[cfe-dev] Adding Support for APINotes

[Gábor Márton via cfe-dev]

Hi Saleem,

About the technical aspects. The feature to be able to add extra
information to library functions would be really helpful in the Clang
Static Analyzer. APINotes might be a way forward to achieve that.

We'd like to add the following to functions

   - Argument constraints
      - Not null
      - Range, e.g. isalpha(int x) x must be in [0,255].
      - Buffer size, e.g. fread(x1, x2, x3)  x1 is a buffer with a size
      denoted by x2 * x3
   - Taint rules
      - propagation
          int x; // x is tainted
        int y;
        myPropagator(x, &y); // y is tainted
      - filter
          int x; // x is tainted
        isOutOfRange(&x); // x is not tainted anymore
      - sink
          int x; // x is tainted
        myNamespace::mySink(x); // It will warn
      - Error return rules, e.g. the return value of mktime() should always
   be checked against -1.
   <https://wiki.sei.cmu.edu/confluence/display/c/ERR33-C.+Detect+and+handle+standard+library+errors>
   (D72705 <https://reviews.llvm.org/D72705>)
   - Indicate which functions we should consider with statistical checkers
   <https://www.youtube.com/watch?v=IM1DYZ-xn-k> (WIP, not upstreamed yet).

Note to taint analysis: we might want to tag global variables as sources.
E.g. std::cin.

I think that we could extend the APINote implementation that you have in
the referenced commit, but with a CSA specific attribute:
def CSANotes : InheritableAttr {
  let Spellings = [GNU<"csa">];
  let Args = [StringArgument<"FreeFormatOrSomeYamlMaybe">];
  let Subjects = SubjectList<[Tag, Function, Var],
                             ErrorDiag>;
}
The string argument could be parsed specifically to the CSA developers'
needs in a CSA specific implementation file. IMHO it would be a flexible
solution because we could avoid adding many CSA specific attributes to
Attrs.td and it would allow us to make experiments.

My concerns about the referenced APINotes implementation:

   - Specifically with the `'Name' key`. How could we match in C++
      - overloaded functions
      - member functions
      - functions in namespaces
      - function templates
      - member functions of class templates (e.g. std::vector::begin)
   - Do we have a mechanism to test/indicate if a note is not applied but
   it should have been?


Adding CSA guys who might want to comment.
+Artem Dergachev <noqnoqneo at gmail.com>
+Gábor Horváth <xazax.hun at gmail.com>

Thanks,
Gabor

On Mon, Sep 28, 2020 at 11:10 PM Saleem Abdulrasool via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> Hi!
>
> I'd like to revive the effort around merging APINotes support into the
> llvm.org repository.  This was previously discussed at
> http://lists.llvm.org/pipermail/cfe-dev/2017-May/053860.html nearly 3
> years ago.  The overall consensus seemed neutral to slightly positive.  Now
> that the Swift specific attributes have been merged, the APINotes seem like
> a good next step towards converging the fork.
>
> I've put up https://reviews.llvm.org/D88446 to add initial documentation
> on the feature before trying to add the actual implementation with the
> goal of gathering commits on the technical aspects of the feature.
>
> Thanks.
>
> --
> Saleem Abdulrasool
> compnerd (at) compnerd (dot) org
> _______________________________________________
> cfe-dev mailing list
> cfe-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>
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