Chained initrds were concatenated back to back. Linux only finds a cpio
archive at a 4-byte aligned offset when it unpacks concatenated
initrds, so a compressed initramfs with an odd length followed by
another archive, like a microcode or overlay cpio, failed to unpack.
Pad each initrd with zeros to a 4-byte boundary, as GRUB and
systemd-boot do.
Linux autoconfiguration only looked for an initramfs named with the
kernel suffix, like initrd.img-6.1 or initramfs-lts. Arch Linux
(initramfs-linux.img), and Fedora or Gentoo using dracut without BLS
(initramfs-<version>.img) add .img to the name, so their kernels were
booted without an initramfs and failed to mount the root filesystem.
Also try each candidate with .img added.
File names are lowercased before matching kernel prefixes, but the
arm64 prefix was "Image", so it could never match and arm64 kernels
were not autoconfigured. Use a lowercase "image" prefix.
alex
Benjamin Leggett