Cross compiler fw_printenv

source /opt/poky/environment... 

Create a cross-compiler environment.

更改u-boot/tools/env/Make 

Add 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))

Compile:

make ARCH=arm CROSS_COMPILE=aarch64-poky-linux- envtools