Steps to reproduce

1. Clone Qt sources

    
   git clone --branch 5.12.3 https://code.qt.io/qt/qt5 
   cd qt5 
   

2. Initialize repositories

    
   perl init-repository --module-subset=default,-qtwebengine --branch 
   

3. If your Apple Account also does not like the profile "com.yourcompany" you have to change it manually to something else:
   Open file

   <source-code-dir>/qt5/qtbase/mkspecs/features/mac/default_post.prf

   and search for the line

   xcode_product_bundle_identifier_setting.value = "com.yourcompany"

   Modify it to "com.mycompany" (for example). Make sure to add this profile to your Apple-ID!

4. Set environmental variable to allow automatic update of provisioning profiles

    
   export XCODEBUILD_FLAGS = -allowProvisioningUpdates 
   

5. Configure build (with -shared option!)

    
   ./configure -xplatform macx-ios-clang -shared -sdk iphoneos -opensource -nomake examples -nomake tests -shared -skip qtwebengine -skip qtwebglplugin 
   

6. Compile code

    
   make -j 4 
   

Actual behaviour

When qmltime gets linked, the linker throws an error that the symbol lcEventDispatcher() is not defined:

 
Undefined symbols for architecture arm64: 
  "lcEventDispatcher()", referenced from: 
      _qt_main_wrapper in libqios.a(qioseventdispatcher.o) 
      +[QIOSApplicationStateTracker applicationDidFinishLaunching:] in libqios.a(qioseventdispatcher.o) 
      user_main_trampoline() in libqios.a(qioseventdispatcher.o) 
      +[QIOSApplicationStateTracker applicationWillTerminate] in libqios.a(qioseventdispatcher.o) 
      QIOSJumpingEventDispatcher::interruptEventLoopExec() in libqios.a(qioseventdispatcher.o) 
ld: symbol(s) not found for architecture arm64 

Expected behaviour

Compilation without any error

Investigation of the problem

Searching a lot through the code resulted in the following observations:

• lcEventDispatcher is declared as extern in qeventdispatcher_cf_p.h
• lcEventDispatcher gets defined by the macro Q_LOGGING_CATEGORY in qeventdispatcher_cf.mm
• The symbol cannot be found by the linker because in the compiled framework (<build-directory>/qtbase/lib/QtCore.framework/QtCore) the symbol is defined internal but not external
  This can be validated by using nm tool one time with and one time without the -g option:

   
  nm -g --demangle QtCore.framework/QtCore 
  

Suggested Bugfix

Adding Q_CORE_EXPORT in front of the definition of lcEventDispatcher makes the symbol external in the resulting QtCore.framework and fixed the problem for me. In the attachments you can find a patch for the qtbase repository that contains the suggested bugfix.

Open Questions

Why does the symbol do not have automatically external linkage when it is declared external and is not defined with the static keyword?