Wasm64 support

[theSherwood]

Hi! Thanks for this great library!

Just a heads up that I've run into an issue around BigInts when using 64-bit wasm. I know this is to be expected but figured I'd flag it all the same just to get it on your radar.

TypeError: Cannot mix BigInt and other types, use explicit conversions
    at Ciovec.read_bytes_array (file:///Users/stuff/node_modules/@bjorn3/browser_wasi_shim/dist/wasi_defs.js:1:4249)
    at fd_write (file:///Users/stuff/node_modules/@bjorn3/browser_wasi_shim/dist/wasi.js:1:8534)
    at wasm://wasm/00091766:wasm-function[206]:0x1ccc0
    at wasm://wasm/00091766:wasm-function[198]:0x1c83c
    at wasm://wasm/00091766:wasm-function[150]:0x14cf4
    at wasm://wasm/00091766:wasm-function[53]:0x878a
    at wasm://wasm/00091766:wasm-function[191]:0x196d9

[bjorn3]

AFAIK WASI doesn't have a wasm64 version. How did you compile this wasm module?

[theSherwood]

Emscripten. I didn't realize WASI didn't support wasm64. Are there any alternative standard interfaces?

[bjorn3]

Emscripten originally used a fully custom ABI, but moved to a subset of WASI + extra methods for functionality not part of WASI. Wasm64 support for WASI is probably an Emscripten specific extensions. I'm curious why you are trying to use browser_wasi_shim with an Emscripten compiled wasm module though. Emscripten already emits javascript for handling their entire ABI including all those extra methods and extensions.

[theSherwood]

I've been using the WASI api (using PURE_WASI compiler flag) because I want to use a larger standard than Emscripten's custom ABI. I don't know how Emscripten supports Wasm64. I just set the MEMORY64 compiler flag. I'm using the browser_wasi_shim at the moment while I figure out what capabilities I want to support. Currently, I'm mostly just using it for printing, as I'm not doing a lot of communication between js and wasm yet.

Emscripten's glue code generation creates a lot of stuff I don't necessarily want. I'm using Nim->C->Wasm. So the resulting Emscripten glue code for passing data to and from JS ends up being pretty mismatched with Nim semantics. At the point that I need to pass data to and from JS, I'm just going to write the JS code myself to match the semantics I want in a perf-conscious way. I've experimented with this a bit and I much prefer it to Emscripten's generated stuff.

So I may be heading in an unusual direction and you don't want to support 64-bit memory because it would entail a bunch of extra code for something that may or may not see much use in the near term. That makes sense. I just wanted to flag this as a limitation.

[bjorn3]

I see. I've asked on the wasm discord if there is any documentation about the wasm64 extension to WASI of Emscripten. I'm not sure yet if I want to support wasm64. I think I will have to try implementing it once I know what to actually implement to see how much extra code it needs.

[bjorn3]

Got a reply. Seems like support for the combination of PURE_WASI and MEMORY64 is purely accidental and the resulting ABI is not documented.

[theSherwood]

Okay. Good to know. Thanks for your time with all this!