[CMake] Proper way to support 64bit and 32bit builds

[Konstantin Tokarev]

29.10.2016, 16:46, "cen" <imbacen at gmail.com>:
> I tried setting CXXFLAGS and CMAKE_CXX_FLAGS to -m32 before the
> project() call but nothing changed. I could make it fail with
> "CXXFLAGS=-m32 cmake -G ..." from command line but this seems wrong. A
> minimal CMakeLists.txt example would be nice.

Use toolchain file

>
> Hendrik Sattler je 29. 10. 2016 ob 15:25 napisal:
>>  You need to set these compiler flags BEFORE the project() call to let CMake detect all stuff properly. There is a CMake variable telling you the size of a void*.
>>
>>  Am 29. Oktober 2016 12:22:07 MESZ, schrieb cen <imbacen at gmail.com>:
>>>  Hi
>>>
>>>  Once I switch to 32bit builds, CMake fails to recognise that
>>>  glibc-devel.i686 is not installed resulting in an error when running
>>>  make.
>>>  In the same way, my own FindGMP fails to recognize that gmp-devel.i686
>>>  is not installed. I need CMake to fail if these things are missing.
>>>  At least for the compiler part, I'm pretty sure I am missing some var
>>>  or
>>>  flag to tell CMake I expect a 32 bit build.
>>>
>>>  This is what I use to switch between builds in CMakeLists.txt (ARCH var
>>>
>>>  is irrelevant here, I use it later on for CPack):
>>>
>>>  if (BUILD_32)
>>>          set_target_properties(${PROJECT_NAME} PROPERTIES COMPILE_FLAGS
>>>  "-m32" LINK_FLAGS "-m32")
>>>           MESSAGE(STATUS "Excluding 64bit library paths from search.")
>>>           set_property(GLOBAL PROPERTY FIND_LIBRARY_USE_LIB64_PATHS OFF)
>>>           set(ARCH i686)
>>>  elseif (BUILD_64)
>>>          set_target_properties(${PROJECT_NAME} PROPERTIES COMPILE_FLAGS
>>>  "-m64" LINK_FLAGS "-m64")
>>>           set(ARCH amd64)
>>>  else()
>>>           set(ARCH amd64)
>>>  endif()
>>>
>>>  For the FindGMP module, I am not really sure what the best practice
>>>  is.Does the BUILD_32 and BUILD_64 flag propagate into the FindGMP? Do I
>>>
>>>  explicitly specify paths for 32bit libs (eg: /usr/lib64) or can cmake
>>>  be smarter than this?
>
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-- 
Regards,
Konstantin