Model-checking software library API usage rules

Modern software increasingly relies on using libraries which are accessed via Application Programming Interfaces (APIs). Libraries usually impose constraints on how API functions can be used (API usage rules) and programmers have to obey these API usage rules. However, API usage rules often are not well-documented or documented informally. In this work, we show how to use the SCTPL logic to precisely specify API usage rules in libraries, where SCTPL can be seen as an extension of the branching-time temporal logic CTL with variables, quantifiers, and predicates over the stack. This allows library providers to formally describe API usage rules without knowing how their libraries will be used by programmers. We also propose an approach to automatically check whether programs using libraries violate or not the corresponding API usage rules. Our approach consists in modeling programs as pushdown systems (PDSs), and checking API usage rules on programs using SCTPL model checking for PDSs. To make the model-checking procedure more efficient, we propose an abstraction that reduces drastically the size of the program model. Moreover, we characterize a sub-logic rSCTPL of SCTPL preserved by the abstraction. rSCTPL is sufficient to precisely specify all the API usage rules we met. We implemented our techniques in a tool and applied it to check several API usage rules. Our tool detected several previously unknown errors in well-known programs, such as Nssl, Verbs, Acacia+, Walksat and Getafix. Our experimental results are encouraging.