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

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Date:	Thu, 29 Oct 2009 09:27:18 +0100
From:	Arnd Bergmann <arndbergmann@...glemail.com>
To:	"Maciej W. Rozycki" <macro@...ux-mips.org>
Cc:	Andi Kleen <andi@...stfloor.org>, Dave Airlie <airlied@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	DRI Development Mailing List 
	<dri-devel@...ts.sourceforge.net>,
	David Miller <davem@...emloft.net>
Subject: Re: is avoiding compat ioctls possible?

On Wednesday 28 October 2009, Maciej W. Rozycki wrote:
> 
> 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).

Such conversion should *only* ever take place in compat_ptr().

	Arnd <><
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