linux-kernel - [PATCH v2] rust: kernel: add support for bits/genmask macros

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Message-Id: <20241024-topic-panthor-rs-genmask-v2-1-85237c1f0cea@collabora.com>
Date: Thu, 24 Oct 2024 11:17:47 -0300
From: Daniel Almeida <daniel.almeida@...labora.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>
Cc: linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org, 
 Daniel Almeida <daniel.almeida@...labora.com>
Subject: [PATCH v2] rust: kernel: add support for bits/genmask macros

These macros are converted from their kernel equivalent.

---
- Added ticks around `BIT`, and `h >=l` (Thanks, Benno).
- Decided to keep the arguments as `expr`, as I see no issues with that
- Added a proper example, with an assert_eq!() (Thanks, Benno)
- Fixed the condition h <= l, which should be h >= l.
- Checked that the assert for the condition above is described in the
  docs.

Signed-off-by: Daniel Almeida <daniel.almeida@...labora.com>
---
 rust/kernel/bits.rs | 36 ++++++++++++++++++++++++++++++++++++
 rust/kernel/lib.rs  |  1 +
 2 files changed, 37 insertions(+)

diff --git a/rust/kernel/bits.rs b/rust/kernel/bits.rs
new file mode 100644
index 0000000000000000000000000000000000000000..479883984f995f6b44272fa4566a08f1c1e6b143
--- /dev/null
+++ b/rust/kernel/bits.rs
@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Bit manipulation macros.
+//!
+//! C header: [`include/linux/bits.h`](srctree/include/linux/bits.h)
+
+/// Produces a literal where bit `n` is set.
+///
+/// Equivalent to the kernel's `BIT` macro.
+///
+#[macro_export]
+macro_rules! bit {
+    ($n:expr) => {
+        (1 << $n)
+    };
+}
+
+/// Create a contiguous bitmask starting at bit position `l` and ending at
+/// position `h`, where `h >= l`.
+///
+/// # Examples
+/// ```
+///     use kernel::genmask;
+///     let mask = genmask!(39, 21);
+///     assert_eq!(mask, 0x000000ffffe00000);
+/// ```
+///
+#[macro_export]
+macro_rules! genmask {
+    ($h:expr, $l:expr) => {{
+        const _: () = {
+            assert!($h >= $l);
+        };
+        ((!0u64 - (1u64 << $l) + 1) & (!0u64 >> (64 - 1 - $h)))
+    }};
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index b5f4b3ce6b48203507f89bcc4b0bf7b076be6247..4f256941ac8fbd1263d5c014a0ce2f5ffb9d1849 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -27,6 +27,7 @@
 extern crate self as kernel;
 
 pub mod alloc;
+pub mod bits;
 #[cfg(CONFIG_BLOCK)]
 pub mod block;
 mod build_assert;

---
base-commit: 91e21479c81dd4e9e22a78d7446f92f6b96a7284
change-id: 20241023-topic-panthor-rs-genmask-fabc573fef43

Best regards,
-- 
Daniel Almeida <daniel.almeida@...labora.com>