Compile CI kernels from Amazon Linux repository

Use the amazon linux downstream of the linux kernel to derive our CI
kernels from, as this is closer to an actual production setup than just
taking the tip of upstream releases.

Signed-off-by: Patrick Roy <roypat@amazon.co.uk>

Author: roypat

resources/rebuild.sh

@@ -134,46 +134,35 @@ EOF
     rm -rf $INITRAMFS_BUILD
 }
 
-
-function get_linux_git {
-    # git clone -s -b v$KV ../../linux
-    # --depth 1
-    cd linux
-    LATEST_TAG=$(git tag -l "v$KV.*" --sort=v:refname |tail -1)
-    git clean -fdx
-    git checkout $LATEST_TAG
+function clone_amazon_linux_repo {
+    [ -d linux ] || git clone https://github.com/amazonlinux/linux linux
 }
 
-
-# Download the latest kernel source for the given kernel version
-function get_linux_tarball {
+# prints the git tag corresponding to the newest and best matching the provided kernel version $1
+# this means that if a microvm kernel exists, the tag returned will be of the form
+#
+#    microvm-kernel-$1.<patch number>.amzn2[023]
+#
+# otherwise choose the newest tag matching
+#
+#    kernel-$1.<patch number>.amzn2[023]
+function get_tag {
     local KERNEL_VERSION=$1
-    echo "Downloading the latest patch version for v$KERNEL_VERSION..."
-    local major_version="${KERNEL_VERSION%%.*}"
-    local url_base="https://cdn.kernel.org/pub/linux/kernel"
-    local LATEST_VERSION=$(
-        curl -fsSL $url_base/v$major_version.x/ \
-        | grep -o "linux-$KERNEL_VERSION\.[0-9]*\.tar.xz" \
-        | sort -rV \
-        | head -n 1 || true)
-    # Fetch tarball and sha256 checksum.
-    curl -fsSLO "$url_base/v$major_version.x/sha256sums.asc"
-    curl -fsSLO "$url_base/v$major_version.x/$LATEST_VERSION"
-    # Verify checksum.
-    grep "${LATEST_VERSION}" sha256sums.asc | sha256sum -c -
-    echo "Extracting the kernel source..."
-    tar -xaf $LATEST_VERSION
-    local DIR=$(basename $LATEST_VERSION .tar.xz)
-    ln -svfT $DIR linux
+
+    # list all tags from newest to oldest
+    (git --no-pager tag -l --sort=-creatordate | grep "microvm-kernel-$1\..*\.amzn2" \
+        || git --no-pager tag -l --sort=-creatordate | grep "kernel-$1\..*\.amzn2") | head -n1
 }
 
-function build_linux {
+function build_al_kernel {
     local KERNEL_CFG=$1
     # Extract the kernel version from the config file provided as parameter.
-    local KERNEL_VERSION=$(grep -Po "^# Linux\/\w+ \K(\d+\.\d+)" "$KERNEL_CFG")
+    local KERNEL_VERSION=$(echo $KERNEL_CFG | grep -Po "microvm-kernel-ci-$ARCH-\K(\d+\.\d+)")
 
-    get_linux_tarball $KERNEL_VERSION
     pushd linux
+    make distclean
+
+    git checkout $(get_tag $KERNEL_VERSION)
 
     arch=$(uname -m)
     if [ "$arch" = "x86_64" ]; then
@@ -187,8 +176,8 @@ function build_linux {
 
         # Patch 6.1 kernels on ARM with 6.10 patches for supporting VMGenID
         # via DeviceTree bindings.
-        # TODO: drop this (and remove the patches from the repo) when we switch
-        # to building kernels from AL tree.
+        # TODO: drop this (and remove the patches from the repo) when AL backports the
+        # patches to 6.1.
         if [[ $KERNEL_VERSION == "6.1" ]]; then
             for i in ../patches/vmgenid_dt/* ; do
                 patch -p1 < $i
@@ -204,9 +193,13 @@ function build_linux {
     make -j $(nproc) $target
     LATEST_VERSION=$(cat include/config/kernel.release)
     flavour=$(basename $KERNEL_CFG .config |grep -Po "\d+\.\d+\K(-.*)" || true)
-    OUTPUT_FILE=$OUTPUT_DIR/vmlinux-$LATEST_VERSION$flavour
+    # Strip off everything after the last number - sometimes AL kernels have some stuff there.
+    # e.g. vmlinux-4.14.348-openela -> vmlinux-4.14.348
+    normalized_version=$(echo "$LATEST_VERSION" | sed -E "s/(.*[[:digit:]]).*/\1/g")
+    OUTPUT_FILE=$OUTPUT_DIR/vmlinux-$normalized_version$flavour
     cp -v $binary_path $OUTPUT_FILE
     cp -v .config $OUTPUT_FILE.config
+
     popd &>/dev/null
 }
 
@@ -226,11 +219,13 @@ fi
 build_rootfs ubuntu-22.04 jammy
 build_initramfs
 
-build_linux $PWD/guest_configs/microvm-kernel-ci-$ARCH-4.14.config
-build_linux $PWD/guest_configs/microvm-kernel-ci-$ARCH-5.10.config
+clone_amazon_linux_repo
+
+build_al_kernel $PWD/guest_configs/microvm-kernel-ci-$ARCH-4.14.config
+build_al_kernel $PWD/guest_configs/microvm-kernel-ci-$ARCH-5.10.config
 if [ $ARCH == "x86_64" ]; then
-    build_linux $PWD/guest_configs/microvm-kernel-ci-$ARCH-5.10-no-acpi.config
+    build_al_kernel $PWD/guest_configs/microvm-kernel-ci-$ARCH-5.10-no-acpi.config
 fi
-build_linux $PWD/guest_configs/microvm-kernel-ci-$ARCH-6.1.config
+build_al_kernel $PWD/guest_configs/microvm-kernel-ci-$ARCH-6.1.config
 
 tree -h $OUTPUT_DIR