A recurring theme of the plan9 port, this time due to duffzero being called from goexitsall.

Disabling duffzero on plan9 is an option, but I'm considering if we could hack around using the normal zero and copy routines in plan9 note handling, so that duffzero/duffcopy can be enabled for plan9 without issues. This might reduce the chance of new cases of FP in note handlers popping up. I am not sure whether this can be done in any sane manner, but I'll keep thinking about it for a while and experiment a bit.

I'll post the error messages and trace later (I don't have them available right now), but it is goexitsall that fails, which seems very plausible seeing that it starts with a XORPS and a call to duffzero, most likely inserted by zerorange() to clear buf.

Test code
Anything that returns from main it seems.

Platform
9front amd64

Revision
f28bbb7