compiler.h: add __visible

gcc 4.6+ has support for a externally_visible attribute that prevents the
optimizer from optimizing unused symbols away.  Add a __visible macro to
use it with that compiler version or later.

This is used (at least) by the "Link Time Optimization" patchset.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/include/linux/compiler-gcc4.h b/include/linux/compiler-gcc4.h
index 2f4079175afb..934bc34d5f99 100644
--- a/include/linux/compiler-gcc4.h
+++ b/include/linux/compiler-gcc4.h
@@ -49,6 +49,13 @@
 #endif
 #endif
 
+#if __GNUC_MINOR__ >= 6
+/*
+ * Tell the optimizer that something else uses this function or variable.
+ */
+#define __visible __attribute__((externally_visible))
+#endif
+
 #if __GNUC_MINOR__ > 0
 #define __compiletime_object_size(obj) __builtin_object_size(obj, 0)
 #endif