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SubjectRe: kfree(0) - ok?
Date
On Aug 15, 2007, at 06:20:27, Jan Engelhardt wrote:
> On Aug 15 2007 11:58, Rene Herman wrote:
>>>> NULL is not 0 though.
>>> It is. Its representation isn't guaranteed to be all-bits-zero,
>>
>> He said the null _pointer_ isn't guaranteed to be all-bits zero.
>> And it isn't. Read the standard or the faq.
>
> 0 is all-bits-zero.
> NULL is 0. ("It is.", above)
>
> Transitively, this would make NULL all-bits-zero. I might have
> missed something, though, perhaps that the cast to void* makes it
> intransitive. But leave it at whatever the standard says.
>
>> but the constant value 0 when used in pointer context is always a
>> null pointer (and in fact the standard requires that NULL be
>> #defined as 0 or a cast thereof).

Irrespective of whatever the standard says, EVERY platform and
compiler anybody makes nowadays has a NULL pointer value with all
bits clear. Theoretically the standard allows otherwise, but such a
decision would break so much code. Linux especially, we rely on the
uninitialized data to have all bits clear and we depend on that
producing NULL pointers; if a NULL pointer was not bitwise exactly 0
then the test "if (some_ptr != NULL)" would fail and we would start
dereferencing garbage.

Cheers,
Kyle Moffett

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