src/cmd/link/elf_test.go - go - Git at Google

 // Copyright 2019 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.

 //go:build dragonfly || freebsd || linux || netbsd || openbsd

 package main

 import (
 	"cmd/internal/buildid"
 	"cmd/internal/hash"
 	"cmd/link/internal/ld"
 	"debug/elf"
 	"fmt"
 	"internal/platform"
 	"internal/testenv"
 	"os"
 	"os/exec"
 	"path/filepath"
 	"runtime"
 	"strings"
 	"sync"
 	"testing"
 	"text/template"
 )

 func getCCAndCCFLAGS(t *testing.T, env []string) (string, []string) {
 	goTool := testenv.GoToolPath(t)
 	cmd := testenv.Command(t, goTool, "env", "CC")
 	cmd.Env = env
 	ccb, err := cmd.Output()
 	if err != nil {
 		t.Fatal(err)
 	}
 	cc := strings.TrimSpace(string(ccb))

 	cmd = testenv.Command(t, goTool, "env", "GOGCCFLAGS")
 	cmd.Env = env
 	cflagsb, err := cmd.Output()
 	if err != nil {
 		t.Fatal(err)
 	}
 	cflags := strings.Fields(string(cflagsb))

 	return cc, cflags
 }

 var asmSource = `
 	.section .text1,"ax"
 s1:
 	.byte 0
 	.section .text2,"ax"
 s2:
 	.byte 0
 `

 var goSource = `
 package main
 func main() {}
 `

 var goSourceWithData = `
 package main
 var globalVar = 42
 func main() { println(&globalVar) }
 `

 // The linker used to crash if an ELF input file had multiple text sections
 // with the same name.
 func TestSectionsWithSameName(t *testing.T) {
 	testenv.MustHaveGoBuild(t)
 	testenv.MustHaveCGO(t)
 	t.Parallel()

 	objcopy, err := exec.LookPath("objcopy")
 	if err != nil {
 		t.Skipf("can't find objcopy: %v", err)
 	}

 	dir := t.TempDir()

 	gopath := filepath.Join(dir, "GOPATH")
 	env := append(os.Environ(), "GOPATH="+gopath)

 	if err := os.WriteFile(filepath.Join(dir, "go.mod"), []byte("module elf_test\n"), 0666); err != nil {
 		t.Fatal(err)
 	}

 	asmFile := filepath.Join(dir, "x.s")
 	if err := os.WriteFile(asmFile, []byte(asmSource), 0444); err != nil {
 		t.Fatal(err)
 	}

 	goTool := testenv.GoToolPath(t)
 	cc, cflags := getCCAndCCFLAGS(t, env)

 	asmObj := filepath.Join(dir, "x.o")
 	t.Logf("%s %v -c -o %s %s", cc, cflags, asmObj, asmFile)
 	if out, err := testenv.Command(t, cc, append(cflags, "-c", "-o", asmObj, asmFile)...).CombinedOutput(); err != nil {
 		t.Logf("%s", out)
 		t.Fatal(err)
 	}

 	asm2Obj := filepath.Join(dir, "x2.syso")
 	t.Logf("%s --rename-section .text2=.text1 %s %s", objcopy, asmObj, asm2Obj)
 	if out, err := testenv.Command(t, objcopy, "--rename-section", ".text2=.text1", asmObj, asm2Obj).CombinedOutput(); err != nil {
 		t.Logf("%s", out)
 		t.Fatal(err)
 	}

 	for _, s := range []string{asmFile, asmObj} {
 		if err := os.Remove(s); err != nil {
 			t.Fatal(err)
 		}
 	}

 	goFile := filepath.Join(dir, "main.go")
 	if err := os.WriteFile(goFile, []byte(goSource), 0444); err != nil {
 		t.Fatal(err)
 	}

 	cmd := testenv.Command(t, goTool, "build")
 	cmd.Dir = dir
 	cmd.Env = env
 	t.Logf("%s build", goTool)
 	if out, err := cmd.CombinedOutput(); err != nil {
 		t.Logf("%s", out)
 		t.Fatal(err)
 	}
 }

 var cSources35779 = []string{`
 static int blah() { return 42; }
 int Cfunc1() { return blah(); }
 `, `
 static int blah() { return 42; }
 int Cfunc2() { return blah(); }
 `,
 }

 // TestMinusRSymsWithSameName tests a corner case in the new
 // loader. Prior to the fix this failed with the error 'loadelf:
 // $WORK/b001/_pkg_.a(ldr.syso): duplicate symbol reference: blah in
 // both main(.text) and main(.text)'. See issue #35779.
 func TestMinusRSymsWithSameName(t *testing.T) {
 	testenv.MustHaveGoBuild(t)
 	testenv.MustHaveCGO(t)
 	t.Parallel()

 	dir := t.TempDir()

 	gopath := filepath.Join(dir, "GOPATH")
 	env := append(os.Environ(), "GOPATH="+gopath)

 	if err := os.WriteFile(filepath.Join(dir, "go.mod"), []byte("module elf_test\n"), 0666); err != nil {
 		t.Fatal(err)
 	}

 	goTool := testenv.GoToolPath(t)
 	cc, cflags := getCCAndCCFLAGS(t, env)

 	objs := []string{}
 	csrcs := []string{}
 	for i, content := range cSources35779 {
 		csrcFile := filepath.Join(dir, fmt.Sprintf("x%d.c", i))
 		csrcs = append(csrcs, csrcFile)
 		if err := os.WriteFile(csrcFile, []byte(content), 0444); err != nil {
 			t.Fatal(err)
 		}

 		obj := filepath.Join(dir, fmt.Sprintf("x%d.o", i))
 		objs = append(objs, obj)
 		t.Logf("%s %v -c -o %s %s", cc, cflags, obj, csrcFile)
 		if out, err := testenv.Command(t, cc, append(cflags, "-c", "-o", obj, csrcFile)...).CombinedOutput(); err != nil {
 			t.Logf("%s", out)
 			t.Fatal(err)
 		}
 	}

 	sysoObj := filepath.Join(dir, "ldr.syso")
 	t.Logf("%s %v -nostdlib -r -o %s %v", cc, cflags, sysoObj, objs)
 	if out, err := testenv.Command(t, cc, append(cflags, "-nostdlib", "-r", "-o", sysoObj, objs[0], objs[1])...).CombinedOutput(); err != nil {
 		t.Logf("%s", out)
 		t.Fatal(err)
 	}

 	cruft := [][]string{objs, csrcs}
 	for _, sl := range cruft {
 		for _, s := range sl {
 			if err := os.Remove(s); err != nil {
 				t.Fatal(err)
 			}
 		}
 	}

 	goFile := filepath.Join(dir, "main.go")
 	if err := os.WriteFile(goFile, []byte(goSource), 0444); err != nil {
 		t.Fatal(err)
 	}

 	t.Logf("%s build", goTool)
 	cmd := testenv.Command(t, goTool, "build")
 	cmd.Dir = dir
 	cmd.Env = env
 	if out, err := cmd.CombinedOutput(); err != nil {
 		t.Logf("%s", out)
 		t.Fatal(err)
 	}
 }

 func TestGNUBuildID(t *testing.T) {
 	testenv.MustHaveGoBuild(t)

 	t.Parallel()

 	tmpdir := t.TempDir()
 	goFile := filepath.Join(tmpdir, "notes.go")
 	if err := os.WriteFile(goFile, []byte(goSource), 0444); err != nil {
 		t.Fatal(err)
 	}

 	// Use a specific Go buildid for testing.
 	const gobuildid = "testbuildid"
 	h := hash.Sum32([]byte(gobuildid))
 	gobuildidHash := string(h[:20])

 	tests := []struct{ name, ldflags, expect string }{
 		{"default", "", gobuildidHash},
 		{"gobuildid", "-B=gobuildid", gobuildidHash},
 		{"specific", "-B=0x0123456789abcdef", "\x01\x23\x45\x67\x89\xab\xcd\xef"},
 		{"none", "-B=none", ""},
 	}
 	if testenv.HasCGO() && runtime.GOOS != "solaris" && runtime.GOOS != "illumos" {
 		// Solaris ld doesn't support --build-id. So we don't
 		// add it in external linking mode.
 		for _, test := range tests {
 			t1 := test
 			t1.name += "_external"
 			t1.ldflags += " -linkmode=external"
 			tests = append(tests, t1)
 		}
 	}
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
 			exe := filepath.Join(tmpdir, test.name)
 			cmd := testenv.Command(t, testenv.GoToolPath(t), "build", "-ldflags=-buildid="+gobuildid+" "+test.ldflags, "-o", exe, goFile)
 			if out, err := cmd.CombinedOutput(); err != nil {
 				t.Fatalf("%v: %v:\n%s", cmd.Args, err, out)
 			}
 			gnuBuildID, err := buildid.ReadELFNote(exe, string(ld.ELF_NOTE_BUILDINFO_NAME), ld.ELF_NOTE_BUILDINFO_TAG)
 			if err != nil {
 				t.Fatalf("can't read GNU build ID")
 			}
 			if string(gnuBuildID) != test.expect {
 				t.Errorf("build id mismatch: got %x, want %x", gnuBuildID, test.expect)
 			}
 		})
 	}
 }

 func TestMergeNoteSections(t *testing.T) {
 	testenv.MustHaveGoBuild(t)
 	expected := 1

 	switch runtime.GOOS {
 	case "linux", "dragonfly":
 	case "openbsd", "netbsd", "freebsd":
 		// These OSes require independent segment
 		expected = 2
 	default:
 		t.Skip("We should only test on elf output.")
 	}
 	t.Parallel()

 	goFile := filepath.Join(t.TempDir(), "notes.go")
 	if err := os.WriteFile(goFile, []byte(goSource), 0444); err != nil {
 		t.Fatal(err)
 	}
 	outFile := filepath.Join(t.TempDir(), "notes.exe")
 	goTool := testenv.GoToolPath(t)
 	// sha1sum of "gopher"
 	id := "0xf4e8cd51ce8bae2996dc3b74639cdeaa1f7fee5f"
 	cmd := testenv.Command(t, goTool, "build", "-o", outFile, "-ldflags",
 		"-B "+id, goFile)
 	cmd.Dir = t.TempDir()
 	if out, err := cmd.CombinedOutput(); err != nil {
 		t.Logf("%s", out)
 		t.Fatal(err)
 	}

 	ef, err := elf.Open(outFile)
 	if err != nil {
 		t.Fatalf("open elf file failed:%v", err)
 	}
 	defer ef.Close()
 	sec := ef.Section(".note.gnu.build-id")
 	if sec == nil {
 		t.Fatalf("can't find gnu build id")
 	}

 	sec = ef.Section(".note.go.buildid")
 	if sec == nil {
 		t.Fatalf("can't find go build id")
 	}
 	cnt := 0
 	for _, ph := range ef.Progs {
 		if ph.Type == elf.PT_NOTE {
 			cnt += 1
 		}
 	}
 	if cnt != expected {
 		t.Fatalf("want %d PT_NOTE segment, got %d", expected, cnt)
 	}
 }

 const pieSourceTemplate = `
 package main

 import "fmt"

 // Force the creation of a lot of type descriptors that will go into
 // the .data.rel.ro section.
 {{range $index, $element := .}}var V{{$index}} interface{} = [{{$index}}]int{}
 {{end}}

 func main() {
 {{range $index, $element := .}}	fmt.Println(V{{$index}})
 {{end}}
 }
 `

 func TestPIESize(t *testing.T) {
 	testenv.MustHaveGoBuild(t)

 	// We don't want to test -linkmode=external if cgo is not supported.
 	// On some systems -buildmode=pie implies -linkmode=external, so just
 	// always skip the test if cgo is not supported.
 	testenv.MustHaveCGO(t)

 	if !platform.BuildModeSupported(runtime.Compiler, "pie", runtime.GOOS, runtime.GOARCH) {
 		t.Skip("-buildmode=pie not supported")
 	}

 	t.Parallel()

 	tmpl := template.Must(template.New("pie").Parse(pieSourceTemplate))

 	writeGo := func(t *testing.T, dir string) {
 		f, err := os.Create(filepath.Join(dir, "pie.go"))
 		if err != nil {
 			t.Fatal(err)
 		}

 		// Passing a 100-element slice here will cause
 		// pieSourceTemplate to create 100 variables with
 		// different types.
 		if err := tmpl.Execute(f, make([]byte, 100)); err != nil {
 			t.Fatal(err)
 		}

 		if err := f.Close(); err != nil {
 			t.Fatal(err)
 		}
 	}

 	var linkmodes []string
 	if platform.InternalLinkPIESupported(runtime.GOOS, runtime.GOARCH) {
 		linkmodes = append(linkmodes, "internal")
 	}
 	linkmodes = append(linkmodes, "external")

 	for _, linkmode := range linkmodes {
 		t.Run(fmt.Sprintf("TestPieSize-%v", linkmode), func(t *testing.T) {
 			t.Parallel()

 			dir := t.TempDir()

 			writeGo(t, dir)

 			binexe := filepath.Join(dir, "exe")
 			binpie := filepath.Join(dir, "pie")
 			binexe += linkmode
 			binpie += linkmode

 			build := func(bin, mode string) error {
 				cmd := testenv.Command(t, testenv.GoToolPath(t), "build", "-o", bin, "-buildmode="+mode, "-ldflags=-linkmode="+linkmode)
 				cmd.Args = append(cmd.Args, "pie.go")
 				cmd.Dir = dir
 				t.Logf("%v", cmd.Args)
 				out, err := cmd.CombinedOutput()
 				if len(out) > 0 {
 					t.Logf("%s", out)
 				}
 				if err != nil {
 					t.Log(err)
 				}
 				return err
 			}

 			var errexe, errpie error
 			var wg sync.WaitGroup
 			wg.Add(2)
 			go func() {
 				defer wg.Done()
 				errexe = build(binexe, "exe")
 			}()
 			go func() {
 				defer wg.Done()
 				errpie = build(binpie, "pie")
 			}()
 			wg.Wait()
 			if errexe != nil || errpie != nil {
 				if runtime.GOOS == "android" && runtime.GOARCH == "arm64" {
 					testenv.SkipFlaky(t, 58806)
 				}
 				t.Fatal("link failed")
 			}

 			var sizeexe, sizepie uint64
 			if fi, err := os.Stat(binexe); err != nil {
 				t.Fatal(err)
 			} else {
 				sizeexe = uint64(fi.Size())
 			}
 			if fi, err := os.Stat(binpie); err != nil {
 				t.Fatal(err)
 			} else {
 				sizepie = uint64(fi.Size())
 			}

 			elfexe, err := elf.Open(binexe)
 			if err != nil {
 				t.Fatal(err)
 			}
 			defer elfexe.Close()

 			elfpie, err := elf.Open(binpie)
 			if err != nil {
 				t.Fatal(err)
 			}
 			defer elfpie.Close()

 			// The difference in size between exe and PIE
 			// should be approximately the difference in
 			// size of the .text section plus the size of
 			// the PIE dynamic data sections plus the
 			// difference in size of the .got and .plt
 			// sections if they exist.
 			// We ignore unallocated sections.
 			// There may be gaps between non-writeable and
 			// writable PT_LOAD segments. We also skip those
 			// gaps (see issue #36023).

 			textsize := func(ef *elf.File, name string) uint64 {
 				for _, s := range ef.Sections {
 					if s.Name == ".text" {
 						return s.Size
 					}
 				}
 				t.Fatalf("%s: no .text section", name)
 				return 0
 			}
 			textexe := textsize(elfexe, binexe)
 			textpie := textsize(elfpie, binpie)

 			dynsize := func(ef *elf.File) uint64 {
 				var ret uint64
 				for _, s := range ef.Sections {
 					if s.Flags&elf.SHF_ALLOC == 0 {
 						continue
 					}
 					switch s.Type {
 					case elf.SHT_DYNSYM, elf.SHT_STRTAB, elf.SHT_REL, elf.SHT_RELA, elf.SHT_HASH, elf.SHT_GNU_HASH, elf.SHT_GNU_VERDEF, elf.SHT_GNU_VERNEED, elf.SHT_GNU_VERSYM:
 						ret += s.Size
 					}
 					if s.Flags&elf.SHF_WRITE != 0 && (strings.Contains(s.Name, ".got") || strings.Contains(s.Name, ".plt")) {
 						ret += s.Size
 					}
 				}
 				return ret
 			}

 			dynexe := dynsize(elfexe)
 			dynpie := dynsize(elfpie)

 			extrasize := func(ef *elf.File) uint64 {
 				var ret uint64
 				// skip unallocated sections
 				for _, s := range ef.Sections {
 					if s.Flags&elf.SHF_ALLOC == 0 {
 						ret += s.Size
 					}
 				}
 				// also skip gaps between PT_LOAD segments
 				var prev *elf.Prog
 				for _, seg := range ef.Progs {
 					if seg.Type != elf.PT_LOAD {
 						continue
 					}
 					if prev != nil {
 						ret += seg.Off - prev.Off - prev.Filesz
 					}
 					prev = seg
 				}
 				return ret
 			}

 			extraexe := extrasize(elfexe)
 			extrapie := extrasize(elfpie)

 			if sizepie < sizeexe || sizepie-extrapie < sizeexe-extraexe {
 				return
 			}
 			diffReal := (sizepie - extrapie) - (sizeexe - extraexe)
 			diffExpected := (textpie + dynpie) - (textexe + dynexe)

 			t.Logf("real size difference %#x, expected %#x", diffReal, diffExpected)

 			if diffReal > (diffExpected + diffExpected/10) {
 				t.Errorf("PIE unexpectedly large: got difference of %d (%d - %d), expected difference %d", diffReal, sizepie, sizeexe, diffExpected)
 			}
 		})
 	}
 }

 func TestIssue51939(t *testing.T) {
 	testenv.MustHaveGoBuild(t)
 	t.Parallel()
 	td := t.TempDir()
 	goFile := filepath.Join(td, "issue51939.go")
 	if err := os.WriteFile(goFile, []byte(goSource), 0444); err != nil {
 		t.Fatal(err)
 	}
 	outFile := filepath.Join(td, "issue51939.exe")
 	goTool := testenv.GoToolPath(t)
 	cmd := testenv.Command(t, goTool, "build", "-o", outFile, goFile)
 	if out, err := cmd.CombinedOutput(); err != nil {
 		t.Logf("%s", out)
 		t.Fatal(err)
 	}

 	ef, err := elf.Open(outFile)
 	if err != nil {
 		t.Fatal(err)
 	}

 	for _, s := range ef.Sections {
 		if s.Flags&elf.SHF_ALLOC == 0 && s.Addr != 0 {
 			t.Errorf("section %s should not allocated with addr %x", s.Name, s.Addr)
 		}
 	}
 }

 func TestFlagR(t *testing.T) {
 	// Test that using the -R flag to specify a (large) alignment generates
 	// a working binary.
 	// (Test only on ELF for now. The alignment allowed differs from platform
 	// to platform.)
 	testenv.MustHaveGoBuild(t)
 	t.Parallel()
 	tmpdir := t.TempDir()
 	src := filepath.Join(tmpdir, "x.go")
 	if err := os.WriteFile(src, []byte(goSource), 0444); err != nil {
 		t.Fatal(err)
 	}
 	exe := filepath.Join(tmpdir, "x.exe")

 	cmd := testenv.Command(t, testenv.GoToolPath(t), "build", "-ldflags=-R=0x100000", "-o", exe, src)
 	if out, err := cmd.CombinedOutput(); err != nil {
 		t.Fatalf("build failed: %v, output:\n%s", err, out)
 	}

 	cmd = testenv.Command(t, exe)
 	if out, err := cmd.CombinedOutput(); err != nil {
 		t.Errorf("executable failed to run: %v\n%s", err, out)
 	}
 }

 func TestFlagD(t *testing.T) {
 	// Test that using the -D flag to specify data section address generates
 	// a working binary with data at the specified address.
 	t.Parallel()
 	testFlagD(t, "0x10000000", "", 0x10000000)
 }

 func TestFlagDUnaligned(t *testing.T) {
 	// Test that using the -D flag with an unaligned address errors out
 	t.Parallel()
 	testFlagDError(t, "0x10000123", "", "invalid -D value 0x10000123")
 }

 func TestFlagDWithR(t *testing.T) {
 	// Test that using the -D flag with -R flag errors on unaligned address.
 	t.Parallel()
 	testFlagDError(t, "0x30001234", "8192", "invalid -D value 0x30001234")
 }

 func testFlagD(t *testing.T, dataAddr string, roundQuantum string, expectedAddr uint64) {
 	testenv.MustHaveGoBuild(t)
 	tmpdir := t.TempDir()
 	src := filepath.Join(tmpdir, "x.go")
 	if err := os.WriteFile(src, []byte(goSourceWithData), 0444); err != nil {
 		t.Fatal(err)
 	}
 	exe := filepath.Join(tmpdir, "x.exe")

 	// Build linker flags
 	ldflags := "-D=" + dataAddr
 	if roundQuantum != "" {
 		ldflags += " -R=" + roundQuantum
 	}

 	cmd := testenv.Command(t, testenv.GoToolPath(t), "build", "-ldflags="+ldflags, "-o", exe, src)
 	if out, err := cmd.CombinedOutput(); err != nil {
 		t.Fatalf("build failed: %v, output:\n%s", err, out)
 	}

 	cmd = testenv.Command(t, exe)
 	if out, err := cmd.CombinedOutput(); err != nil {
 		t.Errorf("executable failed to run: %v\n%s", err, out)
 	}

 	ef, err := elf.Open(exe)
 	if err != nil {
 		t.Fatalf("open elf file failed: %v", err)
 	}
 	defer ef.Close()

 	// Find the first data-related section to verify segment placement
 	var firstDataSection *elf.Section
 	for _, sec := range ef.Sections {
 		if sec.Type == elf.SHT_PROGBITS || sec.Type == elf.SHT_NOBITS {
 			// These sections are writable, allocated at runtime, but not executable
 			// nor TLS.
 			isWrite := sec.Flags&elf.SHF_WRITE != 0
 			isExec := sec.Flags&elf.SHF_EXECINSTR != 0
 			isAlloc := sec.Flags&elf.SHF_ALLOC != 0
 			isTLS := sec.Flags&elf.SHF_TLS != 0

 			if isWrite && !isExec && isAlloc && !isTLS {
 				if firstDataSection == nil || sec.Addr < firstDataSection.Addr {
 					firstDataSection = sec
 				}
 			}
 		}
 	}

 	if firstDataSection == nil {
 		t.Fatalf("can't find any writable data sections")
 	}
 	if firstDataSection.Addr != expectedAddr {
 		t.Errorf("data section starts at 0x%x for section %s, expected 0x%x",
 			firstDataSection.Addr, firstDataSection.Name, expectedAddr)
 	}
 }

 func testFlagDError(t *testing.T, dataAddr string, roundQuantum string, expectedError string) {
 	testenv.MustHaveGoBuild(t)
 	tmpdir := t.TempDir()
 	src := filepath.Join(tmpdir, "x.go")
 	if err := os.WriteFile(src, []byte(goSourceWithData), 0444); err != nil {
 		t.Fatal(err)
 	}
 	exe := filepath.Join(tmpdir, "x.exe")

 	// Build linker flags
 	ldflags := "-D=" + dataAddr
 	if roundQuantum != "" {
 		ldflags += " -R=" + roundQuantum
 	}

 	cmd := testenv.Command(t, testenv.GoToolPath(t), "build", "-ldflags="+ldflags, "-o", exe, src)
 	out, err := cmd.CombinedOutput()
 	if err == nil {
 		t.Fatalf("expected build to fail with unaligned data address, but it succeeded")
 	}
 	if !strings.Contains(string(out), expectedError) {
 		t.Errorf("expected error message to contain %q, got:\n%s", expectedError, out)
 	}
 }
	// Copyright 2019 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.

	//go:build dragonfly \|\| freebsd \|\| linux \|\| netbsd \|\| openbsd

	package main

	import (
	"cmd/internal/buildid"
	"cmd/internal/hash"
	"cmd/link/internal/ld"
	"debug/elf"
	"fmt"
	"internal/platform"
	"internal/testenv"
	"os"
	"os/exec"
	"path/filepath"
	"runtime"
	"strings"
	"sync"
	"testing"
	"text/template"
	)

	func getCCAndCCFLAGS(t *testing.T, env []string) (string, []string) {
	goTool := testenv.GoToolPath(t)
	cmd := testenv.Command(t, goTool, "env", "CC")
	cmd.Env = env
	ccb, err := cmd.Output()
	if err != nil {
	t.Fatal(err)
	}
	cc := strings.TrimSpace(string(ccb))

	cmd = testenv.Command(t, goTool, "env", "GOGCCFLAGS")
	cmd.Env = env
	cflagsb, err := cmd.Output()
	if err != nil {
	t.Fatal(err)
	}
	cflags := strings.Fields(string(cflagsb))

	return cc, cflags
	}

	var asmSource = `
	.section .text1,"ax"
	s1:
	.byte 0
	.section .text2,"ax"
	s2:
	.byte 0
	`

	var goSource = `
	package main
	func main() {}
	`

	var goSourceWithData = `
	package main
	var globalVar = 42
	func main() { println(&globalVar) }
	`

	// The linker used to crash if an ELF input file had multiple text sections
	// with the same name.
	func TestSectionsWithSameName(t *testing.T) {
	testenv.MustHaveGoBuild(t)
	testenv.MustHaveCGO(t)
	t.Parallel()

	objcopy, err := exec.LookPath("objcopy")
	if err != nil {
	t.Skipf("can't find objcopy: %v", err)
	}

	dir := t.TempDir()

	gopath := filepath.Join(dir, "GOPATH")
	env := append(os.Environ(), "GOPATH="+gopath)

	if err := os.WriteFile(filepath.Join(dir, "go.mod"), []byte("module elf_test\n"), 0666); err != nil {
	t.Fatal(err)
	}

	asmFile := filepath.Join(dir, "x.s")
	if err := os.WriteFile(asmFile, []byte(asmSource), 0444); err != nil {
	t.Fatal(err)
	}

	goTool := testenv.GoToolPath(t)
	cc, cflags := getCCAndCCFLAGS(t, env)

	asmObj := filepath.Join(dir, "x.o")
	t.Logf("%s %v -c -o %s %s", cc, cflags, asmObj, asmFile)
	if out, err := testenv.Command(t, cc, append(cflags, "-c", "-o", asmObj, asmFile)...).CombinedOutput(); err != nil {
	t.Logf("%s", out)
	t.Fatal(err)
	}

	asm2Obj := filepath.Join(dir, "x2.syso")
	t.Logf("%s --rename-section .text2=.text1 %s %s", objcopy, asmObj, asm2Obj)
	if out, err := testenv.Command(t, objcopy, "--rename-section", ".text2=.text1", asmObj, asm2Obj).CombinedOutput(); err != nil {
	t.Logf("%s", out)
	t.Fatal(err)
	}

	for _, s := range []string{asmFile, asmObj} {
	if err := os.Remove(s); err != nil {
	t.Fatal(err)
	}
	}

	goFile := filepath.Join(dir, "main.go")
	if err := os.WriteFile(goFile, []byte(goSource), 0444); err != nil {
	t.Fatal(err)
	}

	cmd := testenv.Command(t, goTool, "build")
	cmd.Dir = dir
	cmd.Env = env
	t.Logf("%s build", goTool)
	if out, err := cmd.CombinedOutput(); err != nil {
	t.Logf("%s", out)
	t.Fatal(err)
	}
	}

	var cSources35779 = []string{`
	static int blah() { return 42; }
	int Cfunc1() { return blah(); }
	`, `
	static int blah() { return 42; }
	int Cfunc2() { return blah(); }
	`,
	}

	// TestMinusRSymsWithSameName tests a corner case in the new
	// loader. Prior to the fix this failed with the error 'loadelf:
	// $WORK/b001/_pkg_.a(ldr.syso): duplicate symbol reference: blah in
	// both main(.text) and main(.text)'. See issue #35779.
	func TestMinusRSymsWithSameName(t *testing.T) {
	testenv.MustHaveGoBuild(t)
	testenv.MustHaveCGO(t)
	t.Parallel()

	dir := t.TempDir()

	gopath := filepath.Join(dir, "GOPATH")
	env := append(os.Environ(), "GOPATH="+gopath)

	if err := os.WriteFile(filepath.Join(dir, "go.mod"), []byte("module elf_test\n"), 0666); err != nil {
	t.Fatal(err)
	}

	goTool := testenv.GoToolPath(t)
	cc, cflags := getCCAndCCFLAGS(t, env)

	objs := []string{}
	csrcs := []string{}
	for i, content := range cSources35779 {
	csrcFile := filepath.Join(dir, fmt.Sprintf("x%d.c", i))
	csrcs = append(csrcs, csrcFile)
	if err := os.WriteFile(csrcFile, []byte(content), 0444); err != nil {
	t.Fatal(err)
	}

	obj := filepath.Join(dir, fmt.Sprintf("x%d.o", i))
	objs = append(objs, obj)
	t.Logf("%s %v -c -o %s %s", cc, cflags, obj, csrcFile)
	if out, err := testenv.Command(t, cc, append(cflags, "-c", "-o", obj, csrcFile)...).CombinedOutput(); err != nil {
	t.Logf("%s", out)
	t.Fatal(err)
	}
	}

	sysoObj := filepath.Join(dir, "ldr.syso")
	t.Logf("%s %v -nostdlib -r -o %s %v", cc, cflags, sysoObj, objs)
	if out, err := testenv.Command(t, cc, append(cflags, "-nostdlib", "-r", "-o", sysoObj, objs[0], objs[1])...).CombinedOutput(); err != nil {
	t.Logf("%s", out)
	t.Fatal(err)
	}

	cruft := [][]string{objs, csrcs}
	for _, sl := range cruft {
	for _, s := range sl {
	if err := os.Remove(s); err != nil {
	t.Fatal(err)
	}
	}
	}

	goFile := filepath.Join(dir, "main.go")
	if err := os.WriteFile(goFile, []byte(goSource), 0444); err != nil {
	t.Fatal(err)
	}

	t.Logf("%s build", goTool)
	cmd := testenv.Command(t, goTool, "build")
	cmd.Dir = dir
	cmd.Env = env
	if out, err := cmd.CombinedOutput(); err != nil {
	t.Logf("%s", out)
	t.Fatal(err)
	}
	}

	func TestGNUBuildID(t *testing.T) {
	testenv.MustHaveGoBuild(t)

	t.Parallel()

	tmpdir := t.TempDir()
	goFile := filepath.Join(tmpdir, "notes.go")
	if err := os.WriteFile(goFile, []byte(goSource), 0444); err != nil {
	t.Fatal(err)
	}

	// Use a specific Go buildid for testing.
	const gobuildid = "testbuildid"
	h := hash.Sum32([]byte(gobuildid))
	gobuildidHash := string(h[:20])

	tests := []struct{ name, ldflags, expect string }{
	{"default", "", gobuildidHash},
	{"gobuildid", "-B=gobuildid", gobuildidHash},
	{"specific", "-B=0x0123456789abcdef", "\x01\x23\x45\x67\x89\xab\xcd\xef"},
	{"none", "-B=none", ""},
	}
	if testenv.HasCGO() && runtime.GOOS != "solaris" && runtime.GOOS != "illumos" {
	// Solaris ld doesn't support --build-id. So we don't
	// add it in external linking mode.
	for _, test := range tests {
	t1 := test
	t1.name += "_external"
	t1.ldflags += " -linkmode=external"
	tests = append(tests, t1)
	}
	}
	for _, test := range tests {
	t.Run(test.name, func(t *testing.T) {
	exe := filepath.Join(tmpdir, test.name)
	cmd := testenv.Command(t, testenv.GoToolPath(t), "build", "-ldflags=-buildid="+gobuildid+" "+test.ldflags, "-o", exe, goFile)
	if out, err := cmd.CombinedOutput(); err != nil {
	t.Fatalf("%v: %v:\n%s", cmd.Args, err, out)
	}
	gnuBuildID, err := buildid.ReadELFNote(exe, string(ld.ELF_NOTE_BUILDINFO_NAME), ld.ELF_NOTE_BUILDINFO_TAG)
	if err != nil {
	t.Fatalf("can't read GNU build ID")
	}
	if string(gnuBuildID) != test.expect {
	t.Errorf("build id mismatch: got %x, want %x", gnuBuildID, test.expect)
	}
	})
	}
	}

	func TestMergeNoteSections(t *testing.T) {
	testenv.MustHaveGoBuild(t)
	expected := 1

	switch runtime.GOOS {
	case "linux", "dragonfly":
	case "openbsd", "netbsd", "freebsd":
	// These OSes require independent segment
	expected = 2
	default:
	t.Skip("We should only test on elf output.")
	}
	t.Parallel()

	goFile := filepath.Join(t.TempDir(), "notes.go")
	if err := os.WriteFile(goFile, []byte(goSource), 0444); err != nil {
	t.Fatal(err)
	}
	outFile := filepath.Join(t.TempDir(), "notes.exe")
	goTool := testenv.GoToolPath(t)
	// sha1sum of "gopher"
	id := "0xf4e8cd51ce8bae2996dc3b74639cdeaa1f7fee5f"
	cmd := testenv.Command(t, goTool, "build", "-o", outFile, "-ldflags",
	"-B "+id, goFile)
	cmd.Dir = t.TempDir()
	if out, err := cmd.CombinedOutput(); err != nil {
	t.Logf("%s", out)
	t.Fatal(err)
	}

	ef, err := elf.Open(outFile)
	if err != nil {
	t.Fatalf("open elf file failed:%v", err)
	}
	defer ef.Close()
	sec := ef.Section(".note.gnu.build-id")
	if sec == nil {
	t.Fatalf("can't find gnu build id")
	}

	sec = ef.Section(".note.go.buildid")
	if sec == nil {
	t.Fatalf("can't find go build id")
	}
	cnt := 0
	for _, ph := range ef.Progs {
	if ph.Type == elf.PT_NOTE {
	cnt += 1
	}
	}
	if cnt != expected {
	t.Fatalf("want %d PT_NOTE segment, got %d", expected, cnt)
	}
	}

	const pieSourceTemplate = `
	package main

	import "fmt"

	// Force the creation of a lot of type descriptors that will go into
	// the .data.rel.ro section.
	{{range $index, $element := .}}var V{{$index}} interface{} = [{{$index}}]int{}
	{{end}}

	func main() {
	{{range $index, $element := .}} fmt.Println(V{{$index}})
	{{end}}
	}
	`

	func TestPIESize(t *testing.T) {
	testenv.MustHaveGoBuild(t)

	// We don't want to test -linkmode=external if cgo is not supported.
	// On some systems -buildmode=pie implies -linkmode=external, so just
	// always skip the test if cgo is not supported.
	testenv.MustHaveCGO(t)

	if !platform.BuildModeSupported(runtime.Compiler, "pie", runtime.GOOS, runtime.GOARCH) {
	t.Skip("-buildmode=pie not supported")
	}

	t.Parallel()

	tmpl := template.Must(template.New("pie").Parse(pieSourceTemplate))

	writeGo := func(t *testing.T, dir string) {
	f, err := os.Create(filepath.Join(dir, "pie.go"))
	if err != nil {
	t.Fatal(err)
	}

	// Passing a 100-element slice here will cause
	// pieSourceTemplate to create 100 variables with
	// different types.
	if err := tmpl.Execute(f, make([]byte, 100)); err != nil {
	t.Fatal(err)
	}

	if err := f.Close(); err != nil {
	t.Fatal(err)
	}
	}

	var linkmodes []string
	if platform.InternalLinkPIESupported(runtime.GOOS, runtime.GOARCH) {
	linkmodes = append(linkmodes, "internal")
	}
	linkmodes = append(linkmodes, "external")

	for _, linkmode := range linkmodes {
	t.Run(fmt.Sprintf("TestPieSize-%v", linkmode), func(t *testing.T) {
	t.Parallel()

	dir := t.TempDir()

	writeGo(t, dir)

	binexe := filepath.Join(dir, "exe")
	binpie := filepath.Join(dir, "pie")
	binexe += linkmode
	binpie += linkmode

	build := func(bin, mode string) error {
	cmd := testenv.Command(t, testenv.GoToolPath(t), "build", "-o", bin, "-buildmode="+mode, "-ldflags=-linkmode="+linkmode)
	cmd.Args = append(cmd.Args, "pie.go")
	cmd.Dir = dir
	t.Logf("%v", cmd.Args)
	out, err := cmd.CombinedOutput()
	if len(out) > 0 {
	t.Logf("%s", out)
	}
	if err != nil {
	t.Log(err)
	}
	return err
	}

	var errexe, errpie error
	var wg sync.WaitGroup
	wg.Add(2)
	go func() {
	defer wg.Done()
	errexe = build(binexe, "exe")
	}()
	go func() {
	defer wg.Done()
	errpie = build(binpie, "pie")
	}()
	wg.Wait()
	if errexe != nil \|\| errpie != nil {
	if runtime.GOOS == "android" && runtime.GOARCH == "arm64" {
	testenv.SkipFlaky(t, 58806)
	}
	t.Fatal("link failed")
	}

	var sizeexe, sizepie uint64
	if fi, err := os.Stat(binexe); err != nil {
	t.Fatal(err)
	} else {
	sizeexe = uint64(fi.Size())
	}
	if fi, err := os.Stat(binpie); err != nil {
	t.Fatal(err)
	} else {
	sizepie = uint64(fi.Size())
	}

	elfexe, err := elf.Open(binexe)
	if err != nil {
	t.Fatal(err)
	}
	defer elfexe.Close()

	elfpie, err := elf.Open(binpie)
	if err != nil {
	t.Fatal(err)
	}
	defer elfpie.Close()

	// The difference in size between exe and PIE
	// should be approximately the difference in
	// size of the .text section plus the size of
	// the PIE dynamic data sections plus the
	// difference in size of the .got and .plt
	// sections if they exist.
	// We ignore unallocated sections.
	// There may be gaps between non-writeable and
	// writable PT_LOAD segments. We also skip those
	// gaps (see issue #36023).

	textsize := func(ef *elf.File, name string) uint64 {
	for _, s := range ef.Sections {
	if s.Name == ".text" {
	return s.Size
	}
	}
	t.Fatalf("%s: no .text section", name)
	return 0
	}
	textexe := textsize(elfexe, binexe)
	textpie := textsize(elfpie, binpie)

	dynsize := func(ef *elf.File) uint64 {
	var ret uint64
	for _, s := range ef.Sections {
	if s.Flags&elf.SHF_ALLOC == 0 {
	continue
	}
	switch s.Type {
	case elf.SHT_DYNSYM, elf.SHT_STRTAB, elf.SHT_REL, elf.SHT_RELA, elf.SHT_HASH, elf.SHT_GNU_HASH, elf.SHT_GNU_VERDEF, elf.SHT_GNU_VERNEED, elf.SHT_GNU_VERSYM:
	ret += s.Size
	}
	if s.Flags&elf.SHF_WRITE != 0 && (strings.Contains(s.Name, ".got") \|\| strings.Contains(s.Name, ".plt")) {
	ret += s.Size
	}
	}
	return ret
	}

	dynexe := dynsize(elfexe)
	dynpie := dynsize(elfpie)

	extrasize := func(ef *elf.File) uint64 {
	var ret uint64
	// skip unallocated sections
	for _, s := range ef.Sections {
	if s.Flags&elf.SHF_ALLOC == 0 {
	ret += s.Size
	}
	}
	// also skip gaps between PT_LOAD segments
	var prev *elf.Prog
	for _, seg := range ef.Progs {
	if seg.Type != elf.PT_LOAD {
	continue
	}
	if prev != nil {
	ret += seg.Off - prev.Off - prev.Filesz
	}
	prev = seg
	}
	return ret
	}

	extraexe := extrasize(elfexe)
	extrapie := extrasize(elfpie)

	if sizepie < sizeexe \|\| sizepie-extrapie < sizeexe-extraexe {
	return
	}
	diffReal := (sizepie - extrapie) - (sizeexe - extraexe)
	diffExpected := (textpie + dynpie) - (textexe + dynexe)

	t.Logf("real size difference %#x, expected %#x", diffReal, diffExpected)

	if diffReal > (diffExpected + diffExpected/10) {
	t.Errorf("PIE unexpectedly large: got difference of %d (%d - %d), expected difference %d", diffReal, sizepie, sizeexe, diffExpected)
	}
	})
	}
	}

	func TestIssue51939(t *testing.T) {
	testenv.MustHaveGoBuild(t)
	t.Parallel()
	td := t.TempDir()
	goFile := filepath.Join(td, "issue51939.go")
	if err := os.WriteFile(goFile, []byte(goSource), 0444); err != nil {
	t.Fatal(err)
	}
	outFile := filepath.Join(td, "issue51939.exe")
	goTool := testenv.GoToolPath(t)
	cmd := testenv.Command(t, goTool, "build", "-o", outFile, goFile)
	if out, err := cmd.CombinedOutput(); err != nil {
	t.Logf("%s", out)
	t.Fatal(err)
	}

	ef, err := elf.Open(outFile)
	if err != nil {
	t.Fatal(err)
	}

	for _, s := range ef.Sections {
	if s.Flags&elf.SHF_ALLOC == 0 && s.Addr != 0 {
	t.Errorf("section %s should not allocated with addr %x", s.Name, s.Addr)
	}
	}
	}

	func TestFlagR(t *testing.T) {
	// Test that using the -R flag to specify a (large) alignment generates
	// a working binary.
	// (Test only on ELF for now. The alignment allowed differs from platform
	// to platform.)
	testenv.MustHaveGoBuild(t)
	t.Parallel()
	tmpdir := t.TempDir()
	src := filepath.Join(tmpdir, "x.go")
	if err := os.WriteFile(src, []byte(goSource), 0444); err != nil {
	t.Fatal(err)
	}
	exe := filepath.Join(tmpdir, "x.exe")

	cmd := testenv.Command(t, testenv.GoToolPath(t), "build", "-ldflags=-R=0x100000", "-o", exe, src)
	if out, err := cmd.CombinedOutput(); err != nil {
	t.Fatalf("build failed: %v, output:\n%s", err, out)
	}

	cmd = testenv.Command(t, exe)
	if out, err := cmd.CombinedOutput(); err != nil {
	t.Errorf("executable failed to run: %v\n%s", err, out)
	}
	}

	func TestFlagD(t *testing.T) {
	// Test that using the -D flag to specify data section address generates
	// a working binary with data at the specified address.
	t.Parallel()
	testFlagD(t, "0x10000000", "", 0x10000000)
	}

	func TestFlagDUnaligned(t *testing.T) {
	// Test that using the -D flag with an unaligned address errors out
	t.Parallel()
	testFlagDError(t, "0x10000123", "", "invalid -D value 0x10000123")
	}

	func TestFlagDWithR(t *testing.T) {
	// Test that using the -D flag with -R flag errors on unaligned address.
	t.Parallel()
	testFlagDError(t, "0x30001234", "8192", "invalid -D value 0x30001234")
	}

	func testFlagD(t *testing.T, dataAddr string, roundQuantum string, expectedAddr uint64) {
	testenv.MustHaveGoBuild(t)
	tmpdir := t.TempDir()
	src := filepath.Join(tmpdir, "x.go")
	if err := os.WriteFile(src, []byte(goSourceWithData), 0444); err != nil {
	t.Fatal(err)
	}
	exe := filepath.Join(tmpdir, "x.exe")

	// Build linker flags
	ldflags := "-D=" + dataAddr
	if roundQuantum != "" {
	ldflags += " -R=" + roundQuantum
	}

	cmd := testenv.Command(t, testenv.GoToolPath(t), "build", "-ldflags="+ldflags, "-o", exe, src)
	if out, err := cmd.CombinedOutput(); err != nil {
	t.Fatalf("build failed: %v, output:\n%s", err, out)
	}

	cmd = testenv.Command(t, exe)
	if out, err := cmd.CombinedOutput(); err != nil {
	t.Errorf("executable failed to run: %v\n%s", err, out)
	}

	ef, err := elf.Open(exe)
	if err != nil {
	t.Fatalf("open elf file failed: %v", err)
	}
	defer ef.Close()

	// Find the first data-related section to verify segment placement
	var firstDataSection *elf.Section
	for _, sec := range ef.Sections {
	if sec.Type == elf.SHT_PROGBITS \|\| sec.Type == elf.SHT_NOBITS {
	// These sections are writable, allocated at runtime, but not executable
	// nor TLS.
	isWrite := sec.Flags&elf.SHF_WRITE != 0
	isExec := sec.Flags&elf.SHF_EXECINSTR != 0
	isAlloc := sec.Flags&elf.SHF_ALLOC != 0
	isTLS := sec.Flags&elf.SHF_TLS != 0

	if isWrite && !isExec && isAlloc && !isTLS {
	if firstDataSection == nil \|\| sec.Addr < firstDataSection.Addr {
	firstDataSection = sec
	}
	}
	}
	}

	if firstDataSection == nil {
	t.Fatalf("can't find any writable data sections")
	}
	if firstDataSection.Addr != expectedAddr {
	t.Errorf("data section starts at 0x%x for section %s, expected 0x%x",
	firstDataSection.Addr, firstDataSection.Name, expectedAddr)
	}
	}

	func testFlagDError(t *testing.T, dataAddr string, roundQuantum string, expectedError string) {
	testenv.MustHaveGoBuild(t)
	tmpdir := t.TempDir()
	src := filepath.Join(tmpdir, "x.go")
	if err := os.WriteFile(src, []byte(goSourceWithData), 0444); err != nil {
	t.Fatal(err)
	}
	exe := filepath.Join(tmpdir, "x.exe")

	// Build linker flags
	ldflags := "-D=" + dataAddr
	if roundQuantum != "" {
	ldflags += " -R=" + roundQuantum
	}

	cmd := testenv.Command(t, testenv.GoToolPath(t), "build", "-ldflags="+ldflags, "-o", exe, src)
	out, err := cmd.CombinedOutput()
	if err == nil {
	t.Fatalf("expected build to fail with unaligned data address, but it succeeded")
	}
	if !strings.Contains(string(out), expectedError) {
	t.Errorf("expected error message to contain %q, got:\n%s", expectedError, out)
	}
	}