Comment by voltagex_

Not a dockerfile, but it may be worth looking at buildroot [0] and qemu [1]. I'd like to say that I started 5 years ago with these tools and ended up working on embedded systems, but it's more like I started 5 years ago and ended up with drawers full of unsupported ARM boards.

0: https://buildroot.org

1: https://www.qemu.org/