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

[Christophe Leroy]

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.le...@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__ */