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

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Message-ID: <CAJ-ks9m45p9FHCvbuOS0zJvZfHMcXOLvN+rfjQfyNTHzDovspA@mail.gmail.com>
Date: Sun, 29 Jun 2025 12:04:11 -0400
From: Tamir Duberstein <tamird@...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

On Sat, Jun 28, 2025 at 10:43 PM Antonio Hickey
<contact@...oniohickey.com> wrote:
>
> This commit creates a macro for overflow assertions, the use of this
> macro will avoid local `#ifdef`s by encapsulating the conditional
> behavior (like `#[cfg(CONFIG_RUST_OVERFLOW_CHECKS)]`) to the macro.
>
> In addition this macro allows us to document the intent of the assertion
> more clearly.
>
> 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>
> ---
>  rust/kernel/lib.rs             |  1 +
>  rust/kernel/overflow_assert.rs | 32 ++++++++++++++++++++++++++++++++
>  2 files changed, 33 insertions(+)
>  create mode 100644 rust/kernel/overflow_assert.rs
>
> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index 6b4774b2b1c3..e395adb6b293 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -92,6 +92,7 @@
>  pub mod of;
>  #[cfg(CONFIG_PM_OPP)]
>  pub mod opp;
> +pub mod overflow_assert;
>  pub mod page;
>  #[cfg(CONFIG_PCI)]
>  pub mod pci;
> diff --git a/rust/kernel/overflow_assert.rs b/rust/kernel/overflow_assert.rs
> new file mode 100644
> index 000000000000..5164339813cb
> --- /dev/null
> +++ b/rust/kernel/overflow_assert.rs
> @@ -0,0 +1,32 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Overflow assertion.
> +
> +/// Verifies at runtime that an expression is within an expected bound.

This is a strange comment, imo. The only thing special about this
macro relative to a plain `assert` is that it disabled when
CONFIG_RUST_OVERFLOW_CHECKS=n.

> +///
> +/// This macro is only active when `CONFIG_RUST_OVERFLOW_CHECKS` is enabled.
> +///
> +/// # 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.");
> +/// ```
> +#[macro_export]
> +macro_rules! overflow_assert {
> +    ($cond:expr $(,$arg:literal)?) => {
> +        if cfg!(CONFIG_RUST_OVERFLOW_CHECKS) {
> +            ::core::assert!($cond $(,$arg)?);
> +        }
> +    };
> +}
> --
> 2.50.0
>
>
>