preparing for GCC 5/libstdc++6 (and GCC 6)
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Hi,
it's time to prepare for GCC 5 as the default compiler in unstable. Compared
to earlier version bumps, the switch to GCC 5 is a bit more complicated
because libstdc++6 sees a few ABI incompatibilities, partially depending on
the C++ standard version used for the builds. For some C++11 language
requirements, changes on some core C++ classes are needed, resulting in an ABI
change.
Details for the whole transition, including the C11 and GFortran parts are
outlined in
https://wiki.debian.org/GCC5
There are two set of bug reports filed for issues regarding GCC 5:
http://bugs.debian.org/cgi-bin/pkgreport.cgi?tag=ftbfs-gcc-5;users=debian-gcc@lists.debian.org
These are build failures seen when building with GCC 5. Those which can be
fixed now, have an RC priority, those that require changes on other packages,
or only can be uploaded once GCC 5 is the default, have priority important.
http://bugs.debian.org/cgi-bin/pkgreport.cgi?tag=libstdc%2B%2B-cxx11;users=debian-gcc@lists.debian.org
These are issues which need a decision/investigation if the libstdc++ library
transition propagates to these libraries.
While GCC 5 won't be the default compiler for stretch, there won't be another
libstdc++6 transition with GCC 6. However GCC 6 will change the default C++
standard to C++14. If you know that your package doesn't build using c++11 or
c++14, please consider changing the packaging to explicitly build with
- -std=c++98 or -std=gnu++98.
My goal is to make the GCC version bump on July 31, and use the time until
then to prepare libstdc++6 depending packages to get ready for GCC 5 and
investigate followup transitions until then.
How can you help?
- Don't wait until GCC 5 is the default, start fixing and helping now.
- Please fix the above mentioned GCC 5 issues. Consider uploading
the fix in a NMU.
- Investigate if followup transitions for libraries are needed.
- Upload packages which have a patch, but no feedback from the
package maintainers.
- Please don't ask if the GCC maintainers can rebuild your package
when you didn't check that for yourself when uploading a new
upstream version.
- Join #debian-toolchain on OFTC to coordinate uploads, and ask
questions. At least Martin Michlmayr (tbm) and myself (doko)
will be there.
The libstdc++6 transition will be a large one, having a large fun/pain factor
depending on your point of view. In either case, please help it by addressing
the outstanding issues.
Thanks, Matthias
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