Martin P. Ward

Assembler to C migration using the FermaT transformation system

The FermaT transformation system, based on research carried out over the last twelve years (1987-99) at Durham University and Software Migrations Ltd., is an industrial-strength formal transformation engine with many applications in program comprehension and language migration. The paper describes one application of the system: the migration of IBM 370 Assembler code to equivalent, maintainable C code. We present an example of using the tool to migrate a small, but complex, assembler module to C with no manual intervention required. We briefly discuss a mass migration exercise where 1925 assembler modules were successfully migrated to C code.

Abstracting a specification from code

Much of the work on developing program transformation systems has concentrated on systems to assist in program development. However, the four separate surveys carried out between 1977 and 1990 (Foster and Kiekuth, 1990; Lientz and Swanson, 1980; Morton, 1988; Nosek and Palvia, 1990), summarized in Foster (1991), show that between 40% and 60% of all commercial software effort is devoted to software maintenance rather than the development of new systems. In this paper we describe a joint project between the University of Durham and CSM Ltd to develop a method and tool for reverse-engineering and software maintenance based on program transformation theory. We present an example which illustrates how such a tool can extract a high-level abstract specification from the low-level source code of a program by a process of formal program transformation based on a theory of program equivalence (Ward, 1989a). All the code-level reverse-engineering of the example program was carried out on the prototype tool with the resulting code pasted directly into the paper.

Slicing as a program transformation

The aim of this article is to provide a unified mathematical framework for program slicing which places all slicing work for sequential programs on a sound theoretical foundation. The main advantage to a mathematical approach is that it is not tied to a particular representation. In fact the mathematics provides a sound basis for any particular representation. We use the WSL (wide-spectrum language) program transformation theory as our framework. Within this framework we define a new semantic relation, semirefinement, which lies between semantic equivalence and semantic refinement. Combining this semantic relation, a syntactic relation (called reduction), and WSLs remove statement, we can give mathematical definitions for backwards slicing, conditioned slicing, static and dynamic slicing, and semantic slicing as program transformations in the WSL transformation theory. A novel technique of “encoding” operational semantics within a denotational semantics allows the framework to handle “operational slicing”. The theory also enables the concept of slicing to be applied to nondeterministic programs. These transformations are implemented in the industry-strength FermaT transformation system.

Formal methods for legacy systems

A method is described for obtaining useful information from legacy code. The approach uses formal proven program transformations, which preserve or refine the semantics of a construct while changing its form. The applicability of a transformation in a particular syntactic context is checked before application. By using an appropriate sequence of transformations, the extracted representation is guaranteed to be equivalent to the code. In this paper, we focus on the results of using this approach in the reverse-engineering of medium-scale, industrial software, written mostly in languages such as assembler and JOVIAL. Results from both benchmark algorithms and heavily modified, geriatric software are summarized. It is concluded that the approach is viable, for self-contained code, and that useful design information may be extracted from legacy systems at economic cost. We conclude that formal methods have an important practical role in the reverse-engineering process.

A practical program transformation system for reverse engineering

Program transformation systems provide one means of formally deriving a program from its specification. A tool called ReForm is described. It is designed to address the inverse problem to support the extraction of a specification from existing program code, using transformations. This is an important activity during software maintenance. One of the problems of transformation systems is the scarcity of practical tools which can address industrial scale problems, rather than contrived laboratory problems. An analysis of the important software engineering factors that contribute to a successful transformation based tool is provided. Results from using the tool are also presented.<<ETX>>

Formal methods to aid the evolution of software.

There is a vast collection of operational software systems which are vitally important to their users, yet are becoming increasingly difficult to maintain, enhance, and keep up to date with rapidly changing requirements. For many of these so-called legacy systems, the option of throwing the system away and rewriting it from scratch is not economically viable. Methods are therefore urgently required which enable these systems to evolve in a controlled manner. The approach described in this paper uses formal proven program transformations, which preserve or refine the semantics of a program while changing its form. These transformations are applied to restructure and simplify the legacy systems and to extract higher-level representations. By using an appropriate sequence of transformations, the extracted representation is guaranteed to be equivalent to the code. The method is based on a formal wide spectrum language, called WSL, with an accompanying formal method. Over the last ten years we have developed a large catalog of proven transformations, together with mechanically verifiable applicability conditions. These have been applied to many software development, reverse engineering, and maintenance problems. In this paper, we focus on the results of using this approach in the reverse engineering of medium scale, industrial software, written mostly in languages such as assembler and JOVIAL. Results from both benchmark algorithms and heavily modified, geriatric software are summarized. We conclude that formal methods have an important practical role in software evolution.

A multipurpose backtracking algorithm

Abstract A backtracking algorithm with element order selection is presented, and its efficiency discussed in relation both to standard examples and to examples concerning relation-preserving maps which the algorithm was derived to solve.

Reverse Engineering through Formal Transformation: Knuth's ‘Polynomial Addition’ Algorithm

In this paper we will take a detailed look at a larger example of program analysis by transformation. We will be considering Algorithm 2.3.3.A from Knuths «Fundamental Algorithms» Knuth (1968) (p. 357) which is an algorithm for the addition of polynomials represented using four-directional links. Knuth (1974) describes this as having «a complicated structure with excessively unrestrained goto statements» and goes on to say «I hope someday to see the algorithm cleaned up without loss of its efficiency». Our aim is to manipulate the program, using semantics-preserving operations, into an equivalent, high-level specification. The transformations are carried out in the WSL language, a «wide spectrum language» which includes both low-level program operations and high level specifications, and which has been specifically designed to be easy to transform

Reverse engineering from assembler to formal specifications via program transformations

The FermaT transformation system, based on research carried out over the last sixteen years at Durham University, De Montfort University and Software, Migrations Ltd., is an industrial-strength formal transformation engine with many applications in program comprehension and language migration. This paper is a case study which uses automated plus manually-directed transformations and abstractions to convert an IBM 370 assembler code program into a very high-level abstract specification.

The FermaT assembler re-engineering workbench

Research into the working practices of software engineers has shown the need for integrated browsing and searching tools which include graphical visualisations linked back to the source code under investigation. In addition, for assembler maintenance and re-engineering there is an even greater need for sophisticated control flow analysis, data flow analysis, slicing and migration technology. All these technologies are provided by the FermaT Workbench: an industrial-strength assembler re-engineering workbench consisting of a number of integrated tools for program comprehension, migration and re-engineering. The various program analysis and migrations tools are based on research carried out over the last sixteen years at Durham University, De Montfort University and Software Migrations Ltd., and make extensive use of program transformation theory.