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Re: [Xen-devel] Loading a 32 bit kernel from 64 bit grub-xen
On 1 Jul 2014 20:28, "Phillip Susi" <psusi@xxxxxxxxxx> wrote:
>
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> On 7/1/2014 12:18 PM, Andrey Borzenkov wrote:
> > Ð Tue, 01 Jul 2014 12:06:08 -0400 Phillip Susi <psusi@xxxxxxxxxx>
> > ÐÐÑÐÑ:
> >
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> >> I have been trying to fix grub to load a 32 bit kernel from the
> >> 64 bit xen build. ÂAfter fixing up one or two minor issues with
> >> the elf loader, I believe I now have it to the point where it
> >> jumps correctly to the 32 bit kernel and it crashes there, since
> >> it is 32 bit code still executing on a cpu in 64 bit mode. ÂThe
> >> question is how to return the cpu to 32 bit mode *under xen*?
> >
> >
> > IIRC it was already discussed not long ago and it seems to be Xen
> > limitation. You probably need to ask on xen-devel to be sure.
> >
> > Is it not more simple to use 32 bit grub with 32 bit kernel to
> > start with?
>
> The problem with that is that you have to know in advance which kernel
> you are going to boot. ÂThat makes configuring virtual hosts harder;
> they just want one grub image they can use to chainload whatever the
> guest wants to install in their domain.
>
> Also there must be a way to do this otherwise a 64 bit kernel running
> under xen wouldn't be able to execute a 32 bit binary.
Binaries don't have to use e.g. paging table or hypercall mechanism. You need to either make xen switch all those structures or port kernels to fake-32-xen mode. When either is done GRUB part will be trivial but either of those tasks is outside of grub scope.
>ÂI suppose I'll
> Cc xen-devel.
>
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