linux-kernel - Re: is avoiding compat ioctls possible?

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Message-ID: <alpine.LFD.2.00.0910282055330.9323@eddie.linux-mips.org>
Date:	Wed, 28 Oct 2009 21:05:08 +0000 (GMT)
From:	"Maciej W. Rozycki" <macro@...ux-mips.org>
To:	Andi Kleen <andi@...stfloor.org>
cc:	Dave Airlie <airlied@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	DRI Development Mailing List 
	<dri-devel@...ts.sourceforge.net>, Arnd Bergmann <arnd@...db.de>,
	David Miller <davem@...emloft.net>
Subject: Re: is avoiding compat ioctls possible?

On Wed, 28 Oct 2009, Andi Kleen wrote:

> > I'm just amazed that compat_ioctl should be required for all new code.
> > 
> > DrNick on irc suggested just doing:
> > if (is_compat_task()) ptr &= 0x00000000FFFFFFFF;
> 
> Such hacks often have problems on BE.

 And then some platforms (i.e. MIPS) require sign-extension rather than 
zero-extension, that is:

if (is_compat_task()) ptr = ((ptr & 0xffffffff) ^ 0x80000000) - 0x80000000;

if doing this explicitly (with compat stuff hardware will do the right 
thing automagically).

  Maciej
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