Now that we've done one section manually, let's graduate and use the `readelf -S` of the other sections:
``
  [Nr] Name              Type             Address           Offset
       Size              EntSize          Flags  Link  Info  Align
  [ 2] .text             PROGBITS         0000000000000000  00000210
       0000000000000027  0000000000000000  AX       0     0     16
``

`.text` is executable but not writable: if we try to write to it Linux segfaults. Let's see if we really have some code there:
``
objdump -d hello_world.o
``
gives:
``
hello_world.o:     file format elf64-x86-64


Disassembly of section .text:

0000000000000000 <_start>:
   0:       b8 01 00 00 00          mov    $0x1,%eax
   5:       bf 01 00 00 00          mov    $0x1,%edi
   a:       48 be 00 00 00 00 00    movabs $0x0,%rsi
  11:       00 00 00
  14:       ba 0d 00 00 00          mov    $0xd,%edx
  19:       0f 05                   syscall
  1b:       b8 3c 00 00 00          mov    $0x3c,%eax
  20:       bf 00 00 00 00          mov    $0x0,%edi
  25:       0f 05                   syscall
``

If we grep `b8 01 00 00` on the `hd`, we see that this only occurs at `00000210`, which is what the section says. And the Size is 27, which matches as well. So we must be talking about the right section.

This looks like the right code: a `write` followed by an `exit`.

The most interesting part is line `a` which does:
``
movabs $0x0,%rsi
``
to pass the address of the string to the system call. Currently, the `0x0` is just a placeholder. After linking happens, it will be modified to contain:
``
4000ba: 48 be d8 00 60 00 00    movabs $0x6000d8,%rsi
``
This modification is possible because of the data of the `.rela.text` section.


 Discussion on ".text section" by Ciro Santilli (@cirosantilli, 34)

 Discussion on "`.text` section" by Ciro Santilli (@cirosantilli, 34)