eden/docs/CrossCompile.md

Cross compiling

General guide for cross compiling.

Debian ARM64

A painless guide for cross compilation (or to test NCE) from a x86_64 system without polluting your main.

• Install QEMU: sudo pkg install qemu
• Download Debian 13: wget https://cdimage.debian.org/debian-cd/current/arm64/iso-cd/debian-13.0.0-arm64-netinst.iso
• Create a system disk: qemu-img create -f qcow2 debian-13-arm64-ci.qcow2 30G
• Run the VM: qemu-system-aarch64 -M virt -m 2G -cpu max -bios /usr/local/share/qemu/edk2-aarch64-code.fd -drive if=none,file=debian-13.0.0-arm64-netinst.iso,format=raw,id=cdrom -device scsi-cd,drive=cdrom -drive if=none,file=debian-13-arm64-ci.qcow2,id=hd0,format=qcow2 -device virtio-blk-device,drive=hd0 -device virtio-gpu-pci -device usb-ehci -device usb-kbd -device intel-hda -device hda-output -nic user,model=virtio-net-pci

Gentoo

Gentoo's cross-compilation setup is relatively easy, provided you're already familiar with portage. A cross toolchain file is provided. Throughout this section, replace aarch64 with whatever target architecture you desire.

Crossdev

First, emerge crossdev via sudo emerge -a sys-devel/crossdev.

Now, set up the environment depending on the target architecture; e.g.

sudo crossdev aarch64

QEMU

If you don't have a host Gentoo system of your target architecture, you should install a QEMU user setup for testing. To do so, enable the relevant USE flags for app-emulation/qemu:

app-emulation/qemu static-user qemu_user_targets_aarch64

To use cross-emerged shared libraries, you will also need to tell qemu where the sysroot is. You can do this with an alias:

alias qemu-aarch64="qemu-aarch64 -L /usr/aarch64-unknown-linux-gnu"

Dependencies

Dependencies are the same as normal Gentoo; simply replace the emerge command with emerge-<target>-unknown-linux-gnu (e.g. emerge-aarch64-unknown-linux-gnu). However, there are a few caveats:

Enabling GURU

Since Crossdev sysroots are effectively isolated from the system w.r.t Portage, you must manually enable GURU in your sysroot. Run the following as root:

mkdir -p /usr/aarch64-unknown-linux-gnu/etc/portage/repos.conf
cat << EOF > /usr/aarch64-unknown-linux-gnu/etc/portage/repos.conf/guru.conf
[guru]
location = /var/db/repos/guru
auto-sync = no
priority = 1
EOF

Package Errata

Crossdev is not perfect, and you may face some challenges with package that are not properly keyworded or have issues on specific architectures. These behaviors are, unfortunately, not well documented, and certain build systems such as Meson--and certain troublesome packages like GTK--are generally unfriendly towards cross-compilation.

Thus, it may be desirable to emerge a minimal set of dependencies and allow Eden's build system to handle the rest for you. At a minimum, you only need standard system libraries (Crossdev does this for you) and Qt:

sudo emerge-aarch64-unknown-linux-gnu dev-qt/qtbase:6 dev-qt/qtcharts:6

From here, CPMUtil will take care of everything else. For extra insurance, you may want to set -DCPMUTIL_FORCE_BUNDLED=ON in your configure command.

Building

From here, building is relatively standard. The cross toolchain file contains a few additional configurations, but generally all you need to do is set CROSS_TARGET and CMAKE_TOOLCHAIN_FILE. Disabling OpenGL is strongly recommended as well.

cmake -S . -B build/aarch64 -DCMAKE_TOOLCHAIN_FILE=CMakeModules/toolchains/GentooCross.cmake -GNinja -DCROSS_TARGET=aarch64 -DENABLE_OPENGL=OFF

With that done, you can build as normal:

cmake --build build/aarch64

And finally, run the compiled executable with QEMU!

qemu-aarch64 build/aarch64/bin/eden