linux-kernel - Re: [PATCH] x86_32: add support for 64 bit __get

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Date:	Wed, 9 Mar 2016 12:50:16 -0500
From:	Benjamin LaHaise <bcrl@...ck.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Russell King <rmk@....linux.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86_32: add support for 64 bit __get_user()

On Wed, Mar 09, 2016 at 09:36:30AM -0800, H. Peter Anvin wrote:
> On March 9, 2016 9:22:25 AM PST, Benjamin LaHaise <bcrl@...ck.org> wrote:
> >The existing __get_user() implementation does not support fetching
> >64 bit values on 32 bit x86.  Implement this in a way that does not 
> >generate any incorrect warnings as cautioned by Russell King.  Test 
> >code available at http://www.kvack.org/~bcrl/x86_32-get_user.tar .  
...
> Weird.  I could swear we had already fixed this a few years ago.

That surprised me as well, but Russell raised the fact that the approaches 
previously tried on 32 bit architectures had caused various incorrect 
compiler warnings for certain obscure cases -- see the code in test_module.c 
in that URL that Russell provided to demonstrate the problem across all the 
corner cases.

		-ben
-- 
"Thought is the essence of where you are now."