[lttng-dev] traces omissions

[Sébastien Barthélémy]

Hello all,

I have yet another difficulty using LTTng.

I run a program which dlopens a module (called DCM) which is
instrumented with ust (provider == qi_dcm), and which calls functions
from a processsyncclient library (PSC for short), also instrumented
with ust (provider == qi_bn_ipc_psc).

When I run the program, I ld_preload the two probes provider as in

LD_PRELOAD="$PREFIX/lib/libtp_processsyncclient_pipe.so
$PREFIX/lib/libtp_dcm.so" LD_LIBRARY_PATH=$PREFIX/lib
$PREFIX/bin/naoqi-bin &

This used to work, but when I run it now, I only get traces from the
processsyncclient probes, not from the DCM ones. However, they are
triggered by the same code paths, so I expect to get events from both
of them.

I checked that the probes are correctly registered:

libust[3739/3739]: just registered probe qi_dcm containing 2 events
(in ltt_probe_register() at ltt-probes.c:109)
libust[3739/3739]: just registered probe qi_bn_ipc_psc containing 3
events (in ltt_probe_register() at ltt-probes.c:109)

and that I have symbols from both of them in the DCM module (so it not
a simple #define error):

$ nm libdcm_hal.so |grep _qi_
0005cab4 r _ZL26__tp_strtab_qi_dcm___state
0006c22c d _ZL31__tracepoint_ptr_qi_dcm___state
0005cad8 r _ZL35__tp_strtab_qi_bn_ipc_psc___waiting
0005cac1 r _ZL35__tp_strtab_qi_dcm___clock_realtime
0005cb0f r _ZL38__tp_strtab_qi_bn_ipc_psc___notify_end
0006c234 d _ZL40__tracepoint_ptr_qi_bn_ipc_psc___waiting
0006c230 d _ZL40__tracepoint_ptr_qi_dcm___clock_realtime
0006c23c d _ZL43__tracepoint_ptr_qi_bn_ipc_psc___notify_end
0005caf0 r _ZL44__tp_strtab_qi_bn_ipc_psc___finished_waiting
0006c238 d _ZL49__tracepoint_ptr_qi_bn_ipc_psc___finished_waiting
00040566 t __tracepoint_cb_qi_dcm___clock_realtime
000404c7 t __tracepoint_cb_qi_dcm___state
0006c214 D __tracepoint_qi_bn_ipc_psc___finished_waiting
0006c220 D __tracepoint_qi_bn_ipc_psc___notify_end
0006c208 D __tracepoint_qi_bn_ipc_psc___waiting
0006c1fc D __tracepoint_qi_dcm___clock_realtime
0006c1f0 D __tracepoint_qi_dcm___state


I also get these messages (not sure what they mean):

liblttng_ust_tracepoint[3739/3739]: just registered a tracepoints
section from 0xb1fa1860 and having 1 tracepoints (in
tracepoint_register_lib() at tracepoint.c:610)
liblttng_ust_tracepoint[3739/3739]: just registered a tracepoints
section from 0xb203822c and having 5 tracepoints (in
tracepoint_register_lib() at tracepoint.c:610)
liblttng_ust_tracepoint[3739/3739]: just registered a tracepoints
section from 0xb04b06f4 and having 2 tracepoints (in
tracepoint_register_lib() at tracepoint.c:610)

Is this use case expected?

I fear I'm running out of ideas, how could investigate the matter further?