improve handling of API calls provided by loaded modules through use of some GCC features; this makes app_stack's usage of AGI APIs even cleaner, and will allow it to work 'as expected' either with or without res_agi being loaded

reviewed at http://reviewboard.digium.com/r/62



git-svn-id: http://svn.digium.com/svn/asterisk/trunk@159631 f38db490-d61c-443f-a65b-d21fe96a405b

9 files changed, 810 insertions, 38 deletions

diff --git a/apps/app_stack.c b/apps/app_stack.c
index cebe161af..0a911e5ec 100644
--- a/apps/app_stack.c
+++ b/apps/app_stack.c
@@ -38,9 +38,6 @@ ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
 #include "asterisk/app.h"
 #include "asterisk/manager.h"
 #include "asterisk/channel.h"
-
-/* usage of AGI is optional, so indicate that to the header file */
-#define ASTERISK_AGI_OPTIONAL
 #include "asterisk/agi.h"
 
 /*** DOCUMENTATION
@@ -576,9 +573,7 @@ static int unload_module(void)
 {
 	struct ast_context *con;
 
-	if (ast_agi_unregister) {
-		ast_agi_unregister(ast_module_info->self, &gosub_agi_command);
-
+	if (ast_agi_unregister(ast_module_info->self, &gosub_agi_command) == 1) {
 		if ((con = ast_context_find("app_stack_gosub_virtual_context"))) {
 			ast_context_remove_extension2(con, "s", 1, NULL, 0);
 			ast_context_destroy(con, "app_stack"); /* leave nothing behind */
@@ -598,19 +593,13 @@ static int load_module(void)
 {
 	struct ast_context *con;
 
-	/* usage of AGI is optional, so check to see if the ast_agi_register()
-	   function is available; if so, use it.
-	*/
-	if (ast_agi_register) {
-		con = ast_context_find_or_create(NULL, NULL, "app_stack_gosub_virtual_context", "app_stack");
-		if (!con) {
+	if (ast_agi_register(ast_module_info->self, &gosub_agi_command) == 1) {
+		if (!(con = ast_context_find_or_create(NULL, NULL, "app_stack_gosub_virtual_context", "app_stack"))) {
 			ast_log(LOG_ERROR, "Virtual context 'app_stack_gosub_virtual_context' does not exist and unable to create\n");
 			return AST_MODULE_LOAD_DECLINE;
 		} else {
 			ast_add_extension2(con, 1, "s", 1, NULL, NULL, "KeepAlive", ast_strdup(""), ast_free_ptr, "app_stack");
 		}
-
-		ast_agi_register(ast_module_info->self, &gosub_agi_command);
 	}
 
 	ast_register_application_xml(app_pop, pop_exec);
diff --git a/autoconf/ast_gcc_attribute.m4 b/autoconf/ast_gcc_attribute.m4
index 167bb4e79..c4488454d 100644
--- a/autoconf/ast_gcc_attribute.m4
+++ b/autoconf/ast_gcc_attribute.m4
@@ -1,17 +1,31 @@
 # Helper function to check for gcc attributes.
-# AST_GCC_ATTRIBUTE([attribute name])
+# AST_GCC_ATTRIBUTE([attribute name], [attribute syntax])
 
 AC_DEFUN([AST_GCC_ATTRIBUTE],
 [
 AC_MSG_CHECKING(for compiler 'attribute $1' support)
 saved_CFLAGS="$CFLAGS"
 CFLAGS="$CFLAGS -Werror"
+
+if test "x$2" = "x"
+then
 AC_COMPILE_IFELSE(
 	AC_LANG_PROGRAM([void __attribute__(($1)) *test(void *muffin, ...) {}],
 			[]),
 	AC_MSG_RESULT(yes)
 	AC_DEFINE_UNQUOTED([HAVE_ATTRIBUTE_$1], 1, [Define to 1 if your GCC C compiler supports the '$1' attribute.]),
-	AC_MSG_RESULT(no))
-]
+	AC_MSG_RESULT(no)
+)
+else
+AC_COMPILE_IFELSE(
+	AC_LANG_PROGRAM([void __attribute__(($2)) *test(void *muffin, ...) {}],
+			[]),
+	AC_MSG_RESULT(yes)
+	AC_DEFINE_UNQUOTED([HAVE_ATTRIBUTE_$1], 1, [Define to 1 if your GCC C compiler supports the '$1' attribute.]),
+	AC_MSG_RESULT(no)
+)
+fi
+
 CFLAGS="$saved_CFLAGS"
+]
 )
diff --git a/configure b/configure
index e78c69730..de4cc7c00 100755
--- a/configure
+++ b/configure
@@ -17093,6 +17093,9 @@ rm -f core conftest.err conftest.$ac_objext conftest_ipa8_conftest.oo \
 echo $ECHO_N "checking for compiler 'attribute pure' support... $ECHO_C" >&6; }
 saved_CFLAGS="$CFLAGS"
 CFLAGS="$CFLAGS -Werror"
+
+if test "x" = "x"
+then
 cat >conftest.$ac_ext <<_ACEOF
 /* confdefs.h.  */
 _ACEOF
@@ -17138,17 +17141,73 @@ sed 's/^/| /' conftest.$ac_ext >&5
 
 	{ echo "$as_me:$LINENO: result: no" >&5
 echo "${ECHO_T}no" >&6; }
+
+fi
+
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+else
+cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+void __attribute__(()) *test(void *muffin, ...) {}
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext
+if { (ac_try="$ac_compile"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval "echo \"\$as_me:$LINENO: $ac_try_echo\"") >&5
+  (eval "$ac_compile") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest.$ac_objext; then
+  { echo "$as_me:$LINENO: result: yes" >&5
+echo "${ECHO_T}yes" >&6; }
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_ATTRIBUTE_pure 1
+_ACEOF
+
+else
+  echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	{ echo "$as_me:$LINENO: result: no" >&5
+echo "${ECHO_T}no" >&6; }
+
 fi
 
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+fi
 
 CFLAGS="$saved_CFLAGS"
 
 
+
 { echo "$as_me:$LINENO: checking for compiler 'attribute malloc' support" >&5
 echo $ECHO_N "checking for compiler 'attribute malloc' support... $ECHO_C" >&6; }
 saved_CFLAGS="$CFLAGS"
 CFLAGS="$CFLAGS -Werror"
+
+if test "x" = "x"
+then
 cat >conftest.$ac_ext <<_ACEOF
 /* confdefs.h.  */
 _ACEOF
@@ -17194,17 +17253,73 @@ sed 's/^/| /' conftest.$ac_ext >&5
 
 	{ echo "$as_me:$LINENO: result: no" >&5
 echo "${ECHO_T}no" >&6; }
+
+fi
+
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+else
+cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+void __attribute__(()) *test(void *muffin, ...) {}
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext
+if { (ac_try="$ac_compile"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval "echo \"\$as_me:$LINENO: $ac_try_echo\"") >&5
+  (eval "$ac_compile") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest.$ac_objext; then
+  { echo "$as_me:$LINENO: result: yes" >&5
+echo "${ECHO_T}yes" >&6; }
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_ATTRIBUTE_malloc 1
+_ACEOF
+
+else
+  echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	{ echo "$as_me:$LINENO: result: no" >&5
+echo "${ECHO_T}no" >&6; }
+
 fi
 
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+fi
 
 CFLAGS="$saved_CFLAGS"
 
 
+
 { echo "$as_me:$LINENO: checking for compiler 'attribute const' support" >&5
 echo $ECHO_N "checking for compiler 'attribute const' support... $ECHO_C" >&6; }
 saved_CFLAGS="$CFLAGS"
 CFLAGS="$CFLAGS -Werror"
+
+if test "x" = "x"
+then
 cat >conftest.$ac_ext <<_ACEOF
 /* confdefs.h.  */
 _ACEOF
@@ -17250,17 +17365,73 @@ sed 's/^/| /' conftest.$ac_ext >&5
 
 	{ echo "$as_me:$LINENO: result: no" >&5
 echo "${ECHO_T}no" >&6; }
+
+fi
+
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+else
+cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+void __attribute__(()) *test(void *muffin, ...) {}
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext
+if { (ac_try="$ac_compile"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval "echo \"\$as_me:$LINENO: $ac_try_echo\"") >&5
+  (eval "$ac_compile") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest.$ac_objext; then
+  { echo "$as_me:$LINENO: result: yes" >&5
+echo "${ECHO_T}yes" >&6; }
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_ATTRIBUTE_const 1
+_ACEOF
+
+else
+  echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	{ echo "$as_me:$LINENO: result: no" >&5
+echo "${ECHO_T}no" >&6; }
+
 fi
 
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+fi
 
 CFLAGS="$saved_CFLAGS"
 
 
+
 { echo "$as_me:$LINENO: checking for compiler 'attribute unused' support" >&5
 echo $ECHO_N "checking for compiler 'attribute unused' support... $ECHO_C" >&6; }
 saved_CFLAGS="$CFLAGS"
 CFLAGS="$CFLAGS -Werror"
+
+if test "x" = "x"
+then
 cat >conftest.$ac_ext <<_ACEOF
 /* confdefs.h.  */
 _ACEOF
@@ -17306,17 +17477,73 @@ sed 's/^/| /' conftest.$ac_ext >&5
 
 	{ echo "$as_me:$LINENO: result: no" >&5
 echo "${ECHO_T}no" >&6; }
+
+fi
+
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+else
+cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+void __attribute__(()) *test(void *muffin, ...) {}
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext
+if { (ac_try="$ac_compile"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval "echo \"\$as_me:$LINENO: $ac_try_echo\"") >&5
+  (eval "$ac_compile") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest.$ac_objext; then
+  { echo "$as_me:$LINENO: result: yes" >&5
+echo "${ECHO_T}yes" >&6; }
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_ATTRIBUTE_unused 1
+_ACEOF
+
+else
+  echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	{ echo "$as_me:$LINENO: result: no" >&5
+echo "${ECHO_T}no" >&6; }
+
 fi
 
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+fi
 
 CFLAGS="$saved_CFLAGS"
 
 
+
 { echo "$as_me:$LINENO: checking for compiler 'attribute always_inline' support" >&5
 echo $ECHO_N "checking for compiler 'attribute always_inline' support... $ECHO_C" >&6; }
 saved_CFLAGS="$CFLAGS"
 CFLAGS="$CFLAGS -Werror"
+
+if test "x" = "x"
+then
 cat >conftest.$ac_ext <<_ACEOF
 /* confdefs.h.  */
 _ACEOF
@@ -17362,17 +17589,73 @@ sed 's/^/| /' conftest.$ac_ext >&5
 
 	{ echo "$as_me:$LINENO: result: no" >&5
 echo "${ECHO_T}no" >&6; }
+
+fi
+
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+else
+cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+void __attribute__(()) *test(void *muffin, ...) {}
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext
+if { (ac_try="$ac_compile"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval "echo \"\$as_me:$LINENO: $ac_try_echo\"") >&5
+  (eval "$ac_compile") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest.$ac_objext; then
+  { echo "$as_me:$LINENO: result: yes" >&5
+echo "${ECHO_T}yes" >&6; }
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_ATTRIBUTE_always_inline 1
+_ACEOF
+
+else
+  echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	{ echo "$as_me:$LINENO: result: no" >&5
+echo "${ECHO_T}no" >&6; }
+
 fi
 
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+fi
 
 CFLAGS="$saved_CFLAGS"
 
 
+
 { echo "$as_me:$LINENO: checking for compiler 'attribute deprecated' support" >&5
 echo $ECHO_N "checking for compiler 'attribute deprecated' support... $ECHO_C" >&6; }
 saved_CFLAGS="$CFLAGS"
 CFLAGS="$CFLAGS -Werror"
+
+if test "x" = "x"
+then
 cat >conftest.$ac_ext <<_ACEOF
 /* confdefs.h.  */
 _ACEOF
@@ -17418,17 +17701,73 @@ sed 's/^/| /' conftest.$ac_ext >&5
 
 	{ echo "$as_me:$LINENO: result: no" >&5
 echo "${ECHO_T}no" >&6; }
+
 fi
 
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+else
+cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+void __attribute__(()) *test(void *muffin, ...) {}
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext
+if { (ac_try="$ac_compile"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval "echo \"\$as_me:$LINENO: $ac_try_echo\"") >&5
+  (eval "$ac_compile") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest.$ac_objext; then
+  { echo "$as_me:$LINENO: result: yes" >&5
+echo "${ECHO_T}yes" >&6; }
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_ATTRIBUTE_deprecated 1
+_ACEOF
+
+else
+  echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	{ echo "$as_me:$LINENO: result: no" >&5
+echo "${ECHO_T}no" >&6; }
+
+fi
+
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+fi
 
 CFLAGS="$saved_CFLAGS"
 
 
+
 { echo "$as_me:$LINENO: checking for compiler 'attribute sentinel' support" >&5
 echo $ECHO_N "checking for compiler 'attribute sentinel' support... $ECHO_C" >&6; }
 saved_CFLAGS="$CFLAGS"
 CFLAGS="$CFLAGS -Werror"
+
+if test "x" = "x"
+then
 cat >conftest.$ac_ext <<_ACEOF
 /* confdefs.h.  */
 _ACEOF
@@ -17474,17 +17813,73 @@ sed 's/^/| /' conftest.$ac_ext >&5
 
 	{ echo "$as_me:$LINENO: result: no" >&5
 echo "${ECHO_T}no" >&6; }
+
+fi
+
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+else
+cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+void __attribute__(()) *test(void *muffin, ...) {}
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext
+if { (ac_try="$ac_compile"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval "echo \"\$as_me:$LINENO: $ac_try_echo\"") >&5
+  (eval "$ac_compile") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest.$ac_objext; then
+  { echo "$as_me:$LINENO: result: yes" >&5
+echo "${ECHO_T}yes" >&6; }
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_ATTRIBUTE_sentinel 1
+_ACEOF
+
+else
+  echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	{ echo "$as_me:$LINENO: result: no" >&5
+echo "${ECHO_T}no" >&6; }
+
 fi
 
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+fi
 
 CFLAGS="$saved_CFLAGS"
 
 
+
 { echo "$as_me:$LINENO: checking for compiler 'attribute warn_unused_result' support" >&5
 echo $ECHO_N "checking for compiler 'attribute warn_unused_result' support... $ECHO_C" >&6; }
 saved_CFLAGS="$CFLAGS"
 CFLAGS="$CFLAGS -Werror"
+
+if test "x" = "x"
+then
 cat >conftest.$ac_ext <<_ACEOF
 /* confdefs.h.  */
 _ACEOF
@@ -17530,17 +17925,73 @@ sed 's/^/| /' conftest.$ac_ext >&5
 
 	{ echo "$as_me:$LINENO: result: no" >&5
 echo "${ECHO_T}no" >&6; }
+
+fi
+
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+else
+cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+void __attribute__(()) *test(void *muffin, ...) {}
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext
+if { (ac_try="$ac_compile"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval "echo \"\$as_me:$LINENO: $ac_try_echo\"") >&5
+  (eval "$ac_compile") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest.$ac_objext; then
+  { echo "$as_me:$LINENO: result: yes" >&5
+echo "${ECHO_T}yes" >&6; }
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_ATTRIBUTE_warn_unused_result 1
+_ACEOF
+
+else
+  echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	{ echo "$as_me:$LINENO: result: no" >&5
+echo "${ECHO_T}no" >&6; }
+
 fi
 
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+fi
 
 CFLAGS="$saved_CFLAGS"
 
 
+
 { echo "$as_me:$LINENO: checking for compiler 'attribute weak' support" >&5
 echo $ECHO_N "checking for compiler 'attribute weak' support... $ECHO_C" >&6; }
 saved_CFLAGS="$CFLAGS"
 CFLAGS="$CFLAGS -Werror"
+
+if test "x" = "x"
+then
 cat >conftest.$ac_ext <<_ACEOF
 /* confdefs.h.  */
 _ACEOF
@@ -17586,13 +18037,178 @@ sed 's/^/| /' conftest.$ac_ext >&5
 
 	{ echo "$as_me:$LINENO: result: no" >&5
 echo "${ECHO_T}no" >&6; }
+
 fi
 
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+else
+cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+void __attribute__(()) *test(void *muffin, ...) {}
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext
+if { (ac_try="$ac_compile"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval "echo \"\$as_me:$LINENO: $ac_try_echo\"") >&5
+  (eval "$ac_compile") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest.$ac_objext; then
+  { echo "$as_me:$LINENO: result: yes" >&5
+echo "${ECHO_T}yes" >&6; }
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_ATTRIBUTE_weak 1
+_ACEOF
+
+else
+  echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	{ echo "$as_me:$LINENO: result: no" >&5
+echo "${ECHO_T}no" >&6; }
+
+fi
+
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+fi
 
 CFLAGS="$saved_CFLAGS"
 
 
+
+{ echo "$as_me:$LINENO: checking for compiler 'attribute alias' support" >&5
+echo $ECHO_N "checking for compiler 'attribute alias' support... $ECHO_C" >&6; }
+saved_CFLAGS="$CFLAGS"
+CFLAGS="$CFLAGS -Werror"
+
+if test "xalias("foo")" = "x"
+then
+cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+void __attribute__((alias)) *test(void *muffin, ...) {}
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext
+if { (ac_try="$ac_compile"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval "echo \"\$as_me:$LINENO: $ac_try_echo\"") >&5
+  (eval "$ac_compile") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest.$ac_objext; then
+  { echo "$as_me:$LINENO: result: yes" >&5
+echo "${ECHO_T}yes" >&6; }
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_ATTRIBUTE_alias 1
+_ACEOF
+
+else
+  echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	{ echo "$as_me:$LINENO: result: no" >&5
+echo "${ECHO_T}no" >&6; }
+
+fi
+
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+else
+cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+void __attribute__((alias("foo"))) *test(void *muffin, ...) {}
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext
+if { (ac_try="$ac_compile"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval "echo \"\$as_me:$LINENO: $ac_try_echo\"") >&5
+  (eval "$ac_compile") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest.$ac_objext; then
+  { echo "$as_me:$LINENO: result: yes" >&5
+echo "${ECHO_T}yes" >&6; }
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_ATTRIBUTE_alias 1
+_ACEOF
+
+else
+  echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	{ echo "$as_me:$LINENO: result: no" >&5
+echo "${ECHO_T}no" >&6; }
+
+fi
+
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+fi
+
+CFLAGS="$saved_CFLAGS"
+
+
+
 { echo "$as_me:$LINENO: checking for -ffunction-sections support" >&5
 echo $ECHO_N "checking for -ffunction-sections support... $ECHO_C" >&6; }
 saved_CFLAGS="${CFLAGS}"
diff --git a/configure.ac b/configure.ac
index 37b192284..30113c154 100644
--- a/configure.ac
+++ b/configure.ac
@@ -480,6 +480,7 @@ AST_GCC_ATTRIBUTE(deprecated)
 AST_GCC_ATTRIBUTE(sentinel)
 AST_GCC_ATTRIBUTE(warn_unused_result)
 AST_GCC_ATTRIBUTE(weak)
+AST_GCC_ATTRIBUTE(alias, [alias("foo")])
 
 AC_MSG_CHECKING(for -ffunction-sections support)
 saved_CFLAGS="${CFLAGS}"
diff --git a/contrib/asterisk-ng-doxygen b/contrib/asterisk-ng-doxygen
index ef96f0d36..0c34ba14a 100644
--- a/contrib/asterisk-ng-doxygen
+++ b/contrib/asterisk-ng-doxygen
@@ -1098,7 +1098,9 @@ EXPAND_AS_DEFINED      = \
 			AST_RWDLLIST_HEAD_STATIC \
 			AST_DLLIST_ENTRY \
 			AST_RWDLLIST_ENTRY \
-			AST_CLI_DEFINE
+			AST_CLI_DEFINE \
+			AST_OPTIONAL_API \
+			AST_OPTIONAL_API_ATTR
 
 # If the SKIP_FUNCTION_MACROS tag is set to YES (the default) then 
 # doxygen's preprocessor will remove all function-like macros that are alone 
diff --git a/include/asterisk/agi.h b/include/asterisk/agi.h
index c92ab3c66..9c7759576 100644
--- a/include/asterisk/agi.h
+++ b/include/asterisk/agi.h
@@ -28,6 +28,7 @@ extern "C" {
 #endif
 
 #include "asterisk/cli.h"
+#include "asterisk/optional_api.h"
 
 typedef struct agi_state {
 	int fd;		        /*!< FD for general output */
@@ -60,26 +61,31 @@ typedef struct agi_command {
 	AST_LIST_ENTRY(agi_command) list;
 } agi_command;
 
-#if defined(ASTERISK_AGI_OPTIONAL)
-#define AGI_WEAK attribute_weak
-#else
-#define AGI_WEAK
-#endif
+/*!
+ * \brief
+ *
+ * Registers an AGI command.
+ *
+ * \param mod Pointer to the module_info structure for the module that is registering the command
+ * \param cmd Pointer to the descriptor for the command
+ * \return 1 on success, 0 if the command is already registered
+ *
+ */
+AST_OPTIONAL_API(int, ast_agi_register, (struct ast_module *mod, agi_command *cmd),
+		 { return AST_OPTIONAL_API_UNAVAILABLE; });
 
 /*!
  * \brief
  *
- * Sends a string of text to an application connected via AGI.
+ * Unregisters an AGI command.
  *
- * \param fd The file descriptor for the AGI session (from struct agi_state)
- * \param chan Pointer to an associated Asterisk channel, if any
- * \param fmt printf-style format string
- * \return 0 for success, -1 for failure
+ * \param mod Pointer to the module_info structure for the module that is unregistering the command
+ * \param cmd Pointer to the descriptor for the command
+ * \return 1 on success, 0 if the command was not already registered
  *
  */
-int AGI_WEAK ast_agi_send(int fd, struct ast_channel *chan, char *fmt, ...) __attribute__((format(printf, 3, 4)));
-int AGI_WEAK ast_agi_register(struct ast_module *mod, agi_command *cmd);
-int AGI_WEAK ast_agi_unregister(struct ast_module *mod, agi_command *cmd);
+AST_OPTIONAL_API(int, ast_agi_unregister, (struct ast_module *mod, agi_command *cmd),
+		 { return AST_OPTIONAL_API_UNAVAILABLE; });
 
 /*!
  * \brief
@@ -88,15 +94,16 @@ int AGI_WEAK ast_agi_unregister(struct ast_module *mod, agi_command *cmd);
  * entries.
  *
  * \param mod Pointer to the module_info structure for the module that is registering the commands
- * \param cmd Pointer to the first entry in the array of commands
+ * \param cmd Pointer to the first entry in the array of command descriptors
  * \param len Length of the array (use the ARRAY_LEN macro to determine this easily)
- * \return 0 on success, -1 on failure
+ * \return 0 on success, -1 on failure, AST_OPTIONAL_API_UNAVAILABLE if res_agi is not loaded
  *
  * \note If any command fails to register, all commands previously registered during the operation
  * will be unregistered. In other words, this function registers all the provided commands, or none
  * of them.
  */
-int AGI_WEAK ast_agi_register_multiple(struct ast_module *mod, struct agi_command *cmd, unsigned int len);
+AST_OPTIONAL_API(int, ast_agi_register_multiple, (struct ast_module *mod, struct agi_command *cmd, unsigned int len),
+		 { return AST_OPTIONAL_API_UNAVAILABLE; });
 
 /*!
  * \brief
@@ -105,14 +112,29 @@ int AGI_WEAK ast_agi_register_multiple(struct ast_module *mod, struct agi_comman
  * entries.
  *
  * \param mod Pointer to the module_info structure for the module that is unregistering the commands
- * \param cmd Pointer to the first entry in the array of commands
+ * \param cmd Pointer to the first entry in the array of command descriptors
  * \param len Length of the array (use the ARRAY_LEN macro to determine this easily)
- * \return 0 on success, -1 on failure
+ * \return 0 on success, -1 on failure, AST_OPTIONAL_API_UNAVAILABLE if res_agi is not loaded
  *
  * \note If any command fails to unregister, this function will continue to unregister the
  * remaining commands in the array; it will not reregister the already-unregistered commands.
  */
-int AGI_WEAK ast_agi_unregister_multiple(struct ast_module *mod, struct agi_command *cmd, unsigned int len);
+AST_OPTIONAL_API(int, ast_agi_unregister_multiple, (struct ast_module *mod, struct agi_command *cmd, unsigned int len),
+		 { return AST_OPTIONAL_API_UNAVAILABLE; });
+
+/*!
+ * \brief
+ *
+ * Sends a string of text to an application connected via AGI.
+ *
+ * \param fd The file descriptor for the AGI session (from struct agi_state)
+ * \param chan Pointer to an associated Asterisk channel, if any
+ * \param fmt printf-style format string
+ * \return 0 for success, -1 for failure, AST_OPTIONAL_API_UNAVAILABLE if res_agi is not loaded
+ *
+ */
+AST_OPTIONAL_API_ATTR(int, format(printf, 3, 4), ast_agi_send, (int fd, struct ast_channel *chan, char *fmt, ...),
+		      { return AST_OPTIONAL_API_UNAVAILABLE; });
 
 #if defined(__cplusplus) || defined(c_plusplus)
 }
diff --git a/include/asterisk/autoconfig.h.in b/include/asterisk/autoconfig.h.in
index 0f032b5ba..d6b3f8971 100644
--- a/include/asterisk/autoconfig.h.in
+++ b/include/asterisk/autoconfig.h.in
@@ -91,6 +91,9 @@
 /* Define to 1 if you have the `atexit' function. */
 #undef HAVE_ATEXIT
 
+/* Define to 1 if your GCC C compiler supports the 'alias' attribute. */
+#undef HAVE_ATTRIBUTE_alias
+
 /* Define to 1 if your GCC C compiler supports the 'always_inline' attribute.
    */
 #undef HAVE_ATTRIBUTE_always_inline
diff --git a/include/asterisk/optional_api.h b/include/asterisk/optional_api.h
new file mode 100644
index 000000000..ad7169cc4
--- /dev/null
+++ b/include/asterisk/optional_api.h
@@ -0,0 +1,123 @@
+/*
+ * Asterisk -- An open source telephony toolkit.
+ *
+ * Copyright (C) 2008, Digium, Inc.
+ *
+ * Kevin P. Fleming <kpfleming@digium.com>
+ *
+ * See http://www.asterisk.org for more information about
+ * the Asterisk project. Please do not directly contact
+ * any of the maintainers of this project for assistance;
+ * the project provides a web site, mailing lists and IRC
+ * channels for your use.
+ *
+ * This program is free software, distributed under the terms of
+ * the GNU General Public License Version 2. See the LICENSE file
+ * at the top of the source tree.
+ */
+
+#ifndef __ASTERISK_OPTIONAL_API_H
+#define __ASTERISK_OPTIONAL_API_H
+
+/*!
+ * \file
+ * \brief Optional API function macros
+ *
+ * Some Asterisk API functions are provided by loadable modules, thus,
+ * they may or may not be available at run time depending on whether the
+ * providing module has been loaded or not. In addition, there are some
+ * modules that are consumers of these APIs that *optionally* use them; they
+ * have only a part of their functionality dependent on the APIs, and can
+ * provide the remainder even if the APIs are not available.
+ *
+ * To accomodate this situation, the AST_OPTIONAL_API macro allows an API
+ * function to be declared in a special way, if Asterisk being built on a
+ * platform that supports the GCC 'weak' and 'alias' attributes. If so,
+ * the API function is actually a weak symbol, which means if the provider
+ * of the API is not loaded, the symbol can still be referenced (unlike a
+ * strong symbol, which would cause an immediate fault if not defined when
+ * referenced), but it will return NULL signifying the linker/loader was
+ * not able to resolve the symbol. In addition, the macro defines a hidden
+ * 'stub' version of the API call, using a provided function body, and uses
+ * the alias attribute to make the API function symbol actually resolve to
+ * that hidden stub, but only when the *real* provider of the symbol has
+ * not been found.
+ *
+ * An example can be found in agi.h:
+ *
+ * \code
+ * AST_OPTIONAL_API(int, ast_agi_register, (struct ast_module *mod, agi_command *cmd),
+ *                  { return AST_OPTIONAL_API_UNAVAILABLE; });
+ * \endcode
+ *
+ * This defines the 'ast_agi_register' function as an optional API; if a
+ * consumer of this API is loaded when there is no provider of it, then
+ * calling this function will actually call the hidden stub, and return
+ * the value AST_OPTIONAL_API_UNAVAILABLE. This allows the consumer to
+ * safely know that the API is not available, and to avoid using any
+ * other APIs from the not-present provider.
+ *
+ * In the module providing the API, the AST_OPTIONAL_API macro must
+ * be informed that it should not build the hidden stub function or
+ * apply special aliases to the function prototype; this can be done
+ * by defining AST_API_MODULE just before including the header file
+ * containing the AST_OPTIONAL_API macro calls.
+ *
+ * \note If the GCC 'weak' and 'alias' attributes are not available,
+ * then the AST_OPTIONAL_API macro will result in a non-optional function
+ * definition; this means that any consumers of the API functions so
+ * defined will require that the provider of the API functions be
+ * loaded before they can reference the symbols.
+ */
+
+#define __stringify_1(x)	#x
+#define __stringify(x)		__stringify_1(x)
+
+/*!
+ * \brief A common value for optional API stub functions to return
+ *
+ * This value is defined as INT_MIN, the minimum value for an integer
+ * (maximum negative value), which can be used by any optional API
+ * functions that return a signed integer value and would not be
+ * able to return such a value under normal circumstances.
+ */
+#define AST_OPTIONAL_API_UNAVAILABLE	INT_MIN
+
+#if defined(HAVE_ATTRIBUTE_weak) && defined(HAVE_ATTRIBUTE_alias) && !defined(AST_API_MODULE)
+#define AST_OPTIONAL_API(result, name, proto, stub)	\
+	static result __##name proto stub;		\
+	result __attribute__((weak, alias("__" __stringify(name)))) name proto;
+#define AST_OPTIONAL_API_ATTR(result, attr, name, proto, stub)		\
+	static result __attribute__((attr)) __##name proto stub;	\
+	result __attribute__((weak, alias("__" __stringify(name)), attr)) name proto;
+#else
+/*!
+ * \brief Define an optional API function
+ *
+ * \param result The type of result the function returns
+ * \param name The name of the function
+ * \param proto The prototype (arguments) of the function
+ * \param stub The code block that will be used by the hidden stub when needed
+ *
+ * Example usage:
+ * \code
+ * AST_OPTIONAL_API(int, ast_agi_register, (struct ast_module *mod, agi_command *cmd),
+ *                  { return AST_OPTIONAL_API_UNAVAILABLE; });
+ * \endcode		 
+ */
+#define AST_OPTIONAL_API(result, name, proto, stub) result name proto;
+/*!
+ * \brief Define an optional API function with compiler attributes
+ *
+ * \param result The type of result the function returns
+ * \param attr Any compiler attributes to be applied to the function (without the __attribute__ wrapper)
+ * \param name The name of the function
+ * \param proto The prototype (arguments) of the function
+ * \param stub The code block that will be used by the hidden stub when needed
+ */
+#define AST_OPTIONAL_API_ATTR(result, attr, name, proto, stub) result __attribute__((attr)) name proto;
+#endif
+
+#undef AST_API_MODULE
+
+#endif /* __ASTERISK_OPTIONAL_API_H */
diff --git a/res/res_agi.c b/res/res_agi.c
index ac6a8f85c..4ce871ec2 100644
--- a/res/res_agi.c
+++ b/res/res_agi.c
@@ -51,7 +51,6 @@ ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
 #include "asterisk/utils.h"
 #include "asterisk/lock.h"
 #include "asterisk/strings.h"
-#include "asterisk/agi.h"
 #include "asterisk/manager.h"
 #include "asterisk/ast_version.h"
 #include "asterisk/speech.h"
@@ -60,6 +59,9 @@ ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
 #include "asterisk/term.h"
 #include "asterisk/xmldoc.h"
 
+#define AST_API_MODULE
+#include "asterisk/agi.h"
+
 /*** DOCUMENTATION
 	<agi name="answer" language="en_US">
 		<synopsis>