Verifying Concurrent Programs by Memory Unwinding

We describe a new sequentialization-based approach to the symbolic verification of multithreaded programs with shared memory and dynamic thread creation. Its main novelty is the idea of memory unwinding (MU), i.e., a sequence of write operations into the shared memory. For the verification, we nondeterministically guess an MU and then simulate the behavior of the program according to any scheduling that respects it. This approach is complementary to other sequentializations and explores an orthogonal dimension, i.e., the number of write operations. It also simplifies the implementation of several important optimizations, in particular the targeted exposure of individual writes. We implemented this approach as a code-to-code transformation from multithreaded into nondeterministic sequential programs, which allows the reuse of sequential verification tools. Experiments show that our approach is e↵ective: it found all errors in the concurrency category of SV-COMP15.