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Date:   Sat, 24 Jun 2023 21:05:28 +0000
To:     =?utf-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>
From:   Benno Lossin <benno.lossin@proton.me>
Cc:     Miguel Ojeda <ojeda@kernel.org>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        Alice Ryhl <aliceryhl@google.com>,
        Andreas Hindborg <nmi@metaspace.dk>,
        rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org,
        patches@lists.linux.dev
Subject: Re: [PATCH 4/7] rust: init: wrap type checking struct initializers in a closure
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On 6/24/23 17:03, Bj=C3=B6rn Roy Baron wrote:
> On Saturday, June 24th, 2023 at 11:25, Benno Lossin <benno.lossin@proton.=
me> wrote:
>=20
>> 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@proton.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 fiel=
ds have been mentioned exactly
>>                       // once, this struct initializer will still be typ=
e-checked and complain with a
>>                       // very natural error message if a field is forgot=
ten/mentioned more than once.
>> -                    #[allow(unreachable_code, clippy::diverging_sub_exp=
ression)]
>> +                    #[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(),
>> +                            );
>> +                        })();
>=20
> Is it necessary to call this closure? Typechecking of the closure should =
happen even without calling it.

You are right, I do not need to call it. Will fix.

--=20
Cheers,
Benno

>=20
>>                       }
>>                   }
>>                   Ok(__InitOk)
>> --
>> 2.41.0
>=20
> Cheers,
> Bj=C3=B6rn