[Development] qt-4.8.x gcc5 version/detection issues

[Rex Dieter]

Sune Vuorela wrote:

> On 2015-02-16, Rex Dieter <rdieter at math.unl.edu> wrote:
>> * QT_BUILD_KEY handling
>>
>> Similar to webkit above, the configure bits about QT_BUILD_KEY only
>> handles up to gcc-4.x.
>>
>> For fedora 22, our gcc5 builds are done in a way that is (supposedly) ABI
>> compatible to gcc4, so I'm currently using:
>> http://pkgs.fedoraproject.org/cgit/qt.git/tree/qt-gcc5_compat_qt_build_key.patch
>> to ensure QT_BUILD_KEY matches (ie, it includes the same g++-4 string as
>> before).
>>
>> As far as upstream is concerned, I assume you'd prefer the default here
>> to be g++-5 ?
> 
> The build key is used for ABI checks, so I think the 4 should still be
> used. e.g. you can build a qt plugin with g++-5 and it should still be
> loadable by the qt you buil with g++-4.x
> 
> So I think your current patch is right.

>From my reading of
http://developerblog.redhat.com/2015/02/10/gcc-5-in-fedora/

It may depend on the value of _GLIBCXX_USE_CXX11_ABI macro, but I admittedly 
don't yet fully grasp the implications of it being set either way.

-- Rex