Allow coercing safe-to-call target_feature functions to safe fn pointers #135504

veluca93 · 2025-01-14T21:55:52Z

r? oli-obk

@oli-obk: this is based on your PR #134353 :-)

See #134090 (comment) for the motivation behind this change.

rustbot · 2025-01-14T21:56:04Z

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

bors · 2025-01-15T15:56:15Z

☔ The latest upstream changes (presumably #134353) made this pull request unmergeable. Please resolve the merge conflicts.

tests/ui/rfcs/rfc-2396-target_feature-11/fn-ptr.rs

compiler/rustc_hir_typeck/src/coercion.rs

compiler/rustc_borrowck/src/type_check/mod.rs

oli-obk · 2025-01-16T11:03:59Z

@bors r+

bors · 2025-01-16T11:04:02Z

📌 Commit 8fee6a7 has been approved by oli-obk

It is now in the queue for this repository.

…iaskrgr Rollup of 7 pull requests Successful merges: - rust-lang#134754 (Implement `use` associated items of traits) - rust-lang#135481 (coverage: Completely overhaul counter assignment, using node-flow graphs) - rust-lang#135504 (Allow coercing safe-to-call target_feature functions to safe fn pointers) - rust-lang#135561 (Update docs for `-Clink-dead-code` to discourage its use) - rust-lang#135574 (ci: mirror ubuntu:22.04 to ghcr.io) - rust-lang#135585 (resolve symlinks of LLVM tool binaries before copying them) - rust-lang#135588 (Add license-metadata.json to rustc-src tarball.) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of rust-lang#135504 - veluca93:target-feature-cast-to-fn-ptr, r=oli-obk Allow coercing safe-to-call target_feature functions to safe fn pointers r? oli-obk `@oli-obk:` this is based on your PR rust-lang#134353 :-) See rust-lang#134090 (comment) for the motivation behind this change.

Stabilize target_feature_11 # Stabilization report This is an updated version of rust-lang#116114, which is itself a redo of rust-lang#99767. Most of this commit and report were copied from those PRs. Thanks `@LeSeulArtichaut` and `@calebzulawski!` ## Summary Allows for safe functions to be marked with `#[target_feature]` attributes. Functions marked with `#[target_feature]` are generally considered as unsafe functions: they are unsafe to call, cannot *generally* be assigned to safe function pointers, and don't implement the `Fn*` traits. However, calling them from other `#[target_feature]` functions with a superset of features is safe. ```rust // Demonstration function #[target_feature(enable = "avx2")] fn avx2() {} fn foo() { // Calling `avx2` here is unsafe, as we must ensure // that AVX is available first. unsafe { avx2(); } } #[target_feature(enable = "avx2")] fn bar() { // Calling `avx2` here is safe. avx2(); } ``` Moreover, once rust-lang#135504 is merged, they can be converted to safe function pointers in a context in which calling them is safe: ```rust // Demonstration function #[target_feature(enable = "avx2")] fn avx2() {} fn foo() -> fn() { // Converting `avx2` to fn() is a compilation error here. avx2 } #[target_feature(enable = "avx2")] fn bar() -> fn() { // `avx2` coerces to fn() here avx2 } ``` See the section "Closures" below for justification of this behaviour. ## Test cases Tests for this feature can be found in [`tests/ui/target_feature/`](https://github.com/rust-lang/rust/tree/f6cb952dc115fd1311b02b694933e31d8dc8b002/tests/ui/target-feature). ## Edge cases ### Closures * [target-feature 1.1: should closures inherit target-feature annotations? rust-lang#73631](rust-lang#73631) Closures defined inside functions marked with #[target_feature] inherit the target features of their parent function. They can still be assigned to safe function pointers and implement the appropriate `Fn*` traits. ```rust #[target_feature(enable = "avx2")] fn qux() { let my_closure = || avx2(); // this call to `avx2` is safe let f: fn() = my_closure; } ``` This means that in order to call a function with #[target_feature], you must guarantee that the target-feature is available while the function, any closures defined inside it, as well as any safe function pointers obtained from target-feature functions inside it, execute. This is usually ensured because target features are assumed to never disappear, and: - on any unsafe call to a `#[target_feature]` function, presence of the target feature is guaranteed by the programmer through the safety requirements of the unsafe call. - on any safe call, this is guaranteed recursively by the caller. If you work in an environment where target features can be disabled, it is your responsibility to ensure that no code inside a target feature function (including inside a closure) runs after this (until the feature is enabled again). **Note:** this has an effect on existing code, as nowadays closures do not inherit features from the enclosing function, and thus this strengthens a safety requirement. It was originally proposed in rust-lang#73631 to solve this by adding a new type of UB: “taking a target feature away from your process after having run code that uses that target feature is UB” . This was motivated by userspace code already assuming in a few places that CPU features never disappear from a program during execution (see i.e. https://github.com/rust-lang/stdarch/blob/2e29bdf90832931ea499755bb4ad7a6b0809295a/crates/std_detect/src/detect/arch/x86.rs); however, concerns were raised in the context of the Linux kernel; thus, we propose to relax that requirement to "causing the set of usable features to be reduced is unsafe; when doing so, the programmer is required to ensure that no closures or safe fn pointers that use removed features are still in scope". * [Fix #[inline(always)] on closures with target feature 1.1 rust-lang#111836](rust-lang#111836) Closures accept `#[inline(always)]`, even within functions marked with `#[target_feature]`. Since these attributes conflict, `#[inline(always)]` wins out to maintain compatibility. ### ABI concerns * [The extern "C" ABI of SIMD vector types depends on target features rust-lang#116558](rust-lang#116558) The ABI of some types can change when compiling a function with different target features. This could have introduced unsoundness with target_feature_11, but recent fixes (rust-lang#133102, rust-lang#132173) either make those situations invalid or make the ABI no longer dependent on features. Thus, those issues should no longer occur. ### Special functions The `#[target_feature]` attribute is forbidden from a variety of special functions, such as main, current and future lang items (e.g. `#[start]`, `#[panic_handler]`), safe default trait implementations and safe trait methods. This was not disallowed at the time of the first stabilization PR for target_features_11, and resulted in the following issues/PRs: * [`#[target_feature]` is allowed on `main` rust-lang#108645](rust-lang#108645) * [`#[target_feature]` is allowed on default implementations rust-lang#108646](rust-lang#108646) * [#[target_feature] is allowed on #[panic_handler] with target_feature 1.1 rust-lang#109411](rust-lang#109411) * [Prevent using `#[target_feature]` on lang item functions rust-lang#115910](rust-lang#115910) ## Documentation * Reference: [Document the `target_feature_11` feature reference#1181](rust-lang/reference#1181) --- cc tracking issue rust-lang#69098 cc `@workingjubilee` cc `@RalfJung` r? `@rust-lang/lang`

Stabilize target_feature_11 # Stabilization report This is an updated version of rust-lang#116114, which is itself a redo of rust-lang#99767. Most of this commit and report were copied from those PRs. Thanks ``@LeSeulArtichaut`` and ``@calebzulawski!`` ## Summary Allows for safe functions to be marked with `#[target_feature]` attributes. Functions marked with `#[target_feature]` are generally considered as unsafe functions: they are unsafe to call, cannot *generally* be assigned to safe function pointers, and don't implement the `Fn*` traits. However, calling them from other `#[target_feature]` functions with a superset of features is safe. ```rust // Demonstration function #[target_feature(enable = "avx2")] fn avx2() {} fn foo() { // Calling `avx2` here is unsafe, as we must ensure // that AVX is available first. unsafe { avx2(); } } #[target_feature(enable = "avx2")] fn bar() { // Calling `avx2` here is safe. avx2(); } ``` Moreover, once rust-lang#135504 is merged, they can be converted to safe function pointers in a context in which calling them is safe: ```rust // Demonstration function #[target_feature(enable = "avx2")] fn avx2() {} fn foo() -> fn() { // Converting `avx2` to fn() is a compilation error here. avx2 } #[target_feature(enable = "avx2")] fn bar() -> fn() { // `avx2` coerces to fn() here avx2 } ``` See the section "Closures" below for justification of this behaviour. ## Test cases Tests for this feature can be found in [`tests/ui/target_feature/`](https://github.com/rust-lang/rust/tree/f6cb952dc115fd1311b02b694933e31d8dc8b002/tests/ui/target-feature). ## Edge cases ### Closures * [target-feature 1.1: should closures inherit target-feature annotations? rust-lang#73631](rust-lang#73631) Closures defined inside functions marked with #[target_feature] inherit the target features of their parent function. They can still be assigned to safe function pointers and implement the appropriate `Fn*` traits. ```rust #[target_feature(enable = "avx2")] fn qux() { let my_closure = || avx2(); // this call to `avx2` is safe let f: fn() = my_closure; } ``` This means that in order to call a function with #[target_feature], you must guarantee that the target-feature is available while the function, any closures defined inside it, as well as any safe function pointers obtained from target-feature functions inside it, execute. This is usually ensured because target features are assumed to never disappear, and: - on any unsafe call to a `#[target_feature]` function, presence of the target feature is guaranteed by the programmer through the safety requirements of the unsafe call. - on any safe call, this is guaranteed recursively by the caller. If you work in an environment where target features can be disabled, it is your responsibility to ensure that no code inside a target feature function (including inside a closure) runs after this (until the feature is enabled again). **Note:** this has an effect on existing code, as nowadays closures do not inherit features from the enclosing function, and thus this strengthens a safety requirement. It was originally proposed in rust-lang#73631 to solve this by adding a new type of UB: “taking a target feature away from your process after having run code that uses that target feature is UB” . This was motivated by userspace code already assuming in a few places that CPU features never disappear from a program during execution (see i.e. https://github.com/rust-lang/stdarch/blob/2e29bdf90832931ea499755bb4ad7a6b0809295a/crates/std_detect/src/detect/arch/x86.rs); however, concerns were raised in the context of the Linux kernel; thus, we propose to relax that requirement to "causing the set of usable features to be reduced is unsafe; when doing so, the programmer is required to ensure that no closures or safe fn pointers that use removed features are still in scope". * [Fix #[inline(always)] on closures with target feature 1.1 rust-lang#111836](rust-lang#111836) Closures accept `#[inline(always)]`, even within functions marked with `#[target_feature]`. Since these attributes conflict, `#[inline(always)]` wins out to maintain compatibility. ### ABI concerns * [The extern "C" ABI of SIMD vector types depends on target features rust-lang#116558](rust-lang#116558) The ABI of some types can change when compiling a function with different target features. This could have introduced unsoundness with target_feature_11, but recent fixes (rust-lang#133102, rust-lang#132173) either make those situations invalid or make the ABI no longer dependent on features. Thus, those issues should no longer occur. ### Special functions The `#[target_feature]` attribute is forbidden from a variety of special functions, such as main, current and future lang items (e.g. `#[start]`, `#[panic_handler]`), safe default trait implementations and safe trait methods. This was not disallowed at the time of the first stabilization PR for target_features_11, and resulted in the following issues/PRs: * [`#[target_feature]` is allowed on `main` rust-lang#108645](rust-lang#108645) * [`#[target_feature]` is allowed on default implementations rust-lang#108646](rust-lang#108646) * [#[target_feature] is allowed on #[panic_handler] with target_feature 1.1 rust-lang#109411](rust-lang#109411) * [Prevent using `#[target_feature]` on lang item functions rust-lang#115910](rust-lang#115910) ## Documentation * Reference: [Document the `target_feature_11` feature reference#1181](rust-lang/reference#1181) --- cc tracking issue rust-lang#69098 cc ``@workingjubilee`` cc ``@RalfJung`` r? ``@rust-lang/lang``

Stabilize target_feature_11 # Stabilization report This is an updated version of rust-lang#116114, which is itself a redo of rust-lang#99767. Most of this commit and report were copied from those PRs. Thanks ```@LeSeulArtichaut``` and ```@calebzulawski!``` ## Summary Allows for safe functions to be marked with `#[target_feature]` attributes. Functions marked with `#[target_feature]` are generally considered as unsafe functions: they are unsafe to call, cannot *generally* be assigned to safe function pointers, and don't implement the `Fn*` traits. However, calling them from other `#[target_feature]` functions with a superset of features is safe. ```rust // Demonstration function #[target_feature(enable = "avx2")] fn avx2() {} fn foo() { // Calling `avx2` here is unsafe, as we must ensure // that AVX is available first. unsafe { avx2(); } } #[target_feature(enable = "avx2")] fn bar() { // Calling `avx2` here is safe. avx2(); } ``` Moreover, once rust-lang#135504 is merged, they can be converted to safe function pointers in a context in which calling them is safe: ```rust // Demonstration function #[target_feature(enable = "avx2")] fn avx2() {} fn foo() -> fn() { // Converting `avx2` to fn() is a compilation error here. avx2 } #[target_feature(enable = "avx2")] fn bar() -> fn() { // `avx2` coerces to fn() here avx2 } ``` See the section "Closures" below for justification of this behaviour. ## Test cases Tests for this feature can be found in [`tests/ui/target_feature/`](https://github.com/rust-lang/rust/tree/f6cb952dc115fd1311b02b694933e31d8dc8b002/tests/ui/target-feature). ## Edge cases ### Closures * [target-feature 1.1: should closures inherit target-feature annotations? rust-lang#73631](rust-lang#73631) Closures defined inside functions marked with #[target_feature] inherit the target features of their parent function. They can still be assigned to safe function pointers and implement the appropriate `Fn*` traits. ```rust #[target_feature(enable = "avx2")] fn qux() { let my_closure = || avx2(); // this call to `avx2` is safe let f: fn() = my_closure; } ``` This means that in order to call a function with #[target_feature], you must guarantee that the target-feature is available while the function, any closures defined inside it, as well as any safe function pointers obtained from target-feature functions inside it, execute. This is usually ensured because target features are assumed to never disappear, and: - on any unsafe call to a `#[target_feature]` function, presence of the target feature is guaranteed by the programmer through the safety requirements of the unsafe call. - on any safe call, this is guaranteed recursively by the caller. If you work in an environment where target features can be disabled, it is your responsibility to ensure that no code inside a target feature function (including inside a closure) runs after this (until the feature is enabled again). **Note:** this has an effect on existing code, as nowadays closures do not inherit features from the enclosing function, and thus this strengthens a safety requirement. It was originally proposed in rust-lang#73631 to solve this by adding a new type of UB: “taking a target feature away from your process after having run code that uses that target feature is UB” . This was motivated by userspace code already assuming in a few places that CPU features never disappear from a program during execution (see i.e. https://github.com/rust-lang/stdarch/blob/2e29bdf90832931ea499755bb4ad7a6b0809295a/crates/std_detect/src/detect/arch/x86.rs); however, concerns were raised in the context of the Linux kernel; thus, we propose to relax that requirement to "causing the set of usable features to be reduced is unsafe; when doing so, the programmer is required to ensure that no closures or safe fn pointers that use removed features are still in scope". * [Fix #[inline(always)] on closures with target feature 1.1 rust-lang#111836](rust-lang#111836) Closures accept `#[inline(always)]`, even within functions marked with `#[target_feature]`. Since these attributes conflict, `#[inline(always)]` wins out to maintain compatibility. ### ABI concerns * [The extern "C" ABI of SIMD vector types depends on target features rust-lang#116558](rust-lang#116558) The ABI of some types can change when compiling a function with different target features. This could have introduced unsoundness with target_feature_11, but recent fixes (rust-lang#133102, rust-lang#132173) either make those situations invalid or make the ABI no longer dependent on features. Thus, those issues should no longer occur. ### Special functions The `#[target_feature]` attribute is forbidden from a variety of special functions, such as main, current and future lang items (e.g. `#[start]`, `#[panic_handler]`), safe default trait implementations and safe trait methods. This was not disallowed at the time of the first stabilization PR for target_features_11, and resulted in the following issues/PRs: * [`#[target_feature]` is allowed on `main` rust-lang#108645](rust-lang#108645) * [`#[target_feature]` is allowed on default implementations rust-lang#108646](rust-lang#108646) * [#[target_feature] is allowed on #[panic_handler] with target_feature 1.1 rust-lang#109411](rust-lang#109411) * [Prevent using `#[target_feature]` on lang item functions rust-lang#115910](rust-lang#115910) ## Documentation * Reference: [Document the `target_feature_11` feature reference#1181](rust-lang/reference#1181) --- cc tracking issue rust-lang#69098 cc ```@workingjubilee``` cc ```@RalfJung``` r? ```@rust-lang/lang```

Rollup merge of rust-lang#134090 - veluca93:stable-tf11, r=oli-obk Stabilize target_feature_11 # Stabilization report This is an updated version of rust-lang#116114, which is itself a redo of rust-lang#99767. Most of this commit and report were copied from those PRs. Thanks ```@LeSeulArtichaut``` and ```@calebzulawski!``` ## Summary Allows for safe functions to be marked with `#[target_feature]` attributes. Functions marked with `#[target_feature]` are generally considered as unsafe functions: they are unsafe to call, cannot *generally* be assigned to safe function pointers, and don't implement the `Fn*` traits. However, calling them from other `#[target_feature]` functions with a superset of features is safe. ```rust // Demonstration function #[target_feature(enable = "avx2")] fn avx2() {} fn foo() { // Calling `avx2` here is unsafe, as we must ensure // that AVX is available first. unsafe { avx2(); } } #[target_feature(enable = "avx2")] fn bar() { // Calling `avx2` here is safe. avx2(); } ``` Moreover, once rust-lang#135504 is merged, they can be converted to safe function pointers in a context in which calling them is safe: ```rust // Demonstration function #[target_feature(enable = "avx2")] fn avx2() {} fn foo() -> fn() { // Converting `avx2` to fn() is a compilation error here. avx2 } #[target_feature(enable = "avx2")] fn bar() -> fn() { // `avx2` coerces to fn() here avx2 } ``` See the section "Closures" below for justification of this behaviour. ## Test cases Tests for this feature can be found in [`tests/ui/target_feature/`](https://github.com/rust-lang/rust/tree/f6cb952dc115fd1311b02b694933e31d8dc8b002/tests/ui/target-feature). ## Edge cases ### Closures * [target-feature 1.1: should closures inherit target-feature annotations? rust-lang#73631](rust-lang#73631) Closures defined inside functions marked with #[target_feature] inherit the target features of their parent function. They can still be assigned to safe function pointers and implement the appropriate `Fn*` traits. ```rust #[target_feature(enable = "avx2")] fn qux() { let my_closure = || avx2(); // this call to `avx2` is safe let f: fn() = my_closure; } ``` This means that in order to call a function with #[target_feature], you must guarantee that the target-feature is available while the function, any closures defined inside it, as well as any safe function pointers obtained from target-feature functions inside it, execute. This is usually ensured because target features are assumed to never disappear, and: - on any unsafe call to a `#[target_feature]` function, presence of the target feature is guaranteed by the programmer through the safety requirements of the unsafe call. - on any safe call, this is guaranteed recursively by the caller. If you work in an environment where target features can be disabled, it is your responsibility to ensure that no code inside a target feature function (including inside a closure) runs after this (until the feature is enabled again). **Note:** this has an effect on existing code, as nowadays closures do not inherit features from the enclosing function, and thus this strengthens a safety requirement. It was originally proposed in rust-lang#73631 to solve this by adding a new type of UB: “taking a target feature away from your process after having run code that uses that target feature is UB” . This was motivated by userspace code already assuming in a few places that CPU features never disappear from a program during execution (see i.e. https://github.com/rust-lang/stdarch/blob/2e29bdf90832931ea499755bb4ad7a6b0809295a/crates/std_detect/src/detect/arch/x86.rs); however, concerns were raised in the context of the Linux kernel; thus, we propose to relax that requirement to "causing the set of usable features to be reduced is unsafe; when doing so, the programmer is required to ensure that no closures or safe fn pointers that use removed features are still in scope". * [Fix #[inline(always)] on closures with target feature 1.1 rust-lang#111836](rust-lang#111836) Closures accept `#[inline(always)]`, even within functions marked with `#[target_feature]`. Since these attributes conflict, `#[inline(always)]` wins out to maintain compatibility. ### ABI concerns * [The extern "C" ABI of SIMD vector types depends on target features rust-lang#116558](rust-lang#116558) The ABI of some types can change when compiling a function with different target features. This could have introduced unsoundness with target_feature_11, but recent fixes (rust-lang#133102, rust-lang#132173) either make those situations invalid or make the ABI no longer dependent on features. Thus, those issues should no longer occur. ### Special functions The `#[target_feature]` attribute is forbidden from a variety of special functions, such as main, current and future lang items (e.g. `#[start]`, `#[panic_handler]`), safe default trait implementations and safe trait methods. This was not disallowed at the time of the first stabilization PR for target_features_11, and resulted in the following issues/PRs: * [`#[target_feature]` is allowed on `main` rust-lang#108645](rust-lang#108645) * [`#[target_feature]` is allowed on default implementations rust-lang#108646](rust-lang#108646) * [#[target_feature] is allowed on #[panic_handler] with target_feature 1.1 rust-lang#109411](rust-lang#109411) * [Prevent using `#[target_feature]` on lang item functions rust-lang#115910](rust-lang#115910) ## Documentation * Reference: [Document the `target_feature_11` feature reference#1181](rust-lang/reference#1181) --- cc tracking issue rust-lang#69098 cc ```@workingjubilee``` cc ```@RalfJung``` r? ```@rust-lang/lang```

Stabilize target_feature_11 # Stabilization report This is an updated version of rust-lang/rust#116114, which is itself a redo of rust-lang/rust#99767. Most of this commit and report were copied from those PRs. Thanks ```@LeSeulArtichaut``` and ```@calebzulawski!``` ## Summary Allows for safe functions to be marked with `#[target_feature]` attributes. Functions marked with `#[target_feature]` are generally considered as unsafe functions: they are unsafe to call, cannot *generally* be assigned to safe function pointers, and don't implement the `Fn*` traits. However, calling them from other `#[target_feature]` functions with a superset of features is safe. ```rust // Demonstration function #[target_feature(enable = "avx2")] fn avx2() {} fn foo() { // Calling `avx2` here is unsafe, as we must ensure // that AVX is available first. unsafe { avx2(); } } #[target_feature(enable = "avx2")] fn bar() { // Calling `avx2` here is safe. avx2(); } ``` Moreover, once rust-lang/rust#135504 is merged, they can be converted to safe function pointers in a context in which calling them is safe: ```rust // Demonstration function #[target_feature(enable = "avx2")] fn avx2() {} fn foo() -> fn() { // Converting `avx2` to fn() is a compilation error here. avx2 } #[target_feature(enable = "avx2")] fn bar() -> fn() { // `avx2` coerces to fn() here avx2 } ``` See the section "Closures" below for justification of this behaviour. ## Test cases Tests for this feature can be found in [`tests/ui/target_feature/`](https://github.com/rust-lang/rust/tree/f6cb952dc115fd1311b02b694933e31d8dc8b002/tests/ui/target-feature). ## Edge cases ### Closures * [target-feature 1.1: should closures inherit target-feature annotations? #73631](rust-lang/rust#73631) Closures defined inside functions marked with #[target_feature] inherit the target features of their parent function. They can still be assigned to safe function pointers and implement the appropriate `Fn*` traits. ```rust #[target_feature(enable = "avx2")] fn qux() { let my_closure = || avx2(); // this call to `avx2` is safe let f: fn() = my_closure; } ``` This means that in order to call a function with #[target_feature], you must guarantee that the target-feature is available while the function, any closures defined inside it, as well as any safe function pointers obtained from target-feature functions inside it, execute. This is usually ensured because target features are assumed to never disappear, and: - on any unsafe call to a `#[target_feature]` function, presence of the target feature is guaranteed by the programmer through the safety requirements of the unsafe call. - on any safe call, this is guaranteed recursively by the caller. If you work in an environment where target features can be disabled, it is your responsibility to ensure that no code inside a target feature function (including inside a closure) runs after this (until the feature is enabled again). **Note:** this has an effect on existing code, as nowadays closures do not inherit features from the enclosing function, and thus this strengthens a safety requirement. It was originally proposed in #73631 to solve this by adding a new type of UB: “taking a target feature away from your process after having run code that uses that target feature is UB” . This was motivated by userspace code already assuming in a few places that CPU features never disappear from a program during execution (see i.e. https://github.com/rust-lang/stdarch/blob/2e29bdf90832931ea499755bb4ad7a6b0809295a/crates/std_detect/src/detect/arch/x86.rs); however, concerns were raised in the context of the Linux kernel; thus, we propose to relax that requirement to "causing the set of usable features to be reduced is unsafe; when doing so, the programmer is required to ensure that no closures or safe fn pointers that use removed features are still in scope". * [Fix #[inline(always)] on closures with target feature 1.1 #111836](rust-lang/rust#111836) Closures accept `#[inline(always)]`, even within functions marked with `#[target_feature]`. Since these attributes conflict, `#[inline(always)]` wins out to maintain compatibility. ### ABI concerns * [The extern "C" ABI of SIMD vector types depends on target features #116558](rust-lang/rust#116558) The ABI of some types can change when compiling a function with different target features. This could have introduced unsoundness with target_feature_11, but recent fixes (#133102, #132173) either make those situations invalid or make the ABI no longer dependent on features. Thus, those issues should no longer occur. ### Special functions The `#[target_feature]` attribute is forbidden from a variety of special functions, such as main, current and future lang items (e.g. `#[start]`, `#[panic_handler]`), safe default trait implementations and safe trait methods. This was not disallowed at the time of the first stabilization PR for target_features_11, and resulted in the following issues/PRs: * [`#[target_feature]` is allowed on `main` #108645](rust-lang/rust#108645) * [`#[target_feature]` is allowed on default implementations #108646](rust-lang/rust#108646) * [#[target_feature] is allowed on #[panic_handler] with target_feature 1.1 #109411](rust-lang/rust#109411) * [Prevent using `#[target_feature]` on lang item functions #115910](rust-lang/rust#115910) ## Documentation * Reference: [Document the `target_feature_11` feature reference#1181](rust-lang/reference#1181) --- cc tracking issue rust-lang/rust#69098 cc ```@workingjubilee``` cc ```@RalfJung``` r? ```@rust-lang/lang```

rustbot assigned oli-obk Jan 14, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-rustdoc Relevant to the rustdoc team, which will review and decide on the PR/issue. labels Jan 14, 2025

veluca93 mentioned this pull request Jan 14, 2025

Stabilize target_feature_11 #134090

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oli-obk reviewed Jan 15, 2025

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tests/ui/rfcs/rfc-2396-target_feature-11/fn-ptr.rs Show resolved Hide resolved

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compiler/rustc_hir_typeck/src/coercion.rs Outdated Show resolved Hide resolved

veluca93 force-pushed the target-feature-cast-to-fn-ptr branch from fb5980b to ea653b8 Compare January 15, 2025 16:24

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veluca93 force-pushed the target-feature-cast-to-fn-ptr branch from ea653b8 to 3471d41 Compare January 15, 2025 20:59

oli-obk reviewed Jan 16, 2025

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compiler/rustc_borrowck/src/type_check/mod.rs Outdated Show resolved Hide resolved

Coerce safe-to-call target_feature functions to fn pointers.

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veluca93 force-pushed the target-feature-cast-to-fn-ptr branch from 3471d41 to 8fee6a7 Compare January 16, 2025 09:55

oli-obk reviewed Jan 16, 2025

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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-review Status: Awaiting review from the assignee but also interested parties. labels Jan 16, 2025

matthiaskrgr mentioned this pull request Jan 16, 2025

Rollup of 7 pull requests #135592

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bors merged commit bbc6d16 into rust-lang:master Jan 17, 2025
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Allow coercing safe-to-call target_feature functions to safe fn pointers #135504

Allow coercing safe-to-call target_feature functions to safe fn pointers #135504

veluca93 commented Jan 14, 2025

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oli-obk commented Jan 16, 2025

bors commented Jan 16, 2025

Allow coercing safe-to-call target_feature functions to safe fn pointers #135504

Allow coercing safe-to-call target_feature functions to safe fn pointers #135504

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