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Tracking Issue for `naked_functions_target_feature` #138568

Open

4 tasks

folkertdev opened this issue Mar 16, 2025 · 1 comment

Open

4 tasks

Tracking Issue for `naked_functions_target_feature` #138568

folkertdev opened this issue Mar 16, 2025 · 1 comment

Labels

A-attributes A-naked A-target-feature C-tracking-issue F-naked_functions_target_feature F-naked_functions T-compiler T-lang

Contributor

folkertdev commented Mar 16, 2025 •

edited

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The feature gate for the issue is #![feature(naked_functions_target_feature)].

The #[target_feature(enable = "...")] attribute on standard functions can have two effects:

change the ABI (e.g. how vector types are passed)
change what instructions are accepted in the body (e.g. whether vector instructions are allowed)

At the time of writing, target_feature is ignored when generating code for naked functions even with this feature enabled! Hence, you almost certainly don't need to enable this feature.

If you need to change what instructions are accepted, you can use assembler directives in the naked assembly. See #137720 for examples on how to do that on the most common platforms.

For naked functions, a target_feature does not change the generated code of that function: naked functions must already assume that their registers are in particular registers, and can document assumptions about e.g. the use of vector registers as safety conditions on the naked function itself. Hence, the target feature is useful only as documentation, and currently not strictly needed. Note that there are plans to it a hard requirement that functions using vector types in their signature enable the relevant target features.

About tracking issues

Tracking issues are used to record the overall progress of implementation.
They are also used as hubs connecting to other relevant issues, e.g., bugs or open design questions.
A tracking issue is however not meant for large scale discussion, questions, or bug reports about a feature.
Instead, open a dedicated issue for the specific matter and add the relevant feature gate label.
Discussion comments will get marked as off-topic or deleted.
Repeated discussions on the tracking issue may lead to the tracking issue getting locked.

Steps

Implement the RFC (cc @rust-lang/XXX -- can anyone write up mentoring
instructions?)
Adjust documentation (see instructions on rustc-dev-guide)
Formatting for new syntax has been added to the Style Guide (nightly-style-procedure)
Stabilization PR (see instructions on rustc-dev-guide)

Unresolved Questions

should we try to automatically handle target features at all?
if so, how do we deal with platforms where LLVM has no tools for toggling target features from inline assembly (e.g. wasm simd128)
and how do we deal with the complex interplay of target features with the (different versions of) the target platform (e.g. armv8 has very complex target features)

Implementation history

The text was updated successfully, but these errors were encountered:

folkertdev added the C-tracking-issue label

folkertdev mentioned this issue

add naked_functions_target_feature unstable feature #138570

Merged

Contributor Author

folkertdev commented Mar 16, 2025

@rustbot label +A-naked +F-naked_functions

rustbot added A-naked F-naked_functions labels

matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue


          Rollup merge of rust-lang#138570 - folkertdev:naked-function-target-f…

aa3ec09

…eature-gate, r=Amanieu

add `naked_functions_target_feature` unstable feature

tracking issue: rust-lang#138568

tagging rust-lang#134213 rust-lang#90957

This PR puts `#[target_feature(/* ... */)]` on `#[naked]` functions behind its own feature gate, so that naked functions can be stabilized. It turns out that supporting `target_feature` on naked functions is tricky on some targets, so we're splitting it out to not block stabilization of naked functions themselves. See the tracking issue for more information and workarounds.

Note that at the time of writing, the `target_features` attribute is ignored when generating code for naked functions.

r? `@Amanieu`

matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue


          Rollup merge of rust-lang#138570 - folkertdev:naked-function-target-f…

c354a97

…eature-gate, r=Amanieu

add `naked_functions_target_feature` unstable feature

tracking issue: rust-lang#138568

tagging rust-lang#134213 rust-lang#90957

This PR puts `#[target_feature(/* ... */)]` on `#[naked]` functions behind its own feature gate, so that naked functions can be stabilized. It turns out that supporting `target_feature` on naked functions is tricky on some targets, so we're splitting it out to not block stabilization of naked functions themselves. See the tracking issue for more information and workarounds.

Note that at the time of writing, the `target_features` attribute is ignored when generating code for naked functions.

r? ``@Amanieu``

rust-timer added a commit to rust-lang-ci/rust that referenced this issue


          Unrolled build for rust-lang#138570

9f54074

Rollup merge of rust-lang#138570 - folkertdev:naked-function-target-feature-gate, r=Amanieu

add `naked_functions_target_feature` unstable feature

tracking issue: rust-lang#138568

tagging rust-lang#134213 rust-lang#90957

This PR puts `#[target_feature(/* ... */)]` on `#[naked]` functions behind its own feature gate, so that naked functions can be stabilized. It turns out that supporting `target_feature` on naked functions is tricky on some targets, so we're splitting it out to not block stabilization of naked functions themselves. See the tracking issue for more information and workarounds.

Note that at the time of writing, the `target_features` attribute is ignored when generating code for naked functions.

r? ``@Amanieu``

folkertdev mentioned this issue

Stabilize naked_functions #134213

Open

jieyouxu added T-lang T-compiler A-attributes A-target-feature labels

traviscross added the F-naked_functions_target_feature label

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Labels

A-attributes A-naked A-target-feature C-tracking-issue F-naked_functions_target_feature F-naked_functions T-compiler T-lang