How to specify a compiler in CMake?

Question

I would like to use the IAR compiler. I noticed CMake has already have a bunch of files about this compiler:

https://github.com/jevinskie/cmake/blob/master/Modules/C

Answer 1

You need to create a toolchain file, and use the CmakeForceCompiler module.

Here is an example toolchain file for bare-metal ARM development with IAR:

include(CMakeForceCompiler)

set(CMAKE_SYSTEM_NAME Generic) # Or name of your OS if you have one
set(CMAKE_SYSTEM_PROCESSOR arm) # Or whatever
set(CMAKE_CROSSCOMPILING 1)

set(CMAKE_C_COMPILER iccarm) # Change the arm suffix if appropriate
set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY) # Required to make the previous line work for a target that requires a custom linker file

The last line is necessary because CMake will try to compile a test program with the compiler to make sure it works and to get some version information from preprocessor defines. Without this line, CMake will use add_executable() for the test program, and you will get the error "The C compiler "XXX" is not able to compile a simple test program." This is because the test program fails to link, as it doesn't have your custom linker file (I'm assuming bare-metal development since this is what IAR is usually used for). This line tells CMake to use add_library() instead, which makes the test succeed without the linker file. Source of this workaround: this CMake mailing list post.

Then, assuming that your toolchain file is named iar-toolchain.cmake, invoke CMake like this:

cmake -DCMAKE_TOOLCHAIN_FILE=iar-toolchain.cmake .