GCC BPF support

.github/workflows/kernel-build.yml

@@ -46,6 +46,10 @@ jobs:
     timeout-minutes: 100
     env:
         ARTIFACTS_ARCHIVE: "vmlinux-${{ inputs.arch }}-${{ inputs.toolchain_full }}.tar.zst"
+
+        BUILD_BPF_GCC: ${{ inputs.arch == 'x86_64' && 'true' || '' }}
+        BPF_GCC_INSTALL_DIR: ${{ github.workspace }}/bpf-gcc
+
         BPF_NEXT_BASE_BRANCH: 'master'
         BPF_NEXT_FETCH_DEPTH: 64 # A bit of history is needed to facilitate incremental builds
         BUILD_SCHED_EXT_SELFTESTS: ${{ inputs.arch == 'x86_64' || inputs.arch == 'aarch64' && 'true' || '' }}
@@ -107,11 +111,19 @@ jobs:
           kbuild-output: ${{ env.KBUILD_OUTPUT }}
           max-make-jobs: 32
           llvm-version: ${{ inputs.llvm-version }}
+
+      - if: ${{ env.BUILD_BPF_GCC }}
+        name: Build GCC for BPF selftests
+        uses: ./build-bpf-gcc
+        with:
+          install-dir: ${{ env.BPF_GCC_INSTALL_DIR }}
+
       - name: Build selftests/bpf
         uses: ./build-selftests
         env:
           MAX_MAKE_JOBS: 32
           RELEASE: ${{ inputs.release && '1' || '' }}
+          BPF_GCC: ${{ env.BUILD_BPF_GCC && env.BPF_GCC_INSTALL_DIR || '' }}
         with:
           arch: ${{ inputs.arch }}
           kernel-root: ${{ env.KERNEL_ROOT }}

.github/workflows/test.yml

@@ -26,6 +26,7 @@ jobs:
             - {"test": "test_progs_no_alu32", "continue_on_error": false, "timeout_minutes": 360}
             - {"test": "test_verifier", "continue_on_error": false, "timeout_minutes": 360}
             - {"test": "test_maps", "continue_on_error": false, "timeout_minutes": 360}
+            - {"test": "test_progs-bpf_gcc", "continue_on_error": false, "timeout_minutes": 360}
             # Uncomment this to enable sched_ext selftests jobs
             # - {"test": "sched_ext", "continue_on_error": false, "timeout_minutes": 360}
       fail-fast: false

build-bpf-gcc/README.md

@@ -0,0 +1,15 @@
+# Build BPF GCC
+
+This action grabs latest GCC 15 source code snapshot from
+https://gcc.gnu.org/pub/gcc/snapshots, as well as most recent
+binutils, and builds GCC for BPF backend and installs it into a
+specified directory.
+
+Resulting artifacts are cached with
+[actions/cache](https://github.com/actions/cache), using snapshot
+names as a key.
+
+## Required inputs
+
+* `install-dir` - Path to the directory where built binaries are going to be installed, or restored from cache.
+

build-bpf-gcc/action.yml

@@ -0,0 +1,28 @@
+name: 'Build BPF GCC'
+description: 'Fetch latest GCC and binutils snapshots, bulid GCC and install into the target directory'
+inputs:
+  install-dir:
+    description: "Path to the GCC installation directory"
+    required: true
+
+runs:
+  using: "composite"
+  steps:
+
+    - name: Determine latest snapshots
+      id: latest-snapshots
+      shell: bash
+      run: ${GITHUB_ACTION_PATH}/latest-snapshots.sh
+
+    - uses: actions/cache@v4
+      id: cache
+      with:
+        path: ${{ inputs.install-dir }}
+        key: BPF-GCC-${{ steps.latest-snapshots.outputs.GCC_BASENAME }}-${{ steps.latest-snapshots.outputs.BINUTILS_BASENAME }}
+
+    - if: steps.cache.outputs.cache-hit != 'true'
+      name: Build BPF GCC
+      shell: bash
+      run: |
+        ${GITHUB_ACTION_PATH}/build-and-install.sh ${{ inputs.install-dir }}
+

build-bpf-gcc/build-and-install.sh

@@ -0,0 +1,53 @@
+#!/bin/bash
+set -euo pipefail
+
+source ${GITHUB_ACTION_PATH}/../helpers.sh
+
+INSTALLDIR=$(realpath $1)
+
+if [ -f ${GITHUB_ACTION_PATH}/.env ]; then
+    source ${GITHUB_ACTION_PATH}/.env
+else
+    echo "${GITHUB_ACTION_PATH}/.env is not found, supposed to be produced by latest-snapshots.sh"
+    exit 1
+fi
+
+foldable start download_tarballs "Downloading $BINUTILS_URL and $GCC_URL"
+
+test -f $BINUTILS_TARBALL || wget -q $BINUTILS_URL
+test -f $GCC_TARBALL || wget -q $GCC_URL
+
+foldable end download_tarballs
+
+foldable start build_binutils "Building $BINUTILS_BASENAME"
+
+if [ ! -f  "${INSTALLDIR}/${BINUTILS_BASENAME}.built" ]; then
+  tar xJf $BINUTILS_TARBALL
+  mkdir -p ${BINUTILS_BASENAME}/build-bpf
+  cd ${BINUTILS_BASENAME}/build-bpf
+  ../configure --target=bpf-unknown-none --prefix=$INSTALLDIR
+  make -j$(nproc) && make install
+  touch ${INSTALLDIR}/${BINUTILS_BASENAME}.built
+  cd -
+fi
+
+foldable end build_binutils
+
+foldable start build_gcc "Building $GCC_BASENAME"
+
+if [ ! -f  "${INSTALLDIR}/${GCC_BASENAME}.built" ]; then
+  tar xJf $GCC_TARBALL
+  cd ${GCC_BASENAME}
+  ./contrib/download_prerequisites
+  cd -
+  mkdir -p ${GCC_BASENAME}/build-bpf
+  cd ${GCC_BASENAME}/build-bpf
+  ../configure --target=bpf-unknown-none --prefix=$INSTALLDIR
+  make -j$(nproc) && make install
+  touch ${INSTALLDIR}/${GCC_BASENAME}.built
+  cd -
+fi
+
+foldable end build_gcc
+
+exit 0

build-bpf-gcc/latest-snapshots.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+set -euo pipefail
+
+BINUTILS_TARBALL=`wget https://snapshots.sourceware.org/binutils/trunk/latest/src/sha512.sum -O - -o /dev/null | grep -E 'binutils-[0-9a-f.-]+.tar.xz' | sed -e 's/.*\(binutils-[^<]*\).*/\1/'`
+GCC_TARBALL=`wget https://gcc.gnu.org/pub/gcc/snapshots/LATEST-15 -O - -o /dev/null | grep -E 'gcc-15-[0-9]+.tar.xz' | sed -e 's/.*\(gcc-15-[^<]*\).*/\1/'`
+
+BINUTILS_URL="https://snapshots.sourceware.org/binutils/trunk/latest/src/$BINUTILS_TARBALL"
+GCC_URL="https://gcc.gnu.org/pub/gcc/snapshots/LATEST-15/$GCC_TARBALL"
+
+BINUTILS_BASENAME=$(basename $BINUTILS_TARBALL .tar.xz)
+GCC_BASENAME=$(basename $GCC_TARBALL .tar.xz)
+
+cat > ${GITHUB_ACTION_PATH}/.env <<EOF
+BINUTILS_TARBALL=$BINUTILS_TARBALL
+GCC_TARBALL=$GCC_TARBALL
+BINUTILS_URL=$BINUTILS_URL
+GCC_URL=$GCC_URL
+BINUTILS_BASENAME=$BINUTILS_BASENAME
+GCC_BASENAME=$GCC_BASENAME
+EOF
+
+echo "BINUTILS_BASENAME=${BINUTILS_BASENAME}" >> "$GITHUB_OUTPUT"
+echo "GCC_BASENAME=${GCC_BASENAME}" >> "$GITHUB_OUTPUT"
+
+exit 0

build-selftests/build_selftests.sh

@@ -25,10 +25,17 @@ if [[ $TOOLCHAIN = "llvm" ]]; then
 	TOOLCHAIN="llvm-$LLVM_VERSION"
 fi
 
+if [ -n "${BPF_GCC:-}" ]; then
+    BPF_GCC="${BPF_GCC}/bin/bpf-unknown-none-gcc"
+else
+    BPF_GCC=
+fi
+
 foldable start build_selftests "Building selftests with $TOOLCHAIN"
 
 MAKE_OPTS=$(cat <<EOF
 	ARCH=${ARCH}
+	BPF_GCC=${BPF_GCC}
 	CROSS_COMPILE=${CROSS_COMPILE}
 	CLANG=clang-${LLVM_VERSION}
 	LLC=llc-${LLVM_VERSION}