docs: def _function_add_return_site(self, addr, function_addr):
          """
          Generate CodeNodes for target address, registers node for function to
          function manager as return site
  
          :param int addr: target address
          :param int function_addr: address of function
          :return: None
          """
          try:
              target = self._to_snippet(self._nodes[addr])
          except KeyError:
              target = addr
  
          self.kb.functions._add_return_from(function_addr, target)