Docker (based) Linux Kernel Builder

Docker image for cross-compiling the Linux kernel.

Check the requirements before proceeding.

Initial Setup

Linux kernel Source Code and Toolchain

Put the archives containing the Linux Kernel source code and the toolchain in the files directory.

Here is an example showing how to download Linux Kernel 3.15.37 from kernel.org and a toolchain provided by Bootlin for arm64 architecture.

  curl --output files/kernel.tar.xz https://cdn.kernel.org/pub/linux/kernel/v5.x/linux-5.15.37.tar.xz
  curl --output files/toolchain.tar.bz2 https://toolchains.bootlin.com/downloads/releases/toolchains/aarch64/tarballs/aarch64--glibc--stable-2021.11-1.tar.bz2

See the documentation for more examples and an automated way to download both the Kernel source code and the toolchain.

Variables Setup

Edit file config.env and modify the following variables:

• LK_ARCHIVE_NAME: name of the archive containing the Linux Kernel source code placed in files directory;
• TC_ARCHIVE_NAME: name of the archive containing the toolchain placed in files directory;
• LK_ARCH: name of the target architecture (must match the used toolchain). Examples are arm, arm64 and mips

Building the Docker Image

Building the Docker image is a two steps process. At first, a permanent volume containing both the toolchain and the kernel source code must be created with:

  ./scripts/docker_create_volume.sh

Then, the actual Docker image can be built with:

  ./scripts/docker_build.sh

Configuring and Building the Linux Kernel

It is possible to invoke any available make target on the kernel source code by using the script scripts/make.sh. For example, the following command will print the kernel make help message:

  ./scripts/make.sh help

NOTE: the first time the container is executed it will take more time because a script will take care of extracting the kernel source code and the toolchain contained in the permanent volume.

Configuration

The kernel can be configured as usual. Here are a few examples:

• Use the default configuration for the target architecture:

  ./scripts/make.sh defconfig

• Configure the kernel manually using a menu based program:

  ./scripts/make.sh menuconfig

• Use an existing configuration: save the existing configuration in shared/.config and then run:

  ./scripts/make_olddefconfig.sh

• Configure the tiniest possible kernel for the target architecture (with this configuration kernel modules are usually disabled):

  ./scripts/make.sh tinyconfig

Kernel Build

Build the kernel with:

  ./scripts/make_all_install_retrieve.sh

at the end of the build process, the output artifacts will be placed in shared/install. Here you will find the kernel image (vmlinux), the symbol table (System.map), the used configuration, the kernel headers (in include directory) and the kernel modules (in lib directory).

Cleaning Kernel Build

The kernel build directory can be cleaned as usual using the clean target or the mrproper target (for removing also the configuration file). E.g.,

  ./scripts/make.sh mrproper

Reset Docker Image and Volume

In order to start from scratch (remove the permanent volume, the Docker image and the content of shared directory), you can remove everything with:

  ./scripts/docker_remove_all.sh

TODOs

• Add script for building out-of-tree kernel modules;
• Add support for building Busybox for quick testing in Qemu;
  • see here
• Add support for building the kernel with CLANG;
• Add support for building experimental Rust based kernel modules.