examples-coredump.md

Using Wasm coredump

The following steps describe how to debug using Wasm coredump in Wasmtime:

1. Compile your WebAssembly with debug info enabled; for example:

   rustc foo.rs --target=wasm32-wasip1 -C debuginfo=2
   

foo.rs

fn c(v: usize) {
    a(v - 3);
}

fn b(v: usize) {
    c(v - 3);
}

fn a(v: usize) {
    b(v - 3);
}

pub fn main() {
    a(10);
}

2. Run with Wasmtime and Wasm coredump enabled:

   $ wasmtime -D coredump=/tmp/coredump foo.wasm
   
   thread 'main' panicked at 'attempt to subtract with overflow', foo.rs:10:7
   note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
   Error: failed to run main module `foo.wasm`
   
   Caused by:
       0: Core dumped at /tmp/coredump
       1: failed to invoke command default
       2: error while executing at wasm backtrace:
                   ...
   

3. Use wasmgdb to debug:

   $ wasmgdb foo.wasm /tmp/coredump
   
   wasmgdb> bt
   ...
   #13     000175 as panic () at library/core/src/panicking.rs
   #12     000010 as a (v=???) at /path/to/foo.rs
   #11     000009 as c (v=???) at /path/to/foo.rs
   #10     000011 as b (v=???) at /path/to/foo.rs
   #9      000010 as a (v=???) at /path/to/foo.rs
   #8      000012 as main () at /path/to/foo.rs
   ...