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Date:   Sat, 29 Jul 2023 09:09:53 +0000
To:     Miguel Ojeda <ojeda@kernel.org>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Alex Gaynor <alex.gaynor@gmail.com>
From:   Benno Lossin <benno.lossin@proton.me>
Cc:     Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        =?utf-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>,
        Benno Lossin <benno.lossin@proton.me>,
        Alice Ryhl <aliceryhl@google.com>,
        Andreas Hindborg <nmi@metaspace.dk>,
        rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org,
        Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Subject: [PATCH v3 06/13] rust: init: make initializer values inaccessible after initializing
Message-ID: <20230729090838.225225-7-benno.lossin@proton.me>
In-Reply-To: <20230729090838.225225-1-benno.lossin@proton.me>
References: <20230729090838.225225-1-benno.lossin@proton.me>
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Precedence: bulk

Previously the init macros would create a local variable with the name
and hygiene of the field that is being initialized to store the value of
the field. This would override any user defined variables. For example:
```
struct Foo {
    a: usize,
    b: usize,
}
let a =3D 10;
let foo =3D init!(Foo{
    a: a + 1, // This creates a local variable named `a`.
    b: a, // This refers to that variable!
});
let foo =3D Box::init!(foo)?;
assert_eq!(foo.a, 11);
assert_eq!(foo.b, 11);
```

This patch changes this behavior, so the above code would panic at the
last assertion, since `b` would have value 10.

Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Benno Lossin <benno.lossin@proton.me>
---
v2 -> v3:
- added Reviewed-by's from Martin and Alice.

 rust/kernel/init/macros.rs | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/rust/kernel/init/macros.rs b/rust/kernel/init/macros.rs
index 2bad086cda0a..cfeacc4b3f7d 100644
--- a/rust/kernel/init/macros.rs
+++ b/rust/kernel/init/macros.rs
@@ -1075,13 +1075,13 @@ macro_rules! __init_internal {
         // In-place initialization syntax.
         @munch_fields($field:ident <- $val:expr, $($rest:tt)*),
     ) =3D> {
-        let $field =3D $val;
+        let init =3D $val;
         // Call the initializer.
         //
         // SAFETY: `slot` is valid, because we are inside of an initialize=
r closure, we
         // return when an error/panic occurs.
         // We also use the `data` to require the correct trait (`Init` or =
`PinInit`) for `$field`.
-        unsafe { $data.$field(::core::ptr::addr_of_mut!((*$slot).$field), =
$field)? };
+        unsafe { $data.$field(::core::ptr::addr_of_mut!((*$slot).$field), =
init)? };
         // Create the drop guard:
         //
         // We rely on macro hygiene to make it impossible for users to acc=
ess this local variable.
@@ -1107,12 +1107,12 @@ macro_rules! __init_internal {
         // In-place initialization syntax.
         @munch_fields($field:ident <- $val:expr, $($rest:tt)*),
     ) =3D> {
-        let $field =3D $val;
+        let init =3D $val;
         // Call the initializer.
         //
         // SAFETY: `slot` is valid, because we are inside of an initialize=
r closure, we
         // return when an error/panic occurs.
-        unsafe { $crate::init::Init::__init($field, ::core::ptr::addr_of_m=
ut!((*$slot).$field))? };
+        unsafe { $crate::init::Init::__init(init, ::core::ptr::addr_of_mut=
!((*$slot).$field))? };
         // Create the drop guard:
         //
         // We rely on macro hygiene to make it impossible for users to acc=
ess this local variable.
@@ -1138,11 +1138,13 @@ macro_rules! __init_internal {
         // Init by-value.
         @munch_fields($field:ident $(: $val:expr)?, $($rest:tt)*),
     ) =3D> {
-        $(let $field =3D $val;)?
-        // Initialize the field.
-        //
-        // SAFETY: The memory at `slot` is uninitialized.
-        unsafe { ::core::ptr::write(::core::ptr::addr_of_mut!((*$slot).$fi=
eld), $field) };
+        {
+            $(let $field =3D $val;)?
+            // Initialize the field.
+            //
+            // SAFETY: The memory at `slot` is uninitialized.
+            unsafe { ::core::ptr::write(::core::ptr::addr_of_mut!((*$slot)=
.$field), $field) };
+        }
         // Create the drop guard:
         //
         // We rely on macro hygiene to make it impossible for users to acc=
ess this local variable.
--=20
2.41.0