Returns a concrete state of the flag indicating whether the previous chunk is free or not. Issues a warning if
        that flag is symbolic and has multiple solutions, and then assumes that the previous chunk is free.

        :returns: True if the previous chunk is free; False otherwise

def is_prev_free(self):
        """
        Returns a concrete state of the flag indicating whether the previous chunk is free or not. Issues a warning if
        that flag is symbolic and has multiple solutions, and then assumes that the previous chunk is free.

        :returns: True if the previous chunk is free; False otherwise
        """
        flag = self.state.memory.load(self.base + self._chunk_size_t_size, self._chunk_size_t_size) & CHUNK_P_MASK

        def sym_flag_handler(flag):
            l.warning("A chunk's P flag is symbolic; assuming it is not set")
            return self.state.solver.min_int(flag)

        flag = concretize(flag, self.state.solver, sym_flag_handler)
        return False if flag else True