elf文件中的全局变量在哪里 [英] Where are global variables located in the elf file

问题描述

我想了解elf文件，但是当我想到全局变量，全局静态变量和作用域静态变量时，
会让我有些困惑。例如：

  int a = 2; 
 int b; 
 
静态整数c = 4; 
 static int d; 
 
 void fun（）{
 static int e = 6; 
 static int f; 
} 
 
 
 int main（void）{
 fun（）; 
} 
  

谁能分辨出每个变量属于哪个细分市场？我认为
b ， d 和 f 属于 .bss 段和 a ， c 和 e 属于数据段，但我不知道全局静态变量和elf文件中的全局变量之间的区别。

解决方案

您可以使用 objdump -t 查看符号表：

  $ objdump -t foo | grep -P'\b（a | b | c | d | e | f）\b'
 0000000000601034 l O .data 0000000000000004 c 
 0000000000601040 l O .bss 0000000000000004 d 
 0000000000601044 l O .bss 0000000000000004 f.1710 
 0000000000601038 l O .data 0000000000000004 e.1709 
 0000000000601048 g O .bss 0000000000000004 b 
 0000000000601030 g O .data 0000000000000004 a 
  

您说得对， b ， d 和 f 是 .bss 而 a ， c 和 e 是 .data 。符号是否静态是记录在符号表的单独标志中，即 l 或 g 标志在第二列中。

elf（5）手册页表示这些记录是使用 st_info <的 STB_LOCAL 和 STB_GLOBAL 值记录的/ code>符号表的成员。 /usr/include/elf.h 表示 STB_GLOBAL 为1，而 STB_LOCAL 为0。有一个宏 ST_BIND 来检索 st_info 字段的绑定位。 / p>



---

objdump 还有很多其他标志，请参见< a href = http://linux.die.net/man/1/objdump>手册页。 objdump 适用于所有体系结构，但是还有一个 elfdump 工具可以更好地显示特定于elf的工具东东。 objdump 和底层的 BFD 库在显示某些特定于文件格式的数据方面做得不好。

I want to learn about elf files, but when I think of global variables, global static variables and scope static variables, I have some confusion. For example:

int a = 2;
int b;

static int c = 4;
static int d;

void fun(){
  static int e = 6;
  static int f;
}


int main(void){
   fun();
}

Who can tell which segment each variable belongs to? in my opinion, b, d and f belong to the .bss segment and a,c and e belong to the data segment, but I don't know the difference between global static variables and global variables in elf file.

解决方案

You can use objdump -t to view the symbol table:

$ objdump -t foo | grep -P '      \b(a|b|c|d|e|f)\b'
0000000000601034 l     O .data  0000000000000004              c
0000000000601040 l     O .bss   0000000000000004              d
0000000000601044 l     O .bss   0000000000000004              f.1710
0000000000601038 l     O .data  0000000000000004              e.1709
0000000000601048 g     O .bss   0000000000000004              b
0000000000601030 g     O .data  0000000000000004              a

You are right that b, d, and f are .bss while a, c, and e are .data. Whether the symbol is static or not is recorded in a separate flag of the symbol table—that’s the l or g flag in the second column.

The elf(5) man page says that these are recorded using the STB_LOCAL and STB_GLOBAL values for the st_info member of the symbol table. /usr/include/elf.h says that STB_GLOBAL is 1, while STB_LOCAL is 0. There is a macro ST_BIND to retrieve the binding bits of the st_info field.

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There are tons of other flags for objdump—see the man page. objdump works with all architectures, but there is also an elfdump tool that does a bit better job of showing elf-specific stuff. objdump and the underlying BFD library can do a bad job of showing some file-format-specific data.

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