Fix qemu container integration

.dockerignore

@@ -1,5 +1,6 @@
 .git*
 boards
+.packer_cache
 packer_cache
 scripts
 *.img

.github/workflows/docker.yml

@@ -23,6 +23,10 @@ jobs:
         uses: actions/[email protected]
 
       - name: Set up QEMU
+        # Required only for the multi-arch container builds that are pushed to Dockerhub.
+        # Setting up QEMU during normal PRs prevents testing of the container included
+        # QEMU setup.
+        if: ${{ github.ref == 'refs/heads/master' || startsWith(github.ref, 'refs/tags') }}
         uses: docker/setup-qemu-action@v2
         with:
           platforms: linux/amd64,linux/arm64

docker/Dockerfile

@@ -1,4 +1,10 @@
-FROM tonistiigi/binfmt:qemu-v7.0.0 AS binfmt
+# Source for qemu-user-static >7.0
+FROM public.ecr.aws/ubuntu/ubuntu:kinetic as qemu_binaries
+
+# hadolint ignore=DL3008
+RUN apt-get update -qq \
+ && apt-get install -qqy --no-install-recommends qemu-user-static
+
 FROM golang:1.19-bullseye AS builder
 
 # hadolint ignore=DL3008
@@ -49,7 +55,8 @@ WORKDIR /build
 
 COPY docker/entrypoint.sh /entrypoint.sh
 COPY --from=builder /build/packer-builder-arm /bin/packer /bin/
-COPY --from=binfmt /usr/bin/ /usr/bin
+# Only copy relevant qemu binaries to save container space
+COPY --from=qemu_binaries /usr/bin/qemu-arm-static /usr/bin/qemu-aarch64-static /usr/bin/
 
 # Enable detailed logging
 ENV PACKER_LOG=1

docker/entrypoint.sh

@@ -4,10 +4,34 @@ set -o errtrace -o nounset -o pipefail -o errexit
 
 echo "uname -a: $(uname -a)"
 
-/usr/bin/binfmt --install all
-
 PACKER=/bin/packer
 
+setup_qemu() {
+    # See also:
+    #   * https://github.com/qemu/qemu/blob/master/scripts/qemu-binfmt-conf.sh
+    #   * https://github.com/tonistiigi/binfmt/blob/master/cmd/binfmt/main.go
+    #   * https://docs.kernel.org/admin-guide/binfmt-misc.html
+
+    # mount binfmt_misc to be able to register qemu binaries
+    mount binfmt_misc -t binfmt_misc /proc/sys/fs/binfmt_misc
+
+    # reset
+    find /proc/sys/fs/binfmt_misc -type f -name 'qemu-*' -exec sh -c 'echo -1 > "$1"' shell {} \;
+
+    uname_m="$(uname -m)"
+    if [ "$uname_m" != "aarch64" ]; then
+        echo "Register qemu-aarch64"
+        echo ":qemu-aarch64:M::\x7fELF\x02\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\xb7\x00:\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff:/usr/bin/qemu-aarch64-static:F" > /proc/sys/fs/binfmt_misc/register
+    fi
+    echo "Register qemu-arm"
+    echo ":qemu-arm:M::\x7fELF\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x28\x00:\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff:/usr/bin/qemu-arm-static:F" > /proc/sys/fs/binfmt_misc/register
+}
+
+do_qemu_setup=${SETUP_QEMU:-true}
+if [ "$do_qemu_setup" = true ]; then
+    setup_qemu
+fi
+
 declare -a EXTRA_SYSTEM_PACKAGES=()
 for arg do
     shift