Fedora 39 will ship its arm64 kernels in the new generic EFI zboot
format, using gzip compression for the payload.

For doing EFI boot in QEMU, this is completely transparent, as the
firmware or bootloader will take care of this. However, for direct
kernel boot without firmware, we will lose the ability to boot such
distro kernels unless we deal with the new format directly.

EFI zboot images contain metadata in the header regarding the placement
of the compressed payload inside the image, and the type of compression
used. This means we can wire up the existing gzip support without too
much hassle, by parsing the header and grabbing the payload from inside
the loaded zboot image.

Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: Alex Bennée <alex.bennee@linaro.org>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Message-id: 20230303160109.3626966-1-ardb@kernel.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
[PMM: tweaked comment formatting, fixed checkpatch nits]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>