linux-kernel - Re: [PATCH v4 1/2] rust: kernel: create `overflow

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Message-ID: <CANiq72mAODXhvakhvbSAWXi+Hb6AvVS+yRXGcqQtkykq5qTzcA@mail.gmail.com>
Date: Sun, 20 Jul 2025 18:58:23 +0200
From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To: Antonio Hickey <contact@...oniohickey.com>
Cc: 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>, 
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, 
	Danilo Krummrich <dakr@...nel.org>, Daniel Cote <danielstonecote@...il.com>, 
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v4 1/2] rust: kernel: create `overflow_assert!` macro

Hi Antonio,

Since you are sending likely a new version, a couple quick comments...

On Sun, Jun 29, 2025 at 4:43 AM Antonio Hickey
<contact@...oniohickey.com> wrote:
>
> Co-developed-by: Daniel Cote <danielstonecote@...il.com>
> Signed-off-by: Daniel Cote <danielstonecote@...il.com>
> Signed-off-by: Antonio Hickey <contact@...oniohickey.com>
> Link: https://github.com/Rust-for-Linux/linux/issues/1159
> Suggested-by: Miguel Ojeda <ojeda@...nel.org>

The usual order of the tags would be:

Suggested-by: Miguel Ojeda <ojeda@...nel.org>
Link: https://github.com/Rust-for-Linux/linux/issues/1159
Co-developed-by: Daniel Cote <danielstonecote@...il.com>
Signed-off-by: Daniel Cote <danielstonecote@...il.com>
Signed-off-by: Antonio Hickey <contact@...oniohickey.com>

> /// This macro is only active when `CONFIG_RUST_OVERFLOW_CHECKS` is enabled.

I would probably add another paragraph to clarify/warn that,
therefore, one can only use this macro to add extra checks for users
that don't mind panics in such a case, but that it cannot be relied
for things that need to be always tested for (to prevent UB, access
checks, etc.), similar to what the standard library says for
`debug_assert!` like Tamir mentions or the `WARN*()` docs in C.

> +/// # Examples
> +///
> +/// ```
> +/// overflow_assert!(3 <= 10);
> +/// overflow_assert!(5 <= 5);
> +///
> +/// const X: u8 = 5;
> +/// overflow_assert!(X + 3 < 10);
> +///
> +/// const MAX: i32 = 42;
> +/// const fn f(x: i32) -> i32 {
> +///     x + 1
> +/// }
> +/// overflow_assert!(f(40) < MAX);
> +/// overflow_assert!(f(40) < MAX, "f(x) must not overflow the max value.");
> +/// ```

Since now the macro takes just a `bool`, I would probably try to keep
two or so of these, and I would add a couple comments and try to have
a more "real life" example if possible.

Thanks!

Cheers,
Miguel