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Re: Zero-length allocation with posix_memalign()

by Jason Evans-2 :: Rate this Message:

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Fabian Keil wrote:

> Rémi Denis-Courmont, one of the vlc developers, pointed out
> that passing a zero size to posix_memalign() should actually
> work, though:
>
> | In principle, while useless, there is no reason why allocating an empty
> | picture should not be possible. posix_memalign() does support zero-length
> | allocation anyway:
> | http://www.opengroup.org/onlinepubs/9699919799/functions/posix_memalign.html
> | | If the size of the space requested is 0, the behavior is
> | | implementation-defined; the value returned in memptr shall be either a
> | | null pointer or a unique pointer.

Standards: So many to choose from.  This behavior for posix_memalign was
only defined as of the 2008 standard (see the Issue 7 notes for
posix_memalign):

https://www.opengroup.org/austin/interps/uploads/40/14543/AI-152.txt

Such requirements are unfortunate, because they induce a performance
penalty for every call, just so that programs can avoid proper handling
of edge cases in the rare situations for which such edge cases are a
real possibility.

I will add the pessimization to posix_memalign once the 8.0 freeze is
over.  It will be quite some time before this behavior becomes
ubiquitous, so in the meanwhile it's probably a good idea to modify vlc
to avoid such allocation requests.

Thanks,
Jason
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