[CMake] IBM Fortran and the C Preprocessor

[Brad King]

Will Dicharry wrote:
> The toolchain file looks like this (the project is actually mixed
> C/Fortran code so there's some C/C++ stuff in the actual toolchain file, 
> but this simple toolchain with a simple Fortran exe reproduces the 
> problem):
> 
> set( CMAKE_SYSTEM_NAME AIX )
> set( CMAKE_Fortran_COMPILER mpxlf90 )
> set( CMAKE_Fortran_FLAGS "-qfixed=72" CACHE STRING "" )
> 
> We do this because we need a quick way to choose our compiler (cmake
> chooses GNU on this system by default, and we have to use an MPI wrapper 
> compiler) and because we want those particular Fortran flags when the 
> MPI wrapper compiler is being used.

The usual way to do this is

$ export FC=mpxlf90
$ export FFLAGS="-qfixed=72"
$ cmake /path/to/source

> When I use this toolchain file, the Fortran compiler ID is unknown (I 
> failed to see this before, the C and CXX compiler IDs were correct).
> 
> However if I comment out the set CMAKE_Fortran_FLAGS line or if I skip
> the toolchain file altogether and just pass
> -DCMAKE_Fortran_COMPILER=mpxlf90 into the cmake command, the compiler ID
> is VisualAge and everything works fine.
> 
> Am I misusing the toolchain file capability?

As Bill said, the toolchain file is meant for cross compiling.  It can
probably be used for normal configuration, but that is not well-tested.
I just tried something similar to your example and the compiler id check
works.

$ cat mytool.cmake
set(CMAKE_SYSTEM_NAME AIX)
set(CMAKE_Fortran_COMPILER xlf90)
set(CMAKE_Fortran_FLAGS "-q64" CACHE STRING "")
$ cat CMakeLists.txt
cmake_minimum_required(VERSION 2.6)
project(FOO Fortran)
add_definitions(-DTADA)
add_executable(foo foo.f)
$ mkdir b; cd b
$ cmake .. -DCMAKE_TOOLCHAIN_FILE=../mytool.cmake

-Brad