libGL exported __glX* symbols (Was: glucose and xgl progress)

[Michel Dänzer]

On Thu, 2007-09-20 at 13:50 +0100, José Fonseca wrote:
> On 9/19/07, Gabor Gombas <gombasg at sztaki.hu> wrote:
> > On Wed, Sep 19, 2007 at 10:20:49AM +0000, José Fonseca wrote:
> > > However, when loaded, references to __glXFreeContext *inside*
> > > libglxgext.so are linked to the external __glXFreeContext in libGL.so:
> >
> > If you have multiple definitions for a symbol it is completely random
> > which a given reference will resolve to.
> >
> > Now, the two underscores are a good hint that these are internal symbols
> > and they should not be exported at all or if they have to, one of them
> > must be renamed.
> >
> > > libtool's -export-dynamic flag is not being used. Using libtool's -module
> > > flag doesn't change anything.
> >
> > Does this symbol have to be exported? If no, you should use libtool's
> > --export-symbol feature to explicitely declare which symbols should be
> > visible and which should not. In fact, it is always wise to use
> > --export-symbol when creating shared libraries to prevent ABI breakage
> > by accidentally exporting private symbols.
> >
> > If __glXFreeContext should be exported, then it should be decided which
> > library owns this symbol, and the other must be modified not to export
> > it.
> >
> > If it is the case that libGL.so exports __glXFreeContext but
> > libglxgext.so wants to locally override it, and for some reason you
> > absolutely cannot rename it, then you must use gcc's
> > __visibility__((__protected__)) attribute when declaring __glXFreeContext
> > in libglgxext.so, but that is not portable to non-ELF platforms and
> > other compilers and also has run-time performance costs IIRC.
> 
> I agree in principle with your suggestions. But I'm not entitled to
> decide if __glX* symbols should or not  be exported, [...]

Neither am I :), but AFAICT they aren't currently referenced outside of
their respective modules, and they probably shouldn't be.


-- 
Earthling Michel Dänzer           |          http://tungstengraphics.com
Libre software enthusiast         |          Debian, X and DRI developer