linux-kernel - Re: [PATCH v3] rust: kernel: add support for bits/genmask macros

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAH5fLgjKgAB9vC-XxW5jCaJ5yGaHuDK3po9y2PmzC6kALR8J3g@mail.gmail.com>
Date: Tue, 21 Jan 2025 16:38:01 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Daniel Almeida <daniel.almeida@...labora.com>
Cc: 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>, 
	Trevor Gross <tmgross@...ch.edu>, linux-kernel@...r.kernel.org, 
	rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v3] rust: kernel: add support for bits/genmask macros

On Tue, Jan 21, 2025 at 4:30 PM Daniel Almeida
<daniel.almeida@...labora.com> wrote:
>
> In light of bindgen being unable to generate bindings for macros,
> manually define the bit and genmask C macros in Rust.
>
> Bit and genmask are frequently used in drivers, and are simple enough to
> just be redefined. Their implementation is also unlikely to ever change.
>
> These macros are converted from their kernel equivalent. Since
> genmask_u32 and genmask_u64 are thought to suffice, these two versions
> are implemented as const fns instead of declarative macros.

Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>

> Changes in v3:
> - Changed from declarative macro to const fn
> - Added separate versions for u32 and u64
> - Link to v2: https://lore.kernel.org/r/20241024-topic-panthor-rs-genmask-v2-1-85237c1f0cea@collabora.com
>
> Changes in v2:
>
> - 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>

Seems like this got mixed up? You may be missing a --- line somewhere
in your b4 cover letter.

>  rust/kernel/bits.rs | 42 ++++++++++++++++++++++++++++++++++++++++++
>  rust/kernel/lib.rs  |  1 +
>  2 files changed, 43 insertions(+)
>
> diff --git a/rust/kernel/bits.rs b/rust/kernel/bits.rs
> new file mode 100644
> index 0000000000000000000000000000000000000000..32049abd2078525be25b57b8e6b5948d1eecbf9f
> --- /dev/null
> +++ b/rust/kernel/bits.rs
> @@ -0,0 +1,42 @@
> +// 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.
> +pub const fn bit(n: u32) -> u64 {
> +    1 << n
> +}
> +
> +/// Create a contiguous bitmask starting at bit position `l` and ending at
> +/// position `h`, where `h >= l`.
> +///
> +/// # Examples
> +/// ```
> +///     use kernel::bits::genmask_u64;
> +///     let mask = genmask_u64(39, 21);
> +///     assert_eq!(mask, 0x000000ffffe00000);
> +/// ```
> +///
> +pub const fn genmask_u64(h: u32, l: u32) -> u64 {
> +    assert!(h >= l);
> +    (!0u64 - (1u64 << l) + 1) & (!0u64 >> (64 - 1 - h))
> +}
> +
> +/// Create a contiguous bitmask starting at bit position `l` and ending at
> +/// position `h`, where `h >= l`.
> +///
> +/// # Examples
> +/// ```
> +///     use kernel::bits::genmask_u32;
> +///     let mask = genmask_u32(9, 0);
> +///     assert_eq!(mask, 0x000003ff);
> +/// ```
> +///
> +pub const fn genmask_u32(h: u32, l: u32) -> u32 {
> +    assert!(h >= l);
> +    (!0u32 - (1u32 << l) + 1) & (!0u32 >> (32 - 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>
>