Changes in contributing-architecture.md

192f2fcd - Replace setjmp/longjmp usage in Wasmtime (#11592)

Mon, 08 Sep 2025 14:33:31 +0000

Replace setjmp/longjmp usage in Wasmtime (#11592)Since Wasmtime's inception it's used the `setjmp` and `longjmp`functions in C to implement handling of traps. While this solution waseasy to implement, relatively portable, and performant enough, there area number of downsides that have evolved over time to make this anunattractive approach in the long run:* Using `setjmp` fundamentally requires using C because Rust does not understand a function that returns twice. It's fundamentally unsound to invoke `setjmp` in Rust meaning that Wasmtime has forever needed a C compiler configured and set up to build. This notably means that `cargo check` cannot check other targets easily.* Using `longjmp` means that Rust function frames are unwound on the stack without running destructors. This is a dangerous operation of which we get no protection from the compiler about. Both frames entering wasm and frames exiting wasm are all skipped. Absolutely minimizing this has been beneficial for portability to platforms such as Pulley.* Currently the no_std implementation of Wasmtime requires embedders to provide `wasmtime_{setjmp,longjmp}` which is a thorn in the side of what is otherwise a mostly entirely independent implementation of Wasmtime.* There is a performance floor to using `setjmp` and `longjmp`. Calling `setjmp` requires using C but Wasmtime is otherwise written in Rust meaning that there's a Rust->C->Rust->Wasm boundary which fundamentally can't be inlined without cross-language LTO which is difficult to configure.* With the implementation of the WebAssembly exceptions proposal Wasmtime now has two means of unwinding the stack. Ideally Wasmtime would only have one, and the more general one is the method of exceptions.* Jumping out of a signal handler on Unix is tricky business. While we've made it work it's generally most robust of the signal handler simply returns which it now does.With all of that in mind the purpose of this commit is to replace thesetjmp/longjmp mechanism of handling traps with the recently implementedsupport for exceptions in Cranelift. That is intended to resolve all ofthe above points in one swoop.One point in particular though that's nice about setjmp/longjmp is thatunwinding the stack on a trap is an O(1) operation. For situations suchas stack overflow that's a particularly nice property to have as we canguarantee embedders that traps are a constant time (albeit somewhatexpensive with signals) operation. Exceptions naively require unwindingthe entire stack, and although frame pointers mean we're just traversinga linked list I wanted to preserve the O(1) property here nonetheless.To achieve this a solution is implemented where the array-to-wasm(host-to-wasm) trampolines setup state in `VMStoreContext` so looking upthe current trap handler frame is an O(1) operation. Namely the sp/fp/pcvalues for a `Handler` are stored inline.Implementing this feature required supportingrelocations-to-offsets-in-functions which was not previously supportedby Wasmtime. This required Cranelift refactorings such as #11570, #11585,and #11576. This then additionally required some more refactoring inthis commit which was difficult to split out as it otherwise wouldn't betested.Apart from the relocation-related business much of this change is aboutupdating the platform signal handlers to use exceptions instead oflongjmp to return. For example on Unix this means updating the`ucontext_t` with register values that the handler specifies. Windowsinvolves updating similar contexts, and macOS mach ports ended up notneeding too many changes.In terms of overall performance the relevant benchmark from thisrepository, compared to before this commit, is: sync/no-hook/core - host-to-wasm - typed - nop time: [10.552 ns 10.561 ns 10.571 ns] change: [−7.5238% −7.4011% −7.2786%] (p = 0.00 < 0.05) Performance has improved.Closes #3927cc #10923prtest:full List of files: /wasmtime-44.0.1/docs/contributing-architecture.md

c21353bd - Modernize architecture documentation on linear memory (#10364)

Mon, 10 Mar 2025 22:48:06 +0000

Modernize architecture documentation on linear memory (#10364)The previous docs had fallen a bit behind the times. List of files: /wasmtime-44.0.1/docs/contributing-architecture.md

72004aad - Turn the `wasmtime-runtime` crate into the `wasmtime::runtime::vm` module (#8501)

Tue, 30 Apr 2024 18:52:45 +0000

Turn the `wasmtime-runtime` crate into the `wasmtime::runtime::vm` module (#8501)* Expose `wasmtime-runtime` as `crate::runtime::vm` internally for the `wasmtime` crate* Rewrite uses of `wasmtime_runtime` to `crate::runtime::vm`* Remove dep on `wasmtime-runtime` from `wasmtime-cli`* Move the `wasmtime-runtime` crate into the `wasmtime::runtime::vm` module* Update labeler for merged crates* Fix `publish verify`prtest:full List of files: /wasmtime-44.0.1/docs/contributing-architecture.md

2fcf41f0 - Remove `wasmtime-jit` (#7769)

Tue, 16 Jan 2024 17:49:50 +0000

Remove `wasmtime-jit` (#7769)* Move `jit` crate to `environ`Move the platform agnostic parts of the crate `wasmtime-jit` to`wasmtime-environ`. This is the first part of the refactoring discussedhere: https://github.com/bytecodealliance/wasmtime/issues/7652 and afollow up will move the remaining parts of `wasmtime-jit` so that thecrate can be deleted.* Move `jit` crate to `wasmtime`Move the remaining parts of `wasmtime-jit` to the `wasmtime` crate andremove `wasmtime-jit`. This is part of the refactoring discussed inhttps://github.com/bytecodealliance/wasmtime/issues/7652.* undo toml formatting* Trigger pipeline: prtest:full* Remove `jit` directory* move `ProfilingAgent` out of `profiling` feature* add links to ELF_NAME_DATA List of files: /wasmtime-44.0.1/docs/contributing-architecture.md

738d41ea - Correct grammar (#7224)

Thu, 12 Oct 2023 11:27:02 +0000

Correct grammar (#7224)* Update cli-install.mdCorrect grammar.* Update contributing-architecture.mdCorrect grammar. List of files: /wasmtime-44.0.1/docs/contributing-architecture.md

ed634b29 - Update notes about 64-bit memory support (#6868)

Mon, 21 Aug 2023 15:52:08 +0000

Update notes about 64-bit memory support (#6868)Closes #6865 List of files: /wasmtime-44.0.1/docs/contributing-architecture.md

317cc513 - Rename `VMCallerCheckedAnyfunc` to `VMCallerCheckedFuncRef` (#5738)

Tue, 07 Feb 2023 22:09:02 +0000

Rename `VMCallerCheckedAnyfunc` to `VMCallerCheckedFuncRef` (#5738)At some point what is now `funcref` was called `anyfunc` and the spec changed, but we didn't update our internal names. This does that. Co-authored-by: Jamey Sharp List of files: /wasmtime-44.0.1/docs/contributing-architecture.md

59a9bd62 - Chore fix typo in docs/contributing-architecture.md (#3449)

Wed, 13 Oct 2021 14:56:56 +0000

Chore fix typo in docs/contributing-architecture.md (#3449) List of files: /wasmtime-44.0.1/docs/contributing-architecture.md

1ee2af00 - Remove the lightbeam backend (#3390)

Mon, 27 Sep 2021 17:27:19 +0000

Remove the lightbeam backend (#3390)This commit removes the Lightbeam backend from Wasmtime as per [RFC 14]. This backend hasn't received maintenance in quite some time, and as [RFC 14] indicates this doesn't meet the threshold for keeping the code in-tree, so this commit removes it. A fast "baseline" compiler may still be added in the future. The addition of such a backend should be in line with [RFC 14], though, with the principles we now have for stable releases of Wasmtime. I'll close out Lightbeam-related issues once this is merged. [RFC 14]: https://github.com/bytecodealliance/rfcs/pull/14 List of files: /wasmtime-44.0.1/docs/contributing-architecture.md

93b7cdd6 - Fix a few typos in the architecture doc (#3054)

Fri, 02 Jul 2021 18:09:58 +0000

Fix a few typos in the architecture doc (#3054) List of files: /wasmtime-44.0.1/docs/contributing-architecture.md

aa5d8374 - Start a high-level architecture document for Wasmtime (#3019)

Fri, 02 Jul 2021 14:02:26 +0000

Start a high-level architecture document for Wasmtime (#3019)* Start a high-level architecture document for Wasmtime This commit cleands up some existing documentation by removing a number of "noop README files" and starting a high-level overview of the architecture of Wasmtime. I've placed this documentation under the contributing section of the book since it seems most useful for possible contributors. I've surely left some things out in this pass, and am happy to add more! * Review comments * More rewording * typos List of files: /wasmtime-44.0.1/docs/contributing-architecture.md