Revert "cmd/go: remove support for -buildmode=shared"

This reverts CL 359096.

Updates #47788.

Reason for revert: -buildmode=shared may have actually been working in a few very specific cases. We should not remove -buildmode=shared until we have implemented an alternative to support those few cases.

Change-Id: Ia962b06abacc11f6f29fc29d092773be175e32f1
Reviewed-on: https://go-review.googlesource.com/c/go/+/359575
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

35 files changed, 1726 insertions, 0 deletions

diff --git a/misc/cgo/testshared/overlaydir_test.go b/misc/cgo/testshared/overlaydir_test.go
new file mode 100644
index 0000000000..eb587a2d44
--- /dev/null
+++ b/misc/cgo/testshared/overlaydir_test.go
@@ -0,0 +1,78 @@
+// 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.
+
+package shared_test
+
+import (
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// overlayDir makes a minimal-overhead copy of srcRoot in which new files may be added.
+//
+// TODO: Once we no longer need to support the misc module in GOPATH mode,
+// factor this function out into a package to reduce duplication.
+func overlayDir(dstRoot, srcRoot string) error {
+	dstRoot = filepath.Clean(dstRoot)
+	if err := os.MkdirAll(dstRoot, 0777); err != nil {
+		return err
+	}
+
+	srcRoot, err := filepath.Abs(srcRoot)
+	if err != nil {
+		return err
+	}
+
+	return filepath.Walk(srcRoot, func(srcPath string, info os.FileInfo, err error) error {
+		if err != nil || srcPath == srcRoot {
+			return err
+		}
+
+		suffix := strings.TrimPrefix(srcPath, srcRoot)
+		for len(suffix) > 0 && suffix[0] == filepath.Separator {
+			suffix = suffix[1:]
+		}
+		dstPath := filepath.Join(dstRoot, suffix)
+
+		perm := info.Mode() & os.ModePerm
+		if info.Mode()&os.ModeSymlink != 0 {
+			info, err = os.Stat(srcPath)
+			if err != nil {
+				return err
+			}
+			perm = info.Mode() & os.ModePerm
+		}
+
+		// Always copy directories (don't symlink them).
+		// If we add a file in the overlay, we don't want to add it in the original.
+		if info.IsDir() {
+			return os.MkdirAll(dstPath, perm|0200)
+		}
+
+		// If the OS supports symlinks, use them instead of copying bytes.
+		if err := os.Symlink(srcPath, dstPath); err == nil {
+			return nil
+		}
+
+		// Otherwise, copy the bytes.
+		src, err := os.Open(srcPath)
+		if err != nil {
+			return err
+		}
+		defer src.Close()
+
+		dst, err := os.OpenFile(dstPath, os.O_WRONLY|os.O_CREATE|os.O_EXCL, perm)
+		if err != nil {
+			return err
+		}
+
+		_, err = io.Copy(dst, src)
+		if closeErr := dst.Close(); err == nil {
+			err = closeErr
+		}
+		return err
+	})
+}
diff --git a/misc/cgo/testshared/shared_test.go b/misc/cgo/testshared/shared_test.go
new file mode 100644
index 0000000000..672811fe0e
--- /dev/null
+++ b/misc/cgo/testshared/shared_test.go
@@ -0,0 +1,1080 @@
+// 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"
+	"strings"
+	"testing"
+	"time"
+)
+
+var gopathInstallDir, gorootInstallDir 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 {
+		newargs = append(newargs, "-x")
+	}
+	newargs = append(newargs, args[1:]...)
+	c := exec.Command("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) {
+	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)
+	}
+
+	// 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
+	runtimeP, err := myContext.Import("runtime", ".", build.ImportComment)
+	if err != nil {
+		return 0, fmt.Errorf("import failed: %v", err)
+	}
+	gorootInstallDir = runtimeP.PkgTargetRoot + "_dynlink"
+
+	// 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...)...)
+
+	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 {
+	oldGOROOT := strings.TrimSpace(goCmd(nil, "env", "GOROOT"))
+	if oldGOROOT == "" {
+		return fmt.Errorf("go env GOROOT returned an empty string")
+	}
+
+	// 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)
+	checkSize(t, "../../bin/trivial", 100000) // it is 19K on linux/amd64, 100K should be enough
+}
+
+// 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)
+	checkSize(t, "./trivial.pie", 100000) // it is 19K on linux/amd64, 100K should be enough
+}
+
+// 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) {
+	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)
+	}
+	if string(output) < "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")
+}
diff --git a/misc/cgo/testshared/testdata/dep2/dep2.go b/misc/cgo/testshared/testdata/dep2/dep2.go
new file mode 100644
index 0000000000..94f38cf507
--- /dev/null
+++ b/misc/cgo/testshared/testdata/dep2/dep2.go
@@ -0,0 +1,15 @@
+package dep2
+
+import "testshared/depBase"
+
+var W int = 1
+
+var hasProg depBase.HasProg
+
+type Dep2 struct {
+	depBase.Dep
+}
+
+func G() int {
+	return depBase.F() + 1
+}
diff --git a/misc/cgo/testshared/testdata/dep3/dep3.go b/misc/cgo/testshared/testdata/dep3/dep3.go
new file mode 100644
index 0000000000..6b02ad2ee5
--- /dev/null
+++ b/misc/cgo/testshared/testdata/dep3/dep3.go
@@ -0,0 +1,22 @@
+package dep3
+
+// The point of this test file is that it references a type from
+// depBase that is also referenced in dep2, but dep2 is loaded by the
+// linker before depBase (because it is earlier in the import list).
+// There was a bug in the linker where it would not correctly read out
+// the type data in this case and later crash.
+
+import (
+	"testshared/dep2"
+	"testshared/depBase"
+)
+
+type Dep3 struct {
+	dep  depBase.Dep
+	dep2 dep2.Dep2
+}
+
+func D3() int {
+	var x Dep3
+	return x.dep.X + x.dep2.X
+}
diff --git a/misc/cgo/testshared/testdata/depBase/asm.s b/misc/cgo/testshared/testdata/depBase/asm.s
new file mode 100644
index 0000000000..0f1111f392
--- /dev/null
+++ b/misc/cgo/testshared/testdata/depBase/asm.s
@@ -0,0 +1,10 @@
+// Copyright 2014 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.
+
+// +build gc
+
+#include "textflag.h"
+
+TEXT ·ImplementedInAsm(SB),NOSPLIT,$0-0
+       RET
diff --git a/misc/cgo/testshared/testdata/depBase/dep.go b/misc/cgo/testshared/testdata/depBase/dep.go
new file mode 100644
index 0000000000..e7cc7c81eb
--- /dev/null
+++ b/misc/cgo/testshared/testdata/depBase/dep.go
@@ -0,0 +1,37 @@
+// Copyright 2016 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 depBase
+
+import (
+	"os"
+	"reflect"
+)
+
+var SlicePtr interface{} = &[]int{}
+
+var V int = 1
+
+var HasMask []string = []string{"hi"}
+
+type HasProg struct {
+	array [1024]*byte
+}
+
+type Dep struct {
+	X int
+}
+
+func (d *Dep) Method() int {
+	// This code below causes various go.itab.* symbols to be generated in
+	// the shared library. Similar code in ../exe/exe.go results in
+	// exercising https://golang.org/issues/17594
+	reflect.TypeOf(os.Stdout).Elem()
+	return 10
+}
+
+func F() int {
+	defer func() {}()
+	return V
+}
diff --git a/misc/cgo/testshared/testdata/depBase/gccgo.go b/misc/cgo/testshared/testdata/depBase/gccgo.go
new file mode 100644
index 0000000000..2b02a1e83b
--- /dev/null
+++ b/misc/cgo/testshared/testdata/depBase/gccgo.go
@@ -0,0 +1,9 @@
+// Copyright 2016 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.
+
+// +build gccgo
+
+package depBase
+
+func ImplementedInAsm() {}
diff --git a/misc/cgo/testshared/testdata/depBase/stubs.go b/misc/cgo/testshared/testdata/depBase/stubs.go
new file mode 100644
index 0000000000..c77953803b
--- /dev/null
+++ b/misc/cgo/testshared/testdata/depBase/stubs.go
@@ -0,0 +1,9 @@
+// Copyright 2016 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.
+
+// +build gc
+
+package depBase
+
+func ImplementedInAsm()
diff --git a/misc/cgo/testshared/testdata/division/division.go b/misc/cgo/testshared/testdata/division/division.go
new file mode 100644
index 0000000000..bb5fc98460
--- /dev/null
+++ b/misc/cgo/testshared/testdata/division/division.go
@@ -0,0 +1,17 @@
+// Copyright 2017 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 main
+
+//go:noinline
+func div(x, y uint32) uint32 {
+	return x / y
+}
+
+func main() {
+	a := div(97, 11)
+	if a != 8 {
+		panic("FAIL")
+	}
+}
diff --git a/misc/cgo/testshared/testdata/exe/exe.go b/misc/cgo/testshared/testdata/exe/exe.go
new file mode 100644
index 0000000000..ee95f97bc9
--- /dev/null
+++ b/misc/cgo/testshared/testdata/exe/exe.go
@@ -0,0 +1,45 @@
+package main
+
+import (
+	"os"
+	"reflect"
+	"runtime"
+
+	"testshared/depBase"
+)
+
+// Having a function declared in the main package triggered
+// golang.org/issue/18250
+func DeclaredInMain() {
+}
+
+type C struct {
+}
+
+func F() *C {
+	return nil
+}
+
+var slicePtr interface{} = &[]int{}
+
+func main() {
+	defer depBase.ImplementedInAsm()
+	// This code below causes various go.itab.* symbols to be generated in
+	// the executable. Similar code in ../depBase/dep.go results in
+	// exercising https://golang.org/issues/17594
+	reflect.TypeOf(os.Stdout).Elem()
+	runtime.GC()
+	depBase.V = depBase.F() + 1
+
+	var c *C
+	if reflect.TypeOf(F).Out(0) != reflect.TypeOf(c) {
+		panic("bad reflection results, see golang.org/issue/18252")
+	}
+
+	sp := reflect.New(reflect.TypeOf(slicePtr).Elem())
+	s := sp.Interface()
+
+	if reflect.TypeOf(s) != reflect.TypeOf(slicePtr) {
+		panic("bad reflection results, see golang.org/issue/18729")
+	}
+}
diff --git a/misc/cgo/testshared/testdata/exe2/exe2.go b/misc/cgo/testshared/testdata/exe2/exe2.go
new file mode 100644
index 0000000000..433f331e36
--- /dev/null
+++ b/misc/cgo/testshared/testdata/exe2/exe2.go
@@ -0,0 +1,8 @@
+package main
+
+import "testshared/dep2"
+
+func main() {
+	d := &dep2.Dep2{}
+	dep2.W = dep2.G() + 1 + d.Method()
+}
diff --git a/misc/cgo/testshared/testdata/exe3/exe3.go b/misc/cgo/testshared/testdata/exe3/exe3.go
new file mode 100644
index 0000000000..533e3a9e3d
--- /dev/null
+++ b/misc/cgo/testshared/testdata/exe3/exe3.go
@@ -0,0 +1,7 @@
+package main
+
+import "testshared/dep3"
+
+func main() {
+	dep3.D3()
+}
diff --git a/misc/cgo/testshared/testdata/execgo/exe.go b/misc/cgo/testshared/testdata/execgo/exe.go
new file mode 100644
index 0000000000..0427be8bdf
--- /dev/null
+++ b/misc/cgo/testshared/testdata/execgo/exe.go
@@ -0,0 +1,8 @@
+package main
+
+/*
+ */
+import "C"
+
+func main() {
+}
diff --git a/misc/cgo/testshared/testdata/explicit/explicit.go b/misc/cgo/testshared/testdata/explicit/explicit.go
new file mode 100644
index 0000000000..af969fcb23
--- /dev/null
+++ b/misc/cgo/testshared/testdata/explicit/explicit.go
@@ -0,0 +1,9 @@
+package explicit
+
+import (
+	"testshared/implicit"
+)
+
+func E() int {
+	return implicit.I()
+}
diff --git a/misc/cgo/testshared/testdata/gcdata/main/main.go b/misc/cgo/testshared/testdata/gcdata/main/main.go
new file mode 100644
index 0000000000..394862fd94
--- /dev/null
+++ b/misc/cgo/testshared/testdata/gcdata/main/main.go
@@ -0,0 +1,37 @@
+// 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.
+
+// Test that GC data is generated correctly for global
+// variables with types defined in a shared library.
+// See issue 39927.
+
+// This test run under GODEBUG=clobberfree=1. The check
+// *x[i] == 12345 depends on this debug mode to clobber
+// the value if the object is freed prematurely.
+
+package main
+
+import (
+	"fmt"
+	"runtime"
+	"testshared/gcdata/p"
+)
+
+var x p.T
+
+func main() {
+	for i := range x {
+		x[i] = new(int)
+		*x[i] = 12345
+	}
+	runtime.GC()
+	runtime.GC()
+	runtime.GC()
+	for i := range x {
+		if *x[i] != 12345 {
+			fmt.Printf("x[%d] == %d, want 12345\n", i, *x[i])
+			panic("FAIL")
+		}
+	}
+}
diff --git a/misc/cgo/testshared/testdata/gcdata/p/p.go b/misc/cgo/testshared/testdata/gcdata/p/p.go
new file mode 100644
index 0000000000..1fee75429e
--- /dev/null
+++ b/misc/cgo/testshared/testdata/gcdata/p/p.go
@@ -0,0 +1,7 @@
+// 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 p
+
+type T [10]*int
diff --git a/misc/cgo/testshared/testdata/global/main.go b/misc/cgo/testshared/testdata/global/main.go
new file mode 100644
index 0000000000..f43e7c3fb3
--- /dev/null
+++ b/misc/cgo/testshared/testdata/global/main.go
@@ -0,0 +1,71 @@
+// Copyright 2017 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 main
+
+import (
+	"testshared/globallib"
+)
+
+//go:noinline
+func testLoop() {
+	for i, s := range globallib.Data {
+		if s != int64(i) {
+			panic("testLoop: mismatch")
+		}
+	}
+}
+
+//go:noinline
+func ptrData() *[1<<20 + 10]int64 {
+	return &globallib.Data
+}
+
+//go:noinline
+func testMediumOffset() {
+	for i, s := range globallib.Data[1<<16-2:] {
+		if s != int64(i)+1<<16-2 {
+			panic("testMediumOffset: index mismatch")
+		}
+	}
+
+	x := globallib.Data[1<<16-1]
+	if x != 1<<16-1 {
+		panic("testMediumOffset: direct mismatch")
+	}
+
+	y := &globallib.Data[1<<16-3]
+	if y != &ptrData()[1<<16-3] {
+		panic("testMediumOffset: address mismatch")
+	}
+}
+
+//go:noinline
+func testLargeOffset() {
+	for i, s := range globallib.Data[1<<20:] {
+		if s != int64(i)+1<<20 {
+			panic("testLargeOffset: index mismatch")
+		}
+	}
+
+	x := globallib.Data[1<<20+1]
+	if x != 1<<20+1 {
+		panic("testLargeOffset: direct mismatch")
+	}
+
+	y := &globallib.Data[1<<20+2]
+	if y != &ptrData()[1<<20+2] {
+		panic("testLargeOffset: address mismatch")
+	}
+}
+
+func main() {
+	testLoop()
+
+	// SSA rules commonly merge offsets into addresses. These
+	// tests access global data in different ways to try
+	// and exercise different SSA rules.
+	testMediumOffset()
+	testLargeOffset()
+}
diff --git a/misc/cgo/testshared/testdata/globallib/global.go b/misc/cgo/testshared/testdata/globallib/global.go
new file mode 100644
index 0000000000..b4372a2e9e
--- /dev/null
+++ b/misc/cgo/testshared/testdata/globallib/global.go
@@ -0,0 +1,17 @@
+// Copyright 2017 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 globallib
+
+// Data is large enough to that offsets into it do not fit into
+// 16-bit or 20-bit immediates. Ideally we'd also try and overrun
+// 32-bit immediates, but that requires the test machine to have
+// too much memory.
+var Data [1<<20 + 10]int64
+
+func init() {
+	for i := range Data {
+		Data[i] = int64(i)
+	}
+}
diff --git a/misc/cgo/testshared/testdata/iface/main.go b/misc/cgo/testshared/testdata/iface/main.go
new file mode 100644
index 0000000000..d26ebbcc9c
--- /dev/null
+++ b/misc/cgo/testshared/testdata/iface/main.go
@@ -0,0 +1,17 @@
+// Copyright 2017 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 main
+
+import "testshared/iface_a"
+import "testshared/iface_b"
+
+func main() {
+	if iface_a.F() != iface_b.F() {
+		panic("empty interfaces not equal")
+	}
+	if iface_a.G() != iface_b.G() {
+		panic("non-empty interfaces not equal")
+	}
+}
diff --git a/misc/cgo/testshared/testdata/iface_a/a.go b/misc/cgo/testshared/testdata/iface_a/a.go
new file mode 100644
index 0000000000..e2cef1ecda
--- /dev/null
+++ b/misc/cgo/testshared/testdata/iface_a/a.go
@@ -0,0 +1,17 @@
+// Copyright 2017 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 iface_a
+
+import "testshared/iface_i"
+
+//go:noinline
+func F() interface{} {
+	return (*iface_i.T)(nil)
+}
+
+//go:noinline
+func G() iface_i.I {
+	return (*iface_i.T)(nil)
+}
diff --git a/misc/cgo/testshared/testdata/iface_b/b.go b/misc/cgo/testshared/testdata/iface_b/b.go
new file mode 100644
index 0000000000..dd3e027b37
--- /dev/null
+++ b/misc/cgo/testshared/testdata/iface_b/b.go
@@ -0,0 +1,17 @@
+// Copyright 2017 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 iface_b
+
+import "testshared/iface_i"
+
+//go:noinline
+func F() interface{} {
+	return (*iface_i.T)(nil)
+}
+
+//go:noinline
+func G() iface_i.I {
+	return (*iface_i.T)(nil)
+}
diff --git a/misc/cgo/testshared/testdata/iface_i/i.go b/misc/cgo/testshared/testdata/iface_i/i.go
new file mode 100644
index 0000000000..31c80387c7
--- /dev/null
+++ b/misc/cgo/testshared/testdata/iface_i/i.go
@@ -0,0 +1,17 @@
+// Copyright 2017 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 iface_i
+
+type I interface {
+	M()
+}
+
+type T struct {
+}
+
+func (t *T) M() {
+}
+
+// *T implements I
diff --git a/misc/cgo/testshared/testdata/implicit/implicit.go b/misc/cgo/testshared/testdata/implicit/implicit.go
new file mode 100644
index 0000000000..5360188c56
--- /dev/null
+++ b/misc/cgo/testshared/testdata/implicit/implicit.go
@@ -0,0 +1,5 @@
+package implicit
+
+func I() int {
+	return 42
+}
diff --git a/misc/cgo/testshared/testdata/implicitcmd/implicitcmd.go b/misc/cgo/testshared/testdata/implicitcmd/implicitcmd.go
new file mode 100644
index 0000000000..4d4296738e
--- /dev/null
+++ b/misc/cgo/testshared/testdata/implicitcmd/implicitcmd.go
@@ -0,0 +1,10 @@
+package main
+
+import (
+	"testshared/explicit"
+	"testshared/implicit"
+)
+
+func main() {
+	println(implicit.I() + explicit.E())
+}
diff --git a/misc/cgo/testshared/testdata/issue25065/a.go b/misc/cgo/testshared/testdata/issue25065/a.go
new file mode 100644
index 0000000000..979350ff24
--- /dev/null
+++ b/misc/cgo/testshared/testdata/issue25065/a.go
@@ -0,0 +1,20 @@
+// Copyright 2018 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 issue25065 has a type with a method that is
+//  1) referenced in a method expression
+//  2) not called
+//  3) not converted to an interface
+//  4) is a value method but the reference is to the pointer method
+// These cases avoid the call to makefuncsym from typecheckfunc, but we
+// still need to call makefuncsym somehow or the symbol will not be defined.
+package issue25065
+
+type T int
+
+func (t T) M() {}
+
+func F() func(*T) {
+	return (*T).M
+}
diff --git a/misc/cgo/testshared/testdata/issue30768/issue30768lib/lib.go b/misc/cgo/testshared/testdata/issue30768/issue30768lib/lib.go
new file mode 100644
index 0000000000..9e45ebe683
--- /dev/null
+++ b/misc/cgo/testshared/testdata/issue30768/issue30768lib/lib.go
@@ -0,0 +1,11 @@
+// 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.
+
+package issue30768lib
+
+// S is a struct that requires a generated hash function.
+type S struct {
+	A string
+	B int
+}
diff --git a/misc/cgo/testshared/testdata/issue30768/x_test.go b/misc/cgo/testshared/testdata/issue30768/x_test.go
new file mode 100644
index 0000000000..1bbd139d3e
--- /dev/null
+++ b/misc/cgo/testshared/testdata/issue30768/x_test.go
@@ -0,0 +1,22 @@
+// 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.
+
+package issue30768_test
+
+import (
+	"testing"
+
+	"testshared/issue30768/issue30768lib"
+)
+
+type s struct {
+	s issue30768lib.S
+}
+
+func Test30768(t *testing.T) {
+	// Calling t.Log will convert S to an empty interface,
+	// which will force a reference to the generated hash function,
+	// defined in the shared library.
+	t.Log(s{})
+}
diff --git a/misc/cgo/testshared/testdata/issue39777/a/a.go b/misc/cgo/testshared/testdata/issue39777/a/a.go
new file mode 100644
index 0000000000..c7bf835951
--- /dev/null
+++ b/misc/cgo/testshared/testdata/issue39777/a/a.go
@@ -0,0 +1,9 @@
+// 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 a
+
+import "testshared/issue39777/b"
+
+func F() { b.F() }
diff --git a/misc/cgo/testshared/testdata/issue39777/b/b.go b/misc/cgo/testshared/testdata/issue39777/b/b.go
new file mode 100644
index 0000000000..4e681965e6
--- /dev/null
+++ b/misc/cgo/testshared/testdata/issue39777/b/b.go
@@ -0,0 +1,7 @@
+// 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 b
+
+func F() {}
diff --git a/misc/cgo/testshared/testdata/issue44031/a/a.go b/misc/cgo/testshared/testdata/issue44031/a/a.go
new file mode 100644
index 0000000000..48827e682f
--- /dev/null
+++ b/misc/cgo/testshared/testdata/issue44031/a/a.go
@@ -0,0 +1,9 @@
+// Copyright 2021 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 a
+
+type ATypeWithALoooooongName interface { // a long name, so the type descriptor symbol name is mangled
+	M()
+}
diff --git a/misc/cgo/testshared/testdata/issue44031/b/b.go b/misc/cgo/testshared/testdata/issue44031/b/b.go
new file mode 100644
index 0000000000..ad3ebec2b9
--- /dev/null
+++ b/misc/cgo/testshared/testdata/issue44031/b/b.go
@@ -0,0 +1,17 @@
+// Copyright 2021 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 b
+
+import "testshared/issue44031/a"
+
+type T int
+
+func (T) M() {}
+
+var i = a.ATypeWithALoooooongName(T(0))
+
+func F() {
+	i.M()
+}
diff --git a/misc/cgo/testshared/testdata/issue44031/main/main.go b/misc/cgo/testshared/testdata/issue44031/main/main.go
new file mode 100644
index 0000000000..47f2e3a98e
--- /dev/null
+++ b/misc/cgo/testshared/testdata/issue44031/main/main.go
@@ -0,0 +1,20 @@
+// Copyright 2021 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 main
+
+import "testshared/issue44031/b"
+
+type t int
+
+func (t) m() {}
+
+type i interface{ m() } // test that unexported method is correctly marked
+
+var v interface{} = t(0)
+
+func main() {
+	b.F()
+	v.(i).m()
+}
diff --git a/misc/cgo/testshared/testdata/issue47837/a/a.go b/misc/cgo/testshared/testdata/issue47837/a/a.go
new file mode 100644
index 0000000000..68588eda2f
--- /dev/null
+++ b/misc/cgo/testshared/testdata/issue47837/a/a.go
@@ -0,0 +1,19 @@
+// Copyright 2021 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 a
+
+type A interface {
+	M()
+}
+
+//go:noinline
+func TheFuncWithArgA(a A) {
+	a.M()
+}
+
+type ImplA struct{}
+
+//go:noinline
+func (A *ImplA) M() {}
diff --git a/misc/cgo/testshared/testdata/issue47837/main/main.go b/misc/cgo/testshared/testdata/issue47837/main/main.go
new file mode 100644
index 0000000000..77c6f34379
--- /dev/null
+++ b/misc/cgo/testshared/testdata/issue47837/main/main.go
@@ -0,0 +1,14 @@
+// Copyright 2021 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 main
+
+import (
+	"testshared/issue47837/a"
+)
+
+func main() {
+	var vara a.ImplA
+	a.TheFuncWithArgA(&vara)
+}
diff --git a/misc/cgo/testshared/testdata/trivial/trivial.go b/misc/cgo/testshared/testdata/trivial/trivial.go
new file mode 100644
index 0000000000..6ade47ce36
--- /dev/null
+++ b/misc/cgo/testshared/testdata/trivial/trivial.go
@@ -0,0 +1,9 @@
+package main
+
+func main() {
+	// This is enough to make sure that the executable references
+	// a type descriptor, which was the cause of
+	// https://golang.org/issue/25970.
+	c := make(chan int)
+	_ = c
+}