objc_init分析
objc_init源码
/***********************************************************************
* _objc_init
* Bootstrap initialization. Registers our image notifier with dyld.
* Called by libSystem BEFORE library initialization time
**********************************************************************/
__attribute__((constructor)) void objcFunc(){
printf("来了 : %s \n",__func__);
}
void _objc_init(void)
{
static bool initialized = false;
if (initialized) return;
initialized = true;
// fixme defer initialization until an objc-using image is found?
environ_init();//环境变量的初始化，可以通过在xode中配置相关的环境变量开关，查看需要的信息
tls_init();//线程相关
/****************************************************
* static_init
* Run C++ static constructor functions.
* libc calls _objc_init() before dyld would call our static constructors,
* so we have to do it ourselves.
***************************************************/
static_init();//c++全局构造函数调用
runtime_init();
/**************************************************
* exception_init
* Initialize libobjc's exception handling system.
* Called by map_images().
************************************************/
exception_init();
#if __OBJC2__
cache_t::init();//缓存条件初始化
#endif
_imp_implementationWithBlock_init();
_dyld_objc_notify_register(&map_images, load_images, unmap_image);
// map_images()
// load_images()
#if __OBJC2__
didCallDyldNotifyRegister = true;
#endif
}
打印环境变量帮助：代码资源
以上相关函数的解释：
_dyld_objc_notify_register
read_images流程
map_images
/***********************************************************************
* map_images
* Process the given images which are being mapped in by dyld.
* Calls ABI-agnostic code after taking ABI-specific locks.
*
* Locking: write-locks runtimeLock
**********************************************************************/
void
map_images(unsigned count, const char * const paths[],
const struct mach_header * const mhdrs[])
{
mutex_locker_t lock(runtimeLock);
return map_images_nolock(count, paths, mhdrs);
}
/***********************************************************************
* map_images_nolock
* Process the given images which are being mapped in by dyld.
* All class registration and fixups are performed (or deferred pending
* discovery of missing superclasses etc), and +load methods are called.
*
* info[] is in bottom-up order i.e. libobjc will be earlier in the
* array than any library that links to libobjc.
*
* Locking: loadMethodLock(old) or runtimeLock(new) acquired by map_images.
**********************************************************************/
void
map_images_nolock(unsigned mhCount, const char * const mhPaths[],
const struct mach_header * const mhdrs[])
{
...
if (hCount > 0) {
_read_images(hList, hCount, totalClasses, unoptimizedTotalClasses);
}
firstTime = NO;
// Call image load funcs after everything is set up.
for (auto func : loadImageFuncs) {
for (uint32_t i = 0; i < mhCount; i++) {
func(mhdrs[i]);
}
}
}
read_images
/*********************************************************
* _read_images
* Perform initial processing of the headers in the linked
* list beginning with headerList.
*
* Called by: map_images_nolock
*
* Locking: runtimeLock acquired by map_images
***********************************************************/
void _read_images(header_info **hList, uint32_t hCount, int totalClasses, int unoptimizedTotalClasses)
{
...
ts.log("IMAGE TIMES: first time tasks");
ts.log("IMAGE TIMES: fix up selector references");
ts.log("IMAGE TIMES: discover classes");
ts.log("IMAGE TIMES: remap classes");
ts.log("IMAGE TIMES: fix up objc_msgSend_fixup");
ts.log("IMAGE TIMES: discover protocols");
ts.log("IMAGE TIMES: fix up @protocol references");
ts.log("IMAGE TIMES: discover categories");
ts.log("IMAGE TIMES: realize non-lazy classes");
ts.log("IMAGE TIMES: realize future classes");
...
}
readClass分析
/***********************************************************************
* readClass
* Read a class and metaclass as written by a compiler.
* Returns the new class pointer. This could be:
* - cls
* - nil (cls has a missing weak-linked superclass)
* - something else (space for this class was reserved by a future class)
*
* Note that all work performed by this function is preflighted by
* mustReadClasses(). Do not change this function without updating that one.
*
* Locking: runtimeLock acquired by map_images or objc_readClassPair
**********************************************************************/
Class readClass(Class cls, bool headerIsBundle, bool headerIsPreoptimized)
{
const char *mangledName = cls->nonlazyMangledName();
const char *LGPersonName = "LGPerson";
if (strcmp(mangledName, LGPersonName) == 0) {
// 自己写得类，是如何加载到内存的
printf("%s -KC: 要研究的: - %s\n",__func__,mangledName);
}
...
cls->fixupBackwardDeployingStableSwift();
//自己写的类不会进入下面的判断里面
Class replacing = nil;
if (mangledName != nullptr) {
if (Class newCls = popFutureNamedClass(mangledName)) {
// This name was previously allocated as a future class.
// Copy objc_class to future class's struct.
// Preserve future's rw data block.
if (newCls->isAnySwift()) {
_objc_fatal("Can't complete future class request for '%s' "
"because the real class is too big.",
cls->nameForLogging());
}
class_rw_t *rw = newCls->data();
const class_ro_t *old_ro = rw->ro();
memcpy(newCls, cls, sizeof(objc_class));
// Manually set address-discriminated ptrauthed fields
// so that newCls gets the correct signatures.
newCls->setSuperclass(cls->getSuperclass());
newCls->initIsa(cls->getIsa());
rw->set_ro((class_ro_t *)newCls->data());
newCls->setData(rw);
freeIfMutable((char *)old_ro->getName());
free((void *)old_ro);
addRemappedClass(cls, newCls);
replacing = cls;
cls = newCls;
}
}
if (headerIsPreoptimized && !replacing) {
// class list built in shared cache
// fixme strict assert doesn't work because of duplicates
// ASSERT(cls == getClass(name));
ASSERT(mangledName == nullptr || getClassExceptSomeSwift(mangledName));
} else {
if (mangledName) { //some Swift generic classes can lazily generate their names
addNamedClass(cls, mangledName, replacing);
} else {
Class meta = cls->ISA();
const class_ro_t *metaRO = meta->bits.safe_ro();
ASSERT(metaRO->getNonMetaclass() && "Metaclass with lazy name must have a pointer to the corresponding nonmetaclass.");
ASSERT(metaRO->getNonMetaclass() == cls && "Metaclass nonmetaclass pointer must equal the original class.");
}
addClassTableEntry(cls);
}
// for future reference: shared cache never contains MH_BUNDLEs
if (headerIsBundle) {
cls->data()->flags |= RO_FROM_BUNDLE;
cls->ISA()->data()->flags |= RO_FROM_BUNDLE;
}
return cls;
}
小结
本次知识内容，从 dyld 进入 objc_init, 重点分析了 objc_init 内部的部分方法，包括一些初始化的内容，其中重点是 _dyld_objc_notify_register ，在这里有两个重要的方法执行 map_images 和 load_images，然后深入分析了 map_images方法，接下来继续探索map_images里面的内容。
