Re: [Xen-devel] Hvm_emulate_one() and guest_cpu_user_regs()->eip

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 17.10.13 at 08:50, Razvan Cojocaru <rzvncj@xxxxxxxxx> wrote:
> I've noticed that an hvm_emulate_one() call (that uses
> guest_cpu_user_regs() for it's context) will succeed _without_ modifying
> guest_cpu_user_regs()->eip. Again, this is not only happening when
> hvm_emulate_one() returns X86EMUL_RETRY (which I'd expect), but also, in
> some cases, when it returns no error.
> 
> Why would that happen, and what might be an example of an instruction
> that could cause that if that's normal behaviour?

If you've noticed it, you're in a much better position to tell us for
which instructions this _is_ happening than we are. As for when
this is validly happening - off the top of my head I can only think of
repeated string instructions as candidates (where the progress
being made is expressed in decreasing [RE]CX) or, in similar ways,
LOOPs having their own address as jump target.

Jan


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