On 10/20/14 12:21, "Paweł Hajdan, Jr." wrote:
On 10/20/14 12:53 AM, Anthony G. Basile wrote:
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.
This seems to focus on the Gentoo user adding -std=c++11 to CXXFLAGS.
Do we consider this #1 problem with gcc-4.8 or 4.7+?
As far as I'm concerned, the big issue is e.g.
<https://bugs.gentoo.org/show_bug.cgi?id=513386>, where having gcc-4.7
and gcc-4.8 installed on the same system (and using gcc-4.7 as the
active gcc version) is known to be broken.
This is one step beyond the news item. In addition to the
incompatibility between c++98 abi and c++11, you can expect c++11 code
compiled with gcc-4.7 to not work with c++11 compiled with 4.8 and vice
versa. But this is our problem, not the users'. When we start to
support c++11 in full force, we may need to block earlier versions of
gcc on certain packages to avoid the above mismatch, maintain patches,
etc. Its premature to say.
Another concern I have with the above news item is it might actually
encourage "crazy" users to add -std=c++11 to CXXFLAGS, even though
otherwise they wouldn't even know about the flag.
If you tell a child "don't touch!" they will. I agree with you, and
debated for exactly this reason, but in the end, I think its better to
have a informed public. We'll get better bug reports and better
co-operation.
This is the problem with a "form source" distro. We can't control how
the users will build their executables and this is one case where you
can break things.
To summarize, my suggestion is to make sure we clearly communicate known
bugs reported to Gentoo, like example above one.
I could add another sentence that the resulting abi is also gcc version
dependant, but I don't want to go too far because we aren't supporting
c++11 yet.
Paweł
--
Anthony G. Basile, Ph. D.
Chair of Information Technology
D'Youville College
Buffalo, NY 14201
(716) 829-8197
