diff --git a/kernel/Makefile b/kernel/Makefile
index 69c9fc1..b625918 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -98,133 +98,134 @@ export DTB = $(dtb)
 qemu_opts := \
 	-smp cores=$(smp)
 qemu_net_opts :=
-qemu_ui_opts := 
+qemu_ui_opts :=
 
 ifeq ($(arch), x86_64)
-qemu_opts += \
-	-drive format=raw,file=$(bootimage) \
-	-serial mon:stdio \
-	-m 4G \
-	-device isa-debug-exit
-ifeq ($(board), none)
-qemu_opts += \
-	-drive format=qcow2,file=$(SFSIMG),media=disk,cache=writeback,id=sfsimg,if=none \
-	-device ahci,id=ahci0 \
-	-device ide-drive,drive=sfsimg,bus=ahci0.0
-endif
-ifeq ($(pci_passthru), )
-qemu_net_opts += \
-	-netdev type=tap,id=net0,script=no,downscript=no \
-	-device e1000e,netdev=net0
-else
-qemu_opts += \
-	-machine accel=kvm
-qemu_net_opts += \
-	-device vfio-pci,host=$(pci_passthru)
-qemu_ui_opts += \
-	-vga std
-endif
-ifeq ($(extra_nic), on)
-qemu_net_opts += \
-	-netdev type=tap,id=net1,script=no,downscript=no \
-	-device e1000e,netdev=net1
-endif
+	qemu_opts += \
+		-drive format=raw,file=$(bootimage) \
+		-serial mon:stdio \
+		-m 4G \
+		-device isa-debug-exit
+	ifeq ($(board), none)
+		qemu_opts += \
+			-drive format=qcow2,file=$(SFSIMG),media=disk,cache=writeback,id=sfsimg,if=none \
+			-device ahci,id=ahci0 \
+			-device ide-drive,drive=sfsimg,bus=ahci0.0
+	endif
+
+	ifeq ($(pci_passthru), )
+		qemu_net_opts += \
+			-netdev type=tap,id=net0,script=no,downscript=no \
+			-device e1000e,netdev=net0
+	else
+		qemu_opts += \
+			-machine accel=kvm
+		qemu_net_opts += \
+			-device vfio-pci,host=$(pci_passthru)
+		qemu_ui_opts += \
+			-vga std
+	endif
+
+	ifeq ($(extra_nic), on)
+		qemu_net_opts += \
+			-netdev type=tap,id=net1,script=no,downscript=no \
+			-device e1000e,netdev=net1
+	endif
 
 else ifeq ($(arch), riscv32)
-qemu_opts += \
-	-machine virt \
-	-serial mon:stdio \
-	-kernel ../tools/opensbi/virt_rv32.elf \
-	-device loader,addr=0x80400000,file=$(kernel_img) \
-	-drive file=$(SFSIMG),format=qcow2,id=sfs \
-	-device virtio-blk-device,drive=sfs
-qemu_net_opts += \
-	-netdev type=tap,id=net0,script=no,downscript=no \
-	-device virtio-net-device,netdev=net0
-qemu_ui_opts += \
-	-device virtio-gpu-device \
-	-device virtio-mouse-device
+	qemu_opts += \
+		-machine virt \
+		-serial mon:stdio \
+		-kernel ../tools/opensbi/virt_rv32.elf \
+		-device loader,addr=0x80400000,file=$(kernel_img) \
+		-drive file=$(SFSIMG),format=qcow2,id=sfs \
+		-device virtio-blk-device,drive=sfs
+	qemu_net_opts += \
+		-netdev type=tap,id=net0,script=no,downscript=no \
+		-device virtio-net-device,netdev=net0
+	qemu_ui_opts += \
+		-device virtio-gpu-device \
+		-device virtio-mouse-device
 
 else ifeq ($(arch), riscv64)
-ifeq ($(board), u540)
-qemu_opts += \
-	-machine virt \
-	-serial mon:stdio \
-	-kernel ../tools/opensbi/fu540.elf \
-	-device loader,addr=0x80200000,file=$(kernel_img)
-else
-qemu_opts += \
-	-machine virt \
-	-serial mon:stdio \
-	-kernel ../tools/opensbi/virt_rv64.elf \
-	-device loader,addr=0x80200000,file=$(kernel_img) \
-	-drive file=$(SFSIMG),format=qcow2,id=sfs \
-	-device virtio-blk-device,drive=sfs
-endif
-qemu_net_opts += \
-	-netdev type=tap,id=net0,script=no,downscript=no \
-	-device virtio-net-device,netdev=net0
-qemu_ui_opts += \
-	-device virtio-gpu-device \
-	-device virtio-mouse-device
-
+	ifeq ($(board), u540)
+		qemu_opts += \
+			-machine virt \
+			-serial mon:stdio \
+			-kernel ../tools/opensbi/fu540.elf \
+			-device loader,addr=0x80200000,file=$(kernel_img)
+	else
+		qemu_opts += \
+			-machine virt \
+			-serial mon:stdio \
+			-kernel ../tools/opensbi/virt_rv64.elf \
+			-device loader,addr=0x80200000,file=$(kernel_img) \
+			-drive file=$(SFSIMG),format=qcow2,id=sfs \
+			-device virtio-blk-device,drive=sfs
+	endif
+
+	qemu_net_opts += \
+		-netdev type=tap,id=net0,script=no,downscript=no \
+		-device virtio-net-device,netdev=net0
+	qemu_ui_opts += \
+		-device virtio-gpu-device \
+		-device virtio-mouse-device
 else ifeq ($(arch), aarch64)
-qemu_opts += \
-	-machine $(board) \
-	-serial null -serial mon:stdio \
-	-kernel $(kernel_img)
-ifneq ($(u_boot), )
-qemu_opts += \
-	-sd $(bootloader)
-endif
-
+	qemu_opts += \
+		-machine $(board) \
+		-serial null -serial mon:stdio \
+		-kernel $(kernel_img)
+	ifneq ($(u_boot), )
+		qemu_opts += \
+			-sd $(bootloader)
+	endif
 else ifeq ($(arch), mipsel)
-ifeq ($(board), malta)
-qemu_opts += \
-	-machine $(board) -device VGA \
-	-serial null -serial null -serial mon:stdio \
-	-kernel $(kernel_img)
-endif
-ifeq ($(board), mipssim)
-qemu_opts += \
-	-machine $(board) \
-	-serial mon:stdio \
-	-kernel $(kernel_img)
-endif
+	ifeq ($(board), malta)
+		qemu_opts += \
+			-machine $(board) -device VGA \
+			-serial null -serial null -serial mon:stdio \
+			-kernel $(kernel_img)
+	endif
+	ifeq ($(board), mipssim)
+		qemu_opts += \
+			-machine $(board) \
+			-serial mon:stdio \
+			-kernel $(kernel_img)
+	endif
 endif
 
 ifdef d
-qemu_opts += -d $(d)
+	qemu_opts += -d $(d)
 endif
 
 ifeq ($(graphic), off)
-qemu_opts += -nographic
+	qemu_opts += -nographic
 endif
 
 ### build args ###
 ifeq ($(graphic), off)
-features += nographic
+	features += nographic
 endif
 
 ifeq ($(graphic), console)
-features += consolegraphic
+	features += consolegraphic
 endif
 
 ifneq ($(init), )
-features += run_cmdline
+	features += run_cmdline
 endif
 
 ifeq ($(board), raspi3)
-# qemu only has generic timer
-# TODO: configure system/generic timer automatically
-raspi3_timer ?= generic
-ifeq ($(raspi3_timer), generic)
-features += raspi3_use_generic_timer
-endif
+	# qemu only has generic timer
+	# TODO: configure system/generic timer automatically
+	raspi3_timer ?= generic
+	ifeq ($(raspi3_timer), generic)
+		features += raspi3_use_generic_timer
+	endif
 endif
 
 ifneq ($(board), none)
-features += board_$(board)
+	features += board_$(board)
 endif
 
 features += $(extra_features)
@@ -232,25 +233,25 @@ features += $(extra_features)
 build_args := --target targets/$(target).json --features "$(features)"
 
 ifeq ($(mode), release)
-build_args += --release
+	build_args += --release
 endif
 
 ### prefix ###
 ifeq ($(arch), x86_64)
-ifeq ($(uname), Darwin)
-prefix := x86_64-elf-
-endif
+	ifeq ($(uname), Darwin)
+		prefix := x86_64-elf-
+	endif
 else ifeq ($(arch), riscv32)
-prefix := riscv64-unknown-elf-
+	prefix := riscv64-unknown-elf-
 else ifeq ($(arch), riscv64)
-prefix := riscv64-unknown-elf-
+	prefix := riscv64-unknown-elf-
 else ifeq ($(arch), mipsel)
-prefix ?= mipsel-linux-musln32-
+	prefix ?= mipsel-linux-musln32-
 else ifeq ($(arch), aarch64)
-prefix ?= aarch64-none-elf-
-ifeq (,$(shell which $(prefix)ld))
-	prefix := aarch64-elf-
-endif
+	prefix ?= aarch64-none-elf-
+	ifeq (,$(shell which $(prefix)ld))
+		prefix := aarch64-elf-
+	endif
 endif
 
 gdb := $(prefix)gdb
@@ -374,9 +375,9 @@ ifeq ($(board), raspi3)
 sd_card ?=
 
 ifeq ($(shell uname), Darwin)
-sd_card := /Volumes/boot
+	sd_card := /Volumes/boot
 else ifeq ($(shell uname), Linux)
-sd_card := /media/$(shell whoami)/boot
+	sd_card := /media/$(shell whoami)/boot
 endif
 
 ifdef sd_card