Jason Merrill wrote:
Nice to see this stuff getting improved!
> #pragma GCC visibility push(hidden)
> class __attribute((visibility("default"))) A
> {
> void f ();
> };
>
> void A::f() { }
>
> Here I think we'd all agree that f should get default visibility.
Agreed.
> class A
> {
> void f ();
> };
>
> #pragma GCC visibility push(hidden)
> void A::f() { }
> #pragma GCC visibility pop
>
> This case is less clear; A does not have a specified visibility, but the
> context of f's definition does. However, we don't want to encourage
> this kind of code; the visibility should be specified as early as
> possible so that callers use the right calling convention. Waiting
> until the definition to specify visibility is bad practice. Also, the
> status quo is that f gets A's visibility. I would preserve that and
> possibly give a warning to tell the user that they might want to add
> __attribute((visibility)) to the declaration of f in A.
Agreed.
> Now, templates:
>
> template<class T> __attribute((visibility ("hidden")) T f(T);
> #pragma GCC visibility push(default)
> extern template int f(int);
> #pragma GCC visibility pop
>
> This could really go either way. It could be considered similar to the
> above case in that f<int> is in a way "part" of f<T>, but there isn't
> the same scoping relationship. Also, there isn't the
> declaration/definition problem, as the extern template directive is the
> first declaration of the instantiation. In this case I am inclined to
> respect the #pragma rather than the attribute on the template.
I'd tend to say that the attribute wins, and that if you want to specify
the visibility on the template instantiation, you must use the attribute
on the instantiation, as you suggest:
> Using an attribute would be less ambiguous:
>
> extern template __attribute ((visibility ("default")) int f(int);
>
> In a PR Geoff asked if we really want to allow different visibility for
> different instantiations. I think we do; perhaps one instantiation is
> part of the interface of an exported class, but we want other
> instantiations to be generated locally in each shared object.
Agreed.
--
Mark Mitchell
CodeSourcery
[EMAIL PROTECTED]
(650) 331-3385 x713
