Re: 329-gary-allow-RTLD_GLOBAL

[Gary V. Vaughan]

On 22 May 2007, at 13:48, Ralf Wildenhues wrote:

> * Gary V. Vaughan wrote on Tue, May 22, 2007 at 02:24:25PM CEST:
> > On 22 May 2007, at 13:16, Ralf Wildenhues wrote:
> > > * Gary V. Vaughan wrote on Tue, May 22, 2007 at 02:11:03PM CEST:
> > > > I'm wondering how to best warn people who have their project
> > > > build rely on RTLD_GLOBAL that what they are doing is inherently
> > > > non-portable.
> > >
> > > Erm, relying on RTLD_LOCAL is non-portable.
> >
> > It is?  You mean that relying on identical symbols from two dlopened
> > modules to not clash is non-portable?
>
> Well.  I should have been more specific.  Relying on lt_dladvise_local
> to provide you with symbol hiding is not portable.   Simply because
> dlpreopening will not do that.
>
> > On what architectures?
>
> In most static-only settings.  (With glibc you can sometimes still use
> dlopen in a static link but only if you have the shared libc available
> at runtime.)
>
> It seems to me that dld does not provide symbol locality either, see
> eleven-year-old <http://www.delorie.com/gnu/docs/dld/dld.html>.

ACK.  Thanks for clarifying :-)

> > > Relying on RTLD_GLOBAL is not; after all, dlpreloading offers  
> > > similar.
> >
> > Relying on RTLD_GLOBAL exported symbols to resolve undefined symbols
> > in subsequently dlopened modules doesn't work on windows, or AIX.   
> > That
> > seems pretty non-portable to me...
>
> It doesn't work on AIX with runtimelinking?  That would be news to me.
> Using modules on AIX without runtimelinking seems pretty obscure to  
> me.

RTLD_GLOBAL can be passed to dlopen, but (assuming my recollection  
that AIX
is one of the hosts that requires all symbols to be resolved at link  
time is
correct) in the test case I just patched, AIX can't build moddepend with
undefined symbols.

> > > But also relying on
> > > allowing undefined symbols in your link is non-portable.  I don't  
> > > see
> > > how you can distinguish cases here reliably, in an automatic way.
> >
> > Except for annoyance to the end-user, I was originally thinking that
> > we don't need to distinguish.  When the developer's libltdl client
> > code calls lt_dladvise_global, we could have it emit a warning to
> > stderr that says: If what you are trying to do won't work without
> > calling lt_dladvise_global(), then you're code will not be fully
> > portable.
>
> Hmm.  That will be informative the first time, and annoying the next
> million times, if the user chose to accept this limitation.  So yes,
> a documentation patch is better.  That way not only the fact about
> some unportability but also its intensity may be conveyed.  ;-)

Indeed!

Cheers,
        Gary
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