CMake Fortran Issues

Introduction

CMake has a number of Fortran issues that have been discussed many different times on list and duplicated a fair number of times in the bug tracker as well.

Maik Beckmann is trying to make sense of all the confusion by collecting information on all Fortran issues at http://www.cmake.org/Bug/view.php?id=5809

Please join the work there by

• Contributing patches.
• Testing the patches that already exist there.
• Reporting things that don't work.
• Sending simplified examples of things which don't work.
• Sharing your expert knowledge of CMake.

Concepts expressed using Makefiles

This section is intended to discuss the makefile rules which CMake has to generate.

A simple program

A f9x program which is build by compiling in linking two source files a.f90 and main.f90. The tree structure is:

• example_simpleProgram
  • build
    • Makefile
    • prog.dir
      • build.make
  • main.f90
  • a.f90

a.f90:

SUBROUTINE printHello
    WRITE(*,*) "Hello f9x world"	
END SUBROUTINE

main.f90:

PROGRAM hello 
    CALL printHello
END PROGRAM

Makefile:

all: prog.dir/all

prog.dir/all:
	$(MAKE) -f prog.dir/build.make prog.dir/all

clean:
	$(MAKE) -f prog.dir/build.make prog.dir/clean

build.make:

prog.dir/all: prog.dir/prog

prog.dir/prog:  prog.dir/a.o prog.dir/main.o
	gfortran -o prog.dir/prog  prog.dir/a.o prog.dir/main.o
	
prog.dir/a.o: ../a.f90
	gfortran -o prog.dir/a.o  -c ../a.f90
	
prog.dir/main.o: ../main.f90 
	gfortran -o prog.dir/main.o  -c ../main.f90 
	
prog.dir/clean:
	rm prog.dir/a.o prog.dir/main.o prog.dir/prog

Now change into build and type

$ make

to build. The current CMake is able to build the same without any problems. This is also valid for any fortran code that doesn't use modules.

You can download this example as tarball example_simpleProgram.tar.gz at http://www.cmake.org/Bug/view.php?id=5809

A simple program with module

The same as before, but now a.f90 provides a module which main.f90 uses. The tree structure is:

• example_simpleProgram_withModule
  • build
    • Makefile
    • prog.dir
      • build.make
  • main.f90
  • a.f90

a.f90:

MODULE localMod 
!
CONTAINS
    SUBROUTINE printHello
        WRITE(*,*) "Hello f9x world"
    END SUBROUTINE
END MODULE

main.f90:

PROGRAM hello 
    USE localMod
    CALL printHello
END PROGRAM

Makefile:

all: prog.dir/all

prog.dir/all:
	$(MAKE) -f prog.dir/build.make prog.dir/all

clean:
	$(MAKE) -f prog.dir/build.make prog.dir/clean

build.make:

prog.dir/all: prog.dir/prog


prog.dir/prog:  prog.dir/a.o prog.dir/main.o
	gfortran -o prog.dir/prog  prog.dir/a.o prog.dir/main.o 

prog.dir/a.o: ../a.f90
	gfortran -o prog.dir/a.o  -c ../a.f90 -M prog.dir
	
prog.dir/localmod.mod: prog.dir/a.o	
	
prog.dir/main.o: ../main.f90 prog.dir/localmod.mod
	gfortran -o prog.dir/main.o	 -c ../main.f90 -I prog.dir 
	
prog.dir/clean:
	rm prog.dir/localmod.mod prog.dir/a.o prog.dir/main.o prog.dir/prog

Now change into build and type

$ make

to build. This is nothing the current CMake can't do. Now do (you're at the build directory)

 $ touch ../a.f90

and enter

 $ make

again. You'll see that a.f90 is recompiled, like the current CMake does, but main.f90 is recompiled too! This is different from current CMake, but its the right way, since a module dependency is a compile time dependency like an include.