./lib/iotkitALI/libiot_sdk.a(utils_net.o): In function `read_tcp':
(.text+0x34): undefined reference to `HAL_TCP_Read'
./lib/iotkitALI/libiot_sdk.a(utils_net.o): In function `write_tcp':
(.text+0x7c): undefined reference to `HAL_TCP_Write'
./lib/iotkitALI/libiot_sdk.a(utils_net.o): In function
`disconnect_tcp':
(.text+0xc4): undefined reference to `HAL_TCP_Destroy'
./lib/iotkitALI/libiot_sdk.a(utils_net.o): In function `connect_tcp':
(.text+0x134): undefined reference to `HAL_TCP_Establish'
./lib/iotkitALI/libiot_sdk.a(utils_net.o): In function `read_ssl':
(.text+0x1d0): undefined reference to `HAL_SSL_Read'
./lib/iotkitALI/libiot_sdk.a(utils_net.o): In function `write_ssl':
(.text+0x248): undefined reference to `HAL_SSL_Write'
./lib/iotkitALI/libiot_sdk.a(utils_net.o): In function
`disconnect_ssl':
(.text+0x2a8): undefined reference to `HAL_SSL_Destroy'
./lib/iotkitALI/libiot_sdk.a(utils_net.o): In function `connect_ssl':
(.text+0x32c): undefined reference to `HAL_SSL_Establish'
collect2: error: ld returned 1 exit status
make: *** [all] Error 1
可以看出 libiot_sdk.a 只是链接到头文件却没有把函数内容拷到自己的库里，
又不进能行外部调用，于是就产生了未定义函数错误，结局方法如下。
解决办法：
如图位置的 makefile 里添加 platform 和 tls 两个源码的路径（拉伸图像方便
看）。
