Re: pcb offset into uarea

[David Holland <dholland-tech%netbsd.org@localhost>]

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
dholland%netbsd.org@localhost