从 elf 获取动态符号 table 信息

Question

我正在尝试从 elf 获取动态和静态符号 table 信息。

那是我写的代码：

void symbols(){
    int  i;
    Elf32_Ehdr *header; /* this will point to the header structure */
    header = (Elf32_Ehdr *) map_start;

    Elf32_Shdr *shdr = (Elf32_Shdr *)(map_start + header->e_shoff);

    int shnum = header->e_shnum;
    const char * str_p =NULL;
    Elf32_Shdr *sh_strtab = &shdr[header->e_shstrndx];

    const char *const sh_strtab_p = map_start + sh_strtab->sh_offset;
    int j;

    int k;

    for (i = 0; i < shnum; ++i) {
       if ((shdr[i].sh_type == SHT_SYMTAB)||(shdr[i].sh_type==SHT_DYNSYM)){
          str_p =(char *) shdr[shdr[i].sh_link].sh_offset;
          Elf32_Sym *symboler =(Elf32_Sym *)(map_start + shdr[i].sh_offset);
          for(j=0;j<(shdr[i].sh_size/shdr[i].sh_entsize);j++){
              printf("%u ", symboler->st_size); 
              printf("%x ", symboler->st_value); 
              printf("%u ", symboler->st_shndx);
              printf("%s\n",(char *) ((int)map_start+ (int)str_p + symboler->st_name));
              symboler++;
          }
       }
    }
}

问题出在动态符号 table，例如：

 0 0 0 
 0 0 0 __gmon_start__
 0 0 0 __libc_start_main
 0 0 0 fopen
 0 0 0 fgetc
 0 0 0 printf
 0 0 0 atoi
 4 80485dc 15 _IO_stdin_used

当我使用 readelf 时，我得到这个名字：

 0: 00000000     0 NOTYPE  LOCAL  DEFAULT  UND 
 1: 00000000     0 NOTYPE  WEAK   DEFAULT  UND __gmon_start__
 2: 00000000     0 FUNC    GLOBAL DEFAULT  UND __libc_start_main@GLIBC_2.0 (2)
 3: 00000000     0 FUNC    GLOBAL DEFAULT  UND fopen@GLIBC_2.1 (3)
 4: 00000000     0 FUNC    GLOBAL DEFAULT  UND fgetc@GLIBC_2.0 (2)
 5: 00000000     0 FUNC    GLOBAL DEFAULT  UND printf@GLIBC_2.0 (2)
 6: 00000000     0 FUNC    GLOBAL DEFAULT  UND atoi@GLIBC_2.0 (2)
 7: 080485dc     4 OBJECT  GLOBAL DEFAULT   15 _IO_stdin_used

为什么我的版本是 atoi 而 readelf 是 atoi@GLIBC_2.0 (2)？我该如何解决这个问题？

Answer 1

readelf 显示有关符号版本及其名称的信息。

解释了符号版本控制here。

Symbol versioning - simple explanation

Symbol versioning allows a library to define its exported symbols through the use of a map file. It also allows one library to provide multiple versions of the same symbol. In the past, without symbol versioning, this was accomplished by bumping the shared library version (libfoo.so.1, libfoo.so.2, etc.). Now one library version can provide multiple versions of the same symbol.

有关详细信息，请参阅 this page。

从 elf 获取动态符号 table 信息

getting dynamic symbol table information from elf

c

elf

Symbol versioning - simple explanation