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

[Aaron Ballman via cfe-dev]

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