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SubjectRe: [PATCH v2 02/31] arm64: Kernel booting and initialisation
On Fri, 17 Aug 2012, Arnd Bergmann wrote:

> On Thursday 16 August 2012, Nicolas Pitre wrote:
> > Some people will want to use bzip2 or whatever other decompressor du
> > jour. Maybe this shouldn't be gzip specific, or just presented as a
> > possible option?
>
> Good point. Whether this should be part of this document depends on
> what assumptions we make about the boot loader getting the image
> in the first place.
>
> In the strict sense, we are documenting the interface between the boot
> loader and the kernel here, which already specifies that the kernel
> must be uncompressed by the time we enter it. If the boot loader wants
> to add its own encryption or compression methods, or its own headers
> in front of the binary, the boot protocol isn't really impacted.

Right. And someone else will insist on wrapping the kernel into a boot
loader specific image format e.g. u-Boot. If all those variations could
be kept out of the kernel build that would be a good thing.

That means the kernel should be wrapped/compressed/scrambled at
installation time, not at build time. This way the kernel image remains
universal and flexibility in its installation is possible.

> That said, I think it's a good idea to also specify what kind of
> format we want to be used, e.g. a stripped ELF Image compressed with
> one of gzip/bzip2/lzo/xz and with no other headers added, on a
> vfat/ext4/btrfs formatted file system. There are probably a lot of
> other things one might want to specify if we go down this route. Or we
> could refer to the UEFI spec and mandate that the same format that
> UEFI uses should be used here independent of what boot loader is used.
> I think we can still allow other ways to get to the image for deeply
> embedded systems, e.g. linking the kernel into the boot loader as a
> blob on tightly constrained systems. For that case, we'd only specify
> the interface between boot loader and kernel as described above.

I don't think we'll have to concern ourselves with tightly constrained
systems that much on ARM64.


Nicolas


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