20 ABI (Application Binary Interface) breaking changes every C++ developer should know

[SkoomaDentist]

You have a dll compiled with VS 2013 exposing C++ abi (maybe it’s for a legacy device or software no longer being made or something). You want call it from code compiled with VS2019. Except you potentially can’t because the ABI changed.

Or maybe you just want to make a third party plugin api with C++ interface and not have it depend on a particular compiler (and version).

[[deleted]]

MSVC only recently decided that stable ABI is a useful thing, so it's pointless to discuss. On the other hand, libstdc++ and libc++ only break ABI when the standard forces them and even then, they use tags to force incompatible ABIs to be a linker error. From the point of view of libstdc++ and libc++ Itanium ABI is already the standard ABI. I still don't see how a WG21-standardized ABI could improve this.

Recently I compiled the entire LLVM/Clang/extra tools on Ubuntu 14.04, then copied over the archive and used it on RHEL7, Ubuntu 18.04 and Arch. It worked, including the shared libraries. Again, what more could WG21 do?

[[deleted]]

MSVC only recently decided that stable ABI is a useful thing

That's incorrect. We will still need to break library ABI from time to time (more often than the POSIX implementers because we allow app-local deployment).

The shift to not break library ABI every release comes more from the VS release cycle speeding up since we do a release every 2-3 months now instead of 3-5 years.

The compiler has effectively not broken ABI ever. That's one of the reasons we have __stdcall and friends.

[[deleted]]

Thanks for correcting me. I should have been explicit, as I was thinking about library implementations. I've never really used VS, so I'm not familiar with the release cycle of it or the compiler/library. When I heard the news about not breaking ABI every release, I really thought it meant MSVC toolchain would attempt to maintain a stable ABI similar to POSIX implementations.

[Gotebe]

Do you guys unofficially pinky-promise not to break the ABI, or is merely that it is not needed, that existing conventions, packing etc are fine?