Re: [PATCH] docs/devel: Add cross-compiling doc

[Alistair Francis]

On Wed, Jul 26, 2023 at 10:08 PM Andrew Jones <ajones@ventanamicro.com> wrote:
>
> Add instructions for how to cross-compile QEMU for RISC-V. The
> file is named generically because there's no reason not to collect
> other architectures steps into the same file, especially because
> several subsections like those for cross-compiling QEMU dependencies
> using meson and a cross-file could be shared. Additionally, other
> approaches to creating sysroots, such as with debootstrap, may be
> documented in this file in the future.
>
> Signed-off-by: Andrew Jones <ajones@ventanamicro.com>

Acked-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

> ---
>  docs/devel/cross-compiling.rst | 221 +++++++++++++++++++++++++++++++++
>  1 file changed, 221 insertions(+)
>  create mode 100644 docs/devel/cross-compiling.rst
>
> diff --git a/docs/devel/cross-compiling.rst b/docs/devel/cross-compiling.rst
> new file mode 100644
> index 000000000000..1b988ba54e4c
> --- /dev/null
> +++ b/docs/devel/cross-compiling.rst
> @@ -0,0 +1,221 @@
> +.. SPDX-License-Identifier: GPL-2.0-or-later
> +
> +====================
> +Cross-compiling QEMU
> +====================
> +
> +Cross-compiling QEMU first requires the preparation of a cross-toolchain
> +and the cross-compiling of QEMU's dependencies. While the steps will be
> +similar across architectures, each architecture will have its own specific
> +recommendations. This document collects architecture-specific procedures
> +and hints that may be used to cross-compile QEMU, where typically the host
> +environment is x86.
> +
> +RISC-V
> +======
> +
> +Toolchain
> +---------
> +
> +Select a root directory for the cross environment
> +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> +
> +Export an environment variable pointing to a root directory
> +for the cross environment. For example, ::
> +
> +  $ export PREFIX="$HOME/opt/riscv"
> +
> +Create a work directory
> +^^^^^^^^^^^^^^^^^^^^^^^
> +
> +Tools and several components will need to be downloaded and built. Create
> +a directory for all the work, ::
> +
> +  $ export WORK_DIR="$HOME/work/xqemu"
> +  $ mkdir -p "$WORK_DIR"
> +
> +Select and prepare the toolchain
> +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> +
> +Select a toolchain such as [riscv-toolchain]_ and follow its instructions
> +for building and installing it to ``$PREFIX``, e.g. ::
> +
> +  $ cd "$WORK_DIR"
> +  $ git clone https://github.com/riscv/riscv-gnu-toolchain
> +  $ cd riscv-gnu-toolchain
> +  $ ./configure --prefix="$PREFIX"
> +  $ make -j$(nproc) linux
> +
> +Set the ``$CROSS_COMPILE`` environment variable to the prefix of the cross
> +tools and add the tools to ``$PATH``, ::
> +
> +$ export CROSS_COMPILE=riscv64-unknown-linux-gnu-
> +$ export PATH="$PREFIX/bin:$PATH"
> +
> +Also set ``$SYSROOT``, where all QEMU cross-compiled dependencies will be
> +installed. The toolchain installation likely created a 'sysroot' directory
> +at ``$PREFIX/sysroot``, which is the default location for most cross
> +tools, making it a good location, ::
> +
> +  $ mkdir -p "$PREFIX/sysroot"
> +  $ export SYSROOT="$PREFIX/sysroot"
> +
> +Create a pkg-config wrapper
> +^^^^^^^^^^^^^^^^^^^^^^^^^^^
> +
> +The build processes of QEMU and some of its dependencies depend on
> +pkg-config. Create a wrapper script for it which works for the cross
> +environment: ::
> +
> +  $ cat <<EOF >"$PREFIX/bin/${CROSS_COMPILE}pkg-config"
> +  #!/bin/sh
> +
> +  [ "\$SYSROOT" ] || exit 1
> +
> +  export PKG_CONFIG_PATH=
> +  export 
> PKG_CONFIG_LIBDIR="\${SYSROOT}/usr/lib/pkgconfig:\${SYSROOT}/usr/lib64/pkgconfig:\${SYSROOT}/usr/share/pkgconfig"
> +
> +  exec pkg-config "\$@"
> +  EOF
> +  $ chmod +x "$PREFIX/bin/${CROSS_COMPILE}pkg-config"
> +
> +Create a cross-file for meson builds
> +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> +
> +meson setup, used by some of QEMU's dependencies, needs a "cross-file" to
> +configure the cross environment. Create one, ::
> +
> +  $ cd "$WORK_DIR"
> +  $ cat <<EOF >cross_file.txt
> +  [host_machine]
> +  system = 'linux'
> +  cpu_family = 'riscv64'
> +  cpu = 'riscv64'
> +  endian = 'little'
> +
> +  [binaries]
> +  c = '${CROSS_COMPILE}gcc'
> +  cpp = '${CROSS_COMPILE}g++'
> +  ar = '${CROSS_COMPILE}ar'
> +  ld = '${CROSS_COMPILE}ld'
> +  objcopy = '${CROSS_COMPILE}objcopy'
> +  strip = '${CROSS_COMPILE}strip'
> +  pkgconfig = '${CROSS_COMPILE}pkg-config'
> +  EOF
> +
> +Cross-compile dependencies
> +--------------------------
> +
> +glibc
> +^^^^^
> +
> +If [riscv-toolchain]_ was selected for the toolchain then this step is
> +already complete and glibc has already been installed into ``$SYSROOT``.
> +Otherwise, cross-compile glibc and install it to ``$SYSROOT``.
> +
> +libffi
> +^^^^^^
> +
> +::
> +
> +  $ cd "$WORK_DIR"
> +  $ git clone https://gitlab.freedesktop.org/gstreamer/meson-ports/libffi.git
> +  $ cd libffi
> +  $ meson setup --cross-file ../cross_file.txt --prefix="$SYSROOT/usr" _build
> +  $ ninja -C _build
> +  $ ninja -C _build install
> +
> +*Building libffi seperately avoids a compilation error generated when
> +building it as a subproject of glib.*
> +
> +glib
> +^^^^
> +
> +::
> +
> +  $ cd "$WORK_DIR"
> +  $ git clone https://github.com/GNOME/glib.git
> +  $ cd glib
> +  $ meson setup --cross-file ../cross_file.txt --prefix="$SYSROOT/usr" _build
> +  $ ninja -C _build
> +  $ ninja -C _build install
> +
> +libslirp [optional]
> +^^^^^^^^^^^^^^^^^^^
> +
> +::
> +
> +  $ cd "$WORK_DIR"
> +  $ git clone https://gitlab.com/qemu-project/libslirp.git
> +  $ cd libslirp
> +  $ meson setup --cross-file ../cross_file.txt --prefix="$SYSROOT/usr" _build
> +  $ ninja -C _build
> +  $ ninja -C _build install
> +
> +pixman
> +^^^^^^
> +
> +First ensure the 'libtool' package is installed, e.g.
> +``sudo dnf install libtool`` or ``sudo apt install libtool``
> +
> +::
> +
> +  $ cd "$WORK_DIR"
> +  $ git clone https://gitlab.freedesktop.org/pixman/pixman
> +  $ cd pixman
> +  $ ./autogen.sh
> +  $ ./configure --prefix="$SYSROOT/usr" --host=riscv64-unknown-linux-gnu
> +  $ make -j$(nproc)
> +  $ make install
> +
> +Cross-compile QEMU
> +------------------
> +
> +::
> +
> +  $ cd "$WORK_DIR"
> +  $ git clone https://gitlab.com/qemu-project/qemu.git
> +  $ cd qemu
> +  $ mkdir -p build/install_dir
> +  $ cd build
> +  $ ../configure --target-list=riscv64-softmmu --cross-prefix=$CROSS_COMPILE 
> --prefix="$PWD/install_dir"
> +  $ make -j$(nproc)
> +  $ make install
> +
> +*Cross-compiling QEMU with different configurations may require more
> +dependencies to be built and installed in the sysroot.*
> +
> +Running QEMU
> +------------
> +
> +``build/install_dir`` may now be copied to the target and its bin
> +directory may be added to the target user's PATH. Prior to running
> +QEMU, ensure all the libraries it depends on are present, ::
> +
> +  $ ldd /path/to/bin/qemu-system-riscv64
> +
> +For example, it may necessary to install zlib libraries, e.g.
> +``sudo dnf install zlib-devel`` or ``sudo apt install zlib1g-dev``
> +
> +Subsequent QEMU Cross-compiling
> +-------------------------------
> +
> +Unless it's necessary to update and recompile the toolchain or
> +dependencies, then most steps do not need to be repeated for subsequent
> +compiles. Simply ensure the toolchain is in ``$PATH``, ``$SYSROOT`` points
> +at the sysroot, and then follow the QEMU cross-compile steps in
> +"Cross-compile QEMU". For example, ::
> +
> +  $ export PATH="$HOME/opt/riscv/bin:$PATH"
> +  $ export SYSROOT="$HOME/opt/riscv/sysroot"
> +  $ cd /path/to/qemu
> +  $ mkdir -p build/install_dir
> +  $ cd build
> +  $ ../configure --target-list=riscv64-softmmu 
> --cross-prefix=riscv64-unknown-linux-gnu- --prefix="$PWD/install_dir"
> +  $ make -j
> +  $ make install
> +
> +References
> +----------
> +
> +.. [riscv-toolchain] https://github.com/riscv/riscv-gnu-toolchain
> --
> 2.41.0
>
>