30分钟
3.9.1 Delve入门
首先根据官方的文档正确安装Delve调试器。我们会先构造一个简单的Go语言代码，用于熟悉下Delve的简单用法。
创建main.go文件，main函数先通过循初始化一个切片，然后输出切片的内容：
package main
import (
"fmt"
)
func main() {
nums := make([]int, 5)
for i := 0; i < len(nums); i++ {
nums[i] = i * i
}
fmt.Println(nums)
}命令行进入包所在目录，然后输入dlv debug命令进入调试：
$ dlv debug
Type 'help' for list of commands.
(dlv)输入help命令可以查看到Delve提供的调试命令列表：
(dlv) help
The following commands are available:
args ------------------------ Print function arguments.
break (alias: b) ------------ Sets a breakpoint.
breakpoints (alias: bp) ----- Print out info for active breakpoints.
clear ----------------------- Deletes breakpoint.
clearall -------------------- Deletes multiple breakpoints.
condition (alias: cond) ----- Set breakpoint condition.
config ---------------------- Changes configuration parameters.
continue (alias: c) --------- Run until breakpoint or program termination.
disassemble (alias: disass) - Disassembler.
down ------------------------ Move the current frame down.
exit (alias: quit | q) ------ Exit the debugger.
frame ----------------------- Set the current frame, or execute command...
funcs ----------------------- Print list of functions.
goroutine ------------------- Shows or changes current goroutine
goroutines ------------------ List program goroutines.
help (alias: h) ------------- Prints the help message.
list (alias: ls | l) -------- Show source code.
locals ---------------------- Print local variables.
next (alias: n) ------------- Step over to next source line.
on -------------------------- Executes a command when a breakpoint is hit.
print (alias: p) ------------ Evaluate an expression.
regs ------------------------ Print contents of CPU registers.
restart (alias: r) ---------- Restart process.
set ------------------------- Changes the value of a variable.
source ---------------------- Executes a file containing a list of delve...
sources --------------------- Print list of source files.
stack (alias: bt) ----------- Print stack trace.
step (alias: s) ------------- Single step through program.
step-instruction (alias: si) Single step a single cpu instruction.
stepout --------------------- Step out of the current function.
thread (alias: tr) ---------- Switch to the specified thread.
threads --------------------- Print out info for every traced thread.
trace (alias: t) ------------ Set tracepoint.
types ----------------------- Print list of types
up -------------------------- Move the current frame up.
vars ------------------------ Print package variables.
whatis ---------------------- Prints type of an expression.
Type help followed by a command for full documentation.
(dlv)每个Go程序的入口是main.main函数，我们可以用break在此设置一个断点：
(dlv) break main.main
Breakpoint 1 set at 0x10ae9b8 for main.main() ./main.go:7然后通过breakpoints查看已经设置的所有断点：
(dlv) breakpoints
Breakpoint unrecovered-panic at 0x102a380 for runtime.startpanic()
/usr/local/go/src/runtime/panic.go:588 (0)
print runtime.curg._panic.arg
Breakpoint 1 at 0x10ae9b8 for main.main() ./main.go:7 (0)我们发现除了我们自己设置的main.main函数断点外，Delve内部已经为panic异常函数设置了一个断点。
通过vars命令可以查看全部包级的变量。因为最终的目标程序可能含有大量的全局变量，我们可以通过一个正则参数选择想查看的全局变量：
(dlv) vars main
main.initdone· = 2
runtime.main_init_done = chan bool 0/0
runtime.mainStarted = true
(dlv)然后就可以通过continue命令让程序运行到下一个断点处：
(dlv) continue
> main.main() ./main.go:7 (hits goroutine(1):1 total:1) (PC: 0x10ae9b8)
2:
3: import (
4: "fmt"
5: )
6:
=> 7: func main() {
8: nums := make([]int, 5)
9: for i := 0; i < len(nums); i++ {
10: nums[i] = i * i
11: }
12: fmt.Println(nums)
(dlv)输入next命令单步执行进入main函数内部：
(dlv) next
> main.main() ./main.go:8 (PC: 0x10ae9cf)
3: import (
4: "fmt"
5: )
6:
7: func main() {
=> 8: nums := make([]int, 5)
9: for i := 0; i < len(nums); i++ {
10: nums[i] = i * i
11: }
12: fmt.Println(nums)
13: }
(dlv)进入函数之后可以通过args和locals命令查看函数的参数和局部变量：
(dlv) args
(no args)
(dlv) locals
nums = []int len: 842350763880, cap: 17491881, nil因为main函数没有参数，因此args命令没有任何输出。而locals命令则输出了局部变量nums切片的值：此时切片还未完成初始化，切片的底层指针为nil，长度和容量都是一个随机数值。
再次输入next命令单步执行后就可以查看到nums切片初始化之后的结果了：
(dlv) next
> main.main() ./main.go:9 (PC: 0x10aea12)
4: "fmt"
5: )
6:
7: func main() {
8: nums := make([]int, 5)
=> 9: for i := 0; i < len(nums); i++ {
10: nums[i] = i * i
11: }
12: fmt.Println(nums)
13: }
(dlv) locals
nums = []int len: 5, cap: 5, [...]
i = 17601536
(dlv)此时因为调试器已经到了for语句行，因此局部变量出现了还未初始化的循环迭代变量i。
下面我们通过组合使用break和condition命令，在循环内部设置一个条件断点，当循环变量i等于3时断点生效：
(dlv) break main.go:10
Breakpoint 2 set at 0x10aea33 for main.main() ./main.go:10
(dlv) condition 2 i==3
(dlv)然后通过continue执行到刚设置的条件断点，并且输出局部变量：
(dlv) continue
> main.main() ./main.go:10 (hits goroutine(1):1 total:1) (PC: 0x10aea33)
5: )
6:
7: func main() {
8: nums := make([]int, 5)
9: for i := 0; i < len(nums); i++ {
=> 10: nums[i] = i * i
11: }
12: fmt.Println(nums)
13: }
(dlv) locals
nums = []int len: 5, cap: 5, [...]
i = 3
(dlv) print nums
[]int len: 5, cap: 5, [0,1,4,0,0]
(dlv)我们发现当循环变量i等于3时，nums切片的前3个元素已经正确初始化。
我们还可以通过stack查看当前执行函数的栈帧信息：
(dlv) stack
0 0x00000000010aea33 in main.main
at ./main.go:10
1 0x000000000102bd60 in runtime.main
at /usr/local/go/src/runtime/proc.go:198
2 0x0000000001053bd1 in runtime.goexit
at /usr/local/go/src/runtime/asm_amd64.s:2361
(dlv)或者通过goroutine和goroutines命令查看当前Goroutine相关的信息：
(dlv) goroutine
Thread 101686 at ./main.go:10
Goroutine 1:
Runtime: ./main.go:10 main.main (0x10aea33)
User: ./main.go:10 main.main (0x10aea33)
Go: /usr/local/go/src/runtime/asm_amd64.s:258 runtime.rt0_go (0x1051643)
Start: /usr/local/go/src/runtime/proc.go:109 runtime.main (0x102bb90)
(dlv) goroutines
[4 goroutines]
* Goroutine 1 - User: ./main.go:10 main.main (0x10aea33) (thread 101686)
Goroutine 2 - User: /usr/local/go/src/runtime/proc.go:292 \
runtime.gopark (0x102c189)
Goroutine 3 - User: /usr/local/go/src/runtime/proc.go:292 \
runtime.gopark (0x102c189)
Goroutine 4 - User: /usr/local/go/src/runtime/proc.go:292 \
runtime.gopark (0x102c189)
(dlv)最后完成调试工作后输入quit命令退出调试器。至此我们已经掌握了Delve调试器器的简单用法。
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