build: publish a pinned kernel build environment image

.github/workflows/buildenv-diff.yml

@@ -0,0 +1,71 @@
+name: Buildenv Package Diff
+on:
+  # When a PR bumps the kernel-buildenv digest pin (normally dependabot), show
+  # what actually changed between the two images: each image carries its own
+  # package manifest at /usr/share/buildenv/packages.tsv, so the diff is just
+  # two pulls and a compare, posted to the check summary for the reviewer.
+  pull_request:
+    paths:
+      - "Dockerfile"
+permissions:
+  contents: read
+  packages: read
+jobs:
+  diff:
+    name: package diff
+    runs-on: ubuntu-latest
+    steps:
+      - name: Harden the runner (Audit all outbound calls)
+        uses: step-security/harden-runner@9af89fc71515a100421586dfdb3dc9c984fbf411 # v2.19.4
+        with:
+          egress-policy: audit
+      - name: checkout repository
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v4
+      - name: docker login ghcr.io
+        uses: Wandalen/wretry.action@e68c23e6309f2871ca8ae4763e7629b9c258e1ea # v3.8.0
+        with:
+          action: docker/login-action@b45d80f862d83dbcd57f89517bcf500b2ab88fb2 # v4.0.0
+          with: |
+            registry: ghcr.io
+            username: "${{github.actor}}"
+            password: "${{secrets.GITHUB_TOKEN}}"
+      - name: diff package manifests
+        run: |
+          extract_ref() {
+            grep -oE 'ghcr\.io/edera-dev/kernel-buildenv[^[:space:]]*@sha256:[0-9a-f]+' "$1" | head -1 || true
+          }
+          git fetch --depth 1 origin "${{ github.base_ref }}"
+          git show FETCH_HEAD:Dockerfile > Dockerfile.base 2>/dev/null || : > Dockerfile.base
+          OLD_REF="$(extract_ref Dockerfile.base)"
+          NEW_REF="$(extract_ref Dockerfile)"
+          if [ -z "${NEW_REF}" ] || [ "${OLD_REF}" = "${NEW_REF}" ]; then
+            echo "kernel-buildenv pin unchanged; nothing to diff"
+            exit 0
+          fi
+          MANIFEST=/usr/share/buildenv/packages.tsv
+          docker run --rm "${NEW_REF}" cat "${MANIFEST}" > packages-new.tsv
+          {
+            echo "## kernel-buildenv package changes"
+            echo ""
+          } >> "${GITHUB_STEP_SUMMARY}"
+          if [ -z "${OLD_REF}" ]; then
+            {
+              echo "New pin \`${NEW_REF}\` (no previous pin to diff against);"
+              echo "$(wc -l < packages-new.tsv) packages in the image."
+            } >> "${GITHUB_STEP_SUMMARY}"
+            exit 0
+          fi
+          docker run --rm "${OLD_REF}" cat "${MANIFEST}" > packages-old.tsv
+          {
+            echo "\`${OLD_REF}\`"
+            echo "→ \`${NEW_REF}\`"
+            echo ""
+            if diff -u packages-old.tsv packages-new.tsv > packages.diff; then
+              echo "No package version changes (image metadata/base layer only)."
+            else
+              echo '```diff'
+              # Skip the +++/--- header noise; keep only the package changes.
+              grep -E '^[+-][^+-]' packages.diff
+              echo '```'
+            fi
+          } >> "${GITHUB_STEP_SUMMARY}"

.github/workflows/buildenv.yml

@@ -0,0 +1,124 @@
+name: Build Environment Image
+on:
+  # Rebuild on a schedule so toolchain updates land as deliberate, dated image
+  # releases (which dependabot then proposes as digest bumps in the kernel
+  # Dockerfile) instead of drifting silently into every kernel build. The
+  # cadence balances cache stability (each new image is a cold sccache build)
+  # against sitting too long on Debian toolchain fixes.
+  schedule:
+    - cron: "0 0 1,15 * *"
+  workflow_dispatch:
+  push:
+    branches:
+      - main
+    paths:
+      - "Dockerfile.buildenv"
+      - ".github/workflows/buildenv.yml"
+permissions:
+  contents: read
+  packages: write
+  id-token: write
+concurrency:
+  group: "buildenv-publish"
+env:
+  IMAGE: ghcr.io/edera-dev/kernel-buildenv
+jobs:
+  build:
+    name: "build ${{ matrix.arch }}"
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - arch: amd64
+            platform: linux/amd64
+            runner: ubuntu-latest
+          - arch: arm64
+            platform: linux/arm64
+            runner: ubuntu-24.04-arm
+    runs-on: "${{ matrix.runner }}"
+    steps:
+      - name: Harden the runner (Audit all outbound calls)
+        uses: step-security/harden-runner@9af89fc71515a100421586dfdb3dc9c984fbf411 # v2.19.4
+        with:
+          egress-policy: audit
+      - name: checkout repository
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v4
+      - name: docker setup buildx
+        uses: docker/setup-buildx-action@d7f5e7f509e45cec5c76c4d5afdd7de93d0b3df5 # v4.1.0
+      - name: docker login ghcr.io
+        uses: Wandalen/wretry.action@e68c23e6309f2871ca8ae4763e7629b9c258e1ea # v3.8.0
+        with:
+          action: docker/login-action@b45d80f862d83dbcd57f89517bcf500b2ab88fb2 # v4.0.0
+          with: |
+            registry: ghcr.io
+            username: "${{github.actor}}"
+            password: "${{secrets.GITHUB_TOKEN}}"
+      - name: build and push by digest
+        run: |
+          docker buildx build \
+            -f Dockerfile.buildenv \
+            --platform "${{ matrix.platform }}" \
+            --metadata-file metadata.json \
+            --output "type=image,name=${IMAGE},push-by-digest=true,name-canonical=true,push=true" \
+            .
+          jq -r '."containerimage.digest"' metadata.json > "digest-${{ matrix.arch }}"
+      - name: extract package manifest
+        run: |
+          docker run --rm "${IMAGE}@$(cat digest-${{ matrix.arch }})" \
+            cat /usr/share/buildenv/packages.tsv > "packages-${{ matrix.arch }}.tsv"
+      - name: upload digest
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
+        with:
+          name: "buildenv-digest-${{ matrix.arch }}"
+          path: "digest-${{ matrix.arch }}"
+          if-no-files-found: error
+          compression-level: 0
+          retention-days: 1
+      - name: upload package manifest
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
+        with:
+          name: "buildenv-packages-${{ matrix.arch }}"
+          path: "packages-${{ matrix.arch }}.tsv"
+          if-no-files-found: error
+          compression-level: 0
+  merge:
+    name: merge and publish
+    needs: build
+    runs-on: ubuntu-latest
+    steps:
+      - name: Harden the runner (Audit all outbound calls)
+        uses: step-security/harden-runner@9af89fc71515a100421586dfdb3dc9c984fbf411 # v2.19.4
+        with:
+          egress-policy: audit
+      - name: install cosign
+        uses: sigstore/cosign-installer@6f9f17788090df1f26f669e9d70d6ae9567deba6 # v4.1.2
+      - name: docker setup buildx
+        uses: docker/setup-buildx-action@d7f5e7f509e45cec5c76c4d5afdd7de93d0b3df5 # v4.1.0
+      - name: docker login ghcr.io
+        uses: Wandalen/wretry.action@e68c23e6309f2871ca8ae4763e7629b9c258e1ea # v3.8.0
+        with:
+          action: docker/login-action@b45d80f862d83dbcd57f89517bcf500b2ab88fb2 # v4.0.0
+          with: |
+            registry: ghcr.io
+            username: "${{github.actor}}"
+            password: "${{secrets.GITHUB_TOKEN}}"
+      - name: download digests
+        uses: actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c # v8.0.1
+        with:
+          pattern: "buildenv-digest-*"
+          merge-multiple: true
+      - name: assemble and tag manifest list
+        run: |
+          TAG="$(date -u +%Y%m%d)"
+          docker buildx imagetools create \
+            -t "${IMAGE}:${TAG}" \
+            -t "${IMAGE}:latest" \
+            "${IMAGE}@$(cat digest-amd64)" \
+            "${IMAGE}@$(cat digest-arm64)"
+          DIGEST="$(docker buildx imagetools inspect "${IMAGE}:${TAG}" --format '{{.Manifest.Digest}}')"
+          cosign sign --yes "${IMAGE}@${DIGEST}"
+          {
+            echo "published \`${IMAGE}:${TAG}\`"
+            echo ""
+            echo "pin as: \`${IMAGE}:${TAG}@${DIGEST}\`"
+          } >> "${GITHUB_STEP_SUMMARY}"

Dockerfile.buildenv

@@ -0,0 +1,61 @@
+# Kernel build environment image, published as ghcr.io/edera-dev/kernel-buildenv.
+#
+# This exists so the toolchain is a deliberate, reviewed input to kernel builds
+# rather than whatever the Debian archive serves on build day: sccache keys
+# cache entries on the compiler binary's content hash, so an unplanned gcc
+# update silently turns a build into a 100% cache miss. The image is rebuilt on
+# a schedule (see .github/workflows/buildenv.yml); the kernel Dockerfile pins
+# it by digest and dependabot proposes bumps as reviewable PRs.
+FROM debian:bookworm@sha256:ed4fcc40bb1162b6d2d32e7bec15044d13963779abbe63f67f1cd62b06220519
+
+RUN export DEBIAN_FRONTEND=noninteractive && apt-get update && apt-get install -y \
+      build-essential squashfs-tools python3-yaml \
+      patch diffutils sed mawk findutils zstd \
+      python3 python3-packaging curl rsync cpio gpg grep \
+      flex bison pahole libssl-dev libelf-dev bc kmod && \
+      rm -rf /var/lib/apt/lists/*
+ARG TARGETARCH
+RUN if [ "${TARGETARCH}" = "amd64" ]; then \
+      apt-get update && apt-get install -y linux-headers-amd64 g++-aarch64-linux-gnu gcc-aarch64-linux-gnu && rm -rf /var/lib/apt/lists/*; fi
+RUN if [ "${TARGETARCH}" = "arm64" ]; then \
+      apt-get update && apt-get install -y linux-headers-arm64 g++-x86-64-linux-gnu gcc-x86-64-linux-gnu && rm -rf /var/lib/apt/lists/*; fi
+
+ARG SCCACHE_VERSION=0.16.0
+ARG SCCACHE_SHA256_AMD64=aec995a83ad3dff3d14b6314e08858b7b73d35ca85a5bcf3d3a9ec07dee35588
+ARG SCCACHE_SHA256_ARM64=f73a5c39f96bb6ebb89cc7915cf182260d4cbf30765322c5e793d0fe8bd80784
+# The wrappers must reference the real compiler by absolute path: /usr/lib/sccache
+# is first in PATH, so a bare compiler name would resolve back to the wrapper
+# itself and recurse.
+RUN case "${TARGETARCH}" in \
+      amd64) SCCACHE_ARCH=x86_64 SCCACHE_SHA256="${SCCACHE_SHA256_AMD64}" ;; \
+      arm64) SCCACHE_ARCH=aarch64 SCCACHE_SHA256="${SCCACHE_SHA256_ARM64}" ;; \
+      *) echo "unsupported TARGETARCH ${TARGETARCH}" >&2; exit 1 ;; \
+    esac && \
+    SCCACHE_DIST="sccache-v${SCCACHE_VERSION}-${SCCACHE_ARCH}-unknown-linux-musl" && \
+    curl -Lf -o /tmp/sccache.tar.gz "https://github.com/mozilla/sccache/releases/download/v${SCCACHE_VERSION}/${SCCACHE_DIST}.tar.gz" && \
+    echo "${SCCACHE_SHA256}  /tmp/sccache.tar.gz" | sha256sum -c - && \
+    tar -xz -C /tmp -f /tmp/sccache.tar.gz && \
+    install -m 0755 "/tmp/${SCCACHE_DIST}/sccache" /usr/local/bin/sccache && \
+    rm -rf /tmp/sccache.tar.gz "/tmp/${SCCACHE_DIST}" && \
+    mkdir -p /usr/lib/sccache && \
+    for compiler in cc c++ gcc g++ \
+      x86_64-linux-gnu-gcc x86_64-linux-gnu-g++ \
+      aarch64-linux-gnu-gcc aarch64-linux-gnu-g++; do \
+      [ -x "/usr/bin/${compiler}" ] || continue; \
+      printf '#!/bin/sh\nexec /usr/local/bin/sccache /usr/bin/%s "$@"\n' "${compiler}" >"/usr/lib/sccache/${compiler}"; \
+      chmod 0755 "/usr/lib/sccache/${compiler}"; \
+    done
+ENV PATH="/usr/lib/sccache:${PATH}"
+
+RUN useradd -ms /bin/sh build
+
+# Self-describing package manifest: lets any two image digests be diffed
+# without external records (docker run <image> cat /usr/share/buildenv/packages.tsv).
+# The buildenv-diff workflow uses this to summarize dependabot digest bumps.
+RUN mkdir -p /usr/share/buildenv && \
+    { dpkg-query -W -f '${Package}\t${Version}\t${Architecture}\n' | sort; \
+      printf 'sccache\t%s\tgithub-release\n' "${SCCACHE_VERSION}"; } \
+      >/usr/share/buildenv/packages.tsv
+
+LABEL org.opencontainers.image.source="https://github.com/edera-dev/linux-kernel-oci"
+LABEL org.opencontainers.image.description="Edera kernel build environment (toolchain + sccache)"