K 10
svn:author
V 3
jhb
K 8
svn:date
V 27
2018-02-05T18:10:28.055581Z
K 7
svn:log
V 371
Fix makecontext() on MIPS O32.

The GP register can be clobbered by the callback, so save it in S1
while invoking the callback function.

While here, add a comment expounding on the treatment of GP for the
various ABIs and the assumptions made.

Reviewed by:	jmallett (earlier version)
Sponsored by:	DARPA / AFRL
Differential Revision:	https://reviews.freebsd.org/D14179

END