Makefile always rebuilding

Question

I am using the following simple Makefile to build some simple files. I am really new to making Makefile. I don't know why it keeps in rebuilding even though the files are built after first make and I am not editing any of the file.

EXE    = nextgenrsm
CC     = gcc
LIBS   = StarterWare_Files/
CFLAGS = -c 

INCLUDE_PATH =  StarterWare_Files/

MAIN_SRC = $(wildcard *.c)
MAIN_OBS = $(patsubst %.c,%.o,$(MAIN_SRC))

LIB_SRC = $(wildcard StarterWare_Files/*.c)
LIB_OBS = $(patsubst StarterWare_Files/%.c,%.o,$(LIB_SRC))

output: $(EXE)

$(EXE): $(MAIN_OBS) $(LIB_OBS)
    $(CC) $(MAIN_OBS) $(LIBS)$(LIB_OBS) -o $(EXE) 

$(MAIN_OBS): $(MAIN_SRC) 
    $(CC) $(CFLAGS) *.c -I$(INCLUDE_PATH)

$(LIB_OBS): $(LIB_SRC) 
    cd $(LIBS); \
    $(CC) $(CFLAGS) *.c -I../

clean:
    rm -rf $(LIBS)*.o $(EXE) *.o

NEW EDITED MAKEFILE

EXE    = nextgenrsm
CC     = gcc
LIBS   = StarterWare_Files/
CPPFLAGS = _IStarterWare_Files/


MAIN_OBS = $(patsubst %.c,%.o,$(wildcard *.c))
LIB_OBS  = $(patsubst %.c,%.o,$(wildcard StarterWare_Files/*.c))

all: $(EXE)

$(EXE): $(MAIN_OBS) $(LIB_OBS)
   $(CC) -o $@ $(LDFLAGS) $(MAIN_OBS) $(LIB_OBS) $(LDLIBS)

%.o: %.c 
   $(CC) -o $@ -MD -MP $(CPPFLAGS) $(CFLAGS) -c $^

ALL_DEPS = $(patsubst %.o,%.d,$(MAIN_OBS), $(LIB_OBS))
-include $(ALL_DEPS)

clean:
   rm -f $(LIB_OBS) $(EXE) $(MAIN_OBS) $(ALL_DEPS)

.PHONY: all clean

Whenever I do touch StarterWare_Files/example.h and try to do make again it throws me error that gcc cannot specify -o with -c or -S with Multiple files. Basically the command becomes something like this gcc -o main.o -IStarterWare_Files -c main.c StarterWare_Files/test.h StarterWare_Files/add.h..

Answer 1

Your default target is output but your makefile never produces such a file, so that every time you invoke make it tries to build output file.

The solution is to mark output target as a phony target. As well as clean target:

.PHONY: output clean

---

You can take advantage of built-in rules that compile .o from .c and automatic variables to reduce your makefile to:

EXE    := nextgenrsm
CC     := gcc
LIBS   := StarterWare_Files/
CPPFLAGS := -IStarterWare_Files

MAIN_OBS := $(patsubst %.c,%.o,$(wildcard *.c))
LIB_OBS  := $(patsubst %.c,%.o,$(wildcard StarterWare_Files/*.c))

all: $(EXE)
$(EXE) : $(MAIN_OBS) $(LIB_OBS)
    $(CC) -o $@ $(LDFLAGS) $^ $(LDLIBS)

clean:
    rm -f $(MAIN_OBS) $(LIB_OBS) $(EXE)

.PHONY: all clean   

And if you would like automatic header dependency generation add:

# This rule produces .o and also .d (-MD -MP) from .c.
%.o : %.c
    $(CC) -o $@ -MD -MP $(CPPFLAGS) $(CFLAGS) -c $<

# This includes all .d files produced along when building .o.
# On the first build there are not going to be any .d files.
# Hence, ignore include errors with -.
ALL_DEPS := $(patsubst %.o,%.d,$(MAIN_OBS) $(LIB_OBS))
-include $(ALL_DEPS)

clean:
    rm -f $(MAIN_OBS) $(LIB_OBS) $(EXE) $(ALL_DEPS)