On Aug 2, 2018, at 2:57 AM, Jakub Jelinek <jakub(a)redhat.com>
> On Thu, Aug 02, 2018 at 11:45:00AM +0200, Dominique Martinet wrote:
> Wearing a lib developer hat, I don't see how you can make a .pc that
> doesn't overlink if you provide something a bit entangled with other
> The problem is that if your headers use any sub-lib type you need to add
> that lib in Requires: so that --cflags will pull that lib's include
> path; and that will in turn add that sub-lib to the linked libs even if
> the program likely doesn't care about it (either because they didn't
> even use that part of your lib, or because all uses of that lib will be
> done through your own anyway so it wasn't required in the first place)
Then it is clearly a task for pkg-config (and libtool) to handle it better.
If the --libs it provides contains some mandatory and some optionally needed
libraries, then it should differentiate between them and use
-Wl,--push-state,--as-needed ... -Wl,--pop-state
around those that are optionally needed. If all libraries from those tools
are optional, perhaps it should use it always.
Changing the behavior of say -lpthread on the command line is a bad idea,
many projects really expect it to mean that the mentioned library is linked
in and if it no longer does, it causes silent breakage. Forcing users to do
-Wl,--push-state,--no-as-needed ... -Wl,--pop-state
whenever they really mean to link some library is too hostile.
Maybe pkg-config could learn to push state and use —as-needed? Some
explicit options in gcc and ld like —link-as-needed=libname and
—always-link=libname would be nice, too. It seems that the toolchain
folks (like you) want -lpthread and the like to keep working, and the
package people want a sane default where symbols are made available
but the DT_NEEDED entry is only used if needed.
On the other hand, switching to as-needed linking seems like it's a
step in the right direction in general, but ISTM it would be much
nicer to switch to as-needed direct binding. Do glibc and binutils
even support Solaris-style direct binding yet?