[CMake] How to do platform specific setup?

[Mario Werner]

Hi Robert,

I usually do all my platform and compiler specific customization in a
toolchain file [1]. Such a toolchain file is more or less standard CMake
script which get executed before the root CMakeLists.txt from the
project is processed. When invoking cmake for the first time you simply
specify which toolchain file you want to use by adding
`-DCMAKE_TOOLCHAIN_FILE=<path-to-file>` as parameter.

Note that the idea of a toolchain file is that the file is customized
exactly for your environment.

Best regards,
Mario


[1] https://cmake.org/Wiki/CMake_Cross_Compiling#The_toolchain_file

On 2017-07-19 21:22, Robert Dailey wrote:
> So in one of my top level CMake scripts, I have this:
> 
> ```
> if( ANDROID )
>     include( android )
>     _setup_android_platform()
> elseif( UNIX )
>     include( unix )
>     _setup_unix_platform()
> endif()
> 
> if( CMAKE_CXX_COMPILER_ID STREQUAL "Clang" )
>     include( clang )
>     _setup_clang_toolchain()
> elseif( CMAKE_CXX_COMPILER_ID STREQUAL "MSVC" )
>     include( msvc )
>     _setup_msvc_toolchain()
> endif()
> ```
> 
> This allows me to set up various global things used by all targets
> defined by CMake. An example of what android's does:
> 
> ```
> macro( _setup_android_platform )
>     # Forward the android ABI from CMake to a custom variable for
> portability to other toolchains
>     if( CMAKE_ANDROID_ARCH_ABI )
>         set( ANDROID_ABI ${CMAKE_ANDROID_ARCH_ABI} )
>     endif()
> 
>     # Forcefully disable testing while cross compiling for Android
> platform. It doesn't make sense
>     # to build tests, since we can't run them natively. We build tests
> on a separate platform.
>     set( BUILD_TESTING OFF CACHE BOOL "Do not build unit tests when
> cross compiling for Android" FORCE )
> 
>     android_ndk_import_module_cpufeatures()
>     android_ndk_import_module_native_app_glue()
> 
>     # Export ANativeActivity_onCreate(),
>     # Refer to: https://github.com/android-ndk/ndk/issues/381.
>     set( CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -u
> ANativeActivity_onCreate" )
> 
>     add_definitions(
>         -DANDROID
>     )
> endmacro()
> ```
> 
> And clang:
> 
> ```
> macro( _setup_clang_toolchain )
>     # Disable certain clang warnings
>     # These spam like crazy; disable for now
>     add_compile_options(
>         -Wno-inconsistent-missing-override
>     )
> 
>     # Clang 3.8.0 on Ubuntu was failing with -Wno-expansion-to-defined.
>     # Version 3.8.2 in NDK r14b seems ok with it.
>     if( CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 3.8.2 )
>         add_compile_options(
>             -Wno-expansion-to-defined
>         )
>     endif()
> 
>     set( CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS}
> -Wl,--no-undefined" )
> endmacro()
> ```
> 
> I feel like there is a better way. I recall there being some built-in
> way to override CMake's platform specific setup modules, but I don't
> know anything about it. Can someone offer some advice on if there is a
> built in way to do this?
>