KRust: A Formal Executable Semantics of Rust

Abstract

Rust is a new and promising high-level system programming language. It provides both memory safety and thread safety through its novel mechanisms such as ownership, moves and borrows. Ownership system ensures that at any point there is only one owner of any given resource. The ownership of a resource can be moved or borrowed according to the lifetimes. The ownership system establishes a clear lifetime for each value and hence Rust does not necessarily need garbage collection. These novel features bring Rust high performance, fine-grained low-level control over memory without garbage collection, which differentiate Rust from other existing prevalent languages. For formal analysis of Rust programs and helping programmers learn its new mechanisms and features, a formal semantics of Rust is desired and useful as a fundament for developing related tools. In this paper, we present a formal executable operational semantics of a subset of Rust, called KRust. The semantics is defined in K, a rewriting-based executable semantic framework for programming languages. The executable semantics yields automatically a formal interpreter and verification tools for Rust programs. KRust has been validated by testing with 182 tests, including 157 tests from the official Rust test suite. We individually found an error in the Rust compiler.