WGSLsmith: Randomised Testing for the WebGPU Shading Language

Abstract

We present WGSLsmith, a tool for randomised testing of compilers for the WebGPU Shading Language (WGSL). Under the WebGPU API---now supported by all three major browsers---GPU programs are written in the WebGPU Shading Language (WGSL), and every implementation ships a WGSL compiler that validates shaders and translates them to platform-specific code. Because shaders may come from untrusted websites, these compilers can be exercised by arbitrary web pages, making them a security-critical target for testing. WGSLsmith generates random shaders to find compiler crashes and cross-implementation mismatches. We describe its architecture and usage, and how we have broadened its language feature coverage to keep up to date with the evolving WGSL specification and support features absent from the original design. We report on a campaign that uncovered 12 bugs (all confirmed, 8 fixed) in various parts of the WebGPU stack, and evaluate the thoroughness of WGSLsmith via coverage analysis.