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This commit is contained in:
Ralf Jung 2023-09-09 17:06:10 +02:00
parent 69b62ecc69
commit 275d5c8251
1 changed files with 13 additions and 9 deletions
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22
library/core/src/sync/atomic.rs
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@ -87,18 +87,21 @@
//! atomic `load`s might be implemented using compare-exchange operations, even a `load` can fault
//! on read-only memory.
//!
//! For the purpose of this section, "read-only memory" is defined as memory that is read-only in
//! (For the purpose of this section, "read-only memory" is defined as memory that is read-only in
//! the underlying target, i.e., the pages are mapped with a read-only flag and any attempt to write
//! will cause a page fault. In particular, an `&u128` reference that points to memory that is
//! read-write mapped is *not* considered to point to "read-only memory". In Rust, almost all memory
//! is read-write; the only exceptions are memory created by `const` items or `static` items without
//! interior mutability.
//! interior mutability, and memory that was specifically marked as read-only by the operating
//! system via platform-specific APIs.)
//!
//! However, as an exception from this general rule, Rust guarantees that "sufficiently small"
//! atomic loads are implemented in a way that works on read-only memory. This threshold of
//! "sufficiently small" depends on the architecture:
//! However, as an exception from this general rule, "sufficiently small" atomic loads are
//! implemented in a way that works on read-only memory. The exact threshold for what makes a load
//! "sufficiently small" varies depending on the architecture and feature flags, but Rust guarantees
//! that atomic loads that do not exceed the size documented in the following table are guaranteed
//! to be read-only:
//!
//! | Target architecture | Maximal atomic `load` size that is guaranteed read-only |
//! | Target architecture | Atomic loads no larger than this are guaranteed read-only |
//! |---------------|---------|
//! | `x86` | 4 bytes |
//! | `x86_64` | 8 bytes |
@ -106,10 +109,11 @@
//! | `aarch64` | 8 bytes |
//! | `riscv32` | 4 bytes |
//! | `riscv64` | 8 bytes |
//! | `powerpc64le` | 8 bytes |
//! | `powerpc64` | 8 bytes |
//!
//! Any atomic `load` on read-only memory larger than the given size are Undefined Behavior. For
//! architectures not listed above, all atomic `load` on read-only memory are Undefined Behavior.
//! Atomics loads that are larger than this threshold (and *all* atomic loads on targets not listed
//! in the table) might still be read-only under certain conditions, but that is not a stable
//! guarantee and should not be relied upon.
//!
//! # Examples
//!