runtime: fix cgo signals detection

CL 64070 removed lockOSThread from the cgocall path, but didn't update
the signal-in-cgo detection in sighandler. As a result, signals that
arrive during a cgo call are treated like they arrived during Go
execution, breaking the traceback.

Update the cgo detection to fix the backtrace.

Fixes #47522

Change-Id: I61d77ba6465f55e3e6187246d79675ba8467ec23
Reviewed-on: https://go-review.googlesource.com/c/go/+/339989
Trust: Michael Pratt <mpratt@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

src/runtime/crash_cgo_test.go

@@ -536,6 +536,29 @@ func TestCgoTracebackSigpanic(t *testing.T) {
 	}
 }
 
+func TestCgoPanicCallback(t *testing.T) {
+	t.Parallel()
+	got := runTestProg(t, "testprogcgo", "PanicCallback")
+	t.Log(got)
+	want := "panic: runtime error: invalid memory address or nil pointer dereference"
+	if !strings.Contains(got, want) {
+		t.Errorf("did not see %q in output", want)
+	}
+	want = "panic_callback"
+	if !strings.Contains(got, want) {
+		t.Errorf("did not see %q in output", want)
+	}
+	want = "PanicCallback"
+	if !strings.Contains(got, want) {
+		t.Errorf("did not see %q in output", want)
+	}
+	// No runtime errors like "runtime: unexpected return pc".
+	nowant := "runtime: "
+	if strings.Contains(got, nowant) {
+		t.Errorf("did not see %q in output", want)
+	}
+}
+
 // Test that C code called via cgo can use large Windows thread stacks
 // and call back in to Go without crashing. See issue #20975.
 //
@@ -603,6 +626,28 @@ func TestSegv(t *testing.T) {
 	}
 }
 
+func TestAbortInCgo(t *testing.T) {
+	switch runtime.GOOS {
+	case "plan9", "windows":
+		// N.B. On Windows, C abort() causes the program to exit
+		// without going through the runtime at all.
+		t.Skipf("no signals on %s", runtime.GOOS)
+	}
+
+	t.Parallel()
+	got := runTestProg(t, "testprogcgo", "Abort")
+	t.Log(got)
+	want := "SIGABRT"
+	if !strings.Contains(got, want) {
+		t.Errorf("did not see %q in output", want)
+	}
+	// No runtime errors like "runtime: unknown pc".
+	nowant := "runtime: "
+	if strings.Contains(got, nowant) {
+		t.Errorf("did not see %q in output", want)
+	}
+}
+
 // TestEINTR tests that we handle EINTR correctly.
 // See issue #20400 and friends.
 func TestEINTR(t *testing.T) {

src/runtime/signal_unix.go

@@ -688,9 +688,11 @@ func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	}
 
 	print("PC=", hex(c.sigpc()), " m=", _g_.m.id, " sigcode=", c.sigcode(), "\n")
-	if _g_.m.lockedg != 0 && _g_.m.ncgo > 0 && gp == _g_.m.g0 {
+	if _g_.m.incgo && gp == _g_.m.g0 && _g_.m.curg != nil {
 		print("signal arrived during cgo execution\n")
-		gp = _g_.m.lockedg.ptr()
+		// Switch to curg so that we get a traceback of the Go code
+		// leading up to the cgocall, which switched from curg to g0.
+		gp = _g_.m.curg
 	}
 	if sig == _SIGILL || sig == _SIGFPE {
 		// It would be nice to know how long the instruction is.

src/runtime/signal_windows.go

@@ -218,11 +218,11 @@ func winthrow(info *exceptionrecord, r *context, gp *g) {
 	print("Exception ", hex(info.exceptioncode), " ", hex(info.exceptioninformation[0]), " ", hex(info.exceptioninformation[1]), " ", hex(r.ip()), "\n")
 
 	print("PC=", hex(r.ip()), "\n")
-	if _g_.m.lockedg != 0 && _g_.m.ncgo > 0 && gp == _g_.m.g0 {
+	if _g_.m.incgo && gp == _g_.m.g0 && _g_.m.curg != nil {
 		if iscgo {
 			print("signal arrived during external code execution\n")
 		}
-		gp = _g_.m.lockedg.ptr()
+		gp = _g_.m.curg
 	}
 	print("\n")
 

src/runtime/testdata/testprogcgo/panic.go

@@ -0,0 +1,29 @@
+package main
+
+import "C"
+
+// This program will crash.
+// We want to test unwinding from a cgo callback.
+
+/*
+void panic_callback();
+
+static void call_callback(void) {
+	panic_callback();
+}
+*/
+import "C"
+
+func init() {
+	register("PanicCallback", PanicCallback)
+}
+
+//export panic_callback
+func panic_callback() {
+	var i *int
+	*i = 42
+}
+
+func PanicCallback() {
+	C.call_callback()
+}

src/runtime/testdata/testprogcgo/sigthrow.go

@@ -0,0 +1,20 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+// This program will abort.
+
+/*
+#include <stdlib.h>
+*/
+import "C"
+
+func init() {
+	register("Abort", Abort)
+}
+
+func Abort() {
+	C.abort()
+}