Re: [PATCH v3 1/6] arm/mpu: Find MPU region by range

["Orzel, Michal" <michal.orzel@xxxxxxx>]

On 15/07/2025 10:36, Hari Limaye wrote:
> Hi Michal,
> 
>>> +int mpumap_contains_region(pr_t *table, uint8_t nr_regions, paddr_t base,
>>> +                           paddr_t limit, uint8_t *index)
>>> +{
>>> +    ASSERT(index);
>>> +    *index = INVALID_REGION_IDX;
>>> +
>>> +    /*
>>> +     * The caller supplies a half-open interval [base, limit), i.e. limit 
>>> is the
>>> +     * first byte *after* the region. Require limit strictly greater than 
>>> base,
>>> +     * which is necessarily a non-empty region.
>>> +     */
>>> +    ASSERT(base < limit);
>> Well, that does not guarantee a non-empty region.
>> Consider passing [x, x+1). The assert will pass, even though the region is 
>> empty.
>>
>> ~Michal
>>
> 
> Apologies, I may well be missing something here! Please could you suggest a 
> code snippet to understand your expectation here / what you would prefer the 
> assert to be?
> 
> As I understand it, with a half-open interval [base, limit) as is passed to 
> this function, the size is  `limit - base` and so the region [x, x+1) will 
> have size 1. The empty region starting at the same address would be [x, x). 
> But perhaps I am making the off-by-one error here.
Hmm, I think I made a mistake here. Region of size 1B would have base == limit
in registers. All good then.

~Michal