Fwd: Re: Fix for --as-needed

[Thiago Macieira]

Hello,

I've come up with a patch for the problems people were having with 
--as-needed. 

Description of the problem:
- meinproc uses libkio
- libkio uses libkdeui
- meinproc does not use libkdeui directly

When linking meinproc, libtool builds the whole dependency list, so that 
both libkdeui and libkio are listed. In special, note that since libkdeui 
is a dependency of libkio, it comes first.

The linker then links meinproc and, without --as-needed, adds to the 
file's header:
	NEEDED libkdeui.so.4
	NEEDED libkio.so.4

With that, libkdeui is loaded first. When meinproc is used before the 
libraries are installed, libtool relinks the program and add 
$(builddir)/kdeui/.libs to the executable's RPATH. When the program is 
then run, the correct version of libkdeui is found.

What happened when --as-needed got introduced is that, since meinproc 
doesn't use libkdeui directly, the linker does not add the NEEDED symbol 
to the program's header. Therefore, libkdeui is loaded only because 
libkio uses it. 

The problem in that case is that meinproc's RPATH does *not* influence the 
search path for libkdeui. What's worse, libkio.so.4's RPATH cannot be 
overriden.

My solution consists in:
1) adding the --enable-new-dtags flag to the linker, if supported. This 
makes GNU ld emit RUNPATH directives as well as RPATH. The consequence is 
twofold:
	a) RPATH is ignored
	b) RUNPATH is overrideable by LD_LIBRARY_PATH at run-time

2) making libtool's stub script use LD_LIBRARY_PATH as well as relinking. 
(In truth, it probably doesn't have to relink, but I didn't want to make 
such an intrusive change)

These two changes make the correct library be loaded.

3) make the --as-needed flag usage default to yes only if 
--enable-new-dtags is present as well

The patch is attached. Tests here and with a guin...err... "test subject" 
show it solves the problem. It changes kde-common/admin/acinclude.m4.in, 
so I can't commit. Someone please review, test and commit if acceptable.

----------    ----------

Subject: Re: Fix for --as-needed
Date: Dom 21 Nov 2004 20:19
From: Mauricio Bahamonde <elkrammer at vtr.net>
To: Thiago Macieira <thiago at macieira.info>

Thiago,

	Your patch seems to succesfully correct the problem, it worked fine
 here. You should commit.
Thanks a lot for all your help.

Greetings,

--
Mauricio Bahamonde
<elkrammer at vtr.net>

-------------------------------------------------------

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  Thiago Macieira  -  Registered Linux user #65028
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