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-5.4.y, rpi-5.10.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-5.4.y and rpi-5.10.y LTS branches are being built.
• Bis: Same as their non-bis releases, but with a few extra kernel config features enabled. ("Bis" is Latin for second, secondary, etc.)

Installation

Download the desired tarball, understanding the options above. For this example, we'll assume bcm2711 (Raspberry Pi 4), arm64, rpi-5.4-y, no bis (Raspberry Pi-developer kernel config).

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-bis0.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.