[PATCH] Allow dlopen self test to work with gcc's -fvisibility=hidden.

[Ralf Wildenhues]

Hello,

What do you think of this patch as a fix for
<http://www.open-mpi.org/community/lists/devel/2009/08/6590.php>?

The critical point here being of course, that if the end-user adds
-fvisibility=hidden to CFLAGS, then the package author would have had to
take care of annotating all needed symbols properly with
  __attribute__((visibility("default")))

I'm not sure what would be a good alternative way for the developer to
specify "you can use hidden visibility with this program".

Other than that, I have no idea when GCC introduced the visibility
attribute (didn't find any changes web sites older than
<http://gcc.gnu.org/gcc-3.1/changes.html>) so the 3.0 border is merely a
guess.  Does anybody know better?

OK to apply (and add Josh to THANKS)?

Thanks,
Ralf

   Allow dlopen self test to work with gcc's -fvisibility=hidden.

   * libltdl/m4/libtool.m4 (_LT_TRY_DLOPEN_SELF): Declare default
   visibility for the symbol we are going to test dlopen (NULL)
   when a GCC version is used that understands the visibility
   attribute, under the assumption that if -fvisibility=hidden
   will be used, the user code will be sufficiently annotated
   for visibility of needed symbols from the main executable.
   * THANKS: Update.
   Report by Josh Hursey against OpenMPI.

diff --git a/libltdl/m4/libtool.m4 b/libltdl/m4/libtool.m4
index bff1218..eebe990 100644
--- a/libltdl/m4/libtool.m4
+++ b/libltdl/m4/libtool.m4
@@ -1624,7 +1624,13 @@ else
 #  endif
 #endif
 
-void fnord() { int i=42;}
+/* When -fvisbility=hidden is used, assume the code has been annotated
+   correspondingly for the symbols needed.  */
+#if defined(__GNUC__) && (__GNUC__ >= 3)
+void fnord () __attribute__((visibility("default")));
+#endif
+
+void fnord () { int i=42;}
 int main ()
 {
   void *self = dlopen (0, LT_DLGLOBAL|LT_DLLAZY_OR_NOW);
@@ -1633,7 +1639,11 @@ int main ()
   if (self)
     {
       if (dlsym (self,"fnord"))       status = $lt_dlno_uscore;
-      else if (dlsym( self,"_fnord")) status = $lt_dlneed_uscore;
+      else
+        {
+         if (dlsym( self,"_fnord"))  status = $lt_dlneed_uscore;
+          else puts (dlerror ());
+       }
       /* dlclose (self); */
     }
   else