diff --git a/code/asm/build.mk b/code/asm/build.mk
index 0c1fcc4..d61acaf 100644
--- a/code/asm/build.mk
+++ b/code/asm/build.mk
@@ -1,3 +1,6 @@
+# Note: The Makefile for each project is just a symbol-link to the build.mk
+#       under the "asm" folder.
+
 EXEC = test
 
 SRC = ${EXEC}.s
diff --git a/code/asm/rule.mk b/code/asm/rule.mk
index 23e88bd..db197af 100644
--- a/code/asm/rule.mk
+++ b/code/asm/rule.mk
@@ -1,4 +1,15 @@
-include ../../common.mk
+# This file will be included by the build.mk.
+
+CROSS_COMPILE = riscv64-unknown-elf-
+CFLAGS = -nostdlib -fno-builtin -march=rv32g -mabi=ilp32 -g -Wall
+
+QEMU = qemu-system-riscv32
+QFLAGS = -nographic -smp 1 -machine virt -bios none
+
+GDB = gdb-multiarch
+CC = ${CROSS_COMPILE}gcc
+OBJCOPY = ${CROSS_COMPILE}objcopy
+OBJDUMP = ${CROSS_COMPILE}objdump
 
 .DEFAULT_GOAL := all
 all:
diff --git a/code/common.mk b/code/common.mk
deleted file mode 100644
index 3e6cd46..0000000
--- a/code/common.mk
+++ /dev/null
@@ -1,10 +0,0 @@
-CROSS_COMPILE = riscv64-unknown-elf-
-CFLAGS = -nostdlib -fno-builtin -march=rv32g -mabi=ilp32 -g -Wall
-
-QEMU = qemu-system-riscv32
-QFLAGS = -nographic -smp 1 -machine virt -bios none
-
-GDB = gdb-multiarch
-CC = ${CROSS_COMPILE}gcc
-OBJCOPY = ${CROSS_COMPILE}objcopy
-OBJDUMP = ${CROSS_COMPILE}objdump
\ No newline at end of file
diff --git a/code/os/00-bootstrap/Makefile b/code/os/00-bootstrap/Makefile
index 92431c5..3ef9ace 100644
--- a/code/os/00-bootstrap/Makefile
+++ b/code/os/00-bootstrap/Makefile
@@ -1,4 +1,4 @@
-include ../../common.mk
+LDFLAGS = -Ttext=0x80000000
 
 SRCS_ASM = \
 	start.S \
@@ -6,41 +6,4 @@ SRCS_ASM = \
 SRCS_C = \
 	kernel.c \
 
-OBJS = $(SRCS_ASM:.S=.o)
-OBJS += $(SRCS_C:.c=.o)
-
-.DEFAULT_GOAL := all
-all: os.elf
-
-# start.o must be the first in dependency!
-os.elf: ${OBJS}
-	${CC} ${CFLAGS} -Ttext=0x80000000 -o os.elf $^
-	${OBJCOPY} -O binary os.elf os.bin
-
-%.o : %.c
-	${CC} ${CFLAGS} -c -o $@ $<
-
-%.o : %.S
-	${CC} ${CFLAGS} -c -o $@ $<
-
-run: all
-	@${QEMU} -M ? | grep virt >/dev/null || exit
-	@echo "Press Ctrl-A and then X to exit QEMU"
-	@echo "------------------------------------"
-	@${QEMU} ${QFLAGS} -kernel os.elf
-
-.PHONY : debug
-debug: all
-	@echo "Press Ctrl-C and then input 'quit' to exit GDB and QEMU"
-	@echo "-------------------------------------------------------"
-	@${QEMU} ${QFLAGS} -kernel os.elf -s -S &
-	@${GDB} os.elf -q -x ../gdbinit
-
-.PHONY : code
-code: all
-	@${OBJDUMP} -S os.elf | less
-
-.PHONY : clean
-clean:
-	rm -rf *.o *.bin *.elf
-
+include ../common.mk
diff --git a/code/os/01-helloRVOS/Makefile b/code/os/01-helloRVOS/Makefile
index b056e9a..a98b28c 100644
--- a/code/os/01-helloRVOS/Makefile
+++ b/code/os/01-helloRVOS/Makefile
@@ -1,4 +1,4 @@
-include ../../common.mk
+LDFLAGS = -Ttext=0x80000000
 
 SRCS_ASM = \
 	start.S \
@@ -7,41 +7,4 @@ SRCS_C = \
 	kernel.c \
 	uart.c \
 
-OBJS = $(SRCS_ASM:.S=.o)
-OBJS += $(SRCS_C:.c=.o)
-
-.DEFAULT_GOAL := all
-all: os.elf
-
-# start.o must be the first in dependency!
-os.elf: ${OBJS}
-	${CC} ${CFLAGS} -Ttext=0x80000000 -o os.elf $^
-	${OBJCOPY} -O binary os.elf os.bin
-
-%.o : %.c
-	${CC} ${CFLAGS} -c -o $@ $<
-
-%.o : %.S
-	${CC} ${CFLAGS} -c -o $@ $<
-
-run: all
-	@${QEMU} -M ? | grep virt >/dev/null || exit
-	@echo "Press Ctrl-A and then X to exit QEMU"
-	@echo "------------------------------------"
-	@${QEMU} ${QFLAGS} -kernel os.elf
-
-.PHONY : debug
-debug: all
-	@echo "Press Ctrl-C and then input 'quit' to exit GDB and QEMU"
-	@echo "-------------------------------------------------------"
-	@${QEMU} ${QFLAGS} -kernel os.elf -s -S &
-	@${GDB} os.elf -q -x ../gdbinit
-
-.PHONY : code
-code: all
-	@${OBJDUMP} -S os.elf | less
-
-.PHONY : clean
-clean:
-	rm -rf *.o *.bin *.elf
-
+include ../common.mk
diff --git a/code/os/02-memanagement/Makefile b/code/os/02-memanagement/Makefile
index 259b9ce..7dbfecb 100644
--- a/code/os/02-memanagement/Makefile
+++ b/code/os/02-memanagement/Makefile
@@ -1,5 +1,3 @@
-include ../../common.mk
-
 SRCS_ASM = \
 	start.S \
 	mem.S \
@@ -10,41 +8,4 @@ SRCS_C = \
 	printf.c \
 	page.c \
 
-OBJS = $(SRCS_ASM:.S=.o)
-OBJS += $(SRCS_C:.c=.o)
-
-.DEFAULT_GOAL := all
-all: os.elf
-
-# start.o must be the first in dependency!
-os.elf: ${OBJS}
-	${CC} ${CFLAGS} -T os.ld -o os.elf $^
-	${OBJCOPY} -O binary os.elf os.bin
-
-%.o : %.c
-	${CC} ${CFLAGS} -c -o $@ $<
-
-%.o : %.S
-	${CC} ${CFLAGS} -c -o $@ $<
-
-run: all
-	@${QEMU} -M ? | grep virt >/dev/null || exit
-	@echo "Press Ctrl-A and then X to exit QEMU"
-	@echo "------------------------------------"
-	@${QEMU} ${QFLAGS} -kernel os.elf
-
-.PHONY : debug
-debug: all
-	@echo "Press Ctrl-C and then input 'quit' to exit GDB and QEMU"
-	@echo "-------------------------------------------------------"
-	@${QEMU} ${QFLAGS} -kernel os.elf -s -S &
-	@${GDB} os.elf -q -x ../gdbinit
-
-.PHONY : code
-code: all
-	@${OBJDUMP} -S os.elf | less
-
-.PHONY : clean
-clean:
-	rm -rf *.o *.bin *.elf
-
+include ../common.mk
diff --git a/code/os/03-contextswitch/Makefile b/code/os/03-contextswitch/Makefile
index 4d76913..01d18cb 100644
--- a/code/os/03-contextswitch/Makefile
+++ b/code/os/03-contextswitch/Makefile
@@ -1,5 +1,3 @@
-include ../../common.mk
-
 SRCS_ASM = \
 	start.S \
 	mem.S \
@@ -12,41 +10,4 @@ SRCS_C = \
 	page.c \
 	sched.c \
 
-OBJS = $(SRCS_ASM:.S=.o)
-OBJS += $(SRCS_C:.c=.o)
-
-.DEFAULT_GOAL := all
-all: os.elf
-
-# start.o must be the first in dependency!
-os.elf: ${OBJS}
-	${CC} ${CFLAGS} -T os.ld -o os.elf $^
-	${OBJCOPY} -O binary os.elf os.bin
-
-%.o : %.c
-	${CC} ${CFLAGS} -c -o $@ $<
-
-%.o : %.S
-	${CC} ${CFLAGS} -c -o $@ $<
-
-run: all
-	@${QEMU} -M ? | grep virt >/dev/null || exit
-	@echo "Press Ctrl-A and then X to exit QEMU"
-	@echo "------------------------------------"
-	@${QEMU} ${QFLAGS} -kernel os.elf
-
-.PHONY : debug
-debug: all
-	@echo "Press Ctrl-C and then input 'quit' to exit GDB and QEMU"
-	@echo "-------------------------------------------------------"
-	@${QEMU} ${QFLAGS} -kernel os.elf -s -S &
-	@${GDB} os.elf -q -x ../gdbinit
-
-.PHONY : code
-code: all
-	@${OBJDUMP} -S os.elf | less
-
-.PHONY : clean
-clean:
-	rm -rf *.o *.bin *.elf
-
+include ../common.mk
diff --git a/code/os/04-multitask/Makefile b/code/os/04-multitask/Makefile
index fef6caf..a3e946d 100644
--- a/code/os/04-multitask/Makefile
+++ b/code/os/04-multitask/Makefile
@@ -1,5 +1,3 @@
-include ../../common.mk
-
 SRCS_ASM = \
 	start.S \
 	mem.S \
@@ -13,41 +11,4 @@ SRCS_C = \
 	sched.c \
 	user.c \
 
-OBJS = $(SRCS_ASM:.S=.o)
-OBJS += $(SRCS_C:.c=.o)
-
-.DEFAULT_GOAL := all
-all: os.elf
-
-# start.o must be the first in dependency!
-os.elf: ${OBJS}
-	${CC} ${CFLAGS} -T os.ld -o os.elf $^
-	${OBJCOPY} -O binary os.elf os.bin
-
-%.o : %.c
-	${CC} ${CFLAGS} -c -o $@ $<
-
-%.o : %.S
-	${CC} ${CFLAGS} -c -o $@ $<
-
-run: all
-	@${QEMU} -M ? | grep virt >/dev/null || exit
-	@echo "Press Ctrl-A and then X to exit QEMU"
-	@echo "------------------------------------"
-	@${QEMU} ${QFLAGS} -kernel os.elf
-
-.PHONY : debug
-debug: all
-	@echo "Press Ctrl-C and then input 'quit' to exit GDB and QEMU"
-	@echo "-------------------------------------------------------"
-	@${QEMU} ${QFLAGS} -kernel os.elf -s -S &
-	@${GDB} os.elf -q -x ../gdbinit
-
-.PHONY : code
-code: all
-	@${OBJDUMP} -S os.elf | less
-
-.PHONY : clean
-clean:
-	rm -rf *.o *.bin *.elf
-
+include ../common.mk
diff --git a/code/os/05-traps/Makefile b/code/os/05-traps/Makefile
index 1289de3..270218b 100644
--- a/code/os/05-traps/Makefile
+++ b/code/os/05-traps/Makefile
@@ -1,5 +1,3 @@
-include ../../common.mk
-
 SRCS_ASM = \
 	start.S \
 	mem.S \
@@ -14,41 +12,4 @@ SRCS_C = \
 	user.c \
 	trap.c \
 
-OBJS = $(SRCS_ASM:.S=.o)
-OBJS += $(SRCS_C:.c=.o)
-
-.DEFAULT_GOAL := all
-all: os.elf
-
-# start.o must be the first in dependency!
-os.elf: ${OBJS}
-	${CC} ${CFLAGS} -T os.ld -o os.elf $^
-	${OBJCOPY} -O binary os.elf os.bin
-
-%.o : %.c
-	${CC} ${CFLAGS} -c -o $@ $<
-
-%.o : %.S
-	${CC} ${CFLAGS} -c -o $@ $<
-
-run: all
-	@${QEMU} -M ? | grep virt >/dev/null || exit
-	@echo "Press Ctrl-A and then X to exit QEMU"
-	@echo "------------------------------------"
-	@${QEMU} ${QFLAGS} -kernel os.elf
-
-.PHONY : debug
-debug: all
-	@echo "Press Ctrl-C and then input 'quit' to exit GDB and QEMU"
-	@echo "-------------------------------------------------------"
-	@${QEMU} ${QFLAGS} -kernel os.elf -s -S &
-	@${GDB} os.elf -q -x ../gdbinit
-
-.PHONY : code
-code: all
-	@${OBJDUMP} -S os.elf | less
-
-.PHONY : clean
-clean:
-	rm -rf *.o *.bin *.elf
-
+include ../common.mk
diff --git a/code/os/06-interrupts/Makefile b/code/os/06-interrupts/Makefile
index 6c434c0..e3b6326 100644
--- a/code/os/06-interrupts/Makefile
+++ b/code/os/06-interrupts/Makefile
@@ -1,5 +1,3 @@
-include ../../common.mk
-
 SRCS_ASM = \
 	start.S \
 	mem.S \
@@ -15,41 +13,4 @@ SRCS_C = \
 	trap.c \
 	plic.c \
 
-OBJS = $(SRCS_ASM:.S=.o)
-OBJS += $(SRCS_C:.c=.o)
-
-.DEFAULT_GOAL := all
-all: os.elf
-
-# start.o must be the first in dependency!
-os.elf: ${OBJS}
-	${CC} ${CFLAGS} -T os.ld -o os.elf $^
-	${OBJCOPY} -O binary os.elf os.bin
-
-%.o : %.c
-	${CC} ${CFLAGS} -c -o $@ $<
-
-%.o : %.S
-	${CC} ${CFLAGS} -c -o $@ $<
-
-run: all
-	@${QEMU} -M ? | grep virt >/dev/null || exit
-	@echo "Press Ctrl-A and then X to exit QEMU"
-	@echo "------------------------------------"
-	@${QEMU} ${QFLAGS} -kernel os.elf
-
-.PHONY : debug
-debug: all
-	@echo "Press Ctrl-C and then input 'quit' to exit GDB and QEMU"
-	@echo "-------------------------------------------------------"
-	@${QEMU} ${QFLAGS} -kernel os.elf -s -S &
-	@${GDB} os.elf -q -x ../gdbinit
-
-.PHONY : code
-code: all
-	@${OBJDUMP} -S os.elf | less
-
-.PHONY : clean
-clean:
-	rm -rf *.o *.bin *.elf
-
+include ../common.mk
diff --git a/code/os/07-hwtimer/Makefile b/code/os/07-hwtimer/Makefile
index d1aedf9..ec933db 100644
--- a/code/os/07-hwtimer/Makefile
+++ b/code/os/07-hwtimer/Makefile
@@ -1,5 +1,3 @@
-include ../../common.mk
-
 SRCS_ASM = \
 	start.S \
 	mem.S \
@@ -16,41 +14,4 @@ SRCS_C = \
 	plic.c \
 	timer.c \
 
-OBJS = $(SRCS_ASM:.S=.o)
-OBJS += $(SRCS_C:.c=.o)
-
-.DEFAULT_GOAL := all
-all: os.elf
-
-# start.o must be the first in dependency!
-os.elf: ${OBJS}
-	${CC} ${CFLAGS} -T os.ld -o os.elf $^
-	${OBJCOPY} -O binary os.elf os.bin
-
-%.o : %.c
-	${CC} ${CFLAGS} -c -o $@ $<
-
-%.o : %.S
-	${CC} ${CFLAGS} -c -o $@ $<
-
-run: all
-	@${QEMU} -M ? | grep virt >/dev/null || exit
-	@echo "Press Ctrl-A and then X to exit QEMU"
-	@echo "------------------------------------"
-	@${QEMU} ${QFLAGS} -kernel os.elf
-
-.PHONY : debug
-debug: all
-	@echo "Press Ctrl-C and then input 'quit' to exit GDB and QEMU"
-	@echo "-------------------------------------------------------"
-	@${QEMU} ${QFLAGS} -kernel os.elf -s -S &
-	@${GDB} os.elf -q -x ../gdbinit
-
-.PHONY : code
-code: all
-	@${OBJDUMP} -S os.elf | less
-
-.PHONY : clean
-clean:
-	rm -rf *.o *.bin *.elf
-
+include ../common.mk
diff --git a/code/os/08-preemptive/Makefile b/code/os/08-preemptive/Makefile
index d1aedf9..ec933db 100644
--- a/code/os/08-preemptive/Makefile
+++ b/code/os/08-preemptive/Makefile
@@ -1,5 +1,3 @@
-include ../../common.mk
-
 SRCS_ASM = \
 	start.S \
 	mem.S \
@@ -16,41 +14,4 @@ SRCS_C = \
 	plic.c \
 	timer.c \
 
-OBJS = $(SRCS_ASM:.S=.o)
-OBJS += $(SRCS_C:.c=.o)
-
-.DEFAULT_GOAL := all
-all: os.elf
-
-# start.o must be the first in dependency!
-os.elf: ${OBJS}
-	${CC} ${CFLAGS} -T os.ld -o os.elf $^
-	${OBJCOPY} -O binary os.elf os.bin
-
-%.o : %.c
-	${CC} ${CFLAGS} -c -o $@ $<
-
-%.o : %.S
-	${CC} ${CFLAGS} -c -o $@ $<
-
-run: all
-	@${QEMU} -M ? | grep virt >/dev/null || exit
-	@echo "Press Ctrl-A and then X to exit QEMU"
-	@echo "------------------------------------"
-	@${QEMU} ${QFLAGS} -kernel os.elf
-
-.PHONY : debug
-debug: all
-	@echo "Press Ctrl-C and then input 'quit' to exit GDB and QEMU"
-	@echo "-------------------------------------------------------"
-	@${QEMU} ${QFLAGS} -kernel os.elf -s -S &
-	@${GDB} os.elf -q -x ../gdbinit
-
-.PHONY : code
-code: all
-	@${OBJDUMP} -S os.elf | less
-
-.PHONY : clean
-clean:
-	rm -rf *.o *.bin *.elf
-
+include ../common.mk
diff --git a/code/os/09-lock/Makefile b/code/os/09-lock/Makefile
index b5d872a..4dc0582 100644
--- a/code/os/09-lock/Makefile
+++ b/code/os/09-lock/Makefile
@@ -1,5 +1,3 @@
-include ../../common.mk
-
 SRCS_ASM = \
 	start.S \
 	mem.S \
@@ -17,41 +15,4 @@ SRCS_C = \
 	timer.c \
 	lock.c \
 
-OBJS = $(SRCS_ASM:.S=.o)
-OBJS += $(SRCS_C:.c=.o)
-
-.DEFAULT_GOAL := all
-all: os.elf
-
-# start.o must be the first in dependency!
-os.elf: ${OBJS}
-	${CC} ${CFLAGS} -T os.ld -o os.elf $^
-	${OBJCOPY} -O binary os.elf os.bin
-
-%.o : %.c
-	${CC} ${CFLAGS} -c -o $@ $<
-
-%.o : %.S
-	${CC} ${CFLAGS} -c -o $@ $<
-
-run: all
-	@${QEMU} -M ? | grep virt >/dev/null || exit
-	@echo "Press Ctrl-A and then X to exit QEMU"
-	@echo "------------------------------------"
-	@${QEMU} ${QFLAGS} -kernel os.elf
-
-.PHONY : debug
-debug: all
-	@echo "Press Ctrl-C and then input 'quit' to exit GDB and QEMU"
-	@echo "-------------------------------------------------------"
-	@${QEMU} ${QFLAGS} -kernel os.elf -s -S &
-	@${GDB} os.elf -q -x ../gdbinit
-
-.PHONY : code
-code: all
-	@${OBJDUMP} -S os.elf | less
-
-.PHONY : clean
-clean:
-	rm -rf *.o *.bin *.elf
-
+include ../common.mk
diff --git a/code/os/10-swtimer/Makefile b/code/os/10-swtimer/Makefile
index b5d872a..4dc0582 100644
--- a/code/os/10-swtimer/Makefile
+++ b/code/os/10-swtimer/Makefile
@@ -1,5 +1,3 @@
-include ../../common.mk
-
 SRCS_ASM = \
 	start.S \
 	mem.S \
@@ -17,41 +15,4 @@ SRCS_C = \
 	timer.c \
 	lock.c \
 
-OBJS = $(SRCS_ASM:.S=.o)
-OBJS += $(SRCS_C:.c=.o)
-
-.DEFAULT_GOAL := all
-all: os.elf
-
-# start.o must be the first in dependency!
-os.elf: ${OBJS}
-	${CC} ${CFLAGS} -T os.ld -o os.elf $^
-	${OBJCOPY} -O binary os.elf os.bin
-
-%.o : %.c
-	${CC} ${CFLAGS} -c -o $@ $<
-
-%.o : %.S
-	${CC} ${CFLAGS} -c -o $@ $<
-
-run: all
-	@${QEMU} -M ? | grep virt >/dev/null || exit
-	@echo "Press Ctrl-A and then X to exit QEMU"
-	@echo "------------------------------------"
-	@${QEMU} ${QFLAGS} -kernel os.elf
-
-.PHONY : debug
-debug: all
-	@echo "Press Ctrl-C and then input 'quit' to exit GDB and QEMU"
-	@echo "-------------------------------------------------------"
-	@${QEMU} ${QFLAGS} -kernel os.elf -s -S &
-	@${GDB} os.elf -q -x ../gdbinit
-
-.PHONY : code
-code: all
-	@${OBJDUMP} -S os.elf | less
-
-.PHONY : clean
-clean:
-	rm -rf *.o *.bin *.elf
-
+include ../common.mk
diff --git a/code/os/11-syscall/Makefile b/code/os/11-syscall/Makefile
index b933edc..face96f 100644
--- a/code/os/11-syscall/Makefile
+++ b/code/os/11-syscall/Makefile
@@ -1,5 +1,3 @@
-include ../../common.mk
-
 SYSCALL = y
 
 ifeq (${SYSCALL}, y)
@@ -25,41 +23,4 @@ SRCS_C = \
 	lock.c \
 	syscall.c
 
-OBJS = $(SRCS_ASM:.S=.o)
-OBJS += $(SRCS_C:.c=.o)
-
-.DEFAULT_GOAL := all
-all: os.elf
-
-# start.o must be the first in dependency!
-os.elf: ${OBJS}
-	${CC} ${CFLAGS} -T os.ld -o os.elf $^
-	${OBJCOPY} -O binary os.elf os.bin
-
-%.o : %.c
-	${CC} ${CFLAGS} -c -o $@ $<
-
-%.o : %.S
-	${CC} ${CFLAGS} -c -o $@ $<
-
-run: all
-	@${QEMU} -M ? | grep virt >/dev/null || exit
-	@echo "Press Ctrl-A and then X to exit QEMU"
-	@echo "------------------------------------"
-	@${QEMU} ${QFLAGS} -kernel os.elf
-
-.PHONY : debug
-debug: all
-	@echo "Press Ctrl-C and then input 'quit' to exit GDB and QEMU"
-	@echo "-------------------------------------------------------"
-	@${QEMU} ${QFLAGS} -kernel os.elf -s -S &
-	@${GDB} os.elf -q -x ../gdbinit
-
-.PHONY : code
-code: all
-	@${OBJDUMP} -S os.elf | less
-
-.PHONY : clean
-clean:
-	rm -rf *.o *.bin *.elf
-
+include ../common.mk
diff --git a/code/os/common.mk b/code/os/common.mk
new file mode 100644
index 0000000..ddf2518
--- /dev/null
+++ b/code/os/common.mk
@@ -0,0 +1,53 @@
+# This file will be included by the Makefile of each project.
+
+CROSS_COMPILE = riscv64-unknown-elf-
+CFLAGS += -nostdlib -fno-builtin -march=rv32g -mabi=ilp32 -g -Wall
+LDFLAGS ?= -T os.ld
+
+QEMU = qemu-system-riscv32
+QFLAGS = -nographic -smp 1 -machine virt -bios none
+
+GDB = gdb-multiarch
+CC = ${CROSS_COMPILE}gcc
+OBJCOPY = ${CROSS_COMPILE}objcopy
+OBJDUMP = ${CROSS_COMPILE}objdump
+
+# SRCS_ASM & SRCS_C are defined in the Makefile of each project.
+OBJS = $(SRCS_ASM:.S=.o)
+OBJS += $(SRCS_C:.c=.o)
+
+.DEFAULT_GOAL := all
+all: os.elf
+
+# start.o must be the first in dependency!
+os.elf: ${OBJS}
+	${CC} ${CFLAGS} ${LDFLAGS} -o os.elf $^
+	${OBJCOPY} -O binary os.elf os.bin
+
+%.o : %.c
+	${CC} ${CFLAGS} -c -o $@ $<
+
+%.o : %.S
+	${CC} ${CFLAGS} -c -o $@ $<
+
+run: all
+	@${QEMU} -M ? | grep virt >/dev/null || exit
+	@echo "Press Ctrl-A and then X to exit QEMU"
+	@echo "------------------------------------"
+	@${QEMU} ${QFLAGS} -kernel os.elf
+
+.PHONY : debug
+debug: all
+	@echo "Press Ctrl-C and then input 'quit' to exit GDB and QEMU"
+	@echo "-------------------------------------------------------"
+	@${QEMU} ${QFLAGS} -kernel os.elf -s -S &
+	@${GDB} os.elf -q -x ../gdbinit
+
+.PHONY : code
+code: all
+	@${OBJDUMP} -S os.elf | less
+
+.PHONY : clean
+clean:
+	rm -rf *.o *.bin *.elf
+