proc/variables: fix infinite recursion with pointer loop (#725)

loadValue didn't react correctly to pointer loops going through
slice -> interface{} -> slice or pointer -> interface{} -> pointer.

_fixtures/testvariables2.go

@@ -212,6 +212,14 @@ func main() {
 	ninf := math.Inf(-1)
 	nan := math.NaN()
 
+	var iface6 interface{}
+	var ptrinf *interface{}
+	iface6 = &ptrinf
+	ptrinf = &iface6
+
+	sliceinf := make([]interface{}, 1)
+	sliceinf[0] = sliceinf
+
 	var amb1 = 1
 	runtime.Breakpoint()
 	for amb1 := 0; amb1 < 10; amb1++ {

pkg/proc/proc_test.go

@@ -1440,14 +1440,17 @@ func TestIssue305(t *testing.T) {
 	})
 }
 
-func TestIssue341(t *testing.T) {
-	// pointer loop through map entries
+func TestPointerLoops(t *testing.T) {
+	// Pointer loops through map entries, pointers and slices
+	// Regression test for issue #341
 	withTestProcess("testvariables2", t, func(p *Process, fixture protest.Fixture) {
 		assertNoError(p.Continue(), t, "Continue()")
-		t.Logf("requesting mapinf")
-		mapinf, err := evalVariable(p, "mapinf")
-		assertNoError(err, t, "EvalVariable()")
-		t.Logf("mapinf: %v\n", mapinf)
+		for _, expr := range []string{"mapinf", "ptrinf", "sliceinf"} {
+			t.Logf("requesting %s", expr)
+			v, err := evalVariable(p, expr)
+			assertNoError(err, t, fmt.Sprintf("EvalVariable(%s)", expr))
+			t.Logf("%s: %v\n", expr, v)
+		}
 	})
 }
 

pkg/proc/variables.go

@@ -812,7 +812,12 @@ func (v *Variable) loadValueInternal(recurseLevel int, cfg LoadConfig) {
 		v.Children = []Variable{*v.maybeDereference()}
 		if cfg.FollowPointers {
 			// Don't increase the recursion level when dereferencing pointers
-			v.Children[0].loadValueInternal(recurseLevel, cfg)
+			// unless this is a pointer to interface (which could cause an infinite loop)
+			nextLvl := recurseLevel
+			if v.Children[0].Kind == reflect.Interface {
+				nextLvl++
+			}
+			v.Children[0].loadValueInternal(nextLvl, cfg)
 		} else {
 			v.Children[0].OnlyAddr = true
 		}
@@ -1630,7 +1635,7 @@ func (v *Variable) loadInterface(recurseLevel int, loadData bool, cfg LoadConfig
 	data = data.newVariable("data", data.Addr, typ)
 
 	v.Children = []Variable{*data}
-	if loadData {
+	if loadData && recurseLevel <= cfg.MaxVariableRecurse {
 		v.Children[0].loadValueInternal(recurseLevel, cfg)
 	} else {
 		v.Children[0].OnlyAddr = true

service/api/prettyprint.go

@@ -87,7 +87,9 @@ func (v *Variable) writeTo(buf io.Writer, top, newlines, includeType bool, inden
 		}
 		data := v.Children[0]
 		if data.Kind == reflect.Ptr {
-			if data.Children[0].Addr == 0 {
+			if len(data.Children) == 0 {
+				fmt.Fprintf(buf, "...")
+			} else if data.Children[0].Addr == 0 {
 				fmt.Fprintf(buf, "nil")
 			} else if data.Children[0].OnlyAddr {
 				fmt.Fprintf(buf, "0x%x", v.Children[0].Addr)