Re: [Qemu-devel] kqemu processor feature question

["John R. Hogerhuis" <jhoger@pobox.com>]

On Wed, 2005-10-19 at 00:34 +0400, Brad Campbell wrote:

> After re-installing windows 2000 SP3 & SP4 about 25 times on different machines, its looking wierd..
> SP4 has a problem when configuring COM+ with no kqemu, but works fine with kqemu on all 3 machines 
> (PIII, Sempron 2400+ Athlon XP 2800+).

kqemu avoids emulating instructions, so the instructions run natively.
So, this would seem to imply an issue in the (software) cpu emulation
(that is, in the situation with no kqemu).

It would rule out the system emulation (ancillary hardware) since the
system emulation is the same in both cases w/ and w/out kqemu.

> Any Win2k SP3 or SP4 image created on the Athlons will not boot on the PIII, but an image created on 
> the PIII seems to boot fine on all the machines..

AFAIK qemu doesn't implement Athlon extensions. So this is not
surprising if your theory is true. W/ kqemu would not work since it will
try to run Athlon instructions natively on a Pentium. w/out kqemu would
not work assuming qemu doesn't implement Athlon extensions in the cpu
emulation.

> Now to top it off, I have actually used identical qemu binaries on all the machines. Compiled on the 
> PIII and copied to the Athlons, in addition to locally compiled copies... I'm using a vanilla qemu 
> CVS with the DMA and Concurrent IO Patches. I have yet to remove those patches and try again.. it 
> just keeps on getting stranger.
> 

Strange? I'm not surprised that Athlon-only intructions do not run on
Pentium machines. It would be nice if qemu+kqemu could detect this
circumstance, but you've determined the obvious workaround: install OSes
that optimize themselves for specific x86 variant on install to a
lowest-common-denominator host under kqemu, or on an arbitrary host
under no-kqemu.

> Problem has been worked around by creating the whole image on the laptop. Now it works anywhere, but 
> I'm baffled as to why the images created on the Athlons won't boot on the laptop.
> 

Anyway everything seems to be fitting your theory about Athlon
extensions. It would be nice to catch it in the act of trying to run an
Athlon instruction on a Pentium.

-- John.