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SubjectRe: MMX emulator ?
On Sun, 28 Jun 1998, Sylvain Pion wrote:

>On Sun, Jun 28, 1998 at 06:51:00PM +0200, Andrea Arcangeli wrote:
>> >I wondered whether there has been some thoughts about implementing an MMX
>> >emulator in the kernel, something like the FPU emulator. It sounds like a
>>
>> Intel say that it' s impossible. From 24319201.pdf section 10.1:
>>
>> 10.1. EMULATION OF THE MMX™ INSTRUCTION SET
>>
>> The Intel Architecture does not support emulation of the MMX
>> technology, as it does for floating-point instructions. The EM
>> flag in control register CR0 (provided to invoke emulation of
>> floating-point instructions) cannot be used for MMX instruction
>> emulation. If an MMX instruction is executed when the EM flag is
>> set, an invalid opcode (UD#) exception is generated.
>>
>> Andrea[s] Arcangeli
>
>Well, I already have a prototype (very very very alpha/dirty) that begins to
>work. Cf http://www.inria.fr/prisme/personnel/pion/progs/linux if you're
>interested. The emulation is actually done via the invalid opcode exception,
>caught by the kernel, which in turn sends SIGILL to the process. What Intel
>says is that they do not support hardware help for the emulation (and I don't
>know what's the benefit of that anyway), but we don't need it.

Yes, I agree. Only sound me strange that Intel declare that is not
possible. The phrase "The Intel Architecture does not support emulation of
the MMX technology as it does..." sound me as -> "impossible at
architecture level". Maybe it' s only yet another mistaken due my usual
bad English ;-).

Andrea[s] Arcangeli


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