RE: [ft-devel] Re: xorg crashes with freetype2-2.1.10

[Turner, David]

Hello everyone,

I'm back from vacation and have some hints regarding this infamous
crash.

- First of all, the reason why some pointers have been set to NULL in
  the latest package is really that:

     * the functions were _not_ used by the rest of the library,
       nor exposed through a public API. And I couldn't reasonnably
       guess what the X.org code was doing

     * the functions are completely removed in the heap-optimized
       version of the library.

  If you want to correct it safely, line 370 of 'src/sfnt/sfdriver.c' 
  should read instead:

          #ifdef FT_OPTIMIZE_MEMORY
            0 /* tt_find_sbit_image */,
            0 /* tt_load_sbit_metrics */,
          #else
            tt_find_sbit_image,
            tt_load_sbit_metrics,
          #endif


- The real problem is that the X.org code relies on features that
  are internal to the library. This is ok as long as its sources
  are embedded within the X Server (or X Font Server), but breaks
  when trying to rely on the library installed on the system.


There aren't that many solutions, but they do exist:

A/ Forget about the "optimization", load the glyphs twice
   and be done with it.

B/ Keep a copy of the FreeType sources within X.org, and never
   use the system-installed version of the library.

C/ Ask for a dedicated public API for the problem, which will
   appear in a later release of the library (e.g. 2.2.0). Do
   some twisted magic at compile-time:

     - if the version of FreeType headers used at compile time
       are < 2.2.0, forget about the optimization

This is the only way to generate correct code that will never
break in the future.

By the way, I don't think I'll be able to produce a patch for
X.org in the coming weeks !!

Hope this helps,

- David Turner
- The FreeType Project  (www.freetype.org)



> -----Message d'origine-----
> De : address@hidden
> [mailto:address@hidden 
> la part de
> Werner LEMBERG
> Envoyé : dimanche 24 juillet 2005 21:44
> À : address@hidden
> Cc : address@hidden; address@hidden;
> address@hidden
> Objet : Re: [ft-devel] Re: xorg crashes with freetype2-2.1.10
> 
> 
> 
> > > > My test of the freetype module showed that I could cause a crash
> > > > by loading any -iso10646-1 ttf font I tried; but using an eight
> > > > bit encoding never caused a crash.  I didn't try any other
> > > > sixteen bit encodings (such as legacy CJK encodings) and I
> > > > didn't try otf or type1 fonts in that test.
> > > 
> > > Thanks for all your tests, but to really find out the problem we
> > > need backtraces, which I was told is not an easy thing with X.
> > 
> > We have one in my original report.  It has full debugging symbols,
> > and shows exactly where in xorg the symbol is being dereferenced.
> 
> There are two problems.  The one with your backtrace shows that this
> particular xorg version uses an internal function of FreeType which
> has changed.  I think David T. can answer this better (after returning
> from his vacation) since he has already written some patches for main
> applications to avoid FreeType internals.
> 
> The other problem (reported by James) could be a different bug,
> probably in the cmap code of FreeType, and for his particular problem
> I would like to see a backtrace.
> 
> 
>     Werner
> 
> 
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