proc: bugfix: Truncate stacktrace when FDE of a frame can not be found

Instead of returning an error when FDE of a frame can not be found,
just truncate the stack trace.

Fixes #462

dwarf/frame/entries.go

@@ -65,6 +65,14 @@ func NewFrameIndex() FrameDescriptionEntries {
 	return make(FrameDescriptionEntries, 0, 1000)
 }
 
+type NoFDEForPCError struct {
+	PC uint64
+}
+
+func (err *NoFDEForPCError) Error() string {
+	return fmt.Sprintf("could not find FDE for PC %#v", err.PC)
+}
+
 // Returns the Frame Description Entry for the given PC.
 func (fdes FrameDescriptionEntries) FDEForPC(pc uint64) (*FrameDescriptionEntry, error) {
 	idx := sort.Search(len(fdes), func(i int) bool {
@@ -77,7 +85,7 @@ func (fdes FrameDescriptionEntries) FDEForPC(pc uint64) (*FrameDescriptionEntry,
 		return true
 	})
 	if idx == len(fdes) {
-		return nil, fmt.Errorf("could not find FDE for PC %#v", pc)
+		return nil, &NoFDEForPCError{pc}
 	}
 	return fdes[idx], nil
 }

proc/proc_test.go

@@ -1655,3 +1655,33 @@ func TestPanicBreakpoint(t *testing.T) {
 		}
 	})
 }
+
+func TestIssue462(t *testing.T) {
+	// Stacktrace of Goroutine 0 fails with an error
+	if runtime.GOOS == "windows" {
+		return
+	}
+	withTestProcess("testnextnethttp", t, func(p *Process, fixture protest.Fixture) {
+		go func() {
+			for !p.Running() {
+				time.Sleep(50 * time.Millisecond)
+			}
+
+			// Wait for program to start listening.
+			for {
+				conn, err := net.Dial("tcp", "localhost:9191")
+				if err == nil {
+					conn.Close()
+					break
+				}
+				time.Sleep(50 * time.Millisecond)
+			}
+
+			p.RequestManualStop()
+		}()
+
+		assertNoError(p.Continue(), t, "Continue()")
+		_, err := p.CurrentThread.Stacktrace(40)
+		assertNoError(err, t, "Stacktrace()")
+	})
+}

proc/stack.go

@@ -4,6 +4,7 @@ import (
 	"encoding/binary"
 	"errors"
 	"fmt"
+	"github.com/derekparker/delve/dwarf/frame"
 )
 
 // NoReturnAddr is returned when return address
@@ -101,6 +102,12 @@ func (it *StackIterator) Next() bool {
 	}
 	it.frame, it.err = it.dbp.frameInfo(it.pc, it.sp, it.top)
 	if it.err != nil {
+		if _, nofde := it.err.(*frame.NoFDEForPCError); nofde && !it.top {
+			it.frame = Stackframe{ Current: Location{ PC: it.pc, File: "?", Line: -1  }, Call: Location{ PC: it.pc, File: "?", Line: -1 }, CFA: 0, Ret: 0 }
+			it.atend = true
+			it.err = nil
+			return true
+		}
 		return false
 	}
 

proc/threads.go

@@ -3,6 +3,7 @@ package proc
 import (
 	"debug/gosym"
 	"encoding/binary"
+	"errors"
 	"fmt"
 	"path/filepath"
 	"reflect"
@@ -353,6 +354,9 @@ func (thread *Thread) Scope() (*EvalScope, error) {
 	if err != nil {
 		return nil, err
 	}
+	if len(locations) < 1 {
+		return nil, errors.New("could not decode first frame")
+	}
 	return locations[0].Scope(thread), nil
 }
 

proc/variables.go

@@ -422,11 +422,13 @@ func (g *G) UserCurrent() Location {
 	it := newStackIterator(g.dbp, pc, sp)
 	for it.Next() {
 		frame := it.Frame()
+		if frame.Call.Fn != nil {
 			name := frame.Call.Fn.Name
 			if (strings.Index(name, ".") >= 0) && (!strings.HasPrefix(name, "runtime.") || isExportedRuntime(name)) {
 				return frame.Call
 			}
 		}
+	}
 	return g.CurrentLoc
 }