Re: -dlopen self and optimizing away symbols

[Ralf Wildenhues]

* Albert Chin wrote on Thu, Aug 17, 2006 at 07:55:14AM CEST:
> On Thu, Aug 17, 2006 at 07:42:00AM +0200, Ralf Wildenhues wrote:
> 
> > But say, why is -Wl,-E not passed to the link line?  It should be
> > export_dynamic_flag_spec.  And it should have the desired effect:
> > |  -E             Mark all symbols defined by a program for export
> > |                 to shared libraries.  In a +compat mode link, ld
> > |                 marks only those symbols that are actually
> > |                 referenced by a shared library seen at link time.
> > |                 In a +std link, all symbols are exported by
> > |                 default, so -E is not necessary to make symbols
> > |                 visible.  However, it has an additional side
> > |                 effect of identifying all exported symbols as
> > |                 necessary, so that they will not be removed when
> > |                 using dead code elimination (+Oprocelim).
> 
> Because -export-dynamic is not specified.

It should not need to be.  IOW, either the Libtool documentation or the
implementation is broken:
| `-dlopen FILE'
|      Same as `-dlpreopen FILE', if native dlopening is not supported on
|      the host platform (*note Dlopened modules::) or if the program is
|      linked with `-static', `-static-libtool-libs', or `-all-static'.
|      Otherwise, no effect.  If FILE is `self' Libtool will make sure
|      that the program can `dlopen' itself, either by enabling
|      `-export-dynamic' or by falling back to `-dlpreopen self'.

But anyway, if you have other modules, you should specify
-export-dynamic, I think.  At least I can't infer from the above snippet
that `-dlopen self' would be sufficient.  What do you think?

> > Otherwise, -Wl,+Onoprocelim should be the hammer we're looking for, I
> > guess; but that should not even be necessary, given above documentation
> > (from ld(1)).
> 
> Well, export_dynamic_flag_spec isn't even looked at when -dlopen self
> is being handled. Maybe it should and only use the -dlopen self code
> when export_dynamic_flag_spec is empty?

I still need to look at that code.

> If not, looks like we'll need to add +Onoprocelim to the cc
> command-line for HP-UX. What's the best way to do this? A new
> variable?

Let's better not go that route, if we can avoid it.  But yes, then a new
variable would be good.

Cheers,
Ralf