binwalk -e firmware 对固件进行提取，得到的目录下有squashfs-root（分析的固件为squash文件系统）
进入到该目录下，可以看到该firmware的文件，如下
root:~/IoT/firmware/adm5120/_openwrt-adm5120-p-334wt-squashfs-webui.bin.extracted/squashfs-root# ls
bin etc lib64 overlay qemu-mips root sys usr www
dev lib mnt proc rom sbin tmp var

ldd查看qemu-mips的依赖，并解决依赖问题
qemu-mips -L ./bin/busywork
执行chroot ./ ./qemu-mips ./bin/busybox ash

BusyBox v1.15.3 (2010-04-06 03:13:32 CEST) built-in shell (ash)
Enter 'help' for a list of built-in commands.

/ # help
Built-in commands:

. : [ [[ alias bg break cd chdir command continue echo eval exec
exit export false fg getopts hash help jobs kill let local printf
pwd read readonly return set shift source test times trap true
type ulimit umask unalias unset wait

/ # exit