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From: Namhyung Kim <namhyung@gmail.com>
To: Andi Kleen <andi@firstfloor.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86: remove __phys_reloc_hide
Date: Mon, 09 Aug 2010 16:47:39 +0900	[thread overview]
Message-ID: <1281340059.976.27.camel@leonhard> (raw)
In-Reply-To: <20100809072226.GD29524@basil.fritz.box>

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



  reply	other threads:[~2010-08-09  7:47 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-08-08 21:38 [PATCH] x86: remove __phys_reloc_hide Namhyung Kim
2010-08-09  6:22 ` Andi Kleen
2010-08-09  6:40   ` Namhyung Kim
2010-08-09  6:44     ` Andi Kleen
2010-08-09  7:04       ` Namhyung Kim
2010-08-09  7:22         ` Andi Kleen
2010-08-09  7:47           ` Namhyung Kim [this message]
2010-08-09 18:56           ` H. Peter Anvin
2010-08-10  7:05             ` Ingo Molnar
2010-08-10 10:46               ` Namhyung Kim
2010-08-11  5:44                 ` Namhyung Kim
2010-08-11 19:09                   ` H. Peter Anvin
2010-08-11  6:37               ` [PATCH] x86: add a comment to __pa_symbol Namhyung Kim
2010-08-11  7:44                 ` [tip:x86/urgent] x86: Document __phys_reloc_hide() usage in __pa_symbol() tip-bot for Namhyung Kim
2018-06-19 23:00   ` [PATCH] x86: remove __phys_reloc_hide Thomas Gleixner
2010-08-09  8:07 ` Ingo Molnar
2010-08-09 18:56   ` H. Peter Anvin

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