R devel - Feb 2007 - How to customize the list of exported functions in a shared library

Dear R users,

I am writing binding from C library to R.
I use R 2.4.1, windows XP, and MinGW.

commands

set PKG_CPPFLAGS="-I../sources" "-I." 
set PKG_LIBS="-Lc:/mingw/lib" -lfl -liberty
set DEBUG=T

R CMD SHLIB -d --output=Rsnns.dll  [ list of all C sources]

produce the DLL having all defined functions in the export list.
This doesn't satisfy me, as I would like to hide most of defined functions
and export only a couple of functions from the library and interface
functions which I have written in order to call them from R.

The ../sources directory contains also two compiled libraries, created with
ar. 
If I try to link my DLL with them,  that is

R CMD SHLIB -d --output Rsnns.dll Rsnns.c
-Wl,-Lc:/mingw/lib,-lfl,-L../sources,-lkernel,-lfunc

desired functions from the library are not exported, export list gets only
interface functions in the C file.

And GCC seems to ignore the .def file, which I create.

Thank you.
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On Mon, Feb 05, 2007 at 01:28:24AM -0800, Vladimir Eremeev
wrote:
> I am writing binding from C library to R.
> I use R 2.4.1, windows XP, and MinGW.
> R CMD SHLIB -d --output=Rsnns.dll  [ list of all C sources]
> R CMD SHLIB -d --output Rsnns.dll Rsnns.c
-Wl,-Lc:/mingw/lib,-lfl,-L../sources,-lkernel,-lfunc
You should probably also show us the actual compiler/linker commands
that "R CMD SHLIB" is generating, so we can be sure of what's
really
going on.

I'm not sure what you may have to do differently with MinGW on Windows
(what linker does that use anyway?), but for comparison, here's how I
do it for R 2.2.1, on Linux (Ubuntu Dapper 6.06), with gcc 4.0.3, and
Gnu ld 2.16.91:

For my own custom R package's C code, my Makefile says:

  OBJ = ../foo.o $(patsubst %.c,%.o,$(wildcard ../source/[a-z]*.c))
  $(OBJ): %.o:  %.c $(HDRS)
  R.so: $(OBJ) Makevars vis.map
          R CMD SHLIB -o my_pkg_name_R.so $(OBJ)

My Makevars includes this:

  PKG_LIBS = -Wl,--version-script=vis.map

And when I build my R package, the R.so make target above generates
this link command:

  gcc -shared -o my_pkg_name_R.so [lots of *.o filenames here]
-Wl,--version-script=vis.map -L/usr/lib/R/lib -lR

My vis.map file, which uses Gnu ld syntax, looks like this:

  {
     global: my_pkg_*;
     local:*;
  };

That works, my shared library exports ONLY the symbols starting with
"my_pkg_", everything else remains private.

It's the "--version-script" linker option doing the magic.  Even
with
Gnu ld, there are definitely other ways to control symbol visibility,
but that one seemed most convenient in my case.

-- 
Andrew Piskorski <atp at piskorski.com>
http://www.piskorski.com/