[M3devel] a note on user thread -- *context not 'universal'

[Olaf Wagner]

Quoting Jay <jay.krell at cornell.edu>:

> Do we really need the assembly _fpsetjmp?

IIRC, I introduced fpsetjmp/fplongjmp when I made the first FreeBSD code,
as FreeBSD does not care about storing the floating point state,
and spurious FP errors occured when switching threads by longjmp.
I think Bruce Evans contributed the FreeBSD assembler code.

It may be that Darwin, which is derived from FreeBSD in certain areas,
has inherited this problem (I don't remember offhand, and I haven't
done much BSD or M3 programming in recent months). I think no other
systems needed to use specially crafted setjmp/longjmp pairs to
accomodate the M3 user threads.

Olaf
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