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Re: [Xen-devel] [PATCH 1 of 2] Add the support for Xen to include OVMF UEFI support and directly use it

On Fri, 2012-02-24 at 08:35 +0000, Jan Beulich wrote:
> >>> On 23.02.12 at 16:37, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> > On Thu, 2012-02-23 at 14:48 +0000, Jan Beulich wrote:
> >> >>> Attilio Rao <attilio.rao@xxxxxxxxxx> 02/23/12 11:18 AM >>>
> >> >On 23/02/12 10:07, Ian Campbell wrote:
> >> >> On Wed, 2012-02-22 at 19:17 +0000, Attilio Rao wrote:
> >> >> Can you confirm that you need an OVMF which matches the OS bit-width you
> >> >> are installing. i..e that there is no support for booting a 32 bit EFI
> >> >> OS (or bootloader, shell, whatever it is called) on a 64 bit OVMF?
> >> >
> >> >I didn't test this case, really, but I would think OVMF-64 / OS-32 could 
> >> >possibly work.
> >> 
> >> Native EFI requires bit-matched OS loaders,
> > 
> > Is that a shortcoming of EFI generally or just this implementation?
> I'd assume more the former.
> > Surely people don't reflash their "BIOS" to be able to run a 32 vs 64
> > bit OS? Or do most OSes (even 32 bit ones) have a 64 bit loader capable
> > of loading a 32 bit OS?
> When I asked the same question, I was told that the assumption is that
> on modern (read: UEFI) systems people aren't expected to run 32-bit
> OSes.

Doesn't that apply to running those OSes under Xen to some extent as
well? Can we get away with only supporting 64 bit EFI?

> And no, I don't think any 32-bit OS comes with a 64-bit bootloader.
> Furthermore, to make EFI really work, such an OS would also need
> 64-bit stubs to call the EFI services - not something that's realistically
> going to happen I would think.
> If anything, I would have expected that things could work out the
> other way around: A 64-bit OS having a 32-bit loader and 32-bit
> stubs (which is how we implemented this when, on x86, there was
> no 64-bit EFI yet).

Yes, that does sound more plausible. Does anyone still do that though?
What about in a situation where they could just as easily run a
traditional BIOS (like in a Xen HVM guest)? Why would anyone insist on
being able to use 32 bit EFI if they could just use SeaBIOS? I suppose
the underlying question is: are there any OSes which _only_ support 32
bit EFI and don't support a traditional BIOS?


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