Dynamic Linking with emscripten.

Hi,

I have been trying to experiment with dynamic linking of wasm modules i.e. module 1 would export func foo, and module 2 would import foo.

I have primarily referred to https://webassembly.org/docs/dynamic-linking/ and https://github.com/emscripten-core/emscripten/wiki/Linking.

My code is,
square.c

#include <emscripten.h>
#  define EXPORT __attribute__ ((visibility ("default")))
EXPORT EMSCRIPTEN_KEEPALIVE
int square(int x) {	
  return x * x;
}

cube.c

#  define EXPORT __attribute__ ((visibility ("default")))
#  define IMPORT __attribute__ ((visibility ("default")))
typedef int (**PF)(int);
IMPORT PF square();
EXPORT int cube(int x) { return (*square())(x) * x; }

The emcc commands used are,
emcc square.c -Os -s WASM=1 -s -s SIDE_MODULE=1 -s EXPORTED_FUNCTIONS='["_square"]' -o square.wasm
emcc cube.c -Os -s WASM=1 -s SIDE_MODULE=1 -s EXPORTED_FUNCTIONS='["_cube"]' -o cube.wasm

The JS to load the module is based on https://gist.github.com/kripken/59c67556dc03bb6d57052fedef1e61ab

  <script>
    // Check for wasm support.
    if (!('WebAssembly' in window)) {
      alert('you need a browser with wasm support enabled :(');
    }
    // Loads a WebAssembly dynamic library, returns a promise.
    // imports is an optional imports object
    function loadWebAssembly(filename, imports) {
      // Fetch the file and compile it
      return fetch(filename)
        .then(response => response.arrayBuffer())
        .then(buffer => WebAssembly.compile(buffer))
        .then(module => {
          // Create the imports for the module, including the
          // standard dynamic library imports
          imports = imports || {};
          imports.env = imports.env || {};
          imports.env.__memory_base = imports.env.__memory_base || 0;
          imports.env.__table_base = imports.env.__table_base || 0;
          if (!imports.env.memory) {
            imports.env.memory = new WebAssembly.Memory({ initial: 256 });
          }
          if (!imports.env.table) {
            imports.env.table = new WebAssembly.Table({ initial: 0, element: 'anyfunc' });
          }
          // Create the instance.
          return new WebAssembly.Instance(module, imports);
        });
    }

    loadWebAssembly('square.wasm')
      .then(instance => {
        var exports = instance.exports; 
        var square = exports._square; 
       
        var button = document.getElementById('run');
        button.value = 'Call a method in the WebAssembly module';
        button.addEventListener('click', function() {
          var input = 21;
          alert(input + ' square is ' + square(input));
        }, false);
      }
    );
    
    loadWebAssembly('cube.wasm')
      .then(instance => {
        var exports = instance.exports;
        var cube = exports._cube; 
      
        var button = document.getElementById('run');
        button.value = 'Call a method in the WebAssembly module';
        button.addEventListener('click', function() {
          var input = 21;
          alert(input + ' cube is ' + cube(input));
        }, false);
      }
    );   
  </script>

But i get error in cube.wasm instantiation as,
Uncaught (in promise) LinkError: WebAssembly Instantiation: Import #0 module="env" function="abort" error: function import requires a callable

If I change cube.wasm compile command to have the flag, -s ONLY_MY_CODE=1, then the exported function is not found.
Uncaught (in promise) LinkError: WebAssembly Instantiation: Import #0 module="env" function="_square" error: function import requires a callable

Can anyone help me. Where i am going wrong ?

Thanks.

Start with square.c, cube.c, the two emcc commands, and the loadWebAssembly script; compare them with the WebAssembly dynamic-linking and Emscripten Linking references included in the issue. Reproduce the abort and _square import errors, then verify that both modules instantiate and cube can call square.