Procedural abstraction reduces code size by replacing repeated code fragments with call instructions to a subroutine that executes the repeated fragment. However, in order to build a subroutine, extra instructions are necessary to support the procedural call mechanism. In this paper, we present an operating system level technique which improves the space efficiency of a procedural abstraction- based code compaction technique. The callrelated extra instructions are not used in the proposed technique because operating system routines implicitly supports the procedure call and return. The proposed technique consists of three execution modes including one applicable to ROM-based systems. The experimental results show the proposed technique reduces the code size significantly while increasing the execution time slightly.