6.18. GCC-16.1.0 - Pass 2

#### Linux From Scratch - Version r13.0-154-systemd

### Chapter 6. Cross Compiling Temporary Tools

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# 6.18. GCC-16.1.0 - Pass 2

The GCC package contains the GNU compiler collection, which includes the C and C++ compilers.

Approximate build time: 4.5 SBU
Required disk space: 6.0 GB

## 6.18.1. Installation of GCC

As in the first build of GCC, the GMP, MPFR, and MPC packages are required. Unpack the tarballs and move them into the required directories:

    tar -xf ../mpfr-4.2.2.tar.xz
    mv -v mpfr-4.2.2 mpfr
    tar -xf ../gmp-6.3.0.tar.xz
    mv -v gmp-6.3.0 gmp
    tar -xf ../mpc-1.4.1.tar.xz
    mv -v mpc-1.4.1 mpc

If you are building on x86_64, change the default directory name for 64-bit libraries to “lib”:

    case $(uname -m) in
      x86_64)
        sed -e '/m64=/s/lib64/lib/' \
            -i.orig gcc/config/i386/t-linux64
      ;;
    esac

Create a separate build directory again:

    mkdir -v build
    cd       build

Before starting to build GCC, remember to unset any environment variables that override the default optimization flags.

Now prepare GCC for compilation:

    ../configure                   \
        --build=$(../config.guess) \
        --host=$LFS_TGT            \
        --target=$LFS_TGT          \
        --prefix=/usr              \
        --with-build-sysroot=$LFS  \
        --enable-default-pie       \
        --enable-default-ssp       \
        --disable-fixincludes      \
        --disable-nls              \
        --disable-multilib         \
        --disable-libatomic        \
        --disable-libgomp          \
        --disable-libquadmath      \
        --disable-libsanitizer     \
        --disable-libssp           \
        --disable-libvtv           \
        --enable-languages=c,c++   \
        LDFLAGS_FOR_TARGET=-L$PWD/$LFS_TGT/libgcc \
        target_configargs=gcc_cv_target_thread_file=posix

The meaning of the new configure options:

`--target=$LFS_TGT`

  We are cross-compiling GCC, so it's impossible to build target libraries (`libgcc` and `libstdc++`) with the GCC binaries compiled in this pass—those binaries won't run on the host. The GCC build system will attempt to use the host's C and C++ compilers as a workaround by default. Building the GCC target libraries with a different version of GCC is not supported, so using the host's compilers may cause the build to fail. This parameter ensures the libraries are built by GCC pass 1.

`--with-build-sysroot=$LFS`

  Normally, using `--host` ensures that a cross-compiler is used for building GCC, and that compiler knows that it has to look for headers and libraries in `$LFS`. However, the build system for GCC uses additional tools which are not aware of this location. This switch is needed so those tools will find the needed files in `$LFS`, and not on the host.

`--disable-fixincludes`

  By default, during the installation of GCC some system headers would be “fixed” to be used with GCC. This is not necessary for a modern Linux system, and potentially harmful if a package is reinstalled after installing GCC. This switch prevents GCC from “fixing” the headers.

`--disable-libsanitizer`

  Disable GCC sanitizer runtime libraries. They are not needed for the temporary installation. In gcc-pass1 it was implied by `--disable-libstdcxx`, and now we can explicitly pass it.

`LDFLAGS_FOR_TARGET=...`

  Allow `libstdc++` to use the `libgcc` being built in this pass, instead of the previous version built in gcc-pass1. The previous version cannot properly support C++ exception handling because it was built without libc support.

`target_configargs=gcc_cv_target_thread_file=posix`

  Build the target libraries libgcc and libstdc++ with POSIX thread support enabled. The default is following the configuration of the compiler used for building the target library (in this case, gcc-pass1 which was configured with none thread support).

Compile the package:

    make

Install the package:

    make DESTDIR=$LFS install

As a finishing touch, create a utility symlink. Many programs and scripts run cc instead of gcc, which is used to keep programs generic and therefore usable on all kinds of UNIX systems where the GNU C compiler is not always installed. Running cc leaves the system administrator free to decide which C compiler to install:

    ln -sv gcc $LFS/usr/bin/cc

Details on this package are located in Section 8.32.2, “Contents of GCC.”

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