Re: i387/FPU init issues...

[Arjan van de Ven]

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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