From: Michael Petlan [mailto:mpet...@redhat.com]
>
>On Tue, 2015-11-24 at 12:08 -0300, Arnaldo Carvalho de Melo wrote:
>> Em Tue, Nov 24, 2015 at 12:18:22PM +0100, Michael Petlan escreveu:
>> > I have been playing with perf-probe tool and I found out that some bogus
>> > values of a function argument are obtained by perf-record.
>> >
>> > How to reproduce:
>> >
>> > gcc -O0 -g -o dummy dummy.c
>> > perf probe -x ./dummy --add 'isprime a'
>> > perf record -e probe_dummy:isprime ./dummy
>> > perf script
>> >
>> > The actual output looks like the following:
>> >
>> > dummy 32476 [000] 3534401.838454: probe_dummy:isprime: (400530) a=32767
>> > dummy 32476 [000] 3534401.838504: probe_dummy:isprime: (400530) a=32714
>> > dummy 32476 [000] 3534401.838513: probe_dummy:isprime: (400530) a=3
>> > dummy 32476 [000] 3534401.838519: probe_dummy:isprime: (400530) a=4
>> > dummy 32476 [000] 3534401.838525: probe_dummy:isprime: (400530) a=5
>> > dummy 32476 [000] 3534401.838531: probe_dummy:isprime: (400530) a=6
>> > dummy 32476 [000] 3534401.838537: probe_dummy:isprime: (400530) a=7
>> > dummy 32476 [000] 3534401.838543: probe_dummy:isprime: (400530) a=13
>> > dummy 32476 [000] 3534401.838561: probe_dummy:isprime: (400530) a=17
Hmm, very odd.
Could you try to use ftrace with user stacktrace on that event?
# echo 1 > (debugfs)/tracing/options/stacktrace
# echo 1 > (debugfs)/tracing/options/userstacktrace
# echo 1 > events/probe_dummy/isprime/enable
# ./dummy
# cat trace
And decode the stack address by using (eu-)addr2line ?
Thank you,
>> >
>> > But if you look into the source, you can see that the function isprime()
>> > is called with the following arguments:
>> >
>> > int numbers[] = { 2, 3, 4, 5, 6, 7, 13, 17, 19 };
>> >
>> > So the first and last ones are omitted, there are some bogus numbers
>> > instead
>> > of them and all that is shifted somehow.
>> >
>> > Note that when I probe for %ax register it looks correct.
>> >
>> > The version of kernel/perf is 4.3.0. The architecture is x86_64.
>> > Am I missing something or is it a bug?
>>
>> I'm now trying to bisect that register error I found while trying to
>> reproduce the problem reported above, but please consider writing a
>> 'perf test' entry that does exactly what you did, i.e. have a simple
>> program that you build with a known set of compile flags, then run it
>> using perf probe to catch a specific function, its argument, and then
>> check that the values it produces are the ones expected.
>>
>> We would catch bugs in 'perf probe', the DWARF code, etc, much more
>> quickly with something like that in place. :-)
>
>Hi Arnaldo,
>
>thanks for investigating the issue. I do not use fedora kernel, I use
>what I build from git, but of course I am some versions back. So I use
>4.3.0 and 4.3.0-rc5 and both do the same thing.
>
>I have met this when writing new tests for perf-probe into the testsuite
>I had been speaking about some time ago [1]. But if needed, I may add it
>as a perf-test entry as you wish.
>
>Michael
>
>>
>> - Arnaldo
>
