R: hide unexported functions

[gaborcsardi]

From @gaborcsardi on October 7, 2013 16:26

To avoid name clashes with other packages. See http://cran.us.r-project.org/doc/manuals/r-devel/R-exts.html#Controlling-visibility

Essentially, we need to add

PKG_CFLAGS=$(C_VISIBILITY)
PKG_FFLAGS=$(F77_VISIBILITY)

to Makevars, and then prefix each entry point with attribute_visible, e.g (from the docs):

void attribute_visible R_init_stats(DllInfo *dll)
...

Copied from original issue: igraph/igraph#525

[ntamas]

I'm trying to address this in cfc46d9

[szhorvat]

Doesn't every function that is directly called by R need to be made visible as well? I.e., the visibility spec needs to be added by stimulus?

[ntamas]

No, only the init function needs to be visible. The remaining functions are all referred to by the CallEntries table that you can find in init.c (also mostly autogenerated). You only need to get a handle on R_init_igraph() and call it; the function will register everything else.

[szhorvat]

This is not working properly on macOS. The output of nm -gU igraph.so contains all symbols.

[ntamas]

This is because the R toolchain does not support it yet on Windows or macOS; see here:

Header R_ext/Visibility.h has some definitions for controlling the visibility of entry points. These are only effective when ‘HAVE_VISIBILITY_ATTRIBUTE’ is defined – this is checked when R is configured and recorded in header Rconfig.h (included by R_ext/Visibility.h). It is often defined on modern Unix-alikes with a recent compiler 159, but not supported on macOS nor Windows.

Also:

The visibility mechanism is not available on Windows, but there is an equally effective way to control which entry points are visible, by supplying a definitions file pkgnme/src/pkgname-win.def: only entry points listed in that file will be visible.

I'm experimenting with this but no promises for the next version yet.

[szhorvat]

For reference, here is Visibility.h.

It's strange that they state that it is not supported on macOS because these attributes definitely do work there and we do use them in the C core (granted, CMake checks for them, but they must have been working for quite a long time on macOS now). What we do in the C core is build with -fvisibility=hidden and then selectively unhide symbols using __attribute__ ((visibility ("default")))

[szhorvat]

I checked my local Rconfig.h and it does not define HAVE_VISIBILITY_ATTRIBUTE. If R doesn't support this properly, I think we don't need to bother either, and this can be closed.

[ntamas]

We've done what we could so if R gains support for this on macOS, it will automatically start working in igraph.