This retains the desirable quality of not including paths to CUDA libraries
from the build system into the config files, and has two major advantages:
* It removes the need to use link_directories, which doesn't guarantee that
the libraries from the supplied directory will be used (there may be
libraries with the same names earlier in the search path).
* It removes the need to put -L entries into OPENCV_LINKER_LIBS. This variable
is used with target_link_libraries, where such entries are treated as linker
flags, so doing this is unportable. I remove the support for -L entries
from OpenCVGenPkgconfig.cmake, as well, to discourage adding them in the
future.
Using absolute path to locate the components in the "Libs:" field of the
*.pc can badly break cross-compilation, especially when building
statically linked objects.
Indeed, pkg-config automatically replaces the '-I...' and '-L...' paths
when the PKG_CONFIG_SYSROOT_DIR and PKG_CONFIG_LIBDIR environment
variables are set [1]. This feature is very helpful and common in
cross-compilation framework like Buildroot [2,3].
When there are absolute paths in the *.pc files, pkg-config won't be
able to do the path substitions for these paths when the afromentioned
environment variables are set.
In such case, since the prefix is the target one, not the sysroot one,
these libraries' abolute paths will point to:
- in the best case: a non-existing file (i.e. these files do not exists
on the host system;
- at worst: the host system's libraries. This will make the linking
failed because these host system's libraries will most likely not be
build for the target architecture [4].
So, this patch replace the components' absolute paths by the form:
-L<libdir> -l<libname>
This way, the linker will be able to resolve each dependency path,
whatever the kind of objects/build (shared object or static build) it
is dealing with.
Note that for static link, the library order does matter [5]. The order
of the opencv components has been carefully chosen to comply with this
requirement.
Fixes#3931
[1] http://linux.die.net/man/1/pkg-config
[2] http://buildroot.org/
[3] http://git.buildroot.net/buildroot/tree/package/pkgconf/pkg-config.in
[4] http://autobuild.buildroot.net/results/e8a/e8a859276db34aff87ef181b0cce98916b0afc90/build-end.log
[5] http://stackoverflow.com/questions/45135/linker-order-gcc
Signed-off-by: Samuel Martin <s.martin49@gmail.com>
---
Note: this patch properly applies on top of the master branch, though it
has been written on top of the 2.4 branch.
[~] Automatically tracked dependencies between modules
[+] Support for optional module dependencies
[+] Options to choose modules to build
[~] Removed hardcoded modules lists from OpenCVConfig.cmake, opencv.pc and OpenCV.mk
[+] Added COMPONENTS support for FIND_PACKAGE(OpenCV)
[~] haartraining and traincascade are moved outside of modules folder since they aren't the modules
