linux-kernel - Re: [PATCH] x86: remove __phys_reloc

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Date:	Mon, 09 Aug 2010 16:47:39 +0900
From:	Namhyung Kim <namhyung@...il.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: remove __phys_reloc_hide

2010-08-09 (월), 09:22 +0200, Andi Kleen:

> The original reason was that the C standard allows the compiler
> to make some assumptions on the pointer arithmetic that is done 
> on symbol addresses (e.g. no wrapping). This is exploited
> by the optimizer in the compiler to generate better code.
> 
> This lead to a miscompilation on PowerPC a couple of years back at 
> least with the va->pa conversion.
> 
> After that RELOC_HIDE was introduced after funelling the
> symbol address through an empty asm statement was recommended 
> as the official way to do this by the gcc developers.
> 
> I think x86-64 does not normally wrap here, but it's 
> still safer to do it this way.
> 
> -Andi

OK, then. Thanks for the comment.

p.s. The funny thing I found is there's no use of RELOC_HIDE on
arch/powerpc. Hmm...

-- 
Regards,
Namhyung Kim


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