uint32_t read_magic(FILE *obj_file, int offset)
{
  uint32_t magic;
  fseek(obj_file, offset, SEEK_SET);
  fread(&magic, sizeof(uint32_t), 1, obj_file);
  printf("%x\n", magic);
  return magic;
}
gives feedfacf as expected.

With bitstring:

let () =
  let file = Sys.argv.(1) in
  let b = Bitstring.bitstring_of_file file in
  bitmatch b with
| { magic : 32 : littleendian} -> Printf.printf "%x\n" (Int32.to_int magic)
| { _ } -> ()

getting 7ffffffffeedfacf
where I understand the 7ffffff means NaN