kubesolo-os/build/scripts/build-kernel-arm64.sh

#!/bin/bash
# build-kernel-arm64.sh — Build ARM64 kernel for Raspberry Pi 4/5
#
# Uses the official raspberrypi/linux kernel fork with bcm2711_defconfig
# as the base, overlaid with container-critical config options.
#
# Output is cached in $CACHE_DIR/custom-kernel-arm64/ and reused across builds.
#
# Requirements:
#   - gcc-aarch64-linux-gnu (cross-compiler)
#   - Standard kernel build deps (bc, bison, flex, etc.)
set -euo pipefail

SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
PROJECT_ROOT="$(cd "$SCRIPT_DIR/../.." && pwd)"
CACHE_DIR="${CACHE_DIR:-$PROJECT_ROOT/build/cache}"

# shellcheck source=../config/versions.env
. "$SCRIPT_DIR/../config/versions.env"

CUSTOM_KERNEL_DIR="$CACHE_DIR/custom-kernel-arm64"
CUSTOM_IMAGE="$CUSTOM_KERNEL_DIR/Image"
CUSTOM_MODULES="$CUSTOM_KERNEL_DIR/modules"
CUSTOM_DTBS="$CUSTOM_KERNEL_DIR/dtbs"

mkdir -p "$CACHE_DIR" "$CUSTOM_KERNEL_DIR"

# --- Skip if already built ---
if [ -f "$CUSTOM_IMAGE" ] && [ -d "$CUSTOM_MODULES" ]; then
    echo "==> ARM64 kernel already built (cached)"
    echo "    Image: $CUSTOM_IMAGE ($(du -h "$CUSTOM_IMAGE" | cut -f1))"
    exit 0
fi

# --- Verify cross-compiler ---
if ! command -v aarch64-linux-gnu-gcc >/dev/null 2>&1; then
    echo "ERROR: aarch64-linux-gnu-gcc not found"
    echo "Install: apt-get install gcc-aarch64-linux-gnu"
    exit 1
fi

echo "==> Building ARM64 kernel for Raspberry Pi..."
echo "    Branch: $RPI_KERNEL_BRANCH"
echo "    Repo:   $RPI_KERNEL_REPO"

# --- Download kernel source ---
KERNEL_SRC_DIR="$CACHE_DIR/rpi-linux-${RPI_KERNEL_BRANCH}"
if [ ! -d "$KERNEL_SRC_DIR" ]; then
    echo "==> Downloading RPi kernel source (shallow clone)..."
    git clone --depth 1 --branch "$RPI_KERNEL_BRANCH" \
        "$RPI_KERNEL_REPO" "$KERNEL_SRC_DIR"
else
    echo "==> Kernel source already cached"
fi

# --- Build in /tmp for case-sensitivity ---
KERNEL_BUILD_DIR="/tmp/kernel-build-arm64"
rm -rf "$KERNEL_BUILD_DIR"
cp -a "$KERNEL_SRC_DIR" "$KERNEL_BUILD_DIR"

cd "$KERNEL_BUILD_DIR"

# --- Apply base config (Pi 4 = bcm2711) ---
echo "==> Applying bcm2711_defconfig..."
make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- bcm2711_defconfig

# --- Apply container config overrides ---
CONFIG_FRAGMENT="$PROJECT_ROOT/build/config/rpi-kernel-config.fragment"
if [ -f "$CONFIG_FRAGMENT" ]; then
    echo "==> Applying KubeSolo config overrides..."
    while IFS= read -r line; do
        # Skip comments and empty lines
        case "$line" in \#*|"") continue ;; esac
        key="${line%%=*}"
        value="${line#*=}"
        case "$value" in
            y)   ./scripts/config --enable "$key" ;;
            m)   ./scripts/config --module "$key" ;;
            n)   ./scripts/config --disable "${key#CONFIG_}" ;;
            *)   ./scripts/config --set-str "$key" "$value" ;;
        esac
    done < "$CONFIG_FRAGMENT"
fi

# Handle "is not set" comments as disables
if [ -f "$CONFIG_FRAGMENT" ]; then
    while IFS= read -r line; do
        case "$line" in
            "# CONFIG_"*" is not set")
                key=$(echo "$line" | sed -n 's/^# \(CONFIG_[A-Z_]*\) is not set$/\1/p')
                [ -n "$key" ] && ./scripts/config --disable "${key#CONFIG_}"
                ;;
        esac
    done < "$CONFIG_FRAGMENT"
fi

# Resolve dependencies
make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- olddefconfig

# --- Build kernel + modules + DTBs ---
NPROC=$(nproc 2>/dev/null || echo 4)
echo ""
echo "==> Building ARM64 kernel (${NPROC} parallel jobs)..."
echo "    This may take 20-30 minutes..."

make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- -j"$NPROC" Image modules dtbs 2>&1

echo "==> ARM64 kernel build complete"

# --- Install to staging ---
echo "==> Installing Image..."
cp arch/arm64/boot/Image "$CUSTOM_IMAGE"

echo "==> Installing modules (stripped)..."
rm -rf "$CUSTOM_MODULES"
mkdir -p "$CUSTOM_MODULES"
make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- \
    INSTALL_MOD_STRIP=1 modules_install INSTALL_MOD_PATH="$CUSTOM_MODULES"

# Remove build/source symlinks
KVER=$(ls "$CUSTOM_MODULES/lib/modules/" | head -1)
rm -f "$CUSTOM_MODULES/lib/modules/$KVER/build"
rm -f "$CUSTOM_MODULES/lib/modules/$KVER/source"

# Run depmod
depmod -a -b "$CUSTOM_MODULES" "$KVER" 2>/dev/null || true

echo "==> Installing Device Tree Blobs..."
rm -rf "$CUSTOM_DTBS"
mkdir -p "$CUSTOM_DTBS/overlays"
# Pi 4 DTBs
cp arch/arm64/boot/dts/broadcom/bcm2711*.dtb "$CUSTOM_DTBS/" 2>/dev/null || true
# Pi 5 DTBs
cp arch/arm64/boot/dts/broadcom/bcm2712*.dtb "$CUSTOM_DTBS/" 2>/dev/null || true
# Overlays we need
for overlay in disable-wifi disable-bt; do
    [ -f "arch/arm64/boot/dts/overlays/${overlay}.dtbo" ] && \
        cp "arch/arm64/boot/dts/overlays/${overlay}.dtbo" "$CUSTOM_DTBS/overlays/"
done

# Save config for reference
cp .config "$CUSTOM_KERNEL_DIR/.config"

# --- Clean up ---
echo "==> Cleaning kernel build directory..."
cd /
rm -rf "$KERNEL_BUILD_DIR"

# --- Summary ---
echo ""
echo "==> ARM64 kernel build complete:"
echo "    Image:        $CUSTOM_IMAGE ($(du -h "$CUSTOM_IMAGE" | cut -f1))"
echo "    Kernel ver:   $KVER"
MOD_COUNT=$(find "$CUSTOM_MODULES/lib/modules/$KVER" -name '*.ko*' 2>/dev/null | wc -l)
echo "    Modules:      $MOD_COUNT"
echo "    Modules size: $(du -sh "$CUSTOM_MODULES/lib/modules/$KVER" 2>/dev/null | cut -f1)"
echo "    DTBs:         $(ls "$CUSTOM_DTBS"/*.dtb 2>/dev/null | wc -l)"
echo ""