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Fri, 01 Aug 2025 06:48:44 -0700 (PDT) Date: Fri, 1 Aug 2025 19:19:09 +0530 From: Ritvik Gupta To: Miguel Ojeda Cc: Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?utf-8?B?QmrDtnJu?= Roy Baron , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , Danilo Krummrich , skhan@linuxfoundation.org, linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org Subject: Re: [PATCH v3] rust: kernel: introduce `unsafe_precondition_assert!` macro Message-ID: References: <20250731111234.28602-1-ritvikfoss@gmail.com> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Thu, Jul 31, 2025 at 01:42:42PM +0200, Miguel Ojeda wrote: > On Thu, Jul 31, 2025 at 1:12 PM Ritvik Gupta wrote: > > > > +/// /// - `buf` must be non-null. > > +/// /// - `buf` must be 16-byte aligned. > > We don't know since the full body is not shown, but it is likely this > would need to also be a valid pointer, i.e. it may be an uncommon > example. I believe this is a valid use-case for `unsafe_precondition_assert!`. Should we add similar example? ```cpu.rs /// Creates a new [`CpuId`] from the given `id` without checking bounds. /// /// # Safety /// /// The caller must ensure that `id` is a valid CPU ID (i.e., `0 <= id < nr_cpu_ids()`). #[inline] pub unsafe fn from_u32_unchecked(id: u32) -> Self { debug_assert!(id < nr_cpu_ids()); // Ensure the `id` fits in an [`i32`] as it's also representable that way. debug_assert!(id <= i32::MAX as u32); // INVARIANT: The function safety guarantees `id` is a valid CPU id. Self(id) } ``` > More importantly, could we have a user of the macro introduced in a > second patch so that it gets already used? I believe the `debug_assert!` calls inside the `unsafe fn` (excluding 'const fn' and 'CONFIG_RUST_OVERFLOW_CHECKS' flag) are the intended targets for `unsafe_precondition_assert!`. A quick grep (`git grep -B 15 -A 10 "debug_assert"`), I could find 6 relevant callers in `alloc/kvec.rs` (2) and `cpu.rs` (4), unless I'm missing something. I'll send another patch for this, after getting the example correct. Thanks for the feedback :)