linux-kernel - Re: [PATCH] MIPS: use 32-bit wrapper for compat_sys

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Message-ID: <4E4D3C8D.1040707@cavium.com>
Date:	Thu, 18 Aug 2011 09:23:41 -0700
From:	David Daney <david.daney@...ium.com>
To:	Yong Zhang <yong.zhang@...driver.com>
CC:	linux-mips@...ux-mips.org, linux-kernel@...r.kernel.org,
	Ralf Baechle <ralf@...ux-mips.org>
Subject: Re: [PATCH] MIPS: use 32-bit wrapper for compat_sys_futex

On 08/17/2011 07:32 PM, Yong Zhang wrote:
> On Wed, Aug 17, 2011 at 10:17:52AM -0700, David Daney wrote:
>>> diff --git a/arch/mips/kernel/scall64-o32.S b/arch/mips/kernel/scall64-o32.S
>>> index 46c4763..f48b18e 100644
>>> --- a/arch/mips/kernel/scall64-o32.S
>>> +++ b/arch/mips/kernel/scall64-o32.S
>>> @@ -441,7 +441,7 @@ sys_call_table:
>>>   	PTR	sys_fremovexattr		/* 4235 */
>>>   	PTR	sys_tkill
>>>   	PTR	sys_sendfile64
>>> -	PTR	compat_sys_futex
>>> +	PTR	sys_32_futex
>>
>> This change is redundant, scall64-o32.S already does the right thing
>
> My first virsion(not sent out) doesn't include scall64-o32.S either.
>
>> so additional zero extending is not needed and is just extra
>> instructions to execute for no reason.
>
> Why I'm adding it here is for:
> 1)code consistent, otherwise we must move SYSCALL_DEFINE6(32_futex,...)
>    under CONFIG_MIPS32_N32;

No, you don't have to move it.  Just don't call it.


> 2)I'm afraid there may be some other way to touch the high 32-bit of a
>    register, so touching scall64-o32.S is also for safety(due to unknown
>    reason, fix me if I'm wrong).

OK: You are mistaken.  You claim you don't understand what the code 
does.  That is really a poor justification for modifying it.

David Daney
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