How to display the symbol's type like the nm command?

Question

I'm studying the ELF format right now. I have to code a simple nm fonction (without the options). I'm already printing on the output the symbol's value and the symbol's name.

Here's the nm output :

value             type    name
0000000000600e30  D       __DTOR_END__

I have the same one, but without the 'type'. I am using the ELF64_Sym structure, as follow :

typedef struct {
    Elf64_Word      st_name;
    unsigned char   st_info;
    unsigned char   st_other;
    Elf64_Half      st_shndx;
    Elf64_Addr      st_value;
    Elf64_Xword     st_size; 
} Elf64_Sym;

I know that I have to use the st_info variable and this macro :

#define ELF64_ST_TYPE(info)          ((info) & 0xf)

to get the symbol's type. But, the symbol type can be a macro as follow :

NAME            VALUE
STT_NOTYPE      0
STT_OBJECT      1
STT_FUNC        2
STT_SECTION     3
STT_FILE        4
STT_LOPROC      13
STT_HIOPROC     15

And I would like to know is how can I get from these macros the letters printed by nm, example:

 U, u, A, a, T, t, R, r, W, w

Answer 1

Ok I did some researchs and here's my function to get the correct character depending on the symbol. Feel free to add / edit some characters.

char            print_type(Elf64_Sym sym, Elf64_Shdr *shdr)
{
  char  c;

  if (ELF64_ST_BIND(sym.st_info) == STB_GNU_UNIQUE)
    c = 'u';
  else if (ELF64_ST_BIND(sym.st_info) == STB_WEAK)
    {
      c = 'W';
      if (sym.st_shndx == SHN_UNDEF)
        c = 'w';
    }
  else if (ELF64_ST_BIND(sym.st_info) == STB_WEAK && ELF64_ST_TYPE(sym.st_info) == STT_OBJECT)
    {
      c = 'V';
      if (sym.st_shndx == SHN_UNDEF)
        c = 'v';
    }
  else if (sym.st_shndx == SHN_UNDEF)
    c = 'U';
  else if (sym.st_shndx == SHN_ABS)
    c = 'A';
  else if (sym.st_shndx == SHN_COMMON)
    c = 'C';
  else if (shdr[sym.st_shndx].sh_type == SHT_NOBITS
       && shdr[sym.st_shndx].sh_flags == (SHF_ALLOC | SHF_WRITE))
    c = 'B';
  else if (shdr[sym.st_shndx].sh_type == SHT_PROGBITS
       && shdr[sym.st_shndx].sh_flags == SHF_ALLOC)
    c = 'R';
  else if (shdr[sym.st_shndx].sh_type == SHT_PROGBITS
       && shdr[sym.st_shndx].sh_flags == (SHF_ALLOC | SHF_WRITE))
    c = 'D';
  else if (shdr[sym.st_shndx].sh_type == SHT_PROGBITS
       && shdr[sym.st_shndx].sh_flags == (SHF_ALLOC | SHF_EXECINSTR))
    c = 'T';
  else if (shdr[sym.st_shndx].sh_type == SHT_DYNAMIC)
    c = 'D';
  else
    c = '?';
  if (ELF64_ST_BIND(sym.st_info) == STB_LOCAL && c != '?')
    c += 32;
  return c;
}

I'm missing the s, n, p and i. I'm quite sure the 'R' is not good. I'll will edit this when I find it.