Re: [PATCH] MIPS: prevent compiler warning from cop2_{save,restore}

[Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>]

Hello.

On 9/25/2014 1:26 PM, Paul Burton wrote:

> The no-op cases of cop2_save & cop2_restore lead to the following
> warnings being emitted during build with recent versions of gcc (tested
> using gcc 4.8.3 from the Mentor Sourcery CodeBench 2014.05 toolchain):

>    In file included from ./arch/mips/include/asm/switch_to.h:18:0,
>                     from kernel/sched/core.c:78:
>    kernel/sched/core.c: In function 'finish_task_switch':
>    include/asm-generic/current.h:6:45: warning: value computed is not used [-Wunused-value]
>     #define get_current() (current_thread_info()->task)
                                                 ^
>    ./arch/mips/include/asm/cop2.h:48:32: note: in definition of macro 'cop2_restore'
>     #define cop2_restore(r)  do { (r); } while (0)
>                                    ^
>    include/asm-generic/current.h:7:17: note: in expansion of macro 'get_current'
>     #define current get_current()
>                     ^
>    ./arch/mips/include/asm/switch_to.h:114:16: note: in expansion of macro 'current'
>       cop2_restore(current);     \
>                    ^
>    kernel/sched/core.c:2225:2: note: in expansion of macro 'finish_arch_switch'
>      finish_arch_switch(prev);
>      ^

> Avoid the warning by "using" the value by casting to void.

> Signed-off-by: Paul Burton <paul.burton@imgtec.com>
> ---
>   arch/mips/include/asm/cop2.h | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)

> diff --git a/arch/mips/include/asm/cop2.h b/arch/mips/include/asm/cop2.h
> index 51f80bd..63b3468 100644
> --- a/arch/mips/include/asm/cop2.h
> +++ b/arch/mips/include/asm/cop2.h
> @@ -37,15 +37,15 @@ extern void nlm_cop2_restore(struct nlm_cop2_state *);
>
>   #define cop2_present		1
>   #define cop2_lazy_restore	1
> -#define cop2_save(r)		do { (r); } while (0)
> -#define cop2_restore(r)		do { (r); } while (0)
> +#define cop2_save(r)		do { (void)(r); } while (0)
> +#define cop2_restore(r)		do { (void)(r); } while (0)
>
>   #else
>
>   #define cop2_present		0
>   #define cop2_lazy_restore	0
> -#define cop2_save(r)		do { (r); } while (0)
> -#define cop2_restore(r)		do { (r); } while (0)
> +#define cop2_save(r)		do { (void)(r); } while (0)
> +#define cop2_restore(r)		do { (void)(r); } while (0)
>   #endif

    Looks like the definition are identical between 2 arms of #if, so why not 
move the macro definition out of #if, perhaps in later cleanup patch?

WBR, Sergei