linux-kernel - Re: [RFC 8/8] ARM64: Add uprobe support

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Date:	Mon, 12 Jan 2015 12:15:34 +0530
From:	Pratyush Anand <panand@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	tixy@...aro.org, linux@....linux.org.uk, ananth@...ibm.com,
	sandeepa.prabhu@...aro.org, catalin.marinas@....com,
	will.deacon@....com, linux-kernel@...r.kernel.org,
	anil.s.keshavamurthy@...el.com, masami.hiramatsu.pt@...achi.com,
	wcohen@...hat.com, linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC 8/8] ARM64: Add uprobe support

Hi Oleg,

How can I generate a scenario to test:

a) arch_uprobe_xol_was_trapped
b) arch_uprobe_abort_xol

~Pratyush

On Monday 12 January 2015 10:34 AM, Pratyush Anand wrote:
>
>
> On Friday 09 January 2015 11:29 PM, Oleg Nesterov wrote:
>> On 12/31, Pratyush Anand wrote:
>>>
>>> +int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct
>>> mm_struct *mm,
>>> +        unsigned long addr)
>>> +{
>>> +    probe_opcode_t insn;
>>> +
>>> +    insn = *(probe_opcode_t *)(&auprobe->insn[0]);
>>> +
>>> +    switch (arm_probe_decode_insn(insn, &auprobe->ainsn)) {
>>> +    case INSN_REJECTED:
>>> +        return -EINVAL;
>>> +
>>> +    case INSN_GOOD_NO_SLOT:
>>> +        auprobe->simulate = true;
>>> +        if (auprobe->ainsn.prepare)
>>> +            auprobe->ainsn.prepare(insn, &auprobe->ainsn);
>>> +        break;
>>> +
>>> +    case INSN_GOOD:
>>> +    default:
>>> +        break;
>>> +    }
>>> +
>>> +    return 0;
>>> +}
>>
>> forgot to mention... shouldn't it also check IS_ALIGNED(addr,
>> AARCH64_INSN_SIZE) ?
>>
>> I do not know if unaligned insn address is valid on arm64 or not, but
>> please
>
> AARCH64 instructions are always of fixed lenght ie 4 bytes. I do not see
> possibility of addr being unaligned. Please let me know, if I am missing
> something.
>
>> note that at least it should not cross the page boundary, set_swbp()
>> needs to
>> write AARCH64_INSN_SIZE == UPROBE_SWBP_INSN bytes and it assumes that
>> this
>> should fit the single page.
>
> So, again I do not see the possibility of crossing of page boundary for
> any instruction address.
>
> ~Pratyush
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