musl/arch/aarch64/atomic_arch.h

#define a_ll a_ll
static inline int a_ll(volatile int *p)
{
	int v;
	__asm__ __volatile__ ("ldaxr %w0,%1" : "=r"(v) : "Q"(*p));
	return v;
}

#define a_sc a_sc
static inline int a_sc(volatile int *p, int v)
{
	int r;
	__asm__ __volatile__ ("stlxr %w0,%w2,%1" : "=&r"(r), "=Q"(*p) : "r"(v) : "memory");
	return !r;
}

#define a_barrier a_barrier
static inline void a_barrier()
{
	__asm__ __volatile__ ("dmb ish" : : : "memory");
}

#define a_cas a_cas
static inline int a_cas(volatile int *p, int t, int s)
{
	int old;
	do {
		old = a_ll(p);
		if (old != t) {
			a_barrier();
			break;
		}
	} while (!a_sc(p, s));
	return old;
}

static inline void *a_ll_p(volatile void *p)
{
	void *v;
	__asm__ __volatile__ ("ldaxr %0, %1" : "=r"(v) : "Q"(*(void *volatile *)p));
	return v;
}

static inline int a_sc_p(volatile int *p, void *v)
{
	int r;
	__asm__ __volatile__ ("stlxr %w0,%2,%1" : "=&r"(r), "=Q"(*(void *volatile *)p) : "r"(v) : "memory");
	return !r;
}

#define a_cas_p a_cas_p
static inline void *a_cas_p(volatile void *p, void *t, void *s)
{
	void *old;
	do {
		old = a_ll_p(p);
		if (old != t) {
			a_barrier();
			break;
		}
	} while (!a_sc_p(p, s));
	return old;
}

#define a_ctz_64 a_ctz_64
static inline int a_ctz_64(uint64_t x)
{
	__asm__(
		"	rbit %0, %1\n"
		"	clz %0, %0\n"
		: "=r"(x) : "r"(x));
	return x;
}