preparing for GCC 5, especially libstdc++6

[Lisandro Damián Nicanor Pérez Meyer]

On Tuesday 16 June 2015 23:37:41 Matthias Klose wrote:
> 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.  libstdc++6 will
> support two ABI's, the classic cxx98 ABI (currently in testing/unstable)
> and the new cxx11 ABI (currently enabled in experimental as the default
> ABI).

Hi Matthias!

[snip]

> My goal is to make the GCC version bump in early July, and use the time
> until then to prepare libstdc++6 depending packages to get ready for GCC 5,
> and avoiding version bumps for C++ libraries until this time.

As you already know we the Qt/KDE team, in order to avoid an ABI break, need 
to either:

a) Push Qt 5.4.2 to unstable before gcc5 becomes the default compiler. This is 
currently not an option due to #787689.

b) Push Qt 5.4.2 to unstable at the same time as gcc5 becomes the default 
(well, one or two dinstalls later maybe). If some package gets compiled with 
gcc5 and Qt < 5.4.2 in the meantime we can binNMU it.

c) Push Qt 5.4.2 to unstable a couple of days before gcc5 becomes the default. 
Once gcc5 becomes the default ask for a give back in armhf.

d) Push Qt 5.4.2 to unstable either by forcing gcc5 as default at build time 
or working around the bug. I would definitely would like to avoid this option 
as:
  - The current Qt stack is comprised of 25 source packages. I don't think me
    or my teammates will have the time to hack all of them before beginnings
    of July.
  - I don't know if some other lib/app that build depends on qt5 will still
    have the issue on armhf if we workaround it.
  - I don't know what happens if Qt5 gets built against gcc5 but apps against
    gcc4.9. Possibly and hopefully nothing, but I just don't know.

My current preference would be acb (totally discarding d), but I'm open to 
suggestions too.

Kinds regards, Lisandro.

-- 
El futuro es WIN95.... A no ser que hagamos algo a tiempo.

Lisandro Damián Nicanor Pérez Meyer
http://perezmeyer.com.ar/
http://perezmeyer.blogspot.com/
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