switch to specify -a spec file. - -@dfn{Spec files} are plain-text files that are used to construct spec -strings. They consist of a sequence of directives separated by blank -lines. The type of directive is determined by the first non-whitespace -character on the line, which can be one of the following: - -@table @code -@item %@var{command} -Issues a @var{command} to the spec file processor. The commands that can -appear here are: - -@table @code -@item %include <@var{file}> -@cindex @code{%include} -Search for @var{file} and insert its text at the current point in the -specs file. - -@item %include_noerr <@var{file}> -@cindex @code{%include_noerr} -Just like @samp{%include}, but do not generate an error message if the include -file cannot be found. - -@item %rename @var{old_name} @var{new_name} -@cindex @code{%rename} -Rename the spec string @var{old_name} to @var{new_name}. - -@end table - -@item *[@var{spec_name}]: -This tells the compiler to create, override or delete the named spec -string. All lines after this directive up to the next directive or -blank line are considered to be the text for the spec string. If this -results in an empty string then the spec is deleted. (Or, if the -spec did not exist, then nothing happens.) Otherwise, if the spec -does not currently exist a new spec is created. If the spec does -exist then its contents are overridden by the text of this -directive, unless the first character of that text is the @samp{+} -character, in which case the text is appended to the spec. - -@item [@var{suffix}]: -Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive -and up to the next directive or blank line are considered to make up the -spec string for the indicated suffix. When the compiler encounters an -input file with the named suffix, it processes the spec string in -order to work out how to compile that file. For example: - -@smallexample -.ZZ: -z-compile -input %i -@end smallexample - -This says that any input file whose name ends in @samp{.ZZ} should be -passed to the program @samp{z-compile}, which should be invoked with the -command-line switch @option{-input} and with the result of performing the -@samp{%i} substitution. (See below.) - -As an alternative to providing a spec string, the text following a -suffix directive can be one of the following: - -@table @code -@item @@@var{language} -This says that the suffix is an alias for a known @var{language}. This is -similar to using the @option{-x} command-line switch to GCC to specify a -language explicitly. For example: - -@smallexample -.ZZ: -@@c++ -@end smallexample - -Says that .ZZ files are, in fact, C++ source files. - -@item #@var{name} -This causes an error messages saying: - -@smallexample -@var{name} compiler not installed on this system. -@end smallexample -@end table - -GCC already has an extensive list of suffixes built into it. -This directive adds an entry to the end of the list of suffixes, but -since the list is searched from the end backwards, it is effectively -possible to override earlier entries using this technique. - -@end table - -GCC has the following spec strings built into it. Spec files can -override these strings or create their own. Note that individual -targets can also add their own spec strings to this list. - -@smallexample -asm Options to pass to the assembler -asm_final Options to pass to the assembler post-processor -cpp Options to pass to the C preprocessor -cc1 Options to pass to the C compiler -cc1plus Options to pass to the C++ compiler -endfile Object files to include at the end of the link -link Options to pass to the linker -lib Libraries to include on the command line to the linker -libgcc Decides which GCC support library to pass to the linker -linker Sets the name of the linker -predefines Defines to be passed to the C preprocessor -signed_char Defines to pass to CPP to say whether @code{char} is signed - by default -startfile Object files to include at the start of the link -@end smallexample - -Here is a small example of a spec file: - -@smallexample -%rename lib old_lib - -*lib: ---start-group -lgcc -lc -leval1 --end-group %(old_lib) -@end smallexample - -This example renames the spec called @samp{lib} to @samp{old_lib} and -then overrides the previous definition of @samp{lib} with a new one. -The new definition adds in some extra command-line options before -including the text of the old definition. - -@dfn{Spec strings} are a list of command-line options to be passed to their -corresponding program. In addition, the spec strings can contain -@samp{%}-prefixed sequences to substitute variable text or to -conditionally insert text into the command line. Using these constructs -it is possible to generate quite complex command lines. - -Here is a table of all defined @samp{%}-sequences for spec -strings. Note that spaces are not generated automatically around the -results of expanding these sequences. Therefore you can concatenate them -together or combine them with constant text in a single argument. - -@table @code -@item %% -Substitute one @samp{%} into the program name or argument. - -@item %" -Substitute an empty argument. - -@item %i -Substitute the name of the input file being processed. - -@item %b -Substitute the basename for outputs related with the input file being -processed. This is often the substring up to (and not including) the -last period and not including the directory but, unless %w is active, it -expands to the basename for auxiliary outputs, which may be influenced -by an explicit output name, and by various other options that control -how auxiliary outputs are named. - -@item %B -This is the same as @samp{%b}, but include the file suffix (text after -the last period). Without %w, it expands to the basename for dump -outputs. - -@item %d -Marks the argument containing or following the @samp{%d} as a -temporary file name, so that that file is deleted if GCC exits -successfully. Unlike @samp{%g}, this contributes no text to the -argument. - -@item %g@var{suffix} -Substitute a file name that has suffix @var{suffix} and is chosen -once per compilation, and mark the argument in the same way as -@samp{%d}. To reduce exposure to denial-of-service attacks, the file -name is now chosen in a way that is hard to predict even when previously -chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s} -might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches -the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is -treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g} -was simply substituted with a file name chosen once per compilation, -without regard to any appended suffix (which was therefore treated -just like ordinary text), making such attacks more likely to succeed. - -@item %u@var{suffix} -Like @samp{%g}, but generates a new temporary file name -each time it appears instead of once per compilation. - -@item %U@var{suffix} -Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a -new one if there is no such last file name. In the absence of any -@samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share -the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s} -involves the generation of two distinct file names, one -for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was -simply substituted with a file name chosen for the previous @samp{%u}, -without regard to any appended suffix. - -@item %j@var{suffix} -Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is -writable, and if @option{-save-temps} is not used; -otherwise, substitute the name -of a temporary file, just like @samp{%u}. This temporary file is not -meant for communication between processes, but rather as a junk -disposal mechanism. - -@item %|@var{suffix} -@itemx %m@var{suffix} -Like @samp{%g}, except if @option{-pipe} is in effect. In that case -@samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at -all. These are the two most common ways to instruct a program that it -should read from standard input or write to standard output. If you -need something more elaborate you can use an @samp{%@{pipe:@code{X}@}} -construct: see for example @file{gcc/fortran/lang-specs.h}. - -@item %.@var{SUFFIX} -Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args -when it is subsequently output with @samp{%*}. @var{SUFFIX} is -terminated by the next space or %. - -@item %w -Marks the argument containing or following the @samp{%w} as the -designated output file of this compilation. This puts the argument -into the sequence of arguments that @samp{%o} substitutes. - -@item %V -Indicates that this compilation produces no output file. - -@item %o -Substitutes the names of all the output files, with spaces -automatically placed around them. You should write spaces -around the @samp{%o} as well or the results are undefined. -@samp{%o} is for use in the specs for running the linker. -Input files whose names have no recognized suffix are not compiled -at all, but they are included among the output files, so they are -linked. - -@item %O -Substitutes the suffix for object files. Note that this is -handled specially when it immediately follows @samp{%g, %u, or %U}, -because of the need for those to form complete file names. The -handling is such that @samp{%O} is treated exactly as if it had already -been substituted, except that @samp{%g, %u, and %U} do not currently -support additional @var{suffix} characters following @samp{%O} as they do -following, for example, @samp{.o}. - -@item %I -Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}), -@option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}), -@option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options) -and @option{-imultilib} as necessary. - -@item %s -Current argument is the name of a library or startup file of some sort. -Search for that file in a standard list of directories and substitute -the full name found. The current working directory is included in the -list of directories scanned. - -@item %T -Current argument is the name of a linker script. Search for that file -in the current list of directories to scan for libraries. If the file -is located insert a @option{--script} option into the command line -followed by the full path name found. If the file is not found then -generate an error message. Note: the current working directory is not -searched. - -@item %e@var{str} -Print @var{str} as an error message. @var{str} is terminated by a newline. -Use this when inconsistent options are detected. - -@item %n@var{str} -Print @var{str} as a notice. @var{str} is terminated by a newline. - -@item %(@var{name}) -Substitute the contents of spec string @var{name} at this point. - -@item %x@{@var{option}@} -Accumulate an option for @samp{%X}. - -@item %X -Output the accumulated linker options specified by a @samp{%x} spec string. - -@item %Y -Output the accumulated assembler options specified by @option{-Wa}. - -@item %Z -Output the accumulated preprocessor options specified by @option{-Wp}. - -@item %M -Output @code{multilib_os_dir}. - -@item %R -Output the concatenation of @code{target_system_root} and @code{target_sysroot_suffix}. - -@item %a -Process the @code{asm} spec. This is used to compute the -switches to be passed to the assembler. - -@item %A -Process the @code{asm_final} spec. This is a spec string for -passing switches to an assembler post-processor, if such a program is -needed. - -@item %l -Process the @code{link} spec. This is the spec for computing the -command line passed to the linker. Typically it makes use of the -@samp{%L %G %S %D and %E} sequences. - -@item %D -Dump out a @option{-L} option for each directory that GCC believes might -contain startup files. If the target supports multilibs then the -current multilib directory is prepended to each of these paths. - -@item %L -Process the @code{lib} spec. This is a spec string for deciding which -libraries are included on the command line to the linker. - -@item %G -Process the @code{libgcc} spec. This is a spec string for deciding -which GCC support library is included on the command line to the linker. - -@item %S -Process the @code{startfile} spec. This is a spec for deciding which -object files are the first ones passed to the linker. Typically -this might be a file named @file{crt0.o}. - -@item %E -Process the @code{endfile} spec. This is a spec string that specifies -the last object files that are passed to the linker. - -@item %C -Process the @code{cpp} spec. This is used to construct the arguments -to be passed to the C preprocessor. - -@item %1 -Process the @code{cc1} spec. This is used to construct the options to be -passed to the actual C compiler (@command{cc1}). - -@item %2 -Process the @code{cc1plus} spec. This is used to construct the options to be -passed to the actual C++ compiler (@command{cc1plus}). - -@item %* -Substitute the variable part of a matched option. See below. -Note that each comma in the substituted string is replaced by -a single space. - -@item %<S -Remove all occurrences of @code{-S} from the command line. Note---this -command is position dependent. @samp{%} commands in the spec string -before this one see @code{-S}, @samp{%} commands in the spec string -after this one do not. - -@item %<S* -Similar to @samp{%<S}, but match all switches beginning with @code{-S}. - -@item %>S -Similar to @samp{%<S}, but keep @code{-S} in the GCC command line. - -@item %:@var{function}(@var{args}) -Call the named function @var{function}, passing it @var{args}. -@var{args} is first processed as a nested spec string, then split -into an argument vector in the usual fashion. The function returns -a string which is processed as if it had appeared literally as part -of the current spec. - -The following built-in spec functions are provided: - -@table @code -@item @code{getenv} -The @code{getenv} spec function takes two arguments: an environment -variable name and a string. If the environment variable is not -defined, a fatal error is issued. Otherwise, the return value is the -value of the environment variable concatenated with the string. For -example, if @env{TOPDIR} is defined as @file{/path/to/top}, then: - -@smallexample -%:getenv(TOPDIR /include) -@end smallexample - -expands to @file{/path/to/top/include}. - -@item @code{if-exists} -The @code{if-exists} spec function takes one argument, an absolute -pathname to a file. If the file exists, @code{if-exists} returns the -pathname. Here is a small example of its usage: - -@smallexample -*startfile: -crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s -@end smallexample - -@item @code{if-exists-else} -The @code{if-exists-else} spec function is similar to the @code{if-exists} -spec function, except that it takes two arguments. The first argument is -an absolute pathname to a file. If the file exists, @code{if-exists-else} -returns the pathname. If it does not exist, it returns the second argument. -This way, @code{if-exists-else} can be used to select one file or another, -based on the existence of the first. Here is a small example of its usage: - -@smallexample -*startfile: -crt0%O%s %:if-exists(crti%O%s) \ -%:if-exists-else(crtbeginT%O%s crtbegin%O%s) -@end smallexample - -@item @code{if-exists-then-else} -The @code{if-exists-then-else} spec function takes at least two arguments -and an optional third one. The first argument is an absolute pathname to a -file. If the file exists, the function returns the second argument. -If the file does not exist, the function returns the third argument if there -is one, or NULL otherwise. This can be used to expand one text, or optionally -another, based on the existence of a file. Here is a small example of its -usage: - -@smallexample --l%:if-exists-then-else(%:getenv(VSB_DIR rtnet.h) rtnet net) -@end smallexample - -@item @code{sanitize} -The @code{sanitize} spec function takes no arguments. It returns non-NULL if -any address, thread or undefined behavior sanitizers are active. - -@smallexample -%@{%:sanitize(address):-funwind-tables@} -@end smallexample - -@item @code{replace-outfile} -The @code{replace-outfile} spec function takes two arguments. It looks for the -first argument in the outfiles array and replaces it with the second argument. Here -is a small example of its usage: - -@smallexample -%@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@} -@end smallexample - -@item @code{remove-outfile} -The @code{remove-outfile} spec function takes one argument. It looks for the -first argument in the outfiles array and removes it. Here is a small example -its usage: - -@smallexample -%:remove-outfile(-lm) -@end smallexample - -@item @code{version-compare} -The @code{version-compare} spec function takes four or five arguments of the following -form: - -@smallexample -<comparison-op> <arg1> [<arg2>] <switch> <result> -@end smallexample - -It returns @code{result} if the comparison evaluates to true, and NULL if it doesn't. -The supported @code{comparison-op} values are: - -@table @code -@item >= -True if @code{switch} is a later (or same) version than @code{arg1} - -@item !> -Opposite of @code{>=} - -@item < -True if @code{switch} is an earlier version than @code{arg1} - -@item !< -Opposite of @code{<} - -@item >< -True if @code{switch} is @code{arg1} or later, and earlier than @code{arg2} - -@item <> -True if @code{switch} is earlier than @code{arg1}, or is @code{arg2} or later -@end table - -If the @code{switch} is not present at all, the condition is false unless the first character -of the @code{comparison-op} is @code{!}. - -@smallexample -%:version-compare(>= 10.3 mmacosx-version-min= -lmx) -@end smallexample - -The above example would add @option{-lmx} if @option{-mmacosx-version-min=10.3.9} was -passed. - -@item @code{include} -The @code{include} spec function behaves much like @code{%include}, with the advantage -that it can be nested inside a spec and thus be conditionalized. It takes one argument, -the filename, and looks for it in the startfile path. It always returns NULL. - -@smallexample -%@{static-libasan|static:%:include(libsanitizer.spec)%(link_libasan)@} -@end smallexample - -@item @code{pass-through-libs} -The @code{pass-through-libs} spec function takes any number of arguments. It -finds any @option{-l} options and any non-options ending in @file{.a} (which it -assumes are the names of linker input library archive files) and returns a -result containing all the found arguments each prepended by -@option{-plugin-opt=-pass-through=} and joined by spaces. This list is -intended to be passed to the LTO linker plugin. - -@smallexample -%:pass-through-libs(%G %L %G) -@end smallexample - -@item @code{print-asm-header} -The @code{print-asm-header} function takes no arguments and simply -prints a banner like: - -@smallexample -Assembler options -================= - -Use "-Wa,OPTION" to pass "OPTION" to the assembler. -@end smallexample - -It is used to separate compiler options from assembler options -in the @option{--target-help} output. - -@item @code{gt} -The @code{gt} spec function takes two or more arguments. It returns @code{""} (the -empty string) if the second-to-last argument is greater than the last argument, and NULL -otherwise. The following example inserts the @code{link_gomp} spec if the last -@option{-ftree-parallelize-loops=} option given on the command line is greater than 1: - -@smallexample -%@{%:gt(%@{ftree-parallelize-loops=*:%*@} 1):%:include(libgomp.spec)%(link_gomp)@} -@end smallexample - -@item @code{debug-level-gt} -The @code{debug-level-gt} spec function takes one argument and returns @code{""} (the -empty string) if @code{debug_info_level} is greater than the specified number, and NULL -otherwise. - -@smallexample -%@{%:debug-level-gt(0):%@{gdwarf*:--gdwarf2@}@} -@end smallexample -@end table - -@item %@{S@} -Substitutes the @code{-S} switch, if that switch is given to GCC@. -If that switch is not specified, this substitutes nothing. Note that -the leading dash is omitted when specifying this option, and it is -automatically inserted if the substitution is performed. Thus the spec -string @samp{%@{foo@}} matches the command-line option @option{-foo} -and outputs the command-line option @option{-foo}. - -@item %W@{S@} -Like %@{@code{S}@} but mark last argument supplied within as a file to be -deleted on failure. - -@item %@@@{S@} -Like %@{@code{S}@} but puts the result into a @code{FILE} and substitutes -@code{@@FILE} if an @code{@@file} argument has been supplied. - -@item %@{S*@} -Substitutes all the switches specified to GCC whose names start -with @code{-S}, but which also take an argument. This is used for -switches like @option{-o}, @option{-D}, @option{-I}, etc. -GCC considers @option{-o foo} as being -one switch whose name starts with @samp{o}. %@{o*@} substitutes this -text, including the space. Thus two arguments are generated. - -@item %@{S*&T*@} -Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options -(the order of @code{S} and @code{T} in the spec is not significant). -There can be any number of ampersand-separated variables; for each the -wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}. - -@item %@{S:X@} -Substitutes @code{X}, if the @option{-S} switch is given to GCC@. - -@item %@{!S:X@} -Substitutes @code{X}, if the @option{-S} switch is @emph{not} given to GCC@. - -@item %@{S*:X@} -Substitutes @code{X} if one or more switches whose names start with -@code{-S} are specified to GCC@. Normally @code{X} is substituted only -once, no matter how many such switches appeared. However, if @code{%*} -appears somewhere in @code{X}, then @code{X} is substituted once -for each matching switch, with the @code{%*} replaced by the part of -that switch matching the @code{*}. - -If @code{%*} appears as the last part of a spec sequence then a space -is added after the end of the last substitution. If there is more -text in the sequence, however, then a space is not generated. This -allows the @code{%*} substitution to be used as part of a larger -string. For example, a spec string like this: - -@smallexample -%@{mcu=*:--script=%*/memory.ld@} -@end smallexample - -@noindent -when matching an option like @option{-mcu=newchip} produces: - -@smallexample ---script=newchip/memory.ld -@end smallexample - -@item %@{.S:X@} -Substitutes @code{X}, if processing a file with suffix @code{S}. - -@item %@{!.S:X@} -Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}. - -@item %@{,S:X@} -Substitutes @code{X}, if processing a file for language @code{S}. - -@item %@{!,S:X@} -Substitutes @code{X}, if not processing a file for language @code{S}. - -@item %@{S|P:X@} -Substitutes @code{X} if either @code{-S} or @code{-P} is given to -GCC@. This may be combined with @samp{!}, @samp{.}, @samp{,}, and -@code{*} sequences as well, although they have a stronger binding than -the @samp{|}. If @code{%*} appears in @code{X}, all of the -alternatives must be starred, and only the first matching alternative -is substituted. - -For example, a spec string like this: - -@smallexample -%@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@} -@end smallexample - -@noindent -outputs the following command-line options from the following input -command-line options: - -@smallexample -fred.c -foo -baz -jim.d -bar -boggle --d fred.c -foo -baz -boggle --d jim.d -bar -baz -boggle -@end smallexample - -@item %@{%:@var{function}(@var{args}):X@} - -Call function named @var{function} with args @var{args}. If the -function returns non-NULL, then @code{X} is substituted, if it returns -NULL, it isn't substituted. - -@item %@{S:X; T:Y; :D@} - -If @code{S} is given to GCC, substitutes @code{X}; else if @code{T} is -given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can -be as many clauses as you need. This may be combined with @code{.}, -@code{,}, @code{!}, @code{|}, and @code{*} as needed. - - -@end table - -The switch matching text @code{S} in a @samp{%@{S@}}, @samp{%@{S:X@}} -or similar construct can use a backslash to ignore the special meaning -of the character following it, thus allowing literal matching of a -character that is otherwise specially treated. For example, -@samp{%@{std=iso9899\:1999:X@}} substitutes @code{X} if the -@option{-std=iso9899:1999} option is given. - -The conditional text @code{X} in a @samp{%@{S:X@}} or similar -construct may contain other nested @samp{%} constructs or spaces, or -even newlines. They are processed as usual, as described above. -Trailing white space in @code{X} is ignored. White space may also -appear anywhere on the left side of the colon in these constructs, -except between @code{.} or @code{*} and the corresponding word. - -The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are -handled specifically in these constructs. If another value of -@option{-O} or the negated form of a @option{-f}, @option{-m}, or -@option{-W} switch is found later in the command line, the earlier -switch value is ignored, except with @{@code{S}*@} where @code{S} is -just one letter, which passes all matching options. - -The character @samp{|} at the beginning of the predicate text is used to -indicate that a command should be piped to the following command, but -only if @option{-pipe} is specified. - -It is built into GCC which switches take arguments and which do not. -(You might think it would be useful to generalize this to allow each -compiler's spec to say which switches take arguments. But this cannot -be done in a consistent fashion. GCC cannot even decide which input -files have been specified without knowing which switches take arguments, -and it must know which input files to compile in order to tell which -compilers to run). - -GCC also knows implicitly that arguments starting in @option{-l} are to be -treated as compiler output files, and passed to the linker in their -proper position among the other output files. - -@node Environment Variables -@section Environment Variables Affecting GCC -@cindex environment variables - -@c man begin ENVIRONMENT -This section describes several environment variables that affect how GCC -operates. Some of them work by specifying directories or prefixes to use -when searching for various kinds of files. Some are used to specify other -aspects of the compilation environment. - -Note that you can also specify places to search using options such as -@option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These -take precedence over places specified using environment variables, which -in turn take precedence over those specified by the configuration of GCC@. -@xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint, -GNU Compiler Collection (GCC) Internals}. - -@table @env -@item LANG -@itemx LC_CTYPE -@c @itemx LC_COLLATE -@itemx LC_MESSAGES -@c @itemx LC_MONETARY -@c @itemx LC_NUMERIC -@c @itemx LC_TIME -@itemx LC_ALL -@findex LANG -@findex LC_CTYPE -@c @findex LC_COLLATE -@findex LC_MESSAGES -@c @findex LC_MONETARY -@c @findex LC_NUMERIC -@c @findex LC_TIME -@findex LC_ALL -@cindex locale -These environment variables control the way that GCC uses -localization information which allows GCC to work with different -national conventions. GCC inspects the locale categories -@env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do -so. These locale categories can be set to any value supported by your -installation. A typical value is @samp{en_GB.UTF-8} for English in the United -Kingdom encoded in UTF-8. - -The @env{LC_CTYPE} environment variable specifies character -classification. GCC uses it to determine the character boundaries in -a string; this is needed for some multibyte encodings that contain quote -and escape characters that are otherwise interpreted as a string -end or escape. - -The @env{LC_MESSAGES} environment variable specifies the language to -use in diagnostic messages. - -If the @env{LC_ALL} environment variable is set, it overrides the value -of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE} -and @env{LC_MESSAGES} default to the value of the @env{LANG} -environment variable. If none of these variables are set, GCC -defaults to traditional C English behavior. - -@item TMPDIR -@findex TMPDIR -If @env{TMPDIR} is set, it specifies the directory to use for temporary -files. GCC uses temporary files to hold the output of one stage of -compilation which is to be used as input to the next stage: for example, -the output of the preprocessor, which is the input to the compiler -proper. - -@item GCC_COMPARE_DEBUG -@findex GCC_COMPARE_DEBUG -Setting @env{GCC_COMPARE_DEBUG} is nearly equivalent to passing -@option{-fcompare-debug} to the compiler driver. See the documentation -of this option for more details. - -@item GCC_EXEC_PREFIX -@findex GCC_EXEC_PREFIX -If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the -names of the subprograms executed by the compiler. No slash is added -when this prefix is combined with the name of a subprogram, but you can -specify a prefix that ends with a slash if you wish. - -If @env{GCC_EXEC_PREFIX} is not set, GCC attempts to figure out -an appropriate prefix to use based on the pathname it is invoked with. - -If GCC cannot find the subprogram using the specified prefix, it -tries looking in the usual places for the subprogram. - -The default value of @env{GCC_EXEC_PREFIX} is -@file{@var{prefix}/lib/gcc/} where @var{prefix} is the prefix to -the installed compiler. In many cases @var{prefix} is the value -of @code{prefix} when you ran the @file{configure} script. - -Other prefixes specified with @option{-B} take precedence over this prefix. - -This prefix is also used for finding files such as @file{crt0.o} that are -used for linking. - -In addition, the prefix is used in an unusual way in finding the -directories to search for header files. For each of the standard -directories whose name normally begins with @samp{/usr/local/lib/gcc} -(more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries -replacing that beginning with the specified prefix to produce an -alternate directory name. Thus, with @option{-Bfoo/}, GCC searches -@file{foo/bar} just before it searches the standard directory -@file{/usr/local/lib/bar}. -If a standard directory begins with the configured -@var{prefix} then the value of @var{prefix} is replaced by -@env{GCC_EXEC_PREFIX} when looking for header files. - -@item COMPILER_PATH -@findex COMPILER_PATH -The value of @env{COMPILER_PATH} is a colon-separated list of -directories, much like @env{PATH}. GCC tries the directories thus -specified when searching for subprograms, if it cannot find the -subprograms using @env{GCC_EXEC_PREFIX}. - -@item LIBRARY_PATH -@findex LIBRARY_PATH -The value of @env{LIBRARY_PATH} is a colon-separated list of -directories, much like @env{PATH}. When configured as a native compiler, -GCC tries the directories thus specified when searching for special -linker files, if it cannot find them using @env{GCC_EXEC_PREFIX}. Linking -using GCC also uses these directories when searching for ordinary -libraries for the @option{-l} option (but directories specified with -@option{-L} come first). - -@item LANG -@findex LANG -@cindex locale definition -This variable is used to pass locale information to the compiler. One way in -which this information is used is to determine the character set to be used -when character literals, string literals and comments are parsed in C and C++. -When the compiler is configured to allow multibyte characters, -the following values for @env{LANG} are recognized: - -@table @samp -@item C-JIS -Recognize JIS characters. -@item C-SJIS -Recognize SJIS characters. -@item C-EUCJP -Recognize EUCJP characters. -@end table - -If @env{LANG} is not defined, or if it has some other value, then the -compiler uses @code{mblen} and @code{mbtowc} as defined by the default locale to -recognize and translate multibyte characters. - -@item GCC_EXTRA_DIAGNOSTIC_OUTPUT -@findex GCC_EXTRA_DIAGNOSTIC_OUTPUT -If @env{GCC_EXTRA_DIAGNOSTIC_OUTPUT} is set to one of the following values, -then additional text will be emitted to stderr when fix-it hints are -emitted. @option{-fdiagnostics-parseable-fixits} and -@option{-fno-diagnostics-parseable-fixits} take precedence over this -environment variable. - -@table @samp -@item fixits-v1 -Emit parseable fix-it hints, equivalent to -@option{-fdiagnostics-parseable-fixits}. In particular, columns are -expressed as a count of bytes, starting at byte 1 for the initial column. - -@item fixits-v2 -As @code{fixits-v1}, but columns are expressed as display columns, -as per @option{-fdiagnostics-column-unit=display}. -@end table - -@end table - -@noindent -Some additional environment variables affect the behavior of the -preprocessor. - -@include cppenv.texi - -@c man end - -@node Precompiled Headers -@section Using Precompiled Headers -@cindex precompiled headers -@cindex speed of compilation - -Often large projects have many header files that are included in every -source file. The time the compiler takes to process these header files -over and over again can account for nearly all of the time required to -build the project. To make builds faster, GCC allows you to -@dfn{precompile} a header file. - -To create a precompiled header file, simply compile it as you would any -other file, if necessary using the @option{-x} option to make the driver -treat it as a C or C++ header file. You may want to use a -tool like @command{make} to keep the precompiled header up-to-date when -the headers it contains change. - -A precompiled header file is searched for when @code{#include} is -seen in the compilation. As it searches for the included file -(@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the -compiler looks for a precompiled header in each directory just before it -looks for the include file in that directory. The name searched for is -the name specified in the @code{#include} with @samp{.gch} appended. If -the precompiled header file cannot be used, it is ignored. - -For instance, if you have @code{#include "all.h"}, and you have -@file{all.h.gch} in the same directory as @file{all.h}, then the -precompiled header file is used if possible, and the original -header is used otherwise. - -Alternatively, you might decide to put the precompiled header file in a -directory and use @option{-I} to ensure that directory is searched -before (or instead of) the directory containing the original header. -Then, if you want to check that the precompiled header file is always -used, you can put a file of the same name as the original header in this -directory containing an @code{#error} command. - -This also works with @option{-include}. So yet another way to use -precompiled headers, good for projects not designed with precompiled -header files in mind, is to simply take most of the header files used by -a project, include them from another header file, precompile that header -file, and @option{-include} the precompiled header. If the header files -have guards against multiple inclusion, they are skipped because -they've already been included (in the precompiled header). - -If you need to precompile the same header file for different -languages, targets, or compiler options, you can instead make a -@emph{directory} named like @file{all.h.gch}, and put each precompiled -header in the directory, perhaps using @option{-o}. It doesn't matter -what you call the files in the directory; every precompiled header in -the directory is considered. The first precompiled header -encountered in the directory that is valid for this compilation is -used; they're searched in no particular order. - -There are many other possibilities, limited only by your imagination, -good sense, and the constraints of your build system. - -A precompiled header file can be used only when these conditions apply: - -@itemize -@item -Only one precompiled header can be used in a particular compilation. - -@item -A precompiled header cannot be used once the first C token is seen. You -can have preprocessor directives before a precompiled header; you cannot -include a precompiled header from inside another header. - -@item -The precompiled header file must be produced for the same language as -the current compilation. You cannot use a C precompiled header for a C++ -compilation. - -@item -The precompiled header file must have been produced by the same compiler -binary as the current compilation is using. - -@item -Any macros defined before the precompiled header is included must -either be defined in the same way as when the precompiled header was -generated, or must not affect the precompiled header, which usually -means that they don't appear in the precompiled header at all. - -The @option{-D} option is one way to define a macro before a -precompiled header is included; using a @code{#define} can also do it. -There are also some options that define macros implicitly, like -@option{-O} and @option{-Wdeprecated}; the same rule applies to macros -defined this way. - -@item If debugging information is output when using the precompiled -header, using @option{-g} or similar, the same kind of debugging information -must have been output when building the precompiled header. However, -a precompiled header built using @option{-g} can be used in a compilation -when no debugging information is being output. - -@item The same @option{-m} options must generally be used when building -and using the precompiled header. @xref{Submodel Options}, -for any cases where this rule is relaxed. - -@item Each of the following options must be the same when building and using -the precompiled header: - -@gccoptlist{-fexceptions} - -@item -Some other command-line options starting with @option{-f}, -@option{-p}, or @option{-O} must be defined in the same way as when -the precompiled header was generated. At present, it's not clear -which options are safe to change and which are not; the safest choice -is to use exactly the same options when generating and using the -precompiled header. The following are known to be safe: - -@gccoptlist{-fmessage-length= -fpreprocessed -fsched-interblock @gol --fsched-spec -fsched-spec-load -fsched-spec-load-dangerous @gol --fsched-verbose=@var{number} -fschedule-insns -fvisibility= @gol --pedantic-errors} - -@item Address space layout randomization (ASLR) can lead to not binary identical -PCH files. If you rely on stable PCH file contents disable ASLR when generating -PCH files. - -@end itemize - -For all of these except the last, the compiler automatically -ignores the precompiled header if the conditions aren't met. If you -find an option combination that doesn't work and doesn't cause the -precompiled header to be ignored, please consider filing a bug report, -see @ref{Bugs}. - -If you do use differing options when generating and using the -precompiled header, the actual behavior is a mixture of the -behavior for the options. For instance, if you use @option{-g} to -generate the precompiled header but not when using it, you may or may -not get debugging information for routines in the precompiled header. - -@node C++ Modules -@section C++ Modules -@cindex speed of compilation - -Modules are a C++20 language feature. As the name suggests, they -provides a modular compilation system, intending to provide both -faster builds and better library isolation. The ``Merging Modules'' -paper @uref{https://wg21.link/p1103}, provides the easiest to read set -of changes to the standard, although it does not capture later -changes. - -@emph{G++'s modules support is not complete.} Other than bugs, the -known missing pieces are: - -@table @emph - -@item Private Module Fragment -The Private Module Fragment is recognized, but an error is emitted. - -@item Partition definition visibility rules -Entities may be defined in implementation partitions, and those -definitions are not available outside of the module. This is not -implemented, and the definitions are available to extra-module use. - -@item Textual merging of reachable GM entities -Entities may be multiply defined across different header-units. -These must be de-duplicated, and this is implemented across imports, -or when an import redefines a textually-defined entity. However the -reverse is not implemented---textually redefining an entity that has -been defined in an imported header-unit. A redefinition error is -emitted. - -@item Translation-Unit local referencing rules -Papers p1815 (@uref{https://wg21.link/p1815}) and p2003 -(@uref{https://wg21.link/p2003}) add limitations on which entities an -exported region may reference (for instance, the entities an exported -template definition may reference). These are not fully implemented. - -@item Standard Library Header Units -The Standard Library is not provided as importable header units. If -you want to import such units, you must explicitly build them first. -If you do not do this with care, you may have multiple declarations, -which the module machinery must merge---compiler resource usage can be -affected by how you partition header files into header units. - -@end table - -Modular compilation is @emph{not} enabled with just the -@option{-std=c++20} option. You must explicitly enable it with the -@option{-fmodules-ts} option. It is independent of the language -version selected, although in pre-C++20 versions, it is of course an -extension. - -No new source file suffixes are required or supported. If you wish to -use a non-standard suffix (@pxref{Overall Options}), you also need -to provide a @option{-x c++} option too.@footnote{Some users like to -distinguish module interface files with a new suffix, such as naming -the source @code{module.cppm}, which involves -teaching all tools about the new suffix. A different scheme, such as -naming @code{module-m.cpp} would be less invasive.} - -Compiling a module interface unit produces an additional output (to -the assembly or object file), called a Compiled Module Interface -(CMI). This encodes the exported declarations of the module. -Importing a module reads in the CMI. The import graph is a Directed -Acyclic Graph (DAG). You must build imports before the importer. - -Header files may themselves be compiled to header units, which are a -transitional ability aiming at faster compilation. The -@option{-fmodule-header} option is used to enable this, and implies -the @option{-fmodules-ts} option. These CMIs are named by the fully -resolved underlying header file, and thus may be a complete pathname -containing subdirectories. If the header file is found at an absolute -pathname, the CMI location is still relative to a CMI root directory. - -As header files often have no suffix, you commonly have to specify a -@option{-x} option to tell the compiler the source is a header file. -You may use @option{-x c++-header}, @option{-x c++-user-header} or -@option{-x c++-system-header}. When used in conjunction with -@option{-fmodules-ts}, these all imply an appropriate -@option{-fmodule-header} option. The latter two variants use the -user or system include path to search for the file specified. This -allows you to, for instance, compile standard library header files as -header units, without needing to know exactly where they are -installed. Specifying the language as one of these variants also -inhibits output of the object file, as header files have no associated -object file. - -The @option{-fmodule-only} option disables generation of the -associated object file for compiling a module interface. Only the CMI -is generated. This option is implied when using the -@option{-fmodule-header} option. - -The @option{-flang-info-include-translate} and -@option{-flang-info-include-translate-not} options notes whether -include translation occurs or not. With no argument, the first will -note all include translation. The second will note all -non-translations of include files not known to intentionally be -textual. With an argument, queries about include translation of a -header files with that particular trailing pathname are noted. You -may repeat this form to cover several different header files. This -option may be helpful in determining whether include translation is -happening---if it is working correctly, it behaves as if it isn't -there at all. - -The @option{-flang-info-module-cmi} option can be used to determine -where the compiler is reading a CMI from. Without the option, the -compiler is silent when such a read is successful. This option has an -optional argument, which will restrict the notification to just the -set of named modules or header units specified. - -The @option{-Winvalid-imported-macros} option causes all imported macros -to be resolved at the end of compilation. Without this, imported -macros are only resolved when expanded or (re)defined. This option -detects conflicting import definitions for all macros. - -For details of the @option{-fmodule-mapper} family of options, -@pxref{C++ Module Mapper}. - -@menu -* C++ Module Mapper:: Module Mapper -* C++ Module Preprocessing:: Module Preprocessing -* C++ Compiled Module Interface:: Compiled Module Interface -@end menu - -@node C++ Module Mapper -@subsection Module Mapper -@cindex C++ Module Mapper - -A module mapper provides a server or file that the compiler queries to -determine the mapping between module names and CMI files. It is also -used to build CMIs on demand. @emph{Mapper functionality is in its -infancy and is intended for experimentation with build system -interactions.} - -You can specify a mapper with the @option{-fmodule-mapper=@var{val}} -option or @env{CXX_MODULE_MAPPER} environment variable. The value may -have one of the following forms: - -@table @gcctabopt - -@item @r{[}@var{hostname}@r{]}:@var{port}@r{[}?@var{ident}@r{]} -An optional hostname and a numeric port number to connect to. If the -hostname is omitted, the loopback address is used. If the hostname -corresponds to multiple IPV6 addresses, these are tried in turn, until -one is successful. If your host lacks IPv6, this form is -non-functional. If you must use IPv4 use -@option{-fmodule-mapper='|ncat @var{ipv4host} @var{port}'}. - -@item =@var{socket}@r{[}?@var{ident}@r{]} -A local domain socket. If your host lacks local domain sockets, this -form is non-functional. - -@item |@var{program}@r{[}?@var{ident}@r{]} @r{[}@var{args...}@r{]} -A program to spawn, and communicate with on its stdin/stdout streams. -Your @var{PATH} environment variable is searched for the program. -Arguments are separated by space characters, (it is not possible for -one of the arguments delivered to the program to contain a space). An -exception is if @var{program} begins with @@. In that case -@var{program} (sans @@) is looked for in the compiler's internal -binary directory. Thus the sample mapper-server can be specified -with @code{@@g++-mapper-server}. - -@item <>@r{[}?@var{ident}@r{]} -@item <>@var{inout}@r{[}?@var{ident}@r{]} -@item <@var{in}>@var{out}@r{[}?@var{ident}@r{]} -Named pipes or file descriptors to communicate over. The first form, -@option{<>}, communicates over stdin and stdout. The other forms -allow you to specify a file descriptor or name a pipe. A numeric value -is interpreted as a file descriptor, otherwise named pipe is opened. -The second form specifies a bidirectional pipe and the last form -allows specifying two independent pipes. Using file descriptors -directly in this manner is fragile in general, as it can require the -cooperation of intermediate processes. In particular using stdin & -stdout is fraught with danger as other compiler options might also -cause the compiler to read stdin or write stdout, and it can have -unfortunate interactions with signal delivery from the terminal. - -@item @var{file}@r{[}?@var{ident}@r{]} -A mapping file consisting of space-separated module-name, filename -pairs, one per line. Only the mappings for the direct imports and any -module export name need be provided. If other mappings are provided, -they override those stored in any imported CMI files. A repository -root may be specified in the mapping file by using @samp{$root} as the -module name in the first active line. Use of this option will disable -any default module->CMI name mapping. - -@end table - -As shown, an optional @var{ident} may suffix the first word of the -option, indicated by a @samp{?} prefix. The value is used in the -initial handshake with the module server, or to specify a prefix on -mapping file lines. In the server case, the main source file name is -used if no @var{ident} is specified. In the file case, all non-blank -lines are significant, unless a value is specified, in which case only -lines beginning with @var{ident} are significant. The @var{ident} -must be separated by whitespace from the module name. Be aware that -@samp{<}, @samp{>}, @samp{?}, and @samp{|} characters are often -significant to the shell, and therefore may need quoting. - -The mapper is connected to or loaded lazily, when the first module -mapping is required. The networking protocols are only supported on -hosts that provide networking. If no mapper is specified a default is -provided. - -A project-specific mapper is expected to be provided by the build -system that invokes the compiler. It is not expected that a -general-purpose server is provided for all compilations. As such, the -server will know the build configuration, the compiler it invoked, and -the environment (such as working directory) in which that is -operating. As it may parallelize builds, several compilations may -connect to the same socket. - -The default mapper generates CMI files in a @samp{gcm.cache} -directory. CMI files have a @samp{.gcm} suffix. The module unit name -is used directly to provide the basename. Header units construct a -relative path using the underlying header file name. If the path is -already relative, a @samp{,} directory is prepended. Internal -@samp{..} components are translated to @samp{,,}. No attempt is made -to canonicalize these filenames beyond that done by the preprocessor's -include search algorithm, as in general it is ambiguous when symbolic -links are present. - -The mapper protocol was published as ``A Module Mapper'' -@uref{https://wg21.link/p1184}. The implementation is provided by -@command{libcody}, @uref{https://github.com/urnathan/libcody}, -which specifies the canonical protocol definition. A proof of concept -server implementation embedded in @command{make} was described in -''Make Me A Module'', @uref{https://wg21.link/p1602}. - -@node C++ Module Preprocessing -@subsection Module Preprocessing -@cindex C++ Module Preprocessing - -Modules affect preprocessing because of header units and include -translation. Some uses of the preprocessor as a separate step either -do not produce a correct output, or require CMIs to be available. - -Header units import macros. These macros can affect later conditional -inclusion, which therefore can cascade to differing import sets. When -preprocessing, it is necessary to load the CMI. If a header unit is -unavailable, the preprocessor issues a warning and continue (when -not just preprocessing, an error is emitted). Detecting such imports -requires preprocessor tokenization of the input stream to phase 4 -(macro expansion). - -Include translation converts @code{#include}, @code{#include_next} and -@code{#import} directives to internal @code{import} declarations. -Whether a particular directive is translated is controlled by the -module mapper. Header unit names are canonicalized during -preprocessing. - -Dependency information can be emitted for macro import, extending the -functionality of @option{-MD} and @option{-MMD} options. Detection of -import declarations also requires phase 4 preprocessing, and thus -requires full preprocessing (or compilation). - -The @option{-M}, @option{-MM} and @option{-E -fdirectives-only} options halt -preprocessing before phase 4. - -The @option{-save-temps} option uses @option{-fdirectives-only} for -preprocessing, and preserve the macro definitions in the preprocessed -output. Usually you also want to use this option when explicitly -preprocessing a header-unit, or consuming such preprocessed output: - -@smallexample -g++ -fmodules-ts -E -fdirectives-only my-header.hh -o my-header.ii -g++ -x c++-header -fmodules-ts -fpreprocessed -fdirectives-only my-header.ii -@end smallexample - -@node C++ Compiled Module Interface -@subsection Compiled Module Interface -@cindex C++ Compiled Module Interface - -CMIs are an additional artifact when compiling named module -interfaces, partitions or header units. These are read when -importing. CMI contents are implementation-specific, and in GCC's -case tied to the compiler version. Consider them a rebuildable cache -artifact, not a distributable object. - -When creating an output CMI, any missing directory components are -created in a manner that is safe for concurrent builds creating -multiple, different, CMIs within a common subdirectory tree. - -CMI contents are written to a temporary file, which is then atomically -renamed. Observers either see old contents (if there is an -existing file), or complete new contents. They do not observe the -CMI during its creation. This is unlike object file writing, which -may be observed by an external process. - -CMIs are read in lazily, if the host OS provides @code{mmap} -functionality. Generally blocks are read when name lookup or template -instantiation occurs. To inhibit this, the @option{-fno-module-lazy} -option may be used. - -The @option{--param lazy-modules=@var{n}} parameter controls the limit -on the number of concurrently open module files during lazy loading. -Should more modules be imported, an LRU algorithm is used to determine -which files to close---until that file is needed again. This limit -may be exceeded with deep module dependency hierarchies. With large -code bases there may be more imports than the process limit of file -descriptors. By default, the limit is a few less than the per-process -file descriptor hard limit, if that is determinable.@footnote{Where -applicable the soft limit is incremented as needed towards the hard limit.} - -GCC CMIs use ELF32 as an architecture-neutral encapsulation mechanism. -You may use @command{readelf} to inspect them, although section -contents are largely undecipherable. There is a section named -@code{.gnu.c++.README}, which contains human-readable text. Other -than the first line, each line consists of @code{@var{tag}: @code{value}} -tuples. - -@smallexample -> @command{readelf -p.gnu.c++.README gcm.cache/foo.gcm} - -String dump of section '.gnu.c++.README': - [ 0] GNU C++ primary module interface - [ 21] compiler: 11.0.0 20201116 (experimental) [c++-modules revision 20201116-0454] - [ 6f] version: 2020/11/16-04:54 - [ 89] module: foo - [ 95] source: c_b.ii - [ a4] dialect: C++20/coroutines - [ be] cwd: /data/users/nathans/modules/obj/x86_64/gcc - [ ee] repository: gcm.cache - [ 104] buildtime: 2020/11/16 15:03:21 UTC - [ 127] localtime: 2020/11/16 07:03:21 PST - [ 14a] export: foo:part1 foo-part1.gcm -@end smallexample - -Amongst other things, this lists the source that was built, C++ -dialect used and imports of the module.@footnote{The precise contents -of this output may change.} The timestamp is the same value as that -provided by the @code{__DATE__} & @code{__TIME__} macros, and may be -explicitly specified with the environment variable -@code{SOURCE_DATE_EPOCH}. For further details -@pxref{Environment Variables}. - -A set of related CMIs may be copied, provided the relative pathnames -are preserved. - -The @code{.gnu.c++.README} contents do not affect CMI integrity, and -it may be removed or altered. The section numbering of the sections -whose names do not begin with @code{.gnu.c++.}, or are not the string -section is significant and must not be altered. |