[lttng-dev] 32-bit application crash

[jamie explorer]

Hi All,
i looked into this further, generated .c file with expanded macros for
debugging
Some of the function pointer are not populated correctly.
as i mentioned this issue is only seen using g++ compiler and not seen with
gcc

please see the following GDB analysis:


(gdb) bt

#0  0x00000000 in ?? ()
#1  0x080490a0 in __event_probe__sample_tracepoint___message
(__tp_data=0x80512d0,
    text=0x804ca64 "Hello World\n") at sample_tracepoint.c:8567

#2  0x0804ba23 in __tracepoint_cb_sample_tracepoint___message (
    text=0x804ca64 "Hello World\n")
    at /build/home/jam/gentp/src/sample.c:4026
#3  main (argc=1, argv=0xffffdd74)
    at /build/home/jam/gentp/src/sample.c:4731

****bc_runtime->filter* --- is not populated correctly, because of which it
crashes
*(gdb) frame 1*
#1  0x080490a0 in __event_probe__sample_tracepoint___message
(__tp_data=0x80512d0,
    text=0x804ca64 "Hello World\n") at sample_tracepoint.c:8567
8567     if (__builtin_expect(!!(*bc_runtime->filter*(bc_runtime,
__stackvar.__filter_stack_data) & LTTNG_FILTER_RECORD_FLAG), 0))


*(gdb) list*
8562     (__stackvar.__filter_stack_data, __tp_data,text);
8563     for (bc_runtime = ((__typeof__(*bc_runtime) *) ((char *)
((reinterpret_cast<__typeof__((&__event->bytecode_runtime_head)->next)>(tracepoint_dlopen.rcu_dereference_sym_bp((reinterpret_cast<void
*>((&__event->bytecode_runtime_head)->next)))))) - (unsigned long)
(&((__typeof__(*bc_runtime) *) 0)->node)));
8564     &bc_runtime->node != (&__event->bytecode_runtime_head);
8565     bc_runtime = ((__typeof__(*bc_runtime) *) ((char *)
((reinterpret_cast<__typeof__(bc_runtime->node.next)>(tracepoint_dlopen.rcu_dereference_sym_bp((reinterpret_cast<void
*>(bc_runtime->node.next)))))) - (unsigned long)
(&((__typeof__(*bc_runtime) *) 0)->node))))
8566     {
*8567     if (__builtin_expect(!!(bc_runtime->filter(bc_runtime,
__stackvar.__filter_stack_data) & LTTNG_FILTER_RECORD_FLAG), 0))*
8568      __filter_record = 1;
8569     } if (__builtin_expect(!!(!__filter_record), 1)) return;
8570     } __event_len =
8571


*printing bc_runtime shows filter is 0*
*(gdb) p *bc_runtime *
$3 = {bc = 0x0,* filter = 0x0,* link_failed = 0, node = {next = 0x8051304,
    prev = 0x8051304}}


*also i see __event->bytecode_runtime_head->prev = 0x1 which may be wrong*
*(gdb) p *__event*
$4 = {id = 2, chan = 0xf6c047c0, enabled = 1,
  desc = 0x804c700 <__event_desc___sample_tracepoint_message>, _deprecated1
= 0x0,
  ctx = 0x0, instrumentation = LTTNG_UST_TRACEPOINT, u = {<No data
fields>}, node = {
    next = 0x8051344, prev = 0x0}, _deprecated2 = {next = 0x0, prev = 0x0},
  _deprecated3 = 0x0, _deprecated4 = 0,
*bytecode_runtime_head = {next = 0x8051304,     prev = 0x1}*,
has_enablers_without_bytecode = 134552592, enablers_ref_head = {
    next = 0x8051c10, prev = 0x0}, hlist = {next = 0xf6c00ea0, prev = 0x1},
  registered = 89}


I guess this structure is populated in tracepoint_register using urcu.
Can anyone give me more pointers to debug this. Is this a known issue and
is there any patch which i can use


/Jam





On Mon, Aug 3, 2015 at 4:19 PM, jamie explorer <jamieexplorer at gmail.com>
wrote:

> Hi,
> i am trying to run 32-bit application and see crash at the the line where
> "tracepoint" is used.
> i am using sample application given in lttng-ust-2.6.0/doc/examples/gen-tp/
> Not able to understand why the problem is seen only with 32-bit apps? Can
> experts here pls help me fix this.
>
> Have tried using ELF 32-bit app on Intel 80386 and PowerPC and see the
> crash. Where as 64-bit applications have no problem.
>
> following is the code where it crashes
>         for (i = 0; i < 100000; i++) {
>                 tracepoint(sample_tracepoint, message,  "Hello World\n");
>  <<<< Crash here
>                 usleep(1);
>         }
>
> GDB output:
>
> #0  0x00000000 in ?? ()
> #1  0x10001e54 in __event_probe__sample_tracepoint___message (
>     __tp_data=0x10015420, text=0x100034a4 "Hello World\n")
>     at /build/home/jam/gentp/sample_tracepoint.h:13
> #2  0x10000b9c in __tracepoint_cb_sample_tracepoint___message (
>     text=0x100034a4 "Hello World\n")
>     at //build/home/jam/gentp/sample_tracepoint.h:13
> #3  main (argc=<optimized out>, argv=<optimized out>)
>     at /build/home/jam/gentp/sample.c:115
>
>
> i am running 32-bit version of lttng-sessiond
> root at host:~# ps aux | grep lttng
> root      4224  0.0  0.0  92212  1648 ?        Ssl  00:42   0:00
> /usr/bin/lttng-sessiond --consumerd32-path
> /usr/lib/lttng/libexec/lttng-consumerd --consumerd32-libdir /usr/lib/ -b
> --no-kernel
> root      4243  0.0  0.0  64212   956 ?        Sl   00:42   0:00
> lttng-consumerd  -u --consumerd-cmd-sock
> /var/run/lttng/ustconsumerd32/command --consumerd-err-sock
> /var/run/lttng/ustconsumerd32/error --group tracing
>
>
>
> /Jam
>
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