From e4b522d7ef144fb2ad6a4cb23d9cb5ec154be8bc Mon Sep 17 00:00:00 2001 From: Duncan Sands Date: Thu, 7 Dec 2006 02:14:13 +0100 Subject: [PATCH] [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 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 Signed-off-by: Andi Kleen Cc: Andi Kleen Acked-by: David Howells Signed-off-by: Andrew Morton --- include/asm-i386/atomic.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/include/asm-i386/atomic.h b/include/asm-i386/atomic.h index 51a166242522..6aab7a105fad 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 -- 2.39.5