code: def sys_munmap(self, addr, size):
          
          self.current.memory.munmap(addr, size)
          return 0
docs: Unmaps a file from memory. It deletes the mappings for the specified address range
          :rtype: int
  
          :param addr: the starting address to unmap.
          :param size: the size of the portion to unmap.
          :return: C{0} on success.