Re: [PATCH -tip ] [BUGFIX/URGENT] perf-probe: Do not add offset touprobe address

[Masami Hiramatsu]

(2014/02/06 16:48), Namhyung Kim wrote:
> Hi Masami,
> 
> On Wed, 05 Feb 2014 05:18:58 +0000, Masami Hiramatsu wrote:
>> Fix perf-probe not to add offset value to uprobe probe
>> address when post processing.
>> tevs[i].point.address is the address of symbol+offset,
>> but current perf-probe adjusts the point.address by
>> adding the offset. As a result, the probe address becomes
>> symbol+offset+offset. This may cause unexpected
>> code corruption. Urgent fix is needed.
>>
>> Without this fix
>>   ---
>>   # ./perf probe -x ./perf dso__load_vmlinux+4
>>   # ./perf probe -l
>>     probe_perf:dso__load_vmlinux (on 0x000000000006d2b8)
>>   # nm ./perf.orig | grep dso__load_vmlinux\$
>>   000000000046d0a0 T dso__load_vmlinux
> 
> Shouldn't the original symbol address be
> 
>     000000000046d2b0

Oops, Yes, I missed my ./perf and ./perf.orig...
Since the uprobe doesn't track binary change, I usually use a
copy of original binary. Here is the correct test results;


Without this fix
  ---
  # ./perf probe -x ./perf.orig dso__load_vmlinux+4
  # ./perf probe -l
    probe_perf:dso__load_vmlinux (on 0x000000000006d2b8)
  # nm ./perf.orig | grep dso__load_vmlinux\$
  000000000046d2b0 T dso__load_vmlinux
  ---
You can see the given offset is 4 but the actual probed
address is dso__load_vmlinux+8.

With this fix
  ---
  # ./perf probe -x ./perf.orig dso__load_vmlinux+4
  # ./perf probe -l
    probe_perf:dso__load_vmlinux (on 0x000000000006d2b4)
  ---
Now the problem is fixed.


> 
>>   ---
>> You can see the given offset is 3 but the actual probed
> 
> s/3/4/ ?

Yes, it's a typo. :(

Thank you!!



-- 
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@xxxxxxxxxxx


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