[Development] QNX broken on 5.7

[Rafael Roquetto]

Hi Simon,

You are right, I completely forgot about that thread. Thanks for the feedback.

Cheers,
Rafael

On Tue, Mar 08, 2016 at 06:31:15PM +0000, Hausmann Simon wrote:
> Hi,
> 
> When building Qt 5.7 for QNX a special patch is applied in the CI that fixes the Dinkumware headers. You were CCed when this was discussed (Subject was "‎QNX and Dinkumware support for constexpr and nullptr").
> 
> Simon
> 
>   Original Message
> From: Rafael Roquetto
> Sent: Tuesday, March 8, 2016 18:39
> To: development at qt-project.org
> Subject: [Development] QNX broken on 5.7
> 
> 
> Hello everyone,
> 
> I would like to point out that QNX is unable to build the 5.7 branch. The
> commit that probably triggered the breakage is:
> 
>     d6bb01e1779f1840dfbab57c6ecd615587bbde62
>     Force inclusion of <atomic> on QNX systems.
> 
> 
> This raises my first question: should this not have been reported by the CI?
> This is not the first time that changes go in and break QNX, in spite of
> having the CI in place. Would anyone have a clue about what is going on?
> 
> 
> Now, concerning the issue itself, it seems to be a bigger problem:
> 
>     /usr/include/cpp/xxatomic: In instantiation of 'std::atomic<_Ty*>::atomic(_Ty*) [with _Ty = void(QtMsgType, const char*)]':
>     /usr/include/cpp/xxatomic:336:3: error: invalid conversion from 'void (*)(QtMsgType, const char*)' to 'void*' [-fpermissive]
>     /usr/include/cpp/xxatomic:873:15: error:   initializing argument 1 of 'void* std::_Atomic_address::operator=(void*)' [-fpermissive]
> 
> 
> Caused by the following line inside qlogging.cpp:
> 
> static QBasicAtomicPointer<void (QtMsgType, const char*)> msgHandler = Q_BASIC_ATOMIC_INITIALIZER(qDefaultMsgHandler);
> 
> The problem can be traced to the Dinkumware's std::atomic implementation.
> Ultimately, qDefaultMsgHandler will be passed as an argument to std::atomic's
> default ctor, which looks like this:
> 
>         _CONST_FUN atomic(_Ty *_Right) _NOEXCEPT
>         {   // construct from _Right
>             _Atomic_address::operator=(_Right);
>         }
> 
> 
> _Atomic_address is a base class. As you can see, this ctor is implemented
> using operator=, which looks like this:
> 
> 
>     inline _ITYPE _ATOMIC_ITYPE::operator=(_ITYPE _Value) _NOEXCEPT
>     {   // assign _Value to *this
>         atomic_store(this, _Value);
>         return _Value;
>     }
>                 `
> 
> where _TYPE expands to (void *), thus effectively causing the conversion from
> void (*)(QtMsgType, const char*) to (void *), which is the error.
> 
> Interestingly, Dinkumware's std::atomic does provide operator= in terms of
> _Ty:
> 
> 
>     _Ty *operator=(_Ty *_Right) _NOEXCEPT
>     {   // assign from _Right
>         return static_cast<_Ty *>(_Atomic_address::operator=((void *)_Right));
>     }
> 
> 
> which makes me think that the ctor is wrongly implemented, since it bypasses
> this and calls the base class operator= explicitly.
> 
> 
> I am not sure how to work around this. QBasicAtomicPointer won't let me
> initialize it with some ugly (void *) pointer.
> 
> Does it make sense to revert this patch? Is there a way to fall back to the
> old non-C++11 implementation?
> 
> Thanks,
> Rafael
> 
> --
> Rafael Roquetto | rafael.roquetto at kdab.com | Software Engineer
> Klarälvdalens Datakonsult AB, a KDAB Group company
> Tel. Sweden (HQ) +46-563-540090, USA +1-866-777-KDAB(5322)
> KDAB - Qt Experts

-- 
Rafael Roquetto | rafael.roquetto at kdab.com | Software Engineer
Klarälvdalens Datakonsult AB, a KDAB Group company
Tel. Sweden (HQ) +46-563-540090, USA +1-866-777-KDAB(5322)
KDAB - Qt Experts
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