_oldn; \
})
+/* Abstractions to access atomically (i.e. "once") i64/u64 variables */
+#ifdef CONFIG_ATOMIC64
+static inline int64_t atomic_read_i64(const int64_t *ptr)
+{
+ /* use __nocheck because sizeof(void *) might be < sizeof(u64) */
+ return atomic_read__nocheck(ptr);
+}
+
+static inline uint64_t atomic_read_u64(const uint64_t *ptr)
+{
+ return atomic_read__nocheck(ptr);
+}
+
+static inline void atomic_set_i64(int64_t *ptr, int64_t val)
+{
+ atomic_set__nocheck(ptr, val);
+}
+
+static inline void atomic_set_u64(uint64_t *ptr, uint64_t val)
+{
+ atomic_set__nocheck(ptr, val);
+}
+
+static inline void atomic64_init(void)
+{
+}
+#else /* !CONFIG_ATOMIC64 */
+int64_t atomic_read_i64(const int64_t *ptr);
+uint64_t atomic_read_u64(const uint64_t *ptr);
+void atomic_set_i64(int64_t *ptr, int64_t val);
+void atomic_set_u64(uint64_t *ptr, uint64_t val);
+void atomic64_init(void);
+#endif /* !CONFIG_ATOMIC64 */
+
#endif /* QEMU_ATOMIC_H */
--- /dev/null
+/*
+ * Copyright (C) 2018, Emilio G. Cota <cota@braap.org>
+ *
+ * License: GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+#include "qemu/osdep.h"
+#include "qemu/atomic.h"
+#include "qemu/thread.h"
+
+#ifdef CONFIG_ATOMIC64
+#error This file must only be compiled if !CONFIG_ATOMIC64
+#endif
+
+/*
+ * When !CONFIG_ATOMIC64, we serialize both reads and writes with spinlocks.
+ * We use an array of spinlocks, with padding computed at run-time based on
+ * the host's dcache line size.
+ * We point to the array with a void * to simplify the padding's computation.
+ * Each spinlock is located every lock_size bytes.
+ */
+static void *lock_array;
+static size_t lock_size;
+
+/*
+ * Systems without CONFIG_ATOMIC64 are unlikely to have many cores, so we use a
+ * small array of locks.
+ */
+#define NR_LOCKS 16
+
+static QemuSpin *addr_to_lock(const void *addr)
+{
+ uintptr_t a = (uintptr_t)addr;
+ uintptr_t idx;
+
+ idx = a >> qemu_dcache_linesize_log;
+ idx ^= (idx >> 8) ^ (idx >> 16);
+ idx &= NR_LOCKS - 1;
+ return lock_array + idx * lock_size;
+}
+
+#define GEN_READ(name, type) \
+ type name(const type *ptr) \
+ { \
+ QemuSpin *lock = addr_to_lock(ptr); \
+ type ret; \
+ \
+ qemu_spin_lock(lock); \
+ ret = *ptr; \
+ qemu_spin_unlock(lock); \
+ return ret; \
+ }
+
+GEN_READ(atomic_read_i64, int64_t)
+GEN_READ(atomic_read_u64, uint64_t)
+#undef GEN_READ
+
+#define GEN_SET(name, type) \
+ void name(type *ptr, type val) \
+ { \
+ QemuSpin *lock = addr_to_lock(ptr); \
+ \
+ qemu_spin_lock(lock); \
+ *ptr = val; \
+ qemu_spin_unlock(lock); \
+ }
+
+GEN_SET(atomic_set_i64, int64_t)
+GEN_SET(atomic_set_u64, uint64_t)
+#undef GEN_SET
+
+void atomic64_init(void)
+{
+ int i;
+
+ lock_size = ROUND_UP(sizeof(QemuSpin), qemu_dcache_linesize);
+ lock_array = qemu_memalign(qemu_dcache_linesize, lock_size * NR_LOCKS);
+ for (i = 0; i < NR_LOCKS; i++) {
+ QemuSpin *lock = lock_array + i * lock_size;
+
+ qemu_spin_init(lock);
+ }
+}