Title: GCC 4.7 Introduced the New C++11 ABI 
Author: Anthony G. Basile <blueness@gentoo.org>
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Posted: 2014-10-26
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GCC 4.7 introduced the new experimental 2011 ISO C++ standard [1], along with
its GNU variant.  This new standard is not the default in gcc-4.7, 4.8 or 4.9,
the default is still gnu++98, but it can be enabled by passing -std=c++11 or
-std=gnu++11 to CXXFLAGS.

Users that wish to try C++11 should exercise caution because it is not
ABI-compatible with C++98.  Nor is C++11 code compiled with gcc-4.7 guaranteed
to be ABI-compatible with C++11 compiled with 4.8, or vice versa [2].  Thus
linking C++98 and C++11, or C++11 compiled with different versions of gcc, is
likely to cause breakage.  For packages which are self-contained or do not link
against any libraries written in C++, there is no problem.  However, switching
to C++11 and then building packages which link against any of the numerous
libraries in an incompatible ABI can lead to a broken system.

This is a precautionary news item and the typical user need not do anything.
However, as C++11 gains in popularity and the number of packages using it
increases, it is important that users understand these issues [3].

For an ABI compliance checker, and more information about C++ ABIs, see [4].  

Ref.

[1] http://www.stroustrup.com/C++11FAQ.html

[2] Upstream GCC does not support ABI-compatibility between gcc-4.x and 4.y for
any x != y .  See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61758.  Even
having different versions of gcc installed simultaneously may lead to problems,
especially if the older version of gcc is active.  An example is
https://bugs.gentoo.org/show_bug.cgi?id=513386.  

[3] Note that some packages like www-client/chromium and net-libs/webkit-gtk
are already using C++11 features.

[4] http://ispras.linuxbase.org/index.php/ABI_compliance_checker