A Verification-Based Approach to Memory Fence Insertion in Relaxed Memory Systems

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Abstract

This paper addresses the problem of verifying and correcting programs when they are moved from a sequential consistency execution environment to a relaxed memory context. Specifically, it considers the TSO (Total Store Order) relaxation, which corresponds to the use of store buffers, and its extension x86-TSO, which in addition allows synchronization and lock operations.

The proposed approach uses a previously developed verification tool that uses finite automata to symbolically represent the possible contents of the store buffers. Its starting point is a program that is correct for the usual sequential consistency memory model, but that might be incorrect under x86-TSO. This program is then analyzed for this relaxed memory model and when errors are found (with respect to safety properties), memory fences are inserted in order to avoid these errors. The approach proceeds iteratively and heuristically, inserting memory fences until correctness is obtained, which is guaranteed to happen.

An advantage of our technique is that the underlying symbolic verification tool makes a full exploration possible even for cyclic programs, which makes our approach broadly applicable. The method has been tested with an experimental implementation and can effectively handle a series of classical examples.

This work is supported by the Interuniversity Attraction Poles program MoVES of the Belgian Federal Science Policy Office, and by the grant 2.4545.11 of the Belgian Fund for Scientific Research (F.R.S.-FNRS).