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Re: C++98/C++11 ABI compatibility for gcc-4.7
- From: Jonathan Wakely <jwakely dot gcc at gmail dot com>
- To: James Y Knight <foom at fuhm dot net>
- Cc: jyasskin at googlers dot com, gcc at gcc dot gnu dot org
- Date: Thu, 14 Jun 2012 14:37:38 +0100
- Subject: Re: C++98/C++11 ABI compatibility for gcc-4.7
- References: <firstname.lastname@example.org>
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:
That appears to be a strict aliasing violation. Boost.Python has lots
of warnings about them when built.
> 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
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