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Re: [PATCH] MIPS: use 32-bit wrapper for compat_sys_futex

To: Yong Zhang <yong.zhang@windriver.com>
Subject: Re: [PATCH] MIPS: use 32-bit wrapper for compat_sys_futex
From: David Daney <david.daney@cavium.com>
Date: Thu, 18 Aug 2011 09:23:41 -0700
Cc: linux-mips@linux-mips.org, linux-kernel@vger.kernel.org, Ralf Baechle <ralf@linux-mips.org>
In-reply-to: <20110818023247.GA3750@windriver.com>
References: <1313546094-11882-1-git-send-email-yong.zhang@windriver.com> <4E4BF7C0.80703@cavium.com> <20110818023247.GA3750@windriver.com>
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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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