Guide: Discovering Assembly

To follow this guide, you will need to navigate to the guides/discovering-assembly/support directory.

  1. Open the ex1.asm file and read the comments. Assemble it by using the make utility and run it. Using gdb, go through the program line by line (the start command followed by next) and observe the changes in register values after executing the mov and add instructions. Ignore the sequence of PRINTF32 instructions.

  2. Open the ex2.asm file and read the comments. Assemble it by using the make utility and run it. Using gdb, observe the change in the eip register when executing the jmp instruction. To skip the PRINTF32 instructions, add a breakpoint at the jump_incoming label (the break command followed by run).

  3. Open the ex3.asm file and read the comments. Assemble it by using the make utility and run it. Using gdb, navigate through the program using breakpoints. Follow the program flow. Why is 15 displayed first and then 3? Because of the jump at line 9. Where does the jump at line 25 point to? To the zone1 label.

  4. Open the ex4.asm file and read the comments. Assemble it by using the make utility and run it. Using gdb, go through the program. Why isn’t the jump at line 12 taken? Because the je instruction jumps if the ZF bit in the FLAGS register is set. This bit is set by the cmp instruction, which calculates the difference between the values of the eax and ebx registers without storing the result. However, the add instruction at line 11 clears this flag because the result of the operation is different from 0.