How to find the offset of the section header string table of an elf file?

Question

I have to write a C program that prints an ELF file. I\'m having trouble figuring out where the section header string table is.

Let\'s say I have a file that gave me

Answer 1

This is what I do:

#pragma pack(push,1)

typedef struct
{
  uint8  e_ident[16];
  uint16 e_type;
  uint16 e_machine;
  uint32 e_version;
  uint32 e_entry;
  uint32 e_phoff;
  uint32 e_shoff;
  uint32 e_flags;
  uint16 e_ehsize;
  uint16 e_phentsize;
  uint16 e_phnum;
  uint16 e_shentsize;
  uint16 e_shnum;
  uint16 e_shstrndx;
} Elf32Hdr;

typedef struct
{
  uint32 sh_name;
  uint32 sh_type;
  uint32 sh_flags;
  uint32 sh_addr;
  uint32 sh_offset;
  uint32 sh_size;
  uint32 sh_link;
  uint32 sh_info;
  uint32 sh_addralign;
  uint32 sh_entsize;
} Elf32SectHdr;

#pragma pack(pop)

{
  FILE* ElfFile = NULL;
  char* SectNames = NULL;
  Elf32Hdr elfHdr;
  Elf32SectHdr sectHdr;
  uint idx;

  // ...

  // read ELF header
  fread(&elfHdr, 1, sizeof elfHdr, ElfFile);

  // read section name string table
  // first, read its header
  fseek(ElfFile, elfHdr.e_shoff + elfHdr.e_shstrndx * sizeof sectHdr, SEEK_SET);
  fread(§Hdr, 1, sizeof sectHdr, ElfFile);

  // next, read the section, string data
  SectNames = malloc(sectHdr.sh_size);
  fseek(ElfFile, sectHdr.sh_offset, SEEK_SET);
  fread(SectNames, 1, sectHdr.sh_size, ElfFile);

  // read all section headers
  for (idx = 0; idx < elfHdr.e_shnum; idx++)
  {
    const char* name = "";

    fseek(ElfFile, elfHdr.e_shoff + idx * sizeof sectHdr, SEEK_SET);
    fread(§Hdr, 1, sizeof sectHdr, ElfFile);

    // print section name
    if (sectHdr.sh_name);
      name = SectNames + sectHdr.sh_name;
    printf("%2u %s\n", idx, name);
  }

  // ...
}