Re: [PATCH v5 21/38] rust: ptr: add const_align_up() and enable inline_const feature

[Gary Guo]

On 2026-02-23 11:07, Danilo Krummrich wrote:
> On Sun Feb 22, 2026 at 8:04 PM CET, John Hubbard wrote:
>> On 2/21/26 11:46 PM, Gary Guo wrote:
>>> On 2026-02-21 02:09, John Hubbard wrote:
>>>> Add const_align_up<ALIGN>() to kernel::ptr as the const-compatible
>>>> equivalent of Alignable::align_up(). This uses inline_const to validate
>>>> the alignment at compile time with a clear error message.
>>>>
>> ...
>>
>>>> +#[inline(always)]
>>>> +pub const fn const_align_up<const ALIGN: usize>(value: usize) -> usize {
>>>> +    const { assert!(ALIGN.is_power_of_two(), "ALIGN must be a power of two") };
>>>> +    match value.checked_add(ALIGN - 1) {
>>>> +        Some(v) => v & !(ALIGN - 1),
>>>> +        None => panic!("const_align_up: overflow"),
>>> 
>>> This is wrong. Either this function is always used in const context, in which case
>>> you take `ALIGN` as normal function parameter and use `build_assert` and `build_error`,
>>> or this function can be called from runtime and you shouldn't have a panic call here.
> 
> I think the most common case is that ALIGN is const, but value is not.
> 
> What about keeping the function as is (with the panic() replaced with a Result)
> and also add
> 
> 	#[inline(always)]
> 	pub const fn const_expect<T: Copy>(opt: Result<T>, &'static str) -> T {
> 	    match opt {
> 	        Ok(v) => v,
> 	        Err(_) => panic!(""),
> 	    }
> 	}
> 

We already have `Alignable::align_up` for non-const cases, so this would only be used
in const context and I don't see the need of having explicit const_expect?

Best,
Gary

> for when it is entirely called from const context, e.g.
> 
> 	pub(crate) const PMU_RESERVED_SIZE: u32 =
> 	    const_expect(const_align_up::<SZ_128K>(SZ_8M + SZ_16M + SZ_4K), "...");
> 
>> I will have another go at this, and put it in nova-core as per Miguel's
>> comment as well.
> 
> I think Miguel didn't mean to say it should not be in this file. I think the
> current place makes sense, let's keep it there.