Index: kernel/Makefile
===================================================================
--- kernel/Makefile	(revision c9f3e7e90bf5ef1a7d8f76f8717c35a796152375)
+++ kernel/Makefile	(revision d4da8601eeecd6ff5bc2be80760523864c341a26)
@@ -84,5 +84,5 @@
 COMMON_CFLAGS = $(INCLUDES_FLAGS) -O$(OPTIMIZATION) -imacros $(CONFIG_HEADER) \
 	-ffreestanding -fno-builtin -nostdlib -nostdinc \
-	-fexec-charset=UTF-8 -finput-charset=UTF-8
+	-fexec-charset=UTF-8 -finput-charset=UTF-8 -fno-common
 
 GCC_CFLAGS = -std=gnu99 -Wall -Wextra -Wno-unused-parameter \
@@ -112,5 +112,5 @@
 #
 AFLAGS =
-LFLAGS = -n -T $(LINK) -M --fatal-warnings
+LFLAGS = -n -T $(LINK) -M --fatal-warnings --warn-common
 
 # FIXME: This condition is a workaround for issues #693 and #694.
Index: kernel/generic/src/ipc/sysipc_ops.c
===================================================================
--- kernel/generic/src/ipc/sysipc_ops.c	(revision c9f3e7e90bf5ef1a7d8f76f8717c35a796152375)
+++ kernel/generic/src/ipc/sysipc_ops.c	(revision d4da8601eeecd6ff5bc2be80760523864c341a26)
@@ -38,13 +38,13 @@
 
 /* Forward declarations. */
-sysipc_ops_t ipc_m_connect_to_me_ops;
-sysipc_ops_t ipc_m_connect_me_to_ops;
-sysipc_ops_t ipc_m_page_in_ops;
-sysipc_ops_t ipc_m_share_out_ops;
-sysipc_ops_t ipc_m_share_in_ops;
-sysipc_ops_t ipc_m_data_write_ops;
-sysipc_ops_t ipc_m_data_read_ops;
-sysipc_ops_t ipc_m_state_change_authorize_ops;
-sysipc_ops_t ipc_m_debug_ops;
+extern sysipc_ops_t ipc_m_connect_to_me_ops;
+extern sysipc_ops_t ipc_m_connect_me_to_ops;
+extern sysipc_ops_t ipc_m_page_in_ops;
+extern sysipc_ops_t ipc_m_share_out_ops;
+extern sysipc_ops_t ipc_m_share_in_ops;
+extern sysipc_ops_t ipc_m_data_write_ops;
+extern sysipc_ops_t ipc_m_data_read_ops;
+extern sysipc_ops_t ipc_m_state_change_authorize_ops;
+extern sysipc_ops_t ipc_m_debug_ops;
 
 static sysipc_ops_t *sysipc_ops[] = {