Dependency file generation - rebuild if a header file is updated

src/kernel/Makefile

@@ -6,6 +6,7 @@ CC := x86_64-elf-gcc
 
 SRC := $(wildcard **/*.[cS])
 OBJ := $(patsubst %, %.o, $(basename $(SRC)))
+DEP := $(OBJ:.o=.d)
 
 CFLAGS ?= -Wall -Wextra
 CFLAGS += -ffreestanding
@@ -17,6 +18,13 @@ kernel: LDFLAGS += -n -nostdlib -T Link.ld
 kernel: $(OBJ)
 	$(LINK.c) $^ -o $@
 
+DEPFLAGS = -MT $@ -MMD -MP -MF $*.d
+%.o: %.c $.d
+	$(COMPILE.c) $(DEPFLAGS) -o $@ $<
+%.o: %.S %.d
+	$(COMPILE.S) $(DEPFLAGS) -o $@ $<
+%.d: ;
+
 
 # Copy kernel to sysroot
 /opt/sysroot/kernel: kernel
@@ -26,6 +34,8 @@ kernel: $(OBJ)
 install: /opt/sysroot/kernel
 
 clean:
-	rm -rf $(OBJ) kernel
+	rm -rf $(OBJ) $(DEP) kernel
 
 .PHONY: install
+
+include $(DEP)