libgo: update to Go1.18beta2

gotools/
	* Makefile.am (go_cmd_cgo_files): Add ast_go118.go
	(check-go-tool): Copy golang.org/x/tools directories.
	* Makefile.in: Regenerate.

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/384695

87 files changed, 632 insertions, 507 deletions

diff --git a/libgo/go/os/env_test.go b/libgo/go/os/env_test.go
index 4b860157b4c..f8d56ef8e02 100644
--- a/libgo/go/os/env_test.go
+++ b/libgo/go/os/env_test.go
@@ -66,7 +66,7 @@ func TestExpand(t *testing.T) {
 	}
 }
 
-var global interface{}
+var global any
 
 func BenchmarkExpand(b *testing.B) {
 	b.Run("noop", func(b *testing.B) {
@@ -166,3 +166,39 @@ func TestLookupEnv(t *testing.T) {
 		t.Errorf("smallpox release failed; world remains safe but LookupEnv is broken")
 	}
 }
+
+// On Windows, Environ was observed to report keys with a single leading "=".
+// Check that they are properly reported by LookupEnv and can be set by SetEnv.
+// See https://golang.org/issue/49886.
+func TestEnvironConsistency(t *testing.T) {
+	for _, kv := range Environ() {
+		i := strings.Index(kv, "=")
+		if i == 0 {
+			// We observe in practice keys with a single leading "=" on Windows.
+			// TODO(#49886): Should we consume only the first leading "=" as part
+			// of the key, or parse through arbitrarily many of them until a non-=,
+			// or try each possible key/value boundary until LookupEnv succeeds?
+			i = strings.Index(kv[1:], "=") + 1
+		}
+		if i < 0 {
+			t.Errorf("Environ entry missing '=': %q", kv)
+		}
+
+		k := kv[:i]
+		v := kv[i+1:]
+		v2, ok := LookupEnv(k)
+		if ok && v == v2 {
+			t.Logf("LookupEnv(%q) = %q, %t", k, v2, ok)
+		} else {
+			t.Errorf("Environ contains %q, but LookupEnv(%q) = %q, %t", kv, k, v2, ok)
+		}
+
+		// Since k=v is already present in the environment,
+		// setting it should be a no-op.
+		if err := Setenv(k, v); err == nil {
+			t.Logf("Setenv(%q, %q)", k, v)
+		} else {
+			t.Errorf("Environ contains %q, but SetEnv(%q, %q) = %q", kv, k, v, err)
+		}
+	}
+}
diff --git a/libgo/go/os/env_unix_test.go b/libgo/go/os/env_unix_test.go
index 0336323e8b6..c82a558c6e8 100644
--- a/libgo/go/os/env_unix_test.go
+++ b/libgo/go/os/env_unix_test.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build aix || darwin || dragonfly || freebsd || hurd || linux || netbsd || openbsd || solaris
-// +build aix darwin dragonfly freebsd hurd linux netbsd openbsd solaris
 
 package os_test
 
diff --git a/libgo/go/os/error_errno.go b/libgo/go/os/error_errno.go
index 580e915b73c..c8140461a4d 100644
--- a/libgo/go/os/error_errno.go
+++ b/libgo/go/os/error_errno.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !plan9
-// +build !plan9
 
 package os
 
diff --git a/libgo/go/os/error_posix.go b/libgo/go/os/error_posix.go
index 7a7c8609e27..eb4f54bc610 100644
--- a/libgo/go/os/error_posix.go
+++ b/libgo/go/os/error_posix.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build aix || darwin || dragonfly || freebsd || hurd || (js && wasm) || linux || netbsd || openbsd || solaris || windows
-// +build aix darwin dragonfly freebsd hurd js,wasm linux netbsd openbsd solaris windows
 
 package os
 
diff --git a/libgo/go/os/error_unix_test.go b/libgo/go/os/error_unix_test.go
index 3f419d54702..012e053883f 100644
--- a/libgo/go/os/error_unix_test.go
+++ b/libgo/go/os/error_unix_test.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build aix || darwin || dragonfly || freebsd || hurd || (js && wasm) || linux || netbsd || openbsd || solaris
-// +build aix darwin dragonfly freebsd hurd js,wasm linux netbsd openbsd solaris
 
 package os_test
 
diff --git a/libgo/go/os/error_windows_test.go b/libgo/go/os/error_windows_test.go
index aa0c14b7d46..86c8a985bb3 100644
--- a/libgo/go/os/error_windows_test.go
+++ b/libgo/go/os/error_windows_test.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build windows
-// +build windows
 
 package os_test
 
diff --git a/libgo/go/os/exec.go b/libgo/go/os/exec.go
index bc75d4dd66c..9eb3166ecb7 100644
--- a/libgo/go/os/exec.go
+++ b/libgo/go/os/exec.go
@@ -149,6 +149,8 @@ func (p *ProcessState) SystemTime() time.Duration {
 }
 
 // Exited reports whether the program has exited.
+// On Unix systems this reports true if the program exited due to calling exit,
+// but false if the program terminated due to a signal.
 func (p *ProcessState) Exited() bool {
 	return p.exited()
 }
@@ -162,7 +164,7 @@ func (p *ProcessState) Success() bool {
 // Sys returns system-dependent exit information about
 // the process. Convert it to the appropriate underlying
 // type, such as syscall.WaitStatus on Unix, to access its contents.
-func (p *ProcessState) Sys() interface{} {
+func (p *ProcessState) Sys() any {
 	return p.sys()
 }
 
@@ -171,6 +173,6 @@ func (p *ProcessState) Sys() interface{} {
 // type, such as *syscall.Rusage on Unix, to access its contents.
 // (On Unix, *syscall.Rusage matches struct rusage as defined in the
 // getrusage(2) manual page.)
-func (p *ProcessState) SysUsage() interface{} {
+func (p *ProcessState) SysUsage() any {
 	return p.sysUsage()
 }
diff --git a/libgo/go/os/exec/exec.go b/libgo/go/os/exec/exec.go
index 0c495755116..845b737e28f 100644
--- a/libgo/go/os/exec/exec.go
+++ b/libgo/go/os/exec/exec.go
@@ -216,7 +216,7 @@ func (c *Cmd) String() string {
 
 // interfaceEqual protects against panics from doing equality tests on
 // two interfaces with non-comparable underlying types.
-func interfaceEqual(a, b interface{}) bool {
+func interfaceEqual(a, b any) bool {
 	defer func() {
 		recover()
 	}()
@@ -748,12 +748,11 @@ func dedupEnvCase(caseInsensitive bool, env []string) []string {
 	out := make([]string, 0, len(env))
 	saw := make(map[string]int, len(env)) // key => index into out
 	for _, kv := range env {
-		eq := strings.Index(kv, "=")
-		if eq < 0 {
+		k, _, ok := strings.Cut(kv, "=")
+		if !ok {
 			out = append(out, kv)
 			continue
 		}
-		k := kv[:eq]
 		if caseInsensitive {
 			k = strings.ToLower(k)
 		}
@@ -775,11 +774,10 @@ func addCriticalEnv(env []string) []string {
 		return env
 	}
 	for _, kv := range env {
-		eq := strings.Index(kv, "=")
-		if eq < 0 {
+		k, _, ok := strings.Cut(kv, "=")
+		if !ok {
 			continue
 		}
-		k := kv[:eq]
 		if strings.EqualFold(k, "SYSTEMROOT") {
 			// We already have it.
 			return env
diff --git a/libgo/go/os/exec/exec_linux_test.go b/libgo/go/os/exec/exec_linux_test.go
index 3cfa30ee724..4a37c96e63a 100644
--- a/libgo/go/os/exec/exec_linux_test.go
+++ b/libgo/go/os/exec/exec_linux_test.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build linux && cgo
-// +build linux,cgo
 
 // On systems that use glibc, calling malloc can create a new arena,
 // and creating a new arena can read /sys/devices/system/cpu/online.
diff --git a/libgo/go/os/exec/exec_posix_test.go b/libgo/go/os/exec/exec_posix_test.go
index 7b2c0c0c111..fd7fb42d36a 100644
--- a/libgo/go/os/exec/exec_posix_test.go
+++ b/libgo/go/os/exec/exec_posix_test.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris
-// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris
 
 package exec_test
 
diff --git a/libgo/go/os/exec/exec_test.go b/libgo/go/os/exec/exec_test.go
index d854e0de843..73aa35f1aed 100644
--- a/libgo/go/os/exec/exec_test.go
+++ b/libgo/go/os/exec/exec_test.go
@@ -21,7 +21,9 @@ import (
 	"net/http/httptest"
 	"os"
 	"os/exec"
+	"os/exec/internal/fdtest"
 	"path/filepath"
+	"reflect"
 	"runtime"
 	"strconv"
 	"strings"
@@ -29,15 +31,10 @@ import (
 	"time"
 )
 
-// haveUnexpectedFDs is set at init time to report whether any
-// file descriptors were open at program start.
+// haveUnexpectedFDs is set at init time to report whether any file descriptors
+// were open at program start.
 var haveUnexpectedFDs bool
 
-// unfinalizedFiles holds files that should not be finalized,
-// because that would close the associated file descriptor,
-// which we don't want to do.
-var unfinalizedFiles []*os.File
-
 func init() {
 	if os.Getenv("GO_WANT_HELPER_PROCESS") == "1" {
 		return
@@ -49,21 +46,10 @@ func init() {
 		if poll.IsPollDescriptor(fd) {
 			continue
 		}
-		// We have no good portable way to check whether an FD is open.
-		// We use NewFile to create a *os.File, which lets us
-		// know whether it is open, but then we have to cope with
-		// the finalizer on the *os.File.
-		f := os.NewFile(fd, "")
-		if _, err := f.Stat(); err != nil {
-			// Close the file to clear the finalizer.
-			// We expect the Close to fail.
-			f.Close()
-		} else {
-			fmt.Printf("fd %d open at test start\n", fd)
+
+		if fdtest.Exists(fd) {
 			haveUnexpectedFDs = true
-			// Use a global variable to avoid running
-			// the finalizer, which would close the FD.
-			unfinalizedFiles = append(unfinalizedFiles, f)
+			return
 		}
 	}
 }
@@ -166,12 +152,10 @@ func TestCatGoodAndBadFile(t *testing.T) {
 	if _, ok := err.(*exec.ExitError); !ok {
 		t.Errorf("expected *exec.ExitError from cat combined; got %T: %v", err, err)
 	}
-	s := string(bs)
-	sp := strings.SplitN(s, "\n", 2)
-	if len(sp) != 2 {
-		t.Fatalf("expected two lines from cat; got %q", s)
+	errLine, body, ok := strings.Cut(string(bs), "\n")
+	if !ok {
+		t.Fatalf("expected two lines from cat; got %q", bs)
 	}
-	errLine, body := sp[0], sp[1]
 	if !strings.HasPrefix(errLine, "Error: open /bogus/file.foo") {
 		t.Errorf("expected stderr to complain about file; got %q", errLine)
 	}
@@ -379,50 +363,21 @@ func TestStdinCloseRace(t *testing.T) {
 
 // Issue 5071
 func TestPipeLookPathLeak(t *testing.T) {
-	// If we are reading from /proc/self/fd we (should) get an exact result.
-	tolerance := 0
-
-	// Reading /proc/self/fd is more reliable than calling lsof, so try that
-	// first.
-	numOpenFDs := func() (int, []byte, error) {
-		fds, err := os.ReadDir("/proc/self/fd")
-		if err != nil {
-			return 0, nil, err
-		}
-		return len(fds), nil, nil
+	if runtime.GOOS == "windows" {
+		t.Skip("we don't currently suppore counting open handles on windows")
 	}
-	want, before, err := numOpenFDs()
-	if err != nil {
-		// We encountered a problem reading /proc/self/fd (we might be on
-		// a platform that doesn't have it). Fall back onto lsof.
-		t.Logf("using lsof because: %v", err)
-		numOpenFDs = func() (int, []byte, error) {
-			// Android's stock lsof does not obey the -p option,
-			// so extra filtering is needed.
-			// https://golang.org/issue/10206
-			if runtime.GOOS == "android" {
-				// numOpenFDsAndroid handles errors itself and
-				// might skip or fail the test.
-				n, lsof := numOpenFDsAndroid(t)
-				return n, lsof, nil
-			}
-			lsof, err := exec.Command("lsof", "-b", "-n", "-p", strconv.Itoa(os.Getpid())).Output()
-			return bytes.Count(lsof, []byte("\n")), lsof, err
-		}
-
-		// lsof may see file descriptors associated with the fork itself,
-		// so we allow some extra margin if we have to use it.
-		// https://golang.org/issue/19243
-		tolerance = 5
 
-		// Retry reading the number of open file descriptors.
-		want, before, err = numOpenFDs()
-		if err != nil {
-			t.Log(err)
-			t.Skipf("skipping test; error finding or running lsof")
+	openFDs := func() []uintptr {
+		var fds []uintptr
+		for i := uintptr(0); i < 100; i++ {
+			if fdtest.Exists(i) {
+				fds = append(fds, i)
+			}
 		}
+		return fds
 	}
 
+	want := openFDs()
 	for i := 0; i < 6; i++ {
 		cmd := exec.Command("something-that-does-not-exist-executable")
 		cmd.StdoutPipe()
@@ -432,59 +387,10 @@ func TestPipeLookPathLeak(t *testing.T) {
 			t.Fatal("unexpected success")
 		}
 	}
-	got, after, err := numOpenFDs()
-	if err != nil {
-		// numOpenFDs has already succeeded once, it should work here.
-		t.Errorf("unexpected failure: %v", err)
-	}
-	if got-want > tolerance {
-		t.Errorf("number of open file descriptors changed: got %v, want %v", got, want)
-		if before != nil {
-			t.Errorf("before:\n%v\n", before)
-		}
-		if after != nil {
-			t.Errorf("after:\n%v\n", after)
-		}
-	}
-}
-
-func numOpenFDsAndroid(t *testing.T) (n int, lsof []byte) {
-	raw, err := exec.Command("lsof").Output()
-	if err != nil {
-		t.Skip("skipping test; error finding or running lsof")
-	}
-
-	// First find the PID column index by parsing the first line, and
-	// select lines containing pid in the column.
-	pid := []byte(strconv.Itoa(os.Getpid()))
-	pidCol := -1
-
-	s := bufio.NewScanner(bytes.NewReader(raw))
-	for s.Scan() {
-		line := s.Bytes()
-		fields := bytes.Fields(line)
-		if pidCol < 0 {
-			for i, v := range fields {
-				if bytes.Equal(v, []byte("PID")) {
-					pidCol = i
-					break
-				}
-			}
-			lsof = append(lsof, line...)
-			continue
-		}
-		if bytes.Equal(fields[pidCol], pid) {
-			lsof = append(lsof, '\n')
-			lsof = append(lsof, line...)
-		}
-	}
-	if pidCol < 0 {
-		t.Fatal("error processing lsof output: unexpected header format")
-	}
-	if err := s.Err(); err != nil {
-		t.Fatalf("error processing lsof output: %v", err)
+	got := openFDs()
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("set of open file descriptors changed: got %v, want %v", got, want)
 	}
-	return bytes.Count(lsof, []byte("\n")), lsof
 }
 
 func TestExtraFilesFDShuffle(t *testing.T) {
@@ -794,7 +700,7 @@ func TestHelperProcess(*testing.T) {
 	cmd, args := args[0], args[1:]
 	switch cmd {
 	case "echo":
-		iargs := []interface{}{}
+		iargs := []any{}
 		for _, s := range args {
 			iargs = append(iargs, s)
 		}
@@ -1048,6 +954,14 @@ func TestContext(t *testing.T) {
 }
 
 func TestContextCancel(t *testing.T) {
+	if runtime.GOOS == "netbsd" && runtime.GOARCH == "arm64" {
+		testenv.SkipFlaky(t, 42061)
+	}
+
+	// To reduce noise in the final goroutine dump,
+	// let other parallel tests complete if possible.
+	t.Parallel()
+
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 	c := helperCommandContext(t, ctx, "cat")
@@ -1072,14 +986,25 @@ func TestContextCancel(t *testing.T) {
 	// Calling cancel should have killed the process, so writes
 	// should now fail.  Give the process a little while to die.
 	start := time.Now()
+	delay := 1 * time.Millisecond
 	for {
 		if _, err := io.WriteString(stdin, "echo"); err != nil {
 			break
 		}
+
 		if time.Since(start) > time.Minute {
-			t.Fatal("canceling context did not stop program")
+			// Panic instead of calling t.Fatal so that we get a goroutine dump.
+			// We want to know exactly what the os/exec goroutines got stuck on.
+			panic("canceling context did not stop program")
+		}
+
+		// Back off exponentially (up to 1-second sleeps) to give the OS time to
+		// terminate the process.
+		delay *= 2
+		if delay > 1*time.Second {
+			delay = 1 * time.Second
 		}
-		time.Sleep(time.Millisecond)
+		time.Sleep(delay)
 	}
 
 	if err := c.Wait(); err == nil {
diff --git a/libgo/go/os/exec/exec_unix.go b/libgo/go/os/exec/exec_unix.go
index 467c069e1ca..c20f35276c6 100644
--- a/libgo/go/os/exec/exec_unix.go
+++ b/libgo/go/os/exec/exec_unix.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !plan9 && !windows
-// +build !plan9,!windows
 
 package exec
 
diff --git a/libgo/go/os/exec/exec_windows_test.go b/libgo/go/os/exec/exec_windows_test.go
index fbccffec0e9..8e31e47190f 100644
--- a/libgo/go/os/exec/exec_windows_test.go
+++ b/libgo/go/os/exec/exec_windows_test.go
@@ -3,13 +3,13 @@
 // license that can be found in the LICENSE file.
 
 //go:build windows
-// +build windows
 
 package exec_test
 
 import (
 	"io"
 	"os"
+	"os/exec"
 	"strconv"
 	"syscall"
 	"testing"
@@ -41,3 +41,16 @@ func TestPipePassing(t *testing.T) {
 		t.Error(err)
 	}
 }
+
+func TestNoInheritHandles(t *testing.T) {
+	cmd := exec.Command("cmd", "/c exit 88")
+	cmd.SysProcAttr = &syscall.SysProcAttr{NoInheritHandles: true}
+	err := cmd.Run()
+	exitError, ok := err.(*exec.ExitError)
+	if !ok {
+		t.Fatalf("got error %v; want ExitError", err)
+	}
+	if exitError.ExitCode() != 88 {
+		t.Fatalf("got exit code %d; want 88", exitError.ExitCode())
+	}
+}
diff --git a/libgo/go/os/exec/internal/fdtest/exists_js.go b/libgo/go/os/exec/internal/fdtest/exists_js.go
new file mode 100644
index 00000000000..a7ce33c74f4
--- /dev/null
+++ b/libgo/go/os/exec/internal/fdtest/exists_js.go
@@ -0,0 +1,18 @@
+// 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.
+
+//go:build js
+
+package fdtest
+
+import (
+	"syscall"
+)
+
+// Exists returns true if fd is a valid file descriptor.
+func Exists(fd uintptr) bool {
+	var s syscall.Stat_t
+	err := syscall.Fstat(int(fd), &s)
+	return err != syscall.EBADF
+}
diff --git a/libgo/go/os/exec/internal/fdtest/exists_plan9.go b/libgo/go/os/exec/internal/fdtest/exists_plan9.go
new file mode 100644
index 00000000000..8886e060271
--- /dev/null
+++ b/libgo/go/os/exec/internal/fdtest/exists_plan9.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.
+
+//go:build plan9
+
+package fdtest
+
+import (
+	"syscall"
+)
+
+const errBadFd = syscall.ErrorString("fd out of range or not open")
+
+// Exists returns true if fd is a valid file descriptor.
+func Exists(fd uintptr) bool {
+	var buf [1]byte
+	_, err := syscall.Fstat(int(fd), buf[:])
+	return err != errBadFd
+}
diff --git a/libgo/go/os/exec/internal/fdtest/exists_test.go b/libgo/go/os/exec/internal/fdtest/exists_test.go
new file mode 100644
index 00000000000..a02dddf7f7d
--- /dev/null
+++ b/libgo/go/os/exec/internal/fdtest/exists_test.go
@@ -0,0 +1,21 @@
+// 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 fdtest
+
+import (
+	"os"
+	"runtime"
+	"testing"
+)
+
+func TestExists(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("Exists not implemented for windows")
+	}
+
+	if !Exists(os.Stdout.Fd()) {
+		t.Errorf("Exists(%d) got false want true", os.Stdout.Fd())
+	}
+}
diff --git a/libgo/go/os/exec/internal/fdtest/exists_unix.go b/libgo/go/os/exec/internal/fdtest/exists_unix.go
new file mode 100644
index 00000000000..49f264cebda
--- /dev/null
+++ b/libgo/go/os/exec/internal/fdtest/exists_unix.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.
+
+//go:build aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris
+
+// Package fdtest provides test helpers for working with file descriptors across exec.
+package fdtest
+
+import (
+	"syscall"
+)
+
+// Exists returns true if fd is a valid file descriptor.
+func Exists(fd uintptr) bool {
+	var s syscall.Stat_t
+	err := syscall.Fstat(int(fd), &s)
+	return err != syscall.EBADF
+}
diff --git a/libgo/go/os/exec/internal/fdtest/exists_windows.go b/libgo/go/os/exec/internal/fdtest/exists_windows.go
new file mode 100644
index 00000000000..72b8ccfd23c
--- /dev/null
+++ b/libgo/go/os/exec/internal/fdtest/exists_windows.go
@@ -0,0 +1,12 @@
+// 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.
+
+//go:build windows
+
+package fdtest
+
+// Exists is not implemented on windows and panics.
+func Exists(fd uintptr) bool {
+	panic("unimplemented")
+}
diff --git a/libgo/go/os/exec/lp_js.go b/libgo/go/os/exec/lp_js.go
index 4eac25fe6f4..54ddc4d5b48 100644
--- a/libgo/go/os/exec/lp_js.go
+++ b/libgo/go/os/exec/lp_js.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build js && wasm
-// +build js,wasm
 
 package exec
 
diff --git a/libgo/go/os/exec/lp_unix.go b/libgo/go/os/exec/lp_unix.go
index ebecc74d2a1..0935ab9ae4c 100644
--- a/libgo/go/os/exec/lp_unix.go
+++ b/libgo/go/os/exec/lp_unix.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build aix || darwin || dragonfly || freebsd || hurd || linux || netbsd || openbsd || solaris
-// +build aix darwin dragonfly freebsd hurd linux netbsd openbsd solaris
 
 package exec
 
diff --git a/libgo/go/os/exec/lp_unix_test.go b/libgo/go/os/exec/lp_unix_test.go
index fe4df1a0610..bf602fcedb7 100644
--- a/libgo/go/os/exec/lp_unix_test.go
+++ b/libgo/go/os/exec/lp_unix_test.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build aix || darwin || dragonfly || freebsd || hurd || linux || netbsd || openbsd || solaris
-// +build aix darwin dragonfly freebsd hurd linux netbsd openbsd solaris
 
 package exec
 
diff --git a/libgo/go/os/exec/read3.go b/libgo/go/os/exec/read3.go
index a8c71831d88..10cbfbd54ab 100644
--- a/libgo/go/os/exec/read3.go
+++ b/libgo/go/os/exec/read3.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build ignore
-// +build ignore
 
 // This is a test program that verifies that it can read from
 // descriptor 3 and that no other descriptors are open.
@@ -19,12 +18,15 @@ import (
 	"io"
 	"os"
 	"os/exec"
+	"os/exec/internal/fdtest"
 	"runtime"
 	"strings"
 )
 
 func main() {
 	fd3 := os.NewFile(3, "fd3")
+	defer fd3.Close()
+
 	bs, err := io.ReadAll(fd3)
 	if err != nil {
 		fmt.Printf("ReadAll from fd 3: %v\n", err)
@@ -38,65 +40,52 @@ func main() {
 	// descriptor from parent == 3
 	// All descriptors 4 and up should be available,
 	// except for any used by the network poller.
-	var files []*os.File
-	for wantfd := uintptr(4); wantfd <= 100; wantfd++ {
-		if poll.IsPollDescriptor(wantfd) {
+	for fd := uintptr(4); fd <= 100; fd++ {
+		if poll.IsPollDescriptor(fd) {
 			continue
 		}
-		f, err := os.Open(os.Args[0])
-		if err != nil {
-			fmt.Printf("error opening file with expected fd %d: %v", wantfd, err)
-			os.Exit(1)
+
+		if !fdtest.Exists(fd) {
+			continue
 		}
-		if got := f.Fd(); got != wantfd {
-			fmt.Printf("leaked parent file. fd = %d; want %d\n", got, wantfd)
-			fdfile := fmt.Sprintf("/proc/self/fd/%d", wantfd)
-			link, err := os.Readlink(fdfile)
-			fmt.Printf("readlink(%q) = %q, %v\n", fdfile, link, err)
-			var args []string
-			switch runtime.GOOS {
-			case "plan9":
-				args = []string{fmt.Sprintf("/proc/%d/fd", os.Getpid())}
-			case "aix", "solaris", "illumos":
-				args = []string{fmt.Sprint(os.Getpid())}
-			default:
-				args = []string{"-p", fmt.Sprint(os.Getpid())}
-			}
 
-			// Determine which command to use to display open files.
-			ofcmd := "lsof"
-			switch runtime.GOOS {
-			case "dragonfly", "freebsd", "netbsd", "openbsd":
-				ofcmd = "fstat"
-			case "plan9":
-				ofcmd = "/bin/cat"
-			case "aix":
-				ofcmd = "procfiles"
-			case "solaris", "illumos":
-				ofcmd = "pfiles"
-			}
+		fmt.Printf("leaked parent file. fdtest.Exists(%d) got true want false\n", fd)
+
+		fdfile := fmt.Sprintf("/proc/self/fd/%d", fd)
+		link, err := os.Readlink(fdfile)
+		fmt.Printf("readlink(%q) = %q, %v\n", fdfile, link, err)
 
-			cmd := exec.Command(ofcmd, args...)
-			out, err := cmd.CombinedOutput()
-			if err != nil {
-				fmt.Fprintf(os.Stderr, "%s failed: %v\n", strings.Join(cmd.Args, " "), err)
-			}
-			fmt.Printf("%s", out)
-			os.Exit(1)
+		var args []string
+		switch runtime.GOOS {
+		case "plan9":
+			args = []string{fmt.Sprintf("/proc/%d/fd", os.Getpid())}
+		case "aix", "solaris", "illumos":
+			args = []string{fmt.Sprint(os.Getpid())}
+		default:
+			args = []string{"-p", fmt.Sprint(os.Getpid())}
 		}
-		files = append(files, f)
-	}
 
-	for _, f := range files {
-		f.Close()
-	}
+		// Determine which command to use to display open files.
+		ofcmd := "lsof"
+		switch runtime.GOOS {
+		case "dragonfly", "freebsd", "netbsd", "openbsd":
+			ofcmd = "fstat"
+		case "plan9":
+			ofcmd = "/bin/cat"
+		case "aix":
+			ofcmd = "procfiles"
+		case "solaris", "illumos":
+			ofcmd = "pfiles"
+		}
 
-	// Referring to fd3 here ensures that it is not
-	// garbage collected, and therefore closed, while
-	// executing the wantfd loop above. It doesn't matter
-	// what we do with fd3 as long as we refer to it;
-	// closing it is the easy choice.
-	fd3.Close()
+		cmd := exec.Command(ofcmd, args...)
+		out, err := cmd.CombinedOutput()
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "%s failed: %v\n", strings.Join(cmd.Args, " "), err)
+		}
+		fmt.Printf("%s", out)
+		os.Exit(1)
+	}
 
 	os.Stdout.Write(bs)
 }
diff --git a/libgo/go/os/exec_plan9.go b/libgo/go/os/exec_plan9.go
index cc84f976696..69714ff7983 100644
--- a/libgo/go/os/exec_plan9.go
+++ b/libgo/go/os/exec_plan9.go
@@ -115,11 +115,11 @@ func (p *ProcessState) success() bool {
 	return p.status.ExitStatus() == 0
 }
 
-func (p *ProcessState) sys() interface{} {
+func (p *ProcessState) sys() any {
 	return p.status
 }
 
-func (p *ProcessState) sysUsage() interface{} {
+func (p *ProcessState) sysUsage() any {
 	return p.status
 }
 
diff --git a/libgo/go/os/exec_posix.go b/libgo/go/os/exec_posix.go
index eb5cbc8a953..9514f07acf0 100644
--- a/libgo/go/os/exec_posix.go
+++ b/libgo/go/os/exec_posix.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build aix || darwin || dragonfly || freebsd || hurd || (js && wasm) || linux || netbsd || openbsd || solaris || windows
-// +build aix darwin dragonfly freebsd hurd js,wasm linux netbsd openbsd solaris windows
 
 package os
 
@@ -88,11 +87,11 @@ func (p *ProcessState) success() bool {
 	return p.status.ExitStatus() == 0
 }
 
-func (p *ProcessState) sys() interface{} {
+func (p *ProcessState) sys() any {
 	return p.status
 }
 
-func (p *ProcessState) sysUsage() interface{} {
+func (p *ProcessState) sysUsage() any {
 	return p.rusage
 }
 
diff --git a/libgo/go/os/exec_unix.go b/libgo/go/os/exec_unix.go
index 4ada050f5b6..e777de44ee2 100644
--- a/libgo/go/os/exec_unix.go
+++ b/libgo/go/os/exec_unix.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build aix || darwin || dragonfly || freebsd || hurd || (js && wasm) || linux || netbsd || openbsd || solaris
-// +build aix darwin dragonfly freebsd hurd js,wasm linux netbsd openbsd solaris
 
 package os
 
diff --git a/libgo/go/os/exec_unix_test.go b/libgo/go/os/exec_unix_test.go
index f14b3519fbe..fa332bf1ed8 100644
--- a/libgo/go/os/exec_unix_test.go
+++ b/libgo/go/os/exec_unix_test.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris
-// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris
 
 package os_test
 
diff --git a/libgo/go/os/executable_path.go b/libgo/go/os/executable_path.go
index 625430ecfca..d6161bcb08b 100644
--- a/libgo/go/os/executable_path.go
+++ b/libgo/go/os/executable_path.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build aix || openbsd
-// +build aix openbsd
 
 package os
 
diff --git a/libgo/go/os/executable_plan9.go b/libgo/go/os/executable_plan9.go
index ad7a4410dcd..8d8c83260f5 100644
--- a/libgo/go/os/executable_plan9.go
+++ b/libgo/go/os/executable_plan9.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build plan9
-// +build plan9
 
 package os
 
diff --git a/libgo/go/os/executable_procfs.go b/libgo/go/os/executable_procfs.go
index fdb239474c4..eaa9d92a37e 100644
--- a/libgo/go/os/executable_procfs.go
+++ b/libgo/go/os/executable_procfs.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build hurd || linux || netbsd || (js && wasm)
-// +build hurd linux netbsd js,wasm
 
 package os
 
diff --git a/libgo/go/os/executable_sysctl.go b/libgo/go/os/executable_sysctl.go
index 039448b5573..3c2aeacf7da 100644
--- a/libgo/go/os/executable_sysctl.go
+++ b/libgo/go/os/executable_sysctl.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build freebsd || dragonfly
-// +build freebsd dragonfly
 
 package os
 
diff --git a/libgo/go/os/export_unix_test.go b/libgo/go/os/export_unix_test.go
index dd2f8ec94a5..3a72db8542e 100644
--- a/libgo/go/os/export_unix_test.go
+++ b/libgo/go/os/export_unix_test.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build aix || darwin || dragonfly || freebsd || hurd || (js && wasm) || linux || netbsd || openbsd || solaris
-// +build aix darwin dragonfly freebsd hurd js,wasm linux netbsd openbsd solaris
 
 package os
 
diff --git a/libgo/go/os/fifo_test.go b/libgo/go/os/fifo_test.go
index 007ed291293..de709279613 100644
--- a/libgo/go/os/fifo_test.go
+++ b/libgo/go/os/fifo_test.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build darwin || dragonfly || freebsd || linux || netbsd || openbsd
-// +build darwin dragonfly freebsd linux netbsd openbsd
 
 package os_test
 
diff --git a/libgo/go/os/file.go b/libgo/go/os/file.go
index e717f171e72..28231285542 100644
--- a/libgo/go/os/file.go
+++ b/libgo/go/os/file.go
@@ -109,7 +109,7 @@ func (e *LinkError) Unwrap() error {
 	return e.Err
 }
 
-// Read reads up to len(b) bytes from the File.
+// Read reads up to len(b) bytes from the File and stores them in b.
 // It returns the number of bytes read and any error encountered.
 // At end of file, Read returns 0, io.EOF.
 func (f *File) Read(b []byte) (n int, err error) {
@@ -166,7 +166,7 @@ type onlyWriter struct {
 	io.Writer
 }
 
-// Write writes len(b) bytes to the File.
+// Write writes len(b) bytes from b to the File.
 // It returns the number of bytes written and an error, if any.
 // Write returns a non-nil error when n != len(b).
 func (f *File) Write(b []byte) (n int, err error) {
diff --git a/libgo/go/os/file_plan9.go b/libgo/go/os/file_plan9.go
index 604aea607bc..887e1c88923 100644
--- a/libgo/go/os/file_plan9.go
+++ b/libgo/go/os/file_plan9.go
@@ -139,7 +139,7 @@ func openFileNolog(name string, flag int, perm FileMode) (*File, error) {
 
 // Close closes the File, rendering it unusable for I/O.
 // On files that support SetDeadline, any pending I/O operations will
-// be canceled and return immediately with an error.
+// be canceled and return immediately with an ErrClosed error.
 // Close will return an error if it has already been called.
 func (f *File) Close() error {
 	if err := f.checkValid("close"); err != nil {
diff --git a/libgo/go/os/file_posix.go b/libgo/go/os/file_posix.go
index 21831a7031b..8612bb37966 100644
--- a/libgo/go/os/file_posix.go
+++ b/libgo/go/os/file_posix.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build aix || darwin || dragonfly || freebsd || hurd || (js && wasm) || linux || netbsd || openbsd || solaris || windows
-// +build aix darwin dragonfly freebsd hurd js,wasm linux netbsd openbsd solaris windows
 
 package os
 
@@ -17,7 +16,7 @@ func sigpipe() // implemented in package runtime
 
 // Close closes the File, rendering it unusable for I/O.
 // On files that support SetDeadline, any pending I/O operations will
-// be canceled and return immediately with an error.
+// be canceled and return immediately with an ErrClosed error.
 // Close will return an error if it has already been called.
 func (f *File) Close() error {
 	if f == nil {
diff --git a/libgo/go/os/file_unix.go b/libgo/go/os/file_unix.go
index a31800bd6aa..188ccda29ce 100644
--- a/libgo/go/os/file_unix.go
+++ b/libgo/go/os/file_unix.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build aix || darwin || dragonfly || freebsd || hurd || (js && wasm) || linux || netbsd || openbsd || solaris
-// +build aix darwin dragonfly freebsd hurd js,wasm linux netbsd openbsd solaris
 
 package os
 
diff --git a/libgo/go/os/os_test.go b/libgo/go/os/os_test.go
index 0cde45423b8..e90b89dfa1b 100644
--- a/libgo/go/os/os_test.go
+++ b/libgo/go/os/os_test.go
@@ -52,34 +52,31 @@ var sysdir = func() *sysDir {
 				"libpowermanager.so",
 			},
 		}
-	case "darwin", "ios":
-		switch runtime.GOARCH {
-		case "arm64":
-			wd, err := syscall.Getwd()
-			if err != nil {
-				wd = err.Error()
-			}
-			sd := &sysDir{
-				filepath.Join(wd, "..", ".."),
-				[]string{
-					"ResourceRules.plist",
-					"Info.plist",
-				},
-			}
-			found := true
-			for _, f := range sd.files {
-				path := filepath.Join(sd.name, f)
-				if _, err := Stat(path); err != nil {
-					found = false
-					break
-				}
-			}
-			if found {
-				return sd
+	case "ios":
+		wd, err := syscall.Getwd()
+		if err != nil {
+			wd = err.Error()
+		}
+		sd := &sysDir{
+			filepath.Join(wd, "..", ".."),
+			[]string{
+				"ResourceRules.plist",
+				"Info.plist",
+			},
+		}
+		found := true
+		for _, f := range sd.files {
+			path := filepath.Join(sd.name, f)
+			if _, err := Stat(path); err != nil {
+				found = false
+				break
 			}
-			// In a self-hosted iOS build the above files might
-			// not exist. Look for system files instead below.
 		}
+		if found {
+			return sd
+		}
+		// In a self-hosted iOS build the above files might
+		// not exist. Look for system files instead below.
 	case "windows":
 		return &sysDir{
 			Getenv("SystemRoot") + "\\system32\\drivers\\etc",
@@ -113,20 +110,16 @@ func size(name string, t *testing.T) int64 {
 	if err != nil {
 		t.Fatal("open failed:", err)
 	}
-	defer file.Close()
-	var buf [100]byte
-	len := 0
-	for {
-		n, e := file.Read(buf[0:])
-		len += n
-		if e == io.EOF {
-			break
-		}
-		if e != nil {
-			t.Fatal("read failed:", e)
+	defer func() {
+		if err := file.Close(); err != nil {
+			t.Error(err)
 		}
+	}()
+	n, err := io.Copy(io.Discard, file)
+	if err != nil {
+		t.Fatal(err)
 	}
-	return int64(len)
+	return n
 }
 
 func equal(name1, name2 string) (r bool) {
@@ -142,13 +135,8 @@ func equal(name1, name2 string) (r bool) {
 // localTmp returns a local temporary directory not on NFS.
 func localTmp() string {
 	switch runtime.GOOS {
-	case "android", "windows":
+	case "android", "ios", "windows":
 		return TempDir()
-	case "darwin", "ios":
-		switch runtime.GOARCH {
-		case "arm64":
-			return TempDir()
-		}
 	}
 	return "/tmp"
 }
@@ -572,15 +560,12 @@ func TestReaddirnamesOneAtATime(t *testing.T) {
 	switch runtime.GOOS {
 	case "android":
 		dir = "/system/bin"
-	case "darwin", "ios":
-		switch runtime.GOARCH {
-		case "arm64":
-			wd, err := Getwd()
-			if err != nil {
-				t.Fatal(err)
-			}
-			dir = wd
+	case "ios":
+		wd, err := Getwd()
+		if err != nil {
+			t.Fatal(err)
 		}
+		dir = wd
 	case "plan9":
 		dir = "/bin"
 	case "windows":
@@ -1401,22 +1386,19 @@ func TestChdirAndGetwd(t *testing.T) {
 		dirs = []string{"/system/bin"}
 	case "plan9":
 		dirs = []string{"/", "/usr"}
-	case "darwin", "ios":
-		switch runtime.GOARCH {
-		case "arm64":
-			dirs = nil
-			for _, d := range []string{"d1", "d2"} {
-				dir, err := os.MkdirTemp("", d)
-				if err != nil {
-					t.Fatalf("TempDir: %v", err)
-				}
-				// Expand symlinks so path equality tests work.
-				dir, err = filepath.EvalSymlinks(dir)
-				if err != nil {
-					t.Fatalf("EvalSymlinks: %v", err)
-				}
-				dirs = append(dirs, dir)
+	case "ios":
+		dirs = nil
+		for _, d := range []string{"d1", "d2"} {
+			dir, err := os.MkdirTemp("", d)
+			if err != nil {
+				t.Fatalf("TempDir: %v", err)
+			}
+			// Expand symlinks so path equality tests work.
+			dir, err = filepath.EvalSymlinks(dir)
+			if err != nil {
+				t.Fatalf("EvalSymlinks: %v", err)
 			}
+			dirs = append(dirs, dir)
 		}
 	}
 	oldwd := Getenv("PWD")
@@ -1763,8 +1745,8 @@ func TestHostname(t *testing.T) {
 	// and the /bin/hostname only returns the first component
 	want := runBinHostname(t)
 	if hostname != want {
-		i := strings.Index(hostname, ".")
-		if i < 0 || hostname[0:i] != want {
+		host, _, ok := strings.Cut(hostname, ".")
+		if !ok || host != want {
 			t.Errorf("Hostname() = %q, want %q", hostname, want)
 		}
 	}
@@ -2440,8 +2422,6 @@ func TestRemoveAllRace(t *testing.T) {
 // Test that reading from a pipe doesn't use up a thread.
 func TestPipeThreads(t *testing.T) {
 	switch runtime.GOOS {
-	case "freebsd":
-		t.Skip("skipping on FreeBSD; issue 19093")
 	case "illumos", "solaris":
 		t.Skip("skipping on Solaris and illumos; issue 19111")
 	case "windows":
diff --git a/libgo/go/os/os_unix_test.go b/libgo/go/os/os_unix_test.go
index 95ceb0daa36..10056daa7e1 100644
--- a/libgo/go/os/os_unix_test.go
+++ b/libgo/go/os/os_unix_test.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build aix || darwin || dragonfly || freebsd || hurd || (js && wasm) || linux || netbsd || openbsd || solaris
-// +build aix darwin dragonfly freebsd hurd js,wasm linux netbsd openbsd solaris
 
 package os_test
 
diff --git a/libgo/go/os/path_test.go b/libgo/go/os/path_test.go
index 4535abbc527..59f72834859 100644
--- a/libgo/go/os/path_test.go
+++ b/libgo/go/os/path_test.go
@@ -96,13 +96,8 @@ func TestMkdirAllWithSymlink(t *testing.T) {
 
 func TestMkdirAllAtSlash(t *testing.T) {
 	switch runtime.GOOS {
-	case "android", "plan9", "windows":
+	case "android", "ios", "plan9", "windows":
 		t.Skipf("skipping on %s", runtime.GOOS)
-	case "darwin", "ios":
-		switch runtime.GOARCH {
-		case "arm64":
-			t.Skipf("skipping on darwin/arm64, mkdir returns EPERM")
-		}
 	}
 	RemoveAll("/_go_os_test")
 	const dir = "/_go_os_test/dir"
diff --git a/libgo/go/os/path_unix.go b/libgo/go/os/path_unix.go
index bb0b0a05da7..26574f6a2e1 100644
--- a/libgo/go/os/path_unix.go
+++ b/libgo/go/os/path_unix.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build aix || darwin || dragonfly || freebsd || hurd || (js && wasm) || linux || netbsd || openbsd || solaris
-// +build aix darwin dragonfly freebsd hurd js,wasm linux netbsd openbsd solaris
 
 package os
 
diff --git a/libgo/go/os/pipe2_bsd.go b/libgo/go/os/pipe2_bsd.go
index bf6d081db5b..7eb1350d025 100644
--- a/libgo/go/os/pipe2_bsd.go
+++ b/libgo/go/os/pipe2_bsd.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build dragonfly || freebsd || netbsd || openbsd
-// +build dragonfly freebsd netbsd openbsd
 
 package os
 
diff --git a/libgo/go/os/pipe2_illumos.go b/libgo/go/os/pipe2_illumos.go
index 71b8cb8e25b..354b35cc462 100644
--- a/libgo/go/os/pipe2_illumos.go
+++ b/libgo/go/os/pipe2_illumos.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build illumos
-// +build illumos
 
 package os
 
diff --git a/libgo/go/os/pipe_bsd.go b/libgo/go/os/pipe_bsd.go
index 097b32e7eb3..554d62111a5 100644
--- a/libgo/go/os/pipe_bsd.go
+++ b/libgo/go/os/pipe_bsd.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build aix || darwin || (js && wasm) || (solaris && !illumos)
-// +build aix darwin js,wasm solaris,!illumos
 
 package os
 
diff --git a/libgo/go/os/pipe_test.go b/libgo/go/os/pipe_test.go
index 41a1e9c78aa..20716bce1e1 100644
--- a/libgo/go/os/pipe_test.go
+++ b/libgo/go/os/pipe_test.go
@@ -4,7 +4,6 @@
 
 // Test broken pipes on Unix systems.
 //go:build !plan9 && !js
-// +build !plan9,!js
 
 package os_test
 
@@ -151,11 +150,6 @@ func TestStdPipeHelper(t *testing.T) {
 }
 
 func testClosedPipeRace(t *testing.T, read bool) {
-	switch runtime.GOOS {
-	case "freebsd":
-		t.Skip("FreeBSD does not use the poller; issue 19093")
-	}
-
 	limit := 1
 	if !read {
 		// Get the amount we have to write to overload a pipe
diff --git a/libgo/go/os/rawconn.go b/libgo/go/os/rawconn.go
index ffc598b0618..14a495d9c0a 100644
--- a/libgo/go/os/rawconn.go
+++ b/libgo/go/os/rawconn.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !plan9
-// +build !plan9
 
 package os
 
diff --git a/libgo/go/os/rawconn_test.go b/libgo/go/os/rawconn_test.go
index 8aebaf87a60..fd2038a2332 100644
--- a/libgo/go/os/rawconn_test.go
+++ b/libgo/go/os/rawconn_test.go
@@ -4,7 +4,6 @@
 
 // Test use of raw connections.
 //go:build !plan9 && !js
-// +build !plan9,!js
 
 package os_test
 
diff --git a/libgo/go/os/readfrom_stub.go b/libgo/go/os/readfrom_stub.go
index 826760f3df6..8b7d5fb8f9e 100644
--- a/libgo/go/os/readfrom_stub.go
+++ b/libgo/go/os/readfrom_stub.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !linux
-// +build !linux
 
 package os
 
diff --git a/libgo/go/os/removeall_at.go b/libgo/go/os/removeall_at.go
index 4e55577dc2a..bc5376f1cbc 100644
--- a/libgo/go/os/removeall_at.go
+++ b/libgo/go/os/removeall_at.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build aix || darwin || dragonfly || freebsd || hurd || linux || netbsd || openbsd || solaris
-// +build aix darwin dragonfly freebsd hurd linux netbsd openbsd solaris
 
 package os
 
diff --git a/libgo/go/os/removeall_noat.go b/libgo/go/os/removeall_noat.go
index 966f3f59bc1..a85b1f95669 100644
--- a/libgo/go/os/removeall_noat.go
+++ b/libgo/go/os/removeall_noat.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !aix && !darwin && !dragonfly && !freebsd && !hurd && !linux && !netbsd && !openbsd && !solaris
-// +build !aix,!darwin,!dragonfly,!freebsd,!hurd,!linux,!netbsd,!openbsd,!solaris
 
 package os
 
diff --git a/libgo/go/os/signal/example_unix_test.go b/libgo/go/os/signal/example_unix_test.go
index 3f7795b8cf9..b279ee9491f 100644
--- a/libgo/go/os/signal/example_unix_test.go
+++ b/libgo/go/os/signal/example_unix_test.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris
-// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris
 
 package signal_test
 
diff --git a/libgo/go/os/signal/internal/pty/pty.go b/libgo/go/os/signal/internal/pty/pty.go
index 4ed3eb44e17..e5ee3f6dc01 100644
--- a/libgo/go/os/signal/internal/pty/pty.go
+++ b/libgo/go/os/signal/internal/pty/pty.go
@@ -2,9 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build (aix || darwin || dragonfly || freebsd || hurd || (linux && !android) || netbsd || openbsd || solaris) && cgo
-// +build aix darwin dragonfly freebsd hurd linux,!android netbsd openbsd solaris
-// +build cgo
+//go:build (aix || darwin || dragonfly || freebsd || hurd || (linux && !android) || netbsd || openbsd) && cgo
 
 // Package pty is a simple pseudo-terminal package for Unix systems,
 // implemented by calling C functions via cgo.
diff --git a/libgo/go/os/signal/signal_cgo_test.go b/libgo/go/os/signal/signal_cgo_test.go
index e1e4509e2a7..67bad66e0b2 100644
--- a/libgo/go/os/signal/signal_cgo_test.go
+++ b/libgo/go/os/signal/signal_cgo_test.go
@@ -3,8 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build (darwin || dragonfly || freebsd || (linux && !android) || netbsd || openbsd) && cgo
-// +build darwin dragonfly freebsd linux,!android netbsd openbsd
-// +build cgo
 
 // Note that this test does not work on Solaris: issue #22849.
 // Don't run the test on Android because at least some versions of the
diff --git a/libgo/go/os/signal/signal_linux_test.go b/libgo/go/os/signal/signal_linux_test.go
index 7abe1ec5a0a..f70f108442b 100644
--- a/libgo/go/os/signal/signal_linux_test.go
+++ b/libgo/go/os/signal/signal_linux_test.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build linux
-// +build linux
 
 package signal
 
diff --git a/libgo/go/os/signal/signal_test.go b/libgo/go/os/signal/signal_test.go
index c653c344fa1..7c8162ec7d7 100644
--- a/libgo/go/os/signal/signal_test.go
+++ b/libgo/go/os/signal/signal_test.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build aix || darwin || dragonfly || freebsd || hurd || linux || netbsd || openbsd || solaris
-// +build aix darwin dragonfly freebsd hurd linux netbsd openbsd solaris
 
 package signal
 
@@ -137,6 +136,9 @@ func TestSignal(t *testing.T) {
 	// Using 10 is arbitrary.
 	c1 := make(chan os.Signal, 10)
 	Notify(c1)
+	// Stop relaying the SIGURG signals. See #49724
+	Reset(syscall.SIGURG)
+	defer Stop(c1)
 
 	// Send this process a SIGWINCH
 	t.Logf("sigwinch...")
diff --git a/libgo/go/os/signal/signal_unix.go b/libgo/go/os/signal/signal_unix.go
index a0c7ffbdb54..45675780555 100644
--- a/libgo/go/os/signal/signal_unix.go
+++ b/libgo/go/os/signal/signal_unix.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build aix || darwin || dragonfly || freebsd || hurd || (js && wasm) || linux || netbsd || openbsd || solaris || windows
-// +build aix darwin dragonfly freebsd hurd js,wasm linux netbsd openbsd solaris windows
 
 package signal
 
diff --git a/libgo/go/os/stat_js.go b/libgo/go/os/stat_js.go
index 3badf5ba575..c3e9b5b5e53 100644
--- a/libgo/go/os/stat_js.go
+++ b/libgo/go/os/stat_js.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build js && wasm
-// +build js,wasm
 
 package os
 
diff --git a/libgo/go/os/stat_plan9.go b/libgo/go/os/stat_plan9.go
index 57ae6fb0bbd..e20accf1913 100644
--- a/libgo/go/os/stat_plan9.go
+++ b/libgo/go/os/stat_plan9.go
@@ -43,7 +43,7 @@ func fileInfoFromStat(d *syscall.Dir) *fileStat {
 }
 
 // arg is an open *File or a path string.
-func dirstat(arg interface{}) (*syscall.Dir, error) {
+func dirstat(arg any) (*syscall.Dir, error) {
 	var name string
 	var err error
 
diff --git a/libgo/go/os/stat_unix.go b/libgo/go/os/stat_unix.go
index 6ae26ad540f..b4ab62019dd 100644
--- a/libgo/go/os/stat_unix.go
+++ b/libgo/go/os/stat_unix.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build aix || darwin || dragonfly || freebsd || hurd || (js && wasm) || linux || netbsd || openbsd || solaris
-// +build aix darwin dragonfly freebsd hurd js,wasm linux netbsd openbsd solaris
 
 package os
 
diff --git a/libgo/go/os/sticky_bsd.go b/libgo/go/os/sticky_bsd.go
index ab23d8111d3..e71daf7c749 100644
--- a/libgo/go/os/sticky_bsd.go
+++ b/libgo/go/os/sticky_bsd.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build aix || darwin || dragonfly || freebsd || (js && wasm) || netbsd || openbsd || solaris
-// +build aix darwin dragonfly freebsd js,wasm netbsd openbsd solaris
 
 package os
 
diff --git a/libgo/go/os/sticky_notbsd.go b/libgo/go/os/sticky_notbsd.go
index 9979b43e8e6..9a87fbde92c 100644
--- a/libgo/go/os/sticky_notbsd.go
+++ b/libgo/go/os/sticky_notbsd.go
@@ -3,14 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !aix && !darwin && !dragonfly && !freebsd && (!js || !wasm) && !netbsd && !openbsd && !solaris
-// +build !aix
-// +build !darwin
-// +build !dragonfly
-// +build !freebsd
-// +build !js !wasm
-// +build !netbsd
-// +build !openbsd
-// +build !solaris
 
 package os
 
diff --git a/libgo/go/os/sys_bsd.go b/libgo/go/os/sys_bsd.go
index 1e245eb53a2..e272c245717 100644
--- a/libgo/go/os/sys_bsd.go
+++ b/libgo/go/os/sys_bsd.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build darwin || dragonfly || freebsd || (js && wasm) || netbsd || openbsd
-// +build darwin dragonfly freebsd js,wasm netbsd openbsd
 
 package os
 
diff --git a/libgo/go/os/sys_js.go b/libgo/go/os/sys_js.go
index 4d6a64e8ebe..4fd0e2d7c7d 100644
--- a/libgo/go/os/sys_js.go
+++ b/libgo/go/os/sys_js.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build js && wasm
-// +build js,wasm
 
 package os
 
diff --git a/libgo/go/os/sys_unix.go b/libgo/go/os/sys_unix.go
index aab683e4db8..273fc0351e0 100644
--- a/libgo/go/os/sys_unix.go
+++ b/libgo/go/os/sys_unix.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build aix || darwin || dragonfly || freebsd || hurd || linux || netbsd || openbsd || solaris
-// +build aix darwin dragonfly freebsd hurd linux netbsd openbsd solaris
 
 package os
 
diff --git a/libgo/go/os/timeout_test.go b/libgo/go/os/timeout_test.go
index 6d65e420f04..2ff58110d65 100644
--- a/libgo/go/os/timeout_test.go
+++ b/libgo/go/os/timeout_test.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !js && !plan9 && !windows
-// +build !js,!plan9,!windows
 
 package os_test
 
diff --git a/libgo/go/os/types_plan9.go b/libgo/go/os/types_plan9.go
index 125da661b79..ccf4fd932e7 100644
--- a/libgo/go/os/types_plan9.go
+++ b/libgo/go/os/types_plan9.go
@@ -15,13 +15,13 @@ type fileStat struct {
 	size    int64
 	mode    FileMode
 	modTime time.Time
-	sys     interface{}
+	sys     any
 }
 
 func (fs *fileStat) Size() int64        { return fs.size }
 func (fs *fileStat) Mode() FileMode     { return fs.mode }
 func (fs *fileStat) ModTime() time.Time { return fs.modTime }
-func (fs *fileStat) Sys() interface{}   { return fs.sys }
+func (fs *fileStat) Sys() any           { return fs.sys }
 
 func sameFile(fs1, fs2 *fileStat) bool {
 	a := fs1.sys.(*syscall.Dir)
diff --git a/libgo/go/os/types_unix.go b/libgo/go/os/types_unix.go
index e9b8b8ba3ac..1b90a5a1415 100644
--- a/libgo/go/os/types_unix.go
+++ b/libgo/go/os/types_unix.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !windows && !plan9
-// +build !windows,!plan9
 
 package os
 
@@ -24,7 +23,7 @@ type fileStat struct {
 func (fs *fileStat) Size() int64        { return fs.size }
 func (fs *fileStat) Mode() FileMode     { return fs.mode }
 func (fs *fileStat) ModTime() time.Time { return fs.modTime }
-func (fs *fileStat) Sys() interface{}   { return &fs.sys }
+func (fs *fileStat) Sys() any           { return &fs.sys }
 
 func sameFile(fs1, fs2 *fileStat) bool {
 	return fs1.sys.Dev == fs2.sys.Dev && fs1.sys.Ino == fs2.sys.Ino
diff --git a/libgo/go/os/types_windows.go b/libgo/go/os/types_windows.go
index 59bf5ca3814..5443dfedc8c 100644
--- a/libgo/go/os/types_windows.go
+++ b/libgo/go/os/types_windows.go
@@ -138,7 +138,7 @@ func (fs *fileStat) ModTime() time.Time {
 }
 
 // Sys returns syscall.Win32FileAttributeData for file fs.
-func (fs *fileStat) Sys() interface{} {
+func (fs *fileStat) Sys() any {
 	return &syscall.Win32FileAttributeData{
 		FileAttributes: fs.FileAttributes,
 		CreationTime:   fs.CreationTime,
diff --git a/libgo/go/os/user/cgo_listgroups_unix.go b/libgo/go/os/user/cgo_listgroups_unix.go
new file mode 100644
index 00000000000..5621c1a63aa
--- /dev/null
+++ b/libgo/go/os/user/cgo_listgroups_unix.go
@@ -0,0 +1,43 @@
+// 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.
+
+//go:build (dragonfly || darwin || freebsd || (!android && linux) || netbsd || openbsd || (solaris && !illumos)) && cgo && !osusergo
+
+package user
+
+import (
+	"fmt"
+	"strconv"
+	"syscall"
+	"unsafe"
+)
+
+const maxGroups = 2048
+
+func listGroups(u *User) ([]string, error) {
+	ug, err := strconv.Atoi(u.Gid)
+	if err != nil {
+		return nil, fmt.Errorf("user: list groups for %s: invalid gid %q", u.Username, u.Gid)
+	}
+	userGID := syscall.Gid_t(ug)
+	nameC := make([]byte, len(u.Username)+1)
+	copy(nameC, u.Username)
+
+	n := int32(256)
+	gidsC := make([]syscall.Gid_t, n)
+	rv := getGroupList((*byte)(unsafe.Pointer(&nameC[0])), userGID, &gidsC[0], &n)
+	if rv == -1 {
+		// Mac is the only Unix that does not set n properly when rv == -1, so
+		// we need to use different logic for Mac vs. the other OS's.
+		if err := groupRetry(u.Username, nameC, userGID, &gidsC, &n); err != nil {
+			return nil, err
+		}
+	}
+	gidsC = gidsC[:n]
+	gids := make([]string, 0, n)
+	for _, g := range gidsC[:n] {
+		gids = append(gids, strconv.Itoa(int(g)))
+	}
+	return gids, nil
+}
diff --git a/libgo/go/os/user/cgo_lookup_unix.go b/libgo/go/os/user/cgo_lookup_unix.go
index 3f4014c3633..17eee9ef4bd 100644
--- a/libgo/go/os/user/cgo_lookup_unix.go
+++ b/libgo/go/os/user/cgo_lookup_unix.go
@@ -3,9 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build (aix || darwin || dragonfly || freebsd || hurd || (!android && linux) || netbsd || openbsd || solaris) && cgo && !osusergo
-// +build aix darwin dragonfly freebsd hurd !android,linux netbsd openbsd solaris
-// +build cgo
-// +build !osusergo
 
 package user
 
@@ -114,9 +111,7 @@ func buildUser(pwd *syscall.Passwd) *User {
 	// say: "It is expected to be a comma separated list of
 	// personal data where the first item is the full name of the
 	// user."
-	if i := strings.Index(u.Name, ","); i >= 0 {
-		u.Name = u.Name[:i]
-	}
+	u.Name, _, _ = strings.Cut(u.Name, ",")
 	return u
 }
 
diff --git a/libgo/go/os/user/cgo_unix_test.go b/libgo/go/os/user/cgo_unix_test.go
index 9ec32b3a788..6d16aa20b30 100644
--- a/libgo/go/os/user/cgo_unix_test.go
+++ b/libgo/go/os/user/cgo_unix_test.go
@@ -3,9 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build (darwin || dragonfly || freebsd || (!android && linux) || netbsd || openbsd || solaris) && cgo && !osusergo
-// +build darwin dragonfly freebsd !android,linux netbsd openbsd solaris
-// +build cgo
-// +build !osusergo
 
 package user
 
diff --git a/libgo/go/os/user/decls_solaris.go b/libgo/go/os/user/decls_solaris.go
index 43b6a044047..92c83328912 100644
--- a/libgo/go/os/user/decls_solaris.go
+++ b/libgo/go/os/user/decls_solaris.go
@@ -22,6 +22,3 @@ func libc_getgrnam_r(name *byte, grp *syscall.Group, buf *byte, buflen syscall.S
 
 //extern __posix_getgrgid_r
 func libc_getgrgid_r(gid syscall.Gid_t, grp *syscall.Group, buf *byte, buflen syscall.Size_t, result **syscall.Group) int
-
-//extern getgrouplist
-func libc_getgrouplist(user *byte, group syscall.Gid_t, groups *syscall.Gid_t, ngroups *int32) int
diff --git a/libgo/go/os/user/getgrouplist_unix.go b/libgo/go/os/user/getgrouplist_unix.go
new file mode 100644
index 00000000000..527d941308e
--- /dev/null
+++ b/libgo/go/os/user/getgrouplist_unix.go
@@ -0,0 +1,30 @@
+// 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.
+
+//go:build (dragonfly || freebsd || (!android && linux) || netbsd || openbsd || (solaris && !illumos)) && cgo && !osusergo
+
+package user
+
+import (
+	"fmt"
+	"syscall"
+)
+
+//extern-sysinfo getgrouplist
+func getGroupList(name *byte, userGID syscall.Gid_t, gids *syscall.Gid_t, n *int32) int32
+
+// groupRetry retries getGroupList with much larger size for n. The result is
+// stored in gids.
+func groupRetry(username string, name []byte, userGID syscall.Gid_t, gids *[]syscall.Gid_t, n *int32) error {
+	// More than initial buffer, but now n contains the correct size.
+	if *n > maxGroups {
+		return fmt.Errorf("user: %q is a member of more than %d groups", username, maxGroups)
+	}
+	*gids = make([]syscall.Gid_t, *n)
+	rv := getGroupList(&name[0], userGID, &(*gids)[0], n)
+	if rv == -1 {
+		return fmt.Errorf("user: list groups for %s failed", username)
+	}
+	return nil
+}
diff --git a/libgo/go/os/user/listgroups_aix.go b/libgo/go/os/user/listgroups_aix.go
deleted file mode 100644
index 93feb80924c..00000000000
--- a/libgo/go/os/user/listgroups_aix.go
+++ /dev/null
@@ -1,14 +0,0 @@
-// 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.
-
-//go:build cgo && !osusergo
-// +build cgo,!osusergo
-
-package user
-
-import "fmt"
-
-func listGroups(u *User) ([]string, error) {
-	return nil, fmt.Errorf("user: list groups for %s: not supported on AIX", u.Username)
-}
diff --git a/libgo/go/os/user/listgroups_illumos.go b/libgo/go/os/user/listgroups_illumos.go
deleted file mode 100644
index d25e0339b99..00000000000
--- a/libgo/go/os/user/listgroups_illumos.go
+++ /dev/null
@@ -1,18 +0,0 @@
-// 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.
-
-//go:build cgo && !osusergo
-// +build cgo,!osusergo
-
-// Even though this file requires no C, it is used to provide a
-// listGroup stub because all the other illumos calls work.  Otherwise,
-// this stub will conflict with the lookup_stubs.go fallback.
-
-package user
-
-import "fmt"
-
-func listGroups(u *User) ([]string, error) {
-	return nil, fmt.Errorf("user: list groups for %s: not supported on illumos", u.Username)
-}
diff --git a/libgo/go/os/user/listgroups_stub.go b/libgo/go/os/user/listgroups_stub.go
new file mode 100644
index 00000000000..4cf808b65de
--- /dev/null
+++ b/libgo/go/os/user/listgroups_stub.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.
+
+//go:build android || (js && !wasm)
+
+package user
+
+import (
+	"errors"
+)
+
+func init() {
+	groupListImplemented = false
+}
+
+func listGroups(*User) ([]string, error) {
+	return nil, errors.New("user: list groups not implemented")
+}
diff --git a/libgo/go/os/user/listgroups_unix.go b/libgo/go/os/user/listgroups_unix.go
index 38bf807f52a..b3cf839b3ec 100644
--- a/libgo/go/os/user/listgroups_unix.go
+++ b/libgo/go/os/user/listgroups_unix.go
@@ -1,61 +1,114 @@
-// Copyright 2016 The Go Authors. All rights reserved.
+// 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.
 
-//go:build (dragonfly || darwin || freebsd || hurd || (!android && linux) || netbsd || openbsd || (solaris && !illumos)) && cgo && !osusergo
-// +build dragonfly darwin freebsd hurd !android,linux netbsd openbsd solaris,!illumos
-// +build cgo
-// +build !osusergo
+//go:build ((darwin || dragonfly || freebsd || hurd || (js && wasm) || (!android && linux) || netbsd || openbsd || solaris) && (!cgo || osusergo)) || aix || illumos
 
 package user
 
 import (
+	"bufio"
+	"bytes"
+	"errors"
 	"fmt"
+	"io"
+	"os"
 	"strconv"
 	"syscall"
 )
 
-/*
-#include <unistd.h>
-#include <sys/types.h>
-*/
+const groupFile = "/etc/group"
 
-const maxGroups = 2048
+var colon = []byte{':'}
 
-func listGroups(u *User) ([]string, error) {
-	ug, err := strconv.Atoi(u.Gid)
-	if err != nil {
-		return nil, fmt.Errorf("user: list groups for %s: invalid gid %q", u.Username, u.Gid)
+func listGroupsFromReader(u *User, r io.Reader) ([]string, error) {
+	if u.Username == "" {
+		return nil, errors.New("user: list groups: empty username")
 	}
-	userGID := syscall.Gid_t(ug)
-	nameC, err := syscall.BytePtrFromString(u.Username)
+	primaryGid, err := strconv.Atoi(u.Gid)
 	if err != nil {
-		return nil, fmt.Errorf("user: invalid user name %q: %v", strconv.Quote(u.Username), err)
+		return nil, fmt.Errorf("user: list groups for %s: invalid gid %q", u.Username, u.Gid)
 	}
 
-	n := int32(256)
-	gidsC := make([]syscall.Gid_t, n)
-	syscall.Entersyscall()
-	rv := libc_getgrouplist(nameC, userGID, &gidsC[0], &n)
-	syscall.Exitsyscall()
-	if rv == -1 {
-		// More than initial buffer, but now n contains the correct size.
-		const maxGroups = 2048
-		if n > maxGroups {
-			return nil, fmt.Errorf("user: list groups for %s: member of more than %d groups", u.Username, maxGroups)
+	userCommas := []byte("," + u.Username + ",")  // ,john,
+	userFirst := userCommas[1:]                   // john,
+	userLast := userCommas[:len(userCommas)-1]    // ,john
+	userOnly := userCommas[1 : len(userCommas)-1] // john
+
+	// Add primary Gid first.
+	groups := []string{u.Gid}
+
+	rd := bufio.NewReader(r)
+	done := false
+	for !done {
+		line, err := rd.ReadBytes('\n')
+		if err != nil {
+			if err == io.EOF {
+				done = true
+			} else {
+				return groups, err
+			}
+		}
+
+		// Look for username in the list of users. If user is found,
+		// append the GID to the groups slice.
+
+		// There's no spec for /etc/passwd or /etc/group, but we try to follow
+		// the same rules as the glibc parser, which allows comments and blank
+		// space at the beginning of a line.
+		line = bytes.TrimSpace(line)
+		if len(line) == 0 || line[0] == '#' ||
+			// If you search for a gid in a row where the group
+			// name (the first field) starts with "+" or "-",
+			// glibc fails to find the record, and so should we.
+			line[0] == '+' || line[0] == '-' {
+			continue
+		}
+
+		// Format of /etc/group is
+		// 	groupname:password:GID:user_list
+		// for example
+		// 	wheel:x:10:john,paul,jack
+		//	tcpdump:x:72:
+		listIdx := bytes.LastIndexByte(line, ':')
+		if listIdx == -1 || listIdx == len(line)-1 {
+			// No commas, or empty group list.
+			continue
 		}
-		gidsC = make([]syscall.Gid_t, n)
-		syscall.Entersyscall()
-		rv := libc_getgrouplist(nameC, userGID, &gidsC[0], &n)
-		syscall.Exitsyscall()
-		if rv == -1 {
-			return nil, fmt.Errorf("user: list groups for %s failed (changed groups?)", u.Username)
+		if bytes.Count(line[:listIdx], colon) != 2 {
+			// Incorrect number of colons.
+			continue
 		}
+		list := line[listIdx+1:]
+		// Check the list for user without splitting or copying.
+		if !(bytes.Equal(list, userOnly) || bytes.HasPrefix(list, userFirst) || bytes.HasSuffix(list, userLast) || bytes.Contains(list, userCommas)) {
+			continue
+		}
+
+		// groupname:password:GID
+		parts := bytes.Split(line[:listIdx], colon)
+		if len(parts) != 3 || len(parts[0]) == 0 {
+			continue
+		}
+		gid := string(parts[2])
+		// Make sure it's numeric and not the same as primary GID.
+		numGid, err := strconv.Atoi(gid)
+		if err != nil || numGid == primaryGid {
+			continue
+		}
+
+		groups = append(groups, gid)
 	}
-	gidsC = gidsC[:n]
-	gids := make([]string, 0, n)
-	for _, g := range gidsC[:n] {
-		gids = append(gids, strconv.Itoa(int(g)))
+
+	return groups, nil
+}
+
+func listGroups(u *User) ([]string, error) {
+	f, err := os.Open(groupFile)
+	if err != nil {
+		return nil, err
 	}
-	return gids, nil
+	defer f.Close()
+
+	return listGroupsFromReader(u, f)
 }
diff --git a/libgo/go/os/user/listgroups_unix_test.go b/libgo/go/os/user/listgroups_unix_test.go
new file mode 100644
index 00000000000..a9f79ec6bb0
--- /dev/null
+++ b/libgo/go/os/user/listgroups_unix_test.go
@@ -0,0 +1,107 @@
+// 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.
+
+//go:build ((darwin || dragonfly || freebsd || (js && wasm) || (!android && linux) || netbsd || openbsd || solaris) && (!cgo || osusergo)) || aix || illumos
+
+package user
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+	"testing"
+)
+
+var testGroupFile = `# See the opendirectoryd(8) man page for additional
+# information about Open Directory.
+##
+nobody:*:-2:
+nogroup:*:-1:
+wheel:*:0:root
+emptyid:*::root
+invalidgid:*:notanumber:root
++plussign:*:20:root
+-minussign:*:21:root
+# Next line is invalid (empty group name)
+:*:22:root
+      
+daemon:*:1:root
+    indented:*:7:root
+# comment:*:4:found
+     # comment:*:4:found
+kmem:*:2:root
+manymembers:x:777:jill,jody,john,jack,jov,user777
+` + largeGroup()
+
+func largeGroup() (res string) {
+	var b strings.Builder
+	b.WriteString("largegroup:x:1000:user1")
+	for i := 2; i <= 7500; i++ {
+		fmt.Fprintf(&b, ",user%d", i)
+	}
+	return b.String()
+}
+
+var listGroupsTests = []struct {
+	// input
+	in   string
+	user string
+	gid  string
+	// output
+	gids []string
+	err  bool
+}{
+	{in: testGroupFile, user: "root", gid: "0", gids: []string{"0", "1", "2", "7"}},
+	{in: testGroupFile, user: "jill", gid: "33", gids: []string{"33", "777"}},
+	{in: testGroupFile, user: "jody", gid: "34", gids: []string{"34", "777"}},
+	{in: testGroupFile, user: "john", gid: "35", gids: []string{"35", "777"}},
+	{in: testGroupFile, user: "jov", gid: "37", gids: []string{"37", "777"}},
+	{in: testGroupFile, user: "user777", gid: "7", gids: []string{"7", "777", "1000"}},
+	{in: testGroupFile, user: "user1111", gid: "1111", gids: []string{"1111", "1000"}},
+	{in: testGroupFile, user: "user1000", gid: "1000", gids: []string{"1000"}},
+	{in: testGroupFile, user: "user7500", gid: "7500", gids: []string{"1000", "7500"}},
+	{in: testGroupFile, user: "no-such-user", gid: "2345", gids: []string{"2345"}},
+	{in: "", user: "no-such-user", gid: "2345", gids: []string{"2345"}},
+	// Error cases.
+	{in: "", user: "", gid: "2345", err: true},
+	{in: "", user: "joanna", gid: "bad", err: true},
+}
+
+func TestListGroups(t *testing.T) {
+	for _, tc := range listGroupsTests {
+		u := &User{Username: tc.user, Gid: tc.gid}
+		got, err := listGroupsFromReader(u, strings.NewReader(tc.in))
+		if tc.err {
+			if err == nil {
+				t.Errorf("listGroups(%q): got nil; want error", tc.user)
+			}
+			continue // no more checks
+		}
+		if err != nil {
+			t.Errorf("listGroups(%q): got %v error, want nil", tc.user, err)
+			continue // no more checks
+		}
+		checkSameIDs(t, got, tc.gids)
+	}
+}
+
+func checkSameIDs(t *testing.T, got, want []string) {
+	t.Helper()
+	if len(got) != len(want) {
+		t.Errorf("ID list mismatch: got %v; want %v", got, want)
+		return
+	}
+	sort.Strings(got)
+	sort.Strings(want)
+	mismatch := -1
+	for i, g := range want {
+		if got[i] != g {
+			mismatch = i
+			break
+		}
+	}
+	if mismatch != -1 {
+		t.Errorf("ID list mismatch (at index %d): got %v; want %v", mismatch, got, want)
+	}
+}
diff --git a/libgo/go/os/user/lookup_android.go b/libgo/go/os/user/lookup_android.go
index 151aab49c20..0ae31fd8189 100644
--- a/libgo/go/os/user/lookup_android.go
+++ b/libgo/go/os/user/lookup_android.go
@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build android
-// +build android
 
 package user
 
diff --git a/libgo/go/os/user/lookup_plan9.go b/libgo/go/os/user/lookup_plan9.go
index 33ae3a6adf4..07939363e73 100644
--- a/libgo/go/os/user/lookup_plan9.go
+++ b/libgo/go/os/user/lookup_plan9.go
@@ -18,7 +18,9 @@ const (
 )
 
 func init() {
+	userImplemented = false
 	groupImplemented = false
+	groupListImplemented = false
 }
 
 func current() (*User, error) {
diff --git a/libgo/go/os/user/lookup_stubs.go b/libgo/go/os/user/lookup_stubs.go
index c975a11964c..ce1617d2507 100644
--- a/libgo/go/os/user/lookup_stubs.go
+++ b/libgo/go/os/user/lookup_stubs.go
@@ -3,22 +3,16 @@
 // license that can be found in the LICENSE file.
 
 //go:build (!cgo && !windows && !plan9) || android || (osusergo && !windows && !plan9)
-// +build !cgo,!windows,!plan9 android osusergo,!windows,!plan9
 
 package user
 
 import (
-	"errors"
 	"fmt"
 	"os"
 	"runtime"
 	"strconv"
 )
 
-func init() {
-	groupImplemented = false
-}
-
 func current() (*User, error) {
 	uid := currentUID()
 	// $USER and /etc/passwd may disagree; prefer the latter if we can get it.
@@ -64,13 +58,6 @@ func current() (*User, error) {
 	return u, fmt.Errorf("user: Current requires cgo or %s set in environment", missing)
 }
 
-func listGroups(*User) ([]string, error) {
-	if runtime.GOOS == "android" || runtime.GOOS == "aix" {
-		return nil, fmt.Errorf("user: GroupIds not implemented on %s", runtime.GOOS)
-	}
-	return nil, errors.New("user: GroupIds requires cgo")
-}
-
 func currentUID() string {
 	if id := os.Getuid(); id >= 0 {
 		return strconv.Itoa(id)
diff --git a/libgo/go/os/user/lookup_unix.go b/libgo/go/os/user/lookup_unix.go
index 28b96340e15..090fad20e30 100644
--- a/libgo/go/os/user/lookup_unix.go
+++ b/libgo/go/os/user/lookup_unix.go
@@ -3,8 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build (aix || darwin || dragonfly || freebsd || hurd || (js && wasm) || (!android && linux) || netbsd || openbsd || solaris) && (!cgo || osusergo)
-// +build aix darwin dragonfly freebsd hurd js,wasm !android,linux netbsd openbsd solaris
-// +build !cgo osusergo
 
 package user
 
@@ -18,17 +16,10 @@ import (
 	"strings"
 )
 
-const groupFile = "/etc/group"
 const userFile = "/etc/passwd"
 
-var colon = []byte{':'}
-
-func init() {
-	groupImplemented = false
-}
-
 // lineFunc returns a value, an error, or (nil, nil) to skip the row.
-type lineFunc func(line []byte) (v interface{}, err error)
+type lineFunc func(line []byte) (v any, err error)
 
 // readColonFile parses r as an /etc/group or /etc/passwd style file, running
 // fn for each row. readColonFile returns a value, an error, or (nil, nil) if
@@ -36,7 +27,7 @@ type lineFunc func(line []byte) (v interface{}, err error)
 //
 // readCols is the minimum number of colon-separated fields that will be passed
 // to fn; in a long line additional fields may be silently discarded.
-func readColonFile(r io.Reader, fn lineFunc, readCols int) (v interface{}, err error) {
+func readColonFile(r io.Reader, fn lineFunc, readCols int) (v any, err error) {
 	rd := bufio.NewReader(r)
 
 	// Read the file line-by-line.
@@ -107,7 +98,7 @@ func matchGroupIndexValue(value string, idx int) lineFunc {
 		leadColon = ":"
 	}
 	substr := []byte(leadColon + value + ":")
-	return func(line []byte) (v interface{}, err error) {
+	return func(line []byte) (v any, err error) {
 		if !bytes.Contains(line, substr) || bytes.Count(line, colon) < 3 {
 			return
 		}
@@ -154,7 +145,7 @@ func matchUserIndexValue(value string, idx int) lineFunc {
 		leadColon = ":"
 	}
 	substr := []byte(leadColon + value + ":")
-	return func(line []byte) (v interface{}, err error) {
+	return func(line []byte) (v any, err error) {
 		if !bytes.Contains(line, substr) || bytes.Count(line, colon) < 6 {
 			return
 		}
@@ -181,9 +172,7 @@ func matchUserIndexValue(value string, idx int) lineFunc {
 		// say: "It is expected to be a comma separated list of
 		// personal data where the first item is the full name of the
 		// user."
-		if i := strings.Index(u.Name, ","); i >= 0 {
-			u.Name = u.Name[:i]
-		}
+		u.Name, _, _ = strings.Cut(u.Name, ",")
 		return u, nil
 	}
 }
diff --git a/libgo/go/os/user/lookup_unix_test.go b/libgo/go/os/user/lookup_unix_test.go
index 060cfe186f5..77917677fc1 100644
--- a/libgo/go/os/user/lookup_unix_test.go
+++ b/libgo/go/os/user/lookup_unix_test.go
@@ -3,36 +3,15 @@
 // license that can be found in the LICENSE file.
 
 //go:build (aix || darwin || dragonfly || freebsd || (!android && linux) || netbsd || openbsd || solaris) && !cgo
-// +build aix darwin dragonfly freebsd !android,linux netbsd openbsd solaris
-// +build !cgo
 
 package user
 
 import (
-	"fmt"
 	"reflect"
 	"strings"
 	"testing"
 )
 
-var testGroupFile = `# See the opendirectoryd(8) man page for additional 
-# information about Open Directory.
-##
-nobody:*:-2:
-nogroup:*:-1:
-wheel:*:0:root
-emptyid:*::root
-invalidgid:*:notanumber:root
-+plussign:*:20:root
--minussign:*:21:root
-      
-daemon:*:1:root
-    indented:*:7:
-# comment:*:4:found
-     # comment:*:4:found
-kmem:*:2:root
-` + largeGroup()
-
 var groupTests = []struct {
 	in   string
 	name string
@@ -51,19 +30,10 @@ var groupTests = []struct {
 	{testGroupFile, "indented", "7"},
 	{testGroupFile, "# comment", ""},
 	{testGroupFile, "largegroup", "1000"},
+	{testGroupFile, "manymembers", "777"},
 	{"", "emptyfile", ""},
 }
 
-// Generate a proper "largegroup" entry for testGroupFile string
-func largeGroup() (res string) {
-	var b strings.Builder
-	b.WriteString("largegroup:x:1000:user1")
-	for i := 2; i <= 7500; i++ {
-		fmt.Fprintf(&b, ",user%d", i)
-	}
-	return b.String()
-}
-
 func TestFindGroupName(t *testing.T) {
 	for _, tt := range groupTests {
 		got, err := findGroupName(tt.name, strings.NewReader(tt.in))
diff --git a/libgo/go/os/user/user.go b/libgo/go/os/user/user.go
index c1b8101c862..0307d2ad6a1 100644
--- a/libgo/go/os/user/user.go
+++ b/libgo/go/os/user/user.go
@@ -6,11 +6,13 @@
 Package user allows user account lookups by name or id.
 
 For most Unix systems, this package has two internal implementations of
-resolving user and group ids to names. One is written in pure Go and
-parses /etc/passwd and /etc/group. The other is cgo-based and relies on
-the standard C library (libc) routines such as getpwuid_r and getgrnam_r.
+resolving user and group ids to names, and listing supplementary group IDs.
+One is written in pure Go and parses /etc/passwd and /etc/group. The other
+is cgo-based and relies on the standard C library (libc) routines such as
+getpwuid_r, getgrnam_r, and getgrouplist.
 
-When cgo is available, cgo-based (libc-backed) code is used by default.
+When cgo is available, and the required routines are implemented in libc
+for a particular platform, cgo-based (libc-backed) code is used.
 This can be overridden by using osusergo build tag, which enforces
 the pure Go implementation.
 */
@@ -20,9 +22,12 @@ import (
 	"strconv"
 )
 
+// These may be set to false in init() for a particular platform and/or
+// build flags to let the tests know to skip tests of some features.
 var (
-	userImplemented  = true // set to false by lookup_stubs.go's init
-	groupImplemented = true // set to false by lookup_stubs.go's init
+	userImplemented      = true
+	groupImplemented     = true
+	groupListImplemented = true
 )
 
 // User represents a user account.
diff --git a/libgo/go/os/user/user_test.go b/libgo/go/os/user/user_test.go
index 49920317bed..80251749a7d 100644
--- a/libgo/go/os/user/user_test.go
+++ b/libgo/go/os/user/user_test.go
@@ -5,7 +5,6 @@
 package user
 
 import (
-	"runtime"
 	"testing"
 )
 
@@ -56,10 +55,6 @@ func compare(t *testing.T, want, got *User) {
 func TestLookup(t *testing.T) {
 	checkUser(t)
 
-	if runtime.GOOS == "plan9" {
-		t.Skipf("Lookup not implemented on %q", runtime.GOOS)
-	}
-
 	want, err := Current()
 	if err != nil {
 		t.Fatalf("Current: %v", err)
@@ -77,10 +72,6 @@ func TestLookup(t *testing.T) {
 func TestLookupId(t *testing.T) {
 	checkUser(t)
 
-	if runtime.GOOS == "plan9" {
-		t.Skipf("LookupId not implemented on %q", runtime.GOOS)
-	}
-
 	want, err := Current()
 	if err != nil {
 		t.Fatalf("Current: %v", err)
@@ -127,14 +118,15 @@ func TestLookupGroup(t *testing.T) {
 	}
 }
 
-func TestGroupIds(t *testing.T) {
-	checkGroup(t)
-	if runtime.GOOS == "aix" {
-		t.Skip("skipping GroupIds, see golang.org/issue/30563")
-	}
-	if runtime.GOOS == "illumos" {
-		t.Skip("skipping GroupIds, see golang.org/issue/14709")
+func checkGroupList(t *testing.T) {
+	t.Helper()
+	if !groupListImplemented {
+		t.Skip("user: group list not implemented; skipping test")
 	}
+}
+
+func TestGroupIds(t *testing.T) {
+	checkGroupList(t)
 	user, err := Current()
 	if err != nil {
 		t.Fatalf("Current(): %v", err)
diff --git a/libgo/go/os/wait_unimp.go b/libgo/go/os/wait_unimp.go
index 783a66f77e0..b11bbc04c75 100644
--- a/libgo/go/os/wait_unimp.go
+++ b/libgo/go/os/wait_unimp.go
@@ -2,8 +2,11 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build aix || darwin || hurd || (js && wasm) || openbsd || solaris
-// +build aix darwin hurd js,wasm openbsd solaris
+// aix, darwin, js/wasm, openbsd and solaris don't implement
+// waitid/wait6. netbsd implements wait6, but that is causing test
+// failures, see issue #48789.
+
+//go:build aix || darwin || hurd || (js && wasm) || netbsd || openbsd || solaris
 
 package os
 
@@ -11,7 +14,9 @@ package os
 // succeed immediately, and reports whether it has done so.
 // It does not actually call p.Wait.
 // This version is used on systems that do not implement waitid,
-// or where we have not implemented it yet.
+// or where we have not implemented it yet. Note that this is racy:
+// a call to Process.Signal can in an extremely unlikely case send a
+// signal to the wrong process, see issue #13987.
 func (p *Process) blockUntilWaitable() (bool, error) {
 	return false, nil
 }
diff --git a/libgo/go/os/wait_wait6.go b/libgo/go/os/wait_wait6.go
index 45b370a802e..d395dac40b4 100644
--- a/libgo/go/os/wait_wait6.go
+++ b/libgo/go/os/wait_wait6.go
@@ -2,8 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build dragonfly || freebsd || netbsd
-// +build dragonfly freebsd netbsd
+//go:build dragonfly || freebsd
 
 package os
 
diff --git a/libgo/go/os/wait_waitid.go b/libgo/go/os/wait_waitid.go
index d7c97518b7a..31f4e77d38c 100644
--- a/libgo/go/os/wait_waitid.go
+++ b/libgo/go/os/wait_waitid.go
@@ -6,7 +6,6 @@
 // waitid returns if the process is stopped, even when using WEXITED.
 
 //go:build linux
-// +build linux
 
 package os