Re: [Qemu-devel] [PATCH] pc.c: Add UEFI IA32 & X64 machine types.

[Jordan Justen <jljusten@gmail.com>]

On Mon, Aug 10, 2009 at 11:52 AM, Anthony Liguori<anthony@codemonkey.ws> wrote:
> Jordan Justen wrote:
>>
>> For i386, this change adds a 'uefi' machine type.  For x86_64, this
>> change adds 'uefi' and 'uefi32' machine types.
>>
>
> Why are uefi32 machines explicitly needed?

In UEFI systems, the OS architecture is assumed to be the same as the
firmware architecture.  So, when booting a 32-bit x86 UEFI OS, you
need to use a firmware that runs in 32-bit mode.

So, you could either run the 32-bit qemu:
$ qemu -M uefi
or, achieve similar results from the x86_64 qemu:
$ qemu-system-x86_64 -M uefi32

I am not sure if this is desirable for qemu in general, but I often
test the 32-bit OVMF via qemu-system-x86_64.

> How does one build the uefi roms?

I work for Intel on the OVMF project, which supports UEFI for qemu:
* https://edk2.tianocore.org/OVMF.html
(Currently this project is considered at an alpha stage.)

It is not a trivial process to build OVMF, but it can be done on
Linux, OS X or Windows.  This page is a decent starting point, but it
will call out from pre-requisite setup instructions from other web
pages.
* https://edk2.tianocore.org/build-ovmf.html

Also, binary builds are available at:
* https://edk2.tianocore.org/servlets/ProjectDocumentList?folderID=101

> Is uefi all that useful in the absence of a CSM?  Wouldn't it make more
> sense to add a CSM to uefi and then switch the default pc to use uefi?

CSM is an interface that layers on top of a UEFI firmware to provide
legacy BIOS support.

Considering that UEFI is attempting to replace the legacy BIOS
interfaces with non-legacy interfaces, obviously it should be useful
without a CSM. :)  You can boot a UEFI OS without a CSM, and I have
been making good progress on booting Fedora 11 (UEFI) on qemu with
OVMF.

---

Regarding CSM, I have a few more points, but I should mention that
these might involve my personal opinions, and not represent Intel...

Firstly, I don't think there is an open-source CSM available.  I think
tianocore.org could benefit from an open source CSM, even if it was
limited compared to other commercial CSM offerings.

I think something like a bochs BIOS based CSM is definitely possible.
But since I think the bochs BIOS is GPL licensed, it would more
difficult for us to use it on tianocore.org, since we try to stick
with BSD licensed code.

>
>> These machine types will load different bios and video bios images:
>>
>
> Regards,
>
> Anthony Liguori
>