linux-kernel - Re: [PATCH V2]sh: cmpxchg: fix a bit shift bug in big

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Date:	Tue, 26 Apr 2016 18:07:37 +0800
From:	Pan Xinhui <xinhui@...ux.vnet.ibm.com>
To:	Rich Felker <dalias@...c.org>
CC:	linux-kernel@...r.kernel.org, ysato@...rs.sourceforge.jp,
	mst@...hat.com, peterz@...radead.org, linux-sh@...r.kernel.org
Subject: Re: [PATCH V2]sh: cmpxchg: fix a  bit shift bug in big_endian os


On 2016年04月26日 09:39, Rich Felker wrote:
> On Wed, Apr 20, 2016 at 02:41:00PM +0800, Pan Xinhui wrote:
>> From: Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
>>
>> Correct bitoff in big endian OS.
>> Current code works correctly for 1 byte but not for 2 bytes.
>>
>> Fixes: 3226aad81aa6 ("sh: support 1 and 2 byte xchg")
>> Signed-off-by: Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
>> Acked-by: Michael S. Tsirkin <mst@...hat.com>
>> ---
>> changes from V1:
>> 	just add some patch comments. no code changes.
> 
> Looks good. Are you aware of any code affected by this bug that would
> make it a regression in 4.6? If so I'll try to get this in now as a
> bugfix; otherwise I'll include it in stuff for 4.7.
> 
no idea about what code is affected.
4.7 is okay I think. :)

xinhui
> Rich
> 
> 
>> ---
>>  arch/sh/include/asm/cmpxchg-xchg.h | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/sh/include/asm/cmpxchg-xchg.h b/arch/sh/include/asm/cmpxchg-xchg.h
>> index 7219719..1e881f5 100644
>> --- a/arch/sh/include/asm/cmpxchg-xchg.h
>> +++ b/arch/sh/include/asm/cmpxchg-xchg.h
>> @@ -21,7 +21,7 @@ static inline u32 __xchg_cmpxchg(volatile void *ptr, u32 x, int size)
>>  	int off = (unsigned long)ptr % sizeof(u32);
>>  	volatile u32 *p = ptr - off;
>>  #ifdef __BIG_ENDIAN
>> -	int bitoff = (sizeof(u32) - 1 - off) * BITS_PER_BYTE;
>> +	int bitoff = (sizeof(u32) - size - off) * BITS_PER_BYTE;
>>  #else
>>  	int bitoff = off * BITS_PER_BYTE;
>>  #endif
>> -- 
>> 1.9.1 
>