您好，我正在尝试执行Contiki RTOS包中包含的示例程序。我尝试使用命令make TARGET=cooja clean执行hello-world程序，然后键入make TARGET=cooja，这导致终端上的以下输出：
I../../core/loader -I../../core/. -DAUTOSTART_ENABLE -c hello-world.c -o hello-world.co
hello-world.c: In function ‘process_thread_hello_world_process’:
hello-world.c:52:3: warning: variable ‘PT_YIELD_FLAG’ set but not used [-Wunused-but-set-variable]
ld hello-world.co contiki-cooja.a -o hello-world.cooja
ld: warning: cannot find entry symbol _start; defaulting to 0000000008048094
contiki-cooja.a(log.o): In function `simlog':
/home/contiki/contiki-2.5/examples/hello-world/../../platform/cooja/sys/log.c:78: undefined reference to `strlen'
/home/contiki/contiki-2.5/examples/hello-world/../../platform/cooja/sys/log.c:83: undefined reference to `strlen'
/home/contiki/contiki-2.5/examples/hello-world/../../platform/cooja/sys/log.c:83: undefined reference to `memcpy'
/home/contiki/contiki-2.5/examples/hello-world/../../platform/cooja/sys/log.c:84: undefined reference to `strlen'
contiki-cooja.a(log.o): In function `printf':
/home/contiki/contiki-2.5/examples/hello-world/../../platform/cooja/sys/log.c:128: undefined reference to `vsnprintf'
make: *** [hello-world.cooja] Error 1
rm hello-world.co
root@ubuntu:/home/contiki/contiki-2.5/examples/hello-world#
有人可以告诉我流程出错的地方。我没有对原始示例代码进行任何更改，我打算让程序在COOJA模拟器上运行。谢谢