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[Xen-devel] Re: [patch 13/26] Xen-paravirt_ops: Consistently wrap paravi

To: Zachary Amsden <zach@xxxxxxxxxx>
Subject: [Xen-devel] Re: [patch 13/26] Xen-paravirt_ops: Consistently wrap paravirt ops callsites to make them patchable
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Mon, 19 Mar 2007 18:45:21 -0700
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, akpm@xxxxxxxxxxxxxxxxxxxx, virtualization@xxxxxxxxxxxxxx, netdev@xxxxxxxxxxxxxxx, rusty@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, chrisw@xxxxxxxxxxxx, Andi Kleen <ak@xxxxxx>, anthony@xxxxxxxxxxxxx, mingo@xxxxxxx, torvalds@xxxxxxxxxxxxxxxxxxxx, David Miller <davem@xxxxxxxxxxxxx>
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Zachary Amsden wrote:
> Jeremy Fitzhardinge wrote:
>>  If we then work out in each direction and see matched push/pops,
>> then we know what registers can be trashed in the call.  This also
>> allows us to determine the callsite size, and therefore how much space
>> we need for inlining.
> No, that is a very dangerous suggestion.  You absolutely *cannot* do
> this safely without explicitly marking the start EIP of this code. 
> You *must* use metadata to do that.  It is never safe to disassemble
> backwards or "rewind" EIP for x86 code. 

What do you mean the instruction before is "mov $0x52515000,%eax"?

Yeah, you're right.  Oh well.


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