Debugging WebAssembly

The following steps describe a common way to debug a WebAssembly module in Wasmtime:

  1. Compile your WebAssembly with debug info enabled, usually -g; for example:

    clang foo.c -g -o foo.wasm
  2. Run Wasmtime with the debug info enabled; this is -g from the CLI and Config::debug_info(true) in an embedding (e.g. see debugging in a Rust embedding)

  3. Use a supported debugger:

    lldb -- wasmtime run -g foo.wasm
    gdb --args wasmtime run -g foo.wasm

If you run into trouble, the following discussions might help:

  • On MacOS with LLDB you may need to run: settings set plugin.jit-loader.gdb.enable on (#1953)
  • With LLDB, call __vmctx.set() to set the current context before calling any dereference operators (#1482):
    (lldb) p __vmctx->set()
    (lldb) p *foo