On Wed, Feb 12, 2025 at 10:40 AM Danilo Krummrich <dakr@xxxxxxxxxx> wrote:
>
> On Wed, Feb 12, 2025 at 09:43:02AM -0500, Tamir Duberstein wrote:
> > diff --git a/rust/kernel/alloc/allocator_test.rs b/rust/kernel/alloc/allocator_test.rs
> > index e3240d16040b..17a475380253 100644
> > --- a/rust/kernel/alloc/allocator_test.rs
> > +++ b/rust/kernel/alloc/allocator_test.rs
> > @@ -62,6 +62,26 @@ unsafe fn realloc(
> > ));
> > }
> >
> > + // ISO C (ISO/IEC 9899:2011) defines `aligned_alloc`:
> > + //
> > + // > The value of alignment shall be a valid alignment supported by the implementation
> > + // [...].
> > + //
> > + // As an example of the "supported by the implementation" requirement, POSIX.1-2001 (IEEE
> > + // 1003.1-2001) defines `posix_memalign`:
> > + //
> > + // > The value of alignment shall be a power of two multiple of sizeof (void *).
> > + //
> > + // and POSIX-based implementations of `aligned_alloc` inherit this requirement. At the time
> > + // of writing, this is known to be the case on macOS (but not in glibc).
> > + //
> > + // Satisfy the stricter requirement to avoid spurious test failures on some platforms.
> > + let min_align = core::mem::size_of::<*const crate::ffi::c_void>();
> > + let layout = layout.align_to(min_align).unwrap_or_else(|_err| {
> > + crate::build_error!("invalid alignment")
>
> That's not what I thought this patch will look like. I thought you'll directly
> follow Gary's proposal, which is why I said you can keep the ACK.
>
> build_error!() doesn't work here, there is no guarantee that this can be
> evaluated at compile time.
It's not guaranteed, but it does work. I could use some clarification
on the appropriate use of `build_error`. Here I'm using it to mean "I
want the compiler to let me know if the guarantees change". When is
that inappropriate?
> I think this should just be:
>
> let layout = layout.align_to(min_align).map_err(|_| AllocError)?.pad_to_align();
>
> - Danilo
>
> > + });
> > + let layout = layout.pad_to_align();
> > +
> > // SAFETY: Returns either NULL or a pointer to a memory allocation that satisfies or
> > // exceeds the given size and alignment requirements.
> > let dst = unsafe { libc_aligned_alloc(layout.align(), layout.size()) } as *mut u8;
