Translation Validation for JIT Compiler in the V8 JavaScript Engine

We present TurboTV, a translation validator for the JavaScript (JS) just-in-time (JIT) compiler of V8. While JS engines have become a crucial part of various software systems, their emerging adaption of JIT compilation makes it increasingly challenging to ensure their correctness. We tackle this problem with an SMT-based translation validation (TV) that checks whether a specific compilation is semantically correct. We formally define the semantics of IR of TurboFan (JIT compiler of V8) as SMT encoding. For efficient validation, we design a staged strategy for JS JIT compilers. This allows us to decompose the whole correctness checking into simpler ones. Furthermore, we utilize fuzzing to achieve practical TV. We generate a large number of JS functions using a fuzzer to trigger various optimization passes of TurboFan and validate their compilation using TurboTV. Lastly, we demonstrate that TurboTV can also be used for cross-language TV. We show that TurboTV can validate the translation chain from LLVM IR to TurboFan IR, collaborating with an off-the-shelf TV tool for LLVM. We evaluated TurboTV on various sets of JS and LLVM programs. TurboTV effectively validated a large number of compilations of TurboFan with a low false positive rate and discovered a new miscompilation in LLVM.