Re: [PATCH] powerpc/32: Remove memory clobber asm constraint on dcbX() functions

Christophe Leroy
2019-05-03T14:14:16Z

Segher,

A while ago I proposed the following patch, and didn't get any comment
back on it.

Do you have any opinion on it ? Is it good and worth it ?

Thanks
Christophe

Le 09/01/2018 à 07:57, Christophe Leroy a écrit :
> Instead of just telling GCC that dcbz(), dcbi(), dcbf() and dcbst()
> clobber memory, tell it what it clobbers:
> * dcbz(), dcbi() and dcbf() clobbers one cacheline as output
> * dcbf() and dcbst() clobbers one cacheline as input
>
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
> ---
> arch/powerpc/include/asm/cache.h | 17 +++++++++++++----
> 1 file changed, 13 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/cache.h b/arch/powerpc/include/asm/cache.h
> index c1d257aa4c2d..fc8fe18acf8c 100644
> --- a/arch/powerpc/include/asm/cache.h
> +++ b/arch/powerpc/include/asm/cache.h
> @@ -82,22 +82,31 @@ extern void _set_L3CR(unsigned long);
>
> static inline void dcbz(void *addr)
> {
> - __asm__ __volatile__ ("dcbz 0, %0" : : "r"(addr) : "memory");
> + __asm__ __volatile__ ("dcbz 0, %1" :
> + "=m"(*(char (*)[L1_CACHE_BYTES])addr) :
> + "r"(addr) :);
> }
>
> static inline void dcbi(void *addr)
> {
> - __asm__ __volatile__ ("dcbi 0, %0" : : "r"(addr) : "memory");
> + __asm__ __volatile__ ("dcbi 0, %1" :
> + "=m"(*(char (*)[L1_CACHE_BYTES])addr) :
> + "r"(addr) :);
> }
>
> static inline void dcbf(void *addr)
> {
> - __asm__ __volatile__ ("dcbf 0, %0" : : "r"(addr) : "memory");
> + __asm__ __volatile__ ("dcbf 0, %1" :
> + "=m"(*(char (*)[L1_CACHE_BYTES])addr) :
> + "r"(addr), "m"(*(char (*)[L1_CACHE_BYTES])addr) :
> + );
> }
>
> static inline void dcbst(void *addr)
> {
> - __asm__ __volatile__ ("dcbst 0, %0" : : "r"(addr) : "memory");
> + __asm__ __volatile__ ("dcbst 0, %0" : :
> + "r"(addr), "m"(*(char (*)[L1_CACHE_BYTES])addr) :
> + );
> }
> #endif /* !__ASSEMBLY__ */
> #endif /* __KERNEL__ */
>