Messages in this thread Patch in this message |  | | Date | Fri, 16 Dec 2022 14:15:16 -0800 | From | Boqun Feng <> | Subject | Re: [PATCH] rust: kernel: drop repetition in offset_of macro |
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On Fri, Dec 16, 2022 at 06:26:57PM +0000, Wedson Almeida Filho wrote: > On Fri, 16 Dec 2022 at 17:49, Wei Liu <wei.liu@kernel.org> wrote: > > > > It doesn't make sense to allow multiple fields to be specified in > > offset_of. > > Why do you say it doesn't make sense? > > Here's what I had in mind: > ``` > struct Y { > z: u32 > } > struct X { > y: Y > } > offset_of!(X, y.z)
For me, it's not very obvious that "y.z" is multiples of token trees rather a single token tree ;-)
Maybe some examples of the match pattern of macros can help people catch up faster? Like
"y.z" => tt [y], tt [.], tt [z]
I will defer to Gary or Bjorn for a better quick guide of Rust macros ;-)
Regards, Boqun
> ``` > > Which is something very plausible. > > > No functional change. > > > > Signed-off-by: Wei Liu <wei.liu@kernel.org> > > --- > > Cc: Miguel Ojeda <ojeda@kernel.org> > > Cc: Alex Gaynor <alex.gaynor@gmail.com> > > Cc: Wedson Almeida Filho <wedsonaf@gmail.com> > > Cc: Boqun Feng <boqun.feng@gmail.com> > > Cc: Gary Guo <gary@garyguo.net> > > Cc: Björn Roy Baron <bjorn3_gh@protonmail.com> > > --- > > rust/kernel/lib.rs | 10 ++++++---- > > 1 file changed, 6 insertions(+), 4 deletions(-) > > > > diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs > > index 6a322effa60c..2f3601e4e27e 100644 > > --- a/rust/kernel/lib.rs > > +++ b/rust/kernel/lib.rs > > @@ -208,7 +208,7 @@ impl<'a> Drop for KParamGuard<'a> { > > /// ``` > > #[macro_export] > > macro_rules! offset_of { > > - ($type:ty, $($f:tt)*) => {{ > > + ($type:ty, $f:tt) => {{ > > let tmp = core::mem::MaybeUninit::<$type>::uninit(); > > let outer = tmp.as_ptr(); > > // To avoid warnings when nesting `unsafe` blocks. > > @@ -216,12 +216,14 @@ macro_rules! offset_of { > > // 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).$($f)*) } as *const u8; > > + let inner = unsafe { core::ptr::addr_of!((*outer).$f) } 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) } > > - }} > > + unsafe { > > + inner.offset_from(outer as *const u8) > > + } > > + }}; > > } > > > > /// Produces a pointer to an object from a pointer to one of its fields. > > -- > > 2.35.1 > >
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