]> git.saurik.com Git - apple/dyld.git/blobdiff - src/ImageLoader.cpp
dyld-851.27.tar.gz
[apple/dyld.git] / src / ImageLoader.cpp
index 1723c0677d3abe76348508bd506cb8216edf395b..764b3b89fb3215f0faad5ce64627216f6d313b8b 100644 (file)
@@ -36,6 +36,7 @@
 #include <sys/mount.h>
 #include <sys/sysctl.h>
 #include <libkern/OSAtomic.h>
+#include <string_view>
 
 #include <atomic>
 
@@ -83,6 +84,9 @@ ImageLoader::ImageLoader(const char* path, unsigned int libCount)
        fPathOwnedByImage(false), fIsReferencedDownward(false), 
        fWeakSymbolsBound(false)
 {
+#if __x86_64__
+       fAotPath = NULL;
+#endif
        if ( fPath != NULL )
                fPathHash = hash(fPath);
        if ( libCount > 512 )
@@ -102,6 +106,10 @@ ImageLoader::~ImageLoader()
                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)
@@ -388,7 +396,7 @@ uintptr_t ImageLoader::interposedAddress(const LinkContext& context, uintptr_t a
                //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) && (inImage != it->neverImage) && ((it->onlyImage == NULL) || (inImage == it->onlyImage)) ) {
+               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);
                        }
@@ -401,12 +409,14 @@ uintptr_t ImageLoader::interposedAddress(const LinkContext& context, uintptr_t a
 void ImageLoader::applyInterposingToDyldCache(const LinkContext& context) {
        if (!context.dyldCache)
                return;
-#if !__arm64e__ // until arm64e cache builder sets builtFromChainedFixups
        if (!context.dyldCache->header.builtFromChainedFixups)
                return;
-#endif
        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;
@@ -474,7 +484,7 @@ void ImageLoader::addDynamicInterposingTuples(const struct dyld_interpose_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 __arm__ || __arm64__
+#if TARGET_OS_IPHONE && !TARGET_OS_SIMULATOR
        static bool sVmAccountingSuspended = false;
        if ( suspend == sVmAccountingSuspended )
                return;
@@ -509,7 +519,7 @@ void ImageLoader::link(const LinkContext& context, bool forceLazysBound, bool pr
 
        uint64_t t1 = mach_absolute_time();
        context.clearAllDepths();
-       this->recursiveUpdateDepth(context.imageCount());
+       this->updateDepth(context.imageCount());
 
        __block uint64_t t2, t3, t4, t5;
        {
@@ -629,7 +639,8 @@ void ImageLoader::bindAllLazyPointers(const LinkContext& context, bool recursive
                        }
                }
                // bind lazies in this image
-               this->doBindJustLazies(context);
+               DyldSharedCache::DataConstLazyScopedWriter patcher(context.dyldCache, mach_task_self(), context.verboseMapping ? &dyld::log : nullptr);
+               this->doBindJustLazies(context, patcher);
        }
 }
 
@@ -663,7 +674,19 @@ void ImageLoader::markedUsedRecursive(const std::vector<DynamicReference>& dynam
        
 }
 
-unsigned int ImageLoader::recursiveUpdateDepth(unsigned int maxDepth)
+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
@@ -676,17 +699,29 @@ unsigned int ImageLoader::recursiveUpdateDepth(unsigned int maxDepth)
                unsigned int minDependentDepth = maxDepth;
                for(unsigned int i=0; i < libraryCount(); ++i) {
                        ImageLoader* dependentImage = libImage(i);
-                       if ( (dependentImage != NULL) && !libIsUpward(i) ) {
-                               unsigned int d = dependentImage->recursiveUpdateDepth(maxDepth);
-                               if ( d < minDependentDepth )
-                                       minDependentDepth = d;
+                       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;
 }
 
@@ -798,22 +833,21 @@ void ImageLoader::recursiveLoadLibraries(const LinkContext& context, bool prefli
                // tell each to load its dependents
                for(unsigned int i=0; i < libraryCount(); ++i) {
                        ImageLoader* dependentImage = libImage(i);
-                       if ( dependentImage != NULL ) { 
+                       if ( dependentImage != NULL ) {
                                dependentImage->recursiveLoadLibraries(context, preflightOnly, thisRPaths, libraryInfos[i].name);
                        }
                }
-               
                // do deep prebind check
                if ( fAllLibraryChecksumsAndLoadAddressesMatch ) {
                        for(unsigned int i=0; i < libraryCount(); ++i){
                                ImageLoader* dependentImage = libImage(i);
-                               if ( dependentImage != NULL ) { 
+                               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;
@@ -911,11 +945,11 @@ void ImageLoader::recursiveMakeDataReadOnly(const LinkContext& context)
 
 void ImageLoader::recursiveBindWithAccounting(const LinkContext& context, bool forceLazysBound, bool neverUnload)
 {
-       this->recursiveBind(context, forceLazysBound, neverUnload);
+       this->recursiveBind(context, forceLazysBound, neverUnload, nullptr);
        vmAccountingSetSuspended(context, false);
 }
 
-void ImageLoader::recursiveBind(const LinkContext& context, bool forceLazysBound, bool neverUnload)
+void ImageLoader::recursiveBind(const LinkContext& context, bool forceLazysBound, bool neverUnload, const ImageLoader* parent)
 {
        // Normally just non-lazy pointers are bound immediately.
        // The exceptions are:
@@ -929,11 +963,15 @@ void ImageLoader::recursiveBind(const LinkContext& context, bool forceLazysBound
                        // bind lower level libraries first
                        for(unsigned int i=0; i < libraryCount(); ++i) {
                                ImageLoader* dependentImage = libImage(i);
-                               if ( dependentImage != NULL )
-                                       dependentImage->recursiveBind(context, forceLazysBound, neverUnload);
+                               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->doBind(context, forceLazysBound, parent);
                        // mark if lazys are also bound
                        if ( forceLazysBound || this->usablePrebinding(context) )
                                fAllLazyPointersBound = true;
@@ -968,12 +1006,27 @@ static const char* const sTreatAsWeak[] = {
     "__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];
@@ -991,7 +1044,313 @@ void ImageLoader::weakBind(const LinkContext& context)
 
        // 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 __MAC_OS_X_VERSION_MIN_REQUIRED
+               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]));
+               }
+               
+               // 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
@@ -1043,6 +1402,8 @@ void ImageLoader::weakBind(const LinkContext& context)
                                        }
                                }
                                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());
@@ -1052,7 +1413,7 @@ void ImageLoader::weakBind(const LinkContext& context)
                }
          }
          else
-#endif // __MAC_OS_X_VERSION_MIN_REQUIRED
+#endif // TARGET_OS_OSX
          {
                // make symbol iterators for each
                ImageLoader::CoalIterator iterators[count];
@@ -1063,9 +1424,9 @@ void ImageLoader::weakBind(const LinkContext& context)
                        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 
+
+               // 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)
@@ -1073,7 +1434,7 @@ void ImageLoader::weakBind(const LinkContext& context)
                        //dyld::log("\n");
                        // increment iterator with lowest symbol
                        if ( sortedIts[0]->image->incrementCoalIterator(*sortedIts[0]) )
-                               ++doneCount; 
+                               ++doneCount;
                        // re-sort iterators
                        for(int i=1; i < count; ++i) {
                                int result = strcmp(sortedIts[i-1]->symbolName, sortedIts[i]->symbolName);
@@ -1132,9 +1493,12 @@ void ImageLoader::weakBind(const LinkContext& context)
                                                                                        nameToCoalesce, iterators[i].image->getIndexedShortName((unsigned)iterators[i].imageIndex),
                                                                                        targetAddr, targetImage->getIndexedShortName(targetImageIndex));
                                                        }
-                                                       if ( ! iterators[i].image->weakSymbolsBound(imageIndexes[i]) )
+                                                       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; 
+                                                       }
+                                                       iterators[i].symbolMatches = false;
                                                }
                                        }
                                }
@@ -1151,20 +1515,21 @@ void ImageLoader::weakBind(const LinkContext& context)
                                // 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);
+                                       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);
+                                       imagesNeedingCoalescing[i]->resolveWeak(context, coaler.symbolName, true, false, &dummy, patcher);
                                        imagesNeedingCoalescing[i]->incrementCoalIterator(coaler);
                                }
                        }
@@ -1180,7 +1545,7 @@ void ImageLoader::weakBind(const LinkContext& context)
 
        uint64_t t2 = mach_absolute_time();
        fgTotalWeakBindTime += t2  - t1;
-       
+
        if ( context.verboseWeakBind )
                dyld::log("dyld: weak bind end\n");
 }
@@ -1575,11 +1940,25 @@ intptr_t ImageLoader::read_sleb128(const uint8_t*& p, const uint8_t* end)
                bit += 7;
        } while (byte & 0x80);
        // sign extend negative numbers
-       if ( (byte & 0x40) != 0 )
+       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);