转自:http://blog.csdn.net/mrjy1475726263/article/details/44116289
源自:http://andyniu.iteye.com/blog/1965571
core dump的概念:
A core dump is the recorded state of the working memory of a computer program at a specific time, generally when the program has terminated abnormally (crashed). In practice, other key pieces of program state are usually dumped at the same time, including the processor registers, which may include the program counter and stack pointer, memory management information, and other processor and operating system flags and information. The name comes from the once-standard memory technology core memory. Core dumps are often used to diagnose or debug errors in computer programs.
On many operating systems, a fatal error in a program automatically triggers a core dump, and by extension the phrase "to dump core" has come to mean, in many cases, any fatal error, regardless of whether a record of the program memory is created.
在linux平台下,设置core dump文件生成的方法:
如何产生Core Dump
发生doredump一般都是在进程收到某个信号的时候,Linux上现在大概有60多个信号,可以使用 kill -l 命令全部列出来。
sagi@sagi-laptop:~$ kill -l
1) SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL 5) SIGTRAP
6) SIGABRT 7) SIGBUS 8) SIGFPE 9) SIGKILL 10) SIGUSR1
11) SIGSEGV 12) SIGUSR2 13) SIGPIPE 14) SIGALRM 15) SIGTERM
16) SIGSTKFLT 17) SIGCHLD 18) SIGCONT 19) SIGSTOP 20) SIGTSTP
21) SIGTTIN 22) SIGTTOU 23) SIGURG 24) SIGXCPU 25) SIGXFSZ
26) SIGVTALRM 27) SIGPROF 28) SIGWINCH 29) SIGIO 30) SIGPWR
31) SIGSYS 34) SIGRTMIN 35) SIGRTMIN+1 36) SIGRTMIN+2 37) SIGRTMIN+3
38) SIGRTMIN+4 39) SIGRTMIN+5 40) SIGRTMIN+6 41) SIGRTMIN+7 42) SIGRTMIN+8
43) SIGRTMIN+9 44) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12 47) SIGRTMIN+13
48) SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14 51) SIGRTMAX-13 52) SIGRTMAX-12
53) SIGRTMAX-11 54) SIGRTMAX-10 55) SIGRTMAX-9 56) SIGRTMAX-8 57) SIGRTMAX-7
58) SIGRTMAX-6 59) SIGRTMAX-5 60) SIGRTMAX-4 61) SIGRTMAX-3 62) SIGRTMAX-2
63) SIGRTMAX-1 64) SIGRTMAX
针对特定的信号,应用程序可以写对应的信号处理函数。如果不指定,则采取默认的处理方式, 默认处理是coredump的信号如下:
3)SIGQUIT 4)SIGILL 6)SIGABRT 8)SIGFPE 11)SIGSEGV 7)SIGBUS 31)SIGSYS
5)SIGTRAP 24)SIGXCPU 25)SIGXFSZ 29)SIGIOT
我们看到SIGSEGV在其中,一般数组越界或是访问空指针都会产生这个信号。另外虽然默认是这样的,但是你也可以写自己的信号处理函数改变默认行为,更多信号相关可以看参考链接33。
上述内容只是产生coredump的必要条件,而非充分条件。要产生core文件还依赖于程序运行的shell,可以通过ulimit -a命令查看,输出内容大致如下:
sagi@sagi-laptop:~$ ulimit -a
core file size (blocks, -c) 0
data seg size (kbytes, -d) unlimited
scheduling priority (-e) 20
file size (blocks, -f) unlimited
pending signals (-i) 16382
max locked memory (kbytes, -l) 64
max memory size (kbytes, -m) unlimited
open files (-n) 1024
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) unlimited
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited
看到第一行了吧,core file size,这个值用来限制产生的core文件大小,超过这个值就不会保存了。我这里输出是0,也就是不会保存core文件,即使产生了,也保存不下来==! 要改变这个设置,可以使用ulimit -c unlimited。
OK, 现在万事具备,只缺一个能产生Core的程序了,介个对C程序员来说太容易了。
- <span style="margin:0px;padding:0px;border:0px;color:rgb(51,153,51);vertical-align:baseline;background-color:transparent;">#include <stdio.h>;</span>
- <span style="margin:0px;padding:0px;border:0px;color:rgb(51,153,51);vertical-align:baseline;background-color:transparent;">#include <stdlib.h>;</span>
- <span style="margin:0px;padding:0px;border:0px;color:rgb(153,51,51);vertical-align:baseline;background-color:transparent;">int</span> crash<span style="margin:0px;padding:0px;border:0px;color:rgb(0,153,0);vertical-align:baseline;background-color:transparent;">(</span><span style="margin:0px;padding:0px;border:0px;color:rgb(0,153,0);vertical-align:baseline;background-color:transparent;">)</span>
- <span style="margin:0px;padding:0px;border:0px;color:rgb(0,153,0);vertical-align:baseline;background-color:transparent;">{</span>
- <span style="margin:0px;padding:0px;border:0px;color:rgb(153,51,51);vertical-align:baseline;background-color:transparent;">char</span> <span style="margin:0px;padding:0px;border:0px;color:rgb(51,153,51);vertical-align:baseline;background-color:transparent;">*</span>xxx <span style="margin:0px;padding:0px;border:0px;color:rgb(51,153,51);vertical-align:baseline;background-color:transparent;">=</span> <span style="margin:0px;padding:0px;border:0px;color:rgb(255,0,0);vertical-align:baseline;background-color:transparent;">"crash!!"</span><span style="margin:0px;padding:0px;border:0px;color:rgb(51,153,51);vertical-align:baseline;background-color:transparent;">;</span>
- xxx<span style="margin:0px;padding:0px;border:0px;color:rgb(0,153,0);vertical-align:baseline;background-color:transparent;">[</span><span style="margin:0px;padding:0px;border:0px;color:rgb(0,0,221);vertical-align:baseline;background-color:transparent;">1</span><span style="margin:0px;padding:0px;border:0px;color:rgb(0,153,0);vertical-align:baseline;background-color:transparent;">]</span> <span style="margin:0px;padding:0px;border:0px;color:rgb(51,153,51);vertical-align:baseline;background-color:transparent;">=</span> <span style="margin:0px;padding:0px;border:0px;color:rgb(255,0,0);vertical-align:baseline;background-color:transparent;">‘D‘</span><span style="margin:0px;padding:0px;border:0px;color:rgb(51,153,51);vertical-align:baseline;background-color:transparent;">;</span> <span style="margin:0px;padding:0px;border:0px;color:rgb(102,102,102);font-style:italic;vertical-align:baseline;background-color:transparent;">// 写只读存储区!</span>
- <span style="margin:0px;padding:0px;border:0px;color:rgb(177,177,0);vertical-align:baseline;background-color:transparent;">return</span> <span style="margin:0px;padding:0px;border:0px;color:rgb(0,0,221);vertical-align:baseline;background-color:transparent;">2</span><span style="margin:0px;padding:0px;border:0px;color:rgb(51,153,51);vertical-align:baseline;background-color:transparent;">;</span>
- <span style="margin:0px;padding:0px;border:0px;color:rgb(0,153,0);vertical-align:baseline;background-color:transparent;">}</span>
- <span style="margin:0px;padding:0px;border:0px;color:rgb(153,51,51);vertical-align:baseline;background-color:transparent;">int</span> foo<span style="margin:0px;padding:0px;border:0px;color:rgb(0,153,0);vertical-align:baseline;background-color:transparent;">(</span><span style="margin:0px;padding:0px;border:0px;color:rgb(0,153,0);vertical-align:baseline;background-color:transparent;">)</span>
- <span style="margin:0px;padding:0px;border:0px;color:rgb(0,153,0);vertical-align:baseline;background-color:transparent;">{</span>
- <span style="margin:0px;padding:0px;border:0px;color:rgb(177,177,0);vertical-align:baseline;background-color:transparent;">return</span> crash<span style="margin:0px;padding:0px;border:0px;color:rgb(0,153,0);vertical-align:baseline;background-color:transparent;">(</span><span style="margin:0px;padding:0px;border:0px;color:rgb(0,153,0);vertical-align:baseline;background-color:transparent;">)</span><span style="margin:0px;padding:0px;border:0px;color:rgb(51,153,51);vertical-align:baseline;background-color:transparent;">;</span>
- <span style="margin:0px;padding:0px;border:0px;color:rgb(0,153,0);vertical-align:baseline;background-color:transparent;">}</span>
- <span style="margin:0px;padding:0px;border:0px;color:rgb(153,51,51);vertical-align:baseline;background-color:transparent;">int</span> main<span style="margin:0px;padding:0px;border:0px;color:rgb(0,153,0);vertical-align:baseline;background-color:transparent;">(</span><span style="margin:0px;padding:0px;border:0px;color:rgb(0,153,0);vertical-align:baseline;background-color:transparent;">)</span>
- <span style="margin:0px;padding:0px;border:0px;color:rgb(0,153,0);vertical-align:baseline;background-color:transparent;">{</span>
- <span style="margin:0px;padding:0px;border:0px;color:rgb(177,177,0);vertical-align:baseline;background-color:transparent;">return</span> foo<span style="margin:0px;padding:0px;border:0px;color:rgb(0,153,0);vertical-align:baseline;background-color:transparent;">(</span><span style="margin:0px;padding:0px;border:0px;color:rgb(0,153,0);vertical-align:baseline;background-color:transparent;">)</span><span style="margin:0px;padding:0px;border:0px;color:rgb(51,153,51);vertical-align:baseline;background-color:transparent;">;</span>
- <span style="margin:0px;padding:0px;border:0px;color:rgb(0,153,0);vertical-align:baseline;background-color:transparent;">}</span>
上手调试
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#include <stdio.h> int func( int
*p) { *p = 0; } int main() { func(NULL); return
0; } |
Segmentation fault (core dumped)
#0 0x080483ba in func ()
如何定位到行?
#0 0x080483ba in func (p=0x0) at a.c:5
5 *p = 0;
上边的程序编译的时候有一点需要注意,需要带上参数-g, 这样生成的可执行程序中会带上足够的调试信息。编译运行之后你就应该能看见期待已久的“Segment Fault(core dumped)”或是“段错误 (核心已转储)”之类的字眼了。看看当前目录下是不是有个core或是core.xxx的文件。祭出linux下经典的调试器GDB,首先带着core文件载入程序:gdb exefile core,这里需要注意的这个core文件必须是exefile产生的,否则符号表会对不上。载入之后大概是这个样子的:
sagi@sagi-laptop:~$ gdb coredump core
Core was generated by ./coredump‘.
Program terminated with signal 11, Segmentation fault.
#0 0x080483a7 in crash () at coredump.c:8
8 xxx[1] = ‘D‘;
(gdb)
我们看到已经能直接定位到出core的地方了,在第8行写了一个只读的内存区域导致触发Segment Fault信号。在载入core的时候有个小技巧,如果你事先不知道这个core文件是由哪个程序产生的,你可以先随便找个代替一下,比如/usr/bin/w就是不错的选择。比如我们采用这种方法载入上边产生的core,gdb会有类似的输出:
sagi@sagi-laptop:~$ gdb /usr/bin/w core
Core was generated by ./coredump‘.
Program terminated with signal 11, Segmentation fault.
#0 0x080483a7 in ?? ()
(gdb)
可以看到GDB已经提示你了,这个core是由哪个程序产生的。
GDB 常用操作
上边的程序比较简单,不需要另外的操作就能直接找到问题所在。现实却不是这样的,常常需要进行单步跟踪,设置断点之类的操作才能顺利定位问题。下边列出了GDB一些常用的操作。
- 启动程序:run
- 设置断点:b 行号|函数名
- 删除断点:delete 断点编号
- 禁用断点:disable 断点编号
- 启用断点:enable 断点编号
- 单步跟踪:next 也可以简写 n
- 单步跟踪:step 也可以简写 s
- 打印变量:print 变量名字
- 设置变量:set var=value
- 查看变量类型:ptype var
- 顺序执行到结束:cont
- 顺序执行到某一行: util lineno
- 打印堆栈信息:bt