如何启动gdb调试异常程序

目录

• gdb调试机制
  • 调试信息
  • 进程ID
  • core文件
• gdb调试的启动与停止
  • 目标程序
  • 指定进程
  • core dump文件
• 结论

gdb调试机制

调试的过程中可以清晰的了解上下文，以便分析程序原理与产生错误的原因。

• 代码
• 堆栈信息
• 进程与线程状态

调试信息

1. 使用gcc或者makefile时编译过程中加上-g选项表示编译过程中保留调试符号信息，此方法编译的程序明显比平时编译的程序要大的多

$ g++ -g -o core_dump2 core_dump2.cpp
$ g++ -o core_dump22 core_dump2.cpp
-rwxrwxr-x 1 fl fl  56K 1月  15 17:59 core_dump2*
-rwxrwxr-x 1 fl fl  19K 1月  15 18:18 core_dump22*

2. cmake中集成gdb

## gdb
set(CMAKE_BUILD_TYPE "Debug")
set(CMAKE_CXX_FLAGS_DEBUG "$ENV{CXXFLAGS} -O0 -Wall -g2 -ggdb")
set(CMAKE_CXX_FLAGS_RELEASE "$ENV{CXXFLAGS} -O3 -Wall")

进程ID

$ ps -ef | grep core_dump2
fl         71382   71367  0 17:59 pts/1    00:00:00 ./core_dump2
fl         71393   69623  0 18:00 pts/0    00:00:00 grep --color=auto core_dump2

core文件

1. 利用命令ulimit -a查看程序崩溃后是否会保存core文件，如果保留来core文件就可以用来定位问题了。

2. 利用命令ulimit -option value来编辑指定参数，如ulimit -c unlimited编辑core file size选项的值为unlimited。

3. 编辑完成后，利用source /etc/profile来刷新指定文件包含的环境配置信息。

$ 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) 31113
max locked memory       (kbytes, -l) 65536
max memory size         (kbytes, -m) unlimited
open files                      (-n) 8192
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) 31113
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited
$ ulimit -c unlimited
$ source /etc/profile
$ ulimit -a
core file size          (blocks, -c) unlimited
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 31113
max locked memory       (kbytes, -l) 65536
max memory size         (kbytes, -m) unlimited
open files                      (-n) 8192
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) 31113
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

4. core dump的核心转储文件目录与命令规则

   • 默认在应用程序的执行目录下或者程序启动后调用来chdir之后的目录

   • 在/etc/sysctl.conf中写入core dump文件路径

     kernel.core_pattern=/home/aaa/core_dump/core_%e-%p-%u-%s-%t

     %e:应用程序名称
     %p:应用程序进程id
     %u:应用程序线程id
     %s:导致dump的信号id
     %t:产生dump的事件戳
     

   • 执行命令是配置生效

     sudo sysctl -p /etc/sysctl.conf

   • 创建core_dump目录

     mkdir /home/aaa/core_dump

gdb调试的启动与停止

目标程序

确认符号信息加载成功

• 加载失败情况显示

fl@fl:~/tmp/test$ gdb ./core_dump
GNU gdb (Ubuntu 9.2-0ubuntu1~20.04) 9.2
Copyright (C) 2020 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-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:
    <http://www.gnu.org/software/gdb/documentation/>.

For help, type "help".
Type "apropos word" to search for commands related to "word"...
./core_dump: No such file or directory. <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
(gdb) 

• 加载成功情况显示

fl@fl:~/tmp/test$ gdb ./core_dump
GNU gdb (Ubuntu 9.2-0ubuntu1~20.04) 9.2
Copyright (C) 2020 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-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:
    <http://www.gnu.org/software/gdb/documentation/>.

For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from ./core_dump...  <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
(gdb) 

指定进程

1. 运行程序./core_dump22

$ ./core_dump22
1
2
3
...

2. 查询该程序的进程id

$ ps -ef | grep core_dump22
fl         75837   69623  0 18:48 pts/0    00:00:00 ./core_dump22
fl         76089   71367  0 18:50 pts/1    00:00:00 grep --color=auto core_dump22

3. attach进程，此操作需要root权限，sudo gdb attach 75837

$ sudo gdb attach 75837   
GNU gdb (Ubuntu 9.2-0ubuntu1~20.04) 9.2
Copyright (C) 2020 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-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:
    <http://www.gnu.org/software/gdb/documentation/>.

For help, type "help".
Type "apropos word" to search for commands related to "word"...
attach: No such file or directory.
Attaching to process 75837
Reading symbols from /home/fl/tmp/test/core_dump22...
(No debugging symbols found in /home/fl/tmp/test/core_dump22)
Reading symbols from /lib/x86_64-linux-gnu/libstdc++.so.6...
(No debugging symbols found in /lib/x86_64-linux-gnu/libstdc++.so.6)
Reading symbols from /lib/x86_64-linux-gnu/libc.so.6...
Reading symbols from /usr/lib/debug//lib/x86_64-linux-gnu/libc-2.31.so...
Reading symbols from /lib/x86_64-linux-gnu/libm.so.6...
Reading symbols from /usr/lib/debug//lib/x86_64-linux-gnu/libm-2.31.so...
Reading symbols from /lib64/ld-linux-x86-64.so.2...
(No debugging symbols found in /lib64/ld-linux-x86-64.so.2)
Reading symbols from /lib/x86_64-linux-gnu/libgcc_s.so.1...
(No debugging symbols found in /lib/x86_64-linux-gnu/libgcc_s.so.1)
--Type <RET> for more, q to quit, c to continue without paging-- 

4. 此时，程序进入挂起状态
5. 执行具体的调试操作，需要继续执行程序使用continue命令
6. 调试完成后使用命令detach指定进程，使用命令quit退出gdb

(gdb) detach
Detaching from program: /home/fl/tmp/test/core_dump22, process 75837
[Inferior 1 (process 75837) detached]
(gdb) q
$ 

core dump文件

1. 获取core文件和应用程序
2. 使用命令gdb 应用程序 core文件调试，获取crash原因

$ gdb ./core_dump ~/core_dump/core_core_dump-77936-1000-8-1642244418
GNU gdb (Ubuntu 9.2-0ubuntu1~20.04) 9.2
Copyright (C) 2020 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-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:
    <http://www.gnu.org/software/gdb/documentation/>.

For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from ./core_dump...
[New LWP 77936]
Core was generated by `./core_dump'.
Program terminated with signal SIGFPE, Arithmetic exception.
#0  0x0000560c0c46719f in main (argc=1, argv=0x7fff72528708) at core_dump.c:9
9           c         = a / b;
(gdb) 

3. 调试。。。找到carsh原因。

结论

不论是gdb还是windbg，差别是命令语法不一致，调试原理大同小异。