On 2016.03.24 at 07:25 -0400, Jeffrey Walton wrote: > On Thu, Mar 24, 2016 at 6:54 AM, Markus Trippelsdorf > <markus@xxxxxxxxxxxxxxx> wrote: > > On 2016.03.24 at 06:50 -0400, Jeffrey Walton wrote: > >> We caught a report due to _GLIBCXX_USE_CXX11_ABI and abi:cxx11. We are > >> upstream, and it appears Debian built the library using GCC and > >> _GLIBCXX_USE_CXX11_ABI was in effect. A user then came along with > >> Clanf and compiled the userland program. The link failed. This is > >> expected given our understanding of the landscape. > >> > >> We found "GCC5 and the C++11 ABI", > >> https://developerblog.redhat.com/2015/02/05/gcc5-and-the-c11-abi/. The > >> pages says: > >> > >> Providers of such libraries or interfaces need to consider > >> whether they want to provide ABI coexistence, like libstdc++ > >> does, or require their users to rebuild. > >> > >> I read the Red Hat blog post, but its not clear to me how to > >> accomplish the coexistence. That is, I want to ensure the library that > >> Debian builds has a symbol in both namespace so linking can occur with > >> either GCC or Clang and "things just work" for the user. > >> > >> How is libstdc++ providing symbols in both namespaces? How do I ensure > >> the symbol is present in both namesspaces so "things just work" for a > >> user? > > > > It will not work until this clang bug gets fixed: > > https://llvm.org/bugs/show_bug.cgi?id=23529 > > Thanks Markus. > > 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 -- Markus
