Overriding Qt 4.8.1's OpenGL Selection

Question

I have two different libGL libraries on the same Ubuntu 11.04 machine. One library was installed for the Nvidia's graphics card at /usr/lib/libGL.so the other is the default that came installed with Ubuntu, located at usr/lib/x86_64-linux-gnu/mesa/libGL.so.

Now, the problem I have is the Qt library downloaded from Ubuntu's repositories links against the mesa library, but I want to link against Nvidia's library. This will probably give better performance, and there have been issues using mesa's libGL when compiling a program. Those have been fixed by:

export LIBGL_ALWAYS_INDIRECT=1

To my knowledge this forces X11 to choose the openGL library, and it is choosing the correct one. But, I would much rather have Qt and the program that is compiled with QtOpenGL be linking directly with the correct library.

I downloaded Qt and compiled it myself using these options:

./configure -nomake examples -nomake demos -nomake tools -release -no-webkit

I hoped the linker would use the correct library. No dice. Next, I tried editing the mkspec/linux-g++-64/qmake.conf with these variables set:

QMAKE_LIBDIR_X11      = /usr/lib/x86_64-linux-gnu
QMAKE_LIBDIR_OPENGL   = /usr/lib

Is there an option where I can force the linking of a specific library instead of another (specifically when the configure script is run)? I would prefer not to configure the linker in any specific way. I would also rather not remove the mesa library.

If there is no such configure script flag to do so, is there a way to set precedence of libraries the linker uses?

Worst case scenario, I could probably change all the Makefiles after ./configure is run. Grep the entire Qt tree for use of -lGL and change it to /usr/lib/libGL.so. I feel this is quite a hack though.

Update

Some success. I did a grep on the Qt tree for lGL and found that other mkspecs (besides linux-g++-64) used other variables to specify OpenGL path. So I added them to linux-g++-64's mkspec, here's the result of mkspec/linux-g++-64/qmake.conf:

QMAKE_LIBS_OPENGL     = /usr/lib/libGL.so
QMAKE_LIBS_OPENGL_QT  = /usr/lib/libGL.so

So I set the path to the library I wanted directly thinking it would link properly. Indeed it was good news, during the compilation, -lGL was never used. However, the ultimate result was lib/libQtOpenGL.so is still linked with the wrong library:

$ ldd lib/libQtOpenGL.so
    linux-vdso.so.1 =>  (0x00007fffd83ff000)
    libQtGui.so.4 => (edited)lib/libQtGui.so.4 (0x00007f554c684000)
    libQtCore.so.4 => (edited)lib/libQtCore.so.4 (0x00007f554c19c000)
    libfreetype.so.6 => /usr/lib/x86_64-linux-gnu/libfreetype.so.6 (0x00007f554beda000)
    libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f554bcd6000)
    **libGL.so.1 => /usr/lib/x86_64-linux-gnu/mesa/libGL.so.1 (0x00007f554ba7a000)**
    libXrender.so.1 => /usr/lib/x86_64-linux-gnu/libXrender.so.1 (0x00007f554b86e000)
    libX11.so.6 => /usr/lib/x86_64-linux-gnu/libX11.so.6 (0x00007f554b536000)
    libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f554b22f000)
    libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f554afaa000)
    libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f554ad94000)
    libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f554a9f5000)
    libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f554a7d7000)
    libglib-2.0.so.0 => /lib/x86_64-linux-gnu/libglib-2.0.so.0 (0x00007f554a4e1000)
    libpng12.so.0 => /lib/x86_64-linux-gnu/libpng12.so.0 (0x00007f554a2ba000)
    libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007f554a0a1000)
    libSM.so.6 => /usr/lib/x86_64-linux-gnu/libSM.so.6 (0x00007f5549e99000)
    libICE.so.6 => /usr/lib/x86_64-linux-gnu/libICE.so.6 (0x00007f5549c7f000)
    libfontconfig.so.1 => /usr/lib/x86_64-linux-gnu/libfontconfig.so.1 (0x00007f5549a48000)
    libXext.so.6 => /usr/lib/x86_64-linux-gnu/libXext.so.6 (0x00007f5549835000)
    libgthread-2.0.so.0 => /usr/lib/x86_64-linux-gnu/libgthread-2.0.so.0 (0x00007f554962f000)
    librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007f5549427000)
    /lib64/ld-linux-x86-64.so.2 (0x00007f554d66f000)
    libglapi.so.0 => /usr/lib/x86_64-linux-gnu/libglapi.so.0 (0x00007f5549203000)
    libXdamage.so.1 => /usr/lib/x86_64-linux-gnu/libXdamage.so.1 (0x00007f5548fff000)
    libXfixes.so.3 => /usr/lib/x86_64-linux-gnu/libXfixes.so.3 (0x00007f5548df9000)
    libXxf86vm.so.1 => /usr/lib/x86_64-linux-gnu/libXxf86vm.so.1 (0x00007f5548bf3000)
    libdrm.so.2 => /usr/lib/x86_64-linux-gnu/libdrm.so.2 (0x00007f55489e7000)
    libxcb.so.1 => /usr/lib/x86_64-linux-gnu/libxcb.so.1 (0x00007f55487cb000)
    libpcre.so.3 => /lib/x86_64-linux-gnu/libpcre.so.3 (0x00007f554858e000)
    libuuid.so.1 => /lib/x86_64-linux-gnu/libuuid.so.1 (0x00007f5548389000)
    libexpat.so.1 => /lib/x86_64-linux-gnu/libexpat.so.1 (0x00007f554815f000)
    libXau.so.6 => /usr/lib/x86_64-linux-gnu/libXau.so.6 (0x00007f5547f5b000)
    libXdmcp.so.6 => /usr/lib/x86_64-linux-gnu/libXdmcp.so.6 (0x00007f5547d55000)

I have no idea why, I specified directly what library to use and it was passed correctly to g++, but the linker apparently ignored it. I believe it is no longer a Qt problem, but a linker problem.

Is there any way with ldconfig or other tools to specify what library to link to in case of -lGL? I know other libraries have a program which will organize what library to use (libusb-config comes to mine), but I do not think this is the case with openGL.

Answer 1

The linker needs reconfigured to find the correct library for openGL. One such option, often frowned upon is changing the LD_LIBRARY_PATH variable to include the path of the openGL library that you wish you use. In my case it was located at /usr/lib so I changed the variable accordingly.

export LD_LIBRARY_PATH=/usr/lib/fsl/4.1:/usr/lib

After running the ./configure script with the same options and making it, it was finally pointing to the correct library.

ldd lib/libQtOpenGL.so
    linux-vdso.so.1 =>  (0x00007fff04ebf000)
    libQtGui.so.4 => (edited)Qt4.8.1/lib/libQtGui.so.4 (0x00007fad8826c000)
    libQtCore.so.4 => (edited)Qt4.8.1/lib/libQtCore.so.4 (0x00007fad87d84000)
    libfreetype.so.6 => /usr/lib/x86_64-linux-gnu/libfreetype.so.6 (0x00007fad87ac2000)
    libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007fad878be000)
    **libGL.so.1 => /usr/lib/libGL.so.1 (0x00007fad875a8000)**
    libXrender.so.1 => /usr/lib/x86_64-linux-gnu/libXrender.so.1 (0x00007fad8739c000)
    libX11.so.6 => /usr/lib/x86_64-linux-gnu/libX11.so.6 (0x00007fad87064000)
    libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007fad86d5d000)
    libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007fad86ad8000)
    libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007fad868c2000)
    libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fad86523000)
    libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007fad86305000)
    libglib-2.0.so.0 => /lib/x86_64-linux-gnu/libglib-2.0.so.0 (0x00007fad8600f000)
    libpng12.so.0 => /lib/x86_64-linux-gnu/libpng12.so.0 (0x00007fad85de8000)
    libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007fad85bcf000)
    libSM.so.6 => /usr/lib/x86_64-linux-gnu/libSM.so.6 (0x00007fad859c7000)
    libICE.so.6 => /usr/lib/x86_64-linux-gnu/libICE.so.6 (0x00007fad857ad000)
    libfontconfig.so.1 => /usr/lib/x86_64-linux-gnu/libfontconfig.so.1 (0x00007fad85576000)
    libXext.so.6 => /usr/lib/x86_64-linux-gnu/libXext.so.6 (0x00007fad85363000)
    libgthread-2.0.so.0 => /usr/lib/x86_64-linux-gnu/libgthread-2.0.so.0 (0x00007fad8515d000)
    librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007fad84f55000)
    /lib64/ld-linux-x86-64.so.2 (0x00007fad89257000)
    libnvidia-tls.so.290.10 => /usr/lib/tls/libnvidia-tls.so.290.10 (0x00007fad84d52000)
    libnvidia-glcore.so.290.10 => /usr/lib/libnvidia-glcore.so.290.10 (0x00007fad82a4a000)
    libxcb.so.1 => /usr/lib/x86_64-linux-gnu/libxcb.so.1 (0x00007fad8282e000)
    libpcre.so.3 => /lib/x86_64-linux-gnu/libpcre.so.3 (0x00007fad825f1000)
    libuuid.so.1 => /lib/x86_64-linux-gnu/libuuid.so.1 (0x00007fad823ec000)
    libexpat.so.1 => /lib/x86_64-linux-gnu/libexpat.so.1 (0x00007fad821c2000)
    libXau.so.6 => /usr/lib/x86_64-linux-gnu/libXau.so.6 (0x00007fad81fbe000)
    libXdmcp.so.6 => /usr/lib/x86_64-linux-gnu/libXdmcp.so.6 (0x00007fad81db8000)

I believe there is one other possible and probably better alternative. With Ubuntu 11.04, the linker is configured to look in the /usr/lib/x86_64-linux-gnu/mesa/ directory with a configuration file located at /etc/ld.so.conf.d/x86_64-linux-gnu_GL.conf.

If this file is edited to reflect a different path, the linker will probably choose that library instead. It appears that the linker's library search priority is:

LD_LIBRARY_PATH => files located in /etc/ld.so.conf.d => Finally resorting to searching for libraries in default paths.

It is probably a better solution to edit the files accordingly in /etc/ld.so.conf.d, but in my case I do not have the privileges to edit those files so editing LD_LIBRARY_PATH did the trick.