应用程序加载

应用程序加载原理
库：可执行的二进制文件，加载到内存
文件类型：
静态库 .a
动态库 .so .dll
两者是链接的区别

编译过程

我们可以直接打开工程目录Products下的.app文件找到可执行文件拖到终端可以直接运行

加载过程

库- 映射到内存 images

//输出
+[ViewController load]
(lldb) image list
[  0] 404C4B96-E4D1-3501-BBDA-B6895DA2626A 0x000000010080c000
[  1] 1AC76561-4F9A-34B1-BA7C-4516CACEAED7 0x0000000101122000 /usr/lib/dyld 
[  2] 2A92FC99-72A9-38ED-8DDD-AF4C25080124 0x0000000100820000 /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/usr/lib/dyld_sim 
[  3] C2A18288-4AA2-3189-A1C6-5963E370DE4C 0x00007fff2071f000 /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/Frameworks/Foundation.framework/Foundation 

接下来看dyld 动态链接器

ViewController.m bt

dyldbootstrap jump 查找start

//重点看返回
return dyld::_main((macho_header*)appsMachHeader, appsSlide, argc, argv, envp, apple, startGlue);

_main jump

getHostInfo jump

//instantiateFromLoadedImage   镜像文件加载器
CRSetCrashLogMessage(sLoadingCrashMessage);
        // instantiate ImageLoader for main executable
        sMainExecutable = instantiateFromLoadedImage(mainExecutableMH, mainExecutableSlide, sExecPath);
        gLinkContext.mainExecutable = sMainExecutable;
        gLinkContext.mainExecutableCodeSigned = hasCodeSignatureLoadCommand(mainExecutableMH);

instantiateFromLoadedImage jump

addImage jump

instantiateMainExecutable jump

allImagesCount 拿到所有镜像文件个数

再执行runInitializers
runInitializers jump

//重点代码
processInitializers(context, thisThread, timingInfo, up);
context.notifyBatch(dyld_image_state_initialized, false);

processInitializers jump

recursiveInitialization jump

//重点代码  
context.notifySingle(dyld_image_state_dependents_initialized, this, &timingInfo);           
// initialize this image        
bool hasInitializers = this->doInitialization(context);

notifySingle jump
void (notifySingle)(dyld_image_states, const ImageLoader image, InitializerTimingList*);

单一注册通知

notifyMonitoringDyld
sNotifyObjCInit

registerObjCNotifiers jump

sNotifyObjCInit = init;

单个镜像文件加载->_dyld_objc_notify_register

registerObjCNotifiers

_os_object_init jump

libdispatch_init jump

发现了_os_object_init();

libSystem_initializer jump

//重点代码 调用libdispatch_init
    libdispatch_init();
    _libSystem_ktrace_init_func(LIBDISPATCH);

doModInitFunctions jump

//重点代码 libSystemInitialized
if ( ! dyld::gProcessInfo->libSystemInitialized ) {
    // <rdar://problem/17973316> libSystem initializer must run first
        const char* installPath = getInstallPath();
        if ( (installPath == NULL) || (strcmp(installPath, libSystemPath(context)) != 0) )
            dyld::throwf("initializer in image (%s) that does not link with libSystem.dylib\n", this->getPath());
            }
                            
func(context.argc, context.argv, context.envp, context.apple, &context.programVars);

ImageLoaderMachO 里调用了 doModInitFunctions
初始化镜像文件 调用doModInitFunctions

流程梳理

_os_object_init (libdispatch) -> _objc_init (libobjc)

未完待续......