Sample Project 2 Write-up
Jonathan Misurda
1 Lab Program
1.1 Procedure
Since the programs are all written in C, they will have a main function, so I initially placed a breakpoint
at main and did a disassembly. I noticed there were many call instructions and gdb showed that one in
particular was a call to strcmp. Thinking that this was probably where the input was compared with
the solution, I placed a breakpoint here. I examined the contents of the registers that had been moved to the
stack, knowing that these will be the parameters according to the calling convention we have discussed in
class.
The first parameter I examined proved to be the string “bcdefg”. I tried to enter this as my solution
string, but was told this wasn’t correct. I went back to the breakpoint at strcmp and saw the “bcdefg” as I
had seen before, but the second parameter was “cdefgh” which was not the string I had entered. The code
between the input and the comparison was changing the string in some way.
1.2 Solution
I reasoned that the transformation was simply that every letter was being increased by one. I entered the
string “abcdef” and was told that the solution was “bcdefg”.
1.3 Post-Mortem/Notes
•By the large size of the file and the fact that gdb was able to resolve the calls to their library function
names, the executable was most likely statically linked.
•The strings command would have shown the “bcdefg” constant in the program.
•It is easy to recognize parameters by small negative offsets of $esp or $ebp.
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