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Qt 6 undefined reference to WinMain on MinGW

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  • Christian EhrlicherC Christian Ehrlicher

    I've not problems with Qt6.0.3 (binaries installed through installer). Maybe try to explicitly link against Qt6::EntryPoint. All this magic with WinMain (=subsystem Windows) or main (=subsystem Console) is done in qtentrypoint_win.cpp

    VRoninV Offline
    VRoninV Offline
    VRonin
    wrote on last edited by
    #3

    @Christian-Ehrlicher This was a good guess but unfortunately didn't fix the problem

    "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
    ~Napoleon Bonaparte

    On a crusade to banish setIndexWidget() from the holy land of Qt

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    • Christian EhrlicherC Offline
      Christian EhrlicherC Offline
      Christian Ehrlicher
      Lifetime Qt Champion
      wrote on last edited by
      #4

      But this really has to do something with the subsystem. Maybe you have to add WIN32 (or accidentally added it): https://cmake.org/cmake/help/latest/prop_tgt/WIN32_EXECUTABLE.html#prop_tgt:WIN32_EXECUTABLE . But strange that it works fine for me...

      Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
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      • VRoninV Offline
        VRoninV Offline
        VRonin
        wrote on last edited by
        #5

        I still don't understand why, if the library target is a static lib, everything works fine.
        Qt 6.1 exibits the same problem.

        I created a minimal example repository. If someone is using Qt 6 on MinGW 8.1 64 bits, can please clone it, add the CMake variable BUILD_SHARED_LIBS=ON and build it?
        I'm starting to think it might be a problem of the CI machine

        "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
        ~Napoleon Bonaparte

        On a crusade to banish setIndexWidget() from the holy land of Qt

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        • Christian EhrlicherC Offline
          Christian EhrlicherC Offline
          Christian Ehrlicher
          Lifetime Qt Champion
          wrote on last edited by Christian Ehrlicher
          #6

          As expected it's the WIN32 keyword in add_executable()
          Without this the linking works fine (because then the entry point is main and not WinMain). Now I've something to play with.

          btw: you forgot to specify the BUILD_SHARED_LIBS as OPTION.

          /edit: now it compiles and links fine without any changes on my side !?

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

          VRoninV 1 Reply Last reply
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          • Christian EhrlicherC Christian Ehrlicher

            As expected it's the WIN32 keyword in add_executable()
            Without this the linking works fine (because then the entry point is main and not WinMain). Now I've something to play with.

            btw: you forgot to specify the BUILD_SHARED_LIBS as OPTION.

            /edit: now it compiles and links fine without any changes on my side !?

            VRoninV Offline
            VRoninV Offline
            VRonin
            wrote on last edited by
            #7

            @Christian-Ehrlicher said in Qt 6 undefined reference to WinMain on MinGW:

            As expected it's the WIN32 keyword in add_executable()

            Yes, confirmed, but it's not acceptable, without that keyword the executable will be a console application (the equivalent of CONFIG += console in qmake).

            btw: you forgot to specify the BUILD_SHARED_LIBS as OPTION.

            It's not an option it's built into CMake

            "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
            ~Napoleon Bonaparte

            On a crusade to banish setIndexWidget() from the holy land of Qt

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            • Christian EhrlicherC Offline
              Christian EhrlicherC Offline
              Christian Ehrlicher
              Lifetime Qt Champion
              wrote on last edited by Christian Ehrlicher
              #8

              @VRonin said in Qt 6 undefined reference to WinMain on MinGW:

              It's not an option it's built into CMake

              'This variable is often added to projects as an option() so that each user of a project can decide if they want to build the project using shared or static libraries.'

              I'm lazy and just want to activate an option :)

              And your new project again gives the linker error when WIN32 is specified

              Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
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              • Christian EhrlicherC Offline
                Christian EhrlicherC Offline
                Christian Ehrlicher
                Lifetime Qt Champion
                wrote on last edited by
                #9

                And one more, please try:

                -target_link_libraries(MyLib PRIVATE Qt6::Core Qt6::Gui Qt6::Widgets)
                +target_link_libraries(MyLib PUBLIC Qt6::Core Qt6::Gui Qt6::Widgets)

                :)

                A cmake problem with some dependencies when a library is linked PRIVATE in a lib and then directly in an application?

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

                VRoninV 1 Reply Last reply
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                • Christian EhrlicherC Offline
                  Christian EhrlicherC Offline
                  Christian Ehrlicher
                  Lifetime Qt Champion
                  wrote on last edited by
                  #10

                  Found it - link order problem: libQt6EntryPoint.a must be after -lmingw32 in the link order (linklibs.rsp). Will dig deeper how to fix it.

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

                  VRoninV 1 Reply Last reply
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                  • Christian EhrlicherC Christian Ehrlicher

                    Found it - link order problem: libQt6EntryPoint.a must be after -lmingw32 in the link order (linklibs.rsp). Will dig deeper how to fix it.

                    VRoninV Offline
                    VRoninV Offline
                    VRonin
                    wrote on last edited by
                    #11

                    @Christian-Ehrlicher ABSOLUTE LEGEND!

                    "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
                    ~Napoleon Bonaparte

                    On a crusade to banish setIndexWidget() from the holy land of Qt

                    1 Reply Last reply
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                    • Christian EhrlicherC Christian Ehrlicher

                      And one more, please try:

                      -target_link_libraries(MyLib PRIVATE Qt6::Core Qt6::Gui Qt6::Widgets)
                      +target_link_libraries(MyLib PUBLIC Qt6::Core Qt6::Gui Qt6::Widgets)

                      :)

                      A cmake problem with some dependencies when a library is linked PRIVATE in a lib and then directly in an application?

                      VRoninV Offline
                      VRoninV Offline
                      VRonin
                      wrote on last edited by
                      #12

                      @Christian-Ehrlicher said in Qt 6 undefined reference to WinMain on MinGW:

                      -target_link_libraries(MyLib PRIVATE Qt6::Core Qt6::Gui Qt6::Widgets)
                      +target_link_libraries(MyLib PUBLIC Qt6::Core Qt6::Gui Qt6::Widgets)

                      This fixes the build for some reason

                      "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
                      ~Napoleon Bonaparte

                      On a crusade to banish setIndexWidget() from the holy land of Qt

                      Christian EhrlicherC 1 Reply Last reply
                      0
                      • VRoninV VRonin

                        @Christian-Ehrlicher said in Qt 6 undefined reference to WinMain on MinGW:

                        -target_link_libraries(MyLib PRIVATE Qt6::Core Qt6::Gui Qt6::Widgets)
                        +target_link_libraries(MyLib PUBLIC Qt6::Core Qt6::Gui Qt6::Widgets)

                        This fixes the build for some reason

                        Christian EhrlicherC Offline
                        Christian EhrlicherC Offline
                        Christian Ehrlicher
                        Lifetime Qt Champion
                        wrote on last edited by
                        #13

                        @VRonin said in Qt 6 undefined reference to WinMain on MinGW:

                        This fixes the build for some reason

                        Linking all Qt libraries private for a shared lib somehow confuses cmake so INTERFACE_LINK_LIBRARIES is not interpreted when linking against this lib and the Qt libraries later on.

                        btw: PRIVATE is not correct, it should be PUBLIC and therefore it was not noticed until now.

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

                        VRoninV 1 Reply Last reply
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                        • Christian EhrlicherC Christian Ehrlicher

                          @VRonin said in Qt 6 undefined reference to WinMain on MinGW:

                          This fixes the build for some reason

                          Linking all Qt libraries private for a shared lib somehow confuses cmake so INTERFACE_LINK_LIBRARIES is not interpreted when linking against this lib and the Qt libraries later on.

                          btw: PRIVATE is not correct, it should be PUBLIC and therefore it was not noticed until now.

                          VRoninV Offline
                          VRoninV Offline
                          VRonin
                          wrote on last edited by VRonin
                          #14

                          @Christian-Ehrlicher said in Qt 6 undefined reference to WinMain on MinGW:

                          PRIVATE is not correct, it should be PUBLIC

                          In this particular case it is indeed wrong but if you think of a library not exposing Qt (for example, a library to read/write xml files that internally uses QXmlStreamReader/QXmlStreamWriterer), the application linking to it might or might not link to Qt itself so PUBLIC in that case would be wrong.
                          If this is unclear I can change the minimal example to show what I mean

                          "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
                          ~Napoleon Bonaparte

                          On a crusade to banish setIndexWidget() from the holy land of Qt

                          Christian EhrlicherC 1 Reply Last reply
                          0
                          • VRoninV VRonin

                            @Christian-Ehrlicher said in Qt 6 undefined reference to WinMain on MinGW:

                            PRIVATE is not correct, it should be PUBLIC

                            In this particular case it is indeed wrong but if you think of a library not exposing Qt (for example, a library to read/write xml files that internally uses QXmlStreamReader/QXmlStreamWriterer), the application linking to it might or might not link to Qt itself so PUBLIC in that case would be wrong.
                            If this is unclear I can change the minimal example to show what I mean

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

                            @VRonin It's not unclear. Just a reason why noone noticed until now :)

                            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 Offline
                              Christian EhrlicherC Offline
                              Christian Ehrlicher
                              Lifetime Qt Champion
                              wrote on last edited by
                              #16

                              https://bugreports.qt.io/browse/QTBUG-93671

                              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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                              • S Offline
                                S Offline
                                supa5000
                                wrote on last edited by
                                #17

                                Dear all,

                                i write here for fellow googlers.

                                I stumbled to this thread with setup of msys2 - toolchain + qt6 binaries "mingw81_64". The project compiled fine under QT5 (and it compiles fine with qt6 on linux / ubuntu 20.04) - but with qt6.1.0 it failed on windows.

                                I did have a library, but it was not qt6 depending, like

                                add_library( foo_common STATIC )
                                add_library( foo_engine  STATIC )
                                target_link_libraries( foo_engine PRIVATE foo_common )
                                ...
                                add_executable( ${NAME} ... )
                                target_link_libraries( ${NAME} PUBLIC Qt6::Widgets )
                                target_link_libraries( ${NAME} PRIVATE foo_common foo_engine )
                                

                                I did try few swap places but it had no effect. Finally i added suggested

                                target_link_libraries( ${NAME} PUBLIC Qt6::EntryPoint)
                                

                                after the existing target_link_libraries calls and it did work.

                                VRoninV 1 Reply Last reply
                                0
                                • S supa5000

                                  Dear all,

                                  i write here for fellow googlers.

                                  I stumbled to this thread with setup of msys2 - toolchain + qt6 binaries "mingw81_64". The project compiled fine under QT5 (and it compiles fine with qt6 on linux / ubuntu 20.04) - but with qt6.1.0 it failed on windows.

                                  I did have a library, but it was not qt6 depending, like

                                  add_library( foo_common STATIC )
                                  add_library( foo_engine  STATIC )
                                  target_link_libraries( foo_engine PRIVATE foo_common )
                                  ...
                                  add_executable( ${NAME} ... )
                                  target_link_libraries( ${NAME} PUBLIC Qt6::Widgets )
                                  target_link_libraries( ${NAME} PRIVATE foo_common foo_engine )
                                  

                                  I did try few swap places but it had no effect. Finally i added suggested

                                  target_link_libraries( ${NAME} PUBLIC Qt6::EntryPoint)
                                  

                                  after the existing target_link_libraries calls and it did work.

                                  VRoninV Offline
                                  VRoninV Offline
                                  VRonin
                                  wrote on last edited by
                                  #18

                                  @supa5000 said in Qt 6 undefined reference to WinMain on MinGW:

                                  I did try few swap places

                                  Try replacing

                                  target_link_libraries( ${NAME} PUBLIC Qt6::Widgets )
                                  target_link_libraries( ${NAME} PRIVATE foo_common foo_engine )
                                  

                                  with

                                  target_link_libraries( ${NAME} PRIVATE foo_common foo_engine Qt6::Widgets)
                                  

                                  while it is a workaround it worked for me

                                  "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
                                  ~Napoleon Bonaparte

                                  On a crusade to banish setIndexWidget() from the holy land of Qt

                                  S 1 Reply Last reply
                                  0
                                  • VRoninV VRonin

                                    @supa5000 said in Qt 6 undefined reference to WinMain on MinGW:

                                    I did try few swap places

                                    Try replacing

                                    target_link_libraries( ${NAME} PUBLIC Qt6::Widgets )
                                    target_link_libraries( ${NAME} PRIVATE foo_common foo_engine )
                                    

                                    with

                                    target_link_libraries( ${NAME} PRIVATE foo_common foo_engine Qt6::Widgets)
                                    

                                    while it is a workaround it worked for me

                                    S Offline
                                    S Offline
                                    supa5000
                                    wrote on last edited by
                                    #19

                                    @VRonin said in Qt 6 undefined reference to WinMain on MinGW:

                                    while it is a workaround it worked for me

                                    Thanks for the detail - i tried but the result remained for some reason the same. I did - to be sure - try fresh (rm -rf build && cd build && cmake ../ && make) build but no effect.

                                    To give the full details the actual link line was (that did not work until the entrypoint explicitly linked below)

                                    target_link_libraries( ${name} PRIVATE foo_common foo_engine Qt6::Widgets Qt6::Qml Qt6::Quick)
                                    # Try2: target_link_libraries( ${name} PRIVATE foo_common foo_engine Qt6::Qml Qt6::Quick Qt6::Widgets)
                                    # enabling this makes the link go ok.
                                    # target_link_libraries( ${name PUBLIC Qt6::EntryPoint)
                                    

                                    i tried also (as comment try2) move the Widgets as the last item but it seemed not have effect.

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                                    • S Offline
                                      S Offline
                                      supa5000
                                      wrote on last edited by
                                      #20

                                      I just pulled 6.2.0 and i stumbled again this; this time the Qt6::Entrypoint target was not found during CMake - so i removed it -- and now i am back with the missing WinMain issue.

                                      Any ideas or updates? The linked bug https://bugreports.qt.io/browse/QTBUG-93671 seems stalled..

                                      1 Reply Last reply
                                      0
                                      • J Offline
                                        J Offline
                                        j255
                                        wrote on last edited by j255
                                        #21

                                        I'm running into this in windows. I've been looking at the qmake -d 2>&1 of a Qt example vs a QWT example. At some point in the QWT qmake generation it seems to loose the entrypoint_private module.

                                        qt example: DEBUG 1: C:/tools/Qt/6.4.2/msvc2019_64/mkspecs/features/qt_functions.prf:379: modules := core gui entrypoint_private
                                        qwt example: DEBUG 1: C:/tools/Qt/6.4.2/msvc2019_64/mkspecs/features/qt_functions.prf:379: modules := core gui printsupport concurrent opengl openglwidgets svg

                                        I haven't been able to figure out the clean fix yet. I ended up diffing the makefiles between the examples and one the major differences was that the QWT example was missing the lib: Qt6EntryPoint.lib
                                        So I added it to the qwt example pro like:
                                        LIBS += C:\Qt\6.4.2\msvc2019_64\lib\Qt6EntryPoint.lib

                                        and then the release version at least built successfully.

                                        note: for diffing the qmake -d output it's handy to do a cut like this (powershell):
                                        qmake -d 2>&1 | % { $_ -split ':' | select -last 1 }

                                        this strips out a lot of paths making the diff easier to scan.
                                        This was using Qwt 6.2.0, git sha:92baef.

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