A Program Logic for First-Order Encapsulated WebAssembly.

WebAssembly (Wasm) is the first new programming language in over 20 years to be natively supported on the web. A small-step semantics of Wasm was formally introduced by Haas et al. 2017 and mechanised in Isabelle by Watt 2018. In this report, we introduce a big-step semantics for Wasm, as well as a sound program logic for first-order, encapsulated Wasm. All definitions and soundness results are mechanised in Isabelle and will be released publicly under a BSD-style license shortly. An equivalence result between our big-step semantics and the small-step semantics of Haas et al. 2017 is in development.