The current (2021-Feb-05) aarch64 Arch Linux ARM image has issues on 8GB Raspberry Pi 4 models: It does not bring up the network interface, and the USB ports are not working, making any interactive fix difficult (without serial cable).

A possible fix is to replace the default kernel with a Raspberry specific one. It still results in a 64bit system, only with a non-upstream kernel. If there’s a different ARM system available, it is trivial to mount/boot the SD card there and apply the required changes. The solution below, however, only requires a single working, linux supported hardware, e.g: x86. This description is Arch Linux specific. For ubuntu, see this blogpost on Disconnected Systems.

Install Qemu

Qemu makes it possible to run arm binaries on x86 (and many more combinations). Install qemu-user-static from AUR. To make the resulting package smaller, add --target-list=aarch64-linux-user to the configure invocation in the PKGBUILD file. This package requires glib-static and pcre-static, the former takes some time to build. Due to the number of dependencies, consider building in a clean chroot. (Do not forget to set -j in MAKEFLAGS)

Install the built qemu-user-static package. Read the introduction of binfmt, then setup the config accordingly:

$ cat /etc/binfmt.d/qemu-static.conf
:qemu-aarch64:M::\x7fELF\x02\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\xb7:\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff:/usr/bin/qemu-aarch64-static:CF

Finally, restart the service that - if there’s a config file - mounts the filesystem described by the doc above:

$ sudo systemctl restart systemd-binfmt

Now the system can run aarch64 binaries using qemu.

Install Arch Linux ARM

Follow the install guide. Use the ArchLinuxARM-rpi-aarch64-latest.tar.gz archive, but do not change /etc/fstab! Also, before unmounting root and boot, do:

$ sudo arch-chroot root

This will drop you into the installed ARM system. Add the alarm repos, and install the raspberry kernel:

$ pacman-key --init
$ pacman-key --populate archlinuxarm
$ pacman -S --needed linux-raspberrypi4 raspberrypi-bootloader raspberrypi-bootloader-x raspberrypi-firmware firmware-raspberrypi

This is a good time to also complete the official Installation Guide. After done, copy root/boot over boot again, and unmount the partitions. Again, do not modify etc/fstab, contrary to the alarm docs.

With everything done correctly, using the patched image, the network and USB ports of the 8GB Raspberry Pi 4 are fine again!