以前经常用gdb调试C/C++程序，当学习golang的时候，发现golang的程序也是支持gdb调试的，然而还是遇到一些问题。比如说调试etcd程序就遇到如下问题：
【问题1】 info goroutines，提示找不到Undefined info command: "goroutines". Try "help info".
解决方法：启动gdb后，运行目标程序之前（输入r之前），手动加载runtime/runtime-gdb.py，执行如下命令：source /usr/lib/golang/src/runtime/runtime-gdb.py
原因：对于golang相关的特性，gdb本身并不熟知，因此需要通过插件方式使gdb感知到。
验证：
(gdb) b 28
Breakpoint 1 at 0xcc032b: file /root/etcd/src/github.com/coreos/etcd/gopath/src/github.com/coreos/etcd/cmd/etcd/main.go, line 28.(gdb) r
Starting program: /root/etcd/src/github.com/coreos/etcd/bin/etcd
(gdb) info goroutines
* 1 running runtime.systemstack_switch
2 waiting runtime.gopark
17 waiting runtime.gopark
33 waiting runtime.gopark
* 49 running runtime.gopark
42 runnable runtime.gopark
* 40 syscall runtime.notetsleepg
43 runnable runtime.gopark
* 74 syscall runtime.notetsleepg
(gdb) n
39 startEtcdOrProxyV2()
(gdb) s
github.com/coreos/etcd/cmd/vendor/github.com/coreos/etcd/etcdmain.startEtcdOrProxyV2 ()
at /root/etcd/src/github.com/coreos/etcd/gopath/src/github.com/coreos/etcd/cmd/vendor/github.com/coreos/etcd/etcdmain/etcd.go:57
57 func startEtcdOrProxyV2() {
(gdb) n
58 grpc.EnableTracing = false
(gdb) p grpc
No symbol "grpc" in current context.
【问题2】打印全局变量是提示No symbol "XXX" in current context.
原因：对于golang语言的程序，并不能像C/C++直接打印全局变量，需要通过路径+变量名字才可以打印出来
解决方法：
1）先查看全局变量所在位置，通过info variables XXX
(gdb) info variables grpc.EnableTracing
All variables matching regular expression "grpc.EnableTracing":
File go:
bool github.com/coreos/etcd/cmd/vendor/google.golang.org/grpc.EnableTracing;
2）打印全局变量
(gdb) p 'github.com/coreos/etcd/cmd/vendor/google.golang.org/grpc.EnableTracing'
$1 = true注意打印一定要有双引号/单引号
【问题3】打印变量长度，不能p len(XXX)必须是p $len(XXX)