Comment on myself...

> ... either of scratch register K0 or K1 could be thrown away,
> while the remainings be squashed in other ways, but...

BTW, the existence of struct kernframe has been painful in
many senses and not optimal (IMHO) for good engineering.
I propose to abandon the scheme and merge exception dispatchs
between user mode and kernel mode.  Though this merge might
stir argues, I know, it was the 4.4BSD heritage not a NetBSD
invention.

Toru Nishimura/ALKYL Technology