RISCV_ACQUIRE_BARRIER
__asm__ __volatile__(RISCV_ACQUIRE_BARRIER "" ::: "memory")
RISCV_ACQUIRE_BARRIER, RISCV_ACQUIRE_BARRIER)
SC_PREPEND(""), SC_APPEND(RISCV_ACQUIRE_BARRIER), \
CAS_PREPEND(""), CAS_APPEND(RISCV_ACQUIRE_BARRIER))