BIN_DIR=bin
BUILD_DIR=build
SRC_DIR=src

KERNEL := sen.elf
 
# It is highly recommended to use a custom built cross toolchain to build a kernel.
# We are only using "cc" as a placeholder here. It may work by using
# the host system's toolchain, but this is not guaranteed.
ifeq ($(origin CC), default)
CC := cc
endif
 
# Likewise, "ld" here is just a placeholder and your mileage may vary if using the
# host's "ld".
ifeq ($(origin LD), default)
LD := ld
endif
 
CFLAGS ?= -O2 -g -Wall -Wextra -pipe -fno-pie -no-pie
LDFLAGS ?=
 
# Internal C flags that should not be changed by the user.
INTERNALCFLAGS :=   \
	-I$(SRC_DIR)                \
	-std=gnu11           \
	-ffreestanding       \
	-fno-stack-protector \
	-no-pie              \
	-mabi=sysv           \
	-mno-80387           \
	-mno-mmx             \
	-mno-3dnow           \
	-mno-sse             \
	-mno-sse2            \
	-mno-red-zone        \
	-mcmodel=kernel      \
	-MMD	
 
# Internal linker flags that should not be changed by the user.
INTERNALLDFLAGS :=    \
	-T$(SRC_DIR)/linker.ld         \
	-nostdlib              \
	-zmax-page-size=0x1000 \
	-static

rwildcard=$(foreach d,$(wildcard $(1:=/*)),$(call rwildcard,$d,$2) $(filter $(subst *,%,$2),$d))

CFILES := $(shell find ./$(SRC_DIR) -type f -name '*.c')
OBJ := $(subst $(SRC_DIR),$(BUILD_DIR),$(CFILES:.c=.o))
HEADER_DEPS := $(OBJ:.o=.d))

.PHONY: all
all: $(KERNEL)

$(KERNEL): $(OBJ) | $(BIN_DIR)
	$(LD) $(OBJ) $(LDFLAGS) $(INTERNALLDFLAGS) -o $(BIN_DIR)/$@

-include $(HEADER_DEPS)
$(BUILD_DIR)/%.o: $(SRC_DIR)/%.c | $(BUILD_DIR)
	@mkdir -p $(@D)
	$(CC) $(CFLAGS) $(INTERNALCFLAGS) -c $< -o $@

# create directories if they don't exist
$(BIN_DIR):
	mkdir -p $@

$(BUILD_DIR):
	mkdir -p $@

# Remove object files and the final executable.
.PHONY: clean
clean:
	rm -rf $(BIN_DIR)/$(KERNEL) $(OBJ) $(HEADER_DEPS)