In this lab you learn how code and data are represented in memory and how to make low-level changes to a program in an assembly language. You will create modifications (mods) to a game.

• Download the ZIP file with the the material for this lab from http://www.disco.ethz.ch/lectures/ti2fp/exercises/disassembly.zip. Unpack it to some local folder.

• 1) Find the correct input to defuse the “bomb”.

• 2) When you run this program, a pop-up will appear that asks you to pay for a license. Disable this pop-up (or postpone it for a long time).

• 3) Now, you are ready to hack into SuperTuxKart! The game is installed on your machines. Show us your abilities by modifying the game in cool ways. For instance, make your kart faster, get better items, etc. Before you start modifying the binary, we recommend you to save a backup copy of it so when you break the game, you always have a clean copy. If you prefer, you can also modify a different game.
  Hint: Have a look at the --demangle option of objdump.

• Text editor: Geany
• Hex editor: Bless
• Disassembler: objdump
• Web assembler/disassembler: https://defuse.ca/online-x86-assembler.htm (Attention: Uses Intel syntax, which has arguments in different order than objdump)

• IA-32 cheat sheet (GNU format): http://www.cs.utsa.edu/~clark/cs3843/IA32cheatSheet.pdf
• Intel IA-32 instruction set reference: http://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-instruction-set-reference-manual-325383.pdf

• We have written a tool which allows you to insert your own machine code (produced e.g. with as) into SuperTuxKart. It is contained in the same zip folder as the other executables.
  Usage: ./elf_tool <executable_file> <new_machine_code_file (inject_code.bin)> <insertion_address>.
  The tool inserts the code into the executable, and writes a jump to the new code at the specified insertion_address (given in hexadecimal, e.g. 80487f0). Note that the inserted jump will overwrite 6 bytes of the code, so if the overwritten code is still needed, you have to repeat it in your new code.
• Assembling: Write assembly in a file called inject_code.s and execute the following command to get the machine code binary file required for the elf_tool: as --32 -o inject_code.o inject_code.s && objcopy -O binary inject_code.o inject_code.bin && rm inject_code.o