CMake not recognizing compiler on MacOS with Xcode Generator

Usage
1

Hi,

I have installed CMake 3.17.1, gcc 9.3.0, openmpi 3.1.5 and other tools on my Mac (10.15.4) using spack. I am able to configure and build my code with the following options

cmake ../ \
 -DMPI_C_COMPILER=mpicc -DMPI_CXX_COMPILER=mpicxx \
 -DCMAKE_BUILD_TYPE=Release \
 -DCMAKE_C_COMPILER=gcc \
 -DCMAKE_CXX_COMPILER=g++ \
 -DCMAKE_Fortran_COMPILER=gfortran

However, when I add the Xcode generator option:

cmake -G Xcode ../ \
 -DMPI_C_COMPILER=mpicc -DMPI_CXX_COMPILER=mpicxx \
 -DCMAKE_BUILD_TYPE=Release \
 -DCMAKE_C_COMPILER=gcc \
 -DCMAKE_CXX_COMPILER=g++ \
 -DCMAKE_Fortran_COMPILER=gfortran

cmake is unable to identify the compiler and gives the following errors. Is there a way to resolve this and get cmake to generate the workspace for Xcode?

-- The C compiler identification is unknown
-- The CXX compiler identification is unknown
<edited>
-- Configuring incomplete, errors occurred!
2

It looks like the build command that Cmake is using to compile the test code is adding options that are valid for clang, but not for gcc.

gcc -x c -target x86_64-apple-macos10.15 -fdiagnostics-show-note-include-stack -fmacro-backtrace-limit=0 -fpascal-strings -fasm-blocks --serialize-diagnostics <among other options>

The gcc compiler is complaining about these. Where/How does cmake decide which options to use? Is there a way to suppress these offending options?

3

The executables “gcc” and “g++” on macOS are actually symlinks to AppleClang by default. Have you tried setting absolute paths to your compiler, eg. /usr/local/bin/gcc-9 (if installed via Homebrew)?

1 Like
4

@alex Lifesaver. Thanks for pointing that out.