Re: [GIT PULL] x86 setup: correct booting on 486 (revised)

H. Peter Anvin
2007-11-06T01:12:18Z

Jeremy Fitzhardinge wrote:
>> I'm not so sure about that. Xen PV is rather fundamentally a
>> different beast, hence the platform field recently added to the protocol.
>
> Hm, OK. So make this predicated on "hardware subarchitecture == PC".

Yes; specifically, boot_params.hdr.hardware_subarch == 0 (as opposed to
compile-time subarchitectures, like Voyager, which still boots the same
way as far as I know.)

It would definitely be good to document what other values in this field
changes, of course.

>> This is addressed by the "don't reload segments" bit in LOADFLAGS.
>
> OK.

Specifically, with this bit set the decompression code won't touch the
segment registers at all, and it's up to the caller to have all code and
data segments set up with suitable descriptors. The kernel will still
try to install its own GDT when the kernel proper starts; this becomes a
hardware_subarch issue.

-hpa