Miscellaneous debug_line improvements (#1999)

* dwarf/line: implement DW_LNE_set_discriminator

We don't use the discriminator field in any way but we need to at least
parse it to support debub_line programs that use it.

* dwarf/line: support parsing DWARF4 debug_line sections

There is an extra field maximum_operations_per_instruction that is used
for VLIW CPUs. We don't support this feature but we have to at least
parse the field to not crash.

pkg/dwarf/line/line_parser.go

@@ -14,6 +14,7 @@ type DebugLinePrologue struct {
 	Version        uint16
 	Length         uint32
 	MinInstrLength uint8
+	MaxOpPerInstr  uint8
 	InitialIsStmt  uint8
 	LineBase       int8
 	LineRange      uint8
@@ -102,6 +103,11 @@ func parseDebugLinePrologue(dbl *DebugLineInfo, buf *bytes.Buffer) {
 	p.Version = binary.LittleEndian.Uint16(buf.Next(2))
 	p.Length = binary.LittleEndian.Uint32(buf.Next(4))
 	p.MinInstrLength = uint8(buf.Next(1)[0])
+	if p.Version == 4 {
+		p.MaxOpPerInstr = uint8(buf.Next(1)[0])
+	} else {
+		p.MaxOpPerInstr = 1
+	}
 	p.InitialIsStmt = uint8(buf.Next(1)[0])
 	p.LineBase = int8(buf.Next(1)[0])
 	p.LineRange = uint8(buf.Next(1)[0])

pkg/dwarf/line/line_parser_test.go

@@ -1,6 +1,7 @@
 package line
 
 import (
+	"compress/zlib"
 	"debug/elf"
 	"debug/macho"
 	"debug/pe"
@@ -342,3 +343,38 @@ func TestDebugLineC(t *testing.T) {
 		}
 	}
 }
+
+func TestDebugLineDwarf4(t *testing.T) {
+	p, err := filepath.Abs("../../../_fixtures/zdebug_line_dwarf4")
+	if err != nil {
+		t.Fatal("Could not find test data", p, err)
+	}
+	fh, err := os.Open(p)
+	if err != nil {
+		t.Fatal("Could not open test data", err)
+	}
+	defer fh.Close()
+	fh.Seek(12, 0) // skip "ZLIB" magic signature and length
+	r, err := zlib.NewReader(fh)
+	if err != nil {
+		t.Fatal("Could not open test data (zlib)", err)
+	}
+	data, err := ioutil.ReadAll(r)
+	if err != nil {
+		t.Fatal("Could not read test data", err)
+	}
+
+	debugLines := ParseAll(data, nil, 0, true, 8)
+
+	for _, dbl := range debugLines {
+		if dbl.Prologue.Version == 4 {
+			if dbl.Prologue.LineBase != -5 {
+				t.Errorf("Wrong LineBase %d\n", dbl.Prologue.LineBase)
+			}
+			if dbl.Prologue.LineRange != 14 {
+				t.Errorf("Wrong LineRange %d\n", dbl.Prologue.LineRange)
+			}
+		}
+	}
+
+}

pkg/dwarf/line/state_machine.go

@@ -80,6 +80,7 @@ const (
 	DW_LINE_end_sequence      = 1
 	DW_LINE_set_address       = 2
 	DW_LINE_define_file       = 3
+	DW_LINE_set_discriminator = 4
 )
 
 var standardopcodes = map[byte]opcodefn{
@@ -101,6 +102,7 @@ var extendedopcodes = map[byte]opcodefn{
 	DW_LINE_end_sequence:      endsequence,
 	DW_LINE_set_address:       setaddress,
 	DW_LINE_define_file:       definefile,
+	DW_LINE_set_discriminator: setdiscriminator,
 }
 
 func newStateMachine(dbl *DebugLineInfo, instructions []byte, ptrSize int) *StateMachine {
@@ -548,6 +550,10 @@ func setaddress(sm *StateMachine, buf *bytes.Buffer) {
 	sm.address = addr + sm.dbl.staticBase
 }
 
+func setdiscriminator(sm *StateMachine, buf *bytes.Buffer) {
+	_, _ = util.DecodeULEB128(buf)
+}
+
 func definefile(sm *StateMachine, buf *bytes.Buffer) {
 	entry := readFileEntry(sm.dbl, sm.buf, false)
 	sm.definedFiles = append(sm.definedFiles, entry)