The Itanium ABI it is not just whatever GCC does; while it is not an ISO standard, it is an intervendor ABI documented independently of any compiler implementation and changes are agreed among compiler teams. It is continually updated to track the C++ evolution.
The standard library ABI it is not covered the the Itanum ABI (outside of some basic functionality), but it is defined necessarily by the platform. For linux that would be libstdc++.
The LSB references the Itanium ABI and defines libstdc++ as the ABI for the C++ standard library on linux platforms; it is again not an ISO standard, but it is as close as you can get on Linux.
And of course the C++ ABI being a very complex and both the ABI document itself and compilers have bugs from time to time, especially if you live close to the bleeding edge.
The standard library ABI it is not covered the the Itanum ABI (outside of some basic functionality), but it is defined necessarily by the platform. For linux that would be libstdc++.
The LSB references the Itanium ABI and defines libstdc++ as the ABI for the C++ standard library on linux platforms; it is again not an ISO standard, but it is as close as you can get on Linux.
And of course the C++ ABI being a very complex and both the ABI document itself and compilers have bugs from time to time, especially if you live close to the bleeding edge.