linux-kernel - Re: [PATCH v3 1/9] rust: add offset

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Message-ID: <874jksp71i.fsf@metaspace.dk>
Date:   Mon, 21 Aug 2023 20:43:08 +0200
From:   "Andreas Hindborg (Samsung)" <nmi@...aspace.dk>
To:     Alice Ryhl <aliceryhl@...gle.com>
Cc:     rust-for-linux@...r.kernel.org, Tejun Heo <tj@...nel.org>,
        Miguel Ojeda <ojeda@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        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>,
        linux-kernel@...r.kernel.org, patches@...ts.linux.dev,
        Wedson Almeida Filho <walmeida@...rosoft.com>,
        Martin Rodriguez Reboredo <yakoyoku@...il.com>
Subject: Re: [PATCH v3 1/9] rust: add offset_of! macro


Hi Alice,

Alice Ryhl <aliceryhl@...gle.com> writes:

> From: Wedson Almeida Filho <walmeida@...rosoft.com>
>
> This macro is used to compute the offset of a field in a struct.
>
> This commit enables an unstable feature that is necessary for using
> the macro in a constant. However, this is not a problem as the macro
> will become available from the Rust standard library soon [1]. The
> unstable feature can be disabled again once that happens.
>
> The macro in this patch does not support sub-fields. That is, you cannot
> write `offset_of!(MyStruct, field.sub_field)` to get the offset of
> `sub_field` with `field`'s type being a struct with a field called
> `sub_field`. This is because `field` might be a `Box<SubStruct>`, which
> means that you would be trying to compute the offset to something in an
> entirely different allocation. There's no easy way to fix the current
> macro to support subfields, but the version being added to the standard
> library should support it, so the limitation is temporary and not a big
> deal.

I think `#![feature(offset_of)]` is available in 1.71.0, can we use that directly?

BR Andreas