[Plplot-devel] Linking solution for static drivers that has just been implemented is discussed. Rapid changes in new configuration scheme should now be over

[Alan W. I. <ir...@be...>]

I have just finished implementing the configuration of static drivers using
autotools.  The tough part was figuring out how I wanted to link everything
together (see below).  The easy part (couple of hours work) was implementing
my linking ideas using autotools.  Just to let you know that the autotools
effort has already more than paid off, that part would have been much more
difficult (= virtually impossible for someone with my skill set)
with the previous autoconf approach.

Here is the linking situation with dynamic drivers.  The arrows indicate the
linking direction that must occur in order to satisfy the undefined symbols
in a given library on the left.  Those symbols are resolved by referring to
the libraries on the right using the usual -l syntax during each library
link step.

(1) libplplottcltk ==> libplplot, libtclmatrix

(2) libtclmatrix ==>

(3) libplplotcxx ==> libplplot

(4) libplplotf77 ==> libplplot

(5) plplotc_module.so ==> libplplot

(6) libplplotjava ==> libplplot  (libplplotjava not done yet)

(7) libplplot ==>

(8) tk_drv.so ==> libplplottcltk

(9) tk_drv.so ==> libplplottcltk

(10) ps_drv.so ==> libplplot

This all works with dynamic drivers because libplplot dlopens the pre-linked
driver tk_drv.so (or tkwin_drv.so).  Also, libplplot is small which is an
advantage since that is the one most applications and libraries link to.
Also note that a tcl application only needs to link to libplplottcltk, and
everything else is automatically linked in as required.

However, with static linking you cannot naively use the same scheme since
you get a circular chain.  All driver codes are now put inside
libplplot.  That satisfies linking requirement for most drivers such as
ps_drv.so, but because of tk and tkwin we have

(7a) libplplot ==> libplplottcltk

which becomes circular with (1) which makes a mess.

Here is the solution I have implemented.  To cut the circular chain, I add
all the libplplottcltk and libtclmatrix objects into the convenience library
that also contains the static driver objects.  The configuration is set up
so that libtool automatically puts all the objects in the convenience
library into libplplot so libplplot ends up being self-contained as before
with no additional linking required to resolve its symbols (other than the
usual additional "driver" links to libraries such as libgd, etc.).  Of
course, libplplot is a little larger in this case, but those who use static
drivers on Unix machines get what they deserve.....

Note all other linking for the static drivers case is done as in the dynamic
drivers case which means that tcl executables can continue to get all their
symbols resolved and drivers found if they simply link to libplplottcltk as
before.  Similarly, normal non-tcl executables like x01c simply need to be
linked to libplplot as before.

I have tested these static drivers, and AFAIK they produce identical results
to the dynamic drivers case.  Dynamic loading under tclsh and wish still
works as before from the user perspective although internally an extra
search was implemented to find the initialization routines in the static
drivers case since those routines appear in a different shared object
location. Also, plrender, and pltcl work fine.

The "works as in the dynamic driver case" also extends to -dev tk not
working in exactly the same way.  Since the library linking of the driver is
quite changed, I believe this problem is something fundamental which has
nothing to do with linking.

I declare the current phase of rapid changes to our configuration as
officially over.  From now on, I expect to see considerably more gradual
changes as the cross-platform tests start rolling in.

Alan

email: ir...@be...
phone: 250-727-2902	FAX: 250-721-7715
snail-mail:
Dr. Alan W. Irwin
Department of Physics and Astronomy,
University of Victoria, P.O. Box 3055,
Victoria, British Columbia, Canada, V8W 3P6
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Linux-powered astrophysics
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