Re: gcc visibility used by moz

[Geoffrey Keating <geoffk at apple dot com>]

Gabriel Dos Reis <gdr@integrable-solutions.net> writes:

> Jason Merrill <jason@redhat.com> writes:
> 
> [...]
> 
> | > | - I don't recall suggesting that
> | > | multiple types with the same name should be able to exist.
> | > then you have to consider that suggestion and come with an answer.
> | 
> | I don't see why.  The point is that visibility is orthogonal to
> | linkage; a class S with external linkage is still required by the ODR
> | to be unique across multiple shared objects even if some of the
> | symbols that refer to it can't be referenced from outside their
> | defining object.  The visibility restrictions place practical limits
> | on how other objects can use the type, but that doesn't mean it isn't
> | the same type.
> 
> So, -concretely- what happens to a class S (e.g. associated type info object
> address, address of member functions, etc.) with external linkage,
> defined in multiple translation units, with say hidden visibility?

Under the current definition, this is impossible.  If you have a class
S defined in one object with hidden visibility, and you try to define
it in a different object, you get a different class named S, just as if
you'd defined it in a different namespace or similar.

Thus, the type info objects are different, the member functions have
different addresses, and so on.

This is achived by giving the various pieces hidden visibility.