Question

我在V8中反汇编了这样的javascript函数。

function A() {
  a = 1;
  b = 2;
  c = a + b;
}

我得到了反汇编的代码。在x86机器（64位）

Instructions (size = 228)
0x35ca73465740     0  488b4c2408     REX.W movq rcx,[rsp+0x8]
0x35ca73465745     5  493b4da8       REX.W cmpq rcx,[r13-0x58]
0x35ca73465749     9  750d           jnz 24  (0x35ca73465758)
0x35ca7346574b    11  488b4e27       REX.W movq rcx,[rsi+0x27]
0x35ca7346574f    15  488b492f       REX.W movq rcx,[rcx+0x2f]
0x35ca73465753    19  48894c2408     REX.W movq [rsp+0x8],rcx
0x35ca73465758    24  e88358fdff     call MakeQuadragenarianCodeYoungAgainOddMarking  (0x35ca7343afe0)
0x35ca7346575d    29  90             nop
0x35ca7346575e    30  493ba5b0070000 REX.W cmpq rsp,[r13+0x7b0]
0x35ca73465765    37  7305           jnc 44  (0x35ca7346576c)
0x35ca73465767    39  e83456fdff     call StackCheck  (0x35ca7343ada0)    ;; debug: statement 19
                                                         ;; code: BUILTIN
0x35ca7346576c    44  4c89e0         REX.W movq rax,r12
0x35ca7346576f    47  48b9111d111f770a0000 REX.W movq rcx,0xa771f111d11    ;; object: 0xa771f111d11 <String[1]: a>
0x35ca73465779    57  488b5627       REX.W movq rdx,[rsi+0x27]
0x35ca7346577d    61  e83e0ffdff     call 0x35ca734366c0     ;; debug: statement 26
                                                         ;; debug: position 27
                                                         ;; code: STORE_IC, PREMONOMORPHIC
0x35ca73465782    66  4b8d0424       REX.W leaq rax,[r12+r12*1]
0x35ca73465786    70  48b9311d111f770a0000 REX.W movq rcx,0xa771f111d31    ;; object: 0xa771f111d31 <String[1]: b>
0x35ca73465790    80  488b5627       REX.W movq rdx,[rsi+0x27]
0x35ca73465794    84  e8270ffdff     call 0x35ca734366c0     ;; debug: statement 33
                                                         ;; debug: position 34
                                                         ;; code: STORE_IC, PREMONOMORPHIC
0x35ca73465799    89  48b9111d111f770a0000 REX.W movq rcx,0xa771f111d11    ;; object: 0xa771f111d11 <String[1]: a>
0x35ca734657a3    99  488b5627       REX.W movq rdx,[rsi+0x27]
0x35ca734657a7   103  e8940ffdff     call 0x35ca73436740     ;; debug: statement 40
                                                         ;; debug: position 42
                                                         ;; code: contextual, LOAD_IC, PREMONOMORPHIC
0x35ca734657ac   108  50             push rax
0x35ca734657ad   109  48b9311d111f770a0000 REX.W movq rcx,0xa771f111d31    ;; object: 0xa771f111d31 <String[1]: b>
0x35ca734657b7   119  488b5627       REX.W movq rdx,[rsi+0x27]
0x35ca734657bb   123  e8800ffdff     call 0x35ca73436740     ;; debug: position 44
                                                         ;; code: contextual, LOAD_IC, PREMONOMORPHIC
0x35ca734657c0   128  5a             pop rdx
0x35ca734657c1   129  e89aeefaff     call 0x35ca73414660     ;; debug: position 43
                                                         ;; code: BINARY_OP_IC, MONOMORPHIC, NORMAL (id = 31)
0x35ca734657c6   134  90             nop
0x35ca734657c7   135  48b9511d111f770a0000 REX.W movq rcx,0xa771f111d51    ;; object: 0xa771f111d51 <String[1]: c>
0x35ca734657d1   145  488b5627       REX.W movq rdx,[rsi+0x27]
0x35ca734657d5   149  e8e60efdff     call 0x35ca734366c0     ;; debug: position 41
                                                         ;; code: STORE_IC, PREMONOMORPHIC
0x35ca734657da   154  498b45a8       REX.W movq rax,[r13-0x58]
0x35ca734657de   158  48bb214b4060ff110000 REX.W movq rbx,0x11ff60404b21    ;; object: 0x11ff60404b21 Cell for 6097
0x35ca734657e8   168  83430bd1       addl [rbx+0xb],0xd1
0x35ca734657ec   172  791f           jns 205  (0x35ca7346580d)
0x35ca734657ee   174  50             push rax
0x35ca734657ef   175  e86c54fdff     call InterruptCheck  (0x35ca7343ac60)    ;; code: BUILTIN
0x35ca734657f4   180  58             pop rax
0x35ca734657f5   181  48bb214b4060ff110000 REX.W movq rbx,0x11ff60404b21    ;; object: 0x11ff60404b21 Cell for 6097
0x35ca734657ff   191  49ba0000000000180000 REX.W movq r10,0x180000000000
0x35ca73465809   201  4c895307       REX.W movq [rbx+0x7],r10
0x35ca7346580d   205  488be5         REX.W movq rsp,rbp      ;; debug: statement 47
                                                         ;; js return
                                                         ;; code_age_sequence

＆＃34;功能A＆＃34;中没有明确的函数调用。但是有两个函数（MakeQuadragenarianCodeYoungAgainOddMarking，StackCheck）和未知＆＃34; call＆＃34;反汇编汇编代码中的指令（＆＃34;调用0x35ca734366c0＆＃34;）。这些是什么？他们为什么需要？他们在哪里定义？

Answer 1

生成的JIT代码不是完全独立的。它在VM（v8运行时）的上下文中运行。

StackCheck：

循环需要是可中断的，V8通过放置堆栈来实现检查每个循环迭代的开始。如果运行时想要中断循环，它重置进程的堆栈限制，然后等待进程的下一次堆栈检查。

(Andy Wingo's blog)

也会在函数开头插入堆栈检查。你明白了。

MakeQuadragenarianCodeYoungAgainOddMarking可能与垃圾收集有关。 V8具有世代GC，具有年轻和老一代的物体。 JIT代码是一个堆对象。

为什么需要它们？他们在哪里定义？

它们在V8源中定义。如果您想了解更多，我鼓励您为v8内部提供网络服务。有quite a few articles。

反汇编的javascript jit代码调用未知函数

1 个答案: