[Development] Summary ABI compabilty

[Thiago Macieira]

On quarta-feira, 23 de novembro de 2016 00:07:35 PST Allan Sandfeld Jensen 
wrote:
> Can't we statically link to it, so that it doesn't matter which version the
> application is using?

No, same problem, which is exactly what the Linux distros are doing wrong.

C++ requires certain symbols to be shared and obey ODR: the typeinfo for the 
base types and the virtual tables for some classes (notably, std::exception). 
If we statically link one of the libraries that contains those, then 
applications may or may not link to them at runtime. Breaking ODR for those is 
problematic.

The solution is simple: we need to dynamically link to a library that provides 
those and just those. Both libc++ and libstdc++ have such a library: 
respectively, libc++abi and libsupc++. Linux distros need to make sure that 
only one of those exists and that both libc++ and libstdc++ link to it.

But even if we do that, it doesn't solve the problem of using the std types in 
our ABI, like std::function which we desperately want to use. If our objective 
is to do that, then you can't replace.

-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center