Whistler Oxidation 2019

Metadata

• Oxidation meeting, Whistler 2019 All Hands
• 10am, June 19, 2019
• Oxidation wiki: https://wiki.mozilla.org/Oxidation
  • Keep this up-to-date, plz!
• Notes from the previous meeting: https://github.com/servo/servo/wiki/Orlando-Oxidation-2018
• Chair: erahm
• Notes: lina, plus other attendees

Compile time

• njn: Cargo pipelining works in Nightly, use CARGO_PIPELINING=true
• Sample speedups for opt builds: Webrender 1.27x, Cranelift 1.20x, Firefox 1.07x
• On the path to stabilization
• niko: any reason not to turn on?
  • njn: not really; doesn't slow things down because it just changes the order in which work is done
  • requires Nightly, some people don't want to use that because it sometimes breaks Firefox compilation

Code optimization

• erahm: Cross-language LTO
  • Firefox: enabled on windows
  • clang8 + rust 1.34
  • export RUSTFLAGS=-Clinker-plugin-lto
  • Still issues w/macOS: https://bugzilla.mozilla.org/show_bug.cgi?id=1486042#c63
• erahm: PGO
  • Should be stabilized in 1.37: https://github.com/rust-lang/rust/pull/61268
  • Firefox: work has been done to enable, we need to verify that things are working: https://bugzilla.mozilla.org/show_bug.cgi?id=1437452

Rust XPCOM components

• lina: we have a few now!
• documentation:
  • Build a component in 5 minutes: https://docs.google.com/presentation/d/1qkPwISU1BvsTVyqLuVhisSMuIS_DiXb8X09-boszcu0/edit?usp=sharing
  • dev-platform thread with helper crates to make working with XPCOM interfaces nicer: https://groups.google.com/forum/#!topic/mozilla.dev.platform/u8scZop3FkM
• kvstore: https://searchfox.org/mozilla-central/source/toolkit/components/kvstore
• Wraps rkv (LMDB binding) for key-value storage
• New XUL store: https://searchfox.org/mozilla-central/source/toolkit/components/xulstore
• Certificate store: https://searchfox.org/mozilla-central/source/security/manager/ssl/cert_storage
• Bookmark sync: https://searchfox.org/mozilla-central/source/toolkit/components/places/bookmark_sync
  • Shared between Desktop, Fenix, and FxiOS

Things in progress

• niko: rustc:
  • Parallelized rustc "coming soon"
  • not yet enabled or available, but we're in "data measure and document"
  • if you're editing Rust code (or just running mach cargo check), potentially a win
• dragana: neqo - QUIC implentation in rust
  • Now integrated with platform code! (Not in m-c yet, but getting close)

New (proposed) Rust code in Firefox

• erahm: Rewriting crash reporting in Rust
  • Can use ecosystem for parsing object files, which should make things much easier for us. (Leveraging Sentry's crates)
• ashley: considering rewriting Spidermonkey frontend in Rust (parser, etc.)
  • Currently 60k lines of C++

Oxidation wiki

• njn: Please update https://wiki.mozilla.org/Oxidation#Rust_Components with new Rust projects, or tell me and I'll do it

Difficulties with Rust in Firefox

• erahm: Compilation is sloooowww. File bugs if you find specific scenarios!
• gandalf: Using WebIDL maplikes in Rust is hard...and, in general, WebIDL needs better Rust bindings!
  • We basically need a structure with the same layout as an nsTHashtable in Rust! (Like ThinVec and nsTArray)
    • froydnj: I might be able to do that, though hashtable are obviously more complex than vectors
• lina: Using jsvals in Rust!
  • We have Rust bindings for SpiderMonkey in the tree...in theory!
  • It'd be nice to use promises, access JS object properties...
• bryce: Valgrind false positives due to optimized Rust code branching on an uninitialized value in the MP4 parser tripped fuzzing
  • Hard to verify if it's actually safe!
  • njn: LLVM generates code violating valgrind's assumptions
    • I will talk to jseward to see if anything has improved, might be no good answers
      • Update: jseward has a plan, but it's a non-trivial amount of work and may take some time

Questions

• lina: Do we have a policy for vendoring non-Mozilla crates?
  • froydnj: mostly a licensing question
    • Whoever does main review should also take a look at the crate, especially if it involves unsafe code.
    • No formal signoff, :glob is working on requirements for this.
• lina: Do we support building standalone Rust code (not linked into libxul)?
  • glandium: Yes...in theory. GeckoDriver is a binary, for example.
  • froydnj: We have examples of host and target programs.
    • Search for RUST_PROGRAMS
• lina: How do we test in-tree Rust crates?
  • rust-test job runs on Treeherder (mostly Stylo tests, maybe something else now?)
    • Runs cargo test
    • Search for RUST_TESTS in moz.build
  • froydnj: GTest + FFI is probably best.
  • We don't run third-party tests.
  • Side note: for vendored crates, exclude large test fixtures from Cargo packages! We don't want 5 different copies of Sherlock Holmes in m-c.
• yury: question about wasm
  • devtools uses two crates, would be nice to vendor them?
  • froydnj: should be doable, file a bug
• jld: any Rust-related issues with IPC? IPC is currently only C++-to-C++, pretty much
  • gsvelto: I would use it!