optional_api: Fix linking problems between modules that export global symbols

With the new work in Asterisk 12, there are some uses of the
optional_api that are prone to failure. The details are rather involved,
and captured on [the wiki][1].

This patch addresses the issue by removing almost all of the magic from
the optional API implementation. Instead of relying on weak symbol
resolution, a new optional_api.c module was added to Asterisk core.

For modules providing an optional API, the pointer to the implementation
function is registered with the core. For modules that use an optional
API, a pointer to a stub function, along with a optional_ref function
pointer are registered with the core. The optional_ref function pointers
is set to the implementation function when it's provided, or the stub
function when it's now.

Since the implementation no longer relies on magic, it is now supported
on all platforms. In the spirit of choice, an OPTIONAL_API flag was
added, so we can disable the optional_api if needed (maybe it's buggy on
some bizarre platform I haven't tested on)

The AST_OPTIONAL_API*() macros themselves remained unchanged, so
existing code could remain unchanged. But to help with debugging the
optional_api, the patch limits the #include of optional API's to just
the modules using the API. This also reduces resource waste maintaining
optional_ref pointers that aren't used.

Other changes made as a part of this patch:
 * The stubs for http_websocket that wrap system calls set errno to
   ENOSYS.

 * res_http_websocket now properly increments module use count.

 * In loader.c, the while() wrappers around dlclose() were removed. The
   while(!dlclose()) is actually an anti-pattern, which can lead to
   infinite loops if the module you're attempting to unload exports a
   symbol that was directly linked to.

 * The special handling of nonoptreq on systems without weak symbol
   support was removed, since we no longer rely on weak symbols for
   optional_api.

 [1]: https://wiki.asterisk.org/wiki/x/wACUAQ

(closes issue ASTERISK-22296)
Reported by: Matt Jordan
Review: https://reviewboard.asterisk.org/r/2797/
........

Merged revisions 397989 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@397990 65c4cc65-6c06-0410-ace0-fbb531ad65f3

1 files changed, 74 insertions, 122 deletions

diff --git a/configure b/configure
index 2d04b6d11..3dff95f60 100755
--- a/configure
+++ b/configure
@@ -1,5 +1,5 @@
 #! /bin/sh
-# From configure.ac Revision: 395985 .
+# From configure.ac Revision: 397868 .
 # Guess values for system-dependent variables and create Makefiles.
 # Generated by GNU Autoconf 2.69 for asterisk trunk.
 #
@@ -684,6 +684,7 @@ PKG_CONFIG_PATH
 PKG_CONFIG
 PBX_DLADDR
 PBX_IP_MTU_DISCOVER
+PBX_RTLD_NOLOAD
 PBX_GLOB_BRACE
 PBX_GLOB_NOMAGIC
 AST_RPATH
@@ -696,7 +697,6 @@ AST_TRAMPOLINES
 AST_DECLARATION_AFTER_STATEMENT
 GC_LDFLAGS
 GC_CFLAGS
-PBX_WEAKREF
 PBX_PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP
 PBX_PTHREAD_RWLOCK_INITIALIZER
 AST_ASTERISKSSL
@@ -16564,28 +16564,17 @@ CFLAGS="$saved_CFLAGS"
 
 
 
-# Support weak symbols on a platform specific basis.  The Mac OS X
-# (Darwin) support must be isolated from the other platforms because
-# it has caused other platforms to fail.
-#
-case "${OSARCH}" in
-	darwin*)
-	# Allow weak symbol support on Darwin platforms only because there
-	# is active community support for it.
-	# However, Darwin seems to break weak symbols for each new version.
-	#
-
-{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for compiler 'attribute weak_import' support" >&5
-$as_echo_n "checking for compiler 'attribute weak_import' support... " >&6; }
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for compiler 'attribute may_alias' support" >&5
+$as_echo_n "checking for compiler 'attribute may_alias' support... " >&6; }
 saved_CFLAGS="$CFLAGS"
 CFLAGS="$CFLAGS -Wall -Wno-unused -Werror"
-PBX_WEAKREF=0
+
 
 if test "x" = "x"
 then
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
- void __attribute__((weak_import)) *test(void *muffin, ...) {return (void *) 0;}
+ void __attribute__((may_alias)) *test(void *muffin, ...) {return (void *) 0;}
 int
 main ()
 {
@@ -16597,10 +16586,10 @@ _ACEOF
 if ac_fn_c_try_compile "$LINENO"; then :
   { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
 $as_echo "yes" >&6; }
-	PBX_WEAKREF=1
+
 
 cat >>confdefs.h <<_ACEOF
-#define HAVE_ATTRIBUTE_weak_import 1
+#define HAVE_ATTRIBUTE_may_alias 1
 _ACEOF
 
 else
@@ -16624,10 +16613,10 @@ _ACEOF
 if ac_fn_c_try_compile "$LINENO"; then :
   { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
 $as_echo "yes" >&6; }
-	PBX_WEAKREF=1
+
 
 cat >>confdefs.h <<_ACEOF
-#define HAVE_ATTRIBUTE_weak_import 1
+#define HAVE_ATTRIBUTE_may_alias 1
 _ACEOF
 
 else
@@ -16643,21 +16632,17 @@ CFLAGS="$saved_CFLAGS"
 
 
 
-	# Several other platforms including Linux have GCC versions that
-	# define the weak attribute.  However, this attribute is only
-	# setup for use in the code by Darwin.
-
-{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for compiler 'attribute weak' support" >&5
-$as_echo_n "checking for compiler 'attribute weak' support... " >&6; }
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for compiler 'attribute constructor' support" >&5
+$as_echo_n "checking for compiler 'attribute constructor' support... " >&6; }
 saved_CFLAGS="$CFLAGS"
 CFLAGS="$CFLAGS -Wall -Wno-unused -Werror"
-PBX_WEAKREF=0
+
 
 if test "x" = "x"
 then
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
- void __attribute__((weak)) *test(void *muffin, ...) {return (void *) 0;}
+ void __attribute__((constructor)) *test(void *muffin, ...) {return (void *) 0;}
 int
 main ()
 {
@@ -16669,10 +16654,10 @@ _ACEOF
 if ac_fn_c_try_compile "$LINENO"; then :
   { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
 $as_echo "yes" >&6; }
-	PBX_WEAKREF=1
+
 
 cat >>confdefs.h <<_ACEOF
-#define HAVE_ATTRIBUTE_weak 1
+#define HAVE_ATTRIBUTE_constructor 1
 _ACEOF
 
 else
@@ -16696,82 +16681,10 @@ _ACEOF
 if ac_fn_c_try_compile "$LINENO"; then :
   { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
 $as_echo "yes" >&6; }
-	PBX_WEAKREF=1
-
-cat >>confdefs.h <<_ACEOF
-#define HAVE_ATTRIBUTE_weak 1
-_ACEOF
-
-else
-  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
-$as_echo "no" >&6; }
-
-fi
-rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
-fi
-
-
-CFLAGS="$saved_CFLAGS"
-
-
-	;;
-	linux-gnu)
-	# Primarily support weak symbols on Linux platforms.
-	#
-
-{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for compiler 'attribute weakref' support" >&5
-$as_echo_n "checking for compiler 'attribute weakref' support... " >&6; }
-saved_CFLAGS="$CFLAGS"
-CFLAGS="$CFLAGS -Wall -Wno-unused -Werror"
-PBX_WEAKREF=0
-
-if test "xweakref("foo")" = "x"
-then
-cat confdefs.h - <<_ACEOF >conftest.$ac_ext
-/* end confdefs.h.  */
-static void __attribute__((weakref)) *test(void *muffin, ...) {return (void *) 0;}
-int
-main ()
-{
 
-  ;
-  return 0;
-}
-_ACEOF
-if ac_fn_c_try_compile "$LINENO"; then :
-  { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
-$as_echo "yes" >&6; }
-	PBX_WEAKREF=1
 
 cat >>confdefs.h <<_ACEOF
-#define HAVE_ATTRIBUTE_weakref 1
-_ACEOF
-
-else
-  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
-$as_echo "no" >&6; }
-
-fi
-rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
-else
-cat confdefs.h - <<_ACEOF >conftest.$ac_ext
-/* end confdefs.h.  */
-static void __attribute__((weakref("foo"))) *test(void *muffin, ...) {return (void *) 0;}
-int
-main ()
-{
-
-  ;
-  return 0;
-}
-_ACEOF
-if ac_fn_c_try_compile "$LINENO"; then :
-  { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
-$as_echo "yes" >&6; }
-	PBX_WEAKREF=1
-
-cat >>confdefs.h <<_ACEOF
-#define HAVE_ATTRIBUTE_weakref 1
+#define HAVE_ATTRIBUTE_constructor 1
 _ACEOF
 
 else
@@ -16786,24 +16699,18 @@ fi
 CFLAGS="$saved_CFLAGS"
 
 
-	;;
-	*)
-	# Allow weak symbols on other platforms.  However, any problems
-	# with this feature on other platforms must be fixed by the
-	# community.
-	#
 
-{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for compiler 'attribute weakref' support" >&5
-$as_echo_n "checking for compiler 'attribute weakref' support... " >&6; }
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for compiler 'attribute destructor' support" >&5
+$as_echo_n "checking for compiler 'attribute destructor' support... " >&6; }
 saved_CFLAGS="$CFLAGS"
 CFLAGS="$CFLAGS -Wall -Wno-unused -Werror"
-PBX_WEAKREF=0
 
-if test "xweakref("foo")" = "x"
+
+if test "x" = "x"
 then
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
-static void __attribute__((weakref)) *test(void *muffin, ...) {return (void *) 0;}
+ void __attribute__((destructor)) *test(void *muffin, ...) {return (void *) 0;}
 int
 main ()
 {
@@ -16815,10 +16722,10 @@ _ACEOF
 if ac_fn_c_try_compile "$LINENO"; then :
   { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
 $as_echo "yes" >&6; }
-	PBX_WEAKREF=1
+
 
 cat >>confdefs.h <<_ACEOF
-#define HAVE_ATTRIBUTE_weakref 1
+#define HAVE_ATTRIBUTE_destructor 1
 _ACEOF
 
 else
@@ -16830,7 +16737,7 @@ rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 else
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
-static void __attribute__((weakref("foo"))) *test(void *muffin, ...) {return (void *) 0;}
+ void __attribute__(()) *test(void *muffin, ...) {return (void *) 0;}
 int
 main ()
 {
@@ -16842,10 +16749,10 @@ _ACEOF
 if ac_fn_c_try_compile "$LINENO"; then :
   { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
 $as_echo "yes" >&6; }
-	PBX_WEAKREF=1
+
 
 cat >>confdefs.h <<_ACEOF
-#define HAVE_ATTRIBUTE_weakref 1
+#define HAVE_ATTRIBUTE_destructor 1
 _ACEOF
 
 else
@@ -16860,8 +16767,6 @@ fi
 CFLAGS="$saved_CFLAGS"
 
 
-	;;
-esac
 
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for -ffunction-sections support" >&5
 $as_echo_n "checking for -ffunction-sections support... " >&6; }
@@ -17454,6 +17359,53 @@ rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 
 
 
+    if test "x${PBX_RTLD_NOLOAD}" != "x1"; then
+	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for RTLD_NOLOAD in dlfcn.h" >&5
+$as_echo_n "checking for RTLD_NOLOAD in dlfcn.h... " >&6; }
+	saved_cppflags="${CPPFLAGS}"
+	if test "x${RTLD_NOLOAD_DIR}" != "x"; then
+	    RTLD_NOLOAD_INCLUDE="-I${RTLD_NOLOAD_DIR}/include"
+	fi
+	CPPFLAGS="${CPPFLAGS} ${RTLD_NOLOAD_INCLUDE}"
+
+	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+ #include <dlfcn.h>
+int
+main ()
+{
+#if defined(RTLD_NOLOAD)
+				int foo = 0;
+			        #else
+			        int foo = bar;
+			        #endif
+				0
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+     { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+$as_echo "yes" >&6; }
+		PBX_RTLD_NOLOAD=1
+
+$as_echo "#define HAVE_RTLD_NOLOAD 1" >>confdefs.h
+
+
+
+else
+     { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+	CPPFLAGS="${saved_cppflags}"
+    fi
+
+
+
+
     if test "x${PBX_IP_MTU_DISCOVER}" != "x1"; then
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for IP_MTU_DISCOVER in netinet/in.h" >&5
 $as_echo_n "checking for IP_MTU_DISCOVER in netinet/in.h... " >&6; }