rpi-kernel-build

rpi-kernel-build is a script which builds Raspberry Pi kernel tarballs. It was originally built as a pseudo-fork of sakaki-'s kernel builds to build Raspberry Pi 4 64-bit kernels, but is currently capable of building all variants: 32-bit or 64-bit, bcm2709/bcm2711/bcmrpi/bcmrpi3, multiple tracked upstream branches (e.g. rpi-5.10.y, rpi-5.15.y), and feature-enhanced config patches.

Binary images

There is a scheduled weekly GitHub workflow which builds most combinations. The following parameters are available:

• Architecture: arm (32-bit) or arm64 (64-bit). Note that a 64-bit kernel will work with a 32-bit userland provided by Raspberry Pi OS (on 64-bit CPUs that is; Raspberry Pi 3 and later).
• Platform: bcmrpi (Raspberry Pi 0/1/2), bcm2709/bcmrpi3 (Raspberry Pi 3), bcm2711 (Raspberry Pi 4). Note that the Raspberry Pi 3 platform is called bcm2709 for arm (32-bit) kernels, but bcmrpi3 for arm64 (64-bit) kernels, but are otherwise the same platform.
• Branch: rpi-5.15.y LTS branch is being built.

Installation

Download the desired tarball, understanding the options above. For this example, we'll assume bcm2711 (Raspberry Pi 4), arm64, rpi-5.4-y.

Unfortunately, GitHub actions wrap the build artifacts in a zip file, so it will need to be unzipped to get the tarball:

$ unzip images-build-174991421.2-rpi-5.4.y-bcm2711.zip

Then, extract the resulting tarball to the root directory of the Raspberry Pi OS installation:

$ sudo tar axvf rpi-kernel-5.4.51-20200717-g9d49ae69a144-arm64-bcm2711.tar.xz -C /

Modify /boot/config.txt:

[all]
# Needed for arm64 kernels; omit for arm kernels
arm_64bit=1
# Adjust architecture and platform based on what was chosen
kernel=kernel.img-arm64-bcm2711

Reboot, and hopefully everything has gone correctly.

Building from source

A clone of raspberrypi/linux is needed, in the linux/ subdirectory by default (configurable). Beware that a full clone is needed; --depth=1 will not work as raspberrypi will often rebase rather far back. I currently have a mega centralized linux tree on my build machine, with several remotes, including an "rpi" remote corresponding to the raspberrypi repository. rpi-kernel-build supports alternative remote and branch names.

You can build directly on an arm64 machine, such as a Raspberry Pi 4 with an arm64 kernel, and kernel builds will take about an hour. Minimum build environment on a Debian/Ubuntu system should be:

sudo apt-get install build-essential flex bison libssl-dev

If you want to cross-compile on an x86-64 system, you also want:

sudo apt-get install \
  gcc-aarch64-linux-gnu libc6-dev-arm64-cross \
  gcc-arm-linux-gnueabi libc6-dev-armel-cross

And then set CROSS_COMPILE=yes in your rpi-kernel-build.rc config. On an AMD Ryzen 2700X, kernel builds take about 5 minutes. (Normally CROSS_COMPILE takes a cross compiler prefix such as CROSS_COMPILE="aarch64-linux-gnu-", but CROSS_COMPILE=yes is a special case which sets the prefix based on the target architecture.)

Sources

If built with ASSEMBLE_SOURCE=1 (default), a source tarball is also built. To use, extract it to /usr/src/, install the build prerequisites above, then run:

make -C /lib/modules/$(uname -r)/build prepare

(The kernel tarball's /lib/modules/$(uname -r)/build is a symlink to /usr/src/linux-$(uname -r).)

This source tree may be used to build DKMS modules. An example DKMS module is hello-dkms.