Next steps are to merge the LLVM upgrade, get @kripken to finish upgrading fastcomp, upgrade my ‘empscripten’ branch of Rust, port our LLVM patches onto fastcomp and submit that as a Rust PR, submit patches to turn on emscripten support in Rust, set up automation to keep emscripten target building.
The LLVM upgrade has now landed
Next @kripken is going to upgrade the emscripten incoming branch to the same merge base. But we don’t need to wait for that probably. He’s already prepared a rebase that should be in the ballpark of the same commit: the fastcomp next-merge branch.
So our next step is to take all of their patches, apply them to our tree and merge that into Rust.
Unfortunately, there’s a gotcha - @kripken didn’t realize that our plan was to apply the emscripten LLVM fork to all of our targets and he’s a bit worried about it. The reason is that the fastcomp branch is only tested for the emscripten target, and it’s based on the old pnacl fork, which has a bunch of ancillary patches of unknown value. So we may run into unanticipated problems (and in fact last time we had this working the x86_64 backend miscompiled things).
Furthermore, the fastcomp history is lengthy and messy, with all that pnacl legacy. So we are going to need to scrutinize it carefully and see e.g. if it’s doing anything to the x86 backend. We might, e.g just squash their entire history into one ‘emscripten’ commit, then revert large chunks of it. It could be a big mess. (We also have the option of pursuing a strategy where rustc can optionally use an emscripten-specific LLVM).
It’s also worth noting that the upstream LLVM wasm backend is still in progress and the last I heard the wasm team is trying to have it ready for the wasm launch late this year. So the longer this process goes on the more likely we are to just end up on the upstream wasm backend and skip the asm.js backend completely. Still, I think it’s worth continuing on the path we’re on and seeing how far we can get.
OK, another tantalizing avenue of attack here.
The LLVM wasm backend, while it isn’t fully working, and there are still changes to the wasm spec incoming, works to a relatively large degree, and Rust has it in tree now.
It would be very interesting to see what happens if we turn it on, start laying the groundwork for a
Emscripten already has experimental support, documented here. Might be some useful leads there.
Another idea: even though the road to getting working support for emscripten in-tree is still a bit off on the horizon, we’ve already proven it works, and it would be relatively easy to get it working out of tree again. With a working build it would be incredibly valuable for somebody to sprint ahead and begin implementing a
How does WebAssembly communicate with the “environment” (like canvas, WebAudio, fullscreen, etc.)? I imagine all the interfaces that the W3C defines (like this or this for example) will be accessible, but I can’t find any document that describes how.
That was my plan indeed. There’s some old code around I want to re-use for the dom-rs thingy. I will work on compiling emscripten out-of-tree again in the coming days. I will post instructions once I have a successful build.
@tomaka wasm v1 itself does not provide any facilities for calling web APIs, but emscripten does and will. Here’s the user facing documentation on it. Doing the same thing in Rust will require some digging into how the mechanism works under the hood.
That’s interesting. I wonder how we could integrate such a JS glue file in Rust/Cargo’s build system. Everything will probably remain a bit blurry until we have some sort of prototype.
I think this is the same as the approach I linked previously. You treat it like web-specific assembly code and emscripten packages it up for you.
@brson yes probably, maybe some of it can even be generated by emscripten (was it the WebIDL binder maybe?)
So it seems to me the obvious thing to do, and the most maintainable long term, would be to piggyback on Servo’s bindings generator so we get the benefit of their ongoing work. I’m sure that today it’s pretty tightly coupled to Servo internals, so it could be quite a task getting started. One might be able to imagine creating an adapter layer that basically implements Servo’s API on top of emscripten.
@kripken has some opinions about the right way to do this.
OK, just one more idea.
@kripken just reminded me that one of the early ways we can promote Rust on the web is the exact same way we promote Rust for other software stacks - write a high-performance module in Rust and call it from JS. This plays to our strengths for all the usual reasons, doesn’t require solving DOM bindings. And we’ve got quite a few crates these days that are approaching world-class performance for their domains.
I have several high-priority tasks on my plate still for the immediate future, but I hope I can turn the corner on those and pitch in technically myself.
I cheated and copy’n’pasted a definition, but unless it fails, it works. I will write down simple instructions now.
If anyone can help with eliminating that hack in
libpanic_unwind that would be appreciated. Is there a way to disable it completely and rely on
I will go through @tomaka’s old PR and see which changes from there we need.
There we go, a simple 20-step recipe to build an up-to-date Rust with Emscripten support: https://gist.github.com/badboy/2086757d09b7019e9f4ec8e98ee17054
Someone had already done exactly the same thing a few months ago: http://ashleysommer.com.au/how-to/articles/asm-js-code-using-rust-and-emscripten
Eventually the instructions became outdated. Your Rust fork will unfortunately become outdated as well in a few weeks. Ideally we should avoid repeating this circle again.
D’oh! Didn’t see that at all.
I’d like to get as much of the changes into upstream. Once
next-merge becomes the incoming/master branch for emscripten, the whole setup will be easier again.
If we have that we might get to a point where we can provide an external LLVM to Rust and it will be able to enable Emscripten on the fly.
Update: AFAIK next-merge has been merged into the incoming branch in emscripten. Getting closer!
That will make my 20-step guide a little bit shorter as now a
emsdk install sdk-incoming-64bit && emsdk activate sdk-incoming-64bit should do.