Re: [PATCH] rust: alloc: add missing trait item MIN_ALIGN to Cmalloc

["Danilo Krummrich" <dakr@kernel.org>]

On Sun Aug 24, 2025 at 2:36 PM CEST, Alice Ryhl wrote:
> On Sun, Aug 24, 2025 at 2:07 PM Danilo Krummrich <dakr@kernel.org> wrote:
>> +    const MIN_ALIGN: usize = bindings::ARCH_KMALLOC_MINALIGN;
>
> Is this the right value for normal malloc?

Heh! ARCH_KMALLOC_MINALIGN should be correct, because the Cmalloc implementation
should (ideally) enforce a minimum alignment of ARCH_KMALLOC_MINALIGN for
compatibility reasons.

However, double checking the existing code, it doesn't. Hence, the correct value
must either be

	const MIN_ALIGN: usize = align_of::<crate::ffi::c_ulonglong>();

instead. Or, we have to actually enforce ARCH_KMALLOC_MINALIGN.

Given that this fix is only for within the -rc cycles, i.e. we will remove
allocator_test.rs before the MIN_ALIGN stuff ever hits an actual release, just
using align_of::<crate::ffi::c_ulonglong>() should be fine.