使用GDB分析core dump文件

首先需要对环境进行配置，即配置core文件的输出：
运行命令：ulimit -c unlimited 
该命令用于设置core文件大小不限制
修改/etc/sysctl.conf文件，在文件末尾添加下面一行
kernel.core_pattern=/tmp/core-%e
并修改kernel.core_uses_pid = 1 为
kernel.core_uses_pid = 0 这样core文件的格式就是
core-可执行文件的名字，这里我把进程号去掉了，觉得进程号在此处没多大用处。文件所在目录为/tmp下，也可以自己修改为可执行文件所在目录，这样比较直观。
然后运行命令：sysctl -p /etc/sysctl.conf

假设将其值改变为："/home/duanbei/corefile/core-%e-%p-%t"， 那么所有的core文件将保存在"/home/duanbei/corefile"目录下，文件名格式为“core-程序名-pid-时间戳”

格式参数列表

[plain] view plaincopyprint?
%p - insert pid into filename 
%u - insert current uid into filename 
%g - insert current gid into filename 
%s - insert signal that caused the coredump into the filename 
%t - insert UNIX time that the coredump occurred into filename 
%h - insert hostname where the coredump happened into filename 
%e - insert coredumping executable name into filename 
%p - insert pid into filename
%u - insert current uid into filename
%g - insert current gid into filename
%s - insert signal that caused the coredump into the filename
%t - insert UNIX time that the coredump occurred into filename
%h - insert hostname where the coredump happened into filename
%e - insert coredumping executable name into filename
注：如果设置了“%p”，而“/proc/sys/kernel/core_uses_pid”值又为1，则不会添加PID后缀，因文件名中已含该信息

到此配置工作完成，下面对core文件进行分析。
比如我们运行的代码出现段错误，如下：
[root@localhost mywork]# ./testGdb
Segmentation fault (core dumped)
[root@localhost mywork]#
[root@localhost mywork]# gdb testGdb core-testGdb

GNU gdb (GDB) Fedora (7.0-3.fc12)
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later
This is free software: you are free to change and redistribute it.
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and "show warranty" for details.
This GDB was configured as "i686-redhat-linux-gnu".
For bug reporting instructions, please see:
...
Reading symbols from /home/mywork/testGdb...done.

warning: .dynamic section for "/lib/libc.so.6" is not at the expected address

warning: difference appears to be caused by prelink, adjusting expectations
Reading symbols from /lib/libc.so.6...(no debugging symbols found)...done.
Loaded symbols for /lib/libc.so.6
Reading symbols from /lib/ld-linux.so.2...(no debugging symbols found)...done.
Loaded symbols for /lib/ld-linux.so.2
Core was generated by `./testGdb'.
Program terminated with signal 11, Segmentation fault.//显示出了程序崩溃的原因如下
#0  0x0804839a in copy (t=0x0) at testGdb.c:5
5        *t = 10;
Missing separate debuginfos, use: debuginfo-install glibc-2.11-2.i686
(gdb) bt //显示函数调用堆栈，显然是main函数调用copy函数
#0  0x0804839a in copy (t=0x0) at testGdb.c:5
#1  0x080483b0 in main () at testGdb.c:11
(gdb) f 1 //打印栈号为1的堆栈，显示main函数是怎么调用copy函数，f的全名为frame
#1  0x080483b0 in main () at testGdb.c:11
11        copy(s);
(gdb) p s  //打印变量的值
$1 = 0x0