C ABI Changes for wasm32-unknown-unknown
#1531
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This adds a post for changes discussed in rust-lang/rust#122532 and rust-lang/rust#138601, notably as a result of this decision: rust-lang/rust#122532 (comment)
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I'll note that at this time I'm opening this up to share with folks and get feedback, there's no concrete timeline for when to publish this. My hope for now is "soon after rust-lang/rust#138601" |
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I'll also note, wow, this issue has a huge and sprawling history. I've surely missed something and wanted to clarify that it's not intentional. Let me know! |
Manishearth
reviewed
Mar 21, 2025
| with `-Zwasm-c-abi=spec`. If all that passes then you're good to go and the | ||
| upcoming change to the C ABI will not affect your project. | ||
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| ## I'm affected, now what? |
ehuss
reviewed
Mar 21, 2025
RalfJung
reviewed
Mar 21, 2025
Co-authored-by: Ralf Jung <[email protected]> Co-authored-by: Eric Huss <[email protected]>
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I believe I've addressed all feedback here and I've also marked this as ready-to-go, but I'll drop a comment here after a nightly is available since I think it would be best to wait for a compiler first before publishing this. |
tgross35
added a commit
to tgross35/rust
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Mar 22, 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
matthiaskrgr
added a commit
to matthiaskrgr/rust
that referenced
this pull request
Mar 24, 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
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
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 26, 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
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rust-lang/rust#138601 has now landed, but it didn't make today's nightly, so best to wait one more day for this |
github-actions bot
pushed a commit
to rust-lang/rustc-dev-guide
that referenced
this pull request
Mar 27, 2025
add FCW to warn about wasm ABI transition See rust-lang/rust#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/rust#138762 Transition plan blog post: rust-lang/blog.rust-lang.org#1531 try-job: dist-various-2
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Ok I've added the date of a rustc that has this change now, and this should be good to go |
ehuss
reviewed
Mar 28, 2025
| @@ -0,0 +1,273 @@ | |||
| +++ | |||
| layout = "post" | |||
| date = 2024-03-20 | |||
There was a problem hiding this comment.
The date should be updated to whatever date it goes out.
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And make sure it is the correct year. 😜
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Oop yes thanks! Updated to tomorrow, but happy to update this again if needed
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Just to ensure this doesn't block without a clear owner, I assume this is on behalf of the compiler team, so @davidtwco or @wesleywiser I assume this would be yours to approve? |
bjorn3
reviewed
Mar 28, 2025
| @@ -194,7 +194,7 @@ To determine the impact to your project there are a few tools at your disposal: | |||
| Code can use `-Zwasm-c-abi=spec` to use the standard definition of the C ABI | |||
| for a crate to test out if changes work. | |||
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| The best way to test your crate is to compile with the most recent Nightly | |||
| The best way to test your crate is to compile with a `nightly-2025-03-27` | |||
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This adds a post for changes discussed in
rust-lang/rust#122532 and rust-lang/rust#138601, notably as a result of this decision:
rust-lang/rust#122532 (comment)