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GCC(1) GNU GCC(1)

NAME
gcc - GNU project C and C++ compiler

SYNOPSIS
gcc [-c|-S|-E] [-std=standard]
[-g] [-pg] [-Olevel]
[-Wwarn...] [-Wpedantic]
[-Idir...] [-Ldir...]
[-Dmacro[=defn]...] [-Umacro]
[-foption...] [-mmachine-option...]
[-o outfile] [@file] infile...

Only the most useful options are listed here; see below for the
remainder. g++ accepts mostly the same options as gcc.

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 -c option says not
to run the linker. Then the output consists of object files output by
the assembler.

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.

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.

The usual way to run GCC is to run the executable called gcc, or
machine-gcc when cross-compiling, or machine-gcc-version to run a
specific version of GCC. When you compile C++ programs, you should
invoke GCC as g++ instead.

The gcc program accepts options and file names as operands. Many
options have multi-letter names; therefore multiple single-letter
options may not be grouped: -dv is very different from -d -v.

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 -L more than once, the
directories are searched in the order specified. Also, the placement
of the -l option is significant.

Many options have long names starting with -f or with -W---for example,
-fmove-loop-invariants, -Wformat and so on. Most of these have both
positive and negative forms; the negative form of -ffoo is -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 (=) 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 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 "kB" and
"KiB" for kilobyte and kibibyte, respectively, "MB" and "MiB" for
megabyte and mebibyte, "GB" and "GiB" for gigabyte and gigibyte, and so
on. Such arguments are designated by 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.

OPTIONS
Option Summary
Here is a summary of all the options, grouped by type. Explanations
are in the following sections.

Overall Options
-c -S -E -o file -dumpbase dumpbase -dumpbase-ext auxdropsuf
-dumpdir dumppfx -x language -v -### --help[=class[,...]]
--target-help --version -pass-exit-codes -pipe -specs=file
-wrapper @file -ffile-prefix-map=old=new -fcanon-prefix-map
-fplugin=file -fplugin-arg-name=arg -fdump-ada-spec[-slim]
-fada-spec-parent=unit -fdump-go-spec=file

C Language Options
-ansi -std=standard -aux-info filename -fno-asm -fno-builtin
-fno-builtin-function -fcond-mismatch -ffreestanding -fgimple
-fgnu-tm -fgnu89-inline -fhosted -flax-vector-conversions
-fms-extensions -fpermitted-flt-eval-methods=standard
-fplan9-extensions -fsigned-bitfields -funsigned-bitfields
-fsigned-char -funsigned-char -fstrict-flex-arrays[=n]
-fsso-struct=endianness

C++ Language Options
-fabi-version=n -fno-access-control -faligned-new=n
-fargs-in-order=n -fno-assume-sane-operators-new-delete -fchar8_t
-fcheck-new -fconcepts -fconstexpr-depth=n
-fconstexpr-cache-depth=n -fconstexpr-loop-limit=n
-fconstexpr-ops-limit=n -fno-elide-constructors
-fno-enforce-eh-specs -fno-gnu-keywords -fno-immediate-escalation
-fno-implicit-templates -fno-implicit-inline-templates
-fno-implement-inlines -fmodule-header[=kind] -fmodule-only
-fmodules -fmodule-implicit-inline -fno-module-lazy
-fmodule-mapper=specification -fmodule-version-ignore
-fms-extensions -fnew-inheriting-ctors -fnew-ttp-matching
-fno-nonansi-builtins -fnothrow-opt -fno-operator-names
-fno-optional-diags -fno-pretty-templates -frange-for-ext-temps
-fno-rtti -fsized-deallocation -ftemplate-backtrace-limit=n
-ftemplate-depth=n -fno-threadsafe-statics -fuse-cxa-atexit
-fno-weak -nostdinc++ -fvisibility-inlines-hidden
-fvisibility-ms-compat -fext-numeric-literals
-flang-info-include-translate[=header]
-flang-info-include-translate-not -flang-info-module-cmi[=module]
-stdlib=libstdc++,libc++ -Wabi-tag -Wcatch-value -Wcatch-value=n
-Wno-class-conversion -Wclass-memaccess -Wcomma-subscript
-Wconditionally-supported -Wno-conversion-null
-Wctad-maybe-unsupported -Wctor-dtor-privacy -Wdangling-reference
-Wno-defaulted-function-deleted -Wno-delete-incomplete
-Wdelete-non-virtual-dtor -Wno-deprecated-array-compare
-Wdeprecated-copy -Wdeprecated-copy-dtor
-Wno-deprecated-enum-enum-conversion
-Wno-deprecated-enum-float-conversion -Weffc++
-Wno-elaborated-enum-base -Wno-exceptions -Wextra-semi
-Wno-global-module -Wno-inaccessible-base
-Wno-inherited-variadic-ctor -Wno-init-list-lifetime
-Winvalid-constexpr -Winvalid-imported-macros -Wno-invalid-offsetof
-Wno-literal-suffix -Wmismatched-new-delete -Wmismatched-tags
-Wmultiple-inheritance -Wnamespaces -Wnarrowing -Wnoexcept
-Wnoexcept-type -Wnon-virtual-dtor -Wpessimizing-move
-Wno-placement-new -Wplacement-new=n -Wrange-loop-construct
-Wredundant-move -Wredundant-tags -Wreorder -Wregister
-Wstrict-null-sentinel -Wno-subobject-linkage -Wtemplates
-Wno-non-template-friend -Wold-style-cast -Woverloaded-virtual
-Wno-pmf-conversions -Wself-move -Wsign-promo -Wsized-deallocation
-Wsuggest-final-methods -Wsuggest-final-types -Wsuggest-override
-Wno-template-body -Wno-template-id-cdtor
-Wtemplate-names-tu-local -Wno-terminate -Wno-vexing-parse
-Wvirtual-inheritance -Wno-virtual-move-assign -Wvolatile
-Wzero-as-null-pointer-constant

Objective-C and Objective-C++ Language Options
-fconstant-string-class=class-name -fgnu-runtime -fnext-runtime
-fno-nil-receivers -fobjc-abi-version=n -fobjc-call-cxx-cdtors
-fobjc-direct-dispatch -fobjc-exceptions -fobjc-gc -fobjc-nilcheck
-fobjc-std=objc1 -fno-local-ivars
-fivar-visibility=[public|protected|private|package]
-freplace-objc-classes -fzero-link -gen-decls -Wassign-intercept
-Wno-property-assign-default -Wno-protocol -Wobjc-root-class
-Wselector -Wstrict-selector-match -Wundeclared-selector

OpenMP and OpenACC Options
-foffload=arg -foffload-options=arg -fopenacc -fopenacc-dim=geom
-fopenmp -fopenmp-simd -fopenmp-target-simd-clone[=device-type]

Diagnostic Message Formatting Options
-fmessage-length=n -fdiagnostics-plain-output
-fdiagnostics-show-location=[once|every-line]
-fdiagnostics-color=[auto|never|always]
-fdiagnostics-urls=[auto|never|always]
-fdiagnostics-format=[text|sarif-stderr|sarif-file|json|json-
stderr|json-file] -fdiagnostics-add-output=DIAGNOSTICS-OUTPUT-SPEC
-fdiagnostics-set-output=DIAGNOSTICS-OUTPUT-SPEC
-fno-diagnostics-json-formatting -fno-diagnostics-show-option
-fno-diagnostics-show-caret -fno-diagnostics-show-event-links
-fno-diagnostics-show-labels -fno-diagnostics-show-line-numbers
-fno-diagnostics-show-cwe -fno-diagnostics-show-rules
-fno-diagnostics-show-highlight-colors
-fdiagnostics-minimum-margin-width=width
-fdiagnostics-parseable-fixits -fdiagnostics-generate-patch
-fdiagnostics-show-template-tree -fno-elide-type
-fdiagnostics-path-format=[none|separate-events|inline-events]
-fdiagnostics-show-path-depths -fno-show-column
-fdiagnostics-column-unit=[display|byte]
-fdiagnostics-column-origin=origin
-fdiagnostics-escape-format=[unicode|bytes]
-fdiagnostics-text-art-charset=[none|ascii|unicode|emoji]

Warning Options
-fsyntax-only -fmax-errors=n -Wpedantic -pedantic-errors
-fpermissive -w -Wextra -Wall -Wabi=n -Waddress
-Wno-address-of-packed-member -Waggregate-return -Walloc-size
-Walloc-size-larger-than=byte-size -Walloc-zero -Walloca
-Walloca-larger-than=byte-size -Wno-aggressive-loop-optimizations
-Warith-conversion -Warray-bounds -Warray-bounds=n
-Warray-compare -Warray-parameter -Warray-parameter=n
-Wno-attributes -Wattribute-alias=n -Wno-attribute-alias
-Wno-attribute-warning -Wbidi-chars=[none|unpaired|any|ucn]
-Wbool-compare -Wbool-operation -Wno-builtin-declaration-mismatch
-Wno-builtin-macro-redefined -Wc90-c99-compat -Wc99-c11-compat
-Wc11-c23-compat -Wc23-c2y-compat -Wc++-compat -Wc++11-compat
-Wc++14-compat -Wc++17-compat -Wc++20-compat -Wno-c++11-extensions
-Wno-c++14-extensions -Wno-c++17-extensions -Wno-c++20-extensions
-Wno-c++23-extensions -Wcalloc-transposed-args -Wcast-align
-Wcast-align=strict -Wcast-function-type -Wcast-qual
-Wchar-subscripts -Wclobbered -Wcomment
-Wcompare-distinct-pointer-types -Wno-complain-wrong-lang
-Wconversion -Wno-coverage-mismatch -Wno-cpp -Wdangling-else
-Wdangling-pointer -Wdangling-pointer=n -Wdate-time
-Wno-deprecated -Wno-deprecated-declarations -Wno-designated-init
-Wdisabled-optimization -Wno-discarded-array-qualifiers
-Wno-discarded-qualifiers -Wno-div-by-zero -Wdouble-promotion
-Wduplicated-branches -Wduplicated-cond -Wempty-body
-Wno-endif-labels -Wenum-compare -Wenum-conversion
-Wenum-int-mismatch -Werror -Werror=* -Wexpansion-to-defined
-Wfatal-errors -Wflex-array-member-not-at-end -Wfloat-conversion
-Wfloat-equal -Wformat -Wformat=2 -Wno-format-contains-nul
-Wno-format-extra-args -Wformat-nonliteral -Wformat-overflow=n
-Wformat-security -Wformat-signedness -Wformat-truncation=n
-Wformat-y2k -Wframe-address -Wframe-larger-than=byte-size
-Wno-free-nonheap-object -Wheader-guard -Wno-if-not-aligned
-Wno-ignored-attributes -Wignored-qualifiers
-Wno-incompatible-pointer-types -Whardened -Wimplicit
-Wimplicit-fallthrough -Wimplicit-fallthrough=n
-Wno-implicit-function-declaration -Wno-implicit-int
-Winfinite-recursion -Winit-self -Winline -Wno-int-conversion
-Wint-in-bool-context -Wno-int-to-pointer-cast
-Wno-invalid-memory-model -Winvalid-pch -Winvalid-utf8
-Wno-unicode -Wjump-misses-init -Wlarger-than=byte-size
-Wleading-whitespace=kind -Wlogical-not-parentheses -Wlogical-op
-Wlong-long -Wno-lto-type-mismatch -Wmain -Wmaybe-uninitialized
-Wmemset-elt-size -Wmemset-transposed-args
-Wmisleading-indentation -Wmissing-attributes -Wmissing-braces
-Wmissing-field-initializers -Wmissing-format-attribute
-Wmissing-include-dirs -Wmissing-noreturn -Wno-missing-profile
-Wno-multichar -Wmultistatement-macros -Wnonnull
-Wnonnull-compare -Wnormalized=[none|id|nfc|nfkc]
-Wnull-dereference -Wno-odr -Wopenacc-parallelism -Wopenmp
-Wopenmp-simd -Wno-overflow -Woverlength-strings
-Wno-override-init-side-effects -Wpacked
-Wno-packed-bitfield-compat -Wpacked-not-aligned -Wpadded
-Wparentheses -Wno-pedantic-ms-format -Wpointer-arith
-Wno-pointer-compare -Wno-pointer-to-int-cast -Wno-pragmas
-Wno-pragma-once-outside-header -Wno-prio-ctor-dtor
-Wredundant-decls -Wrestrict -Wno-return-local-addr
-Wreturn-type -Wno-scalar-storage-order -Wsequence-point -Wshadow
-Wshadow=global -Wshadow=local -Wshadow=compatible-local
-Wno-shadow-ivar -Wno-shift-count-negative
-Wno-shift-count-overflow -Wshift-negative-value
-Wno-shift-overflow -Wshift-overflow=n -Wsign-compare
-Wsign-conversion -Wno-sizeof-array-argument -Wsizeof-array-div
-Wsizeof-pointer-div -Wsizeof-pointer-memaccess -Wstack-protector
-Wstack-usage=byte-size -Wstrict-aliasing -Wstrict-aliasing=n
-Wstrict-overflow -Wstrict-overflow=n -Wstring-compare
-Wno-stringop-overflow -Wno-stringop-overread
-Wno-stringop-truncation -Wstrict-flex-arrays
-Wsuggest-attribute=attribute-name -Wswitch -Wno-switch-bool
-Wswitch-default -Wswitch-enum -Wno-switch-outside-range
-Wno-switch-unreachable -Wsync-nand -Wsystem-headers
-Wtautological-compare -Wtrailing-whitespace
-Wtrailing-whitespace=kind -Wtrampolines -Wtrigraphs
-Wtrivial-auto-var-init -Wno-tsan -Wtype-limits -Wundef
-Wuninitialized -Wunknown-pragmas -Wunsuffixed-float-constants
-Wunterminated-string-initialization -Wunused
-Wunused-but-set-parameter -Wunused-but-set-variable
-Wunused-const-variable -Wunused-const-variable=n
-Wunused-function -Wunused-label -Wunused-local-typedefs
-Wunused-macros -Wunused-parameter -Wno-unused-result
-Wunused-value -Wunused-variable -Wuse-after-free
-Wuse-after-free=n -Wuseless-cast -Wno-varargs -Wvariadic-macros
-Wvector-operation-performance -Wvla -Wvla-larger-than=byte-size
-Wno-vla-larger-than -Wvolatile-register-var -Wwrite-strings
-Wno-xor-used-as-pow -Wzero-length-bounds

Static Analyzer Options
-fanalyzer -fanalyzer-call-summaries -fanalyzer-checker=name
-fno-analyzer-feasibility -fanalyzer-fine-grained
-fanalyzer-show-events-in-system-headers -fno-analyzer-state-merge
-fno-analyzer-state-purge -fno-analyzer-suppress-followups
-fanalyzer-transitivity -fno-analyzer-undo-inlining
-fanalyzer-verbose-edges -fanalyzer-verbose-state-changes
-fanalyzer-verbosity=level -fdump-analyzer
-fdump-analyzer-callgraph -fdump-analyzer-exploded-graph
-fdump-analyzer-exploded-nodes -fdump-analyzer-exploded-nodes-2
-fdump-analyzer-exploded-nodes-3 -fdump-analyzer-exploded-paths
-fdump-analyzer-feasibility -fdump-analyzer-infinite-loop
-fdump-analyzer-json -fdump-analyzer-state-purge
-fdump-analyzer-stderr -fdump-analyzer-supergraph
-fdump-analyzer-untracked -Wno-analyzer-double-fclose
-Wno-analyzer-double-free
-Wno-analyzer-exposure-through-output-file
-Wno-analyzer-exposure-through-uninit-copy
-Wno-analyzer-fd-access-mode-mismatch -Wno-analyzer-fd-double-close
-Wno-analyzer-fd-leak -Wno-analyzer-fd-phase-mismatch
-Wno-analyzer-fd-type-mismatch -Wno-analyzer-fd-use-after-close
-Wno-analyzer-fd-use-without-check -Wno-analyzer-file-leak
-Wno-analyzer-free-of-non-heap
-Wno-analyzer-imprecise-fp-arithmetic -Wno-analyzer-infinite-loop
-Wno-analyzer-infinite-recursion -Wno-analyzer-jump-through-null
-Wno-analyzer-malloc-leak -Wno-analyzer-mismatching-deallocation
-Wno-analyzer-null-argument -Wno-analyzer-null-dereference
-Wno-analyzer-out-of-bounds -Wno-analyzer-overlapping-buffers
-Wno-analyzer-possible-null-argument
-Wno-analyzer-possible-null-dereference
-Wno-analyzer-putenv-of-auto-var -Wno-analyzer-shift-count-negative
-Wno-analyzer-shift-count-overflow
-Wno-analyzer-stale-setjmp-buffer
-Wno-analyzer-tainted-allocation-size
-Wno-analyzer-tainted-assertion -Wno-analyzer-tainted-array-index
-Wno-analyzer-tainted-divisor -Wno-analyzer-tainted-offset
-Wno-analyzer-tainted-size -Wanalyzer-symbol-too-complex
-Wanalyzer-too-complex -Wno-analyzer-undefined-behavior-ptrdiff
-Wno-analyzer-undefined-behavior-strtok
-Wno-analyzer-unsafe-call-within-signal-handler
-Wno-analyzer-use-after-free
-Wno-analyzer-use-of-pointer-in-stale-stack-frame
-Wno-analyzer-use-of-uninitialized-value
-Wno-analyzer-va-arg-type-mismatch -Wno-analyzer-va-list-exhausted
-Wno-analyzer-va-list-leak -Wno-analyzer-va-list-use-after-va-end
-Wno-analyzer-write-to-const -Wno-analyzer-write-to-string-literal

C and Objective-C-only Warning Options
-Wbad-function-cast -Wdeprecated-non-prototype -Wfree-labels
-Wmissing-declarations -Wmissing-parameter-name
-Wmissing-parameter-type -Wdeclaration-missing-parameter-type
-Wmissing-prototypes -Wmissing-variable-declarations
-Wnested-externs -Wold-style-declaration -Wold-style-definition
-Wstrict-prototypes -Wtraditional -Wtraditional-conversion
-Wdeclaration-after-statement -Wpointer-sign

Debugging Options
-g -glevel -gdwarf -gdwarf-version -gbtf -gctf -gctflevel
-gprune-btf -gno-prune-btf -ggdb -grecord-gcc-switches
-gno-record-gcc-switches -gstrict-dwarf -gno-strict-dwarf
-gas-loc-support -gno-as-loc-support -gas-locview-support
-gno-as-locview-support -gcodeview -gcolumn-info -gno-column-info
-gdwarf32 -gdwarf64 -gstatement-frontiers
-gno-statement-frontiers -gvariable-location-views
-gno-variable-location-views -ginternal-reset-location-views
-gno-internal-reset-location-views -ginline-points
-gno-inline-points -gvms -gz[=type] -gsplit-dwarf -gdescribe-dies
-gno-describe-dies -fdebug-prefix-map=old=new
-fdebug-types-section -fno-eliminate-unused-debug-types
-femit-struct-debug-baseonly -femit-struct-debug-reduced
-femit-struct-debug-detailed[=spec-list]
-fno-eliminate-unused-debug-symbols -femit-class-debug-always
-fno-merge-debug-strings -fno-dwarf2-cfi-asm -fvar-tracking
-fvar-tracking-assignments

Optimization Options
-faggressive-loop-optimizations -falign-functions[=n[:m:[n2[:m2]]]]
-falign-jumps[=n[:m:[n2[:m2]]]] -falign-labels[=n[:m:[n2[:m2]]]]
-falign-loops[=n[:m:[n2[:m2]]]] -fmin-function-alignment=[n]
-fno-allocation-dce -fallow-store-data-races -fassociative-math
-fauto-profile -fauto-profile[=path] -fauto-inc-dec
-fbranch-probabilities -fcaller-saves -fcombine-stack-adjustments
-fconserve-stack -ffold-mem-offsets -fcompare-elim
-fcprop-registers -fcrossjumping -fcse-follow-jumps
-fcse-skip-blocks -fcx-fortran-rules -fcx-limited-range
-fdata-sections -fdce -fdelayed-branch
-fdelete-null-pointer-checks -fdevirtualize
-fdevirtualize-speculatively -fdevirtualize-at-ltrans -fdse
-fearly-inlining -fipa-sra -fexpensive-optimizations
-ffat-lto-objects -ffast-math -ffinite-math-only -ffloat-store
-fexcess-precision=style -ffinite-loops -fforward-propagate
-ffp-contract=style -ffunction-sections -fgcse
-fgcse-after-reload -fgcse-las -fgcse-lm -fgraphite-identity
-fgcse-sm -fhoist-adjacent-loads -fif-conversion -fif-conversion2
-findirect-inlining -finline-stringops[=fn] -finline-functions
-finline-functions-called-once -finline-limit=n
-finline-small-functions -fipa-modref -fipa-cp -fipa-cp-clone
-fipa-bit-cp -fipa-vrp -fipa-pta -fipa-profile -fipa-pure-const
-fipa-reference -fipa-reference-addressable -fipa-stack-alignment
-fipa-icf -fira-algorithm=algorithm -flate-combine-instructions
-flifetime-dse -flive-patching=level -fira-region=region
-fira-hoist-pressure -fira-loop-pressure -fno-ira-share-save-slots
-fno-ira-share-spill-slots -fisolate-erroneous-paths-dereference
-fisolate-erroneous-paths-attribute -fivopts
-fkeep-inline-functions -fkeep-static-functions
-fkeep-static-consts -flimit-function-alignment
-flive-range-shrinkage -floop-block -floop-interchange
-floop-strip-mine -floop-unroll-and-jam -floop-nest-optimize
-floop-parallelize-all -flra-remat -flto -flto-compression-level
-flto-partition=alg -flto-incremental=path
-flto-incremental-cache-size=n -fmalloc-dce -fmerge-all-constants
-fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves
-fmove-loop-invariants -fmove-loop-stores -fno-branch-count-reg
-fno-defer-pop -fno-fp-int-builtin-inexact -fno-function-cse
-fno-guess-branch-probability -fno-inline -fno-math-errno
-fno-peephole -fno-peephole2 -fno-printf-return-value
-fno-sched-interblock -fno-sched-spec -fno-signed-zeros
-fno-toplevel-reorder -fno-trapping-math
-fno-zero-initialized-in-bss -fomit-frame-pointer -foptimize-crc
-foptimize-sibling-calls -fpartial-inlining -fpeel-loops
-fpredictive-commoning -fprefetch-loop-arrays -fprofile-correction
-fprofile-use -fprofile-use=path -fprofile-partial-training
-fprofile-values -fprofile-reorder-functions -freciprocal-math
-free -frename-registers -freorder-blocks
-freorder-blocks-algorithm=algorithm -freorder-blocks-and-partition
-freorder-functions -frerun-cse-after-loop
-freschedule-modulo-scheduled-loops -frounding-math
-fsave-optimization-record -fsched2-use-superblocks
-fsched-pressure -fsched-spec-load -fsched-spec-load-dangerous
-fsched-stalled-insns-dep[=n] -fsched-stalled-insns[=n]
-fsched-group-heuristic -fsched-critical-path-heuristic
-fsched-spec-insn-heuristic -fsched-rank-heuristic
-fsched-last-insn-heuristic -fsched-dep-count-heuristic
-fschedule-fusion -fschedule-insns -fschedule-insns2
-fsection-anchors -fselective-scheduling -fselective-scheduling2
-fsel-sched-pipelining -fsel-sched-pipelining-outer-loops
-fsemantic-interposition -fshrink-wrap -fshrink-wrap-separate
-fsignaling-nans -fsingle-precision-constant
-fsplit-ivs-in-unroller -fsplit-loops -fsplit-paths
-fsplit-wide-types -fsplit-wide-types-early -fssa-backprop
-fssa-phiopt -fstdarg-opt -fstore-merging -fstrict-aliasing
-fipa-strict-aliasing -fthread-jumps -ftracer -ftree-bit-ccp
-ftree-builtin-call-dce -ftree-ccp -ftree-ch -ftree-coalesce-vars
-ftree-copy-prop -ftree-dce -ftree-dominator-opts -ftree-dse
-ftree-forwprop -ftree-fre -fcode-hoisting -ftree-loop-if-convert
-ftree-loop-im -ftree-phiprop -ftree-loop-distribution
-ftree-loop-distribute-patterns -ftree-loop-ivcanon
-ftree-loop-linear -ftree-loop-optimize -ftree-loop-vectorize
-ftree-parallelize-loops=n -ftree-pre -ftree-partial-pre
-ftree-pta -ftree-reassoc -ftree-scev-cprop -ftree-sink
-ftree-slsr -ftree-sra -ftree-switch-conversion -ftree-tail-merge
-ftree-ter -ftree-vectorize -ftree-vrp -ftrivial-auto-var-init
-funconstrained-commons -funit-at-a-time -funroll-all-loops
-funroll-loops -funsafe-math-optimizations -funswitch-loops
-fipa-ra -fvariable-expansion-in-unroller -fvect-cost-model
-fvpt -fweb -fwhole-program -fwpa -fuse-linker-plugin
-fzero-call-used-regs --param name=value -O -O0 -O1 -O2 -O3
-Os -Ofast -Og -Oz

Program Instrumentation Options
-p -pg -fprofile-arcs --coverage -ftest-coverage
-fcondition-coverage -fpath-coverage -fprofile-abs-path
-fprofile-dir=path -fprofile-generate -fprofile-generate=path
-fprofile-info-section -fprofile-info-section=name
-fprofile-note=path -fprofile-prefix-path=path
-fprofile-update=method -fprofile-filter-files=regex
-fprofile-exclude-files=regex
-fprofile-reproducible=[multithreaded|parallel-runs|serial]
-fsanitize=style -fsanitize-recover -fsanitize-recover=style
-fsanitize-trap -fsanitize-trap=style -fasan-shadow-offset=number
-fsanitize-sections=s1,s2,... -fsanitize-undefined-trap-on-error
-fbounds-check -fcf-protection=[full|branch|return|none|check]
-fharden-compares -fharden-conditional-branches -fhardened
-fharden-control-flow-redundancy -fhardcfr-skip-leaf
-fhardcfr-check-exceptions -fhardcfr-check-returning-calls
-fhardcfr-check-noreturn-calls=[always|no-xthrow|nothrow|never]
-fstack-protector -fstack-protector-all -fstack-protector-strong
-fstack-protector-explicit -fstack-check
-fstack-limit-register=reg -fstack-limit-symbol=sym
-fno-stack-limit -fsplit-stack -fstrub=disable -fstrub=strict
-fstrub=relaxed -fstrub=all -fstrub=at-calls -fstrub=internal
-fvtable-verify=[std|preinit|none] -fvtv-counts -fvtv-debug
-finstrument-functions -finstrument-functions-once
-finstrument-functions-exclude-function-list=sym,sym,...
-finstrument-functions-exclude-file-list=file,file,...
-fprofile-prefix-map=old=new -fpatchable-function-entry=N[,M]

Preprocessor Options
-Aquestion=answer -A-question[=answer] -C -CC -Dmacro[=defn] -dD
-dI -dM -dN -dU -fdebug-cpp -fdirectives-only
-fdollars-in-identifiers -fexec-charset=charset
-fextended-identifiers -finput-charset=charset
-fmacro-prefix-map=old=new -fmax-include-depth=depth
-fno-canonical-system-headers -fpch-deps -fpch-preprocess
-fpreprocessed -ftabstop=width -ftrack-macro-expansion
-fwide-exec-charset=charset -fworking-directory -H -imacros file
-include file -M -MD -MF -MG -MM -MMD -MP -MQ -MT
-Mno-modules -no-integrated-cpp -P -pthread -remap -traditional
-traditional-cpp -trigraphs -Umacro -undef -Wp,option
-Xpreprocessor option

Assembler Options
-Wa,option -Xassembler option

Linker Options
object-file-name -fuse-ld=linker -llibrary -nostartfiles
-nodefaultlibs -nolibc -nostdlib -nostdlib++ -e entry
--entry=entry -pie -pthread -r -rdynamic -s -static
-static-pie -static-libgcc -static-libstdc++ -static-libasan
-static-libtsan -static-liblsan -static-libubsan -shared
-shared-libgcc -symbolic -T script -Wl,option -Xlinker option -u
symbol -z keyword

Directory Options
-Bprefix -Idir -I- -idirafter dir -imacros file -imultilib dir
-iplugindir=dir -iprefix file -iquote dir -isysroot dir -isystem
dir -iwithprefix dir -iwithprefixbefore dir --embed-dir=dir -Ldir
-no-canonical-prefixes --no-sysroot-suffix -nostdinc -nostdinc++
--sysroot=dir

Code Generation Options
-fcall-saved-reg -fcall-used-reg -ffixed-reg -fexceptions
-fnon-call-exceptions -fdelete-dead-exceptions -funwind-tables
-fasynchronous-unwind-tables -fno-gnu-unique
-finhibit-size-directive -fcommon -fno-ident -fpcc-struct-return
-fpic -fPIC -fpie -fPIE -fno-plt -fno-jump-tables
-fno-bit-tests -frecord-gcc-switches -freg-struct-return
-fshort-enums -fshort-wchar -fverbose-asm -fpack-struct[=n]
-fleading-underscore -ftls-model=model -fstack-reuse=reuse_level
-ftrampolines -ftrampoline-impl=[stack|heap] -ftrapv -fwrapv
-fvisibility=[default|internal|hidden|protected]
-fstrict-volatile-bitfields -fsync-libcalls
-fzero-init-padding-bits=value

Developer Options
-dletters -dumpspecs -dumpmachine -dumpversion -dumpfullversion
-fcallgraph-info[=su,da] -fchecking -fchecking=n -fdbg-cnt-list
-fdbg-cnt=counter-value-list -fdisable-ipa-pass_name
-fdisable-rtl-pass_name -fdisable-rtl-pass-name=range-list
-fdisable-tree-pass_name -fdisable-tree-pass-name=range-list
-fdump-debug -fdump-earlydebug -fdump-noaddr -fdump-unnumbered
-fdump-unnumbered-links -fdump-final-insns[=file] -fdump-ipa-all
-fdump-ipa-cgraph -fdump-ipa-inline -fdump-lang-all
-fdump-lang-switch -fdump-lang-switch-options
-fdump-lang-switch-options=filename -fdump-passes -fdump-rtl-pass
-fdump-rtl-pass=filename -fdump-statistics -fdump-tree-all
-fdump-tree-switch -fdump-tree-switch-options
-fdump-tree-switch-options=filename -fcompare-debug[=opts]
-fcompare-debug-second -fenable-kind-pass -fenable-kind-pass=range-
list -fira-verbose=n -flto-report -flto-report-wpa
-fmem-report-wpa -fmem-report -fpre-ipa-mem-report
-fpost-ipa-mem-report -fopt-info -fopt-info-options[=file]
-fmultiflags -fprofile-report -frandom-seed=string
-fsched-verbose=n -fsel-sched-verbose -fsel-sched-dump-cfg
-fsel-sched-pipelining-verbose -fstats -fstack-usage
-ftime-report -ftime-report-details
-fvar-tracking-assignments-toggle -gtoggle
-print-file-name=library -print-libgcc-file-name
-print-multi-directory -print-multi-lib -print-multi-os-directory
-print-prog-name=program -print-search-dirs -Q -print-sysroot
-print-sysroot-headers-suffix -save-temps -save-temps=cwd
-save-temps=obj -time[=file]

Machine-Dependent Options
AArch64 Options (AArch64 Options) -mabi=name -mbig-endian
-mlittle-endian -mgeneral-regs-only -mcmodel=tiny -mcmodel=small
-mcmodel=large -mstrict-align -mno-strict-align
-momit-leaf-frame-pointer -mtls-dialect=desc
-mtls-dialect=traditional -mtls-size=size -mfix-cortex-a53-835769
-mfix-cortex-a53-843419 -mlow-precision-recip-sqrt
-mlow-precision-sqrt -mlow-precision-div
-mpc-relative-literal-loads -msign-return-address=scope
-mbranch-protection=none|standard|pac-ret[+leaf +b-key]|bti|gcs
-mharden-sls=opts -march=name -mcpu=name -mtune=name
-moverride=string -mverbose-cost-dump
-mstack-protector-guard=guard -mstack-protector-guard-reg=sysreg
-mstack-protector-guard-offset=offset -mtrack-speculation
-moutline-atomics -mearly-ldp-fusion -mlate-ldp-fusion
-Wexperimental-fmv-target

Adapteva Epiphany Options (Adapteva Epiphany Options)
-mhalf-reg-file -mprefer-short-insn-regs -mbranch-cost=num
-mcmove -mnops=num -msoft-cmpsf -msplit-lohi -mpost-inc
-mpost-modify -mstack-offset=num -mround-nearest -mlong-calls
-mshort-calls -msmall16 -mfp-mode=mode -mvect-double
-max-vect-align=num -msplit-vecmove-early -m1reg-reg

AMD GCN Options (AMD GCN Options) -march=gpu -mtune=gpu
-mstack-size=bytes

ARC Options (ARC Options) -mbarrel-shifter -mjli-always -mcpu=cpu
-mA6 -mARC600 -mA7 -mARC700 -mdpfp -mdpfp-compact -mdpfp-fast
-mno-dpfp-lrsr -mea -mno-mpy -mmul32x16 -mmul64 -matomic -mnorm
-mspfp -mspfp-compact -mspfp-fast -msimd -msoft-float -mswap
-mcrc -mdsp-packa -mdvbf -mlock -mmac-d16 -mmac-24 -mrtsc
-mswape -mtelephony -mxy -misize -mannotate-align -marclinux
-marclinux_prof -mlong-calls -mmedium-calls -msdata
-mirq-ctrl-saved -mrgf-banked-regs -mlpc-width=width -G num
-mvolatile-cache -mtp-regno=regno -malign-call -mauto-modify-reg
-mbbit-peephole -mno-brcc -mcase-vector-pcrel -mcompact-casesi
-mno-cond-exec -mearly-cbranchsi -mexpand-adddi -mindexed-loads
-mlra -mlra-priority-none -mlra-priority-compact
-mlra-priority-noncompact -mmillicode -mmixed-code -mq-class
-mRcq -mRcw -msize-level=level -mtune=cpu -mmultcost=num
-mcode-density-frame -munalign-prob-threshold=probability
-mmpy-option=multo -mdiv-rem -mcode-density -mll64 -mfpu=fpu
-mrf16 -mbranch-index

ARM Options (ARM Options) -mapcs-frame -mno-apcs-frame -mabi=name
-mapcs-stack-check -mno-apcs-stack-check -mapcs-reentrant
-mno-apcs-reentrant -mgeneral-regs-only -msched-prolog
-mno-sched-prolog -mlittle-endian -mbig-endian -mbe8 -mbe32
-mfloat-abi=name -mfp16-format=name -mthumb-interwork
-mno-thumb-interwork -mcpu=name -march=name -mfpu=name
-mtune=name -mprint-tune-info -mstructure-size-boundary=n
-mabort-on-noreturn -mlong-calls -mno-long-calls -msingle-pic-base
-mno-single-pic-base -mpic-register=reg -mnop-fun-dllimport
-mpoke-function-name -mthumb -marm -mflip-thumb -mtpcs-frame
-mtpcs-leaf-frame -mcaller-super-interworking
-mcallee-super-interworking -mtp=name -mtls-dialect=dialect
-mword-relocations -mfix-cortex-m3-ldrd
-mfix-cortex-a57-aes-1742098 -mfix-cortex-a72-aes-1655431
-munaligned-access -mneon-for-64bits -mslow-flash-data
-masm-syntax-unified -mrestrict-it -mverbose-cost-dump -mpure-code
-mcmse -mfix-cmse-cve-2021-35465 -mstack-protector-guard=guard
-mstack-protector-guard-offset=offset -mfdpic
-mbranch-protection=none|standard|pac-ret[+leaf] [+bti]|bti[+pac-
ret[+leaf]]

AVR Options (AVR Options) -mmcu=mcu -mabsdata -maccumulate-args
-mcvt -mbranch-cost=cost -mfuse-add=level -mfuse-move=level
-mcall-prologues -mgas-isr-prologues -mint8 -mflmap
-mdouble=bits -mlong-double=bits -mno-call-main -mn_flash=size
-mfract-convert-truncate -mno-interrupts -mmain-is-OS_task
-mrelax -mrmw -mstrict-X -mtiny-stack -mrodata-in-ram
-msplit-bit-shift -msplit-ldst -mshort-calls -mskip-bug
-muse-nonzero-bits -nodevicelib -nodevicespecs
-Waddr-space-convert -Wmisspelled-isr

Blackfin Options (Blackfin Options) -mcpu=cpu[-sirevision] -msim
-momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer
-mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly
-mno-csync-anomaly -mlow-64k -mno-low64k -mstack-check-l1
-mid-shared-library -mno-id-shared-library -mshared-library-id=n
-mleaf-id-shared-library -mno-leaf-id-shared-library -msep-data
-mno-sep-data -mlong-calls -mno-long-calls -mfast-fp
-minline-plt -mmulticore -mcorea -mcoreb -msdram -micplb

C6X Options (C6X Options) -mbig-endian -mlittle-endian -march=cpu
-msim -msdata=sdata-type

CRIS Options (CRIS Options) -mcpu=cpu -march=cpu -mtune=cpu
-mmax-stack-frame=n -metrax4 -metrax100 -mpdebug -mcc-init
-mno-side-effects -mstack-align -mdata-align -mconst-align
-m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -melf -maout
-sim -sim2 -mmul-bug-workaround -mno-mul-bug-workaround

C-SKY Options (C-SKY Options) -march=arch -mcpu=cpu -mbig-endian
-EB -mlittle-endian -EL -mhard-float -msoft-float -mfpu=fpu
-mdouble-float -mfdivdu -mfloat-abi=name -melrw -mistack -mmp
-mcp -mcache -msecurity -mtrust -mdsp -medsp -mvdsp -mdiv
-msmart -mhigh-registers -manchor -mpushpop -mmultiple-stld
-mconstpool -mstack-size -mccrt -mbranch-cost=n -mcse-cc
-msched-prolog -msim

Cygwin and MinGW Options (Cygwin and MinGW Options) -mconsole
-mcrtdll=library -mdll -mnop-fun-dllimport -mthread -municode
-mwin32 -mwindows -fno-set-stack-executable

Darwin Options (Darwin Options) -all_load -allowable_client -arch
-arch_errors_fatal -arch_only -bind_at_load -bundle
-bundle_loader -client_name -compatibility_version
-current_version -dead_strip -dependency-file -dylib_file
-dylinker_install_name -dynamic -dynamiclib
-exported_symbols_list -filelist -flat_namespace
-force_cpusubtype_ALL -force_flat_namespace
-headerpad_max_install_names -iframework -image_base -init
-install_name -keep_private_externs -multi_module
-multiply_defined -multiply_defined_unused -noall_load
-no_dead_strip_inits_and_terms -nodefaultrpaths -nofixprebinding
-nomultidefs -noprebind -noseglinkedit -pagezero_size -prebind
-prebind_all_twolevel_modules -private_bundle -read_only_relocs
-sectalign -sectobjectsymbols -whyload -seg1addr -sectcreate
-sectobjectsymbols -sectorder -segaddr -segs_read_only_addr
-segs_read_write_addr -seg_addr_table -seg_addr_table_filename
-seglinkedit -segprot -segs_read_only_addr -segs_read_write_addr
-single_module -static -sub_library -sub_umbrella
-twolevel_namespace -umbrella -undefined -unexported_symbols_list
-weak_reference_mismatches -whatsloaded -F -gused -gfull
-mmacosx-version-min=version -mkernel -mone-byte-bool

DEC Alpha Options (DEC Alpha Options) -mno-fp-regs -msoft-float
-mieee -mieee-with-inexact -mieee-conformant -mfp-trap-mode=mode
-mfp-rounding-mode=mode -mtrap-precision=mode -mbuild-constants
-mcpu=cpu-type -mtune=cpu-type -mbwx -mmax -mfix -mcix
-msafe-bwa -msafe-partial -mfloat-vax -mfloat-ieee
-mexplicit-relocs -msmall-data -mlarge-data -msmall-text
-mlarge-text -mmemory-latency=time

eBPF Options (eBPF Options) -mbig-endian -mlittle-endian
-mframe-limit=bytes -mxbpf -mco-re -mno-co-re -mjmpext -mjmp32
-malu32 -mv3-atomics -mbswap -msdiv -msmov -mcpu=version
-masm=dialect -minline-memops-threshold=bytes

FR30 Options (FR30 Options) -msmall-model -mno-lsim

FT32 Options (FT32 Options) -msim -mlra -mnodiv -mft32b
-mcompress -mnopm

FRV Options (FRV Options) -mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64
-mhard-float -msoft-float -malloc-cc -mfixed-cc -mdword
-mno-dword -mdouble -mno-double -mmedia -mno-media -mmuladd
-mno-muladd -mfdpic -minline-plt -mgprel-ro
-multilib-library-pic -mlinked-fp -mlong-calls -malign-labels
-mlibrary-pic -macc-4 -macc-8 -mpack -mno-pack -mno-eflags
-mcond-move -mno-cond-move -moptimize-membar -mno-optimize-membar
-mscc -mno-scc -mcond-exec -mno-cond-exec -mvliw-branch
-mno-vliw-branch -mmulti-cond-exec -mno-multi-cond-exec
-mnested-cond-exec -mno-nested-cond-exec -mtomcat-stats -mTLS
-mtls -mcpu=cpu

GNU/Linux Options (GNU/Linux Options) -mglibc -muclibc -mmusl
-mbionic -mandroid -tno-android-cc -tno-android-ld

H8/300 Options (H8/300 Options) -mrelax -mh -ms -mn -mexr
-mno-exr -mint32 -malign-300

HPPA Options (HPPA Options) -march=architecture-type
-matomic-libcalls -mbig-switch -mcaller-copies -mdisable-fpregs
-mdisable-indexing -mordered -mfast-indirect-calls -mgas
-mgnu-ld -mhp-ld -mfixed-range=register-range -mcoherent-ldcw
-mjump-in-delay -mlinker-opt -mlong-calls -mlong-load-store
-mno-atomic-libcalls -mno-disable-fpregs -mno-disable-indexing
-mno-fast-indirect-calls -mno-gas -mno-jump-in-delay
-mno-long-load-store -mno-portable-runtime -mno-soft-float
-mno-space-regs -msoft-float -mpa-risc-1-0 -mpa-risc-1-1
-mpa-risc-2-0 -mportable-runtime -mschedule=cpu-type -mspace-regs
-msoft-mult -msio -mwsio -munix=unix-std -nolibdld -static
-threads

IA-64 Options (IA-64 Options) -mbig-endian -mlittle-endian
-mgnu-as -mgnu-ld -mno-pic -mvolatile-asm-stop -mregister-names
-msdata -mno-sdata -mconstant-gp -mauto-pic -mfused-madd
-minline-float-divide-min-latency
-minline-float-divide-max-throughput -mno-inline-float-divide
-minline-int-divide-min-latency -minline-int-divide-max-throughput
-mno-inline-int-divide -minline-sqrt-min-latency
-minline-sqrt-max-throughput -mno-inline-sqrt -mdwarf2-asm
-mearly-stop-bits -mfixed-range=register-range -mtls-size=tls-size
-mtune=cpu-type -milp32 -mlp64 -msched-br-data-spec
-msched-ar-data-spec -msched-control-spec -msched-br-in-data-spec
-msched-ar-in-data-spec -msched-in-control-spec -msched-spec-ldc
-msched-spec-control-ldc -msched-prefer-non-data-spec-insns
-msched-prefer-non-control-spec-insns
-msched-stop-bits-after-every-cycle
-msched-count-spec-in-critical-path
-msel-sched-dont-check-control-spec -msched-fp-mem-deps-zero-cost
-msched-max-memory-insns-hard-limit -msched-max-memory-insns=max-
insns

LM32 Options (LM32 Options) -mbarrel-shift-enabled
-mdivide-enabled -mmultiply-enabled -msign-extend-enabled
-muser-enabled

LoongArch Options (LoongArch Options) -march=arch-type
-mtune=tune-type -mabi=base-abi-type -mfpu=fpu-type -msimd=simd-
type -msoft-float -msingle-float -mdouble-float -mlsx -mno-lsx
-mlasx -mno-lasx -mbranch-cost=n -maddr-reg-reg-cost=n
-mcheck-zero-division -mno-check-zero-division -mcond-move-int
-mno-cond-move-int -mcond-move-float -mno-cond-move-float -memcpy
-mno-memcpy -mstrict-align -mno-strict-align -G num
-mmax-inline-memcpy-size=n -mexplicit-relocs=style
-mexplicit-relocs -mno-explicit-relocs -mdirect-extern-access
-mno-direct-extern-access -mcmodel=code-model -mrelax
-mpass-mrelax-to-as -mrecip -mrecip=opt -mfrecipe -mno-frecipe
-mdiv32 -mno-div32 -mlam-bh -mno-lam-bh -mlamcas -mno-lamcas
-mld-seq-sa -mno-ld-seq-sa -mtls-dialect=opt -mannotate-tablejump
-mno-annotate-tablejump

M32C Options (M32C Options) -mcpu=cpu -msim -memregs=number

M32R/D Options (M32R/D Options) -m32r2 -m32rx -m32r -mdebug
-malign-loops -mno-align-loops -missue-rate=number
-mbranch-cost=number -mmodel=code-size-model-type -msdata=sdata-
type -mno-flush-func -mflush-func=name -mno-flush-trap
-mflush-trap=number -G num

M680x0 Options (M680x0 Options) -march=arch -mcpu=cpu -mtune=tune
-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 -m68060
-mcpu32 -m5200 -m5206e -m528x -m5307 -m5407 -mcfv4e
-mbitfield -mno-bitfield -mc68000 -mc68020 -mnobitfield -mrtd
-mno-rtd -mdiv -mno-div -mshort -mno-short -mhard-float
-m68881 -msoft-float -mpcrel -malign-int -mstrict-align
-msep-data -mno-sep-data -mshared-library-id=n
-mid-shared-library -mno-id-shared-library -mxgot -mno-xgot
-mlong-jump-table-offsets

MCore Options (MCore Options) -mhardlit -mno-hardlit -mdiv
-mno-div -mrelax-immediates -mno-relax-immediates
-mwide-bitfields -mno-wide-bitfields -m4byte-functions
-mno-4byte-functions -mcallgraph-data -mno-callgraph-data
-mslow-bytes -mno-slow-bytes -mno-lsim -mlittle-endian
-mbig-endian -m210 -m340 -mstack-increment

MicroBlaze Options (MicroBlaze Options) -msoft-float -mhard-float
-msmall-divides -mcpu=cpu -mmemcpy -mxl-soft-mul -mxl-soft-div
-mxl-barrel-shift -mxl-pattern-compare -mxl-stack-check
-mxl-gp-opt -mno-clearbss -mxl-multiply-high -mxl-float-convert
-mxl-float-sqrt -mbig-endian -mlittle-endian -mxl-reorder
-mxl-mode-app-model -mpic-data-is-text-relative

MIPS Options (MIPS Options) -EL -EB -march=arch -mtune=arch
-mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips32r3
-mips32r5 -mips32r6 -mips64 -mips64r2 -mips64r3 -mips64r5
-mips64r6 -mips16 -mno-mips16 -mflip-mips16
-minterlink-compressed -mno-interlink-compressed
-minterlink-mips16 -mno-interlink-mips16 -mabi=abi -mabicalls
-mno-abicalls -mshared -mno-shared -mplt -mno-plt -mxgot
-mno-xgot -mgp32 -mgp64 -mfp32 -mfpxx -mfp64 -mhard-float
-msoft-float -mno-float -msingle-float -mdouble-float -modd-spreg
-mno-odd-spreg -mabs=mode -mnan=encoding -mdsp -mno-dsp -mdspr2
-mno-dspr2 -mmcu -mmno-mcu -meva -mno-eva -mvirt -mno-virt -mxpa
-mno-xpa -mcrc -mno-crc -mginv -mno-ginv -mmicromips
-mno-micromips -mmsa -mno-msa -mloongson-mmi -mno-loongson-mmi
-mloongson-ext -mno-loongson-ext -mloongson-ext2
-mno-loongson-ext2 -mfpu=fpu-type -msmartmips -mno-smartmips
-mpaired-single -mno-paired-single -mdmx -mno-mdmx -mips3d
-mno-mips3d -mmt -mno-mt -mllsc -mno-llsc -mlong64 -mlong32
-msym32 -mno-sym32 -Gnum -mlocal-sdata -mno-local-sdata
-mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt
-membedded-data -mno-embedded-data -muninit-const-in-rodata
-mno-uninit-const-in-rodata -mcode-readable=setting
-msplit-addresses -mno-split-addresses -mexplicit-relocs
-mno-explicit-relocs -mexplicit-relocs=release
-mcheck-zero-division -mno-check-zero-division -mdivide-traps
-mdivide-breaks -mload-store-pairs -mno-load-store-pairs
-mstrict-align -mno-strict-align -mno-unaligned-access
-munaligned-access -mmemcpy -mno-memcpy -mlong-calls
-mno-long-calls -mmad -mno-mad -mimadd -mno-imadd -mfused-madd
-mno-fused-madd -nocpp -mfix-24k -mno-fix-24k -mfix-r4000
-mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 -mfix-r5900
-mno-fix-r5900 -mfix-r10000 -mno-fix-r10000 -mfix-rm7000
-mno-fix-rm7000 -mfix-vr4120 -mno-fix-vr4120 -mfix-vr4130
-mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1 -mflush-func=func
-mno-flush-func -mbranch-cost=num -mbranch-likely
-mno-branch-likely -mcompact-branches=policy -mfp-exceptions
-mno-fp-exceptions -mvr4130-align -mno-vr4130-align -msynci
-mno-synci -mlxc1-sxc1 -mno-lxc1-sxc1 -mmadd4 -mno-madd4
-mrelax-pic-calls -mno-relax-pic-calls -mmcount-ra-address
-mframe-header-opt -mno-frame-header-opt

MMIX Options (MMIX Options) -mlibfuncs -mno-libfuncs -mepsilon
-mno-epsilon -mabi=gnu -mabi=mmixware -mzero-extend -mknuthdiv
-mtoplevel-symbols -melf -mbranch-predict -mno-branch-predict
-mbase-addresses -mno-base-addresses -msingle-exit
-mno-single-exit

MN10300 Options (MN10300 Options) -mmult-bug -mno-mult-bug
-mno-am33 -mam33 -mam33-2 -mam34 -mtune=cpu-type
-mreturn-pointer-on-d0 -mno-crt0 -mrelax -mliw -msetlb

Moxie Options (Moxie Options) -meb -mel -mmul.x -mno-crt0

MSP430 Options (MSP430 Options) -msim -masm-hex -mmcu= -mcpu=
-mlarge -msmall -mrelax -mwarn-mcu -mcode-region= -mdata-region=
-msilicon-errata= -msilicon-errata-warn= -mhwmult= -minrt
-mtiny-printf -mmax-inline-shift=

NDS32 Options (NDS32 Options) -mbig-endian -mlittle-endian
-mreduced-regs -mfull-regs -mcmov -mno-cmov -mext-perf
-mno-ext-perf -mext-perf2 -mno-ext-perf2 -mext-string
-mno-ext-string -mv3push -mno-v3push -m16bit -mno-16bit
-misr-vector-size=num -mcache-block-size=num -march=arch
-mcmodel=code-model -mctor-dtor -mrelax

Nvidia PTX Options (Nvidia PTX Options) -m64 -mmainkernel
-moptimize

OpenRISC Options (OpenRISC Options) -mboard=name -mnewlib
-mhard-mul -mhard-div -msoft-mul -msoft-div -msoft-float
-mhard-float -mdouble-float -munordered-float -mcmov -mror
-mrori -msext -msfimm -mshftimm -mcmodel=code-model

PDP-11 Options (PDP-11 Options) -mfpu -msoft-float -mac0
-mno-ac0 -m40 -m45 -m10 -mint32 -mno-int16 -mint16 -mno-int32
-msplit -munix-asm -mdec-asm -mgnu-asm -mlra

PowerPC Options See RS/6000 and PowerPC Options.

PRU Options (PRU Options) -mmcu=mcu -minrt -mno-relax -mloop
-mabi=variant

RISC-V Options (RISC-V Options) -mbranch-cost=N-instruction -mplt
-mno-plt -mabi=ABI-string -mfdiv -mno-fdiv -mfence-tso
-mno-fence-tso -mdiv -mno-div -misa-spec=ISA-spec-string
-march=ISA-string -mtune=processor-string
-mpreferred-stack-boundary=num -msmall-data-limit=N-bytes
-msave-restore -mno-save-restore -mshorten-memrefs
-mno-shorten-memrefs -mstrict-align -mno-strict-align
-mcmodel=medlow -mcmodel=medany -mcmodel=large -mexplicit-relocs
-mno-explicit-relocs -mrelax -mno-relax -mriscv-attribute
-mno-riscv-attribute -malign-data=type -mbig-endian
-mlittle-endian -mstack-protector-guard=guard
-mstack-protector-guard-reg=reg
-mstack-protector-guard-offset=offset -mcsr-check -mno-csr-check
-mmovcc -mno-movcc -minline-atomics -mno-inline-atomics
-minline-strlen -mno-inline-strlen -minline-strcmp
-mno-inline-strcmp -minline-strncmp -mno-inline-strncmp
-mtls-dialect=desc -mtls-dialect=trad

RL78 Options (RL78 Options) -msim -mmul=none -mmul=g13 -mmul=g14
-mallregs -mcpu=g10 -mcpu=g13 -mcpu=g14 -mg10 -mg13 -mg14
-m64bit-doubles -m32bit-doubles -msave-mduc-in-interrupts

RS/6000 and PowerPC Options (RS/6000 and PowerPC Options)
-mcpu=cpu-type -mtune=cpu-type -mcmodel=code-model -mpowerpc64
-maltivec -mno-altivec -mpowerpc-gpopt -mno-powerpc-gpopt
-mpowerpc-gfxopt -mno-powerpc-gfxopt -mmfcrf -mno-mfcrf
-mpopcntb -mno-popcntb -mpopcntd -mno-popcntd -mfprnd
-mno-fprnd -mcmpb -mno-cmpb -mhard-dfp -mno-hard-dfp -mfull-toc
-mminimal-toc -mno-fp-in-toc -mno-sum-in-toc -m64 -m32
-mxl-compat -mno-xl-compat -mpe -malign-power -malign-natural
-msoft-float -mhard-float -mmultiple -mno-multiple -mupdate
-mno-update -mavoid-indexed-addresses -mno-avoid-indexed-addresses
-mfused-madd -mno-fused-madd -mbit-align -mno-bit-align
-mstrict-align -mno-strict-align -mrelocatable -mno-relocatable
-mrelocatable-lib -mno-relocatable-lib -mtoc -mno-toc -mlittle
-mlittle-endian -mbig -mbig-endian -mdynamic-no-pic -mswdiv
-msingle-pic-base -mprioritize-restricted-insns=priority
-msched-costly-dep=dependence_type -minsert-sched-nops=scheme
-mcall-aixdesc -mcall-eabi -mcall-freebsd -mcall-linux
-mcall-netbsd -mcall-openbsd -mcall-sysv -mcall-sysv-eabi
-mcall-sysv-noeabi -mtraceback=traceback_type -maix-struct-return
-msvr4-struct-return -mabi=abi-type -msecure-plt -mbss-plt
-msplit-patch-nops -mlongcall -mno-longcall -mpltseq -mno-pltseq
-mblock-move-inline-limit=num -mblock-compare-inline-limit=num
-mblock-compare-inline-loop-limit=num -mno-block-ops-unaligned-vsx
-mstring-compare-inline-limit=num -misel -mno-isel -mvrsave
-mno-vrsave -mmulhw -mno-mulhw -mdlmzb -mno-dlmzb -mprototype
-mno-prototype -msim -mmvme -mads -myellowknife -memb -msdata
-msdata=opt -mreadonly-in-sdata -mvxworks -G num -mrecip
-mrecip=opt -mno-recip -mrecip-precision -mno-recip-precision
-mveclibabi=type -mfriz -mno-friz -mpointers-to-nested-functions
-mno-pointers-to-nested-functions -msave-toc-indirect
-mno-save-toc-indirect -mpower8-fusion -mno-mpower8-fusion
-mcrypto -mno-crypto -mhtm -mno-htm -mquad-memory
-mno-quad-memory -mquad-memory-atomic -mno-quad-memory-atomic
-mcompat-align-parm -mno-compat-align-parm -mfloat128
-mno-float128 -mfloat128-hardware -mno-float128-hardware
-mgnu-attribute -mno-gnu-attribute -mstack-protector-guard=guard
-mstack-protector-guard-reg=reg
-mstack-protector-guard-offset=offset -mprefixed -mno-prefixed
-mpcrel -mno-pcrel -mmma -mno-mmma -mrop-protect -mno-rop-protect
-mprivileged -mno-privileged

RX Options (RX Options) -m64bit-doubles -m32bit-doubles -fpu
-nofpu -mcpu= -mbig-endian-data -mlittle-endian-data -msmall-data
-msim -mno-sim -mas100-syntax -mno-as100-syntax -mrelax
-mmax-constant-size= -mint-register= -mpid -mallow-string-insns
-mno-allow-string-insns -mjsr -mno-warn-multiple-fast-interrupts
-msave-acc-in-interrupts

S/390 and zSeries Options (S/390 and zSeries Options) -mtune=cpu-
type -march=cpu-type -mhard-float -msoft-float -mhard-dfp
-mno-hard-dfp -mlong-double-64 -mlong-double-128 -mbackchain
-mno-backchain -mpacked-stack -mno-packed-stack -msmall-exec
-mno-small-exec -mmvcle -mno-mvcle -m64 -m31 -mdebug
-mno-debug -mesa -mzarch -mhtm -mvx -mzvector -mtpf-trace
-mno-tpf-trace -mtpf-trace-skip -mno-tpf-trace-skip -mfused-madd
-mno-fused-madd -mwarn-framesize -mwarn-dynamicstack -mstack-size
-mstack-guard -mhotpatch=halfwords,halfwords

SH Options (SH Options) -m1 -m2 -m2e -m2a-nofpu -m2a-single-only
-m2a-single -m2a -m3 -m3e -m4-nofpu -m4-single-only -m4-single
-m4 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al -mb -ml
-mdalign -mrelax -mbigtable -mfmovd -mrenesas -mno-renesas
-mnomacsave -mieee -mno-ieee -mbitops -misize
-minline-ic_invalidate -mpadstruct -mprefergot -musermode
-multcost=number -mdiv=strategy -mdivsi3_libfunc=name
-mfixed-range=register-range -maccumulate-outgoing-args
-matomic-model=atomic-model -mbranch-cost=num -mzdcbranch
-mno-zdcbranch -mcbranch-force-delay-slot -mfused-madd
-mno-fused-madd -mfsca -mno-fsca -mfsrra -mno-fsrra
-mpretend-cmove -mtas

Solaris 2 Options (Solaris 2 Options) -mclear-hwcap
-mno-clear-hwcap -mimpure-text -mno-impure-text -pthreads

SPARC Options (SPARC Options) -mcpu=cpu-type -mtune=cpu-type
-mcmodel=code-model -mmemory-model=mem-model -m32 -m64 -mapp-regs
-mno-app-regs -mfaster-structs -mno-faster-structs -mflat
-mno-flat -mfpu -mno-fpu -mhard-float -msoft-float
-mhard-quad-float -msoft-quad-float -mstack-bias -mno-stack-bias
-mstd-struct-return -mno-std-struct-return -munaligned-doubles
-mno-unaligned-doubles -muser-mode -mno-user-mode -mv8plus
-mno-v8plus -mvis -mno-vis -mvis2 -mno-vis2 -mvis3 -mno-vis3
-mvis3b -mno-vis3b -mvis4 -mno-vis4 -mvis4b -mno-vis4b -mcbcond
-mno-cbcond -mfmaf -mno-fmaf -mfsmuld -mno-fsmuld -mpopc
-mno-popc -msubxc -mno-subxc -mfix-at697f -mfix-ut699
-mfix-ut700 -mfix-gr712rc

System V Options (System V Options) -Qy -Qn -YP,paths -Ym,dir

V850 Options (V850 Options) -mlong-calls -mno-long-calls -mep
-mno-ep -mprolog-function -mno-prolog-function -mspace -mtda=n
-msda=n -mzda=n -mapp-regs -mno-app-regs -mdisable-callt
-mno-disable-callt -mv850e2v3 -mv850e2 -mv850e1 -mv850es -mv850e
-mv850 -mv850e3v5 -mloop -mrelax -mlong-jumps -msoft-float
-mhard-float -mgcc-abi -mrh850-abi -mbig-switch

VAX Options (VAX Options) -munix -mgnu -md -md-float -mg
-mg-float -mlra

Visium Options (Visium Options) -mdebug -msim -mfpu -mno-fpu
-mhard-float -msoft-float -mcpu=cpu-type -mtune=cpu-type
-msv-mode -muser-mode

VMS Options (VMS Options) -mvms-return-codes -mdebug-main=prefix
-mmalloc64 -mpointer-size=size

VxWorks Options (VxWorks Options) -mrtp -msmp -non-static
-Bstatic -Bdynamic -Xbind-lazy -Xbind-now

x86 Options (x86 Options) -mtune=cpu-type -march=cpu-type
-mtune-ctrl=feature-list -mdump-tune-features -mno-default
-mfpmath=unit -masm=dialect -mno-fancy-math-387 -mno-fp-ret-in-387
-m80387 -mhard-float -msoft-float -mno-wide-multiply -mrtd
-malign-double -mpreferred-stack-boundary=num
-mincoming-stack-boundary=num -mcld -mcx16 -msahf -mmovbe
-mcrc32 -mmwait -mrecip -mrecip=opt -mvzeroupper -mprefer-avx128
-mprefer-vector-width=opt -mpartial-vector-fp-math -mmove-max=bits
-mstore-max=bits -mnoreturn-no-callee-saved-registers -mmmx -msse
-msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx -mavx2
-mavx512f -mavx512cd -mavx512vl -mavx512bw -mavx512dq
-mavx512ifma -mavx512vbmi -msha -maes -mpclmul -mfsgsbase
-mrdrnd -mf16c -mfma -mpconfig -mwbnoinvd -mptwrite
-mclflushopt -mclwb -mxsavec -mxsaves -msse4a -m3dnow -m3dnowa
-mpopcnt -mabm -mbmi -mtbm -mfma4 -mxop -madx -mlzcnt -mbmi2
-mfxsr -mxsave -mxsaveopt -mrtm -mhle -mlwp -mmwaitx -mclzero
-mpku -mthreads -mgfni -mvaes -mwaitpkg -mshstk -mmanual-endbr
-mcet-switch -mforce-indirect-call -mavx512vbmi2 -mavx512bf16
-menqcmd -mvpclmulqdq -mavx512bitalg -mmovdiri -mmovdir64b
-mavx512vpopcntdq -mavx512vnni -mprfchw -mrdpid -mrdseed -msgx
-mavx512vp2intersect -mserialize -mtsxldtrk -mamx-tile -mamx-int8
-mamx-bf16 -muintr -mhreset -mavxvnni -mamx-fp8 -mavx512fp16
-mavxifma -mavxvnniint8 -mavxneconvert -mcmpccxadd -mamx-fp16
-mprefetchi -mraoint -mamx-complex -mavxvnniint16 -msm3 -msha512
-msm4 -mapxf -musermsr -mavx10.1 -mavx10.1-256 -mavx10.1-512
-mevex512 -mavx10.2 -mamx-avx512 -mamx-tf32 -mamx-transpose -mmovrs
-mamx-movrs -mcldemote -mms-bitfields -mno-align-stringops
-minline-all-stringops -minline-stringops-dynamically
-mstringop-strategy=alg -mkl -mwidekl -mmemcpy-strategy=strategy
-mmemset-strategy=strategy -mpush-args -maccumulate-outgoing-args
-m128bit-long-double -m96bit-long-double -mlong-double-64
-mlong-double-80 -mlong-double-128 -mregparm=num -msseregparm
-mveclibabi=type -mvect8-ret-in-mem -mpc32 -mpc64 -mpc80
-mdaz-ftz -mstackrealign -momit-leaf-frame-pointer -mno-red-zone
-mno-tls-direct-seg-refs -mcmodel=code-model -mabi=name
-maddress-mode=mode -m32 -m64 -mx32 -m16 -miamcu
-mlarge-data-threshold=num -msse2avx -mfentry -mrecord-mcount
-mnop-mcount -m8bit-idiv -minstrument-return=type
-mfentry-name=name -mfentry-section=name
-mavx256-split-unaligned-load -mavx256-split-unaligned-store
-malign-data=type -mstack-protector-guard=guard
-mstack-protector-guard-reg=reg
-mstack-protector-guard-offset=offset
-mstack-protector-guard-symbol=symbol -mgeneral-regs-only
-mcall-ms2sysv-xlogues -mrelax-cmpxchg-loop
-mindirect-branch=choice -mfunction-return=choice
-mindirect-branch-register -mharden-sls=choice
-mindirect-branch-cs-prefix -mneeded -mno-direct-extern-access
-munroll-only-small-loops -mlam=choice

x86 Windows Options See Cygwin and MinGW Options.

Xstormy16 Options (Xstormy16 Options) -msim

Xtensa Options (Xtensa Options) -mconst16 -mno-const16
-mfused-madd -mno-fused-madd -mforce-no-pic -mserialize-volatile
-mno-serialize-volatile -mtext-section-literals
-mno-text-section-literals -mauto-litpools -mno-auto-litpools
-mtarget-align -mno-target-align -mlongcalls -mno-longcalls
-mabi=abi-type -mextra-l32r-costs=cycles -mstrict-align
-mno-strict-align

zSeries Options See S/390 and zSeries Options.

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.

For any given input file, the file name suffix determines what kind of
compilation is done:

file.c
C source code that must be preprocessed.

file.i
C source code that should not be preprocessed.

file.ii
C++ source code that should not be preprocessed.

file.m
Objective-C source code. Note that you must link with the libobjc
library to make an Objective-C program work.

file.mi
Objective-C source code that should not be preprocessed.

file.mm
file.M
Objective-C++ source code. Note that you must link with the
libobjc library to make an Objective-C++ program work. Note that
.M refers to a literal capital M.

file.mii
Objective-C++ source code that should not be preprocessed.

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 -fdump-ada-spec switch).

file.cc
file.cp
file.cxx
file.cpp
file.CPP
file.c++
file.C
C++ source code that must be preprocessed. Note that in .cxx, the
last two letters must both be literally x. Likewise, .C refers to
a literal capital C.

file.mm
file.M
Objective-C++ source code that must be preprocessed.

file.mii
Objective-C++ source code that should not be preprocessed.

file.hh
file.H
file.hp
file.hxx
file.hpp
file.HPP
file.h++
file.tcc
C++ header file to be turned into a precompiled header or Ada spec.

file.f
file.for
file.ftn
file.fi
Fixed form Fortran source code that should not be preprocessed.

file.F
file.FOR
file.fpp
file.FPP
file.FTN
Fixed form Fortran source code that must be preprocessed (with the
traditional preprocessor).

file.f90
file.f95
file.f03
file.f08
file.fii
Free form Fortran source code that should not be preprocessed.

file.F90
file.F95
file.F03
file.F08
Free form Fortran source code that must be preprocessed (with the
traditional preprocessor).

file.cob
file.COB
file.cbl
file.CBL
COBOL source code.

file.go
Go source code.

file.d
D source code.

file.di
D interface file.

file.dd
D documentation code (Ddoc).

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 specs.

file.adb
Ada source code file containing a library unit body (a subprogram
or package body). Such files are also called bodies.

file.s
Assembler code.

file.S
file.sx
Assembler code that must be preprocessed.

other
An object file to be fed straight into linking. Any file name with
no recognized suffix is treated this way.

You can specify the input language explicitly with the -x option:

-x language
Specify explicitly the 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 -x option. Possible values for language are:

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
cobol
d
f77 f77-cpp-input f95 f95-cpp-input
go

Note that -x does not imply a particular language standard. For
example -x f77 may also require -std=legacy for some older source
codes.

-x none
Turn off any specification of a language, so that subsequent files
are handled according to their file name suffixes (as if -x has not
been used at all).

If you only want some of the stages of compilation, you can use -x (or
filename suffixes) to tell gcc where to start, and one of the options
-c, -S, or -E to say where gcc is to stop. Note that some combinations
(for example, -x cpp-output -E) instruct gcc to do nothing at all.

-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 .c, .i, .s, etc., with .o.

Unrecognized input files, not requiring compilation or assembly,
are ignored.

-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 .c, .i, etc., with .s.

Input files that don't require compilation are ignored.

-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.

-o file
Place the primary output in file 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 -o is not specified, the default is to put an executable file in
a.out, the object file for source.suffix in source.o, its assembler
file in source.s, a precompiled header file in source.suffix.gch,
and all preprocessed C source on standard output.

Though -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.

gcc -c foo.c ...

will use foo.o as the primary output, and place aux outputs and
dumps next to it, e.g., aux file foo.dwo for -gsplit-dwarf, and
dump file foo.c.???r.final for -fdump-rtl-final.

If a non-linker output file is explicitly specified, aux and dump
files by default take the same base name:

gcc -c foo.c -o dir/foobar.o ...

will name aux outputs dir/foobar.* and dump outputs dir/foobar.c.*.

A linker output will instead prefix aux and dump outputs:

gcc foo.c bar.c -o dir/foobar ...

will generally name aux outputs dir/foobar-foo.* and
dir/foobar-bar.*, and dump outputs dir/foobar-foo.c.* and
dir/foobar-bar.c.*.

The one exception to the above is when the executable shares the
base name with the single input:

gcc foo.c -o dir/foo ...

in which case aux outputs are named dir/foo.* and dump outputs
named dir/foo.c.*.

The location and the names of auxiliary and dump outputs can be
adjusted by the options -dumpbase, -dumpbase-ext, -dumpdir,
-save-temps=cwd, and -save-temps=obj.

-dumpbase 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:

gcc -save-temps -S foo.c

saves the (no longer) temporary preprocessed file in foo.i, and
then compiles to the (implied) output file foo.s, whereas:

gcc -save-temps -dumpbase save-foo -c foo.c

preprocesses to in save-foo.i, compiles to save-foo.s (now an
intermediate, thus auxiliary output), and then assembles to the
(implied) output 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
-fdump-* options) with the input name suffix, and aux output files
(those requested by other non-dump options, e.g. "-save-temps",
"-gsplit-dwarf", "-fcallgraph-info") without it.

Similar suffix differentiation of dump and aux outputs can be
attained for explicitly-given -dumpbase basename.suf by also
specifying -dumpbase-ext .suf.

If dumpbase is explicitly specified with any directory component,
any dumppfx specification (e.g. -dumpdir or -save-temps=*) is
ignored, and instead of appending to it, dumpbase fully overrides
it:

gcc foo.c -c -o dir/foo.o -dumpbase alt/foo \
-dumpdir pfx- -save-temps=cwd ...

creates auxiliary and dump outputs named alt/foo.*, disregarding
dir/ in -o, the ./ prefix implied by -save-temps=cwd, and pfx- in
-dumpdir.

When -dumpbase is specified in a command that compiles multiple
inputs, or that compiles and then links, it may be combined with
dumppfx, as specified under -dumpdir. Then, each input file is
compiled using the combined dumppfx, and default values for
dumpbase and auxdropsuf are computed for each input file:

gcc foo.c bar.c -c -dumpbase main ...

creates foo.o and bar.o as primary outputs, and avoids overwriting
the auxiliary and dump outputs by using the dumpbase as a prefix,
creating auxiliary and dump outputs named main-foo.* and
main-bar.*.

An empty string specified as dumpbase avoids the influence of the
output basename in the naming of auxiliary and dump outputs during
compilation, computing default values :

gcc -c foo.c -o dir/foobar.o -dumpbase " ...

will name aux outputs dir/foo.* and dump outputs 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:

gcc foo.c bar.c -o dir/foobar -dumpbase " -flto ...

The compilation of the source files will name auxiliary outputs
dir/foo.* and dir/bar.*, and dump outputs dir/foo.c.* and
dir/bar.c.*. LTO recompilation during linking will use dir/foobar.
as the prefix for dumps and auxiliary files.

-dumpbase-ext auxdropsuf
When forming the name of an auxiliary (but not a dump) output file,
drop trailing auxdropsuf from dumpbase before appending any
suffixes. If not specified, this option defaults to the suffix of
a default dumpbase, i.e., the suffix of the input file when
-dumpbase is not present in the command line, or dumpbase is
combined with dumppfx.

gcc foo.c -c -o dir/foo.o -dumpbase x-foo.c -dumpbase-ext .c ...

creates dir/foo.o as the main output, and generates auxiliary
outputs in dir/x-foo.*, taking the location of the primary output,
and dropping the .c suffix from the dumpbase. Dump outputs retain
the suffix: dir/x-foo.c.*.

This option is disregarded if it does not match the suffix of a
specified dumpbase, except as an alternative to the executable
suffix when appending the linker output base name to dumppfx, as
specified below:

gcc foo.c bar.c -o main.out -dumpbase-ext .out ...

creates main.out as the primary output, and avoids overwriting the
auxiliary and dump outputs by using the executable name minus
auxdropsuf as a prefix, creating auxiliary outputs named main-foo.*
and main-bar.* and dump outputs named main-foo.c.* and
main-bar.c.*.

-dumpdir dumppfx
When forming the name of an auxiliary or dump output file, use
dumppfx as a prefix:

gcc -dumpdir pfx- -c foo.c ...

creates foo.o as the primary output, and auxiliary outputs named
pfx-foo.*, combining the given dumppfx with the default dumpbase
derived from the default primary output, derived in turn from the
input name. Dump outputs also take the input name suffix:
pfx-foo.c.*.

If dumppfx is to be used as a directory name, it must end with a
directory separator:

gcc -dumpdir dir/ -c foo.c -o obj/bar.o ...

creates obj/bar.o as the primary output, and auxiliary outputs
named dir/bar.*, combining the given dumppfx with the default
dumpbase derived from the primary output name. Dump outputs also
take the input name suffix: dir/bar.c.*.

It defaults to the location of the output file, unless the output
file is a special file like "/dev/null". Options -save-temps=cwd
and -save-temps=obj override this default, just like an explicit
-dumpdir option. In case multiple such options are given, the last
one prevails:

gcc -dumpdir pfx- -c foo.c -save-temps=obj ...

outputs foo.o, with auxiliary outputs named foo.* because
-save-temps=* overrides the dumppfx given by the earlier -dumpdir
option. It does not matter that =obj is the default for
-save-temps, nor that the output directory is implicitly the
current directory. Dump outputs are named foo.c.*.

When compiling from multiple input files, if -dumpbase is
specified, dumpbase, minus a auxdropsuf suffix, and a dash are
appended to (or override, if containing any directory components)
an explicit or defaulted dumppfx, so that each of the multiple
compilations gets differently-named aux and dump outputs.

gcc foo.c bar.c -c -dumpdir dir/pfx- -dumpbase main ...

outputs auxiliary dumps to dir/pfx-main-foo.* and
dir/pfx-main-bar.*, appending dumpbase- to dumppfx. Dump outputs
retain the input file suffix: dir/pfx-main-foo.c.* and
dir/pfx-main-bar.c.*, respectively. Contrast with the single-input
compilation:

gcc foo.c -c -dumpdir dir/pfx- -dumpbase main ...

that, applying -dumpbase to a single source, does not compute and
append a separate dumpbase per input file. Its auxiliary and dump
outputs go in dir/pfx-main.*.

When compiling and then linking from multiple input files, a
defaulted or explicitly specified dumppfx also undergoes the
dumpbase- transformation above (e.g. the compilation of foo.c and
bar.c above, but without -c). If neither -dumpdir nor -dumpbase
are given, the linker output base name, minus auxdropsuf, if
specified, or the executable suffix otherwise, plus a dash is
appended to the default dumppfx instead. Note, however, that
unlike earlier cases of linking:

gcc foo.c bar.c -dumpdir dir/pfx- -o main ...

does not append the output name main to dumppfx, because -dumpdir
is explicitly specified. The goal is that the explicitly-specified
dumppfx may contain the specified output name as part of the
prefix, if desired; only an explicitly-specified -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
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 -dumpdir that inhibits the
combination, even if overridden by -save-temps=*:

gcc foo.c -dumpdir alt/pfx- -o dir/main.exe -save-temps=cwd ...

Auxiliary outputs are named foo.*, and dump outputs foo.c.*, in the
current working directory as ultimately requested by
-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; dumppfx is set to the former, unless overridden by
-dumpdir or -save-temps=*, and dumpbase is set to the latter,
unless overriden by -dumpbase. If there are multiple inputs or
linking, this dumpbase may be combined with dumppfx and taken from
each input file. Auxiliary output names for each input are formed
by combining dumppfx, dumpbase minus suffix, and the auxiliary
output suffix; dump output names are only different in that the
suffix from dumpbase is retained.

When it comes to auxiliary and dump outputs created during LTO
recompilation, a combination of dumppfx and 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 -dumpdir option to lto-wrapper; being
involved in linking, this program does not normally get any
-dumpbase and -dumpbase-ext, and it ignores them.

When running sub-compilers, lto-wrapper appends LTO stage names to
the received dumppfx, ensures it contains a directory component so
that it overrides any -dumpdir, and passes that as -dumpbase to
sub-compilers.

-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.

-###
Like -v except the commands are not executed and arguments are
quoted unless they contain only alphanumeric characters or "./-_".
This is useful for shell scripts to capture the driver-generated
command lines.

--help
Print (on the standard output) a description of the command-line
options understood by gcc. If the -v option is also specified then
--help is also passed on to the various processes invoked by gcc,
so that they can display the command-line options they accept. If
the -Wextra option has also been specified (prior to the --help
option), then command-line options that have no documentation
associated with them are also displayed.

--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.

--help={class|[^]qualifier}[,...]
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:

optimizers
Display all of the optimization options supported by the
compiler.

warnings
Display all of the options controlling warning messages
produced by the compiler.

target
Display target-specific options. Unlike the --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 --help= syntax.

params
Display the values recognized by the --param option.

language
Display the options supported for language, where 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 common class.

common
Display the options that are common to all languages.

These are the supported qualifiers:

undocumented
Display only those options that are undocumented.

joined
Display options taking an argument that appears after an equal
sign in the same continuous piece of text, such as:
--help=target.

separate
Display options taking an argument that appears as a separate
word following the original option, such as: -o output-file.

Thus for example to display all the undocumented target-specific
switches supported by the compiler, use:

--help=target,undocumented

The sense of a qualifier can be inverted by prefixing it with the ^
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:

--help=warnings,^joined,^undocumented

The argument to --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
target. For example, to display all the target-specific
optimization options, use:

--help=target,optimizers

The --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 --help is also
specified anywhere on the command line then this takes precedence
over any --help= option.

If the -Q option appears on the command line before the --help=
option, then the descriptive text displayed by --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
--help= option is used).

Here is a truncated example from the ARM port of gcc:

% gcc -Q -mabi=2 --help=target -c
The following options are target specific:
-mabi= 2
-mabort-on-noreturn [disabled]
-mapcs [disabled]

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 -O2 by using:

-Q -O2 --help=optimizers

Alternatively you can discover which binary optimizations are
enabled by -O3 by using:

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

--version
Display the version number and copyrights of the invoked GCC.

-pass-exit-codes
Normally the gcc program exits with the code of 1 if any phase of
the compiler returns a non-success return code. If you specify
-pass-exit-codes, the 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.

-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.

-specs=file
Process file after the compiler reads in the standard specs file,
in order to override the defaults which the gcc driver program uses
when determining what switches to pass to cc1, cc1plus, as, ld,
etc. More than one -specs=file can be specified on the command
line, and they are processed in order, from left to right.

-wrapper
Invoke all subcommands under a wrapper program. The name of the
wrapper program and its parameters are passed as a comma separated
list.

gcc -c t.c -wrapper gdb,--args

This invokes all subprograms of gcc under gdb --args, thus the
invocation of cc1 is gdb --args cc1 ....

-ffile-prefix-map=old=new
When compiling files residing in directory old, record any
references to them in the result of the compilation as if the files
resided in directory new instead. Specifying this option is
equivalent to specifying all the individual -f*-prefix-map options.
This can be used to make reproducible builds that are location
independent. Directories referenced by directives are not affected
by these options. See also -fmacro-prefix-map, -fdebug-prefix-map,
-fprofile-prefix-map and -fcanon-prefix-map.

-fcanon-prefix-map
For the -f*-prefix-map options normally comparison of old prefix
against the filename that would be normally referenced in the
result of the compilation is done using textual comparison of the
prefixes, or ignoring character case for case insensitive
filesystems and considering slashes and backslashes as equal on DOS
based filesystems. The -fcanon-prefix-map causes such comparisons
to be done on canonicalized paths of old and the referenced
filename.

-fplugin=name.so
Load the plugin code in file 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 -fplugin-arg-name-key=value below). Each plugin
should define the callback functions specified in the Plugins API.

-fplugin-arg-name-key=value
Define an argument called key with a value of value for the plugin
called name.

-fdump-ada-spec[-slim]
For C and C++ source and include files, generate corresponding Ada
specs.

-fada-spec-parent=unit
In conjunction with -fdump-ada-spec[-slim] above, generate Ada
specs as child units of parent unit.

-fdump-go-spec=file
For input files in any language, generate corresponding Go
declarations in file. This generates Go "const", "type", "var",
and "func" declarations which may be a useful way to start writing
a Go interface to code written in some other language.

@file
Read command-line options from file. The options read are inserted
in place of the original @file option. If file does not exist, or
cannot be read, then the option will be treated literally, and not
removed.

Options in file are separated by whitespace. A whitespace
character may be included in an option by surrounding the entire
option in either single or double quotes. Any character (including
a backslash) may be included by prefixing the character to be
included with a backslash. The file may itself contain additional
@file options; any such options will be processed recursively.

Compiling C++ Programs
C++ source files conventionally use one of the suffixes .C, .cc, .cpp,
.CPP, .c++, .cp, or .cxx; C++ header files often use .hh, .hpp, .H, or
(for shared template code) .tcc; preprocessed C++ files use the suffix
.ii; and C++20 module interface units sometimes use .ixx, .cppm, .cxxm,
.c++m, or .ccm.

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 gcc).

However, the use of gcc does not add the C++ library. g++ is a program
that calls GCC and automatically specifies linking against the C++
library. It treats .c, .h and .i files as C++ source files instead of
C source files unless -x is used. This program is also useful when
precompiling a C header file with a .h extension for use in C++
compilations. On many systems, g++ is also installed with the name
c++.

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.

Options Controlling C 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:

-ansi
In C mode, this is equivalent to -std=c90. In C++ mode, it is
equivalent to -std=c++98.

-std=
Determine the language standard. This option is currently only
supported when compiling C or C++.

The compiler can accept several base standards, such as c90 or
c++98, and GNU dialects of those standards, such as gnu90 or
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, -std=c90 turns
off certain features of GCC that are incompatible with ISO C90,
such as the "asm" and "typeof" keywords, but not other GNU
extensions that do not have a meaning in ISO C90, such as omitting
the middle term of a "?:" 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 -Wpedantic to
identify which features are GNU extensions given that version of
the standard. For example -std=gnu90 -Wpedantic warns about C++
style // comments, while -std=gnu99 -Wpedantic does not.

A value for this option must be provided; possible values are

c90
c89
iso9899:1990
Support all ISO C90 programs (certain GNU extensions that
conflict with ISO C90 are disabled). Same as -ansi for C code.

iso9899:199409
ISO C90 as modified in amendment 1.

c99
c9x
iso9899:1999
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
<https://gcc.gnu.org/c99status.html> for more information. The
names c9x and iso9899:199x are deprecated.

c11
c1x
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 c1x is deprecated.

c17
c18
iso9899:2017
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 -std=c11) and a new
value of "__STDC_VERSION__", and so is supported to the same
extent as C11.

c23
c2x
iso9899:2024
ISO C23, the 2023 revision of the ISO C standard (published in
2024). The name c2x is deprecated.

c2y The next version of the ISO C standard, still under
development. The support for this version is experimental and
incomplete.

gnu90
gnu89
GNU dialect of ISO C90 (including some C99 features).

gnu99
gnu9x
GNU dialect of ISO C99. The name gnu9x is deprecated.

gnu11
gnu1x
GNU dialect of ISO C11. The name gnu1x is deprecated.

gnu17
gnu18
GNU dialect of ISO C17.

gnu23
gnu2x
GNU dialect of ISO C23. This is the default for C code. The
name gnu2x is deprecated.

gnu2y
The next version of the ISO C standard, still under
development, plus GNU extensions. The support for this version
is experimental and incomplete. The name gnu2x is deprecated.

c++98
c++03
The 1998 ISO C++ standard plus the 2003 technical corrigendum
and some additional defect reports. Same as -ansi for C++ code.

gnu++98
gnu++03
GNU dialect of -std=c++98.

c++11
c++0x
The 2011 ISO C++ standard plus amendments. The name c++0x is
deprecated.

gnu++11
gnu++0x
GNU dialect of -std=c++11. The name gnu++0x is deprecated.

c++14
c++1y
The 2014 ISO C++ standard plus amendments. The name c++1y is
deprecated.

gnu++14
gnu++1y
GNU dialect of -std=c++14. The name gnu++1y is deprecated.

c++17
c++1z
The 2017 ISO C++ standard plus amendments. The name c++1z is
deprecated.

gnu++17
gnu++1z
GNU dialect of -std=c++17. This is the default for C++ code.
The name gnu++1z is deprecated.

c++20
c++2a
The 2020 ISO C++ standard plus amendments. Support is
experimental, and could change in incompatible ways in future
releases. The name c++2a is deprecated.

gnu++20
gnu++2a
GNU dialect of -std=c++20. Support is experimental, and could
change in incompatible ways in future releases. The name
gnu++2a is deprecated.

c++23
c++2b
The 2023 ISO C++ standard plus amendments (published in 2024).
Support is experimental, and could change in incompatible ways
in future releases. The name c++2b is deprecated.

gnu++23
gnu++2b
GNU dialect of -std=c++23. Support is experimental, and could
change in incompatible ways in future releases. The name
gnu++2b is deprecated.

c++2c
c++26
The next revision of the ISO C++ standard, planned for 2026.
Support is highly experimental, and will almost certainly
change in incompatible ways in future releases.

gnu++2c
gnu++26
GNU dialect of -std=c++2c. Support is highly experimental, and
will almost certainly change in incompatible ways in future
releases.

-aux-info filename
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 (I, N for new or 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
(C or 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.

-fno-asm
Do not recognize "asm", "inline" or "typeof" as a keyword, so that
code can use these words as identifiers. You can use the keywords
"__asm__", "__inline__" and "__typeof__" instead. In C, -ansi
implies -fno-asm.

In C++, "inline" is a standard keyword and is not affected by this
switch. You may want to use the -fno-gnu-keywords flag instead,
which disables "typeof" but not "asm" and "inline". In C99 mode
(-std=c99 or -std=gnu99), this switch only affects the "asm" and
"typeof" keywords, since "inline" is a standard keyword in ISO C99.
In C23 mode (-std=c23 or -std=gnu23), this switch only affects the
"asm" keyword, since "typeof" is a standard keyword in ISO C23.

-fno-builtin
-fno-builtin-function
Don't recognize built-in functions that do not begin with
__builtin_ as prefix.

GCC normally generates special code to handle certain built-in
functions more efficiently; for instance, calls to "alloca" may
become single instructions which adjust the stack directly, and
calls to "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
-Wformat for bad calls to "printf" when "printf" is built in and
"strlen" is known not to modify global memory.

With the -fno-builtin-function option only the built-in function
function is disabled. function must not begin with __builtin_. If
a function is named that is not built-in in this version of GCC,
this option is ignored. There is no corresponding
-fbuiltin-function option; if you wish to enable built-in functions
selectively when using -fno-builtin or -ffreestanding, you may
define macros such as:

#define abs(n) __builtin_abs ((n))
#define strcpy(d, s) __builtin_strcpy ((d), (s))

-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++.

-ffreestanding
Assert that compilation targets a freestanding environment. This
implies -fno-builtin. A freestanding environment is one in which
the standard library may not exist, and program startup may not
necessarily be at "main". The most obvious example is an OS
kernel. This is equivalent to -fno-hosted.

-fgimple
Enable parsing of function definitions marked with "__GIMPLE".
This is an experimental feature that allows unit testing of GIMPLE
passes.

-fgnu-tm
When the 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,

Note that the transactional memory feature is not supported with
non-call exceptions (-fnon-call-exceptions).

-fgnu89-inline
The option -fgnu89-inline tells GCC to use the traditional GNU
semantics for "inline" functions when in C99 mode.

Using this option is roughly equivalent to adding the "gnu_inline"
function attribute to all inline functions.

The option -fno-gnu89-inline explicitly tells GCC to use the C99
semantics for "inline" when in C99 or gnu99 mode (i.e., it
specifies the default behavior). This option is not supported in
-std=c90 or -std=gnu90 mode.

The preprocessor macros "__GNUC_GNU_INLINE__" and
"__GNUC_STDC_INLINE__" may be used to check which semantics are in
effect for "inline" functions.

-fhosted
Assert that compilation targets a hosted environment. This implies
-fbuiltin. A hosted environment is one in which the entire
standard library is available, and in which "main" has a return
type of "int". Examples are nearly everything except a kernel.
This is equivalent to -fno-freestanding.

-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.

-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.

typedef int UOW;
struct ABC {
UOW UOW;
};

Some cases of unnamed fields in structures and unions are only
accepted with this option.

Note that this option is off for all targets except for x86 targets
using ms-abi.

-fpermitted-flt-eval-methods=style
ISO/IEC TS 18661-3 defines new permissible values for
"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
"FLT_EVAL_METHOD". As such, code conforming to C11 may not have
been written expecting the possibility of the new values.

-fpermitted-flt-eval-methods specifies whether the compiler should
allow only the values of "FLT_EVAL_METHOD" specified in C99/C11, or
the extended set of values specified in ISO/IEC TS 18661-3.

style is either "c11" or "ts-18661-3" as appropriate.

The default when in a standards compliant mode (-std=c11 or
similar) is -fpermitted-flt-eval-methods=c11. The default when in
a GNU dialect (-std=gnu11 or similar) is
-fpermitted-flt-eval-methods=ts-18661-3.

The -fdeps-* options are used to extract structured dependency
information for a source. This involves determining what resources
provided by other source files will be required to compile the
source as well as what resources are provided by the source. This
information can be used to add required dependencies between
compilation rules of dependent sources based on their contents
rather than requiring such information be reflected within the
build tools as well.

-fdeps-file=file
Where to write structured dependency information.

-fdeps-format=format
The format to use for structured dependency information. p1689r5 is
the only supported format right now. Note that when this argument
is specified, the output of -MF is stripped of some information
(namely C++ modules) so that it does not use extended makefile
syntax not understood by most tools.

-fdeps-target=file
Analogous to -MT but for structured dependency information. This
indicates the target which will ultimately need any required
resources and provide any resources extracted from the source that
may be required by other sources.

-fplan9-extensions
Accept some non-standard constructs used in Plan 9 code.

This enables -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. This is only
supported for C, not C++.

-fsigned-bitfields
-funsigned-bitfields
-fno-signed-bitfields
-fno-unsigned-bitfields
These options control whether a bit-field is signed or unsigned,
when the declaration does not use either "signed" or "unsigned".
By default, such a bit-field is signed, because this is consistent:
the basic integer types such as "int" are signed types.

-fsigned-char
Let the type "char" be signed, like "signed char".

Note that this is equivalent to -fno-unsigned-char, which is the
negative form of -funsigned-char. Likewise, the option
-fno-signed-char is equivalent to -funsigned-char.

-funsigned-char
Let the type "char" be unsigned, like "unsigned char".

Each kind of machine has a default for what "char" should be. It
is either like "unsigned char" by default or like "signed char" by
default.

Ideally, a portable program should always use "signed char" or
"unsigned char" when it depends on the signedness of an object.
But many programs have been written to use plain "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 "char" is always a distinct type from each of "signed
char" or "unsigned char", even though its behavior is always just
like one of those two.

-fstrict-flex-arrays (C and C++ only)
-fstrict-flex-arrays=level (C and C++ only)
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 level controls the level of
strictness.

-fstrict-flex-arrays is equivalent to -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 -fno-strict-flex-arrays is equivalent to
-fstrict-flex-arrays=0, which is the least strict. In this case
all trailing arrays of structures are treated as flexible array
members.

There are two more levels in between 0 and 3, which are provided to
support older code that uses the GCC zero-length array extension
([0]) or one-element array as flexible array members ([1]). When
level is 1, the trailing array is treated as a flexible array
member when it is declared as either [], [0], or [1]. When level
is 2, the trailing array is treated as a flexible array member when
it is declared as either [], or [0].

You can control this behavior for a specific trailing array field
of a structure by using the variable attribute "strict_flex_array"
attribute.

The -fstrict_flex_arrays option interacts with the
-Wstrict-flex-arrays option.

-fsso-struct=endianness
Set the default scalar storage order of structures and unions to
the specified endianness. The accepted values are big-endian,
little-endian and native for the native endianness of the target
(the default). This option is not supported for C++.

Warning: the -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.

Options Controlling C++ Dialect
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 firstClass.C like this:

g++ -g -fstrict-enums -O -c firstClass.C

In this example, only -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 -std, are also relevant
for C++ programs.

Here is a list of options that are only for compiling C++ programs:

-fabi-version=n
Use version 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 "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. 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 -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
"__alignof__" to be distinct from that of "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 appeared in G++ 13, fixes manglings of
lambdas that have additional context.

Version 19, which first appeared in G++ 14, fixes manglings of
structured bindings to include ABI tags.

Version 20, which first appeared in G++ 15, fixes manglings of
lambdas in static data member initializers.

See also -Winterference-size.

loop-interchange-max-num-stmts
The maximum number of stmts in a loop to be interchanged.

loop-interchange-stride-ratio
The minimum ratio between stride of two loops for interchange
to be profitable.

min-insn-to-prefetch-ratio
The minimum ratio between the number of instructions and the
number of prefetches to enable prefetching in a loop.

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.

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.

switch-conversion-max-branch-ratio
Switch initialization conversion refuses to create arrays that
are bigger than switch-conversion-max-branch-ratio times the
number of branches in the switch.

switch-lower-slow-alg-max-cases
Maximum number of cases for slow switch lowering algorithms to
be used.

max-partial-antic-length
Maximum length of the partial antic set computed during the
tree partial redundancy elimination optimization (-ftree-pre)
when optimizing at -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.

rpo-vn-max-loop-depth
Maximum loop depth that is value-numbered optimistically. When
the limit hits the innermost rpo-vn-max-loop-depth loops and
the outermost loop in the loop nest are value-numbered
optimistically and the remaining ones not.

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.

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.

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.

ira-loop-reserved-regs
IRA can be used to evaluate more accurate register pressure in
loops for decisions to move loop invariants (see -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.

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.

ira-simple-lra-insn-threshold
Approximate function insn number in 1K units triggering simple
local RA.

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.

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.

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.

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.

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.

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.

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 -fvar-tracking-assignments, but debug insns
may get (non-overlapping) uids above it if the reserved range
is exhausted.

ipa-sra-deref-prob-threshold
IPA-SRA replaces a pointer which is known not be NULL with one
or more new parameters only when the probability (in percent,
relative to function entry) of it being dereferenced is higher
than this parameter.

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
ipa-sra-ptr-growth-factor times the size of the original
pointer parameter.

ipa-sra-ptrwrap-growth-factor
Additional maximum allowed growth of total size of new
parameters that ipa-sra replaces a pointer to an aggregate
with, if it points to a local variable that the caller only
writes to and passes it as an argument to other functions.

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.

sra-max-scalarization-size-Ospeed
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 (sra-max-
scalarization-size-Ospeed) or size (sra-max-scalarization-size-
Osize) respectively.

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.

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 -fgnu-tm.

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.

hardcfr-max-blocks
Disable -fharden-control-flow-redundancy for functions with a
larger number of blocks than the specified value. Zero removes
any limit.

hardcfr-max-inline-blocks
Force -fharden-control-flow-redundancy to use out-of-line
checking for functions with a larger number of basic blocks
than the specified value.

loop-block-tile-size
Loop blocking or strip mining transforms, enabled with
-floop-block or -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 loop-block-tile-size parameter.

ipa-jump-function-lookups
Specifies number of statements visited during jump function
offset discovery.

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. ipa-cp-value-list-size is the
maximum number of values and types it stores per one formal
parameter of a function.

ipa-cp-eval-threshold
IPA-CP calculates its own score of cloning profitability
heuristics and performs those cloning opportunities with scores
that exceed ipa-cp-eval-threshold.

ipa-cp-max-recursive-depth
Maximum depth of recursive cloning for self-recursive function.

ipa-cp-min-recursive-probability
Recursive cloning only when the probability of call being
executed exceeds the parameter.

ipa-cp-profile-count-base
When using -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.

ipa-cp-recursive-freq-factor
The number of times interprocedural copy propagation expects
recursive functions to call themselves.

ipa-cp-recursion-penalty
Percentage penalty the recursive functions will receive when
they are evaluated for cloning.

ipa-cp-single-call-penalty
Percentage penalty functions containing a single call to
another function will receive when they are evaluated for
cloning.

ipa-max-agg-items
IPA-CP is also capable to propagate a number of scalar values
passed in an aggregate. ipa-max-agg-items controls the maximum
number of such values per one parameter.

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 ipa-
cp-loop-hint-bonus to the profitability score of the candidate.

ipa-max-loop-predicates
The maximum number of different predicates IPA will use to
describe when loops in a function have known properties.

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 ipa-max-aa-steps statements modifying memory.

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.

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 ipa-max-param-expr-ops, the expression is
treated as complicated one, and is not handled by IPA analysis.

lto-partitions
Specify desired number of partitions produced during WHOPR
compilation. The number of partitions should exceed the number
of CPUs used for compilation.

lto-min-partition
Size of minimal partition for WHOPR (in estimated
instructions). This prevents expenses of splitting very small
programs into too many partitions.

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.

lto-max-streaming-parallelism
Maximal number of parallel processes used for LTO streaming.

cxx-max-namespaces-for-diagnostic-help
The maximum number of namespaces to consult for suggestions
when C++ name lookup fails for an identifier.

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.

max-stores-to-sink
The maximum number of conditional store pairs that can be sunk.
Set to 0 if either vectorization (-ftree-vectorize) or if-
conversion (-ftree-loop-if-convert) is disabled.

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.

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.

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.

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.

sched-pressure-algorithm
Choose between the two available implementations of
-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 haifa-sched.cc in the
GCC sources for more details.

The default choice depends on the target.

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.

asan-globals
Enable buffer overflow detection for global objects. This kind
of protection is enabled by default if you are using
-fsanitize=address option. To disable global objects
protection use --param asan-globals=0.

asan-stack
Enable buffer overflow detection for stack objects. This kind
of protection is enabled by default when using
-fsanitize=address. To disable stack protection use --param
asan-stack=0 option.

asan-instrument-reads
Enable buffer overflow detection for memory reads. This kind
of protection is enabled by default when using
-fsanitize=address. To disable memory reads protection use
--param asan-instrument-reads=0.

asan-instrument-writes
Enable buffer overflow detection for memory writes. This kind
of protection is enabled by default when using
-fsanitize=address. To disable memory writes protection use
--param asan-instrument-writes=0 option.

asan-memintrin
Enable detection for built-in functions. This kind of
protection is enabled by default when using -fsanitize=address.
To disable built-in functions protection use --param
asan-memintrin=0.

asan-use-after-return
Enable detection of use-after-return. This kind of protection
is enabled by default when using the -fsanitize=address option.
To disable it use --param asan-use-after-return=0.

Note: By default the check is disabled at run time. To enable
it, add "detect_stack_use_after_return=1" to the environment
variable ASAN_OPTIONS.

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 --param
asan-instrumentation-with-call-threshold=0.

asan-kernel-mem-intrinsic-prefix
If nonzero, prefix calls to "memcpy", "memset" and "memmove"
with __asan_ or __hwasan_ for -fsanitize=kernel-address or
-fsanitize=kernel-hwaddress, respectively.

hwasan-instrument-stack
Enable hwasan instrumentation of statically sized stack-
allocated variables. This kind of instrumentation is enabled
by default when using -fsanitize=hwaddress and disabled by
default when using -fsanitize=kernel-hwaddress. To disable
stack instrumentation use --param hwasan-instrument-stack=0,
and to enable it use --param hwasan-instrument-stack=1.

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 -fsanitize=hwaddress and unavailable for
-fsanitize=kernel-hwaddress. To disable it use --param
hwasan-random-frame-tag=0.

hwasan-instrument-allocas
Enable hwasan instrumentation of dynamically sized stack-
allocated variables. This kind of instrumentation is enabled
by default when using -fsanitize=hwaddress and disabled by
default when using -fsanitize=kernel-hwaddress. To disable
instrumentation of such variables use --param
hwasan-instrument-allocas=0, and to enable it use --param
hwasan-instrument-allocas=1.

hwasan-instrument-reads
Enable hwasan checks on memory reads. Instrumentation of reads
is enabled by default for both -fsanitize=hwaddress and
-fsanitize=kernel-hwaddress. To disable checking memory reads
use --param hwasan-instrument-reads=0.

hwasan-instrument-writes
Enable hwasan checks on memory writes. Instrumentation of
writes is enabled by default for both -fsanitize=hwaddress and
-fsanitize=kernel-hwaddress. To disable checking memory writes
use --param hwasan-instrument-writes=0.

hwasan-instrument-mem-intrinsics
Enable hwasan instrumentation of builtin functions.
Instrumentation of these builtin functions is enabled by
default for both -fsanitize=hwaddress and
-fsanitize=kernel-hwaddress. To disable instrumentation of
builtin functions use --param
hwasan-instrument-mem-intrinsics=0.

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.

tsan-distinguish-volatile
Emit special instrumentation for accesses to volatiles.

tsan-instrument-func-entry-exit
Emit instrumentation calls to __tsan_func_entry() and
__tsan_func_exit().

max-fsm-thread-path-insns
Maximum number of instructions to copy when duplicating blocks
on a finite state automaton jump thread path.

threader-debug
threader-debug=[none|all] Enables verbose dumping of the
threader solver.

parloops-chunk-size
Chunk size of omp schedule for loops parallelized by parloops.

parloops-schedule
Schedule type of omp schedule for loops parallelized by
parloops (static, dynamic, guided, auto, runtime).

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.

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.

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.

ranger-debug
Specifies the type of debug output to be issued for ranges.

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.

unroll-jam-max-unroll
The maximum number of times the outer loop should be unrolled
by the unroll-and-jam transformation.

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.

max-variable-expansions-in-unroller
If -fvariable-expansion-in-unroller is used, the maximum number
of times that an individual variable will be expanded during
loop unrolling.

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.

max-tracked-strlens
Maximum number of strings for which strlen optimization pass
will track string lengths.

gcse-after-reload-partial-fraction
The threshold ratio for performing partial redundancy
elimination after reload.

gcse-after-reload-critical-fraction
The threshold ratio of critical edges execution count that
permit performing redundancy elimination after reload.

max-loop-header-insns
The maximum number of insns in loop header duplicated by the
copy loop headers pass.

vect-epilogues-nomask
Enable loop epilogue vectorization using smaller vector size.

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.

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.

vect-induction-float
Enable loop vectorization of floating point inductions.

vect-force-slp
Force the use of SLP when vectorizing, fail if not possible.

vrp-block-limit
Maximum number of basic blocks before VRP switches to a lower
memory algorithm.

vrp-sparse-threshold
Maximum number of basic blocks before VRP uses a sparse bitmap
cache.

vrp-switch-limit
Maximum number of outgoing edges in a switch before VRP will
not process it.

vrp-vector-threshold
Maximum number of basic blocks for VRP to use a basic cache
vector.

avoid-fma-max-bits
Maximum number of bits for which we avoid creating FMAs.

fully-pipelined-fma
Whether the target fully pipelines FMA instructions. If non-
zero, reassociation considers the benefit of parallelizing
FMA's multiplication part and addition part, assuming FMUL and
FMA use the same units that can also do FADD.

sms-loop-average-count-threshold
A threshold on the average loop count considered by the swing
modulo scheduler.

sms-dfa-history
The number of cycles the swing modulo scheduler considers when
checking conflicts using DFA.

graphite-allow-codegen-errors
Whether codegen errors should be ICEs when -fchecking.

sms-max-ii-factor
A factor for tuning the upper bound that swing modulo scheduler
uses for scheduling a loop.

lra-max-considered-reload-pseudos
The max number of reload pseudos which are considered during
spilling a non-reload pseudo.

max-pow-sqrt-depth
Maximum depth of sqrt chains to use when synthesizing
exponentiation by a real constant.

max-dse-active-local-stores
Maximum number of active local stores in RTL dead store
elimination.

asan-instrument-allocas
Enable asan allocas/VLAs protection.

max-iterations-computation-cost
Bound on the cost of an expression to compute the number of
iterations.

max-isl-operations
Maximum number of isl operations, 0 means unlimited.

graphite-max-arrays-per-scop
Maximum number of arrays per scop.

max-vartrack-reverse-op-size
Max. size of loc list for which reverse ops should be added.

fsm-scale-path-stmts
Scale factor to apply to the number of statements in a
threading path crossing a loop backedge when comparing to
--param=max-jump-thread-duplication-stmts.

uninit-control-dep-attempts
Maximum number of nested calls to search for control
dependencies during uninitialized variable analysis.

uninit-max-chain-len
Maximum number of predicates anded for each predicate ored in
the normalized predicate chain.

uninit-max-num-chains
Maximum number of predicates ored in the normalized predicate
chain.

sched-autopref-queue-depth
Hardware autoprefetcher scheduler model control flag. Number
of lookahead cycles the model looks into; at ' ' only enable
instruction sorting heuristic.

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.

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.

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.

store-merging-max-size
Maximum size of a single store merging region in bytes.

store-forwarding-max-distance
Maximum number of instruction distance that a small store
forwarded to a larger load may stall. Value '0' disables the
cost checks for the avoid-store-forwarding pass.

hash-table-verification-limit
The number of elements for which hash table verification is
done for each searched element.

max-find-base-term-values
Maximum number of VALUEs handled during a single find_base_term
call.

analyzer-max-enodes-per-program-point
The maximum number of exploded nodes per program point within
the analyzer, before terminating analysis of that point.

analyzer-max-constraints
The maximum number of constraints per state.

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.

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.

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.

analyzer-max-svalue-depth
The maximum depth of a symbolic value, before approximating the
value as unknown.

analyzer-max-infeasible-edges
The maximum number of infeasible edges to reject before
declaring a diagnostic as infeasible.

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.

analyzer-bb-explosion-factor
The maximum number of 'after supernode' exploded nodes within
the analyzer per supernode, before terminating analysis.

analyzer-text-art-string-ellipsis-threshold
The number of bytes at which to ellipsize string literals in
analyzer text art diagrams.

analyzer-text-art-ideal-canvas-width
The ideal width in characters of text art diagrams generated by
the analyzer.

analyzer-text-art-string-ellipsis-head-len
The number of literal bytes to show at the head of a string
literal in text art when ellipsizing it.

analyzer-text-art-string-ellipsis-tail-len
The number of literal bytes to show at the tail of a string
literal in text art when ellipsizing it.

ranger-logical-depth
Maximum depth of logical expression evaluation ranger will look
through when evaluating outgoing edge ranges.

ranger-recompute-depth
Maximum depth of instruction chains to consider for
recomputation in the outgoing range calculator.

relation-block-limit
Maximum number of relations the oracle will register in a basic
block.

transitive-relations-work-bound
Work bound when discovering transitive relations from existing
relations.

min-pagesize
Minimum page size for warning and early break vectorization
purposes.

openacc-kernels
Specify mode of OpenACC `kernels' constructs handling. With
--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 --param=openacc-kernels=parloops, OpenACC `kernels'
constructs are handled by the parloops pass, en bloc. This is
the current default.

openacc-privatization
Control whether the -fopt-info-omp-note and applicable
-fdump-tree-*-details options emit OpenACC privatization
diagnostics. With --param=openacc-privatization=quiet, don't
diagnose. This is the current default. With
--param=openacc-privatization=noisy, do diagnose.

cycle-accurate-model
Specifies whether GCC should assume that the scheduling
description is mostly a cycle-accurate model of the target
processor the code is intended to run on, in the absence of
cache misses. Nonzero means that the selected scheduling model
is accurate and likely describes an in-order processor, and
that scheduling should aggressively spill to try and fill any
pipeline bubbles. This is the current default. Zero means the
scheduling description might not be available/accurate or
perhaps not applicable at all, such as for modern out-of-order
processors.

The following choices of name are available on AArch64 targets:

aarch64-vect-compare-costs
When vectorizing, consider using multiple different approaches
and use the cost model to choose the cheapest one. This
includes:

* Trying both SVE and Advanced SIMD, when SVE is available.

* Trying to use 64-bit Advanced SIMD vectors for the smallest
data elements, rather than using 128-bit vectors for
everything.

* Trying to use "unpacked" SVE vectors for smaller elements.
This includes storing smaller elements in larger containers
and accessing elements with extending loads and truncating
stores.

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.

aarch64-double-recp-precision
The number of Newton iterations for calculating the reciprocal
for double type. The precision of division is proportional to
this param when division approximation is enabled. The default
value is 2.

aarch64-autovec-preference
Force an ISA selection strategy for auto-vectorization.

default
Use the default heuristics.

asimd-only
Use only Advanced SIMD for auto-vectorization.

sve-only
Use only SVE for auto-vectorization.

prefer-asimd
Use both Advanced SIMD and SVE. Prefer Advanced SIMD when
the costs are deemed equal.

prefer-sve
Use both Advanced SIMD and SVE. Prefer SVE when the costs
are deemed equal.

aarch64-ldp-policy
Fine-grained policy for load pairs. With
--param=aarch64-ldp-policy=default, use the policy of the
tuning structure. This is the current default. With
--param=aarch64-ldp-policy=always, emit ldp regardless of
alignment. With --param=aarch64-ldp-policy=never, do not emit
ldp. With --param=aarch64-ldp-policy=aligned, emit ldp only if
the source pointer is aligned to at least double the alignment
of the type.

aarch64-stp-policy
Fine-grained policy for store pairs. With
--param=aarch64-stp-policy=default, use the policy of the
tuning structure. This is the current default. With
--param=aarch64-stp-policy=always, emit stp regardless of
alignment. With --param=aarch64-stp-policy=never, do not emit
stp. With --param=aarch64-stp-policy=aligned, emit stp only if
the source pointer is aligned to at least double the alignment
of the type.

aarch64-ldp-alias-check-limit
Limit on the number of alias checks performed by the AArch64
load/store pair fusion pass when attempting to form an ldp/stp.
Higher values make the pass more aggressive at re-ordering
loads over stores, at the expense of increased compile time.

aarch64-ldp-writeback
Param to control which writeback opportunities we try to handle
in the AArch64 load/store pair fusion pass. A value of zero
disables writeback handling. One means we try to form pairs
involving one or more existing individual writeback accesses
where possible. A value of two means we also try to
opportunistically form writeback opportunities by folding in
trailing destructive updates of the base register used by a
pair.

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 n, GCC
will not use this heuristic for loops that are known to execute
in fewer than n Advanced SIMD iterations.

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.

The following choices of name are available on GCN targets:

gcn-preferred-vectorization-factor
Preferred vectorization factor: default, 32, 64.

The following choices of name are available on i386 and x86_64
targets:

x86-stlf-window-ninsns
Instructions number above which STFL stall penalty can be
compensated.

x86-stv-max-visits
The maximum number of use and def visits when discovering a STV
chain before the discovery is aborted.

Program Instrumentation Options
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.

-p
-pg Generate extra code to write profile information suitable for the
analysis program prof (for -p) or gprof (for -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 "no_instrument_function" to
suppress profiling of individual functions when compiling with
these options.

-fprofile-arcs
Add code so that program flow 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
auxname.gcda for each source file. The data may be used for
profile-directed optimizations (-fbranch-probabilities), or for
test coverage analysis (-ftest-coverage). Each object file's
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. foo.gcda for input file dir/foo.c, or dir/foo.gcda
for output file specified as -o dir/foo.o).

Note that if a command line directly links source files, the
corresponding .gcda files will be prefixed with the unsuffixed name
of the output file. E.g. "gcc a.c b.c -o binary" would generate
binary-a.gcda and binary-b.gcda files.

-fcondition-coverage
Add code so that program conditions are instrumented. During
execution the program records what terms in a conditional
contributes to a decision, which can be used to verify that all
terms in a Boolean function are tested and have an independent
effect on the outcome of a decision. The result can be read with
"gcov --conditions".

-fpath-coverage
Add code so that the paths taken are tracked. During execution the
program records the prime paths taken. The number of paths grows
very fast with complexity, and to avoid exploding compile times GCC
will give up instrumentation if the approximate number of paths
exceeds the limit controlled by -fpath-coverage-limit. The result
can be read with "gcov --prime-paths --prime-paths-lines
--prime-paths-source",

-fpath-coverage-limit=limit
The threshold at which point -fpath-coverage gives up on
instrumenting a function. This limit is approximate and
conservative, as GCC uses a pessimistic heuristic which slightly
overcounts the running number of paths, and gives up if the
threshold is reached before finding all the paths. This option is
not for fine grained control over which functions to instrument -
rather it is intended to limit the effect of path explosion and
keep compile times reasonable. The default is 250000.

--coverage
This option is used to compile and link code instrumented for
coverage analysis. The option is a synonym for -fprofile-arcs
-ftest-coverage (when compiling) and -lgcov (when linking). See
the documentation for those options for more details.

* Compile the source files with -fprofile-arcs plus optimization
and code generation options. For test coverage analysis, use
the additional -ftest-coverage option. You do not need to
profile every source file in a program.

* Compile the source files additionally with -fprofile-abs-path
to create absolute path names in the .gcno files. This allows
gcov to find the correct sources in projects where compilations
occur with different working directories.

* Link your object files with -lgcov or -fprofile-arcs (the
latter implies the former).

* 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, "fork" calls are detected and correctly
handled without double counting.

Moreover, an object file can be recompiled multiple times and
the corresponding .gcda file merges as long as the source file
and the compiler options are unchanged.

* For profile-directed optimizations, compile the source files
again with the same optimization and code generation options
plus -fbranch-probabilities.

* For test coverage analysis, use gcov to produce human readable
information from the .gcno and .gcda files. Refer to the gcov
documentation for further information.

With -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.

With -fcondition-coverage, for each conditional in your program GCC
creates a bitset and records the exercised boolean values that have
an independent effect on the outcome of that expression.

With -fpath-coverage, GCC finds and enumerates and records the
taken prime paths of each function, unless the number of paths
would exceed the limit controlled by -fpath-coverage-limit. If the
limit is exceeded the function is not instrumented as if
-fpath-coverage was not used. A prime path is the longest sequence
of unique blocks, except possibly the first and last, which is not
a subpath of any other path.

-ftest-coverage
Produce a notes file that the gcov code-coverage utility can use to
show program coverage. Each source file's note file is called
auxname.gcno. Refer to the -fprofile-arcs option above for a
description of auxname and instructions on how to generate test
coverage data. Coverage data matches the source files more closely
if you do not optimize.

-fprofile-abs-path
Automatically convert relative source file names to absolute path
names in the .gcno files. This allows gcov to find the correct
sources in projects where compilations occur with different working
directories.

-fprofile-dir=path
Set the directory to search for the profile data files in to path.
This option affects only the profile data generated by
-fprofile-generate, -ftest-coverage, -fprofile-arcs and used by
-fprofile-use and -fbranch-probabilities and its related options.
Both absolute and relative paths can be used. By default, GCC uses
the current directory as 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 sourcename.gcda file and
use it as the file name of a .gcda file. See details about the
file naming in -fprofile-arcs. See similar 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 path that are exported during run-time:

%p process ID.

%q{VAR}
value of environment variable VAR

-fprofile-generate
-fprofile-generate=path
Enable options usually used for instrumenting application to
produce profile useful for later recompilation with profile
feedback based optimization. You must use -fprofile-generate both
when compiling and when linking your program.

The following options are enabled: -fprofile-arcs,
-fprofile-values, -finline-functions, and -fipa-bit-cp.

If path is specified, GCC looks at the path to find the profile
feedback data files. See -fprofile-dir.

To optimize the program based on the collected profile information,
use -fprofile-use.

-fprofile-info-section
-fprofile-info-section=name
Register the profile information in the specified section instead
of using a constructor/destructor. The section name is name if it
is specified, otherwise the section name defaults to ".gcov_info".
A pointer to the profile information generated by -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:

.gcov_info :
{
PROVIDE (__gcov_info_start = .);
KEEP (*(.gcov_info))
PROVIDE (__gcov_info_end = .);
}

The program could dump the profiling information registered in this
linker set for example like this:

#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;
}

The merge-stream subcommand of gcov-tool may be used to deserialize
the data stream generated by the "__gcov_filename_to_gcfn" and
"__gcov_info_to_gcda" functions and merge the profile information
into .gcda files on the host filesystem.

-fprofile-note=path
If path is specified, GCC saves .gcno file into path location. If
you combine the option with multiple source files, the .gcno file
will be overwritten.

-fprofile-prefix-path=path
This option can be used in combination with
profile-generate=profile_dir and profile-use=profile_dir to inform
GCC where is the base directory of built source tree. By default
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 -fprofile-prefix-path=path with 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.

-fprofile-prefix-map=old=new
When compiling files residing in directory old, record profiling
information (with --coverage) describing them as if the files
resided in directory new instead. See also -ffile-prefix-map and
-fcanon-prefix-map.

-fprofile-update=method
Alter the update method for an application instrumented for profile
feedback based optimization. The method argument should be one of
single, atomic or prefer-atomic. The first one is useful for
single-threaded applications, while the second one prevents profile
corruption by emitting thread-safe code.

Warning: When an application does not properly join all threads (or
creates an detached thread), a profile file can be still corrupted.

Using prefer-atomic would be transformed either to atomic, when
supported by a target, or to single otherwise. The GCC driver
automatically selects prefer-atomic when -pthread is present in the
command line, otherwise the default method is single.

If atomic is selected, then the profile information is updated
using atomic operations on a best-effort basis. Ideally, the
profile information is updated through atomic operations in
hardware. If the target platform does not support the required
atomic operations in hardware, however, libatomic is available,
then the profile information is updated through calls to libatomic.
If the target platform neither supports the required atomic
operations in hardware nor libatomic, then the profile information
is not atomically updated and a warning is issued. In this case,
the obtained profiling information may be corrupt for multi-
threaded applications.

For performance reasons, if 64-bit counters are used for the
profiling information and the target platform only supports 32-bit
atomic operations in hardware, then the performance critical
profiling updates are done using two 32-bit atomic operations for
each counter update. If a signal interrupts these two operations
updating a counter, then the profiling information may be in an
inconsistent state.

-fprofile-filter-files=regex
Instrument only functions from files whose name matches any of the
regular expressions (separated by semi-colons).

For example, -fprofile-filter-files=main\.c;module.*\.c will
instrument only main.c and all C files starting with 'module'.

-fprofile-exclude-files=regex
Instrument only functions from files whose name does not match any
of the regular expressions (separated by semi-colons).

For example, -fprofile-exclude-files=/usr/.* will prevent
instrumentation of all files that are located in the /usr/ folder.

-fprofile-reproducible=[multithreaded|parallel-runs|serial]
Control level of reproducibility of profile gathered by
"-fprofile-generate". This makes it possible to rebuild program
with same outcome which is useful, for example, for distribution
packages.

With -fprofile-reproducible=serial the profile gathered by
-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 "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
"no_instrument_function" function attribute. gcov-dump with -l can
be used to dump gathered data and verify that they are indeed
reproducible.

With -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 "make
-j"). This reduces quality of gathered data, in particular of
indirect call profiling.

-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
-fsanitize-address-use-after-scope. See
<https://github.com/google/sanitizers/wiki/AddressSanitizer> for
more details. The run-time behavior can be influenced using the
ASAN_OPTIONS environment variable. When set to "help=1", the
available options are shown at startup of the instrumented program.
See
<https://github.com/google/sanitizers/wiki/AddressSanitizerFlags#run-time-flags>
for a list of supported options. The option cannot be combined
with -fsanitize=thread or -fsanitize=hwaddress. Note that the only
targets -fsanitize=hwaddress is currently supported on are x86-64
(only with "-mlam=u48" or "-mlam=u57" options) and AArch64, in both
cases only in ABIs with 64-bit pointers.

When compiling with -fsanitize=address, you should also use -g to
produce more meaningful output. To get more accurate stack traces,
it is possible to use options such as -O0, -O1, or -Og (which, for
instance, prevent most function inlining),
-fno-optimize-sibling-calls (which prevents optimizing sibling and
tail recursive calls; this option is implicit for -O0, -O1, or
-Og), or -fno-ipa-icf (which disables Identical Code Folding for
functions). Using -fno-omit-frame-pointer also improves stack
traces. Since multiple runs of the program may yield backtraces
with different addresses due to ASLR (Address Space Layout
Randomization), it may be desirable to turn ASLR off. On Linux,
this can be achieved with setarch `uname -m` -R ./prog.

-fsanitize=kernel-address
Enable AddressSanitizer for Linux kernel. See
<https://github.com/google/kernel-sanitizers> for more details.

-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
-fsanitize-address-use-after-scope. See
<https://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html>
for more details. The run-time behavior can be influenced using
the HWASAN_OPTIONS environment variable. When set to "help=1", the
available options are shown at startup of the instrumented program.
The option cannot be combined with -fsanitize=thread or
-fsanitize=address, and is currently only available on AArch64.

-fsanitize=kernel-hwaddress
Enable Hardware-assisted AddressSanitizer for compilation of the
Linux kernel. Similar to -fsanitize=kernel-address but using an
alternate instrumentation method, and similar to
-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.

Note: This option has different defaults to the
-fsanitize=hwaddress. Instrumenting the stack and alloca calls are
not on by default but are still possible by specifying the command-
line options --param hwasan-instrument-stack=1 and --param
hwasan-instrument-allocas=1 respectively. Using a random frame tag
is not implemented for kernel instrumentation.

-fsanitize=pointer-compare
Instrument comparison operation (<, <=, >, >=) with pointer
operands. The option must be combined with either
-fsanitize=kernel-address or -fsanitize=address The option cannot
be combined with -fsanitize=thread. Note: By default the check is
disabled at run time. To enable it, add
"detect_invalid_pointer_pairs=2" to the environment variable
ASAN_OPTIONS. Using "detect_invalid_pointer_pairs=1" detects
invalid operation only when both pointers are non-null.

-fsanitize=pointer-subtract
Instrument subtraction with pointer operands. The option must be
combined with either -fsanitize=kernel-address or
-fsanitize=address The option cannot be combined with
-fsanitize=thread. Note: By default the check is disabled at run
time. To enable it, add "detect_invalid_pointer_pairs=2" to the
environment variable ASAN_OPTIONS. Using
"detect_invalid_pointer_pairs=1" detects invalid operation only
when both pointers are non-null.

-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
"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 -ffixed-x18, otherwise functions compiled without
-ffixed-x18 might clobber "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
-fno-exceptions to turn off exceptions.

See <https://clang.llvm.org/docs/ShadowCallStack.html> for more
details.

-fsanitize=thread
Enable ThreadSanitizer, a fast data race detector. Memory access
instructions are instrumented to detect data race bugs. See
<https://github.com/google/sanitizers/wiki#threadsanitizer> for
more details. The run-time behavior can be influenced using the
TSAN_OPTIONS environment variable; see
<https://github.com/google/sanitizers/wiki/ThreadSanitizerFlags>
for a list of supported options. The option cannot be combined
with -fsanitize=address, -fsanitize=leak.

When compiling with -fsanitize=thread, you should also use -g to
produce more meaningful output.

Note that sanitized atomic builtins cannot throw exceptions when
operating on invalid memory addresses with non-call exceptions
(-fnon-call-exceptions).

-fsanitize=leak
Enable LeakSanitizer, a memory leak detector. This option only
matters for linking of executables. The executable is linked
against a library that overrides "malloc" and other allocator
functions. See
<https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer>
for more details. The run-time behavior can be influenced using
the LSAN_OPTIONS environment variable. The option cannot be
combined with -fsanitize=thread.

-fsanitize=undefined
Enable UndefinedBehaviorSanitizer, a fast undefined behavior
detector. Various computations are instrumented to detect
undefined behavior at runtime. See
<https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html> for
more details. The run-time behavior can be influenced using the
UBSAN_OPTIONS environment variable. Current suboptions are:

-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, -fsanitize=shift-base and
-fsanitize=shift-exponent.

-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.

-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.

-fsanitize=integer-divide-by-zero
Detect integer division by zero.

-fsanitize=unreachable
With this option, the compiler turns the
"__builtin_unreachable" call into a diagnostics message call
instead. When reaching the "__builtin_unreachable" call, the
behavior is undefined.

-fsanitize=vla-bound
This option instructs the compiler to check that the size of a
variable length array is positive.

-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.

-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.

-fsanitize=signed-integer-overflow
This option enables signed integer overflow checking. We check
that the result of "+", "*", and both unary and binary "-" does
not overflow in the signed arithmetics. This also detects
"INT_MIN / -1" signed division. Note, integer promotion rules
must be taken into account. That is, the following is not an
overflow:

signed char a = SCHAR_MAX;
a++;

-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, with the
exception of flexible array member-like arrays for which
"-fstrict-flex-arrays" or "-fstrict-flex-arrays=" options or
"strict_flex_array" attributes say they shouldn't be treated
like flexible array member-like arrays.

-fsanitize=bounds-strict
This option enables strict instrumentation of array bounds.
Most out of bounds accesses are detected, including flexible
array member-like arrays. Initializers of variables with
static storage are not instrumented.

-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.

-fsanitize=object-size
This option enables instrumentation of memory references using
the "__builtin_dynamic_object_size" function. Various out of
bounds pointer accesses are detected.

-fsanitize=float-divide-by-zero
Detect floating-point division by zero. Unlike other similar
options, -fsanitize=float-divide-by-zero is not enabled by
-fsanitize=undefined, since floating-point division by zero can
be a legitimate way of obtaining infinities and NaNs.

-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,
-fsanitize=float-cast-overflow is not enabled by
-fsanitize=undefined. This option does not work well with
"FE_INVALID" exceptions enabled.

-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 "nonnull" function attribute.

-fsanitize=returns-nonnull-attribute
This option enables instrumentation of return statements in
functions marked with "returns_nonnull" function attribute, to
detect returning of null values from such functions.

-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.

-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.

-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.

-fsanitize=pointer-overflow
This option enables instrumentation of pointer arithmetics. If
the pointer arithmetics overflows, a run-time error is issued.

-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 "__builtin_ctz" or "__builtin_clz" invokes
undefined behavior and is diagnosed by this option.

Note that sanitizers tend to increase the rate of false positive
warnings, most notably those around -Wmaybe-uninitialized. We
recommend against combining -Werror and [the use of] sanitizers.

While -ftrapv causes traps for signed overflows to be emitted,
-fsanitize=undefined gives a diagnostic message. This currently
works only for the C family of languages.

-fno-sanitize=all
This option disables all previously enabled sanitizers.
-fsanitize=all is not allowed, as some sanitizers cannot be used
together.

-fasan-shadow-offset=number
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.

-fsanitize-sections=s1,s2,...
Sanitize global variables in selected user-defined sections. si
may contain wildcards.

-fsanitize-recover[=opts]
-fsanitize-recover= controls error recovery mode for sanitizers
mentioned in comma-separated list of 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 -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 -fsanitize=undefined (and its
suboptions except for -fsanitize=unreachable and
-fsanitize=return), -fsanitize=float-cast-overflow,
-fsanitize=float-divide-by-zero, -fsanitize=bounds-strict,
-fsanitize=kernel-address and -fsanitize=address. For these
sanitizers error recovery is turned on by default, except
-fsanitize=address, for which this feature is experimental.
-fsanitize-recover=all and -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 "halt_on_error=0"
for ThreadSanitizer and UndefinedBehaviorSanitizer, while default
value for AddressSanitizer is "halt_on_error=1". This can be
overridden through setting the "halt_on_error" flag in the
corresponding environment variable.

Syntax without an explicit opts parameter is deprecated. It is
equivalent to specifying an opts list of:

undefined,float-cast-overflow,float-divide-by-zero,bounds-strict

-fsanitize-address-use-after-scope
Enable sanitization of local variables to detect use-after-scope
bugs. The option sets -fstack-reuse to none.

-fsanitize-trap[=opts]
The -fsanitize-trap= option instructs the compiler to report for
sanitizers mentioned in comma-separated list of opts undefined
behavior using "__builtin_trap" rather than a "libubsan" library
routine. If this option is enabled for certain sanitizer, it takes
precedence over the -fsanitizer-recover= for that sanitizer,
"__builtin_trap" will be emitted and be fatal regardless of whether
recovery is enabled or disabled using -fsanitize-recover=.

The advantage of this is that the "libubsan" library is not needed
and is not linked in, so this is usable even in freestanding
environments.

Currently this feature works with -fsanitize=undefined (and its
suboptions except for -fsanitize=vptr),
-fsanitize=float-cast-overflow, -fsanitize=float-divide-by-zero and
-fsanitize=bounds-strict. "-fsanitize-trap=all" can be also
specified, which enables it for "undefined" suboptions,
-fsanitize=float-cast-overflow, -fsanitize=float-divide-by-zero and
-fsanitize=bounds-strict. If "-fsanitize-trap=undefined" or
"-fsanitize-trap=all" is used and "-fsanitize=vptr" is enabled on
the command line, the instrumentation is silently ignored as the
instrumentation always needs "libubsan" support,
-fsanitize-trap=vptr is not allowed.

-fsanitize-undefined-trap-on-error
The -fsanitize-undefined-trap-on-error option is deprecated
equivalent of -fsanitize-trap=all.

-fsanitize-coverage=trace-pc
Enable coverage-guided fuzzing code instrumentation. Inserts a
call to "__sanitizer_cov_trace_pc" into every basic block.

-fsanitize-coverage=trace-cmp
Enable dataflow guided fuzzing code instrumentation. Inserts a
call to "__sanitizer_cov_trace_cmp1", "__sanitizer_cov_trace_cmp2",
"__sanitizer_cov_trace_cmp4" or "__sanitizer_cov_trace_cmp8" for
integral comparison with both operands variable or
"__sanitizer_cov_trace_const_cmp1",
"__sanitizer_cov_trace_const_cmp2",
"__sanitizer_cov_trace_const_cmp4" or
"__sanitizer_cov_trace_const_cmp8" for integral comparison with one
operand constant, "__sanitizer_cov_trace_cmpf" or
"__sanitizer_cov_trace_cmpd" for float or double comparisons and
"__sanitizer_cov_trace_switch" for switch statements.

-fcf-protection=[full|branch|return|none|check]
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 "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 "return"
implements checking of validity at the point of returning from a
function. The value "full" is an alias for specifying both
"branch" and "return". The value "none" turns off instrumentation.

To override -fcf-protection, -fcf-protection=none needs to be added
and then with -fcf-protection=xxx.

The value "check" is used for the final link with link-time
optimization (LTO). An error is issued if LTO object files are
compiled with different -fcf-protection values. The value "check"
is ignored at the compile time.

The macro "__CET__" is defined when -fcf-protection is used. The
first bit of "__CET__" is set to 1 for the value "branch" and the
second bit of "__CET__" is set to 1 for the "return".

You can also use the "nocf_check" attribute to identify which
functions and calls should be skipped from instrumentation.

Currently the x86 GNU/Linux target provides an implementation based
on Intel Control-flow Enforcement Technology (CET) which works for
i686 processor or newer.

-fharden-compares
For every logical test that survives gimple optimizations and is
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 "__builtin_trap" if the results do not match. Use with
-fharden-conditional-branches to cover all conditionals.

-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 "__builtin_trap" if the result is
unexpected. Use with -fharden-compares to cover all conditionals.

-fharden-control-flow-redundancy
Emit extra code to set booleans when entering basic blocks, and to
verify and trap, at function exits, when the booleans do not form
an execution path that is compatible with the control flow graph.

Verification takes place before returns, before mandatory tail
calls (see below) and, optionally, before escaping exceptions with
-fhardcfr-check-exceptions, before returning calls with
-fhardcfr-check-returning-calls, and before noreturn calls with
-fhardcfr-check-noreturn-calls). Tuning options --param hardcfr-
max-blocks and --param hardcfr-max-inline-blocks are available.

Tail call optimization takes place too late to affect control flow
redundancy, but calls annotated as mandatory tail calls by language
front-ends, and any calls marked early enough as potential tail
calls would also have verification issued before the call, but
these possibilities are merely theoretical, as these conditions can
only be met when using custom compiler plugins.

-fhardcfr-skip-leaf
Disable -fharden-control-flow-redundancy in leaf functions.

-fhardcfr-check-exceptions
When -fharden-control-flow-redundancy is active, check the recorded
execution path against the control flow graph at exception escape
points, as if the function body was wrapped with a cleanup handler
that performed the check and reraised. This option is enabled by
default; use -fno-hardcfr-check-exceptions to disable it.

-fhardcfr-check-returning-calls
When -fharden-control-flow-redundancy is active, check the recorded
execution path against the control flow graph before any function
call immediately followed by a return of its result, if any, so as
to not prevent tail-call optimization, whether or not it is
ultimately optimized to a tail call.

This option is enabled by default whenever sibling call
optimizations are enabled (see -foptimize-sibling-calls), but it
can be enabled (or disabled, using its negated form) explicitly,
regardless of the optimizations.

-fhardcfr-check-noreturn-calls=[always|no-xthrow|nothrow|never]
When -fharden-control-flow-redundancy is active, check the recorded
execution path against the control flow graph before "noreturn"
calls, either all of them (always), those that aren't expected to
return control to the caller through an exception (no-xthrow, the
default), those that may not return control to the caller through
an exception either (nothrow), or none of them (never).

Checking before a "noreturn" function that may return control to
the caller through an exception may cause checking to be performed
more than once, if the exception is caught in the caller, whether
by a handler or a cleanup. When -fhardcfr-check-exceptions is also
enabled, the compiler will avoid associating a "noreturn" call with
the implicitly-added cleanup handler, since it would be redundant
with the check performed before the call, but other handlers or
cleanups in the function, if activated, will modify the recorded
execution path and check it again when another checkpoint is hit.
The checkpoint may even be another "noreturn" call, so checking may
end up performed multiple times.

Various optimizers may cause calls to be marked as "noreturn"
and/or "nothrow", even in the absence of the corresponding
attributes, which may affect the placement of checks before calls,
as well as the addition of implicit cleanup handlers for them.
This unpredictability, and the fact that raising and reraising
exceptions frequently amounts to implicitly calling "noreturn"
functions, have made no-xthrow the default setting for this option:
it excludes from the "noreturn" treatment only internal functions
used to (re)raise exceptions, that are not affected by these
optimizations.

-fhardened
Enable a set of flags for C and C++ that improve the security of
the generated code without affecting its ABI. The precise flags
enabled may change between major releases of GCC, but are
currently:

-D_FORTIFY_SOURCE=3 -D_GLIBCXX_ASSERTIONS
-ftrivial-auto-var-init=zero -fPIE -pie -Wl,-z,relro,-z,now
-fstack-protector-strong -fstack-clash-protection
-fcf-protection=full (x86 GNU/Linux only)

The list of options enabled by -fhardened can be generated using
the --help=hardened option.

When the system glibc is older than 2.35, -D_FORTIFY_SOURCE=2 is
used instead.

This option is intended to be used in production builds, not merely
in debug builds.

Currently, -fhardened is only supported on GNU/Linux targets.

-fhardened only enables a particular option if it wasn't already
specified anywhere on the command line. For instance, -fhardened
-fstack-protector will only enable -fstack-protector, but not
-fstack-protector-strong.

-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 "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.

-fstack-protector-all
Like -fstack-protector except that all functions are protected.

-fstack-protector-strong
Like -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.

-fstack-protector-explicit
Like -fstack-protector but only protects those functions which have
the "stack_protect" attribute.

-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: no means no
checking, generic means force the use of old-style checking,
specific means use the best checking method and is equivalent to
bare -fstack-check.

Old-style checking is a generic mechanism that requires no specific
target support in the compiler but comes with the following
drawbacks:

1. 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.

2. 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.

3. Inefficiency: because of both the modified allocation strategy
and the generic implementation, code performance is hampered.

Note that old-style stack checking is also the fallback method for
specific if no target support has been added in the compiler.

-fstack-check= is designed for Ada's needs to detect infinite
recursion and stack overflows. 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
-fstack-clash-protection.

-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 -fstack-clash-protection will protect dynamic
stack allocations. -fstack-clash-protection may also provide
limited protection for static stack allocations if the target
supports -fstack-check=specific.

-fstack-limit-register=reg
-fstack-limit-symbol=sym
-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 0x80000000
and grows downwards, you can use the flags
-fstack-limit-symbol=__stack_limit and
-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
"no_stack_limit" function attribute.

-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 -fsplit-stack calls code compiled without
-fsplit-stack, there may not be much stack space available for the
latter code to run. If compiling all code, including library code,
with -fsplit-stack is not an option, then the linker can fix up
these calls so that the code compiled without -fsplit-stack always
has a large stack. Support for this is implemented in the gold
linker in GNU binutils release 2.21 and later.

-fstrub=disable
Disable stack scrubbing entirely, ignoring any "strub" attributes.
See

-fstrub=strict
Functions default to "strub" mode "disabled", and apply strictly
the restriction that only functions associated with
"strub"-"callable" modes ("at-calls", "callable" and
"always_inline" "internal") are "callable" by functions with
"strub"-enabled modes ("at-calls" and "internal").

-fstrub=relaxed
Restore the default stack scrub ("strub") setting, namely, "strub"
is only enabled as required by "strub" attributes associated with
function and data types. "Relaxed" means that strub contexts are
only prevented from calling functions explicitly associated with
"strub" mode "disabled". This option is only useful to override
other -fstrub=* options that precede it in the command line.

-fstrub=at-calls
Enable "at-calls" "strub" mode where viable. The primary use of
this option is for testing. It exercises the "strub" machinery in
scenarios strictly local to a translation unit. This "strub" mode
modifies function interfaces, so any function that is visible to
other translation units, or that has its address taken, will not be
affected by this option. Optimization options may also affect
viability. See the "strub" attribute documentation for details on
viability and eligibility requirements.

-fstrub=internal
Enable "internal" "strub" mode where viable. The primary use of
this option is for testing. This option is intended to exercise
thoroughly parts of the "strub" machinery that implement the less
efficient, but interface-preserving "strub" mode. Functions that
would not be affected by this option are quite uncommon.

-fstrub=all
Enable some "strub" mode where viable. When both strub modes are
viable, "at-calls" is preferred. -fdump-ipa-strubm adds function
attributes that tell which mode was selected for each function.
The primary use of this option is for testing, to exercise
thoroughly the "strub" machinery.

-fvtable-verify=[std|preinit|none]
This option is only available when compiling C++ code. It turns on
(or off, if using -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 std and preinit control the timing of when these data
structures are built. In both cases the data structures are built
before execution reaches "main". Using -fvtable-verify=std causes
the data structures to be built after shared libraries have been
loaded and initialized. -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, none takes highest priority over both
std and preinit; preinit takes priority over std.

-fvtv-debug
When used in conjunction with -fvtable-verify=std or
-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 vtv_set_ptr_data.log in the directory named by the
environment variable VTV_LOGS_DIR if that is defined or the current
working directory otherwise.

Note: This feature appends data to the log file. If you want a
fresh log file, be sure to delete any existing one.

-fvtv-counts
This is a debugging flag. When used in conjunction with
-fvtable-verify=std or -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
vtv_count_data.log in the directory named by the environment
variable 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
vtv_class_set_sizes.log in the same directory.

Note: This feature appends data to the log files. To get fresh
log files, be sure to delete any existing ones.

-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,
"__builtin_return_address" does not work beyond the current
function, so the call site information may not be available to the
profiling functions otherwise.)

void __cyg_profile_func_enter (void *this_fn,
void *call_site);
void __cyg_profile_func_exit (void *this_fn,
void *call_site);

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 "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 "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).

-finstrument-functions-once
This is similar to -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 "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 least once per process and at
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.

-finstrument-functions-exclude-file-list=file,file,...
Set the list of functions that are excluded from instrumentation
(see the description of -finstrument-functions). If the file that
contains a function definition matches with one of file, then that
function is not instrumented. The match is done on substrings: if
the file parameter is a substring of the file name, it is
considered to be a match.

For example:

-finstrument-functions-exclude-file-list=/bits/stl,include/sys

excludes any inline function defined in files whose pathnames
contain /bits/stl or include/sys.

If, for some reason, you want to include letter , in one of sym,
write ,. For example,
-finstrument-functions-exclude-file-list=',,tmp' (note the single
quote surrounding the option).

-finstrument-functions-exclude-function-list=sym,sym,...
This is similar to -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 "vector<int> blah(const vector<int> &)", not
the internal mangled name (e.g., "_Z4blahRSt6vectorIiSaIiEE"). The
match is done on substrings: if the 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.

-fpatchable-function-entry=N[,M]
Generate N NOPs right at the beginning of each function, with the
function entry point before the Mth NOP. If M is omitted, it
defaults to 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 "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 M, are
additionally collected in the "__patchable_function_entries"
section of the resulting binary.

Note that the value of "__attribute__ ((patchable_function_entry
(N,M)))" takes precedence over command-line 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
"N=0", no pad location is recorded.

The NOP instructions are inserted at---and maybe before, depending
on 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 by default.
See the -msplit-patch-nops option to change this.

The maximum value of N and M is 65535. On PowerPC with the ELFv2
ABI, for a function with dual entry points, the supported values
for M are 0, 2, 6 and 14 when not using -msplit-patch-nops.

Options Controlling the Preprocessor
These options control the C preprocessor, which is run on each C source
file before actual compilation.

If you use the -E option, nothing is done except preprocessing. Some
of these options make sense only together with -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 Directory
Options. Options to control preprocessor diagnostics are listed in
Warning Options.

-D name
Predefine name as a macro, with definition 1.

-D name=definition
The contents of definition are tokenized and processed as if they
appeared during translation phase three in a #define directive. In
particular, the definition is truncated by embedded newline
characters.

If you are invoking the preprocessor from a shell or shell-like
program you may need to use the shell's quoting syntax to protect
characters such as spaces that have a meaning in the shell syntax.

If you wish to define a function-like macro on the command line,
write its argument list with surrounding parentheses before the
equals sign (if any). Parentheses are meaningful to most shells,
so you should quote the option. With sh and csh,
-D'name(args...)=definition' works.

-D and -U options are processed in the order they are given on the
command line. All -imacros file and -include file options are
processed after all -D and -U options.

-U name
Cancel any previous definition of name, either built in or provided
with a -D option.

-include file
Process file as if "#include "file"" appeared as the first line of
the primary source file. However, the first directory searched for
file is the preprocessor's working directory instead of the
directory containing the main source file. If not found there, it
is searched for in the remainder of the "#include "..."" search
chain as normal.

If multiple -include options are given, the files are included in
the order they appear on the command line.

-imacros file
Exactly like -include, except that any output produced by scanning
file is thrown away. Macros it defines remain defined. This
allows you to acquire all the macros from a header without also
processing its declarations.

All files specified by -imacros are processed before all files
specified by -include.

-undef
Do not predefine any system-specific or GCC-specific macros. The
standard predefined macros remain defined.

-pthread
Define additional macros required for using the POSIX threads
library. You should use this option consistently for both
compilation and linking. This option is supported on GNU/Linux
targets, most other Unix derivatives, and also on x86 Cygwin and
MinGW targets.

-M Instead of outputting the result of preprocessing, output a rule
suitable for make describing the dependencies of the main source
file. The preprocessor outputs one make rule containing the object
file name for that source file, a colon, and the names of all the
included files, including those coming from -include or -imacros
command-line options.

Unless specified explicitly (with -MT or -MQ), the object file name
consists of the name of the source file with any suffix replaced
with object file suffix and with any leading directory parts
removed. If there are many included files then the rule is split
into several lines using \-newline. The rule has no commands.

This option does not suppress the preprocessor's debug output, such
as -dM. To avoid mixing such debug output with the dependency
rules you should explicitly specify the dependency output file with
-MF, or use an environment variable like DEPENDENCIES_OUTPUT.
Debug output is still sent to the regular output stream as normal.

Passing -M to the driver implies -E, and suppresses warnings with
an implicit -w.

-MM Like -M but do not mention header files that are found in system
header directories, nor header files that are included, directly or
indirectly, from such a header.

This implies that the choice of angle brackets or double quotes in
an #include directive does not in itself determine whether that
header appears in -MM dependency output.

-MF file
When used with -M or -MM, specifies a file to write the
dependencies to. If no -MF switch is given the preprocessor sends
the rules to the same place it would send preprocessed output.

When used with the driver options -MD or -MMD, -MF overrides the
default dependency output file.

If file is -, then the dependencies are written to stdout.

-MG In conjunction with an option such as -M requesting dependency
generation, -MG assumes missing header files are generated files
and adds them to the dependency list without raising an error. The
dependency filename is taken directly from the "#include" directive
without prepending any path. -MG also suppresses preprocessed
output, as a missing header file renders this useless.

This feature is used in automatic updating of makefiles.

-Mno-modules
Disable dependency generation for compiled module interfaces.

-MP This option instructs CPP to add a phony target for each dependency
other than the main file, causing each to depend on nothing. These
dummy rules work around errors make gives if you remove header
files without updating the Makefile to match.

This is typical output:

test.o: test.c test.h

test.h:

-MT target
Change the target of the rule emitted by dependency generation. By
default CPP takes the name of the main input file, deletes any
directory components and any file suffix such as .c, and appends
the platform's usual object suffix. The result is the target.

An -MT option sets the target to be exactly the string you specify.
If you want multiple targets, you can specify them as a single
argument to -MT, or use multiple -MT options.

For example, -MT '$(objpfx)foo.o' might give

$(objpfx)foo.o: foo.c

-MQ target
Same as -MT, but it quotes any characters which are special to
Make. -MQ '$(objpfx)foo.o' gives

$$(objpfx)foo.o: foo.c

The default target is automatically quoted, as if it were given
with -MQ.

-MD -MD is equivalent to -M -MF file, except that -E is not implied.
The driver determines file based on whether an -o option is given.
If it is, the driver uses its argument but with a suffix of .d,
otherwise it takes the name of the input file, removes any
directory components and suffix, and applies a .d suffix.

If -MD is used in conjunction with -E, any -o switch is understood
to specify the dependency output file, but if used without -E, each
-o is understood to specify a target object file.

Since -E is not implied, -MD can be used to generate a dependency
output file as a side effect of the compilation process.

-MMD
Like -MD except mention only user header files, not system header
files.

-fpreprocessed
Indicate to the preprocessor that the input file has already been
preprocessed. This suppresses things like macro expansion,
trigraph conversion, escaped newline splicing, and processing of
most directives. The preprocessor still recognizes and removes
comments, so that you can pass a file preprocessed with -C to the
compiler without problems. In this mode the integrated
preprocessor is little more than a tokenizer for the front ends.

-fpreprocessed is implicit if the input file has one of the
extensions .i, .ii or .mi. These are the extensions that GCC uses
for preprocessed files created by -save-temps.

-fdirectives-only
When preprocessing, handle directives, but do not expand macros.

The option's behavior depends on the -E and -fpreprocessed options.

With -E, preprocessing is limited to the handling of directives
such as "#define", "#ifdef", and "#error". Other preprocessor
operations, such as macro expansion and trigraph conversion are not
performed. In addition, the -dD option is implicitly enabled.

With -fpreprocessed, predefinition of command line and most builtin
macros is disabled. Macros such as "__LINE__", which are
contextually dependent, are handled normally. This enables
compilation of files previously preprocessed with "-E
-fdirectives-only".

With both -E and -fpreprocessed, the rules for -fpreprocessed take
precedence. This enables full preprocessing of files previously
preprocessed with "-E -fdirectives-only".

-fdollars-in-identifiers
Accept $ in identifiers.

-fextended-identifiers
Accept universal character names and extended characters in
identifiers. This option is enabled by default for C99 (and later
C standard versions) and C++.

-fno-canonical-system-headers
When preprocessing, do not shorten system header paths with
canonicalization.

-fmax-include-depth=depth
Set the maximum depth of the nested #include. The default is 200.

-fsearch-include-path[=kind]
Look for input files on the #include path, not just the current
directory. This is particularly useful with C++20 modules, for
which both header units and module interface units need to be
compiled directly:

g++ -c -std=c++20 -fmodules -fsearch-include-path bits/stdc++.h bits/std.cc

kind defaults to user, which looks on the "#include "..."" search
path; you can also explicitly specify system for the "#include
<...>" search path.

-ftabstop=width
Set the distance between tab stops. This helps the preprocessor
report correct column numbers in warnings or errors, even if tabs
appear on the line. If the value is less than 1 or greater than
100, the option is ignored. The default is 8.

-ftrack-macro-expansion[=level]
Track locations of tokens across macro expansions. This allows the
compiler to emit diagnostic about the current macro expansion stack
when a compilation error occurs in a macro expansion. Using this
option makes the preprocessor and the compiler consume more memory.
The level parameter can be used to choose the level of precision of
token location tracking thus decreasing the memory consumption if
necessary. Value 0 of level de-activates this option. Value 1
tracks tokens locations in a degraded mode for the sake of minimal
memory overhead. In this mode all tokens resulting from the
expansion of an argument of a function-like macro have the same
location. Value 2 tracks tokens locations completely. This value is
the most memory hungry. When this option is given no argument, the
default parameter value is 2.

Note that "-ftrack-macro-expansion=2" is activated by default.

-fmacro-prefix-map=old=new
When preprocessing files residing in directory old, expand the
"__FILE__" and "__BASE_FILE__" macros as if the files resided in
directory new instead. This can be used to change an absolute path
to a relative path by using . for new which can result in more
reproducible builds that are location independent. This option
also affects "__builtin_FILE()" during compilation. See also
-ffile-prefix-map and -fcanon-prefix-map.

-fexec-charset=charset
Set the execution character set, used for string and character
constants. The default is UTF-8. charset can be any encoding
supported by the system's "iconv" library routine.

-fwide-exec-charset=charset
Set the wide execution character set, used for wide string and
character constants. The default is one of UTF-32BE, UTF-32LE,
UTF-16BE, or UTF-16LE, whichever corresponds to the width of
"wchar_t" and the big-endian or little-endian byte order being used
for code generation. As with -fexec-charset, charset can be any
encoding supported by the system's "iconv" library routine;
however, you will have problems with encodings that do not fit
exactly in "wchar_t".

-finput-charset=charset
Set the input character set, used for translation from the
character set of the input file to the source character set used by
GCC. If the locale does not specify, or GCC cannot get this
information from the locale, the default is UTF-8. This can be
overridden by either the locale or this command-line option.
Currently the command-line option takes precedence if there's a
conflict. charset can be any encoding supported by the system's
"iconv" library routine.

-fpch-deps
When using precompiled headers, this flag causes the dependency-
output flags to also list the files from the precompiled header's
dependencies. If not specified, only the precompiled header are
listed and not the files that were used to create it, because those
files are not consulted when a precompiled header is used.

-fpch-preprocess
This option allows use of a precompiled header together with -E.
It inserts a special "#pragma", "#pragma GCC pch_preprocess
"filename"" in the output to mark the place where the precompiled
header was found, and its filename. When -fpreprocessed is in use,
GCC recognizes this "#pragma" and loads the PCH.

This option is off by default, because the resulting preprocessed
output is only really suitable as input to GCC. It is switched on
by -save-temps.

You should not write this "#pragma" in your own code, but it is
safe to edit the filename if the PCH file is available in a
different location. The filename may be absolute or it may be
relative to GCC's current directory.

-fworking-directory
Enable generation of linemarkers in the preprocessor output that
let the compiler know the current working directory at the time of
preprocessing. When this option is enabled, the preprocessor
emits, after the initial linemarker, a second linemarker with the
current working directory followed by two slashes. GCC uses this
directory, when it's present in the preprocessed input, as the
directory emitted as the current working directory in some
debugging information formats. This option is implicitly enabled
if debugging information is enabled, but this can be inhibited with
the negated form -fno-working-directory. If the -P flag is present
in the command line, this option has no effect, since no "#line"
directives are emitted whatsoever.

-A predicate=answer
Make an assertion with the predicate predicate and answer answer.
This form is preferred to the older form -A predicate(answer),
which is still supported, because it does not use shell special
characters.

-A -predicate=answer
Cancel an assertion with the predicate predicate and answer answer.

-C Do not discard comments. All comments are passed through to the
output file, except for comments in processed directives, which are
deleted along with the directive.

You should be prepared for side effects when using -C; it causes
the preprocessor to treat comments as tokens in their own right.
For example, comments appearing at the start of what would be a
directive line have the effect of turning that line into an
ordinary source line, since the first token on the line is no
longer a #.

-CC Do not discard comments, including during macro expansion. This is
like -C, except that comments contained within macros are also
passed through to the output file where the macro is expanded.

In addition to the side effects of the -C option, the -CC option
causes all C++-style comments inside a macro to be converted to
C-style comments. This is to prevent later use of that macro from
inadvertently commenting out the remainder of the source line.

The -CC option is generally used to support lint comments.

-P Inhibit generation of linemarkers in the output from the
preprocessor. This might be useful when running the preprocessor
on something that is not C code, and will be sent to a program
which might be confused by the linemarkers.

-traditional
-traditional-cpp
Try to imitate the behavior of pre-standard C preprocessors, as
opposed to ISO C preprocessors. See the GNU CPP manual for
details.

Note that GCC does not otherwise attempt to emulate a pre-standard
C compiler, and these options are only supported with the -E
switch, or when invoking CPP explicitly.

-trigraphs
Support ISO C trigraphs. These are three-character sequences, all
starting with ??, that are defined by ISO C to stand for single
characters. For example, ??/ stands for \, so '??/n' is a
character constant for a newline.

The nine trigraphs and their replacements are

Trigraph: ??( ??) ??< ??> ??= ??/ ??' ??! ??-
Replacement: [ ] { } # \ ^ | ~

By default, GCC ignores trigraphs, but in standard-conforming modes
it converts them. See the -std and -ansi options.

-remap
Enable special code to work around file systems which only permit
very short file names, such as MS-DOS.

-H Print the name of each header file used, in addition to other
normal activities. Each name is indented to show how deep in the
#include stack it is. Precompiled header files are also printed,
even if they are found to be invalid; an invalid precompiled header
file is printed with ...x and a valid one with ...! .

-dletters
Says to make debugging dumps during compilation as specified by
letters. The flags documented here are those relevant to the
preprocessor. Other letters are interpreted by the compiler
proper, or reserved for future versions of GCC, and so are silently
ignored. If you specify letters whose behavior conflicts, the
result is undefined.

-dM Instead of the normal output, generate a list of #define
directives for all the macros defined during the execution of
the preprocessor, including predefined macros. This gives you
a way of finding out what is predefined in your version of the
preprocessor. Assuming you have no file foo.h, the command

touch foo.h; cpp -dM foo.h

shows all the predefined macros.

If you use -dM without the -E option, -dM is interpreted as a
synonym for -fdump-rtl-mach.

-dD Like -dM except that it outputs both the #define directives and
the result of preprocessing. Both kinds of output go to the
standard output file.

-dN Like -dD, but emit only the macro names, not their expansions.

-dI Output #include directives in addition to the result of
preprocessing.

-dU Like -dD except that only macros that are expanded, or whose
definedness is tested in preprocessor directives, are output;
the output is delayed until the use or test of the macro; and
#undef directives are also output for macros tested but
undefined at the time.

-fdebug-cpp
This option is only useful for debugging GCC. When used from CPP
or with -E, it dumps debugging information about location maps.
Every token in the output is preceded by the dump of the map its
location belongs to.

When used from GCC without -E, this option has no effect.

-Wp,option
You can use -Wp,option to bypass the compiler driver and pass
option directly through to the preprocessor. If 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 -Wp
forcibly bypasses this phase. The preprocessor's direct interface
is undocumented and subject to change, so whenever possible you
should avoid using -Wp and let the driver handle the options
instead.

-Xpreprocessor option
Pass 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
-Xpreprocessor twice, once for the option and once for the
argument.

-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 (cc1, cc1plus, or 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 -B or -wrapper options to specify an alternate preprocessor or
perform additional processing of the program source between normal
preprocessing and compilation.

Passing Options to the Assembler
You can pass options to the assembler.

-Wa,option
Pass option as an option to the assembler. If option contains
commas, it is split into multiple options at the commas.

-Xassembler option
Pass 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
-Xassembler twice, once for the option and once for the argument.

Options for 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.

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.

-c
-S
-E If any of these options is used, then the linker is not run, and
object file names should not be used as arguments.

-flinker-output=type
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 type is exec, code generation produces a static binary. In this
case -fpic and -fpie are both disabled.

If type is dyn, code generation produces a shared library. In this
case -fpic or -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 type is pie, code generation produces an -fpie executable. This
results in similar optimizations as exec except that -fpie is not
disabled if specified at compilation time.

If type is 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 -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 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 -r) the linker plugin defaults to
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 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.

-fuse-ld=bfd
Use the bfd linker instead of the default linker.

-fuse-ld=gold
Use the gold linker instead of the default linker.

-fuse-ld=lld
Use the LLVM lld linker instead of the default linker.

-fuse-ld=mold
Use the Modern Linker (mold) instead of the default linker.

-llibrary
-l library
Search the library named library when linking. (The second
alternative with the library as a separate argument is only for
POSIX compliance and is not recommended.)

The -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 -L.

Static libraries are archives of object files, and have file names
like liblibrary.a. Some targets also support shared libraries,
which typically have names like liblibrary.so. If both static and
shared libraries are found, the linker gives preference to linking
with the shared library unless the -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, foo.o -lz bar.o searches library z
after file foo.o but before bar.o. If bar.o refers to functions in
z, those functions may not be loaded.

-lobjc
You need this special case of the -l option in order to link an
Objective-C or Objective-C++ program.

-nostartfiles
Do not use the standard system startup files when linking. The
standard system libraries are used normally, unless -nostdlib,
-nolibc, or -nodefaultlibs is used.

-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 -static-libgcc
or -shared-libgcc, are ignored. The standard startup files are
used normally, unless -nostartfiles is used.

The compiler may generate calls to "memcmp", "memset", "memcpy" and
"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.

-nolibc
Do not use the C library or system libraries tightly coupled with
it when linking. Still link with the startup files, libgcc or
toolchain provided language support libraries such as libgnat,
libgfortran or libstdc++ unless options preventing their inclusion
are used as well. This typically removes -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 -lpthread or -lm in some configurations. This is intended
for bare-board targets when there is indeed no C library available.

-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 -static-libgcc or -shared-libgcc, are ignored.

One of the standard libraries bypassed by -nostdlib and
-nodefaultlibs is libgcc.a, a library of internal subroutines which
GCC uses to overcome shortcomings of particular machines, or
special needs for some languages.

In most cases, you need libgcc.a even when you want to avoid other
standard libraries. In other words, when you specify -nostdlib or
-nodefaultlibs you should usually specify -lgcc as well. This
ensures that you have no unresolved references to internal GCC
library subroutines. (An example of such an internal subroutine is
"__main", used to ensure C++ constructors are called.)

-nostdlib++
Do not implicitly link with standard C++ libraries.

-e entry
--entry=entry
Specify that the program entry point is entry. The argument is
interpreted by the linker; the GNU linker accepts either a symbol
name or an address.

-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 (-fpie, -fPIE,
or model suboptions) when you specify this linker option.

-no-pie
Don't produce a dynamically linked position independent executable.

-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 (-fpie, -fPIE, or model
suboptions) when you specify this linker option.

-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.

-r Produce a relocatable object as output. This is also known as
partial linking.

-rdynamic
Pass the flag -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 "dlopen" or to allow obtaining backtraces from within
a program.

-s Remove all symbol table and relocation information from the
executable.

-static
On systems that support dynamic linking, this overrides -pie and
prevents linking with the shared libraries. On other systems, this
option has no effect.

-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 (-fpic, -fPIC, or model suboptions) when you
specify this linker option.[1]

-shared-libgcc
-static-libgcc
On systems that provide libgcc as a shared library, these options
force the use of either the shared or static version, respectively.
If no shared version of 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 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
libgcc.

Therefore, the G++ driver automatically adds -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 libgcc.
If GCC finds, at its configuration time, that you have a non-GNU
linker or a GNU linker that does not support option --eh-frame-hdr,
it links the shared version of libgcc into shared libraries by
default. Otherwise, it takes advantage of the linker and optimizes
away the linking with the shared version of 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 -shared-libgcc, such that it is linked with the shared
libgcc.

-static-libasan
When the -fsanitize=address option is used to link a program, the
GCC driver automatically links against libasan. If libasan is
available as a shared library, and the -static option is not used,
then this links against the shared version of libasan. The
-static-libasan option directs the GCC driver to link libasan
statically, without necessarily linking other libraries statically.

-static-libtsan
When the -fsanitize=thread option is used to link a program, the
GCC driver automatically links against libtsan. If libtsan is
available as a shared library, and the -static option is not used,
then this links against the shared version of libtsan. The
-static-libtsan option directs the GCC driver to link libtsan
statically, without necessarily linking other libraries statically.

-static-liblsan
When the -fsanitize=leak option is used to link a program, the GCC
driver automatically links against liblsan. If liblsan is
available as a shared library, and the -static option is not used,
then this links against the shared version of liblsan. The
-static-liblsan option directs the GCC driver to link liblsan
statically, without necessarily linking other libraries statically.

-static-libubsan
When the -fsanitize=undefined option is used to link a program, the
GCC driver automatically links against libubsan. If libubsan is
available as a shared library, and the -static option is not used,
then this links against the shared version of libubsan. The
-static-libubsan option directs the GCC driver to link libubsan
statically, without necessarily linking other libraries statically.

-static-libstdc++
When the g++ program is used to link a C++ program, it normally
automatically links against libstdc++. If libstdc++ is available
as a shared library, and the -static option is not used, then this
links against the shared version of libstdc++. That is normally
fine. However, it is sometimes useful to freeze the version of
libstdc++ used by the program without going all the way to a fully
static link. The -static-libstdc++ option directs the g++ driver
to link libstdc++ statically, without necessarily linking other
libraries statically.

-symbolic
Bind references to global symbols when building a shared object.
Warn about any unresolved references (unless overridden by the link
editor option -Xlinker -z -Xlinker defs). Only a few systems
support this option.

-T script
Use 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 -T option may be required
when linking to avoid references to undefined symbols.

-Xlinker option
Pass 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 -Xlinker twice, once for the option and once for the
argument. For example, to pass -assert definitions, you must write
-Xlinker -assert -Xlinker definitions. It does not work to write
-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=value syntax than as
separate arguments. For example, you can specify -Xlinker
-Map=output.map rather than -Xlinker -Map -Xlinker output.map.
Other linkers may not support this syntax for command-line options.

-Wl,option
Pass option as an option to the linker. If 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,
-Wl,-Map,output.map passes -Map output.map to the linker. When
using the GNU linker, you can also get the same effect with
-Wl,-Map=output.map.

-u symbol
Pretend the symbol symbol is undefined, to force linking of library
modules to define it. You can use -u multiple times with different
symbols to force loading of additional library modules.

-z keyword
-z is passed directly on to the linker along with the keyword
keyword. See the section in the documentation of your linker for
permitted values and their meanings.

Options for Directory Search
These options specify directories to search for header files, for
libraries and for parts of the compiler:

-I dir
-iquote dir
-isystem dir
-idirafter dir
Add the directory dir to the list of directories to be searched for
header files during preprocessing. If dir begins with = or
$SYSROOT, then the = or $SYSROOT is replaced by the sysroot prefix;
see --sysroot and -isysroot.

Directories specified with -iquote apply only to the quote form of
the directive, "#include "file"". Directories specified with -I,
-isystem, or -idirafter apply to lookup for both the
"#include "file"" and "#include <file>" directives.

You can specify any number or combination of these options on the
command line to search for header files in several directories.
The lookup order is as follows:

1. For the quote form of the include directive, the directory of
the current file is searched first.

2. For the quote form of the include directive, the directories
specified by -iquote options are searched in left-to-right
order, as they appear on the command line.

3. Directories specified with -I options are scanned in left-to-
right order.

4. Directories specified with -isystem options are scanned in
left-to-right order.

5. Standard system directories are scanned.

6. Directories specified with -idirafter options are scanned in
left-to-right order.

You can use -I to override a system header file, substituting your
own version, since these directories are searched before the
standard system header file directories. However, you should not
use this option to add directories that contain vendor-supplied
system header files; use -isystem for that.

The -isystem and -idirafter options also mark the directory as a
system directory, so that it gets the same special treatment that
is applied to the standard system directories.

If a standard system include directory, or a directory specified
with -isystem, is also specified with -I, the -I option is ignored.
The directory is still searched but as a system directory at its
normal position in the system include chain. This is to ensure
that GCC's procedure to fix buggy system headers and the ordering
for the "#include_next" directive are not inadvertently changed.
If you really need to change the search order for system
directories, use the -nostdinc and/or -isystem options.

-I- Split the include path. This option has been deprecated. Please
use -iquote instead for -I directories before the -I- and remove
the -I- option.

Any directories specified with -I options before -I- are searched
only for headers requested with "#include "file""; they are not
searched for "#include <file>". If additional directories are
specified with -I options after the -I-, those directories are
searched for all #include directives.

In addition, -I- inhibits the use of the directory of the current
file directory as the first search directory for "#include "file"".
There is no way to override this effect of -I-.

-iprefix prefix
Specify prefix as the prefix for subsequent -iwithprefix options.
If the prefix represents a directory, you should include the final
/.

-iwithprefix dir
-iwithprefixbefore dir
Append dir to the prefix specified previously with -iprefix, and
add the resulting directory to the include search path.
-iwithprefixbefore puts it in the same place -I would; -iwithprefix
puts it where -idirafter would.

-isysroot dir
This option is like the --sysroot option, but applies only to
header files (except for Darwin targets, where it applies to both
header files and libraries). See the --sysroot option for more
information.

-imultilib dir
Use dir as a subdirectory of the directory containing target-
specific C++ headers.

-nostdinc
Do not search the standard system directories for header files.
Only the directories explicitly specified with -I, -iquote,
-isystem, and/or -idirafter options (and the directory of the
current file, if appropriate) are searched.

-nostdinc++
Do not search for header files in the C++-specific standard
directories, but do still search the other standard directories.
(This option is used when building the C++ library.)

--embed-dir=dir
Append dir directory to the list of searched directories for
"#embed" preprocessing directive or "__has_embed" macro. There are
no default directories for "#embed".

If dir begins with = or $SYSROOT, then the = or $SYSROOT is
replaced by the sysroot prefix; see --sysroot and -isysroot.

-iplugindir=dir
Set the directory to search for plugins that are passed by
-fplugin=name instead of -fplugin=path/name.so. This option is not
meant to be used by the user, but only passed by the driver.

-Ldir
Add directory dir to the list of directories to be searched for -l.

-Bprefix
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
cpp, cc1, as and ld. It tries prefix as a prefix for each program
it tries to run, both with and without machine/version/ for the
corresponding target machine and compiler version.

For each subprogram to be run, the compiler driver first tries the
-B prefix, if any. If that name is not found, or if -B is not
specified, the driver tries two standard prefixes, /usr/lib/gcc/
and /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 PATH environment variable.

The compiler checks to see if the path provided by -B refers to a
directory, and if necessary it adds a directory separator character
at the end of the path.

-B prefixes that effectively specify directory names also apply to
libraries in the linker, because the compiler translates these
options into -L options for the linker. They also apply to include
files in the preprocessor, because the compiler translates these
options into -isystem options for the preprocessor. In this case,
the compiler appends include to the prefix.

The runtime support file libgcc.a can also be searched for using
the -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 -B prefix is to use
the environment variable GCC_EXEC_PREFIX.

As a special kludge, if the path provided by -B is [dir/]stageN/,
where N is a number in the range 0 to 9, then it is replaced by
[dir/]include. This is to help with boot-strapping the compiler.

-no-canonical-prefixes
Do not expand any symbolic links, resolve references to /../ or
/./, or make the path absolute when generating a relative prefix.

--sysroot=dir
Use dir as the logical root directory for headers and libraries.
For example, if the compiler normally searches for headers in
/usr/include and libraries in /usr/lib, it instead searches
dir/usr/include and dir/usr/lib.

If you use both this option and the -isysroot option, then the
--sysroot option applies to libraries, but the -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 --sysroot still works, but the
library aspect does not.

--no-sysroot-suffix
For some targets, a suffix is added to the root directory specified
with --sysroot, depending on the other options used, so that
headers may for example be found in dir/suffix/usr/include instead
of dir/usr/include. This option disables the addition of such a
suffix.

Options for Code Generation Conventions
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 -ffoo is -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 no- or adding it.

-fstack-reuse=reuse-level
This option controls stack space reuse for user declared local/auto
variables and compiler generated temporaries. reuse_level can be
all, named_vars, or none. all enables stack reuse for all local
variables and temporaries, named_vars enables the reuse only for
user defined local variables with names, and none disables stack
reuse completely. The default value is 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,

int *p;
{
int local1;

p = &local1;
local1 = 10;
....
}
{
int local2;
local2 = 20;
...
}

if (*p == 10) // out of scope use of local1
{

}

Another example:

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?
}

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.

-ftrapv
This option generates traps for signed overflow on addition,
subtraction, multiplication operations. The options -ftrapv and
-fwrapv override each other, so using -ftrapv -fwrapv on the
command-line results in -fwrapv being effective. Note that only
active options override, so using -ftrapv -fwrapv -fno-wrapv on the
command-line results in -ftrapv being effective.

-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 -ftrapv and -fwrapv
override each other, so using -ftrapv -fwrapv on the command-line
results in -fwrapv being effective. Note that only active options
override, so using -ftrapv -fwrapv -fno-wrapv on the command-line
results in -ftrapv being effective.

-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.

-fstrict-overflow
This option implies -fno-wrapv -fno-wrapv-pointer and when negated
implies -fwrapv -fwrapv-pointer.

-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.

-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
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 "SIGALRM". This
enables -fexceptions.

-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 "pure" or "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.

-funwind-tables
Similar to -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.

-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).

-fno-gnu-unique
On systems with recent GNU assembler and C library, the C++
compiler uses the "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
"RTLD_LOCAL"; this is necessary to avoid problems with a library
used by two different "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 "dlclose" to
be ignored for affected DSOs; if your program relies on
reinitialization of a DSO via "dlclose" and "dlopen", you can use
-fno-gnu-unique.

-fpcc-struct-return
Return "short" "struct" and "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.

Warning: code compiled with the -fpcc-struct-return switch is not
binary compatible with code compiled with the -freg-struct-return
switch. Use it to conform to a non-default application binary
interface.

-freg-struct-return
Return "struct" and "union" values in registers when possible.
This is more efficient for small structures than
-fpcc-struct-return.

If you specify neither -fpcc-struct-return nor -freg-struct-return,
GCC defaults to whichever convention is standard for the target.
If there is no standard convention, GCC defaults to
-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.

Warning: code compiled with the -freg-struct-return switch is not
binary compatible with code compiled with the -fpcc-struct-return
switch. Use it to conform to a non-default application binary
interface.

-fshort-enums
Allocate to an "enum" type only as many bytes as it needs for the
declared range of possible values. Specifically, the "enum" type
is equivalent to the smallest integer type that has enough room.
This option has no effect for an enumeration type with a fixed
underlying type.

Warning: the -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.

-fshort-wchar
Override the underlying type for "wchar_t" to be "short unsigned
int" instead of the default for the target. This option is useful
for building programs to run under WINE.

Warning: the -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.

-fcommon
In C code, this option controls the placement of global variables
defined without an initializer, known as tentative definitions in
the C standard. Tentative definitions are distinct from
declarations of a variable with the "extern" keyword, which do not
allocate storage.

The default is -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 -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.

-fno-ident
Ignore the "#ident" directive.

-finhibit-size-directive
Don't output a ".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 crtstuff.c; you should not need to
use it for anything else.

-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).

-fno-verbose-asm, the default, causes the extra information to be
omitted and is useful when comparing two assembler files.

The added comments include:

* information on the compiler version and command-line options,

* the source code lines associated with the assembly
instructions, in the form FILENAME:LINENUMBER:CONTENT OF LINE,

* hints on which high-level expressions correspond to the various
assembly instruction operands.

For example, given this C source file:

int test (int n)
{
int i;
int total = 0;

for (i = 0; i < n; i++)
total += i * i;

return total;
}

compiling to (x86_64) assembly via -S and emitting the result
direct to stdout via -o -

gcc -S test.c -fverbose-asm -Os -o -

gives output similar to this:

.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

The comments are intended for humans rather than machines and hence
the precise format of the comments is subject to change.

-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 -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 -grecord-gcc-switches for
another way of storing compiler options into the object file.

-fpic
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 -fpic does not work;
in that case, recompile with -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 "__pic__" and "__PIC__" are
defined to 1.

-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 "__pic__" and "__PIC__" are
defined to 2.

-fpie
-fPIE
These options are similar to -fpic and -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 -pie GCC option.

-fpie and -fPIE both define the macros "__pie__" and "__PIE__".
The macros have the value 1 for -fpie and 2 for -fPIE.

-fno-plt
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 -fno-plt all external symbols are resolved at load time.

Alternatively, the function attribute "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.

-fno-jump-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 -fpic or -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.

-fno-bit-tests
Do not use bit tests for switch statements even where it would be
more efficient than other code generation strategies.

-ffixed-reg
Treat the register named 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).

reg must be the name of a register. The register names accepted
are machine-specific and are defined in the "REGISTER_NAMES" macro
in the machine description macro file.

This flag does not have a negative form, because it specifies a
three-way choice.

-fcall-used-reg
Treat the register named 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 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.

-fcall-saved-reg
Treat the register named 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 reg if they use it.

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.

-fpack-struct[=n]
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.

Warning: the -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.

-fleading-underscore
This option and its counterpart, -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.

Warning: the -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.

-ftls-model=model
Alter the thread-local storage model to be used. The model
argument should be one of global-dynamic, local-dynamic, initial-
exec or 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 -fpic is
not given on the command line.

The default without -fpic is initial-exec; with -fpic the default
is global-dynamic.

-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.

-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, -fno-trampolines is enabled
by default only for Ada.

Moreover, code compiled with -ftrampolines and code compiled with
-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 "-ftrampolines" and
"-fno-trampolines" options currently have no effect, and
trampolines are always generated on platforms that need them for
nested functions.

-ftrampoline-impl=[stack|heap]
By default, trampolines are generated on stack. However, certain
platforms (such as the Apple M1) do not permit an executable stack.
Compiling with -ftrampoline-impl=heap generate calls to
"__gcc_nested_func_ptr_created" and "__gcc_nested_func_ptr_deleted"
in order to allocate and deallocate trampoline space on the
executable heap. These functions are implemented in libgcc, and
will only be provided on specific targets: x86_64 Darwin, x86_64
and aarch64 Linux. PLEASE NOTE: Heap trampolines are not
guaranteed to be correctly deallocated if you "setjmp", instantiate
nested functions, and then "longjmp" back to a state prior to
having allocated those nested functions.

-fvisibility=[default|internal|hidden|protected]
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 strongly recommended that you use this in any
shared objects you distribute.

Despite the nomenclature, default always means public; i.e.,
available to be linked against from outside the shared object.
protected and internal are pretty useless in real-world usage so
the only other commonly used option is hidden. The default if
-fvisibility isn't specified is 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
<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
-fvisibility=hidden and "__attribute__ ((visibility("default")))"
instead of "__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
"#pragma GCC visibility" of use. This works by you enclosing the
declarations you wish to set visibility for with (for example)
"#pragma GCC visibility push(hidden)" and "#pragma GCC visibility
pop". Bear in mind that symbol visibility should be viewed 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 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, "operator new" and "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 "#pragma GCC visibility
push(default)" before including any such headers.

"extern" declarations are not affected by -fvisibility, so a lot of
code can be recompiled with -fvisibility=hidden with no
modifications. However, this means that calls to "extern"
functions with no explicit visibility use the PLT, so it is more
effective to use "__attribute ((visibility))" and/or "#pragma GCC
visibility" to tell the compiler which "extern" declarations should
be treated as hidden.

Note that -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 type_info nodes are unified between the DSOs.

An overview of these techniques, their benefits and how to use them
is at <https://gcc.gnu.org/wiki/Visibility>.

-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 "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 "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.

-fsync-libcalls
This option controls whether any out-of-line instance of the
"__sync" family of functions may be used to implement the C++11
"__atomic" family of functions.

The default value of this option is enabled, thus the only useful
form of the option is -fno-sync-libcalls. This option is used in
the implementation of the libatomic runtime library.

-fzero-init-padding-bits=value
Guarantee zero initialization of padding bits in automatic variable
initializers. Certain languages guarantee zero initialization of
padding bits in certain cases, e.g. C23 when using empty
initializers ("{}"), or C++ when using zero-initialization or C
guarantees that fields not specified in an initializer have their
padding bits zero initialized. This option allows to change when
padding bits in initializers are guaranteed to be zero initialized.
The default is "-fzero-init-padding-bits=standard", which makes no
further guarantees than the corresponding standard. E.g.

struct A { char a; unsigned long long b; char c; };
union B { char a; unsigned long long b; };
struct A a = {}; // C23 guarantees padding bits are zero.
struct A b = { 1, 2, 3 }; // No guarantees.
union B c = {}; // C23 guarantees padding bits are zero.
union B d = { 1 }; // No guarantees.

"-fzero-init-padding-bits=unions" guarantees zero initialization of
padding bits in unions on top of what the standards guarantee, if
the initializer of an union is empty (then all bits of the union
are zero initialized) or if the initialized member of the union is
smaller than the size of the union (in that case guarantees padding
bits outside of the initialized member to be zero initialized).
This was the GCC behavior before GCC 15 and in the above example
guarantees zero initialization of last "sizeof (unsigned long long)
- 1" bytes in the union.

"-fzero-init-padding-bits=all" guarantees additionally zero
initialization of padding bits of other aggregates, so the padding
in between "b.a" and "b.b" (if any) and tail padding in the
structure (if any).

GCC Developer Options
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 =filename suffix. You can specify stdout or - to dump to
standard output, and stderr for standard error.

If =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 final, even if
they are executed earlier. The phase letter is one of i (inter-
procedural analysis), l (language-specific), r (RTL), or t (tree). The
files are created in the directory of the output file.

-fcallgraph-info
-fcallgraph-info=MARKERS
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 "su" marker is specified, the
callgraph is decorated with stack usage information; it is
equivalent to -fstack-usage. When the "da" marker is specified,
the callgraph is decorated with information about dynamically
allocated objects.

When compiling with -flto, no callgraph information is output along
with the object file. At LTO link time, -fcallgraph-info may
generate multiple callgraph information files next to intermediate
LTO output files.

-dletters
-fdump-rtl-pass
-fdump-rtl-pass=filename
Says to make debugging dumps during compilation at times specified
by letters. This is used for debugging the RTL-based passes of the
compiler.

Some -dletters switches have different meaning when -E is used for
preprocessing.

Debug dumps can be enabled with a -fdump-rtl switch or some -d
option letters. Here are the possible letters for use in pass and
letters, and their meanings:

-fdump-rtl-alignments
Dump after branch alignments have been computed.

-fdump-rtl-asmcons
Dump after fixing rtl statements that have unsatisfied in/out
constraints.

-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.

-fdump-rtl-barriers
Dump after cleaning up the barrier instructions.

-fdump-rtl-bbpart
Dump after partitioning hot and cold basic blocks.

-fdump-rtl-bbro
Dump after block reordering.

-fdump-rtl-btl1
-fdump-rtl-btl2
-fdump-rtl-btl1 and -fdump-rtl-btl2 enable dumping after the
two branch target load optimization passes.

-fdump-rtl-bypass
Dump after jump bypassing and control flow optimizations.

-fdump-rtl-combine
Dump after the RTL instruction combination pass.

-fdump-rtl-compgotos
Dump after duplicating the computed gotos.

-fdump-rtl-ce1
-fdump-rtl-ce2
-fdump-rtl-ce3
-fdump-rtl-ce1, -fdump-rtl-ce2, and -fdump-rtl-ce3 enable
dumping after the three if conversion passes.

-fdump-rtl-cprop_hardreg
Dump after hard register copy propagation.

-fdump-rtl-csa
Dump after combining stack adjustments.

-fdump-rtl-cse1
-fdump-rtl-cse2
-fdump-rtl-cse1 and -fdump-rtl-cse2 enable dumping after the
two common subexpression elimination passes.

-fdump-rtl-dce
Dump after the standalone dead code elimination passes.

-fdump-rtl-dbr
Dump after delayed branch scheduling.

-fdump-rtl-dce1
-fdump-rtl-dce2
-fdump-rtl-dce1 and -fdump-rtl-dce2 enable dumping after the
two dead store elimination passes.

-fdump-rtl-eh
Dump after finalization of EH handling code.

-fdump-rtl-eh_ranges
Dump after conversion of EH handling range regions.

-fdump-rtl-expand
Dump after RTL generation.

-fdump-rtl-fwprop1
-fdump-rtl-fwprop2
-fdump-rtl-fwprop1 and -fdump-rtl-fwprop2 enable dumping after
the two forward propagation passes.

-fdump-rtl-gcse1
-fdump-rtl-gcse2
-fdump-rtl-gcse1 and -fdump-rtl-gcse2 enable dumping after
global common subexpression elimination.

-fdump-rtl-init-regs
Dump after the initialization of the registers.

-fdump-rtl-initvals
Dump after the computation of the initial value sets.

-fdump-rtl-into_cfglayout
Dump after converting to cfglayout mode.

-fdump-rtl-ira
Dump after iterated register allocation.

-fdump-rtl-jump
Dump after the second jump optimization.

-fdump-rtl-loop2
-fdump-rtl-loop2 enables dumping after the rtl loop
optimization passes.

-fdump-rtl-mach
Dump after performing the machine dependent reorganization
pass, if that pass exists.

-fdump-rtl-mode_sw
Dump after removing redundant mode switches.

-fdump-rtl-rnreg
Dump after register renumbering.

-fdump-rtl-outof_cfglayout
Dump after converting from cfglayout mode.

-fdump-rtl-peephole2
Dump after the peephole pass.

-fdump-rtl-postreload
Dump after post-reload optimizations.

-fdump-rtl-pro_and_epilogue
Dump after generating the function prologues and epilogues.

-fdump-rtl-sched1
-fdump-rtl-sched2
-fdump-rtl-sched1 and -fdump-rtl-sched2 enable dumping after
the basic block scheduling passes.

-fdump-rtl-ree
Dump after sign/zero extension elimination.

-fdump-rtl-seqabstr
Dump after common sequence discovery.

-fdump-rtl-shorten
Dump after shortening branches.

-fdump-rtl-split1
-fdump-rtl-split2
-fdump-rtl-split3
-fdump-rtl-split4
-fdump-rtl-split5
These options enable dumping after five rounds of instruction
splitting.

-fdump-rtl-sms
Dump after modulo scheduling. This pass is only run on some
architectures.

-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.

-fdump-rtl-subreg1
-fdump-rtl-subreg2
-fdump-rtl-subreg1 and -fdump-rtl-subreg2 enable dumping after
the two subreg expansion passes.

-fdump-rtl-vartrack
Dump after variable tracking.

-fdump-rtl-vregs
Dump after converting virtual registers to hard registers.

-fdump-rtl-web
Dump after live range splitting.

-fdump-rtl-regclass
-fdump-rtl-subregs_of_mode_init
-fdump-rtl-subregs_of_mode_finish
-fdump-rtl-dfinit
-fdump-rtl-dfinish
These dumps are defined but always produce empty files.

-da
-fdump-rtl-all
Produce all the dumps listed above.

-dA Annotate the assembler output with miscellaneous debugging
information.

-dD Dump all macro definitions, at the end of preprocessing, in
addition to normal output.

-dH Produce a core dump whenever an error occurs.

-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.

-dP Dump the RTL in the assembler output as a comment before each
instruction. Also turns on -dp annotation.

-dx Just generate RTL for a function instead of compiling it.
Usually used with -fdump-rtl-expand.

-fdump-debug
Dump debugging information generated during the debug generation
phase.

-fdump-earlydebug
Dump debugging information generated during the early debug
generation phase.

-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.

-freport-bug
Collect and dump debug information into a temporary file if an
internal compiler error (ICE) occurs.

-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 -g.

-fdump-unnumbered-links
When doing debugging dumps (see -d option above), suppress
instruction numbers for the links to the previous and next
instructions in a sequence.

-fdump-ipa-switch
-fdump-ipa-switch-options
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:

all Enables all inter-procedural analysis dumps.

cgraph
Dumps information about call-graph optimization, unused
function removal, and inlining decisions.

inline
Dump after function inlining.

strubm
Dump after selecting "strub" modes, and recording the
selections as function attributes.

strub
Dump "strub" transformations: interface changes, function
wrapping, and insertion of builtin calls for stack scrubbing
and watermarking.

Additionally, the options -optimized, -missed, -note, and -all can
be provided, with the same meaning as for -fopt-info, defaulting to
-optimized.

For example, -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 -optimized) together with low-level
details about the analysis.

-fdump-lang
Dump language-specific information. The file name is made by
appending .lang to the source file name.

-fdump-lang-all
-fdump-lang-switch
-fdump-lang-switch-options
-fdump-lang-switch-options=filename
Control the dumping of language-specific information. The options
and filename portions behave as described in the -fdump-tree
option. The following switch values are accepted:

all Enable all language-specific dumps.

class
Dump class hierarchy information. Virtual table information is
emitted unless 'slim' is specified. This option is applicable
to C++ only.

module
Dump module information. Options lineno (locations), graph
(reachability), blocks (clusters), uid (serialization), alias
(mergeable), asmname (Elrond), eh (mapper) & vops (macros) may
provide additional information. This option is applicable to
C++ only.

raw Dump the raw internal tree data. This option is applicable to
C++ only.

-fdump-passes
Print on stderr the list of optimization passes that are turned on
and off by the current command-line options.

-fdump-statistics-option
Enable and control dumping of pass statistics in a separate file.
The file name is generated by appending a suffix ending in
.statistics to the source file name, and the file is created in the
same directory as the output file. If the -option form is used,
-stats causes counters to be summed over the whole compilation unit
while -details dumps every event as the passes generate them. The
default with no option is to sum counters for each function
compiled.

-fdump-tree-all
-fdump-tree-switch
-fdump-tree-switch-options
-fdump-tree-switch-options=filename
Control the dumping at various stages of processing the
intermediate language tree to a file. If the -options form is
used, options is a list of - 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

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.

asmname
If "DECL_ASSEMBLER_NAME" has been set for a given decl, use
that in the dump instead of "DECL_NAME". Its primary use is
ease of use working backward from mangled names in the assembly
file.

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.

raw Print a raw representation of the tree. By default, trees are
pretty-printed into a C-like representation.

details
Enable more detailed dumps (not honored by every dump option).
Also include information from the optimization passes.

stats
Enable dumping various statistics about the pass (not honored
by every dump option).

blocks
Enable showing basic block boundaries (disabled in raw dumps).

graph
For each of the other indicated dump files (-fdump-rtl-pass),
dump a representation of the control flow graph suitable for
viewing with GraphViz to file.passid.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.

vops
Enable showing virtual operands for every statement.

lineno
Enable showing line numbers for statements.

uid Enable showing the unique ID ("DECL_UID") for each variable.

verbose
Enable showing the tree dump for each statement.

eh Enable showing the EH region number holding each statement.

scev
Enable showing scalar evolution analysis details.

optimized
Enable showing optimization information (only available in
certain passes).

missed
Enable showing missed optimization information (only available
in certain passes).

note
Enable other detailed optimization information (only available
in certain passes).

all Turn on all options, except raw, slim, verbose and lineno.

optall
Turn on all optimization options, i.e., optimized, missed, and
note.

To determine what tree dumps are available or find the dump for a
pass of interest follow the steps below.

1. Invoke GCC with -fdump-passes and in the stderr output look for
a code that corresponds to the pass you are interested in. For
example, the codes "tree-evrp", "tree-vrp1", and "tree-vrp2"
correspond to the three Value Range Propagation passes. The
number at the end distinguishes distinct invocations of the
same pass.

2. To enable the creation of the dump file, append the pass code
to the -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 -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.

3. 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 t for tree passes (and the
letter r for RTL passes), and finally the pass code. For
example, the Early VRP pass dump might be in a file named
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.

-fopt-info
-fopt-info-options
-fopt-info-options=filename
Controls optimization dumps from various optimization passes. If
the -options form is used, options is a list of - separated option
keywords to select the dump details and optimizations.

The options can be divided into three groups:

1. options describing what kinds of messages should be emitted,

2. options describing the verbosity of the dump, and

3. options describing which optimizations should be included.

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:

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.

missed
Print information about missed optimizations. Individual passes
control which information to include in the output.

note
Print verbose information about optimizations, such as certain
transformations, more detailed messages about decisions etc.

all Print detailed optimization information. This includes
optimized, missed, and note.

The following option controls the dump verbosity:

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.

One or more of the following option keywords can be used to
describe a group of optimizations:

ipa Enable dumps from all interprocedural optimizations.

loop
Enable dumps from all loop optimizations.

inline
Enable dumps from all inlining optimizations.

omp Enable dumps from all OMP (Offloading and Multi Processing)
optimizations.

vec Enable dumps from all vectorization optimizations.

optall
Enable dumps from all optimizations. This is a superset of the
optimization groups listed above.

If options is omitted, it defaults to optimized-optall, which means
to dump messages about successful optimizations from all the
passes, omitting messages that are treated as "internals".

If the filename is provided, then the dumps from all the applicable
optimizations are concatenated into the filename. Otherwise the
dump is output onto stderr. Though multiple -fopt-info options are
accepted, only one of them can include a filename. If other
filenames are provided then all but the first such option are
ignored.

Note that the output filename is overwritten in case of multiple
translation units. If a combined output from multiple translation
units is desired, stderr should be used instead.

In the following example, the optimization info is output to
stderr:

gcc -O3 -fopt-info

This example:

gcc -O3 -fopt-info-missed=missed.all

outputs missed optimization report from all the passes into
missed.all, and this one:

gcc -O2 -ftree-vectorize -fopt-info-vec-missed

prints information about missed optimization opportunities from
vectorization passes on stderr. Note that -fopt-info-vec-missed is
equivalent to -fopt-info-missed-vec. The order of the optimization
group names and message types listed after -fopt-info does not
matter.

As another example,

gcc -O3 -fopt-info-inline-optimized-missed=inline.txt

outputs information about missed optimizations as well as optimized
locations from all the inlining passes into inline.txt.

Finally, consider:

gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt

Here the two output filenames vec.miss and 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 vec.miss is produced which contains dumps from the vectorizer
about missed opportunities.

-fsave-optimization-record
Write a SRCFILE.opt-record.json.gz file detailing what
optimizations were performed, for those optimizations that support
-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
-fopt-info-all, as a collection of messages with source file, line
number and column number, with the following additional data for
each message:

* 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,

* the function name of the code being optimized, where
applicable,

* 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,

* 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,

* the GCC pass that emitted the message, and

* the location in GCC's own code from which the message was
emitted

Additionally, some messages are logically nested within other
messages, reflecting implementation details of the optimization
passes.

-fsched-verbose=n
On targets that use instruction scheduling, this option controls
the amount of debugging output the scheduler prints to the dump
files.

For n greater than zero, -fsched-verbose outputs the same
information as -fdump-rtl-sched1 and -fdump-rtl-sched2. For n
greater than one, it also output basic block probabilities,
detailed ready list information and unit/insn info. For n greater
than two, it includes RTL at abort point, control-flow and regions
info. And for n over four, -fsched-verbose also includes
dependence info.

-fenable-kind-pass
-fdisable-kind-pass=range-list
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.

-fdisable-ipa-pass
Disable IPA pass pass. 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.

-fdisable-rtl-pass
-fdisable-rtl-pass=range-list
Disable RTL pass pass. 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. 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 uid falls
within one of the specified ranges, the pass is disabled for
that function. The uid is shown in the function header of a
dump file, and the pass names can be dumped by using option
-fdump-passes.

-fdisable-tree-pass
-fdisable-tree-pass=range-list
Disable tree pass pass. See -fdisable-rtl for the description
of option arguments.

-fenable-ipa-pass
Enable IPA pass pass. 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.

-fenable-rtl-pass
-fenable-rtl-pass=range-list
Enable RTL pass pass. See -fdisable-rtl for option argument
description and examples.

-fenable-tree-pass
-fenable-tree-pass=range-list
Enable tree pass pass. See -fdisable-rtl for the description
of option arguments.

Here are some examples showing uses of these options.

# 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

-fchecking
-fchecking=n
Enable internal consistency checking. The default depends on the
compiler configuration. -fchecking=2 enables further internal
consistency checking that might affect code generation.

-frandom-seed=string
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 -frandom-seed option to produce reproducibly
identical object files.

The 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 string should be different for every file you compile.

-save-temps
Store the usual "temporary" intermediate files permanently; name
them as auxiliary output files, as specified described under
-dumpbase and -dumpdir.

When used in combination with the -x command-line 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 -save-temps.

-save-temps=cwd
Equivalent to -save-temps -dumpdir ./.

-save-temps=obj
Equivalent to -save-temps -dumpdir outdir/, where outdir/ is the
directory of the output file specified after the -o option,
including any directory separators. If the -o option is not used,
the -save-temps=obj switch behaves like -save-temps=cwd.

-time[=file]
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:

# cc1 0.12 0.01
# as 0.00 0.01

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:

0.12 0.01 cc1 <options>
0.00 0.01 as <options>

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.

-fdump-final-insns[=file]
Dump the final internal representation (RTL) to file. If the
optional argument is omitted (or if file is "."), the name of the
dump file is determined by appending ".gkd" to the dump base name,
see -dumpbase.

-fcompare-debug[=opts]
If no error occurs during compilation, run the compiler a second
time, adding opts and -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 -gtoggle is used.

The environment variable GCC_COMPARE_DEBUG, if defined, non-empty
and nonzero, implicitly enables -fcompare-debug. If
GCC_COMPARE_DEBUG is defined to a string starting with a dash, then
it is used for opts, otherwise the default -gtoggle is used.

-fcompare-debug=, with the equal sign but without opts, is
equivalent to -fno-compare-debug, which disables the dumping of the
final representation and the second compilation, preventing even
GCC_COMPARE_DEBUG from taking effect.

To verify full coverage during -fcompare-debug testing, set
GCC_COMPARE_DEBUG to say -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 GCC_COMPARE_DEBUG to -w%n-fcompare-debug not overridden
will do.

-fcompare-debug-second
This option is implicitly passed to the compiler for the second
compilation requested by -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 ".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
first compilation to be skipped, which makes it useful for little
other than debugging the compiler proper.

-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 -fcompare-debug.

-fvar-tracking-assignments-toggle
Toggle -fvar-tracking-assignments, in the same way that -gtoggle
toggles -g.

-Q Makes the compiler print out each function name as it is compiled,
and print some statistics about each pass when it finishes.

-ftime-report
Makes the compiler print some statistics to stderr about the time
consumed by each pass when it finishes.

If SARIF output of diagnostics was requested via
-fdiagnostics-format=sarif-file or
-fdiagnostics-format=sarif-stderr then the -ftime-report
information is instead emitted in JSON form as part of SARIF
output. The precise format of this JSON data is subject to change,
and the values may not exactly match those emitted to stderr due to
being written out at a slightly different place within the
compiler.

-ftime-report-details
Record the time consumed by infrastructure parts separately for
each pass.

-fira-verbose=n
Control the verbosity of the dump file for the integrated register
allocator. The default value is 5. If the value n is greater or
equal to 10, the dump output is sent to stderr using the same
format as n minus 10.

-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 -flto).

Disabled by default.

-flto-report-wpa
Like -flto-report, but only print for the WPA phase of link-time
optimization.

-fmem-report
Makes the compiler print some statistics about permanent memory
allocation when it finishes.

-fmem-report-wpa
Makes the compiler print some statistics about permanent memory
allocation for the WPA phase only.

-fpre-ipa-mem-report
-fpost-ipa-mem-report
Makes the compiler print some statistics about permanent memory
allocation before or after interprocedural optimization.

-fmultiflags
This option enables multilib-aware "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 set up by
compiler internals, by the target, or by builders at configure
time.

Like "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 "TFLAGS", the use of specs enables different flags to be
selected for different multilibs. The way to accomplish that is to
build with make TFLAGS=-fmultiflags, after configuring
--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 "TFLAGS" are being used to build
all target libraries, by configuring a non-bootstrap compiler
--with-specs='%{!fmultiflags:%emissing TFLAGS}' and building the
compiler and target libraries.

-fprofile-report
Makes the compiler print some statistics about consistency of the
(estimated) profile and effect of individual passes.

-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 .su to the auxname. 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:

* The name of the function.

* A number of bytes.

* One or more qualifiers: "static", "dynamic", "bounded".

The qualifier "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 "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 "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.

-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.

-fdbg-cnt-list
Print the name and the counter upper bound for all debug counters.

-fdbg-cnt=counter-value-list
Set the internal debug counter lower and upper bound. counter-
value-list is a comma-separated list of
name:lower_bound1-upper_bound1 [:lower_bound2-upper_bound2...]
tuples which sets the name of the counter and list of closed
intervals. The lower_bound is optional and is zero initialized if
not set. For example, with -fdbg-cnt=dce:2-4:10-11,tail_call:10,
"dbg_cnt(dce)" returns true only for second, third, fourth, tenth
and eleventh invocation. For "dbg_cnt(tail_call)" true is returned
for first 10 invocations.

-print-file-name=library
Print the full absolute name of the library file 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.

-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 GCC_EXEC_PREFIX.

-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 ;, and each switch starts with an @ instead of the
-, without spaces between multiple switches. This is supposed to
ease shell processing.

-print-multi-os-directory
Print the path to OS libraries for the selected multilib, relative
to some lib subdirectory. If OS libraries are present in the lib
subdirectory and no multilibs are used, this is usually just ., if
OS libraries are present in libsuffix sibling directories this
prints e.g. ../lib64, ../lib or ../lib32, or if OS libraries are
present in lib/subdir subdirectories it prints e.g. amd64, sparcv9
or ev6.

-print-multiarch
Print the path to OS libraries for the selected multiarch, relative
to some lib subdirectory.

-print-prog-name=program
Like -print-file-name, but searches for a program such as cpp.

-print-libgcc-file-name
Same as -print-file-name=libgcc.a.

This is useful when you use -nostdlib or -nodefaultlibs but you do
want to link with libgcc.a. You can do:

gcc -nostdlib <files>... `gcc -print-libgcc-file-name`

-print-search-dirs
Print the name of the configured installation directory and a list
of program and library directories gcc searches---and don't do
anything else.

This is useful when gcc prints the error message installation
problem, cannot exec cpp0: No such file or directory. To resolve
this you either need to put cpp0 and the other compiler components
where gcc expects to find them, or you can set the environment
variable GCC_EXEC_PREFIX to the directory where you installed them.
Don't forget the trailing /.

-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 --sysroot option, possibly with an extra suffix that
depends on compilation options. If no target sysroot is specified,
the option prints nothing.

-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.

-dumpmachine
Print the compiler's target machine (for example,
i686-pc-linux-gnu)---and don't do anything else.

-dumpversion
Print the compiler version (for example, 3.0, 6.3.0 or 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).

-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.

-dumpspecs
Print the compiler's built-in specs---and don't do anything else.
(This is used when GCC itself is being built.)

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 -m.

Some configurations of the compiler also support additional target-
specific options, usually for compatibility with other compilers on the
same platform.

AArch64 Options

These options are defined for AArch64 implementations:

-mabi=name
Generate code for the specified data model. Permissible values are
ilp32 for SysV-like data model where int, long int and pointers are
32 bits, and 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.

The ilp32 model is deprecated.

-mbig-endian
Generate big-endian code. This is the default when GCC is
configured for an aarch64_be-*-* target.

-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.

-mlittle-endian
Generate little-endian code. This is the default when GCC is
configured for an aarch64-*-* but not an aarch64_be-*-* target.

-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.

-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.

-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 -mcmodel=large option is incompatible with
-mabi=ilp32, -fpic and -fPIC.

-mtp=name
Specify the system register to use as a thread pointer. The valid
values are tpidr_el0, tpidrro_el0, tpidr_el1, tpidr_el2, tpidr_el3.
For backwards compatibility the aliases el0, el1, el2, el3 are also
accepted. The default setting is tpidr_el0. It is recommended to
compile all code intended to interoperate with the same value of
this option to avoid accessing a different thread pointer from the
wrong exception level.

-mstrict-align
-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.

-momit-leaf-frame-pointer
-mno-omit-leaf-frame-pointer
Omit or keep the frame pointer in leaf functions. The former
behavior is the default.

-mstack-protector-guard=guard
-mstack-protector-guard-reg=reg
-mstack-protector-guard-offset=offset
Generate stack protection code using canary at guard. Supported
locations are global for a global canary or sysreg for a canary in
an appropriate system register.

With the latter choice the options -mstack-protector-guard-reg=reg
and -mstack-protector-guard-offset=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.

-mtls-dialect=desc
Use TLS descriptors as the thread-local storage mechanism for
dynamic accesses of TLS variables. This is the default.

-mtls-dialect=traditional
Use traditional TLS as the thread-local storage mechanism for
dynamic accesses of TLS variables.

-mtls-size=size
Specify bit size of immediate TLS offsets. Valid values are 12,
24, 32, 48. This option requires binutils 2.26 or newer.

-mfix-cortex-a53-835769
-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. This flag will be ignored if an architecture or cpu
is specified on the command line which does not need the
workaround.

-mfix-cortex-a53-843419
-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. This
flag will be ignored if an architecture or cpu is specified on the
command line which does not need the workaround.

-mlow-precision-recip-sqrt
-mno-low-precision-recip-sqrt
Enable or disable the reciprocal square root approximation. This
option only has an effect if -ffast-math or
-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.

-mlow-precision-sqrt
-mno-low-precision-sqrt
Enable or disable the square root approximation. This option only
has an effect if -ffast-math or -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 -mlow-precision-recip-sqrt.

-mlow-precision-div
-mno-low-precision-div
Enable or disable the division approximation. This option only has
an effect if -ffast-math or -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.

-mtrack-speculation
-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
"__builtin_speculation_safe_copy" to permit a more efficient code
sequence to be generated.

-moutline-atomics
-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. -march=armv8.1-a
or -march=armv8-a+lse, the ARMv8.1-Atomics instructions will be
used directly. The same applies when using -mcpu= when the
selected cpu supports the lse feature. This option is on by
default.

-march=name
Specify the name of the target architecture and, optionally, one or
more feature modifiers. This option has the form
-march=arch{+[no]feature}*.

The table below summarizes the permissible values for arch and the
features that they enable by default:

arch value : Architecture : Includes by default
armv8-a : Armv8-A : +fp, +simd
armv8.1-a : Armv8.1-A : armv8-a, +crc, +lse, +rdma
armv8.2-a : Armv8.2-A : armv8.1-a
armv8.3-a : Armv8.3-A : armv8.2-a, +pauth, +fcma, +jscvt
armv8.4-a : Armv8.4-A : armv8.3-a, +flagm, +fp16fml, +dotprod,
+rcpc2
armv8.5-a : Armv8.5-A : armv8.4-a, +sb, +ssbs, +predres, +frintts,
+flagm2
armv8.6-a : Armv8.6-A : armv8.5-a, +bf16, +i8mm
armv8.7-a : Armv8.7-A : armv8.6-a, +wfxt, +xs
armv8.8-a : Armv8.8-a : armv8.7-a, +mops
armv8.9-a : Armv8.9-a : armv8.8-a
armv9-a : Armv9-A : armv8.5-a, +sve, +sve2
armv9.1-a : Armv9.1-A : armv9-a, +bf16, +i8mm
armv9.2-a : Armv9.2-A : armv9.1-a, +wfxt, +xs
armv9.3-a : Armv9.3-A : armv9.2-a, +mops
armv9.4-a : Armv9.4-A : armv9.3-a, +sve2p1
armv9.5-a : Armv9.4-A : armv9.4-a, cpa, +faminmax, +lut
armv8-r : Armv8-R : armv8-r

The value 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. When -march=native is given
and no other -mcpu or -mtune is given then GCC will pick the host
CPU as the CPU to tune for as well as select the architecture
features from. That is, -march=native is treated as -mcpu=native.

The permissible values for feature are listed in the sub-section on
aarch64-feature-modifiers,,-march and -mcpu Feature Modifiers.
Where conflicting feature modifiers are specified, the right-most
feature is used.

GCC uses name to determine what kind of instructions it can emit
when generating assembly code. If -march is specified without
either of -mtune or -mcpu also being specified, the code is tuned
to perform well across a range of target processors implementing
the target architecture.

-mtune=name
Specify the name of the target processor for which GCC should tune
the performance of the code. Permissible values for this option
are: generic, cortex-a35, cortex-a53, cortex-a55, cortex-a57,
cortex-a72, cortex-a73, cortex-a75, cortex-a76, cortex-a76ae,
cortex-a77, cortex-a65, cortex-a65ae, cortex-a34, cortex-a78,
cortex-a78ae, cortex-a78c, ares, exynos-m1, emag, falkor, oryon-1,
neoverse-512tvb, neoverse-e1, neoverse-n1, neoverse-n2,
neoverse-v1, neoverse-v2, grace, neoverse-v3, neoverse-v3ae,
neoverse-n3, olympus, cortex-a725, cortex-x925, qdf24xx, saphira,
phecda, xgene1, vulcan, octeontx, octeontx81, octeontx83,
octeontx2, octeontx2t98, octeontx2t96 octeontx2t93, octeontx2f95,
octeontx2f95n, octeontx2f95mm, a64fx, fujitsu-monaka, thunderx,
thunderxt88, thunderxt88p1, thunderxt81, tsv110, thunderxt83,
thunderx2t99, thunderx3t110, zeus, cortex-a57.cortex-a53,
cortex-a72.cortex-a53, cortex-a73.cortex-a35,
cortex-a73.cortex-a53, cortex-a75.cortex-a55,
cortex-a76.cortex-a55, cortex-r82, cortex-r82ae, cortex-x1,
cortex-x1c, cortex-x2, cortex-x3, cortex-x4, cortex-a510,
cortex-a520, cortex-a520ae, cortex-a710, cortex-a715, cortex-a720,
cortex-a720ae, ampere1, ampere1a, ampere1b, cobalt-100 and native.

The values cortex-a57.cortex-a53, cortex-a72.cortex-a53,
cortex-a73.cortex-a35, cortex-a73.cortex-a53,
cortex-a75.cortex-a55, cortex-a76.cortex-a55 specify that GCC
should tune for a big.LITTLE system.

The value 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 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 -mtune=, -mcpu= or -march= are specified, the code is
tuned to perform well across a range of target processors.

This option cannot be suffixed by feature modifiers.

-mcpu=name
Specify the name of the target processor, optionally suffixed by
one or more feature modifiers. This option has the form
-mcpu=cpu{+[no]feature}*, where the permissible values for cpu are
the same as those available for -mtune. The permissible values for
feature are documented in the sub-section on
aarch64-feature-modifiers,,-march and -mcpu Feature Modifiers.
Where conflicting feature modifiers are specified, the right-most
feature is used.

GCC uses name to determine what kind of instructions it can emit
when generating assembly code (as if by -march) and to determine
the target processor for which to tune for performance (as if by
-mtune). Where this option is used in conjunction with -march or
-mtune, those options take precedence over the appropriate part of
this 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 -march, -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 -mtune, -mcpu=neoverse-512tvb tunes code in the same
way as for -mtune=neoverse-512tvb.

-moverride=string
Override tuning decisions made by the back-end in response to a
-mtune= switch. The syntax, semantics, and accepted values for
string in this option are not guaranteed to be consistent across
releases.

This option is only intended to be useful when developing GCC.

-mverbose-cost-dump
Enable verbose cost model dumping in the debug dump files. This
option is provided for use in debugging the compiler.

-mpc-relative-literal-loads
-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 -mcmodel=tiny.

-msign-return-address=scope
Select the function scope on which return address signing will be
applied. Permissible values are none, which disables return
address signing, non-leaf, which enables pointer signing for
functions which are not leaf functions, and all, which enables
pointer signing for all functions. The default value is none. This
option has been deprecated by -mbranch-protection.

-mbranch-protection=none|standard|pac-ret[+leaf+b-key]|bti|gcs
Select the branch protection features to use. none is the default
and turns off all types of branch protection. standard turns on
all types of branch protection features. If a feature has
additional tuning options, then standard sets it to its standard
level. pac-ret[+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 leaf can be used to extend the
signing to include leaf functions. The optional argument b-key can
be used to sign the functions with the B-key instead of the A-key.
bti turns on branch target identification mechanism. gcs turns on
guarded control stack compatible code generation.

-mharden-sls=opts
Enable compiler hardening against straight line speculation (SLS).
opts is a comma-separated list of the following options:

retbr
blr

In addition, -mharden-sls=all enables all SLS hardening while
-mharden-sls=none disables all SLS hardening.

-mearly-ra=scope
Determine when to enable an early register allocation pass. This
pass runs before instruction scheduling and tries to find a spill-
free allocation of floating-point and vector code. It also tries
to make use of strided multi-register instructions, such as SME2's
strided LD1 and ST1.

The possible values of scope are: all, which runs the pass on all
functions; strided, which runs the pass on functions that have
access to strided multi-register instructions; and none, which
disables the pass.

-mearly-ra=all is the default for -O2 and above, and for -Os.
-mearly-ra=none is the default otherwise.

-mearly-ldp-fusion
Enable the copy of the AArch64 load/store pair fusion pass that
runs before register allocation. Enabled by default at -O and
above.

-mlate-ldp-fusion
Enable the copy of the AArch64 load/store pair fusion pass that
runs after register allocation. Enabled by default at -O and
above.

-msve-vector-bits=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 bits are: scalable, 128, 256, 512, 1024 and
2048. Specifying scalable selects vector-length agnostic output.
At present -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 scalable should be
relied on for producing code that is portable across different
hardware SVE vector lengths.

The default is -msve-vector-bits=scalable, which produces vector-
length agnostic code.

-Wexperimental-fmv-target
Warn about use of experimental Function Multi Versioning. The Arm
C Language Extension specification for Function Multi Versioning is
beta and subject to change. Any usage of FMV is caveated that
future behavior change and incompatibility is likely.

-march and -mcpu Feature Modifiers

Feature modifiers used with -march and -mcpu can be any of the
following and their inverses nofeature:

crc Enable CRC extension. This is on by default for -march=armv8.1-a.

crypto
Enable Crypto extension. This also enables Advanced SIMD and
floating-point instructions.

fp Enable floating-point instructions. This is on by default for all
possible values for options -march and -mcpu.

simd
Enable Advanced SIMD instructions. This also enables floating-
point instructions. This is on by default for all possible values
for options -march and -mcpu.

sve Enable Scalable Vector Extension instructions. This also enables
Advanced SIMD and floating-point instructions.

lse Enable Large System Extension instructions. This is on by default
for -march=armv8.1-a.

rdma
Enable Round Double Multiply Accumulate instructions. This is on
by default for -march=armv8.1-a.

fp16
Enable FP16 extension. This also enables floating-point
instructions.

fp16fml
Enable FP16 fmla extension. This also enables FP16 extensions and
floating-point instructions. This option is enabled by default for
-march=armv8.4-a. Use of this option with architectures prior to
Armv8.2-A is not supported.

rcpc
Enable the RCpc extension. This enables the use of the LDAPR
instructions for load-acquire atomic semantics, and passes it on to
the assembler, enabling inline asm statements to use instructions
from the RCpc extension.

dotprod
Enable the Dot Product extension. This also enables Advanced SIMD
instructions.

aes Enable the Armv8-a aes and pmull crypto extension. This also
enables Advanced SIMD instructions.

sha2
Enable the Armv8-a sha2 crypto extension. This also enables
Advanced SIMD instructions.

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.

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.

profile
Enable the Statistical Profiling extension. This option is only to
enable the extension at the assembler level and does not affect
code generation.

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.

memtag
Enable the Armv8.5-a Memory Tagging Extensions. Use of this option
with architectures prior to Armv8.5-A is not supported.

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
-march=armv8.5-a.

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 -march=armv8.5-a.

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 -march=armv8.5-a.

sve2
Enable the Armv8-a Scalable Vector Extension 2. This also enables
SVE instructions.

sve2-bitperm
Enable SVE2 bitperm instructions. This also enables SVE2
instructions.

sve2-sm4
Enable SVE2 sm4 instructions. This also enables SVE2 instructions.

sve2-aes
Enable SVE2 aes instructions. This also enables SVE2 instructions.

sve2-sha3
Enable SVE2 sha3 instructions. This also enables SVE2
instructions.

sve2p1
Enable SVE2.1 instructions. This also enables SVE2 instructions.

tme Enable the Transactional Memory Extension.

i8mm
Enable 8-bit Integer Matrix Multiply instructions. This also
enables Advanced SIMD and floating-point instructions. This option
is enabled by default for -march=armv8.6-a. Use of this option
with architectures prior to Armv8.2-A is not supported.

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.

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.

bf16
Enable brain half-precision floating-point instructions. This also
enables Advanced SIMD and floating-point instructions. This option
is enabled by default for -march=armv8.6-a. Use of this option
with architectures prior to Armv8.2-A is not supported.

ls64
Enable the 64-byte atomic load and store instructions for
accelerators.

mops
Enable the instructions to accelerate memory operations like
"memcpy", "memmove", "memset". This option is enabled by default
for -march=armv8.8-a

flagm
Enable the Flag Manipulation instructions Extension.

flagm2
Enable the FlagM2 flag conversion instructions.

pauth
Enable the Pointer Authentication Extension.

cssc
Enable the Common Short Sequence Compression instructions.

sme Enable the Scalable Matrix Extension.

sme-i16i64
Enable the FEAT_SME_I16I64 extension to SME. This also enables SME
instructions.

sme-f64f64
Enable the FEAT_SME_F64F64 extension to SME. This also enables SME
instructions.

sme2
Enable the Scalable Matrix Extension 2. This also enables SME
instructions.

sme-b16b16
Enable the FEAT_SME_B16B16 extension to SME. This also enables
SME2 and SVE_B16B16 instructions.

sme-f16f16
Enable the FEAT_SME_F16F16 extension to SME. This also enables
SME2 instructions.

sme2p1
Enable the Scalable Matrix Extension version 2.1. This also
enables SME2 instructions.

fcma
Enable the complex number SIMD extensions.

jscvt
Enable the "fjcvtzs" JavaScript conversion instruction.

frintts
Enable floating-point round to integral value instructions.

wfxt
Enable "wfet" and "wfit" instructions.

xs Enable the XS memory attribute extension.

lse128
Enable the LSE128 128-bit atomic instructions extension. This also
enables LSE instructions.

d128
Enable support for 128-bit system register read/write instructions.
This also enables the LSE128 extension.

gcs Enable support for Armv9.4-a Guarded Control Stack extension.

the Enable support for Armv8.9-a/9.4-a translation hardening extension.

rcpc2
Enable the RCpc2 extension.

rcpc3
Enable the RCpc3 (Release Consistency) extension.

fp8 Enable the fp8 (8-bit floating point) extension.

fp8fma
Enable the fp8 (8-bit floating point) multiply accumulate
extension.

ssve-fp8fma
Enable the fp8 (8-bit floating point) multiply accumulate extension
in streaming mode.

fp8dot4
Enable the fp8 (8-bit floating point) to single-precision 4-way dot
product extension.

ssve-fp8dot4
Enable the fp8 (8-bit floating point) to single-precision 4-way dot
product extension in streaming mode.

fp8dot2
Enable the fp8 (8-bit floating point) to half-precision 2-way dot
product extension.

ssve-fp8dot2
Enable the fp8 (8-bit floating point) to half-precision 2-way dot
product extension in streaming mode.

faminmax
Enable the Floating Point Absolute Maximum/Minimum extension.

lut Enable the Lookup Table extension.

cpa Enable the Checked Pointer Arithmetic instructions.

sve-b16b16
Enable the SVE non-widening brain floating-point ("bf16")
extension. This only has an effect when "sve2" or "sme2" are also
enabled.

Feature crypto implies aes, sha2, and simd, which implies fp.
Conversely, nofp implies nosimd, which implies nocrypto, noaes and
nosha2.

Adapteva Epiphany Options

These -m options are defined for Adapteva Epiphany:

-mhalf-reg-file
Don't allocate any register in the range "r32"..."r63". That
allows code to run on hardware variants that lack these registers.

-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.

-mbranch-cost=num
Set the cost of branches to roughly num "simple" instructions.
This cost is only a heuristic and is not guaranteed to produce
consistent results across releases.

-mcmove
Enable the generation of conditional moves.

-mnops=num
Emit num NOPs before every other generated instruction.

-mno-soft-cmpsf
For single-precision floating-point comparisons, emit an "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 -msoft-cmpsf,
which uses slower, but IEEE-compliant, software comparisons.

-mstack-offset=num
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
"sp+0...sp+7" can be used by leaf functions without stack
allocation. Values other than 8 or 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 --with-stack-offset=num option.

-mno-round-nearest
Make the scheduler assume that the rounding mode has been set to
truncating. The default is -mround-nearest.

-mlong-calls
If not otherwise specified by an attribute, assume all calls might
be beyond the offset range of the "b" / "bl" instructions, and
therefore load the function address into a register before
performing a (otherwise direct) call. This is the default.

-mshort-calls
If not otherwise specified by an attribute, assume all direct calls
are in the range of the "b" / "bl" instructions, so use these
instructions for direct calls. The default is -mlong-calls.

-msmall16
Assume addresses can be loaded as 16-bit unsigned values. This
does not apply to function addresses for which -mlong-calls
semantics are in effect.

-mfp-mode=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.

mode can be set to one the following values:

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.

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.

round-nearest
This is the mode used for floating-point calculations with
round-to-nearest-or-even rounding mode.

int This is the mode used to perform integer calculations in the
FPU, e.g. integer multiply, or integer multiply-and-
accumulate.

The default is -mfp-mode=caller

-mno-split-lohi
-mno-postinc
-mno-postmodify
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 msplit-lohi,
-mpost-inc, and -mpost-modify.

-mnovect-double
Change the preferred SIMD mode to SImode. The default is
-mvect-double, which uses DImode as preferred SIMD mode.

-max-vect-align=num
The maximum alignment for SIMD vector mode types. 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.

-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.

-m1reg-reg
Specify a register to hold the constant -1, which makes loading
small negative constants and certain bitmasks faster. Allowable
values for reg are r43 and r63, which specify use of that register
as a fixed register, and none, which means that no register is used
for this purpose. The default is -m1reg-none.

AMD GCN Options

These options are defined specifically for the AMD GCN port.

-march=gpu
-mtune=gpu
Set architecture type or tuning for gpu. Supported values for gpu
are

gfx900
Compile for GCN5 Vega 10 devices (gfx900).

gfx902
Compile for GCN5 Vega gfx902 devices. (Experimental)

gfx904
Compile for GCN5 Vega gfx904 devices. (Experimental)

gfx906
Compile for GCN5 Vega 20 devices (gfx906).

gfx908
Compile for CDNA1 Instinct MI100 series devices (gfx908).

gfx909
Compile for GCN5 Vega gfx909 devices. (Experimental)

gfx90a
Compile for CDNA2 Instinct MI200 series devices (gfx90a).

gfx90c
Compile for GCN5 Vega 7 devices (gfx90c).

gfx9-generic
Compile generic code for Vega devices, executable on the
following subset of GFX9 devices: gfx900, gfx902, gfx904,
gfx906, gfx909 and gfx90c. (Experimental)

gfx1030
Compile for RDNA2 gfx1030 devices (GFX10 series).

gfx1031
Compile for RDNA2 gfx1031 devices (GFX10 series).
(Experimental)

gfx1032
Compile for RDNA2 gfx1032 devices (GFX10 series).
(Experimental)

gfx1033
Compile for RDNA2 gfx1033 devices (GFX10 series).
(Experimental)

gfx1034
Compile for RDNA2 gfx1034 devices (GFX10 series).
(Experimental)

gfx1035
Compile for RDNA2 gfx1035 devices (GFX10 series).
(Experimental)

gfx1036
Compile for RDNA2 gfx1036 devices (GFX10 series).

gfx10-3-generic
Compile generic code for GFX10-3 devices, executable on
gfx1030, gfx1031, gfx1032, gfx1033, gfx1034, gfx1035, and
gfx1036. (Experimental)

gfx1100
Compile for RDNA3 gfx1100 devices (GFX11 series).

gfx1101
Compile for RDNA3 gfx1101 devices (GFX11 series).
(Experimental)

gfx1102
Compile for RDNA3 gfx1102 devices (GFX11 series).
(Experimental)

gfx1103
Compile for RDNA3 gfx1103 devices (GFX11 series).

gfx1150
Compile for RDNA3 gfx1150 devices (GFX11 series).
(Experimental)

gfx1151
Compile for RDNA3 gfx1151 devices (GFX11 series).
(Experimental)

gfx1152
Compile for RDNA3 gfx1152 devices (GFX11 series).
(Experimental)

gfx1153
Compile for RDNA3 gfx1153 devices (GFX11 series).
(Experimental)

gfx11-generic
Compile generic code for GFX11 devices, executable on gfx1100,
gfx1101, gfx1102, gfx1103, gfx1150, gfx1151, gfx1152, and
gfx1153. (Experimental)

-msram-ecc=on
-msram-ecc=off
-msram-ecc=any
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 any, for devices that support it.

-mstack-size=bytes
Specify how many 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.

-mxnack=on
-mxnack=off
-mxnack=any
Compile binaries suitable for devices with the XNACK feature
enabled, disabled, or either mode. Some devices always require
XNACK and some allow the user to configure XNACK. The compiled
code must match the device mode. The default is -mxnack=any on
devices that support Unified Shared Memory, and -mxnack=no
otherwise.

ARC Options

The following options control the architecture variant for which code
is being compiled:

-mbarrel-shifter
Generate instructions supported by barrel shifter. This is the
default unless -mcpu=ARC601 or -mcpu=ARCEM is in effect.

-mjli-always
Force to call a function using jli_s instruction. This option is
valid only for ARCv2 architecture.

-mcpu=cpu
Set architecture type, register usage, and instruction scheduling
parameters for cpu. There are also shortcut alias options
available for backward compatibility and convenience. Supported
values for cpu are

arc600
Compile for ARC600. Aliases: -mA6, -mARC600.

arc601
Compile for ARC601. Alias: -mARC601.

arc700
Compile for ARC700. Aliases: -mA7, -mARC700. This is the
default when configured with --with-cpu=arc700.

arcem
Compile for ARC EM.

archs
Compile for ARC HS.

em Compile for ARC EM CPU with no hardware extensions.

em4 Compile for ARC EM4 CPU.

em4_dmips
Compile for ARC EM4 DMIPS CPU.

em4_fpus
Compile for ARC EM4 DMIPS CPU with the single-precision
floating-point extension.

em4_fpuda
Compile for ARC EM4 DMIPS CPU with single-precision floating-
point and double assist instructions.

hs Compile for ARC HS CPU with no hardware extensions except the
atomic instructions.

hs34
Compile for ARC HS34 CPU.

hs38
Compile for ARC HS38 CPU.

hs38_linux
Compile for ARC HS38 CPU with all hardware extensions on.

hs4x
Compile for ARC HS4x CPU.

hs4xd
Compile for ARC HS4xD CPU.

hs4x_rel31
Compile for ARC HS4x CPU release 3.10a.

arc600_norm
Compile for ARC 600 CPU with "norm" instructions enabled.

arc600_mul32x16
Compile for ARC 600 CPU with "norm" and 32x16-bit multiply
instructions enabled.

arc600_mul64
Compile for ARC 600 CPU with "norm" and "mul64"-family
instructions enabled.

arc601_norm
Compile for ARC 601 CPU with "norm" instructions enabled.

arc601_mul32x16
Compile for ARC 601 CPU with "norm" and 32x16-bit multiply
instructions enabled.

arc601_mul64
Compile for ARC 601 CPU with "norm" and "mul64"-family
instructions enabled.

nps400
Compile for ARC 700 on NPS400 chip.

em_mini
Compile for ARC EM minimalist configuration featuring reduced
register set.

-mdpfp
-mdpfp-compact
Generate double-precision FPX instructions, tuned for the compact
implementation.

-mdpfp-fast
Generate double-precision FPX instructions, tuned for the fast
implementation.

-mno-dpfp-lrsr
Disable "lr" and "sr" instructions from using FPX extension aux
registers.

-mea
Generate extended arithmetic instructions. Currently only "divaw",
"adds", "subs", and "sat16" are supported. Only valid for
-mcpu=ARC700.

-mno-mpy
Do not generate "mpy"-family instructions for ARC700. This option
is deprecated.

-mmul32x16
Generate 32x16-bit multiply and multiply-accumulate instructions.

-mmul64
Generate "mul64" and "mulu64" instructions. Only valid for
-mcpu=ARC600.

-mnorm
Generate "norm" instructions. This is the default if -mcpu=ARC700
is in effect.

-mspfp
-mspfp-compact
Generate single-precision FPX instructions, tuned for the compact
implementation.

-mspfp-fast
Generate single-precision FPX instructions, tuned for the fast
implementation.

-msimd
Enable generation of ARC SIMD instructions via target-specific
builtins. Only valid for -mcpu=ARC700.

-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; -mspfp, -mspfp-compact, or
-mspfp-fast for single precision, and -mdpfp, -mdpfp-compact, or
-mdpfp-fast for double precision.

-mswap
Generate "swap" instructions.

-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.

-mdiv-rem
Enable "div" and "rem" instructions for ARCv2 cores.

-mcode-density
Enable code density instructions for ARC EM. This option is on by
default for ARC HS.

-mll64
Enable double load/store operations for ARC HS cores.

-mtp-regno=regno
Specify thread pointer register number.

-mmpy-option=multo
Compile ARCv2 code with a multiplier design option. You can
specify the option using either a string or numeric value for
multo. wlh1 is the default value. The recognized values are:

0
none
No multiplier available.

1
w 16x16 multiplier, fully pipelined. The following instructions
are enabled: "mpyw" and "mpyuw".

2
wlh1
32x32 multiplier, fully pipelined (1 stage). The following
instructions are additionally enabled: "mpy", "mpyu", "mpym",
"mpymu", and "mpy_s".

3
wlh2
32x32 multiplier, fully pipelined (2 stages). The following
instructions are additionally enabled: "mpy", "mpyu", "mpym",
"mpymu", and "mpy_s".

4
wlh3
Two 16x16 multipliers, blocking, sequential. The following
instructions are additionally enabled: "mpy", "mpyu", "mpym",
"mpymu", and "mpy_s".

5
wlh4
One 16x16 multiplier, blocking, sequential. The following
instructions are additionally enabled: "mpy", "mpyu", "mpym",
"mpymu", and "mpy_s".

6
wlh5
One 32x4 multiplier, blocking, sequential. The following
instructions are additionally enabled: "mpy", "mpyu", "mpym",
"mpymu", and "mpy_s".

7
plus_dmpy
ARC HS SIMD support.

8
plus_macd
ARC HS SIMD support.

9
plus_qmacw
ARC HS SIMD support.

This option is only available for ARCv2 cores.

-mfpu=fpu
Enables support for specific floating-point hardware extensions for
ARCv2 cores. Supported values for fpu are:

fpus
Enables support for single-precision floating-point hardware
extensions.

fpud
Enables support for double-precision floating-point hardware
extensions. The single-precision floating-point extension is
also enabled. Not available for ARC EM.

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.

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.

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.

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.

fpus_div
Enables support for single-precision floating-point, square-
root and divide hardware extensions.

fpud_div
Enables support for double-precision floating-point, square-
root and divide hardware extensions. This option includes
option fpus_div. Not available for ARC EM.

fpus_fma
Enables support for single-precision floating-point and fused
multiply and add hardware extensions.

fpud_fma
Enables support for double-precision floating-point and fused
multiply and add hardware extensions. This option includes
option fpus_fma. Not available for ARC EM.

fpus_all
Enables support for all single-precision floating-point
hardware extensions.

fpud_all
Enables support for all single- and double-precision floating-
point hardware extensions. Not available for ARC EM.

-mirq-ctrl-saved=register-range, blink, lp_count
Specifies general-purposes registers that the processor
automatically saves/restores on interrupt entry and exit.
register-range is specified as two registers separated by a dash.
The register range always starts with "r0", the upper limit is "fp"
register. blink and lp_count are optional. This option is only
valid for ARC EM and ARC HS cores.

-mrgf-banked-regs=number
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.

-mlpc-width=width
Specify the width of the "lp_count" register. Valid values for
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 "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 "__ARC_LPC_WIDTH__" with the value of width.

-mrf16
This option instructs the compiler to generate code for a 16-entry
register file. This option defines the "__ARC_RF16__" preprocessor
macro.

-mbranch-index
Enable use of "bi" or "bih" instructions to implement jump tables.

The following options are passed through to the assembler, and also
define preprocessor macro symbols.

-mdsp-packa
Passed down to the assembler to enable the DSP Pack A extensions.
Also sets the preprocessor symbol "__Xdsp_packa". This option is
deprecated.

-mdvbf
Passed down to the assembler to enable the dual Viterbi butterfly
extension. Also sets the preprocessor symbol "__Xdvbf". This
option is deprecated.

-mlock
Passed down to the assembler to enable the locked load/store
conditional extension. Also sets the preprocessor symbol
"__Xlock".

-mmac-d16
Passed down to the assembler. Also sets the preprocessor symbol
"__Xxmac_d16". This option is deprecated.

-mmac-24
Passed down to the assembler. Also sets the preprocessor symbol
"__Xxmac_24". This option is deprecated.

-mrtsc
Passed down to the assembler to enable the 64-bit time-stamp
counter extension instruction. Also sets the preprocessor symbol
"__Xrtsc". This option is deprecated.

-mswape
Passed down to the assembler to enable the swap byte ordering
extension instruction. Also sets the preprocessor symbol
"__Xswape".

-mtelephony
Passed down to the assembler to enable dual- and single-operand
instructions for telephony. Also sets the preprocessor symbol
"__Xtelephony". This option is deprecated.

-mxy
Passed down to the assembler to enable the XY memory extension.
Also sets the preprocessor symbol "__Xxy".

The following options control how the assembly code is annotated:

-misize
Annotate assembler instructions with estimated addresses.

-mannotate-align
Does nothing. Preserved for backward compatibility.

The following options are passed through to the linker:

-marclinux
Passed through to the linker, to specify use of the "arclinux"
emulation. This option is enabled by default in tool chains built
for "arc-linux-uclibc" and "arceb-linux-uclibc" targets when
profiling is not requested.

-marclinux_prof
Passed through to the linker, to specify use of the "arclinux_prof"
emulation. This option is enabled by default in tool chains built
for "arc-linux-uclibc" and "arceb-linux-uclibc" targets when
profiling is requested.

The following options control the semantics of generated code:

-mlong-calls
Generate calls as register indirect calls, thus providing access to
the full 32-bit address range.

-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
"arc-linux-uclibc" and "arceb-linux-uclibc" targets.

-G num
Put definitions of externally-visible data in a small data section
if that data is no bigger than num bytes. The default value of num
is 4 for any ARC configuration, or 8 when we have double load/store
operations.

-mno-sdata
Do not generate sdata references. This is the default for tool
chains built for "arc-linux-uclibc" and "arceb-linux-uclibc"
targets.

-mvolatile-cache
Use ordinarily cached memory accesses for volatile references.
This is the default.

-mno-volatile-cache
Enable cache bypass for volatile references.

The following options fine tune code generation:

-malign-call
Does nothing. Preserved for backward compatibility.

-mauto-modify-reg
Enable the use of pre/post modify with register displacement.

-mbbit-peephole
Does nothing. Preserved for backward compatibility.

-mno-brcc
This option disables a target-specific pass in arc_reorg to
generate compare-and-branch ("brcc") instructions. It has no
effect on generation of these instructions driven by the combiner
pass.

-mcase-vector-pcrel
Use PC-relative switch case tables to enable case table shortening.
This is the default for -Os.

-mcompact-casesi
Enable compact "casesi" pattern. This is the default for -Os, and
only available for ARCv1 cores. This option is deprecated.

-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 -mmedium-calls instead.

-mearly-cbranchsi
Enable pre-reload use of the "cbranchsi" pattern.

-mexpand-adddi
Expand "adddi3" and "subdi3" at RTL generation time into "add.f",
"adc" etc. This option is deprecated.

-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.

-mlra
Does nothing. Preserved for backward compatibility.

-mlra-priority-none
Don't indicate any priority for target registers.

-mlra-priority-compact
Indicate target register priority for r0..r3 / r12..r15.

-mlra-priority-noncompact
Reduce target register priority for r0..r3 / r12..r15.

-mmillicode
When optimizing for size (using -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 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.

-mcode-density-frame
This option enable the compiler to emit "enter" and "leave"
instructions. These instructions are only valid for CPUs with
code-density feature.

-mmixed-code
Does nothing. Preserved for backward compatibility.

-mq-class
Ths option is deprecated. Enable q instruction alternatives. This
is the default for -Os.

-mRcq
Does nothing. Preserved for backward compatibility.

-mRcw
Does nothing. Preserved for backward compatibility.

-msize-level=level
Fine-tune size optimization with regards to instruction lengths and
alignment. The recognized values for level are:

0 No size optimization. This level is deprecated and treated
like 1.

1 Short instructions are used opportunistically.

2 In addition, alignment of loops and of code after barriers are
dropped.

3 In addition, optional data alignment is dropped, and the option
Os is enabled.

This defaults to 3 when -Os is in effect. Otherwise, the behavior
when this is not set is equivalent to level 1.

-mtune=cpu
Set instruction scheduling parameters for cpu, overriding any
implied by -mcpu=.

Supported values for cpu are

ARC600
Tune for ARC600 CPU.

ARC601
Tune for ARC601 CPU.

ARC700
Tune for ARC700 CPU with standard multiplier block.

ARC700-xmac
Tune for ARC700 CPU with XMAC block.

ARC725D
Tune for ARC725D CPU.

ARC750D
Tune for ARC750D CPU.

core3
Tune for ARCv2 core3 type CPU. This option enable usage of
"dbnz" instruction.

release31a
Tune for ARC4x release 3.10a.

-mmultcost=num
Cost to assume for a multiply instruction, with 4 being equal to a
normal instruction.

-munalign-prob-threshold=probability
Does nothing. Preserved for backward compatibility.

The following options are maintained for backward compatibility, but
are now deprecated and will be removed in a future release:

-margonaut
Obsolete FPX.

-mbig-endian
-EB Compile code for big-endian targets. Use of these options is now
deprecated. Big-endian code is supported by configuring GCC to
build "arceb-elf32" and "arceb-linux-uclibc" targets, for which big
endian is the default.

-mlittle-endian
-EL Compile code for little-endian targets. Use of these options is
now deprecated. Little-endian code is supported by configuring GCC
to build "arc-elf32" and "arc-linux-uclibc" targets, for which
little endian is the default.

-mbarrel_shifter
Replaced by -mbarrel-shifter.

-mdpfp_compact
Replaced by -mdpfp-compact.

-mdpfp_fast
Replaced by -mdpfp-fast.

-mdsp_packa
Replaced by -mdsp-packa.

-mEA
Replaced by -mea.

-mmac_24
Replaced by -mmac-24.

-mmac_d16
Replaced by -mmac-d16.

-mspfp_compact
Replaced by -mspfp-compact.

-mspfp_fast
Replaced by -mspfp-fast.

-mtune=cpu
Values arc600, arc601, arc700 and arc700-xmac for cpu are replaced
by ARC600, ARC601, ARC700 and ARC700-xmac respectively.

-multcost=num
Replaced by -mmultcost.

ARM Options

These -m options are defined for the ARM port:

-mabi=name
Generate code for the specified ABI. Permissible values are: apcs-
gnu, atpcs, aapcs, aapcs-linux and iwmmxt.

-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
-fomit-frame-pointer with this option causes the stack frames not
to be generated for leaf functions. The default is
-mno-apcs-frame. This option is deprecated.

-mapcs
This is a synonym for -mapcs-frame and is deprecated.

-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 -mno-thumb-interwork, since slightly
larger code is generated when -mthumb-interwork is specified. In
AAPCS configurations this option is meaningless.

-mno-sched-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 -msched-prolog.

-mfloat-abi=name
Specifies which floating-point ABI to use. Permissible values are:
soft, softfp and hard.

Specifying soft causes GCC to generate output containing library
calls for floating-point operations. softfp allows the generation
of code using hardware floating-point instructions, but still uses
the soft-float calling conventions. 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.

-mlittle-endian
Generate code for a processor running in little-endian mode. This
is the default for all standard configurations.

-mbig-endian
Generate code for a processor running in big-endian mode; the
default is to compile code for a little-endian processor.

-mbe8
-mbe32
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.

-march=name[+extension...]
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 -mcpu= option.

Permissible names are: armv4t, armv5t, armv5te, armv6, armv6j,
armv6k, armv6kz, armv6t2, armv6z, armv6zk, armv7, armv7-a, armv7ve,
armv8-a, armv8.1-a, armv8.2-a, armv8.3-a, armv8.4-a, armv8.5-a,
armv8.6-a, armv9-a, armv7-r, armv8-r, armv6-m, armv6s-m, armv7-m,
armv7e-m, armv8-m.base, armv8-m.main, armv8.1-m.main, iwmmxt and
iwmmxt2.

Additionally, the following architectures, which lack support for
the Thumb execution state, are recognized but support is
deprecated: armv4.

Many of the architectures support extensions. These can be added
by appending +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 +crypto extension will always enable
the +simd extension. The exception to the additive construction is
for extensions that are prefixed with +no...: these extensions
disable the specified option and any other extensions that may
depend on the presence of that extension.

For example, -march=armv7-a+simd+nofp+vfpv4 is equivalent to
writing -march=armv7-a+vfpv4 since the +simd option is entirely
disabled by the +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 +simd option can be applied to both armv7-a and
armv8-a architectures, but will enable the original ARMv7-A
Advanced SIMD (Neon) extensions for armv7-a and the ARMv8-A variant
for armv8-a.

The table below lists the supported extensions for each
architecture. Architectures not mentioned do not support any
extensions.

armv5te
armv6
armv6j
armv6k
armv6kz
armv6t2
armv6z
armv6zk
+fp The VFPv2 floating-point instructions. The extension
+vfpv2 can be used as an alias for this extension.

+nofp
Disable the floating-point instructions.

armv7
The common subset of the ARMv7-A, ARMv7-R and ARMv7-M
architectures.

+fp The VFPv3 floating-point instructions, with 16 double-
precision registers. The extension +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.

+nofp
Disable the floating-point instructions.

armv7-a
+mp The multiprocessing extension.

+sec
The security extension.

+fp The VFPv3 floating-point instructions, with 16 double-
precision registers. The extension +vfpv3-d16 can be used
as an alias for this extension.

+simd
The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
instructions. The extensions +neon and +neon-vfpv3 can be
used as aliases for this extension.

+vfpv3
The VFPv3 floating-point instructions, with 32 double-
precision registers.

+vfpv3-d16-fp16
The VFPv3 floating-point instructions, with 16 double-
precision registers and the half-precision floating-point
conversion operations.

+vfpv3-fp16
The VFPv3 floating-point instructions, with 32 double-
precision registers and the half-precision floating-point
conversion operations.

+vfpv4-d16
The VFPv4 floating-point instructions, with 16 double-
precision registers.

+vfpv4
The VFPv4 floating-point instructions, with 32 double-
precision registers.

+neon-fp16
The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
instructions, with the half-precision floating-point
conversion operations.

+neon-vfpv4
The Advanced SIMD (Neon) v2 and the VFPv4 floating-point
instructions.

+nosimd
Disable the Advanced SIMD instructions (does not disable
floating point).

+nofp
Disable the floating-point and Advanced SIMD instructions.

armv7ve
The extended version of the ARMv7-A architecture with support
for virtualization.

+fp The VFPv4 floating-point instructions, with 16 double-
precision registers. The extension +vfpv4-d16 can be used
as an alias for this extension.

+simd
The Advanced SIMD (Neon) v2 and the VFPv4 floating-point
instructions. The extension +neon-vfpv4 can be used as an
alias for this extension.

+vfpv3-d16
The VFPv3 floating-point instructions, with 16 double-
precision registers.

+vfpv3
The VFPv3 floating-point instructions, with 32 double-
precision registers.

+vfpv3-d16-fp16
The VFPv3 floating-point instructions, with 16 double-
precision registers and the half-precision floating-point
conversion operations.

+vfpv3-fp16
The VFPv3 floating-point instructions, with 32 double-
precision registers and the half-precision floating-point
conversion operations.

+vfpv4-d16
The VFPv4 floating-point instructions, with 16 double-
precision registers.

+vfpv4
The VFPv4 floating-point instructions, with 32 double-
precision registers.

+neon
The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
instructions. The extension +neon-vfpv3 can be used as an
alias for this extension.

+neon-fp16
The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
instructions, with the half-precision floating-point
conversion operations.

+nosimd
Disable the Advanced SIMD instructions (does not disable
floating point).

+nofp
Disable the floating-point and Advanced SIMD instructions.

armv8-a
+crc
The Cyclic Redundancy Check (CRC) instructions.

+simd
The ARMv8-A Advanced SIMD and floating-point instructions.

+crypto
The cryptographic instructions.

+nocrypto
Disable the cryptographic instructions.

+nofp
Disable the floating-point, Advanced SIMD and cryptographic
instructions.

+sb Speculation Barrier Instruction.

+predres
Execution and Data Prediction Restriction Instructions.

armv8.1-a
+simd
The ARMv8.1-A Advanced SIMD and floating-point
instructions.

+crypto
The cryptographic instructions. This also enables the
Advanced SIMD and floating-point instructions.

+nocrypto
Disable the cryptographic instructions.

+nofp
Disable the floating-point, Advanced SIMD and cryptographic
instructions.

+sb Speculation Barrier Instruction.

+predres
Execution and Data Prediction Restriction Instructions.

armv8.2-a
armv8.3-a
+fp16
The half-precision floating-point data processing
instructions. This also enables the Advanced SIMD and
floating-point instructions.

+fp16fml
The half-precision floating-point fmla extension. This
also enables the half-precision floating-point extension
and Advanced SIMD and floating-point instructions.

+simd
The ARMv8.1-A Advanced SIMD and floating-point
instructions.

+crypto
The cryptographic instructions. This also enables the
Advanced SIMD and floating-point instructions.

+dotprod
Enable the Dot Product extension. This also enables
Advanced SIMD instructions.

+nocrypto
Disable the cryptographic extension.

+nofp
Disable the floating-point, Advanced SIMD and cryptographic
instructions.

+sb Speculation Barrier Instruction.

+predres
Execution and Data Prediction Restriction Instructions.

+i8mm
8-bit Integer Matrix Multiply instructions. This also
enables Advanced SIMD and floating-point instructions.

+bf16
Brain half-precision floating-point instructions. This
also enables Advanced SIMD and floating-point instructions.

armv8.4-a
+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.

+simd
The ARMv8.3-A Advanced SIMD and floating-point instructions
as well as the Dot Product extension.

+crypto
The cryptographic instructions. This also enables the
Advanced SIMD and floating-point instructions as well as
the Dot Product extension.

+nocrypto
Disable the cryptographic extension.

+nofp
Disable the floating-point, Advanced SIMD and cryptographic
instructions.

+sb Speculation Barrier Instruction.

+predres
Execution and Data Prediction Restriction Instructions.

+i8mm
8-bit Integer Matrix Multiply instructions. This also
enables Advanced SIMD and floating-point instructions.

+bf16
Brain half-precision floating-point instructions. This
also enables Advanced SIMD and floating-point instructions.

armv8.5-a
+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.

+simd
The ARMv8.3-A Advanced SIMD and floating-point instructions
as well as the Dot Product extension.

+crypto
The cryptographic instructions. This also enables the
Advanced SIMD and floating-point instructions as well as
the Dot Product extension.

+nocrypto
Disable the cryptographic extension.

+nofp
Disable the floating-point, Advanced SIMD and cryptographic
instructions.

+i8mm
8-bit Integer Matrix Multiply instructions. This also
enables Advanced SIMD and floating-point instructions.

+bf16
Brain half-precision floating-point instructions. This
also enables Advanced SIMD and floating-point instructions.

armv8.6-a
+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.

+simd
The ARMv8.3-A Advanced SIMD and floating-point instructions
as well as the Dot Product extension.

+crypto
The cryptographic instructions. This also enables the
Advanced SIMD and floating-point instructions as well as
the Dot Product extension.

+nocrypto
Disable the cryptographic extension.

+nofp
Disable the floating-point, Advanced SIMD and cryptographic
instructions.

+i8mm
8-bit Integer Matrix Multiply instructions. This also
enables Advanced SIMD and floating-point instructions.

+bf16
Brain half-precision floating-point instructions. This
also enables Advanced SIMD and floating-point instructions.

armv7-r
+fp.sp
The single-precision VFPv3 floating-point instructions.
The extension +vfpv3xd can be used as an alias for this
extension.

+fp The VFPv3 floating-point instructions with 16 double-
precision registers. The extension +vfpv3-d16 can be used
as an alias for this extension.

+vfpv3xd-d16-fp16
The single-precision VFPv3 floating-point instructions with
16 double-precision registers and the half-precision
floating-point conversion operations.

+vfpv3-d16-fp16
The VFPv3 floating-point instructions with 16 double-
precision registers and the half-precision floating-point
conversion operations.

+nofp
Disable the floating-point extension.

+idiv
The ARM-state integer division instructions.

+noidiv
Disable the ARM-state integer division extension.

armv7e-m
+fp The single-precision VFPv4 floating-point instructions.

+fpv5
The single-precision FPv5 floating-point instructions.

+fp.dp
The single- and double-precision FPv5 floating-point
instructions.

+nofp
Disable the floating-point extensions.

armv8.1-m.main
+dsp
The DSP instructions.

+mve
The M-Profile Vector Extension (MVE) integer instructions.

+mve.fp
The M-Profile Vector Extension (MVE) integer and single
precision floating-point instructions.

+fp The single-precision floating-point instructions.

+fp.dp
The single- and double-precision floating-point
instructions.

+nofp
Disable the floating-point extension.

+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.

+pacbti
Enable the Pointer Authentication and Branch Target
Identification Extension.

armv8-m.main
+dsp
The DSP instructions.

+nodsp
Disable the DSP extension.

+fp The single-precision floating-point instructions.

+fp.dp
The single- and double-precision floating-point
instructions.

+nofp
Disable the floating-point extension.

+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.

armv8-r
+crc
The Cyclic Redundancy Check (CRC) instructions.

+fp.sp
The single-precision FPv5 floating-point instructions.

+simd
The ARMv8-A Advanced SIMD and floating-point instructions.

+crypto
The cryptographic instructions.

+nocrypto
Disable the cryptographic instructions.

+nofp
Disable the floating-point, Advanced SIMD and cryptographic
instructions.

-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.

-march=unset causes the compiler to ignore any -march=... options
that appear earlier on the command line and behave as if the option
was never passed. This is useful to avoid warnings about
conflicting CPU and architecture options when the two produce
different architecture specifications.

-mtune=name
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: arm7tdmi, arm7tdmi-s, arm710t,
arm720t, arm740t, strongarm, strongarm110, strongarm1100,
strongarm1110, arm8, arm810, arm9, arm9e, arm920, arm920t, arm922t,
arm946e-s, arm966e-s, arm968e-s, arm926ej-s, arm940t, arm9tdmi,
arm10tdmi, arm1020t, arm1026ej-s, arm10e, arm1020e, arm1022e,
arm1136j-s, arm1136jf-s, mpcore, mpcorenovfp, arm1156t2-s,
arm1156t2f-s, arm1176jz-s, arm1176jzf-s, generic-armv7-a,
cortex-a5, cortex-a7, cortex-a8, cortex-a9, cortex-a12, cortex-a15,
cortex-a17, cortex-a32, cortex-a35, cortex-a53, cortex-a55,
cortex-a57, cortex-a72, cortex-a73, cortex-a75, cortex-a76,
cortex-a76ae, cortex-a77, cortex-a78, cortex-a78ae, cortex-a78c,
cortex-a710, ares, cortex-r4, cortex-r4f, cortex-r5, cortex-r7,
cortex-r8, cortex-r52, cortex-r52plus, cortex-m0, cortex-m0plus,
cortex-m1, cortex-m3, cortex-m4, cortex-m7, cortex-m23, cortex-m33,
cortex-m35p, cortex-m52, cortex-m55, cortex-m85, cortex-x1,
cortex-x1c, cortex-m1.small-multiply, cortex-m0.small-multiply,
cortex-m0plus.small-multiply, exynos-m1, marvell-pj4, neoverse-n1,
neoverse-n2, neoverse-v1, xscale, iwmmxt, iwmmxt2, ep9312, fa526,
fa626, fa606te, fa626te, fmp626, fa726te, star-mc1, xgene1.

Additionally, this option can specify that GCC should tune the
performance of the code for a big.LITTLE system. Permissible names
are: cortex-a15.cortex-a7, cortex-a17.cortex-a7,
cortex-a57.cortex-a53, cortex-a72.cortex-a53,
cortex-a72.cortex-a35, cortex-a73.cortex-a53,
cortex-a75.cortex-a55, cortex-a76.cortex-a55.

-mtune=generic-arch specifies that GCC should tune the performance
for a blend of processors within architecture 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.

-mtune permits the same extension options as -mcpu, but the
extension options do not affect the tuning of the generated code.

-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.

-mcpu=name[+extension...]
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 -march) and the ARM processor type for which to tune
for performance (as if specified by -mtune). Where this option is
used in conjunction with -march or -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
-mfloat-abi and -mfpu must also be considered: floating-point and
Advanced SIMD instructions will only be used if -mfloat-abi is not
set to soft; and any setting of -mfpu other than auto will override
the available floating-point and SIMD extension instructions.

For example, 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 +nosimd and +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 -mtune.

The following extension options are common to the listed CPUs:

+nodsp
Disable the DSP instructions on cortex-m33, cortex-m35p,
cortex-m52, cortex-m55 and cortex-m85. Also disable the
M-Profile Vector Extension (MVE) integer and single precision
floating-point instructions on cortex-m52, cortex-m55 and
cortex-m85.

+nopacbti
Disable the Pointer Authentication and Branch Target
Identification Extension on cortex-m52 and cortex-m85.

+nomve
Disable the M-Profile Vector Extension (MVE) integer and single
precision floating-point instructions on cortex-m52, cortex-m55
and cortex-m85.

+nomve.fp
Disable the M-Profile Vector Extension (MVE) single precision
floating-point instructions on cortex-m52, cortex-m55 and
cortex-m85.

+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 on cortex-m52, cortex-m55 and star-mc1.

+nofp
Disables the floating-point instructions on arm9e, arm946e-s,
arm966e-s, arm968e-s, arm10e, arm1020e, arm1022e, arm926ej-s,
arm1026ej-s, cortex-r5, cortex-r7, cortex-r8, cortex-m4,
cortex-m7, cortex-m33, cortex-m35p, cortex-m52, cortex-m55 and
cortex-m85. Disables the floating-point and SIMD instructions
on generic-armv7-a, cortex-a5, cortex-a7, cortex-a8, cortex-a9,
cortex-a12, cortex-a15, cortex-a17, cortex-a15.cortex-a7,
cortex-a17.cortex-a7, cortex-a32, cortex-a35, cortex-a53 and
cortex-a55.

+nofp.dp
Disables the double-precision component of the floating-point
instructions on cortex-r5, cortex-r7, cortex-r8, cortex-r52,
cortex-r52plus and cortex-m7.

+nosimd
Disables the SIMD (but not floating-point) instructions on
generic-armv7-a, cortex-a5, cortex-a7 and cortex-a9.

+crypto
Enables the cryptographic instructions on cortex-a32,
cortex-a35, cortex-a53, cortex-a55, cortex-a57, cortex-a72,
cortex-a73, cortex-a75, exynos-m1, xgene1,
cortex-a57.cortex-a53, cortex-a72.cortex-a53,
cortex-a73.cortex-a35, cortex-a73.cortex-a53 and
cortex-a75.cortex-a55.

Additionally the generic-armv7-a pseudo target defaults to VFPv3
with 16 double-precision registers. It supports the following
extension options: mp, sec, vfpv3-d16, vfpv3, vfpv3-d16-fp16,
vfpv3-fp16, vfpv4-d16, vfpv4, neon, neon-vfpv3, neon-fp16,
neon-vfpv4. The meanings are the same as for the extensions to
-march=armv7-a.

-mcpu=generic-arch is also permissible, and is equivalent to
-march=arch -mtune=generic-arch. See -mtune for more information.

-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.

-mcpu=unset causes the compiler to ignore any -mcpu=... options
that appear earlier on the command line and behave as if the option
was never passed. This is useful to avoid warnings about
conflicting CPU and architecture options when the two produce
different architecture specifications.

-mfpu=name
This specifies what floating-point hardware (or hardware emulation)
is available on the target. Permissible names are: auto, vfpv2,
vfpv3, vfpv3-fp16, vfpv3-d16, vfpv3-d16-fp16, vfpv3xd,
vfpv3xd-fp16, neon-vfpv3, neon-fp16, vfpv4, vfpv4-d16, fpv4-sp-d16,
neon-vfpv4, fpv5-d16, fpv5-sp-d16, fp-armv8, neon-fp-armv8 and
crypto-neon-fp-armv8. Note that neon is an alias for neon-vfpv3
and vfp is an alias for vfpv2.

The setting 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 -mcpu and -march.

If the selected floating-point hardware includes the NEON extension
(e.g. -mfpu=neon), note that floating-point operations are not
generated by GCC's auto-vectorization pass unless
-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
"target("fpu=")" function attributes or pragmas.

-mfp16-format=name
Specify the format of the "__fp16" half-precision floating-point
type. Permissible names are none, ieee, and alternative; the
default is none, in which case the "__fp16" type is not defined.

-mstructure-size-boundary=n
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.

-mabort-on-noreturn
Generate a call to the function "abort" at the end of a "noreturn"
function. It is executed if the function tries to return.

-mlong-calls
-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 "short_call" attribute, functions that are inside the
scope of a "#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
"long_call" attribute or the "section" attribute, and functions
that are within the scope of a "#pragma long_calls" directive are
always turned into long calls.

This feature is not enabled by default. Specifying -mno-long-calls
restores the default behavior, as does placing the function calls
within the scope of a "#pragma long_calls_off" directive. Note
these switches have no effect on how the compiler generates code to
handle function calls via function pointers.

-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.

-mpic-register=reg
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 R9 if target is
EABI based or stack-checking is enabled, otherwise the default is
R10.

-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
-msingle-pic-base by default.

-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:

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

When performing a stack backtrace, code can inspect the value of
"pc" stored at "fp + 0". If the trace function then looks at
location "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 "((pc[-3]) & 0xff000000)".

-mthumb
-marm
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 --with-mode=state configure option.

You can also override the ARM and Thumb mode for each function by
using the "target("thumb")" and "target("arm")" function attributes
or pragmas.

-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.

-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
-mno-tpcs-frame.

-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
-mno-apcs-leaf-frame.

-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.

-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.

-mtp=name
Specify the access model for the thread local storage pointer. The
model soft generates calls to "__aeabi_read_tp". Other accepted
models are tpidrurw, tpidruro and tpidrprw which fetch the thread
pointer from the corresponding system register directly (supported
from the arm6k architecture and later). These system registers are
accessed through the CP15 co-processor interface and the argument
cp15 is also accepted as a convenience alias of tpidruro. The
argument auto uses the best available method for the selected
processor. The default setting is auto.

-mtls-dialect=dialect
Specify the dialect to use for accessing thread local storage. Two
dialects are supported---gnu and gnu2. The gnu dialect selects the
original GNU scheme for supporting local and global dynamic TLS
models. The 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.

-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 -fpic or -fPIC is specified. This option conflicts with
-mslow-flash-data.

-mfix-cortex-m3-ldrd
Some Cortex-M3 cores can cause data corruption when "ldrd"
instructions with overlapping destination and base registers are
used. This option avoids generating these instructions. This
option is enabled by default when -mcpu=cortex-m3 is specified.

-mfix-cortex-a57-aes-1742098
-mno-fix-cortex-a57-aes-1742098
-mfix-cortex-a72-aes-1655431
-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 -mcpu=cortex-a57 or
-mcpu=cortex-a72 is specified.

-munaligned-access
-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 "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 "__ARM_FEATURE_UNALIGNED" is also defined.

-mneon-for-64bits
This option is deprecated and has no effect.

-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 -mword-relocations.

-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.

-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.

-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.

-mverbose-cost-dump
Enable verbose cost model dumping in the debug dump files. This
option is provided for use in debugging the compiler.

-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
"SHF_ARM_PURECODE". This option is only available when generating
non-pic code for M-profile targets.

-mcmse
Generate secure code as per the "ARMv8-M Security Extensions:
Requirements on Development Tools Engineering Specification", which
can be found on
<https://developer.arm.com/documentation/ecm0359818/latest/>.

-mfix-cmse-cve-2021-35465
Mitigate against a potential security issue with the "VLLDM"
instruction in some M-profile devices when using CMSE
(CVE-2021-365465). This option is enabled by default when the
option -mcpu= is used with "cortex-m33", "cortex-m35p",
"cortex-m52", "cortex-m55", "cortex-m85" or "star-mc1". The option
-mno-fix-cmse-cve-2021-35465 can be used to disable the mitigation.

-mstack-protector-guard=guard
-mstack-protector-guard-offset=offset
Generate stack protection code using canary at guard. Supported
locations are global for a global canary or tls for a canary
accessible via the TLS register. The option
-mstack-protector-guard-offset= is for use with
-fstack-protector-guard=tls and not for use in user-land code.

-mfdpic
-mno-fdpic
Select the FDPIC ABI, which uses 64-bit function descriptors to
represent pointers to functions. When the compiler is configured
for "arm-*-uclinuxfdpiceabi" targets, this option is on by default
and implies -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 -mno-fdpic option is useful (and required) to build
the Linux kernel using the same ("arm-*-uclinuxfdpiceabi")
toolchain as the one used to build the userland programs.

-mbranch-protection=none|standard|pac-ret[+leaf][+bti]|bti[+pac-
ret[+leaf]]
Enable branch protection features (armv8.1-m.main only). none
generate code without branch protection or return address signing.
standard[+leaf] generate code with all branch protection features
enabled at their standard level. pac-ret[+leaf] generate code with
return address signing set to its standard level, which is to sign
all functions that save the return address to memory. leaf When
return address signing is enabled, also sign leaf functions even if
they do not write the return address to memory. +bti Add landing-
pad instructions at the permitted targets of indirect branch
instructions.

If the +pacbti architecture extension is not enabled, then all
branch protection and return address signing operations are
constrained to use only the instructions defined in the
architectural-NOP space. The generated code will remain backwards-
compatible with earlier versions of the architecture, but the
additional security can be enabled at run time on processors that
support the PACBTI extension.

Branch target enforcement using BTI can only be enabled at runtime
if all code in the application has been compiled with at least
-mbranch-protection=bti.

Any setting other than none is supported only on armv8-m.main or
later.

The default is to generate code without branch protection or return
address signing.

AVR Options

These options are defined for AVR implementations:

-mmcu=mcu
Specify the AVR instruction set architecture (ISA) or device type.
The default for this option is "avr2".

The following AVR devices and ISAs are supported. Note: A complete
device support consists of startup code "crtmcu.o", a device header
"avr/io*.h", a device library "libmcu.a" and a device-specs
("https://gcc.gnu.org/wiki/avr-gcc#spec-files") file "specs-mcu".
Only the latter is provided by the compiler according the supported
"mcu"s below. The rest is supported by AVR-LibC
("https://github.com/avrdudes/avr-libc/"), or by means of "atpack"
("https://gcc.gnu.org/wiki/avr-gcc#atpack") files from the hardware
manufacturer.

"avr2"
"Classic" devices with up to 8 KiB of program memory. mcu =
"attiny22", "attiny26", "at90s2313", "at90s2323", "at90s2333",
"at90s2343", "at90s4414", "at90s4433", "at90s4434",
"at90c8534", "at90s8515", "at90s8535".

"avr25"
"Classic" devices with up to 8 KiB of program memory and with
the "MOVW" instruction. mcu = "attiny13", "attiny13a",
"attiny24", "attiny24a", "attiny25", "attiny261", "attiny261a",
"attiny2313", "attiny2313a", "attiny43u", "attiny44",
"attiny44a", "attiny45", "attiny48", "attiny441", "attiny461",
"attiny461a", "attiny4313", "attiny84", "attiny84a",
"attiny85", "attiny87", "attiny88", "attiny828", "attiny841",
"attiny861", "attiny861a", "ata5272", "ata6616c", "at86rf401".

"avr3"
"Classic" devices with 16 KiB up to 64 KiB of program memory.
mcu = "at76c711", "at43usb355".

"avr31"
"Classic" devices with 128 KiB of program memory. mcu =
"atmega103", "at43usb320".

"avr35"
"Classic" devices with 16 KiB up to 64 KiB of program memory
and with the "MOVW" instruction. mcu = "attiny167",
"attiny1634", "atmega8u2", "atmega16u2", "atmega32u2",
"ata5505", "ata6617c", "ata664251", "at90usb82", "at90usb162".

"avr4"
"Enhanced" devices with up to 8 KiB of program memory. mcu =
"atmega48", "atmega48a", "atmega48p", "atmega48pa",
"atmega48pb", "atmega8", "atmega8a", "atmega8hva", "atmega88",
"atmega88a", "atmega88p", "atmega88pa", "atmega88pb",
"atmega8515", "atmega8535", "ata5795", "ata6285", "ata6286",
"ata6289", "ata6612c", "at90pwm1", "at90pwm2", "at90pwm2b",
"at90pwm3", "at90pwm3b", "at90pwm81".

"avr5"
"Enhanced" devices with 16 KiB up to 64 KiB of program memory.
mcu = "atmega16", "atmega16a", "atmega16hva", "atmega16hva2",
"atmega16hvb", "atmega16hvbrevb", "atmega16m1", "atmega16u4",
"atmega161", "atmega162", "atmega163", "atmega164a",
"atmega164p", "atmega164pa", "atmega165", "atmega165a",
"atmega165p", "atmega165pa", "atmega168", "atmega168a",
"atmega168p", "atmega168pa", "atmega168pb", "atmega169",
"atmega169a", "atmega169p", "atmega169pa", "atmega32",
"atmega32a", "atmega32c1", "atmega32hvb", "atmega32hvbrevb",
"atmega32m1", "atmega32u4", "atmega32u6", "atmega323",
"atmega324a", "atmega324p", "atmega324pa", "atmega324pb",
"atmega325", "atmega325a", "atmega325p", "atmega325pa",
"atmega328", "atmega328p", "atmega328pb", "atmega329",
"atmega329a", "atmega329p", "atmega329pa", "atmega3250",
"atmega3250a", "atmega3250p", "atmega3250pa", "atmega3290",
"atmega3290a", "atmega3290p", "atmega3290pa", "atmega406",
"atmega64", "atmega64a", "atmega64c1", "atmega64hve",
"atmega64hve2", "atmega64m1", "atmega64rfr2", "atmega640",
"atmega644", "atmega644a", "atmega644p", "atmega644pa",
"atmega644rfr2", "atmega645", "atmega645a", "atmega645p",
"atmega649", "atmega649a", "atmega649p", "atmega6450",
"atmega6450a", "atmega6450p", "atmega6490", "atmega6490a",
"atmega6490p", "ata5790", "ata5790n", "ata5791", "ata6613c",
"ata6614q", "ata5782", "ata5831", "ata8210", "ata8510",
"ata5787", "ata5835", "ata5700m322", "ata5702m322",
"at90pwm161", "at90pwm216", "at90pwm316", "at90can32",
"at90can64", "at90scr100", "at90usb646", "at90usb647", "at94k",
"m3000".

"avr51"
"Enhanced" devices with 128 KiB of program memory. mcu =
"atmega128", "atmega128a", "atmega128rfa1", "atmega128rfr2",
"atmega1280", "atmega1281", "atmega1284", "atmega1284p",
"atmega1284rfr2", "at90can128", "at90usb1286", "at90usb1287".

"avr6"
"Enhanced" devices with 3-byte PC, i.e. with more than 128 KiB
of program memory. mcu = "atmega256rfr2", "atmega2560",
"atmega2561", "atmega2564rfr2".

"avrxmega2"
"XMEGA" devices with more than 8 KiB and up to 64 KiB of
program memory. mcu = "atxmega8e5", "atxmega16a4",
"atxmega16a4u", "atxmega16c4", "atxmega16d4", "atxmega16e5",
"atxmega32a4", "atxmega32a4u", "atxmega32c3", "atxmega32c4",
"atxmega32d3", "atxmega32d4", "atxmega32e5", "avr64da28",
"avr64da32", "avr64da48", "avr64da64", "avr64db28",
"avr64db32", "avr64db48", "avr64db64", "avr64dd14",
"avr64dd20", "avr64dd28", "avr64dd32", "avr64du28",
"avr64du32", "avr64ea28", "avr64ea32", "avr64ea48",
"avr64sd28", "avr64sd32", "avr64sd48".

"avrxmega3"
"XMEGA" devices with up to 64 KiB of combined program memory
and RAM, and with program memory visible in the RAM address
space. mcu = "attiny202", "attiny204", "attiny212",
"attiny214", "attiny402", "attiny404", "attiny406",
"attiny412", "attiny414", "attiny416", "attiny416auto",
"attiny417", "attiny424", "attiny426", "attiny427",
"attiny804", "attiny806", "attiny807", "attiny814",
"attiny816", "attiny817", "attiny824", "attiny826",
"attiny827", "attiny1604", "attiny1606", "attiny1607",
"attiny1614", "attiny1616", "attiny1617", "attiny1624",
"attiny1626", "attiny1627", "attiny3214", "attiny3216",
"attiny3217", "attiny3224", "attiny3226", "attiny3227",
"atmega808", "atmega809", "atmega1608", "atmega1609",
"atmega3208", "atmega3209", "atmega4808", "atmega4809",
"avr16dd14", "avr16dd20", "avr16dd28", "avr16dd32",
"avr16du14", "avr16du20", "avr16du28", "avr16du32",
"avr16ea28", "avr16ea32", "avr16ea48", "avr16eb14",
"avr16eb20", "avr16eb28", "avr16eb32", "avr32da28",
"avr32da32", "avr32da48", "avr32db28", "avr32db32",
"avr32db48", "avr32dd14", "avr32dd20", "avr32dd28",
"avr32dd32", "avr32du14", "avr32du20", "avr32du28",
"avr32du32", "avr32ea28", "avr32ea32", "avr32ea48",
"avr32sd20", "avr32sd28", "avr32sd32".

"avrxmega4"
"XMEGA" devices with more than 64 KiB and up to 128 KiB of
program memory. mcu = "atxmega64a3", "atxmega64a3u",
"atxmega64a4u", "atxmega64b1", "atxmega64b3", "atxmega64c3",
"atxmega64d3", "atxmega64d4", "avr128da28", "avr128da32",
"avr128da48", "avr128da64", "avr128db28", "avr128db32",
"avr128db48", "avr128db64".

"avrxmega5"
"XMEGA" devices with more than 64 KiB and up to 128 KiB of
program memory and more than 64 KiB of RAM. mcu =
"atxmega64a1", "atxmega64a1u".

"avrxmega6"
"XMEGA" devices with more than 128 KiB of program memory. mcu
= "atxmega128a3", "atxmega128a3u", "atxmega128b1",
"atxmega128b3", "atxmega128c3", "atxmega128d3", "atxmega128d4",
"atxmega192a3", "atxmega192a3u", "atxmega192c3",
"atxmega192d3", "atxmega256a3", "atxmega256a3b",
"atxmega256a3bu", "atxmega256a3u", "atxmega256c3",
"atxmega256d3", "atxmega384c3", "atxmega384d3".

"avrxmega7"
"XMEGA" devices with more than 128 KiB of program memory and
more than 64 KiB of RAM. mcu = "atxmega128a1",
"atxmega128a1u", "atxmega128a4u".

"avrtiny"
"Reduced Tiny" Tiny core devices with only 16 general purpose
registers and 512 B up to 4 KiB of program memory. mcu =
"attiny4", "attiny5", "attiny9", "attiny10", "attiny102",
"attiny104", "attiny20", "attiny40".

"avr1"
This ISA is implemented by the minimal AVR core and supported
for assembler only. mcu = "attiny11", "attiny12", "attiny15",
"attiny28", "at90s1200".

-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 "absdata" AVR Variable
Attributes,variable attribute.

-mcvt
Use a compact vector table. Some devices support a CVT with only
four entries: 0=Reset, 1=NMI, 2=Prio1 IRQ, 3=Prio0 IRQs. This
option will link startup code from "crtmcu-cvt.o" instead of the
usual "crtmcu.o". Apart from providing a compact vector table, the
startup code will set bit "CPUINT_CTRLA.CPUINT_CVT" which enables
the CVT on the device.

When you do not want the startup code to set
"CPUINT_CTRLA.CPUINT_CVT", then you can satisfy symbol "__init_cvt"
so that the respective code is no more pulled in from "libmcu.a".
For example, you can link with "-Wl,--defsym,__init_cvt=0".

The CVT startup code is available since AVR-LibC v2.3
("https://github.com/avrdudes/avr-libc/issues/1010").

-mdouble=bits
-mlong-double=bits
Set the size (in bits) of the "double" or "long double" type,
respectively. Possible values for bits are 32 and 64. Whether or
not a specific value for bits is allowed depends on the
"--with-double=" and "--with-long-double=" configure options
("https://gcc.gnu.org/install/configure.html#avr"), and the same
applies for the default values of the options.

-mgas-isr-prologues
Interrupt service routines (ISRs) may use the "__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
AVR Function Attributes,,"no_gccisr" function attribute. This
feature is activated per default if optimization is on (but not
with -Og, @pxref{Optimize Options}), and if GNU Binutils support
PR21683 ("https://sourceware.org/PR21683").

-mint8
Assume "int" to be 8-bit integer. This affects the sizes of all
types: a "char" is 1 byte, an "int" is 1 byte, a "long" is 2 bytes,
and "long long" is 4 bytes. Please note that this option does not
conform to the C standards, but it results in smaller code size.

-mmain-is-OS_task
Do not save registers in "main". The effect is the same like
attaching attribute AVR Function Attributes,,"OS_task" to "main".
It is activated per default if optimization is on.

-mno-call-main
Don't run "main" by means of

XCALL main
XJMP exit

Instead, put "main" in section ".init9"
("https://avrdudes.github.io/avr-libc/avr-libc-user-manual/mem_sections.html#sec_dot_init")
so that no call is required. By setting this option the user
asserts that "main" will not return.

This option can be used for devices with very limited resources in
order to save a few bytes of code and stack space. It will work as
expected since AVR-LibC v2.3
("https://github.com/avrdudes/avr-libc/issues/1012"). With older
versions, there will be no performance gain.

-mno-interrupts
Generated code is not compatible with hardware interrupts. Code
size is smaller.

-mrelax
Try to replace "CALL" resp. "JMP" instruction by the shorter
"RCALL" resp. "RJMP" instruction if applicable. Setting -mrelax
just adds the --mlink-relax option to the assembler's command line
and the --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 "EIND" and linker stubs below.

-mrodata-in-ram
-mno-rodata-in-ram
Locate the ".rodata" sections for read-only data in RAM resp. in
program memory. For most devices, there is no choice and this
option acts rather like an assertion.

Since v14 and for the AVR64* and AVR128* devices, ".rodata" is
located in flash memory per default, provided the required GNU
Binutils support (PR31124 ("https://sourceware.org/PR31124")) is
available. In that case, -mrodata-in-ram can be used to return to
the old layout with ".rodata" in RAM.

-mtiny-stack
Only change the lower 8 bits of the stack pointer.

-mfract-convert-truncate
Allow to use truncation instead of rounding towards zero for
fractional fixed-point types.

-nodevicelib
Don't link against AVR-LibC's device specific library "libmcu.a".

Notice that since AVR-LibC v2.3, that library contains code that is
essential for the correct functioning of a program. In particular,
it contains parts of the startup code like: "__init_sp"
("https://github.com/avrdudes/avr-libc/issues/1011") to initialize
the stack pointer with symbol "__stack", "__init_cvt"
("https://github.com/avrdudes/avr-libc/issues/1010") to set up the
hardware to use a compact vector table with -mcvt, "__call_main"
("https://github.com/avrdudes/avr-libc/issues/1012") to call "main"
and "exit", and "__do_flmap_init"
("https://github.com/avrdudes/avr-libc/issues/931") to set up FLMAP
according to symbol "__flmap".

-nodevicespecs
Don't add -specs=device-specs/specs-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 -specs=path-to-
specs-file. There is no more need for option -mmcu=mcu.

This option can also serve as a replacement for the older way of
specifying custom device-specs files that needed -B some-path to
point to a directory which contains a folder named "device-specs"
which contains a specs file named "specs-mcu", where mcu was
specified by -mmcu=mcu.

-Waddr-space-convert
Warn about conversions between address spaces in the case where the
resulting address space is not contained in the incoming address
space.

-Wmisspelled-isr
Warn if the ISR is misspelled, i.e. without __vector prefix.
Enabled by default.

AVR Optimization Options

The following options are pure optimization options. Options
-mgas-isr-prologues, -mmain-is-OS_task, -mno-call-main and -mrelax from
above are only almost optimization options, since there are rare
occasions where their different code generation matters.

-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. See also
the -fdefer-pop Optimize Options,,optimization option.

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.

-mbranch-cost=cost
Set the branch costs for conditional branch instructions to cost.
Reasonable values for cost are small, non-negative integers. The
default branch cost is 0.

-mcall-prologues
Functions prologues/epilogues are expanded as calls to appropriate
subroutines. Code size is smaller.

-mfuse-add
-mno-fuse-add
-mfuse-add=level
Optimize indirect memory accesses on reduced Tiny devices. The
default uses "level=1" for optimizations -Og and -O1, and "level=2"
for higher optimizations. Valid values for level are 0, 1 and 2.

-mfuse-move
-mno-fuse-move
-mfuse-move=level
Run a post reload optimization pass that tries to fuse move
instructions and to split multi-byte instructions into 8-bit
operations. The default uses "level=3" for optimization -O1, and
"level=23" for higher optimizations. Valid values for level are in
the range 0 ... 23 which is a 3:2:2:2 mixed radix value. Each
digit controls some aspect of the optimization.

-mstrict-X
Use address register "X" in a way proposed by the hardware. This
means that "X" is only used in indirect, post-increment or pre-
decrement addressing.

Without this option, the "X" register may be used in the same way
as "Y" or "Z" which then is emulated by additional instructions.
For example, loading a value with "X+const" addressing with a small
non-negative "const < 64" to a register Rn is performed as

adiw r26, const ; X += const
ld <Rn>, X ; <Rn> = *X
sbiw r26, const ; X -= const

-msplit-bit-shift
Split multi-byte shifts with a constant offset into a shift with a
byte offset and a residual shift with a non-byte offset. This
optimization is turned on per default for -O2 and higher, including
-Os but excluding -Oz. Splitting of shifts with a constant offset
that is a multiple of 8 is controlled by -mfuse-move.

-msplit-ldst
Split multi-byte loads and stores into several byte loads and
stores. This optimization is turned on per default for -O2 and
higher.

-muse-nonzero-bits
Enable optimizations that are only possible when some bits in a
register are always zero. This optimization is turned on per
default for -O2 and higher.

"EIND" and Devices with More Than 128 Ki Bytes of Flash

Pointers in the implementation are 16 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 Ki words.

In order to facilitate indirect jump on devices with more than 128 Ki
bytes of program memory space, there is a special function register
called "EIND" that serves as most significant part of the target
address when "EICALL" or "EIJMP" instructions are used.

Indirect jumps and calls on these devices are handled as follows by the
compiler and are subject to some limitations:

* The compiler never sets "EIND".

* The compiler uses "EIND" implicitly in "EICALL"/"EIJMP"
instructions or might read "EIND" directly in order to emulate an
indirect call/jump by means of a "RET" instruction.

* The compiler assumes that "EIND" never changes during the startup
code or during the application. In particular, "EIND" is not
saved/restored in function or interrupt service routine
prologue/epilogue.

* For indirect calls to functions and computed goto, the linker
generates stubs. Stubs are jump pads sometimes also called
trampolines. Thus, the indirect call/jump jumps to such a stub.
The stub contains a direct jump to the desired address.

* Linker relaxation must be turned on so that the linker generates
the stubs correctly in all situations. See the compiler option
-mrelax and the linker option --relax. There are corner cases
where the linker is supposed to generate stubs but aborts without
relaxation and without a helpful error message.

* The default linker script is arranged for code with "EIND = 0". If
code is supposed to work for a setup with "EIND != 0", a custom
linker script has to be used in order to place the sections whose
name start with ".trampolines" into the segment where "EIND" points
to.

* The startup code from libgcc never sets "EIND". Notice that
startup code is a blend of code from libgcc and AVR-LibC. For the
impact of AVR-LibC on "EIND", see the AVR-LibC user manual
("https://avrdudes.github.io/avr-libc/avr-libc-user-manual/").

* It is legitimate for user-specific startup code to set up "EIND"
early, for example by means of initialization code located in
section ".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 "EIND" to the segment where
the vector table is located.

#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");
}

The "__trampolines_start" symbol is defined in the linker script.

* Stubs are generated automatically by the linker if the following
two conditions are met:

-<The address of a label is taken by means of the "gs" modifier>
(short for generate stubs) like so:

LDI r24, lo8(gs(<func>))
LDI r25, hi8(gs(<func>))

-<The final location of that label is in a code segment>
outside the segment where the stubs are located.

* The compiler emits such "gs" modifiers for code labels in the
following situations:

-<Taking address of a function or code label.>
-<Computed goto.>
-<If prologue-save function is used, see -mcall-prologues>
command-line option.

-<Switch/case dispatch tables. If you do not want such dispatch>
tables you can specify the -fno-jump-tables command-line
option.

-<C and C++ constructors/destructors called during
startup/shutdown.>
-<If the tools hit a "gs()" modifier explained above.>
* Jumping to non-symbolic addresses like so is not supported:

int main (void)
{
/* Call function at word address 0x2 */
return ((int(*)(void)) 0x2)();
}

Instead, a stub has to be set up, i.e. the function has to be
called through a symbol ("func_4" in the example):

int main (void)
{
extern int func_4 (void);

/* Call function at byte address 0x4 */
return func_4();
}

and the application be linked with -Wl,--defsym,func_4=0x4.
Alternatively, "func_4" can be defined in the linker script.

Handling of the "RAMPD", "RAMPX", "RAMPY" and "RAMPZ" Special Function
Registers

Some AVR devices support memories larger than the 64 KiB range that can
be accessed with 16-bit pointers. To access memory locations outside
this 64 KiB range, the content of a "RAMP" register is used as high
part of the address: The "X", "Y", "Z" address register is concatenated
with the "RAMPX", "RAMPY", "RAMPZ" special function register,
respectively, to get a wide address. Similarly, "RAMPD" is used
together with direct addressing.

* The startup code initializes the "RAMP" special function registers
with zero.

* If a AVR Named Address Spaces,named address space other than
generic or "__flash" is used, then "RAMPZ" is set as needed before
the operation.

* If the device supports RAM larger than 64 KiB and the compiler
needs to change "RAMPZ" to accomplish an operation, "RAMPZ" is
reset to zero after the operation.

* If the device comes with a specific "RAMP" register, the ISR
prologue/epilogue saves/restores that SFR and initializes it with
zero in case the ISR code might (implicitly) use it.

* RAM larger than 64 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 "RAMP" registers, you must
reset it to zero after the access.

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 -mmcu= command-line option.

For even more AVR-specific built-in macros see AVR Named Address Spaces
and AVR Built-in Functions.

"__AVR_ARCH__"
Build-in macro that resolves to a decimal number that identifies
the architecture and depends on the -mmcu=mcu option. Possible
values are:

2, 25, 3, 31, 35, 4, 5, 51, 6

for mcu="avr2", "avr25", "avr3", "avr31", "avr35", "avr4", "avr5",
"avr51", "avr6",

respectively and

100, 102, 103, 104, 105, 106, 107

for mcu="avrtiny", "avrxmega2", "avrxmega3", "avrxmega4",
"avrxmega5", "avrxmega6", "avrxmega7", respectively. If mcu
specifies a device, this built-in macro is set accordingly. For
example, with -mmcu=atmega8 the macro is defined to 4.

"__AVR_Device__"
Setting -mmcu=device defines this built-in macro which reflects the
device's name. For example, -mmcu=atmega8 defines the built-in
macro "__AVR_ATmega8__", -mmcu=attiny261a defines
"__AVR_ATtiny261A__", etc.

The built-in macros' names follow the scheme "__AVR_Device__" where
Device is the device name as from the AVR user manual. The
difference between Device in the built-in macro and device in
-mmcu=device is that the latter is always lowercase.

If device is not a device but only a core architecture like avr51,
this macro is not defined.

"__AVR_DEVICE_NAME__"
Setting -mmcu=device defines this built-in macro to the device's
name. For example, with -mmcu=atmega8 the macro is defined to
"atmega8".

If device is not a device but only a core architecture like avr51,
this macro is not defined.

"__AVR_CVT__"
The code is being compiled with option "-mcvt" to use a compact
vector table.

"__AVR_XMEGA__"
The device / architecture belongs to the XMEGA family of devices.

"__AVR_HAVE_ADIW__"
The device has the "ADIW" and "SBIW" instructions.

"__AVR_HAVE_ELPM__"
The device has the "ELPM" instruction.

"__AVR_HAVE_ELPMX__"
The device has the "ELPM Rn,Z" and "ELPM Rn,Z+" instructions.

"__AVR_HAVE_LPMX__"
The device has the "LPM Rn,Z" and "LPM Rn,Z+" instructions.

"__AVR_HAVE_MOVW__"
The device has the "MOVW" instruction to perform 16-bit register-
register moves.

"__AVR_HAVE_MUL__"
The device has a hardware multiplier.

"__AVR_HAVE_JMP_CALL__"
The device has the "JMP" and "CALL" instructions. This is the case
for devices with more than 8 KiB of program memory.

"__AVR_HAVE_EIJMP_EICALL__"
"__AVR_3_BYTE_PC__"
The device has the "EIJMP" and "EICALL" instructions. This is the
case for devices with more than 128 KiB of program memory. This
also means that the program counter (PC) is 3 bytes wide.

"__AVR_2_BYTE_PC__"
The program counter (PC) is 2 bytes wide. This is the case for
devices with up to 128 KiB of program memory.

"__AVR_HAVE_8BIT_SP__"
"__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 -mtiny-stack.

"__AVR_HAVE_SPH__"
"__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 -mmcu= and in the cases
of -mmcu=avr2 and -mmcu=avr25 also by -msp8.

"__AVR_HAVE_RAMPD__"
"__AVR_HAVE_RAMPX__"
"__AVR_HAVE_RAMPY__"
"__AVR_HAVE_RAMPZ__"
The device has the "RAMPD", "RAMPX", "RAMPY", "RAMPZ" special
function register, respectively.

"__NO_INTERRUPTS__"
This macro reflects the -mno-interrupts command-line option.

"__AVR_ERRATA_SKIP__"
"__AVR_ERRATA_SKIP_JMP_CALL__"
Some AVR devices (AT90S8515, ATmega103) must not skip 32-bit
instructions because of a hardware erratum. Skip instructions are
"SBRS", "SBRC", "SBIS", "SBIC" and "CPSE". The second macro is
only defined if "__AVR_HAVE_JMP_CALL__" is also set.

"__AVR_ISA_RMW__"
The device has Read-Modify-Write instructions (XCH, LAC, LAS and
LAT).

"__AVR_SFR_OFFSET__=offset"
Instructions that can address I/O special function registers
directly like "IN", "OUT", "SBI", etc. may use a different address
as if addressed by an instruction to access RAM like "LD" or "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
address.

"__AVR_SHORT_CALLS__"
The -mshort-calls command line option is set.

"__AVR_PM_BASE_ADDRESS__=addr"
Some devices support reading from flash memory by means of "LD*"
instructions. The flash memory is seen in the data address space
at an offset of "__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 ".rodata" into RAM.
This is handled by the default linker description file, and is
currently available for "avrtiny" and "avrxmega3". Even more
convenient, there is no need to use address spaces like "__flash"
or features like attribute "progmem" and "pgm_read_*".

"__AVR_HAVE_FLMAP__"
This macro is defined provided the following conditions are met:

*<The device has the "NVMCTRL_CTRLB.FLMAP" bitfield.>
This applies to the AVR64* and AVR128* devices.

*<It's not known at assembler-time which emulation will be used.>

This implies the compiler was configured with GNU Binutils that
implement PR31124 ("https://sourceware.org/PR31124").

"__AVR_RODATA_IN_RAM__"
This macro is undefined when the code is compiled for a core
architecture.

When the code is compiled for a device, the macro is defined to 1
when the ".rodata" sections for read-only data is located in RAM;
and defined to 0, otherwise.

"__WITH_AVRLIBC__"
The compiler is configured to be used together with AVR-LibC. See
the --with-avrlibc configure option.

"__HAVE_SIGNAL_N__"
The compiler supports the "signal(num)" and "interrupt(num)" AVR
Function Attributes,,function attributes with an argument num that
specifies the number of the interrupt service routine.

"__HAVE_DOUBLE_MULTILIB__"
Defined if -mdouble= acts as a multilib option.

"__HAVE_DOUBLE32__"
"__HAVE_DOUBLE64__"
Defined if the compiler supports 32-bit double resp. 64-bit double.
The actual layout is specified by option -mdouble=.

"__DEFAULT_DOUBLE__"
The size in bits of "double" if -mdouble= is not set. To test the
layout of "double" in a program, use the built-in macro
"__SIZEOF_DOUBLE__".

"__HAVE_LONG_DOUBLE32__"
"__HAVE_LONG_DOUBLE64__"
"__HAVE_LONG_DOUBLE_MULTILIB__"
"__DEFAULT_LONG_DOUBLE__"
Same as above, but for "long double" instead of "double".

"__WITH_DOUBLE_COMPARISON__"
Reflects the "--with-double-comparison={tristate|bool|libf7}"
configure option ("https://gcc.gnu.org/install/configure.html#avr")
and is defined to 2 or 3.

"__WITH_LIBF7_LIBGCC__"
"__WITH_LIBF7_MATH__"
"__WITH_LIBF7_MATH_SYMBOLS__"
Reflects the "--with-libf7={libgcc|math|math-symbols}"
configure option
("https://gcc.gnu.org/install/configure.html#avr").

AVR Internal Options

The following options are used internally by the compiler and to
communicate between device specs files and the compiler proper. You
don't need to set these options by hand, in particular they are not
optimization options. Using these options in the wrong way may lead to
sub-optimal or wrong code. They are documented for completeness, and
in order to get a better understanding of device specs
("https://gcc.gnu.org/wiki/avr-gcc#spec-files") files.

-mn-flash=num
Assume that the flash memory has a size of num times 64 KiB. This
determines which "__flashN" address spaces are available.

-mflmap
The device has the "FLMAP" bit field located in special function
register "NVMCTRL_CTRLB".

-mrmw
Assume that the device supports the Read-Modify-Write instructions
"XCH", "LAC", "LAS" and "LAT".

-mshort-calls
Assume that "RJMP" and "RCALL" can target the whole program memory.
This option is used for multilib generation and selection for the
devices from architecture "avrxmega3".

-mskip-bug
Generate code without skips ("CPSE", "SBRS", "SBRC", "SBIS",
"SBIC") over 32-bit instructions.

-msp8
Treat the stack pointer register as an 8-bit register, i.e. assume
the high byte of the stack pointer is zero. This option is used by
the compiler to select and build multilibs for architectures "avr2"
and "avr25". These architectures mix devices with and without
"SPH".

Blackfin Options

-mcpu=cpu[-sirevision]
Specifies the name of the target Blackfin processor. Currently,
cpu can be one of bf512, bf514, bf516, bf518, bf522, bf523, bf524,
bf525, bf526, bf527, bf531, bf532, bf533, bf534, bf536, bf537,
bf538, bf539, bf542, bf544, bf547, bf548, bf549, bf542m, bf544m,
bf547m, bf548m, bf549m, bf561, bf592.

The optional sirevision specifies the silicon revision of the
target Blackfin processor. Any workarounds available for the
targeted silicon revision are enabled. If sirevision is none, no
workarounds are enabled. If sirevision is any, all workarounds for
the targeted processor are enabled. The "__SILICON_REVISION__"
macro is defined to two hexadecimal digits representing the major
and minor numbers in the silicon revision. If sirevision is none,
the "__SILICON_REVISION__" is not defined. If sirevision is any,
the "__SILICON_REVISION__" is defined to be 0xffff. If this
optional sirevision is not used, GCC assumes the latest known
silicon revision of the targeted Blackfin processor.

GCC defines a preprocessor macro for the specified cpu. For the
bfin-elf toolchain, this option causes the hardware BSP provided by
libgloss to be linked in if -msim is not given.

Without this option, bf532 is used as the processor by default.

Note that support for bf561 is incomplete. For bf561, only the
preprocessor macro is defined.

-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 bfin-elf toolchain. Certain other
options, such as -mid-shared-library and -mfdpic, imply -msim.

-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.

-mspecld-anomaly
When enabled, the compiler ensures that the generated code does not
contain speculative loads after jump instructions. If this option
is used, "__WORKAROUND_SPECULATIVE_LOADS" is defined.

-mno-specld-anomaly
Don't generate extra code to prevent speculative loads from
occurring.

-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, "__WORKAROUND_SPECULATIVE_SYNCS"
is defined.

-mno-csync-anomaly
Don't generate extra code to prevent CSYNC or SSYNC instructions
from occurring too soon after a conditional branch.

-mlow64k
When enabled, the compiler is free to take advantage of the
knowledge that the entire program fits into the low 64k of memory.

-mno-low64k
Assume that the program is arbitrarily large. This is the default.

-mstack-check-l1
Do stack checking using information placed into L1 scratchpad
memory by the uClinux kernel.

-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 -fPIC. With a bfin-elf target, this option implies -msim.

-mno-id-shared-library
Generate code that doesn't assume ID-based shared libraries are
being used. This is the default.

-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.

-mno-leaf-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.

-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.

-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.

-mno-sep-data
Generate code that assumes that the data segment follows the text
segment. This is the default.

-mlong-calls
-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 -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.

-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.

-minline-plt
Enable inlining of PLT entries in function calls to functions that
are not known to bind locally. It has no effect without -mfdpic.

-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 "__BFIN_MULTICORE". It
can only be used with -mcpu=bf561[-sirevision].

This option can be used with -mcorea or -mcoreb, which selects the
one-application-per-core programming model. Without -mcorea or
-mcoreb, the single-application/dual-core programming model is
used. In this model, the main function of Core B should be named as
"coreb_main".

If this option is not used, the single-core application programming
model is used.

-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
"__BFIN_COREA" is defined. This option can only be used in
conjunction with -mmulticore.

-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
"__BFIN_COREB" is defined. When this option is used, "coreb_main"
should be used instead of "main". This option can only be used in
conjunction with -mmulticore.

-msdram
Build a standalone application for SDRAM. Proper start files and
link scripts are used to put the application into SDRAM, and the
macro "__BFIN_SDRAM" is defined. The loader should initialize
SDRAM before loading the application.

-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.

C6X Options

-march=name
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: c62x, c64x,
c64x+, c67x, c67x+, c674x.

-mbig-endian
Generate code for a big-endian target.

-mlittle-endian
Generate code for a little-endian target. This is the default.

-msim
Choose startup files and linker script suitable for the simulator.

-msdata=default
Put small global and static data in the ".neardata" section, which
is pointed to by register "B14". Put small uninitialized global
and static data in the ".bss" section, which is adjacent to the
".neardata" section. Put small read-only data into the ".rodata"
section. The corresponding sections used for large pieces of data
are ".fardata", ".far" and ".const".

-msdata=all
Put all data, not just small objects, into the sections reserved
for small data, and use addressing relative to the "B14" register
to access them.

-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 ".fardata" section, and all uninitialized
data in the ".far" section. Put all constant data into the
".const" section.

CRIS Options

These options are defined specifically for the CRIS ports.

-march=architecture-type
-mcpu=architecture-type
Generate code for the specified architecture. The choices for
architecture-type are v3, v8 and v10 for respectively ETRAX 4,
ETRAX 100, and ETRAX 100 LX. Default is v0.

-mtune=architecture-type
Tune to architecture-type everything applicable about the generated
code, except for the ABI and the set of available instructions.
The choices for architecture-type are the same as for
-march=architecture-type.

-mmax-stack-frame=n
Warn when the stack frame of a function exceeds n bytes.

-metrax4
-metrax100
The options -metrax4 and -metrax100 are synonyms for -march=v3 and
-march=v8 respectively.

-mmul-bug-workaround
-mno-mul-bug-workaround
Work around a bug in the "muls" and "mulu" instructions for CPU
models where it applies. This option is disabled by default.

-mpdebug
Enable CRIS-specific verbose debug-related information in the
assembly code. This option also has the effect of turning off the
#NO_APP formatted-code indicator to the assembler at the beginning
of the assembly file.

-mcc-init
Do not use condition-code results from previous instruction; always
emit compare and test instructions before use of condition codes.

-mno-side-effects
Do not emit instructions with side effects in addressing modes
other than post-increment.

-mstack-align
-mno-stack-align
-mdata-align
-mno-data-align
-mconst-align
-mno-const-align
These options (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.

-m32-bit
-m16-bit
-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.

-mno-prologue-epilogue
-mprologue-epilogue
With -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.

-melf
Legacy no-op option.

-sim
This option arranges to link with input-output functions from a
simulator library. Code, initialized data and zero-initialized
data are allocated consecutively.

-sim2
Like -sim, but pass linker options to locate initialized data at
0x40000000 and zero-initialized data at 0x80000000.

C-SKY Options

GCC supports these options when compiling for C-SKY V2 processors.

-march=arch
Specify the C-SKY target architecture. Valid values for arch are:
ck801, ck802, ck803, ck807, and ck810. The default is ck810.

-mcpu=cpu
Specify the C-SKY target processor. Valid values for cpu are:
ck801, ck801t, ck802, ck802t, ck802j, ck803, ck803h, ck803t,
ck803ht, ck803f, ck803fh, ck803e, ck803eh, ck803et, ck803eht,
ck803ef, ck803efh, ck803ft, ck803eft, ck803efht, ck803r1, ck803hr1,
ck803tr1, ck803htr1, ck803fr1, ck803fhr1, ck803er1, ck803ehr1,
ck803etr1, ck803ehtr1, ck803efr1, ck803efhr1, ck803ftr1,
ck803eftr1, ck803efhtr1, ck803s, ck803st, ck803se, ck803sf,
ck803sef, ck803seft, ck807e, ck807ef, ck807, ck807f, ck810e,
ck810et, ck810ef, ck810eft, ck810, ck810v, ck810f, ck810t, ck810fv,
ck810tv, ck810ft, and ck810ftv.

-mbig-endian
-EB
-mlittle-endian
-EL Select big- or little-endian code. The default is little-endian.

-mfloat-abi=name
Specifies which floating-point ABI to use. Permissible values are:
soft, softfp and hard.

-mhard-float
-msoft-float
Select hardware or software floating-point implementations. The
default is soft float.

-mdouble-float
-mno-double-float
When -mhard-float is in effect, enable generation of double-
precision float instructions. This is the default except when
compiling for CK803.

-mfdivdu
-mno-fdivdu
When -mhard-float is in effect, enable generation of "frecipd",
"fsqrtd", and "fdivd" instructions. This is the default except
when compiling for CK803.

-mfpu=fpu
Select the floating-point processor. This option can only be used
with -mhard-float. Values for fpu are fpv2_sf (equivalent to
-mno-double-float -mno-fdivdu), fpv2 (-mdouble-float -mno-divdu),
and fpv2_divd (-mdouble-float -mdivdu).

-melrw
-mno-elrw
Enable the extended "lrw" instruction. This option defaults to on
for CK801 and off otherwise.

-mistack
-mno-istack
Enable interrupt stack instructions; the default is off.

The -mistack option is required to handle the "interrupt" and "isr"
function attributes.

-mmp
Enable multiprocessor instructions; the default is off.

-mcp
Enable coprocessor instructions; the default is off.

-mcache
Enable coprocessor instructions; the default is off.

-msecurity
Enable C-SKY security instructions; the default is off.

-mtrust
Enable C-SKY trust instructions; the default is off.

-mdsp
-medsp
-mvdsp
Enable C-SKY DSP, Enhanced DSP, or Vector DSP instructions,
respectively. All of these options default to off.

-mdiv
-mno-div
Generate divide instructions. Default is off.

-msmart
-mno-smart
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.

-mhigh-registers
-mno-high-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.

-manchor
-mno-anchor
Generate code using global anchor symbol addresses.

-mpushpop
-mno-pushpop
Generate code using "push" and "pop" instructions. This option
defaults to on.

-mmultiple-stld
-mstm
-mno-multiple-stld
-mno-stm
Generate code using "stm" and "ldm" instructions. This option
isn't supported on CK801 but is enabled by default on other
processors.

-mconstpool
-mno-constpool
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.

-mstack-size
-mno-stack-size
Emit ".stack_size" directives for each function in the assembly
output. This option defaults to off.

-mccrt
-mno-ccrt
Generate code for the C-SKY compiler runtime instead of libgcc.
This option defaults to off.

-mbranch-cost=n
Set the branch costs to roughly "n" instructions. The default is
1.

-msched-prolog
-mno-sched-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.

-msim
Links the library libsemi.a which is in compatible with simulator.
Applicable to ELF compiler only.

Cygwin and MinGW Options

These additional options are available for Microsoft Windows targets:

-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.

-mcrtdll=library
Preprocess, compile or link with specified C RunTime DLL library.
This option adjust predefined macros "__CRTDLL__", "__MSVCRT__",
"_UCRT" and "__MSVCRT_VERSION__" for specified CRT library, choose
start file for CRT library and link with CRT library. Recognized
CRT library names for proprocessor are: "crtdll*", "msvcrt10*",
"msvcrt20*", "msvcrt40*", "msvcr40*", "msvcrtd*", "msvcrt-os*",
"msvcr70*", "msvcr71*", "msvcr80*", "msvcr90*", "msvcr100*",
"msvcr110*", "msvcr120*" and "ucrt*". If this options is not
specified then the default MinGW import library "msvcrt" is used
for linking and no other adjustment for preprocessor is done. MinGW
import library "msvcrt" is just a symlink to (or a copy of) another
MinGW CRT import library chosen during MinGW compilation. MinGW
import library "msvcrt-os" is for Windows system CRT DLL library
"msvcrt.dll" and in most cases is the default MinGW import library.
Generally speaking, changing the CRT DLL requires recompiling the
entire MinGW CRT. This option is for experimental and testing
purposes only. This option is available for MinGW targets.

-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.

-mnop-fun-dllimport
This option is available for Cygwin and MinGW targets. It
specifies that the "dllimport" attribute should be ignored.

-mthreads
This option is available for MinGW targets. It specifies that
MinGW-specific thread support is to be used.

-municode
This option is available for MinGW-w64 targets. It causes the
"UNICODE" preprocessor macro to be predefined, and chooses Unicode-
capable runtime startup code.

-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.

-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.

-fno-set-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.

-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
".data" section. This is a necessary for older runtimes not
supporting modification of ".rdata" sections for pseudo-relocation.

-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.

See also under x86 Options for standard options.

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 -arch options
are used; it does so by running the compiler or linker multiple times
and joining the results together with lipo.

The subtype of the file created (like ppc7400 or ppc970 or i686) is
determined by the flags that specify the ISA that GCC is targeting,
like -mcpu or -march. The -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, 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 ppc750 object file. The linker for shared
libraries, /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 ppc970 object file in a ppc7400
library). The linker for executables, ld, quietly gives the executable
the most restrictive subtype of any of its input files.

-Fdir
Add the framework directory dir to the head of the list of
directories to be searched for header files. These directories are
interleaved with those specified by -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 Headers and/or PrivateHeaders
directory contained directly in it that ends in .framework. The
name of a framework is the name of this directory excluding the
.framework. Headers associated with the framework are found in one
of those two directories, with Headers being searched first. A
subframework is a framework directory that is in a framework's
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
/System/Library/Frameworks and /Library/Frameworks. An example
include looks like "#include <Framework/header.h>", where Framework
denotes the name of the framework and header.h is found in the
PrivateHeaders or Headers directory.

-iframeworkdir
Like -F except the directory is a treated as a system directory.
The main difference between this -iframework and -F is that with
-iframework the compiler does not warn about constructs contained
within header files found via dir. This option is valid only for
the C family of languages.

-gused
Emit debugging information for symbols that are used. For stabs
debugging format, this enables -feliminate-unused-debug-symbols.
This is by default ON.

-gfull
Emit debugging information for all symbols and types.

-fconstant-cfstrings
The -fconstant-cfstrings is an alias for -mconstant-cfstrings.

-mconstant-cfstrings
When the NeXT runtime is being used (the default on these systems),
override any -fconstant-string-class setting and cause "@"...""
literals to be laid out as constant CoreFoundation strings.

-mmacosx-version-min=version
The earliest version of MacOS X that this executable will run on is
version. Typical values supported for version include 12, 10.12,
and 10.5.8.

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.

-mkernel
Enable kernel development mode. The -mkernel option sets -static,
-fno-common, -fno-use-cxa-atexit, -fno-exceptions,
-fno-non-call-exceptions, -fapple-kext, -fno-weak and -fno-rtti
where applicable. This mode also sets -mno-altivec, -msoft-float,
-fno-builtin and -mlong-branch for PowerPC targets.

-mone-byte-bool
Override the defaults for "bool" so that "sizeof(bool)==1". By
default "sizeof(bool)" is 4 when compiling for Darwin/PowerPC and 1
when compiling for Darwin/x86, so this option has no effect on x86.

Warning: The -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.

-mfix-and-continue
-ffix-and-continue
-findirect-data
Generate code suitable for fast turnaround development, such as to
allow GDB to dynamically load .o files into already-running
programs. -findirect-data and -ffix-and-continue are provided for
backwards compatibility.

-all_load
Loads all members of static archive libraries. See man ld(1) for
more information.

-arch_errors_fatal
Cause the errors having to do with files that have the wrong
architecture to be fatal.

-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.

-bundle
Produce a Mach-o bundle format file. See man ld(1) for more
information.

-bundle_loader executable
This option specifies the executable that will load the build
output file being linked. See man ld(1) for more information.

-dynamiclib
When passed this option, GCC produces a dynamic library instead of
an executable when linking, using the Darwin libtool command.

-force_cpusubtype_ALL
This causes GCC's output file to have the ALL subtype, instead of
one controlled by the -mcpu or -march option.

-nodefaultrpaths
Do not add default run paths for the compiler library directories
to executables, modules or dynamic libraries. On macOS 10.5 and
later, the embedded runpath is added by default unless the user
adds -nodefaultrpaths to the link line. Run paths are needed (and
therefore enforced) to build on macOS version 10.11 or later.

-allowable_client client_name
-client_name
-compatibility_version
-current_version
-dead_strip
-dependency-file
-dylib_file
-dylinker_install_name
-dynamic
-exported_symbols_list
-filelist
-flat_namespace
-force_flat_namespace
-headerpad_max_install_names
-image_base
-init
-install_name
-keep_private_externs
-multi_module
-multiply_defined
-multiply_defined_unused
-noall_load
-no_dead_strip_inits_and_terms
-nofixprebinding
-nomultidefs
-noprebind
-noseglinkedit
-pagezero_size
-prebind
-prebind_all_twolevel_modules
-private_bundle
-read_only_relocs
-sectalign
-sectobjectsymbols
-whyload
-seg1addr
-sectcreate
-sectobjectsymbols
-sectorder
-segaddr
-segs_read_only_addr
-segs_read_write_addr
-seg_addr_table
-seg_addr_table_filename
-seglinkedit
-segprot
-segs_read_only_addr
-segs_read_write_addr
-single_module
-static
-sub_library
-sub_umbrella
-twolevel_namespace
-umbrella
-undefined
-unexported_symbols_list
-weak_reference_mismatches
-whatsloaded
These options are passed to the Darwin linker. The Darwin linker
man page describes them in detail.

DEC Alpha Options

These -m options are defined for the DEC Alpha implementations:

-mno-soft-float
-msoft-float
Use (do not use) the hardware floating-point instructions for
floating-point operations. When -msoft-float is specified,
functions in 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.

-mfp-reg
-mno-fp-regs
Generate code that uses (does not use) the floating-point register
set. -mno-fp-regs implies -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 $0 instead of $f0. This is a non-standard
calling sequence, so any function with a floating-point argument or
return value called by code compiled with -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.

-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 except that the inexact-flag is not maintained (see
below). If this option is turned on, the preprocessor macro
"_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
-ieee_with_no_inexact.

-mieee-with-inexact
This is like -mieee except the generated code also maintains the
IEEE inexact-flag. Turning on this option causes the generated
code to implement fully-compliant IEEE math. In addition to
"_IEEE_FP", "_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 inexact-flag, you
should normally not specify this option. Other Alpha compilers
call this option -ieee_with_inexact.

-mfp-trap-mode=trap-mode
This option controls what floating-point related traps are enabled.
Other Alpha compilers call this option -fptm trap-mode. The trap
mode can be set to one of four values:

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).

u In addition to the traps enabled by n, underflow traps are
enabled as well.

su Like u, but the instructions are marked to be safe for software
completion (see Alpha architecture manual for details).

sui Like su, but inexact traps are enabled as well.

-mfp-rounding-mode=rounding-mode
Selects the IEEE rounding mode. Other Alpha compilers call this
option -fprm rounding-mode. The rounding-mode can be one of:

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.

m Round towards minus infinity.

c Chopped rounding mode. Floating-point numbers are rounded
towards zero.

d Dynamic rounding mode. A field in the floating-point control
register (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 fpcr, d corresponds to
round towards plus infinity.

-mtrap-precision=trap-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:

p Program precision. This option is the default and means a trap
handler can only identify which program caused a floating-point
exception.

f Function precision. The trap handler can determine the
function that caused a floating-point exception.

i Instruction precision. The trap handler can determine the
exact instruction that caused a floating-point exception.

Other Alpha compilers provide the equivalent options called
-scope_safe and -resumption_safe.

-mieee-conformant
This option marks the generated code as IEEE conformant. You must
not use this option unless you also specify -mtrap-precision=i and
either -mfp-trap-mode=su or -mfp-trap-mode=sui. Its only effect is
to emit the line .eflag 48 in the function prologue of the
generated assembly file.

-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 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.

-mbwx
-mno-bwx
-mcix
-mno-cix
-mfix
-mno-fix
-mmax
-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 -mcpu=
option or that of the CPU on which GCC was built if none is
specified.

-msafe-bwa
-mno-safe-bwa
Indicate whether in the absence of the optional BWX instruction set
GCC should generate multi-thread and async-signal safe code for
byte and aligned word memory accesses.

-msafe-partial
-mno-safe-partial
Indicate whether GCC should generate multi-thread and async-signal
safe code for partial memory accesses, including piecemeal accesses
to unaligned data as well as block accesses to leading and trailing
parts of aggregate types or other objects in memory that do not
respectively start and end on an aligned 64-bit data boundary.

-mfloat-vax
-mfloat-ieee
Generate code that uses (does not use) VAX F and G floating-point
arithmetic instead of IEEE single and double precision.

-mexplicit-relocs
-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.

-msmall-data
-mlarge-data
When -mexplicit-relocs is in effect, static data is accessed via
gp-relative relocations. When -msmall-data is used, objects 8
bytes long or smaller are placed in a small data area (the ".sdata"
and ".sbss" sections) and are accessed via 16-bit relocations off
of the $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 -mlarge-data. With this option the data area is
limited to just below 2GB. Programs that require more than 2GB of
data must use "malloc" or "mmap" to allocate the data in the heap
instead of in the program's data segment.

When generating code for shared libraries, -fpic implies
-msmall-data and -fPIC implies -mlarge-data.

-msmall-text
-mlarge-text
When -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 -msmall-data is used,
the compiler can assume that all local symbols share the same $gp
value, and thus reduce the number of instructions required for a
function call from 4 to 1.

The default is -mlarge-text.

-mcpu=cpu_type
Set the instruction set and instruction scheduling parameters for
machine type cpu_type. You can specify either the 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 cpu_type are

ev4
ev45
21064
Schedules as an EV4 and has no instruction set extensions.

ev5
21164
Schedules as an EV5 and has no instruction set extensions.

ev56
21164a
Schedules as an EV5 and supports the BWX extension.

pca56
21164pc
21164PC
Schedules as an EV5 and supports the BWX and MAX extensions.

ev6
21264
Schedules as an EV6 and supports the BWX, FIX, and MAX
extensions.

ev67
21264a
Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX
extensions.

Native toolchains also support the value native, which selects the
best architecture option for the host processor. -mcpu=native has
no effect if GCC does not recognize the processor.

-mtune=cpu_type
Set only the instruction scheduling parameters for machine type
cpu_type. The instruction set is not changed.

Native toolchains also support the value native, which selects the
best architecture option for the host processor. -mtune=native has
no effect if GCC does not recognize the processor.

-mmemory-latency=time
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 time are

number
A decimal number representing clock cycles.

L1
L2
L3
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.

eBPF Options

-mframe-limit=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 32767. Defaults to whatever limit is imposed by the
version of the Linux kernel targeted.

-mbig-endian
Generate code for a big-endian target.

-mlittle-endian
Generate code for a little-endian target. This is the default.

-mjmpext
-mno-jmpext
Enable or disable generation of extra conditional-branch
instructions. Enabled for CPU v2 and above.

-mjmp32
-mno-jmp32
Enable or disable generation of 32-bit jump instructions. Enabled
for CPU v3 and above.

-malu32
-mno-alu32
Enable or disable generation of 32-bit ALU instructions. Enabled
for CPU v3 and above.

-mv3-atomics
-mno-v3-atomics
Enable or disable instructions for general atomic operations
introduced in CPU v3. Enabled for CPU v3 and above.

-mbswap
-mno-bswap
Enable or disable byte swap instructions. Enabled for CPU v4 and
above.

-msdiv
-mno-sdiv
Enable or disable signed division and modulus instructions.
Enabled for CPU v4 and above.

-msmov
-mno-smov
Enable or disable sign-extending move and memory load instructions.
Enabled for CPU v4 and above.

-mcpu=version
This specifies which version of the eBPF ISA to target. Newer
versions may not be supported by all kernels. The default is v4.

Supported values for version are:

v1 The first stable eBPF ISA with no special features or
extensions.

v2 Supports the jump extensions, as in -mjmpext.

v3 All features of v2, plus:

-<32-bit jump operations, as in -mjmp32>
-<32-bit ALU operations, as in -malu32>
-<general atomic operations, as in -mv3-atomics>
v4 All features of v3, plus:

-<Byte swap instructions, as in -mbswap>
-<Signed division and modulus instructions, as in -msdiv>
-<Sign-extending move and memory load instructions, as in
-msmov>
-mco-re
Enable BPF Compile Once - Run Everywhere (CO-RE) support. Requires
and is implied by -gbtf.

-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.

-mxbpf
Generate code for an expanded version of BPF, which relaxes some of
the restrictions imposed by the BPF architecture:

-<Save and restore callee-saved registers at function entry and>
exit, respectively.

-masm=dialect
Outputs assembly instructions using eBPF selected dialect. The
default is pseudoc.

Supported values for dialect are:

normal
Outputs normal assembly dialect.

pseudoc
Outputs pseudo-c assembly dialect.

-minline-memops-threshold=bytes
Specifies a size threshold in bytes at or below which memmove,
memcpy and memset shall always be expanded inline. Operations
dealing with sizes larger than this threshold would have to be
implemented using a library call instead of being expanded inline,
but since BPF doesn't allow libcalls, exceeding this threshold
results in a compile-time error. The default is 1024 bytes.

FR30 Options

These options are defined specifically for the FR30 port.

-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.

-mno-lsim
Assume that runtime support has been provided and so there is no
need to include the simulator library (libsim.a) on the linker
command line.

FT32 Options

These options are defined specifically for the FT32 port.

-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.

-mlra
Does nothing. Preserved for backward compatibility.

-mnodiv
Do not use div and mod instructions.

-mft32b
Enable use of the extended instructions of the FT32B processor.

-mcompress
Compress all code using the Ft32B code compression scheme.

-mnopm
Do not generate code that reads program memory.

FRV Options

-mgpr-32
Only use the first 32 general-purpose registers.

-mgpr-64
Use all 64 general-purpose registers.

-mfpr-32
Use only the first 32 floating-point registers.

-mfpr-64
Use all 64 floating-point registers.

-mhard-float
Use hardware instructions for floating-point operations.

-msoft-float
Use library routines for floating-point operations.

-malloc-cc
Dynamically allocate condition code registers.

-mfixed-cc
Do not try to dynamically allocate condition code registers, only
use "icc0" and "fcc0".

-mdword
Change ABI to use double word insns.

-mno-dword
Do not use double word instructions.

-mdouble
Use floating-point double instructions.

-mno-double
Do not use floating-point double instructions.

-mmedia
Use media instructions.

-mno-media
Do not use media instructions.

-mmuladd
Use multiply and add/subtract instructions.

-mno-muladd
Do not use multiply and add/subtract instructions.

-mfdpic
Select the FDPIC ABI, which uses function descriptors to represent
pointers to functions. Without any PIC/PIE-related options, it
implies -fPIE. With -fpic or -fpie, it assumes GOT entries and
small data are within a 12-bit range from the GOT base address;
with -fPIC or -fPIE, GOT offsets are computed with 32 bits. With a
bfin-elf target, this option implies -msim.

-minline-plt
Enable inlining of PLT entries in function calls to functions that
are not known to bind locally. It has no effect without -mfdpic.
It's enabled by default if optimizing for speed and compiling for
shared libraries (i.e., -fPIC or -fpic), or when an optimization
option such as -O3 or above is present in the command line.

-mTLS
Assume a large TLS segment when generating thread-local code.

-mtls
Do not assume a large TLS segment when generating thread-local
code.

-mgprel-ro
Enable the use of "GPREL" relocations in the FDPIC ABI for data
that is known to be in read-only sections. It's enabled by
default, except for -fpic or -fpie: even though it may help make
the global offset table smaller, it trades 1 instruction for 4.
With -fPIC or -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, -mno-gprel-ro can be used to disable it.

-multilib-library-pic
Link with the (library, not FD) pic libraries. It's implied by
-mlibrary-pic, as well as by -fPIC and -fpic without -mfdpic. You
should never have to use it explicitly.

-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 -mno-linked-fp.

-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.

-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.

-mlibrary-pic
Generate position-independent EABI code.

-macc-4
Use only the first four media accumulator registers.

-macc-8
Use all eight media accumulator registers.

-mpack
Pack VLIW instructions.

-mno-pack
Do not pack VLIW instructions.

-mno-eflags
Do not mark ABI switches in e_flags.

-mcond-move
Enable the use of conditional-move instructions (default).