debug/elf: support zstd compression

Test cases added to debug/dwarf because that is where it matters in practice.

The new test binary line-gcc-zstd.elf built with

    gcc -g -no-pie -Wl,--compress-debug-sections=zstd line[12].c

using

    gcc (Debian 12.2.0-10) 12.2.0

with a development version of the GNU binutils.

Fixes #55107

Change-Id: I48507c96902e1f83a174e5647b5cc403d965b52b
Reviewed-on: https://go-review.googlesource.com/c/go/+/473256
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>

Author: ianlancetaylor

api/next/55107.txt

@@ -0,0 +1,2 @@
+pkg debug/elf, const COMPRESS_ZSTD = 2 #55107
+pkg debug/elf, const COMPRESS_ZSTD CompressionType #55107

src/cmd/dist/buildtool.go

@@ -78,6 +78,7 @@ var bootstrapDirs = []string{
 	"internal/types/errors",
 	"internal/unsafeheader",
 	"internal/xcoff",
+	"internal/zstd",
 	"math/big",
 	"math/bits",
 	"sort",

src/debug/dwarf/entry_test.go

@@ -69,6 +69,12 @@ func TestReaderSeek(t *testing.T) {
 		{0x40117e, nil},
 	}
 	testRanges(t, "testdata/line-clang-dwarf5.elf", want)
+
+	want = []wantRange{
+		{0x401126, [][2]uint64{{0x401126, 0x40116a}}},
+		{0x40116a, [][2]uint64{{0x40116a, 0x401180}}},
+	}
+	testRanges(t, "testdata/line-gcc-zstd.elf", want)
 }
 
 func TestRangesSection(t *testing.T) {
@@ -156,6 +162,15 @@ func TestReaderRanges(t *testing.T) {
 				{"f2", [][2]uint64{{0x401180, 0x401197}}},
 			},
 		},
+		{
+			"testdata/line-gcc-zstd.elf",
+			subprograms{
+				{"f2", nil},
+				{"main", [][2]uint64{{0x40114b, 0x40116a}}},
+				{"f1", [][2]uint64{{0x401126, 0x40114b}}},
+				{"f2", [][2]uint64{{0x40116a, 0x401180}}},
+			},
+		},
 	}
 
 	for _, test := range tests {

src/debug/dwarf/line_test.go

@@ -48,6 +48,44 @@ func TestLineELFGCC(t *testing.T) {
 	testLineTable(t, want, files, elfData(t, "testdata/line-gcc.elf"))
 }
 
+func TestLineELFGCCZstd(t *testing.T) {
+	// Generated by:
+	//   # gcc --version | head -n1
+	//   gcc (Debian 12.2.0-10) 12.2.0
+	//   # gcc -g -no-pie -Wl,--compress-debug-sections=zstd line*.c
+
+	zfile1H := &LineFile{Name: "/home/iant/go/src/debug/dwarf/testdata/line1.h"}
+	zfile1C := &LineFile{Name: "/home/iant/go/src/debug/dwarf/testdata/line1.c"}
+	zfile2C := &LineFile{Name: "/home/iant/go/src/debug/dwarf/testdata/line2.c"}
+
+	// Line table based on readelf --debug-dump=rawline,decodedline
+	want := []LineEntry{
+		{Address: 0x401126, File: zfile1H, Line: 2, Column: 1, IsStmt: true},
+		{Address: 0x40112a, File: zfile1H, Line: 5, Column: 8, IsStmt: true},
+		{Address: 0x401131, File: zfile1H, Line: 5, Column: 2, IsStmt: true},
+		{Address: 0x401133, File: zfile1H, Line: 6, Column: 10, IsStmt: true, Discriminator: 3},
+		{Address: 0x40113d, File: zfile1H, Line: 5, Column: 22, IsStmt: true, Discriminator: 3},
+		{Address: 0x401141, File: zfile1H, Line: 5, Column: 15, IsStmt: true, Discriminator: 1},
+		{Address: 0x401147, File: zfile1H, Line: 7, Column: 1, IsStmt: true},
+		{Address: 0x40114b, File: zfile1C, Line: 6, Column: 1, IsStmt: true},
+		{Address: 0x40114f, File: zfile1C, Line: 7, Column: 2, IsStmt: true},
+		{Address: 0x401159, File: zfile1C, Line: 8, Column: 2, IsStmt: true},
+		{Address: 0x401168, File: zfile1C, Line: 9, Column: 1, IsStmt: true},
+		{Address: 0x40116a, EndSequence: true},
+
+		{Address: 0x40116a, File: zfile2C, Line: 4, Column: 1, IsStmt: true},
+		{Address: 0x40116e, File: zfile2C, Line: 5, Column: 2, IsStmt: true},
+		{Address: 0x40117d, File: zfile2C, Line: 6, Column: 1, IsStmt: true},
+		{Address: 0x401180, EndSequence: true},
+	}
+	files := [][]*LineFile{
+		{zfile1C, zfile1H, zfile1C},
+		{zfile2C, zfile2C},
+	}
+
+	testLineTable(t, want, files, elfData(t, "testdata/line-gcc-zstd.elf"))
+}
+
 func TestLineGCCWindows(t *testing.T) {
 	// Generated by:
 	//   > gcc --version
@@ -277,7 +315,7 @@ func testLineTable(t *testing.T, want []LineEntry, files [][]*LineFile, d *Data)
 	}
 
 	// Compare line tables.
-	if !compareLines(got, want) {
+	if !compareLines(t, got, want) {
 		t.Log("Line tables do not match. Got:")
 		dumpLines(t, got)
 		t.Log("Want:")
@@ -312,8 +350,10 @@ func dumpFiles(t *testing.T, files []*LineFile) {
 	}
 }
 
-func compareLines(a, b []LineEntry) bool {
+func compareLines(t *testing.T, a, b []LineEntry) bool {
+	t.Helper()
 	if len(a) != len(b) {
+		t.Errorf("len(a) == %d, len(b) == %d", len(a), len(b))
 		return false
 	}
 
@@ -326,11 +366,13 @@ func compareLines(a, b []LineEntry) bool {
 			continue
 		}
 		if al.File.Name != bl.File.Name {
+			t.Errorf("%d: name %v != name %v", i, al.File.Name, bl.File.Name)
 			return false
 		}
 		al.File = nil
 		bl.File = nil
 		if al != bl {
+			t.Errorf("%d: %#v != %#v", i, al, bl)
 			return false
 		}
 	}

src/debug/dwarf/testdata/line-gcc-zstd.elf

@@ -728,6 +728,7 @@ type CompressionType int
 
 const (
 	COMPRESS_ZLIB   CompressionType = 1          /* ZLIB compression. */
+	COMPRESS_ZSTD   CompressionType = 2          /* ZSTD compression. */
 	COMPRESS_LOOS   CompressionType = 0x60000000 /* First OS-specific. */
 	COMPRESS_HIOS   CompressionType = 0x6fffffff /* Last OS-specific. */
 	COMPRESS_LOPROC CompressionType = 0x70000000 /* First processor-specific type. */
@@ -736,6 +737,7 @@ const (
 
 var compressionStrings = []intName{
 	{1, "COMPRESS_ZLIB"},
+	{2, "COMPRESS_ZSTD"},
 	{0x60000000, "COMPRESS_LOOS"},
 	{0x6fffffff, "COMPRESS_HIOS"},
 	{0x70000000, "COMPRESS_LOPROC"},

src/debug/elf/elf.go

@@ -38,7 +38,7 @@ var nameTests = []nameTest{
 	{R_SPARC_GOT22, "R_SPARC_GOT22"},
 	{ET_LOOS + 5, "ET_LOOS+5"},
 	{ProgFlag(0x50), "0x50"},
-	{COMPRESS_ZLIB + 1, "COMPRESS_ZLIB+1"},
+	{COMPRESS_ZLIB + 2, "COMPRESS_ZSTD+1"},
 }
 
 func TestNames(t *testing.T) {

src/debug/elf/elf_test.go

@@ -23,6 +23,7 @@ import (
 	"errors"
 	"fmt"
 	"internal/saferio"
+	"internal/zstd"
 	"io"
 	"os"
 	"strings"
@@ -164,6 +165,10 @@ func (s *Section) Open() io.ReadSeeker {
 	switch s.compressionType {
 	case COMPRESS_ZLIB:
 		zrd = zlib.NewReader
+	case COMPRESS_ZSTD:
+		zrd = func(r io.Reader) (io.ReadCloser, error) {
+			return io.NopCloser(zstd.NewReader(r)), nil
+		}
 	}
 
 	if zrd == nil {

src/debug/elf/file.go

@@ -251,7 +251,7 @@ var depsRules = `
 	< index/suffixarray;
 
 	# executable parsing
-	FMT, encoding/binary, compress/zlib, internal/saferio
+	FMT, encoding/binary, compress/zlib, internal/saferio, internal/zstd
 	< runtime/debug
 	< debug/dwarf
 	< debug/elf, debug/gosym, debug/macho, debug/pe, debug/plan9obj, internal/xcoff