.got和.got.plt节有什么区别? [英] What is the difference between .got and .got.plt section?

问题描述

ELF格式的.got和.got.plt节有什么区别?

What is the difference between .got and .got.plt section in ELF format?

推荐答案

我先前的评论是正确的:

My previous comment turns to be right:

我认为.got用于与全局变量"有关的重定位，而.got.plt是在解析过程绝对地址时与.plt一起起作用的辅助部分.

I think .got is for relocations regarding global 'variables' while .got.plt is a auxiliary section to act together with .plt when resolving procedures absolute addresses.

下面的示例使事情变得很清楚.

The example below makes things a bit clear.

这些是我的32位i686-linux/lib/libm.so的重定位

These are the relocations for my 32 bits i686-linux /lib/libm.so

Relocation section '.rel.dyn' at offset 0x32b8 contains 8 entries:
 Offset     Info    Type            Sym.Value  Sym. Name
00025030  00000008 R_386_RELATIVE   
00024fd8  00005706 R_386_GLOB_DAT    00025034   _LIB_VERSION
00024fdc  00000406 R_386_GLOB_DAT    00000000   __gmon_start__
00024fe0  00000506 R_386_GLOB_DAT    00000000   _Jv_RegisterClasses
00024fe4  00000806 R_386_GLOB_DAT    00000000   _rtld_global_ro
00024fe8  00000906 R_386_GLOB_DAT    00000000   stderr
00024fec  00013006 R_386_GLOB_DAT    0002507c   signgam
00024ff0  00000e06 R_386_GLOB_DAT    00000000   __cxa_finalize

Relocation section '.rel.plt' at offset 0x32f8 contains 12 entries:
 Offset     Info    Type            Sym.Value  Sym. Name
00025000  00000107 R_386_JUMP_SLOT   00000000   fputs
00025004  00000207 R_386_JUMP_SLOT   00000000   __errno_location
00025008  00000307 R_386_JUMP_SLOT   00000000   sprintf
0002500c  00000407 R_386_JUMP_SLOT   00000000   __gmon_start__
00025010  00000607 R_386_JUMP_SLOT   00000000   strtod
00025014  00000707 R_386_JUMP_SLOT   00000000   __assert_fail
00025018  00000a07 R_386_JUMP_SLOT   00000000   strlen
0002501c  00000b07 R_386_JUMP_SLOT   00000000   strtof
00025020  00000c07 R_386_JUMP_SLOT   00000000   fwrite
00025024  00000d07 R_386_JUMP_SLOT   00000000   strtold
00025028  00005e07 R_386_JUMP_SLOT   00005970   matherr
0002502c  00000e07 R_386_JUMP_SLOT   00000000   __cxa_finalize

请注意，正如您所指出的，有两个重定位部分，即.rel.dyn和.rel.plt.您可以看到，.rel.plt的所有重定位都是R_386_JUMP_SLOT类型，这意味着它们是分支重定位，而.rel.dyn中的几乎所有重定位都是R_386_GLOB_DAT，这意味着全局变量的重定位.

Look that as you noted there are two relocation sections, namely .rel.dyn and .rel.plt. You can see that all relocations for .rel.plt are of type R_386_JUMP_SLOT which means that they are branch relocations on the other hand almost all relocations in .rel.dyn are R_386_GLOB_DAT which means relocation for global variables.

.symtab和.dynsym之间存在另一个细微差别.虽然第一个包含对静态链接编辑期间使用的所有符号的引用，但后面一个仅包含动态链接所需的那些符号.因此，上面提到的重定位仅引用.dynsym部分.

Another subtle difference exist between .symtab and .dynsym. While the first contain references for all symbols used during static link editing the later contain only those symbols needed for dynamic linking. Thus, the relocations mentioned above refer only to .dynsym section.

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