--- a/gcc/gcc-plugin.h	Tue May 25 18:58:51 2010 +0900
+++ b/gcc/gcc-plugin.h	Tue Mar 22 17:18:12 2011 +0900
@@ -26,6 +26,7 @@
 
 #include "config.h"
 #include "system.h"
+#include "coretypes.h"
 #include "highlev-plugin-common.h"
 #include "hashtab.h"
 
@@ -38,6 +39,12 @@
   PLUGIN_EVENT_FIRST_DYNAMIC
 };
 
+/* All globals declared here have C linkage to reduce link compatibility
+   issues with implementation language choice and mangling.  */
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 extern const char **plugin_event_name;
 
 struct plugin_argument
@@ -96,16 +103,10 @@
 typedef int (*plugin_init_func) (struct plugin_name_args *plugin_info,
                                  struct plugin_gcc_version *version);
 
-#ifdef __cplusplus
-extern "C" {
-#endif
 /* Declaration for "plugin_init" function so that it doesn't need to be
    duplicated in every plugin.  */
 extern int plugin_init (struct plugin_name_args *plugin_info,
                         struct plugin_gcc_version *version);
-#ifdef __cplusplus
-}
-#endif
 
 /* Function type for a plugin callback routine.
 
@@ -147,4 +148,19 @@
    -iplugindir program argument to cc1.  */
 extern const char* default_plugin_dir_name (void);
 
+#ifdef __cplusplus
+}
+#endif
+
+/* In case the C++ compiler does name mangling for globals, declare
+   plugin_is_GPL_compatible extern "C" so that a later definition
+   in a plugin file will have this linkage.  */
+#ifdef __cplusplus
+extern "C" {
+#endif
+extern int plugin_is_GPL_compatible;
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* GCC_PLUGIN_H */