fix riscv64 atomic asm constraints

most egregious problem was the lack of memory clobber and lack of
volatile asm; this made the atomics memory barriers but not compiler
barriers. use of "+r" rather than "=r" for a clobbered temp was also
wrong, since the initial value is indeterminate.

diff --git a/arch/riscv64/atomic_arch.h b/arch/riscv64/atomic_arch.h
index 98f12fc..d0228a3 100644 (file)
--- a/arch/riscv64/atomic_arch.h
+++ b/arch/riscv64/atomic_arch.h
@@ -8,13 +8,15 @@ static inline void a_barrier()
 static inline int a_cas(volatile int *p, int t, int s)
 {
        int old, tmp;
-       __asm__("\n1:   lr.w.aqrl %0, %2\n"
+       __asm__ __volatile__ (
+               "\n1:   lr.w.aqrl %0, %2\n"
                "       bne %0, %3, 1f\n"
                "       sc.w.aqrl %1, %4, %2\n"
                "       bnez %1, 1b\n"
                "1:"
-               : "=&r"(old), "+r"(tmp), "+A"(*p)
-               : "r"(t), "r"(s));
+               : "=&r"(old), "=r"(tmp), "+A"(*p)
+               : "r"(t), "r"(s)
+               : "memory");
        return old;
 }
 
@@ -23,12 +25,14 @@ static inline void *a_cas_p(volatile void *p, void *t, void *s)
 {
        void *old;
        int tmp;
-       __asm__("\n1:   lr.d.aqrl %0, %2\n"
+       __asm__ __volatile__ (
+               "\n1:   lr.d.aqrl %0, %2\n"
                "       bne %0, %3, 1f\n"
                "       sc.d.aqrl %1, %4, %2\n"
                "       bnez %1, 1b\n"
                "1:"
-               : "=&r"(old), "+r"(tmp), "+A"(*(long *)p)
-               : "r"(t), "r"(s));
+               : "=&r"(old), "=r"(tmp), "+A"(*(long *)p)
+               : "r"(t), "r"(s)
+               : "memory");
        return old;
 }