Pi Kernel Makefile

#-------------------------------------#
#          OS Kernel Makefile         #
#-------------------------------------#

#
# Current functionality:
#
#   Creation of binary images to be
#   loaded by bootloader
#

# Toolchain to use
ARMGNU ?= arm-none-eabi

# Directory for misc build objects
BUILD = build/

# Directory for c build objs
CBUILD = build/c/

# Directory for assembly build objs
ASBUILD = build/as/

# Directory for src objects
SOURCE = src/

# Name of output file
TARGET = harpos.bin

# Name of assembler list file to generate
LIST = $(BUILD)harpos.list

# Name of map file to generate
MAP = $(BUILD)harpos.map

# Name of linker script to use
LINKER = memorymap.ld

# Additional libraries
LIBRARIES =
#csud

# Additional compiler flags for c files
# General warning flags (wall), midlevel optimisations (02), no standard system startup files or libraries (nostdlib nostartfiles)
# assert freestanding environment where stdlib may not exist and program startup may not be at main (freestanding) treat wchar as 16bit value (short-wchar)
COPTS = -Wall -O2 -nostdlib -nostartfiles -ffreestanding -fshort-wchar

# Names of object files to be built
# Uses pattern substitute to find source files and add object names
# Assembly files then c files
OBJS = $(patsubst $(SOURCE)%.s,$(ASBUILD)%.o,$(wildcard $(SOURCE)*.s)) $(patsubst $(SOURCE)%.c,$(CBUILD)%.o,$(wildcard $(SOURCE)*.c))

# Rule for all
all: $(TARGET)

# Rule to make target image : depends on elf
# Objcopy elf to binary image
$(TARGET) : $(BUILD)harpos.elf
    $(ARMGNU)-objcopy $(BUILD)harpos.elf -O binary $(TARGET)

# Rule to make elf : depends on objects and linker script
# Link all objects, link to additional libraries, create map file, output to harpos.elf, replace default linker script with ours
# Objdump elf to list file
# Objcopy elf to hex file
$(BUILD)harpos.elf : $(LINKER) $(OBJS)
    echo $(OBJS)
    $(ARMGNU)-ld $(OBJS) -L. $(patsubst %,-l %,$(LIBRARIES)) -Map $(MAP) -o $(BUILD)harpos.elf -T $(LINKER)
    $(ARMGNU)-objdump -D $(BUILD)harpos.elf > $(LIST)
    $(ARMGNU)-objcopy $(BUILD)harpos.elf -O ihex $(BUILD)harpos.hex

# Rule to make the c object files.
$(CBUILD)%.o: $(SOURCE)%.c
    $(ARMGNU)-gcc $(COPTS) -c $< -o $@

# Rule to make the assembly object files.
$(ASBUILD)%.o: $(SOURCE)%.s
    $(ARMGNU)-as -I $(SOURCE) $< -o $@

# Rule to clean
clean:
    rm -f $(CBUILD)*.o
    rm -f $(ASBUILD)*.o
    rm -f $(BUILD)*.elf
    rm -f $(BUILD)*.hex
    rm -f $(TARGET)
    rm -f $(LIST)
    rm -f $(MAP)