Add build infra

Mostly a copy over from vmtest repo with a few pathing changes.

.github/workflows/kernels.yml

@@ -0,0 +1,68 @@
+# This job builds test kernels and uploads them to the `assets` dummy release.
+#
+# It works by looking at the KERNELS file in the repository and checks it
+# against all the already-uploaded kernels.
+
+name: Kernels
+
+on:
+  push:
+    branches: [ "master" ]
+
+concurrency:
+  # Ensure only a single instance of this job is run at any time
+  group: ${{ github.ref }}
+
+permissions:
+  contents: write
+
+jobs:
+  build-upload:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v3
+
+    - name: Calculate needed kernels
+      id: calculate
+      env:
+        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+      run: |
+        existing=$(gh release view test_assets --json assets --jq '.[][].name')
+
+        # Begin multiline output parameter
+        echo "NEEDED_KERNELS<<MULTILINE_EOF" >> "$GITHUB_OUTPUT"
+
+        echo "$existing" | python3 -c '
+        import sys
+
+        # Calculate kernels that have already been uploaded
+        existing = {line.strip() for line in sys.stdin}
+        with open("./KERNELS", "r") as f:
+            lines = {line.strip() for line in f if line.strip()}
+
+        # Print to stdout kernel we need to build and upload
+        for line in lines:
+            version = line.strip()
+            name = f"bzImage-{version}"
+            if name not in existing:
+                print(line)
+        ' | tee -a "$GITHUB_OUTPUT"
+
+        # End multiline output parameter
+        echo "MULTILINE_EOF" >> "$GITHUB_OUTPUT"
+
+    - name: Build needed kernels
+      run: |
+        while IFS= read -r version; do
+            echo "Building: ${version}"
+            ./build.sh "$version"
+        done <<< "${{ steps.calculate.outputs.NEEDED_KERNELS }}"
+
+    - name: Upload freshly built kernels
+      env:
+        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+      run: |
+        for kernel in bzImage-*; do
+          gh release upload test_assets "$kernel"
+        done

KERNELS

@@ -0,0 +1 @@
+v5.15

build.sh

@@ -0,0 +1,49 @@
+#!/bin/bash
+#
+# Build a vmtest ready kernel.
+#
+# Usage:
+#   ./build.sh v6.2
+
+set -eu
+
+# Formats a version string to a comparable number
+# eg. v1.2.3 => 1002003
+function version {
+	# Strip the leading 'v'
+	local vstripped="${1:1}"
+	echo "$vstripped" | awk -F. '{ printf("%d%03d%03d\n", $1,$2,$3); }'
+}
+
+# Go to repo root
+cd "$(git rev-parse --show-toplevel)"
+
+if [[ $# -ne 1 ]]; then
+	echo "Usage: $0 <kernel-tag>"
+	exit 1
+fi
+
+VERSION="$1"
+
+# Anything older than 5.15 we need to use alpine 3.16, which at the time of
+# writing is the oldest supported alpine version that contains all the build
+# deps (pahole in particular).  We need old alpines to use an older GCC. Newer
+# GCCs have better warnings and they break old kernel builds.
+ALPINE_VERSION=3.18
+if [[ $(version "$1") -le $(version "v5.15") ]]; then
+	ALPINE_VERSION=3.16
+fi
+
+# Build builder
+docker build \
+	--build-arg ALPINE_VERSION="$ALPINE_VERSION" \
+	--build-arg KERNEL_TAG="$1" \
+	-t vmtest-kernel-builder-"$VERSION" \
+	-f docker/Dockerfile.kernel \
+	.
+
+# Run builder
+docker run --rm -v "$(pwd):/output" vmtest-kernel-builder-"$VERSION"
+
+# Rename bzImage appropriately
+mv -f bzImage bzImage-"$VERSION"

build_kernel.sh

@@ -0,0 +1,49 @@
+#!/bin/bash
+#
+# Build a vmtest ready kernel.
+#
+# Usage:
+#   ./build.sh v6.2
+
+set -eu
+
+# Formats a version string to a comparable number
+# eg. v1.2.3 => 1002003
+function version {
+	# Strip the leading 'v'
+	local vstripped="${1:1}"
+	echo "$vstripped" | awk -F. '{ printf("%d%03d%03d\n", $1,$2,$3); }'
+}
+
+# Go to repo root
+cd "$(git rev-parse --show-toplevel)"
+
+if [[ $# -ne 1 ]]; then
+	echo "Usage: $0 <kernel-tag>"
+	exit 1
+fi
+
+VERSION="$1"
+
+# Anything older than 5.15 we need to use alpine 3.16, which at the time of
+# writing is the oldest supported alpine version that contains all the build
+# deps (pahole in particular).  We need old alpines to use an older GCC. Newer
+# GCCs have better warnings and they break old kernel builds.
+ALPINE_VERSION=3.18
+if [[ $(version "$1") -le $(version "v5.15") ]]; then
+	ALPINE_VERSION=3.16
+fi
+
+# Build builder
+docker build \
+	--build-arg ALPINE_VERSION="$ALPINE_VERSION" \
+	--build-arg KERNEL_TAG="$1" \
+	-t vmtest-kernel-builder-"$VERSION" \
+	-f docker/Dockerfile.kernel \
+	.
+
+# Run builder
+docker run --rm -v "$(pwd):/output" vmtest-kernel-builder-"$VERSION"
+
+# Rename bzImage appropriately
+mv -f bzImage bzImage-"$VERSION"

config/config.x86_64

@@ -44,6 +44,7 @@ CONFIG_CRYPTO_XXHASH=y
 CONFIG_DCB=y
 CONFIG_DEBUG_INFO_BTF=y
 CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y
+CONFIG_X86_DECODER_SELFTEST=n
 CONFIG_DEFAULT_FQ_CODEL=y
 CONFIG_DEFAULT_RENO=y
 CONFIG_DEFAULT_SECURITY_DAC=y

docker/Dockerfile.kernel

@@ -0,0 +1,36 @@
+ARG ALPINE_VERSION
+FROM alpine:${ALPINE_VERSION}
+
+RUN apk update && apk add \
+  bash \
+  bison \
+  build-base \
+  diffutils \
+  elfutils-dev \
+  findutils \
+  flex \
+  git \
+  gzip \
+  linux-headers \
+  pahole \
+  perl \
+  python3 \
+  openssl \
+  openssl-dev \
+  xz \
+  zstd
+
+WORKDIR /
+
+ARG KERNEL_REPO=https://github.com/torvalds/linux.git
+ARG KERNEL_TAG
+
+RUN git clone --depth 1 ${KERNEL_REPO} linux --branch ${KERNEL_TAG}
+WORKDIR linux
+
+COPY ./docker/config_kernel.sh config_kernel.sh
+COPY ./docker/build_kernel_container.sh build_kernel_container.sh
+COPY ./config config
+RUN ./config_kernel.sh
+
+ENTRYPOINT ["./build_kernel_container.sh"]

docker/build_kernel_container.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+#
+# Build kernel from inside container.
+#
+# Note this script expects the bind mounted output directly to be mounted
+# at /output.
+
+set -eux
+
+make -j "$(nproc)" bzImage
+bzimage=$(find . -type f -name bzImage)
+cp "$bzimage" /output

docker/config_kernel.sh

@@ -0,0 +1,11 @@
+#!/bin/bash
+#
+# Configure a vmtest ready kernel.
+#
+# Run this inside kernel source tree root.
+
+set -eux
+
+# Set kconfig
+cat config/config config/config.x86_64 config/config.vm > .config
+make olddefconfig