use of -fno-common on Darwin (was: use of program_name)

[Ralf Wildenhues]

[ This is http://article.gmane.org/gmane.comp.lib.gnulib.bugs/5080
  Please remove bug-gnulib from followups.  Thank you. ]

* Paul Eggert wrote on Fri, Jan 06, 2006 at 12:06:59AM CET:
> address@hidden (Karl Berry) writes:
> 
> > Is it a problem in practice, ie, what are these non-Unix linkers?
> 
> I've run into it on IBM mainframe platforms.  You can run into it even
> with GCC, if you use -fno-common.  Googling a bit reveals that libtool
> 1.5 uses -fno-common on Mac OS X (why, I don't know; see
> <http://www.tug.org/pipermail/tex-k/2003-June/000723.html>).

A couple of observations on this topic: It was introduced here
http://lists.gnu.org/archive/html/libtool-patches/2001-03/msg00053.html
as "necessary to build shared libraries", and this documentation
http://developer.apple.com/documentation/DeveloperTools/Conceptual/MachOTopics/Articles/executing_files.html
mentions this for multi-module shared libraries.

Now we've had this discussion recently
http://lists.gnu.org/archive/html/libtool-patches/2005-12/msg00004.html
to use -single_module by default, which would enable us to kill
-fno-common, except we don't know at compile time whether the user will
specify -multi_module at link time.  In any case changing pic_flag may
break ABI of some libraries (but also enable to build some others, esp.
Fortran ones).

Comments?

(FWIW, if you are interested in my opinion about changing program_name:
don't use the same symbol for a different entity, ever, even less so
when you carry `lib' in your name; and get rid of data objects as soon
as you can.)

Cheers,
Ralf