linux-kernel - Re: page->_count build failure [was: mmotm 2011-07-08-12-50 uploaded]

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Message-ID: <4E1B615B.3040509@gmail.com>
Date:	Mon, 11 Jul 2011 22:47:23 +0200
From:	Jiri Slaby <jirislaby@...il.com>
To:	Pekka Enberg <penberg@...nel.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, cl@...ux.com,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: page->_count build failure [was: mmotm 2011-07-08-12-50 uploaded]

On 07/11/2011 10:45 PM, Pekka Enberg wrote:
> On Mon, Jul 11, 2011 at 11:41 PM, Andrew Morton
> <akpm@...ux-foundation.org> wrote:
>> On Mon, 11 Jul 2011 22:27:22 +0200
>> Jiri Slaby <jirislaby@...il.com> wrote:
>>
>>> On 07/08/2011 09:50 PM, akpm@...ux-foundation.org wrote:
>>>> The mm-of-the-moment snapshot 2011-07-08-12-50 has been uploaded to
>>>
>>> Hi, am I the only one encountering a build failure due to double
>>> definition of _count in page struct introduced by:
>>> commit fc9bb8c768abe7ae10861c3510e01a95f98d5933
>>> Author: Christoph Lameter <cl@...ux.com>
>>> Date:   Wed Jun 1 12:25:48 2011 -0500
>>>
>>>     mm: Rearrange struct page
>>>
>>> in the -next tree?
>>>
>>> $ make
>>> ...
>>>   CC      arch/x86/kernel/asm-offsets.s
>>> In file included from include/linux/sched.h:64:0,
>>>                  from arch/x86/kernel/asm-offsets.c:9:
>>> include/linux/mm_types.h:74:15: error: duplicate member ____count___
>>> make[1]: *** [arch/x86/kernel/asm-offsets.s] Error 1
>>> make: *** [prepare0] Error 2
>>> $ gcc --version
>>> gcc (SUSE Linux) 4.6.0 20110607 [gcc-4_6-branch revision 174741]
>>>
>>
>> Oh dear.  Yes, I would call that an error.  Afacit the two `_count's
>> end up at the same offset in the page struct.  Perhaps that makes it
>> legal and your compiler got it wrong.  Or perhaps it is illegal and all
>> other compilers got it wrong.
>>
>> Still, we should fix it.  It's daft to have two distinct page->_count's.
>>
>> To fix it, we could rename one of them.  Which means that we're going
>> to need to work out which references to page->_count are referring to
>> which field.  Which demonstrates the problem!
>>
>>
>> hmm, let's jiggle the offset:
>>
>> --- a/include/linux/mm_types.h~a
>> +++ a/include/linux/mm_types.h
>> @@ -71,6 +71,7 @@ struct page {
>>                                         * Kernel may make use of this field even when slub
>>                                         * uses the rest of the double word!
>>                                         */
>> +                                       int foo;
>>                                        atomic_t _count;
>>                                };
>>                        };
>> _
>>
>> nope, it still compiles OK.  It has to be gcc bustification I think.
>> Fixed in gcc-4.6.0.
> 
> Didn't commit ea6bd8ee1a2ccdffc38b2b1fcfe941addfafaade fix the issue?

Which repo is that from? Git doesn't know it here.

thanks,
-- 
js
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