gdb 调试mysql - 技术栈

gdb 调试mysql,这里调试用户登陆报错
powershell 复制代码
窗口1 用gdb 挂住 my_error 函数
[root@node1 ~]# ps -ef|grep mysql 
root      4688     1  0 Mar22 ?        00:00:00 /bin/sh /usr/local/mysql//bin/mysqld_safe --datadir=/data/mysql/mysql3306/data --pid-file=/data/mysql/mysql3306/data/node1.pid
mysql     5814  4688  0 Mar22 ?        00:15:23 /usr/local/mysql/bin/mysqld --basedir=/usr/local/mysql/ --datadir=/data/mysql/mysql3306/data --plugin-dir=/usr/local/mysql//lib/plugin --user=mysql --log-error=/data/mysql/mysql3306/logs/error.log --open-files-limit=65536 --pid-file=/data/mysql/mysql3306/data/node1.pid --socket=/tmp/mysql3306.sock --port=3306
root     28275 27829  0 23:33 pts/4    00:00:00 grep --color=auto mysql

[root@node1 ~]# gdb -p 5814

--- 挂住my_error函数
(gdb) b my_error
Breakpoint 1 at 0x20729c4
(gdb) bt
#0  0x00007f1813fc1ddd in poll () from /lib64/libc.so.6
#1  0x0000000001059098 in Mysqld_socket_listener::listen_for_connection_event() ()
#2  0x0000000000e28151 in mysqld_main(int, char**) ()
#3  0x00007f1813ef0555 in __libc_start_main () from /lib64/libc.so.6
#4  0x0000000000e0c185 in _start ()


窗口2 模拟登陆报错 ,卡住
[root@node1 ~]# mysql -uroot -perror -S /tmp/mysql3306.sock 
mysql: [Warning] Using a password on the command line interface can be insecure.


窗口1 执行 c 继续往下走
(gdb) c
Continuing.
[Switching to Thread 0x7f1798288700 (LWP 1646)]

Breakpoint 1, 0x00000000020729c4 in my_error(int, int, ...) ()
(gdb) info threads
  Id   Target Id         Frame 
  42   Thread 0x7f1805356700 (LWP 5822) "mysqld" 0x00007f1814cc8644 in __io_getevents_0_4 () from /lib64/libaio.so.1
  41   Thread 0x7f1805b57700 (LWP 5823) "mysqld" 0x00007f1814cc8644 in __io_getevents_0_4 () from /lib64/libaio.so.1
  40   Thread 0x7f1806358700 (LWP 5824) "mysqld" 0x00007f1814cc8644 in __io_getevents_0_4 () from /lib64/libaio.so.1
  39   Thread 0x7f1806b59700 (LWP 5825) "mysqld" 0x00007f1814cc8644 in __io_getevents_0_4 () from /lib64/libaio.so.1
  38   Thread 0x7f17ad3a2700 (LWP 5826) "mysqld" 0x00007f1814cc8644 in __io_getevents_0_4 () from /lib64/libaio.so.1
  37   Thread 0x7f17acba1700 (LWP 5827) "mysqld" 0x00007f1814cc8644 in __io_getevents_0_4 () from /lib64/libaio.so.1
  36   Thread 0x7f17ac3a0700 (LWP 5828) "mysqld" 0x00007f1814cc8644 in __io_getevents_0_4 () from /lib64/libaio.so.1
  35   Thread 0x7f17abb9f700 (LWP 5829) "mysqld" 0x00007f1814cc8644 in __io_getevents_0_4 () from /lib64/libaio.so.1
  34   Thread 0x7f17ab39e700 (LWP 5830) "mysqld" 0x00007f1814cc8644 in __io_getevents_0_4 () from /lib64/libaio.so.1
  33   Thread 0x7f17aab9d700 (LWP 5831) "mysqld" 0x00007f1814cc8644 in __io_getevents_0_4 () from /lib64/libaio.so.1
  32   Thread 0x7f17aa39c700 (LWP 5832) "mysqld" 0x00007f1815eebde2 in pthread_cond_timedwait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  31   Thread 0x7f17a9b9b700 (LWP 5833) "mysqld" 0x00007f1815eeba35 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  30   Thread 0x7f17a939a700 (LWP 5834) "mysqld" 0x00007f1815eeba35 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  29   Thread 0x7f17a8b99700 (LWP 5835) "mysqld" 0x00007f1815eeba35 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  28   Thread 0x7f179f396700 (LWP 5836) "mysqld" 0x00007f1815eebde2 in pthread_cond_timedwait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  27   Thread 0x7f179eb95700 (LWP 5837) "mysqld" 0x00007f1815eebde2 in pthread_cond_timedwait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  26   Thread 0x7f179e394700 (LWP 5838) "mysqld" 0x00007f1815eebde2 in pthread_cond_timedwait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  25   Thread 0x7f179db93700 (LWP 5839) "mysqld" 0x00007f1815eebde2 in pthread_cond_timedwait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  24   Thread 0x7f179d392700 (LWP 5840) "mysqld" 0x00007f1815eebde2 in pthread_cond_timedwait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  23   Thread 0x7f179cb91700 (LWP 5841) "mysqld" 0x00007f1815eebde2 in pthread_cond_timedwait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  22   Thread 0x7f179c390700 (LWP 5842) "mysqld" 0x00007f1815eebde2 in pthread_cond_timedwait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  21   Thread 0x7f179bb8f700 (LWP 5843) "mysqld" 0x00007f1815eebde2 in pthread_cond_timedwait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  20   Thread 0x7f179b38e700 (LWP 5845) "mysqld" 0x00007f1815eeba35 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  19   Thread 0x7f179ab8d700 (LWP 5846) "mysqld" 0x00007f1815eeee9d in nanosleep () from /lib64/libpthread.so.0
  18   Thread 0x7f179a38c700 (LWP 5847) "mysqld" 0x00007f1815eebde2 in pthread_cond_timedwait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  17   Thread 0x7f1799b8b700 (LWP 5848) "mysqld" 0x00007f1815eebde2 in pthread_cond_timedwait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  16   Thread 0x7f180405f700 (LWP 5849) "xpl_worker0" 0x00007f1815eebde2 in pthread_cond_timedwait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  15   Thread 0x7f17ae20b700 (LWP 5850) "xpl_worker1" 0x00007f1815eebde2 in pthread_cond_timedwait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  14   Thread 0x7f17ae1c4700 (LWP 5851) "mysqld" 0x00007f1815eeba35 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  13   Thread 0x7f1807e27700 (LWP 5855) "mysqld" 0x00007f1815eeba35 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  12   Thread 0x7f179938a700 (LWP 5856) "mysqld" 0x00007f1815eebde2 in pthread_cond_timedwait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  11   Thread 0x7f1798b89700 (LWP 5857) "mysqld" 0x00007f1815eeba35 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  10   Thread 0x7f178bfff700 (LWP 5858) "mysqld" 0x00007f1815eeba35 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  9    Thread 0x7f178b7fe700 (LWP 5859) "mysqld" 0x00007f1815eeba35 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  8    Thread 0x7f178affd700 (LWP 5860) "mysqld" 0x00007f1815eeba35 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
---Type <return> to continue, or q <return> to quit--- 
  7    Thread 0x7f17ae17d700 (LWP 5861) "mysqld" 0x00007f1815eeba35 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  6    Thread 0x7f17ae135700 (LWP 5862) "mysqld" 0x00007f1813f0558a in sigwaitinfo () from /lib64/libc.so.6
  5    Thread 0x7f17ae0ed700 (LWP 5863) "mysqld" 0x00007f1813fcd0e3 in epoll_wait () from /lib64/libc.so.6
  4    Thread 0x7f178a7fc700 (LWP 5865) "mysqld" 0x00007f1815eeba35 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  3    Thread 0x7f17ae05f700 (LWP 5951) "mysqld" 0x00007f1815eeba35 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
* 2    Thread 0x7f1798288700 (LWP 1646) "mysqld" 0x00000000020729c4 in my_error(int, int, ...) ()
  1    Thread 0x7f1816309840 (LWP 5814) "mysqld" 0x00007f1813fc1ddd in poll () from /lib64/libc.so.6
(gdb) 
(gdb) 


这里 2 带星号的就是my_error 函数了



############ gdb 用法

1. 安装 gdb 和带调试符号的 MySQL
安装 gdb
如果你的系统没有 gdb，先安装它：

yum install -y gdb
或者，如果你使用 dnf：

dnf install -y gdb
确保 MySQL 具有调试符号

2. 启动 MySQL 并附加 gdb
2.1 启动 MySQL
如果 MySQL 还未运行，可以先启动它：

systemctl start mysqld
然后找到 mysqld 进程 ID：

ps aux | grep mysqld
例如：

mysql    1234  2.3  0.5 /usr/sbin/mysqld
记住 1234（进程 ID）。

2.2 附加 gdb

gdb -p 1234
如果 gdb 报错 ptrace: Operation not permitted，请执行：

echo 0 > /proc/sys/kernel/yama/ptrace_scope
3. 调试 MySQL
3.1 设置断点

(gdb) b sql_parse.cc:100   # 在 sql_parse.cc 第 100 行设置断点
(gdb) b my_function_name    # 在特定函数上设置断点
3.2 继续运行

(gdb) c  # 继续执行
3.3 打印变量值

(gdb) p some_variable
3.4 查看调用栈

(gdb) bt
3.5 单步执行

(gdb) n  # 执行下一行
(gdb) s  # 进入函数
3.6 解除断点

(gdb) delete 1
3.7 退出 gdb

(gdb) q
4. 在 MySQL 运行 SQL 语句进行调试
如果你想调试某个 SQL 语句的执行过程：

附加到 mysqld 进程。

在 dispatch_command 或 mysql_parse 处设置断点：


(gdb) b dispatch_command
在 MySQL 客户端执行 SQL 语句：

mysql -u root -p -e "SELECT * FROM test;"
gdb 会在 dispatch_command 处暂停，你可以查看调用栈：

(gdb) bt
5. 使用 gdb 运行 mysqld
你也可以直接用 gdb 启动 MySQL：

gdb --args /usr/sbin/mysqld --defaults-file=/etc/my.cnf --user=mysql
然后在 gdb 中输入：

(gdb) run
这样，你可以在 MySQL 进程启动时调试它的执行。

结论：
使用 gdb 调试 MySQL 主要包括：

确保 MySQL 具有调试符号。

使用 gdb -p 附加到 mysqld 进程。

设置断点、查看变量、执行 SQL 语句进行调试。

也可以直接用 gdb 启动 mysqld 以便深入分析