Department of Computer Science
CPSC 513: Playing with an SMT Solver

Please email me your sorting program (in any convenient procedural language, or pseudo-code), your program for generating the CVC4 scripts (preferably in C, C++, Perl, Python, etc. -- basically, anything that will run easily on a CS Department Linux machine), your generated CVC4 scripts, and a brief description of what you thought of the assignment. (BTW, please send this to me as plain ASCII text. Not as a PDF, not as a Word file, etc. And please don't email me the binaries.)

OK, so what is the assignment? The goal of this assignment is to give you an understanding of how to write a symbolic execution engine to verify software with an SMT solver, but to save you (and me) the pain of writing a symbolic execution engine. Instead, you will:

The SMT solver we'll use for this assignment is called CVC4 . This is a completely free, open-source SMT solver, written by some of the top people in the SMT community. CVC4 traces its history back to the solvers that launched the recent interest and success of SMT solvers, but for a long time, the earlier solvers (CVC, CVC-Lite, CVC3) had a reputation for being flexible, but slow. CVC4 is much faster, and is now competitive with the best solvers available. (However, if you do a project using an SMT solver, you might also consider trying Z3 , which is generally considered the fastest SMT solver. Z3 used to have licensing issues (free for non-commercial use only, and only supporting Windows), which is why I had standardized on CVC, but Z3 is now under the MIT license and more generally available. You can always go to the SMT Competition website to see lists of solvers, the logics they support, and how they did in competition.)

You can download pre-built binaries (for Linux and Windows, too), from the CVC4 downloads page. You can also download source and build your own copy, if you'd like. I have a 64-bit Linux version on the departmental machines at /isd/users/software/cvc4-1.5-x86_64-linux-opt This will only run on CS departmental Linux machines. See this link for a list of servers available to you. (Or use your own machines, or from your research labs...)

There's pretty good on-line documentation at the CVC4 homepage. In particular, the user manual is a must-read, as well as the description of CVC4's input language . Before you start the assignment itself, you'll probably want to play with the solver a bit. You'll want to use the -im options to put the solver in incremental mode as well as allow it to generate counter-examples (models):
/isd/users/software/cvc4-1.5-x86_64-linux-opt -im
(By the way, for those of you new to Unix/Linux, ask or read up about symbolic links. You'll probably want to create a link to the CVC4 solver, so you don't have to keep typing the full pathname.) You can do things like ask whether 1 plus 1 equals 2:
QUERY (1 + 1 = 2);
or try:
a, b, c: INT;
ASSERT (a < b);
ASSERT (b < c);
QUERY (a < c);
QUERY (c <= a);

Here's an example in pseudo-C that sorts three integers. . (You may want to use an array for more data entries, instead of separately named variables as I did here.) And here's an example of a CVC4 script that would be appropriate for that example. (Note that CVC4 wants input files to have the extension .cvc if the input language is the CVC native language.) You'll probably want to play with this example a bit, to get used to the syntax, and CVC4, before you start writing your code.

That's it! I hope this is fun!

By the way, I have always intended to make this assignment just like Assignment 2, where you (or actually, I) would write a symbolic execution engine for a simple programming language, and this would generate queries to the SMT solver. Then, I would give you a sorting program written in that simple programming language, and you'd use the symbolic execution engine to generate SMT queries, and solve them with the SMT solver. However, this would require me to make up a simple programming language and write up a parser and interpreter for it, and I keep running out of time. Fortunately, each time I have used this assignment, student feedback has actually been quite positive. Furthermore, using scripts to generate inputs to other programs is actually a common and useful way to tackle problems, so it's fun to give that a go, too. I'll appreciate your feedback on whether you think I should make the time to do the assignment more like Assignment 2 in future years.