前言
之前，我们研究了很多关于iOS底层相对零碎的知识。
而iOS对用户来说，最重要的就是每一个APP。
今天，我们来研究一下APP的启动入口。
- 首先，我们新建一个
SingleViewApp - 我们在
main()函数处打一个断点。 - 我们在
ViewController.m中实现一个load方法
+ (void)load{
NSLog(@"%s",__func__);
}
同时在此处也打一个断点。
通常意义上，我们说一个APP的入口就是main()或者+(void)load
所以，我们在此处打断点看看在入口前，系统为我们做了什么
在两个断点处，可以看见先进入了+(void)load方法。
使用lldb bt 打印栈信息
(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 2.1
* frame #0: 0x00000001060e3e77 002-应用程加载分析`+[ViewController load](self=ViewController, _cmd="load") at ViewController.m:17:5
frame #1: 0x00000001069be317 libobjc.A.dylib`call_load_methods + 691
frame #2: 0x00000001069bf814 libobjc.A.dylib`load_images + 77
frame #3: 0x00000001060f207e dyld_sim`dyld::notifySingle(dyld_image_states, ImageLoader const*, ImageLoader::InitializerTimingList*) + 420
frame #4: 0x00000001060ff3e7 dyld_sim`ImageLoader::recursiveInitialization(ImageLoader::LinkContext const&, unsigned int, char const*, ImageLoader::InitializerTimingList&, ImageLoader::UninitedUpwards&) + 303
frame #5: 0x00000001060fe5d3 dyld_sim`ImageLoader::processInitializers(ImageLoader::LinkContext const&, unsigned int, ImageLoader::InitializerTimingList&, ImageLoader::UninitedUpwards&) + 133
frame #6: 0x00000001060fe665 dyld_sim`ImageLoader::runInitializers(ImageLoader::LinkContext const&, ImageLoader::InitializerTimingList&) + 73
frame #7: 0x00000001060f2379 dyld_sim`dyld::initializeMainExecutable() + 199
frame #8: 0x00000001060f6434 dyld_sim`dyld::_main(macho_header const*, unsigned long, int, char const**, char const**, char const**, unsigned long*) + 4384
frame #9: 0x00000001060f1630 dyld_sim`start_sim + 136
frame #10: 0x000000010775785c dyld`dyld::useSimulatorDyld(int, macho_header const*, char const*, int, char const**, char const**, char const**, unsigned long*, unsigned long*) + 2308
frame #11: 0x00000001077554f4 dyld`dyld::_main(macho_header const*, unsigned long, int, char const**, char const**, char const**, unsigned long*) + 837
frame #12: 0x0000000107750227 dyld`dyldbootstrap::start(dyld3::MachOLoaded const*, int, char const**, dyld3::MachOLoaded const*, unsigned long*) + 453
frame #13: 0x0000000107750025 dyld`_dyld_start + 37
随后跳过断点继续运行，断点走到main()
使用lldb bt 打印栈信息
(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
* frame #0: 0x00000001060e40fd 002-应用程加载分析`main(argc=1, argv=0x00007ffee9b1b180) at main.m:16:16
frame #1: 0x0000000108dfe541 libdyld.dylib`start + 1
通过两处的bt打印，我们可以看到，入口都是在dyld中
对照前面的栈方法信息，我们来研究一下dyld的流程
dyld简介
dyld（the dynamic link editor）是苹果的动态链接器，是苹果操作系统一个重要组成部分，在系统内核做好程序准备工作之后，交由dyld负责余下的工作。
dyld下载地址：http://opensource.apple.com/tarballs/dyld。
这里，我们下载一份官方的开源代码来参考研究，这里的版本是750.6.0.
dyld代码分析
从之前的bt方法打印中，我们能看到dyld在load加载前的大概流程
bt方法打印简图.png
现在，我们就按照这个流程来研究一下dyld源码
_dyld_start:
#if __arm64__
.text
.align 2
.globl __dyld_start
__dyld_start:
mov x28, sp
and sp, x28, #~15 // force 16-byte alignment of stack
mov x0, #0
mov x1, #0
stp x1, x0, [sp, #-16]! // make aligned terminating frame
mov fp, sp // set up fp to point to terminating frame
sub sp, sp, #16 // make room for local variables
#if __LP64__
ldr x0, [x28] // get app's mh into x0
ldr x1, [x28, #8] // get argc into x1 (kernel passes 32-bit int argc as 64-bits on stack to keep alignment)
add x2, x28, #16 // get argv into x2
#else
ldr w0, [x28] // get app's mh into x0
ldr w1, [x28, #4] // get argc into x1 (kernel passes 32-bit int argc as 64-bits on stack to keep alignment)
add w2, w28, #8 // get argv into x2
#endif
adrp x3,___dso_handle@page
add x3,x3,___dso_handle@pageoff // get dyld's mh in to x4
mov x4,sp // x5 has &startGlue
// call dyldbootstrap::start(app_mh, argc, argv, dyld_mh, &startGlue)
bl __ZN13dyldbootstrap5startEPKN5dyld311MachOLoadedEiPPKcS3_Pm
mov x16,x0 // save entry point address in x16
#if __LP64__
ldr x1, [sp]
#else
ldr w1, [sp]
#endif
cmp x1, #0
b.ne Lnew
// LC_UNIXTHREAD way, clean up stack and jump to result
#if __LP64__
add sp, x28, #8 // restore unaligned stack pointer without app mh
#else
add sp, x28, #4 // restore unaligned stack pointer without app mh
#endif
#if __arm64e__
braaz x16 // jump to the program's entry point
#else
br x16 // jump to the program's entry point
#endif
// LC_MAIN case, set up stack for call to main()
Lnew: mov lr, x1 // simulate return address into _start in libdyld.dylib
#if __LP64__
ldr x0, [x28, #8] // main param1 = argc
add x1, x28, #16 // main param2 = argv
add x2, x1, x0, lsl #3
add x2, x2, #8 // main param3 = &env[0]
mov x3, x2
Lapple: ldr x4, [x3]
add x3, x3, #8
#else
ldr w0, [x28, #4] // main param1 = argc
add x1, x28, #8 // main param2 = argv
add x2, x1, x0, lsl #2
add x2, x2, #4 // main param3 = &env[0]
mov x3, x2
Lapple: ldr w4, [x3]
add x3, x3, #4
#endif
cmp x4, #0
b.ne Lapple // main param4 = apple
#if __arm64e__
braaz x16
#else
br x16
#endif
#endif // __arm64__
在汇编源码中，我们可以看到
// call dyldbootstrap::start(app_mh, argc, argv, dyld_mh, &startGlue)
bl __ZN13dyldbootstrap5startEPKN5dyld311MachOLoadedEiPPKcS3_Pm
指向了dyldbootstrap::start
dyldbootstrap::start
全局搜索dyldbootstrap，找到其作用域，然后找到其中的start方法
uintptr_t start(const dyld3::MachOLoaded* appsMachHeader, int argc, const char* argv[],
const dyld3::MachOLoaded* dyldsMachHeader, uintptr_t* startGlue)
{
// Emit kdebug tracepoint to indicate dyld bootstrap has started
dyld3::kdebug_trace_dyld_marker(DBG_DYLD_TIMING_BOOTSTRAP_START, 0, 0, 0, 0);
// if kernel had to slide dyld, we need to fix up load sensitive locations
// we have to do this before using any global variables
rebaseDyld(dyldsMachHeader);
// kernel sets up env pointer to be just past end of agv array
const char** envp = &argv[argc+1];
// kernel sets up apple pointer to be just past end of envp array
const char** apple = envp;
while(*apple != NULL) { ++apple; }
++apple;
// set up random value for stack canary
__guard_setup(apple);
#if DYLD_INITIALIZER_SUPPORT
// run all C++ initializers inside dyld
runDyldInitializers(argc, argv, envp, apple);
#endif
// now that we are done bootstrapping dyld, call dyld's main
uintptr_t appsSlide = appsMachHeader->getSlide();
return dyld::_main((macho_header*)appsMachHeader, appsSlide, argc, argv, envp, apple, startGlue);
}
start()函数中做了很多dyld初始化相关的工作，包括：
-
rebaseDyld()dyld重定位。 -
mach_init()mach消息初始化。 -
__guard_setup()栈溢出保护。
完成初始化后，我们直接翻到return
// now that we are done bootstrapping dyld, call dyld's main
uintptr_t appsSlide = appsMachHeader->getSlide();
return dyld::_main((macho_header*)appsMachHeader, appsSlide, argc, argv, envp, apple, startGlue);
能看见这里，返回了dyld的main方法
dyld::_main()
跳转到dyld::_main后，
//
// Entry point for dyld. The kernel loads dyld and jumps to __dyld_start which
// sets up some registers and call this function.
//
// Returns address of main() in target program which __dyld_start jumps to
//
uintptr_t
_main(const macho_header* mainExecutableMH, uintptr_t mainExecutableSlide,
int argc, const char* argv[], const char* envp[], const char* apple[],
uintptr_t* startGlue)
{
if (dyld3::kdebug_trace_dyld_enabled(DBG_DYLD_TIMING_LAUNCH_EXECUTABLE)) {
launchTraceID = dyld3::kdebug_trace_dyld_duration_start(DBG_DYLD_TIMING_LAUNCH_EXECUTABLE, (uint64_t)mainExecutableMH, 0, 0);
}
//Check and see if there are any kernel flags
dyld3::BootArgs::setFlags(hexToUInt64(_simple_getenv(apple, "dyld_flags"), nullptr));
// Grab the cdHash of the main executable from the environment
//第一步，设置运行环境
uint8_t mainExecutableCDHashBuffer[20];
const uint8_t* mainExecutableCDHash = nullptr;
if ( hexToBytes(_simple_getenv(apple, "executable_cdhash"), 40, mainExecutableCDHashBuffer) )
// 获取主程序的hash
mainExecutableCDHash = mainExecutableCDHashBuffer;
#if !TARGET_OS_SIMULATOR
// Trace dyld's load
notifyKernelAboutImage((macho_header*)&__dso_handle, _simple_getenv(apple, "dyld_file"));
// Trace the main executable's load
notifyKernelAboutImage(mainExecutableMH, _simple_getenv(apple, "executable_file"));
#endif
uintptr_t result = 0;
// 获取主程序的macho_header结构
sMainExecutableMachHeader = mainExecutableMH;
// 获取主程序的slide值
sMainExecutableSlide = mainExecutableSlide;
// Set the platform ID in the all image infos so debuggers can tell the process type
// FIXME: This can all be removed once we make the kernel handle it in rdar://43369446
if (gProcessInfo->version >= 16) {
__block bool platformFound = false;
((dyld3::MachOFile*)mainExecutableMH)->forEachSupportedPlatform(^(dyld3::Platform platform, uint32_t minOS, uint32_t sdk) {
if (platformFound) {
halt("MH_EXECUTE binaries may only specify one platform");
}
gProcessInfo->platform = (uint32_t)platform;
platformFound = true;
});
if (gProcessInfo->platform == (uint32_t)dyld3::Platform::unknown) {
// There were no platforms found in the binary. This may occur on macOS for alternate toolchains and old binaries.
// It should never occur on any of our embedded platforms.
#if __MAC_OS_X_VERSION_MIN_REQUIRED
gProcessInfo->platform = (uint32_t)dyld3::Platform::macOS;
#else
halt("MH_EXECUTE binaries must specify a minimum supported OS version");
#endif
}
}
#if __MAC_OS_X_VERSION_MIN_REQUIRED
// Check to see if we need to override the platform
const char* forcedPlatform = _simple_getenv(envp, "DYLD_FORCE_PLATFORM");
if (forcedPlatform) {
if (strncmp(forcedPlatform, "6", 1) != 0) {
halt("DYLD_FORCE_PLATFORM is only supported for platform 6");
}
const dyld3::MachOFile* mf = (dyld3::MachOFile*)sMainExecutableMachHeader;
if (mf->allowsAlternatePlatform()) {
gProcessInfo->platform = PLATFORM_IOSMAC;
}
}
// if this is host dyld, check to see if iOS simulator is being run
const char* rootPath = _simple_getenv(envp, "DYLD_ROOT_PATH");
if ( (rootPath != NULL) ) {
// look to see if simulator has its own dyld
char simDyldPath[PATH_MAX];
strlcpy(simDyldPath, rootPath, PATH_MAX);
strlcat(simDyldPath, "/usr/lib/dyld_sim", PATH_MAX);
int fd = my_open(simDyldPath, O_RDONLY, 0);
if ( fd != -1 ) {
const char* errMessage = useSimulatorDyld(fd, mainExecutableMH, simDyldPath, argc, argv, envp, apple, startGlue, &result);
if ( errMessage != NULL )
halt(errMessage);
return result;
}
}
else {
((dyld3::MachOFile*)mainExecutableMH)->forEachSupportedPlatform(^(dyld3::Platform platform, uint32_t minOS, uint32_t sdk) {
if ( dyld3::MachOFile::isSimulatorPlatform(platform) )
halt("attempt to run simulator program outside simulator (DYLD_ROOT_PATH not set)");
});
}
#endif
CRSetCrashLogMessage("dyld: launch started");
// 设置上下文信息
setContext(mainExecutableMH, argc, argv, envp, apple);
// Pickup the pointer to the exec path.
// 获取主程序路径
sExecPath = _simple_getenv(apple, "executable_path");
// Remove interim apple[0] transition code from dyld
if (!sExecPath) sExecPath = apple[0];
#if __IPHONE_OS_VERSION_MIN_REQUIRED && !TARGET_OS_SIMULATOR
// kernel is not passing a real path for main executable
if ( strncmp(sExecPath, "/var/containers/Bundle/Application/", 35) == 0 ) {
if ( char* newPath = (char*)malloc(strlen(sExecPath)+10) ) {
strcpy(newPath, "/private");
strcat(newPath, sExecPath);
sExecPath = newPath;
}
}
#endif
// 获取进程名称
if ( sExecPath[0] != '/' ) {
// have relative path, use cwd to make absolute
char cwdbuff[MAXPATHLEN];
if ( getcwd(cwdbuff, MAXPATHLEN) != NULL ) {
// maybe use static buffer to avoid calling malloc so early...
char* s = new char[strlen(cwdbuff) + strlen(sExecPath) + 2];
strcpy(s, cwdbuff);
strcat(s, "/");
strcat(s, sExecPath);
sExecPath = s;
}
}
// Remember short name of process for later logging
sExecShortName = ::strrchr(sExecPath, '/');
if ( sExecShortName != NULL )
++sExecShortName;
else
sExecShortName = sExecPath;
// 配置进程受限模式
configureProcessRestrictions(mainExecutableMH, envp);
// Check if we should force dyld3. Note we have to do this outside of the regular env parsing due to AMFI
if ( dyld3::internalInstall() ) {
if (const char* useClosures = _simple_getenv(envp, "DYLD_USE_CLOSURES")) {
if ( strcmp(useClosures, "0") == 0 ) {
sClosureMode = ClosureMode::Off;
} else if ( strcmp(useClosures, "1") == 0 ) {
#if __MAC_OS_X_VERSION_MIN_REQUIRED
#if __i386__
// don't support dyld3 for 32-bit macOS
#else
// Also don't support dyld3 for iOSMac right now
if ( gProcessInfo->platform != PLATFORM_IOSMAC ) {
sClosureMode = ClosureMode::On;
}
#endif // __i386__
#else
sClosureMode = ClosureMode::On;
#endif // __MAC_OS_X_VERSION_MIN_REQUIRED
} else {
dyld::warn("unknown option to DYLD_USE_CLOSURES. Valid options are: 0 and 1\n");
}
}
}
#if __MAC_OS_X_VERSION_MIN_REQUIRED
if ( !gLinkContext.allowEnvVarsPrint && !gLinkContext.allowEnvVarsPath && !gLinkContext.allowEnvVarsSharedCache ) {
pruneEnvironmentVariables(envp, &apple);
// set again because envp and apple may have changed or moved
setContext(mainExecutableMH, argc, argv, envp, apple);
}
else
#endif
{
// 检测环境变量
checkEnvironmentVariables(envp);
defaultUninitializedFallbackPaths(envp);
}
#if __MAC_OS_X_VERSION_MIN_REQUIRED
if ( gProcessInfo->platform == PLATFORM_IOSMAC ) {
gLinkContext.rootPaths = parseColonList("/System/iOSSupport", NULL);
gLinkContext.iOSonMac = true;
if ( sEnv.DYLD_FALLBACK_LIBRARY_PATH == sLibraryFallbackPaths )
sEnv.DYLD_FALLBACK_LIBRARY_PATH = sRestrictedLibraryFallbackPaths;
if ( sEnv.DYLD_FALLBACK_FRAMEWORK_PATH == sFrameworkFallbackPaths )
sEnv.DYLD_FALLBACK_FRAMEWORK_PATH = sRestrictedFrameworkFallbackPaths;
}
else if ( ((dyld3::MachOFile*)mainExecutableMH)->supportsPlatform(dyld3::Platform::driverKit) ) {
gLinkContext.driverKit = true;
gLinkContext.sharedRegionMode = ImageLoader::kDontUseSharedRegion;
}
#endif
// 如果设置了DYLD_PRINT_OPTS则调用printOptions()打印参数
if ( sEnv.DYLD_PRINT_OPTS )
printOptions(argv);
// 如果设置了DYLD_PRINT_ENV则调用printEnvironmentVariables()打印环境变量
if ( sEnv.DYLD_PRINT_ENV )
printEnvironmentVariables(envp);
// Parse this envirionment variable outside of the regular logic as we want to accept
// this on binaries without an entitelment
#if !TARGET_OS_SIMULATOR
if ( _simple_getenv(envp, "DYLD_JUST_BUILD_CLOSURE") != nullptr ) {
#if TARGET_OS_IPHONE
const char* tempDir = getTempDir(envp);
if ( (tempDir != nullptr) && (geteuid() != 0) ) {
// Use realpath to prevent something like TMPRIR=/tmp/../usr/bin
char realPath[PATH_MAX];
if ( realpath(tempDir, realPath) != NULL )
tempDir = realPath;
if (strncmp(tempDir, "/private/var/mobile/Containers/", strlen("/private/var/mobile/Containers/")) == 0) {
sJustBuildClosure = true;
}
}
#endif
// If we didn't like the format of TMPDIR, just exit. We don't want to launch the app as that would bring up the UI
if (!sJustBuildClosure) {
_exit(EXIT_SUCCESS);
}
}
#endif
if ( sJustBuildClosure )
sClosureMode = ClosureMode::On;
// 获取当前程序架构
getHostInfo(mainExecutableMH, mainExecutableSlide);
//-------------第一步结束-------------
// load shared cache
// 第二步，加载共享缓存
// 检查共享缓存是否开启，iOS必须开启
checkSharedRegionDisable((dyld3::MachOLoaded*)mainExecutableMH, mainExecutableSlide);
if ( gLinkContext.sharedRegionMode != ImageLoader::kDontUseSharedRegion ) {
#if TARGET_OS_SIMULATOR
if ( sSharedCacheOverrideDir)
mapSharedCache();
#else
mapSharedCache();
#endif
}
// If we haven't got a closure mode yet, then check the environment and cache type
if ( sClosureMode == ClosureMode::Unset ) {
// First test to see if we forced in dyld2 via a kernel boot-arg
if ( dyld3::BootArgs::forceDyld2() ) {
sClosureMode = ClosureMode::Off;
} else if ( inDenyList(sExecPath) ) {
sClosureMode = ClosureMode::Off;
} else if ( sEnv.hasOverride ) {
sClosureMode = ClosureMode::Off;
} else if ( dyld3::BootArgs::forceDyld3() ) {
sClosureMode = ClosureMode::On;
} else {
sClosureMode = getPlatformDefaultClosureMode();
}
}
#if !TARGET_OS_SIMULATOR
if ( sClosureMode == ClosureMode::Off ) {
if ( gLinkContext.verboseWarnings )
dyld::log("dyld: not using closure because of DYLD_USE_CLOSURES or -force_dyld2=1 override\n");
} else {
const dyld3::closure::LaunchClosure* mainClosure = nullptr;
dyld3::closure::LoadedFileInfo mainFileInfo;
mainFileInfo.fileContent = mainExecutableMH;
mainFileInfo.path = sExecPath;
// FIXME: If we are saving this closure, this slice offset/length is probably wrong in the case of FAT files.
mainFileInfo.sliceOffset = 0;
mainFileInfo.sliceLen = -1;
struct stat mainExeStatBuf;
if ( ::stat(sExecPath, &mainExeStatBuf) == 0 ) {
mainFileInfo.inode = mainExeStatBuf.st_ino;
mainFileInfo.mtime = mainExeStatBuf.st_mtime;
}
// check for closure in cache first
if ( sSharedCacheLoadInfo.loadAddress != nullptr ) {
mainClosure = sSharedCacheLoadInfo.loadAddress->findClosure(sExecPath);
if ( gLinkContext.verboseWarnings && (mainClosure != nullptr) )
dyld::log("dyld: found closure %p (size=%lu) in dyld shared cache\n", mainClosure, mainClosure->size());
}
// We only want to try build a closure at runtime if its an iOS third party binary, or a macOS binary from the shared cache
bool allowClosureRebuilds = false;
if ( sClosureMode == ClosureMode::On ) {
allowClosureRebuilds = true;
} else if ( (sClosureMode == ClosureMode::PreBuiltOnly) && (mainClosure != nullptr) ) {
allowClosureRebuilds = true;
}
if ( (mainClosure != nullptr) && !closureValid(mainClosure, mainFileInfo, mainExecutableCDHash, true, envp) )
mainClosure = nullptr;
// If we didn't find a valid cache closure then try build a new one
if ( (mainClosure == nullptr) && allowClosureRebuilds ) {
// if forcing closures, and no closure in cache, or it is invalid, check for cached closure
if ( !sForceInvalidSharedCacheClosureFormat )
mainClosure = findCachedLaunchClosure(mainExecutableCDHash, mainFileInfo, envp);
if ( mainClosure == nullptr ) {
// if no cached closure found, build new one
mainClosure = buildLaunchClosure(mainExecutableCDHash, mainFileInfo, envp);
}
}
// exit dyld after closure is built, without running program
if ( sJustBuildClosure )
_exit(EXIT_SUCCESS);
// try using launch closure
if ( mainClosure != nullptr ) {
CRSetCrashLogMessage("dyld3: launch started");
bool launched = launchWithClosure(mainClosure, sSharedCacheLoadInfo.loadAddress, (dyld3::MachOLoaded*)mainExecutableMH,
mainExecutableSlide, argc, argv, envp, apple, &result, startGlue);
if ( !launched && allowClosureRebuilds ) {
// closure is out of date, build new one
mainClosure = buildLaunchClosure(mainExecutableCDHash, mainFileInfo, envp);
if ( mainClosure != nullptr ) {
launched = launchWithClosure(mainClosure, sSharedCacheLoadInfo.loadAddress, (dyld3::MachOLoaded*)mainExecutableMH,
mainExecutableSlide, argc, argv, envp, apple, &result, startGlue);
}
}
if ( launched ) {
gLinkContext.startedInitializingMainExecutable = true;
#if __has_feature(ptrauth_calls)
// start() calls the result pointer as a function pointer so we need to sign it.
result = (uintptr_t)__builtin_ptrauth_sign_unauthenticated((void*)result, 0, 0);
#endif
if (sSkipMain)
result = (uintptr_t)&fake_main;
return result;
}
else {
if ( gLinkContext.verboseWarnings ) {
dyld::log("dyld: unable to use closure %p\n", mainClosure);
}
}
}
}
#endif // TARGET_OS_SIMULATOR
// could not use closure info, launch old way
// install gdb notifier
stateToHandlers(dyld_image_state_dependents_mapped, sBatchHandlers)->push_back(notifyGDB);
stateToHandlers(dyld_image_state_mapped, sSingleHandlers)->push_back(updateAllImages);
// make initial allocations large enough that it is unlikely to need to be re-alloced
sImageRoots.reserve(16);
sAddImageCallbacks.reserve(4);
sRemoveImageCallbacks.reserve(4);
sAddLoadImageCallbacks.reserve(4);
sImageFilesNeedingTermination.reserve(16);
sImageFilesNeedingDOFUnregistration.reserve(8);
#if !TARGET_OS_SIMULATOR
#ifdef WAIT_FOR_SYSTEM_ORDER_HANDSHAKE
// Add gating mechanism to dyld support system order file generation process
WAIT_FOR_SYSTEM_ORDER_HANDSHAKE(dyld::gProcessInfo->systemOrderFlag);
#endif
#endif
try {
// add dyld itself to UUID list
addDyldImageToUUIDList();
#if SUPPORT_ACCELERATE_TABLES
#if __arm64e__
// Disable accelerator tables when we have threaded rebase/bind, which is arm64e executables only for now.
if (sMainExecutableMachHeader->cpusubtype == CPU_SUBTYPE_ARM64E)
sDisableAcceleratorTables = true;
#endif
bool mainExcutableAlreadyRebased = false;
if ( (sSharedCacheLoadInfo.loadAddress != nullptr) && !dylibsCanOverrideCache() && !sDisableAcceleratorTables && (sSharedCacheLoadInfo.loadAddress->header.accelerateInfoAddr != 0) ) {
struct stat statBuf;
if ( ::stat(IPHONE_DYLD_SHARED_CACHE_DIR "no-dyld2-accelerator-tables", &statBuf) != 0 )
sAllCacheImagesProxy = ImageLoaderMegaDylib::makeImageLoaderMegaDylib(&sSharedCacheLoadInfo.loadAddress->header, sSharedCacheLoadInfo.slide, mainExecutableMH, gLinkContext);
}
reloadAllImages:
#endif
#if __MAC_OS_X_VERSION_MIN_REQUIRED
gLinkContext.strictMachORequired = false;
// be less strict about old macOS mach-o binaries
((dyld3::MachOFile*)mainExecutableMH)->forEachSupportedPlatform(^(dyld3::Platform platform, uint32_t minOS, uint32_t sdk) {
if ( (platform == dyld3::Platform::macOS) && (sdk >= DYLD_PACKED_VERSION(10,15,0)) ) {
gLinkContext.strictMachORequired = true;
}
});
if ( gLinkContext.iOSonMac )
gLinkContext.strictMachORequired = true;
#else
// simulators, iOS, tvOS, watchOS, are always strict
gLinkContext.strictMachORequired = true;
#endif
CRSetCrashLogMessage(sLoadingCrashMessage);
// instantiate ImageLoader for main executable
// 第三步 实例化主程序
sMainExecutable = instantiateFromLoadedImage(mainExecutableMH, mainExecutableSlide, sExecPath);
gLinkContext.mainExecutable = sMainExecutable;
gLinkContext.mainExecutableCodeSigned = hasCodeSignatureLoadCommand(mainExecutableMH);
#if TARGET_OS_SIMULATOR
// check main executable is not too new for this OS
{
if ( ! isSimulatorBinary((uint8_t*)mainExecutableMH, sExecPath) ) {
throwf("program was built for a platform that is not supported by this runtime");
}
uint32_t mainMinOS = sMainExecutable->minOSVersion();
// dyld is always built for the current OS, so we can get the current OS version
// from the load command in dyld itself.
uint32_t dyldMinOS = ImageLoaderMachO::minOSVersion((const mach_header*)&__dso_handle);
if ( mainMinOS > dyldMinOS ) {
#if TARGET_OS_WATCH
throwf("app was built for watchOS %d.%d which is newer than this simulator %d.%d",
mainMinOS >> 16, ((mainMinOS >> 8) & 0xFF),
dyldMinOS >> 16, ((dyldMinOS >> 8) & 0xFF));
#elif TARGET_OS_TV
throwf("app was built for tvOS %d.%d which is newer than this simulator %d.%d",
mainMinOS >> 16, ((mainMinOS >> 8) & 0xFF),
dyldMinOS >> 16, ((dyldMinOS >> 8) & 0xFF));
#else
throwf("app was built for iOS %d.%d which is newer than this simulator %d.%d",
mainMinOS >> 16, ((mainMinOS >> 8) & 0xFF),
dyldMinOS >> 16, ((dyldMinOS >> 8) & 0xFF));
#endif
}
}
#endif
#if SUPPORT_ACCELERATE_TABLES
sAllImages.reserve((sAllCacheImagesProxy != NULL) ? 16 : INITIAL_IMAGE_COUNT);
#else
sAllImages.reserve(INITIAL_IMAGE_COUNT);
#endif
// Now that shared cache is loaded, setup an versioned dylib overrides
#if SUPPORT_VERSIONED_PATHS
checkVersionedPaths();
#endif
// dyld_all_image_infos image list does not contain dyld
// add it as dyldPath field in dyld_all_image_infos
// for simulator, dyld_sim is in image list, need host dyld added
#if TARGET_OS_SIMULATOR
// get path of host dyld from table of syscall vectors in host dyld
void* addressInDyld = gSyscallHelpers;
#else
// get path of dyld itself
void* addressInDyld = (void*)&__dso_handle;
#endif
char dyldPathBuffer[MAXPATHLEN+1];
int len = proc_regionfilename(getpid(), (uint64_t)(long)addressInDyld, dyldPathBuffer, MAXPATHLEN);
if ( len > 0 ) {
dyldPathBuffer[len] = '\0'; // proc_regionfilename() does not zero terminate returned string
if ( strcmp(dyldPathBuffer, gProcessInfo->dyldPath) != 0 )
gProcessInfo->dyldPath = strdup(dyldPathBuffer);
}
// load any inserted libraries
// 第四步 加载插入的动态库
if ( sEnv.DYLD_INSERT_LIBRARIES != NULL ) {
for (const char* const* lib = sEnv.DYLD_INSERT_LIBRARIES; *lib != NULL; ++lib)
loadInsertedDylib(*lib);
}
// record count of inserted libraries so that a flat search will look at
// inserted libraries, then main, then others.
// 记录插入的动态库数量
sInsertedDylibCount = sAllImages.size()-1;
// link main executable
// 第五步 链接主程序
gLinkContext.linkingMainExecutable = true;
#if SUPPORT_ACCELERATE_TABLES
if ( mainExcutableAlreadyRebased ) {
// previous link() on main executable has already adjusted its internal pointers for ASLR
// work around that by rebasing by inverse amount
sMainExecutable->rebase(gLinkContext, -mainExecutableSlide);
}
#endif
link(sMainExecutable, sEnv.DYLD_BIND_AT_LAUNCH, true, ImageLoader::RPathChain(NULL, NULL), -1);
sMainExecutable->setNeverUnloadRecursive();
if ( sMainExecutable->forceFlat() ) {
gLinkContext.bindFlat = true;
gLinkContext.prebindUsage = ImageLoader::kUseNoPrebinding;
}
// link any inserted libraries
// do this after linking main executable so that any dylibs pulled in by inserted
// dylibs (e.g. libSystem) will not be in front of dylibs the program uses
// 第六步 链接插入的动态库
if ( sInsertedDylibCount > 0 ) {
for(unsigned int i=0; i < sInsertedDylibCount; ++i) {
ImageLoader* image = sAllImages[i+1];
link(image, sEnv.DYLD_BIND_AT_LAUNCH, true, ImageLoader::RPathChain(NULL, NULL), -1);
image->setNeverUnloadRecursive();
}
if ( gLinkContext.allowInterposing ) {
// only INSERTED libraries can interpose
// register interposing info after all inserted libraries are bound so chaining works
for(unsigned int i=0; i < sInsertedDylibCount; ++i) {
ImageLoader* image = sAllImages[i+1];
image->registerInterposing(gLinkContext);
}
}
}
if ( gLinkContext.allowInterposing ) {
// dyld should support interposition even without DYLD_INSERT_LIBRARIES
for (long i=sInsertedDylibCount+1; i < sAllImages.size(); ++i) {
ImageLoader* image = sAllImages[I];
if ( image->inSharedCache() )
continue;
image->registerInterposing(gLinkContext);
}
}
#if SUPPORT_ACCELERATE_TABLES
if ( (sAllCacheImagesProxy != NULL) && ImageLoader::haveInterposingTuples() ) {
// Accelerator tables cannot be used with implicit interposing, so relaunch with accelerator tables disabled
ImageLoader::clearInterposingTuples();
// unmap all loaded dylibs (but not main executable)
for (long i=1; i < sAllImages.size(); ++i) {
ImageLoader* image = sAllImages[I];
if ( image == sMainExecutable )
continue;
if ( image == sAllCacheImagesProxy )
continue;
image->setCanUnload();
ImageLoader::deleteImage(image);
}
// note: we don't need to worry about inserted images because if DYLD_INSERT_LIBRARIES was set we would not be using the accelerator table
sAllImages.clear();
sImageRoots.clear();
sImageFilesNeedingTermination.clear();
sImageFilesNeedingDOFUnregistration.clear();
sAddImageCallbacks.clear();
sRemoveImageCallbacks.clear();
sAddLoadImageCallbacks.clear();
sAddBulkLoadImageCallbacks.clear();
sDisableAcceleratorTables = true;
sAllCacheImagesProxy = NULL;
sMappedRangesStart = NULL;
mainExcutableAlreadyRebased = true;
gLinkContext.linkingMainExecutable = false;
resetAllImages();
goto reloadAllImages;
}
#endif
// apply interposing to initial set of images
for(int i=0; i < sImageRoots.size(); ++i) {
sImageRoots[i]->applyInterposing(gLinkContext);
}
ImageLoader::applyInterposingToDyldCache(gLinkContext);
// Bind and notify for the main executable now that interposing has been registered
uint64_t bindMainExecutableStartTime = mach_absolute_time();
sMainExecutable->recursiveBindWithAccounting(gLinkContext, sEnv.DYLD_BIND_AT_LAUNCH, true);
uint64_t bindMainExecutableEndTime = mach_absolute_time();
ImageLoaderMachO::fgTotalBindTime += bindMainExecutableEndTime - bindMainExecutableStartTime;
gLinkContext.notifyBatch(dyld_image_state_bound, false);
// Bind and notify for the inserted images now interposing has been registered
if ( sInsertedDylibCount > 0 ) {
for(unsigned int i=0; i < sInsertedDylibCount; ++i) {
ImageLoader* image = sAllImages[i+1];
image->recursiveBind(gLinkContext, sEnv.DYLD_BIND_AT_LAUNCH, true);
}
}
// do weak binding only after all inserted images linked
// 第七步 执行弱符号绑定
sMainExecutable->weakBind(gLinkContext);
gLinkContext.linkingMainExecutable = false;
sMainExecutable->recursiveMakeDataReadOnly(gLinkContext);
CRSetCrashLogMessage("dyld: launch, running initializers");
#if SUPPORT_OLD_CRT_INITIALIZATION
// Old way is to run initializers via a callback from crt1.o
if ( ! gRunInitializersOldWay )
initializeMainExecutable();
#else
// run all initializers
// 第八步 执行初始化方法
initializeMainExecutable();
#endif
// notify any montoring proccesses that this process is about to enter main()
notifyMonitoringDyldMain();
if (dyld3::kdebug_trace_dyld_enabled(DBG_DYLD_TIMING_LAUNCH_EXECUTABLE)) {
dyld3::kdebug_trace_dyld_duration_end(launchTraceID, DBG_DYLD_TIMING_LAUNCH_EXECUTABLE, 0, 0, 2);
}
ARIADNEDBG_CODE(220, 1);
#if __MAC_OS_X_VERSION_MIN_REQUIRED
if ( gLinkContext.driverKit ) {
result = (uintptr_t)sEntryOveride;
if ( result == 0 )
halt("no entry point registered");
*startGlue = (uintptr_t)gLibSystemHelpers->startGlueToCallExit;
}
else
#endif
{
// find entry point for main executable
// 第九步 查找入口点并返回
result = (uintptr_t)sMainExecutable->getEntryFromLC_MAIN();
if ( result != 0 ) {
// main executable uses LC_MAIN, we need to use helper in libdyld to call into main()
if ( (gLibSystemHelpers != NULL) && (gLibSystemHelpers->version >= 9) )
*startGlue = (uintptr_t)gLibSystemHelpers->startGlueToCallExit;
else
halt("libdyld.dylib support not present for LC_MAIN");
}
else {
// main executable uses LC_UNIXTHREAD, dyld needs to let "start" in program set up for main()
result = (uintptr_t)sMainExecutable->getEntryFromLC_UNIXTHREAD();
*startGlue = 0;
}
}
#if __has_feature(ptrauth_calls)
// start() calls the result pointer as a function pointer so we need to sign it.
result = (uintptr_t)__builtin_ptrauth_sign_unauthenticated((void*)result, 0, 0);
#endif
}
catch(const char* message) {
syncAllImages();
halt(message);
}
catch(...) {
dyld::log("dyld: launch failed\n");
}
CRSetCrashLogMessage("dyld2 mode");
#if !TARGET_OS_SIMULATOR
if (sLogClosureFailure) {
// We failed to launch in dyld3, but dyld2 can handle it. synthesize a crash report for analytics
dyld3::syntheticBacktrace("Could not generate launchClosure, falling back to dyld2", true);
}
#endif
if (sSkipMain) {
notifyMonitoringDyldMain();
if (dyld3::kdebug_trace_dyld_enabled(DBG_DYLD_TIMING_LAUNCH_EXECUTABLE)) {
dyld3::kdebug_trace_dyld_duration_end(launchTraceID, DBG_DYLD_TIMING_LAUNCH_EXECUTABLE, 0, 0, 2);
}
ARIADNEDBG_CODE(220, 1);
result = (uintptr_t)&fake_main;
*startGlue = (uintptr_t)gLibSystemHelpers->startGlueToCallExit;
}
return result;
}
其中重要的地方加了一些注释，而整个流程大概分为九步
-
设置运行环境。 -
加载共享缓存。 -
实例化主程序。 -
加载插入的动态库。 -
链接主程序。 -
链接插入的动态库。 -
执行弱符号绑定。 -
执行初始化方法。 -
查找入口点并返回。
设置运行环境
这一步主要是设置运行参数、环境变量等。代码在开始的时候，将入参mainExecutableMH赋值给了sMainExecutableMachHeader，这是一个macho_header结构体，表示的是当前主程序的Mach-O头部信息，加载器依据Mach-O头部信息就可以解析整个Mach-O文件信息。接着调用setContext()设置上下文信息，包括一些回调函数、参数、标志信息等
分段代码
setContext
static void setContext(const macho_header* mainExecutableMH, int argc, const char* argv[], const char* envp[], const char* apple[])
{
gLinkContext.loadLibrary = &libraryLocator;
gLinkContext.terminationRecorder = &terminationRecorder;
gLinkContext.flatExportFinder = &flatFindExportedSymbol;
gLinkContext.coalescedExportFinder = &findCoalescedExportedSymbol;
gLinkContext.getCoalescedImages = &getCoalescedImages;
gLinkContext.undefinedHandler = &undefinedHandler;
gLinkContext.getAllMappedRegions = &getMappedRegions;
gLinkContext.bindingHandler = NULL;
gLinkContext.notifySingle = ¬ifySingle;
gLinkContext.notifyBatch = ¬ifyBatch;
gLinkContext.removeImage = &removeImage;
gLinkContext.registerDOFs = dyld3::Loader::dtraceUserProbesEnabled() ? ®isterDOFs : NULL;
gLinkContext.clearAllDepths = &clearAllDepths;
gLinkContext.printAllDepths = &printAllDepths;
gLinkContext.imageCount = &imageCount;
gLinkContext.setNewProgramVars = &setNewProgramVars;
gLinkContext.inSharedCache = &inSharedCache;
gLinkContext.setErrorStrings = &setErrorStrings;
#if SUPPORT_OLD_CRT_INITIALIZATION
gLinkContext.setRunInitialzersOldWay= &setRunInitialzersOldWay;
#endif
gLinkContext.findImageContainingAddress = &findImageContainingAddress;
gLinkContext.addDynamicReference = &addDynamicReference;
#if SUPPORT_ACCELERATE_TABLES
gLinkContext.notifySingleFromCache = ¬ifySingleFromCache;
gLinkContext.getPreInitNotifyHandler= &getPreInitNotifyHandler;
gLinkContext.getBoundBatchHandler = &getBoundBatchHandler;
#endif
gLinkContext.bindingOptions = ImageLoader::kBindingNone;
gLinkContext.argc = argc;
gLinkContext.argv = argv;
gLinkContext.envp = envp;
gLinkContext.apple = apple;
gLinkContext.progname = (argv[0] != NULL) ? basename(argv[0]) : "";
gLinkContext.programVars.mh = mainExecutableMH;
gLinkContext.programVars.NXArgcPtr = &gLinkContext.argc;
gLinkContext.programVars.NXArgvPtr = &gLinkContext.argv;
gLinkContext.programVars.environPtr = &gLinkContext.envp;
gLinkContext.programVars.__prognamePtr=&gLinkContext.progname;
gLinkContext.mainExecutable = NULL;
gLinkContext.imageSuffix = NULL;
gLinkContext.dynamicInterposeArray = NULL;
gLinkContext.dynamicInterposeCount = 0;
gLinkContext.prebindUsage = ImageLoader::kUseAllPrebinding;
gLinkContext.sharedRegionMode = ImageLoader::kUseSharedRegion;
}
configureProcessRestrictions()用来配置进程是否受限
static void configureProcessRestrictions(const macho_header* mainExecutableMH, const char* envp[])
{
uint64_t amfiInputFlags = 0;
#if TARGET_OS_SIMULATOR
amfiInputFlags |= AMFI_DYLD_INPUT_PROC_IN_SIMULATOR;
#elif __MAC_OS_X_VERSION_MIN_REQUIRED
if ( hasRestrictedSegment(mainExecutableMH) )
amfiInputFlags |= AMFI_DYLD_INPUT_PROC_HAS_RESTRICT_SEG;
#elif __IPHONE_OS_VERSION_MIN_REQUIRED
if ( isFairPlayEncrypted(mainExecutableMH) )
amfiInputFlags |= AMFI_DYLD_INPUT_PROC_IS_ENCRYPTED;
#endif
uint64_t amfiOutputFlags = 0;
const char* amfiFake = nullptr;
if ( dyld3::internalInstall() && dyld3::BootArgs::enableDyldTestMode() ) {
amfiFake = _simple_getenv(envp, "DYLD_AMFI_FAKE");
}
if ( amfiFake != nullptr ) {
amfiOutputFlags = hexToUInt64(amfiFake, nullptr);
}
if ( (amfiFake != nullptr) || (amfi_check_dyld_policy_self(amfiInputFlags, &amfiOutputFlags) == 0) ) {
gLinkContext.allowAtPaths = (amfiOutputFlags & AMFI_DYLD_OUTPUT_ALLOW_AT_PATH);
gLinkContext.allowEnvVarsPrint = (amfiOutputFlags & AMFI_DYLD_OUTPUT_ALLOW_PRINT_VARS);
gLinkContext.allowEnvVarsPath = (amfiOutputFlags & AMFI_DYLD_OUTPUT_ALLOW_PATH_VARS);
gLinkContext.allowEnvVarsSharedCache = (amfiOutputFlags & AMFI_DYLD_OUTPUT_ALLOW_CUSTOM_SHARED_CACHE);
gLinkContext.allowClassicFallbackPaths = (amfiOutputFlags & AMFI_DYLD_OUTPUT_ALLOW_FALLBACK_PATHS);
gLinkContext.allowInsertFailures = (amfiOutputFlags & AMFI_DYLD_OUTPUT_ALLOW_FAILED_LIBRARY_INSERTION);
#ifdef AMFI_RETURNS_INTERPOSING_FLAG
gLinkContext.allowInterposing = (amfiOutputFlags & AMFI_DYLD_OUTPUT_ALLOW_LIBRARY_INTERPOSING);
#else
gLinkContext.allowInterposing = true;
#endif
}
else {
#if __MAC_OS_X_VERSION_MIN_REQUIRED
// support chrooting from old kernel
bool isRestricted = false;
bool libraryValidation = false;
// any processes with setuid or setgid bit set or with __RESTRICT segment is restricted
if ( issetugid() || hasRestrictedSegment(mainExecutableMH) ) {
isRestricted = true;
}
bool usingSIP = (csr_check(CSR_ALLOW_TASK_FOR_PID) != 0);
uint32_t flags;
if ( csops(0, CS_OPS_STATUS, &flags, sizeof(flags)) != -1 ) {
// On OS X CS_RESTRICT means the program was signed with entitlements
if ( ((flags & CS_RESTRICT) == CS_RESTRICT) && usingSIP ) {
isRestricted = true;
}
// Library Validation loosens searching but requires everything to be code signed
if ( flags & CS_REQUIRE_LV ) {
isRestricted = false;
libraryValidation = true;
}
}
gLinkContext.allowAtPaths = !isRestricted;
gLinkContext.allowEnvVarsPrint = !isRestricted;
gLinkContext.allowEnvVarsPath = !isRestricted;
gLinkContext.allowEnvVarsSharedCache = !libraryValidation || !usingSIP;
gLinkContext.allowClassicFallbackPaths = !isRestricted;
gLinkContext.allowInsertFailures = false;
gLinkContext.allowInterposing = true;
#else
halt("amfi_check_dyld_policy_self() failed\n");
#endif
}
}
checkEnvironmentVariables()检测环境变量，如果sEnvMode为envNone就直接返回，否则调用processDyldEnvironmentVariable()处理并设置环境变量
static void checkEnvironmentVariables(const char* envp[])
{
if ( !gLinkContext.allowEnvVarsPath && !gLinkContext.allowEnvVarsPrint )
return;
const char** p;
for(p = envp; *p != NULL; p++) {
const char* keyEqualsValue = *p;
if ( strncmp(keyEqualsValue, "DYLD_", 5) == 0 ) {
const char* equals = strchr(keyEqualsValue, '=');
if ( equals != NULL ) {
strlcat(sLoadingCrashMessage, "\n", sizeof(sLoadingCrashMessage));
strlcat(sLoadingCrashMessage, keyEqualsValue, sizeof(sLoadingCrashMessage));
const char* value = &equals[1];
const size_t keyLen = equals-keyEqualsValue;
char key[keyLen+1];
strncpy(key, keyEqualsValue, keyLen);
key[keyLen] = '\0';
if ( (strncmp(key, "DYLD_PRINT_", 11) == 0) && !gLinkContext.allowEnvVarsPrint )
continue;
processDyldEnvironmentVariable(key, value, NULL);
}
}
else if ( strncmp(keyEqualsValue, "LD_LIBRARY_PATH=", 16) == 0 ) {
const char* path = &keyEqualsValue[16];
sEnv.LD_LIBRARY_PATH = parseColonList(path, NULL);
}
}
#if SUPPORT_LC_DYLD_ENVIRONMENT
checkLoadCommandEnvironmentVariables();
#endif // SUPPORT_LC_DYLD_ENVIRONMENT
#if SUPPORT_ROOT_PATH
// DYLD_IMAGE_SUFFIX and DYLD_ROOT_PATH cannot be used together
if ( (gLinkContext.imageSuffix != NULL && *gLinkContext.imageSuffix != NULL) && (gLinkContext.rootPaths != NULL) ) {
dyld::warn("Ignoring DYLD_IMAGE_SUFFIX because DYLD_ROOT_PATH is used.\n");
gLinkContext.imageSuffix = NULL; // this leaks allocations from parseColonList
}
#endif
}
随后是getHostInfo()获取cpu的框架信息
static void getHostInfo(const macho_header* mainExecutableMH, uintptr_t mainExecutableSlide)
{
#if CPU_SUBTYPES_SUPPORTED
#if __ARM_ARCH_7K__
sHostCPU = CPU_TYPE_ARM;
sHostCPUsubtype = CPU_SUBTYPE_ARM_V7K;
#elif __ARM_ARCH_7A__
sHostCPU = CPU_TYPE_ARM;
sHostCPUsubtype = CPU_SUBTYPE_ARM_V7;
#elif __ARM_ARCH_6K__
sHostCPU = CPU_TYPE_ARM;
sHostCPUsubtype = CPU_SUBTYPE_ARM_V6;
#elif __ARM_ARCH_7F__
sHostCPU = CPU_TYPE_ARM;
sHostCPUsubtype = CPU_SUBTYPE_ARM_V7F;
#elif __ARM_ARCH_7S__
sHostCPU = CPU_TYPE_ARM;
sHostCPUsubtype = CPU_SUBTYPE_ARM_V7S;
#elif __ARM64_ARCH_8_32__
sHostCPU = CPU_TYPE_ARM64_32;
sHostCPUsubtype = CPU_SUBTYPE_ARM64_32_V8;
#elif __arm64e__
sHostCPU = CPU_TYPE_ARM64;
sHostCPUsubtype = CPU_SUBTYPE_ARM64E;
#elif __arm64__
sHostCPU = CPU_TYPE_ARM64;
sHostCPUsubtype = CPU_SUBTYPE_ARM64_V8;
#else
struct host_basic_info info;
mach_msg_type_number_t count = HOST_BASIC_INFO_COUNT;
mach_port_t hostPort = mach_host_self();
kern_return_t result = host_info(hostPort, HOST_BASIC_INFO, (host_info_t)&info, &count);
if ( result != KERN_SUCCESS )
throw "host_info() failed";
sHostCPU = info.cpu_type;
sHostCPUsubtype = info.cpu_subtype;
mach_port_deallocate(mach_task_self(), hostPort);
#if __x86_64__
// host_info returns CPU_TYPE_I386 even for x86_64. Override that here so that
// we don't need to mask the cpu type later.
sHostCPU = CPU_TYPE_X86_64;
#if !TARGET_OS_SIMULATOR
sHaswell = (sHostCPUsubtype == CPU_SUBTYPE_X86_64_H);
// x86_64h: Fall back to the x86_64 slice if an app requires GC.
if ( sHaswell ) {
if ( isGCProgram(mainExecutableMH, mainExecutableSlide) ) {
// When running a GC program on a haswell machine, don't use and 'h slices
sHostCPUsubtype = CPU_SUBTYPE_X86_64_ALL;
sHaswell = false;
gLinkContext.sharedRegionMode = ImageLoader::kDontUseSharedRegion;
}
}
#endif
#endif
#endif
#endif
}
加载共享缓存
- 首先调用
checkSharedRegionDisable()检查是否禁用了共享缓存
static void checkSharedRegionDisable(const dyld3::MachOLoaded* mainExecutableMH, uintptr_t mainExecutableSlide)
{
#if __MAC_OS_X_VERSION_MIN_REQUIRED
// if main executable has segments that overlap the shared region,
// then disable using the shared region
if ( mainExecutableMH->intersectsRange(SHARED_REGION_BASE, SHARED_REGION_SIZE) ) {
gLinkContext.sharedRegionMode = ImageLoader::kDontUseSharedRegion;
if ( gLinkContext.verboseMapping )
dyld::warn("disabling shared region because main executable overlaps\n");
}
#if __i386__
if ( !gLinkContext.allowEnvVarsPath ) {
// use private or no shared region for suid processes
gLinkContext.sharedRegionMode = ImageLoader::kUsePrivateSharedRegion;
}
#endif
#endif
// iOS cannot run without shared region
}
根据注释内容，我们判断iOS的程序时，共享缓存必须开启。
- 然后调用
mapSharedCache()加载共享缓存
static void mapSharedCache()
{
dyld3::SharedCacheOptions opts;
opts.cacheDirOverride = sSharedCacheOverrideDir;
opts.forcePrivate = (gLinkContext.sharedRegionMode == ImageLoader::kUsePrivateSharedRegion);
#if __x86_64__ && !TARGET_OS_SIMULATOR
opts.useHaswell = sHaswell;
#else
opts.useHaswell = false;
#endif
opts.verbose = gLinkContext.verboseMapping;
loadDyldCache(opts, &sSharedCacheLoadInfo);
// update global state
if ( sSharedCacheLoadInfo.loadAddress != nullptr ) {
gLinkContext.dyldCache = sSharedCacheLoadInfo.loadAddress;
dyld::gProcessInfo->processDetachedFromSharedRegion = opts.forcePrivate;
dyld::gProcessInfo->sharedCacheSlide = sSharedCacheLoadInfo.slide;
dyld::gProcessInfo->sharedCacheBaseAddress = (unsigned long)sSharedCacheLoadInfo.loadAddress;
sSharedCacheLoadInfo.loadAddress->getUUID(dyld::gProcessInfo->sharedCacheUUID);
dyld3::kdebug_trace_dyld_image(DBG_DYLD_UUID_SHARED_CACHE_A, sSharedCacheLoadInfo.path, (const uuid_t *)&dyld::gProcessInfo->sharedCacheUUID[0], {0,0}, {{ 0, 0 }}, (const mach_header *)sSharedCacheLoadInfo.loadAddress);
}
}
其中主要靠loadDyldCache(opts, &sSharedCacheLoadInfo)
bool loadDyldCache(const SharedCacheOptions& options, SharedCacheLoadInfo* results)
{
results->loadAddress = 0;
results->slide = 0;
results->errorMessage = nullptr;
#if TARGET_OS_SIMULATOR
// simulator only supports mmap()ing cache privately into process
return mapCachePrivate(options, results);
#else
if ( options.forcePrivate ) {
// mmap cache into this process only
//仅加载到当前进程
return mapCachePrivate(options, results);
}
else {
// fast path: when cache is already mapped into shared region
//快速：共享缓存已加载
bool hasError = false;
if ( reuseExistingCache(options, results) ) {
hasError = (results->errorMessage != nullptr);
} else {
// slow path: this is first process to load cache
//慢速：首次加载共享缓存
hasError = mapCacheSystemWide(options, results);
}
return hasError;
}
#endif
}
可见加载共享缓存分三种情况
- 仅加载到当前进程 调用
mapCachePrivate(options, results) - 快速路径， 共享缓存已加载
- 慢速路径， 首次当前进程首次加载共享缓存
mapCacheSystemWide(options, results)
实例化主程序
将主程序的Mach-O加载进内存，并实例化一个ImageLoader。
static ImageLoaderMachO* instantiateFromLoadedImage(const macho_header* mh, uintptr_t slide, const char* path)
{
// try mach-o loader
if ( isCompatibleMachO((const uint8_t*)mh, path) ) {
ImageLoader* image = ImageLoaderMachO::instantiateMainExecutable(mh, slide, path, gLinkContext);
addImage(image);
return (ImageLoaderMachO*)image;
}
throw "main executable not a known format";
}
- 首先会判断
Mach-O头部的magic、cputype、cpusubtype的属性是否兼容
// This is used to validate if a non-fat (aka thin or raw) mach-o file can be used
// on the current processor. //
bool isCompatibleMachO(const uint8_t* firstPage, const char* path)
{
#if CPU_SUBTYPES_SUPPORTED
// It is deemed compatible if any of the following are true:
// 1) mach_header subtype is in list of compatible subtypes for running processor
// 2) mach_header subtype is same as running processor subtype
// 3) mach_header subtype runs on all processor variants
//如果符合以下条件，则视为兼容：
//1）mach_header subtype在运行处理器的兼容子类型列表中
//2）mach_header subtype与运行处理器子类型相同
//3）mach_header subtype在所有处理器变体上运行
const mach_header* mh = (mach_header*)firstPage;
if ( mh->magic == sMainExecutableMachHeader->magic ) {
if ( mh->cputype == sMainExecutableMachHeader->cputype ) {
if ( mh->cputype == sHostCPU ) {
// get preference ordered list of subtypes that this machine can use
const cpu_subtype_t* subTypePreferenceList = findCPUSubtypeList(mh->cputype, sHostCPUsubtype);
if ( subTypePreferenceList != NULL ) {
// if image's subtype is in the list, it is compatible
for (const cpu_subtype_t* p = subTypePreferenceList; *p != CPU_SUBTYPE_END_OF_LIST; ++p) {
if ( *p == mh->cpusubtype )
return true;
}
// have list and not in list, so not compatible
throwf("incompatible cpu-subtype: 0x%08X in %s", mh->cpusubtype, path);
}
// unknown cpu sub-type, but if exact match for current subtype then ok to use
if ( mh->cpusubtype == sHostCPUsubtype )
return true;
}
// cpu type has no ordered list of subtypes
switch (mh->cputype) {
case CPU_TYPE_I386:
case CPU_TYPE_X86_64:
// subtypes are not used or these architectures
return true;
}
}
}
#else
// For architectures that don't support cpu-sub-types
// this just check the cpu type.
const mach_header* mh = (mach_header*)firstPage;
if ( mh->magic == sMainExecutableMachHeader->magic ) {
if ( mh->cputype == sMainExecutableMachHeader->cputype ) {
return true;
}
}
#endif
return false;
}
- 然后调用
ImageLoaderMachO::instantiateMainExecutable(mh, slide, path, gLinkContext)实例化主程序的ImageLoader。ImageLoader是抽象类，其子类负责把Mach-O文件实例化为image，当sniffLoadCommands()解析完以后，根据compressed的值来决定调用哪个子类进行实例化
// create image for main executable
ImageLoader* ImageLoaderMachO::instantiateMainExecutable(const macho_header* mh, uintptr_t slide, const char* path, const LinkContext& context)
{
//dyld::log("ImageLoader=%ld, ImageLoaderMachO=%ld, ImageLoaderMachOClassic=%ld, ImageLoaderMachOCompressed=%ld\n",
// sizeof(ImageLoader), sizeof(ImageLoaderMachO), sizeof(ImageLoaderMachOClassic), sizeof(ImageLoaderMachOCompressed));
bool compressed;
unsigned int segCount;
unsigned int libCount;
const linkedit_data_command* codeSigCmd;
const encryption_info_command* encryptCmd;
sniffLoadCommands(mh, path, false, &compressed, &segCount, &libCount, context, &codeSigCmd, &encryptCmd);
// instantiate concrete class based on content of load commands
if ( compressed )
return ImageLoaderMachOCompressed::instantiateMainExecutable(mh, slide, path, segCount, libCount, context);
else
#if SUPPORT_CLASSIC_MACHO
return ImageLoaderMachOClassic::instantiateMainExecutable(mh, slide, path, segCount, libCount, context);
#else
throw "missing LC_DYLD_INFO load command";
#endif
}
- 在调用完
ImageLoaderMachO::instantiateMainExecutable()后继续调用addImage()，将image加入到sAllImages全局镜像列表，并将image映射到申请的内存中
static void addImage(ImageLoader* image)
{
// add to master list
allImagesLock();
sAllImages.push_back(image);
allImagesUnlock();
// update mapped ranges
uintptr_t lastSegStart = 0;
uintptr_t lastSegEnd = 0;
for(unsigned int i=0, e=image->segmentCount(); i < e; ++i) {
if ( image->segUnaccessible(i) )
continue;
uintptr_t start = image->segActualLoadAddress(i);
uintptr_t end = image->segActualEndAddress(i);
if ( start == lastSegEnd ) {
// two segments are contiguous, just record combined segments
lastSegEnd = end;
}
else {
// non-contiguous segments, record last (if any)
if ( lastSegEnd != 0 )
addMappedRange(image, lastSegStart, lastSegEnd);
lastSegStart = start;
lastSegEnd = end;
}
}
if ( lastSegEnd != 0 )
addMappedRange(image, lastSegStart, lastSegEnd);
if ( gLinkContext.verboseLoading || (sEnv.DYLD_PRINT_LIBRARIES_POST_LAUNCH && (sMainExecutable!=NULL) && sMainExecutable->isLinked()) ) {
const char *imagePath = image->getPath();
uuid_t imageUUID;
if ( image->getUUID(imageUUID) ) {
uuid_string_t imageUUIDStr;
uuid_unparse_upper(imageUUID, imageUUIDStr);
dyld::log("dyld: loaded: <%s> %s\n", imageUUIDStr, imagePath);
}
else {
dyld::log("dyld: loaded: %s\n", imagePath);
}
}
}
到这里实例化主程序完成
加载插入的动态库
这一步是加载环境变量DYLD_INSERT_LIBRARIES中配置的动态库，先判断是否存在需要加载的动态库，如果有，则调用loadInsertedDylib()
if ( sEnv.DYLD_INSERT_LIBRARIES != NULL ) {
for (const char* const* lib = sEnv.DYLD_INSERT_LIBRARIES; *lib != NULL; ++lib)
loadInsertedDylib(*lib);
}
loadInsertedDylib内部实现
通过设置一个LoadContext参数，然后调用load()实现
static void loadInsertedDylib(const char* path)
{
unsigned cacheIndex;
try {
LoadContext context;
context.useSearchPaths = false;
context.useFallbackPaths = false;
context.useLdLibraryPath = false;
context.implicitRPath = false;
context.matchByInstallName = false;
context.dontLoad = false;
context.mustBeBundle = false;
context.mustBeDylib = true;
context.canBePIE = false;
context.origin = NULL; // can't use @loader_path with DYLD_INSERT_LIBRARIES
context.rpath = NULL;
load(path, context, cacheIndex);
}
catch (const char* msg) {
if ( gLinkContext.allowInsertFailures )
dyld::log("dyld: warning: could not load inserted library '%s' into hardened process because %s\n", path, msg);
else
halt(dyld::mkstringf("could not load inserted library '%s' because %s\n", path, msg));
}
catch (...) {
halt(dyld::mkstringf("could not load inserted library '%s'\n", path));
}
}
链接主程序
这一步主要调用了link()函数
void link(ImageLoader* image, bool forceLazysBound, bool neverUnload, const ImageLoader::RPathChain& loaderRPaths, unsigned cacheIndex)
{
// add to list of known images. This did not happen at creation time for bundles
if ( image->isBundle() && !image->isLinked() )
addImage(image);
// we detect root images as those not linked in yet
if ( !image->isLinked() )
addRootImage(image);
// process images
try {
const char* path = image->getPath();
#if SUPPORT_ACCELERATE_TABLES
if ( image == sAllCacheImagesProxy )
path = sAllCacheImagesProxy->getIndexedPath(cacheIndex);
#endif
image->link(gLinkContext, forceLazysBound, false, neverUnload, loaderRPaths, path);
}
catch (const char* msg) {
garbageCollectImages();
throw;
}
}
作用是将实例化后的主程序进行动态化修正让二进制变为可正常执行的状态。
其中load()内部重要通过ImageLoader 的link方法
查看一下源码
void ImageLoader::link(const LinkContext& context, bool forceLazysBound, bool preflightOnly, bool neverUnload, const RPathChain& loaderRPaths, const char* imagePath)
{
//dyld::log("ImageLoader::link(%s) refCount=%d, neverUnload=%d\n", imagePath, fDlopenReferenceCount, fNeverUnload);
// clear error strings
(*context.setErrorStrings)(0, NULL, NULL, NULL);
uint64_t t0 = mach_absolute_time();
// 递归加载加载主程序所需依赖库
this->recursiveLoadLibraries(context, preflightOnly, loaderRPaths, imagePath);
context.notifyBatch(dyld_image_state_dependents_mapped, preflightOnly);
// we only do the loading step for preflights
if ( preflightOnly )
return;
uint64_t t1 = mach_absolute_time();
context.clearAllDepths();
// 递归刷新依赖库的层级
this->recursiveUpdateDepth(context.imageCount());
__block uint64_t t2, t3, t4, t5;
{
dyld3::ScopedTimer(DBG_DYLD_TIMING_APPLY_FIXUPS, 0, 0, 0);
t2 = mach_absolute_time();
// 递归进行rebase
this->recursiveRebaseWithAccounting(context);
context.notifyBatch(dyld_image_state_rebased, false);
t3 = mach_absolute_time();
if ( !context.linkingMainExecutable )
// 递归绑定符号表
this->recursiveBindWithAccounting(context, forceLazysBound, neverUnload);
t4 = mach_absolute_time();
if ( !context.linkingMainExecutable )
// 弱符号绑定
this->weakBind(context);
t5 = mach_absolute_time();
}
// interpose any dynamically loaded images
if ( !context.linkingMainExecutable && (fgInterposingTuples.size() != 0) ) {
dyld3::ScopedTimer timer(DBG_DYLD_TIMING_APPLY_INTERPOSING, 0, 0, 0);
this->recursiveApplyInterposing(context);
}
// now that all fixups are done, make __DATA_CONST segments read-only
if ( !context.linkingMainExecutable )
this->recursiveMakeDataReadOnly(context);
if ( !context.linkingMainExecutable )
context.notifyBatch(dyld_image_state_bound, false);
uint64_t t6 = mach_absolute_time();
if ( context.registerDOFs != NULL ) {
std::vector dofs;
this->recursiveGetDOFSections(context, dofs);
context.registerDOFs(dofs);
}
uint64_t t7 = mach_absolute_time();
// clear error strings
(*context.setErrorStrings)(0, NULL, NULL, NULL);
fgTotalLoadLibrariesTime += t1 - t0;
fgTotalRebaseTime += t3 - t2;
fgTotalBindTime += t4 - t3;
fgTotalWeakBindTime += t5 - t4;
fgTotalDOF += t7 - t6;
// done with initial dylib loads
fgNextPIEDylibAddress = 0;
}
其主要做的几件事情
-
recursiveLoadLibraries()根据LC_LOAD_DYLIB加载命令把所有依赖库加载进内存。 -
recursiveUpdateDepth()递归刷新依赖库的层级。 -
recursiveRebaseWithAccounting()由于ASLR的存在，必须递归对主程序以及依赖库进行重定位操作。 -
recursiveBindWithAccounting()把主程序二进制和依赖进来的动态库全部执行符号表绑定。 -
weakBind()如果链接的不是主程序二进制的话，会在此时执行弱符号绑定，主程序二进制则在link()完后再执行弱符号绑定，后面会进行分析。 -
recursiveGetDOFSections()、context.registerDOFs()注册DOF（DTrace Object Format）节。
链接插入的动态库
和链接主程序一样，调用link()函数去进行链接，不过这里需要从i+1个元素开始，第一个是主程序
ImageLoader* image = sAllImages[i+1];
执行弱符号绑定
sMainExecutable->weakBind(gLinkContext);
- 通过
getCoalescedImages()合并所有动态库的弱符号到一个列表里 - 调用
initializeCoalIterator()对需要绑定的弱符号进行排序 - 调用
incrementCoalIterator()读取dyld_info_command结构的weak_bind_off和weak_bind_size字段，确定弱符号的数据偏移与大小
执行初始化方法
void initializeMainExecutable()
{
// record that we've reached this step
gLinkContext.startedInitializingMainExecutable = true;
// run initialzers for any inserted dylibs
ImageLoader::InitializerTimingList initializerTimes[allImagesCount()];
initializerTimes[0].count = 0;
const size_t rootCount = sImageRoots.size();
if ( rootCount > 1 ) {
for(size_t i=1; i < rootCount; ++i) {
sImageRoots[i]->runInitializers(gLinkContext, initializerTimes[0]);
}
}
// run initializers for main executable and everything it brings up
sMainExecutable->runInitializers(gLinkContext, initializerTimes[0]);
// register cxa_atexit() handler to run static terminators in all loaded images when this process exits
if ( gLibSystemHelpers != NULL )
(*gLibSystemHelpers->cxa_atexit)(&runAllStaticTerminators, NULL, NULL);
// dump info if requested
if ( sEnv.DYLD_PRINT_STATISTICS )
ImageLoader::printStatistics((unsigned int)allImagesCount(), initializerTimes[0]);
if ( sEnv.DYLD_PRINT_STATISTICS_DETAILS )
ImageLoaderMachO::printStatisticsDetails((unsigned int)allImagesCount(), initializerTimes[0]);
}
这一步由initializeMainExecutable()完成。
dyld会优先初始化动态库，然后初始化主程序.
initializeMainExecutable()内部主要方法为runInitializers()
再内部跳转为processInitializers()->recursiveInitialization()->ImageLoader::recursiveInitialization()
void ImageLoader::recursiveInitialization(const LinkContext& context, mach_port_t this_thread, const char* pathToInitialize,
InitializerTimingList& timingInfo, UninitedUpwards& uninitUps)
{
recursive_lock lock_info(this_thread);
recursiveSpinLock(lock_info);
if ( fState < dyld_image_state_dependents_initialized-1 ) {
uint8_t oldState = fState;
// break cycles
fState = dyld_image_state_dependents_initialized-1;
try {
// initialize lower level libraries first
for(unsigned int i=0; i < libraryCount(); ++i) {
ImageLoader* dependentImage = libImage(i);
if ( dependentImage != NULL ) {
// don't try to initialize stuff "above" me yet
if ( libIsUpward(i) ) {
uninitUps.imagesAndPaths[uninitUps.count] = { dependentImage, libPath(i) };
uninitUps.count++;
}
else if ( dependentImage->fDepth >= fDepth ) {
dependentImage->recursiveInitialization(context, this_thread, libPath(i), timingInfo, uninitUps);
}
}
}
// record termination order
if ( this->needsTermination() )
context.terminationRecorder(this);
// let objc know we are about to initialize this image
uint64_t t1 = mach_absolute_time();
fState = dyld_image_state_dependents_initialized;
oldState = fState;
context.notifySingle(dyld_image_state_dependents_initialized, this, &timingInfo);
// initialize this image
bool hasInitializers = this->doInitialization(context);
// let anyone know we finished initializing this image
fState = dyld_image_state_initialized;
oldState = fState;
context.notifySingle(dyld_image_state_initialized, this, NULL);
if ( hasInitializers ) {
uint64_t t2 = mach_absolute_time();
timingInfo.addTime(this->getShortName(), t2-t1);
}
}
catch (const char* msg) {
// this image is not initialized
fState = oldState;
recursiveSpinUnLock();
throw;
}
}
recursiveSpinUnLock();
}
然后在recursiveInitialization()中我们看到了notifySingle()函数
context.notifySingle(dyld_image_state_initialized, this, NULL);
这个流程刚好对应了我们之前bt打印的信息
if ( (state == dyld_image_state_dependents_initialized) && (sNotifyObjCInit != NULL) && image->notifyObjC() ) {
uint64_t t0 = mach_absolute_time();
dyld3::ScopedTimer timer(DBG_DYLD_TIMING_OBJC_INIT, (uint64_t)image->machHeader(), 0, 0);
(*sNotifyObjCInit)(image->getRealPath(), image->machHeader());
uint64_t t1 = mach_absolute_time();
uint64_t t2 = mach_absolute_time();
uint64_t timeInObjC = t1-t0;
uint64_t emptyTime = (t2-t1)*100;
if ( (timeInObjC > emptyTime) && (timingInfo != NULL) ) {
timingInfo->addTime(image->getShortName(), timeInObjC);
}
}
其中，我们需要关心的东西是sNotifyObjCInit
下面全局搜索一下给他赋值的地方
void registerObjCNotifiers(_dyld_objc_notify_mapped mapped, _dyld_objc_notify_init init, _dyld_objc_notify_unmapped unmapped)
{
// record functions to call
sNotifyObjCMapped = mapped;
sNotifyObjCInit = init;
sNotifyObjCUnmapped = unmapped;
// call 'mapped' function with all images mapped so far
try {
notifyBatchPartial(dyld_image_state_bound, true, NULL, false, true);
}
catch (const char* msg) {
// ignore request to abort during registration
}
// call 'init' function on all images already init'ed (below libSystem)
for (std::vector::iterator it=sAllImages.begin(); it != sAllImages.end(); it++) {
ImageLoader* image = *it;
if ( (image->getState() == dyld_image_state_initialized) && image->notifyObjC() ) {
dyld3::ScopedTimer timer(DBG_DYLD_TIMING_OBJC_INIT, (uint64_t)image->machHeader(), 0, 0);
(*sNotifyObjCInit)(image->getRealPath(), image->machHeader());
}
}
}
接下来我们找一下谁调用了registerObjCNotifiers()
全局搜索后在dyldAPIs.cpp中找到方法
void _dyld_objc_notify_register(_dyld_objc_notify_mapped mapped,
_dyld_objc_notify_init init,
_dyld_objc_notify_unmapped unmapped)
{
dyld::registerObjCNotifiers(mapped, init, unmapped);
}
接下来继续找_dyld_objc_notify_register并没有找到调用了。
我们回到之前使用的objc源码，全局搜索后发现
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();
tls_init();
static_init();
runtime_init();
exception_init();
cache_init();
_imp_implementationWithBlock_init();
_dyld_objc_notify_register(&map_images, load_images, unmap_image);
#if __OBJC2__
didCallDyldNotifyRegister = true;
#endif
}
一切，就回到了_objc_init了
这里注册的init回调函数就是load_images()，回调里面调用了call_load_methods()来执行所有的+ load方法
在notifySingle()之后是doInitialization()
bool hasInitializers = this->doInitialization(context);
-
doInitialization()内部首先调用doImageInit来执行镜像的初始化函数，也就是LC_ROUTINES_COMMAND中记录的函数， - 然后再执行
doModInitFunctions()方法来解析并执行_DATA_,__mod_init_func这个section中保存的函数
_mod_init_funcs中保存的是全局C++对象的构造函数以及所有带__attribute__((constructor)的C函数。
我们之前在工程中添加了一个
__attribute__((constructor)) void kcFunc(){
printf("来了 : %s \n",__func__);
}
现在我们在machOView中验证一下
machOView验证.jpg
这也是为什么这个方法在main()函数之前打印的原因。
查找入口点并返回
result = (uintptr_t)sMainExecutable->getEntryFromLC_MAIN();
这一步调用主程序镜像的getEntryFromLC_MAIN()，从加载命令读取LC_MAIN入口，如果没有LC_MAIN就调用getEntryFromLC_UNIXTHREAD读取LC_UNIXTHREAD，找到后就跳到入口点指定的地址并返回
void* ImageLoaderMachO::getEntryFromLC_MAIN() const
{
const uint32_t cmd_count = ((macho_header*)fMachOData)->ncmds;
const struct load_command* const cmds = (struct load_command*)&fMachOData[sizeof(macho_header)];
const struct load_command* cmd = cmds;
for (uint32_t i = 0; i < cmd_count; ++i) {
if ( cmd->cmd == LC_MAIN ) {
entry_point_command* mainCmd = (entry_point_command*)cmd;
void* entry = (void*)(mainCmd->entryoff + (char*)fMachOData);
// verify entry point is in image
if ( this->containsAddress(entry) )
return entry;
else
throw "LC_MAIN entryoff is out of range";
}
cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
}
return NULL;
}
void* ImageLoaderMachO::getEntryFromLC_UNIXTHREAD() const
{
const uint32_t cmd_count = ((macho_header*)fMachOData)->ncmds;
const struct load_command* const cmds = (struct load_command*)&fMachOData[sizeof(macho_header)];
const struct load_command* cmd = cmds;
for (uint32_t i = 0; i < cmd_count; ++i) {
if ( cmd->cmd == LC_UNIXTHREAD ) {
#if __i386__
const i386_thread_state_t* registers = (i386_thread_state_t*)(((char*)cmd) + 16);
void* entry = (void*)(registers->eip + fSlide);
// verify entry point is in image
if ( this->containsAddress(entry) )
return entry;
#elif __x86_64__
const x86_thread_state64_t* registers = (x86_thread_state64_t*)(((char*)cmd) + 16);
void* entry = (void*)(registers->rip + fSlide);
// verify entry point is in image
if ( this->containsAddress(entry) )
return entry;
#elif __arm64__ && !__arm64e__
// temp support until is fixed
const uint64_t* regs64 = (uint64_t*)(((char*)cmd) + 16);
void* entry = (void*)(regs64[32] + fSlide); // arm_thread_state64_t.__pc
// verify entry point is in image
if ( this->containsAddress(entry) )
return entry;
#endif
}
cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
}
throw "no valid entry point";
}
总结
这次的分析大概就到这里，源代码太多，可读性较差，主要流程可以直接按照之前的bt打印的流程来参考