Tim Teitelbaum

The Cornell program synthesizer: a syntax-directed programming environment

Programs are not text; they are hierarchical compositions of computational structures and should be edited, executed, and debugged in an environment that consistently acknowledges and reinforces this viewpoint. The Cornell Program Synthesizer demands a structural perspective at all stages of program development. Its separate features are unified by a common foundation: a grammar for the programming language. Its full-screen derivation-tree editor and syntax-directed diagnostic interpreter combine to make the Synthesizer a powerful and responsive interactive programming tool.

The synthesizer generator

Programs are hierarchical compositions of formulae satisfying structural and extra-structural relationships. A program editor can use knowledge of such relationships to detect and provide immediate feedback about violations of them. The Synthesizer Generator is a tool for creating such editors from language descriptions. An editor designer specifies the desired relationships and the feedback to be given when they are violated, as well as a user interface; from the specification, the Synthesizer Generator creates a full-screen editor for manipulating programs in the language.

Incremental Context-Dependent Analysis for Language-Based Editors

Knowledge of a programming languages grammar allows language-based editors to enforce syntactic correctness at all times during development by restricting editing operations to legitimate modifications ot ~ the programs context-free derivation tree; however, not all language constraints can be enforced in this way because not all features can be described by the context-free formalism. Attribute grammars permit context-dependent language features to be expressed in a modular, declarative fashion and thus are a good basis for specifying language-based editors. Such editors represent programs as attributed trees, Which are modified by operations such as subtree pruning and grafting. Incremental analysis is performed by updating attribute values after every modification. This paper discusses how updating can be carried out and presents several algorithms for the task, including one that is asymptotically optimal in time.

WYSINWYX: What You See Is Not What You eXecute

What You See Is Not What You eXecute: computers do not execute source-code programs; they execute machine-code programs that are generated from source code. Not only can the WYSINWYX phenomenon create a mismatch between what a programmer intends and what is actually executed by the processor, it can cause analyses that are performed on source code to fail to detect certain bugs and vulnerabilities. This issue arises regardless of whether ones favorite approach to assuring that programs behave as desired is based on theorem proving, model checking, or abstract interpretation.

Incremental evaluation for attribute grammars with application to syntax-directed editors

A syntax-directed editor is a tool for structured program development. Such an editor can enforce syntactic correctness incrementally by restricting editing operations to legitimate modifications of the programs context-free derivation tree. However, not all language features can be described by the context-free formalism. To build editors that enforce non-context-free correctness, a more powerful specification technique is needed. In this paper we discuss the advantages of attribute grammars as a specification technique for a syntax-directed editing system. We also present an efficient algorithm for incrementally evaluating attributes as a program tree is derived.

CodeSurfer/x86—A platform for analyzing x86 executables

CodeSurfer/x86 is a prototype system for analyzing x86 executables. It uses a static-analysis algorithm called value-set analysis (VSA) to recover intermediate representations that are similar to those that a compiler creates for a program written in a high-level language. A major challenge in building an analysis tool for executables is in providing useful information about operations involving memory. This is difficult when symbol-table and debugging information is absent or untrusted. CodeSurfer/x86 overcomes these challenges to provide an analyst with a powerful and flexible platform for investigating the properties and behaviors of potentially malicious code (such as COTS components, plugins, mobile code, worms, Trojans, and virus-infected code) using (i) CodeSurfer/x86s GUI, (ii) CodeSurfer/x86s scripting language, which provides access to all of the intermediate representations that CodeSurfer/x86 builds for the executable, and (iii) GrammaTechs Path Inspector, which is a tool that uses a sophisticated pattern-matching engine to answer questions about the flow of execution in a program.

Generating editing environments based on relations and attributes

The ability to generate language-based editors depends on the existence of a powerful, language-independent model of editing. A model is proposed in which programs are represented as attributed abstract-syntax trees with an associated relational database. Relations can depend on the state of the attributed tree, and attributes can depend on the values in relations, provided there are no circular dependencies. The power and the limitations of relational operations are demonstrated with respect to the support of static-semantic checking, anomaly detection, an interrogation facility, and the ability to define alternative program displays. The advantages of the hybrid system over both the purely relational and purely attribute-based systems are presented, and new algorithms are given for query evaluation and incremental view updating motivated by the efficiency requirements of interactive editing under the defined model. A prototype implementation of an editor generator is described, and suggestions for future research are made.

Static caching for incremental computation

A systematic approach is given for deriving incremental programs that exploit caching. The cache-and-prune method presented in the article consists of three stages: (I) the original program is extended to cache the results of all its intermediate subcomputations as well as the final result, (II)) the extended program is incrementalized so that computation on a new input can use all intermediate results on an old input, and (III) unused results cached by the extended program and maintained by the incremental program are pruned away, leaving a pruned extended program that caches only useful intermediate results and a pruned incremental program that uses and maintains only useful results. All three stages utilize static analyses and semantics-preserving transformations. Stages I and III are simple, clean, and fully automatable. The overall method has a kind of optimality with respect to the techniques used in Stage II. The method can be applied straightfowardly to provide a systematic approach to program improvement via caching.

Program Slicing of Hardware Description Languages

Hardware description languages (HDLs) are used today to describe circuits at all levels. In large HDL programs, there is a need for source code reduction techniques to address a myriad of problems in formal verification, design, simulation, and testing. Program slicing is a static program analysis technique that allows an analyst to automatically extract portions of programs relevant to the aspects being analyzed. We extend program slicing to HDLs, thus allowing for automatic program reduction to allow the user to focus on relevant code portions. We have implemented a VHDL slicing tool composed of a general inter-procedural slicer and a front-end that captures VHDL execution semantics. This paper provides an overview of program slicing, a discussion of how to slice VHDL programs, a description of the resulting tool, and a brief overview of some applications and experimental results.

Design and implementation of a fine-grained software inspection tool

Although software inspection has led to improvements in software quality, many software systems continue to be deployed with unacceptable numbers of errors, even when software inspection is part of the development process. The difficulty of manually verifying that the software under inspection conforms to the rules is partly to blame. We describe the design and implementation of a tool designed to help alleviate this problem. The tool provides mechanisms for fine-grained inspection of software by exposing the results of sophisticated whole-program static analysis to the inspector. The tool computes many static-semantic representations of the program, including an accurate call graph and dependence graph. A whole-program pointer analysis is used to make sure that the representation is precise with respect to aliases induced by pointer usage. Views on the dependence graph and related representations are supported. Queries on the dependence graph allow an inspector to answer detailed questions about the semantics of the program. Facilities for openness and extensibility permit the tool to be integrated with many software development processes. The main challenge of the approach is to provide facilities to navigate and manage the enormous complexity of the dependence graph.