Reasoning about program control-flow paths is an important functionality of a number of recent program matching languages and associated searching and transformation tools. Temporal logic provides a well-defined means of expressing properties of control-flow paths in programs, and indeed an extension of the temporal logic CTL has been applied to the problem of specifying and verifying the transformations commonly performed by optimizing compilers. Nevertheless, in developing the Coccinelle program transformation tool for performing Linux collateral evolutions in systems code, we have found that existing variants of CTL do not adequately support rules that transform subterms other than the ones matching an entire formula.
Being able to transform any of the subterms of a matched term seems essential in the domain targeted by Coccinelle. In this work, we propose an extension to CTL named CTL-VW (CTL with variables and witnesses) that is a suitable basis for the semantics and implementation of the Coccinelle's program matching language. Our extension to CTL includes existential quantification over program fragments, which allows metavariables in the program matching language to range over different values within different control-flow paths, and a notion of witnesses that record such existential bindings for use in the subsequent program transformation process. We formalize CTL-VW and describe its use in the context of Coccinelle. We then assess the performance of the approach in practice, using a transformation rule that fixes several reference count bugs in Linux code.
About the Speaker
Julia Lawall is a Lektor (Associate Professor) at the University of Copenhagen. Her interests are primarily in the area of programming languages and operating systems, in particular in applying programming language techniques to improve the robustness and extensibility of
operating systems code. She has in particular worked on domain specific languages for ubiquitous computing, process scheduling, network protocol parsing, and network gateway construction. Her work on Coccinelle is supported by the Danish Council for Independent Research | Technology and Production Sciences. She is currently an INRIA visiting professor in the Regal Group.
Talk
December 10, 2009 - 13:30 - Ada Lovelace, INRIA Bordeaux A29
