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Subject: Re: kmalloc() alignment
In-Reply-To: <E14Zh5G-0005tP-00@the-village.bc.nu> from Alan Cox at "Mar 4, 2001
 10:34:31 pm"
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Date: Mon, 5 Mar 2001 10:40:05 +0100 (MET)
CC: Kenn Humborg <kenn@linux.ie>, Linux-Kernel <linux-kernel@vger.kernel.org>
From: R.E.Wolff@BitWizard.nl (Rogier Wolff)
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Alan Cox wrote:
> > Does kmalloc() make any guarantees of the alignment of allocated
> > blocks?  Will the returned block always be 4-, 8- or 16-byte
> > aligned, for example?
 
> There are people who assume 16byte alignment guarantees. I dont
> think anyone has formally specified the guarantee beyond 4 bytes tho

What does "formally specified" mean? 

As far as I know, you can count on 16-bytes alignment from
kmalloc. The trouble is that you would have to keep the original
pointer and free that if you have to do the "round" yourself. 

I once wrote a kmalloc(*) that would allow you to free any pointer
inside the kmalloc-ed area. This is dangerous as freeing a random
pointer is more likely to "work". But in this case it would be very
convenient.

			Roger.

(*) Too buggy for anyone but me. 

-- 
** R.E.Wolff@BitWizard.nl ** http://www.BitWizard.nl/ ** +31-15-2137555 **
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