code: def _find_return_target(self, target):
          
  
          for i, frame in enumerate(self):
              if frame.ret_addr == target:
                  return i
          return None
docs: Check if the return target exists in the stack, and return the index if exists. We always search from the most
          recent call stack frame since the most recent frame has a higher chance to be hit in normal CFG recovery.
  
          :param int target: Target of the return.
          :return: The index of the object
          :rtype: int