密码学简介
//------------------------------------ 源码 ------------------------------------
int main(int argc, char * argv[]) {
//p = nil
Person * p = [[Person alloc] init];
p.name = @"hank";
p.age = 18;
//[Person alloc]
//objc_msgSend(Person.class,@selector(alloc));
}
/* 总结：上面👆
所有OC中使用Strong 修饰的对象,实际上是调用了这个函数 objc_storeStrong（强引用）
以下是objc_storeStrong的源码实现过程：
void objc_storeStrong(id *location, id obj)
{
id perv = *lopcation;//本地对象 location，obj 是传进来的对象
if(obj == prev){
return;
}
objc_retain(obj); // 保存对象不释放，为了后面的可能使用，如果穿进来的obj= nil, -->看下面👇
*location = obj; // --> 则：让指针指向nil，即 *location = nil (*p = nil, //释放p之前，先让 p = nil)
objc_release(prev); // 释放 判断时使用的对象 prev = nil
}
p（对象）创建后，后面可能会使用，栈空间系统会自动回收，指针会立刻没有了，对象应该释放，malloc 创建的必须free，
但是这里只有：retain、release
*/
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内存指令分析
Debug Workflow - Always Show Disassembly
Debug Workflow Always Show Disassembly 内存指令分析-
LLDB汇编调试
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MachOView 汇编分析
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最后附上分析的源码
**************** 内存指令分析****************
002--OC方法`main:
0x104cd6680 <+0>: sub sp, sp, #0x30 ; =0x30 // 0x104cd6000 --> 0x104cd6680 地址空间布局随机化 aslr 是偏移地址
0x104cd6684 <+4>: stp x29, x30, [sp, #0x20]
0x104cd6688 <+8>: add x29, sp, #0x20 ; =0x20
0x104cd668c <+12>: adrp x8, 2
0x104cd6690 <+16>: add x8, x8, #0xe18 ; =0xe18 //0x104cd668c --> 0x104cd8e18
0x104cd6694 <+20>: adrp x9, 2
0x104cd6698 <+24>: add x9, x9, #0xe38 ; =0xe38 //0x104cd6694 --> 0x104cd8e38
0x104cd669c <+28>: stur w0, [x29, #-0x4]
0x104cd66a0 <+32>: str x1, [sp, #0x10]
-> 0x104cd66a4 <+36>: ldr x9, [x9] //x9是对象或类
0x104cd66a8 <+40>: ldr x1, [x8] //x8是指针， x1 是方法名称
0x104cd66ac <+44>: mov x0, x9
0x104cd66b0 <+48>: bl 0x104cd6b20 ; symbol stub for: objc_msgSend
0x104cd66b4 <+52>: adrp x8, 2
0x104cd66b8 <+56>: add x8, x8, #0xe20 ; =0xe20
0x104cd66bc <+60>: ldr x1, [x8]
0x104cd66c0 <+64>: bl 0x104cd6b20 ; symbol stub for: objc_msgSend
0x104cd66c4 <+68>: adrp x8, 2
0x104cd66c8 <+72>: add x8, x8, #0x38 ; =0x38
0x104cd66cc <+76>: adrp x9, 2
0x104cd66d0 <+80>: add x9, x9, #0xe28 ; =0xe28
0x104cd66d4 <+84>: str x0, [sp, #0x8]
0x104cd66d8 <+88>: ldr x0, [sp, #0x8]
0x104cd66dc <+92>: ldr x1, [x9]
0x104cd66e0 <+96>: mov x2, x8
0x104cd66e4 <+100>: bl 0x104cd6b20 ; symbol stub for: objc_msgSend
0x104cd66e8 <+104>: mov w2, #0x12
0x104cd66ec <+108>: adrp x8, 2
0x104cd66f0 <+112>: add x8, x8, #0xe30 ; =0xe30
0x104cd66f4 <+116>: ldr x9, [sp, #0x8]
0x104cd66f8 <+120>: ldr x1, [x8]
0x104cd66fc <+124>: mov x0, x9
0x104cd6700 <+128>: bl 0x104cd6b20 ; symbol stub for: objc_msgSend
0x104cd6704 <+132>: mov x8, #0x0
0x104cd6708 <+136>: add x9, sp, #0x8 ; =0x8
0x104cd670c <+140>: mov x0, x9
0x104cd6710 <+144>: mov x1, x8
0x104cd6714 <+148>: bl 0x104cd6b44 ; symbol stub for: objc_storeStrong
0x104cd6718 <+152>: mov w2, #0x0
0x104cd671c <+156>: mov x0, x2
0x104cd6720 <+160>: ldp x29, x30, [sp, #0x20]
0x104cd6724 <+164>: add sp, sp, #0x30 ; =0x30 // 释放p
0x104cd6728 <+168>: ret
注意： adrp、add 取地址，要么是全局变量，要么是常量，要么是方法名，x8 保存8个字节的数据
0x104cd668c <+12>: adrp x8, 2
0x104cd6690 <+16>: add x8, x8, #0xe18 ; =0xe18 //0x104cd668c --> 0x104cd8e18
**************** LLDB 汇编调试 指令 ****************
//------------------------------------ LLDB 汇编调试 ------------------------------------
(lldb) x 0x104cd8e18
0x104cd8e18: cc 72 fe 8c 01 00 00 00 30 72 fe 8c 01 00 00 00 .r......0r......
0x104cd8e28: c8 c7 fe 8c 01 00 00 00 1f ea c0 88 01 00 00 00 ................
(lldb) p (SEL) 0x104cd8e18 // 1
(SEL) $0 = "alloc"
(lldb) p (char *)0x018cfe72cc // 2 （1同2）
(char *) $1 = 0x000000018cfe72cc "alloc"
(lldb) x 0x104cd8e38
0x104cd8e38: d0 8e cd 04 01 00 00 00 58 8e cd 04 01 00 00 00 ........X.......
0x104cd8e48: 10 00 00 00 08 00 00 00 08 00 00 00 00 00 00 00 ................
(lldb) po 0x0104cd8ed0
Person
(lldb) register read x0
x0 = 0x00000001c0033560
(lldb) x 0x00000001c0033560
0x1c0033560: d5 8e cd 04 a1 01 00 00 00 00 00 00 00 00 00 00 ................
0x1c0033570: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
(lldb) po 01a104cd8ed5
error: invalid digit 'a' in octal constant
(lldb) po 0x00000001c0033560 //对象
<Person: 0x1c0033560>
(lldb) po p
nil
(lldb) register read x1
x1 = 0x000000018cfe7230 "init" // init 方法
(lldb) n
(lldb) po p
<Person: 0x1c0033560>
(lldb)
// 对此行断点
-> 0x104cd6714 <+148>: bl 0x104cd6b44 ; symbol stub for: objc_storeStrong
(lldb) register read x0
x0 = 0x000000016b12f968
(lldb) po 0x000000016b12f968
6091372904
(lldb) x 0x000000016b12f968 //二级指针，是p的指针
0x16b12f968: 60 35 03 c0 01 00 00 00 c8 f9 12 6b 01 00 00 00 `5.........k....
0x16b12f978: 00 00 00 00 01 00 00 00 a0 f9 12 6b 01 00 00 00 ...........k....
(lldb) po 0x01c0033560 //一级级指针，是p的对象
<Person: 0x1c0033560>
(lldb) register read x1
x1 = 0x0000000000000000 //释放p之前，先让 p = nil //
(lldb)
**************** MachOView 汇编分析源码 ****************
*Mach64 Header：头
Load Commands：加载的指令集，库、数据表，描述了下面的数据
Section64：全是数据
Section64（__TEXT__）：代码段
Section64（__DATA__）：数据段
*************************************************
__text:0000000100006680 _main
__text:0000000100006680
__text:0000000100006680 var_18 = -0x18
__text:0000000100006680 var_10 = -0x10
__text:0000000100006680 var_4 = -4
__text:0000000100006680 var_s0 = 0
__text:0000000100006680
__text:0000000100006680 SUB SP, SP, #0x30
__text:0000000100006684 STP X29, X30, [SP,#0x20+var_s0]
__text:0000000100006688 ADD X29, SP, #0x20
__text:000000010000668C ADRP X8, #selRef_alloc@PAGE // x8的地址是 sel 指针
__text:0000000100006690 ADD X8, X8, #selRef_alloc@PAGEOFF
__text:0000000100006694 ADRP X9, #classRef_Person@PAGE // x9的地址 calss 类指针
__text:0000000100006698 ADD X9, X9, #classRef_Person@PAGEOFF
__text:000000010000669C STUR W0, [X29,#var_4]
__text:00000001000066A0 STR X1, [SP,#0x20+var_10]
__text:00000001000066A4 LDR X9, [X9] ; _OBJC_CLASS_$_Person // objc_class 对象 Person
__text:00000001000066A8 LDR X1, [X8] ; "alloc" // alloc
__text:00000001000066AC MOV X0, X9 ; void *
__text:00000001000066B0 BL _objc_msgSend // init
__text:00000001000066B4 ADRP X8, #selRef_init@PAGE
__text:00000001000066B8 ADD X8, X8, #selRef_init@PAGEOFF
__text:00000001000066BC LDR X1, [X8] ; "init"
__text:00000001000066C0 BL _objc_msgSend // setName
__text:00000001000066C4 ADRP X8, #cfstr_Hank@PAGE ; "hank"
__text:00000001000066C8 ADD X8, X8, #cfstr_Hank@PAGEOFF ; "hank"
__text:00000001000066CC ADRP X9, #selRef_setName_@PAGE
__text:00000001000066D0 ADD X9, X9, #selRef_setName_@PAGEOFF
__text:00000001000066D4 STR X0, [SP,#0x20+var_18]
__text:00000001000066D8 LDR X0, [SP,#0x20+var_18] ; void *
__text:00000001000066DC LDR X1, [X9] ; "setName:"
__text:00000001000066E0 MOV X2, X8
__text:00000001000066E4 BL _objc_msgSend // setAge
__text:00000001000066E8 MOV W2, #0x12
__text:00000001000066EC ADRP X8, #selRef_setAge_@PAGE
__text:00000001000066F0 ADD X8, X8, #selRef_setAge_@PAGEOFF
__text:00000001000066F4 LDR X9, [SP,#0x20+var_18]
__text:00000001000066F8 LDR X1, [X8] ; "setAge:"
__text:00000001000066FC MOV X0, X9 ; void *
__text:0000000100006700 BL _objc_msgSend //
__text:0000000100006704 MOV X8, #0
__text:0000000100006708 ADD X9, SP, #0x20+var_18
__text:000000010000670C MOV X0, X9
__text:0000000100006710 MOV X1, X8
__text:0000000100006714 BL _objc_storeStrong //
__text:0000000100006718 MOV W2, #0
__text:000000010000671C MOV X0, X2
__text:0000000100006720 LDP X29, X30, [SP,#0x20+var_s0]
__text:0000000100006724 ADD SP, SP, #0x30
__text:0000000100006728 RET
__text:0000000100006728 ; End of function _main
__text:0000000100006728