runtime: add explicit `INT $3` at end of Darwin amd64 sigtramp

The omission of this instruction could confuse the traceback code if a
SIGPROF occurred during a signal handler.  The traceback code would
trace up to sigtramp, but would then get confused because it would see a
PC address that did not appear to be in the function.

Fixes #16453.

Change-Id: I2b3d53e0b272fb01d9c2cb8add22bad879d3eebc
Reviewed-on: https://go-review.googlesource.com/25104
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

diff --git a/src/runtime/sys_darwin_amd64.s b/src/runtime/sys_darwin_amd64.s
index e09b906ba571f227308773ac40c87e6e0ec603f7..e4837ce2915ba126c19f2ef9234bb339f70a49c3 100644 (file)
--- a/src/runtime/sys_darwin_amd64.s
+++ b/src/runtime/sys_darwin_amd64.s
@@ -244,6 +244,7 @@ TEXT runtime·sigtramp(SB),NOSPLIT,$32
        MOVQ R8, 24(SP) // ctx
        MOVQ $runtime·sigtrampgo(SB), AX
        CALL AX
+       INT $3 // not reached (see issue 16453)
 
 TEXT runtime·mmap(SB),NOSPLIT,$0
        MOVQ    addr+0(FP), DI          // arg 1 addr