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

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Date:   Sat, 24 Jun 2023 09:25:16 +0000
From:   Benno Lossin <benno.lossin@...ton.me>
To:     Miguel Ojeda <ojeda@...nel.org>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Alex Gaynor <alex.gaynor@...il.com>
Cc:     Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Benno Lossin <benno.lossin@...ton.me>,
        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: [PATCH 4/7] rust: init: wrap type checking struct initializers in a closure

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(),
+                            );
+                        })();
                     }
                 }
                 Ok(__InitOk)
--
2.41.0