linux-kernel - Re: [BUG] percpu misaligned allocation

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Message-ID: <4BA39CD1.8060900@rsk.demon.co.uk>
Date:	Fri, 19 Mar 2010 15:48:33 +0000
From:	Richard Kennedy <richard@....demon.co.uk>
To:	David Miller <davem@...emloft.net>
CC:	tj@...nel.org, fweisbec@...il.com, sparclinux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [BUG] percpu misaligned allocation

On 19/03/10 03:02, David Miller wrote:
> From: Tejun Heo <tj@...nel.org>
> Date: Fri, 19 Mar 2010 11:18:51 +0900
> 
>> On 03/19/2010 10:57 AM, David Miller wrote:
>>> I would use u64 so something like:
>>>
>>> 	u64 [FTRACE_MAX_PROFILE_SIZE / sizeof(u64)]
>>
>> <paranoid>DIV_ROUND_UP() would be safer than division</paranoid>
> 
> There's potential real trouble if it isn't a multiple of sizeof(u64)
> so better:
> 
> 	BUILD_BUG_ON(FTRACE_MAX_PROFILE_SIZE % sizeof(u64));
> 
> :-)
> 
> What a mess, just because this thing can't be typed properly :-/
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> 

Couldn't you use a union?

For example if you have
union test {
	long t;
	char buffer[50];
};
gcc will then do the right thing.

on x86_64 sizeof(union test) = 56
but on x86_32 it's only 52.

regards
Richard

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