Re: [PATCH 0/5] Boot protocol changes

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Jeremy Fitzhardinge wrote:
H. Peter Anvin wrote:
This series looks like a good start for Xen, but we still need to work
out where to stash the metadata which normally lives in ELF notes. Using ELF is convenient for Xen because it lets a large chunk of domain
builder code be reused; on the other hand, loading a plain bzImage is
pretty simple, so maybe it isn't such a big deal.

HPA, Eric: if we don't go the "embed ELF" path, where's a good
backwards-compatible place to stash the note data?  If we do go with
"embed ELF", how should we go about doing it?  Arrange to put the ELF
headers before the 1M mark?

This sounds like another good reason to do the ELF image as the
postcompression image.  The interface to the embedded compression
routine is then unchanged, and we get the "full vmlinux" with any
notes that belongs there.

I'll try to get an implementation of that done -- it really shouldn't
be very hard.

Please explain what you're proposing again, because my memory of your
plan from last time wouldn't help in this case.  Are you proposing that
the bzImage contains compressed data that its expecting the bootloader
to decompress?  Won't that completely break backwards compatibility?  If
we don't care about backwards compatibility with old bootloaders, then
it doesn't matter what we do one way or the other.


No, not at all.

I'm proposing that the existing bzImage format be retained, but that the payload of the decompressor (already a gzip file) simply be vmlinux.gz -- i.e. a gzip compressed ELF file, notes and all. A pointer in the header will point to the offset of the payload (this is new, obviously.)

The decompression stub is adjusted to expect an ELF image, instead of a raw binary.

Existing bootloaders (16- or 32-bit) simply load the bzImage the way they do now; new bootloaders have the option of accessing the vmlinux.gz directly if they either want to load it themselves or want to examine the notes.

	-hpa

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