[parisc-linux] xchg implementation

[LaMont Jones]

> > IIRC, CR24 and 25 are readable from user space (not writable), and can be
> > quite useful for thread specific data, thread id, etc...  It might do to
> > leave them available for such a use.
> You're thinking of CR26 and 27 (ref: Kane's PA-RISC 2.0 Architecture,
> page 2-17).  CR31 _is_ used, I didn't read carefully enough:

And the worst of it is that I knew that.  Sigh...

thanks for the clarification,
lamont