bashor
commented
1 year ago The general idea is to help non-experienced devs in JavaScriptCore (JSC), like me😊, to dive into the topic and try to fix the first wasm issue in JSC.
More experienced folks are also super welcome! You can start your hackathon earlier while others are exploring JSC internals. Or help others with their diving into JSC.
Agenda:
- Overview of Wasm implementation in JSC. (@dbezhetskov)
- Try to fix something simple, preferably around Wasm GC. (All together or in groups, or individually)
- Make sure everyone built JSC in advance.
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Preparation:
Since we are limited in time, ask participants to do a few things in advance:
-
Read or watch materials about Wasm GC to become familiar.
- Wasm Spec: https://webassembly.github.io/spec/core/
- Wasm GC proposal
- Overview
- MVP
- Spec for Prototype Implementation v.6
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Check out and build JSC
- Check out https://github.com/WebKit/WebKit
- For faster checkout
git clone -b main --single-branch --depth=1 https://github.com/WebKit/WebKi
- For faster checkout
- Contributing Code to WebKit https://webkit.org/contributing-code/
- Best/fastest way to build JSC https://trac.webkit.org/wiki/JSCOnly
- Check out https://github.com/WebKit/WebKit
-
Other useful links:
- JSC internals in general https://webkit.org/blog/category/javascript/ and particularly https://webkit.org/blog/10308/speculation-in-javascriptcore/
- WebKit Slack workspace. Link to join.
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List of (simple) issues to look at during the session (mostly around Wasm GC)
With comments from @catamorphism.
Bug 254760 - Enforce operand limit for array.new_canon_fixed
The next two are less simple, but might be pretty self-contained for people who already understand the basic idea of inline caching: Bug 244388 - Inline struct allocation Bug 245405 - Inline Wasm array operations & allocation
Bug 246981 - [Wasm-GC] Implement packed types in struct fields This is not too hard in principle - I already did it for arrays: https://github.com/WebKit/WebKit/commit/04de71ca40b4832b65e5c6861c399d91735c309c , and I think someone could look at the code for arrays and adapt it to structs pretty easily.
Bug 250107 - [Wasm-GC] Add support for final attribute How hard this one is probably depends on whether it only requires static checking or also requires changing the runtime type information that is used for dynamic checks. I haven't looked at this feature enough to know.
Bug 254694 - [Wasm-GC] Implement br_on_cast and br_on_cast_fail
Naïvely, I can imagine this not being too hard, since you can look at how br is implemented and at how ref.cast is implemented and combine the two.
Bug 254695 - [Wasm-GC] Add nullexternref and nullfuncref types
Probably not too hard either, since you can use nullref as a model.
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_Also, you could recommend as pre-work that participants look at the test suite for the reference interpreter -- for example, the tests for br_on_cast are here: https://github.com/WebAssembly/gc/blob/main/test/core/gc/br_on_cast.wast_
and import those tests into the JSC GC test suite: https://github.com/WebKit/WebKit/tree/main/JSTests/wasm/gc
Of course, the tests will fail, but getting to the point where the test fails with the expected CompileError will be a way for people to validate that they have properly built WebKit. Then you'll already have the tests on a local branch, and can work during the hackfest on getting the tests to pass.
(There's also a way to automatically export spec tests into the JSC test suite -- see https://github.com/WebKit/WebKit/tree/main/JSTests/wasm/gc-spec-tests -- but for the purposes of this exercise it's probably easier to manually copy/paste code, following the structure of, for example, https://github.com/WebKit/WebKit/blob/main/JSTests/wasm/gc/casts.js .)
dbezhetskov
spectranaut
mrego
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