Unable to build Ryuk with s390x (buildkit/qemu)

[rnorth]

The multi-arch buildkit build is currently failing for the s390x platform, with a segmentation fault. This is despite no changes since #21, which was working in December.

This is replicable with GitHub Actions and Docker for Mac 3.3.0 (not tried older versions).

Many go subcommands fail (e.g. build, vet, fmt). mod download fails when using newer versions of Go.

So far all of the following avenues have proved fruitless:

• Pinning buildkit/binfmt to various versions
• Changing the tag used for golang build up to 1.16.3
• Changing the golang base image (from buster to alpine)

Quick analysis of the core dumps doesn't yield anything obvious to me.

[rnorth]

We could:

• investigate further and maybe find out the source of the problem; Ryuk release is blocked during that time
• wait; again Ryuk release is blocked
• disable build for s390x; this unblocks release but would give us uneven version/platform coverage

None of these options seems particularly good.

One alternative course of action would be to perform all of the multi-arch binary builds using go's multi-arch targetting, and just use buildx's to copy the right binary into an image. Essentially, we'd eliminate QEMU execution from the container build.

This would be a pain, but might be to most pragmatic approach.

[rnorth]

The passage of time may have fixed things; tonistiigi/binfmt:master (or a pinned equivalent) is now allowing the build to pass, it seems.