Re: --as-needed change wrt undefined weak symbols

[Alan Modra <amodra at gmail dot com>]

On Mon, Jan 14, 2013 at 07:30:24PM -0800, H.J. Lu wrote:
> On Mon, Jan 14, 2013 at 6:23 PM, Alan Modra <amodra@gmail.com> wrote:
> > On Mon, Jan 14, 2013 at 07:30:54AM -0800, H.J. Lu wrote:
> >> Given then the behavior of pr14862 is changed,
> >> I don't think it is a good idea.
> >
> > You added a testcase in November last year that (possibly
> > accidentally) depends on the current --as-needed behaviour for weak
> > references.  Now you claim that testcase as a reason to not change
> > --as-needed.  How is that a reasonable objection?
> >
> 
> It shows that this patch will change the behavior of some
> programs.  Adding DT_NEEDED is one thing. Change
> program behavior is another. I don't think we should do it
> by default.

Of course this patch potentially changes program behaviour.  I'd
argue that people using undefined weak symbols are prepared for and
indeed expect such changes in behaviour.  The PR12549 reporter and
another commenter quite reasonably call ld --as-needed buggy in that
we get a library added to DT_NEEDED only to satify an undefined weak
symbol.  If the same program were linked against archive libraries
supplying the same functionality you'd find the undefined weak symbols
would stay undefined.

-- 
Alan Modra
Australia Development Lab, IBM