[Qt-interest] Qt 4.6.1, Qt JPEG plugin and macdeploy: bus error because it loads two copies of the Qt frameworks

[Marco Molteni]

It was one of the strangest bugs ever: QSettings.

I had Qsettings as a static member of a class, allocated via new.  
Well, I learned the hard way: don't do that.

marco

On 2 Feb 2010, at 11:20, Marco Molteni wrote:

> Hi all,
>
> here is my setup: MacOSX 10.5, Qt 4.6.1 (carbon), project built with  
> cmake. I do not play any trick at all in the compilation or linking  
> phase.
> The code loads some JPEG images, and so it uses the libqjpeg.dylib  
> Qt plugin.
>
> The bundle runs correctly as built, with all the references to the  
> Qt frameworks resolved to /Library/Frameworks/QtXXX.
>
> The problem comes if I try to prepare the bundle for deployment,  
> using macdeployqt.
>
> Running macdeployqt works fine, and it creates correctly the  
> Frameworks directory below the bundle directory and also Resources/ 
> qt.conf, mapping the plugins to the local, macdeplyqt-created  
> directory PlugIns. Running otool -L on the various libraries, and  
> also on the plugins seem to give the expected result.
>
> But, when running the bundle prapared by macdeployqt, it gets a bus  
> error. The debug output, by setting DYLD_PRINT_LIBRARIES and  
> QT_DEBUG_PLUGINS is as follows:
>
> $ DYLD_PRINT_LIBRARIES=1 QT_DEBUG_PLUGINS=1 ./Octopus.app/Contents/ 
> MacOS/Octopus 2> q
>
> $ cat q | grep Qt | head -14 | cat -n
>    1	dyld: loaded: /Users/mmolteni/src/octopus-hgsvn/qtcreator-build/ 
> octopus-gui/./Octopus.app/Contents/MacOS/../Frameworks/ 
> QtGui.framework/Versions/4/QtGui
>    2	dyld: loaded: /Users/mmolteni/src/octopus-hgsvn/qtcreator-build/ 
> octopus-gui/./Octopus.app/Contents/MacOS/../Frameworks/ 
> QtXml.framework/Versions/4/QtXml
>    3	dyld: loaded: /Users/mmolteni/src/octopus-hgsvn/qtcreator-build/ 
> octopus-gui/./Octopus.app/Contents/MacOS/../Frameworks/ 
> QtNetwork.framework/Versions/4/QtNetwork
>    4	dyld: loaded: /Users/mmolteni/src/octopus-hgsvn/qtcreator-build/ 
> octopus-gui/./Octopus.app/Contents/MacOS/../Frameworks/ 
> QtCore.framework/Versions/4/QtCore
>    5	QFactoryLoader::QFactoryLoader() looking at "/Developer/ 
> Applications/Qt/plugins/imageformats/libqgif.dylib"
>    6	QFactoryLoader::QFactoryLoader() looking at "/Developer/ 
> Applications/Qt/plugins/imageformats/libqico.dylib"
>    7	QFactoryLoader::QFactoryLoader() looking at "/Developer/ 
> Applications/Qt/plugins/imageformats/libqjpeg.dylib"
>    8	QFactoryLoader::QFactoryLoader() looking at "/Developer/ 
> Applications/Qt/plugins/imageformats/libqmng.dylib"
>    9	QFactoryLoader::QFactoryLoader() looking at "/Developer/ 
> Applications/Qt/plugins/imageformats/libqsvg.dylib"
>   10	QFactoryLoader::QFactoryLoader() looking at "/Developer/ 
> Applications/Qt/plugins/imageformats/libqtiff.dylib"
>   11	dyld: loaded: /Developer/Applications/Qt/plugins/imageformats/ 
> libqjpeg.dylib
>   12	dyld: loaded: /Library/Frameworks/QtGui.framework/Versions/4/ 
> QtGui
>   13	dyld: loaded: /Library/Frameworks/QtCore.framework/Versions/4/ 
> QtCore
>   14	On Mac OS X, you might be loading two sets of Qt binaries into  
> the same process. Check that all plugins are compiled against the  
> right Qt binaries. Export DYLD_PRINT_LIBRARIES=1 and check that only  
> one set of binaries are being loaded.
>
>
> So as you can see, lines 1-4 are what I would expect, the linker is  
> loading the right frameworks, but then at line 5, Qt for some  
> reasons doesn't follow the qt.conf file and instead loads the system- 
> installed Qt plugins, that then, at line 12, cause to load a second  
> copy of QtGui, and so on.
>
> I spent a lot of time trying to debug this, I would appreciate any  
> help before giving up and compiling Qt static from source :-(
>
> thanks
> marco