Constraint-Based BMC: A Backjumping Strategy

Safety property checking is mandatory in the validation process of critical software. When formal verification tools fail to prove some properties, the automatic generation of counterexamples for a given loop depth is an important issue in practice. We investigate in this paper the capabilities of constraint-based bounded model checking for program verification and counterexample generation on real applications. We introduce DPVS (Dynamic Post-condition Variable driven Strategy), a new backjumping strategy we developed to handle an industrial application from a car manufacturer, the Flasher Manager. This backjumping strategy is used to search a faulty path and to collect the constraints of such a path. The simplified control flow graph (CFG) of the program is explored in a backward way, starting from the post-condition and jumping to the most promising node where the variables of the post-condition are defined. In other words, the constraints are collected by exploring the CFG in a dynamic and non-sequential backward way. The Flasher Manager application has been designed and simulated using the Simulink platform. However, this module is concretely embedded as a C program in a car computer, thus we have to check that the safety properties are preserved on this C code. We report experiments on the Flasher Manager with our constraint-based bounded model checker, and with CBMC, a state-of-the-art bounded model checker. Experiments show that DPVS and CBMC have similar performances on one property of the Flasher Manager; DPVS outperforms CBMC to find a counterexample for two properties; two of the properties of the Flasher Manager remain intractable for CBMC and DPVS