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/Compiler/IAR.cmake

From what I read the common solution is to specify manually ALL the toolchain in my CMakeLists.txt:

set(CMAKE_C_COMPILER iccarm)
set(CMAKE_CPP_COMPILER iccarm)

How CMake can link these definitions with `Modules/Compiler/IAR.cmake"?

I thought I would just have to do

include("Modules/Compiler/IAR.cmake")

What is the correct way to specify my IAR compiler?

When I do

cmake .

It still tries to use gcc instead of my IAR compiler. Why?

Answer 1

If you don't want to use your PC's standard compiler, you have to give CMake the path to the compiler. You do this via environment variables, a toolchain file or direct definitions in the CMake command line (see e.g. CMake Error at CMakeLists.txt:30 (project): No CMAKE_C_COMPILER could be found).

Putting the compiler's name/path into your CMakeLists.txt would stop your project from being cross-platform.

CMake does check for the compiler ids by compiling special C/C++ files. So no need to manually include from Module/Compiler or Module/Platform.

This will be automatically done by CMake based on its compiler and platform checks.

References

• CMake: In which Order are Files parsed (Cache, Toolchain, …)?
• CMake GitLab Commit: Add support files for C, C++ and ASM for the IAR toolchain.

Answer 2

You can call cmake like this:

cmake -DCMAKE_C_COMPILER=iccarm ...

or

cmake -DCMAKE_CXX_COMPILER=...

Answer 3

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 .

Answer 4

To select a specific compiler, you have several solutions, as exaplained in CMake wiki:

Method 1: use environment variables

For C and C++, set the CC and CXX environment variables. This method is not guaranteed to work for all generators. (Specifically, if you are trying to set Xcode's GCC_VERSION, this method confuses Xcode.) For example:

CC=gcc-4.2 CXX=/usr/bin/g++-4.2 cmake -G "Your Generator" path/to/your/source

Method 2: use cmake -D

Set the appropriate CMAKE_FOO_COMPILER variable(s) to a valid compiler name or full path on the command-line using cmake -D. For example:

cmake -G "Your Generator" -D CMAKE_C_COMPILER=gcc-4.2 -D CMAKE_CXX_COMPILER=g++-4.2 path/to/your/source

Method 3 (avoid): use set()

Set the appropriate CMAKE_FOO_COMPILER variable(s) to a valid compiler name or full path in a list file using set(). This must be done before any language is set (ie: before any project() or enable_language() command). For example:

set(CMAKE_C_COMPILER "gcc-4.2")
set(CMAKE_CXX_COMPILER "/usr/bin/g++-4.2")

project("YourProjectName")

The wiki doesn't provide reason why 3rd method should be avoided...