dwarf,proc: various fixes to support DWARFv5 (#3893)

Miscellaneous fixes to our DWARFv5 implementation, several contributed by @thanm.

pkg/dwarf/line/line_parser.go

@@ -116,7 +116,11 @@ func Parse(compdir string, buf *bytes.Buffer, debugLineStr []byte, logfn func(st
 	//   - dbl.Prologue.UnitLength is the length of the entire unit, not including the 4 bytes to represent that length.
 	//   - dbl.Prologue.Length is the length of the prologue not including unit length, version or prologue length itself.
 	//   - So you have UnitLength - PrologueLength - (version_length_bytes(2) + prologue_length_bytes(4)).
-	dbl.Instructions = buf.Next(int(dbl.Prologue.UnitLength - dbl.Prologue.Length - 6))
+	verDelta := uint32(6)
+	if dbl.Prologue.Version >= 5 {
+		verDelta = uint32(8)
+	}
+	dbl.Instructions = buf.Next(int(dbl.Prologue.UnitLength - dbl.Prologue.Length - verDelta))
 
 	return dbl
 }

pkg/dwarf/line/line_parser_test.go

@@ -63,6 +63,7 @@ const (
 	lineRangeGo18   uint8  = 10
 	versionGo14     uint16 = 2
 	versionGo111    uint16 = 3
+	versionGo125    uint16 = 5
 	opcodeBaseGo14  uint8  = 10
 	opcodeBaseGo111 uint8  = 11
 )
@@ -79,7 +80,7 @@ func testDebugLinePrologueParser(p string, t *testing.T) {
 	for _, dbl := range debugLines {
 		prologue := dbl.Prologue
 
-		if prologue.Version != versionGo14 && prologue.Version != versionGo111 {
+		if prologue.Version != versionGo14 && prologue.Version != versionGo111 && prologue.Version != versionGo125 {
 			t.Fatal("Version not parsed correctly", prologue.Version)
 		}
 

pkg/dwarf/line/state_machine.go

@@ -106,7 +106,7 @@ func newStateMachine(dbl *DebugLineInfo, instructions []byte, ptrSize int) *Stat
 	}
 	var file string
 	if len(dbl.FileNames) > 0 {
-		file = dbl.FileNames[0].Path
+		file = dbl.defaultFile()
 	}
 	dbl.endSeqIsValid = true
 	sm := &StateMachine{
@@ -123,6 +123,22 @@ func newStateMachine(dbl *DebugLineInfo, instructions []byte, ptrSize int) *Stat
 	return sm
 }
 
+func (dbl *DebugLineInfo) defaultFile() string {
+	// The default file is always file 1, however DWARFv5 starts numbering the
+	// entries of the files table from 0 but prior versions started with 1
+	// which means that for DWARFv4 and earlier the default file is the first
+	// entry of the table where in DWARFv5 the default is the second entry.
+	// See DWARFv4 and DWARFv5 section 6.2.4 at the end.
+	if dbl.Prologue.Version < 5 {
+		return dbl.FileNames[0].Path
+	}
+	if len(dbl.FileNames) == 1 {
+		// DWARFv5 doesn't say what should happen in this case.
+		return dbl.FileNames[0].Path
+	}
+	return dbl.FileNames[1].Path
+}
+
 // AllPCsForFileLines Adds all PCs for a given file and set (domain of map) of lines
 // to the map value corresponding to each line.
 func (lineInfo *DebugLineInfo) AllPCsForFileLines(f string, m map[int][]uint64) {
@@ -390,7 +406,7 @@ func (sm *StateMachine) next() error {
 	}
 	if sm.endSeq {
 		sm.endSeq = false
-		sm.file = sm.dbl.FileNames[0].Path
+		sm.file = sm.dbl.defaultFile()
 		sm.line = 1
 		sm.column = 0
 		sm.isa = 0

pkg/dwarf/parseutil.go

@@ -131,7 +131,7 @@ func ReadUnitVersions(data []byte) map[dwarf.Offset]uint8 {
 
 			switch unitType {
 			case _DW_UT_compile, _DW_UT_partial:
-				headerSize = 5 + secoffsz
+				headerSize = 4 + secoffsz
 
 			case _DW_UT_skeleton, _DW_UT_split_compile:
 				headerSize = 4 + secoffsz + 8

pkg/proc/bininfo.go

@@ -42,7 +42,7 @@ import (
 
 const (
 	dwarfGoLanguage    = 22   // DW_LANG_Go (from DWARF v5, section 7.12, page 231)
-	dwarfAttrAddrBase  = 0x74 // debug/dwarf.AttrAddrBase in Go 1.14, defined here for compatibility with Go < 1.14
+	dwarfAttrAddrBase  = 0x73 // debug/dwarf.AttrAddrBase in Go 1.14, defined here for compatibility with Go < 1.14
 	dwarfTreeCacheSize = 512  // size of the dwarfTree cache of each image
 )
 

pkg/proc/proc_general_test.go

@@ -136,7 +136,7 @@ func TestDwarfVersion(t *testing.T) {
 	const fakeEntryPoint = 1
 	assertNoError(bi.LoadBinaryInfo(fixture.Path, fakeEntryPoint, nil), t, "LoadBinaryInfo")
 	for _, cu := range bi.Images[0].compileUnits {
-		if cu.Version != 4 {
+		if cu.Version != 4 && cu.Version != 5 {
 			t.Errorf("compile unit %q at %#x has bad version %d", cu.name, cu.entry.Offset, cu.Version)
 		}
 	}

pkg/proc/proc_test.go

@@ -720,13 +720,13 @@ func TestStacktrace(t *testing.T) {
 			locations, err := proc.ThreadStacktrace(p, p.CurrentThread(), 40)
 			assertNoError(err, t, "Stacktrace()")
 
-			if len(locations) != len(stacks[i])+2 {
-				t.Fatalf("Wrong stack trace size %d %d\n", len(locations), len(stacks[i])+2)
-			}
-
 			t.Logf("Stacktrace %d:\n", i)
 			for i := range locations {
-				t.Logf("\t%s:%d\n", locations[i].Call.File, locations[i].Call.Line)
+				t.Logf("\t%s (%#x) %s:%d\n", locations[i].Call.Fn.Name, locations[i].Call.PC, locations[i].Call.File, locations[i].Call.Line)
+			}
+
+			if len(locations) != len(stacks[i])+2 {
+				t.Fatalf("Wrong stack trace size %d %d\n", len(locations), len(stacks[i])+2)
 			}
 
 			for j := range stacks[i] {
@@ -3193,6 +3193,7 @@ func testDeclLineCount(t *testing.T, p *proc.Target, lineno int, tgtvars []strin
 
 	assertLineNumber(p, t, lineno, "Program did not continue to correct next location")
 	scope, err := proc.GoroutineScope(p, p.CurrentThread())
+	t.Logf("scope PC: %#x\n", scope.PC)
 	assertNoError(err, t, fmt.Sprintf("GoroutineScope (:%d)", lineno))
 	vars, err := scope.Locals(0, "")
 	assertNoError(err, t, fmt.Sprintf("Locals (:%d)", lineno))