_arch_xchg
_arch_xchg(ptr, x, "", "", "", "", "")
_arch_xchg(ptr, x, "", "", "", \
_arch_xchg(ptr, x, "", "", RISCV_RELEASE_BARRIER, "", "")
_arch_xchg(ptr, x, ".rl", ".aqrl", "", RISCV_FULL_BARRIER, "")