diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 944f08c2..1be6baa5 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -58,4 +58,4 @@ jobs:
     - name: Download prebuilt user image
       run: cd user && make sfsimg arch=${{ matrix.arch }} prebuilt=1 && cd ..
     - name: Build kernel
-      run: cd kernel && make build arch=${{ matrix.arch }} && cd ..
+      run: cd kernel && make build ARCH=${{ matrix.arch }} && cd ..
diff --git a/README.md b/README.md
index e6e9211d..736fbb53 100644
--- a/README.md
+++ b/README.md
@@ -20,7 +20,6 @@ Supported architectures and boards:
 ### Environment
 
 * [Rust](https://www.rust-lang.org) toolchain
-* Cargo tools: [cargo-binutils](https://github.com/rust-embedded/cargo-binutils)
 * [QEMU](https://www.qemu.org) >= 4.1.0
 * [musl-based GCC toolchains](https://musl.cc/) (only for building [user programs](https://github.com/rcore-os/rcore-user))
 
@@ -41,11 +40,13 @@ $ docker run -it -v $PWD:$PWD -w $PWD wangrunji0408/rcore
 ```bash
 $ git clone https://github.com/rcore-os/rCore.git --recursive
 $ cd rCore/user
-$ make sfsimg prebuilt=1 arch={riscv32,riscv64,x86_64,aarch64,mipsel}
+$ make sfsimg prebuilt=1 arch=x86_64
 $ cd ../kernel
-$ make run arch={riscv32,riscv64,x86_64,aarch64,mipsel}
+$ make run ARCH=x86_64 LOG=info
 ```
 
+See [Makefile](kernel/Makefile) for more usages.
+
 ## Maintainers
 
 | Module | Maintainer            |
diff --git a/kernel/Cargo.toml b/kernel/Cargo.toml
index cda68c9e..7c9475bd 100644
--- a/kernel/Cargo.toml
+++ b/kernel/Cargo.toml
@@ -20,6 +20,7 @@ authors = [
 
 [features]
 default = []
+board_qemu = []
 board_u540 = ["link_user"]
 board_k210 = ["link_user"]
 board_rocket_chip = ["link_user"]
diff --git a/kernel/Makefile b/kernel/Makefile
index 0b17db63..3513f3ff 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -11,37 +11,37 @@
 #   make clean                  Clean
 #
 # Options:
-#   arch    = x86_64 | riscv32 | riscv64 | aarch64 | mipsel
-#   d    = int | in_asm | ...   QEMU debug info
-#   mode = debug | release
+#   ARCH = x86_64 | riscv32 | riscv64 | aarch64 | mipsel
+#   D    = int | in_asm | ...   QEMU debug info
+#   MODE = debug | release
 #   LOG  = off | error | warn | info | debug | trace
-#   USER_IMG = <sfsimg>          image path of user programs
-#   smp     = 1 | 2 | ...        SMP core number
-#   graphic = on | off | console Enable/disable qemu graphical output, or print console to graphic output
-#   board   = none               Running on QEMU
-#         | pc                   Only available on x86_64, run on real pc
-#         | u540                 Only available on riscv64, run on HiFive U540, use Sv39
-#         | k210                 Only available on riscv64, run on K210, use Sv39
-#         | rocket_chip          Only available on riscv64, run on Rocket Chip, use Sv39
-#         | raspi3               Only available on aarch64, run on Raspberry Pi 3 Model B/B+
-#   net = on | off               Only available on x86_64, enable NIC
-#   pci_passthru = 0000:00:00.1  Only available on x86_64, passthrough the specified PCI device
-#   init = /bin/ls               Only available on riscv64, run specified program instead of user shell
-#   extra_nic = on | off         Only available on x86_64, add an additional e1000 nic
-# . extra_features = profile | ... Add additional features
+#   USER_IMG = <sfsimg>         Image path of user programs
+#   SMP  = 1 | 2 | ...          SMP core number
+#   GRAPHIC = on | off | console Enable/disable qemu graphical output, or print console to graphic output
+#   BOARD = qemu                Run on QEMU
+#         | pc                  [ x86_64 only] Run on real pc
+#         | u540                [riscv64 only] Run on HiFive U540, use Sv39
+#         | k210                [riscv64 only] Run on K210, use Sv39
+#         | rocket_chip         [riscv64 only] Run on Rocket Chip, use Sv39
+#         | raspi3              [aarch64 only] Run on Raspberry Pi 3 Model B/B+
+#   NET = on | off              [ x86_64 only] Enable NIC
+#   PCI_PASSTHRU = 0000:00:00.1 [ x86_64 only] Passthrough the specified PCI device
+#   INIT = /bin/ls              [riscv64 only] Run specified program instead of user shell
+#   EXTRA_NIC = on | off        [ x86_64 only] Add an additional e1000 nic
+#   FEATURES = profile | ...    Add additional features
 
-arch ?= riscv64
-mode ?= release
+ARCH ?= riscv64
+MODE ?= release
 LOG  ?=
-graphic ?= off
-smp  ?= 4
-pci_passthru ?=
-init ?=
-extra_nic ?= off
+GRAPHIC ?= off
+SMP  ?= 4
+PCI_PASSTHRU ?=
+INIT ?=
+EXTRA_NIC ?= off
 
-qemu := qemu-system-$(arch)
-target := $(arch)
-build_path := target/$(target)/$(mode)
+qemu := qemu-system-$(ARCH)
+target := $(ARCH)
+build_path := target/$(target)/$(MODE)
 kernel := $(build_path)/rcore
 kernel_img := $(build_path)/kernel.img
 ESP := $(build_path)/esp
@@ -51,55 +51,49 @@ user_dir := ../user
 
 ### export environments ###
 
-export USER_IMG = $(user_dir)/build/$(arch).img
-export USER_QCOW2 = $(user_dir)/build/$(arch).qcow2
+export USER_IMG = $(user_dir)/build/$(ARCH).img
+export USER_QCOW2 = $(user_dir)/build/$(ARCH).qcow2
 
-ifeq ($(arch), aarch64)
-board ?= raspi3
-else ifeq ($(arch), mipsel)
-board ?= malta
+ifeq ($(ARCH), aarch64)
+BOARD ?= raspi3
+else ifeq ($(ARCH), mipsel)
+BOARD ?= malta
 else
-board ?= none
+BOARD ?= qemu
 endif
 
 # currently only mipsel architecture and rocket-chip need DTB linked to the kernel
-ifeq ($(arch), mipsel)
-dtb := src/arch/$(arch)/board/$(board)/device.dtb
+ifeq ($(ARCH), mipsel)
+DTB := src/arch/$(ARCH)/board/$(BOARD)/device.dtb
 endif
-ifeq ($(board), rocket_chip)
-dtb := src/arch/riscv/board/$(board)/device.dtb
+ifeq ($(BOARD), rocket_chip)
+DTB := src/arch/riscv/board/$(BOARD)/device.dtb
 endif
 
 # mipssim does not support SMP
-ifeq ($(board), mipssim)
-smp := 1
+ifeq ($(BOARD), mipssim)
+SMP := 1
 endif
 
-export ARCH = $(arch)
-export BOARD = $(board)
-export SMP = $(smp)
-export DTB = $(dtb)
-
-
 ### qemu options ###
 qemu_opts := \
-	-smp cores=$(smp)
+	-smp cores=$(SMP)
 qemu_net_opts :=
 
-ifeq ($(arch), x86_64)
+ifeq ($(ARCH), x86_64)
 qemu_opts += \
 	-bios $(OVMF) \
 	-drive format=raw,file=fat:rw:$(ESP) \
 	-serial mon:stdio \
 	-m 4G \
 	-device isa-debug-exit
-ifeq ($(board), none)
+ifeq ($(BOARD), qemu)
 qemu_opts += \
 	-drive format=qcow2,file=$(USER_QCOW2),media=disk,cache=writeback,id=sfsimg,if=none \
 	-device ahci,id=ahci0 \
 	-device ide-drive,drive=sfsimg,bus=ahci0.0
 endif
-ifeq ($(pci_passthru), )
+ifeq ($(PCI_PASSTHRU), )
 qemu_net_opts += \
 	-netdev type=tap,id=net0,script=no,downscript=no \
 	-device e1000e,netdev=net0
@@ -107,17 +101,17 @@ else
 qemu_opts += \
 	-machine accel=kvm
 qemu_net_opts += \
-	-device vfio-pci,host=$(pci_passthru)
+	-device vfio-pci,host=$(PCI_PASSTHRU)
 qemu_ui_opts += \
 	-vga std
 endif
-ifeq ($(extra_nic), on)
+ifeq ($(EXTRA_NIC), on)
 qemu_net_opts += \
 	-netdev type=tap,id=net1,script=no,downscript=no \
 	-device e1000e,netdev=net1
 endif
 
-else ifeq ($(arch), riscv32)
+else ifeq ($(ARCH), riscv32)
 qemu_opts += \
 	-machine virt \
 	-serial mon:stdio \
@@ -131,8 +125,8 @@ qemu_net_opts += \
 	-netdev type=tap,id=net0,script=no,downscript=no \
 	-device virtio-net-device,netdev=net0
 
-else ifeq ($(arch), riscv64)
-ifeq ($(board), u540)
+else ifeq ($(ARCH), riscv64)
+ifeq ($(BOARD), u540)
 qemu_opts += \
 	-machine virt \
 	-serial mon:stdio \
@@ -153,79 +147,78 @@ qemu_net_opts += \
 	-netdev type=tap,id=net0,script=no,downscript=no \
 	-device virtio-net-device,netdev=net0
 
-else ifeq ($(arch), aarch64)
+else ifeq ($(ARCH), aarch64)
 qemu_opts += \
-	-machine $(board) \
+	-machine $(BOARD) \
 	-smp 4 \
 	-serial null -serial mon:stdio \
 	-kernel $(kernel_img) \
 	-drive file=$(USER_QCOW2),format=qcow2,id=sfs
 
-else ifeq ($(arch), mipsel)
-ifeq ($(board), malta)
+else ifeq ($(ARCH), mipsel)
+ifeq ($(BOARD), malta)
 qemu_opts += \
-	-machine $(board) -device VGA \
+	-machine $(BOARD) -device VGA \
 	-serial null -serial null -serial mon:stdio \
 	-kernel $(kernel_img)
 endif
-ifeq ($(board), mipssim)
+ifeq ($(BOARD), mipssim)
 qemu_opts += \
-	-machine $(board) \
+	-machine $(BOARD) \
 	-serial mon:stdio \
 	-kernel $(kernel_img)
 endif
 endif
 
-ifdef d
-qemu_opts += -d $(d)
+ifdef D
+qemu_opts += -d $(D)
 endif
 
-ifeq ($(graphic), off)
+ifeq ($(GRAPHIC), off)
 qemu_opts += -nographic
 endif
 
-ifeq ($(net), on)
+ifeq ($(NET), on)
 qemu_opts += $(qemu_net_opts)
 qemu := sudo $(qemu)
 endif
 
 ### build args ###
-ifeq ($(graphic), off)
-features += nographic
+ifeq ($(GRAPHIC), off)
+FEATURES += nographic
 endif
 
-ifeq ($(graphic), console)
-features += consolegraphic
+ifeq ($(GRAPHIC), console)
+FEATURES += consolegraphic
 endif
 
-ifneq ($(init), )
-features += run_cmdline
+ifneq ($(INIT), )
+FEATURES += run_cmdline
 endif
 
-ifneq ($(board), none)
-features += board_$(board)
-endif
+FEATURES += board_$(BOARD)
 
-features += $(extra_features)
+build_args := \
+	-Z build-std=core,alloc \
+	--target targets/$(target).json \
+	--features "$(FEATURES)"
 
-build_args := -Z build-std=core,alloc --target targets/$(target).json --features "$(features)"
-
-ifeq ($(mode), release)
+ifeq ($(MODE), release)
 build_args += --release
 endif
 
 ### prefix ###
-ifeq ($(arch), x86_64)
-ifeq ($(uname), Darwin)
+ifeq ($(ARCH), x86_64)
+ifeq ($(shell uname), Darwin)
 prefix := x86_64-linux-musl-
 endif
-else ifeq ($(arch), riscv32)
+else ifeq ($(ARCH), riscv32)
 prefix := riscv64-linux-musl-
-else ifeq ($(arch), riscv64)
+else ifeq ($(ARCH), riscv64)
 prefix := riscv64-linux-musl-
-else ifeq ($(arch), mipsel)
+else ifeq ($(ARCH), mipsel)
 prefix ?= mipsel-linux-musln32-
-else ifeq ($(arch), aarch64)
+else ifeq ($(ARCH), aarch64)
 prefix ?= aarch64-linux-musl-
 endif
 
@@ -256,7 +249,7 @@ justrun:
 
 justtest:
 	# unavailable now
-	@#$(qemu) $(filter-out -serial mon:stdio, $(qemu_opts)) --append $(init) -serial file:../tests/stdout -monitor null
+	@#$(qemu) $(filter-out -serial mon:stdio, $(qemu_opts)) --append $(INIT) -serial file:../tests/stdout -monitor null
 
 debug: $(kernel) $(kernel_img)
 	@$(qemu) $(qemu_opts) -s -S &
@@ -284,31 +277,31 @@ sym:
 ### bootloader and kernel image ###
 
 bootloader: $(kernel)
-ifeq ($(arch), x86_64)
+ifeq ($(ARCH), x86_64)
 	@cd ../rboot && make build
 endif
 
 $(kernel_img): kernel bootloader
-ifeq ($(arch), x86_64)
+ifeq ($(ARCH), x86_64)
 	@mkdir -p $(ESP)/EFI/rCore $(ESP)/EFI/Boot
 	@cp ../rboot/target/x86_64-unknown-uefi/release/rboot.efi $(ESP)/EFI/Boot/BootX64.efi
 	@cp ../rboot/rboot.conf $(ESP)/EFI/Boot/rboot.conf
 	@cp $(kernel) $(ESP)/EFI/rCore/kernel.elf
-else ifeq ($(arch), $(filter $(arch), riscv32 riscv64))
+else ifeq ($(ARCH), $(filter $(ARCH), riscv32 riscv64))
 	@$(objcopy) $(kernel) --strip-all -O binary $@
-else ifeq ($(arch), aarch64)
+else ifeq ($(ARCH), aarch64)
 	@$(objcopy) $(kernel) --strip-all -O binary $@
-else ifeq ($(arch), mipsel)
+else ifeq ($(ARCH), mipsel)
 # qemu-system-mipsel accepts ELF file only, so objcopy is not needed
 	@$(strip) $(kernel) -o $@
 endif
 
-kernel: $(dtb)
-	@echo Building $(arch) kernel
-ifeq ($(arch), $(filter $(arch), riscv32 riscv64))
-ifeq ($(board), k210)
+kernel: $(DTB)
+	@echo Building $(ARCH) kernel
+ifeq ($(ARCH), $(filter $(ARCH), riscv32 riscv64))
+ifeq ($(BOARD), k210)
 	@cp src/arch/riscv/board/k210/linker.ld src/arch/riscv/boot/linker64.ld
-else ifeq ($(board), rocket_chip)
+else ifeq ($(BOARD), rocket_chip)
 	@cp src/arch/riscv/board/rocket_chip/linker.ld src/arch/riscv/boot/linker64.ld
 else
 	@cp src/arch/riscv/board/u540/linker.ld src/arch/riscv/boot/linker64.ld
@@ -316,11 +309,11 @@ endif
 	@-patch -p0 -N -b \
 		$(sysroot)/lib/rustlib/src/rust/src/libcore/sync/atomic.rs \
 		src/arch/riscv/atomic.patch
-else ifeq ($(arch), mipsel)
+else ifeq ($(ARCH), mipsel)
 	@for file in context entry trap ; do \
-	    $(hostcc) -Dboard_$(board) -E src/arch/$(arch)/boot/$${file}.S -o src/arch/$(arch)/boot/$${file}.gen.s ; \
+	    $(hostcc) -Dboard_$(BOARD) -E src/arch/$(ARCH)/boot/$${file}.S -o src/arch/$(ARCH)/boot/$${file}.gen.s ; \
 	done
-	$(hostcc) -Dboard_$(board) -E src/arch/$(arch)/boot/linker.ld.S -o src/arch/$(arch)/boot/linker.ld
+	$(hostcc) -Dboard_$(BOARD) -E src/arch/$(ARCH)/boot/linker.ld.S -o src/arch/$(ARCH)/boot/linker.ld
 endif
 	@cargo build $(build_args)
 
@@ -331,7 +324,7 @@ sfsimg:
 
 
 ### install ###
-ifeq ($(board), raspi3)
+ifeq ($(BOARD), raspi3)
 sd_card ?=
 
 ifeq ($(shell uname), Darwin)
@@ -349,7 +342,7 @@ endif
 
 endif
 
-ifeq ($(board), u540)
+ifeq ($(BOARD), u540)
 .PHONY:
 install: $(kernel_img)
 	@$(objcopy) -S -O binary ../tools/opensbi/fu540.elf $(build_path)/bin
@@ -357,7 +350,7 @@ install: $(kernel_img)
 	@../tools/u540/mkimg.sh $(build_path)/bin $(build_path)/u540.img
 endif
 
-ifeq ($(board), k210)
+ifeq ($(BOARD), k210)
 .PHONY:
 install: $(kernel_img)
 	@$(objcopy) -S -O binary ../tools/opensbi/k210.elf $(build_path)/k210.img
@@ -367,4 +360,4 @@ endif
 
 .PHONY:
 addr2line:
-	@python3.7 ../tools/addr2line.py $(prefix)addr2line $(arch) $(mode)
+	@python3.7 ../tools/addr2line.py $(prefix)addr2line $(ARCH) $(MODE)
diff --git a/kernel/build.rs b/kernel/build.rs
index 6c5fb419..6efd5f8f 100644
--- a/kernel/build.rs
+++ b/kernel/build.rs
@@ -10,7 +10,6 @@ fn main() {
     println!("cargo:rerun-if-env-changed=USER_IMG");
 
     let arch: String = std::env::var("ARCH").unwrap();
-    let _board: String = std::env::var("BOARD").unwrap();
     if let Ok(user_img) = std::env::var("USER_IMG") {
         println!("cargo:rerun-if-changed={}", user_img);
     }