Crash Reporting for WebAssembly Games

WebAssembly lets games written in C++, Rust, or other languages run at near-native speed in the browser, compiled to wasm and executed in the browser sandbox. This power comes with web-specific failure modes: WebAssembly traps when the code hits an error condition, out-of-memory failures when the linear memory grows beyond its limit, and errors at the boundary between the wasm module and the surrounding JavaScript. Whatever language the game is built in, a WebAssembly game fails as a browser application with wasm characteristics. Setting up crash reporting for a WebAssembly game means capturing the traps, memory failures, and boundary errors with the browser context.

WebAssembly runs compiled code in the browser

A WebAssembly game is code, often written in C++, Rust, or another language, compiled to wasm and run in the browser at near-native speed, inside the browser sandbox alongside JavaScript. This gives games the performance of compiled code with the reach of the web, but it means the game fails in a combination of native-code and web ways: the compiled code can hit error conditions that become WebAssembly traps, and the web environment imposes memory limits and the browser sandbox.

This hybrid nature, compiled code in a web sandbox, shapes WebAssembly crash reporting. A wasm trap is the WebAssembly form of a crash, raised when the code hits an unrecoverable condition like an out-of-bounds memory access or an integer divide by zero, and it surfaces as an abort. The linear memory the wasm module uses has limits, producing out-of-memory failures when it grows too far. And the boundary with JavaScript, where the wasm and JS call each other, introduces its own errors. Understanding these wasm-specific failure modes is the foundation for capturing WebAssembly game crashes.

Capture traps and aborts

The WebAssembly form of a crash is a trap, raised when the wasm code hits an unrecoverable error, an out-of-bounds memory access, an invalid operation, an explicit abort, which typically surfaces in the browser as a thrown error or an Emscripten-style abort. Capture these traps and aborts by hooking the browser error handling, since the trap propagates out of the wasm module as a browser-level error you can catch.

Capture the error and any stack trace or abort message, since the trap carries information about what went wrong, and for wasm compiled with source maps or symbol information, you can map the trap back to the source location in the original language. The trap is the wasm crash, and capturing it, with symbolication where available, gives you the wasm equivalent of a native crash report. Capturing the traps and aborts that the WebAssembly code raises is the core of wasm crash reporting, providing the crash signal that the compiled code produces when it fails.

Watch the linear memory

WebAssembly uses a linear memory, a contiguous block that the wasm module allocates from, and it has limits, so an out-of-memory failure occurs when the module tries to grow the memory beyond its maximum, much like the fixed-heap issue of Unity WebGL. This memory failure is a common wasm crash, especially for memory-intensive games, and it is distinct from a logic trap.

Capture the memory state at crash time, the current linear memory size and usage, so you can see whether a crash is an out-of-memory failure as the memory hits its limit. A crash that occurs when the linear memory cannot grow further is an out-of-memory crash, and the fix is reducing the memory footprint or raising the limit, a different response than a logic trap. Watching the linear memory and capturing its state on crashes lets you identify the out-of-memory failures that are a common wasm crash mode, distinct from the traps the code logic raises.

Capture the JavaScript boundary and browser

A WebAssembly game has a boundary with JavaScript, where the wasm module and the surrounding JS call each other, passing data across, and errors occur there, a wrong type crossing the boundary, a JS function the wasm calls that fails, a JS error in the loader or glue code. Capture errors at this boundary by hooking the JavaScript error handling, which catches the JS-side errors and the glue-code failures the wasm trap handling alone does not.

Capture the browser context too, the browser and version, OS, device, since a WebAssembly game runs across the browser matrix and crashes can be browser-specific, with wasm support and behavior varying somewhat across browsers. The browser context lets you cluster wasm crashes by environment. Capturing the JavaScript boundary errors, alongside the wasm traps, and the browser context, gives you complete coverage of how a WebAssembly game fails: the traps from the compiled code, the memory failures, the boundary errors, and the browser-specific issues, which together are the wasm crash landscape.

Setting it up with Bugnet

Bugnet web SDK hooks the browser error handling, capturing the WebAssembly traps and aborts that propagate out of the wasm module, the JavaScript boundary errors, and, with the memory context, the out-of-memory failures, all with the browser and device context. With source maps or symbol information, the traps can map back to the source location in the original language, making them readable.

Add custom fields for your game state, and group identical crashes into occurrence counts. Because WebAssembly games fail through traps, memory limits, and boundary errors, the captured wasm-and-browser context is what makes them diagnosable: it lets you see whether a crash is a logic trap in the compiled code, an out-of-memory failure at the linear-memory limit, or a JavaScript boundary error, which determines how you fix it across the browsers your wasm game runs on, just as for any web game but with the wasm-specific failure modes covered.

Keep source maps and test the matrix

To make WebAssembly traps readable, keep the source maps or symbol information that map the wasm back to the original source, since a trap without symbolication points at a wasm location that is hard to relate to your source code. Generate and keep this mapping per build, so a captured trap can be symbolicated to the function and line in your original C++, Rust, or other source, much as native shipping builds need symbols.

Test across the browser matrix, since WebAssembly support and behavior vary across browsers, and a wasm game can hit browser-specific issues, plus the memory limits differ on mobile browsers where the constraints are tighter. Pair the cross-browser testing with your captured crash data, which surfaces the traps, memory failures, and boundary errors across the browsers and devices players use. Together they let you ship a WebAssembly game that holds up across the web, with the wasm-specific crashes, readable through your source maps and clustered by the browser context, kept diagnosable and fixable.

WebAssembly is compiled code in a web sandbox. Capture the traps, the linear memory, and the JS boundary, symbolicated.