Subject: Re: [v5][PATCH 2/3] powerpc/kprobe: complete kprobe and migrate exception frame

From: "tiejun.chen" <[email-masked]>
Date: Tue, 18 Sep 2012 14:13:00 +0800

On 09/18/2012 01:09 PM, Benjamin Herrenschmidt wrote:
> On Tue, 2012-09-18 at 15:05 +1000, Benjamin Herrenschmidt wrote:
>> On Mon, 2012-09-17 at 17:54 +0800, Tiejun Chen wrote:
>>> -#ifdef CONFIG_PREEMPT
>>>   	b	restore
>>>
>>>   /* 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
>>> +
>>> +	addi	r8,r1,INT_FRAME_SIZE	/* Get the kprobed function entry */
>>> +
>>> +	lwz	r3,GPR1(r1)
>>> +	subi	r3,r3,INT_FRAME_SIZE	/* dst: Allocate a trampoline exception frame */
>>> +	mr	r4,r1			/* src:  current exception frame */
>>> +	li	r5,INT_FRAME_SIZE	/* size: INT_FRAME_SIZE */
>>> +	li	r6,0			/* start offset: 0 */
>>> +	mr	r1,r3			/* Reroute the trampoline frame to r1 */
>>> +
>>> +	/* Copy from the original to the trampoline. */
>>> +	li	r6,0
>>
>> You just did that li r6,0 2 lines above :-) I'll fix it up manually
>> while applying.
>
> In fact the srwi can be dropped completely, we can just load r5 with the
> divided value. Committed, will push later today, please test.

I retest to kprobe do_fork() and show_interrupts() with/without enabling 
CONFIG_PREEMPT, separately, looks still work.

For 32-bit:
------------
+       /* Copy from the original to the trampoline. */
+       lwz     r3,GPR1(r1)
+       subi    r3,r3,INT_FRAME_SIZE    /* dst: Allocate a trampoline exception 
frame */
+       mr      r4,r1                   /* src:  current exception frame */
+       li      r5,INT_FRAME_SIZE/4     /* size: INT_FRAME_SIZE */
+       li      r6,0                    /* start offset: 0 */
+       mr      r1,r3                   /* Reroute the trampoline frame to r1 */
+       mtctr   r5
+2:     lwzx    r0,r6,r4
+       stwx    r0,r6,r3
+       addi    r6,r6,4
+       bdnz    2b

And for 64-bit:
---------------
+       /* Copy from the original to the trampoline. */
+       lwz     r3,GPR1(r1)
+       subi    r3,r3,INT_FRAME_SIZE    /* dst: Allocate a trampoline exception 
frame */
+       mr      r4,r1                   /* src:  current exception frame */
+       li      r5,INT_FRAME_SIZE/8     /* size: INT_FRAME_SIZE */
+       li      r6,0                    /* start offset: 0 */
+       mr      r1,r3                   /* Reroute the trampoline frame to r1 */
+       mtctr   r5
+2:     ldx     r0,r6,r4
+       stdx    r0,r6,r3
+       addi    r6,r6,8
+       bdnz    2b

Thanks
Tiejun