Implement decoding of SLEB128 numbers

dwarf/frame.go

@@ -106,7 +106,7 @@ func decodeULEB128(buf *bytes.Buffer) (uint64, uint32) {
 	for {
 		b, err := buf.ReadByte()
 		if err != nil {
-			panic("Could not parse LEB128 value")
+			panic("Could not parse ULEB128 value")
 		}
 		length++
 
@@ -123,6 +123,38 @@ func decodeULEB128(buf *bytes.Buffer) (uint64, uint32) {
 	return result, length
 }
 
+// decodeSLEB128 decodes an signed Little Endian Base 128
+// represented number.
+func decodeSLEB128(buf *bytes.Buffer) (int64, uint32) {
+	var (
+		b      byte
+		err    error
+		result int64
+		shift  uint64
+		length uint32
+	)
+
+	for {
+		b, err = buf.ReadByte()
+		if err != nil {
+			panic("Could not parse SLEB128 value")
+		}
+		length++
+
+		result |= int64((int64(b) & 0x7f) << shift)
+		shift += 7
+		if b&0x80 == 0 {
+			break
+		}
+	}
+
+	if (shift < 8*uint64(length)) && (b&0x40 > 0) {
+		result |= -(1 << shift)
+	}
+
+	return result, length
+}
+
 func cieEntry(data []byte) bool {
 	return bytes.Equal(data, []byte{0xff, 0xff, 0xff, 0xff})
 }

dwarf/frame_test.go

@@ -32,7 +32,7 @@ func grabDebugFrameSection(fp string, t *testing.T) []byte {
 	return data
 }
 
-func TestdecodeULEB128(t *testing.T) {
+func TestDecodeULEB128(t *testing.T) {
 	var leb128 = bytes.NewBuffer([]byte{0xE5, 0x8E, 0x26})
 
 	n, c := decodeULEB128(leb128)
@@ -41,6 +41,15 @@ func TestdecodeULEB128(t *testing.T) {
 	}
 }
 
+func TestDecodeSLEB128(t *testing.T) {
+	sleb128 := bytes.NewBuffer([]byte{0x9b, 0xf1, 0x59})
+
+	n, c := decodeSLEB128(sleb128)
+	if n != -624485 {
+		t.Fatal("Number was not decoded properly, got: ", n, c)
+	}
+}
+
 func TestParseString(t *testing.T) {
 	bstr := bytes.NewBuffer([]byte{'h', 'i', 0x0, 0xFF, 0xCC})
 	str, _ := parseString(bstr)