【VSC】ERROR：GDB exited unexpectedly.

记录一次调试所遇bug的查找历程

问题描述

ERROR: GDB exited unexpectedly. Debugging will now abort.

The program has exited with code -1 (0xffffffff).

vscode成功进入gdb调试，运行过程中意外退出。

bug案发现场

图1 案发现场

源代码

main.cpp

#include <iostream>

#include "13.h"

int main()

{

    Solution soLuTion;

    std::cout << soLuTion.romanToInt("MCMXCIV") << std::endl;

    std::cout << sizeof("MCMXCIV") << std::endl;

    return 0;

}

13.cpp

#include <iostream>

#include <string>

#include "13.h"

int Solution::romanToInt(std::string s)

{

    // std::cout << s[0] << std::endl;

    int tempNum = 0;

    char tempChar = '0';

    for (int getC = 0; getC < s.size(); getC++)

    {

        switch (s[getC])

        {

        case 'I':

            tempNum += 1;

            break;

        case 'V':

            if (tempChar == 'I')

            {

                tempNum += 4 - 1;

            }

            else

            {

                tempNum += 5;

            }

            break;

        case 'X':

            if (tempChar == 'I')

            {

                tempNum += 9 - 1;

            }

            else

            {

                tempNum += 10;

            }

            break;

        case 'L':

            if (tempChar == 'X')

            {

                tempNum += 40 - 10;

            }

            else

            {

                tempNum += 50;

            }

            break;

        case 'C':

            if (tempChar == 'X')

            {

                tempNum += 90 - 10;

            }

            else

            {

                tempNum += 100;

            }

            break;

        case 'D':

            if (tempChar == 'C')

            {

                tempNum += 400 -100;

            }

            else

            {

                tempNum += 500;

            }

            break;

        case 'M':

            if (tempChar == 'C')

            {

                tempNum += 900 - 100;

            }

            else

            {

                tempNum += 1000;

            }

            break;

        default:

            break;

        }

        tempChar = s[getC];

    }

    return tempNum;

}

13.h

#pragma once

#include <string>

class Solution

{

public:

    int romanToInt(std::string s);

};

launch.json文件配置

{

    // Use IntelliSense to learn about possible attributes.

    // Hover to view descriptions of existing attributes.

    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387

    "version": "0.2.0",

    "configurations": [

        {

            "name": "g++.exe - Build and debug active file",

            "type": "cppdbg",

            "request": "launch",

            "program": "${workspaceFolder}\\build\\13",

            "args":  [],

            "stopAtEntry": false,

            "cwd": "${workspaceFolder}",

            "environment": [],

            "externalConsole": false,

            "MIMode": "gdb",

            "miDebuggerPath": "D:\\solfware\\mingw64\\mingw64\\bin\\gdb.exe",

            "setupCommands": [

                {

                    "description": "Enable pretty-printing for gdb",

                    "text": "-enable-pretty-printing",

                    "ignoreFailures": true

                }

            ]

        }

    ]

}

使用平台

OS: WIN 10 64bit

g++ --version: g++.exe (x86_64-posix-seh-rev0, Built by MinGW-W64 project) 8.1.0

gdb --version: GNU gdb (GDB) 8.1

vscode version: 1.67.0

问题排查

看看是不是gdb的问题

使用gdb命令行调试

gdb .\13.exe

调试过程

(gdb) b 6

Breakpoint 2 at 0x401563: file D:\myproject\CPP\learn\leecode\main.cpp, line 6.

(gdb) r

Starting program: D:\myproject\CPP\learn\leecode\build\13.exe

[New Thread 5436.0x241c]

[New Thread 5436.0x3e9c]

[New Thread 5436.0x2b38]

[New Thread 5436.0x2ec0]

Thread 1 hit Breakpoint 2, main () at D:\myproject\CPP\learn\leecode\main.cpp:6

6           std:: cout << soLuTion.romanToInt("MCMXCIV") << std::endl;

(gdb) s

Solution::romanToInt (this=0x62fddf, s="MCMXCIV") at D:\myproject\CPP\learn\leecode\13.cpp:7

7           int tempNum = 0;

(gdb) watch tempNum

Hardware watchpoint 3: tempNum

(gdb) n

8           char tempChar = '0';

(gdb) n

9           for (int getC = 0; getC < s.size(); getC++)

(gdb) n

11              switch (s[getC])

(gdb) c

Continuing.

Thread 1 hit Hardware watchpoint 3: tempNum

Old value = 0

New value = 1000

Solution::romanToInt (this=0x62fddf, s="MCMXCIV") at D:\myproject\CPP\learn\leecode\13.cpp:75

75                  break;

(gdb) c

Continuing.

Thread 1 hit Hardware watchpoint 3: tempNum

Old value = 1000

New value = 1100

Solution::romanToInt (this=0x62fddf, s="MCMXCIV") at D:\myproject\CPP\learn\leecode\13.cpp:55

55                  break;

(gdb) c

Continuing.

Thread 1 hit Hardware watchpoint 3: tempNum

Old value = 1100

New value = 1900

Solution::romanToInt (this=0x62fddf, s="MCMXCIV") at D:\myproject\CPP\learn\leecode\13.cpp:75

75                  break;

(gdb) c

Continuing.

Thread 1 hit Hardware watchpoint 3: tempNum

Old value = 1900

New value = 1910

Solution::romanToInt (this=0x62fddf, s="MCMXCIV") at D:\myproject\CPP\learn\leecode\13.cpp:35

35                  break;

(gdb) c

Continuing.

Thread 1 hit Hardware watchpoint 3: tempNum

Old value = 1910

New value = 1990

Solution::romanToInt (this=0x62fddf, s="MCMXCIV") at D:\myproject\CPP\learn\leecode\13.cpp:55

55                  break;

(gdb) c

Continuing.

Thread 1 hit Hardware watchpoint 3: tempNum

Old value = 1990

New value = 1991

Solution::romanToInt (this=0x62fddf, s="MCMXCIV") at D:\myproject\CPP\learn\leecode\13.cpp:15

15                  break;

(gdb) c

Continuing.

Thread 1 hit Hardware watchpoint 3: tempNum

Old value = 1991

New value = 1994

Solution::romanToInt (this=0x62fddf, s="MCMXCIV") at D:\myproject\CPP\learn\leecode\13.cpp:25

25                  break;

(gdb) c

Continuing.

Watchpoint 3 deleted because the program has left the block in

which its expression is valid.

0x0000000000401599 in main () at D:\myproject\CPP\learn\leecode\main.cpp:6

6           std:: cout << soLuTion.romanToInt("MCMXCIV") << std::endl;

(gdb) c

Continuing.

1994

[Thread 5436.0x2ec0 exited with code 0]

[Thread 5436.0x2b38 exited with code 0]

[Thread 5436.0x3e9c exited with code 0]

[Inferior 1 (process 5436) exited normally]

可以看出gdb是可以正常调试的，那么应该不是gdb的问题（误）

看看是不是平台的问题

同样的程序我跑到ubuntu虚拟机上用VSCdebug，是可以正常调试的。

内核版本

LINUX: 5.4.0-109-generic

Ubuntu:18.04.1

GCC: 7.5.0

GDB: 8.1.1

成功快照

图2 linux虚拟机平台

ok,真相了，是平台的差异导致的。那到底是哪里的差异呢？

灵机一动：如果我不watch变量看看

我不watch特定变量，在WIN10下试试debug

图3 不用watch

是可行的！那么找到突破口了，经过我的测试，我找到了引起意外退出的罪魁祸首，s[getC]。

Howerver

在我的虚拟机里，在创建getC这个变量的时候，会先给getC赋个值，具体可以观察图2，这个是是随机的一长串数字，有时是正，有时是负，大概有-996661983，有297860271等，一开始我想到了越界的问题，但是对于虚拟机来讲，它是可以正常调试的，getC的值在创建前的那一刹那会附一个上述的那些值，但这应该不是重点，因为创建完它就被赋予了0，然后我watch s[getC]也不应该有影响。

会不会是gdb版本的问题

回到我的WIN10环境，我不禁陷入了沉思，我又看了看两种环境下gdb的版本，决定再验证一下是不是gdb的问题。

再一次使用gdb命令行调试，我特意watch 了 s[getC]，你猜怎么着，也闪退了。

调试过程

(gdb) l

1       #include <iostream>

2       #include "13.h"

3       int main()

4       {

5           Solution soLuTion;

6           std::cout << soLuTion.romanToInt("MCMXCIV") << std::endl;

7           std::cout << sizeof("MCMXCIV") << std::endl;

8           return 0;

9       }(gdb) b 6

Breakpoint 1 at 0x401563: file D:\myproject\CPP\learn\leecode\main.cpp, line 6.

(gdb) r

Starting program: D:\myproject\CPP\learn\leecode\build\13.exe

[New Thread 17844.0x18a4]

[New Thread 17844.0x33c]

[New Thread 17844.0x2960]

[New Thread 17844.0x4300]

Thread 1 hit Breakpoint 1, main () at D:\myproject\CPP\learn\leecode\main.cpp:6

6           std::cout << soLuTion.romanToInt("MCMXCIV") << std::endl;

(gdb) s

Solution::romanToInt (this=0x62fddf, s="MCMXCIV") at D:\myproject\CPP\learn\leecode\13.cpp:7

7           int tempNum = 0;

(gdb) watch s[getC]

No symbol "getC" in current context.

(gdb) n

8           char tempChar = '0';

(gdb) n

9           for (int getC = 0; getC < s.size(); getC++)

(gdb) watch s[getC]

PS D:\myproject\CPP\learn\leecode\build>

嗯，我大概找到原因了，ERROR: GDB exited unexpectedly.这个错误是由

gdb 8.1 在调试我程序里的变量 s[getC] 时造成的。

结论

gdb 8.1极有可能存在某个bug会造成我所遇到的 gdb exited unexpected。

在网上冲了会浪，发现有人也遇到了和我同样的问题。某不知名人士所遇得bug。他的问题几乎和我相同，同样的string，同样的去watch string里的一个字符，同样的for循环，哈哈，这是变相遇到知音了。

github里也有个issue差不多佐证了我的想法。