runtime: handle empty stack in expandFinalInlineFrame

Fixes #37967

Change-Id: I6fc22bdd65f0263d5672731b73d09249201ab0aa
Reviewed-on: https://go-review.googlesource.com/c/go/+/224458
Reviewed-by: Michael Pratt <[email protected]>

Author: randall77

src/runtime/pprof/proto_test.go

@@ -422,3 +422,16 @@ func TestFakeMapping(t *testing.T) {
 		}
 	}
 }
+
+// Make sure the profiler can handle an empty stack trace.
+// See issue 37967.
+func TestEmptyStack(t *testing.T) {
+	b := []uint64{
+		3, 0, 500, // hz = 500
+		3, 0, 10, // 10 samples with an empty stack trace
+	}
+	_, err := translateCPUProfile(b)
+	if err != nil {
+		t.Fatalf("translating profile: %v", err)
+	}
+}

src/runtime/symtab.go

@@ -153,6 +153,9 @@ func (ci *Frames) Next() (frame Frame, more bool) {
 //
 //go:linkname runtime_expandFinalInlineFrame runtime/pprof.runtime_expandFinalInlineFrame
 func runtime_expandFinalInlineFrame(stk []uintptr) []uintptr {
+	if len(stk) == 0 {
+		return stk
+	}
 	pc := stk[len(stk)-1]
 	tracepc := pc - 1