runtime: add msan calls before calling traceback functions

Tell msan that the arguments to the traceback functions are initialized,
in case the traceback functions are compiled with -fsanitize=memory.

Change-Id: I3ab0816604906c6cd7086245e6ae2e7fa62fe354
Reviewed-on: https://go-review.googlesource.com/24856
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/traceback.go

@@ -1077,6 +1077,9 @@ func callCgoSymbolizer(arg *cgoSymbolizerArg) {
 		// or when on the system stack.
 		call = asmcgocall
 	}
+	if msanenabled {
+		msanwrite(unsafe.Pointer(arg), unsafe.Sizeof(cgoSymbolizerArg{}))
+	}
 	call(cgoSymbolizer, noescape(unsafe.Pointer(arg)))
 }
 
@@ -1096,5 +1099,8 @@ func cgoContextPCs(ctxt uintptr, buf []uintptr) {
 		buf:     (*uintptr)(noescape(unsafe.Pointer(&buf[0]))),
 		max:     uintptr(len(buf)),
 	}
+	if msanenabled {
+		msanwrite(unsafe.Pointer(&arg), unsafe.Sizeof(arg))
+	}
 	call(cgoTraceback, noescape(unsafe.Pointer(&arg)))
 }