Abstract Contract Synthesis and Verification in the Symbolic 𝕂 Framework

In this article, we propose a symbolic technique that can be used for automatically inferring software contracts from programs that are written in a non-trivial fragment of C, called KERNELC, that supports pointer-based structures and heap manipulation. Starting from the semantic definition of KERNELC in the 𝕂 semantic framework, we enrich the symbolic execution facilities recently provided by 𝕂 with novel capabilities for contract synthesis that are based on abstract subsumption. Roughly speaking, we define an abstract symbolic technique that axiomatically explains the execution of any (modifier) C function by using other (observer) routines in the same program. We implemented our technique in the automated tool KINDSPEC 2.1, which generates logical axioms that express pre- and post-condition assertions which define the precise input/output behavior of the C routines. Thanks to the integrated support for symbolic execution and deductive verification provided by 𝕂, some synthesized axioms that cannot be guaranteed to be correct by construction due to abstraction can finally be verified in our setting with little effort.

24. Contractual liability for defective software

This chapter begins with a discussion of the nature of software defects. It then covers the legal status of software and software contracts; implied terms in software contracts; remedies for breach of the implied terms; the approach adopted by the courts in the limited number of cases which have reached the High Court or Court of Appeal; exclusion or limitation of liability; and the enforceability of shrink-wrap licences.