Verifying concurrent programs by memory unwinding

We describe a new sequentialization-based approach to the symbolic verification of multi-threaded programs with shared memory and dynamic thread creation. Its main novelty is the idea of memory unwinding, i.e., an explicit representation of the sequence of write operations into the shared memory. For the verification, we nondeterministically guess this unwinding and then simulate the behavior of the program according to any scheduling that respects this guess. 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 code-to-code transformation from multi-threaded into nondeterministic sequential programs, which allows the reuse of sequential verification tools. Experiments show that our approach is very promising: it found all errors in the concurrency category of SV-COMP15