if pidfd == -1 {
		t.Skip("pidfd not supported")
	}
	defer syscall.Close(pidfd)

	// Use pidfd to send a signal to the child.
	sig := syscall.SIGINT
	if err := unix.PidFDSendSignal(uintptr(pidfd), sig); err != nil {
		if err != syscall.EINVAL && testenv.SyscallIsNotSupported(err) {
			t.Skip("pidfd_send_signal syscall not supported:", err)
		}
		t.Fatal("pidfd_send_signal syscall failed:", err)