You can now run WebAssembly on Cloudflare Workers

  // Really trivial malloc() implementation. We just allocate bytes sequentially from the start of
  // the heap, and reset the whole heap to empty at the start of each request.
  extern byte __heap_base;   // Start of heap -- symbol provided by compiler.

  byte* heap = NULL;         // Current heap position.
  void* last_malloc = NULL;  // Last value returned by malloc(), for trivial optimizations.

  void* malloc(size_t n) {
    last_malloc = heap;
    heap += n;
    return last_malloc;
  }

Shouldn't it be:

  byte *heap = &__heap_base;

I haven't read the rest of the code, nor know how WebAssembly works, but I can't make sense of that snippet.

http://cs241.cs.illinois.edu/malloc.html

There is (or at least was) a score board you can compare against. By the end of the MP, there are usually handful beating libc.

The thing is.. libc is battle tested, so I'd always trust it over a hand rolled solution. It's always interesting to see improvements though (usually at a cost).

Traditionally, all WebAssembly modules are essentially eval()ed. You need JavaScript to download the module into an ArrayBuffer or the like, then pass that to the WebAssembly API to compile it.

However, in Cloudflare Workers, we didn't want you to have to fetch WebAssembly remotely at startup. Instead, you upload your WASM module to the Cloudflare configuration UI/API together with your JavaScript code. At startup, the WASM is compiled and the resulting `WebAssembly.Module` appears as a global variable in your script, which you can then instantiate.

Emscripten normally automatically generates JavaScript for you to load your WASM. But Emscripten's generated script doesn't understand this delivery model where the module shows up as a global variable. It should be trivial to add support, but it would be awkward for us to try to submit a patch upstream without the functionality being public yet.