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

[Rafael Auler]

I checked out the trunk version and updated my source code in two places:
* include the OwningPtr header, which was previously unnecessary
* changed to instantiate the BugType using the new constructor interface,
passing a pointer to the checker instance in the first argument

Afterwards I tested again and got the same output. I will continue testing
here to figure out why this is happening only to me.

Thanks for helping!

Rafael


On Mon, May 26, 2014 at 10:36 PM, 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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