加载内核模块时，有未解析的符号怎么办

加载内核模块时，有未解析的符号如下
# insmod main.o
main.o: unresolved symbol scull_sngl_fops
main.o: unresolved symbol scull_p_buffer
main.o: unresolved symbol scull_user_fops
main.o: unresolved symbol scull_p_init
main.o: unresolved symbol scull_p_cleanup
main.o: unresolved symbol scull_pipe_fops
main.o: unresolved symbol scull_priv_fops
main.o: unresolved symbol scull_access_init
main.o: unresolved symbol scull_access_cleanup
main.o: unresolved symbol scull_wusr_fops
main.o:
Hint: You are trying to load a module without a GPL compatible license
and it has unresolved symbols. The module may be trying to access
GPLONLY symbols but the problem is more likely to be a coding or
user error. Contact the module supplier for assistance, only they
can help you.