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xen-devel
RE: [Xen-devel] VT/ioemu: vga memory access?
> -----Original Message-----
> From: Keir Fraser [mailto:Keir.Fraser@xxxxxxxxxxxx]
> Sent: 16 May 2006 17:58
> To: Petersson, Mats
> Cc: Xen devel list; Gerd Hoffmann
> Subject: Re: [Xen-devel] VT/ioemu: vga memory access?
>
>
> On 16 May 2006, at 17:20, Petersson, Mats wrote:
>
> >> I think I found the bug. It's actually in handle_mmio()
> ;) The "case
> >> INSTR_MOVS" has code which deals with page boundaries. The code
> >> allways _adds_ the count (ecx) to figure whenever the "repz movsb"
> >> crosses a page boundary or not. In case the direction flag is set
> >> this isn't correct, it should subtract instead. Subsequently it
> >> mis-calculates count, making it _larger_ than it was
> because the copy
> >> wouldn't have crossed a page boundary, leading to the negative ecx
> >> value in the register dump ...
> >
> > I think you're right...
> >
> > I'll write some simple test code to check it out, and let
> you know...
>
> Hmmm... wouldn't it be nice if we didn't have a bespoke,
> buggy & incomplete emulator for hvm mmio. ;-)
Yup, that would be rather nice if we didn't have bugs like this...
And by the way, I think IOIO is buggy in exactly the same way...
I'm still working on a test-case that can be used - it'll come in handy
for testing later on when I have FIXED the code by reusing the
x86_emulate.c in QEMU too...
--
Mats
>
> -- Keir
>
>
>
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