I have this makefile.
CC = arm-none-eabi-gcc -c LD = arm-none-eabi-gcc OC = arm-none-eabi-objcopy OS = arm-none-eabi-size TARGET = cli_stm32f4 LIBNAME_OPENCM3 = opencm3_stm32f4 OPT = -Os DEFS += -DSTM32F4 DIR_OPENCM3 = ./libopencm3 DIR_CLI = ./embedded-cli DIR_OBJ = ./obj DEBUG = -ggdb3 LDSCRIPT = stm32f4.ld DIR_FLAGS = -I$(DIR_CLI) ARCH_FLAGS = -mthumb -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16 LDFLAGS += --static -nostartfiles LDFLAGS += -T$(LDSCRIPT) LDFLAGS += $(ARCH_FLAGS) $(DEBUG) LDFLAGS += -Wl,-Map=$(TARGET).map -Wl,--cref LDFLAGS += -Wl,--gc-sections ifeq ($(V),99) LDFLAGS += -Wl,--print-gc-sections endif LDFLAGS += -u _printf_float LDFLAGS += -L$(DIR_OPENCM3)/lib LDLIBS += -l$(LIBNAME_OPENCM3) LDLIBS += -Wl,--start-group -lc -lgcc -lnosys -Wl,--end-group CFLAGS += $(OPT) $(DEBUG) $(ARCH_FLAGS) CFLAGS += -Wextra -Wshadow -Wimplicit-function-declaration CFLAGS += -Wredundant-decls -Wmissing-prototypes -Wstrict-prototypes CFLAGS += -fno-common -ffunction-sections -fdata-sections CFLAGS += -std=c11 -MMD -MP DEFS += -I$(DIR_OPENCM3)/include PREPFLAGS = -MD -Wall -Wundef $(DEFS) BINFLAGS = -O binary OBJS = $(DIR_OBJ)/main.o \ $(DIR_OBJ)/cli.o all : $(TARGET).bin $(TARGET).bin : $(OBJS) $(LDSCRIPT) $(LD) $(LDFLAGS) $(OBJS) $(LDLIBS) -o $(TARGET).elf $(OC) $(TARGET).elf $(BINFLAGS) $@ $(DIR_OBJ)/%.o : %.c mkdir -p $(DIR_OBJ) $(CC) $(CFLAGS) $(DIR_FLAGS) $(PREPFLAGS) $< -o $@ clean : rm -rf $(DIR_OBJ) *.bin *.elf *.map *.d -include $(OBJS:.o=.d) I thought that with this instruction, two object files would be created: main.o and cli.o.
OBJS = $(DIR_OBJ)/main.o \ $(DIR_OBJ)/cli.o cli.c and main.c are in different folders. The former is inside a folder named embedded-cli within the main folder, and the latter is in the main folder with the makefile. 
I already added embedded-cli folder with this instruction.
DIR_FLAGS = -I$(DIR_CLI) But I get this.
make: *** No rule to make target 'obj/cli.o', needed by 'cli_stm32f4.bin'. Stop.
