Trying to configure libktorrent (the KF5 version from the master branch) fails to find the GMP library even though a compatible version (6.0.0) is installed: -- Installing in the same prefix as Qt, adopting their path scheme. -- Looking for __GLIBC__ -- Looking for __GLIBC__ - found -- Performing Test _OFFT_IS_64BIT -- Performing Test _OFFT_IS_64BIT - Success -- Found KF5Archive: /usr/kde5/lib64/cmake/KF5Archive/KF5ArchiveConfig.cmake (found version "5.21.0") -- Found KF5Crash: /usr/kde5/lib64/cmake/KF5Crash/KF5CrashConfig.cmake (found version "5.21.0") -- Found Gettext: /usr/bin/msgmerge (found version "0.19.4") -- Found PythonInterp: /usr/bin/python (found version "2.7.10") -- Found KF5I18n: /usr/kde5/lib64/cmake/KF5I18n/KF5I18nConfig.cmake (found version "5.21.0") -- Found KF5KIO: /usr/kde5/lib64/cmake/KF5KIO/KF5KIOConfig.cmake (found version "5.21.0") -- Found KF5Solid: /usr/kde5/lib64/cmake/KF5Solid/KF5SolidConfig.cmake (found version "5.21.0") -- Found KF5: success (found suitable version "5.21.0", minimum required is "5.15") found components: Archive Crash I18n KIO Solid -- Boost version: 1.56.0 CMake Error at /usr/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:148 (message): Could NOT find LibGMP: Found unsuitable version "..", but required is at least "6.0.0" (found /usr/include) Call Stack (most recent call first): /usr/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:386 (_FPHSA_FAILURE_MESSAGE) cmake/FindLibGMP.cmake:75 (find_package_handle_standard_args) CMakeLists.txt:60 (find_package) -- Configuring incomplete, errors occurred! libktorrent's cmake/FindGMP.cmake tries to find the version by searching through the located gmp.h (/usr/include/gmp.h) to find the _GNU_MP_VERSION macros. Unfortunately (although I don't know whether this problem applies to other architecures or distros), on a Gentoo multiarch system - one supporting both 32-bit and 64-bit executables and libraries - the GMP include file at /usr/include/gmp.h is a forwarding header which includes ARCH/gmp.h as appropriate for the architecture being built. It does not itself contain the __GNU_MP_VERSION macros and so the version test fails. Reproducible: Always libktorrent version (from the top level CMakeLists.txt) is "2.0.1". Git HEAD is a18974f58c12c90c3e4e0acfd387d6a37dd6ca98 This is not an elegant solution, but one workaround that I have found is to additionally look for the include file in the architecture include subdirectory: execute_process(COMMAND ${CMAKE_CXX_COMPILER} -dumpmachine OUTPUT_VARIABLE CXX_MACHTYPE OUTPUT_STRIP_TRAILING_WHITESPACE ERROR_QUIET) find_path(LibGMP_INCLUDE_DIRS NAMES gmp.h PATH_SUFFIXES ${CXX_MACHTYPE} "") which should be benign if the compiler is not GCC or the system is not multiarch.
Ditto on fedora, doing regex's on header files is very fragile. Best practice is generally to employ try_compile Here's an example from digikam used to check libjpeg versions https://quickgit.kde.org/?p=digikam.git&a=blob&f=cmake%2Fmodules%2FMacroJPEG.cmake&o=plain