[Interest] Qt 5.8.0 RC build under windows

Thiago Macieira thiago.macieira at intel.com
Thu Jan 19 01:08:48 CET 2017

On quinta-feira, 19 de janeiro de 2017 00:40:22 PST Prav wrote:
> Hello, Thiago.
> > -no-rtti is not tested and clearly someone broke it. I've submitted a
> > change to remove that option from configure starting with Qt 5.8.1.
> I  was  thinking  that without RTTI compiled programs became lighter and
> faster (but never saw values of how much)

Yes, the option causes the compiler not to emit the RTTI structures for 
polymorphic classes. That may save you a bit of read-only, sharable data in 
the Qt libraries.

> As I can see Qt tries to be
> lighter now to be used in embedded systems. You still think that total
> remove of -no-rtti flag is OK in this case? 

The option only did anything on Windows, where a couple hundred bytes per 
library make much of a difference. It would make more sense on embedded 
systems, but it seems like it wasn't active for them. I don't know why.

My guess is that it use to work for Qt for Embedded Linux back in Qt 4 days, 
but with the conversion to Qt 5 and QPA, the option was lost. And no one 

> And why Qt now needs RTTI? Qt  5.7.0 was building fine without RTTI. What
> features added to 5.8.0 made RTTI mandatory I wonder?

Someone added a dynamic_cast. That's all.

Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center

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