Aram Hăvărneanu 2019 11 10 2025 8 11 https://xw.is/gcc-sysroot-build/ gcc-sysroot-build /gcc-sysroot-build/ Toolchains › Build GCC targeting user space Aram Hăvărneanu 2019 11 10 2025 8 11 Create source and build directories We use a suffix for the build directories so we can build for multiple targets at the same time. The name is arbitrary, we just choose the target name for convenience. mkdir -p ${HOME}/src mkdir -p ${HOME}/obj/binutils-2.45-s390x-linux-gnu mkdir -p ${HOME}/obj/gcc-15.2.0-s390x-linux-gnu Aram Hăvărneanu 2019 11 10 2025 8 11 Download the source code curl https://sourceware.org/pub/binutils/releases/binutils-2.45.tar.xz | tar -C $HOME/src -xJf - curl https://sourceware.org/pub/gcc/releases/gcc-15.2.0/gcc-15.2.0.tar.xz | tar -C $HOME/src -xJf - Aram Hăvărneanu 2019 11 10 2025 8 11 Download GCC prerequisites cd ${HOME}/src/gcc-15.2.0 ./contrib/download_prerequisites Aram Hăvărneanu 2019 11 10 2025 8 11 Prepare the sysroot You will need header files and libraries for the target system (here s390x-linux-gnu). You can either obtain those files from an existing system, or you can prepare a sysroot on an unrelated system. We will assume the sysroot is installed in ${HOME}/cross/s390x-linux-gnu/sys-root, which is the default location for GCC sysroots. Aram Hăvărneanu 2019 11 10 2025 8 11 Build and install Aram Hăvărneanu 2019 11 10 2025 8 11 Binutils Build and install GNU Binutils. cd ${HOME}/obj/binutils-2.45-s390x-linux-gnu ../../src/binutils-2.45/configure --prefix ${HOME}/cross --with-system-zlib --target s390x-linux-gnu --enable-multiarch --disable-multilib --with-sysroot make -j12 && make install Aram Hăvărneanu 2019 11 10 2025 8 11 GCC Build and install GNU GCC. If we use multiarch sysroot (such as from Debian), we must pass --enable-multiarch otherwise GCC will not find the target headers and libraries. Additionally, if the sysroot doesn't make use of multilib, we must explicitly disable via --disable-multilib as otherwise GCC might default to enabling it. Failure to set --enable-multiarch --disable-multilib will result in a failed build. cd ${HOME}/obj/gcc-15.2.0-s390x-linux-gnu ../../src/gcc-15.2.0/configure --prefix ${HOME}/cross --with-system-zlib --target s390x-linux-gnu --enable-languages=c,c++ --enable-multiarch --disable-multilib --with-sysroot make -j12 && make install Note that don't pass a specific directory to --with-sysroot because we placed out sysroot in the default location where GCC expects it. References Context Backlinks Aram Hăvărneanu 2025 8 12 https://xw.is/gdb-build/ gdb-build /gdb-build/ Toolchains › Build GDB and gdbserver(1) Aram Hăvărneanu 2025 8 12 Create source and build directories We use a suffix for the build directories so we can build for multiple targets at the same time. The name is arbitrary, we just choose the target name for convenience. mkdir -p ${HOME}/src mkdir -p ${HOME}/obj/gdb-16.3 mkdir -p ${HOME}/obj/gdb-16.3-riscv64-unknown-elf mkdir -p ${HOME}/obj/gdbserver-16.3-riscv64-linux-gnu Aram Hăvărneanu 2025 8 12 Download the source code curl https://sourceware.org/pub/gdb/releases/gdb-16.3.tar.xz | tar -C $HOME/src -xJf - Aram Hăvărneanu 2025 8 12 Build and install Aram Hăvărneanu 2025 8 12 GDB Make sure you have GMP 4.2+ and GNU MPFR 3.1.0+ installed. Set the path in --with-gmp and/or --with-mpfr, if needed. Aram Hăvărneanu 2025 8 12 Native debugging As we are building, running, and debugging binaries for the same architecture, we do not need to set host or target. Also note that we install it in a different prefix than the cross-debugging case below (${HOME} vs. ${HOME}/xgcc). cd ${HOME}/obj/gdb-16.3 ../../src/gdb-16.3/configure --prefix ${HOME} make -j12 && make install Aram Hăvărneanu 2025 8 12 Cross-debugging Set --target to your desired platform, here we use riscv64-unknown-elf representing bare-metal 64-bit RISC-V. It is fine for multiple cross toolchains to share the same --prefix and --bindir. cd ${HOME}/obj/gdb-16.3-riscv64-unknown-elf ../../src/gdb-16.3/configure --prefix ${HOME}/cross --with-system-zlib --target riscv64-unknown-elf --with-gmp=/opt/homebrew make -j12 && make install Aram Hăvărneanu 2025 8 12 gdbserver(1) gdbserver(1) is a program that runs on the same machine as the binaries you are debugging (the target machine above). You have two options, either compile gdbserver(1) natively on the target machine, or cross-compile it on the build machine and move it to the host machine (which for gdbserver(1) means the target machine). Of course if you can compile it natively you might as well compile GDB itself on the target machine and use that directly. Consult the GCC documentation if you are confused by this paragraph. Aram Hăvărneanu 2025 8 12 Native compilation gdbserver(1) is part of GDB, so just install GDB on the host as described above. Aram Hăvărneanu 2025 8 12 Cross compilation You need a GCC cross compiler targetting the host system (the one running gdbserver, here riscv64-linux-gnu). cd ${HOME}/obj/gdbserver-16.3-riscv64-linux-gnu ../../src/gdbserver-16.3/configure --prefix=/ --disable-gdb --disable-nls --host riscv64-linux-gnu LDFLAGS="-static" make -j12 all-gdbserver make DESTDIR=/tmp install-gdbserver We're building a statically-linked gdbserver so that it works on every system. For example, we might run gdbserver on a musl-based system, even though our Debian sysroot is based on GNU libc. The binary is available in /tmp/bin/gdbserver and can be moved to the host system. Related https://xw.is/binutils/ binutils /binutils/ GNU Binutils Software https://www.gnu.org/software/binutils/ Collection of low-level binary tools such as linkers and assemblers. https://xw.is/gcc/ gcc /gcc/ GNU Compiler Collection Software https://gcc.gnu.org GNU compiler suite. Aram Hăvărneanu 2019 11 28 2025 8 13 https://xw.is/debian-sysroot/ debian-sysroot /debian-sysroot/ Toolchains › Create Debian sysroots We'll create Debian sysroots suitable for a GCC cross compiler. Aram Hăvărneanu 2019 11 28 2025 8 13 Debootstrap machine Everything below runs on the debootstrap machine as root: sudo -i Aram Hăvărneanu 2019 11 28 2025 8 13 Prerequisites Debian or Ubuntu or any system that can run mmdebstrap(1) (modern alternative to debootstrap(8)), with a configured QEMU user emulator. Aram Hăvărneanu 2019 11 28 2025 8 13 Install debootstrap and associated tools apt install -y binfmt-support qemu-user-static mmdebstrap Aram Hăvărneanu 2019 11 28 2025 8 13 Run debootstrap We're going to create sysroots for riscv64 and s390x (see the list of supported Debian ports.). Add more packages to --include, if needed. archs="riscv64 s390x" for arch in ${archs}; do mmdebstrap --variant=buildd --include="zlib1g-dev libgmp-dev libmpfr-dev" --architectures=${arch} stable /tmp/sysroot-${arch}.tar.xz done Note that Debian images are multiarch, which means that libraries and header files are in a different location than the usual one. GCC must be made aware of this via --enable-multiarch when running the top-level configure script. Failure to set --enable-multiarch will result in a failed build. Additionally, GCC for the host should be configured just as the the GCC on the target (in the sysroot). For example, some platforms do not make use of multilib (even though GCC might support it), so in those cases multilib should be explicitly disabled on the build machine with --disable-multilib, because otherwise it might default to being enabled leading to build failure. Aram Hăvărneanu 2019 11 28 2025 8 13 Host machine The following runs on the host machine (the machine where you'll compile and run your cross compiler). It can be the same machine as the debootstrap machine. Aram Hăvărneanu 2019 11 28 2025 8 13 Create directories targets="riscv64-linux-gnu s390x-linux-gnu" for target in ${targets}; do mkdir -p $HOME/cross/${target}/sys-root done Note that when we created the sysroots we used the Debian architecture names (riscv64, s390x), but here we use the GCC target triple (riscv64-linux-gnu, s390x-linux-gnu). Aram Hăvărneanu 2019 11 28 2025 8 13 Copy sysroots Copy the sysroots from the debootstrap machine (here debian@194.182.186.188) to the host machine. targets="riscv64-linux-gnu s390x-linux-gnu" for target in ${targets}; do arch=$(echo ${target} | cut -d '-' -f 1) ssh debian@194.182.186.230 "cat /tmp/sysroot-${arch}.tar.xz" | tar -C ${HOME}/cross/${target}/sys-root -xJf - done Aram Hăvărneanu 2019 11 28 2025 8 13 Debootstrap machine (again) Aram Hăvărneanu 2019 11 28 2025 8 13 Cleanup Still as root: rm -rf /tmp/sysroot-*.tar.xz Contributions