An Executable Operational Semantics for Rust with the Formalization of Ownership and Borrowing

Rust is an emergent systems programming language highlighting memory safety by its Ownership and Borrowing System (OBS). The existing formal semantics for Rust only covers limited subsets of the major language features of Rust. Moreover, they formalize OBS as type systems at the language-level, which can only be used to conservatively analyze programs against the OBS invariants at compile-time. That is, they are not executable, and thus cannot be used for automated verification of runtime behavior. In this paper, we propose RustSEM, a new executable operational semantics for Rust. RustSEM covers a much larger subset of the major language features than existing semantics. Moreover, RustSEM provides an operational semantics for OBS at the memory-level, which can be used to verify the runtime behavior of Rust programs against the OBS invariants. We have implemented RustSEM in the executable semantics modeling tool K-Framework. We have evaluated the semantics correctness of RustSEM wrt. the Rust compiler using around 700 tests. In particular, we have proposed a new technique for testing semantic consistency to ensure the absence of semantic ambiguities on all possible execution selections. We have also evaluated the potential applications of RustSEM in automated runtime and formal verification for both functional and memory properties. Experimental results show that RustSEM can enhance the memory safety mechanism of Rust, as it is more powerful than OBS in detecting memory errors.