linux-kernel - Re: [PATCH v2 1/7] rust: build_assert: add instructions for use with function arguments

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Message-ID: <46b5eef7-2e8d-4801-93d0-6cea10f62dc9@nvidia.com>
Date: Sun, 30 Nov 2025 14:00:45 -0800
From: John Hubbard <jhubbard@...dia.com>
To: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc: Alexandre Courbot <acourbot@...dia.com>,
 Danilo Krummrich <dakr@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>,
 Daniel Almeida <daniel.almeida@...labora.com>,
 Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>,
 Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>,
 Benno Lossin <lossin@...nel.org>, Andreas Hindborg <a.hindborg@...nel.org>,
 Trevor Gross <tmgross@...ch.edu>, "Rafael J. Wysocki" <rafael@...nel.org>,
 Viresh Kumar <viresh.kumar@...aro.org>, Will Deacon <will@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>, Mark Rutland <mark.rutland@....com>,
 rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-pm@...r.kernel.org
Subject: Re: [PATCH v2 1/7] rust: build_assert: add instructions for use with
 function arguments

On 11/30/25 1:56 PM, Miguel Ojeda wrote:
> On Sun, Nov 30, 2025 at 10:44 PM John Hubbard <jhubbard@...dia.com> wrote:
>>
>> Very interesting. So by adding a partially faulty build_assert!() call,
>> these functions were actually wrong when they created! Maybe a Fixes:
>> tag is warranted.
> 
> To clarify: it is the lack of optimization in certain configs (-Os,
> CLIPPY=1...) as well as possibly certain code patterns that may
> trigger it, not that the calls were faulty (note that `always` doesn't

It seems pretty clear that if one writes a *build* assertion about
a function argument, then that is just conceptually wrong unless it
is inlined. Because it can only really be a run-time assertion.

This is what Alex pointed out, and looking at the code I agree.

Thoughts?

> guarantee it either anyway).

Yes, understood. So maybe "Fixes" is too strong. It's more like
"Mitigates:".  :)

thanks,
-- 
John Hubbard

> 
> Daniel suggested Fixes in #0 -- if any of these trigger a build error
> (like the `Bounded` one), then yeah. Cc: stable@ too.
> 
> Thanks!
> 
> Cheers,
> Miguel