Makefile does not find rules despire of available files - gcc

Question

Currently I am trying to get a rather big project of mine to work with a Makefile. I used Make before but in a rather crude way and not really "dynamic", this means I am pretty new to good Makefiles.
My Makefile looks like this:
INCLUDE_DIR = /inc
SOURCE_DIR = /src
BUILD_DIR = /build
BUILD_NAME = build
CC = arm-none-eabi-gcc
CFLAGS = -I$(INCLUDE_DIR)
_INCLUDES = main.h pfc.h
INCLUDES = $(patsubst %, $(INCLUDE_DIR)/%, $(_INCLUDES))
_OBJ = main.o pfc.o
OBJ = $(patsubst %, $(BUILD_DIR)/%, $(_OBJ))
$(BUILD_DIR)/%.o: $(SOURCE_DIR)/%.c $(INCLUDES)
$(CC) -c -o $# $< $(CFLAGS)
$(BUILD_NAME): $(OBJ)
$(CC) -o $# $^ $(CFLAGS)
all: $(BUILD_NAME)
.PHONY: clean
clean:
rm -rf $(BUILD_DIR)/*
When I make the file I get this:
make: *** No rule to make target '/build/main.o', needed by 'build'. Stop.
I guess it is an error in this recipe:
$(BUILD_DIR)/%.o: $(SOURCE_DIR)/%.c $(INCLUDES)
$(CC) -c -o $# $< $(CFLAGS)
Sadly I am not able to get this done on my own.
All files a available in the correct folders.
I really appreciate all the help!
Tristan

Answer 1

You have a few issues here that I can see. But first off - just check (just incase) that all your rules are only indented with tabs and not spaces..... this can be a real "silent" killer of makefiles as they give crap error messages.
Ok so - lets assume you have:
INCLUDE_DIR = inc
SOURCE_DIR = src
BUILD_DIR = build
instead of /src etc.. as mentioned in the comments.
Do you really have inc/main.h and inc/pfc.h?
I copied and pasted your makefile added your src and inc folders (but I used gcc instead of arm-none-eabi-gcc. It did the compile lines correctly, but failed at the linker stage because you are trying to build an output file called build when there is already a folder called build (not allowed in linux - maybe ok for windows but I don't recommend).
I made an answer for another question - but it might be a better start point then you have here in the case where you have nested src/inc directories and you want to be able to clean your output folders - ill put it here for convenience:
# Get your source list (use wildcard or what ever, but just for clarity you should end up with a list of files with full paths to start with):
# Output folders/targets
SRC_DIR = src
OBJ_DIR = obj
BIN_DIR = bin
OUTPUT_FILE = output
# Generate list of source files - this is a linux command - but you can do this in pure make using wildcard and such).
SOURCES := $(shell find $(SOURCEDIR) -name '*.c')
# Create your objects list in the obj directory
OBJECTS = $(addprefix $(OBJ_DIR)/,$(addsuffix .o,$(basename $(SOURCES))))
# Create list of unique folders to create
DIRS = $(sort $(dir $(OBJECTS))) $(BIN_DIR)
# Create list of include paths
INCS = $(addprefix -I,$(sort $(dir $(SOURCES))))
# Main target rule
$(BIN_DIR)/$(OUTPUT_FILE): $(OBJECTS) | $(DIRS)
#echo linker: gcc $(OBJECTS) -o $#
#touch $#
# Rule to build your object file - ensure that the folders are created first (also create a dummy obj file) - note this works for parallel builds too (make -j
$(OBJ_DIR)/%.o: %.c | $(DIRS)
#echo compile: gcc $(INCS) -c $? -o $#
#touch $#
# Create your directories here
$(DIRS):
#echo Creating dir: $#
#mkdir -p $#
# Clean if needed
.PHONY: clean
clean:
rm -rf $(OBJ_DIR) $(BIN_DIR)
Note this is just a template, you still need to fill in the gcc/makefile flags - but its a decent start point...
Debugging
$(info ...) is your friend - for example you could do:
$(info OBJ = $(OBJ))
$(info objrule = $(BUILD_DIR)/%.o: $(SOURCE_DIR)/%.c $(INCLUDES))
To print our what make has expanded these variables / lines to be - this can yield useful debug.

Answer 2

Here is another version of your makefile with automatic dependency generation:
INCLUDE_DIR := inc
SOURCE_DIR := src
BUILD_DIR := build
CC := arm-none-eabi-gcc
CPPFLAGS := -I$(INCLUDE_DIR)
exes := build
build.obj := main.o pfc.o
all : ${exes:%=${BUILD_DIR}/%}
.SECONDEXPANSION:
${BUILD_DIR}:
mkdir -p $#
# Rule to link all exes.
${exes:%=${BUILD_DIR}/%} : ${BUILD_DIR}/% : $$(addprefix ${BUILD_DIR}/,$${$$*.obj}) | $${#D}
${CC} -o $# ${LDFLAGS} $^ ${LDLIBS}
# Rule to compile C sources. And generate header dependencies.
${BUILD_DIR}/%.o : ${SOURCE_DIR}/%.c | $${#D}
${CC} -o $# -c ${CPPFLAGS} ${CFLAGS} -MD -MP $<
# Include automatically generated header dependencies.
ifneq ($(MAKECMDGOALS),clean)
-include $(foreach exe,${exes},$(patsubst %.o,${BUILD_DIR}/%.d,${${exe}.obj}))
endif
clean:
rm -rf $(BUILD_DIR)
.PHONY: all clean
To add another executable target do:
exes += another
another.obj := another_main.o another_pfc.o