libgo: update to Go1.16beta1 release

This does not yet include support for the //go:embed directive added
in this release.

	* Makefile.am (check-runtime): Don't create check-runtime-dir.
	(mostlyclean-local): Don't remove check-runtime-dir.
	(check-go-tool, check-vet): Copy in go.mod and modules.txt.
	(check-cgo-test, check-carchive-test): Add go.mod file.
	* Makefile.in: Regenerate.

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/280172

10 files changed, 457 insertions, 119 deletions

diff --git a/libgo/go/debug/dwarf/const.go b/libgo/go/debug/dwarf/const.go
index b11bf90..c607091 100644
--- a/libgo/go/debug/dwarf/const.go
+++ b/libgo/go/debug/dwarf/const.go
@@ -461,3 +461,15 @@ const (
 	utSplitCompile = 0x05
 	utSplitType    = 0x06
 )
+
+// Opcodes for DWARFv5 debug_rnglists section.
+const (
+	rleEndOfList    = 0x0
+	rleBaseAddressx = 0x1
+	rleStartxEndx   = 0x2
+	rleStartxLength = 0x3
+	rleOffsetPair   = 0x4
+	rleBaseAddress  = 0x5
+	rleStartEnd     = 0x6
+	rleStartLength  = 0x7
+)
diff --git a/libgo/go/debug/dwarf/dwarf5ranges_test.go b/libgo/go/debug/dwarf/dwarf5ranges_test.go
new file mode 100644
index 0000000..8bc50bc
--- /dev/null
+++ b/libgo/go/debug/dwarf/dwarf5ranges_test.go
@@ -0,0 +1,41 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package dwarf
+
+import (
+	"encoding/binary"
+	"os"
+	"reflect"
+	"testing"
+)
+
+func TestDwarf5Ranges(t *testing.T) {
+	rngLists, err := os.ReadFile("testdata/debug_rnglists")
+	if err != nil {
+		t.Fatalf("could not read test data: %v", err)
+	}
+
+	d := &Data{}
+	d.order = binary.LittleEndian
+	if err := d.AddSection(".debug_rnglists", rngLists); err != nil {
+		t.Fatal(err)
+	}
+	u := &unit{
+		asize: 8,
+		vers:  5,
+		is64:  true,
+	}
+	ret, err := d.dwarf5Ranges(u, nil, 0x5fbd, 0xc, [][2]uint64{})
+	if err != nil {
+		t.Fatalf("could not read rnglist: %v", err)
+	}
+	t.Logf("%#v", ret)
+
+	tgt := [][2]uint64{{0x0000000000006712, 0x000000000000679f}, {0x00000000000067af}, {0x00000000000067b3}}
+
+	if reflect.DeepEqual(ret, tgt) {
+		t.Errorf("expected %#v got %#x", tgt, ret)
+	}
+}
diff --git a/libgo/go/debug/dwarf/entry.go b/libgo/go/debug/dwarf/entry.go
index 01f2190..3fc73b8 100644
--- a/libgo/go/debug/dwarf/entry.go
+++ b/libgo/go/debug/dwarf/entry.go
@@ -423,6 +423,47 @@ func (b *buf) entry(cu *Entry, atab abbrevTable, ubase Offset, vers int) *Entry
 		Children: a.children,
 		Field:    make([]Field, len(a.field)),
 	}
+
+	// If we are currently parsing the compilation unit,
+	// we can't evaluate Addrx or Strx until we've seen the
+	// relevant base entry.
+	type delayed struct {
+		idx int
+		off uint64
+		fmt format
+	}
+	var delay []delayed
+
+	resolveStrx := func(strBase, off uint64) string {
+		off += strBase
+		if uint64(int(off)) != off {
+			b.error("DW_FORM_strx offset out of range")
+		}
+
+		b1 := makeBuf(b.dwarf, b.format, "str_offsets", 0, b.dwarf.strOffsets)
+		b1.skip(int(off))
+		is64, _ := b.format.dwarf64()
+		if is64 {
+			off = b1.uint64()
+		} else {
+			off = uint64(b1.uint32())
+		}
+		if b1.err != nil {
+			b.err = b1.err
+			return ""
+		}
+		if uint64(int(off)) != off {
+			b.error("DW_FORM_strx indirect offset out of range")
+		}
+		b1 = makeBuf(b.dwarf, b.format, "str", 0, b.dwarf.str)
+		b1.skip(int(off))
+		val := b1.string()
+		if b1.err != nil {
+			b.err = b1.err
+		}
+		return val
+	}
+
 	for i := range e.Field {
 		e.Field[i].Attr = a.field[i].attr
 		e.Field[i].Class = a.field[i].class
@@ -453,38 +494,31 @@ func (b *buf) entry(cu *Entry, atab abbrevTable, ubase Offset, vers int) *Entry
 			case formAddrx4:
 				off = uint64(b.uint32())
 			}
-			if len(b.dwarf.addr) == 0 {
+			if b.dwarf.addr == nil {
 				b.error("DW_FORM_addrx with no .debug_addr section")
 			}
 			if b.err != nil {
 				return nil
 			}
-			addrsize := b.format.addrsize()
-			if addrsize == 0 {
-				b.error("unknown address size for DW_FORM_addrx")
-			}
-			off *= uint64(addrsize)
 
 			// We have to adjust by the offset of the
 			// compilation unit. This won't work if the
 			// program uses Reader.Seek to skip over the
 			// unit. Not much we can do about that.
+			var addrBase int64
 			if cu != nil {
-				cuOff, ok := cu.Val(AttrAddrBase).(int64)
-				if ok {
-					off += uint64(cuOff)
-				}
-			}
-
-			if uint64(int(off)) != off {
-				b.error("DW_FORM_addrx offset out of range")
+				addrBase, _ = cu.Val(AttrAddrBase).(int64)
+			} else if a.tag == TagCompileUnit {
+				delay = append(delay, delayed{i, off, formAddrx})
+				break
 			}
 
-			b1 := makeBuf(b.dwarf, b.format, "addr", 0, b.dwarf.addr)
-			b1.skip(int(off))
-			val = b1.addr()
-			if b1.err != nil {
-				b.err = b1.err
+			var err error
+			val, err = b.dwarf.debugAddr(b.format, uint64(addrBase), off)
+			if err != nil {
+				if b.err == nil {
+					b.err = err
+				}
 				return nil
 			}
 
@@ -621,38 +655,16 @@ func (b *buf) entry(cu *Entry, atab abbrevTable, ubase Offset, vers int) *Entry
 			// compilation unit. This won't work if the
 			// program uses Reader.Seek to skip over the
 			// unit. Not much we can do about that.
+			var strBase int64
 			if cu != nil {
-				cuOff, ok := cu.Val(AttrStrOffsetsBase).(int64)
-				if ok {
-					off += uint64(cuOff)
-				}
+				strBase, _ = cu.Val(AttrStrOffsetsBase).(int64)
+			} else if a.tag == TagCompileUnit {
+				delay = append(delay, delayed{i, off, formStrx})
+				break
 			}
 
-			if uint64(int(off)) != off {
-				b.error("DW_FORM_strx offset out of range")
-			}
+			val = resolveStrx(uint64(strBase), off)
 
-			b1 := makeBuf(b.dwarf, b.format, "str_offsets", 0, b.dwarf.strOffsets)
-			b1.skip(int(off))
-			if is64 {
-				off = b1.uint64()
-			} else {
-				off = uint64(b1.uint32())
-			}
-			if b1.err != nil {
-				b.err = b1.err
-				return nil
-			}
-			if uint64(int(off)) != off {
-				b.error("DW_FORM_strx indirect offset out of range")
-			}
-			b1 = makeBuf(b.dwarf, b.format, "str", 0, b.dwarf.str)
-			b1.skip(int(off))
-			val = b1.string()
-			if b1.err != nil {
-				b.err = b1.err
-				return nil
-			}
 		case formStrpSup:
 			is64, known := b.format.dwarf64()
 			if !known {
@@ -699,11 +711,32 @@ func (b *buf) entry(cu *Entry, atab abbrevTable, ubase Offset, vers int) *Entry
 		case formRnglistx:
 			val = b.uint()
 		}
+
 		e.Field[i].Val = val
 	}
 	if b.err != nil {
 		return nil
 	}
+
+	for _, del := range delay {
+		switch del.fmt {
+		case formAddrx:
+			addrBase, _ := e.Val(AttrAddrBase).(int64)
+			val, err := b.dwarf.debugAddr(b.format, uint64(addrBase), del.off)
+			if err != nil {
+				b.err = err
+				return nil
+			}
+			e.Field[del.idx].Val = val
+		case formStrx:
+			strBase, _ := e.Val(AttrStrOffsetsBase).(int64)
+			e.Field[del.idx].Val = resolveStrx(uint64(strBase), del.off)
+			if b.err != nil {
+				return nil
+			}
+		}
+	}
+
 	return e
 }
 
@@ -717,6 +750,7 @@ type Reader struct {
 	d            *Data
 	err          error
 	unit         int
+	lastUnit     bool   // set if last entry returned by Next is TagCompileUnit/TagPartialUnit
 	lastChildren bool   // .Children of last entry returned by Next
 	lastSibling  Offset // .Val(AttrSibling) of last entry returned by Next
 	cu           *Entry // current compilation unit
@@ -774,13 +808,18 @@ func (r *Reader) Seek(off Offset) {
 // maybeNextUnit advances to the next unit if this one is finished.
 func (r *Reader) maybeNextUnit() {
 	for len(r.b.data) == 0 && r.unit+1 < len(r.d.unit) {
-		r.unit++
-		u := &r.d.unit[r.unit]
-		r.b = makeBuf(r.d, u, "info", u.off, u.data)
-		r.cu = nil
+		r.nextUnit()
 	}
 }
 
+// nextUnit advances to the next unit.
+func (r *Reader) nextUnit() {
+	r.unit++
+	u := &r.d.unit[r.unit]
+	r.b = makeBuf(r.d, u, "info", u.off, u.data)
+	r.cu = nil
+}
+
 // Next reads the next entry from the encoded entry stream.
 // It returns nil, nil when it reaches the end of the section.
 // It returns an error if the current offset is invalid or the data at the
@@ -799,12 +838,14 @@ func (r *Reader) Next() (*Entry, error) {
 		r.err = r.b.err
 		return nil, r.err
 	}
+	r.lastUnit = false
 	if e != nil {
 		r.lastChildren = e.Children
 		if r.lastChildren {
 			r.lastSibling, _ = e.Val(AttrSibling).(Offset)
 		}
 		if e.Tag == TagCompileUnit || e.Tag == TagPartialUnit {
+			r.lastUnit = true
 			r.cu = e
 		}
 	} else {
@@ -830,6 +871,11 @@ func (r *Reader) SkipChildren() {
 		return
 	}
 
+	if r.lastUnit && r.unit+1 < len(r.d.unit) {
+		r.nextUnit()
+		return
+	}
+
 	for {
 		e, err := r.Next()
 		if err != nil || e == nil || e.Tag == 0 {
@@ -874,6 +920,7 @@ func (r *Reader) SeekPC(pc uint64) (*Entry, error) {
 		r.err = nil
 		r.lastChildren = false
 		r.unit = unit
+		r.cu = nil
 		u := &r.d.unit[unit]
 		r.b = makeBuf(r.d, u, "info", u.off, u.data)
 		e, err := r.Next()
@@ -922,53 +969,186 @@ func (d *Data) Ranges(e *Entry) ([][2]uint64, error) {
 		ret = append(ret, [2]uint64{low, high})
 	}
 
-	ranges, rangesOK := e.Val(AttrRanges).(int64)
-	if rangesOK && d.ranges != nil {
-		// The initial base address is the lowpc attribute
-		// of the enclosing compilation unit.
-		// Although DWARF specifies the lowpc attribute,
-		// comments in gdb/dwarf2read.c say that some versions
-		// of GCC use the entrypc attribute, so we check that too.
-		var cu *Entry
-		if e.Tag == TagCompileUnit {
-			cu = e
-		} else {
-			i := d.offsetToUnit(e.Offset)
-			if i == -1 {
-				return nil, errors.New("no unit for entry")
+	var u *unit
+	if uidx := d.offsetToUnit(e.Offset); uidx >= 0 && uidx < len(d.unit) {
+		u = &d.unit[uidx]
+	}
+
+	if u != nil && u.vers >= 5 && d.rngLists != nil {
+		// DWARF version 5 and later
+		field := e.AttrField(AttrRanges)
+		if field == nil {
+			return ret, nil
+		}
+		switch field.Class {
+		case ClassRangeListPtr:
+			ranges, rangesOK := field.Val.(int64)
+			if !rangesOK {
+				return ret, nil
 			}
-			u := &d.unit[i]
-			b := makeBuf(d, u, "info", u.off, u.data)
-			cu = b.entry(nil, u.atable, u.base, u.vers)
-			if b.err != nil {
-				return nil, b.err
+			cu, base, err := d.baseAddressForEntry(e)
+			if err != nil {
+				return nil, err
 			}
+			return d.dwarf5Ranges(u, cu, base, ranges, ret)
+
+		case ClassRngList:
+			// TODO: support DW_FORM_rnglistx
+			return ret, nil
+
+		default:
+			return ret, nil
+		}
+	}
+
+	// DWARF version 2 through 4
+	ranges, rangesOK := e.Val(AttrRanges).(int64)
+	if rangesOK && d.ranges != nil {
+		_, base, err := d.baseAddressForEntry(e)
+		if err != nil {
+			return nil, err
 		}
+		return d.dwarf2Ranges(u, base, ranges, ret)
+	}
+
+	return ret, nil
+}
 
-		var base uint64
-		if cuEntry, cuEntryOK := cu.Val(AttrEntrypc).(uint64); cuEntryOK {
-			base = cuEntry
-		} else if cuLow, cuLowOK := cu.Val(AttrLowpc).(uint64); cuLowOK {
-			base = cuLow
+// baseAddressForEntry returns the initial base address to be used when
+// looking up the range list of entry e.
+// DWARF specifies that this should be the lowpc attribute of the enclosing
+// compilation unit, however comments in gdb/dwarf2read.c say that some
+// versions of GCC use the entrypc attribute, so we check that too.
+func (d *Data) baseAddressForEntry(e *Entry) (*Entry, uint64, error) {
+	var cu *Entry
+	if e.Tag == TagCompileUnit {
+		cu = e
+	} else {
+		i := d.offsetToUnit(e.Offset)
+		if i == -1 {
+			return nil, 0, errors.New("no unit for entry")
+		}
+		u := &d.unit[i]
+		b := makeBuf(d, u, "info", u.off, u.data)
+		cu = b.entry(nil, u.atable, u.base, u.vers)
+		if b.err != nil {
+			return nil, 0, b.err
 		}
+	}
 
-		u := &d.unit[d.offsetToUnit(e.Offset)]
-		buf := makeBuf(d, u, "ranges", Offset(ranges), d.ranges[ranges:])
-		for len(buf.data) > 0 {
-			low = buf.addr()
-			high = buf.addr()
+	if cuEntry, cuEntryOK := cu.Val(AttrEntrypc).(uint64); cuEntryOK {
+		return cu, cuEntry, nil
+	} else if cuLow, cuLowOK := cu.Val(AttrLowpc).(uint64); cuLowOK {
+		return cu, cuLow, nil
+	}
 
-			if low == 0 && high == 0 {
-				break
+	return cu, 0, nil
+}
+
+func (d *Data) dwarf2Ranges(u *unit, base uint64, ranges int64, ret [][2]uint64) ([][2]uint64, error) {
+	buf := makeBuf(d, u, "ranges", Offset(ranges), d.ranges[ranges:])
+	for len(buf.data) > 0 {
+		low := buf.addr()
+		high := buf.addr()
+
+		if low == 0 && high == 0 {
+			break
+		}
+
+		if low == ^uint64(0)>>uint((8-u.addrsize())*8) {
+			base = high
+		} else {
+			ret = append(ret, [2]uint64{base + low, base + high})
+		}
+	}
+
+	return ret, nil
+}
+
+// dwarf5Ranges interpets a debug_rnglists sequence, see DWARFv5 section
+// 2.17.3 (page 53).
+func (d *Data) dwarf5Ranges(u *unit, cu *Entry, base uint64, ranges int64, ret [][2]uint64) ([][2]uint64, error) {
+	var addrBase int64
+	if cu != nil {
+		addrBase, _ = cu.Val(AttrAddrBase).(int64)
+	}
+
+	buf := makeBuf(d, u, "rnglists", 0, d.rngLists)
+	buf.skip(int(ranges))
+	for {
+		opcode := buf.uint8()
+		switch opcode {
+		case rleEndOfList:
+			if buf.err != nil {
+				return nil, buf.err
+			}
+			return ret, nil
+
+		case rleBaseAddressx:
+			baseIdx := buf.uint()
+			var err error
+			base, err = d.debugAddr(u, uint64(addrBase), baseIdx)
+			if err != nil {
+				return nil, err
 			}
 
-			if low == ^uint64(0)>>uint((8-u.addrsize())*8) {
-				base = high
-			} else {
-				ret = append(ret, [2]uint64{base + low, base + high})
+		case rleStartxEndx:
+			startIdx := buf.uint()
+			endIdx := buf.uint()
+
+			start, err := d.debugAddr(u, uint64(addrBase), startIdx)
+			if err != nil {
+				return nil, err
+			}
+			end, err := d.debugAddr(u, uint64(addrBase), endIdx)
+			if err != nil {
+				return nil, err
+			}
+			ret = append(ret, [2]uint64{start, end})
+
+		case rleStartxLength:
+			startIdx := buf.uint()
+			len := buf.uint()
+			start, err := d.debugAddr(u, uint64(addrBase), startIdx)
+			if err != nil {
+				return nil, err
 			}
+			ret = append(ret, [2]uint64{start, start + len})
+
+		case rleOffsetPair:
+			off1 := buf.uint()
+			off2 := buf.uint()
+			ret = append(ret, [2]uint64{base + off1, base + off2})
+
+		case rleBaseAddress:
+			base = buf.addr()
+
+		case rleStartEnd:
+			start := buf.addr()
+			end := buf.addr()
+			ret = append(ret, [2]uint64{start, end})
+
+		case rleStartLength:
+			start := buf.addr()
+			len := buf.uint()
+			ret = append(ret, [2]uint64{start, start + len})
 		}
 	}
+}
 
-	return ret, nil
+// debugAddr returns the address at idx in debug_addr
+func (d *Data) debugAddr(format dataFormat, addrBase, idx uint64) (uint64, error) {
+	off := idx*uint64(format.addrsize()) + addrBase
+
+	if uint64(int(off)) != off {
+		return 0, errors.New("offset out of range")
+	}
+
+	b := makeBuf(d, format, "addr", 0, d.addr)
+	b.skip(int(off))
+	val := b.addr()
+	if b.err != nil {
+		return 0, b.err
+	}
+	return val, nil
 }
diff --git a/libgo/go/debug/dwarf/entry_test.go b/libgo/go/debug/dwarf/entry_test.go
index 4c9aad2..b54f8b4 100644
--- a/libgo/go/debug/dwarf/entry_test.go
+++ b/libgo/go/debug/dwarf/entry_test.go
@@ -7,6 +7,7 @@ package dwarf_test
 import (
 	. "debug/dwarf"
 	"encoding/binary"
+	"path/filepath"
 	"reflect"
 	"testing"
 )
@@ -54,6 +55,20 @@ func TestReaderSeek(t *testing.T) {
 		{0x400611, nil},
 	}
 	testRanges(t, "testdata/line-gcc.elf", want)
+
+	want = []wantRange{
+		{0x401122, [][2]uint64{{0x401122, 0x401166}}},
+		{0x401165, [][2]uint64{{0x401122, 0x401166}}},
+		{0x401166, [][2]uint64{{0x401166, 0x401179}}},
+	}
+	testRanges(t, "testdata/line-gcc-dwarf5.elf", want)
+
+	want = []wantRange{
+		{0x401130, [][2]uint64{{0x401130, 0x40117e}}},
+		{0x40117d, [][2]uint64{{0x401130, 0x40117e}}},
+		{0x40117e, nil},
+	}
+	testRanges(t, "testdata/line-clang-dwarf5.elf", want)
 }
 
 func TestRangesSection(t *testing.T) {
@@ -96,44 +111,72 @@ func testRanges(t *testing.T, name string, want []wantRange) {
 }
 
 func TestReaderRanges(t *testing.T) {
-	d := elfData(t, "testdata/line-gcc.elf")
-
-	subprograms := []struct {
+	type subprograms []struct {
 		name   string
 		ranges [][2]uint64
+	}
+	tests := []struct {
+		filename    string
+		subprograms subprograms
 	}{
-		{"f1", [][2]uint64{{0x40059d, 0x4005e7}}},
-		{"main", [][2]uint64{{0x4005e7, 0x400601}}},
-		{"f2", [][2]uint64{{0x400601, 0x400611}}},
+		{
+			"testdata/line-gcc.elf",
+			subprograms{
+				{"f1", [][2]uint64{{0x40059d, 0x4005e7}}},
+				{"main", [][2]uint64{{0x4005e7, 0x400601}}},
+				{"f2", [][2]uint64{{0x400601, 0x400611}}},
+			},
+		},
+		{
+			"testdata/line-gcc-dwarf5.elf",
+			subprograms{
+				{"main", [][2]uint64{{0x401147, 0x401166}}},
+				{"f1", [][2]uint64{{0x401122, 0x401147}}},
+				{"f2", [][2]uint64{{0x401166, 0x401179}}},
+			},
+		},
+		{
+			"testdata/line-clang-dwarf5.elf",
+			subprograms{
+				{"main", [][2]uint64{{0x401130, 0x401144}}},
+				{"f1", [][2]uint64{{0x401150, 0x40117e}}},
+				{"f2", [][2]uint64{{0x401180, 0x401197}}},
+			},
+		},
 	}
 
-	r := d.Reader()
-	i := 0
-	for entry, err := r.Next(); entry != nil && err == nil; entry, err = r.Next() {
-		if entry.Tag != TagSubprogram {
-			continue
-		}
+	for _, test := range tests {
+		d := elfData(t, test.filename)
+		subprograms := test.subprograms
 
-		if i > len(subprograms) {
-			t.Fatalf("too many subprograms (expected at most %d)", i)
-		}
+		r := d.Reader()
+		i := 0
+		for entry, err := r.Next(); entry != nil && err == nil; entry, err = r.Next() {
+			if entry.Tag != TagSubprogram {
+				continue
+			}
 
-		if got := entry.Val(AttrName).(string); got != subprograms[i].name {
-			t.Errorf("subprogram %d name is %s, expected %s", i, got, subprograms[i].name)
-		}
-		ranges, err := d.Ranges(entry)
-		if err != nil {
-			t.Errorf("subprogram %d: %v", i, err)
-			continue
-		}
-		if !reflect.DeepEqual(ranges, subprograms[i].ranges) {
-			t.Errorf("subprogram %d ranges are %x, expected %x", i, ranges, subprograms[i].ranges)
+			if i > len(subprograms) {
+				t.Fatalf("%s: too many subprograms (expected at most %d)", test.filename, i)
+			}
+
+			if got := entry.Val(AttrName).(string); got != subprograms[i].name {
+				t.Errorf("%s: subprogram %d name is %s, expected %s", test.filename, i, got, subprograms[i].name)
+			}
+			ranges, err := d.Ranges(entry)
+			if err != nil {
+				t.Errorf("%s: subprogram %d: %v", test.filename, i, err)
+				continue
+			}
+			if !reflect.DeepEqual(ranges, subprograms[i].ranges) {
+				t.Errorf("%s: subprogram %d ranges are %x, expected %x", test.filename, i, ranges, subprograms[i].ranges)
+			}
+			i++
 		}
-		i++
-	}
 
-	if i < len(subprograms) {
-		t.Errorf("saw only %d subprograms, expected %d", i, len(subprograms))
+		if i < len(subprograms) {
+			t.Errorf("%s: saw only %d subprograms, expected %d", test.filename, i, len(subprograms))
+		}
 	}
 }
 
@@ -209,3 +252,44 @@ func Test64Bit(t *testing.T) {
 		}
 	}
 }
+
+func TestUnitIteration(t *testing.T) {
+	// Iterate over all ELF test files we have and ensure that
+	// we get the same set of compilation units skipping (method 0)
+	// and not skipping (method 1) CU children.
+	files, err := filepath.Glob(filepath.Join("testdata", "*.elf"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, file := range files {
+		t.Run(file, func(t *testing.T) {
+			d := elfData(t, file)
+			var units [2][]interface{}
+			for method := range units {
+				for r := d.Reader(); ; {
+					ent, err := r.Next()
+					if err != nil {
+						t.Fatal(err)
+					}
+					if ent == nil {
+						break
+					}
+					if ent.Tag == TagCompileUnit {
+						units[method] = append(units[method], ent.Val(AttrName))
+					}
+					if method == 0 {
+						if ent.Tag != TagCompileUnit {
+							t.Fatalf("found unexpected tag %v on top level", ent.Tag)
+						}
+						r.SkipChildren()
+					}
+				}
+			}
+			t.Logf("skipping CUs:     %v", units[0])
+			t.Logf("not-skipping CUs: %v", units[1])
+			if !reflect.DeepEqual(units[0], units[1]) {
+				t.Fatal("set of CUs differ")
+			}
+		})
+	}
+}
diff --git a/libgo/go/debug/dwarf/line.go b/libgo/go/debug/dwarf/line.go
index 7692f05..c4937ca 100644
--- a/libgo/go/debug/dwarf/line.go
+++ b/libgo/go/debug/dwarf/line.go
@@ -814,7 +814,11 @@ func pathJoin(dirname, filename string) string {
 		// Drives are the same. Ignore drive on filename.
 	}
 	if !(strings.HasSuffix(dirname, "/") || strings.HasSuffix(dirname, `\`)) && dirname != "" {
-		dirname += `\`
+		sep := `\`
+		if strings.HasPrefix(dirname, "/") {
+			sep = `/`
+		}
+		dirname += sep
 	}
 	return drive + dirname + filename
 }
diff --git a/libgo/go/debug/dwarf/line_test.go b/libgo/go/debug/dwarf/line_test.go
index 1fd9b19..b13818e 100644
--- a/libgo/go/debug/dwarf/line_test.go
+++ b/libgo/go/debug/dwarf/line_test.go
@@ -341,6 +341,14 @@ var joinTests = []joinTest{
 	{`\\host\share\`, `foo\bar`, `\\host\share\foo\bar`},
 	{`//host/share/`, `foo/bar`, `//host/share/foo/bar`},
 
+	// Note: the Go compiler currently emits DWARF line table paths
+	// with '/' instead of '\' (see issues #19784, #36495). These
+	// tests are to cover cases that might come up for Windows Go
+	// binaries.
+	{`c:/workdir/go/src/x`, `y.go`, `c:/workdir/go/src/x/y.go`},
+	{`d:/some/thing/`, `b.go`, `d:/some/thing/b.go`},
+	{`e:\blah\`, `foo.c`, `e:\blah\foo.c`},
+
 	// The following are "best effort". We shouldn't see relative
 	// base directories in DWARF, but these test that pathJoin
 	// doesn't fail miserably if it sees one.
diff --git a/libgo/go/debug/dwarf/open.go b/libgo/go/debug/dwarf/open.go
index d6d4f78..b1a4d3a 100644
--- a/libgo/go/debug/dwarf/open.go
+++ b/libgo/go/debug/dwarf/open.go
@@ -7,7 +7,10 @@
 // http://dwarfstd.org/doc/dwarf-2.0.0.pdf
 package dwarf
 
-import "encoding/binary"
+import (
+	"encoding/binary"
+	"errors"
+)
 
 // Data represents the DWARF debugging information
 // loaded from an executable file (for example, an ELF or Mach-O executable).
@@ -26,6 +29,7 @@ type Data struct {
 	addr       []byte
 	lineStr    []byte
 	strOffsets []byte
+	rngLists   []byte
 
 	// parsed data
 	abbrevCache map[uint64]abbrevTable
@@ -36,6 +40,8 @@ type Data struct {
 	unit        []unit
 }
 
+var errSegmentSelector = errors.New("non-zero segment_selector size not supported")
+
 // New returns a new Data object initialized from the given parameters.
 // Rather than calling this function directly, clients should typically use
 // the DWARF method of the File type of the appropriate package debug/elf,
@@ -108,6 +114,7 @@ func (d *Data) AddTypes(name string, types []byte) error {
 // so forth. This approach is used for new DWARF sections added in
 // DWARF 5 and later.
 func (d *Data) AddSection(name string, contents []byte) error {
+	var err error
 	switch name {
 	case ".debug_addr":
 		d.addr = contents
@@ -115,7 +122,9 @@ func (d *Data) AddSection(name string, contents []byte) error {
 		d.lineStr = contents
 	case ".debug_str_offsets":
 		d.strOffsets = contents
+	case ".debug_rnglists":
+		d.rngLists = contents
 	}
 	// Just ignore names that we don't yet support.
-	return nil
+	return err
 }
diff --git a/libgo/go/debug/dwarf/testdata/debug_rnglists b/libgo/go/debug/dwarf/testdata/debug_rnglists
new file mode 100644
index 0000000..985ec6c
--- /dev/null
+++ b/libgo/go/debug/dwarf/testdata/debug_rnglists
diff --git a/libgo/go/debug/dwarf/testdata/line-clang-dwarf5.elf b/libgo/go/debug/dwarf/testdata/line-clang-dwarf5.elf
new file mode 100644
index 0000000..7b80c9c
--- /dev/null
+++ b/libgo/go/debug/dwarf/testdata/line-clang-dwarf5.elf
diff --git a/libgo/go/debug/dwarf/testdata/line-gcc-dwarf5.elf b/libgo/go/debug/dwarf/testdata/line-gcc-dwarf5.elf
new file mode 100644
index 0000000..34ce17c
--- /dev/null
+++ b/libgo/go/debug/dwarf/testdata/line-gcc-dwarf5.elf