[ltt-dev] LTT UserSpace Tracer, broken?
Pierre-Marc Fournier
pierre-marc.fournier at polymtl.ca
Fri May 21 14:49:31 EDT 2010
jpaul at gdrs.com wrote:
> 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
> }
Yes you need glibc 2.6 to have sched_getcpu. However, on my system, it
is a vsyscall, therefore you cannot call it with syscall().
>
> 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
Hmmm... what is the use of the "3" you are passing as argument to
syscall()? This appears to be an invalid pointer, which results in -1
being returned by the syscall and consequently a segfault.
>
> # 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
Thanks, fixed in the manual.
> 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.
Good idea. In the meantime, you can start your program with the
UST_AUTOPROBE=1 environment var, which will have the same effect. When
you use usttrace, this is done automatically.
>
> Thanks
>
> JP
>
>
>
>
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