[CMake] RPATH cross-compile issue with CHECK_*_EXISTS

[Jörg Krause]

On Mon, 2017-02-27 at 16:33 -0500, Brad King wrote:
> On 02/27/2017 03:50 PM, Jörg Krause wrote:
> > The problem is...
> 
> Thanks.  I've opened an issue for this here:
> 
>  https://gitlab.kitware.com/cmake/cmake/issues/16682

Great!

> > > These are set on by default in `Modules/Platform/UnixPaths.cmake`
> > > but
> > > disabled on Debian by `Modules/Platform/Linux.cmake` except when
> > > cross compiling.  If a toolchain file specifies CMAKE_SYSTEM_NAME
> > > such that a custom `Platform/MySystem.cmake` file is loaded then
> > > the latter can set them as needed for the target platform.
> > 
> > Thanks for the hint. We are discussing this setting as a
> > workaround.
> 
> It sounds like this target platform does not want the lib32/lib64
> suffixes to be searched so this would be an appropriate setting
> for the projects to use regardless of what is done about this in
> upstream CMake.  That will also fix it for using CMake 3.7.

Buildroot does not have any problems with searching for libraries in
lib32. It does have a problem with having a host rpath used for linking
with libraries.

So, turning of the search for lib32 is really just a workaround to get
rid of the host rpath.

>From my understanding, there are some possibilities to fix this issue:
1) Prefer to search in lib if FIND_LIBRARY_USE_LIB32_PATHS is enabled,
and only search in lib32 in case the target is not found in lib.
2) Make sure, in case lib32 is a symlink, to follow the symlink.
3) Make sure, in case lib32 is a symlink to lib and is not included in
the linker search paths, to add it to the implicit runtime search
paths.

Any thoughts?

Jörg