linux-kernel - Re: [PATCH 4/7] rust: init: wrap type checking struct initializers in a closure

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Message-ID: <zLJ2TSszsTrjSQ39Y8JsZLnZQ2qe8JLp_dK7vSArkClDKOzaCzO94OXwYdco6FLBNTr-MeRp0c75a-aKm_8wKlb9aPgfvf9nz2Ha5XbrutE=@protonmail.com>
Date:   Sat, 24 Jun 2023 15:03:20 +0000
From:   Björn Roy Baron <bjorn3_gh@...tonmail.com>
To:     Benno Lossin <benno.lossin@...ton.me>
Cc:     Miguel Ojeda <ojeda@...nel.org>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Alice Ryhl <aliceryhl@...gle.com>,
        Andreas Hindborg <nmi@...aspace.dk>,
        rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
        patches@...ts.linux.dev
Subject: Re: [PATCH 4/7] rust: init: wrap type checking struct initializers in a closure

On Saturday, June 24th, 2023 at 11:25, Benno Lossin <benno.lossin@...ton.me> wrote:

> In the implementation of the init macros there is a `if false` statement
> that type checks the initializer to ensure every field is initialized.
> Since the next patch has a stack variable to store the struct, the
> function might allocate too much memory on debug builds. Putting the
> struct into a closure ensures that even in debug builds no stack
> overflow error is caused. In release builds this was not a problem since
> the code was optimized away due to the `if false`.
> 
> Signed-off-by: Benno Lossin <benno.lossin@...ton.me>
> ---
>  rust/kernel/init/macros.rs | 18 +++++++++++-------
>  1 file changed, 11 insertions(+), 7 deletions(-)
> 
> diff --git a/rust/kernel/init/macros.rs b/rust/kernel/init/macros.rs
> index df4281743175..1e0c4aca055a 100644
> --- a/rust/kernel/init/macros.rs
> +++ b/rust/kernel/init/macros.rs
> @@ -1037,14 +1037,18 @@ macro_rules! __init_internal {
>                      // We use unreachable code to ensure that all fields have been mentioned exactly
>                      // once, this struct initializer will still be type-checked and complain with a
>                      // very natural error message if a field is forgotten/mentioned more than once.
> -                    #[allow(unreachable_code, clippy::diverging_sub_expression)]
> +                    #[allow(unreachable_code,
> +                            clippy::diverging_sub_expression,
> +                            clippy::redundant_closure_call)]
>                      if false {
> -                        $crate::__init_internal!(make_initializer:
> -                            @slot(slot),
> -                            @type_name($t),
> -                            @munch_fields($($fields)*,),
> -                            @acc(),
> -                        );
> +                        (|| {
> +                            $crate::__init_internal!(make_initializer:
> +                                @slot(slot),
> +                                @type_name($t),
> +                                @munch_fields($($fields)*,),
> +                                @acc(),
> +                            );
> +                        })();

Is it necessary to call this closure? Typechecking of the closure should happen even without calling it.

>                      }
>                  }
>                  Ok(__InitOk)
> --
> 2.41.0

Cheers,
Björn