https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85222
--- Comment #13 from Richard Biener <rguenth at gcc dot gnu.org> --- Just to mention the testcase fails in the same way if you build and run it with GCC 7 and libstdc++ from GCC 7 when that was configured with the gcc-4 compatible ABI by default. Just in case that wasn't obvious... Dropping the // Determines the version of ios_base::failure thrown by __throw_ios_failure. // If !_GLIBCXX_USE_DUAL_ABI this will get undefined automatically. #define _GLIBCXX_USE_CXX11_ABI 1 from src/c++11/ios.cc probably makes that more "consistent", matching the default ABI. The PR66145 changed that from an unconditional #define to 0 to an unconditional #define to 1. While, as the comment now says, a build without the dual-abi will use the old behavior switching the ABI default does not influence the behavior. I realize PR66145 is exactly about "fixing" the case of the user not using the default ABI but now we have still exactly the same situation when the user does #define _GLIBCXX_USE_CXX11_ABI 0 with a compiler defaulted to the new ABI. So IMHO the original change was totally pointless... :/ I'm probably going to locally patch it to be consistent with the default ABI choice - that at least keeps programs working that do not explicitely choose the ABI via #define _GLIBCXX_USE_CXX11_ABI and is consistent with the system integrators choice of the default ABI to keep compatibility to older GCC versions.
