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    SubjectRe: [PATCH 0/5] Boot protocol changes
    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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