Re: [RFC] perf probe: -x option position issue

[Arnaldo Carvalho de Melo <acme@infradead.org>]

Em Tue, Mar 31, 2015 at 05:04:18PM +0900, Masami Hiramatsu escreveu:
> (2015/03/31 4:48), Arnaldo Carvalho de Melo wrote:
> > 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]#

> OK, finally we should support that.

> > 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).

> Yes, both are bugs. I'll fix that.

> BTW, let me check that the below behaviors are OK for you.

> perf probe -x BIN -a XXX
> 	 -> setup XXX on BIN

Ok

> perf probe -a XXX -x BIN
> 	 -> setup XXX on BIN
> perf probe -a XXX -x BIN -a YYY
> 	 -> setup XXX on kernel and YYY on BIN

The two above are inconsistent, I think, first one, for me, doesn't make
sense, i.e. it says: Add XXX to the selected DSO, which, as none was
specified at that point, should be the kernel, right?

I.e. if we do:

> perf probe -a XXX

Without that extra -x that is coming _after_ the command to add a probe
to XXX (-a XXX), what is that the tool should do (does from day 1, when
'probe' was first introduced in tools/perf/):

Add a probe to XXX _in the kernel_, i.e. not specifying a DSO means: its
for the kernel.

So, for me:

> perf probe -a XXX -x BIN
> 	 -> setup XXX on BIN

Is invalid (or inocuous if what one wants is to add a probe for XXX on
the BIN dso), because it doesn't make sense _if you want to support
adding multiple probes for different DSOs on the same command line_,
because it would mean:

  Add a probe to XXX _in the kernel_, then select BIN as the DSO for
which probes will be then specified, but in this example, none are
specified after that "-x BIN", so, I think that:

 perf probe -a XXX -x BIN

and:

 perf probe -a XXX

Mean the same thing, i.e. add a probe for XXX in the kernel.

> perf probe -x BIN -a XXX -x BIN2 -a YYY
> 	 -> setup XXX on BIN and YYY on BIN2
 
Ok.

Also, more generically, I think that:

perf probe -a AAA -a BBB -a CCC -a DDD -x /lib64/libc-2.17.so -a malloc -a free \
           -x /usr/lib64/libthread_db-1.0.so -a td_lookup -a td_thr_event_enable

Should add kprobes for AAA, BBB, CCC and DDD in the kernel, uprobes for
malloc and free on libc and uprobes for td_lookup and
td_thr_event_enable on libthread_db.

Making it even more compact would be a bonus:

perf probe -a AAA,BBB,CCC,DDD -x /lib64/libc-2.17.so -a malloc,free \
           -x /usr/lib64/libthread_db-1.0.so -a td_lookup,td_thr_event_enable

:-)

- Arnaldo