常用命令

如果希望程序可以调试，在编译时需要加入-g选项，该选项告诉编译器生成调试信息，包括行号、变量名、变量值等；并且不能同时使用-O的优化选项，这可能会改变代码的原始结构和执行流程，进而影响调试。
进入调试的方式：
gdb target-program或gdb -q target-program。-q表示不打印gdb版本信息，界面较为干净。

命令	简写	说明
set args		设置程序运行的参数如需要运行：./demo aa bb cc 则设置方式：set args aa bb cc
break	b	设置断点 b 20 表示在第20行设置断点，可以设置多个断点
info breakpoints		显示断点
delete breakpoints	d	删除断点 d 20 表示删除序号为20的断点，不加序号则删除所有断点
run	r	开始/重新运行程序, 程序运行到断点的位置会停下来，如果没有遇到断点，程序一直运行下去
next	n	执行当前行语句，如果该语句为函数调用，不会进入函数内部
step	s	执行当前行语句，如果该语句为函数调用，则进入函数内部。如果是库函数或者第三方库函数，则进不到函数内部，因为没有源代码，只要有源码的地方都能进去
print	p	显示变量或表达式的值，如果是指针变量则显示指针指向的变量的地址。如果p后面是表达式，会执行这个表达式。还可以作为变量的赋值语句来用
continue	c	继续运行程序，遇到下一个断点停止，如果没有遇到断点，程序将一直运行
set var		设置变量的值存在变量 int i; char name[21]; 设置值 set var i = 10086 set var name = "JacksonWang"
quit	q	退出gdb
start		单步执行，运行程序，并停留在第一个执行语句
finish		在进入到函数内部的情况下，结束当前函数，回到函数调用点
backtrace	bt	查函数调用堆栈
until		当你厌倦了在一个循环体内单步跟踪时，这个命令可以运行程序直到退出循环体。 until 行号：运行至某行，不仅仅用来跳出循环
b 23 if a＞b		条件断点设置， if后面跟着条件

示例

源码

#include <iostream>
#include <string>

using namespace std;

void func(int i, string &s)
{
    cout << "i = " << i << " s = " << s << endl;
}

int main(int argc, char *argv[])
{
    if (argc != 3)
    {
        cout << "执行方式：test 编号 姓名" << endl;
        cout << "如：test 100 张三" << endl;
        return -1;
    }

    int i = stoi(argv[1]);
    string s = argv[2];

    func(i, s);

    func(i, s);

    for (auto i = 0; i < 10; ++i)
    {
        string s = "第" + to_string(i)+ "个编号";
        cout << s << endl;
    }

    return 0;
}

调试过程

[devuser@Rocky8-online gdb调试]$ gdb test
GNU gdb (GDB) Rocky Linux 8.2-20.el8.0.1
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
--Type <RET> for more, q to quit, c to continue without paging--
    <http://www.gnu.org/software/gdb/documentation/>.

For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from test...done.
(gdb) set args 100 张三
(gdb) b 23
Breakpoint 1 at 0x4018aa: file main.cpp, line 23.
(gdb) b 25
Breakpoint 2 at 0x4018be: file main.cpp, line 25.
(gdb) b 27
Breakpoint 3 at 0x4018d2: file main.cpp, line 27.
(gdb) info breakpoints
Num     Type           Disp Enb Address            What
1       breakpoint     keep y   0x00000000004018aa in main(int, char**) at main.cpp:23
2       breakpoint     keep y   0x00000000004018be in main(int, char**) at main.cpp:25
3       breakpoint     keep y   0x00000000004018d2 in main(int, char**) at main.cpp:27
(gdb) d 27
No breakpoint number 27.
(gdb) d 3
(gdb) info breakpoints
Num     Type           Disp Enb Address            What
1       breakpoint     keep y   0x00000000004018aa in main(int, char**) at main.cpp:23
2       breakpoint     keep y   0x00000000004018be in main(int, char**) at main.cpp:25
(gdb) r
Starting program: /home/devuser/workspace/c_c++/test/gdb调试/test 100 张三

Breakpoint 1, main (argc=3, argv=0x7fffffffded8) at main.cpp:23
23          func(i, s);
Missing separate debuginfos, use: yum debuginfo-install glibc-2.28-251.el8_10.2.x86_64 libgcc-8.5.0-22.el8_10.x86_64 libstdc++-8.5.0-22.el8_10.x86_64
(gdb) n
i = 100 s = 张三

Breakpoint 2, main (argc=3, argv=0x7fffffffded8) at main.cpp:25
25          func(i, s);
(gdb) p i
$1 = 100
(gdb) p s
$2 = "张三"
(gdb) set var i = 200
(gdb) s
func (i=200, s="张三") at main.cpp:8
8           cout << "i = " << i << " s = " << s << endl;
(gdb) n
i = 200 s = 张三
9       }
(gdb) n
main (argc=3, argv=0x7fffffffded8) at main.cpp:27
27          for (auto i = 0; i < 10; ++i)
(gdb) n
29              string s = "第" + to_string(i)+ "个编号";
(gdb) n
30              cout << s << endl;
(gdb) n
第0个编号
29              string s = "第" + to_string(i)+ "个编号";
(gdb) n
27          for (auto i = 0; i < 10; ++i)
(gdb) n
29              string s = "第" + to_string(i)+ "个编号";
(gdb) n
30              cout << s << endl;
(gdb) n
第1个编号
29              string s = "第" + to_string(i)+ "个编号";
(gdb) n
27          for (auto i = 0; i < 10; ++i)
(gdb) n
29              string s = "第" + to_string(i)+ "个编号";
(gdb) n
30              cout << s << endl;
(gdb) n
第2个编号
29              string s = "第" + to_string(i)+ "个编号";
(gdb) n
27          for (auto i = 0; i < 10; ++i)
(gdb) n
29              string s = "第" + to_string(i)+ "个编号";
(gdb) n
30              cout << s << endl;
(gdb) n
第3个编号
29              string s = "第" + to_string(i)+ "个编号";
(gdb) until
27          for (auto i = 0; i < 10; ++i)
(gdb) 
第4个编号
第5个编号
第6个编号
第7个编号
第8个编号
第9个编号
33          return 0;
(gdb) q
A debugging session is active.

        Inferior 1 [process 1959176] will be killed.

Quit anyway? (y or n) y
[devuser@Rocky8-online gdb调试]$

调试core文件

如果程序在运行时发生了内存错误，会被内核强行终止，提示“段错误”，内存的状态可保存在core文件中，方便进一步分析查找问题。
注：默认情况下，不会生成core文件，需要修改系统参数。
调试方式如下：

首先使用ulimit -a查看系统限制参数

[devuser@Rocky8-online gdb调试]$ ulimit -a
core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 6955
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
open files                      (-n) 262144
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 8192
cpu time               (seconds, -t) unlimited
max user processes              (-u) 6955
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

使用ulimit -c unlimited把core file size改为unlimited
运行程序，产生core文件
运行gdb target-program core-file
在gdb中，使用bt查看函数调用栈

示例

源码

#include <iostream>
#include <string>
#include <cstring>

using namespace std;

void func(int i, string &s)
{
    cout << "i = " << i << " s = " << s << endl;
}

void corefunc()
{
    char *p = nullptr;
    *p = 'A';
    strcpy(p, "cplusplus");
    cout << "p = " << p << endl;
}

int main(int argc, char *argv[])
{
    if (argc != 3)
    {
        cout << "执行方式：test 编号 姓名" << endl;
        cout << "如：test 100 张三" << endl;
        return -1;
    }

    int i = stoi(argv[1]);
    string s = argv[2];

    func(i, s);

    func(i, s);

    corefunc();

    for (auto i = 0; i < 10; ++i)
    {
        string s = "第" + to_string(i)+ "个编号";
        cout << s << endl;
    }

    return 0;
}

调试过程
使用systemd的系统不会直接产生core文件，可按如下方法使用coredumpctl命令生成

[devuser@Rocky8-online gdb调试]$ cat /proc/sys/kernel/core_pattern 
|/usr/lib/systemd/systemd-coredump %P %u %g %s %t %c %h %e
[devuser@Rocky8-online gdb调试]$ coredumpctl
TIME                            PID   UID   GID SIG COREFILE  EXE
Sat 2024-11-09 16:12:16 CST  1959992  1000  1000  11 present   /home/devuser/workspace/c_c++/test/gdb调试/test
Sat 2024-11-09 16:16:17 CST  1960127  1000  1000  11 present   /home/devuser/workspace/c_c++/test/gdb调试/test
Sat 2024-11-09 16:22:23 CST  1960569  1000  1000  11 present   /home/devuser/workspace/c_c++/test/gdb调试/test
[devuser@Rocky8-online gdb调试]$ coredumpctl -o core dump 1960569
           PID: 1960569 (test)
           UID: 1000 (devuser)
           GID: 1000 (devuser)
        Signal: 11 (SEGV)
     Timestamp: Sat 2024-11-09 16:22:23 CST (7min ago)
  Command Line: ./test 100
    Executable: /home/devuser/workspace/c_c++/test/gdb调试/test
 Control Group: /user.slice/user-1000.slice/session-727.scope
          Unit: session-727.scope
         Slice: user-1000.slice
       Session: 727
     Owner UID: 1000 (devuser)
       Boot ID: 3715d4f161824bbf9481b064cc42f893
    Machine ID: 74da068e81f448da853c64463d64e826
      Hostname: Rocky8-online
       Storage: /var/lib/systemd/coredump/core.test.1000.3715d4f161824bbf9481b064cc42f893.1960569.1731140543000000.lz4
       Message: Process 1960569 (test) of user 1000 dumped core.
                
                Stack trace of thread 1960569:
                #0  0x00000000004017b7 n/a (/home/devuser/workspace/c_c++/test/gdb调试/test)
                #1  0x0000000000401936 n/a (/home/devuser/workspace/c_c++/test/gdb调试/test)
                #2  0x00007f182025d7e5 __libc_start_main (libc.so.6)
                #3  0x000000000040168e n/a (/home/devuser/workspace/c_c++/test/gdb调试/test)
[devuser@Rocky8-online gdb调试]$ ls -l
total 704
-rw-rw-r--. 1 devuser devuser 499712 Nov  9 16:29 core
drwxrwxr-x. 2 devuser devuser      6 Nov  9 15:12 include
drwxrwxr-x. 2 devuser devuser      6 Nov  9 15:12 lib
-rw-rw-r--. 1 devuser devuser    724 Nov  9 16:11 main.cpp
-rw-rw-r--. 1 devuser devuser 117328 Nov  9 16:12 main.o
-rw-rw-r--. 1 devuser devuser   1428 Nov  9 15:43 Makefile
-rwxrwxr-x. 1 devuser devuser  92672 Nov  9 16:12 test

[devuser@Rocky8-online gdb调试]$ gdb test core
GNU gdb (GDB) Rocky Linux 8.2-20.el8.0.1
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
--Type <RET> for more, q to quit, c to continue without paging--
    <http://www.gnu.org/software/gdb/documentation/>.

For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from test...done.
[New LWP 1960569]
Core was generated by `./test 100 张三'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00000000004017b7 in corefunc () at main.cpp:15
15          *p = 'A';
Missing separate debuginfos, use: yum debuginfo-install glibc-2.28-251.el8_10.2.x86_64 libgcc-8.5.0-22.el8_10.x86_64 libstdc++-8.5.0-22.el8_10.x86_64
(gdb) bt
#0  0x00000000004017b7 in corefunc () at main.cpp:15
#1  0x0000000000401936 in main (argc=3, argv=0x7fff0d021a78) at main.cpp:36
(gdb)

调试正在运行中的程序

gdb target-program -p pid

示例

源码

#include <iostream>
#include <chrono>
#include <thread>

using namespace std;

int main(int argc, char *argv[])
{
    for (auto i = 0; i < 1000000; ++i)
    {
        string s = "第" + to_string(i)+ "个编号";
        cout << s << endl;
        std::this_thread::sleep_for(std::chrono::seconds(5));
    }

    return 0;
}

调试过程

[devuser@Rocky8-online gdb调试]$ ps -ef | grep test
devuser  1954586 1952692  0 13:35 pts/0    00:00:00 gdb test
devuser  1962014 1954938  0 19:00 pts/1    00:00:00 ./test
devuser  1962280 1962066  0 19:01 pts/2    00:00:00 grep --color=auto test
[devuser@Rocky8-online gdb调试]$ gdb test -p 1962014
GNU gdb (GDB) Rocky Linux 8.2-20.el8.0.1
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
--Type <RET> for more, q to quit, c to continue without paging--
    <http://www.gnu.org/software/gdb/documentation/>.

For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from test...done.
Attaching to program: /home/devuser/workspace/c_c++/test/gdb调试/test, process 1962014
Reading symbols from /lib64/libstdc++.so.6...Reading symbols from .gnu_debugdata for /lib64/libstdc++.so.6...(no debugging symbols found)...done.
(no debugging symbols found)...done.
Reading symbols from /lib64/libm.so.6...Reading symbols from .gnu_debugdata for /lib64/libm.so.6...(no debugging symbols found)...done.
(no debugging symbols found)...done.
Reading symbols from /lib64/libgcc_s.so.1...Reading symbols from .gnu_debugdata for /lib64/libgcc_s.so.1...(no debugging symbols found)...done.
(no debugging symbols found)...done.
Reading symbols from /lib64/libc.so.6...(no debugging symbols found)...done.
Reading symbols from /lib64/ld-linux-x86-64.so.2...done.
0x00007fdb54a00068 in nanosleep () from /lib64/libc.so.6
Missing separate debuginfos, use: yum debuginfo-install glibc-2.28-251.el8_10.2.x86_64 libgcc-8.5.0-22.el8_10.x86_64 libstdc++-8.5.0-22.el8_10.x86_64
(gdb) n
Single stepping until exit from function nanosleep,
which has no line number information.
std::this_thread::sleep_for<long, std::ratio<1l, 1l> > (__rtime=...) at /usr/include/c++/8/thread:379
379             while (::nanosleep(&__ts, &__ts) == -1 && errno == EINTR)
(gdb) n
384           }
(gdb) n
main (argc=1, argv=0x7ffef61ed998) at main.cpp:11
11              string s = "第" + to_string(i)+ "个编号";
(gdb) n
9           for (auto i = 0; i < 1000000; ++i)
(gdb) n
11              string s = "第" + to_string(i)+ "个编号";
(gdb) n
12              cout << s << endl;
(gdb) n
13              std::this_thread::sleep_for(std::chrono::seconds(5));
(gdb) n
n
n
11              string s = "第" + to_string(i)+ "个编号";
(gdb) n
9           for (auto i = 0; i < 1000000; ++i)
(gdb) n
11              string s = "第" + to_string(i)+ "个编号";
(gdb) n
12              cout << s << endl;
(gdb) n
13              std::this_thread::sleep_for(std::chrono::seconds(5));
(gdb) n
n
n
n
n
11              string s = "第" + to_string(i)+ "个编号";
(gdb) n
9           for (auto i = 0; i < 1000000; ++i)
(gdb) n
11              string s = "第" + to_string(i)+ "个编号";
(gdb) n
12              cout << s << endl;
(gdb) n
13              std::this_thread::sleep_for(std::chrono::seconds(5));
(gdb) c
Continuing.

gdb的简单使用

常用命令

调试core文件

调试正在运行中的程序

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