diff options
| -rw-r--r-- | library/core/src/primitive_docs.rs | 32 |
1 files changed, 6 insertions, 26 deletions
diff --git a/library/core/src/primitive_docs.rs b/library/core/src/primitive_docs.rs index 4a6fca5085c..e105ceadff7 100644 --- a/library/core/src/primitive_docs.rs +++ b/library/core/src/primitive_docs.rs @@ -1746,11 +1746,10 @@ mod prim_ref {} /// alignment, they might be passed in different registers and hence not be ABI-compatible. /// /// ABI compatibility as a concern only arises in code that alters the type of function pointers, -/// code that imports functions via `extern` blocks, and in code that combines `#[target_feature]` -/// with `extern fn`. Altering the type of function pointers is wildly unsafe (as in, a lot more -/// unsafe than even [`transmute_copy`][mem::transmute_copy]), and should only occur in the most -/// exceptional circumstances. Most Rust code just imports functions via `use`. `#[target_feature]` -/// is also used rarely. So, most likely you do not have to worry about ABI compatibility. +/// and code that imports functions via `extern` blocks. Altering the type of function pointers is +/// wildly unsafe (as in, a lot more unsafe than even [`transmute_copy`][mem::transmute_copy]), and +/// should only occur in the most exceptional circumstances. Most Rust code just imports functions +/// via `use`. So, most likely you do not have to worry about ABI compatibility. /// /// But assuming such circumstances, what are the rules? For this section, we are only considering /// the ABI of direct Rust-to-Rust calls (with both definition and callsite visible to the @@ -1762,9 +1761,8 @@ mod prim_ref {} /// types from `core::ffi` or `libc`**. /// /// For two signatures to be considered *ABI-compatible*, they must use a compatible ABI string, -/// must take the same number of arguments, the individual argument types and the return types must -/// be ABI-compatible, and the target feature requirements must be met (see the subsection below for -/// the last point). The ABI string is declared via `extern "ABI" fn(...) -> ...`; note that +/// must take the same number of arguments, and the individual argument types and the return types +/// must be ABI-compatible. The ABI string is declared via `extern "ABI" fn(...) -> ...`; note that /// `fn name(...) -> ...` implicitly uses the `"Rust"` ABI string and `extern fn name(...) -> ...` /// implicitly uses the `"C"` ABI string. /// @@ -1834,24 +1832,6 @@ mod prim_ref {} /// Behavior since transmuting `None::<NonZero<i32>>` to `NonZero<i32>` violates the non-zero /// requirement. /// -/// #### Requirements concerning target features -/// -/// Under some conditions, the signature used by the caller and the callee can be ABI-incompatible -/// even if the exact same ABI string and types are being used. As an example, the -/// `std::arch::x86_64::__m256` type has a different `extern "C"` ABI when the `avx` feature is -/// enabled vs when it is not enabled. -/// -/// Therefore, to ensure ABI compatibility when code using different target features is combined -/// (such as via `#[target_feature]`), we further require that one of the following conditions is -/// met: -/// -/// - The function uses the `"Rust"` ABI string (which is the default without `extern`). -/// - Caller and callee are using the exact same set of target features. For the callee we consider -/// the features enabled (via `#[target_feature]` and `-C target-feature`/`-C target-cpu`) at the -/// declaration site; for the caller we consider the features enabled at the call site. -/// - Neither any argument nor the return value involves a SIMD type (`#[repr(simd)]`) that is not -/// behind a pointer indirection (i.e., `*mut __m256` is fine, but `(i32, __m256)` is not). -/// /// ### Trait implementations /// /// In this documentation the shorthand `fn(T₁, T₂, …, Tₙ)` is used to represent non-variadic |