[cfe-dev] [analyzer]

Gábor Horváth via cfe-dev cfe-dev at lists.llvm.org
Wed Oct 24 20:34:45 PDT 2018


Hi!

Do you have something in mind like this: https://reviews.llvm.org/D33672 ?

Regards,
Gábor

Artem Dergachev via cfe-dev <cfe-dev at lists.llvm.org> ezt írta (időpont:
2018. okt. 25., Cs 4:32):

> Hi,
>
> Your overall plan sounds good, and i believe that such checker will be
> very useful, i'd love to have such check in the analyzer. If you want to
> post it upstream, i encourage you to start early by publishing
> prototypes on Phabricator for code reviews, even when you think they're
> not ready, just because code reviews are cool!
>
> Path-sensitive analysis is indeed useful here because sometimes it's not
> immediately obvious from the code which values are possible for the
> sub-expression. Defining the buggy state can be a bit annoying because
> enum values can be non-contiguous and/or numerous; the former means that
> you'll potentially need to make a lot of State->assume(...) calls and
> see if none of the states with assumptions are null; the latter means
> that you'll need to make sure you identify segments of values to avoid
> calling assume() for *every* enum item. I also recommend
> ConstraintManager::assumeInclusiveRange() for direct assumptions over
> segments.
>
> Your questions so far are AST questions, not specific to the analyzer.
> First of all, notice that every expression has a (qualified) type, which
> is the type of the value it evaluates to, and it can always be obtained
> via Expr::getType(). It may be void (eg., call expression for a function
> that returns void), but it's always there.
>
> For cast-expression, as you might have already guessed, the type of the
> expression is the target type of the cast. Because, well, that's the
> whole point of the cast. This takes care of question 2.
>
> Most functions return not raw Types but QualType objects that are types
> with qualifiers. You can always use the overloaded operator->() on the
> QualType to access the underlying Type; there's also
> QualType::getTypePtr(), but if you think you need it - most likely you
> don't.
>
> Now, types, like statements or declarations, are a hierarchy. Some types
> are integer types, some are array or structure types, some are enum
> types. Enum types are represented by the EnumType class, to which you
> can try to dyn_cast<>() your type. Or, even better, use Type::getAs<>(),
> which can be accessed directly with operator->() on QualType.
>
> If dyn_cast<>()/getAs<>() is successful - your type is an enum and you
> have a pointer to an EnumType object, so you can call
> EnumType::getDecl() to find the *declaration* of the enum in the code.
>
> Also if the enum hides under a typedef, then the type wouldn't be an
> EnumType but it'd be a TypedefType, so the cast would fail. The easy way
> to get rid of typedefs is to do QualType::getCanonicalType().
>
> Some declarations are forward declarations. You might need to do
> EnumDecl::getDefinition() to find the actual definition. Maybe you don't
> need that: i don't remember what operations are allowed on incomplete
> enum types.
>
> Once you have your EnumDecl that is the definition, you can iterate over
> EnumDecl::enumerators() to see what values are present.
>
> In Clang there are a lot more cast kinds of expressions than you
> probably expect, so you might want to take a look at the list of casts
> in clang/AST/OperationKinds.def and see which ones do you need; i don't
> think it'll be important at first, but just in case.
>
> In order to quickly catch up on the basics, i also recommend the AST
> tutorial by Manuel Klimek at https://www.youtube.com/watch?v=VqCkCDFLSsc
>
>
> On 10/24/18 5:16 PM, Alexander Zaitsev via cfe-dev wrote:
> >
> > Hello. I am newbie in Clang Static Analyzer and I am trying to write
> > new Clang Static Analyzer check, which is aimed to find issues with
> > casting values to enum: if we cast anything which is no presented in
> > target enum it will be unspecified/undefined behavior(depends on C++
> > version).
> >
> > So my plan is:
> >
> >  1. Find all casts in source code. Seems like
> >     'check::PreStmt<CastExpr>>' it's what I need.
> >  2. In my implementation of `checkPreStmt` method I must get target
> >     type from CastExpr, but I don't know, how to do it - can you help
> >     with it?
> >  3. Then if target type in Cast is Enum, I must get all values from
> >     this Enum and compare it with all possible values which can be
> >     presented by CastExpr->getSubExpr() - here I don't know how to
> >     evaluate CastExpr->getSubExpr() and how to get all values from Enum.
> >
> > Do you have any ideas?
> >
> > --
> > Best regards,
> > Alexander Zaitsev
> >
> >
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> > cfe-dev at lists.llvm.org
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>
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