From: Arnaldo Carvalho de Melo [mailto:a...@kernel.org]
>Em Tue, Nov 03, 2015 at 12:50:46AM +0000, Alex Bagehot escreveu:
>> Hello,
>>
>> I get this error with perf probe, :
>>
>> perf probe -vvv -x /opt/jdk1.8.0_60/jre/lib/amd64/server/libjvm.so
>> '_ZN13CollectedHeap24common_mem_allocate_initE11KlassHandlemP6Thread'
Ah, I've never thought that the symbol name gets so long :(
BTW, is that oracle's jdk package? I'd like to reproduce the bug.
>>
>> probe-definition(0):
>> _ZN13CollectedHeap24common_mem_allocate_initE11KlassHandlemP6Thread
>> symbol:_ZN13CollectedHeap24common_mem_allocate_initE11KlassHandlemP6Thread
>> file:(null) line:0 offset:0 return:0 lazy:(null)
>> 0 arguments
>> Opening /sys/kernel/debug/tracing/uprobe_events write=1
>> Added new event:
>> snprintf() failed: -7
>> Error: Failed to add events. Reason: Argument list too long (Code: -7)
>>
>>
>> it looks like it's failing here: ./util/probe-event.c
>> probe_trace_event__set_name
>>
>> /* Get an unused new event name */
>> ret = get_new_event_name(buf, 64, event,
>> namelist, allow_suffix);
>
>Masami, do we really need to cap it at 64 bytes? And would it be
>possible to improve that error reporting? I.e. this isn't an "argument
>list", right?
No, but it is used for event name whose maximum length is 63+\0.
There is actually no reason for 64, but we need a limitation for event name.
And, yeah, the error message comes from E2BIG.
#define E2BIG 7 /* Argument list too long */
So, the "argument" means argument of snprintf.
>> It works with a function 63 chars long not 64.
>> Knowing it is the event name erroring, It also works if I give the
>> event a short name eg. 'a'. I don't understand why it creates 3 probes
>> though?
>
>Masami? You gave this explanation at some point, but I forgot, aliases?
>Inlining?
Yes, I guess it is because of inlined function. If there are several different
instances at different addresses, perf probe tries to define probes for each
address.
>
>Would be interesting to warn the user why multiple probes are being
>created, no?
Hmm, ok. it is usually done by probing inlined function, or the target line
has multiple instructions. It may be better to show the reason why.
>Alex, you can try using wildcards in this case, i.e.:
>
> perf record -e probe_libjvm:a* your-workload
>
>That if you don't have other probes in place starting with the same
>prefix :-\
>
>- Arnaldo
>
>
>> objdump -t /opt/jdk1.8.0_60/jre/lib/amd64/server/libjvm.so|grep
>> \.text|awk 'length($NF) == 63 {print length($NF)" "$NF}'|head -1
>>
>> 63 _ZL34bulk_revoke_or_rebias_at_safepointP7oopDescbbP10JavaThread
>>
>>
>>
>> perf probe -vvv -x /opt/jdk1.8.0_60/jre/lib/amd64/server/libjvm.so
>> '_ZL34bulk_revoke_or_rebias_at_safepointP7oopDescbbP10JavaThread'
>>
>> probe-definition(0):
>> _ZL34bulk_revoke_or_rebias_at_safepointP7oopDescbbP10JavaThread
>> symbol:_ZL34bulk_revoke_or_rebias_at_safepointP7oopDescbbP10JavaThread
>> file:(null) line:0 offset:0 return:0 lazy:(null)
>> 0 arguments
>> Opening /sys/kernel/debug/tracing/uprobe_events write=1
>> Added new event:
>> Writing event:
>> p:probe_libjvm/_ZL34bulk_revoke_or_rebias_at_safepointP7oopDescbbP10JavaThread
>> /opt/jdk1.8.0_60/jre/lib/amd64/server/libjvm.so:0x325a20
>>
>> probe_libjvm:_ZL34bulk_revoke_or_rebias_at_safepointP7oopDescbbP10JavaThread
>> (on _ZL34bulk_revoke_or_rebias_at_safepointP7oopDescbbP10JavaThread in
>> /opt/jdk1.8.0_60/jre/lib/amd64/server/libjvm.so)
>>
>> You can now use it in all perf tools, such as:
>>
>> perf record -e
>> probe_libjvm:_ZL34bulk_revoke_or_rebias_at_safepointP7oopDescbbP10JavaThread
>> -aR sleep 1
>>
>>
>>
>> perf probe -vvv -x /opt/jdk1.8.0_60/jre/lib/amd64/server/libjvm.so
>> 'a=_Z17do_write_prologueIP17GlobalTraceBufferEvR15JfrBufferWriterT_'
>>
>> probe-definition(0):
>> a=_Z17do_write_prologueIP17GlobalTraceBufferEvR15JfrBufferWriterT_
>> symbol:_Z17do_write_prologueIP17GlobalTraceBufferEvR15JfrBufferWriterT_
>> file:(null) line:0 offset:0 return:0 lazy:(null)
>> 0 arguments
>> Opening /sys/kernel/debug/tracing/uprobe_events write=1
>> Added new events:
>> Writing event: p:probe_libjvm/a
>> /opt/jdk1.8.0_60/jre/lib/amd64/server/libjvm.so:0x8ca940
>> probe_libjvm:a (on
>> _Z17do_write_prologueIP17GlobalTraceBufferEvR15JfrBufferWriterT_ in
>> /opt/jdk1.8.0_60/jre/lib/amd64/server/libjvm.so)
>> Writing event: p:probe_libjvm/a_1
>> /opt/jdk1.8.0_60/jre/lib/amd64/server/libjvm.so:0x9c07fe
>> probe_libjvm:a_1 (on
>> _Z17do_write_prologueIP17GlobalTraceBufferEvR15JfrBufferWriterT_ in
>> /opt/jdk1.8.0_60/jre/lib/amd64/server/libjvm.so)
>> Writing event: p:probe_libjvm/a_2
>> /opt/jdk1.8.0_60/jre/lib/amd64/server/libjvm.so:0x9c25c1
>> probe_libjvm:a_2 (on
>> _Z17do_write_prologueIP17GlobalTraceBufferEvR15JfrBufferWriterT_ in
>> /opt/jdk1.8.0_60/jre/lib/amd64/server/libjvm.so)
>>
>> You can now use it in all perf tools, such as:
>>
>> perf record -e probe_libjvm:a_2 -aR sleep 1
>>
>>
>> perf probe -l
>>
>> probe_libjvm:a (on
>> _Z17do_write_prologueIP17GlobalTraceBufferEvR15JfrBufferWriterT_ in
>> /opt/jdk1.8.0_60/jre/lib/amd64/server/libjvm.so)
>> probe_libjvm:a_1 (on
>> _Z17do_write_prologueIP17GlobalTraceBufferEvR15JfrBufferWriterT_ in
>> /opt/jdk1.8.0_60/jre/lib/amd64/server/libjvm.so)
>> probe_libjvm:a_2 (on
>> _Z17do_write_prologueIP17GlobalTraceBufferEvR15JfrBufferWriterT_ in
>> /opt/jdk1.8.0_60/jre/lib/amd64/server/libjvm.so)
>>
>>
>>
>> uname -a
>>
>> Linux vagrant-ubuntu-trusty-64 4.3.0-999-generic #201510112200 SMP Mon
>> Oct 12 02:01:41 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
>>
>>
>> Thanks,
>>
>> Alex
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