linux-kernel - Re: [PATCH v6 9/9] rust: sync: atomic: Add Atomic<{usize,isize}>

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Message-ID: <CANiq72m9AeqFKHrRniQ5Nr9vPv2MmUMHFTuuj5ydmqo+OYn60A@mail.gmail.com>
Date: Fri, 11 Jul 2025 15:45:32 +0200
From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To: Benno Lossin <lossin@...nel.org>
Cc: 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, 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>, 
	Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v6 9/9] rust: sync: atomic: Add Atomic<{usize,isize}>

On Fri, Jul 11, 2025 at 11:00 AM Benno Lossin <lossin@...nel.org> wrote:
>
> Do we have a static assert with these cfgs that `isize` has the same
> size as these?
>
> If not, then it would probably make sense to add them now.

Yeah, according to e.g. Matthew et al., we may end up with 128-bit
pointers in the kernel fairly soon (e.g. a decade):

    https://lwn.net/Articles/908026/

I rescued part of what I wrote in the old `mod assumptions` which I
never got to send back then -- most of the `static_asserts` are
redundant now that we define directly the types in the `ffi` crate (I
mean, we could still assert that `size_of::<c_char>() == 1` and so on,
but they are essentially a tautology now), so I adapted the comments.
Please see below (draft).

Cheers,
Miguel

View attachment "0001-rust-ffi-assert-sizes-and-clarify-128-bit-situation.patch" of type "text/x-patch" (2026 bytes)