Re: -dlopen self on AIX

[Howard Chu]

Albert Chin wrote:
> On Sun, Oct 30, 2005 at 11:38:26AM -0800, Howard Chu wrote:
> > Albert Chin wrote:
> > > On Sun, Oct 30, 2005 at 11:14:14AM -0600, Albert Chin wrote:
> > > > [snip ...]
> > > >
> > > > This means the method libtool uses to support -dlopen self on AIX
> > > > won't work (by building a list of symbols into some xxS.o file and
> > > > linking it with the executable). The real solution is to -bE the
> > > > symbol list. What's the cleanest way to do this?
> > > >
> > > > Dynamic module support in openldap-2.3.x isn't working on AIX for the
> > > > above reason. Using -bexpall or -bE when linking the main binary does
> > > > work though. While the main binary, slapd, doesn't dlopen itself,
> > > > modules it dlopen()'s cannot resolve symbols in slapd because they
> > > > weren't exported.
> > > Seems the openldap folks should really use -export-dynamic, which
> > > isn't defined for AIX. We could make it -bexpall but as documented in
> > > the previous mail, it doesn't export everything. So, should we create
> > > a new variable, export_dynamic_cmds? If so, and temporary files are
> > > created by it, how do we clean up?
> > Wait. The fact that -bexpall "doesn't export everything" is A Good 
> > Thing. Symbol tables on AIX include a lot of junk that other modules 
> > simply don't need to see. The symbols they omit are generally not useful 
> > for user code anyway.
>
> It might be a "A Good Thing" in terms of being "pure", but it's
> different than the behavior on Solaris, HP-UX, Tru64 UNIX, IRIX, and
> Linux. It's just not worth it being that different today. AIX
> certainly has no advantage because of it.

Yes, it's a given that AIX is different from every other Unix in the 
world. But you have no idea what you're asking for here. If -bexpall 
actually exported every symbol, it would be utterly unusable. As someone 
who has been (suffering through) building dynamic modules on AIX since 
3.2.0, I know what I'm talking about. The fact that the linker hides 
extraneous symbols today merely brings it inline with normal 
expectations / behavior on other platforms. You aren't missing anything 
with the symbols that aren't exported, none of them are user-level. 
E.g., in AIX, an exported function appears two or three times in the 
symbol table. Once for the actual body of the function, and a couple 
more times in the Data or BSS segments, as function pointers that are 
relocated in the calling modules address space. These extra symbols are 
only of importance to the dynamic loader, and it always knows how to 
find them. On older versions of AIX, that actually exported everything 
with -bexpall, you got duplicate symbols and clashes. The only usable 
way to link anything was using an explicit exports file. The current 
behavor of -bexpall is a significant improvement. It ain't broke, leave 
it alone.

--
  -- Howard Chu
  Chief Architect, Symas Corp.  http://www.symas.com
  Director, Highland Sun        http://highlandsun.com/hyc
  OpenLDAP Core Team            http://www.openldap.org/project/