Change `dynamic-link' to return a global handle when the argument is omitted.

* libguile/dynl.c (sysdep_dynl_link): Handle FNAME == NULL.
  (scm_dynamic_link): Make argument optional.  Adjust body accordingly.

* test-suite/standalone/test-ffi (global, strerror, strlen): New
  bindings.
  Add test for these bindings.

* doc/ref/api-modules.texi (Low level dynamic linking): Update
  description of `dynamic-link'.

doc/ref/api-modules.texi

@@ -1,6 +1,6 @@
 @c -*-texinfo-*-
 @c This is part of the GNU Guile Reference Manual.
-@c Copyright (C)  1996, 1997, 2000, 2001, 2002, 2003, 2004, 2007, 2008, 2009
+@c Copyright (C)  1996, 1997, 2000, 2001, 2002, 2003, 2004, 2007, 2008, 2009, 2010
 @c   Free Software Foundation, Inc.
 @c See the file guile.texi for copying conditions.
 
@@ -1029,7 +1029,7 @@ When using the low level procedures to do your dynamic linking, you have
 complete control over which library is loaded when and what gets done
 with it.
 
-@deffn {Scheme Procedure} dynamic-link library
+@deffn {Scheme Procedure} dynamic-link [library]
 @deffnx {C Function} scm_dynamic_link (library)
 Find the shared library denoted by @var{library} (a string) and link it
 into the running Guile application.  When everything works out, return a
@@ -1040,6 +1040,11 @@ dependent.
 Normally, @var{library} is just the name of some shared library file
 that will be searched for in the places where shared libraries usually
 reside, such as in @file{/usr/lib} and @file{/usr/local/lib}.
+
+When @var{library} is omitted, a @dfn{global symbol handle} is returned.  This
+handle provides access to the symbols available to the program at run-time,
+including those exported by the program itself and the shared libraries already
+loaded.
 @end deffn
 
 @deffn {Scheme Procedure} dynamic-object? obj

libguile/dynl.c

@@ -77,16 +77,23 @@ static void *
 sysdep_dynl_link (const char *fname, const char *subr)
 {
   lt_dlhandle handle;
-  handle = lt_dlopenext (fname);
+
+  if (fname != NULL)
+    handle = lt_dlopenext (fname);
+  else
+    /* Return a handle for the program as a whole.  */
+    handle = lt_dlopen (NULL);
+
   if (NULL == handle)
     {
       SCM fn;
       SCM msg;
 
-      fn = scm_from_locale_string (fname);
+      fn = fname != NULL ? scm_from_locale_string (fname) : SCM_BOOL_F;
       msg = scm_from_locale_string (lt_dlerror ());
       scm_misc_error (subr, "file: ~S, message: ~S", scm_list_2 (fn, msg));
     }
+
   return (void *) handle;
 }
 
@@ -155,7 +162,7 @@ dynl_obj_print (SCM exp, SCM port, scm_print_state *pstate)
 }
 
 
-SCM_DEFINE (scm_dynamic_link, "dynamic-link", 1, 0, 0, 
+SCM_DEFINE (scm_dynamic_link, "dynamic-link", 0, 1, 0,
             (SCM filename),
 	    "Find the shared object (shared library) denoted by\n"
 	    "@var{filename} and link it into the running Guile\n"
@@ -165,18 +172,33 @@ SCM_DEFINE (scm_dynamic_link, "dynamic-link", 1, 0, 0,
 	    "Searching for object files is system dependent.  Normally,\n"
 	    "if @var{filename} does have an explicit directory it will\n"
 	    "be searched for in locations\n"
-	    "such as @file{/usr/lib} and @file{/usr/local/lib}.")
+	    "such as @file{/usr/lib} and @file{/usr/local/lib}.\n\n"
+	    "When @var{filename} is omitted, a @dfn{global symbol handle} is\n"
+	    "returned.  This handle provides access to the symbols\n"
+	    "available to the program at run-time, including those exported\n"
+	    "by the program itself and the shared libraries already loaded.\n")
 #define FUNC_NAME s_scm_dynamic_link
 {
   void *handle;
   char *file;
 
   scm_dynwind_begin (0);
-  file = scm_to_locale_string (filename);
-  scm_dynwind_free (file);
+
+  if (SCM_UNBNDP (filename))
+    file = NULL;
+  else
+    {
+      file = scm_to_locale_string (filename);
+      scm_dynwind_free (file);
+    }
+
   handle = sysdep_dynl_link (file, FUNC_NAME);
   scm_dynwind_end ();
-  SCM_RETURN_NEWSMOB2 (scm_tc16_dynamic_obj, SCM_UNPACK (filename), handle);
+
+  SCM_RETURN_NEWSMOB2 (scm_tc16_dynamic_obj,
+		       SCM_UNBNDP (filename)
+		       ? SCM_UNPACK (SCM_BOOL_F) : SCM_UNPACK (filename),
+		       handle);
 }
 #undef FUNC_NAME
 

test-suite/standalone/test-ffi

@@ -168,6 +168,31 @@ exec guile -q -s "$0" "$@"
               '(0 1 2 3 4 5 6 7 0 0 0 0 0 0 0 0))
       (error "unexpected dest")))
 
+
+;;;
+;;; Global symbols.
+;;;
+
+(use-modules ((rnrs bytevector) #:select (utf8->string)))
+
+(if (defined? 'setlocale)
+    (setlocale LC_ALL "C"))
+
+(define global (dynamic-link))
+
+(define strerror
+  (make-foreign-function '* (dynamic-func "strerror" global)
+                         (list int)))
+
+(define strlen
+  (make-foreign-function size_t (dynamic-func "strlen" global)
+                         (list '*)))
+
+(let* ((ptr (strerror ENOENT))
+       (len (strlen ptr))
+       (bv  (foreign->bytevector ptr 'u8 0 len))
+       (str (utf8->string bv)))
+  (test #t (not (not (string-contains str "file")))))
 
 ;; Local Variables:
 ;; mode: scheme