WebAssembly Setup Issue (LinkError)

edggy

I compiled the code from https://docs.screeps.com/modules.html#Build-wasm-file and tried to run it in the simulation.

Here is my "main" (Copy and pasted from the tutorial):

module.exports.loop = function () {

    // This will return an ArrayBuffer with `addTwo.wasm` binary contents
    const bytecode = require('addTwo');

    const wasmModule = new WebAssembly.Module(bytecode);

    const imports = {};

    // Some predefined environment for Emscripten. See here:
    // https://github.com/WebAssembly/tool-conventions/blob/master/DynamicLinking.md
    imports.env = {
        memoryBase: 0,
        tableBase: 0,
        memory: new WebAssembly.Memory({ initial: 256 }),
        table: new WebAssembly.Table({ initial: 0, element: 'anyfunc' })    
    };

    const wasmInstance = new WebAssembly.Instance(wasmModule, imports);

    console.log(wasmInstance.exports._addTwo(2,3));
}

My wasm file is uploaded as the module "addTwo", here is the addTwo.c file i compiled:

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

The compile command was:

emcc -s WASM=1 -s SIDE_MODULE=1 -O3 addTwo.c -o addTwo.wasm

When I run the code the console outputs:

LinkError: WebAssembly Instantiation: table import 0 is smaller than initial 2, got 0
    at Object.module.exports.loop:20:26
    at __mainLoop:1:15733
    at eval:2:4
    at Object.r.run:2:144134

Does anyone know how to fix this issue?

wtfrank

I also get this issue when I run the same example code. I have emcc v1.38.12

I was able to look at the required imports of the wasm module to see what was missing:

const wasmModule = new WebAssembly.Module(bytecode);
console.log("imports", WebAssembly.Module.imports(wasmModule));

This output:

imports [ { module: 'env', name: 'table', kind: 'table' },
  { module: 'env', name: 'memoryBase', kind: 'global' },
  { module: 'env', name: 'tableBase', kind: 'global' },
  { module: 'env', name: 'abort', kind: 'function' } ]

So perhaps it needs an abort function to be defined.

I added a new member to imports.env:

abort: _ => { throw new Error('abort');},

I think that needed to be done, but it wasn't the problem, it turns out that WebAssemblyTable needs to have initial set to 2 instead of 0.

table: new WebAssembly.Table({ initial: 2, element: 'anyfunc' })