malloc(0) crashing with SIGABRT
Kaz Kylheku
920-082-4242@kylheku.com
Thu Sep 12 11:33:00 GMT 2019
On 2019-09-11 20:59, Brian Inglis wrote:
> On 2019-09-09 11:13, Petr SkoÄÃk wrote:
>> There's been a twitter discussion on how different POSIX platforms
>> handle malloc(0):
>> https://twitter.com/sortiecat/status/1170697927804817412 .
>>
>> As for Cygwin, the answer appears to be "not well", but this should be
>> easy to fix.
>
> POSIX SUS V4 2018 says:
>
> "RETURN VALUE
>
> Upon successful completion with size not equal to 0, malloc() shall
> return a
> pointer to the allocated space. If size is 0, either:
>
> A null pointer shall be returned [CX] [Option Start] and errno may be
> set to
> an implementation-defined value, [Option End] or
>
> A pointer to the allocated space shall be returned. The application
> shall
> ensure that the pointer is not used to access an object.
>
> Otherwise, it shall return a null pointer [CX] [Option Start] and set
> errno to
> indicate the error. [Option End]"
>
> The second option could be implemented by a pointer to an unmapped
> page, or a
> reference to an inaccessible mmap-ed area length zero.
That's easy: the null pointer, plus some small offset that observes
alignment, like 16.
(Alignment is important even if the memory isn't accessed, because
nonportable programs
depend on it for other reasons, like being able to use the least
significant few bits
of a pointer for tagging.)
--
Problem reports: http://cygwin.com/problems.html
FAQ: http://cygwin.com/faq/
Documentation: http://cygwin.com/docs.html
Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
More information about the Cygwin
mailing list