[cxx-abi-dev] Finding the type of a virtual table

[Jason Merrill]

>>>>>   <Kevin.Backhouse at arm.com> writes:

> For the purposes of performing a static analysis, I am interested to know
> whether it is possible to determine the type of an object by looking at its
> vtable. VTables contain RTTI information so it ought to be possible, but I
> am unsure about secondary vtables and I wonder if anyone can help.

> To illustrate, here is an example of a class hierarchy:

>      class A
>      class B
>      class C : A, B
>      class D : B, C

> If I understand the C++ ABI for Itanium correctly, class D will have the
> following vtables:

>      D's primary vtable (which extends B's vtable)
>      Secondary vtable for C in D (which extends A's vtable)
>      Secondary vtable for B in C in D

> Given (say) the secondary vtable for B in C in D and nothing else, is it
> possible to determine that objects with this vtable have type B?

Why would you want to?  The only way to get at that vtable would be through
a pointer of type B*.  If you're using a B*, then you know that the
(sub)object referred to has type B.

Can you be more specific about the analysis you're trying to perform?

Jason