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

[Olivier Goffart]

On Monday 16 February 2015 13:22:30 Rex Dieter wrote:
> 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_ke
> >> y.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.

As far as I understand, _GLIBCXX_USE_CXX11_ABI only makes a difference in the 
ABI of the standard library. (libstdc++)
Since the Qt ABI should not contains anything from the standard library, this 
macro should not have an impact on the binary compatibility with Qt.

-- 
Olivier 

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