LLDB 快速入门

如果调试是删除 bug 的过程，那么编程就是引入 bug 的过程。

—— Edsger W. Dijkstra

LLDB 是什么？

LLDB（ Low level Debug ）是 MacOS 默认进行调试 C/C++ 程序的调试工具，能帮开发者进行更加丰富地流程控制和栈帧数据监测。

简言之，LLDB 是一个有着 REPL 的特性和 C++ 、Python 插件的开源调试器。

在此，我们以几个简单的程序为例子，对 LLDB 进行快速入门。

目录

  • 启动 LLDB

  • 断点操作

    • 设置断点
    • 查看断点
    • 删除断点

  • 分步调试

    • 启动调试
    • 进入，跳过和继续
    • 跳出当前函数

  • 查看变量

  • 结束调试

启动 LLDB

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// demo.cpp
#include <iostream>

using namespace std;

int fact(int n) {
    if (n == 0) {
        return 1;
    }
    else {
        return n * fact(n - 1);
    }
}


int main() {

    int x = 2;
    int y = 3;
    int z = x + y;

    cout << fact(z) << endl;


    return 0;
}

编译 C/C++ 程序时使其可以被 LLDB 调试工具设置断点，需要添加 -g ，以 C++ 文件 demo.cpp 为例：

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clang++ -g demo.cpp

lldb a.out

断点操作

设置断点
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br s -f [文件名] -l [行号]			# 在文件的某一行设置断点
br s -n [函数名]							# 给函数设置断点
查看断点
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br list					# 显示所有断点和其序号
删除断点
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br del [断点序号]
br del 					# 删除所有断点

示例：

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(lldb) br s -f demo.cpp -l 17
Breakpoint 1: where = a.out`main + 28 at demo.cpp:17:9, address = 0x0000000100003d80
(lldb) br s -f demo.cpp -l 21
Breakpoint 2: where = a.out`main + 56 at demo.cpp:21:18, address = 0x0000000100003d9c
(lldb) br s -n fact
Breakpoint 3: where = a.out`fact(int) + 16 at demo.cpp:6:9, address = 0x0000000100003d18
(lldb) br list
Current breakpoints:
1: file = 'demo.cpp', line = 17, exact_match = 0, locations = 1
  1.1: where = a.out`main + 28 at demo.cpp:17:9, address = a.out[0x0000000100003d80], unresolved, hit count = 0 

2: file = 'demo.cpp', line = 21, exact_match = 0, locations = 1
  2.1: where = a.out`main + 56 at demo.cpp:21:18, address = a.out[0x0000000100003d9c], unresolved, hit count = 0 

3: name = 'fact', locations = 1
  3.1: where = a.out`fact(int) + 16 at demo.cpp:6:9, address = a.out[0x0000000100003d18], unresolved, hit count = 0 

(lldb) br del 3
1 breakpoints deleted; 0 breakpoint locations disabled.
(lldb) br list
Current breakpoints:
1: file = 'demo.cpp', line = 17, exact_match = 0, locations = 1
  1.1: where = a.out`main + 28 at demo.cpp:17:9, address = a.out[0x0000000100003d80], unresolved, hit count = 0 

2: file = 'demo.cpp', line = 21, exact_match = 0, locations = 1
  2.1: where = a.out`main + 56 at demo.cpp:21:18, address = a.out[0x0000000100003d9c], unresolved, hit count = 0

分步调试

启动调试
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r

输入 run 或者 r 后程序便会开始启动调试

进入，跳过和继续
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# 进入	单步执行，中间如果有函数调用会跳转到目标函数
s

# 跳过	单步执行，中间的函数执行过程会跳过
n

# 继续	跳转到下一个断点
c
跳出当前函数
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finish

查看变量

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# 查看某个变量：
p [变量名]


# 查看当前栈帧所有变量
fr v


# 切换栈帧
fr s [栈帧序号]


# 打印当前线程的栈帧信息
bt


# 打印所有线程的栈帧信息
bt all

综合案例：在 demo.cpp 的 17 行和 21 行设置断点，使用 r 开始调试

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* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
    frame #0: 0x0000000100003d80 a.out`main at demo.cpp:17:9
   14  
   15   int main() {
   16  
-> 17       int x = 2;
   18       int y = 3;
   19       int z = x + y;
   20  
Target 0: (a.out) stopped.
(lldb) s
Process 31435 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = step in
    frame #0: 0x0000000100003d88 a.out`main at demo.cpp:18:9
   15   int main() {
   16  
   17       int x = 2;
-> 18       int y = 3;
   19       int z = x + y;
   20  
   21       cout << fact(z) << endl;
Target 0: (a.out) stopped.
(lldb) s
Process 31435 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = step in
    frame #0: 0x0000000100003d8c a.out`main at demo.cpp:19:13
   16  
   17       int x = 2;
   18       int y = 3;
-> 19       int z = x + y;
   20  
   21       cout << fact(z) << endl;
   22  
Target 0: (a.out) stopped.
(lldb) s
Process 31435 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 2.1
    frame #0: 0x0000000100003d9c a.out`main at demo.cpp:21:18
   18       int y = 3;
   19       int z = x + y;
   20  
-> 21       cout << fact(z) << endl;
   22  
   23       return 0;
   24   }
Target 0: (a.out) stopped.
(lldb) fr v
(int) x = 2
(int) y = 3
(int) z = 5
(lldb) s
Process 31435 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = step in
    frame #0: 0x0000000100003d18 a.out`fact(n=5) at demo.cpp:6:9
   3    using namespace std;
   4   
   5    int fact(int n) {
-> 6        if (n == 0) {
   7            return 1;
   8        }
   9        else {
Target 0: (a.out) stopped.
(lldb) finish
Process 31435 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = step out
Return value: (int) $0 = 120

    frame #0: 0x0000000100003da4 a.out`main at demo.cpp:21:13
   18       int y = 3;
   19       int z = x + y;
   20  
-> 21       cout << fact(z) << endl;
   22  
   23       return 0;
   24   }
Target 0: (a.out) stopped.
(lldb) c
Process 31435 resuming
120
Process 31435 exited with status = 0 (0x00000000)

结束调试

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q

输入 quit 或者 q 结束 LLDB 调试

以上就是对 LLDB 的一个简单介绍了，如果想了解更多 LLDB 指令，可以查看官网的 LLDB command map

C/C++
#C++ #调试器 #LLDB
LLDB 快速入门
https://goer17.github.io/2023/02/22/LLDB 快速入门/
作者
Captain_Lee
发布于
2023年2月22日
许可协议