Re: [Xenomai-help] Are xmm-registers saved with a (task) context

["M. Koehrer" <mathias_koehrer@domain.hid>]

Hi Gilles,

thanks for your response.
With the MMX registers, you are right. They are actually aliased with the FPU registers.
However, the XMM registers (SSE, SSE2) are not aliased. 
The aliased MMX registers AND the not-aliased XMM registers are available with today's CPUs,
i.e. you still have to take card when using MMX registers.
(All information according to Intel's 64 and IA-32 Architectures
Software Developer’s Manual, Volume 1, Chapters 9,10,11)

>From your mail before I assume that the (not-aliased) XMM registers are saved with the switching routine
and can be used without have to save/restore them.

Regards

Mathias


> > The xmm register are saved by the FPU switching routines. Note
> > however, that depending on the x86 you are using the xmm registers are
> > aliased to the FPU register or are separate registers. So, on machines
> > where the xmm registers are aliased to normal FPU registers, you have
> > to do the save restore on your own if you want to use MMX, SSE, or
> > SSE2 and use FPU instructions in the same thread.
> 
> This probably applies to very old CPUs, xmm are separate registers now.
> 


-- 
Mathias Koehrer
mathias_koehrer@domain.hid


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