Altivec context was Re: Multilib swamp

Joel Sherrill <> joel.sherrill at
Wed Mar 2 18:12:52 UTC 2005

> Brings me right back to the question I asked originally - how could we 
> best add hooks for
> altivec register context switching [ without introducing an ugly #ifdef 
> __PPC__ into cpukit]?
> Ideas?

I thought I had emailed you privately with a suggestion based upon
what I thought would be most general to other architectures.
Multimedia/vector extensions are not uncommon in architectures
anymore.  Although some only consist of instructions which are
an alternate view of FP or 64-bit integer registers.

I propose a 3rd type of context to be added to the integer and
FPU ones we have now and a task attribute which is comparable to
that for has floating point.  It could be disabled on CPUs without
this capability just like FP is done now.

As always the issue is whether one can control the compiler well
enough to limit these architectural extensions to a subset of

Joel Sherrill, Ph.D.             Director of Research & Development
joel at                 On-Line Applications Research
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