title: ELF, PIE ASLR and everything in between, specifically within Linux
body: <p>Before asking my question, I would like to cover some few technical details I want to make sure I've got correct:</p>
  <ul>
  <li><p>A Position Independent Executable (PIE) is a program that would be able to execute regardless of which memory address it is loaded into, right?</p>
  </li>
  <li><p>ASLR (Address Space Layout Randomization) pretty much states that in order to keep addresses static, we would randomize them in some manner,</p>
  </li>
  </ul>
  <p>I've read that specifically within Linux and Unix based systems, implementing ASLR is possible regardless of if our code is a PIE, if it is PIE, all jumps, calls and offsets are relative hence we have no problem.
  If it's not, code somehow gets modified and addresses are edited regardless of whether the code is an executable or a shared object.</p>
  <p>Now this leads me to ask a few questions</p>
  <ol>
  <li><p>If ASLR is possible to implement within codes that aren't PIE and are executables AND NOT SHARED / RELOCATABLE OBJECT (<strong>I KNOW HOW RELOCATION WORKS WITHIN RELOCATABLE OBJECTS!!!!</strong>), how is it done? ELF format should hold no section that states where within the code sections are functions so the kernel loader could modify it, right? ASLR should be a kernel functionality so how on earth could, for example, an executable containing, for example, these instructions.</p>
  <p><strong>pseudo code:</strong></p>
  <pre><code> inc_eax:
    add eax, 5
    ret
  
   main:
    mov eax, 5
    mov ebx, 6
    call ABSOLUTE_ADDRES{inc_eax}
  </code></pre>
  <p>How would the kernel executable loader know how to change the
  addresses if they aren't stored in some relocatable table within the ELF
  file and aren't relative in order to load the executable into some
  random address?</p>
  </li>
  <li><p>Let's say I'm wrong, and in order to implement ASLR you must have a
  PIE executable.  All segments are relative. How would one compile a
  C++ OOP code and make it work, for example, if I have some instance
  of a class using a pointer to a virtual table within its struct,
  and that virtual table should hold absolute addresses, hence I
  wouldn't be able to compile a pure PIE for C++ programs that have
  usage of run time virtual tables, and again ASLR isn't possible....
  I doubt  that virtual tables would contain relative addresses and
  there would be a different virtual table for each call of some
  virtual function...</p>
  </li>
  <li><p>My last and least significant question is regarding ELF and PIE — is there some special way to detect an ELF executable is PIE? I'm familiar with the ELF format so I doubt that there is a way, but I might be wrong.  Anyway, if there isn't a way, how does the kernel loader know if our executable is PIE hence it could use ASLR on it.</p>
  </li>
  </ol>
  <p>I've got this all messed up in my head and I'd love it if someone could help me here.</p>