From: Gary Guo <gary@garyguo.net>
To: Alice Ryhl <aliceryhl@google.com>
Cc: rust-for-linux@vger.kernel.org, "Miguel Ojeda" <ojeda@kernel.org>,
"Wedson Almeida Filho" <wedsonaf@gmail.com>,
"Tejun Heo" <tj@kernel.org>,
"Lai Jiangshan" <jiangshanlai@gmail.com>,
"Alex Gaynor" <alex.gaynor@gmail.com>,
"Boqun Feng" <boqun.feng@gmail.com>,
"Björn Roy Baron" <bjorn3_gh@protonmail.com>,
"Benno Lossin" <benno.lossin@proton.me>,
linux-kernel@vger.kernel.org, patches@lists.linux.dev,
"Wedson Almeida Filho" <walmeida@microsoft.com>,
"Martin Rodriguez Reboredo" <yakoyoku@gmail.com>
Subject: Re: [PATCH v2 2/8] rust: add offset_of! macro
Date: Thu, 1 Jun 2023 18:17:42 +0100 [thread overview]
Message-ID: <20230601181742.5538460f.gary@garyguo.net> (raw)
In-Reply-To: <20230601134946.3887870-3-aliceryhl@google.com>
On Thu, 1 Jun 2023 13:49:40 +0000
Alice Ryhl <aliceryhl@google.com> wrote:
> From: Wedson Almeida Filho <walmeida@microsoft.com>
>
> This macro is used to compute the offset of a field in a struct.
>
> This commit enables an unstable feature that is necessary for using
> the macro in a constant. However, this is not a problem as the macro
> will become available from the Rust standard library soon [1]. The
> unstable feature can be disabled again once that happens.
>
> The macro in this patch does not support sub-fields. That is, you cannot
> write `offset_of!(MyStruct, field.sub_field)` to get the offset of
> `sub_field` with `field`'s type being a struct with a field called
> `sub_field`. This is because `field` might be a `Box<SubStruct>`, which
> means that you would be trying to compute the offset to something in an
> entirely different allocation. There's no easy way to fix the current
> macro to support subfields, but the version being added to the standard
> library should support it, so the limitation is temporary and not a big
> deal.
>
> Link: https://github.com/rust-lang/rust/issues/106655 [1]
> Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
> Co-developed-by: Alice Ryhl <aliceryhl@google.com>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
> ---
> rust/kernel/lib.rs | 35 +++++++++++++++++++++++++++++++++++
> scripts/Makefile.build | 2 +-
> 2 files changed, 36 insertions(+), 1 deletion(-)
>
> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index eaded02ffb01..7ea777b731e6 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -14,6 +14,7 @@
> #![no_std]
> #![feature(allocator_api)]
> #![feature(coerce_unsized)]
> +#![feature(const_refs_to_cell)]
> #![feature(dispatch_from_dyn)]
> #![feature(new_uninit)]
> #![feature(receiver_trait)]
> @@ -98,3 +99,37 @@ fn panic(info: &core::panic::PanicInfo<'_>) -> ! {
> // instead of `!`. See <https://github.com/rust-lang/rust-bindgen/issues/2094>.
> loop {}
> }
> +
> +/// Calculates the offset of a field from the beginning of the struct it belongs to.
> +///
> +/// # Examples
> +///
> +/// ```
> +/// #[repr(C)]
> +/// struct Test {
> +/// a: u64,
> +/// b: u32,
> +/// }
> +///
> +/// assert_eq!(kernel::offset_of!(Test, b), 8);
> +/// ```
> +#[macro_export]
> +macro_rules! offset_of {
> + ($type:path, $field:ident) => {{
> + let $type { $field: _, .. };
> + let tmp = ::core::mem::MaybeUninit::<$type>::uninit();
> + let outer = tmp.as_ptr();
> + // To avoid warnings when nesting `unsafe` blocks.
> + #[allow(unused_unsafe)]
> + // SAFETY: The pointer is valid and aligned, just not initialised; `addr_of` ensures that
> + // we don't actually read from `outer` (which would be UB) nor create an intermediate
> + // reference.
> + let inner = unsafe { ::core::ptr::addr_of!((*outer).$field) } as *const u8;
> + // To avoid warnings when nesting `unsafe` blocks.
> + #[allow(unused_unsafe)]
> + // SAFETY: The two pointers are within the same allocation block.
> + unsafe {
> + inner.offset_from(outer as *const u8) as usize
> + }
> + }};
> +}
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 78175231c969..819510694769 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -277,7 +277,7 @@ $(obj)/%.lst: $(src)/%.c FORCE
> # Compile Rust sources (.rs)
> # ---------------------------------------------------------------------------
>
> -rust_allowed_features := new_uninit
> +rust_allowed_features := const_refs_to_cell,new_uninit
>
> rust_common_cmd = \
> RUST_MODFILE=$(modfile) $(RUSTC_OR_CLIPPY) $(rust_flags) \
next prev parent reply other threads:[~2023-06-01 17:17 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-01 13:49 [PATCH v2 0/8] rust: workqueue: add bindings for the workqueue Alice Ryhl
2023-06-01 13:49 ` [PATCH v2 1/8] rust: workqueue: add low-level workqueue bindings Alice Ryhl
2023-06-01 14:29 ` Martin Rodriguez Reboredo
2023-06-02 14:39 ` Andreas Hindborg (Samsung)
2023-06-06 23:36 ` Boqun Feng
2023-06-07 15:18 ` Alice Ryhl
2023-06-11 15:45 ` Benno Lossin
2023-06-01 13:49 ` [PATCH v2 2/8] rust: add offset_of! macro Alice Ryhl
2023-06-01 17:17 ` Gary Guo [this message]
2023-06-02 10:33 ` Andreas Hindborg (Samsung)
2023-06-07 15:15 ` Alice Ryhl
2023-06-11 15:47 ` Benno Lossin
2023-06-01 13:49 ` [PATCH v2 3/8] rust: sync: add `Arc::{from_raw, into_raw}` Alice Ryhl
2023-06-01 17:26 ` Gary Guo
2023-06-02 10:51 ` Andreas Hindborg (Samsung)
2023-06-05 14:31 ` Gary Guo
2023-06-05 14:49 ` Andreas Hindborg (Samsung)
2023-06-05 15:00 ` Boqun Feng
2023-06-05 15:20 ` Boqun Feng
2023-06-05 18:34 ` Andreas Hindborg (Samsung)
2023-06-11 15:48 ` Benno Lossin
2023-06-01 13:49 ` [PATCH v2 4/8] rust: workqueue: define built-in queues Alice Ryhl
2023-06-01 17:30 ` Gary Guo
2023-06-01 17:52 ` Martin Rodriguez Reboredo
2023-06-02 8:32 ` Alice Ryhl
2023-06-02 14:46 ` Andreas Hindborg (Samsung)
2023-06-11 15:49 ` Benno Lossin
2023-06-01 13:49 ` [PATCH v2 5/8] rust: workqueue: add helper for defining work_struct fields Alice Ryhl
2023-06-01 14:50 ` Martin Rodriguez Reboredo
2023-06-01 18:44 ` Boqun Feng
2023-06-02 8:38 ` Alice Ryhl
2023-06-02 16:32 ` Boqun Feng
2023-06-01 21:09 ` Boqun Feng
2023-06-02 9:37 ` Alice Ryhl
2023-06-02 14:41 ` Andreas Hindborg (Samsung)
2023-06-11 15:59 ` Benno Lossin
2023-06-27 8:42 ` Alice Ryhl
2023-06-01 13:49 ` [PATCH v2 6/8] rust: workqueue: implement `WorkItemPointer` for pointer types Alice Ryhl
2023-06-01 14:51 ` Martin Rodriguez Reboredo
2023-06-02 14:42 ` Andreas Hindborg (Samsung)
2023-06-11 16:01 ` Benno Lossin
2023-06-01 13:49 ` [PATCH v2 7/8] rust: workqueue: add `try_spawn` helper method Alice Ryhl
2023-06-01 14:53 ` Martin Rodriguez Reboredo
2023-06-02 14:43 ` Andreas Hindborg (Samsung)
2023-06-11 16:10 ` Benno Lossin
2023-06-01 13:49 ` [PATCH v2 8/8] rust: workqueue: add examples Alice Ryhl
2023-06-01 14:58 ` Martin Rodriguez Reboredo
2023-06-01 17:32 ` Gary Guo
2023-06-02 9:39 ` Alice Ryhl
2023-06-02 14:44 ` Andreas Hindborg (Samsung)
2023-06-02 14:48 ` Andreas Hindborg (Samsung)
2023-06-11 16:15 ` Benno Lossin
2023-06-27 8:38 ` Alice Ryhl
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