From 1e76bd58cc9ddce2e889a3782642a9fd82d35c57 Mon Sep 17 00:00:00 2001
From: Misha Sakhnov <misha@neon.tech>
Date: Thu, 5 Sep 2024 17:55:04 +0300
Subject: [PATCH] neonvm: makefile targets to introduce cross-compilation of
 the linux kernel

Signed-off-by: Misha Sakhnov <misha@neon.tech>
---
 Makefile                                     | 24 ++++++++++++++---
 neonvm/hack/kernel/Dockerfile.kernel-builder | 27 ++++++++++++++++----
 2 files changed, 43 insertions(+), 8 deletions(-)

diff --git a/Makefile b/Makefile
index 8adb85c1f..2234c5c38 100644
--- a/Makefile
+++ b/Makefile
@@ -12,9 +12,14 @@ GO_BASE_IMG ?= autoscaling-go-base:dev
 E2E_TESTS_VM_IMG ?= vm-postgres:15-bullseye
 PG16_DISK_TEST_IMG ?= pg16-disk-test:dev
 
-## Golang details
+## Golang details (for local tooling)
 GOARCH ?= $(shell go env GOARCH)
 GOOS ?= $(shell go env GOOS)
+
+# The target architecture for linux kernel. Possible values: amd64 or arm64. 
+# Any other supported by linux kernel architecture could be added by introducing new build step into neonvm/hack/kernel/Dockerfile.kernel-builder
+KERNEL_TARGET_ARCH ?= amd64
+
 # Get the currently used golang base path
 GOPATH=$(shell go env GOPATH)
 # Get the currently used golang install path (in GOPATH/bin, unless GOBIN is set)
@@ -244,8 +249,21 @@ ifndef ignore-not-found
   ignore-not-found = false
 endif
 
+# Build the kernel for the amd64 architecture. Uses generic target.
+.PHONY: kernel_amd64
+kernel_amd64: KERNEL_TARGET_ARCH=amd64
+kernel_amd64: kernel
+
+# Build the kernel for the arm64 architecture. Uses generic target.
+.PHONY: kernel_arm64
+kernel_arm64: KERNEL_TARGET_ARCH=arm64
+kernel_arm64: kernel
+
+# Build the kernel for the target architecture.
+# The builder image platform is not specified because the kernel is built for the target architecture using crosscompilation.
+# Target is generic and can be used for any supported architecture by specifying the KERNEL_TARGET_ARCH variable.
 .PHONY: kernel
-kernel: ## Build linux kernel.
+kernel:
 	rm -f neonvm/hack/kernel/vmlinuz; \
 	linux_config=$$(ls neonvm/hack/kernel/linux-config-*) \
 	kernel_version=$${linux_config##*-} \
@@ -253,7 +271,7 @@ kernel: ## Build linux kernel.
 	trap "rm $$iidfile" EXIT; \
 	docker buildx build \
 	    --build-arg KERNEL_VERSION=$$kernel_version \
-		--platform linux/amd64 \
+		--target "kernel_${KERNEL_TARGET_ARCH}" \
 		--pull \
 		--load \
 		--iidfile $$iidfile \
diff --git a/neonvm/hack/kernel/Dockerfile.kernel-builder b/neonvm/hack/kernel/Dockerfile.kernel-builder
index 74b03ef9d..3c314638f 100644
--- a/neonvm/hack/kernel/Dockerfile.kernel-builder
+++ b/neonvm/hack/kernel/Dockerfile.kernel-builder
@@ -15,6 +15,8 @@ RUN apt-get update && apt-get -y install \
     curl \
     ca-certificates \
     build-essential \
+    gcc-x86-64-linux-gnu \
+    gcc-aarch64-linux-gnu \
     flex \
     bison \
     libelf-dev \
@@ -46,16 +48,31 @@ RUN set -e \
     && tar --strip-components=1 -C linux-${KERNEL_VERSION} -xf linux-${KERNEL_VERSION}.tar.xz
 
 
-FROM build-deps AS build
 
-ARG KERNEL_VERSION
+### Cross-compilation related steps
 
+# Build the kernel on amd64
+FROM build-deps AS build_amd64
+ARG KERNEL_VERSION
 ADD linux-config-${KERNEL_VERSION} linux-${KERNEL_VERSION}/.config
+RUN cd linux-${KERNEL_VERSION} && make ARCH=x86_64 CROSS_COMPILE=x86_64-linux-gnu- -j `nproc`
+
+# Copy the kernel image to a separate step
+# Use alpine so that `cp` is available when loading custom kernels for the runner pod.
+# See the neonvm controller's pod creation logic for more detail.
+FROM alpine:3.19 AS kernel_amd64
+ARG KERNEL_VERSION
+COPY --from=build_amd64 /build/linux-${KERNEL_VERSION}/arch/x86/boot/bzImage /vmlinuz
 
-RUN cd linux-${KERNEL_VERSION} && make -j `nproc`
+# Build the kernel on amd64
+FROM build-deps AS build_arm64
+ARG KERNEL_VERSION
+ADD linux-config-${KERNEL_VERSION} linux-${KERNEL_VERSION}/.config
+RUN cd linux-${KERNEL_VERSION} && make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- -j `nproc`
 
+# Copy the kernel image to a separate step
 # Use alpine so that `cp` is available when loading custom kernels for the runner pod.
 # See the neonvm controller's pod creation logic for more detail.
-FROM alpine:3.19
+FROM alpine:3.19 AS kernel_arm64
 ARG KERNEL_VERSION
-COPY --from=build /build/linux-${KERNEL_VERSION}/arch/x86/boot/bzImage /vmlinuz
+COPY --from=build_arm64 /build/linux-${KERNEL_VERSION}/arch/arm64/boot/Image /vmlinuz