compiler: introduce __used and __maybe_unused

__used is defined to be __attribute__((unused)) for all pre-3.3 gcc
compilers to suppress warnings for unused functions because perhaps they
are referenced only in inline assembly.  It is defined to be
__attribute__((used)) for gcc 3.3 and later so that the code is still
emitted for such functions.

__maybe_unused is defined to be __attribute__((unused)) for both function
and variable use if it could possibly be unreferenced due to the evaluation
of preprocessor macros.  Function prototypes shall be marked with
__maybe_unused if the actual definition of the function is dependant on
preprocessor macros.

No update to compiler-intel.h is necessary because ICC supports both
__attribute__((used)) and __attribute__((unused)) as specified by the gcc
manual.

__attribute_used__ is deprecated and will be removed once all current
code is converted to using __used.

Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Adrian Bunk <bunk@stusta.de>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/include/linux/compiler-gcc3.h b/include/linux/compiler-gcc3.h
index ecd621fd27d2..a9e2863c2dbf 100644
--- a/include/linux/compiler-gcc3.h
+++ b/include/linux/compiler-gcc3.h
@@ -4,9 +4,11 @@
 #include <linux/compiler-gcc.h>
 
 #if __GNUC_MINOR__ >= 3
-# define __attribute_used__     __attribute__((__used__))
+# define __used                 __attribute__((__used__))
+# define __attribute_used__     __used                          /* deprecated */
 #else
-# define __attribute_used__     __attribute__((__unused__))
+# define __used                 __attribute__((__unused__))
+# define __attribute_used__     __used                          /* deprecated */
 #endif
 
 #if __GNUC_MINOR__ >= 4