musl/arch/riscv64/atomic_arch.h

#define a_barrier a_barrier
static inline void a_barrier()
{
	__asm__ __volatile__ ("fence rw,rw" : : : "memory");
}

#define a_cas a_cas
static inline int a_cas(volatile int *p, int t, int s)
{
	int old, tmp;
	__asm__("\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));
	return old;
}

#define a_cas_p a_cas_p
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"
		"	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));
	return old;
}