[Bug other/15000] Support setting the default symbol visibility for ELF

[bryner at brianryner dot com]

------- Additional Comments From bryner at brianryner dot com  2004-04-19 15:01 -------
(In reply to comment #4)
> So I really think we need to
> > provide an easy way for the user to ensure that declarations of functions in
> > external DSOs are treated as default visibility.
> 

Local binding is not the same as hidden visibility.  Your patch changes the
default visibility for declarations.  Consider this simple test:

foo.c:
#include <stdlib.h>

int gtk_init (int *argc, char ***argv) __attribute__ ((visibility ("hidden")));

void foo ()
{
  gtk_init (NULL, NULL);
}

gcc -shared -fPIC -o libfoo.so foo.c `pkg-config --libs gtk+-2.0`

readelf -d libfoo.so|grep TEXTREL
 0x00000016 (TEXTREL)                    0x0

I expect if you run readelf -d on the library you compiled with this patch you
will notice the TEXTREL there as well.  If you read drepper's paper you'll see
that's something we want to avoid.  And to avoid that, we have to distinguish
between a declaration of a function that will be defined inside the same DSO as
the caller, and one that will be defined in a DSO that is linked against.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15000