[ltt-dev] LTT UserSpace Tracer, broken?

[jpaul@gdrs.com (jpaul@gdrs.com)]

So, I'm switching modes and attempting to get the "user space tracer" up and running. I'm following the instructions provided here:

http://lttng.org/files/ust/manual/ust.html

I've downloaded and built the following packages:

    libkcompat-0.2.tar.gz
    ust-0.4.tar.gz
    userspace-rcu-0.4.3.tar.bz2
    lttv-0.12.31-04072010.tar.gz

First issue: ust-0.4 will not compile due to an undefined reference to sched_getcpu(). I'm using the latest version of Redhat Enterprise 5.5 and my installed glibc doesn't have that method defined (gcc version=4.3.4, glibc version=2.5-49 .. believe this method came into being around glibc-2.6?). Knowing that upgrading glibc is not a trivial process (as I've actually taken down a machine by doing so incorrectly), I'm not confident that most users may not want to go that route. I've downloaded glib2-2.11 and pulled some code out of that library to place the following in serialize.c:

// Added to avoid upgrading glibc
int
sched_getcpu (void)
{
#ifdef __NR_getcpu
  unsigned int cpu;
//  int r = INLINE_SYSCALL (getcpu, 3, &cpu, NULL, NULL);
  int r = syscall(SYS_getcpu, 3, &cpu, NULL, NULL);

  return r == -1 ? r : cpu;
#else
  __set_errno (ENOSYS);
  return -1;
#endif
}

That may or may not be the cause of some follow-on issues. Maybe glibc "really" needs to be upgraded to effectively use the userspace tracer .. please comment if so and I go that route next. Also, note that I'm doing all this work at "root", so there should be no permissions issues.

Next, I attempted to build and run the "quick start" code as detailed in the instructions (copying that code into ustTest.c):

gcc -o ustTest -g -Wall ustTest.c -lust

# usttrace ./ustTest
/usr/local/bin/usttrace: line 156: 23606 Segmentation fault      $CMD 2>&1
Waiting for ustd to shutdown...
Trace was output in:  /root/.usttraces/machineName-20100520172047665580280

# lttv -m textDump -t  /root/.usttraces/machineName-20100520172047665580280
** (process:23613): WARNING **: Trace /root/.usttraces/machineName-20100520172047665580280 has no metadata tracefile
** (process:23613): CRITICAL **: cannot open trace /root/.usttraces/machineName-20100520172047665580280
/usr/local/bin/lttv: line 15: 23613 Segmentation fault      $0.real $*

So, next I gave up on the command line attempts and tried to get things up and running manually (still using the provided instructions).

mkdir /tmp/ustsocks   <- not sure this is correct anymore, may have changed to: /tmp/ust-app-socks
mkdir /tmp/trace
ustd &
./ustTest &
[7] 23652

My ustTest was changed as follows before running that executable:

int main(int argc, char **argv)
{
    int v = 23;
    char *st = "test23";

    for(;;)
    {
    trace_mark(main, 23, "firstarg %d secondarg %s", v, st);

    /* another marker without arguments: */
    trace_mark(main, 24, MARK_NOARGS);
    sleep(30);
    }

    return 0;
}

# ustctl --list-markers 23652
{PID: 23652, channel/marker: metadata/core_marker_id, state: 1, fmt: "channel %s name %s event_id %hu int #1u%zu long #1u%zu pointer #1u%zu size_t #1u%zu alignment #1u%u" 0x3301d0}
{PID: 23652, channel/marker: metadata/core_marker_format, state: 1, fmt: "channel %s name %s format %s" 0x3301e3}
{PID: 23652, channel/marker: metadata/core_marker_format, state: 1, fmt: "channel %s name %s format %s" 0x330d63}
{PID: 23652, channel/marker: metadata/core_marker_id, state: 1, fmt: "channel %s name %s event_id %hu int #1u%zu long #1u%zu pointer #1u%zu size_t #1u%zu alignment #1u%u" 0x331483}
{PID: 23652, channel/marker: metadata/core_marker_format, state: 1, fmt: "channel %s name %s format %s" 0x332b35}
{PID: 23652, channel/marker: metadata/core_marker_id, state: 1, fmt: "channel %s name %s event_id %hu int #1u%zu long #1u%zu pointer #1u%zu size_t #1u%zu alignment #1u%u" 0x332be6}
{PID: 23652, channel/marker: ust/potential_exec, state: 0, fmt: " " 0x33d9b6}
{PID: 23652, channel/marker: main/23, state: 0, fmt: "firstarg %d secondarg %s" 0x8048763}
{PID: 23652, channel/marker: main/24, state: 0, fmt: " " 0x80487aa}
{PID: 23652, channel/marker: ust/dummymark, state: 0, fmt: " " 0x8048893}

ustctl --enable-marker main/23 23652

# ustctl --create-trace 23652
# ustctl --start-trace 23652
ustd[23630/23663]: Error: failed to connect to buffer (in consumer_thread() at ustd.c:581)
libustcomm[23630/23666]: Error: connect (path=/tmp/ust-app-socks/23652): Connection refused (in ustcomm_connect_path() at ustcomm.c:581)
ustd[23630/23666]: Warning: unable to connect to process, it probably died before we were able to connect (in connect_buffer() at ustd.c:250)
ustd[23630/23666]: Error: failed to connect to buffer (in consumer_thread() at ustd.c:581)
ustd[23630/23664]: Error: failed to connect to buffer (in consumer_thread() at ustd.c:581)
libustcomm[23630/23665]: Error: connect (path=/tmp/ust-app-socks/23652): Connection refused (in ustcomm_connect_path() at ustcomm.c:581)
ustd[23630/23665]: Warning: unable to connect to process, it probably died before we were able to connect (in connect_buffer() at ustd.c:250)
ustd[23630/23665]: Error: failed to connect to buffer (in consumer_thread() at ustd.c:581)
[7]+  Segmentation fault      ./ustTest

# ustctl --stop-trace 23652
libustcomm[23668/23668]: Error: connect (path=/tmp/ust-app-socks/23652): Connection refused (in ustcomm_connect_path() at ustcomm.c:581)
ustctl[23668/23668]: Error: could not connect to PID 23652 (in ustcmd_send_cmd() at ../libustcmd/ustcmd.c:439)
ustctl[23668/23668]: Error: error while trying to stop trace for PID 23652
 (in main() at ustctl.c:230)

Machine info (non-RT kernel): Intel Core2 Duo
# uname -a
Linux machineName 2.6.18-194.3.1.el5PAE #1 SMP Sun May 2 04:42:25 EDT 2010 i686 i686 i386 GNU/Linux

So ... could the above be related to my glibc patch (or not having a later version of glibc) or are things more broken as they appear?  Maybe I'm missing additional steps that are not documented?

Also a suggestion: for large programs, of many developers and lots of code, it might be somewhat of a hassle to have to enable each and every marker. I would suggest adding a "--enable-all-markers" capability to ustctl.

Thanks

JP




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