[Xen-devel] Re: [patch 13/26] Xen-paravirt_ops: Consistently wrap paravirt ops callsites to make them patchable

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

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.

    J

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