[cfe-dev] Does clang now emit [abi:cxx11] unconditionally when used with libstdc++?

Renato Golin via cfe-dev cfe-dev at lists.llvm.org
Wed Aug 17 05:16:43 PDT 2016

On 16 August 2016 at 19:41, Maria Gottschalk via cfe-dev
<cfe-dev at lists.llvm.org> wrote:
> If major version < 5: never emit abi tags.
> If major version >=5: emit abi tags if requested with __attribute ((__abi_tag__ ("..."))).

I don't think that's appropriate, as that would change the behaviour
based on the library's version, not its source code.

If the source has abi tags, and we support abi tags, we *must* emit
abi tags in the mangling.

> This on the assumption that there is something to fix. Richard said there isn't. I wouldn't know.

The new c++11 functions were added to support the new abi, so old abi
library consumers would never hit them, making this "not a problem".

If library consumers do hit them, than they're aware of the problem
and intend to, in which case, exposing it is only logical.

This looks like a behavioural problem, not a compiler problem, so
fixing it in the compiler is a bad move.

If you don't want abi tags support, stick to Clang 3.8.

If you want Clang 3.9+ without abi tag support, revert the two patches
and use that. Of course, any bug in that toolchain would have to be
reproduced in an upstream release to be considered.


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