GCC

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GCC or the GNU Compiler Collection is among the most widely used compiler toolchains in the world with support for: C, C++, Objective-C, Fortran, Ada, Go, and D.

Installation

USE flags

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

ada Build the ADA language (GNAT) frontend
cet Enable support for Intel Control Flow Enforcement Technology (CET). Only effective on amd64/x86. 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. When combined with USE=hardened, 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.
custom-cflags Build with user-specified CFLAGS (unsupported)
cxx Build support for C++ (bindings, extra libraries, code generation, ...)
d Enable support for the D programming language
debug Enable extra debug codepaths, like asserts and extra output. If you want to get meaningful backtraces see https://wiki.gentoo.org/wiki/Project:Quality_Assurance/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!)
fortran Add support for fortran
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.
multilib On 64bit systems, if you want to be able to compile 32bit and 64bit binaries
nls Add Native Language Support (using gettextGNU locale utilities)
nptl Enable support for Native POSIX Threads Library, the new threading module (requires linux-2.6 or better usually)
objc Build support for the Objective C code language
objc-gc Build support for the Objective C code language Garbage Collector
openmp Build support for the OpenMP (support parallel computing), requires >=sys-devel/gcc-4.2 built with USE="openmp"
pch Enable precompiled header support for faster compilation at the expense of disk space and memory (>=sys-devel/gcc-3.4 only)
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.
pie Build programs as Position Independent Executables (a security hardening technique)
rust Build support for the Rust language, installs gccrs.
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
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)
valgrind Enable valgrind annotations for gcc internals (useful for gcc debugging).
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

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.
  --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.
  -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/>.

Removal

Unmerge

Warning
Danger, Will Robinson! While it is technically possible to remove GCC doing so is a very bad idea. Because Gentoo is source-based removing sys-devel/gcc will break your system and render you unable to install software.
root #emerge --ask --depclean --verbose sys-devel/gcc

See also

  • Clang — a "LLVM native" C/C++/Objective-C compiler using LLVM as a backend and optimizer.
  • GCC_optimization — an introduction to optimizing compiled code using safe, sane CFLAGS and CXXFLAGS.
  • Upgrading_GCC