Automatic Ordering of Object Files "*.o" in a Fortran Makefile

While gcc does have -M and related flags for doing exactly this with C/C++ files, they unfortunately do not work with gfortran. Actually, it is possible, but only if you already know the dependencies. Therefore you will need an external program to generate your dependencies.

In my projects, I use this python script, and add the following to my makefile:

# Script to generate the dependencies
MAKEDEPEND=/path/to/fort_depend.py

# $(DEP_FILE) is a .dep file generated by fort_depend.py
DEP_FILE = my_project.dep

# Source files to compile
OBJECTS = mod_file1.f90 \
          mod_file2.f90

# Make sure everything depends on the .dep file
all: $(actual_executable) $(DEP_FILE)

# Make dependencies
.PHONY: depend
depend: $(DEP_FILE)

# The .dep file depends on the source files, so it automatically gets updated
# when you change your source
$(DEP_FILE): $(OBJECTS)
    @echo "Making dependencies!"
    cd $(SRCPATH) && $(MAKEDEPEND) -w -o /path/to/$(DEP_FILE) -f $(OBJECTS)

include $(DEP_FILE)

fort_depend.py basically just makes a list of all the modules USEd in a given file.

... Specify them in your rules.

main_mod2.o: main_mod.o