Stream: git-wasmtime

Topic: wasmtime / issue #3684 Help needed: Instantiate only one ...

Wasmtime GitHub notifications bot (Jan 12 2022 at 18:54):

al3xfischer opened issue #3684:

Hey @all!

I want to instantiate a module that has multiple import.
My gotcha is that I'm only interested in one function of the module that does not need any of the imports.

Is there a way to instantiate the module but ignore the fact that I'm not providing the imports?

I used the following code:

fn main() -> Result<(), Box<dyn Error>> {
    let e = Engine::default();
    let module = Module::from_file(&e,"awam.wasm")?;
    let mut store = Store::new(&e,());

    let instance = Instance::new(&mut store, &module, &[])?;

    let say = instance.get_typed_func::<(),(i32,i32),_>(&mut store,"say")?;
    let (ptr,length) = say.call(&mut store,())?;
    dbg!(ptr,length);
    Ok(())
}

But I get the error msg: expected 3 import, found 0

I also thought about the Linker but I was not able to find an API that might help.

Thanks in advance!

Wasmtime GitHub notifications bot (Jan 12 2022 at 18:57):

bjorn3 commented on issue #3684:

You could provide dummy functions that panic as imports. Or you could use a wasm parser to extract the function you need and produce a new wasm module with this function. A wasm module can only be instantiated as a unit, not in parts.

Wasmtime GitHub notifications bot (Jan 12 2022 at 19:01):

al3xfischer commented on issue #3684:

If I create a fake function does it have to match the types of the imports or is that not validated when instantiated?

Wasmtime GitHub notifications bot (Jan 12 2022 at 19:15):

al3xfischer edited a comment on issue #3684:

@bjorn3 If I create a fake function does it have to match the types of the imports or is that not validated when instantiated?

Wasmtime GitHub notifications bot (Jan 12 2022 at 19:33):

al3xfischer deleted a comment on issue #3684:

@bjorn3 If I create a fake function does it have to match the types of the imports or is that not validated when instantiated?

Wasmtime GitHub notifications bot (Jan 12 2022 at 20:52):

al3xfischer commented on issue #3684:

@bjorn3 Thanks for the help.

I was able to instantiate the module by creating "fake" functions.

Wasmtime GitHub notifications bot (Jan 12 2022 at 20:52):

al3xfischer closed issue #3684:

Hey @all!

I want to instantiate a module that has multiple import.
My gotcha is that I'm only interested in one function of the module that does not need any of the imports.

Is there a way to instantiate the module but ignore the fact that I'm not providing the imports?

I used the following code:

fn main() -> Result<(), Box<dyn Error>> {
    let e = Engine::default();
    let module = Module::from_file(&e,"awam.wasm")?;
    let mut store = Store::new(&e,());

    let instance = Instance::new(&mut store, &module, &[])?;

    let say = instance.get_typed_func::<(),(i32,i32),_>(&mut store,"say")?;
    let (ptr,length) = say.call(&mut store,())?;
    dbg!(ptr,length);
    Ok(())
}

But I get the error msg: expected 3 import, found 0

I also thought about the Linker but I was not able to find an API that might help.

Thanks in advance!

Wasmtime GitHub notifications bot (Jan 12 2022 at 20:53):

alexcrichton commented on issue #3684:

As mentioned there's no way you can instantiate only some parts of a module, it's an all-or-nothing process. If your module only imports functions and you'd like to make them all "dummy" imports you can do so with something like:

fn instantiate<T>(module: &Module, store: &mut Store<T>) -> Result<Instance> {
    let mut imports = Vec::new();
    for i in module.imports() {
        let ty = match i.ty() {
            ExternType::Func(t) => t,
            _ => bail!("non-function import"),
        };
        let func = Func::new(&mut *store, ty, |_, _, _| unimplemented!());
        imports.push(func.into());
    }
    Instance::new(store, module, &imports)
}

Otherwise though you'll need to make sure that all imports are provided when instantiating a module, and when providing "real" imports it's recommended to use the Linker type.

Also as a side node @ALL doesn't actually ping project members, it pings this user: https://github.com/ALL

Wasmtime GitHub notifications bot (Jan 12 2022 at 20:56):

al3xfischer commented on issue #3684:

Thanks for the help.

And also the side node!

Last updated: Dec 23 2024 at 12:05 UTC