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Cross-platform Builds

Cross-platform builds are a bit tricky to setup, especially inside virtualizations such as lxc containers. This is still a bit work in progress, so expect some bugs.

How it works​

This feature depends on Qemu binfmt_misc support (QEMU user space emulation)(https://www.qemu.org/docs/master/user/main.html).

For every build a new buildcontainer is spawned, either on docker host or inside the aurcache-container with the selected target platform. Docker uses binfmt_misc to register the qemu interpreter for the target platform. This should happen automatically when the container is started.

Supported platforms​

  • x86_64 (default)
  • aarch64
  • armv7

Those platforms are limited to those 3 for now, because the archlinux baseimage is only available for those platforms. Which is required for the build container.

Limitations​

qemu-binfmt only supports x86_64. So this can only be used to cross compile from an x86_64 host to other platforms.

Troubleshooting​

If your output looks like this:

Pulling image: ghcr.io/lukas-heiligenbrunner/aurcache-builder:latest
{"msg":"exec container process (missing dynamic library?) `/usr/sbin/sh`: No such file or directory","level":"error","time":"2024-10-25T19:56:14.842412Z"}
Docker container wait error

You have misconfigured qemu-binfmt.

You might have a look at: https://dshcherb.github.io/2017/12/04/qemu-kvm-virtual-machines-in-unprivileged-lxd.html

binfmt_misc should be enabled in the kernel or as a kernel module. You can check this by running cat /proc/sys/fs/binfmt_misc/status. If it is not enabled, you can enable it by running mount binfmt_misc -t binfmt_misc /proc/sys/fs/binfmt_misc.