source /opt/poky/environment...
创建交叉编译环境。
更改u-boot/tools/env/Make
添加CC
9 CC=aarch64-poky-linux-gcc -march=armv8-a -mtune=cortex-a57.cortex-a53 --sysroot=/opt/poky/2.4.2/sysroots/aarch64-poky-linux
10 override HOSTCC = $(CC)
$(warning $(HOSTCC))
编译：
make ARCH=arm CROSS_COMPILE=aarch64-poky-linux- envtools