The University of Queensland
School of Information Technology and Electrical Engineering
CSSE2310/CSSE7231 — Semester 1, 2021
Assignment 2 (v1.0)
Marks: 50
Weighting: 10%
Due: 3:59pm 1 April, 2021
Introduction
The goal of this assignment is to ensure you have gained familiarity and skills with both the C programming
language and using a debugger (such as gdb(1)) to examine various characteristics of running programs. These
will be essential skills in later assignments for this course. For this assignment you will be given an executable
program (the “bomb”) which you have to “defuse” by entering the correct defusing phrases into the program
for each of the 10 bomb phases.
Student conduct
This is an individual assignment. You should work on defusing your own bomb by yourself. You should feel
free to discuss aspects of C programming and the use of debuggers with your fellow students, but you shouldn’t
actively help (or seek help from) anyone with the defusing of particular phases. Do not share your approaches
to solving the bomb phases - even after the assignment deadline (as extensions may be given to other students).
You should note that each student will receive a different bomb and the strings that defuse your bomb will
be different to the strings that defuse another student’s bomb.
In short - don’t risk it! If you’re having trouble, seek help early from a member of the teaching staff. Don’t
be tempted to cheat. You should read and understand the statements on student misconduct in the course profile
and on the school website: https://www.itee.uq.edu.au/itee-student-misconduct-including-plagiarism
Obtaining the “Bomb”
Whilst logged in to moss.labs.eait.uq.edu.au, you should type the following command:
getbomb
This will create a subdirectory within your current directory named csse2310a2 and place the bomb files into
that directory. The files will include an executable called bomb and a number of source files (.h and .c files).
Your bomb (executable and source) will be different to the bombs for all other students. You will not receive
all of the source files – just some of them. There is enough information contained within the bomb executable
and the supplied source files in order for you to successfully defuse all phases (although some of them are more
difficult than others). You should note that some of the bomb’s modules have been compiled with debugging
support (-g flag to gcc) and some haven’t.
Running the “Bomb”
The bomb program will only run on moss.labs.eait.uq.edu.au and you are the only user who can run your bomb
program. Any attempt to run the program on another host or to run another user’s bomb will cause the bomb
to exit immediately. Whilst in your csse2310a2 directory, you can execute the bomb by typing
./bomb
You may not want to do this until you are ready to try defusing the bomb. When you start the bomb program,
it will print out details of any phases you have already defused and it will print your current mark (out of 50)
and the maximum mark you can obtain based on your attempts to date.
The bomb will then prompt you to enter the number of the phase to defuse next, followed by the string that
you believe defuses that phase (or a test string). You will be prompted for confirmation before that string is
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tested. If you confirm your attempt and the string is incorrect then the bomb will “explode” and exit. If the
string is correct, then that phase is defused and you will not be able to solve it again. You will lose marks for
every time the bomb “explodes”.
You should note that the bomb is booby trapped. You are warned against modifying the internal data
structures of the bomb – you never know what might happen and any loss of marks you incur will not be
reversed.
Hints
There are two demo phases that do not count for marks. You may attempt these as many times as you like by
entering either “demo1” or “demo2” when prompted for a phase to defuse. There is no mark penalty if either
of these demo phases “explodes.”
You should carefully read the supplied source code and be familiar with the use of gdb before attempting
to run the bomb. It is suggested you run the bomb from within a debugger rather than standalone. Note that
you may get a warning message about “Missing separate debuginfos...” – you can safely ignore this message.
All phases have associated code and some debugging information and you will need to use a debugger to set
breakpoints, examine various variables etc in order to determine the defusing strings. You may need to learn
about and use a number of features of gdb including watchpoints, automatic display, conditional breakpoints,
and/or breakpoint command lists to solve the phases more efficiently.
You should note that the code that determines each defusing string is not executed until AFTER the defusing
text is read from the user so you may need to enter some arbitrary text, debug the code to determine the defusing
string, quit the program and then run it again to enter the defusing string for that phase.
The bomb is deterministic – the same sequence of inputs will result in the same operation each time, so the
defusing string for each phase will not vary over time. However, many of the functions within the bomb are not
deterministic – they may return something different each time they are called.
Submission
Every time you run the bomb, a record is kept of your interactions with it and your success/failure at defusing
each phase. Your submission time for the assignment will be considered to be the time of your last attempt
to defuse any phase of the bomb. You must make at least one attempt in order to be considered to have
made a submission. An attempt means either that the bomb explodes or a phase is defused.
Late penalties will apply as described in the CSSE2310/CSSE7231 course profile. Any attempt to defuse
the bomb after the deadline will result in a late penalty being applied to your whole assignment mark.
Marks
There are 10 phases, each worth 5 marks. The mark you achieve for each phase is determined by the number
of attempts taken before you successfully defuse that phase. If you do not defuse a phase you will receive zero
marks for that phase. If you defuse a phase on the first attempt, you will receive 5 marks for that phase. If it
takes you longer than one attempt, your mark for that phase will be
5 × 0.8
(number of attempts−1)
i.e. if it takes you 2 attempts, your mark for that phase will be 4 out of 5, 3 attempts gives you 3.2 out of 5, 4
attempts gives you 2.56 out of 5, etc. There is no limit on the number of attempts you can make at any phase
before succeeding. You should note that although each phase is worth the same number of marks, they are
not of equal difficulty. All marks are subject to an audit of our logs to ensure that you have correctly entered
the defusing strings and haven’t tampered with the bomb to defuse it in some other way. Tampering with the
bomb to make it appear as though you have defused a phase when you have not correctly defused it will result
in zero marks for that phase.