This project allows you to build docker files, that run on one architecture (HOST_ARCH) but execute commands on a different architecture (GUEST_ARCH).

For example, you could build a Docker image, that runs on your x86_64 host CI, using which you can run/build aarch64 binaries.

• GUEST_ARCH, the architecture the container is supposed to emulate (can be any of the architectures, that have an alpine chroot available. You can find a list here).
• ALPINE_VERSION, allows you to specify which alpine version the chroot runs on. (Might be limited depending on which GUEST_ARCH you chose)
• CHROOT_DIR, where the chroot is located inside of the Docker container. This is set to /chroot by default, and you probably won't need to change this.

As of writing the docker image can be build by marking the Dockerfile as executable, and then executing it:

chmod +x Dockerfile
./Dockerfile
# if you do not have docker setup to run rootless,
# you might have to prepend sudo or doas to the previous command

If you do not feel comfortable with marking Dockerfiles as executable, you can use the following command instead:

docker build . -t alpine-cross
# if you do not have docker setup to run rootless,
# you might have to prepend sudo or doas to the previous command

docker buildx build --platform linux/arm64 . -t alpine-cross
# if you do not have docker setup to run rootless,
# you might have to prepend sudo or doas to the previous command

To run the container, you have to add the --privileged option to docker run.

For example to validate your setup, you could run the following command.

docker run --privileged -it alpine-cross uname -m
# if you do not have docker setup to run rootless,
# you might have to prepend sudo or doas to the previous command

This should print the architecture name of the GUEST_ARCH

As you may have noticed from the command above, the chroot accepts command line parameters. By using them, you can also start a shell:

docker run --privileged -it alpine-cross ash
# if you do not have docker setup to run rootless,
# you might have to prepend sudo or doas to the previous command

For more information on binfmt_misc, I found the following websites helpful:

• alpine binfmt chroot guide
• ktprograms gist
• pmbootstrap source