From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: linux-next: manual merge of the rr tree
Date: Thu, 8 Jan 2009 12:50:31 -0800
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On Thu, 8 Jan 2009 21:48:35 +0100
Andi Kleen <andi@firstfloor.org> wrote:

> +/*
> + * This macro obfuscates arithmetic on a variable address so that gcc
> + * shouldn't recognize the original var, and make assumptions about it.
> + *
> + * This is needed because the C standard makes it undefined to do
> + * pointer arithmetic on "objects" outside their boundaries and the
> + * gcc optimizers assume this is the case. In particular they
> + * assume such arithmetic does not wrap.
> + *
> + * A miscompilation has been observed because of this on PPC.
> + * To work around it we hide the relationship of the pointer and the object
> + * using this macro.
> + *

wow, thanks.  I always wondered.