[patch v1] malloc: add malloc_zero_aborts tunable

[Florian Weimer]

* DJ Delorie:

> Paul Eggert <eggert@cs.ucla.edu> writes:
>> On 2/12/26 11:15, DJ Delorie wrote:
>>> +  if (bytes == 0 && mp_.malloc_zero_aborts)
>>> +    abort();
>>
>> This would cause malloc to fail to conform to the C standard, something 
>> that is far more likely to cause problems (even as an option) than to 
>> cure it. Nobody should use such an option.
>
> Agreed, but it's a tool for people who want to know if that part of the
> standard is affecting their code, and thus giving them a list of places
> to audit to make sure they're handling it correctly.
>
>> Also, it would slow down malloc.
>
> As I mentioned, I'd work on the tail recursion issue later.  The size
> would already be in a register (usually) and comparing it to zero is
> cheap enough, I'd add all the likelies etc.  I just had this thought and
> wanted to get feedback on it before I forgot it ;-)

We should really be using IFUNCs to select the entry points to the
malloc code.  Then this check can be part of a lightweight debug malloc
(along with the perturb code and other similar behaviors).  The IFUNC
resolvers would activate this code only if the tunables require it.

Thanks,
Florian