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With all users specifying their desired register type now, >> propagate the specified type and restrict I/O access only when type >> matches. >> >> Also, add an `io_project!` example which is enabled by this change. >> >> Signed-off-by: Gary Guo >> --- >> rust/kernel/io.rs | 13 +++++++++++ >> rust/kernel/io/register.rs | 55 ++++++++++++++++++++++++++++++++-------= ------- >> rust/macros/io/register.rs | 34 ++++++++++++++-------------- >> 3 files changed, 68 insertions(+), 34 deletions(-) >> >> diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs >> index 84dd876b3407..4542187d6b91 100644 >> --- a/rust/kernel/io.rs >> +++ b/rust/kernel/io.rs >> @@ -1692,21 +1692,34 @@ pub fn project_loc(self, location: L) -> <= T::Backend as IoBackend>::View<' >> /// The syntax is of form `io_project!(io, proj)` where `io` is an expr= ession to a type that >> /// implements [`Io`] and `proj` is a [projection specification](kernel= ::ptr::project!). >> /// >> +/// `io_project!` can also project to subview of registers defined with= [`register!`] macro. > > nit: "to a subview". > > <...> >> +/// Helper function for register alias implementation. >> +/// >> +/// This is used to enforce base matching. Only called during const eva= l. >> +#[doc(hidden)] >> +#[inline(always)] >> +pub const fn alias_offset>= () -> usize { >> + Alias::OFFSET >> +} >> + >> +/// Helper function for register element alias implementation. >> +/// >> +/// This is used to enforce base matching and provide bounds checking. = Only called during const >> +/// eval. >> +#[doc(hidden)] >> +#[inline(always)] >> +pub const fn element_alias_offset>( >> + idx: usize, >> +) -> usize { >> + build_assert!(idx < Alias::SIZE); >> + Alias::OFFSET + idx * Alias::STRIDE >> +} > > You could convert the `build_assert!` (always good to eschew) into a > `const_assert!` if you turn `idx` into a generic parameter: > > pub const fn element_alias_offset< > Base: ?Sized, > Alias: RegisterArray, > const IDX: usize, > >() -> usize { > crate::const_assert!(IDX < Alias::SIZE); > Alias::OFFSET + IDX * Alias::STRIDE > } > > You get a better error message, the const parameter is used in a > very controlled environment well within the expressive power of const > generics, and that function is not public interface anyway. > > If you don't like it (recent discussions make me think you might not > :)), then let's remove the `build_assert!` and keep the `static_assert` > emitted by the macro until this patch; it's not as elegant as checking > the condition into the same block of code that uses it, but again we are > in a controlled environment and static_assert > const_assert > > build_assert so this may actually be my preferred solution. You can > document the invariant in `element_alias_offset`. The error message should be identical? This function is only called during = const evaluation, so even if I replace this build_assert to assert it'll be fine = and never actually cause linker error or runtime panic. I wonder if I should add assert_in_const_eval() or maybe #[const_eval_only] fn ... which expands to #[inline(always)] fn const ... { assert_in_const_eval() } so that it's clear to reader that this is a const-eval-only function. Best, Gary