Assembler restructuring in FermaT

The FermaT transformation system has proved to be a very successful tool for migrating from assembler to high level languages, including C and COBOL. One of the more challenging aspects facing automated migration, specifically when the aim is to produce maintainable code from unstructured “spaghetti” code, is to restructure assembler subroutines into semantically equivalent high level language procedures. In this paper we describe some of the many varieties of assembler subroutine structures and the techniques used by the migration engine to transform these into structured code. These transformations require a deep analysis of both control flow and data flow in order to guarantee the correctness of the result. Two separate case studies, involving over 10,000 assembler modules from commercial systems, demonstrate that these techniques are able to restructure over 99% of hand-written assembler, with no human intervention required.