musl/arch/riscv32/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__ __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)
		: "r"(p), "r"((long)t), "r"((long)s)
		: "memory");
	return old;
}