def function(self, addr=None, name=None, create=False, syscall=False, plt=None):
        """
        Get a function object from the function manager.

        Pass either `addr` or `name` with the appropriate values.

        :param int addr: Address of the function.
        :param str name: Name of the function.
        :param bool create: Whether to create the function or not if the function does not exist.
        :param bool syscall: True to create the function as a syscall, False otherwise.
        :param bool or None plt: True to find the PLT stub, False to find a non-PLT stub, None to disable this
                                 restriction.
        :return: The Function instance, or None if the function is not found and create is False.
        :rtype: Function or None
        """
        if addr is not None:
            try:
                f = self._function_map.get(addr)
                if plt is None or f.is_plt == plt:
                    return f
            except KeyError:
                if create:
                    # the function is not found
                    f = self._function_map[addr]
                    if name is not None:
                        f.name = name
                    if syscall:
                        f.is_syscall=True
                    return f
        elif name is not None:
            for func in self._function_map.values():
                if func.name == name:
                    if plt is None or func.is_plt == plt:
                        return func

        return None