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

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Date:	Mon, 12 Jan 2015 10:34:58 +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



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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