go/misc/cgo/testshared/shared_test.go

// Copyright 2015 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 shared_test

import (
	"bufio"
	"bytes"
	"debug/elf"
	"encoding/binary"
	"flag"
	"fmt"
	"go/build"
	"io"
	"log"
	"os"
	"os/exec"
	"path/filepath"
	"regexp"
	"runtime"
	"sort"
	"strconv"
	"strings"
	"testing"
	"time"
)

var gopathInstallDir, gorootInstallDir string
var oldGOROOT string

// This is the smallest set of packages we can link into a shared
// library (runtime/cgo is built implicitly).
var minpkgs = []string{"runtime", "sync/atomic"}
var soname = "libruntime,sync-atomic.so"

var testX = flag.Bool("testx", false, "if true, pass -x to 'go' subcommands invoked by the test")
var testWork = flag.Bool("testwork", false, "if true, log and do not delete the temporary working directory")

// run runs a command and calls t.Errorf if it fails.
func run(t *testing.T, msg string, args ...string) {
	runWithEnv(t, msg, nil, args...)
}

// runWithEnv runs a command under the given environment and calls t.Errorf if it fails.
func runWithEnv(t *testing.T, msg string, env []string, args ...string) {
	c := exec.Command(args[0], args[1:]...)
	if len(env) != 0 {
		c.Env = append(os.Environ(), env...)
	}
	if output, err := c.CombinedOutput(); err != nil {
		t.Errorf("executing %s (%s) failed %s:\n%s", strings.Join(args, " "), msg, err, output)
	}
}

// goCmd invokes the go tool with the installsuffix set up by TestMain. It calls
// t.Fatalf if the command fails.
func goCmd(t *testing.T, args ...string) string {
	newargs := []string{args[0]}
	if *testX && args[0] != "env" {
		newargs = append(newargs, "-x", "-ldflags=-v")
	}
	newargs = append(newargs, args[1:]...)
	c := exec.Command(filepath.Join(oldGOROOT, "bin", "go"), newargs...)
	stderr := new(strings.Builder)
	c.Stderr = stderr

	if testing.Verbose() && t == nil {
		fmt.Fprintf(os.Stderr, "+ go %s\n", strings.Join(args, " "))
		c.Stderr = os.Stderr
	}
	output, err := c.Output()

	if err != nil {
		if t != nil {
			t.Helper()
			t.Fatalf("executing %s failed %v:\n%s", strings.Join(c.Args, " "), err, stderr)
		} else {
			// Panic instead of using log.Fatalf so that deferred cleanup may run in testMain.
			log.Panicf("executing %s failed %v:\n%s", strings.Join(c.Args, " "), err, stderr)
		}
	}
	if testing.Verbose() && t != nil {
		t.Logf("go %s", strings.Join(args, " "))
		if stderr.Len() > 0 {
			t.Logf("%s", stderr)
		}
	}
	return string(bytes.TrimSpace(output))
}

// TestMain calls testMain so that the latter can use defer (TestMain exits with os.Exit).
func testMain(m *testing.M) (int, error) {
	cwd, err := os.Getwd()
	if err != nil {
		log.Fatal(err)
	}
	oldGOROOT = filepath.Join(cwd, "../../..")

	workDir, err := os.MkdirTemp("", "shared_test")
	if err != nil {
		return 0, err
	}
	if *testWork || testing.Verbose() {
		fmt.Printf("+ mkdir -p %s\n", workDir)
	}
	if !*testWork {
		defer os.RemoveAll(workDir)
	}

	// -buildmode=shared fundamentally does not work in module mode.
	// (It tries to share package dependencies across builds, but in module mode
	// each module has its own distinct set of dependency versions.)
	// We would like to eliminate it (see https://go.dev/issue/47788),
	// but first need to figure out a replacement that covers the small subset
	// of use-cases where -buildmode=shared still works today.
	// For now, run the tests in GOPATH mode only.
	os.Setenv("GO111MODULE", "off")

	// Some tests need to edit the source in GOPATH, so copy this directory to a
	// temporary directory and chdir to that.
	gopath := filepath.Join(workDir, "gopath")
	modRoot, err := cloneTestdataModule(gopath)
	if err != nil {
		return 0, err
	}
	if testing.Verbose() {
		fmt.Printf("+ export GOPATH=%s\n", gopath)
		fmt.Printf("+ cd %s\n", modRoot)
	}
	os.Setenv("GOPATH", gopath)
	// Explicitly override GOBIN as well, in case it was set through a GOENV file.
	os.Setenv("GOBIN", filepath.Join(gopath, "bin"))
	os.Chdir(modRoot)
	os.Setenv("PWD", modRoot)

	// The test also needs to install libraries into GOROOT/pkg, so copy the
	// subset of GOROOT that we need.
	//
	// TODO(golang.org/issue/28553): Rework -buildmode=shared so that it does not
	// need to write to GOROOT.
	goroot := filepath.Join(workDir, "goroot")
	if err := cloneGOROOTDeps(goroot); err != nil {
		return 0, err
	}
	if testing.Verbose() {
		fmt.Fprintf(os.Stderr, "+ export GOROOT=%s\n", goroot)
	}
	os.Setenv("GOROOT", goroot)

	myContext := build.Default
	myContext.GOROOT = goroot
	myContext.GOPATH = gopath

	// All tests depend on runtime being built into a shared library. Because
	// that takes a few seconds, do it here and have all tests use the version
	// built here.
	goCmd(nil, append([]string{"install", "-buildmode=shared"}, minpkgs...)...)

	shlib := goCmd(nil, "list", "-linkshared", "-f={{.Shlib}}", "runtime")
	if shlib != "" {
		gorootInstallDir = filepath.Dir(shlib)
	}

	myContext.InstallSuffix = "_dynlink"
	depP, err := myContext.Import("./depBase", ".", build.ImportComment)
	if err != nil {
		return 0, fmt.Errorf("import failed: %v", err)
	}
	if depP.PkgTargetRoot == "" {
		gopathInstallDir = filepath.Dir(goCmd(nil, "list", "-buildmode=shared", "-f", "{{.Target}}", "./depBase"))
	} else {
		gopathInstallDir = filepath.Join(depP.PkgTargetRoot, "testshared")
	}
	return m.Run(), nil
}

func TestMain(m *testing.M) {
	log.SetFlags(log.Lshortfile)
	flag.Parse()

	exitCode, err := testMain(m)
	if err != nil {
		log.Fatal(err)
	}
	os.Exit(exitCode)
}

// cloneTestdataModule clones the packages from src/testshared into gopath.
// It returns the directory within gopath at which the module root is located.
func cloneTestdataModule(gopath string) (string, error) {
	modRoot := filepath.Join(gopath, "src", "testshared")
	if err := overlayDir(modRoot, "testdata"); err != nil {
		return "", err
	}
	if err := os.WriteFile(filepath.Join(modRoot, "go.mod"), []byte("module testshared\n"), 0644); err != nil {
		return "", err
	}
	return modRoot, nil
}

// cloneGOROOTDeps copies (or symlinks) the portions of GOROOT/src and
// GOROOT/pkg relevant to this test into the given directory.
// It must be run from within the testdata module.
func cloneGOROOTDeps(goroot string) error {
	// Before we clone GOROOT, figure out which packages we need to copy over.
	listArgs := []string{
		"list",
		"-deps",
		"-f", "{{if and .Standard (not .ForTest)}}{{.ImportPath}}{{end}}",
	}
	stdDeps := goCmd(nil, append(listArgs, minpkgs...)...)
	testdataDeps := goCmd(nil, append(listArgs, "-test", "./...")...)

	pkgs := append(strings.Split(strings.TrimSpace(stdDeps), "\n"),
		strings.Split(strings.TrimSpace(testdataDeps), "\n")...)
	sort.Strings(pkgs)
	var pkgRoots []string
	for _, pkg := range pkgs {
		parentFound := false
		for _, prev := range pkgRoots {
			if strings.HasPrefix(pkg, prev) {
				// We will copy in the source for pkg when we copy in prev.
				parentFound = true
				break
			}
		}
		if !parentFound {
			pkgRoots = append(pkgRoots, pkg)
		}
	}

	gorootDirs := []string{
		"pkg/tool",
		"pkg/include",
	}
	for _, pkg := range pkgRoots {
		gorootDirs = append(gorootDirs, filepath.Join("src", pkg))
	}

	for _, dir := range gorootDirs {
		if testing.Verbose() {
			fmt.Fprintf(os.Stderr, "+ cp -r %s %s\n", filepath.Join(oldGOROOT, dir), filepath.Join(goroot, dir))
		}
		if err := overlayDir(filepath.Join(goroot, dir), filepath.Join(oldGOROOT, dir)); err != nil {
			return err
		}
	}

	return nil
}

// The shared library was built at the expected location.
func TestSOBuilt(t *testing.T) {
	_, err := os.Stat(filepath.Join(gorootInstallDir, soname))
	if err != nil {
		t.Error(err)
	}
}

func hasDynTag(f *elf.File, tag elf.DynTag) bool {
	ds := f.SectionByType(elf.SHT_DYNAMIC)
	if ds == nil {
		return false
	}
	d, err := ds.Data()
	if err != nil {
		return false
	}
	for len(d) > 0 {
		var t elf.DynTag
		switch f.Class {
		case elf.ELFCLASS32:
			t = elf.DynTag(f.ByteOrder.Uint32(d[0:4]))
			d = d[8:]
		case elf.ELFCLASS64:
			t = elf.DynTag(f.ByteOrder.Uint64(d[0:8]))
			d = d[16:]
		}
		if t == tag {
			return true
		}
	}
	return false
}

// The shared library does not have relocations against the text segment.
func TestNoTextrel(t *testing.T) {
	sopath := filepath.Join(gorootInstallDir, soname)
	f, err := elf.Open(sopath)
	if err != nil {
		t.Fatal("elf.Open failed: ", err)
	}
	defer f.Close()
	if hasDynTag(f, elf.DT_TEXTREL) {
		t.Errorf("%s has DT_TEXTREL set", soname)
	}
}

// The shared library does not contain symbols called ".dup"
// (See golang.org/issue/14841.)
func TestNoDupSymbols(t *testing.T) {
	sopath := filepath.Join(gorootInstallDir, soname)
	f, err := elf.Open(sopath)
	if err != nil {
		t.Fatal("elf.Open failed: ", err)
	}
	defer f.Close()
	syms, err := f.Symbols()
	if err != nil {
		t.Errorf("error reading symbols %v", err)
		return
	}
	for _, s := range syms {
		if s.Name == ".dup" {
			t.Fatalf("%s contains symbol called .dup", sopath)
		}
	}
}

// The install command should have created a "shlibname" file for the
// listed packages (and runtime/cgo, and math on arm) indicating the
// name of the shared library containing it.
func TestShlibnameFiles(t *testing.T) {
	pkgs := append([]string{}, minpkgs...)
	pkgs = append(pkgs, "runtime/cgo")
	if runtime.GOARCH == "arm" {
		pkgs = append(pkgs, "math")
	}
	for _, pkg := range pkgs {
		shlibnamefile := filepath.Join(gorootInstallDir, pkg+".shlibname")
		contentsb, err := os.ReadFile(shlibnamefile)
		if err != nil {
			t.Errorf("error reading shlibnamefile for %s: %v", pkg, err)
			continue
		}
		contents := strings.TrimSpace(string(contentsb))
		if contents != soname {
			t.Errorf("shlibnamefile for %s has wrong contents: %q", pkg, contents)
		}
	}
}

// Is a given offset into the file contained in a loaded segment?
func isOffsetLoaded(f *elf.File, offset uint64) bool {
	for _, prog := range f.Progs {
		if prog.Type == elf.PT_LOAD {
			if prog.Off <= offset && offset < prog.Off+prog.Filesz {
				return true
			}
		}
	}
	return false
}

func rnd(v int32, r int32) int32 {
	if r <= 0 {
		return v
	}
	v += r - 1
	c := v % r
	if c < 0 {
		c += r
	}
	v -= c
	return v
}

func readwithpad(r io.Reader, sz int32) ([]byte, error) {
	data := make([]byte, rnd(sz, 4))
	_, err := io.ReadFull(r, data)
	if err != nil {
		return nil, err
	}
	data = data[:sz]
	return data, nil
}

type note struct {
	name    string
	tag     int32
	desc    string
	section *elf.Section
}

// Read all notes from f. As ELF section names are not supposed to be special, one
// looks for a particular note by scanning all SHT_NOTE sections looking for a note
// with a particular "name" and "tag".
func readNotes(f *elf.File) ([]*note, error) {
	var notes []*note
	for _, sect := range f.Sections {
		if sect.Type != elf.SHT_NOTE {
			continue
		}
		r := sect.Open()
		for {
			var namesize, descsize, tag int32
			err := binary.Read(r, f.ByteOrder, &namesize)
			if err != nil {
				if err == io.EOF {
					break
				}
				return nil, fmt.Errorf("read namesize failed: %v", err)
			}
			err = binary.Read(r, f.ByteOrder, &descsize)
			if err != nil {
				return nil, fmt.Errorf("read descsize failed: %v", err)
			}
			err = binary.Read(r, f.ByteOrder, &tag)
			if err != nil {
				return nil, fmt.Errorf("read type failed: %v", err)
			}
			name, err := readwithpad(r, namesize)
			if err != nil {
				return nil, fmt.Errorf("read name failed: %v", err)
			}
			desc, err := readwithpad(r, descsize)
			if err != nil {
				return nil, fmt.Errorf("read desc failed: %v", err)
			}
			notes = append(notes, &note{name: string(name), tag: tag, desc: string(desc), section: sect})
		}
	}
	return notes, nil
}

func dynStrings(t *testing.T, path string, flag elf.DynTag) []string {
	t.Helper()
	f, err := elf.Open(path)
	if err != nil {
		t.Fatalf("elf.Open(%q) failed: %v", path, err)
	}
	defer f.Close()
	dynstrings, err := f.DynString(flag)
	if err != nil {
		t.Fatalf("DynString(%s) failed on %s: %v", flag, path, err)
	}
	return dynstrings
}

func AssertIsLinkedToRegexp(t *testing.T, path string, re *regexp.Regexp) {
	t.Helper()
	for _, dynstring := range dynStrings(t, path, elf.DT_NEEDED) {
		if re.MatchString(dynstring) {
			return
		}
	}
	t.Errorf("%s is not linked to anything matching %v", path, re)
}

func AssertIsLinkedTo(t *testing.T, path, lib string) {
	t.Helper()
	AssertIsLinkedToRegexp(t, path, regexp.MustCompile(regexp.QuoteMeta(lib)))
}

func AssertHasRPath(t *testing.T, path, dir string) {
	t.Helper()
	for _, tag := range []elf.DynTag{elf.DT_RPATH, elf.DT_RUNPATH} {
		for _, dynstring := range dynStrings(t, path, tag) {
			for _, rpath := range strings.Split(dynstring, ":") {
				if filepath.Clean(rpath) == filepath.Clean(dir) {
					return
				}
			}
		}
	}
	t.Errorf("%s does not have rpath %s", path, dir)
}

// Build a trivial program that links against the shared runtime and check it runs.
func TestTrivialExecutable(t *testing.T) {
	goCmd(t, "install", "-linkshared", "./trivial")
	run(t, "trivial executable", "../../bin/trivial")
	AssertIsLinkedTo(t, "../../bin/trivial", soname)
	AssertHasRPath(t, "../../bin/trivial", gorootInstallDir)
	// It is 19K on linux/amd64, with separate-code in binutils ld and 64k being most common alignment
	// 4*64k should be enough, but this might need revision eventually.
	checkSize(t, "../../bin/trivial", 256000)
}

// Build a trivial program in PIE mode that links against the shared runtime and check it runs.
func TestTrivialExecutablePIE(t *testing.T) {
	goCmd(t, "build", "-buildmode=pie", "-o", "trivial.pie", "-linkshared", "./trivial")
	run(t, "trivial executable", "./trivial.pie")
	AssertIsLinkedTo(t, "./trivial.pie", soname)
	AssertHasRPath(t, "./trivial.pie", gorootInstallDir)
	// It is 19K on linux/amd64, with separate-code in binutils ld and 64k being most common alignment
	// 4*64k should be enough, but this might need revision eventually.
	checkSize(t, "./trivial.pie", 256000)
}

// Check that the file size does not exceed a limit.
func checkSize(t *testing.T, f string, limit int64) {
	fi, err := os.Stat(f)
	if err != nil {
		t.Fatalf("stat failed: %v", err)
	}
	if sz := fi.Size(); sz > limit {
		t.Errorf("file too large: got %d, want <= %d", sz, limit)
	}
}

// Build a division test program and check it runs.
func TestDivisionExecutable(t *testing.T) {
	goCmd(t, "install", "-linkshared", "./division")
	run(t, "division executable", "../../bin/division")
}

// Build an executable that uses cgo linked against the shared runtime and check it
// runs.
func TestCgoExecutable(t *testing.T) {
	goCmd(t, "install", "-linkshared", "./execgo")
	run(t, "cgo executable", "../../bin/execgo")
}

func checkPIE(t *testing.T, name string) {
	f, err := elf.Open(name)
	if err != nil {
		t.Fatal("elf.Open failed: ", err)
	}
	defer f.Close()
	if f.Type != elf.ET_DYN {
		t.Errorf("%s has type %v, want ET_DYN", name, f.Type)
	}
	if hasDynTag(f, elf.DT_TEXTREL) {
		t.Errorf("%s has DT_TEXTREL set", name)
	}
}

func TestTrivialPIE(t *testing.T) {
	if strings.HasSuffix(os.Getenv("GO_BUILDER_NAME"), "-alpine") {
		t.Skip("skipping on alpine until issue #54354 resolved")
	}
	name := "trivial_pie"
	goCmd(t, "build", "-buildmode=pie", "-o="+name, "./trivial")
	defer os.Remove(name)
	run(t, name, "./"+name)
	checkPIE(t, name)
}

func TestCgoPIE(t *testing.T) {
	name := "cgo_pie"
	goCmd(t, "build", "-buildmode=pie", "-o="+name, "./execgo")
	defer os.Remove(name)
	run(t, name, "./"+name)
	checkPIE(t, name)
}

// Build a GOPATH package into a shared library that links against the goroot runtime
// and an executable that links against both.
func TestGopathShlib(t *testing.T) {
	goCmd(t, "install", "-buildmode=shared", "-linkshared", "./depBase")
	shlib := goCmd(t, "list", "-f", "{{.Shlib}}", "-buildmode=shared", "-linkshared", "./depBase")
	AssertIsLinkedTo(t, shlib, soname)
	goCmd(t, "install", "-linkshared", "./exe")
	AssertIsLinkedTo(t, "../../bin/exe", soname)
	AssertIsLinkedTo(t, "../../bin/exe", filepath.Base(shlib))
	AssertHasRPath(t, "../../bin/exe", gorootInstallDir)
	AssertHasRPath(t, "../../bin/exe", filepath.Dir(gopathInstallDir))
	// And check it runs.
	run(t, "executable linked to GOPATH library", "../../bin/exe")
}

// The shared library contains a note listing the packages it contains in a section
// that is not mapped into memory.
func testPkgListNote(t *testing.T, f *elf.File, note *note) {
	if note.section.Flags != 0 {
		t.Errorf("package list section has flags %v, want 0", note.section.Flags)
	}
	if isOffsetLoaded(f, note.section.Offset) {
		t.Errorf("package list section contained in PT_LOAD segment")
	}
	if note.desc != "testshared/depBase\n" {
		t.Errorf("incorrect package list %q, want %q", note.desc, "testshared/depBase\n")
	}
}

// The shared library contains a note containing the ABI hash that is mapped into
// memory and there is a local symbol called go.link.abihashbytes that points 16
// bytes into it.
func testABIHashNote(t *testing.T, f *elf.File, note *note) {
	if note.section.Flags != elf.SHF_ALLOC {
		t.Errorf("abi hash section has flags %v, want SHF_ALLOC", note.section.Flags)
	}
	if !isOffsetLoaded(f, note.section.Offset) {
		t.Errorf("abihash section not contained in PT_LOAD segment")
	}
	var hashbytes elf.Symbol
	symbols, err := f.Symbols()
	if err != nil {
		t.Errorf("error reading symbols %v", err)
		return
	}
	for _, sym := range symbols {
		if sym.Name == "go:link.abihashbytes" {
			hashbytes = sym
		}
	}
	if hashbytes.Name == "" {
		t.Errorf("no symbol called go:link.abihashbytes")
		return
	}
	if elf.ST_BIND(hashbytes.Info) != elf.STB_LOCAL {
		t.Errorf("%s has incorrect binding %v, want STB_LOCAL", hashbytes.Name, elf.ST_BIND(hashbytes.Info))
	}
	if f.Sections[hashbytes.Section] != note.section {
		t.Errorf("%s has incorrect section %v, want %s", hashbytes.Name, f.Sections[hashbytes.Section].Name, note.section.Name)
	}
	if hashbytes.Value-note.section.Addr != 16 {
		t.Errorf("%s has incorrect offset into section %d, want 16", hashbytes.Name, hashbytes.Value-note.section.Addr)
	}
}

// A Go shared library contains a note indicating which other Go shared libraries it
// was linked against in an unmapped section.
func testDepsNote(t *testing.T, f *elf.File, note *note) {
	if note.section.Flags != 0 {
		t.Errorf("package list section has flags %v, want 0", note.section.Flags)
	}
	if isOffsetLoaded(f, note.section.Offset) {
		t.Errorf("package list section contained in PT_LOAD segment")
	}
	// libdepBase.so just links against the lib containing the runtime.
	if note.desc != soname {
		t.Errorf("incorrect dependency list %q, want %q", note.desc, soname)
	}
}

// The shared library contains notes with defined contents; see above.
func TestNotes(t *testing.T) {
	goCmd(t, "install", "-buildmode=shared", "-linkshared", "./depBase")
	shlib := goCmd(t, "list", "-f", "{{.Shlib}}", "-buildmode=shared", "-linkshared", "./depBase")
	f, err := elf.Open(shlib)
	if err != nil {
		t.Fatal(err)
	}
	defer f.Close()
	notes, err := readNotes(f)
	if err != nil {
		t.Fatal(err)
	}
	pkgListNoteFound := false
	abiHashNoteFound := false
	depsNoteFound := false
	for _, note := range notes {
		if note.name != "Go\x00\x00" {
			continue
		}
		switch note.tag {
		case 1: // ELF_NOTE_GOPKGLIST_TAG
			if pkgListNoteFound {
				t.Error("multiple package list notes")
			}
			testPkgListNote(t, f, note)
			pkgListNoteFound = true
		case 2: // ELF_NOTE_GOABIHASH_TAG
			if abiHashNoteFound {
				t.Error("multiple abi hash notes")
			}
			testABIHashNote(t, f, note)
			abiHashNoteFound = true
		case 3: // ELF_NOTE_GODEPS_TAG
			if depsNoteFound {
				t.Error("multiple dependency list notes")
			}
			testDepsNote(t, f, note)
			depsNoteFound = true
		}
	}
	if !pkgListNoteFound {
		t.Error("package list note not found")
	}
	if !abiHashNoteFound {
		t.Error("abi hash note not found")
	}
	if !depsNoteFound {
		t.Error("deps note not found")
	}
}

// Build a GOPATH package (depBase) into a shared library that links against the goroot
// runtime, another package (dep2) that links against the first, and an
// executable that links against dep2.
func TestTwoGopathShlibs(t *testing.T) {
	goCmd(t, "install", "-buildmode=shared", "-linkshared", "./depBase")
	goCmd(t, "install", "-buildmode=shared", "-linkshared", "./dep2")
	goCmd(t, "install", "-linkshared", "./exe2")
	run(t, "executable linked to GOPATH library", "../../bin/exe2")
}

func TestThreeGopathShlibs(t *testing.T) {
	goCmd(t, "install", "-buildmode=shared", "-linkshared", "./depBase")
	goCmd(t, "install", "-buildmode=shared", "-linkshared", "./dep2")
	goCmd(t, "install", "-buildmode=shared", "-linkshared", "./dep3")
	goCmd(t, "install", "-linkshared", "./exe3")
	run(t, "executable linked to GOPATH library", "../../bin/exe3")
}

// If gccgo is not available or not new enough, call t.Skip.
func requireGccgo(t *testing.T) {
	t.Helper()

	gccgoName := os.Getenv("GCCGO")
	if gccgoName == "" {
		gccgoName = "gccgo"
	}
	gccgoPath, err := exec.LookPath(gccgoName)
	if err != nil {
		t.Skip("gccgo not found")
	}
	cmd := exec.Command(gccgoPath, "-dumpversion")
	output, err := cmd.CombinedOutput()
	if err != nil {
		t.Fatalf("%s -dumpversion failed: %v\n%s", gccgoPath, err, output)
	}
	dot := bytes.Index(output, []byte{'.'})
	if dot > 0 {
		output = output[:dot]
	}
	major, err := strconv.Atoi(string(output))
	if err != nil {
		t.Skipf("can't parse gccgo version number %s", output)
	}
	if major < 5 {
		t.Skipf("gccgo too old (%s)", strings.TrimSpace(string(output)))
	}

	gomod, err := exec.Command("go", "env", "GOMOD").Output()
	if err != nil {
		t.Fatalf("go env GOMOD: %v", err)
	}
	if len(bytes.TrimSpace(gomod)) > 0 {
		t.Skipf("gccgo not supported in module mode; see golang.org/issue/30344")
	}
}

// Build a GOPATH package into a shared library with gccgo and an executable that
// links against it.
func TestGoPathShlibGccgo(t *testing.T) {
	requireGccgo(t)

	libgoRE := regexp.MustCompile("libgo.so.[0-9]+")

	goCmd(t, "install", "-compiler=gccgo", "-buildmode=shared", "-linkshared", "./depBase")

	// Run 'go list' after 'go install': with gccgo, we apparently don't know the
	// shlib location until after we've installed it.
	shlib := goCmd(t, "list", "-compiler=gccgo", "-buildmode=shared", "-linkshared", "-f", "{{.Shlib}}", "./depBase")

	AssertIsLinkedToRegexp(t, shlib, libgoRE)
	goCmd(t, "install", "-compiler=gccgo", "-linkshared", "./exe")
	AssertIsLinkedToRegexp(t, "../../bin/exe", libgoRE)
	AssertIsLinkedTo(t, "../../bin/exe", filepath.Base(shlib))
	AssertHasRPath(t, "../../bin/exe", filepath.Dir(shlib))
	// And check it runs.
	run(t, "gccgo-built", "../../bin/exe")
}

// The gccgo version of TestTwoGopathShlibs: build a GOPATH package into a shared
// library with gccgo, another GOPATH package that depends on the first and an
// executable that links the second library.
func TestTwoGopathShlibsGccgo(t *testing.T) {
	requireGccgo(t)

	libgoRE := regexp.MustCompile("libgo.so.[0-9]+")

	goCmd(t, "install", "-compiler=gccgo", "-buildmode=shared", "-linkshared", "./depBase")
	goCmd(t, "install", "-compiler=gccgo", "-buildmode=shared", "-linkshared", "./dep2")
	goCmd(t, "install", "-compiler=gccgo", "-linkshared", "./exe2")

	// Run 'go list' after 'go install': with gccgo, we apparently don't know the
	// shlib location until after we've installed it.
	dep2 := goCmd(t, "list", "-compiler=gccgo", "-buildmode=shared", "-linkshared", "-f", "{{.Shlib}}", "./dep2")
	depBase := goCmd(t, "list", "-compiler=gccgo", "-buildmode=shared", "-linkshared", "-f", "{{.Shlib}}", "./depBase")

	AssertIsLinkedToRegexp(t, depBase, libgoRE)
	AssertIsLinkedToRegexp(t, dep2, libgoRE)
	AssertIsLinkedTo(t, dep2, filepath.Base(depBase))
	AssertIsLinkedToRegexp(t, "../../bin/exe2", libgoRE)
	AssertIsLinkedTo(t, "../../bin/exe2", filepath.Base(dep2))
	AssertIsLinkedTo(t, "../../bin/exe2", filepath.Base(depBase))

	// And check it runs.
	run(t, "gccgo-built", "../../bin/exe2")
}

// Testing rebuilding of shared libraries when they are stale is a bit more
// complicated that it seems like it should be. First, we make everything "old": but
// only a few seconds old, or it might be older than gc (or the runtime source) and
// everything will get rebuilt. Then define a timestamp slightly newer than this
// time, which is what we set the mtime to of a file to cause it to be seen as new,
// and finally another slightly even newer one that we can compare files against to
// see if they have been rebuilt.
var oldTime = time.Now().Add(-9 * time.Second)
var nearlyNew = time.Now().Add(-6 * time.Second)
var stampTime = time.Now().Add(-3 * time.Second)

// resetFileStamps makes "everything" (bin, src, pkg from GOPATH and the
// test-specific parts of GOROOT) appear old.
func resetFileStamps() {
	chtime := func(path string, info os.FileInfo, err error) error {
		return os.Chtimes(path, oldTime, oldTime)
	}
	reset := func(path string) {
		if err := filepath.Walk(path, chtime); err != nil {
			log.Panicf("resetFileStamps failed: %v", err)
		}

	}
	reset("../../bin")
	reset("../../pkg")
	reset("../../src")
	reset(gorootInstallDir)
}

// touch changes path and returns a function that changes it back.
// It also sets the time of the file, so that we can see if it is rewritten.
func touch(t *testing.T, path string) (cleanup func()) {
	t.Helper()
	data, err := os.ReadFile(path)
	if err != nil {
		t.Fatal(err)
	}
	old := make([]byte, len(data))
	copy(old, data)
	if bytes.HasPrefix(data, []byte("!<arch>\n")) {
		// Change last digit of build ID.
		// (Content ID in the new content-based build IDs.)
		const marker = `build id "`
		i := bytes.Index(data, []byte(marker))
		if i < 0 {
			t.Fatal("cannot find build id in archive")
		}
		j := bytes.IndexByte(data[i+len(marker):], '"')
		if j < 0 {
			t.Fatal("cannot find build id in archive")
		}
		i += len(marker) + j - 1
		if data[i] == 'a' {
			data[i] = 'b'
		} else {
			data[i] = 'a'
		}
	} else {
		// assume it's a text file
		data = append(data, '\n')
	}

	// If the file is still a symlink from an overlay, delete it so that we will
	// replace it with a regular file instead of overwriting the symlinked one.
	fi, err := os.Lstat(path)
	if err == nil && !fi.Mode().IsRegular() {
		fi, err = os.Stat(path)
		if err := os.Remove(path); err != nil {
			t.Fatal(err)
		}
	}
	if err != nil {
		t.Fatal(err)
	}

	// If we're replacing a symlink to a read-only file, make the new file
	// user-writable.
	perm := fi.Mode().Perm() | 0200

	if err := os.WriteFile(path, data, perm); err != nil {
		t.Fatal(err)
	}
	if err := os.Chtimes(path, nearlyNew, nearlyNew); err != nil {
		t.Fatal(err)
	}
	return func() {
		if err := os.WriteFile(path, old, perm); err != nil {
			t.Fatal(err)
		}
	}
}

// isNew returns if the path is newer than the time stamp used by touch.
func isNew(t *testing.T, path string) bool {
	t.Helper()
	fi, err := os.Stat(path)
	if err != nil {
		t.Fatal(err)
	}
	return fi.ModTime().After(stampTime)
}

// Fail unless path has been rebuilt (i.e. is newer than the time stamp used by
// isNew)
func AssertRebuilt(t *testing.T, msg, path string) {
	t.Helper()
	if !isNew(t, path) {
		t.Errorf("%s was not rebuilt (%s)", msg, path)
	}
}

// Fail if path has been rebuilt (i.e. is newer than the time stamp used by isNew)
func AssertNotRebuilt(t *testing.T, msg, path string) {
	t.Helper()
	if isNew(t, path) {
		t.Errorf("%s was rebuilt (%s)", msg, path)
	}
}

func TestRebuilding(t *testing.T) {
	goCmd(t, "install", "-buildmode=shared", "-linkshared", "./depBase")
	goCmd(t, "install", "-linkshared", "./exe")
	info := strings.Fields(goCmd(t, "list", "-buildmode=shared", "-linkshared", "-f", "{{.Target}} {{.Shlib}}", "./depBase"))
	if len(info) != 2 {
		t.Fatalf("go list failed to report Target and/or Shlib")
	}
	target := info[0]
	shlib := info[1]

	// If the source is newer than both the .a file and the .so, both are rebuilt.
	t.Run("newsource", func(t *testing.T) {
		resetFileStamps()
		cleanup := touch(t, "./depBase/dep.go")
		defer func() {
			cleanup()
			goCmd(t, "install", "-linkshared", "./exe")
		}()
		goCmd(t, "install", "-linkshared", "./exe")
		AssertRebuilt(t, "new source", target)
		AssertRebuilt(t, "new source", shlib)
	})

	// If the .a file is newer than the .so, the .so is rebuilt (but not the .a)
	t.Run("newarchive", func(t *testing.T) {
		resetFileStamps()
		AssertNotRebuilt(t, "new .a file before build", target)
		goCmd(t, "list", "-linkshared", "-f={{.ImportPath}} {{.Stale}} {{.StaleReason}} {{.Target}}", "./depBase")
		AssertNotRebuilt(t, "new .a file before build", target)
		cleanup := touch(t, target)
		defer func() {
			cleanup()
			goCmd(t, "install", "-v", "-linkshared", "./exe")
		}()
		goCmd(t, "install", "-v", "-linkshared", "./exe")
		AssertNotRebuilt(t, "new .a file", target)
		AssertRebuilt(t, "new .a file", shlib)
	})
}

func appendFile(t *testing.T, path, content string) {
	t.Helper()
	f, err := os.OpenFile(path, os.O_WRONLY|os.O_APPEND, 0660)
	if err != nil {
		t.Fatalf("os.OpenFile failed: %v", err)
	}
	defer func() {
		err := f.Close()
		if err != nil {
			t.Fatalf("f.Close failed: %v", err)
		}
	}()
	_, err = f.WriteString(content)
	if err != nil {
		t.Fatalf("f.WriteString failed: %v", err)
	}
}

func createFile(t *testing.T, path, content string) {
	t.Helper()
	f, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0644)
	if err != nil {
		t.Fatalf("os.OpenFile failed: %v", err)
	}
	_, err = f.WriteString(content)
	if closeErr := f.Close(); err == nil {
		err = closeErr
	}
	if err != nil {
		t.Fatalf("WriteString failed: %v", err)
	}
}

func TestABIChecking(t *testing.T) {
	goCmd(t, "install", "-buildmode=shared", "-linkshared", "./depBase")
	goCmd(t, "install", "-linkshared", "./exe")

	// If we make an ABI-breaking change to depBase and rebuild libp.so but not exe,
	// exe will abort with a complaint on startup.
	// This assumes adding an exported function breaks ABI, which is not true in
	// some senses but suffices for the narrow definition of ABI compatibility the
	// toolchain uses today.
	resetFileStamps()

	createFile(t, "./depBase/break.go", "package depBase\nfunc ABIBreak() {}\n")
	defer os.Remove("./depBase/break.go")

	goCmd(t, "install", "-buildmode=shared", "-linkshared", "./depBase")
	c := exec.Command("../../bin/exe")
	output, err := c.CombinedOutput()
	if err == nil {
		t.Fatal("executing exe did not fail after ABI break")
	}
	scanner := bufio.NewScanner(bytes.NewReader(output))
	foundMsg := false
	const wantPrefix = "abi mismatch detected between the executable and lib"
	for scanner.Scan() {
		if strings.HasPrefix(scanner.Text(), wantPrefix) {
			foundMsg = true
			break
		}
	}
	if err = scanner.Err(); err != nil {
		t.Errorf("scanner encountered error: %v", err)
	}
	if !foundMsg {
		t.Fatalf("exe failed, but without line %q; got output:\n%s", wantPrefix, output)
	}

	// Rebuilding exe makes it work again.
	goCmd(t, "install", "-linkshared", "./exe")
	run(t, "rebuilt exe", "../../bin/exe")

	// If we make a change which does not break ABI (such as adding an unexported
	// function) and rebuild libdepBase.so, exe still works, even if new function
	// is in a file by itself.
	resetFileStamps()
	createFile(t, "./depBase/dep2.go", "package depBase\nfunc noABIBreak() {}\n")
	goCmd(t, "install", "-buildmode=shared", "-linkshared", "./depBase")
	run(t, "after non-ABI breaking change", "../../bin/exe")
}

// If a package 'explicit' imports a package 'implicit', building
// 'explicit' into a shared library implicitly includes implicit in
// the shared library. Building an executable that imports both
// explicit and implicit builds the code from implicit into the
// executable rather than fetching it from the shared library. The
// link still succeeds and the executable still runs though.
func TestImplicitInclusion(t *testing.T) {
	goCmd(t, "install", "-buildmode=shared", "-linkshared", "./explicit")
	goCmd(t, "install", "-linkshared", "./implicitcmd")
	run(t, "running executable linked against library that contains same package as it", "../../bin/implicitcmd")
}

// Tests to make sure that the type fields of empty interfaces and itab
// fields of nonempty interfaces are unique even across modules,
// so that interface equality works correctly.
func TestInterface(t *testing.T) {
	goCmd(t, "install", "-buildmode=shared", "-linkshared", "./iface_a")
	// Note: iface_i gets installed implicitly as a dependency of iface_a.
	goCmd(t, "install", "-buildmode=shared", "-linkshared", "./iface_b")
	goCmd(t, "install", "-linkshared", "./iface")
	run(t, "running type/itab uniqueness tester", "../../bin/iface")
}

// Access a global variable from a library.
func TestGlobal(t *testing.T) {
	goCmd(t, "install", "-buildmode=shared", "-linkshared", "./globallib")
	goCmd(t, "install", "-linkshared", "./global")
	run(t, "global executable", "../../bin/global")
	AssertIsLinkedTo(t, "../../bin/global", soname)
	AssertHasRPath(t, "../../bin/global", gorootInstallDir)
}

// Run a test using -linkshared of an installed shared package.
// Issue 26400.
func TestTestInstalledShared(t *testing.T) {
	goCmd(t, "test", "-linkshared", "-test.short", "sync/atomic")
}

// Test generated pointer method with -linkshared.
// Issue 25065.
func TestGeneratedMethod(t *testing.T) {
	goCmd(t, "install", "-buildmode=shared", "-linkshared", "./issue25065")
}

// Test use of shared library struct with generated hash function.
// Issue 30768.
func TestGeneratedHash(t *testing.T) {
	goCmd(t, "install", "-buildmode=shared", "-linkshared", "./issue30768/issue30768lib")
	goCmd(t, "test", "-linkshared", "./issue30768")
}

// Test that packages can be added not in dependency order (here a depends on b, and a adds
// before b). This could happen with e.g. go build -buildmode=shared std. See issue 39777.
func TestPackageOrder(t *testing.T) {
	goCmd(t, "install", "-buildmode=shared", "-linkshared", "./issue39777/a", "./issue39777/b")
}

// Test that GC data are generated correctly by the linker when it needs a type defined in
// a shared library. See issue 39927.
func TestGCData(t *testing.T) {
	goCmd(t, "install", "-buildmode=shared", "-linkshared", "./gcdata/p")
	goCmd(t, "build", "-linkshared", "./gcdata/main")
	runWithEnv(t, "running gcdata/main", []string{"GODEBUG=clobberfree=1"}, "./main")
}

// Test that we don't decode type symbols from shared libraries (which has no data,
// causing panic). See issue 44031.
func TestIssue44031(t *testing.T) {
	goCmd(t, "install", "-buildmode=shared", "-linkshared", "./issue44031/a")
	goCmd(t, "install", "-buildmode=shared", "-linkshared", "./issue44031/b")
	goCmd(t, "run", "-linkshared", "./issue44031/main")
}

// Test that we use a variable from shared libraries (which implement an
// interface in shared libraries.). A weak reference is used in the itab
// in main process. It can cause unreacheble panic. See issue 47873.
func TestIssue47873(t *testing.T) {
	goCmd(t, "install", "-buildmode=shared", "-linkshared", "./issue47837/a")
	goCmd(t, "run", "-linkshared", "./issue47837/main")
}

// Test that we can build std in shared mode.
func TestStd(t *testing.T) {
	if testing.Short() {
		t.Skip("skip in short mode")
	}
	t.Parallel()
	// Use a temporary pkgdir to not interfere with other tests, and not write to GOROOT.
	// Cannot use goCmd as it runs with cloned GOROOT which is incomplete.
	runWithEnv(t, "building std", []string{"GOROOT=" + oldGOROOT},
		filepath.Join(oldGOROOT, "bin", "go"), "install", "-buildmode=shared", "-pkgdir="+t.TempDir(), "std")
}