Emil finds its first defect!

I earlier described the nature of my work at TKK tcslab. My job is to write a tool for automatically testing C programs using a technique called dynamic symbolic execution basing the implementation on LLVM. I call my tool Emil (that is ucfirst(reverse(lower(Lime))) after a similar tool called Lime for testing Java programs, developed here as well).

Emil is currently at 2.9 KLOC, and for the first time, I wrote a test case that should fail, and it failed on the first attempt! This is somewhat a milestone so I now celebrate it by showing the test case and the failing inputs found by Emil. This is of course all trivial and useless, but I believe Emil is going to the right direction.

==divzero.c==

int input(void);
int main() {
    int i = input();
    int j = input();
    if (i > j) {
        i = i / (0*j); // ouch
    } else {
        i = j;
    }
    return i;
}

==Values for i, j by Emil that will lead to division by zero==
{i: 892648572, j: -1285173836}

I hope this is just the beginning for Emil. The future of Emil will be out of my hands, though, because I will (in my current knowledge) leave Emil in the hands of others before next year and be searching for new challenges in the software industry.

Back to work

Ah, my week-long summer vacation is now over. I mostly spent the time in a friend's summer cottage in Sysmä and in the beautiful archipelago of Sipoo. Last two days I was in Porvoo. Vacation reading included works from Hesse and Solzhenitsyn, but I especially want to raise Erlend Loe's Naive, Super that I fell in love with when sitting in a bus.

As for work, I'm now familiar with LLVM optimization pass architecture and implementation. It all feels intuitive. On the negative side, C++ frequently demonstrates its clumsiness in basic tasks. Also, the LLVM API is poorly documented, so I constantly find myself grepping (actually, ack'ing) around the LLVM tree and reading code rather than the doxygen (huh) generated API. However, all in all I'm definitely thankful for LLVM.org/docs.