runtime: show panics in traceback

We used to include panic calls in tracebacks; however, when
runtime.panic was renamed to runtime.gopanic in the conversion of the
runtime to Go, we missed the special case in showframe that includes
panic calls even though they're in package runtime.

Fix the function name check in showframe (and, while we're here, fix
the other check for "runtime.panic" in runtime/pprof). Since the
"runtime.gopanic" name doesn't match what users call panic and hence
isn't very user-friendly, make traceback rewrite it to just "panic".

Updates #5832, #13857. Fixes #14315.

Change-Id: I8059621b41ec043e63d5cfb4cbee479f47f64973
Reviewed-on: https://go-review.googlesource.com/19492
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

src/runtime/crash_test.go

@@ -317,3 +317,22 @@ func TestNetpollDeadlock(t *testing.T) {
 		t.Fatalf("output does not start with %q:\n%s", want, output)
 	}
 }
+
+func TestPanicTraceback(t *testing.T) {
+	output := runTestProg(t, "testprog", "PanicTraceback")
+	want := "panic: hello"
+	if !strings.HasPrefix(output, want) {
+		t.Fatalf("output does not start with %q:\n%s", want, output)
+	}
+
+	// Check functions in the traceback.
+	fns := []string{"panic", "main.pt1.func1", "panic", "main.pt2.func1", "panic", "main.pt2", "main.pt1"}
+	for _, fn := range fns {
+		re := regexp.MustCompile(`(?m)^` + regexp.QuoteMeta(fn) + `\(.*\n`)
+		idx := re.FindStringIndex(output)
+		if idx == nil {
+			t.Fatalf("expected %q function in traceback:\n%s", fn, output)
+		}
+		output = output[idx[1]:]
+	}
+}

src/runtime/pprof/pprof.go

@@ -346,7 +346,7 @@ func printStackRecord(w io.Writer, stk []uintptr, allFrames bool) {
 			name := f.Name()
 			// Hide runtime.goexit and any runtime functions at the beginning.
 			// This is useful mainly for allocation traces.
-			wasPanic = name == "runtime.panic"
+			wasPanic = name == "runtime.gopanic"
 			if name == "runtime.goexit" || !show && strings.HasPrefix(name, "runtime.") {
 				continue
 			}

src/runtime/testdata/testprog/deadlock.go

@@ -29,7 +29,7 @@ func init() {
 	register("GoexitInPanic", GoexitInPanic)
 	register("PanicAfterGoexit", PanicAfterGoexit)
 	register("RecoveredPanicAfterGoexit", RecoveredPanicAfterGoexit)
-
+	register("PanicTraceback", PanicTraceback)
 }
 
 func SimpleDeadlock() {
@@ -171,3 +171,21 @@ func RecoveredPanicAfterGoexit() {
 	}()
 	runtime.Goexit()
 }
+
+func PanicTraceback() {
+	pt1()
+}
+
+func pt1() {
+	defer func() {
+		panic("panic pt1")
+	}()
+	pt2()
+}
+
+func pt2() {
+	defer func() {
+		panic("panic pt2")
+	}()
+	panic("hello")
+}

src/runtime/traceback.go

@@ -380,7 +380,11 @@ func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max in
 				if (n > 0 || flags&_TraceTrap == 0) && frame.pc > f.entry && !waspanic {
 					tracepc--
 				}
-				print(funcname(f), "(")
+				name := funcname(f)
+				if name == "runtime.gopanic" {
+					name = "panic"
+				}
+				print(name, "(")
 				argp := (*[100]uintptr)(unsafe.Pointer(frame.argp))
 				for i := uintptr(0); i < frame.arglen/sys.PtrSize; i++ {
 					if i >= 10 {
@@ -617,10 +621,10 @@ func showframe(f *_func, gp *g) bool {
 	level, _, _ := gotraceback()
 	name := funcname(f)
 
-	// Special case: always show runtime.panic frame, so that we can
+	// Special case: always show runtime.gopanic frame, so that we can
 	// see where a panic started in the middle of a stack trace.
 	// See golang.org/issue/5832.
-	if name == "runtime.panic" {
+	if name == "runtime.gopanic" {
 		return true
 	}