linux-kernel - Re: [PATCH] rust: check type of `$ptr` in `container

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Message-ID: <CAH5fLgioEPTrh0vYt5zdmj8POCMyDdV+Bd=j_M3PZ-EdKLZtTQ@mail.gmail.com>
Date: Fri, 11 Apr 2025 16:36:26 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Tamir Duberstein <tamird@...il.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 <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rust: check type of `$ptr` in `container_of!`

On Fri, Apr 11, 2025 at 4:31 PM Tamir Duberstein <tamird@...il.com> wrote:
>
> Add a compile-time check that `*$ptr` is of the type of `$type->$($f)*`.
>
> Suggested-by: Alice Ryhl <aliceryhl@...gle.com>
> Link: https://lore.kernel.org/all/CAH5fLgh6gmqGBhPMi2SKn7mCmMWfOSiS0WP5wBuGPYh9ZTAiww@mail.gmail.com/
> Signed-off-by: Tamir Duberstein <tamird@...il.com>
> ---
>  rust/kernel/lib.rs | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index 1df11156302a..da9e36aa7967 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -200,7 +200,10 @@ fn panic(info: &core::panic::PanicInfo<'_>) -> ! {
>  macro_rules! container_of {
>      ($ptr:expr, $type:ty, $($f:tt)*) => {{
>          let offset: usize = ::core::mem::offset_of!($type, $($f)*);
> -        $ptr.byte_sub(offset).cast::<$type>()
> +        let container = $ptr.byte_sub(offset).cast::<$type>();
> +        fn assert_same_type<T>(_: T, _: T) {}
> +        assert_same_type($ptr, ::core::mem::addr_of!((*container).$($f)*).cast_mut());

Perhaps it would be better to wrap the type check in an `if false` to
avoid evaluating the expressions at runtime?

> +        container
>      }}
>  }
>
>
> ---
> base-commit: 0af2f6be1b4281385b618cb86ad946eded089ac8
> change-id: 20250411-b4-container-of-type-check-06af1c204f59
> prerequisite-change-id: 20250409-container-of-mutness-b153dab4388d:v1
> prerequisite-patch-id: 53d5889db599267f87642bb0ae3063c29bc24863
>
> Best regards,
> --
> Tamir Duberstein <tamird@...il.com>
>