linux-kernel - kprobe pre_handler change return IP

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Message-ID: <E4ABEE53CC34664FA3F0BD8AEAF50A1941474DB1@szxeml511-mbs.china.huawei.com>
Date:	Thu, 17 Oct 2013 12:57:40 +0000
From:	Liuyongan <liuyongan@...wei.com>
To:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:	Qianhuibin <qianhuibin@...wei.com>
Subject: kprobe pre_handler change return IP

I use kprobe to probe a function suppose: 
          int is_winter(int num) { ... }
          int replace_is_winter(int num) { ...} 
I want to replace is_winter() with replace_is_winter(), so when we call is_winter, replace_is_winter will be called.
                                                                                                                  
so:  
   int my_pre_handler(struct kprobe *p, struct pt_regs *regs)
   { 
        regs->ip = (unsigned long)&replace_is_winter;
        return 1;
   } 

and echo 0 > /proc/sys/debug/kprobes-optimization so that jump instruction will not be used.

I got a exception in fault_handler, and trap number is 14.

   fault_handler: p->addr = 0xffffffffa08e201a, ip = ffffffff8021c59d, trap #14n

Anyone here can help me ?