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authorDuncan Sands <baldrick@free.fr>2006-12-07 02:14:13 +0100
committerAndi Kleen <andi@basil.nowhere.org>2006-12-07 02:14:13 +0100
commite4b522d7ef144fb2ad6a4cb23d9cb5ec154be8bc (patch)
tree707cbc03cd332aa87eff7ff33d85ee3a8fd6ac95 /include/asm-i386
parentd263b213577a1e8f166b0a7212d85175e36d6c19 (diff)
[PATCH] x86-64: fix asm constraints in i386 atomic_add_return
Since v->counter is both read and written, it should be an output as well as an input for the asm. The current code only gets away with this because counter is volatile. Also, according to Documents/atomic_ops.txt, atomic_add_return should provide a memory barrier, in particular a compiler barrier, so the asm should be marked as clobbering memory. Test case: #include <stdio.h> typedef struct { int counter; } atomic_t; /* NB: no "volatile" */ #define ATOMIC_INIT(i) { (i) } #define atomic_read(v) ((v)->counter) static __inline__ int atomic_add_return(int i, atomic_t *v) { int __i = i; __asm__ __volatile__( "lock; xaddl %0, %1;" :"=r"(i) :"m"(v->counter), "0"(i)); /* __asm__ __volatile__( "lock; xaddl %0, %1" :"+r" (i), "+m" (v->counter) : : "memory"); */ return i + __i; } int main (void) { atomic_t a = ATOMIC_INIT(0); int x; x = atomic_add_return (1, &a); if ((x!=1) || (atomic_read(&a)!=1)) printf("fail: %i, %i\n", x, atomic_read(&a)); } Signed-off-by: Duncan Sands <baldrick@free.fr> Signed-off-by: Andi Kleen <ak@suse.de> Cc: Andi Kleen <ak@suse.de> Acked-by: David Howells <dhowells@redhat.com> Signed-off-by: Andrew Morton <akpm@osdl.org>
Diffstat (limited to 'include/asm-i386')
-rw-r--r--include/asm-i386/atomic.h6
1 files changed, 3 insertions, 3 deletions
diff --git a/include/asm-i386/atomic.h b/include/asm-i386/atomic.h
index 51a16624252..6aab7a105fa 100644
--- a/include/asm-i386/atomic.h
+++ b/include/asm-i386/atomic.h
@@ -187,9 +187,9 @@ static __inline__ int atomic_add_return(int i, atomic_t *v)
/* Modern 486+ processor */
__i = i;
__asm__ __volatile__(
- LOCK_PREFIX "xaddl %0, %1;"
- :"=r"(i)
- :"m"(v->counter), "0"(i));
+ LOCK_PREFIX "xaddl %0, %1"
+ :"+r" (i), "+m" (v->counter)
+ : : "memory");
return i + __i;
#ifdef CONFIG_M386