探索Objective-C对象调用方法最终生成C语言

在OC 对象调用实例方法的时候最终都会转为 objc_msgSend
例如在viewController 对象调用如下方法：

[self testString:@"哈哈" intValue:100 stringValue:@"溜溜"];

在实例对象调用的时候会被转为

objc_msgSend(self,@selector(testString:intValue:stringValue:),@"哈哈",100,@"溜溜");

在arm64架构显示汇编如下：

LLDB_stady`objc_msgSend:
->  0x1000f2978 <+0>: nop    
    0x1000f297c <+4>: ldr    x16, #0x16b4              ; (void *)0x0000000196d75bc0: objc_msgSend
    0x1000f2980 <+8>: br     x16

在arm64架构查看寄存器

(lldb) register read
General Purpose Registers:
        x0 = 0x0000000154549790
        x1 = 0x00000001000f2b08  "testString:intValue:stringValue:"
        x2 = 0x00000001000f4078  @
        x3 = 0x0000000000000064
        x4 = 0x00000001000f4098  @
        x5 = 0x000000016fd11c40
        x6 = 0x0000000000000000
        x7 = 0x0000000000000250
        x8 = 0x00000001000f4078  @
        x9 = 0x00000001000f4098  @
       x10 = 0x00000001000f4f08  "testString:intValue:stringValue:"
       x11 = 0x0000000154549790
       x12 = 0x0028be000028be00
       x13 = 0x0000000000000000
       x14 = 0x0000000022a28888
       x15 = 0x0000000154600000
       x16 = 0x000000019779564c  libsystem_pthread.dylib`pthread_mutex_unlock
       x17 = 0x00000001878b3500  UIKit`-[UIViewController viewDidLoad]
       x18 = 0x0000000000000000
       x19 = 0x000000019e05ffe0  UIKit`_UIApplicationLinkedOnVersion
       x20 = 0x0000000154549790
       x21 = 0x00000001882055fc  "countByEnumeratingWithState:objects:count:"
       x22 = 0x000000018820586a  "count"
       x23 = 0x000000019d3a8000  UIKit`_UIFocusEngine._smallSoundPool
       x24 = 0x0000000000000000
       x25 = 0x0000000000000010
       x26 = 0x0000000000000001
       x27 = 0x0000000000000018
       x28 = 0x0000000000000000
        fp = 0x000000016fd11e40
        lr = 0x00000001000f2370  LLDB_stady`-[ViewController viewDidLoad] + 116 at ViewController.m:69:1
        sp = 0x000000016fd11e20
        pc = 0x00000001000f2978  LLDB_stady`symbol stub for: objc_msgSend
      cpsr = 0x60000000

查看具体参数

(lldb) po 0x0000000154549790


(lldb) po $x0

 x1 = 0x00000001000f2b08  "testString:intValue:stringValue:"

(lldb) po $x2
哈哈
(lldb) po $x3
100
(lldb) po $x4
溜溜

总结：方法在被实例对象调用的时候，寄存器x0 存放的是实例对象，x1存放被调用的方法，参数往后的寄存器按顺序排放