From: Austin Clements <austin@google.com>
Date: Wed, 7 Aug 2019 01:37:37 +0000 (-0400)
Subject: runtime: fix debuglog traceback printing off-by-one
X-Git-Tag: go1.15beta1~305
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=45cd312394ebbcdce956952f0e269a82d89e6639;p=gostls13.git

runtime: fix debuglog traceback printing off-by-one

The debuglog traceback printer wasn't adjusting for call/return PCs.

Change-Id: I98dda1c0f22cd78651d88124ea51dc166dc91c7a
Reviewed-on: https://go-review.googlesource.com/c/go/+/227646
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
---

diff --git a/src/runtime/debuglog.go b/src/runtime/debuglog.go
index 100f2d370a..3ce3273f4d 100644
--- a/src/runtime/debuglog.go
+++ b/src/runtime/debuglog.go
@@ -665,13 +665,17 @@ func (r *debugLogReader) printVal() bool {
 		print("..(", r.uvarint(), " more bytes)..")
 
 	case debugLogPC:
-		printDebugLogPC(uintptr(r.uvarint()))
+		printDebugLogPC(uintptr(r.uvarint()), false)
 
 	case debugLogTraceback:
 		n := int(r.uvarint())
 		for i := 0; i < n; i++ {
 			print("\n\t")
-			printDebugLogPC(uintptr(r.uvarint()))
+			// gentraceback PCs are always return PCs.
+			// Convert them to call PCs.
+			//
+			// TODO(austin): Expand inlined frames.
+			printDebugLogPC(uintptr(r.uvarint()), true)
 		}
 	}
 
@@ -794,9 +798,17 @@ func printDebugLog() {
 	printunlock()
 }
 
-func printDebugLogPC(pc uintptr) {
-	print(hex(pc))
+// printDebugLogPC prints a single symbolized PC. If returnPC is true,
+// pc is a return PC that must first be converted to a call PC.
+func printDebugLogPC(pc uintptr, returnPC bool) {
 	fn := findfunc(pc)
+	if returnPC && (!fn.valid() || pc > fn.entry) {
+		// TODO(austin): Don't back up if the previous frame
+		// was a sigpanic.
+		pc--
+	}
+
+	print(hex(pc))
 	if !fn.valid() {
 		print(" [unknown PC]")
 	} else {