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segmentation fault

Scheduled Pinned Locked Moved Unsolved Mobile and Embedded
qt 4.8cross-compilingarmv7mqtt
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  • M Milav
    15 Oct 2019, 05:56

    @jsulm

    it means build successful.

    but it is not run, it is crashes application.

    means while running the application, the application are crash.

    with following error.

    "segmentation fault"

    and i debug the application via qDebug(), the application are crash on following line of code.

    mosq->subscribe(NULL, "sensors/temprature", 1); // Segmentation falut
    
    J Offline
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    J.Hilk
    Moderators
    wrote on 15 Oct 2019, 05:58 last edited by
    #17

    @Milav well, did you press connect before you pressed subscribe?

    If not it will crash...


    Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


    Q: What's that?
    A: It's blue light.
    Q: What does it do?
    A: It turns blue.

    M 1 Reply Last reply 15 Oct 2019, 06:05
    0
    • J J.Hilk
      15 Oct 2019, 05:58

      @Milav well, did you press connect before you pressed subscribe?

      If not it will crash...

      M Offline
      M Offline
      Milav
      wrote on 15 Oct 2019, 06:05 last edited by
      #18

      @J-Hilk

      I press first Connect button and than after i press subscribed button.

      but it is crash...

      J 1 Reply Last reply 15 Oct 2019, 06:10
      0
      • M Milav
        15 Oct 2019, 05:08

        @jsulm

        when i build the project it give me only warning like follow.

        /home/tdp0009/Teq_Projects/Aug_2019/HMI/Firmware/QT/12_oct_hmi/qt-mosquitto-master/qtmosq.h:14: warning: 'mosqpp::mosquittopp::mosquittopp(const char*, bool)' is deprecated (declared at ../../../../CC_Lib/mosquitto/phytec_wega_build_websockets/usr/local/include/mosquittopp.h:94) [-Wdeprecated-declarations]
        
        /home/tdp0009/Teq_Projects/Aug_2019/HMI/Firmware/QT/12_oct_hmi/qt-mosquitto-master/mainwindow.cpp:57: warning: 'int mosqpp::mosquittopp::connect_async(const char*, int, int)' is deprecated (declared at ../../../../CC_Lib/mosquitto/phytec_wega_build_websockets/usr/local/include/mosquittopp.h:103) [-Wdeprecated-declarations]
        
        /home/tdp0009/Teq_Projects/Aug_2019/HMI/Firmware/QT/12_oct_hmi/qt-mosquitto-master/mainwindow.cpp:80: warning: 'int mosqpp::mosquittopp::subscribe(int*, const char*, int)' is deprecated (declared at ../../../../CC_Lib/mosquitto/phytec_wega_build_websockets/usr/local/include/mosquittopp.h:110) [-Wdeprecated-declarations]
        

        but i face segmentation fault error when i run that project, an i found the line at where i face segmentation fault.

        it is ...

        mosq->subscribe(NULL, "sensors/temprature", 1); // Segmentation falut
        
        M Offline
        M Offline
        mvuori
        wrote on 15 Oct 2019, 06:10 last edited by
        #19

        If temprature is supposed to be temperature, this is a bug:
        mosq->subscribe(NULL, "sensors/temprature", 1);

        M 1 Reply Last reply 15 Oct 2019, 06:29
        0
        • M Milav
          15 Oct 2019, 06:05

          @J-Hilk

          I press first Connect button and than after i press subscribed button.

          but it is crash...

          J Offline
          J Offline
          jsulm
          Lifetime Qt Champion
          wrote on 15 Oct 2019, 06:10 last edited by
          #20

          @Milav Did you debug to see whether mosq is not a nullptr? If it's not please provide stack trace after crash.
          Also, in connectPressed it does a return if port is not set - is it set if you press connect?
          You should really run through debugger...

          https://forum.qt.io/topic/113070/qt-code-of-conduct

          M 1 Reply Last reply 15 Oct 2019, 06:28
          0
          • J jsulm
            15 Oct 2019, 06:10

            @Milav Did you debug to see whether mosq is not a nullptr? If it's not please provide stack trace after crash.
            Also, in connectPressed it does a return if port is not set - is it set if you press connect?
            You should really run through debugger...

            M Offline
            M Offline
            Milav
            wrote on 15 Oct 2019, 06:28 last edited by
            #21

            @jsulm

            i debug the size of mosq pointer through following code.

             int size = sizeof(*mosq);
                qDebug() << size;
            

            and output is 20;

            and in connectpressed button slot are run succesfully.

            port value are shown correctly.

            when i run debugger it shows following error.

            The inferior stopped because it received a signal from the Operating System.
            
            Signal name : 
            SIGILL
            Signal meaning : 
            Illegal instruction
            
            

            hope you got my point.

            J 1 Reply Last reply 15 Oct 2019, 06:48
            0
            • M mvuori
              15 Oct 2019, 06:10

              If temprature is supposed to be temperature, this is a bug:
              mosq->subscribe(NULL, "sensors/temprature", 1);

              M Offline
              M Offline
              Milav
              wrote on 15 Oct 2019, 06:29 last edited by
              #22

              @mvuori

              no it is supposed to be sensors/temprature.

              1 Reply Last reply
              0
              • M Milav
                15 Oct 2019, 06:28

                @jsulm

                i debug the size of mosq pointer through following code.

                 int size = sizeof(*mosq);
                    qDebug() << size;
                

                and output is 20;

                and in connectpressed button slot are run succesfully.

                port value are shown correctly.

                when i run debugger it shows following error.

                The inferior stopped because it received a signal from the Operating System.
                
                Signal name : 
                SIGILL
                Signal meaning : 
                Illegal instruction
                
                

                hope you got my point.

                J Offline
                J Offline
                jsulm
                Lifetime Qt Champion
                wrote on 15 Oct 2019, 06:48 last edited by
                #23

                @Milav said in segmentation fault:

                i debug the size of mosq pointer through following code.

                The size of a pointer is fixed, it doesn't matter whether it contains nullptr or something else.
                Do

                qDebug() << mosq;
                

                instead to see the value of the pointer.
                Without stack trace I can't tell you what is going on...

                https://forum.qt.io/topic/113070/qt-code-of-conduct

                M J 2 Replies Last reply 15 Oct 2019, 07:14
                0
                • J jsulm
                  15 Oct 2019, 06:48

                  @Milav said in segmentation fault:

                  i debug the size of mosq pointer through following code.

                  The size of a pointer is fixed, it doesn't matter whether it contains nullptr or something else.
                  Do

                  qDebug() << mosq;
                  

                  instead to see the value of the pointer.
                  Without stack trace I can't tell you what is going on...

                  M Offline
                  M Offline
                  Milav
                  wrote on 15 Oct 2019, 07:14 last edited by
                  #24

                  @jsulm

                  when i execute "qDebug() << mosq;" it gives following output.

                  qtmosq(0xac50b0)
                  

                  how i see stack trace in qt?

                  can you please explore me more about stack trace?

                  J 1 Reply Last reply 15 Oct 2019, 07:20
                  0
                  • J jsulm
                    15 Oct 2019, 06:48

                    @Milav said in segmentation fault:

                    i debug the size of mosq pointer through following code.

                    The size of a pointer is fixed, it doesn't matter whether it contains nullptr or something else.
                    Do

                    qDebug() << mosq;
                    

                    instead to see the value of the pointer.
                    Without stack trace I can't tell you what is going on...

                    J Offline
                    J Offline
                    JonB
                    wrote on 15 Oct 2019, 07:16 last edited by
                    #25

                    @Milav

                    int size = sizeof(*mosq);

                    @jsulm

                    The size of a pointer is fixed,

                    A slight slip of the tongue there. I think what my colleague @jsulm meant to clarify is: sizeof(...) is a compile-time calculation, it does not matter what the value of mosq is or what it points at run-time, rather this statement just assigns sizeof(qtmosq) regardless. As he says, show us what is in the mosq.

                    M 1 Reply Last reply 15 Oct 2019, 07:18
                    0
                    • J JonB
                      15 Oct 2019, 07:16

                      @Milav

                      int size = sizeof(*mosq);

                      @jsulm

                      The size of a pointer is fixed,

                      A slight slip of the tongue there. I think what my colleague @jsulm meant to clarify is: sizeof(...) is a compile-time calculation, it does not matter what the value of mosq is or what it points at run-time, rather this statement just assigns sizeof(qtmosq) regardless. As he says, show us what is in the mosq.

                      M Offline
                      M Offline
                      Milav
                      wrote on 15 Oct 2019, 07:18 last edited by
                      #26

                      @JonB

                      when i execute "qDebug() << mosq;" it gives following output.

                      qtmosq(0xac50b0)

                      1 Reply Last reply
                      0
                      • M Milav
                        15 Oct 2019, 07:14

                        @jsulm

                        when i execute "qDebug() << mosq;" it gives following output.

                        qtmosq(0xac50b0)
                        

                        how i see stack trace in qt?

                        can you please explore me more about stack trace?

                        J Offline
                        J Offline
                        JonB
                        wrote on 15 Oct 2019, 07:20 last edited by JonB
                        #27

                        @Milav

                        when i execute "qDebug() << mosq;" it gives following output.
                        qtmosq(0xac50b0)

                        I'm not sure this is actually trying to deference the pointer, it may just print its value. I would try something likeqDebug() << mosq->something;, where something is some field you know is supposed to exist & be valid in a qtmosq. Or try qDebug() << *mosq (note the *)?

                        how i see stack trace in qt?
                        can you please explore me more about stack trace?

                        I don't know how you run in your "Embedded Custom Board", but can you run the app from inside a debugger? then when it seg faults you will see a "stack trace" in the debugger showing the call stack when the fault occurred.

                        J M 2 Replies Last reply 15 Oct 2019, 07:25
                        1
                        • J JonB
                          15 Oct 2019, 07:20

                          @Milav

                          when i execute "qDebug() << mosq;" it gives following output.
                          qtmosq(0xac50b0)

                          I'm not sure this is actually trying to deference the pointer, it may just print its value. I would try something likeqDebug() << mosq->something;, where something is some field you know is supposed to exist & be valid in a qtmosq. Or try qDebug() << *mosq (note the *)?

                          how i see stack trace in qt?
                          can you please explore me more about stack trace?

                          I don't know how you run in your "Embedded Custom Board", but can you run the app from inside a debugger? then when it seg faults you will see a "stack trace" in the debugger showing the call stack when the fault occurred.

                          J Offline
                          J Offline
                          jsulm
                          Lifetime Qt Champion
                          wrote on 15 Oct 2019, 07:25 last edited by jsulm
                          #28

                          @JonB said in segmentation fault:

                          I'm not sure this is actually trying to deference the pointer

                          It does not, but I wanted to see its value :-)
                          Looks like it's not NULL.

                          https://forum.qt.io/topic/113070/qt-code-of-conduct

                          J 1 Reply Last reply 15 Oct 2019, 07:27
                          1
                          • J jsulm
                            15 Oct 2019, 07:25

                            @JonB said in segmentation fault:

                            I'm not sure this is actually trying to deference the pointer

                            It does not, but I wanted to see its value :-)
                            Looks like it's not NULL.

                            J Offline
                            J Offline
                            JonB
                            wrote on 15 Oct 2019, 07:27 last edited by JonB
                            #29

                            @jsulm
                            Indeedy :) So now let's see how qDebug() << *mosq fares?

                            M 1 Reply Last reply 15 Oct 2019, 07:32
                            0
                            • J JonB
                              15 Oct 2019, 07:20

                              @Milav

                              when i execute "qDebug() << mosq;" it gives following output.
                              qtmosq(0xac50b0)

                              I'm not sure this is actually trying to deference the pointer, it may just print its value. I would try something likeqDebug() << mosq->something;, where something is some field you know is supposed to exist & be valid in a qtmosq. Or try qDebug() << *mosq (note the *)?

                              how i see stack trace in qt?
                              can you please explore me more about stack trace?

                              I don't know how you run in your "Embedded Custom Board", but can you run the app from inside a debugger? then when it seg faults you will see a "stack trace" in the debugger showing the call stack when the fault occurred.

                              M Offline
                              M Offline
                              Milav
                              wrote on 15 Oct 2019, 07:30 last edited by
                              #30

                              @JonB said in segmentation fault:

                              qDebug() << *mosq

                              gives error :-

                              /home/tdp0009/Teq_Projects/Aug_2019/HMI/Firmware/QT/12_oct_hmi/qt-mosquitto-master/mainwindow.cpp:54: note:   'qtmosq' is not derived from 'const QFlags<T>'
                              

                              @JonB said in segmentation fault:

                              qDebug() << mosq->something

                              i tried following things and it output are '0'.

                              1. qDebug() << mosq->connect_async(host.data(), port);
                              2. qDebug() << mosq->loop_start();
                              3. qDebug() << mosq->subscribe(NULL, "sensors/temprature", 1);

                              the output of all above command are zero (0).

                              @JonB said in segmentation fault:

                              app from inside a debugge

                              i am not able to run the debugger because it gives following error.

                              The inferior stopped because it received a signal from the Operating System.
                              
                              Signal name : 
                              SIGILL
                              Signal meaning : 
                              Illegal instruction
                              
                              

                              hope you got your answer.

                              J 1 Reply Last reply 15 Oct 2019, 07:34
                              0
                              • J JonB
                                15 Oct 2019, 07:27

                                @jsulm
                                Indeedy :) So now let's see how qDebug() << *mosq fares?

                                M Offline
                                M Offline
                                Milav
                                wrote on 15 Oct 2019, 07:32 last edited by
                                #31

                                @JonB said in segmentation fault:

                                @jsulm
                                Indeedy :) So now let's see how qDebug() << *mosq fares?

                                sorry the error is as following not previous one.

                                /home/tdp0009/Teq_Projects/Aug_2019/HMI/Firmware/QT/12_oct_hmi/qt-mosquitto-master/mainwindow.cpp:54: error: no match for 'operator<<' in 'qDebug()() << *((MainWindow*)this)->MainWindow::mosq'
                                
                                M 1 Reply Last reply 15 Oct 2019, 07:34
                                0
                                • M Milav
                                  15 Oct 2019, 07:30

                                  @JonB said in segmentation fault:

                                  qDebug() << *mosq

                                  gives error :-

                                  /home/tdp0009/Teq_Projects/Aug_2019/HMI/Firmware/QT/12_oct_hmi/qt-mosquitto-master/mainwindow.cpp:54: note:   'qtmosq' is not derived from 'const QFlags<T>'
                                  

                                  @JonB said in segmentation fault:

                                  qDebug() << mosq->something

                                  i tried following things and it output are '0'.

                                  1. qDebug() << mosq->connect_async(host.data(), port);
                                  2. qDebug() << mosq->loop_start();
                                  3. qDebug() << mosq->subscribe(NULL, "sensors/temprature", 1);

                                  the output of all above command are zero (0).

                                  @JonB said in segmentation fault:

                                  app from inside a debugge

                                  i am not able to run the debugger because it gives following error.

                                  The inferior stopped because it received a signal from the Operating System.
                                  
                                  Signal name : 
                                  SIGILL
                                  Signal meaning : 
                                  Illegal instruction
                                  
                                  

                                  hope you got your answer.

                                  J Offline
                                  J Offline
                                  JonB
                                  wrote on 15 Oct 2019, 07:34 last edited by
                                  #32

                                  @Milav
                                  First you wrote

                                  and i debug the application via qDebug(), the application are crash on following line of code.
                                  mosq->subscribe(NULL, "sensors/temprature", 1); // Segmentation falut

                                  Now you write

                                  qDebug() << mosq->subscribe(NULL, "sensors/temprature", 1);
                                  the output of all above command are zero (0).

                                  This is a problem if you say sometimes it seg faults and sometimes it returns 0? Is that the case? You need to be very specific in your answers!

                                  i am not able to run the debugger because it gives following error.

                                  That is indeed a big problem. There is little for us to answer from what you have posted. Is a debugger supposed to work for your "Embedded Custom Board" (I don't know about this)? You really need one. Otherwise you are likely to have to try printing out all sorts of information in your code to try to diagnose what is going on....

                                  1 Reply Last reply
                                  0
                                  • M Milav
                                    15 Oct 2019, 07:32

                                    @JonB said in segmentation fault:

                                    @jsulm
                                    Indeedy :) So now let's see how qDebug() << *mosq fares?

                                    sorry the error is as following not previous one.

                                    /home/tdp0009/Teq_Projects/Aug_2019/HMI/Firmware/QT/12_oct_hmi/qt-mosquitto-master/mainwindow.cpp:54: error: no match for 'operator<<' in 'qDebug()() << *((MainWindow*)this)->MainWindow::mosq'
                                    
                                    M Offline
                                    M Offline
                                    Milav
                                    wrote on 15 Oct 2019, 07:34 last edited by
                                    #33

                                    Screenshot from 2019-10-15 13-03-18.png

                                    J 1 Reply Last reply 15 Oct 2019, 07:37
                                    0
                                    • M Milav
                                      15 Oct 2019, 07:34

                                      Screenshot from 2019-10-15 13-03-18.png

                                      J Offline
                                      J Offline
                                      jsulm
                                      Lifetime Qt Champion
                                      wrote on 15 Oct 2019, 07:37 last edited by
                                      #34

                                      @Milav Forget about

                                      qDebug() << *mosq;
                                      

                                      it's only going to work if operator<< was overloaded for that class, apparently it isn't, but this is not an issue.
                                      Can you try to run the app directly with gdb?

                                      https://forum.qt.io/topic/113070/qt-code-of-conduct

                                      J M 2 Replies Last reply 15 Oct 2019, 07:41
                                      1
                                      • J jsulm
                                        15 Oct 2019, 07:37

                                        @Milav Forget about

                                        qDebug() << *mosq;
                                        

                                        it's only going to work if operator<< was overloaded for that class, apparently it isn't, but this is not an issue.
                                        Can you try to run the app directly with gdb?

                                        J Offline
                                        J Offline
                                        JonB
                                        wrote on 15 Oct 2019, 07:41 last edited by
                                        #35

                                        @jsulm

                                        Can you try to run the app directly with gdb?

                                        I know this is not the place for a long explanation. But when OP says

                                        I make a qt application for Embedded Custom Board

                                        I thought (knowing nothing about this) it meant he is doing something like )cross-)compiling of whatever but the app runs "on the board", so he might not have/be able to use a debugger? Can you explain to me in one sentence what the OP's enthronement actually is, I'd like to have the vaguest understanding....

                                        1 Reply Last reply
                                        0
                                        • J jsulm
                                          15 Oct 2019, 07:37

                                          @Milav Forget about

                                          qDebug() << *mosq;
                                          

                                          it's only going to work if operator<< was overloaded for that class, apparently it isn't, but this is not an issue.
                                          Can you try to run the app directly with gdb?

                                          M Offline
                                          M Offline
                                          Milav
                                          wrote on 15 Oct 2019, 07:41 last edited by
                                          #36

                                          @jsulm said in segmentation fault:

                                          Forget about
                                          qDebug() << *mosq;

                                          okay thank you.

                                          @jsulm said in segmentation fault:

                                          Can you try to run the app directly with gdb?

                                          yes i tried but , debugger give me error,

                                          the error is shown in below image.

                                          Screenshot from 2019-10-15 13-11-13.png

                                          J J 2 Replies Last reply 15 Oct 2019, 07:43
                                          0

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