linux-kernel - [PATCH v2 1/1] rust: kernel: create `overflow

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Message-ID: <20250504165612.86459-2-contact@antoniohickey.com>
Date: Sun,  4 May 2025 12:56:11 -0400
From: Antonio Hickey <contact@...oniohickey.com>
To: 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 <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>,
	Trevor Gross <tmgross@...ch.edu>,
	Danilo Krummrich <dakr@...nel.org>
Cc: Antonio Hickey <contact@...oniohickey.com>,
	linux-kernel@...r.kernel.org,
	rust-for-linux@...r.kernel.org
Subject: [PATCH v2 1/1] rust: kernel: create `overflow_assert!`

This commit creates a macro for overflow assertions, the use of this
macro will avoid local `#ifdef`s by encapsulating the conditional
behavior to the macro. In addition this macro allows us to document
the intent of the assertion more clearly.

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 | 42 ++++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+)
 create mode 100644 rust/kernel/overflow_assert.rs

diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index de07aadd1ff5..feeb99fc4bbd 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -64,6 +64,7 @@
 #[cfg(CONFIG_NET)]
 pub mod net;
 pub mod of;
+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..aa4438bb0165
--- /dev/null
+++ b/rust/kernel/overflow_assert.rs
@@ -0,0 +1,42 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Overflow assert.
+
+/// Overflow assert (i.e. runtime bound check).
+///
+/// Verifies at runtime that an expression is within an expected bound.
+///
+/// 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 + 1, 10);
+///
+/// const fn f(x: i32) -> i32 {
+///     x + 2
+/// }
+/// overflow_assert!(f(40), 42);
+/// ```
+#[macro_export]
+#[cfg(CONFIG_RUST_OVERFLOW_CHECKS)]
+macro_rules! overflow_assert {
+    ($x:expr, $y:expr) => {
+        core::assert!($x <= $y, "overflow assertion failed: {} > {}", $x, $y);
+    };
+}
+
+/// Disabled overflow assertion (no-op).
+///
+/// This macro exists to allow code using `overflow_assert!` to compile when
+/// `CONFIG_RUST_OVERFLOW_CHECKS` is **not** enabled. It expands to nothing
+/// so it performs no checks and emits no code.
+#[macro_export]
+#[cfg(not(CONFIG_RUST_OVERFLOW_CHECKS))]
+macro_rules! assert_no_overflow {
+    ($x:expr, $y:expr) => {};
+}
-- 
2.49.0