cdefs: Rework and augment visibility attributes

One macro based on GCC visibility functions was already defined,
__exported.  However, it was marked as available for all GCC versions
when it fact it was introduced with gcc 4.0.

There was no macro for hidden visibility attributes, so the macros
__dso_hidden and __dso_public were borrowed from NetBSD.  __dso_public
is an alias for __exported.  The definition for all three macros were
made on the condition that the gcc version used is 4.0 or later.

diff --git a/sys/sys/cdefs.h b/sys/sys/cdefs.h
index 5b76100..a737c18 100644 (file)
--- a/sys/sys/cdefs.h
+++ b/sys/sys/cdefs.h
@@ -41,12 +41,6 @@
 #ifndef        _SYS_CDEFS_H_
 #define        _SYS_CDEFS_H_
 
-#if defined(__GNUC__)
-#define __exported __attribute__((__visibility__("default")))
-#else
-#define __exported
-#endif
-
 #if defined(__cplusplus)
 #define        __BEGIN_DECLS   extern "C" {
 #define        __END_DECLS     }
@@ -299,6 +293,16 @@
 #define __ARRAY_ZERO
 #endif
 
+#if __GNUC_PREREQ__(4, 0)
+#define __exported     __attribute__((__visibility__("default")))
+#define __dso_public   __attribute__((__visibility__("default")))
+#define __dso_hidden   __attribute__((__visibility__("hidden")))
+#else
+#define __exported
+#define __dso_public
+#define __dso_hidden
+#endif
+
 /*
  * A convenient constructor macro, GCC 4.3.0 added priority support to
  * constructors, provide a compatible interface for both.