使用GDB调试Go代码。 转到扩展名“要调用的函数的数据类型无效。”

Using GDB with golang is an exciting thing~~ Base on the document, Go Extensions was provided. It can print the length of maps,string and slice.

However, when I executed "p $len(var)", I got an error "Invalid data type for function to be called". I am sure that the type of var is map.

Maybe, not many people pay attention to this problem? Or, should I ask this quesion in Go's forum?