Remove unnecessary cast in prefetch()

4ecbca85 · Serge Belyshev <[email protected]> · 2007-10-04 23:10:04 +02:00

It is ok to call prefetch() function with NULL argument, as specifically
commented in include/linux/prefetch.h.  But in standard C, it is invalid
to dereference NULL pointer (see C99 standard 6.5.3.2 paragraph 4 and
note #84).

prefetch() has a memory reference for its argument.

Newer gcc versions (4.3 and above) will use that to conclude that "x"
argument is non-null and thus wreaking havok everywhere prefetch() was
inlined.

Fixed by removing cast and changing asm constraint.

[ It seems in theory gcc 4.2 could miscompile this too; although no
  cases known.  In 2.6.24 we should probably switch to
  __builtin_prefetch() instead, but this is a simpler fix for now.
				-- AK ]

Signed-off-by: Serge Belyshev <[email protected]>
Signed-off-by: Andi Kleen <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Commit: 4ecbca8554d0f643351ee07d3284138a5e85ba81
Parents: 9cdcaa2c

Changes

1 files changed · +1 −1

File	Status	Add	Del	Content
include/asm-x86_64/processor.h	modified	+1	−1	View file

include/asm-x86_64/processor.h

View file

diff --git a/include/asm-x86_64/processor.h b/include/asm-x86_64/processor.h
index 1952517..31f579b 100644
--- a/include/asm-x86_64/processor.h
+++ b/include/asm-x86_64/processor.h
@@ -371,7 +371,7 @@ static inline void sync_core(void)
 #define ARCH_HAS_PREFETCH
 static inline void prefetch(void *x) 
 { 
-	asm volatile("prefetcht0 %0" :: "m" (*(unsigned long *)x));
+	asm volatile("prefetcht0 (%0)" :: "r" (x));
 } 
 
 #define ARCH_HAS_PREFETCHW 1