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define 'read-only memory'

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Ralf Jung 2023-09-08 10:35:09 +02:00
parent 07b8c10ed8
commit 69b62ecc69
1 changed files with 8 additions and 1 deletions
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9
library/core/src/sync/atomic.rs
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@ -81,12 +81,19 @@
//!
//! # Atomic accesses to read-only memory
//!
//! In general, atomic accesses on read-only memory are Undefined Behavior. For instance, attempting
//! In general, *all* atomic accesses on read-only memory are Undefined Behavior. For instance, attempting
//! to do a `compare_exchange` that will definitely fail (making it conceptually a read-only
//! operation) can still cause a page fault if the underlying memory page is mapped read-only. Since
//! 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
//! 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.
//!
//! 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: