I have a FORTRAN source code consisting of many different .F and .h files. I need to build an executable from it, but I'm having some problems. The makefile that I produced so far (which may have errors as I'm new to this) is:

 # compiler
 FC = /usr/bin/gfortran-4.5

 # compile flags
 FCFLAGS = -g -c -fdefault-real-8 -fbacktrace -fno-align-commons
 # link flags
 FLFLAGS = -g -fbacktrace

 # source files and objects
 SRCS = $(patsubst %.F, %.o, $(wildcard *.F)) \
        $(patsubst %.h, %.mod, $(wildcard *.h))

 # program name
 PROGRAM = blah

 all: $(PROGRAM)

 $(PROGRAM): $(SRCS)
    $(FC) $(FCFLAGS) $@ $<

 %.o: %.F
    $(FC) $(FLFLAGS) -o $@ $<

 %.mod: %.h
    $(FC) $(FLFLAGS) -o $@ $<

 clean:
    rm -f *.o *.mod

When I try to make the program, however, I'm getting a slew of undefined reference errors. I mean, every function and subroutine call in the very first compiled .F file gives back an undefined reference error. I thought this was because gfortran was trying to link the files instead of just compiling them and then linking at the end, but I thought the '-c' option was supposed to prevent that.

UPDATE:

As commenters have pointed out, I mixed up the compile and link flags. Furthermore, you shouldn't compile *.h files. Here is the latest, corrected makefile:

# compiler
FC = /usr/bin/gfortran-4.4

# compile flags
FCFLAGS = -g -c -fdefault-real-8 -fbacktrace -fno-align-commons -fbounds-check -std=legacy
# link flags
FLFLAGS =

# source files and objects
SRCS = $(patsubst %.F, %.o, $(wildcard *.F))

# program name
PROGRAM = blah

all: $(PROGRAM)

$(PROGRAM): $(SRCS)
    $(FC) $(FLFLAGS) -o $@ $<

%.o: %.F
    $(FC) $(FCFLAGS) -o $@ $<

clean:
    rm -f *.o *.mod

Now when I run make, it will compile each *.F file in the code, but it fails at the linking stage. I get a bunch of undefined reference errors in the very first *.F file. The compiler seems to

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