linux-kernel - Re: [PATCH v2] rust: check type of `$ptr` in `container

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Message-ID: <CAJ-ks9mRUpw5gV54rbQD0Qbju6k+mhjXUHw1JZQiaV+r2RaWzw@mail.gmail.com>
Date: Sat, 12 Apr 2025 14:19:36 -0400
From: Tamir Duberstein <tamird@...il.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: rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] rust: check type of `$ptr` in `container_of!`

On Sat, Apr 12, 2025 at 2:16 PM Tamir Duberstein <tamird@...il.com> wrote:
>
> [...]
>
> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index 1df11156302a..6fbd4cc5afff 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -198,9 +198,14 @@ fn panic(info: &core::panic::PanicInfo<'_>) -> ! {
>  /// ```
>  #[macro_export]
>  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>()
> +    ($field_ptr:expr, $Container:ty, $($fields:tt)*) => {{
> +        let offset: usize = ::core::mem::offset_of!($Container, $($fields)*);
> +        let container_ptr = $field_ptr.byte_sub(offset).cast::<$Container>();
> +        if false {
> +            let field_ptr = ::core::ptr::addr_of!((*container_ptr).$($fields)*).cast_mut();
> +            [$field_ptr, field_ptr]; // typeof(`$ptr_to_field`) == typeof(`$Container.$($fields)*`)

The comment here should be s/ptr_to_field/field_ptr/. I missed this
when renaming this placeholder for clarity.

> +        }
> +        container_ptr
>      }}
>  }