When you build a Docker image with docker buildx build and specify ‘–platform=linux/arm/v6’, the build container runs as arm7l rather than the expected arm6l, which creates issues if the build process assumes the observed CPU architecture is the actual target.

When running a Docker image, one can set the environment variable QEMU_CPU to arm1176 as in:

docker run -it --rm --platform linux/arm/v6 -e QEMU_CPU=arm1176 debian:testing-slim /bin/arch

Resulting in arm6l, but that doesn’t seem possible with docker build. Setting the QEMU_CPU varible before running docker buildx build will have no effect on the build container, and it’ll still identify the CPU architecture as arm7l.

Is there a way to pass the QEMU_CPU variable down to the build container?