linux-kernel - Re: [PATCH v7 9/9] rust: sync: atomic: Add Atomic<{usize,isize}>

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Message-Id: <DBBQ9SLMWA2K.33BWRE1ME65MG@kernel.org>
Date: Mon, 14 Jul 2025 13:06:08 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Boqun Feng" <boqun.feng@...il.com>, <linux-kernel@...r.kernel.org>,
 <rust-for-linux@...r.kernel.org>, <lkmm@...ts.linux.dev>,
 <linux-arch@...r.kernel.org>
Cc: "Miguel Ojeda" <ojeda@...nel.org>, "Alex Gaynor"
 <alex.gaynor@...il.com>, "Gary Guo" <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, "Andreas
 Hindborg" <a.hindborg@...nel.org>, "Alice Ryhl" <aliceryhl@...gle.com>,
 "Trevor Gross" <tmgross@...ch.edu>, "Danilo Krummrich" <dakr@...nel.org>,
 "Will Deacon" <will@...nel.org>, "Peter Zijlstra" <peterz@...radead.org>,
 "Mark Rutland" <mark.rutland@....com>, "Wedson Almeida Filho"
 <wedsonaf@...il.com>, "Viresh Kumar" <viresh.kumar@...aro.org>, "Lyude
 Paul" <lyude@...hat.com>, "Ingo Molnar" <mingo@...nel.org>, "Mitchell Levy"
 <levymitchell0@...il.com>, "Paul E. McKenney" <paulmck@...nel.org>, "Greg
 Kroah-Hartman" <gregkh@...uxfoundation.org>, "Linus Torvalds"
 <torvalds@...ux-foundation.org>, "Thomas Gleixner" <tglx@...utronix.de>,
 "Alan Stern" <stern@...land.harvard.edu>
Subject: Re: [PATCH v7 9/9] rust: sync: atomic: Add Atomic<{usize,isize}>

On Mon Jul 14, 2025 at 7:36 AM CEST, Boqun Feng wrote:
> +// Defines an internal type that always maps to the integer type which has the same size alignment
> +// as `isize` and `usize`, and `isize` and `usize` are always bi-directional transmutable to
> +// `isize_atomic_repr`, which also always implements `AtomicImpl`.
> +#[allow(non_camel_case_types)]
> +#[cfg(not(CONFIG_64BIT))]
> +type isize_atomic_repr = i32;
> +#[allow(non_camel_case_types)]
> +#[cfg(CONFIG_64BIT)]
> +type isize_atomic_repr = i64;
> +
> +// Ensure size and alignment requirements are checked.
> +crate::static_assert!(core::mem::size_of::<isize>() == core::mem::size_of::<isize_atomic_repr>());
> +crate::static_assert!(core::mem::align_of::<isize>() == core::mem::align_of::<isize_atomic_repr>());
> +crate::static_assert!(core::mem::size_of::<usize>() == core::mem::size_of::<isize_atomic_repr>());
> +crate::static_assert!(core::mem::align_of::<usize>() == core::mem::align_of::<isize_atomic_repr>());

This is fine for now, but I would prefer for this to go into an
`assumptions` module like Miguel proposed some time ago.

---
Cheers,
Benno