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SubjectRe: i387/FPU init issues...
H. Peter Anvin wrote:
> Maciej W. Rozycki wrote:
>> On Sat, 3 May 2008, H. Peter Anvin wrote:
>>
>>> Intel explicitly documents "all processors with family 6 or F."
>>
>> It depends (as usually with Intel) on what document you are looking
>> at. Based on my short research, the instruction has been
>> retroactively added
>> to the list of supported opcodes. Even my somewhat dated P4 manual does
>> not list it, never mind its predecessors. It could have been
>> accidentally
>> omitted or even buggy in some early members of the P6 family and this
>> could have been the reason for not documenting it from the beginning (the
>> case of FFREEP comes to mind).
>>
>
> 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

>
> -hpa



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