How to transfer arguments to WebAssembly binary generated from C?

Hello, I converted below C code to WebAssembly binary using wasi-sdk-14 (I downloaded wasi-sdk-14.0-macos.tar.gz)

#include <stdlib.h>
#include <stdio.h>
#include <string.h>

int main (int argc, char ** argv) {
    char * buf = (char *) malloc(100);
    memcpy(buf, argv[1], 100);
    printf("buf: %s\n", buf); 
    return 0;
}

And I am using below script to run the WebAssembly binary file which name is prog.wasm.

open System
open Wasmtime

[<EntryPoint>]
let main _ =
  let path = "prog.wasm"
  let engine = new Engine()
  let wm = Module.FromFile(engine, path)
  let linker = new Linker(engine)
  let store = new Store(engine)

  let cfg = new WasiConfiguration()

  linker.DefineWasi()
  store.SetWasiConfiguration(cfg)

  let instance = linker.Instantiate(store, wm)
  let func = instance.GetFunction(store, "_start")
  let result = func.Invoke(store)
  0

What I want is to transfer arguments to the binary. But _start function does not have any arguments. I guess _start function is entry point of code which executes main function…

So my question is how to transfer arguments to the binary generated from C code? Additionally, I also wonder that how to pass standard input.

[iwate]

@kimdora

When you add WithInheritedArgs() config, the args of your app will be passed to wasmtime. So, WithInheritedArgs() equals to .WithArgs(Environment.GetCommandLineArgs()) https://github.com/bytecodealliance/wasmtime-dotnet/blob/9fad6c4e5918798c9b221e42980c6e524984f54c/src/WasiConfiguration.cs#L96-L102

The screenshot’s program and command line arguments print this output.

[|"C:\Users\iwate\works\iwate\WasmtimeSample\WasmtimeSample\bin\Debug\net6.0\WasmtimeSample.dll";
  "Hello"|]
buf: Hello

So, -- is placeholder for arg0 which is insted of path/to/the/app.dll.

[iwate]

I think WithArgs can do it.

let cfg = (new WasiConfiguration()).WithArgs("--", "Hello,World!")

This is my code for learning. I hope this will help. https://github.com/iwate/learn-wasm-with-dotnet/blob/ede974d438e908bb36eb6587bbd3e6835cf96836/challenge04/dotnet/Iwate.WasmtimeChallenge04/Program.cs#L56