linux-kernel - Re: SLUB: Return ZERO_SIZE

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Message-ID: <20070604154424.5c4750f7@the-village.bc.nu>
Date:	Mon, 4 Jun 2007 15:44:24 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Matt Mackall <mpm@...enic.com>
Cc:	Christoph Lameter <clameter@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	jeremy@...p.org
Subject: Re: SLUB: Return ZERO_SIZE_PTR for kmalloc(0)

> > > I agree the risk is low, but if something _does_ blow up, it will do so subtly.
> 
> Arguable the proposed badptr behavior is correct. It's basically "how many
> angels can dance on the head of a pin"? All the returned pointers are
> at least 0 bytes away from the previous one.

C++ very carefully keeps objects of zero size at differing addresses to
avoid exactly this kind of pointer confusion. Given the trivial fix is
simply

	size += !size;

at the start of malloc what is there worth arguing about ?

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