Comment on Silent Hill decompilation just surpased 80%

• elvith@feddit.org ⁨2⁩ ⁨weeks⁩ ago

  I don’t know.

  The gist is… When you write a program/game/… You write source code and then compile it - that means translating the source code into machine readable code. While certain things do usually get lost in this process (e.g. function names, variable names, etc.) you can see the resulting machine code and make a valid assumption about how the original code looked like. This is not a 1:1 reconstruction, but will yield code that should compile to the (basically) same result as the original game.

  If you hit a Jackpot, you find a version of the program/game that was used for testing. Those often contain many pieces of information that would otherwise be stripped from the end result (e.g. aforementioned variable names, function names and so on). If not, it’s a puzzle solved with guess work and experience.

  If you know some specifics about the game (which language was it written in, what compiler was used in which version,…) you can get some better results, as you can take patterns in the machine code and translate them back into what the original code was probably looking like based on the tools used.

  In the end it’s sadly almost everytime still a manual process in which you look at the resulting source code, make some educated guesses based on patterns that are usually used when programming and specific functions that are probably contained in a game and then check those assumptions by changing the code and see if your changes affect the part of the program you thought you were dealing with.

  Say you assume a specific variable/value is the maximum walking speed of the character. Then you change it and try to play the game and see if you can walk faster now. If so, label this value accordingly and go on to the next unknown piece of the puzzle.

  source

  • diabetic_porcupine@lemmy.world ⁨2⁩ ⁨weeks⁩ ago

    Sounds like something that can easily be done with some powerful ai. So the reason it takes so long (why this post is claiming it’s 80%completed) is because of all the manual work. The code is already fully “decompiled” technically as the process of doing so is automatic and only as slow as the device it runs on. If my understanding is correct 80% is roughly how much of the code is rewritten with human readable code. In other words - we understand most of it and we could literally ship it like this with the remaining 20% obfuscated, we just can’t make any changes to that part because we don’t know wtf it does

    source

    • elvith@feddit.org ⁨2⁩ ⁨weeks⁩ ago

      Im inclined to answer with “Yesn’t”

      Yes, the problem is readability. You can get “better” code of you know the exact tooling and settings for compilation, as you can then better guess what optimisations and tricks were used (by the compiler) and you may be able to “undo” them. There are so many places where this will only let you make guesses. You write a loop in your code, the compiler removes the loop and replaced it with another construct that may be a bit faster to execute, but may be way harder to understand - or tedious to change if you need to edit it especially if it’s not a simple change (character can now run faster!) but needs new functionality that would completely break this optimisation (but it’d be trivial to add in the original code).

      Also all context is removed. You won’t work with code like this:

      (Both pseudocode, not bothered to make a real example that maybe even compiles)

      if keyPressed(MOVE_RIGHT){
        player.speed = min(player.MAX_SPEED, player.speed + player.acceleration*frametime)
      }
      else{
         player.speed = player.speed * player.MOVEMENT_DAMPENING * frametime
      }
      

      You’d get something like this:

      int *fi93836290= 0x7363728
      int *fi22425 = &fi93836290+0x23
      fi22425 = fun7362782(0x63627)? fun42638(...)
      //and so on
      

      source
  • QuarterSwede@lemmy.world ⁨2⁩ ⁨weeks⁩ ago

    Thanks for the detailed explanation. That is what I assumed but it’s clearer now.

    source