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Re: [Xen-devel] Re: domU: 32-bit emulation seems to be broken

To: Christoph Egger <Christoph.Egger@xxxxxxx>
Subject: Re: [Xen-devel] Re: domU: 32-bit emulation seems to be broken
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Fri, 14 Aug 2009 13:55:27 -0700
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Milan Holzäpfel <listen@xxxxxxxx>
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On 08/10/09 05:59, Christoph Egger wrote:
>> I still notice this problem with vanilla domU under Xen 3.3.2
>> (32 bit binaries on a 64 bit domU kernel segfault, AMD CPU).  vdso32=0
>> still helps.
>> Any news?
> What does Linux use w/o vdso32=0 on your box ? Does it use sysenter, syscall
> or int 0x80 ?
> Do you boot the DomU directly or does this happen after migration from
> an Intel box ?

There appears to be a bug in the 64-bit xen_sysret32, which attempts to
take the sysret environment and turn it into an iret hypercall (since
iret is the only way to do a 64-bit kernel -> 32-bit user return).

I don't have an AMD test machine on hand, so I haven't had a chance to
work out what's actually failing.  I couldn't see anything wrong by
staring at the code, but that probably means I was either starting hard
at the bug, or looking right next to the bug...

Could you try looking at this?


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