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

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Message-ID: <20110818023247.GA3750@windriver.com>
Date:	Thu, 18 Aug 2011 10:32:47 +0800
From:	Yong Zhang <yong.zhang@...driver.com>
To:	David Daney <david.daney@...ium.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 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;
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).

Thanks,
Yong
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