Re: Function signatures in extern "C".

[Florian Weimer <fweimer@redhat.com>]

* Jakub Jelinek via Gcc:

> On Mon, Sep 07, 2020 at 10:27:13AM +0100, Jonathan Wakely via Gcc wrote:
>> On Mon, 7 Sep 2020 at 09:18, Iain Sandoe wrote:
>> >
>> > Perhaps the PR should be reopened with “accepts invalid”?
>> 
>> My impression from the PR is that the reporter was using a different
>> ABI, where the name isn't reserved. Maybe the testcase should only be
>> accepted with -fno-threadsafe-statics or -ffreestanding or something
>> to say "I'm doing things differently".
>> 
>> Or we could just say that G++ reserves the Itanium ABI names
>> unconditionally, even if it doesn't need to use them, in which case it
>> would be accepts-invalid.
>
> All identifiers starting with two underscores are reserved for the
> implementation already.

But which implementation?

__ identifiers are used heavily across the GNU project, not just in GCC
and glibc (as one would expect).  A lot of C software outside the GNU
project is similar.  I think this attempt at namespace management has
failed.

For the Itanium C++ ABI symbols, it would be useful to document which
ones can be user-defined (which can be very interesting to avoid a
dependency on libstdc++).  I do not know how much value there is in
supporting a semantically different definition, or a declaration with
different types (probably not much).

Thanks,
Florian
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