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Re: [Qemu-devel] qemu/pc-bios ppc_rom.bin


From: Natalia Portillo
Subject: Re: [Qemu-devel] qemu/pc-bios ppc_rom.bin
Date: Fri, 5 Oct 2007 20:23:44 +0100

Hi all,

Just to resume,
I'm in position with Fabrice, Thiemo and Jocelyn.

And, to note.

Current BIOS are very bloated assembler hacks that everytime I use them make me think "miracle, it POSTs!"

No way, in a far far away galaxy, there was a simple BIOS, that WONT RUN UNDER QEMU.

Why?
Timing?
Doesn't matter to it.

Strange hardware bugs?
Too early for ever knowing they were there.

Source available?
Yes, it is, I don't know the license, but Compaq used it to make the cloned BIOS, so we should be able to use it to make QEMU able to POST-It (trademark lol)

And if any firmware wants to be an alternative open-source firmware it should meet the following requirements:
1.- Be able to boot, unmodified, in real hardware (REAL!)
2.- Be able to boot the same operating systems a closed-source firmware for that platform will be. (in REAL hardware)

It is desiderable for QEMU,
no way,
IT IS A MUST FOR QEMU,
to be able to boot real firmware that boots in the real hardware QEMU is emulating.

(That is, if QEMU emulates a PIIX4 with Pentium II, it must support booting a BIOS for P2+PIIX4, but must not support booting a BIOS for a Athlon+nForce)

And, extrapolate what I say to PowerPC, MIPS, ARM, Alpha, Sparc, so on!

Regards,
Natalia Portillo

----- Original Message ----- From: "Thiemo Seufer" <address@hidden>
To: "Blue Swirl" <address@hidden>
Cc: <address@hidden>; <address@hidden>
Sent: Monday, October 01, 2007 10:57 PM
Subject: Re: [Qemu-devel] qemu/pc-bios ppc_rom.bin


Blue Swirl wrote:
[snip]
> > Qemu is not also aimed for 100% accurate emulation of the hardware.
> > There are no caches or cycle counters and hardware devices run
> > unrealistically fast from CPU standpoint. Emulating performance
> > counters or the errata the most CPUs have would be extremely
> > difficult. I doubt Qemu CPU emulation can ever pass POST of real
> > BIOSes.
>
> I am working on making the Malta emulation boot a unaltered YAMON
> image. I don't see why a PC BIOS would be harder to accomodate.

Emulating microcode, or firmware blobs loaded to misc devices. Think
writing a BIOS for Transmeta,

Writing the emulation for a transmeta is IMHO more challenging than
writing the "BIOS". Btw, if you are interested in the x86 mode, you can
handle the transmeta just as a x86 variant (with a much more standard BIOS).

Alpha or a SoC.

Writing "Firmware for a SoC" is part of my dayjob.

> > Real BIOSes are also closed source, proprietary binary blobs.
>
> At least YAMON, CFE and PMON are not closed source. YAMON has a funny
> license which - I hope - will change.
>
> > Making open source BIOSes a viable alternative is in my opinion a > > much
> > more important goal.
>
> The one doesn't exclude the other. That said, I regard the ability to
> boot unaltered real-world firmare as an important test of the quality
> of a system emulation.

Maybe. The CPU probes for cacheline size, checks for errata #42 vs
#45, reads debug registers, attempts to identify the bus speed by
comparing I/O access times, tries to verify the system using a TPM and
fails all cases. What can you do?

Improve the emulation to handle at least one probing path.


Thiemo









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