[poppler] Compiling poppler with clang

Sun Nov 18 14:01:58 PST 2012

El Dimecres, 14 de novembre de 2012, a les 18:48:26, Adam Reichold va 
escriure:
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> Hello again,
> 
> The attached patch should rework the function copy constructors.

Doesn't seem to apply on current master, can you please rebase it and make 
sure it applies?

Cheers,
  Albert

> 
> Best regards, Adam.
> 
> On 14.11.2012 12:58, Albert Astals Cid wrote:
> > El Dimecres, 14 de novembre de 2012, a les 07:28:21, Adam Reichold
> > va escriure: Hello Albert,
> > 
> > Before I try the other classes, could you have a look at the
> > attached patch for SampledFunction and tell if this is what you are
> > looking for?
> > 
> > Would something like memcpy(sampleSize, func->sampleSize,
> > funcMaxInputs * sizeof(int)); be preferred to the plain for-loops?
> > 
> >> Yes. it's what the other functions use, right?
> > 
> > Regards, Adam.
> > 
> > P.S.: By the way, is there a reason to use the signature
> > Function(const Function*) for the "what would be a copy
> > constructor" instead of "Function(const Function&)"?
> > 
> >> No clue, ask the guy that wrote them (hint, he's not around)
> >> 
> >> Cheers, Albert
> > 
> > On 13.11.2012 23:28, Albert Astals Cid wrote:
> >>>> El Dilluns, 27 d'agost de 2012, a les 22:31:13, Albert Astals
> >>>> Cid
> >>>> 
> >>>> va escriure:
> >>>>> El Dilluns, 27 d'agost de 2012, a les 08:29:40, Thomas
> >>>>> Freitag va
> >>>>> 
> >>>>> escriure:
> >>>>>> On 27.08.2012 00:56, Albert Astals Cid wrote:
> >>>>>>> El Diumenge, 26 d'agost de 2012, a les 15:48:37, He Liu
> >>>>>>> va
> >>>>>>> 
> >>>>>>> escriure:
> >>>>>>>>>> 5. vtable pointer will be overwritten
> >>>>>>>>>> Function.cc:422:10: warning: destination for
> >>>>>>>>>> this 'memcpy' call is a pointer to dynamic class
> >>>>>>>>>> 'SampledFunction'; vtable pointer will be
> >>>>>>>>>> overwritten [-Wdynamic-class-memaccess]
> >>>>>>>>>> 
> >>>>>>>>>> memcpy(this, func, sizeof(SampledFunction));
> >>>>>>>>>> ~~~~~~ ^
> >>>>>>>>>> 
> >>>>>>>>>> Function.cc:422:10: note: explicitly cast the
> >>>>>>>>>> pointer to silence this warning
> >>>>>>>>>> 
> >>>>>>>>>> At least categrory 5. sound serious to me, I
> >>>>>>>>>> would never have copied instances of C++ objects
> >>>>>>>>>> in that way, because it depends on the compiler
> >>>>>>>>>> and the class if this causes problems on runtime,
> >>>>>>>>>> s. i.e.
> >>>>>>>>>> http://weseetips.com/tag/afx_zero_init_object/,
> >>>>>>>>> 
> >>>>>>>>> Note this is memset-ing to 0, not memcpy-ing a
> >>>>>>>>> class to itself. To be honest i agree memcpy'in a
> >>>>>>>>> SampledFunction to a SampledFunction is ugly, but i
> >>>>>>>>> fail to see why it would not work.
> >>>>>> 
> >>>>>> It works, at least with the actual used compilers. But it
> >>>>>> works only, because the allocated members of
> >>>>>> SampledFunction are overwriten after doing the memcpy.
> >>>>>> And this behaviour makes it just more ugly in my eyes.
> >>>>>> And this is the same with the other memcpy's in
> >>>>>> ExponentialFunction, StitchingFunction and
> >>>>>> PostScriptFunction. And it will work till such time as
> >>>>>> everybody who changes the class will not forget to do it
> >>>>>> in the same way. So if You are not willing to change it
> >>>>>> (or let somebody else change it, I know, never change
> >>>>>> running code), we could use the hint: explicitly cast the
> >>>>>> pointer to silence this warning.
> >>>>> 
> >>>>> I'm fine with someone fixing the code. Less warnings is
> >>>>> always good, but for master, there's no need to introduce a
> >>>>> pontential breaker just because clang complains.
> >>>> 
> >>>> So at the end noone volunteered to re-rewite those functions
> >>>> not to use memcpy over classes with virtuals?
> >>>> 
> >>>> Cheers, Albert
> >>>> 
> >>>>> Cheers, Albert
> >>>>> 
> >>>>>> Cheers, Thomas
> >>>>>> 
> >>>>>>>> Hi Albert,
> >>>>>>>> 
> >>>>>>>> :-)
> >>>>>>>> 
> >>>>>>>> A pointer of type SampleFunction* could be pointing
> >>>>>>>> to an instance of a SampleFunction sub-class, which
> >>>>>>>> has different vtable contents.
> >>>>>>> 
> >>>>>>> No, it could not, SampledFunction does not have any
> >>>>>>> childs and the function doing that memcopy is private
> >>>>>>> anyway.
> >>>>>>> 
> >>>>>>>> As a result, one could construct a SampleFunction
> >>>>>>>> with SampleFunction(SampleFunction *) using a pointer
> >>>>>>>> to a sub-class instance, and overwrite the
> >>>>>>>> SampleFunction's vtable address with the sub-class's
> >>>>>>>> vtable address.
> >>>>>>>> 
> >>>>>>>> I am not sure if it will lead to any
> >>>>>>>> bugs/vulnerabilities in this case, but it is not safe
> >>>>>>>> practice in general.
> >>>>>>> 
> >>>>>>> Sure, i never said it was. I'm just saying i don't see
> >>>>>>> why it would not work in our case.
> >>>>>>> 
> >>>>>>>> Since the vtable structure depends on how the
> >>>>>>>> compiler is implemented, memcpy or memset on object
> >>>>>>>> pointers will generally lead to undefined behaviors.
> >>>>>>> 
> >>>>>>> I'm far from a compiler expert, but one would hope that
> >>>>>>> for a given class the compiler stores always the
> >>>>>>> "stuff" in the same order in memory, so again, i fail
> >>>>>>> to see why this should fail in our case.
> >>>>>>> 
> >>>>>>> Cheers,
> >>>>>>> 
> >>>>>>> Albert
> >>>>>>> 
> >>>>>>>> Thanks.
> >>>>>>>> _______________________________________________
> >>>>>>>> poppler mailing list poppler at lists.freedesktop.org
> >>>>>>>> http://lists.freedesktop.org/mailman/listinfo/poppler
> 
> _______________________________________________ poppler
> 
> >>>>>>> mailing list poppler at lists.freedesktop.org
> >>>>>>> http://lists.freedesktop.org/mailman/listinfo/poppler
> >>>>>>> 
> >>>>>>> .
> >>>>>> 
> >>>>>> _______________________________________________ poppler
> >>>>>> mailing list poppler at lists.freedesktop.org
> >>>>>> http://lists.freedesktop.org/mailman/listinfo/poppler
> >>>>> 
> >>>>> _______________________________________________ poppler
> >>>>> mailing list poppler at lists.freedesktop.org
> >>>>> http://lists.freedesktop.org/mailman/listinfo/poppler
> >>>> 
> >>>> _______________________________________________ poppler
> >>>> mailing list poppler at lists.freedesktop.org
> >>>> http://lists.freedesktop.org/mailman/listinfo/poppler
> > 
> > _______________________________________________ poppler mailing
> > list poppler at lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/poppler
> 
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