Formal Replay of Translation Validation for Highly Optimised C

In previous work~\cite{sewell2013translation} we have implemented a translation validation mechanism for checking that a C compiler is adhering to the expected semantics of a verified program. We used this apparatus to check the compilation of the seL4 verified operating system kernel~\cite{Klein_EHACDEEKNSTW_09} by GCC 4.5.1. To get this result, we carefully chose a problem representation that worked well with certain highly optimised SMT solvers. This raises a question of correctness. While we are confident the result is correct, we still aim to replay this result with the most dependable tools available.

In this work we present a formalisation of the proof rules needed to replay the translation check within the theorem prover Isabelle/HOL. This is part of an ongoing effort to bring the entire translation validation result within a single trusted proof engine and derive a single correctness theorem, thus reaching the gold standard level of trustworthiness for program verification.

We had hoped to present the formal rule set in action through a worked example. Unfortunately while we have all the theory we need, the mechanisms for selecting and applying the rules and discharging certain side conditions remain a work in progress, and our example proof is incomplete.