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add FCW to warn about wasm ABI transition by RalfJung · Pull Request #138601 · rust-lang/rust

@rustbot rustbot added S-waiting-on-review

Status: Awaiting review from the assignee but also interested parties.

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Relevant to the compiler team, which will review and decide on the PR/issue.

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Mar 17, 2025

RalfJung

bjorn3

bjorn3

alexcrichton

@jieyouxu jieyouxu added the O-wasm

Target: WASM (WebAssembly), http://webassembly.org/

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Mar 17, 2025

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Mar 21, 2025

bjorn3

@RalfJung

bors added a commit to rust-lang-ci/rust that referenced this pull request

Mar 25, 2025 
add FCW to warn about wasm ABI transition

See rust-lang#122532 for context: the "C" ABI on wasm32-unk-unk will change. The goal of this lint is to warn about any function definition and calls whose behavior will be affected by the change. My understanding is the following:
- scalar arguments are fine
  - including 128 bit types, they get passed as two `i64` arguments in both ABIs
- `repr(C)` structs (recursively) wrapping a single scalar argument are fine (unless they have extra padding due to over-alignment attributes)
- all return values are fine

`@bjorn3` `@alexcrichton` `@Manishearth` is that correct?

I am making this a "show up in future compat reports" lint to maximize the chances people become aware of this. OTOH this likely means warnings for most users of Diplomat so maybe we shouldn't do this?

IIUC, wasm-bindgen should be unaffected by this lint as they only pass scalar types as arguments.

Tracking issue: rust-lang#138762
Transition plan blog post: rust-lang/blog.rust-lang.org#1531

try-job: dist-various-2

bors added a commit to rust-lang-ci/rust that referenced this pull request

Mar 25, 2025 
add FCW to warn about wasm ABI transition

See rust-lang#122532 for context: the "C" ABI on wasm32-unk-unk will change. The goal of this lint is to warn about any function definition and calls whose behavior will be affected by the change. My understanding is the following:
- scalar arguments are fine
  - including 128 bit types, they get passed as two `i64` arguments in both ABIs
- `repr(C)` structs (recursively) wrapping a single scalar argument are fine (unless they have extra padding due to over-alignment attributes)
- all return values are fine

`@bjorn3` `@alexcrichton` `@Manishearth` is that correct?

I am making this a "show up in future compat reports" lint to maximize the chances people become aware of this. OTOH this likely means warnings for most users of Diplomat so maybe we shouldn't do this?

IIUC, wasm-bindgen should be unaffected by this lint as they only pass scalar types as arguments.

Tracking issue: rust-lang#138762
Transition plan blog post: rust-lang/blog.rust-lang.org#1531

try-job: dist-various-2

@bors bors added S-waiting-on-bors

Status: Waiting on bors to run and complete tests. Bors will change the label on completion.

and removed S-waiting-on-author

Status: This is awaiting some action (such as code changes or more information) from the author.

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Mar 25, 2025

@bors bors mentioned this pull request

Mar 26, 2025

github-actions bot pushed a commit to model-checking/verify-rust-std that referenced this pull request

Apr 2, 2025 
add FCW to warn about wasm ABI transition

See rust-lang#122532 for context: the "C" ABI on wasm32-unk-unk will change. The goal of this lint is to warn about any function definition and calls whose behavior will be affected by the change. My understanding is the following:
- scalar arguments are fine
  - including 128 bit types, they get passed as two `i64` arguments in both ABIs
- `repr(C)` structs (recursively) wrapping a single scalar argument are fine (unless they have extra padding due to over-alignment attributes)
- all return values are fine

`@bjorn3` `@alexcrichton` `@Manishearth` is that correct?

I am making this a "show up in future compat reports" lint to maximize the chances people become aware of this. OTOH this likely means warnings for most users of Diplomat so maybe we shouldn't do this?

IIUC, wasm-bindgen should be unaffected by this lint as they only pass scalar types as arguments.

Tracking issue: rust-lang#138762
Transition plan blog post: rust-lang/blog.rust-lang.org#1531

try-job: dist-various-2

alexcrichton added a commit to alexcrichton/blog.rust-lang.org that referenced this pull request

Apr 3, 2025