概述

通常公司发布的可执行程序和动态共享库（.SO）里面的符号表都被移除了，所以每次遇到core dump的时候，都需要将符号表导入到/usr/lib/debug目录下。一直没弄明白为啥是这个目录，能不能是其他目录，这篇文章探索一下相关的知识，做个记录。

我们要给我们生成的可执行文件和.SO瘦身，因为这样可以节省更多的磁盘空间，所以我们移除了debug信息，移除了符号表信息，同时我们还希望万一出事了，比如coredump了，我们能获取更多的信息，这时候我们又希望有符号表。

我们等不能做到呢。Linux下是怎么解决这个矛盾的呢？先看第一个问题，程序减肥。

1.程序减肥

1.1下面是简单的代码

main调用了foo，foo调用了bar，其中bar故意访问了非法地址，为了引起core dump。

tsh@tsh-virtual-machine:~/codeTest/segmentErr/stripTest$ cat stripTest.c 
#include<stdio.h>
#include<stdlib.h>


int bar()
{
    char *p = NULL;
    fprintf(stderr,"I am bar，I will core dump\n");
    fprintf(stderr,"%s",p);
    return 0;
}

int foo()
{
    int i ;
    fprintf(stderr, "I am foo,I will call bar\n");
    bar();
    return 0;
}
int main()
{
    fprintf(stderr,"I am main, I wll can foo\n");
    foo();
    return 0;
}
tsh@tsh-virtual-machine:~/codeTest/segmentErr/stripTest$ 

1.2 编译debug版本

先编译出一个debug版本来，然后我们看下可执行程序的大小

tsh@tsh-virtual-machine:~/codeTest/segmentErr/stripTest$ gcc -g -o stripTest stripTest.c 
tsh@tsh-virtual-machine:~/codeTest/segmentErr/stripTest$ ll
total 24
drwxrwxr-x 2 tsh tsh  4096 Apr 30 10:23 ./
drwxrwxr-x 5 tsh tsh  4096 Apr 30 09:42 ../
-rwxrwxr-x 1 tsh tsh 11152 Apr 30 10:23 stripTest*
-rw-rw-r-- 1 tsh tsh   361 Apr 30 09:43 stripTest.c
tsh@tsh-virtual-machine:~/codeTest/segmentErr/stripTest$ 

1.3 查看section信息

tsh@tsh-virtual-machine:~/codeTest/segmentErr/stripTest$ readelf -S stripTest
There are 36 section headers, starting at offset 0x2290:

Section Headers:
  [Nr] Name              Type             Address           Offset
       Size              EntSize          Flags  Link  Info  Align
  [ 0]                   NULL             0000000000000000  00000000
       0000000000000000  0000000000000000           0     0     0
  [ 1] .interp           PROGBITS         0000000000400238  00000238
       000000000000001c  0000000000000000   A       0     0     1
  [ 2] .note.ABI-tag     NOTE             0000000000400254  00000254
       0000000000000020  0000000000000000   A       0     0     4
  [ 3] .note.gnu.build-i NOTE             0000000000400274  00000274
       0000000000000024  0000000000000000   A       0     0     4
  [ 4] .gnu.hash         GNU_HASH         0000000000400298  00000298
       0000000000000024  0000000000000000   A       5     0     8
  [ 5] .dynsym           DYNSYM           00000000004002c0  000002c0
       0000000000000090  0000000000000018   A       6     1     8
  [ 6] .dynstr           STRTAB           0000000000400350  00000350
       000000000000004c  0000000000000000   A       0     0     1
  [ 7] .gnu.version      VERSYM           000000000040039c  0000039c
       000000000000000c  0000000000000002   A       5     0     2
  [ 8] .gnu.version_r    VERNEED          00000000004003a8  000003a8
       0000000000000020  0000000000000000   A       6     1     8
  [ 9] .rela.dyn         RELA             00000000004003c8  000003c8
       0000000000000030  0000000000000018   A       5     0     8
  [10] .rela.plt         RELA             00000000004003f8  000003f8
       0000000000000048  0000000000000018  AI       5    24     8
  [11] .init             PROGBITS         0000000000400440  00000440
       000000000000001a  0000000000000000  AX       0     0     4
  [12] .plt              PROGBITS         0000000000400460  00000460
       0000000000000040  0000000000000010  AX       0     0     16
  [13] .plt.got          PROGBITS         00000000004004a0  000004a0
       0000000000000008  0000000000000000  AX       0     0     8
  [14] .text             PROGBITS         00000000004004b0  000004b0
       0000000000000222  0000000000000000  AX       0     0     16
  [15] .fini             PROGBITS         00000000004006d4  000006d4
       0000000000000009  0000000000000000  AX       0     0     4
  [16] .rodata           PROGBITS         00000000004006e0  000006e0
       0000000000000055  0000000000000000   A       0     0     4
  [17] .eh_frame_hdr     PROGBITS         0000000000400738  00000738
       0000000000000044  0000000000000000   A       0     0     4
  [18] .eh_frame         PROGBITS         0000000000400780  00000780
       0000000000000134  0000000000000000   A       0     0     8
  [19] .init_array       INIT_ARRAY       0000000000600e10  00000e10
       0000000000000008  0000000000000000  WA       0     0     8
  [20] .fini_array       FINI_ARRAY       0000000000600e18  00000e18
       0000000000000008  0000000000000000  WA       0     0     8
  [21] .jcr              PROGBITS         0000000000600e20  00000e20
       0000000000000008  0000000000000000  WA       0     0     8
  [22] .dynamic          DYNAMIC          0000000000600e28  00000e28
       00000000000001d0  0000000000000010  WA       6     0     8
  [23] .got              PROGBITS         0000000000600ff8  00000ff8
       0000000000000008  0000000000000008  WA       0     0     8
  [24] .got.plt          PROGBITS         0000000000601000  00001000
       0000000000000030  0000000000000008  WA       0     0     8
  [25] .data             PROGBITS         0000000000601030  00001030
       0000000000000010  0000000000000000  WA       0     0     8
  [26] .bss              NOBITS           0000000000601040  00001040
       0000000000000010  0000000000000000  WA       0     0     32
  [27] .comment          PROGBITS         0000000000000000  00001040
       0000000000000035  0000000000000001  MS       0     0     1
  [28] .debug_aranges    PROGBITS         0000000000000000  00001075
       00000000000000