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

[Markus Trippelsdorf <markus at trippelsdorf dot de>]

On 2016.03.24 at 07:57 -0400, 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).

There is no way to make it work at the moment. You have to wait until
the clang bug gets finally fixed.

-- 
Markus