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QFontDatabase causes Segfault [Solved]

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  • P Offline
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    Pippin
    wrote on last edited by Pippin
    #1

    Hello,

    I was getting a segmentation fault out of the line

    auto s = QFontDatabase::addApplicationFont("construct/Type.ttf");

    and I wasn't sure why that was. After some testing, I tried the line

    QFontDatabase k;

    and I got a segmentation fault out of it, too. (Valgrind tells me there's something in the constructor that causes the segfault.) I don't understand. I'm including <QFontDatabase> and all. Any ideas?

    Thanks in advance.

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    • SGaistS Offline
      SGaistS Offline
      SGaist
      Lifetime Qt Champion
      wrote on last edited by
      #2

      Hi,

      What does the debugger tell you ?

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      Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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      • SGaistS SGaist

        Hi,

        What does the debugger tell you ?

        P Offline
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        Pippin
        wrote on last edited by
        #3

        @SGaist What do you mean?

        Valgrind says

        ==5551==    at 0x672E3FA: ??? (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.2.1)
        ==5551==    by 0x672E460: QFontDatabase::QFontDatabase() (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.2.1)
        
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        • SGaistS Offline
          SGaistS Offline
          SGaist
          Lifetime Qt Champion
          wrote on last edited by SGaist
          #4

          I mean: what is the stack trace when you run your application through the debugger ? In your case, gdb

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          Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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          • P Offline
            P Offline
            Pippin
            wrote on last edited by
            #5

            I get this:

            ./Menu[0x4611fd]
            /lib/x86_64-linux-gnu/libpthread.so.0(+0x10340)[0x7fe46bebc340]
            /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5(+0x1743fa)[0x7fe46c8e43fa]
            /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5(_ZN13QFontDatabaseC2Ev+0x41)[0x7fe46c8e4461]
            ./Menu[0x429172]
            ./Menu[0x412b3d]
            /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf5)[0x7fe46b26fec5]
            ./Menu[0x412f10]
            
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            • SGaistS Offline
              SGaistS Offline
              SGaist
              Lifetime Qt Champion
              wrote on last edited by
              #6

              You should run a debug build of your application, it will give more precise information.

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              Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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              • SGaistS SGaist

                You should run a debug build of your application, it will give more precise information.

                P Offline
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                Pippin
                wrote on last edited by
                #7

                @SGaist I'm already compiling with QMAKE_CXXFLAGS += -std=c++14 -Wall -Wextra -pedantic -g -ggdb -rdynamic, what exactly would you like me to do?

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                • SGaistS Offline
                  SGaistS Offline
                  SGaist
                  Lifetime Qt Champion
                  wrote on last edited by
                  #8

                  Did you set these flags your self or use Qt Creator Run in debug mode ?

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                  Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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                  • P Offline
                    P Offline
                    Pippin
                    wrote on last edited by Pippin
                    #9

                    I set these flags myself, I never use Qt Creator for anything. I compile and run everything through the terminal with qmake and make

                    There was also this line though: QMutex: destroying locked mutex but I'm not using any mutex.

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                    • SGaistS Offline
                      SGaistS Offline
                      SGaist
                      Lifetime Qt Champion
                      wrote on last edited by
                      #10

                      Try again with CONFIG+=debug. You currently build a debug version of your app running against a release build of Qt.

                      You might not be using mutex directly but depending on what part of Qt you use, Qt is.

                      Interested in AI ? www.idiap.ch
                      Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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                      • SGaistS SGaist

                        Try again with CONFIG+=debug. You currently build a debug version of your app running against a release build of Qt.

                        You might not be using mutex directly but depending on what part of Qt you use, Qt is.

                        P Offline
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                        Pippin
                        wrote on last edited by
                        #11

                        @SGaist I've added CONFIG+=debug in the .pro file but the outcome is the same.:S

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                        • SGaistS Offline
                          SGaistS Offline
                          SGaist
                          Lifetime Qt Champion
                          wrote on last edited by
                          #12

                          Do you have the Qt debug package for your distribution installed ?

                          Interested in AI ? www.idiap.ch
                          Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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                          • SGaistS SGaist

                            Do you have the Qt debug package for your distribution installed ?

                            P Offline
                            P Offline
                            Pippin
                            wrote on last edited by
                            #13

                            @SGaist I've just installed qtbase5-dbg to make sure, but the result remains the same.

                            Anyway, do we really need to get more information about what exactly is causing the segmentation fault in QFontDatabase::QFontDatabase ? It seems that almost anything in <QFontDatabase> causes a segmentation fault. Well, at least QFontDatabase::QFontDatabase and QFontDatabase::addApplicationFont do.

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                            • P Offline
                              P Offline
                              Pippin
                              wrote on last edited by Pippin
                              #14

                              Wait, Valgrind seems to be more accurate than the stack trace for some reason.

                              ==2786==    at 0x672E3FA: initializeDb() (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.2.1)
                              ==2786==    by 0x672E460: QFontDatabase::QFontDatabase() (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.2.1)
                              

                              I don't know how to get more info.

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                              • SGaistS Offline
                                SGaistS Offline
                                SGaist
                                Lifetime Qt Champion
                                wrote on last edited by
                                #15

                                When are you using it in your application ?

                                Interested in AI ? www.idiap.ch
                                Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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                                • SGaistS SGaist

                                  When are you using it in your application ?

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                                  Pippin
                                  wrote on last edited by Pippin
                                  #16

                                  @SGaist

                                  int main(int argc, char *argv[])
                                  {
                                  	DS::Initialize();
                                  	\\ ...
                                  }
                                  

                                  where DS::Initialize is a static function of the class DSĀ :

                                  void DS::Initialize(void)
                                  {
                                  	struct sigaction act;
                                  	sigemptyset(&act.sa_mask);
                                  	act.sa_handler = ::Handler;
                                  	act.sa_flags = 0;
                                  	sigaction(SIGSEGV, &act, 0);
                                  	
                                  	QFontDatabase k;
                                  	std::cout << "foo" << std::endl;
                                  	auto s = QFontDatabase::addApplicationFont("construct/Type.ttf");
                                  	std::cout << "foo" << std::endl;
                                  	\\ ...
                                  }
                                  
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                                  • SGaistS Offline
                                    SGaistS Offline
                                    SGaist
                                    Lifetime Qt Champion
                                    wrote on last edited by
                                    #17

                                    You're missing a QGuiApplication in order to use QFontDatabase

                                    Interested in AI ? www.idiap.ch
                                    Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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                                    • SGaistS SGaist

                                      You're missing a QGuiApplication in order to use QFontDatabase

                                      P Offline
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                                      Pippin
                                      wrote on last edited by Pippin
                                      #18

                                      @SGaist So it was only a matter of order! It works now, thank you so much! How do I add <Solved> ?

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                                      • SGaistS Offline
                                        SGaistS Offline
                                        SGaist
                                        Lifetime Qt Champion
                                        wrote on last edited by
                                        #19

                                        You're welcome !

                                        Just edit the thread title a prepend it or rather [solved] so that the forum can pick it up and modify the view accordingly :)

                                        Interested in AI ? www.idiap.ch
                                        Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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