Re: [SeaBIOS] WinXP 32 installation failure with new SeaBIOS in QEMU

[Avi Kivity]

On 08/19/2012 12:27 PM, Avi Kivity wrote:
> On 08/17/2012 08:53 AM, Gerd Hoffmann wrote:
> > Hi,
> > > It might be instruction emulator bug in KVM.
> > > Attached is the trace.
> >         qemu-2047  [000] d..2   261.999076: kvm_entry: vcpu 0
> >         qemu-2047  [000] ...1   261.999077: kvm_emulate_insn:
> >
> > f0000:6201:fb (real)
> >             qemu-2047  [000] d..2   261.999078: kvm_entry: vcpu 0
> > ##### CPU 3 buffer started ####
> >             qemu-2047  [003] ...1   411.367592: kvm_emulate_insn:
> > 20000:26c:cb (prot16)
> >             qemu-2047  [003] ...1   411.367593: kvm_inj_exception: #GP
> > (0x844)
> >             qemu-2047  [003] d..2   411.367594: kvm_entry: vcpu 0
> >
> > This looks suspious.  vcpu migration issue?  Or just something missing
> > in the trace?
>
> Looks like tracing with a too-small buffer size.  I generally trace using
>
> trace-cmd record -e kvm -b 100000
>
> and with fingers crossed.
>
> The RET FAR instruction failure (which trace-cmd report decodes) is
> probably not the original failure.

In fact it is, we mis-emulated stack operations when SS.B=0 but the
address size was 32-bits, and there are bits set in the top 16 bits of ESP.

Why ESP has bits set in the top 16 bits is another question.  Is seabios
polluting those bits?