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Commit 0d7ebbbc authored by David Rientjes's avatar David Rientjes Committed by Linus Torvalds
Browse files

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: default avatarDavid Rientjes <rientjes@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent f7e4217b

include/linux/compiler-gcc.h

+1 −0
Original line number Diff line number Diff line
@@ -40,3 +40,4 @@ 
#define  noinline			__attribute__((noinline))

#define __attribute_pure__		__attribute__((pure))

#define __attribute_const__		__attribute__((__const__))

#define __maybe_unused			__attribute__((unused))

include/linux/compiler-gcc3.h

+4 −2
Original line number Diff line number Diff line
@@ -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

include/linux/compiler-gcc4.h

+2 −1
Original line number Diff line number Diff line
@@ -12,7 +12,8 @@ 
# define __inline		__inline	__attribute__((always_inline))

#endif



#define __attribute_used__	__attribute__((__used__))

#define __used			__attribute__((__used__))

#define __attribute_used__	__used			/* deprecated */

#define __must_check 		__attribute__((warn_unused_result))

#define __compiler_offsetof(a,b) __builtin_offsetof(a,b)

#define __always_inline		inline __attribute__((always_inline))

include/linux/compiler.h

+18 −3
Original line number Diff line number Diff line
@@ -108,15 +108,30 @@ extern void __chk_io_ptr(const void __iomem *); 
 * Allow us to avoid 'defined but not used' warnings on functions and data,

 * as well as force them to be emitted to the assembly file.

 *

 * As of gcc 3.3, static functions that are not marked with attribute((used))

 * may be elided from the assembly file.  As of gcc 3.3, static data not so

 * As of gcc 3.4, static functions that are not marked with attribute((used))

 * may be elided from the assembly file.  As of gcc 3.4, static data not so

 * marked will not be elided, but this may change in a future gcc version.

 *

 * NOTE: Because distributions shipped with a backported unit-at-a-time

 * compiler in gcc 3.3, we must define __used to be __attribute__((used))

 * for gcc >=3.3 instead of 3.4.

 *

 * In prior versions of gcc, such functions and data would be emitted, but

 * would be warned about except with attribute((unused)).

 *

 * Mark functions that are referenced only in inline assembly as __used so

 * the code is emitted even though it appears to be unreferenced.

 */

#ifndef __attribute_used__

# define __attribute_used__	/* unimplemented */

# define __attribute_used__	/* deprecated */

#endif



#ifndef __used

# define __used			/* unimplemented */

#endif



#ifndef __maybe_unused

# define __maybe_unused		/* unimplemented */

#endif



/*