[cfe-dev] Adding Support for APINotes

[Artem Dergachev via cfe-dev]

Static analyzer applications are indeed a long-term dream, cf. 
http://lists.llvm.org/pipermail/cfe-dev/2015-December/046354.html - 
We're super interested in attaching arbitrary annotations to functions 
in headers that we can't change directly, or possibly even let our users 
inject annotations into headers they have to use but can't change.

On 9/29/20 9:11 AM, Gábor Márton wrote:
> 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
>       o Not null
>       o Range, e.g. isalpha(int x) x must be in [0,255].
>       o Buffer size, e.g. fread(x1, x2, x3)  x1 is a buffer with a
>         size denoted by x2 * x3
>   * Taint rules
>       o propagation
>         int x; // x is tainted
>           int y;
>           myPropagator(x, &y); // y is tainted
>       o filter
>         int x; // x is tainted
>           isOutOfRange(&x); // x is not tainted anymore
>       o 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++
>       o overloaded functions
>       o member functions
>       o functions in namespaces
>       o function templates
>       o 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 <mailto:noqnoqneo at gmail.com>
> +Gábor Horváth <mailto: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 <mailto:cfe-dev at lists.llvm.org>> wrote:
>
>     Hi!
>
>     I'd like to revive the effort around merging APINotes support into
>     the llvm.org <http://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
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>

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