wasmtime / issue #14594 Guest-debug doesn't guest fuel co... · git-wasmtime

Similar to the other fuel issues we've seen recently -- mutations to fuel in the debug handler don't have any effect. This program panics because the guest ran to completion:

use wasmtime::*;

#[derive(Clone)]
struct Handler;

impl DebugHandler for Handler {
    type Data = ();
    async fn handle(&self, mut store: StoreContextMut<'_, ()>, event: DebugEvent<'_>) {
        if let DebugEvent::Breakpoint = event {
            store.set_fuel(0).unwrap();
        }
    }
}

#[tokio::main(flavor = "current_thread")]
async fn main() -> Result<()> {
    let mut config = Config::new();
    config.guest_debug(true);
    config.consume_fuel(true);
    let engine = Engine::new(&config)?;
    let module = Module::new(
        &engine,
        r#"(module
            (func (export "count") (param $n i32) (result i32)
              (local $i i32)
              (loop $l
                (local.set $i (i32.add (local.get $i) (i32.const 1)))
                (br_if $l (i32.lt_u (local.get $i) (local.get $n))))
              (local.get $i)))"#,
    )?;
    let mut store = Store::new(&engine, ());
    store.set_fuel(1_000_000)?;
    store.set_debug_handler(Handler);
    store.edit_breakpoints().unwrap().single_step(true)?;

    let instance = Instance::new_async(&mut store, &module, &[]).await?;
    let count = instance.get_typed_func::<i32, i32>(&mut store, "count")?;
    let result = count.call_async(&mut store, 100).await;

    println!(
        "result = {result:?}, fuel afterwards = {}",
        store.get_fuel()?
    );
    assert!(result.is_err(), "set_fuel(0) in debug handler was ignored");
    Ok(())
}

Stream: git-wasmtime

Topic: wasmtime / issue #14594 Guest-debug doesn't guest fuel co...

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