Build foreign arch target Flatpak in a Docker instance (Docker optional though)

flatpak_mutliarch.md

Multiarch Flatpak in Docker

• (Optional if on Docker) Run your docker instance
  • Ensure that you include --privileged flag
  • Ensure to have qemu-user-static package in your Dockerfile
• Add --arch flag to flatpak's manifest or build-init, runtime --install, runtime --update, build-export, and build-bundle stages if doing it manually.
• Add new binfmt for your target arch. This is because you won't have qemu within the Sdk probably and you can't bindmount /usr into the flatpak container
  • WARNING! This will change handling of those arch QEMU emulators on your host too!
  • Mount binfmt with mount -t binfmt_misc none /proc/sys/fs/binfmt_misc
  • Remove old qemu mapping with echo -1 > /proc/sys/fs/binfmt_misc/qemu-<arch_name>
  • Add your new mapping with echo 'magic string' > /proc/sys/fs/binfmt_misc/register. You can use this as a template for them but make sure to append 'OC' as flags on them.
• Add --bind-mount=/var/opt/qemu-<arch_name>-static=/usr/bin/qemu-<arch_name>-static to your flatpak build step

That's it!