Messages in this thread | | | Date | Mon, 30 Mar 2015 16:48:49 -0300 | From | Arnaldo Carvalho de Melo <> | Subject | Re: [RFC] perf probe: -x option position issue |
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Em Mon, Mar 30, 2015 at 07:46:55PM +0200, Jiri Olsa escreveu: > hi, > Martin found out following issue.. having following ex binary: > > --- > int main(void) > { > return 0; > } > --- > > following will create uprobe on main: > > [root@dell-per510-01 perf]# gcc -g -o ex ex.c > [root@dell-per510-01 perf]# ./perf probe -x ./ex -a main > Added new event: > probe_ex:main (on main in /root/linux/tools/perf/ex) > > You can now use it in all perf tools, such as: > > perf record -e probe_ex:main -aR sleep 1 > > [root@dell-per510-01 perf]# cat /sys/kernel/debug/tracing/uprobe_events > p:probe_ex/main /root/linux/tools/perf/ex:0x00000000000004f6 > > > while following will create (?) kprobe with complain in dmesg:
Right, it looks like it will create the probe on the currently selected DSO, which, if you have none, will be the kernel, thus the kprobe (probe:main), while if you do a '-x ./ex -a main' you are selecting the 'ex' DSO and then asking for the probe to be added to a function named 'main', on that DSO, that 'perf probe' realizes is a userspace binary, thus creates a uprobe: probe_%DSONAME:%FUNCTIONAME.
I wonder if I can do:
[root@ssdandy acme]# perf probe -a icmp_rcv -x ./ex -a main Probe point 'icmp_rcv' not found. Error: Failed to add events.
No, I can't, I'd say we should support that, i.e. inserting multiple probes per command line, for different DSOs, etc. I.e. the above would be equivalent to these two calls:
[root@ssdandy acme]# perf probe -a icmp_rcv Added new event: probe:icmp_rcv (on icmp_rcv)
You can now use it in all perf tools, such as:
perf record -e probe:icmp_rcv -aR sleep 1
[root@ssdandy acme]# perf probe -x ./ex -a main Added new event: probe_ex:main (on main in /home/acme/ex)
You can now use it in all perf tools, such as:
perf record -e probe_ex:main -aR sleep 1
[root@ssdandy acme]#
But it isn't like that, so, yes, what you report is a bug, both for your expectation (that I think is that it should put a uprobes with both your examples) and for mine (that it would add the first to the kernel, and the second to the selected DSO via -x).
- Arnaldo
> [root@dell-per510-01 perf]# gcc -g -o ex ex.c > [root@dell-per510-01 perf]# ./perf probe -a main -x ./ex > Added new event: > probe:main (on main in ex) > > You can now use it in all perf tools, such as: > > perf record -e probe:main -aR sleep 1 > > [root@dell-per510-01 perf]# dmesg | tail -2 > [16986.182159] Could not insert probe at ex:main+0: -2 > [16986.187030] This probe might be able to register aftertarget module is loaded. Continue. > > > that does not seem as an expected behaviour, or am I missing something? > > thanks, > jirka
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