linux-kernel - Re: asm-x86/byteorder.h: clean up for userspace

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Date:	Wed, 2 Jan 2008 03:31:26 +0200
From:	Adrian Bunk <bunk@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Mike Frysinger <vapier@...too.org>, tglx@...utronix.de,
	mingo@...hat.com, Andi Kleen <andi@...stfloor.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: asm-x86/byteorder.h: clean up for userspace

On Tue, Jan 01, 2008 at 01:19:42PM -0800, H. Peter Anvin wrote:
> Christoph Hellwig wrote:
>> On Mon, Dec 31, 2007 at 01:12:45PM -0500, Mike Frysinger wrote:
>>> Since asm-x86/byteorder.h is exported to userspace, use __asm__ rather than
>>> asm in its code.
>>
>> The correct fix is to not export it to userspace.
>
> Unfortunately, it's historically been provided, for over 15 years.  It's 
> also trivial to export, without funnies, and it's *useful* to userspace, as 
> it provides an interface sorely lacking from the stock libc interfaces.
>...

Userspace either has to #define CONFIG_X86_BSWAP or it'll get the slow 
versions of these functions...

Leaking CONFIG_ variables to userspace is not really funny - I remember 
e.g. what tricks MySQL does (did?) for (ab)using asm-i386/atomic.h in 
userspace.

> 	-hpa

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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