From: David Rientjes __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 Cc: Adrian Bunk Signed-off-by: David Rientjes Signed-off-by: Andrew Morton --- include/linux/compiler-gcc.h | 1 + include/linux/compiler-gcc3.h | 6 ++++-- include/linux/compiler-gcc4.h | 3 ++- include/linux/compiler.h | 21 ++++++++++++++++++--- 4 files changed, 25 insertions(+), 6 deletions(-) diff -puN include/linux/compiler-gcc.h~compiler-introduce-__used-and-__maybe_unused include/linux/compiler-gcc.h --- a/include/linux/compiler-gcc.h~compiler-introduce-__used-and-__maybe_unused +++ a/include/linux/compiler-gcc.h @@ -40,3 +40,4 @@ #define noinline __attribute__((noinline)) #define __attribute_pure__ __attribute__((pure)) #define __attribute_const__ __attribute__((__const__)) +#define __maybe_unused __attribute__((unused)) diff -puN include/linux/compiler-gcc3.h~compiler-introduce-__used-and-__maybe_unused include/linux/compiler-gcc3.h --- a/include/linux/compiler-gcc3.h~compiler-introduce-__used-and-__maybe_unused +++ a/include/linux/compiler-gcc3.h @@ -4,9 +4,11 @@ #include #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 diff -puN include/linux/compiler-gcc4.h~compiler-introduce-__used-and-__maybe_unused include/linux/compiler-gcc4.h --- a/include/linux/compiler-gcc4.h~compiler-introduce-__used-and-__maybe_unused +++ a/include/linux/compiler-gcc4.h @@ -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)) diff -puN include/linux/compiler.h~compiler-introduce-__used-and-__maybe_unused include/linux/compiler.h --- a/include/linux/compiler.h~compiler-introduce-__used-and-__maybe_unused +++ a/include/linux/compiler.h @@ -108,15 +108,30 @@ extern void __chk_io_ptr(const void __io * 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 /* _