How to debug and test WebAssembly code?

Debugging and testing WebAssembly is relatively complex, but there are various tools and methods to support it:

1. Browser DevTools Support

• Chrome DevTools:
  • Sources panel can view WebAssembly source code
  • Supports setting breakpoints, step-by-step execution
  • Can view call stacks and variable values
  • Performance panel analyzes performance bottlenecks
• Firefox DevTools:
  • Debugger panel supports WebAssembly debugging
  • Can view decompiled WebAssembly code
  • Memory panel monitors memory usage

2. Source Maps

• Generate source map files along with .wasm files
• Allows debugging in original source code instead of binary code
• Supports source maps for Rust, C++, AssemblyScript, and other languages

bash
# Rust generate source maps
cargo build --release
# Generates .wasm file and .d.ts type definitions

# Emscripten generate source maps
emcc source.cpp -o output.html -s WASM=1 -g

3. Testing Frameworks

• Rust:
  • Use standard cargo test framework
  • wasm-bindgen-test supports WebAssembly unit testing

  rust
  #[cfg(test)]
  mod tests {
      use super::*;
      #[wasm_bindgen_test]
      fn test_add() {
          assert_eq!(add(2, 3), 5);
      }
  }

• JavaScript:
  • Use Jest, Mocha, and other JavaScript testing frameworks
  • Test exported functions of WebAssembly modules

  javascript
  test('add function', () => {
      expect(wasm.exports.add(2, 3)).toBe(5);
  });

4. Debugging Tools

• wasm-bindgen: Binding tool from Rust to WebAssembly
• wasm-pack: Simplifies Rust WebAssembly project building
• wasm2wat: Converts WebAssembly binary to text format (WAT)

bash
wasm2wat module.wasm -o module.wat

• wat2wasm: Converts text format back to binary format

5. Performance Analysis

• Browser Performance Panel:
  • Records execution time of WebAssembly functions
  • Analyzes CPU usage
  • Identifies performance bottlenecks
• console.time: Measures execution time of specific code sections

javascript
console.time('wasm-function');
wasm.exports.heavyComputation();
console.timeEnd('wasm-function');

6. Memory Debugging

• Chrome Memory Panel: Monitor WebAssembly memory usage
• Memory Snapshots: Analyze memory leaks
• Heap Profiler: View memory allocation

7. Error Handling

• try-catch: Catch exceptions in WebAssembly

javascript
try {
    wasm.exports.functionThatMightFail();
} catch (error) {
    console.error('WebAssembly error:', error);
}

• Error Messages: WebAssembly provides limited error information
• Bounds Check Errors: Memory access violations throw exceptions

8. Logging Debugging

• console.log: Use imported console functions in WebAssembly

rust
#[wasm_bindgen]
extern "C" {
    #[wasm_bindgen(js_namespace = console)]
    fn log(s: &str);
}

9. Best Practices

• Use source maps for debugging instead of debugging binary code directly
• Write comprehensive unit tests and integration tests
• Use performance analysis tools to identify bottlenecks
• Enable debug information in development environment
• Use TypeScript definition files to improve type safety

10. Common Problem Solving

• Compilation errors: Check compiler version and configuration
• Runtime errors: Check memory access and bounds
• Performance issues: Use performance analysis tools to locate bottlenecks
• Memory leaks: Use memory analysis tools to detect