os/signal: avoid calling ioctl via syscall.Syscall on BSDs

Provide appropriate implementations of internal/syscall/unix.Tcsetpgrp
and use this for runSessionLeader in os/signal/signal_cgo_test.go.
This avoids calling syscall.Syscall with SYS_IOCTL on BSDs.

Updates #59667
Updates #63900

Change-Id: Ifa4696bba9f1eb68e81e7103f030bc254adaf0af
Reviewed-on: https://go-review.googlesource.com/c/go/+/540020
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Joel Sing <joel@sing.id.au>

src/internal/syscall/unix/tcsetpgrp_bsd.go

@@ -0,0 +1,22 @@
+// Copyright 2024 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 || netbsd || openbsd
+
+package unix
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+//go:linkname ioctlPtr syscall.ioctlPtr
+func ioctlPtr(fd int, req uint, arg unsafe.Pointer) (err error)
+
+// Note that pgid should really be pid_t, however _C_int (aka int32) is
+// generally equivalent.
+
+func Tcsetpgrp(fd int, pgid int32) (err error) {
+	return ioctlPtr(fd, syscall.TIOCSPGRP, unsafe.Pointer(&pgid))
+}

src/internal/syscall/unix/tcsetpgrp_linux.go

@@ -0,0 +1,21 @@
+// Copyright 2024 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 unix
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+// Note that pgid should really be pid_t, however _C_int (aka int32) is
+// generally equivalent.
+
+func Tcsetpgrp(fd int, pgid int32) (err error) {
+	_, _, errno := syscall.Syscall6(syscall.SYS_IOCTL, uintptr(fd), uintptr(syscall.TIOCSPGRP), uintptr(unsafe.Pointer(&pgid)), 0, 0, 0)
+	if errno != 0 {
+		return errno
+	}
+	return nil
+}

src/os/signal/signal_cgo_test.go

@@ -14,6 +14,7 @@ import (
 	"context"
 	"encoding/binary"
 	"fmt"
+	"internal/syscall/unix"
 	"internal/testenv"
 	"internal/testpty"
 	"os"
@@ -23,7 +24,6 @@ import (
 	"syscall"
 	"testing"
 	"time"
-	"unsafe"
 )
 
 const (
@@ -304,9 +304,8 @@ func runSessionLeader(t *testing.T, pause time.Duration) {
 
 		// Take TTY.
 		pgrp := int32(syscall.Getpgrp()) // assume that pid_t is int32
-		_, _, errno := syscall.Syscall(syscall.SYS_IOCTL, ptyFD, syscall.TIOCSPGRP, uintptr(unsafe.Pointer(&pgrp)))
-		if errno != 0 {
-			return fmt.Errorf("error setting tty process group: %w", errno)
+		if err := unix.Tcsetpgrp(ptyFD, pgrp); err != nil {
+			return fmt.Errorf("error setting tty process group: %w", err)
 		}
 
 		// Give the kernel time to potentially wake readers and have
@@ -315,9 +314,8 @@ func runSessionLeader(t *testing.T, pause time.Duration) {
 
 		// Give TTY back.
 		pid := int32(cmd.Process.Pid) // assume that pid_t is int32
-		_, _, errno = syscall.Syscall(syscall.SYS_IOCTL, ptyFD, syscall.TIOCSPGRP, uintptr(unsafe.Pointer(&pid)))
-		if errno != 0 {
-			return fmt.Errorf("error setting tty process group back: %w", errno)
+		if err := unix.Tcsetpgrp(ptyFD, pid); err != nil {
+			return fmt.Errorf("error setting tty process group back: %w", err)
 		}
 
 		// Report that we are done and SIGCONT can be sent. Note that