linux-kernel - Re: [PATCH 1/3] perf events: fix WARN_ON

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Date:	Fri, 18 Feb 2011 10:15:14 -0700
From:	David Ahern <daahern@...co.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	mingo@...e.hu, paulus@...ba.org
Subject: Re: [PATCH 1/3] perf events: fix WARN_ON_ONCE for 64-bit raw data,
 SW events



On 02/18/11 10:13, Peter Zijlstra wrote:
> On Fri, 2011-02-18 at 15:04 -0200, Arnaldo Carvalho de Melo wrote:
>> Em Fri, Feb 18, 2011 at 04:01:31PM +0100, Peter Zijlstra escreveu:
>>> On Fri, 2011-02-18 at 12:53 -0200, Arnaldo Carvalho de Melo wrote:
>>>>> So size should be changed to u64 rather than modifying the
>>>> WARN_ON_ONCE?
>>>>
>>>> Yeah, I guess so, 32-bit has to die it seems, gets in the way of
>>>> testing
>>>> :-) 
>>>
>>> No!
>>>
>>> 1) don't use RAW unless you have to
>>> 2) you don't have to, goto 1
>>> 3) if you do anyway, ensure its properly padded
>>
>> Ok, but using that struct definition on 32-bit land, will lead to non 8 byte
>> alignment, right?
> 
> Nope, its just fine.. it defaults to an empty 4byte payload ;-)
> 
> Its just that any custom payload must be of size 4+8*n bytes.

4 + 8*n != 8-byte aligned for any whole number n.

David
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