runtime: don't print "unexpected SPWRITE" when printing traceback

cherrymui · cherrymui · commit 15a274b621b3 · 2023-10-12T20:11:47.000Z
The system stack often starts with a stack transition function like "systemstack" or "mcall", which is marked as SPWRITE. When unwinding a system stack for printing, we want the traceback stop at the stack switching frame, but not print the "unexpected SPWRITE" message. Previously before CL 525835, we don't print the "unexpected SPWRITE" message if unwindPrintErrors is set, i.e. printing a stack trace. This CL restores this behavior. Another possibility is not printing the message only on the system stack. We don't expect a stack transition function to appear in a user G. Change-Id: I173e89ead2cd4fbf1f0f8cca225f28718b5baebe Reviewed-on: https://go-review.googlesource.com/c/go/+/531815 LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Michael Pratt <mpratt@google.com> Reviewed-by: Michael Knyszek <mknyszek@google.com>
diff --git a/src/runtime/crash_unix_test.go b/src/runtime/crash_unix_test.go
@@ -216,6 +216,12 @@ func TestPanicSystemstack(t *testing.T) {
 	if nUser != 2 || nSys != 2 {
 		t.Fatalf("want %d user stack frames in %s and %d system stack frames in %s, got %d and %d:\n%s", 2, userFunc, 2, sysFunc, nUser, nSys, string(tb))
 	}
+
+	// Traceback should not contain "unexpected SPWRITE" when
+	// unwinding the system stacks.
+	if bytes.Contains(tb, []byte("unexpected SPWRITE")) {
+		t.Errorf("unexpected \"unexpected SPWRITE\" in traceback:\n%s", tb)
+	}
 }
 
 func init() {
diff --git a/src/runtime/traceback.go b/src/runtime/traceback.go
@@ -356,15 +356,12 @@ func (u *unwinder) resolveInternal(innermost, isSyscall bool) {
 		//
 		// uSE uPE inn | action
 		//  T   _   _  | frame.lr = 0
-		//  F   T   F  | frame.lr = 0; print
-		//  F   T   T  | frame.lr = 0
+		//  F   T   _  | frame.lr = 0
 		//  F   F   F  | print; panic
 		//  F   F   T  | ignore SPWrite
-		if u.flags&unwindSilentErrors == 0 && !innermost {
+		if u.flags&(unwindPrintErrors|unwindSilentErrors) == 0 && !innermost {
 			println("traceback: unexpected SPWRITE function", funcname(f))
-			if u.flags&unwindPrintErrors == 0 {
-				throw("traceback")
-			}
+			throw("traceback")
 		}
 		frame.lr = 0
 	} else {

Original file line number	Diff line number	Diff line change
`@@ -216,6 +216,12 @@ func TestPanicSystemstack(t *testing.T) {`
`216`	`216`	`if nUser != 2 \|\| nSys != 2 {`
`217`	`217`	`t.Fatalf("want %d user stack frames in %s and %d system stack frames in %s, got %d and %d:\n%s", 2, userFunc, 2, sysFunc, nUser, nSys, string(tb))`
`218`	`218`	`}`
	`219`	`+`
	`220`	`+ // Traceback should not contain "unexpected SPWRITE" when`
	`221`	`+ // unwinding the system stacks.`
	`222`	`+ if bytes.Contains(tb, []byte("unexpected SPWRITE")) {`
	`223`	`+ t.Errorf("unexpected \"unexpected SPWRITE\" in traceback:\n%s", tb)`
	`224`	`+ }`
`219`	`225`	`}`
`220`	`226`
`221`	`227`	`func init() {`