linux-kernel - Re: [PATCH v10 2/2] ARM: kprobes: enable OPTPROBES for ARM 32

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Date:	Mon, 1 Dec 2014 16:59:42 +0800
From:	Wang Nan <wangnan0@...wei.com>
To:	"Jon Medhurst (Tixy)" <tixy@...aro.org>
CC:	<masami.hiramatsu.pt@...achi.com>, <linux@....linux.org.uk>,
	<will.deacon@....com>, <taras.kondratiuk@...aro.org>,
	<ben.dooks@...ethink.co.uk>, <cl@...ux.com>, <rabin@....in>,
	<davem@...emloft.net>, <lizefan@...wei.com>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v10 2/2] ARM: kprobes: enable OPTPROBES for ARM 32


>>> +/*
>>> + * NOTE: the first sub and add instruction will be modified according
>>> + * to the stack cost of the instruction.
>>> + */
>>> +asm (
>>> +			".global optprobe_template_entry\n"
>>> +			"optprobe_template_entry:\n"
>>> +			"	sub	sp, sp, #0xff\n"
>>> +			"	stmia	sp, {r0 - r14} \n"
>>
>> AEABI requires that the stack be aligned to a multiple of 8 bytes at
>> function call boundaries, however kprobes can be inserted in the middle
>> of functions where such alignment isn't guaranteed to be maintained.
>> Therefore, this trampoline code needs to make adjust SP if necessary to
>> ensure that alignment. See svc_entry in arch/arm/kernel/entry-armv.S for
>> an example of how this is done; though note, we can't use that exact
>> method because we can't change the flags value without saving them
>> first. (Exception handlers don't have to worry about that because the
>> flags are saved in spsr).
>>
> 
> So I think we have to push a flag into stack for it.
> 

By more thinking I found another method on it. Please see my version 11 patch:

http://lists.infradead.org/pipermail/linux-arm-kernel/2014-December/307562.html


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