How to provide coexisting std::string's (with and without abi:cxx11) in GCC 5.1 and above?

[Marc Glisse]

On Thu, 24 Mar 2016, Jeffrey Walton wrote:

>>> Please forgive my ignorance... What is the "coexistence" that is
>>> discussed? Naively, I thought it would have been something like this
>>> contrived example:
>>>
>>>   $ cat test.cxx
>>>   #include <string>
>>>
>>>   std::string foo __attribute__ ((visibility ("default")));
>>>   std::string bar __attribute__ ((visibility ("default")));
>>>
>>>   $ g++ -g3 -O2 -shared test.cxx -o test.so
>>>
>>>   $ nm test.so | grep _Z3
>>>   ...
>>>   0000201c B _Z3barB5cxx11
>>>   00002034 B _Z3fooB5cxx11
>>>
>>>   $ echo _Z3fooB5cxx11 _Z3barB5cxx11 | c++filt
>>>   foo[abi:cxx11]  bar[abi:cxx11]
>>>   foo  bar
>>>
>>> In the above contrived example, foo and bar are in both namespaces.
>>> That is, the symbol coexists and "things just work".
>>
>> Consider the following example:
>>
>> markus@x4 /tmp % cat test.cpp
>> #include <string>
>>
>> struct Test {
>>   __attribute__((used)) std::string foo() { return "foo"; };
>> };
>>
>> markus@x4 /tmp % g++ -c test.cpp && nm test.o | grep _ZN4Test
>> 0000000000000000 W _ZN4Test3fooB5cxx11Ev
>> markus@x4 /tmp % clang++ -c test.cpp && nm test.o | grep _ZN4Test
>> 0000000000000000 W _ZN4Test3fooEv
>
> Exactly! How do I get both _ZN4Test3fooB5cxx11Ev and _ZN4Test3fooEv
> into the shared object so both GCC and Clang "just work". I thought
> that's what "coexistence" meant, but it appears to mean something else
> (that I have not been able to nail down).

You compile one object file using one compiler/ABI and another one using 
the other ABI, then link them both...

(sorry, I did try to argue against this whole situation but failed)

-- 
Marc Glisse