package uncompressed vmlinux

This allows for easier gdb integration, which expects an uncompressed
vmlinux.

Enable CONFIG_PVH so that qemu can boot the uncompressed image. Only
available on >= 5.0 kernels.

Disable CONFIG_RANDOMIZE_BASE since KASLR breaks the ability to set
breakpoints in gdb.

Only package source code references by the resulting vmlinux to reduce
the size of the image.

Signed-off-by: Lorenz Bauer <[email protected]>

Author: lmb

.github/workflows/build-and-push.yml

@@ -36,10 +36,10 @@ jobs:
       uses: docker/setup-buildx-action@v3
 
     - name: Cache ccache output
-      uses: actions/cache@v3
+      uses: actions/cache@v4
       with:
         path: ccache
-        key: ccache-${{ inputs.kernel_version }}-${{ hashFiles('config') }}
+        key: ccache-${{ inputs.kernel_version }}-${{ hashFiles('config-*') }}
 
     - name: Inject ccache into builder
       uses: reproducible-containers/[email protected]
@@ -63,6 +63,22 @@ jobs:
         annotations: |
           org.opencontainers.image.licenses=GPLv2
 
+    - name: Kernel metadata (debug)
+      id: debug-meta
+      uses: docker/metadata-action@v5
+      with:
+        images: ghcr.io/${{ github.repository_owner }}/ci-kernels
+        flavor: latest=false
+        tags: |
+          type=raw,value=${{ inputs.kernel_version }},suffix=-debug
+          type=match,pattern=^\d+\.\d+,group=0,value=${{ inputs.kernel_version }},suffix=-debug
+          type=raw,value=${{ inputs.static_tag }},enable=${{ inputs.static_tag != '' }},suffix=-debug
+
+        labels: |
+          org.opencontainers.image.licenses=GPLv2
+        annotations: |
+          org.opencontainers.image.licenses=GPLv2
+
     - name: Selftests metadata
       id: selftests-meta
       uses: docker/metadata-action@v5
@@ -72,7 +88,22 @@ jobs:
         tags: |
           type=raw,value=${{ inputs.kernel_version }},suffix=-selftests
           type=match,pattern=^\d+\.\d+,group=0,value=${{ inputs.kernel_version }},suffix=-selftests
-          type=raw,value=${{ inputs.static_tag }},suffix=-selftests,enable=${{ inputs.static_tag != '' }}
+          type=raw,value=${{ inputs.static_tag }},enable=${{ inputs.static_tag != '' }},suffix=-selftests
+        labels: |
+          org.opencontainers.image.licenses=GPLv2
+        annotations: |
+          org.opencontainers.image.licenses=GPLv2
+
+    - name: Selftests metadata (debug)
+      id: selftests-debug-meta
+      uses: docker/metadata-action@v5
+      with:
+        images: ghcr.io/${{ github.repository_owner }}/ci-kernels
+        flavor: latest=false
+        tags: |
+          type=raw,value=${{ inputs.kernel_version }},suffix=-selftests-debug
+          type=match,pattern=^\d+\.\d+,group=0,value=${{ inputs.kernel_version }},suffix=-selftests-debug
+          type=raw,value=${{ inputs.static_tag }},enable=${{ inputs.static_tag != '' }},suffix=-selftests-debug
         labels: |
           org.opencontainers.image.licenses=GPLv2
         annotations: |
@@ -101,6 +132,21 @@ jobs:
         annotations: ${{ steps.meta.outputs.annotations }}
         outputs: ${{ github.ref == 'refs/heads/main' && 'type=registry' || 'type=local,dest=/tmp/build/vmlinux' }}
 
+    - name: Build kernel (debug)
+      uses: docker/build-push-action@v5
+      with:
+        target: vmlinux-debug
+        provenance: false
+        platforms: |
+          linux/amd64
+          ${{ inputs.build_arm64 && 'linux/arm64' || '' }}
+        build-args: |
+          KERNEL_VERSION=${{ inputs.kernel_version }}
+        tags: ${{ steps.debug-meta.outputs.tags }}
+        labels: ${{ steps.debug-meta.outputs.labels }}
+        annotations: ${{ steps.debug-meta.outputs.annotations }}
+        outputs: ${{ github.ref == 'refs/heads/main' && 'type=registry' || 'type=local,dest=/tmp/build/vmlinux-debug' }}
+
     - name: Build selftests
       if: inputs.build_selftests
       uses: docker/build-push-action@v5
@@ -116,9 +162,24 @@ jobs:
         annotations: ${{ steps.selftests-meta.outputs.annotations }}
         outputs: ${{ github.ref == 'refs/heads/main' && 'type=registry' || 'type=local,dest=/tmp/build/selftests-bpf' }}
 
+    - name: Build selftests (debug)
+      if: inputs.build_selftests
+      uses: docker/build-push-action@v5
+      with:
+        target: selftests-bpf-debug
+        provenance: false
+        platforms: |
+          linux/amd64
+        build-args: |
+          KERNEL_VERSION=${{ inputs.kernel_version }}
+        tags: ${{ steps.selftests-debug-meta.outputs.tags }}
+        labels: ${{ steps.selftests-debug-meta.outputs.labels }}
+        annotations: ${{ steps.selftests-debug-meta.outputs.annotations }}
+        outputs: ${{ github.ref == 'refs/heads/main' && 'type=registry' || 'type=local,dest=/tmp/build/selftests-bpf-debug' }}
+
     - name: Store artifacts
       if: github.ref != 'refs/heads/main'
-      uses: actions/upload-artifact@v3
+      uses: actions/upload-artifact@v4
       with:
         name: Artifacts (${{ inputs.kernel_version }})
         if-no-files-found: error

Dockerfile

@@ -7,7 +7,7 @@ COPY download.sh .
 
 RUN --mount=type=cache,target=/tmp/kernel ./download.sh
 
-WORKDIR /usr/src/linux-${KERNEL_VERSION}
+WORKDIR /usr/src/linux
 
 COPY ccache.conf /etc/ccache.conf
 
@@ -39,6 +39,14 @@ RUN if [ -d tools/testing/selftests/bpf/bpf_testmod ]; then \
         ln -s usr/lib /tmp/output/lib; \
     fi
 
+FROM build-vmlinux as build-vmlinux-debug
+
+# Package debug info
+RUN mkdir -p /tmp/debug/boot
+
+COPY copy-debug.sh filter-debug.awk .
+RUN ./copy-debug.sh /tmp/debug
+
 # Build selftests
 FROM build-vmlinux as build-selftests
 
@@ -64,9 +72,23 @@ LABEL org.opencontainers.image.licenses=GPL-2.0-only
 
 COPY --from=build-vmlinux /tmp/output /
 
+# Debug
+FROM vmlinux as vmlinux-debug
+
+LABEL org.opencontainers.image.licenses=GPL-2.0-only
+
+COPY --from=build-vmlinux-debug /tmp/debug /
+
 # Prepare the selftests image
 FROM vmlinux as selftests-bpf
 
 LABEL org.opencontainers.image.licenses=GPL-2.0-only
 
 COPY --from=build-selftests /tmp/selftests /usr/src/linux
+
+# Debug
+FROM vmlinux-debug as selftests-bpf-debug
+
+LABEL org.opencontainers.image.licenses=GPL-2.0-only
+
+COPY --from=build-selftests /tmp/selftests /usr/src/linux

config

@@ -22,6 +22,9 @@ CONFIG_VIRTIO_PCI=y
 CONFIG_VIRTIO=y
 CONFIG_VT=y
 
+# Make debugging in gdb work.
+CONFIG_RANDOMIZE_BASE=n
+
 # Enable BPF related things
 # Please sort lines by alphabet ascending.
 CONFIG_BPF_JIT_ALWAYS_ON=y

config-x86_64

@@ -8,6 +8,7 @@ CONFIG_HYPERVISOR_GUEST=y
 CONFIG_KVM_GUEST=y
 CONFIG_MAXSMP=y
 CONFIG_PARAVIRT=y
+CONFIG_PVH=y
 
 # Get rid of some drivers and obsolete features
 CONFIG_AGP=n

copy-debug.sh

@@ -0,0 +1,15 @@
+#!/bin/bash
+# copy-debug.sh DEST
+
+set -eux
+set -o pipefail
+
+readonly output="${1}"
+
+# Retain vmlinux which includes debug symbols
+cp vmlinux "$output/boot/"
+
+# Retain only the sources referenced by dwarf debug info
+"${LLVM_DWARFDUMP}" "$output/boot/vmlinux" | \
+	awk -f filter-debug.awk | \
+	xargs cp -v --no-clobber --parents --target-directory="$output"

download.sh

@@ -12,4 +12,5 @@ fi
 
 cd /tmp/kernel
 curl --fail -L --time-cond "linux-${KERNEL_VERSION}.tar.${KERNEL_URL##*.}" -o "linux-${KERNEL_VERSION}.tar.${KERNEL_URL##*.}" "$KERNEL_URL"
-tar -xf "linux-${KERNEL_VERSION}.tar.${KERNEL_URL##*.}" -C /usr/src
+mkdir /usr/src/linux
+tar -xf "linux-${KERNEL_VERSION}.tar.${KERNEL_URL##*.}" --strip-components=1 -C /usr/src/linux

filter-debug.awk

@@ -0,0 +1,6 @@
+# Parse the output of llvm-dwarfdump to extract unique file names.
+
+/DW_AT_(call|decl)_file/ {
+	if ($2 ~ /<built-in>/) next;
+	if (!seen[$2]++) print substr($2, 3, length($2)-4)
+}