一、查看OC方法汇编

准备如下代码：

//  Person.h
@interface Person : NSObject

@property (nonatomic, copy) NSString *name;
@property (nonatomic, assign) NSInteger age;

+ (instancetype)person;

@end

//  Person.m
@implementation Person

+ (instancetype)person {
    return [[Person alloc] init];
}

@end

//  main.m
int main(int argc, char * argv[]) {
    Person *p = [Person person];
    return 0;
}

汇编如下：

OC-Method`main:
    0x1021f1ed0 <+0>:   sub    sp, sp, #0x30             ; =0x30 
    0x1021f1ed4 <+4>:   stp    x29, x30, [sp, #0x20]
    0x1021f1ed8 <+8>:   add    x29, sp, #0x20            ; =0x20 
    0x1021f1edc <+12>:  stur   wzr, [x29, #-0x4]
    0x1021f1ee0 <+16>:  stur   w0, [x29, #-0x8]
    0x1021f1ee4 <+20>:  str    x1, [sp, #0x10]
    0x1021f1ee8 <+24>:  adrp   x8, 8
    0x1021f1eec <+28>:  add    x8, x8, #0x3d0            ; =0x3d0 
    0x1021f1ef0 <+32>:  ldr    x0, [x8]
    0x1021f1ef4 <+36>:  adrp   x8, 8
    0x1021f1ef8 <+40>:  add    x8, x8, #0x3c0            ; =0x3c0 
    0x1021f1efc <+44>:  ldr    x1, [x8]
    0x1021f1f00 <+48>:  bl     0x1021f2250               ; symbol stub for: objc_msgSend
    这里objc_msgSend方法有两个参数：id、SEL、汇编中通过x0和x1寄存器传递参数

    0x1021f1f04 <+52>:  mov    x29, x29
    0x1021f1f08 <+56>:  bl     0x1021f2274               ; symbol stub for: objc_retainAutoreleasedReturnValue
    0x1021f1f0c <+60>:  add    x8, sp, #0x8              ; =0x8 
    0x1021f1f10 <+64>:  str    x0, [sp, #0x8]
->  0x1021f1f14 <+68>:  stur   wzr, [x29, #-0x4]
    0x1021f1f18 <+72>:  mov    x0, x8
    0x1021f1f1c <+76>:  mov    x8, #0x0
    0x1021f1f20 <+80>:  mov    x1, x8
    0x1021f1f24 <+84>:  bl     0x1021f228c               ; symbol stub for: objc_storeStrong
    第一个参数为p（实例对象）的地址，第二参数为0x0（nil）
    调用objc_storeStrong相当于将p（实例对象）释放了
    
    0x1021f1f28 <+88>:  ldur   w0, [x29, #-0x4]
    0x1021f1f2c <+92>:  ldp    x29, x30, [sp, #0x20]
    0x1021f1f30 <+96>:  add    sp, sp, #0x30             ; =0x30 
    0x1021f1f34 <+100>: ret

查看x0和x1寄存器中的值：

objc_storeStrong：

void
objc_storeStrong(id *location, id obj)
{
    id prev = *location;
    if (obj == prev) {
        return;
    }
    objc_retain(obj);
    *location = obj;
    objc_release(prev);
}

二、使用反汇编工具分析汇编

修改main中的代码：

int main(int argc, char * argv[]) {
    Person *p = [Person person];
    p.name = @"differ";
    p.age  = 18;
    
    return 0;
}

编译-->将编译后的可执行文件拖到Hopper中:

三、Block反汇编

int main(int argc, char * argv[]) {
    void (^block)(void) = ^() {
        NSLog(@"block");
    };
    
    block();

    return 0;
}

由于block中的实现代码保存到invoke中的，所以分析block汇编代码主要找到invoke

struct Block_ layout {
    void *isa; // 8字节
    volatile int32_t flags; // contains ref count  4字节
    int32_t reserved; // 4字节
    BlockInvokeFunction invoke; // 因此invoke变量地址就是block地址+16字节
    struct Block_descriptor_1 *descriptor;
    // imported variables
};