Build wasm maps from C++ file

README.md

Binaryen and patches

Build binaryen with https://github.com/WebAssembly/binaryen/commit/0b67e96f598c817061e243aa922783b49f0cecab

Compile a program using emscripten

emcc -s SIDE_MODULE=1 fib.c -O1 --separate-asm -g -o fib.js
cat fib.asm.js | grep " //@line "

Create a wasm file with text map

asm2wasm -g fib.asm.js -o fib.wasm -bm fib.wasm.txtmap -bu http://example.org/fib.wasm.map
cat fib.wasm.txtmap

Convert to JSON map

(If the txt2map4wasm not install, you can install it via npm install txt2map4wasm)

txt2map4wasm fib.wasm.txtmap -o fib.wasm.map

fib.c

int fib(int n) {
  int i, t, a = 0, b = 1;
  for (i = 0; i < n; i++) {
    t = a + b;
    a = b;
    b = t;
  }
  return b;
}

fib.index.html

<script>
  var emGlue = {
    env: {
      DYNAMICTOP_PTR: 0,
      tempDoublePtr: 0,
      ABORT: 0,
      STACKTOP: 0,
      STACK_MAX: 10,
      gb: 0,
      fb: 0,
      memory: new WebAssembly.Memory({initial: 256, maximum: 256}),
      table: new WebAssembly.Table({element: "anyfunc", initial: 0, maximum: 0}),
      memoryBase: 0,
      tableBase: 0,
    },
    global: {
      NaN: window.NaN,
      Infinity: window.Infinity,
    }
  };

  fetch('fib.wasm').then(req => req.arrayBuffer())
                   .then(res => WebAssembly.instantiate(res, emGlue))
                   .then(({instance}) => run(instance));

  function run(instance) {
    console.log(instance.exports._fib(4));
  }
</script>

fib.wasm.base64

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

fib.wasm.map

{"version":3,"sources":["fib.c"],"names":[],"mappings":"moBAEA,4BAKA,QAJA,OADA,OAAA,uCAKA"}

Update:
You can generate a source map straight from emcripten with the -g4 flag

 emcc -s SIDE_MODULE=1 fib.c -g4 -o fib.js

does Node (any version, presumably just the bleeding edge ones though) know how to handle these? I have been trying to step from JS into CPP all morning to no avail.