在节头 elf 文件中获取 sh_name 成员 [英] getting the sh_name member in a section header elf file

问题描述

我正在尝试通过访问 elf 文件的 sh_name 成员来获取部分名称的正确偏移量，但它一直给我零或空...

I'm trying to get the correct offset to the section name by accessing the sh_name member of an elf file, but it keep giving me zero, or null...

我应该只使用 mmap() 和 elf.h - 没有辅助函数

I'm supposed to only use mmap() and the elf.h - no helper functions

所以我做到了:

void* map_start = mmap(0, fd_stat.st_size, PROT_READ | PROT_WRITE , MAP_SHARED, fd, 0))
header = (Elf32_Ehdr *) map_start;  
secoff = header->e_shoff;    
section = (Elf32_Shdr *)(map_start + secoff); 

但是当我这样做时:

printf("name offset = %d
", (section->sh_name));

它一直给我 0...我做错了什么?

it keeps giving me 0... what am I doing wrong?

推荐答案

当我做 printf("name offset = %d ", (section->sh_name)); 时它一直给我 0...我做错了什么?>

when i do printf("name offset = %d ", (section->sh_name)); it keeps giving me 0... what am I doiing wrong?

你没有做错任何事情.

sh_name 不是指针，它是 .shstrtab 部分的偏移量，其中包含实际的部分名称.

The sh_name is not a pointer, it's an offset into .shstrtab section, which contains the actual section name.

您可以从 header->e_shstrndx 中找到 .shstrtab 部分.

You can find the .shstrtab section from header->e_shstrndx.

更新:

是不是假设将偏移量打印为整数?

isnt it suppose to print the offset as an int?

它打印0.是什么让您相信 0 不是整数?

It prints 0. What made you believe that 0 is not an int?

但是我要打印名字吗?

也许这个例子会解释?

#include <sys/stat.h>
#include <sys/mman.h>
#include <elf.h>
#include <stdio.h>
#include <fcntl.h>


int print_shdr(const char *const fname, size_t size) {
  int fd = open(fname, O_RDONLY);
  char *p = mmap(0, size, PROT_READ, MAP_PRIVATE, fd, 0);

  Elf32_Ehdr *ehdr = (Elf32_Ehdr*)p;
  Elf32_Shdr *shdr = (Elf32_Shdr *)(p + ehdr->e_shoff);
  int shnum = ehdr->e_shnum;

  Elf32_Shdr *sh_strtab = &shdr[ehdr->e_shstrndx];
  const char *const sh_strtab_p = p + sh_strtab->sh_offset;

  for (int i = 0; i < shnum; ++i) {
    printf("%2d: %4d '%s'
", i, shdr[i].sh_name,
           sh_strtab_p + shdr[i].sh_name);
  }

  return 0;
}

int main(int argc, char *argv[])
{
  struct stat st;
  const char *fname = "/proc/self/exe";

  if (argc > 1)
    fname = argv[1];

  if (stat(fname, &st) != 0) {
    perror("stat");
    return 1;
  }
  return print_shdr(fname, st.st_size);
}

$ gcc -g dump_shdr.c -m32 -std=c99
$ ./a.out
 0:    0 ''
 1:   27 '.interp'
 2:   35 '.note.ABI-tag'
 3:   49 '.note.gnu.build-id'
 4:   72 '.hash'
 5:   68 '.gnu.hash'
 6:   78 '.dynsym'
 7:   86 '.dynstr'
 8:   94 '.gnu.version'
 9:  107 '.gnu.version_r'
10:  122 '.rel.dyn'
11:  131 '.rel.plt'
12:  140 '.init'
13:  135 '.plt'
14:  146 '.text'
15:  152 '.fini'
16:  158 '.rodata'
17:  166 '.eh_frame'
18:  176 '.ctors'
19:  183 '.dtors'
20:  190 '.jcr'
21:  195 '.dynamic'
22:  204 '.got'
23:  209 '.got.plt'
24:  218 '.data'
25:  224 '.bss'
26:  229 '.comment'
27:  238 '.debug_aranges'
28:  253 '.debug_pubnames'
29:  269 '.debug_info'
30:  281 '.debug_abbrev'
31:  295 '.debug_line'
32:  307 '.debug_frame'
33:  320 '.debug_str'
34:  331 '.debug_loc'
35:   17 '.shstrtab'
36:    1 '.symtab'
37:    9 '.strtab'

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