fix broken constraints for powerpc atomic cas asm

the register constraint for the address to be accessed did not convey
that the asm can access the pointed-to object. as far as the compiler
could tell, the result of the asm was just a pure function of the
address and the values passed in, and thus the asm could be hoisted
out of loops or omitted entirely if the result was not used.

diff --git a/arch/powerpc/atomic.h b/arch/powerpc/atomic.h
index d52ee0c..05951a2 100644 (file)
--- a/arch/powerpc/atomic.h
+++ b/arch/powerpc/atomic.h
@@ -31,7 +31,7 @@ static inline int a_cas(volatile int *p, int t, int s)
                "       stwcx. %3, 0, %1\n"
                "       bne- 1b\n"
                "1:     \n"
-               : "=&r"(t) : "r"(p), "r"(t), "r"(s) : "cc", "memory" );
+               : "=&r"(t), "+m"(*p) : "r"(t), "r"(s) : "cc", "memory" );
         return t;
 }