Zirconium Linux From Scratch - Version r12.4-45-systemd

Chapter 3. Cross Compiling Temporary Tools

GCC-15.2.0 - 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
SHA256 Checksum: 438fd996826b0c82485a29da03a72d71d6e3541a83ec702df4271f6fe025d24e
Additional Packages: https://mirror.csclub.uwaterloo.ca/gnu/gmp/gmp-6.3.0.tar.xz
Additional Packages: https://mirror.csclub.uwaterloo.ca/gnu/mpc/mpc-1.3.1.tar.gz
Additional Packages: https://mirror.csclub.uwaterloo.ca/gnu/mpfr/mpfr-4.2.2.tar.xz

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-1.3.1.tar.gz
mv -v mpc-1.3.1 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

Override the build rules of the libgcc and libstdc++ headers to allow building these libraries with POSIX threads support:

sed '/thread_header =/s/@.*@/gthr-posix.h/' \
    -i libgcc/Makefile.in libstdc++-v3/include/Makefile.in

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-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

The meaning of the new configure options:

--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.

--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.

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.

--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.

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 the section called “Contents of GCC.”