Abstract. Bounded model checking (BMC) has successfully been used for many practical program verification problems, but concurrency still poses a challenge. Here we describe a new approach to BMC of sequentially consistent C programs using POSIX threads. Our approach first translates a multi-threaded C program into a nondeterministic sequential C program that preserves reachability for all round-robin schedules with a given bound on the number of rounds. It then re-uses existing high-performance BMC tools as backends for the sequential verification problem. Our translation is carefully designed to introduce very small memory overheads and very few sources of nondeterminism, so that it produces tight SAT/SMT formulae, and is thus very effective in practice: our prototype won the concurrency category of SV-COMP14. It solved all verification tasks successfully and was 30x faster than the best tool with native concurrency handling.

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Abstract-Lazy-CSeq is a context-bounded verification tool for sequentially consistent C programs using POSIX threads. It first translates a multi-threaded C program into a bounded nondeterministic sequential C program that preserves bounded reachability for all round-robin schedules up to a given number of rounds. It then reuses existing high-performance bounded model checkers as sequential verification backends. Lazy-CSeq handles the full C language and the main parts of the POSIX thread API, such as dynamic thread creation and deletion, and synchronization via thread join, locks, and condition variables. It supports assertion checking and deadlock detection, and returns counterexamples in case of errors. Lazy-CSeq outperforms other concurrency verification tools and has won the concurrency category of the last two SV-COMP verification competitions.

Abstract. 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.

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Abstract-Lazy sequentialization is one of the most effective approaches for the bounded verification of concurrent programs. Existing tools assume sequential consistency (SC), thus the feasibility of lazy sequentializations for weak memory models (WMMs) remains untested. Here, we describe the first lazy sequentialization approach for the total store order (TSO) and partial store order (PSO) memory models. We replace all shared memory accesses with operations on a shared memory abstraction (SMA), an abstract data type that encapsulates the semantics of the underlying WMM and implements it under the simpler SC model. We give efficient SMA implementations for TSO and PSO that are based on temporal circular doubly-linked lists, a new data structure that allows an efficient simulation of the store buffers. We show experimentally, both on the SV-COMP concurrency benchmarks and a real world instance, that this approach works well in combination with lazy sequentialization on top of bounded model checking.

We describe a version of the lazy sequentialization schema by La Torre, Madhusudan, and Parlato that is optimized for bounded programs, and avoids the re-computation of the local state of each process at each context switch. Lazy-CSeq implements this sequentialization schema for sequentially consistent C programs using POSIX threads. Experiments show that it is very competitive.

Sequentialization translates concurrent programs into equivalent nondeterministic sequential programs so that the different concurrent schedules no longer need to be handled explicitly. It can thus be used as a concurrency preprocessor for many sequential program verification techniques. CSeq implements sequentialization for C and uses ESBMC as sequential verification backend [5].