Trouble cross compiling OpenCV for ARM9 Montavista Linux

Question

I'm trying to cross-compile the OpenCV library for using it on an embedded system running Montavista Linux(the system has an ARM926 processor). I've managed to configure and generate the makefiles; the sources are built OK, including the 3rd party libraries. The trouble comes at link time. For some reason libtool picks some libraries from the host system (libjpeg, libtiff, libpng) and tries to link them against the ARM9 object files(which evidently is wrong). The error I get is

/usr/lib/libpng12.so: could not read symbols: File in wrong format.

I couldn't and I still can't figure out what exactly is wrong with my setup(I even tried to build the library directly on the ARM9 system but unfortunately it has a very small amount of RAM and gcc chokes). I also modified the LD_LIBRARY_PATH envvar to contain the target's system libraries and exported it before running configure and make. Below is what I pass to configure:

LDFLAGS="-L/opt/Montavista/pro/devkit/arm/v5t_le/target/usr/lib" CFLAGS="-I/opt
/Montavista/pro/devkit/arm/v5t_le/target/usr/include -fsigned-char -march=armv5te
-mtune=arm926ej-s -ffast-math -fomit-frame-pointer -funroll-loops" CC=/opt/Montavista
/pro/devkit/arm/v5t_le/bin/arm_v5t_le-gcc CXXFLAGS="-fsigned-char -march=armv5te 
-mtune=arm926ej-s -ffast-math -fomit-frame-pointer -funroll-loops" CXX=/opt/Montavista
/pro/devkit/arm/v5t_le/bin/arm_v5t_le-g++ ./configure --host=armv5tl-montavista-linux-
gnueabi --without-gtk --without-v4l --without-carbon --without-quicktime --without-
1394libs --without-ffmpeg --without-imageio --without-python --without-swig --enable-
static --enable-shared --disable-apps --prefix=/home/dev/Development/lib

I found this question on SO but unfortunately it does not provide a solution for me.

I'm using gcc version 4.2.0 (MontaVista 4.2.0-16.0.32.0801914 2008-08-30) on Montavista Linux for ARM(Leopard board powered by a TI DM365), OpenCV 2.0.0. My host system is Ubuntu 10.4. Any pointers on how to tackle this issue would be of very much help.

Thanks

[UPDATE][SOLVED]: The autotools based method of generating the makefiles for OpenCV 2.0.0 seems to be broken when trying cross-compiling(or for some odd reason it did not work for me). I used the CMake GUI and specified a proper toolchain.cmake file and everything went smooth.

Answer 1

It seems you are using an old version of OpenCv since it still uses the .configure mechanism. This is good in a sense, because CMake is not known to be cross-compilation friendly.

LDFLAGS="-L/opt/Montavista/pro/devkit/arm/v5t_le/target/usr/lib"

This is were the linker will look for libraries. It should be enough. Are you sure the libraries needed by OpenCV are in this PATH ?

A first Hack would be to rename the libraries in /usr/lib, so that the linker don't find them, and see if it find the target libraries. This is ugly, maybe more than ugly. Don't do it. Yet.

A second solution is to do native compilation. But it an emulated ARM box, not on real, slow and memory poor hardware. I have no experience either with this kind of cross-compile method, but here is a link to get you started.

EDIT Wait !!, Which version of OpenCV are you using ? I thought OpenCV was not using .configure et al. ? There is probably a more elegant solution using .configure flags. Or maybe non optionnal libraries are somehow hardcoded.

Answer 2

Interestingly I'm currently trying to get version 2.1.0 to build for ARM. It relies on cmake which is a real pain to try to get ready for cross-compiling. There's no way to specify what toolchain to use, I have to spot the variable names for all binutils, hoping not to forget any. There are still a bunch of magically defined variables that prevent it from building, I'm giving up right now. I'm still seeing some -march=i686 magically appended and some libs referenced from my build system. What a mess !

Maybe when I have time I'll try to downgrade to an older version making use of more standard tools, but cmake clearly complicates the situation here.