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Re: C++98/C++11 ABI compatibility for gcc-4.7


On 31 May 2012 22:35, James Y Knight wrote:
> You've missed at least one ABI incompatibility in GCC 4.7 and later, as
> demonstrated in real life by (at least) libboost_python, and distilled
> into this test case.
>
> At least these bug reports are probably caused by this ABI incompatibility:
> https://svn.boost.org/trac/boost/ticket/6919

That appears to be a strict aliasing violation. Boost.Python has lots
of warnings about them when built.

> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53455
> https://svn.boost.org/trac/boost/ticket/6895
>
> As I've said before, I really wish GCC devs would take the ABI
> incompatibility problem more seriously.

Those two reports and your test case are the same as
http://gcc.gnu.org/PR53646 and http://gcc.gnu.org/PR53657 and should
be fixable.
It might also be the cause of http://gcc.gnu.org/PR53490 (I couldn't
reproduce that one so I'm not sure.)

It seems to be an inadvertent incompatibility caused by the
interaction of a libstdc++ workaround for a bug and g++ behaviour that
may not have been known to the libstdc++ devs, so not something that
could have been prevented by making it a linker error, because noone
knew it was even broken.  Testing and reporting bugs and analysing the
problem should lead to it being fixed.  I think the problem was GCC
devs not knowing the problem existed, rather than not taking it
seriously.


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