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rust/library/core/src/lib.rs
Jacob Pratt 575405161f
Rollup merge of #134090 - veluca93:stable-tf11, r=oli-obk 
Stabilize target_feature_11

# Stabilization report

This is an updated version of https://github.com/rust-lang/rust/pull/116114, which is itself a redo of https://github.com/rust-lang/rust/pull/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 https://github.com/rust-lang/rust/pull/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/`](f6cb952dc1/tests/ui/target-feature).

## Edge cases
### Closures
 * [target-feature 1.1: should closures inherit target-feature annotations? #73631](https://github.com/rust-lang/rust/issues/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. 2e29bdf908/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](https://github.com/rust-lang/rust/pull/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](https://github.com/rust-lang/rust/issues/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](https://github.com/rust-lang/rust/issues/108645)
* [`#[target_feature]` is allowed on default implementations #108646](https://github.com/rust-lang/rust/issues/108646)
* [#[target_feature] is allowed on #[panic_handler] with target_feature 1.1 #109411](https://github.com/rust-lang/rust/issues/109411)
* [Prevent using `#[target_feature]` on lang item functions #115910](https://github.com/rust-lang/rust/pull/115910)

## Documentation
 * Reference: [Document the `target_feature_11` feature reference#1181](https://github.com/rust-lang/reference/pull/1181)
---

cc tracking issue https://github.com/rust-lang/rust/issues/69098
cc ```@workingjubilee```
cc ```@RalfJung```
r? ```@rust-lang/lang```
2025-02-12 20:09:56 -05:00

438 lines
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Rust
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//! # The Rust Core Library
//!
//! The Rust Core Library is the dependency-free[^free] foundation of [The
//! Rust Standard Library](../std/index.html). It is the portable glue
//! between the language and its libraries, defining the intrinsic and
//! primitive building blocks of all Rust code. It links to no
//! upstream libraries, no system libraries, and no libc.
//!
//! [^free]: Strictly speaking, there are some symbols which are needed but
//! they aren't always necessary.
//!
//! The core library is *minimal*: it isn't even aware of heap allocation,
//! nor does it provide concurrency or I/O. These things require
//! platform integration, and this library is platform-agnostic.
//!
//! # How to use the core library
//!
//! Please note that all of these details are currently not considered stable.
//!
// FIXME: Fill me in with more detail when the interface settles
//! This library is built on the assumption of a few existing symbols:
//!
//! * `memcpy`, `memmove`, `memset`, `memcmp`, `bcmp`, `strlen` - These are core memory routines
//! which are generated by Rust codegen backends. Additionally, this library can make explicit
//! calls to `strlen`. Their signatures are the same as found in C, but there are extra
//! assumptions about their semantics: For `memcpy`, `memmove`, `memset`, `memcmp`, and `bcmp`, if
//! the `n` parameter is 0, the function is assumed to not be UB, even if the pointers are NULL or
//! dangling. (Note that making extra assumptions about these functions is common among compilers:
//! [clang](https://reviews.llvm.org/D86993) and [GCC](https://gcc.gnu.org/onlinedocs/gcc/Standards.html#C-Language) do the same.)
//! These functions are often provided by the system libc, but can also be provided by the
//! [compiler-builtins crate](https://crates.io/crates/compiler_builtins).
//! Note that the library does not guarantee that it will always make these assumptions, so Rust
//! user code directly calling the C functions should follow the C specification! The advice for
//! Rust user code is to call the functions provided by this library instead (such as
//! `ptr::copy`).
//!
//! * Panic handler - This function takes one argument, a `&panic::PanicInfo`. It is up to consumers of this core
//! library to define this panic function; it is only required to never
//! return. You should mark your implementation using `#[panic_handler]`.
//!
//! * `rust_eh_personality` - is used by the failure mechanisms of the
//! compiler. This is often mapped to GCC's personality function, but crates
//! which do not trigger a panic can be assured that this function is never
//! called. The `lang` attribute is called `eh_personality`.
// Since core defines many fundamental lang items, all tests live in a
// separate crate, coretests (library/coretests), to avoid bizarre issues.
//
// Here we explicitly #[cfg]-out this whole crate when testing. If we don't do
// this, both the generated test artifact and the linked libtest (which
// transitively includes core) will both define the same set of lang items,
// and this will cause the E0152 "found duplicate lang item" error. See
// discussion in #50466 for details.
//
// This cfg won't affect doc tests.
#![cfg(not(test))]
//
#![stable(feature = "core", since = "1.6.0")]
#![doc(
html_playground_url = "https://play.rust-lang.org/",
issue_tracker_base_url = "https://github.com/rust-lang/rust/issues/",
test(no_crate_inject, attr(deny(warnings))),
test(attr(allow(dead_code, deprecated, unused_variables, unused_mut)))
)]
#![doc(rust_logo)]
#![doc(cfg_hide(
not(test),
no_fp_fmt_parse,
target_pointer_width = "16",
target_pointer_width = "32",
target_pointer_width = "64",
target_has_atomic = "8",
target_has_atomic = "16",
target_has_atomic = "32",
target_has_atomic = "64",
target_has_atomic = "ptr",
target_has_atomic_equal_alignment = "8",
target_has_atomic_equal_alignment = "16",
target_has_atomic_equal_alignment = "32",
target_has_atomic_equal_alignment = "64",
target_has_atomic_equal_alignment = "ptr",
target_has_atomic_load_store = "8",
target_has_atomic_load_store = "16",
target_has_atomic_load_store = "32",
target_has_atomic_load_store = "64",
target_has_atomic_load_store = "ptr",
))]
#![no_core]
#![rustc_coherence_is_core]
#![rustc_preserve_ub_checks]
//
// Lints:
#![deny(rust_2021_incompatible_or_patterns)]
#![deny(unsafe_op_in_unsafe_fn)]
#![deny(fuzzy_provenance_casts)]
#![warn(deprecated_in_future)]
#![warn(missing_debug_implementations)]
#![warn(missing_docs)]
#![allow(explicit_outlives_requirements)]
#![allow(incomplete_features)]
#![warn(multiple_supertrait_upcastable)]
#![allow(internal_features)]
#![deny(ffi_unwind_calls)]
#![warn(unreachable_pub)]
// Do not check link redundancy on bootstraping phase
#![allow(rustdoc::redundant_explicit_links)]
#![warn(rustdoc::unescaped_backticks)]
//
// Library features:
// tidy-alphabetical-start
#![feature(array_ptr_get)]
#![feature(asm_experimental_arch)]
#![feature(bigint_helper_methods)]
#![feature(bstr)]
#![feature(bstr_internals)]
#![feature(closure_track_caller)]
#![feature(const_carrying_mul_add)]
#![feature(const_eval_select)]
#![feature(core_intrinsics)]
#![feature(coverage_attribute)]
#![feature(disjoint_bitor)]
#![feature(internal_impls_macro)]
#![feature(ip)]
#![feature(is_ascii_octdigit)]
#![feature(lazy_get)]
#![feature(link_cfg)]
#![feature(non_null_from_ref)]
#![feature(offset_of_enum)]
#![feature(panic_internals)]
#![feature(ptr_alignment_type)]
#![feature(ptr_metadata)]
#![feature(set_ptr_value)]
#![feature(slice_as_array)]
#![feature(slice_as_chunks)]
#![feature(slice_ptr_get)]
#![feature(str_internals)]
#![feature(str_split_inclusive_remainder)]
#![feature(str_split_remainder)]
#![feature(ub_checks)]
#![feature(unchecked_neg)]
#![feature(unchecked_shifts)]
#![feature(utf16_extra)]
#![feature(variant_count)]
// tidy-alphabetical-end
//
// Language features:
// tidy-alphabetical-start
#![feature(abi_unadjusted)]
#![feature(adt_const_params)]
#![feature(allow_internal_unsafe)]
#![feature(allow_internal_unstable)]
#![feature(auto_traits)]
#![feature(cfg_sanitize)]
#![feature(cfg_target_has_atomic)]
#![feature(cfg_target_has_atomic_equal_alignment)]
#![feature(cfg_ub_checks)]
#![feature(const_precise_live_drops)]
#![feature(const_trait_impl)]
#![feature(decl_macro)]
#![feature(deprecated_suggestion)]
#![feature(doc_cfg)]
#![feature(doc_cfg_hide)]
#![feature(doc_notable_trait)]
#![feature(extern_types)]
#![feature(f128)]
#![feature(f16)]
#![feature(freeze_impls)]
#![feature(fundamental)]
#![feature(generic_arg_infer)]
#![feature(if_let_guard)]
#![feature(intra_doc_pointers)]
#![feature(intrinsics)]
#![feature(lang_items)]
#![feature(let_chains)]
#![feature(link_llvm_intrinsics)]
#![feature(macro_metavar_expr)]
#![feature(marker_trait_attr)]
#![feature(min_specialization)]
#![feature(multiple_supertrait_upcastable)]
#![feature(must_not_suspend)]
#![feature(negative_impls)]
#![feature(never_type)]
#![feature(no_core)]
#![feature(no_sanitize)]
#![feature(optimize_attribute)]
#![feature(prelude_import)]
#![feature(repr_simd)]
#![feature(rustc_allow_const_fn_unstable)]
#![feature(rustc_attrs)]
#![feature(rustdoc_internals)]
#![feature(simd_ffi)]
#![feature(staged_api)]
#![feature(stmt_expr_attributes)]
#![feature(strict_provenance_lints)]
#![feature(trait_alias)]
#![feature(transparent_unions)]
#![feature(try_blocks)]
#![feature(unboxed_closures)]
#![feature(unsized_fn_params)]
#![feature(with_negative_coherence)]
// tidy-alphabetical-end
//
// Target features:
// tidy-alphabetical-start
#![feature(arm_target_feature)]
#![feature(avx512_target_feature)]
#![feature(hexagon_target_feature)]
#![feature(loongarch_target_feature)]
#![feature(mips_target_feature)]
#![feature(powerpc_target_feature)]
#![feature(riscv_target_feature)]
#![feature(rtm_target_feature)]
#![feature(sha512_sm_x86)]
#![feature(sse4a_target_feature)]
#![feature(tbm_target_feature)]
#![feature(wasm_target_feature)]
#![feature(x86_amx_intrinsics)]
// tidy-alphabetical-end
// allow using `core::` in intra-doc links
#[allow(unused_extern_crates)]
extern crate self as core;
#[prelude_import]
#[allow(unused)]
use prelude::rust_2021::*;
#[cfg(not(test))] // See #65860
#[macro_use]
mod macros;
// We don't export this through #[macro_export] for now, to avoid breakage.
// See https://github.com/rust-lang/rust/issues/82913
#[cfg(not(test))]
#[unstable(feature = "assert_matches", issue = "82775")]
/// Unstable module containing the unstable `assert_matches` macro.
pub mod assert_matches {
#[unstable(feature = "assert_matches", issue = "82775")]
pub use crate::macros::{assert_matches, debug_assert_matches};
}
// We don't export this through #[macro_export] for now, to avoid breakage.
#[unstable(feature = "autodiff", issue = "124509")]
/// Unstable module containing the unstable `autodiff` macro.
pub mod autodiff {
#[unstable(feature = "autodiff", issue = "124509")]
pub use crate::macros::builtin::autodiff;
}
#[cfg(not(bootstrap))]
#[unstable(feature = "contracts", issue = "128044")]
pub mod contracts;
#[unstable(feature = "cfg_match", issue = "115585")]
pub use crate::macros::cfg_match;
#[macro_use]
mod internal_macros;
#[path = "num/shells/int_macros.rs"]
#[macro_use]
mod int_macros;
#[rustc_diagnostic_item = "i128_legacy_mod"]
#[path = "num/shells/i128.rs"]
pub mod i128;
#[rustc_diagnostic_item = "i16_legacy_mod"]
#[path = "num/shells/i16.rs"]
pub mod i16;
#[rustc_diagnostic_item = "i32_legacy_mod"]
#[path = "num/shells/i32.rs"]
pub mod i32;
#[rustc_diagnostic_item = "i64_legacy_mod"]
#[path = "num/shells/i64.rs"]
pub mod i64;
#[rustc_diagnostic_item = "i8_legacy_mod"]
#[path = "num/shells/i8.rs"]
pub mod i8;
#[rustc_diagnostic_item = "isize_legacy_mod"]
#[path = "num/shells/isize.rs"]
pub mod isize;
#[rustc_diagnostic_item = "u128_legacy_mod"]
#[path = "num/shells/u128.rs"]
pub mod u128;
#[rustc_diagnostic_item = "u16_legacy_mod"]
#[path = "num/shells/u16.rs"]
pub mod u16;
#[rustc_diagnostic_item = "u32_legacy_mod"]
#[path = "num/shells/u32.rs"]
pub mod u32;
#[rustc_diagnostic_item = "u64_legacy_mod"]
#[path = "num/shells/u64.rs"]
pub mod u64;
#[rustc_diagnostic_item = "u8_legacy_mod"]
#[path = "num/shells/u8.rs"]
pub mod u8;
#[rustc_diagnostic_item = "usize_legacy_mod"]
#[path = "num/shells/usize.rs"]
pub mod usize;
#[path = "num/f128.rs"]
pub mod f128;
#[path = "num/f16.rs"]
pub mod f16;
#[path = "num/f32.rs"]
pub mod f32;
#[path = "num/f64.rs"]
pub mod f64;
#[macro_use]
pub mod num;
/* The core prelude, not as all-encompassing as the std prelude */
pub mod prelude;
/* Core modules for ownership management */
pub mod hint;
pub mod intrinsics;
pub mod mem;
pub mod ptr;
#[unstable(feature = "ub_checks", issue = "none")]
pub mod ub_checks;
/* Core language traits */
pub mod borrow;
pub mod clone;
pub mod cmp;
pub mod convert;
pub mod default;
pub mod error;
pub mod marker;
pub mod ops;
/* Core types and methods on primitives */
pub mod any;
pub mod array;
pub mod ascii;
pub mod asserting;
#[unstable(feature = "async_iterator", issue = "79024")]
pub mod async_iter;
#[unstable(feature = "bstr", issue = "134915")]
pub mod bstr;
pub mod cell;
pub mod char;
pub mod ffi;
#[unstable(feature = "core_io_borrowed_buf", issue = "117693")]
pub mod io;
pub mod iter;
pub mod net;
pub mod option;
pub mod panic;
pub mod panicking;
#[unstable(feature = "pattern_type_macro", issue = "123646")]
pub mod pat;
pub mod pin;
#[unstable(feature = "random", issue = "130703")]
pub mod random;
#[unstable(feature = "new_range_api", issue = "125687")]
pub mod range;
pub mod result;
pub mod sync;
#[unstable(feature = "unsafe_binders", issue = "130516")]
pub mod unsafe_binder;
pub mod fmt;
pub mod hash;
pub mod slice;
pub mod str;
pub mod time;
pub mod unicode;
/* Async */
pub mod future;
pub mod task;
/* Heap memory allocator trait */
#[allow(missing_docs)]
pub mod alloc;
// note: does not need to be public
mod bool;
mod escape;
mod tuple;
mod unit;
#[stable(feature = "core_primitive", since = "1.43.0")]
pub mod primitive;
// Pull in the `core_arch` crate directly into core. The contents of
// `core_arch` are in a different repository: rust-lang/stdarch.
//
// `core_arch` depends on core, but the contents of this module are
// set up in such a way that directly pulling it here works such that the
// crate uses the this crate as its core.
#[path = "../../stdarch/crates/core_arch/src/mod.rs"]
#[allow(
missing_docs,
missing_debug_implementations,
dead_code,
unused_imports,
unsafe_op_in_unsafe_fn,
ambiguous_glob_reexports,
deprecated_in_future,
unreachable_pub
)]
#[allow(rustdoc::bare_urls)]
mod core_arch;
#[stable(feature = "simd_arch", since = "1.27.0")]
pub mod arch;
// Pull in the `core_simd` crate directly into core. The contents of
// `core_simd` are in a different repository: rust-lang/portable-simd.
//
// `core_simd` depends on core, but the contents of this module are
// set up in such a way that directly pulling it here works such that the
// crate uses this crate as its core.
#[path = "../../portable-simd/crates/core_simd/src/mod.rs"]
#[allow(missing_debug_implementations, dead_code, unsafe_op_in_unsafe_fn)]
#[allow(rustdoc::bare_urls)]
#[unstable(feature = "portable_simd", issue = "86656")]
mod core_simd;
#[unstable(feature = "portable_simd", issue = "86656")]
pub mod simd {
#![doc = include_str!("../../portable-simd/crates/core_simd/src/core_simd_docs.md")]
#[unstable(feature = "portable_simd", issue = "86656")]
pub use crate::core_simd::simd::*;
}
include!("primitive_docs.rs");
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