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Qt 6 undefined reference to WinMain on MinGW

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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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    0
    • 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
      0
      • 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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        0
        • 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/
          Visit the Qt Academy at https://academy.qt.io/catalog

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          1
          • 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
              4
              • 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
                1
                • 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
                    0
                    • 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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                        0
                        • 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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                          2
                          • 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.

                                1 Reply Last reply
                                0
                                • 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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