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Message-Id: <20250423-b4-container-of-type-check-v3-1-7994c56cf359@gmail.com>
Date: Wed, 23 Apr 2025 13:40:10 -0400
From: Tamir Duberstein <tamird@...il.com>
To: Miguel Ojeda <ojeda@...nel.org>, 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>,
Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>,
Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>
Cc: rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
Tamir Duberstein <tamird@...il.com>
Subject: [PATCH v3] rust: check type of `$ptr` in `container_of!`
Add a compile-time check that `*$ptr` is of the type of `$type->$($f)*`.
Rename those placeholders for clarity.
Given the incorrect usage:
> diff --git a/rust/kernel/rbtree.rs b/rust/kernel/rbtree.rs
> index 8d978c896747..6a7089149878 100644
> --- a/rust/kernel/rbtree.rs
> +++ b/rust/kernel/rbtree.rs
> @@ -329,7 +329,7 @@ fn raw_entry(&mut self, key: &K) -> RawEntry<'_, K, V> {
> while !(*child_field_of_parent).is_null() {
> let curr = *child_field_of_parent;
> // SAFETY: All links fields we create are in a `Node<K, V>`.
> - let node = unsafe { container_of!(curr, Node<K, V>, links) };
> + let node = unsafe { container_of!(curr, Node<K, V>, key) };
>
> // SAFETY: `node` is a non-null node so it is valid by the type invariants.
> match key.cmp(unsafe { &(*node).key }) {
this patch produces the compilation error:
> error[E0308]: mismatched types
> --> rust/kernel/lib.rs:207:25
> |
> 207 | [field_ptr, container_field_ptr]; // typeof(`$field_ptr`) == typeof(`$Container.$($fields)*`)
> | ^^^^^^^^^^^^^^^^^^^ expected `*mut rb_node`, found `*mut K`
> |
> ::: rust/kernel/rbtree.rs:270:6
> |
> 270 | impl<K, V> RBTree<K, V>
> | - found this type parameter
> ...
> 332 | let node = unsafe { container_of!(curr, Node<K, V>, key) };
> | ------------------------------------ in this macro invocation
> |
> = note: expected raw pointer `*mut bindings::rb_node`
> found raw pointer `*mut K`
> = note: this error originates in the macro `container_of` (in Nightly builds, run with -Z macro-backtrace for more info)
>
> error: aborting due to 1 previous error
Reviewed-by: Benno Lossin <benno.lossin@...ton.me>
Suggested-by: Alice Ryhl <aliceryhl@...gle.com>
Link: https://lore.kernel.org/all/CAH5fLgh6gmqGBhPMi2SKn7mCmMWfOSiS0WP5wBuGPYh9ZTAiww@mail.gmail.com/
Signed-off-by: Tamir Duberstein <tamird@...il.com>
---
I also considered an implementation using a function, but the resulting
compilation error was not as concise:
> error[E0308]: mismatched types
> --> rust/kernel/lib.rs:207:42
> |
> 207 | assert_same_type($field_ptr, field_ptr);
> | ---------------- ^^^^^^^^^ expected `*const rb_node`, found `*mut K`
> | |
> | arguments to this function are incorrect
> |
> ::: rust/kernel/rbtree.rs:270:6
> |
> 270 | impl<K, V> RBTree<K, V>
> | - found this type parameter
> ...
> 332 | let node = unsafe { container_of!(curr, Node<K, V>, key) };
> | ------------------------------------ in this macro invocation
> |
> = note: expected raw pointer `*const bindings::rb_node`
> found raw pointer `*mut K`
> note: function defined here
> --> rust/kernel/lib.rs:205:16
> |
> 205 | fn assert_same_type<T>(_: *const T, _: *const T) {}
> | ^^^^^^^^^^^^^^^^ -----------
> |
> ::: rust/kernel/rbtree.rs:332:33
> |
> 332 | let node = unsafe { container_of!(curr, Node<K, V>, key) };
> | ------------------------------------ in this macro invocation
> = note: this error originates in the macro `container_of` (in Nightly builds, run with -Z macro-backtrace for more info)
>
> error: aborting due to 1 previous error
---
Changes in v3:
- Fix comment typo.
- s/^;/ / in commit message and cover letter. (Miguel Ojeda)
- Evaluate $ptr only once. (Alice Ryhl)
- Link to v2: https://lore.kernel.org/r/20250412-b4-container-of-type-check-v2-1-f3cc9934c160@gmail.com
Changes in v2:
- Wrap in `if false` to improve unoptimized codegen. (Alice Ryhl)
- Shrink implementation using an array literal instead of a function.
- Link to v1: https://lore.kernel.org/r/20250411-b4-container-of-type-check-v1-1-08262ef67c95@gmail.com
---
rust/kernel/lib.rs | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 1df11156302a..d14ed86efb68 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -198,9 +198,15 @@ fn panic(info: &core::panic::PanicInfo<'_>) -> ! {
/// ```
#[macro_export]
macro_rules! container_of {
- ($ptr:expr, $type:ty, $($f:tt)*) => {{
- let offset: usize = ::core::mem::offset_of!($type, $($f)*);
- $ptr.byte_sub(offset).cast::<$type>()
+ ($field_ptr:expr, $Container:ty, $($fields:tt)*) => {{
+ let offset: usize = ::core::mem::offset_of!($Container, $($fields)*);
+ let field_ptr = $field_ptr;
+ let container_ptr = field_ptr.byte_sub(offset).cast::<$Container>();
+ if false {
+ let container_field_ptr = ::core::ptr::addr_of!((*container_ptr).$($fields)*).cast_mut();
+ [field_ptr, container_field_ptr]; // typeof(`$field_ptr`) == typeof(`$Container.$($fields)*`)
+ }
+ container_ptr
}}
}
---
base-commit: 0af2f6be1b4281385b618cb86ad946eded089ac8
change-id: 20250411-b4-container-of-type-check-06af1c204f59
prerequisite-change-id: 20250409-container-of-mutness-b153dab4388d:v1
prerequisite-patch-id: 53d5889db599267f87642bb0ae3063c29bc24863
Best regards,
--
Tamir Duberstein <tamird@...il.com>
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