How to pass a function pointer param to wasm export function through c-api?

[DbettKK]

Hi, I have been working on calling wasm export functions recently, and I'm trying to make it though wasmer-c-api. But I've run into a problem that I can't solve.

One wasm export funtion I'd like to call receives a funtion pointer as parameter, the origin C code is here.

int call_add(int a, int b, int (*add)(int, int)) {
    // ...
}

And I'll compile it into wasm(wasi) via clang. And it'll be like this in wat.

(func $call_add (type 3) (param i32 i32 i32) (result i32)

And now I want to call this call_add function in another C file through wasmer-c-api, the relative code shows below.

int add(int a, int b) { return a + b; }

void call_function() {
    // construct the `args` and `results`
    // how to pass `add`?
    wasm_val_t args_val[3] = { WASM_I32_VAL(1), WASM_I32_VAL(2), WASM_I32_VAL(1) };
    wasm_val_vec_t args = WASM_ARRAY_VEC(args_val);
    wasm_val_t results_val[1] = { WASM_INIT_VAL };
    wasm_val_vec_t res = WASM_ARRAY_VEC(results_val);
    // get the function ...
    // ...
    // call the function
    wasm_func_call(call_add, &args, &res);
}

You may notice that the thrid args should be wrong here. It should be the index of function add in the wasm table. But the problem is that wasmer-c-api doesn't support wasm_table_get or wasm_table_set yet. Except for that, we should also grow the table and put the function to the table which is not supported either. I know this is a problem about the unsupported interfaces. But I just want to know any other ways to make it work.

And in real situation, the function pointer is much more complicated. So trying to implement it in the origin wasm is hard as well.

Thanks.