Ladybird WebAssembly Update #1

It's been a little over a week since my first post regarding the Ladybird web browser! For a quick recap: I've set a goal to get the Ladybird WebAssembly virtual machine to full spec compliance by the end of the summer. Why, and what is WebAssembly? I think the original post explains it pretty well, so go check it out if you're interested in that.1

Anyway, some great progress has been made, and not just by me! Here's a short list of the things I've done:

  1. Finish the UTF-8 validation fix. Update #0 explains my troubles with this PR
  2. Finish the new spec test generator (see PR and my last update)
  3. Validate imports more thoroughly (see PR)
  4. Make loops work (see PR)
  5. Tighten validation algorithm (see PR)
  6. Tiny memory.fill fix (see PR)
  7. Miscellaneous validator fixes (see this PR and this PR)

Reflection

From these PRs, we've gone from 1k+ failing tests2 to just over 200! I'd say the most impactful PRs were 1 through 5. 6 and 7 were pretty small, fixing at most 3 tests per commit included.

The largest changes code-wise were definitely 3 and 5.

In 3, I validated that import and export types matched. This was my first real foray into the code base, because it required me to write more code than I was getting rid of.

In 5, I rewrote one of the core aspects of the validation algorithm (stack polymorphism support). This allowed for some pretty important validation checks to be made, like stack height validation.

It's worth noting that some of the most impactful changes I made required very little changes code-wise. Take the fourth PR I listed (making loops work). I added two lines of code and deleted seven, but loops are fully spec-compliant now, and we no longer have to skip the test file in CI! Pretty much all the framework for the VM is already in place, but it just has a lot of minor issues that cause major bugs. Another good example of small things making major issues is PR 6 (memory.fill). The bug here was a result of a typo and a small spec misunderstanding (probably). Yet, it cut down the number of failed tests by 200 alone.

New WebAssembly contributor

A user named Enverbalalic has been contributing to the SIMD side of the Wasm VM! With their help, we might actually be able to get full spec compliance (SIMD included) by the end of the summer! I hope they keep working on it, because I know absolutely nothing about SIMD nor how it works in WebAssembly!

Conclusion

And that's it for this update! I'm trying to keep these small and easily digestible by intention. I'm not going into the weeds about the changes I'm making, but I recommend reading my PRs and the relevant spec pages if you're interested. The specification isn't too hard to read if you're just getting into it!

As always, if you have any feedback or questions, make sure to submit an issue on this blog's GitHub repository!

  1. Or don't. ↩︎

  2. I'm not including SIMD as part of the spec-compliance goal. ↩︎