[CMake] absolute library path, sorry for the question

[Mario Emmenlauer]

Dear cmake users,

I have found good documentation on the cmake wiki about RPATH and
its different variables, and also on the mailing lists. But somehow
it still does not add up for me. Can you please help?

I use cmake 3.9.5 on different platforms, CentOS 6 and Ubuntu 14.04
amongst others. I build many standard libraries (like tiff and jpeg)
into my own thirdparty directory, and set CMAKE_PREFIX_PATH to find
them there. On newer Linux and Windows, cmake uses always the absolute
path to those libraries, and everything works fine. But on older Linux
like Ubuntu 14.04 and CentOS 6 it does not. cmake will first find the
library in the correct absolute thirdparty directory, and I can confirm
this by printing the 'XXX_LIBRARIES' variable in the find script. But
later the Makefile will link with '-lxxx' instead of the full path.
This makes 'ld' use the system library instead!

I completely fail to understand at what point cmake changes XXX_LIBRARIES
from an absolute path to '-lxxx', for example for libjpeg.

I have experimented with CMAKE_SKIP_BUILD_RPATH, but it does not help.
The only workaround I could find is to add the thirdparty directory to
LDFLAGS. Then 'ld' will also find the correct library.


Is this a bug, or an expected behavior? What parameters should I add
when I invoke cmake so that it will always use libraries with their
full path?


Cheers,

    Mario Emmenlauer



PS: since I build thirdparty libraries, I prefer not to change their
CMakeLists.txt but would rather prefer to set better cmake command line
parameters.


References:
https://cmake.org/Wiki/CMake_RPATH_handling
https://cmake.org/pipermail/cmake/2015-September/061462.html



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