build esp32 images for both amd64 and arm64

[nikwest]

This will build images for esp32 both for amd64 and arm64.

• use official gcc docker image for building instead of mgos/cc
• use docker builder for building the images (buildx, builder needs to be setup before being able to build, see https://docs.docker.com/desktop/multi-arch/)
• TOOLCHAIN_URL moved into Dockerfile as it is arch dependent now and I couldn't figure out a way to pass arch specific build-args to docker
• Caveat: when building images they are not easily accessible locally from docker before pushing to registry, essentially there is also no separate push command. I was only be able to load single arch images into docker directly.
• also added xz-utils to Dockerfile as it looks like Espressif is using xz compression from next release. Prerequesites:
• rojer/fsync-stub library need to be updated with the pull request I submitted there to also build arm64 lib
• run docker buildx create --name mybuilder --use to create a new builder

TODO:

• also create multi arch images for esp8266 and others, if possible

[nikwest]

Yes, this seems to be like that. The registry is handling the multiarch images. Docker daemon doesn't know anything about it. I also was kind of surprised, see https://github.com/docker/buildx/issues/59.

If you want to load a freshly built image into docker directly you can use the --load command. But this only works for single arch images.

I think podman/buildah alternative doesnt have this restrictions like docker has. The only option I see for testing is to run a local registry container and push the images there. Looks straightforward but I haven't tried it. But I can look at it. Might be an useful addition.

[pimvanpelt]

Cool work, @nikwest, thanks for adding arm64 for Mongoose OS. I'm sure that the raspberry pi folks will appreciate it :-)

[rojer]

Yes, this seems to be like that. The only option I see for testing is to run a local registry container and push the images there.

what, what? this sucks. being able to iterate locally on images without uploading them is important - to me, personally :) can we have a special target that uses build and not buildx? build-local or whatever. or, if we set PLATFORMS = amd64, does it become a single-platform image and then we can --load?

[nikwest]

Yes, if you set PLATFORMS to a single arch then --load works.

[nikwest]

I also adapted things for the other device platforms:

• ESP8266: some mirror for isl isn't available not sure, if temporarily or for good, so build fails.
• for the other platforms I only changed the mklfs et al. to copy from the arch specific build folder I also added a target docker-load-% which will build and install an image for the native local platform

[rojer]

ok, let's go with this. thanks!