Flowback analysis is a powerful technique for debugging programs. It allows the programmer to examine dynamic dependences in a program's execution history without having to re-execute the program. The goal is to present to the programmer a graphical view of the dynamic program dependences. We are building a system, called PPD, that performs flowback analysis while keeping the execution time overhead low. We also extend the semantics of flowback analysis to parallel programs. This paper describes details of the graphs and algorithms needed to implement efficient flowback analysis for parallel programs. Execution time overhead is kept low by recording only a small amount of trace during a program's execution. We use semantic analysis and a technique called incremental tracing to keep the time and space overhead low. As part of the semantic analysis, PPD uses a static program dependence graph structure that reduces the amount of work done at compile time and takes advantage of the dynamic...

We give a formal definition of the notion of information flow for a simple guarded command language. We propose an axiomatisation of security properties based on this notion of information flow and we prove its soundness with respect to the operational semantics of the language. We then identify the sources of non determinism in proofs and we derive in successive steps an inference algorithm which is both sound and complete with respect to the inference system. Keywords: formal verification, program analysis, verification tools, computer security, information flow. 1 Introduction The context of the work described in this paper is the application of formal methods to the verification of information flow properties in programs. In contrast with most previous contributions in this area we put emphasis on the design of mechanical tools. Rather than considering a general (and undecidable) logic in which the development of proofs requires some interaction with the user, we start with a rest...

The Parallel Program Debugger (PPD) allows a programmer to find bugs by following dynamic dependences in a program's execution; this technique is called flowback analysis. Flowback analysis requires the tracing of all variable references and modifications. PPD avoids the overhead of this tracing by recording only a subset of the program's state during execution, and incrementally filling in the missing details when the programmer makes queries about execution dependences. There is a trade-off between overhead of the tracing during program execution and the speed of generating the missing details during user queries. Our compiler is divided into four phases. This separation of phases allows us to first compile separate files, and to generate code for these files. Second, we perform interprocedural analysis using the data structures generated by the first phase. Third, we modify the individual assembly files to account for optimizations to the tracing, and to generate tracing for shared ...

: We give a formal definition of the notion of information flow for a simple guarded command language. We propose an axiomatisation of security properties based on this notion of information flow and we prove its soundness with respect to the operational semantics of the language. We then identify the sources of non determinism in proofs and we derive in successive steps an inference algorithm which is both sound and complete with respect to the inference system. The complexity of the resulting algorithm is linear in terms of the size of the program and the analysis can realistically be integrated within a compiler. Thus, the contribution of the paper is the derivation of a formally based and effective tool for checking security properties of sequential programs. Key-words: formal verification, program analysis, verification tools, computer security, information flow. (R'esum'e : tsvp) email :jpbanatre, bryce, lemetayer@irisa.fr Centre National de la Recherche Scientifique Institut ...

1.77> N \Gamma fn 0 g D(n) = fng S " p2pred(n) D(p) Computing idom ffl invert dom to get idom ffl simple; requires some bookkeeping Aho, Sethi, and Ullman -- Algorithm 10.16 Comp 512, Spring 1998 Lecture 15, Dominance frontiers Definition The dominance frontier of x is the set of nodes y where x dominates a predecessor of y but does not strictly dominate y df(x) = fy j 9 p 2 pred(y); xAEp and x 6 AEyg Computing df