LTTng » LTTng-UST

When enabling some perf counters context in UST in a virtual machine (where all the perf counters are not available), we can make the target application crash.
Example in a KVM with Ubuntu precise 12.04 :
$ lttng create
$ lttng enable-event -u -a
$ lttng add-context -u -t perf:thread:cache-misses
$ lttng start
$ ./tests/utils/testapp/gen-ust-events/gen-ust-events 1 1
Aborted (core dumped)

(gdb) bt full
#0 0x00007f2f357d7425 in raise () from /lib/x86_64-linux-gnu/libc.so.6
No symbol table info available.
#1 0x00007f2f357dab8b in abort () from /lib/x86_64-linux-gnu/libc.so.6
No symbol table info available.
#2 0x00007f2f35d9f54d in add_thread_field (perf_thread=<optimized out>,
perf_field=<optimized out>) at lttng-context-perf-counters.c:231
oldmask = {__val = {0, 18446744073709551615 <repeats 15 times>}}
ret = <optimized out>
thread_field = <optimized out>
newmask = {__val = {18446744067267100671, 18446744073709551615 <repeats 15 times>}}
#3 get_thread_field (field=0x7f2f2c008f50) at lttng-context-perf-counters.c:251
perf_thread = <optimized out>
thread_field = <optimized out>
#4 wrapper_perf_counter_read (field=<optimized out>) at lttng-context-perf-counters.c:261
perf_field = 0x7f2f2c008f50
perf_thread_field = 0x1f58640
#5 0x00007f2f35d9f620 in perf_counter_record (field=<optimized out>, ctx=0x7fff6eae1400,
chan=0x7f2f2c008d20) at lttng-context-perf-counters.c:272
value = <optimized out>
#6 0x00007f2f35d87eb0 in ctx_record (bufctx=0x7fff6eae1400, chan=0x7f2f2c008d20,
ctx=0x7f2f2c008fb0) at lttng-ring-buffer-client.h:94
No locals.
#7 0x00007f2f35da1d6e in ctx_record (ctx=<optimized out>, chan=0x7f2f2c008d20,
bufctx=0x7fff6eae1400) at lttng-ring-buffer-client.h:91
No locals.
#8 lttng_write_event_header_slow (event_id=1, ctx=0x7fff6eae1400, config=<optimized out>)
at lttng-ring-buffer-client.h:294
event = 0x1f584d0
config = 0x7f2f35fc6700
#9 lttng_write_event_header (event_id=<optimized out>, ctx=0x7fff6eae1400,
config=0x7f2f35fc6700) at lttng-ring-buffer-client.h:228
lttng_chan = 0x7f2f2c008d20
event = 0x1f584d0
#10 lttng_event_reserve (ctx=0x7fff6eae1400, event_id=<optimized out>)
at lttng-ring-buffer-client.h:583
ret = 738232832
func = "lttng_event_reserve"
#11 0x000000000040121b in event_probe__tptptest (tp_data=0x1f584d0, anint=0, netint=0,
values=0x7fff6eae14f0, text=0x7fff6eae1510 "test", textlen=<optimized out>, doublearg=2,
floatarg=2222) at ././tp.h:22
__event = 0x1f584d0
__chan = 0x7f2f2c008d20
__ctx = {chan = 0x7f2f2c008a00, priv = 0x1f584d0, handle = 0x7f2f2c008da0,
data_size = 99, largest_align = 1, cpu = 0, buf = 0x7f2f36342000, slot_size = 120,
buf_offset = 81, pre_offset = 68, tsc = 2062361541160, rflags = 1, padding1 = 0,
ip = 0x400e5c, padding2 = '\000' <repeats 11 times>}
---Type <return> to continue, or q <return> to quit---
__dynamic_len_idx = 0
__stackvar = {_dynamic_len = {4, 4, 5, 139840750280704, 139840750280720, 16,
72340172838076673, 139840730935097, 139840750280704, 139840730937568, 0, 0},
__filter_stack_data = "\004\000\000\000\000\000\000\000\004\000\000\000\000\000\000\000\005\000\000\000\000\000\000\000\000\340>6/\177\000\000\020\340>6/\177\000\000\020\000\000\000\000\000\000\000\001\001\001\001\001\001\001\001\071\257\027\065/\177\000\000\000\340>6/\177\000\000\340\270\027\065/\177", '\000' <repeats 113 times>}
__ret = <optimized out>
#12 0x0000000000400e5c in __tracepoint_cb_tp_tptest (floatarg=2222, doublearg=2, textlen=4,
text=0x7fff6eae1510 "test", values=0x7fff6eae14f0, netint=0, anint=0) at tp.h:22
__tp_cb = <optimized out>
__tp_data = <optimized out>
__tp_probe = 0x1f585f0
#13 main (argc=<optimized out>, argv=<optimized out>) at gen-ust-events.c:74
i = <optimized out>
netint = 0
values = {1, 2, 3}
text = "test\000\000\000\000\000"
nr_iter = <optimized out>
nr_usec = <optimized out>
tmp_file_path = <optimized out>