> > > It would, in principle, be possible to save/restore k0 > > > or k1 (but not both) if no other clever solution can be found. > > > There are other VM OSes that manage to do so for MIPS, > > > for other outside-the-old-ABI reasons. It does, of course, > > > add some instructions and some memory traffic to the > > > low-level exception handling , and we would have to look > > > at whether we would want to make such a feature standard > > > or specific to a "thread-ready" kernel build. > > > > I like the read-only k0 idea. We just need to make a system call to > > tell kernel what value to put in k0 before returning to the user space. > > It shouldn't be too hard to implement. I will try it next week. > > You could, I guess, wire a TLB entry to map the thread register into > the highest virtual memory region of the machine (the top of 'kseg2'), > which is accessible in a single instruction as a negative offset from > $0. Funny you should mention this. I was thinking about it yesterday in this context as something else that I've seen done in some non-Linux MIPS OSes, and something that I think would be a better solution for CPU-specific fast storage in SMP configurations than some of the hacks that I've seen proposed for SMP MIPS/Linux so far.
