diff --git a/kernel/Makefile b/kernel/Makefile
index 9ba6c2c..faff60a 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -42,17 +42,11 @@ build_path := target/$(target)/$(mode)
 kernel := $(build_path)/rcore
 kernel_img := $(build_path)/kernel.img
 bootimage := $(build_path)/bootimage.bin
-dtb := src/arch/$(arch)/boot/dts/$(board).dtb
 bootloader_dir = ../bootloader
 bootloader := $(bootloader_dir)/target/$(target)/$(mode)/rcore-bootloader
 bbl_path := $(PWD)/../riscv-pk
 user_dir := ../user
 
-ifeq ($(arch), aarch64)
-board := raspi3
-
-ifeq ($(arch), mipsel)
-board := malta
 
 ### export environments ###
 export ARCH = $(arch)
@@ -60,9 +54,17 @@ export BOARD = $(board)
 export SMP = $(smp)
 export DTB = $(dtb)
 export SFSIMG = $(user_dir)/build/$(arch).qcow2
+
+ifeq ($(arch), aarch64)
+board := raspi3
 export SFSIMG = $(user_dir)/build/$(arch).img
+else ifeq ($(arch), mipsel)
+board := malta
 endif
 
+dtb := src/arch/$(arch)/boot/dts/$(board).dtb
+
+
 ### qemu options ###
 qemu_opts := \
 	-smp cores=$(smp)
@@ -108,7 +110,6 @@ qemu_opts += \
 	-machine $(board) \
 	-serial null -serial mon:stdio \
 	-kernel $(kernel_img)
-endif
 
 else ifeq ($(arch), mipsel)
 qemu_opts += \
diff --git a/kernel/build.rs b/kernel/build.rs
index 9602b9b..be0e3b3 100644
--- a/kernel/build.rs
+++ b/kernel/build.rs
@@ -2,6 +2,7 @@ extern crate cc;
 
 use std::fs::File;
 use std::io::{Result, Write};
+use std::path::Path;
 
 fn main() {
 	println!("cargo:rerun-if-env-changed=LOG");
@@ -19,7 +20,7 @@ fn main() {
 		"riscv64" => {
 		}
 		"mipsel" => {
-			gen_dtb_asm().unwrap();
+			gen_dtb_asm(&arch, &board).unwrap();
 		}
 		"aarch64" => {
 		}
@@ -52,10 +53,8 @@ fn gen_vector_asm() -> Result<()> {
 }
 
 
-fn gen_dtb_asm() -> Result<()> {
-	let arch = std::env::var("ARCH").unwrap();
+fn gen_dtb_asm(arch: &String, board: &String) -> Result<()> {
     let dtb = std::env::var("DTB").unwrap();
-	let board = std::env::var("BOARD").unwrap();
 
     if !Path::new(&dtb).is_file() {
         panic!("DTB `{}` not found", dtb)