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1 objcopy + gdb的使用

1.1 创建一个debug.c文件，内容如下：

#include 
   
    int main (void){        printf ("Hello world.\n");        return 0;}
   

1.1.1 编译release版本，该版本不支持gdb调试

gcc debug.c -o debug_release

1.1.2 编译debug版本

gcc -g debug.c -o debug_debug

$ lltotal 36drwxr-xr-x 2 guang guang  4096 6月  16 15:14 ./drwxr-xr-x 6 guang guang  4096 6月  16 15:10 ../-rw-r--r-- 1 guang guang    79 6月  16 15:13 debug.c-rwxr-xr-x 1 guang guang 10744 6月  16 15:14 debug_debug*-rwxr-xr-x 1 guang guang  8296 6月  16 15:14 debug_release*

1.1.3 使用objcopy从debug_debug里面提取debug信息

$ objcopy --only-keep-debug debug_debug debug.dbg$ lsdebug.c  debug.dbg  debug_debug  debug_release

1.1.4 使用如下方法让release版本的elf文件支持gdb调试

$ gdb -q --symbol=debug.dbg --exec=debug_releaseReading symbols from debug.dbg...done.(gdb) rStarting program: /home/guang/Develop/trainning/debug/debug_release warning: Probes-based dynamic linker interface failed.Reverting to original interface.Hello world.[Inferior 1 (process 3603) exited normally](gdb)

1.1.5 也可以将debug.dbg合并到debug_release文件中

guang@guang-ubuntu:~/Develop/trainning/debug$ gdb debug_release GNU gdb (Ubuntu 8.1-0ubuntu3) 8.1.0.20180409-gitCopyright (C) 2018 Free Software Foundation, Inc.License GPLv3+: GNU GPL version 3 or later 
   
    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:
    .Find the GDB manual and other documentation resources online at:
    .For help, type "help".Type "apropos word" to search for commands related to "word"...Reading symbols from debug_release...Reading symbols from /home/guang/Develop/trainning/debug/debug.dbg...done.done.(gdb) rStarting program: /home/guang/Develop/trainning/debug/debug_release Hello world.[Inferior 1 (process 3679) exited normally](gdb)
   

2 printk

2.1 打印数据格式，不支持浮点型数据打印

2.2 打印指针

%p：打印指针地址%pF：打印函数指针的函数名和偏移地址%pf：只打印函数指针的函数名，不打印偏移地址

2.3 打印文件名、函数名、行号

2.4 打印等级

2.4.1 打印等级定义

include/linux/kern_levels.h0  KERN_EMERG1  KERN_ALERT2  KERN_CRIT3  KERN_ERR4  KERN_WARNNING5  KERN_NOTICE6  KERN_INFO7  KERN_DEBUG

2.4.2 控制台打印等级修改

方法1：echo 8 > /proc/sys/kernel/printk方法2：dmesg –n 8

3 动态调试

3.1 menuconfig配置内核，使能动态打印

4 内核转储(core dump)

4.1 内核转储的功能

系统会将该程序运行时的：

4.2 造成core dump的原因

内存访问越界 // 数组访问越界多线程读写的数据未加锁保护非法指针    // 空指针、野指针堆栈溢出    // 函数内使用大的数组、大的局部变量

4.2 core dump调试

4.2.1 core dump调试

ulimit –c    // 查看core dump文件记录是否开启ulimit –c 0  // 关闭ulimit –c <1~max> // 设置core文件大小ulimit –c unlimited   // 文件大小不设限

// 调试程序实例#include 
   
    int main (void){        char *p = "hello world";        printf ("%s\n", p);        char *np = NULL;        printf ("%c\n", *np); //访问非法指针        return 0;}
   

guang@guang-net:~/develop/share/debug$ gcc -g -o dump dump.c guang@guang-net:~/develop/share/debug$ ./dumphello worldSegmentation fault (core dumped)guang@guang-net:~/develop/share/debug$ lscore  dump  dump.cguang@guang-net:~/develop/share/debug$ readelf -h core ELF Header:  Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00   Class:                             ELF32  Data:                              2's complement, little endian  Version:                           1 (current)  OS/ABI:                            UNIX - System V  ABI Version:                       0  Type:                              CORE (Core file)  Machine:                           Intel 80386  Version:                           0x1  Entry point address:               0x0  Start of program headers:          52 (bytes into file)  Start of section headers:          0 (bytes into file)  Flags:                             0x0  Size of this header:               52 (bytes)  Size of program headers:           32 (bytes)  Number of program headers:         17  Size of section headers:           0 (bytes)  Number of section headers:         0  Section header string table index: 0  guang@guang-net:~/develop/share/debug$ gdb dump core       // 启动core文件调试 GNU gdb (Ubuntu 7.7.1-0ubuntu5~14.04.2) 7.7.1Copyright (C) 2014 Free Software Foundation, Inc.License GPLv3+: GNU GPL version 3 or later 
   
    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 "i686-linux-gnu".Type "show configuration" for configuration details.For bug reporting instructions, please see:
    .Find the GDB manual and other documentation resources online at:
    .For help, type "help".Type "apropos word" to search for commands related to "word"...Reading symbols from dump...done.[New LWP 3443]Core was generated by `./dump'.Program terminated with signal SIGSEGV, Segmentation fault.#0  0x08048476 in main () at dump.c:99       printf ("%c\n", *np);(gdb) bt                          //用bt指令调试，发现代码在dump.c第9行出现了问题#0  0x08048476 in main () at dump.c:9(gdb)
   

4.2.2 core dump文件格式设置

查看文件格式：cat /proc/sys/kernel/core_pattern设置文件格式：echo ./core.%e.%p> /proc/sys/kernel/core_pattern    Core dump文件格式：        %p 所dump进程的进程ID        %u 所dump进程的实际用户ID        %g 所dump进程的实际组ID        %s 导致本次core dump的信号        %t core dump的时间 (由1970年1月1日计起的秒数)        %h 主机名        %e 程序文件名

4.2.3 core dump文件系统自启动生效

系统自启动生效：/etc/rc.local //在文件中加入上述命令行即可

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