During the last decade, static analyzers of source code have improved greatly. Today, precise analyzers that propagate values for the program's variables, for instance with interval arithmetic, are used in the industry. The simultaneous propagation of sets of values, while computationally efficient, is a source of approximations, and ultimately of false positives. When the loss of precision is detrimental to the user's goals, a user needs to provide some kind of manual guidance. Frama-C, a framework for the static analysis of C programs, provides a sound value analyzer. This analyzer can optionally be guided by skillfully placed user annotations. This article describes SPALTER, a Frama-C plug-in that uses a variation of the Skelboe-Moore algorithm from the field of interval arithmetic to guide Frama-C's value analyzer towards a high-level objective set by the user. SPALTER reproduces the results of a case study that used Frama-C's value analysis and required extensive manual guidance. In difference, our approach with SPALTER required no guidance, except preparation of the analyzed program by slicing.

To report a compiler bug, one must often find a small test case that triggers the bug. The existing approach to automated test-case reduction, delta debugging, works by removing substrings of the original input; the result is a concatenation of substrings that delta cannot remove. We have found this approach less than ideal for reducing C programs because it typically yields test cases that are too large or even invalid (relying on undefined behavior). To obtain small and valid test cases consistently, we designed and implemented three new, domain-specific test-case reducers. The best of these is based on a novel framework in which a generic fixpoint computation invokes modular transformations that perform reduction operations. This reducer produces outputs that are, on average, more than 25 times smaller than those produced by our other reducers or by the existing reducer that is most commonly used by compiler developers. We conclude that effective program reduction requires more than straightforward delta debugging.

This experience report describes the choice of OCaml as the implementation language for Frama-C, a framework for the static analysis of C programs. OCaml became the implementation language for Frama-C because it is expressive. Most of the reasons listed in the remaining of this article are secondary reasons, features which are not specific to OCaml (modularity, availability of a C parser, control over the use of resources...) but could have prevented the use of OCaml for this project if they had been missing.

We demonstrate the value analysis of Frama-C. Frama-C is an Open Source static analysis framework for the C language. In Frama-C, each static analysis technique, approach or idea can be implemented as a new plug-in, with the opportunity to obtain information from other plug-ins, and to leave the verification of difficult properties to yet other plug-ins. The new analysis may in turn provide access to the data it has computed. The value analysis of Frama-C is a plug-in based on abstract interpretation. It computes and stores supersets of possible values for all the variables at each statement of the analyzed program. It handles pointers, arrays, structs, and heterogeneous pointer casts. Besides producing supersets of possible values for the variables at each point of the execution, the value analysis produces run-time-error alarms. An alarm is emitted for each operation in the analyzed program where the value analysis cannot guarantee that there will not be a run-time error.