Tools to modify shared libraries

[Dan Nelson]

In the last episode (Jun 17), Marcel Moolenaar said:
> On Tue, Jun 17, 2003 at 01:02:36PM -0400, Alexander Kabaev wrote:
> > On Tue, 17 Jun 2003 09:01:41 -0700
> > Marcel Moolenaar <marcel at xcllnt.net> wrote:
> > > On Tue, Jun 17, 2003 at 08:49:23AM -0700, Joe Kelsey wrote: Linux
> > > uses the same linker (GNU ld). Fixing the linker will have the
> > > same effect on Linux as it will have on FreeBSD and hence will
> > > prevent unnecessary dependencies in Linux libraries to Linux
> > > libraries and thus remove the need to patch ELF files in the long
> > > run.
> > > 
> > 
> > LD putting a library in DT_NEEDED regardless of whether or not
> > library exports any required symbols as long as it appears on
> > command line is a feature, not a bug AFAIK.
> 
> It's a bug because DT_NEEDED serves the purpose of recording library
> dependencies. Any library that does not contribute to symbol
> resolution is by definition not a dependency. Hence, its presence in
> DT_NEEDED only makes the dependency information wrong. Dependency
> information that's wrong is untrustworthy and unreliable and thus
> unusable. Hence, a bug. Immediate consequences of broken dependency
> information is the increased startup time of shared binaries, the
> restriction in use of libraries in cases where they can be used and
> the obstruction in replacing libraries with different implementations
> by possibly causing artificial conflicts due to unnecessary loading
> of libraries.
> 
> Only explicit user directives should allow adding libraries to DT_NEEDED
> regardless of whether there's actually a dependency.

Dependencies can change after a program is linked, though.  How about
the contrived case of a program needing the openpty function, so -lutil
is linked in.  Then 6 months later openpty is moved to libc, making the
dependency on libutil unneeded.  The end result is the same as if a new
program is unnecessarily linked with -lutil, but cannot be "fixed" with
ld because at the time it was linked, the first program actually did
need libutil.

-- 
	Dan Nelson
	dnelson at allantgroup.com