[cfe-dev] Writing simple checkers for the static analyzer

[Jordan Rose]

It's worth noting that running without the core checkers enabled isn't really a sane state for the analyzer. You should either pass "core,alpha.mychecker.MyChecker" to -analyzer-checker, or use "clang --analyze" instead of "clang -cc1 -analyze" and use "-Xanalyzer" to pass down the -analyzer-checker option.

Jordan

On May 26, 2014, at 18:36 , Rafael Auler <rafaelauler at gmail.com> wrote:

> Hi Jordan,
> 
> I'm using the tagged version 3.4, do  you think it is an issue that got fixed in trunk? I am quite sure that I have it enabled, since I put some debugging printfs and saw the results:
> 
> -1 = doNotCallTwice() has not been called before
> 0 = doNotCallTwice() has been called before
> 
> rafael$ clang -cc1 -analyze -analyzer-checker=alpha.mychecker.MyChecker mytest.c
> doNotCallTwice! -1
> doNotCallTwice! -1
> doNotCallTwice! -1
> rafael$ vim mytest.c  # change to avoid folding
> rafael$ clang -cc1 -analyze -analyzer-checker=alpha.mychecker.MyChecker mytest.c
> doNotCallTwice! -1
> doNotCallTwice! -1
> doNotCallTwice! -1
> doNotCallTwice! 0
> mytest.c:8:5: warning: Called twice
>     doNotCallTwice();
>     ^~~~~~~~~~~~~~~~
> 1 warning generated.
> 
> 
> In the first case, I use only function calls in the test case. In the second, I put the extra statement that forces the engine to avoid folding, and the detection finally works.
> 
> Thanks,
> Rafael
> 
> 
> On Mon, May 26, 2014 at 5:52 PM, Jordan Rose <jordan_rose at apple.com> wrote:
> Hm, if I drop this into my clang sources (and update it to match changes in trunk), I don't see any issues with what you've written—building and running it on your sample input works fine. Are you sure you have it enabled? (I forgot to pass -analyzer-checker on my first test, so I have to ask.)
> 
> Jordan
> 
> On May 25, 2014, at 7:28 , Rafael Auler <rafaelauler at gmail.com> wrote:
> 
>> Hi Jordan,
>> 
>> Sure, it is attached. Thanks for taking a look at this. 
>> 
>> Cheers,
>> Rafael
>> 
>> 
>> On Sun, May 25, 2014 at 4:13 AM, Jordan Rose <jordan_rose at apple.com> wrote:
>> Hi, Rafael. From your description, this sounds like a bug in the analyzer—two program states with differing user data should not be folded. Can you attach your checker so I can take a look and see if there are any obvious mistakes? (on your part or ours).
>> 
>> Thanks,
>> Jordan
>> 
>> On May 24, 2014, at 22:01 , Rafael Auler <rafaelauler at gmail.com> wrote:
>> 
>> > Hello,
>> >
>> > I am trying to write a very simple checker for the clang static analyzer for the sake of writing a first exercise on this topic. Its goal is to simply alert whether a specific function has been called twice in a given path. Let's assume the name of this specific function that I am tracking is "doNotCallTwice()".
>> >
>> > In order to record state information, I use the REGISTER_TRAIT_WITH_PROGRAMSTATE macro to register an unsigned together with the program state. This integer indicates whether the function "doNotCallTwice()" has been called in a path and, if it is equal to 1 in a node where I detect yet another call, I prepare to report a "double call" bug. I use "checkPostCall" for changing the state.
>> >
>> > However, something strange happens. My extra integer registered in the program state is not sufficient to differentiate two ProgramStates with the same ProgramPoint: the engine fold the two nodes anyway, ignoring my new state information. On the other hand, the information *is* propagated. If I use other ways to avoid the nodes being folded, the checker works fine.
>> >
>> > An example where it does not work:
>> >
>> > void myfunc (int x, int y) {
>> >   if (x)
>> >     doNotCallTwice();
>> >   if (y)
>> >     doNotCallTwice();
>> >   doNotCallTwice();
>> > }
>> >
>> > Since programstates get folded in the ExplodedGraph, I never detect any path where two calls to doNotCallTwice() happen. However, change the code in the following way avoids the folding and make my checker work:
>> >
>> > void myfunc (int x, int y) {
>> >   if (x)
>> >     doNotCallTwice();
>> >   if (y)
>> >     doNotCallTwice();
>> >   y = x;  // Now x and y are not dead anymore and this won't be folded
>> >   doNotCallTwice();
>> > }
>> >
>> > I based my checker on SimpleStreamChecker.cpp. Am I doing something conceptually wrong?
>> >
>> > Best regards,
>> > Rafael
>> > _______________________________________________
>> > cfe-dev mailing list
>> > cfe-dev at cs.uiuc.edu
>> > http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
>> 
>> 
>> <MyChecker.cpp><mytest.c>
> 
> 

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