user: 请从给定的汇编指令推导出C源代码:

```asm
<rdtsc_ordered>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  nop
  nop
  nop
  mov    $0x0,%eax
  call   <rdtsc@plt>
  cltq
  pop    %rbp
  ret
```

assistant: ```c
__attribute__((always_)) unsigned long long rdtsc_ordered(void) {
  asm volatile("661:\n\t"
               ""
               "\n662:\n"
               ".skip -(("
               "(("
               "665"
               "1"
               "f-"
               "664"
               "1"
               "f"
               ") ^ ((("
               "665"
               "1"
               "f-"
               "664"
               "1"
               "f"
               ") ^ ("
               "665"
               "2"
               "f-"
               "664"
               "2"
               "f"
               ")) & -(-(("
               "665"
               "1"
               "f-"
               "664"
               "1"
               "f"
               ") - ("
               "665"
               "2"
               "f-"
               "664"
               "2"
               "f"
               ")))))"
               " - ("
               "662b-661b"
               ")) > 0) * "
               "("
               "(("
               "665"
               "1"
               "f-"
               "664"
               "1"
               "f"
               ") ^ ((("
               "665"
               "1"
               "f-"
               "664"
               "1"
               "f"
               ") ^ ("
               "665"
               "2"
               "f-"
               "664"
               "2"
               "f"
               ")) & -(-(("
               "665"
               "1"
               "f-"
               "664"
               "1"
               "f"
               ") - ("
               "665"
               "2"
               "f-"
               "664"
               "2"
               "f"
               ")))))"
               " - ("
               "662b-661b"
               ")), 0x90\n"
               "663"
               ":\n"
               ".pushsection .altinstructions,\"a\"\n"
               " .long 661b - .\n"
               " .long "
               "664"
               "1"
               "f - .\n"
               " .word "
               "( 3*32+17)"
               "\n"
               " .byte "
               "663"
               "b-661b"
               "\n"
               " .byte "
               "665"
               "1"
               "f-"
               "664"
               "1"
               "f"
               "\n"
               " .byte "
               "663"
               "b-662b"
               "\n"
               " .long 661b - .\n"
               " .long "
               "664"
               "2"
               "f - .\n"
               " .word "
               "( 3*32+18)"
               "\n"
               " .byte "
               "663"
               "b-661b"
               "\n"
               " .byte "
               "665"
               "2"
               "f-"
               "664"
               "2"
               "f"
               "\n"
               " .byte "
               "663"
               "b-662b"
               "\n"
               ".popsection\n"
               ".pushsection .altinstr_replacement, \"ax\"\n"
               "664"
               "1"
               ":\n\t"
               "mfence"
               "\n"
               "665"
               "1"
               ":\n\t"
               "664"
               "2"
               ":\n\t"
               "lfence"
               "\n"
               "665"
               "2"
               ":\n\t"
               ".popsection" ::
                   : "memory");
  return rdtsc();
}
```