dtrace/amd64: Fix probe argument fetching

[markj]

Summary

dtrace_getarg() previously walked the call stack looking for a frame
matching the dtrace_invop_callsite symbol, in order to look for a
trapframe corresponding to an invop (i.e., FBT or kinst) probe. Commit
3ba8e9dc4a0e broke this in some cases by breaking the expected alignment
of the dtrace_invop_callsite symbol.

Rather than groveling around the stack to find invop probe arguments,
simply use the trapframe reference saved by dtrace_invop(). This is
simpler and less fragile.

Reported by: avg
MFC after: 2 weeks
Fixes: 3ba8e9dc4a0e ("dtrace/amd64: Implement emulation of call instructions")

[avg]

I like how using t_dtrace_trapframe both eliminates the search for the frame below the trap frame and the assumption on the position of the trap frame.

The change looks good to me.

sys/cddl/dev/dtrace/amd64/dtrace_isa.c

35

Just curious, what requires this header?

[markj]

sys/cddl/dev/dtrace/amd64/dtrace_isa.c

35

This is for the t_dtrace_trapframe macro and per-thread struct kdtrace_thread.

It's a bit silly having these in a separate cddl header. I'd like to get rid of it someday.