Improve 'next': return into deferred func

_fixtures/testnextdefer.go

@@ -0,0 +1,10 @@
+package main
+
+import "fmt"
+
+func main() {
+	defer func() {
+		fmt.Println("hi")
+	}()
+	fmt.Println("bye")
+}

dwarf/reader/reader.go

@@ -87,6 +87,9 @@ func (reader *Reader) AddrForMember(member string, initialInstructions []byte) (
 		if err != nil {
 			return 0, err
 		}
+		if entry == nil {
+			return 0, fmt.Errorf("nil entry for member named %s", member)
+		}
 		name, ok := entry.Val(dwarf.AttrName).(string)
 		if !ok || name != member {
 			continue

proctl/proctl.go

@@ -249,6 +249,13 @@ func (dbp *DebuggedProcess) next() error {
 		return err
 	}
 
+	if curg.DeferPC != 0 {
+		_, err = dbp.TempBreak(curg.DeferPC)
+		if err != nil {
+			return err
+		}
+	}
+
 	var goroutineExiting bool
 	var waitCount int
 	for _, th := range dbp.Threads {

proctl/proctl_test.go

@@ -226,8 +226,8 @@ type nextTest struct {
 	begin, end int
 }
 
-func testnext(testcases []nextTest, initialLocation string, t *testing.T) {
-	withTestProcess("testnextprog", t, func(p *DebuggedProcess, fixture protest.Fixture) {
+func testnext(program string, testcases []nextTest, initialLocation string, t *testing.T) {
+	withTestProcess(program, t, func(p *DebuggedProcess, fixture protest.Fixture) {
 		bp, err := p.BreakByLocation(initialLocation)
 		assertNoError(err, t, "Break()")
 		assertNoError(p.Continue(), t, "Continue()")
@@ -277,7 +277,7 @@ func TestNextGeneral(t *testing.T) {
 		{26, 27},
 		{27, 34},
 	}
-	testnext(testcases, "main.testnext", t)
+	testnext("testnextprog", testcases, "main.testnext", t)
 }
 
 func TestNextGoroutine(t *testing.T) {
@@ -285,7 +285,7 @@ func TestNextGoroutine(t *testing.T) {
 		{46, 47},
 		{47, 42},
 	}
-	testnext(testcases, "main.testgoroutine", t)
+	testnext("testnextprog", testcases, "main.testgoroutine", t)
 }
 
 func TestNextFunctionReturn(t *testing.T) {
@@ -293,7 +293,15 @@ func TestNextFunctionReturn(t *testing.T) {
 		{13, 14},
 		{14, 35},
 	}
-	testnext(testcases, "main.helloworld", t)
+	testnext("testnextprog", testcases, "main.helloworld", t)
+}
+
+func TestNextFunctionReturnDefer(t *testing.T) {
+	testcases := []nextTest{
+		{5, 9},
+		{9, 6},
+	}
+	testnext("testnextdefer", testcases, "main.main", t)
 }
 
 func TestRuntimeBreakpoint(t *testing.T) {

proctl/variables.go

@@ -50,6 +50,9 @@ type G struct {
 	File string
 	Line int
 	Func *gosym.Func
+
+	// PC of entry to top-most deferred function.
+	DeferPC uint64
 }
 
 // Returns whether the goroutine is blocked on
@@ -89,7 +92,7 @@ func parseG(thread *ThreadContext, addr uint64) (*G, error) {
 
 	rdr := thread.Process.DwarfReader()
 	rdr.Seek(0)
-	_, err = rdr.SeekToTypeNamed("runtime.g")
+	entry, err := rdr.SeekToTypeNamed("runtime.g")
 	if err != nil {
 		return nil, err
 	}
@@ -97,6 +100,37 @@ func parseG(thread *ThreadContext, addr uint64) (*G, error) {
 	// Let's parse all of the members we care about in order so that
 	// we don't have to spend any extra time seeking.
 
+	// Parse defer
+	deferAddr, err := rdr.AddrForMember("_defer", initialInstructions)
+	if err != nil {
+		return nil, err
+	}
+	var deferPC uint64
+	// Dereference *defer pointer
+	deferAddrBytes, err := thread.readMemory(uintptr(deferAddr), thread.Process.arch.PtrSize())
+	if err != nil {
+		return nil, fmt.Errorf("error derefing *G %s", err)
+	}
+	if binary.LittleEndian.Uint64(deferAddrBytes) != 0 {
+		initialDeferInstructions := append([]byte{op.DW_OP_addr}, deferAddrBytes...)
+		_, err = rdr.SeekToTypeNamed("runtime._defer")
+		if err != nil {
+			return nil, err
+		}
+		deferPCAddr, err := rdr.AddrForMember("fn", initialDeferInstructions)
+		deferPC, err = thread.readUintRaw(uintptr(deferPCAddr), 8)
+		if err != nil {
+			return nil, err
+		}
+		deferPC, err = thread.readUintRaw(uintptr(deferPC), 8)
+		if err != nil {
+			return nil, err
+		}
+		err = rdr.SeekToEntry(entry)
+		if err != nil {
+			return nil, err
+		}
+	}
 	// Parse sched
 	schedAddr, err := rdr.AddrForMember("sched", initialInstructions)
 	if err != nil {
@@ -149,6 +183,7 @@ func parseG(thread *ThreadContext, addr uint64) (*G, error) {
 		Line:       l,
 		Func:       fn,
 		WaitReason: waitreason,
+		DeferPC:    deferPC,
 	}
 	return g, nil
 }