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

[Aaron Ballman via cfe-dev]

On Tue, Oct 20, 2015 at 8:52 PM, Evgenii Stepanov
<eugeni.stepanov at gmail.com> wrote:
> 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>).

Eric was asking for it specifically, so I am assuming that was
something he might want to do. I would certainly be curious what the
semantics would be for it.

I mostly would like to avoid replacing one solution that clutters
libc++ with another one that clutters equally, if we can avoid it.

~Aaron

>
>
> 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