Re: [Mingw-cross-env-list] QT 4.7.0 p1 qjpeg plug-in missing symbols problem

[Mark Brand]

 HI,

> Hit a snag with qjpeg plug-in on Qt 4.7.0 on mingw-cross, happens on both Linux 
> and OSX qt builds.
> > /opt/mingw/usr/bin/i686-pc-mingw32-qmake -o Makefile qjpeg-test.pro
> > make -f Makefile.Release
> > i686-pc-mingw32-g++ -enable-stdcall-fixup -Wl,-enable-auto-import 
> > -Wl,-enable-runtime-pseudo-reloc -static -Wl,-s -Wl,-subsystem,console 
> > -mthreads -Wl -o release/qjpeg-test.exe release/main.o  
> > -L'/opt/mingw/usr/i686-pc-mingw32/lib' 
> > -L/opt/mingw/usr/i686-pc-mingw32/plugins/imageformats -lqjpeg -lqgif -lqico 
> > -lqsvg -lQtSvg -lQtGui -lgdi32 -lcomdlg32 -loleaut32 -limm32 -lwinmm -lwinspool 
> > -lmsimg32 -lQtCore -lpng -lkernel32 -luser32 -lshell32 -luuid -lole32 
> > -ladvapi32 -lws2_32 -lz
> > /opt/mingw/usr/i686-pc-mingw32/plugins/imageformats/libqjpeg.a(qjpeghandler.o):qjpeghandler.cpp:(.text+0x31a):
> >  undefined reference to `_jpeg_destroy_decompress'
...

> Seems like qjpeg plugin library can not find the symbols in libjpeg.a, though 
> libjpeg.a is definitely there and has the symbols in question.

The problem is that "-ljpeg" is missing from the g++ call. It's not your 
fault. I guess we should blame qmake for not realizing that the qjpeg  
plug-in depends on this.

The same thing happens for qtiff too if you add "qtiff" to QTPLUGIN.

You can help qmake by adding "jpeg" to your QTPLUGIN directive in the 
.pro file.  I think this will work in your .pro file:

QTPLUGIN += qtiff tiff \
            qjpeg jpeg \
            qgif \
            qico \
            qsvg

Of course, if you are willing to use Qt as a shared library you can 
avoid these problems altogether.

> Removing qjpeg plugin from the project allows it to build... so svg, gif and 
> ico plugins are okay.

I'm guessing svg works because of -lQtSvg and that gif and ico work 
because of -lQtGui.

> I wonder could it be trying to link against the native libs as  I see "      
> -system-libjpeg \" in qt.mk:66?  Would that cause the linker to barf as if there 
> were no symbols?

No, "-system-libjpeg" just configures Qt to use the "system" jpeg 
library instead of the jpeg code that ships with Qt.  In our case, the 
"system" jpeg is the one provided by mingw-cross-env.


regards,

Mark