Re: [Xen-devel] unstable changeset 16667 introduced regression

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

Oh, you really do mean that the EIP is incremented by 2 bytes rather than 1.
This is explained by the fact that Xen receives a GPF fault, determines this
is due to a software-interrupt/exception attempt by the guest, and
'emulates' the instruction by reflecting the interrupt to the guest and
incrementing EIP across 'INT <n>', which happens to be a two-byte
instruction.

I'll fix this for 3.2.0.

 -- Keir

On 15/1/08 08:21, "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx> wrote:

> Can you explain the scenario in more detail? Do you mean the EIP has not
> been incremented past the 0xcc opcode? I think the change from
> set_system_gate() to set_intr_gate() in that patch is very dubious, now I
> take another look at it. I should probably at least revert that, as it's
> probably causing guest INT3s to be delivered to Xen as GPFs, with no
> corresponding increment of EIP.
> 
> I can't see how any other change in the patch would affect guest execution
> when gdbstub is not involved as almost all other changes are to gdbstub
> code. And probably you are not building Xen with crash_debug=y?
> 
>  -- Keir
> 
> On 14/1/08 22:57, "Bruce Rogers" <BROGERS@xxxxxxxxxx> wrote:
> 
>> Keir,
>> I've narrowed down a problem we are now seeing with Virtualized NetWare when
>> run on current unstable.
>> It started occurring with changeset 16667, which dealt with debugger changes.
>> When encountering the INT 3 instruction (opcode 0xcc), the EIP value provided
>> in the exception frame is supposed to be at the next instruction following
>> the
>> INT 3 instruction.  With this patch included, the EIP value ends up being one
>> byte further into the instruction stream.
>> 
>> I haven't seen where in this patch the problem is coming from, but will keep
>> looking.
>> 
>> - Bruce
>> 
>> 
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> 
> 
> 
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