In article <[email protected]>, Joerg Sonnenberger <[email protected]> wrote: >Hello everyone, >during the developer summit, I was made aware that we got the fancy dual >ABI for libstdc++ with the GCC 5 import. I thought that $#%#$% was >disabled from the start, but alas, it isn't. > >What does dual ABI mean? Long story. std::string in libstdc++ had >a performance "feature" for ages where it avoided string copying by >using reference counting. This has a number of implications, one of them >is that in-place modifications will invalidate iterators. Since this >makes the behavior highly unpredictable especially in multithreaded >programs, C++11 forbids it. Since changing central parts of std::string >requires an ABI change, GCC decided to provide both old and new >interface in the same code and introduce a fancy hack in the name >mangler. Inline namespaces as used by libc++ wouldn't allow both ABIs to >coexist, since functions using std::string only in the return type >wouldn't be mangled different as that case is not allowed in C++. > >Why is this bad? It means that if libfoo is compiled with -std=c++11 and >foobar is compiled with -std=c++03, they can't be linked together and >vice versa. While many libraries are starting to adopt C++11 features, >not everyone does. The dual ABI makes interaction between the standards >*worse*, just to avoid a major bump. > >What should we do? I want to take the time before the 8.0 release and >switch GCC over to always use the new ABI. This means recompiling all >C++ code, but I consider it the lesser evil of having to deal with the >fallout in pkgsrc for years to come.
Please go for it! christos
