Golang GDB调试

1. 调试过程

1.1. 示例代码

package main import (     "fmt"     "time" ) func counting(c chan<- int) {     for i := 0; i < 10; i++ {         time.Sleep(2 * time.Second)         c <- i     }     close(c) } func main() {     msg := "Starting main"     fmt.Println(msg)     bus := make(chan int)     msg = "starting a gofunc"     go counting(bus)     for count := range bus {         fmt.Println("count:", count)     } }

1.2. 调试步骤

编译文件，生成可执行文件gdbfile:

 

go build -gcflags "-N -l" gdbfile.go

 

通过gdb命令启动调试：

 

gdb gdbfile

 

启动之后首先看看这个程序是不是可以运行起来，只要输入run命令回车后程序就开始运行，程序正常的话可以看到程序输出如下，和我们在命令行直接执行程序输出是一样的：

 

(gdb) run Starting program: /home/xiemengjun/gdbfile Starting main count: 0 count: 1 count: 2 count: 3 count: 4 count: 5 count: 6 count: 7 count: 8 count: 9 [LWP 2771 exited] [Inferior 1 (process 2771) exited normally]

 

好了，现在我们已经知道怎么让程序跑起来了，接下来开始给代码设置断点：

 

(gdb) b 23 Breakpoint 1 at 0x400d8d: file /home/xiemengjun/gdbfile.go, line 23. (gdb) run Starting program: /home/xiemengjun/gdbfile Starting main [New LWP 3284] [Switching to LWP 3284]   Breakpoint 1, main.main () at /home/xiemengjun/gdbfile.go:23 23          fmt.Println("count:", count)

 

上面例子b 23表示在第23行设置了断点，之后输入run开始运行程序。现在程序在前面设置断点的地方停住了，我们需要查看断点相应上下文的源码，输入list就可以看到源码显示从当前停止行的前五行开始：

 

(gdb) list 18      fmt.Println(msg) 19      bus := make(chan int) 20      msg = "starting a gofunc" 21      go counting(bus) 22      for count := range bus { 23          fmt.Println("count:", count) 24      } 25  }

 

现在GDB在运行当前的程序的环境中已经保留了一些有用的调试信息，我们只需打印出相应的变量，查看相应变量的类型及值：

 

(gdb) info locals count = 0 bus = 0xf840001a50 (gdb) p count $1 = 0 (gdb) p bus $2 = (chan int) 0xf840001a50 (gdb) whatis bus type = chan int

 

接下来该让程序继续往下执行，请继续看下面的命令

 

(gdb) c Continuing. count: 0 [New LWP 3303] [Switching to LWP 3303]   Breakpoint 1, main.main () at /home/xiemengjun/gdbfile.go:23 23 fmt.Println("count:", count) (gdb) c Continuing. count: 1 [Switching to LWP 3302]   Breakpoint 1, main.main () at /home/xiemengjun/gdbfile.go:23 23 fmt.Println("count:", count)

 

每次输入c之后都会执行一次代码，又跳到下一次for循环，继续打印出来相应的信息。设想目前需要改变上下文相关变量的信息，跳过一些过程，并继续执行下一步，得出修改后想要的结果：

 

(gdb) info locals count = 2 bus = 0xf840001a50 (gdb) set variable count=9 (gdb) info locals count = 9 bus = 0xf840001a50 (gdb) c Continuing. count: 9 [Switching to LWP 3302]   Breakpoint 1, main.main () at /home/xiemengjun/gdbfile.go:23 23 fmt.Println("count:", count)

 

最后稍微思考一下，前面整个程序运行的过程中到底创建了多少个goroutine，每个goroutine都在做什么：

 

(gdb) info goroutines * 1 running runtime.gosched * 2 syscall runtime.entersyscall 3 waiting runtime.gosched 4 runnable runtime.gosched (gdb) goroutine 1 bt #0 0x000000000040e33b in runtime.gosched () at /home/xiemengjun/go/src/pkg/runtime/proc.c:927 #1 0x0000000000403091 in runtime.chanrecv (c=void, ep=void, selected=void, received=void) at /home/xiemengjun/go/src/pkg/runtime/chan.c:327 #2 0x000000000040316f in runtime.chanrecv2 (t=void, c=void) at /home/xiemengjun/go/src/pkg/runtime/chan.c:420 #3 0x0000000000400d6f in main.main () at /home/xiemengjun/gdbfile.go:22 #4 0x000000000040d0c7 in runtime.main () at /home/xiemengjun/go/src/pkg/runtime/proc.c:244 #5 0x000000000040d16a in schedunlock () at /home/xiemengjun/go/src/pkg/runtime/proc.c:267 #6 0x0000000000000000 in ?? ()