On 10/24/14 4:31 PM, Anthony G. Basile wrote: > I've update the c++ news item for your consideration. I incorporated > suggestions, in particular a note about incompatibility between c++11 > compiled with different version of gcc differing in minor number (eg 4.7 > and 4.8).
Thanks, I think this is an improvement. I'd still prefer an explicit mention that having gcc-4.7 and 4.8 installed simultaneously leads to known breakages, especially if 4.7 is the active gcc version. The text of the news item implies this, but it's just not obvious. Also consider explicitly mentioning <https://bugs.gentoo.org/show_bug.cgi?id=513386>. Obviously this wouldn't be a complete list of issues, but from the CC list it's a pretty common bug. If in doubt, consider this question: what would be bad about including the info I suggested above? Paweł > Title: GCC 4.7 Introduces New c++11 ABI > Author: Anthony G. Basile <bluen...@gentoo.org> > Content-Type: text/plain > Posted: 2014-10-20 > Revision: 1 > News-Item-Format: 1.0 > Display-If-Installed: >=sys-devel/gcc-4.7.0 > Display-If-Keyword: amd64 > Display-If-Keyword: arm > Display-If-Keyword: mips > Display-If-Keyword: ppc > Display-If-Keyword: ppc64 > Display-If-Keyword: x86 > Display-If-Keyword: amd64-fbsd > Display-If-Keyword: x86-fbsd > > 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 > ABI-compatible > with c++11 compiled with 4.8, and vice versa. 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 > increase, it is important that users understand these issues. > > For an ABI compliance checker, and more information about C++ ABIs, see [2]. > > Ref. > [1] http://www.stroustrup.com/C++11FAQ.html > [2] http://ispras.linuxbase.org/index.php/ABI_compliance_checker >
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