mirror of https://github.com/rust-lang/rfcs.git
35 lines
1.5 KiB
Markdown
35 lines
1.5 KiB
Markdown
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- Feature Name: volatile
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- Start Date: 2016-01-18
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- RFC PR: [rust-lang/rfcs#1467](https://github.com/rust-lang/rfcs/pull/1467)
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- Rust Issue: [rust-lang/rust#31756](https://github.com/rust-lang/rust/issues/31756)
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# Summary
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[summary]: #summary
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Stabilize the `volatile_load` and `volatile_store` intrinsics as `ptr::read_volatile` and `ptr::write_volatile`.
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# Motivation
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[motivation]: #motivation
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This is necessary to allow volatile access to memory-mapping I/O in stable code. Currently this is only possible using unstable intrinsics, or by abusing a bug in the `load` and `store` functions on atomic types which gives them volatile semantics ([rust-lang/rust#30962](https://github.com/rust-lang/rust/pull/30962)).
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# Detailed design
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[design]: #detailed-design
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`ptr::read_volatile` and `ptr::write_volatile` will work the same way as `ptr::read` and `ptr::write` respectively, except that the memory access will be done with volatile semantics. The semantics of a volatile access are already pretty well defined by the C standard and by LLVM. In documentation we can refer to http://llvm.org/docs/LangRef.html#volatile-memory-accesses.
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# Drawbacks
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[drawbacks]: #drawbacks
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None.
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# Alternatives
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[alternatives]: #alternatives
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We could also stabilize the `volatile_set_memory`, `volatile_copy_memory` and `volatile_copy_nonoverlapping_memory` intrinsics as `ptr::write_bytes_volatile`, `ptr::copy_volatile` and `ptr::copy_nonoverlapping_volatile`, but these are not as widely used and are not available in C.
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# Unresolved questions
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[unresolved]: #unresolved-questions
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None.
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