On 07/09/2013 09:21 AM, Wedson Almeida Filho wrote:
> On Sat, Jul 6, 2013 at 9:59 PM, Joe Perches <j...@perches.com> wrote:
>>
>> Not correct.
>>
>>> while (start < end) {
>>> - size_t mid = start + (end - start) / 2;
>>> + size_t mid = (start + end) / 2;
>>
>> size_t start = 0x80000000;
>> size_t end = 0x80000001;
>
> Good point, they aren't equivalent in all cases.
>
> For the overflow to happen though, we need an array with at least
> N/2+1 entries, where N is the address space size. The array wouldn't
> fit in addressable memory if the element size is greater than 1, so
> this can only really happen when the element size is 1. Even then, it
> would require the kernel range to be greater than half of all
> addressable memory, and allow an allocation taking that much memory. I
> don't know all architectures where linux runs, but I don't think such
> configuration is likely to exist.
>
It does. In ARC port (arch/arc), the untranslated address space starts at
0x8000_0000 and this is where kernel is linked at. So all ARC kernel addresses
(code/data) lie in that range. This means you don't need special corner case for
this trip on ARC - it will break rightaway - unless I'm missing something.
P.S. Sorry for not replying earlier than ur v2.
-Vineet
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