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We describe a simple, but powerful, program logic for reasoning about C11 relaxed accesses used in conjunction with release and acquire memory fences. Our logic, called fenced separation logic (FSL), extends relaxed separation logic with special modalities for describing state that has to be protected by memory fences. Like its precursor, FSL allows ownership transfer over synchronizations and can be used to verify the message-passing idiom and other similar programs. The soundness of FSL has been established in Coq.

Concurrent libraries are the building blocks for concurrency. They encompass a range of abstractions (e.g. locks, exchangers, stacks, queues, sets) built in a layered fashion: more advanced libraries are built out of simpler ones. While there has been a lot of work on verifying such libraries in a sequentially consistent (SC) environment, little is known about how to specify and verify them under weak memory consistency (WMC). We propose a general declarative framework that allows us to specify concurrent libraries declaratively, and to verify library implementations against their specifications compositionally. Our framework is sufficient to encode standard models such as SC, (R)C11 and TSO. Additionally, we specify several concurrent libraries, including mutual exclusion locks, reader-writer locks, exchangers, queues, stacks and sets. We then use our framework to verify multiple weakly consistent implementations of locks, exchangers, queues and stacks. CCS Concepts: • Software and its engineering → General programming languages; • Theory of computation → Semantics and reasoning; Concurrency;

We present SLR, the first expressive program logic for reasoning about concurrent programs under a weak memory model addressing the out-of-thin-air problem. Our logic includes the standard features from existing logics, such as RSL and GPS, that were previously known to be sound only under stronger memory models: (1) separation, (2) per-location invariants, and (3) ownership transfer via release-acquire synchronisation-as well as novel features for reasoning about (4) the absence of out-of-thin-air behaviours and (5) coherence. The logic is proved sound over the recent "promising" memory model of Kang et al., using a substantially different argument to soundness proofs of logics for simpler memory models.

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