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src/ImageLoader.cpp dyld-95.3 dyld-852.2
--- dyld/dyld-95.3/src/ImageLoader.cpp
+++ dyld/dyld-852.2/src/ImageLoader.cpp
@@ -1,6 +1,6 @@
 /* -*- mode: C++; c-basic-offset: 4; tab-width: 4 -*-
  *
- * Copyright (c) 2004-2006 Apple Computer, Inc. All rights reserved.
+ * Copyright (c) 2004-2010 Apple Inc. All rights reserved.
  *
  * @APPLE_LICENSE_HEADER_START@
  * 
@@ -24,6 +24,7 @@
 
 #define __STDC_LIMIT_MACROS
 #include <stdint.h>
+#include <stdlib.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <mach/mach.h>
@@ -33,17 +34,21 @@
 #include <sys/mman.h>
 #include <sys/param.h>
 #include <sys/mount.h>
+#include <sys/sysctl.h>
 #include <libkern/OSAtomic.h>
+#include <string_view>
+
+#include <atomic>
+
+#include "Tracing.h"
 
 #include "ImageLoader.h"
 
-// in libc.a
-extern "C" void _spin_lock(uint32_t*);
-extern "C" void _spin_unlock(uint32_t*);
 
 uint32_t								ImageLoader::fgImagesUsedFromSharedCache = 0;
 uint32_t								ImageLoader::fgImagesWithUsedPrebinding = 0;
-uint32_t								ImageLoader::fgImagesRequiringNoFixups = 0;
+uint32_t								ImageLoader::fgImagesRequiringCoalescing = 0;
+uint32_t								ImageLoader::fgImagesHasWeakDefinitions = 0;
 uint32_t								ImageLoader::fgTotalRebaseFixups = 0;
 uint32_t								ImageLoader::fgTotalBindFixups = 0;
 uint32_t								ImageLoader::fgTotalBindSymbolsResolved = 0;
@@ -52,103 +57,72 @@
 uint32_t								ImageLoader::fgTotalPossibleLazyBindFixups = 0;
 uint32_t								ImageLoader::fgTotalSegmentsMapped = 0;
 uint64_t								ImageLoader::fgTotalBytesMapped = 0;
-uint64_t								ImageLoader::fgTotalBytesPreFetched = 0;
 uint64_t								ImageLoader::fgTotalLoadLibrariesTime;
+uint64_t								ImageLoader::fgTotalObjCSetupTime = 0;
+uint64_t								ImageLoader::fgTotalDebuggerPausedTime = 0;
+uint64_t								ImageLoader::fgTotalRebindCacheTime = 0;
 uint64_t								ImageLoader::fgTotalRebaseTime;
 uint64_t								ImageLoader::fgTotalBindTime;
+uint64_t								ImageLoader::fgTotalWeakBindTime;
+uint64_t								ImageLoader::fgTotalDOF;
 uint64_t								ImageLoader::fgTotalInitTime;
-uintptr_t								ImageLoader::fgNextSplitSegAddress = 0x90000000;
 uint16_t								ImageLoader::fgLoadOrdinal = 0;
-uintptr_t								Segment::fgNextPIEDylibAddress = 0;
-
-
-void ImageLoader::init(const char* path, uint64_t offsetInFat, dev_t device, ino_t inode, time_t modDate)
-{
-	fPathHash = 0;
-	fPath = path;
-	fLogicalPath = NULL;
+uint32_t								ImageLoader::fgSymbolTrieSearchs = 0;
+std::vector<ImageLoader::InterposeTuple>ImageLoader::fgInterposingTuples;
+uintptr_t								ImageLoader::fgNextPIEDylibAddress = 0;
+
+
+
+ImageLoader::ImageLoader(const char* path, unsigned int libCount)
+	: fPath(path), fRealPath(NULL), fDevice(0), fInode(0), fLastModified(0),
+	fPathHash(0), fDlopenReferenceCount(0), fInitializerRecursiveLock(NULL), 
+	fLoadOrder(fgLoadOrdinal++), fDepth(0), fObjCMappedNotified(false), fState(0), fLibraryCount(libCount),
+	fMadeReadOnly(false), fAllLibraryChecksumsAndLoadAddressesMatch(false), fLeaveMapped(false), fNeverUnload(false),
+	fHideSymbols(false), fMatchByInstallName(false),
+	fInterposed(false), fRegisteredDOF(false), fAllLazyPointersBound(false), 
+    fBeingRemoved(false), fAddFuncNotified(false),
+	fPathOwnedByImage(false), fIsReferencedDownward(false), 
+	fWeakSymbolsBound(false)
+{
+#if __x86_64__
+	fAotPath = NULL;
+#endif
+	if ( fPath != NULL )
+		fPathHash = hash(fPath);
+	if ( libCount > 512 )
+		dyld::throwf("too many dependent dylibs in %s", path);
+}
+
+
+void ImageLoader::deleteImage(ImageLoader* image)
+{
+	delete image;
+}
+
+
+ImageLoader::~ImageLoader()
+{
+	if ( fRealPath != NULL ) 
+		delete [] fRealPath;
+	if ( fPathOwnedByImage && (fPath != NULL) ) 
+		delete [] fPath;
+#if __x86_64__
+	if ( fAotPath != NULL )
+		delete [] fAotPath;
+#endif
+}
+
+void ImageLoader::setFileInfo(dev_t device, ino_t inode, time_t modDate)
+{
 	fDevice = device;
 	fInode = inode;
 	fLastModified = modDate;
-	fOffsetInFatFile = offsetInFat;
-	fLibraries = NULL;
-	fLibrariesCount = 0;
-	fDlopenReferenceCount = 0;
-	fStaticReferenceCount = 0;
-	fDynamicReferenceCount = 0;
-	fDynamicReferences = NULL;
-	fDepth = 0;
-	fLoadOrder = fgLoadOrdinal++;
-	fState = 0;
-	fAllLibraryChecksumsAndLoadAddressesMatch = false;
-	fLeaveMapped = false;
-	fNeverUnload = false;
-	fHideSymbols = false;
-	fMatchByInstallName = false;
-	fRegisteredDOF = false;
-#if IMAGE_NOTIFY_SUPPORT
-	fAnnounced = false;
-#endif
-	fAllLazyPointersBound = false;
-	fBeingRemoved = false;
-	fPathOwnedByImage = false;
-#if RECURSIVE_INITIALIZER_LOCK
-	fInitializerRecursiveLock = NULL;
-#else
-	fInitializerLock = 0;
-#endif
-	if ( fPath != NULL )
-		fPathHash = hash(fPath);
-}
-
-
-ImageLoader::ImageLoader(const char* path, uint64_t offsetInFat, const struct stat& info)
-{
-	init(path, offsetInFat, info.st_dev, info.st_ino, info.st_mtime);
-}
-
-ImageLoader::ImageLoader(const char* moduleName)
-{
-	init(moduleName, 0, 0, 0, 0);
-}
-
-
-ImageLoader::~ImageLoader()
-{
-	if ( fPathOwnedByImage && (fPath != NULL) ) 
-		delete [] fPath;
-	if ( fLogicalPath != NULL ) 
-		delete [] fLogicalPath;
-	if ( fLibraries != NULL ) {
-		for (uint32_t i = 0; i < fLibrariesCount; ++i) {
-			if ( fLibraries[i].image != NULL )
-				fLibraries[i].image->fStaticReferenceCount--;
-		}
-		delete [] fLibraries;
-	}
-	if ( fDynamicReferences != NULL ) {
-		for (std::set<const ImageLoader*>::iterator it = fDynamicReferences->begin(); it != fDynamicReferences->end(); ++it ) {
-			const_cast<ImageLoader*>(*it)->fDynamicReferenceCount--;
-		}
-		delete fDynamicReferences;
-	}
 }
 
 void ImageLoader::setMapped(const LinkContext& context)
 {
 	fState = dyld_image_state_mapped;
-	context.notifySingle(dyld_image_state_mapped, this->machHeader(), fPath, fLastModified);
-}
-
-void ImageLoader::addDynamicReference(const ImageLoader* target)
-{
-	if ( fDynamicReferences == NULL )
-		fDynamicReferences = new std::set<const ImageLoader*>();
-	if ( fDynamicReferences->count(target) == 0 ) {	
-		fDynamicReferences->insert(target);
-		const_cast<ImageLoader*>(target)->fDynamicReferenceCount++;
-	}
-	//dyld::log("dyld: addDynamicReference() from %s to %s, fDynamicReferences->size()=%lu\n", this->getPath(), target->getPath(), fDynamicReferences->size());
+	context.notifySingle(dyld_image_state_mapped, this, NULL);  // note: can throw exception
 }
 
 int ImageLoader::compare(const ImageLoader* right) const
@@ -171,12 +145,16 @@
 
 void ImageLoader::setPath(const char* path)
 {
-	if ( fPathOwnedByImage && (fPath != NULL) ) 
+	if ( fPathOwnedByImage && (fPath != NULL) )
 		delete [] fPath;
 	fPath = new char[strlen(path)+1];
 	strcpy((char*)fPath, path);
 	fPathOwnedByImage = true;  // delete fPath when this image is destructed
 	fPathHash = hash(fPath);
+	if ( fRealPath != NULL ) {
+		delete [] fRealPath;
+		fRealPath = NULL;
+	}
 }
 
 void ImageLoader::setPathUnowned(const char* path)
@@ -185,30 +163,22 @@
 		delete [] fPath;
 	}
 	fPath = path;
-	fPathOwnedByImage = false;  
+	fPathOwnedByImage = false;
 	fPathHash = hash(fPath);
 }
 
-void ImageLoader::setLogicalPath(const char* path)
-{
-	if ( fPath == NULL ) {
-		// no physical path set yet, so use this path as physical
-		this->setPath(path);
-	}
-	else if ( strcmp(path, fPath) == 0 ) {
-		// do not set logical path because it is the same as the physical path
-		fLogicalPath = NULL;
-	}
-	else {
-		fLogicalPath = new char[strlen(path)+1];
-		strcpy((char*)fLogicalPath, path);
-	}
-}
-
-const char* ImageLoader::getLogicalPath() const
-{
-	if ( fLogicalPath != NULL )
-		return fLogicalPath;
+void ImageLoader::setPaths(const char* path, const char* realPath)
+{
+	this->setPath(path);
+	fRealPath = new char[strlen(realPath)+1];
+	strcpy((char*)fRealPath, realPath);
+}
+
+
+const char* ImageLoader::getRealPath() const
+{
+	if ( fRealPath != NULL )
+		return fRealPath;
 	else
 		return fPath;
 }
@@ -239,20 +209,20 @@
 	return ( (this->fDevice == stat_buf.st_dev) && (this->fInode == stat_buf.st_ino) );	
 }
 
-const char* ImageLoader::getShortName() const
+const char* ImageLoader::shortName(const char* fullName)
 {
 	// try to return leaf name
-	if ( fPath != NULL ) {
-		const char* s = strrchr(fPath, '/');
+	if ( fullName != NULL ) {
+		const char* s = strrchr(fullName, '/');
 		if ( s != NULL ) 
 			return &s[1];
 	}
-	return fPath; 
-}
-
-uint64_t ImageLoader::getOffsetInFatFile() const
-{
-	return fOffsetInFatFile;
+	return fullName;
+}
+
+const char* ImageLoader::getShortName() const
+{
+	return shortName(fPath);
 }
 
 void ImageLoader::setLeaveMapped()
@@ -282,13 +252,10 @@
 
 bool ImageLoader::containsAddress(const void* addr) const
 {
-	if ( ! this->isLinked() )
-		return false;
-	for(ImageLoader::SegmentIterator it = this->beginSegments(); it != this->endSegments(); ++it ) {
-		Segment* seg = *it;
-		const uint8_t* start = (const uint8_t*)seg->getActualLoadAddress(this);
-		const uint8_t* end = start + seg->getSize();
-		if ( (start <= addr) && (addr < end) && !seg->unaccessible() )
+	for(unsigned int i=0, e=segmentCount(); i < e; ++i) {
+		const uint8_t* start = (const uint8_t*)segActualLoadAddress(i);
+		const uint8_t* end = (const uint8_t*)segActualEndAddress(i);
+		if ( (start <= addr) && (addr < end) && !segUnaccessible(i) )
 			return true;
 	}
 	return false;
@@ -296,10 +263,16 @@
 
 bool ImageLoader::overlapsWithAddressRange(const void* start, const void* end) const
 {
-	for(ImageLoader::SegmentIterator it = this->beginSegments(); it != this->endSegments(); ++it ) {
-		Segment* seg = *it;
-		const uint8_t* segStart = (const uint8_t*)(seg->getActualLoadAddress(this));
-		const uint8_t* segEnd = segStart + seg->getSize();
+	for(unsigned int i=0, e=segmentCount(); i < e; ++i) {
+		const uint8_t* segStart = (const uint8_t*)segActualLoadAddress(i);
+		const uint8_t* segEnd = (const uint8_t*)segActualEndAddress(i);
+		if ( strcmp(segName(i), "__UNIXSTACK") == 0 ) {
+			// __UNIXSTACK never slides.  This is the only place that cares
+			// and checking for that segment name in segActualLoadAddress()
+			// is too expensive.
+			segStart -= getSlide();
+			segEnd -= getSlide();
+		}
 		if ( (start <= segStart) && (segStart < end) )
 			return true;
 		if ( (start <= segEnd) && (segEnd < end) )
@@ -312,13 +285,22 @@
 
 void ImageLoader::getMappedRegions(MappedRegion*& regions) const
 {
-	for(ImageLoader::SegmentIterator it = this->beginSegments(); it != this->endSegments(); ++it ) {
-		Segment* seg = *it;
+	for(unsigned int i=0, e=segmentCount(); i < e; ++i) {
 		MappedRegion region;
-		region.address = seg->getActualLoadAddress(this);
-		region.size = seg->getSize();
+		region.address = segActualLoadAddress(i);
+		region.size = segSize(i);
 		*regions++ = region;
 	}
+}
+
+
+
+bool ImageLoader::dependsOn(ImageLoader* image) {
+	for(unsigned int i=0; i < libraryCount(); ++i) {
+		if ( libImage(i) == image )
+			return true;
+	}
+	return false;
 }
 
 
@@ -330,37 +312,48 @@
 	return true;
 }
 
+bool ImageLoader::findExportedSymbolAddress(const LinkContext& context, const char* symbolName,
+											const ImageLoader* requestorImage, int requestorOrdinalOfDef,
+											bool runResolver, const ImageLoader** foundIn, uintptr_t* address) const
+{
+	const Symbol* sym = this->findExportedSymbol(symbolName, true, foundIn);
+	if ( sym != NULL ) {
+		*address = (*foundIn)->getExportedSymbolAddress(sym, context, requestorImage, runResolver);
+		return true;
+	}
+	return false;
+}
+
 
 // private method that handles circular dependencies by only search any image once
 const ImageLoader::Symbol* ImageLoader::findExportedSymbolInDependentImagesExcept(const char* name, 
 			const ImageLoader** dsiStart, const ImageLoader**& dsiCur, const ImageLoader** dsiEnd, const ImageLoader** foundIn) const
 {
 	const ImageLoader::Symbol* sym;
-	
 	// search self
 	if ( notInImgageList(this, dsiStart, dsiCur) ) {
-		sym = this->findExportedSymbol(name, NULL, false, foundIn);
+		sym = this->findExportedSymbol(name, false, this->getPath(), foundIn);
 		if ( sym != NULL )
 			return sym;
 		*dsiCur++ = this;
 	}
 
 	// search directly dependent libraries
-	for (uint32_t i=0; i < fLibrariesCount; ++i) {
-		ImageLoader* dependentImage = fLibraries[i].image;
+	for(unsigned int i=0; i < libraryCount(); ++i) {
+		ImageLoader* dependentImage = libImage(i);
 		if ( (dependentImage != NULL) && notInImgageList(dependentImage, dsiStart, dsiCur) ) {
-			const ImageLoader::Symbol* sym = dependentImage->findExportedSymbol(name, NULL, false, foundIn);
+			sym = dependentImage->findExportedSymbol(name, false, libPath(i), foundIn);
 			if ( sym != NULL )
 				return sym;
 		}
 	}
 	
 	// search indirectly dependent libraries
-	for (uint32_t i=0; i < fLibrariesCount; ++i) {
-		ImageLoader* dependentImage = fLibraries[i].image;
+	for(unsigned int i=0; i < libraryCount(); ++i) {
+		ImageLoader* dependentImage = libImage(i);
 		if ( (dependentImage != NULL) && notInImgageList(dependentImage, dsiStart, dsiCur) ) {
 			*dsiCur++ = dependentImage; 
-			const ImageLoader::Symbol* sym = dependentImage->findExportedSymbolInDependentImagesExcept(name, dsiStart, dsiCur, dsiEnd, foundIn);
+			sym = dependentImage->findExportedSymbolInDependentImagesExcept(name, dsiStart, dsiCur, dsiEnd, foundIn);
 			if ( sym != NULL )
 				return sym;
 		}
@@ -372,7 +365,7 @@
 
 const ImageLoader::Symbol* ImageLoader::findExportedSymbolInDependentImages(const char* name, const LinkContext& context, const ImageLoader** foundIn) const
 {
-	unsigned int imageCount = context.imageCount();
+	unsigned int imageCount = context.imageCount()+2;
 	const ImageLoader* dontSearchImages[imageCount];
 	dontSearchImages[0] = this; // don't search this image
 	const ImageLoader** cur = &dontSearchImages[1];
@@ -381,56 +374,208 @@
 
 const ImageLoader::Symbol* ImageLoader::findExportedSymbolInImageOrDependentImages(const char* name, const LinkContext& context, const ImageLoader** foundIn) const
 {
-	unsigned int imageCount = context.imageCount();
+	unsigned int imageCount = context.imageCount()+2;
 	const ImageLoader* dontSearchImages[imageCount];
 	const ImageLoader** cur = &dontSearchImages[0];
 	return this->findExportedSymbolInDependentImagesExcept(name, &dontSearchImages[0], cur, &dontSearchImages[imageCount], foundIn);
 }
 
-
-void ImageLoader::link(const LinkContext& context, bool forceLazysBound, bool preflightOnly, const RPathChain& loaderRPaths)
-{
-	//dyld::log("ImageLoader::link(%s) refCount=%d, neverUnload=%d\n", this->getPath(), fStaticReferenceCount, fNeverUnload);
+// this is called by initializeMainExecutable() to interpose on the initial set of images
+void ImageLoader::applyInterposing(const LinkContext& context)
+{
+	dyld3::ScopedTimer timer(DBG_DYLD_TIMING_APPLY_INTERPOSING, 0, 0, 0);
+	if ( fgInterposingTuples.size() != 0 )
+		this->recursiveApplyInterposing(context);
+}
+
+
+uintptr_t ImageLoader::interposedAddress(const LinkContext& context, uintptr_t address, const ImageLoader* inImage, const ImageLoader* onlyInImage)
+{
+	//dyld::log("interposedAddress(0x%08llX), tupleCount=%lu\n", (uint64_t)address, fgInterposingTuples.size());
+	for (std::vector<InterposeTuple>::iterator it=fgInterposingTuples.begin(); it != fgInterposingTuples.end(); it++) {
+		//dyld::log("    interposedAddress: replacee=0x%08llX, replacement=0x%08llX, neverImage=%p, onlyImage=%p, inImage=%p\n", 
+		//				(uint64_t)it->replacee, (uint64_t)it->replacement,  it->neverImage, it->onlyImage, inImage);
+		// replace all references to 'replacee' with 'replacement'
+		if ( (address == it->replacee) && (it->neverImage != inImage) && ((it->onlyImage == NULL) || (it->onlyImage == inImage)) ) {
+			if ( context.verboseInterposing ) {
+				dyld::log("dyld interposing: replace 0x%lX with 0x%lX\n", it->replacee, it->replacement);
+			}
+			return it->replacement;
+		}
+	}
+	return address;
+}
+
+void ImageLoader::applyInterposingToDyldCache(const LinkContext& context) {
+	if (!context.dyldCache)
+		return;
+	if (!context.dyldCache->header.builtFromChainedFixups)
+		return;
+	if (fgInterposingTuples.empty())
+		return;
+
+	// make the cache writable for this block
+	DyldSharedCache::DataConstScopedWriter patcher(context.dyldCache, mach_task_self(), (context.verboseMapping ? &dyld::log : nullptr));
+
+	// For each of the interposed addresses, see if any of them are in the shared cache.  If so, find
+	// that image and apply its patch table to all uses.
+	uintptr_t cacheStart = (uintptr_t)context.dyldCache;
+	for (std::vector<InterposeTuple>::iterator it=fgInterposingTuples.begin(); it != fgInterposingTuples.end(); it++) {
+		if ( context.verboseInterposing )
+			dyld::log("dyld: interpose: Trying to interpose address 0x%08llx\n", (uint64_t)it->replacee);
+		uint32_t imageIndex;
+		uint32_t cacheOffsetOfReplacee = (uint32_t)(it->replacee - cacheStart);
+		if (!context.dyldCache->addressInText(cacheOffsetOfReplacee, &imageIndex))
+			continue;
+		dyld3::closure::ImageNum imageInCache = imageIndex+1;
+		if ( context.verboseInterposing )
+			dyld::log("dyld: interpose: Found shared cache image %d for 0x%08llx\n", imageInCache, (uint64_t)it->replacee);
+		context.dyldCache->forEachPatchableExport(imageIndex, ^(uint32_t cacheOffsetOfImpl, const char* exportName) {
+			// Skip patching anything other than this symbol
+			if (cacheOffsetOfImpl != cacheOffsetOfReplacee)
+				return;
+			if ( context.verboseInterposing ) {
+				const dyld3::closure::Image* image = context.dyldCache->cachedDylibsImageArray()->imageForNum(imageInCache);
+				dyld::log("dyld: interpose: Patching uses of symbol %s in shared cache binary at %s\n", exportName, image->path());
+			}
+			uintptr_t newLoc = it->replacement;
+			context.dyldCache->forEachPatchableUseOfExport(imageIndex, cacheOffsetOfImpl, ^(dyld_cache_patchable_location patchLocation) {
+				uintptr_t* loc = (uintptr_t*)(cacheStart+patchLocation.cacheOffset);
+#if __has_feature(ptrauth_calls)
+				if ( patchLocation.authenticated ) {
+					dyld3::MachOLoaded::ChainedFixupPointerOnDisk ptr = *(dyld3::MachOLoaded::ChainedFixupPointerOnDisk*)loc;
+					ptr.arm64e.authRebase.auth      = true;
+					ptr.arm64e.authRebase.addrDiv   = patchLocation.usesAddressDiversity;
+					ptr.arm64e.authRebase.diversity = patchLocation.discriminator;
+					ptr.arm64e.authRebase.key       = patchLocation.key;
+					*loc = ptr.arm64e.signPointer(loc, newLoc + DyldSharedCache::getAddend(patchLocation));
+					if ( context.verboseInterposing )
+						dyld::log("dyld: interpose: *%p = %p (JOP: diversity 0x%04X, addr-div=%d, key=%s)\n",
+								  loc, (void*)*loc, patchLocation.discriminator, patchLocation.usesAddressDiversity, DyldSharedCache::keyName(patchLocation));
+					return;
+				}
+#endif
+				if ( context.verboseInterposing )
+					dyld::log("dyld: interpose: *%p = 0x%0llX (dyld cache patch) to %s\n", loc, newLoc + DyldSharedCache::getAddend(patchLocation), exportName);
+				*loc = newLoc + (uintptr_t)DyldSharedCache::getAddend(patchLocation);
+			});
+		});
+	}
+}
+
+void ImageLoader::addDynamicInterposingTuples(const struct dyld_interpose_tuple array[], size_t count)
+{
+	for(size_t i=0; i < count; ++i) {
+		ImageLoader::InterposeTuple tuple;
+		tuple.replacement		= (uintptr_t)array[i].replacement;
+		tuple.neverImage		= NULL;
+		tuple.onlyImage		    = this;
+		tuple.replacee			= (uintptr_t)array[i].replacee;
+		// chain to any existing interpositions
+		for (std::vector<InterposeTuple>::iterator it=fgInterposingTuples.begin(); it != fgInterposingTuples.end(); it++) {
+			if ( (it->replacee == tuple.replacee) && (it->onlyImage == this) ) {
+				tuple.replacee = it->replacement;
+			}
+		}
+		ImageLoader::fgInterposingTuples.push_back(tuple);
+	}
+}
+
+// <rdar://problem/29099600> dyld should tell the kernel when it is doing root fix-ups
+void ImageLoader::vmAccountingSetSuspended(const LinkContext& context, bool suspend)
+{
+#if TARGET_OS_IPHONE && !TARGET_OS_SIMULATOR
+	static bool sVmAccountingSuspended = false;
+	if ( suspend == sVmAccountingSuspended )
+		return;
+    if ( context.verboseBind )
+        dyld::log("set vm.footprint_suspend=%d\n", suspend);
+    int newValue = suspend ? 1 : 0;
+    int oldValue = 0;
+    size_t newlen = sizeof(newValue);
+    size_t oldlen = sizeof(oldValue);
+    int ret = sysctlbyname("vm.footprint_suspend", &oldValue, &oldlen, &newValue, newlen);
+    if ( context.verboseBind && (ret != 0) )
+		dyld::log("vm.footprint_suspend => %d, errno=%d\n", ret, errno);
+	sVmAccountingSuspended = suspend;
+#endif
+}
+
+
+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();
-	this->recursiveLoadLibraries(context,loaderRPaths);
-	context.notifyBatch(dyld_image_state_dependents_mapped);
-	
+	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();
-	this->recursiveUpdateDepth(context.imageCount());
-
-	uint64_t t2 = mach_absolute_time();
- 	this->recursiveRebase(context);
-	context.notifyBatch(dyld_image_state_rebased);
-	
-	uint64_t t3 = mach_absolute_time();
- 	this->recursiveBind(context, forceLazysBound);
-	context.notifyBatch(dyld_image_state_bound);
-
-	uint64_t t4 = mach_absolute_time();	
-	std::vector<DOFInfo> dofs;
-	this->recursiveGetDOFSections(context, dofs);
-	context.registerDOFs(dofs);
-
-	
+	this->updateDepth(context.imageCount());
+
+	__block uint64_t t2, t3, t4, t5;
+	{
+		dyld3::ScopedTimer(DBG_DYLD_TIMING_APPLY_FIXUPS, 0, 0, 0);
+		t2 = mach_absolute_time();
+		this->recursiveRebaseWithAccounting(context);
+		context.notifyBatch(dyld_image_state_rebased, false);
+
+		t3 = mach_absolute_time();
+		if ( !context.linkingMainExecutable )
+			this->recursiveBindWithAccounting(context, forceLazysBound, neverUnload);
+
+		t4 = mach_absolute_time();
+		if ( !context.linkingMainExecutable )
+			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<DOFInfo> 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
-	Segment::fgNextPIEDylibAddress = 0;
+	fgNextPIEDylibAddress = 0;
 }
 
 
 void ImageLoader::printReferenceCounts()
 {
-	dyld::log("      dlopen=%d, static=%d, dynamic=%d for %s\n", 
-				fDlopenReferenceCount, fStaticReferenceCount, fDynamicReferenceCount, getPath() );
+	dyld::log("      dlopen=%d for %s\n", fDlopenReferenceCount, getPath() );
 }
 
 
@@ -442,18 +587,39 @@
 	return false;
 }
 
-void ImageLoader::runInitializers(const LinkContext& context)
-{
-#if IMAGE_NOTIFY_SUPPORT
-	ImageLoader* newImages[context.imageCount()];
-	ImageLoader** end = newImages;
-	this->recursiveImageAnnouncement(context, end);	 // build bottom up list images being added
-	context.notifyAdding(newImages, end-newImages);	// tell anyone who cares about these
-#endif
-
+
+// <rdar://problem/14412057> upward dylib initializers can be run too soon
+// To handle dangling dylibs which are upward linked but not downward, all upward linked dylibs
+// have their initialization postponed until after the recursion through downward dylibs
+// has completed.
+void ImageLoader::processInitializers(const LinkContext& context, mach_port_t thisThread,
+									 InitializerTimingList& timingInfo, ImageLoader::UninitedUpwards& images)
+{
+	uint32_t maxImageCount = context.imageCount()+2;
+	ImageLoader::UninitedUpwards upsBuffer[maxImageCount];
+	ImageLoader::UninitedUpwards& ups = upsBuffer[0];
+	ups.count = 0;
+	// Calling recursive init on all images in images list, building a new list of
+	// uninitialized upward dependencies.
+	for (uintptr_t i=0; i < images.count; ++i) {
+		images.imagesAndPaths[i].first->recursiveInitialization(context, thisThread, images.imagesAndPaths[i].second, timingInfo, ups);
+	}
+	// If any upward dependencies remain, init them.
+	if ( ups.count > 0 )
+		processInitializers(context, thisThread, timingInfo, ups);
+}
+
+
+void ImageLoader::runInitializers(const LinkContext& context, InitializerTimingList& timingInfo)
+{
 	uint64_t t1 = mach_absolute_time();
-	this->recursiveInitialization(context, mach_thread_self());
-	context.notifyBatch(dyld_image_state_initialized);
+	mach_port_t thisThread = mach_thread_self();
+	ImageLoader::UninitedUpwards up;
+	up.count = 1;
+	up.imagesAndPaths[0] = { this, this->getPath() };
+	processInitializers(context, thisThread, timingInfo, up);
+	context.notifyBatch(dyld_image_state_initialized, false);
+	mach_port_deallocate(mach_task_self(), thisThread);
 	uint64_t t2 = mach_absolute_time();
 	fgTotalInitTime += (t2 - t1);
 }
@@ -466,94 +632,18 @@
 
 		if ( recursive ) {
 			// bind lower level libraries first
-			for(unsigned int i=0; i < fLibrariesCount; ++i){
-				DependentLibrary& libInfo = fLibraries[i];
-				if ( libInfo.image != NULL )
-					libInfo.image->bindAllLazyPointers(context, recursive);
-			}
-		}
-		// bind lazys in this image
-		this->doBind(context, true);
-	}
-}
-
-
-intptr_t ImageLoader::assignSegmentAddresses(const LinkContext& context)
-{
-	// preflight and calculate slide if needed
-	intptr_t slide = 0;
-	if ( this->segmentsCanSlide() && this->segmentsMustSlideTogether() ) {
-		bool needsToSlide = false;
-		uintptr_t lowAddr = UINTPTR_MAX;
-		uintptr_t highAddr = 0;
-		for(ImageLoader::SegmentIterator it = this->beginSegments(); it != this->endSegments(); ++it ) {
-			Segment* seg = *it;
-			const uintptr_t segLow = seg->getPreferredLoadAddress();
-			const uintptr_t segHigh = (segLow + seg->getSize() + 4095) & -4096;
-			if ( segLow < lowAddr )
-				lowAddr = segLow;
-			if ( segHigh > highAddr )
-				highAddr = segHigh;
-				
-			if ( !seg->hasPreferredLoadAddress() || !Segment::reserveAddressRange(seg->getPreferredLoadAddress(), seg->getSize()) )
-				needsToSlide = true;
-		}
-		if ( needsToSlide ) {
-			// find a chunk of address space to hold all segments
-			uintptr_t addr = Segment::reserveAnAddressRange(highAddr-lowAddr, context);
-			slide = addr - lowAddr;
-		}
-	} 
-	else if ( ! this->segmentsCanSlide() ) {
-		for(ImageLoader::SegmentIterator it = this->beginSegments(); it != this->endSegments(); ++it ) {
-			Segment* seg = *it;
-			if ( strcmp(seg->getName(), "__PAGEZERO") == 0 )
-				continue;
-			if ( !Segment::reserveAddressRange(seg->getPreferredLoadAddress(), seg->getSize()) )
-				throw "can't map";
-		}
-	}
-	else {
-		// mach-o does not support independently sliding segments
-	}
-	return slide;
-}
-
-
-void ImageLoader::mapSegments(int fd, uint64_t offsetInFat, uint64_t lenInFat, uint64_t fileLen, const LinkContext& context)
-{
-	if ( context.verboseMapping )
-		dyld::log("dyld: Mapping %s\n", this->getPath());
-	// find address range for image
-	intptr_t slide = this->assignSegmentAddresses(context);
-	// map in all segments
-	for(ImageLoader::SegmentIterator it = this->beginSegments(); it != this->endSegments(); ++it ) {
-		Segment* seg = *it;
-		seg->map(fd, offsetInFat, slide, this, context);		
-	}
-	// update slide to reflect load location			
-	this->setSlide(slide);
-}
-
-void ImageLoader::mapSegments(const void* memoryImage, uint64_t imageLen, const LinkContext& context)
-{
-	if ( context.verboseMapping )
-		dyld::log("dyld: Mapping memory %p\n", memoryImage);
-	// find address range for image
-	intptr_t slide = this->assignSegmentAddresses(context);
-	// map in all segments
-	for(ImageLoader::SegmentIterator it = this->beginSegments(); it != this->endSegments(); ++it ) {
-		Segment* seg = *it;
-		seg->map(memoryImage, slide, this, context);		
-	}
-	// update slide to reflect load location			
-	this->setSlide(slide);
-	// set R/W permissions on all segments at slide location
-	for(ImageLoader::SegmentIterator it = this->beginSegments(); it != this->endSegments(); ++it ) {
-		Segment* seg = *it;
-		seg->setPermissions(context, this);		
-	}
-}
+			for(unsigned int i=0; i < libraryCount(); ++i) {
+				ImageLoader* dependentImage = libImage(i);
+				if ( dependentImage != NULL )
+					dependentImage->bindAllLazyPointers(context, recursive);
+			}
+		}
+		// bind lazies in this image
+		DyldSharedCache::DataConstLazyScopedWriter patcher(context.dyldCache, mach_task_self(), context.verboseMapping ? &dyld::log : nullptr);
+		this->doBindJustLazies(context, patcher);
+	}
+}
+
 
 bool ImageLoader::allDependentLibrariesAsWhenPreBound() const
 {
@@ -561,7 +651,42 @@
 }
 
 
-unsigned int ImageLoader::recursiveUpdateDepth(unsigned int maxDepth)
+void ImageLoader::markedUsedRecursive(const std::vector<DynamicReference>& dynamicReferences)
+{
+	// already visited here
+	if ( fMarkedInUse )
+		return;
+	fMarkedInUse = true;
+	
+	// clear mark on all statically dependent dylibs
+	for(unsigned int i=0; i < libraryCount(); ++i) {
+		ImageLoader* dependentImage = libImage(i);
+		if ( dependentImage != NULL ) {
+			dependentImage->markedUsedRecursive(dynamicReferences);
+		}
+	}
+	
+	// clear mark on all dynamically dependent dylibs
+	for (std::vector<ImageLoader::DynamicReference>::const_iterator it=dynamicReferences.begin(); it != dynamicReferences.end(); ++it) {
+		if ( it->from == this )
+			it->to->markedUsedRecursive(dynamicReferences);
+	}
+	
+}
+
+unsigned int ImageLoader::updateDepth(unsigned int maxDepth)
+{
+	STACK_ALLOC_ARRAY(ImageLoader*, danglingUpwards, maxDepth);
+	unsigned int depth = this->recursiveUpdateDepth(maxDepth, danglingUpwards);
+	for (auto& danglingUpward : danglingUpwards) {
+		if ( danglingUpward->fDepth != 0)
+			continue;
+		danglingUpward->recursiveUpdateDepth(maxDepth, danglingUpwards);
+	}
+	return depth;
+}
+
+unsigned int ImageLoader::recursiveUpdateDepth(unsigned int maxDepth, dyld3::Array<ImageLoader*>& danglingUpwards)
 {
 	// the purpose of this phase is to make the images sortable such that 
 	// in a sort list of images, every image that an image depends on
@@ -572,34 +697,43 @@
 		
 		// get depth of dependents
 		unsigned int minDependentDepth = maxDepth;
-		for(unsigned int i=0; i < fLibrariesCount; ++i) {
-			DependentLibrary& libInfo = fLibraries[i];
-			if ( libInfo.image != NULL ) {
-				unsigned int d = libInfo.image->recursiveUpdateDepth(maxDepth);
-				if ( d < minDependentDepth )
-					minDependentDepth = d;
-			}
-		}
-	
+		for(unsigned int i=0; i < libraryCount(); ++i) {
+			ImageLoader* dependentImage = libImage(i);
+			if ( dependentImage != NULL ) {
+				if ( libIsUpward(i) ) {
+					if ( dependentImage->fDepth == 0) {
+						if ( !danglingUpwards.contains(dependentImage) )
+							danglingUpwards.push_back(dependentImage);
+					}
+				} else {
+					unsigned int d = dependentImage->recursiveUpdateDepth(maxDepth, danglingUpwards);
+					if ( d < minDependentDepth )
+						minDependentDepth = d;
+				}
+			}
+			// <rdar://problem/60878811> make sure need to re-bind propagates up
+			if ( dependentImage != NULL ) {
+				if ( fAllLibraryChecksumsAndLoadAddressesMatch && !dependentImage->fAllLibraryChecksumsAndLoadAddressesMatch ) {
+					fAllLibraryChecksumsAndLoadAddressesMatch = false;
+				}
+			}
+		}
 		// make me less deep then all my dependents
 		fDepth = minDependentDepth - 1;
-	}
-	
+
+	}
 	return fDepth;
 }
 
 
-void ImageLoader::recursiveLoadLibraries(const LinkContext& context, const RPathChain& loaderRPaths)
+void ImageLoader::recursiveLoadLibraries(const LinkContext& context, bool preflightOnly, const RPathChain& loaderRPaths, const char* loadPath)
 {
 	if ( fState < dyld_image_state_dependents_mapped ) {
 		// break cycles
 		fState = dyld_image_state_dependents_mapped;
 		
 		// get list of libraries this image needs
-		fLibrariesCount = this->doGetDependentLibraryCount();
-		fLibraries = new DependentLibrary[fLibrariesCount];
-		bzero(fLibraries, sizeof(DependentLibrary)*fLibrariesCount);
-		DependentLibraryInfo libraryInfos[fLibrariesCount]; 
+		DependentLibraryInfo libraryInfos[fLibraryCount]; 
 		this->doGetDependentLibraries(libraryInfos);
 		
 		// get list of rpaths that this image adds
@@ -609,79 +743,111 @@
 		
 		// try to load each
 		bool canUsePrelinkingInfo = true; 
-		for(unsigned int i=0; i < fLibrariesCount; ++i){
-			DependentLibrary& requiredLib = fLibraries[i];
+		for(unsigned int i=0; i < fLibraryCount; ++i){
+			ImageLoader* dependentLib;
+			bool depLibReExported = false;
 			DependentLibraryInfo& requiredLibInfo = libraryInfos[i];
+			if ( preflightOnly && context.inSharedCache(requiredLibInfo.name) ) {
+				// <rdar://problem/5910137> dlopen_preflight() on image in shared cache leaves it loaded but not objc initialized
+				// in preflight mode, don't even load dylib that are in the shared cache because they will never be unloaded
+				setLibImage(i, NULL, false, false);
+				continue;
+			}
 			try {
-				bool depNamespace = false;
-				requiredLib.image = context.loadLibrary(requiredLibInfo.name, true, depNamespace, this->getPath(), &thisRPaths);
-				if ( requiredLib.image == this ) {
+				unsigned cacheIndex;
+				dependentLib = context.loadLibrary(requiredLibInfo.name, true, this->getPath(), &thisRPaths, cacheIndex);
+				if ( dependentLib == this ) {
 					// found circular reference, perhaps DYLD_LIBARY_PATH is causing this rdar://problem/3684168 
-					requiredLib.image = context.loadLibrary(requiredLibInfo.name, false, depNamespace, NULL, NULL);
-					if ( requiredLib.image != this )
+					dependentLib = context.loadLibrary(requiredLibInfo.name, false, NULL, NULL, cacheIndex);
+					if ( dependentLib != this )
 						dyld::warn("DYLD_ setting caused circular dependency in %s\n", this->getPath());
 				}
 				if ( fNeverUnload )
-					requiredLib.image->setNeverUnload();
-				requiredLib.image->fStaticReferenceCount += 1;
-				LibraryInfo actualInfo = requiredLib.image->doGetLibraryInfo();
-				requiredLib.required = requiredLibInfo.required;
-				requiredLib.checksumMatches = ( actualInfo.checksum == requiredLibInfo.info.checksum );
-				requiredLib.isReExported = requiredLibInfo.reExported;
-				if ( ! requiredLib.isReExported ) {
-					requiredLib.isSubFramework = requiredLib.image->isSubframeworkOf(context, this);
-					requiredLib.isReExported = requiredLib.isSubFramework || this->hasSubLibrary(context, requiredLib.image);
+					dependentLib->setNeverUnload();
+				if ( requiredLibInfo.upward ) {
+				}
+				else { 
+					dependentLib->fIsReferencedDownward = true;
+				}
+				LibraryInfo actualInfo = dependentLib->doGetLibraryInfo(requiredLibInfo.info);
+				depLibReExported = requiredLibInfo.reExported;
+				if ( ! depLibReExported ) {
+					// for pre-10.5 binaries that did not use LC_REEXPORT_DYLIB
+					depLibReExported = dependentLib->isSubframeworkOf(context, this) || this->hasSubLibrary(context, dependentLib);
 				}
 				// check found library version is compatible
-				if ( actualInfo.minVersion < requiredLibInfo.info.minVersion ) {
+				// <rdar://problem/89200806> 0xFFFFFFFF is wildcard that matches any version
+				if ( (requiredLibInfo.info.minVersion != 0xFFFFFFFF) && (actualInfo.minVersion < requiredLibInfo.info.minVersion)
+						&& ((dyld3::MachOFile*)(dependentLib->machHeader()))->enforceCompatVersion() ) {
+					// record values for possible use by CrashReporter or Finder
 					dyld::throwf("Incompatible library version: %s requires version %d.%d.%d or later, but %s provides version %d.%d.%d",
 							this->getShortName(), requiredLibInfo.info.minVersion >> 16, (requiredLibInfo.info.minVersion >> 8) & 0xff, requiredLibInfo.info.minVersion & 0xff,
-							requiredLib.image->getShortName(), actualInfo.minVersion >> 16, (actualInfo.minVersion >> 8) & 0xff, actualInfo.minVersion & 0xff);
-				}
-				// prebinding for this image disabled if any dependent library changed or slid
-				if ( !requiredLib.checksumMatches || (requiredLib.image->getSlide() != 0) )
+							dependentLib->getShortName(), actualInfo.minVersion >> 16, (actualInfo.minVersion >> 8) & 0xff, actualInfo.minVersion & 0xff);
+				}
+				// prebinding for this image disabled if any dependent library changed
+				//if ( !depLibCheckSumsMatch )
+				//	canUsePrelinkingInfo = false;
+				// prebinding for this image disabled unless both this and dependent are in the shared cache
+				if ( !dependentLib->inSharedCache() || !this->inSharedCache() )
 					canUsePrelinkingInfo = false;
+					
 				//if ( context.verbosePrebinding ) {
 				//	if ( !requiredLib.checksumMatches )
 				//		fprintf(stderr, "dyld: checksum mismatch, (%u v %u) for %s referencing %s\n", 
-				//			requiredLibInfo.info.checksum, actualInfo.checksum, this->getPath(), 	requiredLib.image->getPath());		
-				//	if ( requiredLib.image->getSlide() != 0 )
-				//		fprintf(stderr, "dyld: dependent library slid for %s referencing %s\n", this->getPath(), requiredLib.image->getPath());		
+				//			requiredLibInfo.info.checksum, actualInfo.checksum, this->getPath(), 	dependentLib->getPath());		
+				//	if ( dependentLib->getSlide() != 0 )
+				//		fprintf(stderr, "dyld: dependent library slid for %s referencing %s\n", this->getPath(), dependentLib->getPath());		
 				//}
 			}
 			catch (const char* msg) {
 				//if ( context.verbosePrebinding )
-				//	fprintf(stderr, "dyld: exception during processing for %s referencing %s\n", this->getPath(), requiredLib.image->getPath());		
+				//	fprintf(stderr, "dyld: exception during processing for %s referencing %s\n", this->getPath(), dependentLib->getPath());		
 				if ( requiredLibInfo.required ) {
 					fState = dyld_image_state_mapped;
-					dyld::throwf("Library not loaded: %s\n  Referenced from: %s\n  Reason: %s", requiredLibInfo.name, this->getPath(), msg);
-				}
+					// record values for possible use by CrashReporter or Finder
+					if ( strstr(msg, "Incompatible library version") != NULL )
+						(*context.setErrorStrings)(DYLD_EXIT_REASON_DYLIB_WRONG_VERSION, this->getPath(), requiredLibInfo.name, NULL);
+					else if ( strstr(msg, "architecture") != NULL )
+						(*context.setErrorStrings)(DYLD_EXIT_REASON_DYLIB_WRONG_ARCH, this->getPath(), requiredLibInfo.name, NULL);
+					else if ( strstr(msg, "file system sandbox") != NULL )
+						(*context.setErrorStrings)(DYLD_EXIT_REASON_FILE_SYSTEM_SANDBOX, this->getPath(), requiredLibInfo.name, NULL);
+					else if ( strstr(msg, "code signature") != NULL )
+						(*context.setErrorStrings)(DYLD_EXIT_REASON_CODE_SIGNATURE, this->getPath(), requiredLibInfo.name, NULL);
+					else if ( strstr(msg, "malformed") != NULL )
+						(*context.setErrorStrings)(DYLD_EXIT_REASON_MALFORMED_MACHO, this->getPath(), requiredLibInfo.name, NULL);
+					else
+						(*context.setErrorStrings)(DYLD_EXIT_REASON_DYLIB_MISSING, this->getPath(), requiredLibInfo.name, NULL);
+					const char* newMsg = dyld::mkstringf("Library not loaded: %s\n  Referenced from: %s\n  Reason: %s", requiredLibInfo.name, this->getRealPath(), msg);
+					free((void*)msg); 	// our free() will do nothing if msg is a string literal
+					throw newMsg;
+				}
+				free((void*)msg); 	// our free() will do nothing if msg is a string literal
 				// ok if weak library not found
-				requiredLib.image = NULL;
+				dependentLib = NULL;
 				canUsePrelinkingInfo = false;  // this disables all prebinding, we may want to just slam import vectors for this lib to zero
 			}
+			setLibImage(i, dependentLib, depLibReExported, requiredLibInfo.upward);
 		}
 		fAllLibraryChecksumsAndLoadAddressesMatch = canUsePrelinkingInfo;
 
 		// tell each to load its dependents
-		for(unsigned int i=0; i < fLibrariesCount; ++i){
-			DependentLibrary& lib = fLibraries[i];
-			if ( lib.image != NULL ) {	
-				lib.image->recursiveLoadLibraries(context, thisRPaths);
-			}
-		}
-		
+		for(unsigned int i=0; i < libraryCount(); ++i) {
+			ImageLoader* dependentImage = libImage(i);
+			if ( dependentImage != NULL ) {
+				dependentImage->recursiveLoadLibraries(context, preflightOnly, thisRPaths, libraryInfos[i].name);
+			}
+		}
 		// do deep prebind check
 		if ( fAllLibraryChecksumsAndLoadAddressesMatch ) {
-			for(unsigned int i=0; i < fLibrariesCount; ++i){
-				const DependentLibrary& libInfo = fLibraries[i];
-				if ( libInfo.image != NULL ) {
-					if ( !libInfo.image->allDependentLibrariesAsWhenPreBound() )
+			for(unsigned int i=0; i < libraryCount(); ++i){
+				ImageLoader* dependentImage = libImage(i);
+				if ( dependentImage != NULL ) {
+					if ( !dependentImage->allDependentLibrariesAsWhenPreBound() )
 						fAllLibraryChecksumsAndLoadAddressesMatch = false;
 				}
 			}
 		}
-		
+
 		// free rpaths (getRPaths() malloc'ed each string)
 		for(std::vector<const char*>::iterator it=rpathsFromThisImage.begin(); it != rpathsFromThisImage.end(); ++it) {
 			const char* str = *it;
@@ -689,6 +855,13 @@
 		}
 		
 	}
+}
+
+
+void ImageLoader::recursiveRebaseWithAccounting(const LinkContext& context)
+{
+	this->recursiveRebase(context);
+	vmAccountingSetSuspended(context, false);
 }
 
 void ImageLoader::recursiveRebase(const LinkContext& context)
@@ -699,30 +872,84 @@
 		
 		try {
 			// rebase lower level libraries first
-			for(unsigned int i=0; i < fLibrariesCount; ++i){
-				DependentLibrary& libInfo = fLibraries[i];
-				if ( libInfo.image != NULL )
-					libInfo.image->recursiveRebase(context);
+			for(unsigned int i=0; i < libraryCount(); ++i) {
+				ImageLoader* dependentImage = libImage(i);
+				if ( dependentImage != NULL )
+					dependentImage->recursiveRebase(context);
 			}
 				
 			// rebase this image
 			doRebase(context);
 			
 			// notify
-			context.notifySingle(dyld_image_state_rebased, this->machHeader(), fPath, fLastModified);
+			context.notifySingle(dyld_image_state_rebased, this, NULL);
 		}
 		catch (const char* msg) {
 			// this image is not rebased
 			fState = dyld_image_state_dependents_mapped;
+            CRSetCrashLogMessage2(NULL);
 			throw;
 		}
 	}
 }
 
-
-
-
-void ImageLoader::recursiveBind(const LinkContext& context, bool forceLazysBound)
+void ImageLoader::recursiveApplyInterposing(const LinkContext& context)
+{ 
+	if ( ! fInterposed ) {
+		// break cycles
+		fInterposed = true;
+		
+		try {
+			// interpose lower level libraries first
+			for(unsigned int i=0; i < libraryCount(); ++i) {
+				ImageLoader* dependentImage = libImage(i);
+				if ( dependentImage != NULL )
+					dependentImage->recursiveApplyInterposing(context);
+			}
+				
+			// interpose this image
+			doInterpose(context);
+		}
+		catch (const char* msg) {
+			// this image is not interposed
+			fInterposed = false;
+			throw;
+		}
+	}
+}
+
+void ImageLoader::recursiveMakeDataReadOnly(const LinkContext& context)
+{
+	if ( ! fMadeReadOnly ) {
+		// break cycles
+		fMadeReadOnly = true;
+
+		try {
+			// handle lower level libraries first
+			for(unsigned int i=0; i < libraryCount(); ++i) {
+				ImageLoader* dependentImage = libImage(i);
+				if ( dependentImage != NULL )
+					dependentImage->recursiveMakeDataReadOnly(context);
+			}
+
+			// if this image has __DATA_CONST, make that segment read-only
+			makeDataReadOnly();
+		}
+		catch (const char* msg) {
+			fMadeReadOnly = false;
+			throw;
+		}
+	}
+}
+
+
+void ImageLoader::recursiveBindWithAccounting(const LinkContext& context, bool forceLazysBound, bool neverUnload)
+{
+	this->recursiveBind(context, forceLazysBound, neverUnload, nullptr);
+	vmAccountingSetSuspended(context, false);
+}
+
+void ImageLoader::recursiveBind(const LinkContext& context, bool forceLazysBound, bool neverUnload, const ImageLoader* parent)
 {
 	// Normally just non-lazy pointers are bound immediately.
 	// The exceptions are:
@@ -734,53 +961,596 @@
 	
 		try {
 			// bind lower level libraries first
-			for(unsigned int i=0; i < fLibrariesCount; ++i){
-				DependentLibrary& libInfo = fLibraries[i];
-				if ( libInfo.image != NULL )
-					libInfo.image->recursiveBind(context, forceLazysBound);
+			for(unsigned int i=0; i < libraryCount(); ++i) {
+				ImageLoader* dependentImage = libImage(i);
+				if ( dependentImage != NULL )  {
+					const ImageLoader* reExportParent = nullptr;
+					if ( libReExported(i) )
+						reExportParent = this;
+					dependentImage->recursiveBind(context, forceLazysBound, neverUnload, reExportParent);
+				}
 			}
 			// bind this image
-			this->doBind(context, forceLazysBound);	
-			this->doUpdateMappingPermissions(context);
+			this->doBind(context, forceLazysBound, parent);
 			// mark if lazys are also bound
 			if ( forceLazysBound || this->usablePrebinding(context) )
 				fAllLazyPointersBound = true;
+			// mark as never-unload if requested
+			if ( neverUnload )
+				this->setNeverUnload();
 				
-			context.notifySingle(dyld_image_state_bound, this->machHeader(), fPath, fLastModified);
+			context.notifySingle(dyld_image_state_bound, this, NULL);
 		}
 		catch (const char* msg) {
 			// restore state
 			fState = dyld_image_state_rebased;
+            CRSetCrashLogMessage2(NULL);
 			throw;
 		}
 	}
 }
 
 
-#if IMAGE_NOTIFY_SUPPORT
-void ImageLoader::recursiveImageAnnouncement(const LinkContext& context, ImageLoader**& newImages)
-{
-	if ( ! fAnnounced ) {
-		// break cycles
-		fAnnounced = true;
+
+// These are mangled symbols for all the variants of operator new and delete
+// which a main executable can define (non-weak) and override the
+// weak-def implementation in the OS.
+static const char* const sTreatAsWeak[] = {
+    "__Znwm", "__ZnwmRKSt9nothrow_t",
+    "__Znam", "__ZnamRKSt9nothrow_t",
+    "__ZdlPv", "__ZdlPvRKSt9nothrow_t", "__ZdlPvm",
+    "__ZdaPv", "__ZdaPvRKSt9nothrow_t", "__ZdaPvm",
+    "__ZnwmSt11align_val_t", "__ZnwmSt11align_val_tRKSt9nothrow_t",
+    "__ZnamSt11align_val_t", "__ZnamSt11align_val_tRKSt9nothrow_t",
+    "__ZdlPvSt11align_val_t", "__ZdlPvSt11align_val_tRKSt9nothrow_t", "__ZdlPvmSt11align_val_t",
+    "__ZdaPvSt11align_val_t", "__ZdaPvSt11align_val_tRKSt9nothrow_t", "__ZdaPvmSt11align_val_t"
+};
+
+size_t ImageLoader::HashCString::hash(const char* v) {
+    // FIXME: Use hash<string_view> when it has the correct visibility markup
+    return std::hash<std::string_view>{}(v);
+}
+
+bool ImageLoader::EqualCString::equal(const char* s1, const char* s2) {
+    return strcmp(s1, s2) == 0;
+}
+
+void ImageLoader::weakBind(const LinkContext& context)
+{
+
+	if (!context.useNewWeakBind) {
+		weakBindOld(context);
+		return;
+	}
+
+	if ( context.verboseWeakBind )
+		dyld::log("dyld: weak bind start:\n");
+	uint64_t t1 = mach_absolute_time();
+
+	// get set of ImageLoaders that participate in coalecsing
+	ImageLoader* imagesNeedingCoalescing[fgImagesRequiringCoalescing];
+	unsigned imageIndexes[fgImagesRequiringCoalescing];
+	int count = context.getCoalescedImages(imagesNeedingCoalescing, imageIndexes);
+	
+	// count how many have not already had weakbinding done
+	int countNotYetWeakBound = 0;
+	int countOfImagesWithWeakDefinitionsNotInSharedCache = 0;
+	for(int i=0; i < count; ++i) {
+		if ( ! imagesNeedingCoalescing[i]->weakSymbolsBound(imageIndexes[i]) )
+			++countNotYetWeakBound;
+		if ( ! imagesNeedingCoalescing[i]->inSharedCache() )
+			++countOfImagesWithWeakDefinitionsNotInSharedCache;
+	}
+
+	// don't need to do any coalescing if only one image has overrides, or all have already been done
+	if ( (countOfImagesWithWeakDefinitionsNotInSharedCache > 0) && (countNotYetWeakBound > 0) ) {
+		if (!context.weakDefMapInitialized) {
+			// Initialize the weak def map as the link context doesn't run static initializers
+			new (&context.weakDefMap) dyld3::Map<const char*, std::pair<const ImageLoader*, uintptr_t>, ImageLoader::HashCString, ImageLoader::EqualCString>();
+			context.weakDefMapInitialized = true;
+		}
+
+		// We might have to patch the shared cache __DATA_CONST.  In that case, we'll create just a single
+		// patcher when needed.
+		DyldSharedCache::DataConstLazyScopedWriter patcher(context.dyldCache, mach_task_self(), context.verboseMapping ? &dyld::log : nullptr);
+
+#if TARGET_OS_OSX
+	  // only do alternate algorithm for dlopen(). Use traditional algorithm for launch
+	  if ( !context.linkingMainExecutable ) {
+		  // Don't take the memory hit of weak defs on the launch path until we hit a dlopen with more weak symbols to bind
+		  if (!context.weakDefMapProcessedLaunchDefs) {
+			  context.weakDefMapProcessedLaunchDefs = true;
+
+			  // Walk the nlist for all binaries from launch and fill in the map with any other weak defs
+			  for (int i=0; i < count; ++i) {
+				  const ImageLoader* image = imagesNeedingCoalescing[i];
+				  // skip images without defs.  We've processed launch time refs already
+				  if ( !image->hasCoalescedExports() )
+					  continue;
+				  // Only process binaries which have had their weak symbols bound, ie, not the new ones we are processing now
+				  // from this dlopen
+				  if ( !image->weakSymbolsBound(imageIndexes[i]) )
+					  continue;
+
+				  Diagnostics diag;
+				  const dyld3::MachOAnalyzer* ma = (const dyld3::MachOAnalyzer*)image->machHeader();
+				  ma->forEachWeakDef(diag, ^(const char *symbolName, uint64_t imageOffset, bool isFromExportTrie) {
+					  uintptr_t targetAddr = (uintptr_t)ma + (uintptr_t)imageOffset;
+					  if ( isFromExportTrie ) {
+						  // Avoid duplicating the string if we already have the symbol name
+						  if ( context.weakDefMap.find(symbolName) != context.weakDefMap.end() )
+							  return;
+						  symbolName = strdup(symbolName);
+					  }
+					  context.weakDefMap.insert({ symbolName, { image, targetAddr } });
+				  });
+			  }
+		  }
+
+		  // Walk the nlist for all binaries in dlopen and fill in the map with any other weak defs
+		  for (int i=0; i < count; ++i) {
+			  const ImageLoader* image = imagesNeedingCoalescing[i];
+			  if ( image->weakSymbolsBound(imageIndexes[i]) )
+				  continue;
+			  // skip images without defs.  We'll process refs later
+			  if ( !image->hasCoalescedExports() )
+				  continue;
+			  Diagnostics diag;
+			  const dyld3::MachOAnalyzer* ma = (const dyld3::MachOAnalyzer*)image->machHeader();
+			  ma->forEachWeakDef(diag, ^(const char *symbolName, uint64_t imageOffset, bool isFromExportTrie) {
+				  uintptr_t targetAddr = (uintptr_t)ma + (uintptr_t)imageOffset;
+				  if ( isFromExportTrie ) {
+					  // Avoid duplicating the string if we already have the symbol name
+					  if ( context.weakDefMap.find(symbolName) != context.weakDefMap.end() )
+						  return;
+					  symbolName = strdup(symbolName);
+				  }
+				  context.weakDefMap.insert({ symbolName, { image, targetAddr } });
+			  });
+		  }
+		// for all images that need weak binding
+		for (int i=0; i < count; ++i) {
+			ImageLoader* imageBeingFixedUp = imagesNeedingCoalescing[i];
+			if ( imageBeingFixedUp->weakSymbolsBound(imageIndexes[i]) )
+				continue; // weak binding already completed
+			bool imageBeingFixedUpInCache = imageBeingFixedUp->inSharedCache();
+
+			if ( context.verboseWeakBind )
+				dyld::log("dyld: checking for weak symbols in %s\n", imageBeingFixedUp->getPath());
+			// for all symbols that need weak binding in this image
+			ImageLoader::CoalIterator coalIterator;
+			imageBeingFixedUp->initializeCoalIterator(coalIterator, i, imageIndexes[i]);
+			while ( !imageBeingFixedUp->incrementCoalIterator(coalIterator) ) {
+				const char*         nameToCoalesce = coalIterator.symbolName;
+				uintptr_t           targetAddr     = 0;
+				const ImageLoader*  targetImage;
+				// Seatch the map for a previous definition to use
+				auto weakDefIt = context.weakDefMap.find(nameToCoalesce);
+				if ( (weakDefIt != context.weakDefMap.end()) && (weakDefIt->second.first != nullptr) ) {
+					// Found a previous defition
+					targetImage = weakDefIt->second.first;
+					targetAddr = weakDefIt->second.second;
+				} else {
+					// scan all images looking for definition to use
+					for (int j=0; j < count; ++j) {
+						const ImageLoader* anImage = imagesNeedingCoalescing[j];
+						bool anImageInCache = anImage->inSharedCache();
+						// <rdar://problem/47986398> Don't look at images in dyld cache because cache is
+						//  already coalesced.  Only images outside cache can potentially override something in cache.
+						if ( anImageInCache && imageBeingFixedUpInCache )
+							continue;
+
+						//dyld::log("looking for %s in %s\n", nameToCoalesce, anImage->getPath());
+						const ImageLoader* foundIn;
+						const Symbol* sym = anImage->findExportedSymbol(nameToCoalesce, false, &foundIn);
+						if ( sym != NULL ) {
+							targetAddr = foundIn->getExportedSymbolAddress(sym, context);
+							targetImage = foundIn;
+							if ( context.verboseWeakBind )
+								dyld::log("dyld:   found weak %s at 0x%lX in %s\n", nameToCoalesce, targetAddr, foundIn->getPath());
+							break;
+						}
+					}
+				}
+				if ( (targetAddr != 0) && (coalIterator.image != targetImage) ) {
+					if ( coalIterator.image->inSharedCache() )
+						patcher.makeWriteable();
+					coalIterator.image->updateUsesCoalIterator(coalIterator, targetAddr, (ImageLoader*)targetImage, 0, context);
+					if (weakDefIt == context.weakDefMap.end()) {
+						if (targetImage->neverUnload()) {
+							// Add never unload defs to the map for next time
+							context.weakDefMap.insert({ nameToCoalesce, { targetImage, targetAddr } });
+							if ( context.verboseWeakBind ) {
+								dyld::log("dyld: weak binding adding %s to map\n", nameToCoalesce);
+							}
+						} else {
+							// Add a placeholder for unloadable symbols which makes us fall back to the regular search
+							context.weakDefMap.insert({ nameToCoalesce, { targetImage, targetAddr } });
+							if ( context.verboseWeakBind ) {
+								dyld::log("dyld: weak binding adding unloadable placeholder %s to map\n", nameToCoalesce);
+							}
+						}
+					}
+					if ( context.verboseWeakBind )
+						dyld::log("dyld:     adjusting uses of %s in %s to use definition from %s\n", nameToCoalesce, coalIterator.image->getPath(), targetImage->getPath());
+				}
+			}
+			imageBeingFixedUp->setWeakSymbolsBound(imageIndexes[i]);
+		}
+	  }
+	  else
+#endif // TARGET_OS_OSX
+	  {
+		// make symbol iterators for each
+		ImageLoader::CoalIterator iterators[count];
+		ImageLoader::CoalIterator* sortedIts[count];
+		for(int i=0; i < count; ++i) {
+			imagesNeedingCoalescing[i]->initializeCoalIterator(iterators[i], i, imageIndexes[i]);
+			sortedIts[i] = &iterators[i];
+			if ( context.verboseWeakBind )
+				dyld::log("dyld: weak bind load order %d/%d for %s\n", i, count, imagesNeedingCoalescing[i]->getIndexedPath(imageIndexes[i]));
+		}
 		
-		// announce lower level libraries first
-		for(unsigned int i=0; i < fLibrariesCount; ++i){
-			DependentLibrary& libInfo = fLibraries[i];
-			if ( libInfo.image != NULL )
-				libInfo.image->recursiveImageAnnouncement(context, newImages);
-		}
-		
-		// add to list of images to notify about
-		*newImages++ = this;
-		//dyld::log("next size = %d\n", newImages.size());
-		
-		// remember that this image wants to be notified about other images
-		 if ( this->hasImageNotification() )
-			context.addImageNeedingNotification(this);
-	}
-}
+		// walk all symbols keeping iterators in sync by 
+		// only ever incrementing the iterator with the lowest symbol 
+		int doneCount = 0;
+		while ( doneCount != count ) {
+			//for(int i=0; i < count; ++i)
+			//	dyld::log("sym[%d]=%s ", sortedIts[i]->loadOrder, sortedIts[i]->symbolName);
+			//dyld::log("\n");
+			// increment iterator with lowest symbol
+			if ( sortedIts[0]->image->incrementCoalIterator(*sortedIts[0]) )
+				++doneCount; 
+			// re-sort iterators
+			for(int i=1; i < count; ++i) {
+				int result = strcmp(sortedIts[i-1]->symbolName, sortedIts[i]->symbolName);
+				if ( result == 0 )
+					sortedIts[i-1]->symbolMatches = true;
+				if ( result > 0 ) {
+					// new one is bigger then next, so swap
+					ImageLoader::CoalIterator* temp = sortedIts[i-1];
+					sortedIts[i-1] = sortedIts[i];
+					sortedIts[i] = temp;
+				}
+				if ( result < 0 )
+					break;
+			}
+			// process all matching symbols just before incrementing the lowest one that matches
+			if ( sortedIts[0]->symbolMatches && !sortedIts[0]->done ) {
+				const char* nameToCoalesce = sortedIts[0]->symbolName;
+				// pick first symbol in load order (and non-weak overrides weak)
+				uintptr_t targetAddr = 0;
+				ImageLoader* targetImage = NULL;
+				unsigned targetImageIndex = 0;
+				for(int i=0; i < count; ++i) {
+					if ( strcmp(iterators[i].symbolName, nameToCoalesce) == 0 ) {
+						if ( context.verboseWeakBind )
+							dyld::log("dyld: weak bind, found %s weak=%d in %s \n", nameToCoalesce, iterators[i].weakSymbol, iterators[i].image->getIndexedPath((unsigned)iterators[i].imageIndex));
+						if ( iterators[i].weakSymbol ) {
+							if ( targetAddr == 0 ) {
+								targetAddr = iterators[i].image->getAddressCoalIterator(iterators[i], context);
+								if ( targetAddr != 0 ) {
+									targetImage = iterators[i].image;
+									targetImageIndex = (unsigned)iterators[i].imageIndex;
+								}
+							}
+						}
+						else {
+							targetAddr = iterators[i].image->getAddressCoalIterator(iterators[i], context);
+							if ( targetAddr != 0 ) {
+								targetImage = iterators[i].image;
+								targetImageIndex = (unsigned)iterators[i].imageIndex;
+								// strong implementation found, stop searching
+								break;
+							}
+						}
+					}
+				}
+				// tell each to bind to this symbol (unless already bound)
+				if ( targetAddr != 0 ) {
+					if ( context.verboseWeakBind ) {
+						dyld::log("dyld: weak binding all uses of %s to copy from %s\n",
+									nameToCoalesce, targetImage->getIndexedShortName(targetImageIndex));
+					}
+					for(int i=0; i < count; ++i) {
+						if ( strcmp(iterators[i].symbolName, nameToCoalesce) == 0 ) {
+							if ( context.verboseWeakBind ) {
+								dyld::log("dyld: weak bind, setting all uses of %s in %s to 0x%lX from %s\n",
+											nameToCoalesce, iterators[i].image->getIndexedShortName((unsigned)iterators[i].imageIndex),
+											targetAddr, targetImage->getIndexedShortName(targetImageIndex));
+							}
+							if ( ! iterators[i].image->weakSymbolsBound(imageIndexes[i]) ) {
+								if ( iterators[i].image->inSharedCache() )
+									patcher.makeWriteable();
+								iterators[i].image->updateUsesCoalIterator(iterators[i], targetAddr, targetImage, targetImageIndex, context);
+							}
+							iterators[i].symbolMatches = false; 
+						}
+					}
+					if (targetImage->neverUnload()) {
+						// Add never unload defs to the map for next time
+						context.weakDefMap.insert({ nameToCoalesce, { targetImage, targetAddr } });
+						if ( context.verboseWeakBind ) {
+							dyld::log("dyld: weak binding adding %s to map\n",
+										nameToCoalesce);
+						}
+					}
+				}
+
+			}
+		}
+
+		for (int i=0; i < count; ++i) {
+			if ( imagesNeedingCoalescing[i]->weakSymbolsBound(imageIndexes[i]) )
+				continue;	// skip images already processed
+
+			if ( imagesNeedingCoalescing[i]->usesChainedFixups() ) {
+				// during binding of references to weak-def symbols, the dyld cache was patched
+				// but if main executable has non-weak override of operator new or delete it needs is handled here
+				for (const char* weakSymbolName : sTreatAsWeak) {
+					const ImageLoader* dummy;
+					imagesNeedingCoalescing[i]->resolveWeak(context, weakSymbolName, true, false, &dummy, patcher);
+				}
+			}
+#if __arm64e__
+			else {
+				// support traditional arm64 app on an arm64e device
+				// look for weak def symbols in this image which may override the cache
+				ImageLoader::CoalIterator coaler;
+				imagesNeedingCoalescing[i]->initializeCoalIterator(coaler, i, 0);
+				imagesNeedingCoalescing[i]->incrementCoalIterator(coaler);
+				while ( !coaler.done ) {
+					const ImageLoader* dummy;
+					// a side effect of resolveWeak() is to patch cache
+					imagesNeedingCoalescing[i]->resolveWeak(context, coaler.symbolName, true, false, &dummy, patcher);
+					imagesNeedingCoalescing[i]->incrementCoalIterator(coaler);
+				}
+			}
 #endif
+		}
+
+		// mark all as having all weak symbols bound
+		for(int i=0; i < count; ++i) {
+			imagesNeedingCoalescing[i]->setWeakSymbolsBound(imageIndexes[i]);
+		}
+	  }
+	}
+
+	uint64_t t2 = mach_absolute_time();
+	fgTotalWeakBindTime += t2  - t1;
+	
+	if ( context.verboseWeakBind )
+		dyld::log("dyld: weak bind end\n");
+}
+
+
+void ImageLoader::weakBindOld(const LinkContext& context)
+{
+	if ( context.verboseWeakBind )
+		dyld::log("dyld: weak bind start:\n");
+	uint64_t t1 = mach_absolute_time();
+	// get set of ImageLoaders that participate in coalecsing
+	ImageLoader* imagesNeedingCoalescing[fgImagesRequiringCoalescing];
+	unsigned imageIndexes[fgImagesRequiringCoalescing];
+	int count = context.getCoalescedImages(imagesNeedingCoalescing, imageIndexes);
+
+	// count how many have not already had weakbinding done
+	int countNotYetWeakBound = 0;
+	int countOfImagesWithWeakDefinitionsNotInSharedCache = 0;
+	for(int i=0; i < count; ++i) {
+		if ( ! imagesNeedingCoalescing[i]->weakSymbolsBound(imageIndexes[i]) )
+			++countNotYetWeakBound;
+		if ( ! imagesNeedingCoalescing[i]->inSharedCache() )
+			++countOfImagesWithWeakDefinitionsNotInSharedCache;
+	}
+
+	// don't need to do any coalescing if only one image has overrides, or all have already been done
+	if ( (countOfImagesWithWeakDefinitionsNotInSharedCache > 0) && (countNotYetWeakBound > 0) ) {
+		// We might have to patch the shared cache __DATA_CONST.  In that case, we'll create just a single
+		// patcher when needed.
+		DyldSharedCache::DataConstLazyScopedWriter patcher(context.dyldCache, mach_task_self(), context.verboseMapping ? &dyld::log : nullptr);
+
+#if TARGET_OS_OSX
+	  // only do alternate algorithm for dlopen(). Use traditional algorithm for launch
+	  if ( !context.linkingMainExecutable ) {
+		// for all images that need weak binding
+		for (int i=0; i < count; ++i) {
+			ImageLoader* imageBeingFixedUp = imagesNeedingCoalescing[i];
+			if ( imageBeingFixedUp->weakSymbolsBound(imageIndexes[i]) )
+				continue; // weak binding already completed
+			bool imageBeingFixedUpInCache = imageBeingFixedUp->inSharedCache();
+
+			if ( context.verboseWeakBind )
+				dyld::log("dyld: checking for weak symbols in %s\n", imageBeingFixedUp->getPath());
+			// for all symbols that need weak binding in this image
+			ImageLoader::CoalIterator coalIterator;
+			imageBeingFixedUp->initializeCoalIterator(coalIterator, i, imageIndexes[i]);
+			while ( !imageBeingFixedUp->incrementCoalIterator(coalIterator) ) {
+				const char*         nameToCoalesce = coalIterator.symbolName;
+				uintptr_t           targetAddr     = 0;
+				const ImageLoader*  targetImage;
+				// scan all images looking for definition to use
+				for (int j=0; j < count; ++j) {
+					const ImageLoader* anImage = imagesNeedingCoalescing[j];
+					bool anImageInCache = anImage->inSharedCache();
+					// <rdar://problem/47986398> Don't look at images in dyld cache because cache is
+					//  already coalesced.  Only images outside cache can potentially override something in cache.
+					if ( anImageInCache && imageBeingFixedUpInCache )
+						continue;
+
+					//dyld::log("looking for %s in %s\n", nameToCoalesce, anImage->getPath());
+					const ImageLoader* foundIn;
+					const Symbol* sym = anImage->findExportedSymbol(nameToCoalesce, false, &foundIn);
+					if ( sym != NULL ) {
+						if ( (foundIn->getExportedSymbolInfo(sym) & ImageLoader::kWeakDefinition) == 0 ) {
+							// found non-weak def, use it and stop looking
+							targetAddr = foundIn->getExportedSymbolAddress(sym, context);
+							targetImage = foundIn;
+							if ( context.verboseWeakBind )
+								dyld::log("dyld:   found strong %s at 0x%lX in %s\n", nameToCoalesce, targetAddr, foundIn->getPath());
+							break;
+						}
+						else {
+							// found weak-def, only use if no weak found yet
+							if ( targetAddr == 0 ) {
+								targetAddr = foundIn->getExportedSymbolAddress(sym, context);
+								targetImage = foundIn;
+								if ( context.verboseWeakBind )
+									dyld::log("dyld:   found weak %s at 0x%lX in %s\n", nameToCoalesce, targetAddr, foundIn->getPath());
+							}
+						}
+					}
+				}
+				if ( (targetAddr != 0) && (coalIterator.image != targetImage) ) {
+					if ( coalIterator.image->inSharedCache() )
+						patcher.makeWriteable();
+					coalIterator.image->updateUsesCoalIterator(coalIterator, targetAddr, (ImageLoader*)targetImage, 0, context);
+					if ( context.verboseWeakBind )
+						dyld::log("dyld:     adjusting uses of %s in %s to use definition from %s\n", nameToCoalesce, coalIterator.image->getPath(), targetImage->getPath());
+				}
+			}
+			imageBeingFixedUp->setWeakSymbolsBound(imageIndexes[i]);
+		}
+	  }
+	  else
+#endif // TARGET_OS_OSX
+	  {
+		// make symbol iterators for each
+		ImageLoader::CoalIterator iterators[count];
+		ImageLoader::CoalIterator* sortedIts[count];
+		for(int i=0; i < count; ++i) {
+			imagesNeedingCoalescing[i]->initializeCoalIterator(iterators[i], i, imageIndexes[i]);
+			sortedIts[i] = &iterators[i];
+			if ( context.verboseWeakBind )
+				dyld::log("dyld: weak bind load order %d/%d for %s\n", i, count, imagesNeedingCoalescing[i]->getIndexedPath(imageIndexes[i]));
+		}
+
+		// walk all symbols keeping iterators in sync by
+		// only ever incrementing the iterator with the lowest symbol
+		int doneCount = 0;
+		while ( doneCount != count ) {
+			//for(int i=0; i < count; ++i)
+			//	dyld::log("sym[%d]=%s ", sortedIts[i]->loadOrder, sortedIts[i]->symbolName);
+			//dyld::log("\n");
+			// increment iterator with lowest symbol
+			if ( sortedIts[0]->image->incrementCoalIterator(*sortedIts[0]) )
+				++doneCount;
+			// re-sort iterators
+			for(int i=1; i < count; ++i) {
+				int result = strcmp(sortedIts[i-1]->symbolName, sortedIts[i]->symbolName);
+				if ( result == 0 )
+					sortedIts[i-1]->symbolMatches = true;
+				if ( result > 0 ) {
+					// new one is bigger then next, so swap
+					ImageLoader::CoalIterator* temp = sortedIts[i-1];
+					sortedIts[i-1] = sortedIts[i];
+					sortedIts[i] = temp;
+				}
+				if ( result < 0 )
+					break;
+			}
+			// process all matching symbols just before incrementing the lowest one that matches
+			if ( sortedIts[0]->symbolMatches && !sortedIts[0]->done ) {
+				const char* nameToCoalesce = sortedIts[0]->symbolName;
+				// pick first symbol in load order (and non-weak overrides weak)
+				uintptr_t targetAddr = 0;
+				ImageLoader* targetImage = NULL;
+				unsigned targetImageIndex = 0;
+				for(int i=0; i < count; ++i) {
+					if ( strcmp(iterators[i].symbolName, nameToCoalesce) == 0 ) {
+						if ( context.verboseWeakBind )
+							dyld::log("dyld: weak bind, found %s weak=%d in %s \n", nameToCoalesce, iterators[i].weakSymbol, iterators[i].image->getIndexedPath((unsigned)iterators[i].imageIndex));
+						if ( iterators[i].weakSymbol ) {
+							if ( targetAddr == 0 ) {
+								targetAddr = iterators[i].image->getAddressCoalIterator(iterators[i], context);
+								if ( targetAddr != 0 ) {
+									targetImage = iterators[i].image;
+									targetImageIndex = (unsigned)iterators[i].imageIndex;
+								}
+							}
+						}
+						else {
+							targetAddr = iterators[i].image->getAddressCoalIterator(iterators[i], context);
+							if ( targetAddr != 0 ) {
+								targetImage = iterators[i].image;
+								targetImageIndex = (unsigned)iterators[i].imageIndex;
+								// strong implementation found, stop searching
+								break;
+							}
+						}
+					}
+				}
+				// tell each to bind to this symbol (unless already bound)
+				if ( targetAddr != 0 ) {
+					if ( context.verboseWeakBind ) {
+						dyld::log("dyld: weak binding all uses of %s to copy from %s\n",
+									nameToCoalesce, targetImage->getIndexedShortName(targetImageIndex));
+					}
+					for(int i=0; i < count; ++i) {
+						if ( strcmp(iterators[i].symbolName, nameToCoalesce) == 0 ) {
+							if ( context.verboseWeakBind ) {
+								dyld::log("dyld: weak bind, setting all uses of %s in %s to 0x%lX from %s\n",
+											nameToCoalesce, iterators[i].image->getIndexedShortName((unsigned)iterators[i].imageIndex),
+											targetAddr, targetImage->getIndexedShortName(targetImageIndex));
+							}
+							if ( ! iterators[i].image->weakSymbolsBound(imageIndexes[i]) ) {
+								if ( iterators[i].image->inSharedCache() )
+									patcher.makeWriteable();
+								iterators[i].image->updateUsesCoalIterator(iterators[i], targetAddr, targetImage, targetImageIndex, context);
+							}
+							iterators[i].symbolMatches = false;
+						}
+					}
+				}
+
+			}
+		}
+
+		for (int i=0; i < count; ++i) {
+			if ( imagesNeedingCoalescing[i]->weakSymbolsBound(imageIndexes[i]) )
+				continue;	// skip images already processed
+
+			if ( imagesNeedingCoalescing[i]->usesChainedFixups() ) {
+				// during binding of references to weak-def symbols, the dyld cache was patched
+				// but if main executable has non-weak override of operator new or delete it needs is handled here
+				for (const char* weakSymbolName : sTreatAsWeak) {
+					const ImageLoader* dummy;
+					imagesNeedingCoalescing[i]->resolveWeak(context, weakSymbolName, true, false, &dummy, patcher);
+				}
+			}
+#if __arm64e__
+			else {
+				// support traditional arm64 app on an arm64e device
+				// look for weak def symbols in this image which may override the cache
+				patcher.makeWriteable();
+				ImageLoader::CoalIterator coaler;
+				imagesNeedingCoalescing[i]->initializeCoalIterator(coaler, i, 0);
+				imagesNeedingCoalescing[i]->incrementCoalIterator(coaler);
+				while ( !coaler.done ) {
+					const ImageLoader* dummy;
+					// a side effect of resolveWeak() is to patch cache
+					imagesNeedingCoalescing[i]->resolveWeak(context, coaler.symbolName, true, false, &dummy, patcher);
+					imagesNeedingCoalescing[i]->incrementCoalIterator(coaler);
+				}
+			}
+#endif
+		}
+
+		// mark all as having all weak symbols bound
+		for(int i=0; i < count; ++i) {
+			imagesNeedingCoalescing[i]->setWeakSymbolsBound(imageIndexes[i]);
+		}
+	  }
+	}
+
+	uint64_t t2 = mach_absolute_time();
+	fgTotalWeakBindTime += t2  - t1;
+
+	if ( context.verboseWeakBind )
+		dyld::log("dyld: weak bind end\n");
+}
+
+
 
 void ImageLoader::recursiveGetDOFSections(const LinkContext& context, std::vector<DOFInfo>& dofs)
 {
@@ -789,27 +1559,43 @@
 		fRegisteredDOF = true;
 		
 		// gather lower level libraries first
-		for(unsigned int i=0; i < fLibrariesCount; ++i){
-			DependentLibrary& libInfo = fLibraries[i];
-			if ( libInfo.image != NULL )
-				libInfo.image->recursiveGetDOFSections(context, dofs);
+		for(unsigned int i=0; i < libraryCount(); ++i) {
+			ImageLoader* dependentImage = libImage(i);
+			if ( dependentImage != NULL )
+				dependentImage->recursiveGetDOFSections(context, dofs);
 		}
 		this->doGetDOFSections(context, dofs);
 	}
 }
 
+void ImageLoader::setNeverUnloadRecursive() {
+	if ( ! fNeverUnload ) {
+		// break cycles
+		fNeverUnload = true;
+		
+		// gather lower level libraries first
+		for(unsigned int i=0; i < libraryCount(); ++i) {
+			ImageLoader* dependentImage = libImage(i);
+			if ( dependentImage != NULL )
+				dependentImage->setNeverUnloadRecursive();
+		}
+	}
+}
 
 void ImageLoader::recursiveSpinLock(recursive_lock& rlock)
 {
 	// try to set image's ivar fInitializerRecursiveLock to point to this lock_info
 	// keep trying until success (spin)
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdeprecated-declarations"
 	while ( ! OSAtomicCompareAndSwapPtrBarrier(NULL, &rlock, (void**)&fInitializerRecursiveLock) ) {
 		// if fInitializerRecursiveLock already points to a different lock_info, if it is for
 		// the same thread we are on, the increment the lock count, otherwise continue to spin
 		if ( (fInitializerRecursiveLock != NULL) && (fInitializerRecursiveLock->thread == rlock.thread) )
 			break;
 	}
-	++(fInitializerRecursiveLock->count); 
+#pragma clang diagnostic pop
+	++(fInitializerRecursiveLock->count);
 }
 
 void ImageLoader::recursiveSpinUnLock()
@@ -818,63 +1604,77 @@
 		fInitializerRecursiveLock = NULL;
 }
 
-
-void ImageLoader::recursiveInitialization(const LinkContext& context, mach_port_t this_thread)
-{
-#if RECURSIVE_INITIALIZER_LOCK
+void ImageLoader::InitializerTimingList::addTime(const char* name, uint64_t time)
+{
+	for (int i=0; i < count; ++i) {
+		if ( strcmp(images[i].shortName, name) == 0 ) {
+			images[i].initTime += time;
+			return;
+		}
+	}
+	images[count].initTime = time;
+	images[count].shortName = name;
+	++count;
+}
+
+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);
-#else
-	_spin_lock(&fInitializerLock);
-#endif
 
 	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 < fLibrariesCount; ++i){
-				DependentLibrary& libInfo = fLibraries[i];
-				// don't try to initialize stuff "above" me
-				if ( (libInfo.image != NULL) && (libInfo.image->fDepth >= fDepth) )
-					libInfo.image->recursiveInitialization(context, this_thread);
+			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 initalize this image
+
+			// 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->machHeader(), fPath, fLastModified);
-
+			context.notifySingle(dyld_image_state_dependents_initialized, this, &timingInfo);
+			
 			// initialize this image
-			this->doInitialization(context);
-			// let anyone know we finished initalizing 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->machHeader(), fPath, fLastModified);
+			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;
-		#if RECURSIVE_INITIALIZER_LOCK
 			recursiveSpinUnLock();
-		#else
-			_spin_unlock(&fInitializerLock);
-		#endif
 			throw;
 		}
 	}
 	
-#if RECURSIVE_INITIALIZER_LOCK
 	recursiveSpinUnLock();
-#else
-	_spin_unlock(&fInitializerLock);
-#endif
 }
 
 
@@ -883,21 +1683,26 @@
 	static uint64_t sUnitsPerSecond = 0;
 	if ( sUnitsPerSecond == 0 ) {
 		struct mach_timebase_info timeBaseInfo;
-		if ( mach_timebase_info(&timeBaseInfo) == KERN_SUCCESS ) {
-			sUnitsPerSecond = 1000000000ULL * timeBaseInfo.denom / timeBaseInfo.numer;
-		}
+		if ( mach_timebase_info(&timeBaseInfo) != KERN_SUCCESS )
+			return;
+		sUnitsPerSecond = 1000000000ULL * timeBaseInfo.denom / timeBaseInfo.numer;
 	}
 	if ( partTime < sUnitsPerSecond ) {
-		uint32_t milliSecondsTimeTen = (partTime*10000)/sUnitsPerSecond;
-		uint32_t milliSeconds = milliSecondsTimeTen/10;
-		uint32_t percentTimesTen = (partTime*1000)/totalTime;
+		uint32_t milliSecondsTimesHundred = (uint32_t)((partTime*100000)/sUnitsPerSecond);
+		uint32_t milliSeconds = (uint32_t)(milliSecondsTimesHundred/100);
+		uint32_t percentTimesTen = (uint32_t)((partTime*1000)/totalTime);
 		uint32_t percent = percentTimesTen/10;
-		dyld::log("%s: %u.%u milliseconds (%u.%u%%)\n", msg, milliSeconds, milliSecondsTimeTen-milliSeconds*10, percent, percentTimesTen-percent*10);
+		if ( milliSeconds >= 100 )
+			dyld::log("%s: %u.%02u milliseconds (%u.%u%%)\n", msg, milliSeconds, milliSecondsTimesHundred-milliSeconds*100, percent, percentTimesTen-percent*10);
+		else if ( milliSeconds >= 10 )
+			dyld::log("%s:  %u.%02u milliseconds (%u.%u%%)\n", msg, milliSeconds, milliSecondsTimesHundred-milliSeconds*100, percent, percentTimesTen-percent*10);
+		else
+			dyld::log("%s:   %u.%02u milliseconds (%u.%u%%)\n", msg, milliSeconds, milliSecondsTimesHundred-milliSeconds*100, percent, percentTimesTen-percent*10);
 	}
 	else {
-		uint32_t secondsTimeTen = (partTime*10)/sUnitsPerSecond;
+		uint32_t secondsTimeTen = (uint32_t)((partTime*10)/sUnitsPerSecond);
 		uint32_t seconds = secondsTimeTen/10;
-		uint32_t percentTimesTen = (partTime*1000)/totalTime;
+		uint32_t percentTimesTen = (uint32_t)((partTime*1000)/totalTime);
 		uint32_t percent = percentTimesTen/10;
 		dyld::log("%s: %u.%u seconds (%u.%u%%)\n", msg, seconds, secondsTimeTen-seconds*10, percent, percentTimesTen-percent*10);
 	}
@@ -925,20 +1730,45 @@
 }
 
 
-
-void ImageLoader::printStatistics(unsigned int imageCount)
-{
-	uint64_t totalTime = fgTotalLoadLibrariesTime + fgTotalRebaseTime + fgTotalBindTime + fgTotalInitTime;
+void ImageLoader::printStatistics(unsigned int imageCount, const InitializerTimingList& timingInfo)
+{
+	uint64_t totalTime = fgTotalLoadLibrariesTime  + fgTotalRebaseTime + fgTotalBindTime + fgTotalWeakBindTime + fgTotalDOF + fgTotalInitTime;
+
+	uint64_t totalDyldTime = totalTime - fgTotalDebuggerPausedTime - fgTotalRebindCacheTime;
+	printTime("Total pre-main time", totalDyldTime, totalDyldTime);
+	printTime("         dylib loading time", fgTotalLoadLibrariesTime-fgTotalDebuggerPausedTime, totalDyldTime);
+	printTime("        rebase/binding time", fgTotalRebaseTime+fgTotalBindTime+fgTotalWeakBindTime-fgTotalRebindCacheTime, totalDyldTime);
+	printTime("            ObjC setup time", fgTotalObjCSetupTime, totalDyldTime);
+	printTime("           initializer time", fgTotalInitTime-fgTotalObjCSetupTime, totalDyldTime);
+	dyld::log("           slowest intializers :\n");
+	for (uintptr_t i=0; i < timingInfo.count; ++i) {
+		uint64_t t = timingInfo.images[i].initTime;
+		if ( t*50 < totalDyldTime )
+			continue;
+		dyld::log("%30s ", timingInfo.images[i].shortName);
+		if ( strncmp(timingInfo.images[i].shortName, "libSystem.", 10) == 0 )
+			t -= fgTotalObjCSetupTime;
+			printTime("", t, totalDyldTime);
+	}
+	dyld::log("\n");
+}
+
+void ImageLoader::printStatisticsDetails(unsigned int imageCount, const InitializerTimingList& timingInfo)
+{
+	uint64_t totalTime = fgTotalLoadLibrariesTime  + fgTotalRebaseTime + fgTotalBindTime + fgTotalWeakBindTime + fgTotalDOF + fgTotalInitTime;
 	char commaNum1[40];
 	char commaNum2[40];
 
-	printTime("total time", totalTime, totalTime);
-	dyld::log("total images loaded:  %d (%u from dyld shared cache, %u needed no fixups)\n", imageCount, fgImagesUsedFromSharedCache, fgImagesRequiringNoFixups);
-	dyld::log("total segments mapped: %u, into %llu pages with %llu pages pre-fetched\n", fgTotalSegmentsMapped, fgTotalBytesMapped/4096, fgTotalBytesPreFetched/4096);
-	printTime("total images loading time", fgTotalLoadLibrariesTime, totalTime);
-	dyld::log("total rebase fixups:  %s\n", commatize(fgTotalRebaseFixups, commaNum1));
-	printTime("total rebase fixups time", fgTotalRebaseTime, totalTime);
-	dyld::log("total binding fixups: %s\n", commatize(fgTotalBindFixups, commaNum1));
+	printTime("  total time", totalTime, totalTime);
+	dyld::log("  total images loaded:  %d (%u from dyld shared cache)\n", imageCount, fgImagesUsedFromSharedCache);
+	dyld::log("  total segments mapped: %u, into %llu pages\n", fgTotalSegmentsMapped, fgTotalBytesMapped/4096);
+	printTime("  total images loading time", fgTotalLoadLibrariesTime, totalTime);
+	printTime("  total load time in ObjC", fgTotalObjCSetupTime, totalTime);
+	printTime("  total debugger pause time", fgTotalDebuggerPausedTime, totalTime);
+	printTime("  total dtrace DOF registration time", fgTotalDOF, totalTime);
+	dyld::log("  total rebase fixups:  %s\n", commatize(fgTotalRebaseFixups, commaNum1));
+	printTime("  total rebase fixups time", fgTotalRebaseTime, totalTime);
+	dyld::log("  total binding fixups: %s\n", commatize(fgTotalBindFixups, commaNum1));
 	if ( fgTotalBindSymbolsResolved != 0 ) {
 		uint32_t avgTimesTen = (fgTotalBindImageSearches * 10) / fgTotalBindSymbolsResolved;
 		uint32_t avgInt = fgTotalBindImageSearches / fgTotalBindSymbolsResolved;
@@ -946,9 +1776,21 @@
 		dyld::log("total binding symbol lookups: %s, average images searched per symbol: %u.%u\n", 
 				commatize(fgTotalBindSymbolsResolved, commaNum1), avgInt, avgTenths);
 	}
-	printTime("total binding fixups time", fgTotalBindTime, totalTime);
-	dyld::log("total bindings lazily fixed up: %s of %s\n", commatize(fgTotalLazyBindFixups, commaNum1), commatize(fgTotalPossibleLazyBindFixups, commaNum2));
-	printTime("total init time time", fgTotalInitTime, totalTime);
+	printTime("  total binding fixups time", fgTotalBindTime, totalTime);
+	printTime("  total weak binding fixups time", fgTotalWeakBindTime, totalTime);
+	printTime("  total redo shared cached bindings time", fgTotalRebindCacheTime, totalTime);
+	dyld::log("  total bindings lazily fixed up: %s of %s\n", commatize(fgTotalLazyBindFixups, commaNum1), commatize(fgTotalPossibleLazyBindFixups, commaNum2));
+	printTime("  total time in initializers and ObjC +load", fgTotalInitTime-fgTotalObjCSetupTime, totalTime);
+	for (uintptr_t i=0; i < timingInfo.count; ++i) {
+		uint64_t t = timingInfo.images[i].initTime;
+		if ( t*1000 < totalTime )
+			continue;
+		dyld::log("%42s ", timingInfo.images[i].shortName);
+		if ( strncmp(timingInfo.images[i].shortName, "libSystem.", 10) == 0 )
+			t -= fgTotalObjCSetupTime;
+		printTime("", t, totalTime);
+	}
+	
 }
 
 
@@ -982,129 +1824,144 @@
 }
 
 
-void Segment::map(int fd, uint64_t offsetInFatWrapper, intptr_t slide, const ImageLoader* image, const ImageLoader::LinkContext& context)
-{
-	vm_offset_t fileOffset = this->getFileOffset() + offsetInFatWrapper;
-	vm_size_t size = this->getFileSize();
-	void* requestedLoadAddress = (void*)(this->getPreferredLoadAddress() + slide);
-	int protection = 0;
-	if ( !this->unaccessible() ) {
-		if ( this->executable() )
-			protection   |= PROT_EXEC;
-		if ( this->readable() )
-			protection   |= PROT_READ;
-		if ( this->writeable() )
-			protection   |= PROT_WRITE;
-	}
-#if __i386__
-	// initially map __IMPORT segments R/W so dyld can update them
-	if ( this->readOnlyImportStubs() )
-		protection |= PROT_WRITE;
-#endif
-	// wholly zero-fill segments have nothing to mmap() in
-	if ( size > 0 ) {
-		void* loadAddress = mmap(requestedLoadAddress, size, protection, MAP_FIXED | MAP_PRIVATE, fd, fileOffset);
-		if ( loadAddress == ((void*)(-1)) )
-			dyld::throwf("mmap() error %d at address=0x%08lX, size=0x%08lX segment=%s in Segment::map() mapping %s", errno, (uintptr_t)requestedLoadAddress, (uintptr_t)size, this->getName(), image->getPath());
-	}
-	// update stats
-	++ImageLoader::fgTotalSegmentsMapped;
-	ImageLoader::fgTotalBytesMapped += size;
-	if ( context.verboseMapping )
-		dyld::log("%18s at %p->%p with permissions %c%c%c\n", this->getName(), requestedLoadAddress, (char*)requestedLoadAddress+this->getFileSize()-1,
-			(protection & PROT_READ) ? 'r' : '.',  (protection & PROT_WRITE) ? 'w' : '.',  (protection & PROT_EXEC) ? 'x' : '.' );
-}
-
-void Segment::map(const void* memoryImage, intptr_t slide, const ImageLoader* image, const ImageLoader::LinkContext& context)
-{
-	vm_address_t loadAddress = this->getPreferredLoadAddress() + slide;
-	vm_address_t srcAddr = (uintptr_t)memoryImage + this->getFileOffset();
-	vm_size_t size = this->getFileSize();
-	kern_return_t r = vm_copy(mach_task_self(), srcAddr, size, loadAddress);
-	if ( r != KERN_SUCCESS ) 
-		throw "can't map segment";
-		
-	if ( context.verboseMapping )
-		dyld::log("%18s at %p->%p\n", this->getName(), (char*)loadAddress, (char*)loadAddress+this->getFileSize()-1);
-}
-
-void Segment::setPermissions(const ImageLoader::LinkContext& context, const ImageLoader* image)
-{
-	vm_prot_t protection = 0;
-	if ( !this->unaccessible() ) {
-		if ( this->executable() )
-			protection   |= VM_PROT_EXECUTE;
-		if ( this->readable() )
-			protection   |= VM_PROT_READ;
-		if ( this->writeable() )
-			protection   |= VM_PROT_WRITE;
-	}
-	vm_address_t addr = this->getActualLoadAddress(image);
-	vm_size_t size = this->getSize();
-	const bool setCurrentPermissions = false;
-	kern_return_t r = vm_protect(mach_task_self(), addr, size, setCurrentPermissions, protection);
-	if ( r != KERN_SUCCESS ) 
-		throw "can't set vm permissions for mapped segment";
-	if ( context.verboseMapping ) {
-		dyld::log("%18s at %p->%p altered permissions to %c%c%c\n", this->getName(), (char*)addr, (char*)addr+this->getFileSize()-1,
-			(protection & PROT_READ) ? 'r' : '.',  (protection & PROT_WRITE) ? 'w' : '.',  (protection & PROT_EXEC) ? 'x' : '.' );
-	}
-}	
-
-void Segment::tempWritable(const ImageLoader::LinkContext& context, const ImageLoader* image)
-{
-	vm_address_t addr = this->getActualLoadAddress(image);
-	vm_size_t size = this->getSize();
-	const bool setCurrentPermissions = false;
-	vm_prot_t protection = VM_PROT_WRITE | VM_PROT_READ;
-	if ( this->executable() )
-		protection |= VM_PROT_EXECUTE;
-	kern_return_t r = vm_protect(mach_task_self(), addr, size, setCurrentPermissions, protection);
-	if ( r != KERN_SUCCESS ) 
-		throw "can't set vm permissions for mapped segment";
-	if ( context.verboseMapping ) {
-		dyld::log("%18s at %p->%p altered permissions to %c%c%c\n", this->getName(), (char*)addr, (char*)addr+this->getFileSize()-1,
-			(protection & PROT_READ) ? 'r' : '.',  (protection & PROT_WRITE) ? 'w' : '.',  (protection & PROT_EXEC) ? 'x' : '.' );
-	}
-}
-
-
-bool Segment::hasTrailingZeroFill()
-{
-	return ( this->writeable() && (this->getSize() > this->getFileSize()) );
-}
-
-
-uintptr_t Segment::reserveAnAddressRange(size_t length, const ImageLoader::LinkContext& context)
-{
-	vm_address_t addr = 0;
-	vm_size_t size = length;
-	// in PIE programs, load initial dylibs after main executable so they don't have fixed addresses either
-	if ( fgNextPIEDylibAddress != 0 ) {
-		addr = fgNextPIEDylibAddress + (arc4random() & 0x3) * 4096; // add small random padding between dylibs
-		kern_return_t r = vm_allocate(mach_task_self(), &addr, size, VM_FLAGS_FIXED);
-		if ( r == KERN_SUCCESS ) {
-			fgNextPIEDylibAddress = addr + size;
-			return addr;
-		}
-		fgNextPIEDylibAddress = 0;
-	}
-	kern_return_t r = vm_allocate(mach_task_self(), &addr, size, VM_FLAGS_ANYWHERE);
-	if ( r != KERN_SUCCESS ) 
-		throw "out of address space";
+//
+// This function is the hotspot of symbol lookup.  It was pulled out of findExportedSymbol()
+// to enable it to be re-written in assembler if needed.
+//
+const uint8_t* ImageLoader::trieWalk(const uint8_t* start, const uint8_t* end, const char* s)
+{
+	//dyld::log("trieWalk(%p, %p, %s)\n", start, end, s);
+	++fgSymbolTrieSearchs;
+	const uint8_t* p = start;
+	while ( p != NULL ) {
+		uintptr_t terminalSize = *p++;
+		if ( terminalSize > 127 ) {
+			// except for re-export-with-rename, all terminal sizes fit in one byte
+			--p;
+			terminalSize = read_uleb128(p, end);
+		}
+		if ( (*s == '\0') && (terminalSize != 0) ) {
+			//dyld::log("trieWalk(%p) returning %p\n", start, p);
+			return p;
+		}
+		const uint8_t* children = p + terminalSize;
+		if ( children > end ) {
+			dyld::log("trieWalk() malformed trie node, terminalSize=0x%lx extends past end of trie\n", terminalSize);
+			return NULL;
+		}
+		//dyld::log("trieWalk(%p) sym=%s, terminalSize=%lu, children=%p\n", start, s, terminalSize, children);
+		uint8_t childrenRemaining = *children++;
+		p = children;
+		uintptr_t nodeOffset = 0;
+		for (; childrenRemaining > 0; --childrenRemaining) {
+			const char* ss = s;
+			//dyld::log("trieWalk(%p) child str=%s\n", start, (char*)p);
+			bool wrongEdge = false;
+			// scan whole edge to get to next edge
+			// if edge is longer than target symbol name, don't read past end of symbol name
+			char c = *p;
+			while ( c != '\0' ) {
+				if ( !wrongEdge ) {
+					if ( c != *ss )
+						wrongEdge = true;
+					++ss;
+				}
+				++p;
+				c = *p;
+			}
+			if ( wrongEdge ) {
+				// advance to next child
+				++p; // skip over zero terminator
+				// skip over uleb128 until last byte is found
+				while ( (*p & 0x80) != 0 )
+					++p;
+				++p; // skip over last byte of uleb128
+				if ( p > end ) {
+					dyld::log("trieWalk() malformed trie node, child node extends past end of trie\n");
+					return NULL;
+				}
+			}
+			else {
+ 				// the symbol so far matches this edge (child)
+				// so advance to the child's node
+				++p;
+				nodeOffset = read_uleb128(p, end);
+				if ( (nodeOffset == 0) || ( &start[nodeOffset] > end) ) {
+					dyld::log("trieWalk() malformed trie child, nodeOffset=0x%lx out of range\n", nodeOffset);
+					return NULL;
+				}
+				s = ss;
+				//dyld::log("trieWalk() found matching edge advancing to node 0x%lx\n", nodeOffset);
+				break;
+			}
+		}
+		if ( nodeOffset != 0 )
+			p = &start[nodeOffset];
+		else
+			p = NULL;
+	}
+	//dyld::log("trieWalk(%p) return NULL\n", start);
+	return NULL;
+}
+
+
 	
-	return addr;
-}
-
-bool Segment::reserveAddressRange(uintptr_t start, size_t length)
-{
-	vm_address_t addr = start;
-	vm_size_t size = length;
-	kern_return_t r = vm_allocate(mach_task_self(), &addr, size, false /*only this range*/);
-	if ( r != KERN_SUCCESS ) 
-		return false;
-	return true;
-}
-
-
-
+uintptr_t ImageLoader::read_uleb128(const uint8_t*& p, const uint8_t* end)
+{
+	uint64_t result = 0;
+	int		 bit = 0;
+	do {
+		if (p == end)
+			dyld::throwf("malformed uleb128");
+
+		uint64_t slice = *p & 0x7f;
+
+		if (bit > 63)
+			dyld::throwf("uleb128 too big for uint64, bit=%d, result=0x%0llX", bit, result);
+		else {
+			result |= (slice << bit);
+			bit += 7;
+		}
+	} while (*p++ & 0x80);
+	return (uintptr_t)result;
+}
+
+
+intptr_t ImageLoader::read_sleb128(const uint8_t*& p, const uint8_t* end)
+{
+	int64_t result = 0;
+	int bit = 0;
+	uint8_t byte;
+	do {
+		if (p == end)
+			throw "malformed sleb128";
+		byte = *p++;
+		result |= (((int64_t)(byte & 0x7f)) << bit);
+		bit += 7;
+	} while (byte & 0x80);
+	// sign extend negative numbers
+	if ( ((byte & 0x40) != 0) && (bit < 64) )
+		result |= (~0ULL) << bit;
+	return (intptr_t)result;
+}
+
+void ImageLoader::forEachReExportDependent( void (^callback)(const ImageLoader*, bool& stop)) const
+{
+	bool stop = false;
+	for (unsigned int i=0; i < libraryCount(); ++i) {
+		if ( libReExported(i) ) {
+			if ( ImageLoader* dependentImage = libImage(i) ) {
+				callback(dependentImage, stop);
+			}
+		}
+		if (stop)
+			break;
+	}
+}
+
+
+VECTOR_NEVER_DESTRUCTED_IMPL(ImageLoader::InterposeTuple);
+VECTOR_NEVER_DESTRUCTED_IMPL(ImagePair);
+
+
+