linux-kernel - Re: x86-64: __pa_symbol() vs. _

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Message-ID: <20081209111508.GB23556@one.firstfloor.org>
Date:	Tue, 9 Dec 2008 12:15:08 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Jan Beulich <jbeulich@...ell.com>
Cc:	mingo@...e.hu, Andi Kleen <andi@...stfloor.org>,
	tglx@...utronix.de, hpa@...or.com, linux-kernel@...r.kernel.org
Subject: Re: x86-64: __pa_symbol() vs. __pa()

On Tue, Dec 09, 2008 at 10:05:02AM +0000, Jan Beulich wrote:
> Can any of you recall the reason for the comment accompanying the
> __pa_symbol() definition:
> 
> /* __pa_symbol should be used for C visible symbols.
>    This seems to be the official gcc blessed way to do such arithmetic. */

gcc assumes that such symbol arithmetic doesn't wrap. iirc there was a 
miscompilation on PPC64 because of that and then it was fixed
everywhere. On x86-64 there are normally no wraps, but there might
be in some cases.

-Andi
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