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List:       gcc
Subject:    Re: KDE hackers, please read (was [nathan@codesourcery.com: Re: GCC
From:       Nathan Sidwell <nathan () codesourcery ! com>
Date:       2001-12-10 9:44:33
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Waldo Bastian wrote:
> 
> On Tuesday 04 December 2001 02:50 pm, Joe Buck wrote:
> > > The alternative, banning RTTI from KDE, isn't very attractive either.
> >
> > What if you only use RTLD_GLOBAL for those libraries that define base
> > classes that you'll want to do RTTI with?  Or use it everywhere except
> > with libraries that you know are problematic and sloppy with name spaces,
> > like the flash plugin and OpenGL.
> 
> The problem that we had was with things like templates. If two plugins use the
> same template, they will get the same symbol-names. When the symbols are
> loaded in the global namespace, it can happen that plugin A resolves against
> the symbols of plugin B. When you now unload plugin B you will get a crash
> the next time you access plugin A.
Isn't this a bug in the DL machinery. Why can't it track the dependency
DAG? (or is unloading specifically undefined in such a case?)

> To what _extent_ does linking without RTLD_GLOBAL break RTTI? Looking at
> PR3993 breakage there seems to happen because the module that does the
> dlopen'ing doesn't strongly define class B (how do you call that, "class B
> isn't being emitted"?)  That situation could be prevented most of the time I
> think. (I believe such classes also have a negative impact on prelinking)
Not saying RTLD_GLOBAL (and linking the main executable with -E), effectively
places each dlopen'd library in its own namespace. RTTI across library
boundaries would not work.

nathan

-- 
Dr Nathan Sidwell   ::   http://www.codesourcery.com   ::   CodeSourcery LLC
         'But that's a lie.' - 'Yes it is. What's your point?'
nathan@codesourcery.com : http://www.cs.bris.ac.uk/~nathan/ : nathan@acm.org
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