runtime: fail silently if we unwind over sigpanic into C code

If we're running C code and the code panics, the runtime will inject a
call to sigpanic into the C code just like it would into Go code.
However, the return PC from this sigpanic will be in C code. We used
to silently abort the traceback if we didn't recognize a return PC, so
this went by quietly. Now we're much louder because in general this is
a bad thing. However, in this one particular case, it's fine, so if
we're in cgo and are looking at the return PC of sigpanic, silence the
debug output.

Fixes #23576.

Change-Id: I03d0c14d4e4d25b29b1f5804f5e9ccc4f742f876
Reviewed-on: https://go-review.googlesource.com/90896
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 21 insertions, 0 deletions

diff --git a/src/runtime/crash_cgo_test.go b/src/runtime/crash_cgo_test.go
index 8993a75ad3..3b9fedc7a4 100644
--- a/src/runtime/crash_cgo_test.go
+++ b/src/runtime/crash_cgo_test.go
@@ -481,3 +481,24 @@ func TestSigStackSwapping(t *testing.T) {
 		t.Errorf("expected %q got %v", want, got)
 	}
 }
+
+func TestCgoTracebackSigpanic(t *testing.T) {
+	// Test unwinding over a sigpanic in C code without a C
+	// symbolizer. See issue #23576.
+	if runtime.GOOS == "windows" {
+		// On Windows if we get an exception in C code, we let
+		// the Windows exception handler unwind it, rather
+		// than injecting a sigpanic.
+		t.Skip("no sigpanic in C on windows")
+	}
+	t.Parallel()
+	got := runTestProg(t, "testprogcgo", "TracebackSigpanic")
+	want := "runtime.sigpanic"
+	if !strings.Contains(got, want) {
+		t.Fatalf("want failure containing %q. output:\n%s\n", want, got)
+	}
+	nowant := "unexpected return pc"
+	if strings.Contains(got, nowant) {
+		t.Fatalf("failure incorrectly contains %q. output:\n%s\n", nowant, got)
+	}
+}