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Date: Mon, 17 Sep 2012 18:19:04 +0800
From: "tiejun.chen" <tiejun.chen@windriver.com>
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To: David Laight <David.Laight@ACULAB.COM>
Subject: Re: [v5][PATCH 2/3] powerpc/kprobe: complete kprobe and migrate
 exception frame
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On 09/17/2012 06:02 PM, David Laight wrote:
>>   /* N.B. the only way to get here is from the beq following ret_from_except. */
>>   resume_kernel:
>> -	/* check current_thread_info->preempt_count */
>> +	/* check current_thread_info, _TIF_EMULATE_STACK_STORE */
>>   	CURRENT_THREAD_INFO(r9, r1)
>> +	lwz	r8,TI_FLAGS(r9)
>> +	andis.	r8,r8,_TIF_EMULATE_STACK_STORE@h
>> +	beq+	1f
> ...
>> +1:
>
> Does this add a statically mispredicted branch to every
> return to userspace ?

Return usersapce? No, this is just follow 'resume_kernel'.

Note I add this 'unlikely' here since I assume often Kprobe is always disabled 
by default and especially its also rare to kprobe 'stwu' in many kprobe cases.

Tiejun