[cfe-dev] [RFC] __attribute__((internal_linkage))

[Evgenii Stepanov via cfe-dev]

Do we really want to apply the attribute to the entire namespace? We'd
need to skip at least extern template methods (like
char_traits<char>).


On Tue, Oct 20, 2015 at 5:28 PM, Aaron Ballman <aaron.ballman at gmail.com> wrote:
> On Fri, Oct 16, 2015 at 2:07 PM, Reid Kleckner <rnk at google.com> wrote:
>> On Thu, Oct 15, 2015 at 6:55 PM, Eric Fiselier <eric at efcs.ca> wrote:
>>>
>>> 1. What would happen if the user attempts to take the address of a
>>> function marked
>>> `__attribute__((internal_linkage))`? Wouldn't this case required external
>>> linkage?
>>> For libc++ it's sufficient if it causes a compile error because users
>>> aren't allowed
>>> to take the address of functions in the standard library.
>>
>>
>> Addresses of such functions would just compare not equal across TUs. I think
>> that's pretty reasonable, and probably conformant. There are many ways that
>> STL functions can be called indirectly (std::function's vtable), so I don't
>> think we want to try to forbid that.
>>
>>>
>>> 2. It would be great if we could apply the attribute to a namespace, that
>>> in turn applies it to
>>>    all of the symbols within. Would this be possible?
>>
>>
>> The Clang attribute machinery *appears* to support attributes on namespace,
>> but there doesn't seem to be a single test for it in the test suite. I don't
>> think we can do that yet. Anyway, this feels like a separate feature request
>> to me.
>
> C++ attributes are supported on namespaces, but I'm not certain about
> GNU attributes on them. I'm not aware of any GNU attributes that
> appertain to a namespace, so I'm not surprised about a lack of test
> coverage.
>
> As for the feature itself, I think it's possibly a related feature
> instead of a separate one, but I don't feel strongly. Given the use
> case is "let's remove a bunch of not-really-working" libc++ code, I
> can see the namespace being the better approach for those needs, with
> a declaration attribute that happens to be the underlying
> implementation of the namespace attribute.
>
> ~Aaron