$ sudo dtrace -s nil.d -p

File: “nil.d”
——

#pragma D option quiet

BEGIN
{
        globalNilMsgIndex = 0;
        globalVtime = vtimestamp;
        globalWtime = walltimestamp;
}

pid$target::objc_msgSend:entry
/ arg0 == 0 /
{
        this->mIndex = ++globalNilMsgIndex;

        printf("%7d: [nil %s] (thread: %08x)\n", this->mIndex, copyinstr(arg1), tid);
        @nilAgg[ustack()] = count();
        @selCounter[copyinstr(arg1)] = count();
}

END
{
        printf("Nil-calling sites:\n");
        printa(@nilAgg);

        printf("Selectors frequently sent to nil:\n");
        printa(@selCounter);
}