Thought about a Qt port

[Thiago Macieira]

On domingo, 31 de março de 2013 20.20.46, Alberto Mardegan wrote:
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> On 03/31/2013 12:11 AM, Thiago Macieira wrote:
> > Great. You'll need to query QtCore for "reduce_relocations":
> > 
> > ifneq ($(shell $(PKGCONFIG) --variable qt_config $(QTCORE) | grep
> > reduce_relocations), ) 
> > CXXFLAGS += -fPIE endif
> 
> Can you briefly explain (or just give a pointer to a web page) what
> this does? The gcc man page doesn't tell me much (other then I should
> probably add -pie to the linker flags; is this correct?).

QtCore.pc and Qt5Core.pc have a qt_config variable stored, which contains a 
list of Qt settings that might be relevant for applications, such as what 
features were enabled at compile time. The "reduce_relocations" feature 
corresponds to the -reduce-relocations configure option.

On Qt 4, it was not enabled by default. In Qt 5, it is. And it produces an 
error if you compile without -fPIE or -fPIC:

qglobal.h:974:4: error: #error "You must build your code with position 
independent code if Qt was built with -reduce-relocations. " "Compile your 
code with -fPIC or -fPIE."

Strictly speaking, what we need is to disable copy relocations in the 
executable. There's no option for that, but -fPIC and -fPIE do accomplish it. 
That also means you do not need to pass -pie to the linker.

For more information
http://www.macieira.org/blog/2012/01/sorry-state-of-dynamic-libraries-on-linux/
http://www.macieira.org/blog/2012/01/update-and-benchmark-on-the-dynamic-library-proposals/

-- 
Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
   Software Architect - Intel Open Source Technology Center
      PGP/GPG: 0x6EF45358; fingerprint:
      E067 918B B660 DBD1 105C  966C 33F5 F005 6EF4 5358
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