Re: Patch ping

[Paolo Carlini <pcarlini at suse dot de>]

Ian Lance Taylor wrote:

> It would be easy to add a single instance of the mutex in
> src/locale_init.cc.  But then code compiled with a newer version of
> libstdc++ would not work with older versions of libstdc++.so, as there
> would be an undefined symbol at link time.  Does that count as a bad
> ABI change?  It would continue to be possible to use code compiled
> with older versions of libstdc++ with the new libstdc++.so; the older
> code just wouldn't use the mutex when initializing the cache.
>  
I think this kind of "incompatibility" *in principle* is possible: i.e., 
the .so number of mainline is 6.0.6 whereas 3.4.0 had 6.0.0 
(http://gcc.gnu.org/onlinedocs/libstdc++/abi.html) and certainly the 
same difficulty is experienced by someone trying to use the 3.4.0 .so 
together with code compiled with the mainline - or 4_0-branch for that 
matter - headers.

However, I think Benjamin espressed some concerns about symbol exports 
(only one for your approach, right?) I'm not sure whether there are 
specific problems with exporting mutex objects or whether he is 
referring to our more general policy lately of adding exports only if 
really, really, needed.

Paolo.