Re: [PATCH 0/5] Split the emulator: decode & execute

[Laurent Vivier <Laurent.Vivier-6ktuUTfB/bM@public.gmane.org>]

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Avi Kivity wrote:
> Laurent Vivier wrote:
>> Avi Kivity wrote:
>>   
>>> Laurent Vivier wrote:
>>>     
>>>> These patches split the emulator in two parts: one to decode the
>>>> instruction,
>>>> the other to execute it. The decode part is then called only when needed.
>>>>
>>>>   
>>>>       
>>> Patchset looks good, but fails booting FC6 x86-64 on Intel.  It may be a
>>> merge error (did not apply cleanly due to other changes).  I pushed this
>>> as a 'split-emulator' branch on the kvm.git repository.
>>>
>>>     
>> I think I found the bug (not a merge error...): I just supposed that an
>> instruction fetch cannot failed.
>>
>>   
> 
> Interesting.  I don't see how an instruction fetch can fail on
> uniprocessor.  Can you give details of the failure?
> 
> Instruction fetches can fail on SMP so a fix is certainly needed.

OK, I spoke too fast.

x86_decode_insn() fails because it is not able to decode:

0xffffffff8110b7ef <__copy_user_nocache+47>:    movnti %r11,(%rdi)
or
0xffffffff8110b7ef <__copy_user_nocache+47>:    0x4c    0x0f    0xc3    0x1f

0x4c is decoded as a REX prefix.
0x0f is decoded as a Two-byte opcode
but 0xc3 is unknown in twobyte_table, so we exit because of an unrecognized
opcode ("Cannot emulate").

Some comments ?

Laurent
-- 
------------- Laurent.Vivier-6ktuUTfB/bM@public.gmane.org  --------------
          "Software is hard" - Donald Knuth


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