K 10
svn:author
V 2
kp
K 8
svn:date
V 27
2020-09-11T09:15:49.133423Z
K 7
svn:log
V 511
dtrace: fix fbt return probes on RISC-V

Return values are passed in a0, so read it from there. We also pass a1 through
to userspace, as the ABI allows small structs to be returned in registers
a0/a1. While here read the register values directly from the trapframe rather
than rtval, and remove the now unneeded argument from dtrace_invop().

Set fbtp_roffset so that we get the correct return location in arg0.

Reviewed by:	markj
Sponsored by:	Axiado
Differential Revision:	https://reviews.freebsd.org/D26389

END