On Mon, Feb 17, 2014 at 09:25:49PM +0000, David Laight wrote: > > > I'm adding code to i386 and amd64 to save the ymm registers on process > > > switch - allowing userspace to use the AVX instructions. > > > [ensuing crap about the u area] > > > > Why put it in the u area at all? It's a legacy concept of little > > continuing value. > > Certainly most of the stuff that is in the pcb could be put into the lwp > structure. Apart form the fp save area it isn't even very big. > > Putting the FP save area at the low address of the kernel stack pages > saves you having to worry about how bit it is. > (for 'stack grows down' systems).
On the other hand, varying the size of the kernel stack unpredictably doesn't sound like such a great plan. I suppose it's not by that much though. I dunno, I just tend to think the u area is an anachronism and we'd be better off abolishing it. -- David A. Holland dholl...@netbsd.org