linux-kernel - Re: kfree(0)

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Date:	Wed, 15 Aug 2007 16:06:49 +0200 (CEST)
From:	Jan Engelhardt <jengelh@...putergmbh.de>
To:	Kyle Moffett <mrmacman_g4@....com>
cc:	Rene Herman <rene.herman@...il.com>,
	Jason Uhlenkott <jasonuhl@...onuhl.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Tim Bird <tim.bird@...sony.com>,
	linux kernel <linux-kernel@...r.kernel.org>
Subject: Re: kfree(0) - ok?


On Aug 15 2007 09:58, Kyle Moffett wrote:
>
> 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.

But if kmalloc returns NULL on failure, then testing for NULL
(irrespective of being 0 or 0xDEADBEEF) is ok.
What would actually concern me then is what "if (!some_ptr)" would do.
Probably not the right thing.


	Jan
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