Using zig to compile C to web assembly

Question

I believe that it should be possible to use zig to compile a simple c library to web assembly.

I am using the following c code

// add.c
int add (int first, int second)
{
  return first + second;
}

Once compiled to web assembly I am trying to run it in the browser using the following HTML.

<!DOCTYPE html>
<!-- add.html -->
<html>
  <head></head>
  <body>
    <script type="module">
      (async() => {
        const response = await fetch('add.wasm');
        const bytes = await response.arrayBuffer();
        const { instance } = await WebAssembly.instantiate(bytes);

        console.log('The answer is: ' + instance.exports.add(1, 2));
      })();
    </script>
  </body>
</html>

To compile the code I have been using a command similar to:

$ zig cc --target=wasm32-freestanding -Wl,--no-entry -Wl,--export-all-symbols -o add.wasm add.c

However when I look at the output in the browser console I get the error message Uncaught (in promise) TypeError: instance.exports.add is not a function. This implies that the function add is being optimised away or not exported.

I have tried adding the -shared and -dynamic switches to the command line and these are not supported for the web assembly target (at least for the version of zig I am using).

Is there a way to ensure that add gets exported?

I serve up the HTML and compiled add.wasm using python -m http.server.

I am using zig 0.15.1. At the time of writing this is the latest release other than the nightly build.

robertklep · Accepted Answer · 2025-09-27 14:59:55Z

5

You can explicitly export functions:

zig cc -target wasm32-freestanding -Wl,--no-entry -Wl,--export=add -o add.wasm add.c

(found here)

I don't know why --export-all-symbols doesn't work (the documentation I can find on it says it's for PE targets only, but it does export some additional, internal, symbols to the WASM file).

answered Sep 27 at 14:59

robertklep

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