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Segfault when calling QWidget::show (on Debian 9)

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  • B Bart_Vandewoestyne

    @JonB said in Segfault when calling QWidget::show (on Debian 9):

    Meanwhile I see now you go MyApplication::mfParseArguments(int, char**) (), etc. It ends up calling your MyApplication::mfRun(int, char**, QString&) (). What does that do with argv?

    Well, actually, in MyApplication::mfParseArguments(int argc, char** argv) the argv from main is taken and a copy of it is created. This copy has one extra -e argument and is thus one element longer. Something in essence like this (original code slightly modified):

     char** newArgvs;
     newArgvs = new char*[argc+1];
     for(i = 0; i < argc + 1; i++)
     {
        newArgvs[i] = new char[256];
    }
    
    strcpy(newArgvs[0], argv[0]);
    strcpy(newArgvs[1], "-e");		
    for(i = 1; i < argc; i++)
    {
        strcpy(newArgvs[i+1], argv[i]);
    }
    argc++;
    

    and then at the end of MyApplication::mfParseArguments that newArgvs is passed to ICService::mfParseArguments:

    return ICService::mfParseArguments(argc, newArgvs, false);
    

    which in its turn then passes this info through to ICService::mfExec and that one then passes it to MyApplication::mfRun which calls QWidget::show that segfaults.

    JonBJ Online
    JonBJ Online
    JonB
    wrote on last edited by JonB
    #13

    @Bart_Vandewoestyne said in Segfault when calling QWidget::show (on Debian 9):

    for(i = 1; i < argc; i++)
    {
    strcpy(newArgvs[i+1], argv[i]);
    }

    I shall be surprised if it is this, but....

    I think your code is not 100% technically correct. You do not NULL terminate your new vector. Technically you should find your original argv had an extra element at the end: argv[argc] == NULL. You do not copy this or NULL terminate your new newArgvs. E.g. https://stackoverflow.com/questions/16418932/is-argvargc-equal-to-null-pointer

    The Standard (C99 5.1.2.2.1p2) mandates that:

    If they are declared, the parameters to the main function shall obey the following constraints:

    — The value of argc shall be nonnegative.

    — argv[argc] shall be a null pointer.

    Note the last point. I doubt it's that, but worth a try on your new copy?

    1 Reply Last reply
    1
    • B Bart_Vandewoestyne

      @JonB said in Segfault when calling QWidget::show (on Debian 9):

      Meanwhile I see now you go MyApplication::mfParseArguments(int, char**) (), etc. It ends up calling your MyApplication::mfRun(int, char**, QString&) (). What does that do with argv?

      Well, actually, in MyApplication::mfParseArguments(int argc, char** argv) the argv from main is taken and a copy of it is created. This copy has one extra -e argument and is thus one element longer. Something in essence like this (original code slightly modified):

       char** newArgvs;
       newArgvs = new char*[argc+1];
       for(i = 0; i < argc + 1; i++)
       {
          newArgvs[i] = new char[256];
      }
      
      strcpy(newArgvs[0], argv[0]);
      strcpy(newArgvs[1], "-e");		
      for(i = 1; i < argc; i++)
      {
          strcpy(newArgvs[i+1], argv[i]);
      }
      argc++;
      

      and then at the end of MyApplication::mfParseArguments that newArgvs is passed to ICService::mfParseArguments:

      return ICService::mfParseArguments(argc, newArgvs, false);
      

      which in its turn then passes this info through to ICService::mfExec and that one then passes it to MyApplication::mfRun which calls QWidget::show that segfaults.

      kshegunovK Offline
      kshegunovK Offline
      kshegunov
      Moderators
      wrote on last edited by
      #14

      @Bart_Vandewoestyne said in Segfault when calling QWidget::show (on Debian 9):

      strcpy(newArgvs[0], argv[0]);
      

      This could easily overflow. What's the result of strlen(argv[0])?

      Read and abide by the Qt Code of Conduct

      B 1 Reply Last reply
      2
      • B Bart_Vandewoestyne

        @Bart_Vandewoestyne said in Segfault when calling QWidget::show (on Debian 9):

        @Christian-Ehrlicher said in Segfault when calling QWidget::show (on Debian 9):

        The question is - where do you pass it to your Q(Core)Application.

        That is indeed a good question... it is currently not yet clear to me where the single instance of the QApplication class is created. I'll have to spend some more time with the code to figure that out, and report back once I know more.

        OK. For as far as I can see it now, the call to QApplication(argc, argv) happens in ICService::mfExec before the call to MyApplication::mfRun and is with the new argc and argv, where the new argc is one more than the old argc (passed to main), and the new argv has one element (-e) more than the old argv (that was passed to main).

        Is it troublesome if in a call to QApplication(newArgc, newArgv) we have that newArgc != argc and newArgv is not the same as argv, where argc and argv were the arguments passed to main?

        Christian EhrlicherC Online
        Christian EhrlicherC Online
        Christian Ehrlicher
        Lifetime Qt Champion
        wrote on last edited by Christian Ehrlicher
        #15

        @Bart_Vandewoestyne said in Segfault when calling QWidget::show (on Debian 9):

        the call to QApplication(argc, argv) happens in ICService::mfExec

        Some code would be good...
        You already posted a link with the solution but ignored it constantly - Q(Core)Application takes a reference to an int so the callers should pass this to. Otherwise there might be a dangling reference. But without code...

        wrt to your strange copy stuff (whyever you need to modify your command line - sounds like a strange hack for me):

        std::vector<char*> newArgs;
        newArgs.push_back(argv[0]);
        newArgs.push_back(const_cast<char*>("-e"));
        for (int i = 1; i < argc; ++i)
          newArgs.push_back(argv[i]);
        argc += 1;
        ...mfParseArguments(argc, newArgs.data());
        

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        B 2 Replies Last reply
        2
        • kshegunovK kshegunov

          @Bart_Vandewoestyne said in Segfault when calling QWidget::show (on Debian 9):

          strcpy(newArgvs[0], argv[0]);
          

          This could easily overflow. What's the result of strlen(argv[0])?

          B Offline
          B Offline
          Bart_Vandewoestyne
          wrote on last edited by
          #16

          @kshegunov said in Segfault when calling QWidget::show (on Debian 9):

          This could easily overflow. What's the result of strlen(argv[0])?

          I've added

          std::cout << "strlen(argv[0]) = " << strlen(argv[0]) << std::endl;
          

          right before the strcpy statement and the result is 14. Knowing that newArgvs[0] was allocated with new char[256] I would assume this is not causing trouble.

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          0
          • Christian EhrlicherC Christian Ehrlicher

            @Bart_Vandewoestyne said in Segfault when calling QWidget::show (on Debian 9):

            the call to QApplication(argc, argv) happens in ICService::mfExec

            Some code would be good...
            You already posted a link with the solution but ignored it constantly - Q(Core)Application takes a reference to an int so the callers should pass this to. Otherwise there might be a dangling reference. But without code...

            wrt to your strange copy stuff (whyever you need to modify your command line - sounds like a strange hack for me):

            std::vector<char*> newArgs;
            newArgs.push_back(argv[0]);
            newArgs.push_back(const_cast<char*>("-e"));
            for (int i = 1; i < argc; ++i)
              newArgs.push_back(argv[i]);
            argc += 1;
            ...mfParseArguments(argc, newArgs.data());
            
            B Offline
            B Offline
            Bart_Vandewoestyne
            wrote on last edited by
            #17

            @Christian-Ehrlicher said in Segfault when calling QWidget::show (on Debian 9):

            Some code would be good...

            Sorry for not posting code here, @Christian-Ehrlicher, but my question is related to code I work on professionally and for as far as I know I am not allowed to share any code.

            Christian EhrlicherC 1 Reply Last reply
            0
            • B Bart_Vandewoestyne

              @Christian-Ehrlicher said in Segfault when calling QWidget::show (on Debian 9):

              Some code would be good...

              Sorry for not posting code here, @Christian-Ehrlicher, but my question is related to code I work on professionally and for as far as I know I am not allowed to share any code.

              Christian EhrlicherC Online
              Christian EhrlicherC Online
              Christian Ehrlicher
              Lifetime Qt Champion
              wrote on last edited by
              #18

              @Bart_Vandewoestyne said in Segfault when calling QWidget::show (on Debian 9):

              allowed to share any code.

              Then good luck. We can't guess your code...

              Apart from this you already shared code.

              Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
              Visit the Qt Academy at https://academy.qt.io/catalog

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              • Christian EhrlicherC Christian Ehrlicher

                @Bart_Vandewoestyne said in Segfault when calling QWidget::show (on Debian 9):

                mpMainWindow

                I would guess this is either a nullptr or not initialized. Build your app with debug information, go to stack frame 7 and print out the value of mpMainWindow .

                B Offline
                B Offline
                Bart_Vandewoestyne
                wrote on last edited by
                #19

                @Christian-Ehrlicher said in Segfault when calling QWidget::show (on Debian 9):

                I would guess this is either a nullptr or not initialized. Build your app with debug information, go to stack frame 7 and print out the value of mpMainWindow .

                I've added the -g option to our release build and when I run the application in gdb it now segfaults with the following call stack:

                user@debianvbox:~/SVN/PolarisRel/Apps$ gdb ./PolarisSlave 
                GNU gdb (Debian 7.12-6) 7.12.0.20161007-git
                Copyright (C) 2016 Free Software Foundation, Inc.
                License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
                This is free software: you are free to change and redistribute it.
                There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
                and "show warranty" for details.
                This GDB was configured as "x86_64-linux-gnu".
                Type "show configuration" for configuration details.
                For bug reporting instructions, please see:
                <http://www.gnu.org/software/gdb/bugs/>.
                Find the GDB manual and other documentation resources online at:
                <http://www.gnu.org/software/gdb/documentation/>.
                For help, type "help".
                Type "apropos word" to search for commands related to "word"...
                Reading symbols from ./PolarisSlave...done.
                (gdb) r
                Starting program: /home/user/SVN/PolarisRel/Apps/PolarisSlave 
                [Thread debugging using libthread_db enabled]
                Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
                
                Program received signal SIGSEGV, Segmentation fault.
                strlen () at ../sysdeps/x86_64/strlen.S:106
                106	../sysdeps/x86_64/strlen.S: No such file or directory.
                (gdb) bt
                #0  strlen () at ../sysdeps/x86_64/strlen.S:106
                #1  0x00007ffff3e101ed in XSetCommand () from /usr/lib/x86_64-linux-gnu/libX11.so.6
                #2  0x00007ffff3e147f0 in XSetWMProperties () from /usr/lib/x86_64-linux-gnu/libX11.so.6
                #3  0x00007ffff659007d in QWidgetPrivate::create_sys(unsigned long, bool, bool) () from /home/user/SVN/PolarisRel/ThirdParty/Qt/qt-install/lib/libQtGui.so.4
                #4  0x00007ffff6548769 in QWidget::create(unsigned long, bool, bool) () from /home/user/SVN/PolarisRel/ThirdParty/Qt/qt-install/lib/libQtGui.so.4
                #5  0x00007ffff6550697 in QWidget::setVisible(bool) () from /home/user/SVN/PolarisRel/ThirdParty/Qt/qt-install/lib/libQtGui.so.4
                #6  0x000055555594a1fd in QWidget::show (this=<optimized out>) at ../../ThirdParty/Qt/qt-install/include/QtGui/qwidget.h:497
                #7  BSPPolarisSlave::mfRun (this=0x7fffffffe0e0, argc=<optimized out>, argv=<optimized out>, errormsg=...) at BSPPolarisSlave.cpp:443
                #8  0x0000555555c010da in ICService::mfExec(int, char**, QString&, bool) ()
                #9  0x0000555555bfd90e in ICService::mfParseArguments(int, char**, bool) ()
                #10 0x000055555594dbb3 in BSPPolarisSlave::mfParseArguments (this=0x7fffffffe0e0, argc=2, argv=0x7fffffffe258) at BSPPolarisSlave.cpp:659
                #11 0x000055555592a3ad in main (argc=1, argv=0x7fffffffe258) at BSPPolarisSlaveMain.cpp:71
                (gdb) f 7
                #7  BSPPolarisSlave::mfRun (this=0x7fffffffe0e0, argc=<optimized out>, argv=<optimized out>, errormsg=...) at BSPPolarisSlave.cpp:443
                443			mpMainWindow->show();
                (gdb) p mpMainWindow
                $1 = (BSPPolarisSlaveMainWindow *) 0x555556627c40
                

                Some things I noticed are:

                • mpMainWindow is not nullptr.
                • In the call to BSPPolarisSlave::mfRun argc and argv are marked as 'optimized out'... and similarly, in the call to QWidget::show, the this parameter is also 'optimized out'. I have not much experience with gdb (most of the time, I debug in the Visual Studio debugger)... but could this 'optimizing out' be the problem?
                J.HilkJ 1 Reply Last reply
                0
                • B Bart_Vandewoestyne

                  @Christian-Ehrlicher said in Segfault when calling QWidget::show (on Debian 9):

                  I would guess this is either a nullptr or not initialized. Build your app with debug information, go to stack frame 7 and print out the value of mpMainWindow .

                  I've added the -g option to our release build and when I run the application in gdb it now segfaults with the following call stack:

                  user@debianvbox:~/SVN/PolarisRel/Apps$ gdb ./PolarisSlave 
                  GNU gdb (Debian 7.12-6) 7.12.0.20161007-git
                  Copyright (C) 2016 Free Software Foundation, Inc.
                  License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
                  This is free software: you are free to change and redistribute it.
                  There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
                  and "show warranty" for details.
                  This GDB was configured as "x86_64-linux-gnu".
                  Type "show configuration" for configuration details.
                  For bug reporting instructions, please see:
                  <http://www.gnu.org/software/gdb/bugs/>.
                  Find the GDB manual and other documentation resources online at:
                  <http://www.gnu.org/software/gdb/documentation/>.
                  For help, type "help".
                  Type "apropos word" to search for commands related to "word"...
                  Reading symbols from ./PolarisSlave...done.
                  (gdb) r
                  Starting program: /home/user/SVN/PolarisRel/Apps/PolarisSlave 
                  [Thread debugging using libthread_db enabled]
                  Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
                  
                  Program received signal SIGSEGV, Segmentation fault.
                  strlen () at ../sysdeps/x86_64/strlen.S:106
                  106	../sysdeps/x86_64/strlen.S: No such file or directory.
                  (gdb) bt
                  #0  strlen () at ../sysdeps/x86_64/strlen.S:106
                  #1  0x00007ffff3e101ed in XSetCommand () from /usr/lib/x86_64-linux-gnu/libX11.so.6
                  #2  0x00007ffff3e147f0 in XSetWMProperties () from /usr/lib/x86_64-linux-gnu/libX11.so.6
                  #3  0x00007ffff659007d in QWidgetPrivate::create_sys(unsigned long, bool, bool) () from /home/user/SVN/PolarisRel/ThirdParty/Qt/qt-install/lib/libQtGui.so.4
                  #4  0x00007ffff6548769 in QWidget::create(unsigned long, bool, bool) () from /home/user/SVN/PolarisRel/ThirdParty/Qt/qt-install/lib/libQtGui.so.4
                  #5  0x00007ffff6550697 in QWidget::setVisible(bool) () from /home/user/SVN/PolarisRel/ThirdParty/Qt/qt-install/lib/libQtGui.so.4
                  #6  0x000055555594a1fd in QWidget::show (this=<optimized out>) at ../../ThirdParty/Qt/qt-install/include/QtGui/qwidget.h:497
                  #7  BSPPolarisSlave::mfRun (this=0x7fffffffe0e0, argc=<optimized out>, argv=<optimized out>, errormsg=...) at BSPPolarisSlave.cpp:443
                  #8  0x0000555555c010da in ICService::mfExec(int, char**, QString&, bool) ()
                  #9  0x0000555555bfd90e in ICService::mfParseArguments(int, char**, bool) ()
                  #10 0x000055555594dbb3 in BSPPolarisSlave::mfParseArguments (this=0x7fffffffe0e0, argc=2, argv=0x7fffffffe258) at BSPPolarisSlave.cpp:659
                  #11 0x000055555592a3ad in main (argc=1, argv=0x7fffffffe258) at BSPPolarisSlaveMain.cpp:71
                  (gdb) f 7
                  #7  BSPPolarisSlave::mfRun (this=0x7fffffffe0e0, argc=<optimized out>, argv=<optimized out>, errormsg=...) at BSPPolarisSlave.cpp:443
                  443			mpMainWindow->show();
                  (gdb) p mpMainWindow
                  $1 = (BSPPolarisSlaveMainWindow *) 0x555556627c40
                  

                  Some things I noticed are:

                  • mpMainWindow is not nullptr.
                  • In the call to BSPPolarisSlave::mfRun argc and argv are marked as 'optimized out'... and similarly, in the call to QWidget::show, the this parameter is also 'optimized out'. I have not much experience with gdb (most of the time, I debug in the Visual Studio debugger)... but could this 'optimizing out' be the problem?
                  J.HilkJ Offline
                  J.HilkJ Offline
                  J.Hilk
                  Moderators
                  wrote on last edited by
                  #20

                  @Bart_Vandewoestyne said in Segfault when calling QWidget::show (on Debian 9):

                  mpMainWindow is not nullptr

                  are you sure it is initialised then ? gdb, in contrast to its MSVC equivalent, does no null initialisations during debug runs. So an uninitialised pointer is very rarely a nullptr


                  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.

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                  • J.HilkJ J.Hilk

                    @Bart_Vandewoestyne said in Segfault when calling QWidget::show (on Debian 9):

                    mpMainWindow is not nullptr

                    are you sure it is initialised then ? gdb, in contrast to its MSVC equivalent, does no null initialisations during debug runs. So an uninitialised pointer is very rarely a nullptr

                    B Offline
                    B Offline
                    Bart_Vandewoestyne
                    wrote on last edited by
                    #21

                    @J-Hilk said in Segfault when calling QWidget::show (on Debian 9):

                    are you sure it is initialised then ? gdb, in contrast to its MSVC equivalent, does no null initialisations during debug runs. So an uninitialised pointer is very rarely a nullptr

                    For as far as I can see yes, because right before the call to show(), the pointer is initialized:

                    mpMainWindow = new BSPPolarisSlaveMainWindow(this, windowsCaption, 0, true, Qt::Window | Qt::WindowTitleHint | Qt::WindowSystemMenuHint);
                    connect(mpApplication, SIGNAL(lastWindowClosed()), mpApplication, SLOT(quit()));
                    mpMainWindow->show();
                    
                    1 Reply Last reply
                    0
                    • Christian EhrlicherC Christian Ehrlicher

                      @Bart_Vandewoestyne said in Segfault when calling QWidget::show (on Debian 9):

                      allowed to share any code.

                      Then good luck. We can't guess your code...

                      Apart from this you already shared code.

                      B Offline
                      B Offline
                      Bart_Vandewoestyne
                      wrote on last edited by
                      #22

                      @Christian-Ehrlicher said in Segfault when calling QWidget::show (on Debian 9):

                      Then good luck. We can't guess your code...

                      Apart from this you already shared code.

                      In the past on this forum, I've had good answers leading to a solution even without sharing code. I do believe that's possible :-)

                      And you are right: I have shared some code snippets. That is indeed not consistent with what I wrote, but I am somehow assuming that I am allowed to share small, non meaningful snippets of code that do not reveal any company secrets, if that can help us get to a solution quicker. I hope no one in our company will blame me for that... Finding the right balance between what you can share in order to get to a solution quicker is not always easy, but I try to find that balance.

                      1 Reply Last reply
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                      • B Offline
                        B Offline
                        Bart_Vandewoestyne
                        wrote on last edited by
                        #23

                        Some more info on this problem:

                        • It is only a release build on Debian 9 that segfaults. As mentioned earlier, the debug build on Debian 9 runs fine.
                        • Release builds and debug builds on Debian 8 and Red Hat Enterprise Linux 8.5 run fine!
                        J.HilkJ 1 Reply Last reply
                        0
                        • Christian EhrlicherC Christian Ehrlicher

                          @Bart_Vandewoestyne said in Segfault when calling QWidget::show (on Debian 9):

                          the call to QApplication(argc, argv) happens in ICService::mfExec

                          Some code would be good...
                          You already posted a link with the solution but ignored it constantly - Q(Core)Application takes a reference to an int so the callers should pass this to. Otherwise there might be a dangling reference. But without code...

                          wrt to your strange copy stuff (whyever you need to modify your command line - sounds like a strange hack for me):

                          std::vector<char*> newArgs;
                          newArgs.push_back(argv[0]);
                          newArgs.push_back(const_cast<char*>("-e"));
                          for (int i = 1; i < argc; ++i)
                            newArgs.push_back(argv[i]);
                          argc += 1;
                          ...mfParseArguments(argc, newArgs.data());
                          
                          B Offline
                          B Offline
                          Bart_Vandewoestyne
                          wrote on last edited by
                          #24

                          @Christian-Ehrlicher said in Segfault when calling QWidget::show (on Debian 9):

                          wrt to your strange copy stuff (whyever you need to modify your command line - sounds like a strange hack for me):

                          std::vector<char*> newArgs;
                          newArgs.push_back(argv[0]);
                          newArgs.push_back(const_cast<char*>("-e"));
                          for (int i = 1; i < argc; ++i)
                            newArgs.push_back(argv[i]);
                          argc += 1;
                          ...mfParseArguments(argc, newArgs.data());
                          

                          I totally agree that that modification of the command line is strange. Note that this was not my idea, but I inherited this legacy code from my predecessors :-(
                          I tried your suggestion using std::vector instead of using an array of char*, but that also didn't solve the segfault.

                          JonBJ 1 Reply Last reply
                          0
                          • B Bart_Vandewoestyne

                            @Christian-Ehrlicher said in Segfault when calling QWidget::show (on Debian 9):

                            wrt to your strange copy stuff (whyever you need to modify your command line - sounds like a strange hack for me):

                            std::vector<char*> newArgs;
                            newArgs.push_back(argv[0]);
                            newArgs.push_back(const_cast<char*>("-e"));
                            for (int i = 1; i < argc; ++i)
                              newArgs.push_back(argv[i]);
                            argc += 1;
                            ...mfParseArguments(argc, newArgs.data());
                            

                            I totally agree that that modification of the command line is strange. Note that this was not my idea, but I inherited this legacy code from my predecessors :-(
                            I tried your suggestion using std::vector instead of using an array of char*, but that also didn't solve the segfault.

                            JonBJ Online
                            JonBJ Online
                            JonB
                            wrote on last edited by JonB
                            #25

                            @Bart_Vandewoestyne
                            Just so you know. Your segfault emanates from this line: https://code.woboq.org/kde/qt4/src/gui/kernel/qwidget_x11.cpp.html#804

                                    XSetWMProperties(dpy, id, 0, 0,
                                                     qApp->d_func()->argv, qApp->d_func()->argc,
                                                     &size_hints, &wm_hints, &class_hint);
                            

                            (Doubtless some sort of X set window manager properties on start up?) It's on a strlen() from there, so presumably some element in qApp->d_func()->argv is wrong. So you're still on the argv issue. Try to print out everything in the last argv you pass on.

                            1 Reply Last reply
                            1
                            • B Bart_Vandewoestyne

                              Some more info on this problem:

                              • It is only a release build on Debian 9 that segfaults. As mentioned earlier, the debug build on Debian 9 runs fine.
                              • Release builds and debug builds on Debian 8 and Red Hat Enterprise Linux 8.5 run fine!
                              J.HilkJ Offline
                              J.HilkJ Offline
                              J.Hilk
                              Moderators
                              wrote on last edited by J.Hilk
                              #26

                              @Bart_Vandewoestyne new debian, huh. New/updated compiler then as well?

                              I assume you have tried the release build with -O0 ?


                              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.

                              Christian EhrlicherC B 2 Replies Last reply
                              0
                              • J.HilkJ J.Hilk

                                @Bart_Vandewoestyne new debian, huh. New/updated compiler then as well?

                                I assume you have tried the release build with -O0 ?

                                Christian EhrlicherC Online
                                Christian EhrlicherC Online
                                Christian Ehrlicher
                                Lifetime Qt Champion
                                wrote on last edited by
                                #27

                                @J-Hilk or run it with valgrind (compile with -O2 and -g)

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                                J.HilkJ B 3 Replies Last reply
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                                • Christian EhrlicherC Christian Ehrlicher

                                  @J-Hilk or run it with valgrind (compile with -O2 and -g)

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                                  J.Hilk
                                  Moderators
                                  wrote on last edited by
                                  #28

                                  @Christian-Ehrlicher never used valgrind before, as I usually don't do linux stuff. But I trust your expertise :D


                                  oh it also now supports macOS, maybe I should give it a try sometime soon than!


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                                  • J.HilkJ J.Hilk

                                    @Bart_Vandewoestyne new debian, huh. New/updated compiler then as well?

                                    I assume you have tried the release build with -O0 ?

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                                    Bart_Vandewoestyne
                                    wrote on last edited by
                                    #29

                                    @J-Hilk said in Segfault when calling QWidget::show (on Debian 9):

                                    @Bart_Vandewoestyne new debian, huh. New/updated compiler then as well?

                                    Yes, due to the switch from Debian 8 to Debian 9, a new compiler as well. Debian 8 (where everything works) has

                                    dev@debian8:~$ g++ --version | head -1
                                    g++ (Debian 4.9.2-10+deb8u2) 4.9.2
                                    

                                    while Debian 9 (where the release build segfaults) has

                                    user@debianvbox:~$ g++ --version | head -1
                                    g++ (Debian 6.3.0-18+deb9u1) 6.3.0 20170516
                                    

                                    I assume you have tried the release build with -O0 ?

                                    I hadn't, but now I have ;-) And I have interesting news: when using -O0 the segfault is gone! From -O1 and further, we get the segfault.

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                                    • Christian EhrlicherC Christian Ehrlicher

                                      @J-Hilk or run it with valgrind (compile with -O2 and -g)

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                                      Bart_Vandewoestyne
                                      wrote on last edited by
                                      #30

                                      @Christian-Ehrlicher said in Segfault when calling QWidget::show (on Debian 9):

                                      @J-Hilk or run it with valgrind (compile with -O2 and -g)

                                      I have no experience with valgrind, but looks like a good suggestion so I will try and report back.

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                                      • Christian EhrlicherC Christian Ehrlicher

                                        @J-Hilk or run it with valgrind (compile with -O2 and -g)

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                                        Bart_Vandewoestyne
                                        wrote on last edited by
                                        #31

                                        @Christian-Ehrlicher said in Segfault when calling QWidget::show (on Debian 9):

                                        @J-Hilk or run it with valgrind (compile with -O2 and -g)

                                        OK, so I compiled with -O2 and -g and ran my program through valgrind. This is what I got:

                                        user@debianvbox:~/SVN/PolarisRel/Apps$ valgrind ./PolarisSlave
                                        ==5165== Memcheck, a memory error detector
                                        ==5165== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
                                        ==5165== Using Valgrind-3.12.0.SVN and LibVEX; rerun with -h for copyright info
                                        ==5165== Command: ./PolarisSlave
                                        ==5165== 
                                        ==5165== Invalid read of size 8
                                        ==5165==    at 0x8B3B205: XSetCommand (in /usr/lib/x86_64-linux-gnu/libX11.so.6.3.0)
                                        ==5165==    by 0x8B3F7EF: XSetWMProperties (in /usr/lib/x86_64-linux-gnu/libX11.so.6.3.0)
                                        ==5165==    by 0x5EE707C: QWidgetPrivate::create_sys(unsigned long, bool, bool) (in /home/user/SVN/PolarisRel/ThirdParty/Qt/qt-install/lib/libQtGui.so.4.8.7)
                                        ==5165==    by 0x5E9F768: QWidget::create(unsigned long, bool, bool) (in /home/user/SVN/PolarisRel/ThirdParty/Qt/qt-install/lib/libQtGui.so.4.8.7)
                                        ==5165==    by 0x5EA7696: QWidget::setVisible(bool) (in /home/user/SVN/PolarisRel/ThirdParty/Qt/qt-install/lib/libQtGui.so.4.8.7)
                                        ==5165==    by 0x4FE1FC: show (qwidget.h:497)
                                        ==5165==    by 0x4FE1FC: BSPPolarisSlave::mfRun(int, char**, QString&) (BSPPolarisSlave.cpp:443)
                                        ==5165==    by 0x7B50D9: ICService::mfExec(int, char**, QString&, bool) (in /home/user/SVN/PolarisRel/Apps/PolarisSlave)
                                        ==5165==    by 0x7B190D: ICService::mfParseArguments(int, char**, bool) (in /home/user/SVN/PolarisRel/Apps/PolarisSlave)
                                        ==5165==    by 0x501BB2: BSPPolarisSlave::mfParseArguments(int, char**) (BSPPolarisSlave.cpp:659)
                                        ==5165==    by 0x4DE3AC: main (BSPPolarisSlaveMain.cpp:71)
                                        ==5165==  Address 0xbe71780 is 0 bytes after a block of size 16 alloc'd
                                        ==5165==    at 0x4C2C93F: operator new[](unsigned long) (vg_replace_malloc.c:423)
                                        ==5165==    by 0x501A27: BSPPolarisSlave::mfParseArguments(int, char**) (BSPPolarisSlave.cpp:637)
                                        ==5165==    by 0x4DE3AC: main (BSPPolarisSlaveMain.cpp:71)
                                        ==5165== 
                                        ==5165== Invalid read of size 1
                                        ==5165==    at 0x4C2EDA2: strlen (vg_replace_strmem.c:454)
                                        ==5165==    by 0x8B3B1EC: XSetCommand (in /usr/lib/x86_64-linux-gnu/libX11.so.6.3.0)
                                        ==5165==    by 0x8B3F7EF: XSetWMProperties (in /usr/lib/x86_64-linux-gnu/libX11.so.6.3.0)
                                        ==5165==    by 0x5EE707C: QWidgetPrivate::create_sys(unsigned long, bool, bool) (in /home/user/SVN/PolarisRel/ThirdParty/Qt/qt-install/lib/libQtGui.so.4.8.7)
                                        ==5165==    by 0x5E9F768: QWidget::create(unsigned long, bool, bool) (in /home/user/SVN/PolarisRel/ThirdParty/Qt/qt-install/lib/libQtGui.so.4.8.7)
                                        ==5165==    by 0x5EA7696: QWidget::setVisible(bool) (in /home/user/SVN/PolarisRel/ThirdParty/Qt/qt-install/lib/libQtGui.so.4.8.7)
                                        ==5165==    by 0x4FE1FC: show (qwidget.h:497)
                                        ==5165==    by 0x4FE1FC: BSPPolarisSlave::mfRun(int, char**, QString&) (BSPPolarisSlave.cpp:443)
                                        ==5165==    by 0x7B50D9: ICService::mfExec(int, char**, QString&, bool) (in /home/user/SVN/PolarisRel/Apps/PolarisSlave)
                                        ==5165==    by 0x7B190D: ICService::mfParseArguments(int, char**, bool) (in /home/user/SVN/PolarisRel/Apps/PolarisSlave)
                                        ==5165==    by 0x501BB2: BSPPolarisSlave::mfParseArguments(int, char**) (BSPPolarisSlave.cpp:659)
                                        ==5165==    by 0x4DE3AC: main (BSPPolarisSlaveMain.cpp:71)
                                        ==5165==  Address 0x50 is not stack'd, malloc'd or (recently) free'd
                                        ==5165== 
                                        ==5165== 
                                        ==5165== Process terminating with default action of signal 11 (SIGSEGV)
                                        ==5165==  Access not within mapped region at address 0x50
                                        ==5165==    at 0x4C2EDA2: strlen (vg_replace_strmem.c:454)
                                        ==5165==    by 0x8B3B1EC: XSetCommand (in /usr/lib/x86_64-linux-gnu/libX11.so.6.3.0)
                                        ==5165==    by 0x8B3F7EF: XSetWMProperties (in /usr/lib/x86_64-linux-gnu/libX11.so.6.3.0)
                                        ==5165==    by 0x5EE707C: QWidgetPrivate::create_sys(unsigned long, bool, bool) (in /home/user/SVN/PolarisRel/ThirdParty/Qt/qt-install/lib/libQtGui.so.4.8.7)
                                        ==5165==    by 0x5E9F768: QWidget::create(unsigned long, bool, bool) (in /home/user/SVN/PolarisRel/ThirdParty/Qt/qt-install/lib/libQtGui.so.4.8.7)
                                        ==5165==    by 0x5EA7696: QWidget::setVisible(bool) (in /home/user/SVN/PolarisRel/ThirdParty/Qt/qt-install/lib/libQtGui.so.4.8.7)
                                        ==5165==    by 0x4FE1FC: show (qwidget.h:497)
                                        ==5165==    by 0x4FE1FC: BSPPolarisSlave::mfRun(int, char**, QString&) (BSPPolarisSlave.cpp:443)
                                        ==5165==    by 0x7B50D9: ICService::mfExec(int, char**, QString&, bool) (in /home/user/SVN/PolarisRel/Apps/PolarisSlave)
                                        ==5165==    by 0x7B190D: ICService::mfParseArguments(int, char**, bool) (in /home/user/SVN/PolarisRel/Apps/PolarisSlave)
                                        ==5165==    by 0x501BB2: BSPPolarisSlave::mfParseArguments(int, char**) (BSPPolarisSlave.cpp:659)
                                        ==5165==    by 0x4DE3AC: main (BSPPolarisSlaveMain.cpp:71)
                                        ==5165==  If you believe this happened as a result of a stack
                                        ==5165==  overflow in your program's main thread (unlikely but
                                        ==5165==  possible), you can try to increase the size of the
                                        ==5165==  main thread stack using the --main-stacksize= flag.
                                        ==5165==  The main thread stack size used in this run was 8388608.
                                        ==5165== 
                                        ==5165== HEAP SUMMARY:
                                        ==5165==     in use at exit: 1,121,308 bytes in 9,104 blocks
                                        ==5165==   total heap usage: 22,310 allocs, 13,206 frees, 4,039,124 bytes allocated
                                        ==5165== 
                                        ==5165== LEAK SUMMARY:
                                        ==5165==    definitely lost: 2,944 bytes in 6 blocks
                                        ==5165==    indirectly lost: 13,190 bytes in 537 blocks
                                        ==5165==      possibly lost: 54,718 bytes in 437 blocks
                                        ==5165==    still reachable: 1,050,456 bytes in 8,124 blocks
                                        ==5165==         suppressed: 0 bytes in 0 blocks
                                        ==5165== Rerun with --leak-check=full to see details of leaked memory
                                        ==5165== 
                                        ==5165== For counts of detected and suppressed errors, rerun with: -v
                                        ==5165== ERROR SUMMARY: 5 errors from 2 contexts (suppressed: 0 from 0)
                                        Segmentation fault
                                        

                                        I'll try to decipher this myself, but if in the meanwhile someone more experienced with valgrind can point me in the right direction, that would be nice :-)

                                        kshegunovK 1 Reply Last reply
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                                        • J.HilkJ Offline
                                          J.HilkJ Offline
                                          J.Hilk
                                          Moderators
                                          wrote on last edited by
                                          #32

                                          from my point of view, I would say the issue is with your strange string manipulation stuff.

                                          You have to be very careful, when working with stringliterals, it is super easy to run into undefined behaviour, when you try to modify them.


                                          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.

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