原理：
1.Page Fault
进程直接访问物理内存是不安全的，所以操作系统在物流内存上又建立了一层虚拟内存，虚拟内存进行了分页。
当进程访问一个虚拟内存Page而物流内存不存在，会触发一次缺页中断（Page Fault），分配物理内存，有需要还要从磁盘mmap读入数据
通过App Store渠道分发的App，Page Fault还会进行签名验证，所以一次Page Fault的耗时比想象的要多：
2.重排：
编译器生成二进制代码时，默认按照链接的.o顺序写文件，按照.o内部顺序写函数，如果函数跨页了，就会触发多次Page Fault，所以把函数排到一个Page里，只需要一次Page Fault
重排：
1.build Setting中搜索order file
2.添加自定义的.order地址
3.程序按照order里的内容调用方法
那如何获取程序启动时方法调用顺序
插桩：
1.Build Settings 搜索 other c flags，添加-fsanitize-coverage=trace-pc-guard参数
2.粘贴如下代码到项目
/#import "Hook.h"
/#import <dlfcn.h>
/#import <libkern/OSAtomic.h>
//原子队列
static OSQueueHead symbolList = OS_ATOMIC_QUEUE_INIT;
//定义符号结构体
typedef struct {
void *pc;
void *next;
}SYNode;
void __sanitizer_cov_trace_pc_guard_init(uint32_t *start,
uint32_t *stop) {
static uint64_t N; // Counter for the guards.
if (start == stop || *start) return; // Initialize only once.
printf("INIT: %p %p\n", start, stop);
for (uint32_t *x = start; x < stop; x++)
*x = ++N; // Guards should start from 1.
}
void __sanitizer_cov_trace_pc_guard(uint32_t *guard) {
// if (!*guard) return; // Duplicate the guard check.
// // If you set *guard to 0 this code will not be called again for this edge.
// // Now you can get the PC and do whatever you want:
// // store it somewhere or symbolize it and print right away.
// // The values of `*guard` are as you set them in
// // __sanitizer_cov_trace_pc_guard_init and so you can make them consecutive
// // and use them to dereference an array or a bit vector.
// void *PC = __builtin_return_address(0);
// Dl_info info;
// dladdr(PC, &info);
// printf("fname:%s \nfbase:%p \nsname:%s \nsaddr:%p\n",
// info.dli_fname,
// info.dli_fbase,
// info.dli_sname,
// info.dli_saddr);
//
//
// char PcDescr[1024];
// // This function is a part of the sanitizer run-time.
// // To use it, link with AddressSanitizer or other sanitizer.
//// __sanitizer_symbolize_pc(PC, "%p %F %L", PcDescr, sizeof(PcDescr));
// printf("guard: %p %x PC %s\n", guard, *guard, PcDescr);
// if (!*guard) return; // Duplicate the guard check.
/* 精确定位 哪里开始 到哪里结束! 在这里面做判断写条件!*/
void *PC = __builtin_return_address(0);
Dl_info info;
dladdr(PC, &info);
printf("fname:%s \nfbase:%p \nsname:%s \nsaddr:%p\n",
info.dli_fname,
info.dli_fbase,
info.dli_sname,
info.dli_saddr);
if (![[[NSString alloc] initWithUTF8String:info.dli_sname] containsString:@"createOrderFile"]){
// [ViewController createOrderFile];
SYNode *node = malloc(sizeof(SYNode));
*node = (SYNode){PC,NULL};
//进入,因为该函数可能在子线程中操作，所以用原子性操作，保证线程安全
OSAtomicEnqueue(&symbolList, node, offsetof(SYNode, next));
}
//
}
@implementation Hook
+(void)createOrderFile{
NSMutableArray <NSString *> * symbolNames = [NSMutableArray array];
while (YES) {
SYNode * node = OSAtomicDequeue(&symbolList, offsetof(SYNode, next));
if (node == NULL) {
break;
}
Dl_info info;
dladdr(node->pc, &info);
NSString * name = @(info.dli_sname);
BOOL isObjc = [name hasPrefix:@"+["] || [name hasPrefix:@"-["];
NSString * symbolName = isObjc ? name: [@"_" stringByAppendingString:name];
[symbolNames addObject:symbolName];
}
//取反
NSEnumerator * emt = [symbolNames reverseObjectEnumerator];
//去重
NSMutableArray<NSString *> *funcs = [NSMutableArray arrayWithCapacity:symbolNames.count];
NSString * name;
while (name = [emt nextObject]) {
if (![funcs containsObject:name]) {
[funcs addObject:name];
}
}
//干掉自己!
[funcs removeObject:[NSString stringWithFormat:@"%s",__FUNCTION__]];
//将数组变成字符串
NSString * funcStr = [funcs componentsJoinedByString:@"\n"];
NSString * filePath = [NSTemporaryDirectory() stringByAppendingPathComponent:@"hank.order"];
NSData * fileContents = [funcStr dataUsingEncoding:NSUTF8StringEncoding];
[[NSFileManager defaultManager] createFileAtPath:filePath contents:fileContents attributes:nil];
NSLog(@"##########################################funcStr");
NSLog(@"%@",funcStr);
NSLog(@"%@",filePath);
}
@end
3.- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
里面调用+(void)createOrderFile
4.把得到的hank.order文件拷贝到项目的根目录下。
5.Build Settings中搜索order file，添加hank.order文件的地址(./hank.order或者${SRCROOT}/hank.order)
6.Build Settings 中搜索 link map,如果是Yes则改回No
7.去掉 Other C Flags的参数 -fsanitize-coverage=func,trace-pc-guard
8.去掉 Other Swift Flags的参数 -sanitize-coverage=func 和 -sanitize=undefined
9.注销__sanitizer_cov_trace_pc_guard_init和__sanitizer_cov_trace_pc_guard方法
参考：https://www.jianshu.com/p/ccfa14d64b0a
