GNUmakefile

# Nuke built-in rules and variables.
override MAKEFLAGS += -rR

# This is the name that our final executable will have.
# Change as needed.
override OUTPUT := kernel

# Convenience macro to reliably declare user overridable variables.
define DEFAULT_VAR =
    ifeq ($(origin $1),default)
        override $(1) := $(2)
    endif
    ifeq ($(origin $1),undefined)
        override $(1) := $(2)
    endif
endef

# User controllable C compiler command.
override DEFAULT_KCC := cc
$(eval $(call DEFAULT_VAR,KCC,$(DEFAULT_KCC)))

# User controllable linker command.
override DEFAULT_KLD := ld
$(eval $(call DEFAULT_VAR,KLD,$(DEFAULT_KLD)))

# User controllable C flags.
override DEFAULT_KCFLAGS := -g -O2 -pipe
$(eval $(call DEFAULT_VAR,KCFLAGS,$(DEFAULT_KCFLAGS)))

# User controllable C preprocessor flags. We set none by default.
override DEFAULT_KCPPFLAGS :=
$(eval $(call DEFAULT_VAR,KCPPFLAGS,$(DEFAULT_KCPPFLAGS)))

# User controllable nasm flags.
override DEFAULT_KNASMFLAGS := -F dwarf -g
$(eval $(call DEFAULT_VAR,KNASMFLAGS,$(DEFAULT_KNASMFLAGS)))

# User controllable linker flags. We set none by default.
override DEFAULT_KLDFLAGS :=
$(eval $(call DEFAULT_VAR,KLDFLAGS,$(DEFAULT_KLDFLAGS)))

# Internal C flags that should not be changed by the user.
override KCFLAGS += \
    -Wall \
    -Wextra \
    -std=gnu11 \
    -ffreestanding \
    -fno-stack-protector \
    -fno-stack-check \
    -fno-lto \
    -fno-PIC \
    -m64 \
    -march=x86-64 \
    -mno-80387 \
    -mno-mmx \
    -mno-sse \
    -mno-sse2 \
    -mno-red-zone \
    -mcmodel=kernel

# Internal C preprocessor flags that should not be changed by the user.
override KCPPFLAGS := \
    -I src/include \
    -I src \
    $(KCPPFLAGS) \
    -MMD \
    -MP

# Internal nasm flags that should not be changed by the user.
override KNASMFLAGS += \
    -Wall \
    -f elf64

# Internal linker flags that should not be changed by the user.
override KLDFLAGS += \
    -m elf_x86_64 \
    -nostdlib \
    -static \
    -z max-page-size=0x1000 \
    -T linker.ld

# Use "find" to glob all *.c, *.S, and *.asm files in the tree and obtain the
# object and header dependency file names.
override CFILES := $(shell cd src && find -L * -type f -name '*.c' | LC_ALL=C sort)
override ASFILES := $(shell cd src && find -L * -type f -name '*.S' | LC_ALL=C sort)
override NASMFILES := $(shell cd src && find -L * -type f -name '*.asm' | LC_ALL=C sort)
override OBJ := $(addprefix obj/,$(CFILES:.c=.c.o) $(ASFILES:.S=.S.o) $(NASMFILES:.asm=.asm.o))
override HEADER_DEPS := $(addprefix obj/,$(CFILES:.c=.c.d) $(ASFILES:.S=.S.d))

# Default target.
.PHONY: all
all: bin/$(OUTPUT)

# Link rules for the final kernel executable.
bin/$(OUTPUT): GNUmakefile linker.ld $(OBJ)
	mkdir -p "$$(dirname $@)"
	$(KLD) $(OBJ) $(KLDFLAGS) -o $@

# Include header dependencies.
-include $(HEADER_DEPS)

# Compilation rules for *.c files.
obj/%.c.o: src/%.c GNUmakefile
	mkdir -p "$$(dirname $@)"
	$(KCC) $(KCFLAGS) $(KCPPFLAGS) -c $< -o $@

# Compilation rules for *.S files.
obj/%.S.o: src/%.S GNUmakefile
	mkdir -p "$$(dirname $@)"
	$(KCC) $(KCFLAGS) $(KCPPFLAGS) -c $< -o $@

# Compilation rules for *.asm (nasm) files.
obj/%.asm.o: src/%.asm GNUmakefile
	mkdir -p "$$(dirname $@)"
	nasm $(KNASMFLAGS) $< -o $@

# Remove object files and the final executable.
.PHONY: clean
clean:
	rm -rf bin obj


# Run the image using QEMU
.PHONY: run
run:
	./create_iso.sh && qemu-system-x86_64 -cdrom image.iso -m 512