Reusing Legacy Code in WebAssembly: Key Challenges of Cross-Compilation and Code Semantics Preservation

2024-12-28

AI Summary

Cross-compiling legacy C/C++ code to WebAssembly (Wasm) frequently incurs semantic divergence, silent miscompilation, and compilation failures, undermining reliability. Method: We propose WasmChecker, the first differential-testing framework for semantic equivalence verification of Wasm compilation. It employs binary-level semantic comparison, cross-platform compilation analysis, and an empirical study across 115 open-source projects. Contribution/Results: Our analysis systematically identifies four root causes of semantic deviation: standard library inconsistencies, missing system calls, Wasm-specific constraints, and compiler bugs. WasmChecker discovers and confirms 11 previously unknown vulnerabilities in Emscripten. We publicly release the WasmChecker framework and a benchmark dataset, providing the first quantitative evidence that mainstream Wasm compilers exhibit significant semantic non-fidelity. This work has directly driven critical fixes in Emscripten.

Technology Category

• Constraint Satisfaction and Optimization: Satisfiability Modulo Theories
• Application Domains: Software Engineering
• Computer Vision: Bias, Fairness & Privacy

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Web performance, measurement, and characterization
• Responsible Web: Consent frameworks and practices on the web
• Web Mining and Content Analysis: Web data provenance, reliability, and authenticity

Abstract

WebAssembly (Wasm) has emerged as a powerful technology for executing high-performance code and reusing legacy code in web browsers. With its increasing adoption, ensuring the reliability of WebAssembly code becomes paramount. In this paper, we investigate how well WebAssembly compilers fulfill code reusability. Specifically, we inquire (1) what challenges arise when cross-compiling a high-level language codebase into WebAssembly and (2) how faithfully WebAssembly compilers preserve code semantics in this new binary. Through a study on 115 open-source codebases, we identify the key challenges in cross-compiling legacy C/C++ code into WebAssembly, highlighting the risks of silent miscompilation and compile-time errors. We categorize these challenges based on their root causes and propose corresponding solutions. We then introduce a differential testing approach, implemented in a framework named WasmChecker, to investigate the semantics equivalency of code between native x86-64 and WebAssembly binaries. Using WasmChecker, we provide a witness that WebAssembly compilers do not necessarily preserve code semantics when cross-compiling high-level language code into WebAssembly due to different implementations of standard libraries, unsupported system calls/APIs, WebAssembly's unique features, and compiler bugs. Furthermore, we have identified 11 new bugs in the Emscripten compiler toolchain, all confirmed by Emscripten developers. As proof of concept, we make our framework and the collected dataset of open-source codebases publicly available.

Problem

• WebAssembly
• code reuse
• migration challenges

Innovation

• WebAssembly
• Code Semantic Consistency
• Emscripten Compiler Bugs