Part 4: Building the Cross-Compilation Toolchain

Overview

The cross-compilation toolchain allows you to build programs for your LFS system from your host system. This chapter builds the initial compiler and libraries in $LFS/tools.

Prerequisites

Completed Part 1-3
Logged in as lfs user
$LFS variable set
All packages downloaded to $LFS/sources

Build Order

Binutils-2.45 (Pass 1)
GCC-15.2.0 (Pass 1)
Linux-6.16.1 API Headers
Glibc-2.42
Libstdc++ from GCC-15.2.0

General Build Instructions

For each package:

# Extract package
cd $LFS/sources
tar -xf <package>.tar.xz
cd <package-directory>

# Create build directory (if recommended)
mkdir -v build
cd build

# Configure, build, install
../ configure <options>
make
make install

# Clean up
cd $LFS/sources
rm -rf <package-directory>

1. Binutils-2.45 - Pass 1

Purpose: Cross-linker and assembler

Build Time: 1 SBU Disk Space: 700 MB

cd $LFS/sources
tar -xf binutils-2.45.tar.xz
cd binutils-2.45

# Create dedicated build directory
mkdir -v build
cd build

# Configure
../configure --prefix=$LFS/tools \
             --with-sysroot=$LFS \
             --target=$LFS_TGT \
             --disable-nls \
             --enable-gprofng=no \
             --disable-werror \
             --enable-new-dtags \
             --enable-default-hash-style=gnu

# Build
make

# Install
make install

# Cleanup
cd $LFS/sources
rm -rf binutils-2.45

Configure Options Explained:

--prefix=$LFS/tools - Install to tools directory
--with-sysroot=$LFS - Tell linker where to find libraries
--target=$LFS_TGT - Cross-compile for LFS target
--disable-nls - Disable internationalization (not needed)
--enable-gprofng=no - Don't build gprofng (not needed)
--disable-werror - Don't stop on warnings
--enable-new-dtags - Use modern RPATH tag
--enable-default-hash-style=gnu - Use GNU hash style

2. GCC-15.2.0 - Pass 1

Purpose: Cross-compiler

Build Time: 11 SBU Disk Space: 4.2 GB

cd $LFS/sources
tar -xf gcc-15.2.0.tar.xz
cd gcc-15.2.0

# Extract required dependencies
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

# For x86_64, set default directory to lib (not lib64)
case $(uname -m) in
  x86_64)
    sed -e '/m64=/s/lib64/lib/' \
        -i.orig gcc/config/i386/t-linux64
 ;;
esac

# Create build directory
mkdir -v build
cd build

# Configure
../configure \
    --target=$LFS_TGT \
    --prefix=$LFS/tools \
    --with-glibc-version=2.42 \
    --with-sysroot=$LFS \
    --with-newlib \
    --without-headers \
    --enable-default-pie \
    --enable-default-ssp \
    --disable-nls \
    --disable-shared \
    --disable-multilib \
    --disable-threads \
    --disable-libatomic \
    --disable-libgomp \
    --disable-libquadmath \
    --disable-libssp \
    --disable-libvtv \
    --disable-libstdcxx \
    --enable-languages=c,c++

# Build
make

# Install
make install

# Create limits.h header
cd ..
cat gcc/limitx.h gcc/glimits.h gcc/limity.h > \
  `dirname $($LFS_TGT-gcc -print-libgcc-file-name)`/include/limits.h

# Cleanup
cd $LFS/sources
rm -rf gcc-15.2.0

Configure Options Explained:

--target=$LFS_TGT - Cross-compile for LFS target
--with-glibc-version=2.42 - Specify glibc version
--with-newlib - No C library available yet
--without-headers - No C headers available yet
--enable-default-pie - Position Independent Executables
--enable-default-ssp - Stack Smashing Protector
--disable-shared - Build static libraries only
--disable-multilib - Disable multi-arch support
--enable-languages=c,c++ - Only C and C++

3. Linux-6.16.1 API Headers

Purpose: Kernel headers for glibc

Build Time: <0.1 SBU Disk Space: 1.6 GB

cd $LFS/sources
tar -xf linux-6.16.1.tar.xz
cd linux-6.16.1

# Ensure tree is clean
make mrproper

# Extract headers
make headers

# Install to temporary location
find usr/include -type f ! -name '*.h' -delete
cp -rv usr/include $LFS/usr

# Cleanup
cd $LFS/sources
rm -rf linux-6.16.1

4. Glibc-2.42

Purpose: GNU C Library

Build Time: 4.5 SBU Disk Space: 850 MB

cd $LFS/sources
tar -xf glibc-2.42.tar.xz
cd glibc-2.42

# Create symlink for LSB compliance
case $(uname -m) in
    i?86)   ln -sfv ld-linux.so.2 $LFS/lib/ld-lsb.so.3
    ;;
    x86_64) ln -sfv ../lib/ld-linux-x86-64.so.2 $LFS/lib64
            ln -sfv ../lib/ld-linux-x86-64.so.2 $LFS/lib64/ld-lsb-x86-64.so.3
    ;;
esac

# Apply patch (if needed - check LFS docs)
# patch -Np1 -i ../glibc-2.42-fhs-1.patch

# Create build directory
mkdir -v build
cd build

# Ensure proper tools are used
echo "rootsbindir=/usr/sbin" > configparms

# Configure
../configure \
      --prefix=/usr \
      --host=$LFS_TGT \
      --build=$(../scripts/config.guess) \
      --enable-kernel=5.4 \
      --with-headers=$LFS/usr/include \
      --disable-nscd \
      libc_cv_slibdir=/usr/lib

# Build
make

# Install
make DESTDIR=$LFS install

# Fix hardcoded path
sed '/RTLDLIST=/s@/usr@@g' -i $LFS/usr/bin/ldd

# Sanity check
echo 'int main(){}' | $LFS_TGT-gcc -xc -
readelf -l a.out | grep ld-linux
# Should show: [Requesting program interpreter: /lib64/ld-linux-x86-64.so.2]
# or [Requesting program interpreter: /lib/ld-linux.so.2] for 32-bit

rm -v a.out

# Cleanup
cd $LFS/sources
rm -rf glibc-2.42

Configure Options Explained:

--host=$LFS_TGT - Cross-compile for LFS
--build=$(../scripts/config.guess) - Auto-detect build system
--enable-kernel=5.4 - Minimum kernel version
--with-headers=$LFS/usr/include - Use Linux headers
--disable-nscd - Don't build name service cache daemon
libc_cv_slibdir=/usr/lib - Install shared libraries to /usr/lib

5. Libstdc++ from GCC-15.2.0

Purpose: C++ standard library

Build Time: 0.4 SBU Disk Space: 1.1 GB

cd $LFS/sources
tar -xf gcc-15.2.0.tar.xz
cd gcc-15.2.0

# Create build directory
mkdir -v build
cd build

# Configure
../libstdc++-v3/configure \
    --host=$LFS_TGT \
    --build=$(../config.guess) \
    --prefix=/usr \
    --disable-multilib \
    --disable-nls \
    --disable-libstdcxx-pch \
    --with-gxx-include-dir=/tools/$LFS_TGT/include/c++/15.2.0

# Build
make

# Install
make DESTDIR=$LFS install

# Remove libtool archive files
rm -v $LFS/usr/lib/lib{stdc++{,exp,fs},supc++}.la

# Cleanup
cd $LFS/sources
rm -rf gcc-15.2.0

Verification

After completing the cross-toolchain, verify it works:

# Test compiler
echo 'int main(){}' | $LFS_TGT-gcc -xc -
readelf -l a.out | grep ld-linux
rm a.out

# Expected output:
# [Requesting program interpreter: /lib64/ld-linux-x86-64.so.2]
# or
# [Requesting program interpreter: /lib/ld-linux.so.2]

Troubleshooting

Issue: configure fails with "C compiler cannot create executables"

Solution: Verify $LFS and $LFS_TGT are set:

echo $LFS
echo $LFS_TGT

Issue: make fails with permission errors

Solution: Ensure you're the lfs user and directories have correct ownership:

whoami  # Should be: lfs
ls -ld $LFS/tools

Issue: Cannot find headers

Solution: Verify Linux headers installed:

ls $LFS/usr/include/linux

Next Steps

Cross-toolchain complete! Proceed to:

Part 5: Build temporary tools using cross-compiler
Part 6: Enter chroot environment
Part 7: Build final LFS system

Important Notes

Never skip sanity checks
Save build logs for troubleshooting
Each package should be built in the order shown
Clean up source directories after each build to save space

Part 04 Cross Toolchain Build

Part 4: Building the Cross-Compilation Toolchain

Overview

Prerequisites

Build Order

General Build Instructions

1. Binutils-2.45 - Pass 1

2. GCC-15.2.0 - Pass 1

3. Linux-6.16.1 API Headers

4. Glibc-2.42

5. Libstdc++ from GCC-15.2.0

Verification

Troubleshooting

Issue: configure fails with "C compiler cannot create executables"

Issue: make fails with permission errors

Issue: Cannot find headers

Next Steps

Important Notes

References