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Subject: Re: [OMPI devel] adding new functions to a BTL
From: Eugene Loh (Eugene.Loh_at_[hidden])
Date: 2008-10-22 18:06:43


Ralf Wildenhues wrote:
Jeff Squyres wrote:
    
We use lt_dlopen() to open the plugins (Libtool's wrapper for a   
portable dlopen).  It opens all plugins (DSOs) in a private scope.    
That private scope is kept deep in the OPAL MCA base and not exposed   
elsewhere in the code base.  So if you manually dlopen a plugin again,  
I'll bet that the linker realizes that that DSO has already been  
loaded into the process space and doesn't actually load it again (but  
doesn't fail).  So the dlsyms fail because you don't have access to  
the private scope from where Libtool originally opened the DSO.
      
Shouldn't it work to re-dlopen the lib with RTLD_GLOBAL?
  
I used dlopen("...", RTLD_LAZY | RTLD_GLOBAL).  It gave me a non-NULL handle, but subsequent dlsyms failed.
Also, recent libltdl should allow you to choose which scope you want in
the first place, local or global, through lt_dladvise.
I'm just learning all this dl stuff right now.  Jeff's --enable-static seems to do exactly what I want (namely, make things work in the way that I'm familiar with!).  I did try to figure out what OMPI was doing and it seemed to me it was using RTLD_LAZY | RTLD_GLOBAL, which is why I chose that.

For now, --enable-static seems to do exactly what I want.  Further workarounds probably don't make any sense.