[Rd] Problem with dyn.load'ed code

[Matt Calder]

Andrew,
	Thanks! The version script worked like a charm. Specifically I now
build using:

g++ -shared -Wl,--version-script=ver.map to_dyn_load.cc -o to_dyn_load.so -larpack

where ver.map is the file:

{
     global: R_func_*;
     local:*;
};

and any function I want exported to R is named R_func_*. This is going
to be my new SOP. 
	Thanks again Andrew, and also Simon. I greatly appreciate you taking
your time to solve this problem for me.

	Matt

	
On Mon, 2007-12-31 at 15:30 -0500, Andrew Piskorski wrote:
> On Sun, Dec 30, 2007 at 10:43:50PM -0500, Matt Calder wrote:
> > Simon,
> > 	Thanks for the reply. Indeed, declaring the function static fixes the
> > example. Unfortunately, the real problem that gave rise to the example
> > arises in a large Fortran library that is not under my control (ARPACK).
> > The author is providing BLAS and LAPACK functionality intentionally.
> > That may or may not be good practice, but it is a given in this case.
> 
> Ok, so R is calling its one "dnrm2_" function, let's call this "A",
> while ARPACK defines a second, different "dnrm2_", which we'll call
> "B".  You want to call function A from your own C code, while R keeps
> calling function A as before without any change or interference.  And
> of course, A and B are two C-coded functions with different behaviors
> but the exact same name.  You can make that work, it just requires
> some tricks.
> 
> > 	I still feel like the linker ought to be able to solve this problem for
> > me. My impression was that the static keyword passed to the linker
> 
> It can, you just need to tell it exactly what you want.  I assume you
> are building your own custom C code into a shared library, which you
> then load into R.
> 
> Thus, one solution is to statically link the ARPACK library into your
> own shared library, and then carefully tell the linker which symbols
> to export and which to keep private inside your shared library.  As
> long as the symbol ARPACK's "B" dnrm2_ function is kept private inside
> your own shared library (not exported), R will never see it and will
> happily keep using dnrm2_ "A" as before.
> 
> That's how I've solved this sort of name collision problem in the
> past.  In your "src/Makevars", you may want something like to this:
> 
>   PKG_LIBS = -Wl,--version-script=vis.map -Wl,-Bstatic -L/usr/local/lib/ARPACK -lARPACK -Wl,-Bdynamic
> 
> You may also need a PG_PKG_LIBS with the same stuff, but I don't
> remember why.  The '--version-script=' and related matters were also
> disccussed here back in February:
> 
>   https://stat.ethz.ch/pipermail/r-devel/2007-February/044531.html
>