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SubjectRe: i387/FPU init issues...
Arjan van de Ven wrote:
>>
>> It has retroactively been added to the documented list for all P6 core
>> chips - that should mean it works on all of them. The most common
>> reason for not documenting something (other than various Pure Evil NDA
>> schemes) is that it hasn't been properly verified. However,
>> verification can be done a posteori.
>
> the other reason is that certain groups of "unknown" opcodes will act as
> NOP.
> Which for this purpose is .. exactly the right thing retroactive
>

Specifically, I believe the P6 added a whole class of instructions which
would act as NOP's if used on older chips. It has been used for
prefetch instructions, etc. At some point, the 0F 1F /0 group was
declared to be NOP, and nothing else, for all future.

-hpa



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