[CMake] CMake 3.11.3: set properties on the command line?

[Craig Scott]

On Tue, Dec 18, 2018 at 7:42 AM Paul Smith <paul at mad-scientist.net> wrote:

> Hi all.
>
> I'm using cmake with a cross-compiler environment, but building third
> party packages that are configured with CMake.  So when I invoke cmake
> for those packages I add this options to the command line:
>
>   -DCMAKE_FIND_ROOT_PATH=/my/sysroot
>
> However, this is not working because it's finding 32bit libraries.  For
> example if the package's CMakeLists.txt file contains this:
>
>   find_package(ZLIB REQUIRED)
>
> then my link line ends up containing:
>
>   /my/sysroot/usr/lib/libz.so
>
> which is the 32bit version and the link fails.  The 64bit version DOES
> exist exactly as it should:
>
>   $ ls -1 /my/sysroot/usr/lib*/libz.so*
>   /my/sysroot/tools/usr/lib/libz.so
>   /my/sysroot/tools/usr/lib64/libz.so
>
> and the link works if I do it by hand with the right path.  I don't
> know why it's not automatically looking for lib64; I checked and CMake
> knows I want a 64bit build.  For example I see this after running:
>
>   CMakeFiles/3.11.3/CMakeCXXCompiler.cmake:set(CMAKE_CXX_SIZEOF_DATA_PTR
> "8")
>
> Actually I wish cmake would just add "-lz" to the command line and let
> the linker figure it all out rather than trying to second-guess things.
> Then it would "just work".
>
> In any event, if I edit the CMakeLists.txt in the package to set the
> global property FIND_LIBRARY_USE_LIB64_PATHS to ON, then it all works
> fine:
>
>   set_property(GLOBAL PROPERTY FIND_LIBRARY_USE_LIB64_PATHS ON)
>
> But I can't see any way to set that property from the command line,
> without editing the package's CMakeLists.txt file which I obviously
> don't want to do.
>
> Help for either (a) figuring out why cmake incorrectly chooses 32bit
> libraries or (b) setting the property without editing third-party
> CMakeLists.txt files would be much appreciated!!
>


If you are setting your own sysroot, are you using a toolchain file? You
could put your set_property() command in your toolchain file if you're
using one.

If you're not using a toolchain file and don't want to go that route, you
could potentially inject the commands you want using the
CMAKE_PROJECT_<projectName>_INCLUDE
<https://cmake.org/cmake/help/latest/variable/CMAKE_PROJECT_PROJECT-NAME_INCLUDE.html>
feature. It allows you to effectively include a file immediately after a
project() command without having to actually edit the CMakeLists.txt that
contains that project() command.

Those techniques aside, it's interesting that you need to add this manual
workaround at all. I suspect this code
<https://gitlab.kitware.com/cmake/cmake/blob/v3.13.2/Modules/Platform/Linux.cmake#L55>
might be why it is being turned off for you, but without more detail about
your build setup, it's hard to say. If you use a toolchain file and set
CMAKE_SYSTEM_NAME to anything (even the same as the
CMAKE_HOST_SYSTEM_NAME), CMAKE_CROSSCOMPILING will be TRUE, which I suspect
would prevent the problem you're seeing.

-- 
Craig Scott
Melbourne, Australia
https://crascit.com

New book released: Professional CMake: A Practical Guide
<https://crascit.com/professional-cmake/>
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