setjmp/longjmp and sparc

well, i might as well reveal my stupidity now, and
get it over with.

i don't understand how setjmp/longjmp are used to
switch contexts in sched.c.

on a sparc, setjmp just saves the caller's stack pointer,
frame pointer, and return pc; longjmp simply unwinds the
call stack by popping register windows until it finds the
matching frame.

i take it that a jmp_buf saves a lot more stuff (like an
almost-complete copy of the register file) on other
architectures? i think my ignorance of how setjmp/longjmp
works on other machines is part of my problem in understanding
what's going on.

-matt

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