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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>
This commit is contained in:
David Rientjes 2007-05-09 02:35:27 -07:00 committed by Linus Torvalds
parent f7e4217b00
commit 0d7ebbbc6e
4 changed files with 25 additions and 6 deletions
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1
include/linux/compiler-gcc.h
View File

@ -40,3 +40,4 @@
#define noinline __attribute__((noinline))
#define __attribute_pure__ __attribute__((pure))
#define __attribute_const__ __attribute__((__const__))
#define __maybe_unused __attribute__((unused))

6
include/linux/compiler-gcc3.h
View File

@ -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

3
include/linux/compiler-gcc4.h
View File

@ -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))

21
include/linux/compiler.h
View File

@ -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
/*