[lttng-dev] SIGSEGV __event_probe, C++ application (static linking)

[Dilong Zheng]

Hi,


I have instrumented a C++ application with user space tracepoints. When I run the application and do a: "lttng list -u" command, I am able to see all my available tracepoints for the application. However when I enable those user space tracepoints and then start the trace, a core gets dumped and examining the core file in gdb I see the following error:


Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00000000 in ?? ()

...

(gdb) bt
#0  0x00000000 in ?? ()
#1  0x08dd1088 in __event_probe__mike___sem_wait_entry (__tp_data=0xef92d818)
    at /localhome/zhengd/override_mcd/System/SS_Inc/./sem_wrapper.h:67
#2  0x08dd44d9 in __tracepoint_cb_mike___sem_wait_entry () at /localhome/zhengd/override_mc /System/SS_Inc/sem_wrapper.h:67
#3  __wrap_sem_wait (sem=0xf43014c8) at /localhome/zhengd/override_mcd/System/System_Services/SysServices_Linux/SystemLinux.cpp:1877


Contextual Information: I would like to trace all calls to sem_wait() in my application. I am simply using a wrapper sem_wait function where I can place tracepoint() calls. Here's what the sem_wait wrapper looks like:


extern "C" int __real_sem_wait(sem_t*);

extern "C" int __wrap_sem_wait(sem_t* sem)

{

    tracepoint(mike, sem_wait_entry);

    int ret = __real_sem_wait(sem);

    tracepoint(mike, sem_wait_exit, ret);


    return ret;

}


Here is the TRACEPOINT_EVENT macro found in my tracepoint provider header file (which was generated using lttng-gen-tp command line utility):


TRACEPOINT_EVENT(mike,

    sem_wait_entry,

    TP_ARGS(),

    TP_FIELDS()

)


And I am statically linking by using an existing CPP file (file with the __wrap_sem_wait() function) to create probes. I would just like to know any possible reasons why this error may be happening given the above mentioned circumstances and what I may be able to try in order to fix this.


Thanks,


Dilong
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