Program Checking with Less Hassle

The simple and often imprecise specifications that programmers may write are a significant limit to a wider application of rigorous program verification techniques. Part of the reason why non-specialists find writing good specification hard is that, when verification fails, they receive little guidance as to what the causes might be, such as implementation errors or inaccurate specifications. To address these limitations, this paper presents

two-step verification

, a technique that combines implicit specifications, inlining, and loop unrolling to provide improved user feedback when verification fails. Two-step verification performs two independent verification attempts for each program element: one using standard modular reasoning, and another one after inlining and unrolling; comparing the outcomes of the two steps suggests which elements should be improved. Two-step verification is implemented in AutoProof, our static verifier for Eiffel programs integrated in EVE (the Eiffel Verification Environment) and available online.