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

From: Mark Brand
Subject: Re: [Mingw-cross-env-list] QT 4.7.0 p1 qjpeg plug-in missing symbols problem
Date: Mon, 21 Jun 2010 21:30:14 +0200
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20100608 SUSE/3.1.0 Thunderbird/3.1


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/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
 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 \

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.



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