Re: [Qemu-devel] [PATCH v3 6/7] hw/arm: pass pristine kernel image to guest firmware over fw_cfg

[Laszlo Ersek <lersek@redhat.com>]

On 12/12/14 14:57, Peter Maydell wrote:
> On 12 December 2014 at 13:52, Laszlo Ersek <lersek@redhat.com> wrote:
>> On 12/12/14 14:20, Peter Maydell wrote:
>>> If we have a real bootloader in the UEFI firmware, why do we need
>>> to do decompression for it? We only do this in the builtin bootloader
>>> because QEMU is acting as the bootloader and has to support the
>>> feature itself. I would have thought that the UEFI builtin kernel
>>> booting support already supported decompressing the kernel...
>>
>> The "UEFI builtin kernel booting support" will qualify as "builtin" only
>> after my 2500 line patch series is merged in edk2.
> 
> I had in mind the support for UEFI loading kernels off
> hard disks, which presumably is already present.

Ah, I see.

Sure, if you have a kernel image (with the EFI stub) that is an
*immediately executable* EFI binary, then you can just go to the UEFI
shell, navigate to the filesystem / directory that hosts that image, and
run it. (Similarly, PXE boot it etc.)

But in this case the EFI binary is compressed with gzip (for aarch64
kernels); you couldn't even run it from the UEFI shell.

Or else, if you thought of grub2 loading a kernel from the disk with
UEFI protocols -- that works too, but then it's grub that does the
decompression.

(There's a plethora of ways to boot UEFI kernels, and I've recently
asked Matt Fleming if he could write up a comprehensive blog post or
similar about all of them. Hopefully the community will be able to refer
to an authoritative summary sometime next year.)

> 
>> Zlib decompression is not present in edk2 (it only has a TianoCore
>> variant of LZMA), and I didn't want to impede (in the community sense)
>> my edk2 patchset even more (ie. beyond its current size) by importing
>> libz too.
> 
> Fair enough. This avoids odd inconsistency in compressed kernel
> support between the f/w and non f/w setups, anyway.
> 
> If you fix the stray space then
> Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
> 
> thanks
> -- PMM
> 

Awesome!

Thanks
Laszlo