GCC

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GCC or the GNU Compiler Collection is among the most widely used compiler toolchains in the world with official support for: C, C++, Objective-C, Objective-C++, Modula-2 Fortran, Ada, Go, and D. Third-party front ends exist for the Pascal, Modula-3, and VHDL programming languages.[1]

Installation

USE flags

USE flags for sys-devel/gcc The GNU Compiler Collection

+cxx Build support for C++ (bindings, extra libraries, code generation, ...)
+fortran Add support for fortran
+nls Add Native Language Support (using gettext - GNU locale utilities)
+openmp Build support for the OpenMP (support parallel computing), requires >=sys-devel/gcc-4.2 built with USE="openmp"
+pie Build programs as Position Independent Executables (a security hardening technique)
+sanitize Build support for various sanitizer functions (ASAN/TSAN/etc...) to find runtime problems in applications.
+ssp Build packages with stack smashing protection on by default
ada Build the ADA language (GNAT) frontend
cet Enable support for control flow hijacking protection. On amd64, this provides Intel Control Flow Enforcement Technology (CET). On arm64, this provides Branch Target Identification (BTI) and Pointer Authentication Code (PAC) support. This is only effective on amd64 or arm64. Only provides benefits on newer CPUs. For Intel, the CPU must be at least as new as Tiger Lake. For AMD, it must be at least as new as Zen 3. This is harmless on older CPUs, but provides no benefit either. For ARM64, PAC was introduced in armv8.3-a, and BTI was introduced in armv8.5-a. When combined with USE=hardened on amd64, GCC will set -fcf-protection by default when building software. The effect is minimal on systems which do not support it, other than a possible small increase in codesize for the NOPs. The generated code is therefore compatible with i686 at the earliest. On arm64, GCC will set -mbranch-protection=standard by default when building software.
custom-cflags Build with user-specified CFLAGS (unsupported)
d Enable support for the D programming language
debug Enables GCC's 'checking' facility via --enable-checking=yes,extra,rtl. This adds checks to various compiler passes for integrity and input validation. This can help catch possible miscompilations early as well as latent bugs which could become real problems in future, but at the cost of slower compile times when using GCC. Unrelated to backtraces.
default-stack-clash-protection Build packages with stack clash protection on by default as a hardening measure. This enables -fstack-clash-protection by default which protects against large memory allocations allowing stack smashing. May cause slightly increased codesize, but modern compilers have been adapted to optimize well for this case, as this mitigation is now quite common. See https://developers.redhat.com/blog/2020/05/22/stack-clash-mitigation-in-gcc-part-3 and https://www.qualys.com/2017/06/19/stack-clash/stack-clash.txt.
default-znow Request full relocation on start from ld.so by default. This sets the -z,now (BIND_NOW) flag by default on all linker invocations. By resolving all dynamic symbols at application startup, parts of the program can be made read-only as a hardening measure. This is closely related to RELRO which is also separately enabled by default. In some applications with many unresolved symbols (heavily plugin based, for example), startup time may be impacted.
doc Add extra documentation (API, Javadoc, etc). It is recommended to enable per package instead of globally
fixed-point Enable fixed-point arithmetic support for MIPS targets in gcc (Warning: significantly increases compile time!)
go Build the GCC Go language frontend.
graphite Add support for the framework for loop optimizations based on a polyhedral intermediate representation
hardened Activate default security enhancements for toolchain (gcc, glibc, binutils)
ieee-long-double Use accelerated 128-bit IEEE long double ABI (ppc64le only)
jit Enable libgccjit so other applications can embed gcc for Just-In-Time compilation.
libssp Build SSP support into a dedicated library rather than use the code in the C library (DO NOT ENABLE THIS IF YOU DON'T KNOW WHAT IT DOES)
lto Build using Link Time Optimizations (LTO). Note that GCC is always built with support for building other programs with LTO. This USE flag is for whether GCC itself is built and optimized with LTO.
modula2 Build the GCC Modula-2 language frontend.
multilib On 64bit systems, if you want to be able to compile 32bit and 64bit binaries
objc Build support for the Objective C code language
objc++ Build support for the Objective C++ language
objc-gc Build support for the Objective C code language Garbage Collector
pch Enable precompiled header support for faster compilation at the expense of disk space and memory
pgo Build GCC using Profile Guided Optimization (PGO). GCC will build itself and then analyze the just-built binary and then rebuild itself using the data obtained from analysis of codepaths taken. It does not affect whether GCC itself supports PGO when building other software. This substantially increases the build time needed for building GCC itself.
rust Build support for the Rust language, installs gccrs.
systemtap enable systemtap static probe points
test Enable dependencies and/or preparations necessary to run tests (usually controlled by FEATURES=test but can be toggled independently)
time64 Use 64-bit time_t type instead of the regular 32-bit type. This flag is forced on time64 profiles, and masked elsewhere. It should be only used when detection of type width is not possible (e.g. for SRC_URI)
valgrind Enable annotations for accuracy. May slow down runtime slightly. Safe to use even if not currently using dev-debug/valgrind
vanilla Do not add extra patches which change default behaviour; DO NOT USE THIS ON A GLOBAL SCALE as the severity of the meaning changes drastically
vtv Build support for virtual table verification (a C++ hardening feature). This does not control whether GCC defaults to using VTV> Note that actually using VTV breaks ABI and hence the whole system must be built with -fvtable-verify.
zstd Enable support for ZSTD compression
Data provided by the Gentoo Package Database · Last update: 2024-11-03 22:53 More information about USE flags

The graphite USE flag is needed for the -ftree-loop-optimize, -fgraphite-identity, -floop-nest-optimize, and -floop-parallelize-all options. [2]

Emerge

root #emerge --ask sys-devel/gcc

Invocation

user $gcc --help
Usage: gcc [options] file...
Options:
  -pass-exit-codes         Exit with highest error code from a phase.
  --help                   Display this information.
  --target-help            Display target specific command line options (including assembler and linker options).
  --help={common|optimizers|params|target|warnings|[^]{joined|separate|undocumented}}[,...].
                           Display specific types of command line options.
  (Use '-v --help' to display command line options of sub-processes).
  --version                Display compiler version information.
  -dumpspecs               Display all of the built in spec strings.
  -dumpversion             Display the version of the compiler.
  -dumpmachine             Display the compiler's target processor.
  -foffload=<targets>      Specify offloading targets.
  -print-search-dirs       Display the directories in the compiler's search path.
  -print-libgcc-file-name  Display the name of the compiler's companion library.
  -print-file-name=<lib>   Display the full path to library <lib>.
  -print-prog-name=<prog>  Display the full path to compiler component <prog>.
  -print-multiarch         Display the target's normalized GNU triplet, used as
                           a component in the library path.
  -print-multi-directory   Display the root directory for versions of libgcc.
  -print-multi-lib         Display the mapping between command line options and
                           multiple library search directories.
  -print-multi-os-directory Display the relative path to OS libraries.
  -print-sysroot           Display the target libraries directory.
  -print-sysroot-headers-suffix Display the sysroot suffix used to find headers.
  -Wa,<options>            Pass comma-separated <options> on to the assembler.
  -Wp,<options>            Pass comma-separated <options> on to the preprocessor.
  -Wl,<options>            Pass comma-separated <options> on to the linker.
  -Xassembler <arg>        Pass <arg> on to the assembler.
  -Xpreprocessor <arg>     Pass <arg> on to the preprocessor.
  -Xlinker <arg>           Pass <arg> on to the linker.
  -save-temps              Do not delete intermediate files.
  -save-temps=<arg>        Do not delete intermediate files.
  -no-canonical-prefixes   Do not canonicalize paths when building relative
                           prefixes to other gcc components.
  -pipe                    Use pipes rather than intermediate files.
  -time                    Time the execution of each subprocess.
  -specs=<file>            Override built-in specs with the contents of <file>.
  -std=<standard>          Assume that the input sources are for <standard>.
  --sysroot=<directory>    Use <directory> as the root directory for headers
                           and libraries.
  -B <directory>           Add <directory> to the compiler's search paths.
  -v                       Display the programs invoked by the compiler.
  -###                     Like -v but options quoted and commands not executed.
  -E                       Preprocess only; do not compile, assemble or link.
  -S                       Compile only; do not assemble or link.
  -c                       Compile and assemble, but do not link.
  -o <file>                Place the output into <file>.
  -pie                     Create a dynamically linked position independent
                           executable.
  -shared                  Create a shared library.
  -x <language>            Specify the language of the following input files.
                           Permissible languages include: c c++ assembler none
                           'none' means revert to the default behavior of
                           guessing the language based on the file's extension.

Options starting with -g, -f, -m, -O, -W, or --param are automatically
 passed on to the various sub-processes invoked by gcc.  In order to pass
 other options on to these processes the -W<letter> options must be used.

For bug reporting instructions, please see:
<https://bugs.gentoo.org/>.

Tips

Skip stage 1 build

Warning
This is unsupported and can break the system so this should not be used lightly. Refer to bug #705406 for more info.

It is possible to skip building stage 1 in the 3 stage build process by adding EXTRA_ECONF="--disable-bootstrap" via /etc/portage/package.env.

See also

References

  1. ↑ Wikipedia:GNU_Compiler_Collection
  2. ↑ https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html#Optimize-Options Retrieved on Feb 7 2023
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