Re: [RESEND PATCH v5] rust: kernel: introduce `unsafe_precondition_assert!` macro

["Benno Lossin" <lossin@kernel.org>]

On Wed Aug 27, 2025 at 8:00 AM CEST, Ritvik Gupta wrote:
> diff --git a/rust/kernel/safety.rs b/rust/kernel/safety.rs
> new file mode 100644
> index 000000000000..e78d49e3e7c8
> --- /dev/null
> +++ b/rust/kernel/safety.rs
> @@ -0,0 +1,54 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Safety related APIs.

I think this looks fine to start out with.

> +
> +/// Checks that preconditions of an unsafe function are followed.
> +///
> +/// The check is enabled at runtime if debug assertions (`CONFIG_RUST_DEBUG_ASSERTIONS`)
> +/// are enabled. Otherwise, this macro is no-op.
> +///
> +/// # Examples
> +///
> +/// ```no_run
> +/// use kernel::unsafe_precondition_assert;
> +///
> +/// struct RawBuffer<T: Copy, const N: usize> {
> +///     data: [T; N],
> +/// }
> +///
> +/// impl<T: Copy, const N: usize> RawBuffer<T, N> {
> +///     /// # Safety
> +///     ///
> +///     /// The caller must ensure that `index` is less than `N`
> +///     unsafe fn set_unchecked(&mut self, index: usize, value: T) {
> +///         unsafe_precondition_assert!(
> +///             index < N,
> +///             "RawBuffer::set_unchecked requires index ({}) < N ({})",
> +///             index,
> +///             N,

You can move the names into the `{}`:

    unsafe_precondition_assert!(
        index < N,
        "RawBuffer::set_unchecked requires index ({index}) < N ({N})",
    );

> +///         );
> +///
> +///         // SAFETY: By the safety requirements of this function, `index` is valid
> +///         unsafe {
> +///             *self.data.get_unchecked_mut(index) = value;
> +///         }
> +///     }
> +/// }
> +/// ```
> +///
> +/// # Panics
> +///
> +/// Panics if the expression is evaluated to `false` at runtime.
> +#[macro_export]
> +macro_rules! unsafe_precondition_assert {
> +    ($cond:expr $(,)?) => {
> +        $crate::unsafe_precondition_assert!(@inner $cond, ::core::stringify!($cond))
> +    };
> +
> +    ($cond:expr, $($arg:tt)+) => {
> +        $crate::unsafe_precondition_assert!(@inner $cond, $crate::prelude::fmt!($($arg)+))
> +    };
> +
> +    (@inner $cond:expr, $msg:expr) => {
> +        ::core::debug_assert!($cond, "unsafe precondition(s) violated: {}", $msg) };

The closing `}` should be on the next line.

---
Cheers,
Benno

> +}
>
> base-commit: 8f5ae30d69d7543eee0d70083daf4de8fe15d585