启动优化优秀文章和部分内容摘录

https://mp.weixin.qq.com/s/LSj63THjgt2XKxkapAQpCg

首先在other C flag中增加下面这段：-fsanitize-coverage=func,trace-pc-guard

#import <dlfcn.h>
#import <libkern/OSAtomicQueue.h>
#import <pthread.h>

typedef struct {
    void *ptr;
    NSInteger number;
} CLRCall;

static OSQueueHead sQueueData = OS_ATOMIC_QUEUE_INIT;
static OSQueueHead *sQueue = &sQueueData;
static BOOL sStopCollecting = NO;
static BOOL sInitDidOccur = NO;

typedef struct {
    void *pointer;
    void *next;
} PointerNode;

void __sanitizer_cov_trace_pc_guard_init(uint32_t *start, uint32_t *stop) {
    sInitDidOccur = YES;
    for (uint32_t *x = start; x < stop; x++) {
        *x = 1;
    }
}

void __sanitizer_cov_trace_pc_guard(uint32_t *guard) {
    // If initialization has not occurred yet (meaning that guard is uninitialized), that means that initial functions like +load are being run. These functions will only be run once anyways, so we should always allow them to be recorded and ignore guard
    if (sStopCollecting || (!(*guard) && sInitDidOccur)) {
        return;
    }
    *guard = 0;
    void *pointer = __builtin_return_address(0);
    PointerNode *node = malloc(sizeof(PointerNode));
    *node = (PointerNode){pointer, NULL};
    OSAtomicEnqueue(sQueue, node, offsetof(PointerNode, next));
}

extern NSArray <NSString *> *CLRCollectCalls(void) {
    sStopCollecting = YES;
    __sync_synchronize();
    // Hopefully, any other threads for which sStopCollecting was NO when they entered and are still preempted will get to preempt
    // during this sleep and finish up
    sleep(1);
    NSMutableArray <NSString *> *functions = [NSMutableArray array];
    while (YES) {
        PointerNode *node = OSAtomicDequeue(sQueue, offsetof(PointerNode, next));
        if (node == NULL) {
            break;
        }
        Dl_info info = {0};
        dladdr(node->pointer, &info);
        NSString *name = @(info.dli_sname);
        BOOL isObjc = [name hasPrefix:@"+["] || [name hasPrefix:@"-["];
        NSString *symbolName = isObjc ? name : [@"_" stringByAppendingString:name];
        [functions addObject:symbolName];
    }
    return [[functions reverseObjectEnumerator] allObjects];
}