Re: Re: [RFC PATCH 4/6] uprobes/x86: Emulate rip-relative call's

[Masami Hiramatsu]

(2014/04/10 23:28), Oleg Nesterov wrote:
> On 04/10, Masami Hiramatsu wrote:
>>
>> (2014/04/10 22:41), Denys Vlasenko wrote:
>>> On 04/09/2014 05:43 PM, Oleg Nesterov wrote:
>>>> On 04/08, Jim Keniston wrote:
>>>>>
>>>>> On Sun, 2014-04-06 at 22:16 +0200, Oleg Nesterov wrote:
>>>>>> 0xe8. Anything else?
>>>>>
>>>>> No, I think e8 is the only call instruction uprobes will see.
>>>>
>>>> Good.
>>>
>>> There is this monstrosity, "16-bit override for branches" in 64-mode:
>>>
>>> 66 e8 nn nn       callw   <offset16>
>>>
>>> Nobody sane uses it because it truncates instruction pointer.
>>
>> No problem, insn.c can handle that too. :)
> 
> Does it?
> 
> 	"callw 1f; 1:\n"
> 	"rep; nop\n"
> 
> objdump:
> 
> 	66 e8 00 00             callw  485 <_init-0x3ffed3>
> 	f3 90                   pause
> 
> 
> if we probe this "callw", we copy MAX_INSN_BYTES into auprobe->insn,
> and after insn_get_length() (insn_complete() == T)
> 
> 	// this is correct
> 	OPCODE1() == e8	
> 
> 	// this all looks wrong
> 	insn->length == 6
> 	insn->immediate.value == -1863122944
> 	insn->immediate.nbytes == 4



Oops, that should be a bug in insn.c!
I'll fix that asap!

Thank you,


> 
> so it seems that lib/insn.c treats the next "pause" insn as the high
> 16 bits of address.
> 
> Oleg.
> 
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-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@xxxxxxxxxxx


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