Refactor frame API

dwarf/frame_entries.go

@@ -15,7 +15,17 @@ type CommonInformationEntry struct {
 	InitialInstructions   []byte
 }
 
-type FrameDescriptionEntries []*FrameDescriptionEntry
+type addrange struct {
+	begin, end uint64
+}
+
+func (r *addrange) Cover(addr uint64) bool {
+	if (addr - r.begin) < r.end {
+		return true
+	}
+
+	return false
+}
 
 // Represents a Frame Descriptor Entry in the
 // Dwarf .debug_frame section.
@@ -26,25 +36,19 @@ type FrameDescriptionEntry struct {
 	Instructions []byte
 }
 
-type addrange struct {
-	begin, end uint64
+func (fde *FrameDescriptionEntry) ReturnAddressOffset(pc uint64) int64 {
+	frame := executeDwarfProgram(fde, pc)
+	return frame.cfa.offset
 }
 
-func (r *addrange) Cover(addr uint64) bool {
-	if (addr - r.begin) < r.end {
-		return true
-	}
-
-	return false
-}
+type FrameDescriptionEntries []*FrameDescriptionEntry
 
-func (fdes FrameDescriptionEntries) FindReturnAddressOffset(pc uint64) (uint64, error) {
+func (fdes FrameDescriptionEntries) FDEForPC(pc uint64) (*FrameDescriptionEntry, error) {
 	for _, fde := range fdes {
 		if fde.AddressRange.Cover(pc) {
-			offset := unwind(fde, pc)
-			return offset, nil
+			return fde, nil
 		}
 	}
 
-	return 0, fmt.Errorf("Could not find return address.")
+	return nil, fmt.Errorf("Could not find FDE for %#v", pc)
 }

dwarf/frame_table.go

@@ -113,7 +113,7 @@ var fnlookup = map[byte]instruction{
 }
 
 // Unwind the stack to find the return address register.
-func unwind(fde *FrameDescriptionEntry, pc uint64) uint64 {
+func executeDwarfProgram(fde *FrameDescriptionEntry, pc uint64) *FrameContext {
 	frame := &FrameContext{
 		address:       pc,
 		cie:           fde.CIE,
@@ -129,7 +129,7 @@ func unwind(fde *FrameDescriptionEntry, pc uint64) uint64 {
 	dwarfexec(frame, fde.CIE.InitialInstructions)
 	dwarfexec(frame, fde.Instructions)
 
-	return uint64(frame.cfa.offset)
+	return frame
 }
 
 // Execute dwarf instructions.

dwarf/frame_table_test.go

@@ -82,17 +82,22 @@ func TestFindReturnAddress(t *testing.T) {
 			t.Fatal(err)
 		}
 
+		fde, err := fdes.FDEForPC(start)
+		if err != nil {
+			t.Fatal(err)
+		}
+
 		end, _, err := gsd.LineToPC(testsourcefile, 19)
 		if err != nil {
 			t.Fatal(err)
 		}
 
-		ret, err := fdes.FindReturnAddressOffset(start)
+		ret := fde.ReturnAddressOffset(start)
 		if err != nil {
 			t.Fatal(err)
 		}
 
-		addr := regs.Rsp + ret
+		addr := uint64(int64(regs.Rsp) + ret)
 		data := make([]byte, 8)
 
 		syscall.PtracePeekText(p.Pid, uintptr(addr), data)