[cfe-dev] A proposal for ABI migrations in libc++

[Peter Collingbourne]

On Tue, Oct 01, 2013 at 08:51:19PM -0500, Chandler Carruth wrote:
> Brief thoughts... I think it would be desirable to be able to have more
> than one stable ABI along side the"next" ABI. For example, FreeBSD and Mac
> might want to different stable ABIs.

I think that should a particular platform need anything more granular
than _LIBCPP_ABI_NEXT, we could do something like put a specific ABI
change behind its own macro and make sure that that macro is defined
on the platforms that need it or if _LIBCPP_ABI_NEXT is defined.
(Or whatever is appropriate for the specific change.)  But I think
that can be done incrementally after _LIBCPP_ABI_NEXT is introduced
and on an as-needed basis.

> Also, I'd like a more friendly interface for users of the unstable ABI than
> an internal libc++ macro... Maybe a clang switch could house it?

+1.  Such a flag could also cause the unstable-ABI version of the
library to be linked to.

Thanks,
-- 
Peter